BRPI0203609B1 - Apparatus for the execution of an electronic electroanalysis and method for analyzing a test object - Google Patents

Description

APPLIANCES FOR THE IMPLEMENTATION OF AN ELECTRONIC SHOCKING AND METHOD FOR ANALYZING A TEST OBJECT

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation in part of co-pending US Patent Application No. 09 / 835,598 filed April 16, 2001, which is a continuation of US Patent Application No. 09 / 334,311 filed on June 16, 1999, issued as US Patent No. 6,219,143.

FIELD OF INVENTION

The present invention relates generally to the field of non-destructive testing. Specifically, the present invention relates to the electronic shear technique.

BACKGROUND OF THE INVENTION

[003] The shear interferometry technique, or shear technique, involves the interference of two laterally displaced images of the same object to form an interference image. Conventional shear methods require that a first interference image (or a baseline image) be taken while the object is in an untensioned or first stressed condition, and that another interference image be taken while object is in a second tensioned condition. Comparison of these two interference images (preferably by image subtraction methods) reveals information about the stress concentrations and thus the integrity of the object in a single image, called a shear. In particular, shear has been found to be useful for detecting stress concentrations and thus defects in vehicle tires, especially retreaded vehicle tires.

In conventional electronic shear, interference images are stored in a computer memory and are compared electronically for the production of single static shear. Because all data is processed electronically, the analysis results can be viewed in "real time". "Real time" as used in the prior art refers to the almost instantaneous visualization of the shalhogram after the second interference image has been taken.

An apparatus and method for performing an electronic shear are described in U.S. Patent No. 4,887,899 issued to Hung. The apparatus described in the cited patent produces a light-reflecting interference image reflected from the test object through a birefringent material and a polarizer. The birefringent material, which may be a calcite crystal, divides the reflected ray of light from the object into two rays, and the polarizer makes it possible for reflected light rays from one pair of points to interfere with one another. Thus each point in the object generates two rays, and the result is an interference image formed by the optical interference of two laterally displaced images of the same object.

Prior to the development shown in the Hung patent, the spatial frequency of the interference image produced in the shear analysis was relatively high, requiring the use of a high resolution photographic film for recording a useful interference image. The development shown in the Hung patent produces an interference image with a relatively low spatial frequency because the effective angles between the interfering rays are small. Therefore, interference images can be recorded by a camcorder, a camcorder typically having much less resolution capability than a high density or high resolution photographic film. By storing an interference image of the object in its initial untensioned condition, and comparing that interference image virtually instantaneously by computer to another interference image taken at a different voltage level, an image at "real time" or a shearogram of the resulting deformations in the object can be observed. Each point on the actual interference image is generated by light interference emanating from a couple of distinct points on the object. Therefore, each pixel of the camcorder is illuminated by a light reflected from those two points. If the total illumination remains constant, then any variations in pixel intensity in the interference image are due solely to changes in the phase relationship of the two light points.

When the initial video image of the interference image is stored, an initial intensity for each pixel is recorded as described above. If differential deformations occur on the object, these deformations will cause changes in the subsequent interference image. In particular, the intensity of a given pixel will change according to a change in the phase relationship between the two rays of light, reflected from the two points on the object, which illuminate the pixel. Phase differences can be positive changes, making the pixel brighter, or negative changes, making the pixel darker. The pixel becoming brighter or darker depends on the initial phase ratio and the direction of the phase shift. Due to the cyclic nature of phase interference, as the deformation of the object continuously increases, the intensity in a given pixel may go through a complete cycle. That is, the pixel intensity could increase to a maximum (positive) difference, then return to the original intensity, and then continue to a maximum (negative) difference, and so on.

[008] In prior art systems, a single shear is derived from two single static interference images taken at two distinct voltage levels. The single shalhogram is then viewed by an operator for analysis; If multiple shalhograms are taken, the analysis is done one shalhogram at a time. Thus, the operator service time required to perform a complete stress analysis is substantial. In addition, a single ciscalogram may falsely show light aspects that appear to be defects (referred to as "false positives"). These "false positives" are caused by different reflective characteristics on the surface of the test object, and appear as defects when a static cishalogram is viewed. Moreover, on a static cishalogram some actual defects may be "washed out" and thus not visible (referred to as "negative negatives") at certain stress levels (particularly at highs). These "washed out" effects are caused by fringe lines that are not spatially separated enough to be visibly distinguishable and thus appear to be freak light effects rather than actual defects in the test object. Thus, a single static shalogram may contain inaccurate information regarding the defects actually present. Moreover, an operator having to analyze a large number of shear lines requires a large amount of operator assistance time.

SUMMARY OF THE INVENTION

The present invention relates to an apparatus for performing an electronic shear on a test object, such as a tire. The shear test apparatus of the present invention may include a tire handling system which loads a tire and automatically centers it relative to the shear chamber. The tire handling system also utilizes a pivoting loading movement that facilitates tire loading and minimizes the required tread space.

The shear test apparatus of the present invention may also include a vacuum chamber, which has an air handling system, which may reduce the relative humidity within the vacuum chamber during a test cycle. This may prevent the formation of a fog condition, which could substantially reduce the quality of interference images taken by the shear camera.

Another aspect of the present invention may comprise a system and method for archiving animated images created during shear tests so that they may be reviewed at a later time. Animated image data is compressed prior to storage in the file medium in such a way as to allow more efficient storage of test results without significant degradation of image quality. Thus, data can be archived more cost-effectively without sacrificing any loss of accuracy in test results.

These and other advantages of the invention, as well as additional inventive aspects, will be apparent from the description of the invention provided herein.

BRIEF DESCRIPTION OF DRAWINGS

[013] The invention will hereinafter be described with reference to the accompanying drawings, where like reference numerals denote like elements in the various drawings, and: [014] Figure 1 is a schematic block diagram of a system of shear image formation.

[015] Figure 2 is a schematic diagram of a shear imaging system showing a cross section of a tire as the test object.

[016] Figure 3 is a schematic diagram of a shear camera in two different orientations relative to the tire; and [017] Figure 4 is a graphical representation of the deformation of a test object, showing the corresponding shear fringe pattern produced.

[018] Figure 5 is a schematic diagram of an example display for displaying a plurality of shear animations.

Figure 6 is a schematic diagram of a shear imaging system adapted for archiving test data in accordance with one aspect of the invention.

