Eyeglass lens processing apparatus

An eyeglass lens processing apparatus for processing an eyeglass lens includes: a lens chuck that holds the lens; a regular-grooving tool; a first moving unit that moves the lens held by the lens chuck; a grooving data input unit that inputs grooving data including a width and depth of the groove to be formed in the lens; a controller that controls the first moving unit to perform regular-grooving on the basis of the grooving data; a fine-grooving tool; a second moving unit that moves the lens held by the lens chuck; and a selector that selects whether fine-grooving is to be performed. When performance of fine-grooving is selected, the controller performs the regular-grooving on the lens so that a bottom and side surfaces of the groove have a fine-grooving margin, and controls the second moving unit to perform the fine-grooving on the basis of the grooving data.

BACKGROUND OF THE INVENTION

The present invention relates to an eyeglass lens processing apparatus for processing an eyeglass lens.

When an eyeglass lens is fixed to an eyeglass frame by wires made of nylon or the like, grooving is performed to form a groove, into which the wire is fitted, on a peripheral surface (an edge surface) of the lens on which roughing and flat-finishing are performed. For this purpose, an eyeglass lens processing apparatus including a grooving unit has been proposed in recent years.

However, according to the grooving in the related art, processing speed has been prior to other conditions and the appearance (quality in shape) of the groove to be formed has not been regarded as an important factor. Accordingly, a grooving grindstone having a granularity of about #400 has been used as a grooving tool. However, in this case, even though polishing (mirror-finishing) is performed on the peripheral surface of the lens, the groove to be formed becomes whitish, so that the appearance is poor. Further, variation in use of grooves, that is, the use not for the purpose of fitting of the wires but decoration of the eyeglass has been regarded.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an eyeglass lens processing apparatus that can form a groove having an excellent appearance on a peripheral surface of an eyeglass lens.

In order to achieve the above-mentioned object, the invention provides an eyeglass lens processing apparatus having the following structure.(1) An eyeglass lens processing apparatus for processing an eyeglass lens, the apparatus comprising;

a lens chuck that holds the lens;

a first moving unit that relatively moves the lens-held by the lens chuck with respect to the regular-grooving tool;

a grooving data input unit that inputs grooving data, the grooving data including a width and depth of the groove to be formed in the lens;

a controller that controls the first moving unit to perform regular-grooving on the lens on the basis of the input grooving data;

a second moving unit that relatively moves the lens held by the lens chuck with respect to the fine-grooving tool; and

a selector that selects whether or not fine-grooving is to be performed,

wherein when performance of the fine-grooving is selected, the controller performs the regular-grooving on the lens so that a bottom and side surfaces of the groove have a margin for the fine-grooving, and controls the second moving unit to perform the fine-grooving on the lens on the basis of the input grooving data.(2) The eyeglass lens processing apparatus according to (1), wherein a processing width of the regular-grooving tool is smaller than a processing width of the fine-grooving tool by the fine-grooving margin on each of the side surfaces of the groove.(3) The eyeglass lens processing apparatus according to (2), wherein

when non-performance of the fine-grooving is selected, a minimum value of the groove width allowed to be input is limited to the processing width of the regular-grooving tool, and

when the performance of the fine-grooving is selected, the minimum value of the groove width allowed to be input is limited to the processing width of the fine-grooving tool.(4) The eyeglass lens processing apparatus according to (1), wherein

a granularity of the regular-grooving tool is in a range of #300 to #800, and

a granularity of the fine-grooving tool is in a range of #1000 to #3000.(5) The eyeglass lens processing apparatus according to (1), wherein the regular-grooving tool and the fine-grooving tool have a same outer diameter and are fixed to a same spindle.(6) The eyeglass lens processing apparatus according to (1), further comprising:

a roughing tool;

a third moving unit that relatively moves the lens held by the lens chuck with respect to the roughing tool;

a fourth moving unit that relatively moves the lens held by the lens chucks with respect to the flat-finishing tool; and

