A few months ago I entered a prototyping competition, The ProtoHype Challenge, with some coworkers. This competition is being sponsored by both TechShop and the University of Pittsburgh’s Clinical and Translational Science Institute. The goal of the competition was to pair people with good prototyping skills (TechShop Members) with ideas for a medical device or biomedical research tool. Ten groups from Pitt provided challenges from which the prototyping teams could submit proposals. Our team was lucky enough to be chosen to prototype our favorite challenge: calibration of commercial motion capture IMUs (Inertial Measurement Units).
Our companion team at Pitt is using the IMUs to capture the motion of physical therapy patients to track progress the patients are making and to ensure that the patients are performing exercises correctly. The issue they run into is that over time, the IMUs position drifts and the readings of patient motion become inaccurate. This drift is due to the accelerometer data accruing small errors over time.
To mitigate this drift the IMUs use magnetometers to maintain global orientation. In order for this to work, the magnetometers need to be accurately calibrated with respect to the accelerometers. This process can be very difficult, involving positioning the IMU in a series of known orientations and reading the magnetic field to generate calibration data. Our goal is to create a mechanism to simplify the calibration process.
Our Proposed Solution
The mechanism we are planning on building is a device that will allow the IMU to be automatically positioned in the necessary orientations for calibration. The mechanism itself will be very similar to a gyroscope or spherical wrist joint with three stacked rotational axis. The image at the start of the post depicts the mechanism. We will have control software that will control the positioning of the IMU and will communicate with it to trigger calibration when the IMU is in each position correctly.
We are working on the actual mechanical, electrical, and software architecture designs for our first prototype. More updates will follow.