When it comes to quality control in manufacturing, the human eye can prove to be an unreliable detective. Automated vision systems are proving to be speedier and more reliable ‘inspectors’ – solving the trickiest of cases to save costs and improve product quality
Plastics manufacturer Logoplaste is showing how machine vision can make eliminating rejects seem ‘elementary’ at its blow-moulding plant. Working closely with Sick UK, it has reduced to nearly zero the number of defective two-litre milk containers delivered to its customer – a major UK dairy products company.
By replacing manual batch quality checking with Sick Inspector I20 vision cameras, the production team has almost completely eliminated the number of problem bottles that used to slip through the net and end up with the customer. Not only has this improved Logoplaste’s relationship with the customer, it has saved on the potential for punitive fines.
Logoplaste is a major industrial group which manufactures rigid plastic bottles ‘in-house’ in 62 factories located in 18 countries worldwide serving the food and beverage, personal care, household care and oil and lubricants sectors.
For more than 35 years, the company has pioneered the ‘hole in the wall’ concept, supplying plastic bottles ‘just-in-time’ from factories installed directly on the site of the client.
At its plant in Hatfield Peverel, the two 500 metre lines produce 6,000 milk bottles an hour each from HDPE resin with an added white pigment. Two Sick Inspector I20 vision cameras are positioned on each line to inspect every single moulded container at full line speed, replacing the human batch inspection rate of just 14 units per hour.
“Sick was very supportive and helped us to run a two-day trial which demonstrated how effective the Inspector I20 would be for this application,” explains Logoplaste plant manager Jon Hart. “We were then able to build the mounting frames, install the cameras and get the system up and running within two weeks.
“We found the Sick system was very easy to set up, calibrate and commission. The Inspector I20 also offered a degree of precision which enabled us to search for patterns that other cameras might have found difficult to detect.
“The Inspector I20 vision cameras are positioned at close range to scan the top and handle of each container. We have been able to move from 10-15 related customer complaints per year down to only one since installation – almost a 100 per cent reduction.”
“Very quickly we had total quality control on each line, removing the need for human inspection with all the problems of error, fatigue and capacity. Whilst our manpower levels have remained unchanged, we have been able to remove five minutes per hour from QC checks.
“Most importantly, we know instantly if there are problems and we can rectify plant faults in real time. With the previous batch inspection there was a time lag and we could only work back to faults retrospectively.”
The blow-moulded bottles are conveyed to the customers’ plant as aseptic fully-enclosed containers. The ring of material at the neck – known as the moil – is removed later in the customers’ process prior to filling.
During the moulding process, flashings occur at the moil and the handle. Automatic trimming removes the flashings before the containers are conveyed to the customer.
“During trimming, it is possible for the small pieces of flashing to be left attached to the moil or entire handle slugs left in place,” comments Trevor Seabrook, production manager at Logoplaste. “These can be a problem on the filling line, where the moil is removed prior to filling.
“Sometimes the moil and the handle may be damaged during the de-flashing process. If the moil is dented or deformed, it may affect the clean removal of the moils. If there are pieces of flashing on the moil or handle, they could possibly enter the bottle at this point. Holes, tears or weak points on faulty handles will cause the loss of sterility, or could leak after filling.
“It is in our interest to eliminate any problems as soon as detected in order to supply our customer with zero quality issues.”
Each line has one SICK Inspector I20 scanning the container necks and one scanning the section of the handle where untrimmed flashings remain. Set at 40mm from the target, the Inspector I20 compares each scan against a pre-programmed image.
If a fault is identified, an alarm is triggered and the faulty unit can be removed from the line before palletising. Faulty containers are recycled.
While the Inspector I20 cameras may be controlled via its integral digital IO or PC interface, Logoplaste took the decision to add an Inspector Viewer HMI for each line. As well as easy control and overview, the Viewer enables the collection of data and trends, as well as images, and improves the versatility of the quality control system.
“The Inspector I20 vision cameras have now been running for 18 months without issues. We are going to recommend this approach for similar lines at a company technical forum in the near future,” adds Seabrook.
David Hannaby, Sick UK’s product manager for imaging and measurement says: “Using the Inspector I20 gave Logoplaste all the power and functionality of an advanced machine vision solution, whilst being extremely easy to use and affordable.
“The solution is also the result of our close working relationship with the Logoplaste production team and we were able to prove the effectiveness of the system through a trial, before the order was placed.”
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