1. What is a stepper motor?
Stepping motor is an actuator that converts electrical pulses into angular displacement. In layman's terms: 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 angular displacement by controlling the number of pulses, so as to achieve the purpose of accurate positioning; at the same time, you can control the speed and acceleration of the motor rotation by controlling the pulse frequency, so as to achieve the purpose 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 stepping is generally two-phase, with small torque and volume, and the stepping angle is generally 7.5 degrees or 15 degrees;
The reactive step is generally three-phase, which can achieve large torque output. The step angle is generally 1.5 degrees, but the noise and vibration are very high.
Big. It has been eliminated in the 1980s in developed countries such as Europe and the United States; hybrid stepping refers to the combination of the advantages of permanent magnet and reactive. It is divided into two-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 kind of stepper motor is the most widely used.
3. What is HOLDING TORQUE?
Holding torque (HOLDING TORQUE) refers to the torque at which the stator locks the rotor when the stepper motor is energized but not rotating. It is one of the most important parameters of a stepper motor. Usually, the torque of a stepper motor at low speed is close to the holding torque. Since the output torque of a stepping motor decays continuously with the increase of speed, and the output power also changes with the increase of speed, the holding torque has become one of the most important parameters to measure the stepping motor. For example, when people say a 2N.m stepper motor, it refers to a stepper motor with a holding torque of 2N.m unless otherwise specified.
4. What is DETENT TORQUE?
DETENT TORQUE refers to the torque at which the stator locks the rotor when the stepper motor is not energized.
DETENT TORQUE does not have a unified translation method in China, which is easy to cause misunderstandings;
Since the rotor of the reactive stepping motor is not a permanent magnet material, it does not have DETENT TORQUE.
5. What is the accuracy of the stepper motor? Does it accumulate?
Generally, the accuracy of a stepping motor is 3-5% of the step angle, and it does not accumulate.
6. What is the allowable surface temperature of the stepper motor?
The high temperature of the stepper motor will first demagnetize the magnetic material of the motor, which will cause the torque to drop and even lose step. Therefore, the maximum allowable temperature of the motor surface should depend on the demagnetization point of different motor magnetic materials; generally speaking, the demagnetization of magnetic materials The points are all above 130 degrees Celsius, and some are even as high as 200 degrees Celsius, so the external temperature of the stepping motor is completely normal at 80-90 degrees Celsius.
7. Why does the torque of the stepper motor varyRotating speedRise and fall?
When the stepper motor rotates, the inductance of each phase winding of the motor will form a back electromotive force; the higher the frequency, the greater the back 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 the stepper motor can run normally at low speed, but cannot start if it is higher than a certain speed, accompanied by howling?
The stepper motor has a technical parameter: no-load start frequency, that is, the pulse frequency that 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. In the case of load, the starting frequency should be lower. If the motor is to rotate at a high speed, the pulse frequency should have an acceleration process, that is, the start frequency is low, and then increase to the desired high frequency according to a certain acceleration (the motor speed increases from low speed to high speed).
9. How to overcome the vibration and noise of the two-phase hybrid stepping motor at low speed?
Large vibration and noise when the stepper motor rotates at low speed are its inherent shortcomings. Generally, the following solutions can be used to overcome:
A. If the stepper motor is working in the resonance zone, the resonance zone can be avoided by changing the reduction ratio and other mechanical transmission;
B. Use a drive with subdivision function, which is the most commonly used and easiest method;
C. Change to a stepping motor with a smaller step angle, such as a three-phase or five-phase stepping motor;
D. Changing to an AC servo motor can almost completely overcome vibration and noise, but the cost is higher;
E. Add a magnetic damper to the motor shaft. There are such products on the market, but the mechanical structure has changed a lot.
10.Does the subdivision number of the subdivision drive represent the accuracy?
The subdivision technology of the stepper motor is essentially an electronic damping technology (please refer to the relevant literature). Its main purpose is to reduce or eliminate the low-frequency vibration of the stepper motor. Improving the operation accuracy of the motor is only a side function of the subdivision technology. For example, for a two-phase hybrid stepping motor with a step angle of 1.8°, if the subdivision number of the subdivision driver is set to 4, then the motor's operating resolution is 0.45° per pulse. Can the accuracy of the motor reach or approach? 0.45°, also depends on other factors such as the subdivision current control accuracy of the subdivision driver. The precision of subdivision drivers of different manufacturers may vary greatly; the greater the subdivision number, the more difficult it is to control the precision.
11.What is the difference between the series connection and parallel connection of the four-phase hybrid stepping motor and the driver?
The four-phase hybrid stepping motor is generally driven by a two-phase driver. Therefore, the four-phase motor can be connected into two phases by using a series connection method or a parallel connection method when connecting. The series connection method is generally used in the occasions where the motor speed is relatively high. At this time, the driver output current required is 0.7 times of the motor phase current, so the motor heat is small; the parallel connection method is generally used in the occasions where the motor speed is high (also known as the high-speed connection method). ), the required driver output current is 1.4 times of the motor phase current, so the motor generates more heat.
12. How to determine the DC power supply of the stepper motor driver?
A. Determination of voltage
The power supply voltage of the hybrid stepping motor driver is generally a wide range (such as the power supply of IM483
The voltage is 12～48VDC), and the power supply voltage is usually selected according to the working speed and response requirements of the motor. If the motor's working speed is high or the response requirement is quicker, then the voltage value is also high, but note that the ripple of the power supply voltage cannot exceed the maximum input voltage of the drive, otherwise the drive 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 a linear power supply is used, the power supply
Flow can generally be 1.1 to 1.3 times of I; if usedswitchPower supply, the power supply current can generally be 1.5 to 2.0 times I.
