Design And Control Of A Compliant Robotic Actuator With Parallel Spring-Damping Transmission

As the developments of robotic technologies,robots are moving from industrial applications to unstructured environments,such as service,medical and rescue.These new applications require robots with better environmental adaptation and humanrobot interaction safety,as well as better force and position control ability,which is difficult for the conventional rigid robots consisting of rigid actuators.By using physically compliant actuators to drive the robot’s joints,the robot’s environmental adaptability and human-robot interaction safety can be improved,as well as its force control stability.Although the physical compliant actuators can improve the compliance and force control stability of the robots,the introduction of compliant elements will reduce the mechanical bandwidth of the system,resulting in a reduction in the dynamic response of the force control.In addition,the introduction of compliant elements may also induce oscillations to the system,which can affect the position control capability of the actuator.To address these issues,this paper proposes a parallel spring-damping actuation scheme based on a conventional series elastic actuator.This paper first analyses the dynamics of this actuation scheme in the frequency and time domains and finds that it can improve the force and position control performance while maintaining the compliance of the actuator.A parallel spring-damping actuator with variable damping is then designed.The variable damping function is achieved by varying the size of the orifices via a variable damping adjustment mechanism,which is embedded in the shaft of the actuator to ensure the compactness of the actuator.In addition,because of the parallel springdamping structure of the actuator,it can be converted from a compliant actuator to a rigid one when the orifices are fully closed.Based on the variable damping characteristics of the actuator,this paper first proposes a variable damping control algorithm that can effectively control the physical damping of the actuator,and then proposes a variable damping force control algorithm and a variable damping position control algorithm that can both incorporate the variable damping control algorithm.Through simulation analysis and experimental verification,it is demonstrated that the proposed parallel springdamping actuator with variable damping can improve the force control and position control performance of the actuator while ensuring the compliance.This research provides new ideas and methods to support the practical application of physical compliant actuators in robots.