Patent Publication Number: US-2003234471-A1

Title: Press apparatus

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a press apparatus.  
       [0003] 2. Description of the Related Art  
       [0004] Conventionally, molding articles from, for example, glass or resin is carried out by the steps of placing glass material or resin material in a mold of a press apparatus; softening the material through application of heat; and press-molding the softened material. In this case, a molded glass or resin article assumes the shape of a cavity of the mold, which consists of an upper mold and a lower mold. After the molded glass or resin article is obtained, the upper mold is raised so as to open the mold. The molded glass or resin article is unloaded from the lower mold by means of a transfer member having a vacuum means or the like. The thus-unloaded article is transported to the subsequent process.  
       [0005] In such a press apparatus, when positional deviation arises between the upper and lower molds, the following problems arise: a molded article fails to assume a predetermined shape, the upper and lower molds fail to engage with each other, or the upper or lower mold is broken. In order to avoid such problems, when the upper mold is moved vertically, the axis of the upper mold must not deviate or be inclined, and the upper mold must not move in the circumferential direction; i.e., rotate.  
       [0006] In order to meet the above requirements, the conventional press apparatus employs a linear guide mechanism configured such that two to four guide rods are disposed around the upper mold so as to guide a vertical movement of the upper mold (as disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. H08-206895). In this case, guide holes are formed in an upper-mold-mounting member adapted to support the upper mold. The guide rods are inserted into the corresponding guide holes, so that the inner surfaces of the guide holes slide on the corresponding outer surfaces of the guide rods. Generally, bushes are fitted into the corresponding guide holes. Thus, the linear guide mechanism is usually called a linear bush.  
       [0007] When the upper mold is moved vertically, the linear guide mechanism prevents deviation of the axis of the upper mold and rotation of the upper mold.  
       [0008] However, in the conventional press apparatus, the linear bush involves large frictional resistance and great variations in the frictional resistance. Thus, heavy load is imposed on a drive unit for vertically moving the upper mold; therefore, the drive unit must be of large output, resulting in an increase in the cost of manufacturing the press apparatus and running cost.  
       [0009] Even when the drive unit is operated in such a manner as to maintain constant output, variations in frictional resistance lead to variations in a force imposed on the upper mold. Thus, a pressing force which the upper mold applies to a glass or resin material varies; i.e., press-molding cannot be performed at a predetermined pressing force, resulting in impairment in the quality of a molded glass or resin article.  
       [0010] Furthermore, since a gap is unavoidably present between the guide rod and the bush fitted in the guide hole, the guide hole is inclined with respect to the guide rod. Accordingly, the upper mold is inclined, with a resultant failure to maintain parallelism between the mating surface of the upper mold and that of the lower mold. This failure leads to uneven surface of a molded article, variations in thickness among molded articles, or impairment in profile transfer to a molded article. As a result, molded articles fail to exhibit consistent quality. The angle of inclination of the guide hole with respect to the guide rod can be reduced through increasing the length of the sliding surface of the bush. However, in this case, frictional resistance increases.  
       SUMMARY OF THE INVENTION  
       [0011] An object of the present invention is to solve the above-mentioned problems in the conventional press apparatus and to provide a press apparatus in which a movable member is not in contact with a guide member, so as to avoid involvement of frictional resistance; to enhance positioning accuracy for the movable member; to reduce load imposed on a drive unit for moving the movable member; and to avoid involvement of positional deviation and inclination of a mold attached to the movable member, thereby enhancing quality of a molded article.  
       [0012] To achieve the above object, a press apparatus of the present invention has a movable member having a mold-mounting surface for mounting a movable mold thereon and at least four guide surfaces; and a guide member having at least four guide surfaces facing the corresponding guide surfaces of the movable member. Fluid is injected into a space formed between the guide surfaces of the movable member and the corresponding guide surfaces of the guide member such that the mutually facing guide surfaces are held in a noncontacting condition.  
       [0013] In this case, since the four guide surfaces of the movable member receive equal forces which are imposed perpendicularly to the guide surfaces, the locus of movement of the movable member does not deviate horizontally. Also, the movable member does not rotate about its axis.  
       [0014] Thus, at the time of mold closing, the movable mold is smoothly engaged with a stationary mold, since a positional relationship is accurately maintained between the mating surface of the movable mold and that of the stationary mold. Also, breakage of the mold can be avoided.  
       [0015] Furthermore, since the movable member and the guide member permit accurate positioning of the mating surfaces of the movable and stationary molds, an engagement mechanism which would otherwise be provided on the molds is not required.  
       [0016] Preferably, the guide surfaces of the movable member or the guide surfaces of the guide member are equipped with corresponding hydrostatic bearings. In this case, since the hydrostatic bearings hold, hydrostatically and in a noncontacting condition, the guide surfaces of the movable member or the guide surfaces of the guide member which face the corresponding hydrostatic bearings, no frictional resistance arises. Thus, the movable member can be moved smoothly in the vertical direction. Therefore, load imposed on the drive unit and the like can be reduced.  
       [0017] Preferably, the movable member has a hollow portion. In this case, the weight of the movable member can be reduced. Thus, the movable member can be move smoothly in the vertical direction and can be positioned accurately by means of the hydrostatic bearings.  
       [0018] Preferably, the movable member has a reinforcement member disposed within the hollow portion. In this case, the weight of the movable member can be reduced. Also, since a beam-like member extends across the hollow portion, even when the guide surfaces of the movable member receive external forces, deflection of the guide surfaces can be reduced to the greatest possible extent.  
       [0019] Preferably, the movable member has a plurality of the hollow portions.  
       [0020] Preferably, a pressure chamber of a drive unit is formed between the guide surfaces of the movable member and the corresponding guide surfaces of the guide member; the movable member has partition walls disposed within the corresponding pressure chambers; and the partition walls are moved by means of pressure of fluid to be supplied into the pressure chambers.  
       [0021] Preferably, piping for supplying fluid to the hydrostatic bearings or pressure chambers runs in the hollow portion.  
       [0022] Preferably, the reinforcement member is disposed within the hollow portion at a position corresponding to the position of the partition walls disposed within the corresponding pressure chambers. In this case, distortion of the movable member stemming from pressure of fluid for driving the partition walls and the hydrostatic bearings can be reduced to the greatest possible extent.  
       [0023] Preferably, the guide member has a pair of opposed first guide members, and a pair of opposed second guide members held between the first guide members, and the distance between the opposed first guide members and the distance between the opposed second guide members can be adjusted.  
       [0024] Preferably, the partition walls are formed on corresponding surfaces of the movable member which face the corresponding first guide members.  
