Polishing tools, polishing machines and methods of polishing a workpiece

Abstract

The invention relates to a sub-aperture polishing tool, comprising a support member including an attachment feature for attachment to a sub-aperture polishing machine. At an end of the support member is a polishing head comprising: a base structure attached to or integral with the support member, the base structure being arranged to provide a non-flat surface. The polishing head also comprises an outer shell, at least part of the outer surface of which defines the working surface of the polishing tool, the outer shell being affixed to the base structure so as to enclose a cavity between the outer shell and the non-flat surface. A viscoelastic material filling the cavity, located between the outer shell and the base structure.

1 . A sub-aperture polishing tool, comprising:
 a support member including an attachment feature for attachment to a sub-aperture polishing machine; and   at an end of the support member, a polishing head comprising:   a base structure attached to or integral with the support member, the base structure being arranged to provide a non-flat surface;   an outer shell, at least part of the outer surface of which defines the working surface of the polishing tool, the outer shell being affixed to the base structure so as to enclose a cavity between the outer shell and the non-flat surface; and   a viscoelastic material filling the cavity, located between the outer shell and the base structure.   
     
     
         2 . The sub-aperture polishing tool of  claim 1 , wherein the outer shell comprises a layer of polishing material forming the outer surface and being suitable for sub-aperture polishing of a workpiece, wherein preferably:
 the polishing material is in direct contact with the viscoelastic material, or   the outer shell further comprises an elastic layer located between the layer of polishing material and the viscoelastic material, wherein preferably the elastic layer is in direct contact with the viscoelastic material.   
     
     
         3 . (canceled) 
     
     
         4 . (canceled) 
     
     
         5 . The sub-aperture polishing tool of  claim 1 , wherein the non-flat surface defines a macro-structure which is rigid in use and has a surface profile which varies on a scale of the same order of magnitude as that of the outer shell, the macro-structure being shaped so as to determine the thickness of the viscoelastic material between the outer shell and the non-flat surface at each location on the outer surface, wherein preferably:
 the macro-structure and the outer shell are configured such that the viscoelastic material forms a layer having a substantially constant thickness between the non-flat surface and the outer shell, the surface profile of the macro-structure preferably including a region which follows the shape of the outer shell, wherein most preferably the layer has a thickness in the range of 2 to 200 mm, and/or   the macro-structure and the outer shell are shaped differently relative to one another such that the thickness of the viscoelastic material between varies across different locations on the working surface, and/or   the macro-structure has at least in part a convex or concave curved shape, preferably part-spherical, part-ellipsoidal, part-parabolic or part-toroidal.   
     
     
         6 . (canceled) 
     
     
         7 . (canceled) 
     
     
         8 . (canceled) 
     
     
         9 . The sub-aperture polishing tool of  claim 5 , wherein the macro-structure is formed at least in part by a core which extends towards the outer shell and is configurable to be rigid in use. 
     
     
         10 . The sub-aperture polishing tool of  claim 1 , wherein the non-flat surface defines a micro-structure in the form of a surface texture arranged to grip the shear-stiffening and/or shear-thickening material when the sub-aperture polishing tool is rotated in use, wherein preferably the micro-structure is defined integrally in the base structure and/or is defined in part by a plurality of protrusions affixed to the base structure. 
     
     
         11 . The sub-aperture polishing tool of  claim 1 , wherein the working surface is non-flat when not pressed against a surface. 
     
     
         12 . The sub-aperture polishing tool of  claim 1 , wherein the viscoelastic material is a shear-thickening and/or stress-stiffening viscoelastic material, or
 the viscoelastic material is a shear-thinning and/or stress-softening viscoelastic material.   
     
     
         13 . (canceled) 
     
     
         14 . A sub-aperture polishing machine comprising:
 the sub-aperture polishing tool of  claim 1 ;
 a workpiece holder for holding, in use, a workpiece; and 
 an actuating mechanism in mechanical communication with the attachment feature, wherein the actuating mechanism is configured to rotate, in use, the sub-aperture polishing tool about a first rotational axis passing through the tool while at least a portion of the working surface is in contact with a surface of the workpiece such that the working surface moves against the surface of the workpiece. 
   
