JP2005126318A - Press molding apparatus and method for press-molding optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a press molding apparatus where molding accuracy can be improved because the inclination of a main shaft to support a molding die and the like are eliminated and where a large-sized apparatus is not needed if the stroke at die opening or closing is large. <P>SOLUTION: The press molding apparatus 1 has freely openable and closable upper and lower molding dies 22, 23 and a drive part 3 for opening or closing by moving one of the upper and lower molding dies 22, 23. The drive part 3 has the main shaft 24 to support the freely movable molding die 23, a vertically moving member 32 supporting the main shaft 24, a plurality of screw shafts 33 positioned to be eccentric from the shaft line of the main shaft 24 and threaded with a screw part 32b on the vertically moving member 32, drivers M1, M2 to rotate the screw shafts 33 respectively and synchronously and a control unit to control the drivers M1, M2. The screw shafts 33 are rotated while being controlled with the drivers M1, M2 not to cause the inclination of the main shaft 24 when a material is molded in the closed molding die 23. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention supplies a material such as a glass preform between a pair of molds that can be opened and closed, press-molds a molded product of a predetermined shape by closing the mold and pressurizing the material. The present invention relates to an apparatus and a method for molding an optical element using the press molding apparatus.

  2. Description of the Related Art There is known a press molding apparatus that has a pair of molds that can be opened and closed, supplies a material between the molds, and closes the mold to form a molded product having a predetermined shape. As such a press molding apparatus used for molding an optical element such as a lens, the heat-softened material is supplied between a pair of upper and lower molds, and the pair of molds are brought close to each other. There are some which are moved in the direction of molding (for example, see Patent Document 1).

  As a method of raising the lower die and bringing the pair of upper and lower molds closer, there are a method of raising the lower die with a screw shaft (for example, Patent Document 2) and a method of raising the lower die with a cylinder (for example, patents). Reference 3).

Japanese Patent Laid-Open No. 6-16432 (refer to the description of [0002] in the specification). Japanese Utility Model Publication No. 7-6242 JP-A-3-265527

The technique described in Patent Document 2 has an advantage that since the main shaft and the screw shaft are on the same axis, the main shaft is hardly inclined and the molding accuracy can be improved.
However, since the screw shaft is arranged on the same axis as the main shaft, the length of the vertical device with the length of the screw shaft added to the main shaft increases as the lifting / lowering stroke of the mold increases. There is a problem that the workability becomes worse as the size increases.

  Furthermore, in the technique described in Patent Document 2, the longer the lifting stroke of the molding die, the greater the deflection of the screw shaft due to the buckling load acting in the axial direction during molding, which adversely affects the molding accuracy. There is a problem of affecting. That is, due to the buckling load, horizontal displacement (shift) and angular displacement (tilt, tilt) occur between the molding surfaces of the pair of molds, and the molding accuracy is lowered.

Further, in the technique described in Patent Document 3, for example, as shown in FIG. 2, the driving force and the applied pressure at the time of molding are transmitted to the shaft center of the lower end surface of the holding shaft in a point contact state. Therefore, there is an advantage that an unnecessary moment in the axial diameter direction does not act at the time of molding, and the inclination of the holding shaft can be suppressed.
However, even in this technique, as shown in FIG. 3, if the driving body is provided directly below the holding shaft, there is a problem that the apparatus becomes large and the workability deteriorates. Further, in order to reduce the size of the apparatus, as shown in FIGS. 1 and 2, if the drive body and the screw drive shaft are provided at positions deviated from the hold shaft, the moment generated between the hold shaft and the screw drive shaft is generated. As a result, there is a problem that the holding shaft is inclined and the molding accuracy is lowered.

  The inventor has conducted research in order to solve the above problems. First, in order to solve the problem caused by placing the lower mold screw shaft on the same axis as the main shaft, the press molding apparatus shown in FIG. 6 in which the main shaft and the lower mold screw shaft are arranged eccentrically is prototyped, Various studies were made.

A press molding apparatus 300 shown in FIG. 6 drives a molding unit 320 including a pair of upper and lower molding dies 322 and 323 inside a molding chamber 321 and a main shaft 324 supporting a lower molding 323 in the vertical direction. Part 330.
The drive unit 330 is attached to a servo motor M, a screw shaft 333 that rotates by driving of the servo motor M, and a lower end of the main shaft 324, and includes a nut 332a that forms a ball screw / nut mechanism together with the screw shaft 333. Member 332.

The drive unit 330 includes a support member 334a attached to the base 331, guide rails 334b vertically provided on the support member 334a, and an elevating member 332 fitted to the guide rail 334b. A guide 334 including a fitting groove 332b is provided.
With the above configuration, when the servo motor M is driven to rotate the screw shaft 333, this rotation is converted into vertical vertical movement parallel to the axis of the main shaft 324 by the nut 332 a of the elevating member 332, while being guided by the guide 334. The main shaft 324 and the mold 323 are moved up and down in the vertical direction.

  According to the press molding apparatus shown in FIG. 6, since the height of the apparatus in the vertical direction can be suppressed, there is an advantage that the apparatus can be downsized and the workability is improved. On the other hand, in the driving unit 330 as shown in the figure, the screw shaft 333 is provided at a position eccentric with respect to the main shaft 324. Therefore, when the load during press molding of the material acts in the direction indicated by the arrow I in the figure, It has been found that there is a new problem that the lifting member 332 is inclined due to the force in the direction of the arrow II acting on the screw shaft 333, and the mold 323 is inclined together with the main shaft 324.

