Scanners Find the Code

04/01/1999



Omron Electronics



Many, if not most, manufacturing facilities incorporate bar coding on some level. Applications range from parts tracking and quality control to finished goods identification. The question is, are manufacturers using bar-code scanners best suited to the application? Just as there are many bar-code symbologies, different types of bar-code scanners are available.

A bar-code scanner is composed of a light source and a light detector. No matter what the form factor, all types of bar-code scanners work by scanning and detecting the contrast between the dark bars and the spaces on a bar code label. The first requirement for a good read is a nicely contrasting print with a minimum of smudging.

The data signal is converted from analog to digital so it can be processed by a decoder, which is either built into the scanner or is a separate plug-in device. If the bar code is legible and the symbology is recognized as valid, the symbol is decoded. The decoded data is then transmitted to application-based software and can be displayed on a CRT, batch terminal, or other screen, or used in other enterprise database operations.

All scanners are available in one of two form factors--handheld or fixed position. Handheld scanners are pointed at stationary items. Fixed position scanners read bar codes from items as the items themselves pass by the scanner. In industrial applications, items with bar-code labels generally pass by the scanner on a conveyor belt.

Handheld or fixed position
Handheld and fixed position scanners for industrial applications operate using one of two technologies: CCD (charged-coupled device) and laser. CCD scanners operate by flooding the bar code with light which reflects the bar-code symbol back to an array of sensors. Laser scanners use a beam created by a laser diode that is scanned across the bar code via a rapidly moving mirror.

Handheld CCD scanners are available in single line array and 2-dimensional, while fixed position CCD scanners are available in single line array and 2-dimensional array (vision systems). Handheld and fixed position laser scanners are available in single line (or linear), raster (used when the bar code is not precisely positioned and when readability must be increased), vibrating vane (sweeps a laser across a bar code for better readability and to read some 2-dimensional bar codes), and omnidirectional (can read a bar code regardless of orientation).

While the most common bar code is a single line array, two-dimensional codes see increasing use. The bar code on a retail product may only contain two numbers--a vendor identification number and a unique product part number. Two-dimensional codes are capable of packing much larger amounts of data into a small space. This is useful, for example, in tracking work in process in a manufacturing plant.

Advantages and shortcomings of scanner types

CCD

Laser

Less expensive

Shorter scanning range (up to about 6')
Less field of view
Slower scan rates
Can read 1D and some 2D bar codes
Not omnidirectional (if labels are skewed or slightly blurred, reliability can be impaired)

More expensive

Longer
Greater field of view
Faster scan rates
Can read 1D and some 2D bar codes
Omnidirectional (can read skewed or slightly blurred labels)

Source: Control Engineering with input from Omron Electronics


Bar code application matrix

Scanner type

Characteristics

Manufacturing

Warehousing

Inventory

Retail

Distribution

Laser Handheld

Linear barcodes, Stationary product

*

*

*

*

Laser Fixed position

Linear barcodes, Moving product

*

*

Single line array CCD Handheld

Linear barcodes, Stationary product, Short read ranges

*

*

Single line array CCD Fixed position

Linear barcodes, 2D barcodes, Moving product

*

*

2D Array CCD Handheld

2D barcodes, Linear barcodes

*

*

2D Array CCD Fixed position

2D barcodes, Linear barcodes, Moving product

*

*

*

*

Source: Control Engineering with input from Omron Electronics






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