JP2007114217A - Measurement method for lens shape or formed surface shape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of a precise shape measurement for a lens or a form block, having a curved surface which exceeds 35 degrees for the tilt angle. <P>SOLUTION: The method of measuring a lens shape and a formed surface shape, measures the shape from a center part to an effective diameter of the lens surface, exceeding 35 degrees tilt angle by using a shape measuring machine using a contactor. The measurement is performed in such a way that the contactor travels along the lens surface or the formed surface in an ascending direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for manufacturing a mold used for molding a lens by a press and a method for measuring a lens shape or a molding surface shape that can be used in a method for manufacturing a lens using a mold obtained by this manufacturing method.
In particular, a manufacturing method of a molding die that can obtain a lens having high shape accuracy and surface accuracy without grinding or polishing after molding by a precision press, and a pickup optical system used for a high-density optical disk using this molding die, etc. The present invention relates to a method for measuring a lens shape or a molding surface shape, which can be used in a manufacturing method of an ultra-high precision aspherical lens used in the invention.

There are the following prior arts for producing a mold for molding a lens having a predetermined optical performance, and determining and correcting the accuracy thereof.
Japanese Patent Application Laid-Open No. 2002-96332 discloses a method for designing a lens mold. In this method, a reference lens is first created using a reference mold as a step before making a mass production mold. Then, a mass production provisional mold is created based on the data collected from the reference mold and the reference lens, a provisional mass production lens molded by the created mass production provisional mold is assumed, and the provisional mass production lens is optically evaluated by optical simulation. The design and creation of the mass production provisional mold are repeated until the mass production provisional mold can produce a lens having a spherical aberration within an allowable range. In this method, the mass production mold can be designed without pressing the mass production provisional mold. However, in order to apply this method, it is first necessary to prepare a reference mold having optical performance within an allowable range and measure its shape. However, this publication does not disclose a method for producing a reference mold and measuring a shape, but only by trial and error.

  Japanese Patent Application Laid-Open No. 2002-96344 also discloses a method for designing a lens molding die. In this method, a temporary molding die is created based on a predetermined shape design value, thereby forming a lens, and measuring the optical characteristics of the molded temporary lens. The obtained measured value is compared with the desired optical characteristic, and the difference between the spherical aberrations is detected. As a result of detection, the amount of deviation of the aspherical aberration value from the desired optical characteristic is determined in advance by the relationship between the slight change amount of the high-order term and the variation amount of the spherical aberration value in the aspherical constant of the equation defining the aspherical surface. Compared with the obtained table, the slight change amount of the high-order term among the corresponding aspheric constants is used as the adjustment amount, and the adjustment amount is added to the aspheric constant of the aspheric type of the temporary molding die to create a new shape design Design the mold as a value.

  In this method, it is necessary to prepare in advance a table for determining the relationship between the amount of change in the high-order term of the aspherical aspheric constant and the amount of variation in the spherical aberration value. In order to verify the accuracy of this table Requires processing many molds, thereby pressing many different lenses to measure optical performance. Furthermore, this prior art does not disclose verification of whether or not the mold is processed according to the design shape.

  In the design stage of molding a lens having a spherical surface or an aspherical surface, the optical constant (refractive index, dispersion) of the lens material is determined based on the optical performance required for the lens, and the first surface of the lens, Lens shape design values including the shape of the two surfaces and the lens thickness are determined. Then, based on the obtained lens shape design value, the shape design value of the mold for molding the lens is determined. In this case, for example, in the case of a glass lens, the coefficient of thermal expansion of the glass and the coefficient of thermal expansion of the mold are different, so that the lens shape design value is determined after incorporating factors that affect molding, such as shrinkage of the glass after pressing. Based on this, the shape design value of the mold is determined.

  When the shape design value of the mold is determined, the machining input value is input to the processing machine based on the design value, and the mold is processed to produce a temporary mold. For example, the machining input value can be made equal to the mold shape design value. However, the shape of the processed temporary mold may not match the mold shape design value. Depending on factors such as temperature, humidity, and atmospheric pressure, the physical properties of the mold material and the accuracy of the processing machine used for mold processing fluctuate, and depending on the position of the mold material to be processed (near the optical axis and the periphery) This is caused by a slight change in the processing amount due to the difference in resistance. Therefore, in such a case, it is necessary to correct the shape of the processed temporary mold. At this time, in order to confirm the accuracy of the die machining, the shape of the provisional die must be measured precisely and the measured value and the die shape design value must be compared. Here, the processing machine is a grinding machine, a cutting machine or the like.

