Rotary Encoder : Types, Working Principle and Signal Output

 

The rotary encoder is a device used to measure the rotational speed and cooperate with PWM technology to realize fast speed regulation. Through photoelectric conversion, the photoelectric rotary encoder can convert the angular displacement, angular speed and other mechanical quantities of the output shaft into corresponding electrical pulses and output them in digital quantity (REP).

It is divided into single output and double output. Technical parameters mainly include the number of pulses per revolution (from dozens to thousands), and power supply voltage. Single-channel output means that the output of rotary encoder is a group of pulses, while the dual-channel output rotary encoder outputs two groups of pulses with A/B phase difference of 90 degrees. Through these two groups of pulses, not only the speed can be measured, but also the direction of rotation can be judged.

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.

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

Shaft sleeve type: the shaft sleeve type can be divided into half-empty type, full-empty type and large-diameter type.

According to the working principle of encoder, it can be divided into photoelectric type, magnetic type and contact brush type.

Encoders can be classified into incremental and absolute encoders according to the different ways of hole engraving on the code disk.

A photoelectric coder with an axis in the center, on which there are annular open and dark lines, and photoelectric transmitting and receiving devices to read, obtains four groups of sine wave signals, which are combined into A, B, C and D, and each sine wave has a phase difference of 90 degrees (360 degrees relative to a cycle). Reverse the C and D signals and superimpose them on the A and B phases to enhance the stable signal; Another Z-phase pulse is output per revolution to represent the zero reference position. Since phase A and phase B differ by 90 degrees, the forward rotation and reverse rotation of the encoder can be determined by comparing whether phase A is in front or phase B is in front. The zero reference position of the encoder can be obtained through the zero pulse.

Encoder code disk is made of glass, metal and plastic. The glass code disk is a thin scribed line deposited on the glass. It has good thermal stability and high accuracy. The metal code disk is directly through and without scribed lines and is not fragile. However, due to the thickness of the metal, the accuracy is limited, and its thermal stability is one order of magnitude worse than that of the glass. The plastic code disk 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 known as analytical graduation, or direct graduation, typically between 5 and 10000 lines per revolution

Rotary encoder signal output:
The signal output includes sine wave (current or voltage), square wave (TTL, HTL), open collector (PNP, NPN), and push-pull type. TTL is a long-line differential drive (symmetrical A, A -; B, B -; Z, Z -), and HTL is also known as push-pull or push-pull output. The signal receiving equipment interface of the encoder should correspond to the encoder.

 

Signal connection - The pulse signal of the encoder is generally connected to the counter, PLC and computer. The modules connected by PLC and computer can be divided into low-speed modules and high-speed modules, and the switching frequency can vary from low to high.

For example, single-phase connection is used for one-way counting and one-way speed measurement.

A. B Two-phase connection is used for forward and reverse counting, judgment of forward and reverse directions and speed measurement.

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

 

A, A -, B -, B -, Z, Z - connections. Because of the connection with symmetrical negative signals, common mode noise will be suppressed in the subsequent differential input circuit, and only useful differential mode signals will be taken, so its anti-interference ability is strong, and it 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, it may damage the internal function, and full attention should be paid to its use.