Patent Document

FIELD OF THE INVENTION 
   The invention relates to optical inspection of objects to determine whether they meet required manufacturing specifications, and in particular to the optical inspection of fasteners. 
   BACKGROUND OF THE INVENTION 
   It is known to optically inspect manufactured items for defects that would render the item unusable, such as by combining a fastener inspection system with a single camera. The inspection of fasteners may include examining threaded fasteners to ensure that the threaded portion is correctly formed, that the fastener head is correctly formed, that the junction of the head and shank is correctly formed, that the shank is correctly formed at the terminal end, and other suitable examinations. 
   One drawback to prior methods and systems is that the optical inspection software must be able to match the object against a library of acceptable objects regardless of its orientation and lighting, and this must be done in a rapid manner. While some of these problems can be solved by initially orienting the object in only one position and then moving it to other pre-determined positions, the recognition software must still track the object and recognise it once it has reached the new orientation. This process requires a computationally intensive operation that can be the limiting factor in the production and quality control of the fasteners. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, a system and method for inspecting fasteners are provided that overcome known problems with systems and methods for inspecting fasteners. 
   In particular, a system and method for inspecting fasteners are provided which utilize dual inspection angles and on-the-fly selection of comparison images to provide additional inspection capabilities and flexibility. 
   In accordance with an exemplary embodiment of the present invention, a method of optically inspecting a fastener to determine whether it meets two or more dimensional parameters is provided. The method includes using centrifugal force to place the fastener in a predetermined location. Two or more sets of image data of the fastener are generated from two or more corresponding different angles. Fastener pass/fail data is generated using a dimensional requirement associated with each set of image data. 
   The present invention provides many important technical advantages. One important technical advantage of the present invention is a fastener inspection system that utilizes images of the fasteners from two different axes and that selects comparison image data on the fly, so as to provide additional inspection capabilities and flexibility. 
   Those skilled in the art will further appreciate the advantages and superior features of the invention together with other important aspects thereof on reading the detailed description that follows in conjunction with the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram an inspection station in accordance with an exemplary embodiment of the present invention; 
       FIG. 2  is a diagram of an inspection station showing a horizontal vision system in accordance with an exemplary embodiment of the present invention; 
       FIG. 3  is a diagram of an inspection station showing a vertical vision system in accordance with an exemplary embodiment of the present invention; 
       FIG. 4  is a diagram of an inspection station showing a rejection mechanism in accordance with an exemplary embodiment of the present invention; 
       FIG. 5  is an overhead view of the fastener locating mechanism on the rotating turntable in accordance with an exemplary embodiment of the present invention; 
       FIG. 6  is a breakaway view of the fastener locating mechanism on the rotating turntable in accordance with an exemplary embodiment of the present invention; and 
       FIG. 7  is a diagram of an inspection system in accordance with an exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures might not be to scale, and certain components can be shown in generalized or schematic form and identified by commercial designations in the interest of clarity and conciseness. 
     FIG. 1  is a diagram an inspection station  100  in accordance with an exemplary embodiment of the present invention. Inspection station  100  allows the top dimension of fasteners to be inspected, with compensation for variations in surface finish. 
   Inspection station  100  includes base  101  having on it a rotating turntable  102 . Singulating feed mechanism  106  provides fasteners  104  to rotating turntable  102 , and the fasteners  104  are fed into fastener retaining slots  103  by centrifugal force, where they can be inspected by inspection system  700  (not explicitly shown) using image data generated by horizontal vision system  200 , vertical vision system  300 , and other suitable systems. Inspection system  700  generates rejection data, which causes rejection mechanism  400  to actuate and to eject fasteners  104  that do not meet inspection criteria. If rejection data is not generated, the fasteners  104  are accepted at an acceptance position that includes stationary wiper  115 , which removes the acceptable fasteners  104  that remain after the rejected fasteners  104  have been removed. 
   Rotating turntable  102  has fastener retaining slots  103  around the periphery. Fasteners  104  are fed into the fastener retaining slots  103  from feed chute  105  by singulating feed mechanism  106 , which biases a fastener  104  against the turntable so that it locates in one of fastener retaining slots  103 . Rotating turntable  102  rotates continuously as fasteners  104  feed into it. View AA of  FIG. 1  is shown in greater detail in  FIG. 2 . VIEW BB of  FIG. 1  is shown in greater detail in  FIG. 3 . View CC of  FIG. 1  is shown in greater detail in  FIG. 4 . 
