Abstract:
The present invention discloses a sensing device for measuring the three dimension shape and its measuring method. The said sensing device includes a projecting device, an observing device, a projecting localizer, an observing localizer and a computer for data processing. The optic axis of the projecting device and the optic axis of the observing device are crossed on the surface of the object by the relative motion and the focusing of the projecting device and the observing device, such that the viewing field of the whole field measurement and the position of the zero-order fringe are determined. The projecting device and the observing device are focused automatically by means of the object distance and the image distance of the projecting device in this viewing field, and the object distance and the image distance of the observing device in this viewing field. The camera in the observing device records the fringe patterns respectively after phase shifting and the computer calculates the three dimension surface shape of the object. The present invention achieves whole-field high accuracy and high speed absolute measurement of the three dimension object shape in the variable viewing field.

Description:
TECHNOLOGICAL FIELD 
   This invention is about a kind of sensing device for 3-D shape measurement and its measuring method, in particular, a sensing device for absolute measurement of object 3-D shape with structured light and its measuring method. 
   BACKGROUND TECHNOLOGY  
   The structured light 3-D shape measurement is a kind of technique available for whole-field measurement of object shape. It can adopt parallel optical axes structure or cross-optical axes structure. The structured light in question includes projected grating and projected moire. These two are often used as the same owing to indefinite difference other than the quantity of gratings between them. 
   Takade and other persons publish the “Fourier Transform Profilometry For The Automatic Measurement Of 3-D Object Shapes” on  Applied Optics  (vol.22, No.24, Dec. 15, 1983,P3977-3982), and Opton Company shows these two structures in the  Moiré Report  issued on its website. Drawing  1  is sketch of parallel optical axes structure, in which the ray from light source  1  is on grating  2 , projective imaging lens  3  projects the grating line image onto object surface  5 ,  4  is virtual reference plane. CCD camera images object surface  5  with deformed grating fringes onto CCD target  7  by observer imaging lens  6 . The key point of this structure is that projection device  8 &#39;s optical axis  9  is coplanar with and parallel to CCD camera&#39;s optical axis  10 , so the projected grating lines received by CCD camera are coplanar contours, which can facilitate to provide intuitional information about height, but the grating must be placed far away from the optical axis of projector so as to image the grating within the field range of observe camera. Parallel optical axes structure has following problems: (1) It is difficult to keep optical axes parallel; (2) the central parts of optical components of projector and camera are out of work, for the large aberration on their edges will bring about large measuring error. 
   Cross-optical axes structure is showed in Drawing  2 . Its components are same to parallel optical axes structure. The ray from light source  1  is on grating  2 , projective imaging lens  3  projects the grating line image on object surface  5 , CCD camera images the object surface  5  with grating fringes on it onto CCD target  7  by observer imaging lens  6 . The difference lies in that projection device&#39;s optical axis  9  crosses CCD camera&#39;s optical axis  10  at the point  0  on virtual reference plane  4  to form conjugate image of grating line. Because the image of grating on virtual reference plane  4  are not uniformly spaced fringes, unless pupil is at infinite distance, i.e., telemetric optical system. The projected grating lines received by CCD camera is non-coplanar contours. Cross-optical axes structure is easy to be produced and it utilizes effectively projection device and CCD camera&#39;s field of view to decrease measuring error. 
   American U.S. Pat. No. 5,175,601 declares a high-speed 3-D surface measurement, surface inspection and reverse CAD system. It uses cross-optical axes projected grating to measure 3-D object shape in a fixed field of view. 
   3-D shape phase measurement technique often adopts FFT and phase-shift methods to deal with data. In the case of FFT, the initial phase modulation on reference plane can be removed automatically, so FFT is applicable for both parallel optical axes structure and cross-optical axes structure. However, because the high-frequency components are filtered with FFT, the resolution of small shape changes at hole or edge is lower. 
   The phase-shift method of technique above, compared with FFT, has a higher depth resolution and horizontal resolution, and also can measure small shape changes such as hole and edge of surface. But phase-shift method is only applicable for parallel optical axes structure. 
   There are two puzzles in the application of phase-shift method on cross-optical axes 3-D shape measurement technique. (1) Like that in  Scanning moiré method and automatic measurement of  3- D shapes  by Masanori Idesawa on  Applied Optics  (vol. 16, No.8 August1977, pp2152-2162), the contours described by grating fringes on object surface form a function of fringe order, and the difference in height of contours is not equidistant, instead, it is also a function of fringe order. Therefore, in order to get absolute measurement of 3-D object shape, the absolute fringe order of grating lines must be measured accurately, that is to say, to determine the position of zero-order fringe. But at present we have not the equipment or method to determine the position of zero-order fringe. (2) As a whole-field-of-view measuring device, its optical system shall have a variable field of view. Under a certain field of view, the distances from projection optical system and viewing optical system to object (object distance) and to projected grating and observation plane (image distance) need be measured accurately. But all these can&#39;t be settled by technology of today. As a result, the existing cross optical axes measuring device takes a field of view with a certain operating distance as fixed field of view, and gives parameters under the said field of view and marks corresponding relationship between phase and height. Because the calibrated error will influence measurement accuracy, the high-precision whole-field measurement of 3-D object shape is impossible. 
   CONTENT OF THE INVENTION 
   The purpose of this invention is to make up the disadvantages of existing structured light object shape measuring method and device with cross optical axes and to provide a new sensing device for 3-D shape measurement. The projection device and observation device of the sensing device in question can be pancratic through their relative motion to realize the crossing of optical axes, change projected object distance and image distance, observed object distance and image distance, determine the position of zero-order fringe, and achieve the high-precision whole-field measurement of variable field of view under the precondition of structured light real-time measurement. 
