The information in a barcode is contained in the relative thickness and relative position of the lines and spaces within the specific data characters. Scanners convert the bars and spaces into usable information for data entry.
Barcodes streamline data entry. They are used to increase the speed and accuracy of reading and entering data.
BAR CODE BASICS
Bar codes are the most popular of the automatic data entry methods. It is a pattern of parallel bars and spaces of variable widths arranged in a specific predetermined pattern to represent a corresponding number, letter, or symbol. The information in a bar code is contained in the relative thickness and relative position of the lines and spaces within the specific data characters. Scanners convert the bars and spaces into usable information for data entry.
Why bar codes are used
Bar codes streamline data entry. They are used to increase the speed and accuracy of reading and entering data. It is primarily intended as a machine-readable data management system. Bar codes have received wide spread acceptance because of their low susceptibility to errors in data input. The error rate in human reading of hand written data is 7-14%. The error rate in human reading of preprinted data is 1/300 characters. There is a one in two million error rate for scanner read bar codes. It is considered the most effective data entry method. Most new bar code installations have a payback of less than one year. Credited with accuracy, speed, control, reliability and portability, bar code technology is the most popular method of tracking and transmitting data and is replacing other methods of tracking and transmitting data.
Bar code advantages
Easy to print
Not language dependent
Low error rate
Variety of print methods
Full character set
Bar code disadvantages
Low density except for new 2D code
Bar code applications
In industrial and business-to-business settings, there are four applications that are common to all businesses: materials management, information management, labor management, and asset management. The use of bar codes is rapidly increasing in document management. Documents are either filmed or entered into an electronic imaging system. Automatic data entry can be provided with bar coded documents (i.e. the bar code could contain an invoice number a number of pages, and a page number). Since bar code reading is highly accurate, less data entry errors will occur and faster data entry will result. Data that can be entered automatically can be either numeric or alphanumeric depending on the bar code symbology selected. Document sorting can also be reduced if a document code is included in the bar code. A bar code should be considered as an alternative to OCR in many indexing applications.
How it works
Standard bar codes are read by a light source, illuminating the bars and spaces. This involves moving the read head over the code symbol, or if the read head is in a fixed-position (as in the supermarket), then the code is presented to the read head. The light is absorbed by the black bars and reflected by the white spaces and/or background, in a specific sequence with orientation being determined by the start and stop codes. A sensor detects the reflected light from the spaces and produces a “high” signal output for each space and a “low” signal output for each bar where the light has been absorbed. The duration of the high and low signals indicates whether the bars and spaces are wide or narrow. The thickness is always in reference to a line or space contained with the bar code. The reference thickness is called the “x” dimension, or the narrow element width.
It is then necessary to determine what this pattern of wide and narrow elements symbology is to decode the bar code. This is accomplished with decoding software. The decoder performs 4 basic functions. It times the duration of the electrical pulses and classifies them as wide or narrow bars or spaces. A determination is made regarding which bar code symbology is being used. Once this is done it translates the bar and space pattern into the actual characters that make up the bar code. The last function is to transmit the bar code data to some other device that will use the data. Transmitting the data through a computer interface to various computer devices usually does this.
The data stored in the bar code is a unique identifier that provides access to data stored in a central computer system. By keeping the data separate from the bar-coded identifier and centrally located, you also simplify updating the information. However, the “license plate” method only works if everyone has access to the same database. This is not usually a problem for internal operations; when the code crosses into another environment, the database may not be accessible.
BAR CODE DESIGN
Start by listing the constraints within the project. These would be the components that cannot be changed. These may include the scanning distance required, the number of characters to be encoded, the type of characters to be encoded (alpha and/or numeric), the size and orientation of the area to which the label or tag will be affixed, and (if printed on site) the width of the print head.
Once the constraints have been identified, the rest of the process can be designed. Depending upon the constraints identified, you can start by defining the label size or the bar code size. Remember, in both instances, to include the quiet zone requirements of the bar code chosen. If you start with the bar code size required, you can then design the label/tag size around it. Conversely, if you start with the label/tag size, you must design the bar code within it. Once these steps are completed, you can move on to adding fields to the label/tag format and determining data sources for the identified fields.
Designing for maximum scanning success
The following four (4) elements and their compatibility contribute to the successful, high (99.99%) first read rate and high (99.5%) read rate, use of bar codes in any data collection application.
The most critical relationship in these elements is the density of the bar code, which determines the scanning depth-of-field. The density of the bar code is determined by the size of the “X” dimension (the width of the narrow bar or element) and the ratio of wide to narrow elements within the symbol. The compatibility of the “X” dimension of the bar code to the light source of the scanner determines the system requirements for scanning distance.
Each scanning device has a depth-of-field for each increment in the size of the “X” dimension. For a standard range distance scanner a 20 mil “X” dimension can be scanned from about 2 inches to 18 inches. A 50 mil “X” dimension can be scanned from about 3 inches to 36 inches. This would be with standard white material with or without a laminate. The long range distance scanner has a greater depth of field which can be extended even more when using retro reflective material extending the scanning distance to over 28′ using a 100 mil “X” dimension. Each scanning device manufacturer has its own specifications for each of their distance options. Testing is always recommended because of the other elements than contribute to successful bar code scanning.
It is imperative that the system development and implementation teams match the actual scanning requirements with the proper bar code configuration and scanning devices. Many times the system requirements for scanning a bar code are discussed after the scanning equipment has been chosen and the bar code configuration has been determined because of constraints on the size of the label.
The coordination of these four elements determines the success or failure of all scanning systems. The data collection software and hardware can be the best but if the bar codes either cannot be read or are difficult to read, the system will not achieve its anticipated benefits and savings.
A description of each of these four elements and how they relate to each other is given below. It is like five fingers fitting perfectly in the five fingers of a glove. Each is important by itself but they work together as a hand to complete tasks.
1. Bar code:
- The type of bar code symbology to use is dependent on whether you are scanning numeric or alphanumeric information (see symbology selection below).
- Narrow Element / “X” dimension and ratio where applicable to determine density and the area required for the bar code including quiet zones at both ends. The quiet zone, the clear area to the left and right of the bar code is a function of the “X” dimension (see “x” dimension, ratio, resolution, and quiet zone sections below).
- Height (redundancy) of bars for quicker scanning.