  If the main shaft 324 and the mold 323 are inclined, the horizontality of the contact surfaces of the upper and lower molds 322 and 323 is lost. This means that the fitting accuracy of the upper and lower molds 322 and 323 is deteriorated. That is, an angle shift (tilt) occurs in the center axis of the molding surfaces of the pair of molding dies 322 and 323, and the eccentric accuracy of the optical element to be molded is deteriorated. Further, when positioning members (for example, sleeves and guide pins) of the upper and lower molds 322 and 323 are provided so as to protrude from the contact surfaces of the upper and lower molds 322 and 323, the molds 322 and 323 are opened and closed. There is a problem that these are rubbed and galling each time. In order to prevent this, if the fitting clearance is increased, the horizontal misalignment (decenter) of the upper and lower molds 322 and 323 is also deteriorated, and the eccentric accuracy of the optical element is impaired.

Recently, there has been a demand for higher accuracy of optical elements used in these optical devices by increasing the number of pixels of a digital camera or increasing the recording density of an optical recording medium such as a DVD. In particular, in the molding of aspherical lenses, one central axis (which connects the aspherical center and the aspherical curvature center) is defined by one molding surface shape, so that the central axes of the upper and lower molding surfaces coincide. The positional accuracy of the pair of molding surfaces is extremely important.
For example, these optical elements are required to be molded under a condition that the tilt is within 2 minutes. However, it is not easy to always perform the continuous pressing by controlling the tilt within a predetermined range.

  The present inventor analyzed the factor of tilt deterioration, found that there was room for improvement in the drive mechanism accompanying the raising and lowering of the mold, and also took into account the problems caused by the press molding apparatus shown in FIG. , Repeated research. As a result, it has been found that the above problem can be solved by adopting a configuration in which the main shaft that supports the mold is moved up and down by a plurality of screw shafts provided at positions eccentric from the main shaft.

Therefore, an object of the present invention is to improve the molding accuracy by using a structure that does not cause eccentricity of a molded product such as an optical element in the drive unit that opens and closes the mold. It is another object of the present invention to provide a molding apparatus and a molding method capable of preventing an increase in the size of the apparatus and a deterioration in workability without causing an inclination in a main shaft that is a moving direction of a movable mold.
Furthermore, when exchanging and inspecting the mold in the non-operating state, supplying the material in the operational state, and when the unloading means enters and exits between the molds to carry out the molded optical element, it is sufficient. It is necessary to open the upper and lower molds in this way. Thus, even if the mold opening of the mold is sufficiently large, it is possible to provide a press molding apparatus and a molding method capable of making the press molding apparatus relatively compact. Objective.

In order to achieve the above object, the invention according to claim 1 is characterized in that an openable upper and lower molds having opposed molding surfaces and at least one of the upper and lower molds are moved in the vertical direction. In the press molding apparatus having a drive unit that opens and closes the mold, the drive unit includes a main shaft that supports the movable mold, a lifting member that supports the main shaft and moves up and down, and the main shaft. A plurality of screw shafts that are arranged at positions deviated from the axis of the shaft and screwed with a plurality of screw portions formed on the lifting member, respectively, and the screw shafts are rotated in synchronization with each other. The driving body and a control device that controls driving of the driving body are provided.
According to this configuration, the elevating member can be precisely raised and lowered in the vertical vertical direction without causing a tilt due to a moment on the main shaft. Further, since each of the screw shafts is rotated by the driving body, it is possible to correct a bad influence due to a pitch error or the like for each screw shaft for each screw shaft and press-mold the material with high accuracy.

  The invention according to claim 2 is configured such that the plurality of screw portions of the elevating member are provided at symmetrical positions with the main shaft as a center. In this way, in order to maintain the level of the elevating member, the load acting on the plurality of screw shafts can be made uniform, load control can be easily performed during pressure molding, and the level of the molding die is highly accurate. It is possible to maintain. Further, even if bending occurs due to the rigidity and thickness of the elevating member, since the screw portion is in a symmetrical position with respect to the main shaft portion, the elevating member is not inclined and the main shaft portion is kept horizontal. .

  According to a third aspect of the present invention, it is preferable that the plurality of screw shafts are configured so as to equally receive a load when the mold is closed and press-molded. In this way, the press load is evenly applied to the plurality of screw shafts, so that the main shaft can be prevented from being inclined, and the level of the mold can be maintained with high accuracy.

According to a fourth aspect of the present invention, a driving body may be provided corresponding to each of the plurality of screw shafts, and drive control of each driving body may be performed by the control device. This is advantageous in that application is possible even when high torque (load) is required, and synchronization can be secured with the highest accuracy.
In this case, as described in claim 5, the control device preferably performs position control for controlling a moving position of the elevating member by rotation of the plurality of screw shafts when the molding material is molded. .
According to this configuration, the mold can be closed by the position control while keeping the molding die horizontal with high accuracy.

The invention of claim 6 is a method for molding an optical element using the press molding apparatus according to any one of claims 1 to 5, wherein the mold is preheated to a predetermined temperature and softened by heating. A step of conveying the material and supplying the material to the lower mold of the mold in an open state; and a step of pressure-molding the material by closing the mold. In the pressure forming step, the position of the forming die is controlled by rotating a plurality of screw shafts.
According to these methods, an optical element such as a lens can be molded with high molding accuracy.

