Spherical grinding method and spherical grinding apparatus

Abstract

To provide a spherical surface grinding method and a spherical surface grinding device which can grind a work-piece with high accuracy.SOLUTION: A spherical surface grinding method includes: a first step in which a shape of a grindstone is measured by a shape measuring mechanism in a state where the grindstone is not inclined with respect to a turning center shaft for turning the grindstone; a second step in which the shape of the grindstone is measured by the shape measuring mechanism in a state where the grindstone is inclined with respect to the turning center shaft; a third step in which shape data on the grindstone obtained in the first step is synthesized with shape data on the grindstone obtained in the second step to obtain estimated shape data in a state where the grindstone is inclined with respect to the turning center shaft; a fourth step in which a contact point between the grindstone and a work-piece with a desired curvature radius is calculated, on the basis of the estimated shape data; a fifth step in which an inclination angle of the grindstone with respect to the turning center shaft, which is set in actual processing, is calculated, on the basis of the contact point ; and a sixth step in which the grindstone is inclined at the inclination angle to grind the work-piece into a spherical shape.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a spherical grinding method and a spherical grinding apparatus.

Background Art

[0002] Patent Document 1 discloses a technique for performing spherical grinding of a workpiece to be processed using a cup-shaped grindstone.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In spherical grinding of a workpiece, the grinding is performed by bringing a grindstone into contact with the workpiece in a state where the grindstone is inclined at a predetermined angle and rotating both the grindstone and the workpiece. At this time, in order to achieve high-precision grinding, it is important to grasp the contact point between the grindstone and the workpiece and appropriately set the positional relationship between the two.

[0005] However, in conventional techniques including Patent Document 1, it is difficult to grasp the exact contact point between the grindstone and the workpiece, and there is a problem that high-precision grinding cannot be performed.

[0006] The present invention has been made in view of the above, and an object thereof is to provide a spherical grinding method and a spherical grinding apparatus capable of grinding a workpiece with high precision.

Means for Solving the Problems

[0007] In order to solve the above-described problems and achieve the object, a spherical grinding method according to the present invention includes: a first step of measuring the shape of a cup-shaped grinding wheel by a shape measurement mechanism in a state where the grinding wheel is not inclined with respect to a turning center axis for turning the grinding wheel; a second step of measuring the shape of the grinding wheel by the shape measurement mechanism in a state where the grinding wheel is inclined with respect to the turning center axis; a third step of obtaining estimated shape data when the grinding wheel is inclined with respect to the turning center axis by synthesizing the shape data of the grinding wheel obtained in the first step and the shape data of the grinding wheel obtained in the second step; a fourth step of calculating a contact point between the grinding wheel and a workpiece having a desired curvature based on the estimated shape data; a fifth step of calculating an inclination angle of the grinding wheel with respect to the turning center axis, which is set in actual machining, based on the contact point; and a sixth step of setting the grinding wheel at the inclination angle and performing spherical grinding of the workpiece.

[0008] Further, in the spherical grinding method according to the present invention, in the above invention, the third step includes: a feature point extraction step of extracting feature points common to the shape data of the grinding wheel obtained in the first step and the shape data of the grinding wheel obtained in the second step; and an estimated shape data acquisition step of synthesizing the shape data of the grinding wheel obtained in the first step and the shape data of the grinding wheel obtained in the second step based on the feature points to obtain the estimated shape data.

[0009] Further, in the spherical grinding method according to the present invention, in the above invention, the second step further includes a turning center axis estimation step of measuring the shape of the grinding wheel by the shape measurement mechanism in a state where the grinding wheel is inclined at a plurality of different angles with respect to the turning center axis, and estimating a true turning center axis based on the shape data of the grinding wheel measured in the first step and the shape data of the plurality of grinding wheels measured in the second step, and the fifth step calculates the inclination angle by further using the true turning center axis.

