JP4166619B2 - Optical element molding method and molding apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technology for manufacturing an optical element such as a lens, and more particularly to a technology for manufacturing an optical element by pressure molding.
[0002]
[Prior art]
In the technology of manufacturing optical elements by pressure molding in a state where the molding material, which is a glass material, is heated and softened, it is caused by the thermal contraction of the molded body in the cooling process after pressure molding once In order to suppress a decrease in molding accuracy due to sink marks or the like generated in the past, a technique for applying pressure to the molded body in the cooling process has been proposed.
[0003]
For example, in Patent Document 1 and Patent Document 2, a first body mold having a high thermal expansion coefficient and a second body mold having a lower height between the upper and lower sides than the first body mold at high temperatures are referred to as upper and lower molds. Place it in between and press the material to be molded while the upper and lower molds are in contact with the first body mold at a high molding temperature where the material to be molded is soft. As a result of the thermal contraction of the first body mold while cooling, the distance between the upper and lower molds is narrowed, and eventually the upper and lower molds come into contact with the second body mold to complete the molding of the desired shape. .
[0004]
Also, for example, in Patent Document 3, an upper and lower mold that can be moved independently in the vertical direction is prepared, and the upper mold is lowered to a predetermined position where the spacer abuts while fixing the position of the lower mold at the molding temperature. Pressurization with the first predetermined pressure is performed, and in the subsequent cooling step, the upper mold is fixed at the predetermined position and the lower mold is lifted to perform pressurization with the second predetermined pressure to form a desired shape. The method of completing is disclosed.
[0005]
Furthermore, for example, in Patent Document 4, when a material to be molded that has been heated to a molding temperature that is higher than the transition point and lower than the softening point is pressed from the lower mold and molded, the position is first controlled by a servo motor. Start the torque control after moving the mold to the set position slightly before the final mold closed state, pressurize the material to be molded at the first predetermined pressure, and then continue pressurizing with the slight pressure from the lower mold Then, cooling is started while maintaining the shape of the molding material, and after reaching a temperature near the transition point, the molding material is pressed from the lower mold with a second predetermined pressure until the transition point is reached. There has been proposed a method of completing the molding.
[0006]
[Patent Document 1]
JP-A-6-256025
[Patent Document 2]
JP 2002-29763 A
[Patent Document 3]
JP-A-6-16432
[Patent Document 4]
Japanese Patent No. 3143575
[0007]
[Problems to be solved by the invention]
In the methods disclosed in Patent Document 1 and Patent Document 2 described above, when the amount of heat shrinkage of the material to be molded exceeds the amount of heat shrinkage of the second body mold, for example, molding of a thick optical element is performed. In the case of performing the process, it is conceivable that release of the material to be molded from the mold occurs in the cooling process, which causes a decrease in the molding accuracy of the optical element.
[0008]
Further, in the methods disclosed in Patent Document 1, Patent Document 2, and Patent Document 3, control of the deformation amount of the shape of the molded body in accordance with the temperature during the cooling step performed after pressurization at the molding temperature. Therefore, it is conceivable that the individual performance of the optical element finally formed varies due to variations in the cooling rate in the cooling process.
[0009]
Furthermore, in the method disclosed in Patent Document 4 described above, a press in which pressing with a molding die that is continued until the temperature near the transition point is reached in the cooling step performed after pressing under the molding temperature is very small. If the material to be molded has a large amount of thermal shrinkage, for example, when molding an optical element including a thick part, so-called sink marks are formed due to uneven temperature drop in the cooling process. It is thought that it will occur. In order to prevent this sinking, for example, it is effective to reduce the cooling rate of the material to be molded. However, reducing the cooling rate causes a decrease in the production efficiency of the optical element.
[0010]
In order to cancel such sink marks, it is possible to take a technique of further increasing the pressing force of pressurization or performing pressurization over a long time, for example, in final press molding performed later. However, if the pressing force of pressurization is excessively increased, the internal stress of the optical element to be formed will remain non-uniformly, the optical refractive index will become non-uniform, and the performance of the optical element will be degraded. Moreover, if the pressurization time is lengthened, the production efficiency of the optical element is eventually lowered.
