JP2946003B2 - Method and apparatus for molding optical element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for press-molding an optical element such as a glass lens or a prism using a mold, and more particularly to improving the precision of an optical element to be manufactured.

[0002]

2. Description of the Related Art Conventionally, in press molding of an optical element, generally, at least one of a pair of upper and lower molds is detected, and this mold is heated to a temperature higher than a transition temperature of a glass material and lower than a softening point thereof. As a result, the glass material is heated to a temperature at which the glass material can be formed, and thereafter, a pressing pressure is applied to form the glass material. That is, the timing of applying the pressing pressure is determined by the temperature of the mold.

[0003]

By the way, the thermal expansion coefficient of the glass shows a very large value several times higher than that of the lower temperature region in the high temperature region after the transition point, and the thermal expansion coefficient in this high temperature region. Is larger than the coefficient of thermal expansion of the mold material such as ceramics and metal, so when pressed in a high temperature range, even if it is molded to a specified accuracy immediately after pressing, it is molded from the mold while the temperature falls to the transition point. The product (optical element) shrinks more, causing so-called "sink". This "sink" appears greatly with the increase in the size of the optical element to be molded, and reduces the accuracy of the optical element. Therefore, solving the "sink" is an important issue for improving the accuracy of the optical element.

In order to solve this problem, at least the temperature of the glass material (formed optical element) at the time of closing the final mold in the press molding should be made as close as possible to the transition point temperature. It cannot be measured directly and must be inferred from the temperature of the mold.Because the temperature varies depending on the measurement position of the mold, accurate molding could not be performed by the method of controlling press molding by the temperature of the mold. .

According to the present invention, a high-precision optical element is formed by more accurately grasping the actual temperature of a glass material, and a non-defective product is formed stably without causing damage to the mold and the glass material. It is an object of the present invention to provide a method and an apparatus for molding an optical element that can be used.

[0006]

According to the present invention, there is provided a method for forming an optical element, comprising: placing a glass material between a pair of upper and lower dies; detecting and controlling the temperature of the dies; In the molding method of an optical element in which a glass material is heated and press-molded, after the glass material is disposed between a pair of upper and lower molds, the glass material has a gap with the upper mold or a set position S1 where the glass material contacts with a very small force. At least one of the upper and lower molds is moved to S2, and then the mold and the glass material are heated. When the temperature of the mold reaches a set temperature T1 lower than the transition temperature T2 of the glass material,
If the glass material has a gap with the upper mold, move the mold
The glass material and the upper mold are brought into contact with each other , and then when the glass material reaches a transition point temperature T2 or a temperature T3 before or after the transition temperature T2, a pair of upper and lower members are set at a relatively low set pressure P1 capable of starting deformation of the glass material. The glass material is pressed and held by the mold, and then, when the temperature of the glass material reaches the temperature T2 or T3 is detected from the start of movement of the mold accompanying the start of deformation of the glass material, and then the temperature of the mold at the time of the detection is detected. T
a, the temperature of the glass material is set to the temperature T2 or T2.
Set temperature T4 not less than 3 and not more than softening point Tm of glass material
Heating control to consists in press-molded by the pair of upper and lower mold, prior Symbol set temperature T1 is the set pressure P1
Is a temperature at which the glass material is not damaged even if the glass material is held under pressure.

In the press molding, when the pair of upper and lower molds is closed to a set position S3 slightly before the final mold closed state, the heating of the mold and the glass material is switched to cooling, and then the glass and the glass material are cooled. The temperature of the material is equal to the temperature T2 or T3
It is preferable to control the movement and cooling of the mold so that the mold is brought into the final mold closed state when it is lowered to the vicinity. When performing the press molding, when the pair of upper and lower molds is closed to a set position S3 slightly before the final mold closed state,
The heating of the mold and the glass material is switched to cooling and the movement of the mold is stopped. When the temperature of the glass material falls to a temperature slightly higher than the temperature T2 or T3, the mold is moved to a final mold closed state. You may make it do. Further, in the method of molding an optical element, it is preferable to control the position, movement and press pressure of the mold using a servomotor.

Further, in order to achieve the above object, the optical element molding apparatus according to the present invention arranges a glass material between a pair of upper and lower molds, detects and controls the temperature of the mold, and heats the mold and the glass material. In a molding apparatus for an optical element to be press-molded, means for setting and controlling at least the pressing pressure to a molding pressure P2 and a lower set pressure P1, and the mold starts moving with the press pressure set to the set pressure P1. Detecting means for detecting the temperature, means for storing the temperature of the mold at the time of receiving the signal from the signal from the detecting means, means for calculating and storing a set temperature relating to the press molding operation based on the temperature of the mold. And an operation command means for performing a press forming operation in accordance with the set temperature. Preferably, the driving source of the mold is a servomotor capable of controlling the position, speed and torque, respectively.

