Miniature photoelectric sensor detects fill level during secondary packaging operations

Summary

In the food processing industry, shingling, or overlapped layering, is a common technique for optimizing space utilization during secondary packaging operations. Confectionery, sealed in gusseted bags with predominantly triangular profiles, is packed in alternating, overlapping layers in preformed cardboard cartons. Once each carton is full, it passes to a case-sealing station prior to palletization and dispatch.

Prealigned bags of confectionery arrive at the packing station in regularly spaced rows. At each station, a multi-axis pick-and-place packing robot lifts a row of bags, aligns it and lowers it into a preformed carton. Successive layers overlap each other, ensuring that space within the carton is fully utilized. Once the predetermined number of layers has been packed, the carton is conveyed to the sealing station.

From time to time, one or more incorrectly formed layers occur. Individual bags may be missing from a row on arrival at the packing station, or may be damaged or misaligned. A non-contact sensor system is needed to sense the height of the top layer of bags, rejecting any defective cartons. It must be reliable and require minimal maintenance.

Customer Solution

Rugged photoelectric sensors with background suppression from the Contrinex C23 range are ideal for this application. A pinpoint red LED with a 10mm-diameter light spot at the maximum sensing range of 300mm ensures highly reliable detection of objects of almost any color against light or dark backgrounds. These sensors are well suited to both the task and the environment.

Immediately after packing, a single sensor is mounted centrally above the conveyor. As each carton passes below on its way to the sealing station, the sensor detects the top surface of the packed bags. If the height of the top layer falls outside preset limits, the sensor triggers a reject mechanism that diverts the carton to a holding area for investigation.

Mounted in 20mm x 30mm x 10mm miniature plastic housings, C23 photoelectric sensors  are available with industry-standard PNP or NPN 3‑wire or 4-wire output. Connection to the customer’s control system is via a PVC-sheathed cable with the choice of an integral M12 connector or a hermetically sealed entry. A second output provides a stability alarm in the event of reduced sensitivity, flagging the need for preventative maintenance before any performance degradation occurs.

Locating sensors optimally is simple thanks to a custom-designed range of multi-position mounting brackets. An operating range between 15mm and 250mm accommodates a variety of carton sizes without any need to reposition the sensor. A simple electrical adjustment via an onboard potentiometer suffices, while remote adjustment via IO-Link, a standardized point-to-point serial connection protocol, is available as standard at no extra cost for PNP versions.