Basic classification of encoders
Encoder is a precise measuring device which is closely combined with machinery and electronics. It encodes and converts signals or data for communication, transmission and storage of signal data.According to different characteristics, encoder classification is as follows:
Code tray and yardstick.The encoder which converts linear displacement into electrical signal is called code ruler, and the encoder which converts angular displacement into telecommunication is code disk.
Incremental encoders.Provide information such as position, Angle and winding number. Define the separation rate by the number of pulses per winding.
Absolute value encoder.Provides information such as position, Angle, and winding number in the form of Angle increments, each of which is assigned a unique code.
Hybrid absolute value encoder.The hybrid absolute value encoder outputs two groups of information: one group of information is used to detect the magnetic pole position, with the function of absolute information;The other group has exactly the same output information as the incremental encoder.
The difference between incremental and absolute encoders
The incremental encoder converts the displacement into a periodic electrical signal, which is then converted into a counting pulse.In absolute encoder, each position corresponds to a certain number code, and the value expressed is only related to the starting and ending positions of measurement, but has nothing to do with the middle process of measurement.
With an incremental encoder, the position is determined by the number of pulses calculated from the zero mark, while the position of an absolute encoder is determined by the reading of the output code.In a circle, the output code reading at each position is unique;Therefore, when the power supply is disconnected, the absolute encoder is not separated from the actual position.If the power is switched on again, the position reading remains current and valid.
The parameters to be determined in the selection of the encoder
Installation size, outgoing mode and protection.It includes two aspects: locating the stop, axle diameter, mounting hole position and cable outgoing mode.Installation space volume;Whether the protection level of working environment meets the requirements.
Resolution.The number of pulses per turn when the encoder is working.
Electrical interface for encoder output.Common push and pull output, voltage output, open collector, line - driven output.The output mode shall match the interface circuit of the control system.
Common motor encoder
Three groups of square wave pulses A, B and Z phase are directly output by photoelectric conversion principle.The phase difference between A and B is 90o, which can easily determine the rotation direction.One pulse per revolution of the Z phase is used for reference point positioning.Its advantage: the principle structure is simple, the average life of the machine can be more than tens of thousands of hours, strong anti-interference ability, high reliability, suitable for long distance transmission.Disadvantages: unable to output the absolute position information of shaft rotation.
Absolute value encoder
Direct digital output of the sensor, the sensor on along radial there are a number of concentric circular encoder code, each consisting of pervious to light and opaque and sector, relationship between adjacent code number of sectors is double, the code number on the encoder is the binary digital digits, in the side of the encoder is a light source, the other side corresponding to every yard a photosensitive element;When the code plate is in different positions, each photosensitive element converts the corresponding level signal according to the illumination or not, and forms the binary number.
This encoder is characterized by no counter, in any position of the shaft can be read a fixed position corresponding to the digital code.Obviously, the more code channels, the higher the resolution, for an encoder with N bit binary resolution, the code disk must have N bar code channels.At present, China has 16 absolute encoder products.