JP2001220156A - Method and device for forming optical element, and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming an optical element, by which the optical element having a functional surface with high precision can be obtained. SOLUTION: A glass base material is cooled while nearly completely relaxing thermal stress generated in the glass base material 4 in the temperature range of not less that the transition point, where the relaxation action being the viscoelastic property of the glass itself is active, and while hardly relaxing the stress in the glass base material 4 in the temperature range of not mort that the transition point, where the relaxation action hardly functions, so as to prevent stress distribution from being complicated due to incomplete relaxation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding an optical element having a complicated shape, such as an aspherical lens, by press molding.

[0002]

2. Description of the Related Art In recent years, as optical devices have become smaller and lighter, aspherical lenses have been desired as glass lenses used in optical systems. As a method of molding the glass lens having the aspherical shape, a method of molding an optical element by sandwiching an optical element material in a molding die having a predetermined surface accuracy and press molding has been proposed.

This method is disclosed, for example, in Japanese Patent Publication No. 61-3226.
As disclosed in Japanese Unexamined Patent Application Publication No. 3 (1999) -1995, a glass material is sandwiched in a mold having an internal shape exactly corresponding to the final shape of a desired optical element, and the viscosity of the glass material is 108 to 5
Press molding is performed at a temperature in the range of × 1010 dPa · s, and then the temperature difference between the glass material and the mold is at least 2
This is a method of obtaining a high-precision optical element by taking out the glass material from between the molds in a temperature range where the viscosity of the glass material is less than 1012 dPa · s, by cooling so that the temperature does not become 0 ° C. or more.

[0004]

However, even in the molding method of the prior art disclosed in the above publication, the viscosity of the glass material is 108
Since a temperature change from a temperature in the range of ~ 5 × 1010 dPa · s to room temperature is required, and a thermal expansion coefficient between the glass material and the mold member is significantly different, thermal stress occurs in the glass material during cooling. Would. Furthermore, due to the viscoelastic physical properties of glass, the generated thermal stress is relaxed in a form proportional to the distribution of temperature and stress.

As a result, when cooling proceeds to a temperature range in which the glass material is taken out, a complicated stress distribution is generated in the glass material, and the stress is generated when the close contact between the mold member and the glass material is released. However, there is a problem that the optical function surface of the optical element is deformed and the optical accuracy is deteriorated.

The present invention has been made in consideration of the above-described conventional problems, and has as its object to provide a method of forming an optical element and the like capable of obtaining high functional surface accuracy of the optical element. It is another object of the present invention to provide a method for molding an optical element and the like in which the stress in the glass material is controlled by the cooling rate and high functional surface accuracy of the optical element can be obtained. It is a further object of the present invention to provide an optical element molding method and the like that can shorten the molding tact while maintaining high functional surface accuracy of the optical element.

[0007]

In order to achieve the above object, in a method for molding an optical element according to the present invention, a glass material in a softened state is pressed by a molding die member, and then the glass material is pressed. In the method for molding an optical element, which performs a cooling step of cooling a glass material, the cooling step is performed such that a stress relaxation rate in the glass material becomes 90% or more in a temperature range equal to or higher than a transition point of the glass material. In the temperature range below the transition point, cooling is performed such that the stress relaxation rate becomes 10% or less.

According to a second aspect of the present invention, in the method for molding an optical element according to the first aspect, the cooling step includes the step of reducing the stress relaxation rate of the glass material to 9%.
0 ° C. or more until the transition point of the glass material reaches 10 ° C./min. Cooling is performed at the following rate, and then 50% or less at the transition point or lower so that the stress relaxation rate is 10% or less.
° C / min. It is characterized by cooling at the above speed.

According to a third aspect of the present invention, in the method for molding an optical element according to the first aspect, the cooling step is carried out by 60 degrees from a transition point of the glass material.
50 ° C./min. From a temperature set high in the range of 40 ° C. to 40 ° C. to a temperature set high in the range of 20 ° C. to 5 ° C. above the transition point. After cooling at the above rate, the temperature is set to be higher than the transition point in the range of 20 ° C. to 5 ° C. from the transition point to 10 ° C./° C. so that the stress relaxation rate of the glass material becomes 90% or more. min. Cool at the following speed, and then reduce the stress relaxation rate to 10% or less.
Below the transition point, 50 ° C./min. It is characterized by cooling at the above speed.