  According to the present invention, it is possible to increase the molding accuracy of a press-molded product, in particular, the eccentric accuracy (determination of molding tilt and molding shift) without causing an inclination or the like in the main shaft of the press molding apparatus. Even if the stroke of movement of the mold is increased, the apparatus is not increased in size.

[Embodiment of the Invention]
Preferred embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic plan sectional view of a glass optical element manufacturing apparatus when the press molding apparatus of the present invention is applied to a glass optical element manufacturing apparatus.
The manufacturing apparatus shown in FIG. 1 is for manufacturing a small collimator lens by pressing a spherical glass preform (inhibition of molding material).

  As shown in FIG. 1, the glass optical element manufacturing apparatus includes a heating chamber 100 and a molding chamber 200 provided adjacent to the heating chamber 100. The heating chamber 100 and the molding chamber 200 are connected to each other through a passage 130 having an opening / closing valve 131, and the heating chamber 100, the molding chamber 200, and the passage 130 form a single sealed space that is blocked from the outside. ing. The outer wall of the sealed space is formed of stainless steel or other members, and the hermeticity is maintained by a sealing material. The sealed space formed by the heating chamber 100, the molding chamber 200, and the passage 130 is set to an inert gas atmosphere when the glass optical element is molded.

  The heating chamber 100 is an area for preheating prior to pressing the glass preform to be supplied. In this area, the glass preform is supplied into the heating chamber 100 from the outside of the heating chamber 100. A reform supply unit 111, a preform transfer unit 112 that transfers a glass preform from the preform supply unit 111 to the molding chamber 200, and a preform heating unit 113 that preheats the glass preform transferred to the molding chamber 200 are installed. Has been.

The preform conveying means 112 is provided in the heating chamber 100, receives the glass preform supplied from the preform supply means 111, conveys it to a heating region by the preform heating means 113, and further heat-softened glass. The preform is transferred to the molding chamber 200. The preform conveying means 112 includes four plates 112d at the tip of the arm 112c, and holds the glass preform thereon.
In the embodiment, an arm 112c including a tray 112d is horizontally supported by a drive base 112b that moves on a sliding portion 112a fixed in the heating chamber 100, and the arm 112c has a rotation angle of approximately 90 degrees. Is configured to rotate in the horizontal direction.

The preform conveying means 112 is provided with an arm opening / closing mechanism (not shown) inside the drive base 112b, thereby opening the tip of the arm 112c and dropping the glass preform on the plate 112d onto the mold.
When the glass preform is preheated and transported in a softened state, if the glass surface is defective due to contact with the transport jig, the shape accuracy of the optical element after molding is impaired. 112c is a levitation conveyance type that conveys the glass preform in a state where the glass preform is floated.
Then, for example, the arm 112c is constituted by a pair of arm divided bodies that can be divided in the width direction, and the front ends of the arm divided bodies are opened to each other, so that the glass plate on the plate 112d is opened from the opened gap. It is advisable that the reform is dropped onto the mold.

  The preform heating means 113 is for heating the supplied glass preform to a temperature corresponding to a predetermined viscosity. The preform heating unit 113 has a substantially U-shape when viewed from the side, and includes heater members on the upper and lower surfaces thereof. The preform heating means 113 is installed on the moving path of the glass preform held on the arm 112d.

  In this manufacturing apparatus, the heater surface temperature of the preform heating means 113 is preferably about 1100 ° C., and the atmosphere in the furnace, that is, the atmosphere between the upper and lower heaters is preferably about 700 to 800 ° C. In the present embodiment, the arm 112c is prevented from warping in the vertical direction by providing a temperature difference between the upper and lower heaters.

On the other hand, the molding chamber 200 includes a press molding apparatus 1 for molding a glass optical element having a desired shape by pressing the glass preform preliminarily heated in the heating chamber 100, and a suction pad. Unloading means 220 for automatically taking out the optical element from the press molding apparatus 1 and conveying it to the element taking-out means 230 is provided.
The element taking-out means 230 carries out the press-molded glass optical element to the outside of the molding chamber 200.

2 and 3 are diagrams showing details of the press forming apparatus provided in the above manufacturing apparatus, FIG. 2 is a side sectional view for explaining the schematic configuration, and FIG. 3 is a sectional view taken along the line II in FIG. FIG.
The press molding apparatus 1 is provided below the molding unit 2 that performs press molding of the glass preform and the molding unit 2, and moves up and down the lower molding die 23 among the upper and lower molding dies 22 and 23 of the molding unit 2. And a driving unit 3 to be operated.
The molding unit 2 includes a heating chamber 100 (see FIG. 1) for heating the glass preform, a molding chamber 200 communicating with each other via a passage 130, and a pair of upper and lower molding dies 22 provided in the molding chamber 200. , 23. The upper mold 22 is fixed to the ceiling portion of the molding chamber 200, and the lower mold 23 is attached to the upper end of the main shaft 24 that can be moved up and down in the vertical vertical direction.

  The number of optical elements molded by one cycle of press molding may be one or more. Any number of the molds 22 and 23 may be arranged on the master dies 20a and 20b according to the number of optical elements. However, when the areas of the master dies 20a and 20b are increased, it is caused by thermal deformation due to high temperature during pressing. Molding accuracy deteriorates due to the effect of warping. In particular, in the molds 22 and 23 arranged near the ends on the mother dies 20a and 20b, the eccentric accuracy is deteriorated due to the vertical axis deviation. Further, the fitting accuracy of the upper and lower molds 22 and 23 is poor, and the positioning member is galled or rubbed. Furthermore, if the clearance of the positioning member is increased in order to solve these problems, the eccentricity accuracy is deteriorated. Therefore, the number of molding dies 22 and 23 is the inclination of the central axis of the molding surface of the upper and lower molding dies 22 and 23 in the optical element molded by all the molding dies 22 and 23 on the mother dies 20a and 20b (here. In this case, it is preferable to select a number in which the molding tilt is less than 2 minutes. Although depending on the material of the mother dies 20a and 20b, the size of the dies 22 and 23, the arrangement interval, etc., the number of the dies 22 and 23 arranged on one mother dies 20a and 20b is preferably 1 to 4.

