Abstract:
A lubrication apparatus that lubricates mechanism of a molding machine. The lubrication apparatus includes a tank for collecting lubrication oil therein, and a lubrication oil supply route for supplying lubrication oil from the tank.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an apparatus and method for lubricating a feed mechanism of a forming machine. Description of the  
         [0003]     2. Related Art  
         [0004]     Conventionally, in a forming machine, such as an injection molding machine, resin heated and melted in a heating cylinder is injected into a cavity of a mold apparatus under high pressure so that the cavity is filled with the molten resin. The molten resin is then cooled and solidified within the cavity so as to produce a molded article.  
         [0005]     The mold apparatus consists of a stationary mold and a movable mold. A mold clamping apparatus for advancing and retracting the movable mold is provided so as to bring the movable mold into contact with the stationary mold and separate the same from the stationary mold, to thereby effect mold closing, mold clamping, and mold opening.  
         [0006]     The mold clamping apparatus has a toggle mechanism for advancing and retracting the movable mold. The toggle mechanism is operated through drive of a drive source, such as an electric motor or a servomotor, disposed at a drive section.  
         [0007]      FIG. 1  is a sectional view of a drive section of a conventional mold clamping apparatus.  
         [0008]     In  FIG. 1 , reference numeral  51  denotes a servomotor serving as a drive source. The servomotor  51  is attached to an unillustrated stationary member, such as a toggle support, and has a rotary shaft  52 . The front end (right-hand end in  FIG. 1 ) of the rotary shaft  52  is coupled to the rear end (left-hand end in  FIG. 1 ) of a ball-screw shaft  56  via a coupling  53 . A key groove is formed on each of the outer circumferential surface of the rotary shaft  52 , the outer circumferential surface of the ball-screw shaft  56 , and the inner circumferential surface of the coupling  53 ; and keys  54  are fitted into the key grooves. Thus, rotation of the rotary shaft  52  is transmitted to the ball-screw shaft  56  via the coupling  53 .  
         [0009]     The ball-screw shaft  56  is rotatably supported by bearings  57  accommodated within a bearing housing  58 , which is attached to the unillustrated stationary member, such as a toggle support. The outer rings of the bearings  57  are retained by means of a plate  59  attached to the bearing housing  58 . The ball-screw shaft  56  is fixedly attached to the inner rings of the bearings  57  by means of a nut  60 , so that the ball-screw shaft  56  cannot move along the axial direction.  
         [0010]     A screw groove is formed on the outer circumference of the ball-screw shaft  56  over substantially the entire length thereof, and the ball-screw shaft  56  is in screw-engagement with a ball-screw nut  61 . The ball-screw shaft  56  and the ball-screw nut  61  constitute a ball-screw-type feed mechanism. The ball-screw nut  61  is attached to a cross head  62  of a toggle mechanism, which is slidable along guide bars  63 .  
         [0011]     Therefore, when the servomotor  51  is operated, rotation of the rotary shaft  52  is transmitted to the ball-screw shaft  56 , and the ball-screw nut  61  in screw-engagement with the ball-screw shaft  56  moves along the axis of the ball-screw shaft  56 . As a result, the cross head  62  is moved leftward and rightward in  FIG. 1 . When the cross head  62  is advanced (moved rightward in  FIG. 1 ), the toggle mechanism extends so as to advance an unillustrated movable platen, to thereby perform mold closing and mold clamping. When the cross head  62  is retracted (moved leftward in  FIG. 1 ), the toggle mechanism contracts so as to retract the movable platen, to thereby perform mold opening.  
         [0012]     Since large torque is required to effect mold closing, mold clamping, and mold opening, heavy load acts on a ball screw that is constituted by the ball-screw shaft  56  and the ball-screw nut  61 . In view of this, grease serving as a lubricant is supplied to the ball screw in order to enable smooth movement of the ball screw serving as a feed mechanism and prevent wear of the ball screw to thereby prolong the service life of the ball screw.  