[0009]

[Function] A glass material has a viscosity of about 10 ²⁰ poise at room temperature, and is hard, brittle, and easily damaged, and at the same time, the mold is easily damaged. However, as the temperature increases, the viscosity decreases and reaches a transition point. And the viscosity becomes about 10 ¹³ poise, and it becomes deformable by applying an external force. The present invention prevents the mold and the glass material from being damaged by starting the heating of the mold and the glass material so that the glass material has a gap with the upper mold or contacts with an extremely small force. The viscosity of the glass material decreases as the temperature increases. Therefore, as described above, when the temperature of the mold reaches the set temperature T1 at which the glass material is not damaged even when the glass material is pressurized and held at the set pressure P1, the glass material is removed by a pair of molds. Pressing is held at the clamping force P1. The set temperature T1 is set lower than the transition point temperature T2, and the set pressure P1 does not deform the glass material at the set temperature T1,
The glass material is at or near the transition temperature T2
Is defined so as to deform the glass material when it reaches.

Therefore, when the glass material reaches the transition point temperature T2 or the temperature T3 before and after the transition point temperature T2, the set pressing force P1
The glass material starts to deform. The start of the deformation is detected by the start of the movement of the mold, and the temperature Ta of the shape at this time is extracted and stored. The movement start type temperature Ta is equal to the temperature T.
Although there is usually a deviation from 2 or T3, it can be specified from the characteristics of the glass material that the temperature of the glass material is T2 or T3 when the temperature of the mold is Ta.
That is, the relationship between the mold temperature and the glass material temperature can be grasped. Therefore, it is possible to press-mold the glass material by controlling the temperature of the glass material to a desired set temperature T4 which is equal to or higher than the temperature T2 or T3 and equal to or lower than the softening point temperature Tm of the glass material, based on the movement start temperature Ta. Thus, more accurate molding can be performed. Since the temperature of the glass material can be more accurately detected with reference to the movement start mold temperature Ta as described above, the heating is switched to cooling slightly before the end of the press forming, and the final mold closing state is reached. Sometimes, if the temperature of the glass material is reduced to the temperature T2 or T3 or its vicinity, "sink" can be suppressed more completely. The position, movement and press pressure of the mold are controlled by driving the mold with a servomotor.
Can be performed accurately.

[0011]

1 to 3 show an embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 shows an example of an optical element molding apparatus according to the present invention, in which a fixed shaft 2 extends downward from an upper portion of a frame 1 and has a heat insulating cylinder 3a made of ceramic such as Si ₃ N ₄ at its lower end. The upper die assembly 4 is attached by a bolt or the like (not shown) via a heat insulating ring 3b that transmits infrared rays such as transparent quartz glass. The upper die assembly 4 includes a metal die plate 5, an upper die 6 made of ceramics or the like, and the upper die 6
And a stationary die 7 which forms part of the mold.

[0012] drive 8 in the lower part of the frame 1 which is a drive source of the servo motor 8a is provided, giving a controllable pressing force to the desired value with the speed and position controllably moved up and down by the device 8 The moving shaft 9 extends upward facing the fixed shaft 2. At the upper end of the moving shaft 9, a lower mold assembly 11 that is paired with the upper mold assembly 4 is attached via a heat insulating cylinder 10a and a heat insulating ring 10b similar to the heat insulating cylinder 3a and the heat insulating ring 3b. Lower mold assembly 11
Is a die plate 12, a lower mold 13 and a movable die 14.
Consists of

A bracket 15 which is vertically moved by a driving device (not shown) is movably engaged with the fixed shaft 2. A transparent quartz tube 16 surrounding the pair of mold assemblies 4 and 11 is attached to the bracket 15. The lower end of the transparent quartz tube 16 is an intermediate plate 1A through which the moving shaft 9 passes.
And a molding chamber 17 which is cut off from the atmosphere around the mold assemblies 4 and 11 in an airtight manner. An outer cylinder 18 surrounding the transparent quartz tube 16 is attached to the bracket 15, and a lamp unit 19 is provided on the outer cylinder 18. The lamp unit 19 includes an infrared lamp 20 and a reflecting mirror 21 disposed behind the infrared lamp 20.
11 is heated. Reference numeral 22 denotes a water cooling pipe for cooling the reflection mirror 21 and the like.

