Patent Publication Number: US-7713108-B2

Title: Eyeglass lens processing apparatus

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an eyeglass lens processing apparatus for processing a peripheral edge of an eyeglass lens. 
   In a eyeglass lens processing apparatus for processing a peripheral edge of an eyeglass lens by a plurality of grindstones such as a roughing grindstone for a glass lens, a roughing grindstone for a plastic lens and a finishing grindstone for beveling and flat-processing are attached to a grindstone rotating shaft side by side in a parallel relation with lens chuck shafts, and the plurality of grindstones are integrally rotated (for example, see U.S. Pat. No. 6,095,896 (JP-A-11-70451)). Further, there is a structure in which a polishing grindstone is coaxially attached thereto. The peripheral edge of the eyeglass lens held by the lens chuck shafts is first processed by the roughing grindstone. At this time, an axis-to-axis distance between an axis of the lens chuck shafts and an axis of the grindstone rotating shaft varies based on target lens shape data to rough the peripheral edge of the lens while a predetermined finish margin remains. 
   In recent years, the design of an eyeglass frame has been diversified and many eyeglass frames having a steep frame curve have been proposed. In this case, the eyeglass lens also has a steep lens curve according to the frame curve (“high curve lens”). 
   However, as in the above-described apparatus, when the high curve lens having the steep lens curve is to be roughed by only controlling the axis-to-axis distance between the lens chuck shafts and the grindstone rotating shaft, there is a possibility that the lens protrudes (deviates) from a width of the roughing grindstone. If the periphery edge of the lens is roughed while the lens protrudes from the width of the roughing grindstone, the periphery edge of the lens may be brought into contact with the finishing grindstone provided next to the roughing grindstone, or the processing moves to the finishing processing in a state that a part which should be roughed remains. In this case, there is a feat that an excess load, an axial deviation, or deformation and crack of the lens occurs at the time of the processing. If the width of the roughing grindstone is made sufficiently wide, a size of the apparatus becomes large. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an eyeglass lens processing, apparatus which can suitably perform roughing of a high curve lens while protrusion of the lens from a width of a roughing grindstone is eliminated without using wide grindstone. 
   In order to resolve the above-described situation, the invention is characterized in providing the following structures. 
   (1) An eyeglass lens processing apparatus for processing a peripheral edge of an eyeglass lens based on target lens shape data, the apparatus comprising: 
   a lens rotating unit that rotates a lens chuck shaft for holding the lens; 
   a grindstone rotating unit that rotates a grindstone rotating shaft to which a plurality of grindstones including a roughing grindstone is attached; 
   a X-axis moving unit that relatively moves the lens chuck shaft in an axial direction of the lens shuck shaft with respect to the grindstone rotating shaft based on X-axis moving information; 
   a Y-axis moving unit that relatively moves the lens chuck shaft in a direction in which an axis-to-axis distance between an axis of the lens chuck shaft and an axis of the grindstone rotating shaft varies based on Y-axis moving information; 
   a lens curve data input unit that inputs curve data of at least one of a front refractive surface and a rear refractive surface of the lens, the curve data being generated by calculation based on a detected position of the refractive surface of the lens or input as known data by an operator in advance; and 
   a computing unit obtains the X-axis moving information corresponding to the Y-axis moving information for each rotation angle of the lens chuck shaft so that a contact surface of the lens with the roughing grindstone is located within a width of the roughing grindstone from the beginning of the roughing until the end of the roughing based on the target lens shape data, layout data, and the curve data. 
   (2) The apparatus according to (1), wherein the computing unit computes the X-axis moving information corresponding to the Y-axis moving information so that the front surface of the lens is located at a predetermined position set at a lens front surface side of the roughing grindstone.
 
(3) The apparatus according to (1), wherein the computing unit computes the X-axis moving information corresponding to the Y-axis moving information so that the rear surface of the lens is located at a predetermined position set at a lens rear surface side of the roughing grindstone.
 
