Method and system for measuring the relief of an object

Abstract

A method and a system for measuring the relief of an object are described herein. The system includes a grid projecting for projecting a grid, an image acquisition apparatus that includes a camera, and a computer. Providing a reference object having common elements with the object to measure, the method includes the steps of a) positioning the grid at three different known positions relative to the camera and the common elements; b) for each position of the grid, projecting the grid unto the reference object and, with the camera, taking an image of the reference object to yield three images having values for each pixel of the camera and c) computing the reference object phase for each pixel using the three reference object intensity values for the corresponding pixel. Steps a), b) and c) are repeated by replacing the reference object by the object to be measured. The difference of height between the object to be measured and the reference object for each pixel are then computed by subtracting the reference object phase and the object phase for the corresponding pixel.

1. A method for measuring the relief of an object using a camera provided with an array of pixels, said method comprising the steps of:
 a) projecting a grid on a reference object; the grid being located at a first position relative to the camera and to the reference object; 
 b) taking, with the camera, an image of the reference object illuminated by said projected grid; said image of the reference object having an intensity values value for each pixel of the reference object image; 
 c) repeating steps a) and b) at least two times with the grid being located each time at two different known positions relative to the camera and to the reference object to yield at least three intensity values for each pixel of the reference object image; 
 d) computing the  a reference object phase for each pixel of the reference object image using three reference object intensity values selected from the at least three reference object intensity values for the corresponding pixel; 
 e) projecting the grid on the object; the grid being located at said first position; 
 f) taking with the camera an image of the object illuminated by said projected grid; said image of the object having an intensity values value for each pixel position of the object image; 
 g) repeating steps e) and f) at least two times with the grid being located each time at said two different known positions to yield at least three intensity values for each pixel of the object image; 
 h) computing the an object phase for each pixel position of the object image using three object intensity values selected from the at least three object intensity values for the corresponding pixel; and 
 i) computing the a difference of height between the object and the reference object for each pixel using said reference object phase and said object phase for the corresponding pixel; and 
 j) using said difference of heights height between the object and the reference object for each said pixel to determine the relief of the object;  
 wherein at least one of the reference object phase and the object phase is computed, in step d) or step h), for each pixel by selecting the three most advantageous intensity values from at least four intensity values. 
 
     
     
       2. A The method as recited in  claim 1 , wherein, in at least one of steps d) and h), the phase ΔΦ is computed for each pixel by solving the following system of equations:
   I n =A+B·cos(ΔΦ+Δφ n )
 
 where I n  represent the at least three intensity values, A and B are known coefficients and Δφ n  are phase variations caused by the different known locations of the grid. 
 
     
     
       3. A The method as recited in  claim 2 , wherein said system of equations is solved using a numerical method. 
     
     
       4. A  The method as recited in  claim 1 , wherein, in step c), steps a) and b) are repeated more than two times with the grid being located at more the than two different known positions relative to the camera and to the reference object to yield said at least three intensity values and at least one additional intensity value for each pixel of the reference object image and, in step d), a selection is performed among the at least three intensity values and the at least one additional values value to yield the three most advantageous intensity values; said three most advantageous intensity values being used to compute the reference object phase for each pixel. 
     
     
       5. A The method as recited in claim  4  1, wherein, in step c), steps a) and b) are repeated more than two times with the grid being located at more than two different known positions relative to the camera and to the reference object to yield more than tree intensity values and, in step d), the three most advantageous values from said more than three most advantageous intensity values are used selected to compute the reference object phase for each pixel of the reference object image. 
     
     
       6. A The method as recited in  claim 1 , wherein, in step g), steps e) and f) are repeated more than two times with the grid being located at more than two different known positions relative to the camera and to the object to yield said at least three intensity values and at least one additional intensity value for each pixel of the object image and, in step h), a selection is performed among the at least three intensity values and the at least one additional values value to yield the three most advantageous intensity values and said three most advantageous intensity values are used to compute the object phase for each pixel. 
     
     
       7. A The method as recited in  claim 1 , wherein, in step g), steps a) e) and b) f) are repeated more than two times with the grid being located at more than two different known positions relative to the camera and to the object to yield more than three intensity values and, in step c) h) the three most advantageous values form from said more than three intensity values are used selected to compute the object phase for each pixel of the objet image. 
     
     
       8. A The method as recited in  claim 1 , wherein, in step c) g), said two different known positions of the grid are chosen so as to provide at least two images of the object having a 180 degrees difference in phase therebetween. 
     
     
       9. A The method as recited in  claim 8 , wherein a two-dimensional image of the object is computed by subtracting adding intensity values for each pixel of said at least two images of the object having a 180 degrees difference in phase therebetween; said two dimensional image being used to perform a preliminary analysis of the object. 
     
     
       10. A The method as recited in  claim 1 , wherein, in step g) c), said two different known positions of the grid are chosen so as to provide at least two images of the reference object having a 180 degrees difference in phase therebetween. 
     
