1. What is a stepper motor? In what situations should a stepper motor be used?
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 (the step angle) in a set direction. You can control the amount of angular displacement by controlling the number of pulses, thus achieving accurate positioning; similarly, you can control the motor's speed and acceleration by controlling the pulse frequency, thus achieving speed regulation. Therefore, stepper motors can be considered when accurate positioning or speed control is required.
2. What are the different types of stepper motors? What are the differences between them?
Stepper motors are classified into three types: permanent magnet (PM), reactive (VR), and hybrid (HB). Permanent magnet stepper motors are generally two-phase, with smaller torque and size, and a step angle typically of 7.5 or 15 degrees. Reactive stepper motors are generally three-phase, capable of high torque output, with a step angle typically of 1.5 degrees, but they generate significant noise and vibration. They were phased out in developed countries like those in Europe and America in the 1980s. Hybrid stepper motors combine the advantages of both permanent magnet and reactive motors. They are further divided into two-phase, four-phase, and five-phase types: two-phase stepper motors typically have a step angle of 1.8 degrees, while five-phase stepper motors typically have a step angle of 0.72 degrees. This type of stepper motor is the most widely used.
3. What is holding torque?
Holding torque refers to the torque with which the stator locks the rotor in place when a stepper motor is energized but not rotating. It is one of the most important parameters of a stepper motor, and the torque at low speeds is typically close to the holding torque. A higher holding torque indicates a stronger load-carrying capacity. Since the output torque of a stepper motor decreases with increasing speed, and the output power also varies with speed, holding torque becomes a crucial parameter for evaluating stepper motors. For example, when people say a 2 N·m stepper motor, unless otherwise specified, they are referring to a stepper motor with a holding torque of 2 N·m.
4. What are the different ways to drive a stepper motor?
Generally speaking, stepper motors are driven by either constant voltage or constant current. Constant voltage drive is almost obsolete, and constant current drive is now the most common type.
5. What is the accuracy of the stepper motor? Is it cumulative?
The accuracy of a typical stepper motor is 3-5% of the step angle. The deviation of a single step in a stepper motor does not affect the accuracy of the next step; therefore, the accuracy of a stepper motor does not accumulate.
6. What is the permissible surface temperature of a stepper motor?
Overheating of a stepper motor will first cause the motor's magnetic materials to demagnetize, leading to a decrease or even loss of torque. Therefore, the maximum allowable temperature of the motor's surface depends on the demagnetization point of the magnetic materials used in the motor. Generally, the demagnetization point of magnetic materials is above 130 degrees Celsius, so a stepper motor surface temperature of 80-90 degrees Celsius is perfectly normal.
7. Why does the torque of a stepper motor decrease as the speed increases?
When a stepper motor rotates, the inductance of each phase winding generates a back electromotive force (EMF); the higher the frequency, the greater the back EMF. Under its influence, the phase current of the motor decreases as the frequency (or speed) increases, resulting in a decrease in torque.
8. Why can a stepper motor run normally at low speeds, but fail to start and make a whistling sound if it exceeds a certain speed?
Stepper motors have a technical parameter: the 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 will not start normally and may lose steps or stall. Under load, the starting frequency should be even lower. To achieve high-speed rotation, the pulse frequency should have an acceleration process, i.e., a low starting frequency followed by a gradual increase to the desired high frequency (motor speed increasing from low to high). We recommend setting the no-load starting frequency to twice the number of pulses required for one revolution of the motor.
9. How to overcome the vibration and noise of a two-phase hybrid stepper motor when it is running at low speed?
The inherent drawback of stepper motors is high vibration and noise at low speeds, which can generally be overcome by the following solutions:
A. If the stepper motor is operating in the resonance zone, the stepper motor speed can be increased by changing the reduction ratio.
B. Using a driver with microstepping function is the most common and simplest method. This is because the phase current change of the motor is smoother with a microstepping driver than with a half-step driver.
C. Replace with a stepper motor with a smaller step angle, such as a three-phase or five-phase stepper motor, or a two-phase microstepping stepper motor.
D. Replacing it with a DC or AC servo motor can almost completely overcome vibration and noise, but the cost is higher.
E. Add a magnetic damper to the motor shaft. Such products are already available on the market, but the mechanical structure is significantly altered.
10. Does the microstepping value of a microstepping driver represent precision?
Microstepping technology for stepper motors is essentially an electronic damping technology (please refer to relevant literature). Its main purpose is to reduce or eliminate low-frequency vibrations in the stepper motor; improving the motor's operating accuracy is only a secondary function. For example, for a two-phase hybrid stepper motor with a step angle of 1.8 degrees, if the microstepping driver is set to 4 microsteps, the motor's operating resolution is 0.45 degrees per pulse. Whether the motor's accuracy can reach or approach 0.45 degrees depends on other factors such as the microstepping driver's microstepping current control accuracy. The accuracy of microstepping drivers from different manufacturers can vary greatly; the higher the microstepping number, the more difficult it is to control the accuracy.
11. What are the differences between series connection and parallel connection of a four-phase drive stepper motor and its driver?
Four-phase hybrid stepper motors are generally driven by two-phase drivers. Therefore, they can be connected in series or parallel to function as two-phase motors. Series connection is generally used for applications with relatively high motor speeds. In this case, the required driver output current is 0.7 times the motor phase current, resulting in less motor heat generation. Parallel connection is generally used for applications with relatively high motor speeds (also known as high-speed connection), requiring a driver output current of 1.4 times the motor phase current, resulting in greater motor heat generation.
12. How to determine the DC power supply for a stepper motor driver?
A. Determining the Power Supply Voltage: The power supply voltage for a hybrid stepper motor driver generally falls within a wide range. The voltage is typically selected based on the motor's operating speed and response requirements. If the motor operates at a higher speed or requires a faster response, a higher voltage is preferable. However, it's crucial that the power supply voltage ripple does not exceed the driver's maximum input voltage; otherwise, the driver may be damaged. If the motor operates at a lower speed, a lower voltage value can be considered.
B. Determining the Output Current of the Power Supply 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 taken as 1.1-1.3 times I; if a switching power supply is used, the power supply current can generally be taken as 1.5-2.0 times I. If a power supply simultaneously powers several drivers, the power supply current should be appropriately doubled.
13. Under what circumstances is the enable signal Ena of a hybrid stepper motor driver typically used?
When the enable signal Ena 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 automated equipment, if it is required to manually rotate the motor shaft without interrupting power to the driver, Ena can be set low to take the motor offline for manual operation or adjustment. After manual operation is completed, the Ena signal is set high again to resume automatic control.
14. How to adjust the rotation direction of a two-phase stepper motor after it is powered on using a simple method?
Simply swap the A+ and A- (or B+ and B-) wires of the motor and driver connections.