(4). The apparatus according to (1), wherein
 
   the lens curve data input unit inputs the curve data of the lens front surface and the rear surface of the lens, and 
   the computing unit computes the X-axis moving information corresponding to the Y-axis moving information so that the front surface of the lens is located at a position inner than a lens front surface side end of the roughing grindstone and the rear surface of the lens is located at a position inner than a lens rear surface side end of the roughing grindstone. 
   (5) The apparatus according to (1), wherein 
   the computing unit judges whether or not the contact surface of the lens deviates from the width of the roughing grindstone when the lens is roughed while the lens chuck shaft is fixed in the axial direction, and computes the X-axis moving information which moves the lens chuck shaft in the axial direction only where the contact surface of the lens is judged to deviate from the width of the roughing grindstone. 
   (6) The apparatus according to (1) further comprising a mode selector for selecting a high curve processing mode for processing a high curve lens and a low curve processing mode for processing a low curve lens, 
   wherein, when the roughing is started in the low curve mode, the computing unit computes the Y-axis moving information while the movement of the lens chuck shaft in the axial direction is fixed based on the target lens shape data and the layout data. 
   (7). The apparatus according to (1), wherein the computing unit computes the X-axis moving information based on the target lens shape data, the layout data, the curve data and diameter data of the lens, 
   wherein the diameter data is obtained by measuring the held lens by a measuring unit or is obtained as known data. 
   (8) The apparatus according to (7), wherein the measuring unit includes a feeler brought into contact with a refractive surface of the lens. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a view for explaining the processing unit of an eyeglass lens processing apparatus according to the present invention. 
       FIG. 2  is a view for explaining a measuring unit. 
       FIG. 3  is a view for the construction of a grindstone group. 
       FIG. 4  is a view for explaining a control system. 
       FIGS. 5A to 5B  are views for explaining measurement of the edge position of an eyeglass lens. 
       FIGS. 6A to 6B  are views for explaining measurement of the edge position of an eyeglass lens. 
       FIGS. 7A to 7C  are views for explaining control of an eyeglass lens rotating speed. 
       FIG. 8  is a view for explaining a simulation screen of a bevel shape. 
       FIG. 9  is a view for explaining the positional relationship between an eyeglass lens and a grindstone group. 
       FIG. 10A  to  FIG. 10B  are second views for explaining the positional relationship between an eyeglass lens and a grindstone group. 
       FIGS. 11A to 11B  are views for explaining acquisition of the outer shape size before lens processing. 
       FIG. 12  is a second view for explaining acquisition of the outer shape size before lens processing. 
       FIG. 13  is a third view for explaining acquisition of the outer shape size before lens processing. 
       FIG. 14  is a view for explaining formation of a bevel of a high curve lens. 
       FIGS. 15A to 15B  are views for explaining the manner for acquiring beveling data. 
       FIGS. 16A to 16B  are views for explaining the bevel on the front side. 
       FIG. 17  is a view for explaining another construction of a grindstone group. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Now referring to the drawings, an embodiment of the invention will be explained as follows.  FIG. 1  is a schematic structure view of a processing unit in an eyeglass lens peripheral edge processing apparatus according to the invention. 
   A carriage portion  100  is mounted on a base  170 . An eyeglass lens LE to be processed is held (chucked) by lens chuck shafts (lens rotating axes)  102 L,  102 R of a carriage  101 , and a peripheral edge of the lens is pressed and processed by a grindstone group  168  coaxially attached to a grindstone spindle  161   a . The grindstone group  168  is constituted by a roughing grindstone  162  for a glass, a high curve bevel-finishing (beveling) grindstone  163  for having a bevel slope to form a bevel in a high curve lens, a finishing grindstone  164  having a V-groove (bevel groove) VG and a flat processing plane to form the bevel in a low curve lens, a flat-polishing grindstone  165  and a roughing grindstone  166  for plastic. The grindstone  161   a  is rotated by a motor  160 . 
   The lens chuck axis  102 L is held by a left arm  101 L of the carriage  101  and the lens chuck axis  102 R is held by a right arm  101 R of the carriage  101  rotatably and coaxially. The lens chuck axis  102 R is moved toward the lens chuck axis  102 L by a motor  110  attached to the right arm  101 R, and the lens LE is held by the lens chuck shafts  102 R and  102 L. Further, the two lens chuck shafts  102 R and  102 L are rotated in synchronization with each other by a motor  120  attached to the left arm  101 L through a rotation transmission mechanism such as a gear. These components constitute a lens rotating unit. 
   The carriage  101  is mounted on a moving support base  140  which is movable along shafts  103  and  104  extending in parallel to the lens chuck shafts  102 R,  102 L and grindstone spindle  161   a . A ball screw (not shown) extending in parallel to the shaft  103  is attached to the rear of the moving support base  140 . The ball screw is attached to the rotating shaft of an X axis direction moving motor  145 . By the rotation of the motor  145 , the carriage  101  as well as the moving support base  140  is linearly moved in the X-axis direction (axial direction of the lens chuck shafts). These components constitute an X-axis direction moving unit. The rotating shaft of the motor  145  is provided with an encoder  146  for detecting the X-axis direction movement of the carriage  101 . 
   The supporting base  140  is fixed with shafts  156  and  157  extending in the Y-axis direction (direction in which the axis-to-axis distance between the lens chuck shafts  102 R,  102 L and the grindstone spindle  161   a  is changed). The carriage  101  is mounted on the supporting base  140  so that it is movable in the Y-axis direction along the shafts  156  and  157 . In the supporting base  140 , a Y-axis direction moving motor  150  is fixed. The rotation of the motor  150  is transmitted to a ball screw  155  extending in the Y-axis direction. By the rotation of the ball screw  155 , the carriage  101  is moved in the Y-axis direction. These components constitute a Y-axis direction moving unit. The rotating shaft of the motor  150  is provided with an encoder  158  for detecting the Y-axis direction movement of the carriage  101 . 
   Referring to  FIG. 1 , a chamfering mechanism  200  is arranged on the front side of the apparatus body. The chamfering mechanism  200 , which is well known, will not be explained here (see, for example, JP-A-2006-239782). 
   Referring to  FIG. 1 , lens edge position measuring portions (lens shape measuring portions)  300 F and  300 R are arranged on the carriage  101 .  FIG. 2  is a schematic structure view of the lens measuring portion  300 F for measuring the lens edge position on the lens front surface. An attached support base  301 F is fixed to a support base block  300   a  fixed on the base  170  in  FIG. 1 . A slider  303 F is slidably attached on a rail  302 F fixed on the attached support base  301 F. A slide base  310 F is attached to the slider  303 F. A tracing stylus arm  304 F is fixed to the slide base  310 F. An L-shape hand  305 F is fixed to the tip of the tracing stylus arm  304 F, and a tracing stylus (feeler)  306 F is fixed to the tip of the hand  305 F. The tracing stylus  306 F is brought into contact with the front reflecting surface of the eyeglass lens LE. 
   A lower end of the slide base  310 F is fixed with a rack  311 F. The rack  311 F is brought in mesh with a pinion  312 F of an encoder  313 F fixed to the attached support base  301 F. Rotation of the motor  316 F is transmitted to the rack  311 F by way of a gear  315 F, an idle gear  314 F and the pinion  312 F, and slide base  310 F is moved in the X axis direction. While the lens edge position is measured, the motor  316 F presses the tracing stylus  306 F to the eyeglass lens LE always by a constant force. The tracing stylus  306 F is pressed to a lens refractive surface with a light force by the motor  316 F so that the lens refractive surface is not scratched. The means for giving the pressing force of the tracing stylus  306 F to the lens refractive surface may be a well known pressure giving means such as a spring. The encoder  313 F detects the moving position of the slide base  310 F thereby to detect the moving position of the tracing stylus  306 F in the X-axis direction. The edge position (inclusive of the lens front surface position) on the front surface of the eyeglass lens LE is measured using the information on the moving position, the information on the rotating angle of the lens chuck shafts  102 L and  102 R and their moving information in the Y-axis direction. 
   The lens measuring portion  300 R for measuring the edge position of a rear surface of the eyeglass lens LE is symmetrical with the lens measuring portion  300 F in a left and right direction, and therefore, with “R” substituted for “F” at the ends of the symbols appended to the respective constituent elements of the measuring portion  300 F in  FIG. 2 , an explanation of the structure thereof will be omitted. 
   The lens edge position will be measured in such a manner that the tracing stylus  306 F is brought into contact with the front surface of the eyeglass lens LE and the tracing stylus  306 R is brought into contact with the rear surface of the eyeglass lens LE. In this state, the carriage  101  is moved in the Y-axis direction on the basis of a target lens shape data, and the eyeglass lens LE is rotated to thereby simultaneously measure edge data of the front surface of the eyeglass lens LE and the rear surface of the lens for processing the lens peripheral edge. In an edge position measuring unit in which the tracing stylus  306 F and the tracing stylus  306 R are integrally movable in the X-axis direction, the lens front surface and lens rear surface are measured separately. Further, in the lens edge position measuring portion, it is assumed that the lens chuck shafts  102 L and  102 R move in the Y-axis direction, but the tracing styluses  306 F and  306 R may move relatively in the Y-axis direction. The lens edge position may be acquired by computation on the basis of design data of the eyeglass lens LE. 
   Referring to  FIG. 1 , a drilling and grooving mechanism  400  is arranged on a rear side of the carriage portion  100 . The structure of the carriage portion  100 , the lens edge position measuring portion  300 F and  300 R and the drilling and grooving mechanism  400 , which may be those described in U.S. Pat. No. 6,790,124 (JP-A-2003-145328), will not be explained in detail. 
