Section 1: Bar Code Printing Basics
There are two primary activities associated with bar code systems, printing the symbols and reading them. Both are equally important even though they are separate activities, performed at different times at different locations, and many times by different companies.
It is essential that these two activities be coordinated if acceptable results are to be obtained. Something must be used to make sure both activities are operating under the same rules.
Of the two activities, printing and reading, the first to be performed is the printing. After all, if something is be read, it must first be available in a readable form. Someone else may be printing the bar code symbol for you, as in the case of the UPC codes
printed on items in the grocery store. Or you may be printing the symbol for someone else to read, such as would be the case if you were providing a product to be resold in the grocery store.
Text vs. Bar Code
In our modern information age, enormous amounts of data are moved from computer to computer every day. But computers have difficulty recognizing mistakes, giving rise to the phrase "garbage in, garbage out." If you are depending upon the data to make
important business decisions, it must be accurate, dependable and timely. Bar code systems are used to replace human data entry techniques because of two main attributes;
- The technology is very reliable, with extremely low read rate errors.
- They are easily and inexpensively automated, increasing speed and productivity.
SATO CL Series Thermal Transfer Printers
To realize the benefits offered by bar codes, their capabilities and limitations must be understood. Bar code systems are not designed to duplicate the human visual capabilities, like OCR (Optical Character Recognition) systems which require complex imaging and
recognition schemes, but to replace it with components designed with readily available and low cost technology.
The human visual system is capable of deciphering very complex signals. It can decipher a symbol completely illegible to the machine. But the same visual system has great difficulty in taking large quantities of simple information, such as that represented by a bar
code symbol, and reducing it to a single character. On the other end of the spectrum, the limited operational range of a machine scanner dictates that it operate under a very rigid and simple set of conditions. It can process huge quantities of simple information but requires very definable
elements. For example, it wants to interpret a non-reflective part of a symbol as a bar. It is very poor at deciding if what was seen was a bar or a space with some garbage in it. To compensate for this deficiency, bar code label printers are optimized for printing simple symbols such as the
"bars" in a bar code.
Bar code printers are designed to produce the simple character elements that can be easily read by a machine scanner. Human text fonts in contrast are designed to fit the needs of the human that is interpreting them. Humans like to see all of those curlicues and
serifs hanging off the end of the characters which makes it easier for the eye to string them together into words. Machine readers are more like the engineers that designed them, they see little use in anything that does not contain information. To them perfection is found in nice straight edges
and consistent spacing. A simple matrix font formed from dots is sufficient to convey the necessary information. If larger characters are needed for visibility, simply expand the size by creating larger matrix elements using multiple dots to form each element. This results in the familiar
"stair-stepped" characters that were characteristic of early dot matrix printers. However, humans have become accustomed to seeing smooth and nicely rounded characters that have been printed on their modern laser printers where they have a choice of fonts with which to express their
individuality. Since most labels also contain information in a human readable form, it is necessary for us to compromise somewhere.
Trying to make the human readable characters pleasing to the eye comes at a price, which is paid in increased memory storage requirements and/or reduced print speed. To store a number of large matrix fonts defining a complete range of character sizes requires a lot
of memory. Memory storage can be reduced if the outline font approach is employed, like that used to define TrueType or PostScript fonts. Using this implementation, only the font definition is stored and is expanded by the processor when needed, but the time required to image a label becomes
longer. If items are coming down a conveyor belt at a rate of one every five seconds, a slow printer that cannot keep up is not the correct answer.
Specifications
Application specifications perform the coordination task between the two activities. They are used to delineate the conditions under which a bar code symbol is to be printed and read later. At a minimum, the specifications should contain the following information:
- The symbology to be used.
- The density and size of the symbols.
- The allowable printing tolerances.
- Any check characters to be used to increase data integrity.
- The message content of the encoded data.
- Any data identifier characters to be included in the symbol.
- The size of the label. � The location of each symbol on the label. � Human readable information or graphic images to be included.
- The environmental conditions to which the label will be exposed.
- The material used for the label.
The initial step in label printing is to carefully read the specification. If no specification exists, then the first order of business is to write one. It may be a simple one page memo or a document containing many pages. No matter how simple or controlled your
application, you are asking for disaster without a specification. It establishes the ground rules under which everything must operate. Even though your scanner can read the labels your present printer is producing, there is no guarantee this will be the case if you should ever replace either with
different equipment, or even if you change ribbon manufacturers.
