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What are the classification and characteristics of stepper m

time:2019-06-11 Browse:


  What are the classification and characteristics of stepper motors?


  As the importance of controlling motors increases, the amount of control motors used increases year by year. The stepping motor is a kind of control motor, and the speed control and positioning control can be performed without using the feedback loop, so-called motor open loop control.

  Its application is mainly based on OA machines and FA machines with strong office business capabilities, and is widely used in medical equipment, measuring instruments, automobiles, game consoles, etc. In terms of quantity, the 0A machine application accounts for about 75% of the total number of stepper motors.

  一、Classification of Stepper Motors


The classification of stepper motors

Classification of Stepper Motor

  There are various classification methods for motors. For example, when driving by voltage type, there are AC drive and DC drive. When the relationship between rotary speed and power frequency is classified, there are synchronous motor and asynchronous motor.

  The following figure shows the positional relationship of the stepper motor in the small motor series.

  As can be seen from the above figure, the stepping motor is a DC-driven synchronous motor, but it cannot be directly driven by DC or AC power. It needs to be equipped with a driver. Therefore, the operation of the stepper motor requires a drive circuit. This is the same as the brushless DC motor. The brushless DC motor uses a drive circuit that connects the motor stator to the DC power supply.

  二、Characteristics of Stepper Motor

  The basic characteristics of a stepper motor include the static characteristics of the motor, continuous motion characteristics (dynamic characteristics), motor starting characteristics, and motor braking characteristics (transient characteristics). The following are introduced separately:

  1. Characteristics of Static Torque

  When the coil of the stepping motor is through direct current, the relationship between the electromagnetic torque of the loaded rotor (the recovered electromagnetic torque generated by balancing the load torque is called static torque or static torque) and the rotor power angle is called angle-still. Torque characteristics, this is the static characteristics of the motor. As shown below:

  Since the rotor is a permanent magnet and the resulting air gap magnetic density is sinusoidal, the theoretical static torque curve is a sine wave. This angle-stationary torque characteristic is an important indicator of the ability of the stepping motor to generate electromagnetic torque. The larger the maximum torque, the better, and the closer the torque waveform is to the sinusoid, the better. In fact, there is cogging torque under the magnetic pole, which causes the combined torque to be distorted. For example, the cogging torque of the two-phase motor is 4 times harmonic of the static torque angle period, and is added to the sinusoidal static torque. The torque shown is:


  Wherein TL and TM each represent a load torque and a maximum static torque (or a holding torque), and the corresponding power angles are θL and θM, and the change of the displacement angle determines the positional accuracy of the stepping motor. According to the above formula:


  The step angle θs of the PM permanent magnet stepper motor and the HB hybrid stepping motor is described in the previous lesson: θs=180°/PNr, and the angle is changed to the mechanical angle (radian), then it becomes:


  The above formula Nr is the number of rotor teeth or the number of pole pairs, so the two-phase motor θM = θs.


  2. Characteristics of Dynamic Torque

  Dynamic torque characteristics include drive pulse frequency-torque characteristics and drive pulse frequency-inertia characteristics.

  1) Pulse frequency-torque characteristics

  The pulse frequency-torque characteristic is an important feature of the stepper motor. As shown in the figure below, the vertical axis is the dynamic torque, the horizontal axis is the response pulse frequency, and the response pulse frequency is expressed in pps, that is, the number of pulses per second.
  Stepping motor pulse frequency-torque characteristic
  As shown, the dynamic torque generation of the stepper motor includes two factors: pull-out-torque and pull-in-torque. The former is called out-of-step or lost torque, and the latter is called starting or pulling torque. The pull-in torque range is from zero to the maximum self-start pulse frequency or the maximum self-start frequency range. The area enclosed by the curve is called the self-starting area. The motor synchronously starts the forward and reverse start operation, and is the running zone between the pull-in and the out-of-step zone. The motor can run synchronously with the corresponding load in this zone. The load torque outside the range will not run continuously, and the step-out phenomenon will occur. . The stepping motor is open-loop drive control, and there is a margin between the load torque and the electromagnetic torque, and the value should be 50%~80%.


 Pulse frequency-torque characteristics

Pulse Frequency-Torque Characteristics of Stepper Motor


  2) Pulse frequency-inertia characteristic

  Stepper motors must have sufficient starting acceleration when starting with inertia loads. Therefore, if the inertia of the load increases, the starting pulse frequency decreases. For this reason, both of them should be considered comprehensively when selecting the stepping motor.



       The vertical axis of the figure below shows the maximum self-starting frequency, the horizontal axis is the load inertia, and the curve shows the relationship between the load inertia and the maximum self-starting pulse frequency. Here, a PM type claw pole stepping motor (two phases, step angle 7.5°) is taken as an example. Under the load PL, the relationship between the maximum self-start pulse frequency PL and the load inertia Jc is as follows:

  In the formula, JR stepper motor rotor inertia, Ps is the maximum self-starting frequency of no-load.

  3. Characteristics of transient torque 

  Due to the inertia of the stepper motor, even if the idler runs one step, it will produce an over-shoot and oscillate back and forth between the overshoot and the under-shoot. After the sorrow, it will be at a fixed angle. This is the transient response characteristic of the stepper motor.

  The figure below shows the transient characteristics of a stepper motor. The vertical axis takes the rotor movement angle and the horizontal axis takes the time. ΔT is the rise time, Δθ is the overshoot angle, and the time when the rotor is free to rest to the set position (usually the time to reach the error range of 5% of the step angle) is called the setting time.

  The shorter the settling time, the faster the speed. In order to speed up the operation of the mechanism and shorten the settling time, the damping (braking) of the stepping motor becomes important. The method of shortening the stabilization time includes changing the friction or changing the inertia drive, etc., which will be described in detail later.



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