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51 SCM Proportional Electromagnet Control Technology

Proportional electromagnets as actuators are one of the key products of electromechanical integration. They are widely used in various automation control systems. Proportional electromagnets have large thrust, simple structure, convenient maintenance, and low cost, and are widely used in electric appliances. Mechanical converter [1]; Proportional electromagnet characteristics and working reliability, has a very important impact on the entire control system, is one of the key components to determine the quality of the control system. The proportional electromagnet acts as an electro-mechanical conversion element whose function is to convert the current signal delivered by the proportional control amplifier to a displacement or force signal output.
Proportional electromagnets are used in control circuits with 24 V DC proportional control amplifiers as power components that continuously and proportionally control the movement, speed and direction of the system's actuators. The proportional electromagnet's thrust within its rated travel range is proportional to the current flowing into its coil. It can be used as a linear power element on other devices that require automatic control of force, such as automatic throttle control. When the electromagnet and the single-chip microcomputer form an automatic control system, the design of the interface circuit between the single-chip microcomputer and the proportional electromagnet is a key because the operating voltage of the electromagnet is relatively high and the operating current is large.
With the development of microelectronics and computer technology, the demand for proportional electromagnets is increasing day by day, and there are applications in various control fields. The following describes the proportional solenoid control technology.
1 PWM Driver Basics and Features
PWM (Pulse Width Modulation, Pulse Width Modulation) technology is the use of semiconductor switching devices on and off, the DC voltage into a voltage pulse train, and by controlling the voltage pulse width and pulse train cycle to achieve voltage conversion, frequency conversion purposes A control technique [2]. That is, a series of equal-amplitude rectangular pulses with different pulse widths are used to approximate a desired current or voltage signal.
The PWM drive circuit is a drive form widely used in high-precision control systems. This circuit enables a wide range of speed and position control, providing unparalleled advantages over conventional drive methods. The PWM drive circuit has the advantages of simple circuit, high speed, good linearity, and high efficiency, making it widely used in many fields of measurement, communication, power control and conversion. This design uses the PWM drive circuit requires low power controllable devices, wide speed range, good fast, high efficiency, low power consumption, the PWM signal directly output by the C8051F005 microcontroller through the drive circuit, and then with the appropriate control The algorithm (PID algorithm or fuzzy control algorithm, etc.) to control the proportional electromagnet can realize the precise control of the clutch, and has a good reference value for the research of the electronically controlled clutch control system.
2 proportional solenoid and microcontroller interface circuit
2.1 MCU Overview
The single-chip microcomputer used in this control system is the C8051F005 single-chip microcomputer [3] introduced by Silabs of the United States. It is a fully integrated mixed-signal system-level MCU chip with a true 12-bit multi-channel ADC, a programmable gain amplifier, two 12-bit DACs, two voltage comparators, a voltage reference, and one 32 KB Flash memory and 8051-compatible microcontroller core, hardware-implemented (not bit-operation analog in user software) I2C/SMBus, UART, SPI serial interface and 1 capture/compare module with 5 Programmable Counter/Timer Array (PCA), as well as 4 general-purpose 16-bit timers and 4-byte wide general-purpose digital I/O ports. The C8051F005 has 2 304 bytes of RAM and an execution speed of 25 MIPS. It features on-chip VDD monitor, WDT, and clock oscillator. It is a truly on-chip system that can effectively manage analog and digital peripherals. Flash memory also has system reprogrammability that can be used for nonvolatile data storage and allows 8051 firmware to be updated on site. The MCU can turn off any or all peripherals to reduce power consumption.
The C8051F005 type microcomputer can work with a voltage of 2.7 to 3.6 V within the industrial temperature range (-45 to +85 °C). The port I/O, RST, and JTAG pins all accept a 5 V input signal voltage.
2.2 PWM signal output and proportional solenoid drive circuit
The C8051F005 MCU has an on-chip programmable counter/timer array PCA. The PCA includes a dedicated 16-bit counter/timer time reference and five programmable capture/compare modules. The time base clock can be one of the following four clock sources: system clock/12, system clock/4, timer 0 overflow, or external clock input (ECI).
Each capture/compare module has its own I/O line (CEXn line). When it is allowed to work, the CEXn line is connected to a pin of the port through the function selection switch. Each capture/compare module has four operating modes: edge-triggered capture, software timer, high-speed output, and pulse width modulation (PWM). The I/O and external clock inputs of the PCA capture/compare module can be connected to the MCU's port I/O pins through digital crossbars.