[0010] In order to solve the above-described problems and achieve the object, a spherical grinding apparatus according to the present invention includes a work holding mechanism for holding a work, a work rotation mechanism for rotating the work holding mechanism around a work rotation axis, a grindstone holding mechanism for holding a cup-shaped grindstone, a grindstone rotation mechanism for rotating the grindstone around a grindstone rotation axis, a grindstone turning mechanism for turning the grindstone rotation mechanism around a turning center axis perpendicular to the grindstone rotation axis, a shape measurement mechanism having an axis parallel to the work rotation axis as an optical axis, an NC movement mechanism for moving the shape measurement mechanism in three-dimensional directions, a retraction mechanism for retracting the work holding mechanism to a position away from the grindstone rotation axis, a measurement control mechanism for controlling the shape measurement mechanism and the NC movement mechanism in order to measure the shape of the grindstone in a state where the grindstone holding mechanism is not inclined with respect to the turning center axis and the shape of the grindstone in a state where the grindstone holding mechanism is inclined with respect to the turning center axis, respectively, a data processing device for synthesizing the shape data of the grindstone acquired by the measurement control mechanism and calculating an inclination angle of the grindstone holding mechanism for obtaining a work having a desired curvature from data of a contact point between the work and the grindstone when the grindstone holding mechanism is inclined at a desired angle with respect to the turning center axis, and a machining control mechanism for controlling the grindstone turning mechanism based on an output result of the data processing device.

Effect of the Invention

[0011] In the spherical grinding method and the spherical grinding apparatus according to the present invention, by estimating shape data of the grindstone when the grindstone is inclined with respect to the turning center axis, accurate contact point data between the grindstone and the work can be acquired. Thereby, the work can be ground with high precision.

Brief Description of the Drawings

[0012]

Figure 1

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Figure 14

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the spherical grinding method and spherical grinding apparatus according to the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiments, and the constituent elements in the following embodiments include those that can be replaced and are easy for those skilled in the art, or those that are substantially the same.

[0014] Here, in spherical grinding of a glass lens or the like, the work to be processed and a cup-shaped grindstone brought into line contact with the work are rotated respectively to process the work. At this time, by changing the inclination of the grindstone, the curvature of the work to be processed can be changed. However, when the work is continuously processed, the shape of the grindstone changes due to wear, so it was necessary to adjust the inclination of the grindstone while observing the finish of the work.

[0015] Therefore, conventionally, each time the work is processed, the shape of the grindstone is measured using a shape measurement mechanism having an optical axis parallel to the rotation axis of the work (hereinafter referred to as the "work rotation axis"), thereby grasping the contact point between the grindstone and the work, and adjusting the movement amount of the work such as the inclination angle and the depth of cut of the grindstone.

[0016] When measuring the shape of the grindstone, for example, as shown in part A of FIG. 1, it is measured by the shape measurement mechanism 22 from above the grindstone 14. On the other hand, when processing the work W, as shown in part B of the same figure, the grindstone 14 is used while being inclined with respect to the turning center axis Ac. Therefore, for example, due to limitations in equipment accuracy, etc., there may be an error between the theoretically (simulationally) turning center axis Ac and the actual turning center axis (true turning center axis) Ac. As a result, the contact point between the grindstone and the work measured by the shape measurement mechanism 22 and the actual contact point will be different.

[0017] Therefore, when actually machining the workpiece W, for example, it is conceivable to measure the shape of the grinding wheel 14 in a state where the grinding wheel 14 is tilted at an angle (see B in FIG. 1) by the shape measuring mechanism 22. However, in such a state where the grinding wheel 14 is tilted, as shown in FIG. 2 for example, only the shape of one end (the left side in the drawing) of the cup-shaped grinding wheel 14 can be measured, and in some cases, the shape of the other end cannot be measured. Therefore, it becomes unclear which position information of the measured shape of the grinding wheel 14 is from the center of the grinding wheel, and the absolute position of the grinding wheel 14 in the coordinate system of the entire apparatus cannot be grasped. That is, the shape and position of the entire machining area when the grinding wheel 14 is tilted for machining cannot be grasped.

[0018] Thus, when measuring the shape of the grinding wheel from above, an error occurs with respect to the assumed position of the grinding wheel when tilted at a predetermined angle. On the other hand, when trying to measure in a state where the grinding wheel is tilted assuming the machining of the workpiece, the shape and position of the entire grinding wheel become unclear. As a result, in either case, there arises a problem that the contact point when the grinding wheel is tilted at a predetermined angle cannot be grasped.

