Patent Abstract:
A magnetic indexer for locating a device producing a magnetic field in a blind or inaccessible position of a work piece. A magnet is initially placed on a first side of the work piece such that a magnetic field produced by the magnet extends through the work piece and substantially perpendicular to a surface of the work piece. A device comprising a plurality of probes for sensing magnetic fields is then positioned over a second surface of the work piece. The probes are then moved over the second surface to determine the location of the axis of the magnet via the strength of the sensed magnetic field. Once the position of the axis of the magnet is determined, the work surface is either marked or worked on through the platform on which the probes are positioned. In particular, a hole may be accurately drilled or otherwise formed directly over the magnet even when the first surface of the work piece cannot be seen. Additionally, the present invention allows a very accurate positioning of a work tool on the second surface without the need to first visualize the first surface of the work piece.

Full Description:
This application is a continuation of U.S. patent application Ser. No. 10/448,560 filed on May 3, 2003, now U.S. Pat. No. 6,927,560 issued on Aug. 9, 2005, which is a continuation-in-part of Ser. No. 10/143,242 filed on May 9, 2002, now U.S. Pat. No. 7,498,796 issued on Mar. 3, 2009, the disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a system to precisely form holes, and more particularly to a system to locate a device and indicate a location to form a hole. 
     BACKGROUND OF THE INVENTION 
     It is often desirable to locate, with a high degree of accuracy and specificity, locations in a blind area of a working surface. In particular, if it is desired to affix together two portions of a structure, where only an outside surface is visible to a work person, it is often difficult, if not impossible, to precisely and reproducibly place a fastener between the two portions. This is particularly relevant in regards to aircraft where the skin of the aircraft is placed over an internal frame structure and must be affixed thereto. Once the skin is in place, it is often very difficult to properly locate a fastener that must first go through the skin to be affixed to the internal structure of the aircraft. This situation arises in other construction and manufacturing instances as well. 
     One solution has been the attempt to back drill from inside the structure. That is, to have a work person physically place themselves inside the structure and then cut through the sub-structure through the skin. This, however, often creates impreciseness in the hole creation. For example, the full sized hole which is formed normal to the skin of the air craft, which is following the back drilled pilot hole, may be angular. That is because the hole formed from the inside of the skin can not be easily formed exactly normal to the skin of the aircraft. In particular the internal structures of the part may not be normal to the skin while the hole on through the outside of the skin must be normal to the skin. Furthermore, it is very hard on the work person who must crawl into the usually small areas to produce the holes. 
     Backmarkers are widely used in the aircraft industry to transfer holes from the understructure to the outside surface. Backmarkers consist of a long split piece of thin metal with a pin on one side and a hole on the other that are in alignment. The pin side is slipped under the skin to line up with a pilot hole, in the understructure, and a pilot hole is drilled into the outer skin. This method does not work on wide parts and thick parts. Deflection of the split plates and the difficulty of installing the device on thick parts limits the use to thin sheet metal areas near the edge of the skin. 
     Another method is to use a probe or locating device to determine a precise position on the skin. In particular, the device is first programmed with locations in three dimensional space. Therefore, when a surface is placed within reach of the probe, the probe can determine the location of a point which the probe touches. This, however, requires an extensive pre-programming and precise placement of the surface which is to be probed. Using such special orientation probes increases time and manufacturing costs for many applications. Also, probing the understructure before drilling has several shortcomings. When a skin is placed over a built up structure, the weight of the skin causes the structure and tooling to deform. It is possible that probed holes will move between measurements and drilling. Also, temperature changes between probing and drilling can cause the holes to not align due to growth or shrinkage to the part and differences in growth between the upper and lower surfaces. Fastener induced growth and coldworking of holes in aircraft structure can also shift positions of the holes between probing and drilling. 
