Patent Publication Number: US-2010120601-A1

Title: Manufacturing method of glass molded body, manufacturing apparatus of glass molded body, and glass molded body

Description:
TECHNICAL FIELD 
     The present invention relates to a manufacturing method of a glass molded body which can be used as various kinds of optical elements, a manufacturing apparatus of a glass molded body and a glass molded body. 
     BACKGROUND ART 
     In recent years, as lenses for digital cameras, optical pickup lenses for DVD, etc., lenses for cameras of mobile phones, coupling lenses for optical communications, and the like, optical elements made of glass are used widely. As such optical elements made of glass, glass molded bodies manufactured by a process of conducting press molding for glass materials with a shaping mold have been used more often. 
     In the conventional method (hereafter, referred to as “reheat-pressing method”) which has been used widely as a manufacturing method of a glass molded body, a glass material used for manufacturing a molded body is produced preliminary to have a specified weight and shape, and is heated together with a shaping mold to a temperature at which the shape of the glass material becomes changeable, and thereafter the glass material is pressed and shaped by a shaping mold. 
     According to the reheat-pressing method, since the press shaping can be conducted while controlling the temperature of a glass material or a shaping mold precisely, dispersion in the performance of the manufactured glass molded body can be suppressed to be comparatively small. However, this method needs to repeat heating and cooling a glass molded body and a shaping mold for each shaping shot, and in order to suppress dispersion in temperature at the time of conducting press shaping and to conduct the shaping with sufficient reproducibility, it has a fundamental problem that the shaping for one time takes a very long time. 
     On the other hand, in a well-know method as another manufacturing method, a shaping mold is heated preliminary to a prescribed temperature, a molten glass droplet is supplied to the surface of the shaping mold, and a press molding is conducted for the supplied molten glass droplet with the shaping mold while the temperature of the molten glass droplet is still a temperature at which the shape of the molten glass droplet is changeable (for example, refer to Patent Document 1). In such a method of conducting press molding for a molten glass droplet, it is not necessary to repeat heating and cooling a shaping mold, etc. and a glass molded body can be manufactured directly from a molten glass droplet. Therefore, a time necessary for conducting a molding process at one time can be shortened so much. 
     Furthermore, the following method is proposed in order to conduct press molding for a minute molten glass droplet so as to manufacture a minute glass molded body: a molten glass droplet dropped from a nozzle is made to collide with a member provided with a small through hole, and a part of the collided molten glass droplet as a minute droplet is made to pass through the small through hole and is supplied to a lower mold (for example, refer to Patent Document 2). 
     Patent documents 1: Japanese Patent Unexamined Publication No. 1-308840 
     Patent documents 2: Japanese Patent Unexamined Publication No. 2002-154834 
     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     The methods described in Patent Documents 1 and 2 are a method of supplying a molten glass droplet to a lower mold by causing the molten glass droplet to drop from a nozzle and conducting press molding. In these methods, when a predetermined amount of molten glass is accumulated at a tip portion of a nozzle, a molten glass drops naturally from the nozzle. Therefore, the dropping intervals can be adjusted to some extent by the heating temperature of the nozzle. However, since the temperature of the nozzle is easily influenced by disturbances, such as temperature in the vicinity of the nozzle and a flow of air, it is difficult to keep the dropping intervals of a molten glass droplet constant perfectly. 
     In these methods, to a lower mold heated to a predetermined temperature, supplied is a molten glass droplet having a temperature higher than that of the lower mold. Therefore, the supplied molten glass droplet is quickly cooled by heat release from its contact portion with the lower mold. Therefore, when the process is repeated to manufacture many glass shaped-bodies, if dispersion arises in dropping intervals, dispersion is further caused in a period of time after a molten glass droplet has been supplied to a lower mold until the molten glass droplet is subjected to press molding, and the temperature of a molten glass droplet at the time of press molding will vary greatly. As a result, the dispersion in the temperature of the molten glass droplet at the time of press molding is directly linked with dispersion in the quality of a obtained glass molded body. 
     Moreover, as the volume of a molten glass droplet becomes small, the molten glass droplet supplied to the lower mold is cooled quickly. Therefore, in the case of conducting press molding for a minute droplet produced by the method described in Patent Document 2, dispersion in the temperature of a molten glass droplet at the time of press molding becomes large especially. Therefore, it was difficult to manufacture a glass molded body with stable quality. 