       [0025] Preferably, forces imposed on the movable member from the corresponding hydrostatic bearings are directed toward the center of the movable member and cancel each other. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0026] The structure and features of the press apparatus according to the present invention will be readily appreciated as the same becomes better understood by referring to the drawings, in which:  
     [0027]FIG. 1 is a vertical sectional view showing the configuration of a press apparatus according to a first embodiment of the present invention;  
     [0028]FIG. 2 is a sectional view taken along line I-I of FIG. 1;  
     [0029]FIG. 3 is a sectional view showing the structure of the guide surface of a hydrostatic bearing unit in the first embodiment of the present invention;  
     [0030]FIG. 4 is a plan view or view taken along line II-II of FIG. 3 showing the guide surface of the hydrostatic bearing unit in the first embodiment of the present invention;  
     [0031]FIG. 5 is a transverse sectional view showing the configuration of a press apparatus according to a second embodiment of the present invention;  
     [0032]FIG. 6 is a vertical sectional view showing the configuration of a press apparatus according to a third embodiment of the present invention;  
     [0033]FIG. 7 is a sectional view taken along line III-III of FIG. 6;  
     [0034]FIG. 8 is a sectional view taken along line IV-IV of FIG. 6;  
     [0035]FIG. 9 is a sectional view taken along line IV-IV of FIG. 6, showing a fourth embodiment of the present invention;  
     [0036]FIG. 10 is a sectional view taken along line IV-IV of FIG. 6, showing a fifth embodiment of the present invention;  
     [0037]FIG. 11 is a sectional view taken along line III-III of FIG. 6, showing the fifth embodiment of the present invention;  
     [0038]FIG. 12 is a vertical sectional view showing the configuration of a press apparatus according to a sixth embodiment of the present invention;  
     [0039]FIG. 13 is a sectional view taken along line V-V of FIG. 12;  
     [0040]FIG. 14 is a sectional view taken along line VI-VI of FIG. 12;  
     [0041]FIG. 15 is a sectional view taken along line V-V of FIG. 12, showing a modification of the sixth embodiment;  
     [0042]FIG. 16 is a sectional view taken along line V-V of FIG. 12, showing another modification of the sixth embodiment;  
     [0043]FIG. 17 is a vertical sectional view showing the configuration of a press apparatus according to a seventh embodiment of the present invention; and  
     [0044]FIG. 18 is a sectional view taken along line VII-VII of FIG. 17. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
     [0045] Embodiments of the present invention will next be described in detail with reference to the drawings. Press apparatus according to the embodiments of the present invention are suited for molding articles from, for example, glass or resin by the major steps of placing glass material or resin material in a mold; softening the material through application of heat; and press-molding the softened material. In molding by use of the press apparatus, no particular limitation is imposed on material for molded articles. Specifically, the press apparatus can be used to mold articles from, for example, metal, ceramic, paper, fiber, or an appropriate mixture of these materials, in addition to glass and resin. For convenience, description of the embodiments refers to the case of molding an article from glass.  
     [0046]FIG. 1 is a vertical sectional view showing the configuration of a press apparatus according to a first embodiment of the present invention. FIG. 2 is a sectional view taken along line I-I of FIG. 1.  
     [0047] In FIG. 1, reference numeral  10  denotes a press apparatus; reference numeral  11  denotes a base frame, which serves as a portion of the frame of the press apparatus  10 ; and reference numeral  12  denotes a guide frame, which serves as a portion of the frame of the press apparatus  10 . The guide frame  12  assumes the form of a rectangular prismatic tube in a standing condition, and a lower end portion thereof is attached to the upper surface of the base frame  11 .  
     [0048] A ceiling frame  13 , which serves as a portion of the frame of the press apparatus  10 , is attached to an upper end portion of the guide frame  12 . The base frame  11  and the ceiling frame  13  assume the form of a rectangular plate so as to close opposite end openings of the guide frame  12  in the form of a rectangular prismatic tube.  
     [0049] A stationary member  21  is mounted on the upper surface of the base frame  11  and within the guide frame  12 . A lower mold  22 , which serves as a stationary mold, is mounted on the upper surface of the stationary member  21 , the upper surface serving as a mold-mounting surface. The lower mold  22  is mounted directly on the upper surface of the stationary member  21 ; however, the lower mold  22  may be mounted via an unillustrated mounting member. The upper surface of the lower mold  22  includes a flat mating surface, and the surface of a cavity formed in such a manner as to form a substantially lower half of a molded article. Reference numeral  27  denotes material for a molded article. As mentioned previously, for convenience, description of the present embodiment refers to the case of molding an article from glass. Therefore, the material  27  is glass material. Examples of molded articles include optical elements such as lenses, prisms, filters, and mirrors; storage media for use with computers such as disks; and optical-fiber-coupling members.  
     [0050] A drive unit  25  is mounted on the upper surface of the ceiling frame  13 . A connecting rod  26  of the drive unit  25  extends downward through an unillustrated through-hole formed in the ceiling frame  13 . A movable member  24  is attached to a lower end portion of the connecting rod  26 . In the present embodiment, as shown in FIG. 2, the movable member  24  assumes the form of a prism having a rectangular cross section, preferably a square cross section. The vertically extending four side wall surfaces of the movable member  24  function as guide surfaces  24   a.  Notably, the movable member  24  may assume the form of a prismatic tube instead of a prism. An upper mold  23 , which serves as a movable mold, is mounted on the lower surface of the movable member  24 , the lower surface serving as a mold-mounting surface. The upper mold  23  is mounted directly on the lower surface of the movable member  24 ; however, the upper mold  23  may be mounted via an unillustrated mounting member. The lower surface of the upper mold  23  includes a flat mating surface, and the surface of a cavity formed in such a manner as to form a substantially upper half of a molded article.  
     [0051] The drive unit  25  is, for example, a cylinder unit including a piston to be driven by compressed fluid of high pressure. In this case, a lower end portion of the piston rod attached to the piston is connected to an upper end portion of the connecting rod  26 . Through changeover of flow of compressed fluid supplied to the cylinder unit, the piston is moved upward or downward. Accordingly, the connecting rod  26  and the movable member  24  are moved upward or downward. Fluid for use as the compressed fluid is, for example, air, but may be other gas such as nitrogen gas. Also, liquid such as oil may be used.  
     [0052] The drive unit  25  may be an electric motor instead of the cylinder unit. For example, a linear motor may serve as the drive unit  25 . In this case, a lower end of a reciprocating member (a slider), which corresponding to a rotor of a rotary motor, is connected to an upper end portion of the connecting rod  26 . Through changeover of current supplied to the linear motor, the slider is moved upward or downward with respect to a stationary member, which corresponds to a stator of a rotary motor. Accordingly, the connecting rod  26  and the movable member  24  are moved upward or downward. Alternatively, the drive unit  25  may be a rotary electric motor such as a servomotor. In this case, rotation of a rotary shaft is converted to reciprocating motion by means of motion direction conversion device such as a combination mechanism of a ball screw and a nut. The reciprocating motion is transmitted to the connecting rod  26 .  
     [0053] In the mold open state as shown in FIG. 1, the upper mold  23  is positioned above the lower mold  22 . As the movable member  24  is moved downward, the upper mold  23  moves downward and approaches the lower mold  22 . Subsequently, the mating surface of the upper mold  23  comes into contact with that of the lower mold  22 ; i.e., mold closing is performed. Furthermore, the upper mold  23  is pressed against the lower mold  22 ; i.e., mold clamping is performed. When mold closing and mold clamping are performed, the upper mold  23  and the lower mold  22  are integrally combined. As a result, the material  27  is vertically pressed while being confined in an unillustrated cavity defined by the upper mold  23  and the lower mold  22 , thereby yielding a molded article assuming the shape of the cavity. When the material  27  is glass material, the material  27  is generally heated to a high temperature of about 300-500° C. and is in a softened condition.  
     [0054] The upper mold  23  and the lower mold  22  are made of, for example, a tungsten alloy, a stainless steel alloy, or cemented carbide. However, no particular limitation is imposed on material for the upper and lower molds  23  and  22 . When the material  27  is glass material, preferably, a single-layer or multilayer thin film is formed on the surface of at least the cavity in order to prevent adhesion of glass material to the surface. The thin film is formed from, for example, hydrogenated amorphous carbon, diamond, titanium nitride, tantalum nitride, platinum-iridium, or platinum-silicon. However, no particular limitation is imposed on material for the thin film.  
     [0055] Work holes  14  are formed in side walls of the guide frame  12  for loading the material  27  on the lower mold  22  and unloading a molded article. In the present embodiment, a single work hole  14  is formed in each of the four side walls of the guide frame  12 . However, no particular limitation is imposed on the form of the work hole  14 . The work hole  14  may be designed as appropriate in terms of position, shape, size, quantity, among other characteristics.  
