Aug 25, 2022
Rotary Encoder Classification, Working Principle and Installation Matters
The rotary encoder is a device used to measure the speed and cooperate with PWM technology to realize rapid speed regulation. The photoelectric rotary encoder can convert the angular displacement, angular velocity and other mechanical quantities of the output shaft into corresponding electrical pulses through photoelectric conversion. output (REP).

Divided into single output and dual output. The technical parameters mainly include the number of pulses per revolution (dozens to thousands), and the supply voltage. Single output means that the output of the rotary encoder is a set of pulses, while the rotary encoder with double output outputs two sets of pulses with A/B phase difference of 90 degrees. Through these two sets of pulses, not only the speed can be measured, but also the rotation can be judged. direction.
According to the output type of the signal, it is divided into: voltage output, open collector output, push-pull complementary output and long-line drive output
Form classification

Shaft type: Shaft type can be divided into clamping flange type, synchronous flange type and servo mounting type.

Bushing type: The bushing type can be divided into semi-empty type, full-empty type and large-diameter type.
According to the working principle of the encoder, it can be divided into photoelectric type, magnetoelectric type and contact brush type.

According to the different ways of carving holes in the code disc, encoders can be divided into two types: incremental and absolute.
The incremental encoder converts the displacement into a periodic electrical signal, and then converts the electrical signal into a count pulse, and the number of pulses represents the magnitude of 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 the measurement, and has nothing to do with the intermediate process of the measurement.
Rotate the incremental encoder to output pulses when rotating, and know its position through the counting device. When the encoder does not move or power failure, it relies on the internal memory of the counting device to remember the position. In this way, when the power is cut off, the encoder can not have any movement. When the power is on, the encoder output pulse process, there is no interference and the pulse is lost, otherwise, the zero point memorized by the counting device will be offset, and this offset The amount of shift is impossible to know, only after the wrong result occurs.
The solution is to increase the reference point. Every time the encoder passes the reference point, the reference position is corrected into the memory position of the counting device. Before the reference point, the accuracy of the position cannot be guaranteed. For this reason, in the industrial control, there are methods such as finding the reference point for each operation, and starting the machine to find the change.

For example, the positioning of the printer scanner is based on the principle of incremental encoder. Every time we turn it on, we can hear a crackling sound, it is looking for the reference zero point, and then it works.

This method is more troublesome for some industrial control projects, and it is not even allowed to start the change (the exact position must be known after the startup), so there is the emergence of the absolute encoder.
Absolute rotary photoelectric encoders have been more and more widely used in angle, length measurement and positioning control in various industrial systems because each position is absolutely unique, anti-interference, and no power-off memory.
There are many engraved lines on the absolute encoder optical disc, and each engraved line is arranged in 2, 4, 8, and 16 lines in turn. In this way, at each position of the encoder, by reading the Pass, dark, and obtain a set of unique binary codes (Gray code) from the zero power of 2 to the n-1 power of 2, which is called an n-bit absolute encoder. Such an encoder is determined by the mechanical position of the code disc, and it is not affected by power failure and interference.
The uniqueness of each position determined by the mechanical position of the absolute encoder, it does not need to remember, does not need to find a reference point, and does not need to count all the time, when you need to know the position, you can read its position. In this way, the anti-interference characteristic of the encoder and the reliability of the data are greatly improved.

Since absolute encoders are obviously superior to incremental encoders in positioning, they have been increasingly used in industrial control positioning. Because of its high precision, the absolute encoder has a large number of output bits. If parallel output is still used, each output signal must be well connected. For more complex working conditions, it must be isolated and the number of connecting cable cores is large. It brings a lot of inconvenience and reduces reliability. Therefore, in the multi-digit output type, absolute encoders generally use serial output or bus output. The most commonly used serial output of absolute encoders produced in Germany is SSI (synchronous serial output). line output)
From a photoelectric code disc with an axis in the center, on which there are ring-shaped and dark scribe lines, and read by photoelectric transmitting and receiving devices, four sets of sine wave signals are obtained and combined into A, B, C, D, each sine wave The phase difference is 90 degrees (360 degrees relative to one cycle), the C and D signals are reversed and superimposed on the A and B phases to enhance the stable signal; in addition, a Z-phase pulse is output per revolution to represent the zero reference bit. Since the phase A and B differ by 90 degrees, the forward rotation and reverse rotation of the encoder can be judged by comparing the phase A or phase B before, and the zero reference position of the encoder can be obtained through the zero pulse.
The materials of the encoder code disc are glass, metal, plastic. The glass code disc is a thin engraved line deposited on the glass, which has good thermal stability and high precision. However, because the metal has a certain thickness, the accuracy is limited, and its thermal stability is an order of magnitude worse than that of glass. The plastic code disc is economical and its cost is low, but its accuracy, thermal stability, and life are worse. .