     The present invention is made in view of the above technical themes, and an object of the present invention is to provide a glass molded body manufacturing method capable of manufacturing a glass molded body with stable quality efficiently by suppressing dispersion in the temperature of a molten glass droplet at the time of press molding to the minimum, to provide a manufacturing apparatus for use in the manufacturing method, and a glass molded body manufactured by the manufacturing method. 
     Means for Solving the Problem 
     In order to solve the above-mentioned theme, the present invention has the following features. 
     1. In a glass molded body manufacturing method of manufacturing a glass molded body by conducting press molding for a molten glass droplet by using a shaping mold having a lower mold and an upper mold, the glass molded body manufacturing method is characterized by comprising: 
     a supplying process of causing a molten glass droplet to drop from an upper portion toward the lower mold thereby supplying the molten glass droplet to the lower mold; 
     a detecting process of detecting that the dropped molten glass droplet has reached a predetermined position; and 
     a pressing process of starting pressing for the molten glass droplet after a predetermined time has elapsed from the detection in the detection process. 
     2. The glass molded body manufacturing method described in the item 1 is characterized in that the detecting process is a process of detecting that the dropped molten glass droplet has passed through a predetermined position above the lower mold. 
     3. The glass molded body manufacturing method described in the item 1 is characterized in that the detecting process is a process of detecting an impulse force generated due to the collision of the molten glass droplet with the lower mold by a weight sensor provided in a lower part of the lower mold. 
     4. The glass molded body manufacturing method described in any one of the items 1 through 3 is characterized in that the supplying process is a process of causing a molten glass droplet dropped from the above portion to collide with a member provided with a small through hole, causing a part of the collided molten glass droplet to pass through the small through hole, and supplying the part to the lower mold. 
     5. The glass molded body manufacturing method described in the item 1 is characterized in that the supplying process is a process of causing a molten glass droplet dropped from the above portion to collide with a member provided with a small through hole, causing a part of the collided molten glass droplet to pass through the small through hole, and supplying the part to the lower mold and the detecting process is a process of detecting the molten glass droplet has collided with the member provided with the small through hole. 
     6. The glass molded body manufacturing method described in any one of the items 1 through 5 is characterized in that when a predetermined time has elapsed from the detection in the detecting process, the pressing of the molten glass droplet has been completed. 
     7. The glass molded body manufacturing method described in the item 2 is characterized in that the passage of the molten glass droplet through the predetermined position is detected by an optical sensor comprising a light emitting section and a light receiving section to receive the light emitted from the light emitting section. 
     8. In a glass molded body manufacturing apparatus having a shaping mold having a lower mold and an upper mold and for manufacturing a glass molded body by conducting press molding for a molten glass droplet, the glass molded body manufacturing apparatus is characterized by comprising: 
     a supplying section for causing a molten glass droplet to drop from an upper portion toward the lower mold thereby supplying the molten glass droplet to the lower mold; 
     a detecting section for detecting that the dropped molten glass droplet has reached a predetermined position; and 
     a control section for controlling actions of the shaping mold to start pressing for the molten glass droplet after a predetermined time has elapsed from the detection in the detection process. 
     9. A glass molded body characterized by being manufactured by the glass molded body manufacturing method described in any one of the items 1 through 7. 
     EFFECT OF THE INVENTION 
     According to the present invention, when a predetermined time has elapsed after detecting that a dropped molten glass droplet has reached a predetermined position, pressing for the molten glass droplet by a shaping mold is stated. Therefore, a period of time after the molten glass droplet has come in contact with the lower mold until press molding is started is maintained constant with high accuracy. Therefore, at the time of manufacturing many glass shaped-bodies repeatedly, even if dispersion arises in dropping intervals, dispersion in the temperature of the molten glass droplet at the time of press molding can be suppressed to the minimum, whereby a glass molded body can be manufactured efficiently with stable quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic diagram showing a glass molded body manufacturing apparatus  10  used in Embodiment 1. 
         FIG. 2  is a schematic diagram showing a glass molded body manufacturing apparatus  10  used in Embodiment 1. 
         FIG. 3  is a flowchart showing a glass molded body manufacturing method in Embodiment 1. 
         FIG. 4  is a schematic diagram showing a glass molded body manufacturing apparatus  20  used in Embodiment 2. 
         FIG. 5  is a schematic diagram showing a glass molded body manufacturing apparatus  30  used in Embodiment 3. 