     FIG. 2  is a diagram of inspection station  100  showing horizontal vision system  200  in accordance with an exemplary embodiment of the present invention. After the fasteners  104  are fed onto rotating turntable  102 , it turns to present the fasteners  104  first to horizontal inspection camera  107  of the horizontal vision system  200 , which views the fastener  104  through optics  108 , as illuminated by transmitted light from light source  109  and collimator  110 . In this manner, silhouette or shadowgraph data can be generated, the data can be compared against a library of acceptable parameters both to categorize the fastener  104 , for the presence of a screw thread of the correct type and pitch, and for the correct dimensions for the fastener type. The light source  109  can have adjustable luminance, and can be adjusted to provide an optimum level of illumination where the contrast of the lighting is approximately the same as the maximum grey scale range of horizontal inspection camera  107 . 
   It is not necessary that rotating turntable  102  remain stationary while the fastener  104  is imaged and categorized since capture of the image can be near instantaneous and once the image is captured the categorization and labeling for rejection will occur while the rotating turntable  102  is indexing onwards. 
     FIG. 3  is a diagram of inspection station  100  showing vertical vision system  300  in accordance with an exemplary embodiment of the present invention. Further rotation of rotating turntable  102  presents the fastener  104  to vertical vision system camera  111 , which can include adjustable lighting head  112  to illuminate fastener  104  using reflected light. Adjustable lighting head  112  provides illumination from a range of directions at variable levels in each direction, so as to illuminate each fastener  104  to provide optimum contrast regardless of the finish on the fastener head. In this manner, vertical vision system camera  111  can be used to determine the delineation of depressions on the fastener head, the outline of the exterior of the head, or other fastener dimensions that may be required to allow the fastener to fit a fastener driving tool. Detection of the optimum contrast is by detection of the best differentiation of edges in the viewed image, and requires a pre-programmed illumination routine to vary the illumination from adjustable lighting head  112  so as to narrow the range of choices of illumination. 
   In one exemplary embodiment, the luminance of adjustable lighting head  112  can be varied rapidly by inspection system  700  or other suitable systems until a level of illumination that provides the greatest contrast is achieved in image data corresponding to the edges found in the fastener  104 . The fastener  104 , which was initially inspected at the horizontal vision system, can now be further inspected as necessary in terms of external drive profile, internal drive profile, overall diameter, or other suitable data. In another exemplary embodiment, rejection data can be associated with the fastener  104  by inspection system  700  or other suitable systems if the dimensions of the fastener  104  fail to fall within a valid category, for instance because the internal drive socket does not meet specifications. 
     FIG. 4  is a diagram of inspection station  100  showing rejection mechanism  400 , in accordance with an exemplary embodiment of the present invention. Motor  118  can be a servomotor, a stepping motor, or other suitable motors. Rotating turntable  102  is turned by motor  118  and is mounted on base  101 . Motor  118  allows the position of the fastener retaining slots  103  as shown in  FIG. 1  to be tracked with accuracy so that the fastener retaining slots  103  can be indexed. 
   As rotating turntable  102  progresses, a fastener  104  that has been determined to be faulty rotates to a position opposite reject solenoid  113 , which is controlled so as to operate and eject the fastener  104  down reject chute  114 . The remaining fasteners  104  are directed by stationary wiper  115  as shown in  FIG. 1  to accept chute  116 . Likewise, other suitable processes can be used, such as the use of an accept solenoid in conjunction with controls over singulating feed mechanism  106  of  FIG. 1  to allow a fastener  104  to be inspected multiple times, such as when image data of the fastener was not adequately obtained and where additional inspection time is required. 
   While one accept chute  116  is shown (and can be disposed within element  117 , as shown), two or more accept chutes  116  can be used, where suitable. Inspection station  100  can thus act as a sorter using mechanisms similar to the reject mechanism  400 , as inspection station  100  can be used to classify the fasteners  104  it inspects as opposed to only determining pass/fail criteria. In one exemplary embodiment, reject mechanism  400  can include a solenoid  113 . 
     FIG. 5  is an overhead view of the fastener locating mechanism on the rotating turntable  102  in accordance with an exemplary embodiment of the present invention. Fasteners  104  are located in fastener retaining slots  103 , which are formed by locating fingers  120  of outer turntable ring  122  and locating fingers  119  of inner turntable ring  121 . Locating fingers  119  of inner turntable ring  121  are configured so as to guide the fasteners  104  into fastener retaining slots  103 . In one exemplary embodiment, inner turntable ring  121  and outer turntable ring  122  can be controllably adjusted so as to increase or decrease the size of fastener retaining slots  103 . 
