(12) Ulllted States Patent (10) Patent N0.: US 8,269,970 B2 P0lid0r et a]. (45) Date of Patent: Sep. 18, 2012

Transcription

1 US B2 (12) Ulllted States Patent (10) Patent N0.: P0ld0r et a]. (45) Date of Patent: Sep. 18, 12 (54) OPTICAL COMPARATOR WITH DIGITAL 6,945,652 B2 9/05 sakqta et a1 GAGE 7,058,109 B2* 6/06 Davs /56 7,064,880 B2* 6/06 Mushka /237 (75) Inventors: Edward T. Poldor, Webster, NY(US); 7,142,7 B2* 11/06 C 11' t l /744 7,6,339 B2 12/07 K ? a1 Bors Gelman, Farport, NY (US) 7,433,796 B2 10/08 Behan et a1. 7,519,501 B2* 4/09 Palmateer /150 (73) ,528,968 B2* 5/09 Matsumya et al. 6/6 Assgnee. QualltyVlslon Internat10nal,Inc., 7,901, * 011 Klepp 3/l22 ROCheSIe/LNYWS) 02/00675 Al* 6/02 TreZZa 9/298 03/ A1* 9/03 Lee /393 ( * ) Notce: Subject to any dsclamer, the term of ths (Contnued) patent s extended or adjusted under U.S.C. 154(b) by 0 days. FOREIGN PATENT DOCUMENTS CA A1 4/1994 (21) Appl. No.. 12/497,097 (Contnued) (22) Fled: Jul. 2, 09 OTHER PUBLICATIONS (65) Pror Publcaton Data VISIONX Inc., VsonGuage Dgtal Optcal Comparator/Dgtal Pro?le Projector, Us 11/ A1 Jan' 6 11 chnes/dgtal-optcal-comparators.html, 5 pages. (51) Int. Cl. G01B 9/08 (06.01) (Contnued) (52) us. Cl /392; 6/393 Prmary Examner * Gregory J Toa?ey (58) Feld of Class?caton Search AssslanlExamner * Jarreas C Underwood See applcaton?le for complete search hstory. (74) Attorney. Agenl, 01 F f"! * Stephen B- S8181; ThOmaS B. Ryan; Harter Secrest & Emery LLP (56) References Cted (57) ABSTRACT U.S. PATENT DOCUMENTS A /444 3,339,076 3,888,593 Hlal A Kempf /393 4,567,478 A Schwab 5,715,021 A Gbeau et al. 5,886,788 A 3/1999 Kobayash 6,000,801 A * 12/1999 Dllon et al /28 6,147,758 A 11/00 Okabe et a1. 6,175,417 B1 1/01 Do et al. 6,195,165 B1* 2/01 6,6,0 B1* 3/02 6,424,332 B1* 7/02 6,597,410 B1* 7/03 An optcal comparator arranged for rear projecton onto a Vewng screen combnes an optcal projector that projects an optcal mage of a test part under nspecton onto the Vewng screen Wth a Vdeo projector that projects an optcal mage of a pxlated template pattern contanng llustrated spec?ca tons of the test part onto the same Vewng screen. The mages of the test part and the pxlated template pattern are projected concurrently onto the Vewng screen for Vsually comparng the form of the test part aganst ts spec?ed form. Clams, 6 Drawng Sheets

2 Page 2 US. PATENT DOCUMENTS FOREIGN PATENT DOCUMENTS 05/0l7l707 Al 8/05 Easley et al. EP Al 7/ /06890 A1 9/05 Hurst et al. 06/ A1 5/06 Carver et al. 06/ A1 07/ A1 11/06 Ktamura et al. l/07 Hajjar et al. OTHER PUBLICATIONS 07/ A1 Zoos/ Al 5/07 Hardng et al. V08 Klepp - -. MICROVU, Projecteue de pro?l numerque, Extract from the artcle Zoos/ A1 * 6/08 Mtsu 438/16 n Machnery Producton 869 (May 15, 08), P 15 and Google 08/ A1 10/08 Matsumya et a1 Englsh Translaton of artcle extract (2 pages plus translaton). 09/ A1 5/09 Nagashma et al. 09/ A1 5/09 Nagashma et al. 10/02666 A1 9/10 Beauchemn * cted by examner

3 US. Patent Sep. 18, 12 Sheet 1 of6? 3 E 1 : w. v, v

4 US. Patent Sep. 18, 12 Sheet 2 of6

5 US. Patent Sep. 18, 12 Sheet 3 of6 $4 92 FG. 4

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7 US. Patent Sep. 18, 12 Sheet 5 of6 mm.... mmw

8 US. Patent Sep. 18, 12 Sheet 6 of6 38

9 1 OPTICAL COMPARATOR WITH DIGITAL GAGE TECHNICAL FIELD The nventon relates to the?eld of optcal metrology and partcularly to the gagng of test parts through optcal magng systems that provde for comparng the test parts aganst templates or other representatons of the test parts. BACKGROUND OF THE INVENTION Optcal comparators, partcularly of a type that project a shadow mage (e.g., a negatve mage) or an oblquely llu mnated mage of a test part onto a screen overlad by a template of the test part, have enjoyed Wdespread acceptance as robust and relable forms of measurement by provdng measurement results n a vsually ver?able form. Dfferences between projected edge features of the test part and one or more tolerance boundares of the same features nscrbed on the templates are readly apparent on the comparator screens. Whle numercal data can also be extracted by montorng motons of the test parts aganst calbrated mages of the test parts appearng on the comparator screens, the numercal data can be ver?ed for reasonableness aganst estmates made by vsually nspectng the edges of the test part aganst the tem plate boundares or other edge features of at least approx mately known sze appearng on the screens. The accuracy Wth Whch vsual comparsons can be made depends largely on the accuracy Wth Whch the templates can be made. The optcs of the optcal comparators can be care fully calbrated and optcally corrected to present largely dstorton-free mages of test parts mounted Wthn the vew ng apertures of the optcal projecton systems. However, dfferent templates can be requred for dfferent test parts or more complex templates n the form of chart gages can be constructed for measurng ranges of related edge features among correspondng sets of test parts. More than one tem plate can be requred for measurng multple vews or edge features of the same test parts. The templates can be expensve to manufacture to requred accuracy and can requre specal storage and handlng provsons to preserve the templates n Workng condton. Tme must be allotted for orderng new or replacement templates, and even mnor revsons to the ntended form or tolerance de?ntons of test parts can requre the orderng of new templates. Efforts have been made to replace optcal projecton com parators Wth dgtal camera based comparators for makng smlar vsual comparsons on computer montors. Most advantageously, physcal templates can be replaced by dgtal representatons of the test parts generated on the computer montors by extractng boundary nformaton from computer aded desgn (CAD) spec?catons that de?ne the ntended outlnes of the test parts. Dgtal mages of the test parts captured by dgtal cameras are also generated on the same computer montors for makng comparsons aganst the dg tally generated templates. HoWever, the computer montors present pxlated mages that sgn?cantly lmt the precson Wth Whch the comparsons can be made for gven sze mages appearng on the computer screen. Snce both the templates and the test parts must be matched to the same scale on the computer screens, the resoluton of the templates and test parts match each other at dfferent dgtal magn?catons. Thus,?ne comparsons can be df?cult to make to customary certanty and can requre vsual nspecton of smaller seg ments of the test parts Wthn the same sze?eld of vew. The dgtal converson of the test part mages contrbutes add tonal systematc and random errors that reduce the relablty of the measurements as Well as the perceved robustness prevously derved from comparng actual mages of test parts aganst reference datum. SUMMARY OF THE INVENTION The nventon among ts preferred embodments dgtally generates templates for optcal projecton onto the vewng screens of optcal comparators concurrently Wth the optcal projecton of mages of test parts onto the same vewng screens. The accuracy Wth Whch the mages of the test parts are projected onto the vewng screens s largely a functon of the llumnatng and projecton optcs and s not constraned by any ntervenng dgtal pxlaton of test part mages. Although optcally projected onto the same vewng screens, the templates are dgtally generated havng regard to the projected pxel sze on the vewng screens. As such, the nventon preserves the relablty and robustness long asso cated Wth optcal comparators Whle obvatng the need for physcal templates. The combned optcal projectons of the test part and the dgtally generated template also allow for overlappng color based comparsons for provdng more eas ly dscemable ndcatons as to Whether test parts are Wthn tolerance. One example of an optcal comparator n accordance Wth ths nventon ncludes a vewng screen, an optcal projector for projectng an optcal mage of a test part under nspecton onto the vewng screen, and a vdeo projector for projectng an optcal mage of a pxlated template pattern contanng llustrated spec?catons of the test part onto the vewng screen. The vdeo projector preferably ncludes a dgtal ds play engne for generatng the pxlated template pattern. A?rst llumnator llumnates the test part and a second llum nator llumnates the dgtal dsplay engne. The optcal pro jector and the vdeo projector are related so that the mages of the test part and the pxlated template pattern are projected concurrently onto the vewng screen at a matchng scale. A program-drven nterface between (a) one or more dgtal CAD?les contanng spec?catons of the test part and (b) the dgtal dsplay engne of the vdeo projector can be arranged to convert the spec?catons n the dgtal CAD?le nto the pxlated template pattern n an llustrated form amenable to comparson Wth the projected optcal mage of the test part. For example, nformaton concernng the boundares of the test part, such as may be represented n the dgtal CAD?le as a nomnal boundary havng a numercally de?ned tolerance, can be converted nto a tolerance Zone band approprately postoned Wth respect to other CAD-referenced features of the test part n the pxlated template pattern. For enhancng the optcal comparson, the optcal mage of the test part and the optcal mage of the pxlated template pattern can be projected n dfferent colors. For example, a negatve mage of the test part can be projected n a?rst color, such as green, and an mage of pxlated tolerance Zone bands can be projected n a second color, such as red. The projec tons are preferably color addtve, and portons of the pro jected negatve mage of the test part that are Wthn the projected tolerance Zones of the test part appear as a thrd color, such as yellow. A feature, such as a bore hole, can be seen to be Wthn tolerance When an annular red band sur rounds an annular yellow band. The unnterrupted outer red band s an ndcaton that the outer lmt of the tolerance Zone has not been breached as Would be ndcated by a green break n the red band outsde the Zone. The unnterrupted nterme date yellow band s an ndcaton that the nner lmt of the tolerance Zone has not been breached as t Would also be