         FIG. 6  is a flowchart showing a glass molded body manufacturing method in Embodiment 3. 
     
    
    
     EXPLANATION OF REFERENCE SYMBOLS 
     
         
         
           
               10 ,  20  and  30  Glass molded body manufacturing apparatus 
               11  and  31  Lower mold 
               12  and  32  Upper mold 
               13  Optical Sensor 
               13   a  Light emitting section 
               13   b  Light receiving section 
               14  Controller 
               15  and  35  Shaping mold 
               16  Timer 
               21  Weight Sensor 
               33  Molten glass droplet 
               34  Small through hole 
               36  Member provided with small through hole  34   
               41  Nozzle 
               42  Melting Bath 
               43  Molten glass droplet 
             P 1  Dropping position 
             P 2  Molding position 
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereafter, embodiments of the present invention will be explained in detail with reference to drawings. 
     Embodiment 1 
     The manufacturing method of a glass molded body according to the first embodiment of the present invention will be explained with reference to  FIGS. 1 to 3 .  FIGS. 1 and 2  are schematic diagrams showing a manufacturing apparatus  10  of a glass molded body, which is used in this embodiment.  FIG. 1  shows the state of a supplying process of dropping a molten glass droplet from a nozzle and supplying it to a lower mold, and  FIG. 2  shows the state of a pressing process of pressing the supplied molten glass droplet with a shaping mold, respectively. Further,  FIG. 3  is a flowchart showing the manufacturing method of a glass molded body in this embodiment. 
     The manufacturing apparatus  10  of the glass molded body shown in  FIGS. 1 and 2  has a shaping mold  15  which includes a lower mold  11  and a upper mold  12  and is used to conduct press molding for a molten glass droplet  43 . Further, as a supplying section to supply a molten glass droplet  43  to the lower mold  11 , the manufacturing apparatus  10  has a melting bath  42  to store glass  44  in a molten state and a nozzle  41  provided in the lower part of the melting bath  42 . The lower mold  11  is structured to be moved by a driving section (not shown) between a position (dropping position P 1 ) beneath a nozzle  41  for receiving a molten glass droplet  43  and a position (shaping position P 2 ) opposite to the upper mold  12  for conducting press molding for a molten glass droplet  43 . Also, the upper mold  12  is structured to be moved by a driving section (not shown) in the direction (the vertical direction in the drawing) to press a molten glass droplet between it and the lower molds  11 . 
     Further, the manufacturing apparatus  10  of a glass molded body has an optical sensor  13  as a detecting section to detect the state that a dropped molten glass droplet  43  has arrived at a predetermined position and a controller  14  as a control section to control actions of the shaping mold  15 . The optical sensor  13  has a light emitting section  13   a  and a light receiving section  13   b  to receive light emitted from the light emitting section  13   a . The controller  14  has a timer  16  to measure the time after the optical sensor  13  has detected a molten glass droplet  43 . 
     The material of the shaping mold  15  may be chosen from well-known materials of a shaping mold for manufacturing a glass molded body by conducting press molding and used suitably. Examples of the material of the shaping mold  15  include ultrahard materials containing various heat-resistant alloys (stainless steel, etc.) and tungsten carbide as main components, various ceramics (silicon carbide, silicon nitride, aluminium nitride, etc.), and composite materials containing carbon, and the like. Further, materials in which a protective layer of various metals, ceramics, and carbon is formed on the above materials, are employable. 
     The shaping mold  15  is structured to be heated to a prescribed temperature by a heating section (not illustrated). In this case, it may be preferable that the lower mold  11  and the upper mold  12  are subjected to a temperature control independently, respectively. As the heating section, well-known heating sections can be chosen and used suitably. For example, the well-known heating sections include a cartridge heater used in such a way that it is embedded in the inside of a member to be heated, a sheet-shaped heater used in such a way that it is brought in contact with the outside of a member to be heated, an infrared heating device, a high-frequency induction heating device, and the like. 
     Hereafter, each of processes will be explained in the order in accordance with the flowchart shown in  FIG. 3 . 
