JP2010184340A - Processing method for lens and grinding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens processing method and a grinding device eliminating the need for a centering machine. <P>SOLUTION: A bi-axial grinding machine provided with a grinding stone shaft attached with a grinding stone for rough grinding and a grinding stone shaft attached with a grinding stone for precise grinding is used. A lens material is charged in a first bi-axial grinding machine 10a and rough grinding and precise grinding of a first surface are performed. Subsequently, the lens material is conveyed to a second bi-axial grinding machine 10b, and rough grinding, precise grinding and outer periphery processing of a second surface are performed by the second bi-axial grinding machine 10b. A holder 12a of the first bi-axial grinding machine 10a is made to a holder with a chuck structure, and a holder of the second bi-axial grinding machine is made to a holder with a suction structure. The second bi-axial grinding machine retains the lens material making the roughly ground surface as reference, and since rough grinding, precise grinding and outer periphery processing of the second surface are performed while keeping the retaining, centering of the lens material is made possible by outer periphery processing. Thereafter, polishing of the first surface and the second surface is performed, and washing of the polished lens is finally performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lens processing method and a grinding apparatus, and relates to the above-described method and apparatus applied to lens processing including a rough grinding process, a fine grinding process and a polishing process, and a centering process of a lens spherical surface.

  The lens is processed for rough grinding, fine grinding and polishing (polishing) and centering (centering) of both spherical surfaces (hereinafter referred to as “first surface” and “second surface”) of the lens. And a plurality of machines are used to perform these processing steps. Conventionally, the first and second surfaces are roughly ground with a cup grinder of a rough grinder, the first and second surfaces are finely ground with a pellet pan of a fine grinder, and the first with a polishing pan of a grinder. The first surface and the second surface are polished, the outer periphery is processed by a centering machine, and then the cleaning is performed to wash away the oil-based grinding liquid used in the outer periphery processing.

  Rough grinding is generally performed by a grinding method called CG processing (spherical surface generation processing). That is, the lens material is mounted on the lens holder provided at the upper end of the vertical workpiece axis, and the downward cup-shaped grindstone that is in circular contact with the surface of the lens material (exactly in contact with the circle protruding from the lens periphery) is mounted at the lower end. The grindstone shaft is tilted according to the curvature of the lens surface to be ground, and the grindstone shaft is positioned at a position where the contact circle between the cup grindstone and the lens surface passes through the center of the lens axis. Then, the workpiece shaft and the grinding wheel shaft are rotated, the workpiece is fed upward by a servo motor, and the spherical surface of the lens is created by the combined motion of the revolution and rotation of the cup grinding stone with respect to the lens surface. . As a cup grindstone for rough grinding, a grindstone having a particle size of about 100 to 350 is used.

  Precision grinding, on the other hand, is a process of transferring the spherical surface of the pellet dish to the lens. A pellet dish corresponding to the curvature of the lens spherical surface to be processed is attached to the lower end of the grindstone shaft that is pivotally supported on the rocking table, and the upper end of the workpiece axis is mounted. Mount the lens material that has been ground to the lens holder. Then, in a state where the rocking center of the rocking table and the center of curvature of the lens spherical surface coincide with each other, the lens surface is pressed against the pellet pan with a constant pressure with an air cylinder or the like, and the rotation of the work shaft 1 and the grindstone shaft 25a, The surface of the lens is ground by the combined motion of the rotation of 25b and the reciprocating swing.

  Conventionally, rough grinding and fine grinding of lens materials have been performed by separate machines, but the applicant of the present application provides a grinding wheel shaft for rough grinding and a grinding stone shaft for fine grinding on the same machine stand, A lens spherical grinding method and apparatus (hereinafter referred to as “biaxial grinding machine”) capable of continuously performing rough grinding and fine grinding without changing the workpiece is proposed (Patent Document 1). . Lens processing using the proposed apparatus is performed by continuing rough grinding and fine grinding of the first surface with a cup grindstone and pellet pan of a biaxial grinding machine, then reversing the lens material on the machine base, Perform rough grinding and fine grinding of the surface, then transfer the lens material to the polishing machine, polish the first and second surfaces with the polishing dish, then transfer the lens material to the centering machine and process the outer circumference Then, the processed lens is processed by being transported to a cleaning machine and cleaned.