[020] Figure 7 is a flow chart of an example archiving process according to an aspect of the invention.

[021] Figure 8 is a perspective view of an exemplary shear test apparatus in accordance with another aspect of the present invention with the vacuum chamber in an open position and the tire handling system in the open position. loading.

Figure 9 is a front elevational view of the shear test apparatus of Figure 8 with the vacuum chamber in an open position and the tire handling system in the loading position.

Figure 10 is a side elevational view of the shear test apparatus of Figure 8, with the vacuum chamber in an open position and the tire handling system in the loading position.

[11] Figure 11 is a perspective view of the shear test apparatus of Figure 8, with the vacuum chamber in an open position and the tire handling system in the inspection position.

[12] Figure 12 is a front elevational view of the shear test apparatus of Figure 8, with the vacuum chamber in an open position and the tire handling system in the inspection position.

[026] Figure 13 is a side elevational view of the shear test apparatus of Figure 8, with the vacuum chamber in an open position and the tire handling system in the inspection position.

Figure 14 is a top plan view of an exemplary assembly of a tire handling system for the shear test apparatus of Figure 8 in the inspection position.

[15] Figure 15 is a front elevational view of the tire handling system of figure 14 in the inspection position.

Fig. 16 is a cross-sectional view of the tire handling system of Fig. 14 taken along line 16-16 in Fig. 15.

Figure 17 is a cross-sectional view of the tire handling system of Figure 14 taken along line 17-17 in Figure 15.

[18] Figure 18 is a side elevational view of the tire handling system of Figure 14 taken on the plane of line 18-18 in Figure 15.

Figure 19 is a cross-sectional view of the tire handling system of Figure 14 taken along line 19-19 in Figure 18.

Figure 20 is a schematic diagram of an exemplary air handling system for the shear testing apparatus of Figure 8.

DETAILED DESCRIPTION OF EXAMPLE ASSEMBLIES

[034] The present invention utilizes the basic concepts of electronic shear. Further details of electronic shalography are given in U.S. Patent No. 4,887,899, the disclosure of which is incorporated herein by reference.

Referring now to Figure 1, a schematic block diagram of an arrangement for the practice of electronic shearing is described. Coherent electromagnetic radiation or coherent light is produced by a laser 10, the laser light being directed through a fiber optic cable 15 (or, alternatively, directed by a mirror or mirror array, or provided directly) to a beam expander or illuminator 20. The beam expander 20 directs coherent light onto a test object 25. The surface of the test object 25 is illuminated and reflects light to a shear camera 30. The shear camera 30 includes an optical element 35, a light focusing lens 40, and a detector 45. The optical element 35 may be a birefringent material and a polarizer, the birefringent material being a calcite material, such as a Wallestein prism. The optical element, however, is not limited to a birefringent material and a polarizer, other elements such as a defrosting grid, a Mickelson mirror, or an appropriate wave board may be applied. Further, the optical element 35 may contain other optical items, such as, but not limited to a quarter-wave plate. The detector 45 may be a traditional video camera, a digital video camera, a charge coupled device (CCD), or other photosensitive detection equipment.

The output of detector 45 is coupled to an animation device such as a computer 50. Computer 50 includes a video capture circuit 55, a central processing unit 60 and a memory 65. Alternatively, computer 50 may include a logical extractor that is configured to extract shear images from memory in a predetermined manner. The logic puller may be realized in hardware or alternatively in software on computer 50. Video capture circuit 55 may be a dedicated video card or frame grabber preferably capable of capturing entire video images at a rate at least 15 frames per second. However, a video capture circuit 55 may be able to capture video images at any suitable rate. The central processing unit 60 may be any of several conventional microprocessors, or a dedicated microprocessor device. Detector 45 is coupled to central processing unit 60, central processing unit 60 being coupled to video capture circuit 55 and memory device 65. Central processing unit 60 is still coupled to a display unit 70, which may be a CRT (cathode ray tube) display, an LCD (liquid crystal display), or the like.

[037] In operation, the coherent light emanating from the beam expander 20 is reflected from the test object 25. Optical element 35 collects the reflected light from object 25, causing an interference image to be created. The interference image is focused on a detector 45 through lens 40. Conventionally, a first interference image is taken while the test object 25 is in a first stressed condition, and a second interference image is taken with the object. 25 in a second stressed condition. The two interference images, then, are compared by a process of differentiating one image from another, and the shalogram is created and displayed on a monitor.

In the present invention, the test object 25 undergoes a sequence of or a continuum of varying voltage levels. Detector 45 continuously captures the interference image from optical element 35, and communicates the interference image to computer 50 during the voltage cycle. Capture circuit 55 electronically captures all interference images at a rate of at least 15 frames per second. Capture circuit 55 communicates the interference images to the central processing unit 60. The central processing unit 60 compares the interference image with a baseline interference image of the object in the untensioned or nearly untensioned state (or , alternatively, at any chosen stress state), by a process of differentiating an interference image from the baseline interference image, thereby forming a cishalogram. Each shalogram image is simultaneously displayed on display unit 70 and stored on memory device 65. After the series of variable voltage levels has been completed, microprocessor 60 (or, alternatively, a logic puller) recalls the sequence. shear images captured by capture circuit 55 and redisplay them sequentially on display unit 70. The sequential display of these shear images at a rate of at least 15 frames per second produces a shear animation of the shear produced during or after tensioning of the test object 25.

Test object 25 may be a relatively large object, such as a tire 200, as described in Figure 2. A shear camera 230, which is rotatable within the bead 202 of tire 200, is described in Figure 2. (Alternatively, tire 200 can be rotated and camera 230 can be stationary.) Shear camera 230 includes a laser 235, which produces a coherent beam of light, to illuminate the interior of tire 200. Shear camera 235 is attached, in addition to a computer 240 having a display 245, computer 240 and display 245 being used for data acquisition and animation of the resulting shear images.

[040] When used for tire or retread defect detection, the shear imaging camera 230 may be positioned inside the tire, described as position A in Figure 3, or outside the tire described in Figure 3 by position B. Having the shear camera 230 in position A allows detection of defects in the tire tread area 200. Having the shear camera 230 in position B provides examination of the bead area and tire sidewall area 200.

