A Barcode Primer for Manufacturers Dr. Peter Green BellHawk Systems Corporation

Transcription

1 A Barcode Primer for Manufacturers Dr. Peter Green BellHawk Systems Corporation Introduction This document is an introduction to the principles and practice of barcode scanning as it relates to a manufacturing operation. Some of the topics covered includes types of barcode, why do we use them, and different types of barcode equipment. Different Types of Barcode Linear barcodes have different width bars and stripes that are used to encode letters and numbers. You are probably familiar with UPC barcodes that are used to identify items at a grocery store. These barcodes are all numeric, with the first five digits indicating the manufacturer and the remaining digits identifying the product. UPC Barcode The most commonly used barcodes in manufacturing are called code 128 barcodes. This is because the barcodes can contain all 128 ascii keyboard characters of a standard computer. A typical one inch wide code 128 barcode can hold about 16 ascii characters. There are other linear barcodes in use, such as code 39 and 3 of 8, which have different ways of encoding the numbers and letters into bars and stripes. In general, these are not as flexible as code 128 barcodes. All of these Industrial Code 128 Barcode industrial barcodes have guard bars at either end and usually use a checksum for error detection. As a result they have a very high accuracy in being read. These linear barcodes are used within manufacturing plants as they can be scanned using rugged low-cost scanners. 2D Barcodes normally are used on containers being sent between manufacturing plants or from a manufacturing plant to a distribution warehouse. Instead of bars and stripes, they have different sized squares to represent the data. As a result they can hold 1,000 to 2,000 ascii characters. This is normally used to encode data such as Vendor, PO Number, Part Number, and Quantity inside the container. 2D Barcode August 27, 2001 Page 1 of 8 Copyright 2001 BellHawk Systems Corporation

2 What Do We Use Barcodes for? Tracking material containers - linear barcode on container is a "license plate" tag that references a database record that has all the information about the container, such as the material in the container, the quantity, and the location of the container. Database Server Computer Tracking jobs through the use of barcodes on job traveler work sheets. A typical traveler has a barcode to identify the job and then a barcode to identify each operation. It may also have barcodes corresponding to each item of material consumed August 27, 2001 Page 2 of 8 Copyright 2001 BellHawk Systems Corporation

3 Identifying people by scanning the barcodes on their badges. Identifying inventory locations by scanning barcodes on bins and racks. Identifying machines by scanning barcodes on machines Controlling the actions of factory-floor information system computer programs by scanning action barcodes. Selecting scrap, rework, and job cancellation reasons by scanning barcode from list. Why Use Barcodes? 1. Get rid of paperwork Today, many people on the factory floor are still using pencil and paper to record information about jobs and materials. This is then keyed into the computer, often a day later. This is a very error prone process and also results in information being available too late to be useful. Instead of writing information down, employees scan the information directly into the computer. 2. Reduced data entry errors. Statistically keyboarding from hand-written records results in at least one error in 40. This means that, if you use a 10 digit part number, every fourth entry will be wrong on average. This can result in totally inaccurate inventories, for example, that require frequent shut-downs for cycle counting. Scanning a barcode to get the same information results in less than one error in 10 Million characters. In practice the barcode scanner either scans the barcode correctly or beeps at you to tell you that it was unable to successfully scan the barcode. 3. Reduced data entry time. It takes less than a second to scan a barcode, whereas it can take tens of seconds to write down a part number, or the like, and then to keyboard it into the computer. 4. Reduced training. It is much easier to train someone to point and scan than it is to record the same data manually or to key it into a computer. Today, many of the people on the factory-floor do not read or write good English. It is much easier to teach these people to scan data than to write it down. August 27, 2001 Page 3 of 8 Copyright 2001 BellHawk Systems Corporation

4 How Barcodes Work Scanner Decoder Barcode scanners work on a number of principles. In its simples form, a laser beam is scanned across the barcode and the reflected light is collected and converted into a digital data stream. This is then decoded into a string of ascii characters, which are fed to the computer. The scanning may also be done electronically using a solid-state CCD element like those in a digital camera. It may also be done by manually moving a wand over the barcode or swiping a barcode through a reader. In the case of 2D barcodes, the barcode may be scanned by a laser moving in a two dimensional raster pattern. It may also be scanned by a two dimensional CCD element. Some 2D scanners use a linear scanner and then have the user manually move the scan beam up and down the barcode, thus simulating a raster scan. Corded Scanners The most commonly used scanner is the CCD scanner. It has a linear CCD element inside a tough plastic case. This is a contact scanner, that is held over the barcode. Scanning commences when the user presses a button and a beep is heard when a successful scan is completed. These are very rugged and can stand repeated 6 foot drops onto concrete. Type typically come with a 6 foot long cord although this can be extended to 12 feet. This unit contains the scanner and the decoder unit inside its handle. Variants of this scanner are available for scanning 2D barcodes with a two dimensional CCD array. A linear CCD scanner will typically cost $175 and a 2D corder CCD scanner will cost around????? Many wands are still in use in factories, although they are now falling out of favor. They used to be much cheaper than the CCD units but August 27, 2001 Page 4 of 8 Copyright 2001 BellHawk Systems Corporation

