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More Answers From John Salls
Hi, i have an application where I need to carry out colour inspection. How to handle such task? What kind of cameras and machine vision algorithms do you recommend? So far I have found out that comparing RGB values is not a good way.
Color inspection is a difficult task as it is so lighting dependent. Start with a GREAT really stable White light and Color Balance Target. If you want to verify color quality at the beginning of a run (to make sure your color is perfect), use a spectrophotometer. If you are trying to inspect during production, you would be looking at a color vision system. There is a pretty broad variation in the tools available from one manufacturer to the next. You can usually make RGB systems work, but it can be really confusing. I would look for one that supports HSI (Hue Saturation Intensity) or a variation of this. It makes more sense to human beings that way. For tools Color Histogram or Color meters will generally tell you what color you are looking at in a specific area. Color filters will also help with the tasks looking for variations. Color Blob is great for locating colors (for example sorting Skittles by color). I mostly use Cognex InSight for this. Good Luck!
We are examining the capabilities of vision systems to perform blemish inspections on molded plastic bottles and are seeking to understand the achievable results within the realms of repeat-ability, reproduce-ability, and stability. Are there any published guidelines or whitepapers that address the art of the doable within the industry?
I am not aware of any white papers on what you are trying to do. Typically defect detection capability varies widely depending on your materials, vision system/camera used, lighting/optics, etc. What i would suggest instead is you get an evaluation on your application performed by several machine vision manufacturers. Typically they will do these evaluations for free or for some small fee depending on how difficult the inspection is going to be. The critical step for this is to gather some representative sample for the manufacturers to look at. Some good sample selected from different batches so they get an idea of your normal process variation, some reject samples from the same batches. Ideally if possible you want to get some borderline good and some borderline bad samples. These marginal samples are absolute gold for the application evaluations. At a minimum this will tell you if your application is possible or completely impossible with very low investment.
I've been working with laser profiling sensors to generate 3D images and inspecting them with vision tools. Usually these devices only give you what is called a height image. Using this image I can measure almost anything I want but I cannot read a 2D code printed on an object or inspect the color/grayscale value of the same object. Is there a device that can deliver both Height Image and "normal image" (similar to one from a camera) or should I just use a profile sensor and camera at the same time?
Gocator also gives a 2D and 3D Image. Not sure how easy it will be to pull those into a Keyence System or if that is cheaper than using 2 cameras, but something to look into.
Hello - I need to image a relatively large area (1mx1m) with about 0.5mm resolution. I think this means that the camera/lens system should be no less than about 4 megapixel, but of course higher resolution is preferred. I also need to stand the camera off the part by about 2m. The application is indoors where the lighting can be controlled reasonably well. It can be considered a static application - speed is not a concern. This is essentially a metrology problem where I am trying to measure a roughly 5mm wide x 1m long feature on the part. Are there industrial camera solutions with this type of resolution?
Yes there are industrial camera solutions that will work for you. Many manufacturers do 5MP Industrial Cameras and a few have higher resolution available. You'll want a good lens. Edmund is a good place to start. The rule of thumb you want to be 5x - 10x your resolution. In this case you would get 1M/2448 pixels = 0.4mm/pixel (Target 0.05mm). You might consider 2 lower resolution cameras with a known calibrated distance between them? Unless you need to measure 0m-1m you can save money and get better resolution. The other important thing would be your budget. I'd suggest Cognex because they are relatively easy to program and have the 5MP camera, but you are looking at about $12K of hardware plus. There are lower cost alternatives, but they are harder to program. I'd look at Cognex VisionPro, Data Logic, or Halcon if you want to go that route, particularly multi-camera. No matter what leave some money for good lights. Never Skimp on Lights. Good Luck!!!