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

Transcription

1 Auto-ID 321

2 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 spinoff of automation. 322

3 Manual data collection: Job traveler: Employee time sheets: Operation tear strips: Preprinted cards 323

4 Problems with manual methods: 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 324

5 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 immediate access to data. 325

6 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 use is declining due to disadvantages 326

7 Optical Character Recognition Specially designed characters are machine readable example: numbers at bottom of bank checks more advanced technology can read even standardlooking character sets. Advantages: readable by humans too cheap printing Disadvantages: near-contact scanning lower scanning rates lower density compared to barcodes higher error rates compared to barcoding 327

8 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. Example Use: automobile painting 328

9 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 millions of possible ID signatures possible. 329

10 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 MHz available for longer read ranges 256bit non-volatile memory with read/write 330

11 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 Many different barcode codes exist 331

12 Basic concept of barcoding Basic concept: different absorbtion or reflection of light 332

13 Classifications: 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: also powerful for distance, but less power and less heat 333

14 Infrared: 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 334

15 Scanning method: single detector: issues spot size in relation to bar size CCD: Charge Coupled Device: can use flash illumination 335

16 autoid class 2 336

17 Review of last class Auto-ID technologies: magnetic stripe optical character recognition barcode RF tags Each has advantages/disadvantages Compared to manual: each offers accuracy, automation, speed 337

18 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 But what about the codes themselves? 338

19 Many different barcode symbologies possible: 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 readability at different distances 339

20 Basic terminology: Barcodes are either conventional (one-dimension) or 2D (twodimensional) We focus on one-dimensional codes: one-dimension: code represents a binary sequence Bars: foreground color (black) Spaces: background (white) 2 types of codes: Delta codes Width codes 340

21 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) Delta codes have a fixed width for n bits 341

22 Width Codes Width codes: information is not stored in the color, but in the width. Thus, variable width of characters. Example: 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 and government) 342

23 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. 343

24 Examples: (Pavlidis et al, IEEE Computer, April 1990) 344

25 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: 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 345

26 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 346

27 UPC is a Delta code with 2 bars, 2 spaces, 7 modules 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. Advantage: we can scan by halfs, and reassemble later. 347

28 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. 348

29 Code 39 patterns chosen such that changing a single bit in 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. 349