The stepping motor is a special motor used for control. Its rotation is operated step by step at a fixed angle (called "step angle"). It is characterized by no accumulation error (accuracy is 100%), so it is widely used. Used in a variety of open loop control. The operation of the stepping motor is driven by an electronic device. This device is a stepping motor driver, which converts the pulse signal from the control system into the angular displacement of the stepping motor, or, for each pulse signal sent by the control system. The stepper motor is rotated one step angle by the drive. Therefore, the speed of the stepper motor is proportional to the frequency of the pulse signal. Therefore, controlling the frequency of the stepping pulse signal can accurately adjust the speed of the motor; controlling the number of stepping pulses can accurately position the motor. When the stepping motor is driven by the subdivision driver, the step angle becomes smaller. For example, when the driver works in the 10 subdivision state, the step angle is only one tenth of the "inherent step angle of the motor", that is to say, When the driver works in the whole step state without subdivision, the control system sends a step pulse every time, the motor rotates 1.8°; while the subdivision driver works in the 10 subdivision state, the motor only rotates 0.18°, which is The basic concept of subdivision. The subdivision function is completely generated by the drive by precisely controlling the phase current of the motor, independent of the motor.
The main advantage of the driver subdivision is that the low frequency oscillation of the motor is completely eliminated. Low-frequency oscillation is an inherent characteristic of stepper motors (especially reactive motors), and subdivision is the only way to eliminate it. If your stepper motor sometimes needs to work in the resonance zone (such as arcing), select the subdivision driver. Is the only choice. The output torque of the motor is increased. Especially for a three-phase reactive motor, the torque is increased by about 30-40% compared to when it is not subdivided. Improve the resolution of the motor. It is self-evident that the resolution of the motor is improved by reducing the step angle and increasing the uniformity of the step.
The above is the basic principle of the stepper motor. Next, it summarizes the design and selection experience of the stepper motor drive:
Select holding torque (HOLDINGTORQUE)
The holding torque is also called the static torque, which refers to the moment that the stator locks the rotor when the stepping motor is energized but does not rotate. Since the torque of the stepping motor at low speed is close to the holding torque, the torque of the stepping motor is rapidly attenuated as the speed increases, and the output power also changes with the increase of the speed, so the holding torque is a measure of the stepping. One of the most important parameters of the motor load capacity. For example, the stepping motor of 1N.m is generally mentioned without explanation, and it can be understood that the holding torque is 1N.m.
Select the number of phases
The two-phase stepping motor has low cost, the step angle is at least 1.8 degrees, the vibration at low speed is large, the torque is fast at high speed, and it is suitable for high speed and low precision and stability requirements; three-phase stepping motor step The angle is at least 1.5 degrees, the vibration is smaller than the two-phase stepping motor, and the low speed performance is better than the two-phase stepping motor. The maximum speed is 30 to 50% higher than that of the two-phase stepping motor, which is suitable for high speed and accuracy and stability requirements. In higher occasions, the 5-phase stepping motor has a smaller step angle, and the low-speed performance is better than that of the 3-phase stepping motor, but the cost is high, which is suitable for the middle and low speed sections and requires high precision and stability.
Select stepper motor
The principle of selecting the motor after selecting the motor should be followed, firstly, the load characteristics should be clearly defined, and then the static torque and the torque frequency curve of the different types of stepping motors can be compared to find the stepping motor that best matches the load characteristics; when the precision requirement is high, the machine should be used. Deceleration device to make the motor work in the highest efficiency and lowest noise state; avoid working the motor in the vibration zone, if necessary, by changing the voltage, current or increasing the damping; in terms of power supply voltage, it is recommended that the motor be DC 24V- 36V, 86 motor adopts DC 46V, 110 motor adopts higher than DC 80V; large inertia load should select motor with larger frame number; when high inertia load and working speed are higher, the motor should adopt gradually increasing frequency to increase speed. Prevent motor out of step, reduce noise, improve positioning accuracy when stopping; in view of the stepper motor torque is generally below 40Nm, beyond this torque range, and the running speed is greater than 1000RPM, you should consider the choice of servo motor, general AC servo motor can Normal operation at 3000RPM, DC servo motor can run normally at 10000RPM.
Select drive and subdivision
It is best not to choose the whole step state, because the vibration is larger in the whole step state; try to choose a small current, large inductance, low voltage driver; use a driver larger than the working current, and use subdivision when low vibration or high precision is required. Type driver, high-voltage type driver for high-torque motor to obtain good high-speed performance; in the case where the actual motor speed is usually high and the accuracy and stability are not high, it is not necessary to select a high-dividing number driver. In order to save costs; in the condition that the actual running speed of the motor is usually very low, a large number of subdivisions should be selected to ensure smooth operation and reduce vibration and noise. In short, when selecting the subdivision number, the actual operation of the motor should be considered comprehensively. Speed, load torque range, gearbox settings, accuracy requirements, vibration and noise requirements.
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