Precision Measurement - Final Thoughts
This is the third and last entry, for now, in my discussion of precision measurement. I'm hoping this series helps eliminate that question that always seems to come up: "How accurately can Camera X measure something?" It should be clear now that the camera or camera brand is not the key gating technology in a measurement application, and that one cannot know the potential precision of a measurement until the target field of view is defined and the resolution capability is known. And to review, we noted that "accuracy" is a term often misused when we really mean "precision" and "repeatability".
In conclusion, consider the following thoughts about lighting and part features and presentation.
Choose The Correct Illumination
In metrology, the choice of illumination may plays a critical role. Unfortunately there is no specific rule that can be applied to illumination. Many metrology applications benefit from backlighting (taking care in part presentation as noted below), though the physical implementation of a backlight in automation on the production line may be a challenge. Front lighting may [more…]
Is machine vision becoming too difficult? I don't mean that machine vision itself is somehow getting harder to use or implement. But is there a trend towards specifying inspection tasks that are so difficult only a few machine vision professionals can actually come up with and implement a viable solution?
In a recent meeting with a group of very wise and seasoned automation systems project managers, account managers and engineers, I heard a familiar refrain: "the machine vision component sales people always come in and tell us their systems can do everything and anything for $5,000, but after twenty-five years we know better!" (Don't send scathing comments - I'm only sharing an actual conversation.) "Hurray", I sort of thought; "a little resistance to over-promising of machine vision capabilities, cost, and ease of integration."
In the days that followed, however, a more sobering thought emerged. It seems that the savvy customer base knows now that there are appropriate and viable applications for inexpensive smart cameras and smart sensors, and that these components cannot be applied to any and every inspection task. [more…]
Precision Measurement Depends Upon Resolution
A determining factor for delivering high precision and low uncertainty in machine vision metrology is the resolution of the acquired image. In this context, the term resolution (or image resolution) means the size of an individual pixel in real-world units. Simply put, if a camera sensor contained 1000 pixels in the horizontal direction, and optics were incorporated that acquired an image that covered an area in the real-world scene that were 1 inch in width, a single pixel would represent 0.001”. Note that this is a fundamental metric that does not change with camera manufacturer or analysis software.
How many pixels are enough for a specific application?
As a gauge, the smallest unit of measurement (some exceptions noted later) in a machine vision system is the single pixel. As with any measurement system, in order to make a repeatable and reliable measurement one must use a gauge where the smallest measurement unit (as a general rule of thumb) is one tenth of the required measurement tolerance band. In the example just described, the system could [more…]
Having just wrapped up a webinar for the AIA on "Machine Vision Technology in High Precision Online Inspection and Measurement" (register and view here), I decided to expand upon the material here over the next 3 posts about precision measurement using machine vision.
Understanding Precision Measurement Concepts
Precision measurement using machine vision technology is a valuable application for online production inspection. A good place to start in addressing how to successfully perform machine vision metrology is to understand precision measurement concepts. The term metrology often is used interchangeably with measurement and indeed they are closely linked. Actually, metrology is the “science of measurement”. When we talk about metrology in an industrial process, it refers to “applied metrology” or “industrial metrology”; the application of the science of metrology for manufacturing. As we consider metrology in this sense, let’s review some terms and concepts used in measurement and metrology.
The terms precision and accuracy are used in the specification and qualification of a measurement system. Precision is the ability to repeat a certain measurement, while accuracy is how well a measurement agrees [more…]