2. Scanner (Hardware):
- Wand / Slot (Contact)
- CCD (minimal non contact, .5″ up to 3″)
- Single Line
- Single Line Moving
- Standard, Long Range & Extended Long Range optics for scanning up to 18 feet with standard material and 28′ with retro-reflective material using a 100 mil “X” dimension.
- Paper: Lowest cost but should be laminated for durability (see Materials in Reference Center).
- Plastic: More durable and many times doesn’t need lamination
(see Materials in Reference Center)
- Retro Reflective: Includes imbedded glass beads to enhance distance scanning (see Materials in Reference Center).
- Lamination: Matte laminate can perform better with wand readers
(see Materials in Reference Center).
- Indoors: Light Source is important, as you don’t want too much or too little light. Certain lights, mercury vapor & helium neon, can affect scanning performance.
- Outdoors: Sunlight can affect scanning so special optics have been developed for this purpose.
Which symbology to select
The goal is to maintain the highest degree of data integrity usually in the smallest area possible. The denser the code, the smaller the space required. However, denser codes can result in lower read rates. Check digits can offset some read failures. Several questions need to be answered before a symbology can be selected:
1. What character set needs to be encoded?
- Numeric only
- Special characters
2. How much data needs to be encoded?
- Different symbologies have different densities. Depending on the amount of data and the space available on the document, some codes are more appropriate.
- The space available on the document defines how many characters can be encoded or what symbology, density and ratios may be used.
- If the scanning resolution is high, more characters can be encoded.
- What is the tolerance for misread bar codes?
3. Do you want to have a check digit/check character?
- Some bar code symbologies have this feature built in and don’t need an extra check digit.
4. What is the position in the document?
- Some bar code symbologies are more tolerant on quiet zone requirements. If the bar code is on the edge, some misreads can happen because the bar code can be cut.
- Content of human readable label information.
- Label or document graphic requirements.
5. Determine if there is a standard for the industry.
Consider the simplest symbology that solves the problem. These symbologies offer more accuracy and provide faster reading. Choose the symbology with the highest inherent message density, if possible. If you will be encoding only numeric data, try I 2/5 or code 128C. If you are encoding alphanumeric data, consider 128B. If you are encoding large amounts of data, try using one of the two dimensional symbologies such as PDF 417. The disadvantage of two-dimensional symbologies is the limited number o readers available to decode the code. In addition, the cost of a reader capable of decoding two-dimensional bar codes is more expensive and allows fewer input options then standard readers.
With the development of scanners that can auto discriminate among several linear symbologies, many companies are using two or more linear symbologies on the same label. Substantial cost savings can be realized when two requirements are satisfied with one label. Another valid reason for using different symbologies on the same label is to assure that the correct bar code will be scanned. Auto discriminating scanners can be programmed to read only a specific code, thereby reducing errors from scanning the wrong code.
Label design should allow for modifications over time as departmental needs change or as industry standards evolve. For the ease and simplicity of scanning, use the shortest possible encoded fields even if a directory file is required.
The smallest element in a bar code is called the “x” dimension. This is the narrowest bar or space in the code. The choice of this dimension is based not only on the space available on the document to print the code, but also on the type of scanner and environment in which the label will be scanned. The minimum “x” dimension for Code 39, Codabar, Code 93, Code 128, I 2/5, Code 49, and Code 16K is .0075 inches. Usually, the larger the “x” dimension, the more forgiving the bar code is when scanned. For the most effective and reliable scanning, use the lowest possible density.
The most reliable and effective scanning takes place with a wide-to-narrow element ratio as close to 3 to 1 as possible. A larger “x” dimension requires a larger label area. Most applications use “x” dimensions in the range of 10 mils to 25 mils. It is preferred practice to have all bars and spaces in whole multiples of the “x” dimension. For the most effective and reliable scanning, use the 3.0:1 element ratio whenever possible.
Resolution of a scanner refers to the smallest element it can see. If the resolution of a scanner is not high enough, it will not be able to see small elements in high-density bar codes. On the other hand, a high-resolution scanner will see “defects” in low-density symbols that would be ignored by a properly matched scanner. One of the problems end users have is the failure to match the resolution of the scanner to the density of the media. The size of the spot of light emitted by a scanning device should be slightly less (80-100%) than the narrowest element. If the spot of light is significantly larger than the narrowest element, a distraction occurs when scanning is attempted. Therefore, scanning becomes more difficult. If the spot of light is significantly smaller than the narrowest element, scanning is not only difficult but errors can readily occur. For the most reliable scanning, be certain that the resolution of scanning devices be matched properly to the narrowest element of any one symbol.
Density is usually measured in one of two methods. Density is measured in either characters per inch or by the narrow bar size. The character per inch density is determined by the combination of the “x” dimension and the element ratio. The wider the “x” dimension (bars) and/or the larger the ratio, the fewer characters per inch (lower density). Narrower bars provide greater density, however they are more vulnerable to print voids, stains, and dirt, which can affect bar width interpretation.
To enable a scanner to distinguish between the wide and narrow elements, a minimum ratio is needed depending upon which resolution has been used for printing the bar code. The width of the wide element should be at least twice the narrow element. A range of 2.2:1 to 3.0:1 is recommended. Some symbologies have fixed element ratio options. Code 39 allows the user to determine the element ratio. The width of bars and spaces can and do vary unintentionally as a result of the printing process. As long as this variance is within accepted tolerance ranges, the deviations are not detrimental. However, the smaller the element ratio, the lower the tolerance range. The most reliable scanning takes place with a wide-to-narrow element ratio as close to 3:1 as possible. It is preferred practice to have all bars and spaces in whole multiples of the “x” dimension.
Code designers specify a zone be just to the right and left of a bar code that shall be free from all printing. This “quiet zone” gives the scanner time to adjust its opto-electronic measurement circuits to properly determine the critical width of each bar in the code message and determine the contrast between the bar and the space between each bar. Quiet zones at the beginning and end of a code signal the scanner where to begin and end. The quiet zone should be 10X the “x” dimension of the symbol, or one-quarter inch, whichever is greater. A clearance of 1/16” above and below the code is recommended.
Bar code scanning takes place by focusing light on a pattern of bars and spaces. The bars should absorb most of the light, and the spaces should reflect most of the light back to the scanning device. The two primary ways of measuring the correct absorption and reflection factors is by print contrast signal (PCS) or minimum reflectance difference (MRD). The result of these calculations must be substantial enough that scanners are able to properly distinguish between bars and spaces. The higher the difference between light and dark spaces, the better the read.
