Soft Gripper Gloves with Mirroring System Design for Hand Rehabilitation ^†

Abstract

Over the last decade, soft robotic gripper systems, such as grippers, have been used in a variety of applications, particularly in human rehabilitation. This study aims to enhance the rehabilitation process by creating a mirroring system glove for hand paralysis patients due to injury, stroke, hemiplegia, and others. A soft and flexible liquid silicone rubber (LSR) was used to develop and build a pair of gloves to improve comfort and safety compared with rigid rehabilitation equipment. The non-affected hand’s sensory glove, equipped with flex sensors, detects motion by measuring the bending angle at each finger. The other glove uses Arduino and a pneumatic system to help the afflicted hand accomplish training exercises. The new design of a gripper is important for manufacturing gloves that provide acceptable gripping behavior.

1. Introduction

A multitude of individuals are experiencing mobility impairments and neurological disorders in various body parts, necessitating specialized rehabilitation or substantial assistance for the partial or complete functionality of the affected limb for the performance of activities of daily living (ADLs). Over 50 million people globally have mobility challenges, while younger individuals experience mobility challenges caused by accidents or neurological disorders [1]. Consequently, functional rehabilitation is essential for them.

Recent advancements in exoskeleton technology have enabled hand rehabilitation, facilitated by the integration and evolution of medical and engineering technology. The advancement of wearable hand exoskeleton technology has enhanced hand function treatment [2]. Rehabilitative therapies utilizing assistive devices are effective in treating paralysis associated with limb problems, especially with pneumatic or motor function and extremity functionality. Nonetheless, the rehabilitation of refined motor abilities, including finger movement and coordination, necessitates a considerable duration and continues to pose challenges [3]. Despite these endeavors, many issues with hand rehabilitation equipment persist unresolved.

Hand rehabilitation exoskeletons prioritize functional execution while neglecting user device interaction with diverse movements. To increase the rehabilitation process, we developed mirroring system gloves for hand paralysis patients who experienced injury, stroke, and hemiplegia. The developed optimal assistive rehabilitation equipment for hand function is cost-effective and portable to enable home-based rehabilitation. It is user-friendly and pleasant to promote ease of use during prolonged training sessions.

2. Design and Manufacture

2.1. Soft Gripper Actuator

Many soft gripper actuators are used in hand rehabilitation exoskeletons. Most of them are still manufactured, not in a single process, using wax or two times molding [4]. The created design in this study can be manufactured in one single shot as a cost-effective product. The design adopts a cylindrical, segmented gripper mechanism with uniformly distributed curved parts. The portions are delineated by grooves, facilitating flexibility and mobility. The outside is smooth and contoured for flexion and extension movements. The interior facilitates the application of air pressure, resulting in the gripper’s ability to extend (straightening) or bend depending on the pressure distribution. The gripper design was refined from the previous study by employing a Taguchi-based Gray Relational Analysis (GRA) method to achieve multi-quality target optimization in deformation and maximum principal stress. The gripper serves as a proxy for grasping force in practical applications by identifying the optimal design parameters [5]. Figure 1 shows the gripper design and its internal structure.

This gripper was manufactured by an injection molding process using liquid silicone rubber CN-251 material, which possesses enough elongation (400%), hardness (Shore A 25), and viscosity (22,000 cps) to accommodate significant deformation and avert material failure in the application. In the molding process, LSR was cured in a chemical reaction without the application of heat, resulting in a solidification product. CN-251 underwent crosslinking to transform it from a liquid state to a solid elastomer. This approach significantly influences the rheological characteristics of the material, such as viscosity through the curing process [6].

2.2. Hand Rehabilitation System

The schematic design of the hand rehabilitation system is shown in Figure 2. It comprises a sensory glove and a pneumatic-based glove and is controlled by an Arduino-embedded system. The sensory glove is donned on the unaffected hand to gather force and flexion data for hand motion detection.

3. Result and Discussion

3.1. Bending Angle Experiment

Given the geometry and motility similarities of five fingers, a singular finger-like device affixed to patients’ hands was developed. To reduce computational complexity and provide room for pneumatic actuation, the soft gripper was configured as a hollow cuboid with a central cuboid actuation tube. The grooves provided regulated flexibility, enabling the gripper to flex or elongate in response to air pressure changes within the chamber. The dimensions of the gripper can be personalized to the patient’s specifications. Figure 3 presents the bending result of the gripper. Even with a small pressure difference, the result showed a big gap difference. The gripper bend can be bent 180°, following the human finger behavior.

3.2. Mirror Therapy Test Training Result

Figure 4 displays the images in training with the plastic sensor in the prototype stage. The strain gauge sensor was constructed using graphite pencil markings. Pencil markings on printed paper were used for strain gauges. Standard graphite pencils left residues made of interconnected tiny graphite particle networks, which demonstrated reversible resistance variations under compressive or tensile stress. Pencil-on-paper devices are inexpensive, straightforward, and quick to manufacture. They are lightweight, adaptable, portable, and disposable and do not have potentially adverse environmental effects during processing and device manufacturing [7].

Continued enhancement of this prototype is necessary to provide superior performance and comfort for patients. In this experiment, Velcro tape and soft gloves were utilized as the base holder of the gripper to obtain excellent contact. On the left-hand side, the stain gauge sensor is attached. At the right-hand side, the gripper and soft glove indicated the injured hand.

4. Conclusions

In this study, we have developed a hand rehabilitation device that facilitates mirror therapy for the recovery of post-stroke patients. The gloves, utilizing a sensing actuation combination, employed flexible and wearable technologies, offering a safe, comfortable, portable, and cost-effective alternative to rigid exoskeleton systems. The intuitive application software enables patients or non-professionals to perform daily training and engage in therapies. The developed device potentially automates healthcare applications for home-based hand rehabilitation by using an open-source microcontroller board.

The developed device needs to be upgraded using a professional membrane bending sensor and an appropriate layout arrangement combined with traditional mirror therapy. Mirror therapy employs particular arrangements of mirrors to generate the illusion of movement in the affected limb; this technique activates the brain regions associated with the motion of the impaired limb, thereby expediting the rehabilitation process. Therefore, the glove developed in this study enhances mirror treatment, activating additional brain regions and preventing muscular ankylosis through the actual movement of the afflicted limb.