Abstract:
An eyeglass lens grinding apparatus, which is designed to process an eyeglass lens so that the lens fits into an eyeglass frame. Frame shape data of an eyeglass frame is input, and a lens edge position on the lens is measured based on said frame shape data. Lens processing data is calculated based on the lens edge position and the frame shape data. The processing data is stored. The grinding wheels are controlled to process a plurality of lenses consecutively based on the same processing data until a signal requiring different processing data is issued. If a next set of lenses are to be processed, i.e. a different processing data is required, a made is switch to measure a lens edge position to newly obtain processing data.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an eyeglass lens grinding apparatus which grinds a lens to be processed, so that the lens fits into an eyeglass frame. 
     An eyeglass lens grinding apparatus is known, which, on the basis of input frame shape data obtained by a measurement of the shape of an eyeglass frame, grinds a lens to be processed to fit into the eyeglass frame. The apparatus is provided with lens measuring means for measuring the shape of the lens (the peripheral edge position) on the basis of the input frame shape data. The lens measuring means includes two detecting mechanisms respectively having first and second feelers that are movable in the direction of a lens rotary shaft and that are brought into abutment with the front and rear surfaces of the lens to detect their peripheral edge positions. Alternatively, the lens measuring means includes a single detecting mechanism by which the front and rear faces of the lens are sequentially measured. Such a lens measurement is performed for each of the lenses to be processed. 
     In a manufacturer of sunglass lenses, the sunglass lenses are generally processed such that lenses of the same specifications are continuously processed into the same shape. When the measurement of the lens shape is performed prior to each processing of a lens, there arises a problem in that the production efficiency is low. 
     Such an eyeglass lens grinding apparatus is known, which has a rough grinding wheel having a particle size of about #100 to #120 depending on the material of a lens to be processed, and a finishing grinding wheel having a particle size of about #400. These rough grinding and finishing grinding wheels are coaxially mounted on a grinding wheel rotary shaft. The finishing grinding wheel is provided with a single bevel groove. In the lens grinding apparatus, the lens to be processed is held on the lens rotary shaft, and pressingly contacted with the grinding wheels so that a bevel is finally formed in a peripheral portion of the lens. That is, the lens is roughly processed by the rough grinding wheel and then processed by the finishing grinding wheel having the bevel groove, into a final shape in which the lens fits into an eyeglass frame. 
     When the number of lenses to be processed is large, the degree of wear of a grinding wheel is increased in proportion to the number. Particularly when the finishing grinding wheel which is used in the final finishing processing is largely worn, this wear tends to produce an error in the finished size. Furthermore, wear of a grinding wheel reduces the processing accuracy due to a lowered processing performance of the grinding wheel. 
     In order to avoid the size error and reduction of the processing accuracy, the finished size must be periodically checked to make an appropriate size adjustment. For lenses such as sunglass lenses which are processed in large quantities by the manufacturer, however, frequent size checks result in a reduced production efficiency. 
     SUMMARY OF THE INVENTION 
     In view of the problem discussed above, it is an object of the invention to provide an apparatus which can efficiently process a large number of lenses. 
     It is another object of the invention to provide an apparatus which can process a large number of lenses efficiently while suppressing a size error. 
     To achieve the above-noted objects, the present invention provides the followings: 
     (1) An eyeglass lens grinding apparatus for processing an eyeglass lens to fit into an eyeglass frame, the apparatus comprising: 
     frame shape data input means for inputting frame shape data of an eyeglass frame; 
     lens edge measuring means for obtaining a lens edge position based on the frame shape data input by the frame shape data input means; 
     processing data calculating means for obtaining lens processing data based on the lens edge position obtained by the lens edge measuring means and the frame shape data; 
     mode switching means for newly activating the lens edge measuring means to newly obtain processing data; 
     data storing means for storing the processing data obtained by the processing data calculating means; 
     grinding means for grinding a lens; 
     processing control means for controlling the grinding means to process a plurality of lenses consecutively based on the same processing data until the control means receives a signal requiring different processing data. 
     (2) An eyeglass lens grinding apparatus according to (1), wherein the lens edge measuring means includes: 
     input means for inputting a lens shape data including lens thickness information; and 
     detecting means for detecting the lens edge position on either one of front and rear surfaces of a lens; 
     (3) An eyeglass lens grinding apparatus according to (2), wherein the lens includes a sunglass lens. 