[0011]
In the method disclosed in Patent Document 4, the absolute position of the lower mold is controlled by a servo motor during pressurization at the molding temperature, so that the upper and lower molds are thermally deformed and the upper and lower molds are held. It is conceivable that the molding accuracy of the optical element finally formed decreases due to the thermal deformation of the shaft.
[0012]
The present invention has been made in view of the above-described problems, and a problem to be solved is to improve molding accuracy in pressure molding of optical elements.
[0013]
[Means for Solving the Problems]
  An optical element molding method according to one aspect of the present invention includes:In a method for molding an optical element, which is an optical element formed by pressure-molding a glass material to be molded with a pair of molds,The material that has been softened by being heated to a temperature higher than the yield point temperature of the glass material itself.The pair ofPress with a mold,A pressing step of setting the thickness of the material to a set thickness that is thicker than a thickness desired for an optical element; and maintaining the pressure on the glass material to be molded while maintaining the pressing The thickness of the material is formed to the desired thickness before cooling to a temperature below the yield point temperature and above the transition temperature of the material itself.In addition, the thickness of the material is controlled by controlling the temperature of the material based on the elapsed time from the time when the thickness of the material reaches the set thickness and the distance between the pair of molding dies at that time. Is a constant time from the set thickness to the desired thicknessA cooling molding step, and the above-described problems are solved by using this method.
[0014]
  According to this method, since the material is molded to a desired thickness before being cooled to the temperature described above while maintaining the pressure on the glass material to be molded, the occurrence of sink marks is prevented, and as a result, molding accuracy is improved. improves.
  In addition, as a result of being able to suppress variations in time required to form the material to a desired thickness due to variations in the glass material itself, variations in temperature around the molding apparatus, etc., the molded optical element Variations in the optical characteristics are reduced.
  In the cooling molding step of the optical element molding method according to the present invention described above, when the temperature of the glass material to be molded reaches a temperature below the intermediate point between the yield point temperature and the transition point temperature, the material is formed. The raw material can be molded to the desired thickness while maintaining the temperature of the material.
[0015]
  According to the results of experiments described later, this can significantly improve the molding accuracy..
[0019]
  Also,In the pressurizing step in the optical element molding method according to the present invention described above, the determination that the thickness of the glass material to be molded has reached the set thickness is based on the output of the sensor that detects the position of the mold. Can be made based on.
[0020]
By doing so, it is possible to detect that the thickness of the glass material to be molded, which is difficult to detect directly, has reached the set thickness.
Further, in the cooling molding step of the optical element molding method according to the present invention described above, the determination that the thickness of the glass material to be molded has been molded to the desired thickness is determined by a pair of opposing surfaces. It can be performed based on detection of the contact of the mold.
[0021]
  By doing so, it becomes possible to detect that the thickness of the glass material to be molded, which is difficult to detect directly, is formed to a desired thickness..
[0022]
  BookAn optical element molding apparatus according to another aspect of the invention includes:In an optical element molding apparatus that press-molds a glass material to be molded into an optical element,Opposing to form by pressing the glass material to be softened by heatingA pair ofA mold,A mold for detecting that the distance between the pair of molds approaches a predetermined distance, and that the thickness of the material has reached a set thickness that is thicker than the thickness desired for the optical element. An approach detection means; a mold contact detection means for detecting that the distance between the pair of molds has approached a predetermined distance and the thickness of the material has reached the desired thickness; and In order to make the time from detection of the mold approach detection means to detection of the mold contact detection means constant, based on the elapsed time from the detection of the mold approach detection means and the distance between the pair of molds at that time SaidAnd a temperature control means for controlling the temperature of the material. By using this apparatus, the above-mentioned problems are solved.
[0023]
According to this apparatus, the apparatus is used for the optical element molding method according to the present invention described above by controlling the temperature of the glass material to be molded based on the positional relationship between the molds facing the temperature control means. Can be implemented. Therefore, by using this apparatus, the molding accuracy of the optical element to be molded is improved.
[0026]
  According to this configuration, in the optical element molding method according to the present invention described above, the glass material to be molded has the above-described desired thickness when the opposing molds come into contact with each other. Enables detection of completion of cooling molding process.
[0027]
  ThisAccording to the configuration of the present invention, the glass material to be molded has the set thickness described above when the distance between the facing molds is the predetermined interval described above. It is possible to detect the completion of the pressing step in the optical element molding method.