a target lens shape data input unit that inputs target lens shape data,

wherein the control unit controls the third and fourth moving units to perform roughing and flat-finishing on the lens on the basis of the input target lens shape data.(7) The eyeglass lens processing apparatus according to (6) further comprising an operation unit that obtains the grooving data based on the input target lens shape data, wherein the grooving data input unit inputs the obtained grooving data.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments according to the invention will be described with reference to accompanying drawings.FIG. 1is a view showing a schematic appearance of an eyeglass lens processing apparatus according to an embodiment of the invention. An eyeglass lens processing apparatus1includes an eyeglass frame measuring device2. A measuring device disclosed in U.S. Pat. No. 6,325,700B1 (JP-A-2000-314617), etc. can be used as eh measuring device2) A touch screen display (A display unit)10, and a switch panel (an operation unit)20including a processing start switch and the like are provided on the upper surface of the processing apparatus1. Reference numeral3indicates a cover for opening and closing a processing chamber. Further, the measuring device2, display10, switch panel20, and the like may be separately formed from the processing apparatus1.

FIG. 2is a view showing a schematic structure of a lens processing unit provided in the processing apparatus1. A lens LE to be processed is rotated while being held (chucked) by lens chucks111L and111R included in a carriage110, and is ground (processed, edged) by a grindstone151used as a processing (grinding, edging) tool that is attached to a grindstone spindle150and rotated. The grindstone151according to the present embodiment includes three grindstones of a roughing grindstone151afor plastic, a regular-finishing grindstone151b, and a polishing grindstone151c. Each of the grindstones151band151chas a V-shaped-groove for beveling and a plane-processing surface. The grindstone spindle150is rotated by a grindstone rotating motor153via torque transmission members such as a belt.

A block114capable of rotating about a rotation axis of the lens chuck111L is attached to a left arm110L of the carriage110. A lens rotating motor115is fixed to the block114, and the torque of the motor115is transmitted to the lens chuck111L provided to the left arm110L via torque transmission members such as a gear, so that the lens chuck111L is rotated. Further, the torque of the lens chuck111L is transmitted to the lens chuck111R provided to a right arm110R of the carriage110via torque transmission members such as a belt disposed in the carriage110, so that the lens chuck111R is rotated in synchronization with the lens chuck111L.

When the processing is performed, a cup used as a fixing jig is attached to the front surface (front refracting surface) of the lens LE by an adhesive tape, so that a base of the cup is mounted on a lens receiver provided at the end of the lens chuck111L. A lens holding (chucking) motor112for moving the lens chuck111R in an axial direction of the lens chuck111R is fixed to the right arm110R, and the torque of the motor112is transmitted to the lens chuck111R via torque transmission members such as a belt and axial movement members disposed in the carriage110, so that the lens chuck111R is moved in a direction in which it approaches the lens chuck111L. A lens retainer is fixed to the end of the lens chuck111R and the lens retainer comes in contact with the rear surface (rear refracting surface) of the lens LE, so that the lens LE is held (chucked) by the lens chucks111L and111R.

The carriage110is rotatably and slidably mounted on a carriage shaft130parallel to the lens chucks111L and111R, and is moved together with a moving arm131toward the left or right side (hereinafter, referred to as an “X-direction”) that is an axial direction of the carriage shaft130by a motor132for moving the carriage toward the left or right side. Further, a block140capable of being rotated about a rotation axis of the grindstone spindle150is attached to the moving arm131. A motor141for moving the carriage vertically and two guide shafts145are fixed to the block140, and a lead screw142is rotatably attached to the block140. The torque of the motor141is transmitted to the lead screw142via torque transmission members such as a belt, so that the lead screw142is rotated. A guide block143coming in contact with the lower surface of the block114is fixed to the upper end of the lead screw142. The guide block143is moved along the guide shafts145. The carriage110is rotated about the carriage shaft130in the vertical direction (in a direction in which a distance between the rotating axis of the lens chucks111L and111R and the rotation axis of the grindstone spindle150is changed. Hereinafter, referred to as a “Y-direction”) due to the movement of the guide block143. Further, a spring is elastically provided between the carriage110and the moving arm131, and the carriage110is always pushed downward, so that the lens LE is pressed against the grindstone151. A known structure of a carriage may be used as the above-mentioned structure of the carriage, which is disclosed in U.S. Pat. No. 6,478,657B (JP-A-2001-18155) which is hereby incorporated by reference.

