28 things all about servo motors you should know

28 things all about servo motors you should know

28 things all about servo motors you should know

The general structure of the industrial robot electric servo system is three closed-loop control, namely current loop, speed loop and position loop. In general, for AC servo drives, a variety of functions such as position control, speed control, and torque control can be achieved by manually setting their internal functional parameters. So what do you need to know about servo motors? The following summary of the servo motor 28 you may not know the problem, together with a look at it.


1. How to choose the correct servo motor and stepper motor?

A: Depending on the specific application, simply to determine: the nature of the load (such as horizontal or vertical load, etc.), torque, inertia, speed, accuracy, acceleration and deceleration requirements, the upper control requirements (such as the requirements for the port interface and communication), the main control mode is the position, torque or speed mode. The power supply is DC or AC power, or battery power, voltage range. Accordingly to determine the motor and with the driver or controller model.


2. Choose stepper motor or servo motor system?

A: In fact, the choice of what kind of motor should be based on the specific application, each has its own characteristics.


3. How to use a stepper motor driver?

A: According to the current of the motor, with greater than or equal to the current of the driver. If you need low vibration or high precision, you can use a subdivision type driver. For large torque motor, use high voltage type driver as much as possible to get good high speed performance.


4.2 phase and 5 phase stepper motor what is the difference, how to choose?

A: 2 phase motor is low cost, but the vibration at low speed is higher, and the torque drops quickly at high speed. 5 phase motor is less vibration, high speed performance, than 2 phase motor speed 30 ~ 50% higher, can replace the servo motor in some occasions.


5. When to choose DC servo system, what is the difference between it and AC servo?

A: DC servo motors are divided into brushed and brushless motors.

Brush motor is low cost, simple structure, large starting torque, wide speed range, easy control, requires maintenance, but easy maintenance (change carbon brush), generates electromagnetic interference, and has requirements for the environment. Therefore it can be used in cost-sensitive general industrial and civil applications.

Brushless motor is small in size, light in weight, large output, fast response, high speed, small inertia, smooth rotation and stable torque. The control is complex, easy to realize intelligent, and its electronic phase change is flexible, can be square wave phase change or sine wave phase change. The motor is maintenance-free, with high efficiency, low operating temperature, low electromagnetic radiation, long life, and can be used in various environments.

AC servo motor is also brushless motor, divided into synchronous and asynchronous motor, at present, synchronous motor is generally used in motion control, which has a large power range and can do a lot of power. Large inertia, low maximum rotation speed, and rapidly decreases as the power increases. Therefore, it is suitable for doing low-speed smooth running applications.


6. What should I pay attention to when using the motor?

A: The following checks should be made before powering up and running.

(1) whether the power supply voltage is appropriate (overvoltage is likely to cause damage to the drive module); for the DC input +/- polarity must not be connected to the wrong, the drive controller on the motor model or current setting value is appropriate (not too large at the beginning).

2) control signal lines connected securely, industrial sites to consider shielding (such as the use of twisted pair).

(3) do not start with the need to connect all the lines, only the most basic system, after good operation, and then gradually connected.

4) Be sure to figure out the grounding method, or the use of floating air not connected.

(5) start running within half an hour to closely observe the state of the motor, such as whether the movement is normal, sound and temperature rise, and find problems immediately stop to adjust.


7. stepper motor start running, sometimes move a little on the motion or back and forth in place, and sometimes lose step when running, what is the problem?

Generally, the following aspects should be considered for inspection.

(1) whether the motor torque is large enough to drive the load, so we generally recommend that users select the torque than the actual need to choose 50% to 100% of the motor, because the stepper motor can not run over the load, even for a moment, will cause a loss of step, serious stalling or irregular in situ repeatedly moving.

(2) the upper controller to the input stepping pulse current is large enough (generally > 10mA), in order to make the optocoupler stable conduction, the frequency of the input is too high, resulting in the reception is not, if the output circuit of the upper controller is CMOS circuit, then also use CMOS input type driver.

3) whether the starting frequency is too high, whether the acceleration process is set on the starting program, start accelerating to the set frequency from within the starting frequency specified by the motor, even if the acceleration time is very short, otherwise it may be unstable, or even in an idle state.  

4) When the motor is not fixed, sometimes this condition will occur, then it is normal. Because, in fact, it causes the motor to resonate strongly at this time and cause it to enter the out-of-step state. The motor must be fixed.

5) For a 5-phase motor, the motor will not work even if the phase is connected wrong.


8. I want to control the servo motor directly by communication, is it possible?

Yes, it is convenient, but it is a matter of speed, for applications that do not require high response speed. If you require a fast response to control parameters, servo motion control card, which generally has a DSP and high speed logic processing circuit to achieve high-speed, high-precision motion control. Such as S acceleration, multi-axis interpolation, etc.


9. How about using switching power supplies to power stepper and DC motor systems?

Generally do not, especially for large torque motors, unless the choice of switching power supply more than double the required power. Because, when the motor work is a large inductive load, will form an instantaneous high voltage on the power supply side. And the switching power supply overload performance is not good, will protect the shutdown, and its precision voltage regulation performance and do not need, sometimes may cause damage to the switching power supply and driver. Can be used with conventional toroidal or R-type transformer-variable DC power supply.


10. Want to use ± 10V or 4 ~ 20mA DC voltage to control the stepper motor, can it?

Yes, but a separate conversion module is required.


11. There is a servo motor with encoder feedback, can it be controlled by a servo driver with only a speed measuring machine port?

Yes, you need an encoder to tachometer signal module.


12. Can the code plate part of the servo motor be disassembled?

It is forbidden to disassemble it, because the quartz chip inside the code plate is easy to break, and after entering the dust, the life and accuracy will not be guaranteed, so professional personnel are needed to overhaul it.


13. Can the stepper and servo motor be disassembled for overhaul or modification?

Do not, let the manufacturer to do, disassembled without professional equipment is difficult to install back to the original, the gap between the motor’s rotor stator can not be guaranteed. The performance of the magnet material is destroyed, or even cause a loss of magnetism, the motor torque is greatly reduced.


14. Can the servo controller sense the change of external load?

Such as stopping, returning or keeping a certain thrust to follow up when encountering set resistance.


15. Can the domestic drive or motor and foreign high-quality motor or drive be used together?

In principle, it is possible, but only after clarifying the technical parameters of the motor, otherwise it will greatly reduce the proper effect, and even affect the long-term operation and life. Consult with the supplier before deciding.


16. Is it safe to use DC power supply voltage greater than the rated voltage value to drive the motor?

Normally this is not a problem, as long as the motor runs within the set speed and current limits. Because motor speed is proportional to motor line voltage, selecting a certain supply voltage will not cause overspeed, but malfunctions such as drive may occur.

In addition, it is important to ensure that the motor meets the minimum inductance coefficient requirements of the drive, and also that the current limit set is less than or equal to the rated current of the motor.

In fact, it is good if you can have the motor run slower (below rated voltage) in the device you are designing.

Running at a lower voltage (and therefore lower speed) will result in less brush run bounce, and less brush/commutator wear, lower current draw and longer motor life.

On the other hand, if the motor size and performance requirements require additional torque and speed, overdriving the motor is possible, but at the expense of product life.


17. How do I select the proper power supply for my application?

It is recommended to select a power supply voltage value that is 10%-50% higher than the voltage required for the. This percentage varies depending on Kt, Ke, and the voltage drop in the system. The current value of the driver should be sufficient to deliver the power required by the application. Remember that the output voltage value of the driver is different from the supply voltage, so the driver output current is also different from the input current. To determine the appropriate supply current, calculate all the power requirements for the application and add 5%. The required current value can be calculated using the I = P/V formula.

It is recommended to choose a supply voltage value that is 10% to 50% higher than the required voltage. This percentage varies depending on Kt, Ke, and the voltage drop in the system. The current value of the driver should be sufficient to deliver the energy required by the application. Remember that the output voltage value of the driver is different from the supply voltage, so the driver output current is also different from the input current. To determine the appropriate supply current, calculate all the power requirements for the application and add 5%. The required current value can be calculated by the formula I = P/V.


