21 common FAQs about stepper motor

1 The service life of the motor?

The key factor affecting the life of the motor is the two bearings inside the motor. Generally, the service life of standard bearings is about 6,000 hours of continuous operation.

If you need a longer life, we can replace better quality bearings and custom shafts to achieve this, please contact our technical team for more details.

2 What is holding torque?

Holding torque refers to the torque at which the stator locks the rotor when the stepper motor is energized but not rotating. It is one of the most important parameters of a stepper motor. Generally, the output torque of the stepping motor at low speed is close to the holding torque. Since the output torque of a stepping motor decreases with increasing speed, the holding torque has become one of the most important parameters for measuring a stepping motor. For example, a 2Nm stepping motor generally refers to a stepping motor having a holding torque of 2Nm.

3 What is detent torque(static torque)?

Detent torque refers to the torque that the stator locks the rotor when the stepper motor is not energized.

4 What is the accuracy of the stepper motor?

Generally, the accuracy of a stepper motor is 3% to 5% of the step angle, which is not cumulative.

5 Why the stepper motor gets stuck when starting?

Usually there are the following reasons: the motor load is too heavy, the power supply voltage is reduced, the motor acceleration time is too short and the given command frequency is too high

6 Why is the stepper motor unstable

Command pulse failure, pulse frequency and mechanical resonance

7 What is the allowable surface temperature of a stepper motor?

The high temperature of the stepping motor will first demagnetize the magnetic material of the motor, which will cause the torque to drop or even lose step. Therefore, the maximum temperature allowed on the motor surface should depend on the demagnetization point of different motor magnetic materials. Generally speaking, the degaussing point of magnetic materials is higher than 130 degrees Celsius, and some are even as high as 200 degrees Celsius, so the external temperature of the stepper motor is within the normal range of 80 to 90 degrees Celsius.

8 Classification of stepper motors?

Stepper motors are divided into three types: permanent magnet (PM), reactive power (VR) and hybrid power (HB)

Permanent magnet stepping is usually two-phase, with small torque and volume, and the stepping angle is generally 7.5 degrees or 15 degrees;

The reactive power step is usually three-phase, which can achieve large torque output. The step angle is generally 1.5 degrees, but the noise and vibration are large;

Hybrid step refers to the combination of the advantages of permanent magnets and reactance. Divided into two-phase, four-phase and five-phase: the two-phase step angle is 1.8 degrees, the four-phase step angle is 0.9 degrees, and the five-phase step angle is 0.72 degrees, which have been widely used.

9 Why does the torque of a stepping motor decrease with increasing speed?

When the stepping motor rotates, the inductance of each phase winding of the motor will form the back electromotive force; the higher the frequency, the greater the back electromotive force. Under its action, the phase current of the motor decreases as the frequency (or speed) increases, resulting in a decrease in torque.

10 Why a stepper motor can run normally at low speed, but if it is higher than a certain speed, it will not start with howling sound?

The stepper motor has a technical parameter: no-load starting frequency, that is, the pulse frequency that can normally start the stepping frequency under no-load conditions. If the pulse frequency is higher than this value, the motor will not start normally, and may lose step or stall. 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 start frequency is very low, and then increase to the required high frequency according to a certain acceleration (the motor speed increases from low speed). speed). high speed).

11 What is a stepper motor?

Stepper motors are actuators that convert electrical pulse signals into angular displacement. When the stepper driver receives the pulse signal, it will drive the stepper motor to rotate a fixed angle (step angle) in the set direction. The actual angular displacement can be controlled by controlling the number of pulses to achieve precise positioning. At the same time, the speed and acceleration of the motor can be controlled by controlling the pulse frequency to achieve the purpose of speed regulation.