     (4) An eyeglass lens grinding apparatus according to (2), wherein: 
     the lens includes a sunglass lens; and 
     the detecting means detects two different paths in relation to the same radius vectors, one of the paths being indicative of a position of a bevel bottom. 
     (5) An eyeglass lens grinding apparatus according to (4), wherein the other of the paths is indicative of a position of a bevel apex. 
     (6) An eyeglass lens grinding apparatus according to (1), wherein: 
     the data storing means stores plural sets of processing data, obtained by the processing data calculating means, in relation to respective identification data; and 
     the apparatus further comprises reading-out means for selectively reading out one set of processing data from the storing means; and 
     the processing control means controls the grinding means to process a lens based on the set of processing data read out by the reading-out means. 
     (7) An eyeglass lens grinding apparatus according to (1), wherein: 
     the data storing means is rewritable; and 
     the processing control means controls the grinding means to process a plurality of lenses consecutively based on the same processing data until the processing data is updated. 
     (8) An eyeglass lens grinding apparatus according to (1), wherein: 
     the grinding means includes a rough processing wheel and a finishing processing wheel having a plurality of bevel grooves each for forming a bevel; and 
     the processing control means controls the finishing processing wheel to perform processing with a sequentially selected one of the bevel grooves. 
     (9) An eyeglass lens grinding apparatus for processing an eyeglass lens to fit into an eyeglass frame, the apparatus comprising: 
     frame shape data input means for inputting frame shape data of an eyeglass frame; 
     lens edge measuring means for obtaining a lens edge position based on the frame shape data input by the frame shape data input means; 
     processing data calculating means for obtaining lens processing data based on the lens edge position obtained by the lens edge measuring means and the frame shape data; 
     data storing means for storing plural sets of processing data, obtained by the processing data calculating means, together with respective identification data; 
     mode switching means for newly activating the lens edge measuring means to newly obtain processing data; 
     grinding means for grinding a lens; 
     reading-out means for reading out one set of processing data from the storing means; and 
     processing control means for controlling the grinding means to process a lens based on the one set of processing data read out by the reading-out means. 
     According to the invention, a large number of lenses can be processed efficiently. 
     Further, even when a large number of lenses are processed, a size error can be reduced to a very low level and the processing can be efficiently performed. 
     The present disclosure relates to the subject matter contained in Japanese patent application Nos. Hei. 9-337995 and Hei. 9-337997 (both filed on Nov. 21, 1997), which are expressly incorporated herein by reference in their entireties. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view illustrating the general configuration of a lens grinding apparatus according to an embodiment of the present invention. 
     FIG. 2 is a view illustrating the configuration of grinding wheels in the lens grinding apparatus. 
     FIG. 3 is a side view showing the upper and lower parts of a lens chuck in the lens grinding apparatus. 
     FIG. 4 is a perspective view illustrating a mechanism for moving a lens grinding part  300 R. 
     FIG. 5 is a view illustrating a mechanism for horizontally moving the lens grinding part  300 R and detecting the completion of processing. 
     FIG. 6 is a sectional side view showing the configuration of the lens grinding part  300 R. 
     FIG. 7 is a sectional side view illustrating a lens thickness (shape) measuring section  400  in the lens grinding apparatus. 
     FIG. 8 is a schematic block diagram showing a control system in the lens grinding apparatus. 
     FIG. 9 is a diagram illustrating a calculation of a bevel employed in the lens grinding apparatus. 
     FIG. 10 is a view showing an example of a setting screen used when a size adjustment or the like is performed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A lens grinding apparatus according to an embodiment of the present invention will be hereinafter described with reference to the accompanying drawings. 
     Configuration of Whole Apparatus 
     In FIG. 1, reference numeral  1  denotes a main base, and  2  denotes a sub-base that is fixed to the main base  1 . A lens chuck upper part  100  and a lens chuck lower part  150  hold a lens to be processed by means of their respective chuck shafts during processing it. A lens thickness (shape) measuring section  400  is accommodated below the lens chuck upper part  100  in the depth of the sub-base  2 . 
