JP4170204B2 - Polishing method - Google Patents

Description

The present invention relates to a mold polishing how for molding an optical element such as a lens.

  FIG. 17 is an explanatory view showing an embodiment of a conventional polishing method. Metal molds, particularly molds for molding optical elements, are required to have high precision and are manufactured by processing steps such as cutting and polishing, grinding and polishing, or only cutting and only grinding. Among them, the processing method by polishing has a small unit removal amount and is a pressure transfer processing based on the pre-processed surface, so that highly accurate processing can be realized. Therefore, the polishing method is adopted as the final finish of the optical element molding die 50.

  FIG. 18 shows a conventional method for processing a mold having a free-form surface and an embodiment of a mold having a free-form surface (see, for example, Japanese Patent Application Laid-Open No. 2001-79742). What improves the polishing accuracy of the free-form surface 63 is described. A method of processing a mold for molding a molded article having a free curved surface 63 will be described. A guide member 66 is formed by a solidified material 64 on the extended surface of the curved surface of the mold having a curved surface that is the basis of the free curved surface 63. Let it form. Using the guide member 66 as a guide, the processing tool 68 is moved to process the base curved surface so as to create a predetermined free curved surface 63.

  19 (a) and 19 (b) show an embodiment of a conventional polishing method (see, for example, Patent Document 2 and JP-A-2002-66888). A polishing method is described that can prevent the shape accuracy from deteriorating at the outer peripheral portion 71a of the optically effective range of an optical element such as the lens 71 (FIG. 19A). The small-diameter polishing tool 72 (FIG. 19B) is scanned in the Y-axis direction 70Y along the polishing locus 70A while swinging in the X-axis direction 70X with respect to the lens 71 (FIG. 19A). At the outer peripheral portion 71a of the lens 71, the oscillating polishing tool 72 cannot completely pass through the optical effective range 70B, and the polishing removal shape becomes high. Therefore, the outer peripheral portion 71a of the lens 71 is polished and removed based on the polishing locus 70A in advance. In order to predict and correct the shape error, the dwell time, polishing load, or swing speed of the polishing tool 72 is weighted.

  20 (a) to 20 (c) show an embodiment of a conventional polishing tool manufacturing method, polishing method, polishing tool and optical element or mold thereof (for example, Patent Document 3, JP 2001-2001). No. 138196). A method of manufacturing a polishing tool capable of finishing a curved optical element or its mold into a mirror surface that can be used as an optical component, a polishing tool, and an optical element or its mold are described.

  The polishing tool portion 82 of the polishing tool 81 (FIG. 20 (a)) for polishing the workpieces 80I (FIG. 20 (b)) and 80II (FIG. 20 (c)) is made of a pulverized powder member of wood. A material obtained by kneading and thermocompressing a thermosetting resin mainly composed of any of urethane resin, epoxy resin, and phenol resin is molded as a raw material. About the material of the polishing tool part 82, the ratio with respect to the thermosetting resin of the powdered member of wood shall be 10% or more by weight ratio. The cross section of the polishing tool portion 82 is formed in an arc-shaped tire shape, and a shank 83 as a shaft is joined to the center portion of the arc shape.

  The polishing tool 81 is excellent in truing property. Moreover, the surface of the tool part 82 can be made precise. Further, the polishing tool 81 has water absorbency, prevents squeezing during processing, has appropriate hardness and plasticity, and has good abrasive bite. Further, the radius of curvature of the polishing tool portion 82 is set so that the uncut portion 80f of the workpiece 80I (FIG. 20B) by polishing or the workpiece 80II by turning back of the polishing tool 81 (FIG. 20A). The level difference 80p in FIG. 20 (c) is set to a size that can be accommodated in an optically unnecessary area.

In addition, processing of optical elements that can achieve a predetermined shape accuracy over the entire effective light range of an optical element such as a lens or a mirror, and can efficiently use the material by reducing the difference between the effective light range and the outer diameter. A method is also disclosed (see, for example, Patent Document 4 and Japanese Patent Application Laid-Open No. 2001-322063).
JP 2001-79742 A (page 1-2, FIG. 8) JP 2002-66888 A (page 1-2, FIGS. 1 and 2) JP 2001-138196 A (page 1-2, FIGS. 1, 10, 11) Japanese Patent Laid-Open No. 2001-322063 (pages 1, 3 and 1-6)

  However, when the conventional pressure transfer polishing method shown in FIG. 17 is performed, a defect region 52 is generated on the outer periphery of the polishing region 51. For example, as shown in FIG. 17, when the cross section of the polishing region 51 is viewed, the complete polishing region 51, that is, the region 51 that can be polished with a desired accuracy, and the defect regions 52 exist at both ends thereof. Since the polishing region 51 is formed by superimposing the unit processing marks 53, defect regions 52 having a width substantially corresponding to the width of the unit processing marks 53 are formed at both ends where the superimposition is incomplete.

  In the optical element molding die 50, it is necessary to set a width outside the effective range of the defect width 52 or more in the optical element. In general, the width outside the effective region of the optical element molding die 50 is substantially equal to the width outside the effective region of the optical element to be molded. Here, in order to reduce the cost by reducing the material for forming the optical element, it is desired to reduce the width outside the effective area, particularly the width outside the effective area in the sub-scanning direction. However, it is necessary to determine the width outside this effective range in consideration of restrictions from the molding technique. When the optical element is molded, a molding transfer error inevitably occurs toward the end of the optical element. Since the width is about 0.7 to 1 mm on one side, the width outside the effective range is desirably set to about 1 mm on one side. Therefore, it is desired that the defect width 52 by polishing be 1 mm or less on one side. In the conventional one, since the defect width 52 due to polishing is larger than the error width of molding transfer, the width outside the effective area of the optical element is determined by the polishing defect width 52, and the optical element corresponding to the width is determined. Since many materials to be formed were used, it was a cause of cost increase.

