JP2004141983A - Working method of molding die, molding die, and optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a working method of a molding die, wherein a fine molding surface for an optical surface is efficiently and certainly obtained, while the number of corrective polishing works is reduced, and also to provide a molding die manufactured by the working method and an optical element molded with the molding die. <P>SOLUTION: The working method of the molding die comprises processes of: creating by cutting the molding surface 2 for the optical surface of the molding die 1 corresponding to an optical surface of a free curved surface with a predetermined cutting pitch; preliminarily working to form on the molding surface 2 for the optical surface finer polishing traces 13 than cutting traces 5 formed by the previous process so that the cutting traces are erased; measuring the surface shape of the molding surface 2 for the optical surface; and finishing to remove from the molding surface 2 for the optical surface a shape deviation component corresponding to a wavelength band of 2-8mm out of shape deviations between the surface shape based on measurement result obtained and the free curved surface. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical element such as a scanning lens, a prism, and a mirror used for a polygon scanner optical system of a laser printer, a molding die for molding an optical surface of the optical element, and a method of processing the molding die. About.
[0002]
[Prior art]
Optical elements, such as lenses and prisms, have optical surfaces through which light enters and exits. An optical element such as a mirror has an optical surface for reflecting light. These optical surfaces must accurately input or output or reflect light in order to exhibit desired optical characteristics. Therefore, it is necessary to precisely form the optical surfaces.
[0003]
For example, in a scanning lens used in a polygon scanner optical system of a laser printer, an incident spot position of a laser moves with scanning, and if the optical surface is undulated, image defects such as vertical streaks will be caused. Therefore, in the optical element such as the scanning lens, it is necessary to sufficiently remove the undulation from the optical surface to provide a precise optical surface.
[0004]
In recent years, the optical surface of such an optical element may be formed by a molding die. In this case, in order to eliminate the undulation of the optical surface of the optical element and obtain a precise optical surface, the undulation of the surface on which the optical surface is molded (hereinafter referred to as an optical surface molding surface) is removed by using a molding die. It is necessary to have a good optical surface molding surface.
[0005]
Removal of the undulation of the optical surface molding surface, after processing the surface shape of the optical surface molding surface as rough processing, calculate the amount of undulation and its wavelength to be measured by measuring the surface shape of the optical surface molding surface, It is often the case that finishing is further performed based on the calculated undulation. For example, as shown in FIG. 20, a desired shape is created by cutting the optical surface molding surface (S.11), and the surface shape of the optical surface molding surface is measured using a contact probe (S.12). ), The small diameter polishing tool is point-contacted and its residence time is controlled to correct the shape of the optical surface molding surface and remove undulations based on the measurement result of the surface shape (S.13), and the contact probe is again turned on. Then, the surface shape of the optical surface molding surface is measured (S.14), and it is determined whether or not the surface accuracy or undulation satisfies the target accuracy (S.15). A method of repeating the steps (S.13) and (S.14) has been conventionally performed.
[0006]
As an example of the conventional method of polishing the optical surface molding surface, by using a modified polishing tool having a tool diameter shorter than the wavelength of the undulation, the peak of the undulation is selectively polished and converted into a secondary undulation having a short wavelength. After that, the main polishing tool having a tool diameter twice or more the wavelength of the secondary undulation is moved relative to the object to be polished, and the surface to be polished (the optical surface forming surface) on which the secondary undulation is formed is polished. A method has been proposed (for example, Patent Document 1).
[0007]
In addition, an error shape measuring step of measuring the shape of the surface of the workpiece before processing and obtaining an error shape with respect to the target shape, an approximation step of approximating the obtained error shape with a higher-order polynomial, and approximation with a higher-order polynomial A dwell time calculating step of calculating a dwell time distribution on the surface of the workpiece of the first polishing tool necessary for polishing and removing a residual shape which is a difference between the obtained approximated curved surface and the error shape; A first polishing step of relatively moving the first polishing tool with respect to the surface of the workpiece so as to realize the time distribution, and a second polishing step in which the polishing surface is larger than that of the first polishing tool; There has also been proposed a method including a second polishing step of correcting and polishing a low-frequency error shape at a spatial frequency using a polishing tool (for example, Patent Document 2).
[0008]
Furthermore, the pressing mechanism and the processing and polishing head are supported at the center of gravity, and a load measuring device is laid out on the normal line at the processing point to make the normal direction at the processing point coincide with the pressing direction by the pressing mechanism. A curved surface polishing apparatus that performs control has also been proposed (for example, Patent Document 3).
[0009]
Patent Document 1 discloses a method in which a polishing tool is brought into contact with a surface to be polished with a contact width longer than the wavelength of the undulation, and the polishing tool is vibrated by rotating or swinging the polishing tool. The undulation is removed by averaging the surface to be polished. According to this method, the shape of the surface to be polished is measured using an interferometer, but when the shape is a toric shape or a free-form surface shape, the measurement probe such as an optical probe or a stylus probe is polished. A method of continuously acquiring point coordinates by operating on a surface is used.
[0010]
Patent Documents 2 and 3 disclose a polishing tool in contact with a surface to be polished with a contact width shorter than the wavelength of the undulation, and control the residence time of polishing to reduce the undulation of the polished surface. It is to let.
[0011]
According to these, the undulation caused by the processing of the surface to be polished is accurately measured, and the removal processing (correction polishing) for canceling the undulation based on the measurement data is further performed to thereby improve the surface of the surface to be polished. Improve accuracy. Therefore, the measurement accuracy of the waviness greatly affects the finishing accuracy of the optical surface molding surface.
[0012]
As a polishing tool for finishing a curved optical element or its mold into a mirror surface usable as an optical component, a polishing tool portion of a polishing tool for polishing a workpiece, a powdery member obtained by grinding wood, a urethane resin A thermosetting resin, which is mainly composed of any one of epoxy resin and phenol resin, is kneaded and heated and compressed to form a material. There has also been proposed a resin having a weight ratio of not less than 10% to the resin (for example, Patent Document 4).
