| A significant limitation on the fabrication of precision parts is the inherent inaccuracy of the machining process due to the thermal deformation of the machine tool structure. The problem has begun to receive considerable attention as the threshold for machining tolerances has dropped, and automated machine tools have become widespread. At the present time, the only commercially viable method of reducing the operational thermal deformation of a machine tool structure is fluid showering, a costly and inconvenient process that is only available for exceptional applications.; This thesis presents a technique for reducing thermally induced machining error by measuring the structural deformation of the machine tool while it is in operation, and compensating for it on-line. The structural thermal deformation is indirectly measured by relating it to point temperatures on the structure through a process model. A technique for determining the approximate analytical form for the temperature distribution in the structure will be developed in the thesis.; The thermally induced deflection of the structure is compensated by an array of artificial electric heaters, attached to the surface of the structure, and controlled by a PC based numerical control system. The control system manipulates the artificial heaters to calibrate a deflection pattern in the structure that eliminates the natural deformation at key points.; The performance of the control system is evaluated using a finite-element test model of a simulated machine tool structure. The control system approach tested in this thesis provides a reduction of thermally induced effect that is comparable to the commercial method of fluid showering, but at a fraction of the cost and complexity. |
