Contrinex sensors provide ‘sweet’ label checking

Sealed cartons of bagged sweets in a high-volume production process travel by conveyor to a labelling station. Contrinex’s versatile photoelectric contrast sensor, mounted beside the conveyor, checks the label alignment and confirms the presence of print markings as each carton leaves the labelling area. If a label is blank, illegible or wrongly positioned, the carton is diverted to a holding area for investigation.

Advantages include:

  • Reliable, repeatable in-line detection on a non-contact basis
  • Real-time rejection of unidentified or untraceable products
  • Remote set-up via IO-Link reduces need for manual intervention
  • Operating range up to 12mm with three-colour RGB emission technology
  • Automatic selection of best emission colour
  • IO-Link connectivity available at no extra cost
  • High switching frequency up to 10kHzVersatile industry-standard push-pull 4-wire output
  • High tolerance to object position variation around 12 mm

In the food-processing industry, packaged consumer products require labelling, for identification and for batch control, before final packing. In this application, in confectionery production, sealed cartons of bagged sweets travel by conveyor from carton-taping stations to a label printer and applicator, before passing to the final packing area.

The printer-applicator, which is located at one side of the conveyor, produces a continuous feed of printed labels from roll-stock. As each carton passes the applicator head, the label-stock advances, peeling a single label and applying it to the side of the carton.

From time to time, misfeeds or malfunctions occur within the printer-applicator, which consequently applies labels that are either blank, illegible or wrongly positioned. Failure to detect these errors results in unidentified or untraceable products arriving at subsequent operations or, critically, at the customer’s premises.

A reliable non-contact sensor system is needed. The sensor must detect the alignment of labels and confirm the presence of print markings as cartons leave the printer-applicator, rejecting any defective cartons.

A Contrinex photoelectric contrast sensor is ideal for this application - Its versatile design incorporates a single-lens autocollimator, delivering a narrow optical beam that allows detection of very small features. The choice of red, green or blue LED light, auto-selectable during set-up, ensures optimal contrast resolution.

Immediately after the applicator, a single sensor is mounted beside the conveyor with adjustable mounting brackets making for easy positioning. As the label on each carton passes the detection point, changes in contrast trigger the sensor. The transition from carton surface to label body identifies the position and alignment of the label itself, while the well-defined contrast between printed content and the label body ensures reliable detection of even the smallest print marks.

If the label is wrongly aligned or the print markings missing, the sensor triggers a reject mechanism that diverts the carton to a holding area for investigation. An operating range up to 12mm allows adequate clearance between sensor and target, while the compact 40mm x 50mm x 15mm PBTB plastic housing is both mechanically robust and small enough to accommodate any space constraints.

Set-up is accomplished either using a three-button keypad on the sensor, or via IO-Link, a standardized point-to-point serial connection protocol. Photoelectric contrast sensors are available with industry-standard push-pull 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.

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