Abstract:
A method and system for measuring thread products and determining product conformance to predefined specifications are provided. The measuring system includes a measuring device electrically coupled to a computer-based component. The measuring device senses width information of a thread product and senses rotational and length information relative to the sensed width information. The computer-based component receives the sensed information, compares the sensed information to previously-defined quality specification information for the product, and determines if the product is within an uncertainty limit of the specification information based on the comparison.

Description:
FIELD OF THE INVENTION 
   This invention relates generally to fasteners and, more specifically, to fastener quality. 
   BACKGROUND OF THE INVENTION 
   For many years, the U.S. government has provided fastener quality guidelines for various industries. Recent audits of adherence to these guidelines have highlighted areas for improvement in fastener quality in certain fields. For example, a Federal Aviation Administration (FAA) document number AS9100 presents quality guidelines for screws, bolts, and other fasteners for the commercial aviation industry. 
   Screw and bolt quality is currently measured with gauges. Current gauges, such as those produced by Greenslade, Southern, and Johnson, for measuring screw and bolt quality, such as thread features, are unable to meet measurement uncertainty limits set forth in AS9100. Further, these gauges do not provide traceability of the information they gather with respect to the fastener. 
   Therefore, there exists an unmet need for gauges that meet measurement uncertainty limits. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method and system for direct differential measurements of thread products and determining product conformance to predefined specifications. 
   The measuring system includes a measuring device electrically coupled to a computer-based component. The measuring device senses width information of a thread product and senses rotational and length information relative to the sensed width information. The computer-based component receives the sensed information, compares the sensed information to previously-defined quality specification information for the product, and determines if the product is within an uncertainty limit of the specification information based on the comparison. 
   In an aspect of the invention, the measuring device suitably includes two contact probes that sense width information, two scales that sense length information of the probes relative to the product, and a spindle that holds the product and senses rotational information of the probes relative to the product. 
   In another aspect of the invention, the probes are suitably air activated probes, the scales are suitably airbearing scales, and the spindle is suitably an airbearing spindle. 
   In still another aspect of the invention, the computer-based component suitably determines a concentricity error value based on a portion of the sensed information and determines an angularity error value based on a portion of the sensed information. The computer-based component uses the concentricity error value and the angularity error value to determine if the object is within an uncertainty limit of the specification information. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings. 
       FIG. 1  illustrates a non-limiting example block diagram of a measuring system formed in accordance with the present invention; 
       FIGS. 2 and 3  are perspective views of a non-limiting example measuring device formed in accordance with the present invention; and 
       FIGS. 4 and 5  illustrate an example process performed by the system shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a block diagram of a measuring system  20  that determines if thread geometry of a fastener, such as a screw, bolt, threaded rod, or the like, is within measurement uncertainty limits of predefined quality specifications. The measuring system  20  includes a measuring device  24  that is electrically coupled with a controller  26 . The measuring device  24  generates various measurement information of a fastener using probes and scales  30  and a spindle  32 . The controller  26  includes a processor  40  that is coupled with a user interface  42  and a memory  44 . 
   Before a fastener is analyzed by the measuring device  24 , a user enters specifications for the fastener into the controller  26  using the user interface  42 . The user interface  42  includes one of a keyboard, display, mouse, or any other interface device that allows the user to enter information and interact with the processor  40 . After a fastener is inserted into the measuring device  24 , the probes and scales  30  and the spindle  32  are manipulated by the user in order to provide certain digital measurement and position information about the fastener and the threads on the fastener. The digital information provided by the probes and scales  30  and the spindle  32  are supplied to the controller  26 . The processor  40  saves the information received from the measuring device  24  into the memory  44 . The processor  40  executes a comparison program that compares the incoming information from the measuring device  24  with the specification information entered by the user to determine if the stored information is within acceptable limits of the specification information. 
   In one embodiment, the processor  40  continuously generates measurement information including pitch diameters, flank angles, major and minor diameters for a thread of a fastener based on the information provided by the probes and scales  30  and the spindle  32 . The processor  40  geometrically calculates the thread measurement information based on probe information, such as probe tip size, and the entered specification information. 
     FIG. 2  illustrates a non-limiting example of a measuring device  100  that generates information for use by the controller  26 . The device  100  includes first and second base sections  102  and  104 . The first base section  102  is mounted substantially orthogonal to the second base section  104 , thereby creating an L-shaped formation between the two sections  102  and  104 . The first and second base sections  102  and  104  are suitably made of a material that is substantially resistant to thermal expansion, such as without limitation granite. A spindle  110  is suitably mounted on a top surface of the first section  102 . A non-limiting example spindle  110  is a precision airbearing spindle with better than 0.001 arc second resolution and 3 arc seconds accuracy. Spindles of this level of resolution and accuracy are produced by Nelson Air Corporation. The spindle  110  produces highly-accurate digital rotational information. A fastener, such as a bolt or screw  114  is mounted to the spindle  110  using a mounting plate  116  that is sized to securely hold the bolt  114  in place. The plate  116  is attached to a spinning surface of the spindle  110 . The spindle  110  includes a digital data port that electrically connects with the controller  26 . Also, the spindle  110  includes two manual vernier adjustors  120  for adjusting the position of the bolt  114 . 
