* Question
| What is a photoelectric encoder? |
* Answer
| Working principle: When the axis of the photoelectric encoder rotates, both A and B lines produce pulse output. The A and B two-phase pulses are separated by a phase angle of 90 degrees, so that the rotation direction of the photoelectric encoder and the motor speed can be measured.The line is used to measure the number of pulses, and the B line and the A line can be used to measure the direction of rotation. N is the motor speed Δn=ND-ND. For example, the speed of our car is 1.5m/s, the diameter of the wheel is 220mm, C=D*Pi,The number of pulses output per second by the optical code disc is: PD=130×600/60=1300 pulses. When the number of detected pulses deviates from the calculated standard value, the correspondence between the voltage and the number of pulses can be used.Calculate the incremental voltage △U output to the servo system, after D/A conversion, calculate the number of incremental pulses, and then subtract it.At this time, the system starts the position loop, continuously measures the number of pulses output by the photoelectric encoder per second, and compares it with the standard value PD (ideal value) to calculate the increment ΔP and convert it into the corresponding D/A.Output digital quantity, reduce the number of pulses of the motor by the controller, and subtract the increment based on the original output voltage.According to its scale method and signal output form, it can be divided into three types: incremental, absolute and hybrid.Its advantage is that the principle structure is simple, the average mechanical life can be more than tens of thousands of hours, the anti-interference ability is strong, the reliability is high, and it is suitable for long-distance transmission.
The disadvantage is that the absolute position information of the shaft rotation cannot be output.One side of the code wheel is a light source, and the other side has a photosensitive element corresponding to each code channel; when the code wheel is at different positions, each photosensitive element converts a corresponding level signal according to whether it is illuminated or not to form a binary number.Absolute encoders use the natural binary or cyclic binary (Gray code) method for photoelectric conversion.The absolute encoder differs from the incremental encoder in that it has a light-transmissive, opaque line pattern on the disc. The absolute encoder can have several codes, and the absolute position is detected based on the code on the read code disc.However, the resolution is determined by the number of bits in the binary, that is, the accuracy depends on the number of bits, and there are currently 10, 14 and so on.The photoelectric encoder is an angle (angular velocity) detecting device, which converts the angular amount input to the shaft into a corresponding electric pulse or digital quantity by using the photoelectric conversion principle, and has the advantages of small volume, high precision, reliable operation, digital interface, and the like.. |
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