[0019] Therefore, in the spherical grinding method and spherical grinding apparatus according to the present invention, such problems are solved, and high-precision grinding is realized by acquiring data of the accurate contact point of the grinding wheel in the grinding state (tilted state) of the grinding wheel.

[0020] (Spherical grinding apparatus) The spherical grinding apparatus according to an embodiment of the present invention will be described with reference to FIGS. 3 and 4. The spherical grinding apparatus is for performing spherical grinding of the workpiece W. The spherical grinding apparatus can perform both concave machining and convex machining on the workpiece W. In the present embodiment, the case of performing convex machining will be mainly assumed for the description.

[0021] FIG. 3 is a front view of the spherical grinding apparatus 1 according to the embodiment, and FIG. 4 is a side view of the spherical grinding apparatus 1. The spherical grinding apparatus 1 includes a work holding mechanism 11, a work rotation mechanism 12, a retraction mechanism 13, a grinding wheel (first grinding wheel) 14, a grinding wheel holding mechanism 15, a grinding wheel rotation mechanism 16, a grinding wheel turning mechanism 17, a grinding wheel (second grinding wheel) 18, a grinding wheel holding mechanism 19, a grinding wheel rotation mechanism 20, a grinding wheel turning mechanism 21, a shape measurement mechanism 22, an NC movement mechanism 23, a measurement control mechanism 24, a data processing device 25, a machining control mechanism 26, and a reference surface 27.

[0022] The work holding mechanism 11 is a mechanism for holding the work W to be machined. Examples of the work W include a glass lens having a diameter of about Φ1 to 3 mm. The work rotation mechanism 12 is a mechanism for rotating the work holding mechanism 11 around the work rotation axis Aw. The retraction mechanism 13 is a mechanism for retracting the work holding mechanism 11 to a position away from the rotation axes (hereinafter referred to as "grinding wheel rotation axes") At1 and At2 of the grinding wheels 14 and 18. This retraction mechanism 13 can move the work holding mechanism 11 in three-dimensional directions (X-axis direction, Y-axis direction, and Z-axis direction).

[0023] The grinding wheel 14 is a tool for grinding the work W. This grinding wheel 14 is a cup-shaped grinding wheel and is used, for example, during rough grinding. The grinding wheel holding mechanism 15 is a mechanism for holding the grinding wheel 14. The grinding wheel rotation mechanism 16 is a mechanism for rotating the grinding wheel 14 held by the grinding wheel holding mechanism 15 around the grinding wheel rotation axis At1. The grinding wheel turning mechanism 17 is a mechanism for turning (swinging) the grinding wheel rotation mechanism 16 around the turning center axis Ac perpendicular to the grinding wheel rotation axis At1.

[0024] The grinding wheel 18 is a tool for grinding the workpiece W. This grinding wheel 18 is a cup-shaped grinding wheel and is used, for example, during precision grinding. The grinding wheel holding mechanism 19 is a mechanism for holding the grinding wheel 18. The grinding wheel rotation mechanism 20 is a mechanism for rotating the grinding wheel 18 held by the grinding wheel holding mechanism 19 around the grinding wheel rotation axis At2. The grinding wheel turning mechanism 21 is a mechanism for turning the grinding wheel rotation mechanism 20 around the turning center axis Ac perpendicular to the grinding wheel rotation axis At2.

[0025] The shape measurement mechanism 22 is a mechanism for measuring the shapes of the grinding wheels 14 and 18. Examples of such a shape measurement mechanism 22 include a laser displacement meter. Further, the shape measurement mechanism 22 has an optical axis Ao that is parallel to the workpiece rotation axis Aw. The NC movement mechanism 23 is a mechanism for moving the shape measurement mechanism 22 in three-dimensional directions (X-axis direction, Y-axis direction, and Z-axis direction).

[0026] The measurement control mechanism 24 is a mechanism for controlling the shape measurement mechanism 22 and the NC movement mechanism 23 in order to measure the shapes of the grinding wheels 14 and 18 in a state where the grinding wheel holding mechanisms 15 and 19 are not inclined with respect to the turning center axis Ac (before inclination) and the shapes of the grinding wheels 14 and 18 in a state where the grinding wheel holding mechanisms 15 and 19 are inclined with respect to the turning center axis Ac (after inclination).

