UV transparent-object detection solves medical packaging problem

Transparent plastic packaging is commonly used in the packaging of a wide variety of products. However, it poses a challenge for high-speed automated packaging machinery, which was the challenge faced by a manufacturing packaging medical products. For a solution, it turned to Contrinex’s family of transparent-object detection sensors which utilise UV light.

The clear plastic thermoformed blister packs formed in this application are used to hold pharmaceutical and surgical products. They typically comprise a recessed, semi-rigid tray base, vacuum-formed from clear thermoplastic material, into which the product is placed, before it is sealed with a metal or plastic film to provide hygienic packaging.

Typically, blister-packaging lines for surgical products operate in sterile conditions and therefore minimal manual intervention is permitted, to minimise the risk of contamination. If defective bases are identified and rejected after forming, the flow of tray bases to the loading station is not continuous. In this event, a sensor system must suspend the loading cycle until a base is in position.

A sensor is therefore used to detect the presence of transparent tray bases, enabling the loading cycle to proceed with minimal delay as soon as a tray is present at the loading station in-feed. Standard photoelectric sensors, which use red-light, proved to be unreliable as they are unable to differentiate reliably between ‘tray present’ and ‘tray not present’ conditions.

Therefore, an alternative sensor was sought that could reliably detect the presence of a transparent plastic target. Ideally, the sensor would have a sensing range that would enable it to be mounted some distance above the blister trays to provide access for operators or cleaning.

The use of an ultraviolet light source in Contrinex’s C23PA UV transparent-object detection sensors is ideal for this application. Part of the family of small C23PA sensors, the sensor’s performance enables it to be mounted above the machine’s conveyor, and reliably detect the presence of transparent tray bases. Positioning the sensor is simple thanks to a range of adjustable mounting brackets, and their auto-collimated optics ensure there are no blind zones.

These transparent-object detection sensors use a patented reflex operating principle with polarised ultraviolet light with a 275 nm wavelength. This wavelength is chosen because it is where the absorption of the polarized UV light by a range of commonly used plastics is maximised. A choice of size and shape of the custom-designed UV reflectors which use high-tech plastic materials with excellent reflective properties simplifies installation.

The customer makes use of both the PNP normally-open output and the IO-Link digital interface. IO-Link is a standardised serial connection protocol for sensors and actuators, which is included within the sensors for no additional cost.

An additional option across the C23PA family of photoelectric sensors is to have a second switched output to provide a ‘stability alarm’ in the event of less than ideal detection. The alarms flags the need for preventative maintenance, such as cleaning the sensor’s lens, well before any performance degradation occurs. Proving this extra functionality on a separately switched output makes it simple and low cost to implement within the machine.

The robust sensors feature Ecolab-certified plastic housings and a sensing range up to 1200 mm, adjustable using a teach button or IO-Link to accommodate a wide range of applications. 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.

The C23PA family of sensors also benefits from having a range of complementary low-cost stainless-steel mounting and protection bracketry options.