Design and Development of A Physiotherapy Robot for Rehabilitation of Stroke Patients

Abstract

The motivation for this research is the huge disparity between the number of patients and available physiotherapists in developing countries like India. The study of literature on prior research and consultation with physiotherapists showed the requirement of an exoskeleton device to impart repetitive therapy to the elbow joint. The elbow joint required a device that allowed its movement through two degrees of freedom, flexion/extension, and pronation/supination. Initially, a modular exoskeleton is built to impart a one-degree of-freedom flexion/extension motion to the elbow joint. The literature and preliminary study showed that pneumatic actuators or McKibben muscles best suit this application. The drawbacks of the commercial muscle, such as smaller contraction and longer formfactor(length), led to the development of an inhouse designed muscle actuator. The inhouse developed muscle has been designed with a unique pair of end-fittings that facilitated its easy assembly/disassembly. As the muscle is developed for a critical medical application, the muscle must be tested and characterized. The characterization process led to the design and development of two test rigs to conduct all tests with minor adjustments to the setup. The test results revealed the influence of the size and material of the bladder and braided sleeve used in the muscle's construction, on the behaviour of the muscle. The tests also showed a lower hysteresis error in the developed muscle compared to the commercial muscle. The lifecycle test on the developed pneumatic muscle successfully endured a life of over 200000 cycles at maximum pressure and loading conditions. The 12 mm styrene-based muscle with a larger braided sleeve is most effective in space-constraint applications requiring large contraction and compliance characteristics. On the other hand, the 12 mm latex-based muscle with a larger braided sleeve is most effective in applications requiring a balance of accuracy, high load capacity and compliance. The research also involves the comparison of three mathematical models to find a model that best represents the behaviour of the developed muscle. The initial design of the exoskeleton has a direct actuator-mounted arrangement. The drawbacks of the direct actuator-mounted exoskeleton such as smaller range of motion iii(ROM) led to the development of the EXPHYSIO. EXPHYSIO is short for exoskeleton for physiotherapy, which is an indirectly actuated exoskeleton system designed to impart repetitive motion to the elbow joint through two degrees of freedom. The indirectly actuated EXPHYSIO is tested for performance using the 12 mm latex muscles. The EXPHYSIO shows a 20% increase in flexion in comparison to the direct actuator mounted arrangement. It is observed that the exoskeleton executed repetitive tasks with ease, allowing the control of the elbow joint through its two degrees of freedom motion. Therefore, this research accomplished a safe, easy-to-teach, and compliant exoskeleton system for the repetitive therapy of the elbow joint through two degrees of freedom.