Source: James Abundis & Globe Staff, Boston Globe, August 30, 2010

Inertial tracking systems have an unfortunate tendency to slowly drift over time. University of Michigan Professor Johann Borenstein has developed a very effective solution to that problem. First, he places a MEMS sensor in a boot. With every step, the sensor is momentarily stationary,  allowing drift to be completely reset. According to Prof. Borenstein:

…during the brief moment of being stationary (i.e., the boot having zero velocities) we can compare that known condition with the velocities computed from the accelerometer data. This allows us not only to estimate the accelerometer drift with great accuracy, but also to remove that drift from the next step (and, in part, retroactively from the previous step). This way our accelerometer drift is fully “reset” with every step. The result is that we can estimate distance traveled with an accuracy of 1% of distance traveled for unlimited walks. The ability to reset accelerometer drift with every step and thus roughly once every second is unique to walking. Designers of missiles and submarines would kill for that benefit…

Borenstein developed a patent-pending Heuristic Drift Elimination (HDE) algorithm to eliminate effects of MEMS gyros’ sensitivity to linear acceleration and drift. He reports his system has average heading errors near zero in walks of unlimited duration and average position error <1% of distance traveled in walks of less than 30 minutes.

In a simulated rescue exercise held at the Worcester Polytechnic Institute’s campus, Borenstein’s system helped the Worcester Fire Department found a “lost” firefighter in just under ten minutes – compared to an unassisted rescue time of twenty four minutes. [Full disclosure - my company Q-Track, also participated in the exercise. Further details in the links below]. The Boston Globe’s Hiawatha Bray wrote an excellent description of the exercise, including the graphic of Borenstein’s system (above).

Unfortunately, Borenstein has had difficulty finding a commercialization partner for the technology. See: Personal Tracking System Touted as Lifesaver for First Responders (National Defense Magazine) for details.

Previously on ÆtherCzar:

Additional information and a report on the WPI PPL Workshop are available from the TRX Blog, here.

Update (12/8/2010): Deleted: “In typical walking, the boot will be stationary more than half the time, enabling any inertial drift during that period to be ignored.” The explanation above has been corrected. Thanks to Prof. Borenstein for pointing out the error. For additional information, including a video of the system, see:


Hans Schantz is CTO of The Q-Track Corporation, and a co-inventor of NFER® technology. His prior work experience includes stints with IBM, the Lawrence Livermore National Lab, The ElectroScience Lab of the Ohio State University, and Time Domain Corporation. Author of The Art and Science of Ultra-wideband Antennas (Artech House, 2005), his forty U.S. patents include antennas, RF systems, RF-based location systems, and related inventions. He is a Senior Member of the IEEE, a member of the Institute of Navigation, and an amateur radio operator [KC5VLD]. Schantz earned his Ph.D. in physics from the University of Texas at Austin. He also holds degrees in Industrial Engineering and Physics from Purdue University. Dr. Schantz blogs at ÆtherCzar and is @ÆtherCzar on Twitter. His wife, Barbara, invented The Baby Dipper® Bowl. Hans and Barbara have two sets of twins: girls aged ten, and boys six years old. The views expressed are the author's and are not necessarily the views of his employer, clients, investors, sponsors, or customers.

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