Lyapunov function based bilateral control for teleoperation system with time varying delay

Recently, robotic surgical support systems are in clinical use for minimally invasive surgery. In order to improve the operability of the robotic surgical systems, development of haptic forceps teleoperation systems is required to help surgeon´s dexterity. In addition, the motion scaling, which can adequately reduce or enlarge the movements and tactile senses of the operator and the robot, is necessary to assure safety of the surgery. On the other hand, communication time delay is inevitable in teleoperation systems, which may cause instability of the teleoperation systems. Therefore, stability of the system must be guaranteed in the presence of the communication time delay between master device and slave device. We have developed a multi-DOF robotic forceps manipulator using a novel omnidirectional bending mechanism, and for the developed robotic forceps manipulator, we proposed a passivity based bilateral control that enables motion scaling in both position tracking and force tracking, and guarantees the stability of the teleoperation system in the presence of constant time delay, so far. In this paper, the passivity based bilateral control is extended so as to guarantee the stability of the teleoperation system not only in the presence of the constant time delay but also in the presence of the time varying delay.