JP2829103B2 - Cutting method and cutting device for plastic lens - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for cutting a plastic lens suitable for cutting a lens surface of a plastic lens used for spectacles and optical equipment.

(Prior art and problems to be solved) In order to finish a lens surface of a plastic lens used for eyeglasses or optical equipment to a desired spherical or aspherical surface, conventionally, a plastic material is firstly roughened with a grinder. After forming a convex or concave surface, it is common to repeat polishing in the order of rough polishing, medium polishing, and finish polishing, and then apply a coating to the finished optical component.

In such a conventional processing system, it is necessary to go through many complicated steps, and there is a problem that a highly skilled technique is required and processing is time-consuming. Moreover,
When polishing a spectacle lens, a number of lenses with different powers, such as those for myopia, hyperopia, astigmatism, etc.
It is necessary to prepare as many as 1000 types of polishing dies, which requires a large space for accommodating these dies, and there is a problem that the polishing agent scatters around during processing and the working environment is not favorable. Furthermore, considering the setup time for the preparation of the mold and the like, a certain amount of lenses are processed at a time in terms of production efficiency, but there is a problem that the distribution inventory and the amount of work in process increase.

Therefore, it is required to omit a polishing step which requires many steps and finish the material into a required shape only by cutting using an ultra-precision lathe. However, as shown in FIG. 9, the conventionally known curved surface cutting method has the following problems.

In the conventional cutting method shown in FIG. 9, a work, for example,
The material a of the plastic lens is held by a chuck (neither is shown) attached to the main shaft so that the center SCL of the main shaft coincides with the optical axis of the cut material a, and this is rotated to the center SCL of the main shaft. Then, the diamond tool b is moved in the Χ-axis direction and the Z-axis direction to form a required lens surface c. In this case, the cutting tool b moves in a direction perpendicular to the spindle center SCL (主 -axis direction) and in the same direction (Z-axis direction).

In this conventional cutting method, the cutting tool b is sent from the outer periphery of the material a toward the center SCL in the Χ-axis direction, and is also sent in the Z-axis direction, and is moved on an arc in the Χ-Z-axis plane, thereby obtaining rotational symmetry. Can be obtained. However, there is a problem that the cutting speed becomes zero in the vicinity of the center LC of the lens a. In this center LC, a so-called “navel” is easily formed, and it is difficult to increase the processing accuracy near the center LC. .

The present invention has been made in order to solve the problems as described above, and does not require a polishing step, is ultra-precise, and in a short time, a method and a method for cutting a plastic lens that can easily process a lens surface. It is intended to provide a device.

(Means for Solving the Problems) In the method of cutting a plastic lens according to the present invention, the main axis on which the work is mounted is defined by the relative feed direction of the cutting tool to the work, and the に 対 し て -axis direction and the Z-axis direction which are orthogonal to each other. The angle between the optical axis of the cut work and the center line of the main axis is set to 30 ° or more, and preferably, at least a part of the cut surface of the work to be a product is a Χ axis (Z = 0). ) Or the Z-axis (０ = 0) so that the work is rotated, and the coordinate value of the cutting tool is monotonously increased or decreased with respect to any one of the Χ-axis and the Z-axis during the curved surface machining. Direction, and during the feed in one direction, feed only in the direction of monotonically increasing or decreasing the coordinate value of the other axis, and cut the cutting tool made of a material whose crystal structure is a single crystal in the Χ axis direction. Yohi Z axis In which the surface to be cut is cut into a required curved surface.

When the cutting tool is moved on an arc on the Χ-Z axis plane by an arc interpolation method to cut the surface to be cut, and the center of the interpolation radius of the arc coincides with the center line of the main axis, the light When a spherical lens that is rotationally symmetric with respect to the axis does not have the center of the interpolation radius of the arc coincident with the center line of the main axis, an aspheric lens that is rotationally asymmetric with respect to the optical axis can be obtained.

Further, according to the present invention, there is provided a tool rest which holds a cutting tool made of a material having a single crystal structure and is relatively movable with respect to a workpiece in a Χ-axis direction and a Z-axis direction perpendicular to each other. A main shaft that rotates about a center line that is inclined with respect to the axial direction and the Z-axis direction, and an angle formed between the optical axis of the cut work and the center line of the main shaft attached to the main shaft is 30 ° or more, and Work support means for supporting the work at a position where at least a part to be a product out of the cut surface of the work does not intersect the Χ axis (Z = 0) or the Z axis (Χ = 0), and a blade holding the cutting tool A driving means for moving the base relative to the workpiece, rotating the main spindle, and at the time of final finish cutting, the tool post is moved in only one direction of each of the Χ axis and the Z axis to the surface to be cut. Corresponding to the required curved surface to be formed Cutting device of a plastic lens which comprises causing moved is provided.

