An encoder (encoder) is a device that converts signals (such as bit streams) or data into a form that can be used for communication, transmission, and storage. The encoder converts angular or linear displacement into electrical signals. The former is called a code disk, and the latter is called a code scale. According to the reading method, encoders can be divided into contact type and non-contact type; according to the working principle, encoders can be classified into incremental type and absolute type. Incremental encoders convert displacement into periodic electrical signals, and then convert these electrical signals into counting pulses, using the number of pulses to represent the size of the displacement. Absolute encoders have a corresponding unique digital code for each position, so their indication value is only related to the starting and ending positions of the measurement, and is independent of the intermediate process of the measurement.
Main classifications
The encoder can be classified in the following ways.
1. According to the different hole patterns of the encoder disk:
(1) Incremental type: It emits a pulse signal every time a certain unit angle is passed (there are also positive and negative cosine signals, which are then subdivided and chopped to generate higher-frequency pulses). Usually, A-phase, B-phase, and Z-phase outputs are provided. A-phase and B-phase emit pulses that are delayed by 1/4 of a cycle from each other. The delay relationship can be used to distinguish forward and reverse rotations, and the 2 or 4 times frequency can be obtained by taking the rising and falling edges of A-phase and B-phase. Z-phase is a single-circle pulse, that is, one pulse is emitted per circle. Generally, incremental encoders do not have internal storage devices, so they do not have the function of maintaining data after power failure. CNC machines must perform the “return to reference point” operation to determine the counting reference and perform actual position “reset”.
(2) Absolute value type: For each circle, a unique binary value corresponding to the specific angle is emitted. Multiple positions can be recorded and measured through external marking devices. The output of the absolute value encoder can directly reflect the absolute angle within the 360° range. The absolute position can be identified by the amplitude of the output signal or the physical encoding scale of the grating. The former is called a rotating transformer (Rotating Transformer), and the latter is called an absolute value encoder (Absolute-value Encoder). [4]
2. According to the output type of the signal: voltage output, open collector output, push-pull complementary output, and long-line drive output.
3. Classified by the mechanical installation form of the encoder:
(1) Shaft type: Shaft type can be further divided into clamping flange type, synchronous flange type, and servo installation type, etc. [2]
(2) Sleeve type: The sleeve type can be further divided into semi-empty type, fully-empty type and large-diameter type, etc.
4. According to the working principle of the encoder, it can be classified as: photoelectric type, magneto-electric type and contact brush type.
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