The bar code is one of the most critical elements of a label. More and more, fully automated systems are relying on bar codes to streamline all kinds of operations. However, if a bar code is illegible, major hassles are created within the automated environment leading to enormous costs. Therefore, it’s no surprise that astute managers are seeking ways to eliminate bad bar codes from their labels.
This has led several thermal printer manufactures to create elaborate mechanisms to verify each bar code before it is released from the printer. In general, these systems do an excellent job at eliminating bad bar codes, so it makes sense that customers would look for similar solutions when considering a move to color. Therefore, I’m often asked, “Do you have an inline verifier for your color inkjet printer?”
The question brings me back to my days in B-school when I learned that “customers don’t need drills; they need holes.” In our case, customers want valid bar codes. An inline verifier system is one way to achieve this, but it is far from the only way. To find another solution, it’s important to consider what causes bad bar codes.
- Ribbon wrinkle. It’s very difficult to run hundreds of miles of flimsy plastic film without a wrinkle or two.
- Ribbon inconsistency. Perfect thermal ribbon transfers are tough to make on a consistent basis. Ribbons will invariably have areas of thicker, thinner, or missing coating which in turn can cause transient bar code failures.
- Head failure. The heat and physical abrasion of the ribbon grinds thermal heads into submission. Add the fact that the printer doesn’t know its head has failed, and the initial failure mode is almost always caused by a few dropped dots. Although a few missing dots are hard to see, they can kill bar code scan-ability.
- Contamination. Clean heads make good images. Unfortunately, as miles and miles of ribbon rub past the head, it becomes a natural trap for accumulated contaminates.
- Set up issues. A thermal printer requires very careful set up. If the the temperature is set too high, the resulting bars are too thick, which in turn makes every space too thin. Vice versa if the temperature is set too low. Additionally, print speed, head pressure and pressure block location all need to be optimized to ensure bar code quality.
- Ribbon variation. The marketplace is filled with a wide variety of ribbons, each with grossly different characteristics. Therefore, if different ribbons are used, the settings mentioned above need to be re-calibrated. I’ve seen bar code problems caused by a well-meaning purchasing rep who substituted one ribbon for a lower cost one.
Therefore, given all these possible failures, the only practical way for a thermal printer to guarantee bar code quality is through the process of inline post-print inspection.
Now, let’s compare this method to the one used with Epson ink jet printers. There are no ribbons to wrinkle or have have consistency issues. Nothing touches the heads, eliminating a source for wear or contamination. There are no end-user equivalents to heat, pressure, speed settings and such that affect print image dimensional accuracy critical to bar codes. And the head does not wear in the course of normal printing.
This isn’t to say that inkjet technology is infallible. Its most common failure points is a clogged nozzle and in very rare cases, an actual head failure. But these issues can be caught, since both the 3400 and 3500 printers actually use automatic nozzle check systems to monitor head integrity by verifying that every individual nozzle is working properly. Which brings me full circle to my reference to drills and holes. Customers want accurate bar codes and guarding against nozzle failures is the way inkjet printers achieve this goal.