(Function) The angle between the optical axis of the machined workpiece and the center line of the spindle
When the work is rotated around the spindle center line at 30 ° or more, the cut surface of the work is arranged at a position separated from the spindle center line, and the cutting speed on the cut surface becomes zero.
No so-called "navel" does not occur.

Preferably, of the surface to be cut of the work, at least a part to be a product is rotated around the central axis of the main shaft so as not to intersect the Χ axis or the Z axis, and the lens surface which is the surface to be cut is cut. At the time of finish cutting, the cutting tool only needs to be fed in one direction of each of the Χ axis or the Z axis along the surface to be cut, and the problem of backlash occurring in the feed device of the cutting tool can be avoided.

A cutting tool made of a material having a single-crystal structure, preferably a single-crystal diamond tool, has a spherical cutting edge and ensures high cutting accuracy and surface roughness required for finish cutting. When the angle between the optical axis of the cut work and the center line of the main shaft is set to 30 ° or more and the work is rotated around the center line of the main shaft, the difference in the radius of rotation of the cut work due to the mounting location is small, The change rate of the cutting speed generated between the diamond tool and the diamond tool is small, and in combination with the use of the cutting tool having the single crystal structure described above, the surface roughness required for cutting the lens surface is 0.5.
Processing with an accuracy of μm or less is possible.

The angle between the optical axis of the machined workpiece and the center line of the spindle is
If it is less than 30 °, the rate of change of the cutting speed in the surface to be cut becomes large, and the cutting speed becomes excessive in some places, so that the life of the cutting tool is shortened.

In this cutting method, when the cutting tool by the circular interpolation cutting method is moved on the arc of Χ and Z axes with the interpolation radius R, the position where the optical axis of the cut work intersects the center line of the main axis is determined by the above interpolation radius. By making it coincide with the center of R, a rotationally symmetric spherical surface with respect to the optical axis is obtained, and when not making it coincide, a rotationally asymmetric aspherical surface is obtained, which is suitable for cutting these spherical and aspherical surfaces. is there.

(Example) Hereinafter, an example of a method and an apparatus for cutting a plastic lens of the present invention will be described in detail with reference to the drawings.

The processing of the plastic lens is performed according to the procedure shown in FIG. First, an 80 mm round, 10 mm thick lens material is prepared. This lens material is made of a synthetic resin suitable for a spectacle lens, and the material is not particularly limited.

Next, rough cutting is performed by an NC lathe, and both surfaces of the lens material are cut into a curved surface, leaving a required cutting allowance. This rough cutting step does not require a particularly high cutting precision, so that it may be processed by a conventional known NC lathe, or a lathe to which the method of the present invention is applied may be used.

When the rough cutting step is completed, ultra-precision cutting by the method of the present invention is performed. Although the details of the finish cutting process will be described later, each surface of the lens is finished by a double bite feed process using an ultra-precision lathe, and the finishing process is completed, and is the same as that obtained in the conventional finish polishing process. Processing with a certain degree of surface roughness is possible.

After finishing cutting, the lens surface is coated in a coating process as in the conventional case, and a product is obtained.

Next, the ultra-precision cutting and the ultra-precision lathe according to the method of the present invention will be described.

FIG. 2 is a schematic diagram showing a main configuration of an ultra-precision lathe to which the method of the present invention is applied, a headstock 2 rotatably supporting a main shaft 4, a moving device 10 for moving a tool post (not shown),
A chuck (work supporting means) 14 attached to the main shaft 4 and supporting the work W is constituted by a not-shown CNC control device and the like.

The Z-axis table 6 of the moving device 10 is mounted on a bed (not shown), and can be moved only in the Z-axis direction by a Z-axis motor (not shown). The feed speed and the feed amount are also controlled by a control device (not shown). You. The Z-axis table 8 is mounted on the Z-axis table 6, and the Χ-axis table 8 can be moved only in the Χ-axis direction orthogonal to the Z-axis on the Z-axis table 6 by the Χ-axis motor (not shown). The feed speed, feed amount, and the like of the Χ axis table 8 are also controlled by the control device.
A tool post (not shown) is fixedly mounted on the 刃 -axis table 8 of the moving device 10. A diamond tool 12 of a cutting tool, which will be described in detail later, is attached to the tool rest by being held by a tool holder 13.

