Dependence of machining accuracy on acceleration/deceleration and interpolation methods in CNC machine tools

This paper presents the development of a CNC (computer numerical controller) system with an Intel 80486 as the main CPU, a floating point DSP (digital signal processor) TMS320C31 as the motion control CPU, a graphic DSP TMS34020 as the graphic CPU, and a MC68000 as the CPU of the internal PLC (programmable logic controller). Through the milling center equipped with the developed CNC system, the dependence of machining accuracy of the machine tool equipped with the developed CNC system on the acceleration/deceleration method and the interpolation method is investigated. The path error, which actually represents the machining accuracy, due to exponential acceleration/deceleration is shown to be largest for the same acceleration/deceleration time while that due to parabolic acceleration/deceleration is shown to be smallest. It is also shown that the path error for the acceleration/deceleration method before interpolation is smaller than that for the acceleration/deceleration method after interpolation. In addition, the backlash compensation method is discussed, which eliminates quadrant protrusion in circular cutting on reversal of the rotational direction of the motor. Furthermore, experimental results demonstrates that backlash can be compensated to a desirable degree by the developed CNC