Grasps under Artificially-limited Thumb’s Joint Range of Motion –Posture Analysis with ROM Boundary and Muscle Loads–

This paper proposed a method to clarify the features of grasping styles of ROM-limited hands. We measured the contact regions and joint angles of grasping by a ROM-limited hand. The joint angles were analyzed with respect to ROM boundary. Muscle loads of grasps were also estimated. Grasping styles finally selected by the ROM-limited hand tend to use side region of the thumb. In the grasping styles finally selected by the ROM-limited hand, ROM-limited joints tend to be farther from ROM boundary. In addition, the influence of muscle loads is not confirmed.

1. Introduction

On designing a product, usability can be evaluated virtually by estimating grasps for the CAD model of the product using a digital hand [1]. It has two merits. One is cost saving, and the other is to be able to consider various hands’ posture easily. Previous studies on grasp synthesis have been focusing mainly on healthy hands (e.g., [2] [3] [4]). However, in recent years, market size of universal design products tends to expand. Thus, it is important to synthesize grasps by various hand models including non-healthy hands (e.g., whose finger’s range of motion, ROM, is restricted). Therefore, the purpose of this study is proposing a method to clarify the features of grasping styles of ROM-limited hands. This will contribute to grasp synthesis for ROM-limited hands and help to realize the virtual evaluation of universal design products.