   The X-axis direction moving unit and Y-axis direction moving unit in the eyeglass lens peripheral edge processing apparatus shown in  FIG. 1  may have a configuration in which the grindstone  161   a  is moved relatively to the lens chuck shafts ( 102 L,  102 R) in the X-axis direction and Y-axis direction. Further, the lens edge position measuring portion  300 F and  300 R may also have a configuration in which the tracing styluses  306 F and  306 R are moved relatively to the lens chuck shafts ( 102 L,  102 R) in the Y-axis direction. 
   Now, the structure of the grindstone group  168  will be explained.  FIG. 3  is a view when the grindstone group  168  is seen from the direction of an arrow A in  FIG. 1 . The width w 162  of the roughing grindstone  162  for a glass and the width w 166  of the roughing grindstone  166  for plastic are both 17 mm. Usually, since the edge thickness of the eyeglass lens LE is 15 mm or less, correspondingly, the width w 162  and w 166  are made as narrow as possible. 
   With respect to the V-groove for beveling of the finishing grindstone  164  for a low curve, the angle  164 αf of a front surface processing slope and the angle  164 αr of a rear surface processing slope relative to the X-axis direction are both set at 35° in order to give a good appearance when the eyeglass lens LE with a gentle frame curve is fitted in. The depth of the V groove VG is smaller than 1 mm. 
   The high-curve bevel-finishing (beveling) grindstone  163  includes a front surface beveling grindstone having a front surface beveling slope  163 F for processing the bevel slope on the front side of the eyeglass lens LE, and a rear surface beveling grindstone having a rear surface beveling grindstone slope  163 Rs on the rear side of the eyeglass lens LE and a rear bevel foot processing slope  163 Rk for a bevel foot on the rear side of the eyeglass lens LE. In this apparatus, the grindstones for the respective processed slopes are formed integrally, but may be provided individually. 
   The angle  163 αf of the front surface beveling slope  163 F relative to the X-axis direction is smaller than the angle  164 αf of the front surface processing slope of the finishing grindstone  164 , e.g. 30°. Where the front surface bevel is formed in the high curve lens, the frame curve of the eyeglass lens LE (frame curve of the frame in which the eyeglass lens LE is fitted) is steep. Thus, in order to give the good appearance of the front side, the angle  163 αf of the front surface bevel is preferably made small for the low curve lens. On the other hand, the angle  163 αr of rear surface beveling grindstone slope  163 Rs relative to the X-axis direction is larger than the angle  164 αr of the front surface processing slope of the finishing grindstone  164 , e.g. 45°. In the high curve lens, in order that the eyeglass lens LE does not come off on the rear side and is surely held, the angle  163 αr of rear surface bevel is made preferably large as compared with the low curve lens. Further, the angle  163 αk of the rear bevel foot processing slope  163 Rk relative to the X-axis direction is larger than the angle of the rear surface bevel foot processing slope  163 Rk of the finishing grindstone  164  (in  FIG. 3 , 0°, but is set at not larger than 3°), e.g. 15°. Thus, when the eyeglass lens LE is attached to the high curve frame, the eyeglass lens LE provides good appearance and can be easily held. 
   Further, the width w 163 F of the front surface beveling slope  163 F relative to the X-axis direction is set at 9 mm and the width w 163 Rs of the rear surface beveling slope  163 Rs is set at 3.5 mm. As described later, in the case of the high curve lens, the front side bevel slope and the rear side bevel slope are processed separately so that they are set at the width larger than those of the finishing grindstone  164  for a low curve, respectively. The width w 163 Rk of the rear side bevel foot processing slope  163 Rk is set at 4.5 mm. 
     FIG. 4  is a control block diagram of the eyeglass lens peripheral edge processing apparatus. A control unit  50  is connected with an eyeglass frame shape measuring unit  2  (which may be that described in U.S. Pat. No. 533,412 (JP-A-4-93164)), a display  5  serving as a touch panel type of display device and input device, a switch unit  7 , a memory  51 , the carriage portion  100 , the chamfering mechanism  200 , the lens edge position measuring portions  300 F,  300 R, the drilling and grooving mechanism  400  and others. An input signal to the apparatus can be inputted by touching the display on the display  5  with a touch pen (or a finger). The control unit  50  receives the input signal by the touch panel function of the display  5  to control the display of the graphic and information of the display  5 . 
   Next, an explanation will be given of the measuring operation of the lens edge position, roughing operation for the high curve lens and beveling operation for the high curve lens by the apparatus having the construction described above. 
   First, the target lens shape data (m, θn) (n=1, 2, . . . N) of the eyeglass frame measured by the eyeglass frame shape measuring unit  2  are inputted by depressing the switches of the switch unit  7  and stored in the memory  51 . In the target lens shape data, m represents a radius vector length and θn represents a radius vector angle. The target lens shape FT is displayed on the screen  500  of the display  5 . A state where the layout data inclusive of the PD (pupillary distance) value of a wearer, FPD (frame pupillary distance) value of the eyeglass frame and the height of an optical center relative to the geometric center of the target lens shape can be inputted is provided. The layout data can be inputted by manipulating predetermined button keys displayed on the display  5 . Further, the processing conditions such as the material of the eyeglass lens LE, kind of the frame, processing mode (beveling, flat-processing and grooving) and presence or absence of chamfering can be also set by manipulating predetermined button keys displayed on the display  5 . Now, an explanation will be. Given of the case where the beveling mode is set. 
   If it is previously known that the frame curve of the eyeglass lens frame is large, a high curve mode can be selected beforehand by a predetermined button key  501  displayed on the display  5 . If the high curve mode is selected beforehand, using the grindstone  163  for the high curve beveling (hereinafter, referred to as a high curve beveling grindstone) is set. Where the frame curve of the eyeglass lens frame is not steep and so the finishing grindstone  164  is used, the normal processing mode may be selected beforehand. Where the beveling is selected in conformity with the eyeglass lens frame with the high frame curve, the eyeglass lens LE is also selected so as to conform to the high curve. 
   Once the data necessary for the processing could be inputted, the eyeglass lens LE is chucked by the lens chuck shafts  102 R and  102 L and the start switch of the switch unit  7  is depressed to start the apparatus. 
   The control unit  50  actuates the measuring portions  300 F,  300 R on the basis of the target lens shape data to measure the edge positions of the front surface and rear surface of the eyeglass lens LE. 
   Referring to  FIGS. 5A to 5B  and  FIGS. 6A to 6B , an explanation will be given of the edge positions of the lens front surface and lens rear surface.  FIG. 5A  illustrates the target lens shape FT and geometrical center FC. In  FIG. 5A , the position of the target lens shape data (m, θn) (n=1, 2, . . . , N) relative to the geometrical center FC is also illustrated. In the target lens shape data, m represents the radius vector length and θn represents the radius vector angle. As seen from  FIG. 5A , it is assumed that the radius vector angle θn increases counterclockwise with the radius vector angle θn on the right side in the figure being 0° with reference to the geometrical center FC.  FIG. 5B  is a graph showing changes in the radius vector length m for the radius vector angle θn. 
   Further,  FIG. 6A  is a view when the lens edge is seen from the direction of corner C 1  where the eyeglass lens LE is processed with the target lens shape FT.  FIG. 6B  is a graph showing the edge position fxn of the lens front side refractive surface and the edge position rxn of the lens rear-side refractive surface for the radius-vector angle θn of the target lens shape FT shown in  FIG. 5A . These positions represent the distances for the reference position in the X-axis direction. 
   Where the edge position of the eyeglass lens LE is measured on the basis of the target lens shape FT, while rotating the lens chuck shafts  102 R,  102 L, the control unit  50  moves the lens chuck shafts  102 R,  102 L in the Y-axis direction on the basis of the radius vector length m for each radius vector angle θn of the target lens shape (in this case, the radius vector angle θn represents the rotating angle of the eyeglass lens LE) thereby controlling the positions in the Y-axis direction of the tracing stylus  306 F to be in contact with the lens front surface and the tracing stylus  306 R to be in contact with the lens rear surface. During the measurement, the tracing styluses  306 F and  306 R are pressed on the lens refractive surfaces by light force by the motors  316 F and  316 R, respectively. The edge positions fxn and rxn are acquired by the encoders  313 F and  313 R, respectively. 
   Next, an explanation will be given of the case where the lens chuck shafts  102 R,  102 L are rotated at an equiangular speed. If the rotating speed of the lens chuck shafts  102 R,  102 L is increased, the measuring time can be shortened. However, in the vicinity of the corners C 1  to C 4  which are inflecting points where the radius vector length m of the target lens shape FT abruptly changes, as described above, the positions of the tracing styluses  306 F and  306 R in the Y-axis direction abruptly change. Correspondingly, the edge positions fxn and rxn also abruptly change in the vicinity of the corners C 1  to C 4 . Particularly, at the corners C 1  to C 4 , the radius vector length m and the edge positions fxn, rxn turn from “increase” to “decrease”. At this time, if the rotating speed of the eyeglass lens LE is too fast, owing to the influence of e.g. an inertial force, the trackability in the X-axis direction of the tracing styluses  306 F and  306 R for the refractive surfaces of the eyeglass lens LE will be deteriorated. As regards the tracing stylus  306 R for measuring the edge position of the lens rear surface, its trackability after the radius vector length m turns from “increase” to “decrease” at corner C 1  will be deteriorated, thereby deteriorating the measuring accuracy. As regards the tracing stylus  306 F for measuring the edge position of the lens front surface, owing to an abrupt change in the radius vector length Rn in the vicinity of corner C 1 , 
   the edge position also changes abruptly. Thus, its trackability in this vicinity will be deteriorated, thereby deteriorating the measuring accuracy. Further, as the lens curve becomes steep, this tendency increases. 
   In the range where the radius vector m abruptly changes so that it turns from “increase” to “decrease”, the tracing styluses  306 F and  306 R cannot follows abrupt moving control in the Y-axis direction of the lens chuck shafts  102 L and  102 R so that they may come off the radius vector path of the target lens shape FT. 
