JPH10236830A - Method for forming optical element and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the thickness precision of a formed optical element irrespective of the thickness of the optical material to be formed and to stably obtain a high-precision facial shape free of residual stress. SOLUTION: A heated optical material 8 is compressed and compacted by the forming dies 1 and 2 into an optical element. In the process of compacting the optical material 8, the positions of the dies 1 and 2 are detected, the distance between the dies 1 and 2 is kept constant to control the thickness of the material 8 to a specified value, and the pressure of the dies 1 and 2 on the material 8 which contracts with cooling is changed stepwise in process to cool the formed material 8.

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 molding an optical element, and more particularly to a means for ensuring the thickness accuracy of an optical element.

[0002]

2. Description of the Related Art Conventionally, as a method for efficiently mass-producing optical elements such as lenses, there is a molding method using a pressing means such as a precision press molding machine. In the above method, a mass of material that has been heated and softened, for example, an optical material, is supplied into a mold of a press molding machine, and is pressed in this state to obtain an optical element having a predetermined shape. In this case, the thickness of the molded optical element is extremely important in determining the precision of the optical element.

As a method for determining the thickness of an optical element formed by a press forming machine, for example, a technique described in Japanese Patent Application Laid-Open No. 61-205630 is disclosed. In one embodiment (prior art 1), in addition to a control mechanism such as a stopper, in order to prevent local shrinkage and sink due to non-uniform volume shrinkage generated in the process of cooling and solidifying an optical material in a mold, By interposing a pressurizing member (elastic member) between the mold and a piston for driving the mold, the mold presses the optical material in conjunction with shrinkage due to cooling and solidification of the optical material. ing.

In another embodiment (prior art 2), a mold is fixed to an end of a pressing member (hydraulic cylinder), and the optical element contacts the mold at a position where the optical element has a desired thickness. After the optical material is pressed and molded to a desired thickness, the stopper is moved or removed, and the optical material is pressed by a mold in conjunction with the optical material that contracts due to cooling and solidification. There is. Generally, when the thickness of an optical element is to be molded with high precision, in the press molding process, the upper and lower dies are moved to a predetermined position to secure the accuracy of the thickness, and then the process of cooling and solidifying is performed. In
In order to prevent local shrinkage and sink marks of the optical material and obtain a highly accurate surface shape, it is linked to the shrinkage due to cooling and solidification of the optical material,
The mold applies pressure to the optical material.

[0005]

However, according to the prior art 1, since an elastic member is interposed between the mold and the piston, an optical member is provided for preventing sink marks in the cooling and solidifying process of the optical material. The pressure applied to the material depends on the amount of deformation of the elastic member. The amount of deformation of the elastic member varies depending on the thickness (medium thickness) of the optical material in the molding process, and the thickness is not constant as described above.
For this reason, it is difficult to always keep the pressing force for preventing sink marks constant, and there is a problem that the surface accuracy of the formed optical element varies.

In the prior art 2, since there is no means for detecting the start of cooling and solidification of the optical material, pressure is applied before the cooling and solidification starts, and the thickness of the optical material changes. . Furthermore, even if pressure is applied to the optical material after the cooling and solidification is started, the surface accuracy cannot be improved depending on the progress of the cooling and solidification, and sink occurs. The starting point and progress of this cooling and solidification vary depending on the temperature of the heated molding material, the weight, the temperature of the mold for molding, and the like.
Since the pressure cannot be measured at the timing of starting the pressurization, there is a problem that the variation in the surface accuracy of the optical element after molding cannot be suppressed. Further, when the optical material is press-molded in the state of being heated and softened, and then cooled and solidified, the pressure is rapidly reduced, so that there is a problem that a residual stress is generated on the surface of the molded optical element.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and an object of the invention according to claim 1 is that the optical material after molding is not affected by the thickness of the optical material before molding. An object of the present invention is to provide a molding method of an optical element capable of securing the thickness accuracy of the element and stably obtaining a highly accurate surface shape without residual stress. An object of the invention according to claim 2 is to provide an optical element molding apparatus effective for performing the molding method.