Fixed shaft 2, moving shaft 9 and bracket 15
The gas supply passages 23 and 2 for making the interior of the molding chamber 17 an inert gas atmosphere and for cooling the mold assemblies 4 and 11 are provided.
4 and 25 are provided, and an inert gas controlled at a predetermined temperature by a temperature control device (not shown) is supplied to the molding chamber 17 at a predetermined flow rate through a flow control valve (not shown). The gas supplied to the molding chamber 17 is exhausted from the exhaust port 26. Note that 2 7 is a temperature detecting thermocouple provided in the lower mold assembly 11, 2
A control unit 8 controls the infrared lamp 20 and the driving device 8 as described later.

Next, a method for molding the optical element of the present invention using the molding apparatus will be described. The bracket 15 is raised along the fixed shaft 2, the molding chamber 17 is opened, and the glass material 30A is carried onto the lower mold 13 at the mold opening position below the position shown in FIG.

Next, the bracket 15 is lowered, the molding chamber 17 is closed by the transparent quartz tube 16, and the gas supply path 2 is closed.
An inert gas is supplied from 3, 24, 25 to make the inside of the molding chamber 17 an inert gas atmosphere, and the driving device 8 is operated to raise the moving shaft 9. Increasing the amount of moving shaft 9 is controlled by a servo motor 8a, the set position of either the glass material 30A and the upper die 6 has a slight gap, or pole Ku value slightly contact (FIG. 3 (a) S1 or S2). These are upper mold 6, lower mold 13 and glass material 3
This is because the glass material 30A is brought closer to the upper mold 6 and the lower mold 13 while avoiding damage to 0A, and the glass material 30A described below is heated more efficiently. The positioning of the glass material 30A with respect to the upper mold 6 can be performed with high accuracy by the servomotor 8a because the dimensional accuracy of the glass material 30A is generally high.

Next, the upper and lower mold assemblies 4 and 11 and the glass material 30A are heated by the lamp unit 19 through the transparent quartz tube 16. Since the glass material 30A is a transparent glass, the ratio of direct heating by the radiation from the infrared lamp 20 is low, and the ratio of indirect heating through the mold assemblies 4 and 11 is high. By determining the positional relationship with the mold 6 as described above, the glass material 3
OA is more effectively heated by the upper and lower dies 6,13.

The temperatures of the mold assemblies 4 and 11 are detected by a thermocouple 27 for temperature detection, and the temperature is predetermined as lower than the transition temperature T2 of the glass material 30A as shown in FIG. 3 (c). When the set temperature T1 is reached, the driving device 8 is operated again. If the drive device 8 has been stopped at the set position S1 in FIG. 3A until that time, the moving shaft 9 is raised to the position S2 to move the glass material 30A to the upper mold. Then, as shown in FIG. 3 (b), a press pressure of the set pressure P1 is applied. The set pressure P1 is applied by controlling the torque of the servo motor 8a.

The set temperature T1 and the set pressure P1 are determined as follows. At room temperature, the glass material 30A is hard and brittle, having a viscosity of about 10 ²⁰ poise, so that the molds 6 and 13 are easily damaged at the same time as the glass material 30A itself is damaged. , 13 and the glass material 30A are not damaged. The set temperature T1 is a temperature that does not cause the above-described damage from the relationship with the set pressure P1, and is determined from the relationship with the transition point temperature T2 of the glass material 30A. On the other hand, the set pressure P1 is such that the temperature of the glass material 30A reaches the transition point temperature T2 or the temperature T3 before and after the transition point temperature T2, and the viscosity is 10
When the pressure becomes about ¹³ poise, the glass material 30A can be deformed, and when the temperature of the glass material 30A is lower than the temperature T2 or T3, the pressure is such that the glass material 30A cannot be deformed.

As described above, when the glass material 30A is heated by the upper and lower dies 6 and 13 at the set pressing force P1 and the heating is continued, and when the glass material 30A reaches the temperature T2 or T3 at which the deformation starts, FIG. As shown in FIG.
And the movement axis 9 starts moving from the position S2. The start of movement of the moving shaft 9 from the position S2 is detected by detecting means for detecting a change in the output of the position detecting means of the servomotor 8a, and the detection signal is used to detect the temperature Ta of the mold at that time, that is, the temperature detection thermocouple 27. Read the output and control unit 2
8 is stored. The stored movement start temperature Ta is
Normally, the transition point temperature T2 or T3 does not match, and shows a different value. However, since it is clear from the characteristics of glass that the glass material 30A has the temperature T2 or T3,
The movement start mold temperature Ta is regarded as the temperature T2 or T3, and the following molding control is performed based on the temperature.