   On the other hand, assuming that the eyeglass lens LE is rotated at a constant speed, in order to assure the measuring accuracy at the corners C 1  to C 4  where the radius vector length m abruptly changes, if the rotating speed of the eyeglass lens LE is sufficiently reduced, the measuring time will be lengthened. Particularly, in the case of beveling, since the edge positions are measured at two points of the bevel apex and the bevel bottom, if the one round measurement time is lengthened, the total processing time will be further lengthened. 
   Now, in the target lens shape FT, at the areas farther from the corners. C 1  to C 4  (in  FIGS. 5A to 5B , the vicinity of 0°, 90°, 180° and 270°), the changing amount in the radius vector length m is relatively small and the changing amount in the edge position is also small. In these ranges, even if the rotating speed of the eyeglass lens LE is increased, the trackability of the tracing styluses  306 F,  306 R for the lens refractive surfaces can be ensured. 
   In view of the above fact, in order to shorten the measuring time, according to the change in the radius-vector length m, the rotating speed of the lens chuck shafts  102 R,  102 L (the rotating speed of the eyeglass lens LE) is changed. Specifically, in the range where the change in the radius vector length m is large, the rotating speed of the eyeglass lens LE is decreased thereby to ensure the measuring accuracy. On the other hand, in the range where the change in the radius vector length m is small, the rotating speed of the eyeglass lens LE is increased thereby to shorten the measuring time. 
   Now referring to  FIGS. 7A to 7C , an explanation will be given of a preferred example of the lens rotating speed control. The control unit  50  differentiates the radius vector length m of the target lens shape data (m, θn) of the eyeglass lens frame shown in  FIG. 5A  with respect to the radius vector angle θn. Assuming that the edge position on the path of the target lens shape is measured at 1000 points for one turn, the radius vector angle θn is changed for each 0.36°. The relationship of the differentiation result (differentiated value) of rdn with the radius vector angle θn is shown in the graph of  FIG. 7A . Next, the control unit  50  computes the absolute value of the differentiated value thus acquired. The relationship of the absolute value. Ardn thus computed with the radius vector angle θn is shown in  FIG. 7B . As seen from  FIG. 7B , at the corners C 1  to C 4  of four points of the target lens shape FT, the absolute value Ardn is large. 
   The control unit  50  changes the angular speed of rotating the chuck shafts  102 R,  102 L according to the absolute value. Ardn. This changing of the angular speed will be explained. In the control unit  50 , as shown in  FIG. 7C , with respect to the radius vector angle θn, the rotation angular speed Vθn nearly inversely proportional to the absolute value Ardn is acquired. The chuck shafts  102 R,  102 L are rotated at the rotation angular speed thus acquired. Specifically, in the range where the changing rate of the radius vector length m is small, the lens chuck shafts  102 R,  102 L are rotated at a high speed. As the changing rate of the radius vector length increases, they are rotated at a lower speed. The rotation angular speed Vθn can be experimentally determined so that the tracing styluses  306 F,  306 R can track the refractive surfaces even in the range where the absolute value Ardn which represents the changing rate of the radius vector length m (changing amount for a unit rotating angle) is large like the corners C 1  to C 4 . 
   In this way, by rotating the lens chuck shafts  102 R,  102 L at the rotation angular speed Vθn according to the changing rate of the radius vector length m, the speed in the Y-axis direction of the tracing styluses  306 F,  306 R moving along the refractive surfaces of the eyeglass lens LE can be made nearly constant. Thus, while ensuring the measuring accuracy, with the measuring time shortened, the edge positions of the refractive surfaces of the eyeglass lens LE can be measured. 
   Hitherto, the explanation has been given of the case where the refractive surfaces of the eyeglass lens LE are measured using the rotation angular speed Vθn being in an inverse relationship with the absolute value Ardn. However, the computation of the rotation angular speed Vθn according to changes in the radius vector length m is not limited to such a case. For example, the rotation angular speed Vθn in  FIG. 7C  may be changed stepwise so that it is changed in two steps of a high speed VθL and a low speed VθH across the boundary of the rotation angular speed of Vθc. The number of the steps to change is not 2 but may be 3 or over. 
   In the above description, the rotation angular speed Vθn is changed on the basis of the changing rate of the radius vector length m of the target lens shape FT, but may be changed also considering a change in the lens refractive surfaces in the X-direction. With the same target lens shape FT, if the eyeglass lens LE is thick, for example, it is a minus lens with a steep curve, or the high curve lens, the change in the edge position in the X-axis direction for the change in the radius vector angle θn becomes large. In the process measuring the edge position, if the change in the detected result appears as a large amount in either the tracing stylus  306 F or the tracing stylus  306 R as the measured result by the tracing styluses  306 F,  306 R, estimating that the subsequent change also becomes large, the control unit  50  controls the rotation angular speed Vθn to be decreased. Afterward, if the change in the detected result by the tracing styluses  306 F,  306 R appears as a small amount, the control unit  50  controls the rotation angular speed Vθn to be increased as the tracing styluses  306 F,  306 R can easily track the eyeglass lens LE. 
   In place of using the change in the edge position in the X-axis direction obtained in the measuring process, if the lens curve or the frame curve of the eyeglass lens frame is inputted, using this curve, the change in the edge position in the X-axis direction for the radius vector angle θn can be roughly computed. Thus, the rotation angular speed Vθn may be controlled on the basis of this computed result. The control based on both changes is more preferable. 
   In this embodiment, the eyeglass lens LE is chucked by the lens chuck shafts  102 R and  102 L so that it is nearly vertical to the setting-up plane on which the processing apparatus body  1  is set up. The refractive surfaces of the eyeglass lens LE are measured by the tracing styluses  306 F,  306 R located in parallel to the setting-plane. However, the control of the rotation angular speed is not limited to the relationship among these components. 
   For example, where the eyeglass lens LE is chucked so that its refractive surfaces are in nearly parallel to the setting-up plane of the processing apparatus body and measured by bringing the tracing styluses into contact with the eyeglass lens LE in a direction vertical to the setting-up plane (for example, U.S. Pat. No. 6,099,383 (JP-A-10-225855), the above control of the rotation angular speed can be applied. 
   Next, an explanation will be given of the operation after the edge position measurement. In the case of the beveling mode, the edge position measurement is carried out at two points of the bevel apex and the bevel bottom (position where the bevel foot and bevel slope cross) in the same longitudinal direction. Once the edge positions of the lens front surface and lens rear surface have been acquired, along a predetermined program, the control unit  50  executes bevel computation of acquiring the bevel path data to be formed on the eyeglass lens LE on the basis of the target lens shape data and edge position information. The computation of acquiring the bevel path data will be described later. 
   Once the bevel computation has completed, a simulation screen permitting the bevel shape to be changed is displayed on the display  5  (see  FIG. 8 ). On the simulation screen, a bevel curve value (Crv) based on the bevel computation is displayed at a display column  511 . On the simulation screen, the bevel curve value can be changed. Further, the quantity of moving the bevel apex position in parallel toward the lens front surface or lens rear surface can be inputted at an input column  512 . Further, on the simulation screen, the target lens shape FT and a bevel sectional diagram  520  are displayed. By designating the position of a cursor  530  on the target lens shape FT using a button key  513  or  514 , the bevel sectional diagram  520  is changed into the state at a designated position. 
   After the bevel simulation screen has been displayed, when the processing start switch of the switch unit  7  is depressed, the control unit  50  controls the driving of the motors  145 ,  150 , etc, of moving the carriage  101  according to the processing sequence, thereby roughing the peripheral edge of the eyeglass lens LE on the roughing data using the roughing grindstone  166  for plastic. The roughing path of the roughing data is computed as a path of the target lens shape data with a remaining finishing margin. 
   Now, in the processing of the plastic lens in this embodiment, processing is carried out so that the peripheral edge of the lens LE does not protrude from the grindstone width of the grindstone  166  (hereinafter referred to as “grindstone width effectively using processing”) on the way of the roughing. 
   An explanation will be given of the grindstone width effectively using processing.  FIG. 9  and  FIGS. 10A to 10B  are views showing the positional relationship between the high curve lens LE chucked by the lens chuck shafts  102 R,  102 L and grindstone group  168  when seen from the direction of arrow A in  FIG. 1 . The diagonally shaded area on the eyeglass lens LE is the section of the target lens shape FTr (roughing path) of the eyeglass lens LE to be roughed. 
   Prior to explaining the grindstone width effectively using processing, the conventional roughing control will be explained briefly. In processing the target lens shape FTr, the control unit  50  drives the motor  145  to move the carriage  101  in the X-direction so that the lens side end  1030  of the lens chuck axis  102 L is located at a position  166   p  set inside the left side boundary  166   a  of the roughing grindstone  166  by a predetermined distance (e.g. 2 mm). Thereafter, the control unit  50  drives the motor  150  to change the axis-to-axis distance between the lens chuck shafts  102 R,  102 L and the grindstone spindle  161   a  according to the target lens shape FTr, thereby roughing the peripheral edge of the eyeglass lens LE using the roughing grindstone  166 . At this time, in the case of a non-processed high curve lens LE, the outermost area LEO of the eyeglass lens LE protrudes outwardly from the right side boundary  166   b  of the grindstone  166 . If the roughing is continued in this state, with the outermost area LEO being left, the remaining area of the eyeglass lens LE will be roughed. With the progress of processing, when the outermost area LEO comes off from the eyeglass lens LE, the eyeglass lens LE may be cracked. 
