Design and Development of Hand-opening and Pinch Force Sensors

There is growing interest in developing prosthetic limbs capable of providing sensory feedback to amputees. The development of such advanced systems requires accurate, quantitative assessment of the sensation perceived by the amputee. We have designed and fabricated robust, devices to track and record hand-opening distance and pinch force during a series of structured tasks performed by unilateral amputees using their intact hand to mirror perceived sensation in the amputated limb. For hand-opening distance measurement, the subject's thumb and forefinger are coupled to linear potentiometers. While subjects open and close their hand freely, the distance between the thumb and forefinger is estimated in real time by recording the voltage output. For pinch force measurement, a commercially-available mini compression load cell is mounted on a custom-designed aluminum assembly that is adjustable to enable measurement at different hand-opening distances. The load cell generates a voltage signal proportional to the applied pinch force. Calibration was accomplished by applying incremental forces using a compression load testing device while monitoring the voltage output. These measurements will help to quantify the amputee's perception of hand-opening and pinch force and thereby serve towards developing a subject-specific sensor-stimulation map that can be programmed into an advanced prosthesis.