Abstract

The lightness and softness of pneumatic artificial muscles (PAMs) contribute to their safe use in mechanical devices involved with humans. However, a PAM has limited range of motion (ROM) and a stroke-dependent output force. In this paper, a mechanism combined with a PAM and a speed-increasing gear was developed to improve the tradeoff relationship between the ROM and output force and to verify its benefits in order to enhance the convenience of using PAMs. The gear enhanced the ROM and back-drivability of the PAM, which is beneficial for device safety in daily use. We first designed a mechanism consisting of an antagonistic system-driven PAM and the gear, and then simulated the relationship between the ROM and output force of the mechanism. The effectiveness of the mechanism including the gear was compared with a non-gear mechanism with multiple PAMs. We prototyped the PAM mechanism with and without the gear, and their ROMs, impact absorption, and viscoelasticity were experimentally investigated. Results showed that the gear effectively improved both ROM and output torque below a certain load; moreover, the gear ratio and air pressure had large effects on the external static and dynamic forces, respectively. We confirmed comprehensively the effect and feasibility of the mechanism.

Highlights

  • Mechanical devices that are involved with humans, for instance, medical robotic devices pertinent to rehabilitation or diagnosis and treatment of diseases, play an important role in improving and enhancing the quality of life of their users

  • We focus our attention on pneumatic artificial muscles (PAMs), which contain a prismatic actuator that contracts longitudinally by compressed air and have good power-weight, compliance and safety [22] features

  • We developed the PAM’s antagonistic drive system (PADS)-gear mechanism and verified its benefits to enhance the convenience of using PAMs as the actuator in mechanical devices interacting with humans, such as medical robotics or wearable devices

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Summary

Introduction

Mechanical devices that are involved with humans, for instance, medical robotic devices pertinent to rehabilitation or diagnosis and treatment of diseases, play an important role in improving and enhancing the quality of life of their users. The softness (i.e., compliance) and lightness of the devices can contribute to their safety and fit These characteristics can minimize the physical and mental load of users and the effect of collisions with the external environment on the user’s body during daily use. Elements and actuators that are used in the devices have a profound effect on the compliance and lightness of the whole device These include springs, pneumatic artificial muscles (PAMs) [1,2,3,4,5,6,7,8,9,10,11], magnetorheological (MR) dampers [12,13,14], shape memory alloys (SMAs) [15,16,17], soft pneumatic actuators (SPAs) [18], and dielectric elastomer actuators (DEAs) [19].

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