Patent Publication Number: US-6336057-B1

Title: Lens grinding apparatus

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an eyeglass lens grinding apparatus for grinding the periphery of an eyeglass lens. 
     An eyeglass lens grinding apparatus is known which grinds the periphery of an eyeglass lens so that the eyeglass lens fits into an eyeglass frame. In this type of apparatus, a lens to be processed is mounted on one lens rotating shaft via a mounting jig such as a suction cup fixed to a front surface of the lens, while a rear surface of the lens is pressed by a lens holder of another lens rotating shaft, thereby clamping or chucking the lens using the two lens rotating shafts for processing. 
     In general, a chamfering process is performed subsequently to the peripheral processing so as to remove sharp corner portions from peripheral edges of the lens. Conventionally, this chamfering process is effected manually using a so-called hand grinder having a conical grinding wheel after the lens subjected to a finishing process is detached from the grinding apparatus. However, this operation requires expert skill and is not easy to perform. 
     Accordingly, the present applicant or assignee proposed an apparatus which makes it possible to perform the chamfering process efficiently with a simple arrangement, as disclosed in Japanese Unexamined Patent Publication No. 254000/1997 and U.S. Pat. No. 5,803,793. The apparatus has a grinding-wheel rotating shaft on which a chamfering grinding wheel and other processing grinding wheels are disposed coaxially. The apparatus controls the relative movement of the grinding-wheel rotating shaft with respect to the lens rotating shaft as well as the axial movement of the grinding-wheel rotating shaft on the basis of chamfering process data, to thereby perform the chamfering process of the lens front and rear surfaces without dismounting the lens subjected to the finishing process from the lens rotating shaft. The chamfering process data is obtained by measuring edge positions on the front and rear surfaces of the lens on the basis of radius vector data on the eyeglass frame and on the basis of the result of that measurement. 
     However, if the lens to be processed is clamped by the lens rotating shafts, the lens is deflected (deformed) depending on the shape of its front surface side. Generally, if the curve of the lens front surface is gentle with respect to the shape of the lens receiving surface of a mounting jig (in the case of a minus lens), the lens is deformed toward its rear surface side due to a pressing force of the lens holder. In contrast, in a case where the curve of the lens front surface is sharp (in the case of a plus lens), the lens is deformed toward its front surface side. In the case of an unprocessed lens, the stress of this deformation is applied to the overall lens, and is therefore small. If the lens is made smaller by rough grinding, however, since the portion for absorbing the stress is reduced, the deformation is enlarged. The smaller power the lens, that is, smaller the lens thickness becomes, the greater the deformation. The difference of deformation amount before and after rough grinding can reach about 0.2 mm at maximum. For this reason, if the chamfering process is performed on the basis of the lens shape data measured before rough grinding, there are cases where the actual amount of chamfering will differs from an intended amount of chamfering, and the chamfering will not be uniform visually. 
     SUMMARY OF THE INVENTION 
     In view of the above-described problems, it is an object of the present invention to provide an apparatus which makes it possible to perform the chamfering process (the processing of edge corner portions) with high accuracy. 
     The present invention provides the followings: 
     (1) An eyeglass lens grinding apparatus for grinding a periphery of a lens, comprising: 
     a lens holding system which holds a lens while clamping the lens; 
     a data input system which inputs shape data of an eyeglass frame to which the lens is fitted, and layout data of the lens with respect to the eyeglass frame; 
     an edge-position-data calculating system which, on the basis of the data inputted by the data input system, obtains edge position data of the lens after layout; 
     a first measuring system which measures an edge position of the lens before processing that is held by the lens holding system, on the basis of the edge position data obtained by the edge-position-data calculating system; 
     a second measuring system which measures an edge position of the lens after rough grinding, on the basis of the edge position data; 
     a chamfering-process-data calculating system which obtains chamfering process data for processing a corner portion of an edge of the lens after finish processing, on the basis of a result of measurement by the second measuring system; 
     a chamfering process system having a chamfering grinding wheel, which processes the corner portion of the edge of the lens after the finish processing; and 
     a chamfering-process controlling system which controls the chamfering process system on the basis of the chamfering process data obtained by the chamfering-process-data calculating system. 
     (2) The eyeglass lens grinding apparatus according to (1), wherein the edge position data obtained by the edge-position-data calculating system are radius vector data including a radius vector angle and a radius vector length of the lens. 
     (3) The eyeglass lens grinding apparatus according to (1), further comprising: 
     a determining system which determines whether or not the lens can be processed on the basis of a result of measurement by the first measuring system; and 
     a notifying system which notifies a result of determination by the determining system. 
