The Drive Mode of Closed-loop System of Stepper Motor

For the position closed-loop control, although it can improve the precision of position and output torque in the application, yet the specific performance is direct to the drive technology and its characteristic.

In practice, the controller will send directions and pulse signals. After sending the signal, the driver will rotate the rotor of the stepper motor through a step angle. The acceleration, deceleration, start, stop of the stepper motor is related to the frequency and control pulse of the driver.

In terms of motor forward and reverse, it is determined by the controller according to the control signal of the driver. In the closed-loop system, the application of drive technology will directly affect system performance. For hybrid stepper motor, it has the characteristic of the reactive and permanent magnet stepper motor. So, in reality, it has many advantages and becomes a mainstream product.

Unipolar Bipolar Drive

For hybrid stepper motor, it needs to be powered by the way of bipolar in the actual operation. In the middle of the winding, the wire not only can’t be taken out but also can’t be driven by the application of the monopole circuit method. In the early development stage, due to the high cost of electronic devices, to simplify the structure of the driving circuit, the stepper motor uses a single-pole method to supply power to reduce cost.

For single-pole drive mode, the wire is in the middle of the motor windings, which makes windings become two parts. Having a simple driver and structure group, the motor can operate. If there are four power tubes to be used, at the same time, half of each phase can be energized.

Base on the effective reduction of windings inductance, the operation performance in high-speed can be improved. But, because only half of the windings are powered, when the stepper motor operates at medium and low speed, the output of motor torque is relatively poor.

In reality, in terms of control, the two-phase motor needs six outgoing lines, the three-phase needs nine lines, the five-phase needs 15 lines, so it has a very complex character in the actual wiring.

Frequency Rise Voltage Rise Drive

In the mode of constant voltage, the goal of the motion is to make the motor windings operate quickly. In the high-frequency condition, the current will up. But in the low-frequency condition, the performance in reverse. When the stepper motor operates in the low-frequency condition, the current of windings will up. But it will aggravate the low-frequency vibration. At this time, the windings current should have a smooth change characteristic to reduce the possibility of overshoot.

In the condition of high frequency, it is required to change the current to meet the output of torque. So, the method upconversion to rise voltage is used, that is, the driving voltage should be adjusted according to the actual working frequency of the motor. When the working frequency of the motor is high, because of the rise of the driving voltage, the output torque of the motor can be compensated in the high-frequency environment.

When the motor runs at low frequency, the low-frequency vibration can be reduced by reducing the driving voltage. Generally speaking, in the actual processing, the main method is to use an open-loop control method to the output voltage, but the voltage can’t be detected.

When the drive voltage changes, the voltage of the voltage regulator will also change accordingly, and based on the control object, the specific drive mode will be determined. In the actual processing, the windings current can better control the change of the output torque, the mainstream processing method can facilitate the operation of diver.

Constant Current Cut-wave Drive

For the drive mode, no matter what speed the stepper motor runs at, the drive mode can ensure that the current has a good performance in terms of constancy, so it can make up for the problem that in the high-speed, the output torque is lower. The key idea of the drive mode is to use closed-loop to control current. By using a current sensor to detect, the three-phase current of the motor can be detected. By changing the switching frequency and duty cycle of the power tube, the output torque can be controlled.

By using the sensor, the current loop can exert a series process on the resistor with a small resistance value. By detecting the voltage at both ends of the resistance, the loop current value can be obtained. This method has the characteristic of simple structure, but it also exits disadvantages, that is, the voltage at both ends of the resistance is affected by other factors in the application.

Compared with other driving modes, it has the following features:

First, when the stepper motor is rotating, the winding current of each phase has the characteristic of the frequent switch, and the output torque often fluctuates due to the existence of fluctuation. By using the constant current cut-wave drive mode, this problem can be solved, that is, the output of torque stabilizes in the large frequency.

Second, in the constant current cut-wave drive control, by pulse different currents can complete the goal of the voltage supply. Based on the improvement of power supply efficiency, the formation of resonance will be dampened.

Third, by the application of this method, based on the improvement of motor torque characteristics, the range of working frequency will be widened, so the motor has a stronger load capacity.