(I) Classification and structure of pulse encoders Pulse encoders are divided into three types: photoelectric, contact and electromagnetic induction. The precision and reliability of photoelectric type are superior to the other two, so only photoelectric pulse encoder is used on CNC machine tools. Structure of photoelectric pulse encoder. On the circumference of a disk, there are equally spaced lines, which are divided into transparent and opaque parts, which are called circular gratings. The circular grating rotates with the working axis. On the opposite side of the circular grating, a fixed fan-shaped sheet, called the indicator grating, is placed in parallel, and two slits (directional slits) with a spacing difference of 1/4 are made on it. In addition, there is a zero slot (one pulse per revolution). The pulse generator is connected with the servo motor through a cross joint or key.
(II) Working principle of pulse encoder When the circular grating rotates with the working axis, the light passes through the straight parts of the two gratings, forming alternating light and dark stripes. Photoelectric elements receive these alternating optical signals and convert them into alternating electrical signals. The electrical signal is two sets of current signals A and B which are similar to sine waves. The phase difference between A and B signals is 90, which is amplified and shaped into a square wave. The signals passing through the two gratings also have a "pulse per revolution", called Z-phase pulse, which is also obtained through the above processing. Z pulse is used to generate the reference point of the machine tool. Subsequent pulses are sent to the counter, and the rotation angle and speed of the working shaft can be measured according to the number and frequency of pulses. Its resolution depends on the number of circles of the circular grating and the subdivision multiple of the measuring line.
(3) Application of Photoelectric Pulse Encoder As a position detection device on CNC machine tools, the photoelectric pulse encoder feeds back the detection signal to the CNC system. There are two ways to feed back to the numerical control system: one is to meet the requirement that the reversible counter has up-and-down counting, and form up-counting pulses and down-counting pulses; The second is to adapt to the counter with counting control and counting requirements, and form direction control signals and counting pulses.