[0027] The data processing device 25 synthesizes the shape data of the grinding wheels 14 and 18 acquired by the measurement control mechanism 24, and calculates the inclination angle of the grinding wheel holding mechanisms 15 and 19 for obtaining a workpiece W with a desired curvature from the data of the contact points between the workpiece W and the grinding wheels 14 and 18 when the grinding wheel holding mechanisms 15 and 19 are inclined at a desired angle. This data processing device 25 is realized by a general-purpose information processing device such as a personal computer or a workstation.

[0028] The machining control mechanism 26 is a mechanism for controlling the grinding wheel turning mechanisms 17 and 21 based on the output result of the data processing device 25. The reference surface 27 is a surface for taking a reference of the measurement value of the shape measurement mechanism 22. In FIG. 3, the symbol O indicates the equipment origin of the spherical grinding device 1, the symbol St1 indicates the reference point (grinding wheel reference) of the grinding wheel 14, and the symbol St2 indicates the reference point (grinding wheel reference) of the grinding wheel 18, respectively.

[0029] (Spherical grinding method) The spherical grinding method according to the embodiment of the present invention will be described with reference to FIGS. 5 to 14. In the spherical grinding method according to the embodiment, as shown in FIG. 5, a first shape measurement step (step S1), a second shape measurement step (step S2), a shape data acquisition step (step S3), a contact point calculation step (step S4), an inclination angle calculation step (step S5), and a machining step (step S6) are performed.

[0030] <First shape measurement step> In the first shape measurement step, the shapes of the grinding wheels 14 and 18 before inclination are measured (step S1). Specifically, in the first shape measurement step, the cup-shaped grinding wheels 14 and 18 are not inclined with respect to the turning center axis Ac for turning the grinding wheels 14 and 18 (see A in FIG. 1), and the shapes of the grinding wheels 14 and 18 are measured by the shape measurement mechanism 22. Further, in the first shape measurement step, the shapes of the grinding wheels 14 and 18 arranged upward are measured from above by the shape measurement mechanism 22.

[0031] <Second shape measurement step> In the second shape measurement step, the shapes of the grinding wheels 14 and 18 after inclination are measured (step S2). Specifically, in the second shape measurement step, the shapes of the grinding wheels 14 and 18 are measured by the shape measurement mechanism 22 in a state where the grinding wheels 14 and 18 are inclined with respect to the turning center axis Ac. Further, in the second shape measurement step, the shapes of the grinding wheels 14 and 18 arranged at a predetermined angle are measured from above by the shape measurement mechanism 22. Further, in the second shape measurement step, it is preferable to incline the grinding wheels 14 and 18 in a state close to the inclination angle during actual machining and measure the shape data.

[0032] <Shape data acquisition step> In the shape data acquisition step, as shown in FIG. 6, by synthesizing the shape data of the grindstones 14 and 18 acquired in the first shape measurement step and the shape data of the grindstones 14 and 18 acquired in the second shape measurement step, when the grindstones 14 and 18 are inclined with respect to the rotation center axis Ac, estimated shape data is acquired (step S3). Note that the "shape data" refers to point sequence data indicating the shape of the grindstones 14 and 18. Further, this shape data also includes position data (coordinate data) of each point.

[0033] Specifically, the shape data acquisition step includes a feature point extraction step and an estimated shape data acquisition step. In the feature point extraction step, for example, as shown in part C of FIG. 6, feature points common to the shape data of the grindstones 14 and 18 acquired in the first shape measurement step and the shape data of the grindstones 14 and 18 acquired in the second shape measurement step are extracted. Subsequently, in the estimated shape data acquisition step, based on these feature points, by synthesizing the shape data of the grindstones 14 and 18 acquired in the first shape measurement step and the shape data of the grindstones 14 and 18 acquired in the second shape measurement step, estimated shape data is acquired.

[0034] Here, since the shape data of the grindstones 14 and 18 obtained in the second shape measurement step is measured with the grindstones 14 and 18 tilted, it is data only on the shape of a part (one end) of the grindstones 14 and 18, and the overall shape and position of the grindstones 14 and 18 are unknown. On the other hand, in the shape data acquisition step, since the shape data obtained in the second shape measurement step is fitted to the shape data obtained in the first shape measurement step, it becomes possible to accurately grasp the overall shape and position of the grindstones 14 and 18.

