Abstract:
Methods for performing surface lapping using a robotic system are provided. In one embodiment, a method for lapping a surface includes providing a lapping assembly having a first base coupled to a second base by a flexible coupling member, and a lapping medium coupled to the second base, the flexible coupling member being configured to flex to allow the lapping medium to at least partially conform to the surface. The lapping medium is moveably applied to the surface using the lapping assembly. In another embodiment, the method further includes pneumatically controlling a pressure applied by the lapping medium to the surface using a pneumatic device operatively coupled to the second base.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This patent application is a divisional of, commonly-owned U.S. patent application Ser. No. 10/777,388 entitled “Pneumatically Actuated Flexible Coupling End Effectors for Lapping/Polishing” filed on Feb. 12, 2004 (now U.S. Pat. No. 7,118,452), and is related to co-pending, commonly-owned U.S. patent application Ser. No. 10/301,999 entitled “Contour Following End Effectors For Lapping/Polishing” filed on Nov. 21, 2002, U.S. patent application Ser. No. 10/302,042 entitled “Spring-Loaded Contour Following End Effectors for Lapping/Polishing” filed on Nov. 21, 2002 (now Abandoned), and to U.S. patent application Ser. No. 10/302,000 entitled “Automated Lapping System” filed Nov. 21, 2002 and issued as U.S. Pat. No. 6,921,317 on Jul. 26, 2005, which are hereby incorporated by reference. 

   GOVERNMENT LICENSE RIGHTS 
   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 
   This invention relates generally to lapping and polishing surfaces and, more specifically, to robotic lapping and polishing. 
   BACKGROUND OF THE INVENTION 
   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 always ensure that the precise, optic surface finish quality has been met. 
   Therefore, there exists an unmet need to reduce the cost and increase the accuracy of lapping or polishing. 
   SUMMARY OF THE INVENTION 
   The present invention provides methods for performing surface lapping using a robotic system. In one embodiment, a method for lapping a surface includes providing a lapping assembly having a first base coupled to a second base by a flexible coupling member, and a lapping medium coupled to the second base, the flexible coupling member being configured to flex to allow the lapping medium to at least partially conform to the surface. The lapping medium is moveably applied to the surface using the lapping assembly. 
   In another embodiment, a method for lapping a surface includes providing a lapping assembly having a first base coupled to a robotic arm, and a second base moveably coupled to the first base and to a lapping medium; moveably applying the lapping medium to the surface using the lapping assembly; and pneumatically controlling a pressure applied by the lapping medium to the surface using a pneumatic device operatively coupled to the second base. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention are described in detail below with reference to the following drawings. 
       FIG. 1  is a perspective view of an end effector in operation in accordance with an embodiment of the invention; 
       FIG. 2  illustrates a perspective view of an exemplary pneumatic end effector effector in accordance with an embodiment of the invention; 
       FIG. 3  is a cross-sectional view of the pneumatic end effector shown in  FIG. 2 ; 
       FIG. 4  is an exploded view of exemplary materials layered on an end effector; 
       FIGS. 5A-C  illustrate perspective and plan views of the end effector shown in  FIG. 2 ; and 
       FIGS. 6A  and B illustrate side views of the end effector shown in  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention relates to apparatus and methods for providing end effectors for performing surface lapping using a robotic system. Many specific details of certain embodiments of the invention are set forth in the following description and in  FIGS. 1-6  to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that the present invention may be practiced without several of the details described in the following description. 
     FIG. 1  shows an embodiment of an end effector  30  in accordance with an embodiment of the present invention that is attached to a robot  20  for polishing and lapping a work product  32 . A non-limiting example of the product  32  is a core or cavity injection mold for making polycarbonate aircraft canopies. The work product  32  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  30  pivots at an end of the robot  20 , but does not rotate about an axis that is perpendicular to a planar surface of the end effector  30 . In other words, the end effector  30  maintains a substantially orthogonal position relative to the work product  32 . 
   A non-limiting example of the robot  20  includes a Fanuc, Inc. robot with soft float. Soft float allows the robot  20  to apply pressure to a surface without resulting in undesired shut-offs. Because the robot  20  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. 
     FIG. 2  illustrates a perspective view of an exemplary pneumatic end effector  30  in accordance with an embodiment of the invention. 
     FIGS. 3 and 4  illustrate cross-sectional and exploded views, respectively, of the end effector  30  of  FIG. 2 . As shown in  FIG. 3 , in one embodiment, the end effector  30  receives compressed air through an air logic controller  34  as controlled by a proportional integral derivative (PID) controller  36 . The air logic controller  34  receives high pressure air from a source. The air logic controller  34  provides constant pressure between the end effector flexible coupling member  50  and the work product  32 , The PID controller  36  includes a control knob to increase or decrease the air pressure variably by turning the knob. The air logic controller  34  displays a digital readout of the air pressure. commanded by the control knob of the PID controller  36  and senses the pressure through the pneumatic tube  70 . The sensed pressure is constantly monitored by the ND controller  36 . The PID controller  36  compensates for pressure variations by dispensing more or less air pressure through the air logic controller  34  as required to maintain constant pressure at the end effector plate  50 . 
   As further shown in  FIGS. 2-4 , in this embodiment, the end effector  30  includes a fist mounting plate  40 , a piston cylinder  42 , a piston  44 , a second mounting plate  48 , and a flexible coupling member  50 . In one particular embodiment, the flexible coupling member  50  includes a cross-slotted cylinder that acts as a flexible coupling between the second plate  48  and the abrasive lapping medium. The flexible coupling member  50  may be fabricated out of any suitable semi-rigid material. As described more fully below, the end effector  30  having the flexible coupling member  50  may provide significant advantages over the prior art. 