  Further, in the conventional processing method of a mold having a free curved surface and a mold having a free curved surface (Patent Document 1, Japanese Patent Laid-Open No. 2001-79742) shown in FIG. Although the outside of the effective range is not generated, first, there is a problem that it takes time to form the guide member 66 so as to accurately fit the extended surface of the curved surface of the mold.

  Further, the material of the guide member 66 may not be selected from any material. For example, when the chip of the material adheres to the polishing tool 68, when the chip is different from the original mold material, there is a concern that the polishing accuracy is adversely affected and the polishing accuracy is deteriorated.

  Furthermore, when a level difference is caused by the difference in polishing amount between the curved surface of the mold and the guide member 66 and the polishing tool 68 comes into contact with the edge of the level difference part, a sudden load is applied to the tool 68. Therefore, there is a concern that the tool 68 is chipped or the tool 68 is scratched. Thus, the tool 68 is easily damaged.

  Further, by polishing the mold edge, there is a high possibility that large chips such as burrs adhere to the surface of the tool 68. If the tool is damaged by the tool 68 damaged in this way or the tool 68 to which a large amount of swarf adheres, the processing surface may be damaged or scratched, or a desired shape accuracy may not be obtained. .

  For this reason, the material of the guide member 66 is preferably the same material as that of the mold, but even in such a case, the processing area increases, the processing time becomes longer, and the wear of the tool 68 becomes severe. There is concern.

  Further, there is a cost demerit such that extra material for the “quick part” connecting the die piece member 62 and the guide member 66 is required. In particular, when a complicated shape such as a free-form surface 63 or an aspherical shape is used, it is very difficult to manufacture the “fast part”.

  Further, in the conventional polishing method shown in FIG. 19 (Patent Document 2, Japanese Patent Application Laid-Open No. 2002-66888), an error of the polishing removal shape of the outer peripheral portion 71a of the lens 71 is predicted based on the polishing locus 70A in advance, Although a method for correcting this is disclosed, in order to correct the predicted error, if the polishing tool 72 that is considerably smaller than the assumed polishing tool 72 is not used, the error is completely corrected. Is considered difficult. In particular, it is estimated that it is more difficult to correct the polishing defect shown in FIG. Here, the target polishing defect width 70w (FIG. 19A), the width outside the so-called effective region, is 3 mm on one side.

  Further, in the above-described conventional polishing tool manufacturing method, polishing method, polishing tool and optical element or mold thereof (Patent Document 3, Japanese Patent Application Laid-Open No. 2001-138196) shown in FIG. (B)), 80p (FIG. 20 (c)) Although it is described that the radius of the polishing tool portion 82 (FIG. 20 (a)) is reduced in order to reduce the outside of the so-called effective range, the polishing tool portion 82 is described. When the tool contact surface is made small by reducing the radius of the tool, it is necessary to make unit processing traces overlap closely. For this reason, there has been a concern that the tool path becomes long and the time required for polishing is long. For this reason, it is not a good idea to make the radius of the polishing tool 81 (FIG. 20A) smaller than necessary. In addition, when the curvature of the processed surface is 0.01 / mm or more, that is, a concave surface with a radius of 100 mm or less, it is relatively difficult to make the defect widths 80f and 80p be 1 mm or less on one side.

In view of the above problems, the present invention reduces the width outside the effective area of the optical element to be molded by reducing the width outside the effective area of the optical element molding die to, for example, 1 mm or less on one side. In addition to reducing the amount of molding material used, the polishing time is prevented from becoming extremely long, the processing time is shortened, and energy such as electric power is reduced, thereby reducing the cost. as its object to provide a sought abrasive how.

In order to achieve the above object, the present invention according to claim 1 is provided between a polishing tool having a shape of a sphere or a part of a sphere, and a processing surface of an optical element molding die in contact with the polishing tool. In the polishing method for polishing the optical element molding die by generating a load, the processing surface having the maximum curvature and removal depth in the sub-scanning direction of the processing surface was polished with a polishing tool having a different diameter. When the relationship between the defect width in the sub-scanning direction generated by the polishing and the diameter of the polishing tool is acquired in advance, the relationship between the previously acquired defect width in the sub-scanning direction and the diameter of the polishing tool Based on this, the diameter of the polishing tool is determined such that the defect width in the sub-scanning direction of the processing surface of the optical element molding die to be polished is acceptable for the processing surface, and the diameter is equal to or less than the determined diameter. wherein the polishing is performed on the selected polishing tool from the abrasive tool It is a polishing method to. According to this configuration, the diameter of the polishing tool is correlated with the defect width by the polishing, the defect width is increased when the curvature is large, since the greater the removal depth is increased, the sub-scanning of the working surface When the processing surface having the largest curvature and removal depth in both directions is polished with a polishing tool having a different diameter, the relationship between the defect width in the sub-scanning direction generated by the polishing and the diameter of the polishing tool is acquired in advance. In addition, based on the relationship between the previously acquired defect width in the sub-scanning direction and the diameter of the polishing tool, the defect width in the sub-scanning direction of the processing surface of the optical element molding die to be polished is Determine the diameter of the polishing tool that is acceptable for the processing surface, and perform polishing with a polishing tool selected from the polishing tools having a diameter less than the determined diameter, thereby forming an optical element within a width outside the desired effective range. it is possible to polish the mold, Duck, taking into consideration the polishing time can also be in ing to select a tool of the above conditions are satisfied largest diameter.

In addition, the polishing tool has a value allowed for the processing surface based on the relationship between the defect width in the sub-scanning direction obtained by polishing the maximum curvature and removal depth of various processing surfaces and the diameter of the polishing tool. Since the diameter is determined, the relationship between the defect width in the sub-scanning direction and the diameter of the polishing tool can be obtained with a small amount of data, and the defect width in the sub-scanning direction can be obtained even when polishing is performed by selecting the largest diameter tool. Can be polished to ensure that the defect width is less than or equal to the allowable defect width .