     (4) The eyeglass lens grinding apparatus according to (1), further comprising: 
     a storage system which stores an inclination angle of a finishing grinding wheel; and 
     an information inputting system which inputs information on a positional change in at least one of a lens front surface and a lens rear surface with respect to the edge position data, 
     wherein the chamfering-process-data calculating system obtains the chamfering process data on the basis of the edge position obtained by the second measuring system, the information on a positional change inputted by the information inputting system, and the inclination angle stored in the storage system. 
     (5) The eyeglass lens grinding apparatus according to (4), wherein the information on a positional change is information obtained by measuring an edge position different from the edge position measured by the second measuring system on the basis of the edge position data. 
     (6) The eyeglass lens grinding apparatus according to (5), further comprising: 
     a position calculating system which calculates, on the basis of the edge position data, another edge position different from the edge position that is measured by the second measuring system on the basis of the edge position data, 
     wherein the second measuring system also measures the edge position obtained by the position calculating system. 
     (7) The eyeglass lens grinding apparatus according to (1), further comprising: 
     a beveling process system having a beveling grinding wheel for such a finishing operation as to form a bevel in the lens after rough grinding; 
     a beveling-process-data calculating system which obtains beveling process data for forming the bevel in the edge of the lens after rough grinding, on the basis of the result of measurement by the second measuring system; and 
     a beveling-process controlling system which controls the beveling process system on the basis of the beveling process data obtained by the bevel-process-data calculating system. 
     (8) The eyeglass lens grinding apparatus according to (7), further comprising: 
     a storage system which storing an inclination angle of the beveling grinding wheel; and 
     an information inputting system which inputs information on a positional change in at least one of a lens front surface and a lens rear surface with respect to the edge position data, 
     wherein the beveling-process-data calculating system obtains the beveling process data on the basis of the edge position obtained by the second measuring system, the information on the positional change inputted by the information inputting system, and the inclination angle stored in the storage system. 
     (9) The eyeglass lens grinding apparatus according to (8), further comprising: 
     a position calculating system which, on the basis of the edge position data, obtains as the information on a positional change another edge position different from the edge position measured by the second measuring system on the basis of the edge position data, 
     wherein the second measuring system also measures the edge position obtained by the position calculating system. 
     (10) The eyeglass lens grinding apparatus according to (1), further comprising: 
     a selecting system which selects whether or not the chamfering process by the chamfering process system is to be performed; and 
     a measurement controlling system which executes both of the measurement by the first measuring system and the measurement by the second measuring system if it is selected by the selecting system that the chamfering process by the chamfering process system is to be performed. 
     (11) The eyeglass lens grinding apparatus according to (1), further comprising: 
     a selecting system which selects whether or not the chamfering process by the chamfering process system is to be performed; 
     a measurement controlling system which executes both of the measurement by the first measuring system and the measurement by the second measuring system if it is selected by the selecting system that the chamfering process by the chamfering process system is to be performed, and which executes only the measurement by the first measuring system if it is selected by the selecting system that the chamfering process by the chamfering process system is not to be performed; 
     a beveling process system having a beveling grinding wheel for such a finishing operation as to form a bevel in the lens after rough grinding; 
     a beveling-process-data calculating system which obtains beveling process data for forming the bevel in the edge of the lens after rough grinding; and 
     a beveling-process controlling system which controls the beveling process system on the basis of the beveling process data obtained by the bevel-process-data calculating system, 
     wherein if it is selected by the selecting system that the chamfering process is to be performed, the beveling-process-data calculating system obtains the beveling process data on the basis of a result of measurement by the second measuring system, and if it is selected by the selecting system that the chamfering process is not to be performed, the beveling-process-data calculating system obtains the beveling process data on the basis of a result of measurement by the first measuring system. 
     (12) The eyeglass lens grinding apparatus according to (1), further comprising: 
     a rough grinding system having a rough grinding wheel for rough grinding the lens; 
     a rough-grinding-data calculating system which obtains rough grinding data for rough grinding the lens, on the basis of the edge position data; and 
     a rough-grinding controlling system which controls the rough grinding system on the basis of the rough grinding data obtained by the rough-grinding-data calculating system. 
     (13) The eyeglass lens grinding apparatus according to (12), further comprising: 
     a determining system which determines whether or not the lens can be processed on the basis of a result of measurement by the first measuring system; and 
     a notifying system which notifies a result of determination by the determining system, 
     wherein the rough-grinding-data calculating system obtains the rough grinding data if it is determined by the determining system that the lens can be processed; and 
     wherein the rough-grinding controlling system operates the rough grinding system if it is determined by the determining system that the lens can be processed. 
     (14) The eyeglass lens grinding apparatus according to (12), further comprising: 
     a beveling process system having a beveling grinding wheel for such a finishing operation as to form a bevel in the lens subjected to rough grinding by the rough grinding system; 
     a beveling-process-data calculating system which obtains the beveling process data for forming the bevel in the edge of the lens subjected to rough grinding, on the basis of the result of measurement by the second measuring system; and 
     a beveling-process controlling system which controls the beveling process system on the basis of the beveling process data obtained by the bevel-process-data calculating system. 