10 3 ndcated by a black break n the yellow band outsde the Zone. Based on such an easly dscernble color test, multple features of ndvdual test parts can be nspected concurrently or nearly so to determne f the features are Wthn tolerance. The nterface between the dgtal CAD?les and the dgtal dsplay engne of the vdeo projector can produce template structures to compensate for resoluton lmtatons of the pxlated template pattern at a gven magn?caton for makng sub-pxel comparsons Wth the projected mage of the test part. For example, the locaton of a boundary lne can be more precsely represented by laterally staggered sets of pxels n the pxlated template pattern. A nomnal lne, Whch repre sents the ntended boundary, s mplct from the staggered sets of pxels as a lne that can be adjudged on the vewng screen to exactly bsect the staggered sets of pxels. The laterally staggered sets of pxels can also be laterally sepa rated by an amount that straddles an ntended tolerance Zone. The projected mage of the test part contans edges Whose resoluton s not lmted by a pxel count and can dvde the ndvdual staggered sets of pxels appearng on the vewng screen nto dfferent sze areas of fractonal pxel dmensons that can be compared for a more precse determnaton of the locatons of the edges Wth respect to the boundary or toler ance Zones at a resoluton hgher than the resoluton of the pxels representng the boundary or tolerance Zones. Such mult-pxel boundary enhancements can also be used n com bnaton Wth addtve color controls for more easly dstn gushng areas of overlap between the boundares or tolerance Zones projected n one color and the mage of the test part projected n another color. Preferably, the optcs for projectng the mage of the px lated template pattern onto the vewng screen are suf?cently ndependent of the optcs for projectng the mage of the test part onto the vewng screen so that a change n the magn? caton of the mage of the test part does not affect the number of pxels avalable for magng the rescaled pxlated template pattern projected onto the vewng screen. The dgtal dsplay engne of the vdeo projector can magnfy the template pat tern by generatng a dgtal mage of a smaller porton of the template pattern usng the same number of pxels, Whch are projected at the same optcal magn?caton onto the vewng screen. Snce a smaller porton of the template pattern s generated by the same number of avalable pxels, the reso luton of the so-magn?ed template pattern as projected upon the vewng screen s ncreased. In other Words, the same vsble spacng between pxels on the vewng screen repre sents a smaller dstance accordng to the scale of the ncreased magn?caton. The optcal projector can project the mage of the test part to the vewng screen along a?rst optcal axs, and the vdeo projector can project the mage of the pxlated template pattern to the vewng screen along a second optcal axs that s nclned to the?rst optcal axs. An optc, such as a seg mented lens (e.g., Fresnel lens) or gratng, can be overlad on the vewng screen to combne lght energes of the projected mages approachng the vewng screen along the?rst and second optcal axes nto lght energes emanatng from the vewng screen along a common vewng axs. The algnment of lght energes between the mages produced by the optcal and vdeo projectors provdes for more unform comparsons of color and contrast throughout the vewng screen. For purposes of economy and optcal algnment, the optcal projector and the vdeo projector can share some optcs. For example, the optcal paths of the optcal projector and the vdeo projector canbe combned at a beamspltter so that both the optcal mage of a test part and the pxlated template pattern are projected along the same optcal axs to the vew ng screen. A rotatonally adjustable retcle can be algned Wth the vewng screen for measurng angular orentatons of maged features of the test part. A communcaton lnk can be pro vded between the retcle and the vdeo projector so that the mage of the pxlated template pattern rotates on the vewng screen matchng rotatonal adjustments of the retcle. The optcal projector and the vdeo projector are preferably cal brated so that a center pont of the retcle corresponds to a center pont of the pxlated template pattern. The optcal projector preferably ncludes a magn?caton adjuster for changng magn?caton of the mage of the test part projected onto the vewng screen. Another communcatons lnk can be provded between the magn?caton adjuster and the vdeo projector so that the mage of the pxlated template pattern on the vewng screen changes n magn?caton matchng changes n the magn?caton of the mage of the test part on the vewng screen. The vdeo projector s also preferably lnked to a computer so that the vdeo projector can also project other computer generated mages onto the vewng screen, ncludng an nter actve desktop that supports communcaton protocols Wth the computer. For example,?les contanng data relatng to the test part or the optcal comparator can be accessed through the nterface and results dsplayed on the vewng screen. Another example of an optcal comparator for comparng a test part aganst desgn spec?catons n accordance Wth ths nventon ncludes a support for mountng a test part and a dgtal mage generator for generatng a pxlated template pattern contanng llustrated spec?catons of the test part. A?rst llumnator llumnates the test part and a second llum nator llumnates the dgtal mage generator. Imagng optcs project overlappng optcal mages of the test part and the pxlated template pattern on a vewng screen at a matchng scale for vsually comparng the test part to the pxlated template pattern. The magng optcs can nclude a?rst objectve for produc ng an mage of the test part, a second objectve for producng an mage of the pxlated template pattern, and a beam com bner for combnng the mages produced by the?rst and second objectves. The second objectve can have hgher power than the?rst objectve for scalng the pxlated tem plate pattem to the test part. The?rst and second llumnators preferably llumnate the test part and the dgtal mage gen erator Wth dfferent color lght. The dgtal dsplay engnes of the vdeo projectors preferably nclude arrays of addressable elements for generatng the pxlated template patters. Alter natvely, the dgtal dsplay engnes can nclude laser beam steerng devces for tracng the template pattern drectly onto the vewng screen or through the ntermedacy of focusng optcs. BRIEF DESCRIPTION OF THE DRAWING FIGURES FIG. 1 s a dagram of an optcal comparator for nspectng a test part arranged n accordance Wth one embodment of the nventon n Whch an optcal projector and a vdeo projector follow entrely dfferent optcal paths to a common vewng screen. FIGS. 2A, 2B, and 2C present front vews of the vewng screen Wth FIG. 2A showng a projected mage of the test part, FIG. 2B showng a projected mage of a pxlated tem plate pattern, and FIG. 2C showng n an enlarged cut-away

