Influence of joint flexibility in the adjustment of impedance controller parameters

The adjustment of stiffness, damping, and apparent mass in an impedance controller is analyzed for a joint linear model which includes flexibility, modeled as a spring effect in the torque transmission between actuator and load. An approximate model to the fourth-order linear model is utilized to analyze the behavior in free space and to obtain a condition on impedance parameters for a nonoscillatory behavior. Joint impedance has four zeros and two poles. The joint in contact with the environment can be unstable. The analysis shows a lower limit in the stiffness defined by the impedance controller if the behavior in free space is not modified through an increase in apparent mass