Your guide to hand held laser scanners
From extended range scanners to wearable models, industrial hand helds have been tailored for demanding and varied conditions.
By Staff -- Modern Materials Handling, 5/1/1998
The vast majority of bar code scanners used in plants and warehouses these days are portable, hand-held laser scanners. And just as there is a wide range of conditions and data capture needs in industry, there is a broad variety of hand-held laser scanners available to get the various data capture jobs done. A partial list of these models includes standard-, long-, and extended-range scanners as well as cordless, wearable, and non-condensing versions.Regardless of the specific model in use, hand-held laser scanners collect data by passing a beam of laser light over a bar code and measuring the intensity of the light reflected back to the scanner. The reflected light intensity changes as the beam passes over the bars and spaces of the bar code. Since the velocity of the beam's movement is known, the relative widths of the bars and spaces is determined by measuring the duration of each change in light intensity.
In a process called decoding, the information in the bar code is understood when the relative widths of the bars and spaces are analyzed. Some scanners decode data before passing it on to a host computer while others pass on undecoded information for later translation.
While hand-held laser scanners generally work alike, three primary factors affect the specific scanner design:
1. Scanning performance demanded by the application,
2. Human factors, and
3. The working environment.
Scanning-performance factors
The two issues most frequently related to scanner performance are range and bar code characteristics.
Range. The optical design of a laser subsystem determines the range of distances that the scanner can read a bar code of a given density. Density is a measure of the width of lines and spaces. The denser the bar code, the narrower the lines and spaces, and the shorter the range.
Most materials handling applications require scanners be optimized for near-range performance-from contact out to tens of inches on bar codes ranging from 5 mils to 55 mils. Examples include orderpicking, manufacturing, packing, and shipping.
Other applications require far-range performance at tens of feet. For example, bar codes identifying dock doors may be hung from a high-bay warehouse ceiling. As a result, long-range bar code scanners have been developed to read bar codes at nearly 40 ft.
In many of the applications that have a long-range requirement, there is also the need to scan at short range. At a receiving dock, for instance, the operator may need to scan the bar code near the ceiling as well as one on an invoice.
Extended range scanners solve this problem by incorporating not one but two separate lasers, one for near-range scanning and the other for long-range scanning.
Bar code characteristics. There are two critical bar code characteristics that affect the performance of hand-held laser scanners-density and label quality.
Bar code densities in most material-handling applications are between 5 mil and 55 mil, within the capabilities of standard near-range scanners. But for bar codes placed on extremely small parts, high-density scanners are needed. Some of these scan extremely dense 2-mil bar codes.
The quality of bar codes can vary enormously in the plant or warehouse. Some bar codes are printed poorly while others become damaged during handling.
As a result, there are now scanners that can read poorly printed or damaged bar codes. This capability is due to improvements in laser optics and the adaptive logic that processes the light reflected back from the bar code. In addition, digital decoding algorithms have been developed that use fuzzy logic, a method of dealing with mathematical uncertainty-in this case the uncertainty of what's a bar and what's a space.
Dealing with human factors
The designs of hand-held laser scanners are also heavily influenced by the fact that the scanner is usually held in a human hand. As a result, most scanners are gun shaped for ease of use. However, some of the latest designs take the scanner out of the hand in an attempt to maximize worker productivity.
For instance, the use of a conventional hand-held scanner can significantly reduce operator productivity in handling intensive processes that require both hands. Examples include package/parcel handling and order picking.
This problem has been solved with scanners worn on the hand rather than being held in the hand. These wearable scanners are always readily available for the data capture task without the operator having to spend any extra time retrieving and holstering the scanner throughout the day.
Most wearable scanners are designed to mount on the back of the hand. Another highly miniaturized design features a ring scanner small enough to fit on the back of a finger.
Often, a wearable scanner is wired to a host terminal that is also worn by the user. There are, however, other wearable scanners that allow connection to non-wearable hosts.
Yet another human factor challenge comes up when operators must read bar codes that may be located anywhere in a relatively large work space. These might include packing and shipping operations or on the shop floor. In any of these cases, long cables connecting the scanners to the host PC/terminal are often cumbersome.
Battery-powered, cordless radio scanners eliminate the need for a cable tethering the scanner to its host computer. The scanner transmits decoded bar code data via a radio to a radio interface module which is cabled to the host computer. Upon receiving bar code data, the interface module forwards the information to the host and transmits a confirmation message back to the scanner. Data transmission range of these scanners is typically between 30 and 50 ft.
Still another human factor issue in plants and warehouses is the ability of operators to see the laser scan line during use.
Until recently, all of the lasers used in hand-held scanners produced light with a wavelength of 670 nanometers, which is just within the 700 nm limit of human visibility. (A nanometer is a billionth of a meter.)
However, a new generation of laser scanners is now available with a wavelength of 650 nm. Be-cause the retinal receptors in the human eye are more sensitive to this wavelength, 650 nm light appears three times brighter than 670 nm light.
The higher apparent brightness makes the scanner easier for an operator to use in all scanning situations. However, it is particularly valuable in long-range applications and in high ambient-light conditions, where the scan line can become impossible to see.
The working environment
To say the least, most industrial settings are not scanner friendly. Exposure to mechanical shock and external contaminants as well as temperature and humidity ranges are a constant threat.
The danger of mechanical shock has been dealt with by building scanners with a high level of ruggedness and durability. Impact-absorbent materials are used both externally and internally to protect the housing and internal components. Industrial scanners today typically meet a 6-ft drop spec, making them able to survive multiple drops to concrete from a height of 6 ft.
To protect against contamination, gaskets, and O-rings, ultrasonic welds are used to seal housing elements and cable connections. In addition, most scanners are built to operate at temperatures ranging from -20 deg C to 50 deg C, and at humidities from 5% to 95%.
Despite these protections, significant problems can still be encountered when a scanner consistently moves between refrigerated/freezer environments and hot, humid conditions elsewhere in the facility.
When a cold scanner is brought from a freezer into hot, humid air, moisture will condense either on the cold outside or inside surface of the scanning window.
There are two common solutions. The first is a heated enclosure that keeps the scanner warm even inside the freezer. Another design heats the scanning window with a small electric current, much like a rear-window defroster on a car.
As is apparent, there is a wide range of hand-held laser scanners available for materials handling applications. And from all indications, there will be more improvements announced in the near future.
Technical information for this article was provided by John Lert, director of advanced product concepts at Symbol Technologies.
How leading laser scanners stack up
Scanner type Features
All industrial hand held laser scanners
Designed for shock resistance (6 ft drop spec), sealed against wind-blown rain and dust. Also capable of operating over wide temperature and humidity range.
Standard range
Intended for near-range scanning (contact to tens of inches). Capable of scanning poor-quality bar codes.
Long range
Optimized for long-range scanning (out to hundreds of inches).
Extended range
Built with dual lasers, one for near-range reading, the other for long-range data capture.
Fuzzy logic
Suited to scanning extremely poor-quality bar codes as easily as high-quality symbols.
High density
Optimized for reading very dense symbols (down to 2 mils).
Cordless
Intended as a point-to-point radio link in place of a cable to communicate with a host, allowing user to move more freely within a work space.
Wearable
Built to be worn on the user's body (usually hand or finger), minimizing time required for data capture in handling-intensive applications.
High visibility
Suited to read bar codes in high ambient-light conditions such as outdoors in bright sunlight. May use 650-nm laser to enhance visibility of laser beam.
Non-condensing
Designed to prevent or eliminate internal and external condensation caused by movement between cold environments (freezers) and warm, humid environments.
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