Experimental Testing of Passive Linear TMD for Postural Tremor Attenuation

Sarah Gebai,Mohammad Hammoud,Emmanuel Roze,Elodie Hainque,Gilles Foret,Gwendal Cumunel

doi:10.3390/app11219809

Abstract

Research interest to provide a mechanical solution for involuntary tremors is increasing due to the severe side effects caused by the medications used to lessen its symptoms. This paper deals with the design of a cantilever-type tuned mass damper (TMD) used to prove the effectiveness of passive controllers in reducing the involuntary tremor’s vibrational signals transmitted by the muscles to the hand segment. TMD is tested on an experimental arm, reflecting the flexion-extension motion of the wrist, excited by a mechanical shaker with the measured tremor signal of a patient with essential tremor. The designed TMD provides a new operational frequency for each position of the screw fixed to its beam. Modal damping ratios are also calculated using different methods for each position. The effectiveness of the TMD is quantified by measurements using a vibrometer and inertial measurement unit. Three TMDs, representing 15.7% total mass ratio, cause a reduction of 29% for the acceleration, 69% for the velocity, 79% for the displacement, 67% for the angular velocity, and 82% for the angular displacement signals. These encouraging results will allow the improvement of the design of the passive controller in the form of a wearable bracelet suitable for daily life.

Highlights

Essential tremor (ET) is one of the most common tremor diseases [1]
This can be explained by the low modal damping ratios provided by the manufactured tuned mass damper (TMD), which are not high enough to lessen the amplitude of critical peaks
The optimal damping ratios determined numerically are not reached in this study due to a low damping ratio provided by the strain rate of the stainless steel beam material, air damping provided by the beam and the screw, and frictional damping provided by the clamped end and the surface of contact with the attached screw, without the addition of an external damper

Summary

Introduction

Essential tremor (ET) is one of the most common tremor diseases [1]. The muscles of the patient with ET operate in the frequency range of 4–12 Hz [2]. A 200–400 g TMD operating between 4.5–6 Hz is placed near the free end of the beam It causes a 57% reduction in the amplitude of acceleration at the resonance frequency of 5.32 Hz. Buki et al [8] manufactured a forearm as an inertial rod attached rigidly to the hand and excited by a direct-current (DC) motor at the wrist joint to apply a pronation-supination motion. Two TMDs designs as a 109 mm × 72 mm × 9 mm metallic rectangular box each, of 530 g total mass, are placed symmetrically on the top and the bottom of the hand, at the wrist joint, to reduce the motion in the horizontal direction These TMDs were tested on a real patient by tracing the pre-drawn line on a whiteboard. The tremor assistance device was able to mitigate the fluctuation in the water level

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