Question and answer of the hottest stepper motor

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Difficult questions and answers of stepping motor

1 What is a stepper motor

stepping motor is an actuator that converts digital pulse signal into angular displacement. In other words, when the stepping driver receives a pulse signal, it drives the stepping motor to rotate a fixed angle (i.e. step angle and step angle) in the set direction. You can control the angular displacement by controlling the number of pulses, so as to achieve the purpose of accurate positioning; At the same time, you can control the speed and acceleration of the motor by controlling the pulse frequency, so as to achieve the purpose of speed regulation

2. What kinds of stepper motors are there

there are three types of stepping motors: permanent magnet (PM), reactive (VR) and hybrid (HB)

permanent magnet stepping motors are generally two-phase, with small torque and volume, and the stepping angle is generally 7.5 degrees or 15 degrees

the reactive stepping motor is generally three-phase, which can achieve large torque output, and the stepping angle is generally 0.75 degrees. The output torque is large and the speed is high. This kind of motor is widely used in machine tools

the hybrid stepping motor combines the advantages of permanent magnet type and reactive type. It is divided into two-phase, three-phase, four phase and five phase: the two-phase (four phase) step angle is generally 1.8 degrees, the three-phase step angle is usually 1.2 degrees, and the five phase step angle is mostly 0.72 degrees. At present, the hybrid stepping motor is the most widely used

3. What is holding torque

holding torque refers to the torque that the stator locks the rotor when the stepping motor is energized but does not rotate. It is one of the most important parameters of stepper motor. Generally, the torque of stepper motor at low speed is close to the holding torque. As the output torque of stepping motor decreases with the increase of speed, and the output power also changes with the increase of speed, holding torque has become one of the most important parameters to measure stepping motor. For example, when people say 2n M, unless otherwise specified, means that the holding torque is 2n M

4. What is demand torque

demand torque refers to the torque when the stator locks the rotor when the stepping motor is not powered on. It is commonly referred to as "positioning moment". There is no unified translation method for demand torque in China, which is easy to cause misunderstanding; Since the rotor of the reactive stepping motor is not made of permanent magnet, it has no demand torque

5. What is the accuracy of the stepper motor? Cumulative

in general, the motor shall be replaced in time in case of damage in the step. The accuracy is% of the step angle and does not accumulate

6. What is the allowable surface temperature of the stepping motor

if the temperature of the stepping motor is too high, the magnetic material of the motor will be demagnetized first, resulting in torque reduction and even out of step. Therefore, the maximum allowable temperature of the motor surface should depend on the demagnetization point of different motor magnetic materials; Generally speaking, the demagnetization point of magnetic materials is above 130 degrees Celsius, and some are even as high as 200 degrees Celsius. Therefore, the surface temperature of stepping motor is completely normal at degrees Celsius

7. Why does the torque of stepping motor decrease with the increase of rotating speed

when the stepping motor rotates, the inductance of each phase winding of the motor will form a reverse electromotive force; The higher the frequency, the greater the reverse electromotive force. Under its action, the phase current of the motor decreases with the increase of frequency (or speed), resulting in the decrease of torque

8. Why can the stepper motor operate normally at low speed, but cannot be started if it is higher than a certain speed, accompanied by howling

the stepping motor has a technical parameter: no-load starting frequency, that is, the pulse frequency at which the stepping motor can start normally under no-load condition. If the pulse frequency is higher than this value, the motor cannot start normally, and step loss or locked rotor may occur. Under load, the starting frequency should be lower. If the motor is to rotate at a high speed, the pulse frequency should have an acceleration process, that is, the starting frequency is low, and then it will rise to the desired high frequency according to a certain acceleration (the global composite aviation material market will have a broad prospect in the next five years, and the engine speed will rise from low speed to high speed)

9. How to overcome the vibration and noise of two-phase hybrid stepping motor at low speed

high vibration and noise during low-speed rotation of stepping motor are its inherent shortcomings, which can be overcome by the following schemes:

a. if the stepping motor just works in the resonance zone, the resonance zone can be avoided by changing the reduction ratio and other mechanical transmission

b. drive with subdivision function is the most commonly used and easiest method

c. replace with stepper motor with smaller step angle, such as three-phase or five phase stepper motor

d. replacing AC servo motor can almost completely overcome vibration and noise, but the cost is high

e. add magnetic damper to the motor shaft. This product has been available in the market, but the mechanical structure has changed greatly

10. Can the subdivisions of subdivision drives represent precision

the subdivision technology of stepping motor is essentially an electronic damping technology (please refer to the relevant literature). Its main purpose is to reduce or eliminate the low-frequency vibration of stepping motor. Improving the operation accuracy of the motor is only an incidental function of the subdivision technology. For example, for a two-phase hybrid stepping motor with a stepping angle of 1.8 °, if the subdivision of the subdivision driver is set to 4, the operating resolution of the motor is 0.45 ° per pulse, and whether the accuracy of the motor can reach or connect to 0.45 ° depends on other factors such as the Subdivision Current control accuracy of the subdivision driver. The precision of subdivision drives from different manufacturers may vary greatly; The larger the fraction, the more difficult it is to control the precision

