Apparatus and method

Abstract

Apparatus comprising a tool ( 2 ) for forming an aspherical surface on a material ( 14 ), and a support for supporting the material ( 12 ) for rotation about an axis, the arrangement being such that the tool ( 2 ) is restricted to movement with respect to the material ( 14 ) in two substantially linear axes transverse to each other. The apparatus may be a high-performance machine comprising a measuring arrangement ( 18 ) mounted so as to extend substantially across the surface of the material ( 14 ) and serving to measure the distance between the tool ( 2 ) and a referencing region ( 32 ) of the measuring arrangement ( 18 ) which can be in the form of a symmetrical metrology device ( 18 ), the metrology device being structurally unloaded. The apparatus is substantially symmetrical in two substantially vertical planes substantially perpendicular to and intersecting each other.

1 . Apparatus comprising a tool for forming an aspherical surface on a material, and a support for supporting said material for rotation about an axis, the arrangement being such that said tool is restricted to movement with respect to said material in two substantially linear axes transverse to each other. 
   
   
       2 . Apparatus according to  claim 1 , wherein the two substantially linear axes are in a substantially vertical plane in which the rotational axis of the material lies. 
   
   
       3 . Apparatus according to  claim 2 , wherein the two substantially linear axes are constituted by a substantially vertical axis of movement in said vertical plane and a substantially horizontal axis of movement in said vertical plane. 
   
   
       4 . Apparatus according to any preceding claim, wherein said apparatus has a relatively high stiffness loop. 
   
   
       5 . Apparatus according to  claim 4 , wherein the loop of stiffness is a substantially quadrangular stiffness loop between said tool and said material. 
   
   
       6 . Apparatus according to any preceding claim, wherein said tool is a grinding machine tool. 
   
   
       7 . Apparatus according to  claim 6  as appended to  claim 4 , wherein both static loop stiffness and dynamic loop stiffness are at a relatively high level. 
   
   
       8 . Apparatus according to any preceding claim, and further comprising two movement sub-systems by way of which said tool is moved in said two substantially linear axes. 
   
   
       9 . Apparatus according to  claim 8  as appended to  claim 3 , wherein a first movement sub-system moves said tool vertically and a second movement sub-system moves said tool horizontally. 
   
   
       10 . Apparatus according to  claim 8  or  9 , wherein the first movement sub-system is an integral part of the second movement sub-system. 
   
   
       11 . Apparatus according to any one of  claims 8  to  10 , wherein the movement sub-systems are removable from said apparatus. 
   
   
       12 . Apparatus according to any one of  claims 8  to  11 , wherein the movement sub-systems comprise respective pairs of associated linear motors and linear encoders for movement of said tool along respective pairs of bearing rails. 
   
   
       13 . Apparatus according to any preceding claim wherein said tool is a high-performance machine tool further comprising a measuring arrangement mounted so as to extend substantially across a surface of said material and serving to measure the distance between said tool and a referencing region of said measuring arrangement. 
   
   
       14 . Apparatus according to  claim 13 , wherein said measuring arrangement comprises a metrology frame including said referencing region, and a laser interferometer system mounted on the high-performance tool. 
   
   
       15 . Apparatus according to  claim 14 , wherein said referencing region is in the form of a mirror. 
   
   
       16 . Apparatus according to  claim 15 , wherein said mirror is a low-mass straight-edge mirror and the laser interferometer system is a small independent laser interferometer mounted on a carriage unit which carries the tool. 
   
   
       17 . Apparatus according to any one of  claims 14  to  16 , wherein said laser interferometer is mounted on the upper end of an invar support beam, at the lower end of which there is an air-bearing linear variable differential transducer (LVDT) contact probe. 
   
   
       18 . Apparatus according to any one of  claims 14  to  17 , wherein said metrology frame is a symmetrical metrology frame, and said apparatus further comprises a support upon which said metrology frame is mounted, said metrology frame being structurally unloaded. 
   
   
       19 . Apparatus according to  claim 18 , wherein said symmetrical metrology frame is a fully symmetrical metrology frame. 
   
   
       20 . Apparatus according to any one of  claims 14  to  19 , the arrangement being such that the metrology frame is outside of the working volume. 
   
   
       21 . Apparatus according to any preceding claim, wherein said apparatus is substantially symmetrical in two substantially vertical planes substantially perpendicular to and intersecting each other. 
   