  According to lens processing using a biaxial grinding machine, the number of types of processing machines can be reduced by one (two in the conventional processing in which fine grinding of each surface is performed in two steps), and the conveyance of lenses between machines is also possible. One conveyance (or two conveyances) can be reduced, and the occurrence of positioning errors associated with the loading of the lens material into the conveyance destination machine is reduced. Therefore, the accuracy and productivity of lens processing can be improved.

  As for a holder for holding a lens material during grinding, a chuck structure for holding the outer periphery of the lens material with a nail and a suction structure for holding the lower surface of the lens material by vacuum suction are known. In the latter structure, it is necessary to prevent the adsorbed lens material from slipping on the holder, but if the adsorbing surface of the lens material is just a rough ground surface, there will be a shape error between the holder and the support part. Due to the vacuum leakage, sufficient holding force cannot be obtained and high speed grinding cannot be performed. On the other hand, the centering machine employs a structure in which a lens material whose both surfaces are polished is sandwiched between upper and lower annular edges and held in a centered state.

JP 2006-297520 A

  The present invention provides a lens processing method and a grinding apparatus that do not require a centering machine, thereby simplifying the processing steps from rough grinding to cleaning of a polished lens in lens processing, and reducing the types of machines to be used. Therefore, it is an object to improve productivity in lens processing and reduce equipment costs.

  In lens processing including the processing method of the present invention, after rough grinding and fine grinding of the first surface, the machine is changed to perform rough grinding, fine grinding and peripheral processing of the second surface, and then the first surface and The second surface is polished, and finally the polished lens is cleaned.

  In the lens processing including the processing method of the present invention, the lens processing from rough grinding to cleaning of the polished lens is performed by the two biaxial grinding machines 10a and 10b, the polishing machine 20, and the cleaning machine 30. A centering machine is not used. First, the lens material is loaded into the first biaxial grinding machine 10a to perform rough grinding and fine grinding of the first surface, and then the lens material is transported to the second biaxial grinding machine 10b. The shaft grinding machine 10b performs rough grinding, fine grinding, and outer periphery processing on the second surface. The holder 12a of the first biaxial grinding machine 10a is a chuck structure holder, and the second biaxial grinding machine holder is an adsorption structure holder. The chuck-structure holder 12a has a sufficient material holding force that can withstand rough grinding of the first surface. In the second biaxial grinding machine, since the first surface of the lens material adsorbed to the holder 12b is precisely ground, airtightness between the support portions 32a, 34b, and 34c of the holder 12b is ensured, and the first A material holding force necessary for rough grinding of two surfaces can be obtained.

  In the processing method of the present invention performed by the second biaxial grinding machine, the second surface is ground and the outer periphery of the lens is processed. The first surface of the lens material is finely ground, and the second biaxial grinding machine holds the lens material on the basis of this finely ground surface, and the rough grinding of the second surface is performed while maintaining the lens material. In addition, since the fine grinding and the outer periphery processing are performed, the lens material can be centered by the outer periphery processing. Naturally, the rough grinding and the fine grinding of the second surface are performed in this order, but the outer peripheral machining may be performed at any stage. Generally, after the second surface is precisely ground, the outer periphery is processed. The outer periphery processing may be performed on the outer cylindrical surface of the rough grinding cup grindstone 3a, but the grindstone shaft may be three and the third grindstone shaft may be equipped with a grindstone dedicated to outer periphery processing.

  The lens material that has been processed by the second biaxial grinding machine is conveyed to the polishing machine 20 to polish the first surface and the second surface, and finally the processed lens is cleaned by the cleaning machine 30. Since the final process is polishing using an aqueous processing liquid, the cleaning process can be simplified.