     [0056] Upper portions of the vertically extending side walls of the guide frame  12  function as a guide member  15  for guiding the movable member  24 . The guide member  15  assumes the form of a prismatic tube having a rectangular cross section, preferably a square cross section. The inner surfaces of the side walls of the prismatic tube serve as guide surfaces  15   a.  As shown in FIG. 2, the cross-sectional shape of the movable member  24  and that of the guide member  15  are analogous to each other and are substantially square. The movable member  24  has four guide surfaces  24   a,  and adjacent guide surfaces  24   a  are perpendicular to each other. The guide member  15  has four guide surfaces  15   a,  and adjacent guide surfaces  15   a  are perpendicular to each other. The guide surfaces  24   a  of the movable member  24  face the corresponding guide surfaces  15   a  of the guide member  15  in parallel with each other.  
     [0057] The four guide surfaces  24   a  of the movable member  24  and the four guide surfaces  15   a  of the guide member  15  are smooth planes. The outside perimeter of the movable member  24  is slightly smaller than the inside perimeter of the guide member  15 . A gap between the guide surfaces  24   a  of the movable member  24  and the corresponding guide surfaces  15   a  of the guide member  15  is very narrow. However, for convenience of description, FIG. 2 depicts the gap exaggeratingly large.  
     [0058] Hydrostatic bearings  30  are mounted on the corresponding guide surfaces  15   a  of the guide member  15 . In the present embodiment, the hydrostatic bearings  30  each assume the form of a rectangular plate and are mounted on the corresponding guide surface  15   a  of the guide member  15  in an embedded condition. Guide surfaces  30   a  of the hydrostatic bearings  30  are substantially flush with the corresponding guide surfaces  15   a  of the guide member  15 .  
     [0059] The mounting position of the hydrostatic bearings  30  is determined such that the guide surfaces  24   a  face, at least partially, the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  at all times during vertical movement of the movable member  24 . In other words, even when the movable member  24  is at any position of the stroke of its vertical movement, the guide surfaces  24   a  face, at least partially, the corresponding guide surfaces  30   a  of the hydrostatic bearings  30 . Thus, the four guide surfaces  24   a  of the movable member  24  are hydrostatically held by means of the hydrostatic bearings  30  which face the same; therefore, the locus of vertical movement of the movable member  24  does not deviate horizontally. Also, the movable member  24  does not rotate about its vertically extending axis. Furthermore, since the guide surfaces  24   a  of the movable member  24  and the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  are held in parallel with each other at all times, the movable member  24  is not inclined.  
     [0060] Since the guide surfaces  24   a  of the movable member  24  are hydrostatically held by means of the hydrostatic bearings  30  which face the same, the guide surfaces  24   a  do not come into contact with the guide surfaces  15   a  of the guide member  15  and the guide surfaces  30   a  of the hydrostatic bearings  30 . That is, the guide surfaces  24   a  of the movable member  24  are hydrostatically held in a noncontacting condition. Thus, since no frictional resistance arises, the movable member  24  can be smoothly moved in the vertical direction through application of slight force. Therefore, load to be imposed on the drive unit  25  and the connecting rod  26  can be reduced.  
     [0061] Each of the hydrostatic bearings  30  may consist of a single hydrostatic bearing unit or a plurality of hydrostatic bearing units. For example, a plurality of hydrostatic bearing units in a square shape may be combined so as to make the hydrostatic bearing  30  in the form of a rectangular plate. Alternatively, the hydrostatic bearing  30  may partially include the hydrostatic bearing units; for example, the hydrostatic bearing units are disposed at merely corresponding opposite end portions of the hydrostatic bearing  30 .  
     [0062] As shown in FIG. 2, compressed fluid is supplied to the hydrostatic bearings  30  from a compressed-fluid supply source  35  via a supply line  37 , which serves as piping for supplying compressed fluid. The pressure of the compressed fluid to be supplied to the hydrostatic bearings  30  is adjusted by means of a pressure control valve  36  disposed in the supply line  37 . Fluid for use as the compressed fluid is, for example, air, preferably cleaned dry air. Since cleaned dry air used as the compressed fluid contains neither dust nor water vapor, the surface of a molded article is not contaminated. Fluid for use as the compressed fluid may be another gas, preferably inert gas such as nitrogen gas, argon gas, helium gas, or krypton gas.  
     [0063] The compressed-fluid supply source  35  is, for example, a gas cylinder, a pressure tank, a compressor, or a combination thereof. However, no particular limitation is imposed on the compressed-fluid supply source  35 . A plurality of compressed-fluid outlets are formed in the guide surface  30   a  of each of the hydrostatic bearings  30 . The compressed fluid is discharged through the outlets and forms a hydrostatic film between the guide surface  30   a  and the corresponding guide surface  24   a  of the movable member  24 , whereby the hydrostatic bearing  30  functions as a bearing.  
     [0064] Next, the configuration of a hydrostatic bearing unit of the hydrostatic bearing  30  will be described.  
     [0065]FIG. 3 is a sectional view showing the structure of the guide surface of a hydrostatic bearing unit in the first embodiment of the present invention. FIG. 4 is a plan view or view taken along line II-II of FIG. 3 showing the guide surface of the hydrostatic bearing unit in the first embodiment of the present invention.  
     [0066] In FIGS. 3 and 4, reference numeral  31  denotes a hydrostatic bearing unit. For convenience of description, the hydrostatic bearing unit  31  in the present embodiment assumes the form of a square plate. However, no particular limitation is imposed on the shape of the hydrostatic bearing unit  31 . For example, the hydrostatic bearing unit  31  may assume the form of a rectangular or circular plate.  
     [0067] A guide surface  31   a  of the hydrostatic bearing unit  31  has a recess  31   d  formed thereon. The recess  31   d  has a flat bottom surface in parallel with the guide surface  31   a.  As shown in FIG. 4, a plurality of compressed-fluid outlets  31   b;  for example, four outlets  31   b,  are formed in the bottom surface of the recess  31   d.  The recess  31   d  assumes a square shape. The bottom surface of the recess  31   d  is depressed, for example, about 2 or 3 μm from the guide surface  31   a.  A groove  32  is formed around the recess  31   d.    
     [0068] Compressed fluid supplied from the compressed-fluid supply source  35  is discharged downward in FIG. 3 from the outlets  31   b,  whereby a hydrostatic film is formed between the guide surface  31   a  of the hydrostatic bearing unit  31  and the guide surface  24   a  of the movable member  24 , and thus a gap of, for example, about 2 or 3 μm is formed between the guide surface  31   a  and the guide surface  24   a.  Thus, even when a force is exerted on the hydrostatic bearing unit  31  or the movable member  24  in such a manner as to press the hydrostatic bearing unit  31  or the movable member  24  toward the other, a gap is maintained between the guide surface  31   a  and the guide surface  24   a;  i.e., the effect of hydrostatic holding can be obtained. Therefore, the movable member  24  can freely move with respect to the hydrostatic bearing unit  31  in the lateral direction in FIG. 3 or perpendicularly to the paper on which FIG. 3 appears.  
     [0069] The above-mentioned gap can be modified through adjustment of, for example, pressure of compressed fluid. When the gap is, for example, about 0.1-100 μm, the effect of hydrostatic holding can be obtained. The structure of the guide surface  31   a  of the hydrostatic bearing unit  31  can be modified as appropriate. For example, the groove  32  can be eliminated. Furthermore, the recess  31   d  can be eliminated such that the outlets  31   b  are directly formed in the guide surface  31   a  which assumes the form of a single plane. Notably, when the recess  31   d  is formed, pressure loss of compressed fluid decreases in the recess  31   d,  so that hydrostatic holding force can be increased.  
     [0070] Next, the operation of the thus-configured press apparatus  10  will be described.  
     [0071] First, the drive unit  25  is activated beforehand so as to establish a mold open condition in which the upper mold  23  is located above the lower mold  22  with a certain distance established therebetween. By means of a transfer device, such as a manipulator, disposed at the exterior of the press apparatus  10 , or by the hands of a worker, the material  27  is transferred into the guide frame  12  through the work hole  14  and is placed on the lower mold  22  mounted on the upper surface of the stationary member  21 . In the present embodiment, the material  27  is the perform made of silica glass and is preheated to high temperature (e.g., 300-500° C.) to thereby be softened. Thus, the material  27  in a softened condition is placed in the cavity of the lower mold  22 . Subsequently, the material  27  is further heated to a predetermined temperature (e.g., 600° C.) by means of an unillustrated heating unit.  