[0013]
When manufacturing a molding die whose optical surface molding surface shape is an aspherical surface shape or a free-form surface shape, a material obtained by applying electroless nickel plating to the surface of a steel-based material as a mold material is used. Is often cut with a diamond bite.
[0014]
[Patent Document 1]
JP 2000-263391 A
[Patent Document 2]
JP-A-2002-52451
[Patent Document 3]
JP-A-2-131851
[Patent Document 4]
JP 2001-138196 A
[0015]
[Problems to be solved by the invention]
However, there are the following problems in the measurement of the undulation caused by the processing of the polished surface. In other words, when the optical surface molding surface of the molding die is cut with a diamond tool, cutting marks formed by the diamond tool are formed on the surface, and since the surface shape is directional, the optical surface molding surface is different. It has anisotropy.
[0016]
In order to reduce the cutting marks, it is conceivable to reduce the processing width interval of the cutting, that is, the so-called cutting pitch. However, if the cutting pitch is reduced, the number of times of repetitive cutting required for cutting a predetermined area increases. As a result, the total cutting length is increased, and the time required for the cutting is increased, which adversely affects the surface accuracy of the polished surface. Therefore, it is difficult to sufficiently reduce the cutting pitch, and undulation having anisotropy remains on the surface to be polished as a measurement target.
[0017]
When measuring the undulation of the surface of the polished surface having such anisotropy by the scanning of the above-described measurement probe, the measurement probe is inadvertent due to the bending of the cutting mark remaining on the surface of the polished surface and a change in the cutting width. Will be displaced up and down. The displacement is mixed into the measurement data as a swell of a wavelength sufficiently longer than the cutting pitch, even though it does not originally exist. As a result, measurement data that differs from the actual polished surface shape including errors is obtained, and it is difficult to obtain a precise optical surface molding surface by correction polishing performed based on the measurement data. It has become. In order to obtain a more precise optical surface molded surface, it is necessary to repeatedly perform the measurement of the surface to be polished and the correction polishing. It is also unclear whether accuracy can be obtained and the work has become very inefficient.
[0018]
The present invention has been made in view of the above circumstances, a working method of a molding die capable of reliably obtaining a precise optical surface molding surface while reducing the number of times of correction polishing, and that can be reliably obtained. It is an object to provide a molding die manufactured by using a processing method, and an optical element molded by the molding die.
[0019]
[Means for Solving the Problems]
In order to solve the above problem, a method of processing a molding die according to claim 1 of the present invention is a method of processing a molding die for molding an optical surface having a specific surface shape in an optical element, A forming step of forming the optical surface forming surface of the molding die corresponding to the optical surface by cutting at a predetermined cutting pitch, and a finer than the cutting mark so as to cancel the cutting mark formed on the optical surface forming surface by the forming process. Based on the measurement result obtained by the preliminary processing step of forming a processing mark on the optical surface molding surface and performing the preliminary processing, the measurement step of measuring the surface shape of the optical surface molding surface after the preliminary processing step, and the measurement result obtained by the measurement step A finishing step of removing a shape error component corresponding to a predetermined wavelength range from a shape error between a surface shape and a specific surface shape from an optical surface forming surface.
[0020]
According to a second aspect of the present invention, there is provided a method of processing a molding die according to the first aspect, wherein the measuring step is performed by an operation of scanning while bringing the measuring probe into contact with the optical surface molding surface. It is characterized by.
[0021]
According to a third aspect of the present invention, there is provided a method of processing a molding die according to any one of the first and second aspects, wherein at least one of the preliminary processing step and the finishing step is an abrasive. It is characterized by being performed by polishing using grains.
[0022]
According to a fourth aspect of the present invention, there is provided a method of processing a molding die according to the third aspect, wherein a plurality of polishing marks formed on the optical surface molding surface by polishing are formed in a cutting direction and a cutting direction in the generating step. It is characterized in that it extends in a direction different from any of the directions orthogonal to the cutting direction.
[0023]
According to a fifth aspect of the present invention, there is provided a method of processing a molding die according to any one of the third and fourth aspects, wherein the polishing marks are linear or arc-shaped. And
[0024]
According to a sixth aspect of the present invention, there is provided the molding die machining method according to any one of the third to fifth aspects, wherein both the preliminary machining step and the finishing step use abrasive grains. The contact width in the direction orthogonal to the cutting direction between the polishing tool and the optical surface forming surface in the preliminary processing step, and the cutting direction between the polishing tool and the optical surface forming surface in the finishing step The contact width in the direction in which the optical surface is formed is smaller than the width of the optical surface forming surface in the direction perpendicular to the cutting direction.
[0025]
According to a seventh aspect of the present invention, there is provided the molding die machining method according to the sixth aspect, wherein the polishing tool and the optical surface molding surface in the pre-machining step are contacted in a direction orthogonal to the cutting direction. The width is equal to or larger than a contact width in a direction orthogonal to a cutting direction between the polishing tool and the optical surface forming surface in the finishing step.
[0026]
The molding die according to claim 8, which is a molding die for molding an optical surface having a specific surface shape in an optical element, wherein the optical surface molding surface of the molding die corresponding to the optical surface has a predetermined cutting pitch. In the pre-processing, a forming process that is created by cutting in the optical process, and a processing mark finer than the cutting mark is formed on the optical surface forming surface so as to cancel the cutting mark formed on the optical surface forming surface by the generating process Step, after the pre-processing step, a measurement step of measuring the surface shape of the optical surface molding surface, of the shape error between the surface shape and the specific surface shape based on the measurement results obtained in the measurement process, a predetermined wavelength range And a finishing step of removing a corresponding shape error component from the optical surface molding surface.