         [0013]     However, in the conventional ball screw serving as a feed mechanism, since grease is used for lubrication, maintaining a uniform film of lubricant at the contact surfaces between the balls and the screw is difficult. Consequently, lubrication conditions at respective portions of the ball screw become uneven. In particular, when the stroke of movement of the ball-screw shaft relative to the ball-screw nut is short, the grease is pushed out from the contact surfaces between the balls and the screw, and therefore, maintaining the lubricant film is difficult. As a result, there arises a variation in service life among the respective portions of the ball screw, thereby shortening the overall service life of the ball screw.  
         [0014]     When the supply rate of grease is set greater than a required rate in order to guarantee that grease is distributed sufficiently to respective portions of the ball screw, consumption of grease increases. In general, grease is expensive, and therefore, the increased consumption of grease renders maintenance cost of the forming machine extremely high. Further, when the supply rate of grease is increased, excessive grease overflows, scatters, and contaminates the forming machine and an area surrounding the forming machine.  
         [0015]     Further, when the ball screw is used for a long period of time, iron particles generated due to wear contaminate grease. If lubrication is performed by use of grease containing iron particles, contact surfaces are abraded by the iron particles. Therefore, grease containing iron particles must be discharged as soon as possible. However, when the supply rate of grease is increased in order to discharge grease containing iron particles as soon as possible, grease is discharged from the ball screw at a high rate, resulting in increased maintenance cost and contamination of the forming machine and an area surrounding the forming machine, as described above.  
         [0016]     Moreover, since grasping the progress of wear of the ball screw is difficult, the service life of the ball screw cannot be predicted accurately. Therefore, in some cases the ball screw is used even after its service life has been reached. As a result, the feed mechanism of the forming machine operates erratically, whereby the accuracy of formed products decreases, and other components of the forming machine are affected adversely. Meanwhile, when the ball-screw shaft and the ball-screw nut are replaced prematurely in order to avoid use of the ball screw beyond its service life, the maintenance cost of the forming machine increases.  
         [0017]     In view of the foregoing, there has been proposed a method for measuring the amount of iron contained in grease adhering to the ball-screw shaft and the ball-screw nut and predicting the service life of the ball screw. However, this method requires stopping a forming machine so as to collect grease adhering to the ball-screw shaft and the ball-screw nut. When the frequency of operation of collecting grease is increased in order to improve prediction accuracy, the total stoppage time of the forming machine increases, and the productivity of the forming machine decreases. Meanwhile, the frequency of operation of collecting grease is decreased in order to shorten the total stoppage time of the forming machine, prediction accuracy deteriorates.  
       SUMMARY OF THE INVENTION  
       [0018]     An object of the present invention is to solve the above-mentioned problems in conventional techniques and to provide an apparatus and method for lubricating a feed mechanism of a forming machine which can maintain uniform film of lubrication oil on contact surfaces of respective portions of the feed mechanism to thereby prolong service lives of the respective portions of the feed mechanism, reduce maintenance cost, prevent contamination of the forming machine and an area surrounding the forming machine, and prevent wear of the contact surfaces.  
         [0019]     Another object of the present invention is to provide an apparatus and method for lubricating a feed mechanism of a forming machine which can detect the amount of iron contained in lubrication oil and control the forming machine properly on the basis of the detected amount of iron.  
         [0020]     In order to achieve the above objects, the present invention provides an apparatus for lubricating a feed mechanism of a forming machine, comprising a conversion mechanism for converting rotational motion to rectilinear motion or converting rectilinear motion to rotational motion; and a lubrication oil circulation pipe for supplying lubrication oil to the conversion mechanism and collecting the supplied lubrication oil.  
         [0021]     This simple configuration enables maintenance of a uniform film of lubrication oil on contact surfaces of respective portions of the feed mechanism, to thereby prolong the service lives of the respective portions of the feed mechanism.  
         [0022]     Preferably, the conversion mechanism includes a screw shaft having a spiral groove; a screw nut having a spiral groove of the same pitch as that of the spiral groove of the screw shaft; and a power transmission member disposed between the spiral groove of the screw shaft and the spiral groove of the screw nut and adapted to transmit power between the screw shaft and the screw nut.  
