[Abstract] This article explains the feeding principle of a vertical fully automatic continuous vertical packaging machine, introduces the control difficulties and the Delta PLC control implementation program.
【Abstract】This paper expounds the vertical automatic successive vertical
packaging machine blanking principle, and introduces the control
difficulties and delta PLC control realize the program.
[Keywords] Continuous; Intermittent; Vertical automatic packaging machine; Material feeding control
【Keywords】continuous; intermittent; vertical automatic packaging machine; blanking control
A vertical packaging machine is a machine that automatically and continuously completes three functions: forming rolls of flexible packaging material into bags, filling them with material, and sealing them. Combined with metering and filling machinery, vertical packaging machines are commonly used for packaging block, flake, granular, stem, powder, and liquid and semi-liquid materials. Vertical packaging machines are generally divided into continuous packaging machines and intermittent packaging machines.
1. Introduction to the process of continuous vertical packaging machine
Figure 1 Intermittent vertical packaging machine
As shown in Figure 1, the horizontal sealing device of an intermittent vertical packaging machine is fixed in one position. Each time it seals, the film pulling action is customized, and the film can only be released after a certain sealing time before the film pulling continues. In contrast, a continuous vertical packaging machine can continuously pull the film. During the complete pressing action, the entire horizontal sealing platform maintains the same speed as the film traction. After completion, the horizontal sealing platform retracts, quickly returning to its original position. Because continuous production is more efficient, it is currently a trend to replace intermittent machines. However, even within continuous production, there are two methods: one using mechanical cams, and the other using servo motors with electronic cams. The mechanical method is inconvenient when changing the packaging film length, requiring mechanical adjustments, and its large mechanical inertia limits speed. Therefore, the servo method using electronic cams to control continuous packaging machines has become the preferred choice.
Currently, functions such as bag making, sealing, date printing, and bag film cutting have been completed. The customer has participated in the packaging exhibition in Hanover, Germany, and related articles have also been published. This article focuses on the coordination between electronic scale feeding and packaging.
In the past, intermittent filling packaging initiated packaging actions based on material signals; that is, each material signal triggered a corresponding action such as film feeding, longitudinal sealing, and transverse sealing, which was logically simple. However, this method is clearly unsuitable for the current continuous packaging system.
2. Analysis of the difficulties in blanking and filling
Figure 2. Schematic diagram of blanking and filling
As shown in Figure 2, the weighing device is positioned very high above the packaging, approximately 2-3 meters. Powdered substances, such as laundry detergent, take 2-4 seconds to fall from the air into the bag. This presents significant challenges for continuous packaging control. Two scenarios will be described below.
Scenario 1: If the material feeding time is short and can be ignored (with an intermediate hopper, the feeding time is 300ms), the actual operation is shown in Figure 3. The opening solenoid valve is triggered at the fixed angle of the heat sealing servo (the heat sealing of the continuous packaging machine is an electronic cam, and the angle can be set in the program).
Figure 3. Operation diagram when the material feeding time is negligible.
The discharge valve can be triggered by setting the electronic cam cycle from 0 to 360 degrees. For example, if the setting is 50 degrees before starting the machine, material may get stuck. Adjust the trigger angle to 150 degrees until it is suitable. Because the material discharge time is short enough, one cycle is 500ms for 120 bags.
Scenario two often involves customers not using an intermediate hopper. When packaging food-grade granules, to avoid contamination during intermediate steps, an intermediate hopper is often omitted. This means that the time from opening the container to the material falling into the bag is relatively long, ranging from approximately 1 to 4 seconds.
Assume that it takes about 2 seconds from the opening of the solenoid valve to the bag being dropped into it by the feed scale. The actual bag cutting speed is 30 to 120 bags per minute. Taking 60 bags per minute as the control speed, the control process is shown in Figure 4. The left side is the feeding channel. When the set speed is 60 bags, the solenoid valve needs to be opened first. When the bag is about to fall to the bottom, the pulling mold and sealing cutting are started.
