JPH09208239A - Method for forming optical element and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical element having good surface accuracy free from seizing and forming defects without extending tact time. SOLUTION: The glass blank 13 placed on a transporting arm 6 is heated and softened in a heating furnace 4 and is transported to the space between a pair of forming dies 2 and 3 disposed in a forming chamber 1 and, thereafter, the blank is press formed in this method for forming the optical element. An adequate atmosphere temp. lower than the glass transition point temp. is maintained in this forming chamber 1. While the glass blank is controlled in heating to the temp. near the transition point on the track on which the transporting arm 6 moves, the glass blank is press formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to molding of an optical element in which a glass material placed on a transfer arm is softened by heating in a heating furnace and is conveyed between a pair of molding dies provided in a molding chamber and then pressure-molded. The present invention relates to a method and an apparatus therefor, and more particularly to temperature control of a glass material in a forming chamber.

[0002]

2. Description of the Related Art Conventionally, when a glass material that has been heated and softened in a heating furnace is conveyed between a pair of molding dies and an optical element is press-molded by the molding dies, performance deterioration due to oxidation of the molding dies and peripheral members thereof occurs. In order to prevent this, molding is performed in an atmosphere of an inert gas such as nitrogen or argon. Since the inert gas flows in so as to constantly replace the air in the molding chamber of the molding machine, the ambient temperature in the molding chamber does not rise so much and the glass material that has been softened by heating in the heating furnace is transferred between the molds. However, the outer peripheral portion and the surface of the glass material being conveyed during the step of pressing may be rapidly cooled due to the ambient temperature of the molding chamber, which may affect the transferability of the molding surface. These phenomena are more conspicuous especially in a lens having a large outer diameter and a lens having a large thickness deviation.

In order to solve this problem, for example, a molding chamber heater is embedded in the inner wall of the molding chamber to control the ambient temperature of the molding chamber to a temperature near the transition temperature of the glass material used in the preform for molding. Japanese Patent Application Laid-Open No. 2-267127 discloses a method and apparatus for molding an optical element that is molded by the above method. This technique will be described with reference to FIG.

In FIG. 4, reference numeral 101 denotes a molding chamber, and an upper mold 102 and a lower mold 103, which are molding dies, are housed in the molding chamber 101. The upper mold 102 is the molding chamber 101.
The lower mold 103 is fixed to the lower surface of the upper plate 101a, and the lower mold 103 is fixed to the upper surface of the lower mold installation table 104. And the upper mold 10
2. The lower mold 103 is coaxially opposed to each other in a pair, and molding surfaces 102a and 103a having a high surface shape and surface roughness corresponding to a desired optical element are formed on the opposed surfaces. That is, the molding surfaces 102a and 103a are
Upper mold temperature monitor unit 10 for measuring the temperature of the lower mold 103
6. Formed on the tip of the lower mold temperature monitor 107. On the other hand, the lower mold 103 includes the lower plate 101b of the molding chamber 101.
Drive shaft 10 provided through a hole 108 formed in the
It is fixed to the tip of 9 through a lower die installation table 104, and is provided so as to be able to move toward and away from the upper die 102 by the operation of a drive unit 110 connected to the other end of the drive shaft 109. The lower die installation table 104 and the drive shaft 109 are heat insulating materials 1
It is fixed via 11.

On the side wall 101c of the molding chamber 101, a window 11 for loading and unloading a glass material 112 and an optical element (not shown) after press molding into and from the molding chamber 101.
3 are provided. The window 11 is formed on the side wall 101c.
A heating furnace 114 provided with a glass material heater 114 a for heating and softening the glass material 112 to a predetermined temperature is connected to a position corresponding to 3. A heat insulating shutter 115 is provided between the window 113 and the heating furnace 114.
The heat insulating shutter 115 is connected to the driving unit 116 and is vertically moved by the operation of the driving unit 116 so that the window 113 can be opened and closed. Reference numeral 117 denotes a transfer arm for carrying the glass material 112 into a molding point between the heating furnace 114 and the upper and lower molds 102 and 103 in the molding chamber 101, and carrying out the optical element after the press molding from the molding chamber 101. A mounting portion 119 for mounting the glass material 112 and the carrier 118 holding the optical element is formed at the tip of the carrier arm 117.

