Admittance Control Based on a Stiffness Ellipse for Rapid Trajectory Deformation

This study proposes an admittance control method based on a stiffness ellipse. Some assembly tasks in factories are difficult to automate because discontinuous transitions between contact and noncontact phases generate issues. In the contact phase, a control approach is required to handle assembly parts with compliance; in the noncontact phase, a control method follows a trajectory. To achieve an assembly task, it is often necessary to switch control during the contact phase; however, such switchovers often degrade performance. This study aims to solve this problem by adjusting the stiffness ellipse by admittance control. By tilting the stiffness ellipse, external force can be applied in the desired direction during contact without switching the control or adjusting the position/force command. Using the proposed method, tasks having contact and noncontact phases can be achieved with continuous control. Experimental results from a drawing task and simulation results from drawing and peg-in-hole tasks demonstrate the advantages of the proposed method.