It's a stepper motor. It moves a small step when you apply power. If you don't apply electricity, it will stay there. It won't move after the power is cut off.
A stepper motor is an open-loop control component that converts electrical pulse signals into angular displacement or linear displacement. Under non-overload conditions, the motor's speed and stopping position only depend on the frequency and number of pulses of the pulse signal, and are not affected by load changes. That is, if a pulse signal is added to the motor, the motor will rotate through a step angle. The existence of this linear relationship, coupled with the characteristics of the stepper motor that only has periodic errors and no cumulative errors. It makes it very simple to use stepper motors to control speed, position and other control fields.
Although stepper motors have been widely used, stepper motors are not like ordinary DC motors. AC motors are commonly used. It must be used as a control system composed of dual ring pulse signals, power drive circuits, etc. Therefore, it is not easy to make good use of stepper motors. It involves a lot of professional knowledge such as machinery, motors, electronics and computers.
At present, there are indeed many manufacturers producing stepper motors, but there are very few manufacturers with professional and technical personnel who can develop them by themselves. Most manufacturers only have one or twenty people, and even the most basic There are no equipment. It's just a blind imitation stage. This causes a lot of trouble for users in product selection and use. Based on the above situation, we decided to use the wide range of inductive stepper motors as an example. Describe its basic working principle. We hope it can be helpful to the majority of users in selecting, using, and improving the entire machine.
2. Working principle of inductor stepper motor
(1) Principle of reactive stepper motor
Because the working principle of reactive stepper motor is relatively simple . The following first describes the principle of the three-phase reactive stepper motor.
1. Structure: The motor rotor is evenly distributed with many small teeth. The stator teeth have three excitation windings, and their geometric axes are staggered from the rotor tooth axes in turn. 0, 1/3て, 2/3て, (the distance between the axes of two adjacent rotor teeth is the tooth pitch, expressed in て), that is, A and tooth 1 are aligned, and B and tooth 2 are staggered to the right by 1/3て, C and tooth 3 are staggered 2/3 to the right, A' is aligned with tooth 5, (A' is A, tooth 5 is tooth 1) The following is an expanded view of the stator and rotor:
2. Rotation : If phase A is energized and phases B and C are not energized, tooth 1 is aligned with A due to the magnetic field (the same is true below when the rotor is not subject to any force). If phase B is energized and phases A and C are not energized, tooth 2 should be aligned with B. At this time, the rotor moves 1/3て to the right. At this time, tooth 3 and C are offset by 1/3て, and tooth 4 and A Offset (て-1/3て)=2/3て. If phase C is energized and phases A and B are not energized, tooth 3 should be aligned with C. At this time, the rotor moves 1/3 to the right, and tooth 4 is aligned with A by 1/3. For example, phase A is energized, phases B and C are not energized, tooth 4 is aligned with A, and the rotor moves 1/3 to the right. In this way, after A, B, C, and A are energized respectively, tooth 4 (that is, the tooth before tooth 1 ) moves to phase A, and the motor rotor rotates one gear pitch to the right. If you continuously press A, B, C, A... to energize, the motor will rotate to the right by 1/3 て per step (per pulse). If you press A, C, B, A... to energize, the motor will rotate in reverse direction. It can be seen that the position and speed of the motor have a one-to-one correspondence between the number of conductions (number of pulses) and frequency. The direction is determined by the conductive sequence. However, due to considerations such as torque, stability, noise and angle reduction. The conductive state of A-AB-B-BC-C-CA-A is often used, thus changing the original 1/3て to 1/6て per step. Even through different combinations of two-phase currents, 1/3て becomes 1/12て or 1/24て. This is the basic theoretical basis for motor subdivision drive. It is not difficult to deduce: there are m-phase excitation windings on the motor stator, and their axes are offset from the rotor tooth axis by 1/m, 2/m...(m-1)/m,1. And the conductive motor can be controlled to rotate forward and reverse according to a certain phase sequence - this is the physical condition of rotation. As long as this condition is met, we can theoretically manufacture stepper motors of any phase. Due to various considerations such as cost, two, three, four, and five phases are generally used in the market.