According to a second aspect of the present invention, in the polishing method according to the first aspect, a tool path when the polishing tool is turned back outside the effective range in the sub-scanning direction on the processed surface of the optical element molding die. The polishing method is characterized in that the position is outside the center of the width in the sub-scanning direction outside the effective area. According to this configuration, when the shape of the processed surface in the sub-scanning direction is a concave surface, the width of the inner side of the polishing defect outside the effective region increases as the removal depth increases. Therefore, the position of the tool path when the polishing tool turns back outside the effective area in the sub-scanning direction is outside the center of the width in the sub-scanning direction outside the effective area, so that the optical element can be below the width outside the desired effective area. The molding die can be polished.

According to the first aspect of the present invention, the diameter of the polishing tool correlates with the defect width by polishing, and the defect width increases as the curvature increases, and also increases as the removal depth increases. When the polishing of the processing surface having the maximum curvature and removal depth in the sub-scanning direction of the processing surface is performed with a polishing tool having a different diameter, the defect width in the sub-scanning direction generated by the polishing and the diameter of the polishing tool Sub-scanning of the processing surface of the optical element molding die to be polished based on the relationship between the previously acquired defect width in the sub-scanning direction and the diameter of the polishing tool. By determining the diameter of the polishing tool at which the defect width in the direction becomes an allowable value for the processing surface, and performing polishing with a polishing tool selected from the polishing tools having a diameter equal to or less than the determined diameter , Polish the mold for molding optical elements below the width. It can, moreover, it is also possible to ing that in consideration of the polishing time to select a tool of the above conditions are satisfied largest diameter.

In addition, the polishing tool has a value allowed for the processing surface based on the relationship between the defect width in the sub-scanning direction obtained by polishing the maximum curvature and removal depth of various processing surfaces and the diameter of the polishing tool. Since the diameter is determined, the relationship between the defect width in the sub-scanning direction and the diameter of the polishing tool can be obtained with a small amount of data, and the defect width in the sub-scanning direction can be obtained even when polishing is performed by selecting the largest diameter tool. Can be polished to ensure that the defect width is less than or equal to the allowable defect width .

According to the present invention described in claim 2, in which the sub-scanning direction of the shape of the processed surface is a concave surface, the width of polishing defects inside portion of the effective outside increases with the removal depth is increased. Therefore, the position of the tool path when the polishing tool turns back outside the effective area in the sub-scanning direction is outside the center of the width in the sub-scanning direction outside the effective area, so that the optical element can be below the width outside the desired effective area. The molding die can be polished.

Hereinafter, describing the implementation form of abrasive how according to the present invention with reference to the drawings. As an example of a processing apparatus when polishing is performed, a polishing apparatus 9 shown in FIG. 1 is used. A polishing tool 1 having a shape of a rotating sphere or a part of a sphere is attached to a spindle that also serves as a linear slide 3. A predetermined load is applied to the linear motion slide 3 by the load generating mechanism 5, the load is transmitted to the polishing tool 1, and a load is generated between the tool 1 and the processing surface 7 a of the workpiece 7.

  The generated load is detected by the load sensor 4. A command such as a signal is issued from the control unit (not shown) to the load generation mechanism unit 5 so that the load becomes a predetermined load. Examples of the control unit (not shown) include a personal computer (not shown).

  The tool 1 is rotatably mounted on a tool shaft 2 provided on the linear motion slide 3. The load generating mechanism 5 is configured to include the linear motion slide 3, the load sensor 4, and the like. The load generating mechanism 5 is mounted on a column 6 that supports it.

  When the workpiece 7 is subjected to polishing, the workpiece 7 has an X axis, a Y axis, a Z axis, and another axis (not shown) that is a rotation axis parallel to the X axis, the Y axis, It is moved along another axis (not shown). By this movement, the normal line of the machining surface 7a of the workpiece 7 is matched with the tool load loading direction. Thus, the polishing apparatus 9 is capable of normal control. The workpiece 7 is fixed on a three-axis linear motion table 8 that can move along the X-axis, Y-axis, and Z-axis. An optical element molding die 7 is used as the workpiece 7. By polishing the processed surface 7a of the workpiece 7, the processed surface 7a of the optical element molding die 7 is finished.

  FIG. 2 is an explanatory view showing a work surface of a workpiece. As shown in FIG. 2, there is an error in the desired design shape 7d and the shape measurement result 7c before polishing the processed surface 7b. The removal amount or removal depth at each machining point is determined from the error. Before processing the processing surface 7b of the target workpiece 7, by processing a material having the same shape as the processing surface 7b, the relationship between the removal amount or the removal depth and the processing conditions is grasped in advance. It is necessary to keep in. Regarding this relationship, Preston's rule of thumb as shown by the following equation (1) is known.

δ = k × P × V × t (1)
(Δ: removal amount, k: proportionality constant, P: pressure, V: relative speed of tool and machining point (tool peripheral speed), t: dwell time)

  Thereby, a processing condition can be determined with respect to the removal amount or the removal depth at each processing point. Here, δ may be considered as a removal depth, and P may be regarded as a load. In general, the proportionality constant k is a constant determined by the material of the workpiece and the polishing tool.

  FIG. 3A is a plan view showing the optical element molding die, and shows a state where the processing surface of the optical element molding die is viewed from directly above. FIG. 3B is an explanatory diagram showing a state in which polishing processing is performed on the optical element molding die using a polishing tool.

  The longitudinal direction of the optical element molding die 10 is the main scanning direction X of the optical element molding die 10 or the polishing tool 1B, and is orthogonal to the main scanning direction X and is processed by the optical element molding die 10. The direction substantially along the surface 10a or the processing surface 10b is the sub-scanning direction Y of the optical element molding die 10 or the polishing tool 1B. The surface state before the optical element molding die 10 is polished is the processed surface 10b, and the surface state after the optical element molding die 10 is polished is the processed surface 10a. . The processing surface 10a of the optical element molding die 10 is a molding transfer surface 10a for accurately forming the optical element.

