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.
Revisions Revision A B Date 14 January 2011 15 April 2011 By CMO CMO C 15 August 2011 CMO D 4 November 2011 CMO E 14 February 2012 CMO F 9 January 2013 MHA Changes First version. Updated for 3.7 Beta Updated Wireless configuration menu Updated Wireless States Additional Functionality: Stand-by Synchronisation with 3rd party devices + examples Added Rotation Matrix export description Added note about not using maximum update rate to ensure retransmissions are possible during recordings.
Table of Contents 1 Introduction 1 2 Content Overview 2 3 4 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 Getting Started 4 3.1 Hardware Setup 4 3.2 Software Installation 4 3.3 Tips for Best Practice 4 Hardware 8 4.1 Motion Trackers (MTw) 8 4.2 Awinda Station 11 4.3 Awinda USB Dongle 12 4.
6.11 7 Application Software Development for the MTw Xsens Peripheral Software 40 41 7.1 Magnetic Field Mapper (MFM) 41 7.2 Firmware Updater 41 8 Troubleshooting and Support 8.1 9 43 Customer Support 45 Warranty Liability 10 46 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.
Abbreviations and Terms Term Quaternion Euler Angles Awinda Protocol Strap Down Integration Delta Angle Delta Velocity Personal Area Network Body Area Network Abbreviation BAN BNC DOF MT MTB MTM PAN SDI SDK TTL XFF XKF-3 XKF-3w Description An orientation representation of complex numbers. A unit length quaternion is a convenient parameterization of rotations. Representation of the spatial orientation of any frame of the space as a sequence of rotations from a reference frame.
Default Folders Description Main program Documentation Files MT Manager MT SDK MTw User Manual MTw SDK User Manual Tutorials / Help files © Xsens Technologies B.V. v Location C:\Program Files ... \Xsens\MT Manager C:\Program Files ... \Xsens\Documentation C:\Program Files ... \Xsens\MT Manager
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.
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.
2.4 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.
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.
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.
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.
3.3.4.1 Absolute Maximum Rating MTw Shock (any axis) Input Voltage Temperature During operation Temperature During charging 3.3.4.2 TBD -0.3 V … 6 V (note power is supplied only via USB) -10 oC - +60 oC 0 oC - +45 oC Absolute Maximum Rating AWINDA Station DC Input Voltage SYNC (BNC) inputs Operating Temperature -0.3 V … 16 V (Use included DC adapter) -0.5 to 3.8V -20 oC - +80 oC Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
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.
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 ON fully charged 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).
4.1.4 Estimated battery life with stand-by mode activated Bat. Capacity at sleep start Estimated time to full Measuring time left after 8 [%] discharge in standby [hrs] hrs in standby [hrs:min] 100 75 50 25 10 © Xsens Technologies B.V. 88 64 44 20 8 2.
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.
4.2.2 Awinda Station Status LED The Awinda Station has five LED indicators. From right to left, these indicators are: LABEL LED DESCRIPTION CHRG OFF When no mains power supply is connected to the Awinda Station. [CHaRGer functionality] STAT OFF [STATus of the Awinda Station] EXT OFF CONN OFF DATA OFF GREEN: When 12V power supply is connected (mains power supply). OFF: When no USB connection is present and when MT Manager is not started.
4.3.1 Awinda USB Dongle LED The Awinda USB dongle has one white LED. State Description Radio Off LED off. Scanning for Pulsating LED. MTw’s 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.
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.
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.
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.
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.
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.
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.
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.
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 Disconnect COM port1 Scan single port 6.3.1 Scan All Ports All available COM ports are scanned for connected devices. 6.3.
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”.
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.
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.
State Connecting Connected Enabled Transition Station detected Enable Make operational Disable Operational Start measuring Release Measuring Recording Stop measuring Start recording Stop recording Description MT Manager and Station are connected. Next State Connected User indicated that the system can be enabled. User indicated that system can become operational. User indicated that the system is to be disabled. User indicated that the system can start measuring.
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 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.
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: ”. Rejecting an MTw does not cause it to power off; it stops communication between that MTw and the Awinda Master.
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.
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.
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.
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).
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.
Parameter Line Polarity Trigger Once Skip First Skip Factor Description The sync line to activate. Rising or falling edge, or rising and falling. It is not recommended to selected Trigger once, if more than one recording using synchronisation of multiple systems will be made. 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.
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.