[0035] Also, in the first shape measurement step, as shown in part D of FIG. 7 for example, the shape data of the upper surfaces of both ends of the grinding wheel 14 before tilting and its center position (grinding wheel rotation axis At1) can be measured. Further, in the second shape measurement step, as shown in part E of FIG. 8 for example, the shape data of the upper surface of one end (left side of the paper) of the grinding wheel 14 after tilting can be measured. And in the shape data acquisition step, by synthesizing these shape data, as shown in FIG. 9, the estimated shape data of the grinding wheel 14 after tilting and its center position (grinding wheel rotation axis At1) can be obtained. Note that in FIGS. 7 to 9, an example of measuring and synthesizing the shape data of the grinding wheel 14 is given, but the same measurement and synthesis are also performed on the shape data of the grinding wheel 18.

[0036] Also, as shown in FIG. 7 for example, the vicinity of the contact point between the grinding wheel 14 (and the grinding wheel 18) and the work W often tilts, and the error of shape measurement tends to be large. Therefore, in the second shape measurement step, it is preferable to measure the shape data with the grinding wheels 14 and 18 tilted to a state close to the tilting angle during actual machining. By synthesizing the shape data measured in this way with the shape data obtained in the first shape measurement step, the overall shape data of the grinding wheels 14 and 18 can be obtained with high precision. As a result, in the contact point calculation step described later, the contact point during machining can be calculated with high precision.

[0037] <Contact Point Calculation Step> In the contact point calculation step, based on the estimated shape data obtained in the shape data acquisition step, the contact points between the grinding wheels 14 and 18 and the work W with a desired curvature are calculated (step S4). Specifically, the "contact point" refers to the trajectory (also called the turning trajectory) of the contact points between the two when the grinding wheels 14 and 18 are turned around the turning center axis Ac to machine the work W.

[0038] <Tilt Angle Calculation Step> In the tilt angle calculation step, based on the contact points calculated in the contact point calculation step, the tilt angles of the grinding wheels 14 and 18 around the turning center axis Ac set in actual machining are calculated (step S5).

[0039] <Processing Step> In the processing step, the grinding wheels 14 and 18 are set to the inclination angles calculated in the inclination angle calculation step, and spherical grinding of the workpiece W is performed (step S6).

[0040] Here, in the spherical grinding of the workpiece W, as described above, for example, due to limitations in equipment accuracy, etc., there may be an error between the theoretically (simulationally) turning center axis Ac and the actual turning center axis (true turning center axis) Ac. Therefore, in the spherical grinding method according to the embodiment, the true turning center axis Ac may be obtained.

[0041] In this case, in the second shape measurement step, with the grinding wheels 14 and 18 inclined at a plurality of different angles with respect to the turning center axis Ac, the shape of the grinding wheels 14 and 18 is measured by the shape measurement mechanism 22. Then, based on the shape data of the grinding wheels 14 and 18 before inclination measured in the first shape measurement step and the shape data of the plurality of grinding wheels 14 and 18 measured in the second shape measurement step, a turning center axis estimation step for estimating the true turning center axis Ac is performed. Note that this turning center axis estimation step may be performed after the second shape measurement step and before the inclination angle calculation step.

[0042] Subsequently, in the fifth step, using the true turning center axis Ac estimated in the turning center axis estimation step, the inclination angle of the grinding wheels 14 and 18 with respect to the turning center axis Ac, which is set in actual processing, is calculated.

[0043] The method for estimating the true turning center axis Ac in the turning center axis estimation step will be described with reference to FIGS. 10 to 12. Hereinafter, as shown in the same figure, the description will be made on the premise that there is an error between the theoretically turning center axis (denoted as "turning center axis (Sim)") and the true turning center axis (denoted as "turning center axis (actual)"). Further, FIG. 11 shows the case where the inclination angle θ of the grinding wheel is "20°", and FIG. 12 shows the case where the inclination angle θ of the grinding wheel is "40°".