According to a fourth aspect of the present invention, there is provided an optical element molding apparatus, wherein a molding die member for pressing a glass material in a softened state and cooling of the glass material pressed by the molding die member are controlled. A cooling control means for cooling the glass material so that a stress relaxation rate in the glass material becomes 90% or more in a temperature range equal to or higher than a transition point of the glass material. In a temperature range below the transition point, the stress relaxation rate is 10
%.

According to a fifth aspect of the present invention, in the optical element forming apparatus according to the fourth aspect, the cooling control means controls the stress relaxation rate of the glass material to be 90% or more. Up to the transition point of the glass material at 10 ° C./min. Cooling is performed at a rate of not more than 50 ° C./min. It is characterized by a control configuration for cooling at the above speed.

According to a sixth aspect of the present invention, in the apparatus for molding an optical element according to the fourth aspect, the cooling control means is in a range of 60 ° C. to 40 ° C. from a transition point of the glass material. From the temperature set high in the range of 20 ° C. to 5 ° C. from the transition point, at 50 ° C./min. After cooling at the above rate, the stress relaxation rate of the glass material is 90% or more,
From the temperature set higher in the range of 20 ° C. to 5 ° C. than the transition point to the transition point, 10 ° C./min. Cooling is performed at a rate of 50 ° C./min. Below the transition point so that the stress relaxation rate becomes 10% or less. It is characterized by a control configuration for cooling at the above speed.

In the storage medium according to the present invention,
Press the glass material in the softened state with a molding die member,
A storage medium storing a computer-readable program for executing an optical element molding method for cooling the glass material thereafter, wherein the optical element molding method includes a temperature range equal to or higher than a transition point of the glass material. Then, cooling is performed so that the stress relaxation rate in the glass material is 90% or more, and the stress relaxation rate is 10% in a temperature range below the transition point.
%.

[0014] In the storage medium according to the present invention,
8. The storage medium according to claim 7, wherein the cooling control step is performed at 10 ° C./mi up to a transition point of the glass material so that a stress relaxation rate of the glass material is 90% or more.
n. Cool at the following speed, then reduce the stress relaxation rate to 10%
50 ° C./min.
It is characterized by cooling at the above speed.

In the storage medium according to the ninth aspect,
The storage medium according to claim 7, wherein the cooling control step is performed by setting a temperature higher than the transition point of the glass material in a range of 60 ° C. to 40 ° C. to 20 ° C. from the transition point.
Up to 50 ° C / m up to a higher set temperature in the range of 5 ° C
in. After cooling at the above rate, the glass material is shifted from the transition point by 20% so that the stress relaxation rate is 90% or more.
10 ° C./min. From the temperature set high in the range of 5 ° C. to 5 ° C. to the transition point. Cooling is performed at a rate of 50 ° C./min. Below the transition point so that the stress relaxation rate becomes 10% or less. It is characterized by cooling at the above speed.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a flowchart showing a method for molding an optical element according to a first embodiment of the present invention. FIG. 2 is a cross-sectional configuration view of an optical element molding apparatus for realizing the molding method shown in FIG. 1, and a glass lens is molded using a molding body for molding a concave meniscus lens. This shows a substantially completed state.

In this embodiment, a case will be described in which heavy crown glass (SK12) is used as a glass material to form a concave meniscus-shaped optical element shown in FIG.

First, in FIG. 2, a through-hole is formed in a state where the shaping die 1 is vertically penetrated, and a cylindrical upper mold member 2 is fitted into the upper through-hole. In this state, it is slidably inserted along the vertical direction. A disc-shaped flange portion is formed at the upper end of the upper mold member 2, and this flange portion comes into contact with the upper surface of the molding body 1 from above via a spacer for adjusting the thickness of the lens. Defines the press stroke of the upper die member 2. On the lower surface of the upper mold member 2, a molding surface for pressing the glass material 4 and transferring a desired shape to the surface to form an optical function surface is formed.

On the other hand, a lower mold member 3 formed in a columnar shape like the upper mold member 2 is inserted into the lower through hole so as to be slidable in the up and down direction in a fitted state.

On the upper end surface of the lower mold member 3, a molding surface for transferring a desired shape to the lower surface of the glass material 4 to form an optical function surface is formed.

