Development of compact and lightweight brake mechanisms for portable and wearable robots

Abstract

Soft robots have been developed to provide safe human–robot interactions and improve portability. Although soft locking devices are essential components of robotic systems, little research has been conducted on them compared to soft actuators and sensors. Locking devices, including brakes and clutches, are necessary to maintain a stable position, reduce the number of actuators, and prevent unintended movements in robots. Conventional locking devices, such as electromagnetic and electrorheological types, have rigid structures that limit their compactness. Therefore, soft locking devices that use electrostatic (ES) adhesive or pneumatic jamming forces have recently gained popularity. However, their range of motion cannot exceed their sizes, and their application is limited because they require high voltage or a massive compressor to operate. This study proposes two types of tubular brakes that do not restrict the robots’ range of motion while maintaining flexibility and compactness: hygroscopic and shape memory alloy- (SMA-) based brakes. The tubular brakes can also be a guiding tube when used in a tendon-driven robot. Moreover, this study validates the performance of these two types of brakes. In particular, theoretical modeling is introduced in the SMA-based brake to analyze the locking mechanism and performance, which can be used to determine the locking force and response time according to temperature. Improved compactness resulting from the use of the proposed brakes is demonstrated by its application to soft wearable devices.