1、Designation: C1652/C1652M 06C1652/C1652M 14Standard Test Method forMeasuring Optical Distortion in Flat Glass Products UsingDigital Photography of Grids1This standard is issued under the fixed designation C1652/C1652M; the number immediately following the designation indicates theyear of original ad
2、option or, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONTransmitted and reflected distortion in annealed, heat strengthened, a
3、nd tempered glass can bemeasured by several methods.(1, 2, 3, 4,)2 Qualitative 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
4、, some of which are:(1 1) ) Measuring local curvature using mechanical radius gages (1, 5, 6, and Test Method C1651)2)(2 Moire) Moir Fringe analysis (7, 8)3)(3) Double exposure of transmitted grid images (Practice F733)(4 4) ) Projection of an array of round dots (9)(5 5) ) Dual laser beams (10)The
5、user should be familiar with techniques that are available so as 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
6、 lines.Changes in the spacing of lines are used to quantifying the distortion.1. Scope1.1 This test method covers the determination of optical distortion of heat-strengthened and fully tempered architectural glasssubstrates which have been processed in a heat controlled continuous or oscillating con
7、veyance oven. See Specifications C1036and C1048 for discussion of the characteristics of glass so processed. In this test method the reflected image of processed glassis photographed and the photographic image analyzed to quantify the distortion due to surface waviness. The test method is alsouseful
8、 to quantify optical distortion observed in transmitted light in laminated glass assemblies.1.2 The values stated in either SI units or inch-pound units are regarded separately as standard. The values stated in each systemmay not be exact equivalents; therefore, each system shall be used independent
9、ly of the other. Combining values from the twosystems may result in nonconformance with the standard.1.3 There is no known ISO equivalent to this standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of
10、 this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C162 Terminology of Glass and Glass ProductsC1036 Specification for Flat GlassC1048 Specification for Heat-Strengthened
11、 and Fully Tempered Flat Glass1 This test method is under the jurisdiction of ASTM Committee C14 on Glass and Glass Products and is the direct responsibility of Subcommittee C14.11 on OpticalProperties.Current edition approved Oct. 1, 2006May 1, 2014. Published November 2006May 2014. Originally appr
12、oved in 2006. Last previous edition approved in 2006 asC1652/C1652M 06. DOI: 10.1520/C1652_C1652M-06.10.1520/C1652_C1652M-14.2 The boldface numbers in parentheses refer to a list of references at the end of this standard.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contact
13、ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been m
14、ade to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Co
15、pyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1C1651 Test Method for Measurement of Roll Wave Optical Distortion in Heat-Treated Flat GlassF733 Practice for Optical Distortion and Deviation of Transparent Parts Using the Double-Exposur
16、e Method2.2 Other Standards:U.S. Patent 7 345 698 Optical System for Imaging Distortions in Moving Reflective Sheets (2003)3. Terminology3.1 See Terminology C162 Terminology of Glass and Glass ProductsProducts.3.2 Definitions:3.2.1 focal length, FThe focal length of a specular reflector, due to the
17、curvature at a point equals R/2. (See 3.2.3.) Intransmitted light, local thickness changes introduce a convergence or divergence, equivalent to a lens with a focal length F.3.2.2 optical power, DThe optical power due to the curvature at a point is D = 1/F. The optical power is expressed in diopters,
18、(Units 1/m), or as is typical, in millidiopters. The optical power is also used to quantify optical distortion, the deformation ofimages reflected from flat glass, or transmitted by laminated or bent glass, or both.3.2.3 radius of curvature, RThe local radius of curvature at a point on the surface,
19、in meters. Rx and Ry are respectivelymeasured in planes x (usually horizontal) and y (usually vertical)vertical).3.2.4 roll waveA repetitive, wave-like departure from flatness in otherwise flat glass that results from heat-treating the glassin a horizontal conveyance system. Roll wave excludes edge
20、effects such as edge kink, and distortion induced by assembly orinstallation.4. Summary of Test Method4.1 This test procedure was designed to provide an accurate method of quantifying the optical distortion of glass as it is revealedin reflected or transmitted images. The optical distortion in refle
21、cted light can be related to a surface waviness, known as roll wavein tempered glass products, or, in transmitted light, related to curvature and local thickness variations in laminated glass products.The test method is based on the use of a digital camera which is used to record the appearance of a
22、n accurately printed grid patternwhich has been reflected from or transmitted though apiece a lite of glass. Mathematical analyses performed on computer of thechanges in the grid pattern along with the laws of optics and the geometrical arrangement makes it possible to quantify the lenspower or opti
23、cal distortion of each element of the glass surface defined by the grid.4.2 A uniformly spaced set of parallel lines, usually set at 45 angle to horizontal, may be used instead of a grid. If such a setof lines is used, the mathematics of calculation will be slightly altered from those expressed in A
24、ppendix X1.5. Significance and Use5.1 This test method provides accurate data for evaluation of the optical properties of the glass being inspected.5.2 The procedure described is useful for measuring the roll wave introduced during the tempering process of flat architecturalglass. (1)5.3 This test m
25、ethod is also useful for inspection of laminated and tempered automotive glass in transmitted light, in both flatand curved geometries.6. Apparatus6.1 The items shown in Fig. 1 are required to practice this test method:6.2 An accurately printed flat screen containing a pattern of equidistant black l
26、ines on a white background.NOTE 1The ruled area of the screen should have at least twice the dimensions of the area on the glass to be examined.6.2.1 The line spacing or pitch p (center to center or corresponding edge to corresponding edge distance between adjacent lines)defines the spatial resoluti
