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3D motion tracker uses wireless technology

Posted: 27 Oct 2010     Print Version  Bookmark and Share

Keywords:3D motion tracker  kinematic measurements  wireless 

Xsens Technologies B.V. rolls out the MTw miniature wireless inertial motion tracker for ambulatory 3D kinematic measurements that features the Awinda radio protocol for time synchronisation within the wireless network.

MTw 3D motion tracker

The importance of accurate time synchronisation can be explained looking at the arm movement when playing tennis—both the upper and lower arm can move at angular velocities easily reaching 1000°/s. When tracking the 3D elbow joint angle, any error in timing, even of just a few milliseconds, would give rise to errors of several degrees.

The Xsens MTw brings the unobtrusiveness and ease of use of wireless technology to inertial 3D motion tracking. "The goal we have with this product is to further enhance the freedom of movement that inertial sensor technology brings to the field of 3D kinematics measurement systems by making our sensors wireless" says Colleen Monaghan, product manager, Movement Science of Xsens. "Losing the cables makes the system easier to put on and more comfortable to wear; something that is essential when working with patients outside laboratory settings. However, while making the product wireless, there was no question on compromising on accuracy—at any level. In fact, the MTw is our smallest and most accurate motion tracker ever."

Per Slycke, CTO of Xsens explains; "Measuring 3D motion accurately in biomechanics research, sports, and ergonomics is already challenging—you do not want time synchronisation between multiple sensors to be a potential cause of measurement errors. While time synchronisation is relatively easy to address in wired systems, it is not trivial for a wireless sensor network. In order to really tackle this issue at a fundamental level Xsens' R&D team has developed a unique, patent pending radio protocol we call Awinda, based on standard low-cost 2.4GHz ISM chipsets, that takes care of time synchronisation of up to 32 MTw's across the wireless network to within 10µs." Fred Dijkstra, system architect at Xsens adds; "Wireless data transmission is great because of the freedom it gives the user—but from a technical point of view you have to deal with data packets being lost during transmission. Traditional radio protocols reserve a lot of time for acknowledgement of data packet reception and re-transmission of data, which means the network throughput will drop dramatically. With Awinda, specifically developed for inertial sensors, we took a new approach—if a data packet from the sensor is lost in transmission the sensor will not re-transmit that packet but use the embedded processor to integrate the information from the "lost" data packet into the next one. This way, you can keep the accuracy in real-time motion tracking, without any impact on radio network throughput. The benefit for the user is that you do not have to worry about the accuracy of your measurement varying with the quality of the radio link."

The MTw Development Kit includes; multiple MTw's, a combined wireless receiver and charging dock, MT Manager, an easy to use Windows software for recording and real-time visualisation of data and an SDK compatible with amongst others C/C++, MATLAB, LabVIEW. Using the specially designed click-in straps ensures efficient and secure fastening to the body.

The MTw is available for ordering with shipments in place in December 2010. A preview of the MTw will be held at the Neuroscience 2010 conference November 13-17, 2010 in San Diego, USA.

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