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Integrating robots with machine vision

01 October 2008

The usefulness of a machine vision system in a manufacturing plant depends as much on how well it is integrated into the production line as it does on the performance of the system itself.

ABB TrueView
ABB TrueView

Making effective use of the data produced by the vision system and making it easy to set up are key factors, says Martin Walder, Managing Director of ABB Robotics

Users of automated manufacturing lines expect a lot from their installations. Typically, robotic cells are now available for a wide range of application areas, serving large automotive production companies to small food and beverage or plastics manufacturers. Encompassing computer science, optics, mechanical engineering and industrial automation, machine vision systems offer manufacturers the tools to perform narrowly defined tasks such as counting objects on a conveyor, reading serial numbers, and searching for surface defects.

Just as human inspectors working on assembly lines visually inspect parts to judge the quality of workmanship, so machine vision systems use digital and smart cameras, with image processing software, to perform similar inspections.

The central ingredient of the most versatile robotic solution is a machine vision system but, in itself, such a system is not a complete solution. Almost any modern machine vision system from a reputable manufacturer will be capable of producing good quality data, but the real issues are how that data are used, and how easy the system is to work with.

It’s important to bear in mind that machine vision system manufacturers produce equipment that can be used in a wide range of applications; it is not specifically optimised for use with robots. This means that although the equipment offers all of the facilities—such as geometric pattern matching and blob analysis—needed for robot control, it will often be unnecessarily difficult for the end user of the machine to access and use these facilities.

ROBOTIC COMMUNICATIONS

The first problem that needs to be addressed is communication between the vision system and the robot controller, as fast and dependable communication is essential for achieving high levels of productivity.

Users expect today’s manufacturing lines to be productive, but this high speed of operation places considerable demands on the robot controller—powerful processors are needed, coupled with software which implements fast but stable control loops for the robot motion. All of this is, however, of little value if the communication link with the vision system is slow or unreliable.

Even the best software and best communications links are, however, of little value unless end users can to take full advantage of their potential. Until recently, this was more difficult than it sounds—both vision systems and robots had a deserved reputation for being hard to set up.

Fortunately, developments in user interface technology mean that this is no longer the case. The best robotic systems have graphical programming systems which are based on familiar Windows technology and which are very intuitive to use. The days of developing manually coded programs for each application and even each product are over.

In addition, leading suppliers of robotic machines provide their own interface for the vision system. Instead of the user having to grapple with the full range of functions offered by the vision system manufacturer, many of which are irrelevant in robot applications, they are presented with selected functions which have been optimised for use with robots.

AUTOMATING TIME CONSUMING OPERATIONS

Essential operations, such as system calibration and object identification, which have in the past been tedious and time consuming, can be automated. Users can also be provided with a library of functions—such as checking that every position in a tray of products is properly filled—instead of having to program these functions from scratch. The result is big savings in machine set up time.

Tight integration between the robot controller and the vision system can also provide the basis for other benefits, such as the automatic sharing and balancing of the workload between multiple robots used in a manufacturing line. This enables throughput and operating efficiency to be maximised.

TrueView

ABB’s Vision Guided Robotics System, TrueView, combines ABB robots with off-the-shelf hardware and an eVisionFactory (eVF) software platform to form a fully integrated package. The technology using a robot-mounted single camera and variable lighting packages to position in an optimal image capture location. The eVF software processes the image and sends the appropriate path adjustment to the robot via the Ethernet.

This unique approach to vision guidance allows for automatic calibration and part training. It proves itself as a worthy return on investment (ROI) opportunity, whilst offering a range of benefits including reduced labour and capital costs, enhanced flexibility and safety, improved quality, and reduced warranty.

AUTOMATION INSPECTION

We have concentrated on the aspects of machine vision systems that relate directly to motion control, but they can also provide other functions, such as automatic inspection.

A vision system can inspect the product itself, detecting all kinds of visual defects such as incorrect shape and poor colour. The system can also inspect the packaging, revealing problems like missing or illegible date stamps, missing labels and incorrectly filled packs.

Best of all, in most cases, inspection can be accomplished with the same vision system that is being used for control purposes. The incremental cost of this additional functionality is, therefore, minimal but the savings it delivers by doing away with manual inspection can be very substantial.

For manufacturers, vision systems should be considered as an integral part of every robot-based installation. As we’ve seen, however, the performance of the vision system itself is a relatively minor concern when evaluating the installation’s overall capabilities.

Hopefully, we have given a brief insight into some of the other factors that must be taken into account, but it’s by no means exhaustive. It’s always advisable, therefore, to seek guidance from a supplier which has proven robotics expertise and which is able and willing to demonstrate the capabilities of its products.

For more information about the potential benefits of integrating robots into your production process, please email robotics@gb.abb.com.


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