[0008]

According to a first aspect of the present invention, there is provided a method for forming an optical element, wherein a heated optical material is molded while being pressed by a molding die. In the step of pressing and molding, the distance of the mold is kept constant so that the optical material has a desired thickness by detecting the position of the mold, and in the step of cooling the molded optical material, cooling is performed. The pressure of the mold to be applied to the optical material that shrinks with the pressure is changed stepwise. According to a second aspect of the present invention, there is provided an optical element forming apparatus for forming a heated optical material while pressing the heated optical material with a forming die, wherein a driving unit for driving the forming die and a position of the forming die are detected. A first detecting means, a second detecting means for detecting a pressure applied to the optical material from the molding die, and the second detecting means based on an output from the first detecting means or the second detecting means. It is characterized by comprising control means for controlling the position of the driving means in a stepwise manner, and input means for writing an arbitrary program in the control means.

In the operation of the invention according to the first aspect, in the step of press-molding the optical material, the position of the mold is detected to keep the distance of the mold constant so that the optical material has a desired thickness. In the process of cooling the molded optical material, the thickness of the molded optical element is made constant by gradually changing the pressure of the mold applied to the optical material that contracts with cooling, and Pressurization corresponding to the solidified state of the optical material that shrinks accordingly is performed. In the operation of the invention according to claim 2, a driving unit for driving the molding die, a first detecting unit for detecting a position of the molding die, and a detecting unit for detecting a pressure applied to the optical material from the molding die. Second detection means;
Control means for stepwise controlling the position of the driving means based on the output from the first detecting means or the second detecting means, and input means for writing an arbitrary program in the control means Thus, the position of the mold is detected by the first detector, the pressure applied to the optical material from the mold by the second detector is detected, and the output from the first detector or the second detector is output. The position of the driving means for driving the forming die is controlled stepwise by the control means. The mold is driven by this driving means, and the optical material is molded. Note that an arbitrary control program can be previously written in the control means from the input means.

[0010]

FIG. 1 shows an embodiment of the present invention.
It is a schematic structure figure of a shaping device of an optical element. In FIG. 1, a lower mold 1 and an upper mold 2 are disposed to face each other, and the lower mold 1 is held by an upper end of a vertical mechanism as a driving means including a motor 3 and a ball screw 4 so as to be vertically movable. I have.
A displacement sensor 5 as first detection means for detecting displacement of the lower mold 1 is provided on a lower side surface of the lower mold 1, and a pressure sensor 6 as second detection means for detecting pressure is provided at a lower end of the lower mold 1. Are arranged. Further, a controller 7 as a control means for controlling the vertical movement of the lower die 1 based on the displacement of the lower die 1 and the pressure applied to the lower die 1 is provided in the vicinity, and the motor 7, the displacement sensor 5 and the pressure sensor 6 Are electrically connected to each other. Further, a program input device 9 as an input means capable of writing an arbitrary control program in the controller 7 is connected to the controller 7.

A method for molding an optical element using the molding apparatus having the above configuration will be described. The optical material 8 heated and softened to a predetermined temperature is supplied between the upper mold 2 and the lower mold 1, and the lower mold 1 is raised to perform press molding. At this time, the controller 7
Receives the signal of the displacement sensor 5 that detects the displacement of the lower die 1 and controls the lower die 1 to be positioned at a predetermined position.
A medium thickness (thickness between surface vertices) of the molded optical material 8 is obtained.
Thereafter, the pressure applied to the lower mold 1 from the vertical mechanism is detected by the pressure sensor 6, and the optical material 8 is cooled and solidified while controlling the vertical position of the lower mold 1 stepwise so as to apply a predetermined pressure. By this operation, an optical element having no residual stress is obtained by performing a function of annealing by a high-precision surface shape that prevents sink marks and a gradual pressure decrease while ensuring medium accuracy.

(First Embodiment of the Invention) FIGS. 2 to 4 show a first embodiment of the invention, FIG. 2 is a front view showing a part of a molding device for an optical element, and FIG. FIG. 4 is a flow chart showing the molding process, and FIG. 4 is a time chart in which the pressure in the operation of the flow chart of FIG.

