The use of compressed air to promote the movement of multiple groups of combined pneumatic pistons in the actuator, the transmission of force to the beam and the characteristics of the inner curve track, drive the hollow core spindle for rotational movement, compressed air gas disk transmission to each cylinder, change the position of the inlet and outlet air to change the direction of rotation of the spindle, according to the load (valve) the required rotational torque requirements, the number of cylinder combinations can be adjusted to drive the load (valve) work.
Two-position five-way solenoid valve is usually used with double-acting pneumatic actuator, two positions are two controllable: on - off, five-way is a five-channel ventilation, of which one is connected to the air source, two with the double-acting cylinder of the external air chamber inlet and outlet connection, two with the internal air chamber inlet and outlet connection, the specific working principle can be referred to the double-acting pneumatic actuator working principle.
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As there are more and more control methods and means, there are many methods used to control pneumatic actuators in the actual industrial life and industrial control, and the following are commonly used.
(A) Intelligent display instrument control based on microcontroller development
Intelligent display instrument is used to monitor the working status of the valve and control the valve actuator. It monitors the working status of the valve through two position sensors, determines whether the valve is in the open or closed state, records the number of the valve switch through programming, and has two 4-20mA outputs corresponding to the valve opening degree and two normally open and normally closed output contacts. Through these output signals, the switching action of the valve is controlled. According to the requirements of the system, the intelligent valve display instrument can be designed from the hardware into 3 parts: analog part, digital part, and key/display part.
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1. The analog circuit part mainly includes three parts: power supply, analog input circuit, and analog output circuit.
The power supply part supplies energy to the whole circuit, including the energy supply for the analog circuit, digital circuit and display. In order to realize the remote control of valve opening and reading, the valve opening information needs to be transmitted to other control instruments, while the control instrument can formulate the valve for a certain opening degree from a remote location, the system needs 1 analog input signal of 4～20mA and 1～2 analog output signals of 4～20mA. The analog input signal is converted into a digital signal corresponding to the valve opening degree by A/D conversion and sent to the digital part of the microcontroller, which can be output after filtering in the microcontroller. The valve opening information is converted into analog signal output through D/A conversion, which is used to connect to the display meter to show the valve opening or connect to other control devices. In this design system, all digital data are used in serial input and output mode, in order to save chip resources and space, the input 4 ~ 20mA analog in the conversion to digital, using the existing 4-way DA chip and the microcontroller system resources combined for 8-bit AD use.
2, the digital circuit part mainly includes: microcontroller, power-down protection, two-way monitoring pulse input signal, two-way normally open and normally closed conversion contact output.
The AT89C4051 is a low-voltage, high-performance CMOS 8-bit microcontroller with 4K bytes of erasable, reprogrammable, read-only flash memory. By compounding a versatile 8-bit CPU flash memory within a single chip, it is fully compatible with the 80C51 and 80C52 in terms of performance, instruction settings, and pinout.
Considering the need to maintain some valve parameters previously set in the instrument when the system is powered down or restarted, and that the data memory in the microcontroller does not have a power-down storage function, a chip with a power-down save function, X5045, is extended off-chip. X5045 is a programmable circuit that combines three functions: watchdog, power monitoring, and serial EEPROM, and this combined design The watchdog in the X5045 provides protection for the system and will respond to the CPU via the RESET signal when the system sends a fault and the set time is exceeded. x5045 provides three time values for the user to choose to use. The voltage monitoring function it has also protects the system from low voltage. When the supply voltage drops below the allowable range, the system will reset until the supply voltage returns to a stable value. the X5045's memory can be interfaced with the CPU by serial communication. A total of 4069 bits can be used to place data by 512 x 8 bytes.
The pin arrangement of the X5045 is shown in Figure 1. It has 8 pins and the functions of each pin are as follows.
CS: circuit select terminal, active low.
SO: serial data output terminal.
SI: serial data input terminal; SI: serial clock output terminal; SI: serial data input terminal; SI: serial data input terminal.
SCK: serial clock output.
WP: write protect input, active low.
RESET: reset output.
Vcc: power supply terminal; Vcc: power supply terminal; Vcc: power supply terminal; Vcc: power supply terminal.
