Programmable Springs: Developing Compliant Actuators for Autonomous Robots

Conventional approaches to actuation and motion control are designed to eliminate any perturbations from the system and provide smooth precise control of speed or position and a high level of stiffness. By contrast, emerging approaches to autonomous robotics rely on exploiting the environment to aid motion. In passive dynamic systems motion is modulated by interactions between the mechanism and the environment; instead of forcing the actuators to follow pre-planned trajectories the environment is used to guide motion. Developing real robots that can exploit these dynamics requires the use of actuators that can react to the environment, exhibiting behaviour that varies from high stiffness to complete compliance or zero impedance. We will outline our design for an electric actuator, called a programmable spring, which can be configured to emulate many complex sprung and zero impedance systems within its range of movement and mechanical limits. This design forms the basis for a prototype actuator intended as a cost effective `off the shelf¿ component for robotics development. Our design includes a sophisticated control architecture that allows the actuator to exhibit complex autonomous behaviour whilst offering the user a high degree of control. The addition of programmable damping behaviour and possible applications for this type of system beyond the field of robotics are also discussed.