   
       22 . Apparatus according to  claim 21 , wherein said apparatus is substantially box-shaped. 
   
   
       23 . Apparatus according to any preceding claim, wherein said tool is a numerically controlled machine tool having a tool surface of a pre-determined shape, and a data processing system for generating geometric information in relation to said tool surface. 
   
   
       24 . Apparatus according to  claim 23  as appended to  claim 6 , wherein said tool surface is an abrasive surface of said grinding tool. 
   
   
       25 . Apparatus according to  claim 23  or  24 , wherein said data processing system uses Non-Uniform Rational B-Splines (NURBS) to monitor wear of said tool surface. 
   
   
       26 . Apparatus according to any one of  claims 23  to  25 , and further comprising a forming device located in one of said substantially linear axes for forming a desired cross-sectional profile on said tool surface, a conditioning device having a conditioning surface for conditioning the formed tool surface, and an inspecting device for determining a cross-sectional profile of said conditioning surface. 
   
   
       27 . Apparatus according to  claim 26 , wherein said forming device is a forming wheel, the conditioning device is a dressing stick and the inspecting device is a surface-contacting probe which contacts the conditioning surface of the dressing stick. 
   
   
       28 . Apparatus according to  claim 26  or  27  wherein said tool comprises a cup wheel which includes said surface of said tool and which has a symmetrical toric cross-sectional profile when formed, such that said measurement of the cross-sectional profile of the conditioning surface in one direction can be electronically transposed to give measurements in a direction substantially perpendicular to that in which the determination is taken. 
   
   
       29 . Apparatus according to any one of  claims 8  to  28 , wherein the combined mass of said tool and the two movement sub-systems is less than substantially 750 Kg. 
   
   
       30 . Apparatus according to any preceding claim, wherein said material is a free-form optic. 
   
   
       31 . Apparatus according to  claim 30  as appended to  claim 22 , wherein for a 2 m diameter free-form optic, the box-shape structure is substantially 3 m in length by substantially 1.5 m in height and weighs substantially 12 tons. 
   
   
       32 . Apparatus according to any preceding claim, and further comprising a thermal stabilising system for controlling the temperature of said apparatus. 
   
   
       33 . Apparatus according to  claim 32 , wherein said thermal stabilising system comprises high diffusivity materials. 
   
   
       34 . Apparatus according to  claim 32  or  33  as appended to  claim 12 , wherein grating scales of the encoders are of low co-efficient of thermal expansion and are suitably restrained to prevent thermal creep. 
   
   
       35 . A method of forming an asphercial surface on a material, comprising rotating said material about an axis of rotation, moving a tool with respect to said surface, and restricting the movement of said tool to movement in two substantially linear axes transverse to each other. 
   
   
       36 . A method according to  claim 35 , wherein the two substantially linear axes of tool movement are in a substantially vertical plane in which the rotational axis of the material lies. 
   
   
       37 . A method according to  claim 36 , wherein the two substantially linear axes are constituted by a substantially vertical axis of movement in said vertical plane and a substantially horizontal axis of movement in said vertical plane. 
   
   
       38 . A method according to any one of  claims 35  to  37 , wherein said tool is a grinding machine tool. 
   
   
       39 . A method according to any one of  claims 35  to  38 , wherein said moving is by way of two movement sub-systems. 
   
   
       40 . A method according to  claim 37 ,  38  or  39 , wherein a first movement sub-system moves said tool substantially vertically and a second movement sub-system moves said tool substantially horizontally. 
   
   
       41 . A method according to  claim 40 , wherein the first movement sub-system is an integral part of the second movement sub-system. 
   
   
       42 . A method according to any one of  claims 39  to  41 , wherein the two movement sub-systems are removable from said tool. 
   
   
       43 . A method according to any one of  claims 35  to  42 , wherein said tool is a high-performance machine tool and further comprising a measuring arrangement mounted so as to extend substantially across a surface of said material and serving to measure the distance between said tool and a referencing region of said measuring arrangement. 
   
   
       44 . A method according to any one of  claims 35  to  43  and further comprising providing a pre-determined shape to a surface of said tool, operating the tool surface against a surface of said material surface, and generating using a data processing system geometric information in relation to the tool surface. 
   
   
       45 . A method to  claim 44 , wherein said data processing system uses Non-Uniform Rational B-Splines (NURBS) for monitoring wear of said tool surface. 
   
