Some Popular questions about stepper motor

1. What is a stepper motor? A stepper motor is an actuator that converts electrical pulses into angular displacement. In simple terms, when a stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (known as the step angle) in a specified direction. You can control the angular displacement by controlling the number of pulses, achieving precise positioning. Additionally, you can control the motor's speed and acceleration by adjusting the pulse frequency for speed control.

2. What are the types of stepper motors? Stepper motors are classified into three types: Permanent Magnet (PM), Variable Reluctance (VR), and Hybrid (HB). Permanent Magnet stepper motors typically have two phases, with smaller torque and size, and a step angle of 7.5 or 15 degrees. Variable Reluctance stepper motors usually have three phases, providing high torque output but producing significant noise and vibration. They have largely been phased out in developed countries since the 1980s. Hybrid stepper motors combine the advantages of Permanent Magnet and Variable Reluctance types and come in two-phase and five-phase variants, with step angles of 1.8 and 0.72 degrees, respectively, making them widely used in various applications.

3. What is Holding Torque? Holding torque refers to the torque that holds the rotor in place when the stepper motor is powered but not rotating. It is one of the most important parameters of a stepper motor. Typically, the holding torque of a stepper motor is close to the torque at low speeds. Since the output torque of a stepper motor decreases as the speed increases, holding torque becomes a crucial parameter for stepper motor evaluation. For example, when people refer to a 2 N·m stepper motor, it usually means a stepper motor with a holding torque of 2 N·m unless otherwise specified.

4. What is Detent Torque? Detent torque refers to the torque that holds the rotor in place when the stepper motor is not powered. There is no standardized translation for Detent Torque in China, which can lead to misunderstandings. Detent torque is not applicable to Variable Reluctance stepper motors because their rotors are not made of permanent magnet materials.

5. What is the accuracy of stepper motors, and is it cumulative? The typical accuracy of stepper motors is within 3-5% of the step angle, and this accuracy is not cumulative.

6. What is the permissible external temperature for stepper motors? Excessively high temperatures can demagnetize the magnetic materials in stepper motors, leading to decreased torque and potential loss of steps. Therefore, the maximum allowable external temperature of a stepper motor depends on the demagnetization point of the specific magnetic material used. In general, magnetic materials have demagnetization points above 130 degrees Celsius, some even exceeding 200 degrees Celsius, so an external temperature of 80-90 degrees Celsius is typically considered normal.

7. Why does the torque of a stepper motor decrease as the speed increases? When a stepper motor rotates, the inductance of its winding coils generates a reverse electromotive force (EMF). The higher the frequency (or speed), the larger this reverse EMF becomes. As a result, the phase current in the motor decreases with increasing frequency (speed), leading to a decrease in torque.

8. Why can a stepper motor operate normally at low speeds but fail to start at higher speeds with a whining noise? Stepper motors have a technical parameter called "idle start frequency," which refers to the pulse frequency at which a stepper motor can start without load. If the pulse frequency exceeds this value, the motor may fail to start, lose steps, or stall. In situations with a load, the start frequency should be even lower. To achieve high-speed rotation, the pulse frequency should have an acceleration process, starting at a lower frequency and gradually increasing to the desired high frequency (accelerating the motor from low to high speed).

9. How can vibrations and noise be mitigated when two-phase hybrid stepper motors run at low speeds? Vibration and noise are inherent drawbacks of stepper motors when operating at low speeds. To mitigate these issues, you can consider the following solutions: A. Avoiding resonance zones by changing the mechanical transmission ratio if the stepper motor operates within a resonance zone. B. Using drivers with microstepping capability, which is the most common and straightforward approach. C. Switching to stepper motors with smaller step angles, such as three-phase or five-phase stepper motors. D. Transitioning to AC servo motors, which can almost completely eliminate vibration and noise but come at a higher cost. E. Adding magnetic dampers to the motor shaft, although this requires significant mechanical changes.

10. Does the subdivision count of a microstepping driver represent accuracy? The subdivision technology of stepper motors is essentially a form of electronic damping technology (refer to relevant literature). Its primary purpose is to reduce or eliminate low-frequency vibrations in stepper motor operation, and improved accuracy is just an additional benefit. For example, in the case of a two-phase hybrid stepper motor with a step angle of 1.8 degrees, if the subdivision driver is set to 4, the motor's resolution is 0.45 degrees per pulse. Whether the motor's accuracy can reach or approach 0.45 degrees depends on factors such as the precision of current control in the subdivision driver. The accuracy of subdivision drivers can vary significantly between different manufacturers, and higher subdivision counts may make accuracy more challenging to control.

11. What is the difference between series and parallel connection methods for four-phase hybrid stepper motors and drivers? Four-phase hybrid stepper motors are generally driven by two-phase drivers. Therefore, you can connect the four-phase motor in either a series or parallel configuration to make it behave like a two-phase motor. The series connection method is typically used for situations where the motor operates at lower speeds. In this case, the driver's output current should be 70% of the motor's phase current, resulting in lower motor heat generation. The parallel connection method, also known as the high-speed method, is typically used when the motor operates at higher speeds. It requires the driver's output current to be 140% of the motor's phase current, leading to higher motor heat generation.

12. How do you determine the DC power supply for hybrid stepper motor drivers? A. Voltage Determination: The voltage of the power supply for hybrid stepper motor drivers usually falls within a wide range (e.g., 12 to 48VDC). The choice of power supply voltage depends on the motor's operating speed and response requirements. If the motor operates at high speeds or requires fast response, a higher voltage may be selected. However, it's important to ensure that the ripple voltage of the power supply does not exceed the driver's maximum input voltage to avoid damaging the driver. B. Current Determination: The power supply current is generally determined based on the driver's output phase current (I). If using a linear power supply, the power supply current can be set to 1.1-1.3 times the phase current (I). If using a switching power supply, the power supply current can be set to 1.5-2.0 times the phase current (I).