Abstract:
Systems and methods for obtaining dimensions for threaded fasteners are disclosed. In one embodiment, a system includes an apparatus that determines a dimension of a fastener using a probe that senses a linear displacement of the fastener. A probe tip is rotatably disposed on the probe that contacts the fastener. A controller is coupled to the apparatus for receiving the dimensional characteristic. In another embodiment, a measurement apparatus includes a rotating spindle that supports the fastener and a probe that detects a dimension and having a portion that rotatably engages the fastener. A scale is coupled to the probe to determine a displacement. In another embodiment, a method includes positioning a fastener in a spindle that rotates the fastener, engaging the fastener with a probe to sense a dimension of the fastener, the probe having a terminal portion that rotatably conforms to the fastener, and processing the dimension.

Description:
FIELD OF THE INVENTION 
   This invention relates generally to threaded fasteners, and more particularly, to fastener inspection. 
   BACKGROUND OF THE INVENTION 
   Threaded fasteners are commonly available in a variety of sizes, thread configurations, materials and grades. In certain critical fastening applications, the dimensional tolerances of the fastener may be of significant importance. For example, selected fasteners employed in the construction of civil and military aircraft have been identified as critical to the airworthiness of the aircraft. Accordingly, these fasteners are frequently subjected to enhanced inspection procedures to ensure compliance with established government and/or commercial standards for fastener quality. 
   An important aspect of the inspection procedure is a determination of the conformity of the threaded fastener with established dimensional standards. In one known method, threaded fasteners may be individually dimensionally inspected using micrometers and similar devices for the measurement of a shank diameter of the fastener and/or the major and minor thread diameters of the fastener. Thread gages typically configured as a “go” or “no-go” devices may also used to accept or reject threaded fasteners that have conforming or non-conforming thread profiles, respectively. Alternately, other devices, such as an optical comparator, may also be used to inspect the thread profile. 
   Although the foregoing method is suitable for determining the dimensional conformity of threaded fasteners, certain drawbacks nevertheless exist. Manual inspection of relatively large lots of fasteners is generally time consuming, since a reasonable number of the fasteners must be dimensionally inspected in order to attain a statistically significant sample. Moreover, in instances where all of the fasteners in the lot must be inspected for dimensional conformity, significant amounts of inspection time are required. In either case, accurate dimensional measurements may depend upon the skill of the inspector, which may lead to variations in the dimensional data collected from a selected lot of fasteners. 
   Accordingly, there is a need for systems and methods for rapidly and accurately obtaining dimensional information for threaded fasteners. 
   SUMMARY OF THE INVENTION 
   The present invention comprises systems and methods for obtaining dimensional information for threaded fasteners. In one aspect, a measuring system includes a measurement apparatus that determines at least one dimensional characteristic of a fastener, such as a length or an angular dimension, with a probe that senses a linear displacement of the fastener as the fastener is moved relative to the probe. A probe tip is coupled to the probe that extends to a contact portion and permits the contact portion to rotate relative to a longitudinal axis that extends through the probe tip. A controller is coupled to the measurement apparatus for receiving the at least one dimensional characteristic. 
   In another aspect, a measurement apparatus includes a spindle that rotatably supports a threaded fastener, and a probe that detects a linear displacement and having a terminal portion that rotatably engages the fastener. A scale coupled to the probe to determine a linear displacement in a direction aligned with the fastener axis. 
   In still another aspect, a method includes positioning a fastener in a spindle that rotates the fastener about a longitudinal axis of the fastener, and engaging the fastener with a probe to sense a linear displacement corresponding to a dimension of the fastener, the probe having a terminal portion contacting the fastener that rotatably conforms to the fastener, and processing the dimension. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred and alternate embodiments of the present invention are described in detail below with reference to the following drawings. 
       FIG. 1  is a block diagrammatic view of a measurement system for inspecting a fastener according to an embodiment of the invention; 
       FIG. 2  is an isometric view of the measurement apparatus of  FIG. 1 ; 
       FIG. 3  is a partial isometric view of the apparatus of  FIG. 2  that illustrates a probe tip in accordance with another embodiment of the invention; 
       FIG. 4  is a cross sectional view of the probe tip of  FIG. 3  that will be used to describe the probe tip in further detail; 
       FIG. 5  is an isometric view of a blade portion for the probe tip of  FIG. 4  according to still another embodiment of the invention; and 
       FIG. 6  is an isometric view of a blade portion for the probe tip of  FIG. 4  according to still yet another embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   The present invention relates generally relates to a systems and methods for inspecting fasteners. Many specific details of certain embodiments of the invention are set forth in the following description and in  FIGS. 1 through 6  to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that the present invention may be practiced without several of the details described in the following description. 
