| 摘要 |
PURPOSE:To carry out the shift of the stage by use of a D/A converter of a low bit number thereby to reduce the manufacturing cost of the device. CONSTITUTION:A target value is stored in a register 9, and a filip-flop 14 is set through an OR circuit 20. Said target value being compared 12 with the stored value(present position of the stage) of the counter to open an AND gate 15a and to supply a pulse to a motor 8. The rise-up of the output of the flip-flop 14 is detected 17, and a bedplate 6 moves as the beam deflects 5 in a specific quantity 21. When the content of a counter 11 coincides with the stored value of the register, the flip- flop 14 is reset and the gate 15a is closed and stopped. The output of the flip-flop 14 is detected 19 and a difference 13 is examined and a corresponding signal is selected 17 from a constant circuit 21 and deflected 5 therefrom. In this manner, the bedplate 6 is stopped and the difference between the quantity of shift up to the present and the target quantity is discriminated. When the difference is greater than a predetermined value, retransfer of the stage is carried out, and hence the D/A converter 18 for the output of the constant circuit 21 may be sufficient even if the number of bits is small, and the cost for manufacturing the device is greatly reduced. |
