The difference between incremental encoder and absolute encoder

Incremental encoder

The incremental encoder converts the displacement into a periodic electrical signal, and then converts this electrical signal into a counting pulse. The number of pulses is used to indicate the magnitude of the displacement. According to the working principle, the encoder can be divided into incremental and absolute Two types.

　　 When the shaft of the incremental encoder rotates, there is a corresponding pulse output. The determination of the rotation direction and the increase or decrease of the number of pulses are realized by the direction circuit and counter at the rear. The starting point of counting can be set arbitrarily, which can realize unlimited accumulation and measurement of multiple circles. It is also possible to use the Z signal for each pulse transmitted as a reference mechanical zero position. One rotation of the encoder shaft will output a fixed pulse, and the number of pulses is determined by the number of encoder grating lines. When you need to improve the resolution, you can use the A and B signals with a 90-degree phase difference to multiply the original pulse number, or replace the high-resolution encoder

Absolute encoder

The absolute encoder is a sensor that directly outputs numbers. There are several concentric code discs along the radial direction on its circular code disc. Each track is composed of light-transmissive and opaque sectors. The sectors of adjacent code channels The relationship between the trees in the area is doubled. The number of code channels on the code disc is the number of binary digits. On one side of the code disc is the light source, and the other side has a photosensitive element corresponding to each code channel. When the disc is in different positions When, each photosensitive element converts a corresponding level signal according to whether it receives light or not, and forms a binary number. The characteristic of this kind of encoder is that it does not need a counter, and can read a fixed digital code corresponding to the position at any position of the shaft. Obviously, there must be N doctrines. At present, there are 16-bit absolute encoder products in China.

The difference between incremental encoder and absolute encoder

　　 1. Different in nature

　　 1. Incremental encoder: The displacement is converted into a periodic electrical signal, and then the electrical signal is converted into a counting pulse, and the number of pulses is used to indicate the magnitude of the displacement.

　　2. Absolute encoder: Because each position is absolutely unique, anti-interference, and no power-down memory, it has been more and more widely used in angle and length measurement and positioning control in various industrial systems.

　　 2. Different principles

　　1. Incremental encoder: An equal angle gap is opened on the edge of a code disc (divided into transparent and opaque parts), and light sources and photosensitive elements are installed on both sides of the encoder. When the code wheel rotates with the working shaft, every time it rotates a slot, the light and shadow will change.

　　 After shaping and amplifying, an electric pulse output signal with a certain amplitude and power can be obtained, and the number of pulses is equal to the number of slots in rotation. The pulse signal is sent to the counter to count, and the angle of rotation of the disc can be known from the measured number.

2. Absolute encoder: Due to its high precision, the absolute encoder has a large number of output bits. If parallel output is still used, each output signal must ensure a good connection. For more complex conditions, isolation and more cable cores. This brings a lot of inconvenience and reduces reliability.

　　 Therefore, the absolute encoder has multiple numbers. Output type, generally choose serial output or bus type output, the German absolute encoder serial output is the most commonly used SSI (synchronous serial output).