Xsens Technologies AWNDDNG Wireless dongle User Manual Manual

Xsens Technologies B.V. Wireless dongle Manual

Manual

 MTw User Manual MTw Hardware, MT Manager, Awinda Protocol              Xsens HQ (Enschede, NL) Xsens US office (Los Angeles, USA)  Phone +31 88 97367 00 +1 310-481-1800 Fax +31 88 97367 01 +1 310-416-9044 Email info@xsens.com internet www.xsens.com
  © Xsens Technologies B.V.   i Revisions Revision Date By Changes A 14 January 2011 CMO First version. B 15 April 2011 CMO Updated for 3.7 Beta  Updated Wireless configuration menu Updated Wireless States Additional Functionality: Stand-by Synchronisation with 3rd party devices + examples C 15 August 2011 CMO Added Rotation Matrix export description Added note about not using maximum update rate to ensure retransmissions are possible during recordings. D 4 November 2011 CMO Updated for 3.8 Settling time advice added Added Awinda USB dongle-related information Added stand-by mode details Additional 3rd party sync options implemented Update rate default value E 14 February 2012 CMO Updated for 3.8.1 Added Table 1 maximum and typical update rates and buffering times. Added information related to magnetic field disturbances (3.3.1) F 9 January 2013 MHA Added Awinda Station and Awinda Dongle to Declaration of Conformity CE and FCC         ©  2010-2013, Xsens  Technologies B.V.  All rights reserved.  Information in this document is subject to change without notice. Xsens, MVN, MotionGrid, MTi, MTi-G, MTx, MTw, Awinda and  KiC  are  registered  trademarks  or  trademarks  of  Xsens  Technologies  B.V.  and/or  its parent, subsidiaries and/or affiliates in The Netherlands, the USA and/or other countries. All other trademarks are the property of their respective owners.
  © Xsens Technologies B.V.   ii Table of Contents 1 Introduction  1 2 Content Overview  2 2.1 Carrying Case with Contents  2 2.2 Motion Tracker (MTw)  2 2.3 Awinda Station  2 2.4 Awinda USB Dongle  3 2.5 Click-in Body Straps  3 2.6 Software  3 3 Getting Started  4 3.1 Hardware Setup  4 3.2 Software Installation  4 3.3 Tips for Best Practice  4 4 Hardware  8 4.1 Motion Trackers (MTw)  8 4.2 Awinda Station  11 4.3 Awinda USB Dongle  12 4.4 Click-in Body Straps  14 5 Recommended workflow  17 6 MT Manager  19 6.1 Software Installation  19 6.2 Connecting to MT Manager  20 6.3 Connectivity Toolbar  21 6.4 Device List  22 6.5 Wireless Configuration  24 6.6 Preferences  30 6.7 Synchronisation  31 6.8 Orientation Reset  36 6.9 Recording Data  37 6.10 Saved and Exported Data  37
  © Xsens Technologies B.V.   iii 6.11 Application Software Development for the MTw  40 7 Xsens Peripheral Software  41 7.1 Magnetic Field Mapper (MFM)  41 7.2 Firmware Updater  41 8 Troubleshooting and Support  43 8.1 Customer Support  45 9 Warranty Liability  46 10 Regulatory Notices  47 10.1 Radio Frequency Exposure and Emission  47 10.2 FCC Statement  48 10.3 CE Declaration of Conformity  49 10.4 FCC Declaration of Conformity  50 11 Appendices  51 11.1 MTw Technical Specifications  51 11.2 Awinda Station Technical Specifications  53 11.3 Awinda USB Dongle Technical Specifications  54 11.4 Xsens Kalman Filter  58 11.5 Strap Down Integration  59 11.6 Coordinate Systems  61 11.7 Orientation Output Modes  65 11.8 Synchronisation Examples  68
  © Xsens Technologies B.V.   iv Abbreviations and Terms  Abbreviation Description BAN Body Area Network BNC BNC (Bayonet Neill-Concelman) connector. Common type of RF connector used for the coaxial cable. Used to connect Awinda Station to third party devices for synchronisation purposes. DOF Degrees Of Freedom MT Motion Tracker MTB MT Binary Communication Protocol MTM MT Manager PAN Personal Area Network SDI Strap down integration SDK Software Development Kit TTL Transistor–transistor  logic.  Used  in  the  synchronisation  ports  of  the Awinda Station. XFF Xsens Firmware File format XKF-3 Xsens Kalman Filter 3 DOF XKF-3w Xsens Kalman Filter 3 DOF for MTw  Term Description Quaternion An orientation representation of complex numbers. A unit length quaternion is a convenient parameterization of rotations. Euler Angles Representation of the spatial orientation of any frame of the space as a sequence of rotations from a reference frame. Awinda Protocol Patented wireless communication protocol specifically suited for real-time transmission of mathematically integrated data, such as constructed by a Strap Down Integration (SDI) algorithm. Strap Down Integration A method to compute an orientation/ position change given an angular velocity/acceleration of a rigid body. For example computing angle change using MEMS vibrating gyroscopes. Delta Angle Output of strap down integration of the angular velocity data. Delta Velocity Output of strap down integration of the acceleration data. Personal Area Network A personal area network (PAN) is that associated with the MTw development kit. A set of wireless clients communicates with a host wireless receiver that is remove from the subject wearing the wireless clients. The wireless receiver is connected directly to the host PC. Body Area Network Differing slightly from a PAN, with the Body Area Network (BAN), a local wireless receiver is also body-worn, this collects wireless data from all body-worn devices and transmits wireless data to a remote wireless receiver, which is connected directly to a host PC.
  © Xsens Technologies B.V.   v Default Folders Description Files Location Main program MT Manager MT SDK C:\Program Files ... \Xsens\MT Manager Documentation MTw User Manual MTw SDK User Manual C:\Program Files ... \Xsens\Documentation Tutorials / Help files  C:\Program Files ... \Xsens\MT Manager
 © Xsens Technologies B.V.   1 1 Introduction The  MTw™  is  a  miniature  wireless  inertial  measurement  unit  incorporating  3D accelerometers,  gyroscopes,  magnetometers  (3D  compass),  and  a  barometer  (pressure sensor). The  embedded  processor handles sampling,  buffering, calibration and strap down integration  of  the  inertial  data  as  well  as  the  wireless  network  protocol  for  data transmission. Combined with the  MT SDK with Xsens Kalman  Filter on  the host  device the MTw provides real-time 3D orientation for up to 32 wireless motion trackers in a network, while at the same time also providing calibrated 3D linear acceleration, angular velocity and (earth) magnetic field and atmospheric pressure data.  One of the unique features of the MTw is the patent-pending Awinda™ radio protocol. The Awinda protocol is based on the IEEE 802.15.4 PHY. Using this basis ensures that standard 2.4 GHz ISM chipsets can be used. The Awinda protocol ensures time synchronisation of up to 32 MTw’s across the wireless network to within 10 μs. This is in a range comparable to the wired systems of Xsens (i.e. the Xbus). Awinda has been specifically developed with inertial sensor  data  in  mind  and  will  maintain  the  accuracy  of  3D  motion  tracking  even  if  data  is temporarily  lost  in  radio  transmission,  while  maintaining  very  efficient  use  of  the  limited available bandwidth. Traditional radio protocols reserve a lot of time for acknowledgement of  data  packet  reception  and  re-transmission  of  data,  possibly  causing  the  network throughput to drop. With Awinda, the data is initially sampled at 1800Hz, is down-sampled on the processor of the MTw to 600Hz. and using Strap Down Integration (SDI) the  data is transmitted to the Awinda Station. For real-time applications, this means that the accuracy is preserved even if data packets are lost. For post-processing and analysis, it means that there is no missing data. Buffered data at the MTw is made available to the host in a configurable re-transmission scheme that will flush the buffered data to the host when excess bandwidth is available.  The  completely  wireless  nature  of  the  MTw  widens  the  possible  areas  of  applications, improves the speed of donning the motion tracking systems onto test subjects, or patients. Because  inertial  sensor  technology  does  not  rely  on  line  of  sight  and  is  not  influenced  by lighting  conditions,  the  systems  can  be  worn  in  the  field,  with  no  need  for  simulated environments.  Fields of use:  Biomechanics  Rehabilitation  Sports and exercise science  Ergonomics  Virtual reality  Animation  Motion capture
  © Xsens Technologies B.V.   2 2 Content Overview 2.1 Carrying Case with Contents  The MTw Development kit arrives in a case, approximately the size of a common briefcase. A standard MTw Development kit contains:  6 MTw's  1 Awinda Station  1 USB cable  1 power cable  Awinda USB Dongle  1 set of full body Click-in body straps  CD with MT Manager and MT SDK  User manual 2.2 Motion Tracker (MTw)  MTw’s are miniature inertial measurement units containing 3D linear accelerometers, 3D rate gyroscopes, 3D magnetometers and a barometer. The casing has been designed with a click mechanism, to ease positioning on the body using click-in body straps. For more details see Section 4.1. 2.3 Awinda Station  The Awinda Station. It controls the reception of synchronised wireless data from all wirelessly connected MTw’s and charges up to 6 MTw’s simultaneously. It can receive wireless data from up to 32 MTw’s. For more details see Section 4.2.
  © Xsens Technologies B.V.   3 2.4 Awinda USB Dongle  The Awinda USB Dongle has the same wireless capabilities as the Awinda Station. It controls the reception of synchronised wireless data from all wirelessly connected MTw’s. It can receive data from up to 32 MTw’s. For more details see Section 4.3. 2.5 Click-in Body Straps    The MTw Click-in body straps are a one-size fits all mounting system. They have specially designed click mechanism enabling the MTw to be quickly and easily clicked into place and removed again for charging. When clicked in, they maintain a robust connection to the strap. The straps are made from strong elastic material, backed with silicone rubber to ensure comfortable and close fixation to the skin. They are fastened using Velcro. For more details see Section 4.4. 2.6 Software  The MTw development kit is supplied with a visualising and recording software package, MT Manager. This facilitates quick and easy use of the MTw and Awinda Station. In addition, a MT Software Development Kit (SDK) is provided, with example code in C, C++, LabView, MATLAB and Linux.1 The MT SDK is intended to make software application development for the MTw easily accessible. For more details see Section 6.11.                                                             1. Future releases will include example code in Excel.
  © Xsens Technologies B.V.   4 3 Getting Started 3.1 Hardware Setup Dock the MTw’s into the Awinda Station. Connect the Awinda Station to the PC,  using the USB cable provided. The mains power supply is only needed for charging the MTw, turning it on from the Transport (or switched off) mode and while carrying out firmware updates, but we recommend connecting the power supply immediately to charge the MTw’s. For wireless communication between MTw’s, the Awinda Station and the PC, it is not necessary to plug the  Awinda  Station  to  the  mains  power  supply  since  the  wireless  interface  in  the  Awinda Station is powered by USB from the PC.  See Section 4.1 for details about the MTw. See Section 4.2 for details about the Awinda Station. See Section 4.3 for details about the Awinda USB dongle. See Section 4.4 for details about the MTw Click-in body straps. 3.2 Software Installation Insert  the  CD  supplied  to  run  the  MT  Manager  Installer  (setup.exe).  If  using  Windows XP/Vista/7 operating systems, install with 'Administrator' or 'Power User' rights. Follow the on-screen instructions.  See Section 6.1 for detailed MT Manager installation instructions. 3.3 Tips for Best Practice 3.3.1 Magnetic Distortion For  best  results  when  measuring  with  the  Xsens  MTw,  it  is  advised  to  avoid  highly magnetised areas when carrying out measurements; in particular in the beginning. XKF-3w uses the local magnetic field to compute heading. When this signal is distorted due to close proximity of a strong magnet, or ferromagnetic material (iron or steel),  accuracy of results may decrease.  Check  the  magnetic  norm  of  the  environment.  To  check  the  magnetic  norm,  the  system should be installed and running, with at least one MTw active. Open the inertial data graph and look at  the Magnetic Norm curve (black line) while moving  in the  measurement area. Areas for which the magnetic norm variation remains within ±0.2 are best for carrying out measurements.  3.3.1.1 Types of Magnetic Disturbance Figure  1  below  gives  an  indication  of  how  ferromagnetic  objects  lying  in  a  homogenous magnetic  field  cause  magnetic  field  distortions.  It  is  clear  from  this  figure  that  only  when
  © Xsens Technologies B.V.   5 close to the (ferro-)  magnetic material can the material  be  considered  as disturbing, since the  field  lines  bend  towards  the  object  when  in  close  proximity.  For  more  detailed information about the influence of magnetic field on orientation, see the PhD thesis “Inertial and magnetic sensing of human motion” D. Roetenberg 20061.   Figure 1: Simulation of ferromagnetic objects in free space with a homogeneous magnetic field Homogenous magnetic field As  mentioned  above,  it  is  advised  to  avoid,  at  least  starting  a  measurement  in  a  highly disturbed  magnetic  environment  (in  a  magnetic  norm  of  about  2  or  3).  If  however,  the measurement begins with a magnetic norm of around 2 or 3, and remains within ±0.2 of this value, the orientation should remain accurate.  If  the  homogenous  and  highly  disturbed  magnetic  field  is  due  to  the  MTw  fixed  to  an instrument, or a prosthesis, it is best to carry out magnetic field mapping for this MTw (see section 7.1). This instructs XKF-3w algorithm that the magnetic field has a new value.  Varying magnetic field The  XKF-3w  algorithm  can  compensate  for  areas  of  fast  fluctuating  magnetic  fields. However, slow, large (>±0.2) changes are more difficult for the algorithm to compensate for, over periods of  time longer than approximately 30s, since the algorithm will constantly  be updating its new heading value.  NOTE: Do  not  expose  the  MTw  to  very  strong  magnetic  fields.  There  is  a  chance  the  MTw  may become magnetized which  will  render the  calibration  values  of  the magnetic field  sensors                                                            1.http://www.xsens.com/images/stories/PDF/Inertial%20and%20Magnetic%20Sensing%20of%20Human%20Motion.pdf Homogenous magnetic field Disturbed magnetic field
  © Xsens Technologies B.V.   6 inside the MTw inaccurate. Performing a Magnetic Field Mapping on the MTw may recover the calibration if the magnetization is not too strong. 3.3.2 Settling Time As with all filters of its kind, the XKF-3w filter is based on history. For this reason, some time is  needed  for  the  XKF-3w  filters  to  settle  to  a  stable  state,  this  is  referred  to  as  “settling time”. Users should be aware that prior to a measurement, the MTw’s should be allowed to reach  some  filter  stability.  In  practice  this  means,  that  users  should  try  to  minimise movement when making a wireless connection. Furthermore, depending on the update rate, users should minimise movement, or keep any movements to calm and slow movements for the first few seconds, to one minute after entering measurement mode. 3.3.3 Operating Conditions The MTw has been designed to be used or worn close to the human body. Take care when exposing  the  MTw  to  strongly  deviating  environmental  conditions.  The  recommended operating  temperature  is  between  -20°C  and  +55°C  ambient  temperature.  If  operated outside  this  temperature  range  performance  may  decrease  or  the  device  may  become damaged.  Fast  transient  temperature  fluctuations  may  cause  significant  temperature gradients  across  the  device.  Such  gradients  cannot  be  properly  modelled  by  temperature compensation and may therefore decrease performance. Additionally, operating around 0o may cause water particles to freeze and condense around the components, causing potential damage  to  the  internal  electronics.  For  optimal  performance,  the  ambient  temperature should  remain  as  constant  as  possible  during  the  measurement.  Cold  environments  may provide shorter operation time of the trackers.  The MTw and  Awinda Station must be kept  dry at all  times. Condensation  and water  may damage  the  internal  electronics.  Using  the  MTw  with  the  straps  will  protect  the  MTw  to body moisture to a limited degree.  Protect the MTw from violent handling such as drops on hard surfaces. Excessive shocks or violent  handling  may  damage  the  MTw  or  render  the  factory  calibration  no  longer applicable.  When  handling  the  MTw  at  a  desk,  it  is  advised  to  place  cushioning  material between the desk and the MTw.  Do not put MTw’s in the pockets in the suit case while in operation. Due to the high thermal insulation of the foam then surrounding the MTw the device will not be able to dissipate the small amount of heat that it generates during operation and it may become (too) hot. 3.3.4 Absolute Maximum Ratings  Stresses above the absolute maximum ratings to the MTw may cause permanent damage to the device components.