Quality Considerations
The implementation of a successful bar code system starts with the symbol. The code is selected based upon data requirements and the capabilities of the scanning system used. Once selected, the next step in implementing a system is to record the symbol in a manner
that will ensure readability at the proper time. This is a direct measure of the QUALITY of the printed symbol. A quality symbol must not only be within specifications at the time of printing, but must remain readable throughout its life.
Because the symbol is being read by a scanner, its quality level should be judged against what the scanner expects to see. Here is an example of "what you see is not necessarily what you get." The human eye may think the contrast between the bars and spaces
is excellent, but if they are printed with red ink on a white background they will appear indistinguishable to a laser scanner operating in the infrared spectrum. If the bars are created by overprinting with a heavily inked ribbon on a dot matrix printer, then edge bleeding of the printed bars can
result in wide spaces being interpreted by the scanner as narrow spaces.
� MEASURING PRINT QUALITY
For an accurate determination of quality, the symbol should be measured with equipment that evaluates what the scanner will be looking for. There are many pieces of equipment, called verifiers, on the market that can make these measurements. They range from portable units with quick
"Go/No-Go" readouts to ones that analyze the scanner signal and list the level of compliance for each parameter. Some will even make suggestions as to what can be done to improve the quality level of the symbol. Measurements made to the new ANSI standards will be letter graded, ranging
from an "A" for excellent quality to an "F" for bar code symbols that do not fall within the specifications. Using these measurements, it is easy to spot symbols that are slowly deteriorating and take steps to rectify the cause before they become a problem in the field. It is
common for application specifications to call for a letter grade one or two levels higher that the minimum requirements. This way, allowances are made for the symbol to degrade when exposed to environmental conditions and still be within the minimum specification limits when it is time to read
them.
Verifiers should be used with a heavy dose of common sense. Most quality printers designed for bar coding applications have few problems printing consistent symbols if they are maintained within the proper operating parameters (a good ribbon on a dot matrix printer
for example). Therefore, a good sampling program can be used to maintain an acceptable quality level for most applications. Unless mandated by the customer, it is not usually necessary to verify each label as it is printed, unless your printer cannot give consistent results. If that is the case,
it is time to get a better printer. What is important is whether or not the symbol can be read in the days or weeks ahead, after it has been sitting on someone's receiving dock for a couple of weeks.
� QUALITY VS. TECHNOLOGY
Printing quality bar code labels depends upon several factors. First, the print technology chosen must be able to meet the technical requirements of the symbol. Thermal and laser printers can print almost any code density including the new ultra high density symbols, but dot matrix printers can
only be used for low to medium density printing because of the physical size of the print wire. The technology must also meet the needs of the environment. A direct thermal label is of very high quality when it is first printed, but if the label is attached to a part going through a hot air shrink
wrap machine, it can easily become useless. However, the same label is perfectly acceptable for a package of hamburger, neither can stand prolonged exposure to heat or sunlight.
The next consideration is the base label material, which must be matched to both the print technology and the environment. If a symbol is generated by transferring ink to a label surface, then the ink must not only adhere at the time of printing, but throughout the
useful life of the label. It must also provide a method of attachment to the item to be identified. This is commonly done using an adhesive-backed label material, but other methods may be used such as attachment using string or even being stapled to the item. Whatever method is used, it is
critical that the label stay attached to the item. A label lying on the warehouse floor is as useless as one that cannot be read but still attached to the item.
� COMPLIANCE LABELING
Compliance labeling can be most accurately described as a "You don't comply, I don't buy" ultimatum from one of your customers. Your customer has mandated that you put a bar code label on all products shipped to them and have provided a specification. It should describe the symbologies
used, the information encoded, the layout of the label and any additional text information and graphics that may be required. It will also outline the environmental requirements of the label and placement on the shipping cartons.
The specification may follow the general requirements of an industry standard or may be specific to your particular customer. The customer may even level a penalty for labels that do not meet their specifications. Many follow the popular "three strikes and you
are out" arrangement; the first time a label fails, you are fined, the second time one fails, you pay a larger fine, the third time one fails, they remove you from the approved vendor list.
Your customer will undoubtedly institute some type of quality check on incoming labels. This can be as simple as scanning them to see if they read correctly or they may take a statistical sampling of the labels and use a bar code verifier to test them. Obviously you
would like to catch any bad labels before they leave your shipping dock! Now is the time to create your own quality assurance program to make sure you are consistently producing labels to your customer's specifications. The quality assurance program should mirror that of your customer, so that
when problems do occur (and they will occur), you are comparing apples to apples and can immediately identify and correct the problem. It may be that the incorrect ribbons or label stock was purchased. Or that preventive maintenance procedures were not followed, allowing the print quality to
degrade.
