Knowledge of dry goods electric control - difference between stepping motor and servo motor


Small editors often envy the big gods high paid vocational colleges, but after communicating with God, they find that they are very proficient in machinery and electrical. When we see the gap, we know where to make up. Today, we learn the distinction between SCM and PLC; The difference between step motor and servo motor.

PLC is a general control platform for industrial environment, which is developed by users for the final control purpose.

PLC is an intelligent product. The core controller of Small PLC is often single chip microcomputer. To some extent, small PLC can be understood as a special single-chip system.

The conclusion can be drawn as follows:

1) PLC is a product based on single chip microcomputer, which is an integrated circuit, and they are not comparable.

2) PLC is a special case of SCM application system.

3) PLC of different manufacturers has the same working principle, similar functions and indicators, has certain interchangeability, quality assurance, and programming software is moving towards standardization. This is the basis of PLC widely used.

4) The application system of single chip microcomputer is the sea of eight immortals, which is very different in function and quality. It is difficult to learn, use and maintain.

Generally speaking: MCU is like a blank book, you want to write what to write. PLC is like a blank tree with a form drawn, and you fill in whatever you want.

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From the perspective of engineering, the selection of PLC and SCM system is discussed

1) For single project or few projects, PLC is a wise and quick way, with high success rate and good reliability.

2) For large amount of supporting projects, the use of SCM system may have the advantages of low cost and high efficiency, but it needs considerable R & D power and industry experience to make the system run stably and reliably.

Stepping motor is an open-loop control unit which transforms electric pulse signal into angular displacement or linear displacement. Under the condition of no overload, the speed and stop position of the motor only depend on the frequency and number of pulses of the pulse signal, but not affected by the load change. When the stepper actuator receives a pulse signal, It drives the stepping motor to set a fixed angle, called 'step angle', and its rotation is run step by step with a fixed angle. The angular displacement can be controlled by controlling the number of pulses, so as to achieve the goal of accurate positioning, and at the same time, the speed and acceleration of motor rotation can be controlled by controlling the pulse frequency, so as to achieve the purpose of high speed.! U4 s5 N) D# }* w' O

Servo motor is also called executive motor. In automatic control system, it is used as an executive element to convert the received electrical signal into angular displacement or angular speed output on motor shaft. The rotor inside the servo motor is a permanent magnet. The u/v/w three-phase electric field controlled by the driver forms electromagnetic field. The rotor rotates under the action of the magnetic field. Meanwhile, the encoder feedback signal provided by the motor is sent to the driver. The driver compares the feedback value with the target value to adjust the rotor rotation angle. The precision of servo motor is determined by the accuracy of encoder (number of lines), that is, servo motor itself has the function of sending out pulse. Every angle of rotation, it will send out corresponding number of pulses. Thus, the pulse of servo driver and servo motor encoder forms a correspondence, so it is closed-loop control, and step motor is open-loop control.

The difference between step motor and servo motor is as follows:

1. The control accuracy is different; The more the number of phases and beats of the stepping motor, the higher the accuracy of the step motor. The more the encoder scale, the higher the accuracy.

2. The control mode is different; One is open-loop control and the other is closed-loop control.

3. The low frequency characteristics are different; The low frequency vibration is easy to appear in the low speed of the stepping motor. When it works at low speed, damping technology or subdivision technology is generally used to overcome the low frequency vibration phenomenon. The servo motor is running smoothly, even at low speed, it will not appear vibration phenomenon. The AC servo system has resonance suppression function, which can cover the mechanical rigidity deficiency, and the system has frequency analysis function (FFT), which can detect the resonance point of the machine for system adjustment.

4. The characteristics of moment frequency are different; The output torque of the stepper motor will decrease with the increase of the speed, and the AC servo motor is constant torque output.

5. The overload capacity is different; The stepper motor generally does not have the overload capacity, but the AC motor has a strong overload capacity.

6. Different operation performance; The control of stepping motor is open-loop control, which is prone to step loss or blocking when the starting frequency is too high or the load is too large. When the speed is too high, it is easy to overshoot. The AC servo drive system is closed-loop control. The driver can directly sample the feedback signal of the motor encoder. The internal part is composed of position ring and speed ring, and generally, there will be no step loss or overshoot of the stepping motor, The control performance is more reliable.

7. The speed response performance is different; It takes hundreds of milliseconds for stepping motor to accelerate from static to working speed, but the acceleration performance of AC servo system is good, which usually takes only a few milliseconds, which can be used in the control occasions requiring rapid start and stop.

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