Biologically Inspired Soft Robot for Thumb Rehabilitation1

摘要

More than 130,000 people have strokes each year in the United States [1]. Of these victims, 76% are left with disabilities that cost the nation over $54 billion in lost work and medical fees. One prominent disability is upper extremity hemiplegia, which occurs among approximately 50% of stroke sufferers [2]. Robotic technology has the potential to provide an automated platform for controled rehabilitation and assisted, task-oriented therapy.Several systems have been designed to assist in patient articulation of an impaired hand using rigid robotic components. While these products have been successful in articulating the pure bending motions of the four fingers, the limited capabilities of rigid technologies fail to reproduce the complicated motion path [3] of the thumb during opposition grasp (see Fig. 1). This is the most important articulation for normal hand function and specifically for picking up everyday objects. To date, robotic systems for thumb rehabilitation have not been widely investigated [4] apart from some recent work [5] that used a multijoint rigid robot.The soft robotic thumb rehabilitation system presented in this paper is a task-oriented therapeutic device that replicates and restores correct thumb motor function for patients with neurologically caused hand disabilities.Discussions with physical therapists and patients identified a need for a controllable robotic system to assist a neurologically impaired thumb in performing functional operations for at-home task-oriented therapy. First and foremost, the device must follow the motion path of a healthy thumb. The device must also be comfortable, durable, and externally controllable. The final design (see Fig. 2) consisted of a soft robotic actuator, a conformable neoprene padded aluminum attachment with Velcro straps, and a control system.The most essential specification of the design was replicating a healthy thumb's natural motion path during opposition grasp. It was hypothesized that the overall motion path of the thumb during opposition grasp could be represented as a combination of bend (thumb flexion), twist (thumb rotation), and extension (skin stretching). A biological kinematic study using eight independent electromagnetic sensors (3D Guidance TrakSTAR) was performed on a healthy thumb during opposition grasp to the index finger and to the small finger. The motion paths measured were broken down into bend, twist, and extension, and their values became the minimum and maximum functional requirements respectively. These requirements were: 25–70 degrees of bend, 15–25 degrees of twist, and 0.4–0.5 in. of linear extension.Given the inherent limitations of traditional robotic components, soft multimaterial fluidic actuators were investigated for their increased compliance, customizability, and safety. Several different soft robotic actuators exist and were evaluated. For this application, a fiber-reinforced actuator was found to be the most effective and efficient in terms of single actuator durability, force, and motion path customizability.The fiber-reinforced actuator was made from an elastomeric chamber with a flexible strain layer (fiberglass cloth, FG-C0427S, US Composites, FL, USA) adhered to the bottom, which was then wrapped with a strain material (Kevlar thread, KEV693NATL00S, The Thread Exchange, NC, USA) to restrict expansion in certain directions, and covered with a flexible outer protection layer. A cross sectional model of a basic, soft bending, fiber-reinforced actuator can be seen in Fig. 3, exhibiting the inner chamber, the structural elastomer, the strain wrapping, the strain layer, and the protective outer layer.Through experimentation, a fabrication technique was developed to create soft actuators with a maximum inflatable pressure of 50 psi (345 kPa) capable of producing the desired bend, twist, and extension motion paths. An actuator with double helical strain wrapping and a strain layer along the bottom produced a bending motion.