[0044] First, as shown in FIG. 10, draw a circle with a radius rt from the center of rotation axis (Sim) to the end (corner) of the grinding wheel, and a circle with a radius rf from the center of rotation axis (actual) to the end of the grinding wheel. Subsequently, based on the angles θt0 and θf0 from the center of rotation axis (Sim) and the center of rotation axis (actual) to the end of the grinding wheel before tilting, and the tilting angle θ = 20° of the grinding wheel shown in FIG. 11, apply the equation of the circle to obtain the coordinates (yct1, zct1) of the theoretical grinding wheel position (denoted as "grinding wheel position (Sim)") and the coordinates (yft1, zft1) of the actual grinding wheel position (denoted as "grinding wheel position (actual)"). Then, based on these coordinates, obtain the deviation amounts Δy1 and Δz1 of the grinding wheel position (actual) with respect to the grinding wheel position (Sim).

[0045] Subsequently, based on the angles θt0 and θf0 from the center of rotation axis (Sim) and the center of rotation axis (actual) to the end of the grinding wheel before tilting, and the tilting angle θ = 40° of the grinding wheel shown in FIG. 12, apply the equation of the circle to obtain the coordinates (yct2, zct2) of the theoretical grinding wheel position (denoted as "grinding wheel position (Sim)") and the coordinates (yft2, zft2) of the actual grinding wheel position (denoted as "grinding wheel position (actual)"). Then, based on these coordinates, obtain the deviation amounts Δy2 and Δz2 of the grinding wheel position (actual) with respect to the grinding wheel position (Sim). Using the deviation amounts Δy1, Δz1, Δy2, and Δz2 obtained as above, estimate the true center of rotation axis Ac.

[0046] In this way, by comparing the shape data when the grinding wheels 14 and 18 are tilted around the theoretical center of rotation axis Ac with the shape data when the grinding wheels 14 and 18 are tilted around the true center of rotation axis Ac, the coordinates of the true center of rotation axis Ac can be obtained. Thereby, using the coordinates of the true center of rotation axis Ac, the shape and accurate trajectory of the grinding wheels 14 and 18 can be grasped, so that the contact point between the workpiece W and the grinding wheels 14 and 18 and its trajectory (swing trajectory) can be accurately grasped. As a result, the tilting angles of the grinding wheels 14 and 18 required for grinding to a desired curvature can be obtained with high precision. Also, in terms of the curvature and grinding amount of the workpiece W, higher-precision machining quality can be obtained.

[0047] In addition, for example, as shown in FIG. 13, when there is no undulation in the turning orbit around the turning center axis Ac of the grinding wheels 14 and 18, as described above, by calculating the contact point in the contact point calculation step or estimating the true turning center axis Ac in the turning center axis estimation step, the inclination angle of the grinding wheels 14 and 18 can be obtained with high precision. On the other hand, for example, as shown in FIG. 14, when there is undulation in the turning orbit around the turning center axis Ac of the grinding wheels 14 and 18, it is assumed that the inclination angle of the grinding wheels 14 and 18 cannot be obtained with high precision only by calculating the contact point in the contact point calculation step or estimating the true turning center axis Ac in the turning center axis estimation step.

[0048] In this case, as described above, in the second shape measurement step, by using the shape data obtained by tilting the grinding wheels 14 and 18 in a state close to the inclination angle during actual machining, even when there is undulation in the turning orbit, the inclination angle of the grinding wheels 14 and 18 can be obtained with high precision.

[0049] It is also assumed that the inclination angle during actual machining of the actual workpiece W is slightly changed (corrected) from the inclination angle during measurement in the second shape measurement step. In this case, as described above, by estimating the true turning center axis Ac in the turning center axis estimation step, the inclination angle of the grinding wheels 14 and 18 can be obtained with high precision.

[0050] According to the spherical grinding method and the spherical grinding apparatus according to the present embodiment described above, by estimating the shape data of the grinding wheels 14 and 18 when the grinding wheels 14 and 18 are tilted with respect to the turning center axis Ac, data on the exact contact point between the grinding wheels 14 and 18 and the workpiece W can be obtained. Thereby, the workpiece W can be ground with high precision.

