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. One or more end effectors include a base, a plate, a lapping pad attached to the plate, and a pivot joint. The pivot joint allows the plate to pivot about two substantially orthogonal axes. The base is attached to an arm of a robot. The end effector includes a component for absorbing applied pressure, such as a spring-loaded shaft or a pneumatic shaft. In an aspect of the invention, the two axes are substantially parallel to the planar surface.

Description:
RELATED APPLICATION  
       [0001]    This patent application is related to concurrently-filed patent applications entitled “Contour Following End Effectors for Lapping/Polishing”, bearing attorney docket number BOEI-1-1101, and “Automated Lapping System”, bearing attorney docket number BOEI-1-1121, which are hereby incorporated by reference. 
     
    
     GOVERNMENT LICENSE RIGHTS  
       [0002] 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. 
     
    
     
       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 present invention includes one or more end effectors with a base, a plate, a lapping pad attached to the plate, and a pivot joint. The pivot joint allows the plate to pivot about two substantially orthogonal axes. The base is attached to the robotic arm. The end effector includes a component for absorbing applied pressure.  
           [0008]    In an aspect of the invention, the component includes a spring-loaded shaft or a pneumatic shaft.  
           [0009]    In another aspect of the invention, the two axes are substantially parallel to the planar surface. 
       
    
    
