Stepper motor working principle

1. Stepping motor is an open-loop control element that transforms electrical pulse signals into angular or linear displacements. In the case of non-overload, the motor speed, stopping position depends only on the frequency of the pulse signal and the number of pulses, and is not affected by the load change, that is, add a pulse signal to the motor, the motor is turned over a step angle. The existence of this linear relationship, coupled with the stepper motor only periodic error without cumulative error and other characteristics. This makes it very easy to control with stepper motors in the field of speed and position control. Although the stepper motor has been widely used, but the stepper motor can not be like ordinary DC motor, AC motor in the regular use. It must be used by the double ring pulse signal, power drive circuit control system can be used. Therefore, with a good stepper motor is not easy, it involves mechanical, electrical, electronic and computer and many other specialized knowledge. At present, the production of stepper motor manufacturers are indeed many, but with professional and technical personnel, able to develop their own, research and development of manufacturers is very little, most of the manufacturers only one, twenty people, even the most basic equipment are not. Only in a blind imitation stage. This will give the household in the product selection, the use of many problems. Signed in the above situation, we decided to take a wide range of induction sub-stepping motor as an example. Describe its basic working principle. Hope to help the majority of users in the selection, use, and machine improvement.

Two, inductor stepper motor principle

(a) reactive stepper motor principle due to reactive stepper motor working principle is relatively simple. The following first described three-phase reactive stepper motor principle.

1, structure: motor rotor evenly distributed with many small teeth, stator teeth have three excitation winding resistance, its geometric axis in turn, respectively, with the rotor tooth axis staggered. 0, 1/3 て, 2/3 て, (the distance between the axes of two neighboring rotor teeth for the distance between the teeth to て said), that is, the A and the teeth of the 1 relative Qi, B and the teeth of the 2 staggered to the right of the 1/3 て, C and the teeth of the 3 staggered to the right of the 2/3 て, A 'and the teeth of the 5 relative Qi, (A' and the tooth 5), (A' and the tooth 5), (A' and the tooth 5), (A' and the tooth 5). Relatively flush, (A' is A, tooth 5 is tooth 1) the following is the stator-rotor unfolding diagram:

2, rotating: such as A-phase energized, B, C-phase is not energized, due to the role of the magnetic field, the teeth of the 1 and A aligned, (rotor is not subjected to any force the following are the same). If the B phase is energized, A, C phase is not energized, tooth 2 should be aligned with B, at this time the rotor to the right over 1/3 て, at this time, tooth 3 and C offset for 1/3 て, tooth 4 and A offset (て-1/3 て) = 2/3 て. If C is energized, A, B phase is not energized, tooth 3 should be aligned with C. At this time, the rotor is shifted to the right by 1/3 て, at this time, tooth 4 is aligned with A offset by 1/3 て.　If the A phase is energized, B, C phase is not energized, teeth 4 and A alignment, the rotor and moved to the right over 1/3 て so that after A, B, C, A respectively energized state, teeth 4 (that is, the teeth 1 before the first tooth) moved to the A phase, the motor rotor rotated to the right over a tooth distance, if you constantly press A, B, C, A ...... energized, the motor is every step (per pulse) 1/3て,rotates to the right. If A,C,B,A...... is energized, the motor reverses. It can be seen: the position and speed of the motor by the number of conductive (number of pulses) and frequency into a one-to-one relationship. And the direction is determined by the conductive order. However, for torque, smoothness, noise and reduced angle considerations. Often use A-AB-B-BC-C-CA-A this conductive state, so that the original step 1/3 て changed to 1/6 て. Even through the two-phase current different combinations, so that its 1/3 て changed to 1/12 て, 1/24 て, which is the basic theoretical basis of the motor subdivision drive. It is not difficult to introduce: the motor stator has m-phase excitation winding resistance, its axis were offset from the rotor tooth axis 1/m,2/m ......(m-1)/m,1. And conductive according to a certain phase sequence motor can be controlled forward and reverse - this is the stepping motor rotation of the Physical conditions. As long as this condition is met, we can theoretically manufacture any phase of the stepper motor, for cost and other considerations, the market is generally two, three, four, five-phase for more.

