Preliminary studies on force/motion control of intelligent mechanical systems

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Rabindran, Dinesh

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According to a survey conducted by the Robotics Industries Association (RIA), North American robot orders increased 19% in 2003, the best year for robotics since 2000 [RIA Online]. To rationalize the relatively high investment that industrial automation systems entail, research in the field of intelligent machines should target high value functions such as fettling, die-finishing, deburring, fixtureless manufacturing [Butler and Tesar, 1992]. To achieve this goal, past work has concentrated on force control algorithms at the system level without an investigation of the feasibility of performance expansion at the actuator level. We present pertinent literature at both system and component levels in the field of force control. A general overview of the problem we are faced with is presented together with some research areas that will help create a science base that can make significant contributions in the area. Some simple force control experiments are conducted on a modular robot testbed to study the issues involved in force control implementations at the system level and also to present the class of problems this research thread addresses. The goal of this research work is to facilitate efficient execution of robotic contact processes using systems assembled on demand using Multi-Domain Actuators (MDA) and controlled using a model based intelligent Multi-Domain Control (MDC) scheme. The approach at UT Austin has been to maximize the number of choices within the actuator to enhance its intelligence. Drawing on this 20-year research history in electromechanical actuator architecture, in this report we propose a new concept that mixes two distinct subsystems (in motion and force domains respectively with a kinematic scaling of approximately 14:1) within the same actuator called a Force/Motion Actuator (FMA). A detailed kinematic and dynamic model of the FMA is presented. The actuator performance is evaluated with an operational specification in the motion domain using a weighted minimum prime-mover velocity norm criterion. It is shown that the design choice of 14:1 scaling between the motion and force sub-systems results in the selective flow of force- and motion- sub-system attributes to the output. We demonstrate that the velocity side of FMA contributes to the motion predominantly and the force-side contributes to external disturbance rejection. We also present the future work that would draw on this effort to establish a science base for Multi-Domain Control in the system domain


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