     FIG. 1  is a block diagrammatic view of a measurement system  10  for inspecting a fastener according to an embodiment of the invention. Many of the details of the system  10  are disclosed in U.S. application Ser. No. 10/294,079 (U.S. Published Application No. 2004 0093182 A1) filed Nov. 13, 2002, which application is herein incorporated by reference. The system  10  includes a measurement apparatus  12  that is coupled to a controller  14 . The measurement apparatus  12  is operable to generate measurement information for a fastener undergoing inspection. Accordingly, the measurement apparatus  12  includes a first unit  16  that further includes one or more probes that engage the fastener, and scales configured to measure a force imposed on the probes as the probes engage the fastener. The measurement apparatus  12  also includes a second unit  18  that includes a spindle to support and position the fastener relative to the probes. The first unit  16  and the second unit  18  are generally configured to support and measure various threaded fasteners, such as bolts, screws and the like. One skilled in the art will readily appreciate that the measurement apparatus  12  may also be configured to accommodate threaded fasteners of different configurations. For example, the measurement apparatus  12  may be configured to support and measure various specialized threaded fasteners commonly employed in the aircraft industry, such as the well-known HI-LOK, HI-TIGUE and HI-LITE fasteners available from the Hi Shear Corporation of Torrance, Calif. The measurement apparatus  12  will be described in further detail below. 
   The controller  14  includes a memory  20  that is coupled to a processor  22  and a user interface  24 . Prior to the inspection of a fastener in the system  10 , a user may enter data pertaining to the fastener into the controller  14  using the user interface  24 , which may include a keyboard, a display, a mouse, or any other interface device that allows the user to enter information into the system  10  and to further interact with the system  10 . For example, the user interface  24  may also include a stored media reading device, such as a tape drive, a magnetic disk drive, or an optical disk drive operable to read the data for the fastener from a stored media device that is inserted into the reader. 
   When a fastener is inserted into the spindle of the second unit  18 , the probes and scales of the first unit  16  and the spindle are manipulated by the controller  14  to perform dimensional measurements and generate inspection information for the fastener. For example, the dimensional measurements may include the determination of a major diameter, a minor diameter, and a mean diameter. The dimensional measurements may also include one or more angular measurements, including a thread pitch and a thread angle. The inspection information generated by the apparatus  12  is transferred to the processor  22 , which may perform pre-programmed numerical routines, including the generation and compilation of statistical information based upon the acquired dimensional information. The processor  22  may also perform pre-programmed comparison routines wherein the dimensional measurements are compared to previously stored data pertaining to the fastener. In a particular embodiment, the processor  22  is configured to continuously generate measurement information and directly provide the information to the user using a visual display device, a printer, or other similar devices. 
     FIG. 2  is an isometric view of the measurement apparatus  12  of  FIG. 1  that will be used to describe the measurement apparatus  12  in greater detail. The apparatus includes a first base section  30  configured to be positioned on a support surface, such as a floor, and a second base section  32  that is coupled to the first base section  30  and oriented perpendicular the first base section  30  to comprise a generally L-shaped structure. The first base section  30  and the second base section  32  are generally comprised of a material having a relatively high density, which is substantially resistant to thermal expansion, such as granite, or other similar materials. A spindle  34  is positioned on a support portion  36  of the first section  30 . The spindle  34  supports a rotational surface  38  that rotates a fastener  40  that is retained on the rotational surface  38  by a mounting plate  42 . The spindle  34  is operable to accurately resolve angular positions so that rotational information of high accuracy may be generated. In one particular embodiment, the spindle  34  is a precision air-bearing spindle with greater than 0.001 arc-second resolution and at least about 3 arc-second accuracy. Spindles having this level of resolution and accuracy are commercially available from the Nelson Air Corporation of Milford, N.H., although other alternatives exist. The spindle  34  further includes a digital data port that is electrically coupled to the controller  14  of  FIG. 1  so that digital data may be conveniently transferred. The spindle  34  also includes a pair of manual vernier adjustment devices  44  for adjusting the position of the fastener  40  relative to the spindle  34 . 
   Still referring to  FIG. 2 , for geometrical reference, an x-axis is substantially parallel to the spinning surface of the spindle  34  and the surface of the second base section  32  that faces the spindle  34 . A z-axis is substantially parallel to the surface of the second section  32  and substantially perpendicular to the mounting surface of the spindle  34 . The second base section  32  includes a first vertical track  46  and a second vertical track  48 . The first track  46  and the second track  48  are approximately equidistant along the x-axis direction from a centerline that projects outwardly through the spindle  34  and is substantially parallel to the z-axis. The first track  46  and the second track  48  slidably receive a first scale  50  and a second scale  52 , respectively. The first scale  50  and the second scale  52  generate z-axis dimensional information based upon the position of the first scale  50  on the track  46  and the second scale  52  on the track  48 . The generated z-axis information is transferred to the controller  14 . In another particular embodiment of the present invention, the first scale  50  and the second scale  52  may be air-bearing scales having better than 0.2 micro-inch resolution. Suitable air bearing scales are commercially available from the Nelson Air Corporation of Milford, N.H., although other alternatives exist. 
   The first scale  50  and the second scale  52  are coupled to a first probe  54  and a second probe  56 , respectively. The first probe  54  and the second probe  56  are oriented so that a longitudinal axis that projects through the first probe  54  and the second probe  56  is approximately parallel with the x-axis. The first probe  54  and the second probe  56  are configured to couple to probe tips  58  that project inwardly towards the fastener  40 . The first probe  54  and the second probe  56  are operable to accurately resolve linear displacements transferred from the fastener  40  to the first probe  54  and the second probe  56  through the probe tips  58 . In a particular embodiment, the first probe  54  and the second probe  56  are air-activated probes with better than 0.2 micro-inch resolution commercially available from the Heidenhain Corporation of Schaumburg, Ill., although other alternatives exist. 