  When polishing is performed, the tool path TP is sent in the sub-scanning direction Y and picked in the main scanning direction X. The processing surface 10a includes an effective area 10e corresponding to the effective area of the optical element molded using the mold 10 and an outside of the effective area 10f corresponding to the outside of the effective area of the optical element molded using the mold 10. And exist. In order to reduce the width of the optical element in the sub-scanning direction Y, it is desirable to reduce the width 10w of the optical element molding die 10 in the sub-scanning direction Y outside the effective region 10f. Therefore, the width 10w in the sub-scanning direction Y of the defect generated by the polishing is set to be equal to or smaller than the allowable width 10w in the sub-scanning direction Y outside the effective region 10f.

  In order to reduce the defect width 10w outside the effective region 10f formed in the optical element molding die 10 when the polishing process is performed, the polishing tool jigs 1A and 1B shown in FIGS. It is effective to set the radius 1r of the polishing tools 1e and 1f small. The radius 1r of the polishing tools 1e and 1f means a radius 1r of a spherical shape. A numerical value obtained by doubling the radius 1r is defined as a tool diameter 1s. As shown in FIG. 5A, the polishing tool 1A is configured to include a spherical polishing tool 1e and a tool shaft 2 rotatably attached to the polishing tool 1e. Further, as shown in FIG. 5B, the polishing tool 1B includes a part of a sphere, a so-called deformed spherical polishing tool 1f, and a tool shaft 2 rotatably mounted on the polishing tool 1f. It is comprised as provided with.

  FIG. 4 shows the result of investigating the defect width when the flat surface is machined by changing the tool radius of the polishing tool. The tool radius of the polishing tool correlates with the width of a defect formed by many unit machining marks. For example, the width in the sub-scanning direction outside the effective range allowed for the optical element molding die is 0.8 mm on one side. In this case, as shown in FIG. 4, in order for the defect width by polishing to fall within the range of the width numerical value (0.8 mm), the tool radius may be set to 20 mm or less. If a polishing tool capable of processing the defect width generated by the polishing process to 1 mm or less on one side is selected, the width outside the effective area on the processing surface of the optical element molding die can be set to 1 mm or less on one side. Thus, the defect width decreases as the tool radius decreases. Accordingly, when polishing is performed on the processing surface of the optical element molding die using a polishing tool having a small tool radius, it is not necessary to use “Yaito”.

  Without using “Yatoi”, the width 10w of the optical element molding die 10 outside the effective region 10f, that is, the so-called defect width 10w, can be reduced, so the amount and material cost of the material of the optical element molding die 10 can be reduced. Can be reduced. Further, when the defect width 10w in the sub-scanning direction Y is set to 1 mm or less on one side, the width where an error portion of the optical element molding transfer occurs, and the defect of the processing surface 10a of the optical element molding die 10 by polishing. The width 10w becomes substantially equal to the width 10w, and the width 10w outside the effective region 10f of the optical element molding die 10 can be reduced to 1 mm or less on one side.

  As the tool radius (FIG. 4) is reduced, the unit processing trace left on the processing surface 10a of the optical element molding die 10 by the polishing tool 1f (FIG. 3B) decreases. For example, with reference to FIG. 17, in order to form the optical element molding die 50 having a reduced defect width 52, when the tool radius of the polishing tool used for polishing is reduced, the optical element is formed by the polishing tool. The unit machining trace 53 left on the machining surface 50a of the metal mold 50 is also reduced. Since the polishing surface 50a is formed by superimposing the unit processing marks 53, when the unit processing marks 53 are small, it is necessary to overlap so many unit processing marks 53.

  In order to reduce the width (10w) outside the effective region (10f) of the optical element molding die (10) shown in FIG. 3, the unit processing is performed when the optical element molding die (10) is polished. Since the trace (53) (FIG. 17) has to be reduced, the pick amount (Px) (FIG. 3) is reduced, and the polishing tool (1f) on the processing surface (10a) of the optical element molding die (10). It is necessary to increase the residence time of (FIG. 3B) so as to increase the overlap of unit processing traces.

  When the pick amount (Px) decreases, for example, the tool path (TP) shown in FIG. 3 becomes longer, and when the dwell time is further increased, the polishing time is increased accordingly. It takes time to polish. For this reason, the pick amount (Px) is reduced more than necessary, or the residence time of the polishing tool (1f) on the processing surface (10a) of the optical element molding die (10) is increased more than necessary. Doing so is not preferred.

  For example, as shown in FIG. 6, when the unit processing trace is reduced and the pick amount is changed from 0.10 mm to 0.05 mm, the polishing time is approximately twice as long. If the time required for the polishing process increases, the optical element molding die 10 cannot be efficiently manufactured, and power costs and labor costs for manufacturing the optical element molding die 10 (FIG. 3) are required. Since it is difficult to save energy, it is difficult to reduce the cost of the optical element molding die 10. Along with this, it is difficult to reduce the cost of optical elements manufactured using the optical element molding die 10. Therefore, it is desirable not to make the unit processing trace smaller than necessary. Therefore, the width 10w of the polishing defect in the sub-scanning direction Y is ensured to be approximately ½ or more of the width 10w outside the effective range set as 0.8 mm as a guide, that is, 0.4 mm or more as a guide. Is preferred.

  As an optical element, for example, an optical element having only a flat surface can be cited, but in general, most optical elements are formed in a curved surface. In order to form an optical element having a curved surface such as a lens, for example, a molding transfer surface 20a of the optical element molding die 20 (FIG. 12) is also formed in a curved surface shape. In recent years, since the optical element is required to have high optical performance, the molded transfer surface 20a is being formed as a free-form surface.

  In the polishing process of the optical element molding die 20 (FIGS. 12 and 13), the defect widths 20v and 20w (FIG. 13) formed by many unit processing traces are formed and transferred to the optical element molding die 20. As the machining surface curvature of the surface 20a increases, the surface 20a increases. An example of the measurement result is shown in FIG.

  FIG. 7 is a diagram showing the relationship between the machining surface curvature and the polishing defect width. The measurement results in FIG. 7 are the results when using a polishing tool having a tool radius of 11.5 mm. Here, when the processing surface of the optical element molding die is a concave surface, the curvature of the concave surface is positive. Further, when the processing surface of the optical element molding die is a convex surface, the curvature of the convex surface is negative. The defect width is larger on the concave surface than on the convex surface. In addition, among the concave surfaces, the defect width of the one having a larger curvature is assumed to be large.

