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EETE FEB 2015

MEMS TECHNOLOGIES MEMS step up for 3D motion tracking By Per Slycke Microelectromechanical systems (MEMS) are all around us. They can be found in our step counters and our phones. But these inertial motion sensing applications do not really exploit the true potential of the technology, which is capable of detecting changes in orientation as small as 0.01 degrees. However, we are now seeing the emergence of a new generation of 3D motion capture systems that are opening up exciting new dimensions in both consumer applications and scientific and industrial research. Inertial motion sensors were first developed during the Second World War to help stabilize the V-2 rockets. The technology was further refined for the guidance of intercontinental ballistic missiles. Since the late 1980s, mechanical gyros and accelerometers have been replaced progressively by solid state MEMS technology that has enabled the sensors to become ever smaller and lighter. They are found in a host of applications, from triggering the operation of air bags in cars, stabilising aircraft in flight and helping to eliminate motion-shake on hand held video cameras. In recent years, we have started to see these MEMS sensors being used to accurately measure human motion in 3D, with potential applications in entertainment, sports, ergonomics, biomechanical engineering, injury rehabilitation, and many others. One of the benefits of this MEMS based motion capture technology is that it tracks motion in 3D with no external reference such as GPS tracking or using cameras. This means the technology can be deployed outside of the lab or studio, which is especially helpful for industrial and consumer applications. What are MEMS sensors? MEMS are miniature electromechanical systems, able to convert mechanical movements such as rotation and acceleration into electrical signals. The sensors can detect motion in three dimensions, both 3D rotational movement as well as 3D linear movement, therefore sometimes referred to as “6D”. A particular advantage of MEMS sensors is that they are solid state silicon devices. So as long as they are not physically damaged they will operate for long periods of time with almost no degradation in performance. Calibration is of course a very important challenge in designing motion capture systems, and achieving effective autocalibration using advanced “sensor fusion” software algorithms has been an important breakthrough in the design of 3D motion tracking systems. In effect, the system only requires calibration at the factory assembly stage. Another major advantage of the technology is the size. The unobtrusive nature of the devices means they can be easily integrated into clothing or connected to devices to measure both human and robot motion. The trend of increasing integration and decreasing size is set to continue, opening up even more possibilities for this technology. When these highly integrated MEMS motion sensor systems hit certain levels of accuracy they enable exiting new functionalities. For example, applications like tracking 3D human motion in real-time, rather than simple step counting, the utility of which is increasingly being disputed. MEMS for unmanned flight MEMS sensors are being used to stabilise moving objects, in the way that the technology was originally developed for. Area-I, a company specialising in advanced aircraft, has used Xsens MEMS based technology in the development of its unmanned aircraft. The aircraft have a limited payload requiring both an accurate and lightweight navigation system. Highly accurate MEMS sensor systems that provide attitude and navigation data are ideal in this situation. MEMS in healthcare In healthcare and rehabilitation, MEMS sensors can be used to tackle one of the most common medical complaints: lower back pain. As people become increasingly sedentary, spending more time in front of a computer and in cars, lower back pain has become a big problem. At any one time, 40% of the population is suffering from lower back pain but almost everyone (85-90%) of people will experience this pain at some point in their lives. The solution to this is often a series of exercises to be repeated at home but in many cases, the patients don’t complete the treatment. This is down to several reasons. At home, patients don’t have the expertise of their doctors so can’t be certain they are doing the exercises correctly, or if they are working at all. In addition, the exercises are boring and repetitive, putting some patients off. To help patients complete their treatment, Hocoma, a global medical technology company, developed Valedo. The Valedo system uses highly accurate wearable motion trackers to track the movement of the wearer. This is combined with a state of the art gaming experience, giving them the motivation to continue their exercises. The software also provides real time feedback, whether it’s in a clinic or in a home. Hocoma uses low power, high performance MEMS based motion trackers to power the Valedo system, making it suitable for a mass market. The sensors are comprised of a 3D gyroscope, 3D accelerometer and 3D magnetometer which detect a full 360 degree range of movements to within one degree. Weighing only 18 grams and with a battery life of six hours, the sensors are applied to the chest bone and pelvis to measure the movements of the upper body and pelvis. Valedo tracks 17 unique movements within 45 therapeutic exercises to help users reach their therapeutic goals. The movement performance algorithms monitor accuracy, smoothness and precision, ensuring patients are moving correctly. This is all incorporated into a serious gaming experience. The user’s movements control a robot though different landscapes, with the challenge of making the movements are precise and smooth as possible. Hocoma’s Valedo system is enabled by a MEMS motion tracking system. Per Slycke is CTO and General Manager at Xsens – www.xsens.com 36 Electronic Engineering Times Europe February 2015 www.electronics-eetimes.com


EETE FEB 2015
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