Introduction to the closed-loop control system of stepper motor

1. The closed-loop control of the stepper motor was first in the form of encoder

For stepper motors with low split rate, a slotted disc and photoelectric sensor are usually used as the assembly of the reaction encoder, and the number of slots is equal to the number of steps taken by the motor per revolution· for high-resolution stepper motors, high-resolution incremental encoders need to be selected, such as resolver incremental encoders, inductive synchronizer incremental encoders, etc.

Due to the high price of the reactive encoder and the need for a larger volume of the system in order to place the encoder on the axis of the stepper motor, these two major shortcomings constrain the application of the closed-loop control system of the stepper motor in the form of encoder.

In the initial state, the system is stationary by one or several phases of excitation, after starting to work, the target direction is first sent to the subtraction counter, and then, the "start" pulse signal is added to the control unit, and the control unit immediately sends the step instruction to the phase sequence generator under the effect of "starting pulse", so that the excitation changes once, and the subsequent pulse is generated by the encoder device.

Every time the encoder occurs - a pulse, the counter is minus 1, therefore, the subtraction counter records the rotor orientation of the practice, when the count of the subtraction counter is reduced to zero, a stop signal is announced to the control unit, stopping future stepping instructions, and the system stops working.

Introduction to the closed-loop control system of stepper motor

Introduction to the closed-loop control system of stepper motor

2. Closed-loop control system of stepper motor using current detection

Closed-loop operation of stepper motors with current detection is based on the concept that the phase current of some reactive stepper motors exhibits positive or negative extremes over a certain rate range. When the phase current presents an extreme value, a pulse or punctual signal occurs instantaneously in the peak detection line, which is reflected to the control unit as a follow-up pulse to complete the closed-loop control of the stepper motor.

It is worth noting that the conduction phase current and cut-off phase current of the motor may present if there are thousands of peaks, which state should be detected, which can be determined according to the practical operation of the motor, the current detection can be completed by piercing a small resistance with a known resistance value in the current loop, measuring the voltage of the current passage period, the peak detection circuit generally uses the analog differential method, and the peak is indicated by the zero value of di/t.

3. Closed-loop control system of stepper motor in the form of waveform detection

The principle of the stepper motor closed-loop control system in the form of waveform detection is to indirectly obtain the rotor orientation information through the detection of the phase current of the stepper motor or the winding back EMF (or the current caused by the winding back EMF), which reacts to the control pulse of the control unit and controls the movement of the stepper motor.

The waveform detector is composed of a simple electronic circuit, which is inexpensive, and can be installed directly in the logic circuit of the controller if required, and the stepper motor does not need additional mechanical connection.

Introduction to the closed-loop control system of stepper motor

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