Stepper motor knowledge

Stepping common sense

1. What is a stepper motor?

A stepper motor is an actuator that converts electrical pulses into angular displacement. To put it bluntly: 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 to achieve accurate positioning. At the same time, you can control the speed and acceleration of the motor by controlling the pulse frequency to achieve the purpose of speed regulation.

2. What are the types of stepper motors?

There are three types of stepping motors: permanent magnet (PM), reactive (VR) and hybrid (HB) permanent magnets. The stepping is generally two-phase, the torque and volume are small, and the step angle is generally 7.5 degrees or 15 degrees; reactive stepping is generally three-phase, can achieve large torque output, the step angle is generally 1.5 degrees, but the noise and vibration are very large. Developed in Europe and the United States in the 1980s has been eliminated; hybrid stepping refers to the advantages of mixing permanent magnet and reactive. It is divided into two phases and five phases: the two-phase step angle is generally 1.8 degrees and the five-phase step angle is generally 0.72 degrees. This stepper motor is the most widely used.

3. What is holding torque (HOLDING TORQUE)?

HOLDING TORQUE is 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 the stepper motor at low speed is close to the holding torque. Since the output torque of the stepping motor is continuously attenuated as the speed increases, the output power also changes with the increase of the speed, so the holding torque becomes one of the most important parameters for measuring the stepping motor. For example, when people say that a 2N.m stepper motor, unless otherwise specified, is a stepper motor that maintains a torque of 2N.m.

4. What is DETENT TORQUE?

DETENT TORQUE is the torque at which the stator locks the rotor when the stepper motor is not energized. DETENT TORQUE has no unified translation method in China, which is easy to misunderstand. Because the rotor of reactive stepping motor is not permanent magnet material, it does not have DETENT TORQUE.

5. What is the accuracy of the stepper motor? Do you accumulate?

The accuracy of a general stepper motor is 3-5% of the step angle and does not accumulate.

6. What is the allowable temperature of the stepper motor?

If the temperature of the stepping motor is too high, the magnetic material of the motor will be demagnetized firstly, resulting in a torque drop and even out of step. Therefore, the maximum allowable temperature of the motor surface should depend on the demagnetization point of the magnetic material of different motors; in general, the demagnetization of the magnetic material The points are all above 130 degrees Celsius, and some even up to 200 degrees Celsius, so the external temperature of the stepper motor is completely normal at 80-90 degrees Celsius.

7. Why does the torque of the stepper motor decrease with increasing speed?

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 larger the back electromotive force. Under its action, the motor decreases with increasing frequency (or speed), resulting in a drop in torque.

8. Why the stepping motor can run normally at low speed, but if it is higher than a certain speed, it can't start, accompanied by howling?

The stepping motor has a technical parameter: the no-load starting frequency, that is, the pulse frequency that the stepping motor can start normally under no-load conditions. If the pulse frequency is higher than this value, the motor cannot start normally, and lost or blocked may occur. In the case of load, the starting frequency should be lower. If the motor is to be rotated at a high speed, the pulse frequency should have an acceleration process, that is, the starting frequency is low, and then rise to a desired high frequency (the motor speed is increased from a low speed to a high speed) at a certain acceleration.

9. How to overcome the vibration and noise of the two-phase hybrid stepping motor at low speed?

The large vibration and noise of the stepping motor at low speed is its inherent shortcoming. Generally, the following solutions can be used to overcome:
A. If the stepper motor works just in the resonance zone, the resonance zone can be avoided by changing the gear ratio and other mechanical transmissions;
B. Using a drive with subdivision, this is the most common and easiest method;
C. Change to a stepper motor with a smaller step angle, such as a three-phase or five-phase stepper motor;
D. Switching to AC servo motor can almost completely overcome vibration and noise, but the cost is higher;
E. A magnetic damper is added to the motor shaft. This product is available on the market, but the mechanical structure changes greatly.

10. Does the number of subdivisions of the subdivision drive represent accuracy?

The subdivision technology of the stepping 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 stepping motor, and improve the running accuracy of the motor is only a supplementary 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 operating resolution of the motor is 0.45° per pulse, and the accuracy of the motor can be achieved or approached. 0.45° also depends on other factors such as the subdivision current control accuracy of the subdivision driver. The accuracy of subdivision drivers from different manufacturers may vary greatly; the larger the number of subdivisions, the more difficult it is to control.