  Also, as shown in FIG. 8, the relationship between the removal depth on the concave surface and the defect width increases the defect width when the removal depth is large. This tendency is particularly strong when the processed surface is concave. FIG. 8 shows the relationship between the removal depth and the defect width when a grinding tool having a tool radius of 10.5 mm is used on a concave surface having a machining surface curvature of 0.025 / mm, that is, a curvature radius of 40 mm. Has been. As shown in FIGS. 7 and 8, the processing surface curvature and the removal depth are correlated with the defect width.

  In the target optical element molding die, the polishing tool diameter is determined so as to obtain a desired defect width with respect to the maximum curvature and maximum removal depth in the sub-scanning direction of the processed surface. That is, the relationship between the defect width and the polishing tool diameter at the maximum removal depth at the maximum curvature in the sub-scanning direction of the processing surface is acquired before polishing the optical element molding die to determine the polishing tool diameter. . By using such a polishing tool, the optical element molding die can be polished within a width outside the desired effective range.

If these relationships are already acquired, the acquired data is used. If these relationships have not been obtained, a test piece (not shown) corresponding to the maximum curvature in the sub-scanning direction on the processing surface of the optical element molding die is prepared as a preliminary experiment, and polishing of various diameters is performed. Data is acquired by polishing the maximum removal depth with a tool .

  Preliminary experiments are carried out before polishing the optical element molding die for mass production, so the relationship between the defect width generated by polishing and the diameter of the polishing tool can be accurately obtained, and It is efficient because it can focus on experiments on the maximum removal depth at the maximum curvature of the machined surface.

  For example, when the curved molding transfer surface 20a of the optical element molding die 20 shown in FIG. 12 is finished, a polishing tool is used to perform surface finishing, and the polishing tool used at that time is used. A method for determining the tool diameter of the polishing tool having the shape of the tool sphere or a part of the sphere will be described. Even if the machining surface curvature of the optical element molding die 20 is a free-form surface, the approximate curvature is obtained, and the tool diameter is determined with respect to the maximum curvature.

  When examining the defect width 20w in the sub-scanning direction Y of the optical element molding die 20 (FIG. 13), the approximate curvature in the sub-scanning direction Y of the work surface 20b is obtained, and the polishing defect width is determined based on FIG. . When the approximate line for obtaining the approximate curvature is greatly shifted from the processed surface 20a (FIGS. 12 and 13), a portion where a polishing defect occurs, that is, a portion of the end 20h in the sub-scanning direction Y of the optical element molding die 20 A specific curvature is obtained, and the tool radius of the polishing tool is determined with respect to the maximum curvature.

  Even when the maximum removal depth is obviously not the end portion 20h in the sub-scanning direction Y, that is, when the maximum removal depth is not a portion where defects due to polishing occur, the maximum removal depth at the end portion 20h in the sub-scanning direction Y. From this, the tool radius of the polishing tool is determined.

  Explaining how to determine the maximum removal depth in the processing surface 20b of the optical element molding die 20 when polishing is performed, the processing surface 20b of the optical element molding die 20 before polishing is measured, The maximum removal depth of the processing surface 20b of the optical element molding die 20 is determined according to the maximum amount corrected in the polishing process from the measurement value error.

  Further, it is not always necessary to prepare an experimental workpiece (not shown) equal to the maximum curvature of the processing surface 20b of the optical element molding die 20, and a preliminary polishing for polishing a surface having a curvature larger than the maximum curvature. From the experiment, it is also possible to determine the relationship between the width of the defect generated by polishing and the diameter of the polishing tool. By doing so, it is often possible to save the labor for preparing the experimental workpiece and to reduce the material cost.

  For example, when a preliminary experiment is performed under a condition where at least one of the maximum curvature of the processing surface 20a of the optical element molding die 20 and the maximum removal depth is large, the actual optical element molding die 20 is polished. The defect widths 20v (FIGS. 12 and 13) and 20w (FIG. 13) are smaller than the defect widths obtained from the preliminary experiment results. From such a thing, it is also possible to determine the polishing tool diameter.

  By using the selected polishing tool when performing the polishing process, the effective area 30e of the optical element 30 (FIG. 11A) formed using the mold 20 (FIGS. 12 and 13) is obtained. The corresponding effective area 20e (FIG. 13) and the effective area 20f (FIG. 13) corresponding to the effective area 30f of the optical element 30 (FIG. 11A) molded using the mold 20 are processed surfaces 20a. The optical element molding die 20 provided for is efficiently formed.

  As shown in FIG. 12, when the shape of the optical element molding die 20 is a concave molding transfer surface 20a along the main scanning direction X, as shown in FIG. On the other hand, the tool shaft 2 of the polishing tool 1C is polished at an angle 2a to prevent the tool shaft 2 and the optical element molding die 20 from interfering with each other.

  Further, as shown in FIG. 14, the unit machining trace 1t left on the machining surface, that is, the polishing trace 1t, is left in the tool axis direction u by the polishing tool 1C including the polishing tool 1g having a shape of a part of a sphere. It is made into the shape of an elongate along. Therefore, in order to reduce the polishing defect width 20w in the sub-scanning direction Y (FIG. 13), the angle 2a of the tool axis 2 of the polishing tool 1C with respect to the main scanning direction X should be set small (FIG. 13, FIG. 14). Thereby, as shown to Fig.14 (a)-(c), the length of the subscanning direction Y of the grinding | polishing trace 1t by the grinding | polishing tool 1g which carried out the shape of a part of spherical body can be shortened.

  However, the angle 2a is within a range in which the optical element molding die 20 (FIG. 13) does not interfere with the tool shaft 2 of the polishing tool 1C and other parts around the polishing tool (not shown). It must be set. As shown in FIGS. 13 and 14, a polishing tool 1C is mounted on a polishing tool 1g having a shape of a part of a sphere, a so-called special deformed spherical polishing tool 1g, and rotatably mounted on the polishing tool 1g. And a tool shaft 2.

