Design proposal for reducing actuator redundancy in intrinsically compliant manipulators

Variable Stiffness Actuators (VSA) allow for simultaneous position and stiffness control of a joint by the use of two actuators, therefore they are used in the design of intrinsically compliant manipulators. Generally, for a manipulator with n joints n VSAs are used, resulting in 2n actuators. In this work, we propose the design of a two-link intrinsically compliant manipulator using only three actuators (instead than four): one Series Elastic Actuator (SEA) in a mono-articular configuration, and a VSA based on two antagonistic actuators in biarticular (actuators producing simultaneous torque about both joints) configuration. The proposed actuation structure reduces the amount of actuators, while increasing the isotropy of the end effector force (in all the workspace), and end effector stiffness isotropy when the arm extends. Therefore the proposed structure based on monoarticular SEA and biarticular VSA is suitable for light and compliant manipulation, as for example robotic hands, arms and legs.