Laser diode arrays revolutionize fruit labelling

The ability to print variable data on demand brings benefits for both fruit packers and the retail industry

Steve Gorton and Scott Howarth

In October 2009 Sinclair Systems International LLC (www.sinclair-intl.com), the market leader in the field of fresh produce labelling, introduced its VPS laser marking system based on diode laser array technology. The VPS system bolts directly onto Sinclair’s existing labelling machines and allows barcodes, PLU (product look up) codes (FIGURE 1) and graphics to be printed on demand according to the type of fruit being labelled.

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FIGURE 1. Laser marked label applied to navel orange.

At the core of the system is an ultra wide laser diode array module manufactured by Intense Ltd. that delivers several hundred individually addressable laser beams, enabling printing of labels in a single pass without the need for scanning technology. Sinclair has successfully completed field trials in California and is in the process of rolling the product out to its customers.

For some time, the fruit and vegetable industry has recognized a need for print-on-demand technology, i.e. the ability to instantaneously change information on a label as it is being applied. Until now, the vast majority of labels have been pre-printed with both branding information and product variable data. The ability to print variable data on demand brings benefits for both fruit packers and the retail industry.

Fruit packers benefit

With the growing need to add information to fruit labels like PLU, country of origin, bar code, etc., it has been necessary for Sinclair’s customers to carry a large inventory of label types. Print-on-demand technology is able to deliver significant savings in both inventory carrying cost and deliver an improvement in operating efficiencies.

Sinclair’s position as a market leader in the industry created a unique product development challenge once it decided to introduce print on demand technology. The company’s installed equipment inventory represented a major product obsolescence liability if replacement technology was introduced into the field. Therefore, the new technology had to be designed as a retrofit kit for existing labelling machines and require only minimal modifications.

On-demand label printing also reduces the number of label applicators required by fruit packers. Until now several label applicators have been used for each fruit sizer, each carrying a specific label. For example, each fruit sizer may have three applicators – carrying labels for large, medium and small fruit. Fruit are “sized” using automatic systems sited immediately prior to the labellers. This size information is used to instruct one of the three label applicators to apply a label to that specific fruit.

Considering this example, the three label applicators can be replaced by one single applicator plus the VPS retrofit system (FIGURE 2). Now the applicator holds a reel of labels containing just the branding information and a blank patch for variable data. The size data is used to tell the VPS system to print the appropriate PLU code and/or bar code.

In addition to reduced label inventory holdings and quantities of label applicators, the print-on-demand technology also brings a range of efficiency savings. Inventory management is simplified, requiring less SKUs and reducing the level of obsolescence. Short or unexpected product runs are no longer a problem. Similar costs associated with over- or under-stocking are reduced. Operator errors and labor time associated with changing labels is also improved.

Retailers benefit

Food safety and traceability is also becoming increasingly important. A number of food safety scares have been highlighted in the press in recent years. The VPS system allows date and location data to be printed on the label in addition to PLU and bar codes, making track and trace possible down to the individual fruit level.

Available technologies

Sinclair considered a wide range of technologies before deciding to develop a system based on Intense’s DLAM diode array technology.

The table compares some of the available technologies that were considered.

A number of Sinclair’s competitors have attempted to implement systems using technology such as ink jet and thermal printers, but have been unable to produce a system that delivers the required quality and reliability at a commercially viable cost.

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Laser marking of labels provides a solution that overcomes many of the shortcomings of other technologies. Laser marking is non-contact, therefore, wear and degradation of the print quality is not an issue (as is the case in direct thermal applications); no consumable is required (as in inkjet technology where ink viscosity must be carefully monitored and managed); and there is no interaction with the surface of the fruit resulting in fruit damage (as is the case in direct lasing the fruit).

Direct thermal or thermal transfer

Thermal printing systems by definition require the print head to be in contact with the label during printing. This leads to wear of the print head and a drop in print quality. This is especially a problem in the relatively harsh environment of a pack house where dust and fruit derived contaminants are commonplace.

Loss of printing elements is frequently seen as the print head wears. When printing bar codes, this is unacceptable.

The label substrate used by Sinclair is a key part of its technology and product. The flexibility and compliance of the label is critical to its ability to adhere reliably to the fruit once applied. Due to the contact nature of thermal printing, heat is generated. This drives the need to use a thicker and more robust label. However, this also has the side effect of making the label stiffer and reducing adhesion.

