Abstract:
Disclosed is a method that utilizes optics to measure a hole depth in a workpiece. The method involves placing a light recording apparatus and a light source apparatus proximate a hole. Light is then emitted from the light source apparatus and is directed into the hole. This illumination of the hole allows an image of the side surface of the hole that is at the greatest distance from the light recording apparatus to be recorded. Then, the apparent diameter of the image is calculated. The apparent diameter of the image, in turn, is compared to the known diameter of the hole in order to calculate the distance between a reference datum in the light recording apparatus and the far side surface of the hole. Once this distance is determined, the hole depth is calculated by accounting for the distance between the reference datum and the workpiece surface.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to estimating the depth of a hole by the use of optics.  
         BACKGROUND OF THE INVENTION  
         [0002]    Every year, millions of holes are drilled into composite materials by the aircraft industry in order to join various structures together with fasteners. To join these structures efficiently, it is desirable to initially select a properly sized fastener. If the fastener that is selected is too long, then the fastener will need to be ground down, which will result in additional work. On the other hand, if the fastener length that is selected is too short, the fastener must be removed and replaced with a fastener of the appropriate length. Due to the nature of composite materials, the thickness of the materials to be joined often varies significantly from the nominal design size of the materials. Thus, in order to select the proper fastener length, it is desirable to know the approximate depth of the hole that has been created in the composite materials that are to be joined by the fastener.  
           [0003]    A method of estimating the depth of the above-mentioned hole involves the use of feeler gages. These feeler gages can be manual or automatic. Although each of these feeler gages can adequately estimate the depth of the hole, both have undesirable limitations. For manual feeler gages, the undesirable feature is that they are inefficient because they require an operator to make a time consuming break in the manufacturing flow in order to measure the depth of the hole. This break in the manufacturing flow can be reduced by the use of automatic feeler gages that are attached to the robots that create the holes in the composite materials. Automatic feeler gages, however, are also not ideal because these feeler gages are susceptible to being broken during operation since they must physically contact the workpiece. Accordingly, it would be desirable to measure the depth of the hole using a process that does not involve physical contact with the hole.  
         SUMMARY OF THE INVENTION  
         [0004]    In one preferred form, the present invention provides a method that utilizes optics to measure the depth of a hole that has been drilled in a workpiece. The method involves placing a light recording apparatus proximate the drilled hole at a predetermined distance from a surface of the workpiece and placing a light source apparatus proximate the hole. Light is emitted from the light source apparatus and directed into the hole in order to illuminate the side surface of the hole that is at the greatest distance from the light recording apparatus. By illuminating this far side surface of the hole, an image of the far side surface of the hole can be recorded using the light recording apparatus.  
           [0005]    Then, using the image of the side surface of the hole, the apparent diameter of the hole can be calculated. This apparent diameter, in turn, can be compared to the known diameter of the hole in order to calculate the distance between the light recording apparatus and the side surface of the hole that is the greatest from the light recording apparatus. Once this distance is determined, the hole depth can be calculated by simply subtracting the distance between the light recording apparatus and the surface of the workpiece from the distance that has been previously calculated.  
           [0006]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0008]    [0008]FIG. 1 is a schematic of a hole depth measuring apparatus constructed and operated in accordance with the teachings of the present invention;  
         [0009]    [0009]FIG. 2 is an exemplary image of a hole side surface recorded by the depth measuring apparatus of FIG. 1;  
         [0010]    [0010]FIG. 3 is a schematic illustration in flow chart form of one embodiment of the method of the present invention;  
         [0011]    [0011]FIGS. 4A and 4B are views similar to that of FIG. 2 but illustrating changes in the image that are related to the depth of the hole;  
         [0012]    [0012]FIG. 5 is a schematic view similar to that of FIG. 1 but illustrating a hole depth measuring apparatus constructed in accordance with the teachings of an alternate embodiment of the present invention;  
         [0013]    [0013]FIG. 6 is a view that illustrates observing a hole through a reticle; and  
         [0014]    [0014]FIG. 7 is an exemplary image of a hole side surface recorded by a depth measuring apparatus constructed in accordance with a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0016]    Referring to FIG. 1, a workpiece  10  is comprised of a first material  12  and a second material  14  which are to be joined together by means of a fastener that is not shown. Those skilled in the art will understand that the workpiece  10  is merely exemplary and is not intended in any way to limit the scope of the present invention. In this regard, those skilled in the art will understand that the workpiece may be constructed in a manner so as to include a multiciplicity of layers, which may or may not be formed from different materials, and/or special function materials, such as films or pastes, for example, that are configured to fill gaps, thwart corrosion and/or alter characteristics such as chemical resistance and coefficient of friction. To join the first material  12  to the second material  14  with a fastener, a hole  16  with a countersink  18  is created in the workpiece  10 . Those skilled in the art will understand that the countersink  18  may be omitted if desired, or substituted with various other types of slots, counterbores or shaped recesses. In a preferred embodiment, the hole  16  is created by a drill  110  that is attached to a robot  120 .  
