'Seeing' the problem

The trend toward greater use of dark packaging can be seen on a variety of packaged goods. The sleek look of black packaging in particular has become more popular over the past few years, even in the food and beverage industry. According to Michael Coleman, senior vice president of Source/Inc., a Chicago-based international branding consultancy, "black, [is a] color that historically was not us...


The trend toward greater use of dark packaging can be seen on a variety of packaged goods. The sleek look of black packaging in particular has become more popular over the past few years, even in the food and beverage industry. According to Michael Coleman, senior vice president of Source/Inc., a Chicago-based international branding consultancy, "black, [is a] color that historically was not used in packaging for the food and beverage categories, [but] has become popular as an indicator of quality or indulgence. Player's cigarettes were one of the first brands to use black packaging. Minute Maid Orange Juice was also an early adopter of the color black to signify a premium product positioning."

Greater use of darker packaging across industries has had some unintended consequences for OEMs of packaging equipment, particularly stretch packaging machinery. The problem is that dark colors are difficult for many photoelectric sensors, which often do not detect a dark background or false trip on a shiny packaging material. Another problem dark packaging presents for photoelectric sensors is that dark colors absorb more light than they reflect, which can shorten the sensing range.

MacWrap Ltd., an OEM of stretch-wrapping machinery based in Pontypool, ON, Canada, learned of this problem through customer complaints. The solution involved not only a lengthy exploration of photoelectric sensors that could accurately sense dark packaging, but also a search for a sensor that could be a retrofit into existing machinery.

Control Engineering 's editorial director, David Greenfield, spoke with MacWrap's electrical division manager, Kevin Cowan, to learn how MacWrap's engineers solved this problem.

Q Describe your packaging machinery and how you first learned that darker packaging was causing sensing issues with your equipment.

MacWrap produces three types of wrapping machinery: an orbital, a rotary tower, and a turntable. All three are available in semi-automatic or automatic versions. This issue was brought to our attention through sales. When we first heard about the sensing problem, we weren't getting the proper information about what our machines would be wrapping. Eventually, it got fed down through the sales team that the issue involved customers who were wrapping black packages. We had to scurry and find something that would suit their needs. It was certainly a customer-induced change to our engineering process.

Q Are these types of customer issues more typical now?

I've been with the company for eight years, and I do see this more now. We're getting a lot better feedback. I deal with a lot of our customers directly because I deal with the service end of things as well. I'm able to hear from our customers first-hand and then work with our engineers directly to address certain issues. It's helped improve communications within the company.

Q Once the problem was identified, how did the engineers work to resolve the issue and make it part of the end product?

One issue that we had in addressing this problem was limited space. The old photo eyes we used were inside a carriage that rises up and down to sense the load. The photo eye senses the top of load so it knows when to stop. As a result, we were limited to working with the space available in the carriage unit.

Then it was a matter of finding what suppliers could address our needs. It was quite an intensive look at many suppliers to make sure the sensor could "see" at least six feet, be able to "see" black, and fit the mechanical requirements within the carriage.

Inside the carriage, we have a small opening through which the photo eye "sees." Therefore, we needed a very thin, streamlined eye to be able to fit and see through the opening.

Most important, we wanted to change the sensor without having to change the structure of the carriage. We had to be able to send this new eye out to a customer with an 8-year-old machine for retrofitting without difficulty.

Q What was the principal factor affecting your decision?

We selected the Series 28 photoelectric sensor [from Pepperl+Fuchs] because it withstood all our tests. We had several manufacturers bring their "eyes" in here and we tested them on glossy black and flat black. Its [Series 28] sensing range for black is just 5% less than its range for white targets. The model we chose has an infrared beam and operates in a diffused mode that detects light reflected from a target. Diffused mode background suppression ignores the background by using two sensing elements: one designated for the target and one for the background. When the light from the target exceeds that of the background, the output changes state.

Basically, the Pepperl+Fuchs "eye" worked best and was most reliable. It didn't give any false readings because of the background suppression. Other manufacturers that claimed to have the same background suppression ability could not deliver it when we tested it.

Q Describe the testing you performed on your machines.

Once we placed the sensor on the carriage of our top-loading machine, we activated the background suppression mode by adjusting the potentiometer until the sensor ignored the background. We experimented with the range and found the optimal setting was about four feet. The carriage-mounted "eye" senses the contours of the package, which enables the machine to automatically wrap any size package.

We also experimented with the "eye" on our rotary tower machine, where the carriage rotates around the package. We set the sensing range to the width of the conveyor [42 inches] so that the sensor didn't see anything beyond the belt. Since MacWrap products do not have a lot of I/O points, the systems use standard hard wiring with an Allen-Bradley [Rockwell Automation] MicroLogix PLC.

Q Has this experience changed how you and the other MacWrap engineers think about the design and changing use of your products?

This issue has helped me to be more customer-alert and responsive to their needs. Still, as a small company, a lot of our decisions come down to cost. The Pepperl+Fuchs "eye" turned out to be cheaper than the "eye" we were originally using. Beyond cost issues, we do constantly try to devise ways, through programming, to streamline and make our machines as user friendly as possible, whether that means going to touchscreens or adding diagnostic readouts to help customers troubleshoot the machine and get it back on line as quickly as possible. We have improved a lot in that regard, even though the overall operation of the machine hasn't changed that much.

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