   Another purpose of this invention is to provide a method for 3-D object shape measurement by above-mentioned 3-D shape measurement sensing device. This method adopts cross optical axes, changes such operating distances as projected object distance and image distance, observed object distance and image distance to determine the objects of various sizes. Due to its accurate determination of the position of zero-order fringe, it can improve measurement accuracy greatly and achieve a high-precision whole-field measurement of object under the precondition of structured light real-time measurement. In order to reach purposes above, this invention adopts the following technical solution: a sensing device for 3-D shape measurement, including projecting grating or projection device mark point and receiving grating or observation device mark point. The projection device and observation device are placed respectively on projecting positioner and observing positioner that can move relatively to make projection device&#39;s and observation device&#39;s optical axes cross so as to measure projected object distance and image distance, observed object distance and image distance. 
   Where, the relative motion of projection device and observation device includes at least adjusting the relative position of projecting positioner and observing positioner to change the relative distance between projection device and observation device. 
   The change in the position of projection device and observation device above mentioned can be realized by removing either projecting positioner or observing positioner. 
   Where, the relative motion of projection device and observation device also includes relative rotating projection device and observation device to adjust the angle of optical axes of projection device and observation device. This relative rotation refers to at least the running of either projection device or observation device. 
   Where, projection device and observation device rotate do relative one-dimensional rotation around projection device mark point and observation device mark point. 
   Projecting positioner and observing positioner of this invention at least consist of: projection slider, observation slider and rectilinear motion axis. Projection slider and observation slider can be installed sliding on rectilinear motion axis. 
   Or, projecting positioner and observing positioner at least consist of: projection rotary positioning table, observation rotary positioning table and rectilinear motion axis. Projection rotary positioning table and observation rotary positioning table are placed on rectilinear motion axis. 
   Or, projecting positioner and observing positioner consist of: projection slider, observation slider, rectilinear motion axis, projection rotary positioning table and observation rotary positioning table. Projection slider and observation slider are installed sliding at least one rectilinear motion axis. On the sliders place projection rotary positioning table and observation rotary positioning table respectively, on which place projection device and observation device respectively. 
   In terms of the relative motion of projection device and observation device in this invention, mark points of projection device and observation device are on the same straight line before or after the displacement. In such case projection slider and observation slider can be installed sliding on one rectilinear motion axis. 
   Where, the line of rotational centers of two rotary positioning tables is parallel to rectilinear motion axis. 
   Where, projection mark point coincides with the rotational center of projection rotary positioning table, and observation mark point coincides with the rotational center of observation rotary positioning table. 
   Where, projection device and observation device are pancratic and can define the image of mark point sharply by focusing. 
   The projection device of this invention consists of: light source, projection condenser that collects the rays from the light source, movable grating, mark point used to cross optical axes of projection device and observation device, movable pancreatic projective lens that can image grating or mark point. 
   Where, projection device also includes projecting linear positioner that enables projective lens to focus along the optical axis. 
   In addition, projection device includes grating phase-shift linear positioner that enables grating to move in the plane of grating lines. 
   The observation device of this invention consists of: (movable for focusing) observer imaging lens that enables the projective imaging of mark subpoint or grating lines on object, observation mark point aiming at the mark subpoint on object surface, camera imaging lens that receives the image produced by observation lens, and CCD camera that receives image signals. 
   Observation device also includes: movable observer imaging lens that enables the projective imaging of mark subpoint or grating lines on object, observation mark point aiming at the mark subpoint on object surface, observation grating used for interference with projected grating, camera imaging lens that receives the interference fringes formed by observation grating, and CCD camera that receives image signals. 
   Observation device also includes observing linear positioner that enables observation lens to focus along the optical axis. 
   The mark point of this invention may be cross wire, ring or spot. 
   The further-developed sensing device of this invention will also include image capture board for digitization of image signals and computer for data processing. 
   The technical solutions above mentioned can be combined with each other to develop a new one. 
   The above measuring method of 3-D object shape by 3-D shape measurement sensing device involves following steps: 
   1) Utilize the relative motion of projection device and observation device, and the focusing of projection device and observation device to enable projection device&#39;s optical axis and observation device&#39;s optical axis to cross on the object surface, to determine the field of view of whole-field measurement and position of zero-order fringe; 
   2) Utilize the triangle formed by projection device&#39;s mark point, observation device&#39;s mark point and crossing of their optical axes to measure indirectly the projection working distance and observation working distance; 
   3) Calculate projected object distance, projected image distance, observed object distance and observed image distance; 
   4) Projection device will finish AF imaging of grating on object surface, and observation device will finish AF imaging of grating fringes on object surface; 
   5) Data processing. 
   In step 1), projection device finishes the clear imaging of projection mark point on the object. Observation device finishes the clear imaging of mark subpoint on the object and coincides with the mark point of observation device to produce the cross of the said optical axes. 
   Where, the mark subpoint projected by projection device onto object surface is at the position of the said zero-order fringe. 
   In step 2), the said projection working distance is the distance BC between projection device projection mark point and the crossing of optical axes. The said observation working distance is the distance observation device AC between observation mark point and the crossing of optical axes. The said triangle ABC is made of BC, AC and the link line AB from projection device&#39;s mark point to observation device&#39;s mark point. μ is the included angle measured by observing positioner, which is formed by observation optical axis and the link line AB from projection device&#39;s mark point to observation device&#39;s mark point, ν is the included angle measured by projecting positioner, which is formed by projection optical axis and the link line AB from projection device&#39;s mark point to observation device&#39;s mark point, AB is the AB distance measured by projection device positioner and observation device positioner, θ is the included angle formed by optical axes of projection device and observation device. Observation working distance AC and projection working distance BC are measured indirectly by formulas (2) and (3):
 
