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What is an encoder? How does it work?

An encoder is a device that programs and converts signals (such as bitstreams) or data into a signal form that can be used for communication, transmission, and storage. The encoder converts either the angular displacement or the linear displacement into an electrical signal. The former is called a code disk and the latter is called a code ruler.

The encoder is mainly composed of code plate (circular grating, indicating grating), body, light-emitting device, photosensitive device and other components.
(1) The circular grating is composed of radially light and dark stripes coated on transparent materials or depicted on metal materials. An adjacent fringe spacing is called a grating node, and the number of grating nodes is the number of pulses (resolution) of the encoder.

(2) indicating grating is a fixed, but the window fringe line is exactly the same as the circular grating fringe line.


(3) The body is the carrier for assembly of circular grating, indicating grating and other components.

(4) light-emitting devices are generally infrared light-emitting tubes.

(5), photosensitive device is a high frequency photosensitive element; There are generally silicon photocells and photosensitive triodes.
According to the principle of operation, encoders can be divided into two types: incremental and absolute

Incremental encoders
1. The incremental encoder converts the displacement into periodic electrical signals, and then converts the electrical signals into counting pulses. The number of pulses represents the magnitude of displacement.


2. Working principle diagram
3, the advantages and disadvantages of incremental code disk


Advantages:
(1), high accuracy (the frequency doubling circuit can be used to further improve the accuracy);


(2) Single structure cylinder, low cost, suitable for Angle measurement and speed measurement without contact measurement, high reliability, long life


Disadvantages:
¡¤ In the pulse transmission process, the cumulative error generated by interference requires the counter and the speed is limited to a certain extent.

4, use matters needing attention
(1) Consider the zero finding problem

(2) Accumulated errors caused by interference may be considered

(3) Consider the contradiction between maximum speed and resolution

(4) Consider the counter overflow problem

Absolute encoder
1. Absolute pulse coding disk is an absolute Angle position detection device. Its position output signal is a digital signal of a certain type.


2, three parts of the structure, rotating code plate, light source and light sensing element. Optical code channel, each code channel according to a certain regularity of the distribution of transparent and opaque areas.
3, the principle of
The light of the light source passes through the optical system, passes through the transmittance area of the code plate, is received by the photosensitive element behind the narrow slit, and the output is "1"; If it is blocked by the opaque area, the photosensitive element output is "0". The combination of the output codes of each code channel represents the corner position of the code disk.

4, the advantages and disadvantages of absolute code disk
Advantages:
(1) High precision, no contact, long life
(2) Zero search is not required for boot
(3) No cumulative error
(4) No counter is needed and high speed is allowed.

Disadvantages:
(1) Complex structure and large volume
(2) It's expensive

5, use matters needing attention
1, the power supply should be reliable, pay attention to the long line transmission voltage drop
2, consider the handling of error code
3, consider the treatment of zero crossing




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