   Now it is assumed that the arrangement order of the roughing grindstone  166  and the other grindstones is changed so that the finishing grindstone  164  is arranged on the right side of the roughing grindstones  166  (on the rear side of the eyeglass lens LE). In this case, the outermost area LEO protruded from the right side boundary  166   b  of the roughing grindstone  166  is put on the finishing grindstone  164  so that it is brought into pressure contact with the grindstone  164 , thereby increasing the load applied on the eyeglass lens LE. Thus, the axial angle of the actual eyeglass lens LE for the rotation angle of the lens chuck shafts  102 R,  102 L will be changed so that “axis deviation” is likely to occur. Further, this may cause the eyeglass lens LE to be deformed or broken. If the width of the roughing grindstone  166  can be sufficiently increased correspondingly to processing of the high curve lens, the above problem can be solved. However, in addition to the roughing grindstone  166  for plastic and finishing grindstone  164 , a plurality of grindstones such as the roughing grindstone  162  for a glass, and high curve bevel finishing grindstone  163  are coaxially attached to the grindstone rotating axis so that the entire width of the grindstones is large. Therefore, if the width of the roughing grindstones  166 ,  162  is increased, the apparatus must be structured so that the lens chuck shafts  102 L,  102 R can move over the entire grindstone width, and so will be upsized. 
   In order to obviate such inconvenience, the control unit  50  computes the position in the X-axis direction of the lens front surface and/or the lens rear surface on the basis of the lens front curve and/or lens rear curve and the movement information in the Y-axis direction, and effectively using the narrow grindstone width, performs roughing control so that the edge of the eyeglass lens LE falls within the width of the roughing grindstone  166 . 
     FIGS. 10A to 10B  are views for explaining the first method of the grindstone width effectively using processing. 
   First, the control unit  50  substitutes any four points selected from the edge position on the lens front surface measured by the lens shape measuring portions  300 F and  300 R for an equation of sphere, thereby acquiring the radius CRf of the lens front surface curve (lens front surface curve is automatically inputted in the control unit  50 ). In inputting the lens front surface curve data, if the lens front surface curve is previously known (which is obtained through the measurement by a well known curve meter), it may be inputted on the inputting screen of the display  5 . 
   Now, in  FIG. 10A , it is assumed that the curve circle with a radius CRf is LECf. It is assumed that the center of the curve circle LECf is located on a rotating center  102 T of the lens chuck shafts  102 R,  102 L. It is assumed that the moving distance of the lens side end  1030  of the lens chuck axis  102 L for the origin xo in the X-axis direction is xt (movement information in the X-axis direction). It is assumed that the distance in the Y-axis direction from the rotation center  102 T to the roughing grindstone  166  is Ly, and the point on the curve circle LECf apart by the distance Ly from the rotation center  102 T is LEC 1 . Further, it is assumed that the distance in the X-axis direction from the point LEC 1  on the curve circle LECf to the lens side end  1030  is Δxf. The distance Δxf is acquired from the radius CRf of the curve circle LECf of the lens front surface and the distance Ly. The control unit  50  computes the distance xt on the basis of the position  166   p  relative to the origin xo and the distance Δxf so that the point LEC 1  on the curve circle LECf corresponding to the distance Ly in the Y-axis direction is always located on the position  166   p  on the roughing grindstone  166 . 
   In roughing, the control unit  50  controls the movement in the Y-axis direction of the eyeglass lens LE on the basis of the target lens shape FTr, and also controls the movement in the X-axis direction of the eyeglass lens LE on the basis of the distance xt corresponding to the distance Ly. At this time, the lens side end  1030  is moved on a moving path along the curve circle LECf of the lens front surface. Thus, the eyeglass lens LE is moved so that the lens front surface always lies at the position  166   p . Therefore, the front surface of the eyeglass lens LE does not protrude from the left side boundary  166   a  and the rear surface of the eyeglass lens LE also does not protrude from the right side boundary  166   b  because the width of the roughing grindstone  166  is wider than the edge of the eyeglass lens LE. In such a state, the edge of the eyeglass lens LE is roughed. 
   As described above, if the curve circle LECf of the lens front surface is caused to always lie on the predetermined position  166   p  on the roughing grindstone  166 , even the high curve lens can roughed without the lens rear surface position protruding from the width of the roughing grindstone  166 . Even where the width w 166  of the roughing grindstone  166  is narrow, this grindstone width can be effectively used. 
   The above roughing control was carried out with reference to the lens front side. Under the same idea, as shown in  FIG. 10B , the roughing control with reference to the lens rear side can also be adopted. In this case, the control unit  50  acquires the curve circle LECr from the rear surface curve radius CRr of the eyeglass lens LE. The control unit  50  computes the distance xt on the basis of the position  166   q  relative to the origin xo and the distance Δxr so that the point LEC 2  on the curve circle LECr corresponding to the distance Ly in the Y-axis direction is always located on a predetermined position  166   q  (predetermined position on the lens rear side) set inside by a predetermined distance (2 mm) from the right side end surface  166   b  of the roughing grindstone  166 . The control unit  50 , on the basis of the computed result, controls the movement in the Y-axis direction of the eyeglass lens LE and also controls the movement in the X-axis direction thereof. Although the rear surface curve radius CRr acquired through the measurement of the edge position of the lens rear surface is supplied to the control unit  50 , the measurement result of the lens rear surface curve previously made may be supplied thereto. 
   Further, the edge of the eyeglass lens LE is set within the width of the roughing grindstone  166  using both input data of the front surface curve radius CRf and the rear surface curve CRr, and then the movement information in the X-axis direction relative to the movement in the Y-axis direction may be acquired. In this case, for example, by acquiring the curve circle located at the middle between the front surface curve radius. CRf and the rear surface curve radius CRr is acquired, and using the movement information in the X-direction computed so that the curve circle acquired lies on the center position of the width of the roughing grindstone  166 , the roughing is performed. Further, from when the distance in the X-direction between the curve circle LECf and LECr becomes shorter than the width of the roughing grindstone  166 , the movement in the X-axis direction may be determined within a range in which the point where the curve circle LECf of the lens front surface is brought in contact with the roughing grindstone  166  is located inside the position  166   p  and the point where the curve circle LECr of the lens rear surface is brought in contact with the roughing grindstone  166  is located inside the position  166   q.    
   In order to reduce partial abrasion of the grindstone surface of the roughing grindstone  166 , the X-axis movement is preferably controlled so that the edge of the eyeglass lens LE is roughed equally using the surface of the roughing grindstone  166  within a range where both of the curve circle LECf of the lens front surface and the curve circle LECr of the lens rear surface fall within the width of the roughing grindstone (between the position  166   p  and the position  166   q ). 
   The trouble caused when roughing only in the Y-axis direction movement is likely to occur when the eyeglass lens LE has a higher curve. Thus, where the eyeglass lens LE is a high curve lens (for example, the lens curve is 6 or more curve), the above grindstone width effectively using processing may be carried out; and where the curve of the eyeglass lens LE is not so high, like before, the roughing by only the Y-direction movement may be carried out. However, if it is desired that the width of the roughing grindstone  166  is not wide and the processing apparatus body  1  has a compact structure, even if the eyeglass lens LE does not have a high curve, the above grindstone width effectively using processing is preferably adopted. 
   Meanwhile, the method explained referring to  FIGS. 10A to 10B  can be also applied to the case where the outer-size of the eyeglass lens LE before processing is not known. In many cases, the eyeglass lens LE is moved simultaneously in both Y-axis direction and X-direction. Thus, in these cases, the load applied on the eyeglass lens LE may become slightly larger than in the case of the movement in only the Y-axis direction. In order to reduce such load, an explanation will be given of the second roughing method of using the grindstone effectively using processing in which the eyeglass lens LE is moved in the X-axis direction only when the edge of the eyeglass lens LE protrudes from the width of the roughing grindstone  166 . 
   First, in order to know the edge thickness of the eyeglass lens LE before processing, the outer size of the eyeglass lens LE (material lens) before processing will be acquired as follows. In starting the roughing, as shown in  FIGS. 11A to 11B , the control unit  50  drives the motor  145  to move the lens chuck axis  102 L in the X-axis direction so that the lens side end  1030  is located at the position  166   p  of the roughing grindstone  166 . Further, the control unit  50 , as shown in  FIG. 12 , drive the motor  120  to rotate the eyeglass lens LE so that the geometrical center FC of the target lens shape, the optical center Eo of the eyeglass lens LE and the center  166 T of the roughing grindstone  166  are located on the same straight line. In the case of an optical center chuck in which the optical center Eo of the eyeglass lens LE agrees with the rotation center  210 T, it is not necessary to consider the geometrical center FC. In this case without rotating the eyeglass lens LE, the control unit  50  drives the motor  150  to move the lens chuck shafts  102 L,  102 R in the Y-axis direction so that the eyeglass lens LE is brought into contact with the roughing grindstone  166 . At this time, the control unit  50  compares the driving pulse signal of the motor  150  with the pulse signal outputted from the encoder  158  and, when a deviation between both signals is generated, detects that the eyeglass lens LE has been brought into contact with the roughing grindstone  166 . This is because owing to the reaction force applied from the grindstone  166  when the eyeglass lens LE is brought into contact with the grindstone  166 , the quantity of movement of the actual eyeglass lens LE becomes smaller relatively to the quantity of movement of the eyeglass lens LE converted from the driving signal of the motor  150 . 
