適応型フィードフォワード制御によるレーザ出力応答の改善 Adaptive Feedforward Control for Improving Output Power Response of CO_2 Laser
Feedback control has been used to stabilize the steady-state output power of a CO<sub>2</sub> laser to overcome the problems caused by the change in the temperature/deterioration of CO<sub>2</sub> gas. The transient response, however, is as slow as a few hundred milliseconds because of the slow dynamics of a thermopile power sensor. When machining conditions of a CO<sub>2</sub> laser are changed, this rather slow response requires an extra dwell time, resulting in low productivity of the machining.<br>To cope with this problem, the authors have developed adaptive feedforward control for a CO<sub>2</sub> laser in addition to conventional feedback control. The model of a CO<sub>2</sub> laser is described as a gain, which is varied by the setting parameters; laser power, pulse frequency and duty factor, as well as gas conditions. In this paper, two new variables, effective discharge power and threshold discharge power, are introduced to obtain a compact and adjustable model. With the proposed control system, the step response time of a laser power is reduced to less than ten milliseconds without overshoot, and can be set to desired constant time. The effects of such a fast and stable response on the machining speed and machining quality are examined. The experimental results show that for thin metal line-cutting, neither the melt-off area nor dross is observed even in the no-dwell time case. For thin metal hole-cutting, the machining speed is improved by 30%.
計測自動制御学会論文集 34(3), 209/216, 1998-03-31
The Society of Instrument and Control Engineers