  The machining input value is corrected by accurately measuring the shape of the processed temporary mold, calculating the difference from the design value, and feeding back the difference to the machining input value. If mold processing is performed again using this correction value, a practical mold that satisfies an error within an allowable range with respect to the mold shape design value can be processed. If the mold machining is performed again and the difference from the mold shape design value is within an allowable range, the above is repeated. In any case, it is important to accurately measure the shape of the processed temporary mold.

  In order to precisely measure a curved surface such as a molding surface of a mold for molding a lens having a spherical surface or an aspherical surface, a stylus type measuring machine is used. The stylus type measuring machine has, for example, a tip shape as shown in FIG. 2, a tip angle of 12 to 90 °, a tip R (curvature radius) of 2 to 500 μm, diamond, ruby, A stylus (contactor) made of a material such as sapphire or carbide is used. Then, as shown in FIG. 1, the shape of the stylus tip is measured by going down the slope of the molding surface and going up the slope from the bottom. In an existing stylus type measuring machine, as shown in FIG. 3, the tilt angle (θ) between the stylus and the surface to be measured is limited. If θ ≦ 35 °, accurate measurement can be performed. However, if the angle exceeds 35 °, the measured value of the measuring instrument is not guaranteed and accurate data cannot be obtained or the reliability of the data obtained by measurement is not guaranteed. Sex is not guaranteed.

  However, depending on the optical system, a specially shaped lens (for example, an optical pickup lens having a large convex surface in order to achieve high resolution) may be required. Such a specially shaped lens may have a curved surface such that θ> 35 °, which is not guaranteed by a stylus type surface shape measuring instrument, as an optical functional surface, and such an optical functional surface can be molded. It is necessary to process the mold. However, an accurate correction value of the machining input value cannot be obtained unless an accurate measurement value of the mold shape is obtained.

  Moreover, even if a mold is obtained in which an error from the mold shape design value is within an allowable range, even if a glass material is press-molded using the mold to produce a lens, the lens is not always desired. May not have the optical performance. This is due to the difference between the molded lens (provisional lens) and the initially determined lens shape design value exceeding an allowable range. Specifically, the press-molded lens shrinks in the cooling process after press molding, but the behavior of this shrinkage varies depending on the lens shape, and it is difficult to predict when obtaining the mold shape design value.

  At this time, it is necessary to accurately measure the shape of the provisional lens, calculate the difference between the lens shape measurement value and the lens shape design value, and correct the mold shape design value based on the difference. However, as in the case of the molding surface described above, the shape measurement of the lens curved surface having an inclination angle exceeding 35 degrees is out of the guaranteed range, and there is a problem in precise shape measurement.

  On the other hand, in recent years, there is a demanded lens having an inclination angle of 50 degrees to 60 degrees, and it has been a problem to accurately measure the shape of such a lens and a mold for molding these lenses. . However, it cannot be determined whether or not the tip of the stylus follows the measurement object (work), and it cannot be determined whether or not reliable data is obtained.

  As a measuring instrument used for shape measurement, there is a non-contact type in addition to the stylus type, and it is not necessary to consider whether the stylus tip follows if there is no contact. However, when the tilt angle is large, the reflected light cannot be picked up and data cannot be collected.

  The accuracy of the die actually processed is required to have an error of about 0.1 μm or less. Similarly, the lens to be molded is required to have an error of 0.1 μm or less with respect to the lens shape design value. Therefore, although such high-precision surface shape measurement data is more important than conventional methods, high-precision surface shape measurement data cannot be obtained with the conventional method, and a mold having desired optical characteristics is obtained. And the manufacturing method of a lens was difficult.

