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AC Servo Drive Alias: Servo Drive, Servo Motor Drive, Servo Motor Drive, Full Digital AC Servo Drive, Servo drive Servo motor.

Regarding the application of servo: First of all, you have to determine what occasion you are using. If it is used on the machine tool, the hardware of the control part can be designed relatively simple, and the cost is correspondingly lower. If it is used in military industry, the control algorithm should be more flexible when designing the internal firmware, such as providing position loop filtering, velocity loop filtering, nonlinear, optimization or intelligent algorithm. Of course it does not need to be implemented on a hardware part. Object-oriented can be made into several types of products.

AC servo is widely used in machining centers, automatic lathes, electric injection molding machines, manipulators, printing machines, packaging machines, spring machines, CMMs, EDM machines, etc.

There is a big difference in the performance of stepper motors and AC servo motors. A stepper motor is a discrete motion device; it is intrinsically linked to modern digital control technology. In the current domestic digital control system, the application of stepper motor is very extensive. With the emergence of all-digital AC servo systems, AC servo motors are increasingly used in digital control systems. In order to adapt to the development trend of digital control, most of the motion control systems use stepper motors or all-digital AC servo motors as executive motors.

Although the two are similar in control mode (pulse train and direction signal), there are big differences in performance and application. Such as: 1. Different control accuracy; 2. Different low frequency characteristics; 3. Different torque-frequency characteristics; 4. Different overload capacity; 5. Different operating performance; 6. Different speed response performance.

AC servo systems outperform stepper motors in many performance areas. However, in some occasions with low requirements, stepper motors are often used as executive motors. Therefore, in the design process of the control system, various factors such as control requirements and costs should be comprehensively considered, and an appropriate control motor should be selected.

Questions about servo zero switch: There are many ways to find change, which can be selected according to the required accuracy and actual requirements. It can be done by the servo motor itself (some brands of servo motors have a complete back-to-origin function), or it can be done by the host computer with the servo, but the principles of back-to-origin are basically the following.

1. When the servo motor is looking for the origin, when it hits the origin switch, it will decelerate and stop immediately, taking this point as the origin.

2. When returning to the origin, directly look for the Z-phase signal of the encoder. When there is a Z-phase signal, it will decelerate and stop immediately. This homing method is generally only applied to the rotating shaft, and the homing speed is not high and the accuracy is not high.

Does the installation of the synchronous belt also have a great influence on the servo positioning? In this case, we need to know whether the servo is adjusted very softly? Common servos are controlled by pulses. Then, the proportional gain of the position loop, the proportional gain of the speed loop, and the integral time constant How much are each?

Position loop proportional gain: 21rad/s

Speed ​​loop proportional gain: 105rad/s

Speed ​​loop integral time constant: 84ms

Regarding the three control methods of the servo, there are generally three control methods for the servo: speed control method, torque control method, and position control method. What I want to know is what are these three control methods based on?

Both speed control and torque control are controlled by analog quantity. Position control is controlled by sending pulses. The specific control method should be selected according to the requirements of the customer and the motion function to be satisfied. If you have no requirements for the speed and position of the motor, as long as you output a constant torque, of course, use the torque mode.

If there are certain accuracy requirements for position and speed, but you are not very concerned about real-time torque, it is not convenient to use torque mode, and it is better to use speed or position mode. If the upper controller has a better closed-loop control function, the effect of speed control will be better. If the requirements themselves are not very high, or there is basically no real-time requirements, the position control method does not have high requirements on the upper controller.

As far as the response speed of the servo drive is concerned, the torque mode has the smallest amount of computation, and the drive has the fastest response to the control signal; the position mode has the largest amount of computation, and the drive has the slowest response to the control signal.

When there are relatively high requirements for dynamic performance in motion, the motor needs to be adjusted in real time. Then if the operation speed of the controller itself is very slow (such as PLC, or low-end motion controller), it is controlled by position mode. If the operation speed of the controller is relatively fast, you can use the speed method to move the position loop from the driver to the controller to reduce the workload of the driver and improve the efficiency (such as most high-end motion controllers); if there is a better upper control It is also possible to use torque control to remove the speed loop from the drive, which is generally only possible for high-end dedicated controllers, and there is no need to use a servo motor at this time.

In other words:

1. Torque control: The torque control method is to set the external output torque of the motor shaft through external analog input or direct address assignment. When it is set to 5V, the motor shaft output is 2.5Nm: if the motor shaft load is lower than 2.5Nm, the motor rotates forward, when the external load is equal to 2.5Nm, the motor does not rotate, and when it is greater than 2.5Nm, the motor reverses (usually occurs when there is a gravitational load). ). The set torque can be changed by changing the setting of the analog quantity in real time, or the value of the corresponding address can be changed through communication.