     Reference symbols  300 R and  300 L respectively represent right and left lens grinding parts each having grinding wheels for lens grinding on its rotary shaft. Each of the lens grinding parts  300 R and  300 L is held by a moving mechanism (described later) so as to be movable in the vertical and horizontal directions with respect the sub-base  2 . As shown in FIG. 2, a rough grinding wheel  30  for processing on glass lenses, and an intermediate finishing grinding wheel  31  having bevel grooves are mounted concentrically on the rotary shaft of the lens grinding part  300 L. The intermediate finishing grinding wheel  31  is a metal bond grinding wheel having a particle size of #400, which is formed at its grinding surface with four bevel grooves  31   a ,  31   b ,  31   c  and  31   d  having the same V-shaped configurations. The rough grinding wheel  30  for processing on glass lenses, which is the same as that in the lens grinding part  300 L, and an accurate finishing grinding wheel  34  having bevel grooves are mounted concentrically on the rotary shaft of the lens grinding part  300 R. The accurate finishing grinding wheel  34  is a metal bond grinding wheel having a particle size of #600, which is formed at its grinding surface with four bevel grooves  34   a ,  34   b ,  34   c  and  34   d  having the same configurations as the bevel grooves of the intermediate finishing grinding wheel  31 . The diameter of these grinding wheels are relatively small, that is, about 60 mm, thereby improving processing accuracy while ensuring durability of the grinding wheels. With this grinding wheel arrangement, the grinding apparatus is preferably used for beveling refractive-power-less sunglass lenses made of glasses on a large or mass scale. 
     A display unit  10  for displaying processing data and other information and an input unit  11  for allowing a user to input data or an instruction to the lens grinding apparatus are provided in the front surface of a body of the apparatus. Reference numeral  12  denotes a closable door. 
     Structures of Main Parts 
     &lt;Lens Chuck Part&gt; 
     FIG. 3 illustrates the lens chuck upper part  100  and the lens chuck lower part  150 . A fixing block  101  is fixed to the sub-base  2 . A DC motor  103  is mounted on top of the fixing block  101  by means of a mounting plate  102 . The rotational force of the DC motor  103  is transmitted through a pulley  104 , a timing belt  108  and a pulley  107  to a feed screw  105 . As the feed screw  105  is rotated, a chuck shaft holder  120  is moved vertically while being guided by a guide rail  109  fixed to the fixing block  101 . A pulse motor  130  is fixed to the top portion of the chuck shaft holder  120 . The rotational force of the pulse motor  130  is transmitted, via a gear  131 , and a relay gear  132  to a gear  133  to rotate the chuck shaft  121 . Reference numeral  124  denotes a lens depressing member mounted on the chuck shaft  121 . Reference numeral  135  denotes a photosensor and  136  denotes a light-shielding plate that is mounted on the chuck shaft  121 . The photosensor  135  detects a rotation reference position of the chuck shaft  121 . 
     A lower chuck shaft  152  is rotatably held by a chuck shaft holder  151  fixed to the main base  1 . The rotational force of a pulse motor  156  is transmitted to the chuck shaft  152  to rotate the chuck shaft  152 . Reference numeral  159  is a cup receptacle, mounted on the chuck shaft  152 , for receiving a fixing cup fixed to a lens to be processed, thereby holding the lens. Reference numeral  157  denotes a photosensor and  158  denotes a light-shielding plate that is mounted on the gear  155 . The photosensor  157  detects a rotation reference position of the chuck shaft  152 . 
     With the lens chuck part thus constructed, a lens to be processed is placed on the chuck shaft  152  side, and then chucked by lowering the chuck shaft  121 . The control unit  600  (described later in detail) monitors and controls a load current of the DC motor  103  to optimize the chucking pressure. 
     &lt;Moving Mechanism for Lens Grinding Part&gt; 
     FIG. 4 illustrates a mechanism for moving the right lens grinding part  300 R. A vertical slide base  201  is vertically slidable along two guide rails  202  that are fixed to the front surface of the sub-base  2 . A bracket-shaped screw holder  203  is fixed to the side surface of the sub-base  2 . A pulse motor  204 R is fixed to the upper end of the screw holder  203 . A ball screw  205  is coupled to the rotary shaft of the pulse motor  204 R, so that the rotation of the ball screw  205  causes the vertical slide base  201  fixed to a nut block  206  to be moved in the vertical direction while being guided by the guide rails  202 . A spring  207  is provided between the sub-base  2  and the vertical slide base  201 . That is, the spring  207  urges the vertical slide base  201  upward to cancel out the downward load of the vertical slide base  201 , thereby facilitating its vertical movement. Reference numeral  208 R designates a photosensor, and  209  designates a light-shielding plate that is fixed to the nut block  206 . The photosensor  208 R determines a reference position of the vertical movement of the vertical slide base  201  by detecting the position of the light-shielding plate  209 . 