[0027]
The molding die according to claim 9 is the molding die according to claim 8, wherein at least one of the pre-processing step and the finishing step is performed by polishing using abrasive grains, and the polishing is performed by polishing. A plurality of polishing marks formed on the surface forming surface extend in a direction different from any of a cutting direction and a direction orthogonal to the cutting direction in the generating step.
[0028]
According to a tenth aspect of the present invention, in the molding die of the ninth aspect, a plurality of polishing marks extend in the same direction, and an interval between adjacent polishing marks is 100 μm or less. And
[0029]
The molding die according to claim 11 is the molding die according to any one of claim 9 or claim 10, wherein an angle between a direction in which each polishing mark extends and a cutting direction in the generating step and each polishing mark is formed. And a direction perpendicular to the cutting direction is an angle of 5 ° or more.
[0030]
According to a twelfth aspect of the present invention, there is provided a molding die according to any one of the ninth to eleventh aspects, wherein the polishing marks are linear or arc-shaped.
[0031]
The molding die according to claim 13 is the molding die according to any one of claims 8 to 12, wherein the surface roughness of the optical surface molding surface after the finishing step is 80 nm in Ry value. It is characterized by the following.
[0032]
The optical element according to claim 14, which is an optical element having an optical surface of a specific surface shape formed by a molding die, wherein an optical surface molding surface of the molding die corresponding to the optical surface is formed at a predetermined cutting pitch. A pre-processing step of forming a finer than the cutting traces on the optical surface molding surface so as to negate the cutting traces formed on the optical surface molding surface by the generating process And, after the preliminary processing step, a measurement step of measuring the surface shape of the optical surface molding surface, and a shape wavelength corresponding to a predetermined wavelength range among the shape errors between the surface shape and the specific surface shape based on the measurement result obtained in the measurement process. And a finishing step of removing a shape error component from the optical surface molding surface.
[0033]
The optical element according to claim 15 is the optical element according to claim 14, wherein at least one of the preliminary processing step and the finishing step is performed by polishing using abrasive grains, and the optical surface is formed by polishing. A plurality of polishing marks formed on the surface extend in a direction different from any of a cutting direction and a direction orthogonal to the cutting direction in the generating step.
[0034]
An optical element according to a sixteenth aspect is the optical element according to the fifteenth aspect, wherein a plurality of polishing marks extend in the same direction and the interval between adjacent polishing marks is 100 μm or less. .
[0035]
The optical element according to claim 17 is the optical element according to claim 15 or 16, wherein an angle between a direction in which each polishing mark extends and a cutting direction in the creation step and each polishing mark extends. The angle between the direction and the direction perpendicular to the cutting direction is at least 5 °.
[0036]
An optical element according to an eighteenth aspect is characterized in that, in the optical element according to any one of the fifteenth to seventeenth aspects, the polishing mark has a linear shape or an arc shape.
[0037]
The optical element according to claim 19 is the optical element according to any one of claims 14 to 18, wherein the surface roughness of the optical surface molding surface after the finishing step is 80 nm in Ry value. It is characterized by the following.
[0038]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method for processing a molding die according to an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, a method of processing a molding die for molding an optical surface of a scanning lens as an optical element used in a polygon scanner optical system of a laser printer will be described. The optical surface of the scanning lens has a free-form surface as a specific surface shape.
[0039]
FIG. 1 is a flowchart illustrating a method for processing a molding die 1 (see also FIG. 2) according to an embodiment of the present invention. FIG. 1 illustrates a process of processing an optical surface molding surface 2 of the molding die 1 as a molding surface for molding an optical surface. The molding die 1 is made of a steel material having a length of 10 mm (Y direction in FIG. 2) and a width of 200 mm (X direction in FIG. 2), and the optical surface molding surface 2 is subjected to electroless nickel plating. ing. The specific surface shape of the optical surface forming surface 2 is a free-form surface corresponding to the optical surface of the scanning lens.
[0040]
As shown in FIG. 2, the optical surface forming surface 2 is mirror-cut using a diamond cutter 3 by, for example, a fly-cut method, and the shape is created (generation step (S.1)). As shown in the figure, the diamond cutter 3 is provided with a diamond tool 4 made of single crystal diamond around the periphery thereof, and the optical surface forming surface 2 is cut by the diamond tool 4. As an apparatus main body for controlling the position and rotating the diamond cutter 3, a precision cutting apparatus (not shown) having an orthogonal three-axis linear motion slide mechanism and capable of positioning in units of nanometers is used. .
[0041]
While rotating the rotating shaft 3a of the diamond cutter 3, the diamond cutting tool 4 is brought into contact with the optical surface forming surface 2 while moving along the optical surface forming surface 2 from the X direction end 2a to the other end 2b. When it is moved in the middle X direction, a band-shaped cutting mark 5 is formed on the optical surface molding surface 2. The cutting mark 5 has a cutting width corresponding to the width of the diamond cutting tool 4 in the Y direction in the drawing, and the cutting width is smaller than the width of the optical surface molding surface 2 in the Y direction. Therefore, in order to create the shape of the entire optical surface forming surface 2 with the diamond tool 4, the cutting process from the end 2a to the multi-end 2b is performed by setting the position of the diamond tool 4 in the Y direction at a predetermined pitch (pitch). (Feed amount).
[0042]
FIG. 3 shows a state in which a part of the surface of the optical surface molding surface 2 after this creation step is observed with a differential interference microscope. As is clear from the drawing, a plurality of cutting marks 5 are formed on the optical surface forming surface 2 at a predetermined cutting pitch S along the X direction as the cutting direction. If this cutting trace 5 is observed precisely, it will be understood that each of the cutting traces 5 is not straight but slightly winding.