[0029]
According to this configuration, it is possible to suppress variations in time required to form the material into a desired thickness due to variations in the glass material itself or variations in temperature around the molding apparatus. Variations in the optical characteristics of the optical elements are reduced.
[0030]
The optical element molding apparatus according to the present invention described above may further include a distance measuring means for measuring the distance between the opposing molds.
According to this configuration, the temperature control means can control the temperature of the glass material based on the measurement result of the distance measurement means.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described with reference to the drawings.
  FIG. 1 shows the structure of a molding apparatus according to the present invention.
  In FIG.Molding room1 has a heater 3 installed,Molding roomA water-cooled pipe 4 is embedded in the outer cover portion 2 that surrounds 1. When heater 3 operatesMolding room1 is heated, and when a pump (not shown) is operated to flow water into the water-cooled pipe 4.Molding room1 is cooled. A programmable controller (PLC) 5 controls the operation of the heater 3 and the pump.Molding room1 can be heated and cooled to a predetermined temperature,Molding roomIt is also possible to change the speed of temperature change of 1.
[0033]
  Molding room1 includes a fixed-side template 6 attached to the fixed shaft 7 and an operating-side template 9 attached to the moving shaft 10. Here, the fixed side template 6 and the fixed shaft 7 do not move, but the moving shaft 10 moves in a direction approaching or moving away from the fixed side template 6 by operating a driving device (not shown). In accordance with the movement, the working side template 9 also moves in that direction. The PLC 5 also controls the operation of the driving device, and can move the working side template 9 in the above-described direction and can maintain a stopped state at a desired position.
[0034]
An upper die 8 is attached to the fixed side template 6, and a lower die 11 is attached to the working side die 9 so as to face the upper die 8. In FIG. 1, a molding material 12, which is a glass material preformed in a cylindrical shape, is placed on the molding surface of the lower mold 11. Thereafter, the heater 3 is operated to bring the material 12 to be heated and softened, and the above-described driving device is operated to move the lower mold 11 upward to face the molding surface of the upper mold 8 facing each other. The optical element is molded by pressurizing (pressing) the cylindrical surface of the molding material 12 until the molding surface of the mold 11 abuts, and then cooling and curing the molding material 12.
[0035]
As can be seen by referring to the shapes of the molding surfaces of the upper die 8 and the lower die 11 shown in FIG. 1, the optical element formed at this time has a triangular prism shape with one concave side surface. It becomes a glass prism (one-sided spherical prism). The reason why the material 12 that is preformed in a cylindrical shape is used as the material to be molded 12 in this embodiment is that a prism having a prism shape can be formed without trapping air between the mold and the glass.
[0036]
The mold contact detection contact 13 provided on the working side mold plate 9 and the fixed side mold plate contact A14 provided on the fixed side mold plate 6 so as to oppose this constitute a contact sensor. The contact between 8 and the lower mold 11 is detected. When the lower die 11 rises and the upper die 8 and the lower die 11 come into contact with each other, the die contact detection contact 13 and the fixed mold plate contact A14 come into contact with each other and short-circuit, and current flows from the battery A15 to the coil in the relay A16. Flows. At this time, the two contacts in the relay A16 are brought into contact with each other by the magnetic force generated in the coil, so that the two wires connecting the respective contacts and the PLC 5 are electrically connected, so that the lower mold 11 comes into contact with the upper mold 8. It is detected by the PLC 5 that it has been reached.
[0037]
The mold proximity detection contact 17 provided on the working-side template 9 and the fixed-side template contact B18 provided on the fixed-side template 6 opposite thereto constitute a contact sensor. It is detected that the distance between the mold 8 and the lower mold 11 has approached a predetermined interval. When the upper mold 8 and the lower mold 11 approach each other to a predetermined distance, the mold proximity detection contact 17 and the fixed-side mold plate contact B18 come into contact with each other to short-circuit, and a current flows from the battery B19 to the coil in the relay B20. At this time, when the two contacts in the relay B20 come into contact with each other by the magnetic force generated in the coil, the two wires connecting the respective contacts and the PLC 5 are electrically connected, so that the lower mold 11 is separated from the upper mold 8 by a predetermined distance. It has been detected by the PLC 5 that it has reached a position far away from it.
