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Abstract
Nuclear facility dismantlement tasks include disassembly of process equipment, cutting pipe, size reduction of equipment, transport of materials, and decontamination of floors, walls, and remaining equipment. A human performing these tasks would clearly consider a range of options and evaluate these options based on a number of performance criteria. For remote systems to approach this level of sophistication, they must also consider and evaluate options based on performance criteria. For dual-arm robots, these criteria include: joint motion limits (ranges, velocities, accelerations, torques, etc.), dual-arm criteria (relative criteria for load, energy, compliance, etc.), obstacle avoidance (scene model for obstacles), and task criteria (force, deformation, dexterity, etc.). This paper discusses performance criteria and decision making algorithms implemented in software as teleoperator control modes. It includes implementation results for a dual-arm robot with 17 independently driven joints.
KEYWORDS: robots, decision making, dual-arm, dismantlement, teleoperate.
Introduction
The United States Department of Energy (DOE) established the Office of Technology Development with the mission of cultivating technologies that are safer, faster, more effective, and less expensive than current methods. As part of the Robotics Technology Development Program, the Decontamination and Dismantlement (D&D) team designed and recently demonstrated the Dual Arm Work Module (DAWM). The DAWM (Figure 1.) is a robotic manipulator system with 17 Degrees of Freedom (DOF) arranged in 2 serial chains each having 8 independent DOF and sharing 1 common center rotational joint. This arrangement gives the system 5 redundant
DOF.
Red Zone Robotics manufactured and delivered the 5 DOF base unit that includes the common rotational joint and the next two joints in both chains. A pair of Schilling Titan II manipulators form the last 6 DOF in each chain. The DAWM's kinematically redundant design allows it to perform a wide range of tasks, thus amortizing development costs. Currently, a human operator directly deploys the DA WM's 5 base joints using visual feedback, experience, and intuition. Because of obstacles or kinematic coupling among the robot's joints, even an experienced operator may need to reposition the base joints several times while performing a task. This paper describes several levels of computer involvement that should offer improvement.
In the initial operational mode envisioned for the DA WM, the operator directly positions each of the 5 base joints using rate control and then leaves these joints locked while controlling the Schilling arms with a pair of force reflecting manual controllers. This is the classic model of DOE teleoperation; an experienced operator directly controlling a state-ofthe- art robot. The present work develops a configuration control interface that drives a computer optimization algorithm with task requirements and performance criteria to automatically suggest a configuration for the robot's 5 base joints.
Results included in this paper show that the configuration control interface will successfully find collision-free configurations for the DA WM even in complex environments with nested obstacles. By associating a suite of performance criteria with each of the D&D tools the robot will use, the optimization algorithm will automatically prioritize and scale the performance criteria without requiring operator input. The operator retains the opportunity to adjust the ranking and scaling of these parameters if so desired.
The development of the configuration control interface also led to the development of two other useful operational modes. By automatically performing the required geometric transformations, self-motion mode allows the operator to hold the tool point constant while repositioning the base joints. Coupled mode automatically operates the DAWM's entire joint set in concert while the operator controls the tool point placement.
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R. Hooper, C. Kapoor, D. Tesar. “Decision Making Software for Dual-Arm Operations in Nuclear Facility Decontamination and Dismantlement.” Proceedings of the World Automation Congress (WAC), Montpellier, France, 1996. Concurrently published in the Proceedings of the International Symposium on Robotics and Automation (ISRAM), Albuquerque, New Mexico,
1996.
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