11. What is the difference between the series connection method and the parallel connection method 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 to two phases by series connection or parallel connection. The series connection method is generally used in the case where the motor speed is relatively high. At this time, the required output current of the driver is 0.7 times of the motor phase current, so the motor generates little heat; and the connection method is generally used in the case where the motor speed is high (also called high speed connection method). ), the required driver output current is 1.4 times the motor phase current, so the motor generates a large amount of 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 (for example, the power supply voltage of the IM483 is 12 to 48 VDC), and the power supply voltage is usually selected according to the operating speed and response requirements of the motor. If the motor has a higher operating speed or a faster response, the voltage is also higher, but note that the ripple of the supply voltage cannot exceed the maximum input voltage of the drive, otherwise the drive may be damaged.
B. Determination of Current The supply current is generally determined by the output phase current I of the driver. If a linear power supply is used, the supply current can generally be 1.1 to 1.3 times that of I; if a switching power supply is used, the supply current can generally be 1.5 to 2.0 times that of I.

13. Under what circumstances is the offline signal FREE of the hybrid stepper motor driver 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 the motor shaft (manual mode) is required to be directly powered while the drive is uninterrupted, the FREE signal can be set low, the motor can be taken offline, and manually operated or adjusted. After manual completion, set the FREE signal high to continue automatic control.

14. If you use a simple method to adjust the direction of rotation of the two-phase stepper motor after power-on?

Simply swap the A+ and A- (or B+ and B-) wires of the motor to the drive.

About the subdivision principle of the driver and some related instructions
In foreign countries, for stepping systems, two-phase hybrid stepping motors and corresponding subdivision drivers are mainly used. However, in China, the majority of users are not particularly aware of the “segmentation”. Some just think that the subdivision is to improve the accuracy. In fact, the subdivision is mainly to improve the running performance of the motor. The description is as follows: The sub-control is realized by the driver precisely controlling the phase current of the stepping motor. Take the 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 the commonly used constant current chopping method) Every time the motor runs, the current in the winding will be abruptly changed from 0 to 3A or from 3A to 0. The huge change of the phase current will inevitably cause vibration and noise of the motor running. If a subdivision driver is used, the motor is driven in a subdivided state. Each time the motor is operated for one microstep, the current change in the winding is only 0.3A instead of 3A, and the current changes in a sinusoidal manner, which is greatly The vibration and noise of the motor are improved, so the performance advantage is the real advantage of the subdivision. Since the subdivision driver has to accurately control the phase current of the motor, the driver has to have relatively high technical requirements and process requirements, and the cost is also high. Note that some drivers in China use “smoothing” instead of subdivision, and some are also called subdivisions, but this is not a true subdivision. It is hoped that the majority of users must distinguish the essence of the two:

15 . "Smoothing" does not precisely control the phase current of the motor, but only slows the rate of change of the current, so "smoothing" does not produce microsteps, and subdivided microsteps can be used for precise positioning.

16 . When the phase current of the motor is smoothed, it will cause the motor torque to drop, and the subdivision control will not cause the motor torque to drop. On the contrary, the torque will increase.

17. What is the difference between the application of two-phase and five-phase hybrid stepping motors?

Question and answer:
In general, the two-phase motor has a large step angle and good high-speed characteristics, but there is a low-speed vibration region. The five-phase motor has a small step angle and runs smoothly at low speed. Therefore, in the case of high requirements for the operation accuracy of the motor, and mainly in the middle and low speed section (generally less than 600 rev / min), five-phase motor should be used; on the contrary, if the high-speed performance of the motor is pursued, there is no accuracy and stability. Where 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 smoothness can be solved by using a subdivision driver.
Compared with stepper motors, servo motors have the following advantages:
1. Realize closed-loop control of position, speed and torque; overcome the problem of stepping motor out of step;
2, high speed performance is good, the general rated speed can reach 2000 ~ 3000 rpm;
3, strong anti-overload capability, can withstand loads of three times the rated torque, especially suitable for occasions with transient load fluctuations and quick start required;
4. The low speed operation is stable, and the stepping operation phenomenon similar to the stepping motor does not occur when running at low speed. Suitable for occasions with high speed response requirements;
5, the motor acceleration and deceleration dynamic corresponding time is short, generally within tens of milliseconds; 6, heat and noise significantly reduced.