     First, the shaping mold  15  is heated beforehand to a prescribed temperature (Process S 101 ). As the prescribed temperature, appropriately selected is a temperature at which a good transfer surface is formed on a glass molded body by conducting press molding. Generally, when the temperature of the lower mold  11  or the upper mold  12  is too low, it will become difficult to form a good transfer surface on a glass molded body. On the contrary, when temperature is made too high more than needed, there is fear that fusion takes place between a glass droplet and a shaping mold or the life of a shaping mold may become short. Actually, a proper temperature may change depending on various conditions, such as the kind, shape, and size of a glass droplet, the material of a shaping mold, the kind of a protective layer, the shape and size of a glass molded body, and the location of a heater or a temperature sensor. Therefore, it is desirable to obtain the proper temperature experimentally. Usually, it is desirable to set the temperature to about a temperature from (Tg (glass transition point) of a glass droplet−100° C.) to (Tg+100° C.). The heating temperature of the lower mold  11  may be the same with or different from that of the upper mold  12 . 
     Next, the lower mold  11  is moved to the dropping position P 1  (Process S 102 ), and a molten glass droplet  43  is dropped from the nozzle  41  (Process S 103 ). At this time, the melting bath  42  is heated by a heater (not illustrated), and glass  44  in the molten state is stored inside the melting bath  42 . The nozzle  41  is provided at the lower side of the melting bath  42 , and the glass  44  in the molten state passes through a passage provided inside the nozzle  41  with the aid of its own weight and is accumulate at the tip portion of the nozzle  41  with the aid of its surface tension. When a prescribed amount of the molten glass is accumulate at the tip portion of the nozzle  41 , a molten glass droplet  43  is separated naturally from the tip portion of the nozzle  41 , and then the molten glass droplet  43  with a prescribed amount drops downward. At this time, the molten glass droplet  43  is on the condition that its temperature is higher than that of the shaping mold  15 . 
     Generally, the weight of the dropping molten glass droplet  43  is adjustable by the outside diameter of the tip portion of the nozzle  41 . Although such a weight depends on the kind of a molten glass, a molten glass droplet with a weight of 0.1 to 2 g can be made to drop. Further, the dropping intervals of a molten glass droplet can be adjusted by the inside diameter, length, heating temperature and the like of the nozzle  41 . Therefore, if these conditions are set appropriately, it is possible to make a molten glass droplet to drop with a predetermined weight at predetermined intervals. 
     There is no specific restriction in the kind of usable glass, and the well-known kinds of glass can be chosen and used in accordance with usage. For example, optical glasses, such as a phosphoric acid type glass and a lanthanum type glass, and the like may be usable. 
     After the molten glass droplet  43  has dropped from the nozzle  41 , the optical sensor  13  detects that the dropping molten glass droplet  43  has passed through a predetermined position above the lower mold  11  (Process S 104 ). The optical sensor  13  is arranged at a predetermined position above the lower mold  11 , and the optical sensor  13  receives light emitted from a light emitting section  13   a  with a light receiving section  13   b  and monitors the intensity of the received light. When a molten glass droplet  43  dropped from the nozzle  41  passes through the optical path between the light emitting section  13   a  and the light receiving section  13   b , light expected to reach the light receiving section  13   b  is blocked by the molten glass droplet  43 , and the intensity of light received by the light receiving section  13   b  becomes lower, whereby it is possible to detect that the dropped molten glass droplet  43  has passed through the predetermined position. The wavelength of the light used for this detection is not limited specifically and the light may be a visible light or an infrared light. 
     When the passage of the molten glass droplet  43  is detected by the optical sensor  13  and the information of the passage is sent to a controller  14 , a timer  16  of the controller  14  will start measuring time. In the following processes, the actions of the shaping mold  15  are controlled on the basis of the time measured by the timer  16 . Each of specified times T 1 , T 2  and T 3 , which are explained below, represents a period of time measured by the timer  16  from the initial time of 0 second at which the optical sensor  13  detected the passage of the molten glass droplet  43 . 
     As the detecting section for detecting that the dropped molten glass droplet  43  has passed through the predetermined position above the lower mold  11 , it is not limited to the optical sensor  13  and various well-known sensors can be used. For example, sensors utilizing an electric wave, sound, temperature, etc. are usable. Especially, since an optical sensor has the advantage that its response speed is quick and strong to disturbance, it can be used preferably. Further, in order to prevent detection errors caused by fluctuation of the drop position of a molten glass droplet over time, it is desirable to have a device to adjust the position of the detecting section. 
