Influence of time-varying communication delay in adaptive controller based bilateral control system

Abstract

Communication delay between a master robot and a slave robot destabilizes a bilateral control system. And some re cent researches show that an adaptive controller that dynamically determines the master's controller gain depending on a stiffness of a contact object is effective to improve stability. However few researches show an influence of time-varying communication delay in adaptive controller based bilateral control systems. This paper therefore verifies an influence of time-varying communica tion delay. A PI (polynomial interpolation) with a schmitt trigger is utilized to estimate a stiffness of a contact object. Simulation results show that the PI based estimation method has a robust ness against a constant/time-varying communication delay. An experiment of a bilateral control over an IP (Internet Protocol) network emulator also show the validity of the estimation method. I. INT RODUCTIONThe da Vinci Surgical System (Intuitive Surgical, Inc.) or the PackBot (iRobot Corporation) has drawn attention as a practical application of teleoperated robots. The da Vinci is a medical robot for minimally invasive endoscopic surgeries, and more than 3000 robots are utilized in the world. The PackBot was utilized for the probe of Fukushima I Nuclear Power Plant after the Great East Japan Earthquake in 2011. However, since a human operator who manipulates the da Vinci or the PackBot does not feel a reaction force from a contact object, it is difficult to achieve sensitive motions such as a grasping of brittle materials. Hence some researchers have tried to transmit a reaction force to a human operator [1] . This kind of teleoperation is known as a bilateral teleoperation or a bilateral control. A bilateral control is a hybrid control of a position control and a force control. A slave robot tracks a master robot when a human operator manipulates the master robot. This is the position control. When the slave robot contacts with an object, the human operator feels a reaction force from the object. This is the force control. However, a bilateral control system becomes unstable when a feedback loop in the system includes communication delay.There are two kinds of approaches to design a bilateral control system with communication delay. One is an approach to utilize a sufficient condition for stability, and the other is an approach to utilize a necessary and sufficient condition for stability. Small gain theorem based design methods [2] and passivity theorem based design methods [3] have been proposed as sufficient condition based approaches. However, control performance is low. On the other hand, Nyquist the-978-1-4799-8464-0/16/$31.00 ©2016 IEEE orem based design methods have been proposed as necessary and sufficient condition based approaches. These methods fall into two category. One is a design method which does not take into account interference between a position control and a force control. The other is a design method which takes into account interference. Although the first method makes it easy to design a controller,...

Design of Adaptive Controller using Object Position for Bilateral Control System with Communication Delay

“…Reference (11) switched two controllers based on the contact condition: a non-contact state or a contact state. References (12) and (13) designed an adaptive controller that utilized the stiffness of a contact object for a controller gain. However, the delay resulting from the time taken for stiffness estimation degrades control performance.…”