JP2001080924A - Method and device for molding optical glass element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the dispersion in a shape of a molding caused by the weight difference of a glass material, the difference of molding shapes and the difference of setting positions, or the like, by controlling a pressing pressure added to a die while using the die temperature and the shaft position as the conditions to decide the pressing pressure in order to allow the thickness of an optical glass element to have a set value at a press step in the cooling process to mold by a glass molding method. SOLUTION: The pressing pressure is controlled so that the pressure is increased when the difference between the shaft position in the pressing direction of the molding die and the target position is small in comparison with that of the die temperatures and the pressure is decreased when it is large. The device for molding the optical glass element is provided with a detection means for detecting the die temperature and the shaft position, respectively, comparison means for comparing the detected values with the target values, respectively, and a pressing pressure control means for successively deciding/controlling the pressure based on the compared results. The device is also provided with upper and lower molding dies 1, 2, an upper side press shaft 3, a load cell 4 for measuring the pressing pressure, and an electric servomotor 5 for driving the shaft 3. The position of the shaft 3 is decided by a pulse signal to be sent to the servomotor 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for molding an optical glass element by a glass molding method, and more particularly, to a thickness (thickness) of the molded optical glass element.
The present invention relates to a method and apparatus for molding an optical glass element devised so as to maintain a constant.

[0002]

2. Description of the Related Art Conventionally, in a glass molding method, a glass material is heated and softened, and a pressing pressure is applied in the softened state to transfer a mold shape (optically functional surface) to the glass material. At this time, since the linear expansion coefficient of the glass is generally larger than the linear expansion coefficients of the mold and the spacer, even during the cooling process, a pressing pressure is applied to the mold to bring the glass material into contact with the surface of the mold until the final stage. As described above, a method of maintaining under pressure is adopted.

In this glass molding method, when molding a certain kind of optical glass element, molding conditions such as molding amount, molding time, molding pressure, heating temperature and heating time are as follows.
It was set before molding and molding was repeated under the same conditions. In this molding method, if the weight (volume) and shape of the glass material before molding were exactly the same, there was no particular problem, and the same molded product (optical glass element) was obtained.

However, in reality, it is difficult to make the size of the glass material supplied to the molding die exactly the same every time molding is performed, and there is a slight difference in weight (volume) and shape. For this reason, when the molding is repeated under the same molding conditions as described above, the glass material slightly harder than the reference size hardens against the pressing pressure before the molding proceeds to the reference value (that is, the predetermined In the case of a slightly smaller glass material, there is a problem that the molding proceeds more than planned (that is, the glass material becomes thinner than the planned thickness).

[0005] In other words, when the weight (volume) of the glass material is large, the glass is larger than usual at the time of molding and extends to the outer periphery of the mold surface (the diameter becomes large), so that the area to be molded becomes large. The pressing pressure applied per unit area is reduced. Therefore, when press molding is performed for the set standard molding time, a glass molded product (optical glass element) having a thickness greater than the reference value is produced. On the other hand, if the weight (volume) is large, it takes a long time to heat the glass due to a large heat capacity, and the glass is not sufficiently softened by the set heating time, and as a result, the molding amount under the same pressing pressure is insufficient. In addition, an optical glass element having a thickness larger than the reference value is produced. If the weight (volume) of the glass material is small, the reverse is true, and the glass molded product (optical glass element) having a small thickness is obtained.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 3-193630, a method has been proposed in which the molding temperature is changed in accordance with the size (weight) of the glass material to make the wall thickness constant. I have. However, if the molding temperature is changed, the viscosity of the glass, the shape of the molding surface of the molding die during molding, the amount of heat shrinkage between the glass molded product and the molding die during cooling, etc. will differ. Even if the thickness becomes constant, the refractive index and the shape of the formed optical glass element (particularly, lens-based element) vary, which is not preferable.

In consideration of these problems, Japanese Patent Laid-Open No. 10-1
According to the invention described in Japanese Patent Application No. 67737, the weight of a glass material before molding is measured, and one or more molding materials are selected from a moving distance of a molding die, a molding time, a molding pressure, and a heating time in accordance with the weight. A method of changing conditions is employed.