Figure 4 Control process diagram
The second solenoid valve is opened 1 second after the first solenoid valve is opened. This results in two bags of material being in the material hopper at the same time. It is essential to ensure that this timing is perfectly synchronized during the subsequent heat-sealing electronic cam cycle to ensure accuracy, as shown in Figure 5.
Figure 5 Control process diagram
The runtime sequence diagram is shown in Figure 6.
Each time the current horizontal seal is applied, it is for the bag that was previously sealed. Figure 6 shows the timing diagram for a basic 60 bags. The timing diagram for different speeds also needs to be changed. Assuming there are 120 bags, with a cycle of 500ms, the solenoid valves need to be opened sequentially, possibly four times in advance. The first heat-sealing cam heat-seals the first bag that starts to be discharged, which is the fourth bag that has already been discharged. There are already four bags in the air chute before the heat-sealing starts.
Because the cam lags behind by several cycles, the above-mentioned method of triggering at the cam cycle position point cannot be adopted. Instead, the time-triggered feeding solenoid valve must be used according to the set filling speed. The main difficulty lies in the fact that if the setting is 60 bags, assuming the solenoid valve opens every 1 second, the actual film pulling and horizontal sealing speed may not be 1 second; it could be 1.1 seconds, or even 0.9 seconds per bag. Over time, this will lead to greater deviations during operation, resulting in material jamming, as shown in Figure 7.
Figure 7 Runtime sequence diagram
3. Blanking and Filling Solution
The main problem now is that if the solenoid valve is activated based on a time cycle, the actual operating cycle of the cam cannot be perfectly matched with it. Only by activating the solenoid valve based on the actual cam operating cycle can a perfect match be guaranteed. Before the cam starts moving, the solenoid valve is activated based on time. In the first two cycles, the cam has not actually moved, so the solenoid valve is activated based on the time cycle. The cam only starts moving in the third cycle. Switching to a set angle output solenoid valve solves both the problem of the delayed cam start not being able to rely on angle to activate the feeding solenoid valve and the problem of accumulated errors between the feeding cycle and the cam operating cycle over a long period of time when relying solely on time to activate the solenoid valve, as shown in Figure 8.
Figure 8 Runtime sequence diagram
3. Program Implementation
On the HMI screen, select the switch to fill mode, as shown in Figure 9.
Figure 9. Schematic diagram of human-computer interface
Set the material feeding time and filling speed on the HMI, as shown in Figure 10.
Figure 10 Schematic diagram of human-computer interface
The program calculates how many bags actually need to be placed in advance. Assuming a material feeding time of 2 seconds, a speed of 40 bags, and a cycle time of 1.2 seconds per bag, 2 seconds / 1.2 seconds = 1.67. Therefore, two bags need to be released based on the cycle time, as shown in Figures 11, 12, and 13.
Figure 11 Calculation Interface
Figure 13 shows that the solenoid valve is triggered twice during the initial time cycle, and then switched to cam angle triggering.
After actual operation, the packaging filling was stable at test speeds of 40-60-80-120.
3. Conclusion
The vertical automatic packaging machine control system, composed of Delta HMI, PLC, frequency converter and servo, easily meets the requirements of users; stable and reliable product quality and simple and easy operation methods demonstrate the superiority of Delta's integrated electromechanical products; the system realizes fully automatic production and greatly improves production efficiency; rich fault diagnosis functions improve the convenience of operators to maintain the equipment.
About the author:
Yu Qiang, male, born in December 1969, graduated from the Department of Electrical Engineering, Anhui Institute of Mechanical and Electrical Engineering, majoring in Industrial Automation. He previously worked at the Eighth Research Institute of the Ministry of Information Industry and the Engineering Department of the Automation Branch of USTC Innovation Co., Ltd. He currently works at the PLC Product Development Department of Delta Electronics Co., Ltd., mainly focusing on the high-end application of PLC in automation, including the research and market development of precision motion control of various mechanical equipment and process control of engineering projects.
