Compensation of the thermal expansion on milling spindles

Temperature variations on high frequency rotating milling spindles lead to thermal expansion and therefore to incorrect cutting depths. To compensate for these deviations, Micro-Epsilon has developed a highly accurate sensor which acquires thermal displacements and length changes in the spindle shaft using a non-contacting method.

For the measurement a factory-calibrated miniature sensor based on the eddy current principle is used and is directly integrated into the tool spindle. When changing the spindle, a sensor replacement without recalibration or any adjustment work is then possible. Despite the small sensor size, the error level of the sensor is only 1 µm and the temperature stability is 0.1 µm/°C

The sensor signals are conditioned with a digital signal processor which is accommodated in a compact aluminum cast housing suitable for use on machines. Based on this conditioned displacement information, the machine controller carries out compensation of the axial expansion. The specified travel movements of the Z axis are here superimposed by the compensation movement.

The controller unit with the digital signal processor is constructed separately from the sensor and is mounted on the machine. All sensor-specific data are saved in the sensor (EEPROM) so that the measurement system is again immediately ready for operation after a change of spindle.