[0051] Also, according to the spherical grinding method and the spherical grinding apparatus according to the present embodiment, even when machining a micro-diameter lens such as Φ1 mm for an endoscope that requires a high precision of, for example, 1 μm or less, grinding can be completed in one pass without repeating the finish evaluation and the chasing operation by repeated adjustment machining. Therefore, it can lead to an improvement in productivity and a significant cost reduction.

[0052] Further, in the spherical grinding method and spherical grinding apparatus according to the present embodiment, shape data near the contact points between the grinding wheels 14 and 18 and the workpiece W, where optical measurement errors are likely to occur, is synthesized and corrected by measurement data at a plurality of inclination angles, so that a more accurate grinding wheel shape can be obtained. As a result, the estimation error of the contact points between the grinding wheels 14 and 18 and the workpiece W is reduced, and high-precision machining is achieved.

[0053] Also, by using the spherical grinding method and spherical grinding apparatus according to the present embodiment, the shape of the grinding wheels 14 and 18 after machining the workpiece W, that is, the wear amount of the grinding wheels 14 and 18, can be calculated. Therefore, for example, the curvature correction during continuous machining of the workpiece W can be automated and made more accurate.

[0054] That is, conventionally, quality inspection was performed after machining the workpiece, and based on the quality inspection results, the curvature of the next workpiece was corrected each time. On the other hand, in the spherical grinding method and spherical grinding apparatus according to the present embodiment, the wear amount of the grinding wheels 14 and 18 is calculated based on the shape measurement results performed before machining the workpiece W, and based on the wear amount, the curvature of the workpiece W can be automatically corrected.

[0055] Also, conventionally, for example, the curvature of the workpiece was corrected by adjusting the swivel angle of the grinding wheel, but in the spherical grinding method and spherical grinding apparatus according to the present embodiment, by moving the workpiece W in the Y-axis direction, the curvature of the workpiece W can be corrected with high precision. That is, the curvature of the workpiece W can be finely adjusted by shifting the workpiece W in the Y-axis direction (see FIG. 1 for example) by the workpiece holding mechanism 11.

[0056] Also, conventionally, the shape of the grinding wheel was measured every time the workpiece was machined, but in the spherical grinding method and spherical grinding apparatus according to the present embodiment, for example, the shape of the grinding wheels 14 and 18 is measured after machining several workpieces W, and if correction of the curvature of the workpiece W is necessary, the correction can be performed.

[0057] As described above, the spherical grinding method and the spherical grinding apparatus according to the present invention have been specifically described in terms of the embodiments for carrying out the invention. However, the gist of the present invention is not limited to these descriptions and should be broadly interpreted based on the descriptions in the claims. Needless to say, various changes and modifications based on these descriptions are also included in the gist of the present invention.

[0058] For example, in this embodiment, as shown in FIG. 3, the spherical grinding apparatus 1 including the grinding wheel 14 for rough grinding and the grinding wheel 18 for finish grinding has been introduced as an example. However, a configuration including only one of the grinding wheel 14 for rough grinding and the grinding wheel 18 for finish grinding, or a configuration including three or more types of grinding wheels may also be acceptable.

[0059] In addition, the work holding mechanism 11 (see FIG. 3) in this embodiment may adjust the thickness of the work W by controlling the work W in the Z-axis direction. In this embodiment, the description has been made assuming that the work W to be processed is mainly a lens. However, as long as it is an object capable of spherical grinding, it may be other than a lens. Also, the material of the work W can be appropriately selected. For example, of course glass, but also something that can be ground such as sapphire or ceramic may be selected.

[0060] In addition, in this embodiment, a laser displacement meter has been exemplified as the shape measurement mechanism 22 (see FIG. 3). However, in addition to the laser displacement meter, various measurement mechanisms capable of optical, mechanical, surface, strip-shaped or linear measurement can be used. Also, in this embodiment, cup-shaped grinding wheels are used as the grinding wheels 14 and 18. However, the particle size and type of the grinding wheel can be appropriately selected according to the required quality of the work W.

