1、Designation: C 1652/C 1652M 06Standard Test Method forMeasuring Optical Distortion in Flat Glass Products UsingDigital Photography of Grids1This standard is issued under the fixed designation C 1652/C 1652M; the number immediately following the designation indicates theyear of original adoption or,
2、in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONTransmitted and reflected distortion in annealed, heat strengthened, and tempere
3、d glass can bemeasured by several methods.(1,2,7,8,)2Qualitative methods are based on the observation ofwaviness in the glass as viewed in of reflected or transmitted images in a set of equidistant lines, calledZebra Lines. Quantitative measuring techniques are based on several methods, some of whic
4、h are:1) Measuring local curvature using mechanical radius gages (1, 6,9)2) Moire Fringe analysis (3, 4)3) Double exposure of transmitted grid images (Practice F 733)4) Projection of an array of round dots (5)5) Dual laser beams (10)The user should be familiar with techniques that are available so a
5、s to select the most suitable afterconsidering the precision, speed, and test specification requirements. The test method described in thisdocument uses a digital camera to capture a transmitted or reflected image of a set of equidistant lines.Changes in the spacing of lines are used to quantifying
6、the distortion.1. Scope1.1 This test method covers the determination of opticaldistortion of heat-strengthened and fully tempered architecturalglass substrates which have been processed in a heat controlledcontinuous or oscillating conveyance oven. See SpecificationsC 1036 and C 1048 for discussion
7、of the characteristics of glassso processed. In this test method the reflected image ofprocessed glass is photographed and the photographic imageanalyzed to quantify the distortion due to surface waviness.The test method is also useful to quantify optical distortionobserved in transmitted light in l
8、aminated glass assemblies.1.2 The values stated in either SI units or inch-pound unitsare regarded separately as standard. The values stated in eachsystem may not be exact equivalents; therefore, each systemshall be used independently of the other. Combining valuesfrom the two systems may result in
9、nonconformance with thestandard.1.3 There is no known ISO equivalent to this standard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices a
10、nd determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C 162 Terminology of Glass and Glass ProductsC 1036 Specification for Flat GlassC 1048 Specification for Heat-Treated Flat GlassKindHS, Kind FT Coated and Uncoated GlassF 733 Practice fo
11、r Optical Distortion and Deviation ofTransparent Parts Using the Double-Exposure Method3. Terminology3.1 See Terminology C 162 Terminology of Glass and GlassProducts3.23.2.1 focal length, FThe focal length of a specular reflec-tor, due to the curvature at a point equals R/2. (See 3.2.3.) Intransmitt
12、ed light, local thickness changes introduce a conver-gence or divergence, equivalent to a lens with a focal length F.3.2.2 optical power, DThe optical power due to thecurvature at a point is D = 1/F. The optical power is expressed1This test method is under the jurisdiction of ASTM Committee C14 on G
13、lassand Glass Products and is the direct responsibility of Subcommittee C14.11 onOptical Properties.Current edition approved Oct. 1, 2006. Published November 2006.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For referenced ASTM standards, visit the A
14、STM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Uni
15、ted States.in diopters, (Units 1/m), or as is typical, in millidiopters. Theoptical power is also used to quantify optical distortion, thedeformation of images reflected from flat glass, or transmittedby laminated or bent glass, or both.3.2.3 radius of curvature, RThe local radius of curvatureat a p
16、oint on the surface, in meters. Rxand Ryare respectivelymeasured in planes x (usually horizontal) and y (usuallyvertical)3.2.4 roll waveA repetitive, wave-like departure fromflatness in otherwise flat glass that results from heat-treatingthe glass in a horizontal conveyance system. Roll waveexcludes
17、 edge effects such as edge kink, and distortion inducedby assembly or installation.4. Summary of Test Method4.1 This test procedure was designed to provide an accuratemethod of quantifying the optical distortion of glass as it isrevealed in reflected or transmitted images. The optical distor-tion in