[0043]
In a cutting process performed by the precision cutting device based on simultaneous X-axis and 2-axis commands, if the curvature of the optical surface molding surface 2 as the surface to be cut in the Y-axis direction changes, the cutting mark 5 will also bend. However, the bending of the cutting mark 5 in FIG. 3 has a shorter repetition wavelength of the bending and a stronger randomness than the bending expected from the change in the curvature of the optical molding surface 2 in the Y-axis direction. Things.
[0044]
FIG. 4 shows a state in which the optical surface molding surface 2 is cut along the cutting plane P in FIG. 1 and the cut marks 5 on the surface are observed along the X-axis direction. Each of the cutting marks 5 has an uneven shape in which portions having a large cutting depth and portions having a small cutting depth alternately overlap with each other. The boundary between the adjacent cutting marks 5 has a shape such that the cutting depth is shallow and the peak 5a is formed, and the skirt spreads toward the deep cutting valley 5b connecting the peak 5a and the peak 5a. ing.
[0045]
If the surface shape of the optical surface molding surface 2 described later is measured in a state where the cutting mark 5 is formed by an operation of scanning while making the contact type measurement probe 6 contact the optical surface molding surface 2, for example, FIG. As shown in FIG. 5, the measuring probe 6 scans over the meandering cutting mark 5. At this time, if there is a peak 5a of the cutting mark 5 on the scanning trajectory 6a of the measuring probe 6 as shown in FIG. 6, the measuring probe 6 is located on one of the right and left valleys 5b adjacent to the peak 5a. In some cases, a shape error that does not originally exist in the measurement result may be measured as undulation in the X-axis direction due to depression.
[0046]
Since the shape error as the undulation has a wavelength of 2 mm to 8 mm, the wavelength is completely different from the cutting pitch S in the Y-axis direction in units of several tens of μm. If erroneous recognition is made as if there is undulation in the X-axis direction due to this shape error, the accuracy of the subsequent finishing of the optical surface molding surface 2 will not be sufficiently obtained.
[0047]
Therefore, next, preliminary processing is performed so as to cancel the cutting marks 5 so as to form processing marks finer than the cutting marks 5 in the generating step on the optical surface molding surface 2 in the creation step (preliminary processing step (S.2)). This pre-machining step accurately removes the cutting mark 5 which is erroneously recognized as having a warm waviness even though it does not originally exist without substantially affecting the shape measurement of the optical surface molding surface 2. The surface of the optical surface molding surface 2 is polished for the purpose of replacing with processing marks that can perform measurement.
[0048]
FIG. 7 shows a schematic configuration of a polishing apparatus 7 for performing this preliminary processing. The polishing apparatus 7 includes, in addition to XYZ orthogonal linear translation slide mechanisms 7X, 7Y, and 7Z, tilt stages 7A and 7A for controlling a rotation posture in a rotation direction A around the X axis and a rotation direction B around the Y axis, respectively. 7B.
[0049]
The polishing spindle 8 can be moved up and down along the Z-axis via a linear motion guide mechanism using an aerostatic bearing, and the optical cylinder actuator is used to optically control the molding die 1 using a polishing tool 9 as a surface to be polished. It is possible to contact the surface forming surface 2.
[0050]
The molding die 1 is fixed to the polishing device 7 so that the optical surface molding surface 2 faces the polishing tool 9, and the posture can be controlled in five directions of X, Y, Z, A, and B. The outer frame of the molding die 1 is provided with a toy 10 as a guide member so as to cover the periphery of the optical surface molding surface 2. In the case of the toy 10, the entire surface of the optical surface molding surface 2 is sufficiently polished to prevent the polishing of the peripheral portion thereof from becoming insufficient, or the periphery of the optical surface molding surface 2 is sagged by the polishing process. It is made of the same material as the molding die 1 in order to prevent the molding die 1.
[0051]
The surface of the optical surface forming surface 2 is polished while rotating the polishing tool 9. At this time, the optical surface molding surface 2 of the molding die 1 and the toy 10 mounted so as to cover the periphery thereof are polished together.
[0052]
The polishing is performed while the polishing tool 9 is cleaned by the cleaning brush 12 while supplying the polishing liquid 11 to the surface of the optical surface forming surface 2 as shown in FIG. The linear motion slide mechanism 7Y is operated to scan in the Y-axis direction while the polishing tool 9 is in contact with the optical surface molding surface 2, and then the linear motion slide mechanism 7X is operated to move in the X-axis direction by a predetermined processing pitch. After the pick feed, the polishing tool 9 is again scanned in the Y-axis direction. By repeating the scanning in the Y-axis direction and the pick feed in the X-axis direction, the entire optical surface forming surface 2 is polished.
[0053]
In this polishing, the tilt stage is set so that the contact direction of the polishing tool 9 with the optical surface forming surface 2 as the surface to be polished always coincides with the normal direction of the surface to be polished at the contact point (processing point). 7A and 7B. The operation of the tilt stages 7A, 7B and the operation of the linear motion slides 7X, 7Y are linked, and the optical surface molding surface 2 is polished while simultaneously controlling four axes.
[0054]
The polishing tool 9 is formed of a compression molding material obtained by kneading wood and urethane resin. As the polishing liquid 11, a diamond paste obtained by mixing diamond abrasive grains having a particle diameter of about 1 μm and a gel-like oil is used. This diamond paste is applied to the surface of the optical surface molding surface 2 prior to polishing. Is also applied.
[0055]
The purpose of the polishing in this preliminary processing step is to improve the measurement accuracy in the measurement of the surface shape of the optical surface molding surface 2 described later so as to cancel the cutting marks 5. Therefore, the residence time control for controlling the contact time between the polishing tool 9 and the processing point according to the state of the processing point is not performed, and the uniform polishing is performed with the scanning speed on the optical surface molding surface 2 being constant.
