DC motor has wide speed range and smooth stepless speed regulation. The duty cycle of PWM pulse signal is used to determine the average voltage output to DC motor. By adjusting the duty cycle, the output voltage can be adjusted continuously. In this paper, AT89S51 microcontroller as the core, based on the DC motor speed control and speed measurement system design, and then gives the main circuit structure of the system, as well as the drive circuit design and system software design. This scheme makes full use of the advantages of single chip microcomputer and has the characteristics of high frequency and fast response. DC motor is a common driving equipment in industrial production, which has good starting and braking performance. In the early days, the control of DC motor was based on analog circuit, which was composed of operational amplifier, nonlinear integrated circuit and a few digital circuits. The hardware part of the control system is complex, single function and difficult to debug. This scheme adopts single chip microcomputer control system, so that many control functions and algorithms can be completed by software technology, which provides greater flexibility for the control of DC motor and makes the system achieve higher performance.
The main circuit design of speed regulation and speed measurement system
The whole system is composed of input circuit, PWM modulation, speed measuring circuit, driving circuit, control part and display part. AT89S51 single chip microcomputer is selected for PWM modulation, and frequency and duty cycle are adjusted by software. The drive circuit is isolated and protected by optocoupler. The control part is composed of single chip microcomputer and peripheral circuit to realize various control requirements. The peripheral circuit mainly completes the acquisition, operation and speed control of input signal. The display part adopts four bit common positive nixie tube.
In terms of hardware, STC89C51 single chip microcomputer is used as the core, and the minimum system is composed of reset circuit, crystal oscillator circuit, driving circuit, speed measuring circuit, keyboard and LED display module. In software, PWM pulse signal output, keyboard and LED display data transmission are generated by programming with C51 language. Through the keyboard to adjust the given value of speed gear, it can track according to the given value and display it on the LED display. Finally, the single chip microcomputer outputs PWM pulse signal. The speed is fed back to the CPU through the speed measuring circuit, and the speed is displayed on the LED display through the CPU, so as to achieve the desired speed.
Design of DC motor drive circuit
At present, most of the 12V DC motor is driven by H-bridge. In order to make it easier, the driving module uses optocoupler to isolate the control circuit from the main circuit, so as to achieve protection. U3 outputs PWM control signal to drive the motor in reverse phase through triode to realize the speed regulation of the motor. The driving circuit diagram is shown in Figure 3.
Design of speed measuring circuit
The speed measurement module is composed of U-type photoelectric switch, turntable and peripheral circuit. When the motor rotates, it drives the turntable to rotate. There are eight small holes on the turntable. When the turntable rotates for one circle, eight pulse signals are generated. Thus, the physical quantity of the motor can be converted into the changing pulse signal, which is transmitted to the external interrupt p3.3 of the single chip microcomputer for counting, Realize the monitoring of motor speed. The speed measuring circuit is shown in Figure 4.
The common photoelectric speed measurement method is used in the design. The specific method is to fix a disk on the motor shaft and use the U-type optocoupler in the speed measurement module. Through the eight round holes on the turntable, a pulse signal is generated. When the motor turns to the hole, the LED irradiates the light to the photosensitive triode through the gap, and the triode turns on, otherwise the triode turns off. The installation of U-type photoelectric switch and turntable is shown in Figure 5: fix the turntable on the rotating shaft of the motor, install the U-type optocoupler, insert the optocoupler into the turntable, fix it with screws, and install the turntable side in the middle of the slot of the U-type photoelectric switch.
The design of speed measurement and speed control system based on single-chip microcomputer control of DC motor is that the input signal is converted by single-chip microcomputer, the output control signal is adjusted by the drive circuit, and the speed of DC motor can be monitored in real time. Because PWM control technology is used, high precision speed control can be achieved. The photoelectric switch is used in speed measurement to realize speed detection easily. Therefore, the speed measurement and speed control system of DC motor designed in the scheme has the main circuits of speed input, detection, display, pulse width modulation, motor drive, etc., which is convenient for the control and display of motor speed.