Application example of PLC in slice packaging system
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1 Introduction
A set of equipment with an annual output of 150,000 tons of polyester melt, the rear matching device is an annual output of 70,000 tons of short filaments, and the remaining melt is cut into polyester chips by a pelletizer and packaged into a ton bag for export. The packaging machine uses a one-ton bag automatic weighing and packaging system from the 12th Aerospace Department. There are two sets. The system uses a programmable controller for automatic control. This article will focus on the application of PLC in the packaging system.
2 system overall
This packaging system generally uses mechatronics technology. The programmable controller (PLC) and the weighing indicator control unit F701 form a measurement and control system to complete the production process of the weighing, metering and packaging of the slice. The system uses PLC as the control center, with weighing indicator control instrument, pneumatic actuator, electric actuator, automatic control components and mechanical devices to realize the dynamic online weighing measurement and packaging of the slice. The system presidential block diagram is shown in Figure 1.
2.1 Electronic Control System
The control unit of the packaging machine consists of two parts.
(1) Panel part: It consists of main control cabinet, auxiliary control cabinet and two on-site operation boxes. The main control cabinet mainly has PLC and weighing indicator control instrument F701, code wheel setter, bag counter and so on. The auxiliary control cabinets are mainly AC contactors and thermal relays, which respectively control the M1 fan motor, the M2 lifting mechanism motor, and the M4 transmission mechanism motor. Among them, the lifting mechanism uses two contactors because of the rise and fall. The field operation box AR1 is used for the material port lifting control, and the AR2 is used for the transmission control.
(2) On-site part:
3 motors M1, M2, M3;
4 two-position five-way solenoid valves cooperate with the cylinder to control the feeding gate 1 (solenoid valve YV1), the feeding gate 2 (solenoid valve YV2), the discharge gate (solenoid valve YV4) and the pocket clamp release (solenoid valve YV5);
6 limit switches, SQ1 is the closing position of the feeding door, SQ3 is the closing position of the discharge door, and SQ4, SQ5, SQ6 and SQ7 respectively correspond to the upper, lower, upper and lower limits of the material of the bag lifting mechanism;
3 load cells BP1, BP2, BP3;
A photoelectric switch SQ11 is used to detect the material package to the end of the conveyor chain.
The main mechanical devices include weighing hoppers, slab conveyors, bagging mechanisms, control doors, and discharge doors. Since the slice is a granular uniform particle, it has good fluidity and does not adhere to the powdery material, so it can be dropped by its own weight, and the hopper does not need to be specially operated. The control door adopts a double gate, and when the control doors 1 and 2 are fully opened, the feed is fast, and when the control door 2 is closed, the feed is slow.
2.2 Packaging process
(1) Weighing process: This system has two modes of operation, automatic and manual, but the manual mode is also realized by PLC. The manual mode is mainly used for debugging, repairing and troubleshooting, so the automatic operation is taken as an example.
After the PLC deducts the tare signal from F701 (the net weight is immediately set to 0), the control doors 1 and 2 are opened, and the silo is quickly fed to the weighing hopper (fast feeding speed is about 23kg/s), when the preset value is reached. When the control door 2 is closed, the fast feeding is changed to the slow feeding (the speed is about 2 kg/s), and when the material amount reaches the falling value, the control door 1 is closed, and the feeding ends. After stabilization, the PLC sends a data hold signal to the F701. The F701 automatically compares with the set shortage, excess, and upper limit. If the amount is appropriate, the “weighing” light is on. If the amount is excessive or insufficient, the “out of tolerance” light is on and the alarm is issued.
(2) Lifting mechanism action and discharging process: Add the empty bag to the discharge port and press the “feed port” button of AR1 to wait for the “weighing” lamp to light up, then the material 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 to start discharging. When the F701 sends a near zero signal, the discharge door is closed 5 seconds, then the bag mouth clamp is automatically released, and the bag count is incremented by 1. The PLC sends a skin repeat command signal to the F701 (cancel The tare weighting operation), the filled bag is placed on the conveyor from the spout.
(3) Transfer process: Press the “Transfer Start” button of AR2, M4 will automatically transfer a bag to stop, and the mouth will be automatically lowered to the lower position. Each time a bag is weighed, one station is forwarded in the order of the transfer start button bag. This cycle. Use a forklift to fork the bag on the conveyor in time.
When the amount is low, it is allowed to feed by pressing the “slow cast” button and automatically reach the appropriate amount; if there is no corrective action in addition to the alarm when the system is excessive, the “force” button must be pressed to open the discharge door.
3 PLC control system
3.1 Hardware Configuration
The core control part of this packaging system is the PLC. The PLC selects the C200HE of Omron with good cost performance and good expansion.
(1) The CPU selects SYSMACC200HE-CPU42-E, and the program capacity is 7.2k words.
(2) There are 4 digital input cards (DI). Models are DC input units of type B ID212. This card supports 16-point DC voltage input. A total of 32 inputs are used, including the control output signal of the weighing indicator controller F701 and the inputs of buttons, knobs, and limit switches.
(3) There are three digital output cards (DO). The model is B type OC222 relay output unit 2, this card supports 12-point relay output; A-type OD411 transistor output unit, this card supports 8 points output. A total of 20 outputs are shared, including solenoid valves, motor control signals, signal indicators, and control signals sent to the F701.
