Water drops influence negatively the final performances of the Cap Inspection enacted by mean of camera systems.  Refer to the figure on right side, where a green colour scanning line intercepted a water drop scanning, and measured its distance to the bottle’s plastic, greater than toward the closure top surface: a wrong distance.  


“To prevent these false rejects the inspection’s sensitivity could be decreased, but then we’ll have an optic closure inspection no more capable to reject what guaranteed by the Vendor of the electronic inspector and requested by the bottling factory Quality Control Dept.”

Green colour scans intercepting water drops emulating cocked closures, increasing false rejects. A single water drops is the equivalent of many pixels.  Implying an additional false reject, added to the value we’d have had if all closures should have been dry. False rejects you’ve never seen because the camera Vision inspection equipment had  its performances downgraded since commissioning 


When nearly all of the bottles are damped, the effect is a systematic error superimposed to the uncertainty of the measurement system.  If closures are damped, because no drying system is applied, the losses due to water drops amounts to 0.02 %.   0.02 % of false rejects becomes a huge loss on Production under today’s common assumptions:

  1. Bottling Line is an high-speed one (> 30000 bph);
  2. we integrate false rejects over the entire life-time of the Line (> 10 years).


  A commercial Dewatering solution 

Nearly Inertial Dewatering Solution



To prevent these false rejects the inspection’s sensitivity could be decreased, but then we’ll have an optic closure inspection no more capable to reject what guaranteed by the Vendor of the electronic inspector and requested by the Food and Beverage Packaging factory Quality Control and Assurance Department.  Still today: 

dewatering caps
  1. no Inspector has an “intelligence level” adequate to fully compensate water drops.  They really confuse actual water drops with deformed caps or PET bottles’ neck-rings;
  2. trying to assure themselves Bottlers’ new orders, when questioned during pre-order phase about the performances in presence of water drops, many Vendors of Electronic Inspectors guarantee nearly whatever.

  A particularly efficient commercial Dewatering solution



The solution has to be pre-emptive. The video above shows a commercial Dewatering solution (“Mistral" model by SECOMAK Ltd., based at Elstree in the Hertfordshire, United Kingdom).   A one year long deep, extensive testing in 25 high-speed Aseptic Beverage Bottling Lines ranked it the best of six different commercial and non-commercial competing solutions.  A statistical test, involving over 7 billions of PET containers!   The production speed always as high as 1.5 m/s, 52000 bottles-per-hour.  The key point lies in the fact that this system acts by mean of two rows of needles, thus consuming little of air, and does not influence bottles’ own dynamics. Meaning that the total displacement (or, sliding) of the bottles along their journey in those ~400 mm where the needles dewater necks, under-caps and caps’ all-around surface, is limited.  Thorough, statistically significative testing crossed with False Triggers counters’ data provided by each electronic inspection equipment, allowed to set a precise boundary to the induced sliding.   For > 99.5 % of the unstable 500 ml capacity bottles resulted < 20 mm.  Front of bottles’ diameters ~58 mm, we have a maximum sliding which the Inspector shifting-register may recover of 29 mm.  The remaining 0.499 % of the bottles’ slides in the range (20 - 29) mm, still completely recovered by the shifting register system of the Inspector.  And only 0.001 % of the bottles slided over 29 mm then prone to become a container without any identity. 

 In presence of water drops, multiple light refractions, diffractions and reflections define the superior limit to the size of the defect we can detect by a camera system and an inferior limit of the losses (false rejects), to be integrated along the entire Inspector's lifetime


Non-Specific Systems

Containers Dewatering. Water drops influence negatively the final performances of the Cap Inspection enacted by mean of camera systems

Alternative systems are the blowers like the one on side and below, commercialized by Vendors in different sizes until 15 kW of power: power choice is function of the area to de-water and of containers’ speed.  They are commonly visible nearly wherever and it’d be imagined that they are adapt for the special application we are referring to: dewatering systems.  The tunnel solution is thinked for bottles not having any associated identity in a Shifting-Register.  It is a satisfactory dewatering system only for standalone electronic inspectors and not the actual in-the-machine whose Shifting-Registers is extend tens of meters along Conveyors and Machines.

 Closures drying before inspector: blower-controlled air-knives, acoustic insulation and drip accumulation tray



Containers Dewatering. Water drops influence negatively the final performances of the Cap Inspection enacted by mean of camera systems


In the reality, what we are here naming tunnel solution, are systems to dewater:

  • bottles external sidewalls, 
  • cans’ tops and bottom before an ink-jet marking system, 

One more time clearly visible difference between the Secomak technology seen above and the one here on side, in the consumption of air and energy, markedly in favour of the Secomak-like solution. They have to be dry the tops of the closures and the bottles’ plastic rings, say the areas evidenced with red colour in the figure above, then the air-knives have to be carefully directed there.  

  

 The tunnel solution, as seen by a passing bottle. Visibly, it is thinked for bottles not having any associated identity in a Shifting-Register. Then, it can be satisfactory only for standalone electronic inspectors  and not the actual in-the-machine whose Shifting-Register extend themselves tens of meters along Conveyors and Machines





All times the electronic inspection equipment is configured in-the-machine rather than standalone, the air-knives' geometry has to be optimized during startup to respect the most fundamental requirement of shifting-registers, limiting bottles’ sliding to  < 1/2  bottle diameter.  When closures get out damped by the Capper, it is mandatory to interpose a Dewatering system.


Cap Inspection with Camera, without Dewatering










If the dewatering system is absent, the expensive and intrinsically high-performing optic closure inspection based on 1 megapixel camera, shall be reduced to performances closer to a low-performance single analog sensor optic closure inspection, costing one-hundredth times less.  The reason why a single and simple water drop may affect so much a visual inspection with camera, is hinted by the the Worlfram Interactive animation below (Adobe™ Flash Player™ necessary, here available for download).  Here, a single water drop appears represented as an ellipsoidic object.  Water has a refraction index completely different than air.  More, the same water drop deviates the incident light beams toward different directions, by an angle related to  the wavelength of the photons.  Two parallel beams entering the water drop, shall pass through different amounts of water and, if their frequency is different, this second factor shall add further deviation.  The net visible effect, correspondfing to the original couple of light beams, shall be a pair of blurred dots whose distance is different than the original.  A geometric deformation plus a blurring. 


Links to other pages about Closure Inspection:



                                                                                                                                                                                                                                                                                                                                                                                                                                                         
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