1 Introduction
Jinan Zhenghao Chemical Fiber New Material Co., Ltd. No. 3 Chemical Plant has a set of 150,000 tons of polyester melt annually. The following equipment is 70,000 tons of short filament. The remaining melt is cut into polyester chips by a pelletizer Packed into a ton of bags for export. The packaging machine selects a one-ton bag automatic weighing and packaging system from the Twelve Institute of the Ministry of Aerospace, with a total of two sets. The system uses a programmable controller for automatic control. This article will focus on the application of PLC in packaging systems.
2 Overall system
This packaging system generally uses mechatronics technology. The programmable controller (PLC) and weighing indicator controller F701 form a measurement and control system to complete the production process of weighing, measuring and packaging of slices. The system uses PLC as the control center, and is equipped with weighing indicator controller, pneumatic actuator, electric actuator, automatic control components and mechanical devices to realize dynamic online weighing measurement and packaging of slices. The block diagram of the system president is shown in Figure 1.
2.1 Electronic control system
The control part of the packaging machine consists of two parts.
(1) Panel mounting part: It consists of main control cabinet, auxiliary control cabinet and two field operation boxes. The main control cabinet mainly includes PLC and weighing indicator controller F701, code disc setter, bag counter and so on. The auxiliary control cabinet is mainly an AC contactor and a thermal relay, which respectively control the M1 fan motor, M2 lifting mechanism motor, and M4 transmission mechanism motor. Among them, the lifting mechanism uses two contactors because of its rise and fall. The on-site operation box AR1 is used for the lifting control of the material port, and AR2 is used for the transmission control.
(2) On-site part:
3 motors M1, M2, M3;
Four two-position five-way solenoid valves cooperate with the cylinder to control the feeding door 1 (solenoid valve YV1), the feeding door 2 (solenoid valve YV2), the discharge door (solenoid valve YV4) and the bag mouth clamp release (solenoid valve YV5);
6 limit switches, SQ1 is the feeding door closed position, SQ3 is the discharge door closed position, and SQ4, SQ5, SQ6, and SQ7 correspond to the upper, lower, upper, and lower limits of the material opening of the bagging and lifting mechanism, respectively;
3 load cells BP1, BP2, BP3;
One photoelectric switch SQ11 is used to detect the package to the end of the conveyor chain.
The main mechanical devices include weighing hopper, plate conveyor, bagging mechanism, control door, discharge door, etc. Because the slices are granular uniform particles, they have good fluidity and do not stick compared to powdered materials, so they can be dropped by their own weight, and the hopper does not need to do special operations. The control gate adopts a double gate, when the control gates 1 and 2 are fully opened, it is fast feeding, and when the control gate 2 is closed and 1 is opened, it is slow feeding.
Figure 1 overall block diagram of the system
2.2 Packaging process
(1) Weighing process: This system has two operation modes, automatic and manual, but the manual mode is also realized by PLC. The manual mode is mainly used for debugging, maintenance and troubleshooting, so the automatic operation is used as an example.
After PLC sends the tare weight deduction signal to F701 (at this time, the net weight is set to 0 immediately), open the control doors 1 and 2, and quickly feed the material into the weighing hopper from the silo (fast feeding speed is about 23kg / s), when the preset value is reached Close the control door 2 at the time, change the fast feeding to slow feeding (speed is about 2kg / s), close the control door 1 when the amount of material reaches the drop value, and the feeding ends. After stabilization, the PLC sends a data retention signal to F701. F701 automatically compares with the insufficient, excessive, and upper limit values ​​set. If the amount is appropriate, the “Well†light turns on, and if the amount is excessive or underweight, the “Out of tolerance†light turns on and alarms.
(2) Action of lifting mechanism and discharging process: clamp the empty bag on the discharging port and add it, press AR1 "feed port rising" button and wait until the "Well" light is on, the feeding port will automatically rise to the upper position, and the fan will start to inflate for 15s. After the inflation is completed, the discharge door is opened and the discharge is started. When the F701 sends a near zero signal, the discharge door is closed within 5 seconds, and then the bag mouth clip is automatically released, and the bag count is increased by 1. The PLC sends a leather repeat position command signal to the F701 (cancel) Tare weight operation), the bag full of material is separated from the material port and placed on the conveyor.
(3) Transmission process: Press AR2's "transmission start" button, M4 starts to automatically transmit a bag position to stop, the bag mouth is manually tied, and the material mouth is automatically lowered to the lower position. After weighing each bag in the future, press the transfer start button to transfer the bag forward one station in sequence. This cycle goes back and forth. Forklift the bag on the conveyor in time with a forklift.
When the amount is insufficient, it is allowed to replenish the material by pressing the "slow-throw" button and the appropriate amount is automatically reached; when the system is excessive, there is no corrective action except for the alarm, and the "force" button must be pressed to open the discharge door to discharge the material.
3 PLC control system
3.1 Hardware configuration
The core control part of this packaging system is the PLC. PLC chooses Omron's C200HE with high cost performance and good scalability. Its hardware configuration is shown in Figure 2:
Figure 2 PLC layout
(1) The CPU selects SYSMACC200HE-CPU42-E, and the program capacity is 7.2k words.
(2) There are 4 digital input cards (DI). The models are all B type ID212 DC input units. This card supports 16-point DC voltage input. A total of 32 input values ​​are used, including the control output signal of weighing indicator controller F701 and the input of buttons, knobs, and limit switches.
(3) There are 3 digital output cards (DO). The model is B type OC222 relay output unit, this card supports 12 points relay output; A type OD411 transistor output unit, this card supports 8 points output. 20 output quantities are shared, including solenoid valve, motor control signal, signal light indication and control signal sent to F701.
(4) Power supply and backplane. The power supply is PA204, and the bottom plate is 8-slot bottom plate.