[0056]
In order to reduce the time required for polishing, it is desirable that the polishing tool 9 has a large tool radius and a large contact width with the optical surface forming surface 2 and has a low elastic modulus. Thereby, the pick feed amount P (see also FIG. 9) can be increased, and the time required for polishing can be reduced. In the present embodiment, the tool radius of the polishing tool 9 is R30 mm, the tool width is 2 mm, and the pick feed amount is 0.4 mm.
[0057]
As shown in FIG. 9, polishing marks 13 (see also FIG. 11) as processing marks formed on the optical surface molding surface 2 by polishing with the polishing tool 9 are in directions different from both the X-axis direction and the Y-axis direction. The direction in which the rotation center axis 9a extends so as to extend toward the XY plane is set to be at an angle of θ1 with respect to the Y axis. In the present embodiment, θ1 is set to 30 °.
[0058]
FIG. 10 shows a state in which the surface of the optical surface molding surface 2 after polishing in the preliminary processing step is observed with a differential interference microscope. By this polishing, the surface roughness of the optical surface molding surface 2 is reduced to a level that cannot be detected by the white light interferometer.
[0059]
FIG. 11 schematically shows a state of the surface of the optical surface molding surface 2 by the differential interference microscope shown in FIG. The polishing marks 13 extend linearly in a direction in which they are aligned at an angle θ with the X-axis direction as the cutting direction, and the interval W between adjacent polishing marks is 100 μm or less, which is more than the cutting pitch S. It is fine. The angle θ is a value determined by the angle θ1 and the rotation speed of the polishing tool 9 and the scanning speed in the Y-axis direction. That is, when the rotation speed of the polishing tool 9 is sufficiently higher than the scanning speed in the Y-axis direction, the angle θ is substantially the same as the angle θ1, and as the rotation speed of the polishing tool 9 decreases, The angle θ becomes larger than the angle θ1 as the scanning speed in the Y-axis direction of the polishing tool 9 increases.
[0060]
As described above, by adjusting the rotation speed of the polishing tool 9 and the scanning speed in the Y-axis direction, the angle θ can be adjusted, and the rotation speed of the polishing tool 9 is adjusted in the Y-axis direction. When the speed is sufficiently higher than the speed, the angle θ can be adjusted by setting the angle θ1 between the rotation center axis 9a of the polishing tool 9 and the Y axis.
[0061]
FIG. 12 schematically shows the polishing marks 13 when the angle θ1 is set to 0 and the reciprocating polishing is performed on the same scanning locus. By adjusting the rotation speed of the scanning polishing tool 9 and the scanning speed in the Y-axis direction, the angle θ can be adjusted to a desired angle even when the angle θ1 is 0 °, and the reciprocating operation is performed. By doing so, two types of polishing marks 13 can be formed on the optical surface molding surface 2 so that the extending direction extends in a direction symmetrical with respect to the Y axis.
[0062]
After the preliminary processing step, the surface shape of the optical surface molding surface 2 is measured (measurement step (S.3)). The measurement is performed by a scanning operation in which the contact type measurement probe 6 is scanned on the optical surface molding surface 2. FIG. 13 shows the measurement results obtained by measuring the surface shape of the optical surface molding surface 2 by scanning the measurement probe 6 in the X-axis direction at a total of 10 locations at 0.8 mm intervals in the Y-axis direction. FIG. 13 shows the measurement results at ten locations superimposed.
[0063]
In FIG. 13, the horizontal axis indicates the X-axis direction of the optical surface molding surface 2, and the vertical axis indicates the Z-axis direction of the optical surface molding surface 2. Compared to the measurement result (FIG. 14) of measuring the surface shape of the optical surface molding surface 2 under the same conditions when the preliminary processing step is not performed, the measurement result of the present embodiment shown in FIG. The protruding measurement component 14 that is recognized as being recognized is greatly reduced.
[0064]
When the preliminary processing step is completed, a shape error component corresponding to a predetermined wavelength component is removed from the optical surface molding surface 2 (finishing step (S.4)). The removal of the shape error component is performed by polishing based on the shape error between the surface shape based on the measurement result obtained in the measurement process and the free-form surface as the specific surface shape to be finally obtained. Specifically, for example, the polishing amount to be processed at each measurement position is calculated based on the three-dimensional mapping data of the shape error shown in FIG. 15, and polishing is performed.
[0065]
In this polishing, the residence time of the polishing tool is controlled, and the tool radius of the polishing tool is R10 mm, the tool width is 0.6 mm, the pick feed amount is 0.1 mm, and the predetermined wavelength component is 2 mm to 2 mm. The shape error of the wavelength component of 8 mm is removed. Therefore, the contact width in the Y-axis direction in contact with the optical surface forming surface 2 is less than or equal to the Y-axis direction contact width of the polishing tool 9 on the optical surface forming surface 2 in the preliminary processing step.
[0066]
After the finishing step, the surface shape of the optical surface molding surface 2 is measured again (S.5), and the shape error of the wavelength component of 2 mm to 8 mm over a length of 200 mm along the X-axis direction at each measurement position is ± 20 nm. Within the range, and confirm that the desired surface accuracy is secured.
[0067]
According to the processing method of the molding die 1, the maximum height of the surface roughness of the optical surface molding surface 2, that is, the Ry value can be set to 80 nm or less. The surface can be made precise, and sufficient transmittance can be obtained even when this scanning lens is used to transmit laser light having a wavelength of 600 nm to 800 nm to the optical surface.
[0068]
[Modification 1]
In the above-described embodiment, in the pre-processing step, the direction in which the polishing tool 9 abuts on the optical surface forming surface 2 always coincides with the normal direction of the surface to be polished at the contact point (processing point). As shown in FIG. 16, polishing is performed while controlling each axis of the polishing apparatus 7 so that the axial direction of the rotation center axis 20a of the polishing tool 20 always coincides with the normal line at the processing point. Processing may be performed.