  © Xsens Technologies B.V.   7 3.3.4.1 Absolute Maximum Rating MTw Shock (any axis) TBD Input Voltage -0.3 V … 6 V (note power is supplied only via USB) Temperature During operation -10 oC - +60 oC Temperature During charging 0 oC - +45 oC 3.3.4.2 Absolute Maximum Rating AWINDA Station DC Input Voltage -0.3 V … 16 V (Use included DC adapter) SYNC (BNC) inputs -0.5 to 3.8V Operating Temperature -20 oC - +80 oC  Exposure  to  absolute  maximum  rating  conditions  for  extended  periods  may  affect  device reliability.  NOTE:  Drops  onto  hard  surfaces  can  cause  shocks  of  greater  than  20000  m/s2  (2000  g) exceeding the absolute maximum rating of the device. Care should be taken when handling to  avoid  damage.  Drops  causing  shock  greater  than  absolute  maximum  ratings  may  not destroy the device but will permanently alter the properties of the physical motion sensors, which  may  cause  the  device  to  become  inaccurate.  If  this  occurs,  please  contact support@xsens.com to investigate if the MT should be returned for a check. 3.3.5 Keeping the Hardware Clean The housing of  the MTw and  Awinda Station are  waterproof. However, the housing is not watertight. To keep the Awinda Station and the MTw’s clean, use a damp cloth to wipe the surfaces.
  © Xsens Technologies B.V.   8 4 Hardware The MTw Development Kit is comprised of both software and hardware. This section deals with all hardware aspects. The hardware of the MTw development kit includes the motion trackers, the Awinda Station and the click-in body straps. 4.1 Motion Trackers (MTw) The  MTw  provides  3D  angular  velocity  using  rate  gyroscopes,  3D  acceleration  using accelerometers,  3D  earth  magnetic  field  using  magnetometers,  as  well  as  atmospheric pressure using the barometer. Combined with Xsens algorithms, 3D drift-free orientation is provided.  The  MTw  is  an  excellent  measurement  unit  for  orientation  measurement  of human  body  segments,  in  particular  because  it  is  also  designed  to  maintain  very  high accuracy time synchronization of the individual sensor readout across a wireless network of multiple units. This is essential when measuring joint angles accurately.   Front side of the MTw where the micro USB is connected. On the top is LED giving indications of device status.  Back side of the MTw, displaying various regulatory notices and 2D barcodes used by Xsens for quality control and tracking, as well as the MTw product code (MTw-38A70G20) and serial number1 (SN). Note that the last three digits of the SN are displayed in a large font, for the user to easily identify individual MTw’s. This aids the user for example when placing MTw’s on particular body segments.  The  MTw  is powered using  a  LiPo  battery.  The battery  can  be  in  operation  for  up  to  3.5 hours, in stand-by for approximately 90 hours and is fully recharged after one hour docked in the  Awinda  Station  (with  a  power  supply  connected  to  the  Awinda  Station).  For  more technical  details  on  the  MTw,  sensor  component  specifications  and  orientation performance, see Section 11.1.                                                            1 Also known as Device ID.
  © Xsens Technologies B.V.   9 4.1.1 MTw LED Indications The following lists the  LED indications of the  MTw, which are  a combination  of the device states and the Awinda protocol states of the MTw: State  Description Power-up  Blinking.  Docked and fully charged ON Charging Slow fade from ON to OFF as a percentage [%] of battery status. A slow cycle means an almost full battery. A quick cycle means an almost empty battery. Scanning Pulsating. Connected Slow symmetric ON/OFF toggle in sync with Awinda Station (CONN LED). Measuring  Fast symmetric ON/OFF toggle in sync with Awinda Station (CONN LED). Battery Low Quick Triple Pulses, overrides other states until charging again. Flushing  Double pulse in sync with Awinda  Station (CONN LED). Stand-by OFF. Blinks for 3 s, if a change in magnetic field has been detected, while searching for a radio connection. 4.1.2 MTw Stand-by Mode Following a  wireless  connection, the  MTw  is  in  operational  or  measurement mode. When the radio of the Awinda Master has been switched off, for longer than 30 seconds the MTw will  enter  stand-by  mode.  In  this  mode,  the  MTw  will  shut  down  its  power,  but  monitor change in magnetic field every second. See below for exiting standby mode. 4.1.3 Exiting stand-by mode With  MT  SDK  3.8  instead  of  searching  only  for  a  wireless  link,  the  MTw  will  monitor  its magnetic field once every second. If the magnetic field has changed considerably, and there is a wireless link to an Awinda Master available, the MTw will automatically become active again.  To  bring  the  MTw  back  from  stand-by  to  operational  mode,  reactivate  the  radio  of  the Awinda Master, and move the MTw; a simple 90 degree turn, or simply lifting it from the suit case to apply to the subject should be enough. As an alternative, this can also be done by changing  the  magnetic  field  around  the  MTw.  Consider  moving  a  pair  of  stainless  steel scissors (NOT A MAGNET) over the MTw, to change the field and reactivate it.
  © Xsens Technologies B.V.   10 4.1.4 Estimated battery life with stand-by mode activated Bat.  Capacity  at  sleep  start [%] Estimated  time  to  full discharge in standby [hrs] Measuring  time  left  after  8 hrs in standby [hrs:min] 100 88 2.18 75 64 1:45 50 44 1:06 25 20 0:24 10 8 0:00
  © Xsens Technologies B.V.   11 4.2 Awinda Station  Front view of the Awinda Station, showing the LEDs. A description of the LEDs are described in Section 4.2.2 below. On top are docking spaces for 6 MTw’s with regressed micro USB connectors. On the side is a foldable and rotatable 2.4 GHz antenna for maximum range.   Back view of the Awinda Station, showing the DC power connector, the USB connector and 4 BNC sync I/O connectors for synchronisation with external devices 1. See 11.2 for more technical specifications of the Awinda Station.  4.2.1 Awinda Station Synchronisation Ports On the back of the Awinda Station there are four BNC ports, two Sync In ports and two Sync Out. The ports have been configured  to  send (Sync  Out) or receive (Sync  In)  TTL pulses 0-3.3V. For software configuration of the synchronisation channels, see Section 6.7.                                                              1
  © Xsens Technologies B.V.   12 4.2.2 Awinda Station Status LED The Awinda Station has five LED indicators. From right to left, these indicators are: LABEL LED DESCRIPTION CHRG  [CHaRGer functionality] OFF When no mains power supply is connected to the Awinda Station.   GREEN: When 12V power supply is connected (mains power supply). STAT  [STATus of the Awinda Station] OFF OFF: When no USB connection is present and when MT Manager is not started.  GREEN: Both USB connection present and MT Manager running connected to driver.  ORANGE: USB connection to host PC is present.  RED: Only power supply connected or error has occurred, e.g., a short-circuit of an MTw. EXT OFF Remains off unless external connection made.  GREEN: External connection e.g. sync port. CONN OFF OFF: No wireless connection.  GREEN slow blinking: (1 blink per second), radio switched on. When MTw connects, MTw LED and CONN LED blink synchronously. Fast blink: Measurement Mode. DATA OFF OFF: No data received.   GREEN: Measurement mode.  ORANGE: Flushing. Flushing is the action of transferring data that has been stored on the MTw buffer, while the MTw was out of range and unable to transfer data in real-time to the Awinda Station.  RED: Recording mode is active. This allows the remote monitoring that the host PC has initiated a recording successfully.  Note:  The  power  supply  is  needed  to  charge  the  MTw’s  or  to  change  from  power  off  to power on. Only the power supply is needed for charging purposes (USB is not needed in this case). Power supply and USB connection are required for firmware updates. Power supply is not needed for wireless communication (e.g. measurement/recording).  4.3 Awinda USB Dongle  See 11.3 for more technical specifications of the Awinda USB Dongle.
  © Xsens Technologies B.V.   13 4.3.1 Awinda USB Dongle LED The Awinda USB dongle has one white LED. State  Description Radio Off LED off. Scanning for MTw’s Pulsating LED. Connected Slow symmetric ON/OFF toggle (MTw blinks in sync with LED of dongle). Measuring  Fast symmetric ON/OFF toggle (MTw blinks in sync with LED of dongle).
  © Xsens Technologies B.V.   14 4.4 Click-in Body Straps The MTw Click-in body straps have been designed to ensure that the user can enjoy as much flexibility as possible. The user may first insert the MTw into the strap, then fasten the strap to the body (recommended). Alternatively, prepare the subject by first attaching the straps, to the body locations, then insert the MTw’s at the appropriate locations. 4.4.1 Putting MTw’s into Strap Holders Each system is supplied with a series of stickers, with the ID of the MTw printed. The user can use this to fix to the MTw holder on the straps, to enable the user to remember more easily where each MTw is fixed on the body. The user can also set a numerical Location ID in MT Manager Device List (Section 6.4.2) to code Location ID to, e.g., body segments.   To put the MTw into the holder of the straps, slip the MTw, gently into the “cup” of the holder.  Press the clip of the MTw against the MTw housing.  Press the MTw vertically into the housing.  Release the clip into the clasp of the holder. Take care to ensure that the MTw is completely and firmly restrained. 4.4.2 Putting on the Straps It  is  possible  for  the  user  to  put  the  straps  onto  their  own  body  segments,  however,  to ensure tight and stable fit, it is advisable to have someone else fasten them.  Before each use, pre-stretch the straps to remove any initial stiffness.
