21 Key Points About Servo Motor (Note to Engineers) | MachineMFG

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21 Key Points About Servo Motor (Note to Engineers)


Looking to select the right motor for your application? With so many options available, it can be overwhelming to know where to start.

But fear not! Our comprehensive guide will walk you through everything you need to know about selecting and using servo and stepper motors. From understanding load requirements to choosing the right power supply, we’ve got you covered.

So, whether you’re a seasoned engineer or just getting started in the world of motors, read on to learn how to make the right choice for your specific needs.

Key Points About Servo Motor

1. How to correctly select servo motor and stepper motor?

The selection process primarily depends on the specific application.

To begin, it is crucial to determine the nature of the load, including its orientation (horizontal or vertical), torque, inertia, speed, accuracy, acceleration, deceleration, and control requirements (such as port interface and communication).

Furthermore, the main control mode needs to be identified, whether it is position, torque, or speed. It is also necessary to consider the power supply type, such as DC or AC power supply, battery power supply, and voltage range.

By taking these factors into account, the appropriate motor model and matched driver or controller can be determined.

2. Stepper motor or servo motor system, which one to choose?

The selection of the appropriate motor should be based on the specific application as each motor has its unique characteristics that make it suitable for certain tasks.

3. How to use the stepper motor driver?

The motor should be equipped with a driver that is equal to or greater than its current rating.

If high precision or low vibration is required, a subdivision driver can be used.

When using high torque motors, it is recommended to use high voltage drives as much as possible to achieve optimal high-speed performance.

4. What is the difference between 2-phase and 5-phase stepping motors and how to choose them?

The cost of a 2-phase motor is low, but it produces significant vibration at low speeds and experiences rapid torque decrease at high speeds.

In contrast, a 3-phase motor has lower vibration and offers superior high-speed performance, which can be up to 30-50% higher than that of a 2-phase motor. Therefore, it can serve as a viable replacement for a servo motor in certain applications.

5. When to select DC servo system and what is the difference between DC servo system and AC servo system?

A DC servo motor can be divided into two types: brush motor and brushless motor.

The brush motor has several advantages, including low cost, simple structure, high starting torque, wide speed regulation range, and easy control. However, it requires maintenance (carbon brush replacement), produces electromagnetic interference, and has environmental requirements. Therefore, it is suitable for common industrial and civil applications that prioritize cost.

On the other hand, a brushless motor has numerous advantages, such as small size, light weight, high output, fast response, high speed, low inertia, smooth rotation, and stable torque. Although the control is complex, it allows for intellectualization, and the electronic commutation mode is flexible and can be square wave commutation or sine wave commutation. Additionally, this motor is maintenance-free, highly efficient, has a low operating temperature, low electromagnetic radiation, and a long service life, making it suitable for various environments.

An AC servo motor is also a brushless motor, which can be divided into synchronous and asynchronous motors. Currently, the synchronous motor is commonly used in motion control due to its large power range, which can achieve high power. However, it has a large inertia, low maximum rotational speed, and rapidly decreases with increasing power. Therefore, it is suitable for low-speed and smooth operation applications.

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

The following checks shall be made before power on operation:

(1) The power supply voltage must be appropriate since overvoltage can damage the drive module. Also, ensure that the DC input’s + / – polarity is not connected incorrectly, and the motor model or current setting value on the drive controller is appropriate, not too large at the beginning.

(2) Firmly connect the control signal line and consider shielding problems, such as twisted pair, at the industrial site.

(3) Only connect the most basic system’s wires at the beginning and then connect them step by step after the system runs well.

(4) Determine the grounding method or floating non-grounding.

(5) Closely observe the motor’s state, such as normal movement, sound, and temperature rise, within half an hour after starting the operation. If any problem is found, stop the machine immediately for adjustment.

7. When the stepping motor starts and runs, sometimes it stops moving or returns in place, and sometimes it will lose step during operation. What’s the problem?

When conducting inspections, the following aspects should be considered:

(1) Is the motor torque sufficient to drive the load?

