Servo-control knowledge

With regard to the three kinds of servo control mode, generally have three kinds of servo-control mode: Speed control mode, torque control mode, position control mode. Want to know is that these three kinds of control mode specific on what basis to choose from?

Speed control and torque control are the analog volume control. Position control is controlled by sending pulses. What is the specific control method used according to customer requirements, to meet to choose what kind of motor function.

If you are the motor speed and position are not required, as long as the output of a constant torque, of course, is to use torque mode.

If you have a certain position and velocity accuracy requirements, while the real-time torque is not very concerned with the torque model is not convenient, with better speed or position modes. If the upper controller has a better closed-loop control functions, with the speed control results will be better. If the request itself is not very high, or, basically no real time requirements of the position control of the upper controller does not have very high demands.

On the servo drive's response rate, the smallest amount of torque mode operation, the drive for the fastest response to control signals; position mode operation the largest, the drive control signals in response to the slowest.

The dynamic performance of the movement has a relatively high demand, we need time to adjust the motor. So, if the controller itself, the computing speed is very slow (eg, PLC, or low-end motion controller), on the location of control of use. If the controller calculation speed is faster, you can use the speed mode, the position loop controller from the drive to reduce the workload of the drive to improve efficiency (such as most of the high-end motion controller); If you have a better control of the Upper device, it can control the torque, the speed loop away from the drive, which is generally only a high-end dedicated controller can be so dry, but this time completely without the use of servo motors.

2. Servo motion control card to connect the general steps to

Have recently seen many people make with the servo motor control card to connect the basic problems, which obviously should be by the control card's technical support staff to answer any questions. Here I give my clients to write the "control card servo motor speed control of the general steps", in order to avoid the ads as much as possible the card does not involve a specific model, and the control card brand model is different from the specific wiring and instructions are also different, and even some of the features do not necessarily support each control card, your reference bar.

1, initialization parameters

In the wiring before initialization parameters.

In the control card: the selected control; PID parameters will be cleared; to control the card by default when you enable signal power off; this state of preservation, ensure the control card again on the power-that is, for this state.

In the servo motor: Set control mode; setting enabled by an external control; encoder signal output of the gear ratio; set control signal and the ratio between the motor speed. In general, it is recommended to make servo work with a maximum design speed of the control voltage corresponding to 9V. For example, Matsushita is set to 1V voltage corresponding to the speed, factory value is 500, if you are only prepared to allow the motor to switch the following work in 1000, then this parameter is set to 111.

2, wiring

The control card power, the connection between the control card and the servo signal line. The following line is the need to take: the control card analog output lines so that it can signal line, servo encoder output signal line. Review wiring without error, the motor and control card (and PC) electricity. At this time motor should not move, and can easily rotate the outside, if not, check the enable signal setup and wiring. External rotation with the motor control card check whether the motor position can accurately detect the changes in, or check the encoder signal wiring and settings

3, test the direction of

For a closed-loop control system, if the feedback signal of the direction is not correct, the consequences will certainly be disastrous. By controlling the card to open servo enable signal. This is the servo should be a lower rate of rotation, which is the legendary "zero drift." General control card will have a zero-drift suppression commands or parameters. Use this command or parameters to see whether the motor speed and direction by this directive (parameter) control. If you can not control, check the wiring and control analog mode parameter settings. Confirmation is given a positive number, the electrical is being transferred, the encoder count increased; given negative, winding back around in circles, the encoder count decreased. If the motor with the load, travel is limited, do not adopt this approach. Test Do not give too much voltage, it is recommended below 1V. If the direction is inconsistent, you can modify the control card or motor parameters, to achieve consistency.

3. Ask: three-loop control principle

1, the first current loop: current loop input is the speed loop PID regulator that after the output, we called the "current loop to the definition of" bar, and then, this is a given current loop and the "feedback current loop" value to compare After the margin of doing in the current loop PID regulator output to the motor, "current loop output" is the motor phase current of each phase, "current loop feedback" is not the encoder feedback but the internal drive installed in each phase Hall elements (magnetic field induced into a current and voltage signals) back to the current loop.

2, speed loop: speed loop PID position loop input is adjusted to set the output as well as the location of the feed-forward value, we call "speed setting", the "speed setting" and "Speed-loop feedback" value to compare After doing the difference in the speed loop PID regulator (mainly the proportional gain and integral processing) after the output is the above mentioned "current loop given." Speed loop feedback from the encoder feedback and the value after "Speed Arithmetic Unit," to get.

