Scanners find the code

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.

04/01/1999


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.

Source: Omron Electronics

Bar Code Application Matrix

Scanner type Characteristics Manufacturing Warehousing Inventory Retail Distribution
Source: Control Engineering with input from Omron Electronics
Laser HandheldLinear barcodes, Stationary product
Laser Fixed positionLinear barcodes, Moving product
Single line array CCD HandheldLinear barcodes, Stationary product, Short read ranges
Single line array CCD Fixed positionLinear barcodes, 2D barcodes, Moving product
2D Array CCD Handheld2D barcodes, Linear barcodes
2D Array CCD Fixed position2D barcodes, Linear barcodes, Moving product



Advantages and Shortcomings of Scanner Types

CCD

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)

Laser

More expensive

Longer scanning range (6-12' average but can go up to 35')

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



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