θ=180−μ−ν  (1)
 
 AC=AB ×sin ν÷sin θ  (2)
 
 BC=AB ×sin μ÷sin θ  (3)
 
   In step 3), the said observation lens&#39;s focal length is F 2 , observed object distance is ZC, observed image distance is ZCF; projective lens&#39;s focal length is F 1 , projected object distance is L P , projected image distance is L PF , A is the distance between projection device&#39;s mark point and the center of grating, B is the distance between observation device&#39;s mark point and the image surface center of observer imaging lens. A and B are parameters for projection device and observation device. Once the devices are set these parameters will have fixed value. Use formulas (6) and (7) to calculate projected object distance, projected image distance, observed object distance and observed image distance. 
   
     
       
         
           
             
               
                 
                   
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                 4 
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                     C 
                   
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                       CF 
                     
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                     B 
                   
                 
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                 5 
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                     1 
                     
                       L 
                       P 
                     
                   
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                     1 
                     
                       L 
                       PF 
                     
                   
                 
                 = 
                 
                   1 
                   
                     F 
                     1 
                   
                 
               
             
             
               
                 ( 
                 6 
                 ) 
               
             
           
           
             
               
                 
                   
                     1 
                     
                       Z 
                       C 
                     
                   
                   + 
                   
                     1 
                     
                       Z 
                       CF 
                     
                   
                 
                 = 
                 
                   1 
                   
                     F 
                     2 
                   
                 
               
             
             
               
                 ( 
                 7 
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   In step 4), the said automatic focusing (AF) refers to how the focusing projection device forms a clear image of the grating in projection device on object surface on the basis of projected object distance, projected image distance, observed object distance and observed image distance. Focusing observation device will form a clear image of projected grating fringes on object surface. 
   In step 5), the said data processing includes collecting phase-shift striated pattern and calculating phase distribution and height distribution. 
   As for the sensing device and measuring method of this invention, the relative motion and focusing of projection device and observation device in the sensing device are utilized to finish the crossing of optical axes and to change projected object distance and image distance, and observed object distance and image distance, to determine accurately the position of zero-order fringe and realize the 3-D high-precision measurement of variable field of view and whole field of objects with different size. 
   The device and method of this invention can allow for a high-precision whole-field absolute measurement of object surface shape. For the measurement of 300*300 mm field of view, the measurement accuracy is ±0.01 mm, which is 5˜10 times that of existing measuring device, and the measurement can be accomplished within 30 s. It is applicable for the high-precision and high-speed whole-field measurement of 3-D objects with complex shape such as engine leaf. 
   The following is detailed description of the invention with charts and embodiments. The said embodiments are used to describe not to limit this invention. 
   BRIEF DESCRIPTION OF THE INVENTION 
   Chart  1 . Sketch of the principle of existing parallel optical axes 3-D shape measuring device; 
   Chart  2 . Sketch of the principle of existing cross-optical axes 3-D shape measuring device; 
   Chart  3 . Sketch of one embodiment for 3-D shape measuring device of this invention; 
   Chart  4 . Sketch of one embodiment for projection device of this invention; 
   Chart  5 . Sketch of one embodiment for observation device of this invention; 
   Chart  6 . Sketch of parameter calculation of sensing device for 3-D shape measurement of this invention; 
   Chart  7 . Sketch of the principle of sensing device for 3-D shape measurement of this invention; 
   Chart  8 . Method flow chart of sensing device for 3-D shape measurement of this invention; 
   Chart  9 . Sketch of one embodiment for sensing device for 3-D shape measurement of this invention; 
   Chart  10 . Sketch of one embodiment for sensing device for 3-D shape measurement of this invention; 
   Chart  11 . Sketch of another embodiment for projection device of this invention; 
   Chart  12 . Sketch of another embodiment for observation device of this invention; 
   Chart  13 . Sketch of one embodiment for observation device with observation grating of this invention; 
   Chart  14 . Sketch of another embodiment for 3-D shape measuring device of this invention; 
   Chart  15 . Sketch of another embodiment for sensing device for 3-D shape measurement of this invention; 
   Chart  16 . Sketch of variable field of view of sensing device for 3-D shape measurement of this invention. 

