Sensors: A matter for reflection

Sensors which identify individual packs for critical automated processes such as counting, picking or quality monitoring can find many modern pack designs more or less invisible. The use of transparent, reflective, dark or black matt packs could increase a line’s reject and wastage rates to a point where the operation starts to be uneconomic.   Yet, optimal productivity remains critical for food, FMCG (fast moving consumber goods) or pharmaceutical manufacturers supplying competitive markets.  

There’s no need for packaging conveying lines to remain in the ‘dark ages’ with sensors blind to transparency, bedazzled by reflectivity or groping for black matt packs and labels. Packaging designers can explore a glittering world of choices for packs, cartons and bottles without causing major headache for packaging line operation. 

Unusual, angled or rounded pack shapes are also becoming more popular but could cause stoppages and downtime. Similarly, the temptation to maximise capacity to increase throughput and reduce costs per unit could result in crowding packs so close together that some sensors miss the millimetre gaps between packs. The unpalatable solution might have to be spacing out the packs and losing an opportunity for increased profitability.

Black out

Take black as a background colour for a pack design. Tropical butterflies such as the Parides species from South East Asia use matt black on their wings as a way of hiding from their enemies in their jungle habitats. 

The reflectance of light from these wings can be 1% or less thanks to the intricate surface structure.  Even the most matt black cards and paints are around 4 to 5% reflectance. To the average sensor this is still like staring into a black hole.

So, until recently, despite being loved by designers, matt black has been a virtual ‘no-no’ for high-speed pack conveying lines, as many sensors struggle to detect packs, even under bright lighting.

Now, however, it is possible to exploit the style, glitz and glamour of matt black designs. SICK’s new W2S family of high power sub-miniature photoelectric positioning sensors, for example, can cope with reflectance levels down to 1% with ease.

Another issue facing the packing line manager can be overcrowding. Cost pressure to fit more and more packs onto the conveyor can be self-defeating if the detector can’t tell when one pack ends and the next starts.  The same sensor confusion often occurs with stylish rounded, radiused or facetted corners. Artificially increasing the spacing to help detection is an inadequate and expensive option. 

Confronting and solving these problems is the remit of the new DeltaPac multitask photoelectric sensor which boosts packaging productivity by making gap-free pack conveying achievable. Without sacrificing accuracy or risking frequent pile-ups, downstream quality and stoppages, it consistently detects a wide range of pack shapes at high production speeds and eliminates the need to separate packs on a line.

Seeing through packaging problems

SICK’s sensor development engineers have also targeted difficult, transparent, semi-transparent, shiny, highly-reflective and uneven packaging surfaces on high-speed lines.

Transparency allows attractively coloured contents, such as beverages, sauces or condiments, to shine through the bottles and jars, and can substitute for more costly all-over printing or pigmentation. However, many sensors struggle to pick up a clearly-defined signal and heat shrinking on to packing trays can create further multi-reflective clutter.

The new TranspaTect photoelectric sensor delivers reliable and consistent detection of transparent packaging in pharmaceutical, food and beverage processes. A key development was removing the requirement for a traditional reflector for the light beam, which can be inconvenient and difficult to accommodate and replacing this by using a matt surface of a convenient machine component as a reference surface.