  © Xsens Technologies B.V.   15  Insert  each MTw, into  the  correct  strap holder.  Note  the  location of the MTw  ID  with respect to the body location, for future use.  For consistency, it is recommended to display the Xsens text in the correct orientation for reading – this means that the cup should be the lowest point.  Attach the straps to the appropriate body segments.1  Check that the straps are fastened tightly enough to the body.  To do this, the subject wearing the straps should walk or run for a few seconds, or perform  sample  movements  that  will  be  made  during  the  measurements.  If  the straps become loose, re-tighten them and repeat the check.  NOTE:  When  tightening  the  straps,  pull  the  strap  at  the  point  where  it  runs  through  the plastic buckle, not just at the end! 4.4.3 Recommended Locations While inertial sensor technology facilitates freedom of movement and minimises restrictions imposed  by  camera  and  lighting,  users  should  remain  as  vigilant  when  placing  inertial sensors  to  the  body  as when placing any  other  human  measurement system to the body. Users  should  be  aware  of  skin  motion  artefact,  which  can  occur  with  all  forms  of  human (movement) measurement systems. When placing Xsens MTw to the body, using the Click-in body straps helps  to ensure that the MTw is fastened  tightly and robustly  to the skin. The following points should be taken into consideration:  Be aware of muscle contractions that may cause unwanted movement of the MTw  Place MTw’s on areas with least likelihood of moving due to a muscle contraction.  For  measurements  of  the  extremities,  for  example  forearm,  take  into  account  the measurement desired. At  Xsens,  we  place  the  MT  closer  to  the  wrist,  as  this  provides more information about 3D movement. Furthermore, the wrist area has less fatty tissue, decreasing the chances of skin motion artefact. (See 4.4.4 for instructions for fastening the forearm strap.)  For the upper arm, the location is less critical, as the upper arm has more musculature.  On the lower leg, two locations have been described in literature as good placement. 1. On the tibia, close to the knee2. 2. On the lateral side  of the lower leg, aligned with the fibula, 6cm above the lateral malleolus3.  For upper leg measurements, we recommend placing the MTw close to the knee, on the lateral thigh, as this has less probability of having fatty tissue, compared e.g. to closer to                                                            1  Configuration  sheets  with  recommended  MTw  positions  for  full  body  measurement  are available upon request. 2 Cloete, T.;  Scheffer, C.”Repeatability of  an off-the-shelf, full body  inertial motion capture system  during  clinical  gait  analysis”  Engineering  in  Medicine  and  Biology  Society  (EMBC), 2010 Annual International Conference of the IEEE 11 Nov 2010 pp 5125 - 5128 3 Cutti AG, Ferrari A, Garofalo P, et al. ‘Outwalk’: a protocol for clinical gait analysis based on inertial & magnetic sensors. MED BIO ENG COMPUT, 2010; 48(1):17-25.
  © Xsens Technologies B.V.   16 the hips. The silicone backed strap, combined with the pelvis belt, this helps to ensure that this strap does not slide along the leg, during movement e.g. gait measurements.   For pelvis motion measurement, place the MTw at the small of the back. Tightening the pelvis belt  of the pelvis, we recommend using the MTw pelvis 4.4.4 Forearm Strap The  forearm  straps  have  been  designed  slightly  differently  from  the  others,  with  an additional Velcro strap to ensure a tight fit. To fasten the forearm strap to the subject:     Ensure that the rubber touches the skin, to optimise subject comfort. Fasten the inner (broad) Velcro strap. Insert the smaller Velcro strap into buckle. Wrap around, ensuring a tight fit.
  © Xsens Technologies B.V.   17 5 Recommended workflow   To start up, the Awinda Master must be plugged into the USB port of the PC.  The ID of the Master and docked MTw’s is displayed in the device list. See 0.  Go to wireless configuration. Select a radio channel and switch the radio on (enable). See 6.5.  When an MTw is undocked, its radio looks for a station to connect to. The wirelessly connected MTw’s appear in the list.  When all required MTw's are connected, set the update rate and either make operational or enter measurement mode directly.  See 6.5.6 for selecting the best update rate.
  © Xsens Technologies B.V.   18   From operational mode, measurement mode can be initiated.  When “Start Measuring” is clicked, make sure that the MTw is kept still.  For best results, data should be measured and recorded in the same environment as when measurement mode was initiated. Like all filters of its kind, the XKF‐3w filter is based on history. Therefore time is needed for the XKF‐3w filters to settle to a stable state. This time is called settling time, see 3.3.2.  For about one minute after entering measurement mode, make calm, slow movements to warm up the filters (the actual time depends on the amount of trackers in use, but one minute should be sufficient).  To check if the filters have been stabilised, ensure that the orientation of the MTw doesn’t change, when the MTw is stationary (in a magnetically undisturbed environment). When in measurement mode, recording can be made.
  © Xsens Technologies B.V.   19 6 MT Manager Each  MTw  Development  Kit  is  accompanied  with  MT  Manager,  an  easy-to-use  software interface  facilitating  visualisation,  recording  and  exportation  of  inertial  sensor  data. Additionally, the MTw  Software Development Kit (SDK) is  provided, giving full access to all data and configurations of the MTw, with accompanying documentation and example code to enable software developers to create customised (real-time) visualisation and recording application software. For more details about the SDK, please see Section 6.11.  The MT Manager software has been designed for Windows 7. It is easy-to-use software with familiar Windows user interface, which allows the user to:  View and modify device settings and properties  Configure the Awinda wireless interface  Configure synchronisation with third party devices  Real-time visualisation of:  3D Orientation  3D Inertial and magnetic data  Barometric pressure sensor data   Status data  Record native binary log files of data from motion trackers (.MTB files)  Log file export to ASCII  The  MT  Manager  is  therefore  an  easy  way  of  getting  to  know  and  to  demonstrate  the capabilities of the Motion Tracker. 6.1 Software Installation If users  have previously installed Xsens MT  SDK1, first uninstall the previous version of MT SDK, as well as the USB drivers from add or remove programs in the control panel. The USB drivers are listed as 'Windows Driver Package - Xsens USB-serial Converter Driver Package' in Add/Remove Programs. Uninstall all entries of these drivers from the list.  NOTE: Do not connect the Awinda Station to the PC before fully installing the MT SDK.  Insert  CD  provided  to  install  MT  SDK  on  a  computer  running  Windows  using  the  MT  SDK Setup application on the CD provided. The installation will start automatically2 if “Autorun” is enabled on the CD player, otherwise, run the setup.exe file in the location of the CD ROM. Windows  Vista/7  users,  should  choose  “Open  folder to  view  files”  in  the  Autoplay  dialog.                                                            1 Do not uninstall the MT SDK 3.3 if you need to continue to work with your MTi, MTx, MTi-G or Xbus Master since 3.8only officially supports the MTw. 2 If the installation application does not start automatically, double-click “setup.exe” in the root folder of your CD/DVD drive, e.g. E:\
  © Xsens Technologies B.V.   20 Right-click  “Run  setup.exe”  and  “run  as  administrator”.  Follow  the  on-screen  instructions. When prompted, enter the serial number for the product. This number can be found on the letter  accompanying  the  MT  SDK  CD-ROM.  User  the  default  installation  folder  or  select preferred installation folder, and click next. 6.2 Connecting to MT Manager To initialize the Awinda Station and MTw’s, dock the MTw’s in the Awinda Station. Physically connect the Awinda Station, to the PC using the USB cable provided.  6.2.1 Automatic COM Port Scanning Upon  execution  of  the  MT  Manager,  all  available  COM  ports  on  the  host  PC  are automatically  scanned  for  Xsens  hardware.  Progress  is  displayed  during  scanning  in  the status bar on the bottom right corner of the main window. If the PC has a large number of COM-ports (e.g. if Bluetooth drivers are installed) this may take some time.   Upon successful connection1, the “Device List” sub-window appears with a list of connected devices and respective Device ID number (when necessary press the Device List icon).   The  Wireless  Configuration  section  (6.4.2)  describes  how  to  connect  the  MTw’s  as  sub-systems (clients) of Awinda.  NOTE: If synchronisation configuration is needed first enable these settings (See section 6.7) before carrying out the wireless configuration.                                                            1 Please refer to Section 8 in case of problems.
  © Xsens Technologies B.V.   21  If  the  automatic  scanning  at  start  up  does  not  reveal  any  connected  devices,  ensure  that there is a USB connection and manually scan for ports using the functions in the connectivity toolbar. 6.3 Connectivity Toolbar The  following  items  are  available  on  the  connectivity  toolbar,  for  manual  COM  port scanning/disconnecting.    Scan all ports Scan single port Disconnect COM port1 6.3.1 Scan All Ports All available COM ports are scanned for connected devices. 6.3.2 Scan Single Port Choose an active COM port from the appropriate drop down menus to link this port to MT Manager, click “Scan single port”. 6.3.3 Disconnect COM Port To disconnect all hardware connected, select the “Disconnect” button.                                                            1 This can also be used to close an open file.
  © Xsens Technologies B.V.   22 6.4 Device List The Device List contains all of the information about the devices connected to MT Manager. It is possible to connect more than one Awinda Station (and associated MTw’s) at one time to MT Manager.  Single Station: Power On Power Off  Two Awinda Stations Connected  Wireless connection with Awinda USB Dongle 6.4.1 Power On/Off When docked it is possible to power off the MTw’s, to a fully powered down “Transport Mode”. To do this, select Power Off from the drop down, menu and click “Apply”. It is important to “Apply” changes or they are lost after e.g. a rescan or if removed from the Station.  To re-enable the power, simply dock the MTw back into the Awinda Station; it will wake up by the power connection.  It is best to power off unwanted MTw’s before continuing with the wireless configuration. If the user decides to power off the MTw after wireless configuration, it will be necessary to re-dock the MTw, Power Off and then reconfigure the wireless network.
  © Xsens Technologies B.V.   23  When the wireless configuration has been performed, the Device List is updated such that all connected MTw’s are listed, with the indication of whether they are still in the Awinda Station (docked) or wirelessly connected.  MTw’s docked or wirelessly connected is shown as a Connected Device in the Device List. Still docked (and not previously configured wirelessly) have the index “[DOCKED]”. 6.4.2 Location ID  Users can change the numerical Location ID of  docked  MTw’s  in the Device List. This is useful  for  example  if  users  want  to  use  a numerical code for a given body segment.  After  making  changes  in  the  Device  List, click  Apply  to  make  sure  changes  are implemented.
  © Xsens Technologies B.V.   24 6.5 Wireless Configuration When the Awinda Station is connected to the MT Manager, the Awinda system can be in one of the following states: State Description Connecting The Station is plugged into the USB connection and MT Manager tries to establish the link to the Station. Connected The Station is plugged in to the USB and detected by MT Manager. The radio is not transmitting. Enabled The station is broadcasting (i.e. radio enabled) on the specified channel and MTw’s can detect this transmission and connect. MTw’s that connect but should not be part of the configuration can be rejected.  Operational All the necessary MTw’s are connected and no more new MTw’s can connect. The system is ready to start the measurements using the indicated maximum frame rate or the user can specify a lower one. Measuring The MTw’s are measuring and transmitting data to the station. The station relays the measurements to MT Manager. Recording Any missed data packets are retransmitted in this state, provided that the maximum update rate is not selected.  The state transition diagram is illustrated below:
  © Xsens Technologies B.V.   25 State Transition Description Next State Connecting Station detected MT Manager and Station are connected. Connected Connected Enable User indicated that the system can be enabled. Enabled Enabled  Make operational User indicated that system can become operational.  Operational Disable User indicated that the system is to be disabled. Connected Operational Start measuring User indicated that the system can start measuring. Measuring Release User indicates that system is no longer operational, but still enabled. Enabled Measuring Stop measuring User indicates that measuring can be stopped. Operational  Start recording User indicates that the recording is to be started. Recording Recording Stop recording User indicates that the recording can be stopped. Measuring  It is  possible to enable and  disable the  radio link  using the wireless configuration window. Likewise, rejecting and accepting motion trackers for a given Awinda Station. 6.5.1 Setting Up a Wireless Network in MT Manager NOTE: If synchronisation with third party devices is needed first enable these settings (See section 6.7) before carrying out the wireless configuration.  To configure the wireless network to be used, including selection of MTw’s, and the update rates, go to > Tools > Wireless Configuration, or use the shortcut button:    As shown above, the wireless configuration menu is split into two sections: 1. On  the  left  hand  side  are  details  about  the  detected  Awinda  Master(s).  Here  also  the Update Rate and the Radio Channel, per Awinda Master can be configured.  2. On  the  right  hand  side  are  details  about  the  MTw  and  the  associated  radio  signal strength.
  © Xsens Technologies B.V.   26 6.5.2 Choosing a Radio Channel  Figure 2: Overview of channels operating around 2.4GHz; for ease of channel selection Figure 2 provides an overview of the allowed channels for operating on IEEE 802.15.4, the standard that Awinda is based on, around 2.4 GHz. The bottom row of the figure shows the channels  on  the  2.4GHz,  the  top  row  shows  how  WiFi  channels  use  the  spectrum.  This should indicate to the user that the best channels to use when you know which channel WiFi is on. When in an environment where WiFi is also expected to be in prevalent use, but you are not sure which channels, try Channels 11, 15, 20 or 25.  Bluetooth uses all of the spectrum around 2.4 GHz, but will (try to) avoid channels in use by other systems including Awinda channels. 6.5.3 Select Radio Channel for Wireless Connection A number of wireless frequency channels are available to connect the Awinda Master with the MTw’s. When the wireless configuration menu is open, create the wireless network by first  selecting  the  radio  channel  for  communication  between  the  Awinda  Master  and  the MTw’s. To  select  the  radio  channel,  double  click  on  the  value  under  the  heading  “Channel”  and select  the  radio  channel  from  the  drop  down  menu.  This  channel  will  be  enabled  on  the Awinda Master. 6.5.4 Turn Radio On After selecting the radio channel for the wireless communication, click “Radio On”. The radio transceiver  of  the  Awinda  Master  will  turn  on  and  it  which  will  search  for  MTw’s  on  this channel. For  a  wireless  connection  between  the  Awinda  Master  (either  the  Awinda  Station  or  the Awinda USB Dongle) and the MTw’s, the MTw’s should not be docked in the Awinda Station, because while docked, the radio of the MTw is turned off. It is advised to remove the MTw’s one by one instead of all at once.