The spindle 4 is driven to rotate by a spindle motor 4a. The center line SCL is disposed so as to be inclined with respect to both the Χ axis and the Z axis, and the inclination angle α (FIG. 4) with respect to the Z axis is preferably set to 45 degrees for the reason described later. You. The moving device 10 may be placed on a table that rotates on the above-described bed, and the angle α between the spindle center SCL and the Z-axis may be arbitrarily set.

As shown in FIGS. 2 and 3, the chuck 14 attached to the main shaft 4 has a cup shape in which the tool post side is open, and the bottom wall is fixed to the end surface of the main shaft 4 with bolts or the like. A round hole 14a is opened in the peripheral wall of the chuck 14, and a holder (support means) 15 is fitted into the hole 14a and fixed by a bolt, a chuck or the like.

The holder 15 attached to the chuck 14 has the spindle center SCL
The workpiece 1 has a spherical surface 15a having a predetermined curvature for mounting the workpiece W, and the chuck 1 has a normal line passing through the center of the spherical surface 15a, that is, the optical axis of the finished workpiece W is orthogonal to the main axis center SCL.
Mounted on 4. The work W whose one surface is finished to the above-mentioned predetermined spherical surface is attached to the holder 15 by bonding with an adhesive.

As the tool 12 attached to the tool holder 13, a material having a single crystal structure, for example, a tool made of diamond is used. Such a cutting tool has a R
Cutting with high accuracy and high shape accuracy is possible.

As will be described in detail later, the CNC control device, as will be described in detail later, inputs a cutting condition such as an interpolation radius R, a center position coordinate, and a cutting start position coordinate by an arc interpolation cutting method. Table 8, Z axis table 6
Are automatically controlled.

Next, the cutting method of the present invention will be described together with the operation of the cutting device configured as described above.

First, the work W is mounted on the holder 15. In the work W, the convex surface and the concave surface are subjected to rough cutting in the previous process, leaving a required cutting allowance. In the case of the embodiment shown in these figures, the convex surface of the work W is The spherical surface 15a is bonded and fixed with an adhesive. Then, the holder 15 to which the work W is attached is screwed and fixed to the chuck 14. At this time, as shown in FIGS. 3 and 4, the workpiece W has an optical axis LA at the time of cutting the center line of the main shaft 4.
It is attached to the chuck 14 so as to be orthogonal to the SCL.
That is, the optical axis LA and the center line SC of the main shaft 4 when cut.
The intersection angle β formed with L is 90 ° (see FIG. 4). For this reason, the work W is separated from the center line SCL, and the cutting speed is not 0 at any part of the cutting surface of the work W, and the rate of change of the cutting speed in the work cutting surface can be suppressed to a small value. The work W can be rotated at a cutting speed necessary for ensuring cutting accuracy in any part of the plane. At this time, the workpiece W is placed on the workpiece cutting surface 15a.
Is rotated about the center line SCL by the radius _RA .

Then, the cutting tool 12 is fed in the Χ-axis direction and the Z-axis direction along the arc on the Χ-Z-axis plane by a conventionally known arc interpolation cutting method. That is, when the interpolation radius R _B , its center position coordinate, and the cutting start position are input to the above-described CNC control device, circular interpolation calculation is executed, and each feed of the Χ axis and Z axis at each position coordinate on the circular arc of the cutting tool 12 is performed. The quantities are determined sequentially. Then, the respective axis motors of the 軸 -axis table 8 and the Z-axis table 6 are driven in accordance with the determined feed amount, and the cutting tool 12 is sent along the set arc on the Χ-Z-axis plane. .

Various lens is obtained by the center position of the interpolation radius R _B at this time. 5 to 7 show the above radius R _A and
Demonstrating the relationship of R _B , when the centers of these radii are located (R _A = R _B ), a spherical lens rotationally symmetric with respect to the optical axis is obtained, and when they do not match (R _A ≠ R _B ), A rotationally asymmetric aspheric lens is obtained. Also, as shown in FIG. 8, when the center position of the interpolation radius R _I of the concave surface of the work W is shifted from the center line passing through the center position of the interpolation radius R _O of the convex surface, a bifocal spectacle lens can be obtained. become.