The need to maintain precise control of the label as it moves through the thermal printer combined with the mechanical constraints of the applicator system means that labels must be printed in advance of the fruit arriving at the applicator. On average the label is printed ten fruit in advance. This creates problems if the fruit conveyor is stopped, or if a piece of fruit falls off the conveyor.

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FIGURE 2. Retrofitted VPS laser marked label application system.

Perhaps the biggest issue with thermal printing in this application is the cost and management of the consumables. With print heads requiring replacement every 500-750k labels or so, replacement could be a weekly operation.

Ink jet

While ink jet is a non-contact technology, the space between the jet and the media is very small (~5 mm). This is better than thermal transfer or direct thermal methods, but only marginally. Ink jets can get clogged up by dirt and debris in the pack-house environment. Blockages result in missing pixels and consequently unreadable barcodes. Similarly to thermal printing systems, inkjet solutions also need to print the labels in advance of the fruit arriving.

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FIGURE 3. Schematic of VPS laser label marking system.

Inkjet systems can achieve high speeds. However, at the speeds required by Sinclair, drying time becomes an issue. Frequently this results in ink rubbing off during the application process.

As mentioned previously, the polyethylene labels used by Sinclair are a key part of the technology, outperforming paper-based labels. Food grade ink that will dry rapidly on PE labels is very difficult to find. Ink is a consumable and must be maintained by the customer; ink cartridges must be replaced frequently.

Solid state laser

Fiber or diode-pumped solid state (DPSS) laser systems are frequently used in product-marking applications. However, they cannot be applied in Sinclair’s application due to the combined requirements of high speed and wide print width. Scanning technology is unable to move the beam over the full print field and maintain the required linear print speed without losing print quality.

Diode laser marking system

The VPS system is built around a very large emitter diode laser array. This is powered by electronics able to drive each laser individually. Custom optics are used to deliver the laser beams onto the label to be printed (FIGURE 3).

The label itself has been developed by Sinclair and incorporates laser markable layers within its structure. The chemical formulation has been designed to maximize absorption of the laser energy and enable high speed printing. The label is certified as food safe.

The system is designed to retrofit onto Sinclair’s existing label applicator, the RM6. The RM6 machine has been proven over many years to be fast and reliable. The system uses proprietary techniques developed by Sinclair. It is able to pick up a label from a reel and deliver it to the fruit gently and without risk of damage. It achieves this by using a rotating set of extendable rubber bellows.

When fitted to the applicator, the VPS print system directs its array of laser beams onto the label as it is moved from the label reel to the fruit surface. This means that a label is printed only when needed.

Intense Limited (www.intenseco.com) is the leading supplier of diode lasers into the printing industry and supplies to several blue chip companies within CtP, digital printing and direct marking fields. Intense’s DLAM technology is unique within the laser industry in delivering laser arrays with several hundred high power, individually addressable emitters. The diode array technology is highly reliable and has been proven over several years of successful production supply.

Advanced die alignment techniques allow Intense to place multiple laser array chips adjacent to each other while maintaining a constant pitch across the entire array. The technology is modular and capable of creating large arrays of several inches. Laser powers in excess of 500 mW per emitter are available.

Field trials

Sinclair has conducted field trials at a citrus pack house in California. Systems were installed and began operation in August 2009. Labelling trials commenced in earnest in October once the citrus fruit season started. The testing went well, and the system was qualified by the pack house to make production runs in January 2010.

The pack house is using the system to produce three different Databar bar-coded labels for small, medium and large navel oranges. To assess the performance of the system, Sinclair measured two metrics: scan percentage of bar code and labelling percentage. For the last production run, the company saw 100% of bar codes scanned successfully and over 95% of the fruit was labelled (this is typical of a normal labelling operation).

Conclusion

Diode laser array marking systems have been successfully introduced into a highly demanding application. The combination of wide print widths, reliable operation, high linear print speed (>1.5 m/s), and good print quality are expected to open up a range of new product marking opportunities for diode array direct marking technology.

Steve Gorton (steve_gorton@intenseco.com) is product line director with Intense Ltd and M. Scott Howarth, PhD, is director of research and development with Sinclair Systems International LLC.

 

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