Accordingly, an object of the present invention is to be used in a method capable of accurately measuring a shape even with a lens or a mold having a curved surface with an inclination angle exceeding 35 degrees, thereby producing a mold having a desired shape. Another object of the present invention is to provide a method for measuring a lens shape or a molding surface shape.
Furthermore, an object of the present invention is to provide a method for measuring a lens shape or a molded surface shape, which can be used in a method for manufacturing a lens that can be molded into a desired shape even if the lens has a curved surface with an inclination angle exceeding 35 degrees. There is.

The present invention for solving the above problems is as follows.
[Claim 1] A lens shape measuring method for measuring a shape from a central portion of a lens surface having an inclination angle of 35 degrees or more to an effective diameter using a shape measuring machine using a contact, A method for measuring a lens shape, wherein a child is measured in a direction that rises along the lens surface.
[Claim 2] When the lens surface is a convex surface, measurement is performed by moving the contact from the outer periphery of the lens surface toward the optical axis portion. When the lens surface is a concave surface, The lens shape measuring method according to claim 1, wherein the measurement is performed by moving the contact from the optical axis portion toward the outer periphery.
[3] The method for measuring a lens shape according to any one of [1] to [2], wherein the lens surface of the optical pickup lens is measured.
[Claim 4] A molding surface shape measuring method for measuring the shape of a molding surface of a molding die having a surface with an inclination angle of 35 degrees or more by using a shape measuring machine using a contact, wherein the contact is the A method for measuring a shape of a molding surface, characterized by measuring in a direction rising along the molding surface.
[Claim 5] When the molding surface is a convex surface, measurement is performed by moving a contact from the outer periphery of the molding surface toward the mold center. When the molding surface is a concave surface, the outer periphery is measured from the mold center. The method of measuring a molding surface shape according to claim 4, wherein the measurement is performed by moving the contact toward the surface.
[6] The method for measuring a lens shape or a molding surface shape according to any one of [1] to [5], wherein the lens surface or the molding surface has a surface with an inclination angle of 50 to 60 degrees.

In the process of producing a lens having a lens curved surface with an inclination angle exceeding 35 degrees, the inventors have used a stylus type shape measuring machine (stylus type) to determine the shape of the lens curved surface having various shapes and the molding surface of the mold. It was measured using a surface roughness profile measuring machine). And in the case of the shaping | molding surface of a shaping | molding die, I noticed that there was a slight difference between the mold shape measurement value measured in the direction in which the stylus descends the molding surface and the mold shape measurement value measured in the upward direction.
Therefore, a practical mold produced by correcting the machining input value based on the mold shape measurement value measured in the direction down the molding surface, and the machining input value based on the mold shape measurement value measured in the direction up the molding surface. The accuracy of a lens molded using a practical mold produced by correction was verified. As a result, it was found that the accuracy of the lens molded using the practical mold produced by correcting the machining input value based on the measured value of the mold shape measured in the direction of going up the molding surface was good. completed. Here, the processing input value is a shape value input to a processing machine that processes the molding surface of the mold, and may be an aspherical type or a point sequence data.

In the first method for producing a pressing mold, the direction from the mold center to the effective diameter of the molding surface of the prepared temporary mold is measured using a stylus type shape measuring machine in the direction in which the stylus rises along the molding surface. The mold shape measurement value is obtained by measuring the mold shape, and the machining input value of the mold is corrected based on the difference between the obtained mold shape measurement value and the mold shape design value.
Further, in the second method for producing a pressing mold, the shape from the central portion of the produced provisional lens surface to the effective diameter is measured along the surface of the provisional lens using a stylus-type shape measuring machine. The lens shape measurement value is obtained by measuring in the upward direction, and the mold shape design value is corrected based on the difference between the obtained lens shape measurement value and the lens shape design value.

  In the manufacturing method of the first pressing mold, “from the mold center to the effective diameter” means from the center position of the molding surface to the perpendicular drawn toward the circumference of the circle that determines the effective diameter of the lens. This is the projected distance on the molding surface. This corresponds to the right half of the molding surface of the mold shown in FIG.