     (15) The eyeglass lens grinding apparatus according to (14), further comprising: 
     a storage system which stores an inclination angle of the beveling grinding wheel; and 
     an information inputting system which inputs information on a positional change in at least one of a lens front surface and a lens rear surface with respect to the edge position data, 
     wherein the beveling-process-data calculating system obtains the beveling process data on the basis of the edge position obtained by the second measuring system, the information on the positional change inputted by the information inputting system, and the inclination angle stored in the storage system. 
     (16) The eyeglass lens grinding apparatus according to (15), further comprising: 
     a position calculating system which, on the basis of the edge position data, obtains as the information on the positional change another edge position different from the edge position that is measured by the second measuring system on the basis of the edge position data, 
     wherein the second measuring system also measures the edge position obtained by the position calculating system. 
     (17) The eyeglass lens grinding apparatus according to (15), wherein the chamfering-process-data calculating system obtains the chamfering process data on the basis of the edge position obtained by the second measuring system, the information on the positional change inputted by the information inputting system, and the inclination angle stored in the storage system. 
     (18) The eyeglass lens grinding apparatus according to (17), further comprising: 
     a position calculating system which, on the basis of the edge position data, obtains as the information on the positional change another edge position different from the edge position that is measured by the second measuring system on the basis of the edge position data, 
     wherein the second measuring system also measures the edge position obtained by the position calculating system. 
     (19) The eyeglass lens grinding apparatus according to (14), further comprising: 
     a determining system which determines whether or not the lens can be processed on the basis of a result of measurement by the first measuring system; and 
     a notifying system which notifies a result of determination by the determining system, 
     wherein the rough-grinding-data calculating system obtains the rough grinding data if it is determined by the determining system that the lens can be processed; and 
     wherein the rough-grinding controlling system operates the rough grinding system if it is determined by the determining system that the lens can be processed. 
     (20) The eyeglass lens grinding apparatus according to (12), further comprising: 
     a selecting system which selects whether or not the chamfering process by the chamfering process system is to be performed; 
     a measurement controlling system which executes both of the measurement by the first measuring system and the measurement by the second measuring system if it is selected by the selecting system that the chamfering process by the chamfering process system is to be performed, and which executes only the measurement by the first measuring system if it is selected by the selecting system that the chamfering process by the chamfering process system is not to be performed; 
     a beveling process system having a beveling grinding wheel for such a finishing operation as to form a bevel in the lens subjected to rough grinding by the rough grinding system; 
     a beveling-process-data calculating system which obtains the beveling process data for forming the bevel in the edge of the lens subjected to rough grinding; and 
     a beveling-process controlling system which controls the beveling process system on the basis of the beveling process data obtained by the bevel-process-data calculating system, 
     wherein if it is selected by the selecting system that the chamfering process is to be performed, the beveling-process-data calculating system obtains the beveling process data on the basis of the result of measurement by the second measuring system, and if it is selected by the selecting system that the chamfering process is not to be performed, the beveling-process-data calculating system obtains the beveling process data on the basis of a result of measurement by the first measuring system. 
     The present disclosure relates to the subject matter contained in Japanese patent application No. Hei. 10-120914 (filed on Apr. 30, 1998), which is expressly incorporated herein by reference in its entirety. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a diagram illustrating a processing section of an eyeglass lens grinding apparatus; 
     FIG. 2 is a diagram illustrating the arrangement of grinding wheels; 
     FIG. 3 is a diagram illustrating a lens thickness measuring section; 
     FIG. 4 is a schematic block diagram illustrating a control system of the apparatus; 
     FIG. 5 is a flowchart illustrating a processing operation; 
     FIG. 6 is a flowchart illustrating a method of calculating a chamfering process locus; 
     FIG. 7 is a diagram illustrating the calculation of a measurement locus in a second measurement; 
     FIG. 8 is a diagram illustrating the calculation of a correction angle σ of a rear surface inclination angle ρ in a finishing grinding wheel; 
     FIG. 9 is a diagram illustrating the calculation of an edge position P 3  after a finishing process; 
     FIGS.  10 ( a ) and  10 ( b ) are diagrams illustrating a change in the configuration due to peripheral length correction and the calculation of a correction amount w in the direction of a reference line L 3 ; 
     FIG. 11 is a diagram illustrating the calculation of the edge position after a finishing process in the case where a peripheral length correction is performed; 
     FIG. 12 is a diagram illustrating the calculation of the chamfering process locus; 
     FIG. 13 is a diagram illustrating the calculation of a value of a bevel bottom position in a radial direction of the lens; and 
     FIG. 14 is a side view for explaining a rear surface inclination angle ρ of a finishing grinding wheel. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the accompanying drawings, a description will be given of an embodiment of the present invention. FIG. 1 is a diagram illustrating a processing section of an eyeglass lens grinding apparatus. 