  The molding tilt is performed by, for example, press-molding an optical element (lens) having a flange-shaped flat portion on the periphery using upper and lower molds 22 and 23 having a flat portion on the periphery, and the first of the formed optical elements. It can obtain | require by measuring the angle of the flat part of a surface and a 2nd surface. Moreover, you may obtain | require by the angle of the upper and lower shaping | molding type | molds 22 and 23 of the press molding apparatus 1. FIG. The material of the mother dies 20a and 20b is preferably a material having high heat resistance. Further, when heat conduction from the mother dies 20a and 20b is used as a mechanism for heating the molds 22 and 23, the material of the mother dies 20a and 20b can be a material capable of high frequency induction (mainly metal such as iron, cobalt, nickel, etc.). ) And a high frequency induction coil can be used as a heating means for the mother dies 20a and 20b. When a ceramic material is used for the molds 22 and 23, it is preferable to use a tungsten alloy or the like whose thermal expansion coefficient approximates.

  The glass preform carried into the molding chamber 200 from the heating chamber 100 through the passage 130 (see FIG. 1) is conveyed between the upper and lower molding dies 22 and 23 in the mold open state and supplied to the lower molding die 23. Is done. Then, the lower mold 23 rises together with the main shaft 24 to close the mold, whereby the glass preform is press-molded.

In the figure, reference numeral 25 denotes a heater or induction heating coil for heating the molds 22 and 23 to a predetermined temperature prior to press molding, and around the upper mold 22 and the lower mold 23. Each is provided on the lifting path.
Here, it is preferable that the material and the cross-sectional shape of the elevating member 32 have high rigidity and are not easily bent even when a load is applied to the main shaft 24. As the material, for example, carbon steel, rolled steel, or ceramic that is JIS machine structural steel is preferably used. By using such an elevating member 32, the molding accuracy of the molded product can be further increased.

  The main shaft 24 extends through the through-hole formed in the floor portion of the molding chamber 200 to the inside of the drive unit 3. The drive unit 3 is connected to a base 31, two servo motors M 1 and M 2 as drive bodies attached to the lower part of the base 31, and drive shafts of the servo motors M 1 and M 2. A pair of left and right screw shafts 33, 33 that are rotated by driving M2, and screw holes that are attached to the lower ends of the main shaft 24 and screwed with the screw shafts 33, 33 together with the screw shafts 33, 33 to form a ball screw / nut mechanism. Lifting member 32 formed with 32b, 32b (see FIG. 3), first guides 34, 34 for guiding the lifting member 32 from both the left and right sides, and a second guide 36 for guiding the lifting member 32 from the back side, have.

The pair of left and right screw shafts 33, 33 are positions deviated from the axis of the main shaft 24, that is, positions different from the axis of the main shaft 24, and are symmetrically opposed to each other by 180 degrees about the main shaft 24 (the same line in FIG. (X) the upper position).
Since the elevating member 32 is made of a material having high rigidity, even when a load is applied in the axial direction of the main shaft 24 when the glass preform is press-molded, the screw shafts 33 and 33 are arranged in the vertical direction. The lifting member 32 is always maintained in a horizontal state only by applying equal loads to each other, and the main shaft 24 is not inclined.
Even if the screw shafts 33 and 33 are not arranged at symmetrical positions around the main shaft 24, it is possible to maintain the level of the elevating member 32, but the load acting on each of the screw shafts 33 and 33 is different. Therefore, the control becomes complicated. Furthermore, even if the elevating member 32 is bent, the main shaft 24 does not incline, so that it is preferable to arrange it at a symmetrical position.

The upper ends of the above-described screw shafts 33, 33 are rotatably supported on the upper portion of the base 31 by bearings or the like, and the lower ends thereof are connected to the drive shafts of the servo motors M1, M2.
The first guides 34, 34 for guiding the left and right sides of the elevating member 32 are a pair of left and right support members 34 a, 34 a provided vertically from the ceiling portion of the base 31, and the support members 34 a, 34 a. The guide rails 34b and 34b laid in the vertical up and down direction at one end, and guide grooves 32a and 32a (see FIG. 3) formed on the elevating member 32 and fitted to the guide rails 34b and 34b. .

The second guide 36 for guiding the elevating member 32 from the rear is provided with a support member 36a that is suspended from the ceiling portion of the base 31 in the vertical direction, and is laid at substantially the center of the support member 36a. A vertical vertical guide rail 36b provided on an axis Y perpendicular to X and passing through the axis of the main shaft 24, and a guide groove 32c (see FIG. 3) formed in the elevating member 32 and fitted to the guide rail 36b. It is composed of The support member 36a and the support members 34a and 34a are preferably formed integrally as shown in FIG. 3 in order to increase mutual rigidity.
Further, as the first guides 34 and 34 and the second guide 36, it is preferable to use linear guides with high guidance accuracy.

