Integration of variable stiffness actuators in a five-bar device to assist in active rehabilitation of the arm

Active arm rehabilitation involves restoring muscle tone by applying force to the arm to produce traction and compression on the muscles. Devices for rehabilitation assistance can be exoskeleton or end-effector type. This paper uses an end-effector type device, which provides an opposing force to the patient’s arm’s movement to tone their muscles during active rehabilitation. To provide that force, large and expensive motors with high torque are required. In order to avoid the use of motors, it is proposing a variable stiffness actuator integrated into a five-bar mechanism for active arm rehabilitation assistance in this work. The five-bar mechanism has a pantograph attached to amplify the workspace and emulates the arm rehabilitation trajectories, the patient holding onto the end-effector to trace the trajectories. The end-effector provides a constant opposing force to the patient’s arm’s movement, which activates the muscles. Thus, our proposal is the integration of an actuator with variable stiffness to replace the motors. The mechanism synthesis is presented to determine the parameters to vary the stiffness that provides a constant force in the five-bar mechanism end-effector.