Linear multi-degree of freedom variable stiffness actuator for robotic assembly tasks

The series elastic actuators (SEAs) have been popularly applied to various robotic applications. The rigid actuator is vulnerable to applications where back drivability is required despite many automated assembly tasks requiring the function for enhanced robot operation. Since the SEA comprises only one stiffness, there is a limit to the usable application. Therefore, the variable stiffness actuator (VSA) with multiple stiffnesses is to be developed. This study aims to develop a linear multi-degree of freedom VSA. Instead of the conventional rotary-type VSA with one degree of freedom, we propose an actuator that can control stiffness with more than two degrees of freedom. The proposed VSA is advantageous for tasks such as screwing and deburring that require a change in stiffness depending on the circumstances. The mechanism is configured using a linear spring, and the stiffness is controlled by changing the tension spring to a nonlinear form. We also develop the new VSA through this mechanism and perform simulation analysis. In addition, the validity of the proposed VSA is verified through experiments by manufacturing a VSA based on the design.