  The measurement is performed while the stylus contacts the curved surface in the upward direction. The upward direction is the direction in which the stylus climbs the music to be measured. That is, when the molding surface is a convex surface, the direction is from the lens outer periphery toward the mold center, and when the molding surface is a concave surface, the measurement is performed by moving the stylus from the mold center toward the outer periphery. By correcting the machining input value of the mold based on the measured value of the mold shape obtained by measuring in this way, the lens is molded with high accuracy by using a practical mold produced based on the machining input value. be able to.

  The mold shape measurement value measured by the above method is compared with the mold shape design value. At this time, if there is a difference between the two, the machining input value is corrected based on the difference. If there is no difference, the temporary mold is made a practical mold without changing the machining input value.

When the mold shape is measured, the data is compared with the mold design value, and the difference (error amount) between the two is plotted against the distance from the center, a graph such as FIG. 4 is obtained. The amount of error is larger because the processing resistance (here, grinding resistance) is larger in the outer peripheral portion than in the central portion. In order to correct this, the machining input value is corrected so as to increase the grinding amount of the outer peripheral portion from the center, and the die machining is performed again.
Specifically, the machining input value can be corrected by inputting a machining input value that cancels the generated error amount.

  In the second manufacturing method, a lens is formed by actually pressing with a temporary mold, and the shape of the obtained temporary lens is measured. When measuring the shape of the provisional lens, if the lens is convex, the measurement data in the up direction is measured by measuring from the lens outer periphery toward the optical axis, and if the lens is concave, measuring from the optical axis toward the outer periphery. Is adopted.

  The material, shape, and structure of the temporary mold and the practical mold used for the mold manufacturing method are not particularly limited, and conventional ones can be used as they are. However, the mold manufacturing method is particularly suitable for a mold manufacturing method for molding a lens having a surface with an inclination angle of 35 degrees or more. In addition, known methods and apparatuses for grinding, cutting, and polishing used for mold processing for producing a temporary mold and a practical mold can be appropriately used.

  A method for producing a lens having a spherical surface or an aspherical surface, further comprising producing a practical mold by the above production method, supplying a molding material to the obtained practical mold, and obtaining a lens by press molding the molding material Is disclosed.

  The material and shape of the molding material used in the lens manufacturing method, press molding conditions, and the like can be appropriately selected from known ones. Moreover, what is necessary is just to use suitably what is used for the precision press of a glass lens also as the molding apparatus used for press molding.

  The manufacturing method of the lens is particularly suitable for manufacturing a lens having a surface with an inclination angle of 35 degrees or more, such as a lens having a surface with an inclination angle of 35 degrees or more, for example, a lens having a surface with an inclination angle of 50 to 60 degrees. However, there is an effect that a wavefront aberration of 0.04λrms or less can be obtained.

  The present invention includes a method of measuring the shape from the central portion of a lens surface having a surface with an inclination angle of 35 degrees or more to an effective diameter using a shape measuring machine using a contact. This method is characterized by measuring in a direction in which the contact rises along the lens surface. Specifically, the measurement in the upward direction can be performed from the outer periphery of the lens toward the optical axis when the lens is convex, and from the optical axis toward the outer periphery when the lens is concave. A lens having a surface with an inclination angle of 35 degrees or more, for example, a lens having an inclination angle of 35 degrees or more and 60 degrees or less can be measured even with a lens having a surface with an inclination angle of 50 to 60 degrees.

  In addition, the present invention can be used as long as it is not only a precision press of a glass lens but a molding method using a mold.

  The present invention is effectively applied to accurately form a lens having an aspherical surface with a large tilt angle. Conventionally, for example, since reliable shape measurement data of the first surface with a large tilt angle could not be obtained, the first surface that cannot be measured with the shape measurement data of the second surface with a small tilt angle and the wavefront aberration measurement value of the lens. The shape evaluation with high accuracy could be performed only by the method of supplementing the shape data. However, according to the present invention, reliable shape data can be obtained directly, and a mold can be manufactured based on this data.