The drive of the servo motors M1, M2 is controlled by a control device.
FIG. 4 is a block diagram illustrating a configuration of a control device that controls driving of the servo motors M1 and M2.
The control device includes a memory 82 for storing various preset conditions, a control unit 81 for controlling the servomotors M1 and M2 so that an operation in accordance with the set conditions is performed, and a drive command for the control unit 81. Therefore, drivers 84 and 84 that drive each of the servo motors M1 and M2, position detection units 85 and 85 that detect the rotation angles of the screw shafts 33 and 33, and loads (referred to as torque) acting on the screw shafts 33 and 33. And load detectors 86 and 86 that detect the motors M1 and M2 through servomotors M1 and M2.
The controller 81 can control the servo motors M1 and M2 by outputting a drive command (target value signal) at a predetermined cycle.

  As the position detectors 85 and 85 for detecting the rotation angle of the screw shafts 33 and 33, a known encoder can be used. The encoder outputs a detection signal corresponding to the rotation angle of the screw shaft 33. As shown in the figure, in the control device 8 of this embodiment, a detection signal related to the rotation angle detected by the position detectors 85 and 85 is input to the drivers 84 and 84. In addition, information regarding the driving state is constantly input from the drivers 84 and 84 to the control unit 81.

  The drivers 84 and 84 use the detection signal regarding the rotation angle as a feedback signal, and perform feedback control so that the detected value matches the target value. The detection of the detection signal is preferably performed at an interval as short as possible, for example, at an interval of several ms. By doing in this way, rotation of the screw shafts 33 and 33 can be synchronized with high precision, and the raising / lowering member 32 can be maintained horizontally with high precision.

  Further, both information inputted from the drivers 84, 84 to the control unit 81 are compared in the control unit 81, and the rotational positions of the motors M1, M2 driven by the drivers 84, 84 (that is, the screw shaft 33, The drive command to the drivers 84 and 84 is output so that the rotation angle of 33 is substantially the same. In addition, the position of the raising / lowering member 32 or the shaping | molding die 23 may be detected with the optical sensor which is not shown in figure, and the signal may be input into a control part.

  Further, as the load detectors 86 and 86, for example, a detector that detects the increase or decrease of the load from the relationship between the amount of current supplied to the motor and the rotational speed of the motor can be used. As shown in the figure, a detection signal related to the load acting on the screw shafts 33, 33 detected by the load detection units 86, 86 is input to the drivers 84, 84 and the control unit 81, and torque is exceeded when a predetermined load is exceeded. The limiter works so that the motors M1 and M2 can be controlled by the drivers 84 and 84 so that an excessive load is not applied.

Furthermore, the control unit 81 compares whether or not the position of the elevating member 32 calculated based on information from the drivers 84 and 84 has reached a position preset in the memory 82, and whether or not the mold closing has been completed. Judging. Then, when it is confirmed that the mold closing has been completed, a command is issued to the drivers 84 and 84 to stop the driving of the motors M1 and M2.
In controlling the operation of the press molding apparatus of the present invention by the control unit 81, the upper and lower molding dies 22, 23 are placed at predetermined positions while pressing the glass preform supplied between the upper and lower molding dies 22, 23. After the position control is performed until reaching the position, switching from the position control to the load control may be performed. That is, after the molding is started, the screw shafts 33 and 33 are synchronously rotated so that the main shaft 24 is not inclined so that one of the molding dies (here, the lower die 23) is horizontal with respect to the other (the upper die 22). Position control is performed until the position is brought close to a predetermined position while maintaining.

Next, switching to load control in which the load applied between the upper and lower molds 22 and 23 or the press load detected by the press load detecting means is controlled by the control unit 81 is performed. When performing this load control, the servo motors M1 and M2 are driven until a preset load value (for example, 10 MPa) is reached.
The set numerical value may be set in multiple stages over time. Thus, by controlling the press molding apparatus by combining position control and load control, the surface accuracy and thickness accuracy of the optical element to be molded can be increased, and a concave meniscus lens that is difficult to mold or It is effective for forming biconcave lenses.

The press molding process using the above apparatus is performed as follows, for example.
(A) Mold heating step Prior to press molding, the upper and lower molds 20a, 20b are heated to a predetermined temperature by heating means 25, 25, preferably a high frequency induction heating coil, thereby heating the upper and lower molds 22, 23. . In the case of continuous molding, since the upper and lower molds 22 and 23 are cooled to a temperature near Tg (glass transition temperature) in the take-out process at the previous molding, heating is performed to a predetermined temperature for the next molding. Is called. Temperature of the upper and lower molds 22 and 23, ¹⁰ 8 ^{to 10 12} in the viscosity of the glass preform, preferably to ¹⁰ 8 ^{to 10 10} poises equivalent.

(B) Supplying process The pre-ripened glass foam is conveyed between the heated upper and lower mother dies 20a, 20b, and dropped and arranged on the lower forming die 23. In the supplying step, a glass preform preliminarily molded into a predetermined shape having an appropriate weight is heated to an appropriate temperature. It is preferable to heat in advance to a temperature higher than the set temperature of the mold and supply a glass material in a softened state suitable for molding (so-called non-isothermal press). In this case, the mold temperature is particularly precisely controlled. It is necessary to be. This shortens the molding cycle time and improves production efficiency.