Resolution - The number of pass or dark lines provided by the encoder per 360 degrees of rotation is called resolution, also called resolution division, or directly called how many lines, generally 5 to 10,000 lines per rotation

Rotary encoders are speed and displacement sensors that integrate opto-electromechanical technology.
Signal output includes sine wave (current or voltage), square wave (TTL, HTL), open collector (PNP, NPN), push-pull type, among which TTL is a long-line differential drive (symmetric A, A-; B, B -; Z, Z-), HTL is also called push-pull, push-pull output, the signal receiving device interface of the encoder should be connected with the corresponding signal of the encoder - the pulse signal of the encoder is generally connected to the counter, PLC, computer, PLC and computer The connected modules are divided into low-speed modules and high-speed modules, and the switching frequency is low or high.
Such as single-phase connection, it is used for one-way counting and one-way speed measurement.

A.B two-phase connection is used for forward and reverse counting, judging forward and reverse and speed measurement.

A, B, Z three-phase connection for position measurement with reference position correction.

A, A-, B, B-, Z, Z- are connected. Due to the connection with symmetrical negative signal, in the subsequent differential input circuit, the common mode noise is suppressed and only the useful differential mode signal is taken, so its resistance to It has strong interference ability and can transmit a long distance.
For TTL encoders with symmetrical negative signal output, the signal transmission distance can reach 150 meters.

The rotary encoder is composed of precision components, so when it is subjected to a large impact, the internal functions may be damaged, and sufficient attention should be paid to the use.
Do not apply direct shock to the shaft during installation.
The connection between the encoder shaft and the machine should use a flexible connector. When installing the connector on the shaft, do not press in hard. Even if the connector is used, due to poor installation, it is possible to apply a load larger than the allowable load to the shaft, or cause the core to be pulled. Therefore, special attention should be paid.

Bearing life is related to service conditions and is particularly affected by bearing load. If the bearing load is smaller than the specified load, the bearing life can be greatly extended.
Do not disassemble the rotary encoder, as this will impair oil and drip resistance. Anti-drip products should not be immersed in water or oil for a long time, and should be wiped clean when there is water or oil on the surface.

Vibration added to the rotary encoder is often the cause of false pulses. Therefore, pay attention to the installation location and installation location. The more pulses that occur per revolution, the narrower the slot spacing of the rotating slot disc and the more susceptible it is to vibration. When rotating or stopping at low speed, the vibration applied to the shaft or the main body may cause the rotary groove disc to vibrate, and false pulses may occur.

Incorrect wiring and connection may damage the internal circuit, so be careful when wiring: The wiring should be performed with the power OFF. When the power is turned on, if the output line touches the power supply, the output may be damaged. loop. Incorrect wiring may damage the internal circuit, so pay attention to the polarity of the power supply when wiring. If it is wired in parallel with the high-voltage line and power line, it may be damaged due to malfunction due to induction, so separate wiring is required.

When extending the wire, it should be less than 10m. And due to the distribution capacity of the wire, the rise and fall time of the waveform will be long. If there is a problem, the waveform is shaped by using a Schmitt circuit or the like.
To avoid induction noise, etc., use the shortest possible wiring distance. Special attention is required when inputting to integrated circuits. When the wire is extended, due to the influence of the conductor resistance and the capacitance between the lines, the rise and fall time of the waveform is prolonged, which is easy to produce interference (crosstalk) between the signals, so the wire with low resistance and low capacitance between the lines (twisted pair, shielded Wire).
For HTL encoders with symmetrical negative signal output, the signal transmission distance can be up to 300 meters.
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