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How much do you know about stepper motor?

Views: 6     Author: Site Editor     Publish Time: 2023-05-06      Origin: Site Inquire

1. About the stepper motor

As a special motor for precise displacement control and large-scale speed regulation, the stepper motor rotates step by step with its own inherent step angle (determined by the mechanical structure of the rotor and stator). Its characteristic is that each step of rotation, The step angle is always constant, which can keep the precise and accurate position. So no matter how many times you rotate, there is always no quadrature error. Due to the simple control method and low cost, it is widely used in various open-loop controls. The operation of the stepper motor needs to be driven by a power electronic device with pulse distribution, which is the stepper motor driver. It receives the pulse signal sent by the control system, according to the structural characteristics of the stepping motor, distributes the pulse sequentially, and realizes the control of angular displacement, rotation speed, rotation direction, brake loading state, and free state. Every time the control system sends a pulse signal, the driver can drive the stepper motor to rotate a step angle. The speed of the stepper motor is proportional to the frequency of the pulse signal. The angular displacement is related to the number of pulses. When the stepper motor stops rotating, two states can be produced: brake loading can produce maximum or partial holding torque (usually called brake holding, without electromagnetic brake or mechanical brake) and the rotor is in a free state (can be driven by external thrust drive with easy rotation). The stepping motor driver must match the type of the stepping motor. Otherwise, the stepper motor and driver will be damaged.

2. Step angle and subdivision

The step angle of the stepping motor is the angle at which the control system sends a step pulse signal. The step angle of each motor is confirmed when it leaves the factory. It can be called "the inherent step angle of the motor". There are 0.9/1.2/1.8 etc.

The subdivision number of the driver refers to the real step angle when the motor is running, which is a fraction of the inherent step angle (full step). For example, when the driver is working in 10 subdivisions, the actual step angle is only one-tenth of the "motor's natural step angle". The subdivision function is completely generated by the stepper driver by precisely controlling the phase current of the motor, and has nothing to do with the motor.

Under the condition of constant controller pulse, the greater the subdivision, the lower the speed. For example, the controller sends out pulses of 200 pulses per second. When the subdivision is not set, it makes one revolution per second; when the subdivision is set to 4, it takes 800 pulses to make one revolution, so sending 200 pulses per second can only make a quarter of a revolution. Yes, the speed is 1/4 of the original!

3. Driver

As we know before, due to the unique structure of the stepping motor, the inherent step angle of the motor is like 0.9/1.8°, which means that the angle turned by each step is 0.9 for half-step work, and 1.8 for a full step. However, in many precision control and occasions, the angle of the whole step is too large, which affects the control accuracy, and the vibration is too large, so it is required to complete the inherent step angle of the motor in many steps. This is the so-called subdivision drive, which can realize this function. The electronic device is called a subdivision driver.

The stepper motor adopts a subdivision driver, which can eliminate the low-frequency resonance phenomenon of the stepper motor, reduce vibration, reduce working noise, and increase the output torque of the stepper motor. At the same time, the current provided to the stepper motor is "continuous and strong", which greatly reduces the back electromotive force when the stepper motor rotates, and improves the rotational displacement resolution of the stepper motor.

stepper motor drivers


4. Motor pulse

The pulse refers to a cycle of the motor coil level from high to low, or from low to high. The conversion of several cycles is a few pulses, and the frequency is the number of conversions in one second, not the number of energizations in one second. If the frequency of the pulse signal sent by the PLC is 50HZ, it means that the speed at which the stepper motor executes the number of pulses is 50 cycles in one second.

The pulse signal is the power supply of the stepping motor, which is characterized by discontinuity. Every time the stepping motor receives a pulse signal, it rotates at a certain angle, and the controller sends out a certain number of pulse signals, and the motor rotates at a certain angle. The pulse frequency is high. The motor spins fast. One is the total amount and the other is the amount per second, that's the difference.

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