Analysis of Effect of Motion Path on Leg Muscle Load and Evaluation of Device to Support Leg Motion During Robot Operation by Reducing Muscle Load

Hiroki Kato,Masaharu Komori,Ikko Yasuda,Tatsuro Terakawa

doi:10.1109/access.2021.3066192

Abstract

Because the human arm and leg have a similar skeletal structure, it may be possible to use the leg to operate a robot by the master-slave method. However, operation by the leg with six degrees of freedom has two problems. First, people move their ankle with a curved motion despite intending to move it linearly. Second, it is a burden for the operator to suspend their legs in the air during operation. This study dealt with these problems. For the first problem, we hypothesized that one of the reasons was that the muscle load of a curved motion was smaller than that of a linear motion, and we quantitatively compared them by musculoskeletal analysis. The muscle loads of curved motions were 20% smaller in the anteroposterior direction, 3.1% to 23.8% smaller in the lateral direction, and 10% smaller in the vertical direction than linear motions, which showed that the hypothesis was consistent. Further, comparison of the analysis results with the results of a previous study suggested that subjects unconsciously tried to reduce the muscle load and to move closer to a linear line when they moved their ankle while consciously intending to make a linear motion. For the second problem, we developed two different prototypes of a leg support device. An experiment to evaluate the effectiveness of these devices showed that subjective exercise intensity of the tasks in the experiment using the devices was 40% or more less than that without the device, which proved the effectiveness of the devices.

Highlights

Robot arms with multiple degrees of freedom (DOFs) are used in factories and welfare fields
The master-slave operation method has the advantage of being easy to operate because an operator can manipulate a multi-DOF robot arm by only moving his or her body part
Multi-DOF operation by the lower limb has two problems: 1) Even when the operator intends to move a leg linearly, the leg moves in a curved motion when visual feedback is absent, and the reason is not clear

Summary

Introduction

Robot arms with multiple degrees of freedom (DOFs) are used in factories and welfare fields. One of the methods to operate such a robot is master-slave operation, where an operator moves his or her arm to create the same movement in the robot. In this method, the operator can understand the correspondence between the movement of the arm and the movement of the robot, which makes it easy for even an inexperienced person to operate the robot. Various studies have examined robot arm operation by using an exoskeleton-like device [11]-[14] or by using electromyography [15]-[16]. Komori et al proposed a virtual space-based evaluation system to compare the master-slave method with a button operation method and proved the effectiveness of the master-slave method by showing that it can shorten the operation time by 27.7% and increase the subjective operability evaluation by 76.0% during operation of a virtual robot hand [17]

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