  The second biaxial grinding machine in the above processing method is a rotating work shaft 1 and a lens which is attached to the tip of the rotating work shaft 1 and holds the spherical surface by suction with the center of curvature of the lens spherical surface on the rotation center axis. A holder 12b, a plurality of parallel rotating grindstone shafts 25a, 25b, which are mounted on the opposite ends of the holder 12b and mounted with tool holders 29a, 29b, and the rotating grindstone shafts 25a, 25b or the rotating workpiece shaft 1 are rotated with a grindstone. An X moving table 22 that moves in a direction crossing the shafts 25a and 25b, and an axis perpendicular to the moving center axis passing through the swing center P set on the rotating center axis and the moving direction of the X moving table 22 A swing table 23 that swings the rotating grindstone shafts 25a and 25b or the rotary workpiece shaft 1, a Z moving table 13 that moves the tip and the swing center P close to each other, and the Z moving table and the X moving table 22 And a controller 5 for controlling the moving position and the swinging position of the swinging base 23. A grindstone 3a for rough grinding is mounted on one of the tool holders 29a and 29b, and a grindstone 3b for fine grinding is mounted on the other. By mounting, it is possible to perform rough grinding and fine grinding of the lens material spherical surface and outer periphery grinding for centering the lens without re-holding the lens material on the same machine base.

  The suction portions 32a, 32b, and 32c of the lens holder 12b attached to the tip of the work shaft 1 are communicated with a through hole provided in the shaft center of the work shaft 1 and pass through the through hole to the lower end of the work shaft 1. It communicates with the mounted rotary joint, and communicates with a vacuum source connected to the rotary joint, and a vacuum pressure for adsorbing the lens material to the lens holder 12b is supplied from the vacuum source.

  In the above-described biaxial grinding machine, when a cup grindstone that contacts the lens spherical surface with a circle is used as the grindstone 3b for fine grinding, the wear of the cup grindstone for fine grinding is large. Therefore, it is desirable to provide correction means for correcting wear of the grindstone. In this correction, the constant Δt given as the wear amount of the grindstone and the angle formed by the rotating work shaft and the rotating grindstone shaft are θ, and the X moving table 22 and the Z moving table 13 are respectively set to Δx = Δt × tan θ, Δz. This can be realized by registering in the controller 5 correction moving means for correcting and moving by (Δx) and (Δz) calculated by = Δt × 1 / cos θ.

  In this invention, when the first surface 4a of the lens material is ground, the lens material is held with a force that can withstand the reaction force during rough grinding by gripping the outer periphery of the lens material, and the second surface 4b is ground. Makes it possible to hold the lens material with a force that can withstand the processing reaction force during rough grinding of the second surface by holding the finely ground first surface 4a by suction, and the peripheral processing of the lens material is the same machine It becomes possible on a table, and grinding and centering of the second surface of the lens material can be performed by a single machine.

  The first surface 4a is processed up to fine grinding, and the spherical shape is almost finished. Since the surface is adsorbed, spherical processing of the second surface can be performed at a position that matches the sphere center of the first surface 4a. Therefore, if the outer periphery is processed without removing the suction, the centering process is performed. In other words, the finely ground surface of the lens material is held by the suction edge holder 12b provided with the annular edge 34c or the support surfaces 32a and 34b processed into the same shape as the surface, and processing until the fine grinding of the opposite surface is performed. Since there is no error in the surface shape of the lens side and the holder side, and the surface roughness is small, leakage of the suction holder can be prevented, strong suction retention force can be obtained, and high-precision centering is possible at the grinding stage become.

  Therefore, according to the present invention, it is possible to perform lens processing without using a centering machine and capable of simplifying the structure or operation of the processed lens cleaning machine. In addition, the number of times the lens material is transported and repositioned between machines is reduced, and the processing efficiency can be improved by shortening the process. Further, in the second two-axis grinding machine, the outer surface machining, which is rough grinding, fine grinding and centering of the second surface, is performed on the same machine with the first ground surface of the lens material as a reference. Since it can be performed as a series of processing without changing the material, it is possible to realize lens processing with high accuracy, and to reduce the occurrence of defective products due to misalignment that occurs when the lens material is mechanically changed or held.

Schematic diagram showing the processing method of the lens of the present invention Side view showing an example of the grinding apparatus of the present invention Cross-sectional side view showing an example of a lens holder that holds the outer periphery of a lens material Cross-sectional side view showing an example of a lens holder that holds a finely ground surface of a lens material Sectional side view showing another example of a lens holder for holding a finely ground surface of a lens material Sectional side view showing still another example of a lens holder for holding a finely ground surface of a lens material The figure which shows the example of the table which shows the relationship between the number of grinding and the amount of grinding wheel wear Explanatory drawing explaining the principle of grinding wheel wear correction Schematic side view showing an example of a lens spherical surface measurement method

  FIG. 1 is a diagram schematically showing an example of a lens processing step according to the method of the present invention. FIG. 1 shows a configuration in which fine grinding of the first surface and the second surface is performed with a fine grinding cup grindstone, and outer periphery processing is performed with a rough grinding cup grindstone. In the figure, 10a is a first biaxial grinding machine, 10b is a second biaxial grinding machine, 20 is a polishing machine, 30 is a washing machine, 4 is a lens material, 4a is the first surface, and 4b is the first surface. 2 surface, 4c is the outer periphery of the lens material, 3a is a rough grinding cup grindstone, 3b is a fine grinding cup grindstone, 12a is a material holder of the chuck structure of the first biaxial grinding machine 10a (hereinafter referred to as "chuck"). , 12b is a material holder (hereinafter referred to as “suction holder”) having a suction structure of the second biaxial grinding machine 10b.

  The lens material 4 is first loaded on the chuck 12a of the first biaxial grinding machine 10a with the first surface 4a facing upward, and the first surface 4a is roughly ground (FIG. 1 (a)) and finely ground (FIG. 1). (b)) is performed. Next, a lens material whose first surface has been finely ground is loaded into the suction holder 12b of the second biaxial grinding machine 10b with the second surface up, and the second surface 4b is roughly ground (see FIG. c)) and fine grinding ((d) in the figure), and further, grinding of the lens outer peripheral surface by the outer cylindrical surface of the rough grinding wheel 3a while maintaining the holding of the lens material by the suction holder 12b ( The grinding process of the outer peripheral end face by the tip of the rough grinding wheel 3a (FIG. 5 (e)) is performed. The above-described grinding process (FIG. (E)) of the outer peripheral side surface of the lens results in the centering process of the lens.

  The lens material processed by the second biaxial grinding machine 10b is conveyed to the polishing machine 20, where the first surface and the second surface are polished by a conventionally known method, and the lens processing is completed. The processed lens is conveyed from the polishing machine 20 to the cleaning machine 30, and the processing liquid of the polishing machine 20 is washed away. Although the cleaning machine 30 is an independent machine in FIG. 1, the cleaning machine 30 can be attached to the polishing machine 20. In this case, conveyance from the polishing machine 20 to the cleaning machine 30 is not necessary.

  Among the machines shown in FIG. 1, conventionally known machines can be used as the polishing machine 20 and the washing machine 30. A biaxial grinding machine that performs fine grinding with a pellet pan is described in Patent Document 1. Since FIG. 1 illustrates a biaxial grinding machine that performs fine grinding with a cup grindstone, a side view of an example of a biaxial grinding machine that performs both rough grinding and fine grinding with a cup grindstone will be described below. Will be described with reference to FIG.

  In FIG. 2, 1 is a work shaft, 11 is an electric motor for driving the work shaft 1, 12a and 12b are lens holders provided at the tip (upper end) of the work shaft 1, and 13 is a lift that supports the work shaft 1. It is a table (Z-direction moving table). Reference numeral 23 denotes a swing base that swings around the swing center P, 21 denotes a guide provided on the swing base 23, and 22 denotes an X moving base (X direction moving base) that moves along the guide 21. Two grindstone shafts 25a and 25b are supported on the X moving table 22 in parallel with each other. The guide 21 is provided in a direction orthogonal to the two grindstone shafts 25a and 25b.

  As shown in FIG. 3, the lens holder 12 a of the first biaxial grinding machine 10 a is a chuck structure holder that includes a claw 31 that holds the outer periphery 4 c of the lens material 4. As shown in FIGS. 4 to 6, the lens holder 12 b of the second biaxial grinding machine 10 b is a holder having a suction structure including suction portions 32 a, 32 b, and 32 c that suction the finely ground first surface 4 a. . Here, the suction holder of FIG. 4 has the suction portion 32a having the same shape as the finely grounded first surface 4a, and a sheet-like pad 33 made of a material having a high friction coefficient is provided on the suction portion 32a. Sometimes pasted. On the other hand, the suction holder 12b in FIG. 5 has a structure in which the peripheral portion 34b of the suction portion 32b is processed into the same shape as the peripheral portion of the first surface 4a that has been precisely ground, and the central portion is formed as a shallow concave portion that serves as a vacuum reservoir. is there. Further, the suction holder 12b of FIG. 6 has a structure including an annular edge 34c that supports the peripheral portion of the first surface 4a, and the inside of the annular edge is the suction portion 32c. The hole 35 at the center of the suction portion is communicated with a through hole provided in the axis of the work shaft 1 and is communicated with a vacuum source via a rotary joint (not shown) attached to the lower end of the work shaft. 4 and 5, the support surfaces 32a and 34b of the suction holder 12b are mounted with an end mill on the grindstone shaft 25b of the second biaxial grinding machine to which the suction holder 12b is mounted, and a program for supporting surface processing is registered in the controller 5. NC processing is preferable, and by such a method, it is possible to obtain the suction holder 12b having the support surfaces 32a and 34b that are in close contact with the finely grounded first surface 4a without any gaps, and can perform heavy grinding or high-speed grinding. High holding power can be obtained.

  Tool holders 29a and 29b are provided at the lower ends (shaft ends facing the work holder) of the grindstone shafts 25a and 25b, and a rough grinding cup grindstone 3a for rough grinding is mounted on one of the 29a, and the other 29b includes A cup grindstone 3b for fine grinding is mounted. The grindstone shafts 25a and 25b are connected to electric motors 26a and 26b for driving the grindstone shaft.

  The cup grindstones 3a and 3b are grindstones in which the surface of the lens material to be processed and the grindstone are in contact with each other with an arc centering on the rotation center axis of the grindstone. The coarse grinding cup grindstone 3a is a cup grindstone having a grindstone particle size of 100 to 350, and the fine grinding cup grindstone 3b is a grindstone particle size of 1500 to 2500 cup grindstone. The machining allowance of the lens surface (thickness in the direction of the optical axis of the lens surface scraped off by processing) performed in polishing in the next process of fine grinding is 10 to 50 microns. If the surface roughness of precision grinding or the curvature error of the lens protrudes from the range of machining allowance during polishing, the processed lens becomes a defective product. Therefore, it is necessary to process the surface roughness on the sub-micron level in precision grinding, and for that purpose, it is necessary to use a grindstone with a number of about 1500 to 2500.

  On the other hand, such a high-numbered (fine-grained) grindstone is very easily worn compared to a low-numbered coarse grinding grindstone (about 100 to 350). Although it depends on the material of the grindstone and the lens, the amount of wear is on the order of 0.5 microns when processing one lens. In CG processing using a cup grindstone, when the grindstone is worn, the radius of curvature of the lens surface to be processed increases. Therefore, it is necessary to frequently correct the relative positional relationship between the grindstone and the lens material so that the radius of curvature of the lens processed by the abrasion of the grindstone is within an allowable accuracy.

In the apparatus of the embodiment, in order to perform this correction, a table 54 (FIG. 7) showing the wear amount Δt of the cup grindstone 3 in the grindstone axis direction for each predetermined number of machining and the Δt are used for the controller 5. Calculation formula of correction amount of X moving table 22 and lifting table 13 Δx = Δt × tan θ
Δz = Δt × 1 / cosθ
And are registered.

  The table 54 showing the amount of wear Δt in FIG. 7 is processed in accordance with the number of processed lenses 5, 10, 15... After mounting a new precision grinding cup 3b. This is obtained by measuring the wear amount Δt of the grindstone generated in the grinding wheel axis direction as 3 (unit micron), 2.7, 2.5.

  Returning to FIG. 2, the work shaft 1 is pivotally supported by a lifting platform 13 guided so as to be movable up and down on the frame 2, and a bracket 14 integrated with the lifting platform is driven by a Z-axis servomotor 17. The feed screw 18 is screwed. The oscillating table 23 is oscillated by a B-axis servo motor 37. The X moving table 22 is screwed to a feed screw 28 that is rotationally driven by an X-axis servo motor 27 mounted on the swing table 23. Reference numeral 5 denotes an NC device that controls these servomotors, 51, 52, and 53 are servo amplifiers, and 19 is a current controller of the Z-axis servomotor 17.

  Next, a procedure for grinding a lens with the apparatus of FIG. 2 will be described. First, a position where the grindstone shaft 25a mounted with the rough grinding cup grindstone 3a passes the rocking center P of the rocking table 23 is set as the moving origin of the X moving table 22, and an angle θ corresponding to the curvature of the lens spherical surface to be ground is set. The position of the X moving table 22 is set at a position where the contact circle between the rough grinding cup grindstone 3a and the lens spherical surface passes through the optical axis of the lens. Set the grinding completion position to the Z-axis origin. Then, the lens material 4 is loaded into the lens holder 12, and the lens holder 12 is rotated by the revolution of the rough grinding cup grindstone 3a by the rotation of the work shaft 1 and the rotation of the rough grinding cup grindstone 3a by the rotation of the grindstone shaft 25a. The spherical surface of the lens material 4 is created while being held.

  Next, the position where the grindstone shaft 25b passes through the swing center P of the swing table 23 is set as the movement origin of the X shift table 22, and the swing table 23 is tilted to an angle θ corresponding to the curvature of the lens spherical surface to be ground. The position of the X moving table 22 is set at a position (Q1 in FIG. 8) where the contact circle between the cup grindstone 3b and the lens spherical surface passes through the optical axis of the lens, and the grinding completion position of the work shaft 1 according to the machining allowance is set to Z. Set to the axis origin. The coarse grinding-finished lens material 4 held by the lens holder 12 is finely ground by the revolution of the cup grindstone 3b by the rotation of the work shaft 1 and the rotation of the cup grindstone 3b by the rotation of the grindstone shaft 25b.

  When the cup grindstone 3b is worn by the wear amount Δt by grinding the lens, the contact circle between the cup grindstone 3b and the lens spherical surface is displaced from the position passing through the optical axis of the lens (Q2 in FIG. 8). When the cup grindstone 3b is replaced with a new grindstone, the counter that counts the correction timing is reset, and the registered table is referenced each time the number of processed lenses reaches 5, 10, 15,. Then, Δt is read, and the X moving table 22 and the lifting table 13 are moved by Δx and Δz calculated based on the above-described formula.

  By this correction operation, as shown in FIG. 1, the deviation Δx in the X direction and the deviation Δz in the Z direction of the contact circle between the lens material 4 and the cup grinding stone 3b caused by the wear of the cup grinding stone Δt are corrected. The contact circle between the cup grindstone 3b after wear and the lens spherical surface returns to the position passing through the optical axis of the lens (Q3 in FIG. 8), and both the error of the curvature of the lens surface and the error of the lens thickness due to wear are both present. It is corrected.

  Here, the advantages of the method of performing precision grinding with a cup grindstone will be described. In conventional lens processing, fine grinding is performed with a pellet dish. However, since the pellet dish has a structure in which a large number of small grindstone plates are attached to a substrate that has a curved surface (or a concave curved surface when processing a convex lens) that matches the curvature of the lens spherical surface to be processed, Each time the curvature changes, it must be replaced with a pellet dish that matches the curvature, and a dedicated pellet dish must be prepared for each type of lens to be processed.

  On the other hand, in CG processing (spherical surface creation processing) using a cup grindstone, the angle θ of the rotation center axis of the cup grindstone with respect to the optical axis of the lens can be changed to correspond to the curvature of the lens surface to be processed. One type of cup grindstone can be used to process many types of lens surfaces with different curvatures.

  As described above, in the lens processing method of the present invention, a method in which fine grinding is performed with a cup grindstone is preferable. However, the method of the present invention can also be employed in lens processing in which fine grinding is performed with a pellet dish. In this case, as the first and second biaxial grinding machines 10a and 10b, for example, a spherical grinding apparatus proposed in Patent Document 1 may be used. In the above example, the outer periphery of the lens material used for centering is performed with a rough grinding cup grindstone. However, a three-shaft grinder with three grindstone shafts is used to roughly grind the three grindstone shafts. A method in which a cup grindstone for grinding, a cup grindstone for fine grinding, and a grindstone for peripheral processing are respectively mounted and the peripheral processing is performed with a dedicated grindstone is also a good method.

  Next, details of correction of grinding wheel wear during precise grinding of the lens material with the cup grinding wheel described in the above embodiment will be described. In conventional rough grinding, error correction based on wear of a cup grinding wheel for rough grinding is performed as follows. That is, the lens processed periodically or every predetermined number of lenses is extracted, and, as shown in FIG. 9, as shown in FIG. The thickness h (the height in the optical axis direction. The height of the front and back surfaces is shown in the figure) is measured with a micrometer across the lens material 4, and the measured value and the master (reference lens) The deviation from this value is input to the controller of the grinding machine. The controller calculates the correction amount by a predetermined arithmetic expression registered in advance, and corrects the angle θ of the grindstone axis with respect to the workpiece axis so as to cancel the error of the curvature radius R due to the wear of the grindstone.

  However, when this correction method is applied to the wear of a cup grinding wheel for fine grinding, the following problems occur. First, since the wear of the grinding wheel for fine grinding is much larger than the wear of the grinding wheel for rough grinding, a lens sampling inspection must be performed frequently in order to compensate for this, and the operator's work load Becomes very large.

  Secondly, when the wear amount of the grindstone is large, the lens center thickness error must also be corrected. However, the above-mentioned conventional correction is only for the curvature radius of the workpiece, and is different with respect to the workpiece center thickness. Need to be corrected.

  Third, in the correction of the angle θ of the grindstone axis with respect to the workpiece axis, the wear shape of the grindstone does not match the curved surface shape of the lens surface at the end of processing. The contact point between the lens surface and the grindstone shifts (the contact line between the grindstone and the lens surface deviates from an arc centered on the rotation center of the grindstone), and the processed lens surface does not become a spherical surface. These problems are caused by the wear amount of the cup grindstone for fine grinding being much larger than that for the rough grinding.

The above problem can be solved as follows. That is, according to the type of the grinding wheel and the lens to be processed, the relationship between the processing amount (the number of processing or the processing time) and the grinding wheel wear amount is measured in advance by test processing, and a relational expression between them or a table indicating the relationship between the two is obtained. Register in advance in the controller 5. Then, for each predetermined number of lenses or a predetermined time of lens processing, a grindstone wear amount (abrasion dimension in the grindstone axis direction) Δt predicted with reference to the calculation formula or table is predicted. Then, the X moving table 22 is set to Δx = Δt × tanθ with respect to the predicted wear amount Δt.
The movement amount Δz of the lifting platform is expressed as follows: Δz = Δt × 1 / cosθ
The correction movement is performed by Δx and Δz calculated in step (1). As shown in FIG. 1, the correction direction is a direction in which the contact circle between the worn grindstone and the lens spherical surface passes through the center W of the lens ground by the worn grindstone.

  By adopting the above-mentioned means, it becomes possible to correct automatically due to the wear of the cup grinding stone for fine grinding with high wear without frequently bothering the operator, and the shape of the spherical surface processed by the correction operation It was also possible to avoid the phenomenon that became unstable. Furthermore, according to the above correction, it is possible to simultaneously correct both an error in the curvature of the lens surface due to wear of the grinding wheel and an error in the lens thickness at the center portion, and a cup with high wear for precision grinding that requires high machining accuracy. It becomes possible to carry out using a grindstone.

