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 (ie, the 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.
There are three types of stepping motors: permanent magnet (PM), reactive (VR) and hybrid (HB). The permanent magnet stepping is generally two-phase, the torque and volume are small, the step angle is generally 7.5 degrees or 15 degrees; the reactive step is generally three-phase, which can achieve large torque output, and the step angle is generally 1.5. Degree, 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. Hybrid stepper motor is the most widely used 200 stepper motor and servo motor 333332 for the first time to pay attention to the 51 black electronic forum and "microcontroller tutorial network" official WeChat forum black coin reward.
Basic parameters of stepper motor:
1. Inherent step angle of the motor
It represents the angle at which the motor rotates each time the control system sends a step pulse signal. The motor is given a step angle value when it leaves the factory. For example, the 86BYG250A motor gives a value of 0.9°/1.8° (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', it is not necessarily the true step angle of the actual working of the motor, and the true step angle is related to the drive.
The general calculation of the stepping motor step angle β is usually calculated by the following formula.
β=360°/(Z•m•K)
The step angle of the β-stepping motor in the formula;
Z-number of rotor teeth;
M—the number of phases of the stepper motor;
K-control coefficient, which is the proportional coefficient of the number of beats and the number of phases
2. The number of phases of the stepper motor
It refers to the number of coil groups inside the motor. Currently, two-phase, three-phase, four-phase, five-phase stepping motors are commonly used. The number of phases of the motor is different, and the step angle is also different. Generally, the step angle of the two-phase motor is 0.9°/1.8°, the three-phase is 0.75°/1.5°, and the five-phase is 0.36°/0.72°. When there is no subdivision driver, the user mainly chooses the stepping motor with different phase numbers to meet the requirements of the step angle. If you use a subdivision drive, the 'phase number' will become meaningless, and the user can change the step angle by simply changing the number of subdivisions on the drive.
3. Hold torque (HOLDINGTORQUE)
It refers to the moment that the stator locks the rotor when the stepper motor is energized but does not rotate. 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.
DETENTTORQUE: refers to the moment that the stator locks the rotor when the stepper motor is not energized. DETENTTORQUE does not have a unified translation method in China, which is easy to misunderstand. Since the rotor of the reactive stepping motor is not a permanent magnet material, it does not have DETENTTORQUE.
Stepper motor main characteristics
1. The stepping motor must be driven to operate. The driving signal must be a pulse signal. When there is no pulse, the stepping motor is stationary. If an appropriate pulse signal is added, it will rotate at a certain angle (called the step angle). The speed of rotation is proportional to the frequency of the pulse. For example, the stepping motor has a step angle of 7.5 degrees and a 360 degree circle, which requires 48 pulses to complete.
2. Stepper motor has the superior characteristics of instant start and rapid stop.
3. Change the order of the pulses, you can easily change the direction of rotation.
Therefore, current printers, plotters, robots, and other devices are powered by stepper motors.
Stepper motor driver features
It is an ASIC that forms the stepper motor driver system:
A, pulse distributor integrated circuit: such as Sanyo's PMM8713, PMM8723, PMM8714 and so on.
B. Controller integrated circuit including pulse distributor and current chopping: such as L297 and L6506 of SGS Company.
C. Driver integrated circuits containing only power drive (or current control, protection circuit): such as MTD1110 (quadrature chopper drive) and MTD2001 (two-phase, H-bridge, chopper drive) from Japan New Electric Industrial Co., Ltd.
D. Drive controller integrated circuits including pulse distributor, power drive, current control and protection circuits, such as Toshiba's TB6560AHQ, MOTOROLA's SAA1042 (four-phase) and ALLEGRO's UCN5804 (four-phase), etc. .
“Subdivided drive” overview: Subdividing the “inherent step angle of the motor” into several small step drive methods, called subdivision drive, which is realized by the drive precisely controlling the phase current of the stepper motor, and the motor itself. Nothing. The principle is that the stator current phase current does not rise to the first position, and the power phase current does not drop to zero at one time (the winding current waveform is no longer an approximate square wave, but an N-order approximate step wave), then the stator winding current The resultant magnetic field forces the rotor to have N new equilibrium positions (forming N step angles).