   Further, by detecting a change in the driving current of the motor  160  rotating the grindstone (when the eyeglass lens LE is brought into contact with the grindstone  166 , owing to the reaction force applied from the eyeglass lens LE to the grindstone  166 , a current quantity of the motor  160  changes), it can be also detected that the eyeglass lens LE has been brought in contact with the grindstone  166 . Similarly, it can be also detected from a change in the driving current of the motor  150  for the Y-axis movement that the eyeglass lens LE has been brought in contact with the grindstone  166 . By using both deviation in the Y-axis direction and changes in the current quantity of the motor  160 , the reliability of detecting that the eyeglass lens LE has been brought into contact with the grindstone  166  can be enhanced. 
   At this time, as the case may be, the outer periphery of the eyeglass lens LE may protrude from the grindstone  166 . How, because of a very short time, the influence such as axis deviation is negligible. 
   When it is detected that the eyeglass lens LE has been brought into contact with the roughing grindstone  166 , the control unit  50  can acquire the Y-axis position of the rotation center  102 T at this time from the encoder  158  to compute the radius rLE of the eyeglass lens LE before processing on the basis of the radius Rc of the roughing grindstone  166  and the layout data (distant r 10 ) of the optical center Eo relative to the geometrical center FC. 
   Further, as shown in  FIG. 11A , the control unit  50  previously computes the curve circle LECf of the lens front surface and the curve circle LECr of the lens rear surface by inputting curve data. The control unit  50  acquires the distance Ly between the rotation center  102 T and the lens outer periphery from the radius rLE of the eyeglass lens LE. On the basis of the distance Ly and the curve circle LECr of the lens rear surface, the control unit  50  acquires the distance Δxr from the lens side end  1030  to the point LEC 4  of the lens rear surface (on the curve circle LECr) when the eyeglass lens LE is brought into contact with the grindstone  166 . If the distance Δxr is known, it can be decided whether or not the edge point LEC 4  of the lens rear surface protrudes from the predetermined position  166   q  of the lens rear side of the roughing grindstone  166 , and the distance from the predetermined position  166   q  to the point LEC 4  can be also computed. 
   At this time, if the lens rear surface (edge point LEC 4 ) does not protrude from the predetermined position  166   q  of the roughing grindstone  166 , like the conventional manner, while the eyeglass lens LE is being rotated, the roughing is carried out by the movement control in only the Y-axis direction on the basis of the target lens shape data. If the lens rear surface (edge point LEC 4 ) protrudes from the predetermined position  166   q  of the roughing grindstone  166 , the lens chuck axis  102 L is moved toward the left side (lens front side) by the protruding quantity and thereafter the roughing is started (see  FIG. 11B ). 
   Further, the control unit  50  computes the distance Δxf from the lens side end  1030  to the lens front surface (curve circle LECf) according to the distance Ly (movement information in the Y-axis direction) to be changed in the Y-axis direction. When the distance Ly in the Y-axis direction is shortened with the progress of the roughing, the control unit  50  acquires, from the distance Δxf, the position of the lens front surface of the curve circle LECf relative to the predetermined position  166   p  of the lens front side of the roughing grindstone  166 . Before the lens front surface outwardly protrudes from the predetermined position  166   p  of the roughing grindstone  166 , the eyeglass lens LE is moved toward the rear side. Its moving position is set within the range in which the lens rear surface acquired from the curve circle LECr does not protrude from the predetermined position  166   q  of the roughing grindstone  166 . The lens side end  1030  or the lens front surface position LEC 3  of the curve circle LECf acquired from the target lens shape for roughing has only to be moved to the position  166   p  of the roughing grindstone  166 . Thereafter, without moving the eyeglass lens LE in the X-direction, the roughing can be carried out. 
   By the roughing control described above, even with the high curve lens, effectively using the grindstone width of the roughing grindstone with a narrow width, the roughing can be carried out without the lens protruding from the roughing grindstone  166 . Further, according to the roughing technique illustrated in  FIGS. 11A to 11B , the movement in the X-axis direction during the roughing can be reduced so that the redundant load applied on the eyeglass lens LE during the roughing can be reduced. 
   As device for acquiring the outer size of the eyeglass lens LE before processing, the lens edge position measuring portions  300 F,  300 R can be also employed. The control unit  50 , as shown in  FIG. 13 , after the direction of a straight line  180  connecting the optical center Eo and the geometrical center FC (rotation center  102 T) is caused to agree with the Y-axis direction by the rotation of the eyeglass lens LE, brings at least one of the tracing stylus  306 F and  306 R of the eyeglass lens shape measuring portion  300 F into contact with the target lens shape FT. Thereafter, the control unit  50  controls the Y-axis movement of the eyeglass lens LE so that the tracing stylus  306 F (or  306 R) moves outwardly of the target lens shape FT along the straight line  180 . When the tracing stylus  306 F (or  306 R) deviates from the state where it is in contact with the refractive surface of the eyeglass lens LE, the detection information of the edge position of the encoder  313 F (or  313 R) abruptly changes. By acquiring the moving position in the Y-axis direction from the encoder  158 , the radius rLE which is the outer size of the eyeglass lens LE before processing can be computed. Further, if the outer size of the eyeglass lens LE before processing is known beforehand, the operator may input the radius rLE on a predetermined screen of the display  5 . With respect to the optical center Eo, along the direction of a straight line  182  with an orientation opposite to that of the straight line  180 , the tracing stylus  306 F or  306 R may be moved. 
   The explanation has been hitherto given of the grindstone effectively using processing. This processing should not be limited to the manner as described above. As long as the relative movement between the grindstone and the eyeglass lens LE is controlled on the basis of the refractive surface information (at least one curve data on the lens front surface and lens rear surface) in order that when the eyeglass lens LE is roughed by a predetermined grindstone, it does not protrude from the roughing grindstone, such control is included in the technical idea of the grindstone effectively using processing. 
   Next, an explanation will be given of the bevel-finishing after the roughing. As described above, in the beveling mode, according to the curve of the eyeglass lens LE to be fitted in the eyeglass lens frame, the high curve mode or the low curve mode being the normal processing mode can be selected by the button key  501  of the display  5 . 
   When the low curve mode is selected, the beveling by the finishing grindstone  164  with the V-groove is set and the bevel path data are computed by the control unit  50 . On the basis of the edge position data of the lens front surface and lens rear surface by the lens edge position measurement and the target lens shape, the bevel path data are computed from a predetermined computing equation so that the bevel apex is located between the lens front surface and the lens rear surface. For example, it is computed as the path on which the bevel apex is located on the entire periphery to divide the edge thickness at a predetermined ratio (e.g. 3:7) and also the path shifted toward the lens rear side by the bevel curve along the lens front surface curve. The computing of the bevel path data can be realized by the method disclosed in JP-A-2-212059. The beveling by the finishing grindstone  164  with the V-groove will not explained here because it is described in JP-A-2-212059 and others. 
   Next, an explanation will be given of the computing of the bevel path data in the case of the high curve mode (high curve lens). In the case of the high curve mode, the bevel apex path is computed so that it basically runs along the lens front surface curve. The bevel formed when the eyeglass lens LE is fitted in a high curve frame MFR, in order to give the good appearance, as shown in  FIG. 14 , is set so that if the edge thickness of the eyeglass lens LE is not larger than a predetermined value to (e.g. 3 mm), the bevel apex VTP is located on the front surface curve and a bevel slope Vsr is formed on only the lens rear side. The reasons are as follows. Namely, because the high curve lens conforming to the frame curve (the eyeglass lens LE having a steep lens front surface curve) is employed as the eyeglass lens LE fitted in the high curve frame MFR, the lens front surface can be sufficiently served as the front side bevel slope. Further, if the front side bevel slope with an angle different from that of the lens front surface is formed largely, the boundary line therebetween is conspicuous due to the difference in the angle so that the appearance is deteriorated. If the edge thickness is larger than the predetermined value t 0 , setting is made so that the bevel apex VTP is shifted toward the lens rear side according to the edge thickness. Further, on the lens front side, a small plane may be formed as a kind of chamfering by using the front surface beveling grindstone. In this case, the bevel apex is shifted toward the lens rear side. 
   It is assumed that the bevel apex path data are represented by (m, θn, Hn) (n=1, 2, . . . , N) where m is the radius vector of the target lens shape data, θn is the data of the radius vector angle and Hn is the position data in the X-axis direction. In the setting in which the bevel slope VSr is formed on only the lens rear side, as the position data in the X-axis direction, the edge position data of the lens front surface detected by the lens edge position measuring portion  300 F is employed as it is. 
   Next, referring to  FIG. 15A , an explanation will be given to the method of acquiring the rear surface beveling data for forming a bevel slope VSr on the lens rear side using a rear surface beveling slope  163 Rs on the basis of the bevel apex path data (m, θn, Hn). 
   In  FIG. 15A , a bevel height vh (distance in the Y-axis direction from the bevel bottom Vbr where the bevel slope VSr and the bevel foot cross each other to the bevel apex VTP) is previously set. The bevel height vh can be called up from the memory  51  previously storing it by the control unit  50  and also can be arbitrarily set on the display  5 . The control unit  50  acquires a processing point of assuring the bevel bottom Vbr having the bevel height vh thus set. 
   It is assumed that the grindstone radius at the crossing point  163 G on the grindstone  163  to be brought into contact with the bevel bottom Vbr is Rt. The axis-to-axis distance LV (distance between the lens rotation center  102 T and grindstone rotation center) when the processing is performed with the diameter smaller by the bevel height vh than the two dimensional target lens shape data (m, θn) of the bevel apex path data (m, θn, Hn) (n=1, 2, 3, . . . , N) is acquired from
 