  In order to determine the diameter 1s of the polishing tool 1g constituting the polishing tool 1C, a preliminary experiment assuming the optical element molding die 20 is performed. From the experimental result, the tool diameter 1s of the polishing tool 1g constituting the polishing tool 1C is determined.

  A relationship of the polishing tool diameter 1s with respect to the maximum curvature and the maximum removal depth of the processing surface 20a of the optical element molding die 20 is obtained. For example, when polishing the optical element molding die 20 having a maximum curvature of 0.05 / mm and a maximum removal depth of 700 nm, when the defect width 20w outside the effective region 20f in the sub-scanning direction Y is 1 mm. From the preliminary experiment results shown in FIG. 9, the tool radius 1r of the polishing tool 1g in the polishing tool 1C (FIGS. 13 and 14) is selected to be 12 mm or less (FIG. 9). Further, the polishing tool 1g constituting the polishing tool 1C is set so that the defect width 20w (FIG. 13) is approximately ½ or more of the above-described 1 mm, that is, 0.5 mm or more, which is the width of the effective region 20f. The tool radius 1r is selected to be 4 mm or more (FIG. 9).

  Thus, the tool radius within the range of 4 mm or more and 12 mm or less is determined. A polishing tool 1C having a polishing tool 1g having a tool radius 1r (FIG. 14) within the above numerical range is selected. If the tool radius 1r of the polishing tool 1g is set to a small value of 12 mm or less, inadvertent interference between the optical element molding die 20 (FIG. 13) and the polishing tool 1g, tool axis 2, spindle axis, etc. Can be prevented. However, if the tool diameter becomes too small, interference between the tool axis (2) of the polishing tool (1C) and the processing surface (20a) of the optical element molding die (20) may become a problem. . In that case, it is preferable to set the tool diameter 1 s (FIG. 14) to such a size that the interference between the tool shaft 2 and the machining surface 20 a is not generated. Further, if the radius 1r of the polishing tool 1g is set to a large numerical value of 4 mm or more, the radius 1r of the polishing tool 1g is prevented from becoming too small and the polishing time is prolonged due to an increase in the tool path. be able to.

  If, for example, the tool diameter 1s of the polishing tool 1g of the polishing tool 1C shown in FIG. 14 can be determined from the past actual machining results, a preliminary experiment may not be performed. When there is a past actual machining record, it is possible to omit the preliminary experiment. By omitting the preliminary experiment, the labor for preparing the experimental workpiece can be saved and the material cost can be reduced.

  The curvature in the sub-scanning direction Y of the processed surface 20a of the optical element molding die 20 is preferably set within a range of -0.05 / mm to 0.05 / mm. Such a range of curvature almost covers the range of curvature of the optical element molding die that is normally used. Therefore, the optical element molding die 20 capable of reducing the defect width by polishing to 1 mm or less can be provided to the market. In addition, the optical element 30 (FIG. 11A) molded using such an optical element molding die 20 is normally capable of realizing necessary optical performance.

  The polishing tool 1g constituting the polishing tool 1C (FIG. 14) is required to maintain a spherical shape during polishing. FIG. 10 is a diagram showing the relationship between the Young's modulus of the tool material and the defect width. FIG. 10 shows the result of measurement when the curvature of the processed surface 20a of the optical element molding die 20 (FIGS. 12 and 13) is 0.05 / mm. From the relationship between the Young's modulus of the tool material shown in FIG. 10 and the defect width, the Young's modulus of the tool material of the polishing tool having a spherical shape or a part of the spherical shape is about 100 MPa [1.00E + 08 (Pa)] or more. It is preferable.

  The tool material having such a Young's modulus is formed by mixing and hardening a fine powder such as wood with a synthetic resin material such as urethane resin. The spherical polishing tool 1e constituting the polishing tool 1A (FIG. 5A) is formed by mixing fine powder made of wood with urethane resin and solidifying such tool material into a spherical shape. ing. In addition, the polishing tool 1f having a shape of a part of a sphere constituting the polishing tool 1B (FIG. 5B) is also mixed with a fine powder made of wood and urethane resin. It is formed by being hardened into a shape of a part of a sphere. Also, a polishing tool 1g having a shape of a part of a sphere constituting the polishing tool 1C (FIG. 14) is also mixed with a fine powder made of wood and urethane resin. It is formed by being hardened to the shape of the part. Such a tool material has a Young's modulus of 160 MPa [1.60E + 08 (Pa)].

  For example, when a tool material having a Young's modulus smaller than about 100 MPa [1.00E + 08 (Pa)] is used to form the polishing tool (1g) of the polishing tool (1C) (FIG. 14), polishing processing is performed. Is performed, the polishing tool (1g) of the polishing tool (1C) is in a state of being crushed without being able to maintain the spherical shape roughly. For this reason, the contact width (20v, 20w), that is, the defect width (20v, 20w) between the polishing tool (1g) of the polishing tool (1C) (FIG. 13) and the processed surface (20a) is extremely increased. The In this way, the Young's modulus of the sphere or a part of the sphere constituting the polishing tool is set to be less than about 100 MPa [1.00E + 08 (Pa)] (FIG. 10). When used and polished, the defect width (20v, 20w) of the processed surface (20a) of the optical element molding die (20) (FIG. 13) cannot be accommodated within 1 mm (FIG. 10).

  However, the tool radius 1r of the polishing tools 1e, 1f, and 1g is set to 4 mm to 12 mm, and the Young's modulus of the tool material of the polishing tools 1e, 1f, and 1g is 100 MPa [1.00E + 08 (Pa)]. If it is set as the above, the defect width by grinding | polishing can be 1 mm or less (FIG. 4, FIG. 9, FIG. 10). The width outside the effective range along the sub-scanning direction of the optical element molding die, the so-called defect width, is 1 mm or less at each end in the sub-scanning direction of the optical element molding die. The optical element molding die can be polished so as to have such numerical values.

