Balance Exercises Steered by a Patient's Own Weight

The problem

A research study needed to measure how well patients control their balance. Each patient stands with one foot on a platform mounted to a multi-axis force transducer, which measures force in three directions and moments around three axes.

From those signals, the software had to work out the patient’s center of pressure, the point where their weight is actually centered, and show it live on screen. The study also needed a set of reaching and stability exercises built around it, and a full record of every session.

What we built

The transducer’s amplifier feeds a low-cost, multi-channel data acquisition card. Transfer functions convert those voltages into a center-of-pressure position, plotted live on a single X-Y chart: side-to-side movement moves the marker left and right, and front-to-back movement moves it up and down.

The software has four parts:

• Patient calibration: not every patient has the same range of motion, so the researcher and patient calibrate the chart’s axes together. A patient with limited movement can still reach the edges of the screen.
• Exercise configurator: the researcher picks from a library of exercises, each with its own parameters. In reaching exercises, the patient steers their center of pressure onto a target. In stability exercises, they keep it inside boundaries that move.
• Runtime display: the exercise itself, which the researcher can start, stop, restart, or reconfigure at any point.
• Troubleshooting view: charts the raw voltage from each transducer channel, for checking the hardware.

The result

Every exercise is streamed to disk as it runs: the center-of-pressure position, the exercise settings, and where each target was at every moment. Researchers can recreate any session afterward and analyze it however the study requires.