[0038]
When the upper die 8 and the lower die 11 are further brought closer after the die proximity detection contact 17 and the fixed die plate contact B18 come into contact with each other, the die proximity detection contact 17 is projected to a predetermined position protruding from the working side die 9. Since the coil spring 21 holding the die is compressed and the die proximity detection contact 17 is accommodated inside the working side die plate 9, the upper die 8 and the lower die 11 can be brought into contact with each other.
[0039]
The displacement sensor 22 is a sensor that measures the distance between the upper mold 8 and the lower mold 11 and gives the value to the PLC 5. Here, a linear scale used for position detection is used.
Next, the procedure of the optical element molding method embodying the present invention performed using the molding apparatus shown in FIG. 1 will be described.
[0040]
First, FIG. 2 will be described. This figure is a diagram showing a state of control of the molding apparatus shown in FIG. The graph shown in the figure shows, in order from the top, the temperature change of the material 12 to be molded, the change in the press pressure on the material 12 to be molded by the upper die 8 and the lower die 11, and the change in the position of the lower die 11. The horizontal axis indicates the passage of time. In the present embodiment, the PLC 5 performs heating / cooling / pressing on the material 12 and control of the position of the lower mold 11.
[0041]
Before starting the process shown in FIG. 2, the lower mold 11 is lowered, and the material 12 to be molded is placed on the molding surface of the lower mold 11. Note that the position of the lower mold 11 at this time is the position of “displacement 0”. At this time, since the material 12 to be molded is not in contact with the upper mold 8, the pressing force is naturally “0”.
[0042]
  First, in the period of FIG. 2A (nitrogen replacement period), in order to prevent the molding material 12 from being oxidized in a later step,Molding roomNitrogen is sent into 1 to discharge air (oxygen).
  Molding roomWhen the inside of 1 has a sufficient nitrogen atmosphere, the control shifts to the period (b) (heating period), and the PLC 5 operates the heater 3.Molding room1 is heated to a temperature Ta slightly higher than the yield point temperature At. Here, the yield point temperature refers to a temperature at which thermal expansion does not occur when the glass material that is the material to be molded 12 is heated, and contraction starts when heated further.
[0043]
  After moving to period (b)Molding roomWhen a sufficient time has passed so that it can be considered that the temperature of 1 has reached Ta, the control shifts to the period (c) (soaking period), and the PLC 5 controls the operation of the heater 3 to set the temperature Ta at this time. The material to be molded 12 is made uniform at the temperature Ta throughout.
[0044]
When a sufficient time has passed so that it can be considered that the material to be molded 12 has reached the temperature Ta throughout the period after the period (c), the control proceeds to the period (d) (filling period), and the PLC 5 is a heater. 3, while continuing the operation control of 3 and maintaining the temperature of the molding material 12 at this time with Ta, the operation of the driving device (not shown) is started to raise the lower die 11, and the lower die 11 and the upper die 8 The material to be molded 12 is pressed and deformed with a constant press pressure Pa.
[0045]
When the molding material 12 is deformed by this pressurization, the working side mold plate 9 gradually approaches the fixed side mold plate 6 and eventually the mold proximity detection contact 17 and the fixed side mold plate contact B18 come into contact with each other. In FIG. 2, the position of the lower mold 11 when the mold proximity detection contact 17 and the fixed-side mold plate contact B18 first contact each other is indicated as “displacement A”. In addition, the to-be-molded material 12 at this time does not have a shape desired as an optical element as a finished product, and has a wall thickness (the above-described set wall thickness) thicker than the desired one. Yes.
[0046]
  When this contact is detected, the control shifts to the period (e) (first slow cooling period), and the PLC 5 controls the operation of the heater 3 while maintaining the pressurization pressure Pa on the material 12 to be molded. do itMolding roomThe heating amount of 1 is gradually reduced. Then, the material 12 to be molded is gradually cooled, and the temperature gradually falls below the yield point temperature At from Ta, so that the force of pressing the lower mold 11 and the upper mold 8 due to thermal expansion is weakened. The position further rises from “Displacement A”.