Explanation of Reference Numerals

[0061] 1 Spherical grinding apparatus 11 Work holding mechanism 12 Work rotation mechanism 13 Retraction mechanism 14 Grinding wheel (first grinding wheel) 15 Grinding wheel holding mechanism 16 Grinding wheel rotation mechanism 17 Grinding wheel swiveling mechanism 18 Grinding wheel (second grinding wheel) 19 Grinding wheel holding mechanism 20 Grinding wheel rotation mechanism 21 Grinding wheel swiveling mechanism 22 Shape measurement mechanism 23 NC movement mechanism 24 Measurement control mechanism 25 Data processing device 26 Machining control mechanism 27 Reference surface Ac Swiveling center axis Ao Optical axis At1 Grinding wheel rotation axis At2 Grinding wheel rotation axis O Equipment origin St1,St2 Grinding wheel reference W Workpiece

Claims

1. A first step of measuring, from above, the shape of the cup-shaped grinding wheel while the grinding wheel is disposed upward without being inclined with respect to the rotation center axis for rotating the grinding wheel by a shape measuring mechanism; A second step of measuring, from above, the shape of the grinding wheel disposed at a predetermined angle while the grinding wheel is inclined with respect to the rotation center axis by the shape measuring mechanism; A third step of obtaining estimated shape data when the grinding wheel is inclined with respect to the rotation center axis by synthesizing the shape data of the grinding wheel obtained in the first step and the shape data of the grinding wheel obtained in the second step; A fourth step of calculating a contact point between the grinding wheel and a work having a desired curvature based on the estimated shape data; A fifth step of calculating an inclination angle of the grinding wheel with respect to the rotation center axis, which is set in actual machining, based on the contact point; A sixth step of setting the grinding wheel at the inclination angle and performing spherical grinding of the work; A spherical grinding method including the above steps.

2. The third step includes: A feature point extraction step of extracting feature points common to the shape data of the grinding wheel obtained in the first step and the shape data of the grinding wheel obtained in the second step; An estimated shape data acquisition step of synthesizing the shape data of the grinding wheel obtained in the first step and the shape data of the grinding wheel obtained in the second step based on the feature points to obtain the estimated shape data; The spherical grinding method according to claim 1, including the above steps.

3. In the second step, while the grinding wheel is inclined with respect to the rotation center axis at a plurality of different angles respectively, the shape of the grinding wheel is measured by the shape measuring mechanism, The method further includes a rotation center axis estimation step of estimating a true rotation center axis based on the shape data of the grinding wheel measured in the first step and the shape data of the plurality of grinding wheels measured in the second step; The fifth step further uses the true turning center axis to calculate the inclination angle. The spherical grinding method according to claim 1 or claim 2.

4. A work holding mechanism for holding a work, A work rotation mechanism for rotating the work holding mechanism around a work rotation axis, A grindstone holding mechanism for holding a cup-shaped grindstone, A grindstone rotation mechanism for rotating the grindstone around a grindstone rotation axis, A grindstone turning mechanism for turning the grindstone rotation mechanism around a turning center axis perpendicular to the grindstone rotation axis, A shape measurement mechanism having an optical axis as an axis parallel to the work rotation axis, An NC movement mechanism for moving the shape measurement mechanism in three-dimensional directions, A retraction mechanism for retracting the work holding mechanism to a position away from the grindstone rotation axis, A measurement control mechanism for controlling the shape measurement mechanism and the NC movement mechanism to measure the shape of the grindstone in a state where the grindstone holding mechanism is not inclined with respect to the turning center axis and the shape of the grindstone in a state where the grindstone holding mechanism is inclined with respect to the turning center axis, respectively, A data processing device that synthesizes the shape data of the grindstone acquired by the measurement control mechanism and calculates the inclination angle of the grindstone holding mechanism for obtaining a work with a desired curvature from the data of the contact point between the work and the grindstone when the grindstone holding mechanism is inclined at a desired angle with respect to the turning center axis, A processing control mechanism for controlling the grindstone turning mechanism based on the output result of the data processing device, comprising The measurement control mechanism controls the shape measurement mechanism and the NC movement mechanism so that the shape of the upwardly disposed grindstone can be measured from above in a state where the grindstone holding mechanism is not inclined with respect to the turning center axis, Controlling the shape measurement mechanism and the NC movement mechanism so that the shape of the grinding wheel disposed at a predetermined angle can be measured from above in a state where the grinding wheel holding mechanism is inclined with respect to the turning center axis. Spherical grinding device.

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