     A sub-base  2  having a lens chuck upper part  100  and lens grinding parts  300 R and  300 L is fixed on a main base  1 . In addition, a lens thickness measuring section  400  is installed on the farther side in the center of the sub-base  2 . 
     A fixing block  101  which forms a part of the lens chuck upper part  100  is fixed to the center of the sub-base  2 , and a DC motor  103  for vertically moving a chuck shaft holder  120  is mounted on top of the fixing block  101 . The DC motor  103  rotates a vertically extending feed screw, and this rotation causes the chuck shaft holder  120  to move vertically while being guided by a guide rail fixed to the fixing block  101 . A pulse motor  130  for rotating a chuck shaft  121  is fixed on top of the chuck shaft holder  120 . A lens holder  124  is attached to a lower end of the chuck shaft  121  (see FIG.  2 ). 
     A chuck shaft  152  which forms a part of a lens chuck lower part  150  is rotatably held by a holder  151  which is fixed to the main base  1 , and rotation is transmitted thereto by a pulse motor  156 . A cup receiver  159  for mounting a cup fixed to a lens to be processed is attached to an upper end of the chuck shaft  152  (see FIG.  2 ). 
     The lens grinding parts  300 R and  300 L are bilaterally symmetrical, and a housing  305  for rotatably holding therein a rotating shaft having a group of grinding wheels  30  to  33  (or  30  and  34  to  36 ), such as those shown in FIG. 2, is attached to the front portion of each shaft support base  301 . The left and right groups of grinding wheels are respectively rotated by servo motors  310 R and  310 L which are fixed to the respective shaft support bases  301 . 
     As shown in FIG. 2, the rough grinding wheel  30  and the finishing grinding wheel  31  having a bevel groove are attached to the rotating shaft of the lens grinding part  300 L. Further, the conical chamfering grinding wheel  32  for a front surface is coaxially attached to an upper end face of the finishing grinding wheel  31 , while the conical chamfering grinding wheel  33  for a rear surface is coaxially attached to a lower end face of the rough grinding wheel  30 . The rough grinding wheel  30 , the mirror-polishing grinding wheel  34  having a bevel groove, the conical chamfering grinding wheel  35  for a front mirror-polished surface, and the conical chamfering grinding wheel  36  for a rear mirror-polished surface are coaxially attached to the rotating shaft of the lens grinding part  300 R. These groups of grinding wheels use grinding wheels whose diameters are relatively small at 60 mm or thereabouts so as to improve the processing accuracy and ensure the durability of the grinding wheels. It should be noted that, in this embodiment, the angles of inclination (the angle of inclination with respect to the horizontal plane) of the chamfering grinding wheels  33  and  36  for the rear surface are set to 35 degrees, while the angles of inclination of the chamfering grinding wheels  32  and  35  for the front surface are set to 45 degrees. 
     The lens grinding parts  300 R and  300 L are respectively movable in the vertical direction and the horizontal direction, and their moving mechanisms are arranged as follows: The lens grinding part  300 R is fixed to a horizontal slide base  210 , and the horizontal slide base  210  is horizontally movable along two guide rails  211  fixed to a vertical slide base  201 . The vertical slide base  201  is vertically movable along two guide rails  202  fixed to the front surface of the sub-base  2 . A nut block  206  is fixed to the vertical slide base  201 , and the vertical slide base  201  moves vertically together with the nut block  206  as a ball screw  205  coupled to a rotating shaft of a pulse motor  204 R is rotated. The mechanism for horizontally moving the horizontal slide base  210  is arranged in the same way as the vertically moving mechanism, and is actuated by the rotation of a pulse motor  214 R. 
     The mechanism for moving the lens grinding part  300 L is bilaterally symmetrical with the moving mechanism for the lens grinding part  300 R, and it is vertically moved by a pulse motor  204 L and is horizontally moved by a pulse motor  214 L (not shown in FIG.  1 ). 
     It should be noted that, for details of the above-described construction, reference may be made on Japanese Unexamined Patent Publication No. 254000/1997 and U.S. Pat. No. 5,803,793 filed by or assigned to the present assignee. 
