Nowadays, there are step motors and servo motors used for plasma cutting in the market. However, in many cases, the servo motors are significantly more expensive than the stepper motors. Why? What are the characteristics of servo motor in the end? What are its unique features in those places? 9~13kg Single Tub Washing Machine
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The basic concept of servo is accurate, accurate and quick positioning. The frequency conversion is a necessary internal link of the servo control, the same frequency conversion exists in the servo driver (to carry on stepless speed regulation). However, the servo controls the current loop speed loop or position loop to be closed. This is a big difference. In addition, the construction of the servo motor is different from that of an ordinary motor, and it needs to satisfy fast response and accurate positioning. Currently, AC servo motors circulating on the market are mostly permanent magnet synchronous AC servos. However, such motors are difficult to achieve great power due to process limitations. Synchronous servos of more than ten KW are expensive and expensive, so that they can be used in the field. In many cases, AC asynchronous servos are used. In this case, many drives are high-end inverters with encoder feedback closed-loop control. The so-called servo is to meet the accurate, accurate, rapid positioning, as long as there is no contention for servo frequency conversion.
First, the common point of the two:
The technology of AC servo itself is to learn from and apply the technology of frequency conversion. Based on the servo control of DC motor, the frequency conversion PWM method is used to simulate the control method of DC motor, which means that AC servo motor must have frequency conversion. Link: The frequency conversion is to rectify the AC 50, 60HZ power frequency of the power frequency into DC, and then use the controllable gate of various types of transistors (IGBT, IGCT, etc.) to invert the frequency through the carrier frequency and PWM adjustment. The waveform is similar to the adjustable frequency. The sinusoidal pulsating power, as the frequency is adjustable, the AC motor speed is adjustable (n=60f/p, n speed, f frequency, p pole pair)
Second, the inverter:
A simple inverter can only adjust the speed of the AC motor. In this case, it can be open-loop or closed-loop depending on the control method and the frequency converter. This is the traditional V/F control method. Now many frequency conversions have been established through mathematical models, which convert the stator magnetic field UVW3 of an AC motor into two current components that can control the speed and torque of the motor. Nowadays, most of the famous brand inverters that can perform torque control are The torque is controlled in such a way that the output of each phase of the UVW is added with a Hall-effect current detection device, and the PID adjustment of the current loop constituting the closed-loop negative feedback is performed after sampling feedback; ABB's frequency conversion also proposes different direct torque control techniques in this manner. Please refer to the relevant information for details. This can not only control the speed of the motor can control the torque of the motor, and the speed of the control accuracy is better than v / f control, encoder feedback can also be added, when the control accuracy and response characteristics are much better.
Third, servo motor:
Driver: In the premise that the servo driver develops the inverter technology, the current loop, speed loop, and position loop (without the loop in the inverter) of the servo driver perform more precise control techniques and algorithm operations than the normal inverter, It is also much more powerful than traditional frequency conversion, and the main point is precise position control. The speed and position are controlled by the pulse sequence sent by the upper controller (of course, some servos integrate the control unit internally or directly through the bus to set parameters such as position and speed in the drive), and the internal algorithm and speed of the driver are faster. More accurate calculations and better-performing electronic devices make it superior to frequency converters.
Motors: The material, structure, and processing technology of servo motors are much higher than those of AC motors driven by inverters (general AC motors or constant-moment, constant-power, and other variable-frequency motors), that is, when the driver outputs current, voltage, When the frequency changes rapidly, the servo motor can respond to changes in the power supply to produce changes in response. The response characteristics and overload resistance are much higher than those of the AC motor driven by the inverter. The serious difference in the motor is also the fundamental difference between the two. . That is to say, it is not the inverter's output that cannot change as fast as the power signal, but the motor itself cannot react. Therefore, in order to protect the motor when the internal algorithm of the frequency conversion is set, a corresponding overload setting is made. Of course, even if the output capacity of the inverter is not set to be limited, some inverters with excellent performance can directly drive the servo motor! ! !
Fourth, AC motor:
AC motors are generally divided into synchronous and asynchronous motors 1 and AC synchronous motors: that is, the rotor is composed of a permanent magnetic material, so after the rotation, as the rotating magnetic field of the stator of the motor changes, the rotor also changes the speed of response frequency, and the rotor speed = Stator speed, so called "synchronous".
2. AC asynchronous motor: The rotor consists of induction coil and material. After rotation, the stator generates a rotating magnetic field. The magnetic field cuts the induction coil of the stator. The rotor coil generates an induced current. The rotor then generates an induced magnetic field. The induced magnetic field follows the stator's rotating magnetic field, but the magnetic field of the rotor is always smaller than the change of the stator. Once it is equal to No change in the magnetic field cuts the rotor's induction coil, and there is no induced current in the rotor coil. The rotor magnetic field disappears, and the rotor stalls and the stator produces a speed difference and regains the induced current. . . Therefore, a key parameter in the AC asynchronous motor is that the slip ratio is the ratio of the speed difference between the rotor and the stator.
3, corresponding to AC synchronous and asynchronous motor frequency converters have phased synchronous frequency converters and asynchronous frequency converters, servo motors also have AC synchronous servo and AC asynchronous servo, of course, inverter AC frequency asynchronous common, servo is common AC synchronous servo.
Fifth, frequency conversion and servo motor application.
Because of the difference in performance and function between frequency converter and servo, applications are not the same:
1. In the occasions of speed control and torque control, the general inverter is not required to be very high, and the feedback signal of the upper position plus the position feedback signal constitute the closed-loop frequency conversion for position control. The accuracy and response are not high. Some frequency converters also accept the pulse sequence signal to control the speed, but it seems that the position cannot be controlled directly.
2, in the strict position control requirements of the occasion can only use the servo to achieve, there is the servo response speed is much greater than the frequency conversion, some of the speed of the accuracy and response to the occasion also requires high servo control, can use the frequency control Almost all of the sports occasions can be replaced with servos. The key points are two points: First, the price servo is much higher than the frequency conversion, and the second is the reason of the power: the maximum frequency conversion can achieve hundreds of KW, or even higher, the maximum number of servos Ten KW. Now the servo can also achieve hundreds of KW.
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Four advantages of selecting a servo motor