     Reference numeral  210  denotes a horizontal slide base to which the lens grinding part  300 R is fixed. The horizontal slide base  210  is slidable in the horizontal direction along two slide guide rails  211  that are fixed to the front surface of the vertical slide base  201 . A bracket-shaped screw holder  212  is fixed to the lower end of the vertical slide base  201 , and a pulse motor  214 R is fixed to the side surface of the screw holder  212 . The ball screw  213  is coupled to the rotary shaft of the pulse motor  214 R. The ball screw  213  is in threaded engagement with a nut block  215 . As shown in FIG. 5, the nut block  215  is connected through a spring  220  to a protruded portion  210   a  that extends downwardly from the horizontal slide base  210  (note that the mechanism shown in FIG. 5 is located behind the nut block  215  in FIG.  4 ). The spring  220  biases the horizontal slide base  210  toward the lens chuck side. The rotation of the pulse motor  214 R causes the rotation of the ball screw  213 , which moves the nut block  215  in the left-handed direction in FIG.  5 . The horizontal slide base  210  pulled by the spring  220  is moved in the left-handed direction accordingly. If the grinding pressure larger than the biasing force of the spring  220  is caused during processing of the lens, the horizontal slide base  210  is not moved even through the nut block  215  is moved in the left-handed direction, thereby adjusting the grinding pressure to the lens to be processed. When the nut block  215  is moved in the right-handed direction in FIG. 5, the nut block  215  is pushed by the protruded portion  210   a  so as to move the horizontal slide base  210  in the right-handed direction. A photosensor  221 R is attached to the protruded portion  210   a . The photosensor  221 R detects the completion of processing upon detecting a light shielding plate  222  fixed to the nut block  215 . 
     A photosensor  216 R fixed to the screw holder  212  detects a light-shielding plate  217  fixed to the nut block  215 , thereby determining a reference position of the horizontal movement of the horizontal slide base  210 . 
     Since a moving mechanism for the left lens grinding part  300 L is symmetrical with that for the right lens grinding part  300 R, it will not be described. 
     &lt;Lens Grinding Part&gt; 
     FIG. 6 is a side sectional view showing the structure of the right lens grinding part  300 R. A shaft support base  301  is fixed to the horizontal slide base  210 . A housing  305  is fixed to the front portion of the shaft support base  301 , and rotatably holds therein a vertically extending rotary shaft  304 . A group of grinding wheels including a rough grinding wheel  30  and so on are mounted on the lower portion of the rotary shaft  304 . A servo motor  310 R is fixed to the top surface of the shaft support base  301  through a mounting plate  311 . The rotational force of the servo motor  310 R is transmitted via a pulley  312 , a belt  313  and a pulley  306  to the rotary shaft  304 , thereby rotating the group of the grinding wheels. 
     Since the left lens grinding part  300 L is symmetrical with the right lens grinding part  300 R, its structure will not be described. 
     &lt;Lens Thickness (Shape) Measuring Section&gt; 
     FIG. 7 is a sectional side view showing the configuration of the lens thickness (shape) measuring section  400 . A lens measuring unit  401  is suspended on and held by a rail  403 , attached to the lower face of a stationary base  402 , through a movement block  404 , so as to be slidable in the axial direction. A motor  405  for the axial movement is fixed onto the stationary base  402 . The rotation of the motor  405  is transmitted via a pulley  406 , a belt  407 , and a pulley  408  to a feed screw  409 . A female screw is formed inside the movement block  404  and threadingly engaged with the feed screw  409 . The movement block  404  is moved in the axial direction by the rotation of the feed screw  409  while being guided by the rail  403 . 
