Multimodal Tremor Suppression of the Wrist Using FES and Electric Motors–A Simulation Study

Wearable technologies have shown promising results in tremor management, making them a feasible alternative to current treatments. Devices based on active actuation, such as electric motors, show high tremor suppression rate, but are heavy and bulky. In contrast, devices based on functional electrical stimulation (FES) are lightweight and smaller in size, but might cause pain, discomfort, and FES-induced muscle fatigue. Also, when the stimulation parameters do not adapt to the tremor, their suppression performance is compromised. Therefore, a multimodal approach was developed and tested by modeling wrist joint dynamics and simulating the muscle response to FES based on an existing dataset collected from 18 participants with Parkinson's disease. The goal was to evaluate and compare the performance of a multimodal device to that of an FES-only or an electric-motor-only approach. A nonlinear control system allocates the control effort between FES and motor torque based on the tremor level. Results showed an improvement in tremor suppression level (up to 12%) in the multimodal approach compared to FES only when there is voluntary motion. Also, the voluntary motion tracking error was lower in the multimodal approach, compared to the FES-only method (up to 57%). No notable improvement in tremor suppression level or voluntary motion tracking error was observed by comparing the multimodal system and the motor only approach. However, the advantage of using a multimodal system compared to the motor-only system is the reduction of the required motor torque resulting in reduced weight and size of the final device.