     [0072] Subsequently, the drive unit  25  is activated so as to move the connecting rod  26  downward. The four guide surfaces  24   a  of the movable member  24  move downward along the four corresponding guide surfaces  15   a  of the guide member  15 . In this case, the guide surfaces  24   a  of the movable member  24  face, at least partially, the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  at all times. In other words, even when the movable member  24  is at any position of the stroke of its downward movement, the guide surfaces  24   a  face, at least partially, the corresponding guide surfaces  30   a  of the hydrostatic bearings  30 .  
     [0073] Since, while the movable member  24  is moving downward, compressed fluid is discharged from the outlets of the hydrostatic bearings  30  mounted on the guide member  15 , the four guide surfaces  24   a  of the movable member  24  are hydrostatically held at all times, with equal forces, by the four corresponding hydrostatic bearings  30 . The adjacent guide surfaces  24   a  are perpendicular to each other, and the guide surfaces  30   a  of the hydrostatic bearings  30  are in parallel with the corresponding guide surfaces  24   a.  Thus, the movable member  24  is subjected to equal forces which are exerted thereon from directions perpendicular to the four corresponding guides surfaces  24   a  (from horizontally opposite directions and from vertically opposite directions in FIG. 2). Therefore, the locus of downward movement of the movable member  24  does not deviate horizontally. Also, the movable member  24  does not rotate about its vertically extending axis. Furthermore, since the guide surfaces  24   a  of the movable member  24  and the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  are held in parallel with each other at all times, the movable member  24  is not inclined. That is, the vertically extending axis of the movable member  24  is not inclined with respect to the vertically extending axis of the guide frame  12 .  
     [0074] Since the guide surfaces  24   a  of the movable member  24  are hydrostatically held by means of the hydrostatic bearings  30  which face the same, the guide surfaces  24   a  do not come into contact with the guide surfaces  15   a  of the guide member  15  and the guide surfaces  30   a  of the hydrostatic bearings  30 . Thus, since no frictional resistance arises, the movable member  24  can be smoothly moved downward through application of slight force. Therefore, load to be imposed on the drive unit  25  and the connecting rod  26  can be reduced.  
     [0075] As the movable member  24  is moved downward, the upper mold  23  mounted on the lower surface of the movable member  24  moves downward and approaches the lower mold  22 . Then, the mating surface of the upper mold  23  comes into contact with that of the lower mold  22 ; i.e., mold closing is performed. At this time, the locus of downward movement of the movable member  24  does not deviate horizontally, and the movable member  24  does not rotate and is not inclined. Therefore, the locus of downward movement of the upper mold  23  does not deviate horizontally, and the upper mold  23  does not rotate and is not inclined. Thus, at the time of mold closing, the positional relationship is accurately maintained between the mating surface of the upper mold  23  and that of the lower mold  22 , thereby permitting smooth engagement of the upper mold  23  and the lower mold  22 . Also, the upper mold  23  or the lower mold  22  is free from breakage.  
     [0076] Subsequently, the upper mold  23  is pressed against the lower mold  22 ; i.e., mold clamping is performed. Thus, the upper mold  23  and the lower mold  22  are integrally combined. As a result, a glass material which serves as the material  27  is vertically pressed while being confined in a cavity defined by the upper mold  23  and the lower mold  22 , thereby yielding a molded glass article assuming the shape of the cavity. After press molding ends, cooling is performed until the temperature of the molded glass article drops to the transition point of glass or below. During this cooling, the molded glass article confined in the cavity is continuously subjected to a pressing force which is exerted from vertically opposite directions and is smaller than a molding force. When the temperature of the molded glass article drops to the transition point of glass or below, the drive unit  25  stops operating, whereby pressing the molded glass article ends.  
     [0077] In this case, since no frictional resistance arises between the guide surfaces  24   a  of the movable member  24  and the corresponding guide surfaces  15   a  of the guide member  15  and between the guide surfaces  24   a  of the movable member  24  and the corresponding guide surfaces  30   a  of the hydrostatic bearings  30 , output of the drive unit  25  is transmitted to the upper mold  23  without being influenced by frictional resistance. Thus, through control of output of the drive unit  25 , a pressing force to be applied to the material  27  from the upper mold  23  can be appropriately controlled. Therefore, a molded glass article of high quality assuming a predetermined shape can be obtained.  
     [0078] After mold clamping is performed at a predetermined pressing force for a predetermined time, the drive unit  25  is activated so as to move the connecting rod  26  and the movable member  24  upward. As a result, the upper mold  23  moves away from the lower mold  22 ; i.e., mold opening is performed. Also in this case, as in the case where the movable member  24  is moved downward, the locus of upward movement of the movable member  24  does not deviate horizontally, and the movable member  24  does not rotate and is not inclined. Therefore, the locus of upward movement of the upper mold  23  does not deviate horizontally, and the upper mold  23  does not rotate and is not inclined. Thus, at the time of mold opening, the positional relationship is accurately maintained between the mating surface of the upper mold  23  and that of the lower mold  22 , thereby permitting smooth separation of the upper mold  23  and the lower mold  22 . Also, the upper mold  23  or the lower mold  22  is free from breakage.  
     [0079] The movable member  24  is moved upward until the same reaches the top dead center. Also in this case, the locus of upward movement of the movable member  24  does not deviate horizontally, and the movable member  24  does not rotate and is not inclined. Therefore, the locus of upward movement of the upper mold  23  does not deviate horizontally, and the upper mold  23  does not rotate and is not inclined. Thus, vibration is not generated. Also, since no frictional resistance arises, the movable member  24  can be smoothly moved upward through application of slight force. Therefore, load to be imposed on the drive unit  25  and the connecting rod  26  can be reduced.  
     [0080] After mold opening is performed, by means of a transfer device or by the hands of a worker, a molded article is unloaded to the exterior of the guide frame  12  through the work hole  14 , and then the material  27  to be used to mold the next glass article is transferred into the guide frame  12  through the work hole  14  and is placed on the lower mold  22 .  
     [0081] The above-described operation is repeated, thereby yielding a number of molded glass articles.  
     [0082] The present embodiment has been described while mentioning the case of molding an article from glass. In the case of molding an article from glass or resin, the material  27  may be heated or placed in a predetermined atmosphere, for example, in an inert gas atmosphere, immediately before molding. Also, immediately after molding, a molded article may be cooled. In such a case, a heating unit, a cooling unit, an inert gas supply unit, or the like may be disposed in the periphery of the press apparatus  10 . Such arrangement enables direct heating or cooling of the material  27  or a molded article in an inert gas atmosphere, or heating or cooling of the material  27  placed on the lower mold  22 , or heating or cooling of the material  27  or a molded article confined in a cavity defined by the upper mold  23  and the lower mold  22 .  
     [0083] As described above, in the present embodiment, the four guide surfaces  24   a  of the movable member  24  are hydrostatically held, with equal forces, by the four corresponding hydrostatic bearings  30 . The adjacent guide surfaces  24   a  are perpendicular to each other, and the guide surfaces  30   a  of the hydrostatic bearings  30  are in parallel with the corresponding guide surfaces  24   a.  Thus, the movable member  24  is subjected to equal forces which are exerted thereon form directions perpendicular to the four corresponding guide surfaces  24   a.  Therefore, the locus of movement of the movable member  24  does not deviate horizontally. Also, the movable member  24  does not rotate about its vertically extending axis. Furthermore, since the guide surfaces  24   a  of the movable member  24  and the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  are held in parallel with each other at all times, the movable member  24  is not inclined.  