13. Under what circumstances is the offline signal FREE of the hybrid stepper motor driver generally used?
When the offline signal FREE is low, the current output from the drive to the motor is cut off, and the motor rotor is in a free state (offline state). In some automation equipment, if the motor shaft is required to be directly rotated (manual mode) when the drive is powered off, 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 again to continue automatic control. 14. How to adjust the direction of rotation of the two-phase stepper motor after power-on in a simple way?
Just swap the A+ and A- (or B+ and B-) of the motor and driver wiring. Regarding the subdivision principle of the drive and some related instructions (reproduced) abroad, for the stepping system, the two-phase hybrid stepping motor and the corresponding subdivision drive are mainly used. However, in China, the majority of users do not have a special understanding of "subdivision". Some just think that subdivision is to improve accuracy. In fact, it is not true. Subdivision is mainly to improve the running performance of the motor. The description is as follows: Sub-control is realized by the driver accurately controlling the phase current of the stepping motor. Take a two-phase motor as an example. If the rated phase current of the motor is 3A, if the motor is driven by a conventional driver (such as a commonly used constant current chopping method) , Each step of the motor runs, the current in the winding will change from 0 to 3A or from 3A to 0. A huge change in phase current will inevitably cause vibration and noise in the operation of the motor. If you use a subdivision driver and drive the motor in the state of 10 subdivisions, the current in the winding changes only 0.3A instead of 3A for each microstep of the motor, and the current changes in a sinusoidal curve, so it is greatly The vibration and noise of the motor are improved. Therefore, the advantages in performance are the real advantages of subdivision. Since the subdivision drive needs to accurately control the phase current of the motor, it has very high technical requirements and process requirements for the drive, and the cost will also be higher.Note that there are some domestic drives that use "smoothing" to replace subdivision, and some are also called subdivision, but this is not a real subdivision.
We must distinguish the essential differences between the two:
15. "Smoothing" does not precisely control the phase current of the motor, but only slows down the rate of change of the current. Therefore, "smoothing" does not produce microsteps, and subdivided microsteps can be used for precise positioning.
16. After the phase current of the motor is smoothed, it will cause a decrease in the motor torque, and the subdivision control will not cause a decrease in the motor torque, on the contrary, the torque will increase. 17. What is the difference in the application of two-phase and five-phase hybrid stepping motors? Question answering: Generally speaking, two-phase motors have large step angles 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, the five-phase motor should be selected in the occasions where the motor's running accuracy is required to be high, and mainly in the low-to-medium speed range (generally less than 600 rpm); on the contrary, if the high-speed performance of the motor is pursued, there is no need for accuracy and stability. If there are too many requirements, a two-phase motor with a lower cost should be used. 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 drive. Compared with stepper motors, servo motors have the following advantages:
1. Realize the closed-loop control of position, speed and torque; overcome the problem of stepping motor out-of-step;
2. Good high-speed performance, generally rated speed can reach 2000-3000 rpm;
3. Strong anti-overload capability, able to withstand a load three times the rated torque, which is especially suitable for occasions with instant load fluctuations and fast starting requirements;
4. The low-speed operation is stable, and the stepping operation phenomenon similar to the stepping motor will not occur when the low-speed operation is running. Suitable for occasions with high-speed response requirements;
5. The dynamic response time of motor acceleration and deceleration is short, generally within tens of milliseconds; 6. Heat and noise are significantly reduced.
Attachment: dynamic index and terminology of stepper motor:
1. Step angle accuracy:
The error between the actual value and the theoretical value of the step angle each time the stepping motor rotates. Expressed in percentage: error/step angle*100%. The value of different running beats is different, it should be within 5% when running in four beats, and within 15% when running in eight beats.
2. Loss of step:
The number of steps when the motor is running is not equal to the theoretical number of steps. Call it out of step.
3. Misalignment angle:
The angle at which the axis of the rotor teeth deviates from the axis of the stator teeth, and there must be an out-of-adjustment angle in the operation of the motor. The error caused by the out-of-adjustment angle cannot be solved by the use of subdivision driving.
4. Maximum no-load starting frequency:
The maximum frequency at which the motor can be started directly under a certain driving mode, voltage and rated current without load.
5. Maximum no-load operating frequency:
The maximum speed frequency of the motor without load under a certain driving mode, voltage and rated current.
6. Operating torque frequency characteristics:
The curve of the relationship between output torque and frequency measured under certain test conditions is called the operating torque-frequency characteristic. This is the most important of the many dynamic curves of the motor and the fundamental basis for the selection of the motor. As shown below:
Other characteristics include inertia frequency characteristics, starting frequency characteristics and so on.
Once the motor is selected, the static torque of the motor is determined, but the dynamic torque is not. The dynamic torque of the motor depends on the average current (not the static current) of the motor during operation. The greater the average current, the greater the output torque of the motor, which is the The frequency characteristic is harder.
As shown below:
Among them, curve 3 has the largest current or the highest voltage; curve 1 has the smallest current or the lowest voltage, and the intersection of the curve and the load is the maximum speed point of the load.
To make the average current large, increase the drive voltage as much as possible, and use a small inductance and large current motor.
7. The resonance point of the motor:
Stepper motors have a fixed resonance area. The resonance area of two-phase and four-phase induction stepping motors is generally between 180-250pps (step angle of 1.8 degrees) or about 400pps (step angle of 0.9 degrees). The higher the motor drive voltage, the larger the motor current, the lighter the load, and the smaller the size of the motor, the resonance zone will shift upward, and vice versa. In order to make the motor output large torque without losing step and reducing the noise of the entire system, generally The working points should be more offset from the resonance zone.
8. Motor forward and reverse control:
When the power sequence of the motor winding is AB-BC-CD-DA or (), it is forward rotation, and when the power sequence is DA-CA-BC-AB or (), it is reverse.