[0069]
By performing the polishing in this manner, the polishing tool 20 can be brought into contact with the optical surface forming surface 2 with a wide contact area, and the time required for the polishing can be further reduced. The pick feed amount P can be increased to 1 mm by setting the diameter of the rotating circle portion where the polishing tool 20 contacts the optical surface forming surface 2 to 5 mm. Thus, the time required for polishing the entire optical surface molding surface 2 having a length of 10 mm and a width of 200 mm can be reduced to about 10 minutes, and the time required for preliminary processing can be reduced.
[0070]
However, when polishing the optical surface molding surface 2 having a large change in curvature, the tool contact pressure distribution due to the contact position at the contact portion between the polishing tool 20 and the optical surface molding surface 2 tends to fluctuate. Consideration must be given to the elastic deformation of the contact part. As a material of the polishing tool 20, a material such as urethane foam, pitch, and chloroprene rubber is used.
[0071]
When the rotational center axis 20a and the normal direction at the processing point of the optical surface molding surface 2 have high coincidence, polishing marks 21a are formed on the optical surface molding surface 2 as shown in FIG. When the rotation center axis 20a and the normal direction at the processing point of the optical surface molding surface 2 have low coincidence, polishing marks 21b are formed on the optical surface molding surface 2 as shown in FIG.
[0072]
Both of the polishing marks 21a and 21b are arc-shaped and formed continuously so that a part of the rotating arc overlaps and aligns. The polishing marks 21a and 21b vary depending on the combination of the pick feed amount P, the scanning speed of the polishing tool 20, and the like. It is also possible to form a scar.
[0073]
[Modification 2]
In the above-described embodiment, in the preliminary processing step, polishing using the polishing tool 9 is performed. However, as shown in FIG. The blast processing may be performed by spraying (blast particles) on the optical surface forming surface 2 as a surface to be processed. The blast nozzle 30 is formed of, for example, a ceramic having excellent abrasion resistance, and a blast particle 30a as a projection material is, for example, a zinc alloy having a particle diameter of 1 μm.
[0074]
According to this method, the area that can be processed in a short time is large compared to the polishing processing, and even when the curvature change of the optical surface forming surface 2 is large, it is hardly affected by the change, and the preliminary processing can be easily and efficiently performed. It can be carried out.
[0075]
For example, if a blast nozzle 30 having a nozzle diameter of 12 mm is used, the blast nozzle 30 can be scanned once along the X-axis direction without repeatedly scanning the optical surface molding surface 2 having a length of 10 mm. For example, the preliminary processing of the entire optical surface molding surface 2 is completed. Thus, the processing time can be reduced to about one minute, and the time required for the preliminary processing can be further reduced. Here, scanning is performed such that the blast nozzle 30 keeps a constant distance (gap) with respect to the optical surface molding surface 2 while controlling the Z direction position of the molding die 1.
[0076]
FIG. 19 schematically shows a state of the surface of the optical surface molding surface 2 when the preliminary processing is performed by the blast processing. It can be confirmed that uniform dimples 31 with little processing unevenness are formed, and the cutting marks 5 are favorably canceled.
[0077]
【The invention's effect】
As described above, according to the inventions according to claims 1, 8, and 14 of the present application, a processing mark finer than a cutting mark is formed on an optical surface so as to cancel a cutting mark formed on the optical surface forming surface by the creation step. Since there is a pre-processing step of forming on the surface and performing the pre-processing, the measurement probe does not fall into any of the adjacent left and right valleys across the peak of the cutting mark in the measurement step. Therefore, in the measurement of the surface shape of the optical surface molding surface before the finishing step, the measurement result can be accurately performed without introducing a shape error that does not originally exist in the measurement result as undulation. As a result, it is not necessary to repeatedly perform shape measurement and finishing in order to obtain a desired surface accuracy, so that the number of times of processing such as correction polishing can be reduced, and a highly accurate optical surface molded surface can be efficiently and reliably obtained. be able to.
[0078]
According to the second aspect of the present invention, since the measuring step is performed by an operation of scanning while bringing the measuring probe into contact with the optical surface forming surface, for example, the inclination of the generating line becomes 35 ° or more at the end of the optical surface. Even in a molding die for molding an optical surface of a scanning lens having a large inclination, it is possible to measure the surface shape with high accuracy in units of several nm.
[0079]
According to the third aspect of the present invention, at least one of the pre-processing step and the finishing step is performed by polishing using abrasive grains, so that even if the optical surface molding surface is a free-form surface, it is easy and efficient. Processing can be performed Furthermore, when both the preliminary processing step and the finishing step are performed by polishing, there is no need to prepare separate processing apparatuses, which is advantageous in terms of processing efficiency and processing space, and can reduce costs.
[0080]
According to the fourth, ninth, and fifteenth aspects, the plurality of polishing marks formed on the optical surface molding surface by polishing are directed toward a direction different from any of the cutting direction in the generating step and the direction orthogonal to the cutting direction. Since it is extended, when the scanning direction in the measuring step is set to a direction that matches the cutting direction in the generating step or a direction perpendicular to the cutting direction, the unevenness due to the measured polishing marks, that is, the wavelength of the shape error is shortened. be able to. Furthermore, the actual shape error wavelength due to the polishing marks is not erroneously recognized as a shape error having a long wavelength, and can be easily separated and eliminated from the measurement result by, for example, a data filter. As a result, the surface accuracy is not unnecessarily increased based on the erroneous recognition, and a precise optical surface molding surface can be efficiently obtained without waste. An optical element having an optical surface molded based on the optical surface molded surface has high surface precision of the optical surface, and a sampling interval for sample extraction for product inspection in a production line can be increased, which is necessary for inspection. The labor and cost can be reduced.
