Ac Servo drive alias: Servo drive, Servo motor drive, Servo motor drive, ac Servo drive, Servo drive.
On servo applications: first decide what you are using. If used in machine tools, the control part of the hardware can be designed relatively simple, and the cost is correspondingly lower. If used in military industry, the internal firmware should be designed with more flexible control algorithms, such as position loop filtering, velocity loop filtering, nonlinear, optimization or intelligent algorithms. It certainly doesn't have to be implemented on a hardware part. There are several types of products that can be object-oriented.
Ac servo is widely used in machining center, automatic lathe, electric injection molding machine, manipulator, printing machine, packing machine, spring machine, CMM, EDM machine and so on.
The performance of stepper motor and AC servo motor is quite different. Stepper motor is a discrete motion device. It has essential connection with modern digital control technology. In the present domestic digital control system, the stepper motor is widely used. With the appearance of full digital AC servo system, AC servo motor is more and more used in digital control system. In order to adapt to the development trend of digital control, stepper motor or all-digital AC servo motor is used as the executive motor in most motion control systems.
Although they are similar in control mode (pulse train and direction signal), there are great differences in performance and application. Such as: 1, the control precision is different; 2. Different low frequency characteristics 3. Different moment frequency characteristics 4. Different overload capacity 5.
Ac servo system is superior to stepper motor in many aspects of performance. But in some of the less demanding occasions also often use stepper motor to do the executive motor. Therefore, in the design process of the control system to comprehensively consider the control requirements, cost and other factors, choose the appropriate control motor.
The problem about servo zero switch: there are many ways to find zero, which can be selected according to the required accuracy and actual requirements. It can be completed by the servo motor itself (some brand servo motors have a complete function of returning to the origin), or it can be completed by the upper computer with the servo, but the principle of returning to the origin is basically common as follows.
I. When the servo motor is looking for the origin, when it encounters the origin switch, it immediately slows down and stops, taking this point as the origin.
Second, when returning to the origin, directly look for the Z confidence number of the encoder, when there is a Z confidence number, immediately slow down to stop. This reversion method is generally only used in the rotation axis, and the speed of reversion is not high, the accuracy is not high.
Does the installation of the synchronous belt also have a significant impact on servo positioning? In this case, do you want to know if the servo is soft? What is the proportional gain of the position loop, the proportional gain of the speed loop, and the integral time constant?
Position ring proportional gain: 21rad/s
Speed loop proportional gain: 105rad/s
Velocity loop integration time constant: 84ms
About three kinds of servo control, general servo has three kinds of control: speed control, torque control, position control. What I want to know is what the three control methods are based on?
Speed control and torque control are controlled by analog quantities. Position control is controlled by sending pulses. The specific control mode should be selected according to the requirements of customers and the motion function. If you have no requirements on the speed and position of the motor, just output a constant torque, of course, in torque mode.
If the position and speed have certain accuracy requirements, but the real-time torque is not very concerned, using torque mode is not very convenient, using speed or position mode is better. If the upper controller has better closed-loop control function, the speed control effect will be better. If the requirements are not very high, or there is basically no real-time requirements, the position control mode has no high requirements for the upper controller.
In terms of the response speed of the servo driver, the torque mode has the least computation and the response of the driver to the control signal is the fastest. The position mode has the largest computation and the slowest response to the control signal.
It is necessary to adjust the motor in real time when the dynamic performance in motion is highly required. So if the controller itself is slow (such as PLC, or low-end motion controller), use position control. If the operation speed of the controller is relatively fast, the position ring can be moved from the driver to the controller in a speed way to reduce the workload of the driver and improve efficiency (such as most of the middle and high-end motion controllers). If you have a better upper controller, you can use torque control to remove the speed loop from the drive, which is usually only for high-end dedicated controllers, and you don't need servo motors at all.
Or to put it another way:
1. Torque control The torque control method is to set the external output torque of the motor shaft through the input of external analog quantity or the assignment of direct address. Specifically, for example, if 10V corresponds to 5Nm, the output of the motor shaft will be 2.5nm when the external analog quantity is set to 5V. If the motor shaft load is lower than 2.5nm, the motor will run forward. When the external load is equal to 2.5nm, the motor does not run, and when the external load is greater than 2.5nm, the motor reverses (usually in the case of gravity load). The torque can be changed by changing the setting of analog quantity immediately, and the corresponding address value can also be changed through communication.
