| 摘要 |
1465191 Automatic control NATIONAL RESEARCH DEVELOPMENT CORP 4 April 1975 [29 March 1974] 14162/74 Heading G3N Crystal growing apparatus includes an electrically heated crucible and a rod for pulling a crystal from a melt. The crucible is continuously weighed to derive a control signal used to adjust the heat supplied to the melt and thereby control the crosssectional area of the crystal. The heater current is also measured to produce a correction component which is added to the control signal. As shown, a crystal 9 is pulled from a melt 3 in a crucible 5 by a rod 1. The crucible is surrounded by a susceptor 7 heated by eddy currents induced by an RF coil 11, and supported on a load cell 21 producing a signal indicative of changes in weight of the melt 3 due to crystal formation. The load cell signal is subtracted from a fixed signal representing initial weight in a subtractor 25 the output from which is fed to a comparator 27 together with a signal from a potentiometer device 29 responsive to the position of the rod 1 to produce a voltage representing the expected weight of a uniformly growing crystal. Any difference signal produced by the comparator 27 adjusts the temperature of the melt 3 by controlling the power delivered to the coil 11. Variations in the current in the coil produce varying magnetic levitation forces on the crucible 5, introducing error into the weight measured by the cell 21. To correct this, the current is sensed by a transformer (35) in a correction circuit 31, Fig. 2 (not shown), and converted by a rectifier bridge, smoothing circuit and potentiometer, into a compensating voltage which is added into the control loop by a circuit 33. Alternative locations for the adding circuit are shown, 33a-d. In another embodiment, the weight signal from the subtractor 25 is differentiated and then compared with a constant value in the comparator 27. |