Then, as shown in FIG. 2 or FIG. 4, the workpiece W is such that at least a part to be a product of the cut surface does not intersect with the Χ axis (Z = 0) or the Z axis (Χ = 0). And attached to the chuck 14. Even if a part that does not become a product intersects the Χ axis or the Z axis, that part is cut off, so that even if the cutting accuracy of that part is poor, it does not matter. When the surface to be cut is a curved surface like a plastic lens, it is necessary that the curve on the Χ-Z-axis plane of the curved surface monotonically increases or decreases with respect to the Χ-axis or Z-axis coordinates. When the coordinate value monotonically increases or decreases, the tool rest can be moved only in one direction (in a fixed direction) of each of the Χ axis and the Z axis. As a result, it is possible to eliminate adverse effects on cutting accuracy due to backlash which cannot be avoided in this type of lathe device.

On the other hand, the work W 'shown by a virtual line in FIG.
Since the surface to be cut is disposed so as to intersect the Χ axis, the position where the lens surface of the work W ′ intersects the Χ axis (Z =
It is necessary to feed the tool post in the opposite direction with respect to the を axis at (0 position). At this point, the adverse effect of backlash occurs. In addition, at the mounting position of the workpiece W ″ indicated by the imaginary line in FIG. 4 (in this case, the surface to be cut intersects the Z axis), the position where the lens surface intersects the Z axis (position of Χ = 0) It is necessary to feed the tool post in the opposite direction with respect to the Z-axis at the boundary, and the adverse effect of backlash occurs at this point.

In the case of cutting the lens surface, the workpiece W is preferably mounted at a position where the feed amount is substantially the same in each direction of the Χ axis and the Z axis by the axis motor. Therefore, the main shaft 4 is moved in the Χ axis direction and the Z axis direction. It is desirable that each of them is inclined at 45 degrees. In this case, the inclination may be substantially 45 degrees, and the inclination angle may deviate from 45 degrees within a range of several degrees. By doing so, the rate of change of the cutting speed is minimized, and
Since the minimum value of the turning radius of the work becomes large, it is possible to select the tool holder 13 having the largest thickness (turnability).

When the work W is completed as described above,
12 is moved to a position immediately before cutting, and rotation of the spindle 4 is started. The rotation speed of the main shaft 4 at this time depends on the material of the work W, but a plastic lens is cut with a diamond bite, and a proper processing time (for example, 1 minute to 5 minutes to cut one lens surface). In order to obtain the required surface roughness (for example, 0.5 μm or less) in
It is desirable to set it so as to be not less than 00 m / min and not more than 1500 m / min.

When the cutting speed is 200 m / min or less, a long processing time is required. When the speed exceeds 1500m / min, the cutting surface becomes rough,
The life of the diamond tool is shortened.

Next, the control device outputs a drive control signal to the Χ-axis motor and the Z-axis motor, and the cutting tool 12 is operated along the interpolation arc on the Χ-Z-axis plane at the calculated feed speed.
I will send you. At this time, since the cutting edge of the cutting tool 12 used is a diamond having a single crystal structure, the cutting edge R accuracy is high, and the feed rate of the cutting tool 12 is set to 20 to 100 μm / rev. Is obtained.
Then, the finish processing of the surface to be cut can be completed usually by two feeds.

In this manner, the other lens surfaces are cut in the same manner as when the cutting of one lens surface is completed.

In the above-described embodiment, the tool post is used for the workpiece W.
Although it was moved in the axis and Z-axis directions, the tool post is fixed, or for example, it can be moved only in the Χ-axis direction,
On the other hand, the main shaft may be moved in the Χ-axis and Z-axis directions simultaneously with the rotation, or the main shaft may be moved only in the Z-axis direction simultaneously with the rotation.

(Effects of the Invention) As described in detail above, according to the method of cutting a plastic lens of the present invention, the main axis on which the work is mounted is defined by the relative feed direction of the cutting tool to the work, and the Χ-axis direction and the Z direction orthogonal to each other. Each of them is inclined with respect to the axial direction, the angle between the optical axis of the cut work and the center line of the main axis is set to 30 ° or more, and preferably, at least a part of the cut surface of the work, which is to be a product, has a thickness of Χ. The workpiece is rotated so that it does not intersect with the axis (Z = 0) or the Z axis (Χ = 0), and when the curved surface is machined, the cutting value is monotonously adjusted with respect to either the Χ axis or the Z axis. A cutting tool made of a material whose crystal structure is a single crystal, fed only in the direction of increasing or decreasing, and sending only in the direction of monotonically increasing or decreasing the coordinate value with respect to other axes during the feeding in the one direction. The axial direction And in the Z-axis direction to cut the surface to be cut into a required curved surface, so that a polishing step is not required as in the prior art, and the lens surface can be easily formed in an ultra-precise and short time. In the cutting apparatus to which the method according to the present invention can be applied, the tool post is moved relative to the workpiece by the driving means in accordance with a required curved surface to be formed on the surface to be cut. It is possible to relatively move the tool post by simply inputting the interpolation radius and its center position by, for example, an arc interpolation method with a complicated lens surface curved shape. Although various types of polishing dies were required, these dies were not required, and automation of lens production and so-called FM
It is easy to switch to S, and has excellent effects such as the ability to reduce the amount of distribution inventory and the amount of work in process.

