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What is the working principle of the stepper motor?

time:2019-06-11 Browse:

        Today, many friends have heard of stepper motors in their lives. When you hear them, you may be a bit confused. What is a stepper motor? What is the difference between it and the toy car motor we bought? These doubts below will let you know how the stepper motor differs from the toy motor we see in our lives. 
        

  Stepper motor structure and working principle:

 

  1. A stepper motor is an open-loop control element that converts an electrical pulse signal into an angular displacement or a linear displacement. In the case of non-overload, the speed and stop position of the motor depend only on the frequency of the control pulse signal and the number of pulses.
 

  2. The more the number of pulses, the greater the angle at which the motor rotates.
 

  3. The higher the frequency of the pulse, the faster the motor speed, but it cannot exceed the maximum frequency, otherwise the torque of the motor will decrease rapidly and the motor will not rotate.

  

Structure diagram of Stepper motor
Structural diagram of stepper motor



  The principle of generating by torque can be divided into:

  (1) Reactive type: the rotor has no winding, and the reaction torque generated by the excited stator winding realizes step operation

  (2) Excitation type: the stator and rotor have excitation windings (or permanent magnets for rotors), which are stepped by electromagnetic torque.
 

  According to the output torque size can be divided into:

  (1) Servo type: The output torque can only drive a small load in the range of a few tenths to a few tenths (N.m). It must be used with a hydraulic torque amplifier to drive a large load such as a machine table.

  (2) Power type: The output torque is above 5~50 N.m, which can directly drive large load such as machine tool table.
 

  According to the number of stators can be divided into:

  (1) Single stator type (2) Double stator type (3) Three stator type (4) Multi-stator type
 

  According to the distribution of each phase winding can be divided into;

  (1) Radial distribution: the phases of the motor are arranged in a circle

  (2) Axial distribution: the phases of the motor are arranged in the axial direction
 

  Radial distribution of the motor

The working principle of the stepper motor

  Stepper motor working principle:
 

  When the phase A winding is connected to a direct current through the direct current, the magnetic field will generate a magnetic field in the direction of AA. Under the action of the electromagnetic force of the magnetic field, the rotor is attracted to the rotor. The teeth are aligned with the teeth on the stator AA pole. If the A phase is de-energized, the B phase is energized. At this time, the electromagnetic force of the new magnetic field attracts the two poles of the rotor and the BB magnetic pole pair, and the rotor rotates 60° counterclockwise. Generally, the angle at which the rotor turns over each time the on-off state of the stepper motor winding is changed is called the step angle. If the control line keeps pressing the control circuit to continuously control the on/off of the stepper motor windings in the order of A → C → B → ..., the rotor of the stepper motor will rotate clockwise. If the power-on sequence is changed to A → B → C → A ..., the stepper motor is reversed.

  1. The above describes the working process of three-phase single-three-shot, in addition to three-phase double three-shot, three-phase six-shot and other working methods. The three-phase double three-shot power-on mode simultaneously energizes the two-phase winding: such as AB-BC-CA-AB-... The control method of three-phase six-shot is: A→AB→B→BC→C→CA→A→ ...
 

  2. The speed of the motor is related to the frequency of phase sequence switching. The faster the switch is, the faster the motor rotates. The direction of motor rotation is related to the phase sequence.
 

  3. The angle of rotation of each motor is called the step angle θ. The step angle is related to the structure of the motor. θ=360°/mzk where m is the number of phases of the stator winding. Z is the number of teeth of the rotor. K is the energization mode, when m is m-phase, k=1, m-phase is 2m, k=2.
 

 

  

  Stepper motor diagram

  Stepper motor diagram
 

 

 

 

  Stepper motor features:
 

  1. The accuracy of a general stepper motor is 3-5% of the step angle and does not accumulate. Therefore, the stepping motor can be used as a special motor for control, and is widely used in various open loop control.
 

  2. The maximum temperature allowed by the stepper motor appearance is related to the motor demagnetization point:

  If the temperature of the stepping motor is too high, the magnetic material of the motor will be demagnetized firstly, which will cause the torque to drop and even lose the step. Therefore, the maximum temperature allowed by 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 stepper motor's external temperature is completely normal at 80-90 degrees Celsius.
 

  3. The torque of the stepper motor will decrease as the speed increases.

  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.
 

  4. The stepper motor can run normally at low speed, but if it is higher than a certain speed, it can't start, and it is accompanied by howling.

  The stepper 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.

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