The temperature of the glass material at this time is a temperature corresponding to less than 10 ^{10 in} terms of viscosity, preferably less than 10 ⁹ poise, specifically 10 ⁶ to 10 ^8.5 poise. However, as described later, phosphate glass, borate glass, when the refractive index nd used 1.7 or more glass as the glass material is preferably a relatively low temperature, 10 ^7.5 ~ It is preferable to be equivalent to 10 ⁹ poise. Further, the temperature of the glass material is preferably higher than the temperature of the upper and lower molds 22 and 23.
When the heated and softened glass material is transported and placed on the lower mold 23, if the glass material comes into contact with the transport member and a defect occurs on the surface, the surface shape of the optical element to be molded is affected. For this reason, it is preferable to use a conveying means that conveys the softened glass material in a state of being floated in the gas by the above method and drops the glass material on the lower mold 23. Next, the following pressing process is performed.

(C) Pressing process Immediately after the glass material is supplied, the lower mother die 20b is raised while operating the servo motors M1 and M2 which are driving means on the lower mother die 20b side to perform position control. By pressing the lower mold 20b against the mold 20a and transferring the molding surfaces of the upper and lower molds 22, 23 to the glass preform, a glass molded body having a predetermined surface shape is molded. At this time, since the upper master die 20a is fixed to the ceiling portion of the molding chamber 200, the reaction force of the molding load is applied to the main shaft 24 via the lower master die 20b, and further, the lifting member 32 and the screw shaft 33. , 33, a load is applied to the servo motors M1, M2. Loads of the servo motors M1 and M2 are detected by the load detectors 86 and 86. When the detected value exceeds a predetermined value (for example, 400 kgf / cm ² ), the load is provided in the drivers 84 and 84 or the controller 81. The torque limiter is activated to stop the driving of the servo motors M1 and M2.

(D) Cooling / mold release step Cooling of the molds 22 and 23 is started simultaneously with the start of pressurization or thereafter. In other words, while maintaining the pressure so as to maintain the pressure, or in a state where the pressure is reduced, the molded optical element and the molds 22 and 23 are kept in close contact, and the viscosity of the glass is equal to or lower than the temperature equivalent to 10 ¹² poise. After cooling to the end, the lower mold 20b is lowered to separate the upper and lower molds 22, 23 and release them. The mold release temperature is preferably 10 ^12.5 to 10 ^13.5 poise.

(E) Taking-out process The molded optical element is automatically taken out by a conveying means provided with an adsorbing member.

FIG. 5 is a flowchart for explaining a control procedure in the pressing process.
When the glass preform is supplied to the lower mold 23 and a start signal for starting molding is input to the control unit 81 (step S1), the control unit 81 starts position control (step S2). A drive command signal (target value signal) for synchronously driving the servo motors M1 and M2 is output to the drivers 84 and 84 at a predetermined cycle (step S3).
Simultaneously with the driving of the servo motors M1 and M2, the position on the servo motor M1 side and the position on the servo motor M2 side are detected by the position detection means (steps S4 and S5), and each position detection signal is input to the drivers 84 and 84. At this time, information related to the drive state of each servo motor M1, M2 is always input to the control unit 81, and the control unit 81 causes the driver 84 to make the rotational positions of the motors M1, M2 substantially coincide (synchronize). , 84 is output to the drive command signal (step S6). The drivers 84 and 84 having received the drive command generate a drive current based on the difference between the detected position signal and the drive command signal, and drive the servo motors M1 and M2. Thereby, the horizontality of the elevating member 32, that is, the horizontality of the lower mold 23 is maintained.

If the rotation angles of the left and right screw shafts 33 and 33 do not coincide with each other during the ascending process (step S6), it is determined that an abnormality has occurred, an alarm is output, and the servo motors M1 and M2 are stopped. When the rotation angles of the left and right screw shafts 33, 33 coincide with each other, the ascending height (current position) of the elevating member 32 is determined from the rotation angles of the screw shafts 33, 33, and the position preset in the memory 82 It is determined whether or not the target position has been reached (step S7).
The predetermined position when the glass preform supplied to the lower mold 23 comes into contact with the upper mold 22 or when the elevating member 32 is further raised after the contact may be set as the target position. it can. Preferably, after the elevating member 32 is raised and the glass preform starts to be deformed by raising the lower mold 23, a predetermined position at which the glass preform (molded body) has a predetermined thickness is defined as a target position. To do.

  The target position is appropriately determined depending on the shape of the lens to be molded and the material composition to be used. For example, initial pressurization is performed to largely deform the material so as to obtain a shape approximate to the final shape, the molds 22 and 23 are cooled simultaneously with the initial pressurization or after the initial pressurization, and then repressurized (second When the surface shape of the molded body is corrected by pressurizing), the position where the initial pressurization is completed can be set as the target position.

When it is determined that the elevating member 32 has reached the target position (step S7), that is, when it is determined that the initial pressurization has ended, the control unit 81 starts the second position control in order to perform the second pressurization ( Step 8). In the second pressurization, position control is performed so that the applied pressure is smaller than the initial pressurization. For example, the pressurizing force of the second pressurization is set to be in the range of 5 MPa to 30 MPa (about 50 to 300 kgf / cm ² ) so that the load is 5 to 70% of the initial pressurization.
It should be noted that it is preferable to provide a limit value for the torque of the servo motors M1 and M2 so that excessive pressurization and load are not generated even in the second pressurization.

Since the cooling of the molds 22 and 23 is started simultaneously with the application of the initial pressurizing force or after the application, the transition from the initial pressurization to the second pressurization is performed by the temperature of the molds 22 and 23 being the glass viscosity. It is preferably 10 ¹⁰ to 10 ¹³ poise. The transition from the initial pressurization to the second pressurization can be made when the lower mold 23 reaches about 0.1% to 5% of the final thickness of the optical element to be molded.

