Remote Gripping for Effective Bilateral Teleoperation

Remote Gripping for Effective Bilateral Teleoperation

A.M. Harsha S. Abeykoon (University of Moratuwa, Sri Lanka) and R.M. Maheshi Ruwanthika (University of Moratuwa, Sri Lanka)
DOI: 10.4018/978-1-5225-0435-1.ch005
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Abstract

Accessibility for remote locations could be easily overcome by teleoperation. When manipulating an object at a remote place, it is beneficial if the operator is capable of feeling the force and position information including environmental object impedance for successful remote manipulation. In this chapter, bilateral control, based on acceleration architecture is explained from the basics starting from the human's haptic perception. The sensorless sensing mechanism “Reaction Torque Observer” is applied to the gripper which enables the operator to feel the remote environment while on remote manipulation. “Disturbance Observer” which is a popular control tool used to attain robustness is also successfully adopted for this application. Further, authors introduce force lock during bilateral teleoperation, which facilitate handling delicate objects. Practical as well as experimental results are discussed and the chapter concludes with suggestions for possible future research directions.
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Introduction

The prefix tele from Greek origin means at a distance and teleoperation literally means operating a machine at a distance. Teleoperation extends the human capability to manipulate objects remotely by providing the operator with similar conditions as those at the remote location. Most controllers encountered in daily activities are unilateral controllers. As the name implies, communication is performed unilaterally. A simple TV remote controller is an example for a unilateral controller. In a bilateral controller, master (operator) and slave (environment) sides are bilaterally controlled. The intention is to feel the environment at the distance while it is being controlled. Bilateral control system enables the slave side environment to be reflected in the master side and master side operating intention to be reflected in the slave side.

Humans have five sensors for vision, smell, sound, taste, and touch. Sound and visual senses of the human can be stored and reproduced in a remote place, but the sense of the nose (smell) and tongue (taste) cannot normally be transmitted or stored via electronic means. Touch, the fifth sense, can be transmitted and reproduced using the bilateral control concept. Target of bilateral control is the transmission of haptic information by electronic means from a remote location. The term haptic means the sense of touch.

The significant aim in advanced bilateral teleoperation is to achieve high haptic perception and to give the operator the feeling of telepresence (as if the operator is physically present at the remote site). For a perfect bilateral teleoperation, both position tracking and force control should be achieved simultaneously. Consider an example where high precision position control should be achieved. The position of a cutting tool should be maintained despite the changes in the material properties and the variations in cutting forces during high precision machining. Similarly, there are applications that need force control. Contact force has to be maintained carefully while handling fragile objects. In such applications, force need to be controlled regardless of the position. Thus, position control and force control have opposing requirements. In this chapter authors introduce acceleration control to achieve position control and force control simultaneously in realizing bilateral teleoperation.

The bilateral control system is a popular and successful concept behind several engineering applications such as mine excavation, space robots, and medical surgeries. Following applications highlight the importance of haptic feedback in teleoperation.

The Da Vinci Surgical system is designed to facilitate complex surgery using a minimally invasive approach. It is controlled by a surgeon from a console. The surgeon performs operation through small incisions. He sits at the console while operating. On patient-side, cart with four interactive robotic arms are controlled from the console. Da Vinci’s patient-side cart holds up to three EndoWrist instruments and one 3D camera. Surgeon operates by viewing a magnified 3D HD image of the patient’s interior. The surgeon uses controls that work like forceps. As surgeon moves controls, Da Vinci responses in real time, translating hand, wrist and finger movements into smaller, precise movements of EndoWrist instruments at the patient-side cart (Intuitive Surgical Inc, 2015). In this approach there is no haptic feedback to the surgeon from the organs touched through the EndoWrist instruments. The surgeon relies on the vision system and assumes the force applied through EndoWrist instruments on the organ and proceeds the operation. The lack of haptic feedback in Da Vinci Surgical system is a greater risk. If haptic feedback is introduced, the surgeon does not want to rely only on the vision system and it avoids the assumption of force applied through the EndoWrist instruments on organs (Ishii, Katsura, Nishi, & Ohnishi, 2008). With the aging of population, the skill preservation of an expert has been a serious concern especially in fields like handcraft production. The solution of digital skill preservation proposed by Shimono et al (2007) has been developed through nearly a decade and the latest research on motion copying system and haptic database facilitates reliable remote manipulation from another country (Nagata & Katsura, 2015). This is possible to operate few patients at a time by a single expert surgeon (Kebude, Morimitsu, Katsura, & Sabanovic, 2014). This text introduces a successful sensorless haptic feedback method which could be used in minimally invasive surgery in the future.

Key Terms in this Chapter

Teleoperation: Operating a machine at a distance.

Reaction Torque Observer (RTOB): A modified version of disturbance observer to estimate reaction torque/force exerted by external environment on the motor if frictional elements and parameter variations are known beforehand.

Control Stiffness: The change in the force per arbitrary small change in the displacement.

Bilateral Teleoperation: Operating a machine at a distance while exchanging the action and reaction information between the master and the slave bidirectionaly in real time via a communication channel.

Slave: The machine/manipulator following the command signal issued from the remote location.

Disturbance Observer (DOB): An observer use to attain robust operation which is immune to the system disturbances.

Haptic: the sense of touch.

Force Lock: A gripper locking mechanism which is activated after satisfying the assigned force limit and maintains the constant force until object release logic is true.

Master: The operator issuing the commands through a human machine interface to control the remote machine/manipulator.

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