     In aircraft construction, it is often critical to produce a hole, for fastening a portion of the airframe to another portion, within hundredths of an inch. One specific method of construction for internal airframe structure involves the use of sine wave topography on the internal structures or beams of the aircraft. To ensure a sufficiently strong connection, which will withstand the extreme stresses that an aircraft will encounter, the fastener must be placed at a peak of the sine wave. Therefore, placement of a fastener must be extremely precise to ensure that a peak is hit, rather than a valley or a portion adjacent to the peak. It is also desirable to precisely locate edges of hidden structure pieces. In this and many other applications, the precise locating of the fastener becomes critically important. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a magnetic indexer which locates a device that is producing a magnetic field in a blind or inaccessible position. A magnet is initially placed on one side of the work surface such that a magnetic field produced by the magnet extends through the work surface such that the axis of the magnetic field is substantially perpendicular to the work surface. The device, comprising a plurality of probes which are affected by magnetic fields, is positioned over the opposite side of the work surface. The probes are then moved over the work surface to determine the location of the magnet. Once the position of the magnetic field axis is determined, the work surface is either marked or worked on through the platform on which the probes are positioned. In particular, a hole may be reproducibly placed directly over the magnet even when the underside of the work piece is not visible. Additionally, with the present invention, a work tool may be very accurately positioned on the work surface without seeing the underside of the work surface. 
     A first embodiment of the present invention includes a system for determining a location of a device that produces a field having varying strengths depending upon a lateral distance from the device. The system comprises a probe adapted to be affected by the varying strength of the field produced by the device and which assists in locating the device. As the probe is moved a processor determines the field strength affecting the probe. A confirmation system provides a physical confirmation that the processor has determined the location of the device with the probe. 
     A second embodiment of the present invention includes a system to determine a location of a device through a surface. The system comprises a device, which produces a magnetic field, positioned on a first side of the surface. A probe is positioned on a second side of the surface affected by the field. A processor determines the affect produced in the probe by the field. The processor is adapted to determine the position of the device based upon the affect of the field on the probe. 
     The present invention also provides a new method to precisely locate a position. The method involves locating a device, which produces a field, with a probe affected by the field. The device is placed on a first side of a surface. A field is then produced with the device through the surface. A probe is used on a second side of the surface to determine a center axis of the field and to provide a physical confirmation of the center axis of the field. Once the location of the center axis of the field is determined then work may be performed at a precise and predetermined location. 
     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 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a preferred embodiment of the digital magnetizer according to the present invention; 
         FIG. 2  is a side elevational view of the magnetic indexer according to the present invention; 
         FIG. 3  is a perspective view of the magnetic indexer in use; 
         FIG. 4  is a perspective view of the platform of the magnetic indexer after it has been positioned; 
         FIG. 5  is a perspective view of a magnetic indexer according to a second embodiment of the present invention; and 
         FIG. 6  is a perspective view of a third embodiment of the magnetic indexer affixed to a robot. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     With reference to  FIGS. 1 and 2 , a magnetic indexer  10  in accordance with a preferred embodiment of the present invention is shown. The magnetic indexer  10  includes a vacuum attachment member  12 , a work piece platform  14 , a probe platform  16  and a plurality of probes  18 ,  20 , and  22 . The vacuum attachment member  12  generally includes members in which a vacuum may be created, so as to affix the work piece platform  14  to a work piece (described further herein). It will be understood, however, that any appropriate system suitable for attaching the work piece platform  14  to a work piece may be used. Extending generally perpendicular from the work piece platform  14  are stabilizing members  24  ( FIG. 2 ) which engage the work piece to ensure that the work piece platform  14  is substantially parallel to the work piece. A magnet  26  is positioned on an opposite side of the work piece from the work piece platform  14 . The magnet  26  produces a magnetic field which has a central magnetic axis  26   a . Extending from the work piece platform  14  is the probe platform  16 . The probe platform  16  is moveable relative to the work piece platform  14 . A first set of adjustment screws  28  allow for movement of the probe platform  16  in a first axis A. A second set of adjustment screws  30  allow for adjustment of the probe platform  16  along a second axis B. Therefore the probe platform  16  may be moved, relative to the work piece platform  14 , using the first set of adjustment screws  28  and the second set of adjustment screws  30 , in two dimensions. 
     Affixed to the probe platform  16  are probes  18 ,  20  and  22 . The probes  18 ,  20  and  22  are spaced apart so that the probes define a center axis C. The center axis C is an axis equidistant from, but parallel to, an axis along which each of the probes  18 ,  20  and  22  extend. 