11 5 vew of a combnaton of the projected mages of the test part and the pxlated template pattern for makng a vsual com parson. FIGS. 3A and 3B depct alternatng sets of pxels for form ng a boundary and a tolerance Zone aganst Whch a boundary of the test part can be measured to sub-pxel resoluton. FIG. 4 s a sde vew of the vewng screen showng the effect of a Fresnel lens plate for combnng the mages of the test part and the pxlated template pattern for vewng through a range optmal vewng postons. FIG. 5 s a dagram of an alternatve optcal comparator combnng certan optcs of an optcal projector and a vdeo projector for projectng mages of the test part and the px lated template pattern along a common path to the vewng screen. FIG. 6 s a dagram of another alternatve optcal compara tor that combnes an optcal projector and a vdeo projector n advance of a magn?caton lens for projectng mages of the test part and the pxlated template pattern along a common path to the vewng screen. FIG. 7 s a dagram of a laser projector for projectng mages of the template pattern onto the vewng screen. DETAILED DESCRIPTION OF THE INVENTION An optcal comparator 10, Whose outlne s depcted by dashed lnes n FIG. 1, ncludes a mult-axs stage 12 for supportng a test part 14. The mult-axs stage 12 s depcted as havng three orthogonal axes X,Y, and Z of translaton (.e., lnear moton) but could nclude fewer axes of translaton or one or more addtonal axes of rotaton (.e., angular moton), also preferably orthogonal. Varous manual controls (not shown) can be assocated Wth the mult-axs stage 12 to adjust the poston of the test part 14, Whch can also nclude motors, actuators, or the lke for automatcally postonng and/ or movng the test part 14 under nspecton. In addton, at least the lnear moton axes X and Y are preferably equpped Wth graduated lnear encoders (not shown) for measurng the changes n the poston of the test part 14. Abacklght (pro?le) llumnator 15 outputs an llumnaton beam 17. Included Wthn the llustrated backlght llumnator 15 s a lght source 16 for producng the beam 17 and a collmator 18 for collmatng the llumnaton beam 17 along an llumnaton axs 19. The lght source 16 can take a number of forms such as lght emttng dodes or ncandescent or arc lamps. When the lght source 16 s a broadband lght source, a spectral?lter can be used to lmt the spectral content of the llumnatonbeam 17. When the lght source ncompletely or unevenly?lls the desred ext pupl of the backlght llu mnator 15, one or more dffusers (not shown) can be used, such as a?rst dffuser at the focal plane of a collmator 18 and a second dffuser between the collmator 18 and the test part 14 to acheve suf?cent homogenety throughout the llum naton beam 17. A re?ector can also be combned Wth the lght source 16 to mprove ef?cency. Overall, the llumna ton beam 17 output from the llumnator 15 s preferably collmated, homogeneous, and monochromatc, preferably Wthn the green color spectrum, Whch s conventonal for optcal comparators. Other known types of llumnators could also be provded ncludng a brght?eld llumnator for co axal surface llumnaton or a dark?eld llumnator for oblque surface llumnaton. The backlt test part 14, Whch s preferably subject to manufacture accordng to predetermned desgn spec?ca tons, blocks portons of the llumnaton beam 17 n a pattern matchng the physcal pro?le of the test part 14. An optcal projector 21 collects the remanng portons of the llumna ton beam 17 propagatng along the llumnaton axs 19 and projects a negatve optcal mage 24 of the test part 14 onto a vewng screen 38 (.e., a transmttng rear projecton screen) as an optcal projecton beam (see FIG. 2A, for example). The vewng screen 38 preferably has a frostng 36 to provde a vewng plane that renders the projected negatve mage 24 of the test part 14 vsble through a range of vewng angles. A front relay lens 22 of the optcal projector 21 functons as an objectve for recevng the shadow pattern of the test part 14 and for formng a prmary mage of the test part 14, Whch can be ultmately relayed as the negatve mage 24 of the test part 14 onto the vewng screen 38. Located along an optcal pathway 23 of the optcal projector 21 between two beam foldng mrrors 26 and 28, a second relay lens 27 cooperates Wth the?rst relay lens 22 for formng an ntermedate mage 29 of the test part 14. The overall sze of the projected negatve mage 24 n relaton to the sze of the test part 14 can be controlled by a magn?caton lens, Whch ncludes a plu ralty of dfferent power lenses 31 mounted n a turret 32 for rotatng the ndvdual lenses 31 nto algnment Wth the opt cal pathway 23. A large foldng mrror 34 redrects the pro jecton beam along an optcal projecton axs orented normal to the vewng screen 38 for formng the negatve optcal mage 24 of the test part 14 on the vewng screen 38. Also projected onto the vewng screen 38 s a greatly magn?ed optcal mage 54 of a pxlated template pattern 44 (see FIG. 2B), preferably n a color that contrasts Wth the color at Whch the negatve mage 24 of the test part 14 s projected onto the vewng screen 38. The pxlated template pattern 44 can be generated Wthn a vdeo projector by a dgtal dsplay engne 42, Whch s preferably a spatal lght modulator n a form such as a lqud crystal dsplay (LCD) or a dgtal mcromrror devce (DMD). For example, the vdeo projector can be a DLP projector ncorporatng mcro mrror array technology from Texas Instruments. Hgh reso luton pxel counts are generally preferred but the vdeo pro jector can also be selected Wth regard to cost Where pxel resoluton and optcal sharpness can be applcaton matched. A projecton lens 46 of the vdeo projector projects a greatly magn?ed optcal mage 54 of the pxlated template pattern 44 onto the vewng screen 38. A vdeo projecton beam 47 carryng the optcal mage 54 propagates along a vdeo projecton axs 45 that s nclned to a normal of the vewng screen 38. The nclnaton of the vdeo projecton beam 47 Would ordnarly be expected to contrbute a so called keystone (trapezodal) dstorton to the projected mage 54 of the pxlated template pattern 44. HoWever, the projecton lens 46 as related to the pxlated template pattern 44 can be arranged to compensate for the expected keystone dstorton so that the mage 54 of the pxlated template pat tern 44 can be projected onto the vewng screen 38 Wthout any sgn?cant dstorton. For example, the pxlated template pattern 44 could be nclned Wth respect to an object plane of the projecton lens 46 to correct for the expected dstorton or an astgmatc lens could be ncorporated nto the projecton lens 46 to make a smlar correcton. Any resdual keystone error can be corrected by software drvng the vdeo projector at the tme of ntal mage calbraton or a later recalbra ton of the projected mage 54. Although the vdeo projector, as shown n FIG. 1, projects the dgtal mage 54 of the pxlated template pattern 44 drectly onto the back of the vewng screen 38, the mage 54 can also be projected va one or more mrrors (not shown) for orentng the vdeo projector n a dfferent poston Wthn the optcal comparator 1 0. The one or more mrrors can be made adjustable for algnng the center of the dgtal mage 54 Wth the center of the vewng screen 38. The use of such