Further, the thickness of the molded concave meniscus lens (glass material 4) is defined by the flange portion of the upper die member 2 being in contact with the upper surface of the molding die 1, as described above. The thickness of the concave meniscus lens 4 is not changed every time the operation is performed.

On the other hand, an opening hole 1
a, a glass material 4 is supplied to the inside of the shaping die 1 through the opening 1a, and the concave meniscus lens 4 having been formed is taken out of the shaping die 1. It is.

Heaters 5 are arranged in the molding die 1 at the four corners thereof. This heater 5
While heating the molding die 1, the upper die member 2 and the lower die member 3, the molding die 1, the upper die member 2 and the lower die member 3 are heated.
The glass material 4 is heated through. The cooling rate of the glass material 4 is controlled by the programmable temperature controller 10.
Is controlled by

Using the above mold structure, a concave meniscus lens is formed by a forming process according to the present embodiment shown in FIG. The above control method can be realized by storing a program according to the flowchart shown in FIG. 1 in a storage device in the programmable temperature controller 10 and operating the program. FIG. 4 shows a process diagram of the molding temperature and the weight.

The shaping die 1, upper mold member 2 and lower mold member 3 are preheated to a temperature corresponding to predetermined molding conditions (step S11). First, the upper die member 2 is slid upward with respect to the molding die 1. In this state, the glass material 4 heated to a predetermined temperature is supplied onto the molding surface of the lower mold member 3 by an automatic hand or the like (step S1).
2). In this embodiment, the viscosity of the glass material 4 is 10 ^9.5 d.
It is a temperature (620 ° C.) corresponding to Pa · s.

Next, in this embodiment, a load of 4000 N is applied to the glass material 4 and pressed (step S13), and the glass material 4 is gradually crushed in the horizontal direction, and finally, as shown in FIG. The state shown in FIG.
In this state, optical function surfaces to which the shapes of the molding surface of the upper mold member 2 and the molding surface of the lower mold member 3 are transferred are formed above and below the glass material 4.

Thereafter, the molded concave lens (glass material)
4) is cooled (step S14). In this cooling process
In the present embodiment, the glass material 4 is used for the upper and lower mold members 2 and
To prevent uneven peeling between
And the viscosity of glass material 4 is 10 ^10.5Temperature equivalent to dPa · s
Temperature (600 ° C), and apply a 3200N load
Under load, the viscosity of the glass material 4 is 10^13.5dPa ・ s
Cooling is performed to a temperature (530 ° C.) corresponding to the above.

Here, since the transition point of the glass material in this embodiment is 550 ° C., the pressing temperature (620 ° C.)
From 550 ° C. to 550 ° C., cooling is performed at a cooling rate (5 ° C./min.) At which the stress relaxing action of the glass material itself can be expected.

Since the cooling speed is controlled by the programmable temperature controller 10, it is easy to change the cooling speed during the cooling (step S1).
5). After the temperature of the glass material has reached 550 ° C. (transition point), the cooling rate is set to 600 C / min. So that the stress relaxation action of the glass material is hardly involved. The cooling is performed by controlling at a high speed (step S16).

After the above steps, when the temperature has dropped to a predetermined temperature (step S17), the concave meniscus lens (glass material 4) was taken out by an automatic hand or the like (step S18). In this embodiment, the concave lens 4 is taken out at a temperature (500 ° C.) at which the viscosity of the glass material 4 is equal to 10 14 dPa · s.

FIGS. 5A and 5B show the results obtained by examining the optical function surface of the concave meniscus lens formed by the above using a Fizeau interferometer, and the same shape formed by the conventional method without including the process of the present embodiment. FIG. 6 shows the result of the concave meniscus lens shown in FIG. R = 14 in FIG.
6A, axially symmetric deformation in which the center of about three Newton rings becomes high occurs, and R = 15 in FIG.
It can be seen that the surface of No. 5 also has an axially symmetric deformation in which the center of about one Newton ring is lowered. In contrast, the result molded by the process of the present embodiment is:
R = 14 faces (FIG. 5 (a)), R = 155 faces (FIG.
(B)) Both show a clear parallel line with interference fringes,
Almost no deformation has occurred, and by the method of the present invention,
It can be seen that good surface accuracy is obtained.

Further, as a result of continuously forming the concave meniscus lens by the method of the present embodiment, the deformation amount is within one Newton ring or less in the optical function surfaces of all the lenses.

In this embodiment, the stress distribution in the glass material, which is the point of the present invention, is set to 620 ° C. to 550 ° C.
At 5 ° C./min. 60 ° C / 550 ° C to 500 ° C
min. The simulation analysis performed to determine the cooling rate will be described.

For the analysis, general-purpose structural analysis software “MAR
C "(manufactured by Nippon Mark Co., Ltd.) to simulate the thermal stress inside the glass material 4 during the above-described cooling process.

First, as initial data for performing a numerical simulation, data of a model, physical property values, basic boundary conditions, and initial forming conditions are input.

The physical properties of the glass material 4 and the mold members 2, 3 as shown in FIG. 8 are input as data. The relationship between the temperature and the expansion coefficient is as shown in the graph of FIG. 7 for the glass material 4 and the mold members 2 and 3, respectively.

The viscoelastic properties of the glass material 4 shown in FIG. 8 are obtained as follows. That is, first, while maintaining the glass sample in the viscoelastic temperature range at a constant temperature, a bending test is performed in which a constant load is applied in a three-point bending state, and the amount of bending of the sample is measured. Seeking compliance. This is calculated by changing the temperature factor little by little, and as a result, a creep curve shown in FIG. 9 is obtained.

Dc (t, To) = 4bd3 / I3 × v (t) / Wo In the above equation, Dc (t, To) is the creep compliance, b is the width of the test piece, and d is the width of the test piece. Length, I is the distance between spans, v (t) is the deflection at the load point, and Wo is the load.

Since the glass in the viscoelastic temperature range has a simple property in terms of thermorheology, the creep compliance curve at each temperature in FIG. 1 shown
It is summarized in the master curve of the book. In this case, the relationship between temperature and time can be represented by a time / temperature shift factor shown in FIG. That is, the time / temperature shift factor of the glass shown here can be approximated by two straight lines (Alenew's equation) as shown in FIG. 11, and the temperature at the intersection is a temperature slightly lower than the glass transition temperature. is there.

The relaxation modulus (corresponding to the modulus of elasticity of an elastic body) can be taken up as a function of temperature and time due to the effect of a decrease in stress relaxation.
Since the target glass is thermorheologically simple as described above, the master curve shown in FIG. 12 (generally, the master curve of the relaxation modulus in FIG. 12 is the same as the creep compliance in FIG. 10) Approximation by the reciprocal of compliance).

As described above, a viscoelastic substance having a simple thermorheological property, such as glass, is obtained from the master curve of the relaxation modulus shown in FIG. 12 and the time / temperature shift factor shown in FIG. The relaxation elastic coefficient Er (t, To) at a certain temperature and a certain time is obtained, and can be expressed by a hysteresis integral equation (shown below) in the linear viscoelastic theory.

[0043]

(Equation 1) In the above equation, τ is analysis time, σ (t) is stress, ε
(T) is distortion.

Therefore, in order to incorporate the viscoelastic characteristics into the numerical analysis, it is necessary to formulate the master curve of the relaxation elastic coefficient in FIG. 12 and the time / temperature shift factor in FIG. Regarding the time / temperature shift factor in FIG. 11,
Since it can be approximated by the Arenews formula as described above, it is possible to input and analyze the formula of the straight line and the intersection of the straight lines using an analysis program (software program "MARC" manufactured by Nippon Mark Co., Ltd.). It should be noted that the master curve of the relaxation elastic modulus in FIG. 12 can be approximated by the following Plonie expansion.

[0045]

(Equation 2) Here, t'n is an n-th order conversion time, and Ern is an n-th order relaxation elastic coefficient.

Using the above physical property values, the thermal stress in the glass from the start of cooling immediately after the end of the press to the reheating and recooling processes is analyzed.

Since the finite element method is used for the analysis, a model is created by dividing one object into a finite number of regions. FIG. 13 shows a model diagram. The number of regions may be arbitrarily selected according to desired accuracy. In this embodiment, ME as a preprocessor software manufactured by Nippon Mark Co., Ltd.
Using NTAT, the mold part is divided into about 2000 elements and the analysis material part is divided into about 1000 elements. Further, since the object to be studied has an axisymmetric structure, an axisymmetric two-dimensional element is applied to each element.