Referring back to Figure 2 in operation, the shear camera 230 and the tire 200 may be placed in a vacuum chamber capable of subjecting the tire 200 to a vacuum, producing tensions in the tire 200, by producing a positive pressure (relative to the pressure inside the vacuum chamber) in voids in the tire 200, causing a bulging 250. Referring to Figure 4, the bulging may be caused by a defect 260, the defect 260 possibly being but not limited to a delamination between two tire layers or a void in the molded material. When subjected to a vacuum, the bulge 250 appears because of the positive pressure in the gap blank 260. The graph of Fig. 4 depicts the inclination of the bulge 250 by line 270. The graph of Fig. 4 further depicts a fringe pattern. including ring groups 280 and 290, produced by differentiating two optical interference images produced by the shear camera 230. The fringe patterns 280 and 290 of a shear image, which is produced by the computer 240 (by the differentiation method or by any other (another image resolution technique) appear as a set of approximately concentric and substantially circular fringe lines corresponding to bulge 250 slope 270. Fringe patterns 280 and 290 are a contour mapping of the absolute value of bulge 250 slope 270 Therefore, because the bulging 250 is substantially symmetrical, the fringe patterns 280 and 290 appear to be mirror images of each other.

[042] Referring back to Figure 2, in operation, the shear camera 230 takes a series of interference images, which are communicated to the computer 240, while the tire 200 undergoes a vacuum or variable voltage cycle. In a preferred embodiment, tire 200 undergoes a depressurization cycle and then a pressurization cycle to return the tire to an untensioned state. Because the field of view of the 230 shear camera is limited by the field of view of the optics and the size of the tire, a tire must be sectioned in various sectors, ranging from four to twelve or more. In an example assembly, tire 200 is sectioned into nine different sectors. The shear camera 230, therefore, sees an area corresponding to 40 ° of arc 200 of the tire 200. After the depressurization and pressurization cycle, the camera 230 is rotated to the next sector, where the depressurization and pressurization cycle is repeated. The computer 240 continues to collect data and can, in a preferred assembly, simultaneously display data on the display 245, for the entire nine sector cycle. The shalograms are generated and displayed at such a rate that they appear to be animated.

Referring now to Figure 5, a display 300 is described, the display being divided into nine different sectors, each sector 310 corresponding to an approximate 40 ° arc of the interior of a tire. Alternatively, however, each sector 310 could correspond to any tire-specific field of view for a shear camera, such as the shear camera 230. Computer 240, as described in Figure 2, which can be connected to display 300, is capable of displaying a plurality of animations simultaneously, as described in Figure 5. Figure 5 depicts a static screen snapshot of a typical display, although display 300 actually shows animations or a sequential image formation of shear produced images. by computer 240 at a rate providing an animated effect and, in a preferred embodiment, at a rate of 30 frames per second. A display having multiple animation windows or screen sectors provides the clear advantage for an operator to be able to observe the animations simultaneously by looking at indications of deformation due to defects. This simultaneous observation allows less operator assistance time, thus providing substantial time savings without a substantial loss of accuracy. Animation capture and provision, preferably at 30 frames per second (or alternatively at any suitable animation rate) provides animations that are smooth enough to be useful to an operator.

[044] The advantages of image sequence animation is that animation improves the accuracy of defect detection. Light effects, which would appear as "false positives" on a static cishalogram, do not manifest as defects when animated due to the absence of apparent motion induced by animation. A fringe pattern caused by a real defect will tend to "grow" or "retract", and the intensity of the fringe lines will appear to alternate during animation due to the continuously shifting state of stress on the test object. Moreover, the actual defects, which can be "washed out" on a static shear or even an integration of multiple shear images, become apparent with the animation of the shear images.

[045] Shear animation enables visualization of defects in a multiplicity of stress states, some of the stress states may not cause the "wash" effect, and yet the apparent motion created by the animation of the images manifests a real defect as opposite to the light effect. The animation of the shear lines goes through a substantial continuity of stress states, so defects that may not be present in two chosen stress states become apparent in the animation. These advantages in animating shear images provide better defect detection accuracy and provide shorter analysis times by an operator.

[046] It has been recognized that various signal processing techniques, such as, but not limited to the use of multipurpose logic, neural networks, artificial intelligence, and pattern recognition techniques, may be applied to perform automatic identification of a defect. However, systems such as this tend to be inherently complex and substantially expensive. Therefore, maintaining a human operator, but decreasing the operator assistance time required by providing the operator with numerous simultaneous animations, has the effect of providing substantial cost savings.

[047] While animation of shear images may be preferable at a rate of at least 15 frames per second, it should be noted that frame rates of less than 15 frames per second can also be used effectively, although animation may appear discretized, compared to an animation running at least 15 frames per second. In addition, it should be appreciated that frame rates of more than 30 frames per second may be advantageous in specific applications and may become simpler to implement as microprocessor and video capture technology is improved.

It should be appreciated that while a differentiation approach to the production of each shear is described above, the methods and apparatus shown may be applied to different image resolution techniques, including but not limited to continuous integration. Continuous integration describes the process of taking a first interference image and differentiating a second interference image for the production of a first shalhogram. A third interference image is taken and subtracted from the first shalhogram for the production of a third shalhogram. A fourth interference image is then taken and subtracted from the second shear to produce a third shear. This sequence is continued throughout the test cycle. The continuous integration technique and other techniques known to those of ordinary skill in the art lend themselves to the animation techniques shown above and can be applied to them without departing from the spirit and scope of the present invention.

[049] The process and apparatus described above should be considered for the optimization of various competing factors associated with shear imaging, especially when applied to retread tire failure tests (although clearly not limited to this application). These competing factors include, but are not limited to, maximizing data, maximizing accuracy, minimizing operator service time, available light wavelengths, object size, equipment costs, and optical field of view. By animating shear lines in a plurality of sectors on a display screen, several of these competing factors are optimized.

[050] Collected shear image data may be archived to allow the same tire image data used by the operator for tire evaluation during the shear test to be revised at a later date. The ability to archive image data can provide a number of advantages, including allowing a decision regarding the presence of defects in a certain tire to be re-evaluated at a later date, such as when investigating a potential warranty issue. Additionally, archived tire data can be used to assess the condition of a particular tire over time when the tire is tested multiple times.

[051] The advantages associated with image sequence animation during the original tire evaluation also apply to the review of archived image data. Furthermore, in order to reasonably and accurately reassess a decision regarding a particular tire, for example in a warranty situation, the archived data must be substantially the same as the data that was revised during the original evaluation. . Thus, the animation of the images should preferably be part of the archived record.