   DETAILED DESCRIPTION OF THE INVENTION 
   Refer to Chart  15 : in an embodiment of this invention, the projecting positioner and observing positioner are equipped with projection slider  41 , observation slider  42  and rectilinear motion axis  40 . Projection slider  41  and observation slider  42  can be installed sliding on rectilinear motion axis  40 . Projection device  70  is installed on projection slider  41  and observation device  80  is placed on slider  42 . The relative distance between projection device and observation device can be changed by the movement of sliders  41  and  42  on rectilinear motion axis  40  to enable the crossing of optical axes of projection device  70  and observation device  80  on the object surface and to adjust the field of view and operating distance for measurement of objects with different size. In such case, when place projection device  70  and observation device  80  on rectilinear motion axis  40 , their optical axes mustn&#39;t be parallel. 
   Refer to Chart  10 : in another embodiment of this invention, projecting positioner and observing positioner are equipped with rectilinear motion axis  40 , projection rotary positioning table  50  and observation rotary positioning table  60 . Projection rotary positioning table  50  and observation rotary positioning table  60  are placed with a fixed distance directly on rectilinear motion axis  40 . Projection device  70  is installed on projection rotary positioning table  50  and observation device  80  is installed on observation rotary positioning table  60 . Use projection rotary positioning table  50  or observation rotary positioning table  60  to enable the rotation of projection device  70  or observation device  80  to make the optical axes of projection device  70  and observation device  80  cross on object surface and adjust the field of view. Of course, the simultaneous running of projection rotary positioning table  50  and observation rotary positioning table  60  also can make optical axes of projection device  70  and observation device  80  cross on object surface and adjust the field of view and operating distance to measure objects with different size. 
   Refer to Chart  9 : in another embodiment of this invention, projecting positioner and observing positioner are equipped with projection slider  41 , observation slider  42  and rectilinear motion axis  40 . In such case, place a projection rotary positioning table  50  on the said projection slider  41 , and an observation rotary positioning table  60  on observation slider  42 . Projection device  70  is installed on projection rotary positioning table  50  and observation device  80  is installed on observation rotary positioning table  60 . Use rotation of projection rotary positioning table  50  and/or observation rotary positioning table  60  and sliding of sliders to enable the movement or rotation of projection device  70  and/or observation device  80 , make optical axes of projection device  70  and observation device  80  cross on object surface and adjust the field of view, so as to measure objects with different size. 
   Where, the mark point of projection device  70  coincides with the rotating center of projection rotary positioning table  50 , and the mark point of observation device  80  coincides with the rotating center of observation rotary positioning table  60 . 
   Moreover, the link line of rotating centers of projection rotary positioning table  50  and observation rotary positioning table  60  is parallel to rectilinear motion axis  40 . 
   Rotary positioning tables  50  and  60  can move at 0-360°, while the preferred rotation angle is within 180° facing the object. 
   The sensing device for 3-D shape measurement of this invention can be placed on one, two or three-coordinates mobile devices, such as moving arm, tripod or platform of three-coordinates measuring machine to change the field of view and measure projection operating distance and observation working distance of objects with different size by one, two or three-dimensional motion. 
   Refer projection device  70  to Chart  4 : rays from light source  71  are converged by condenser  72 , and then irradiate grating  73  or projection mark point  74  behind the grating. Projective lens linear positioner  76  controls projective lens  75  to moving focus along the optical axis and form the image of grating  73  or mark point  74 . Use projection grating linear positioner  77  to control the movement of grating  73  in grating plane to finish precise phase-shift. 
   The projection mark point  74  and grating  73  in projection device  70  also can be placed on mark point and grating switch  79 , to switch projection mark point or grating into beam path separately. See Chart  11 . 
   Refer observation device  80  to Chart  5 : observing linear positioner  89 A controls observation lens  89  to move along the optical axis to focus the mark subpoint or grating fringes projected by projection device onto the object. Observation mark point splicer  83  can switch mark point  83 A into beam path so as to aim it accurately at the mark subpoint on object surface, make optical axes cross and determine the position of zero-order fringe. The mark subpoint or grating fringes projected onto object surface form their images through observer imaging lens  89  on the image surface of observer imaging lens  89 , and are received through camera imaging lens  82  by camera  81 . 