A lens measuring unit300is disposed on the rear side of the carriage110.FIG. 3is a view showing a schematic structure of the lens measuring unit300(a unit for measuring the position of the edge of the lens LE). An arm305provided with a measuring element303for measuring the rear surface of the lens LE is fixed to the right end of a shaft301. Further, an arm309provided with a measuring element307for measuring the front surface of the lens LE is fixed to the middle of the shaft301. A line extending between a contact point of the measuring element303and a contact point of the measuring element307is parallel to the rotation axis of the lens chucks111L and111R. The shaft301and a slide base310can be moved in the axial direction of the lens chucks111L and111R. The movement of the shaft301(the slide base310) in the lateral direction (in the X-direction) is detected by a detecting unit320that includes a spring pushing the slide310base to a starting point, an encoder, and the like.

When the front shape of the lens LE (the position of the front edge of the lens LE) is measured, the lens LE is moved toward the left side inFIG. 3, so that the measuring element307comes in contact with the front surface of the lens LE. The measuring element307always comes in contact with the front surface of the lens LE due to the spring of the detecting unit320. In this state, while the lens LE is rotated, the carriage110is moved in the Y-direction on the basis of target lens shape data, so that the front shape of the lens LE is measured. Similar to this, when the rear shape of the lens LE (the position of the rear edge of the lens LE) is measured, the lens LE is moved toward the right side inFIG. 3, so that the measuring element303comes in contact with the rear surface of the lens LE. The measuring element303always comes in contact with the rear surface of the lens LE due to the spring of the detecting unit320. In this state, while the lens LE is rotated, the carriage110is moved in the Y-direction on the basis of the target lens shape data, so that the rear shape of the lens LE is measured.

A grooving and chamfering unit400is disposed on the front side of the carriage110(refer toFIG. 2).FIG. 4is a view showing the schematic structure of the grooving and chamfering unit400. A fixing plate402is fixed to a block401(refer toFIG. 2) provided on a base101. A grindstone moving motor405is fixed to the upper portion of the fixing plate402. The motor405rotates an arm420so as to move a grinding (processing) unit440to a process position or a retraction position. A holding member411by which an arm rotating member410is rotatably held is fixed to the fixing plate402, and a gear413is fixed to the arm rotating member410extending over the fixing plate402. A gear407is fixed to a rotation shaft of the motor405, and the torque of the gear407caused by the motor405is transmitted to the gear413via a gear415, so that the arm420fixed to the arm rotating member410is rotated.

A grindstone rotating motor421is fixed to the gear413, and a rotation shaft of the motor421is connected to a rotation shaft423that is rotatably held in the arm rotating member410. A pulley424is fixed to the front end of the rotation shaft423extending to the arm420. A holding member431by which a grindstone spindle430is rotatably held is fixed to the tip of the arm420. A pulley432is fixed to the rear end of the grindstone spindle430. The pulleys432and424are connected with each other via a belt435, and the torque of the motor421is transmitted to the grindstone spindle430, so that the grindstone spindle430is rotated. A chamfering grindstone441, a regular-grooving grindstone443used as a regular-grooving tool, a fine-grooving grindstone (a mirror-grooving grindstone)445used as a fine-grooving tool are concentrically fixed to the grindstone spindle430. It is preferable that the granularity of the regular-grooving grindstone443be in the range of #300 to #800, and it is preferable that the granularity of the fine-grooving grindstone445be in the range of #1000 to #3000.

Further, the chamfering grindstone441may be composed of a chamfering grindstone for chamfering the front surface of the lens and a chamfering grindstone for chamfering the rear surface of the lens, which are integrally formed. Alternatively, the chamfering grindstone441may be composed of a chamfering grindstone for chamfering the front surface of the lens and a chamfering grindstone for chamfering the rear surface of the lens, which are separately formed. Further, a grooving cutter may be used as the regular-grooving grindstone443.

FIG. 5Ais an enlarged view of the regular-grooving grindstone443, andFIG. 5Bis an enlarged view of the fine-grooving grindstone445. The regular-grooving grindstone443has a processing width WM of 0.5 mm and is formed in a semicircular shape having a radius RM of 0.25 mm in a cross section thereof. Meanwhile, the fine-grooving grindstone445has a processing width WF of 0.6 mm and is formed in a semicircular shape having a radius RF of 0.3 mm in a cross section thereof. That is, a margin Δd for the fine-grooving tolerance on one side surface of the groove to be formed is 0.05 mm, and the processing width WM of the regular-grooving grindstone443is smaller than the processing width WF of the fine-grooving grindstone445by 0.1 mm, which is the fine-grooving margin 2Δd on both (opposite) side surfaces of the groove to be formed. Further, each of the regular-grooving grindstone443and the fine-grooving grindstone445has an outer diameter of 30 mm.