Further, in the model diagram shown in FIG. 13 as the boundary condition, the temperature of the molding cycle to be input later as the temperature defining condition is directly input directly to the upper surface of the upper die member and the lower surface of the lower die member. In addition, the other surface portions are set to be insulated.

In this embodiment, since the element used in the model is an axially symmetric two-dimensional element, only a forced constraint point is provided in the rotation axis direction (Y direction), and the displacement restriction Direction) does not require a compulsory constraint point. In view of this, in the model diagram shown in FIG. 13, forcible restraint points that do not cause displacement in the rotation axis direction (Y direction) are provided on the entire lower surface of the lower mold member.
Further, a small load 1N is always applied to the upper surface of the upper die member so that the upper die member and the material for analysis do not cause rigid displacement in the rotation axis direction (Y direction).

At this point, the calculation is started. The analysis proceeds in a minute time Δt, but first, a calculation of a so-called initial state is performed. In the present embodiment, it is assumed that the stress in all models at time 0 is completely zero. Regarding the temperature distribution, there is no distribution in the model at time 0, and the cooling process after pressing is calculated. Therefore, it is assumed that the initial temperature is constant at 620 ° C. which is the pressing temperature for all elements.

Next, the analysis proceeds by Δt at a time.
The progress procedure and the analysis flowchart depend on the analysis software used.

In the software used in the present embodiment, the time is advanced by Δt, and a non-stationary nonlinear heat conduction equation σc = (∂T / ∂t) = k ｛(∂ ² T / ∂x ² ) + (∂ ² T / {Y ² ) + (∂ ² T / ∂z ² )｝ + Q are all solved for each node, and first, a heat conduction analysis for obtaining a temperature distribution in the model is performed.

Where T is temperature and is a function of the space x, y, z and time t. σ is density, c is specific heat, k is thermal conductivity, and σ, c, and k are each a function of temperature T. Q is an internal heat generation value, which is 0 in the present embodiment.

Thereafter, the balance equation of force (力 σ _x / ∂x) + (∂τ _yz / ∂y) + (∂τ _zx / ∂
z) + X = 0 is calculated for each xyz component for each node, and stress deformation analysis is performed.

The above equation is an equation for the x component. Here, σ is stress, τ is shear stress, and x, y, and z represent coordinate components. X is the x component of the external force.

As described above, one step of the analysis is completed, and the next step is calculated by advancing the time by Δt. The analysis ends when the total time for the calculation is reached. In the present embodiment, an analysis is performed on a cooling process from the model pressing temperature of 620 ° C. to room temperature (20 ° C.).

The results of the analysis are shown by expressing the stress distribution in the glass material by contour lines. 14 shows an analysis result obtained by simulating the process of the present embodiment, and FIG.
/ Min. This is the result when cooling is performed at a constant speed.
The maximum and minimum stress values in both figures are 4.52 kg in FIG.
/ Mm ² , minimum 4.33 kg / mm ² , maximum in FIG.
12 kg / mm ^2, was minimal -2.18kg / mm ^2. In the sign, + indicates a compression field, and-indicates a tension field.

From these results, it can be seen that there is not much difference between the maximum values of the stress generated in the glass material in both processes. However, in the above experimental results (FIGS. 5 and 6), there is a clear difference in optical function surface accuracy.

From the above, it can be seen that the accuracy of the optically functional surface is affected by the distribution more than the maximum value of the stress, and the molding process according to the present embodiment is very effective in reducing the stress distribution. It is found that it is effective.

This simulation was performed with various combinations of cooling rates. As a result, for the combination of glass type and lens shape of the present embodiment, the cooling rate above the transition point of the glass material is 5 ° C./min. Before and after is optimal. At a speed higher than this, the stress relaxation effect cannot be provided, and the stress distribution becomes severe. At a speed lower than that, the difference in the stress distribution is so large.
in. To decide.

The cooling rate below the transition point of the glass material is 600 C / min. At the following speeds, the relaxation effect of the glass material itself becomes large, and the stress distribution is also severe. Further, if cooling is performed at an excessively high speed, a molding defect that the glass material is broken in actual molding occurs.
in. Set as Note that this combination of cooling rates does not correspond to all combinations because the state of stress generation varies depending on the type of glass and the shape of the lens. The above cooling rate is optimal for the combination of glass type and lens shape in the present embodiment.

In this way, the cooling rate of the present embodiment is determined from the analysis of the stress in the glass material by simulation.