12 7 mrrors for foldng the path of the vdeo proj ector can produce an mage rotaton on the vewng screen 38 that can be corrected by the software drvng the vdeo projector n the process of calbraton. A rotatable retcle plate (protractor) 48 contanng algn ment marks 49 (see FIGS. 2A-2C) overlays the vewng screen to provde a reference for angularly algnng the mage 54 of the pxlated template pattern 44 to the negatve mage 24 of the test part 14 and for measurng stage motons of the test part 14. An encoder 50 montors the angular poston of the rotatable retcle plate 48, and the measured angular pos ton of the retcle plate 48 can be calbrated to the generated angular orentaton of the pxlated template pattern 44 through a communcatons lnk 51 so that the angular oren taton of the mage 54 of the pxlated template pattern 44 tracks the angular orentaton of the retcle plate 48. Informaton for generatng the pxlated template pattern 44 preferably arses from one or more dgtal machne read able?les 56 contanng desgn spec?catons of the test part 14 such as may be generated by a computer-aded desgn (CAD) system. For example, the nformaton n the dgtal?les 56 can nclude a three-dmensonal model of the test part 14, Whch can be represented n varous Ways ncludng as Wreframe, surface, or soldmodels Wth topology and feature descrptons ntended for gudng the manufacture of the test part 14. Generally, the CAD models nherently de?ne the ntended dmensons of the modeled test part but tolerances must sometmes be appended. The dgtal?les 56 (eg CAD?les) can be receved drectly nto a computer 58 for conver son nto a dsplay template (.e., an ecad template) repro ducble n Whole or part as the desred pxlated template pattern 44, generally from a two-dmensonal pro?le repre sentaton of the test part 14 from a gven perspectve, or can be converted n a separate computer and transferred nto the computer 58 n the converted form. Tolerance nformaton drawn from the dgtal?les 56 or elsewhere can be ncorpo rated nto the two-dmensonal pro?le representaton of the test part 14 Wthn the (ecad) dsplay template replacng or augmentng the ntended pro?le boundares of the test part 14. All or any porton of the pro?le representaton of the test part 14 Wthn the (ecad) dsplay template can be reproduced by the dgtal dsplay engne 42. The tolerance boundary repre sentatons Wthn the (ecad) dsplay template can be adjusted Whle comparng the mages 24 and 54 of the test part 14 and the pxlated template pattern 44 n varous symmetrc or asymmetrc forms, ncludng expandng or contractng the tolerance Zones to ad n comparng the test part 14 aganst ts ntended form. The computer 58 s preferably arranged to perform a num ber of functons, Whch nclude (a) mportng a (DXF) CAD?le of the test part 14, (b) openng the CAD?le on a computer montor 59, (c) checkng the unts of measure and provde a means to change between Englsh and S metrc systems, (d) provdng for elmnatng unwanted CAD features, (e) pro vdng for selectng only Wanted CAD features, (f) provdng for buldng the (ecad) dsplay template, and (g) edtng and storng the (ecad) dsplay template. A two-dmensonal CAD drawng of the test part 14 can be converted nto the desred pro?le representaton Wthn the (ecad) dsplay template by changng the background of the CAD drawng to black and changng the lnes of the CAD drawng to a spec?c color, lne Wdth, and style. For example, certan of the lnes can be gven an enlarged Wdth to represent tolerance Zone bands. Other predetermned styles can be de?ned for convertng the lnes nto a form most approprate for comparson to pro?le mages of the test part In FIG. 2A, the negatve mage 24 of the test part 14 s depcted Wth shaded Zones correspondng to a pattern of llumnaton (preferably n green lght aganst a black back ground) produced by the optcal projecton of the test part 14 onto the vewng screen 38. As shown, the test part 14 has an outer pro?le boundary 62 beyond Whch lght passes and sx bore hole features 64 through Whch lght passes. In FIG. 2B, the pxlated template pattern 44 s shown Wth dashed lnes and shaded Zones representng llumnated features (prefer ably n red lght aganst a black background) ncludng boundary lnes 66 correspondng to the ntended outer pro?le boundary of the test part 14 and tolerance Zone bands 68 settng mnmum and maxmum dmensons of the bore hole features of the test part 14. In the enlarged cut-away vew of FIG. 2C, the projected mage 54 of the pxlated template pattern 44 overles the projected mage 24 of the test part 14. The maged boundary 62 of the test part 14 extends slghtly beyond the maged boundary 66 of the pxlated template pattern 44, Whch can be ndcatve of ether an algnment error or an out of toler ance condton. Regons of overlap 70 between the maged bore hole features 64 of the test part 14 and the maged tolerance Zone bands 68 of the pxlated template pattern 44 are shown n a darker shade of gray ndcatve of color sub tracton. HoWever, the green and red colors of the projected mages 24 and 54 of the test part 14 and the pxlated template pattern 44 preferably combne by color addton nto a brghter color yellow. All but one of the bore hole features 64 are Wthn toler ance, Whch s vsually ndcated n two Ways. Frst, the regons of overlap 70 entrely surround the bore hole features 64, Whch con?rms that the mnmum radal dmensons of the bore hole features 64 are Wthn the tolerance Zone bands 68. Second, the tolerance Zone bands 68 entrely surround the regons of overlap 70 and no portons of the bore hole features 64 extend beyond the tolerance Zone bands 68, Whch con?rms that the maxmum radal dmensons of the bore hole features reman Wthn the tolerance Zone bands 68. HoWever, the bore hole feature referenced as 64' s out of tolerance n both respects. Frst, the regon of overlap 70' does not completely surround the bore hole feature 64'. Second, a porton of the bore hole feature 64' extends beyond the regon of overlap 70'. Thus, one part of the bore hole feature 64' does not meet the mnmum radal dmenson tolerance and another part of the bore hole feature 64' does not meet the maxmum radal dmenson tolerance, both because the bore hole feature 64' s mspostoned. In the red-green-black color scheme representatve of color addton, a black break n the surroundng yellow regon of overlap 70 ndcates an out of tolerance condton Wth respect to the mnmum radal dmenson and a green break n the surroundng red tolerance Zone band 68 ndcates an out of tolerance condton Wth respect to the maxmum radal dmenson. Whle the optcal resoluton of the projected negatve mage 24 of the test part 14 can be qute hgh, lmted largely by the optcal transfer functon of the projector optcs, the resoluton of the projected mage 54 of the pxlated template pattern 44 s lmted by the pxel densty of the dgtal dsplay engne 42, Whch generates the orgnal mage of the pxlated template pattern 44. That s, even f the optcs of the vdeo projector are as good as the optcs of the optcal projector 21, the pxel densty Wth Whch the orgnal pxlated tem plate pattern 44 s generated lmts the resoluton of the pro jected mage 54 of the pxlated template pattern 44. On the vewng screen 38, the spacng between pxels n the pro jected mage 54 s generally a product of the spacng between the pxels n the pxlated template pattern 44 and the magn