Stepper motor packaging machinery application

Stepper motor control gear pumps can also achieve accurate metering. Gear pumps are widely used in the delivery of viscous bodies, such as syrup, bean paste, white wine, oil, ketchup and the like. At present, piston pumps are mostly used for the measurement of these materials, and there are disadvantages such as difficulty in adjustment, complicated structure, inconvenient maintenance, large power consumption, and inaccurate measurement. The gear pump metering is measured by a pair of gear meshing rotations, and the space of the material passing through the teeth and teeth is forcibly sent from the feed port to the discharge port. The power comes from the stepping motor. The position and speed of the stepping motor are controlled by the programmable controller, and the measurement accuracy is higher than that of the piston pump. The stepper motor is suitable for running at low speed. When the speed is increased, the noise of the stepping motor will increase significantly, and other economic indicators will drop significantly. For a gear pump with a relatively high speed, it is better to use a speed-up structure. We started the structure of the stepping motor direct-coupled gear pump on the viscous packaging machine. As a result, the noise is difficult to avoid and the reliability is degraded. Later, the spur gear speed-up method was adopted to reduce the speed of the stepping motor, the noise was controlled, the reliability was also improved, and the metering degree was guaranteed.

Third, the application of stepper motor in the supply of packaging film

In the packaging machine which integrates bag making, filling and sealing, it is required to provide a fixed length supply of the plastic film for packaging, and whether it is intermittent supply or continuous supply, it can be reliably completed by a stepping motor.

1, for intermittent packaging machine

The intermittent packaging machine uses a stepping motor to supply the film, and the reliability can be improved. In the previous packaging film, the method of intermittently pulling the crank linkage mechanism was adopted, and the structure was complicated and the adjustment was difficult. Especially when the product needs to be replaced, not only the adjustment was difficult, but also the packaging film was wasted a lot. The stepping motor and the draw-belt roller are directly connected to the drawstring, which not only simplifies the structure, but also is very convenient to adjust, as long as the button on the control panel can be realized, which saves the adjustment time and saves the packaging material. In the intermittent packaging machine, the feeding control of the packaging material can adopt two modes: a bag length control mode and a color mark control mode. The bag length control mode is suitable for the packaging film without color standard, which is realized by setting the speed of the stepping motor in advance, and the setting of the turning ratio can be realized by the dial switch. The color mark mode is equipped with a photoelectric switch, and the photoelectric switch detects the position of the color mark. When the color mark is detected, a control switch signal is issued, and after the step motor receives the signal, the rotation is stopped, and after a certain time delay, the film is rotated, and the film is re-started. , to ensure that the film is fixed according to the position of the color mark.

2, for continuous packaging machine

In the continuous packaging machine, the stepping motor is continuously rotated, and the packaging film is uniformly and continuously conveyed. When the length of the bag is changed, it can be realized only by the dial switch.

Fourth, the application of stepper motor in horizontal seal

In continuous packaging machines, cross-sealing is an important actuator and one of the more complex mechanisms in packaging machines. Especially for the color-coded packaging film, the sealing and cutting position requirements are extremely strict. In order to improve the cutting accuracy, people have developed the eccentric sprocket mechanism, the crank guide mechanism, etc., but these mechanisms are very troublesome and reliable. Low disadvantages. The main reason for these shortcomings is that the process requires horizontal sealing of the sealing wheel and positioning and cutting. The stepper motor directly drives the transverse seal wheel to achieve speed synchronization. The film supply wheel of the continuous packaging machine is continuously supplied with film. When the horizontal sealing is required, the linear speed of the horizontal sealing is synchronized with the feeding speed of the film to avoid the occurrence of tear film and film accumulation. Since the diameter of the transverse sealing wheel is constant, when changing the length of the bag, it needs to be changed by changing the rotation speed of the horizontal sealing wheel, but the horizontal sealing requires a certain time, that is, the transverse sealing wheel and the film need to be constant from contact to leaving. Time, otherwise the seal is not strict. The total time per revolution of the transverse sealing wheel and the time required for the horizontal sealing are constant. To meet the requirements of speed synchronization, the speed of the stepping motor can be divided into two parts within one week, and some of them first meet the requirements of speed synchronization. In addition, in the continuous packaging machine, the stepping motor is continuously rotated, and the packaging film is uniformly and continuously conveyed. When the length of the bag is changed, it can be realized only by the dial switch.

Fourth, the application of stepper motor in horizontal seal

In continuous packaging machines, cross-sealing is an important actuator and one of the more complex mechanisms in packaging machines. Especially for the color-coded packaging film, the sealing and cutting position requirements are extremely strict. In order to improve the cutting accuracy, people have developed the eccentric sprocket mechanism, the crank guide mechanism, etc., but these mechanisms are very troublesome and reliable. Low disadvantages. The main reason for these shortcomings is that the process requires horizontal sealing of the sealing wheel and positioning and cutting.