The application is mainly used in winding and unwinding devices that have strict requirements on the force of the material, such as wire wrapping devices or optical fiber pulling equipment. The torque setting should be changed at any time according to the change of the winding radius to ensure that the force of the material is not affected. will change with the winding radius.

2. Position control: The position control mode generally determines the rotation speed through the frequency of externally input pulses, and determines the rotation angle through the number of pulses, and some servos can directly assign speed and displacement through communication. Since the position mode can have very strict control on the speed and position, it is generally used in positioning devices.

Application fields such as CNC machine tools, printing machinery and so on.

3. Speed ​​mode: The rotation speed can be controlled by analog input or pulse frequency. The speed mode can also perform positioning when there is an outer loop PID control of the upper control device, but the position signal of the motor or the direct load must be used. The position signal is fed back to the upper position for operation. The position mode also supports the direct load outer loop to detect the position signal. At this time, the encoder at the motor shaft end only detects the motor speed, and the position signal is provided by the direct final load end detection device. The advantage of this is that it can reduce the intermediate transmission process. The error increases the positioning accuracy of the entire system.

How to judge the fault difference between servo motor and servo drive?

Look at the error, alarm number on the drive, and then check the manual. If there is no alarm, it is naturally the drive failure. Of course, it is also possible that the servo is not faulty at all, but the control signal error causes the servo to not move.

In addition to looking at the error and alarm number on the drive, and then checking the manual, sometimes the most direct way to judge is to replace it, such as X and Z axis servo replacement (only the same model can be used). Or modify the parameters, such as locking the X axis to prevent the system from detecting the X axis

But it should be noted that the X axis and the Z axis are interchangeable, even if the model is the same, the imported equipment may cause problems due to different loads and different parameters. Of course, if it is a domestic device, the servo parameters are usually not adjusted according to the usage, and there is generally no problem. However, attention should be paid to whether the power torque of the X-axis and Z-axis motors is the same, whether the motor screw is directly connected, and the electronic gear reduction ratio.

A few questions about AC servo motors:

Question (A): Is the rated speed of AC synchronous servo and AC asynchronous servo related to the number of poles? n1=60f/2p? The output of constant torque below the rated speed and constant power above the rated speed, then the definition of the rated speed is determined by the motor itself Mechanical decision or drive decision?

Related, synchronous speed n1=60f/2p, asynchronous machine has slip s, n=(1-s)n1, synchronous machine n=n1, 2p is the number of pole pairs. The definition of the field weakening speed in the control is judged by the driver.

The rated speed can be determined by several aspects: the back EMF level of the synchronous servo, the allowable driving current alternating frequency of the motor iron core material, the maximum power of the motor under the rated torque, the highest temperature rise, etc. The most important thing is the back EMF; the asynchronous motor mainly Limited by the highest frequency allowed by the material and the number of pole pairs.

The definition of rated speed is determined by the mechanical and electrical characteristics of the motor itself.

Question (B): Does the distinction between AC and DC servo depend on the form of current or voltage between the driver and the motor? But the current direction of DC brushless servo also changes? Can it be understood as AC? Is AC servo based on DC brushless servo? Based on the principle of servo evolution?

Answer: AC servo usually refers to the servo driven by sine wave. The brushless drive is equivalent to the control accuracy of the brushed DC motor with 6 (7) commutators. Generally, the low-speed characteristics are poor. Commercially, it is also called AC servo, just because he got rid of the brush, but the characteristics are probably better than the good AC servo, DC servo, 10,000 times the speed regulation than the brushless motor can never be achieved.

The DC brushless motor is actually a kind of self-controlled permanent magnet synchronous motor, but it is powered by a rectangular wave, while the permanent magnet synchronous motor is usually powered by a sine wave. The reason why it is called "DC motor" is that the controller of the brushless motor is equivalent to the brushes and commutators of the DC brushed motor to achieve "electronic commutation", which is equivalent to a DC motor from the DC bus side.

DC servo is used for DC motor, not DC brushless motor; DC brushless motor and AC servo motor are actually the same thing, that is, AC synchronous motor (AC permanent magnet synchronous servo motor).

Question (C): The number of pole pairs of the motor?

Answer: n1=60*f/2p

p generally represents the number of pole pairs of the motor, and 2p is the number of poles.

One pair of poles includes N pole and S pole, and the number of poles is of course twice the number of pole pairs.