Bar codes produced with carbon-based inks normally ensure a higher PCS or MRD than alcohol-based or dye-based inks, thus providing better scanning characteristics. All scanners can accommodate carbon-based inks. However, infrared scanners are unable to read media produced with alcohol-based or dye-based inks. Using carbon-based ink to create bar code symbols may prove to be a significant asset when the media is used in hostile operating environments. Infrared scanners can often read these symbols even when they are contaminated by marks from ballpoint pens, dirt, or other foreign matter.
Ideally, use black carbon based ink or toner for bars and an opaque white matte finish print surface. Other combinations of code and background color can also be used as long as there is a 50-60% contrast between the light reflectance of the printed code and the background.
Media also contributes to contrast. Opacity must be sufficient to prevent background surfaces from interfering with the scanners ability to read the media. If a dark background shows through a label, the scanner may interpret some spaces as bars. This can readily happen when a white adhesive label is placed on a dark surface. The higher the initial reflectivity of the face sheet, the higher the difference between light and dark spaces and the better the read. Your substrate choice should have high opacity.
Color of substrate can impact contrast. The contrast point of reference for scanning is based on the 633 nanometers of the red-light helium neon laser scanners. Therefore, you must avoid using paper or background label stock that contains any significant blue component that reduces contrast. White substrate should be the first choice. Ideally this would be of OCR quality. However, in some applications where there are multiple bar code labels, there could be operator confusion. Color-coding labels can reduce such confusion. When using label stock other than white, avoid colors with blue content. Pink or yellow background colors are the safest choices. An alternative is to have preprinted colored boxes around a bar code to color identify the specific code. Alternately, a colored stripe can be preprinted on the side of a label.
Horizontal versus vertical orientation
Labels can contain bar codes in two distinctive orientations, called picket fence or ladder codes. Applications that exclusively employ light pens should choose the horizontal orientation to support the more natural motion of the hand sweep.
Bar code height
Hand scanning is not naturally done in straight lines; it is done in arching motions. The MINIMUM bar height should be .24 inches or 15% of the bar code length, whichever is greater for Code 39 and 128. For optimum scanning, it is recommended that the code be .375” tall. UPC and EAN codes should be at least 1.02” tall.
Human readability of a bar code
Ensure that the coded information is printed above or below the bar code in an alphanumeric human readable font. This allows for key entry, if the bar code is not readable.
Bar code print quality standards
In 1990, the American National Standards Institute (ANSI) published ANSIx3.182-1990 Bar Code Print Quality Guidelines. These guidelines define measurement procedures and standardized methods of evaluating bar code print quality. A bar code is measured on an A-F range. A perfect symbol is not always achievable. This can be the result of a variety of reasons. Pointil verifies all work and provides samples pulled periodically during the production process.
Whether preprinted or printed on demand, sampling of printed codes to assure readability is critical. If preprinted, ask your supplier to provide you with a sampling of bar code verification (samples with print outs showing bar code readability and quality). If printed on demand, confirm your customer has the capability to verify codes printed. Additionally, two important measurements of bar code system performance are “first read rate” and “substitution error rate.”
First pass read rate (FPRR) is the ratio of the number of successful reads to the total number of attempted reads on the first attempt. A low first read indicates that the bar code must be scanned multiple times before a successful read is accomplished. A good bar code system should offer a first read rate greater than 85% and a second pass read rate of 95%. This means that a particular bar code can be read on the first scanning attempt 85% of the time. A first read rate, though, is not a measure of the correctness of the “read.” The primary cause of low first read rates is poorly printed bar codes, such as those with insufficient contrast between the bars and spaces, inadequate quiet zones and excessive spots and voids. Operator technique/training directly affect scanning success.
Substitution error rate records the number of characters incorrectly decoded out of the total number of characters scanned. This problem is much more critical because, in most cases, the operator is unaware that an error has been entered into the system. However, many symbologies are self-checking, meaning that codes are designed so that defects render the code unreadable, rather than readable but incorrect.
Many specific industries have established label standards unique to their industry. The automotive industry (AIAG), the health industry (HIBCC), the plumbing industry (IBCA), and the electronics industry (EIA) are a few of the industries establishing such standards. Furthermore, individual companies such as WalMart have developed “company specific” labeling standards.
Such standards tell the “labeler” how to create and apply a label that will meet the “recipients” information and application standards. These standards may include the following:
1. What information is required (i.e. p.o. number, quantity, etc.)?
2. What data content code standard to use.
3. What item to bar code and in what symbology.
4. How to arrange the data.
5. What bar code print quality standards to use?
6. Where to place the label (s)
Data content codes
Preprinted versus on-site
There are situations in which preprinting bar code documents/labels is more appropriate and situations in which on-site printing of bar codes is more appropriate. Part of that evaluation certainly includes cost per unit, cost of printing and verification equipment, and on-site expertise to print bar codes. Additional considerations include:
Specialty materials required High quality labels required
Existing QA programs Moderate quality labels required
Very high-density symbols required Short lead-time
Over laminates Variable data
Service Bureau Capabilities Frequent design changes
Compliance Assistance Short runs
High quality labels required
There are a number of printing methods available to print bar codes. Conventional offset or flexography printing is utilized in the printing of UPC retail bar codes. Mechanical numbering machines can be utilized for discrete bar code symbologies (Code 39), but not continuous or 2D codes. Photocomposition can be used to print extremely small bar codes. This process utilizes photo typesetting to create the bar code, number, and text. This process has a resolution of 2000 DPI providing the highest level of quality and also the highest cost. This production process utilizes photographic paper and can include a coating or laminate over the printed image to provide scuff protection. The former is recommended as the latter tends to delaminate.
However, for more complicated bar code applications such as consecutive numbering, random numbering, or data storage, computerized non-impact printing technologies must be utilized
Laser. Pre die cut labels are processed through laser printers with 300-600 DPI resolution. It is difficult (and expensive) to provide laser labels with protective coatings or laminates. Therefore, a clear protective label or tape must be placed over the label to insure it will withstand normal handling and use. Laser printing can be low to high speed, batch or on-demand production. If the document needs any static printing, it must be preprocessed on a conventional printing press.
Ion Deposition. Labels are both manufactured and printed in the same process. Ion Deposition typically utilizes 240-300 DPI resolution. Labels can be provided with protective coating or over laminates. This is the preferred method for medium to high quantity production.