[0047]
  afterwards,Molding roomWhen the heating amount of 1 continues to decrease and the force decreases due to thermal expansion of the material 12 to be molded, and the position of the lower mold 11 that continues to rise reaches “displacement B” in FIG. 2, the lower mold 11 and the upper mold 8 is detected by the PLC 5 by a short circuit between the mold contact detection contact 13 and the fixed-side template contact A14. When the lower mold 11 and the upper mold 8 come into contact with each other, the shape of the material 12 to be molded is a desired thickness and shape as an optical element as a finished product.
[0048]
Note that the working side template 9 of the mold proximity detection contact 17 is previously set so that the temperature of the molding material 12 when this contact occurs is within the range of the yield point temperature At and below the transition point temperature Tg. Set the amount of protrusion from. Here, the transition point temperature is a value representing a temperature range in which the glass material that is the molding material 12 is transitioned from an elastic state to a viscoelastic state when heated, and specifically, the glass material is in an elastic state. The temperature at the intersection of the thermal expansion line indicating the rate of thermal expansion with respect to the temperature change when the glass material is in the state and the thermal expansion line indicating the rate of thermal expansion with respect to the temperature change when the glass material is in the viscoelastic state. Therefore, when the lower mold 11 and the upper mold 8 are in contact with each other, it can be said that the molding material 12 is in a viscoelastic state.
[0049]
  When the contact between the lower mold 11 and the upper mold 8 is detected, the control shifts to the period (f) (distortion removal period), and the PLC 5 controls the operation of the heater 3.Molding room1 is slightly increased to maintain the molding material 12 at the temperature Tb when the lower mold 11 and the upper mold 8 come into contact with each other, and the operation of a driving device (not shown) is controlled to control the molding material 12. Is continuously pressed with a press pressure Pb smaller than the press pressure Pa described above to maintain the state in which the lower die 11 and the upper die 8 are in contact with each other. By this step, the distortion in the material to be molded 12 that becomes a deterioration factor of the optical characteristics when it remains in the molded optical element is released.
[0050]
  When a sufficient time has passed so that it can be considered that the internal strain of the material to be molded 12 has been released after the period (f), the control proceeds to the period (g) (second slow cooling period), and the PLC 5 is a heater. Control the movement of 3Molding roomThe molding material 12 is gradually cooled by gradually decreasing the heating amount of 1 again so that the temperature is lower than the transition temperature Tg. At this time, the abutting state between the lower mold 11 and the upper mold 8 is maintained, but the force of pressing the lower mold 11 and the upper mold 8 due to thermal expansion gradually decreases by lowering the temperature of the material 12 to be molded. Therefore, in accordance with this, the operation of the driving device (not shown) is controlled so that the press pressure for maintaining the contact state between the lower mold 11 and the upper mold 8 is gradually reduced from the aforementioned value Pb.
[0051]
  When a sufficient time has passed so that it can be considered that the temperature of the material 12 to be molded has fallen below the transition temperature Tg after the period (g), the control proceeds to the period (h) (quenching period), and the PLC 5 is a heater. 3 is stopped and a pump (not shown) is operated to flow water into the water-cooled pipe 4.Molding room1 is rapidly lowered to control the material 12 to be rapidly cooled. Also at this time, in order to maintain the contact state between the lower mold 11 and the upper mold 8, pressurization is continued with a very weak press pressure that maintains the elasticity of the material 12 to be molded.
[0052]
Thereafter, when a sufficient time has passed so that it can be considered that the temperature of the material 12 to be molded has been cooled to a level where it can be taken out after the period (h), the control proceeds to the period (i), and the PLC 5 is not activated. The operation of the illustrated pump is controlled to discharge water in the water cooling pipe 4. Subsequently, the control shifts to the period (j), and the operation of a driving device (not shown) is controlled to lower the lower mold 11 to the position of “displacement 0” which is the initial position. The material 12 is taken out to complete a series of molding.
[0053]
The above procedure is the optical element molding method for carrying out the present invention. In addition, when implementing the shaping | molding method mentioned above, the displacement sensor 22 shown in FIG. 1 is not necessarily required.