     The probes  18 ,  20 ,  22  are affixed to a secondary probe platform  32  which is affixed to the probe platform  16  with a fastener  33 . This allows the secondary probe platform  32  to be removed from the probe platform  16  without moving the work piece platform  14 . 
     With reference to  FIGS. 3 and 4 , the effect of each probe  18 ,  20 ,  22  is determined by a processor  34 . The processor  34  may be any appropriate processor, however, a microprocessor is able to determine the effect of the magnetic field on each of the probes  18 ,  20 ,  22  and to determine the relative orientation of each of the probes  18 ,  20 , and  22  to the magnetic field. The processor&#39;s  34  determination is displayed on a display device  35 . In particular, a CRT or LCD screen may be used as the display device  35 . The processor  34  can display on the display device  35  a confirmation that the center axis C is co-linear with the magnetic axis  26   a    
     The magnetic indexer  10  is affixed to a surface or work piece  36  with the vacuum attachment members  12 . As discussed above, the vacuum attachment members  12  may affix the work piece platform  14  to the work piece  36  through any appropriate means. For example, a vacuum may be created within the vacuum attachment members  12  allowing the work piece platform  14  to be held in place. It will also be understood that more than two vacuum attachment members  12  may be used depending upon the size of the work piece platform  14 . 
     Below the work piece  36  is a sub-structure or support beam  38 . At the position where a hole must be produced, a magnet  26  has been placed. The magnet  26  is placed on the beam  38  in a preliminary manufacturing step before the work piece platform  14  is secured to the work piece  36 . Because of this, the magnet  26  is able to be easily placed in the exact position where a hole must be produced for an attachment between the work piece  36  and the beam  38 . The magnetic indexer  10  is placed over a position relatively close to where the hole must be produced. Then, using the adjustment screws  28 ,  30 , the probe platform  16  is adjusted until the center axis C is directly over or co-linear with the magnetic axis  26   a  (through a process described more fully herein). 
     Once the center axis C is aligned directly over the magnetic axis  26   a , the secondary probe platform  32  is removed so that a drill bit  40  may drill through the probe platform  16  and work piece platform  14  to produce a hole in the work piece  36 . It will be understood that additional drill guide members may be put in place of the secondary probe platform  32  to increase the precision of the drilling step performed by the drill bit  40  as it proceeds through the magnetic indexer  10 . 
     Once the hole is produced through the work piece  36  and the beam  38 , the magnet  26  is removed during a clean up process of the internal area. Furthermore, the magnetic indexer  10  is then removed from the work piece  36  by pressurizing the vacuum attachment members  12  to remove the magnetic indexer  10  from the work piece  36 . Then, any appropriate fastener is used to affix the work piece  36  permanently to the beam  38 . 
     The exact location of the magnet  26  is determined by locating the magnetic axis  26   a  which is a north-south (N-S) pole axis of the magnet  26 . The magnetic axis  26   a , also termed the center or field axis, of the magnet  26  is the center of the magnetic field and the area where the magnetic field is the strongest. The magnet  26  is placed on the beam  38  so that the magnetic axis  26   a  is substantially perpendicular to the surface of the beam  38 . Therefore, once the work piece  36  is affixed to the beam  38 , the magnetic axis  26   a  is also perpendicular to the surface of the work piece  36 . Additionally, the work piece  36  should not interfere with the magnetic field produced by the magnet  26 . It will be understood, however, that as long as the magnetic field of the magnet  26  is powerful enough for the probes  18 ,  20 ,  22  to sense the field produced by the magnet  26 , the work piece  36  may be formed of virtually any non-magnetic material. 
