Types of barcode readers
Methods Scanning methods are distinguished by the amount of operator manipulation required: - Pen or wand-type readers: requires the operator to swipe the pen over the code.
- Semi-automatic handheld readers: The operator need not swipe, but must at least position the reader near the label
- Fix-mount readers for automatic reading: The reading is performed laterally passing the label over the reader. No operator is required, but the position of the code target must coincide with the imaging capability of the reader.
- Reader gates for automatic scanning: The position of the code must be just under the gate for short time, enabling the scanner sweep to capture the code target successfully.
Types of technology The reader types can be distinguished as follows: - Pen type readers consist of a light source and a photodiode that are placed next to each other in the tip of a pen or wand.To read a bar code, the tip of the pen moves across the bars in a steady motion. The photodiode measures the intensity of the light reflected back from the light source and generates a waveform that is used to measure the widths of the bars and spaces in the bar code. Dark bars in the bar code absorb light and white spaces reflect light so that the voltage waveform generated by the photo diode is a representation of the bar and space pattern in the bar code. This waveform is decoded by the scanner in a manner similar to the way Morse code dots and dashes are decoded.
- Laser scanners work the same way as pen type readers except that they use a laser beam as the light source and typically employ either a reciprocating mirror or a rotating prism to scan the laser beam back and forth across the bar code.As with the pen type reader, a photodiode is used to measure the intensity of the light reflected back from the bar code. In both pen readers and laser scanners, the light emitted by the reader is tuned to a specific frequency and the photodiode is designed to detect only this modulated light of the same frequency.
- CCD readers (also referred to as LED scanner) use an array of hundreds of tiny light sensors lined up in a row in the head of the reader. Each sensor measures the intensity of the light immediately in front of it. Each individual light sensor in the CCD reader is extremely small and because there are hundreds of sensors lined up in a row, a voltage pattern identical to the pattern in a bar code is generated in the reader by sequentially measuring the voltages across each sensor in the row. The important difference between a CCD reader and a pen or laser scanner is that the CCD reader is measuring emitted ambient light from the bar code whereas pen or laser scanners are measuring reflected light of a specific frequency originating from the scanner itself.
- 2D imaging scanners are the fourth and newest type of bar code reader currently available. They use a small video camera to capture an image of a bar code. The reader then uses sophisticated digital image processing techniques to decode the bar code. Video cameras use the same CCD technology as in a CCD bar code reader except that instead of having a single row of sensors, a video camera has hundreds of rows of sensors arranged in a two dimensional array so that they can generate an image.
- There are a number of open source libraries for barcode reading from images. These include the ZXing project, which reads one- and two-dimensional barcodes using Android and JavaME, the JJIL project, which includes code for reading EAN-13 barcodes from cellphone cameras using J2ME, and Zebra (Changed name to ZBAR?), which reads various one-dimensional barcodes in C. Even web site integration, either by image uploads (e.g. Folke Ashberg: EAN-13 Image-Scanning and code creation tools) or by use of plugins (e.g. the Barcodepedia uses a flash application and some web cam for querying a database), have been realized options for resolving the given tasks.
- Omni-Directional Barcode Scanners
- Omni-directional scanning uses "series of straight or curved scanning lines of varying directions in the form of a starburst, a lissajous pattern, or other multiangle arrangement are projected at the symbol and one or more of them will be able to cross all of the symbol's bars and spaces, no matter what the orientation."
- Omni-directional scanners almost all use a laser. Unlike the simpler single-line laser scanners, they produce a pattern of beams in varying orientations allowing them to read barcodes presented to it at different angles. Most of them use a single rotating polygonal mirror and an arrangement of several fixed mirrors to generate their complex scan patterns.
- Omni-directional scanners are most familiar through the horizontal scanners in supermarkets, where packages are slid across a glass or sapphire window. There are a range of different omni-directional units available which can be used for differing scanning applications, ranging from retail type applications with the barcodes read only a few centimetres away from the scanner to industrial conveyor scanning where the unit can be a couple of metres away or more from the code.
- Omni-directional scanners are also better at reading poorly printed, wrinkled, or even torn barcodes.
Housing Types The reader packaging can be distinguished as follows : - Handheld scanner : with a handle and typically a trigger button for switching on the light source.
- Pen scanner (or wand scanner) : a pen-shaped scanner that is swiped.
- Stationary scanner : wall- or table-mounted scanners that the barcode is passed under or beside. These are commonly found at the checkout counters of supermarkets and other retailers.
- Fixed position scanner : an industrial barcode reader used to identify products during manufacture or logistics. Often used on conveyor tracks to identify cartons or pallets which need to be routed to another process or shipping location. Another application joins holographic scanners with a checkweigher to read bar codes of any orientation or placement, and weighs the package. Systems like this are used in factory and farm automation for quality management and shipping.
- PDA scanner : a PDA with a built-in barcode reader or attached barcode scanner e.g. Grabba.
- Automatic reader : a back office equipment to read barcoded documents at high speed (50,000/hour) e.g. Multiscan MT31
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