A heat insulating plate 120 is provided on the entire inner wall of the molding chamber 101, and a heat insulating plate 121 is also provided on the upper surface of the lower plate 101b so that the heat in the molding chamber 101 is not released to the outside. There is. A molding chamber heater 122 for heating the inside of the molding chamber 101 to a predetermined temperature is installed on the entire inner wall of the heat insulating plate 121. Further, on the side wall 101d of the molding chamber 101 on the opposite side of the heating furnace 114, a molding room temperature monitor 123 for measuring the temperature in the molding chamber 101 and controlling the heating state by the molding chamber heater 122 is installed. . The molding room temperature monitor 123 is housed and installed in the quartz tube 124, and when the lower die 103 is moved up and down and the transfer arm 117 is carried in and out, the molding room temperature that fluctuates due to the outside air flowing into the molding chamber 101 is displayed. When the measurement is made directly by the molding chamber monitor 123, the molding chamber 101 is prevented from being overheated due to the temperature of the inflowing outside air, that is, the molding chamber 101 is heated to a temperature exceeding the set temperature. I'm supposed to get it.

On the other hand, in the lower plate 101b of the molding chamber 101,
A nitrogen gas heating furnace 126 communicating with the inside of the molding chamber 101 is connected via a stainless pipe 125 covered with a heat insulating material. The nitrogen gas heating furnace 126 is configured in a tubular shape having a nitrogen gas heater 127, one end of which is connected to a nitrogen gas supply device (for example, a nitrogen gas tank) 128, and the other end of which is connected to the stainless pipe 125. A nitrogen gas temperature monitor unit 129 is provided. The nitrogen gas temperature monitor unit 129 measures the temperature of the nitrogen gas fed into the molding chamber 101, controls the nitrogen gas heater 127, and the fed nitrogen gas does not affect the temperature of the molding chamber 101. Thus, the temperature of the molding chamber 101 can be set to almost the same temperature. Then, the temperature-controlled nitrogen gas is passed through the stainless pipe 125 from below the lower die installation table 104 to the molding chamber 10.
1 is fed into the molding chamber 101 with almost no flow velocity so as not to affect the internal temperature and the molding die temperature.

[0008]

However, the above prior art has the following problems. That is, if the ambient temperature of the entire molding chamber is raised to near the glass transition point,
Cooling of the glass during press molding is delayed, the takt time is extended, and productivity is reduced. Furthermore, the mold is usually controlled to a temperature slightly lower than the transition temperature of the glass material, but the surface temperature of the mold rises due to the influence of the high molding chamber temperature, and the glass material burns into the mold, Molding failure of the element occurs and repair of the molding die is required.

The present invention has been made in view of the above-mentioned problems of the prior art. Therefore, the object of the invention according to claim 1 is to obtain good surface accuracy without seizure or molding failure without extending the tact time. It is an object of the present invention to provide a molding method of an optical element that can be manufactured. An object of the invention according to claim 2 or 3 is to provide a molding apparatus for carrying out the above-mentioned method for molding an optical element.

[0010]

In order to solve the above problems, the invention according to claim 1 provides a pair of glass materials placed on a transfer arm, which are softened by heating in a heating furnace and provided in a molding chamber. In a method of molding an optical element in which the material is conveyed between molding dies and then pressure-molded, the molding chamber is maintained at an appropriate ambient temperature lower than the glass transition point temperature, and the glass material is in the vicinity of the transition point on an orbit along which the transport arm moves. It is characterized in that the press molding is performed while controlling the heating to the above temperature. Claim 2 or 3
The invention according to claim 1, the heating furnace for heating and softening the glass material, a molding chamber adjacent to the heating furnace, a pair of molding dies provided in the molding chamber, the heating furnace and the molding chamber on which the glass material is placed. In a molding device of an optical element provided with a transfer arm that moves and, a means for heating and controlling a glass material near a transition temperature is provided around the orbit of the transfer arm adjacent to the heating furnace in the molding chamber. It is characterized by

