Fifteen tips you must know about stepper motors

1.What is a stepper motor?
A stepper motor is an actuator that converts electrical pulses into angular displacement. Simply put, when a stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (and step angle) in the set direction. You can control the angular displacement by controlling the number of pulses to achieve accurate positioning; At the same time, you can control the speed and acceleration of the motor rotation by controlling the pulse frequency, thereby achieving the goal of speed regulation.

2.What are the types of stepper motors?
There are three types of stepper motors: permanent magnet (PM), reactive (VR), and hybrid (HB). Permanent magnet steppers are generally two-phase, with small torque and volume, and a step angle of generally 7.5 degrees or 15 degrees; Reactive stepping is generally three-phase and can achieve high torque output. The stepping angle is generally 1.5 degrees, but both noise and vibration are significant. It has been phased out in developed countries such as Europe and America in the 1980s; Hybrid stepping refers to the combination of the advantages of permanent magnet and reactive methods. It is divided into two phases and five phases: the step angle of the two phases is generally 1.8 degrees, while the step angle of the five phases is generally 0.72 degrees. This type of stepper motor is most widely used.

3. What is Holding TORQUE?
Holding torque refers to the torque at which the stator locks the rotor when a stepper motor is energized but not rotating. It is one of the most important parameters of a stepper motor, and the torque of the stepper motor is usually close to the holding torque at low speeds. Due to the continuous attenuation of the output torque of a stepper motor with increasing speed, and the variation of output power with increasing speed, maintaining torque has become one of the most important parameters for measuring stepper motors. For example, when people say a 2N. m stepper motor, unless otherwise specified, it refers to a stepper motor that maintains a torque of 2N. m.

4. What is DETENT TORQUE?
DETENT TORQUE refers to the torque at which the stator locks the rotor when the stepper motor is not powered on. There is no unified translation method for DETENT TORQUE in China, which can easily lead to misunderstandings; Due to the fact that the rotor of the reactive stepper motor is not made of permanent magnet material, it does not have a DETENT TORQUE.

5.What is the accuracy of the stepper motor? Accumulate?
The accuracy of a typical stepper motor is 3-5% of the step angle and does not accumulate.

6. What is the allowable external temperature of the stepper motor?
If the temperature of the stepper motor is too high, it will first demagnetize the magnetic material of the motor, leading to a decrease in torque and even loss of step. Therefore, the maximum allowable temperature on the surface of the motor should depend on the demagnetization point of different magnetic materials of the motor; Generally speaking, the demagnetization point of magnetic materials is above 130 degrees Celsius, and some even reach as high as 200 degrees Celsius. Therefore, the surface temperature of stepper motors is completely normal at 80-90 degrees Celsius.

7.Why does the torque of a 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 phase current of the motor decreases with the increase of frequency (or speed), resulting in a decrease in torque.

8.Why can the stepper motor operate normally at low speeds, but if it exceeds a certain speed, it cannot start and is accompanied by a whistling sound?
The stepper motor has a technical parameter: no-load starting frequency, which 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 experience step loss or rotor blockage. Under load, the starting frequency should be lower. If the motor is to achieve high-speed rotation, there should be an acceleration process in the pulse frequency, that is, the starting frequency should be lower, and then a certain acceleration should be applied to reach the desired high frequency (the motor speed should increase from low speed to high speed).

9.How to overcome the vibration and noise of two-phase hybrid stepper motors during low-speed operation?
The inherent drawbacks of stepper motors are high vibration and noise during low-speed rotation, which can generally be overcome by the following solutions:
A. If the stepper motor works exactly in the resonance zone, mechanical transmission such as changing the reduction ratio can avoid the resonance zone;
B. The most commonly used and convenient method is to use drivers with subdivision functions;
C. Replace with a stepper motor with a smaller step angle, such as a three-phase or five phase stepper motor;
D. Replacing it with an AC servo motor can almost completely overcome vibration and noise, but the cost is relatively high;
E. Adding a magnetic damper to the motor shaft is a product that is already available on the market, but the mechanical structure has undergone significant changes.

10. Can the subdivision of the driver represent accuracy?
The subdivision technology of stepper motors is essentially an electronic damping technology (please refer to relevant literature), whose main purpose is to weaken or eliminate the low-frequency vibration of stepper motors, and improving the operating accuracy of motors is only an additional function of subdivision technology. For example, for a two-phase hybrid stepper motor with a step angle of 1.8 °, if the subdivision fraction of the subdivision driver is set to 4, the operating resolution of the motor is 0.45 ° per pulse. 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 segmented drives from different manufacturers may vary greatly; The larger the subdivision, the more difficult it is to control accuracy.

11.What is the difference between the series connection and parallel connection of the four phase hybrid stepper motor and driver?
The four phase hybrid stepper motor is generally driven by a two-phase driver. Therefore, series connection or parallel connection can be used to connect the four phase motor into two phases for use. The series connection method is generally used in situations where the motor speed is high, and the required driver output current is 0.7 times the motor phase current, so the motor generates less heat; The parallel connection method is generally used in situations where the motor speed is high (also known as high-speed connection method), and the required driver output current is 1.4 times the motor phase current, so the motor generates more heat.

12.How to determine the DC power supply for the stepper motor driver?
A. Determination of voltage
The power supply voltage of a hybrid stepper motor driver is generally a wide range (for example, the power supply voltage of IM483 is 12-48VDC), and the power supply voltage is usually selected based on the operating speed and response requirements of the motor. If the motor operates at a high speed or requires a fast response, the voltage value is also high. However, it is important to note that the ripple of the power supply voltage should not exceed the maximum input voltage of the driver, otherwise it may damage the driver.
B. Determination of current
The power supply current is generally determined based on the output phase current I of the driver. If a linear power supply is used, the power supply current can generally be 1.1 to 1.3 times that of I; If a switch mode power supply is used, the power supply current can generally be 1.5-2.0 times that of I.

13.Under what circumstances is the offline signal FREE of hybrid stepper motor drivers generally used?
When the offline signal FREE is low, the current output from the driver to the motor is cut off, and the motor rotor is in a free state (offline state). In some automation equipment, if it is required to directly rotate the motor shaft (manually) while the driver is constantly powered on, the FREE signal can be set low to take the motor offline for manual operation or adjustment. After manual completion, set the FREE signal high to continue automatic control.

14. How to adjust the rotation direction of the two-phase stepper motor after being powered on using a simple method?
Just swap the A+and A - (or B+and B -) of the motor and driver wiring.

15.What are the differences in the application scenarios of two-phase and five phase hybrid stepper motors?
Q&A:
Generally speaking, two-phase motors have a large step angle and good high-speed characteristics, but there is a low-speed vibration zone. The five phase motor has a small step angle and runs smoothly at low speeds. Therefore, in situations where high precision is required for the operation of the motor, and mainly in the medium and low speed range (generally below 600 rpm), a five phase motor should be selected; On the contrary, if the pursuit of high-speed performance of the motor does not require much precision and smoothness, a two-phase motor with lower cost should be selected. In addition, the torque of a five phase motor is usually above 2NM. For small torque applications, a two-phase motor is generally used, and the problem of low-speed stability can be solved by using a subdivision driver.