3, position loop: Location is the outer ring of the input pulse (usually the case, a direct address to write data to drive the servo exceptions), the external pulse through the smoothing filter processing and electronic gear calculation as a "position of ring settings," setting and the feedback from the encoder pulse counter is calculated through the deviation of the value of the PID position loop after adjustment (proportional gain adjustment, non-integral-differential links) after the output and location of a given feed-forward signal on the combined value the rate mentioned above constitute a ring given. Position loop feedback also came from the encoder.

Encoder mounted on the tail servo motor, it had no connection and current loop, he sampled from the motor rotation rather than the motor current, and the current loop input, output, feedback without any contact. The current loop is formed within the drive, even without the motor, as long as the dummy load is installed on each phase (for example, a light bulb) will be able to form a feedback loop current work. . .

4. For general questions about servo

First of all, I personally think that the most important issue to do servo system is to have a clear concept. A complete set of servo system, should be completed "current loop", "speed ring" and "position loop" control, speed loop and current loop output directly as a given, the output of position loop speed loop as given. Servo drive according to conditions of use of three different settings mode, then the controller should do according to these three modes of the corresponding control. To put it simply, when the servo drive for position mode, its internal needs to adjust all the parameters of the three rings, the upper controller is just a simple given, the controller is open-loop control and, therefore, there is no quality control parameters need to be adjusted. When the servo drive is the speed mode, the controller general to issue-10v voltage as the speed for a given transmitted to the servo drives, while receiving position loop encoder feedback constitutes a closed-loop control, this time controller with adjustable parameters position-dependent control quality parameters, while the servo drive at this time as long as the adjustment speed loop and current loop-related parameter, the drive inside the position loop parameters does not make sense!

You use TRIO controller, which can pulse output, analog output can also be returned at the same time encoder. If you use pulse output, then you need to set the servo drive for position mode, to adjust the position loop, velocity loop and current loop The PID parameters, in addition you want to set the servo drive electronic gear ratio, at this time there is no PID controller parameters need to be adjusted.

If you use analog output increases to return control of the encoder, servo drives is set to speed mode, need to adjust the speed of servo loop parameters related to pid, controller side p_gain, i_gain, d_gain, vff_gain and other parameters needed to be adjusted in order to achieve a good quality control at this time of the position loop servo drive parameters and the electronic gear ratio parameter has no effect. Pid parameter adjustment from the inside out to follow the principle, first adjust current loop parameters, the speed loop parameters, the final position loop parameters, the general situation, you have to set a good servo used within the load ratio, using the recommended parameters can be used, fine-grained control the quality of mediation in the TRIO software, you can turn on the oscilloscope function, you adjust to any changes, can be seen through the oscilloscope, is very convenient!

Accordingly, only when you use the trio controller analog output plus the location of the encoder feedback closed-loop manner, only open-loop control of position loop controller, say, when the servo = 0, the controller is open-loop control, this when the motion commands do not work, only play a role DAC this directive, DAC is a direct analog output instructions, the direct output-10v to 10v voltage to control the servo speed. (In a manner somewhat like the controlled inverter) their descriptions to help you look carefully. When the servo = 1, the position loop closed-loop control, motion commands to be effective.

In the TRIO has a direct connection servo controller enables the output of the relay-type nodes. When the wdog = 1, the output is ON, so that servo enabled, when the wdog = 0, the disconnect servo enabled. WDOG and open loop does not matter. When the controller in operation process, the system failure, which will automatically wdog = 0!

5. Universal CNC servo and dedicated servo What is the difference

Simply put: NC dedicated servo is the servo and CNC systems are closed, NC dedicated servo you can not be applied in other host computer (such as hair pulse, analog command) occasions. And universal servo (talk UTV servo more professional) can only accept pulse or analog command upper machine, you are no way servo universal application of the NC with dedicated servo systems. an example. Siemens 802C (or S) is a general-purpose servo band, and However, 810,840 to fail you have to use it to their own dedicated servo can not. As for the CNC system made in China or Taiwan production of NC system, which control commands are generally issued by pulse or analog (pulse-fat is probably the most simplest of NC ), so they are (only) with a common servo.

Complex point say: NC-specific servo is a servo power after the class. Servo-driven, and numerical control system has many parts made of one of its signals are PWM signals, mounted on the external drive is only one part of the power supply and power amplifier only. The general-purpose servo is different, its various circuits (such as position, velocity, current) and computing all done in the drive. including motor parameters.