  © Xsens Technologies B.V.   27 When no longer docked to the Awinda Station the MTw will  activate its radio and start to search for an Awinda Master to connect wirelessly to. All possible channels are scanned, but the  MTw  will  connect  to  the  channel,  which  has  an  Awinda  Master  available.  If  multiple Awinda  Masters  are  active,  the  MTw  will  automatically  pick  the  channel  with  the  best (strongest) wireless link. Since each channel is scanned, it will take a few seconds to connect.  NOTE: If you experience a very poor wireless connection, or slow detection of MTw’s, select a different wireless channel in the wireless configuration or turn-off potential sources of 2.4 GHz radiation (Bluetooth, WiFi, walkie-talkies, etc.) 6.5.5 Connecting MTw’s to an Awinda Master  When a connection has been established between the Awinda Master and the MTw’s, each MTw appears in the list on the right hand side, with an indication of the signal strength. As each new MTw is detected, the maximum Update Rate (marked as “Rate (Hz)”) will decrease as appropriate.  The LED on the MTw will blink synchronously with the LED of the Awinda USB Dongle or with the CONN LED of the Awinda Station, when a successful link has been established.  The user should decide which of the detected MTw’s to use in the measurements. To disconnect a given Awinda Master and an MTw, right click over the MTw, and select “Reject for Station: <StationID>”. Where Station ID is the serial number of the Awinda Master in use.
  © Xsens Technologies B.V.   28 Initially, if a user has rejected the MTw for a given station, this is depicted as “Unknown”. A rescan shows that the MTw was rejected by the user “Blacklisted”.  To reconnect a rejected MTw and Awinda Master, right-click the MTw and select “Accept for Station: <Station ID>”.  Rejecting an MTw does not cause it to power off; it stops communication between that MTw and the Awinda Master.  NOTE: To power off the MTw, the user should power it off in the Device List, while docked in the Awinda Station, before starting the wireless configuration. See Section 6.4.1. 6.5.6 Update Rate  As each MTw makes a connection with the Awinda Master, the Maximum Update Rate decreases accordingly.  It is possible to select an update rate, by double clicking the value under “Rate (Hz)”, a drop down menu will appear with the available update rates. NOTE: The default update rate is always one value less than the maximum, to ensure that retransmissions  are  possible  during  recording.  Users  can  increase  this  to  maximum  but caution should be taken as this will reduce or remove the possibility of retransmissions.  Table  1  provides  an  indication  of  the  maximum  and  typical  update  rates  for  a  number  of MTw’s.  The  buffering  time  is  also  indicated.  This  is  the  amount  of  time  that  data  can  be expected to be stored on the MTw, if the user goes beyond the specified radio transmission range. Table 1: Typical and maximum update rates and buffering times Amount of MTw’s UR [Hz] (max – no retransmissions) Buffering time[s] (max) UR [Hz] (typical – allowing retransmissions) Buffering Time [s] (typ) 1 150 7 120 9 2 120 9 100 10 4 100 10 75 14 6 75 14 60 17 12 50 20 40 26 18 40 26 30 34
  © Xsens Technologies B.V.   29 6.5.7 Wireless Connection with the Awinda USB Dongle  The  procedure  to  connect  to  the  Awinda  USB  Dongle  is  the  same  as  connecting  to  the Awinda Station.  Therefore, follow  the  steps  described  above.  One  possible  scenario when using the Dongle is  that it is possible  that both the Station  and the  Dongle (therefore two Awinda Masters) are connected to the PC via the USB port. If only a wireless connection with the  Dongle  is  needed,  then  ensure  that  the  radio  of  the  <Station  ID>  of  the  Dongle  is activated during the wireless configuration procedure. 6.5.8 Wirelessly Connecting More Than One Awinda Master If more than one Awinda Master is in use, the user should first configure the MTw’s of one Master, then click “Operational” to enter operational mode and ensure that the configured MTw’s are bound to that Awinda Station. When in operational mode, no new MTw’s can be added to  the wireless network. Before configuring the second Awinda Station, first ensure that the radio channel is different from the previously configured Station, then proceed with wireless configuration of the second Station. 6.5.9 Operational and Measurement Modes When only one Awinda Station is in use, when all MTw’s have been detected and accepted for  the  measurement,  the  user  can  go  directly  to  recordings,  the  user  does  not  need  to select “Operational” but can go directly to “Start Measuring”.  With  Start  Measuring  command,  MT  Manager  will  close  the  wireless  configuration  menu, rescan the COM ports and update the Device List. Remember to keep MTw’s very still at this time.  The MTw’s are now detected as clients of the active wireless motion tracker network with the Awinda Station as the master device, as shown in the Device List. All MTw’s are time synchronised with each other to a global time base given by the Awinda Station.
  © Xsens Technologies B.V.   30 6.6 Preferences The  graphs  can  be  visualised  as  either  Euler  angles  or  quaternions.  For  more  information about quaternions and Euler angles, see Section 11.7. 6.6.1 Preferences: Graphs     6.6.2 Preferences: Miscellaneous  Show docked MTw’s in Device List (see 6.4). Log and visualize data for docked MTw’s (see 6.6.2.2).
  © Xsens Technologies B.V.   31 6.6.2.1 Show Docked MTw’s in Device List This is related to how the Device List handles docked MTw’s. The default setting is to show docked MTw’s, at all times. If checked (default), docked, and powered on MTw’s will appear in the Device List, even after wireless configuration. In the Device List it will be possible to power off, and to observe the battery level of docked MTw’s. If unchecked, after a wireless configuration, docked MTw’s will not appear in the Device List. 6.6.2.2 Log and Visualize Data for Docked MTw’s This  setting  is  related  to  how  the  recording  function  handles  docked  MTw’s.  The  default setting  is  unchecked,  which  means  that  data  will  not  be  recorded  from  docked  MTw’s.  If checked, data from docked, and powered on MTw’s will be stored in the data files. This may be useful for users wishing to use for example only the barometer  signal from the docked MTw’s, without using battery power. Note: If this option is selected, the update rate of these MTw’s is always 100Hz. 6.6.3 Preferences: Logging   Logging/file names. It is possible to change the naming in which the log files are saved. The Xsens default (and recommended) is “MT_” followed by the device ID and trial number. However the user may input custom text, as well as preset values, such as date, time etc. 6.6.4 Preferences: Exporters  Following a measurement, it is possible to export the values. Section 11.7 provides a description of each Orientation Output Mode.  Note:  1) Acceleration and Angular Velocity are values derived from the SDI values. 2) Orientation is always exported, as default. To undo this, select “none” from the drop-down menu in the list. 6.7 Synchronisation MT  Manager  for  MTw  provides  a  very  easy  to  use  interface,  with  many  possibilities  to facilitate all kinds of synchronisation with third party devices. The user should decide which
  © Xsens Technologies B.V.   32 type  of  synchronisation  to  implement,  based  on  the  synchronisation  possibilities  of  their own  systems.  For  synchronisation,  one  system  must  be  in  control,  therefore  sends  the synchronisation signal (Master/Sync Out), and the other attached systems are controlled by and receive this signal (Slave/Sync In).  The  hardware  clock  of  the  Awinda  Station  is  very  accurate.  As  an  indication  of  the  clock accuracy,  the  error  in  the  Awinda  Station’s  clock has a maximum  of  1  µs  every  second  (1 ppm). Therefore,  in  general,  the  recommended  scenario  is  that  Xsens  is  the  master  sending  the control signals during synchronisation.  There are four synchronisation ports on the Awinda Station, onto which BNC connectors can be attached. Two sync ports (Line 1 and Line 2) are available for Sync  In and two for Sync Out.  For  each  synchronisation  port,  there  are  a  number  of  possible  synchronisation possibilities.  See Section 11.8 for synchronisation examples. 6.7.1 Synchronisation Settings in MT Manager NOTE: Set the synchronisation settings before carrying out the wireless configuration step. NOTE: It is not possible to set synchronisation settings during a wireless connection. To  configure  the  software  for  synchronisation  control,  go  to  >Tools,  >Synchronisation Configuration.
  © Xsens Technologies B.V.   33 6.7.2 Sync In Sync  In  means  that  a  third  party  device sends  a  control  signal  to  the  Awinda  Station.  The Awinda station can detect polarity changes on the input lines. This trigger may be a rising or falling edge as illustrated in the following figures:    When a trigger is detected on one of the input lines, the Awinda station can be configured to perform a certain action. A combination of any of the following are possible, on each Sync In port:  Event Description Start Recording External system sends a start recording trigger. On the Awinda Station, this will be the next frame. Stop Recording External system sends a stop recording trigger. Reset Timer The outgoing timer of the Awinda station will be set to 0. Trigger Indication The  Awinda  Station  receives  a  generic  signal,  determines  the timestamp of a trigger and sends it to MT Manager.  A number of parameters can be set for each action:
  © Xsens Technologies B.V.   34 Parameter Description Line The sync line to activate. Polarity Rising or falling edge, or rising and falling. Trigger Once It is not recommended to selected Trigger once, if more than one recording using synchronisation of multiple systems will be made. Skip First The number of initial occurrences of the sync trigger to skip. This is useful if a well-defined delay is expected, or if the external signal sends the same signal to generate both a start and stop recording. Take for example the command to start recording and stop recording, one signal sent to the Awinda Station can generate two different commands. Therefore if both start and stop are on the same sync line, skip first should be 1 for stop recording, ensuring that the second trigger, not the first, causes recording to stop. Skip Factor The number of occurrences of the sync trigger to skip in between trigger signals. In the same way that was described in Skip First (above), skip factor, for start and stop recording on one sync line should be set to 1, to ensure that the first trigger starts the recording and the second stops etc. 6.7.3 Important Notices for Sync In When  the  Awinda  Station  is  configured  to  start  recording  upon  receipt  of  a  trigger,  it initialises recording at the start of the following frame. The Awinda Station cannot trigger a start recording command between frames since data received in a given frame is measured in the  previous one. Therefore, delaying  the recording in this  way ensures that data is  not recorded prior to the external trigger indication.  Recording should not be stopped between frames, since data received in a given frame was measured  during  the  previous  frame.  Therefore,  the  Awinda  Station  stops  recording immediately after the current frame.  Rising  and  falling  edge  polarity:  This  command  is  particularly  useful  for  the  ''Trigger indication'' action for the following purposes:  An external system is connected and the behaviour with respect to its output signals is not exactly  known.  The  Awinda  system  can  be  configured  to  send  a  trigger  indication  to  the driver at every change of polarity. The user can then set the Awinda system  to record and log the incoming trigger indications (only one MTw is required). These logs can be correlated with the actual actions performed.  Another useful example is to detect when a switch action occurs. An example can be a foot-switch.  A  configured  trigger  indication  with rising  and  falling  edge  sensitivity  could  detect this.
  © Xsens Technologies B.V.   35 6.7.3.1 Sync In in MT Manager: When  Sync  In  is  in  use,  after  configuration,  and  when  ready  to  record,  users  should  click Record,  to  prepare  the  system  for  the  external trigger.  The  record icon  changes  from  the normal red dot to one with the pause symbol overlaid:   6.7.4 Sync Out Sync  Out  is  the  command  that  enable  the  Xsens  system  to  send  a  trigger  pulse  for synchronisation purposes. A control signal is sent via the Awinda Station, from MT Manager to the third party hardware. As with sync In, a combination of events are possible, based on a number of parameters. Event Description Start Recording Upon clicking the record button in MT Manager, the Awinda Station starts the recording and consequently sends a start recording trigger to the third party system. Stop Recording Upon clicking the record button in MT Manager, the Awinda Station stops recording and sends a stop recording trigger to the third party system. Go to Operational This feature gives the maximum flexibility because it speeds up the preparation of the instrumentation and the subject (if synchronising at the time of the operational mode) or, once the preparation is done, to synchronize and record data only when strictly necessary (if synchronising every time you record)  Frame Transition Measurement A frame transition at the station can be used to give a signal to the external system, indicating the end of the strap-down integration interval over which data is calculated. Selecting this option, the frame transition is sent from the moment that “Start Measuring” is selected. Frame Transition Recording See Frame transition Measurement Selecting this option, the frame transition is sent from the moment that a recording is started. This is a very useful option to implement, to ensure that during a recording, the clocks of the synchronised systems are known, ensuring that any drift can be compensated for.  The default polarity of the output line is low. However, for input triggers that assume high polarity,  the  polarity  of  the  line  must  be  set  beforehand.  This  is  possible,  using  'Go  to operational' with a polarity positive pulse and infinite pulse-width.  A number of parameters can be set for each action:
  © Xsens Technologies B.V.   36 Parameter Description Line The sync line to activate. Polarity Positive pulse (where the polarity is initially low [0V] and goes high [3.3V]). Negative pulse (where polarity is initially high [3.3V] and goes low [0V]). Trigger Once It is not recommended to selected Trigger once, if more than one recording using synchronisation of multiple systems will be made.  Skip First Number of initial sync pulses to skip. This command is useful if a well-defined delay is expected between the Xsens and the third party system. It may also be needed if the third party, like the Xsens system uses the same pulse properties to trigger different actions. See description provided above for Sync In. Skip Factor Number of sync pulses, between the sync pulses delivered, to skip. See Sync In Table description. Pulse Width Some systems wait for a signal of a minimum pulse width before generating the desired synchronisation action. The Awinda Station can send a pulse with a duration of up to 99ms to a third party system. It is not recommended to send a signal longer than a frame width.  Specify 0 ms to generate an infinite pulse width. 6.8 Orientation Reset In some situations, it may occur that the MTw sensor axes are not exactly aligned with the axes of the object of which the orientation has to be recorded. It may be desired to output the  orientation  and/or  calibrated  inertial  (and  magnetic)  data  in  an  object-fixed frame,  as opposed  to  a  sensor-fixed  frame.  Four  methods  have  been  added  to  the  software  to facilitate in obtaining the output in the desired coordinate frames.  1. Setting an arbitrary rotation matrix to rotate S to the chosen object coordinate system O. See Section 11.6.3. 2. A  heading  reset  that  redefines  the  X-axis  of  the  global  coordinate  frame  while maintaining  the  Z-axis  along  the  vertical  (also  known  as  “boresighting”).  After  the heading  reset  the  orientation  will  be  expressed with respect  to  the  new  global  (earth fixed) reference frame. See Section 11.6.4 3. An  object  reset  that  defines  how  the  MTw  is  oriented  with  respect  to  the  coordinate axes to which it is attached. After the object reset, both the inertial (and magnetic) and orientation data are expressed with respect to the axes of the object. See Section 11.6.5. 4. A combined object/heading reset, referred to as alignment. See Section 11.6.6.  NOTE:  For  all  co-ordinate  system  reset  functions  it  is  important  to  remember  that  the housing of the MTw cannot be considered an accurate reference. Placement and subsequent aligning must be done very carefully otherwise (alignment) errors may be induced.