 LV=rn ·cos θ n +√{square root over (( Rt−vh ) 2 −( rn ·sin θ n ) 2 )}{square root over (( Rt−vh ) 2 −( rn ·sin θ n ) 2 )}
 
( n= 1, 2, 3 , . . . , N )  Equation 1
 
   The same computation as Equation 1 is carried out with the target lens shape data (m, θn) rotated by any minute angle around the lens rotation center. The rotating angle ξi (i=1, 2, 3, . . . , N) at this time is computed on the entire periphery. By acquiring the maximum value LVi of the distance LV at each rotating angle ξi, the reference processing data (LVi, ξi) of the processing point for assuring the bevel bottom Vbr at each lens rotating angle ξi can be obtained. 
   Next, according to the reference processing data (LVi, ξi), the processing point in the X-axis direction is acquired so that the bevel apex is tangent to the rear surface beveling slope  163 Rs. Now, for brevity of explanation, when considered as an orthogonal coordinate system relatively having an origin of the lens chuck shafts  102 R,  102 L, the bevel apex path data (m, θn, Hn) are replaced by bevel apex path data (xn, yn, zn) where the (m, θn, Hn) is expressed by:
 
 xn=rn ·cos θ n  
 
 yn=rn ·sin θ n  
 
zn=zn
 
( n= 1, 2, 3 , . . . , N )  Equation 2
 
   At this time, the grindstone of the rear surface beveling slope  163 Rs having the same origin as that of the orthogonal coordinate system can be expressed by
 
( x−X ) 2 +( y−Y ) 2 =( z−Z ) 2 ·tan 2 ψ1  Equation 3
 
   The (X, Y, Z) in Equation 3 is placed on a virtual cone apex coordinate constituting the grindstone plane of the rear surface beveling slope  163 Rs. Z in the rear surface beveling slope  163 Rs side is expressed by 
   
     
       
         
           
             
               
                 Z 
                 = 
                 
                   z 
                   + 
                   
                     
                       
                         
                           
                             ( 
                             
                               x 
                               - 
                               X 
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               y 
                               - 
                               Y 
                             
                             ) 
                           
                           2 
                         
                       
                       
                         
                           tan 
                           2 
                         
                         ⁢ 
                         ψ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                     
                   
                 
               
             
             
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 4 
               
             
           
         
       
     
   
   Further, on the orthogonal coordinate system in which ξi in the above reference processing path replaced by θn, Xn and Yn are expressed by
 