   Refer observation device  80  to Chart  12 : set up observing beam path B and measuring beam path A separately. The only difference of measuring beam path A from Chart  5  is that in the beam path there are not observation mark point splicer  83  and mark point  83 A on it. Observing beam path consists of observation lens  89  that is also included by measuring beam path, observation lens linear positioner  89 A that controls observation lens  89  to move along the optical axis, square prism  84  for vertical light splitting from measuring beam path, which is behind observation lens  89 , mark point  85  between square prism  84  and reflector  86 , reflector  86  that changes the beam path direction by 90°, observation camera  88  that forms the image of mark point  85  and observation camera imaging lens  87  in the front of it.  85 A in Chart  12  is the conjugate point of mark point. 
   Refer observation device  80  to Chart  13 : set up observing beam path B and measuring beam path A separately. The only difference of measuring beam path A from Chart  5  is that in the beam path there is observation grating  83 B instead of observation mark point splicer  83  and mark point  83 A on it. Observing beam path consists of observation lens  89  that is also included by measuring beam path, observation lens linear positioner.  89 A that controls observation lens  89  to move along the optical axis, square prism  84  for vertical light splitting from measuring beam path, which is behind observation lens  89 , mark point  85  between square prism  84  and reflector  86 , reflector  86  that changes the beam path direction by 90°, observation camera  88  that forms the image of mark point  85  and observation camera imaging lens  87  in the front of it.  85 A in Chart  13  is the conjugate point of mark point. 
   Chart  8  is the measuring method flow of sensing device for 3-D shape measurement of this invention. When measuring, locate the object at a place where observation device  80  can form its whole-field image. Adjust the imaging lens of projection device  70  and turn or move projection device  70  to enable a clear image of projection mark point  74  on object surface. If the projection mark point and grating in projection device  70  are placed on mark point and grating switch  79 , projection mark point shall be switched into the beam path before the activities above are conducted. 
   When observation device  80  achieves its observation and measurement through the switching of observation mark point switch  83 , firstly switch the observation mark point  83 A into the beam path, adjust the imaging lens of observation device  80 , focus the mark subpoint, to enable the mark subpoint on the object to form a clear image both on the image surface of observer imaging lens  89  and the image surface of camera  81 . Rotate or move observation device  80  to make the mark subpoint on the object coincide with the observation mark point  83 A in observation device  80 . Now the optical axes of projection device and observation device cross, projection device mark point  74 , observation device&#39;s mark point  83 A and the mark subpoint on the object form a triangle Δ ABC, as showed in Chart  6 . 
   When observation device  80  has observing beam path B or measuring beam path A, adjust the imaging lens of observation device  80  to enable the mark subpoint on the object to form a clear image on the image surface of observer imaging lens  89 . After light-splitting by square prism  84 , go through reflector  86  and observation camera imaging lens  87 , mark point  85  and the mark subpoint on the object get their images on observation camera  88 . Rotate or move observation device  80  to make the mark subpoint on the object coincide with the mark point  85  in observation device  80 . Now the optical axes of projection device and observation device cross, projection device mark point  74 , conjugate point of observation device&#39;s mark point  85 A and the mark subpoint on the object form a triangleΔ ABC, as showed in Chart  6 . 
   In fact, in the sensing device for 3-D shape measurement of this invention, the change in the relative position of projection device and observation device is not limited to the movement on a rectilinear motion axis. In order to check 3-D shape of objects with different size, we can change the relative position of projection device and observation device at will. Like that in Chart  16 —a sketch of field of view change of the sensing device for 3-D shape measurement: when check the object, projection device, observation device and object are at A′, B′ and C respectively. If these positions can&#39;t meet the demand for measurement of the object, move projection device and/or observation device to places A and B to satisfy measurement requirements. This movement may be achieved by at least one rectilinear motion axis B′B and/or A′A or other ways available according to existing techniques, which is known by technicians in this field. The measurement of object surface shape at every place is finished by the triangles A′B′C and Δ ABC formed by projection device&#39;s mark point, observation device&#39;s mark point or conjugate point of mark point, and mark subpoint on the object respectively. 
   After the triangle is determined, indirect measurement of projection working distance and observation working distance is available. TakeΔ ABC for example: the included angle ν or μ formed by projection optical axis or observation optical axis and the link line AB from mark point  74  in projection device to mark point  83 A or its conjugate point  85 A in observation device can be measured by rotary positioning positioner. The distance of link line AB from mark point  74  in projection device to mark point  83 A or its conjugate point  85 A in observation device can be measured by rectilinear motion axis  40  with grating ruler or be indirectly measured by rectilinear motion axis. The included angle θ formed by optical centers of projection device and observation device, and the distances BC and AC between projection device&#39;s mark point  74 , observation device&#39;s mark point  83 A or its conjugate point  85 A and the mark subpoint on the object, namely, projection working distance and observation working distance, can be calculated by following formulas (2) and (3):
 