[052] However, storing animated images can require a huge amount of memory space. For example, in one embodiment of the invention, the raw data collected for each tire may comprise about 250 MB of information in the form of animated images, which may substantially limit the number of test results that can be stored in a given medium. of storage. Thus, in the present invention, the archiving aspect may be adapted such that prior to storage, the data is compressed to allow more efficient storage of the test results. For example, in a sample assembly, during a test, all shear image data that is produced is stored in a shear computer memory, such as in computer RAM. As explained above, this data can be displayed as animations to allow analysis of the test object for possible defects by an operator. This data can also be transferred to an archive memory, for example a hard disk, a CD-ROM or a magnetic tape, where the data can be stored on a long-term basis. Prior to this long-term storage, the data is compressed so that substantially more test results can be stored on a given storage medium. Thus, the cost of storing data and the cost of recalling stored data is reduced. As explained below, the data is compressed so that the test results can be stored efficiently without significant degradation in image quality, thereby allowing the test results to be reviewed at a later time without any loss in accuracy. defect detection.

[053] In an exemplary embodiment, for implementing data archiving, an archiving computer 340 is provided which is in communication with the shear computer via a parallel or similar cable as shown, for example, Figure 6. In addition, software on the shear computer, such as, for example, boot software and hardware support software, is modified to support data transfer to the archive computer. Once all data has been collected by the shear computer, the archiving process can be started. A flowchart illustrating a set of exemplary steps to be performed in the archiving process is shown in Figure 7 and described below. As will be appreciated, these steps do not have to be performed in the sequence illustrated. Further, the individual steps may be performed by the shear computer 240, the file computer 340, or any other suitable processor. For example, image processing, compression and data retention could be performed by a single computer or processor. As noted above, the memory in which data is archived may be any suitable memory in which data may be stored, including, for example, the hard disk drive of the shear computer, the file computer, or another computer, a floppy disk loaded into an external floppy disk drive with the shear computer, the file computer, or another computer, a CD-ROM loaded into a CD-ROM drive associated with the shear computer, the file computer, or the another computer, or a magnetic tape loaded on a tape drive associated with the shear computer, the file computer, or another computer.

[054] To associate the tire (or other test object) that has been tested with its corresponding specific test result in the archive database, a unique identifier can be entered once all data has been collected by the shear computer 240. In the example assembly, this is accomplished by switching the display screen to an operator interface, which is rotated by the filing computer 340. Through the interface, the operator is prompted to enter a unique identifier for the tire, which was tested. To ensure that a unique identifier is entered by the operator, the interface program can be adapted so that the test results collected for a tire are not displayed until the identifier is entered. In other words, the operator interface will remain on the display until an appropriate identifier is entered for the tire. Once a tire identifier has been entered, the display can be switched back to the shear computer to display the animated shear images of the newly completed test cycle. The tire identifier may be entered through any suitable input device, including, for example, a keyboard or barcode reader.

[055] The operator interface program may also allow you to enter other tire information such as, for example, a customer ID or banknote. The input of other information may be made optional, so that the tire identifier input is the only operator measure required for data archiving implementation. The operator interface can also display other information regarding the archiving process, such as, for example, a list of archived files and a status of the amount of storage capacity used.

Prior to transferring the data to the archiving computer 340, it may be beneficial to select the raw image data to reduce the number of images that must be transferred to the archiving computer. In particular, we have found that when a significant number of shear images are collected during a test cycle, there is no appreciable loss in animation quality if only images selected from the animation sequence are displayed at a relatively higher rate. slow. For example, in an assembly of the invention, twenty-eight shear images are collected for each section of the tire. During an operator review, these images are displayed at a rate of about 60 frames per second. However, there is no appreciable difference in animation quality if only every third image in the twenty-eight image sequence is displayed at a rate of about 20 frames per second. Thus, storing only ten of the twenty-eight images for that particular section can produce an accurate record of the test.

Once the images to be transferred to the archiving computer are selected, an initial compression sequence can be performed in this case by the shear computer 240. In this initial compression sequence, the individual images of the animation sequence that must be transferred to the 340 file computer may be reduced in size. In one assembly, the image bitmaps stored on the shear computer are 512 pixels wide, 480 pixels high, and are eight bits per pixel. Each image bitmap to be transferred to the 340 file computer can be reduced in size from 9: 1 to 172 pixels wide and 160 pixels high using data from each third column and each third row of the map. bit To help ensure that the archived image looks as close as possible to the original image, a pixel weighting technique can be used to reduce image size. With pixel weighting technique, a single pixel is created, which is the average of the original pixel and the eight pixels that surround the original pixel in the original image. For pixels on the edge of the bitmap, the average of the original pixel and the surrounding five pixels is used. This has the effect of smoothing the data, reducing noise in the image. After the image is reduced, a header is added to the image to instruct an image viewer on how to display the image.

[058] To initiate the transfer of the reduced images from the shear computer 240 to the archive computer 340, communication is established between the two computers. This can be implemented by any suitable software. In the example assembly, at the end of the data collection process, the shear computer 240 sends a message to the archive computer 340, which contains a file name for the image data. Optionally, the message may also include a scale for creating a ridge view grid in the archived data associated with the tire. Once the file name message is received, the archive computer 340 creates a working directory in the root directory of the drive into which the downloaded images will be placed. Then a text file is created in that directory, with a single line saying the file name. The filing computer 340 then responds to the shear computer 240 with the same filename originally sent by the shear computer. This response signals to the shear computer 240 to transfer the files containing the reduced images. The transfer process does not begin until archiving computer 340 sends the appropriate file name response. As each file is transferred, it is stored in the working directory created by the archiving computer 340. Reduced images can be transferred to the archiving computer in a ".BMP" format.

[059] After all image files have been transferred to the archiving computer 340, the archiving computer additionally compresses the data. This can be done by converting the image sets for each tire section into an animated graphic file, for example, a GIF file. Standard GIF compression includes a built-in transparency aspect, which allows one of the colors to be made transparent. In the context of an animation, the transparent color is used when a pixel in an animation frame is the same as in the previous frame. Thus, the first frame of the animated GIF file has the complete image data. However, successive frames may use the transparency bit, which warns the display program not to change the color of the pixel being displayed. This significantly increases the compression ratio, creating more repeating patterns. Additional details regarding GIF files and compression can be found in the Graphic Interchange Form Programming Reference, published by CompuServe Inc., dated July 31, 1990.