[0081]
According to the fifth, twelfth, and eighteenth aspects of the present invention, since the polishing marks are linear or arc-shaped, the polishing marks can be easily formed on the optical surface molding surface using a polishing tool.
[0082]
According to the invention according to claim 6, since the contact width of the polishing tool in the preliminary processing step and the contact width of the polishing tool in the finishing step are both smaller than the width of the optical surface molding surface in the direction orthogonal to the cutting direction, High-precision polishing in nm units can be efficiently performed using a small-diameter polishing tool. Thereby, a precise optical surface molding surface can be efficiently obtained.
[0083]
According to the invention according to claim 7, since the contact width of the polishing tool in the preliminary processing step is equal to or larger than the contact width of the polishing tool in the finishing step, the pick feed amount in the preliminary processing step can be increased. As a result, the time required for the pre-machining step can be shortened, and the work becomes efficient.
[0084]
According to the tenth and sixteenth aspects of the present invention, a plurality of polishing marks extend in the same direction and the interval between adjacent polishing marks is 100 μm or less. From the shape error, for example, even with a filter of -12 dB / octave which is an attenuation rate of a general-purpose surface roughness measuring device, the mixing of the shape error due to polishing marks can be easily reduced to 2% or less.
[0085]
According to the invention according to claims 11 and 17, any of the angle between the direction in which each polishing mark extends and the cutting direction in the generating step and the angle between the direction in which each polishing mark extends and the direction perpendicular to the cutting direction are all set. Since it is an angle of 5 ° or more, when the scanning direction in the measuring step is set to a direction coinciding with the cutting direction in the generating step or a direction orthogonal to the cutting direction, the irregularities due to the polishing marks to be measured, that is, the wavelength of the shape error, It can be short. Furthermore, the actual shape error wavelength due to the polishing marks is not erroneously recognized as a shape error having a long wavelength, and can be easily separated and eliminated from the measurement result by, for example, a data filter. As a result, the surface accuracy is not unnecessarily increased based on the erroneous recognition, and a precise optical surface molding surface can be efficiently obtained without waste. An optical element having an optical surface molded based on the optical surface molded surface has high surface precision of the optical surface, and a sampling interval for sample extraction for product inspection in a production line can be increased, which is necessary for inspection. The labor and cost can be reduced.
[0086]
Since the polishing marks are inclined by 5 ° or more with respect to the cutting direction and the direction perpendicular thereto, it is easy to confirm that the cutting marks are canceled by observing the surface of the optical surface molding surface, and furthermore, the polishing marks are formed by a plurality of polishing marks. By forming the layers in different directions, it is possible to more effectively cancel the cutting marks.
[0087]
According to the thirteenth and nineteenth aspects, since the surface roughness of the optical surface molding surface after the finishing step is 80 nm or less in Ry value, laser light having a wavelength of 600 nm to 800 nm is transmitted through the optical surface. Even when this optical element is used, a sufficient transmittance can be obtained.
[Brief description of the drawings]
FIG. 1 is a flowchart illustrating a method for processing a molding die according to an embodiment of the present invention.
FIG. 2 is a view for explaining a step of creating an optical surface molding surface of a molding die.
FIG. 3 is a diagram showing a state in which the surface of an optical surface molding surface after a creation step is observed with a differential interference microscope.
FIG. 4 is a view showing a state in which a molding die is cut along a P plane in FIG. 1 and cutting marks on an optical surface molding surface are observed along an X-axis direction.
FIG. 5 is a view schematically showing a state in which the shape of the optical-surface molding surface on which cutting marks are formed is measured using a contact-type measurement probe.
FIG. 6 is a diagram showing a state in which a measurement probe drops from a peak of a cutting mark to an adjacent left or right valley.
FIG. 7 is a view showing a schematic configuration of a polishing apparatus for performing preliminary processing.
FIG. 8 is a diagram showing a state of polishing processing in preliminary processing in which a main part thereof is partially enlarged.
FIG. 9 is a plan view of an optical surface forming surface viewed from above, for explaining a state of scanning in polishing processing in preliminary processing.
FIG. 10 is a diagram showing a state in which the surface of an optical surface molding surface after a preliminary processing step is observed with a differential interference microscope.
11 is a diagram schematically illustrating the surface of the optical surface molding surface shown in FIG. 11, and is a diagram illustrating a state where a linear polishing mark is formed on the optical surface molding surface.
FIG. 12 schematically illustrates another example of the surface of the optical surface molding surface after the preliminary processing step, and illustrates a state where two types of linear polishing marks are formed on the optical surface molding surface. FIG.
FIG. 13 is a diagram showing a measurement result obtained by measuring the surface shape of the optical surface molded surface obtained in the measurement step using a contact type measurement probe.
FIG. 14 is a diagram showing a measurement result obtained by measuring the surface shape of the optical surface molding surface using a contact-type measurement probe when a preliminary processing step is not performed.
FIG. 15 is a diagram showing three-dimensional mapping data of a shape error of the optical surface molding surface.
FIG. 16 is a diagram illustrating a polishing process in a pre-machining step according to Modification Example 1 of the present invention while controlling each axis of the polishing apparatus so that the axial direction of the rotation center axis of the polishing tool always coincides with the normal line at the machining point; FIG.
17A and 17B are views showing polishing marks formed on the surface of the optical surface molding surface by the polishing shown in FIG. 16, wherein FIG. 17A shows the relationship between the rotation center axis and the normal direction at the processing point of the optical surface molding surface. (B) shows the case where the coincidence between the rotation center axis and the normal direction at the processing point of the optical surface molding surface is low.
FIG. 18 is a diagram illustrating a state in which blast processing is performed in a preliminary processing step according to Modification 2 of the present invention.