     FIG. 3 illustrates the lens thickness measuring section  400  (FIG.  1 ). The lens thickness measuring section  400  includes a measuring arm  527  having two feelers  523  and  524 , a rotation mechanism such as a DC motor (not shown) for rotating the measuring arm  527 , a sensor plate  510  and photo-switches  504  and  505  for detecting the rotation of the measuring arm  527  to thereby allow control of the rotation of the DC motor, a detection mechanism such as a potentiometer  506  for detecting the amount of rotation of the measuring arm  527  to thereby obtain the shapes of the front and rear surfaces of the lens. The configuration of the lens thickness measuring section  400  is basically the same as that disclosed in Japanese Unexamined Patent Publication No. Hei. 3-20603 and U.S. Patent No. 5,333,412 filed by or assigned to the present assignee, which are referred to for details of the lens thickness measuring section  400 . A difference from that disclosed in Japanese publication 3-20603 is that the lens thickness measuring section  400  of FIG. 3 is so controlled as to move in front-rear direction (indicated by arrows in FIG. 3) relative to the lens grinding apparatus by a front-rear moving means  630  based on radius vector data. The lens thickness is measured such that the measuring arm  527  is rotated upward from its lower initial position and the feelers  523  and  524  are respectively brought into contact with the front and rear refraction surfaces of the lens. Therefore, it is preferable that the rotary shaft of the measuring arm  527  be equipped with a coil spring or the like which cancels out the downward load of the measuring arm  527 . 
     In addition, the lens thickness (edge thickness) measurement is performed in the following manner. The measuring arm  527  is rotated, that is elevated, so that the feeler  523  is brought into contact with the lens front refraction surface. While keeping the feeler  523  in contact with the lens front refraction surface, the lens is rotated as well as the lens thickness measuring section  400  is controlled to move forward or backward by the front-rear moving means  630 , so that the shape of the lens front refraction surface (on the edge of the lens to be formed) is obtained. Then, the shape of the lens rear refraction surface (on the edge of the lens to be formed) is obtained similarly by rotating the lens and by moving the lens thickness measurement section  400  while keeping the feeler  524  in contact with the lens rear refraction surface. The feelers  523  and  524  may be simultaneously brought into contact with the respective front and rear reflection surfaces, to thereby obtain both shapes of the surfaces concurrently. 
     &lt;Control System&gt; 
     FIG. 4 is a block diagram showing a general configuration of a control system of the lens grinding apparatus. Reference character  600  denotes a control unit which controls the whole apparatus. The display unit  10 , input unit  11  having various operation switches, and photosensors for detecting the initial rotational position of the lens chuck shafts and the initial position of the lens grdingint parts  300 R and  300 L are connected to the control unit  600 . The motors for moving or rotating the respective parts are connected to the control unit  600  via drivers  620 - 628 . The drivers  622  and  625 , which are respectively connected to the servo motor  310 R for the right lens grinding part  300 R and the servo motor  310 L for the left lens grinding part  300 L, detect the torque of the servo motors  310 R and  310 L during the processing and feed back the detected torque to the control unit  600 . The control unit  600  uses the torque information to control the movement of the lens grinding parts  300 R and  300 L as well as the rotation of the lens. 
     Reference numeral  601  denotes an interface circuit which serves to transmit and receive data. An eyeglass frame shape measuring apparatus  650  (see U.S. Pat. No. 5,333,412), a host computer  651  for managing lens processing data, a bar code scanner  652 , etc. may be connected to the interface circuit  601 . A main program memory  602  stores a program for operating the lens grinding apparatus. A data memory  603  stores data that are supplied through the interface circuit  601 , and control unit  600  lens thickness measurement data, and other data. 
     Next, a description will be given of the processing operation (seethe flowchart of FIG.  5 ). The shape of the eyeglass frame or the template is measured by the lens frame shape measuring apparatus  650 , and the measured data is inputted. Since the lens shape based on the eyeglass frame data is displayed on the display unit  10 , layout data such as the PD value of the wearer and the optical center height is entered by the switching operation of the input unit  11  with respect to the lens shape. In addition, processing conditions such as the lens material and the processing mode (a beveling process, a plane process, or a mirror-polish process) are entered. When a chamfering process is performed, an instruction for chamfering is entered by a switch  11   g . In the instruction for chamfering, a chamfering ratio (the edge thickness is divided by a ratio over the entire periphery) as well as the offset amount can be set in advance as parameters. Hereafter, a description will be given of the case where the beveling process and the chamfering process are performed. 
     The operator attaches the cup to the front surface of the lens to be processed, and places lens on the cup receiver  159  provided on the chuck shaft  152 . When the preparation for the process is completed, a START switch  11   i  is pressed to start the operation of the apparatus. 
     In response to a start signal, the control unit  600  lowers the chuck shaft  121  to chuck the lens to be processed, and then performs lens measurement prior to the rough-grinding process by driving and controlling the front-rear moving means  630  and the lens thickness measuring section  400  in accordance with radius vector data after the layout. If an instruction for chamfering has been made through the switch  11   g , the lens measurement prior to the rough-grinding process is performed to check whether the lens to be processed has a sufficient diameter (size) or not. 