     
     
         15 . (canceled) 
     
     
         16 . A method of polishing a workpiece, the method comprising:
 (a) providing a sub-aperture polishing tool in accordance with  claim 1 ;   (b) placing the working surface of the sub-aperture polishing tool in contact with a surface of the workpiece; and   (c) moving the working surface against the surface of the workpiece so as to polish the workpiece surface.   
     
     
         17 . The method of  claim 16 , wherein steps (b) and (c) are performed a plurality of times at different locations on the workpiece surface, and wherein the orientation of the sub-aperture tool with respect to the workpiece surface is different at at least some of the locations. 
     
     
         18 . The method of  claim 16 , wherein;
 the viscoelastic material is a shear-thickening and/or stress-stiffening viscoelastic material, and the working surface is moved against the surface of the workpiece so as to reduce and/or remove mid-spatial defects from the surface of the workpiece, or   the viscoelastic material is a shear-thinning and/or stress-weakening viscoelastic material, and the working surface is moved against the surface of the workpiece so as to preferentially smooth relatively flat regions while retaining sharp edges of the workpiece surface.   
     
     
         19 . The method of  claim 18 , wherein steps (b) and (c) are repeated sequentially at two or more different locations on the workpiece surface, each of the plurality of locations comprising mid-spatial defects having a respective wavelength different to those of at least some of the other locations, and wherein step (b) is performed at each location under polishing conditions selected in dependence on the wavelength of the respective mid-spatial defects. 
     
     
         20 . (canceled) 
     
     
         21 . (canceled) 
     
     
         22 . A polishing tool, comprising:
 a support member including an attachment feature for attachment to a polishing machine; and   at an end of the support member, a polishing head comprising:   a base structure attached to or integral with the support member;   an outer shell, at least part of the outer surface of which defines the working surface of the polishing tool, the outer shell being affixed to the base structure so as to enclose a cavity between the outer shell and the base structure; and   a shear-thinning and/or stress-weakening viscoelastic material filling the cavity, located between the outer shell and the base structure.   
     
     
         23 . The polishing tool of  claim 22 , wherein the outer shell comprises a layer of polishing material forming the outer surface and being suitable for polishing of a workpiece, where the polishing material preferably comprises at least one of polyurethane, poromeric cloth, a tar based viscoelastic polymer and/or another compliant material;
 wherein preferably the polishing material is in direct contact with the shear-thinning and/or stress-weakening viscoelastic material.   
     
     
         24 . (canceled) 
     
     
         25 . The polishing tool of  claim 23 , wherein the outer shell further comprises an elastic layer located between the layer of polishing material and the shear-thinning and/or stress-weakening viscoelastic material, wherein preferably the elastic layer is in direct contact with the viscoelastic material. 
     
     
         26 . A polishing machine comprising:
 the polishing tool of  claim 23 ;   a workpiece holder for holding, in use, a workpiece; and   an actuating mechanism in mechanical communication with the attachment feature, wherein the actuating mechanism is configured to move, in use, the polishing tool relative to the workpiece, while at least a portion of the working surface is in contact with a surface of the workpiece.   
     
     
         27 . (canceled) 
     
     
         28 . A method of polishing a workpiece, the method comprising:
 (a) providing a polishing tool in accordance with  claim 23 ;   (b) placing the working surface of the polishing tool in contact with a surface of the workpiece; and   (c) moving the working surface against the surface of the workpiece so as to polish the workpiece surface.   
     
     
         29 . A method of polishing a workpiece according to  claim 28 , wherein the working surface is moved against the surface of the workpiece so as to preferentially smooth relatively flat regions while retaining sharp edges of the workpiece surface. 
     
     
         30 . A method of polishing a workpiece according to  claim 28 , wherein:
 the polishing tool is a sub-aperture polishing tool and the surface of the workpiece has a different shape and/or surface profile to that of the working surface of the sub-aperture polishing tool at least when the sub-aperture polishing tool is not in contact with the surface of the workpiece, or   the polishing tool is a full-aperture polishing tool and the surface of the workpiece to be polished is substantially the same size as the working surface of the polishing tool, or smaller than the working surface of the polishing tool.   
     
     
         31 . (canceled) 
     
     
         32 . An article polished by the method of  claim 16 , wherein the article is preferably any of: an optical element such as a lens or prism, a diffractive optical element, a semiconductor wafer, a screen for an electronic device, a medical prosthetic, or a mould.