3. Torque: Once the motor is energized, a magnetic field (magnetic flux Ф) will be generated between the stator and the rotor. When the rotor and the stator are staggered at a certain angle, the force F generated is proportional to (dФ/dθ) S. Its magnetic flux Ф=Br *S Br is the magnetic density, S is the magnetic permeability area, F is proportional to L*D*Br, L is the effective length of the iron core, D is the rotor diameter Br=N·I/R N·I is the excitation winding ampere-turns (current Multiplied by the number of turns) R is the magnetic resistance. Torque = force * radius Torque is proportional to the effective volume of the motor * ampere-turns * magnetic density (only the linear state is considered). Therefore, the larger the effective volume of the motor, the greater the excitation ampere-turns, the smaller the air gap between the stator and the rotor, and the motor torque The bigger, vice versa.
(2) Inductor type stepper motor
1. Features: Compared with the traditional reaction type, the inductor type has permanent magnets added to the rotor to provide soft magnetic The stator excitation only needs to provide a changing magnetic field without providing energy consumption at the working point of the magnetic material. Therefore, the motor has high efficiency, small current and low heat generation. Due to the presence of permanent magnets, the motor has a strong back electromotive force and its own damping effect is relatively good, making it relatively stable during operation, with low noise and low low-frequency vibration. The inductor type can be regarded as a low-speed synchronous motor to some extent. A four-phase motor can operate in four phases or in two phases. (Must be driven by bipolar voltage), which cannot be the case with reactive motors. For example: four-phase and eight-phase operation (A-AB-B-BC-C-CD-D-DA-A) can completely adopt the two-phase eight-beat operation mode. It is not difficult to find that the conditions are C=, D=. A The internal windings of two-phase motors are exactly the same as those of four-phase motors. Small-power motors are generally directly connected to two-phase, while motors with higher power are often externally connected to eight leads for ease of use and flexible changes in the dynamic characteristics of the motor. (Four-phase), when used in this way, it can be used as a four-phase motor or a two-phase motor with windings connected in series or parallel.
2. Classification
Induction motors can be divided into two-phase motors, three-phase motors, four-phase motors, five-phase motors, etc. based on the number of phases. Based on the frame number (motor outer diameter), it can be divided into: 42BYG (BYG is the code name of the induction stepper motor), 57BYG, 86BYG, 110BYG, (international standard), while 70BYG, 90BYG, 130BYG, etc. are all domestic standards.
3. Terminology of static indicators of stepper motors Phase number: The number of pairs of excitation coils that produce different opposite pole N and S magnetic fields. Commonly expressed by m. Number of beats: The number of pulses or conductive state required to complete a periodic change in the magnetic field is represented by n, or refers to the number of pulses required for the motor to rotate through a pitch angle. Taking a four-phase motor as an example, there is a four-phase four-beat operating mode, namely AB -BC-CD-DA-AB, four-phase eight-beat operation mode, namely A-AB-B-BC-C-CD-D-DA-A. Step angle: corresponds to a pulse signal, the angular displacement of the motor rotor Represented by θ. θ=360 degrees (number of rotor teeth J*number of operating beats), taking a conventional two- and four-phase motor with 50-tooth rotor teeth as an example. When running in four beats, the step angle is θ=360 degrees/(50*4)=1.8 degrees (commonly known as full step). When running in eight beats, the step angle is θ=360 degrees/(50*8)=0.9 degrees (commonly known as full step). half step). Positioning torque: The locking torque of the motor rotor itself when the motor is not energized (caused by the harmonics of the magnetic field tooth shape and mechanical errors) Static torque: When the motor does not rotate under the action of rated static electricity, the motor Locking torque of the rotating shaft. This torque is a measure of motor volume (geometric dimensions) and has nothing to do with drive voltage, drive power, etc. Although the static torque is proportional to the electromagnetic excitation ampere-turns and is related to the air gap between the fixed-gear rotors, it is not advisable to excessively reduce the air gap and increase the excitation ampere-turns to increase the static torque, which will cause the motor to heat up. and mechanical noise.
4. Dynamic indicators and terminology:
1. Step angle accuracy: The error between the actual value and the theoretical value of each step angle of the stepper motor. Expressed as a percentage: error/step angle*100%. The value is different for different running beats. It should be within 5% when running with four beats, and within 15% when running with eight beats.
2. Out-of-step: The number of steps when the motor is running is not equal to the theoretical number of steps. Call it a step-out.
