Lean labelling sees the light
20 June 2013
Glossy foils, PET films and shrink wraps are being used increasingly in case packaging to maximise the on-shelf appeal of products, while minimising the amount of waste and weight in each multi-pack. However, such applications can create a production challenge, as Sick explains
Along the line, strategically-placed optical sensors detect the presence of packs and trigger automated processes. Lasers usually offer a robust sensing solution, but in the case of reflective, metalised or transparent objects, their beams of light can struggle to detect objects reliably.
The end-of-line labelling of shrink wrapped cases, bottles or cans presents particular problems for optical sensors, especially when bottles are transparent. False signals or mis-reflections from the glossy surface or uneven curved shapes of the wrap can lead to a case being applied with the wrong label, two labels or no label at all. Wrongly labelled packs are rejected and subsequently have to be taken off the line and reassigned by an operator; a mislabelling could even stop the line altogether.
The unrelenting drive for maximum uptime means solutions have to be found to avoid unacceptable stoppages and unnecessary human intervention, maximising reliability and availability at every stage.
Labelling machine manufacturer, Markem-Imaje was challenged by a global soft drinks manufacturer to find a solution to ensure maximum uptime of a new 80 packs-per-minute labelling process.
Application technical manager for Markem-Imaje, Robert Keyte explains: "We had read in the press that Sick had developed a new sensing solution that avoids false signals, so we approached them to explore a solution for our Tandem and Tridem print and apply labelling process.
"We already had a close working partnership, so successfully trialling the system at the customer’s new UK factory went very smoothly. Using the Sick MultiPac sensor in configuration with the Tandem Print and Apply system has delivered 100% reliability in removing spurious signals from the application.
"Tandem labelling systems are designed to provide built-in redundancy avoiding downtime completely. Normally two machines print and apply a label to alternate packs, but when one machine is offline, for example while the label roll or printer ribbon is changed, the second machine is instructed by the control system to label every pack. This is vital in ensuring uptime is maintained in a mission critical environment.
"A sensor is positioned before the printers to detect each pack. In most solutions, a laser sensor is positioned horizontally directing a beam of light to a reflector across the conveyor. When the beam is broken, a product is detected and the machine is triggered to apply the label.
"However, in transparent packs the beam may not be broken, or the light may be misdirected by reflecting off a glossy or uneven surface. As a result the printer may receive multiple triggers for a single pack and this can create a 'ghost pack' in a fully integrated control solution.
"At the start of the process we teach a Sick laser barcode reader which is positioned at the end of the control system. In the event of a no read or an incorrect barcode being selected, the resultant pack is rejected and pushed off the line.”
The two companies worked in close partnerships with the customer to develop a new system using the Sick WTB27 MultiPac. This doesn't use a conventional laser. Instead a special PinPoint, high intensity LED produces a very bright and compact light spot similar in dimension to a laser. The MultiPac is positioned vertically, reflecting the light back to the sensor unit. This solution avoids the possibility of the beam being broken accidentally, for example by an operative when replenishing the label machine with supplies or carrying out preventative maintenance.
The Sick sensor has two independent receiver systems positioned either side of the LED, so if the returning beam is deflected at least one of the receivers captures the reflected light. The PinPoint LED technology emits high-intensity light so that even faint reflections are reliably detected.
"We are coming across more and more applications with reflective materials, clear liquids, or shrink wraps,” continues Robert Keyte. "The solution developed is commercially confidential to the customer, but the principal could equally work for a range of our labelling technologies, for single machine or Tandem / Tridem solution in either new or retrofit situations.”
With a scanning distance of up to 500mm, the Sick MultiPac can accommodate differing pack sizes without the need to adjust the mounting height, another advantage for a leaner manufacturing process.
Wayne Morrison, applications engineer for Sick UK, commented: "Sick and Markem-Imaje worked in partnership to deliver 100% reliability to the customer and eliminated the possibility of false signals. The application offers many opportunities for applications using a variety of labelling technologies and dealing with a wide variety of challenging packaging, from clear packs of bottle water, reflective multi-packs of chocolate bars to metallised foil biscuit wraps.
"The solution also promises advantages in logistics to support reliable detection and tracking of bubble wrapped packages, or shrink-wrapped pallets.”