working principle:
In general, the rotor of the motor is a permanent magnet. When a current flows through the stator winding, the stator winding generates a vector magnetic field. The magnetic field will drive the rotor to rotate an angle so that the direction of a pair of magnetic fields of the rotor coincides with the direction of the magnetic field of the stator. When the stator's vector magnetic field rotates an angle. The rotor also turns an angle with the magnetic field. Each time an electric pulse is input, the motor rotates an angle forward. The angular displacement it outputs is proportional to the number of input pulses and the speed is proportional to the pulse frequency. By changing the order in which the windings are energized, the motor will reverse. Therefore, the number of control pulses, the frequency, and the sequence of energization of the motor phases can be used to control the rotation of the stepper motor.
Heating principle:
Commonly seen types of motors have iron cores and winding coils inside. Windings have resistance, and power will produce losses. The loss is proportional to the square of the resistance and current. This is the copper loss we often say. If the current is not a standard DC or sine wave, it will also produce harmonic losses; the core has hysteresis. The eddy current effect also produces losses in an alternating magnetic field. Its magnitude is related to material, current, frequency, and voltage. This is called iron loss. Both copper loss and iron loss are manifested as heat, which affects the efficiency of the motor. Stepping motors generally seek positioning accuracy and torque output, the efficiency is relatively low, the current is generally large, and the harmonic components are high, the frequency of the current alternating changes with the speed, so the stepper motor generally has a heating condition, and the situation is more general Severe AC motor.
Stepper motor use Stepper motor is a kind of special motor for control. As an actuator, it is one of the key products of mechatronics. With the development of microelectronics and computer technology (the performance of stepper motor driver is improved), the demand of stepper motor is required. Increasing day by day. The precision of stepping motor does not accumulate errors during operation, making it widely used in various automatic control systems, especially open-loop control systems. 
Stepper Motor Structure Classification
Stepper motors are also called pulse motors, including reactive stepper motors (VR), permanent magnet stepper motors (PM), and hybrid stepper motors (HB).
(1) Reactive stepping motor:
Also called inductive, hysteresis or reluctance stepper motors. The stator and the rotor are made of soft magnetic material. The large magnetic poles uniformly distributed on the stator are equipped with multi-phase excitation windings, and the stator and rotor are uniformly distributed around the small teeth and slots. After the power is applied, the torque is generated by the change of the magnetic permeability. Generally three, four, five, six phases; can achieve large torque output (power consumption is greater, the current up to 20A, high drive voltage); step angle is small (minimum can be achieved by one-sixth) There is no detent torque when power is off; the internal motor has less damping, single-step operation (referring to when the pulse frequency is very low) has a longer oscillation time; startup and operation frequency is higher.
(2) Permanent Magnet Stepper Motors:
Usually, the rotor of the motor is made of permanent magnetic material. The stator made of soft magnetic material has multi-phase excitation windings. There are no small teeth and slots around the stator and rotor. After the power is applied, the permanent magnets interact with the stator current magnetic field to generate torque. Generally two or four phases; output torque is small (power consumption is small, current is generally less than 2A, drive voltage is 12V); step angle is large (for example, 7.5 degrees, 15 degrees, 22.5 degrees, etc.); it has a certain degree of power failure The holding torque; startup and operating frequency is low.
(3) Hybrid stepper motor:
Also called permanent-magnet reaction type, permanent-magnet induction stepper motor, it combines the advantages of permanent magnet type and reactive type. There is no difference between the stator and the four-phase reaction stepping motor (but the two poles of the same phase oppose each other, and the polarities of the N and S generated by the windings of the two poles must be the same), and the rotor structure is more complicated (the inside of the rotor is cylindrical and permanent. Magnet, both ends of the jacket soft magnetic material, surrounded by small teeth and grooves). Generally two-phase or four-phase; positive and negative pulse signals must be supplied; output torque is larger than permanent magnet type (power consumption is relatively small); step angle is smaller than permanent magnet type (usually 1.8 degrees); when there is no power Positioning torque; high starting and running frequency; it is a kind of stepper motor that develops quickly.
2, stepper motor according to the way of work
(1) Power type: The output torque is large and can directly drive a large load (usually a reactive, hybrid stepper motor).
(2) Servo type: The output torque is small and can only drive a small load (usually a permanent magnet type, hybrid stepper motor).
Produced by STMicroelectronics, the chip is relatively old, with a maximum of 16 subdivisions.
Control interface: parallel port.
Advantages: large drive current.
Disadvantages: The chip is older and has the possibility of stopping production; the circuit is slightly more complicated; and the program control is slightly more complicated.
2.A4988ALLEGRO company production, this company is still very famous for stepper motor driver IC, small package, such as QFN/LQFP; in small instruments, power requirements can be used. A4988 official manual describes the drive current can reach 2A, but in actual use, with 24V power supply, 1A current has been very hot, if you reach 2A current, it is estimated that a good cooling system. The A4988 supports 2, 4, 8, and 16 subdivisions.
Control interface: step/direction
Advantages: simple circuit; simple control; cheap price.
Disadvantages: Test the use of the process, always baffling chip, did not find the problem, the back of the product is not used again; drive current is small, suitable for 42 or less stepper motor.
3.DRV8825Texas Instruments (TI) company, analog device overlord, motor series (step motor, brush motor, brushless motor, etc.) chip a lot, is still good. The overall performance of the DRV8825 is similar to that of the A4988. The subdivision supports 2, 4, 8, 16, and 32 subdivisions. It may be related to the wiring or program control, the noise is very large, and the back product is not used.
Control interface: step/direction
Advantages: simple circuit, simple program control.
Disadvantages: Small drive current and high noise (maybe related to PCB layout).
4. TMC246/TMC249The TRINAMIC company, a German company, specializes in motor-driven chips. The German-made products are really good. 246 is a built-in mos tube, 249 external mos tube, the two control programs are fully compatible, but the circuit difference is relatively large. High demand can be considered, the price is more expensive, the same kind of driver chip is the highest, of course, performance is also basic, as to how to use, who knows who!
Control Interface: SPI
Advantages: simple circuit; simple program control; very high efficiency, 246 built-in mos tube, small heat; 249 external mos tube can drive high current motor; low noise, smooth motion.
Disadvantages: expensive; wiring requirements are high, hardware engineers design are designed 4 layer board;
5. TMC260/TMC2660/TMC262TRINAMIC company, the company's new series of models, all aspects of performance have improved, such as greater drive current, higher subdivision, maximum support 256 subdivision (but such high subdivision is not very useful in general situations), etc. . If the TMC Series is recommended for use with the TMC Series, the price is relatively inexpensive; the TMC262, which requires high power, is an external mos tube and the control program is fully compatible.
Control interface: step/direction and spi, only spi can be used, related configuration parameters can only use spi. The method used by the deaf person is to control the step/direction of the motor and configure the spi bus for the parameters.
Advantages: large drive currents, smooth motion (but not feeling good with TMC246 and 249, possible wiring problems?), the price is actually cheaper than 246 and 249.
Disadvantages: expensive, wiring a little troublesome.
6.L6470Produced by STMicroelectronics (ST), ST New Products. I have not used it. My colleagues have used it for testing. From the manual, it is quite powerful, with high current (peak current 7A), built-in speed curve, hardware origin, etc. Those interested can go to test.
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