     [0084] Thus, at the time of mold closing, the positional relationship is accurately maintained between the mating surface of the upper mold  23  and that of the lower mold  22 , thereby permitting smooth engagement of the upper mold  23  and the lower mold  22 . Also, the upper mold  23  or the lower mold  22  is free from breakage.  
     [0085] Since the guide surfaces  24   a  of the movable member  24  are hydrostatically held by means of the hydrostatic bearings  30  which face the same, the guide surfaces  24   a  do not come into contact with the guide surfaces  15   a  of the guide member  15  and the guide surfaces  30   a  of the hydrostatic bearings  30 . Thus, since no frictional resistance arises, the movable member  24  can be smoothly moved downward through application of slight force. Therefore, load to be imposed on the drive unit  25  and the connecting rod  26  can be reduced. Also, output of the drive unit  25  is transmitted to the upper mold  23  without being influenced by frictional resistance. Thus, through control of output of the drive unit  25 , a pressing force to be applied to the material  27  from the upper mold  23  can be appropriately controlled. Therefore, a molded article of high quality assuming a predetermined shape can be obtained.  
     [0086] Next, a second embodiment of the present invention will be described. Structural features similar to those of the first embodiment are denoted by common reference numerals, and repeated description thereof is omitted. Also, repeated description of actions and effects similar to those of the first embodiment is omitted.  
     [0087]FIG. 5 is a transverse sectional view showing the configuration of a press apparatus according to a second embodiment of the present invention.  
     [0088] In the first embodiment, the hydrostatic bearings  30  are mounted on the corresponding guide surfaces  15   a  of the guide member  15 . The mounting position of the hydrostatic bearings  30  is determined such that the guide surfaces  24   a  face, at least partially, the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  at all times during vertical movement of the movable member  24 . However, in the case where the stroke of vertical movement of the movable member  24  is very long as compared with the vertical dimension of the guide surfaces  24   a,  it is difficult for the guide surfaces  24   a  to face, at least partially, the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  at all times.  
     [0089] Thus, in the present embodiment, the hydrostatic bearings  30  are mounted on the four corresponding guide surfaces  24   a  of the movable member  24  in an embedded condition. The guide surfaces  30   a  of the hydrostatic bearings  30  are substantially flush with the corresponding guide surfaces  24   a  of the movable member  24 . Notably, no hydrostatic bearings  30  are mounted on the four guide surfaces  15   a  of the guide member  15 .  
     [0090] The vertical dimension of the guide surfaces  15   a  of the guide member  15  is determined in such a manner as to be longer than that of the guide surfaces  24   a  of the movable member  24  and to cover the overall stroke of vertical movement of the movable member  24 . Thus, when the movable member  24  is moving vertically, the guide surfaces  15   a  of the guide member  15  face, at least partially, the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  at all times. In other words, even when the stroke of vertical movement of the movable member  24  is very long as compared with the vertical dimension of the guide surfaces  24   a,  the guide surfaces  15   a  of the guide member  15  face, at least partially, the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  at all times.  
     [0091] Thus, since the hydrostatic bearings  30  mounted on the corresponding guide surfaces  24   a  of the movable member  24  are hydrostatically held by means of the four corresponding guide surfaces  15   a  of the guide member  15 , the locus of vertical movement of the movable member  24  does not deviate horizontally. Also, the movable member  24  does not rotate about its vertically extending axis. Furthermore, since the guide surfaces  15   a  of the guide member  15  and the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  are held in parallel with each other at all times, the movable member  24  is not inclined.  
     [0092] Since the hydrostatic bearings  30  mounted on the corresponding guide surfaces  24   a  of the movable member  24  are hydrostatically held by means of the four guide surfaces  15   a  of the guide member  15  which face the same, the four guide surfaces  24   a  of the movable member  24  do not come into contact with the guide surfaces  15   a  of the guide member  15 . Thus, no frictional resistance arises.  
     [0093] Next, a third embodiment of the present invention will be described. Structural features similar to those of the first and second embodiments are denoted by common reference numerals, and repeated description thereof is omitted. Also, repeated description of actions and effects similar to those of the first and second embodiments is omitted.  
     [0094]FIG. 6 is a vertical sectional view showing the configuration of a press apparatus according to a third embodiment of the present invention; FIG. 7 is a sectional view taken along line III-III of FIG. 6; and FIG. 8 is a sectional view taken along line IV-IV of FIG. 6.  
     [0095] A drive unit  40  of the press apparatus  10  of the present embodiment is constituted by portions of side walls of a movable member  41  and portions of side walls of the guide frame  12 . The upper mold  23 , which serves as a movable mold, is mounted on the movable member  41 . As shown in FIG. 7, the movable member  41  assumes the form of a prism having a rectangular cross section, preferably a square cross section. The vertically extending four side wall surfaces of the movable member  41  function as guide surfaces  41   a.  The movable member  41  is made of, for example, ceramic or a stainless steel alloy. However, no particular limitation is imposed on material for the movable member  41 . The upper mold  23  is mounted directly on the lower surface of the movable member  41 ; however, the upper mold  23  may be mounted via an unillustrated mounting member.  
     [0096] Upper portions of the vertically extending side walls of the guide frame  12  function as a guide member  15  for guiding the movable member  41 . The guide member  15  assumes the form of a prismatic tube having a rectangular cross section, preferably a square cross section. The inner surfaces of the side walls of the prismatic tube serve as guide surfaces  15   a.  As shown in FIG. 7, the cross-sectional shape of the movable member  41  and that of the guide member  15  are analogous to each other and are substantially square. The guide surfaces  41   a  of the movable member  41  face the corresponding guide surfaces  15   a  of the guide member  15  in parallel with each other. The four guide surfaces  41   a  of the movable member  41  and the four guide surfaces  15   a  of the guide member  15  are smooth planes. The outside perimeter of the movable member  41  is slightly smaller than the inside perimeter of the guide member  15 . A gap between the guide surfaces  41   a  of the movable member  41  and the corresponding guide surfaces  15   a  of the guide member  15  is very narrow. However, for convenience of description, FIGS. 6 and 7 depict the gap exaggeratingly large.  
     [0097] Hydrostatic bearings  30  are mounted on the corresponding guide surfaces  15   a  of upper and lower portions of the guide member  15 . Since the guide surfaces  41   a  of upper and lower portions of the movable member  41  are hydrostatically held by means of the hydrostatic bearings  30  which face the same, the guide surfaces  41   a  do not come into contact with the guide surfaces  15   a  of the guide member  15  and the guide surfaces  30   a  of the hydrostatic bearings  30 . That is, the guide surfaces  41   a  of the movable member  41  are hydrostatically held in a noncontacting condition. Thus, since no frictional resistance arises, the movable member  41  can be smoothly moved in the vertical direction through application of slight force.  
     [0098] The mounting position of the hydrostatic bearings  30  is determined such that the guide surfaces  41   a  of upper and lower portions of the movable member  41  face, at least partially, the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  at all times during vertical movement of the movable member  41 . In other words, even when the movable member  41  is at any position of the stroke of its vertical movement, the guide surfaces  41   a  of upper and lower portions of the movable member  41  face, at least partially, the corresponding guide surfaces  30   a  of the hydrostatic bearings  30 . Thus, the four guide surfaces  41   a  of upper and lower portions of the movable member  41  are hydrostatically held by means of the hydrostatic bearings  30  which face the same; therefore, the locus of vertical movement of the movable member  41  does not deviate horizontally. Also, the movable member  41  does not rotate about its vertically extending axis. Furthermore, since the guide surfaces  41   a  of upper and lower portions of the movable member  41 —the upper and lower portions being located axially away from each other—are hydrostatically held in corresponding directions perpendicular to the axial direction, inclination of the axis can be more effectively prevented.  
