During automated packaging of fast-moving products in controlled conditions, thermoforming lines produce transparent plastic tray bases from continuous reel-stock material. A small transparent-object sensor with patented UV technology detects the presence of each set of transparent trays after it is formed, initiating a subsequent operation and, optionally, triggering a counting circuit. Manual intervention is avoided, ensuring contamination-free, reliable operation with little or no downtime.

Customer Application:

 Production engineers rely on high-integrity process control to manage operations, particularly on high-volume packaging lines. Thermoforming equipment, frequently deployed in modern process manufacturing across a range of industries from pharmaceuticals to food and beverages, plays a key role in continuous production of plastic packaging, including blister packs and film-sealed trays.

Typically, this type of packaging comprises a recessed, semi-rigid tray base, vacuum-formed in-line from a clear thermoplastic material and sealed with a metal or plastic film after the desired products are loaded. Configurable thermoforming lines are ideal for high-speed production of tray bases from continuous reel-stock material.

After forming, continuous strips of trays pass through the machine towards a slitting and cutting station. Error-free control of trays is essential for managing throughput.

Sensors must detect the presence of the transparent trays as they pass through the machine, initiating subsequent operations, including filling and sealing. Optionally, a sensor must also increment a counter as each set of trays passes the sensing position.

Photoelectric sensors using visible-light sources are unsuitable as they require part-specific set-up to differentiate reliably between a range of different tray profiles. A solution is required that optimizes efficiency by avoiding manual intervention between batches.

Customer Solution:

The Contrinex C23 transparent-object reflex sensor with ultraviolet LED-light source is ideally suited to this application. One of these small cubic devices, mounted opposite a compact rectangular reflector, is positioned beside the strip of trays immediately after they are formed. As each set of trays breaks the reflected UV beam, it triggers the sensor, initiating downstream operations and, where required, incrementing the item count.

Contrinex transparent-object sensors utilize a patented reflex operating principle with polarized ultraviolet light at 275 nm. At this wavelength, absorption of the polarized UV light by a range of commonly used plastics is maximized. Sensor output is insensitive to target geometry, ensuring reliable detection of irregularly shaped targets, including those with ridged and grooved surfaces and those with complex formed shapes – something that cannot be guaranteed with visible-light sensors.

Custom-designed UV reflectors, using high-tech plastic materials with excellent reflective properties in the ultraviolet range, provide a range of sizes and profiles that simplify installation – even where space is limited. Positioning sensors and reflectors is simple thanks to a range of adjustable mounting brackets, and autocollimated optics ensure there are no blind zones.

An industry-standard PNP normally open output ensures optimum flexibility. Additionally, IO-Link, a standardized point-to-point serial connection protocol for sensors and actuators, is enabled on PNP versions at no additional cost. A second output provides a stability alarm in the event of reduced sensitivity, flagging the need for preventative maintenance before any performance degradation occurs.

Robust sensor construction, featuring small (20 mm x 30 mm x 10 mm) Ecolab-certified plastic housings with M8 connectors, ensures reliable operation. A sensing range up to 1200 mm, adjustable via a teach button or via IO-Link, accommodates a range of machine parameters. Sensitivity data is stored on the sensor’s inbuilt memory and may be retrieved or updated remotely via IO-Link, eliminating the need for manual adjustment.

These rugged small sensors meet the customer’s need for reliable operation with little or no manual intervention. The solution is highly cost-effective with minimal non-productive time; throughput is maintained at or above target levels.

Customer benefits:

  • UV sensors ensure reliable detection of transparent, irregularly shaped plastic targets
  • Safe detection of the thinnest transparent materials
  • Maximum operating reserve owing to high absorption factor of UV light by transparent plastics
  • Elimination of multiple switching on a single target
  • Reliable operation without the need for manual intervention
  • Very low sensitivity to dust, liquid droplets and splashes
  • Wide operating range accommodates full range of machine geometries
  • Simple one- or two-step teach procedure optimizes initial sensor set-up
  • Sensitivity parameters are retrieved or updated remotely via IO-Link
  • Stability alarm highlights reduced sensitivity, avoiding unplanned stoppages

Product Specific Advantages:

  • Ultraviolet reflex photoelectric sensors for transparent object detection
  • Very low sensitivity to target shape
  • IO-Link serial-connection protocol enabled on PNP versions at no additional cost
  • Pre-taught sensitivity parameters stored on inbuilt sensor memory
  • Remote sensitivity retrieval or update via IO-Link
  • Highly tolerant of contamination by dust, liquid droplets or splashes
  • Robust, Ecolab approved sensors with IP67-rated small plastic housings