a b s t r a c tIn minimally invasive surgery (MIS) the continuously increasing use of robotic devices allows surgical operations to be conducted more precisely and more efficiently. Safe and accurate interaction between robot instruments and living tissue is an important issue for both successful operation and patient safety. Human tissue, which is generally viscoelastic, nonlinear and anisotropic, is often described as purely elastic for its simplicity in contact force control design and online computation. However, the elastic model cannot reproduce the complex properties of a real tissue. Based on in vitro animal tissue relaxation tests, we identify the Hunt-Crossley viscoelastic model as the most realistic one to describe the soft tissue's mechanical behavior among several candidate models. A force control method based on Hunt-Crossley model is developed following the state feedback design technique with a Kalman filter based active observer (AOB). Both simulation and experimental studies were carried out to verify the performance of developed force controller, comparing with other linear viscoelastic and elastic model based force controllers. The studies and comparisons show that the Hunt-Crossley model based force controller ensures comparable rise time in transient response as the controller based on Kelvin-Boltzmann model which is reported as the most accurate description for robot-tissue interaction in recent literature, but it causes much less overshoot and remains stable for tasks with faster response time requirements.

Tele-surgery has been more and more popular in robotassisted medical intervention. Most existing teleoperation architectures for medical applications adopt 2-channel architectures. The 2-channel architectures have been evaluated in literature and it is shown that some architectures, e.g. position-force (P-F), are able to provide the surgeon a reliable haptic sense of the working environment (transparency). However, stability of these P-F architecture is still a considerable concern especially when physiological disturbances exist in the remote environment. P-PF architecture is proved to provide a convenient alternative. With one more channel 3-channel teleoperation architectures present promising options due to their augmented design flexibility. This paper evaluates stability and transparency of general 3-channel bilateral teleoperation control architectures and provides a design framework guidelines to improve the architectures' stability robustness and optimize the transparency. Simulation evaluations are provided to illustrate how the optimal 3-channel teleoperation architecture is chosen for medical applications given their dedicated requirements.

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