3, torque: once the motor is energized, the stator and rotor will produce a magnetic field (flux Ф) when the rotor and stator staggered at a certain angle to produce a force F and (d Ф/dθ) is proportional to the flux Ф=Br * S Br for the magnetic density, S for the magnetically conductive area of the F is proportional to the L * D * Br L is the effective length of the iron core, D is the diameter of the rotor Br = N-I/RN-I for the excitation winding resistance ampere-turns, the number of turns of the excitation winding resistance ampere-turns. Excitation winding resistance ampere-turns (current multiplied by turns) R is the magnetoresistance. Torque = force * radius torque is proportional to the effective volume of the motor * number of ampere-turns * magnetic density (only linear state is considered) Therefore, the larger the effective volume of the motor, the larger the number of excitation ampere-turns, the smaller the air gap between the stator and rotor, the larger the motor torque, and vice versa.

(B) Induction stepping motor

1, features: induction stepping motor and the traditional reaction stepping motor, compared with the structure of the rotor with permanent magnets to provide a soft magnetic material work point, and the stator excitation only need to provide a changing magnetic field and do not have to provide the magnetic material work point of the dissipation of energy, so that the motor is highly efficient, current is small, and low heat generation. Because of the existence of permanent magnets, the motor has a strong counterpotential, and its own damping effect is better, so that it is smoother, lower noise, low-frequency vibration is small in the operation process. The inductor stepping motor can be regarded as a low-speed synchronous motor to some extent. A four-phase motor can be used for four-phase operation or two-phase operation. (A bipolar voltage drive must be used.) This is not the case with reactive motors. For example, a four-phase, eight-phase operation (A-AB-B-BC-C-C-D-CD-D-DA-A) can be completely two-phase, eight-beat operation. It is not difficult to find the conditions for C= ,D= . A two-phase motor internal winding and four-phase motor is identical, small power motors are generally connected directly to the two-phase, while the power of a larger motor, in order to facilitate the use of the motor to flexibly change the dynamic characteristics of the motor, often the external wiring for the eight leads (four-phase), so that when used, both as a four-phase motor can be used for the use of the motor can be used as a two-phase motor windings in series or in parallel.

2, classification Induction sub-stepping motor to the number of phases can be divided into: two-phase motor, three-phase motor, four-phase motor, five-phase motor. Inductor stepping motor can be divided into: 42BYG (BYG for inductor stepping motor code), 57BYG, 86BYG, 110BYG, (international standard), and like 70BYG, 90BYG, 130BYG and so on are domestic standards.

3, stepper motor static indicators term phase: the number of pairs of excitation coils to produce different poles N, S magnetic field. Commonly used m said. The number of beats: the number of pulses required to complete a periodic change in the magnetic field or the conductive state expressed in n, or the number of pulses required for the motor to rotate through a pitch angle to four-phase motors, for example, there are four-phase, four-beat operation that AB-BC-CD-DA-AB, four-phase, eight-beat operation that A-AB-B-B-BC-C-C-D-CD-DA-A. Pitch Angle: Corresponding to a pulse signal, the motor rotor rotated by the angular displacement expressed in θ. Angular displacement of the motor rotor is expressed by θ. θ=360 degrees (rotor teeth J * number of running beats), with the conventional two-phase, four-phase, rotor teeth for the 50-tooth motor as an example. Four beat operation step angle for θ = 360 degrees / (50 * 4) = 1.8 degrees (commonly known as a whole step), eight beat operation step angle for θ = 360 degrees / (50 * 8) = 0.9 degrees (commonly known as half step). Positioning torque: motor in the non-electrified state, the motor rotor's own locking torque (caused by the harmonics of the magnetic field tooth shape as well as mechanical errors) static torque: motor in the rated static electricity, the motor does not rotate when the motor rotor shaft locking torque. This torque is a measure of the size (geometry) of the motor, independent of the drive voltage and drive power supply. Although the static torque is proportional to the number of electromagnetic excitation ampere-turns, and the air gap between the stator and rotor, but excessive use to reduce the air gap, increase the excitation ampere-turns to improve the static torque is not desirable, which will cause the motor's heat and mechanical noise.

4, stepper motor dynamic indicators and terminology:

1, step angle accuracy: stepper motor every turn of a step angle of the actual value and the theoretical value of the error. Expressed as a percentage: error / step angle * 100%. The value is different for different running beats, four beats should be within 5% when running, eight beats should be within 15% when running.

2, out of step: the number of steps in motor operation, not equal to the theoretical number of steps. It is called out of step.

