| 摘要 |
PURPOSE:To eliminate the variance of phase due to an amplitude difference by arranging two FG heads in such positions that signals due to an FG magnet have the same phase and amplitude modulation components due to a magnetic flux of a motor magnet have phases opposite to each other and averaging detection signals. CONSTITUTION:An FG head consists of the first head 14 and the second head 15. Both heads 14 and 15 are so arranged that their detection outputs due to a motor magnet 12 have phases opposite to each other and FG signals of the same phases are detected. Signals detected by heads 14 and 15 are inputted to amplifiers 17 and 19 respectively to obtain output waveforms 51 and 52. Waveforms 51 and 52 are subjected to amplitude modulation due to the magnetic flux of the magnet 12. These waveforms 51 and 52 are inputted to an FG signal output adding circuit 20 and are averaged to obtain a waveform 53. In the waveform 53, amplitude modulation components due to the magnetic flux of the motor magnet 12 are eliminated. This waveform 53 is shaped by a waveform shaping circuit 21 to input the signal of only rotation information to a speed control circuit 22. |