In FIG. 2, a molding chamber 10 is disposed on a gantry 20, and the molding chamber 10 includes an upper base 21, a lower base 22, and a cover 13. The upper die support 14 is fitted to the upper base 21. The upper die support 14 has a male screw 14 threaded on a lower side surface thereof.
The upper die 12 is fixed by the upper die retainer 16 screwed into a. A vertically movable main shaft 17 is inserted through the central opening 22 a of the lower base 22, and a lower mold support 15 is fixed to the upper end of the main shaft 17. The lower mold support 15 includes
The lower mold 11 is fixed by a lower mold retainer 19 screwed to the male screw 15a threaded on the upper side surface.

The main shaft 17 is fitted to a housing 33 suspended from the lower surface of the gantry 20 via a guide roller 34 so as to be vertically movable. Further, a main bearing 30 is fixed to a lower end of the main shaft 17, and a pressure sensor 26 is continuously provided on a lower surface thereof. On the other hand, a guide 32 is laid vertically on the inner surface of the gantry 20 (not shown).
A table 31 is fitted to 2 so as to be vertically movable.
The table 31 has a receiving surface 31 a protruding in a direction perpendicular to the paper surface, and is connected to the lower surface of the pressure sensor 26. A ball screw 24 is screwed into the table 31, and a motor 23 is connected to a lower end of the ball screw 24. The table 31 is driven up and down by the rotation of the motor 23,
Pressure sensor 26 and main bearing 3 connected to table 31
0, the lower shaft 11 and the lower shaft
Moves up and down.

A displacement sensor 2 is provided at the lowermost portion of the side surface of the spindle 17.
5 is attached, so that the displacement of the lower mold 11 can be measured. The displacement sensor 25 and the pressure sensor 26 are connected to a controller 27, and are configured to receive respective signals. Motor 23 is also the controller 2
7 and a controller 27 is connected to a program input device 29. A controller 2 for inputting a program for controlling the rotation of the motor 23 from the program input device 29 to the controller 27 and executing the control contents
By controlling the motor 23 by the
, And the pressure applied to the optical material 18 is controlled.

A method for molding an optical element using the molding apparatus having the above configuration will be described. The optical material 18 placed on the placing member 35 is heated to a temperature equal to or higher than the softening point of the optical material 18 in a heating furnace (not shown) provided outside the molding chamber 10. Next, the optical material 18 and the mounting member 35 are transported between the upper die 12 and the lower die 11 that are heated near the softening point temperature of the optical material 18 by using a transport means (not shown). Then, the lower die 11 is raised by rotating the motor 23 to raise the table 31,
The optical material 18 is pressed by the upper mold 12 and the lower mold 11. The change in the relative position between the lower mold 11 and the upper mold 12 is measured by the displacement sensor 25, and the pressure applied to the lower mold 11 is:
It is measured by the pressure sensor 26. At this time, lower mold 1
The motor 23 that raises 1 is controlled according to the flow shown in FIG.

First, the lower mold 11 is raised by the motor 23 so that the relative position between the lower mold 11 and the upper mold 12 falls within a predetermined position range, that is, within a thickness range of a desired optical element (step S1). ). Then, it is determined whether or not the distance between the lower mold 11 and the upper mold 12 is within a desired thickness range of the optical element (Step S2). In step S2, the lower mold 11 and the upper mold 12
Is determined to be larger than the desired thickness of the optical element, the lower mold 11 is slightly moved upward (step S3), and the process proceeds to step S2. If it is determined in step S2 that the distance between the lower mold 11 and the upper mold 12 is smaller than the desired thickness of the optical element, the lower mold 11 is slightly moved down (step 4), and the process proceeds to step S2.