     In this embodiment, the detecting section is made to detect that the molten glass droplet  43  has passed through the predetermined position above the lower mold  11 . However, since the molten glass droplet  43  is quickly cooled by contacting the lower mold  11 , it is most ideal to measure the elapsed time after the time when the molten glass droplet  43  has collided with the lower mold  11  was made 0 second. However, it may be considered that a period of time after the molten glass droplet  43  has passed through the predetermined position until it collides with the lower mold  11  may be almost constant and only negligible dispersion occurs in the period of time. Therefore, as in this embodiment, with the method of measuring the elapsed time after the time when the molten glass droplet  43  has passed through the predetermined position was made 0 second, the period of time after a molten glass droplet has come in contact with a lower mold until press molding is started can be kept constant with high accuracy. 
     In this way, the detecting process of the present invention is a process of detecting that a molten glass droplet  43  has arrived at a specified position. Here, the specified position may be a position based on which a period of time after a molten glass droplet  43  has come in contact with the lower mold  11  until press molding is started can be kept constant. For example, as the specified position, the detecting section may detect that a molten glass droplet  43  has actually collided with the lower mold  11 , or may detect that a dropped molten glass droplet  43  has passed through a predetermined position above the lower mold  11 . Also, the detecting section may detect that a molten glass droplet  43  has separated from the tip portion of the nozzle  41  and starts dropping. 
     After the molten glass droplet  43  has reached the lower mold  11  (Process S 105 ), when the measuring time by a timer  16  has become the predetermined time T 1 , the lower mold  11  is moved to the shaping position P 2  (Process S 106 ). Here, in the present invention, since it is not necessary to manage specifically strictly the specified time T 1  for moving the lower mold  11  to the shaping position P 2 , it is not essential for the specified time T 1  to be based on the measuring time by the timer  16 . 
     Subsequently, when the measuring time by the timer  16  has become the specified time T 2 , the upper mold  12  is moved downward and the application of pressure is started (Process S 107 ). As mentioned above, in the manufacturing method of the present invention, since the molten glass droplet  43  having a temperature higher than a prescribed temperature of the heated lower mold  11  is supplied to the lower mold  11 , the supplied molten glass droplet  43  is quickly cooled by heat release from its contact part with the lower mold  11 . Therefore, if there is dispersion in the period of time from the supplying of the molten glass droplet  43  to the press molding, the temperature of the molten glass droplet  43  at the time of the press molding will vary greatly, and the various qualities of a obtained glass molded body will be influenced. For example, the core diameter (thickness on the central axis), the accuracy of a transfer surface, the surface roughness of a transfer surface, the index of refraction and the like are influenced. 
     Among them, the influence to the core diameter is great especially. If the time until press molding is started becomes short, the temperature of the molten glass droplet  43  at the time of the press molding becomes high. Therefore, since the viscosity becomes low, the molten glass droplet  43  becomes difficult to deform, and the core diameter of an obtained glass molded body becomes thin. On the contrary, if the time until press molding is started becomes long, the temperature of the molten glass droplet  43  at the time of the press molding becomes low. Therefore, since the viscosity becomes high, the molten glass droplet  43  becomes difficult to deform, and the core diameter of an obtained glass molded body becomes thick. 
     Accordingly, in order to manufacture a glass molded body with stable quality by suppressing dispersion in the temperature of a molten glass droplet at the time of press molding to the minimum, it is necessary to make a period of time after a molten glass droplet  43  has been supplied to the lower mold  11  until press molding is started, constant as much as possible. In this embodiment, when a predetermined time T 2  has elapsed after the optical sensor  13  detected the passage of a molten glass droplet  43 , press molding is started. Accordingly, even if there is dispersion in dropping intervals, dispersion in the temperature of a molten glass droplet  43  at the time of press molding can be suppressed to the minimum. As a result, a glass molded body can be manufactured efficiently with stable quality. 
     Since a proper time of the predetermined time T 2  may changes depending on various conditions, such as the temperature of the lower mold  11 , the upper mold  12 , nozzle  41  or the like, the kind of glass, the size of a glass molded body, and a core diameter, it is desirable to determine the proper temperature experimentally. Generally, when the predetermined time T 2  is set at a time within the range from about one second to several seconds, a glass molded body can be manufactured with stable quality. 