     It will be understood that a reference to a single probe  18  in the following description is exemplary of each of the probes  18 ,  20 ,  22  and its description as a single probe is merely for clarity. The probe  18  is affected by, that is the probe  18  senses, the magnetic field produced by the magnet  26 . One exemplary probe type is a Hall-Effect probe. In the Hall-Effect probe  18 , the magnetic field produced by the magnet  26  creates a voltage when a current is running perpendicular to the field in the Hall-Effect probe  18 . The Hall-Effect probe  18  measures the induced voltage produced due to the magnetic field of the magnet  26 . Knowing the induced voltage, and the current, the strength of the magnetic field is determined using the equation V H ned/I=B. According to the equation, V H  is equal to the Hall-voltage, n is equal to the charge carrier density, e is equal to the electronic charge, d is equal to the strip width, and I is equal to the current. This equation results in B which is the strength of magnetic field. Once the strength of the magnetic field is known by use of the Hall-Effect probe  18 , the location of the magnetic axis  26   a  may be determined. The closer the Hall-Effect probe  18  is to the magnetic axis  26   a , the greater the response in the Hall-Effect probe  18 . According to the first embodiment, the magnetic axis  26   a  is located co-linear with the center axis C of the probes  18 ,  20 , and  22  when the response by each of the probes  18 ,  20 , and  22  is substantially equal. 
     The processor  34  determines and processes the affect produced on each of the probes  18 ,  20 , and  22 . The display device  35  displays the affect determined by the processor  34 . The processor  34  may also indicate which way the probe platform  16  should be moved, using the adjustment screws  28 ,  30 , to correctly position the center axis C over the magnetic axis  26   a . Then, once each of the probes  18 ,  20 ,  22  indicates an equivalent response, it is known that the center axis C is positioned directly over the magnetic axis  26   a . At this point, the display indicates that the center axis C is over the magnetic axis  26   a  and that the operator should make no further adjustments. In particular, the center axis C is co-linear with the magnetic axis  26   a  of the magnet  26 . Once it is displayed that the center axis C is over the magnetic axis  26   a , the secondary probe platform  32  is removed so that the drill point or bit  40  may be introduced to produce the desired hole. 
     With reference to  FIG. 5 , a second embodiment of a magnetic indexer system  50  includes a moveable sensor canister  52  with directional or signaling LEDs  54 ,  56 ,  58  and  60  affixed to the top of the moveable canister  52 . Each LED  54 ,  56 ,  58 , and  60  may include an array of LEDs such that a strength of the response in a particular direction can be indicated. Placed centrally and along a center axis D is a marker  62  which extends through the moveable canister  52  to selectively engage the work piece  36 . The center axis D relates to probes  64 ,  66  and  68  as center axis C relates to probes  18 ,  20 ,  22  according to the first embodiment. 
     Each of the probes  64 ,  66  and  68  are connected to a processor  70 . The probes  64 ,  66  and  68  work substantially similarly to the probes  18 ,  20  and  22  described in reference to the first embodiment. The processor  70  also works similar to the processor  34  discussed above. In the magnetic indexer  50 , however, the processor  70  determines the location of the center axis D relative to the magnetic axis  26   a  and illuminates the appropriate LED  54 ,  56 ,  58  and  60  indicating the direction the moveable canister  52  must be moved to properly align the center axis D with the magnetic axis  26   a . Once the center axis D is placed substantially co-linear with the magnetic axis  26   a  of the magnet  26 , all four LED arrays  54 ,  56 ,  58  and  60  illuminate to show that the center axis D is properly aligned over the magnetic axis  26   a . That is, when all four LEDs  54 ,  56 ,  58 ,  60  are illuminated, they create a visual confirmation that the magnetic axis  26   a  is positioned substantially co-linear with the center axis D. At this point, the marker  62  may be depressed to form a mark at the position on the work piece  36 . 
     Once the mark has been made, the moveable canister  52  is simply removed from the work piece  36  and proper chucks may be affixed to the work piece  36  to ensure that a properly aligned hole is produced in the work piece  36 . Again, once the hole is formed through the work piece  36  and the beam  38 , the magnet  26  and any debris may be cleaned out of the internal space. 
     With reference to  FIG. 6 , a third embodiment of a magnetic indexer  80  is illustrated. The magnetic indexer  80  includes a single probe  82  which is affixed to an arm  84  of a robot  86 . It will be understood that a plurality of probes can also be used with the robot  86 . Only one probe  82 , however, is necessary if placed next to the surface  88  in one location and then moved to another location along the surface  88  with an exact knowledge of the first location. Therefore, an effective plurality of probes is simulated by simply placing and moving the single probe  82  and exactly recalling the previous placements, and the field measurements, for each of the previous placements. 