[060] The compression provided by standard GIF compression can be further enhanced by modifying the transparency aspect to produce lossy compression. Specifically, we have found that in a shear animation, it can be difficult to discern between pixel values, which change only a relatively small amount of intensity from one frame to the next. Thus, these pixels can be assigned a transparent color without any substantial degradation of animation quality. Specifically, in the input stream feeding the compression agent, the pixel being displayed is constantly being compared to the pixel which is to replace it in the successive frame so that transparent pixels can be generated. According to one aspect of the present invention, the generation of transparent pixels is altered by assigning the transparent color to pixels in an animation frame, which have not changed more than a predetermined level from the preceding frame, as opposed to only those pixels that are identical. Thus, transparent pixels have a much higher tendency to be generated.

[061] GIF compression uses the LZW compression technique, which creates "tokens" that represent longer byte repeat sequences. These tokens are created as compression occurs. Using a tolerance for the generation of transparent pixels increases the tendency for longer strings on the chips, thereby providing greater compression. The decoder program for animations simply swerves in front of the pixels, which have the transparent value, leaving the same color displayed.

[062] For example, when using a scale from 0 to 255 from light to dark, the trigger for assigning a transparent pixel can be adjusted when the brightness level has not changed more than 8 counts of the displayed brightness. With such a trigger, if the displayed pixel of the first frame of the animation has a brightness level of 10 and the corresponding pixel in the second frame has a brightness level of 17, the transparent pixel value (for example, 252) would be assigned. that pixel in the second frame. If in the third frame the corresponding pixel has a brightness level of 24, the transparent pixel value would not be assigned, so the new pixel value of 24 would be saved and later displayed. Using the 0 to 255 scale from light to dark, applicants have found that changes in brightness of less than 16 levels are difficult for the human eye to visually discern. Thus, the compression algorithm of the present invention could use, for example, any brightness level of 16 or less as the trigger for assigning the transparent pixel value during compression. As will be appreciated, if other scales are used for pixel values, considering the invention, a trigger should be selected to reflect a change that is not discernible by the human eye. Thus, the compression algorithm is not limited to any particular trigger value for assigning the transparent pixel value, but may instead involve any value that represents a change in the image that is difficult for the human eye. discern.

[063] At the end of the compression process performed by the archiving computer 340, a series of animated GIF files, each of which may correspond to a particular section of the tire being tested (or another test object), is saved. in the file storage medium, in a directory or subdirectory corresponding to the particular file name. To allow animated GIF files to be displayed, an HTML document is created which allows GIF files to be displayed in a web browser. The HTML document can also contain the tire identifier, customer name, any operator entered notes, date and time. This HTML document can also be saved using the filename and replaced with the GIF files in the file storage medium. An index HTML document is also updated with the filename, tire identifier, and any other desired information to allow searches for test results to be performed. For example, a search function could be provided through the operator interface. Once this is completed, the working directory, which contained the original files transferred from the shear computer, can be removed.

Referring now to Figures 8 to 20 of the drawings, an illustrative apparatus 410 is shown for conducting the shear test on a vehicle tire. It will be appreciated that while the illustrated shear test apparatus 410 may be used for the production of animated shear images of a tire, the apparatus is not limited to performing tests that produce animations. Instead, the shear test apparatus 410 may be configured to perform any desired shear test method. As shown in Figures 8 to 13, the shear test apparatus 410 includes a vacuum chamber 412, in which a tire can be loaded and subjected to a vacuum test cycle (i.e., depressurization and pressurization). In the illustrated embodiment, the vacuum chamber 412 has a generally cylindrical configuration which is divided into upper and lower portions 414, 416. As best shown in figures 8 and 11, the upper and lower portions 414, 416 are closely connected. pivoting together along a rear portion 418 of the vacuum chamber 410, so that in this case the upper portion 414 is movable relative to the lower portion 416 between the open and closed positions. The separation of the vacuum chamber 412 at the upper and lower portions 414, 416 is along an angle to the base 421 of the vacuum chamber. Specifically, vacuum chamber 412 is divided into upper and lower portions 414, 416 along a downwardly sloping plane as it extends from rearward portion 418 to vacuum chamber 420. Thus, when the upper portion 414 is in the open position, the upper and lower portions 414, 416 define an open mouth having a relatively low front edge 422. This low front edge 422 facilitates the loading and unloading of tires such as Described below.

[065] For tire interference imaging, during the vacuum cycle, a shear camera assembly is provided. The camera assembly, which is shown schematically in Figure 2, includes a shear camera 230 and a laser 235 for illumination of the tire with a coherent beam of light. The shear camera 230 is supported on a mast 233, which is arranged in a centralized relationship to the vacuum chamber 412. The mast 233 is extendable along the central axis of the vacuum chamber 412 to allow the camera 230 to be positioned. inside the tire, for examination of the tread area and outside of the tire, for examination of the tire bead and sidewall. Additionally, the mast 233 is rotatable so that the camera 230 can be positioned to view the different sections or sectors of the tire. As described above, after each vacuum cycle, the camera 230 is rotated to see the next tire sector and the vacuum cycle is repeated.

The illustrated shear test apparatus 410 further includes a tire handling system which loads a tire into the vacuum chamber 412 and automatically centers the tire in relation to the chamber and in turn to the shear chamber. . Specifically, the tire handling system provides a simple mechanical centering mechanism which reliably and accurately centers tires of different diameter without the need for any adjustments by an operator. Further, the tire handling system utilizes a pivoting loading assembly 424 which minimizes tread space requirements for loading / unloading operation and substantially facilitates the loading / unloading process by allowing a tire to be loaded and unloaded. in a substantially vertical position. For this purpose, the pivot loading assembly 424 includes a tire support plate 426 which is movable between a loading position and an inspection position when the vacuum chamber 412 is in the open position. In the loading position, the tire support plate 426 is arranged substantially outside and in front of the vacuum chamber 412. In addition, the tire support plate 426 extends at a slight angle from the vertical towards the rear 418. of the vacuum chamber 412, with a lower end 446 of the support plate being disposed generally in front of the low front edge 422 of the vacuum chamber mouth, as shown in figures 8 to 10. In the inspection position, the vacuum support plate The tire 426 is disposed horizontally within the vacuum chamber 412 and centered with respect to the chamber (and, in turn, the shear camera), as shown in figures 11 to 13. The support plate 426 is configured so that its center portion is substantially open so that when the plate is in the inspection position the camera can see the lower tire bead supported on it without any need for manipulation additional tire.

