Complete collection of frequently asked questions about stepper motors and drivers

Complete collection of frequently asked questions about stepper motors and drivers

What is a stepper motor driver?

The operation of a stepper motor requires an electronic device to drive it. This device is a stepper motor driver, which converts the pulse signal sent by the control system into the angular displacement of the stepper motor. In other words, every time the control system sends a pulse signal, the stepper motor rotates a step angle through the driver. In other words, the speed of the stepper motor is proportional to the frequency of the pulse signal. Therefore, by controlling the frequency of the stepper pulse signal, the motor speed can be accurately adjusted; by controlling the number of stepper pulses, the motor can be accurately positioned.

Types of stepper motors?

Types of stepper motors Stepper motors are generally divided into permanent magnet (PM), reactive (VR) and hybrid (HB) according to electromagnetic design. At the same time, according to the different coil excitation designs, stepper motors can be divided into two-phase, three-phase and five-phase; according to their transmission design, stepper motors are divided into rotary stepper, linear stepper, and with or without reduction gears.
Permanent magnet stepper is generally two-phase, with small torque and volume, and the step angle is generally 7.5 degrees or 15 degrees.
Reactive stepper motors are generally three-phase, which can achieve large torque output, and the step angle is generally 1.5 degrees, but the noise and vibration are very large. They have been eliminated in developed countries such as Europe and the United States in the 1980s.
Hybrid stepper motors refer to a combination of the advantages of permanent magnet and reactive types. It is divided into two-phase, four-phase and five-phase: the two-phase step angle is generally 1.8 degrees and the five-phase step angle is generally 0.72 degrees. This type of stepper motor is the most widely used.

Under what circumstances is the stepper motor used?

The stepper motor is a special motor used for control. Its rotation runs step by step at a fixed angle (called the step angle). Its characteristic is that there is no accumulated error, so it is widely used in various open-loop controls. The stepper motor is an actuator that converts electrical pulses into angular displacement. In simple terms: when the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (i.e., the step angle) in the set direction.
The angular displacement can be controlled by controlling the number of pulses 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 to achieve the purpose of speed regulation. Therefore, stepper motors can be considered when accurate positioning or speed control is required.

What is the number of phases of a stepper motor? How do users choose a stepper motor with several phases?

The number of phases of a stepper motor refers to the number of coil groups inside the motor. Currently, two-phase, three-phase, four-phase, and five-phase stepper motors are commonly used. The step angle of a motor is different for different phases. Generally, the step angle of a two-phase motor is 1.8 degrees, that of a three-phase motor is 1.5 degrees, and that of a five-phase motor is 0.72 degrees. When there is no subdivision driver, users mainly rely on selecting stepper motors with different numbers of phases to meet the step angle requirements. If a subdivision driver is used, the number of phases will become meaningless. Users only need to change the number of subdivisions on the driver to change the step angle.

What are the special requirements for the control system when using a subdivision driver?

After the driver is subdivided, the running performance of the motor will have a qualitative leap, but all of this is generated by the driver itself and has nothing to do with the motor and the control system. When using, the only thing that users need to pay attention to is the change of the step angle of the stepper motor, which will affect the frequency of the stepper signal sent by the control system, because the step angle of the stepper motor will become smaller after subdivision, requiring the frequency of the stepper signal to be increased accordingly. Take a 1.8-degree stepper motor as an example: the step angle of the driver is 0.9 degrees when in half-step state, and the step angle is 0.18 degrees when in ten subdivisions. In this way, when the motor speed is required to be the same, the frequency of the stepper signal sent by the control system is 5 times that of the half-step operation when in ten subdivisions.

What is holding torque?

After the driver is subdivided, the running performance of the motor will have a qualitative leap, but all of this is generated by the driver itself and has nothing to do with the motor and the control system. When using, the only thing that users need to pay attention to is the change of the step angle of the stepper motor, which will affect the frequency of the stepper signal sent by the control system, because the step angle of the stepper motor will become smaller after subdivision, requiring the frequency of the stepper signal to be increased accordingly. Take a 1.8-degree stepper motor as an example: the step angle of the driver is 0.9 degrees when in half-step state, and 0.18 degrees when in ten-minute state. In this way, when the motor speed is required to be the same, the frequency of the step signal sent by the control system is 5 times that of the half-step operation when in ten-minute state.

What is the accuracy of the stepper motor? Is it cumulative?

The accuracy of a general stepper motor is 3~5% of the step angle. The deviation of a single step of a stepper motor does not affect the accuracy of the next step, so the accuracy of the stepper motor is not cumulative.


What is the allowable surface temperature of the stepper motor?

If the temperature of the stepper motor is too high, the magnetic material of the motor will be demagnetized first, resulting in a decrease or even loss of torque. Therefore, the maximum allowable temperature of the motor surface should depend on the demagnetization point of the magnetic material of different motors. Generally speaking, the demagnetization point of magnetic materials is above 130 degrees Celsius, so it is completely normal for the surface temperature of the stepper motor to be 80~90 degrees Celsius.

Why does the torque of the stepper motor decrease as the speed increases?

When the stepper 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 motor phase current decreases as the frequency (or speed) increases, resulting in a decrease in torque.

Why can the stepper motor run normally at low speed, but cannot start and whistle if it is higher than a certain speed?

Why can the stepper motor run normally at low speed, but cannot start and whistle if it is higher than a certain speed? The stepper motor has a technical parameter: no-load starting frequency, that is, the pulse frequency at which the stepper motor can start normally under no-load conditions. If the pulse frequency is higher than this value, the motor cannot start normally, and may lose steps or stall. Under load conditions, the starting frequency should have an acceleration process, that is, the starting frequency is low, and then it is increased to the desired high frequency at a certain acceleration (the motor speed increases from low speed to high speed). The no-load starting frequency is generally twice the number of pulses required for the motor to run one circle.

How to overcome the vibration and noise of a two-phase hybrid stepper motor when running at low speed?

The inherent disadvantages of stepper motors are that they vibrate and make a lot of noise when they rotate at low speeds. Generally, the following solutions can be used to overcome them:
A. If the stepper motor happens to work in the resonance zone, the speed of the stepper motor can be increased by changing the reduction ratio
. B. Use a driver with a subdivision function, which is the most commonly used and simplest method. Because the phase current of the subdivision driver motor changes more slowly than that of the half-step type.
C. Replace it with a stepper motor with a smaller step angle, such as a three-phase or five-phase stepper motor, or a two-phase subdivision stepper motor.
D. Replace it with a DC or AC servo motor, which can almost completely overcome vibration and noise, but the cost is higher.
E. Add a magnetic damper to the motor shaft. This product is already available on the market, but the mechanical structure changes significantly.

Can the number of subdivisions of the subdivision driver represent the accuracy?

The subdivision technology of stepper motors is essentially an electronic damping technology, and its main purpose is to reduce or eliminate the low-frequency vibration of stepper motors. Improving the operation accuracy of motors is only a by-product of subdivision technology. For example, for a two-phase hybrid stepper motor with a step angle of 1.8 degrees, if the subdivision number of the subdivision driver is set to 4, the operation resolution of the motor is 0.45 degrees per pulse. Whether the motor's accuracy can reach or approach 0.45 degrees also depends on other factors such as the subdivision current control accuracy of the subdivision driver. The accuracy of subdivision drivers from different manufacturers may vary greatly. The larger the number of subdivisions, the more difficult it is to control the accuracy.