Design and Preliminary Feasibility Study of a Soft Robotic Glove for Hand Function Assistance in Stroke Survivors

Abstract

Various robotic exoskeletons have been proposed for hand function assistance during activities of daily living (ADL) of stroke survivors. However, traditional exoskeletons involve the use of complex rigid systems that impede the natural movement of joints, and thus reduce the wearability and cause discomfort to the user. The objective of this paper is to design and evaluate a soft robotic glove that is able to provide hand function assistance using fabric-reinforced soft pneumatic actuators. These actuators are made of silicone rubber which has an elastic modulus similar to human tissues. Thus, they are intrinsically soft and compliant. Upon air pressurization, they are able to support finger range of motion (ROM) and generate the desired actuation of the finger joints. In this work, the soft actuators were characterized in terms of their blocked tip force, normal and frictional grip force outputs. Combining the soft actuators and flexible textile materials, a soft robotic glove was developed for grasping assistance during ADL for stroke survivors. The glove was evaluated on five healthy participants for its assisted ROM and grip strength. Pilot test was performed in two stroke survivors to evaluate the efficacy of the glove in assisting functional grasping activities. Our results demonstrated that the actuators designed in this study could generate desired force output at a low air pressure. The glove had a high kinematic transparency and did not affect the active ROM of the finger joints when it was being worn by the participants. With the assistance of the glove, the participants were able to perform grasping actions with sufficient assisted ROM and grip strength, without any voluntary effort. Additionally, pilot test on stroke survivors demonstrated that the patient's grasping performance improved with the presence and assistance of the glove. Patient feedback questionnaires also showed high level of patient satisfaction and comfort. In conclusion, this paper has demonstrated the possibility of using soft wearable exoskeletons that are more wearable, lightweight, and suitable to be used on a daily basis for hand function assistance of stroke survivors during activities of daily living.

Keywords: activities of daily living; hand exoskeleton; rehabilitation; soft actuators; soft robotic.

Figure 1

(A) A fabric-reinforced soft actuators with a corrugated fabric layer and an elastic fabric later [Actuator thickness, T = 12 mm, and length, L = 160 mm (Thumb), 170 mm (Little Finger), 180 mm (Index & Ring Fingers), 185 mm (Middle Finger)]. (B) Upon air pressurization, the corrugated fabric layer unfolds and expands due to the inflation of the embedded pneumatic chamber. Radial budging is constrained when the corrugated fabric layer unfolds fully. The elastic fabric elongates during air pressurization and stores elastic energy. The actuator achieves bending and extending motions at the same time. (C) A bending motion is preferred at the finger joints (II, IV, VI). An extending motion is preferred over the bending motion at the finger segments (I, III, V) and the opisthenar (VII).

Figure 2

Schematic of the force measurement system for (A) blocked tip force, (B) normal grip force, and (C) frictional grip force measurement.

Figure 3

(A) Outer view and (B) inner view of the soft robotic glove. (C) Actuators are inserted into actuator pockets. (D) The length of the finger-actuator pockets can be adjusted and attached to the base of the glove via Velcro.

Figure 4

(A) Pump-valve control system integrated into a waist belt pack. (B) Inner view of the control system. (C) Step response of the controller implemented on the pump-valve control system.

Figure 5

(A) Schematic and (B) the real setup of a portable setup with dynamometer to measure the glove-assisted grip strength. Maximum frictional grip force was recorded before the cylinder released from the actuators' grip.

Figure 6

(A) Experimental and theoretical blocked tip force values over increasing pressures. (B) Normal and (C) frictional grip force output-displacement of the cylinder relationships of four actuators gripping cylinder with diameter D = 75 mm and D = 50 mm at a fixed pressure (120 kPa).

Figure 7

(A) Averaged range of motion of individual finger joints of five participants during active and glove-assisted trials. MCP, Metacarpophalangeal joint; PIP, Proximal interphalangeal joint; DIP, Distal interphalangeal joint. (B) Averaged muscle activation profiles of finger flexors and extensors of one representative subject (Subject 2) during active and glove-assisted trials. Exercise Cycle, Hand closing followed by opening.

Figure 8

The glove generated sufficient force to lift a 454 g-weighted can in the (A) vertical and (B) horizontal orientation. (C) Palmar grasp, (D) Pincer grasp achieved with the assistance of the glove.

Figure 9

Evaluation of the glove with stroke patient S1 and S2. (A) Hand conditions of patients. (B) Comparison of grasping performances with and without assistance of glove. (C) Time taken to complete the grasping tasks (n = 6 for each patient; P = 0.06 for S1, P = 0.02 for S2, paired t test, ^*p < 0.05.). The actuators of the glove were pressurized at 120 kPa.