2020.01.21
Summary:The screw feeder adopts distributed control, integrating PLC technology and frequency conversion speed regulation technology. The computer realizes the ratio setting and start-stop action of the weighing instrument. The PLC realizes on-site dynamic pictures and displays the equipment operating status, and can implement fixed value, configuration Ratio and material type settings.
Screw feeder control module design
Carbon black raw material batching process is, a number of raw material storage of resin, carbon black, iron oxide and other raw materials, in accordance with a certain ratio, respectively, through the corresponding feeding equipment, the raw materials will be conveyed to the weighing scale, measured and sent to the raw mill, the raw mill mill into raw material, out of the mill mixture into the separator, selected fine powder into the subsequent operation of carbon black production, the coarse powder back to the raw mill to continue to powder. One of the commonly used feeding equipments for raw meal batching system is screw feeder. Screw feeder is suitable for powder and other materials feeding, smooth operation, feeding uniformity, low noise, easy installation and commissioning, simple control, can be controlled by a frequency converter to achieve variable speed feeding. Screw feeder spiral for the variable pitch, variable diameter, and in the exit with crushing knife, to ensure that the material is uniformly added to the hopper.
With the development of power electronics technology, microelectronics technology and modern control theory, frequency converter has been widely used in AC motor speed control, in order to realize the precise control of various ingredients, the following control circuit selects Mitsubishi FR-A540-0.75KW type frequency converter to control the speed of the motor of the spiral feeder.
The frequency converter adopts photoelectric isolation switch quantity to control the start and stop of the frequency converter, and adopts analog voltage signal to set the frequency of the frequency converter, and the microcontroller adjusts the size of the output frequency of the frequency converter by changing the size of the analog voltage signal to change the rotational speed of the driving motor of the screw conveyor, so as to achieve the purpose of adjusting the amount of material to be fed.
The voltage and frequency setting signal of the inverter is generated by the circuit composed of D/A converter DAC0832 and operational amplifier.DAC0832 works in the single buffer mode and outputs the conversion result in the form of current with unipolarity.The I/V conversion circuit composed of operational amplifier is used to convert the current output of DAC0832 into voltage, and then the voltage is sent to the frequency setting signal ( analog) input of the inverter. Analog) input For the unipolar output circuit, the expression for the output voltage is: YursDVREF256 where D is a decimal input number. Because the conversion result Iouri connected to the inverting terminal of the operational amplifier, there is a negative sign in Eq.
If VEF=-5V, when D=0~255(00H~FFH), there is Vour=0~4.98V. By adjusting the zero potentiometer of the operational amplifier, the D/A chip can be zero compensated.
The start signal of the inverter is controlled by the PA7 terminal of 82C55. In order to effectively inhibit the inverter interference signal into the microcontroller control system, the optocoupler TIL117 is used to optically isolate the PA7 control terminal and the inverter turn-on control terminal STF. When the 82C55 PAT output is 0, the optocoupler TIL117 pass, and then the inverter start signal on, inverter-controlled spiral feeder to start feeding; when the 82C55 PA7 output is 1, the optocoupler TIL117 off, and then the inverter start signal is also off, the spiral feeder to stop feeding. In the spiral feeder operation, by changing the size of the digital input DAC0832 to adjust the frequency of the frequency converter to set the size of the voltage, you can change the feeding speed, to achieve fast and slow feeding.
Screw feeder control program to set the weight of the material given S, when the measured weight of the falling material is less than 90%, so that the screw feeder fast feeding; when the measured weight is greater than 90%, so that the screw feeder slow feeding, so as not to produce overshooting. When the measured weight is equal to Wg-g, stop feeding.
Spiral according to the actual situation, by selecting the electromagnetic vibrating feeder speed controller of the two rate setting value to realize, so as to enhance the flexibility of the system.
The spiral feeder control program is responsible for the weighing and dosing control when the spiral feeder is feeding. Since the operation of the spiral feeder is completely controlled by the frequency converter, and the dosage needs to obtain the raw material weight information from the weighing module to accurately control the weighing process, the program should call the frequency converter control program, the dosage algorithm subroutine, and the A/D interrupt processing. According to the raw material dosage algorithm to prepare the algorithm subroutine, run the program to generate the discharge flag bit, when the initial value of 0, that is, fast feeding; discharge flag position of 1, transfer to slow feeding. Frequency converter control program to complete the variable speed control of the spiral feeder. The values of the fast discharging parameters are usually fixed, and the initial values of the slow discharging parameters are fixed, and they can be stored in the E2PROM of the X5045.
