Automation is one of the most commonly used words in bag-maker marketing. Almost all suppliers say their machines are automated. Few vendors explain what automatic control is, how tolerant it is, or what happens when a system malfunctions.
The difference between a truly automated production line and a machine that requires manual adjustment is in three main ways. First, look at changeover time. Next, it depends on how often the machine shuts down. Third, see how many operators a shift requires.
This paper will explain the automation features of modern Plastic Bag Machine. It also gives key numbers that each feature should meet.
Servo Web Feed and Closed Loop Tension: Foundation
The first level of automation in any Plastic Bag Machine is motion control. Other automation features build on it.
Older machines use crank and cam systems to pull film. The length of the cloth bag is determined by shifting gears or moving connecting rods. This can take 30–60 minutes and usually requires a mechanic. The length of the cloth bag depends on the precision of the mechanism.
A servo-driven feed replaces the system. The operator enters the length of the bag on the screen. The system can be controlled to ±1 mm in length. Replacing a new bag can take less than five minutes in length and require no tools. The servo can also control the start and stop speed of the film. This is important for the membrane. Hard mechanical movements of 100 laps per minute stretch LDPE to 15 microns. This can change the length of the bag during the same production process.
Tension control work with the servo feed. dancer arm or weight cell measures the actual tension of the film. Then release the brake by adjusting the closed-loop system. Depending on the width and thickness of the film, the system usually maintains tension in the 20 -45 N range.
This control affects the length of the bag and the printing position. When the tension is too high, 25 μm LDPE can stretch by several percent. The servo may have the correct count, but the actual cut length can still be changed. Lower tension can also cause the film to move from one side to the other, causing registration problems. On a well-equipped machine, the operator will
Recipe storage and HMI: No a Mechanic transformation
The second level is information automation. It allows the machine to remember how to make each product.
A modern Plastic Bag Machine is stored in its HMI production recipes. Recipes can include bag length, seal temperature per area, sealing stay time, tension setting, stack count, punch time and conveyor belt speed. Each recipe is saved under the product name. Instead of resetting the machine, the operator can choose the next order.
Factories running ten or more SKUs day can save five to 10 production hours a week with this feature. This is common for contract bag producers.
The HMI also handles many tasks that once relied on operators. Before production starts, the machine raises the seal temperature the setpoint. It does not start to cycle until each area is within the tolerance set. The counter tracks production according to the number of orders. When the order is complete, the machine stopped working, so the last stack isn't short.
It also records alerts with timestamps. Operators can see the time of each alarm. This makes it easier to pinpoint the cause of slow production during shifts.
Machines following IEC 60204-1 control circuits can display these diagnoses in a clear format. Factories using ISO 9001:2015 can also add alarm records to their process records without the need for additional paperwork.
Registration, perforation and Inline Quality Monitoring
The third layer holds each bag of printed artwork like the previous bag.
Printing registration tracking makes an automated Plastic Bag Machine suitable for printed film. Photo Eyes read impressions. It sends a signal to a servo system, which moves the movie forward or backward. This keeps the seal and cut in place on the artwork. The system can maintain accuracy of ±0.5 mm when shifting gears.
The waist-handle punch uses the same registration signal on the line printed on the T-shirt bag. The servo keeps the handle punch in position. This will prevent the handle from opening into the seal line. Before servo indexing, the operator must set the punch position by mechanical adjustment and inspect it through the eyes. Automation can eliminate such defects.
Inline monitoring also adds quality control. Sealed temperature zones are always being checked. Modern controllers sound an alarm or stop the machine when an area moves beyond ±2°C from the setpoint. This temperature change can be an early sign of a weak seal.
Sensors also check the stacker for bags. The missing packet detector will find skipped loops that could otherwise go unnoticed in the middle of the stack.
These systems cannot replace operators. They reduce the need for the operator to observe the machine at all times at a rate of 100 laps per minute, which is difficult to do reliably.
Fault Detection, Counting and security layer
The rest of the automation will keep the line running. When something goes wrong with the machine, it shuts down and sends out counted bags.
Self-diagnosis of malfunctions covers issues that can quickly generate waste. These include film breaks, web splice detection, temperature variation of seal, pressure below the 0.4–0.5 MPa level, and loss of print marks. When something goes wrong, the machine stops and shows the problem on HMI. It also records malfunctions. The operator can see where the process has stopped without having to search the entire line.
This increases the averagetime it takesto repair. A clear fault message can take about two minutes to fix. Failures without clear information can take about 20 minutes because operators must check the lines.
Counting and stacking automates the finished bag to a specified quantity. General accuracy is ±1 bag / batch. The system can add tags or different stack position at the end of each batch. It then moves the finished stack at production speed.
When the production line feeds carton packers directly, the batch system works with the downstream conveyor. This will ensure the machine has enough bags to prevent the machine from waiting.
Security features are also part of the automation system. These features are regulated for plastic bag machines sold in Europe. When the machine opens, the interlocking guard stops the machine. Emergency stop circuit is designed to comply with ISO 13849-1 performance levels. The machine can also prevent accidental reboot after failure. These functions are required by Mechanical Directive 2006/42/EC.
Newer machines can also use data interfaces, such as OPC UA, which is standardized as IEC 62541. It sends production counts, alarm states and machine speed to factory monitoring system. The plant scheduler can then check the state of the machine without having to walk to the production floor.
Frequently Asked Questions
What automation feature is paying off the fastest?
Recipe storage with servo feed. With each size change, the replacement time can be reduced from 30–60 minutes to less than 5 minutes. At the plants that run many SKUs, that time can be saved with almost every shift. Operators only need to use the HMI, not special skills.
Does increased automation mean fewer operators?
That means fewer operators per bag, but it doesn't always mean fewer employees. An operator can monitor an automated line rather than the two or three operators needed on a mechanical machine to feed, monitor and stack bags. Planting plants typically uses the labor savings to print, pack or run a second shift, rather than reduce staffing.
Can automation be added to older machines?
Only part. Servo kit and individual counter available. They improve bag length accuracy and counting. However, automatic switching, printing registration and complete fault diagnosis require a servo-based control system. Modifications often donot provide fully cumulative switching and fault diagnosis for machines designed with servo control from the start.
Source of information
- IEC 60204-1 --Mechanical safety: mechanical and electrical equipment, control circuits and diagnostics.
- ISO 13849-1 --Mechanical safety: safety-related aspects of control systems.
- Machinery Directive 2006/42/EC-European Union mechanical safety and guarding requirements.
- IEC 62541 -OPC Unified Architecture, machine data interface standards.
- ISO 9001: 2015 -Quality management and process documentation;
- - KPIs for manufacturing operations (availability, performance, quality).
- Grand View Research and Hemp Bags Production market data.