Generally, press molding of glass is performed at a temperature T4 which is equal to or higher than the temperature T2 or T3 and equal to or lower than the softening point temperature Tm. The control of the set temperature T4 for molding is performed by controlling the mold temperature to be a value obtained by adding the difference between the temperature T2 or T3 and the set temperature T4 to the movement start mold temperature Ta as described above. Good. This makes the glass material 30A
Is accurately controlled by the set temperature T4, and more accurate press forming is enabled. In actual molding, the temperature T2 or T3 is stored in advance in the control unit 28, and the temperature T2 or T3 and the movement start temperature Ta
It is preferable to correct the set temperature T4 also stored in advance in the control unit 28 by the control unit 28 or to correct the mold detection temperature.

When the mold temperature reaches the corrected set temperature T4, as shown in FIG. 3C , the control unit 28 keeps the mold temperature corrected set temperature T4, that is, the glass material 30A at the set temperature T4. The output of the infrared lamp 20 is controlled. After the temperature rise process from the temperature T2 or T3 to the set temperature T4 and after the temperature reaches the set temperature T4, the glass material 30A is softened and the reaction force against the servomotor 8a is small. Until the closed state is reached, the set torque does not act, but the lower mold 13 is raised by torque control and press molding is performed.

In this way, the lower mold 13 may be raised to the final mold closed state and molded at a stretch, but if the set temperature T4 is set relatively higher than the softening point temperature T2, "fall" will occur. In order to keep the value small, it is good to do as follows. That is, as the lower die 13 is raised, the molding proceeds, and as shown in FIG. 2, the position of the servo motor 8a is reached when the set position S3 (see FIG. The heating by the infrared lamp 20 is stopped by this detection signal, and the gas supply path 2 is detected.
An inert gas such as N ₂ gas, preferably controlled to a predetermined temperature, is supplied to the molding chamber 17 at a predetermined flow rate through the heat insulating cylinders 3a, 10a or directly from the gas supply path 25 to the molding chamber 17, and the mold assembly 4, 11 and the cooling of the glass material 30A are started.

Simultaneously with the start of cooling, as shown in FIG. 3A, the movement of the lower mold 13 is stopped, and the mold temperature is a value obtained by adding a relatively small value α of, for example, about 10 ° C. to the T2 or T3. When the mold temperature has decreased to T2 or T3, the lower mold 13 is moved again to close the shape at a stretch, or when the mold temperature has decreased to substantially T2 or T3 as shown in FIG. Control to reach.
The mold temperature at this time is the movement start mold temperature Ta described above.
Is preferably corrected in consideration of the difference between the heating process and the cooling process, and the mold temperature is
A shows a value closer to the temperature of A itself.

As described above, the lower mold 1 is set at the set position S3.
3 is continuously moved without being temporarily stopped as shown in FIG. 3 (a), and the glass material 30A drops to the temperature T2 or T3 or a temperature slightly higher than the temperature T2 just when the final mold is closed. In this way, the moving speed or / and the cooling speed of the lower mold 13 may be controlled.

The dimension e varies depending on the size and shape of the optical element to be molded, the glass and the mold material used, but the glass material 30A contracts from the temperature of the glass material 30A at the set position S3 to the transition point temperature T2. It only needs to be in quantity or slightly larger, in fact it is a small dimension.

When the movement of the lower mold 13 is stopped by reaching the final mold closed state, the molding is controlled by the torque set by the servomotor 8a and the molding pressure P2 is applied to the glass material 30A as shown in FIG. Complete. Note that FIG.
In (a), after maintaining the molding pressure P2 up to the temperature T5 at which the product can be taken out, the mold is opened and the molded product is taken out. However, when the temperature of the glass material 30A drops to some extent from T2 or T3, the pressure is reduced. You may.

In the above-described embodiment, the lower mold 13 is driven by the servo motor 8a to perform press molding. However, the present invention is not limited to this.
The driving may be performed by a hydraulic or pneumatic device. Also, the pressure diagram shown in FIG. 3B is an example, and it goes without saying that the pressure during the movement of the mold is different depending on the moving speed of the mold, the size of the molded product, and the like. Up to the set temperature T4, the maximum pressure is regulated by the set pressure P1, and the set temperature T for molding is set.
After reaching 4, the pressure is controlled so that the maximum pressure is regulated by the molding pressure P2.