By the way, in the slow cooling of the molding material 12 in the first slow cooling period (period (e) of FIG. 2) in the above-described molding method, the amount of protrusion of the mold proximity detection contact 17 from the working side mold plate 9 is set in advance. By setting, the temperature Tb of the material 12 to be molded when the lower mold 11 and the upper mold 8 are in contact with each other is included in the range of the yield point temperature At or lower and the transition point temperature Tg or higher. I was doing. However, in this control, since the temperature is lowered regardless of the degree of deformation of the molding material 12, the mold proximity detection contact 17 and the mold proximity detection contact 17 are caused by variations in the molding material 12 itself and temperature variations around the molding apparatus. There may be variations in the time from when the fixed mold plate contact B18 comes into contact with when the lower mold 11 and the upper mold 8 come into contact. This variation can cause variations in the cycle time during molding and can cause variations in the optical characteristics of the optical element after molding. In order to cope with this problem, it is preferable to control the cooling rate of the molding material 12 based on the degree of deformation of the molding material 12. Hereinafter, this control method will be described with reference to FIG.
[0054]
FIG. 3 shows the temperature change (temperature change from point C to point D) of the molding material 12 in the vicinity of the period (e) (first slow cooling period) of the control state shown in FIG. The change in the position of the mold 11 (change in the position from the displacement A to the displacement B) is shown in an enlarged manner.
[0055]
  (1) in FIG. 3 shows a case where the temperature change speed of the material 12 to be molded varies, and the contact between the mold proximity detection contact 17 and the fixed mold plate contact B18 at point A in FIG. The PLC 5 controls the operation of the heater 3 by being detected.Molding roomAlthough the heating amount of 1 is decreased at a constant rate, the rate of temperature decrease of the molding material 12 varies (from the change of graph C → D-1 to the change of graph C → D-2 in the figure). As a result, the time of contact between the lower mold 11 and the upper mold 8 varies in the range from point B-1 to point B-2 in the figure, and the length of the first slow cooling period is also ( It varies from e) -1 to (e) -2.
[0056]
Therefore, in order to cope with such a case, the PLC 5 detects the contact between the mold proximity detection contact 17 and the fixed mold plate contact B18 between the lower mold 11 and the upper mold 8 when the contact is detected. The measurement of the distance is started, and the measurement result is sequentially acquired from the displacement sensor 22. Further, the PLC 5 has a space between the lower mold 11 and the upper mold 8 in a period from the contact between the mold proximity detection contact 17 and the fixed mold plate contact B 18 to the contact between the lower mold 11 and the upper mold 8. Table data indicating an appropriate relationship between the distance and the elapsed time from the contact between the die proximity detection contact 17 and the fixed-side template contact B18 is prepared in advance.
[0057]
  Here, the distance between the lower mold 11 and the upper mold 8 measured by the displacement sensor 22 when a certain period of time has elapsed from the contact between the mold proximity detection contact 17 and the fixed-side mold plate contact B18 is the table described above. When the distance is shorter than the distance indicated in the data, the PLC 5 controls the operation of the heater 3 to reduce the rate of reduction of the heating amount of the molding chamber 1 and to moderate the rate of temperature decrease of the molding material 12. On the other hand, when the distance between the lower mold 11 and the upper mold 8 measured by the displacement sensor 22 is longer than the distance indicated in the table data described above, the PLC 5 controls the operation of the heater 3.Molding roomThe rate of temperature decrease of the material to be molded 12 is increased by increasing the rate at which the heating amount of 1 is decreased. That is, the distance between the lower mold 11 and the upper mold 8 is regarded as the degree of deformation of the molding material 12, and the PLC 5 is controlled to control the cooling speed of the molding material based on this distance.
[0058]
As a result, the speed of the temperature change of the material 12 to be molded can be made constant (change of graph C → D in the figure) as shown in FIG. The time of contact between the lower mold 11 and the upper mold 8 is always set to point B in the figure, and the length of the first slow cooling period can be stabilized at (e), which is caused by the above-described variation. Variation in optical characteristics of the optical element after molding due to variation in cycle time is suppressed.
[0059]
FIG. 4 shows experimental data when the molding method according to the present invention described above is performed.
In FIG. 4, (1-1) and (1-2) are data of an experiment in which the press pressure Pa in the pressurization to the molding material 12 in the filling period (period (d) in FIG. 2) is changed. (2-1) and (2-2) are experimental data obtained by changing the press pressure Pb in pressurizing the material 12 during the strain removal period (period (f) in FIG. 2), and (3-1) ) And (3-2) show experimental data in which the temperature Tb of the molding material 12 held in the strain removal period (period (f) in FIG. 2) is changed, and (4) shows these data. It is a figure for demonstrating the measuring object in experiment.