     The lens measuring unit  401  having the following configuration is attached to the lower side of the movement block  404 . A guide shaft  412 , a rear post  413 , and a center post  414  are fixed to upper and lower plates  410  and  411 . The guide shaft  412  is passed through a bearing  415  so that the bearing  415  is vertically slidable. A measurement arm  417  is fixed to the bearing  415 . The measurement arm  417  has, at its distal end, a feeler  416  which is to abut against a surface of a lens to be processed. The measurement arm  417  is upward urged by a spring  418 . A rack  419  is fixed via a mounting block  423  to the rear side of the measurement arm  417 . A potentiometer  420  is fixed to the center post  414 . A pinion  421  is attached to a rotary shaft of the potentiometer  420 , and threadingly engaged with the rack  419 . The potentiometer  420  detects the amount of the vertical movement of the measurement arm  417 . The reference numeral  422  denotes a spring which cancels a downward load exerted on the measurement arm  417 . One end of the spring  422  is fixed to the mounting block  423 . A feed screw  430  is rotatably held between the upper and lower plates  410  and  411 . The feed screw  430  is rotated by a motor  431  attached to the lower plate  411 , via a pulley  432 , a belt  433 , and a pulley  434 . The reference numeral  435  denotes a movement block having a female screw that is threadingly engaged with the feed screw  430 . The movement block  435  is slid vertically along the guide shaft  412  in association with the rotation of the feed screw  430 . The downward movement of the movement block  435  causes the lower face of the movement block  435  (on the guide shaft  412  side) to abut against the bearing  415 , thereby depressing the measurement arm  417  downwardly. The initial position, i.e. the lowest position, of the measurement arm  417  is detected by means of a sensor  436  and a light shielding plate  437  fixed to the mounting block  423 . 
     The thus configured lens thickness (shape) measuring section  400  performs a measurement in the following manner. First, the motor  405  is driven on the basis of the frame shape data of the eyeglass frame, to move the lens measuring unit  401  to a measurement position. Next, the motor  431  is rotated forwardly by a predetermined number of pulses to rotate the feed screw  430 , so that the movement block  435  is moved upwardly. In association with this movement, the measurement arm  417  is pulled by the spring  418  to be moved upwardly, so that the feeler  416  abuts against the front surface of the lens. The movement block  435  is moved to an appropriate escape position. The lens is rotated by one turn while maintaining the abutment between the feeler  416  and the front surface of the lens, and concurrently the lens measuring unit  401  is moved in the axial direction on the basis of the frame shape data. The potentiometer  420  detects the amount of the movement of the feeler  416  in the direction of the lens chuck shaft during this operation, so that the shape of the lens is obtained. 
     In the lens measurement in the apparatus of the embodiment, the shape of the front surface of the lens is measured two times in accordance with different measurement paths based on the data of the eyeglass frame. From the two measurements, the inclination of the front surface of the lens at an edge position of the lens in relation to each radius vector is obtained, and the obtained inclination is used in the calculation of the bevel data (the calculation will be described later). The bevel data may be calculated by measuring the front and rear surfaces of the lens, and feelers which are respectively dedicated to the front and rear surfaces of a lens may be dispose, as disclosed in Japanese patent Kokai publication No. Hei. 3-20603, and others. In the case of a refractive-power-less sunglass lense configured by a complete spherical surface, if data of one point (for example, a point on the bevel bottom face) are obtained in relation to each radius vector, it is possible to attain necessary accuracy. For example, if the spherical curve is calculated or obtained as data, the inclination of the surface at the bevel position can be obtained. 
     &lt;Control System&gt; 
     FIG. 8 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 , and photosensors 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 drive  628  detects the load current of the DC motor  103 , and feeds back the detected current to the control unit  600 . The control unit  600  uses these information to control the movement of the lens grinding parts  300 R and  300 L, the rotation of the lens, and the lens chuck pressure. 
     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 , lens thickness measurement data, and other data. 
     Operation 
     The operation of the thus configured apparatus will be described. Hereinafter, the operation in the case where a large number of sunglass lenses with no refractive power and of the same specifications are processed into the same shape will be described. 