Parameter Line Polarity Trigger Once Skip First Skip Factor Pulse Width Description The sync line to activate. 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]). It is not recommended to selected Trigger once, if more than one recording using synchronisation of multiple systems will be made. Number of initial sync pulses to skip.
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.
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.
Abbreviation Counter Temperature VelInc_X VelInc_Y VelInc_Z OriInc_w Acc_X Acc_Y Acc_Z Gyr_X Gyr_Y Gyr_Z Mag_X Data Sample counter Temperature inside housing Velocity increment from SDI, x-axis Velocity increment from SDI, y-axis Velocity increment from SDI, z-axis Orientation increment quaternion from SDI, real component Orientation increment quaternion from SDI, xaxis Orientation increment quaternion from SDI, yaxis Orientation increment quaternion from SDI, zaxis Acceleration x-axis Acceleration y-axis
Abbreviation Data from each connected MTw Unit 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).
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.
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.
8 Troubleshooting and Support Problem Installation is aborted due to previously installed version. Possible cause Drivers are still present from the previous Xsens MT SDK installations. Solution 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.
Problem found in the Device List. Re-entering wireless network after out of range, MTw(s) not detected in MTM. Re-enable radio does not always find trackers used before. RSSI in Wireless configuration is full, while I cannot receive data from the MTw. MTw in Wireless Configuration is shown as disconnected, but RSSI appears to have a good strength. A discrepancy of a sample count is detected between MTw’s at the beginning or end of an exported file. Possible cause Solution it.
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.
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.
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.
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.
10.3 CE Declaration of Conformity We, Xsens Technologies B.V.
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.
11 Appendices 11.1 MTw Technical Specifications 11.1.1 MTw Performance Angular velocity Dimensions 3 axes Full Scale ± 1200 deg/s Linearity 0.1 % of FS 2 Bias stability 20deg/hr Noise 0.05deg/s/√Hz Alignment error 0.1 deg Bandwidth3 100Hz (max.) Acceleration 3 axes ± 160 m/s2 0.2 % of FS 0.003m/s2/√Hz 0.1 deg 100 Hz (max.) Magnetic field 3 axes ± 1.5 Gauss 0.2 % of FS 0.15mGauss/√Hz 0.1 deg 20 Hz (max.) Pressure 300 -1100 mBar1 0.05 % of FS 100 Pa/year 0.85 Pa/√Hz - 11.1.
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.
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.
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.
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.
11.3.1 Schematics Awinda USB Dongle Housing Specifications 11.3.2 Physical, Electrical and RF Properties Communication MTw Wireless 2.4GHz/USB © Xsens Technologies B.V. AWINDA Station Wireless 2.4GHz/ USB 56 Awinda Dongle Wireless 2.
interface Wireless transmit range indoor /outdoor Synchronization accuracy Additional interfaces: Operating voltage Power consumption1 Battery runtime Charge time Temperature Operating Range Specified performance Operating Temperature Range Housing Dimensions Weight ~20m / 70m ~50m USB ~20m < 10µs <1ppm clock drift <1ppm clock drift NA 2 x Sync In (BNC) 2 x Sync Out (BNC) 4.65-5.
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.
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.
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).
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 coordinate 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.
z Z Local vertical y S x MTw default co-ordinate system Z up, default Y G X Local tangent plane Z up, default Local Magnetic North 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.
ROS 0 0 1 0 1 0 1 0 0 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. X Z Y Y Z X a b 11.6.
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).
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 inverse (qSG) is defined by the complex conjugate (†) of qGS. The complex conjugate can be calculated: † qGS (q0 , q1 , q2 , q3 ) qSG As defined here qGS rotates a vector in the sensor co-ordinate system (S) to the global reference co-ordinate system (G). † xG qGS xS qGS qGS xS qSG Hence, qSG rotates a vector in the global reference co-ordinate system (G) to the sensor coordinate system (S), where qSG is the complex conjugate of qGS. 11.7.
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.
RGS a d b e c f g R11 R12 h R21 R22 i R31 R32 RSG a b d e g h c f i R13 R23 R33 Here, also the row-order/column-order is defined. The output definition in rotation matrix (DCM) output mode is: MTData DATA = MID 50 (0x32) a b c d e f g h i All data elements in DATA field are FLOATS (4 bytes) , unless specified otherwise by modifying the OutputSetting Data Format field. 11.8 Synchronisation Examples 11.8.
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
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.
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.
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).
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.
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.
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.
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.
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. © Xsens Technologies B.V.