         [0017]    After the hole  16  has been created in the workpiece  10 , a light recording apparatus  20 , which in a preferred embodiment is also attached to the robot  120 , is placed proximate the hole  16  at a predetermined distance away from the workpiece surface  22 . In a preferred embodiment when placing the light recording apparatus  20  proximate the hole  16 , the optical axis of a light recording apparatus is oriented generally parallel to the axis of the hole  16 . However, the optical axis of a light recording apparatus may also be oriented at an angle form the axis of hole  16 . In a preferred embodiment, the light recording apparatus is a digital camera. However, other well-known conventional light recording apparatuses, such as a conventional camera, a reticle and a human eye, or the like, may also be used.  
         [0018]    To illuminate the hole  16 , a light source apparatus  26  is placed proximate the hole  16 . In a preferred embodiment, the light source apparatus  26  is comprised of a light source  28 , which emits light, and a lens  30  that focuses the light, represented by light paths  32  and  34 , that is emitted from the light source  28 . The light emitted from light source  28  is gathered by lens  30  in order to increase the amount of light that reaches a hole far side surface  36 . After the light emitted from the light source  28  passes through lens  30 , the light, as represented by light paths  32  and  34 , is directed through a beam splitter  38 .  
         [0019]    The beam splitter  38  serves the purpose of redirecting the light emitted from the light source  28  along a path, as represented by light paths  40  and  42 , that is generally parallel to the axis of hole  16 . In a preferred embodiment, the beam splitter  38  is contained within the light recording apparatus  20  and light emitted from the light source  28  is sent into the light recording apparatus  20 . As shown in FIG. 1, the light recording apparatus lens  24  is located between the beam splitter  38  and the hole  16 . Preferably, the path of the light is centered on the beam splitter  38  so as to prevent light from traversing around the beam splitter  38  or light recording apparatus lens  24  on its way to the hole  16 . As those skilled in the art will readily understand, the light recording apparatus lens  24  may be positioned between the beam splitter  38  and the image recorder  44 . Furthermore, the positions of the light source  28  and the light recording apparatus  20  may be swapped in any of the aforementioned configurations, and the beam splitter  38  may be replaced by a mirror which reflects the light from the light source  28  along paths close to  40  and  42 , the mirror having an aperture or other space through which the light that returns from the sides of the hole  16  is permitted to pass and meet the light recording apparatus  20 .  
         [0020]    Once the light has been redirected by the beam splitter  38  towards the hole  16 , it travels along a path as represented by light paths  40  and  42  and illuminates the hole far side surface  36 . Some of the light that reaches the hole far side surface  36  will be reflected off the hole far side surface  36 , travel back along light paths proximate the light paths  40  and  42 , and pass through the light recording apparatus lens  24  to a light-sensitive image recorder  44 , which is used to record an image  46 , as shown in FIG. 2, of the hole far side surface  36 . The light-sensitive image recorder  44  may provide a permanent record of the image, such as a photograph or a video image, or may simply provide a transient image, via a set of lenses, for example, that exists only as long as the hole depth measurement device (i.e., the light source  28 , the light recording apparatus  20 , et al.) are maintained in their position and actively enabled to generate, record or otherwise process the light beam in the manner described above.  
         [0021]    In FIG. 3, the methodology of the present invention is illustrated in flow chart form. With additional reference to FIGS. 1 and 2, the methodology begins at block  302  where a hole image size (i.e., the image diameter  48 ) is determined. A controller  130  that is connected to the light recording apparatus  20  employs photo-processing software that is programmed to determine the image diameter  48 . The methodology then proceeds to block  304 .  