We recommend selecting motors with a torque 50% to 100% greater than the actual demand, as stepping motors cannot operate under excessive load. Instantaneous overload can cause the motor to go out-of-step, stop or move irregularly and repeatedly, leading to serious consequences.

(2) Is the current of the input walking pulse from the upper controller large enough (generally > 10mA)?

Ensure that the optocoupler can be turned on stably and that the input frequency is not too high, as it may result in failure to receive the pulse. If the output circuit of the upper controller is CMOS circuit, a CMOS input driver shall also be selected.

(3) Is the starting frequency too high?

Ensure that the acceleration process is set in the starting procedure. It is best to accelerate from the specified starting frequency of the motor to the set frequency, even if the acceleration time is very short. Otherwise, it may lead to an unstable or idle state.

(4) When the motor is not fixed properly, it may cause strong resonance resulting in the out-of-step state.

Ensure that the motor is properly fixed.

(5) For a 5-phase motor, incorrect phase connection may cause the motor to malfunction.

8. I want to directly control the servo motor through communication, is that OK?

Yes, it is also convenient, but it is mainly a matter of speed. It is typically used for applications that do not require a high response speed.

If fast response control parameters are needed, it is best to use a servo motion control card. These cards typically have DSP and high-speed logic processing circuits that enable high-speed and high-precision motion control. This includes acceleration, multi-axis interpolation, and other features.

9. Is it good to use the switching power supply to supply power to the stepping and DC motor system?

It is generally best not to use high torque motors, especially without selecting a switching power supply with more than twice the required power.

This is because the motor is a large inductive load, which can create an instantaneous high voltage at the power end.

Switching power supplies have poor overload performance, which can lead to shutdowns. Additionally, their precise voltage stabilizing performance is not always necessary and may even cause damage to the switching power supply and driver.

Conventional ring or R-type transformers can be used to transform DC power supply.

10. Do you want to use ± 10V or 4 ~ 20mA DC voltage to control the stepping motor?

Yes, but you will need another conversion module.

11. There is a servo motor with encoder feedback. Can it be controlled by a servo driver with only a tachometer port?

Yes, it requires an encoder tachometer signal module to be installed.

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

Disassembling is prohibited as the quartz sheet in the code disc is prone to breakage. Additionally, if dust enters the mechanism, it may compromise both the accuracy and lifespan of the device. As a result, professional maintenance is required to ensure proper functioning.

13. Can the stepping motor and servo motor be disassembled for maintenance or refitted?

It’s best to let the manufacturer handle it. Without professional equipment and knowledge, it’s difficult to properly install the components back after disassembly. Additionally, the gap between the rotating stators of the motor can’t be guaranteed, which can cause damage to the performance of the magnetic steel material. This damage can result in a loss of excitation and greatly reduce the motor’s torque.

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

In the event of encountering resistance, you may choose to stop, reverse, or maintain a specific level of force.

15. Can domestic drives or motors be used with foreign high-quality motors or drivers?

In principle, it is possible to use the motor. However, it should only be done after the technical parameters of the motor are clear. Otherwise, it could greatly reduce the intended effect and even have a negative impact on the long-term operation and service life.

It is recommended to consult with the supplier before making a decision to ensure that all technical specifications are properly understood.

16. Is it safe to drive the motor with a DC supply voltage greater than the rated voltage?

Typically, there are no issues as long as the motor functions within the set speed and current parameters.

The motor speed is directly proportional to the motor line voltage, so selecting a specific power supply voltage will not cause overspeed, but it may result in faults such as driver malfunctions.

Additionally, it’s essential to ensure that the motor satisfies the minimum inductance coefficient requirement of the driver, and the set current limit is less than or equal to the motor’s rated current.

In fact, it’s beneficial if you can make the motor run at a slower speed (below the rated voltage) in the device you design. Running at a lower voltage (and consequently, a slower speed) results in less brush operation rebound, less brush/commutator wear, lower current consumption, and a longer motor lifespan.

