What is an encoder How does it work

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

The encoder is mainly composed of code disc (circular grating, indicating grating), body, light emitting device, photosensitive device and other components.

(1) The circular grating is composed of radial stripes of light and dark that are coated on a transparent material or a metal material. The pitch of an adjacent fringe is called a grid section, and the number of grid sections in the entire circumference of the grating is the pulse number (resolution) of the encoder.

(2) The indicating grating is a piece of grating sheet that is fixed, but the fringe of the window is exactly the same as the fringe of the circular grating.  

(3) The body is a carrier for assembling circular gratings, indicating gratings and other components.

(4) The light-emitting device is generally an infrared light-emitting tube.  

(5)The photosensitive device is a high-frequency photosensitive element; generally there are silicon photocells and photosensitive triodes.

According to the working principle, the encoder can be divided into two types: incremental and absolute

Incremental encoder

1. Incremental encoder converts the displacement into a periodic electric signal, and then converts this electric signal into a counting pulse, and the number of pulses is used to indicate the magnitude of the displacement.

2.Working principle diagram

3. Advantages and disadvantages of incremental code disc

advantage:

(1) High accuracy (frequency multiplication circuit can be used to further improve accuracy);

(2) Simple structure, low cost, suitable for angle measurement and speed measurement without contact measurement, high reliability and long life

Disadvantages:

Zero search after power-on. In the pulse transmission process, the cumulative error caused by interference requires a counter and the speed is limited.

4. Precautions for use

(1) Consider the zero-finding problem

(2) Consider the cumulative error caused by interference

(3) Consider the contradiction between maximum speed and resolution

(4) Consider the problem of counter overflow

Absolute encoder

1. Absolute pulse encoder disc is an absolute angular position detection device. Its position output signal is a digital signal of a certain standard. It indicates the absolute position reached after displacement. The digital signal of the absolute position of the start and end points is used. , The magnitude of displacement can be obtained after calculation.

3.Three parts of the structure, rotating code disc, light source and optical sensor. Optical code channels, each code channel is distributed with transparent and opaque areas according to a certain rule.

3. Principle

The light from the light source passes through the optical system, passes through the light-transmitting area of the code wheel, and is received by the photosensitive element behind the slit, and the output is "1"; if it is blocked by the opaque area, the photosensitive element outputs "0". The output code combination of each code channel represents the corner position of the code wheel.

4. Advantages and disadvantages of absolute code disc

advantage:

(1) High precision, no contact, long life

(2) No need to find zero after boot

(3) No cumulative error

(4) No counter is required and the allowable speed is high.

Disadvantages:

(1) Complex structure and large volume

(2) The price is expensive

5. Precautions for use

1. The power supply must be reliable and pay attention to the voltage drop during long-term transmission

2. Consider the handling of errors

3. Consider the treatment of zero crossing