Improvement of model-mediated teleoperation using a new hybrid environment estimation technique

In a haptic teleoperation system, the incorporation of knowledge about the remote environment in the controller design can improve stability and performance. Model-mediated teleoperation adopts this idea by rendering an estimated model of the remote environment on local site instead of transmitting force/velocity flows. Thus, the user perceives locally generated forces corresponding to the estimated and transmitted model parameters and the control loop between master and slave is opened. Less conservative stability boundaries and the applicability to teleoperation systems with arbitrary time delay are the main advantages of this approach. In order to guarantee a high fidelity, the estimation has to fit well with the measurements. In this paper, we extend the approach of model-mediated teleoperation to a full 6 degrees-of-freedom (DOF) teleoperation system with negligible time delay. We furthermore propose a hybrid approach for the estimation of the remote environment by combining the classical Kelvin-Voigt model and the nonlinear Hunt-Crossley model. Persistent excitation and device-dependent limitations of the estimation algorithm are discussed. Experimental results show stability and accuracy of the estimation technique as well as a superior fidelity of the proposed approach compared to a position-based admittance controller with fixed parameters even with negligible time delay.