θ=180−μ−ν  (1)
 
 AC=AB ×sin ν÷sin θ  (2)
 
 BC=AB ×sin μ÷sin θ  (3)
 
   In order to avoid any possible personal error and get a clear imaging of grating  73  on the object, the given observed object distance, observed image distance, projected object distance and projected image distance must be accurate. In this invention, we can calculate accurate values of observed object distance, observed image distance, projected object distance and projected image distance, conduct automatic focusing based on these values and use camera  81  to record the clear grating line image on the object. 
   As showed in Chart  7 : suppose the focal length of observation lens is F 2 , observed object distance is ZC, observed image distance is ZCF; the focal length of projective lens is F 1 ,projected object distance is L P , projected image distance is L PF . A and B are known parameters of projection device and observation device, and they have fixed values once the devices are determined. Then: 
   
     
       
         
           
             
               
                 
                   
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   After lens is decided, its focal length F 1  or F 2  is a fixed value. For this invention the focal length of lens is 16-50 mm. 
   Get Z C , Z CF , L PF  and L P  according to equations (4), (5), (6) and (7). 
   Conduct automobile focusing according to calculated values: 
   Adopt the projection device in Chart  4 : utilize projecting linear positioner to move the projective lens  75  of projection device  70 , make rays from the light source in projection device  70  go through grating  73  and then form a clear image on the visual surface of the object; 
   Adopt the projection device in Chart  11 : when the projection mark point  74  and grating  73  in projection device  70  are placed on mark point and grating switch  79 , the grating shall be switched into the beam path; 
   Adopt the observation device in Chart  12 : utilize observing linear positioner  89 A to move the imaging lens  89  of observation device  80  to get a clear image of projected grating fringes on the object surface. Camera  81  in observation device  80  shall record grating fringe image; 
   Adopt the observation device in Chart  5 : when the projection mark point in observation device  80  is placed on mark point switch  83 , mark point  83 A shall be switched out of the beam path. Camera  81  in observation device  80  shall record grating fringe image on object surface; 
   Adopt the observation device in Chart  13 : utilize observing linear positioner  89 A to move the imaging lens  89  of observation device  80  to get a clear image of projected grating fringes on the object surface. Camera  81  in observation device  80  shall record the grating interference fringe image on observation grating surface. 
   CCD camera  81  in observation device  80  will input the image it records in image capture board (that is not showed in Chart) for digitization, and the digitized fringe image is input in computer (not showed in Chart), then get a digitized fringe chart. Move the grating in projection device, collect four fringe image charts by CCD camera  81  at one fourth grating spacing, two fourths grating spacing, three fourths grating spacing and one grating spacing to the direction perpendicular to the optical axis respectively and transfer them into computer by image capture board, then get 0-2π phase diagrams by phase-shift algorithm. 
   
     
       
         
           
             
               
