Transparent and Shaped Stiffness Reflection for Telesurgery

摘要

The main goal of this chapter is to demonstrate the potential benefits of controllers of the third concept, i.e. controllers with model-based haptic feedback, especially for telesurgical applications. Hereto, this chapter describes the practical implementation of the Stiffness Reflecting Controller. The experiments described in Section 5 support the claim that such controllers show good robustness properties. It is shown that, for the SRC, the compliance of the position controller does not influence the stiffness felt by the operator. It is also shown that the introduction of a low-pass filter or non-negligible time-delay only minimally affects the transparency and stability for the SRC. Although not explicitly demonstrated in this chapter, controllers of the third concept can also behave more robust with respect to other hardware-related issues of surgical slave robots that traditionally restrict the applicability of bilateral controllers on such robots. Willaert et al. (2009b) show e.g. that the inertia of the slave has a large influence on the stability properties of the DFF controller and conclude that the slave inertia should be as low as possible. Since current commercial surgical robots are mostly not lightweight robots, the SRC can be a useful controller for these robots. Another, hardware aspect of current surgical robots is the restricted structural stiffness, which influences both transparency and stability (Christiansson & van der Helm, 2007; Tavakoli & Howe, 2009). For the DFF and a slave with flexibilities, the stiffness that the human operator feels is a series connection of the real environment stiffness, the stiffness of the position controller and the structural stiffness of the slave. In this work, the estimation of the environment stiffness is based on the force measurement at the end-effector (Fe ) and the position measurement at the motor (xs xe ). As the 1 d.o.f master and slave behave as a rigid-body for frequencies below 100 Hz, the correct environment stiffness can be estimated. For flexible multi-d.o.f. systems, however, the estimation of k e should be based on the force measurement at the end-effector (Fe ) and the position measurement at the end-effector (xe = xs ). In future research, it will be investigated how the position of the end-effector can be measured or estimated. By doing so, the SRC can be made insensitive to both the compliance of the position controller and the compliance of the slave robot itself. Based on the detailed stability analysis of the DFF and the experiments presented here, it is clear that, compared to the DFF, the SRC will have significantly better stability properties when implemented on multi-d.o.f master-slave setups. But, a detailed analysis of the stability properties of the SRC is not straightforward due to the presence of the Extended Kalman Filter. Thanks to the introduction of a stiffness-depending damping term (see 12), the SRC implemented on the setup described in this chapter is stable for environment stiffnesses up to