Thermal Transfer. This printing technology utilizes 300 DPI resolution. This is the preferred method for on-demand printing requirements, given its relative lost cost and reliable process. It is the slowest of non-impact technologies. Though they have similar DPI resolution, thermal transfer technology provides higher quality bar codes than laser or ion deposition because thermal transfer technology incorporates square dots while laser and ion deposition utilize round dots. Depending upon the particular type of manufacturing equipment, labels can be both manufactured and printed in the same process. Labels can be provided with protective over laminates.
BAR CODE SYMBOLOGIES
Traditional bar codes (1D) – Linear Codes:
Interleaves 2/5 (I 2/5)
Two dimensional bar codes (2D)
Why two dimensional (2D) bar codes?
What are 2D codes?
2D Stacked Code
2D Matrix Codes
Data Matrix Code
Why use 2D codes?
How does 2D work?
BIFOCAL 2D Bar Codes
Who would use 2D?
Where would 2D be used?
How is 2D used?
Why will consumers use2D?
There are over 50 different bar code symbologies each having their own symbol interpretation. Currently, there are only a few code symbologies in wide spread use. Code symbol density ranges from low to mega-density. Low-density symbols have fewer than 3 characters per inch. High-density symbols can contain 100s of characters per square inch. Code symbologies are classified as linear (1D) or two-dimensional (2D). Two types of symbology structure, discrete or continuous, define all bar codes.
Linear Codes (1D)
Linear codes are those in which characters are grouped, one next to another, in one linear direction. Simply put a single row of parallel bars and spaces. While linear bar codes are two dimensional, having both width and height, they are one dimensional in scanning. Only the widths of bars (and sometimes spaces) are measured to interpret the symbol. The height of the code is simply redundancy to enable scanners to more easily scan the symbol. These are most commonly known as “bar” codes. These include UPC, Code 39, Codabar, Code 128, Interleaved 2 of 5, and 2 of 5 code.
Discrete bar codes
There are three main discrete bar codes used in North America: Code 39, Codabar, and Code 2 of 5. Characters in these codes begin and end with a bar. This construction creates spaces between characters that are not part of a character. This inter character gap should be approximately equal to the narrow bar width. Codes with this inter character gap are called discrete since each character is separate and independent from other characters in the same symbol. Because of this inter character gap, impact numbering machines can be used to print bar codes since the space of the inter character gap can be used for ratchets for the individual number wheels in a numbering head. These ratchets are essential for impact numbering devices.
Code 39 was the first alphanumeric code and is the most common non-retail symbology. It is a 43 character alphanumeric binary code (most other discrete codes are not alphanumeric). This bar code is capable of representing all capital letters, numbers, seven special characters (./+%$- and space), and can easily be printed by a variety of technologies.
Code 39 is a two-width symbology; meaning all bars and spaces are either wide or narrow. Each character is composed of nine elements; five bars and four spaces. Three elements are wide (two bars and one space) and six are narrow. Each code begins and ends with an asterisk, which is this symbology’s start/stop code. Code 39 is self-checking; meaning any element erroneously printed or scanned will not result in bad data input. An optional check character is available. Code 39 is the standard symbology for the federal government, automotive industry, and the material handling industry. It is the code of choice in most situations that require alphanumeric coding. It is bi-directional. The maximum density is 9.8 characters per inch. Minimum bar ratio is 2.0:1. If the “x” dimension is less than .02 inches, the minimum ratio should be 2.5:1. Maximum bar ratio is 3.0:1.
Although there are only 43 data characters in Code 39’s character set, it is possible to encode all 128 ASCII characters using Code 39’s full ASCII feature. If a reader is in its full ASCII mode, the symbols $ / % and + are used as precedence codes with the 26 letters.
Also known as USD-4, NW 7, and Code 2of 7, Codabar is a self-checking, numeric only code. It is a bi-directional code. There are 16 characters in the set, 10 digits plus special characters ($-,/ and +). The start/stop characters A,B,C,D,E,*,N, or T must be used in matching pairs and may appear elsewhere in the bar code. Each character is coded independently by means of four bars and three intervening spaces, totaling a fixed width but employing a complex set of individual bar and space widths. It was originally designed for use in retail price labeling. It was one of the original proposed symbologies for the UPC. Instead, it found a niche in several diverse, non-retail applications. It is the code required by the Department of Defense. Other applications include inventory control, libraries, blood banks, photo finishing, and air bill applications. The maximum density is 12.8 characters per inch. The minimum bar width is .075″.
Its specifications allow it to be printed with wide quality tolerances. That is why it was used for package tracking. There is no checksum defined as part of the Codabar standard, but some industries (libraries, for example) have adopted their own checksum standards.
Code 2 of 5
In use since the late 1960’s and is supported by several equipment suppliers. It is used less that Code 39 or Codabar. It is a numeric, discrete, self-checking bar code originally developed for automated warehouse sorting and Photo-finishing envelopes. 2/5 encodes information in five bars, two of which are wide with the remaining three narrow. All spaces separating the bars are about the same width and carry no data, so the code has a much lower information density than the interleaved 2 of 5. Its only advantage is a shorter impression length compared to Code 39 and Codabar.
Continuous bar codes
Other codes are called continuous and will not allow an inter-character gap. Consequently they cannot be used in impact numbering equipment.
Interleaves 2 of 5 (I 2/5, ITF)
Interleaved 2 0f 5 is a numeric-only, bi-directional, self-checking code. It’s the most popular numeric only bar code in non-retail distribution. Its main advantage is its density. Each character is five elements…two wide and three narrow. There must be an even number of characters in this code.
If there are an odd number of digits, a zero must be added in the most significant position. Bars represent odd-numbered digits and even-numbered digits are represented by spaces. This “interleaving” process, in which bars and spaces encode numbers independently, gives the code a higher density. I 2/5 is usually printed with a top and bottom border to prevent a partial scan being interpreted as a complete scan. I 2/5 is often used with a MOD 10 check digit. The standard ITF contains 14 digits, with an optional 6-digit suffix. The IT outer case code with the human readable characters at the base of the code, grouped into country code, supplier code, product code, and check digit.
