Development of A Workpiece Straightness Error Compensation System for NC Turning

The dimensional accuracy of a long workpieces obtained by turning is essentially affected by the thermal expansion of the cutting tools, the geometrical errors of the machine tools, and etc. This paper presents a newly developed photo-electric post-process system for measuring the straightness of a long workpiece on the machine tool, an in-process workpiece dimensional error measurement system, and an error compensation system which is incorporated to a FANUC 3T controller. Three non-contact proximetors are used to develop a three-probe method for dimensional measurement in turning. The measured value is compared with the desired dimension in an IBM PC/XT computer. To carry out the error compensation, the X-axis of the NC lathe is directly controlled by the computer. It is found that a high dimensional accuracy for long workpiece in heavy cutting can be obtained. The errors is reduced to the tolerance limit of approximately 10 μm.