A: We have all spent countless hours staring at webs for any number of reasons, such as inspecting for quality, wrinkles, defects and so on. While all printing presses have great web-inspection points, few other web machines are so well equipped. What a missed opportunity! It is both easy and inexpensive to design a great inspection station on most machines.
First, as seen in the figure above, we must find a location where the operator, seated or standing, can comfortably view the web. Looking straight ahead or slightly down is most ergonomic. Second, that location must be mechanically trustworthy. The adjacent rollers must be quite round and precisely aligned. Third, the location must have good tension control. Finally, a longish span is helpful, though not necessary. Note that none of these requirements are especially onerous.
What light through yonder window breaks
Now we are ready to put in lighting. Here we will add three lights, but not just any hardware store lights will do. Light intensity will need to be somewhat greater than the highest ambient light in the area. The lighting should be soft and diffused. You can tell whether the light is at least moderately soft in that you will not be able to see the filament or tube or lamp. A light meter can do even better checks of uniformity. Finally, the color “temperature” of the lighting should be “daylight balanced” or 5700 Kelvin. This natural light is considered neutral and standard for most purposes.
The overhead light will serve best for most purposes such as defect inspection. The side light will be most useful for inspecting flatness. Finally, the back light will be great for studying the uniformity of formation. Each light should be independently controlled. Of course, we are not limited to three lights. We could add a strobe to look for and study periodic defects.
Don’t overlook this lookout
Now for the most overlooked part. We must shield all ambient lighting from the inspection area. This is to avoid competing lights and, worst of all, shadows from overhead lights passing through framework, rollers and other equipment. Finally, we may even need to shield some of our own light sources so that they don’t compete with the light we are selecting.
There, we have it. Though it will require some study and rearrangement of lighting parts, the equipment itself is simple and cheap. It may even pay for itself by avoiding but a single customer complaint that might be caught with good lighting.