18. What operating mode can I choose for the Servo Drive?

The different modes are not all present in all models of drives


19. How do I ground the drive and the system?

a. If there is no isolation between the AC power supply and the drive DC bus (e.g. transformer), do not ground the non-isolated port of the DC bus or the non-isolated signal, as this may cause equipment damage and personal injury. Because the AC common voltage is not to earth, there may be high voltages between the DC bus ground and earth.

b. In most servo systems, all common grounds and earth are connected together at the signal end. Multiple ways of connecting the earth produce ground loops that are susceptible to noise and generate flow at different reference points.

c. To keep the command reference voltage constant, connect the signal ground of the driver to the signal ground of the controller. It will also be connected to the ground of the external power supply, which will affect the operation of the controller and the driver (e.g. 5V power supply for the encoder).

d. Shield grounding is more difficult and there are several ways to do it. The correct shield grounding is at a reference potential point inside its circuit. This point depends on whether the noise source and reception are grounded at the same time, or floating. Be sure that the shield is grounded at the same point so that ground current does not flow through the shield.


20. Why can’t the gearbox be matched exactly to the motor at the standard torque point?

If you consider the continuous torque generated by the motor through the reducer, many reduction ratios will far exceed the torque rating of the reducer.

If we were to design each reducer to match the full torque, there would be too many combinations of internal gears in the reducer ( larger volume, more material).

This would make the product expensive and violate the “high performance, small size” principle of the product.


21. How do I choose to use a planetary or spur gear reducer?

Planetary gearboxes are generally used when high torque is required in a limited space, i.e. small volume and high torque, and they have better reliability and life than spur gearboxes. Spur gear reducers are used for lower current consumption, low noise and high efficiency low cost applications.


22. What is duty cycle?

Duty cycle is the ratio of operating time / (operating time + non-operating time) of a motor in each operating cycle. If the duty cycle is low, it allows the motor to run at 3 times the continuous current for a short time, thus producing more force than the rated continuous operation.


23. Can the drive circuit of a standard rotary motor be used for a linear motor?

Generally, yes. You can treat linear motors as rotary motors, such as linear stepper motors, brushed, brushless and AC linear motors. Please ask the supplier for details.


24. Can linear motors be mounted vertically for up and down motion?

Yes. According to the user’s requirements, we can add a balancing device for the movable slider or add a brake for the guide rail when installed vertically.


25. Can multiple movers be installed on the same platform?

Yes, you can. As long as several movers do not interfere with each other.


26. Is it possible to mount multiple brushless motors on the same magnetic rail with multiple kinematic coils?

Yes, it is possible. As long as the movers do not interfere with each other.


27. What is the advantage of using linear motor over linear motor with ball screw?

Since there is no mechanical connection between the stator and the movers, backlash, wear, and seizure problems are eliminated, and movement is smoother. It highlights the features of higher precision, high speed, high acceleration, fast response, smooth motion, high control accuracy, good reliability compact size, low profile height, long life, maintenance-free, etc.


28.How to choose electric cylinder, sliding table, precision stage products? How is the cost calculated?

The key to choosing actuator products depends on what kind of requirements you have for the motion parameters, you can determine the specific motion parameters and other technical conditions according to the application you need, these parameters should meet your actual needs, not only to meet the application requirements and leave room, but also do not mention too high, otherwise the cost may be several times higher than the standard products. For example, if 0.1mm accuracy is sufficient, do not choose the parameters of 0.01mm. The same is true for other parameters such as load capacity, speed, etc.

Another recommendation for users is that if it is not necessary, the three main parameters of pushing and pulling force or weight, speed and positioning accuracy should not be required to be high at the same time, because the actuator is a high precision and high technology mechatronics product.

We need to consider and choose the corresponding components of motor, drive and feedback device, as well as different precision and accuracy of the actuator. controller and feedback device, as well as different precision levels of guide rails, screw, support seat and other mechanical systems, so that it can achieve the required overall movement parameters, can be described as a product that involves the whole body. Of course, you have high requirements of the product needs, we can still meet, but the cost will be correspondingly higher.


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