The 8-bit PWM signal (variable duty cycle) output by the PCA is as follows:
$ include (c8051F005.inc)
ORG 0000H
LJMP MAIN
ORG 0073H; Timer 3 interrupt entry
LJMP INTERT33
MAIN:
MOV WDTCN, #0DEH; Disable Watchdog Timer
MOV WDTCN, #0ADH
MOV OSCICN, #84H; Select Internal Oscillator at 12 MHz
MOV XBR0, #08H; select CEX0 pin to connect to P0.0
MOV XBR2, #40H; Allow Function Select Switch
ORL PRT0CF, #00000001B; Select P0.0 as push-pull
MOV TMR3RLL, #0B0H; Assign initial value to timer 3 low byte
MOV TMR3RLH, #0A0H; Assign the initial value to the high byte of timer 3
MOV PCA0CPH0, #0FFH; to PCA capture module high byte initial value
MOV PCA0CPL0, #0FFH; to PCA capture module low byte initial value
MOV PCA0MD, #08H; Select PCA clock source as system clock, disable CF interrupt
MOV PCA0CPM0, #42H; Select 8-bit pulse width modulation output method and start the start
MOV PCA0CN, #40H; Allows PCA to work
MOV IE, #080H; CPU open interrupt
MOV EIE2, #1; T3 open interrupt
MOV TMR3CN, #00000110B; Start T3 operation, T3 use system clock source
SJMP $
INTERT33:
MOV A, TMR3CN; Clear T3 Flag TF3
ANL A, #7FH
MOV TMR3CN, A
DEC PCA0CPH0; Change in duty cycle
RETI
According to the system design requirements, PWM signals with different duty cycles can be obtained by modifying PCA0CPH0.
This control system adopts PCA of C8051F005 one-chip computer to realize the PWM output of 8-bit resolution by software. The PWM signal is connected to the MCU's port I/O pin through the CEXn line by the function selection switch. The PWM output signal drives the proportional solenoid through the drive circuit. The module capture/compare registers PCA0CPLn and PCA0CPHn store the PWM output signal duty cycle high time value. If you need to change the duty cycle, you can change the value of PCA0CPHn during operation. The proportional solenoid's push rod displacement is proportional to the value of PCA0CPHn.
In the driving circuit, the PWM output voltage signal needs to be converted into a proportional electromagnet control current signal, and a better proportional characteristic relationship must be ensured. Using the transfer characteristic of the FET [4], when the voltage VDS between the drain and the source of the FET remains constant, the relationship between the drain current ID and the gate-to-source voltage VGS is called the “transfer characteristic”.
The control circuit uses a high-power field-effect transistor, the IRL3803, whose current output is sufficient to drive the proportional solenoid. IRL3803's drain current ID and gate-source voltage VGS have a good linear relationship, the gate and the P0.0 port of the C8051F005 microcontroller (the PWM signal output pin selected by the software programming PCA), the IRL3803 drain and proportion Electromagnets are connected. In this circuit, the proportional solenoid is the GP80, which has a rated suction force of 120 N, a stroke of 8 mm, and a rated voltage of 24 V.
During control, the magnitude of the control current is achieved by changing the "duty cycle" of the electrical signal input to the proportional solenoid switch. The greater the duty cycle, the greater the control current through the solenoid coil and the greater the displacement of the control output.
Proportional solenoid drive circuit shown in Figure 1. In the driver circuit, R1 is a current limiting resistor that allows the IRL3803 tube to conduct; D1 is a steering diode that provides the correct voltage polarity to the IRL3803 tube; the diode D2 acts as a protection against damage to the proportional solenoid during overvoltage. The proportional solenoid is powered directly from the 24 V voltage.
Conclusion
The C8051F005 microcontroller has a high degree of integration and few peripheral circuits. Its high-speed execution instruction features can precisely control the proportional electromagnet. The C8051F005 core is compatible with the common 51 series, and the instruction is easy to learn, which can shorten the system development cycle. Proportional electromagnets have been widely used as electromechanical switching devices. The proportional electromagnet control system based on the C8051F005 single-chip microcomputer can meet the requirements of high precision and good stability. The hardware circuit is simple and reliable. In the application system, a fixed duty cycle or variable duty cycle PWM signal is output directly from the I/O port of the single-chip microcomputer according to needs, and is matched with a certain control algorithm. The software programming is clear and easy to implement, and has a very good promotion value.

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