PURPOSE: To prevent unnecessary vibration and oscillation by simulating a set transfer function to output a false signal by an adaptive digital filter on the basis of the output of a compensating circuit or a power amplifier, and adding/subtracting this false signal to/from a displacement signal to control magnetic attracting force.
CONSTITUTION: A transfer function is inputted to an adaptive digital filter 15 from the transfer function measuring apparatus 12 of a transfer function setting part 11 so as to simulate the transfer function of a floating table 4 system. This adaptive digital filter 15 receives the output signal of a compensating circuit 7 or a power amplifier 8 and outputs a false signal conformed to the intrinsic, transfer function of the floating table 4 system. The low frequency component is cut by a by-pass circuit 16, and the high frequency component is subtracted by an adder 21 to output the false signal. The outputted false signal is added/subtracted to/from the displacement signal of a displacement sensor 6, and the target value is added/subtracted by an adder 22 and outputted to the compensator 7 or the power amplifier 8.
KANEMITSU YOICHI
WATANABE KAZUHIDE
OSAWA SUSUMU
EBARA CORP