     The shapes of various eyeglass frames into which the sunglass lenses are to be fitted (hereinafter, such a shape is referred to as “a target lens configuration”) are previously measured by a lens frame shape measuring apparatus  650 , and the target lens configuration data are transmitted to a host computer  651 . The target lens configuration data are managed by the host computer  651 . The data relating to a lens shape, such as the thickness of a lens are managed by the host computer  651 . When the lens processing is to be performed, a job card in the form of a bar code, which is attached to the lens to be processed, is read by a bar code scanner  652  connected to the present apparatus (the job card in the form of the bar code is attached in the unit of a lot in which a large number of lenses to be processed into the same frame and having the same specification are bundled). According to the instruction of the job card, the data relating to the lens shape, such as the thickness of each lens, and the target lens configuration data are read out from a management database of the host computer  651 , and then transferred to and stored in a data memory  603 . 
     When a processing is to be initially performed by using the transferred target lens configuration data, the switch  11 e of the input unit  11  is operated so that the measurement mode is switched to“lens measurement” mode. When a lens to be processed is placed on the side of the chuck shaft  152  and the start switch  11   i  is depressed, the chuck shaft  121  is lowered so that the lens is chucked, and the lens measurement is then started. 
     The control unit  600  operates the lens thickness (shape) measuring section  400  on the basis of the target lens configuration data, so that the shape of the front surface of the lens is measured. Along two-dimensional first and second measurement paths obtained based on the target lens configuration (eyeglass frame shape) data, measurement is performed twice on the front face of the lens. For example, the first measurement path is set to be at the position of a bevel apex which is the outermost peripheral portion of the lens, and the second measurement path is set to be a path located inwardly from the bevel apex by an amount corresponding to the bevel height (i.e. an amount corresponding to the depth of the bevel groove in each of the intermediate and accurate finishing grinding wheels  31  and  34 ). 
     The calculation of the bevel will be described. When a bevel is to be formed in a sunglass lens of a constant thickness and having no refractive power, the present embodiment adopts such a processing by which the bevel apex is located at a substantially center position of the thickness of the lens periphery (edge), in order to visually improve the bevel state. If a lens has no curve, the lens, which has undergone the processing and is to be subjected to the beveling, has a constant peripheral (edge) thickness. However, a lens for a sunglass has a curve, and hence the peripheral (edge) thickness of the lens is thicker as the lens surface is more inclined. On the basis of the peripheral (edge) positions of the first and second measurement paths and the thickness of the lens center, the bevel calculation produces data in which the thickness variation is corrected, thereby obtaining bevel path data. Specifically, as shown in FIG. 9, using the points A and B obtained as results of two lens measurements, the lens surface between the points A and B is approximated as a linear line, and the inclination θ of the lens front surface at the lens periphery after processing is obtained. In accordance with the inclination θ of the lens front surface, a correction factor is previously determined. The position of the bevel apex can be obtained from the position of the first measurement path with the use of the correction factor. Accordingly, the bevel apex path data can be obtained. 
     Alternatively, the bevel apex path data may be obtained in the following manner. When the subject lens has a constant thickness, the inclination of the front surface of the lens is equal to that of the rear surface, and hence the thickness t′ of the periphery (edge) which located inwardly from the bevel apex by an amount corresponding to the height of the bevel can be easily obtained from the following expression in relation to the lens thickness t (for example, 2.2 mm): 
     
       
         t′=t/cos θ. 
       
     
     When the peripheral (edge) thickness based on of the target lens configuration data is obtained in relation to each radial vector angle, the path data of the bevel apex which is to be located at the center of the peripheral (edge) thickness are obtained. 
     The bevel path data thus obtained are converted into data on the axis-to-axis distance between the lens rotary shaft and the grinding wheel rotary shaft to provide processing data for the lens processing. The processing data are stored into the data memory  603 , and read out therefrom and used during the processing. 
     Subsequently to the completion of the lens measurement operation of the apparatus, the“lens measurement” mode is canceled by operating the switch  11   e  so that the mode is transferred to the processing mode. By depressing the start switch  11   i , the processing is started. The mode change over signal and the start signal may entered as instruction signals in association with a key operation on the host computer  651  in place of an operation of the switches of the input unit  11 . 