     During the press molding, the heat of the molten glass droplet  43  is taken from the contact surface of the molten glass droplet  43  with the lower mold  11  or the upper mold  12 , and then the cooling of the molten glass droplet  43  is advanced further. When the measuring time by the timer  16  becomes the predetermined time T 3 , the application of pressure is canceled and the upper mold  12  is moved upward (Process S 108 ). The predetermined time T 3  may be set at a time when the molten glass droplet  43  is cooled to the temperature at which the shape of a transfer surface formed on a glass molded body does not collapse even if the application of pressure by the shaping mold  15  is cancelled. Since the influence of the predetermined time T 3  on the quality of a glass molded body is not great as compared with the above-mentioned predetermined time T 2 , the predetermined time T 3  is not necessarily required to be determined based on the measuring time by the timer  16 . However, in order to manufacture efficiently a glass molded body with more stable quality, it is desirable to determine the predetermined time T 3  based on the measuring time by the timer  16 . With regard to the temperature at which the shape of a transfer surface does not collapse even if the application of pressure is cancelled, although the temperature may change depending the kind of glass, the size and shape of a glass molded body and a required accuracy, it may be permissible to cool the molten glass droplet  43  to a temperature near the glass transition point Tg of the glass. 
     The load to be applied onto a molten glass droplet  43  as the application of pressure may be always constant, or may be changed in terms of time. In order to enhance transfer accuracy, it is desirable to apply the load of a predetermined value or more in such a way that the condition that the molten glass droplet  43  and the shaping mold  15  are in close contact with each other can be maintained until the molten glass droplet  43  is cooled to the temperature at which the above-mentioned application of pressure can be canceled. The weight of the load may be appropriately set in accordance with the size, etc. of a glass molded body to be manufactured. There is no specific restriction in the driving section to move the upper mold  12  upward or downward, and well-known drive devices, such as an air cylinder, an oil pressure cylinder, and an electric cylinder using a servo-motor, can be chosen suitably, and can be used as the driving section. 
     After the upper mold  12  has been moved upward, the formed glass molded body is collected (Process S 109 ), whereby the manufacture of a glass molded body is completed. The collecting of a glass molded body can be conducted by a well-known mold releasing apparatus with the utilization of vacuum absorption, etc., for example. Subsequently, when a glass molded body is manufactured successively, the lower mold  11  is moved again to the dropping positions P 1  (Process S 102 ), and the following processes may be repeated. 
     The manufacturing method of a glass molded body of according to the present invention may include another process in addition to the processes having been explained above. For example, after a glass molded body has been collected at Process  5109 , a process of cleaning the shaping mold  15 , etc. may be provided additionally. 
     The glass molded body manufactured by the manufacturing method of the present invention can be used as various optical elements, such as imaging lenses for a digital camera and the like, optical pickup lenses for DVD and the like, and coupling lenses for optical communications. Further, if the glass molded body is further heated, softened and pressed by a shaping mold, various optical elements can also be manufactured from the glass molded body. 
     Embodiment 2 
     Next, the manufacturing method of a glass molded body as the second embodiment of the present invention will be explained with reference to  FIG. 4 .  FIG. 4  is a schematic diagram showing a manufacturing apparatus  20  of a glass molded body, which is used in the second embodiment, and shows the state of a supplying process of dropping a molten glass droplet  43  from a nozzle  41  and supplying it to a lower mold  11 . 
     The difference of the manufacturing apparatus  20  of a glass molded body from the manufacturing apparatus  10  of a glass molded body in the first embodiment explained previously is in a detecting section for detecting that a dropped molten glass droplet  43  has arrived at a predetermined position. The manufacturing apparatus  20  of a glass molded body shown in  FIG. 4  has a weight sensor  21  in the lower part of the lower mold  11 . If the weight sensor  21  detects an impulse force generated when a molten glass droplet  43  dropped from the nozzle  41  collides with the lower mold  11 , the information about the impulse force is sent to a controller  14 , a timer  16  of the controller  14  will be started. 
     As the weight sensor  21 , well-known sensors can be chosen suitably and can be used. For example, a sensor employing a piezoelectric element, a sensor employing a strain gage, etc. are usable. Especially, the sensor employing a piezoelectric element has high sensibility and its response speed is quick. Accordingly, it can be used preferably. The weight sensor  21  may also be provided to the lower part of the lower mold  11  such that it comes in direct contact with the lower mold  11 , or it may also be provided such that other members are inserted between it and the lower mold  11 . For example, it is desirable to provide a heat insulation member between the lower mold  11  and the weight sensor  21  in such a way that the heat of the lower mold  11  is not transferred directly to the weight sensor  21 . 