  The optical element molded by the optical element molding die 20 (FIGS. 12 and 13) is a lens 30 having a cross-sectional shape shown in FIG. The lens 30 is formed to include an effective area 30e and an effective area outside 30f located outside the effective area 30e. Further, as shown in FIG. 11B, a rib 45 is provided on the main body 41 of the optical element 40, and an optical element 40 so-called lens 40 whose strength is supplemented by the rib 45 can also be used. The lens 40 includes an effective area 40e and an effective area outside 40f located outside the effective area 40e. A rib 45 that improves the strength of the lens 40 is provided outside the effective range 40 f of the lens 40.

  These lenses 30 and 40 are formed with molding transfer error portions 30f and 40f toward the ends. The widths 30w and 40w are about 0.7 to 1 mm on one side. For this reason, for example, the widths 20v and 20w outside the effective region 20f of the optical element molding die 20 (FIG. 13) are desirably set to about 0.7 to 1 mm on one side.

  Further, a rib 45 is formed at the end of the lens 40 (FIG. 11B), and due to the presence of the rib 45, there is a region where the shape cannot be measured. The width of such a region is 1 mm or less. For this reason, the width outside the effective range of the optical element molding die for forming the lens 40 was set to 1 mm or less.

  A tool path of the polishing tool 1C when the polishing tool 1C (FIG. 13) is used to polish the optical element molding die 20 will be described. The tool path of the polishing tool 1C in the optical element molding die 20 shown in FIG. 13 is the tool path TP of the polishing tool 1B on the optical element molding die 10 shown in FIG. The operation is almost the same. The tool path of the polishing tool 1C so that the polishing tool 1g of the polishing tool 1C (FIG. 13) does not come into contact with the edge 20h of the optical element molding die 20 when polishing is performed. Set.

  By doing in this way, it can prevent that the polishing tool 1g contacts the edge part 20h of the optical element shaping die 20, and the polishing tool 1g is damaged. Further, by polishing the edge portion 20h of the optical element molding die 20, large chips such as burrs adhere to the surface of the polishing tool 1g of the polishing tool 1C, and the processed surface 20a is formed by the large chips. Thus, it is possible to prevent the occurrence of defects such as scratches and degradation of the removal depth accuracy on the processed surface 20a.

  FIG. 15 is an explanatory view showing a longitudinal section of a polishing region of an optical element molding die. An effective area 25e is formed in the polishing area 25d, and an outside of the effective area 25f is formed outside the effective area 25e. The tool path of the polishing tool 1C in the optical element molding die 25 shown in FIG. 15 is substantially the same as the tool path TP of the polishing tool 1B in the optical element molding die 10 shown in FIG. The same behavior is assumed.

  FIG. 16 is a diagram showing the removal depth on the concave surface, the width of the polishing defect inner part, and the width of the polishing defect outer part. Tool path folding position in the sub-scanning direction Y (FIG. 15) With respect to the so-called tool path turning position, the removal depth of the outer portion 25m of the polishing defect outside the effective region 25f of the polishing region 25d and the removal depth of the inner portion 25n of the polishing defect As shown in FIG. 16, as the removal depth becomes larger, the width of the inner side of the polishing defect becomes wider. Such a tendency is noticeable when the shape of the processed surface in the sub-scanning direction is concave. For this reason, the position of the tool path when the polishing tool 1g of the polishing tool 1C is folded back outside the effective area 25f of the polishing area 25d in the sub-scanning direction Y (FIG. 15) is the sub-scanning outside the effective area 25f. It is set to be outside the center of the width in the direction Y. As a result, the optical element molding die can be polished within a desired width outside the effective range 25f.

  When taking data for determining the diameter of the polishing tool so as to obtain a desired defect width with respect to the maximum curvature and maximum removal depth of the processed surface of the target optical element molding die 25, a polishing region 25d is obtained. The relationship between the width of the polishing defect inner portion 25n and the width of the polishing defect outer portion 25m in the effective region outside 25f is obtained (FIG. 16). Based on the result, the return position of the tool path of the polishing tool 1C with respect to the optical element molding die 25 (FIG. 15) is determined. Thereby, the NC scanning width 3w of the polishing tool 1g of the polishing tool 1C along the sub-scanning direction Y is determined.

  Hereinafter, a polishing method of the optical element molding die 20 (FIGS. 12 and 13) for manufacturing the lens 30 (FIG. 11A), and an image forming apparatus on which the lens 30 (FIG. 11A) is mounted. (Not shown) will be described in detail.

  The polishing tool 1C shown in FIG. 14 was used to polish the optical element molding die 20 having a maximum curvature of 0.02 / mm in the sub-scanning direction Y (FIG. 13). The width 20w in the sub-scanning direction Y outside the effective region 10f of the optical element molding die 20 is 1 mm.

  Before performing the polishing process, the shape of the optical element molding die 20 is measured, and the removal depth at each processing point is determined from the error from the ideal shape of the optical element molding die 20. The maximum removal depth at the end 20h in the sub-scanning direction Y of the optical element molding die 20 was 700 nm. For example, the removal depth may be inferred and determined using FIGS. The polishing conditions were a load of 3N (300 gf) and a tool rotation speed of 100 rpm. In addition, diamond having a diameter of 0.5 μm was used as an abrasive grain used for polishing.

  By defining the maximum removal depth, each polishing condition, and the proportionality constant obtained as data in advance, the residence time at each processing point can be determined using Preston's rule of thumb (1). It is determined. Each of the data is input to a control device (not shown) of the polishing apparatus 9 (FIG. 1), for example.

  Instead of the optical element molding die 7 shown in FIG. 1, an optical element molding die 20 shown in FIGS. 12 and 13 is mounted on the three-axis linear motion table 8 of the polishing apparatus 9 (FIG. 1). Moreover, it replaces with the tool 1 shown in FIG. 1, and the grinding | polishing tool jig 1C (FIG. 13, FIG. 14) is attached to the spindle which served as the linear motion slide 3 of the grinding | polishing apparatus 9 (FIG. 1).

