Abstract:
End effectors are provided for performing surface lapping using a robot. The end effectors allow orthogonal surface contact in order to maintain optimum pressure applied by the robot. The end effectors include a base, a plate having a planar surface, a lapping pad that attaches to the planar surface of the plate, and a pivot-joint. The pivot-joint allows the plate to pivot about two axes. The base is attached to an arm of the robot. The two axes are substantially parallel to the planar surface.

Description:
GOVERNMENT LICENSE RIGHTS  
       [0001] This invention was made with Government support under U.S. Government contract F33615-97-2-3400 awarded by United States Air Force. The Government has certain rights in this invention. 
     
    
     
       RELATED APPLICATIONS  
         [0002]    This patent application is related to concurrently-filed patent applications entitled “Spring-Loaded Contour Following End Effectors for Lapping/Polishing”, bearing attorney docket number BOEI-1-1102, and “Automated Lapping System”, bearing attorney docket number BOEI-1-1121, which are hereby incorporated by reference.  
         FIELD OF THE INVENTION  
         [0003]    This invention relates generally to lapping and polishing surfaces and, more specifically, to robotic lapping and polishing.  
         BACKGROUND OF THE INVENTION  
         [0004]    Injection-molded aircraft canopies and windshields offer tremendous benefits to aircraft in cost, weight, and impact tolerance. A major cost in this manufacturing process is the injection mold itself. Surfaces of canopies and windshields are finished to a quality similar to an optic lens in order to prevent pilots from being subjected to visual distortion. The precise optics for canopies and windshields are built into the injection mold. The injection molds are lapped or polished by hand, section by section, using a diamond plated lapping material. Hand polishing or lapping an injection mold takes several man-years to accomplish. Thus, lapping or polishing is very costly. Hand polishing or lapping also does not ensure that the precise, optic surface finish quality has been met.  
           [0005]    Therefore, there exists an unmet need to reduce the cost and increase the accuracy of lapping or polishing.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides end effectors for performing surface lapping using a robot. The end effectors allow orthogonal surface contact in order to maintain optimum pressure applied by the robot.  
           [0007]    The end effectors include a base, a plate having a planar surface, a lapping pad that attaches to the planar surface of the plate, and a pivot joint. The pivot joint allows the plate to pivot about two axes. The base is attached to an arm of the robot.  
           [0008]    In accordance with an aspect of the invention, the two axes are substantially parallel to the planar surface.  
           [0009]    In accordance with an another aspect of the invention, the pivot joint includes a universal joint, a gimbaled joint, a half-ball and socket joint, or a crossed-pin ball and socket joint. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings.  
         [0011]    [0011]FIG. 1 is a perspective view of an end effector in operation;  
         [0012]    [0012]FIG. 2 is an exploded view of exemplary materials layered on an end effector;  
         [0013]    [0013]FIGS. 3A and B illustrate a universal joint end effector;  
         [0014]    [0014]FIG. 4 illustrates a gimbaled-joint end effector;  
         [0015]    [0015]FIGS. 5A and B illustrate a one-half ball and socket end effector;  
         [0016]    [0016]FIGS. 6A and B illustrate a cross-pinned ball and socket end effector; and  
         [0017]    FIGS.  7 A-C illustrate a multi-end effector support. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    [0018]FIG. 1 shows an embodiment of an end effector  40  according to the present invention that is attached to a robot  42  for polishing and lapping a work product  44 . A non-limiting example of the product  44  is a core or cavity injection mold for making polycarbonate aircraft canopies. The work product  44  suitably entails a high degree of polishing or lapping accuracy. For example, precise optical properties for injection molds must be attained in order to produce optically flawless or near-flawless polycarbonate molded canopies. In order to attain this desired level of accuracy, the end effector  40  pivots at an end of the robot  42 , but does not rotate about an axis that is perpendicular to a planar surface of the end effector  40 . In other words, the end effector  40  maintains a substantially orthogonal position relative to the work product  44 .  
         [0019]    A non-limiting example of the robot  42  includes a Fanuc, Inc. robot with soft float. Soft float allows the robot  42  to apply pressure to a surface without resulting in undesired shut-offs. Because the robot  42  applies continuous, consistent pressure that far exceeds the capabilities of a human operator, lapping and polishing evolutions take a fraction of the time taken by a human operator.  
         [0020]    As shown in FIG. 2, the end effector  40  suitably includes a lapping plate  50  with applied layers of materials that aid in lapping the work product  44 . In one embodiment, the layers of materials include one or more silicone or polysulphide adhesive layers  54  interleaved with one or more solid acrylic rings  56 . A pitch substance  60 , such as tree pitch produced by Universal Photonics, Inc., Adolf Miller, or Zophar Mills, Inc., is applied to the last acrylic ring  56 . A polishing or abrasive material  62 , such as a diamond-plated lapping material, is attached to the pitch  60 . The robot  42  applies pressure to the work product  44  through the end effector  40  in order to for the pitch  60  to conform to the surface of the work product  44 . The robot  42  moves the end effector  40  over a section of the surface of the work product  44  that entails the same curvature to which the pitch  60  conforms.  