13 9?caton of the projecton lens 46 requred to substantally?ll the vewng screen 38. In comparson, any loss n resoluton assocated Wth the magn?caton of the projected mage 24 of the test part 14 by a conventonal optcal projector s expected to the relatvely nconsequental. The optcal comparator 10 s preferably arranged for nspectng the test part 14 at dfferent magn?catons. The magn?caton lens ncludes a turret 32 of dfferent power lenses 31 that can be rotated nto the projecton path. Although the resoluton of the projected mage 54 of the pxlated template pattern 44 s lmted, the resoluton of the projected mage 54 n unts of the dstances represented scales Wth the magn?caton requred to match the magn?caton of the projected negatve mage 24 of the test part 14. Snce the optcs for projectng the mage 54 of the pxlated template pattern 44 are separate from the optcs for projectng the negatve mage 24 of the test part 14, the requred change to the magn?caton of the projected mage 54 can be accom plshed by generatng a smaller porton of the (ecad) dsplay template at a larger sze Wth the dgtal dsplay engne 42. The dgtal dsplay engne 42 of the vdeo projector can magnfy the template pattern 44 by generatng a dgtal mage of a smaller porton of the (ecad) dsplay template usng the same number of pxels, Whch are projected at the same opt cal magn?caton onto the vewng screen 38. Snce the same number and sze of pxels are avalable for?llng the avalable?eld of proj ecton, the resoluton of the projected mage 54 of the template pattern 44 relates drectly to the scale at Whch the pxlated template pattern 44 s generated. For example, f magn?caton s doubled, the resoluton of the projected mage 54 of the pxlated template pattern 44 s also prefer ably doubled. Although template pattern resoluton scales drectly to magn?caton, the resoluton of the projected mage 54 of the pxlated template pattern 44 s lmted at a gven scale for comparng the projected mages 24 and 54 of the test part 14 and the pxlated template pattern 44. For mprovng mea surement precson at a gven magn?caton, the pxels rep resentng the boundary lnes and tolerance Zones can be arranged n laterally staggered sets of pxels as shown n FIGS. 3A and 3B. A segment of a greatly enlarged boundary lne 72 s shown n FIG. 3A composed of laterally staggered sets of pxels 74 and 76 de?nng an mplct nomnal bound ary lne 78 between them. The staggered sets of pxels 74 and 76 de?ne the mplct boundary 78 between adjacent pxels. An edge boundary 80 of a test part 14 dvdes the laterally staggered sets of pxels 74 and 76 nto dfferent sze areas of fractonal pxel dmensons Whose relatve szes can be assessed to more precsely compare the edge boundary 80 to the mplct boundary lne 78. Smlarly, the boundares of a tolerance Zone band 82 can be represented by laterally staggered and offset sets of pxels 84 and 86 as shown n FIG. 3B. The nner edges of the pxel sets 84 and 86 de?ne mplct boundares 88 and 89 at the outer lmts of the tolerance Zone band 82. Any breach of the ntended tolerance Zone band 82 by the edge boundary 90 of the test object s made more readly apparent. Overlappng addtve or subtractve color combnatons between the px lated boundary lnes 72 or tolerance Zone bands 82 and the maged test part 14 can also enhance the vsual comparsons. The mages formed by the dgtal dsplay engne 42 are preferably not lmted to pxlated template patterns but can also nclude any of a number of computer generated graphcs or text. For example, nformaton concernng the test part 14, ncludng nstructons for settng up the comparator and nspectng the test part 14 can be projected onto the vewng screen 38. In fact, the vewng screen 38 can be arranged as an nteractve desktop for the computer 58. For example, a com puter mouse (not shown), Whose locaton s vsble on the vewng screen 38 can be used to operate menus and open or close?les. A keyboard (also not shown) can be smlarly connected to the computer 58 for nputtng nformaton nto the computer 58, Whch can be vsbly represented on the vewng screen 38. In addton to the retcle plate 48, a lens plate 92 as shown n FIG. 4 can also overlay the vewng screen 38 for regulatng the drectons of lght emanatng from the vewng screen 38. The lens plate 92, Whch can take the form of a segmented lens or gratng, s preferably a Fresnel lens arranged for drectng the maged lght through a range of optmum vewng pos tons. The lens plate 92 can be arranged to combne the lght energes of the optcal and vdeo projecton beams and 47, Whch nomnally approach the vewng screen 38 along df ferent projecton axes and 45, and to drect the combned lght energes emanatng from the vewng screen 38 along a common vewng axs 94. The algnment of lght energes between the projecton beams and 47 allows for more unform comparsons of color and contrast over the entre vewng screen 38 throughout the range of optmum vewng postons. An alternatve optcal comparator 100 arranged n accor dance Wth the nventon s depcted n FIG. 5. Components of the optcal comparator 100 n common Wth components of the optcal comparator 10 are labeled by the same reference characters. For example, the comparator 100 ncludes the same mountng stage 12, backlght (pro?le) llumnator 15, and transmttng vewng screen 38. A front relay lens 102 functons as an objectve of an optcal projector 104 for col lectng the patterned lght from the llumnator 15 and form ng a negatve mage of the test part 14. The magn?caton lens reszes the negatve mage for projecton Wthn an optcal projecton beam 106 onto the vewng screen 38. A beamspltter 108 together Wth foldng mrror 110 redrects the optcal projecton beam 106 along a projecton axs 112 normal to the vewng screen 38. Wthn a dgtal dsplay engne 116 of a vdeo projector 118, a separate lght source 114, preferably one or more (red) lght emttng dodes (LEDs), operates through a condenser 1 for llumnatng a dgtal mcromrror devce (DMD) 122. An assocate processor drver 124, Whch receves nstruc tons from the computer 58, controls operaton of the dgtal mcromrror devce 122 for generatng pxlated template pat terns 44 or other dgtal mages. The dgtal mcromrror devce 122 ncludes an array of mrrors that are ndvdually addressable by the processor drver 124 for swtchng between postons for achevng desred spatal dstrbuton of lght Wthn a vdeo projecton beam 126. In one poston, the ndvdually addressable mrrors re?ect portons of the nc dent lght n a drecton along an axs 127 of the vdeo pro jecton beam 126. In another poston, the ndvdually addressable mrrors re?ect the remanng portons of the nc dent lght n a drecton along an axs 129 to a beam dump 1. A projecton lens 132 forms a magn?ed mage 54 of the pxlated pattern 44 generated by the dgtal mcromrror devce 122 for projecton onto the vewng screen 38. The beamspltter 108 combnes the vdeo projecton beam 126 Wth the optcal projecton beam 1 06 for propagaton together along the projecton axs 112 to the vewng screen 38. The ntegraton of the vdeo projector 118 Wth the optcal projector 104 enables both the vdeo projecton beam 126 and the optcal projecton beam 106 to approach the vewng screen 38 along the common projecton axs 112. The relatve lght ntenstes between the projected mages reman conss tent over a Wder range of vewng angles.