However, if the motor size constraints and performance requirements necessitate additional torque and speed, overdriving the motor is possible. But, it will come at the cost of the product’s service life.

17. How to select the appropriate power supply for the application?

For optimal performance, it is advisable to have a power supply voltage that is 10% to 50% higher than the maximum voltage required. However, this percentage may vary depending on factors such as KT, Ke, and the voltage drop within the system.

The current value of the driver should be sufficient to deliver the energy required for the application. Keep in mind that the output voltage of the driver differs from the supply voltage, which means that the output current of the driver will also be different from the input current.

To determine the appropriate supply current, it is necessary to calculate all power requirements for the application and increase them by 5%. The required current value can be determined using the formula I = P / V.

Therefore, to ensure that the system operates smoothly, it is essential to have the right power supply voltage and current values that can provide the required energy to the application.

The percentage of the recommended power supply voltage may vary depending on several factors such as KT, Ke, and voltage drop within the system.

It’s essential to ensure that the current value of the driver is sufficient to deliver the required energy for the application. Note that the output voltage of the driver differs from the supply voltage, which means that the output current of the driver will also be different from the input current.

To determine the appropriate supply current, it’s necessary to calculate all power requirements for the application and increase them by 5%. You can use the formula I = P / V to calculate the required current value.

In summary, it’s crucial to have the correct power supply voltage and current values to ensure that the system operates efficiently and delivers the necessary energy to the application.

18. What kind of working mode can I choose for the servo driver?

Not all models of drives have different modes available.

19. How are drives and systems grounded?

If there is no isolation between the AC power supply and the driver DC bus (such as the transformer), do not ground the non-isolated port of the DC bus or the non-isolated signal, as this may result in equipment damage and personal injury.

Due to the absence of a common voltage between AC and earth, a high voltage may exist between the DC bus ground and earth.

In most servo systems, all common ground and ground are interconnected at the signal end. However, the ground loop generated by various methods of connecting the ground is prone to noise interference and may produce current at different reference points.

To maintain a consistent command reference voltage, the signal ground of the driver must be linked to the signal ground of the controller. Moreover, it should be connected to the external power supply ground, which may impact the controller and driver’s operation (e.g., 5V power supply of the encoder).

Shielding layer grounding can be challenging and requires different methods. The correct shield ground should be at the reference potential point inside the circuit, depending on whether the noise source and receiver are grounded simultaneously or floating.

Make sure to ground the shield at the same point, so the ground current does not flow through the shield.

20. Why can’t the reducer match the motor exactly at the standard torque point?

When considering the maximum continuous torque generated by the motor through the reducer, it becomes apparent that many reduction ratios will exceed the torque capacity of the reducer. If we were to design each reducer to match the full torque, the internal gears of the reducer would require too many combinations, resulting in a large volume and requiring many materials.

This would ultimately increase the product price and violate the principle of “high performance and small volume”.

How to select electric cylinder, slide table and precision platform products? How is the cost calculated?

Choosing the right actuator product depends on your motion parameter requirements. To determine the specific technical conditions and motion parameters for your application, ensure they meet your actual needs, and provide enough room for the application while avoiding excessively high values that can increase costs several times more than standard products.

For instance, if an accuracy of 0.1mm is adequate, avoid selecting a parameter of 0.01mm. The same applies to load capacity, speed, and other parameters.

Another selection suggestion for users is to avoid setting the three primary parameters of push and pull or load, speed, and positioning accuracy very high simultaneously, as the actuator is a high-precision and high-tech mechatronics product.

Therefore, it is essential to consider and choose the appropriate motor, drive controller, and feedback device, as well as guide rails, screw rods, support seats, and other mechanical systems with various accuracy levels based on mechanical structure, electrical performance, material characteristics, and treatment methods.

Achieving the required overall motion parameters can be likened to selecting a product that pulls and launches the whole body. Of course, if you have high requirements, we can still meet them, but the cost will increase accordingly.

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