Quantitative analysis of passive wrist tremor suppression method to minimize voluntary motion deterioration

Abstract

Tremor is rhythmic involuntary oscillation of a body part by quasi-sinusoidal contraction of muscle groups. Patients with tremor suffer from lack of independency in daily activities. Because of the high risk of side effects, medication or surgery is not a perfect solution of tremor suppression. Therefore, mechanical suppression devices became an effective alternative for tremor patients. So far, performance of tremor suppression mechanism or a suppression device has been evaluated only by tremor suppression rate. However, higher suppression with damping also deteriorates intended voluntary motion of the user. To design a favorable tremor suppression device, muscular effort increased to compensate the impeded voluntary motion should be considered in selection of damping parameter. In this research, voluntary motion deterioration during passive tremor suppression was quantitatively analyzed and a wearable tremor suppression device with variable hydraulic damper was designed for optimal suppression for wrist flexion/extension tremor. From kinematic data and electromyography achieved by voluntary tracking tasks with various suppression levels, quantitative relationship between the tremor reduction ratio and the amount of deterioration in voluntary motion was achieved. With a variable hydraulic damper, 4 damping ratios(0.070/0.14/0.19/ 0.37 [N/(rad/s)]) were applied to 4 voluntary motion frequencies(0.2/0.5/1.0/2.0 Hz). Nine healthy volunteers were participated to measure acceleration and sEMG signals during wrist flexion and extension motion. From the data, the power of sEMG, the power of tremor, tracking error, and translation of tremor frequency were computed for quantitative analysis. To simulate pathological tremor in normal person, extreme exercises were performed by 3 participants to induce fatigue-induced tremor. Despite further researches are required for more accurate selection of suppression conditions, this research have suggested an additional guide...