COMPENSATORY CONTROL OF FORM ERROR IN MACHINING

In order to dissolve the existing tie-up between high precision and high costs in machining, a new approach for controlling form errors is proposed in this thesis. The new approach, called "Compensatory Control," is based on mathematical modeling of the variable or variables contributing to the form error, using the Dynamic Data Systems methodology (DDS) and then forecasting the future value of this variable by virtue of the developed model. Compensatory action can then be taken to offset the effect of the forecast value of the variable.;Based on this concept, a microcomputer-based compensatory control system was developed using a spindle error sensing system and an electro-hydraulic drive system to generate the compensation. The resulting system enabled a 50% reduction in roundness error at low work spindle speeds with deteriorating performance at increased work spindle speeds primarily due to the response characteristics of the electro-hydraulic drive system.;The obtained results indicate the feasibility of this approach, together with the possibility of using this technique to correct for other form errors such as cylindricity, straightness, and flatness.;In order to demonstrate the feasibility of this approach, a compensatory control system is developed to improve the roundness error of a component ground in a cylindrical chuck grinding operation. Before this can be attempted, a study is made to determine the major cause of roundness error in that particular operation. This study required a redefinition of the error of roundness compatible to a new measuring technique that was developed to enable on-line and simultaneous measurement of roundness and the variable termed as the error motion of the work-spindle. Consequent analysis established the error motion of the work spindle as a major contributor to the form error of roundness in that particular operation.