  © Xsens Technologies B.V.   37  The  Orientation  Reset  menu  allows  the  orientation  of  the  MTw  to  be  reset  in  a number  of  ways.  To  reset  the  MTw,  align  it  in  the  correct  manner  and  select  the  type  of reset needed from the drop-down menu beside the icon indicated above. Determine if the reset should be applied to one or all MTw’s. If the reset should be applied to only one MTw, select the MTw  to be reset from the Device List, select the “Current Device”  radio button, then click the reset button. 6.9 Recording Data Before recording data, ensure that the directory stated in the File Control menu is correct.  To record data, use the red icon in the Recording & Playback menu.  Record button in the Playback & Recording menu When  the  data  is  recording  the  icon  appears  depressed.  To  stop  the  recording,  click  the same icon. Data is automatically saved in the directory specified. The record button will be depressed until all data is downloaded (flushed) from the trackers.   To review the data, graphically, open the .MTB file, open the desired type of graph (inertial, or  orientation  data)  and  select  the  “Play”  icon  in  the  Playback  &  Recording  menu.  The progress of the recorded file during playback is seen in the green progress bar at the bottom left-hand-side of the screen.  6.10 Saved and Exported Data MT  Manager  can  export  data  logged  in  .MTB  files  to  ASCII  format,  with  the  following content:  Sample Counter  – is always exported to ensure that  data from all MTw’s are correctly allocated.
  © Xsens Technologies B.V.   38  SDI  data  (Velocity  Increment,  Orientation  Increment).  See  Section  11.5  for  more information.  Inertial  (and  magnetic)  calibrated  sensor  data  (3D  acceleration,  angular  velocity, magnetic  field,  pressure).  Please  note  that  while  the  terminology  is  inertial  data,  the data received by MT Manager for the accelerometers and gyroscopes are actually data from the SDI. This means integrated values. This data has been converted to calibrated sensor data.  Orientation data  The output orientation can be presented in different conventions:  Unit normalised Quaternions (also known as Euler parameters)  Euler angles: roll, pitch, yaw (XYZ Earth fixed type, also known as Cardan)  Rotation Matrix (Direction Cosine Matrix)   Awinda wireless network properties  RSSI: Received Signal Strength Indicator (It is advised to use this to check what the signal strength was during measurements)  Trigger In timestamps  Status Byte
  © Xsens Technologies B.V.   39 Abbreviation Data Unit Counter Sample counter (-), wraps at 65535 Temperature Temperature inside housing o C VelInc_X Velocity increment from SDI, x-axis m/s VelInc_Y Velocity increment from SDI, y-axis m/s VelInc_Z Velocity increment from SDI, z-axis m/s OriInc_w Orientation increment quaternion from SDI, real component  Unit quaternion OriInc_x Orientation increment quaternion from SDI, x-axis Unit quaternion OriInc_y Orientation increment quaternion from SDI, y-axis Unit quaternion OriInc_z Orientation increment quaternion from SDI, z-axis Unit quaternion Acc_X Acceleration x-axis m/s2 Acc_Y Acceleration y-axis m/s2 Acc_Z Acceleration z-axis m/s2 Gyr_X Angular rate x-axis rad/s Gyr_Y Angular rate y-axis rad/s Gyr_Z Angular rate z-axis rad/s Mag_X Magnetic field x-axis arbitrary unit; magnetic field strength at Xsens is 1 Mag_Y Magnetic field y-axis arbitrary unit; magnetic field strength at Xsens is 1 Mag_Z Magnetic field z-axis arbitrary unit; magnetic field strength at Xsens is 1 Pressure Atmospheric pressure mBar Roll/Pitch/Yaw Orientation Euler angles format (3) deg Quat * Orientation quaternion format (4) Unit quaternion Mat [R#][C#] Rotation matrix format [Row][Column] (3x3). (Direction Cosine matrix) Unit vectors Trigger In 1 Awinda converted time stamp values of trigger indications sent to Sync In 1 of the Awinda Station Milliseconds Trigger In 2 Awinda converted time stamp values of trigger indications sent to Sync In 2 of the Awinda Station Milliseconds Status N/A for MTw and / or MT SDK 3.7 Beta  RSSI Received  Signal  Strength  Indicator  by  Station dBm
  © Xsens Technologies B.V.   40 Abbreviation Data Unit from each connected MTw  6.11 Application Software Development for the MTw The  MT  Manager  Windows®  GUI  application  software  created  by  Xsens  uses  exactly  the same  SDK/API  available  to  developers  (xsens_cmt.dll)  with  the  dynamic  library  interface. This is the same API that is provided for software development in the Software Development Kit (SDK). Source code for the lower levels of the API (drivers) are supplied for reference but are not recommended to use for application development on Windows or Linux.  Static LIBs as well as DLLs are provided for developers for both 32-bit and 64-bit platforms. The DLL also includes a COM interface for easy application development in applications that support the COM-interface, such as MATLAB, Excel, LabVIEW etc.  For  detailed  documentation  on  the  API  please  refer  to  the  Application  Programming Interface (API) reference documentation made available as HTML and the supplied example source code for C++, C#, LabVIEW and MATLAB.  From MT SDK 3.8 there is also a Linux version of the SDK.
  © Xsens Technologies B.V.   41 7 Xsens Peripheral Software 7.1 Magnetic Field Mapper (MFM) When an MTw is mounted to an object that contains ferromagnetic materials, the measured (Earth)  magnetic  field  can  become  distorted,  causing  errors  in  measured  orientation.  To correct  for  known  magnetic  disturbances,  for  example,  an  MTw  attached  to  a  steel prosthesis,  a  separate  software  product  has  been  developed  to  allow  users  to  remap  the magnetic  field  of  the  MTw.  This  software  is  called  Magnetic  Field  Mapper  (MFM)  and  is located  in  the  installation  file  of  MT  Manager.  In  this  directory  is  also  a  user  manual  for instructions on how to execute MFM, in terms of software steps and how to orientate the MTw  during the  process. The  user manual  for  the MFM  is  generic  since  it  is useful  for  all Xsens products.   First create  a wireless connection for the  given MTw (see Section 6.4.2, but pay particular attention to the instructions below): Note:    MFM  can  be  run  for  one  MTw  at  a  time.  Therefore  for  each  MTw  that  should  be mapped,  use  the  following  instructions,  1-3  depends  on  user  preference,  4-10  applies  to both methods of choice.  In MT Manager do the following:  Power off unnecessary MTw’s Wirelessly reject unnecessary MTw’s 1 Dock all MTw’s Undock all MTw’s 2 Power  off  all  but  one  MTw  in  the  device list Wireless configuration 3 Wireless configuration for remaining MTw Reject all but one MTw 4 Set update rate to 100Hz 5 Start Measuring 6 Close MT Manager 7 Activate MFM 8 Follow instructions for MFM 9 Close MFM 10 Repeat above for remaining MTw’s to be mapped.     7.2 Firmware Updater With  new  software  releases,  it  can  be  expected  that  new  firmware  is  required  for  the Awinda  Station,  Awinda  USB  Dongle  and  MTw’s.  Xsens  supplies  a  firmware  updater.  The firmware updater is found in START> All Programs > Xsens > Firmware Updater.
  © Xsens Technologies B.V.   42  It is important to select Awinda system and to follow the on-screen instructions. There are step by step instructions in the user manual. START > All Programs > Xsens >Documentation >Firmware Updater User Manual.  Note  that  the  maximum  amount  of  devices  that  the  firmware  updater  can  handle  for  an MTw system, is 16 devices. In theory this can be two MTw kits comprising for example: 2x Awinda Stations 2x Awinda USB Dongles 12x MTw’s (6 docked in each Awinda Station).
  © Xsens Technologies B.V.   43 8 Troubleshooting and Support Problem Possible cause Solution Installation is aborted due to previously installed version. Drivers are still present from the previous Xsens MT SDK installations. Use  Add/Remove  Programs  on the  Control  Panel  to  remove the previously installed version. Then  re-try  installing the  desired version.  After Wireless configuration MTw appears to spin.  Too much movement when entering measurement mode. Filter not initialised correctly.  Keep  motion  trackers  as  still  as possible  when  entering measurement  mode  from wireless  configuration.  See Settling  Time  (Section  3.3.2)  for details. Rescan  ports  to  reinitialise  the filters. The MTw is no longer visible in the Device List. It is possible that MTw’s have been removed and replaced too quickly in the Awinda Station, therefore no longer recognised in MT Manager. MTw is powered off. Place the MTw into another station socket. Note: When the MTw is left unplugged for a while (few minutes), the MT Manager will find it again. COM ports have been scanned, but no devices detected. It is possible that an incorrect baudrate has been selected; this means that the device cannot be found. Select “Auto” in the baudrate drop down menu. Then rescan all COM ports.  No Awinda Station/MTw’s found by MT Manager. The host PC/laptop may not have properly installed the USB drivers for the Awinda Station. Check all cable connections. Un-plug the USB cable and power supply from the Awinda Station, close MT Manager. Wait 30 seconds and then re-plug and reopen MT Manager. Awinda Station “freezes”. A corruption has occurred in the USB driver between the Awinda Station and the PC.  Unplug the USB cable and power supply from the Awinda Station, close MT Manager. Wait 30 seconds and then re-plug and reopen MT Manager. Following rescan, no Awinda Station, and /or fewer than expected MTw’s  Check all cable connections. Un-plug the USB cable and power supply from the Awinda Station, wait 30 seconds and then re-plug
  © Xsens Technologies B.V.   44 Problem Possible cause Solution found in the Device List. it. Re-entering wireless network after out of range, MTw(s) not detected in MTM. MTw and Awinda Station lost wireless connection for an undesired length of time. Re-dock the MTw(s) perform Wireless configuration step again (Section 6.4.2). Re-enable radio does not always find trackers used before.  Re-dock the MTw(s), rescan ports and perform Wireless configuration step again (Section 6.4.2). RSSI in Wireless configuration is full, while I cannot receive data from the MTw. MTw and Awinda Station no longer wirelessly connected. Re-dock the MTw(s) perform Wireless configuration step again (Section 6.4.2). MTw in Wireless Configuration is shown as disconnected, but RSSI appears to have a good strength. MTw and Awinda Station are not wirelessly connected.  Related to above issue. Re-dock the MTw(s), rescan ports and perform Wireless configuration step again (Section 6.4.2). A  discrepancy  of  a sample  count  is detected  between MTw’s  at  the beginning or  end  of an exported file. Due  to  the  nature  of  wireless transmission, this may occur. Always allocate exported data to a given sample count.  NB - also to prevent possible problems of missing samples.
  © Xsens Technologies B.V.   45 8.1 Customer Support Xsens  Technologies  B.V.  is  glad  to  help  you  with  any  questions  you  may  have  about  the MTw, or about the use of the technology for your application. Please use the FAQ or contact Xsens Customer Support:   Internet and FAQ: http://www.xsens.com/support  Telephone: Xsens HQ +31 88 97367 00 / Xsens US office 310-481-1800  To be able to help you, please mention your Motion Tracker Device ID (on the back of the device) and software license registration number in your e-mail.
  © Xsens Technologies B.V.   46 9 Warranty Liability Xsens Technologies B.V. warrants the products manufactured by it to be free from defects in material  and  workmanship  for  a  period  of  1  year  from  the  date  of  delivery.  Products  not subjected to misuse will be  repaired, replaced  or credit  issued  at the sole option of  Xsens Technologies  B.V.  Contact  Xsens  via  www.xsens.com/support  for  return  material authorization  (RMA)  prior  to  returning  any  items  for  calibration,  repair  or  exchange.  The product must be returned in its original packaging to prevent damage during shipping.  The warranty shall not apply to products repaired or altered or removed  from the original casing by others than Xsens Technologies B.V. so as, in Xsens Technologies B.V. opinion, to have  adversely  affected  the  product,  products  subjected  to  negligence,  accidents  or damaged by circumstances beyond Xsens Technologies B.V.’s control.  NOTE: Xsens reserves the right to make changes in its products in order to improve design, performance, or reliability.  Subject to the conditions and limitations on liability stated herein, Xsens warrants that the Product as so delivered shall materially conform to Xsens’ then current specifications for the Product, for a period of one year from the date of delivery. ANY LIABILITY OF XSENS WITH RESPECT  TO  THE  SYSTEM  OR  THE  PERFORMANCE  THEREOF  UNDER  ANY  WARRANTY, NEGLIGENCE,  STRICT  LIABILITY  OR  OTHER  THEORY  WILL  BE  LIMITED  EXCLUSIVELY  TO PRODUCT REPAIR, REPLACEMENT OR, IF REPLACEMENT IS INADEQUATE AS A REMEDY OR, IN XSENS' OPINION IMPRACTICAL, TO REFUND THE PRICE PAID FOR THE PRODUCT. XSENS DOES NOT  WARRANT, GUARANTEE,  OR  MAKE  ANY  REPRESENTATIONS REGARDING THE USE,  OR THE  RESULTS  OF  THE  USE,  OF  THE  PRODUCT  OR  WRITTEN  MATERIALS  IN  TERMS  OF CORRECTNESS,  ACCURACY,  RELIABILITY,  OR  OTHERWISE.  Xsens  shall  have  no  liability  for delays or failures beyond its reasonable control.
