Keywords: Control , Haptic interface, telemanipulation, medical robotics, effect of changing operator grip stiffness

ABSTRACT - This article addresses specic issues of force re ected telemanipulating systems and medical robotics. The approach to the robotic assisted surgery presented here is based on the idea of combining the best characteristics of a surgeon and of a robot. From the surgeon, it is expected to use his own senses, experience and judgment to guide the slave robot, while the master robot provides both the geometric accuracy by means of a motion constraint and tactile feedback for the surgeon.
The article consists of two parts. The first one deals with requirements for medical robotics and addresses some changes for the robotic assisted surgical procedures. The abilities of surgeon and robot are compared and the reasons of bringing the robots to the operating theathre are discussed. Some examples of ''in vivo'' robotic systems for orthopaedic and minimally invasive surgery, specific regarding the tactile (force) feedback are presented.
The second part outlines the development of a three degree of freedom (DOF) (x,y,z) force feedback telemanipulating system. This system consists of the PHANTOM Premium 1.5 haptic interface with three active DOF acting, as a master device and the ASEA IRb 6 industrial robot with five DOF acting as a slave robot arm. The robots are connected via serial link. Two different force re ection control schemes are implemented and analyzed: the direct method, suitable for compliant environment and as next the position-error-based force re ection method, suitable for sti er envi- ronments. The system (in)stability depending on the operator's hand compliance and the environment compliance is assessed and found to be the drawback of the direct method. Due to the non-satisfactory practical behavior of the first method, and on the other hand, undesirable damping encountered during the free motion with the second method, a new method was introduced. That is the position-error-based force reflection with variable gain. This method was used for the drilling experiment carried out on various hard and soft materials including aluminium, wood, bone and soap. The geometric accuracy and fixation along the z axis of drilling was achieved by means of a cylindrical motion constraint in software of a master robot arm.

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NOTE: Section 3 provides an example of the effect of a change in grip stiffness of the operator on the open loop gain (and thus stability),.
Only basic control architectures are used in this article