MACCEPA, the mechanically adjustable compliance and controllable equilibrium position actuator: Design and implementation in a biped robot

In this paper a rotational actuator with a novel adaptable compliance (inverse of stiffness) is presented. First, a number of comparable designs are given with their possible drawbacks.

The MACCEPA concept and design is then described in detail. The equation to calculate the generated torque is derived. Depending on the design parameters, it is shown that the torque is a quasi linear function with respect to the angle between the equilibrium position and the actual position. Also, the change of the pre-tension has a quasi linear effect on the torque. Another advantage is that the actuator can be built with standard components, e.g. electrical servo motors. Experiments show independent control of the equilibrium position and compliance.

The use of the MACCEPA in the Controlled Passive Walking biped Veronica is described. Controlled Passive Walking is an approach that combines the advantages of actively controlled robots and passive walkers. By adapting the compliance of the joints, natural motions can be chosen in order to obtain a controllable and energy efficient walking motion. To test the concept, the biped Veronica is built, actuated by six MACCEPAs.