5 now are identical in cost. A wand has a photo-sensor at its tip which is moved manually over the barcode to perform the scanning. This has to be done at about a 60% angle to the barcode surface and requires somewhat of a knack for successful scanning. Today's wands have an integral decoder unit. Wands typically have stainless steel cases which makes them rugged. Unfortunately their weakness lies in their photo detectors. When dropped, the drag of the wand cable often results in the tip of the photo detector hitting the concrete, which can break it. Typical cost of a wand is $175. Laser scanners usually contain a solid-state laser that is mechanically scanned in one dimension or two. The benefit of a laser scanner is range. Laser scanners have a scan distance that varies from about 2 feet to about 25 feet, depending on the model. At longer scan ranges, larger higher reflectivity labels are required. Depending on the model, these are fairly robust, withstanding a several foot drop onto concrete. Laser scanners are more expensive, typically costing $500 for a linear scan model and $1,000 For a 2D scan model. Connecting a Corded Scanner to a PC The most common way of connecting a corded scanner to a PC is through a "wedge" configuration. In this configuration, the scanner has a Y cable. To connect the scanner to the PC, the PC's keyboard is unplugged from the back of the computer and the Y cable is plugged between the keyboard and the computer. In this configuration, when a barcode is scanned, it appears to the computer as if the contents of the barcode were typed on the keyboard. The benefit of the wedge configuration is that no special software needs to be loaded into the PC to read the barcodes. There are scanner models available that connect into the serial and USB ports of PCs. These, however, need special software to be loaded onto the PC for the barcode scanners to perform keyboard emulation. Cordless Scanners Corded scanners are very effective for activities such as scanning barcode badges and job traveler sheets. In a stock room or shipping or receiving situation a long cord can become an OSHA hazard. August 27, 2001 Page 5 of 8 Copyright 2001 BellHawk Systems Corporation

6 Cordless scanners replace the cord with a short-range wireless link. The scanner transmits the barcode contents to a base station, which is connected to a PC in a wedge configuration. Thus the cordless scanner works the same as a corded scanner, except there is no cord. Cordless scanners have a range of about 30 feet. They also have a digital code, like a garage door opener, to uniquely link a scanner with its base station. This enables up to 10 or so (depending on the model) cordless scanners to operate in the same area without interference. Note that, however, each scanner needs its own PC, with which the operator interacts as if they were using a corded scanner. Batch PDA/Scanner Units For tracking material transactions in a warehouse, we need a totally mobile solution to record putting away items and retrieving items. In this situation, we use a Portable Digital Assistant (PDA) with an integrated barcode scanner. These units have a built-in processor as well as a LCD touch sensitive screen. With these units, transactions are recorded and stored in the memory of the PDA. Then, at an appropriate time the PDA is placed in a cradle. The cradle is typically connected to the plant LAN and relays the material transaction data to the factory-floor database server. The cradle also recharges the battery within the PDA. The reason that these are called "Batch" units is that the data is saved up until a batch of data can be transferred to the database. They have the great benefit that there is no limitation to the geographic area that can be covered by these units. In fact, many people give these units to their truck drivers so that they can record deliveries on the road. The batteries within these units are good for one shift and can easily be replaced with charged batteries for the next shift. Most transactions are entered through the touch screen, using a stylus. Typically the unit will contain its own local database so that it can perform real-time validation at data entry time. Some models use the stylus to enter quantities whereas others have a numeric keypad. Some of these units are based around a Palm Pilot and others around a Pocket PC paradigm. At present, the screens are all monochrome to extend battery life. The units normally have linear (1D) barcode scanners but can be ordered with the capability to read 2D barcodes by manually doing the up-down scan. Typical cost of these units is between $1,000 and $1,200 plus the cost of a network cradle at about $500 for a 4 slot version. Wireless PDA Scanners August 27, 2001 Page 6 of 8 Copyright 2001 BellHawk Systems Corporation

7 These are the same PDA/scanners as the batch units, except that they have a wireless LAN link built-in. This enables these units to communicate with the factory-floor database server without being placed in a cradle. Wireless communications has to be line-of-sight between the PDA and the wireless LAN access point. The wireless waves will not go through metal, including racks, or concrete walls with reinforcing steel bars. When the user is in visual range of the access point they can press a button and the accumulated transaction data will be relayed without the need to place the unit in a cradle. The range of these units is about 500 feet. They are moisture and dust proof and can be used outdoors. These units still need to be placed in a cradle to recharge their batteries or their batteries exchanged for recharged units at the end of every shift. With appropriate programming (such as provided by BellHawk ) these units can function in batch mode until they are in range of an access point. Units can also work with multiple access points, seamlessly transitioning between them (as a cell-phone is supposed to do between cell-towers). The cost of these units is about $2,000 depending on memory and the capabilities of the built-in scanner. Industrial access points cost about $850 each. Printing Barcodes Barcodes, such as those on job traveler sheets, can be printed on any laser printer (with the appropriate software). It is not recommended that they be printed on an ink-jet printer as the ink can easily smudge or run. The laser printer heat seals the ink to the paper, making it much more durable. Barcode labels are printed on a barcode printer. PC Printer Driver Label Template Unlike a regular windows printer, an industrial barcode printer is a complex piece of equipment that has its own built-in control processor. The printer uses a wax/resin ribbon that is thermally imaged onto the barcode label stock (which has a base substrate on which there are peel-off labels). The printer takes a series of instructions and internally composes the barcode label image, including generating the specified format for each of the barcodes on the label. August 27, 2001 Page 7 of 8 Copyright 2001 BellHawk Systems Corporation

8 The printer needs a special printer driver, such as that provided by Label Matrix. This printer driver takes in a label template, fills in the data field, typically from a database, and sends the appropriate data to the printer. The label template is generated by a point and click WYSIWYG program from the vendor of the printer driver. Programs such as Label Matrix contain drivers for just about every barcode printer made. They also support control of features such as automatic label alignment and peel and strip (where the label is automatically peeled off the substrate and the substrate is rewound into the printer). A basic industrial barcode printer costs about $1,200. This price increases up to about $5,000 per unit as the speed, ruggedness, and label size increase. Options such as peel and strip also increase the cost. Programs such as Label Matrix cost from $500 to about $800 per license. August 27, 2001 Page 8 of 8 Copyright 2001 BellHawk Systems Corporation