Abstract:
Improved methods and apparatus for cross-sectional scanning of parts employ a scanning station in which the focal plane of the scanning apparatus never moves in the vertical direction, i.e., the direction in which the stage of the part/potting combination moves. Distinct steps of material removal and scanning alternate with an intermediate step of moving the part/potting combination in the vertical direction after a surface layer has been removed, thus placing the newly-created surface back into the non-moving focal plane for the next scanning step. A removal station (not the stage carrying the part/potting combination) repeatedly moves into and out of the field of view of the scanning station between scanning steps. The material removal station is specially configured to remove the desired surface layer of the part/potting combination and the created debris, without requiring the separate environment characteristic of previous commercial applications.

Description:
BACKGROUND 
       [0001]    Cross-sectional scanning of parts, and the processing of the data generated in the same, is described in U.S. Pat. Nos. 5,139,338; 5,261,648; 5,880,961; 6,091,099; and 6,407,735. Such techniques, broadly speaking, involve the repeated optical scanning of a part that has been encased in a potting material so that, as successive layers of the part/potting combination are removed, data regarding the dimensions of the part are generated by a computer processing the scanned data of the image of each successive surface remaining after the preceding layer is removed. The optical contrast between the portions of the surface due to the potting material and those due to the material of the part identifies the dimensions of the part itself. Post-acquisition data processing techniques improve the utility of the data for various purposes. One such technique is described in U.S. Pat. No. 6,407,735. 
       SUMMARY 
       [0002]    Commercial embodiments of the techniques and systems disclosed in the patents listed above generally involve what may be called an “X-Axis” approach, meaning that a stage or shuttle carries the part/potting combination linerally back and forth along an axis between separate scanning and material removal stations. This application discloses various embodiments of improved methods and apparatus for cross-sectional scanning of parts, utilizing a so-called “Z-Axis” approach. These embodiments employ a scanning station in which the focal plane of the scanning apparatus never moves in the vertical or Z direction, i.e., the direction in which the stage of the part/potting combination moves. The distinct steps of material removal and scanning alternate with an intermediate step of moving the part/potting combination in the Z direction after a surface layer has been removed, thus placing the newly-created surface back into the focal plane for the next scanning step. To accomplish this, a removal station (not the stage carrying the part/potting combination) repeatedly moves in the +/−X direction, i.e., into and out of the field of view of the scanning station, between scanning steps. The material removal station is specially configured to remove the desired surface layer of the part/potting combination and the created debris, without requiring the separate environment that previously mandated the use of the X-Axis approach in commercial applications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    The figures illustrate a preferred embodiment and thus it should be understood that minor changes in shape, proportion, size, and the like are not critical to the scope of the disclosure except as specifically noted elsewhere below. 
           [0004]      FIG. 1  is a schematic side view of a system according to the detailed description below. 
           [0005]      FIG. 2  is a close-up upper perspective view of a prototype embodiment of a portion of  FIG. 1 . 
           [0006]      FIG. 3  is a close-up lower perspective view of a portion of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    In general terms, this application pertains to substantially improved versions of the methods and apparatus for cross-sectional scanning disclosed in U.S. Pat. Nos. 5,139,338; 5,261,648; 5,880,961; and 6,091,099. Each of these documents is incorporated by reference and familiarity with the basic operating principles taught in each of these documents is assumed in the following discussion. Thus, details known in the art will be understood, such as those associated with the removal of successive layers of the part/potting combination, generation of data regarding the dimensions of the part (including the computer processing of the scanned data of the image of each successive surface remaining after the preceding layer is removed), and the post-acquisition data processing techniques that improve the utility of the data for various purposes. 
         [0008]    Referring to  FIGS. 1-3 , a prototype cross-sectional scanner system  10  comprises vertically moving stage  11  and fixed-focal plane scanner  12 . In the preferred embodiment, scanner  12  is stationary with respect to system  10  and thus only the vertical motion of stage  11  need be considered explicitly. However, although it is not preferred, it is possible for scanner  12  to move relative to stage  11 , but the remainder of this discussion assumes that only stage  11  moves in the vertical direction with the understanding that the non-preferred approach is also included. Stage  11  supports part/potting combination  13  so that vertical motion of stage  11  advances combination  13  in the vertical direction toward scanner  12 . The initial motion places the upper surface of combination  13  at a position corresponding to the height of one thickness of material to be removed above the fixed location F of the focal plane of scanner  12 . Then such a thickness is removed from the upper (scanner-facing) surface of combination  13  by cutting subsystem  14  described further below. This places the upper surface so created exactly at the position of the fixed focal plane of scanner  12 , and scanning proceeds according to conventional techniques. A repeated series of stepwise motions, each corresponding in distance to the thickness of material to be removed, alternates with removal of such material followed by scanning of the new upper surface created. Thus, each scanning step occurs at the location of the fixed focal plane. The part/potting combination never shuttles in the X or Y directions. 