     FIG. 6  is a breakaway view of the fastener locating mechanism on rotating turntable  102  in accordance with an exemplary embodiment of the present invention. The fastener locating mechanism on rotating turntable  102  can include an outer turntable ring  122  and an inner turntable ring  121 . The outer turntable ring  122  has locating fingers  120 , while the inner turntable ring  121  has locating fingers  119 . Rotation of the inner turntable ring  121  relative to the outer turntable ring  122  allows control of fastener retaining slots  103  within which the fasteners  104  are located. Rotating turntable  102  can thus be adjusted for fasteners  104  of differing diameter. 
   Block  123  locates on dowels  124  on the inner turntable ring  121  and outer turntable ring  122  to positively locate the rings relative to each other. Replacement of block  123  with another of different length allows quick changing of the dimensions of fastener retaining slots  103 . In one exemplary embodiment, a conical block  123  with increasing diameter or other suitable mechanisms can be used to allow the dimension of fastener retaining slots  103  to be altered on-the-fly. 
   In one exemplary embodiment, there may be other vision systems present to inspect the thread form in side view by reflected light to determine if the thread is intact. For example, one can be used around the whole fastener  104 , and another can be used to inspect the lower tip of a fastener  104 . In this exemplary embodiment, the presence of a chisel point in self-drilling fasteners  104  can be detected. 
   The present invention can be used in conjunction with the inspection of any suitable item that has a substantially regular form in two axes, and can be adapted to the inspection of objects of irregular form with limited re-entrant portions. Use in this latter application requires orienting the object on two axes for inspection, rather than the single axis orientation described for the current invention. Such orientation techniques are known. Use of both reflected light and transmitted light to provide sufficient detail of a single axis can also or alternatively be used. 
   In addition to a rotating turntable  102 , other suitable conveying systems can also or alternatively be used, such as ones that are capable of orienting and retaining the object to be recognized. 
   It is to be understood that even though numerous characteristics and advantages of the various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functioning of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail so long as the functioning of the invention is not adversely affected. For example the particular elements of the conveyor or rotating turntable  102  may vary dependent on the particular application for which it is used without variation in the spirit and scope of the present invention. 
     FIG. 7  is a diagram of inspection system  700 , in accordance with an exemplary embodiment of the present invention. Inspection system  700  can be implemented in hardware, software, or a suitable combination of hardware and software, and can be one or more software systems operating on a general-purpose processing platform. Inspection system  700  is coupled to horizontal vision system  200  and vertical vision system  300  and can use suitable image processing techniques to inspect image data of the fasteners  104  that is generated by horizontal vision system  200  and vertical vision system  300 . 
   As used herein, a software system can include one or more objects, agents, threads, lines of code, subroutines, separate software applications, two or more lines of code or other suitable software structures operating in two or more software applications or on two or more processors, or other suitable software structures. In one exemplary embodiment, a software system can include one or more lines of code or other suitable software structures operating in a general purpose software application, such as an operating system, and one or more lines of code or other suitable software structures operating in a specific purpose software application. 
   Inspection system  700  includes fastener image processing system  702 , illumination variation system  704 , and reject control system  706 . In one exemplary embodiment, fastener image processing system  702  includes a library of expected fastener parameters with associated tolerances for the length, diameter, head profile, presence of washer, profile of fastener tip, thread profile and pitch, and other suitable data. Fastener image processing system  702  allows rapid categorization of the currently illuminated fastener  104  and analysis of the dimensional data of the currently illuminated fastener  104 , based on tolerance data. If fastener image processing system  702  determines that the currently illuminated fastener  104  does not meet predetermined tolerance criteria, it generates fastener rejection data. In addition, fastener image processing system  702  can generate illumination variation data if the image data of the currently illuminated fastener does not generate predetermined match data, such as if a match is not found, if one or more critical dimensions can not be determined, or in response to other suitable conditions. 
   Illumination variation system  704  receives illumination variation data and generates control data of one or more lighting devices to controllably vary the luminance generated by the lighting devices. In one exemplary embodiment, illumination variation system  704  can use one or more predetermined settings or functions to vary the luminance of the lighting devices, such as to continuously increase or decrease the luminance, increase or decrease the luminance by a predetermined step, or other suitable settings or functions. 
   Reject control system  706  receives fastener rejection data and generates fastener rejection control data. In one exemplary embodiment, reject control system  706  can receive turntable dimension data, turntable rotation data, inspection position data, reject slot position data, and other suitable data and can generate reject control timing data to allow the rejected fastener  104  to be ejected by a suitable mechanism when it reaches a predetermined position. Likewise, control timing data can be stored, can be associated with an interchangeable turntable, or other suitable processes can be used. 
   Although exemplary embodiments of a system and method of the present invention have been described in detail herein, those skilled in the art will also recognize that various substitutions and modifications can be made to the systems and methods without departing from the scope and spirit of the appended claims.

Technology Category: 4