     In response to the processing start signal, the rough processing is first performed. The control unit  600  drives the servo motors  310 R and  310 L to rotate both the groups of grinding wheels of the lens grinding parts  300 R and  300 L. Furthermore, the control unit  600  drives the right and left pulse motors  204 R and  204 L to lower the right and left vertical slide bases  210  so that both of the right and left rough grinding wheels  30  are located at the same height as the lens to be processed. Then, the pulse motors  214 R and  214 L are rotated so as to slide the lens grinding parts  300 R and  300 L toward the lens, and the upper and lower pulse motors  130  and  156  are synchronously rotated so that the lens chucked by the chuck shafts  121  and  152  are rotated. The right and left rough grinding wheels  30  are moved toward the lens while being rotated, thereby gradually grinding the lens from the two directions. The amounts of movement of the rough grinding wheels  30  toward the lens are controlled independently from each other on the basis of the processing data. In the apparatus of the embodiment, since the axis of the lens chuck shaft is aligned on a linear line connecting the axes of the rotary shafts for the right and left grinding wheel groups, the right and left rough grinding wheels  30  are moved on the basis of the shape information sets which are shifted from each other by 180 degree. 
     Subsequently to the completion of the rough processing, a bevel finishing processing using the intermediate finishing grinding wheel  31  and the accurate finishing grinding wheel  34  is started. The control unit  600  causes the rough grinding wheels  30  to be separated from the lens, then reads the bevel processing data stored in the data memory  603 , and, on the basis of the data, moves the lens grinding parts  300 L and  300 R so that one of the four bevel grooves of each of the intermediate finishing grinding wheel  31  and the accurate finishing grinding wheel  34  is located at the position of the bevel which is to be formed in the lens. In a case of the processing of the first subject lens, the bevel grooves  31   a  and  34   a  are used. The control unit  600  controls the rotating intermediate finishing grinding wheel  31  to be moved toward the lens, so that the bevel groove  31   a  is pressingly contacted with the lens to grind the lens. Subsequently to the completion of the intermediate-finishing at the initial rotational position (i.e., after a portion of the lens at the initial rotational position has be ground until an amount for the accurate finishing remains), the rotation of the lens is started. During the rotation of the lens, the intermediate finishing processing is performed on the whole periphery of the lens by moving the intermediate finishing grinding wheel  31  on the basis of the bevel processing data for intermediate finishing. In the course of the semi-finishing processing, when the lens makes one half of rotation, the accurate finishing grinding wheel  34  is moved toward the lens and the portion of the lens which has been subjected to the intermediate finishing processing is further subjected to the accurate finishing processing using the bevel groove  34   a . On the basis of the bevel processing data for accurate finishing processing, the control unit  600  controls the movement of the accurate finishing grinding wheel  34  in the axial direction and the direction toward the lens until the lens is completely processed. In this operation, it is preferable to set the processing amount (about 0.2 mm) of the accurate finishing process to be smaller than the processing amount (about 1.5 mm) of the intermediate-finishing processing. In the case of the sunglass lens of a thickness of 2.2 mm, even if the lens is not ground to completely remove the amount set for the intermediate finishing processing, the accurate finishing grinding wheel  34  can complete the required processing for the lens by one rotation of the lens. In other words, the whole of the required finishing processing including the accurate finishing can be ended upon the total 1.5 rotations of the lens. 
     By subjecting the portion of lens to the intermediate finishing processing and then to the accurate finishing processing using the accurate finishing grinding wheel of a smaller particle size as described above, it is possible to provide an excellent finished surface without any burrs which are likely to be formed on the lens periphery (edge) in the case of a glass lens. The accurate finishing process may be started after the previous intermediate finishing process is ended over the whole periphery of lens. However, the start of the accurate finishing processing from a time point, at which a portion of the lens, that has been subjected to the intermediate finishing processing, reaches the position where accurate finishing processing is enabled, makes it possible to shorten the entire processing time period, and thus the efficient finishing processing can be attained. Specifically, in the case where the processing using the accurate finishing grinding wheel is started after the intermediate finishing processing is ended completely over the whole periphery of the lens, at least two rotations of lens are required. In contrast, according to the grinding wheel arrangement of the embodiment, only 1.5 rotations of lens can complete the entire finishing processing in the fastest case as described above. 
