Patent Number: 048658006
Section: description

DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like, are words of convenience and are not to be construed as limiting terms. Referring now to the drawings, and particularly to FIG. 1, there is shown a fuel assembly grid inspection apparatus, generally designated by the numeral 10, which includes the combination of a precision noncontact measurement device, generally designated 12, and a universal support fixture 14 which are the components of the apparatus 10 comprising the present invention which cooperate in inspecting a fuel assembly grid 16. As seen in FIG. 1, the precision measurement device 12 per se is in the form of hardware manufactured and sold by View Engineering of Simi, Calif. and identified by the model designation "View 1220 System". The device 12 basically includes a data gathering unit (DGU) 18, a monitor and disk drive assembly (MDDA) 20, a keyboard 22, a joystick 24 and a printer 26. The device 12 measures by viewing or seeing, instead of touching or contacting, the grid 16. The DGU 18 of the device 12 includes a stationary base 28, viewing means 30 in the form of a video camera and lens system, a source of illumination 32 in the form of a ring light, an inspection platform 34 having a retroreflective surface 36 thereon (which is also part of the source of illumination 32), and electromagnetically-actuated X-, Y- and Z-axes stage assemblies 38,40,42 which mount the platform 34 and viewing means 30 on the stationary base 28 for movement relative thereto and to one another along X,Y,Z orthogonal directions. The viewing means 30 is disposed above the retroreflective surface 36 on the inspection platform 34 so as to define an inspection field of view extending generally vertically therebetween. As will be described in greater detail later, the universal fixture 14 is supported by the inspection platform 34 about the perimeter of the inspection field of view. The fixture 14, in turn, supports the grid 16 across and within the field of view. The viewing means 30 and the universal fixture 14 are movable relative to each other in X, Y and Z directions for achieving a complete inspection of all parts of the grid 16 in the vertical field of view. In particular, the Y-axis stage assembly 40 is actuatable for moving the platform 34 in the Y direction (forward or rearward, or toward the front or rear of the DGU 18) relative to the stationary base 28. The viewing means 30 being disposed in spaced relation above the inspection platform 34 is movable in X (left or right) and Z (up or down) directions with respect thereto and to the universal fixture 14 and grid 16 by actuation of the respective X-axis stage assembly 38 and the Z-axis stage assembly 42 which is movably mounted on the X-axis stage assembly 38. The viewing means 30 is adapted to view and record one or more images of the grid 16 located in the field of view and to provide digitized video image information to the MDDA 20 from which actual measurements of the grid 16 being inspected can be calculated. The known standard measurements for the particular grid design being inspected are inputted from either a floppy disk or a permanent hard disk into the MDDA 20 and the actual measurements which have been calculated therein are compared to such known standard measurements to determined whether or not the actual dimensions of the grid 16 being inspected come within acceptable tolerances of the known standard measurements. The fixture 14 is universal in the sense that it is adapted to support any one of a variety of grids of different designs within the field of view. Different programs are stored which contain the known standard measurements of the different grid designs. The one program which corresponds to the grid being inspected will be recalled and loaded into the working memory of the MDDA 20. It is not believed to be necessary for an understanding of the present invention that the operation of the device 12 be described in any greater detail. For more information about the operation of the device 12, one can consult the operator's manual for the View 1220 System available from View Engineering. Turning now to FIGS. 2-11, there is shown the universal grid support fixture 14 in assembled form and in some of its individual component parts. As mentioned above, the universal fixture 14 is adapted to support any one of a plurality of fuel assembly grids of different designs within the inspection field of view of the noncontact measurement device 12. The universal fixture 14 includes a mounting base 44 having first and second pairs of opposing portions 46A,46B and 48A,48B bounding the perimeter of the retroreflective surface 36 of the inspection field of view. The portions 46A,46B and 48A,48B of the mounting base 44 are supported by the inspection platform 34 of the measurement device 12. The universal fixture 14 further includes first and second pairs of upright grid supports 50A,50B, and guide means in the form of a pair of tracks 52A,52B mounted on, and in parallel relation along, the opposing mounting base portions 46A,46B of the first pair thereof. Each of the grid supports 50A,50B is composed of a spacer block 54 and a support assembly 56. The tracks 52A,52B have dovetail cross-sectional configurations which are complementary to and receivable in grooves 55 having dovetail cross-sectional configurations formed across the bottom of the spacer blocks 54. In such manner, the grid supports 50A and 50B of each of the pairs thereof are mounted to the respective tracks 52A and 52B in spaced relation to one another for adjustable slidable movement therealong. A