Abstract:
The invention relates to a machine comprising a train of grinding stones ( 21 ), mounted to rotate about a first axis (A–A′), a lens support ( 15 ), provided with means ( 37 ), for rotating the lens ( 35 ) about a second axis (B–B′) parallel to the first axis (A–A′), means ( 13, 39 ) for relative radial and axial positioning of the lens support ( 15 ) with relation to the train of grinding ( 21 ) and a tool carrier unit ( 17 ) with a tool ( 81; 83; 85 ) fixed to a tool support shaft ( 75 ) rotating about a third axis (C–C′). In an active position the tool is adjacent to the second axis (B–B′) and the third axis (C–C′) with a variable angle with relation to the second axis (B–B′). The tool support unit ( 17 ) further comprises means ( 79 ) for controlling the angle of inclination of the third axis (C–C′) with relation to the second axis (B–B′), when the tool ( 81, 83, 85 ) is at a distance from the lens ( 35 ). Of application to the grinding of ophthalmic lenses.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a machine for grinding optical lenses. 
   Known machines (EP 0 350 216) are used to carry out economically and efficiently back-beveling operations to grind down the sharp edges of an ophthalmic lens blank after it has been ground. 
   Such machines are not entirely satisfactory. Specifically, the extent of the surface machined by the back-beveling grindstone depends on the curvature of the lens. During the back-beveling operation and in the case of greatly curved lenses, the back-beveling grindstone is in contact with the lens over a greater surface area than in the case of flat or virtually flat lenses. The quality of the back-beveling and consequently the appearance of the lens obtained therefore vary depending on the curvature of the lens. 
   Furthermore, the machines of the aforementioned type (see for example JP 8 155 945) are used more precisely to carry out operations of grooving and/or drilling the lens, but are bulky. 
   The main object of the invention is to remedy these disadvantages, that is to say to provide a machine that can be used to simply back-bevel, groove and/or drill optical lenses with a constant quality of operation irrespective of the curvature of the lens, and that is not very bulky. 
   SUMMARY OF THE INVENTION 
   Accordingly, the subject of the invention is a grinding machine of the aforementioned type, characterized in that the control means are suitable for retracting the tool-carrier shaft via the control of the angle of inclination. 
   Furthermore, to carry out the operations of back-beveling, grooving and drilling, the known machines of the aforementioned type require complex mechanisms to move the tool-carrier assembly relative to the lens support. 
   Another object of the invention is to obtain a grinding machine of the aforementioned type whose structure is simplified. 
   As a result, according to another aspect of the invention, the machine of the aforementioned type comprises means for relative movement of the tool-carrier shaft relative to the lens support in translation along the third axis when the tool is in the active position. Further, the means for relative movement comprise means for relative translation of the tool-carrier shaft relative to the second axis in a first direction, parallel to the second axis, means for pseudo-translation of the lens support relative to the second axis in a second direction perpendicular to the second axis, and means for synchronizing the translation and pseudo-translation means. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
     An exemplary embodiment of the invention will now be described with regard to the appended drawings in which: 
       FIG. 1  is a partial three-quarter top view in perspective of the pertinent portions of a grinding machine according to the invention; 
       FIG. 2  is a view in partial section along the line II—II of  FIG. 1 ; 
       FIG. 3  is a view in perspective taken along the arrow III of  FIG. 1  of a detail of the grinding machine according to the invention, with the tool-carrier assembly in the retracted position; 
       FIG. 4  is a partial view in section along the line IV—IV of  FIG. 1  of the grinding machine according to the invention during a drilling operation; and 
       FIG. 5  is a detail view of  FIG. 4 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The grinding machine represented in  FIGS. 1 to 5  is intended to produce a beveled and back-beveled optical lens, and carry out grooving and drilling operations based on a generally circular lens blank. 
   This grinding machine comprises a frame  11 , a grinding assembly  13 , a lens support  15 , a tool-carrier assembly  17  and a control unit  19 . 
   The grinding assembly  13  comprises a grindstone set  21  mounted rotatably about a first horizontal axis A–A′ in a grindstone support  22  and rotated by a grinding motor (not shown). 
   The grindstone set  21  consists of several juxtaposed grindstones  21 A to  21 D. The grindstones are associated with a type of lens to be ground and with various steps of the grinding process: a grindstone  21 A for rough-cutting mineral lenses, a grindstone  21 B for rough-cutting synthetic lenses, a finishing grindstone with beveling  21 C provided with a circular groove  23 , and a grindstone  21 D for polishing with beveling. This grindstone set  21  may where necessary be fitted with finishing or polishing grindstones without beveling. 
   This grindstone set  21  is fixedly mounted on a grindstone shaft  25 , itself mounted freely rotatable in the support  22  about the first axis A–A′. 
   The bottom portion  27  of the grindstone support  22  is mounted slidingly in an axial direction parallel to the first axis A–A′ on a sliding bar  29 . Means (not shown) are used to drive the grinding assembly  13  in translation in this axial direction by sliding the grindstone support  22  along the sliding bar  29 . 