It is a recommended symbology for corrugated shipping containers and has been selected for use on other shipping containers in the grocery industry. It is used in this application to identify the trade selling as opposed to the consumer-selling unit in retail trade. It employs a data format standard identical to that of the regular UPC A code but with two additional digits at the front. The first is an assortment indicator used to indicate the type of selling unit (e.g., case or pallet) or for a single case where the five-digit item code portion matches the five-digit item code of the consumer selling units inside. Quite commonly, the five digits match. This is not possible when there is more than one trade-selling unit for the same consumer item, or where the trade-selling unit contains an assortment of consumer selling units. The second extra digit is always a zero, provided to make the format compatible with EAN.
The code value, as specified by the data format standard, is more widely used than is the bar code symbology. In distribution, sorting and shipment control are usually exercised according to shipment number ID rather than stock keeping unit (SKU) ID. On the other hand, the UPC shipping container code number is the standard way to identify items in a purchase order, shipping advice, invoice, etc. when transmitted between parties using UCS, the grocery industry’s EDI standard.
Though its major application is considered warehouse inventory, it has been accepted in airline ticketing and baggage and cargo handling.
N,K codes are a different type of continuous bar code symbology, which provides greater symbol density. N,K code is proportional, allowing elements to have multiple widths, not just two widths. These symbologies divide the region occupied by a character into N modules. Each bar and space may occupy one or more modules. K refers to the total number of bars and spaces in a character.
UPC (Universal Product Code)
UPC has been successfully employed in the supermarket industry since 1973. It is the most familiar N,K code. It is used in static applications for product identification. UPC is a coding system as well as a symbology; it is designed to uniquely identify a product and its manufacturer. It is important to differentiate between the UPC coding scheme and the UPC symbology. UPC is a fixed length, numeric, continuous symbology employing four element widths. There are three versions of the UPC symbol:
Version A is a 10-digit code: the first five digits represent the manufacturer of the labeled item, and the next five digits are a unique product identifier code. This 10-digit code is preceded with a “number system” digit. Most products will either have a “1” or “7” in this position. It signifies that the product is of a fixed weight and size, as opposed to a variable (i.e. apples) or a product coupon. A Mod 10 DR check digit that is based on the preceding 11 digits of data follows the UPC code. To make matters more complicated, the publishing industry has added a supplemental 2 and 5 digit symbols to the end of the UPC-A symbol. This supplemental symbol contains date-of-issue information or a price.
UPC-E is a shortened and more complicated for of UPC-A, representing a full ten digits using only 6 characters. UPC-E was developed to aid manufacturers who could not fit an entire 12-digit symbol on their small package. A limited number of these symbols were issued, the last of which was given out years ago.
UPC-D is a version used for variable length messages. It is very seldom used.
The UPC code currently used will be replaced by EAN. EAN, initially known as “European Article Numbering”, is gaining worldwide retailing acceptance. In the US its use is largely limited to the encoding of books, though all retailers will adopt the symbology by 2005. EAN-13 encodes 13 digits, one more than UPC. For more information, contact the UPC Code Council at (513) 435-3870 or http://www.uc-council.org. This Council issues the manufacturer and product code numbers used in this symbology.
Code 128 is an N,K code, one specifically designed to encode the entire 128 character ASCII set. This character set includes special control codes necessary for computer communication. The symbology is denser than Code 39 and includes a check character instead of the optional check for Code 39.
Each character is encoded by means of three bars and three spaces with a combined width of 11 modules or units. The total length of 11 modules is made up of an odd number of bar modules and an even number of space modules. The bars and spaces may be 1,2,3, or 4 modules wide. This coding system provides 106 different print characters. Four bars and three spaces define three stop/start characters. Each character requires only 68% of the space required in Code 39 characters.
The symbology provides for three different character sets that are identified by distinct start characters: A, B, or C. 128 C consists of the 100 two-digit pairs 00 through 99. This allows the effective density of 128 to be doubled when printing all numeric data. This provides a maximum density of 24 characters per inch. 128 A and 128 B cover the entire 128 ASCII character set, with a considerable amount of redundancy. 128 B includes both upper and lower case letters as well as numbers and some special characters; 128 A emphasizes the full set of special characters but excludes the lower case letters. As a result, the code can be quite compact when expressing numbers only, yet fully capable of providing all needed ASCII characters as and when needed.
Code 93 is a specially designed code incorporating nine “n” modules, each having 3 bars and 3 spaces. The bars and spaces may be one to four “N” modules wide. Code 93 as designed by Intermec (designers of Code 39) to address density demands by users. Code 93 normally utilizes the same character set as Code 39, but special versions use the complete ASCII file. Code 93 utilizes 2 check digits and has a higher density and Code 128 versions A/B.
Two dimensional bar codes
Why two dimensional (2D) bar codes?
Bar codes became widely used because they increased productivity and were significantly more accurate. Standard linear codes have been primarily used for identifying items. They are typically 20 characters or less. Identification has traditionally been through a “license plate” concept of assigning bar coded numbers to documents or assets. This process has largely remained an intra-organization system, because the data base behind the bar coded identifier is within the organization. As such, the assigned bar code numbers have no meaning to others who may scan them.
As with any technology with widespread appeal, users wanted the ability to do more: store more data, scan it more accurately, store it in a smaller footprint, read it faster, and read it from further distances. While the capability of traditional bar codes improved (i.e. 128C has a higher density capability than Code 39 and an inherent check digit for higher scan reliability), such improvements were relatively marginal in hindsight. Despite some of these improvements other issues arose; for example, if more data was added in a code it meant more space was taken. If the code was compressed to fit in the original footprint, it may be too dense for a scanner to read. These problems may be solvable as a new generation of bar code technology slowly emerges.
What are 2D codes?
2D bar codes were developed in response to the evolving constraints of traditional linear bar codes. Two dimensional (2D) bar codes are printable PDBs (portable data bases). They are stored on paper instead of flash cards or CDs. These formats both used modules to create a vertical and horizontal pattern of data storage (matrix), hence the two dimensional (2D) description. This was a paradigm shift in code symbology as traditional linear codes only store data in one dimension. Some 2D symbols can carry 7000 characters of data as compared to a regular or linear bar code capacity of 20 characters. 2D symbols can also carry binary data, which can be made to run a computer program or generate photographs and drawings, such as passport photos, fingerprints, and signatures. Two-dimensional bar codes are defined as stacked or matrix (pattern). DataMatrix can be used like traditional bar codes as a “license plate” number that accesses a specific file of information on a computer. However, the symbol can also contain that information rather than just a number that “accesses” that information on a storage device (hard drive). Each square in the symbol is a data cell.
