Design and Modeling of Parallel Exoskeleton for Wrist Tremor Suppression

Abstract

Simple Everyday Tasks (SET) such as writing, eating, and object manipulation are a struggle a for patients suffering from Pathological Tremors. Pathological tremors are involuntary, rhythmic, and oscillatory movements that manifest in limbs, the head, and other body parts. Among the existing treatments, mechanical loading through wearable rehabilitation devices is the best way to go due to them being non-invasive and without side-effects to the human body. Along this line, Exoskeletons are being developed to actively mitigate pathological tremors in the forearm and wrist. While these forearm exoskeletons can effectively suppress tremors, they still require significant improvements in ergonomics to assist in SET. The ergonomics of the exoskeleton can be improved via design and motion control pertaining to human biomechanics, which leads to better efficiency, comfort, and safety for the user. The wrist is a complicated biomechanical joint with two coupled degrees of freedom (DOF) pivotal to human manipulation capabilities. Existing exoskeletons either do not provide tremor suppression in all wrist DOFs, or can be restrictive to the natural wrist movement. This motivates us to explore a better exoskeleton solution for wrist tremor suppression. The presented work introduces the design of a Parallel Exoskeleton for Wrist Tremor Suppression (PEWTS). The design features a dual parallel subsystems setup that aim to be compact and suppress tremors in both radial/ulnar deviation (RUD) and flexion/extension (FE) motions of the wrist. When PEWTS is equipped by the user two closed kinematic chains are formed, each with six DOFs to ensure unconstrained natural wrist movements. The parallel setup offers better feasibility and controllability to the design and control. A linear Series Elastic Actuator is employed, to provide better ergonomic comfortness. This also compensated for the rigidness and absence of back-drivability of a simple Linear actuator. The presented study focuses on providing a fundamental understanding of the working of PEWTS and investigating its feasibility through kinematic workspace analysis.