[0029]

As described above, according to the present invention, the temperature of the glass material can be grasped more accurately, accurate molding can be performed, and the "shrinkage" can be suppressed to a small degree, so that a high-precision optical element can be obtained. Can be formed, and the effect of stably forming a good product can be obtained without inducing damage to the mold and the glass material.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of a mold assembly showing a state slightly before a final mold closed state.

FIG. 3 is a curve diagram showing changes in mold position, pressure and temperature in a molding cycle according to one embodiment of the present invention.

[Explanation of symbols]

 2 Fixed shaft 4 Upper die assembly 5 Die plate 6 Upper die 7 Fixed die 8 Drive unit 8a Servo motor 9 Moving shaft 11 Lower die assembly 12 Die plate 13 Lower die 14 Moving die 16 Transparent quartz tube 17 Molding room 19 Lamp unit 20 Infrared ray Lamp 23 Gas supply path 24 Gas supply path 25 Gas supply path 27 Thermocouple for temperature detection 28 Control unit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-149903 (JP, A) JP-A-4-124041 (JP, A) JP-A-3-237022 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) C03B 11/00

Claims (6)

(57) [Claims] 1. A glass material is arranged between a pair of upper and lower molds,
A method for forming an optical element, comprising: detecting and controlling the temperature of the mold to heat and mold the mold and the glass material; After placing a glass material between a pair of upper and lower molds, b. Moving at least one of the upper and lower molds to a set position S1 or S2 where the glass material has a gap with the upper mold or contacts with an extremely small force; c. Then heating the mold and the glass material; d. When the temperature of the mold reaches the set temperature T1 lower than the transition point temperature T2 of the glass material, if the glass material has a gap with the upper mold, the mold is moved to bring the glass material into contact with the upper mold , e. Next, the glass material is pressed and held by the pair of upper and lower molds at a relatively low set pressure P1 capable of starting deformation of the glass material when the glass material reaches the transition point temperature T2 or a temperature T3 before and after the transition temperature T2, f. Thereafter, the point at which the glass material has reached the temperature T2 or T3 is detected from the start of the movement of the mold accompanying the start of deformation of the glass material, and g. Next, based on the temperature Ta of the mold at the time of the detection, the temperature of the glass material is controlled to a set temperature T4 equal to or higher than the temperature T2 or T3 and equal to or lower than the softening point temperature Tm of the glass material, thereby controlling the pair of upper and lower molds. Press forming, h. The method of molding an optical element, wherein the set temperature T1 is a temperature at which the mold and the glass material are not damaged even when the glass material is pressed and held at the set pressure P1. 2. The method of molding an optical element according to claim 1 , wherein: a. In the press molding, when the pair of upper and lower molds is closed to a set position S3 slightly before the final mold closed state, the heating of the mold and the glass material is switched to cooling, b. Next, the temperature of the glass material is set to the temperature T2 or T3.
A method for molding an optical element, comprising: controlling movement and cooling of a mold so that the mold is in a final mold closed state when the mold is lowered to the vicinity. 3. The method for molding an optical element according to claim 1 , wherein: a. In the press forming, when the pair of upper and lower molds is closed to a set position S3 slightly before the final mold closed state, the heating of the mold and the glass material is switched to cooling and the movement of the mold is stopped, b. Next, the temperature of the glass material is set to the temperature T2 or T3.
When the temperature is lowered to a slightly higher temperature, the mold is moved to a final mold closed state. 4. The method for molding an optical element according to claim 1, wherein the position, movement and press pressure of the mold are controlled using a servomotor. 5. A glass material is arranged between a pair of upper and lower molds,
An optical element forming apparatus for detecting and controlling the temperature of the mold and heating and press-molding the mold and the glass material, comprising: a. Means for setting and controlling at least the pressing pressure to a molding pressure P2 and a lower set pressure P1; b. Detecting means for detecting that the mold has started moving with the press pressure set to the set pressure P1, c. Means for storing, in response to a signal from the detecting means, the temperature of the mold at the time of receiving the signal; d. Means for calculating and storing a set temperature for the press forming operation based on the temperature of the mold; e. An apparatus for forming an optical element, comprising: a control unit comprising: an operation command unit for performing a press forming operation in accordance with the set temperature. 6. The optical element molding apparatus according to claim 5, wherein the driving source of the mold is a servomotor capable of controlling position, speed and torque.