  Furthermore, in a lens group (assembled lens) that is configured by a plurality of lenses having an aspherical surface with a large inclination angle and has a predetermined optical performance, it is very important that the surface shape of each lens is evaluated with high accuracy. It is important and the effect of the present invention is further exhibited. This is because even if it is found that the predetermined optical performance is not achieved by measuring the optical performance of the lens group (wavefront aberration, etc.), it cannot be determined how much surface modification of which lens in the group is necessary. Because. Further, in the lens group, it is often impossible to measure the wavefront aberration of each lens, and therefore, the above method (supplementing surface shape data that cannot be measured by measuring the wavefront aberration of the lens) cannot be applied. According to the present invention, each lens shape is compared with its shape design value to modify the lens shape, thereby increasing the shape accuracy of each lens, minimizing the shape error, and consequently increasing the accuracy of the lens group. Because it can be raised. In addition, the present invention can be effectively applied to a lens having an aspheric surface with a large tilt angle on the first surface and the second surface for the same reason as described above.

  According to the present invention, the shape of a lens surface or molding surface having a surface with an inclination angle of 35 degrees or more can be measured with high accuracy. Then, based on the highly accurate shape data, for example, it is possible to manufacture a highly accurate lens or mold so that an error amount with respect to a design value is significantly less than 0.1 μm.

Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1
In measuring the surface shape of the mold, the coordinate data of the curved surface of the mold was measured using a stylus type surface roughness contour shape measuring machine (Form Talysurf manufactured by Taylor Hobson). Specifically, a lens shape design value having desired optical performance was determined, and based on this, a mold shape design value was determined in consideration of the thermal expansion coefficient of the glass and the like. This mold shape design value was input to the grinding machine as a machining input value to perform die machining. The shape of the produced mold was measured as shown in FIG. For shape measurement, after searching for the lowest point of the curved surface of the mold (concave surface in Fig. 1), the stylus is moved to the left flat part, and then the stylus is moved by a predetermined distance as shown by the arrow in Fig. 1 during the automatic measurement. The obtained measurement data was taken in as coordinate data. If the shape of the object to be measured is concave, the stylus is “down” → “up”, and if it is convex, “up” → “down”.

  The measured coordinate data (mold shape measurement value) was compared (fitting) with the mold shape design value, and the difference (error amount) was obtained to obtain the shape measurement data shown in FIG. Based on the amount of error, a shape correction program for grinding is created, and the mold is reworked to process one with a smaller error value.

  According to the shape measurement data shown in FIG. 4, the center (optical axis portion) is a valley, and the error amount is relatively large toward the outer periphery. Although it decreases again near the outer edge, this change is asymmetric.

  Since the grinding machine grinds a rotating object to be ground with a grindstone, a molding die that is an object to be ground has a shape to be rotated. Therefore, the left-right asymmetry in FIG. 4 was thought to be due to inaccurate grinding and not due to non-uniform grinding. Therefore, this data was averaged on the left and right with the optical axis symmetrical (see FIG. 7), and the average data was used in the shape correction program for grinding.

  FIG. 5 shows the amount of error by reworking the mold by this shape correction program and comparing the reworked mold shape with the mold shape design value. Despite correction of the machining input value, the difference (error) exceeds 0.2 μm with respect to the design value at both ends (outer edge periphery).

  On the other hand, a shape correction program for grinding was created using data (see FIG. 7) of only the right half (only the upward direction of the stylus of the measuring machine) without taking the left and right averages in the data of FIG. The shape of the mold machined by this correction is shown in FIG. (In Fig. 6, the left half data obtained by inverting the right half data is also shown side by side.) The amount of error with respect to the design value is significantly less than 0.1 µm, and the shape has been corrected correctly. Was verified.

  As described above, the measurement of the mold shape using the data obtained from the upward movement of the stylus is more accurate, and it has been confirmed that the mold whose shape has been corrected is close to the desired design value. It was.

Example 2
Next, with respect to the plano-convex lens having the shape shown in FIG. 8, a molding die was prepared based on the mold shape design value determined based on the lens shape design value, and press molding was performed using this molding die. The surface inclination angle on the curved surface side (first surface) of this lens is 48 °.

  Based on the required optical performance, the lens shape design value was determined, and based on this, the mold shape design value was determined in consideration of the thermal expansion coefficient of the glass. A provisional mold satisfying this mold shape design value was manufactured, and the wavefront aberration of a glass lens actually press-molded was measured by laser interference measurement (transmitted wavefront aberration measuring device manufactured by Zygo), and the result of FIG. 9 was obtained. It was. Here, the wavefront aberration measured simultaneously was 0.026 λrms.

