When is a system really “broken”?
Remember the service call I mentioned in the previous post? The customer had some vision systems that were “not working”, and even wanted to consider new equipment!
This may sound like too broad a statement, but generally, machine vision systems already operating in an automation environment actually rarely malfunction. Nor does their performance “get worse over time”. Certainly components like lights and cameras and processors and other peripherals will fail (or in the case of illumination, degrade). But the simple truth is that virtually any change in the performance of the machine vision system is the result of some external force. (Ok; I understand that any time the system’s not doing its job one might call it “broken”, but there’s a further point here.)
The most common of these changes affecting performance is a change in the imaging: cameras being moved, lenses de-focused, light intensity changing, and so on. I’ve had customers dramatically change a camera position with respect to dedicated illumination and then wonder why the inspection failed since the camera was “still looking at the same area”. Changes in the part being inspected also have a dramatic effect on performance, particularly when those potential variations were not known in advance and accommodated for in the imaging and processing.
Very often, the end-user maintenance and debug process for a machine vision system producing excessive false rejects or missing actual defects is a poorly organized and usually not documented procedure involving random things like focusing the camera, adjusting the F-stop, changing thresholds, even replacing components. Maybe these actions might actually help in some circumstances. What I’d like to emphasize however, is the need for a better “root cause analysis” of the problem. The question that needs to be answered is “Why did system performance degrade?”. Look first to the obvious and most likely candidates: changes in imaging and/or part features or presentation. With a clear understanding of the real problem, the resolution is often easier than expected, and may only require something like minor adjustment of inspection parameters.
An awareness of the impact of external changes on a vision system could possibly eliminate or reduce problems that otherwise might balloon into emergencies. If changes to a part are planned, incorporate appropriate changes to the inspection system just as one would plan changes to other aspects of the automation. Where appropriate, plan and document preventative maintenance for lighting and optical components so that degradation of illumination or dirty lenses won’t affect day to day inspection performance.
David…
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