2D Stacked code
Stacked codes are constructed of rows of individual characters (that can be individually recognized) including stop/start characters that are stacked upon one another. It also contains an element telling the scanner where it is when it’s reading the code. Stacked code is easier to print and read than matrix code. Like standard linear bar codes, the scanner looks at the width of bars and spaces to read the code.
PDF 417 was the first 2D code. It is a continuous type stacked symbology. Each stacked row contains start/stop patterns and data units called “words.” In each row of a symbol, the first and last words are row indicators. The height and width of PDF 417 is variable. Because rows can vary in length, and the number of rows can be variable, users can define the share or aspect ratio of the symbol, the X and Y dimensions of the elements, and the mode of the symbol. Symbols may be stacked upon one another for almost unlimited data acquisition or truncated for smaller symbols. PDF 417 can encode ASCII, binary or numeric data and can communicate with any operating system. It can be bi-directionally scanned and can be decoded by the computer system and automatically do the document verification either on-line or locally.
2D Matrix codes
Data matrix symbols are rectangular in shape (usually square). They are made of cells that represent data bits. Matrix codes have a checkerboard appearance, with each uniformly spaced square or polygon shaped cell corresponding to a binary bit. They are constructed of a mosaic of light and dark elements that must all be read before any characters can be recognized. Matrix codes contain bars having only one width, so the scanner must read the center of each bar to interpret the code. Matrix codes can store more information per unit area than stack code. Matrix symbols are encoded with a binary code requiring a special scanner.
To an untrained eye, all data-matrix codes look much the same. There are actually several different types of data-matrix codes. The best known include QR Code and DataMatrix Code.
A DataMatrix Code is composed of two solid adjacent borders known as the “finder pattern” and two other borders consisting of alternating black and white modules known as the “timing pattern”. Within the borders are even numbers of rows and columns of cells encoding information. Algorithms contained in each cell identify the information that has been encoded. Upwards of 3000 ASCII characters may be encoded in a symbol. This code is very popular for applications that require a very tiny symbol size. A typical matrix code can be made to hold 60 characters of information in a .12″ square symbol. A special 2D CCD reader or cell phone is required to read the code.
QR codes were developed by and originally used in a factory where there was significant likelihood of damage to the code. Because of this issue, it was designed to include data restoration up to 30%, meaning 30% of the code could be damaged or stained and still provide complete data recovery. It has 3 position detection patterns in 3 of the 4 corners with black and white data modules within. A special 2D CCD reader or cell phone is required to read the code.
Why use 2D codes?
2D codes are capable of storing significantly greater data than conventional bar codes. A traditional linear bar code carries one line of data (linear). It is limited by the length of the sequence of bars that will fit in a given space, typically a maximum of 20 characters. A 10 digit conventional bar code would be approximately 2.8 inches long by .375 inches tall, or about 1 square inch. Data matrix symbologies can store 30 times as much data in the same space. A QR code could contain 600 characters with 25% correction capability.
While traditional bar codes have a bit of redundancy (the height of the bars simply repeat the same data) and/or there is a check digit included, but there is no redundancy should 25% the bar code length be torn off. Probably the most fascinating thing about 2D symbologies is that most can accommodate advanced data redundancy and “error correction methods” (error correction can be defined by the user). By mathematical formulas embedded in the code, data can be mixed in predetermined ways, so the information from a single input/output character is distributed along with other data over pixels scattered over multiple locations. As a result, when the code is damaged “error correction” will “reconstruct” missing portions of the symbol and recreate the missing data. Up to 30% of the label can be destroyed or damaged and still retrieve 100% of the data contained in the symbol when it is scanned. Damage can include worn out and scratched areas, horizontally and/or vertically cut areas, hole punched areas, and folded areas. This is very beneficial for use in environments where symbol damage is likely. 2D bar codes generally have an error rate of less than 1 in 10 million characters scanned. The advantages of 2D codes are:
More information: A traditional linear bar code carries data one line of data (linear). It is limited by the length of the sequence of bars that will fit in a given space, typically a maximum of 20 characters. By adding more information, you add to the length. By contrast, a data-matrix code is a square or rectangle of 2 dimensional information, packing 30 times as much information in about the same relative space.
Fewer errors: While traditional bar codes have a bit of redundancy (the height of the bars simply repeat the same data) and/or there is a check digit included, there is no redundancy should 25% the bar code length be torn off. 2D codes have options for multiple levels of error correction by means of built in redundancy.
Broader reading capability. 2D bar codes cannot be read by traditional linear bar code scanners, BUT they can be read by cell phones with built in digital cameras.
Higher security. Data can be encrypted in 2D codes making it more secure.
How does it work?
Data matrix codes are readable by 2D scanners and cell phones with a camera and an appropriate “app.” QR Codes have detection patterns located in 3 corners that let the scanning device orient the code and hence read from any orientation (omni directional). The omni directional capability guarantees stable high speed reading. DataMatrix Codes have a finder pattern that is used to locate and orient the symbol while the timing pattern provides a count of the number of rows and columns in the symbol.
Bifocal bar codes
Bar code scanners have a specific scanning range called the “depth of field”. A near range scanner may have a “depth of field” range of 0-6”. A long range scanner may have a “depth of field” scan range from 3 feet to 30 feet. What that means is that it cannot scan less than 3 feet or more than 30 feet. A specific bar code size must be used to work within the specific “depth of field” range of the scanner. Some optical scanners have a wide scanning range but need a different size bar code to scan close up versus further away (i.e. one bar code size for under 3 feet and a different bar code size for 30 feet).
This becomes a particular issue in settings like a warehouse where you may want to scan an upper storage rack label from the floor, but later scan it up close when a cherry picker goes to that storage space. This may also occur with labels/tags marking dock doors. You would want to provide a long range scanning capability for forklift drivers so they don’t have to dismount from the forklift to scan the dock door label. In this way they do not have to stop the forklift and walk over to the bar code door bar code tag to scan it. Conversely, if you make the bar code too big, you can’t scan it if you are standing next to it.
What to do? Pointil has developed a BIFOCAL 2D Bar Code. Much like bifocal glasses, this bar code can scan at different distances to accommodate different types of scanners simultaneously. This allows you to scan from short range with a standard scanner or all the way up to the maximum distance scannable by your long range scanner with the same bar code.