 Xn=LV ·cos θ n  
 
 Yn=LV ·sin θ n  
 
( n= 1, 2, 3 , . . . , N )  Equation 5
 
   By using these values and substituting the bevel apex path data (xn, yn, zn) into Equation 2, the maximum value of Z Zmax is acquired. The same computation is performed while rotating the bevel apex path data (xn, yn, zn) by any optional angle ξi (i=1, 2, 3, . . . N) around the lens rotation center over the entire periphery thereby to acquire the maximum value Zmax i of Z at each ξi. Thus, the processing point where the bevel apex is tangent to the rear surface beveling slope  163 Rs is acquired. The Zmax i acquired and the above reference processing data (LVi, ξi) provides the rear surface beveling data of (LVi, Zmax i, ξi)(i=1, 2, 3, . . . N). 
   During the beveling, for each lens rotation angle ξi of the above rear surface beveling data, the control unit  50  controls the Y-axis movement of the carriage  101  on the basis of the data LVi and also controls the X-axis movement of the carriage  101  on the basis of Zmax i. Thus, the bevel slope VSr is formed on only the lens rear side. In this case, without simultaneously processing the bevel slope on the lens front side, only the bevel slope on the lens rear side is processed individually. Thus, even with the high curve bevel, the problem of bevel thinning due to the interference can be solved. In order to avoid that the bevel apex gives an acute angle, before or after the beveling due to the rear surface beveling slope  163 Rs, control is preferably done so that the bevel apex area is flat-finished with a predetermined width of e.g. 0.1 mm by the flat-finishing grindstone plane of the finishing grindstone  164 . 
   In the case of the high curve lens also, the bevel foot is preferably formed by the processing slope  163 Rk. The reason therefor will be explained referring to  FIG. 14 . Where the lens LE has the high curve, if the angle of the rear surface bevel foot processing slope  163 Rk of the grindstone  163  relative to a reference line  1610  is 0°, the bevel foot formed on the rear surface of the eyeglass lens LE is in parallel to the reference line  1610  like a dotted line  1632 . In this case, the dotted line  1632  indicative of the bevel foot and the frame MFR interfere with each other so that the fitness when the eyeglass lens LE is fitted in the frame MFR is not pleasant. Inversely, where the grindstone  163  does not have the rear surface bevel foot processing slope  163 Rk so that the bevel slope is evenly formed at the angle of the rear surface beveling slope  163 Rs from the bevel apex VTP of the eyeglass lens LE to the rear surface of the eyeglass lens LE, the slope is formed like dotted line  1634  and so the bevel foot is not formed (only the bevel slope is formed from the bevel apex VTP to the rear surface of the eyeglass lens LE). In this case, if the eyeglass lens LE is fitted in the frame MFR from the direction of arrow  1636 , a large gap d 1634  will be formed between the edge of the rear surface of the eyeglass lens LE and the frame MFR so that the appearance when framed is not pleasant. For this reason, where the bevel slope is formed on the rear side of the eyeglass lens LE with the high curve, as in this embodiment, the slope  163 Rk for forming the bevel foot is preferably provided at an angle relative to the reference line  1610  smaller than the angle of the rear surface beveling slope  163 Rs relative to the reference line  1610 . 
   In the case of the eyeglass lens LE with the high curve, without the bevel being formed on the lens front side, the lens front surface, because of the front surface beveling slope  163 F, is fitted with sufficient catch for the front surface  1640  of the groove of the frame MFR. Therefore, if the edge thickness of the eyeglass lens LE measured by the lens edge position measuring portions  300 F,  300 R is small, the bevel on the lens front side is not required. Thus, even with the high curve lens, the beveling providing the good appearance can be done without lengthening the processing time as compared with the processing time of the ordinary beveling using the finishing grindstone  164 . 
   However, where the edge thickness of the eyeglass lens LE is large (for example, 3 mm or more), the bevel slope is preferably formed also on the lens front side.  FIG. 16A  shows the case where the eyeglass lens LE with a large edge thickness is fitted in the frame MFR without the bevel being on the lens front side. As seen, when the eyeglass lens LE is fitted in the frame MFR, the eyeglass lens LE protrudes from the rear side of the frame MFR so that the appearance after fitting when seen laterally is not pleasant. 
   On the other hand,  FIG. 16B  shows the case where after the bevel slope VSf is formed with the front surface beveling slope  163 F on the lens front side of the same eyeglass lens LE as shown in  FIG. 16A , the eyeglass lens LE is fitted in the frame MFR. As seen from  FIG. 16B , unlike the case of  FIG. 16A , the eyeglass lens LE does not protrude from the frame MFR, and the eyeglass lens LE can be fitted therein with the good appearance seen laterally. 
   From the point of view of safety of an eyeglass lens wearer, it is not preferred that the eyeglass lens LE comes off the frame MFR in the direction of arrow  1650  (toward the rear side) (see  FIG. 14 ). In view of this, in order to assure the catch for the frame MFR (difficulty of come off after fitting), the inclination angle of the rear surface processing slope  163 Rs relative to the reference line  1610  is made larger than that of the front side bevel formed by the front surface beveling slope  163 F. Moreover, a smaller quantity of the bevel revealing area d 1642  not covered with the frame MFR in the front side bevel slope VSf is preferable from the viewpoint of appearance (if the angle of the front surface beveling slope  163 F relative to the reference line  1610  is excessively large, it is not preferable from the viewpoint of appearance). In view of these facts, in this embodiment, the front surface beveling slope  163 F is formed in the direction of the angle of 30° relative to the reference line  1610 , and the rear surface beveling slope  163 Rs is formed in the direction of the angle of 45° relative to the reference line  1610 . It should be noted that these angles are exemplary. 
   An explanation will be given of the case where the bevel slope is formed on the lens front surface (see  FIG. 15B ). If the thickest area in the edge thicknesses measured by the edge position measuring portions  300 F,  300 R is not smaller than a predetermined value t 0  (3 mm), the control unit  50  makes setting of forming the bevel slope on the lens front side also. At this time, the control unit  50 , if the thickest area is within a range not smaller than 3 mm but smaller than 4 mm, computes the bevel path so that the distance d 192  from the front side of the eyeglass lens LE to the bevel-apex VTP is 0.3 mm. The distance d 192  is shifted so that the distance d 192  is increased by 0.1 mm whenever the thickest area increases by 1 mm in such a fashion that if the thickest area is within a range not smaller than 4 mm but smaller than 5 mm, the distance d 192  is set at 0.4 mm; if the thickest area is within a range not smaller than 5 mm but smaller than 6 mm, the distance d 192  is set at 0.5 mm, . . . . By setting the distance d 192 , the bevel height vh at this time can be acquired from the  163 αf (ψ 2  in  FIG. 15A ) of the front beveling slope  163 F. 
   In beveling the eyeglass lens front surface, it is assumed that the intersecting point of the lens front surface and the bevel slope lies on the position of the same grindstone radius Rt position as in the case of the lens rear surface. Where the bevel slope is formed on the lens front surface of the high curve lens, the presence of the bevel foot on the lens front surface is not preferable from the viewpoint of appearance so that the bevel foot will not be formed. Therefore, in computing the front surface beveling data, by replacing Equation 3 by
 
( x−X ) 2 +( y−Y ) 2 =( z−Z ) 2 ·tan 2 ψ2  Equation 6
 
and replacing Equation 4 by
 
                 Z   =     z   -             (     x   -   X     )     2     +       (     y   -   Y     )     2           tan   2     ⁢   ψ   ⁢           ⁢   2                   Equation   ⁢           ⁢   7               
in the same manner as in the case of the lens rear surface, the front surface beveling data (LVi, Zmax i, ξi) (i=1, 2, 3, . . . , N) can be acquired.
 
   For each lens rotation angle ξi of the above front surface beveling data, the control unit  50  controls the Y-axis movement of the carriage  101  on the basis of the data LVi and also controls the X-axis movement of the carriage  101  on the basis of the data Zmax i so that even with the high curve bevel where the bevel slope VSf is formed on the lens front side by this, the problem of bevel thinning due to the interference can be solved. 
   Hitherto, the setting of the bevel based on the edge thickness of the eyeglass lens LE has been explained, but the setting of the bevel is not limited to the manner as described above. Further, whether or not the front side bevel should be formed is determined with reference to 3 mm of the thickest area. However, this reference should not be limited to 3 mm. Whether or not the front surface bevel should be formed may be selectable by the operator. In this case, the bevel apex position may be changeable on the simulation screen displayed on the display  5  shown in  FIG. 8  by the button key  512 . 
   It is convenient that the bevel height vh of the rear surface described above is set according to the kind of the eyeglass lens frame. In the lens peripheral edge processing, as described referring to  FIG. 4 , the operator selects the kind of the eyeglass lens frame in a state where the target lens shape FT is displayed on the screen  500  of the display  5 . Where metal is selected as the material of the eyeglass lens frame, the bevel height vh is set at 2 mm by the control unit  50 . Where “cell” is selected as the material of the eyeglass lens frame, the bevel height vh is set at 3.5 mm by the control unit  50 . Further, as shown in  FIG. 8 , the height of the rear surface bevel height can be changed by manipulating a button  541   b  displayed on the display  5 . 
   In this way, by the processing with the bevel height of the lens rear surface changed according to the inputted material of the eyeglass lens frame, the appearance when the eyeglass lens LE is fitted in the eyeglass lens frame can be improved. 
   Further, the high curve beveling grindstone  163  includes the front surface beveling slope  163 F and the rear surface beveling slope  163 Rs adjacent to each other, but should not be limited to such structure. As shown in  FIG. 17 , at the one of both ends of the grindstone group  168 , the front surface beveling slope  163 F may be arranged, whereas at the other thereof, the rear surface beveling slope  163 Rs and the rear surface bevel foot processing slope  163 Rk may be arranged. In the arrangement of the grindstones as shown in  FIG. 3 , the vicinity of the boundary between the front surface beveling slope  163 F and the rear surface beveling slope  163 Rs cannot be employed for actual processing. However, in the structure as shown in  FIG. 17 , the entity of the front surface beveling slope  163 F and the rear surface beveling slope  163 Rs can be employed for processing.