Coaxial damping series elastic actuator for improved performance of transmissibility

There are many flexible joint designs that are delivering torque and absorbing shocks simultaneously. One of the most active areas of the research is the Series Elastic Actuator (SEA), which connects the motor and load by lowering the stiffness. The problem, however, is that the non-rigid stiffness causes the system to have a lower bandwidth, thereby slowing down the system's response. On the other hand, the high stiffness of SEA adversely affects energy efficiency and performance of impact relief. In other words, concerning the application of conventional SEAs, it is important to determine the joint stiffness. Therefore, other researchers have developed Variable Stiffness Actuators (VSAs) that can control the stiffness in the system. To improve further the controllability and transmissibility of SEAs, Variable Physical Damping Actuators (VPDAs) that can change the damping element of the system has been developed. Although previous studies have provided valuable findings, VSAs and VPDAs make the system complex so that complicated control theories are required. In this paper, a new Coaxial Damping SEA (CODSEA) that can efficiently adjust the stiffness and dynamic damping is designed. The biggest advantage of CODSEA is that it can change the stiffness and damping efficiently by converting the geometry of the driving shaft and particle materials inside the driving shaft without additional systems. In other words, only the driving shaft becomes the SEA and physical damping system.