It is mainly used in winding and unwinding devices with strict requirements on the force of the material, such as cable device or fiber pulling equipment. The torque setting should be changed at any time according to the change of the radius of the winding to ensure that the force of the material will not change with the change of the radius of the winding.
2, position control: the position control mode is generally through the external input pulse frequency to determine the size of the rotation speed, through the number of pulses to determine the rotation Angle, some servo can directly through the communication mode of speed and displacement assignment. Because position mode can have very strict control of speed and position, it is generally used in positioning devices.
Application areas such as CNC machine tools, printing machinery and so on.
3. Speed mode: the rotation speed can be controlled by the input of analog quantity or the frequency of pulse. The speed mode can also be positioned when there is the outer ring PID control of upper control device, but the position signal of the motor or the position signal of direct load must be fed back to the upper for calculation. In this case, the encoder at the motor shaft end only detects the motor speed, and the position signal is provided by the detection device at the direct final load end. This advantage is to reduce the error in the process of intermediate transmission and increase the positioning accuracy of the whole system.
How to judge the fault difference between servo motor and servo drive?
Look at the error on the drive, the alarm number, and then consult the manual. If there is no alarm, it is naturally a drive failure. Of course, there may be no failure of the servo at all, but the control signal error leads to no servo action.
In addition to the error on the drive, the alarm number, and then refer to the manual, sometimes the most direct way to determine is to replace, such as X and Z axis servo change (the same model can be). Or modify parameters, such as locking the X-axis to prevent the system from detecting the X-axis
However, it should be noted that X axis and Z axis are exchanged, even if the model is the same, imported equipment may also cause problems because of different loads and different parameters. Of course, if it is domestic equipment, usually will not adjust the servo parameters according to the use of the situation, there is generally no problem. However, attention should be paid to whether the motor power torque of X axis and Z axis is the same, whether the motor screw is directly connected and the reduction ratio of electronic gear.
Some questions about AC servo motor:
Question (A) : Is the rated speed of ac synchronous servo and AC asynchronous servo related to the number of poles? n1=60f/2p? Output constant torque below rated speed, constant power above rated speed, then the rated speed is determined by the motor itself or the driver to decide?
Related, synchronous speed N1 =60f/2p, asynchronous machine also has slip s, n=(1-S) N1, synchronous machine n= N1, 2p is polar logarithm. The limit of weak magnetic speed in control is judged by the driver.
Rated speed can be determined by several aspects: synchronous servo back potential level, motor core material allowed driving current alternating frequency, rated torque motor maximum power, maximum temperature rise, the most important or back potential; Induction motors are mainly limited by the maximum frequency permitted by the material and the polar logarithm.
The rated speed is defined by the mechanical and electrical characteristics of the motor itself.
Q (B) : Does the distinction between AC and DC servos depend on the form of current or voltage between the driver and the motor? But the current direction of brushless DC servo also changes? Can it be understood as communication? Is ac servo based on the principle of dc brushless servo evolution?
A: AC servo usually refers to the servo driven by sine wave. Brushless drive is equivalent to the control precision of brushless DC motor with commutator number of 6(7). Generally, low speed characteristics are poor. There is also a commercial called ac servo, just because he got rid of the brush, but I'm afraid the characteristics of ac servo, DC servo gap, 10000 times of speed than brushless motor is absolutely difficult to achieve.
Dc brushless motor is actually a kind of automatic permanent magnet synchronous motor, but it is rectangular wave power supply, and usually said permanent magnet synchronous motor is sine wave power supply. The reason why it is called "DC motor" is mainly taken into account that the controller of the brushless motor is equivalent to the brush and commutator of the DC brush motor to realize "electronic commutation", which is equivalent to the DC motor from the side of the DC bus.
Dc servo for DC motor, not brushless DC motor; Brushless DC motor and AC servo motor are actually the same thing, is ac synchronous motor (AC permanent magnet synchronous servo motor).
Question (C) : The polar logarithm of the motor?
A: n1 = 60 * f / 2 p
P generally represents the number of pole pairs of the motor, and 2P is the number of poles.
1 pair consists of N and S poles, and the number of poles is, of course, twice that of the logarithm.
