Accelerometer-based motion tracker takes position

A novel micromachined inertial navigation system motion tracker, weighing only 60g, offers high accuracy measurement and Bluetooth data transfer.

The IMT6000, manufactured by Imego of Sweden, is the first ultralight inertial navigation system (INS) device able to track motion for 10s with positional accuracy, in x-y-z co-ordinates, of a few centimetres and angular accuracy surpassing 0.3 degrees.

The IMT6000 can track velocity during 20s of motion to within 0.01m/s.

The system consists of a 60g IMU sensor head that collects, digitises, stores and transmits all sensory data.

A standby laptop receives the digital information via a Bluetooth link and computes all requested motion parameters, including positions and angles for all degrees of freedom.

The complete motion event is captured and can be replayed in minute detail, with resolutions of several hundred samples per second.

The digital IMU sensor head builds on commercial micromachined gyros and accelerometers that are boosted with noise removal algorithms to reach noise levels of 0.005deg/s/(rt)Hz and 60ug/(rt)Hz, throughout the generous measuring ranges of 3600deg/s and 50g.

Another important parameter for motion tracking is the bias stability of the sensors.

The IMT6000 is capable of stabilities down to 10deg/h and 100ug.

All sensors are sampled at 2.7kHz and filtered in several stages to finally display information with 200Hz resolution.

Imego can customise the INS platform to a particular application as per customer's specifications.

Imego also develops and customises sensor elements, sensor systems, and their packaging to satisfy further product requirements.

Imego's motion trackers are currently primarily tuned to sports applications, focusing on explosive events that take on the order of a few seconds to complete.

The IMT6000 measures, computes and displays all six motion parameters for all motion directions and all discrete time steps.

The x-y-z accelerations, velocities, positions, angular accelerations, angular velocities, and angles then completely describe the motion and give the most accurate scientific description of the event that can be had.

Imego's specialty is to take advantage of the general knowledge about a particular motion and customising the device to limit the small errors inherent in fine grained motion tracking.

For example, knowing that a race car always turns left on a track, we can tune the gyro scale factors accordingly, dramatically enhancing performance of the tracking.

If the Nascar circuit decided to switch directions one day, then that particular Imego motion tracker would have to be recalibrated.

Another example is the understanding that almost all tennis players hold their racket nearly horizontal just before starting the serve motion.

This kind of information can be exploited to determine specific sensor and navigation parameters, which in the end improves navigation precision.

Imego also uses advanced sensory calibration in a temperature controlled precision rate table, making it possible to compensate for nonlinear behaviour and temperature dependencies always present in MEMS sensors.

The overall result is improved accuracy of all motion parameters, eclipsing tracking predictions based purely on manufacturer's sensor specifications.

Beyond the world of sports, applications range from black boxes for industrial robots, precision positioning of film cameras, and accurate location of drill heads to computer animation and biomechanics.

Basically, the IMT6000 can be applied whenever the problem entails measuring any motion parameter, while it at the same time is essential to use a sensor head that is small and light enough not to disturb the actual motion.

One prime example is Imego's development of a light but accurate position measuring instrument, the GPS Shadow Explorer (GSE).

Geodesic applications require a small and light instrument that quickly measures out a few unknown locations when not enough satellites are visible in the sky to use GPS.

The GSE can then simply pinpoint the x-y-z coordinates, with the precision of a few centimeters, as long as each point can be reached within 25 seconds of walking from the known GPS coordinate.

In a research project, partly financed by Saab Bofors Dynamics and SensoNor, Imego has developed a novel electronics platform, including a fully digital gyro ASIC, which boosts SensoNor's low cost automotive gyroscope to good tactical grade performance.

The combination of new ASIC and commercial gyro succeeded in resolving the rotation of the Earth, about 15 degrees per hour, in late Q2 2004.

This achievement further confirms Imego's position as one of the world's leading MEMS gyro research and prototyping companies.

Less than a handful of research groups have previously been able to demonstrate this performance for silicon MEMS gyros before, and none for a low cost automotive gyro in commercial production.

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