[Brief description of the drawings]

FIG. 1 is a flowchart showing steps in processing an optical lens by the cutting method of the present invention, FIG. 2 is a block diagram showing a main configuration of a lathe to which the method of the present invention is applied,
FIG. 3 is an enlarged sectional view of a main part showing details of a holder 15 and a chuck 14 to which the work W is attached, and FIG.
FIG. 5 is a diagram showing the relationship between the mounting position with respect to the Χ, Z axis and the spindle center line SLC, FIG. 5 is a plan view of a lens which is a workpiece, FIG. 6 is a cross-sectional view taken along line VI-VI of FIG. FIG. 7 is a sectional view taken along the line VII-VII of FIG. 5, FIG. 8 is a sectional view of a bifocal spectacle lens, and FIG. 9 shows a conventional method for cutting a lens surface. FIG. 5 is a diagram showing a relationship between a Χ axis, a Z axis, and the like, which are moving directions. 2 ... headstock, 4 ... spindle, 6 ... Z-axis table, 8 ...
… ΧAxis table, 10 …… Moving device, 12 …… Byte, 12a
…… Single crystal diamond bite, 14 …… Chuck, 15…
… Holder, LA …… Optical axis, SCL …… Spindle center, W …… Work.

Claims (6)

(57) [Claims] 1. A spindle for mounting a workpiece is inclined relative to a Χ-axis direction and a Z-axis direction, which are relative directions of a cutting tool relative to the workpiece, and are orthogonal to each other. The angle of the center line is set to 30 ° or more, the work is rotated around the main axis, and a cutting tool made of a material having a crystal structure of a single crystal is moved in the Χ-axis direction and the Z-axis direction to form the cut surface. Cutting a plastic lens into a required curved surface. 2. A cutting tool at the time of machining a curved surface, wherein the workpiece is rotated so that at least a part to be a product out of the cut surface of the workpiece does not intersect with the Χ axis (Z = 0) or the Z axis (Χ = 0). Is sent only in the direction of monotonically increasing or decreasing the coordinate value with respect to one of the Χ axis and the Z axis, and the coordinate value is also monotonically increased with respect to the other axes during the feed in the one direction. 2. The method of cutting a plastic lens according to claim 1, wherein the feeding is performed only in a direction in which the plastic lens is reduced. 3. The method according to claim 3, wherein the cutting tool is formed by a circular interpolation method.
Cutting on the surface to be cut by moving on an arc on the axial plane,
When the center of the interpolation radius of the arc coincides with the center line of the main axis, the rotationally symmetric spherical lens with respect to the optical axis, when the center of the interpolation radius of the arc does not coincide with the center line of the main axis, 3. The method of cutting a plastic lens according to claim 1, wherein an aspherical lens that is rotationally asymmetric with respect to the optical axis is obtained. 4. The method for cutting a plastic lens according to claim 1, wherein the main axis is inclined at substantially 45 degrees with respect to the Χ-axis direction and the Z-axis direction. . 5. The cutting tool is held by a tool rest movable in the Χ-axis direction and the Z-axis direction, and the tool rest is moved with respect to the workpiece at the time of final finishing cutting in one direction of each of the Χ-axis and the Z-axis. The method for cutting a plastic lens according to any one of claims 1 to 4, wherein the surface to be cut is cut only by relative movement. 6. A tool rest which holds a cutting tool made of a material having a single crystal structure and is relatively movable with respect to a workpiece in a Χ-axis direction and a Z-axis direction orthogonal to each other. A main shaft that rotates about a center line that is inclined with respect to the Z-axis direction, an angle formed between the optical axis of the cut work and the center line of the main shaft attached to the main shaft is 30 ° or more; At least the part that becomes the product in the cutting surface is the Χ axis (Z = 0)
Or a work supporting means for supporting the work at a position not intersecting with the Z axis (Χ = 0); and a driving means for relatively moving the tool rest holding the cutting tool with respect to the work, and rotating the spindle. In the final clean cutting, the tool rest is relatively moved only in one direction of each of the Χ axis and the Z axis in accordance with a required curved surface to be formed on the surface to be cut. Cutting equipment.