Instead of being reserved for end-of-the-line packaging verification, machine vision can now be cost-effectively deployed at various key process points along the way. By distributing vision sensors at multiple points – and using Ethernet communications to tie them together – manufacturers are able to respond more quickly to problems, achieve better process control and minimise production costs says Cognex marketing specialist Leigh Simpson
During recent years there has been an increasing trend in the packaging industry towards the use of machine vision technology for 100%-automated inspection. On today’s high-speed production lines it has become increasingly challenging to check integrity and critical features of packages such as proper marking and logo placement. Frequent line changeovers only further increases the difficulty of ensuring the proper filling, capping, sealing, labelling and packaging of products.
Machine vision manufacturers are meeting these requirements with new self-contained, low-cost high-speed machine vision systems that can handle multiple inspection tasks with greater realms of accuracy and flexibility. Within these new systems the tools are more intelligent and thus tolerant to light level changes, specular reflection, rotation, noise, vibration and part movement.
They can also work a lot faster [due to hardware performance advances] which means they can work on faster lines, or do more checks on existing lines. A complex PC-based vision check in 1996 might take up to five seconds. The same tools could run on today’s PCs at around 250ms.
Easy-to-use software and increasingly small camera units allow new inspection tasks to be reconfigured should production lines change or move. These changes have seen a marked increase in the number of companies using vision systems in the packaging industry but the story doesn’t just stop there.
The packaging industry is embracing machine vision but it is clear that most packaging lines could benefit from automated inspection at several key process points. Until now the traditionally high price of machine vision systems has often proved a deterrent to using vision at any stage other than at the end of the line.
End-of-the-line inspection systems can do a great job at final part checking but, waiting until an item has undergone numerous value-adding stages of production before inspecting it, can result in a number of problems.
First, since problems are not detected at the point of occurrence, a line may need to be shut down for several hours so operators can trace processes back upstream to determine the root cause.
Secondly, should there be a fault caused at the initial filling stages the product may well have undertaken the labelling and capping processes before being discovered as faulty which could mean that several thousand completed bottles or packages simply become waste product, creating further losses.
Manufacturers could, however, expand an end-of-the-line vision system to other points on the production line by multiplexing vision cameras from a single processor.
The benefit here was that the hardware cost associated with each inspection point was minimal. The downside was that, linking off of a single processor, vision processing had to be divided up among multiple cameras, resulting in reduced vision performance at each point.
There was the issue of scalability which, in technological terms, can be defined as how well a solution to a problem will work when the size of the problem increases. With a multiplexed camera configuration, scalability is inherently poor since only an infinite number of cameras can be used, no matter how many additional uses a manufacturer might find for vision.
Finally, there was a great deal of software complexity and integration costs involved in managing and maintaining multiplexed cameras. Special programming was typically required to synchronise camera triggers and outputs, and a problem at one station often meant the entire system had to be taken offline.
Recent advances in machine vision sensor technology have enabled automotive suppliers and manufacturers to distribute vision throughout the manufacturing process without the limitations associated with a multiplexed camera approach.
Vision sensors are compact, online inspection devices that typically combine camera, processing, vision software tools, and communications in a single, self-contained unit.
Because of the affordable nature of many vision sensors available today and improvements in processor technology, it has become feasible to have one processor per camera, resulting in maximum vision performance at every point on the production line where a sensor is placed and greater assurance of uptime. And, since each sensor is an independent device, the complexity associated with synchronising multiple cameras off of one processor is eliminated.
More importantly, it is now cost-justifiable for many manufacturers to add vision in enough places so packing problems are caught at the source. A company that had only used vision at the end of the line to check completed products may now be able to justify the addition of dedicated vision sensors downstream to ensure proper filling, correct packaging and suitably applied labelling.
That way, if individual components are not correct, action can be taken on the spot before time and money is wasted. With a multiplexed camera approach, there are only so many vision cameras one could use without having to absorb the cost of another vision system. With vision sensors, having one camera for every processor means having the scalability to add vision to these points and others in the future.
Because vision sensors can now be distributed cost-effectively throughout the engine assembly process, vision is finding its way into more and more places throughout the factory. As a result, many manufacturers now need a centralised way to maintain and manage the ever-growing number of vision sensors running on the floor.
Running 60 vision sensors across 10 production lines is one thing. Setting up applications on each, and then modifying them during product changeover, is another.
Today’s most advanced vision sensors offer built-in Ethernet net-working capabilities to solve this problem.
Ethernet communications enable users to link multiple vision sensors across the factory, manage vision activity remotely, and share vision results data with all levels of the organisation.
Networked vision can be implemented in two primary ways. First, two or more vision sensors can be linked over Ethernet to form a dedicated vision area network.
In a vision area network, vision sensors can exchange data and can be managed by some type of host, whether it is a PC or another vision sensor. This type of configuration offers a number of key benefits.
Consider the example mentioned earlier, where vision may need to be implemented at numerous assembly stages. To enable data exchange between several PC-based vision systems on this line, one would need to establish a serial communications link by linking several serial cables between each system.
Then, to view inspection results, one would either need to have a separate VGA monitor at each inspection point to view inspection results or have the results sent over serial lines into a single work station where an HMI package would be required to consolidate and present the results.
In contrast, a network of vision sensors linked over Ethernet enables direct peer-to-peer communications between each sensor over a single line so there are no complicated cabling schemes to deal with.
Since a host manages the network of sensors, vision results data from all four sensors can be collected at a central point, and viewed on a single VGA monitor. The host may also be used to archive failed images from each vision sensor, which can be used to better determine why certain failures occurred.
The second way of implementing networked vision is to uplink a vision area network to existing plant and enterprise networks. This can provide a number of benefits. It enables users to manage vision activity from remote locations. One could set up and modify vision applications, share applications with other plant sites, and remotely troubleshoot problems with technicians, all without ever leaving the office.
Additionally, uplinking to plant and enterprise networks enables manufacturers to gain direct access to the data related to the quality of their products directly from the vision sensors from anywhere in the plant, the enterprise, or anywhere within their global organisations.