   
       46 . A method according to  claim 44  or  45 , and further comprising forming with a forming device a desired cross-sectional profile of said surface of said tool arranged to move in one of said substantially linear axes, said forming occurring in one of said substantially linear axes, conditioning said surface of said tool by a conditioning surface of a conditioning device, and determining with an inspection device the cross-sectional profile of said conditioning surface. 
   
   
       47 . A method according to  claim 46 , wherein said forming is by a forming wheel, the conditioning is by a dressing stick and the inspecting is by a surface-contacting probe which contacts the conditioning surface of the dressing stick. 
   
   
       48 . A method according to  claim 46  or  47 , wherein said tool comprises a cup wheel which includes said surface of said tool and which has a symmetrical toric cross-sectional profile when formed, such that said measurement of the cross-sectional profile of the conditioning surface in one direction can be electronically transposed to give measurements in a direction substantially perpendicular to that in which the determination is taken. 
   
   
       49 . A method according to any one of  claims 35  to  48 , and further comprising a thermally stabilising tool. 
   
   
       50 . A high-performance machine comprising a tool for working at a surface of a material, a support which supports said material, and a measuring arrangement mounted so as to extend substantially across said surface and serving to measure the distance between said tool and a referencing region of said measuring arrangement. 
   
   
       51 . A machine according to  claim 50 , wherein said measuring arrangement comprises a metrology frame which includes said referencing region. 
   
   
       52 . A machine according to  claim 51 , wherein said referencing region is in the form of a mirror and said machine further comprises a laser interferometer system mounted on the high-performance tool. 
   
   
       53 . A machine according to  claim 52 , wherein said mirror is a low-mass straight-edge mirror and the laser interferometer system is a small independent laser interferometer mounted on a carriage unit which carries the tool. 
   
   
       54 . A machine according to  claim 52  or  53 , wherein said laser interferometer is mounted on the upper end of an invar support beam, at the lower end of which there is an air-bearing linear variable differential transducer (LVDT) contact probe. 
   
   
       55 . A machine according to any one of  claims 50  to  54 , wherein said measuring arrangement is structurally unloaded. 
   
   
       56 . A machine according to any one of  claims 50  to  55 , the machine being substantially symmetrical in two substantially vertical planes substantially perpendicular to and intersecting each other. 
   
   
       57 . A machine according to any one of  claims 50  to  56 , wherein said machine is a numerically controlled machine having two substantially linear axes and a rotational axis, a tool surface having a predetermined shape, and a data processing system for generating geometric information in relation to said tool surface. 
   
   
       58 . A machine according to  claim 57 , the arrangement being such that said tool is restricted to movement with respect to said material in said two substantially linear axes. 
   
   
       59 . A machine according to  claim 57  or  58 , wherein said tool is substantially linearly movable across said apparatus, and further comprises a forming device located in the substantially linear path of said tool for forming a desired cross-sectional profile on said tool surface, a conditioning device having a conditioning surface for conditioning the formed tool surface, and an inspecting device for determining a cross-sectional profile of said conditioning surface. 
   
   
       60 . Apparatus comprising a tool for working at a surface of a material, a symmetrical metrology device, and a support upon which said metrology device is mounted, said metrology device being structurally unloaded and including a single referencing device for providing positional information of said tool with respect to said surface. 
   
   
       61 . Apparatus according to  claim 60 , wherein said symmetrical metrology device is a fully symmetrical metrology frame. 
   
   
       62 . Apparatus according to  claim 60  or  61 , and further comprising a laser interferometer system mounted on said tool which has only two axes of tool movement. 
   
   
       63 . Apparatus according to  claim 62 , wherein said two axes of tool movement are substantially linear axes transverse to each other. 
   
   
       64 . Apparatus according to any one of  claims 60  to  63 , wherein said metrology device is outside of the working volume. 
   
   
       65 . Apparatus according to any one of  claims 60  to  64 , said apparatus being substantially symmetrical in two substantially vertical planes substantially perpendicular to and intersecting each other. 
   
   
       66 . Apparatus according to any one of  claims 63  to  65 , wherein said tool is a numerically controlled tool having said two substantially linear axes, a tool surface having a pre-determined shape, and a data processing system for generating geometric information in relation to said tool surface. 
   
   
       67 . Apparatus according to  claim 66 , wherein said tool surface is an abrasive surface of a grinding tool. 
   
   
       68 . Apparatus according to  claim 66  or  67 , wherein said data processing system uses Non-Uniform Rational B-Splines (NURBS) to monitor wear of said tool surface. 
   