In the operation of the invention according to claim 1, the inside of the molding chamber is maintained at an appropriate atmospheric temperature lower than the glass transition temperature,
By pressing and molding the glass material while controlling heating to a temperature near the transition point on the orbit along which the transfer arm moves, the glass material during transfer is prevented from quenching and a uniform temperature is maintained until just before press forming. The mold maintains the proper temperature. In the operation of the invention according to claim 2 or 3, the means for controlling the heating of the glass material to near the transition temperature is provided around the orbit of the transfer arm adjacent to the heating furnace in the forming chamber. Avoiding the rapid cooling of the glass material by means of controlling the heating of the glass material transferred to
Keep uniform temperature. Further, since the means for controlling heating is limited to the periphery of the orbit of the transfer arm, it has little influence on the atmosphere of the entire molding chamber. In the operation according to claim 3, in addition to the above-mentioned operation, the heating control means is a cylindrical auxiliary heating device formed so as to surround the orbit of the transfer arm, so that the thermal efficiency is good and the necessary space is saved. Minimize.

[0012]

1 and 2 show an embodiment of the present invention, FIG. 1 is a front sectional view of an optical element molding apparatus, FIG. 2 is a front sectional view of an auxiliary heating apparatus, and FIG. 3 is auxiliary heating. It is a right view of an apparatus.

In FIG. 1, an upper mold 2 and a lower mold 3, which are molding dies, are arranged inside the molding chamber 1 so as to face each other. A main shaft 9 is connected to the lower mold 3, and the lower mold 3 is driven by a driving device 10.
Can be driven up and down. Left wall 1a of molding chamber 1
The heating furnace 4 is attached to the inside of the heating furnace, and the heater 5 is internally provided on the inner wall thereof. The molding chamber 1 and the heating furnace 4 communicate with each other through a through hole 1b, and the through hole 1b is closed by a shutter 15 until just before molding. The shutter 15 is opened and closed by an opening / closing device 16 attached to the upper part outside the molding chamber 1. A gas supply pipe 12 is connected to the lower part of the molding chamber 1,
The gas supply pipe 12 is connected to the nitrogen generator 11. The nitrogen generator 11 supplies an inert gas containing no oxygen, mainly nitrogen or argon, to the molding chamber 1.

The carrier arm 6 carries the glass material 13 and the holder 14 on which the glass material 13 is placed into the heating furnace 4 by a driving means (not shown), and further carries the glass material 13 to the molding position in the molding chamber 1. A cylindrical auxiliary heating device 7 is arranged so as to surround the orbit on the left wall 1a in the orbit of the transfer arm 6 inside the molding chamber 1. 2 and 3 show the auxiliary heating device 7. An infrared heater 8 is provided inside the auxiliary heating device 7, and the infrared heater 8 is a donut type infrared lamp. A reflector plate 17 is formed on the inner wall of the auxiliary heating device 7 in order to improve thermal efficiency. On the right side surface of the auxiliary heating device 7, a small-diameter cylinder 7a is provided upright, and is formed to have a minimum inner diameter through which the transfer arm 6 on which the glass material 13 and the holder 14 are placed can pass.

A method of molding an optical element using the above molding apparatus will be described. First, after the holder 14 on which the glass material 13 is placed is mounted on the transfer arm 6 by a supply device (not shown), the transfer arm 6 is loaded into the heating furnace 4, and the glass material 13 and the holder 14 are removed. Heat until the surface of softens. When the glass material 13 is softened, the shutter 15 is opened by the opening / closing device 16 and the transfer arm 6 is transferred to the molding position inside the molding chamber 1. At this time, the holder 14 and the glass material 13 are the auxiliary heating device 7
To reach the molding position. Next, the main shaft 9 is driven by the driving device 10, and the upper mold 2 and the lower mold 3 perform press molding. After the glass is cooled and solidified, the molded product is released from the upper mold 2 and the lower mold 3, the holder 14 is carried out from the molding chamber, and the molding operation is completed. It should be noted that the inside of the molding chamber 1 is supplied with an inert gas from the nitrogen generator before the transfer arm 6 is carried in, and is in an atmosphere of an appropriate molding temperature.