  © Xsens Technologies B.V.   47 10 Regulatory Notices 10.1 Radio Frequency Exposure and Emission The MTw  contains  a small radio transmitter  and  receiver. During communication  with  the Awinda  Station  it  receives  and  transmits  radio  frequency  (RF)  electromagnetic  fields (microwaves) in the frequency range 2400 of 2500 MHz (IEEE 802.15.4 PHY compliant). The output  power  of  the  radio  transmitter  is  very  low.  When  using  the  system,  you  will  be exposed to some of the transmitted RF energy. This exposure is well below the prescribed limits in all national and international RF safety standards and regulations.  Most modern electronic equipment, for example, in hospitals and cars, is shielded from RF energy. However, certain electronic equipment is not.  Therefore: Note:  This  equipment  emits  RF  energy  in  the  ISM  (Industrial,  Scientific,  Medical)  band. Please  insure  that  all  medical  devices  used  in  proximity  to  this  device  meet  appropriate susceptibility specifications for this type of RF energy (CE or FCC marked).  Turn  off  this  electronic  device  before  entering  an  area  with  potentially  explosive atmosphere. It is very rare, but any electronic device could generate sparks. Sparks in such areas could cause an explosion or fire resulting in bodily injury or even death. Areas with a potentially  explosive  atmosphere  are  often,  but  not  always,  clearly  marked.  They  include fuelling  areas,  such  as  petrol  station,  below  deck  on  boats,  fuel  or  chemical  transfer  or storage facilities, and areas where the air contains chemicals or particles, such as grain, dust, or metal powders.
  © Xsens Technologies B.V.   48 10.2 FCC Statement NOTE:  This  equipment  has  been  tested  and  found  to  comply  with  the  limits  for  a  Class  B digital  device,  pursuant  to  Part  15  of  the  FCC  Rules. These  limits  are  designed  to  provide reasonable  protection  against  harmful  interference  in  a  residential  installation.  This equipment generates, uses and can radiate radio frequency energy and, if not installed and used  in  accordance  with  the  instructions,  may  cause  harmful  interference  to  radio communications.  However,  there  is  no  guarantee  that  interference  will  not  occur  in  a particular  installation.  If  this  equipment  does  cause  harmful  interference  to  radio  or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:  Reorient or relocate the receiving antenna  Increase the separation between the equipment and receiver  Connect  the  equipment  into  an  outlet  on  a  circuit  different  from  that  to  which  the receiver is connected  Consult the dealer or an experienced radio/TV technician for help.
  © Xsens Technologies B.V.   49 10.3 CE Declaration of Conformity We, Xsens Technologies B.V., of Pantheon 6a  7521 PR Enschede The Netherlands  declare under our sole responsibility that our product:  MTw-38A##G## AWNDDNG AW-A  to  which  this  declaration  relates,  conforms  to  the  following  Standards  and  other Normative Documents:  EN 61326-1 (2006)  EN 61326-1 (2006)  EN 61000-3-2 (2006)  EN 61000-3-3 (1995) + A1 (2001) + A2 (2005) EN 60950-1: 2006 Safety of information technology equipment  Environment to be used is light industrial / laboratory  Class of emission is B.   January 13 2011 Enschede, the Netherlands    Per Slycke CTO Xsens Technologies B.V.
  © Xsens Technologies B.V.   50 10.4 FCC Declaration of Conformity We, Xsens Technologies B.V., of Pantheon 6a  7521 PR Enschede The Netherlands  declare under our sole responsibility that our product:  MTw-38A##G## AWNDDNG AW-A  to which this declaration relates, have been tested and found to comply with the limits for  a  Unintentional  Radiator  as  described  in  47  CFR  15  (2007  May,  04  Edition)  Class  B Digital Device, pursuant to Part 15 of the FCC Rules.  Operation is subject to the following two conditions: 1. This device may not cause harmful interference, and  2. This device must accept any interference received, including interference that may cause undesired operation.   January 13 2011 Enschede, the Netherlands    Per Slycke CTO Xsens Technologies B.V.
  © Xsens Technologies B.V.   51 11 Appendices 11.1 MTw Technical Specifications 11.1.1 MTw Performance  Angular velocity Acceleration Magnetic field Pressure Dimensions 3 axes 3 axes 3 axes - Full Scale ± 1200 deg/s ± 160 m/s2 ± 1.5 Gauss 300 -1100 mBar1 Linearity 0.1 % of FS 0.2 % of FS 0.2 % of FS 0.05 % of FS Bias stability 2 20deg/hr - - 100 Pa/year Noise 0.05deg/s/√Hz 0.003m/s2/√Hz 0.15mGauss/√Hz 0.85 Pa/√Hz Alignment error 0.1 deg 0.1 deg 0.1 deg - Bandwidth3 100Hz (max.) 100 Hz (max.) 20 Hz (max.) - 11.1.2 Orientation Performance Dynamic Range all angles in 3D Angular Resolution4 0.05 deg Static  accuracy (Roll/Pitch) <0.5 deg Static Accuracy5 (Heading) 1 deg Dynamic Accuracy6 2 deg RMS 11.1.3 MTw Physical Properties Accelerometers MEMS solid state, capacitative readout Rate gyroscope MEMS solid state, monolithic, beam structure, capacitive readout Magnetometer Magneto-Impedance sensor elements Barometer Piezo-resistive sensor element Weight 27g Housing dimensions 34.5 x 57.8 x 14.5mm (W x L x H)                                                             1 (-500 -.9000 m above sea level) 2 As measured from the Allan variance diagram. 3 Half of the chosen sampling rate. 4 1 σ standard deviation of zero-mean angular random walk 5 In homogenous magnetic environment 6 May depend on type of motion
  © Xsens Technologies B.V.   52 11.1.4 Schematics MTw Housing Specifications  11.1.5 Charging / Discharging MTw’s The MTw’s are equipped with LiPo batteries, with a capacity of 220mAh. Fully charged, it has a  run-time  of  2.5-3.5hrs, depending on  the  data  rate  and  temperature.  Charging  will  take ~1hrs at room temperature. Do not exceed charging ambient temperature of 0 °C to +45 °C.
  © Xsens Technologies B.V.   53  NOTE: If the MTw isn't used for a long time, please put them away half-charged. Store them in a cool and dry place 11.2 Awinda Station Technical Specifications The Awinda Station uses the Awinda protocol to receive and time-synchronize data from up to 32 MTw’s simultaneously.  Data  from  multiple  MTw’s  time-synchronized  to  within  10µs,  with  a  reasonable  radio link.  Charges up to 6 MTw’s simultaneously.  LED indicators for MTw status.  Synchronisation with third party devices The  Awinda  Station  has  four  AUX  sync  I/O  BNC  connectors  for  synchronisation  with  third party devices. These have TTL levels of 0-3.3V.  Power supply A power adapter is  shipped  with the MTw Development kit,  to  power the  Awinda Station (necessary for charging the MTw’s). The power adapters have EU/US/UK plugs and electrical properties: 100-240V AC/12 V DC 1.5A.  Communication The Awinda Station interfaces with the PC using a USB cable, supplied with the system.
  © Xsens Technologies B.V.   54 11.2.1 Schematics Awinda Station Housing Specifications  11.3 Awinda USB Dongle Technical Specifications The  Awinda  USB  Dongle  uses  the  Awinda  protocol  to  receive  and  time-synchronize  data from up to 32 MTw’s simultaneously.
  © Xsens Technologies B.V.   55  Data  from  multiple  MTw’s  time-synchronized  to  within  10µs,  with  a  reasonable  radio link.  LED indicators for MTw connectivity status.  Power supply The  USB  Dongle  uses  only  440mW  therefore  does  not  require  external  power  supply, meaning that it is ideal for outdoor use.  Communication The Awinda Station interfaces with the PC using a USB cable, supplied with the system.
  © Xsens Technologies B.V.   56 11.3.1 Schematics Awinda USB Dongle Housing Specifications  11.3.2 Physical, Electrical and RF Properties  MTw AWINDA Station Awinda Dongle Communication Wireless 2.4GHz/USB Wireless 2.4GHz/ USB Wireless 2.4GHz/
  © Xsens Technologies B.V.   57 interface USB Wireless transmit range indoor /outdoor ~20m / 70m ~50m ~20m Synchronization accuracy < 10µs <1ppm clock drift <1ppm clock drift Additional interfaces: NA 2 x Sync In (BNC) 2 x Sync Out (BNC) NA Operating voltage 4.65-5.25 V 4.65-5.25V / 12V 4.65-5.25V Power consumption1 ~265 mW 10W max2 < 440mW Battery runtime ~3-4 hrs3 NA NA Charge time ~1 hrs NA NA Temperature Operating Range -10oC to 60oC (discharge) -20 to 85oC -20 to 85oC Specified performance Operating Temperature Range 0oC to 55oC 0 to 55 oC 0 to 55 oC Housing Dimensions 34.5 x 57.8 x 14.5mm (W x L x H) 148 x 104 x 61.9 mm (L x W x H)  Note: Awinda dimensions with antenna attached, but not raised. 45x20.4x10.6mm with USB connector 33x20.4x10.6mm without Weight 27g 200g 8g                                                            1 Power consumption for the MTw depends on the chosen frame rate. 2 Power consumption during charging of 6 empty MTw’s. 3  Battery  runtime  when  fully  charged  depends  on  the  chosen  frame  rate  and  ambient temperature.
 © Xsens Technologies B.V.   58 11.4 Xsens Kalman Filter The orientation of  the MTw is  computed by Xsens Kalman Filter for 3  degrees-of-freedom (3DoF) orientation (XKF-3w). XKF-3w uses signals of the rate gyroscopes, accelerometers and magnetometers  to  compute  a  statistical  optimal  3D  orientation  estimate  of  high  accuracy with no drift for both static and dynamic movements.  The design of the XKF-3w algorithm can be explained as a sensor fusion algorithm where the measurement of  gravity  (by  the  3D  accelerometers)  and  Earth  magnetic  north  (by  the  3D magnetometers)  compensate  for  otherwise  slowly,  but  unlimited,  increasing  (drift)  errors from the integration of rate of turn data (angular velocity from the rate gyros). This type of drift  compensation  is  often  called  attitude  and  heading  referenced  and  such  a  system  is often  called  an  Attitude  and  Heading  Reference  System  (AHRS).  For  the  MTw,  a  specific Xsens  Kalman  Filter  (XKF-3-w)  has  been  developed  to  deal  with  the  nature  of  wireless transmissions (e.g. irregular  updates  due  to  temporal  packets  losses) and the use  of  high-accuracy strap down integration. In-depth documentation/whitepapers will be provided at a later date. For specific questions, please contact support@xsens.com. 11.4.1 Using the Acceleration of Gravity to Stabilize Inclination (Roll/Pitch) XKF-3w  stabilizes  the  inclination  (i.e.  roll  and  pitch  combined,  also  known  as  “attitude”) using the accelerometer signals. An accelerometer measures gravitational acceleration plus acceleration due to the movement of the object with respect to its surroundings.  XKF-3w uses the assumption that on average the acceleration due to the movement is zero. Using this assumption, the direction of the gravity can be observed and used to stabilize the attitude. The orientation of the MT in  the gravity field is accounted for so that centripetal accelerations  or  asymmetrical  movements  cannot  cause  a  degraded  orientation  estimate performance.  This assumption is surprisingly powerful, almost all  moving objects  undergo accelerations if they are moving, but in most cases the average acceleration with respect to the environment during some period of time is zero. The key here is the amount of time over which the acceleration must be averaged for the assumption to hold. During this time, the rate  gyroscopes  must  be  able  to  track  the  orientation  to  a  high  degree  of  accuracy.  In practice, this limits the amount of time over which the assumption holds true. For the class of  miniature  MEMS  rate  gyroscopes  used  in  the  MT  this  period  of  time  is  about  10-20 seconds maximum.  However, for some applications this assumption does not hold. For example an accelerating automobile may generate significant accelerations for time  periods lasting longer than the maximum time the MT’s rate gyroscopes can reliably keep track of the orientation. This will severely  degrade  the  accuracy  of  the  orientation  estimates  with  XKF-3,  because  the  use scenario (application) does not match the assumptions made. Note however, that as soon as the movement does again match the assumptions made, XKF-3w will recover and stabilize. The recovery to optimal accuracy can take some time.