  After the second pressurization is started, the respective positions of the servo motors M1 and M2 are detected (steps S9 and S10), and the respective detection signals are input to the drivers 84 and 84 and the control unit 81. The controller 81 determines whether or not the rotational position at the time of the second pressurization has reached a preset target value, and if not, drives the servo motors M1 and M2 to reach the target value. Command signal is output (step S11).

In this way, the molds 22 and 23 and the molded body are moved while continuing the position control until the rotation angle of the screw shafts 33 and 33 rotated by the servo motors M1 and M2 reaches the set value at the time of the second pressurization. When the cooling is performed and the rotation angle of the screw shafts 33 and 33 reaches the set value at the time of the second pressurization, the control unit 81 stops driving the servo motors M1 and M2 and determines that the press molding is completed ( Step S12).
Thereafter, the molds 22 and 23 are cooled to a temperature equal to or lower than, for example, 10 ^12.5 to 10 ^13.5 poise in terms of glass viscosity, and the lower mold 23 is lowered to open the mold and take out the molded product. And in order to shape | mold the next molded product, the process of step S1-S12 is repeated.
As described above, the multistage control is useful for molding a convex meniscus lens, a concave meniscus lens, a biconcave lens, and the like.

According to the press molding method described above, the glass is greatly deformed by the position control while maintaining the level of the mold (that is, the consistency between the upper and lower optical axes of the pair of molds), and the final shape is obtained. The shape is close to. Next, when it is within the predetermined viscosity range during cooling, the surface shape is corrected by performing position control (speed control) again so that an appropriate load (secondary pressurization, etc.) is applied, and the final wall thickness is adjusted. Press towards.
Therefore, an optical element having a high molding difficulty such as a concave meniscus lens or a biconcave lens is likely to cause a deviation in surface accuracy because the glass shrinks unevenly during cooling after press molding. This can be prevented by the molding method.

  There are no particular restrictions on the material to which the present invention is applied. As the glass preform, optical glass made of phosphate glass, borate glass, silicate glass, borosilicate glass, or the like can be used. In particular, phosphate glass and borate glass have high reactivity between the glass and the mold surface, and press molding may be performed at a relatively low temperature (that is, at a high viscosity) to prevent fusion. In such a case, a high pressing force is required. However, since the verticality of the main shaft is maintained even when press forming at a high pressing force as compared with the prior art, the present invention is particularly suitable for forming these materials. It is.

  Further, for example, in a high refractive index optical glass having a refractive index nd of 1.7 or more, the molding surface is similarly formed as described above due to a high refractive index component (W, Nb, Ti, etc.) added in a large amount. The reactivity in becomes high. Accordingly, similarly, the effect of the present invention in which the verticality of the press shaft is maintained even when pressing is performed at a low temperature and a high pressurizing force can be obtained remarkably.

Although the preferred embodiment of the present invention has been described, the present invention is not limited to the above description.
For example, although two screw shafts 33 are provided at symmetrical positions, three or more screw shafts may be provided. Also in this case, for example, the screw shafts are arranged at equal intervals on the same circumference centered on the axis of the main shaft 24 so that no bending moment acts on each screw shaft.
The guides are also provided on both the left and right sides and the rear side of the elevating member 32. For example, the guides may be provided on the left and right and both front and rear sides.

  Furthermore, in the apparatus of this aspect described above, servomotors M1 and M2 are provided for the two screw shafts 33 and 33, respectively, but two ball screws may be driven by one motor. For example, the motor and the ball screw may be connected with a gear. In this case, the synchronization of the rotation of the two ball screws can be easily obtained. Further, the motor and the ball screw may be connected by a pulley. In addition, as long as any one of the molds can be moved, the driving body is not limited to the servo motor, and other types of motors, cylinders, and the like may be used.

  Furthermore, after the second pressurization, a multi-stage pressurization schedule such as secondary pressurization and tertiary pressurization may be used according to the thickness and shape of the optical element to be molded. According to such a multi-stage pressurization schedule, the surface accuracy and thickness accuracy of the optical element to be molded can be increased, and it is particularly effective for high-precision molding of concave meniscus lenses and biconcave lenses that are difficult to mold. It is.

Example 1
A biconvex lens (diameter 12.8 mm, center thickness 2.02 mm) having a flat portion at the periphery was press-molded using the press-molding apparatus shown in FIGS. 1 and 2. The distance between the two ball screws 33 and 33 was 200 mm, four sets of molding dies 22 and 23 were incorporated in the mother dies 20a and 20b, and a high-frequency induction heater 25 was used as a heating means. A glass preform for molding is obtained by hot-forming barium borosilicate glass having a transition temperature Tg of 500 ° C. and a yield temperature Ts of 540 ° C. into a biconvex curved surface in advance, and carbon on the surface thereof. What attached the system membrane was used. The molds 22 and 23 are made of silicon carbide (SiC), and are composed of an upper mold, a lower mold, and a cylindrical body mold that regulates both. Carbon mold release films are applied to the molding surfaces of the upper mold and the lower mold. The molding dies 22 and 23 were assembled to the tungsten alloy mother dies 20a and 20b so that even if the upper and lower mother dies 20a and 20b contacted each other, a load was applied to the molded product.
The glass preform is preheated to 610 ° C., the preheating temperature of the molds 22 and 23 is set to 580 ° C., and the four preheated glass preforms are dropped and supplied to the four lower mold forming surfaces, and then immediately the lower mold 23 Was raised while repeating the position control and brought close to the upper die 22. The two elevating members 32 were raised at a speed of about 2.5 mm / s by rotating the two ball screws 33 and 33 connected to the rotation shafts of the servomotors M1 and M2 in synchronization. The elevating member 32 was raised while maintaining the horizontal with respect to the vertical direction, so that the main shaft 24 on which the lower mother die 20b was placed rose without being inclined.
About 3 seconds after the start of pressing, the upper mother die 20a and the lower mother die 20b were pressed until they contacted each other. After the contact, a preset torque limiter was activated and pressurized with a load of about 400 kgf. Cooling at 80 ° C./min with the upper and lower mother molds in contact with each other, when the temperature reached 480 ° C., the lower mold was lowered and the molded lens was taken out. Immediately after this, the mother die was moved to the heating position to start heating, and the next press cycle was started. This press was repeated 100 times to obtain 400 lenses. 40 pieces were selected from these, and the tilt was measured by measuring the thickness of the flat portion at the periphery. As a result, the tilt was an average of 0.8 minutes and a maximum of 1.5 minutes, both satisfying the standard values.

