How Sensors Improve Counting and Position Control in Individual Straw Packing

Despite being fast, a straw packing line will only be costly if it continues to pack air rather than straws. Speed is not enough, but speed coupled with precision matters. As such, when it comes to the individual straw packing machine, precision boils down to two things: accurately counting straws and placing them in the appropriate position before the wrap is sealed. Fail to do so, and you will end up with wrapped air, misaligned printed straws, straws sticking out, or machines stopping every now and then as an operator clears a jam.

That's how sensors become valuable. In a current individual straw packing machine, sensors play along with the PLC and servo motors. They detect any problem in milliseconds before it gets to the customer. This article walks through how sensors handle counting and position control, what types of sensors do the heavy lifting, and what to look for if you're evaluating a machine.

Why Counting and Position Errors Cost More Than You Think

All the wrappers that come out of the machine are straws for which you have already paid to be extruded, film that you have already paid to be printed, and a rejection for which someone on the assembly line will have to pick up manually. Think of that being repeated thousands of times during each shift, and you can see how a relatively low percentage of rejects becomes expensive very quickly.

Here's where things usually go wrong on a line that isn't well monitored or calibrated:

• Inconsistent feeding: The straws may either come in too early, late, or not at all due to vibrations or a faulty feed system.

• Film tension drift:  In a rolling process, film tension drifts and causes errors in where to cut and seal the straw.

• Dust and residue buildup:  This happens in the lens sensors after prolonged use, which causes erroneous readings.

• Worn or loose parts: mechanical wear changes timing that used to be reliable.

There is also an issue of hygiene here, and it pertains to this particular product only. Straws individually wrapped imply that they have not been handled and are sealed inside the wrapper, so a wrapper that is torn, open at the ends, or even a straw that does not lie straight in the wrapper negates the entire purpose of buying individually wrapped straws.

How Sensors Improve Counting Accuracy

Photoelectric sensors

Photoelectric sensors send out a beam of light and read whether it's broken, reflected, or scattered by a straw passing through. Three types show up most often:

• Through-beam sensors: the transmitter and receiver are located on opposite ends of the straw route, with anything obstructing the light being counted as a detection event. Effective and reliable, yet they require access from both sides of the line.

• Retro-reflective sensors: the transmitter and the receiver are combined into one unit, while the light is bounced off from a reflector. They are easier to fit into smaller spaces, although they have trouble with shiny and transparent straws.

• Diffuse sensors: the light bounces off the surface of the straw, which makes them effective with opaque straws, including paper straws. Yet, they are harder to configure for transparent PLA straws, as the light goes straight through without reflecting back.

This is a crucial factor, as the light-based sensors calibrated for detecting opaque straws will fail to detect transparent ones, since there is nothing to bounce back. The machines intended to manipulate straws of both types require two types of sensors.

Fiber-optic sensors for small, fast targets

Straws are small in size, and at higher speeds, they pass through the detection area rather quickly. The fiber-optic sensing system uses a small fiber-optic head along with an amplifier in order to accommodate itself within a narrow space near the wrapping mechanism and to provide fast and stable operation. This type of sensor is widely used in cases where a bulky sensor housing cannot be accommodated.

Detecting empty and double-fed straws

It should be noted that the real value of a counter sensor lies not only in the detection of the straw but also in the detection of some kind of deviation in the process. For example, empty wrappers on the production line, as well as two straws supplied into one pocket, are detected using the same principle of the PLC analyzing information provided by the sensor in comparison with the cycle.

Speed and response time

While the performance of a sensor will be adequate at a lower testing speed, it might start missing some signals when the same line is run at its full production speed. The reaction time or detection and re-detection time of the sensor becomes the bottleneck in such cases. One reason why high-speed machines with servomotors depend on fast sensors which respond to a signal in near real-time rather than depending only on mechanical timings.

How Sensors Improve Position Control 

Color mark (registration) sensors for printed film

In case the packaging machine uses print on the film, then the color mark sensor or registration sensor is used to detect the printed mark on the film. This information is then used by the PLC to time the sealing and cutting operation so that the print remains in the same place for each individual wrapper produced. This is worth asking about directly if you're evaluating a machine built with printing in mind, like the Full Automatic Individual Straw Packing Machine LG-58YS.

Position feedback from servo systems

While older machines depend on mechanical cams, in the case of a servo-controlled machine, encoders give the PLC data on the precise location of the motor shaft in real-time. This closed-loop design enables the PLC to make adjustments on the spot rather than have to account for the misalignment of worn-out mechanical components. In terms of actual results, it means improved accuracy of the location of the seal and cut.

Film tension and drift

A roll of film will not perform the same way at the beginning of the run as at the end of the run because the diameter changes. In addition, the tension and speed of feed may vary, but the sensor that provides the real-time information to the PLC can make the necessary adjustments to prevent this from being a problem that results in skewed wrappers toward the end of the roll.

