To effectively manage and control a factory, we need information. How do we collect it?

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Auto-ID

• Data-collection needs:

– What is our WIP?

– What is productivity or assignment of employees? – What is utilization of machines?

– What is progress of orders? – What is our inventory?

– What must we track for quality purposes?

• To effectively manage and control a factory, we need information.

– How do we collect it?

– Note information may be required of automation, or a

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– Job traveler:

– Employee time sheets:

– Operation tear strips:

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– require cooperation and accuracy of factory workers – requires later transcription into other forms or into

database

• Error rates of handwritten data average 1/30

– example: dates, order numbers, counts, etc. – forces delay in access of data

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Automated data collection

• Examples of automated data collection:

– magnetic card readers – bar codes

– optical character readers – radio frequency systems – voice recognition

• Automated methods give fewer errors:

– example: barcode error rate is 10,000 times less than

keyboard entry

• automated reduces time workers spend logging data

• faster

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Magnetic Strip autoid

• Magnetic strip attached to a product or container

• Problems:

– cannot be scanned remotely – more expensive than barcodes – risk of erasure via magnetic fields • Advantages

– dense data storage – ability to alter

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Optical Character Recognition

• Specially designed characters are machine readable

– example: numbers at bottom of bank checks

– more advanced technology can read even

standard-looking character sets.

• Advantages:

– readable by humans too – cheap printing

• Disadvantages:

– near-contact scanning – lower scanning rates

– lower density compared to barcodes

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Radio Frequency (RFID)

• (active) RFID: ID “tag” on part or container (or truck or railcar)

– active device emits signals when prompted by an external

source

– usually read-only device -- limited number of characters – receiver then collects the signal and decodes it

– Problems: more expensive than other technologies • generally used only when environment precludes others • active device, so requires removal and reuse.

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Surface Acoustical Wave (SAW)

• SAW: Related to RFID:

– uses specially encoded substrate made of crystaline

material (such as lithium niobate)

– Radio waves (inquiry transmission) hit substrate

--converted into acoustical signal on the substrate, then back to a unique radio signal ID

– Tag is about half size of credit card – requires no battery or power source

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Newest developments in RFID

• Motorola printed tags -- offers 900 bits of storage: conductive ink printing

• Texas Instruments Tag-it

– 0.9in x 1.5in to 1.8in x3in flexible tags – Can be enclosed within paper labels

– Operate at 13.56MHz, but 902-928MHz available for longer

read ranges

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Barcoding

• Barcoding Advantages:

– low error rates

– well developed technology – relatively inexpensive

– can be read from close or from distance

– labels are relatively cheap and easy: can rely on common

printing technologies

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Basic concept of barcoding

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– Contact: must have very close proximity – noncontact: inches to feet away

• Visible light:

– compatible with most printing inks, dyes, etc. – light sources:

• LED

– reliable, cheap, low power, but lowpower requires close proximity

• Laser (example: Helium Neon Laser)

– high power, so longest distances, but more expensive • Visible laser Diode:

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– Works well with labels printed with carbon-based inks,

laser-etched codes on metal, etc.

– Biggest advantage

• readable through oil, grease, grime, visibly-opaque coverings

– so suitable for dirty environments or security situations – Disadvantage:

• Not all inks suitable • not all papers suitable

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– single detector:

• issues spot size in relation to bar size

– CCD: Charge Coupled Device: • can use flash illumination

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Review of last class

• Auto-ID technologies:

– magnetic stripe

– optical character recognition – barcode

– RF tags

– Each has advantages/disadvantages – Compared to manual:

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Barcodes:

• Last class: introductory barcodes:

– Well developed technology

– inexpensive -- can use common inks and papers • Classifications:

– light: visible vs. infrared

– detector: CCD vs. single detector

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– Density: How much information can we represent in a

given space?

– Reliability: How accurate will our reading of information

be?

– Cost: for printing and reading

– Representation: numeric or alphanumeric? – Sub-issues:

• what is a 1 vs. a 0 ? • what is our alphabet ? • direction scanning issues

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Basic terminology:

• Barcodes are either conventional (one-dimension) or 2D (two-dimensional)

• We focus on one-dimensional codes:

– one-dimension: code represents a binary sequence • 10010100010101101110100010...

• Bars: foreground color (black)

• Spaces: background (white)

• 2 types of codes:

– Delta codes – Width codes

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Delta codes

• Delta codes: info is contained in which color is in which location

– Interval is divided into equally sized modules – Each module is either black (1) or white (0)

– Example Delta code: UPC (Universal Product Code)

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Width Codes

• Width codes: information is not stored in the color, but in the width.

– Thus, variable width of characters. – Example: 010010100

• The color alternates between bits, regardless of whether a bit is a one or a zero.

– Example: code 39 (very common code used in industry

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Reading different sizes, distances, speeds

• How can we read the code under variety of size issues, distances, and speeds (and printing accuracy)?

– Solution: code must be “selfclocking”: number of bars

and spaces per code must be fixed, and number of modules or bits must also be fixed.

– Delta codes: already have fixed number of modules, so

must specify how many bars or spaces.

• (n,k) code has n modules and k pairs of bars and spaces • UPC is (7,2)

– Width codes: have fixed number of bars and spaces, but

we must fix the number of wide elements:

• example: code 39 has word length of 9 elements with three of those wide.

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How do we know we have the right direction?

• 2 solutions for detecting scan direction:

– have unique start and stop code words

• example: code 39 uses the “ * ” character: – 010010100

– Make all your codes reversible and identifiable:

• for a delta code, this means that if your code scheme contains a “100”, you cannot have a “001” symbol.

– ---> This means that you can only use half of all possible codes since you can’t use mirror images

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UPC: Universal Product Code

• Universal Product Code:

– used in American supermarkets since 1974 – UPC-A: consists of 12 numeric digits

• first digit is “number system designator”:typically 1 or 7 – fixed-weight/volume product, or variable, or coupon? • Digits 2-6 are manufacturer’s identifying number (assigned

by governing body)

• Digits 7-11 are unique product code assigned by mfgr. • Last digit is a “check” digit -- all digits together satisfy

algebraic equation.

• By year 2005: UPC will be nonexistent: replaced by EAN (originally European Article Numbering) -- adds extra digit

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• How big a code?

– 2 bars and 2 spaces require 3 dividers -- 6 positions possible – 20 ways to choose 3 out of 6

– Thus, depending on whether you start with bar or space,

total of 40 possible “characters”

– But, can’t include mirror images, so only 20 codes allowed • symbols on left half start with space, symbols on right half

start with bar.

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Code 39

• Code 39: Very popular code:

– several versions:

• version A: consists of A-Z, 0-9 only • version D: full ASCII character set • “39” stands for “3 of 9”

– 3 wide elements representing value 1 – 9 elements total: 4 spaces, 5 bars.

– How many times can 3 be selected out of 9? • = 84 characters possible

• 10 digits, 26 letters, hyphen, period, space, *, $, /, +, % • so only 44 code words used

• asterix used only as the first and last word of a symbol: indicates direction of scan.

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bar or space results in illegal code word.

– Example: “1”: bars:10001 spaces:0100

– but, changing one bit gives illegal code: • bars: 11001, spaces: 0000

– Thus, code is self-checking:

• spaces only have odd number of wides, and bars have only even number of wides.