3, out of adjustment angle: rotor tooth axis offset stator tooth axis angle, motor operation must exist out of adjustment angle, by the error generated by the out of adjustment angle, the use of subdivided drive can not be resolved.

4, the maximum no-load starting frequency: motor in a certain drive form, voltage and rated current, in the case of no load, the maximum frequency of direct starting.

5, the maximum no-load running frequency: motor in a certain drive form, voltage and rated current, the maximum speed frequency of the motor without load.

6, running moment frequency characteristics: motor in some test conditions measured in the operation of the output torque and frequency relationship of the curve is called running moment frequency characteristics, this is the motor of many dynamic curve in the most important, but also the fundamental basis for the selection of the motor. As shown in the figure below

Other characteristics include frequency of inertia characteristics, starting frequency characteristics, etc. Once the motor is selected, the static force of the motor will be reduced. Once the motor is selected, the motor's static torque to determine the dynamic torque is not, the motor's dynamic torque depends on the average current when the motor is running (rather than static current), the larger the average current, the larger the motor output torque, that is, the motor's frequency characteristics of the more hard. As shown in the following figure:

Which, curve 3 current is the largest, or the highest voltage; curve 1 current is the smallest, or the lowest voltage, the intersection of the curve and the load is the maximum speed point of the load. To make the average current is large, as much as possible to increase the drive voltage, so that the use of small inductance and high current motor.

7, motor *** vibration point:

stepping motors have a fixed *** vibration area, two-phase, four-phase inductor stepping motor *** vibration area is generally between 180-250pps (step angle of 1.8 degrees) or in the 400pps or so (step angle of 0.9 degrees), the higher the motor drive voltage, the higher the current of the motor, the lighter the load, the smaller the motor volume, then *** vibration point. The higher the motor drive voltage, the higher the motor current, the lighter the load, the smaller the size of the motor, the *** vibration zone upward offset, and vice versa, in order to make the motor output torque is large, not out of step and the noise of the entire system to reduce the general working point should be offset *** vibration zone more. 8, motor forward and reverse control: when the motor winding energized sequence of AB-BC-CD-DA or ( ) for positive rotation, energized sequence of DA-CA-BC-AB or ( ) for reverse rotation. Third, the drive control system composed of the use, control stepper motor must be composed of ring pulse, power amplification and other control systems, the block diagram is as follows:

1, pulse signal generation.

Pulse signals are generally generated by the microcontroller or CPU, the general duty cycle of the pulse signal is 0.3-0.4 or so, the higher the motor speed, the greater the duty cycle.

2, the signal distributor (also known as pulse distributor)

Induction of sub-stepping motors to two-phase, four-phase motor-based, two-phase motor mode of operation of two-phase four-beat and two-phase eight-beat two kinds of specific allocations are as follows: two-phase four-beat, the step angle of 1.8 degrees; two-phase eight-beat, the step angle of 0.9 degrees. Four-phase motors work in two ways, four-phase four-beat AB-BC-CD-DA-AB, step angle of 1.8 degrees; four-phase eight-beat AB-B-BC-C-CD-D-AB, (step angle of 0.9 degrees). 3, power amplification power amplification is the most important part of the drive system. Stepping motor torque at a certain speed depends on its dynamic average current rather than static current (and the current on the sample are static current). The larger the average current, the larger the motor torque, to achieve a large average current which requires the drive system to try to overcome the motor's reverse potential. Therefore, different occasions to take different drive mode, so far, the drive mode generally have the following kinds: constant voltage, constant voltage series resistance, high and low voltage drive, constant current, fine fractions and so on. In order to maximize the dynamic performance of the motor, the signal distribution, power amplification composed of stepper motor drive power. Our SH series two-phase constant current chopper drive power supply with microcontroller and motor wiring diagram is as follows:

Description:

CP connects to CPU pulse signal (negative signal, low level active)

OPTO connects to CPU +5V

FREE offline, connected to CPU ground, the drive power supply does not work DIR Direction control, connected to CPU ground, motor reverse DIR Direction control, connected to CPU ground, motor reversal

VCC DC power supply positive terminal

GND DC power supply negative terminal

A connects to the motor lead red line connects to the motor lead green line

B connects to the motor lead yellow line connects to the motor lead blue line

Once a stepping motor has been finalized, its performance is dependent on the motor's drive power supply. The higher the speed of the stepping motor, the larger the force distance is, the higher the current of the motor is required, and the higher the voltage of the driving power supply. The voltage affects the torque as follows: