Sources of Variation and the Maximum Label Size
Variations in products, the labels and the operator set-up will all statistically add in an automated labeling process to present a worst case label application scenario.
The labeling machine also has minor tolerances of operation that will also add to the worst case scenario.
The label size needs to allow for the worst case scenario so your automated labeling continues uninterrupted with a known and understood expectation of label shift.
1.0 Products variation
THE MORE SAMPLES YOU COLLECT THE MORE TRUE THE PICTURE YOU HAVE AS TO CURRENT PRODUCT VARIATIONS
Variations in product size are invariable; even for Plastic or glass containers.
A product that is say 200mm tall can easily have a height variation of .5% or 1mm
This information is often available from the packaging supplier as a Tolerance
When a product varies in shape this presents the worst kind of variation for Automation and in deed for hand labeling.
Labeling with self-adhesive labels requires that that the label is applied to a surface that is flat OR has a curve in ONLY one direction.
With round bottles the curve is in the direction of the Circumference. In some instances the manufacturers of round containers do not carefully control the shape of their containers and you see variations in the walls of the round bottles which results in complex contours (A surface with a curve in more than one direction).
See the following video link “Complex Contours on Round Products”
2.0 Label Variation
While the die shape of a label may be fixed and invariable; its position on the web will vary:
The label manufacturer should be able to advise of the slitting tolerance of the web they can achieve; this can often be +/- 0.5 or 1.0 mm
These slitting tolerances lead to label position tolerance as the label head that dispenses the labels is fixed in position.
3.0 Operator Setting Variation
A skillful operator is still Human and may not set the machine in its optimum setting.
One difficult the operator faces is knowing if his/her setting is based on the Perfect Bottle and Label.
Ideally the perfect bottle and perfect label lie at the center of a Bell Curve of variation/tolerance.
If the operator set the machine based on samples that are not at the center of their bell curve of variation then the labeling results will offset slightly and the maximum label shift will be more than the theoretical addition of just the product and label tolerances.
It’s a good idea to allow between +/-0.5mm and 1.0mm variation for the Operator set up
4.0 Machine Variation
The Labeling machine variations come from a few different sources
While many variation in machine label placement can be attributed to the set-up the following discussion covers the case where the set-up has been completed to optimal settings.
a) Label Tracking
b) Product Sensing
c) Label Gap Sensing
d) Label speed and product label surface speed mismatch
With Round and Flat Bottles the LabelOn™ variation in label placement will be within +/- 1.0mm usually much better
With Oval Bottles the LabelOn™ variation in label placement width wise will be within +/- 1.5mm usually much better , height variation remains within +/- 1.0mm usually much better
5.0 Example Round Bottle Label Height:
A round bottle with total height 100mm diameter 25mm and label panel height 75mm needs labeling
The manufacturer of the bottles states a height variation +/- 1% = +/- 1mm
The label Manufacturer states a slitting tolerance +/- 1mm
Operator skill allowance of +/- 0.5mm
Labeling Machine tolerance is +/- 1mm
Total tolerance is +/- 3.5mm
Therefore maximum label height should be 75mm less 7mm = 68mm
6.0 Example Flat Bottle
A flat Bottle with total height 150mm, Width 80mm, Depth 40mm has a label panel height 80mm and width 75mm needs labeling
The manufacturer of the bottles states a height and width variation +/- 1% = +/- 1.5 mm height and +/- 0.8mm width
The label Manufacturer states a slitting tolerance +/- 1mm (this affects height placement only)
Operator skill allowance of +/- 0.5mm (this affects both height and width placement)
Labeling Machine tolerance is +/- 1mm(this affects both height and width placement)
Total tolerance is Height +/- 4.0mm , Width +/- 2.3mm
Therefore maximum label size should be Height 80mm less 8.0mm = 72mm, Width 75mm less 4.6mm = 70.4 mm
From LabelOn Modular Manuals