Using the eye is visual. The use of magnified imaging by eye or with a camera is a common part of manufacturing. Some of that use is for inspection. Some is for measurement. Some is online. Some is offline. There are vision-inspection systems. There are video-inspection systems. There isn’t a standard definition of each, and they’re different from each other.

Visual (not vision) inspection
We all know about visual inspection—inspection by the naked eye. Parts are inspected for proper color, fit and finish, presence or absence of labels or other parts, and much more. Visual inspection can be improved by lighting. Colors are most easily seen under bright, white light. Other inspections are done with lights of different wavelengths. For example, certain inks appear only under ultraviolet light. Inspections of these kinds can be performed by unaided observation of the part.

If the part or characteristic of the part being inspected is small, magnification makes such inspection easier. A common tool for this is the single lens magnifier, many times surrounded by a circular fluorescent light. Mounted at the end of an adjustable arm, the lens can be positioned for proper magnification while the part being inspected is held comfortably. The fluorescent light evenly floods the part with light. This, too, is visual inspection.

Other types of inspection devices include microscopes that perform a similar function as a simple lens, but at much higher magnifications. In visual applications, the user looks through an eyepiece to see the magnified image, which can be illuminated from any number of directions and by a variety of light sources.

Visual inspection with a camera
With the pervasiveness of digital cameras, everyone now pretty much understands the basics of how they work. A lens images a scene on a detector that digitizes the image for later viewing. A camcorder is similar, except that it captures a continuous series of scenes. Digital still cameras and camcorders also illuminate and magnify the scenes they image. Let’s apply this to the inspection examples above.

Your digital camera can show the captured image on its display, but the size of that display is usually less than 3 in.—not very practical for inspection. However, displaying that digital image on a video monitor can show great detail enhanced by the size of the monitor. It’s the same for the camcorder images. Vision inspection is basically visual inspection with a camera.

The simplest vision inspection is just the magnified image from a camera shown on a monitor, instead of directly through a lens or eyepiece. There are a number of advantages to this type of inspection. The user doesn’t have to bend over an eyepiece to see the image. He or she can sit at a comfortable distance. In addition, several people can look at the image at the same time, which may not be practical for inspection, but is very useful for training purposes.

Let’s go back to the digital camera. If you take a photograph of an object, you freeze its motion. The still image captures the event at an instant in time. My earlier mention of inspection assumed the inspector was holding the part being inspected. What if the part is still on the production line? Freezing it in time can come in handy.

In-line vision inspection
Many times it’s desirable to inspect parts at various stages of the manufacturing process. However, if tens or hundreds or thousands of parts are being made at a time it can be impractical to pick each one up to inspect it. This is where capturing an event in time comes in handy.

Solid state cameras are small enough to mount on the production line at positions where parts pass by it on a conveyor belt, for example. Inspectors can look at images of the parts on monitors, rather than at the parts themselves. If there are few parts or the belt is moving slowly, it might be possible to inspect them all in real time as they go by. However, if there are lots of parts, or they’re going by too fast to see the detail by eye, images can be captured just like taking pictures with your digital camera. Those still images can be inspected visually (by eye) or by image processing software.

All this leads to two generally accepted definitions. Visual inspection means inspection by eye, either directly or with supplemental lighting, and/or with magnification. In other words, it’s inspection without the use of a camera/lens/electronics (an instrument). Vision inspection, on the other hand, typically means inspection with a camera/lens/electronics where, in addition, the images are analyzed by software, not simply the eye of an observer.

How is video inspection different?
This is where it gets more convoluted. A vision inspection system that displays the camera image on a monitor typically uses video signal standards to present the images. A computer monitor can have separate red-green-blue (RGB) inputs. With a television monitor, the signal is usually the NTSC standard (in North America). In either case, the image is displayed on a video monitor. That vision inspection uses video monitors causes some people to erroneously interchange the words “vision” and “video” when describing the type of inspection. There is yet another difference.

The following definitions are common in the industries that provide such systems. Vision inspection typically means inspection of parts “as they go by.” This means use of a camera and associated electronics to capture images of parts on the production line. Video inspection, on the other hand, usually means off-line inspection, where the parts are taken to the inspection system. In such usage, vision and video are not synonyms.

The three Vs of inspection
So where does all this leave us? I can visually inspect a part directly, or I can visually look at a video image from a vision system. However, if I use a vision inspection system, I’m usually inspecting parts online. On the other hand, I use video inspection to measure parts that are taken to the inspection system. In both cases, those systems might use software to aid the inspection rather than rely on visual interpretation of the images. These distinctions matter when you think about the capabilities of each type of inspection.

What does this have to do with measurement?
Yes, the column is called “Measurement Matters,” and all I’ve talked about is inspection. Well, measurement and inspection are sometimes used interchangeably, yet are very different. Next month I’ll get into the differences between inspection and measurement. I’ll leave you with this thought: Just as you can visually analyze a video image from a vision system to inspect a part, you can also inspect a part to verify its measurements or inspect a part as you measure it.

Yes, measurement matters. Inspection, too.