Q & A on the hottest stepper motor

2022-08-05
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Q & A on stepper motor

1 What is a stepper motor

stepper motor is an actuator that converts electric pulse into angular displacement. To put it more simply: when the stepping driver receives a pulse signal, it drives the stepping motor to rotate a fixed angle (and stepping 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

reactive stepping is generally divided into sprocket chain drive, worm gear drive, gear drive and other three phases according to the difference of regulating beam drive method. It can achieve large torque output. The stepping angle is generally 1.5 degrees, but the noise and vibration are very large. It has been eliminated in developed countries such as Europe and the United States in the 1980s; Hybrid stepping refers to the combination of the advantages of permanent magnet and reactive stepping. It is divided into two phases and five phases: the two-phase stepping angle is generally 1.8 degrees and the five-phase stepping angle is generally 0.72 degrees. When the pendulum cannot be hung or the bolt cannot be detached, the relevant parts can be removed and cleaned with kerosene. This stepping motor is the most widely used

3. What is holdingtorque

holdingtorque 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. if it is used as raw material without special instructions, it means that the holding torque is 2n M

4. What is detenttorque

detenttorque refers to the torque when the stator locks the rotor when the stepping motor is not powered on

detenttorque has no unified translation method in China, which is easy to misunderstand; Since the rotor of the reactive stepping motor is not made of permanent magnet, it does not have detenttorque

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

the accuracy of general stepping motor is% of the stepping 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 motor 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

stepper 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 stepper 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 approach 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

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