Control System For The Equal-Diameter Growth Of Laser Crystal

The keys for laser crystal to grow in the same diameter are the diameter-measure system and control arithmetic, when crystal grow, the temperature is up to thousands of centigrade, and general diameter measure methods can't gain high precision, which will depress the total control effects. And it is difficult to apply general PID control or fuzzy control to the equipment of crystal growth with nonlinear and great pure hysteresis characteristics. This paper aim to design such a control system for crystal to grow in the equal-diameter,which is provided with suitable control arithmetic and high precision diameter-measure method.and it is important to improve quality of crystal.The paper adopts weighing to measure the change of crystal diameter. In growing, the crystal is weighed in an interval T, by right of the relation between diameter and weight, diameter error is figured out. powerful microconverter and high precision sensor-are introduced and the weigh system attain 2/10000 precision,which establish a foundation for the whole system to receive satisfactory control effects.As to control arithmetic,a composite control model combining PID with Fuzzy control is introduced,in which the fuzzy logic relation between parameters KP,KI, Kd and absolute value of windage e and windage change Ae . parameters KP, KI, KD will be adjusted on line.system will possess both favourable dynamic performance and upper stable precision.and receive satisfactory effects.By simulation and test, provided with weighing system and Fuzzy-PID control arithmetic, the diameter control system achieve marked advance in dynamic performance, stable precision and diameter precision.it will have proud application foreground if the system is popularize to crystal growth industry.