     A magnet  90 , which produces a magnetic field having a central magnetic axis  90   a , is placed near the surface  88  opposite the magnetic indexer  80 . A processor  94  determines the response of the probe  82  and controls the robot  86 . In this way, the robot  86  can quickly locate the magnetic axis  90   a , of the magnet  90 , affixed to the support sheet  92 . It will be understood, however, that separate processors may be used to determine the location of the magnetic axis  90   a  and control the robot  86 . In addition, once the processor  94  has determined the exact location of the magnetic axis  90   a , a tool may be placed on the robot arm  84  to produce the hole required. It will also be understood that a plurality of arms may extend from the robot  86  so that once the position of the magnetic axis  90   a  is located, a tool arm simply rotates in place with a tool extending from the tool arm to produce the hole in the surface  88 . When a robot  86  is used, producing a hole serves to confirm that the magnet  90  has been properly located. 
     It will be understood that each embodiment of the present invention does not require a Hall-Effect probe. Any probe which is sensitive to or which can detect the magnetic field produced by the magnet  26 ,  90  may be used in the present invention. One alternative probe is a Three-Axis Magnetic Sensor Hybrid HMC2003 produced by Solid State Electronics Center, a division of Honeywell. The other portions of the magnetic indexer  10  are reproduced while simply replacing the Hall-Effect probe  18  with the alternative probe. If the alternative probe, such as the HMC2003, is able to determine a magnetic axis in more than one relative axis, then only one probe may be necessary on the magnetic indexer  10 . It is still understood, however, that the single alternative probe still defines a central probe axis for determining the magnetic axis  26   a ,  90   a . The alternative probe is still able to detect the field produced by the magnet  26 ,  90  and is able to indicate the magnetic axis  26   a ,  90   a.    
     It will also be understood that the magnet used in the present invention must have their magnetic axis  26   a ,  90   a  properly and precisely aligned. Therefore, it may be desirable to first test the magnet  26 ,  90  using the magnetic indexer  10  to ensure that the magnetic axis  26   a ,  90   a  is properly aligned so that when the magnet  26 ,  90  is affixed to the beam  38  or the support sheet  92 , the magnetic axis  26   a ,  90   a  is substantially perpendicular to the surface of the work piece  36 ,  88 . This is because only when the magnetic axis  26   a ,  90   a  is produced substantially perpendicular to the surface is the strength of the field weakened sequentially as one moves away from the magnetic axis  26   a ,  90   a . It is the magnetic field acting upon the probes which is sensed by the probes  18 ,  20 ,  22 ;  64 ,  66 ,  68 ; and  82 , which are used to determine where the magnets  26 ,  90  are positioned. If the magnetic axis  26   a ,  90   a  is angled to the surface (i.e., not perpendicular), the magnetic field would also not be perpendicular and the precise location of the magnetic axis  26   a ,  90   a  could not be correctly determined. 
     In addition, the magnetic indexer itself can be calibrated or zeroed. This means that the central axis of the magnetic indexer can be precisely determined before performing any tasks with the indexer. Generally, a magnetic source having a known magnetic axis can be placed at a zeroed position relative to the magnetic indexer, so that the magnetic indexer can be zeroed to that magnetic axis. After this, the precise zeroed position of the magnetic indexer is known and even greater preciseness can be attained with the magnetic indexer to locate a magnetic axis. 
     The preferred embodiments of the present invention thus provide a means to quickly and precisely detect the locations where holes need to be drilled in a work piece based on previously made hole location determinations that are otherwise not visible to an operator or optical detection machine. The preferred embodiments also allow for the precise detection of any non-visible landmark as well. That is, the present invention may be used to determine edges of hidden pieces as well. The present invention is especially well suited for aircraft manufacturing applications, but it will be appreciated that the invention will find utility in a wide variety of other manufacturing applications as well. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Technology Classification (CPC): 1