FEATURE Sensors
Transparent-object detection with UV light sensors
Mark Weymouth, Managing Director or Plus Automation, main distributor of Contrinex products in the UK and Ireland, explains the benefits of Contrinex’s C23PA transparent-object detection sensors
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ransparent 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 led Contrinex to develop a unique family of transparent-object detection sensors which utilise UV light. Contrinex’s small 30 x 20 x 10mm C23PA transparent-object detection sensors with their unique patent-protected UV-light technology can easily detect even the most demanding clear objects like transparent thermoformed trays. In a medical packaging application, the sensor is placed immediately after the forming station, and initiates a subsequent operation and triggers a counter. The Ecolab certifi cation of these sensors makes them ideally suited for the packaging of food and medical products.
Pharmaceutical application 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 fi lm to provide hygienic packaging. Typically, blister-packaging lines
for surgical products operate in sterile conditions and therefore minimal manual intervention is permitted, to avoid the risk of contamination. If defective bases are identifi ed and rejected after forming, the fl ow 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 infeed. Standard photoelectric sensors, which use red light, proved to be unreliable as they can’t reliably diff erentiate between ‘tray
18 June 2022 | Automation
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.
Sensor solution
The unique 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 refl ex operating principle with polarised ultraviolet light with a 275nm 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 refl ectors which use high-tech plastic materials with excellent refl ective properties simplifi es installation.
The customer makes use of both the PNP
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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 at 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 fl ag 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-
certifi ed plastic housings and a sensing range up to 1200mm, 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
benefi ts from having a range of complementary low-cost stainless-steel mounting and protection bracketry options.
CONTACT:
Plus Automation
www.plusautomation.co.uk
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