Passivity-based model updating for Model-mediated Teleoperation

We study the stability of three-dimensional (3D) haptic interaction in Model-mediated Teleoperation (MMT) systems. In MMT, a simple object model is employed on the master side to approximate the remote environment. The haptic feedback is rendered locally on the master side based on model parameters which are estimated on the slave side. The main advantage of the MMT approach is that the haptic control loop is running locally which leads to stable behavior even in the presence of communication delays. The local model must be updated when the environment changes, or novel, previously unseen parts are encountered. During the model update, a sudden change of the model parameters leads to model-jump effects and results in unpredictable motion and force. A smooth and stable model update scheme is required to mitigate this effect. To guarantee system stability, we derive a passivity condition for a 3D spring-damper model during the model update phase. Energy generated due to the changes of the model parameters is dissipated through an adaptive damper element. The sampling effect of the haptic device is also taken into account. The performance of the proposed passivity-based model update (PMU) scheme is evaluated through simulations and subjective experiments. Evaluation results show that by using the PMU scheme, system stability during the model update phase is guaranteed. Moreover, subjects feel more comfortable with the model update if the PMU scheme is enabled.