The stepper motor directly drives the transverse seal wheel to achieve speed synchronization. The film supply wheel of the continuous packaging machine is continuously supplied with film. When the horizontal sealing is required, the linear speed of the horizontal sealing is synchronized with the feeding speed of the film to avoid the occurrence of tear film and film accumulation. Since the diameter of the transverse sealing wheel is constant, when changing the length of the bag, it needs to be changed by changing the rotation speed of the horizontal sealing wheel, but the horizontal sealing requires a certain time, that is, the transverse sealing wheel and the film need to be constant from contact to leaving. Time, otherwise the seal is not strict. The total time per revolution of the transverse sealing wheel and the time required for the horizontal sealing are constant. To meet the requirements of speed synchronization, the speed of the stepping motor can be divided into two parts within one week, and some of them first meet the requirements of speed synchronization. In addition, the unloaded part meets the total time of the week.

In order to achieve good sealing quality, the non-equal speed control mode can be realized by the stepping motor on the transverse sealing wheel, that is, the speed synchronization is realized at every point of the horizontal sealing, which is limited to the length, and will not be stated here.

The characteristics of the stepper motor are mainly attributed to three aspects, one is that the overload is good. The speed is not affected by the load size. Unlike ordinary motors, when the load is increased, the speed will drop. Therefore, the stepping motor is used in places where speed and position are strictly required. Second, the control is convenient. The stepping motor rotates in units of “steps”, and the digital features are obvious, which brings great convenience to computer control. In turn, the emergence of computers has opened up a broader market for stepping motors. Third, the structure of the whole machine is simple. The traditional mechanical speed and position control structure is complicated and difficult to adjust. After using the stepping motor, the structure of the whole machine is simple and compact.

The application of stepper motors in packaging machinery has just begun. Many traditional mechanical control methods can be replaced by stepper motors. In addition to some of the applications described above, they are also available in printing, filling, wrapping, etc. The application, I believe that in a relatively short period of time, China's packaging machinery industry will be able to leap to a new level in the stepper motor technology platform.
Partially meet the requirements of the total time of the week.

In order to achieve good sealing quality, the non-equal speed control mode can be realized by the stepping motor on the transverse sealing wheel, that is, the speed synchronization is realized at every point of the horizontal sealing, which is limited to the length, and will not be stated here.

The characteristics of the stepper motor are mainly attributed to three aspects, one is that the overload is good. The speed is not affected by the load size. Unlike ordinary motors, when the load is increased, the speed will drop. Therefore, the stepping motor is used in places where speed and position are strictly required. Second, the control is convenient. The stepping motor rotates in units of “steps”, and the digital features are obvious, which brings great convenience to computer control. In turn, the emergence of computers has opened up a broader market for stepping motors. Third, the structure of the whole machine is simple. The traditional mechanical speed and position control structure is complicated and difficult to adjust. After using the stepping motor, the structure of the whole machine is simple and compact.

The application of stepper motors in packaging machinery has just begun. Many traditional mechanical control methods can be replaced by stepper motors. In addition to some of the applications described above, they are also available in printing, filling, wrapping, etc. The application, I believe that in a relatively short period of time, China's packaging machinery industry will be able to leap to a new level in the stepper motor technology platform.

Introduction to motion control system

2007-6-24

Introduction to Motion Control Systems Motion control is a technique for how to precisely control the position and velocity of an object. A typical motion control system consists of three parts: a control part; a drive part; and an execution part. As shown below:

The motion execution component is usually a stepper motor or a servo motor. A stepper motor is an actuator that converts electrical pulses into angular displacement. It is characterized by no accumulation error and is therefore widely used in various open loop control. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in the set direction, and its rotation is step by step at a fixed angle. The angular displacement can be controlled by controlling the number of pulses to achieve the purpose of accurate positioning. At the same time, the speed and acceleration of the motor rotation can be controlled by controlling the pulse frequency, thereby achieving the purpose of speed regulation.
The operation of the stepper motor is driven by an electronic device. This device is a stepper motor driver that amplifies the pulse signal from the control system to drive the stepper motor. The speed of the stepping motor is proportional to the frequency of the pulse signal. The frequency of the stepping pulse signal can be controlled to accurately adjust the speed of the motor. The number of stepping pulses can be controlled to accurately position the motor. Therefore, the typical stepper motor drive control system is mainly composed of three parts:
1. Step controller, realized by single chip microcomputer.
2. The driver amplifies the pulse outputted by the single chip to drive the stepping motor.
3. Stepper motor.