As described above, according to the method for molding an optical element shown in the present embodiment, in the temperature range above the transition point where the relaxation action, which is the viscoelastic property of the glass itself, is active, it occurs in the glass material. At the transition point below which the thermal stress can be almost completely relaxed and the relaxation action can not be expected, the cooling in the glass material is cooled almost without relaxing the stress in the glass material in order to prevent the stress distribution from becoming complicated due to incomplete relaxation, It becomes possible to mold an optical element, which was conventionally difficult to mold, with high precision.

[Second Embodiment] FIG. 16 shows a second embodiment of the present invention.
5 is a flowchart illustrating a method for molding an optical element according to an embodiment. FIG. 17 is a sectional configuration diagram of an optical element molding apparatus for realizing the molding method shown in FIG.

In the present embodiment, the glass material is made of flint glass (F8), and the optical element to be formed is formed into a convex meniscus shape as shown in FIG. Since the lens shape to be molded is different from that of the first embodiment, the molding apparatus used is different in the molding surface shape of the optical function surface of the upper mold member 2a and the lower mold member 3a as shown in FIG. The parts are the same.

Next, a molding method of the present embodiment using the above-described mold structure will be described with reference to FIG. The above-described control method can be realized by storing and operating the program according to the flowchart shown in FIG. 16 in the storage device in the controller 10.

As compared with the first embodiment, since the glass material 4a is flint glass (F8), the temperature is 520.degree.
It can be molded sufficiently with a load of N. Next, when the temperature reaches 500 ° C., 4
Cool to 30 ° C. (Step S21, Step S2
2. Step S23). FIG. 19 shows a process diagram of temperature and load in the present embodiment. Since the transition point of the glass material used in the present embodiment is 445 ° C., it is 520 ° C. to 46 ° C.
50 ° C / min. Up to 5 ° C (transition point + 200C). (Step S24, Step S25), 465 ° C.
Up to 445 ° C (transition point) at 10 ° C / min. (Step S26, Step S27), and further 445 ° C.
To 430 ° C from 50 ° C / min. (Step S28, Step S29). Thereafter, the formed optical element is taken out (Step S30).

FIGS. 20A and 20B show the results obtained by examining the optical function surface of the concave lens formed by the process of the molding method of the present embodiment using a Fizeau interferometer, and include the process of the present embodiment. FIG. 2 shows the result of a convex meniscus lens having the same shape (FIG. 18) formed by a conventional method.
1 (a) and (b).

Referring to FIGS. 21 (a) and 21 (b), axially symmetric deformation occurs in which the center of about two Newton rings is high in the concave surface of FIG. It can be seen that an axially symmetric deformation in which the center of about one ring is high has occurred. In contrast, the results of FIGS. 20 (a) and (b) formed by the process of the present embodiment show that the interference fringes are parallel lines on both the concave and convex surfaces (FIGS. (A) and (b)). There is almost no deformation, and it can be seen that good surface accuracy is obtained by the molding method of the present embodiment.

Further, as a result of forming the convex meniscus lens continuously by the forming method of the present embodiment, the deformation amount of the Newton ring 1
It fits under the book.

Next, a description will be given of a simulation of stress in the glass material, which is performed to determine the cooling rate according to the present embodiment. FIG. 22 shows a model diagram based on the finite element method. The number of elements is 2000 for the mold member and 1500 for the glass material. The boundary conditions are the same as in the above-described embodiment, and the physical property values are measured for the glass material used in the present embodiment, and are similarly input.

The results of the analysis are shown by expressing the stress distribution in the glass material by contour lines. FIG. 23 shows an analysis result obtained by simulating the process of this embodiment, and FIG.
/ Min. This is the result when cooling is performed at a constant speed.
Both figures clearly show that the stress distribution in the glass material is reduced by the forming process according to the present embodiment.

This simulation was carried out with various combinations of cooling rates. As a result, for the combination of glass type and lens shape of the present embodiment, the cooling rate above the transition point of the glass material is 10 ° C./min. Before and after is optimal. However, from the viewpoint of shortening the tact time, the action of relaxing the glass material in a higher temperature range can be expected, and the transition point + 20 ° C.
In this temperature range, high-speed cooling is performed.

The cooling rate below the transition point of the glass material is 50 ° C./min. Before and after is optimal.