3.2 PLC program
The C200HE program is represented by an easy-to-understand ladder diagram. When using an ordinary programmer, the ladder diagram must be converted into a mnemonic for input. Although the program structure of C200HE is not modular, in this system, by using interlock and interlock release instructions—IL (02) and ILC (03) and jump and jump end instructions—JMP (04) and JME ( 05) Make the program structure similar to modular. The program of this system uses a total of 4 sets of IL and ILC instructions. The first group is used to detect whether the limit switches of the control door and the discharge door are in place. Whether these two limit switches are in place is the key point of the program step. If it is not in place, the program will stop and affect the packaging progress, so it must be Alarm the operator in time. Two sets of JMP and JME instructions are nested in the second group, respectively corresponding to the automatic operation process and manual operation process from weighing to discharging. The third group is used for the automatic transmission process, and the fourth group is used for the manual transmission process.
The weight detection of this packaging system does not use analog input cards, but is detected by using three parallel load cells and a weighing indicator controller F701. F701 is an instrument specially used for weighing and controlling a single material. The analog signal of weight is processed by F701, while PLC and F701 are all digital signals. In this way, the PLC of this system processes all digital signals, which greatly improves the control accuracy and also makes the programming relatively simple. There is no need to use complex commands. Moreover, due to the weight, the power failure and the power failure occur during operation. There is no change after the operation is stopped until the fault is restored and the operation is resumed, so there is no need to consider the data retention function, that is, there is no need to use the special memory and corresponding commands in the PLC. The flow chart of the automatic operation program is shown in Figure 3.
The following describes the automatic feeding process of the packaging system and the relationship between the PLC and the handover signal of the weighing indicator F701 in conjunction with the PLC statement of the feeding program ladder diagram. The DI signals used are 00000 (close to 0), 00001 (preset value), 00002 (drop value), 00003 (insufficient amount), 00004 (excess amount), the above signals are sent from F701 to PLC, and 0009 (Automatic knob switch), 00301 (limit switch SQ1, closed when the feed door is closed), 00303 (limit switch SQ3, closed when the discharge door is closed); DO signals are 00700 (tare signal), 00701 ( Leather repeat bit signal), 00701 (data hold signal), the above signals are sent from PLC to F701, 00600 (feeding door 1 open), 00601 (feeding door 2 open), 00602 (discharge door open), 00603 (bag opening The clip is released). In the PLC program, the drop value signal is sometimes used as the final value signal, because when the weight reaches the drop value, the control door is closed and the feeding is completed. There is only a time interval for the valve to close, and the size of the drop value is after the control door is closed The weight of the slices that did not fall into the hopper. The program ladder diagram is shown in Figure 4.
Feeding conditions: The first and second sentences are the starting conditions when the system is turned on for the first time or when the automatic packaging starts for the first time in each shift. At this time, the feeding door is closed and feeding will be performed. The third sentence is the starting condition for the second pack to start packaging. At this time, the last pack has been fed and the bag door has been released. The feeding door is also closed. The fourth sentence is that when either of the above two conditions is met and the discharge door is closed, the feeding conditions are met.
Feeding process: The fifth sentence is that the PLC sends a 0.12 second pulse to the F701 for tare weight operation before feeding. At this time, F701 sets the net weight to 0 immediately. Sentences 6, 7, 10, and 11, the internal I / O bit 09010 is that the weight has not reached the preset value. Before this, 00600 and 00601 all acted to open the feeding gates 1 and 2. At this time, it is a large feeding; the preset value 00001 arrives 09010 is 0, at this time 00601 power failure feeding door 2 is closed and changed to small feeding. 03009 is the weight has not reached the final value (drop value), before the 00600 action to open the feeding door 1, that is, the preset value has arrived and the final value has not yet reached the feeding door 1 is open, this time for small feeding, the final value is 03009 When the power is 0,00600, the feeding gate 1 is closed, and the feeding is ended.
Discharging process: The 8th and 9th sentence is that after the final value of the weighing hopper has reached 4.5s, the PLC sends a data retention instruction to F701, and the weight is compared at this time. In the 12th and 13th sentences, 03006 is the end-of-inflation sign. The discharge control 09012 is not overweight and 1 after the end of inflation. At this time, 00602 is electrified to open the discharge door to discharge, and 5s09012 is 0 after the discharge is close to 0. 00602 Loss of power to close the discharge door to ensure that the material has been exhausted. The 14th sentence is that the PLC sends a 0.12s pulse to the F701 to perform the tare repetitive bit operation after the discharge is finished, that is, the tare weight removal operation before feeding is cancelled. In this way, the tare-removing operation is carried out after the return, to ensure that the net weight is weighed every time.
Figure 3 Automatic operation program flow chart
Figure 4 Ladder diagram of feeding program
4 Conclusion
Packaging is a necessary condition for products to enter the circulation field, and the main means to achieve packaging is to use packaging machinery. The accuracy of weighing and packaging will directly affect the reputation and economic benefits of the enterprise. Although the C200HE is a relatively early product, because the operator of the packaging machine is on site, there is no need to connect industrial control machines, operation panels and other display operation equipment, and it can be equipped with signal lights and alarm sounds, and the processed signals are all digital. , So C200HE is also a very cost-effective configuration in this packaging system. The maximum packaging capacity of this packaging system is 32 bags / H, the operator only needs 2 to 3 people, and the operation is simple and convenient. The control system adopts PLC control, which can ensure the reliability and control accuracy of the system. The weighing accuracy is designed to be 1000kg ± 0.8k. Since the system has been used, after two tests by the metrology department, the dynamic measurement accuracy of the entire system is better than 0.2 ‰. No customer has reported that the product has weight problems since the device was driven and exported, which has maintained the company's reputation.
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