Synchronous motor mechanical speed=60*operating frequency/number of pole pairs;

Asynchronous motor mechanical speed=60*operating frequency*(1-slip rate)/number of pole pairs

Application Trend of AC Servo Motor

The automatic control system not only develops rapidly in theory, but also changes with each passing day in its application devices. Modular, digital, high-precision, long-life devices are updated every 3 to 5 years. Traditional AC servo motors have soft characteristics, and their output characteristics are not single-valued; stepper motors are generally open-loop control and cannot be accurately positioned. The speed regulation is simple but the accuracy is sometimes insufficient. The DC motor servo system is widely used in the position follow-up system due to its excellent performance, but it also has disadvantages, such as complex structure, prominent dead zone contradiction at ultra-low speed, and commutation. Brushes can create noise and maintenance issues. At present, the new permanent magnet AC servo motor is developing rapidly, especially after the development from square wave control to sine wave control, the system performance is better, its speed regulation range is wide, especially the low speed performance is excellent.

AC/DC servo motor system

The following describes its different characteristics from the DC servo motor system in terms of power drive, performance, protection circuit, etc.

Power drive

For the power amplification part of the drive motor of the DC servo system that is often used in radar, when the antenna is light in weight, slow in rotation speed, and the driving power is small, it is generally tens of watts, and the motor can be directly controlled by the DC power supply. When the driving power is required to be nearly kW or more, selecting the driving scheme, that is, amplifying the armature current of the DC motor, is an important part of designing the servo system. High-power DC power supplies currently use more: transistor power amplifiers, thyristor power amplifiers and motor amplifiers, etc. It is less used for kilowatt-level transistor power amplifiers. The thyristor technology was rapidly developed and widely used in the 1960s and early 1970s, but due to various reasons at that time, such as reliability, many products gave up thyristor control. The current integrated drive modules are generally made of transistors or thyristors. The motor amplifier is a traditional DC servo motor power amplifier device. Because of its simple control and robustness, it is still used in the current new models of radar products. The following mainly takes the amplification motor as an example, and compares its advantages and disadvantages with the AC servo motor.

Amplifying motors are often referred to as amplifiers. Generally, an AC asynchronous induction motor is used to drive a two-stage DC generator set in series to achieve DC control. Two sets of control windings, the input impedance of each set is several thousand ohms. If the input impedance is about 10 kiloohms in series, it is generally a complementary balanced symmetrical input. When the system input is not zero, its balance is broken, so that the amplifying motor has an output signal . When the input current is a dozen to tens of mA, the output can reach a DC voltage of more than 100v and a current of several amperes to tens of amperes, which is directly connected to the armature winding of the DC servo motor. Its main disadvantages are its large volume and weight, and its nonlinearity, especially around the zero point, is not very good, which requires careful handling for demanding systems.

The AC servo motor is equipped with a special driver, which is much smaller than the amplifier motor of the same power in volume and weight. It relies on the switching circuit composed of internal transistors or thyristors, and judges according to the photoelectric encoder or Hall device in the servo motor. The position of the rotor at that time determines the corresponding output states of a, b, and c of the drive motor, so its efficiency and stability are very good. Therefore, it is not necessary to make a special power amplifier circuit to control the amplifier motor. This kind of motor is generally a permanent magnet type, and the three-phase changing current of a, b, and c generated by the driver controls the rotation of the motor, so it is called an AC servo motor; the control signal input by the driver can be a pulse train or a DC voltage. Signal (generally ±10v), so it is also called DC brushless motor.

Simple test comparison of two motors

A simple test comparison of the two motors has been done: as long as the original DC error signal of the system is directly connected to the analog control input of the AC servo driver, the AC servo motor and its driver are used to replace the original differential power amplifier, motor amplifier and DC. The servo motor, but the control part and the angle measuring element are unchanged, and the output characteristics of the two schemes are simply compared.

The original DC servo motor has a rated voltage of 100v, a rated speed of 3000r/min, and a no-load starting voltage of 2v. When the input voltage is 1v, the motor does not rotate and the input voltage is 2 to 2.5v. It can be observed that the motor speed is uneven, which is an unavoidable phenomenon caused by carbon brushes, oil seals, etc. and torque angle. The AC servo motor has low friction force due to the absence of carbon brushes, and its electromagnetic force is always perpendicular to the rotation radius due to the existence of the Hall device (this is the so-called sinusoidal control), so its low-speed performance is significantly better than the former. At that time, the rotation speed of the motor was kept very low, and it was difficult to distinguish the rotation of the motor with the naked eye. It was only possible to observe the rotation of the indicated armature position through its own software interface, and no crawling phenomenon could be observed, nor could it be felt by hand. characteristic soft