Method and apparatus for locating non-visible objects

Abstract

Non-visible objects which differ in their physical properties from their surroundings by association with a variable strength magnetic field may be detected by a suitable array of Hall effect sensors which can be moved relative to the object in question. By analysing the signals from the plurality of the sensors in the array, the position of the object can be deduced relative to the array and the array moved to enable a machining guide thereon to be aligned with the non-visible object. The system is of particular value in locating apertures ( 2 ) in wing spars ( 1 ) when attempting to fix the skin ( 3 ) of the wing on to them where it is important to be able to locate the correct point at which to drill a hole through the skin ( 3 ) to coincide with the hole ( 2 ) in the spar. By locating a magnet ( 4 ) relative to the hole to identify the hole magnetically and using an array of Hall sensors ( 12 ) in a base with an aperture ( 14 ), it is possible to shift the array ( 10 ) so that the aperture ( 14 ) is precisely aligned with the non-visible hole ( 2 ).

1 . A method of locating an object lying behind an opaque surface rendering the object non-visible which comprises providing in the neighbourhood of the object a variable strength magnetic field, sensing the magnetic field strength at a plurality of positions relative to the object using an array of Hall effect magnetic sensors, the array of Hall effect sensors being associated geometrically with a machining guide, such that the machining guide and the array of sensors are fixed positionally one relative to the other, interrogating the sensors to determine the value of the field strength at at least the majority of the sensors, analysing the sensor responses to determine the displacement between the object and the machining guide, and moving the array and machining guide to a position in which the displacement is a minimum.  
   
   
       2 . A method according to  claim 1  wherein once the machining guide is located adjacent the surface at that point of the surface immediately and centrally overlying the object in question, the position of the array and machining guide is fixed.  
   
   
       3 . A method according to  claim 1  wherein the fixation is effected by locking the array on to the surface via vacuum pads.  
   
   
       4 . A method according to any one of  claims 1  to  3  wherein the object is a hole relative to which a magnet or body of ferromagnetic material is located.  
   
   
       5 . Apparatus for locating non-visible objects positioned behind an opaque surface, which apparatus comprises means to generate a variable strength magnetic field, a base member adapted to be placed on or against the surface, means in the base member defining a machining guide, an array of Hall effect sensors located relative to the machining guide, and means for collecting and analysing outputs from at least some of the sensors to provide an indication of the variation of the magnetic field associated with the object relative to the position of the base member.  
   
   
       6 . Apparatus according to  claim 5  wherein the base member is adapted to be moved across the surface to enable the machining guide to be aligned with the object.  
   
   
       7 . Apparatus according to  claim 5  or  6  and including fixing means adapted to lock the position of the base member and the object relative to one another.  
   
   
       8 . Apparatus according to any one of  claims 4  to  6  and wherein the means for analysing includes a visual display means adapted to indicate the location of the object relative to the array of sensors, and accordingly to indicate when the array is positioned with the machining guide associated therewith located closest to the non-visible object.  
   
   
       9 . Apparatus according to any one of  claims 5  to  8  wherein the array of Hall effect sensors is a cruciform array.  
   
   
       10 . Apparatus according to any one of  claims 5  to  9  wherein the signal display is a computer-driven flat display screen adapted to represent in appropriate symbolic fashion the location of the object and the location of the machining guide.  
   
   
       11 . A method of locating an object lying behind an opaque surface rendering the object non-visible which comprises providing in the neighborhood of the object a variable strength magnetic field, sensing the magnetic field strength at a plurality of positions relative to the object using an array of Hall effect magnetic sensors, the array of Hall effect sensors being associated geometrically with a machining guide, such that the machining guide and the array of sensors are fixed positionally one relative to the other, interrogating the sensors to determine the value of the field strength at at least the majority of the sensors, analyzing the sensor responses to determine the displacement between the object and the machining guide, and moving the array and machining guide to a position in which the displacement is a minimum.  
   
   
       12 . The method of  claim 11 , wherein the object is a hole relative to which a magnet or body of ferromagnetic material is located.  
   
   
       13 . The method of  claim 11 , wherein once the machining guide is located adjacent the surface at that point of the surface immediately and centrally overlying the object in question, the position of the array and machining guide is fixed.  
   
   
       14 . The method of  claim 13 , wherein the object is a hole relative to which a magnet or body of ferromagnetic material is located.  
   
   
       15 . The method of  claim 11 , wherein the fixation is effected by locking the array on to the surface via vacuum pads.  
   
   
       16 . The method of  claim 15 , wherein the object is a hole relative to which a magnet or body of ferromagnetic material is located.  
   
   
       17 . An apparatus for locating non-visible objects positioned behind an opaque surface, which apparatus comprises means to generate a variable strength magnetic field, a base member adapted to be placed on or against the surface, means in the base member defining a machining guide, an array of Hall effect sensors located relative to the machining guide, and means for collecting and analyzing outputs from at least some of the sensors to provide an indication of the variation of the magnetic field associated with the object relative to the position of the base member.  
   
   
       18 . The apparatus of  claim 17 , further including fixing means adapted to lock the position of the base member and the object relative to one another.  
   
   
       19 . The apparatus of  claim 17 , wherein the base member is adapted to be moved across the surface to enable the machining guide to be aligned with the object.  
   
   
       20 . The apparatus of  claim 19 , further including fixing means adapted to lock the position of the base member and the object relative to one another.  
   
   
       21 . The apparatus of  claim 19 , wherein the array of Hall effect sensors is a cruciform array.  
   
   
       22 . The apparatus of  claim 19 , wherein the means for analyzing includes a visual display means adapted to indicate the location of the object relative to the array of sensors, and accordingly to indicate when the array is positioned with the machining guide associated therewith located closest to the non-visible object.  
   
   
       23 . The apparatus of  claim 22 , wherein the visual display is a computer-driven flat display screen adapted to represent in appropriate symbolic fashion the location of the object and the location of the machining guide.  
   
   
       24 . The apparatus of  claim 17 , wherein the means for analyzing includes a visual display means adapted to indicate the location of the object relative to the array of sensors, and accordingly to indicate when the array is positioned with the machining guide associated therewith located closest to the non-visible object.  
   
   
       25 . The apparatus of  claim 24 , wherein the visual display is a computer-driven flat display screen adapted to represent in appropriate symbolic fashion the location of the object and the location of the machining guide.  
   
   
       26 . The apparatus of  claim 17 , wherein the array of Hall effect sensors is a cruciform array.