How Sensors, PLC, and HMI Work Together 

None of this works as isolated parts. A sensor by itself only reports what it sees; it's the PLC that turns that signal into action.

Here's the basic loop, and it happens in milliseconds:

• Detection: the sensor senses the straw, film mark, or motor position.

• Decision: the PLC compares the information to the cycle expectation.

• Response: the system can either adjust the servo motor, reject the product, or shut down the production line if there is an issue.

This is the feedback control loop that makes it possible for the machine to recognize an empty wrapper or a poorly cut wrapper before it is packaged and shipped.

The HMI turns raw data into something useful

The human-machine interface (HMI) is where all of this is revealed to you. A great HMI will display real-time counts, record any error that occurs, and allow for modification of sensitivity settings or timing of sensors without having to dive deep into the PLC code. This is important not only for teaching new operators how to use the machines but for reducing changeover times between straw sizes/materials.

Turning stop data into fewer stops

Each and every automatic stop registered by the machine represents a data point. When a machine consistently stops during a particular phase, whether it be the registration sensor registering a misread, then this represents a direction that can help in solving this problem – cleaning/re-calibrating that sensor or checking that film roll.

Common Sensor-Related Issues and How to Solve Them

The typical issues with sensors are usually a few repeat offenders.

• False triggers or missed detections: generally attributed to dust, contamination of the lens with film, or interference with ambient light. Cleaning and checking for sensitivity will correct most of these problems.

• Print mark misreads:  the printed marks tend to be dark or glossy or low in contrast for the color mark sensor to see clearly. Increased sensitivity or changing to an ink mark of higher contrast will resolve the issue.

• Drift after long runs: sensors may slowly lose calibration after thousands of cycles of usage. Scheduling periodic calibrations, rather than only doing so when defects become apparent, prevents this from becoming an issue of wasting product.

A short checklist worth keeping near the line:

• Check the lens: if detection appears inconsistent, clean the lens.

• Confirm sensitivity settings: particularly following changes in straw materials or colors.

• Watch the reject rate: increasing trends generally indicate that a sensor is in need of maintenance prior to replacement.

• Keep spare sensors on hand: if it is the sensor that is not working, it will be a cheap and quick fix if you do not have to wait for parts.

If a problem doesn't clear up with cleaning and recalibration, it's worth checking in with technical support or sourcing a replacement through spare parts rather than letting a line run on guesswork.

What to Look For When Choosing a Straw Packing Machine 

When there are comparisons between the machines, the sensor system deserves to receive as much thought as the speed figure quoted. A few questions to ask of your machine supplier might be:

• What sensors does the machine employ, and where on the production line?

• How does the machine deal with variations in straw material? 

• How convenient is it to clean, calibrate, or replace a sensor without having an engineer available on site?

• What action does the machine take when a sensor detects an issue?

A machine with a well-matched sensor and servo setup, like the Full Automatic Individual Straw Packing Machine LG-58YS, pays for itself in fewer stops and less wasted film over a production run. It's also worth checking what kind of after-sales service comes with the machine, since sensor calibration and troubleshooting go a lot smoother with good documentation and support behind you.

Conclusion

Speed sells the story, but it is the sensors that make the speed count. Counting sensors ensure each wrapper really has a straw in it. Position sensors place the seal, the cut, and the printed mark right where they are supposed to be, again and again. Add these together with a programmable logic controller and servo feedback control system, and you have a line that can check its own mistakes within milliseconds, instead of handing them off to the packaging.

When you're evaluating choices for a straw packing line, or trying to figure out why an existing one has trouble getting it right, you should talk directly about the sensors and servo systems behind it. Contact Hangzhou Fuyang Sunrise Machinery to see the LG-58YS in action or get a quote tailored to your production line.

FAQs

What sensors are used in an individual straw packing machine?

A single unit of a straw packing machine (used for straws wrapped in OPP film or paper) is dependent upon a few core categories of sensors for the coordination between feeding, printing, cutting, and sealing processes. A few such sensors are photoelectric or color mark sensors, proximity sensors, encoders, and temperature sensors.

How does a packing machine avoid empty wrappers?

Packing machines do not have any issue related to empty wrappers, as they detect the presence of products through sensing and automated rejection techniques.

Do clear PLA straws need different sensor settings?

Yes, in the case of clear PLA straws, there may be a requirement for different photoelectric or optical sensor settings from that of clear plastic (PP or PS) straws because, although they look identical in terms of being completely transparent, they actually are different in nature.

How often should sensors be cleaned or calibrated?

How often sensors need cleaning or calibration depends heavily on the sensor type, the environment, and the application requirements (such as industrial safety vs. general use).