As described above, the cooling rate of the present embodiment is determined from the analysis of the stress in the glass material by simulation.

In the present embodiment, since the relaxation action is very active in the temperature range immediately after pressing, a sufficient relaxation action can be expected even if the cooling rate is high in that temperature range. Therefore, since the cooling rate in the temperature range is increased, it is possible to shorten the molding tact while maintaining high functional surface accuracy of the optical element.

The present invention can be applied to a modification or modification of the above embodiment without departing from the gist of the invention. For example, in the first and second embodiments, the case where a meniscus lens is formed has been described. However, the present invention is also applicable to forming an optical element having another shape, such as a concave lens or a flat optical element. . In addition, the gist of the present invention is that the stress relaxation rate in the glass material is 90% or more in a temperature range above the transition point and 10% in a temperature range below the transition point.
Therefore, it is also possible to use a method other than the cooling rate control.

Note that the present invention is not limited to the apparatus of the above-described embodiment, and may be applied to a system including a plurality of devices or an apparatus including a single device.
A storage medium storing program codes of software for realizing the functions of the above-described embodiments is supplied to a system or an apparatus, and a computer (or CPU or MPU) of the system or apparatus reads out and executes the program code stored in the storage medium. It goes without saying that it will be completed by doing so.

In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. As a storage medium for supplying the program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, and a ROM can be used. When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also the OS or the like running on the computer performs the actual processing based on the instruction of the program code. It goes without saying that a case where some or all of the operations are performed and the functions of the above-described embodiments are realized by the processing is also included.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the program code is read based on the next program code. Needless to say, the extended function may be performed by a CPU or the like provided in an expansion board or an expansion unit to perform a part or all of the actual processing, and the processing may realize the functions of the above-described embodiments. No.

[0081]

As described in detail above, according to the first, fourth and seventh aspects of the present invention, it is possible to obtain the functional surface accuracy of an optical element which has been difficult to mold with high accuracy. Becomes easier.

According to the second, fifth and eighth aspects of the present invention, it is possible to easily obtain the functional surface accuracy of the optical element, which has been difficult to form with high accuracy, by controlling the cooling rate. It becomes possible.

According to the third, sixth and ninth aspects of the present invention, it is possible to shorten the molding tact while maintaining high functional surface accuracy of the optical element.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method for molding an optical element according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional configuration diagram of an optical element molding apparatus for realizing the molding method shown in FIG.

FIG. 3 is a cross-sectional view illustrating a shape of the optical element according to the first embodiment.

FIG. 4 is a process diagram of molding temperature and weight according to the first embodiment.

FIG. 5 is a diagram showing a result of examining an optical function surface of a lens by a Fizeau interferometer when molding is performed by the method according to the first embodiment.

FIG. 6 is a diagram showing a result of examining an optical function surface of a lens by a Fizeau interferometer when molding is performed by a conventional method.

FIG. 7 is a graph showing a relationship between a temperature and an expansion coefficient.

FIG. 8 is a view showing data of physical properties of a glass material and a mold member.

FIG. 9 is a graph of creep compliance according to the first embodiment.

FIG. 10 is a graph showing a master curve of creep compliance according to the first embodiment.

FIG. 11 is a graph showing a time / temperature shift factor according to the first embodiment.

FIG. 12 is a graph showing a master curve of a relaxation elastic modulus according to the first embodiment.

FIG. 13 is a model diagram according to the first embodiment.

FIG. 14 is a diagram showing a stress distribution according to the first embodiment.

FIG. 15 is a diagram showing a stress distribution when cooling is performed at a constant speed.

FIG. 16 is a flowchart illustrating a method for molding an optical element according to a second embodiment of the present invention.

FIG. 17 is a cross-sectional configuration diagram of an optical element molding apparatus for realizing the molding method shown in FIG.

FIG. 18 is a cross-sectional view illustrating a shape of an optical element according to a second embodiment.

FIG. 19 is a process diagram of temperature and load according to the second embodiment.

FIG. 20 is a diagram showing a result of examining an optical function surface of a lens according to the second embodiment by a Fizeau interferometer.

FIG. 21 is a view showing a result of examining an optical function surface of a lens by a Fizeau interferometer when molding is performed by a conventional method.

FIG. 22 is a model diagram according to a second embodiment.

FIG. 23 is a diagram showing a stress distribution according to the second embodiment.