   As shown in  FIG. 4 , the piston cylinder  42  includes a piston cavity  68  that receives the piston  44 . An O-ring  76  is positioned around the piston  44  in order to come in contact with the walls of the piston cavity  68  and the piston  44 . The second mounting plate  48  includes bushings  64 , such as polymer bushings, that are mounted within throughholes of the second mounting plate  48 . Guideposts  52  are securely received by the piston cylinder  42 . The bushings  64  slideably receive the guideposts  52 . The second mounting plate  48  is attached to the piston  44  by a plurality of bolts  66  ( FIG. 4 ). 
   As best shown in  FIG. 4 , attached to a lapping end or side of the flexible coupling member  50  is an adhesively bonded polymer bumper  58  for damage control in the event of an abrasive media disbond, flexible adhesive media  90  such as polysulphide or silicone, a layer of pitch  92 , and a lapping abrasive  94 , such as diamond media plated on a flexible cloth gridwork. 
   The first mounting plate  40  includes a cavity  72  ( FIG. 3 ) that communicates at one end with the piston cavity  68 , and at a second end receives a pneumatic tube  70  that is coupled to the air logic controller  34 . Similarly, the second mounting plate  48  includes a slurry cavity  88  that is open at one end to a slurry cavity  82  within the flexible coupling member  50 . A second opening of the slurry cavity  88  receives a slurry tube  80  that receives an abrasive/polishing slurry from a slurry system  96 . In one embodiment, the slurry system  96  is coupled to a computer controller, such as described in copending patent application Automated Lapping System. 
     FIGS. 5A-C  illustrate perspective and plan views of an embodiment of a latch mechanism  110  that attaches the end effector flexible coupling member  50  to the second mounting plate  48  and thus the piston  44 . The latch mechanism  110  includes two halves that are rotatably attached via bolts  116  to a side of the second mounting plate  48  that is opposite the side that is in contact with the piston  44 . Each of the halves include coupling gears ( FIG. 5B ) that cause one of the halves to be activated if the other half is activated. Each of the halves include protruding pins  113  ( FIG. 4 ) that pass through holes in the second mounting plate  48  into a spring cavity  111  that includes a spring  112  ( FIGS. 4 and 5C ). The spring  112  provides a contracting force on the protruding pins  113  that forces the halves of the latch mechanism  110  into a closed position. The base of the second mounting plate  48  includes a recessed area  118  ( FIG. 5A ) between the two halves of the latch mechanism  110 . The recessed area  118  includes a chocking pin  114 . The flexible coupling member  50  includes an external groove  130  and a chocking pin receiving hole  132  ( FIG. 4 ). The flexible coupling member  50  is coupled to the second mounting plate  48  by opening up the latch mechanism  110 , inserting the flexible coupling member  50  into the recessed area  118 , so that the chocking pin  114  is received by the chocking pin hole  132 . Then, the latch mechanism  110  is placed in a closed position whereby portions of each half of the latch mechanism  110  are received within the groove  130 . 
     FIG. 6A  illustrates a side view of the end effector  30  when the piston  44  is in a non-compressed or partially compressed position. In the non-compressed position the piston  44  extends from the piston cylinder  42  with the second mounting plate  48  being guided by the guide posts  52 .  FIG. 6B  illustrates a side view of the end effector  30  when the piston  44  is in a fully compressed position. In the fully compressed position, the piston  44  is fully received within the piston cylinder  42 . The second mounting plate  48  makes contact (or near contact) with the piston cylinder  42  as guided by the guide posts  52 . 
   In operation, the end effector  30  may be positioned proximate the work product  32  by the robot  20  such that the lapping abrasive  94  is engaged against a portion of the work product  32  that is to be polished. As the lapping abrasive  94  engages against the work product  32 , a pressure within the piston cavity  68  is controlled via the pneumatic tube  70  by the air logic controller  34  so that the lapping abrasive  94  is applied with a variably adjustable constant force against the work product  32 . A flow of abrasive slurry may enter the slurry cavity  82  via the slurry tube  80  from the slurry supply system  96 , and may flow onto the work product  32  to facilitate the polishing process. 
   It will be appreciated that the end effector  30  having the flexible coupling member  50  provides a semi-rigid or flexible coupling between the lapping abrasive  94  and the second plate  48 . Thus, the flexible coupling member  50  may flex under pressure to allow the lapping abrasive  94  to at least partially conform to the surface of the work piece  32 . 
   Embodiments of apparatus and methods in accordance with the present invention may provide significant advantages over the prior art. For example, because the end effector  30  includes the flexible coupling member  50  that maintains a semi-rigid state suitable for driving the lapping abrasive  94 , yet still allows a degree of flexure between the end effector  30  and the work product  32 . Thus, unlike alternate polishing systems that assure normality of the lapping head to the work product  32 , the end effector  30  in accordance with the present invention allows the lapping abrasive  94  to conform to the surface of the work product  32 . 
   Furthermore, because the end effector  30  includes a pneumatic piston  44 , the force with which the lapping abrasive  94  is applied to the work product  32  may be adjustably controlled to a desired operating pressure that remains constant as the lapping abrasive  94  is applied over various portions of the work product  32 . Thus, the polishing of the work product  32  may be performed in a controllable, automated manner, and may thereby improve the quality and reduce the costs associated with the polishing process. 
   While preferred and alternate embodiments of the invention have 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 these preferred and alternate embodiments. Instead, the invention should be determined entirely by reference to the claims that follow.