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10 key questions about servo motors!

October 13,2022

How to correctly select servo motor and stepping motor ?

Answer: It mainly depends on the specific application situation. Simply put, it is necessary to determine: the nature of the load (such as horizontal or vertical load, etc.), the requirements of torque, inertia, rotation speed, accuracy, acceleration and deceleration, the upper control requirements (such as requirements for port interface and communication), and whether the main control mode is position, torque or speed. Whether the power supply is DC or AC power supply, or battery power supply, and the voltage range. So as to determine the model of the motor and the matched driver or controller

Choose stepper motor or servo motor system?

Answer: Actually, what kind of motor should be selected depends on the specific application, each with its own characteristics.

 How to match the stepper motor driver?

Answer: According to the current of the motor, use a driver greater than or equal to this current. If low vibration or high precision is required, it can be equipped with subdivision driver. For high-torque motors, high-voltage drivers should be used as much as possible to obtain good high-speed performance.

What is the difference between 4.2-phase stepping motor and 5-phase stepping motor, and how to choose it?

Answer: The cost of 2-phase motor is low, but the vibration is big at low speed, and the torque drops quickly at high speed. The 5-phase motor has small vibration and good high-speed performance, which is 30~50% higher than that of the 2-phase motor, and can replace servo motors in some occasions.

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

Answer: DC servo motors are divided into brushed and brushless motors.
Brushed motor has the advantages of low cost, simple structure, large starting torque, wide speed regulation range, easy control and maintenance, but it is convenient to maintain (carbon brush replacement), which generates electromagnetic interference and requires the environment. Therefore, it can be used in common industrial and civil occasions which are sensitive to cost.
Brushless motor has the advantages of small size, light weight, large output, fast response, high speed, small inertia, smooth rotation and stable torque. The control is complex, it is easy to realize intelligence, and its electronic commutation mode is flexible, which can be square wave commutation or sine wave commutation. The motor is maintenance-free, high in efficiency, low in operating temperature, low in electromagnetic radiation and long in service life, and can be used in various environments.
AC servo motor is also a brushless motor, which is divided into synchronous motor and asynchronous motor. At present, synchronous motor is generally used in motion control, and its power range is large, so it can achieve great power. Large inertia, low maximum rotation speed, and rapid decrease with the increase of power. Therefore, it is suitable for low-speed and stable operation.

Problems to pay attention to when using the motor?

Answer: Before powering on and running, check as follows:
1) Whether the power supply voltage is appropriate (over-voltage is likely to cause damage to the driving module); The+/-polarity of the DC input must not be connected in the wrong way, and whether the motor model or current setting value on the drive controller is appropriate (don’t be too big at the beginning);
2) The control signal line is firmly connected, and it is best to consider the shielding problem (such as twisted pair) in the industrial site;
3) Don’t connect all the lines that need to be connected at the beginning, only connect them into the most basic system, and then connect them step by step after running well.
4) Be sure to find out the grounding method, or use floating and not connecting.
5) Within half an hour after the start of operation, closely observe the state of the motor, such as whether the movement is normal, sound and temperature rise, and immediately stop and adjust when problems are found.

When the stepping motor starts to run, it sometimes stops when it moves or moves back and forth in place, and sometimes it loses its step when it runs. What is the problem?

Generally, the following aspects should be considered for inspection:
1) Whether the torque of the motor is large enough to drive the load, therefore, we generally recommend that users choose the motor whose torque is 50%~100% larger than the actual need when selecting the type, because the stepping motor can’t run over the load, even if it is instantaneous, it will cause out-of-step, or in severe cases, it will stop running or move irregularly in situ.
2) Whether the current of the input walking pulse from the upper controller is large enough (generally > 10mA) to make the optocoupler conduct stably, and whether the input frequency is too high to receive. If the output circuit of the upper controller is a CMOS circuit, the CMOS input driver should also be selected. Micro-signal technical training deserves your attention.
3) Whether the start-up frequency is too high, and whether the acceleration process is set in the start-up procedure, it is best to accelerate from the start-up frequency specified by the motor to the set frequency, even if the acceleration time is short, otherwise it may be unstable or even in an idle state.
4) When the motor is not fixed properly, this situation sometimes occurs, which is normal. Because, in fact, the strong resonance of the motor at this time leads to the out-of-step state. The motor must be fixed.
5) For a 5-phase motor, the phase connection is wrong, and the motor cannot work.

 I want to directly control the servo motor through communication, can I?

Yes, it’s convenient, but it’s just a matter of speed. It’s used for applications that don’t require too much response speed. If it is required to respond quickly to control parameters, it is best to use servo motion control card, which is generally equipped with DSP and high-speed logic processing circuit to realize high-speed and high-precision motion control. Such as S acceleration, multi-axis interpolation, etc.

 Is it good to use switching power supply to supply power to stepping and DC motor systems?

Generally, it’s best not to, especially the high torque motor, unless a switching power supply with more than twice the required power is selected. Because, when the motor works, it is a large inductive load, which will form an instantaneous high voltage to the power supply. However, if the overload performance of the switching power supply is not good, it will protect and shut down, and its precise voltage stabilizing performance is unnecessary, which may sometimes cause damage to the switching power supply and drivers. A DC power supply that can be transformed by a conventional ring or R-type transformer.

10. I want to use ±10V or 4~20mA DC voltage to control the stepping motor. Is it ok?
Yes, but an additional conversion module is required.