         [0022]    In block  304 , a hole size, which is indicative of the diameter of the hole  16 , is determined. Generally, the hole size will be known because the hole  16  is typically formed to a pre-specified diameter. If the diameter of the hole  16  is not known, it is possible to determine the hole size by recording an image of a side surface of the hole  16  that is near the workpiece surface  22  and using this image to calculate to the diameter of hole  16 . The methodology then proceeds to block  306 .  
         [0023]    In block  306 , a first distance  160 , which is indicative of the distance between the workpiece surface  22  and a reference datum  162  that is located in the light recording apparatus  20  (e.g., the datum could by located at the image recorder  44 ), is determined. Generally, the first distance  160  will be known because the light recording apparatus  20  has been placed a predetermined distance from the workpiece surface  22  and the distance from the reference datum  162  to a surface of the light recording apparatus is known. The methodology then proceeds to block  308 .  
         [0024]    In block  308 , a second distance  164 , which is indicative of the distance between the reference datum  162  and the hole far side surface  36 , is calculated utilizing the hole image size, which was determined in block  302 , and the hole size, which was determined in block  304 . The controller  130  is programmed to perform this calculation.  
         [0025]    To understand how the second distance  164  is calculated, the optical principle that this calculation is based upon will be described with reference to FIGS. 4A and 4B, which illustrate a first hole image  50  and a second hole image  52 , respectively. The first hole image  50  and the second hole image  52  are recorded images of the far side surface of two holes with the same diameter but with different depths. Furthermore, both recorded images of the first hole image  50  and the second hole image  52  were taken by a light recording apparatus that was located at the same distance (i.e., the first distance for both images is constant) from the workpiece surface when each image was recorded.  
         [0026]    As is readily apparent, the first hole image diameter  54 , which is an image of the far side surface of the hole with a greater depth, is less than the second hole image diameter  56 . In other words, the hole image size, which is the diameter of the image of the far side surface of a hole, will be a function of the depth of the hole. Thus, given a known hole diameter (i.e., the hole size) and a hole image size, the second distance, which is indicative of the distance between a reference datum in the light recording apparatus and the hole far side surface, can be calculated.  
         [0027]    Referring back to FIG. 3, the methodology then proceeds to block  310 . With additional reference to FIG. 1, in block  310 , the estimated hole depth  166  is calculated by subtracting the first distance, which was determined in block  306 , from the second distance, which was determined in block  308 . The controller  130  is programmed to perform this calculation.  
         [0028]    Referring to FIG. 5, a hole depth measuring apparatus constructed in accordance with the teachings of another embodiment of the present invention is illustrated wherein like elements are indicated and/or referred to by the previously employed reference numerals. A reticle  60  is placed proximate a hole  16  at predetermined distance from the workpiece surface  10 . A light source apparatus  26  is placed proximate the hole  16 . The light source apparatus  26  is comprised of a light source  28  and a lens  30  for gathering the light as represented by light paths  32  and  34  that is emitted from the light source  28 . A beam splitter  38 , which redirects the light emitted from the light source  28  along an axis generally parallel to the axis of the hole  16 , is placed in the path of light as represented by light paths  32  and  34 .  
         [0029]    Because the light illuminates a hole far side surface  36 , an observer  62  can view the hole far side surface  36  through the reticle  60 . With additional reference to FIG. 6, by viewing the hole far side surface  36  through the reticle  60  the observer, using reticle lines  64 A- 64 Q, can determine a hole image size, which is indicative of the apparent diameter of the hole  16 . Once the hole image size is determined by the observer  62 , the hole depth  166  can be determined using a method similar to the one shown in FIG. 3.  
         [0030]    While the method of the present invention has been described thus far as having the light recording apparatus  20  placed a predetermined known distance away from the workpiece surface  22 , those skilled in the art will appreciate that the invention, in its broader aspects, may be performed somewhat differently. For example, the light recording apparatus  20  may, in the alternative, be placed at an unknown distance from the workpiece surface  22 . In this situation, images for the near and far sides of the hole  16  are taken and compared. As the diameter of the hole  16  is known, the image of the near side of the hole  16  can be accurately scaled to determine the depth of the hole  16 .  
         [0031]    In a third such variation, the optical axis of the light recording apparatus may be placed at an angle to the axis of the hole such tat the image looks similar to FIG. 7. In this case the hole depth is calculated based on the angle of the optical axis, the position of the hole image  70  in the field of view, and the image length  72 .  
         [0032]    While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims.