JP2008285337A - Apparatus for molding lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for molding a lens, by which even the thin lens having a small ratio of the central thickness to the outward form can be molded with high precision without being broken. <P>SOLUTION: The apparatus for molding the lens is provided with: a pair of bases 13, 14 any of which has a moving means 11 and a displacement measuring means 12 for measuring the quantity of the base 13 to be displaced by the moving means 11 and which are arranged to be opposed to each other; a pair of molds 15, 16 which are placed respectively on the opposed surfaces of the bases 13, 14 to each other and any of which has a temperature measuring means 19 on the inside thereof; a heating means 18 for heating at least the pair of molds 15, 16; and a controller 20 which is connected to the displacement measuring means 12 and the temperature measuring means 19 and controls the quantity of the base 13 to be displaced by the moving means 11 or the temperature by the heating means 18. Any of molds 15, 16 has a stress measuring means consisting of an ultrasonic transmitter element 21 and an ultrasonic receiver element 22. The stress to be imposed on a vitreous material held between the pair of molds 15, 16 is measured by the stress measuring means and the measured stress is outputted to the controller 20. The lens is molded while controlling the quantity of the base 13 to be displaced by the moving means 11 or the temperature by the heating means 18 so that the measured stress does not exceed a fixed value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a molding apparatus for a lens mounted on an optical pickup or an image pickup device, and more particularly to a molding apparatus for a thin lens such as a meniscus lens, in which the thickness of the central portion is particularly thin with respect to the outer shape.

  Glass lenses are used in optical recording / reproducing pickup devices such as CDs and MDs, and imaging devices mounted on digital cameras and mobile phones in consideration of usage environments such as heat resistance and impact resistance. In order to cope with the reduction in size and thickness of these devices, an aspheric lens is required as a glass lens to be mounted.

  Such a small aspherical lens had its shape transferred by a pair of molds having an aspherical shape after heating and softening a glass material that defines the weight and outer shape. .

  FIG. 4 is a cross-sectional view of a main part in a conventional lens molding apparatus. First, a pair of molds 1 and 2 having molding surfaces 1a and 2a formed with aspherical surfaces are inserted and fixed to sleeves 3 and 4, respectively, and then pressed parts 7 and 8 through die plates 5 and 6, respectively. The bolts 9 are fastened together, and the pressurizing portions 7 and 8 and the dies 1 and 2 are fixed integrally. After the glass material 10 is sandwiched between the molding parts 1a and 2a, the glass material 10 is heated to at least the glass transition temperature (Tg) and maintained for a certain period of time to soften the glass material 10 and pressurize each other by the pressurizing parts 7 and 8. The molding is done. Finally, after the molds 1 and 2 are gradually cooled, the molded glass material 10 is taken out as a lens.

For example, Patent Document 1 and Patent Document 2 are known as prior art document information relating to the invention of this application.
JP-A-8-133766 JP-A-8-231231

  Usually, the glass material 10 is heated to a glass transition temperature (Tg) or higher and then pressed to perform molding. At this time, the glass material 10 is heated to at least 400 degrees or more together with the pair of molds 1 and 2. For this reason, the glass material 10 is subjected to stress caused by the difference in linear expansion coefficient from the pair of molds 1 and 2 and its surroundings along with the pressure from the pressurizing sections 7 and 8 at the time of molding. Become. As a result, the stress exceeding the limit value is applied to the glass material 10, so that when a thin lens having a small center thickness with respect to its outer shape such as a meniscus lens is molded, there is a problem that cracking is likely to occur. It was.

  Accordingly, an object of the present invention is to provide a molding apparatus that can mold a thin lens with high accuracy without cracking.

  In order to achieve the above object, the present invention has a moving means and a displacement measuring means for measuring a displacement amount by the moving means. A pair of molds placed on opposite surfaces and having temperature measuring means inside, a heating means for heating at least the pair of molds, and connected to the displacement measuring means and the temperature measuring means, moving means and heating means The pair of molds includes a stress measuring unit including an ultrasonic oscillation element and an ultrasonic receiving element, and the pair of molds is formed by the stress measuring unit. The stress applied to the glass material sandwiched between the two is measured and output to the control device, and molding is performed while controlling the displacement amount and temperature of the moving means or heating means so that the stress does not exceed a certain value.

  A lens molding apparatus according to the present invention includes a pair of bases having a moving unit, a displacement measuring unit for measuring a displacement amount by the moving unit, a pair of molds for molding a glass material, and at least The heating means for heating the pair of molds, and a control device connected to the moving means and the heating means for controlling the temperature and the amount of displacement thereof. Further, the pair of molds are provided with an ultrasonic oscillation element on one side and an ultrasonic reception element for receiving ultrasonic waves on the other side, facing the surface on which the glass material is formed. During molding, the ultrasonic wave transmitted from the ultrasonic oscillation element propagates through the mold, the glass material, and the mold, and is received by the other ultrasonic receiving element, thereby reducing the stress generated in the glass material. taking measurement. Then, this measurement result is output to the control device, and the molding is performed while controlling the temperature or the displacement amount so that the stress value does not exceed a certain value. As a result, even a thin lens having a small center thickness with respect to the outer shape, such as a meniscus lens, can be molded with high accuracy without cracking.

  Hereinafter, a lens molding apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a configuration diagram illustrating a lens molding apparatus according to the present invention. In particular, the vicinity of the mold, which is the point of the invention, is shown in a sectional view.

  In the lens molding apparatus of this embodiment, a fixed base 14 is fixed on a base 13 having a moving means 11 and a displacement measuring means 12 for measuring a displacement amount by the moving means 11. They are provided facing each other at intervals. The molds 15 and 16 are placed and fixed on the opposing surfaces 13a and 14a of the bases 13 and 14 so that the molding surfaces 15a and 16a face each other. As described above, the molds 15 and 16 placed on the bases 13 and 14 sandwich the glass material 17 with the molding surfaces 15a and 16a paired vertically. A heating means 18 such as a carbon heater, a ceramic heater, or an electromagnetic heating type is provided at least around the molds 15 and 16, and the glass material 17 is heated to a certain temperature together with the molds 15 and 16. The glass material 17 sandwiched between the molding surfaces 15a and 16a is heated to a constant temperature by the heating means 18 and then pressurized by the moving means 11 to be molded into a lens having a shape following the molding surfaces 15a and 16a. It is.

  Further, at least one of the molds 15 and 16 has a temperature measuring means 19 made of a thermocouple or the like, and is connected to the control device 20 together with the displacement measuring means 12, the moving means 11 and the heating means 18. The control device 20 stores a molding profile mainly composed of heating temperature, pressurization, and holding time thereof, and monitors the output signals from the temperature measuring means 19 and the displacement measuring means 12 while setting the molding profile. The temperature and displacement of the moving means 11 and the heating means 18 are controlled along the lines.

  Furthermore, the ultrasonic oscillating element 21 is connected to one of the molds 15 and 16 directly below the molding surfaces 15a and 16a, and the ultrasonic receiving element 22 is connected to the other. The ultrasonic oscillating element 21 and the ultrasonic receiving element 22 are connected to the molds 15 and 16 via the heat insulating material 23 because the molds 15 and 16 are as high as 300 to 800 ° C. during molding. Further, by covering a part of the heat insulating material 23 with the cooling means 24 composed of a Peltier element or the like, the influence of radiant heat from the molds 15 and 16 and the heating means 18 is minimized.

  As the heat insulating material 23, a material having lower thermal conductivity than at least the molds 15 and 16 may be selected. When silicon carbide (SiC), carbide (WC), glassy carbon or the like is used as the molds 15 and 16, for example, gallium arsenide, gallium nitride, sapphire, boron nitride or the like is selected as the heat insulating material 23.

  In addition, as an element used for the ultrasonic oscillation element 21 and the ultrasonic reception element 22, an inorganic piezoelectric material having a high Curie point temperature and hardly losing piezoelectric characteristics even at a high temperature, for example, titanic acid, in consideration of the temperature at the time of use. Select zirconia lead lithium or aluminum nitride.

  What is important here is that the ultrasonic oscillating element 21 and the ultrasonic receiving element 22 are suspended from the molds 15 and 16 via the heat insulating material 23 by providing counterbores in the bases 13 and 14, respectively. To connect. By doing so, the vibration oscillated from the ultrasonic oscillator 21 can be reliably propagated to the other ultrasonic receiver 22 without being absorbed and diffused by the base 13 and attenuated.

  Next, FIG. 2 shows a molding flow using the lens molding apparatus.

  First, a molding condition is set in consideration of the shape accuracy of the glass material 17 and the lens to be molded (25). This molding condition is a molding profile composed of the heating temperature and pressure of the glass material 17 and the holding time thereof.

  Next, after the glass material 17 and the pair of upper and lower molds 15 and 16 are arranged coaxially, molding is started (26). Then, the control unit 20 controls the heating unit 18 and the moving unit 11 so as to satisfy the provisional molding conditions set in (25). That is, while the glass material 17 is heated together with the molds 15 and 16 by the heating means 18 and kept at a constant temperature, the mold 15 is raised together with the lower base 13 by the moving means 11. In this way, the glass material 17 is sandwiched between the molds 15 and 16, and the glass material 17 is pressurized with a constant pressure. At this time, the displacement measuring means 12 measures the amount of displacement of the base 13. Further, during this pressurization, the ultrasonic wave oscillated from the ultrasonic oscillation element 21 propagates to the glass material 17 through the lower mold 15 and is received by the ultrasonic reception element 22 through the upper mold 16. .

  What is important at this time is to dispose two or more sets of the ultrasonic oscillation element 21 and the ultrasonic reception element 22 and shift the timing of oscillating each ultrasonic oscillation element 21. By doing so, it is possible to accurately measure the stress generated in the glass material 17 during molding and its position.

  Further, the arrangement of the ultrasonic oscillation element 21 and the ultrasonic reception element 22 may be set on the central axis of the molds 15 and 16 according to the shape of the lens, and one or more sets concentrically. By doing so, even when the place where the maximum stress is generated at the time of molding the lens changes, it is possible to measure reliably and accurately. As described above, the maximum stress generated in the glass material 17 being molded is calculated using the ultrasonic oscillator 21 and the ultrasonic receiver 22 (27).

  Next, it is determined whether or not the calculated maximum stress exceeds a crack occurrence threshold of the glass material 17 to be formed (28). At this time, determination is made by storing, as a library (29), data on a glass material crack occurrence threshold (fracture stress) obtained in advance by simulation or experiment in a storage unit inside the control device 20, and comparing it with the value. This data can prevent cracking during molding by preparing and storing data at each temperature during molding as well as data at room temperature. In this determination, if the maximum stress generated during the molding is equal to or less than the crack occurrence threshold stored in the library (29), the molding proceeds as it is, and it is cooled to room temperature (30). If the threshold value is exceeded, the heating means 18 and the moving means 11 are controlled via the control device 20, and the molding is continued while controlling the heating temperature or displacement so as not to exceed the crack occurrence threshold value (31). .

In addition, the above control estimates the presence or absence of cracking during molding using a library of molding conditions such as temperature and displacement and crack occurrence threshold values that have been input in advance. Variables may be adjusted. In this case, the stress is estimated at a constant interval Δt, the current stress value is σ _E1 , the cracking threshold at this time is σ _C1 , and the stress value at the time point that is a predetermined interval Δt from the present is σ _E0 , Σ _{C0 is} the threshold value for occurrence of cracks at the time, σ _{E2 is} the predicted stress value after a predetermined interval Δt in the current molding conditions, σ _{C2 is} the threshold value for occurrence of cracks at this time, T _{1 is the} current temperature, and the yield point of the glass material 17 Is T _AT
T ₁ <T _AT +70
| Σ _E2 −σ _C2 | / | σ _E1 −σ _C1 | <1
0.7 ・ σ _C2 <(σ _E1 −σ _E0 ) + σ _E1 <0.9 ・ σ _C2
The temperature and the amount of displacement are controlled so as to satisfy the relationship represented by the above formula.

  Finally, after cooling to room temperature, the lens is taken out from the molds 15 and 16 to finish molding (32). The above steps are repeated to evaluate the shape accuracy of the molded lens and adjust the temporary molding conditions.

  In the present embodiment, the stress generated in the glass material 17 is measured using ultrasonic waves. Since this ultrasonic wave is refracted or reflected at the boundary when propagating through materials having different sound speeds, especially the connection between the heat insulating material 23 and the molds 15 and 16 greatly affects the measurement accuracy. Below, the detail of the arrangement | positioning of the heat insulating material 23 is demonstrated using FIG.

The ultrasonic wave oscillated from the ultrasonic oscillation element 21 is refracted and diffused at a boundary where the material is different and the propagation speed changes, such as the mold 15 and the heat insulating material 23. The refraction angle θ _{out of the} ultrasonic wave at this time is expressed by the following equation, where the sound speed of the emitting side material is v _out , the incident angle θ _in , and the sound speed v _in of the incident side material.

(Sinθ _out ) / v _out = (Sinθ _in ) / v _in
From this equation, it can be seen that when an ultrasonic wave propagates from a material having a high sound velocity to a material having a low sound velocity, the emission angle is smaller than the incident angle.

The sound velocity v _out is inversely proportional to the square root of the density ρ _out of the propagating material and proportional to the square root of the bulk modulus K _out and is expressed by the following equation.

v _out = (K _out / ρ _out ) ^1/2
The above formula makes it possible to calculate the propagation velocity of ultrasonic waves from the density and bulk modulus of the propagating material. Using this value, the shape of the boundary surface can be reduced so that diffusion due to ultrasonic refraction is suppressed. Decide and increase the accuracy of measurement.

The reflectance R at the interface between the molds 15 and 16 and the glass material 17 is the density ρ _out of the incident side material, the acoustic velocity V _out and the acoustic impedance Z _out that is the product of them, and the incident side material. It is expressed as follows by density ρ _in , sound velocity v _in , and acoustic impedance Z _in .

Z _out = ρ _out・ v _out
Z _in = ρ _in · v _{in
R = (Z out -Z in)} / (Z in + Z out)
Depending on the combination of the material of the molds 15 and 16 and the glass material 17, the difference in acoustic impedance between the molds 15 and 16 and the glass material 17 is remarkably large, and the reflection between the molds 15 and 16 and the glass material 17 is significant. When the rate is high, the propagation speed of the reflected wave generated at the interface between the upper mold 16 and the glass material 17 is measured by the ultrasonic oscillation element 21 installed on the bottom surface of the lower mold 15 to increase the rate. Accurate measurement is possible. Further, since reflection also occurs between the molds 15 and 16 and the heat insulating material 23, by selecting a material that reduces the difference in acoustic impedance between the molds 15 and 16 and the heat insulating material 23, the mold 15 , 16 and the heat insulating material 23 can be prevented from being reflected, and the measurement accuracy can be improved.

  At this time, when the sound speed of the molds 15 and 16 is slower than the sound speed of the heat insulating material 23, the boundary shape as shown in FIG. 3A or 3B is obtained, and the sound speed of the molds 15 and 16 is the heat insulating material. When the sound speed is higher than 23, the boundary shape as shown in FIG. 3C or FIG. 3D is used to suppress the diffusion of ultrasonic waves, and the ultrasonic waves oscillated by the ultrasonic oscillator 21 are converted into ultrasonic waves. It is possible to efficiently propagate to the receiving element 22.