12 How to overcome the vibration and noise of low-speed two-phase hybrid stepper motors?

The huge vibration and noise when the stepper motor rotates at low speed are its inherent shortcomings. Generally, the following solutions can be used to overcome:

A. If the stepper motor works in the resonance zone, the resonance zone can be avoided by changing the reduction ratio and other mechanical transmissions;

B. Use a driver with subdivision function, which is the most common and simplest method;

C. Use a stepper motor with a smaller step angle, such as a three-phase or five-phase stepper motor;

D. Changing to an AC servo motor can almost completely overcome vibration and noise, but the cost is higher;

E. Add an electromagnetic damper to the motor shaft. There are such products on the market, but the mechanical structure has undergone great changes.

13 Does the subdivision number of the subdivision drive represent accuracy?

The subdivision technology of the stepper motor is essentially an electronic damping technology. Its main purpose is to reduce or eliminate the low frequency vibration of the stepper motor. Improving the running accuracy of the motor is only a side function of the subdivision technology. For example, for a two-phase hybrid stepping motor with a step angle of 1.8°, if the subdivision number of the subdivision driver is set to 4, the working resolution of the motor is 0.45° per pulse. Whether the accuracy of the motor can reach or approach 0.45° also depends on other factors, such as the subdivision current control accuracy of the subdivision drive. The accuracy of subdivision drivers of different manufacturers may vary greatly; the greater the number of subdivisions, the more difficult the accuracy control is.

14 Why stepper motor overheated?

The working environment temperature of the motor is too high and the voltage is too high

15 stepper motor runs multiple steps or not synchronized

Uneven transmission gap, large load fluctuation, friction between stator and rotor

16 Why is the stepper motor noisy?

The motor is running in the resonance region and the load is too large or too small.

17 What is the difference between series and parallel connection of four-phase hybrid stepping motor and driver?

The four-phase hybrid stepping motor is usually driven by a two-phase driver. Therefore, the four-phase motor can be connected into two phases by using a series connection method or a parallel connection method when connecting.

The series connection method is usually used where the motor speed is relatively high. At this time, the required driver output current is 0.7 times the motor phase current, so the motor generates less heat;

The parallel connection method is usually used where the motor speed is high (also known as the high-speed connection method). The required driver output current is 1.4 times the motor phase current, so the motor generates more heat.

18 How to determine the DC power supply of the stepper motor driver?

Selection of power supply voltage: The power supply voltage of the hybrid stepping motor driver is usually in a wide range, and the power supply voltage is usually selected according to the working speed and response requirements of the motor. Please note that the ripple of the power supply voltage cannot exceed the maximum input voltage of the drive, otherwise the drive may be damaged.

Selection of power supply current: The power supply current is usually determined by the driver. If a linear power supply is used, the power supply current can usually be 1.1 to 1.3 times I; if a linear power supply is used, it can usually be 1.1 times I. If a switching power supply is used, the power supply current is usually 1.5 to 2.0 times I.

19 Why the subdivision function of the drive can make the motor run smoothly and reduce noise?

The subdivision control of the stepping motor is realized by the driver accurately controlling the phase current of the stepping motor. Taking a two-phase motor as an example, if the rated phase current of the motor is 2A, when using a conventional drive, the windings of the motor will be. The internal current will change from 0 to 2A or from 2A to 0. The huge change of phase current will cause vibration and noise of the motor. If you use a subdivision driver and drive the motor in 10 subdivision states, the current change of the winding is only 0.2A instead of 2A per microstep, and the current changes in a sinusoidal curve, which greatly reduces vibration and reduces motor noise.

20 Under what circumstances is the off-line signal of the hybrid stepper motor driver usually used?

When the offline signal is low, the current output from the drive to the motor will be cut off, and the motor rotor is in a free state (offline state). In some automation equipment, if the motor shaft is required to rotate directly when the drive is turned off (manual mode), the offline signal can be set to low level to take the motor offline for manual operation or adjustment. After manual completion, set the offline signal to high again to continue automatic control.

21 How to adjust the rotation direction of the two-phase stepper motor after power-on?

You only need to exchange the A + and A- or B + and B- of the motor and drive phase wires, and only one group can be exchanged (the direction of the two groups will not change).

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