Remarkable though the human eye is, it was never designed to detect small defects on a fast moving packaging line, particularly for lengthy periods, which is why vision technology is so important says Rod Abbott
Machine vision is concerned with the automatic interpretation of images of real scenes in order to obtain information and thereby to control or monitor machines or processes. The images may be visible light, but could also be of X-ray or infra-red energy, and may even be derived from ultrasound information.
Today’s industrial vision systems are digital processing systems using image capture equipment feeding a digitising device which in turn feeds a digital processing system. For the majority of systems supplied by UK Industrial Vision Association members this simplifies to a video camera feeding an analogue-to-digital converter feeding a frame store accessed by a computer or other form of digital processor.
Companies may still question the financial justification for using vision systems but UKIVA director Don Braggins offers 21 valid reasons for their employment, all financially rooted.
These include the saving of time and labour directly concerned with inspection of products; encouraging process automation; contributing to scrap elimination; better process understanding; increasing throughput; minimising raw material usage; reduction of product recall costs; and improved sales through the quality perception of packaging – if the packaging is not perfect, the customer may think that the product is not carefully made.
The more cynical may only choose to be persuaded by application… and why not? A good example is offered by German brewer Emil Petersen. When the company wanted to increase efficiency and ensure that its bottle labels were applied correctly, a complete automation system was installed in 1999 under the supervision of technical director Werner Sauer.
Using two Krones production machines set up in a mirror configuration, the company was able to expand output capability to 70 000 bottles/hr. One particular constituent of the new Krones machines, the Multimatic, is responsible for receiving the beer bottles once they have been packed, cleaned, filled and sealed with a plastic stopper. The Multimatic is then responsible for both labelling the bottles and applying a wire clamp over the stopper to ensure it does not discharge under the build up of pressure.
Each bottle that enters the Multimatic is fed into a 40-bottle capacity magazine and placed on a separate plate in such a way that the clamp faces in one of two orientations. These plates are equipped with a servo-motor that rotates bottles 360 deg to accurately position them prior to labelling. Two retro-reflective sensors are used to recognise the orientation of the clamp on the bottleneck.
An Omron F10 pattern matching advanced sensor recognises the position of the clamp and compensates for error. The F10 consists of two parts. Firstly, the camera head, which projects the “taught area” to the sensor and the area in which the sensor searches for the taught image and, secondly, the evaluation unit which receives the resulting readings and gives a yes/no output.
The camera projects the measurement window over the bottle neck area containing the clamp and compares this with the ‘good’ pattern taught by the user. If the clamp is in the correct position, the bottle will not rotate and the label will be successfully placed. If the sensor does not detect the clamp, the bottle will be rotated until the F10 identifies the correct pattern, after which labelling is executed.
Fast, precise inspection performance
Omron has moved up a gear or two since then, having recently introduced another highly capable vision system that combines flexibility and ease of use with powerful software tools. The F210 can be used to inspect a variety of targets, from orientation of bottles on high speed lines to complex labelling verification and positioning applications and confirming products packed match label descriptors.
It is said to be easy to set up and configure thanks to user-friendly menus and uses advanced algorithms to ensure fast, precise inspection performance.
The standard software package offers about 70 different processing functions. During set-up of an inspection task, any combination of processing functions can be selected from the menu. A macro functions software option allows the user to enhance flow menus by creating macro programs using only a PC text editor. Two cameras can be connected to the F210 to perform different inspection tasks at different locations at the same time.
Lake Image Systems sales manager David Rudeforth takes the discipline a step further. “A vision system can only help to identify faulty product, but what about identifying the cause of the faulty product – whether that is a crumpled package, a loose bottle cap or a missing/misplaced component.
“The cost of manufacturing errors like this is very high and, if the fault causes a line stoppage, it’s a cost well worth avoiding. A high speed imaging system will record the user’s problems, allowing them to see exactly what is happening in slow motion, and enabling faulty machine actions to be identified and corrected.
“Less stoppages and less faulty products mean higher outputs and higher speeds. Calculate the cost of one line stoppage lasting an hour. A high-speed camera can help pinpoint the problem area very quickly, preventing this happening again.”
Connection through firewire interface
The Privo high-speed camera, made by Swiss-based AOS Technologies, is distributed in the UK by Lake and is one of a range of three brand new cameras that connect to the operator’s laptop using a firewire interface. The compact unit incorporates its own battery and is capable of up to 1000 frames/sec in high resolution.
This rate allows the fastest of machine faults to be visualised. The entire system, including lighting, fits into an oversized briefcase and costs less than the early bulky systems.
Meanwhile, Tecscan has introduced an on-line pro-active inspection system to solve two problems that occur in corrugated carton and box production. The system warns about, or rejects, printed cartons automatically that have been printed with missing colours and ensures accuracy of the folding and gluing operation. It relies on high-speed intelligent cameras and can be integrated into any high-speed folder or forming machine.
Primarily for flexible packaging, Cognex has introduced PatFlex, a software tool that enables a vision system to find an object, an identifying characteristic or motif that has been altered due to a perspective change or surface deformations and corrects them. It allows for optical character verification marked on curved surfaces on which the perspective deformations are common and also determines the location and inspection of decorative labels glued on cylindrical surfaces.
It is designed for applications in which the object changes shape during the production process, such as items in pouches or bags. In taking on all of these appearance changes, PatFlex enables vision systems to proceed with rigorous inspection and verification applications.
Cognex has also introduced a new In-Sight 5400 vision sensor which it says is 10 times faster than the previous generation of vision systems, enabling high-speed inspections to be carried out on cans and bottles without sacrificing image quality.
For web printers, converters and label printers, AVT supplies machine vision-based automatic inspection systems – AVT PrintVision solutions are designed for process control [PrintVision/Jupiter, PrintVision/Genesis] and quality assurance [PrintVision/Apollo, PrintVision/Helios].
The PrintVision/Argus combines the two, with a camera that samples the web, and a second LCCD camera that provides 100% inspection, 100% of the time. Process or random faults are detected by the LCCD camera and the second head moves in for a closer look.
New category of vision system
The future of vision technology has much in store for the packaging industry. Like many high-tech disciplines, it is constantly evolving. In the past year a new category of vision system has emerged called machine vision micro-system. This offers the high performance capabilities typical of PC-based vision systems at a lower price, plus some interesting new technologies.
Designed to offer many characteristics of an industrial control system at the price point of an intelligent camera, machine vision micro-systems have already become a popular alternative for high-speed inspection. Manufacturers are increasingly adopting this new technology along with gigabyte ethernet disciplines, chip-on-board LEDs for illumination, layered photodiodes and CMOS camera technology for ultra-high resolution.