[0008]

However, in recent years,
The demand for optical elements such as an aspherical lens and a free-form surface lens is rapidly increasing, and the shape accuracy required for such optical elements is much stricter than that of conventional optical elements. Also, the shapes of optical elements to be molded (particularly, lens-based elements) are also various, and the amount pressed during cooling (the amount of mold movement) depends on the difference in shape of the glass material before molding or the molding die. It is easily affected by the position of the glass material placed inside. Therefore, a method of measuring the weight of a glass material before molding and controlling the press amount, the press pressure, and the like in accordance with the weight cannot be used anymore.

Further, in order to measure the weight of the glass material, a glass weight measuring device is required in addition to the molding machine.
Additional places to install the equipment are also needed extra. In addition, since the glass material conveyance path becomes complicated, continuous molding may be interrupted due to a glass material conveyance error (eg, drop).

[0010] The present invention has been made based on the above circumstances, and the object thereof is to achieve a weight difference between glass materials,
In order to provide a molding method and a molding apparatus for an optical glass element, which can suppress a variation in the shape of a molded article (optical glass element) caused by a difference in shape, placement, and the like, and can obtain a molded article better than a conventional molding method. is there.

[0011]

Therefore, in the present invention,
In a molding method of an optical glass element in which a glass material is heated and softened and press-molded by a molding die, in order to set a thickness of the molded optical glass element to a set value, in a pressing step in a cooling process, The press pressure applied to the mold is controlled by using the temperature and the shaft position as conditions for determining the press pressure.

In this case, as an embodiment of the present invention,
For the temperature of the molding die, if the axial position of the molding die in the pressing direction is smaller than a preset target position, the pressing pressure is increased, and if it is larger than the target value, the pressing pressure is decreased. It is effective to control.

According to the present invention, in a molding apparatus of an optical glass element for heating and softening a glass material and press-molding the glass material by a molding die, a cooling process is performed to set the thickness of the molded optical glass element to a set value. In the pressing step, a detecting means for respectively detecting the temperature and the axial position of the mold, and a comparing means for comparing a value detected by the detecting means with a target value,
It is characterized by comprising a press pressure control means for determining and controlling successive press pressures based on the comparison result.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. Here, the glass material is press-molded at a predetermined temperature at which it can be deformed, and after the load applied to the glass molded product in the mold becomes substantially zero, the process moves to the cooling process, and further, the pressurization is performed again during the cooling process. After that, in the molding method of the optical element for removing the molded product from the mold, the pressure for re-pressing in the cooling step is determined by referring to the position of the press shaft (of the movable molding die) and the set position at the temperature at that time. In comparison, if the amount of pressing (the amount of movement of the mold) is too large, the pressing pressure is reduced, and if the amount of pressing is small, the pressing pressure is increased. Thus, in the temperature range in which the glass is repressurized during the cooling step, the pressure is constantly applied to the glass, and the glass is controlled so as to have a predetermined thickness at the temperature of the end of the repressurization during cooling. A molding apparatus for this purpose will be clarified in the following embodiments.

(First Embodiment) Next, a first embodiment of the present invention will be specifically described with reference to FIG. The molding apparatus here includes upper and lower molding dies 1 and 2, a press shaft 3, a load cell 4 for measuring press pressure, and an electric servomotor 5 for driving the press shaft 3. The position of the press shaft 3 is determined by a pulse signal sent to the electric servomotor 5.

In this molding apparatus, the press shaft 3
Is detected by a suitable detecting means (not shown), and the above detection result is obtained by comparing means (not shown).
Within a predetermined press time, the temperature is compared with a preset reference value of the amount of press movement using the temperature of the molding die at that time as a parameter, and based on the comparison result, press pressure adjustment control (that is, electric servomotor 5 (pulse signal control for the drive of No. 5).

More specifically, when pressure is applied to the press shaft 3 in the press direction by driving the electric servomotor 5, the press shaft 3 and the load cell 4 are compressed or bent, and the frame of the molding machine is elongated. I do. When heat is applied to the mold, the press shaft 3 and the frame of the molding machine undergo thermal expansion.

In this case, since the electric servomotor 5 is located at a position distant from the molding die, the position of the tip of the movable molding die is actually determined by the change in press pressure and temperature, and the pulse applied to the electric servomotor 5 is changed. There is a difference from the electrical display position.

In order to eliminate these effects, first, in a molding apparatus, a dummy mold is attached instead of a mold,
With the dummy type (fixed type and movable type) abutting each other,
Change the press pressure and record each axis position indication. Next, the temperature of the mold is changed, and the same measurement is performed. The results are shown in the graph.
As shown in FIG. 5, it is understood that the mold temperature and the shaft position are in an inversely proportional relationship as shown in FIG. This can be approximated by the following equation.