3. Misalignment angle: The angle at which the axis of the rotor teeth deviates from the axis of the stator teeth. There must be a misalignment angle when the motor is running. The error caused by the misalignment angle cannot be solved by using subdivision drive.
4. Maximum no-load starting frequency: The maximum frequency at which the motor can be started directly without load under a certain drive form, voltage and rated current.
5. Maximum no-load operating frequency: The maximum speed frequency of the motor without load under a certain drive form, voltage and rated current.
6. Operating torque-frequency characteristics: The curve showing the relationship between the output torque and frequency of the motor during operation measured under certain test conditions is called the operating torque-frequency characteristics. This is the most important of the many dynamic curves of the motor. It is also the fundamental basis for motor selection. As shown in the figure below: Other characteristics include inertia frequency characteristics, starting frequency characteristics, etc. 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 (rather than the static current) when the motor is running. The greater the average current, the greater the output torque of the motor, that is, the motor's The frequency characteristics are harder. As shown in the figure below: Among them, curve 3 has the largest current or the highest voltage; curve 1 has the smallest current or the lowest voltage. The intersection between the curve and the load is the maximum speed point of the load. To make the average current large, increase the driving voltage as much as possible and use a motor with small inductance and high current.
7. The maximum vibration point of the motor: Stepper motors have a fixed maximum vibration area. The maximum vibration area of ??two- and four-phase induction subtypes is generally between 180-250pps. (step angle 1.8 degrees) or around 400pps (step angle 0.9 degrees). The higher the motor drive voltage, the greater the motor current, the lighter the load, and the smaller the motor volume, the maximum vibration zone will shift upward. Vice versa, in order to make the motor output a large torque without losing synchronization and reduce the noise of the entire system, the general operating point should be offset from the maximum vibration zone.
8. Motor forward and reverse control: When the motor winding energization sequence is AB-BC-CD-DA or (), it is forward rotation, and when the energization sequence is DA-CA-BC-AB or () for inversion.
As an actuator, stepper motors are one of the key products of mechatronics and are widely used in various automation control systems. With the development of microelectronics and computer technology, the demand for stepper motors is increasing day by day, and they are used in various fields of the national economy.
A stepper motor is an actuator that converts electrical pulses into angular displacement. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (called "step angle") in the set direction, and its rotation runs step by step at a fixed angle. The angular displacement can be controlled by controlling the number of pulses to achieve accurate positioning; at the same time, the speed and acceleration of the motor rotation can be controlled by controlling the pulse frequency to achieve speed regulation. The stepper motor can be used as a special motor for control. It is widely used in various open-loop controls by taking advantage of its characteristics of no accumulated error (accuracy of 100%).
The more commonly used stepper motors now include reactive stepper motors (VR), permanent magnet stepper motors (PM), hybrid stepper motors (HB) and single-phase stepper motors, etc. .
Permanent magnet stepper motors are generally two-phase, with small torque and volume, and the step angle is generally 7.5 degrees or 15 degrees;
Reactive stepper motors are generally Three-phase, large torque output can be achieved, the step angle is generally 1.5 degrees, but the noise and vibration are very large. The rotor magnetic circuit of the reactive stepper motor is made of soft magnetic materials, and the stator has multi-phase excitation windings that use changes in magnetic permeability to generate torque.
Hybrid stepper motor refers to a mixture of the advantages of permanent magnet type and reactive type. It is further 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 and is also the stepper motor selected for this subdivision drive solution.
Some basic parameters of stepper motors:
Motor inherent step angle:
It means that every time the control system sends a step pulse signal, the motor rotates angle.
The motor is given a step angle value when it leaves the factory. For example, the value given by the 86BYG250A motor is 0.9°/1.8° (which means 0.9° for half-step operation and 1.8° for full-step operation). This step angle It can be called the 'inherent step angle of the motor', which is not necessarily the real step angle when the motor is actually working. The real step angle is related to the driver.
The number of phases of a stepper motor:
Refers to the number of coil groups inside the motor. Currently, two-phase, three-phase, four-phase, and five-phase stepper motors are commonly used. The number of motor phases is different, and the step angle is also different. Generally, the step angle of a two-phase motor is 0.9°/1.8°, a three-phase motor is 0.75°/1.5°, and a five-phase motor is 0.36°/0.72°. When there is no subdivision driver, users mainly rely on choosing stepper motors with different numbers of phases to meet their own step angle requirements. If a subdivision driver is used, the 'number of phases' will become meaningless. The user only needs to change the subdivision number on the driver to change the step angle.