[067] An example assembly of a tire handling system is shown in greater detail in Figures 14 to 19. In the example assembly, the tire support plate 426 is mounted on a cart 428 which in turn , is connected to a pivot frame 430 via a pair of arms 432 as shown in figures 16 to 18. In this case, carriage 428 (see, for example, figures 14 and 15) comprises a pair of control elements. parallel brackets 434 which are interconnected by a pair of laterally extending clamps 436 which extend between the support members adjacent to the ends thereof. When the support plate 426 is in the loading position, the support elements 434 are angled slightly backwards from a vertically upright position as shown in figures 8 and 10. The support elements 434 are horizontal, and extend in a front-to-rear relationship to vacuum chamber 412 when the support plate 426 is in the inspection position. Each arm 432 is connected to a respective support member of the support elements 434, and connects the trolley to an axis 438 (Figures 15, 16 and 19), which is rotatably supported by pivot frame 430, and defines the pivot around which arms 432 and cart 428 rotate. The shaft 438 extends laterally between a pair of legs 440 disposed adjacent to a front end of the pivot frame 430 as shown in figure 19.

[068] Pivot loading assembly 424 also includes a linear actuator 442 which is pivotally connected at one end to pivot frame 430 and at the opposite end to one of arms 432 (see, for example, figures 17 and 19). Thus, the extension and retraction of linear actuator 442 pivots shaft 438 and arms 432 relative to pivot frame 430, and thereby pivots carriage 428 and support plate 426 between loading and inspection positions. The low front edge 422 of the vacuum chamber 412 facilitates pivoting movement of the trolley 428 and support plate 426, having a minimum height barrier that the trolley and support plate must pass. Since the trolley 428 and support plate 426 are substantially upright when in the loading position, they consume a relatively small amount of floor space, particularly compared to horizontal conveyor type loading systems. The required tread space is also minimized by the tire being loaded onto and unloaded from the vacuum chamber 412 in the same position.

For the support of a tire as it is loaded onto the plate, the support plate 426 includes a pair of laterally spaced columns 444. The columns 444 are disposed adjacent to the lower end 446 of the support plate 426, and are sufficiently spaced to support different diameter tires. Since the support plate 426 is arranged substantially vertically in the loading position and the columns 444 are at the lower end 446 of the plate, a tire only has to be raised a short distance to be loaded onto the support plate.

[070] The tire handling system automatically centers the tire in relation to the vacuum chamber 412 and thus the shear camera, taking advantage of the tire's circular configuration. Regarding the steering or lateral axis, the columns 444 on the support plate 426 may act as the centering mechanism. In particular, the columns 444 are disposed on the support plate 426, so that when the plate is in the inspection position, the columns 444 are positioned on one side and spaced equidistant from the center of the pressure chamber 412. Thus, Regardless of which tire diameter is placed over the columns 444, the tire will be laterally centered relative to the camera and camera when the support plate 426 is pivoted to the inspection position.

[071] The centering of the tire towards the front or rear axle of the vacuum chamber is accomplished through the tire support plate 426 and a tire detection arm 448 which are movable towards each other. so that a tire can be clipped between them. As shown, for example, in Figures 14, 16, 18, prior to the commencement of a centering / loading operation, sensing arm 448 is disposed adjacent an upper end 450 of cart 428, in lateral alignment with one of Further, the sensing arm 448 and the columns 444 are spaced equidistant from the center of the trolley 428. The sensing arm 448 is longitudinally slidable along the trolley 428 on a rail 452 (Figure 14) provided at Likewise, the support members 434. Likewise, the support plate 426 is longitudinally slidable along the trolley 428 on corresponding rails 454 (Figure 15) provided on the support elements 434.

[072] The support plate 426 and the detection arm 448 are driven along the carriage 428 by means of a spindle drive mechanism in this case. Leading spindle 458 of the drive mechanism extends longitudinally with respect to carriage 428 parallel to the rails and is supported at one end of the carriage by suitable bearings as shown in Figure 14. A motor 460 is disposed at the upper end of carriage 428, for turning spindle 458. Support plate 426 is coupled via a nut to a lower portion 463 of lead spindle 458, while detection arm 448 is coupled via a nut to an upper portion 465 of spindle advance. The lower and upper portions 463, 465 of lead spindle 458 are threaded identically but in opposite directions. Thus, one rotation of lead spindle 458 moves support plate 426 and detection arm 448 in opposite directions at the same speed.

[073] During a tire loading operation, the motor 460 rotates the lead spindle 458 so that the tire support plate 42 6 moves toward the upper end of the carriage 428 while the detection arm 448 moves forward. it moves toward the lower end so that a tire resting on the support posts 444 ends up stapled between the support posts and the sensing arm. The sensing arm 448 is pivotally supported such that when the sensing arm contacts the outer surface of the tire, it is pushed in front of a centralized position. This pivoting movement of the sensing arm 448 triggers a limit switch, which stops the spindle drive motor 460. Since the support plate 426 and the sensing arm 448 moved an equal distance along the cart 428 and started In the laterally aligned and spaced equidistant sequence of the center of the trolley, the tire is in a centralized position relative to the trolley when the sensing arm 448 contacts the tire. Thus, by configuring the cart 428 so that it is centered relative to the vacuum chamber 414, when the cart pivots to the inspection position, the tire will also be centered relative to the camera.

[074] As will be appreciated, the centering sequence can occur at any time prior to the start of the inspection cycle. For example, in order to reduce the time required for the loading operation, the centering sequence may occur at the same time as the cart is pivoting from loading to inspection position. However, the centering sequence can also occur before or after the cart is pivoted.

[075] For subjecting the tire or other test object to a vacuum cycle (i.e., depressurization and pressurization), the illustrated shear test apparatus 410 includes an air handling system 446. The air handling system 446. In this case, air 446 includes a vacuum pump 468 which draws air through an outlet 470 in the vacuum chamber wall 412, as shown in Figure 20. An inlet valve 472 is also provided in the vacuum chamber wall. During the depressurization portion of the vacuum cycle, the inlet valve 472 is closed, and the vacuum pump 468 draws air out of the vacuum chamber 412. When the vacuum chamber 412 is closed, this reduces the pressure. in the vacuum chamber and tension the tire. While the tire is tensioned, the shear camera 230 takes a series of tire interference images. Once a desired number of interference images have been taken, the pressurization portion of the vacuum cycle begins. During chamber pressurization, vacuum pump 468 continues to operate, but inlet valve 472 is open. Thus, air is circulated through the closed vacuum chamber 412, through the air inlet and outlet. This returns the vacuum chamber to normal atmospheric pressure, and returns the tire to an untensioned state. The camera 230 can then be rotated to the next tire sector and the repeated vacuum cycle.