     Since the finishing processing is divided into two steps, i.e. the intermediate finishing processing and the accurate finishing processing, wear of grinding wheels can be dispersed. Further, since the amount to be processed by the final, accurate finishing processing can be reduced, the wear amount of the accurate finishing grinding wheel  34  is smaller in degree than that of the intermediate finishing grinding wheel  31 . Even when a large number of lenses are continuously processed, the reduction of the size accuracy due to wear of the grinding wheels can be suppressed to a very low level. The experiments conducted by the inventors indicated that the wear amount of the intermediate finishing grinding wheel was about 0.05 mm and that of the accurate finishing grinding wheel was not larger than about 0.01 mm when about 1,000 lenses were processed under a condition that the processing amount of 1.5 mm was set for the intermediate finishing grinding wheel and the processing amount of 0.2 mm was set for the accurate finishing grinding wheel was 0.2 mm. Namely, it was confirmed that the size accuracy can be sufficiently maintained. 
     When the processing for one lens is ended as described above, the chuck shaft  121  is raised and the processed lens is detached. Thereafter, the control is transferred to the processing for the next lens. The control unit  600  reads out the previously stored processing data, and performs the rough and finishing processings in the processing mode without the lens measurement. Thus, in comparison to the case in which the lens measurement is performed for each lens, the entire processing time period can be shortened. The processing for sunglass lenses is generally performed such that a large number of lenses of the same specifications are continuously processed using the same target lens configuration. Consequently, the omission of the lens measurement can largely shorten the entire processing time period. 
     The host computer  651  may store and manage plural sets of processing data together with identification symbols, in correspondence with lens specification data and target lens configuration data. In this case, even if the lot of lenses is changed, the host computer  651  can read out processing data corresponding to instructions on a bar code job card to continuously perform the processing in the process mode without the lens measurement. However, it is not required to store plural sets of processing data. Note that since the processing for sunglass lenses is generally performed such that a large number of lenses of the same specifications are continuously processed using the same target lens configuration as described above, the lens measurement at each time when a different processing is to be performed does not lead a serious time loss, so that the storing of the plural sets of processing data is not essential and the rewriting of the processing data at each time when a different processing is to be performed is sufficient. 
     In the finishing processing for the second lens after the rough processing, the control unit  600  controls the apparatus so that the finishing processing is performed using the bevel groove  31   b  of the intermediate finishing grinding wheel  31  and the bevel groove  34   b  of the accurate finishing grinding wheel  34 . Each time when the lens is changed to another one, the bevel grooves to be used in the processing are sequentially changed accordingly. 
     That is, the bevel grooves  31   c  and  34   c  are used in the processing for the third lens, and the bevel grooves  31   d  and  34   d  are used in the processing for the fourth lens. In the embodiment, this can reduce the wear of the grinding wheels to one fourth in comparison to the case in which only one bevel groove is used in the processing. Thus, the life of the grinding wheels can be prolonged. Even when a large number of lenses are continuously processed, the lowering of the size accuracy can be avoided as much as possible. 
     The finished size of a lens may be gradually increased because of wear of the grinding wheels due to repeated processings, or other reasons. The size adjustment is conducted in the following manner. The menu switch lid is depressed so that a parameter setting screen  700  shown in FIG. 10 is displayed on the display unit  10 . The item which is to be adjusted is selected by moving an arrow cursor  701  which is displayed in the left side of the screen. The items correspond to the four bevel grooves  31   a  to  31   d  of the intermediate finishing grinding wheel  31  and the four bevel grooves  34   a  to  34   d  of the accurate finishing grinding wheel  34 , respectively. Any one of the bevel grooves can be selected. The preset size of the selected item is changed by increasing or decreasing the value displayed in the right side, by operating the switch  11   c . Similarly, the bevel positions of the intermediate finishing grinding wheel  31  and the accurate finishing grinding wheel  34  can be adjusted for the bevel grooves independently from one another. When the parameter setting screen  700  is closed, the data stored in the adjust value memory  604  are rewritten by the adjusted values. The input of these values may be realized by a control from the host computer  651  connected to the main unit of the apparatus. The control unit  600  controls the processing by each bevel groove on the basis of the rewritten data. This enables an appropriate setting to cope with the wear of the grinding wheels even if the bevel grooves have different degrees of grinding wheel wear. 
     The present invention has been described by referring to a processing for a sunglass lens with no refractive power. The present invention can also be applied to a processing for an eyeglass lens with a refractive power since the eyeglass lenses with the refractive power can be processed similarly.