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 the stepper motor continues to attenuate as the speed increases, and the output power also changes with the increase of the speed, the holding torque has become one of the most important parameters for measuring the stepper motor. For example, when people say a 2N.m stepper motor, they mean a stepper motor with a holding torque of 2N.m unless otherwise specified.
DETENT TORQUE:
Refers to the torque at which the stator locks the rotor when the stepper motor is not powered on. There is no unified translation method for DETENT TORQUE in China, which can easily lead to misunderstanding. Since the rotor of the reactive stepper motor is not a permanent magnet material, it does not have DETENT TORQUE.
Some characteristics of stepper motors:
1. Generally, the accuracy of stepper motors is 3-5% of the step angle and is not cumulative.
2. The maximum temperature allowed on the surface of the stepper motor.
If the temperature of the stepper motor is too high, it will first demagnetize the magnetic material of the motor, resulting in a decrease in torque and even loss of step. Therefore, the maximum temperature allowed on the surface of the motor should depend on the demagnetization point of the magnetic material of different motors; generally Generally speaking, the demagnetization point of magnetic materials is above 130 degrees Celsius, and some are even as high as above 200 degrees Celsius, so it is completely normal for the surface temperature of the stepper motor to be 80-90 degrees Celsius.
3. The torque of a stepper motor decreases as the speed increases.
When the stepper motor rotates, the inductance of each phase winding of the motor will form a reverse electromotive force; the higher the frequency, the greater the reverse electromotive force. Under its action, the phase current of the motor decreases as the frequency (or speed) increases, resulting in a decrease in torque.
4. The stepper motor can run normally at low speed, but if it is higher than a certain speed, it will not start and will make a whistling sound.
The stepper motor has a technical parameter: 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 cannot start normally, possibly Loss of step or stall occurs. Under load, the starting frequency should be lower. If you want the motor to rotate at high speed, the pulse frequency should have an acceleration process, that is, the starting frequency is low, and then rises to the desired high frequency at a certain acceleration (the motor speed increases from low speed to high speed).
With its remarkable characteristics, stepper motors play an important role in the era of digital manufacturing. With the development of different digital technologies and the improvement of stepper motor technology, stepper motors will be used in more fields.
Little knowledge about stepper motors (newly seen, share with everyone)
1. What is a stepper motor?
Stepper motor It 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 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 speed regulation.
2. What types of stepper motors are there?
There are three types of stepper motors: permanent magnet (PM), reactive (VR) and hybrid (HB) permanent magnets. Magnetic steppers are generally two-phase, with small torque and volume, and the step angle is generally 7.5 degrees or 15 degrees; reactive steppers are generally three-phase, which can achieve large torque output, and the step angle is generally 1.5 degrees. , but the noise and vibration are very large. It has been eliminated in developed countries such as Europe and the United States in the 1980s; hybrid stepper refers to a mixture of the advantages of permanent magnet and reactive types. 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 type of stepper motor is the most widely used.
3. What is the holding torque (HOLDING TORQUE)?
The 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. Usually the torque of a stepper motor at low speed is close to the holding torque. Since the output torque of the stepper motor continues to attenuate as the speed increases, and the output power also changes with the increase of the speed, the holding torque has become one of the most important parameters for measuring the stepper motor. For example, when people say a 2N.m stepper motor, they mean a stepper motor with a holding torque of 2N.m unless otherwise specified.
4. What is DETENT TORQUE?
DETENT TORQUE refers to the torque of the stator locking the rotor when the stepper motor is not powered on. There is no unified translation method for DETENT TORQUE in China, which can easily lead to misunderstanding. Since the rotor of the reactive stepper motor is not a permanent magnet material, it does not have DETENT TORQUE.
5. What is the accuracy of stepper motors? Is it cumulative?
Generally, the accuracy of stepper motors is 3-5% of the step angle, and it is not cumulative.