                 
                   I 
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                 ( 
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                 ( 
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                 ( 
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                 ( 
                 11 
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                 ( 
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   Where, I 0  is ambient light intensity, A is fringe contrast, φ is phase at every point on the object surface. 
   Use unwrapping algorithm to get the principle of phase diagram as follows: 
   For the phase-shifted phase diagram, by the criterion φ 2 −φ 1≧ π, φ 2 =φ 1 −2π; and φ 2 −φ 1≦ −π, φ 2 =φ 1 +2π, they can be unwrapped to continuously changed phase distribution. 
   Suppose the observed object distance Z C , observed image distance Z CF , projected image distance L PF , projected object distance L P , included angel θ of optical centers of projection device and observation device at the place of object, grating spacing P are given, in virtue of the projected grating/moire height and phase formula put forward by Masanori Idesawa in  Scanning moiré method and automatic measurement of  3- D shapes  published on Applied Optics (vol.16, No.8 August.1977, pp2152-2162), we can get the surface shape of 3-D object. 
   Following are detailed embodiments of this invention: 
   Embodiment 1 
   See Charts  3  and  15 . Install projection device  70  on projection slider  41  of rectilinear motion axis  40  with grating ruler and double sliders. Install observation device  80  on observation slider  42  of rectilinear motion axis  40  with double sliders. The rectilinear motion axis  40  with double sliders is hung on three-coordinates moving arm  30  that can do three-dimensional movement, and keeps vertical to Z shaft of three-coordinates moving arm. The optical centers of observation device  80  and projection device  70  are at a same level, the to-be-measured object is installed on the rotary positioning table which can do 360° rotation (German PI Company&#39;s rotary positioner M039). Projection device  70  joins with power supply by cable. The observation camera  81  and observation camera  88  of observation device  80  joins with Matrox Pulser 4-channel image capture board by cable (not showed in the Chart), and the image capture board is plugged in computer (not showed in the Chart). The projective imaging lens linear positioner  76  in projection device  70  adopts German PI Company&#39;s linear positioner M224.20, the grating linear positioner  77  adopts German PI Company&#39;s linear positioner M222.20. The observer imaging lens linear positioner  89 A in observation device  80  adopts German PI Company&#39;s linear positioner M224.20. The linear positioner and rotary positioner are connected by cables with a four-channel DC electric machine control panel C-842.40 produced by German PI Company. The latter is plugged in the computer. 
   Refer projection device  70  to Chart  4 . It consists of light source  71  that produces white light in front of condenser  72 , grating  73  and projective lens  75  in front of the mark point (cross wire  74  in this embodiment). The movement of grating  73  in grating plane is controlled by grating linear positioner  77 , and the movement of projective lens  75  along the optical axis is controlled by projective lens linear positioner  76 . 
   Refer observation device  80  to Chart  12 . It includes measuring beam path and observing beam path. The said observing beam path consists of observation lens  89 , observation lens linear positioner  89 A that controls observation lens  89  to move along the optical axis, square prism  84  for vertical light splitting from measuring beam path, which is behind observation lens  89 , mark point - - - cross wire  85  between square prism  84  and reflector  86 , reflector  86  that changes the beam path direction by 90°, observation camera  88  that forms the image of mark point  85  (cross wire in this embodiment) and observation camera imaging lens  87  in the front of it. Fully aim the mark point in observing beam path at the mark subpoint projected by projection device  70  on the object to achieve the crossing of optical axes of projection device  70  and observation device  80  and to determine the position of zero-order fringe. The said measuring beam path consists of observer imaging lens  89 , linear positioner  89 A that controls observation lens  89  to move along the optical axis, camera  81  used to receive the grating fringes on object surface and camera imaging lens  82  in front of it. The grating fringes projected onto object surface get an image on the image surface of observer imaging lens  89  and will be received by camera  81  with camera imaging lens  82 . The focal length of projective lens  75  is 50 mm, and the focal length of observation lens  89  is 50 mm. 
   Refer to Chart  8 . When measuring, firstly make a three-dimensional adjustment of three-coordinates moving arm  30 , projection slider  41  and/or observation slider  42  to adapt the field of view of projection device  70  and observation device  80  to the size of measured object. Move projective imaging lens linear positioner  77  to enable projective lens  76  to produce a clear image of cross wire  74  on the object surface and get a shadow of cross wire. Adjust the imaging lens linear positioner  89 A of observation device to make the shadow cross wire imaged by projective imaging lens  75  on the object get a clear image on the target of camera  88 . Adjust the slider  41  or  42  of rectilinear motion axis  40  to coincide the shadow cross wire on the object with cross wire  85  of observation device. Now the optical axes of projection device  70  and observation device  80  cross. The rectilinear motion axis with grating ruler will measure the value of link line AB from projection device&#39;s mark point to observation device&#39;s mark conjugate point  85 A. According to the values of included angles ν and μ, which are formed by projection device and the link line AB, and observation device and the link line AB respectively, and the value of AB, the computer will give accurate values of observed object distance, observed image distance, projected object distance and projected image distance by formulas (4)-(7) and do automatic focusing on the basis of above values, namely, readjust projective imaging lens linear positioner  76  to enable projective lens  75  to form a clear image of grating line  73 . Fine adjust observer imaging lens linear positioner  89 A to enable observation lens  89  to form a clear image of grating line  73  on the object. Then move projected grating  73 , when the grating moves at one fourth grating spacing, two fourths grating spacing, three fourths grating spacing and one grating spacing along the direction perpendicular to the optical axis respectively, collect four fringe image samples by viewing camera, input them into image capture board and the digitized fringe image is input in computer, then get a digitized fringe chart. Get 0-2π phase diagrams by phase-shift algorithm, and finally develop the phases with mark subpoint as zero-order phase, calculate the height distribution of the object by relevant formulas to get the values of points Xz, Yz and Z in the field of view in this way. Rotate the rotary stage to change the measurement surface and repeat this process, then we can get the surface shape of 3-D object. 