The distance between the lower mold 11 and the upper mold 12 is within the desired thickness range of the optical element, that is, the lower mold 11 and the upper mold 12
When the relative position of the lower mold 11 falls within the predetermined position range, it is determined whether or not the mold pressure applied to the optical material 18 by the lower mold 11 is the set value 1 (step S5). The set value 1 is the amount of pressurization of the lower mold 11 due to cooling of the optical element, and is set by controlling the rotation of the motor 23 based on a value input from the pressure sensor 26 to the controller 27. Things. If it is determined in step S5 that the mold pressure of the lower mold 11 is larger than the set value 1, the lower mold 11 is slightly moved down (step S6), and the process proceeds to step S5. Step S
If it is determined in step 5 that the mold pressure of the lower mold 11 is smaller than the set value 1, the lower mold 11 is slightly moved up (step S7), and the process proceeds to step S5.

Then, with the mold pressure of the lower mold 11 set to the set value 1, the optical element formed by molding the optical material 18 is
Cool for a predetermined time (see FIG. 4) (step S8). Thereafter, the mold pressure is reduced with the cooling of the optical element, and is set to the set value 2 (step S9). In this state, after waiting for a predetermined time, the mold pressure is further reduced and set to the set value 3 (step S10). Then, after waiting for a certain time, the lower mold 11 is lowered (step 11), and the optical element formed by the conveying means (not shown) is discharged from the forming chamber 10 to the outside.

According to the first embodiment of the present invention, in the process of pressing the optical element, the displacement sensor 25 for detecting the displacement of the lower mold 11 is provided to control the relative position between the upper mold 12 and the lower mold 11. By doing so, the accuracy of the thickness of the optical element after molding is ensured, and the lower die 11
The pressure sensor 26 that detects the pressure applied to the optical element prevents the sink of the optical element after molding by controlling the pressure in a stepwise manner, so that an optical element having a highly accurate surface shape can be molded stably, and The internal stress of the later optical element can be removed.

In the first embodiment of the present invention, the pressure sensor 2
Although 6 is arranged on the lower mold side, it may be arranged on the upper mold side, that is, between the upper mold 12 and the upper mold support 14 or between the upper mold support 14 and the upper base 21. Further, a means for detecting the output torque of the motor 23 is provided instead of the pressure sensor 26, and the same control is performed to obtain the same effect.

(Embodiment 2) FIGS. 5 and 6 show Embodiment 2 of the present invention. FIG. 5 is a front view in which a part of an optical element molding apparatus is broken, and FIG. It is a block diagram of a control system. Embodiment 2 of the present invention relates to Embodiment 1 of the present invention.
Since the basic configuration is the same as that of the first embodiment, only different portions will be described, and drawings and descriptions of the same portions will be omitted. Also, in FIGS. 5 and 6, only portions different from the first embodiment of the invention will be described.
The same members are denoted by the same reference numerals, and description thereof will be omitted.

5 and 6, a cover 13 has a light projector 42 and a light receiver 43 of a laser type outer diameter displacement sensor.
Are disposed facing each other, and the upper mold 1 is placed on the optical path between them.
2 and the lower mold 11 are positioned so as to be present.
The light emitter 42 and the light receiver 43 are connected to a controller 44 of a laser type outer diameter displacement sensor, and when the laser beam passes between the upper mold 12 and the lower mold 11, the upper mold 1 is turned on.
The distance between 2 and lower mold 11 can be measured. The light projector 42, the light receiver 43, and the controller 44 constitute a laser distance measuring device 45. The controller 44 is connected to the controller 27 that controls the vertical movement of the spindle 17. Other configurations are the same as those of the first embodiment.

A method for molding an optical element using the above-described apparatus will be described. The process is the same as that of the first embodiment of the present invention until the optical material 18 and the mounting member 35 are transported between the upper die 12 and the lower die 11 by using a transport unit (not shown). Next, the upper mold 12 and the lower mold 11 immediately before molding are performed.
The distance between the upper mold 12 and the lower mold 11 in a state where the optical material 18 and the mounting member 35 are on standby between them is measured by the laser distance measuring device 45. The measured value is transmitted to the controller 27, and the controller 27 calculates the moving distance of the lower mold 11 to a predetermined pressing position. In the next pressing process of the optical material 18, the motor 23 is driven so that the predetermined accuracy of the optical material 18 is achieved while monitoring the displacement sensor 25. After that, the process after the process of driving the motor 23 so that the pressure applied to the lower mold 11 becomes the pressurized amount accompanying the predetermined cooling and solidification is the same as that of the first embodiment of the invention.