   The lens support  15  comprises a carriage  31  mounted tiltably on the frame  11  and furnished with two half-shafts  33 A and  33 B suitable for gripping the lens blank  35 , a motor  37  for rotating the lens blank  35 , and means  39  for radially positioning the carriage  31  relative to the first axis A–A′. 
   The carriage is articulated by one longitudinal edge  41  about a tilt shaft  43  disposed parallel to the first axis A–A′. 
   The two half-shafts  33 A and  33 B are mounted along the other longitudinal edge  45  of the carriage  31 . These half-shafts  33 A and  33 B are disposed on a second horizontal axis B–B′ which, during grinding, is parallel to the first axis A–A′. Furthermore, these half-shafts  33 A and  33 B are furnished with free ends  47 A and  47 B facing one another, suitable for gripping the lens blank  35 . 
   The drive motor  37  of the lens blank  35  rotates the half-shaft  33 B and the half-shaft  33 A about the second axis B–B′ via a transmission mechanism (not shown). 
   As illustrated in  FIG. 4 , the radial means  39  of positioning the carriage  31  relative to the first axis A–A′ comprise a drive mechanism  51  and a guide rod or button  53 . 
   The drive mechanism  51  comprises a drive worm  55  in interaction with a nut  57 . The worm  55  is mounted rotatably on the frame  11  and disposed in a radial direction perpendicular to the axial direction. In the example illustrated in  FIG. 2 , the drive worm  55  is vertical. 
   This drive worm  55  is rotated by a motor  59  integral with the frame  11 . 
   Furthermore, the bottom end of the actuation rod  53  is attached to the nut  57 . The edge  45  of the carriage  35  adjacent to the second horizontal axis B–B′ is resting on the top end of this rod  55 . 
   When the motor  59  rotates the drive worm  55 , the nut  57  and the actuation rod  53  move in translation in the vertical direction. The action of the rod  53  on the carriage  31  is used to move the second axis B–B′ relative to the first axis A–A′ by tilting the carriage  31 . For tilting movements of small amplitude, the movement of the second axis B–B′ relative to the first axis A–A′ can be likened to a vertical pseudo-translation movement. Furthermore, the carriage  31  is furnished with tracers  61  of the lens blank  35 , connected to the control unit  19 . 
   With reference to  FIGS. 1 ,  2  and  4 , the tool-carrier assembly  17  comprises a support  71  furnished with a protruding link arm  73 , a tool-carrier shaft  75 , a motor  77  for rotating the tool-carrier shaft  75 , and means  79  for actuating the tool-carrier shaft  75 . 
   As illustrated in  FIG. 2 , the support  71  is of generally cylindrical shape. It is mounted rotatably on the grindstone support  22  about a horizontal pivot axis D–D′, perpendicular to the first axis A–A′. 
   The tool-carrier shaft  75  is mounted rotatably about a third axis C–C′ at the free end of the link arm  73 . In the example illustrated in  FIGS. 1 to 5 , the tool-carrier shaft  75  remains in the vertical plane which passes through the first axis A–A′. 
   This shaft  75  supports a grindstone  81  for back-beveling, a grindstone  83  for grooving, and a bit  85  for drilling. 
   The back-beveling grindstone  81  has a much smaller diameter than that of the grindstones  21 A to  21 D of the grindstone set. As illustrated in  FIG. 5 , this back-beveling grindstone has externally a cylindrical mid-surface  87 , surrounded by two frustoconical surfaces  89  and  91  which converge as they move away from this surface. As illustrated in  FIG. 5 , it is a surface  89  having a half-cone angle at the top that is relatively small, for example of the order of 35°, and an opposite surface  91  having a half-cone angle at the top that is relatively large, for example 55°. 
   The grooving grindstone  83  comprises a single, narrow, cylindrical mid-surface  92 . In the example illustrated in  FIG. 5 , the width of the cylindrical mid-surface lies between 0.5 and 1.6 mm. 
   The drill bit  85  is mounted at the free end of the tool-carrier shaft  75  and is aligned with the third axis C–C′. 
   The motor  77  for rotating the tool-carrier shaft  75  is connected to this shaft  75  by transmission means comprising in particular a pulley  93  and a belt  95  ( FIG. 1 ). 
   The means  79  for actuating the tool-carrier shaft  75  comprise ( FIG. 1 ) an actuating motor  101  whose output shaft  103  is furnished at its end with a worm  105 . This worm  105  interacts with a tangential toothed wheel integral with the support  71 . 
   These actuating means  79  rotate the support  71  about the pivot axis through an angular movement of at least 30°, and preferably 180°. 
   Consequently, during this rotary movement, the angle formed between the third axis C–C′ and the first axis A–A′ or the second axis B–B′ varies by at least between 0 and 30° and preferably between 0 and 180°. 
   The control unit  19  is used to control, on the one hand, the movement of the grindstone support  22  in the axial direction and, on the other hand, the movement of the carriage  31  about the articulation shaft  43 . Thus, this control unit  19  coordinates the relative movement of the lens support relative to the grindstone set. Furthermore, this control unit is furnished with synchronization means (not shown) used to control simultaneously the axial movement of the grindstone support  22  and the movement of the carriage  31  about the articulation shaft, according to a predefined control law. 