         [0009]    In general, scanner  12  is any multi-pixel scanner, camera, or similar optical image capture device such as a CCD array, line scan camera, or area scan camera. High resolution (155,000 pixels per square centimeter or greater) (megapixel per square inch or greater) image capture equipment is preferred for scanner  12 . In this case, a preferred, but not limiting, thickness of each slice is 25.4 micrometers [one thousandth (0.001) inch]. This combination results in data points measured at a scale that is 25.4 micrometers [one thousandth (0.001) inch] in each of the three orthogonal primary directions. 
         [0010]    References to thickness measurements should be understood as referring to measurements taken normal to the surface of the part/potting combination  13 . The part itself typically is oriented at some non-orthogonal angle within the potting material and thus distances measured in the principal X, Y, and Z planes may expose amounts of the part that are greater than or less than the thickness as measured normal to the surface of the part at the location of measurement. 
         [0011]    As shown, part/potting combination  13  is generally rectangular in cross-section in each of the three principal directions. It is preferred, but not required, that combination  13  have maximum dimensions on the order of 44.4 millimeters by 63.5 millimeters by 88.9 millimeters (1¾ inch by 2½ inch by 3½ inch). This is only a preference. 
         [0012]    Cutting subsystem  14  is, in general, any means for removing an amount of the upper surface of the part/potting combination. In the embodiment illustrated, it specifically includes a rotating single-end center-cutting end mill supplied by Niagara Cutter of Amherst, N.Y. under their model number A377 as designated by that manufacturer. This device has three flutes in a right-hand orientation at a helix angle of 37° and dimensions (flute diameter by shank diameter by cut length by overall length) of 9.5 millimeters by 9.5 millimeters by 38.1 millimeters by 82.6 millimeters (⅜ inch by ⅜ inch by 1½ inches by 3¼ inches). The device may be uncoated or coated as available from the manufacturer; a preferred coating is TiCN. The use of three flutes is preferred for creation of a smoother surface, but the number of flutes is not by itself a critical parameter. The preferred rotation speed is 1200 rpm. The right-handed orientation, coupled with counter-clockwise rotation (as observed looking at the tip of the device, as illustrated by the curved arrow in  FIG. 2 ) means that the cutting edges advance into the workpiece in the same direction as the advancing hood, i.e., the positive X-direction. It is possible, but not necessary, to continue rotation of the end mill as hood  15  is withdrawn (in the −X direction) so that the rapidly spinning cutting surfaces smooth out the surface of combination  13  to ensure greater accuracy. 
         [0013]    The cutting length of cutting subsystem  14  should be greater than the width of part/potting combination  13  to ensure that the entire width of part/potting combination  13  is cut in a single pass. The position of cutting subsystem  14  with respect to the location of part/potting combination  13  is coordinated accordingly. 
         [0014]    Hood  15  enables conventional vacuum system  16  to quickly and efficiently remove debris  18  from chamber  17  as such debris is created by cutting subsystem  14  when it removes the layer of part/potting combination  13 . The exact shape of hood  15  is not critical. The function of hood  15  is to concentrate the vacuum and keep the debris within a contained volume. In the embodiment illustrated, hood  15  substantially surrounds cutting subsystem  14  but for a relatively small open throat facing the upper surface of the part/potting combination, through which debris will be collected by the vacuum (see especially  FIG. 3 ). 
         [0015]    As with the cutting length of cutting subsystem  14 , the width of hood  15  (measured in the Y-direction) is greater than the width of part/potting combination  13  to ensure that the entire width is cut in a single pass. Hood  15  is mechanically attached or otherwise coordinated with the position of cutting subsystem  14  so that both advance together (in the X-direction) across the face of part/potting combination  13  to remove the surface layer of material (thus generating the debris). 
