Transparent-object sensors with patented UV technology detect presence of clear plastic sheet during thermoforming

Summary

During automated packaging, high-speed thermoforming lines produce transparent plastic blister-trays from continuous reel-stock material. Transparent-object sensors with patented UV technology detect the presence of the transparent plastic sheet as it is unwound, ensuring the material is correctly tensioned as it enters the loading station. False detection is avoided, ensuring reliable operation with little or no downtime. Ecolab-certified, these sensors are also suitable for the packaging of medical products.

Customer Application

Thermoforming equipment is often used in the production of plastic packaging and is particularly suitable for the continuous production of blister-packs. The process involves the in-line vacuum-forming of clear thermoplastic material into semi-rigid blister-trays which, after insertion of the desired products, are sealed with film. Configurable thermoforming lines are ideal for the high-speed production of such blister-trays from continuous reel-stock material.

Coupling a standalone reel-feeder to the loading station of a modular line is quick and simple. In operation, a set of drive rollers draws thermoplastic sheet from the stock reel, creating a continuous loop of material between the feeder and the loading station. Maintaining the size of the loop between defined limits ensures the material is correctly tensioned as it enters the loading station.

Sensors must detect the presence of the transparent material as the loop size varies, initiating or inhibiting operation of the feeder if the loop becomes respectively too small or too large. Photoelectric sensors using visible-light sources are unsuitable as they cannot differentiate reliably between ‘material present’ and ‘material not present’ under normal operating conditions.

Customer Solution

Contrinex C23 transparent-object reflex sensors with ultraviolet LED-light sources are ideally suited to this application. These miniature cubic devices, mounted between the reel feeder and the loading station, detect the presence of the transparent material loop as its size varies. Positioning sensors and reflectors is simple thanks to a range of adjustable mounting brackets, and autocollimated optics ensure there are no blind zones.

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. Custom-designed UV reflectors, using high-tech plastic materials with excellent reflective properties in the ultraviolet range, provide a range of sizes and geometries that simplify installation.

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 miniature (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 geometries. Sensitivity parameters are 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 miniature 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.