Apparatus for growing sapphire single crystals by Kyropoulos method with dynamic weighing device and automatic feedback control

Currently Kyropoulos method (GOI) is the most widely applied for industrial production of single sapphire crystals of optoelectronic quality. The method consists in the fact that growth of the crystal is carried out directly in the melt by gradual temperature decrease. Generally, process control is based on reducing the heating power according to a predetermined function of time which is chosen empirically on the grounds of quality of crystals obtained in preceding processes. In recent years, weight sensors have been used to control the process of crystal growing by Kyropoulos method. The main advantage of the crystallization process control using dynamic weighing is the ability to measure continuously and stabilize the crystallization mass rate using a feedback system. However, implementation this system requires the development of high-precision dynamic weighing apparatus, as well as algorithms for automatic feedback control. In this paper we consider the design features and algorithms for automatic control applied for NIKA-M60 crystal growth machine. These features allow realizing automatic control crystallization process with feedback via the heater power and the pulling rate of the crystal.