14 11 A Zoom lens 134 operatng n reverse through the beam spltter 108 relays mages of both the backlt test part 14 and the frontlet dgtal mcromrror devce 122 to a camera 136. A vdeo processor 138 can be used to lnk the camera 136 to the computer 58 for montorng the nspecton of ndvdual test parts. Snce mages of both the test part 14 and the pxlated template pattern 44 are dgtally captured by the camera 136, drect numerc comparsons can be made to at least approx mately algn and scale the mages, manage nspecton proto cols, and record results. HoWever, the?ner measurements and comparsons are preferably made by vsual reference to the vewng screen 38, Where the resoluton of the mage 24 of the test part 14 has not been subjected to a dgtal approxmaton. Another example of an optcal comparator arranged n accordance Wth the nventon s depcted n FIG. 6. The same reference characters dentfy features n common Wth the optcal comparators 10 or 100. Smlar to the optcal com parator 100, a front relay lens 152 of the depcted optcal comparator 150 functons as an objectve of an optcal pro jector 154 for collectng the patterned lght from the llum nator 15 and formng a negatve mage of the test part 14. The magn?caton lens reszes the negatve mage for projec ton Wthn an optcal projecton beam 156 onto the vewng screen 38. The optcal projecton beam 156 transmts through a beamspltter 158 and s redrected by foldng mrrors 160 and 162 along a projecton axs 164 normal to the vewng screen 38. An alternatve dgtal dsplay engne 166 for a vdeo pro jector 165 ncludes a backlt lqud crystal dsplay (LCD) 168 as a spatal lght modulator. Lght from a lght source 170, preferably formed by one or more (red) lght emttng dodes, passes through a condenser 172 that evenly llumnates the lqud crystal dsplay 168. Lqud crystal cells arranged n an array Wthn the dsplay 168 are ndvdually addressable by the processor drver 174 for swtchng between states of enablng or dsablng the passage of lght through the cells of the lqud crystal dsplay 168. The processor drver 174 receves nformaton from the computer 58 for generatng the desred pxlated template patterns 44 or other mages n the lqud crystal dsplay 168. A projecton lens 176 forms a magn?ed mage of the pxlated template pattern 44 gener ated by the lqud crystal dsplay 168 Wthn a vdeo projec ton beam 178 for projecton onto the vewng screen 38. The beamspltter 158 combnes the vdeo projecton beam 178 Wth the optcal projecton beam 156 for propagaton together along the projecton axs 164 to the vewng screen 38. In contrast to the optcal comparators 10 and 100, the magn?caton lens of the optcal comparator 150 magn?es both the projected mage 24 of the test part 14 and the projected mage 54 of the pxlated template pattern 44 gen erated by the dgtal dsplay engne 166. The arrangement may be useful for smplfyng the combnaton of the optcal and vdeo projecton beams 156 and 178 n stuatons Were a lower resoluton of the pxlated template pattern 44 s toler able at hgher magn?catons. The pxlated template pattern 44 contanng llustrated spec?catons of the test part 14 can be ntegrated to varous degrees Wthn the optcal comparators 10, 100, and 150. For example, the pxlated template pattern 44 can be coupled or not coupled to the mage 24 of the test part 14, coupled or not coupled to the mult-axs stage 12, coupled or not coupled to the rotatable retcle plate 48, and coupled or not coupled to the magn?caton (e.g., rotatonal poston of the turret 32) of the optcal projector 21 or 104. In an uncoupled condton, the magn?caton and orenta ton of the pxlated template pattern 44 can be set Wthn the vdeo projector or 118 and an operator can move the test part 14 Wth respect to a statonary pxlated template pattern 44 for makng vsual comparsons smlar to comparsons made Wth a conventonal over-screen physcal template. If the operator Wants to nspect a porton of the test part 14 beyond the boundares of the pxlated template pattern 44, the pxlated template pattern 44 can be regenerated from the (ecad) dsplay template to represent another (.e., relatvely shfted) porton of the test part 14. Keyboard or mouse (not shown) nputs to the computer 58 can be used to control the correspondng template shft. Wth nput concernng the magn?caton power of the opt cal projector 21 or 104, the (ecad) dsplay template repro ducble n Whole or part as the pxlated template pattern 44 can be automatcally scaled to match. Smlarly, Wth nput concernng the rotatonal poston of the rotatable retcle plate 48, the pxlated template pattern 44 can be automatcally orented to match. The mage 54 of the pxlated template pattern 44 can be algned Wth the mage 24 of the test part 14 by referencng two feature locatons n the (ecad) dsplay template to the same two feature locatons on the test part 14. In addton, translatons supported by the mult-axs stage 12 can be scaled to correspondng translatons of the pxlated template pattern 44 (.e., the regeneraton of dfferent portons of the underlyng (ecad) dsplay template). The feature algnment and stage scalng couples the mages 24 and 54 of the test part 14 and the pxlated template pattern 44, and together, the pxlated template pattern 44 tracks motons of the test part 14 as translated by the stage 12. The couplng of the mages 24 and 54 of the test part 14 and the pxlated template pattern 44 can be accomplshed as follows. Select a?rst reference feature from the (ecad) dsplay template, such as a lne, crcle, or comer. Algn the same correspondng reference feature on the test part 14 to an optcal centerlne of the vewng screen, and send an output strng to the computer 58. The strng, Whch preferably org nates from dgtal readouts (DRO s) collected from onboard encoders, can nclude nformaton for dentfyng the X andy coordnate postons of the mult-axs stage 12 from a home poston, the rotatonal angle 0 of the rotatable retcle plate 48, the magn?caton of the magn?caton lens of the optcal projector 21 or 104, and an ndcaton as to Whether the ecad template s to be coupled or uncoupled to the moton controls of the optcal comparator 10, 100, or 150. Select a second reference feature from the (ecad) dsplay template. Algn correspondng reference feature on the test part 14 to an optcal centerlne of the vewng screen, and send an output strng Wth smlar types of nformaton to the computer 58. Based on ths nformaton, the pxlated template pattern 44 rotates to the angle of the test part 14 on the vewng screen and dsplays a scaled porton of the (ecad) dsplay template at the same magn?caton as the optcal projector 21 or 104 as selected by the operator. In addton, the (ecad) dsplay template can be automatcally scaled and centered relatve to the vewng screen centerlne for closely matchng the pro jected mage 24 of the test part 14. The (ecad) dsplay template, as reproduced by the vdeo projector, 118, 165 as the pxlated template pattern 44 s preferably a negatve of the underlyng CAD drawng. For example, the background of the drawng should be black and the lnes de?nng the test part 14 can be n a color chosen by the operator on the computer 58. Once the test part 14 and the (ecad) dsplay template are coupled together, the computer 58 can be arranged to perodcally poll for any changes n the parameters n the strng to know When the operator has rela tvely moved the test part 14, such as by turnng table poston knobs or by operatng the joystck.

15 13 An operator can make comparsons between the test part 14 and the pxlated template pattern 44 n ether a coupled or uncoupled mode. In the coupled mode, the mage 54 of the pxlated template pattern 44 moves together Wth the mage 24 of the test part 14 as translated by the moton stage 12. In the decoupled mode, the mage 54 of the pxlated template pattern 44 remans statonary on the projector vewng screen 38 Whle the mage 24 of the test part 14 translates across on the vewng screen 38. In ether mode, the mage 54 of the pxlated template pattern 44 can be scaled automatcally to provde a?eld of vew matchng the sze as the projected mage 24 of the test part 14 at the magn?caton selected by the operator. In the uncoupled mode, the angular orentaton of the mage 54 of the pxlated template pattern 44 can be set to track the rotaton of the rotatable retcle plate 48 ndepen dently of the orentaton of the test part 14. The operator can choose to dsplay of the X andy coordnate values of the stage 12 or the rotatonal angle 8 of the rotatable retcle plate 48 as measures taken from a nomnal locaton of a feature or feature group When the operator moves the test part 14 to a best?t poston relatve to the projected pxlated template pattern 44. The projected mage from the dgtal dsplay engne 42 can nclude a WndoW on the dsplay screen 38 for dsplayng nstructons to the operator for set-up and other messages that can be projected onto the vewng screen 38 n a dalog WndoW to gude the nspecton process. Ths faclty can be used to help the operator orent the part for nspecton and call attenton to mportant features on the (ecad) dsplay tem plate. Status nformaton can also be provded such as COUPLED or DECOUPLED to avod confuson. Dmensons and/or tolerances can be attached to features usng?y-outs to provde numerc data about mportant fea tures. SoftWare for the computer 58 can provde a GO TO functon for exercsng computer numerc control (CNC) over the X andy motons of the stage 12 and relatvely movng the test part 14 through a sequence of locatons automatcally. The GO TO functon for the computer numerc control (CNC) over the X and Y motons of the stage 12 can be programmed nto the computer 58 by nputtng varous des tnatons of the test part 14 at Whch comparsons are to be made. The entre (ecad) dsplay template (or at least the porton of the template contanng desred locatons for com parson) can be dsplayed on the vewng screen Whle a?eld of vew (FOV) crcle szed to the selected scale of the ntended comparson overles the (ecad) dsplay template. The?eld of vew (FOV) crcle can be postoned over the mage of the ecad dsplay template and the center of the crcle can become a programmed destnaton When the opera tor saves the poston. For measurng other regons of the test part, the operator can drag the FOV crcle to varous ponts on the ecad ds play template and save these locatons for later or mmedate playback. At run tme, the sequence of stage locatons can be stepped through n turn. When the system s n COUPLED mode, the pxlated template pattern 44 generated from the ecad dsplay template remans n place over the nomnal center of the projected mage 24 of the test part 14 automat cally. After each move, the operator can DECOUPLE and jggle the mage 54 of the test part 24 nto tolerance by movng the stage 12 and rotatng the retcle plate 48 untl a best?t stu aton s found. The operator can select CONTINUE to re couple the mages of the test part 14 and the pxlated template pattern 44 and move to the next pre-programmed stage loca ton Although the dgtal dsplay engnes 42, 116, and 166 of the vdeo projectors, 118, and 165 preferably nclude arrays of addressable elements for producng the pxlated template patterns 44, smlar dgtal template patterns can generated by laser beam steerng devces of conventonal laser projectors. For example, as shown n FIG. 7, a mrror 186 of a laser projector 180, Whch s pvotable about two orthogonal axes y' and 2', can be used to steer a collmated laser beam 184 from a laser source 182 for tracng the template pattern. The com puter 58 can be arranged to convert the desred template pattern derved from the CAD model nto the requred?le format for the laser projector 180. When operated Wth su? cent tracng speed together Wth a suf?cent refresh rate, the controlled trajectory of the laser beam 184 can be used to project a contnuous glowng mage of the template pattern on the vewng screen 38. The mage of the template pattern can be traced drectly onto the vewng screen 38 or through the ntermedacy of focusng optcs 188. A laser projector of a type that could be used for purposes of the subject nventon s dsclosed n US Patent Applcaton Publcaton No. 09/ of Nagashma et al. Although Nagashma et al. s laser projector s arranged for projectng mages n multple colors, a sngle color may su?ce for projectng a template pattern n accordance Wth ths nven ton. US. Pat. No. 7,433,796 to Behan et al. dscloses a laser projector and system for convertng engneerng data con cernng fasteners generated usng tools such as CAD/CAM type applcatons nto both geometrc and non-geometrc data for projecton Wth a laser projector onto objects ntended for manufacture Wth the fasteners. Both the Nagashma et al. applcaton and the Behan et al. patent are hereby ncorpo rated by reference. Instead of projectng mages onto the back of a transms sve vewng screen, the optcal and vdeo projectors of the optcal comparators could be arranged for projectng mages onto the front of a re?ectve vewng screen. Many other such varatons and mod?catons Wll be apparent to those of skll n the art Wthn the overall teachng of ths nventon. The nventon clamed s: 1. An optcal comparator comprsng: a vewng screen, an optcal projector that projects an optcal mage of a test part under nspecton onto the vewng screen, and a vdeo projector that projects an optcal mage of a px lated template pattern contanng llustrated spec?ca tons of the test part onto the vewng screen, the vdeo projector ncludng a dgtal dsplay engne for generatng the pxlated template pattern, a?rst llumnator for llumnatng the test part and a second llumnator for llumnatng the dgtal dsplay engne, the optcal projector and the vdeo projector beng related so that the mages of the test part and the pxlated template pattern are projected concurrently onto the vewng screen at a matchng scale, and a pro gram-drven nterface between (a) one or more dgtal?les contanng spec?catons of the test part and (b) the dgtal dsplay engne of the vdeo projector for convert ng the spec?catons n the dgtal?le nto the pxlated template pattern n an llustrated form for comparson Wth the projected optcal mage of the test part on the vewng screen, Wheren the program-drven nterface converts nformaton concernng one or more boundares of the test part n the dgtal?le nto one or more tolerance Zone bands n the pxlated template pattern. 2. The optcal comparator of clam 1 n Whch the optcal mage of the test part s projected n a?rst color, and the