The arm420is rotated by the motor405during the grooving and chamfering, so that the grindstone spindle430is moved from the retraction position to the process position. The process position of the grindstone spindle430is a position where a rotating axis of the grindstone spindle430becomes parallel to the rotating axes of the lens chucks111L and111R and the rotation axis of the grindstone spindle150on a plane defined by the both rotation axes between the lens chucks111L and111R and the grindstone spindle150. In the same manner as the processing performed by the grindstone151, the lens LE is moved in the X-direction by the motor132, and the lens LE is moved in the Y-direction by the motor141.

Further, a grooving tool, which is moved relative to a lens held by lens chucks, may be used as the grooving unit as disclosed in U.S. Pat. No. 6,942,542B (JP-A-2003-145400) which is hereby incorporated by reference. Further, a regular-grooving tool and a fine-grooving tool may be fixed to separate spindles.

Next, the operation of the present apparatus will be described with reference to a schematic block diagram of a control system of the present apparatus shown inFIG. 6. In this case, the case when the grooving is performed on the peripheral surface (the edge surface) of the lens LE will be mainly described. First, target lens shape data is input. Measurement is performed by the measuring device2for measuring an eyeglass frame, a template (a pattern), a demo lens (model lens), and the like, input is provided from the outside through communication devices, and information previously stored in a data memory51is read, so as to perform the input of the target lens shape data. When the target lens shape data is input, a target lens shape graphic based on the target lens shape data is displayed on the display10, so that layout data and processing conditions can be input (refer toFIG. 6). The displaying on the display10is controlled by an operation control unit50.

The layout data such as a pupillary distance PD of a user, a frame pupillary distance FPD, a height of an optical center o a lens with respect to a geometric center of the target lens shape, and the like is input by using buttons (keys)502displayed in an input field501on an input screen500of the display10. Further, processing conditions, such as a material of a lens, a processing , mode (a bevel-finishing mode or a flat-finishing mode), whether the grooving is performed, whether the polishing is performed, and whether the chamfering is performed, are input by buttons (keys) switches503displayed in the input field501.

When the data required for the processing is input, the lens LE is held (chucked) by the lens chucks111L and111R and the processing start switch of the switch panel20is operated to operate the apparatus. The operation control unit50operates the lens measuring unit300before the processing so as to measure the position of the edge of the front and rear surfaces of the lens LE on the basis of the target lens shape data and the layout data. When the flat-finishing mode is selected, the operation control unit50determines (calculates) flat-finishing data on the basis of the measured edge position data. A processing point when the lens LE is rotated is determined (calculated) on the basis of a radius of the grindstone151, and a distance Li between a rotation center (a processing center) of the lens LE and a rotation center of the grindstone151(a distance between the rotation axis of the lens chucks111L and111R and the rotation axis of the grindstone spindle150), which corresponds to each rotation angle of the lens LE, is determined (calculated), so that the flat-finishing data is obtained. Roughing data is obtained as data that is larger than the flat-finishing data by a margin for the flat-finishing.

Further, when the grooving is selected, the operation control unit50determines (calculates) path data of a groove to be formed on the peripheral surface of the lens LE on the basis of the measured edge position data. For example, the path of the groove is determined (calculated) in the path of the middle of the groove so that the groove middle path divides the measured edge thickness at a predetermined ratio (for example, 5:5).

When the groove path data is obtained, the screen of the display10is changed into the simulation screen (refer toFIG. 7) used to input grooving data. A target lens shape graphic510of the lens LE held by the lens chucks111L and111R is displayed above the screen500, and a cross-sectional graphic520of the groove is displayed at the right side on the screen. An input field530used to input the grooving data is displayed on the lower half of the screen. Further, a graphic corresponding to an edge position, which is designated by a line511displayed in the target lens shape graphic510, is displayed as the cross-sectional graphic520of the groove. It is possible to change the positioned designated by the line511by using buttons (keys)540in the input field530.

