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Design of a Controller for a Platform-Based Automated Finishing System

By Nishant Jhaveri

December, 2000  

Chairman: Dr. Gloria Wiens

Major Department: Department of Mechanical Engineering

             Burrs are sharp and relatively small projections that form along the edges, on the workpieces that are machined or stamped. In most cases, these burrs must be removed for improved product/system performance, safety, cost, ease of assembly, elimination of stress risers, appearance of part, etc. In manual deburring a person moves a deburring knife/file or a high speed cutting tool along the desired edges of the workpiece, maintaining a constant force on the tool. For manual deburring, corporations suffer from large turnover rates and significant health costs because the tasks are repetitive and boring, and the workers are susceptible to cumulative trauma disorders. In general, repetitive motion disorders, large cycle time and the continuing emphasis on quality have increased the search for automated methods. As an alternative, existing robots or machine tools are positioning devices that can move the cutter along a desired trajectory. However, these devices lack the ability to directly control the force on the cutter.

Attaching an active micro-manipulator as end-effector tooling, existing systems can provide controlled compliance in more than one direction irrespective of burr variations or only in one direction with burr variations. In general, the positioning device has to change its orientation continuously to maintain the constant normal force along the desired path trajectory. This results in long cycle time and tedious CNC/robot programming.

To overcome these problems faced by industries, a deburring controller for a two degree of freedom micro-manipulator is presented in this thesis. The deburring controller has been designed to two dimensionally maintain the desired normal (thrust) force on the spindle and tangential contact with the workpiece, as the positioning device moves the deburring head along the desired contours of the workpiece being deburred. The resulting hybrid, event-driven process-based controller provides the micro-manipulator the ability to sense a burr and to change the applied force using an empirically derived process model based controller logic module. When no burr is present, the micro-manipulator operates under hybrid position and constant force control. The micro manipulator’s ‘logic module’ provides the ability to change compliance during the cornering/contouring operation and provides the ability to respond intelligently to burr variations and other operating conditions. The simulation results showed satisfactory results for cornering/contouring operations and significantly reduced the finished surface error during the burr.

The resulting work will extend the capabilities of today’s robots, machine tools and parallel kinematic machines by eliminating tedious orientation motion requirements in finishing complex contours.

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