ingineerng Plant MATERIAL HANDLING -

t t ' t Auxiliary Input

Job Travelers Bar Codes Or Program Cards Electric Scales

CNC Input Voice i

ig. 1. Sbopfloor applications for bar code systems include job costing, :heduling, project tracking, quality and statistical control, and down- me reporting.

utomatic identification systems pro- - vide instantaneous knowledge of

aterial flow from receiving, through manufacturing, to shipping. This information enables the staff to accurately control material resources, which leads to increased productivity, reduced operating expenses, and improved product quality.

Material handling related expenses for bringing an item to market range from 30 to 80% of the product's total cost. Conse- quently, the savings potential realized from improved flow and control is substantial. Now, automatic identification technology has advanced to the point where the princi- ples of measurement and control can be ap- plied effectively to discrete operations.

Once a plant accepts the concept and val- ue of automatic identification, the next step is to match needs with the various technologies on the market, including opti- cal bar code, magnetic, radio frequency, and voice. Of these options, optical bar code technology is probably the most wide- ly accepted because of its accuracy, simple operation, proven performance, and rea- sonable price. Combining bar code technol- ogy with programmable microprocessors further increases system flexibility and re- duces cost to the point where virtually eve- ry industry now uses the concept to some degree.

Applying bar codes effectively requires close examination of the transactions among people, information, and material to maximize tracking and control capabili- ties. Several plant operations should be studied:

Receiving - Inefficient handling of ma- terial at the receiving dock creates a ripple effect through the flow cycle. Poor receiv- ing practices result in backed-up trucks and congestion, acceptance of incorrect materi-

102 PLANT ENGINEERING OCTOBER 17,1991 . FILE 4595 ! I

I

al, and misplaced loads. Bar code technol- ogy offers a fast and accurate way to pro- cess incoming materials with a minimum of labor.

Raw material storage - Accurate counts and locations lead to savings through re- duced inventory levels and knowledge of all available stock.

Production (fabrication and assembly) - Shop floor data collection applications include job costing, scheduling, project tracking, time and attendance, quality and statistical control, and downtime reporting. Plant workers follow prompts on the shop terminal to enter data with bar code wands or laser guns, alphanumeric keypads, card scanners, or badge readers, Fig. 1.

Packaging - Bar codes reduce manpow- er in this labor-intensive operation by per- forming online, realtime verification of packaging labels. Automatic systems, tied to computers or programmable controllers, increase productivity by defining the con- tent of each package and gat r- mation on printing manifests.

Finished goods storage - ic identification virtually eliminates mis- placed products, facilitates the storage of raw material and finished goods, saves cap- ital costs, and minimizes the turnaround time to pick orders.

Shipping - Bar codes, in conjunction with tracking, weighing, and sortation sys- tems and computers, help guarantee that containers get into the right truck. Comput-

specification that spells out exactly how the proposed system performs, reflects reality, and is compatible with existing operati'ons:

Bar code system elements generate4he primary data on which the other system components operate. Elements include readers and scanners, decoders, sortation controls, weigh stations, label printers.

Reader and scanner ty creasing cost and complexity, are m p " , fixed beam, and mdving beam. Ali three choices contain a light source and optical system to develop reflected li t and dark

Readers and scanners also include electron- ic circuitry for interpreting the scanned data.

Manual readers consist .of handheld wands or laser guns attached to portable or stationary units. With wands or pens, the operator provides the scanning action by moving the detector directly over a bar code label, in close proximity to or actual contact with the surface. The more expen- sive laser guns give the operator additional flexibility, because the label is scanned many times a second from a distance. Digi- tal displays and keyboards are available to augment the data collection process of wands or laser guns.

Portable data collection units permit the

5

Bar Code Components '9 d

transitions from a bar code, 9 on a label.

Fig. 2. Bar codes, along with tracking, weighing, and sortation systems and computers, identaa pack- ,

operator to move freely while'capturing data. The operator downloads the data in batches to a host-system. Stationary units

ag rs check the container'sbar code against a ored shipping manifest and prints reports n truck contents and weight, Fig. 2. often connect online with a host system, tents and weight.

rated System Design ere are no universal off-the-ihelf solu- for material flow cycle problems. A s engineering approach determines

red components and optimizes pay- k by integrating a variety of technol-

with existing or proposed plant opera- ments of the automated system include computers, communica- king and control, conveyors, and dentification technologies. s team analyzes the dependency

interaction among many plant parame- ters and system alternatives. People using the system should serve on the team, be- cause they know who needs what informa- tion and when. The team sets the overall design objectives and scope before select- ing individual elements. The group ana- lyzes the tradeoff between various technol- ogies, and assures management of an adequate return on the investment before

The result of this planning is a functional

ds ation. For example, a circle scan pat-

tern is used by tire manufacturers where the bar code appears anywhere on the pe- rimeter. Highly complex patterns handle virtually any orientation of the scanned bar code. Omnidirectional scanners employ a rotating pattern to read bar codes with 360- deg orientations. Figure 3 shows a sam- pling of bar code beam patterns.

More than one scanner, and even differ- ent types, are occasionally used at the same conveyor location. For example, cluster scanner configurations that surround a conveyor ‘are installed in cases where the bar code has multiple orientations. Scan- ners cover the conveyor from a variety of angles so that at least one picks up a passing bar cod ho matter where the label falls on

Higher scan rates generally permit faster co eyor speeds. taster rates also facilitate

a bar code by a “majority voting” logic

the mo‘ 4 ng package.

a r ompanson of multiple reads to validate

aDDrOath. .:’z

Bar code symbol :placement is not as long as the label Dasses within the

data, nimber of vaiid reads, and various error messages.