     [0099] In the present embodiment, the drive unit  40  is disposed between the upper hydrostatic bearings  30  and the lower hydrostatic bearings  30 . Specifically, portions of the guide member  15  located between the upper hydrostatic bearings  30  and the lower hydrostatic bearings  30  are removed so as to form pressure chambers  44 . In the present embodiment, as shown in FIGS. 6 and 8, through-holes are formed in the corresponding side walls of the guide frame  12 , which serves as the guide member  15 . The through-holes are closed with corresponding plate-like cover members  43 , thereby forming the corresponding pressure chambers  44 . The through-holes are closed from the inside with the corresponding guide surfaces  41   a  of the movable member  41 . Notably, in the case where the side walls of the guide frame  12  are made of thick plates, respectively, recesses instead of the through-holes may be formed on the corresponding inner surfaces of the side walls so as to form the pressure chambers  44 . In this case, the cover members  43  are not required, and the recesses are closed from the inside with the corresponding guide surfaces  41   a  of the movable member  41 .  
     [0100] Plate-like partition walls  42  which project outward are formed on the corresponding guide surfaces  41   a  of the movable member  41 . The partition walls  42  may be attached to the movable member  41 ; however, the present embodiment is described while mentioning the partition walls  42  formed integrally with the movable member  41 . The four pressure chambers  44  each assume the form of a prismatic tube having a rectangular cross section. As shown in FIG. 8, the outline of each of the four partition walls  42  and the cross-sectional shape of each of the four pressure chambers  44  are analogous to each other and are rectangular. The inner surface of each of the pressure chambers  44  and the perimetric surface of each of the partition walls  42  are smooth planes. The outside perimeter of each of the partition walls  42  is slightly smaller than the inside perimeter of each of the pressure chambers  44 . A gap between the perimetric surfaces of the partition walls  42  and the corresponding inner surfaces of the pressure chambers  44  is very narrow. However, for convenience of description, FIGS. 6 and 8 depict the gap exaggeratingly large.  
     [0101] Compressed-fluid lines  45   a  and  45   b  are attached to the cover members  43  such that the compressed-fluid line  45   a  communicates with an upper pressure chamber  44   a  located above the partition wall  42  in each of the pressure chambers  44  and such that the compressed-fluid line  45   b  communicates with a lower pressure chamber  44   b  located below the partition wall  42  in each of the pressure chambers  44 . An unillustrated compressed-fluid supply source supplies compressed fluid to the upper pressure chambers  44   a  and the lower pressure chambers  44   b  via the compressed-fluid lines  45   a  and  45   b,  which serve as piping for supplying compressed fluid. Also, the thus-supplied compressed fluid is discharged from the upper and lower pressure chambers  44   a  and  44   b.    
     [0102] Fluid for use as the compressed fluid to be supplied to the upper and lower pressure chambers  44   a  and  44   b  is, for example, air, preferably cleaned dry air. Since cleaned dry air used as the compressed fluid contains neither dust nor water vapor, the surface of a molded article is not contaminated. Fluid for use as the compressed fluid may be another gas, preferably inert gas such as nitrogen gas, argon gas, helium gas, or krypton gas. Preferably, the compressed fluid is identical to compressed fluid to be supplied to the hydrostatic bearings  30 . In this case, the compressed-fluid supply source for the pressure chambers  44  can be the same as the compressed-fluid supply source  35  for the hydrostatic bearings  30 .  
     [0103] The pressure chamber  44  corresponds to the pressure chamber of an ordinary cylinder unit; the partition wall  42  corresponds to the piston of the ordinary cylinder unit; and the movable member  41  corresponds to the piston rod of the ordinary cylinder unit. In this case, through supply of compressed fluid to the upper pressure chambers  44   a  or the lower pressure chambers  44   b,  the partition walls  42  and the movable member  41  can be moved upward or downward. Thus, the upper mold  23  mounted on the lower surface of the movable member  41  can be moved upward and downward.  
     [0104] As in the case of the first embodiment, a gap between the guide surfaces  31   a  of the hydrostatic bearing units  31  and the corresponding guide surfaces  41   a  of the movable member  41  is, for example, about 2 or 3 μm. The gap can be modified through adjustment of, for example, pressure of compressed fluid to be supplied to the hydrostatic bearing units  31 . When the gap is, for example, about 0.1-100 μm, the effect of hydrostatic holding can be obtained. Also, a gap between the guide surfaces  15   a  of the guide member  15  and the corresponding guide surfaces  41   a  of the movable member  41  is similar to that between the guide surfaces  31   a  of the hydrostatic bearing units  31  and the corresponding guide surfaces  41   a  of the movable member  41 ; and a gap between the inner surfaces of the pressure chambers  44  and the corresponding perimetric surfaces of the partition walls  42  is similar to that between the guide surfaces  31   a  of the hydrostatic bearing units  31  and the corresponding guide surfaces  41   a  of the movable member  41 . Therefore, compressed fluid supplied to the upper pressure chambers  44   a  and the lower pressure chambers  44   b  hardly leaks out. When compressed fluid to be supplied to the pressure chambers  44  is identical to that to be supplied to the hydrostatic bearings  30 , leakage of compressed fluid, if any, from the pressure chambers  44  or the hydrostatic bearings  30  raises no mutual influence on the pressure chambers  44  and the hydrostatic bearings  30 .  
     [0105] As mentioned above, in the present embodiment, the drive unit  40  includes the partition walls  42  of the movable member  41  and the pressure chambers  44  formed in the corresponding side walls of the guide member  15 . Through supply of compressed fluid to the upper pressure chambers  44   a  or lower pressure chambers  44   b  of the pressure chambers  44 , the partition walls  42  and the movable member  41  can be moved upward or downward. Thus, through use of the drive unit  40  of simple structure, the upper mold  23  mounted on the lower surface of the movable member  41  can be moved upward and downward. Also, the overall configuration of the press apparatus  10  can be simplified and reduced in size.  
     [0106] The hydrostatic bearings  30  are mounted on corresponding portions of the guide member  15  which are located above and below the pressure chambers  44 ; i.e., on the corresponding guide surfaces  15   a  of upper and lower portions of the guide member  15 . The guide surfaces  41   a  of upper and lower portions of the movable member  41  are hydrostatically held by means of the hydrostatic bearings  30  which face the same. Thus, the guide surfaces  41   a  of the upper and lower portions of the movable member  41 —the upper and lower portions being located axially away from each other—are hydrostatically held in corresponding directions perpendicular to the axial direction, whereby inclination of the axis can be more effectively prevented.  
     [0107] Next, a fourth embodiment of the present invention will be described. Structural features similar to those of the first to third embodiments are denoted by common reference numerals, and repeated description thereof is omitted. Also, repeated description of actions and effects similar to those of the first to third embodiments is omitted.  
     [0108]FIG. 9 is a sectional view taken along line IV-IV of FIG. 6, showing the fourth embodiment of the present invention.  
     [0109] In the present embodiment, as shown in FIG. 9, a single cover member  43  assuming a cylindrical shape is provided, and a single partition wall  42  assuming the form of a disk-like flange surrounding the movable member  41  is provided. The pressure chamber  44  assumes a form resembling a single cylinder. The outline of the partition wall  42  and the cross-sectional shape of the pressure chamber  44  are analogous to each other and are circular. The diameter of the circle is greater than the length of the diagonal of the movable member  41 .  
     [0110] Thus, the drive unit  40  composed of the movable member  41 , the partition wall  42 , and the cover member  43  corresponds to a single cylinder unit. The movable member  41  corresponds to a piston rod disposed at the center of the cylinder unit. In this case, since the partition wall  42  and the pressure chamber  44  are provided singly, the structure is simplified; manufacturing is facilitated; and the number of compressed-fluid lines  45   a  and  45   b  can be reduced. Other features are similar to those of the third embodiment, and thus repeated description thereof is omitted.  
