Photoelectric position sensor
The photoelectric position sensor works by using the principle of photoelectric effect. It consists of a light-emitting tube-photosensitive receiving tube assembly placed on the stator and a light-shielding plate that rotates with the motor rotor.
In a three-phase brushless DC motor, the shading plate has a gap of about 120° (electrical angle), and the number of gaps is equal to the number of pole pairs of the rotor of the brushless DC motor. When the gap faces the phototransistor, the phototransistor receives the light emitted by the light source and produces a "bright current" output. When the light shield blocks the light, the phototransistor has only "dark current" output. The light-shielding plate rotates with the rotor, and the phototransistor outputs "bright current" or "dark current" signals in turn with the rotation of the rotor, so as to detect the rotor magnetic pole position and control the commutation of the three-phase winding of the motor. The disadvantage of the photoelectric position sensor is that the photoelectric signal is easily affected by dust or moisture, and the reliability is low.
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