   A side of the second base section  104  that faces the mounted spindle  110  includes first and second vertical tracks  126  and  128 . For purpose of providing geometric reference, an x-axis is substantially parallel to the spinning surface of the spindle  110  and the surface of the second section  104  that faces the spindle  110 . A z-axis is substantially parallel to the surface of the second section  104  and substantially perpendicular to the mounting surface of the spindle  110 . The first and second tracks  126  and  128  are substantially equidistant along the x-axis direction from a centerline of the spindle  110  that is substantially parallel to the z-axis. The first and second tracks  126  and  128  slidably receive first and second scales  130  and  132 , respectively. Non-limiting examples of the scales  130  and  132  are airbearing scales with better than 0.2 micro inch resolution. Nelson Air Corporation produces Airbearing scales with this level of resolution. The scales  130  and  132  generate z-axis dimension information based on the scale&#39;s position on the tracks  126  and  128 . The generated z-axis information is sent to the controller  26 . 
   As shown in  FIG. 3 , first and second probes  140  and  142  are mounted to the first and second scales  130  and  132 , respectively. The probes  140  and  142  include probe shafts  146  and  148  that attach to respective probe tips  150  and  152 . The probes  140  and  142  are mounted to the scales  130  and  132  in a configuration such that the probe shafts  146  and  148  face each other and are substantially equidistant from the centerline of the spindle  110 . A non-limiting example of the probes  140  and  142  are air activated probes with better than 0.2 micro inch resolution. Heidenhain Corporation produces probes with this level of resolution. 
   In one embodiment, the probe tips  150  and  152  are mounted to a swivel device (not shown) that is suitably connected to the shafts  146  and  148 . The swivel device allows the probe tips  150  and  152  to conform to an offset angle of ridges of the thread relative to a centerline of the shafts  146  and  148 . The probe tips  150  and  152  can also be pivotally mounted to the shafts  146  and  148 . 
   In one embodiment of the invention, as shown in  FIG. 2 , the measuring device  100  is positioned to rest on the first section  102 . The tracks  126  and  128  are vertically oriented. In this position, the scales  130  and  132  with the attached probes  140  and  142  are counterbalanced in order to be nearly weightless. Counterbalance of the scales  130  and  132  allows motion of the scales  130  and  132  up or down the tracks  126  and  128  based on an up or down force the probe tips  150  and  152  receive from pressure the probes  140  and  142  place on threads of the fastener that is being measured. First and second counterweights  160  and  162  are suitably coupled respectively with the first and second scales  130  and  132  via first and second cables  164  and  166  that pass over respective first and second pulleys  170  and  172 . The first and second pulleys  170  and  172  are suitably attached to sides of the second section  104  that are substantially orthogonal to the side of the second section  104  that faces the spindle  110 . 
   In another embodiment, the measuring device  100  suitably rests on the second section  104 . With the device  100  resting on the second section  104 , the scales  130  and  132  advantageously do not require a counterbalance. 
     FIG. 4  illustrates a non-limiting example process  200  performed by the measuring system  100  shown in  FIGS. 2 and 3 . At a block  204 , a user of the system  100  enters previously-defined quality specifications for the threads of a fastener, such as a screw or bolt, that is to be measured. The specifications suitably include values of pitch diameters, flank angles, and major and minor diameters. The specifications may also include form errors, such as lead errors, circularity errors, taper, runout, helix angles, and helix paths. At a block  206 , the bolt or screw is placed into the measuring device  20  and thread measurement information for the placed bolt or screw is generated. The block  206  is described in more detail later in  FIG. 5 . At a block  210 , the processor  40  compares the generated measurements of the fastener with the entered specifications. At a block  212 , the processor  40  generates measurement uncertainty values based on the comparison. 
     FIG. 5  illustrates a process  250  for generating measurement information at the block  206  ( FIG. 4 ). At a block  260 , the probe tips  150  and  152  are placed in contact with and on opposing sides of a non-threaded shank of the fastener  114 . The tips  150  and  152  are placed near as possible to the head of the fastener while still allowing rotation of the spindle  110  without interfering with the probes  140  and  142 . At a block  264 , the fastener is spun and digital information produced by the probes  140  and  142 , scales  130  and  132 , and spindle  110  are sent to the controller  26  for storage in the memory  44 . At a block  270 , the probe tips  150  and  152  are placed in contact with the shank of the fastener near the fastener&#39;s threads. At a block  272 , the fastener is spun and information produced by the probes  140  and  142 , scales  130  and  132 , and spindle  110  are generated and sent to the controller  26 . 
   At a block  280 , the tips of the probes are placed around the fastener such that the tips contact either the beginning or ends of the thread. At a block  282 , the fastener is spun, thereby forcing the probe tips to move up or down the fastener due to pressure placed on the thread. As the probe tips  150  and  152  travel up or down the fastener, the probes  140  and  142  and scales  130  and  132  move along the tracks. The probes  140  and  142 , scales  130  and  132 , and spindle  110  generate information as the probe tips  150  and  152  move up or down the fastener. At a block  288 , all the information generated by the probes  140  and  142 , scales  130  and  132 , and spindle  110  are sent to the controller  26  for analysis. 
   The processor  40  uses the digital information stored at the block  264  to determine a concentricity error value of the placed fastener. The concentricity error value is suitably the location of the longitudinal axis of the fastener relative to the centerline of the spindle  110 . 
   The processor  40  uses the stored digital information stored at the block  272  to determine an angularity error value. The angularity error value is suitably an angular difference between the centerline of the spindle and the centerline of the placed fastener. 
   In one embodiment, the measuring device  100  is adjusted to minimize the concentricity error value and the angularity error value. The spindle  110  includes an adjusting component that allows for 5 degrees of freedom adjustments. The connection between probes  140  and  142  and scales  130  and  132  includes an adjusting component that allows for 3 degrees of freedom adjustments. 
   In another embodiment, the processor  40  mathematically adjusts the thread measurement information stored in the block  282  with the concentricity error value and the angularity error value. 
   While the preferred embodiment of the invention has 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 the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.