Caps' Colour Inspection


To perceive the rationale for the inspection of the Caps’ Colour, we recommended to see the video below. It has been filmed in a PepsiCo plant and in a beverage Bottling Line where, at the time of the film our staff commissioned twelve different formats, personalized by twelve different colours for the cap.  In this conditions the production face the risk of:

  • Operators errors in the special sort bottle + cap: entire cartons of wrong caps reaching the Capper;
  • caps of the wrong colour mixed in the lot of the caps of the correct colour.


 






A solution pass thru the control of the colour of each one cap applied by the Capper Machine. Colour control made illuminating with a source of known spectrum (a halogen lamp) the cap.  Part of the light reflected by the cap enters the lens of a trichromatic detector.  This is a device with three separate channels, referred to the familiar fundamental colours red, green and blue. The signal in the outfeed of each one channel is separately amplified and later digitised and processed, comparing the digitised value with upper and lower limits set during the commissioning.   




















 The signals incoming by three separate channels, each one corresponding to a fundamental colour, are processed to deduce the cap colour. The couple of yellow colour vertical lines are the inspection window, the range of distances measured in millimetres equivalent to Encoder pulses. In the vertical axe of the diagram they appear, digitized in a scale of 4096 bits, the signals’ amplitudes. In the example shown, a cap has been measured thru all three channels with approximately the same amplitude ~1380 bits. The image setup in the meantime specifying a “good colour 1” implies that all caps whose chromatic mix similar to this one shall be considered correctly coloured. Where “correctly” means their colour is coherent with the currect production


As an example, refer to the graphic above at right side:

  • a couple of yellow colour vertical lines represents the inspection window, the range of distances in the Inspector's Shifting-Register, where the three chromatic channels are evaluated;
  • red colour the red chroma signal, whose grey level is normalized (0 - 4096);
  • blue colour the blue chroma signal amplitude, whose grey level is normalized (0 - 4096);
  • green colour the green chroma signal, whose grey level is normalized (0 - 4096);
  • white colour their superimposed amplitude, whose grey level is normalized (0 - 4096).

Caps whose tri-chromatic mix is out of each one of the three allowed ranges, shall be rejected. In the example, a cap has been measured thru all three channels with approximately the same amplitude ~1380 bits. The image setup in the meantime specifying a “good colour 1” implies that all caps whose chromatic mix similar to this one shall be considered correctly coloured. Where “correctly” means their colour is coherent with the currect production.   In the video above it is visible ad addition to the standard configuration of this kind of devices, namely a stainless steel curved screen, opposite to the source of light and trichromatic sensor.    The Sun in some special times of the day, gets into that PepsiCo Bottling Hall, infeeding the thrichromatic sensor.  Knowingly, Sun’s spectrum is continous and centred on yellow colour.  The screen allow to overwhelm these phases, preventing Electronic Inspector’s systematic errors: huge false rejects stopping the entire 50000 bph PET Bottling Line.


Links to other pages about Closure Inspection:

 

                                                                                                                                                                                                                                                                                                                                                                                                                                                         
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