Abstract
As the applications of robots increase, mobility and capability of interaction in unstructured environments have become important. Hence, humanoid robots have been developed to have these capabilities, and recently, compliant motions for safe contact have been studied. The Operational Space Formulation can be an effective method for humanoid robots to realize compliant motion via unified motion and force control. Nevertheless, the implementation of the Operational Space Formulation on humanoid robots has not been successful. One of the challenging issues is low position tracking performance. In this study, a control method for solving this problem is proposed by considering the joint stiffness and joint bandwidth limits. To consider joint stiffness, the Operational Space Formulation was derived using flexible joint robot dynamics. Additionally, an extra torque generation method, which penalizes low performance actuators, is utilized to account for the bandwidth limits. Neither methods requires additional sensors or joint space controllers. Hence, they can be useful for conventional humanoid robots composed of electric motors and gears. By integrating the two methods, the position tracking performance of the Operational Space Formulation on the humanoid robot was significantly improved. The proposed method was demonstrated via position and orientation control experiments using our humanoid robot, TOCABI.
Highlights
T HE demand for robots that are applied to human environments such as social robots and collaborative robots, has been increasing
This study presents a controller that combines the Operational Space Formulation considering joint elasticity and the extra torque generation algorithm for humanoid robots
Considering the joint elasticity and the joint bandwidth limit, which are the main causes of the degradation of tracking performance, the Operational Space Formulation was able to provide sufficient performance in the humanoid robot
Summary
T HE demand for robots that are applied to human environments such as social robots and collaborative robots, has been increasing. Joint space controllers can accomplish high position tracking performance, converting the desired task to the joint space trajectory is difficult to solve for the robots with high degree of freedom (DoF) or complicated structures They may not utilize the advantages of the Operational Space Formulation such as the intrinsic compliance of tasks or dynamically decoupled independent control of each task. The Operational Space Formulation considering joint elasticity was proposed in [24], and the method considering the bandwidth limit of joints to generate additional torque over several steps was proposed in [25] Both methods improved the position tracking performance of the Operational Space Formulation, and they are expected to exhibit a significant effect when they are integrated.
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