  Next, the shape of the first surface of the lens was measured with the same stylus shape measuring machine as in Example 1, and compared with the lens shape design value, the shape error data shown in FIG. 10 was obtained. . In FIG. 10, the left half is the upward direction of the stylus, and the right half is the downward direction. Again, the left and right are asymmetric, but this is due to insufficient accuracy in shape measurement.

  On the other hand, the shape error data and the lens shape design value were taken into optical design software (Code V, etc.), and the wavefront aberration of this lens was simulated. FIG. 11 (a) (wavefront aberration diagram calculated from data in the upward direction) and FIG. 11 (b) (wavefront aberration diagram calculated from the data in the downward direction) show the results. The wavefront aberrations were 0.025λrms and 0.05λrms, respectively.

From these two wavefront aberration diagrams, it can be seen that FIG. 11A substantially matches the measured data of FIG. 9 both in amplitude and in the obtained wavefront aberration value. On the other hand, FIG. 11B is not consistent with FIG.
From the above, it can be seen that the accuracy of the upstream data is sufficiently high because the wavefront aberration calculated from the climbing direction data is very close to the actually measured wavefront aberration even at the guaranteed range of 35 ° or more. It was. The wavefront aberration value of the lens molded at the same time was 0.026 λrms, which satisfied the desired optical performance. As a result, the temporary mold could be a practical mold.

  If the desired optical performance is not satisfied, the mold shape design value is corrected based on the difference between the lens shape measurement value measured in the upward direction of the stylus and the lens shape design value, and the shape for grinding is corrected. A correction program may be created and a practical mold may be processed accordingly. As described above, the measurement of the lens shape using the data obtained by the upward movement of the stylus is more accurate, and thus the shape-corrected mold produces a lens having a desired optical performance. Suitable for

According to the method of the present invention, it is possible to accurately measure a lens shape error after press molding a provisional lens by obtaining a sufficiently reliable lens shape measuring method.
Further, by comparing the measured value by the lens shape measurement with the lens shape design value, it is possible to accurately feed back to the correction of the mold shape, thereby easily reducing the lens shape error generated during molding.

Schematic of shape measurement by stylus. The tip shape of a stylus is shown. The tilt angle (θ) between the stylus and the surface to be measured, which is in contact with the stylus type measuring machine, is shown. Standard program shape measurement data. Shape data after correction (left and right average correction). Shape data after correction (right side data correction). Compensation data comparison. The shape of the plano-convex lens produced in Example 2. The result of having measured the wavefront aberration of the glass lens actually press-molded in Example 2 with the laser interference measuring device. Shape error data. Wavefront aberration diagram.

Claims (6)

A lens shape measuring method for measuring a shape from a central portion of a lens surface having a surface with an inclination angle of 35 degrees or more to an effective diameter using a shape measuring machine using a contact, wherein the contact is the lens surface A method for measuring a lens shape, comprising: When the lens surface is a convex surface, the contact is moved from the outer periphery of the lens surface toward the optical axis portion, and when the lens surface is a concave surface, the outer periphery from the optical axis portion of the lens surface is measured. The lens shape measuring method according to claim 1, wherein the measurement is performed by moving the contact toward the surface. The lens shape measuring method according to claim 1, wherein the lens surface of the optical pickup lens is measured. A molding surface shape measuring method for measuring the shape of a molding surface of a molding die having a surface with an inclination angle of 35 degrees or more using a shape measuring machine using a contact, wherein the contact is along the molding surface A method of measuring a shape of a molding surface, characterized by measuring in an upward direction. When the molding surface is a convex surface, the contact is moved from the outer periphery of the molding surface toward the mold center, and when the molding surface is a concave surface, the contact is measured from the mold center toward the outer periphery. The method for measuring a molding surface shape according to claim 4, wherein the measurement is performed by moving the surface. The method for measuring a lens shape or a molding surface shape according to any one of claims 1 to 5, wherein the lens surface or the molding surface has a surface with an inclination angle of 50 to 60 degrees.

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