Time Delay and Uncertainty Compensation in Bilateral Telerobotic Systems: State-of-Art with Case Studies

1. Introduction

Telerobotics is the subfield of robotics which is concerned with the design operation, and control of teleoperators (Batsomboon & Tosunoglou, 1996; Buss & Schmidt, 1999; Niemeyer, Preusche, & Hirzinger, 2008; Sheridan, 1992). The word “tele” comes from the Greek word “τηλε = tele” which means “distant.” All complex words which have as prefix the word “tele” (e.g., tele-learning, tele-medicine, tele-communication, etc.) have the meaning that the respective operation or task is performed by two distant systems or humans which are physically separated. This separation may be very small (e.g., when an operator and a robot are located in the same room) or very large with a long distance separating them. For convenience of the reader, we first define the basic terms that are used in the general field of telerobotics, namely: teleoperators, telerobot, teleoperation, telemanipulation, local site, remote site, direct or manual control, supervisory control, shared control, unilateral control, bilateral control, telepresence-transparency.

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  Teleoperator: A system or device which enables a human operator to manipulate and sense objects at a distance (i.e., beyond his/her reach).

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  Telerobot: A robot that works using human instructions from a distance and performs live actions at a distant environment via sensors and effectors.

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  Teleoperation: Stresses the task level operations via human intelligence and human-machine interfaces.

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  Telemanipulation: A remote robot (slave), working in a difficult or dangerous environment, tracks the motion of a master manipulator. To this end, two distinct processes are needed, namely: interaction between the operator and the master robot, and the interaction between the slave robot and its environment.

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  Local Site or Master Site: The site where the human operator and the master robot are located.

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  Remote Site or Slave Site: The site where the slave robot and its environment are located. The complete system composed by the local and remote robots is known as master-slave system.

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  Direct (Manual) Control: The operator is controlling the motion of the robot directly without the help of any automatic device.

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  Supervisory Control: The operator is controlling the robot with high-level commands via high-level feedback and substantial intelligence and/or autonomy.

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  Shared Control: A control type that belongs between the two extremes of direct control and supervisory control, i.e., the robot is not fully directly controlled but some degree of intelligent autonomous help is available to assist the operator.

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  Unilateral Control: The type of control where the human operator cannot feel any accurate force from the remote site, i.e., the operator can feel neither the hardness nor the texture of the remote environment (object).

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  Bilateral Control: The control where there exists force feedback, as e.g., in surgical telerobotic systems, where the surgeon can remotely sense the quality of suture and locate veins and bones beneath the tissue, and so is able to exert a proper force control during cutting and puncturing.

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  Telepresence: The ability of the operator not only to manipulate the remote environment, but also to perceive the environment as if encountered directly. In other words, the operator feels himself/herself to be physically present at the remote site. Sheridan called telepresence a compelling illusion and a subjective sensation (Sheridan, 1992).

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  Transparency: The property that specifies how close the operator’s perceived mechanical impedance (force/velocity ratio) comes to recreating the true environment impedance. The medium of the operator-environment interaction is the master-slave system. Obviously, if we have full (perfect) transparency the medium can be considered as absent. It is remarked that the ultimate goal in designing a bilateral control system is to get full transparency.