According to the second embodiment of the present invention, in addition to the effects of the first embodiment of the present invention, in the process of detecting the distance between the upper mold 12 and the lower mold 11, the position of the mold is closer to the mold. Since the distance between the molds can be measured in the same atmosphere, even if the mold expands due to heat, etc., the distance to the press molding position is always calculated, so it has a more accurate filling. An optical element can be obtained.

In the present invention, the following technical ideas can be derived from the above specific embodiments of the invention. (1) In a molding method of an optical element in which a heated optical material is molded while being pressed by a pair of molds heated near the softening point temperature of the optical material, in the step of pressing and molding the optical material, In the process of detecting the position of the mold, keeping the distance of the mold constant so that the optical material has a desired thickness, and cooling the molded optical material,
A method of molding an optical element, wherein a pressure of the mold applied to the optical material that contracts with cooling is changed stepwise. In addition to the effect of the invention according to claim 1, by heating the mold near the softening point temperature of the optical material, rapid cooling of the heated optical material is prevented, and a high-precision optical element with less distortion is obtained. be able to. (2) The optical material is carried between a pair of upper and lower molds heated near the softening point temperature of the optical material, and in a press molding process, the relative position of the pair of upper and lower molds is detected so that the optical material has a predetermined thickness. In the method of molding an optical element in which the distance between a pair of upper and lower molds is maintained so as to be thick, and the optical material is molded while being pressed, in the cooling and solidifying process after press molding, the optical material shrinks with cooling and solidification. A method for molding an optical element, characterized in that the pressure of the mold to be applied is changed stepwise by program control. In addition to the effect of the invention according to claim 1, a high-precision surface shape is obtained by changing the pressure of the mold applied to the optical material that contracts with cooling and solidification in a stepwise manner by program control. An optical element having no residual stress can be easily obtained by simple means.

[0027]

According to the first aspect of the present invention, the thickness of the molded optical element is made constant, and the pressure corresponding to the solidification state of the optical material that contracts with cooling is performed. It is possible to stably obtain an optical element which has a high thickness accuracy, has no surface sink, has a highly accurate surface shape, and has no residual stress. According to the second aspect of the present invention, the method for molding an optical element according to the first aspect of the present invention can be easily performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical element molding apparatus according to an embodiment of the present invention.

FIG. 2 is a front view in which a part of the optical element forming apparatus according to the first embodiment of the present invention is partially broken;

FIG. 3 is a flowchart showing a molding process of the optical element according to the first embodiment of the present invention.

FIG. 4 is a time chart in which the pressure in the operation of the flowchart of FIG. 3 according to the first embodiment of the invention is plotted on the vertical axis.

FIG. 5 is a front view in which a part of a molding device for an optical element according to Embodiment 2 of the present invention is partially broken.

FIG. 6 is a configuration diagram of a control system of a molding apparatus according to Embodiment 2 of the present invention.

[Explanation of symbols]

 1 upper mold 2 lower mold 3 motor 4 ball screw 5 displacement sensor 6 pressure sensor 7 controller 9 program input device

Claims (2)

[Claims] In a molding method of an optical element, wherein a heated optical material is molded while being pressed by a molding die, in a step of press-molding the optical material, a position of the molding die is detected and the desired optical material is obtained. In the process of cooling the molded optical material while keeping the distance of the molding die constant so as to be thick, the pressure of the molding die applied to the optical material that contracts with cooling is changed stepwise. A method for molding an optical element, comprising: 2. A molding device for an optical element for molding a heated optical material while pressing it with a molding die, comprising: a driving unit for driving the molding die; and a first unit for detecting a position of the molding die. Detecting means, a second detecting means for detecting a pressure applied to the optical material from the molding die, and a driving means based on an output from the first detecting means or the second detecting means. An apparatus for molding an optical element, comprising: control means for controlling a position in a stepwise manner; and input means for writing an arbitrary program in the control means.