16 15 optcal mage of the one or more tolerance Zone bands n the pxlated template pattern s projected n a second color. 3. The optcal comparator of clam 2 n Whch the?rst and second colors of the projected test part and the tolerance Zone bands are color addtve, and portons of the projected mage of the test part that are Wthn the projected tolerance Zone bands appear on the vewng screen n a thrd color. 4. An optcal comparator comprsng: a vewng screen, an optcal projector that projects an optcal mage of a test part under nspecton onto the vewng screen, and a vdeo projector that projects an optcal mage of a px lated template pattern contanng llustrated spec?ca tons of the test part onto the vewng screen, the vdeo projector ncludng a dgtal dsplay engne for generatng the pxlated template pattern, a?rst llumnator for llumnatng the test part and a second llumnator for llumnatng the dgtal dsplay engne, the optcal projector and the vdeo projector beng related so that the mages of the test part and the pxlated template pattern are projected concurrently onto the vewng screen at a matchng scale, and a pro gram-drven nterface between (a) one or more dgtal?les contanng spec?catons of the test part and (b) the dgtal dsplay engne of the vdeo projector for convert ng the spec?catons n the dgtal?le nto the pxlated template pattern n an llustrated form for comparson Wth the projected optcal mage of the test part on the vewng screen, Wheren the program-drven nterface between the one or more dgtal?les and the dgtal dsplay engne of the vdeo projector produces template structures that com pensate for resoluton lmtatons of the pxlated tem plate pattern for makng sub-pxel comparsons Wth the projected mage of the test part. 5. The optcal comparator of clam 4 n Whch a boundary lne s represented by laterally staggered sets of pxels n the pxlated template pattern. 6. The optcal comparator of clam 5 n Whch the projected optcal mage of the test part on the vewng screen repro duces an edge feature of the test part to dvde the laterally staggered sets of pxels n the pxlated template pattern nto dfferent sze areas of fractonal pxel dmensons that can be compared for determnng the locaton of the edge feature Wth respect to the boundary lne to a resoluton hgher than the resoluton of the pxels representng the boundary lne. 7. The optcal comparator of clam 4 n Whch a tolerance Zone s represented by laterally separated sets of pxels n the pxlated template pattern. 8. The optcal comparator of clam 7 n Whch the projected optcal mage of the test part on the vewng screen repro duces an edge feature of the test part to dvde the laterally staggered sets of pxels n the pxlated template pattern nto dfferent sze areas of fractonal pxel dmensons that can be compared for determnng the locaton of the edge feature Wth respect to the tolerance Zone to a resoluton hgher than the resoluton of the pxels representng the tolerance Zone. 9. The optcal comparator of clam 1 n Whch optcs of the vdeo projector for projectng the mage of the pxlated tem plate pattern onto the vewng screen are ndependent of optcs of the optcal projector for projectng the mage of the test part onto the vewng screen so that a change n the magn?caton of the mage of the test part does not ncrease a pxel sze of a resealed pxlated template pattern projected onto the vewng screen at a matchng scale An optcal comparator comprsng: a vewng screen, an optcal projector that projects an optcal mage of a test part under nspecton onto the vewng screen, and a vdeo projector that projects an optcal mage of a px lated template pattern contanng llustrated spec?ca tons of the test part onto the vewng screen, the vdeo projector ncludng a dgtal dsplay engne for generatng the pxlated template pattern, a?rst llumnator for llumnatng the test part and a second llumnator for llumnatng the dgtal dsplay engne, the optcal projector and the vdeo projector beng related so that the mages of the test part and the pxlated template pattern are projected concurrently onto the vewng screen at a matchng scale, and optcs of the vdeo projector for projectng the mage of the pxlated template pattern onto the vewng screen beng ndependent of optcs of the optcal projector for pro jectng the mage of the test part onto the vewng screen so that a change n the magn?caton of the mage of the test part does not ncrease a pxel sze of a rescaled pxlated template pattern projected onto the vewng screen at the matchng scale, Wheren the dgtal dsplay engne provdes for magnfyng the pxlated template pattern appearng on the vewng screen by generatng a dgtal mage of a smaller porton of the template pattern such that the smaller porton of the template pattern s reproduced to a hgher resoluton. 11. The optcal comparator of clam 10 n Whch the vdeo projector and the optcal projector share at least one optc for projectng the mages of the pxlated template pattern and the test part along a common optcal axs to the vewng screen. 12. The optcal comparator of clam 11 n Whch the vdeo projector and the optcal projector nclude respectve optcal paths that are combned at a beamspltter. 13. The optcal comparator of clam 10 n Whch the optcal projector projects the mage of the test part to the vewng screen along a?rst optcal axs and the vdeo projector projects the mage of the pxlated template pattern to the vewng screen along a second optcal axs that s nclned to the?rst optcal axs. 14. The comparator of clam 13 further comprsng an optc algned Wth the vewng screen and arranged to combne lght energes of the projected mages approachng the vew ng screen along the?rst and second optcal axes nto lght energes emanatng from the vewng screen along a common vewng axs. 15. The optcal comparator of clam 10 n Whch the?rst llumnator provdes for back lghtng the test part for pro jectng a shadow mage of the test part onto the vewng screen. 16. The optcal comparator of clam 10 n Whch the?rst llumnator llumnates the test part Wth a?rst color lght and the second llumnator llumnates the dgtal dsplay engne Wth a second color lght. 17. An optcal comparator comprsng: a vewng screen, an optcal projector that projects an optcal mage of a test part under nspecton onto the vewng screen, and a vdeo projector that projects an optcal mage of a px lated template pattern contanng llustrated spec?ca tons of the test part onto the vewng screen, the vdeo projector ncludng a dgtal dsplay engne for generatng the pxlated template pattern, a?rst llumnator for llumnatng the test part and a second llumnator for llumnatng the dgtal dsplay engne,