   
       69 . Apparatus according to  claim 67  or  68 , wherein said tool is substantially linearly movable across said apparatus, and further comprises a forming device located in the substantially linear path of said tool for forming a desired cross-sectional profile on said abrasive surface, a conditioning device having a conditioning surface for conditioning the formed abrasive surface, and an inspecting device for determining a cross-sectional profile of said conditioning surface. 
   
   
       70 . Apparatus comprising a tool for working at material, said apparatus being substantially symmetrical in two substantially vertical planes substantially perpendicular to and intersecting each other. 
   
   
       71 . Apparatus according to  claim 70 , wherein said apparatus is substantially box-shaped. 
   
   
       72 . Apparatus according to  claim 70  or  71 , wherein said tool is for forming an aspherical surface on said material, and further comprising a support for supporting said material for rotation about an axis, the arrangement being such that said tool is restricted to movement with respect to said material in two substantially linear axes transverse to each other. 
   
   
       73 . Apparatus according to  claim 72 , and further comprising a measuring arrangement mounted so as to extend substantially across said surface and serving to measure the distance between said tool and a referencing region of said measuring arrangement. 
   
   
       74 . Apparatus according to  claim 73 , wherein said measuring arrangement is a symmetrical metrology device, said metrology device being structurally unloaded and including said referencing region for providing positional information of said tool with respect to said surface. 
   
   
       75 . Apparatus according to any one of  claims 72  to  74 , wherein said tool is a numerically controlled tool having said two substantially linear axes, a tool surface having a pre-determined shape, and a data processing system for generating geometric information in relation to said tool surface. 
   
   
       76 . Apparatus according to  claim 75  wherein said tool is linearly movable across said apparatus, and further comprises a forming device located in the substantially linear path of said tool for forming a desired cross-sectional profile on said tool surface, a conditioning device having a conditioning surface for conditioning the formed tool surface, and an inspecting device for determining a cross-sectional profile of said conditioning surface. 
   
   
       77 . A numerically controlled machine comprising a tool and having two substantially linear axes and a rotational axis, a tool surface having a predetermined shape, and a data processing system for generating geometric information in relation to said tool surface. 
   
   
       78 . A machine according to  claim 77 , wherein said tool surface is an abrasive surface of a grinding tool. 
   
   
       79 . A machine according to  claim 77  or  78 , wherein said data processing system uses Non-Uniform Rational B-Splines (NURBS) to monitor wear of said tool surface. 
   
   
       80 . A machine according to any one of  claims 77  to  79 , wherein said tool is for forming an aspherical surface on a material, and further comprises a support for supporting said material for rotation about an axis, the arrangement being such that said tool is restricted to movement with respect to said material in said two substantially linear axes which are transverse to each other. 
   
   
       81 . A machine according to  claim 80 , and further comprising a measuring arrangement mounted so as to extend substantially across the surface of said material and serving to measure the distance between said tool and a referencing region of said measuring arrangement. 
   
   
       82 . A machine according to any one of  claims 77  to  81 , wherein said numerically controlled machine is a high-performance numerically controlled machine. 
   
   
       83 . A machine according to  claim 81  or  82 , wherein said measuring arrangement comprises a symmetrical metrology device, and a support upon which said metrology device is mounted, said metrology device being structurally unloaded and including said referencing region for providing positional information of said tool with respect to the surface of said material. 
   
   
       84 . A machine according to any one of  claims 77  to  83 , wherein said machine is substantially symmetrical in two substantially vertical planes substantially perpendicular to and intersecting each other. 
   
   
       85 . A machine according to any one of  claims 77  to  84 , said tool being substantially linearly movable across said apparatus, and further comprising a forming device located in the substantially linear path of said tool for forming a desired cross-sectional profile on said tool surface, a conditioning device having a conditioning surface for conditioning the tool surface, and an inspecting device for determining a cross-sectional profile of said conditioning surface. 
   
   
       86 . A method comprising providing a pre-determined shape to a surface of a tool, operating the tool surface against a material surface, and generating using a data processing system geometric information in relation to the tool surface. 
   
   
       87 . A method according to  claim 86 , wherein said data processing system uses Non-Uniform Rational B-Splines (NURBS) for monitoring wear of said tool surface. 
   