Example 2
Using the same press molding apparatus as in Example 1, a convex meniscus lens (diameter 12 mm, center thickness 2.10 mm) having a flat portion at the periphery was press molded. The same material as in Example 1 was used for the glass preform for molding.
After the glass preform preheated to 610 ° C. was dropped and supplied to the molding surface of the lower mold 23 heated to 580 ° C., the lower mold 23 was immediately raised while repeating position control to bring it close to the upper mold 22. At this time, the position was controlled every 4 ms so that the ascending speed (pressing speed) was 2.5 mm / s.
About 2 seconds after the start of pressing, cooling gas was blown onto the molds 22 and 23 and cooling was started at a rate of 80 ° C./min. Even after the cooling was started, the lower mold 23 continued to rise at a constant speed. Eventually, when the center thickness of the compact reached 2.2 mm (immediately before the target value), the lower mold 23 stopped rising (press speed zero) and maintained its position. Then, the cooling was further continued, and the second pressurization was started when the temperature of the molds 22 and 23 reached 550 ° C. At this time, the set value was switched so that the position control was performed every 100 ms so that the pressing speed of the second pressurization was 0.01 mm / s. About 15 seconds after the start of the second pressurization, the upper and lower mother dies 20a and 20b contacted each other.
Cooling was continued in this state, and after the glass molded bodies in the molds 22 and 23 reached the transition point Tg, the lower mold 23 was lowered and the molded lens was taken out. Thereafter, the mother die 20b was moved to the heating position to start heating, and the next press cycle was started. This press was repeated 100 times, 40 pieces were arbitrarily extracted from the obtained lenses, and the tilt was calculated by measuring the thickness of the flat part. As a result, the tilt was 0.7 minutes on average and 1.5 minutes at the maximum, both satisfying the standard values.

  INDUSTRIAL APPLICABILITY The present invention can be applied to press molding of a molded product that requires high molding accuracy, and is particularly suitable for press molding of an optical lens used in an imaging device such as a digital camera or a recording / reproducing device of an optical recording medium such as a DVD. It is.

It is a schematic plan sectional view of the glass optical element manufacturing apparatus when the press molding apparatus of the present invention is applied to the glass optical element manufacturing apparatus. It is side surface sectional drawing explaining schematic structure of the press molding apparatus of this invention. It is the II sectional view taken on the line of FIG. It is a block diagram explaining the structure of the control apparatus which controls the drive of servomotor M1, M2. It is a flowchart explaining the effect | action of the press apparatus of this embodiment. It is a figure which shows schematic structure of a reference press molding apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Press molding apparatus 2 Molding part 22,23 Mold 24 Main shaft 25 Heater 3 Drive part 31 Base 32 Lifting member 33 Screw shaft 34 1st guide 34a Support member 34b Guide rail 36 2nd guide 36a Support member 36b Guide rail

Claims (6)

In a press molding apparatus having an openable upper and lower molds having opposed mold surfaces, and a drive unit that moves at least one of the upper and lower molds in the vertical direction to open and close the mold ,
The drive unit includes a main shaft that supports the movable mold, and
An elevating member that supports the main shaft and moves up and down;
A plurality of screw shafts arranged at positions deviated from the axis of the main shaft, and screwed with a plurality of screw portions formed on the elevating member, respectively, to raise and lower the elevating member;
A driver that rotates each of the screw shafts in synchronization;
Having a control device for controlling the driving of the driving body;
A press molding apparatus characterized by the above.   The press molding apparatus according to claim 1, wherein the plurality of screw portions of the elevating member are provided at symmetrical positions around the main shaft.   The press forming apparatus according to claim 2, wherein the plurality of screw shafts receive the load at the time of press forming by closing the forming die.   The press forming apparatus according to claim 1, wherein a driving body is provided corresponding to each of the plurality of screw shafts, and driving control of each driving body is performed by the control device.   5. The press molding apparatus according to claim 1, wherein the control device performs position control for controlling a moving position of the molding die by rotation of the screw shaft when molding a molding material. . An optical element molding method using the press molding apparatus according to claim 1,
Heating the mold to a predetermined temperature in advance;
Conveying the heat-softened material and supplying the material to the lower mold of the mold in an open state;
Performing the mold closing of the mold and press-molding the material,
In the pressure molding step, performing position control of the mold by rotation of a plurality of screw shafts;
An optical element molding method characterized by the above.

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