(4) Power supply and backplane. The power supply uses PA204, and the bottom plate is an 8-slot backplane.
3.2 PLC program
The C200HE program is represented by an easy-to-understand ladder diagram. When using a normal programmer, the ladder diagram must be converted to a mnemonic for input. Although the program structure of the C200HE is not modular, in this system, the interlocking and interlocking release commands—IL(02) and ILC(03) and the jump and jump termination instructions—JMP(04) and JME( 05) The program structure is similar to modularity. 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 switch of the control door and the discharge door is in place. Whether the two limit switches are in place or not is the key point of the program step. If the program is not stopped, it will affect the packaging progress, so it must be Timely alarm to notify the operator. Two sets of JMP and JME commands are nested in the second group, which correspond to the automatic operation process and the manual operation process from weighing to discharging. The third group is used for the automatic transfer process and the fourth group is used for the manual transfer process.
The weight detection of this packaging system does not use an analog input card, but is detected by using three parallel load cells and a weighing indicator controller F701. F701 is a meter specially used for weight weighing and control of single material. The weight of this analog signal is processed by F701, and PLC and F701 are all digital signal. In this way, the PLC processing of the system is all digital signals, which makes the control precision greatly improved, and the programming is relatively simple, without using complicated commands, and because the weight is lost after power-off and power-off, and malfunctions during operation. There is no change after stopping the operation until the recovery operation is resumed, so the data retention function is not considered, that is, the special memory and corresponding commands in the PLC are not required. The automatic operation program flow chart is shown in Figure 3.
The following describes the relationship between the automatic feeding process of the packaging system and the handover signal of the PLC and the weighing indicator F701 in combination with the ladder program PLC statement of the material program. The used DI signals are 00000 (close to 0), 00001 (preset value), 00002 (drop value), 00003 (insufficient quantity), 00004 (over quantity), the above signals are sent from F701 to PLC, and 00009 (automatic mode knob switch), 00301 (limit switch SQ1, closed when the feed gate is closed), 00303 (limit switch SQ3, closed when the discharge gate is closed); DO signal has 00700 (tare weight signal), 00701 ( Skin repeat bit signal), 00701 (data hold signal), the above signals are sent from PLC to F701, 00600 (feed gate 1 open), 00601 (feed gate 2 open), 00602 (discharge gate open), 00603 (bag mouth) The clip is released). In the PLC program, the signal of the difference value is sometimes used as the final value signal. Because the weight is close to the control value, the control gate is closed. At the time, there is only the interval when the valve is closed. The size of the difference is after the control gate is closed. There is no slice weight falling 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 the first time each batch starts to be automatically packaged. At this time, the feeding door is closed and the feeding is performed. The third sentence is the starting condition for the second package to start packaging. At this time, the previous package has been fed, and the bag opening has been released and the feeding door is closed. The fourth sentence is that the feeding condition is met when either of the last two conditions is satisfied and the discharge door is closed.
Feeding process: The fifth sentence is that the PLC sends a 0.12 second pulse to the F701 before the feeding to perform the tare operation. At this time, the F701 sets the net weight to 0 immediately. In the sixth, seventh, tenth, and eleventh sentences, the internal I/O bit 09010 is the weight that has not reached the preset value. Before this, 00600 and 00601 both open the feeding gates 1, 2, and this time is the large feeding; the preset value is 00001. 09010 is 0. At this time, the 00601 power failure charging door 2 is closed to a small feeding. 03009 is the weight not reached the final value (fall value), before the 00600 action opens the feeding door 1, that is, the preset value has arrived and the feeding door 1 is open when the final value is not reached. At this time, the feeding is small, and the final value is 03009. The feed gate 1 is closed for 0,00600 power failure, and the material is finished.
Discharge process: The 8th and 9th sentences are after the final value of the weighing hopper has reached 4.5s, the PLC sends a data retention command to the F701, and the weight comparison is performed at this time. The 12th and 13th sentences, 03006, are the end of inflation indication. The discharge control 09012 is not overweight and is 1 after the end of inflation. At this time, 00602 is energized to open the discharge door and discharge, and when it is close to 0, 5s09012 is 0. 00602 Loss of electricity and close the discharge door to ensure that the material has been exhausted. The 14th sentence is that after the discharge is completed, the PLC sends a 0.12 s pulse to the F701 to perform the skin repeat operation, that is, the tare weight operation before the feeding is canceled. After the cycle is returned, the tare weight operation is performed to ensure that the net weight is calculated each time.
4 Conclusion
Packaging is a necessary condition for products to enter the circulation field, and the main means of achieving packaging is the use of packaging machinery. The accuracy of weighing packaging will directly affect the reputation and economic benefits of the company. Although the C200HE is a relatively early product, the operator of the packaging machine is on site, and there is no need to connect the display operation equipment such as the industrial computer and the operation panel, and the signal light and the alarm sound can be used, and the processed signals are all digital. Therefore, the C200HE is also a cost-effective configuration in this packaging system. The packaging system has a maximum packaging capacity of 32 bags/H, and the operator only needs 2 to 3 people, which is easy to operate. The control system is controlled by PLC to ensure system reliability and control accuracy. The weighing accuracy is designed to be 1000kg±0.8k. Since the system has been tested twice, the dynamic measurement accuracy of the whole system is better than 0.2‰. Since the export of the device driving products, no customer has reported that the product has weight problems, which has well maintained the company's reputation.