[0060]
First, experimental conditions will be described.
In this experiment, a single-sided spherical prism of 7.5 × 7.5 × 12.0 [mm] is manufactured by the above-described molding method. Among the 100 prisms manufactured under each condition, The number of determined items is counted.
[0061]
In this experiment, a glass material having a transition temperature Tg = 506 ° C. and a yield temperature At = 538 ° C. was used.
Here, regarding the quality determination of the prism, a product having a PV value of 0.2 μm or less on the measurement surface shown in FIG. The PV (Peak-to-Valley) value indicates the amount of deviation of the measurement surface from the design value in the normal direction of the surface. In addition, the plane shown in FIG. 4 (4), that is, the plane formed by the lower mold 11 is selected as the measurement plane as the object for determining the quality of the prism. This is because it appears most prominently.
[0062]
First, (1-1) and (1-2) will be described. In the graph shown in (1-1), the horizontal axis indicates the magnitude of the press pressure Pa, the vertical axis indicates the PV value, and the average value and the maximum value of the PV value of each prism when Pa is a certain value. The minimum value is shown. The table shown in (1-2) shows the number of 100 prisms that are determined to be non-defective based on the above-described pass / fail determination conditions among the 100 prisms manufactured when Pa is a certain value.
[0063]
Referring to (1-1) and (1-2), when the value of Pa is between 10 MPa (megapascal) and 40 MPa, 90% or more of the manufactured prisms are non-defective products, and the case is out of the range. It was found that outstanding results were obtained compared to the yield rate. Here, when Pa falls below the range of this value, a lot of sink marks occur, and when Pa exceeds this value, a lot of burn-in occurs.
[0064]
Next, (2-1) and (2-2) will be described. In the graph shown in (2-1), the horizontal axis indicates the magnitude of the press pressure Pb, the vertical axis indicates the PV value, and the average value and the maximum value of the PV value of each prism when Pb is a certain value. The minimum value is shown. Further, the table shown in (2-2) shows the number of 100 prisms that are determined to be non-defective based on the above-described pass / fail determination conditions among the 100 prisms manufactured when Pb is set to a certain value.
[0065]
Referring to (2-1) and (2-2), if the value of Pb is also between 10 MPa and 40 MPa, 90% or more of the manufactured prisms are non-defective products, It was found that outstanding results were obtained in comparison. Here, when Pb falls below this value range, a lot of sink marks occur, and when Pb exceeds this value, a lot of burn-in occurs.
[0066]
From the above, it can be said that the values of Pa and Pb are preferably between 10 MPa and 40 MPa in terms of improving the molding accuracy of the optical element.
Next, (3-1) and (3-2) will be described. In the graph shown in (3-1), the horizontal axis indicates the value of the holding temperature Tb, the vertical axis indicates the PV value, and the average value, the maximum value, and the minimum value of the PV value of each prism when Tb is a certain value. The value is shown. The table shown in (3-2) indicates the number of 100 prisms that are determined to be non-defective based on the above-described pass / fail determination conditions among the 100 prisms manufactured when Tb is set to a certain value.
[0067]
Referring to (3-1) and (3-2), the value of Tb is between 506 ° C. and 522 ° C., that is, the transition point temperature Tg or more, and the yield point temperature Tg and the transition point temperature At 90% or more of the manufactured prisms are non-defective when the temperature is exactly the intermediate temperature (Tg− (At−Tg) × 0.5) or less, and the result is markedly superior to the non-defective rate when the prism is out of the range. Was found to be obtained. Here, when Tb is less than this value range, many cracks are generated, and when Tb is more than this value, the area degree is often deteriorated.
[0068]
From the above, it can be said that the value of Tb is preferably not less than the transition point temperature Tg and not more than the intermediate temperature between the yield point temperature Tg and the transition point temperature At in terms of improving the molding accuracy of the optical element. .
The present invention is not limited to the above-described embodiments, and various improvements and changes can be made without departing from the spirit of the present invention.
[0069]
For example, in the above-described embodiment, the heating, cooling, and pressurization control for the material to be molded 12 is realized by the PLC 5, but a CPU (Central Processing Unit) provided in the computer performs these controls. This program may be created and executed by causing the CPU to execute the program.
