Methods for finishing surfaces using tool center point shift techniques

Abstract

The described embodiments relate generally to lapping, polishing or sanding operations of three dimensional objects having curved surfaces. More specifically, methods and apparatuses are described for providing a smooth and consistent looking surface along curved or spline shaped features. In some embodiments, a robot arm is used in conjunction with a computer numerical control (CNC) machine. Methods involve varying the location of a tool center point with respect to a finishing tool depending on the location of the finishing tool with respect to the tool control path.

What is claimed is: 
     
         1 . A method for finishing a surface of a part, the method comprising:
 positioning the part in a computer numerical control (CNC) tool, wherein the part has at least one curved surface adjacent to at least one flat surface; and   finishing the surface of the part by moving a finishing tool along a tool control path that travels along the at least one flat surface and the at least one curved surface, wherein the finishing tool rotates about an axis substantially normal to the at least one curved and at least one flat surfaces during the finishing, wherein during the finishing a location of a tool center point (TCP) varies with respect to the finishing tool depending on the location of the finishing tool with respect to the tool control path.   
     
     
         2 . The method of  claim 1 , wherein the tool control path moves the finishing tool in an orientation that is substantially normal to the surface of the part. 
     
     
         3 . The method of  claim 1 , wherein the finishing tool travels along the tool control path a substantially constant speed. 
     
     
         4 . The method of  claim 1 , tool control path moves the finishing tool from a first flat surface to a first curved surface and to a second flat surface. 
     
     
         5 . The method of  claim 4 , wherein the first curved surface is an edge of the part. 
     
     
         6 . The method of  claim 4 , wherein the first curved surface is a corner of the part. 
     
     
         7 . The method of  claim 1 , wherein after the finishing the part has substantially no visually detectable defects related to the finishing process along the tool control path. 
     
     
         8 . The method of  claim 1 , wherein the part is a thermoplastic molded part. 
     
     
         9 . A system for finishing a surface of a part, comprising:
 a computer numerical control (CNC) tool configured to finish the surface of the part; and   a robotic arm positioned on the CNC tool, the robotic arm configured to maneuver a finishing tool positioned on an end of the robotic arm in a three dimensional tool control path along the surface of the part, the three dimensional tool control path including a path that travels along at least one flat surface and the at least one curved surface of the part, the robotic arm configured to rotate the finishing tool about an axis substantially normal to the at least one curved surface and the at least one flat surface during a finishing operation, wherein the CNC tool is configured to vary a tool center point (TCP) of the finishing tool depending on the location of the finishing tool with respect to the three dimensional tool control path during the finishing operation.   
     
     
         10 . The system of  claim 9 , wherein the part has at least one edge that has a curved surface between a first flat surface and a second flat surface, wherein the CNC tool is configured to maneuver the finishing tool in a tool control path that travels from the first flat surface to the curved surface to the second flat surface. 
     
     
         11 . The system of  claim 10 , wherein the CNC tool is configured to maneuver the robotic arm such that the TCP is at a first location while the polishing tool polishes the first flat surface and moves to a second location while the polishing tool polishes the curved surface and moves to a third location while the polishing tool polishes the second flat surface. 
     
     
         12 . The method of  claim 11 , wherein the movement of the TCP from the first location to the second location and to the third location is continuous. 
     
     
         13 . The method of  claim 9 , wherein the part is a thermoplastic molded part. 
     
     
         14 . The method of  claim 9 , wherein the part is a metal part. 
     
     
         15 . The method of  claim 9 , further comprising:
 a dispenser configured to dispense fluid onto the part during the polishing.   
     
     
         16 . A non-transitory computer readable medium for storing a computer program executable by a processor for finishing a surface of a part, comprising:
 computer code for finishing the surface of the part on a computer numerical control (CNC) tool, the computer code configured to maneuver a finishing tool positioned on a robotic arm of the CNC machine along a tool control path that travels along at least one flat surface and at least one curved surface of the part, wherein the computer code is configured to rotate the finishing tool about an axis substantially normal to the at least one flat and at least one curved surfaces during the finishing, wherein during the finishing a location of a tool center point (TCP) varies with respect to the finishing tool depending on the location of the finishing tool with respect to the tool control path.   
     
     
         17 . The method of  claim 16 , wherein the computer code for moving a finishing tool along a tool control path comprises computer code for maneuvering a robotic arm of the CNC tool in three dimensions along the tool control path. 
     
     
         18 . The method of  claim 17 , wherein the tool control path moves the finishing tool in an orientation that is substantially normal to the surface of the part. 
     
     
         19 . The method of  claim 17 , wherein the finishing tool is positioned on an end of the robotic arm. 
     
     
         20 . The method of  claim 17 , wherein the TCP is established as a datum point for orienting the movement of the robot in three dimensions.