11. What is the difference between series connection and parallel connection of four phase hybrid stepping motor and driver

four phase hybrid stepping motor can be driven by unipolar and bipolar. For example, hsm8672 driver is unipolar and HSM driver is bipolar. Usually, a four phase stepping motor can be driven by a two-phase driver. Therefore, the four phase motor can be connected into two phases by series connection or parallel connection. The series connection method is generally used in the case of low motor speed. At this time, the output current of the driver is 0.7 times of the phase current of the motor, so the motor has low heating; The parallel connection method is generally used in occasions with high motor speed (also known as high-speed connection method). The output current of the driver required is 1.4 times of the phase current of the motor, so the motor is hot

12. How to determine the DC power supply of stepping motor driver

a. determination of voltage: the power supply voltage of hybrid stepping motor driver is generally in a wide range (for example, the power supply voltage of HSM is 8 ~ 40VDC), and the power supply voltage is usually selected according to the operating speed and response requirements of the motor. If the motor operates at a high speed or the response is required to be fast, the voltage value is also high. However, note that the ripple of the power supply voltage cannot exceed the maximum input voltage of the driver, otherwise the driver may be damaged

b. determination of current: the power supply current is generally determined according to the output phase current I of the driver. If linear power supply is adopted, the power supply current can generally be 1.1 ~ 1.3 times of I; If switching power supply is adopted, the power supply current can generally be 1.5 ~ 2.0 times of I

13. When is the off-line signal free of hybrid stepping motor driver generally used

when the offline signal free is at low level, the current output from the driver to the motor is cut off, and the motor rotor is in free state (offline state). In some automation equipment, if it is required to directly rotate the motor shaft (manual mode) when the driver is not powered on, the free signal can be set low to make the motor offline for manual operation or adjustment. After manual operation, set the free signal high to continue automatic control

14. How to use a simple method to adjust the rotation direction of the two-phase stepping motor after it is powered on

just switch the a+ and a- (or b+ and b-) of the motor and driver wiring

15. What is the subdivision principle of stepping motor driver

stepping motors used in automatic motion control system mainly include two-phase, three-phase, four phase and five phase hybrid stepping motors. The stepping motor must be matched with the corresponding driver to receive the digital signal of the controller (CPU, PLC, etc.). In order to reduce the working noise of stepping motor, subdivision driver is usually used, especially in the low-speed working state

many people don't know much about "subdivision". Some people just think that subdivision is to improve the accuracy, but in fact it is not. Subdivision is mainly to improve the operating performance of the motor. Now it is explained as follows: the subdivision control of stepper motor which causes the increase of single vehicle cost is realized by the driver accurately controlling the phase current of stepper motor. Taking two-phase motor as an example, if the rated phase current of the motor is 3a, If a conventional driver (such as the common constant current chopping mode) is used to drive the motor, the current in the winding will change from 0 to 3A or from 3a to 0 at each step of motor operation. The huge change of phase current will inevitably cause vibration and noise during motor operation. If a subdivision driver is used to drive the motor in the state of 10 subdivisions, the current in the winding changes by only 0.3A instead of 3A every microstep of the motor, and the current changes in a sinusoidal curve, which greatly improves the vibration and noise of the motor. Therefore, the real advantage of subdivision is its performance advantage. Because the subdivision driver needs to accurately control the phase current of the motor, it has high technical and process requirements for the driver, and the cost will be high. Note that some domestic drivers use "smoothing" to replace subdivision, and some are also called subdivision, but this is not real subdivision. We hope that users must distinguish the essential difference between the two:

1. "smoothing" does not accurately control the phase current of the motor, but only slows down the change rate of the current. Therefore, "smoothing" does not produce micro steps, and the subdivided micro steps can be used for accurate positioning

2. after the phase current of the motor is smoothed, the motor torque will decrease, while the subdivision control will not decrease the motor torque, on the contrary, the torque will increase

16. Can unipolar drives and bipolar drives be common

unipolar driver can not replace bipolar driver, while bipolar driver can replace Unipolar Driver. Because the current distribution of the two drivers depends on their own continuous efforts, the effect of driving the stepping motor is also different. Unipolar Driver (e.g. hsm8672) is a four phase stepping motor specially used for unipolar connection. For example, there are five wire, six wire and eight wire four-phase stepping motors, which can use both unipolar and bipolar drivers (such as HSM). However, to achieve the best efficiency, it is better to select the drive specifically. (end)

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