Towards a robust variable stiffness actuator

Robots with Variable Stiffness Actuators (VSA) are intrinsically flexible in the joints. The built-in mechanical spring not only has the advantage of a higher peak performance, but also leads to a more robust robot. This paper presents and analyzes the threats to a VSA equipped robot that arise from external or internal origin. Influences of mechanical, moisture, electrical, thermal, radiation, and chemical nature are identified. Protection methods from these threats are discussed and the results presented. The results are separated into hardware, observation, control limiters, and reaction strategies. A hierarchical implementation of the control limiters and reaction strategies is presented. The reaction strategies use a motor position deviation and a change in the stiffness setup to reduce the load at high passive deflections in the VSA. Control limiter and reaction strategies have been implemented in the DLR Hand Arm System and evaluated experimentally with impacts on the system.