Preferably, the air between the test object and the shear camera should have a uniform and consistent density during the vacuum tensioning cycle. Applicants have found that if the relative humidity is high during the vacuum cycle, an ambient condition such as mist occurs in vacuum chamber 412. This causes refraction and reflection of light used in the shear process, substantially reducing the quality of interference images. taken by the shear camera 230. The fog condition is produced because the reduction in ambient pressure in the vacuum chamber 412 during the vacuum cycle leads to a corresponding reduction in the ambient air temperature and of any airborne water. . As the air and water temperature is reduced, water comes out of suspension, producing the mist.

In order to prevent the fog condition from developing, the shear test apparatus 410 of the present invention may include a mechanism in communication with the interior of the vacuum chamber 412, which may reduce the relative humidity in the chamber. vacuum during the vacuum cycle. For example, the air handling system 466 may be adapted to heat the air carried to the vacuum chamber 412 through the inlet valve 472, thereby heating the air within the vacuum chamber. This counteracts the heat that is removed as a result of the pressure reduction, allowing the air to hold more water. Thus the relative humidity is reduced and the water vapor remains in suspension. As shown in Figure 20, one way in which this can be accomplished is by providing a heating element 474 in the air inlet to the vacuum chamber 412. Air carried into the vacuum chamber 412 through the inlet passes over the element. 474 and thereby is heated.

[078] Air heating can be performed more efficiently by using the heat generated by the operation of the vacuum pump 468. In particular, a duct may be provided which takes air from the exhaust side of the vacuum pump 4. 68, which was heated by the operation of the vacuum pump, and directs it over the heating element 474. The heated air is then directed to the vacuum chamber 412 through the air inlet valve 472. The heating element 474 can be manually actuated so that it can be activated when desired, such as during high humidity conditions. Additionally, the heating element 474 may be connected to a sensor which actuates the heating element when the relative humidity exceeds a predetermined value. To help prevent overheating, the heating element 474 may be adapted so that it is interrupted when the vacuum pump 468 is not operating. Although the heating element 474 at the inlet to the vacuum chamber 412 is shown, it will be appreciated that the heating element may be arranged anywhere suitable to allow it to heat the air in the vacuum chamber 412, such as inside the vacuum chamber. vacuum chamber itself. Moreover, any suitable type of heating mechanism may be used.

Alternatively, instead of using a heating element, the air handling system 466 may include a dehumidifier for the removal of water vapor from the air in the vacuum chamber. The dehumidifier includes cooling plates, which cool the air as it is circulated during the pressurization portion of the vacuum cycle. This causes water vapor to escape from the suspension on the cooling plates. The air can then be allowed to warm back, producing a lower relative humidity and taken back to the vacuum chamber 412.

All references cited herein, including patents, patent applications and publications are hereby incorporated in their entirety by reference.

Although this invention has been described with an emphasis on preferred embodiments, variations of preferred embodiments may be used, and it is intended that the invention may be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications involved in the spirit and scope of the invention as defined by the claims.

Claims (34)