  An angle 2a formed between the tool axis 2 of the polishing tool 1C (FIG. 13) and the main scanning direction X of the optical element molding die 20 was set to 30 degrees. If the tool axis 2 of the polishing tool 1C (FIG. 13) is set at an angle 2a of 30 degrees with respect to the main scanning direction X of the optical element molding die 20, the polishing tool and the optical element molding The metal mold 20 does not interfere.

  Next, when polishing with a removal depth of 700 nm on the processing surface 20b of the optical element molding die 20 having a curvature of 0.02 / mm, the polishing tool 1g constituting the polishing tool 1C is formed. The relationship between the tool radius 1r (FIG. 14) and the defect widths 20v and 20w (FIG. 13) can be selected from those shown in FIG.

  In order to make the defect width of the optical element molding die 1 mm or less, a tool radius of 12 mm was selected based on FIG. The defect width when the tool radius 1r is 12 mm is about 0.95 mm. By selecting a tool radius of 12 mm, the width 20 w outside the effective range 20 f allowed for the optical element molding die 20 (FIG. 13) is about 0.95 mm. The width 20w of the effective region 20f is 1 mm or less. Further, by selecting a tool radius of 12 mm based on FIG. 9, the defect width is set to about 0.95 mm, and the width 20 w of the outside 20 f of the optical element molding die 20 (FIG. 13) is It is set to a numerical value of approximately 1/2 or more of the 1 mm, that is, 0.5 mm or more.

  In this manner, polishing of the optical element molding die 20 was performed. The polishing process of the optical element molding die 20 was completed without spending more polishing time than necessary. By performing polishing after performing the above settings, it is possible to provide the optical element molding die 20 in which the inside of the effective area 20e is finished with high accuracy.

  A plastic lens 30 (FIG. 11A) molded using the optical element molding die 20 is a printer (not shown) such as a laser beam printer (LBP) as an fθ lens, or a so-called printing device (not shown). ) And used. The plastic lens thus created is installed in an image forming apparatus such as a copying machine or LBP. Since the plastic lens 30 in which the amount of lens material and the material cost are reduced is mounted on the image forming apparatus, an image forming apparatus with low cost and low environmental load is provided.

The present invention is rather intended to be limited to the disclosed embodiments can be modified in various ways without departing from the scope of the present invention.

A polishing apparatus for polishing shows an embodiment of a polishing how according to the present invention; FIG. It is explanatory drawing which shows the to-be-processed surface of a workpiece. (A) is a top view which shows the optical element shaping die, (b) is explanatory drawing which shows the state by which the grinding | polishing process is performed to the optical element shaping die using the polishing tool. It is a figure which shows the relationship between a tool radius and a defect width. (A) is explanatory drawing which shows a spherical-shaped grinding | polishing tool, (b) is explanatory drawing which shows the grinding tool of the shape which carried out a part of spherical body. It is a figure which shows the relationship between pick amount and grinding | polishing time. It is a figure which shows the relationship between a process surface curvature and a grinding | polishing defect width. It is a figure which shows the relationship between the removal depth in a concave surface, and defect width. It is a figure which shows the relationship between a tool radius and a defect width. It is a figure which shows the relationship between the Young's modulus of a tool material, and a defect width. (A) is sectional drawing which shows an optical element without a rib, (b) is sectional drawing which shows an optical element with a rib. It is a front view which shows the optical element shaping die. It is a side view which shows the optical element shaping die. (A)-(c) is explanatory drawing which shows the relationship between the tool axis | shaft of a polishing tool jig provided with a polishing tool, and a grinding | polishing trace. It is explanatory drawing which shows the longitudinal cross-section of the grinding | polishing area | region of the optical element shaping die. It is a figure which shows the removal depth in a concave surface, the width | variety of a polishing defect inner side part, and the width | variety of a polishing defect outer side part. It is explanatory drawing which shows one form of the conventional grinding | polishing method. It is explanatory drawing which shows one form of the metal mold | die which has the conventional processing method of the metal mold | die which has a free-form surface, and a free-form surface. 1 shows an embodiment of a conventional polishing method, (a) is an explanatory view showing a scanning pattern of the polishing tool, and (b) is an explanatory view showing a polishing removal shape of the polishing tool. 1 shows an embodiment of a conventional polishing tool manufacturing method, polishing method, polishing tool and optical element or mold thereof, (a) is a sectional view showing the polishing tool, and (b) is polishing of a polished workpiece. Sectional view showing a state in which the folded part of the tool is deeper than the other part, (c) is a state in which several reciprocating parts near the processing start and processing end of the polished workpiece are incompletely processed. It is sectional drawing which shows a thing.

Explanation of symbols

1 Polishing tool (tool)
1e, 1f, 1g Polishing tool 1r Tool radius (radius)
1s Tool diameter (diameter)
2 Tool axis 2a Angle 7 Optical element molding die (workpiece)
7a Processed surface 10a, 20a Molding transfer surface (processed surface)
10, 20, 25 Optical element molding mold (mold)
10w, 20w Defect width (width)
X Main scanning direction Y Sub scanning direction

Claims (2)

A polishing method for polishing a mold for polishing an optical element by generating a load between a polishing tool having a shape of a sphere or a part of a sphere and a processing surface of an optical element molding mold in contact with the polishing tool In
When polishing a processed surface having the maximum curvature and removal depth in the sub-scanning direction of the processing surface with a polishing tool having a different diameter, the defect width in the sub-scanning direction generated by the polishing and the diameter of the polishing tool Sub-scanning of the processing surface of the optical element molding die to be polished based on the relationship between the previously acquired defect width in the sub-scanning direction and the diameter of the polishing tool. A polishing method comprising: determining a diameter of a polishing tool having a defect width in a direction equal to or less than a value allowed for the processed surface, and performing polishing with a polishing tool selected from the polishing tools having a diameter equal to or less than the determined diameter .   2. The polishing method according to claim 1, wherein a position of a tool path when turning the polishing tool outside the effective area in the sub-scanning direction on the processing surface of the optical element molding die is the sub-scanning outside the effective area. A polishing method characterized by being outside the center of the width in the direction.

Images