     
       11. A The method as recited in claim  1  10, wherein a two-dimensional image of the reference object is computed by subtracting adding intensity values for each pixel of said at least two images of the reference object having a 180 degrees difference in phase therebetween; said two dimensional image being used to perform a preliminary analysis of the reference object. 
     
     
       12. A The method as recited in  claim 1 , wherein said reference object is a plane surface. 
     
     
       13. A The method as recited in  claim 1 , wherein said reference object is said object at a past predetermined time and said reference object phase is computed around said past time; whereby step i) provides the variation of height at each pixel between said past time and take approximate time when the object phase is computed and said step j) yields the variation with time of relief of the object. 
     
     
       14. A method as recited of  claim 1 , for measuring the relief of an object using a camera provided with an array of pixels, said method comprising the steps of:
 a) projecting a grid on a reference object; the grid being located at a first position relative to the camera and to the reference object; 
 b) taking, with the camera, an image of the reference object illuminated by said projected grid; said image of the reference object having an intensity values for each pixel of the reference object image; 
 c) repeating steps a) and b) at least two times with the grid being located each time at different known positions relative to the camera and to the reference object to yield at least three intensity values for each pixel of the reference object image; 
 d) computing a reference object phase for each pixel of the reference object image using three reference object intensity values selected from the at least three reference object intensity values for the corresponding pixel; 
 e) projecting the grid on the object; the grid being located at said first position; 
 f) taking with the camera an image of the object illuminated by said projected grid; said image of the object having an intensity values for each pixel of the object image; 
 g) repeating steps e) and f) at least two times with the grid being located each time at said different known positions to yield at least three intensity values for each pixel of the object image, 
 h) computing an object phase for each pixel of the object image using three object intensity values selected from the at least three object intensity values for the corresponding pixel; 
 i) computing a difference of height between the object and the reference object for each pixel using said reference object phase and said object phase for the corresponding pixel; and 
 j) using said difference of heights between the object and the reference object for each said pixel to determine the relief of the object; 
 wherein said reference object is a CAD of the object; said grid being virtually positioned and projected into said CAD in step a) and said image of said reference object being simulated in step b). 
 
     
     
       15. A system for measuring the relief of an object, said system comprising: a grid projecting assembly; an image acquisition apparatus including a camera provided with an array of pixels; a computer configured for
 a) receiving from the image acquisition apparatus at least three images of the projected grid onto the object and at least three images of the projected grid onto the reference object; each of said images of the projected grid onto the object corresponding to a different known position of the grid; each of said images of the projected grid onto the reference object corresponding to one of said different known positions of the grid; 
 b) computing the a reference object phase for each pixel using the three reference object intensity values selected from at least three reference object intensity values for the corresponding pixel in said at least three images of the projected grid onto the reference object; 
 c) computing the an object phase for each pixel using the three object intensity values selected from at least three object intensity values for the corresponding pixel in said at least three images of the projected grid onto the object; and 
 d) computing the a difference of height between the object and the reference object for each pixel using said reference object phase and said object phase for the corresponding pixel; and 
 e) using said difference of heights height between the object and the reference object for each said pixel to determine the relief of the object; 
 wherein the computer is configured to compute at least one of the reference object phase and the object phase for each pixel by selecting the three most advantageous intensity values from at least four intensity values. 
 
     
     
       16. The use of the method of  claim 1  for A method for measuring the relief of an object using a camera provided with an array of pixels to perform lead-coplanarity inspection., said method comprising the steps of:
 a) projecting a grid on a reference object; the grid being located at a first position relative to the camera and to the reference object; 
 b) taking, with the camera, an image of the reference object illuminated by said projected grid; said image of the reference object having an intensity value for each pixel of the reference object image; 
 c) repeating steps a) and b) at least two times with the grid being located each time at different known positions relative to the camera and to the reference object to yield at least three intensity values for each pixel of the reference object image; 
 d) computing a reference object phase for each pixel of the reference object image using three reference object intensity values selected from the at least three reference object intensity values for the corresponding pixel; 
 e) projecting the grid on the object; the grid being located at said first position; 
 f) taking with the camera an image of the object illuminated by said projected grid; said image of the object having an intensity value for each pixel of the object image; 
 g) repeating steps e) and f) at least two times with the grid being located each time at said different known positions to yield at least three intensity values for each pixel of the object image; 
 h) computing an object phase for each pixel of the object image using three object intensity values selected from the at least three object intensity values for the corresponding pixel; 
 i) computing a difference of height between the object and the reference object for each pixel using said reference object phase and said object phase for the corresponding pixel; and 
 j) using said difference of height between the object and the reference object for each said pixel to determine the relief of the object; 
 
       wherein at least one of the reference object phase and the object phase is computed, in step d) or step h), for each pixel by selecting the three most advantageous intensity values from at least four intensity values. 
     
     
       17. The system as recited in claim 15, wherein said grid projecting assembly is adapted to project onto the object a grid of white light.