Who would use 2D?
DataMatrix Code has its roots in the US and has, to date, been the predominate data matrix symbology used here, primarily in industrial applications. That is beginning to change. QR Code was originally intended for tracking vehicle parts, but innovative marketers have learned it’s power and it has now morphed into a much broader consumer context through the use of cell phones as scanners. Virtually all cell phones in Japan, where the code was developed, have built in QR scanner capability. QR code use is common place there. For phones like the iPhone and the Android, there are reader applications available. In the US, the technology is still largely unknown, but that will change rapidly as people learn the power and convenience it provides.
Where would 2D be used?
In an industrial business setting, data matrix symbologies have substantial power to increase data transmission, particularly for processes that cross company lines. Historically bar code was an internal business application tied to an internal data base. A number in the code would act as a “look up link” to date in the internal data base. Such a code (look up link) would not translate to another company’s internal data base. Now documents with around 1000 words can be transmitted via 2D code. This will change the dynamics of tracking and shipping. The constraint is that conventional bar code scanners in place don’t have the capability to scan this type of code. Until the supply chain upgrades scanners throughout, its use in this capacity is limited. On the consumer side, there will be vast and immediate use due to the widespread use of cell phones.
How is 2D used?
Consumers with a camera equipped cell phone and the correct reader application can scan the image with the camera function to display the contents of the code symbol. The information in the scanned symbol can be redirected to connect to the web via the phone’s web browser. This is called “hard linking.” The iPhone supports this by means of an app available on iTunes. The Android operating system is capable of providing this and its web browser supports the URL redirection. The Nokia operating system also supports QR Code.
Why will consumers use 2D?
Consumers can instantly learn more about companies and their products. They could “hard link” from codes on products, billboards, display posters, business cards, magazines, or newspapers, for example. You could “hard link” from the milk carton at breakfast to get more nutrition facts; the poster at the metro station for the train schedule; download a coupon from a product billboard; link to a movie trailer from a code in the newspaper; do a virtual tour of an apartment for rent via a newspaper ad; scan a clam shell of salad to see if it has been recalled; scan a code on a bottle of wine at dinner to learn about the vintage. The application opportunities for information, entertainment, business, and safety are endless.
BAR CODE PROBLEM SOLVER
Bar code print quality is not as simple as verifying bar code scan-ability. Most users will not have scanners as sophisticated as the verifiers used in manufacturing plants to validate bar code readability. Also, bar codes verified in-plant are new, unused and presumably in perfect condition. Bar codes in live applications may be damaged, stained, etc. Verifying symbol quality only tells you how well the symbol was printed. It doesn’t determine whether the correct symbology or data was printed, whether it was formatted correctly, etc. There are a number of parameters that make up a successful bar code scan. Within the bar code itself, these parameters include:
Print Contrast Signal
Decodability indicates the amount of tolerance remaining in the width of the most deviant element in the symbol. Bar codes are made up of elements (bars and spaces) of different widths. For example, Code 39 has two element widths…one narrow and one wide. Each element within a bar code symbol should be consistent across the symbol. In other words, all of the narrow elements (bars) should be consistent in width and all the wide elements (bars) should be consistent in width.
The decodability grade indicates the amount of error in the width of the most deviant element in the symbol. The lower the deviation, the higher the grade. Optimally, each element size in a bar code symbol would be consistent across the symbol. A decodability failure means that the width of the bars and/or spaces in one of the elements is so inconsistent that it cannot be evaluated. A decodability failure results in an overall symbol failure regardless of the quality of the other parameters.
NOTE: Bar codes printed in the horizontal orientation (picket fence) will be more consistent that bar codes printed in the vertical orientation (ladder), which tend to have dimensional errors.
This is the area immediately preceding the start character and following the stop character in a bar code symbol as specified in a particular application and/or symbology specification. The quiet zone immediately preceding the start character and following the stop character must each be a minimum of ten times the narrow element for all symbologies except UPC, EAN, and 2-D symbologies. Scanners expect the quiet zone to be free of any low reflectance objects (dark areas). If a low reflectance object is detected in the quiet zone then the scanner may not distinguish the start or stop signal resulting in an unsuccessful scan.
NOTE: Do not print bar codes too close to the edge of the label, tag, or document. Do not print other test or lines too close to the leading edge or trailing edge of the bar code. Quiet zone requirements for 2D (two dimensional) bar codes very with each Symbology, but can be as little as .01 inch. 2D bar codes typically require quiet zones on all four sides of the symbol.
Print Contrast Signal
Symbol contrast is the difference in reflectance values on the “lightest” space (including the quiet zone) and the “darkest” bar of the symbol. The greater the difference between light and dark contrast, the higher the performance of the code (bar code colors and/or background colors can have a large effect on this parameter).
NOTE: Substrates with metallic surfaces will reflect as black and are therefore not recommended for use with bar codes. Scanners read bar codes by distinguishing between the bars and spaces. In order to create the best contrast, the bars should be black and the spaces and background should be white. Other combinations work including different bar colors and different background colors, as long as the contrast between the bars and spaces is distinguishable by the scanner. When the contrast gets too low, the scanner will not distinguish between the bars and spaces and will therefore not see the bar code.
The reflectance value of the “lightest” space must be at least twice as great as the reflectance value of the “darkest bar.”
Edge contrast is the difference of the reflectance values of the dark and light components of an edge. Each element of a bar code has two edges that go from dark to light. Therefore, each edge has a dark and light reflectance value component.
Modulation is based on the relationship between the minimum edge contrast and the symbol contrast. Ideally, the edge contrast should be equal to symbol contrast but as an aperture size approaches an element size the amplitude of the signal received will decrease and the edge contrast will decrease. The greater the difference between minimum edge contrast and symbol contrast, the lower the grade.
NOTE: Aperture size has the greatest affect on this parameter. The substrate material can also have a major affect on this.
Defects are irregularities in bars, spaces and quiet zones. Defects are measured based upon the relationship between the largest defect in the symbol and the symbol contrast. The smaller the defect, the better the grade. In general, a small aperture used to analyze very wide elements will cause the largest defects.