     The rough-grinding process is performed if it is confirmed through the lens measurement that the lens has a sufficient diameter (if the lens diameter is insufficient, the display unit  10  indicates so). For the rough-grinding process, the left and right rough grinding wheels  30  are moved vertically to a level where the lens to be processed is held, and then the lens grinding parts  300 R and  300 L are slid toward the lens. The left and right rough grinding wheels  30  gradually grind the lens from two directions while being rotated. At this time, the amounts of movement of the right and left rough grinding wheels  30  toward the lens are controlled independently of each other on the basis of the rough-grinding process data (which is calculated by leaving a finishing allowance in the normal direction with respect to the radius vector data at the bevel apex position) obtained from the radius vector data. 
     After the rough-grinding process is completed, the rotation of the grinding wheels is stopped. After the lens grinding parts  300 R and  300 L are returned to their initial positions, the process proceeds to the lens measurement after the rough-grinding process. The lens measurement after the rough-grinding process is performed to calculate the bevel locus (the bevel path) and the chamfering process locus (the chamfering process path). 
     A description will be given of a method of the lens measurement after the rough-grinding process and the calculation of the bevel locus and the chamfering process locus (see the flowchart of FIG.  6 ). 
     &lt;Lens Measurement&gt; 
     In the lens measurement after the rough-grinding process, the shapes of the lens front and rear surfaces are respectively measured twice in accordance with different measurement loci on the basis of the radius vector data after the layout. 
     In the first measurement of the lens shape, the measurement is performed in accordance with the locus (the path) of the position of the bevel apex (in the specification, this is referred to as the reference shape) to be formed in the lens. This measurement locus (the measurement path) can be obtained from the two-dimensional process data based on the radius vector data after the layout. 
     The second measurement is performed in accordance with the shape (the locus or path) of the bevel bottom (the portion where the bevel slope and the bevel shoulder intersect each other). This measurement locus in this case can be obtained in the following manner. 
     As shown in FIG. 7, when a point a at the bevel apex (reference shape) is to be processed, the line connecting the rotation center of the lens and that of the grinding wheel is indicated as an axis L 1 , the line connecting the process point a and the rotation center of the grinding wheel is indicated as a normal L 2 , the line connecting the process point a and the rotation center of the lens is indicated as a reference line L 3 , and the followings are defined: 
     δ=height of the bevel (the line segment ac) in the direction of the reference line L 3 , 
     θ=angle between the normal L 2  and the reference line L 3 , 
     γ=reference height of the bevel (the line segment ab, and already known from the shape of the bevel groove), and 
     τ=angle formed by the normal L 2  and the axis L 1 . The position of the process point a can be obtained by a process correction calculation (basically identical with that described in U.S. Pat. No. 5,347,762) which calculates the axis-to-axis distance between the lens rotation center and the wheel rotation center during a process, from information indicative of the radius vector angle and length of the lens on the basis of the frame shape data and the layout data, and in correspondence with the radius vector angle (the lens rotation angle during a process). When the position of the process point a is once obtained, θ and τ are known. 
     Assuming that the angle formed by the line segments ab and bc of Δabc of FIG. 7 is approximately rectangular, the following is held: 
     
       
         δ=γ/cos θ 
       
     
     By subtracting the bevel height δ from the reference shape in the direction of the reference line L 3 , the distance of the bevel bottom at the process point a can be obtained. When the distance is calculated at each places in correspondence with the radius vector angle, the measurement locus in the second measurement can be obtained. 
     &lt;Calculation of Bevel Locus&gt; 
     When the lens shape is once measured, it is possible to obtain three-dimensional bevel curve locus data (three-dimensional bevel curve path data) which are to be applied to the lens edge, on the basis of information indicative of the lens shape and in accordance with a predetermined program. As for this calculation, there have been proposed several methods such as that a curve is determined from front and rear surface curves, that the edge thickness is divided, and that the two methods are combinedly performed (the movement or the selection may be performed in response to an input operation by the optician). For details of this calculation, reference may be made on commonly assigned U.S. Pat. No. 5,347,762, etc. 
     &lt;Calculation of Chamfering Process Locus&gt; 
     The calculation of the chamfering process locus is made by determining the edge position locus (the edge position path) after the finishing process and on the basis of this edge position locus. In a case where chamfering is provided for the lens rear refraction surface and the lens front refraction surface, respectively, the edge position loci are determined at the respective surfaces, but a description will be given herein by citing the lens rear surface as an example. 
     The edge locus (the edge path) after the beveling (finishing) process is calculated from the edge position information and the bevel curve locus data, which are obtained through two lens shape measurements. In this calculation, an offset of the edge position is corrected with respect to the inclination angle of the finishing grinding wheel so as to form an edge shoulder. 
     First, a correction angle for the lens rear surface inclination with respect to the rear surface inclination angle ρ (this value is previously known and stored in the main program memory  602 ) of the finishing grinding wheel (as shown in FIG. 14) is calculated. When a lens is processed at the rear surface inclination angle ρ of the finishing grinding wheel, the inclination angle of the lens bevel shoulder in the direction of the normal L 2  becomes as it is to the inclination angle ρ. In order to obtain the edge locus in the direction of the reference line L 3 , however, a correction angle must be considered for the section shape in the direction of the reference line L 3 . From FIG. 8, the correction angle σ for this purpose is obtained as: 
     
       
         σ=arctan (tan ρ/cos θ) 
       
     
     This correction angle σ is obtained for each place in accordance with the radius vector angle. 
