Daisuke Matsuka

Compensation for torque fluctuation caused by temperature change in fast and precise positioning of galvanometer scanners

This paper presents a compensation approach for torque fluctuation caused by temperature change of galvanometer scanners in laser-positioning servomechanisms. The galvanometer scanner is driven by a swaying motor which is used in laser drilling machines because of its precise positioning ability. However, since the motor temperature rises during the high speed motion, the reversible flux loss occurs. As a result, thermal demagnetization decreases a torque constant and the overshoot occurs at the settling waveform, resulting in deterioration of precision positioning performance. The proposed approach can estimate the temperature of a permanent magnet with a high degree of accuracy by detected current value using a pre-identified cooling coefficient. Specifically, the approach considers a rise in heat caused by eddy current loss. Then the approach compensates for torque fluctuation using the estimated temperature of the permanent magnet. The proposed approach has been verified by experiments using galvanometer scanners.

Thermal Demagnetization Compensation for Fast and Precise Positioning in Galvanometer Scanners

To improve the positioning accuracy of galvanometer scanners, we have developed a thermal demagnetization compensation (TDC) approach. In recent years, increase in power consumption of the galvanometer scanner results from high-speed motion; therefore, a magnets temperature rise increases. Generated torque of the galvanometer scanner decreases with a rise in temperature because of demagnetization so that positioning ability of the galvanometer scanner declines. The proposed TDC approach estimates magnet temperature with a high degree of accuracy from the detected current using preidentified thermal characteristics. On the basis of estimated temperature, the TDC approach is able to compensate for generated torque fluctuation caused by the magnets temperature rise without additional thermal sensors. Furthermore, the TDC performs efficiently even so the settling waveform has transient response error caused by continuous movement. In addition, the TDC approach performs for various operating frequencies. When we applied the TDC approach to galvanometer scanners installed on laser-drilling machine, the TDC approach reduced the maximum positioning error by 32%, and all shots were less than an accuracy tolerance.