Synchronous motor mechanical speed =60* operating frequency/polar logarithm;
Asynchronous motor mechanical speed =60* operating frequency *(1- slip)/ polar logarithm
Application trend of AC servo motor
Automatic control system not only develops rapidly in theory, but also changes rapidly in its application devices. Modular, digital, high precision, long life of the device every 3 to 5 years there are updated products on the market. The characteristic of traditional AC servo motor is soft and its output characteristic is not single value. Stepper motor generally unable to pinpoint for open loop control, speed of the motor itself and the resonance zone, PWM speed control system of position tracking performance is poorer, frequency control of motor speed is relatively simple but sometimes not enough accuracy, dc motor servo system, with its excellent performance has been widely used in the position servo system, but its disadvantages, such as complicated structure, the contradiction in dead zone in super-low speed, And reversing brushes can cause noise and maintenance problems. At present, the new permanent magnet ac servo motor develops rapidly, especially after the development from square wave control to sine wave control, the system performance is better, its speed range is wide, especially the low speed performance is superior.
Ac/DC servo motor system
The following describes the different characteristics of dc servo motor system from the aspects of power drive, performance, protection circuit and so on.
Power drive
For the driving motor power amplification part of the DC servo system often used in radar, the line weight is light, the speed is slow, the driving power is small, generally tens of watts, the motor can be directly controlled by the DC power. When the drive power requirement is near kilowatt or above, the selection of the drive scheme, that is, to amplify the armature current of the DC motor, is an important part of the design of the servo system. At present, the high power DC power supply is used more: transistor power amplifier, thyristor power amplifier and motor enlarger and so on. For kilowatt transistor amplifier used less. SCR technology in the last century 60 ~ 70's early rapid development and wide application, but because of various reasons at that time, such as reliability, many products abandoned SCR control. At present, integrated drive modules are generally made of transistors or thyristors. Motor enlarger is a traditional DC servo motor power amplifier device, because of its simple control, strong and durable, the current new type of radar products are still used. The following is mainly to enlarge the motor as an example, and ac servo motor to compare its advantages and disadvantages.
The amplifying motor is often called the expander. It is generally used to drag two dc generator sets in series with ac asynchronous induction motor to achieve DC control. Two groups of control windings, each group of input impedance is several thousand ohms, if the series using input impedance of about 10 thousand Ohms, generally complementary balance symmetrical input, when the system input is not zero break its balance, so that the amplifier motor has output signal. When the input current is more than ten to dozens of milliamps, its output can reach more than 100V DC voltage and several ampere to dozens of ampere current, directly connected to the armature winding of dc servo motor. Its main disadvantages are large volume, heavy weight, nonlinearity, especially near zero point is not very good, which requires careful handling for demanding systems.
And ac servo motor is equipped with special drive, it is far less than in the bulk and weight with the power of motor to enlarge, it depends on the internal composition of transistor and thyristor switch circuit, based on photoelectric encoder or within the servo motor hall device to judge rotor position at that time, decided to drive motor of a, b, c three corresponding state of output, so its efficiency and stability is very good. So unlike control amplifier motor need to do special amplifier circuit. This kind of motor is generally permanent magnet, the driver produces a, B, C three-phase change of current control motor rotation, so it is called ac servo motor; The control signal input by the driver can be pulse series or DC voltage signal (generally ± 10V), so it is also called dc brushless motor.
Simple test comparison of two motors
Made simple test comparison of two kinds of motor: as long as the system of the original dc error signal directly connected to the ac servo drive analog control input, using ac servo motor and its drive instead of the original differential amplifiers, amplidyne and dc servo motor, the control part and the Angle measuring components are the same, simple comparison of two schemes of output characteristic.
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. In no-load condition, when its input voltage is 1V, the motor does not operate and the input voltage is 2-2.5V, the motor speed is uneven, which is inevitable caused by carbon brush, oil seal and torque Angle. However, ac servo motor has low friction due to the absence of carbon brush, and its electromagnetic force is always perpendicular to the radius of rotation due to the existence of Hall device (this is the so-called sinusoidal control), so its low speed performance is obviously better than the former. At that time, when the speed was set at a very low level, it was difficult to distinguish the rotation of the motor with the naked eye, and the armature position indicated could only be observed through its own software interface. Creeping phenomenon could not be observed, and the characteristic soft phenomenon could not be felt by hand
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