         [0016]    Any debris  18  generated by such removal is withdrawn through vacuum hood  15 , which is attached to conventional vacuum system  16 . As illustrated in this embodiment, system  10  further comprises a working chamber  17 , which is optional in the sense that system  10  could be incorporated as a sub-system of a larger system if so desired. 
         [0017]    Thus, the amount of motion required of the various components of system  10  is substantially reduced compared to prior commercial embodiments. To summarize, focal plane F remains fixed at all times; table  11  (and thus part/potting combination  13 ) moves only in the Z direction and not at all in the X or Y directions; hood/vacuum system  15 ,  16  moves only in the +/−X directions and not in the Y or Z directions; and cutting subsystem  14  (in the preferred embodiment illustrated) comprises a rotating end mill, having an axis of symmetry located such that it is coordinated with the Z position of the part/potting combination  13  to thereby remove only the necessary and desired amount of material as that axis moves in only the +/−X direction and not the Y or Z directions. The substantial reduction in the amount of moving subassemblies enables a substantial reduction in the overall size of the system  10 , because it reduces overall structural, mechanical, and electrical supporting equipment. This makes the system  10  highly suitable for use with small part/potting combinations  13  such as those having the non-limiting dimensions given above. 
         [0018]    The techniques described above may be contrasted to the disclosure of the patents listed above, which specifically disclose the use of separate, dedicated locations for the material removal station and the scanning station, such stations being separated from each other along the so-called X axis. The time required to shuttle the stage bearing the part/potting combination back and forth between these physically separate stations reduces the cycle time of the entire process compared to the approach disclosed above. By contrast, very low cycle times of approximately 8-10 seconds are believed possible in commercial production of the approach described above. 
         [0019]    It is well known to use computers to control the operation and location of the system as well as to process the data generated by the scanning subsystem. The preferred, but not required, technique to convert the scanning data is disclosed in the patents incorporated by reference above, as well as U.S. Pat. No. 6,407,735, which is also incorporated by reference. 
       Application to Cross-Sectional Scanning Systems 
       [0020]    The techniques described above may be employed in a cross-sectional scanning system of the following general design. Details of particular embodiments of such systems are in the patents incorporated by reference above. 
         [0021]    The system produces electronic data representations of an object or part. The major components of the system are: (1) a data gathering station having a focal plane, the position of the focal plane being fixed relative to the surface of the part; (2) a material removal station that moves into and out of position over the surface of the part; and (3) a table providing only vertical relative movement of the part to put the surface at the position of the focal plane. The data gathering station typically, but not necessarily, comprises: (1) an image data acquisition device for successively acquiring images of the part after removal of a predetermined contour; and (2) an electronic device operatively associated with the image data acquisition device for receiving and storing the images. The material removal station typically, but not necessarily, comprises: (1) a tool constructed and arranged to remove a predetermined contour of material from the part; and (2) a drive mechanism constructed and arranged to provide relative movement between the tool and the part. The table holds the part and is moved by a drive mechanism constructed and arranged to provide only vertical relative movement of the table; and a means to determine the relative locations of the part and the focal plane along the vertical direction. 
         [0022]    The operation of a typical configuration of such a system is as follows. The image data acquisition device successively acquires images of the part after removal of a predetermined contour. The tool is moved into and out of relative material removing engagement with the part. The relative movement between the table and the tool along the path is such that the part and the tool are moved in material removal alignment for removing a predetermined contour of material from the part and in imaging alignment to the image data acquisition device after removal of a predetermined contour. The position determining apparatus actuates the image data acquisition device at predetermined positions of the part relative to the tool. For example, a linear encoder with a scale, a sensor, and a computer may be arranged to send signals to the computer in response to the relative movement between the sensor and the scale. The computer is programmed to determine the position of the scale relative to the sensor in response to the signals received from the sensor. Thus, because the scale and sensor are operatively associated with each other, the position of the part relative to the tool along the path is incrementally determined by the computer. 
         [0023]    Commercial embodiments of such systems employ visible light (400-700 nm wavelength) for illumination and scanners sensitive to light typically having a wavelength centered on 550 nm. However, such values are not critical provided that sufficient contrast is provided at the detection wavelength chosen. Similarly, while directly impinging illumination and scanning normal to the surface have been illustrated, as is commercially common, more complicated geometries are possible but not preferred. 
         [0024]    While the above description refers to many specific details for the sake of explanation, these details should not be construed as limitations unless explicitly included in the following claims.