Instantaneous model impedance control for robots

Impedance control facilitates the performance of tasks that involve contact with the environment. Two generic strategies for implementing impedance control have been described in the literature: the dynamic based approach [4] and the position based approach [7]. The second method has been introduced to eliminate the inherent sensitivity of the first method to the accuracy of the dynamic model. However, it introduces impedance errors whenever the actual position of the robot differs from that of the model. We propose a new method for implementing impedance control, which is designed to take advantage of the error-correction capabilities of position controllers, while maintaining good impedance tracking performance. The proposed Instantaneous Model Impedance Control re-initializes the impedance model to the current position of the robot so the model does not accumulate position errors. The novelty of the method is in using the position feedback both in the outer loop, to track the desired impedance, and in the inner loop to improve robustness. The proposed method includes the dynamic-based and the position-based methods as specific cases, and can be tuned to trade between their corresponding merits. Using simulations, we demonstrate the performance of the new method in comparison with the previous methods. We consider two scenarios: stiff environment, which challenges the position based approach, and load uncertainties, which challenges the dynamic based approach.