Analysis of the Effect of Common Disturbances on the Safety of a Wearable Tremor Suppression Device

The advent of wearable technology has enabled a large number of externally worn mechatronic devices to be developed and tested on people with movement disorders. The complexity of these disorders and the variety of conditions across different patients have resulted in a pressing demand for the incorporation of intelligent control systems, especially for a wearable tremor suppression device (WTSD) that can suppress tremor without impeding the user's voluntary motion. Several devices have been developed to reduce tremor; however, the evaluations of these devices have only been done in a controlled lab setting, while the functionality and ability to avoid user injury under the effect of disturbances during daily use have not been investigated. In this study, the performance of a WTSD was tested with several commonly used tremor suppression control systems, i.e., Weight-frequency Fourier Linear Combiner (WFLC), Bandlimited Multiple Fourier Linear Combiner, and enhanced High-order WFLC-based Kalman Filter, on a bench-top tremor simulator. These systems were also tested under the influence of three simulated disturbances that are commonly seen in real life, i.e., data mutation, sensor drift, and measurement loss. The experimental evaluation showed that none of these systems are safe under the disturbances. The tremor power suppression ratio (67.8%-94.2%) of the WTSD was not significantly lowered by the disturbances; however, the error when tracking voluntary motion significantly increased by 8.8^°-93.6^°, which may present a safety hazard to the users. The results of this study emphasize the importance of integrating safety measures into intelligent WTSDs.

I. Introduction

The existence of pathological tremor in the extremities of an individual often impairs his/her ability to perform activities of daily living (ADLs). Furthermore, the social embarrassment caused by tremor makes the affected individuals avoid social contact outside of their own family and friends. The most commonly seen pathological tremors are parkinsonian tremor and essential tremor [1]. It has been reported clinically that approximately 65% of the affected individuals’ lives have been severely impacted by living with tremor [2], [3]. Furthermore, nearly 25% of the affected individuals do not respond to traditional treatments [4].