18、 reflected light can be related to a surface waviness,known as roll wave in tempered glass products, or, in trans-mitted light, related to curvature and local thickness variationsin laminated glass products. The test method is based on theuse of a digital camera which is used to record the appearanc
19、eof an accurately printed grid pattern which has been reflectedfrom or transmitted though apiece glass. Mathematical analy-ses performed on computer of the changes in the grid patternalong with the laws of optics and the geometrical arrangementmakes it possible to quantify the lens power or opticald
20、istortion of each element of the glass surface defined by thegrid.4.2 A uniformly spaced set of parallel lines, usually set at45 angle to horizontal, may be used instead of a grid. If sucha set of lines is used, the mathematics of calculation will beslightly altered from those expressed in Appendix
21、X1.5. Significance and Use5.1 This test provides accurate data for evaluation of theoptical properties of the glass being inspected.5.2 The procedure described is useful for measuring the rollwave introduced during the tempering process of flat architec-tural glass. (1)5.3 This test method is also u
22、seful for inspection oflaminated and tempered automotive glass in transmitted light,in both flat and curved geometries.6. Apparatus6.1 The items shown in Fig. 1 are required to practice thistest method:6.2 An accurately printed flat screen containing a pattern ofequidistant black lines on a white ba
23、ckground.NOTE 1The ruled area of the screen should have at least twice thedimensions of the area on the glass to be examined.6.2.1 The line spacing or pitch p (center to center orcorresponding edge to corresponding edge distance betweenadjacent lines) defines the spatial resolution of the system.A50
24、mm 2 in pitch in both horizontal and vertical directionsprovides satisfactory resolution for the examination of tem-pered glass in reflection mode. A smaller pitch can be usedwhen examination of smaller deformations in laminated glassis carried out using this test method. The width of the black line
25、is typically 6 mm 14 in. The line-to-line distance must beuniform, in both horizontal and vertical directions. The unifor-mity of the line-to-line spacing, p, is critical, because theFIG. 1 Test Configurations of Reflective AnalysisC 1652/C 1652M 062system interprets a non-uniform spacing as optical
26、 distortion.Auniformity of the pitch of 0.2 mm 0.008 in is satisfactory inreflective measurements.6.3 A digital camera equipped with an a planar lens and animage pixel resolution compatible with the software require-ments. These requirements are met by most commerciallyavailable digital cameras.6.4
27、A computer using an operating system compatible withthe software and any peripherals needed to satisfy the datalogging and reporting requirements.6.5 A software program capable of performing the evalua-tion of changes in line-spacing, p, and computation of theoptical distortion, D, throughout the in
28、spected region.6.6 Lighting sufficient to provide photographic contrast.6.6.1 A uniform illumination of the screen must be ensured.In average lighting conditions, four Quartz-Halogen flood-lamps, 500 watt each, are satisfactory.6.6.2 In a brightly illuminated area, two times higherillumination power
29、 is needed to assure good photographiccontrast.7. Sampling7.1 The number of specimens and frequency of testing is tobe determined by the user.8. Calibration and Standardization8.1 System calibration is a two-step procedure.8.2 Verification of System Zero8.2.1 Set the camera at a distance 2L from the
30、 screen.Capture the image of the screen without a glass panel in placeand process the image through the analysis software. Theimage analysis should indicate small values of D throughoutthe inspection area, typically less than 5 mdpt.8.3 Verification of Calibration (Span Calibration)8.3.1 This system
31、 calibration is determined by the screenuniformity and distance, L, to the camera as shown in Fig. 1,Fig. 2, and Fig. 3.8.3.2 Place a panel with known distortion in the testposition. Record the screen image and process it through thesoftware. The calculated distortion should not differ from theknown
32、 value by more than 5 mdpt.8.3.3 The known value of distortion should be establishedusing traceable, curvature measuring methods. Dual laser beamand interferometry are suitable for this purpose.9. Procedure9.1 Set up the grid screen:9.1.1 Ruled screen board should be vertical, in an uprightposition.