   
       88 . A method according to  claim 86  or  87 , and further comprising forming an asphercial surface on said material surface, said aspherical spherical surface formed by rotating the material about an axis of rotation, moving said tool with respect to said surface, and restricting the movement of said tool to movement in two substantially linear axes transverse to each other. 
   
   
       89 . A method according to any one of  claims 86  to  88 , and further comprising forming with a forming device a desired cross-sectional profile of the tool surface, the tool being arranged to move in a substantially linear path, said forming occurring in said substantially linear path, conditioning the tool surface by a conditioning surface of a conditioning device, and determining with an inspection device the cross-sectional profile of said conditioning surface. 
   
   
       90 . Apparatus comprising a tool having a material-contacting surface, said tool being substantially linearly movable across said apparatus, a forming device located in the substantially linear path of said tool for forming a desired cross-sectional profile on said material-contacting surface, a conditioning device having a conditioning surface for conditioning the formed material-contacting surface, and an inspecting device for determining a cross-sectional profile of said conditioning surface. 
   
   
       91 . Apparatus according to  claim 90 , wherein said forming device is a forming wheel, the conditioning device is a dressing stick and the inspecting device is a surface-contacting probe which contacts the conditioning surface of the dressing stick. 
   
   
       92 . Apparatus according to  claim 90  or  91 , wherein said material-contacting surface is an abrasive surface of a grinding tool having a cup wheel which has a symmetrical toric cross-sectional profile when formed. 
   
   
       93 . Apparatus according to any one of  claims 90  to  92 , wherein said determining of the cross-sectional profile of the conditioning surface in one direction can be electronically transposed to give measurements in a direction substantially perpendicular to that in which the determination is taken. 
   
   
       94 . Apparatus according to  claim 92  or  93 , wherein said grinding tool is for forming an aspherical surface on a material, and further comprises a support for supporting said material for rotation about an axis, the arrangement being such that said grinding tool is restricted to movement with respect to said material in two substantially linear axes transverse to each other. 
   
   
       95 . Apparatus according to  claim 94 , and further comprising a measuring arrangement mounted so as to extend substantially across said material and serving to measure the distance between said grinding tool and a referencing region of said measuring arrangement. 
   
   
       96 . Apparatus according to any one of  claims 92  to  95 , wherein said grinding tool is a high-performance grinding tool. 
   
   
       97 . Apparatus according to  claim 95  or  96 , wherein said measuring arrangement comprises a symmetrical metrology device, and a support upon which said metrology device is mounted, said metrology device being structurally unloaded and including said referencing region for providing positional information of said grinding tool with respect to the material surface. 
   
   
       98 . Apparatus according to any one of  claims 90  to  97 , wherein said apparatus is substantially symmetrical in two substantially vertical planes substantially perpendicular to and intersecting each other. 
   
   
       99 . Apparatus according to any one of  claims 90  to  98 , wherein said tool is a numerically controlled tool, said material-contacting surface having a predetermined shape, and a data processing system for generating geometric information in relation to said material-contacting surface. 
   
   
       100 . Apparatus according to  claim 99 , wherein said data processing system uses Non-Uniform Rational B-Splines (NURBS) to monitor wear of said material-contacting surface. 
   
   
       101 . A method comprising forming with a forming device a desired cross-sectional profile of a material-contacting surface of a tool arranged to move in a substantially linear path, said forming occurring in said substantially linear path, conditioning said material-contacting surface by a conditioning surface of a conditioning device, and determining with an inspection device the cross-sectional profile of said conditioning surface. 
   
   
       102 . Apparatus according to  claim 101 , wherein said tool is a grinding tool having a cup wheel which has a symmetrical toric cross-sectional profile when formed, said method further comprising electronically transposing the determination of the cross-sectional profile of the conditioning surface taken in one direction to give measurements in a direction substantially perpendicular to that in which the determination is taken. 
   
   
       103 . A method according to  claim 101  or  102 , and further comprising forming an asphercial surface on a material, including rotating said material about an axis of rotation, moving said tool with respect to said surface, and restricting the movement of said tool to movement in two substantially linear axes transverse to each other. 
   
   
       104 . A method according to any one of  claims 101  to  103 , and further comprising providing a pre-determined shape to said material-contacting surface, operating said material-contacting surface against the material surface, and generating using a data processing system geometric information in relation to the tool surface. 
   
   
       105 . A method according to  claim 104 , wherein said data processing system uses Non-Uniform Rational B-Splines (NURBS) for monitoring wear of said material-contacting surface.