     Except that detecting section differ, the processes of manufacturing a glass molded body in this embodiment is the same as the processes in the first embodiment shown in  FIG. 3 . Therefore, if Process  5101  through Process S 109  having been explained previously are conducted sequentially in the order, a glass molded body can be manufactured efficiently with stable quality. 
     Embodiment 3 
     Next, the manufacturing method of a glass molded body as the third embodiment of the present invention will be explained with reference to  FIG. 5  and  FIG. 6 .  FIG. 5  is a schematic diagram showing a manufacturing apparatus  30  of a glass molded body, which is used in the third embodiment, and shows the state of a supplying process of dropping a molten glass and supplying it to a lower mold.  FIG. 6  is a flowchart showing the manufacturing method of a glass molded body in this embodiment. 
     The difference of the manufacturing apparatus  30  of a glass molded body from the manufacturing apparatus  10  of a glass molded body in the first embodiment explained previously is in that the manufacturing apparatus  30  has a member  36  provided with a small through hole  34  in order to supply a minute molten glass droplet  33  to a lower mold. Further, a shaping mold  35  includes a lower mold  31  and an upper mold  32  with respective small molding surfaces. Other structures are the same as those of the manufacturing apparatus  10  of a glass molded body. 
     As with the case of Embodiment 1, a shaping mold  35  is heated beforehand to a predetermined temperature (Process S 301 ), a lower mold  31  is moved to the dropping position P 1  (Process S 302 ), and a molten glass droplet  43  is dropped from a nozzle  41  (Process S 303 ). The passage of the molten glass droplet  43  is detected by an optical sensor  13  and the information about the passage is sent to a controller  14 , then a timer  16  of the controller  14  will be started (Process S 304 ). 
     The molten glass droplet  43  collides with the member  36  provided with the small through hole  34 , and a part of the molten glass droplet  43  passes the small through hole  34  as a minute molten glass droplet  33  (Process S 305 ) and reaches the lower mold  31  (Process S 306 ). 
     In this description, the case where the optical sensor  13  detects that the molten glass droplet  43  dropped from the nozzle  41  has passed through a predetermined position is explained as an example. However, the method of detecting a molten glass droplet is not limited to this example. For example, the detecting method includes the following ways: the optical sensor  13  may detect that the molten glass droplet  33  pushed out from the small through hole  34  has passed through a predetermined position, or the weight sensor provided in the lower part of the lower mold  31  may detect an impulse force generated when the molten glass droplet  33  collides with the lower mold. Further, the detecting method may detect impulse force, sound, etc. generated when the molten glass droplet  43  collides with the member  36  provided with the small through hole  34 . 
     The shape of the member  36  provided with the small through hole  34  is not limited specifically. For example, as disclosed in Patent documents 2, a member provided with a tapered surface, or a member having a guide hole, etc. can also be used. 
     After the molten glass droplet  33  has reached the lower mold  31 , a glass molded body is manufactured by the same processes as Embodiment 1. When the measuring time by the timer  16  becomes the predetermined time T 1 , the lower mold  31  is moved to the shaping position P 2  (Process S 307 ), and when the measuring time by the timer  16  becomes the predetermined time T 2 , the upper mold  32  is moved downward and the application of pressure is started (Process S 308 ). When the volume of the molten glass droplet  33  becomes small, cooling may progress quickly. Therefore, especially in the case that the press molding of a minute molten glass droplet  33  is conducted by the use of the member  36  provided with the small through hole  34  as with this embodiment, the method of the present invention can be used effectively. 
     When the measuring time by the timer  16  becomes the predetermined time T 3 , the application of pressure is canceled and the upper mold  32  is moved upward (Process S 309 ). Then, a glass molded body is collected, whereby the manufacture of a glass molded body (process S 310 ) has been completed. 
     Example 
     Hereafter, examples having been conducted to check the effectiveness of the present invention will be described. However, the present invention is not limited to these examples. 
     Example 1 
     A glass molded body was manufactured in accordance with the flowchart shown in  FIG. 3  in Embodiment 1 by the use of the manufacturing apparatus  10  of a glass molded body. 
     A ultrahard material containing tungsten carbide as main components was used as the material of both the lower mold  11  and the upper mold  12 . The outside diameter of a glass molded body to be manufactured is set to 7 mm in diameter, and the thickness of a core was set to 3.5 mm as a target value. A phosphoric acid type glass having a glass transition point Tg of 480° C. was used as the glass material. The heating temperature of the shaping mold  15  in Process S 101  was set at 500° C. in the lower mold  11  and at 450° C. in the upper mold  12 . 