If the relationship between the acoustic impedance Z _{M of the} molds 15 and 16 and the acoustic impedance Z _G of the glass material 17 is Z _M > Z _G , the lower mold 15 and the glass material 17 are The phase advances 90 degrees at the interface. By subtracting this phase component from the phase component received by the ultrasonic receiving element 22, it is possible to measure the amount of phase change that has occurred in the glass material 17, and the stress generated in the glass material 17 by the acoustoelastic method can be measured. It becomes possible to measure.

  The above embodiment is an example in which a plurality of ultrasonic oscillators 21 are provided and the timing of each oscillation is shifted, but the same effect can be obtained by providing a plurality of ultrasonic oscillators 21 having different oscillation phases.

  By molding using the above-described molding apparatus, it is possible to mold a thin lens such as a meniscus lens having a thin center portion with respect to the outer shape with high accuracy without causing cracks or chipping.

  A lens molding apparatus according to the present invention includes a pair of bases having a moving unit, a displacement measuring unit for measuring a displacement amount by the moving unit, a pair of molds for molding a glass material, and at least The heating means for heating the pair of molds, and a control device connected to the moving means and the heating means for controlling the temperature and the amount of displacement thereof. Further, the pair of molds are provided with an ultrasonic oscillation element on one side and an ultrasonic reception element for receiving ultrasonic waves on the other side, facing the surface on which the glass material is formed. During molding, the ultrasonic wave transmitted from the ultrasonic oscillation element propagates through the mold, the glass material, and the mold, and is received by the other ultrasonic receiving element, thereby reducing the stress generated in the glass material. taking measurement. Then, this measurement result is output to the control device, and the molding is performed while controlling the temperature or the displacement amount so that the stress value does not exceed a certain value. As a result, even a thin lens having a small center thickness with respect to the outer shape, such as a meniscus lens, has the effect of being able to be molded with high precision without cracking. This is useful for an apparatus for forming a thin lens having a small thickness.

1 is a configuration diagram of a lens molding apparatus for explaining an embodiment of the present invention. Flow chart explaining the molding method using the same device (A)-(d) is sectional drawing explaining the connection of a metal mold | die and a heat insulating material Cross-sectional view of relevant parts for explaining a conventional lens molding apparatus

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Moving means 12 Displacement measuring means 13 Base 14 Base 15 Mold 16 Mold 17 Glass material 18 Heating means 19 Temperature measuring means 20 Control device 21 Ultrasonic oscillation element 22 Ultrasonic receiving element 23 Heat insulating material 24 Cooling means

Claims (5)

A moving means and a displacement measuring means for measuring the amount of displacement by the moving means; a pair of bases provided opposite to each other; and placed on opposing surfaces of the base; A pair of molds, a heating unit that heats at least the pair of molds, and a control unit that is connected to the displacement measuring unit and the temperature measuring unit and controls the displacement amount or temperature of the moving unit and the heating unit. The pair of molds includes a stress measurement unit including an ultrasonic oscillation element and an ultrasonic reception element, and the stress measurement unit measures the stress applied to the glass material sandwiched between the pair of molds. A lens molding apparatus that performs molding while controlling the amount of displacement and temperature of the moving means or heating means so that the stress does not exceed a certain value. The lens molding apparatus according to claim 1, wherein the ultrasonic oscillation element and the ultrasonic reception element are connected to a mold through a heat insulating material having a cooling means. The lens molding apparatus according to claim 2, wherein the ultrasonic oscillation element and the ultrasonic reception element are suspended via a heat insulating material on a surface of a mold facing the molding surface. 4. The lens molding apparatus according to claim 3, wherein a plurality of sets of the ultrasonic oscillation element and the ultrasonic reception element are provided concentrically. The lens shaping apparatus according to claim 4, wherein each of the ultrasonic oscillation elements has a phase different from each other.

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