NOTE: Substrates having recycled content can pose problems. Some recycled content may be darker or protrude slightly from the surface. Such characteristics can create misreads of bar codes. Maintenance; Bar code quality degrades as miscellaneous deposits (paper dust, core, adhesive debris) build up in the printer and on the print head. Because of the density of bar code printing, it is probable that printer maintenance be required more frequently that outlined in the manufacturer’s recommendations. Worn print heads or ribbon creases can result in bar code symbols having missing bars or horizontal white streaks through the bars.
Printed bar codes are denser than standard text. As a result more printer consumables are used and few labels/tags/documents can be printed before maintenance is again required. More frequent maintenance will minimize print defects.
BARCODE TROUBLE SHOOTING:
There are a number of general steps that can be performed to identify or isolate a barcode problem. They include:
1. Inspect the label for obvious damage including tears, dirt, or ink/pencil marks.
2. Determine if there are quiet zones at each end of the barcode. There should be a clear area approximately .25 inch or ten times the narrow bar width at the before and after the barcode. For 2D (two dimensional) barcodes, refer to the symbol specifications provided with your software.
3. If there is no obvious damage and there are quiet zones, you will need to verify that the materials and scanner are compatible. Infrared scanners require substrates that are designed for use with infrared scanners.
4. Verify that the scanner you are using is operating correctly, by scanning another similar barcode symbol. If the second barcode symbol can be scanned, then the scanner is not the problem. If the barcode cannot be scanned, it may be the cable, if your scanner is attached to a decoder via a cable. If you can disconnect the cable from the scanner and the decoder, use a different scanner or a different cable in order to isolate whether the cable and/or scanner is operational.
5. If you’re using a scanning terminal or an integrated scanner/decoder and all of the previous steps have failed, make sure the scanner is set to the parameters you need for your application.If there is no visible problem with the barcode and the scanner is confirmed as operating satisfactorily, you will need to confirm that the scanner and decoder are configured to read that barcode Symbology.If the scanner/decoder is configured to read that Symbology, the next step would be barcode analysis. This will require a barcode verifier.
a. Depending on the scanner manufacturer, the dip switches in the scanner may have to be reset. Refer to your scanner manual.
b. Confirm that the Symbology used to encode the barcode is compatible with scanner and decoder.
c. Confirm the scanner’s optical settings are compatible with the barcode you are trying to scan.
NOTE: The aperture size of the scanner can be adjusted to read barcodes more accurately. However, there is not a “one size fits” all solution. An aperture setting appropriate for one barcode size will not necessarily result in the successful scan of a different barcode x dimension.
6. If there is no visible problem with the bar code and the scanner is confirmed as operating satisfactorily, you will need to confirm that the scanner and decoder are configured to read that bar code Symbology.
7. If the scanner/decoder is configured to read that Symbology, the next step would be bar code analysis. This will require a bar code verifier.
8. If the verifier cannot decode the barcode, check for print head defects, printer speed variations, toner variations, ribbon defects, and the printer heat settings.
9. Print quality consists of a number of factors and procedures. If the problem remains unsolved, it may be caused by the choice of Symbology, the format (including the x dimension, the ratio, code height, check digit, etc.), the substrate, and even the data file that was encoded. It may be the printing software did not correctly encode the barcode. This may be the result of converting to new printing software, or utilizing printing software programmed incorrectly. In such cases, a common oversight is the exclusion of start/stop characters.
10. If the barcode is scannable by a verifier, the parameters causing the problem will be identified. A verifier will identify the decodability, print contrast, reflectance, edge contrast, modulation, and defects (see detail above on these subjects).
PRINTER CONSIDERATIONS: Barcode scanning success can be improved by the following:
a. Printer speed: Check speed and heat settings, confirm that the substrate is compatible with the printer, that the ribbons are compatible with the stock.
b. Print-head temperature: Since thermal transfer printing involves imaging through tiny heated prints contacting a ribbon onto a label, the print head temperature has a dramatic effect on symbol quality. If the heat setting is too high, the bars will print too heavy. Conversely, if the setting is too cool, the bars within a symbol will print too light. The heat setting can be adjusted either as a printer function or through a software setting. Adjustment control will vary between software and printers.
c. Printer Speed: The rated print or run speed (normally stated in inches per second) of thermal/thermal transfer printers is rarely achieved when printing barcodes. If the print speed is too fast, the heating elements do not have enough dwell time at the substrate surface to fully transfer an image, typically resulting in bars that are too narrow and/or too light.
2. Laser: Check the toner and density setting, as well as the minimum x dimension (should not be less than 10 mil).
3. Dot Matrix: Check for ribbon/print head spacing to substrate. Spacing needs to be adjusted based upon the thickness of the substrate or document. Barcodes will not be scannable on multiple plies.
The problem solver sections on thermal transfer, thermal, and laser has more specific barcode printing problem solutions as relates specifically to their printing processes.
1. The barcode will not scan.
Review Barcode Quality Parameters.
See the Barcode Trouble Shooting Guidelines
Review Printer Considerations.
2. Go to the printer specific problem solver sections (Thermal Transfer, Thermal, Laser).
3. The barcode scans at a distance, but not up close. This can frequently happen in a warehouse setting where both large and small barcodes are utilized. See depth of field information.
Potential Cause: Different scanners are built to scan barcodes of different x-dimensions from a certain range of distance (depth of field). The scanner may not set or suited to scan a barcode of that x-dimension from the distance attempted.
Potential Solution: Try scanning a barcode with a smaller x-dimension from the desired distance. If this works, the problem was the size of the barcode x-dimension. (see link to depth of field) See depth of field information.
4. The barcode scans up close, but not at a distance. This can frequently happen in a warehouse setting where both large and small barcodes are utilized.
Potential Cause: Different scanners are built to scan barcodes of different x-dimensions from a certain range of distance (depth of field). The scanner may not set or suited to scan a barcode of that x-dimension from the distance attempted.
Potential Solution: Try scanning a barcode with a larger x-dimension from the desired distance. If this works, the problem was the size of the barcode x-dimension. (see link to depth of field)
5. I have relabeled my cartons (new barcode label over old barcode label) and the new codes are not reading correctly now. See depth of field information.
Potential Cause: The label stock is too transparent. The scanner is reading graphics and/or barcode data off the original label (the label that is covered) as well as barcode data off the new label. The “overlay” of dark symbols from both labels creates a nonreadable field.
Potential Solution: The new label should be manufactured with a more opaque material and/or a blockout (black or gray tinted adhesive) that will increase opacity and cover the data from the original label.
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