INTELLIGENT TRANSDUCTION FOR RESPONSE SYNTHESIS IN TELEMANIPULATION

INTERNATIONAL JOURNAL ON SMART SENSING AND INTELLIGENT SYSTEMS VOL. 6, NO. 4, SEPTEMBER 2013 INTELLIGENT TRANSDUCTION FOR RESPONSE SYNTHESIS IN TELEMANIPULATION J. K. Mukherjee Electronics and Instrumentation Services Division, Bhabha Atomic Research Centre , Mumbai 400085 , India Email: Submitted: May 25, 2013 Accepted: July 31, 2013 Published: Sep. 05, 2013 ___________________________________________________________________________ Abstract- A virtual transducer forming technique has been developed with an objective to enhance remote environment perception in tele-robotic systems by adding proximity feel in pre-contact phase during remote manipulation tasks. A fluidics inspired transducer model has been conceived and designed to serve for master side perception creation based on remote robot’s proximity with workspace objects and its dynamics. Robot’s native joint sensors function as primary sensors and active joystick forms the output stage. It induces proximity feel around approachable and unapproachable parts in distinctly different manner. The paper delves in aspects like building reconfigurability for varied transducer characteristics formation and tunable force exertion on operator hand for suiting application context and operator choice. Index terms: proximity, telemanipulator, virtual transducer, force feedback, servo motor , active joystick, remote-perception , operator interface, intelligent sensing 1479 J. K. Mukherjee, INTELLIGENT TRANSDUCTION FOR RESPONSE SYNTHESIS IN TELEMANIPULATION I. INTRODUCTION Tele-operated systems are used for remote working in hazardous environments like radioactive, biologically contaminated and toxic confines. Operations can be for part manipulation or probing of specimen. Such systems employ a slave robot arm in active workspace for reproducing the motions that are performed on another arm of similar type by the operator located at safe location. Conventional tele-control systems rely on kinesthetic feedback [1]. The ability to feel remote environment at master is dependent on transparency but has an associated problem of stability of system [2]. Such system work in two major regimes of workspace interactions namely ‘in free space’ and ‘in part contact’. For the later regime, transparency is created by using instrumented grasp subsystems capable of tactile sensing in gripper and rebuilding them on master side. In ‘free space regime’ no tactile feedback is available and generally bilateral control give self dynamics based feedback [3][4]. Intelligent transducer can play useful role here. Generally the operator perceives the remote state through visuals only and hits are assessed by human intelligence using vision support [5] and virtual reality[6]. If a sensing method is devised to create ‘closeness perception’ for the remote robot end-effector ‘REE’ then operator can have better feel of remote environment and even feel an impending hit. In ‘tele-probing’ involving surface scan of remote located specimen by contact or near contact type sensors like ultrasonic flaw detectors and eddy-current probes, perception of proximity is highly desired in ‘nearcontact’ state as it does not generate any reaction feedback owing to REE’s non contact condition. The objective of this work is to develop a ‘transduction method’ that offers perceivable forms of feedback generation at operator end. Proximity alone is not sufficient parameter to formulate perception and dynamics of REE plays an important role. II. RELATED WORK “Virtual fixture” refers to a general class of guidance modes [7][8] that help a robotic manipulator perform a task by limiting its movement into restricted regions and/or influencing its movement along desired paths and prohibit the motion of a robot manipulator into forbidden regions of geometric or configuration space. Spring action have been proposed[9][10] but they are not passive and tend to react on stationary state REE too. Virtual fixtures have limitations. These introduce abrupt changes in machine response and have been treated as hyper plane in software domain for simulation environments serving for operator training. Though, with some specific adaptation, this approach has been applied for on-line force feedback [11] to develop perception of approaching software configured barrier 1480 INTERNATIONAL JOURNAL ON SMART SENSING AND INTELLIGENT SYSTEMS VOL. 6, NO. 4, SEPTEMBER 2013 parts, limitations in fixture shaping arising from consideration of real-time computation burden, lack of framework for their integration into a tele-managed system, and absence of system assisted or automated method of implementation have restricted their use in training applications where it serves as safety curtain to avoid damage from wrong operator action. III A NEW APPPROACH The desired method must permit motion through it to permit the Robot End Effecter ‘REE’ to reach a part in impact constrained manner by enabling human operator with appropriate perception while working in ‘man-in-loop’ type operating scenario. The method must be automation savvy and should avoid introducing instability in control loop by ensuring passive nature, wherein a ‘zero’ REE motion results in null forces on operator side. The general bilateral control for tele-manipulator is complicated and passivity of system needs to be ensured [12][13]. An economical operator support method can be developed by a ‘virtual transducer’ for slave arms working in CAD modelled workspace, as location of the probe in Figure 1. Feedback developer remote workspace can be determined using kinematic model of the robot and dynamics can be assessed from commands flowing to the slave that define the slave state (fig.1). The proposed transducer develops response parameter ‘RP’ by using modeled impedance on the robotic arm’s approach to a part based on the on-line computed parameters. The transducer is expected to meet several criteria depending on the type of the object REE is in vicinity of. A. DESIRED TRANSDUCER BEHAVIOR FOR APPROACHABLE OBJECTSAn approachable body in workspace opposes REE motion towards it in a manner depicted in figure 2. V is velocity of approach towards the approachable body and F represents response parameter ‘RP’ which mostly is implied as opposition force to the REE but in some 1481 J. K. Mukherjee, INTELLIGENT TRANSDUCTION FOR RESPONSE SYNTHESIS IN TELEMANIPULATION Figure 2 (a,b,c) Desired behavior for approachable objects, (d,e,f) required behavior for approachable objects. Figure 3(right) Preferred behavior for unapproachable objects implementation can be audio-visual effect. Its magnitude is represented by width W. Higher the FEE velocity towards the approachable body higher is the discouragement to the REE operator at master end. This also implies that an approachable body can be reached by REE at very slow speed. It is equivalent to gently touching without impact and is desirable. B. DESIRABLE BEHAVIOR FOR UNAPPROACHABLE OBJE (...truncated)