19 is a diagram showing dimples formed on the optical surface molding surface by the blasting shown in FIG. 18;
FIG. 20 is a flowchart illustrating a method for processing the optical surface molding surface of a conventional optical element molding die.
[Explanation of symbols]
θ, θ1: angle
1: Mold
2: Optical surface molding surface
3: Diamond cutter
4: Diamond bite
5: Cutting marks
5a: Yamabe
5b: Tanibe
6: Measurement probe
7: Polishing device
9: Polishing tool
13: Polishing mark

Claims (19)

A processing method of a molding die for molding an optical surface having a specific surface shape in an optical element,
A creation step of creating an optical surface molding surface of the molding die corresponding to the optical surface by cutting at a predetermined cutting pitch,
A pre-processing step of forming a processing mark finer than the cutting mark on the optical-surface forming surface and performing a pre-processing thereof, so as to cancel the cutting mark formed on the optical-surface forming surface by the generating step;
After the preliminary processing step, a measuring step of measuring the surface shape of the optical surface molding surface,
A finishing step of removing, from the optical surface molding surface, a shape error component corresponding to a predetermined wavelength range among shape errors between the surface shape based on the measurement result obtained in the measurement process and the specific surface shape. A method for processing a molding die. 2. The method according to claim 1, wherein the measuring step is performed by an operation of scanning the optical surface molding surface while bringing the measurement probe into contact with the optical surface molding surface. 3. 3. The method according to claim 1, wherein at least one of the preliminary processing step and the finishing step is performed by polishing using abrasive grains. 4. The plurality of polishing marks formed on the optical surface forming surface by the polishing extend in a direction different from any of a cutting direction in the creation step and a direction orthogonal to the cutting direction. 5. The method for processing a molding die according to 4. The method according to claim 3, wherein the polishing mark has a linear shape or an arc shape. The preliminary processing step and the finishing step are both performed by polishing using abrasive grains, and the contact width of the polishing tool and the optical surface molding surface in the preliminary processing step in a direction perpendicular to the cutting direction, and Wherein the contact width between the polishing tool and the optical surface forming surface in the finishing step in the direction orthogonal to the cutting direction is smaller than the width of the optical surface forming surface in the direction orthogonal to the cutting direction. The method for processing a molding die according to any one of claims 3 to 5. The contact width in the direction orthogonal to the cutting direction between the polishing tool and the optical surface forming surface in the preliminary processing step is in the direction orthogonal to the cutting direction between the polishing tool and the optical surface forming surface in the finishing step. The method for processing a molding die according to claim 6, wherein the contact width is equal to or larger than the contact width. A molding die for molding an optical surface having a specific surface shape in the optical element,
A creation step of creating an optical surface molding surface of the molding die corresponding to the optical surface by cutting at a predetermined cutting pitch,
A pre-processing step of forming a processing mark finer than the cutting mark on the optical-surface forming surface and performing a pre-processing thereof, so as to cancel the cutting mark formed on the optical-surface forming surface by the generating step;
After the preliminary processing step, a measuring step of measuring the surface shape of the optical surface molding surface,
A finishing step of removing, from the optical surface molding surface, a shape error component corresponding to a predetermined wavelength region among the shape errors between the surface shape based on the measurement result obtained in the measurement process and the specific surface shape. A molding die manufactured by using the method. At least one of the preliminary processing step and the finishing step is performed by polishing using abrasive grains, and a plurality of polishing marks formed on the optical surface molding surface by the polishing are cutting directions in the generating step. The molding die according to claim 8, wherein the molding die extends in a direction different from any of a direction perpendicular to the cutting direction. The molding die according to claim 9, wherein the plurality of polishing marks extend in the same direction, and an interval between adjacent polishing marks is 100 µm or less. The angle between the direction in which each of the polishing marks extends and the cutting direction in the creation step and the angle between the direction in which each of the polishing marks extends and the direction perpendicular to the cutting direction are all angles of 5 ° or more. The molding die according to any one of claims 9 to 10, characterized in that: The molding die according to any one of claims 9 to 11, wherein the polishing marks have a linear shape or an arc shape. The molding die according to any one of claims 8 to 12, wherein a surface roughness of the optical surface molding surface after the finishing step is 80 nm or less in Ry value. An optical element having an optical surface of a specific surface shape molded by a molding die,
A creation step of creating an optical surface molding surface of the molding die corresponding to the optical surface by cutting at a predetermined cutting pitch,
A pre-processing step of forming a processing mark finer than the cutting mark on the optical-surface forming surface and performing a pre-processing thereof, so as to cancel the cutting mark formed on the optical-surface forming surface by the generating step;
After the preliminary processing step, a measuring step of measuring the surface shape of the optical surface molding surface,
A finishing step of removing, from the optical surface molding surface, a shape error component corresponding to a predetermined wavelength region among the shape errors between the surface shape based on the measurement result obtained in the measurement process and the specific surface shape. An optical element formed by a molding die manufactured by using the method. At least one of the preliminary processing step and the finishing step is performed by polishing using abrasive grains, and a plurality of polishing marks formed on the optical surface molding surface by the polishing are cutting directions in the generating step. The optical element according to claim 14, wherein the optical element extends in a direction different from any of a direction perpendicular to the cutting direction. 16. The optical element according to claim 15, wherein the plurality of polishing marks extend in the same direction and the interval between adjacent polishing marks is 100 μm or less. The angle between the direction in which each of the polishing marks extends and the cutting direction in the creation step and the angle between the direction in which each of the polishing marks extends and the direction perpendicular to the cutting direction are all angles of 5 ° or more. The optical element according to claim 15, wherein: The molding die according to any one of claims 15 to 17, wherein the polishing marks have a linear shape or an arc shape. The optical element according to any one of claims 14 to 18, wherein a surface roughness of the optical surface molding surface after the finishing step is 80 nm or less in Ry value.

Images