     The temperature near the tip portion of the nozzle  41  was made 1000° C., and the manufacturing apparatus  10  was set such that about 190 mg of a molten glass droplet  43  dropped at intervals of about 10 seconds. In this condition, 100 drops of molten glass droplets  43  were made to drop for a period of time, and dispersion in the dropping intervals was measured during the period of time. As a result, there was a difference of 0.2 seconds between the longest interval and the shortest interval. 
     The predetermined time T 1  at which the lower mold  11  was moved to the shaping position P 2  was set to 3 seconds, the predetermined time T 2  for starting press molding was set to 12 seconds, and the predetermined time T 3  for ending the press molding was set to 27 seconds, and then 100 glass shaped-bodies were manufactured. The load for press molding was 1800 Ns. The molten glass droplets dropped from the nozzle  41  at intervals of about 10 seconds. Among the dropped molten glass droplets, one droplet per five droplets was used for the manufacture of a glass molded body. Therefore, one glass molded body was manufactured every about 50 seconds. 
     The thickness of core of each of 100 manufactured glass shaped-bodies was measured. As a result, the difference between the maximum thickness and the minimum thickness was 0.002 mm. Accordingly, it was confirmed that the thickness of core was remarkably stable. 
     Comparative Example 1 
     In Comparative example 1, the optical sensor  13  was not used. Instead, false signals generated once at 50 seconds were sent to the controller  14 , and a glass molded body was manufactured by a method of starting a timer  16  in response to the false signals. Other conditions were made to the same as Example 1. The thickness of core of each of 100 manufactured glass shaped-bodies was measured. As a result, the difference between the maximum thickness and the minimum thickness was 0.02 mm. Accordingly, it was confirmed that very large dispersion took place as compared with Example 1. 
     Example 2 
     A glass molded body was manufactured in accordance with the flowchart shown in  FIG. 6  in Embodiment 3 by the use of the manufacturing apparatus  30  of a glass molded body. 
     As the material of both the lower mold  11  and the upper mold  12 , silicon nitride was used. The outside diameter of a glass molded body to be manufactured is set to 3.8 mm in diameter, and the thickness of a core was set to 2.6 mm as a target value. A lanthanum type glass having a glass transition point Tg of 640° C. was used as the glass material. The heating temperature of the shaping mold  35  in Process  5301  was set at 580° C. in both the lower mold  31  and the upper mold  32 . 
     The temperature near the tip portion of the nozzle  41  was made 1100° C., and the manufacturing apparatus  30  was set such that about 200 mg of a molten glass droplet  43  dropped at intervals of about 10 seconds. In this condition, 100 drops of molten glass droplets  43  were made to drop for a period of time, and dispersion in the dropping intervals was measured during the period of time. As a result, there was a difference of 0.2 seconds between the longest interval and the shortest interval. In the manufacturing apparatus  30 , the diameter of the small through hole  34  was φ 2.3 mm, and the weight of the molten glass droplet  33  having passed through the small through hole  34  was about 60 mg. 
     The predetermined time T 1  at which the lower mold  31  was moved to the shaping position P 2  was set to 2 seconds, the predetermined time T 2  for starting press molding was set to 6 seconds, and the predetermined time T 3  for ending the press molding was set to 15 seconds, and then 100 glass shaped-bodies were manufactured. The load for press molding was 1800 Ns. The molten glass droplets dropped from the nozzle  41  at intervals of about 10 seconds. Among the dropped molten glass droplets, one droplet per three droplets was used for the manufacture of a glass molded body. Therefore, one glass molded body was manufactured every about 30 seconds. 
     The thickness of core of each of 100 manufactured glass shaped-bodies was measured. As a result, the difference between the maximum thickness and the minimum thickness was less than 0.001 mm. Accordingly, it was confirmed that the thickness of core was remarkably stable. 
     Comparative Example 2 
     In Comparative example 2, the optical sensor  13  was not used. Instead, false signals generated once at 30 seconds were sent to the controller  14 , and a glass molded body was manufactured by a method of starting a timer  16  in response to the false signals. Other conditions were made to the same as Example 2. The thickness of core of each of 100 manufactured glass shaped-bodies was measured. As a result, the difference between the maximum thickness and the minimum thickness was 0.04 mm. Accordingly, it was confirmed that very large dispersion took place as compared with Example 2.