  That is, in the fine grinding of the lens material in the above embodiment, the roughly ground lens material 4 held at the tip of the workpiece shaft 1 whose lift position is NC controlled is moved around the oscillation center P passing through the axis of the workpiece shaft. Of the grinding wheel shafts 25a and 25b, which are pivotally supported by the rocking table 23 controlled by the NC, and the X-moving table 22 which controls the movement position of the grinding wheel shafts 25a and 25b in the direction perpendicular to the axis. In the above precision grinding, the grinding wheel that makes a circular contact with the surface of the lens to be processed is used as the rotary grinding wheel, and the count is 1500-2500. Using the cup grindstone 3b, the grindstone axis is inclined at an angle corresponding to the curvature of the lens spherical surface to be ground, and the position of the X moving table 22 is set at a position where the contact circle between the grindstone 3b and the lens spherical surface passes through the center of the lens. State In the the rotation of the rotary grindstone shaft 25b of the work shaft 1 performs precise grinding of the rough grinding completion lens material 4.

  In the above-described precision grinding method of the lens, an arithmetic expression representing the relationship between the processing amount of the lens and the abrasion amount of the grindstone or a table indicating the relationship is registered in the NC control device, With reference to the calculation formula or table for each processing amount, the wear amount Δt of the grindstone at the time is obtained, and the X moving table 22 and the height of the work shaft are respectively set to Δx = Δt × with respect to the obtained wear amount Δt. It is preferable to perform the next lens processing after correcting and moving by Δx and Δz calculated by tan θ and Δz = Δt × 1 / cos θ.

1 Work axis
3a Cup grinding wheel for rough grinding
3b Cup grinding wheel for precision grinding 4 Lens material
12a Lens holder with chuck structure
12b Lens holder with suction structure
13 Lifting platform (Z-direction moving platform)
22 X moving table (X direction moving table)
23 Swing base
25a Wheel axis for rough grinding
25b Wheel axis for precision grinding

Claims (6)

  The first surface of the lens material that has been subjected to rough grinding and fine grinding of the first surface is sucked and held by a suction holder that holds the center of curvature of the first surface on the central axis, and the lens material is roughened by a rough grinding wheel. A method of processing a lens, characterized in that rough grinding of the second surface, precise grinding of the second surface, and outer periphery processing of the lens material are performed while maintaining the suction and holding.   Spherical grinding comprising a first rotating grindstone shaft equipped with a rough grinding cup grindstone, a second rotating grindstone shaft equipped with the grindstone for fine grinding, and a rotating work shaft equipped with the suction holder The lens processing method according to claim 1, wherein the suction holder holds the center of curvature of the first surface after precise grinding on the rotation center axis of the rotary work shaft.   The precision grinding of the second surface is a cup grindstone that is in circular contact with the surface of the lens material to be processed, and the grindstone having a particle size of 1500 to 2500 is performed according to claim 1 or 2. Lens processing method.   The lens processing method according to claim 1, wherein the outer periphery of the lens material is processed by the rough grinding wheel. A rotating workpiece axis 1;
A lens holder 12b that is attached to the tip of the rotating workpiece shaft and holds the spherical surface by suction with the center of curvature of the lens spherical surface on the rotational center axis;
A plurality of parallel grindstone shafts 25a, 25b that are opposed to the tip and are mounted with tool holders 29a, 29b at opposite ends,
An X moving table 22 for moving the rotating grindstone axis or the rotating workpiece axis in a direction crossing the rotating grindstone axis;
An oscillating table 23 for oscillating the rotating grindstone axis or rotating workpiece axis about an axis orthogonal to the rotational center axis passing through the oscillation center P set on the rotation center axis and the moving direction of the X moving table; ,
A Z-moving base 13 that closely separates the tip and the swing center P;
A controller 5 for controlling the moving position of the Z moving table and the X moving table and the swing position of the swing table;
By mounting a grinding wheel 3a for rough grinding on one side of the tool holder and mounting a grinding wheel 3b for fine grinding on the other side, outer peripheral grinding for rough grinding and fine grinding of the lens material spherical surface and centering of the lens is performed. Lens grinding device that makes it possible.   The controller sets the constant Δt given as the amount of wear of the grindstone and the angle formed by the rotating work shaft and the rotating grindstone shaft as θ, and sets the X moving table 22 and the Z moving table 13 to Δx = Δt × tan θ, 6. The lens grinding apparatus according to claim 5, further comprising correction moving means for correcting and moving by Δx and Δz calculated by Δz = Δt × 1 / cos θ.

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