Use of Compliant Actuators in Robotic Applications

Abstract

In industrial robotics - accurate - positioning of manipulators or end effectors is by far the most common application. The system is designed to meet the high mechanical stiffness and high feedback gains required, which improves the accuracy, the stability and the bandwidth of the position control. A typical DC-drive with gearbox and conventional feedback control often suits this purpose. New robotic technologies emerge, however, in which accurate positioning or trajectory tracking is not the primary design goal or unable to compensate for the many drawbacks- from this different point of view - that comes along with conventional electrical actuators, like high reflective inertia, high stiffness, low force-to-weight ratio. These new robotic applications can strongly benefit from compliant actuator technology. Instead of introducing compliance on the control level through application-specific software, this approach is based on inherent adaptable compliance on a purely mechanical level. In this way intrinsic compliance is assured at all time, enhancing system safety. The equivalent torsion spring stiffness of an actuated joint and the equilibrium position of its end effectors, i.e. the joint's configuration in which the actuator torque is zero, leaves us with two adaptable mechanical parameters to be set for each joint, which evidently increases the complexity of control. This is easily countered with the range of potential benefits, adding value to existing applications and also creating new applications in robotics. An overview of compliant actuator technologies developed by different research groups is given. Different robotic applications are outlined in which these compliant actuators are incorporated.