A motor-assisted recumbent trike for cycling training in neurological patients

Cycling is a widely used rehabilitative method since it is a safe and intensive exercise that shares several similarities with walking. When practiced outdoors, cycling becomes a model of Sport-Therapy, favoring social inclusion and promoting the psychological well-being of the subjects. The aim of this study is to design a motor-assisted recumbent trike in order to allow even severely impaired people to pedal outdoors. The main novelty of the designed system is in the control strategy which implements an assist-as-needed cooperative approach in order to maximize the residual volitional contribution of the pilot. A commercial recumbent trike (CATRIKE 700) was equipped with a DC brushed motor mounted on a custom-made aluminum support and coupled with a free wheel to transmit torque to the main chain without applying any additional resistance. A Proportional Integral Derivative (PID) controller was implemented in order to modulate the PWM duty cycle to keep a constant target cadence. A feasibility study involving three healthy volunteers and three stroke survivors was conducted. The designed setup proved to be suitable for assisting a fully-active exercise as well as for handling completely passive legs movements. Moreover, it proved to be a good solution in assisting the user in compensating for muscle weakness or fatigue. Future works will combine the voluntary effort of the pilot and the assistance of the motor with the action of Functional Electrical Stimulation (FES) and will verify the feasibility of the hybrid motor-FES approach.