| Incremental encoder | Absolute encoder | Grating | Resolver | Rotary inductive synchronizer | |
| principle | Using mechanical principle to turn mechanical angular displacement into electrical signal | Light and dark alternating moiré fringes produced by the diffraction principle of light | An analog angle measuring device using the principle of electromagnetic induction is essentially a transformer with variable mutual inductance. | Using the principle of electromagnetic induction, the mutual inductance of two planar printed windings varies with position, and the working principle is similar to that of a multi-pole rotary transformer. | |
| classification | Principle and structure | material | (1) sine and cosine rotary transformer | (1) Straight line | |
| (1) Contact type | (1) Glass grating | (2) Linear rotary transformer | (2) Rotary | ||
| (2) Photoelectric | (2) Metal grating | (3) Proportional rotary transformer | |||
| (3) Electromagnetic | principle | ||||
| Feedback form | (1) Transmissive | ||||
| (1) Incremental encoder | (2) Reflective | ||||
| (2) Absolute encoder | |||||
| (3) Hybrid encoder | |||||
| basic component | Light-emitting diodes, photoelectric discs, visors, photosensitive elements, | (1) Circular grating | Brushed and brushless, stator core and coil, rotor core and coil, rotor output transformer | Fixed length and slider, winding | |
| Metal ring, ruler grating, readhead | |||||
| (2) Linear grating | |||||
| Scale grating | |||||
| Characteristics | Each increment of an output pulse signal corresponds to an incremental angular displacement | Absolute angular displacement by reading the pattern on the encoder disc | Measuring the angular displacement by measuring the number of moiré movements by the photosensitive element | Output is analog | The induced output electromotive force is an alternating voltage whose amplitude does not change and whose phase varies with the scale and the slider. |
| advantage | (1) No contact wear | High-resolution | Simple structure, strong, heat-resistant, impact-resistant, anti-interference, large signal output, low cost | (1) High-precision and high-resolution line displacement and rotation angle measurement | |
| (2) High speed and high precision | Easy to implement digital measurements and | (2) Strong anti-interference ability, which is little affected by external disturbance electric field and spatial magnetic field changes, and is basically not affected by power fluctuations. | |||
| Automatic control | (3) Simple structure, reliable operation and long service life | ||||
| (4) Long distance displacement measurement | |||||
| (3) most commonly used, easy to install | (3) It is possible to directly read the absolute value of the angular coordinates without having to "zero out" | (5) Good processability, low cost, easy to copy and batch production | |||
| (4) The price is cheaper than absolute | (4) Location information is not easy to lose | ||||
| (5) No cumulative error | |||||
| (6) The maximum allowable rotation speed is higher than the incremental type | |||||
| Disadvantage | (1) complicated structure | It has high requirements on the use environment, requires sealing when used, and must be protected against oil, dust, iron filings, etc. | (1) Low precision, suitable for measurement of medium and low precision angular displacement | (1) The output signal is weak | |
| (2) expensive | (2) The output is analog and cannot be directly digitally controlled. | (2) Signal processing trouble | |||
| (3) Location information will be lost after power failure | (3) The single-turn type can measure the shaft angle range from 0 to 360°, which is not suitable for multi-rotation motion control. Multi-rotation has been developed, but the cost is higher. | (3) Companion electronic equipment (digital display) for signal processing is more complicated and expensive | |||
| (4) The maximum allowable rotation speed is not as high as absolute | (4) There is a time delay in sampling processing, which is not suitable for high-speed control. | ||||
| Range of accuracy | Expressed in resolution, it is related to the number of pulses and the number of octaves generated by one revolution of the code wheel. It is generally 500 to 5000 pulses/r. High precision up to 2 17 pulse counts. The octave number is generally 1, 2, 4, and 8 times. | Expressed in resolution, related to the number of code channels of the code wheel. High-precision absolute code disk is generally 19-bit, with higher precision up to 21 bits | 10nm～10μm | Measurement accuracy 3~5' | (1) Straight line |
| Accuracy ±1μm, resolution 0.05μm, repeatability 0.2μm | |||||
| (2) Rotary type (diameter 300mm) | |||||
| Accuracy ±1", resolution 0.05", repeatability 0.1" | |||||
| Application | Very wide. Various occasions for measuring angle, speed, acceleration, line displacement, and angular quantity | Very wide. Various occasions for angle measurement | Wide range of applications. Metrology and inspection, assembly and testing, linear motors, printing and imaging, scientific instruments, semiconductor manufacturing | Measuring components in a high-precision servo system and solving components in an analog solution | Very wide. |
| Rotary applications such as: gyro platform, servo turntable, artillery control, radar antenna positioning, precision machine tools and other equipment. | |||||
| Linear applications such as coordinate boring machines, coordinate milling machines, and other precision machine tools for positioning, display, and closed-loop control systems for CNC machine tools | |||||
| Main characteristic parameter | Power supply, output signal, output form, pulse number, maximum response frequency, starting torque, rated load on the shaft, maximum speed, shaft diameter / shaft shape, use environment | Power supply, output form, output code, resolution (number of code channels), maximum response frequency, starting torque, rated load on the shaft, maximum speed, shaft diameter / shaft shape, use environment | Resolution, output waveform, range or diameter, measurement period, environmental requirements, DC power supply, protection level, minimum clock frequency, maximum moving speed, size | ordinary: | Structure type, detection period, accuracy, repeatability, slider resistance, slider input voltage, fixed-length impedance, fixed-length input voltage, voltage transfer coefficient |
| Excitation mode, excitation side rated voltage, rated frequency, open circuit input impedance, transformation ratio (output/excitation), multi-pole and dual-channel type and pole-logarithm, maximum no-load output voltage | |||||
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