1. Apparatus for performing an electronic shear on a tire, the apparatus comprising: a pressure chamber (412) having a movable door between open and closed positions; an air handling system (446) in communication with the interior of the pressure chamber for changing ambient pressure in the pressure chamber (412), the air handling system (446) including a moisture reduction mechanism (474) ) communicating with the interior of the pressure chamber (412) and being selectively operable to reduce relative humidity within the pressure chamber (412); a shear camera (230) disposed in the pressure chamber (412) for taking an interference image of a tire; an image processor (60) coupled to the shear camera (30), the image processor (60) being adapted to receive a plurality of sequential interference images from the shear camera (30), producing a set of a plurality of images sequential tire shear from interference images and produce animation from the sequential shear image set to represent dynamically changing stress states in a tire; a file memory for retaining data corresponding to the animation received from the image processor, the retained animation data being compressed such that the retained animation data includes only individual preselected shalogram images from the set of shalogram images sequentials; and a tire loading system (424) for loading a tire into the pressure chamber (412) through the pressure chamber port (414,416), the tire loading system (424) including a support plate 426, which is pivotal between a loading position, wherein the tire support plate (426) is arranged to support a tire in a generally vertical position substantially outside the pressure chamber (412), and a inspection position, where the support plate (426) is arranged to support a tire in a substantially horizontal position within the pressure chamber (412), the support plate (426) being movable along a trolley (428) , which is adapted to automatically center a supported tire on the support plate (426) relative to the shear camera (230). Apparatus according to claim 1, characterized in that the preselected individual shear-hog images comprise shear-hog images taken at a preselected regular interval from the set of sequential shear-hog images. Apparatus according to claim 1, characterized in that the individual preselected shalogram images in the retained animation data are of reduced size using a pixel weighting technique. Apparatus according to claim 1, characterized in that each shear image comprises a plurality of individual pieces of image data and that the retained data is compressed in such a way that it includes only the individual pieces of image data. which changed more than a predetermined amount of the preceding shear image in the sequential shear image set. Apparatus according to claim 1, characterized in that the tire support plate (426) has a central portion which is substantially open. Apparatus according to claim 1, characterized in that the tire loading system (424) includes a pivot frame (430) disposed in the pressure chamber (412) and a pivot arm (432) which extends between the pivot frame (430) and the cart (428). Apparatus according to claim 6, characterized in that the pressure chamber port is defined by an upper portion (414) of the pressure chamber (412) which is pivotally mounted to a lower portion (414). 416) of the pressure chamber (412), and where a joint separates the upper and lower portions of the pressure chamber (412), the joint extending at an upward angle from a front portion (420) of the pressure chamber (412), adjacent to which the tire support plate (426) is disposed in the loading position towards an opposite rear portion (410) of the pressure chamber (412). Apparatus according to claim 1, characterized in that the tire support plate (426) includes a pair of spaced support columns (444) arranged adjacent a lower end of the support plate (426) and adjacent to a lower end of the cart (428). Apparatus according to claim 8, characterized in that the tire loading system (424) includes a sensing arm (448) disposed adjacent an upper end (450) of the trolley (428) opposite to the column posts. (444) and a centering drive mechanism (458), the centering drive mechanism (458) being operable to move the sensing arm (448) and support columns (444) in opposite directions along the cart ( 428) equal distances at equal speeds, and the sensing arm (448) being operable to stop operation of the drive mechanism (458) when the sensing arm (448) contacts a tire supported on the support plate (426). Apparatus according to claim 1, characterized in that the moisture reduction mechanism comprises a heating element (474) operable to supply heated air into the pressure chamber (412). Apparatus according to claim 10, characterized in that the heating element (474) is disposed outside the pressure chamber (412) adjacent to a pressure chamber inlet through which the manipulation system (426) air flows air into the pressure chamber (412). 12. Apparatus for performing an electronic shear on a test object, the apparatus comprising: a pressure chamber (412) within which the test object is bearable; a shear camera (230) disposed in the pressure chamber (412) for taking an interference image of the test object; and an air handling system (446) in communication with the interior of the pressure chamber (412) for changing ambient pressure in the pressure chamber (412), the air handling system (446) including a reduction mechanism humidity (474) communicating with the interior of the pressure chamber (412) and being selectively operable to reduce relative humidity within the pressure chamber (412). Apparatus according to claim 12, characterized in that the moisture reduction mechanism (474) comprises a heating element (474) operable to provide heated air into the pressure chamber (412). Apparatus according to claim 13, characterized in that the heating element (474) is disposed outside the pressure chamber (412) adjacent to an inlet in the pressure chamber (412) through which the manipulation system air (446) sends air into the pressure chamber (412). Apparatus according to claim 14, characterized in that the air handling system (446) includes a vacuum pump (468) in communication with the interior of the pressure chamber (412) and operable to remove air from the pressure chamber (412) through an outlet and bring air into the pressure chamber (412) through the inlet. Apparatus according to claim 15, characterized in that the heating element (474) is arranged to heat the air from an outlet side of the vacuum pump (468) which is brought into the chamber. (412) through the inlet. Apparatus according to claim 12, further including a tire loading system (424) for loading a tire into the pressure chamber (412) through the pressure chamber port (414,416). , the tire loading system (424) including a tire support plate (426), which is pivotable between a loading position, where the tire support plate (426) is arranged to support a tire in one position. generally vertical substantially outside the pressure chamber (412), and an inspection position, where the support plate (426) is arranged to support a tire in a substantially horizontal position within the pressure chamber (412), the pressure plate support (426) being movable along a trolley (428) which is adapted to automatically center a supported tire on the support plate (426) relative to the shear camera (230). Apparatus according to claim 17, characterized in that the tire support plate (426) has a center portion which is substantially open. Apparatus according to claim 17, characterized in that the tire loading system (424) includes a pivot frame (430) disposed in the pressure chamber (412) and an extending pivot arm (432). between the pivot frame (430) and the cart (428). Apparatus according to claim 19, characterized in that the pressure chamber port is defined by an upper portion (414) of the pressure chamber (412) which is pivotally mounted to a lower portion (414). 416) of the pressure chamber (412), and where a joint separates the upper and lower portions of the pressure chamber (412), the joint extending at an upward angle from a front portion (420) of the pressure chamber (412), adjacent to which the tire support plate (426) is disposed in the loading position toward an opposite rear portion (410) of the pressure chamber (412). Apparatus according to claim 17, characterized in that the tire support plate (426) includes a pair of spaced support columns (444) arranged adjacent to a lower end of the support plate (426) and adjacent to a lower end of the cart (428). Apparatus according to claim 21, characterized in that the tire loading system (424) includes a sensing arm (448) disposed adjacent an upper end (450) of the trolley (428) opposite to the tire columns. (444) and a centering drive mechanism (458), the centering drive mechanism (458) being operable to move the sensing arm (448) and support columns (444) in opposite directions along the cart ( 428) equal distances at equal speeds, and the sensing arm (448) being operable to stop operation of the drive mechanism (458) when the sensing arm (448) contacts a tire supported on the support plate (426). Apparatus according to claim 12, further including an image processor (60) coupled to the shear camera (30), the image processor (60) being adapted to receive a plurality of interference images from the shear camera (30), produce a set of a plurality of sequential tire shear images from the interference images, and produce an animation from a sequential shear image set to represent stress states that change dynamically in the test object. Apparatus according to claim 23, characterized in that it includes a file memory for retaining data corresponding to the animation, the retained animation data being compressed such that the retained animation data includes only individual shalogram images. preselected from the sequential shear set and less than all image data associated with each individual preselected A method for analyzing a test object, comprising: (a) taking an interference image of a test object; (b) comparing the interference image with a baseline interference image for the production of a shalhogram image; (c) repeating steps (a) and (b) at varying stress levels of the test object for the production of a set of a plurality of sequential shear images; (d) selecting individual shear images from the sequential shear image set for producing a sequential shear image file set, each of the selected shear images comprising a set of individual chunks of Image; characterized by the fact that it further comprises: (e) compressing the image data associated with each of the selected individual images to produce an animated graphic file, the animated graphic file being compressed such that individual pieces of which changed less than a predetermined amount of the preceding shear image in the sequential shear image file set; (f) the storage of the animated graphic file. Method according to claim 25, characterized in that the individual pieces of image data comprise pixel values. Method according to claim 26, characterized in that the predetermined amount is a change in pixel value, which is not discernible by the human eye in an animation. A method according to claim 25, further including the step of assigning an identifier to the test object. The method of claim 28, further including the step of creating an index file associating the test object identifier with the animated graphic file. Method according to claim 25, characterized in that the step of selecting individual shalhogram images for the sequential shalhogram image file set is performed by taking shalhogram images at a pre-selected regular interval at from the set of sequential shear images. A method according to claim 25, further including the step of decreasing the size of each of the selected shalogram images for compressing the image data. A method according to claim 25, further including the step of displaying the animated graphic file at a frame rate fast enough to generate a representative animation of dynamically changing stress states in the test object. A method according to claim 32, further including the step of displaying the set of plurality of sequential shear images at a frame rate fast enough to generate a representative animation of dynamically changing stress states. on the test object. A method according to claim 33, characterized in that the set of plurality of sequential shear images is displayed at a faster frame rate than the animated graphic file.