Parametric study of an enhanced passive absorber used for tremor suppression

Abstract

Passive absorbers are designed to be attached to upper limb systems to reduce tremor of patients suffering from Parkinson's disease. Several works were done previously to show the effectiveness of the low cost passive controllers, which can reduce the undesired vibrations without power requirements. An improved type of such controllers is suggested in this paper. The mechanical absorber is a two-degree-of-freedom (DOF) system, which is formed by an elastic absorber connected in series to a viscous damper one, naming the system the Series Elastic Viscous Damper (SEVD). It was able to cause a high reduction in the amplitude of the tremor and operate over a wide frequency range. The lumped parameters of each absorber within the SEVD absorber are chosen to satisfy the tuning conditions. The device is tested numerically on the forearm of a biodynamic upper limb structure to check its capability in reducing the tremor at the limb's proximal joints. The limb was modeled as rigid segments with a three DOF flexion-extension angular motion in the horizontal plane. This study seeks to analyze the effect of the SEVD damping coefficient, total mass, and mass distribution on the reduction of the displacement amplitude at the joints, with stiffness chosen to satisfy the tuning condition for the undesired frequency of tremor. It was found that very low damping coefficients are not suitable to provide reduction at all joints simultaneously; high absorber's total mass can slightly increase the performance and equally, distributed dual masses can be a good selection.