     Next, as shown in FIG. 9, the section shape in the direction of the reference line L 3  is considered in accordance with the correction angle σ of the rear surface inclination, and the edge position P 3  of the lens rear surface after the beveling process is obtained. In FIG. 9, P 1  denotes the edge position obtained in the first measurement of the lens edge position, and P 2  denotes the edge position obtained in the second measurement. In this case, h of FIG. 9 is obtained from the result of the measurement of the lens edge position, and δ from the result of the second measurement (the measurement result at the bevel bottom) and the bevel calculation result. When the rear surface is approximately considered as a straight line, therefore, a correction amount μ in the optical axis direction of the lens, and a correction amount ξ in the radial direction of the lens are expressed as follows: 
     [Ex. 1] 
     When the correction amounts are obtained for each place in accordance with the radius vector angle, information of the edge locus on the side of the rear surface after the beveling process is obtained. 
     As described in U.S. Pat. No. 5,347,762, when a lens which has undergone a beveling process is to be mounted to an eyeglass frame, it is preferable to correct the position of the bevel apex so that the curve locus (the curve path) of the eyeglass frame substantially coincides in peripheral length with the bevel curve locus. In the correction (hereinafter, referred to as peripheral length correction), the peripheral length of the bevel curve locus is approximately obtained by calculating distances among the bevel curve locus data obtained in the bevel calculation on the basis of the data, and summing the distances. The correction amount can be obtained from the thus obtained peripheral length, and the peripheral length of the eyeglass frame shape which is similarly obtained from the radius vector information of the frame shape. The calculation of the edge locus after the beveling process in the case where the peripheral length correction is performed will be described. In the above, all the correction calculations are performed on the reference line L 3 . The shape change due to the peripheral length correction occurs in the direction of the axis L 1  (see FIG.  10 ( a )). Consideration will be made with substituting the shape change due to the peripheral length correction for that in the reference line L 3 . It is assumed that, as shown in FIG.  10 ( b ), a point b of the bevel bottom before the peripheral length correction is corrected in the direction of the axis L 1  by a peripheral length correction amount λ, and a point c also is corrected in the direction of the axis L 1  at the point b. In this case, a correction amount ω in the direction of the reference line L 3  can be approximately obtained by: 
     [Ex. 2] 
     In order to obtain the edge locus after the beveling process due to the peripheral length correction, the section shape shown in FIG.  11  and in the direction of the reference line L 3  will be considered in the same manner as described above. Assuming that the edge position P 3  is shifted to P 4  as a result of the peripheral length correction, when the correction amount in the radial direction of the lens is indicated by κ and that in the optical axis direction of the lens is indicated by η, these correction amounts are as follows: 
     [Ex. 3] 
     In the case where the peripheral length correction is performed, therefore, the correction amounts of the edge position after the final beveling process are expressed as follows: 
     [Ex. 4] 
     When the correction amounts are obtained for each place in accordance with the radius vector angle, information of the edge locus on the side of the lens rear surface in the case where the peripheral length correction is performed is obtained. 
     Next, the calculation of the chamfering process locus which is performed during the chamfering process in order to visually uniformalize the chamfer shape will be described with reference to FIG.  12 . Even when the edge locus is obtained as described above and a fixed chamfering amount from the edge end (P 4 ) in the bevel direction is designated (an offset of a fixed amount is applied), the length of the chamfered slope after chamfering (hereinafter, the length is referred to as chamfering width) is changed by influence of the rear surface curve, with the result that the chamfering is visually recognized not to be uniformly performed. In order to visually uniformalize the chamfering width in the case where a fixed chamfering amount is designated, therefore, the chamfering process locus is obtained so that the length of the slope after chamfering is uniform irrespective of the radius vector angle. 
     In FIG. 12, g denotes an offset component of the chamfering amount, j denotes an offset amount after correction, f denotes a correction angle of the inclination angle F of the chamfering grinding wheel (a previously known value, and, in the embodiment, 35 degrees) in the direction of the reference line L 3 , and e denotes a chamfering width in the case where the rear surface of the lens is flat. The chamfering width becomes equal in size to the chamfering width d because of the rear surface curve. In a method of uniformalizing the chamfering width, an offset correction amount k is obtained so as to attain the chamfering width which is equal to that in the case where the rear surface of the lens is flat. In order to perform the method, the correction angle f is first obtained. In the same manner as that of obtaining the correction angle σ in FIG. 8, the correction angle is obtained by: 
     
       
         f=arctan (tan F/cos θ). 