33、9.1.2 When used in reflective mode, the board should havea hole, sufficient for viewing through with a digital camera, cutin its center.9.1.3 When the screen is wall-mounted, so that viewingthrough a hole in its center is not possible, the camera can bemounted next to the screen or above it. In this
34、 configuration(see Fig. 2), a V-shaped line drawn from the center of the glassto the center of the screen (L1), and from the center of the glassto the center of the camera lens (L2) represents a geometric,specular reflection. The screen must be perpendicular to thebisector of line L1and L2and the ca
35、mera back must beperpendicular to line L2.9.1.4 The grid board typically should be somewhat largerthan twice the dimensions of the glass to be measured. Forexample, to analyze a 600mm by 1200 mm 24 in by 48 inglass, use a 1500 mm by 2500 mm 60 in by 100in grid board.9.2 Set up the glass sample:9.2.1
36、 Place the glass parallel to the grid board as shown inFig. 1, at a measured distance L. The distance should be theFIG. 2 Test Configuration for Off-Set CameraC 1652/C 1652M 063largest available, since the sensitivity of the measurement isdirectly proportional to the spacing, L. Four meters 160 inyi
37、elds satisfactory results.9.2.2 For simplicity of computations, the overall distancebetween the screen and the camera should be L, so that, L1=L2= L. Nevertheless, the distances are not required to be equal.9.2.3 Visually inspect the reflected image to assure that theroll wave is oriented horizontal
38、ly or vertically. Fig. 3 illustratesthe transmitted light set-up.9.3 Set up camera:9.3.1 Mount a digital camera on a suitable tripod, as shownin Fig. 2, and Fig. 3.9.3.2 Set the camera to a resolution compatible with thesoftware. Make sure that the image of the screen is in verysharp focus. In the i
39、mage, the edges of the rectangular screenshould be parallel to the edges of the camera frame.9.4 Illuminate grid screen:9.4.1 The illumination should be sufficient that goodcontrast is seen in the image. Use four 500-watt quartz floodlamps as specified in 6.6.1, placing them at an angle to thescreen
40、 as illustrated in Fig. 1. Verify that the lights are notlocated in the field of view of the camera.9.5 Check out the set up:9.5.1 Place the glass to be analyzed in the field of view ofthe camera looking through the hole in the center of the gridboard.9.5.2 Make sure that all of the glass shows a re
41、flection of thegrid and that the grid and glass are on the same centerline andare parallel.9.5.3 Visually inspect the reflected image to assure that theroll wave is oriented horizontally or vertically.9.5.4 Assure a sharp focus.9.5.5 Add an identification number for the glass by printingwith a felt
42、marker on an erasable board just above or below thesample, or by placing a printed label on the screen.9.6 Take a photograph:9.6.1 Take a digital photograph of the grid board patternreflected from the glass or transmitted through it.9.6.2 Transfer the camera images to a computer file, or tothe softw
43、are program.10. Calculations and Analyses10.1 Follow the software manufacturers manual to performthe image analysis. The software should provide the full-fieldinformation on the optical distortion of the inspected item intabular and graphical formats.10.2 Save the results to satisfy the reporting re
44、quirementslisted in Section 11.10.3 When the test objective includes measuring of the rollwave distortion, the analysis must be performed along linesperpendicular to the roll wave direction.10.4 Additional information may be presented in manyways including the maximum distortion within the limits of
45、inspected area, both for the positive and the negative lenspower.10.5 A Graphical, 3D presentation and a table of values foreach grid element on the sample is available in image analysissoftware.10.6 Data, photos, and a quality summary comparing theresults to specified performances is saved in a dat
46、abase in thecomputer for future reference.10.7 The glass surface may be analyzed for (either or both):10.7.1 Cylindrical lens power (uniaxial analysis), typicallyused when measuring the roller wave distortion of flat glass10.7.2 Visual perception (biaxial analysis), typically usedwhen measuring the
47、optical distortion of laminated and curveditems in transmitted light.11. Report11.1 From the measured changes in line spacing, the soft-ware calculates the uniaxial or biaxial optical power, or both,D, a teach point, using equations shown in Appendix X1.11.2 For the roll wave analysis, the maximum o
48、ptical powerD and the location of maximum distortion within the inspectionarea must be calculated and reported. The report must include:11.2.1 Date of the test,11.2.2 Description of the item (Part ID, Serial #, Lot # ),11.2.3 Inspected area,11.2.4 Screen pitch, p,11.2.5 Distance, L, used in the test
49、,11.2.6 Type of analysis, uniaxial or biaxial,11.2.7 Mean optical power,11.2.8 Standard deviation of the optical power within asample,11.2.9 The software used, and,11.2.10 Graphs or photographs or both, of deformed set oflines.FIG. 3 Test Configuration in Transmitted LightC 1652/C 1652M 06411.3 When inspecting laminated or bent glass, or both, intransmission, additional information may be required by thespecification for the part under inspection.12. Precision and Bias12.1 The C14.11 Subcommittee will conduct an inter-laboratory Round Robin Test to determine t
