User Manual

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