       
     
     From the figure, the offset correction amount k is obtained as follows: 
     [Ex. 5] 
     This method is based on the approximation expression. When the offset component g is largely increased, therefore, the error is increased. From the view point of visual uniformalization, when the offset component g is greater than 1 mm, it is preferable to obtain the offset correction amount k while setting g to be 1 (g=1). When the correction angle σ is sufficiently small, the offset correction amount may be expressed as follows: 
     [Ex. 6] 
     (in the correction on the side of the front surface of the lens, particularly, the influence is very small). 
     From the above, it will be seen that the position of a chamfering process point Q in the optical axis direction with respect to the edge position P 4  shown in FIG. 12 can be obtained by an addition of g+k. For the position of the chamfering process point Q in the radial direction of the lens with respect to the edge position P 4 , a correction amount m can be obtained by: 
     
       
         m=j·tan σ. 
       
     
     The thus obtained position of the chamfering process point Q is information which is obtained without considering the position of the bevel bottom. In the case of a beveling process, the chamfering process must be performed so as not to interfere with the bevel. To comply with this, a process is performed in which the position of the bevel bottom is obtained, the position is compared with the chamfering process point, and, if the chamfering process point Q in the optical axis direction is in the inner side with respect to the position of the bevel bottom, the bevel bottom position is substituted for the chamfering process point. 
     As shown in FIG. 13, the value of the bevel bottom position in the radial direction of the lens can be obtained by subtracting t=δ+ω from the reference shape (this is equal to that obtained by subtracting co from the locus of the second measurement). The value of the bevel bottom position in the optical axis direction of the lens is obtained by using q and q′ obtained by splitting the bevel apex. The q and q′ are obtained from the shape of the bevel groove of the finishing grinding wheel. 
     In this way, the chamfering process point Q and the position of the bevel bottom are obtained for the whole periphery in accordance with the radius vector angle, and the chamfering process locus in which the chamfering process does not interfere with the bevel can be obtained. The chamfering process locus on the side of the front surface of the lens can be obtained in the same method. Also in a plane process in which a beveling process is not performed, the chamfering process locus can be obtained in a basically same concept. 
     When the bevel locus data and the chamfering process locus data are obtained as described above, the bevel process and the chamfering process are automatically performed consecutively. The control unit  600  performs the bevel process by controlling the height of the bevel groove of the finishing grinding wheel  31  and its movement in the direction toward the lens on the basis of the bevelling process data stored in the data memory  603 . Since the beveling process data used in the process has been obtained from the result of lens measurement after the rough-grinding process, the bevel is formed at an accurate position. 
     When the beveling process is completed, the operation proceeds to the chamfering process. The control unit  600  performs the chamfering process by controlling the movement of the chamfering grinding wheel  32  for the front surface and the chamfering grinding wheel  33  for the rear surface in the vertical direction and in the direction toward the lens on the basis of the chamfering process data stored in the data memory  603 . Since the chamfering process data has been determined from the edge position obtained by measuring the shape of the actual lens which has been subjected to the rough-grinding process so that the deformation is enlarged, chamfering can be performed for both the front surface and the rear surface with high accuracy. 
     Although in the above description the first measurement and the second measurement are performed twice over the entire periphery in the measurement of the lens edge, the lens data may be used instead if the lens data is available from another source. 
     As described above, since the chamfering locus (processing data of an edge corner portion) is obtained on the basis of the lens measurement data obtained after the rough-grinding process, the edge corner portion can be processed with higher accuracy without being affected by the shape of the lens and its power. In addition, processing can be performed such that the bevel position can be accurately secured. 
      β tan σ=μ{fraction (δ/h)} β=ε−μ  [Ex. 1] 
     Optical axis direction        μ   =       ɛ                 tan                 σ         δ   h     +     tan                 σ                         
     Radial direction 
     
       
         ζ=μ{fraction (δ/h)} 
       
     
     [Ex. 2]       ω   =         γ   +     λ                   cos        (     θ   -   τ     )             cos                 θ       -   δ                     
     [Ex. 3]       κ   =       ω                 δ         h                 tan                 σ     +   δ                      η=k{fraction (h/δ)} 
     [Ex. 4] 
     Radial direction          ζ   +   κ     =         μ                   δ   h       +       ω                 δ         h                 tan                 σ     +   δ         =         ɛ                 tan                 σ     +   ω           h   δ        tan                 σ     +   1                         
     Optical axis direction          μ   +   η     =           ɛ                 tan                 σ         δ   h     +     tan                 σ         +     κ                   h   δ         =         ɛ                 tan                 σ     +   ω         δ   h     +     tan                 σ                           
     [Ex. 5]       k   =       g        (       tan                 f     -     tan                 σ       )           tan                 σ     +     δ   h                         
     [Ex. 6]       k   =       gh   δ        tan                 f