A new force limitation mechanism for risk reduction in rehabilitation robots

In this paper, a new mechanism to reduce the risk of rehabilitation robots contacting with a human is proposed. The device is composed of a force limitation mechanism, a spring and a damper with anisotropic viscosity. A prototype was developed and its basic features were experimentally evaluated. The size of the prototype was too large, but it confirmed that the new mechanism had many advantages. It could avoid using force stronger than a threshold level above which humans are affected. As the arrangement of the mechanism was not restricted to the joints of a robot arm, posture of the robot had no influence upon the threshold force to an end-effector. The anisotropic damper realizes quick response to excessive forces and slow restoration for safe movement.