  © Xsens Technologies B.V.   59 NOTE:  To  be  able  to  accurately  measure  orientations  as  well  as  position  in  applications which can encounter long term accelerations, Xsens offers a solution that incorporates a GPS receiver (the MTi-G). 11.4.2 Using the Earth Magnetic Field to Stabilise Heading (Yaw) By default, the heading is stabilised using the local (earth) magnetic field. In other words, the measured magnetic field is used as a compass. If the local Earth magnetic field is temporarily disturbed,  XKF-3w  will  track  this  disturbance  instead  of  incorrectly  assuming  there  is  no disturbance. However, in case of structural magnetic disturbance (>10 to 20 s) the computed heading will  slowly converge  to  a  solution using  the 'new'  local magnetic north. Note that the magnetic field has no direct effect on the inclination estimate.  If  the  MTw  is  rigidly  strapped  to  an  object  containing  ferromagnetic  materials,  structural magnetic disturbances will be present. Using an Xsens a technique 'magnetic field mapping' (i.e.  a  3D  calibration  for  soft  and  hard  iron  effects),  these  magnetic  disturbances  can  be completely accounted for, allowing the MTw to be used as if it would not be secured to an object containing ferromagnetic materials. 11.4.3 Initialisation The XKF-3w algorithm not only computes orientation, but also keeps track of variables such as  sensor  biases or  properties  of  the  local  magnetic field.  For  this  reason,  the  orientation output may need some time to stabilize once the MTw is put into measurement mode. Time to  obtain  optimal  stable  output  depends  on  a  number  of  factors.  An  important  factor determining stabilizing time is determined by the time to correct for small errors on the bias of the rate gyroscopes. The bias of the rate gyroscope may slowly change due to different effect such as temperature change or exposure to impact. To reduce stabilizing time, the last computed gyroscope bias can be stored in the sensor unit non-volatile memory. If the MT is used after only a short period of power-off the gyro biases will generally not have changed a lot and the stabilizing time will typically be less than 10 seconds. Furthermore, XKF-3w will converge  faster  and  reach  optimal  robustness  faster  if  it  is  started  in  an  area  without magnetic disturbances. 11.5 Strap Down Integration1 Strap down integration (SDI)  is  a method used  to compute an orientation/position change given  an  angular  velocity  and  linear  acceleration  of  a  rigid  body.  Angular  velocity  and acceleration data in the MTw is sampled at a very high frequency to maintain accuracy under very dynamic conditions such as vibrations and impacts. The sampling frequency is too high to  be  transmitted wirelessly,  and  would typically present a computational  load that  is  too high on the receiving host device (e.g. PC). Therefore the data that has been sampled at a high  frequency  is  digitally  filtered  and  down-sampled  to  600  Hz  and  calibrated  using  the                                                            1  Further  information  about  strap  down  integration  for  the  MTw  is  available  in  the  MTw Whitepaper.
  © Xsens Technologies B.V.   60 individual device  calibration1 values on the embedded microprocessor  (MCU) of the  MTw. Based  on  this  data  the  MTw  further  calculates  velocity  increments  and  orientation increments using an SDI algorithm. The main advantage of using the SDI algorithm is that full 3D tracking accuracy can be maintained even if the output update rate from the MTw is very low (<100 Hz). An additional advantage is that the MTw can continue to track the 3D motion internally when facing transient data loss in the RF transmission and immediately report the full 3D velocity and  orientation increment as  soon  as the RF link  is  restored  (data packets again received by the Awinda Station), without the need to re-transmit all the data that was lost which would a) cause a large delay during real-time tracking b) use a lot of precious RF bandwidth  and  consume  unnecessary  power.  The  specific  use  of  SDI  data  in  combination with such a specialized RF protocol, Xsens has named the Awinda protocol2.  NOTE: Velocity and orientation increments resulting from the embedded  SDI can easily be converted  back  to  acceleration  and  angular  velocity  values.  At  high  enough  update  rates there is no or negligible loss  of  accuracy  due to this conversion.  What  is “high enough” is partly also determined by the dynamics of the movement. Xsens recommends the use of SDI values rather  than acceleration and angular velocity values  for further calculations as they represent the highest degree of accuracy.                                                              1  The  devices  are  calibrated  at  the  factory  by  Xsens  and  is  a  highly  sophisticated  process compensating  for  component  errors  that  are  not  stochastic  (i.e.  they  can  be  modeled). Compensation  models  include  bias,  gain,  misalignment,  g  sensitivity,  temperature  effects, etc. 2 Patents pending.
  © Xsens Technologies B.V.   61 11.6 Coordinate Systems 11.6.1 Calibrated Sensor Readings All calibrated sensor readings (accelerations, angular velocity, earth magnetic field, pressure) are in the right handed Cartesian co-ordinate system as defined in the figure below. This co-ordinate system is body-fixed to the device and is defined as the sensor co-ordinate system (S). The 3D orientation output is discussed in Section 11.6.2.  The co-ordinate system is aligned to the external housing of the MTw.   High  accuracy  alignment  between  the  (plastic)  housing  and  the  sensor-fixed  output coordinate system (S) is not possible for the MTw for obvious reasons. The actual alignment between the S co-ordinate system and the bottom part of the plastic housing is guaranteed to <3o.  The non-orthogonality  between  the  axes of the  body-fixed  co-ordinate system,  S,  is <0.1o. This also means that the output of 3D linear acceleration, 3D angular velocity (gyro) and 3D magnetic field data all will have orthogonal XYZ readings within <0.1o. 11.6.2 Orientation Coordinate System The MTw calculates the orientation between the sensor-fixed co-ordinate system, S, and a earth-fixed reference co-ordinate system, G. By default, the local earth-fixed reference co-ordinate system used is defined as a right handed Cartesian co-ordinate system with:      X positive when pointing to the local magnetic North.  Y according to right handed co-ordinates (West).  Z positive when pointing up.  The 3D orientation output (independent of output mode, see Section 11.7) is defined as the orientation between the body-fixed co-ordinate system, S, and the earth-fixed co-ordinate system, G, using the earth-fixed co-ordinate system, G, as the reference co-ordinate system. Z Y X
  © Xsens Technologies B.V.   62   Please refer to Section 11.7 for further details on output co-ordinate systems and different options to redefine the output co-ordinate systems.  True North vs. Magnetic North As defined above the output coordinate system of the MTw is with respect to local Magnetic North.  The  deviation  between  Magnetic  North  and  True  North  (known  as  the  magnetic declination) varies depending on your location on earth and can be roughly obtained from various models of the earth’s magnetic field as a function of latitude and longitude. 11.6.3 Arbitrary Alignment If  the  measured  kinematics  is  required  in  an  object  coordinate  system  (O)  with  a  known orientation  with  respect  to  standard  sensor  coordinate  frame  (S),  the  object  alignment matrix can also be set with an arbitrary but known orientation. This is useful if the MTw can only be fastened in one specific orientation.  The  object  alignment  matrix  (ROS)  is  applied  to  the  output  data  (RGS)  according  to  the following equations. For 3D orientation data:  TGO GS OSR R R For inertial and magnetic data: OSROSss  Example The object alignment matrix is given by: Local Magnetic North Local vertical G  Local tangent plane Z up, default  X Z Y S  MTw default co-ordinate system  Z up, default z x y
  © Xsens Technologies B.V.   63 0 0 10 1 01 0 0OSR  Here  O  represents  the  object  coordinate  system  and  S  the  standard  sensor  coordinate system described in Section 11.6.2. Once the object alignment matrix is set to ROS, the sensor output will be expressed with respect to the object coordinate system  shown in figure (b), below.       a  b 11.6.4 Heading Reset It is often important that the global Z-axis remains along the vertical (defined by local gravity vector), but the global X-axis has to be in another direction. In this case a heading reset may be used,  this is  also known as  “bore sighting”. When performing  a heading reset, the new global  reference  frame  is chosen  such  that  the  global  X-axis points  in  the  direction of the sensor  while  keeping  the  global  Z-axis  vertical  (along  gravity,  pointing  upwards).  In  other words: The new global frame has the Z axis along gravity, pointing upwards, the X-axis in the plane spanned by the vertical and the sensor X-axis, perpendicular to the global Z-axis and the Y-axis such that a right handed coordinate system is formed. NOTE: After a heading reset, the yaw may not be exactly zero, this occurs especially when the X-axis is close to the vertical. This is caused by the definition of the yaw when using Euler angles, which becomes unstable when the pitch approaches ± 90 deg. 11.6.5 Object Reset The object reset function aims to facilitate in aligning the MT coordinate frame (S) with the coordinate frame of the object to which the MT is attached (O). After an object reset, the S coordinate frame is changed to S’ as follows:  the S’ Z-axis is the vertical (up) at time of reset. Z Y X Z X Y
  © Xsens Technologies B.V.   64  the S’ X-axis equals the S X-axis, but projected on the new horizontal plane.  the S’ Y-axis is chosen as to obtain a right handed coordinate frame.  NOTE: Once this object reset is conducted, both inertial (and magnetic) and orientation data will be output in the new coordinate frame (S’).  The object reset can be used to set the MTw coordinate frame to that of the object to which it is attached (see figure below). The MTw has to be fixated in such a way that the X-axis is in the XZ-plane of the object coordinate frame (situation A). This means that the MTw can be used to identify the X-axis of the object. To preserve the global vertical, the object must be oriented such that the object z-axis is vertical. The object reset causes the new S’ coordinate frame and the object coordinate frame to be aligned (situation B).  NOTE: Since the sensor X-axis is used to describe the direction of the object X-axis, the reset will not work if the sensor X-axis is aligned along the Z-axis of the object.  MTw coordinate  frame  before (A) and  after (B) object  reset. The new  Z-axis of the sensor coordinate frame will be along the vertical. The new direction of the X-axis will be the old X–axis that is projected onto the horizontal plane. 11.6.6 Alignment Reset The  alignment  reset  combines  the  Object  reset  and  the  Heading  reset  in  a  single  time instant.  This  has  the  advantage  that  all  co-ordinate  systems  can  be  aligned  with  a  single action. Note that the new global reference x-axis (heading) is defined by the object X-axis (to which XZ-plane of the MTw has been aligned).   NOTE: Once this alignment reset is conducted, both inertial (and magnetic) and orientation data will be output with respect to the new S’ coordinate frame. new  MTw coordinate frame (S’) Object coordinate  frame (O) x x x z B. A. MTw coordinate  frame (S) Object coordinate  frame (O) y x z z z
  © Xsens Technologies B.V.   65 11.7 Orientation Output Modes The  orientation,  calculated  by  the  MTw  is  the  orientation  of  the  sensor-fixed  co-ordinate system  (S)  with  respect  to  a  Cartesian  earth-fixed  co-ordinate  system  (G).  The  output orientation can be presented in different parameterizations:   Unit Quaternions (also known as Euler parameters)  Euler angles1: roll, pitch, yaw (XYZ Earth fixed type, also known as Cardan or aerospace sequence)  Rotation Matrix (directional cosine matrix)  A  positive  rotation  is  always  “right-handed”,  i.e.  defined  according  to  the  right  hand  rule (corkscrew rule). This means a positive rotation is defined as clockwise in the direction of the axis of rotation.  11.7.1 Quaternion Orientation Output A unit quaternion vector can be interpreted to represents a rotation about a unit vector n through an angle α. ( ( ), ( ))22GSq cos sinn A  unit  quaternion  itself  has  unit  magnitude,  and  can  be  written  in  the  following  vector format; qGS = (q0,q1,q2,q3) |q| = 1 Quaternions are an efficient, non-singular description of 3D orientation and a quaternion is unique up to sign: q = -q An  alternative  representation of a  quaternion is as  a  vector  with a  complex  part,  the  real component is the first one, q0.                                                              1 Please note that  due to the definition of Euler  angles there is a mathematical singularity when the sensor-fixed x-axis is pointing up or down in the earth-fixed reference frame (i.e. pitch is close to ±90 deg. This singularity is in no way present in the quaternion or rotation matrix output mode.
  © Xsens Technologies B.V.   66 The inverse (qSG) is defined by the complex conjugate (†) of qGS. The complex conjugate can be calculated: †0 1 2 3( , , , )GS SGq q q q q q     As  defined  here  qGS  rotates  a  vector  in  the  sensor  co-ordinate  system  (S)  to  the  global reference co-ordinate system (G). †GS GS GS SGq q q qG S Sx x x Hence, qSG rotates a vector in the global reference co-ordinate system (G) to the sensor co-ordinate system (S), where qSG is the complex conjugate of qGS. 11.7.2 Euler Angles Orientation Output Mode The  definition  used  for  'Euler-angles'  here  is  equivalent  to  'roll,  pitch,  yaw/heading'  (also known  as  Cardan).  The  Euler-angles  as  orientation  output  are  provided  as  XYZ  Earth fixed type (subsequent rotation around global X, Y and Z axis, also known as aerospace sequence).   φ = roll1 = rotation around XG, defined from [-180o…180 o]  θ = pitch2  = rotation around YG, defined from [-90 o …90 o]  ψ = yaw3 = rotation around ZG, defined from [-180 o …180 o]  NOTE: Due to the definition of Euler angles there is a mathematical singularity (gimbal lock) when the sensor-fixed X-axis is pointing up or down in the earth-fixed reference frame (i.e. pitch approaches ±90o).  This singularity  is  in  no  way present in  the  quaternion or rotation matrix output mode. The singularity cannot be compensated for but only avoided using the rotation  matrix  output,  then  manually  extract  Euler  Angles  by  using  different  Euler sequences4.  The Euler-angles can be interpreted in terms of the components of the rotation matrix, RGS, or in terms of the unit quaternion, qGS;  1132 2 3 0 12233 0 31131 1 3 0 2111 2 0 3212211 0 122tan tan 2 2 1sin ( ) sin (2 2 )22tan tan 2 2 1GSGSGSR q q q qR q qR q q q qq q q qRR q q                                                                             1 “roll” is also known as: “bank” 2  “pitch” is also known as: “elevation” or “tilt” 3 “yaw” is also known as: “heading”, “pan” or “azimuth” 4  Woltring  HJ.  3-D  attitude  representation  of  human  joints:  A  standardization  proposal. Journal of Biomechanics. 1994;27 (12):1399-1414.