   As an example, a description of a grinding operation will now be given followed by an operation of drilling an ophthalmic lens blank using the grinding device of  FIGS. 1 to 5 . 
   Initially and as illustrated in  FIG. 3 , the support  71  is oriented so that the arm  73  and the tool-carrier shaft  75  are in a retracted position beneath the grindstone set  21 . Thus, the space situated above the grindstones  21 A to  21 D is totally clear. 
   As is known, the blank  35  is wedged between the two ends  47 A and  47 B of the half-shafts  33 A and  33 B by an adapter suitably positioned on the blank. 
   Consequently, the motor for rotating the grindstones  21 A to  21 D is activated. The grindstone set  21  is then rotated about the first axis A–A′ by this motor. The control unit  19  controls the means of axial movement of the grindstone support  22  and the means of radial movement  39  of the carriage  31  to position the lens blank  35  in contact with the rough-cutting grindstone  21 A. 
   The motor  37  for rotating the lens blank  35  relative to the second axis B–B′ is then actuated to cause this blank  35  to rotate about this second axis B–B′. 
   Simultaneously, thanks to the mechanism  51 , the distance between the first axis A–A′ and the second axis B–B′ is adjusted according to the angular position of the blank  35  about the second axis B–B′, to suit the shape of the spectacle frame onto which the lens is to be mounted after it has been processed. 
   In the same manner, the lens is then brought to the grindstone for finishing with beveling  21 C. 
   The blank then has its final contour. A drilling operation is then carried out. 
   In a first step, the grindstone support  22  is positioned at the end of axial travel. This end of travel corresponds to a position of the grindstone support  22  at the extreme right of  FIG. 1 . Simultaneously, the carriage  31  is moved away from the grindstone set  21  by upward movement of the guide rod  53  up to an end of radial travel. 
   The motor  101  for actuating the tool-carrier assembly  17  is then activated. The rotation of the output shaft  103  of this motor  101  rotates the worm  105  about an axis parallel to the first axis A–A′. This worm  105  interacts with the toothed wheel provided on the support  71 . The support  71  is then rotated about its pivot axis D–D′. This rotary movement of the support  71  causes the tool-carrier shaft  75  to pivot about the pivot axis D–D′ in the vertical plane passing through the axis A–A′, from the retracted position shown in  FIG. 3 , situated beneath the grindstone set, to an active position shown in  FIG. 4 , situated above the grindstone set. 
   Based on the data received from the tracers  61 , the control unit  19  determines the angle formed by the tangent to the outer or inner surface of the lens blank  35  at the drilling point of this blank  35  and the direction perpendicular to the second axis B–B′ which passes through this drilling point. This angle is marked  α  in  FIG. 5 . The angle α depends on the curvature of the lens blank  35 . 
   The motor  101  for actuating the tool-carrier assembly  17  is deactivated when the angle formed by the third axis C–C′ and the second axis B–B′ is equal to this angle  α . 
   The means for axial movement of the support  22  and the means for radial movement  51  of the carriage  31  are then controlled to bring the end of the bit  85  into contact with the drilling point ( FIG. 4 ). 
   The bit  85  is then perpendicular to the outer surface of the lens blank  35 , irrespective of the curvature of this blank. 
   The motor  77  for rotating the tool-carrier shaft  75  is then activated. The means for axial movement of the support and the means for radial movement  39  of the carriage  31  are then controlled by the means for synchronizing of the control unit  19  to move the tool-carrier shaft  75  in translation along the third axis C–C′ while keeping the inclination of this third axis C–C′ relative to the second axis B–B′ constant and equal to α, throughout the whole drilling operation. More precisely, during the drilling, the support  22  moves leftward and the carriage  31  moves downward so that the drilling point moves exactly along the axis C–C′. 
   As a variant, the angle formed by the third axis C–C′ and the second axis B–B′ is controlled before a back-beveling operation so that the angle of attack between the surface of the back-beveling grindstone  81  and the sharp edge of the lens blank  35  to be ground is equal to a predetermined value irrespective of the curvature of this blank. 
   In another variant, the angle of inclination of the third axis C–C′ relative to the second axis B–B′ is controlled before a grooving operation so that the mid-plane P of the grooving grindstone  85  is for example parallel to the tangent to the convex surface of the lens blank at the sharp edge, or else parallel to a direction mid-way between the tangents of the convex and concave surfaces. 
   This makes it possible to obtain a high degree of uniformity of width of the groove over the whole periphery of the lens irrespective of the shape of the latter (curvatures and peripheral profile). 
   Thanks to the invention that has just been described, it is possible to have a machine which can be used at the same time to grind, back-bevel, groove and drill ophthalmic lens blanks of different curvatures, while maintaining the quality of these operations irrespective of the curvature of the lens blank. 
   This machine can be used to perform all these operations economically and effectively.