Suit-type Wearable Robot Powered by Shape-memory-alloy-based Fabric Muscle

Abstract

A suit-type wearable robot (STWR) is a new type of soft wearable robot (SWR) that can be worn easily anywhere and anytime to assist the muscular strength of wearers because it can be worn like normal clothes and is comfortable to wear even with no power supply. This paper proposes an STWR, in which a shape-memory-alloy-based fabric muscle (SFM) is used as the actuator. The STWR, which weighs less than 1 kg, has a simple structure, with the following components: SFMs, wire encoders for measuring the contraction length of the SFMs, and BOA that fix the actuators on the forearms. In this study, a position controller for the SFM using the wire encoder was developed, and a prototype STWR was fabricated using this position controller. Moreover, by putting the STWR on a mannequin, step-response experiments were performed in which the arms of the mannequin lifted barbells weighing 2 kg and 4 kg to a certain target position. A fast response of moving to the target position in less than 1 s was observed in all steps except for the initial heating step for the 2 kg barbell. The response speed of the SFM was noticeably slower for the 4 kg barbell compared to that for the 2 kg barbell; it moved to the target position in approximately 3 s in all the steps except for the initial heating step. The SFM-applied STWR could overcome the limitations of conventional robots in terms of weight and inconvenience, thereby demonstrating the application potential of STWRs.

A review of soft wearable robots that provide active assistance: Trends, common actuation methods, fabrication, and applications

“…which occupy a certain volume at atmospheric pressure and compress and become stiff when subjected to negative pressure (Robertson and Paik 2017). Another form of actuation method used is the shape-memory alloy (SMA) actuator, which uses electrical current to affect the behavior, shape, and/or length of a material used in designing an actuator (Park and Park 2019). Another method is passive assistance from flexible or relatively soft materials.…”

Design of Shape Memory Alloy-Based Soft Wearable Robot for Assisting Wrist Motion

“…However, the strain that the actuator can produce is relatively low (<8% of its initial length) [46], which is insufficient for the use in making a wearable robot. In order to enhance actuating performance, SMA can be shaped in the shape of coiled springs that result in substantially larger displacement when it is utilized as an actuator [46,[55][56][57][58][59]. The coil spring shaped SMA actuators have large extension strain over 200% [46,55], which is enough for the desired application as the strain of a SMA coil spring is larger than that exhibited by human muscles [60].…”

“…Another shortcoming faced when working with SMA actuators is the slow response due to the difficulty of both heating up and cooling down the SMA rapidly in the same system. Generally, many SMA-based actuators are operated in ambient air, which offers a fast heating rate, but the limitation is a slow cooling rate as well [46][47][48][49]59]. To enhance the response speed of SMA based actuators, a few works have applied water as an alternative coolant during the actuation of the SMA [50,[55][56][57][58].…”

Next Generation Autofocus and Optical Image Stabilization System for Camera Modules Using Magnetic Shape Memory Actuators

“…SMAs are currently gaining popularity in camera [8] and wearable smart robotics [9] applications owing to their large strain and stress output [10]. However, their response time can be several seconds long during heating and even longer (10-30 s) during cooling [9], due to the high inertia of thermal expansion and contraction. Therefore, the application of SMAs in fast-response actuators is nearly impossible.…”