Generally, the transfer arm 6 is rapidly cooled when the holder 14 and the glass material 13 are transferred from the heating furnace 4 into the molding chamber due to the difference between the ambient temperature of the molding chamber 1 and the temperature inside the heating furnace 4. However, this phenomenon progresses from the portion where the amount of heat of glass is small, that is, the central portion in the concave lens and the outer peripheral portion of the lens in the convex lens. If a temperature distribution is generated between the outer peripheral portion and the central portion of the lens in this way, the glass will solidify before the molding is completed (before the glass flow reaches a predetermined amount) during molding, and the surface shape as designed is obtained. May not be obtained. In order to avoid such a phenomenon, it is effective to form the glass before it cools or to delay the cooling of the glass.

In the forming method of the embodiment of the present invention, the auxiliary heating device 7 heats the orbit for conveying the glass material 13 to delay the cooling of the glass and prevent the deterioration of the surface accuracy. Further, since the infrared heater 8 mainly heats the object by radiation, it heats only the transfer arm 6, the holder 14 and the glass material 13 without raising the ambient temperature of the molding chamber 1 more than necessary.

According to the embodiment of the present invention, the cooling of the glass is delayed to prevent the deterioration of the surface accuracy and the ambient temperature in the molding chamber is maintained at a predetermined temperature, so that the takt time is not extended. It is possible to obtain an optical element with good surface accuracy without image sticking or molding failure.

In the embodiment of the present invention, the infrared lamp is used as the heating means of the auxiliary heating device, but an electric heater, a spot heater or the like may be used instead. However, in order to maintain the cleanliness inside the molding chamber 1, it is desirable to have a structure that does not generate soot or dust when deteriorated as much as possible. Further, although the auxiliary heating device is a cylindrical type, it may be a rectangular tube type.

[0020]

Example 1 A case where a convex lens is molded by using the optical element molding apparatus and molding method described in the embodiments of the invention will be described. The glass material 13 has a convex preform finished in advance with a radius of curvature close to a desired lens shape (outer diameter 15 mm, medium thickness 3.5 mm, edge wall 1.
3 mm) was used. The glass material of the glass material 13 was PBH6 (transition temperature 455 ° C.) manufactured by OHARA. The temperature inside the heating furnace 4 was 750 ° C., and the upper and lower molds 2 and 3 were heated to 445 ° C. Further, the auxiliary heating device 7 was set to a central temperature of 440 ° C.

When the glass is molded without the auxiliary heating device 7 in the optical element molding apparatus shown in the embodiment of the invention, the glass is heated to a transition point temperature or higher (in this embodiment, a part is 560 ° C. or higher). The upper and lower molds 2 and 3 (mold temperature 445 ° C.) in which the temperature of the glass material 13 is kept below the transition temperature.
Therefore, the glass material 13 is rapidly cooled by the upper and lower molds 2 and 3 at the time of molding. When molding a convex lens, the glass is solidified from the outer peripheral portion which is thinned and the heat is quickly absorbed by the upper and lower molds 2 and 3. For this reason, if the outer peripheral portion of the convex lens solidifies too quickly, the central portion cannot be deformed before the transfer, and a sink mark occurs. Further, since the glass material 13 of the convex lens has a thin outer peripheral portion, it is cooled even while being conveyed from the heating furnace 4. Therefore, a temperature distribution has already occurred in the glass material 13 at the start of molding. To alleviate this, it is effective to raise the mold temperature or raise the heating temperature, but these may increase the load on the molding die and impair the durability of the molding die. It is not a fundamental solution to reduce the.

Therefore, by delaying the cooling of the heated glass material 13 by using the auxiliary heating device 7, the molding is started in a state where the temperature difference between the outer peripheral portion and the central portion of the glass material 13 is smaller at the start of the molding. This is effective in improving the transferability of the lens surface and the durability of the molding die. In particular, the effect is great when molding a lens having a larger outer diameter or a lens having a large difference between the edge thickness and the inner thickness.

According to this embodiment, it is possible to obtain a lens having fewer sink marks than the conventional one. As a comparative example, when molding was performed under the same conditions with the auxiliary heating device 7 turned off (atmosphere temperature of the measurement result at the same location was 179 ° C.), a sink mark was formed in the center of the lens. Further, due to the heat leaked from the auxiliary heating device 7, a part of the upper and lower molds 2 and 3 was heated, and astigmatism and burn-in did not occur in the lens.