     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 with a robot;  
         [0012]    [0012]FIG. 2 is an exploded view of exemplary materials layered on an end effector;  
         [0013]    [0013]FIGS. 3A and B illustrate a spring-loaded, universal joint end effector;  
         [0014]    [0014]FIGS. 4A and B illustrate a spring-loaded, hexagonal joint end effector;  
         [0015]    [0015]FIGS. 5A and B illustrate a gimbaled joint end effector with a spring-loaded shaft;  
         [0016]    [0016]FIGS. 6A and 6B illustrate a half ball and socket joint end effector with a spring-loaded shaft;  
         [0017]    [0017]FIGS. 7A and 7B illustrate a pneumatic end effector; and  
         [0018]    FIGS.  8 A-C illustrate a multi-end effector support. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    [0019]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 .  
         [0020]    The spring-loaded end effectors  40  are suitable for use with a robot that is configured with rigid motion and fixed positioning as compared to robots configured with soft float functions, such as Fanuc robots. A non-limiting example of the robot  42  is a Cooper robot. Without soft float, shut-offs may occur if the robot  42  applies too much pressure to a surface. The spring-loaded end effectors  40  allow the robot  42  to apply continuous, consistent pressure without incurring unnecessary shut-offs. The present invention far exceeds the capabilities of a human operator, therefore lapping and polishing evolutions take a fraction of the time taken by a human operator. The spring-loaded end effectors  40  include springs or pressure applying/absorbing devices for absorbing a predefined amount of pressure in order to apply pressure-loaded diamond laps on the work surface for accelerated material removal, and to avoid unnecessary robot shutdowns due to over travel.  
         [0021]    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 silicon 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.  
       Spring-Loaded Joints  
       [0022]    [0022]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 .  
         [0023]    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.  
         [0024]    A compression spring  140  encircles the universal joint  104 , thereby putting expanding pressure on the base mount  106  and the lapping plate  110 . When pressure is applied to the lapping plate  110 , the U-shaped lapping plate portion  120  slides the second and third pins  130  and  132  through the compression slots  144  while compressing the compression spring  140 .  
         [0025]    [0025]FIGS. 4A and B illustrate a spring loaded, hexagonal ball and socket joint end effector  200 . The end effector  200  includes a base  204 , a hexagonal ball  202 , and a lapping plate  206  with a hexagonal bushing  210 . FIG. 4B is a cutaway view of the end effector  200 . The hexagonal ball  202  includes a first cavity  212  along the centerline of a shaft of the hexagonal ball  202  and a second cavity  214  within a portion of the base  204 . A single flexible retaining wire  216  is attached at opposing sides of the second cavity  214  by first and second clamp screws  218  and  220 . The flexible retaining wire  216  travels from the first clamp screw  218  through the first cavity  212  and out of the hexagonal ball  202  around a securing pin  222  back into the hexagonal ball  202  to the second clamp screw  220 . The securing pin  222  is securely attached within the hexagonal bushing  210 . A compression spring  208  is wrapped around the shaft of the hexagonal ball  202  and applies an expanding force to the base  204  and the hexagonal bushing  210 .  
         [0026]    When pressure is applied to the lapping plate  206 , the spring  208  compresses and the flexible retaining wire  216  flexes within the second cavity  214 . The flexible retaining wire  216  keeps the hexagonal ball  202  within the hexagonal bushing  210 .  
       Spring-Loaded Shafts  
       [0027]    [0027]FIGS. 5A and B illustrate a gimbaled-joint end effector  150  with a spring-loaded shaft. The gimbaled-joint end effector  150  includes a gimbaled-joint section  156  coupled to a spring-loaded shaft section  158 . The spring-loaded shaft section  158  includes a first base  162 , a second base  164 , first and second shaft bushings  170  and  172 , a spline shaft  176 , and a spring  178 . The second base  164  is securely attached to a base of the gimbaled-joint section  156 . The second base  164  includes a cavity for receiving the second shaft bushing  172 . The second shaft bushing  172  includes a cavity with a toothed wall configured to receive the spline shaft  176 . The spline shaft  176  and the second shaft bushing  172  are suitably secured within the second base  164  by a pin  180  that passes through opposing sidewalls of the second base  164 , the second shaft bushing  172 , and the spline shaft  176 . The first shaft bushing  170  is positioned within a cavity of the first base  162 . The first shaft bushing  170  includes a cavity with toothed walls for receiving the spline shaft  176 . The first shaft bushing  170  includes a vertical notch  186  for receiving a pin  182  that is securely attached to the spline shaft  176 . The vertical notch  186  allows for motion of the spline shaft  176  vertically within the first shaft bushing  170 .  
         [0028]    A spring  178  is positioned around the spline shaft  176  between the first and second shaft bushings  170  and  172 . The spring  178  maintains an expanding force on the first shaft bushing  170  and the second shaft bushing  172 . Thus, when pressure is applied to the gimbaled-joint section  156 , the second shaft bushing  172  moves the spline shaft  176  with the attached pin  182  up the vertical notch  186  and compresses the spring  178 .  
         [0029]    [0029]FIGS. 6A and B illustrate a one-half ball socket end effector  240  with spring-loaded shaft. The one-half ball and socket end effector  240  includes a socket housing  244 , a half-ball lapping plate  246 , and first and second pins  248  and  250 . The lapping plate  246  includes a one-half ball joint portion  256  that is pivotally received by a semi-circular cavity  252  formed by the socket housing  244 . The pins  248  and  250  pass through opposite sides of the socket housing  244  and protrude into the cavity  252 . The distance between the pins  248  and  250  is less than a diameter of a widest part of the one-half ball joint portion  256 . Thus, the one-half ball joint portion  256  swivels within the socket housing  244  and is maintained within the cavity  252  by the pins  248  and  250 .  
         [0030]    The socket housing  244  is coupled to a shaft  260  that is suitably coupled to a robot arm. The shaft  260  receives a spring support washer  262  and a compression spring  264 . A securing pin  266  allows the shaft  260  to be slidably received by a support structure (not shown). When pressure is applied to the half-ball lapping plate  246 , the shaft  260  slides through the support structure and compresses the spring  264  between the spring support washer  262  and the support structure. Therefore, the one-half ball socket end effector  240  absorbs some applied pressure in order to avoid any unnecessary robot shut-offs.  
       Pneumatic Shock  
       [0031]    FIGS.  7 A-C illustrate a one-half ball socket end effector  300  with a pneumatic shock. The end effector  300  includes a pneumatic shock section  304  that connects to a end effector portion  306 . The pneumatic shock section  304  includes a pneumatic housing  310 , a shock  312 , a housing cap  314 , and a connector  316  coupled to a pneumatic input line  320 . The pneumatic input line  320  receives pressurized air from a pneumatic source pump (not shown) that is controlled by a controlling device (not shown). The shock  312  includes a shaft  324  that passes through an opening at a first end of the pneumatic housing  310 . The shock  312  also includes a plunger portion  326  attached to the shaft  324 . The plunger portion  326  is larger in diameter than the shaft  324  and larger than an opening at a first end of the pneumatic housing  310 . The plunger portion  326  is surrounded by a seal  328  that mates with an interior wall of the pneumatic housing  310  for avoiding air leakage pass the plunger portion  326 . A second end of the pneumatic housing  310  that is opposite the first end is capped by the housing cap  314  that includes a receiving cavity for securely connecting to the connector  316 . The connector  316  securely receives the pneumatic input line  320  from the pneumatic source (not shown).  
         [0032]    The lapping plate portion  306  includes a lapping plate housing  330 , a lapping plate cap  334 , a lapping plate  336 , and a pressure sensor  338 . The lapping plate housing  330  includes a first cavity for threadily attaching the housing  330  to the shaft  324  of the shock  312 . The lapping plate housing  330  includes a second cavity  340  that is sized to receive the lapping plate cap  334  and the lapping plate  336 . The lapping plate  336  is suitably a half ball that is attached to the lapping plate cap  334 . When the half ball and lapping plate cap  334  are inserted into the second cavity  340 , cross-pins  344  are inserted along a cord of the swivel plate base  330  near the opening of the second cavity  340 . The cross-pins  344  are separated at a distance that is less than the diameter of the half ball, thereby keeping the half ball within the second cavity  340 . The pressure sensor  338  is mounted at one end of the second cavity  340  opposite the opening of the cavity  340 . The pressure sensor  338  is attached to the controller device (not shown). The pressure sensor  338  senses pressure from the lapping plate cap  334  based upon pressure on the lapping plate  336  causing the lapping plate cap  334  to move within the cavity  340 . The controller device instructs increases or decreases in pneumatic pressure within the pneumatic housing  310  based on the sensed applied load pressure compared to the prescribed pressure.  
       Multiple Unit  
       [0033]    FIGS.  8 A-C illustrate a multi-end effector support  350 . The 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). The types of end effector units that can be used with the multi-end effector support  350  are any one of the ones shown in FIGS.  3 - 7 . In order to accommodate the plurality of arms  356 , multiple size lapping plates are interspersed and attached to the ends of each of the spring-loaded end effector units  240  attached to the arms.  
         [0034]    It will be appreciated that various jointed end effectors can be used at the end of any of the spring-loaded shafts or at the end of the pneumatic shock. An example end effector that can be used is a cross-pinned ball socket joint end effector that is described in the related copending U.S. Patent Application identified above and incorporated by reference.  
         [0035]    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.