To make a few practical application of the distinction it: dedicated servo parameter adjustment is generally to debug the system in NC, while the general-purpose servo servo drives need to debug.

Some special-purpose type servo motor encoder feedback directly back to numerical control system (due to an external power supply and amplifier is just one only), while the general-purpose servo is necessary to take back part of the drive.

Dedicated servo motor encoder number of lines, many of the millions of lines may be poor but far from universal type, and generally that is 2500 and 17BIT (a million used there? Who can receive too come?)

In high-speed high-precision machine tool applications, have to use special-purpose servo and NC can not be, Taiwan and China-made CNC system plus general-purpose servo do not (at least not now). Of course, much cheaper. Something is not how high-end, The Well is that you apply to any occasion. However, in CNC industry, use of special-purpose servo is a trend.

This is why high-end CNC systems with dedicated servo (too many advantages. Does not say), Mitsubishi and General CNC servo two points are also easy to understand.

6. "Location", "Speed," "Torque"

"Position", "Speed," "Torque" is the servo system from the outside to the inside of the three closed-loop control mode.

Position control methods are to complete all of the three closed-loop servo control, the computer need only send a pulse train to the servo unit can be, the computer does not require the completion of the side of the PID control algorithm;

Using the speed control mode, the servo speed and torque to complete (current) two closed-loop control, the computer needs to send analog servo unit, the computer side of the need to complete PID position control algorithm, and then D / A output;

In general, we need to position control system can either use the servo position control mode, you can also use the speed control mode, only the handling of different host computer. In addition, it was considered less susceptible to interference position control mode.

Torque control method is a servo system only for closed-loop torque control, ie a current control, host computer algorithms are simple, just need to send to the servo unit a target torque value, is an analog quantity. Multi-torque control in a single occasion, such as printing system, a motor with the speed or position control methods used to determine the printing location, and the other motor for torque control method is used to form a constant tension.

7. Servo three kinds of control mode

If you are the motor speed and position are not required, as long as the output of a constant torque, of course, is to use torque mode.

If you have a certain position and velocity accuracy requirements, while the real-time torque is not very concerned with the torque model is not convenient, with better speed or position modes. If the upper controller has a better closed-loop control functions, with the speed control results will be better. If the request itself is not very high, or, basically no real time requirements of the position control of the upper controller does not have very high demands.

On the servo drive's response rate, the smallest amount of torque mode operation, the drive for the fastest response to control signals; position mode operation the largest, the drive control signals in response to the slowest.

The dynamic performance of the movement has a relatively high demand, we need time to adjust the motor. So, if the controller itself, the computing speed is very slow (eg, PLC, or low-end motion controller), on the location of control of use. If the controller calculation speed is faster, you can use the speed mode, the position loop controller from the drive to reduce the workload of the drive to improve efficiency (such as most of the high-end motion controller); If you have a better control of the Upper device, it can control the torque, the speed loop away from the drive, which is generally only a high-end dedicated controller can be so dry, but this time completely without the use of servo motors.

8. Will the servo and inverter What is the difference

1, the two things in common:

AC servo technology itself is a draw and the application of frequency conversion technology, in the DC motor servo control based on the way through the conversion of the PWM DC Motor Control imitation to achieve, that is bound to variable frequency AC servo motor, this links: Frequency is the frequency of the 50,60 HZ AC into DC first rectifier, and then can control the gate of the various types of transistors (IGBT, IGCT, etc.) through the carrier frequency and PWM inverter for adjustable frequency adjustable waveform similar to the are cosine pulse of electricity, due to frequency is adjustable, so the speed of AC motor of the adjustable (n = 60f / p, n speed, f the frequency, p the number of pole pairs)

Second, talk about the converter:

A simple inverter can adjust the speed of AC motor, then you can open-loop can be closed-loop control mode and the inverter depending on the setting, which is in the traditional sense of the V / F control mode. Now many of the conversion have been adopted to establish the mathematical model, the AC motor's stator magnetic field UVW3 phase transformation that can control motor speed and torque of the two current components, and now most of the torque control can be carried out well-known brand of inverter are adoption of such control the torque, UVW output of each phase to be Jia Huoer effects of current detection device, the sampling constitutes a closed-loop feedback and current negative feedback loop PID regulator; ABB variable frequency also proposed and such a different way of direct torque control technique , specifically requested access to relevant information. This can not only control the motor speed control motor torque and speed control accuracy of better than v / f control, encoder feedback can also be added from time increases, plus when the control accuracy and response characteristics much better.