6. What is the allowable surface temperature of a stepper motor?
Excessive temperature of a stepper motor will first demagnetize the magnetic material of the motor, resulting in a decrease in torque and even loss of step. Therefore, the maximum allowable temperature on the surface of the motor should depend on the demagnetization point of the magnetic materials of different motors; generally speaking, the demagnetization point of magnetic materials is above 130 degrees Celsius, and some are even as high as above 200 degrees Celsius, so the surface temperature of the stepper motor is between 80-90 degrees Celsius is completely normal.
7. Why does the torque of the stepper motor decrease as the speed increases?
When the stepper motor rotates, the inductance of each phase winding of the motor will form a reverse electromotive force ;The higher the frequency, the greater the reverse electromotive force. Under its action, the phase current of the motor decreases as the frequency (or speed) increases, resulting in a decrease in torque.
8. Why can the stepper motor run normally at low speed, but cannot start if it is higher than a certain speed, accompanied by a whistling sound?
The stepper motor has a technical parameter : No-load starting frequency, that 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 cannot start normally, and may lose steps or stall. Under load, the starting frequency should be lower. If you want the motor to rotate at high speed, the pulse frequency should have an acceleration process, that is, the starting frequency is low, and then rises to the desired high frequency at 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 stepper motor when it rotates at low speed?
The inherent shortcomings of the stepper motor are its high vibration and noise when it rotates at low speed. Generally, the following solutions can be used to overcome:
A. If the stepper motor happens to work in the maximum vibration area, the maximum vibration area can be avoided by changing the reduction ratio and other mechanical transmission;
B. Use a driver with subdivision function, which is the most commonly used and simplest method;
C. Change to a stepper motor with a smaller step angle, such as a three-phase or Five-phase stepper motor;
D. Switch to AC servo motor, which can almost completely overcome vibration and noise, but the cost is higher;
E. Add magnetic damping to the motor shaft There is already such a product on the market, but the mechanical structure has changed significantly.
10. Can the subdivision number of the subdivision driver 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 weaken or eliminate the low-frequency vibration of the stepper motor, and improving the operating accuracy of the motor is only an incidental function of the subdivision technology. For example, for a two-phase hybrid stepper 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. Can the accuracy of the motor reach or be close to 0.45°, it also depends on other factors such as the subdivision current control accuracy of the subdivision driver. The accuracy of subdivision drives from different manufacturers may vary greatly; the larger the number of subdivisions, the more difficult it is to control the accuracy.
11. What is the difference between the series connection method and the parallel connection method of the four-phase hybrid stepper motor and the driver?
The four-phase hybrid stepper motor is generally connected by a two-phase driver. Drive, therefore, the four-phase motor can be connected into two phases using series connection or parallel connection. The series connection method is generally used in situations where the motor speed is high. The required driver output current is 0.7 times the motor phase current, so the motor generates less heat. The parallel connection method is generally used in situations 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 greater 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 stepper motor driver is generally It is a wide range (for example, the power supply voltage of IM483 is 12~48VDC). The power supply voltage is usually selected according to the working speed and response requirements of the motor. If the motor has a high operating speed or a fast response requirement, the voltage value will also be high. However, please note that the ripple of the power supply voltage cannot 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 based on the output phase current I of the driver. If a linear power supply is used, the power supply current can generally be 1.1 to 1.3 times I; if a switching power supply is used, 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 level, the current the driver outputs to the motor is cut off and the motor rotor is in a free state (offline state). In some automation equipment, if it is required to directly rotate the motor shaft (manual mode) when the driver is not powered on, 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 to continue automatic control.
14. What if you use a simple method to adjust the rotation direction of the two-phase stepper motor after it is powered on?
Just connect A+ and A- (or B+ and B) between the motor and the driver. -) Just swap.
The main characteristics of stepper motors:
1 The stepper motor must be driven to operate. The drive model must be a pulse signal. When there is no pulse, the stepper motor is stationary, such as
If appropriate pulse signal is added, it will rotate at a certain angle (called step angle). The speed of rotation is proportional to the frequency of pulses.
2 The stepping angle of the Tamron version stepper motor is 7.5 degrees, and it takes 48 pulses to complete one revolution of 360 degrees.
3 Stepper motors have the superior characteristics of instant start and rapid stop.
4. Changing the sequence of pulses can easily change the direction of rotation.
Therefore, currently printers, plotters, robots, and other equipment use stepper motors as their power core