A button (key)531used to change curve values of the groove, and a button (key)532used to change the position of the groove corresponding to the front surface of the lens LE are provided in the input field530. When the values are changed, a groove position521in the cross-sectional graphic520of the groove is also changed. Further, a groove width W can be input by using a button (key)533, and a groove depth D can be input by using a button (key)534. Numerals input by the buttons531to534can be input by numerical keys. Further, whether the fine-grooving is to be performed can be selected by a button (key)535.

When the non-performance of the fine-grooving is selected (when only regular-grooving is selected), the minimum value of the groove width W allowed to be input by the button533is limited to the processing width WM of the regular-grooving grindstone443. Meanwhile, when the performance of the fine-grooving is selected, the minimum value of the groove width W allowed to be input by the button533is limited to the sum of the processing width WM of the regular-grooving grindstone443and the fine-grooving margin Δd on each of the side surfaces of the groove (2Δd). Further, according to this embodiment, the processing width of the fine-grooving grindstone445is the sum of the processing width of the regular-grooving grindstone443and the fine-grooving margin Δd on each of the side surfaces of the groove (2Δd). For this reason, when the performance of the fine-grooving is selected, the minimum value of the groove width W allowed to be input by the button533is limited to the processing width WF of the fine-grooving grindstone445.

The processing width WM of the regular-grooving grindstone443, the processing width WF of the fine-grooving grindstone445, and the fine-grooving margin Δd are stored in a memory52in advance. The operation control unit50can change the minimum value of the groove width N allowed to be input by the button533, on the basis of the selection of the performance or non-performance of the fine-grooving.

Meanwhile, the maximum value of the groove width W allowed to be input by the button533is limited to the width smaller than the measured minimum edge thickness of the lens LE. If the groove width W that is smaller than the minimum value allowed to be input or larger than the maximum value allowed to be input is input, this is notified to an operator by warning messages, alarm, or the like.

Further, the grooving data such as the groove width W and the groove depth D, and the selection of the performance or non-performance of the fine-grooving may be input from the outside through communication devices.

When the grooving data is input and the processing start switch is again operated, first, the operation control unit50rotates the lens LE and moves the carriage110in the X-direction and Y-direction on the basis of the roughing data, so that the lens LE is processed by the roughing grindstone151a. Next, the operation control unit50rotates the lens LE and moves the carriage110in the X-direction and Y-direction on the basis of the flat-finishing data, so that the lens LE is processed by the plane processing surface of the regular-finishing grindstone151b. When the polishing is selected, the lens LE is further processed by the plane processing surface of the polishing grindstone151c.

When the regular flat-finishing or the flat-polishing is completed, the grooving is performed. The operation control unit50moves the grindstone spindle430of the grooving and chamfering unit400to the process position, and then rotates the lens LE and moves the carriage110in the X-direction and Y-direction on the basis of the grooving data, so that the lens LE is processed by the regular-grooving grindstone443. When the fine-grooving is selected, the lens LE is further processed by the fine-grooving grindstone445.

The grooving data will be described below. The groove path data obtained on the basis of the edge position data is represented by referential symbols Rgn, θn, and Zn (n=1, 2, 3, . . . , N). Rgn indicates a radius formed by the center of the groove, and indicates a radius, which is obtained by subtracting the groove depth D from the radius of the target lens shape representing the shape of the flat-finished lens. θn indicates a radial angle. Zn indicates a position of the center of the groove in the X-direction (the central position of the groove width W). The grooving data in the depth direction of the groove (the Y-direction), which is based on the groove path data Rgn and θn is obtained as Lgi and θi (i=1, 2, 3, . . . , N) by determining a processing point every rotation angle θi of the lens LE on the basis of the radius of the regular-grooving grindstone443and/or fine-grooving grindstone445and determining a distance Lgi between the rotation axis of the lens chucks111L,111R and the rotation axis of the grindstone spindle150at every processing point. The grooving data in the width direction of the groove (the X-direction), which is based on the groove path data Zn and θn is obtained as Zi and θi(i=1, 2, 3, . . . , N) by determining a position Zi of the lens LE in the X-direction at every processing point based on the set groove.

In the case when the non-performance of the fine-grooving is selected (when only regular-grooving is selected), during one rotation of the lens LE, the operation control unit50moves the lens LE in the Y-direction with respect to the regular-grooving grindstone443on the basis of the grooving data Lgi and θi in the Y-direction, which is based on the set groove depth D. In this case, if the groove width W is set equal to the processing width WM of the regular-grooving grindstone443, during one rotation of the lens LE, the operation control unit50moves the lens LE in the X-direction with respect to the regular-grooving grindstone443on the basis of the grooving data Zi and θi in the X-direction.