17 17 the optcal projector and the vdeo projector beng related so that the mages of the test part and the pxlated template pattern are projected concurrently onto the vewng screen at a matchng scale, a rotatonally adjustable retcle algned Wth the vewng screen for measurng angular orentatons of maged features of the test part and a communcaton lnk between the retcle and the vdeo projector so that the mage of the pxlated template pattern rotates on the vewng screen matchng rota tonal adjustments of the retcle. 18. The optcal comparator of clam 17 n Whch the optcal projector and the vdeo projector are calbrated so that a center pont of the retcle corresponds to a center pont of the pxlated template pattern. 19. The optcal comparator of clam 1 further comprsng a magn?caton adjuster Wthn the optcal projector for changng magn?caton of the mage of the test part projected onto the vewng screen and a communcatons lnk between the magn?caton adjuster and the vdeo projector so that the mage of the pxlated template pattern on the vewng screen changes n mag n?caton matchng changes n the magn?caton of the mage of the test part on the vewng screen.. The optcal comparator of clam 1 further comprsng a communcatons lnk between the dgtal dsplay engne of the vdeo projector and a computer so that the vdeo projector can project mages generated by the computer onto the vew ng screen. 21. An optcal comparator comprsng: a vewng screen, an optcal projector that projects an optcal mage of a test part under nspecton onto the vewng screen, and a vdeo projector that projects an optcal mage of a px lated template pattern contanng llustrated spec?ca tons of the test part onto the vewng screen, the vdeo projector ncludng a dgtal dsplay engne for generatng the pxlated template pattern, a?rst llumnator for llumnatng the test part and a second llumnator for llumnatng the dgtal dsplay engne, the optcal projector and the vdeo projector beng related so that the mages of the test part and the pxlated template pattern are projected concurrently onto the vewng screen at a matchng scale, and a communcatons lnk between the dgtal dsplay engne of the vdeo projector and a computer so that the vdeo projector can project mages generated by the computer onto the vewng screen ncludng mages of an nterac tve desktop that supports communcaton protocols Wth the computer. 22. A method of nspectng a test part comprsng steps of llumnatng the test part from a?rst lght source, projectng a magn?ed optcal mage of the llumnated test part onto a vewng screen, llumnatng a dgtal dsplay engne from a second lght source, generatng Wth the dgtal dsplay engne a pxlated tem plate pattern representng the test part, projectng a magn?ed optcal mage of the pxlated tem plate pattern onto the vewng screen at a common scale Wth the projected optcal mage of the test part, comparng the projected optcal mage of the test part to the projected optcal mage of the pxlated template pattern on the vewng screen, and matchng the projected optcal mages of the test part and the pxlated template pattern to a common scale nclud ng changng the sze of the generated pxlated template pattern that s projected onto the vewng screen to match a changed magn?caton of the projected optcal mage of the test part, Wheren the sze of the generated pxlated template pattern s changed by generatng a dgtal mage of a smaller porton of the template pattern such that the smaller porton of the template pattern s reproduced to a hgher resoluton. 23. The method of clam 22 ncludng steps of accessng one or more dgtal?les contanng spec?catons of the test part and convertng the spec?catons from the one or more dgtal?les nto the pxlated template pattern. 24. A method of nspectng a test part comprsng steps of llumnatng the test part from a?rst lght source, projectng an optcal mage of the llumnated test part onto a vewng screen, llumnatng a dgtal dsplay engne from a second lght source, accessng one or more dgtal?les contanng spec?ca tons of the test part, generatng Wth the dgtal dsplay engne a pxlated tem plate pattern representng the test part by convertng the spec?catons from the one or more dgtal?les nto the pxlated template pattern ncludng convertng nforma ton concernng boundares of the test part n the one or more dgtal?les nto one or more tolerance Zone bands n the pxlated template pattern, projectng an optcal mage of the pxlated template pat tern onto the vewng screen, and comparng the projected optcal mage of the test part to the projected optcal mage of the pxlated template pattern on the vewng screen.. The method of clam 24 n Whch the step of proj ectng the optcal mage of the test part ncludes projectng the optcal mage of the test part onto the vewng screen n a?rst color and the step of projectng the optcal mage of the pxlated template pattern ncludes projectng the one or more tolerance Zone bands onto the vewng screen n a second color. 26. The method of clam n Whch portons of the pro jected optcal mage of the test part that overlap Wth the one or more tolerance Zone bands appear on the vewng screen n a thrd color. 27. A method of nspectng a test part comprsng steps of llumnatng the test part from a?rst lght source, projectng an optcal mage of the llumnated test part onto a vewng screen, llumnatng a dgtal dsplay engne from a second lght source, accessng one or more dgtal?les contanng spec?ca tons of the test part, generatng Wth the dgtal dsplay engne a pxlated tem plate pattern representng the test part by convertng the spec?catons from the one or more dgtal?les nto the pxlated template pattern ncludng convertng nforma ton concernng boundares of the test part n the one or more dgtal?les nto laterally staggered sets of pxels n the pxlated template pattern, projectng an optcal mage of the pxlated template pat tern onto the vewng screen, and comparng the projected optcal mage of the test part to the projected optcal mage of the pxlated template pattern on the vewng screen. 28. The method of clam 27 n Whch the step of proj ectng the optcal mage of the test part onto the vewng screen reproduces an edge feature of the test part to dvde the later ally staggered sets of pxels n the pxlated template pattern

18 19 nto dfferent sze areas of fractonal pxel dmensons that can be compared for determnng the locaton of the edge feature Wth respect to the boundary lne to a resoluton hgher than the resoluton of the pxels representng the boundary lne. 29. The method of clam 24 n Whch the step of proj ectng the optcal mage of the test part ncludes projectng the mage of the test part to the vewng screen along a?rst optcal axs and the step of projectng the optcal mage of the pxlated template pattern ncludes projectng the mage of the px lated template pattern to the vewng screen along a second optcal axs.. The method of clam 29 ncludng a step of combnng lght energes of the projected mages approachng the vew ng screen along the?rst and second optcal axes nto lght energes emanatng from the vewng screen along a common vewng axs. 31. The method of clam 24 ncludng a step of lnkng the dgtal dsplay engne of the vdeo projector to a computer so that the vdeo projector can project mages generated by the computer onto the vewng screen. 32. A method of nspectng a test part comprsng steps of llumnatng the test part from a?rst lght source, projectng an optcal mage of the llumnated test part onto a vewng screen, llumnatng a dgtal dsplay engne from a second lght source, generatng Wth the dgtal dsplay engne a pxlated tem plate pattem representng the test part, projectng an optcal mage of the pxlated template pat tern onto the vewng screen, comparng the projected optcal mage of the test part to the projected optcal mage of the pxlated template pattern on the vewng screen, and lnkng the dgtal dsplay engne of the vdeo projector to a computer so that the vdeo projector can project mages generated by the computer onto the vewng screen, Wheren the step of projectng the optcal mage of the pxlated template pattern ncludes projectng onto the vewng screen mages of an nteractve desktop that supports communcaton protocols Wth the computer. 33. The method of clam 24 n Whch the step of llumnat ng the test part ncludes backlghtng the test part and the step of projectng the optcal mage of the llumnated test part ncludes projectng a shadow mage of the llumnated test part onto the vewng screen. 34. The method of clam 33 n Whch the step of generatng a pxlated template pattern ncludes selectvely re?ectng lght from an addressable mcromrror array Wthn the dgtal dsplay engne.. An optcal comparator comprsng a support for mountng a test part, a dgtal mage generator for generatng a template pattern contanng llustrated spec?catons of the test part, a?rst llumnator for llumnatng the test part and a second llumnator for llumnatng the dgtal mage generator, and projecton optcs that project overlappng optcal mages of the test part and the template pattern onto a vewng screen at a matchng scale for vsually comparng the test part to the pxlated template pattern, Wheren the dgtal mage generator ncludes a beam steer ng devce for tracng the template pattern. 36. The comparator of clam n Whch the projecton optcs nclude a?rst objectve for producng an mage of the test part, and a second objectve for producng an mage of the pxlated template pattern. 37. The comparator of clam 36 n Whch the second objec tve ncludes hgher optcal power than the?rst objectve for scalng the pxlated template pattern to the test part. 38. The comparator of clam n Whch the?rst and second llumnators llumnate the test part and the dgtal mage generator Wth dfferent color lght. 39. The comparator of clam 38 n Whch the dgtal mage generator ncludes an array of ndvdually addressable ele ments for generatng the template pattern.. The comparator of clam n Whch the projecton optcs nclude a laser projector and the beam steerng devce s ncorporated nto the laser projector for projectng the mage of the template pattern onto the vewng screen.