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1.1 Photoelectric encoder

Encoder is a kind of sensor, mainly used to detect the speed, position, Angle, distance and count of mechanical motion, many motor control need to be equipped with encoder for motor controller as commutation, speed and position detection, etc., the application range is quite wide. According to different classification methods, encoders can be divided into the following types:

According to the detection principle, it can be divided into optical type, magnetoelectric type, induction type and capacitive type.

According to the output signal form, it can be divided into analog encoder and digital encoder.

Ø According to the encoder method, it is divided into incremental encoder, absolute encoder and hybrid encoder.

Photoelectric encoder is a digital sensor integrating optical, mechanical and electrical technology. It mainly uses the principle of grating diffraction to realize displacement-digital transformation, and converts the mechanical geometric displacement on the output axis into a pulse or digital sensor through photoelectric conversion. A typical photoelectric encoder consists of a code disc, a detection grating, a photoelectric conversion circuit (including a light source, a photosensitive device, a signal conversion circuit), a mechanical component, etc. The photoelectric encoder has the advantages of simple structure, high precision, long life and so on, and is widely used in precision positioning, speed, length, acceleration, vibration and so on.

Here we mainly introduce the incremental encoders and absolute encoders generally supported by SIMATIC S7 series high-speed counting products.

1.2 Incremental encoder

Incremental encoders provide a sensing method for discretization, increment, and displacement change (velocity) of continuous displacement. The characteristic of the incremental encoder is that each output pulse signal is corresponding to an incremental displacement, and it can generate a pulse signal equivalent to the displacement increment. Incremental encoders measure relative increments of position relative to a reference point, and cannot directly detect absolute position information.

As shown in Figure 1-1, the incremental encoder is mainly composed of a light source, a code disk, a detection grating, a photoelectric detection device and a conversion circuit. There are radiative light transmission gaps with equal pitch carved on the code disc, and the interval between the two adjacent light transmission gaps represents an incremental period. The detection grating is engraved with two groups of light transmission gaps corresponding to the code disc, A and B, to pass or block the light between the light source and the photoelectric detection device, their pitch and the pitch on the code disc are equal, and the two groups of light transmission gaps are staggered by 1/4 pitch, so that the photoelectric detection device output signal in phase difference of 90°. When the code disc rotates with the measured axis, the detection grating does not move, and the light shines through the gap between the code disc and the detection grating to the photoelectric detection device, the photoelectric detection device outputs two sets of electrical signals that are approximately sine wave with a phase difference of 90°, and the electrical signals are processed by the conversion circuit to obtain the Angle or speed information of the measured axis.

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