FIG. 24 is a diagram showing a stress distribution when cooling is performed at a constant speed.

[Description of Signs] 1 Molding die 1a Opening hole 2 Upper die member 3 Lower die member 4 Glass material 5 Heater 10 Programmable temperature controller

Claims (9)

[Claims] 1. A molding method for an optical element, wherein a glass material in a softened state is pressed by a molding die member, and then a cooling step of cooling the glass material is performed, wherein the cooling step comprises a transition point of the glass material. In the above temperature range, cooling is performed so that the stress relaxation rate in the glass material becomes 90% or more, and in the temperature range below the transition point, cooling is performed so that the stress relaxation rate becomes 10% or less. Method for forming an optical element. 2. The cooling step is performed at a rate of 10 ° C./min. To a transition point of the glass material so that a stress relaxation rate of the glass material is 90% or more. Cooling is performed at a rate of not more than 50 ° C./min. 2. The method of molding an optical element according to claim 1, wherein the cooling is performed at the above speed. 3. The method according to claim 1, wherein the cooling step comprises: setting a temperature higher than the transition point of the glass material in a range of 60 ° C. to 40 ° C .;
50 ° C./min. Up to the temperature set high in the range of
After cooling at the above rate, the temperature is set to be higher than the transition point in the range of 20 ° C. to 5 ° C. from the transition point to 10 ° C./° C. so that the stress relaxation rate of the glass material becomes 90% or more. min. Cooling is performed at the following rate, and thereafter, the temperature is reduced to 5% or less so that the stress relaxation rate is 10% or less.
0 ° C./min. The method for forming an optical element according to claim 1, wherein the cooling is performed at the above speed. 4. An optical element molding apparatus comprising: a molding die member for pressing a glass material in a softened state; and cooling control means for controlling cooling of the glass material pressed by the molding die member. In the above, the cooling control means may cool the glass material so that the stress relaxation rate in the glass material is 90% or more in a temperature range above the transition point of the glass material, and the stress relaxation rate in a temperature range below the transition point. A molding apparatus for cooling an optical element, wherein the apparatus has a control structure for cooling so as to be 10% or less. 5. The cooling control means according to claim 1, wherein said glass material has a stress relaxation rate of 90% or more. Cooling is performed at a rate of not more than 50 ° C./min. 5. The optical element molding apparatus according to claim 4, wherein the apparatus is configured to control cooling at the above speed. 6. The cooling control means includes: a temperature set higher than a transition point of the glass material in a range of 60 ° C. to 40 ° C .;
50 ° C./min. Up to the temperature set high in the range of
After cooling at the above rate, the temperature is set to be higher than the transition point in the range of 20 ° C. to 5 ° C. from the transition point to 10 ° C./° C. so that the stress relaxation rate of the glass material becomes 90% or more. min. Cooling is performed at the following rate, and thereafter, the temperature is reduced to 5% or less so that the stress relaxation rate is 10% or less.
0 ° C./min. 5. The optical element molding apparatus according to claim 4, wherein the apparatus is configured to control cooling at the above speed. 7. A storage medium storing a computer-readable program for executing a method of molding an optical element for pressing a glass material in a softened state with a molding die member and thereafter cooling the glass material. The method of molding the optical element may include: cooling the glass material so that the stress relaxation rate in the glass material is 90% or more in a temperature range equal to or higher than the transition point of the glass material; A storage medium characterized by comprising a cooling control step of cooling so that a relaxation rate becomes 10% or less. 8. The cooling control step is performed at a rate of 10 ° C./min. To a transition point of the glass material so that a stress relaxation rate of the glass material is 90% or more. Cooling is performed at a rate of not more than 50 ° C./min. The storage medium according to claim 7, wherein the storage medium is cooled at the above speed. 9. The cooling control step includes: starting from a temperature set in the range of 60 ° C. to 40 ° C. higher than the transition point of the glass material, and starting from 20 ° C. to 5 ° C.
50 ° C./min. Up to the temperature set high in the range of
After cooling at the above rate, the temperature is set to be higher than the transition point in the range of 20 ° C. to 5 ° C. from the transition point to 10 ° C./° C. so that the stress relaxation rate of the glass material becomes 90% or more. min. Cooling is performed at the following speed.
0 ° C./min. The storage medium according to claim 7, wherein the storage medium is cooled at the above speed.