     [0111] Next, a fifth embodiment of the present invention will be described. Structural features similar to those of the first to fourth embodiments are denoted by common reference numerals, and repeated description thereof is omitted. Also, repeated description of actions and effects similar to those of the first to fourth embodiments is omitted.  
     [0112]FIG. 10 is a sectional view taken along line IV-IV of FIG. 6, showing the fifth embodiment of the present invention. FIG. 11 is a sectional view taken along line III-III of FIG. 6, showing the fifth embodiment of the present invention.  
     [0113] In the present embodiment, as shown in FIG. 10, a pressure chamber  44  is only formed at each of a pair of opposed portions of the guide member  15 . That is, two pressure chambers  44  are formed in opposition to each other. Similarly, a partition wall  42  is formed at each of a pair of opposed guide surfaces  41   a  of the movable member  41 . In this case, since the number of partition walls  42  and pressure chambers  44  is fewer than that of the third embodiment, the structure is simplified; manufacturing is facilitated; and the number of compressed-fluid lines  45   a  and  45   b  can be reduced.  
     [0114] Preferably, as shown in FIG. 10, the guide member  15  includes wide guide members  15 - 1 , in which the corresponding pressure chambers  44  are formed, and narrow guide members  15 - 2 , in which no pressure chamber  44  is formed. In this case, the width of the narrow guide members  15 - 2  (a horizontal length in FIG. 10) is substantially equal to the distance between the paired, opposed guide surfaces  41   a  on which the corresponding partition walls  42  are formed. The width of the wide guide members  15 - 1  (a vertical length in FIG. 10) is substantially equal to the distance between the paired, opposed guide surfaces  41   a  on which no partition wall  42  is formed, plus the total thickness of the paired narrow guide members  15 - 2 . The narrow guide members  15 - 2  are held at their opposite end surfaces between the mutually facing surfaces of the paired wide guide members  15 - 1 ; i.e., between the guide surfaces  15   a.  As shown in FIG. 11, the wide guide members  15 - 1  and the narrow guide members  15 - 2  are joined together by means of joining members  47  such as bolts. In this case, the joining members  47  cause the guide surfaces  15   a  of the wide guide members  15 - 1  to be pressed against the end surfaces of the narrow guide members  15 - 2 .  
     [0115] In the present embodiment, when the drive unit  40  is activated in order to move the movable member  41  vertically, compressed fluid is introduced into the pressure chambers  44 ; as a result, pressure within the pressure chambers  44  increases. Thus, the wide guide members  15 - 1  are subjected to respective forces which are exerted thereon in such directions as to potentially move them away from each other. In this case, since, as shown in FIG. 11, the joining members  47  cause the guide surfaces  15   a  of the wide guide members  15 - 1  to be pressed against the end surfaces of the narrow guide members  15 - 2 , the distance between the wide guide members  15 - 1  does not increase. Thus, the distance between the guide surfaces  30   a  of the hydrostatic bearings  30  mounted on the corresponding surfaces  15   a  of the paired wide guide members  15 - 1  remains unchanged. Therefore, even when the drive unit  40  is activated, a gap between the guide surfaces  30   a  of the hydrostatic bearings  30  and the corresponding guide surfaces  41   a  of the movable member  41  remains unchanged. Thus, performance of the hydrostatic bearings  30  is not affected.  
     [0116] Notably, if the pressure chambers  44  are formed in the corresponding narrow guide members  15 - 2 , increase in pressure within the pressure chambers  44  causes the narrow guide members  15 - 2  to be subjected to respective forces which are exerted thereon in such directions as to potentially move them away from each other. In this case, as shown in FIG. 11, the joining members  47  are subjected to respective forces which are exerted thereon in shear directions; i.e., in directions perpendicular to their axes. As a result, the joining member  47  may be deformed, potentially increasing the distance between the narrow guide members  15 - 2 . If the distance increases, the distance between the guide surfaces  30   a  of the hydrostatic bearings  30  mounted on the corresponding guide surfaces  15   a  of the paired narrow guide members  15 - 2  will change. Accordingly, a gap between the guide surfaces  30   a  of the hydrostatic bearings  30  and the corresponding guide surfaces  41   a  of the movable member  41  will change; as a result, performance of the hydrostatic bearings  30  will be affected.  
     [0117] Thus, the narrow guide members  15 - 2  are held at their opposite end surfaces between the guide surfaces  15   a  of the paired wide guide members  15 - 1 , and the narrow guide members  15 - 2  and the wide guide members  15 - 1  are joined together by means of joining members  47  such that the guide surfaces  15   a  of the wide guide members  15 - 1  are pressed against the corresponding end surfaces of the narrow guide members  15 - 2 , whereby performance of the hydrostatic bearings  30  can be stabilized. Other features are similar to those of the third embodiment, and thus repeated description thereof is omitted.  
     [0118] Notably, the structure shown in FIG. 11 is also applicable to the first to third embodiments. In the first to third embodiments, all of the four wall surfaces are provided with the respective hydrostatic bearings  30 . That is, the wall surfaces of the wide guide members  15 - 1  and the wall surfaces of the narrow guide members  15 - 2  are provided with the respective pressure chambers  44 .  
     [0119] In this case, preferably, joining-member insertion holes  47   a  formed in the wide guide members  15 - 1  have a relatively large size so as to allow movement of the corresponding joining members  47  in the width direction of the wide guide members  15 - 1  (in the vertical direction in FIG. 11); and distance-between-narrow-guide-members adjustment members  48  with which corresponding adjustment bolts  48   a  are screw-engaged are attached to the wide guide members  15 - 1 . In adjustment, the joining members  47  are loosened, and the adjustment bolts  48   a  are rotated so as to adjust the distance between the guide surfaces  15   a  of the opposed narrow guide members  15 - 2 , thereby appropriately adjusting a gap between the guide surfaces  41   a  of the movable member  41  and the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  mounted on the corresponding guide surfaces  15   a.    
     [0120] When the distance between the guide surfaces  15   a  of the opposed wide guide members  15 - 1  is to be adjusted, a shim(s) is interposed between the end surface of each of the narrow guide members  15 - 2  and the guide surface  15   a  of each of the wide guide members  15 - 1  while the thickness and the number of shims are adjusted. In this manner, a gap between the guide surfaces  41   a  of the movable member  41  and the corresponding guide surfaces  30   a  of the hydrostatic bearings  30  mounted on the corresponding guide surfaces  15   a  of the wide guide members  15 - 1  can be appropriately adjusted.  
     [0121] Next, a sixth embodiment of the present invention will be described. Structural features similar to those of the first to fifth embodiments are denoted by common reference numerals, and repeated description thereof is omitted. Also, repeated description of actions and effects similar to those of the first to fifth embodiments is omitted.  
     [0122]FIG. 12 is a vertical sectional view showing the configuration of a press apparatus according to the sixth embodiment of the present invention; FIG. 13 is a sectional view taken along line V-V of FIG. 12; FIG. 14 is a sectional view taken along line VI-VI of FIG. 12; FIG. 15 is a sectional view taken along line V-V of FIG. 12, showing a modification of the sixth embodiment; and FIG. 16 is a sectional view taken along line V-V of FIG. 12, showing another modification of the sixth embodiment.  
     [0123] In the present embodiment, as shown in FIGS.  12 - 14 , a hollow portion  53  is formed in the movable member  41 . In this case, the hollow portion  53  is an elongated hole having a rectangular cross section and extending axially in the movable member  41 . The upper end of the hollow portion  53  opens at the upper end surface of the movable member  41 , whereas the lower end of the hollow portion  53  is closed in the movable member  41 . Notably, the upper end of the hollow portion  53  may be closed in the movable member  41 . The axis of the hollow portion  53  substantially coincide with that of the movable member  41 . The cross-sectional shape of the hollow portion  53  is analogous to that of the movable member  41 . The length (a vertical dimension in FIG. 12) and cross-sectional area of the hollow portion  53  can be determined as appropriate.  