clamp section 57 in each spacer block 54 is tightened to secure the spacer block to the respective one of the tracks 52A,52B. The support assembly 56 of each of the grid supports 50A,50B is assembled from a base block 58, mounting block 60, a grid support member 62 and a grid support insert 64. The base block 58 has a groove 66 formed across its bottom which is dovetail-shaped and complementary in cross-section to a track 68 formed across the top of each spacer block 54 for mounting the base block 58 to the top of the spacer block 54. A clamp section 70 in the base block 58 is tightened to secure the base block to the spacer block. The mounting block 60 of each support assembly 56 is secured by a dovetail interfitting connection 72 and an adjustment screw 74 to the base block 58 so as to extend in cantilever fashion a short distance inwardly therefrom in overlying relation to a marginal edge portion of the retroreflective surface 36 of the inspection platform 34. The grid support member 62 of each support assembly 56 is slidably mounted by a dovetail groove and track connection 76 to the lower side of the mounting block 60. An adjustment screw 78 is used to move the support member 62 along the X-axis relative to the mounting block 60. At the inner end of each support member 62 is seated one of the grid support inserts 64. When a grid 16 is supported by the fixture 14 as seen in FIG. 1, each of the support members 62 underlies the perimeter of the grid 16 and each of the inserts 64 extends from the bottom side of the grid upwardly into one of the cells thereof. In order for the field of view which encompasses the grid 16 to be transparent except for the grid itself, the grid engaging portions of the fixture 14 which project into the field of view to support the grid 16--the support members 62 and inserts 64--are made of transparent material. For example, the support members 62 are composed of acrylic material and the inserts 64 are scratch-resistant synthetic sapphire material. Further, the universal fixture 14 includes a pair of extendable and retractable actuators 80A,80B, for example, in the form of air cylinders. One actuator 80A is mounted to the one tracks 52A on base portion 46B, whereas the other actuator 80A is mounted to a third track 52C on base portion 48A, by spacer blocks 82 and base blocks 84 being substantially identical, in construction and in their connections together and to the tracks, to the spacer blocks 54 and mounting blocks 60 of the grid supports 50A, 50B. The actuators 80 are actuatable to locate the grid 16 in a desired position with respect to the inspection field of view by causing slight movement of the grid in X and Y directions relative to the grid support members 62 and inserts 64. Still further, the fixture 14 includes a plurality of sensors 86, for instance in the form of microswitch assemblies, mounted to the mounting blocks 60 (above the support members 62) of the first pair of grid supports 50A and to a fourth track 52D by a spacer block 88 and base block 90 being substantially identical, in construction and in their connections together and to the track, to the spacer blocks 54 and mounting blocks 60 of the grid supports 50A,50B. The sensors 86 are responsive to contact by the grid 16 when the latter has been moved to its desired position with respect to the inspection field of view. Turning now to FIGS. 12-16, there is seen two of the many different fuel assembly grid designs adapted to be supported by the universal fixture 14 within the inspection field of view of the noncontact measurement device 12. The grids 16A,16B basically include a multiplicity of interleaved straps 92 having an egg-crate configuration designed to form cells 94. The cells 94 of the grid l6A have opposing dimples 96 formed in the metal of the interleaved straps 92 to support the fuel rods of a fuel assembly which extend through the cells 94. Also, mixing vanes 97 are defined on and extend upwardly from the straps 92. The cells 94 of the grid 16B have opposing dimples 96 and springs 98 which serve the same purpose. In carrying out inspection of the fuel assembly grid 16, the viewing means 30 and source of illumination 32 of the DGU 18 are turned on and moved so as to define the illuminated inspection field of view across the grid as it is supported by the fixture 14. The viewing means 30 views the grid and records multiple images thereof to provide digitized video information to the MDDA 20 from which measurements can be calculated and compared to known standard measurements for the particular grid design stored in the MDDA 20. To view 100% of the grid 16, the viewing means 30 (i.e., video camera and lens system), while maintained pointed in the direction of the field of view toward the retroreflective surface 36, and/or the grid are moved relative to one another. However, the position of the fixture 14 is first sensed to ensure the correctness of the placement thereof before proceeding with inspection of the grid. Typically, as is the case with the grids in FIGS. 12-16, the grid 16A or 16B being inspected has at least a pair of vertically displaced fuel rod contacting dimples 96 disposed in each of a plurality of cells 94 defined in the grid. The dimples 96 are inspected for perpendicularity with respect to each other by using the viewing means 30 to view them at separate instances but from the same location above them and within the field of view. A separate image of each dimple 96 is recorded to provide information from which the degree of offset of one dimple with respect to the other can be determined. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof.