Decision Making Software for Nuclear Facility Decontamination and Dismantlement, page 3

Performance Criteria - Multiple performance criteria form the basis for decision making in this work. These criteria emphasize task-based performance indicators derived from the physical description of the manipulator. The origins of these criteria are from foundation activity in high speed mechanisms for production machinery. There, the issues of precision and modeling of complex non-linear structures forced the development of a geometric understanding for mechanical structures and how to represent them with efficient analytical tools. Thomas and Tesar showed that the concept of kinematic influence coefficients (used in systems with 1 DOF) were effective in spatial manipulator structures with N DOF. An important development in this continuing work on performance criteria has been the association of performance criteria with the D&D tools the DAWM will use while performing its tasks. By choosing a tool, the operator will automatically scale and prioritize the criteria. This automatic process allows the use of multiple performance criteria without distracting the operator from the task at hand or consuming valuable time. The criteria formulations emphasize efficiency and portability. With currently available computational hardware, decisions based on several of these criteria are possible in real-time. Given the rapid pace of advancements in computational speed, it will soon be possible to employ the entire suite of performance criteria in a real-time decision making process. The Jacobian matrix forms the basis for the geometric performance criteria. These criteria are task independent and based only on the geometry of the robot; thus these criteria are formulated once for each robot with no need for reformulation if the task changes. The inertial criteria have their basis in dynamic models of forces and torques within the robot and are essential to the intelligent design and application of robots. These criteria mainly address actuator torques and their rate of change. The rate of change of the actuator torque criterion measures how fast the robot can respond to torque and force demands. It is an especially important criterion because larger actuators or higher gear ratios can supply more torque, but both will slow the overall response of the robot to external disturbances. Consideration of the basic torque demands as well as their rate of change allows the intelligent allocation of the robot's torque resources for enhanced operation. The compliance criteria describe the robot's ability to perform precision operations under load. They also correspond to the vibratory modes of the robot. The potential energy partition values are particularly important compliance criteria. These values measure the distribution of compliance energy and how it changes as the robot moves. An unusually high compliance energy content in any part of the robot indicates a problem with the robot's design. Rapid changes in the compliance energy distribution indicate large local forces, which correspond to large actuator demands and decreased precision. The kinetic energy criteria address high-level issues represented in relatively simply formulations. The rate of change of the kinetic energy criterion corresponds to very large demands on actuator power. Very rapid changes in the kinetic energy distribution represent shocks to the robot.

Conclusion - As robots become more kinematically complex and begin to face more challenging tasks, the algorithms controlling their motion must become correspondingly more sophisticated. In D&D tasks within nuclear facilities, a human wearing protective clothing is the baseline reference for evaluating the performance of robots. A human faced with a decontamination or dismantlement task would clearly consider a number of options for completing the task and then evaluate these options based on a range of performance criteria. For robots to approach this level of sophistication, they must also consider and evaluate options based on performance criteria. This paper discussed a method of multi-criteria decision making entirely general with respect to the number and variety of performance criteria. It showed the application of the decision making method within several different teleoperator control modes for robots. As an example, the paper employed a complex dual-arm robot with 17 DOF designed specifically for D&D operations. For this robot, results show the method is powerful enough to operate the robot in a complex environment with multiple nested obstacles, yet efficient enough to execute at hundreds of cycles per second on common personal computing hardware.