Application – Detecting bags of sweets at buffering station

Updated on Friday 11 September 2020, 11:11 AM

3 Minute Read

During high-speed production of retail bags, a confectionery manufacturer conveys individual bags of sweets to a pick-and-place packing robot for secondary packaging. A highly reliable diffuse-mode photoelectric sensor, mounted beside the conveyor, detects the presence of bags as they approach the packing station and inhibits the pick-and-place sequence if no bags are queued for the packing robots.


In the food-processing industry, consumer products generally require secondary packaging – both for consolidation and for protection, before final dispatch. During confectionery production, individual bags of sweets travel by conveyor from bagging stations to a pick-and-place packing robot for secondary packaging, before passing on to the labelling and packing area.

Ideally, product flow along the conveyor is continuous; in practice, interruptions occur from time to time as bagging machines require attention. In the absence of bagged products arriving at the secondary-packaging station, a plant-wide control system prevents operation of the pick-and-place robot to prevent miss-filling.

Immediately prior to arrival at the secondary-packaging station, custom-formed guide rails align bags for packing. Space is limited and there is no easy access to both sides of the conveyor. A highly reliable non-contact sensor system was needed to detect the presence of bags as they approach the alignment rails; the system must inhibit the pick-and-place sequence if no bags are queued for packing.

Customer Solution

Diffuse-mode photoelectric sensors from the Contrinex C23PA family of sensors are ideal for this application. These highly reliable devices contain both a transmitter and a receiver and do not require a separate reflector, instead relying on the reflective nature of the target. Space constraints are accommodated without compromise, thanks to a maximum sensing range of 3 to 1500mm. This is adjustable via a pre-set potentiometer or via IO-Link, the standardised point-to-point serial connection protocol.

Immediately before the alignment rails, a single sensor is mounted beside the conveyor; positioning sensors is simple thanks to a range of adjustable mounting brackets. As each bag passes in front of the sensor, its presence triggers the device, sending a signal to the customer’s control system. A high-intensity red LED with a 15mm-diameter light spot at the selected 500mm sensing range ensures highly reliable detection of bags in real-time.

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.

The sensors are corrosion-resistant and impervious to water ingress and has the additional benefit of offering a range of low-cost stainless-steel mounting and protection bracketry. The reliability of the sensors in the application has been excellent.

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