Encoder is a kind of equipment that can compile and convert signals (such as bitstream) or data into signals that can be used for communication, transmission and storage. Encoder converts angular displacement or linear displacement into electrical signal. The former is called code disk, and the latter is called code ruler. According to the readout mode, the encoder can be divided into contact type and non-contact type; According to the working principle, encoders can be divided into incremental and absolute. Incremental encoder is to convert the displacement into periodic electrical signal, and then convert the electrical signal into counting pulse, and use the number of pulses to represent the displacement. Each position of the absolute encoder corresponds to a certain digital code, so its indication is only related to the starting and ending positions of measurement, and has nothing to do with the intermediate process of measurement.
Main categories
Encoders can be classified in the following ways.
1. It is classified according to the different ways of engraving
(1) Incremental type: it is to send out a pulse signal (also send sine and cosine signal, and then subdivide it, chopping out the pulse with higher frequency) for every rotation unit angle. It is usually output by phase a, phase B and phase Z. phase A and phase B are pulse output with mutual delay of 1 / 4 cycle. According to the delay relationship, positive and negative rotation can be distinguished, and by taking phase a, phase B and phase Z The rising and falling edge of B phase can be 2 or 4 times frequency; The Z phase is a single cycle pulse, that is, one pulse per cycle.
(2) Absolute value type: corresponding to a circle, each reference angle sends out a binary value corresponding to the angle, and multiple positions can be recorded and measured by external circle recording device.
2. According to the output type of signal, it can be divided into voltage output, open collector output, push-pull complementary output and long line drive output.
3. Classification by mechanical installation form of encoder
(1) Shaft type: shaft type can be divided into clamping flange type, synchronous flange type and servo installation type.
(2) Shaft sleeve type: shaft sleeve type can be divided into half empty type, full empty type and large diameter type.
4. The encoder can be divided into photoelectric type, magnetoelectric type and contact brush type.
working principle
It consists of a photoelectric encoder with an axis, on which there are circular through and dark lines, and photoelectric transmitting and receiving devices to read. Four groups of sine wave signals are obtained and combined into a, B, C and D. each sine wave has a phase difference of 90 degrees (360 degrees relative to a cycle). The C and D signals are reversed and superimposed on a and B to enhance the stable signal; In addition, a z-phase pulse is output per revolution to represent the zero reference bit.
Because the phase difference between a and B is 90 degrees, the forward and reverse rotation of the encoder can be judged by comparing whether a phase is in front or B phase is in front. The zero reference bit of the encoder can be obtained by zero pulse. Encoders are made of glass, metal and plastic. Glass encoders deposit very thin lines on glass, which has good thermal stability and high precision. Metal encoders directly cut lines through and through, which is not fragile. However, due to a certain thickness of metal, the precision is limited, and its thermal stability is one order of magnitude worse than that of glass. Plastic encoders are economical, with low cost, However, the accuracy, thermal stability and service life are poor.
Resolution - the number of through or dark lines provided by the encoder per 360 degrees of rotation is called resolution, which is also called analytical graduation or direct graduation. Generally, the graduation is 5-10000 lines per revolution.
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