   The first scale  50  and the probe  54 , and the second scale  52  and the probe  56  are counterbalanced in order to approximately neutralize the weight of the scale  50  and the probe  54 , and the scale  52  and the probe  56 . Accordingly, a first counterweight  60  and a second counterweight  62  are suitably coupled respectively with the first scale  50  and the second scale  52  through first and second cables  64  and  66  that pass over respective first and second pulleys  68  and  70 . The first and second pulleys  68  and  70  are suitably attached to respective sides of the second section  32 . Consequently, the first scale  50  and the second scale  52  are counterbalanced and may translate along the first track  46  and the second track  48  based solely upon a vertically-directed force imparted to the probe tips  58  by a threaded portion of the fastener  40 . In another embodiment of the invention, the second section  32  is positioned on a horizontal supporting surface, such as a floor, so that an axis of the fastener  40  projects in a horizontal direction. As a result, the first scale  50  and the second scale  52  advantageously do not require counterbalancing. 
     FIG. 3  is a partial isometric view of the apparatus  12  of  FIG. 2  that illustrates the probe tip  58  in accordance with another embodiment of the invention. The probe tip  58  includes a threaded stop  61  that is configured to engage a corresponding threaded portion on the first probe  54  and the second probe  56 , respectively. An opposing end of the probe tip  58  further includes a blade portion  63  that engages a threaded portion of the fastener  40 , or still other portions of the fastener  40 , such as a shank portion. The blade portion  63  will be discussed in greater detail below. A pivotal portion  64  is interposed between the threaded stop  61  and the blade portion  63  that permits the blade portion  63  to freely rotate about an axis extending through the probe tip  58 . Accordingly, the pivotal portion  64  permits the blade portion  63  to advantageously and adjustably conform to geometrical variations present in the threaded portion of the fastener  40  as it is subjected to an inspection procedure, thus producing inspection information having greater accuracy. The pivotal portion  64  will also be described in further detail below. 
     FIG. 4  is a cross sectional view of the probe tip  58  of  FIG. 3  that will be used to describe the probe tip  58  in further detail. The probe tip  58  includes an axial shaft  65  that extends into the pivotal portion  64  and that is configured to threadably engage the blade portion  63 . The axial shaft  65  is supported by a pair of bearings  66  positioned within the pivotal portion  64 . The bearings  66  may be conventional anti-friction bearings, but preferably, the bearings  66  are jeweled bearings having a hard, mineral material such as a ruby, or a sapphire to provide a low-friction support. The axial shaft  65  is retained within the pivotal portion  64  by a collar  68  that is fixedly positioned on the axial shaft  65 . The collar  68  may be fixedly positioned on the shaft  65  by providing an interference fit between the collar  68  and the axial shaft  65 . Alternately, the collar  68  may be fixedly positioned on the shaft  65  using various adhesive compounds. A bearing retainer  70  is positioned on the axial shaft  65  that retains the bearing  66  within the pivotal portion  64 . 
   Still referring to  FIG. 4 , the pivotal portion  64  includes a free-play adjuster  72  that is threadably received into a barrel portion  74  to a desired depth to allow a rounded end  73  of the axial shaft  65  to contact a thrust plate  76  so that any axial free-play in the probe tip  58  is eliminated. The thrust plate  76  may be comprised of any suitably hard, rigid material such as tungsten or other like materials so that the probe tip  58  does not develop a significant amount of axial free-play when in use. The barrel portion  74  also receives the threaded stop  61 , which is retained within the barrel portion  74  by an interference fit between the barrel portion  74  and the stop  61 . 
     FIG. 5  is an isometric view of a blade portion  83  for the probe tip  58  of  FIG. 4  according to still another embodiment of the invention. The blade portion  83  includes a threaded rod  85  configured to threadably engage the axial shaft  65  that is coupled to a planar portion  87  having a tapered engagement portion  89 . Depending on the configuration of the threaded portion of the fastener  40  ( FIG. 2  and  FIG. 3 ), the tapered engagement portion  89  may taper to a relatively acute edge, such as a knife edge, or it may taper to an edge that has a predetermined radius R, as shown in  FIG. 5 . 
     FIG. 6  is an isometric view of a blade portion  93  for the probe tip  58  of  FIG. 4  according to still yet another embodiment of the invention. In this embodiment, the blade portion  93  includes a threaded rod  95  configured to threadably engage the axial shaft  65  that is coupled to a planar portion  97 . The planar portion  97  is coupled to an engagement portion  99  generally comprised of a cylinder having a predetermined diameter configured to engage the threaded portion of the fastener  40  (as shown in  FIG. 2  and  FIG. 3 ). 
   While preferred and alternate embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of these preferred and alternate embodiments. Instead, the invention should be determined entirely by reference to the claims that follow.