         [0021]    [0021]FIGS. 3A and B illustrate a non-limiting example end effector  100  that suitably attaches to the robot  42  (FIG. 1). The end effector  100  includes a universal joint  104  that couples a base mount  106  to a lapping plate  110 . The base mount  106  suitably attaches to the robot  42  (FIG. 1). The universal joint  104  suitably includes a U-shaped receiver portion  114 , a pin housing  116 , and a U-shaped lapping plate portion  120 . The U-shaped receiver portion  114  is part of or is securely attached to the base mount  106 . The U-shaped lapping plate portion  120  is suitably part of or is alternatively securely attached to, the lapping plate  110 .  
         [0022]    A first pin  124  is mounted through the U-shaped receiver portion  114  and the pin housing  116 . The pin housing  116  rotates about a longitudinal axis of the first pin  124 . Second and third pins  130  and  132  are mounted through the U-shaped lapping plate portion  120  and into the pin housing  116  to allow the U-shaped lapping plate portion  120  to rotate about a longitudinal axis of the second and third pins  130  and  132 . The second and third pins  130  and  132  are substantially axially orthogonal to the first pin  124 . Thus, the universal joint  104  allows the lapping plate  110  to rotate about the axis of the first pin  124  and the axis of the second and third pins  130  and  132  without allowing rotation of the lapping plate  110  itself.  
         [0023]    [0023]FIG. 4 illustrates a gimbaled-joint end effector  150 . The gimbaled-joint end effector  150  includes a base  154 , a swivel ring  156 , and a lapping plate  160 . The base  154  is securely attached to the robot  42  (FIG. 1). The swivel ring  156  is suitably ring-shaped and securely receives first and second pins  164  and  166  on opposing sides. The pins  164  and  166  protrude outward from the swivel ring  156 . The base  154  includes a circular cavity for receiving the swivel ring  156 . The first and second pins  164  and  166  are rotatably received by walls that define the cavity of the base  154 , thereby allowing the swivel ring  156  to rotate about a longitudinal axis of the first and second pins  164  and  166 . The swivel ring  156  also receives a third pin  170  with a longitudinal axis that is orthogonal to the longitudinal axis of the first and second pins  164  and  166 . The lapping plate  160  includes a circular extension  172  that is sized to fit within the swivel ring  156 . The circular extension  172  rotatably receives the third pin  170 . The lapping plate  160  rotates about the longitudinal axis of the third pin  170  within the swivel ring  156 . The gimbaled-joint end effector  150  allows the lapping plate  160  to rotate about the longitudinal axis of the first, second, and third pins  164 ,  166 , and  170  without causing rotation of the lapping plate  160  itself.  
         [0024]    [0024]FIGS. 5A and B illustrate a one-half ball socket end effector  190 . The one-half ball and socket end effector  190  includes a socket housing  194 , a half-ball lapping plate  196 , and first and second pins  200  and  204 . The lapping plate  196  includes a one-half ball joint portion  206  that is pivotally received by a semi-circular cavity  208  formed by the housing  194 . The pins  200  and  204  pass through opposite sides of the housing  194  and protrude into the cavity  208 . The distance between the pins  200  and  204  is suitably less than a diameter of a widest part of the one-half ball joint portion  206 . Thus, the one-half ball joint portion  206  swivels within the housing  194  and is maintained within the cavity  208  by the pins  200  and  204 .  
         [0025]    [0025]FIGS. 6A and B illustrate a cross-pinned ball and socket end effector  230 . The cross-pinned ball and socket end effector  230  includes a base  234 , a lapping plate  238 , a ball pin  242 , and securing pins  250  and  252 . The base  234  includes a ball assembly  240  that is substantially spherical and that receives the ball pin  242  through approximately the center of the ball assembly  240 . The ball pin  242  is suitably longer than the diameter of the ball assembly  240 . The lapping plate  238  includes a ball cavity  244  that rotatably receives the ball assembly  240 . The lapping plate  238  also includes pin cavities  246  that are located adjacent to the ball cavity  244  on opposite sides of the ball cavity  244 . The ball pin  242  is inserted into the ball assembly  240 . The ball assembly  240  with ball pin  242  are inserted into the ball cavity  244  with the ball pin  242  being received by the pin cavities  246 . The securing pins  250  and  252  mount through the lapping plate  238  and the pin cavities  246 , respectively. The securing pins  250  and  252  keep the ball pin  242  within the respective ball pin cavities  246 . The lapping plate  238  pivots about a longitudinal axis of the ball pin  242 . The lapping plate  238  also rotates about an axis substantially orthogonal to the longitudinal axis of the ball pin  242 . This is because the ball pin cavities  246  are sized to allow pitching motion of the ball pin  242  therein.  
         [0026]    FIGS.  7 A-C illustrate a multiple end effector support  350 . The multiple end effector support  350  includes a plurality of arms  356  that extend radially from a center shaft  360 . The center shaft  360  is attached to a base (not shown) that is coupled to the robot  42  (FIG. 1). As shown in FIG. 7C, an extension  364  extends from a single end effector unit  366 . The type of end effector unit that can be used is any one of the ones shown in FIGS.  3 - 7 . The multiple end effector support  350  suitably includes two or more arms  356  for polishing and lapping a large area. In another embodiment, small and large lapping plates are alternately connected around the multiple end effector support  350 .  
         [0027]    In one embodiment, the extension  364  is suitably a threaded shaft that is received by a threaded cavity near an end of an arm  356 . The extension  364  is secured to one of the arms  356  by a securing pin  370  that tightens a split at the end of the arm  356 . The split extends to the threaded cavity.  
         [0028]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.