     [0124] The cross-sectional shape of the hollow portion  53  is not necessarily analogous to that of the movable member  41  and may be modified as appropriate. For example, as shown in FIG. 15, the cross-sectional shape of the hollow portion  53  may be circular. Furthermore, the cross-sectional shape of the hollow portion  53  may be elliptical, polygonal such as pentagonal or hexagonal, star-shaped, or indeterminate.  
     [0125] Instead of a single hollow portion  53 , a plurality of hollow portions  53  may be provided. For example, as shown in FIG. 16, a number of hollow portions  53  each having a circular cross section of small diameter may be formed. Furthermore, the hollow portions  53  may each assume a hexagonal cross section and be arranged such that the distance between the adjacent hollow portions  53  is short, whereby the movable member  41  assumes a so-called honeycomb cross section.  
     [0126] In view of strength of the movable member  41 , the cross-sectional shape of the hollow portion  53  is preferably closed as shown in FIGS.  12 - 16 . However, the cross-sectional shape may be partially opened as needed. For example, in FIGS. 13 and 14, a slit may be formed in such a manner as to extend through the movable member  41  between a corner part of the hollow portion  53  and a corner portion of the movable member  41 .  
     [0127] In the present embodiment, since the movable member  41  has the hollow portion  53 , the weight of the movable member  41  can be reduced accordingly. As a result, the movable member  41  can be smoothly moved in the vertical direction.  
     [0128] Since the movable member  41  is of light weight, the movable member  41  is accurately positioned by means of the hydrostatic bearings  30 . Specifically, the four guide surfaces  41   a  of the movable member  41  are subjected to corresponding equal forces which the four hydrostatic bearings  30  exert respectively, whereby a gap between the guide surfaces  41   a  of the movable member  41  and the corresponding guide surfaces  31   a  of the hydrostatic bearings  30  becomes constant, thereby positioning the movable member  41 . When the position of the movable member  41  deviates to thereby cause a change in the gap between the guide surfaces  41   a  and the corresponding guide surfaces  31   a,  the forces which the hydrostatic bearings  30  exert on the guide surfaces  41   a  restore the movable member  41  to its proper position. Therefore, when the movable member  41  is of light weight, the movable member  41  can be restored promptly to its proper position upon subjection to forces exerted by the hydrostatic bearings  30  and is thus positioned accurately.  
     [0129] Furthermore, the hollow portion  53  permits installation of electric wiring and fluid piping therein. For example, in place of the compressed-fluid lines  45   a  and  45   b,  compressed-fluid lines  45   a′  and  45   b′  as represented by the dotted line in FIG. 12 can be attached to the movable member  41  through the hollow portion  53  in such a manner as to communicate with the upper and lower pressure chambers  44   a  and  44   b  via the guide surfaces  41   a.  In the case where the hydrostatic bearings  30  are disposed on the corresponding guide surfaces  41   a  of the movable member  41 , the supply lines  37  for supplying compressed fluid to the hydrostatic bearings  30  can run through the hollow portion  53 . In this case, since there is no need either to attach the compressed-fluid lines  45   a  and  45   b  to the cover member  43  or to attach the supply lines  37  to the guide member  15 , the periphery of the press apparatus  10  can be tidied; the press apparatus  10  can be installed in a small place; and operability of the press apparatus  10  is enhanced. As shown in FIG. 16, when a plurality of hollow portions  53  are provided, not only is the weight of the movable member  41  reduced, but also the following advantage is yielded: since each portion between the hollow portions  53  functions as a member like a beam, even when an external force is imposed on the guide surface  41   a,  deflection of the guide surface  41   a  can be reduced to the greatest possible extent. Other features are similar to those of the third embodiment, and thus repeated description thereof is omitted.  
     [0130] Next, a seventh embodiment of the present invention will be described. Structural features similar to those of the first to sixth embodiments are denoted by common reference numerals, and repeated description thereof is omitted. Also, repeated description of actions and effects similar to those of the first to sixth embodiments is omitted.  
     [0131]FIG. 17 is a vertical sectional view showing the configuration of a press apparatus according to the seventh embodiment of the present invention, and FIG. 18 is a sectional view taken along line VII-VII of FIG. 17.  
     [0132] In the present embodiment, as shown in FIGS. 17 and 18, reinforcement members  56  are disposed within the hollow portion  53 . In this case, the hollow portion  53  is an elongated hole having a rectangular cross section and extending axially in the movable member  41 . As shown in FIG. 18, each of the reinforcement members  56  is a cruciform member extending between each pair of opposed surfaces of the hollow portion  53 . As shown in FIG. 17, the reinforcement members  56  are disposed at a plurality of corresponding positions located along the axial direction of the hollow portion  53 . When the reinforcement members  56  are located at a position corresponding to the partition walls  42  and at positions corresponding to the hydrostatic bearings  30 , distortion of the movable member  41  arising from the pressure of fluid used to drive the partition walls  42  and the hydrostatic bearings  30  can be reduced to the greatest possible extent.  
     [0133] In the present embodiment, the reinforcement members  56  are formed integrally with the movable member  41 . However, the reinforcement members  56  may be formed separately from the movable member  41  and attached to the movable member  41 . Also, the reinforcement member  56  may assume any shape. For example, the reinforcement member  56  may extend continuously along the axial direction of the hollow portion  53 .  
     [0134] As described above, since the present embodiment has the reinforcement members  56  disposed in the hollow portion  53 , the strength of the movable member  41  can be enhanced, thereby preventing deformation of the guide surfaces  41   a.  Other features are similar to those of the sixth embodiment, and thus repeated description thereof is omitted.  
     [0135] The first to seventh embodiments are described while mentioning a vertical press apparatus in which a mold moves in the longitudinal direction (vertical direction). However, the present invention is also applicable to a horizontal press apparatus in which a mold moves in the lateral direction (horizontal direction). Also, the present invention is applicable to not only a press apparatus in which only one of two mold halves moves, but also a press apparatus in which both of the two mold halves move. In this case, a member corresponding to the stationary member used in a press apparatus in which only one of two mold halves moves is made movable through employment of a structure similar to that of the movable member.  
     [0136] The first to seventh embodiments are described while mentioning the guide member and the movable member each having a rectangular cross section. However, no particular limitation is imposed on the cross-sectional shape of the guide member and that of the movable member so long as a plurality of guide surfaces are provided. For example, the cross-sectional shape may consist of a single straight line and a single arc, or two parallel straight lines and two arcs, or may be a polygon having five or more line segments. In this case, the arrangement, size, and the like of the hydrostatic bearings are adjusted such that forces imposed on the guide surfaces of the movable member from the hydrostatic bearings which face the guide surfaces are directed toward the center of the movable member and cancel each other, whereby the resultant of the forces becomes zero. Through employment of this adjustment, even when the guide member and the movable member assume any cross-sectional shape, a gap between the guide surfaces of the movable member and the corresponding guide surfaces of the hydrostatic bearings becomes constant, thereby positioning the movable member.  
     [0137] The above embodiments are described while mentioning the hydrostatic bearings provided on the guide member or the movable member. However, the present invention may provide the function of the hydrostatic bearings without use of the hydrostatic bearings in the following manner: outlet ports for introducing compressed fluid are directly provided in the guide member or the movable member.  
     [0138] The above embodiments are described while mentioning dry air, nitrogen gas, or the like for use as compressed fluid. However, liquid may be used as compressed fluid according to articles to be molded. For example, liquid such as pure water may be used.  
     [0139] The present invention is not limited to the above-described embodiments. Numerous modifications and variations of the present invention are possible in light of the spirit of the present invention, and they are not excluded from the scope of the present invention.  
     [0140] The disclosure of Japanese Patent Application No. 2002-179809 filed Jun. 20, 2002 and No. 2003-87998 filed Mar. 27, 2003 including specification, drawings and claims are incorporated herein by reference in its entirety.