   Embodiment 2  
   Refer to Chart  3 . The sensing device can be installed on three-coordinates moving arm, like that in Chart  10 . The projection rotary positioning table  50  adopts German PI Company&#39;s rotary positioner M039, installed on rectilinear motion axis  40 . The observation rotary positioning table  60  adopts German PI Company&#39;s rotary positioner M039, installed on rectilinear motion axis  40 . Projection device  70  is installed on projection rotary positioning table  50  and observation device  80  is installed on observation rotary positioning table  60 . The mark point  73  of projection device  70  coincides with the rotating center of projection rotary positioning table  50 , and the mark point  83 A of observation device  80  coincides with the rotating center of rotary positioning table  60 . The optical axis of observation device  80  and rectilinear motion axis  40  are crossed as a μ angle, the optical axis of projection device  70  and rectilinear motion axis  40  are crossed as a ν angle, and the optical axes of projection device and observation device are crossed as a θ angle. The measured object is installed on a rotary positioning table (German PI Company&#39;s rotary positioner M039). Projection device  70  is connected by cable with power supply. The measuring camera  81  of observation device  80  is connected by cable with four-channel image capture board (not showed in the Chart), and the image capture board is plugged in the computer (not showed in the Chart). The projective lens linear positioner  76  of projection device  70  adopts German PI Company&#39;s linear positioner M224.20, grating linear positioner  77  adopts German PI Company&#39;s linear positioner M222.20. The observer imaging lens linear positioner  89 A of observation device  80  adopts German PI Company&#39;s linear positioner M224.20. Linear positioner and rotary positioner are connected by cable with German PI Company&#39;s two four-channel DC electric machine control panels C-842.40 respectively, which is plugged in the computer. Other parts that need to be automatically controlled are connected with the computer. 
   Refer projection device  70  to Chart  11 . It consists of light source  71 , condenser  72 , mark point—ring  74  and grating  73  are placed on grating ring switch  79 , projective lens  75 , projective lens linear positioner  76 , and grating linear positioner  77 . 
   Refer observation device  80  to Chart  5 . It consists of observation camera  81 , measuring camera imaging lens  82 , mark point - - - ring  83 A is placed on ring switch  83 , observer imaging lens  89 , and observer imaging lens linear positioner  89 A. 
   The focal length of projective lens  75  is 50 mm, the focal length of observation lens  89  is 50 mm, and the focal length of viewing camera imaging lens  82  is 30 mm. 
   Refer to Chart  8 . When measuring, firstly make a three-dimensional adjustment of three-coordinates moving arm  30  to adapt the field of view of projection device  70  and observation device  80  to the size of measured object. Then splice the ring  74  of projection device grating ring switch  79  into the beam path. Move projective imaging lens linear positioner  76  to enable imaging lens  75  to produce a clear image of ring. Splice the ring  83 A of observation device ring switch  83  into the beam path. Adjust observer imaging lens linear positioner  89 A and projection positioning table  50  or observation positioning table  60  to make the shadow ring imaged by measuring camera imaging lens  89  onto the target of measuring camera  81  coincide with the ring S 3 A of observation device. Now refer to Chart  8  and steps of Embodiment 1, the computer will read the values of angles ν and μ formed by projection device  70  or observation device  80  and AB respectively and input the fixed value of AB to calculate projected object distance and image distance, observed object distance and image distance. Do automatic focusing on the basis of above values, splice grating  73  of grating ring switch  79  in projection device  70  into the beam path, and move ring  83 A of ring switch in observation device  80  out of the beam path. Then move projected grating  73 , when the grating moves at one fourth grating spacing, two fourths grating spacing, three fourths grating spacing and one grating spacing along the direction perpendicular to the optical axis respectively, collect four fringe image samples by viewing camera. See Embodiment 1 for detailed steps. Then we can get the surface shape of 3-D object. 
   Embodiment 3  
   Refer to Chart  3 . The sensing device can be installed on three-coordiniates moving arm, like that in Chart  9 . Projecting positioner and observing positioner are equipped with projection slider  41 , observation slider  42  and rectilinear motion axis  40 . In such case, the said projection slider  41  has a projection rotary positioning table  50  on it, which adopts German PI Company&#39;s rotary positioner M039, and the observation slider  42  has an observation, rotary positioning table  60 , which adopts German PI Company&#39;s rotary positioner M039. Projection device  70  (see Chart  11 ) is installed on projection rotary positioning table  50 , and observation device  80  (see Chart  5 ) is installed on observation rotary positioning table  60 . Utilize projection rotary positioning table  50  and/or observation rotary positioning table  60  and movement of sliders, drive respectively the movement or rotation of projection device  70  and/or observation device  80 , so as to enable the optical axes of projection device  70  and observation device  80  cross on the object surface. Adjust the field of view to measure objects with different size. Projection device  70  is connected by cable with power supply. Measuring camera  81  of observation device  80  is connected by cable with four-channel image capture board (not showed in the Chart), which is plugged in the computer (not showed in the Chart). Projective lens linear positioner  76  of projection device  70  adopts German PI Company&#39;s linear positioner M224.20, grating linear positioner  77  adopts German PI Company&#39;s linear positioner M222.20. Observer imaging lens linear positioner  89 A of observation device  80  adopts German PI Company&#39;s linear positioner M224.20. Both linear positioner and rotary positioner are connected by cable with German PI Company&#39;s two four-channel DC electric machine control panels C-842.40, which is plugged in the computer. Other parts that need to be automatically controlled are connected with the computer. 
   The focal length of projective lens  75  is 50 mm, the focal length of observation lens  89  is 50 mm, and the focal length of viewing camera imaging lens  82  is 30 mm. 
   Its working process is same to Embodiment 2. 
   Embodiment 4  
   Refer to Chart  14 . The sensing device can be installed on a marble platform with rectilinear motion axis. Utilize the movement of sensing device, distance change of projection device  70  and observation device  80  to adapt the field of view of projection device  70  and observation device  80  to the size of the measured object. Other steps are same to Embodiment 1, with only difference of that observation device has an observation grating. See Chart  13 . The image received by measuring camera  81  is grating interference fringe. The calculation is finished by formulas above.