Moving toward Soft Robotics: A Decade Review of the Design of Hand Exoskeletons

Abstract

Soft robotics is a branch of robotics that deals with mechatronics and electromechanical systems primarily made of soft materials. This paper presents a summary of a chronicle study of various soft robotic hand exoskeletons, with different electroencephalography (EEG)- and electromyography (EMG)-based instrumentations and controls, for rehabilitation and assistance in activities of daily living. A total of 45 soft robotic hand exoskeletons are reviewed. The study follows two methodological frameworks: a systematic review and a chronological review of the exoskeletons. The first approach summarizes the designs of different soft robotic hand exoskeletons based on their mechanical, electrical and functional attributes, including the degree of freedom, number of fingers, force transmission, actuation mode and control strategy. The second approach discusses the technological trend of soft robotic hand exoskeletons in the past decade. The timeline analysis demonstrates the transformation of the exoskeletons from rigid ferrous materials to soft elastomeric materials. It uncovers recent research, development and integration of their mechanical and electrical components. It also approximates the future of the soft robotic hand exoskeletons and some of their crucial design attributes.

Keywords: activities of daily living; hand exoskeletons; rehabilitation; soft robotics; systematic and chronological review.

Figure 1

Internal bone structure of a human finger and finger exoskeleton robot, where ‘F’ is the actuation force applied in its respective direction (arrow head). (a) The natural skeletal structure of the human finger. (b) The rigid joint and link mechanism of a hand exoskeleton; distal (DIP), proximal (PIP) and metacarpal (MCP) interphalangeal joints. (c) The pneumatically-actuated hand exoskeleton. (d) The tendon/cable–pulley system in a wearable glove. Reprinted and modified with permission from [27], published under the Creative Commons Attribution license (CC BY 2.0) [32].

Figure 2

Soft wearable gloves for rehabilitation and ADL. (a) Exo-Glove Poly 2.0 (improved version). Reprinted from [52] with permission from Springer Nature. (b) Three fingered GRIPIT with a single actuator with cable routing across the point ‘A to D’ indicated in red. Reprinted with permission from [23] published under the Creative Commons Attribution license (CC BY 4.0) [78]. (c) The iHand system. Reprinted from [59] with permission from Springer Nature. (d) Jarayani glove bending with control unit, Inertial Movement Unit (IMU) sensor and Universal Serial Bus (USB) cable. Reprinted from [48] with permission from IEEE. (e) Prototype of the muscle glove using shape-memory alloy (SMA) spring actuators. Reprinted from [74] with permission from Springer Nature.

Figure 3

Different actuation mechanisms for soft robotic hand exoskeletons. (a) The Harvard Glove 2.0 with fiber-reinforced actuators with fiber-reinforced actuators and light-emitting diode (LED) sensor display. Reprinted from [6] with permission from Elsevier. (b) The NUS prototype glove with fabric as the strain limiting layer. Reprinted from [10] with permission from Taylor & Francis. (c) The NUS glove for rehabilitation. Reprinted from [17] with permission from Springer Nature. (d) The Power-Assist glove. Reprinted from [38] with permission from Fuji Technology Press Ltd.

Figure 4

Mechanical development of soft robotic hand exoskeleton devices since 2008.

Figure 5

Electric development of soft robotic hand exoskeleton devices since 2008.

Figure 6

Functionality trend of soft robotic hand exoskeleton devices since 2008.