Contact Stability Analysis on Some Impedance Control Methods.

This paper aims at the analysis of the contact stability of impedance control implemented to a robot manipulator. It is important for next generation robots to realize compliant motion to environment. Impedance control is one of the compliance control methods. However, there are still contact stability problems that the control system is unstable when the robot arm implemented with impedance control contacts to a stiff environment. In this paper, two methods of impedance control, Hogan's method and acceleration feedback method, are analyzed on the contact stability influenced with the locations of sensor and actuator. The target impedance, and modeling error are also considered. An one d.o.f. arm grasping a fixed stiff object is modeled and simulated under the consideration of unmodeled dynamics of the arm and the elasticity of the contact surface of the arm and its object. The analysis draws the results that the collocation of sensor and actuator does not always stabilize the contact task in the case of the existence of the unmodeled arm dynamics, and the stable regions of target impedance are different on these methods.