Description
Pulse encoder
The pulse encoder is an optical position detection element. The encoding disk is directly installed on the rotating shaft of the motor to measure the rotation Angle position and speed change of the shaft. The output signal is an electrical pulse. It is a commonly used angular displacement sensor. It can also be used as a speed detection device. The advantages of the pulse encoder are no friction and wear, small driving torque and fast response speed. The disadvantage of pulse encoder is poor anti-pollution ability and easy to damage. Classification and structure of pulse encoder Pulse encoders are divided into photoelectric, contact and electromagnetic induction three kinds. The accuracy and reliability of the photoelectric type are better than the other two, so only the photoelectric type pulse encoder is used on the CNC machine tool. The structure of the pulse encoder: the circle of a disk is engraved with equal spacing lines, which are divided into transparent and opaque parts, called circular grating. The circular grating rotates with the working axis. Opposite the circular grating, a fixed fan-shaped slice, called an indicator grating, is placed parallel to the circular grating, with two slits (directional slits) that differ by 1/4 pitch. In addition, there is a zero slit (one pulse per revolution). The pulse generator is connected to the servo motor by a cross connector or key.
The working principle of pulse encoder
When the circular grating is rotated with the working axis, the light passes through the linear part of the two grating, forming a stripe between light and dark. The photoelectric element receives these light signals alternating between light and dark, and converts 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 signal through the two gratings, there is also a "per revolution pulse", called the Z-phase pulse, which is also obtained by the above processing. The Z pulse is used to generate the reference point of the machine tool. The 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 the pulses. Its resolution depends on the number of turns of the circular grating and the subdivision multiple of the measurement line.
Application of pulse encoder
The pulse encoder is used as a position detection device in CNC machine tools, and the detection signal is fed back to the CNC system. There are two ways to feed back to the numerical control system: one is to adapt to the reversible counter with the requirement of addition and subtraction, forming the addition and subtraction pulse; The second is to adapt to the counter with counting control and counting requirements to form direction control signals and counting pulses.
Many people do not understand how the encoder pulse is calculated, and now I will give you the answer.
The specifications of each encoder indicate what the resolution is.
The unit is line/coil;
If it is 1024 lines/turn, it means that the encoder will send 1024 A phase and 1024 B phase pulses for each turn.
At this time, it depends on how your pulse receiver calculates the number of pulses, if it is A double frequency (that is, after receiving a complete A phase pulse rising edge and a B phase pulse rising edge, count a pulse), then it is to receive 1024 pulses; If it is 4 times the frequency (each A and B phase pulse of the rising edge and falling edge count a pulse, then a pair of AB phase pulse, the receiver counts 4)
Ac servo motor
The biggest characteristic element of AC servo motor is the servo mechanism. Can be called "servo motor", in addition to AC servo motor, there are DC servo motor and RC servo motor. The following explains their differences and characteristics, and briefly introduces the indispensable position/speed detection mechanism of servomechanism. Servo mechanism and servo motor Servo mechanism is an automatic control system in which the position, orientation, attitude and other control quantities of the object change with the target (or given value). The English word servo is based on the Latin word servus, which means "slave," meaning control that acts according to instructions. Dc servo motor In general, DC servo motors and DC motors are treated differently. The advantages and disadvantages of DC servo motor are summarized as follows. Advantages of DC servo motor: (1) Small, light weight, high efficiency. (2) Suitable for low voltage work. (3) High efficiency/high power can be obtained by using high-performance permanent magnets. (4) The system price of motor and servo amplifier is low. (5) Through feedback, the basic performance such as rotation accuracy and positioning performance is very high. Disadvantages of DC servo motor: (1) To perform servo control according to the load. (2) There is brush wear, need maintenance. (3) Brush wear will produce dust, not suitable for clean environment. (4) will produce mechanical and motor noise. Coreless DC motor, many manufacturers use it for DC servo motor. The characteristics of coreless DC motor are as follows: (1) The rotor inertia is small. (2) The inductance of the motor coil is small and the rectification characteristics are good. (3) No slot torque is generated. Although the DC servo motor has the disadvantage of brush contact with the commutator, the basic performance can match that of the AC servo motor, and the use is very close to it. Moreover, they have a lot in common in the design and manufacture of motors and servo amplifiers, and many manufacturers sell DC servo motors and AC servo motors together.
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