Stepper motor design reference scheme
This module can be divided into the following three parts:
·Single chip microcomputer system: control stepping motor;
·Peripheral circuit: interface circuit between PIC MCU and stepping motor;
·Pic program: write the interface program of single chip microcomputer controlling} stepping electric power machine to realize the output function of triangular wave signal.
(1) Interface between stepping motor and single chip microcomputer.
Single chip microcomputer is a control processor with excellent performance. When controlling the operation of stepping motor, the interface components must have the following functions.
① Voltage isolation function.
Single chip microcomputer works at 5V, while stepping motor works at dozens of V or even higher. Once the voltage of the stepping motor is connected to the single chip microcomputer, the single chip microcomputer will be damaged; The signal of stepper motor will interfere with the single chip microcomputer and may also lead to system error. Therefore, the interface device must have isolation function.
② Information transmission function.
The interface component shall be able to transfer the control information of the single chip microcomputer to the stepper motor circuit to generate the control information required for operation. Corresponding to different working modes, the interface component shall be able to generate corresponding working control waveform.
③ Generate the required different frequencies.
In order to make the stepping motor work at different speeds to adapt to different purposes, the interface components shall be able to produce different working frequencies.
(2) Voltage isolation interface.
The voltage isolation interface is specially used to isolate the single chip microcomputer of the low-voltage part and the stepping motor driving circuit of the high-voltage part to ensure their normal operation.
The voltage isolation interface can use pulse transformer or photoelectric isolator, which is basically used now. The output signal of single chip microcomputer can be directly sent to the base of transistor through TTL gate circuit, and then the transistor drives the light-emitting diode of photoelectric coupling device.
The light of the LED shines on the photosensitive tube inside the optocoupler, converts it into an electrical signal, and then drives the power amplification circuit of the stepping motor. The current amplification interface is the pre amplification circuit of the power amplification circuit of the stepping motor. Its function is to amplify the output signal of the photoelectric isolator, so as to provide enough driving current to the power amplifier circuit.
(3) Working mode interface and frequency generator.
To control the stepping motor with single chip microcomputer, three I / 0 lines need to be used on the input and output interface to control the stepping motor. At this time, the single chip microcomputer uses Ra0, rai and ra2 of I / O port to control the three phases of the stepping motor.
The control mode of stepper motor is generally divided into open-loop control and closed-loop control. The simplest control mode of open-loop control stepper motor is Ding loop control system. Under this control mode, the input of stepper motor control pulse does not depend on the position of rotor, but sends out control pulse according to a fixed law, The stepper motor only depends on this series of established pulses. This control mode is more suitable for controlling the stepper motor due to the uniqueness of the stepper motor and is suitable for the national conditions of our country. The characteristics of this control mode are: simple control, easy implementation and low price. This control mode, especially in open-loop control, has no feedback on the load position to the control circuit.
Therefore, the stepping motor must accurately respond to each excitation change. If the excitation change is too fast and the motor cannot move to a new position, there will be a deviation between the actual load position and the ideal position. When the load is basically unchanged, the generation of control pulse sequence is relatively simple, but when the load change may be large, The generation of control pulse sequence is difficult to take care of comprehensively, and there may be out of step and other phenomena. At present, with the popularization of microcomputer application, relying on microcomputer, the generation of control pulse sequence of some more complex stepping motors can be realized.