[0070]
In the above-described embodiment, the displacement sensor 22 measures the distance between the lower mold 11 and the upper mold 8. However, since the upper mold 8 is fixed in this embodiment, the displacement sensor 22 22 may measure the displacement of the lower mold 11 and calculate the distance between the lower mold 11 and the upper mold 8 from the measurement result. In addition, the measurement result of the displacement sensor 22 may be used to detect contact between the lower mold 11 and the upper mold 8 or to detect that the position of the lower mold 11 has become “displacement A”. Is possible.
[0071]
【The invention's effect】
As described above in detail, the present invention first pressurizes the material that has been softened by being heated to a temperature higher than the yield point temperature of the glass material to be molded itself, thereby reducing the thickness of the material. A set thickness that is thicker than the thickness desired for the optical element, and subsequently maintaining the pressure on the glass material to be molded while keeping the material below the yield point temperature and The thickness of the material is formed to the desired thickness by cooling until the temperature reaches the transition temperature of the material itself.
[0072]
Thus, according to the present invention, there is an effect that the molding accuracy of the optical element to be formed is improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a molding apparatus according to the present invention.
FIG. 2 is a diagram showing how the molding apparatus shown in FIG. 1 is controlled.
FIG. 3 is a diagram showing a state of cooling control.
FIG. 4 is a diagram showing experimental data when a molding method according to the present invention is performed.
[Explanation of symbols]
1 Molding room
2 outer cover
3 Heater
4 Water-cooled pipe
5 Programmable controller
6 Fixed side template
7 Fixed shaft
8 Upper mold
9 Working side template
10 Movement axis
11 Lower mold
12 Molding material
13 type contact detection contact
14 Fixed side template contact A
15 Battery A
16 Relay A
Type 17 proximity detection contact
18 Fixed side plate contact B
19 Battery B
20 Relay B
21 Coil spring
22 Displacement sensor

Claims (6)

In a method for molding an optical element, which is an optical element formed by pressure-molding a glass material to be molded with a pair of molds,
It pressurizes said workpiece being softened by being heated to a temperature higher than the yield point temperature of the glass molding material itself by the pair of molds, than the thickness that is desired the thickness of said workpiece as an optical element A pressurizing step to set a thick wall thickness,
The thickness of the material is desired until the material is cooled below the yield point temperature and above the transition temperature of the material itself while maintaining the pressurization on the glass material to be molded. By forming the thickness, and controlling the temperature of the material based on the elapsed time from the time when the thickness of the material has reached the set thickness and the distance between the pair of molding dies at that time, A cooling molding step in which the time until the thickness of the material reaches the desired thickness from the set thickness is constant ;
A method for forming an optical element, comprising:   In the cooling and forming step, the desired thickness of the material while maintaining the temperature of the material when the temperature of the glass material to be molded reaches a temperature below the middle of the yield point temperature and the transition temperature. The method for molding an optical element according to claim 1, wherein the molding is performed. The determination that the thickness of the glass material to be molded has reached the set thickness is performed based on an output of a sensor that detects a position of the mold, in the pressing step. 3. A method for molding an optical element according to 1 or 2 . In the cooling molding step, the determination that the thickness of the glass material to be molded has been molded to the desired thickness is made based on detection of contact between the pair of molds facing each other. The method for molding an optical element according to any one of claims 1 to 3, wherein: In an optical element molding apparatus that press-molds a glass material to be molded into an optical element,
A pair of opposing molds that press and mold a glass material to be molded that has been softened by heating; and
A mold for detecting that the distance between the pair of molds approaches a predetermined distance, and that the thickness of the material has reached a set thickness that is thicker than the thickness desired for the optical element. An approach detection means;
A mold contact detection means for detecting that the distance between the pair of molds is close to a predetermined distance and that the thickness of the material has reached the desired thickness;
In order to make the time from the detection of the mold approach detection means to the detection of the mold contact detection means constant, the elapsed time from the detection of the mold approach detection means and the distance between the pair of molds at that time Temperature control means for controlling the temperature of the material based on ;
An optical element molding apparatus comprising: 6. The optical element molding apparatus according to claim 5 , further comprising distance measuring means for measuring a distance between the pair of opposing molds.

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