If the groove width W is larger than the processing width WM of the regular-grooving grindstone443, the processing corresponding to the set grooving width W cannot be performed during one rotation of the lens LE. For this reason, the set groove width W is divided. For example, the lens LE is moved in the X-direction so that the grooving is performed on the front surface of the lens LE at the first rotation thereof, and the lens LE is moved in the X-direction so that the grooving is performed on the rear surface of the lens LE at the second rotation thereof. If the groove width W is set to 0.8 mm, the grooving is performed through the two rotations of the lens LE. For example, the lens LE is moved in the X-direction so that the grooving is performed on the front surface of the lens LE at the first rotation thereof, and the lens LE is moved in the X-direction so that the grooving is performed on the lens LE at the position to be shifted to the rear side of the lens LE by a predetermined width (for example, 0.1 mm). If the groove width W is set to 0.8 mm, the grooving is performed through the four rotations of the lens LE.

When the performance of the fine-grooving is selected, first, the lens LE is processed by the regular-grooving grindstone443. The movement of the lens LE in the Y-direction with respect to the regular-grooving grindstone443is controlled on the basis of the grooving data Lgi and θi in the Y-direction so that the bottom of the groove has the fine-grooving margin Δd. Further, the movement of the lens LE in the X-direction with respect to the regular-grooving grindstone443is controlled on the basis of the grooving data Zi and θi in the X-direction so that each of the side surfaces of the groove has the fine-grooving margin Δd. After the regular-grooving, the lens LE is processed by the fine-grooving grindstone445. The movement of the lens LE in the Y-direction with respect to the fine-grooving grindstone445is controlled so that the fine-grooving margin Δd is removed from the bottom of the groove. Further, the movement of the lens LE in the X-direction with respect to the fine-grooving grindstone445is controlled so that the fine-grooving margin Δd is removed from each of the side surfaces of the groove.

The case when the groove width W is set equal to the processing width WF of the fine-grooving grindstone445will be described. As shown inFIG. 8, the operation control unit50controls the movement of the lens LE in the Y-direction with respect to the regular-grooving grindstone443so that the bottom of the groove has the fine-grooving margin Δd. Further, the operation control unit50controls the movement of the lens LE in the X-direction with respect to the regular-grooving grindstone443so that each of the side surfaces of the groove have the fine-grooving margin Δd. As shown inFIG. 8B, after the regular-grooving, the control unit50controls the movement of the lens LE in the Y-direction with respect to the fine-grooving grindstone445so that the fine-grooving margin Δd is removed from the bottom of the groove. Further, the control unit50controls the movement of the lens LE in the X-direction with respect to the fine-grooving grindstone445so that the fine-grooving margin Δd is removed from each of the opposite side surfaces of the groove.

The case when the groove width W is set to be larger than the processing width WF of the fine-grooving grindstone445will be described. For example, the groove width W is set to 0.6 mm. As shown inFIG. 9, the control unit50controls the movement of the lens LE in the Y-direction with respect to the regular-grooving grindstone443so that the bottom of the groove has the fine-grooving margin Δd. Further, the operation control unit50controls the movement of the lens LE in the X-direction with respect to the regular-grooving grindstone443so that each of the side surfaces of the groove have the fine-grooving margin Δd. In this case, similar to the above-mentioned case when only regular-grooving is selected, a groove width W-Δd, which has -the fine-grooving margin Δd on each of the side surfaces of the groove, is divided.FIG. 9Ashows an example in which the grooving is performed on the lens LE at the position to be shifted to the rear side of the lens LE from the front side thereof by a predetermined width.

As shown inFIG. 9B, after the regular-grooving, the operation control unit50controls the movement of the lens LE in the Y-direction with respect to the fine-grooving grindstone445so that the fine-grooving margin Δd is removed from the bottom of the groove. Further, the control unit50controls the movement of the lens LE in the X-direction with respect to the fine-grooving grindstone445so that the fine-grooving margin Δd is removed from each of the side surfaces of the groove. Even in this case, similar to the above, the groove width W is divided.FIG. 9Bshows an example in which the grooving is performed on the lens LE at the position to be shifted to the rear side of the lens LE from the front side thereof by a predetermined width.