1. What is a stepper motor?
A stepper motor is an actuator that converts electrical pulses into angular displacement. To put it plainly: when the 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 number of pulses to control the angular displacement, so as to achieve the purpose of accurate positioning; at the same time, you can control the frequency of pulses to control the speed and acceleration of motor rotation, so as to achieve the purpose of speed regulation.
2. What kinds of stepper motors are there?
There are three kinds of stepping motors: permanent magnet (PM), reactive (VR) and hybrid (HB). Permanent magnet stepping is generally two-phase, with smaller torque and volume, and the stepping angle is generally 7.5 degrees or 15 degrees; reactive stepping is generally three-phase, with large torque output, and the stepping angle is generally 1.5 degrees, but the noise and vibration are great. In Europe and the United States and other developed countries in the 80's has been eliminated; hybrid stepping refers to a mixture of permanent magnet type and the advantages of the reaction type. It is divided into two-phase and five-phase: two-phase stepping angle is generally 1.8 degrees and five-phase stepping angle is generally 0.72 degrees. This type of stepper motor is the most widely used.
3. What is the holding torque (HOLDING TORQUE)?
Holding torque (HOLDING TORQUE) refers to the torque of the stator locking the rotor when the stepper motor is energized but not rotating. It is one of the most important parameters of a stepper motor, and usually the torque of a stepper motor at low speeds is close to the holding torque. Since the output torque of a stepper motor continues to decay with increasing speed, and the output power changes with increasing speed, the holding torque becomes one of the most important parameters for measuring a stepper motor. For example, when people say 2N.m stepping motor, it means a stepping motor with a holding torque of 2N.m without special instructions.
4. What is DETENT TORQUE?
DETENT TORQUE is the torque that the stator locks the rotor when the stepping motor is not energized.DETENT TORQUE is not translated in a uniform way in China, which is easy to be misunderstood; since the rotor of the reactive stepping motor is not a permanent magnet material, it does not have DETENT TORQUE.
5. What is the precision of the stepping motor? Is it cumulative?
Generally, the precision of stepper motor is 3-5% of the stepping angle, and it is not cumulative.
6. How much temperature is allowed on the exterior of the stepper motor?
The high temperature of stepping motor will firstly demagnetize the magnetic material of the motor, which will lead to torque drop or even out of step, so the maximum temperature allowed for the exterior of the motor should depend on the demagnetization point of the magnetic material of the different motors; in general, the demagnetization point of the magnetic material is over 130 degrees Celsius, and some of them are even up to more than 200 degrees Celsius, so it is completely normal for the exterior of the stepping motor to be in the temperature range of 80-90 degrees Celsius.
7. Why does the torque of the stepper motor decrease with the increase of the rotating speed?
When the stepping motor rotates, the inductance of each phase of the motor winding will form a reverse electromotive force; the higher the frequency, the larger the reverse electromotive force. Under its action, the motor phase current decreases with the increase of frequency (or speed), which leads to the decrease of torque.
8. Why can the stepper motor run normally at low speeds, but if it is higher than a certain speed can not start, and accompanied by a whistling sound?
Stepping motor has a technical parameter: no-load start frequency, that is, the pulse frequency of stepping motor can start normally under no load, if the pulse frequency is higher than this value, the motor can not start normally, and it may lose step or blocking. In the case of a load, the starting frequency should be lower. If the motor is to achieve high speed rotation, the pulse frequency should be accelerated, i.e., the starting frequency is low, and then increased to the desired high frequency (motor speed from low to high) at a certain acceleration.
9. How to overcome the vibration and noise of two-phase hybrid stepping motor at low speed?
Vibration and noise are inherent disadvantages of stepper motors when rotating at low speeds, which can generally be overcome by the following programs:
A. If the stepping motor happens to work in the resonance area, the resonance area can be avoided by changing the mechanical transmission such as the reduction ratio;
B. Adopt the driver with subdivision function, which is the most commonly used and easiest method;
C. Replace with stepping motor with smaller step angle, such as three-phase or five-phase stepping motor;
D. Switch to AC servo motors, which can almost completely overcome vibration and noise, but at a higher cost;
E. In the motor shaft with a magnetic damper, the market has such products, but the mechanical structure of the larger change.
10. Does the subdivision of the drive represent accuracy?
Stepper motor interpolation is essentially an electronic damping technology (please refer to the relevant literature), the main purpose of which is to attenuate or eliminate the low-frequency vibration of the stepper motor, and to improve the motor's running accuracy is only an incidental function of the interpolation technology. For example, for a two-phase hybrid stepping motor with a stepping angle of 1.8°, if the interpolation driver's interpolation number is set to 4, then the motor's running resolution is 0.45° per pulse. Whether the motor's accuracy can reach or approach 0.45° also depends on other factors such as the precision of the interpolation current control of the interpolation driver. Different manufacturers of subdivided drive precision may vary greatly; the larger the subdivided points the more difficult to control the precision.
11. What is the difference between series connection and parallel connection of four-phase hybrid stepping motor and driver?
Four-phase hybrid stepping motor is generally driven by two-phase driver, therefore, the connection can be used in series or parallel connection method to connect the four-phase motor into two-phase use. The series connection method is generally used in occasions where the motor speed is relatively high, and the output current of the driver required is 0.7 times of the phase current of the motor, thus the motor heating is small; the parallel connection method is generally used in occasions where the motor speed is relatively high (also known as the high-speed connection method), and the output current of the driver required is 1.4 times of the phase current of the motor, thus the motor heating is large.
12. How to determine the stepper motor driver DC power supply?
A. Determination of voltage
Hybrid stepper motor driver power supply voltage is generally a wide range (such as IM483 power supply voltage of 12 ~ 48VDC), the power supply voltage is usually selected according to the motor's operating speed and response requirements. If the motor working speed is high or the response requirement is fast, then the voltage value is also high, but pay attention to the ripple of the power supply voltage can not exceed the maximum input voltage of the driver, otherwise the driver may be damaged.
B. Determination of current
The power supply current is generally determined according to the output phase current I of the driver. If the linear power supply is used, the power supply current can be 1.1 to 1.3 times of I. If the switching power supply is used, the power supply current can be 1.5 to 2.0 times of I.
13. Under what circumstances is the offline signal FREE of the hybrid stepping motor driver 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 you are required to rotate the motor shaft directly (manually) when the drive is not energized, you can set the FREE signal low to take the motor offline and perform manual operation or adjustment. After manual operation is completed, set the FREE signal high again to continue automatic control.
14. What is the simple way to adjust the direction of rotation of a two-phase stepping motor when it is energized?
Simply align A+ and A- (or B+ and B-) of the motor and driver wiring.
15. What is the difference between two-phase and five-phase hybrid stepper motors for applications?
Question Answer:
Generally speaking, two-phase motors with large step angles have good high-speed characteristics, but there is a low-speed vibration zone. Five-phase motors have a small step angle and run smoothly at low speeds. Therefore, in the motor running accuracy requirements are high, and mainly in the low-speed section (generally less than 600 rpm) of the occasion should be used five-phase motor; on the contrary, if the pursuit of high-speed performance of the motor, the accuracy and smoothness of the occasion without too many requirements should be selected at a lower cost of two-phase motors. In addition, the torque of five-phase motors is usually more than 2NM, for small torque applications, two-phase motors are generally used, while the problem of low-speed smoothness can be solved by using a subdivided drive.
Post time: Sep-12-2024