27、on of the system. A 50 mm 50 mm 2 in pitch in both horizontal and vertical directions providessatisfactory resolution for the examination of tempered glass in reflection mode. A smaller pitch can be used when examinationof smaller deformations in laminated glass is carried out using this test method
28、. The width of the black line is typically 6 mm 14in. The line-to-line distance must be uniform, in both horizontal and vertical directions. The uniformity of the line-to-line spacing,p, is critical, because the system interprets a non-uniform spacing as optical distortion.Auniformity of the pitch o
29、f 0.2 mm 0.008in is satisfactory in reflective measurements.6.3 A digital camera equipped with an a planar lens and an image pixel resolution compatible with the software requirements.These requirements are met by most commercially available digital cameras.6.4 A computer using an operating system c
30、ompatible with the software and any peripherals needed to satisfy the data loggingand reporting requirements.6.5 A software program capable of performing the evaluation of changes in line-spacing, p, and computation of the opticaldistortion, D, throughout the inspected region.C1652/C1652M 1426.6 Lig
31、hting sufficient to provide photographic contrast.6.6.1 A uniform illumination of the The screen must be ensured. In average lighting conditions, four Quartz-Halogenflood-lamps, 500 watt each, are satisfactory. illuminated with uniform diffused background lighting with a minimum illuminanceof 850 lu
32、x (80 candles), measured at the surface of the screen. Four Quartz-Halogen flood lamps, 500 watts each, can providesatisfactory results.6.6.2 In a brightly illuminated area, two times higher illumination power is needed to assure good photographic contrast.7. Sampling7.1 The number of specimens and
33、frequency of testing is to be 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 2Lfrom the screen. Capture the image of the screen without a glass panel in place and processthe ima
34、ge through the analysis software. The image analysis should indicate small values of D throughout the inspection area,typically less than 5 mdpt.8.3 Verification of Calibration (Span Calibration)8.3.1 This system calibration is determined by the screen uniformity and distance, L, to the camera as sh
35、own in Fig. 1, Fig. 2,and Fig. 3.8.3.2 Place a panel with known distortion in the test position. Record the screen image and process it through the software. Thecalculated distortion should not differ from the known value by more than 5 mdpt.8.3.3 The known value of distortion should be established
36、using traceable, curvature measuring methods. Dual laser beam andinterferometry are suitable for this purpose.9. Procedure9.1 Set up the grid screen:9.1.1 Ruled screen board should be vertical, in an upright position.9.1.2 When used in reflective mode, the board should have a hole, sufficient for vi
37、ewing through with a digital camera, cut inits center.FIG. 1 Test Configurations of Reflective AnalysisC1652/C1652M 1439.1.3 When the screen is wall-mounted, so that viewing through a hole in its center is not possible, the camera can be mountednext to the screen or above it. In this configuration (
38、see Fig. 2), a V-shaped line drawn from the center of the glass to the centerof the screen (L1), and from the center of the glass to the center of the camera lens (L2) represents a geometric, specular reflection.The screen must be perpendicular to the bisector of line L1 and L2 and the camera back m
39、ust be perpendicular to line L2.9.1.4 The grid board typically should be somewhat larger than twice the dimensions of the glass to be measured. For example,to analyze a 600mm by 1200 mm 24 in by 48 in glass, use a 1500 mm by 2500 mm 60 in by 100in grid board.9.2 Set up the glass sample:9.2.1 Place t
40、he glass parallel to the grid board as shown in Fig. 1, at a measured distance L. The distance should be the largestavailable, since the sensitivity of the measurement is directly proportional to the spacing, L. Four meters 160 in yields satisfactoryresults.9.2.2 For simplicity of computations, the
41、overall distance between 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 the roll wave is oriented horizontally or vertically. Fig. 3 illustrates thetransmitted light set-up
42、.9.3 Set up camera:9.3.1 Mount a digital camera on a suitable tripod, as shown in Fig. 2, and Fig. 3.9.3.2 Set the camera to a resolution compatible with the software. Make sure that the image of the screen is in very sharp focus.In the image, the edges of the rectangular screen should be parallel t
43、o the edges of the camera frame.9.4 Illuminate grid screen:FIG. 2 Test Configuration for Off-Set CameraFIG. 3 Test Configuration in Transmitted LightC1652/C1652M 1449.4.1 The illumination should be sufficient that good contrast is seen in the image. Use four 500-watt quartz flood lamps asspecified i
44、n 6.6.1, placing them at an angle to the screen as illustrated in Fig. 1. Verify that the lights are not located in the fieldof 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 of the camera looking through the hole in the center of the grid board
45、.9.5.2 Make sure that all of the glass shows a reflection of the grid and that the grid and glass are on the same centerline andare parallel.9.5.3 Visually inspect the reflected image to assure that the roll wave is oriented horizontally or vertically.9.5.4 Assure a sharp focus.9.5.5 Add an identifi
46、cation number for the glass by printing with a felt 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 pattern reflected from the glass or transmitted through it.9.6.2 Transfer
47、 the camera images to a computer file, or to the software program.10. Calculations and Analyses10.1 Follow the software manufacturers manual to perform the image analysis. The software should provide the full-fieldinformation on the optical distortion of the inspected item in tabular and graphical f
48、ormats.10.2 Save the results to satisfy the reporting requirements listed in Section 11.10.3 When the test objective includes measuring of the roll wave distortion, the analysis must be performed along linesperpendicular to the roll wave direction.10.4 Additional information may be presented in many
49、 ways including the maximum distortion within the limits of inspectedarea, both for the positive and the negative lens power.10.5 A Graphical, 3D presentation and a table of values for each grid element on the sample is available in image analysissoftware.10.6 Data, photos, and a quality summary comparing the results to specified performances is saved in a database in the computerfor future reference.10.7 The glass surface may be analyzed for (either or both):software available for analysis of the glass surface distortion by thismethod provides two analy
