| 摘要 |
PURPOSE:To produce an accurate index signal by using a means which detects a specific part of a rotor or a stator by a magnetic sensor and masks the output of the sensor for a fixed period of time before a DC motor is started and a current is switched. CONSTITUTION:A comparator 9 delivers a waveform 3' to a monostable multivibrator 10 by the signal detected by a Hall device 3. With this input signal, the monostable multivibrator 10 delivers a waveform 4' to an AND circuit 11. The circuit 11 calculates an AND between waveforms 2' and 4' and transfers a waveform 5' to a high rank device as an index signal. In this case, the waveform 5' is not delivered from the circuit 11 since no AND condition is obtained between the position of the noise contained in the waveform 2' and the waveform 4'. Then only the waveform part obtained when a projection 6 of a rotor 1 with which the AND conditions can be obtained is detected and delivered as the waveform 5'. In such a way, an index signal is not delivered erroneously even though the noise produced when the direction of the current flowing to a coil wound round a stator is switched. Thus it is possible to detect an index signal accurately. |