  © Xsens Technologies B.V.   67 Here, the arctangent (tan-1) is the four quadrant inverse tangent function.  NOTE: that the output is in degrees and not radians. 11.7.3 Rotation Matrix Orientation Output Mode The  rotation  matrix  (also  known  as  Direction  Cosine  Matrix,  DCM)  is  a  well-known, redundant  and  complete  representation  of  orientation.  The  rotation  matrix  can  be interpreted as the unit-vector components of the sensor coordinate system S expressed in G. For  RGS  the  unit  vectors  of  S  are  found  in  the  columns  of  the  matrix,  so  column  1  is  XS expressed  in  G  etc.  A  rotation  matrix  norm  is  always  equal  to  one  (1)  and  a  rotation  RGS followed by the inverse rotation RSG naturally yields the identity matrix I3. ||R|| = 1 RGSRSG = I3  The rotation matrix, RGS, can be interpreted in terms of quaternions; 2 2 2 20 1 2 3 1 2 0 3 0 2 1 32 2 2 20 3 1 2 0 1 2 3 2 3 0 12 2 2 21 3 0 2 2 3 0 1 0 1 2 3220 1 1 2 0 3 1 3 0 2221 2 0 3 0 2 2 3 0 1132 2 2 22 2 2 22 2 2 22 2 1 2 2 2 22 2 2 2 1 2 222GSq q q q q q q q q q q qR q q q q q q q q q q q qq q q q q q q q q q q qq q q q q q q q q qq q q q q q q q q qq q q                    220 2 2 3 0 1 0 32 2 2 2 1q q q q q q q    or in terms of Euler-angles (according to the XYZ Euler sequence); cos sin 0 cos 0 sin 1 0 0sin cos 0 0 1 0 0 cos sin0 0 1 sin 0 cos 0 sin coscos cos sin sin cos cos sin cos sin cos sin sincos sin sin sin sin cos cos cos sin siZ Y XGSR R R R                                                       n sin cossin sin cos cos cos        As  defined  here RGS,  rotates  a  vector  in  the  sensor  co-ordinate  system  (S)  to  the  global reference system (G):  ()TGS SGRRG S Sx x x  It follows naturally that, RSG rotates a vector in the global reference co-ordinate system (G) to the sensor co-ordinate system (S).  For the rotation matrix (DCM) output mode it is defined that:
  © Xsens Technologies B.V.   68  11 12 1321 22 2331 32 33GSa d g R R RR b e h R R Rc f i R R R                 SGa b cR d e fg h i  Here, also the row-order/column-order is defined.  11.8 Synchronisation Examples 11.8.1 Start and stop recording of third party devices using single pulse Third party device starting and stopping recording of Xsens system, on Line 1 of the Sync In port.  The output definition in rotation matrix (DCM) output mode is:  MTData DATA =    MID 50 (0x32)   All  data  elements  in  DATA  field  are  FLOATS  (4  bytes)  ,  unless  specified  otherwise  by modifying the OutputSetting Data Format field. ihgfedcba
  © Xsens Technologies B.V.   69  Select Start Recording Check  the  check  box  for Line 1 Polarity: Rising Edge1 Trigger Once: Unchecked2 Skip First = 0 Skip  Factor  =  1  (so  that every other pulse will start a  recording  in  MT Manager)  Select Stop Recording Check  the  check  box  for Line 1 Polarity: Rising Edge  Check  the  check  box  for Trigger Once: Unchecked Skip  First  =  1  (first  trigger starts  recording,  so  it should  not  also  send  a signal  to  stop  -  or  this causes  confusion  for Awinda Station) Skip  Factor  =  1  (so  that every other pulse will stop a  recording  in  MT Manager)  The above example indicates how to allow a signal of 3.3V enter the Sync In 1 port, of the Awinda  Station.  The  first  upward  going  pulse  (and  subsequent  odd  numbered  pulses), received  on  the  Awinda  Station,  will  start  recording  (Polarity  =  rising  edge).  The  second upward  going  pulse  (and  subsequent  even  numbered  pulses),  received  on  the  Awinda Station, will stop recording.  11.8.2 Start and stop recording of third party devices with infinite pulse width It is of course also possible, to configure that for example the upward rising edge causes the start of recording and the negative direction edge causes stop recording, this may be useful in the event that a third party devices sends a pulse of infinite length.   To do this, the following settings should be input:                                                            1 Note that this setting depends on the signal from third party system. 2 To ensure that a series of recordings can be made.
  © Xsens Technologies B.V.   70  Select Start Recording Check  the  check  box  for Line 1 Polarity: Rising Edge Trigger  Once:  Uncheck  (if more  than  one  recording desired) Skip first = 0 Skip factor = 0  Select Stop Recording Check  the  check  box  for Line 1 Polarity: Falling Edge Trigger  Once:  Uncheck  (if more  than  one  recording desired) Skip first = 0 Skip factor = 0 11.8.3 Start and stop recording of third party devices including trigger indication pulses In  some  instances  it  may  be  desired  to  have  a  trigger  indication  in  the  data,  for  example using a manual trigger button, or using an external clock. The following example shows how to do this. Note: The trigger indication below has been indicated in this example as coming through via the Sync In 2 channel, while start, stop recording and reset timer come through in the Sync In  1.if  Sync  In  1  is  also  used  for  the  trigger  indication,  one  should  additionally  insert  the amount  of  pulses expected between  the  start  and  stop  recording,  therefore  changing  the skip factor for stop recording to a large number equivalent to the number of pulses expected between start and stop recording. If this is known, it can be very efficient, otherwise it may be  limiting.  The  example  shows  a  simplified  method,  independent  of  time  needed  for recording or number of trigger pulses expected.
  © Xsens Technologies B.V.   71  Use  the  setting  of  11.8.1. In addition: Select Reset Timer Check  the  check  box  for Line 1 Polarity: Rising Edge Trigger Once: Uncheck Skip first = 0 Skip factor = 1  Select Trigger Indication Check  the  check  box  for Line 2 Polarity: Rising Edge Trigger Once: Uncheck Skip first = 0 Skip factor = 0 Note: Stop recording time may not be on the last sample recorded. Stop recording timestamp  is showed in  both Trigger In 1  and 2,  independent if the trigger was set on Sync In1 or Sync In 2, this is because the signal comes directly from the Awinda Station, independent of the line used. Trigger Indications can be exported to ASCII using the exporter and selecting the Trigger In 1 and / or Trigger In 2 in the preferences menu. Reset  timer resets  the  timer of the sync events  (the amount of milliseconds shown in  the Trigger In events when the data is exported. The exported sample counter, always exported as the first column will not be reset. In any synchronisation situation, there should only be one master. It is necessary to elect a master, either one of the connected Awinda Stations, or a third party device. 11.8.4 Synchronising Two Awinda Stations Using more than one Awinda Station per MT Manager is possible. While the data received from  each  MTw  to  each  Awinda  is  perfectly  time  synchronised,  the  time  synchronisation between the Awinda Stations themselves, running in MT Manager has not been tested. One way  of  ensuring  good  time  synchronisation  between  the  Awinda  Stations  is  to  use  two separate  PCs,  connect  each  Awinda  Station  to  a  given  PC  and  synchronise  the  Awinda Stations as with a third party device.
  © Xsens Technologies B.V.   72 To  do this, select which Awinda Station (and MT Manger)  will provide  the Sync Out  signal (connect  the  BNC  to  the  correct  port)  and  which  will  receive  the  Sync  In  signal  (ensure correct  BNC port connection).  The  following  settings  have  been  successfully  tested  in  MT  Manager  to  start  and  stop  a series of recordings using one Awinda Station as the control: Sync In Sync Out Start Recording Stop Recording  Start Recording Stop Recording   Rising Edge  Skip First = 0  Skip Factor = 1  Rising Edge  Skip First = 1  Skip Factor = 1  Positive Pulse  Skip First = 0  Skip Factor = 0  Pulse Width = 10ms  Positive Pulse  Skip First = 0  Skip Factor = 0  Pulse Width = 10ms 11.8.5 Synchronising with Noraxon EMG Synchronisation  was  successfully  tested  between  MT  Manager  and  Noraxon  TeleMyo system.  The steps described below describe how to make it possible for the Awinda Station to send a synchronisation  signal  (Xsens  is  Sync  Out  and  Noraxon  is  Sync  In)  and  how  to  receive  the synchronisation signal (Noraxon is Sync Out, Xsens Sync In). 11.8.5.1 Awinda Station Sends Sync Signal (Noraxon Receives Sync Signal) Hardware requirements: Noraxon Hardware Xsens Hardware  Wireless EMG transmitters  1 TeleMyo DTS (plus antenna)  MTw  Awinda Station  Both  systems  of  course  also  need  related  cables  to  connect  to  each  other  (with  BNC connectors at each end) and a USB cable to connect to the PC.  In addition to the normal MTw hardware  setup, also connect  the BNC connector  from the TeleMyo DTS to Sync Out 1 on the Awinda Station. Connect the USB connection between the TeleMyo DTS and the PC. When switched on, the DTS will display “USB ready”.
  © Xsens Technologies B.V.   73 11.8.5.2 Software Setup in MT Manager Synchronisation on Sync Out Line 1: Sync Out  Select Start Recording   Check the check box for Line 1  Polarity: Rising Edge  Trigger Once: Uncheck  Skip first = 0  Skip factor = 0  Pulse width = 10 ms  Select Stop Recording  Check the check box for Line 1  Polarity: Rising Edge   Trigger Once: Uncheck  Skip First = 0  Skip Factor = 0  Pulse width = 10 ms   Set up the wireless configuration in MT Manager. 11.8.5.3 Software Setup Noraxon MyoResearch Software: The example given below is for is gait analysis, measuring the medial gastrocnemius, tibialis anterior, semitendinosus and the rectus femoris. For an 8-Channel EMG system, Channel 9 is selected as the synchronisation line in the Noraxon MyoResearch Software. If a 16 channel system is in use, this is the 17th channel.   Return to the main menu, under  >Measuring Options, go  to  >Recording Options,  then  >Triggering tab.   Check the check box beside “Start Recording”;  Go to the drop down menu beside “When Channel”, select “Sync”;  Select  Rises  Above  (ensure  that  this  is  also  the  direction  indicated  on  the  mini-receiver);  Input e.g. 0.5V  Longer than 5ms  Repeat settings for Stop Recording.  Navigate further through the software.
  © Xsens Technologies B.V.   74  The Noraxon software initialises the EMG signals.  When this screen is reached, click record, on the bottom left hand side of the screen on the Noraxon software.  The software indicates that it is waiting for the trigger.
  © Xsens Technologies B.V.   75  Press Record in MT Manager, the button is depressed and the Noraxon software indicates that recording has started.  Repressing record in MT Manager will stop the recording on both systems, where Noraxon will again indicate waiting for start trigger. 11.8.5.4 Awinda Station Receives Sync Signal (Noraxon Sends Sync Signal) For  the  Xsens  system  to  send  the  synchronisation  commands,  the  mini-receiver  from Noraxon is not needed.  Hardware requirements: Noraxon Hardware Xsens Hardware  Wireless EMG transmitters  1 TeleMyo DTS (plus antenna)  1 TeleMyo mini-receiver (plus antenna)  MTw  Awinda Station  Both  systems  of  course  also  need  related  cables  to  connect  to  each  other  (with  BNC connectors at each end) and a USB cable to connect to the PC.  In addition to the normal MTw hardware setup, set up the hardware of the Noraxon system as follows: USB port of TeleMyo mini-receiver to USB of PC. Connect jack connector to Sync Out port of TeleMyo mini-receiver to BNC connection Sync In 1 of Awinda Station.
  © Xsens Technologies B.V.   76 Manual trigger pulse, jack connector to Sync In port of TeleMyo minirecevier. Connect the external antenna to the TeleMyo DTS. When successfully connected and switched on, the TeleMyo DTS will display “WiFi ready”. 11.8.5.5 Software Setup: MT Manager  Synchronisation on the Sync In Line 1 port: Sync In  Select Start Recording  Check the check box for Line 1  Polarity: Rising Edge  Trigger Once: Uncheck  Skip first = 0  Skip factor = 1  Select Stop Recording  Check the check box for Line 1  Polarity: Rising Edge   Trigger Once: Uncheck  Skip First = 1  Skip Factor = 1  Set up the wireless configuration in MT Manager.  To initialise recording, click the Record button. To indicate that MT Manager is waiting for an external  pulse,  the  icon  changes  from  the  normal  red  dot  to  one  with  the  pause  symbol overlaid, as shown in Section 6.7.2. 11.8.5.6 Software Setup: Noraxon MyoResearch Software: Based  on  the  output  settings  described  for  MT  Manager,  the  settings  for  Noraxon MyoResearch  software  can  remain  the  same.  The  difference  is  that  instead  of  the  trigger pulse  coming  from  the  record  button  in  MT  Manager,  this  now  comes  from  the  manual button  connected to  the mini-receiver.  Additionally, the  mini-receiver  should be  set  up  as follows:  Go to the hardware menu;  Select the TeleMyo mini-receiver from the list of icons;  Select: settings;  Select: Configure;  Ensure that the wireless sync is “External Pulse” and Input Range is ±5V
  © Xsens Technologies B.V.   77  The rest of the software setup is the same as described in Section 11.8.5.6 above. However, instead of clicking Record in MT Manager, one should click the hardware trigger supplied by Noraxon, to generate a manual trigger to both systems.

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