[0024]

[Embodiment 2] In this embodiment, a case where a concave lens is molded instead of the convex lens of Embodiment 1 will be described.
The glass material 13 has a concave preform (external diameter 15) finished in advance with a radius of curvature close to a desired lens shape.
mm, medium meat 1.1 mm, and edge meat 3.2 mm) were used.
The glass material of the glass material 13 was PBH6 (transition temperature 455 ° C.) manufactured by OHARA. The furnace temperature of the heating furnace 4 is 750
C., the upper and lower molds 2 and 3 were heated to 445.degree. Further, the auxiliary heating device 7 was set to a central temperature of 460 ° C.

When molding a convex lens, when the glass material 13 comes out of the heating furnace 4, the temperature of the central portion of the glass material 13 decreases rapidly. This is because the central portion of the glass material 13 is thin and the heat capacity is small. For this reason, when molding is performed in a state where the heat distribution is large, the inner wall cannot be crushed or the outer peripheral portion is extremely drawn, and the surface accuracy deteriorates. However, since the temperature distribution in the radial direction can be reduced by using the molding apparatus and the molding method according to the embodiment of the invention, the surface accuracy is improved.

According to the present embodiment, it is possible to obtain a lens having fewer sink marks than the conventional one. As a comparative example, when molding was performed under the same conditions with the auxiliary heating device 7 turned off (atmosphere temperature of the measurement result at the same location was 179 ° C.), a sink mark was formed on the outer peripheral portion of the lens. Further, due to the heat leaked from the auxiliary heating device 7, a part of the upper and lower molds 2 and 3 was heated, and astigmatism and burn-in did not occur in the lens.

[0027]

According to the first aspect of the present invention, the glass material being conveyed is prevented from being rapidly cooled and a uniform temperature is maintained until immediately before press molding, and the molding die maintains an appropriate temperature. It is possible to obtain an optical element having good surface accuracy without seizure or defective molding without extension. Claim 2
According to the invention related to 3, the glass material transferred from the heating furnace to the forming chamber is heated and controlled to a temperature near the transition point, so that the glass material is prevented from being rapidly cooled and kept at a uniform temperature.
Further, since the means for controlling heating is limited to the periphery of the orbit of the transfer arm, it has little effect on the atmosphere of the entire molding chamber. Therefore, if a glass material is molded using this molding device,
It is possible to obtain an optical element having good surface accuracy without seizure or defective molding without extending the tact time. According to the invention of claim 3, in addition to the above effects, the thermal efficiency is good and the required space is minimized, so that the molding apparatus can be made compact.

[Brief description of drawings]

FIG. 1 is a front sectional view of an optical element molding apparatus according to an embodiment of the present invention.

FIG. 2 is a front sectional view of an auxiliary heating device according to an embodiment of the invention.

FIG. 3 is a right side view of the auxiliary heating device according to the embodiment of the invention.

FIG. 4 is a vertical cross-sectional view of a conventional optical element molding apparatus.

[Explanation of symbols]

 1 Molding room 2 Upper mold 3 Lower mold 4 Heating furnace 6 Transfer arm 7 Auxiliary heating device 8 Infrared lamp 13 Glass material

Claims (3)

[Claims] 1. A method for molding an optical element, comprising: softening a glass material placed on a transfer arm in a heating furnace, softening the glass material, transferring the glass material between a pair of molding dies provided in a molding chamber, and then press-molding the glass material. Is maintained at an appropriate ambient temperature lower than the glass transition point temperature, and the glass material is press-molded while controlling the heating to a temperature near the transition point on the track on which the transfer arm moves, . 2. A heating furnace for heating and softening a glass material, a molding chamber adjacent to the heating furnace, a pair of molding dies provided in the molding chamber, the heating furnace on which the glass material is placed, and the molding chamber. In a molding device of an optical element including a transfer arm that moves the and, a means for heating and controlling a glass material near the transition temperature is provided around the orbit of the transfer arm adjacent to the heating furnace in the molding chamber. An optical element molding device characterized by the above. 3. The apparatus for molding an optical element according to claim 2, wherein the heating control means is a cylindrical auxiliary heating device formed so as to surround the orbit of the transfer arm.