Decoder logic is contained in the scanner housing or a separate piece of equipment, depending on the application. A self-con- tained scanner and decoder is probably more economical for an application requir- ing a single read and transmission, with few relay outputs. In other cases, centralized decoding from multiple scan heads is less expensive. Where the application calls for high functionality, the centralized decoder offers a programmed microprocessor to handle a variety of related tasks, such as tracking and production counting. Or the application geometry may dictate a small scan head installed in close quarters that connects to a remote decoder.

Sortation devices integrate bar code scan- ners and tracking systems with the mechan- ical controls of a conveyor. The bar code label on an incoming package determines the destination on a multiple-lane convey- or. The sortation controller checks the scanned label against a table that defines the package’s destination lane.

Photoeyes, combined with a tachometer encoder on the conveyor, track the package to predefined points along the route. The sortation controller activates a mechanism that diverts the package into the assigned lane. Sortation controllers are used to route packages to desired shelving storage or to trucking docks for shipping. Another pho- toeye on the divert lane indicates a success- ful movement.

Multiplexers combine data channels from many sources onto one communica- tions line to a host computer; this approach simplifies the wiring scheme. For example, one serial channel of the multiplexer might

1 1

Depth of field, which is the distance be- tween the minimum and maximum scan- ning range,. is an important parameter. For example, if the scanner sits directly above a

iconveyor, looking down on top-mounted “‘jabels, the depth of field determines the

permissible variation in package height. : Some scanners employ dynamic focusing,

dhanging the depth of field in response to an input signal related to package height.

. depths of field, which means more allowa- ble variability in the distance from label to scanner. For example, a bar width of 0.01 in. generally translates to a 3-in. depth of field. A larger width of 0.015 in. corre- sponds to a 6-in. depth of field. Similarly,

,” ’

Y‘ .e ‘ Larger bar widths permit greater optical

; ’

104 PLANT ENGINEERING OCTOBER 17,1991

collect data by polling from up to 32 local or remote devices, checking for errors, and transmitting in real time to a host comput- er. In other words, one data communica- tions line takes the place of 32 lines run- ning from peripherals to the host computer.

Peripheral devices are manual readers, fixed or moving-beam laser scanners, key input terminals, weigh stations, and micro- computer terminals. Data communications are bidirectional to perform downloading of preprogrammed parameters to the var- ious peripheral terminals.

Transaction rate affects the number of devices realistically connected to the multi-

. i

ly identifies, weighs, tares, and labels pack- ages on the fly. Both systems, shown in 4, are able to read and generate bar co labels with product net and gross weights.

Operators are able to program the in-mo tion scale system with product data, such a tare weights and tolerance limits. An bound laser scanner identifies the cont ers as they pass through the system. The station controller applies the proper tare weights and tolerances, and=s_tpres data on gross and net weights. An ocrtbound scan- ner verifies that the co to the proper containe

Label printers for include conventional

plexer. For example, moving-beam scan- ners transmit a serial message for each box. The message length (number of characters), baud rate, and time between boxes deter- mine the number of moving-beam scanners per serial channel. In practical terms, a multiplexer handles fewer devices if mov- ing-beam scanners are among the

. In static systems, the package a halt on the conveyor for manual . The in-motion scale automatical-

Software d e v e b ~ t ; s and computer integration are continudly improving theper$iormance of bar coding

r for manual weighing; in-mot weigh, tare,

Fig. 5. Bar code labels are prihed in traditional methods and on demand; offset, dot matrix, inkjet, laser, thermal, and electrostatic printing are commonly used.

The combination of printing speed, for. mat variations, quality, and cost dictate the printer chosen for a particular application Figure 5 offers a sampling of label types.

Label printing stock, adhesive, and method of application are also considera- tions. Label stock includes paper and film, such as PVC, Mylar, and acetate. Adhesive possibilities include. permanent, remov- able, pressure sensitive, heat sensitive, and temperature resistant. Hand-applied labels

substrate. h a d e

low degree of specularity (matte finish). Glossy inks tend to reflect back into the scanner, making the bars appear as spaces. Similarly, covering the bar code label with a highly reflective film, such as cellophane, is not advised.

Recent Developments Microprocessors and software tech-

niques permit continuing advances in de- coding technology. A recent development makes it unnecessary to scan the entire bar code in one pass. Partial scans provide use- ful data that are combined with other par- tial reads to rebuild the complete bar code symbol. The scanned bar codes contain a checksum digit to verify code reconstruction.

As for hardware, the current trend is to- ward self-contained scanner and decoder units. Small, sophisticated electronic chips carry more and more of the scanning and decoding circuitry, making the equipment accurate, fast, economical, and smaller, without sacrificing performance.

Another trend is the gradual adoption of the personal computer as a platform on which to base integrated system schemes. The personal computer serves as the hub for scanning, decoding, communications, tracking, and sortation functions.

The accompanying “Bar Code System Checklist” presents some of the many ques- tions that should be answered before the elements are selected.

For more information.. . . . . Ron Holzhauer, Material Handling Editor,

31 2-390-2668.

For information on how to order copies of this article circle 13 on post card

106 PLANT ENGINEERING OCTOBER 17,1991 FILE 4595