Vss: ground terminal.
INA is the input signal, which is the valve pulse signal (<10mA) collected by the photoelectric sensor. The signal is filtered by the bypass capacitor and sent to the optocoupler, which is converted into the output OUT voltage signal to be sent to the microcontroller. The output voltage can go directly to the I/O port of the microcontroller. In the control, it is required that both A and B pulses are received before they are considered to be input by the signal, AB for positive rotation and BA for reverse rotation. It does not count when only one signal is input.
Two-way normally open and normally closed changeover contact output. Used to connect the solenoid valve, through the control of solenoid valve suction to control the pneumatic actuator for the corresponding open or closed valve action.
3、The display part mainly includes: microcontroller, 4-digit LED display, 3 status indicators (auto, forward, reverse), 3 keys (MODE/SET key, up key, down key).
The AT89C4051 microcontroller is used in the display section to control the 4-digit LED display and to communicate with the digital section of the microcontroller, and to select and control the mode of the controller accordingly. Three status indicators are designed on the display to show the status of the actuator: forward, reverse and automatic; three keys: MODE/SET, up and down, control the working mode of the actuator and initialize some parameters. These 3 parts are connected through the interface to form a complete control system, which can control some actuators similar to pneumatic motors and so on. In the actual application, it basically achieves the various performance indicators required in advance.
(II) System using PLC to control
PLC is being used more and more widely in control systems, and since this program is developed on top of OMRON's PLC, OMRON's PLC is used for introduction.
Hardware composition: 1 PC, 1 set of PLC (including CPU, I/O module, ID212, OC224, AD003 module), 2 relays, 2 solenoid valves, 1 pneumatic valve actuator.
The principle of its composition is: the PC is connected to the PLC of OMRON through RS-232 serial communication, and the PLC is programmed and monitored. the I/O modules of the PLC are connected to the input and output signals, where the input module is connected to two position sensors on the valve, and the valve switching status is displayed through the sequence of the light on the input module ID211 of the PLC. The input module receives two valve detection pulse inputs, i.e. pulse A and pulse B. In the operating state, indicator A lights up when pulse A is input and indicator B lights up when pulse B is input. The input sequence is AB, which means open valve. An input sequence of BA indicates a closed valve. The valve detection pulses A and B signals must be partially superimposed, otherwise the valve opening cannot be detected properly.
The PLC output module OC225 controls two relays with two sets of normally open and normally closed output contacts, one for the open valve output contact and one for the closed valve output contact. When the valve is opened, the open output contact operates when the valve opening is greater than or equal to the set valve limit value, the open output contact operates when the valve opening is less than the set valve limit value, and the open output contact resets when the invention opening is less than the set valve limit value. When closing the valve, when the valve is closed to zero position and there is no pulse input within 21s, the closing output contact will be operated; if there is pulse input within 21s, the closing output contact will be delayed for 21s. Through the relay suction to control the two solenoid valve switch, solenoid valve open, you can control the pneumatic valve actuator makes the valve to do the corresponding open or close the valve action. At the same time, the proximity sensor transmits the valve opening and closing situation to the PLC, and compares with the required valve opening degree until it meets the requirements.
Automatic zeroing and automatic full adjustment: The control system has automatic zeroing and automatic full adjustment function, when the valve opening is less than the zeroing range value or the valve opening from the full range is less than the full adjustment range value, and the time is greater than or equal to the set value of the stability time value, the PLC automatically control the valve for zeroing or automatic full adjustment.
In the experiment, the valve opening is calculated by the position sensor on the valve.
When the valve leaves the A sensor first and then leaves the B sensor, it means the valve is closing the valve. When the valve leaves the B sensor first and then the A sensor, it means that the valve is opening. The sensor receives a pulse signal, and the valve's opening and closing status is noted by the collected signal from the position sensor.
The ladder diagram is written in the upper computer with programming software CX-programmer, and then the ladder diagram is downloaded to the PLC to run, and the valve is controlled and monitored in the configuration software of the upper computer, and the amount of valve switching can be determined by the lap value entered in the configuration software interface. After the configuration interface is done, the control and action of controls such as open valve, close valve, stop, and general switch can be operated directly in the configuration interface in a very intuitive image.
