Torsion MACCEPA: a novel compact compliant actuator designed around the drive axis

The Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator (MACCEPA) is a Variable Stiffness Actuator (VSA) where both equilibrium position and stiffness of the actuator can be controlled independently. This actuator uses only one linear spring and has a simple design but its compactness is limited by the spring. For this reason a MACCEPA utilizing torsion spiral springs was designed, reducing the planar dimensions of the actuator. Torsion spiral springs are placed around the joints' axis, allowing a more compact VSA in comparison to previous designs. To the authors' best knowledge, this is the first VSA based on torsion springs. This paper firstly presents the design of the actuator as the static equations and secondly discusses the design and production of the torsion spiral springs. The newly presented actuator is built and experiments are conducted to validate the model and feasibility of the torsion MACCEPA.