Thermal Error Measurement and Compensation with Torque Limit Skip in Swiss-type Lathe Manufacturing

This paper presents a new methodology for the measurement of thermal errors of Swiss -type lathes. The basis of the proposed method is the torque limit skip function integrated in the lathe's control which stops the motion of a linear axis if the torque on the corresponding axis servo is exceeded. The skip signal is triggered via a slow contact between a bar in the lathe's spindle and an artefact in the lathe's tool holder. Experimental results indicate that when a sufficiently low torque override limit is applied, the axis positioning repeatability under the repeated application of the torque limit skip is within +/- 1 mu m. The relative change in position of the axis after the skip measured over several hours is the thermal error which can be compensated. The proposed measurement technique offers significant advantages over conventional thermal error measurement with a touch -trigger probe or linear displacement sensors: if available on the machine's control, it does not require any specialized installation, can be used during production, and delivers comparable results without high additional equipment costs.