Z = a (P / T) + b where Z: axis position,
P: press pressure, T: mold temperature, a, b: constants. From this equation, if the press pressure and temperature are known, the actual position of the molding die (press shaft) can be obtained using the shaft position displayed on the molding machine. This is prepared and put in advance before molding.

Next, the molding process will be described step by step with reference to the process diagram at the time of molding (FIG. 3). First,
The material for the optical glass element (SK12 was used as the glass material) was heated to 580 ° C., kept at that temperature for several minutes, the glass was softened, and the first press (e) was moved to the predetermined axial position (c). ) Until it reaches. Next, a rough estimate of a press allowance to be performed during a press temperature range (550 ° C. to 450 ° C.) during cooling is obtained from data obtained when a conventional molding method is used while molding at a constant press pressure. In this example, the amount pressed during cooling was about 30 microns, so 30 microns was used as the reference value.

Then, 30 microns is pushed during the temperature difference of 100 ° C. to cool from 550 ° C. to 450 ° C.,
The press shaft needs to move at 0.3 microns / ° C.
Here, at the starting temperature (a) of the second press (f), a press pressure of 4000 N is applied and then the mold is
Each time the temperature is cooled by 0 ° C., the position of the measurement axis (the position corrected from the value of the equation obtained first, the same applies hereinafter) is compared with the target axis position (on the line d), and the position of the measurement axis is determined. If the position has not been reached, increase the press pressure (here 5
00N). If the measurement axis position is beyond the target position, the press pressure is reduced (here, 5
00N).

As a result of molding, as described above, in the set temperature range, it is possible to always apply pressure to the glass, and furthermore, it is possible to suppress the variation of the axial position at the pressing end temperature to within ± 2 μm. Was. The molded article using this process could have a thickness accuracy within ± 2 microns.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. Here, reference numerals 6 and 7 denote upper and lower molding dies, 8 and 9 denote upper and lower body dies, 10 denotes an upper press shaft, 12 denotes a lower press shaft, and 13 and 14,
An electric servomotor for each press shaft is shown. Here, by controlling the interval between the molding dies in the first press by lowering the press shaft 10 and abutting the barrel dies, it is possible to make the control more accurate than in the previous embodiment.

Thereafter, the control of the second press during cooling is as follows:
The operation is performed in the same manner as in the first embodiment by raising the press shaft 12. The shaft position of the press shaft 12 at this time is obtained in advance by a calculation formula, and is corrected and set, as in the first embodiment.

[0026]

As described above, according to the present invention,
In the molding by the glass molding method, variations in the refractive index and the shape of the optical glass element to be molded can be reduced, and in particular, the thickness can be controlled to be constant. Further, when the control of the press pressure is continuously changed using the PID control, the molding can be realized with higher accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a molding machine showing a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a molding machine showing a second embodiment of the present invention.

FIG. 3 is a process diagram according to the first embodiment of the present invention.

FIG. 4 is a graph showing a relationship between a press pressure and an axial position according to the present invention.

FIG. 5 is a graph showing the relationship between shoulder temperature and shaft position according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper molding die 2 Lower molding die 3 Upper pressing shaft 4 Load cell 5 Electric servo motor 6 Upper molding die 7 Lower molding die 8 Upper trunk die 9 Lower trunk die 10 Upper press shaft 12 Lower press shaft 13, 14 Electric servo motor

Claims (3)

[Claims] In a method for forming an optical glass element, wherein a glass material is heated and softened and press-formed by a forming die, a pressing step in a cooling process is performed to set a thickness of the formed optical glass element to a set value. The method of molding an optical glass element, wherein the press pressure applied to the mold is controlled using the temperature and the axial position of the mold as conditions for determining the press pressure. 2. The press pressure is increased when the axial position in the press direction of the mold is smaller than a preset target position with respect to the temperature of the mold, and the press pressure is increased when the axial position is larger than the target value. The method for forming an optical glass element according to claim 1, wherein the control is performed so as to reduce the amount. 3. In a molding apparatus for an optical glass element which heats and softens a glass material and press-molds it with a molding die, a pressing step in a cooling process is performed in order to set a thickness of the molded optical glass element to a set value. In, detecting means for detecting the temperature and the axial position of the mold, respectively, comparing means for comparing the detection value by the detecting means with the target value, based on the comparison result, to determine the sequential press pressure And a press pressure control means for controlling.