SATO CL4O8 Demand Label Printer
An on-line verifier system (one that checks each bar code as it is printed and interrupts the printing if an out of spec symbol is detected) may be needed if strict quality control measures are required. For less stringent requirements, a statistical sampling with a
hand-held verifier may be all that is needed.
Demand vs. Batch Printing?
Many times people confuse when something is needed with how fast it is produced. With bar coded labels, it is not important how fast it was printed, but that it is available when the time comes to be used. The real restraint is the amount of time elapsed between when the information is available
for printing and when the label is ready for use. Bar code label applications can be broken down into two time requirement categories, batch and demand, based on when the information is available to print the label relative to the time it is printed.
� BATCH PRINTING
Batch printing implies that the data to be printed on the label is known far enough in advance to have them printed remote to the using location. Sometimes this leads to increased control problems. If the labels are serialized, for example, a voided or lost label can have serious consequences. On
the other hand, if the label is produced at the point of usage at the time it is needed, the chances of it getting lost or placed on the wrong article are greatly reduced. Batch printing can be done in two basic ways, depending upon how much time the label data is known in advance.
- Off-Site Printing - If the information required to print the labels is known weeks or days in advance and the quantities used are sufficiently large, then label production becomes an exercise for the purchasing agent. There is tremendous latitude in label size, materials and
supply format (i.e. rolls, sheets, individual, etc.). This is probably the most cost effective method of generating high quality labels, and most likely the only way of getting some specialty labels. However, an inventory level of labels is required to meet the usage requirements. If a large
number of different labels are required, each must be inventoried with the accompanying increased likelihood that some will be scrapped as products undergo change.
- On-Site Printing - This is similar to the off site classification except the exact data for the labels is not known until hours in advance. Typical of this category would be date coded part number labels for a multi-product production line, only a few hours notice may be
available when the line is converted to a different product. Depending upon the number of labels needed, the choices could range from an in-house press to a high speed label printer. The incidence of scrappage is reduced since a smaller number of each label is printed during each production cycle.
There is less latitude in material selection because prep and print time is limited. There is a wide selection of printer types, but the print technology is restricted to those that can be easily implemented at a remote location. As an example, press printing is not a good on-site choice because
of the requirement for photographic plates, negatives, and other resource consuming tasks.
The Trouble with Batch Printing
�DEMAND PRINTING
Demand label applications require a unique label to be printed and presented at the point of use. This type of label generally contains a predetermined format with variable data sections, e.g. a serialized data field, that makes each label unique. The variable data, while it might be known in
advance, is closely identified with a real time activity. The labels are intended to be used in conjunction with this activity as they are printed, or at least within a short time period after printing.
Printing labels only when they are required has many advantages. It is also more restrictive on how the labels are produced. Demand printers can operate in the real time production environment. They accept data from the system and produce a label with data unique to
that particular article. The variable data can be almost anything; serial numbers, sequence codes, test results, date codes, lot codes, etc. Because the labels are printed on the spot and usually one at a time, the type of printer needed has to meet a number of special requirements that do not
apply to batch printing.
- Speed - The label must be ready when it is needed. This can be very fast, if an automatic applicator is used, or reasonably slow if a human operator takes the label and places it on the article. At the same time, the print process used must be simple and fast. Multi-step
printers do not make good demand printers because of the time needed for set up.
- Presentation - The label must be presented to the applicator ready to be used immediately after it is printed. This could mean stripped with the adhesive back exposed or with the backing liner still attached but separated into individual labels by either tearing or
cutting them apart. The last printed label must be easily accessible without wasting label stock.
- Media - The media must be universally usable for all label requirements supported by that printer. While it is possible to change label supplies to get different label sizes, pre-print information, etc., it is not feasible to change the media except on supply-type basis
(i.e. one roll, one sheet, etc.).
Because of their limited print field and media supply systems, demand label printers cannot efficiently produce text documents such as Bills of Lading and Shipping Notices. These types of applications are best left to ordinary computer printers that are designed to print human readable text
documents with an occasional bar code field.
The applications for which demand label printers are used can be categorized by the following:
- The labels are generated at the point of use.
- Each label or group of labels is unique.
- Labels are used in a real time environment.
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