         [0023]     In this case, no friction is produced between the screw shaft and the screw nut, and thus, power is transmitted smoothly. Therefore, rotational motion of one of the screw shaft and the screw nut is efficiently converted to rectilinear motion of the other of the screw shaft and the screw nut.  
         [0024]     Preferably, the power transmission member is a group of balls or rollers.  
         [0025]     In this case, since a sufficient quantity of lubrication oil is supplied to the peripheral surfaces of the balls or rollers, a lubrication oil film does not break, and therefore, the contact surfaces of the respective portions of the feed mechanism do not wear.  
         [0026]     Preferably, the lubrication apparatus further comprises a storage member for storing lubrication oil in an amount such that at least a portion of the screw shaft is immersed in the lubrication oil.  
         [0027]     In this case, since a sufficient quantity of lubrication oil is supplied to the peripheral surface of the screw shaft, a lubrication oil film does not break, and therefore, the contact surfaces of the respective portions of the feed mechanism do not wear.  
         [0028]     Preferably, the storage member covers at least a portion of the screw shaft to an extent such that the portion is immersed in the lubrication oil.  
         [0029]     Alternatively, the lubrication apparatus further comprises a storage member for storing lubrication oil in an amount such that at least a lower portion of a return tube of the screw nut is immersed in the lubrication oil.  
         [0030]     Preferably, the storage member covers at least the return tube of the screw nut to an extent such that the return tube is immersed in the lubrication oil.  
         [0031]     Preferably, the lubrication apparatus includes filter means disposed in the lubrication oil circulation pipe and adapted to remove impurities contained in the lubrication oil.  
         [0032]     In this case, since impurities, such as iron particles and dust, contained in the lubrication oil are removed by the filter means, the contact surfaces of the feed mechanism are not worn away by the impurities, such as iron particles and dust, contained in the lubrication oil.  
         [0033]     Preferably, the lubrication apparatus includes a cooling unit disposed in the lubrication oil circulation pipe and adapted to cool the lubrication oil  35 .  
         [0034]     In this case, since the respective portions of the feed mechanism are cooled by means of cooled lubrication oil, wear of the feed mechanism can be prevented.  
         [0035]     Preferably, the lubrication apparatus includes an iron-content measurement unit disposed in the lubrication oil circulation pipe and adapted to measure iron content of the lubrication oil.  
         [0036]     In this case, since the service life of the feed mechanism can be grasped in advance, the feed mechanism can be exchanged with a new one at proper timing.  
         [0037]     Preferably, the lubrication apparatus includes control means for controlling the forming machine on the basis of the iron content measured by the iron-content measurement unit.  
         [0038]     Preferably, the control means calculates a service life of the conversion mechanism on the basis of the measured iron content.  
         [0039]     Preferably, the control means produces a warning for prompting exchange of the lubrication oil or the conversion mechanism when the measured iron content exceeds a predetermined level.  
         [0040]     In this case, the timing for exchanging the lubrication oil or the feed mechanism can be grasped reliably.  
         [0041]     The present invention provides a method for lubricating a feed mechanism of a forming machine, comprising supplying lubrication oil to a conversion mechanism for converting rotational motion to rectilinear motion or converting rectilinear motion to rotational motion; and collecting the supplied lubrication oil.  
         [0042]     This method enables smooth and efficient conversion of rotational motion to rectilinear motion.  
         [0043]     Preferably, the conversion mechanism transmits power by means of a screw shaft having a spiral groove; a screw nut having a spiral groove of the same pitch as that of the spiral groove of the screw shaft; and a power transmission member disposed between the spiral groove of the screw shaft and the spiral groove of the screw nut.  
         [0044]     In this case, no friction is produced between the screw shaft and the screw nut, and thus, power is transmitted smoothly. Therefore, rotational motion of one of the screw shaft and the screw nut is efficiently converted to rectilinear motion of the other of the screw shaft and the screw nut.  
         [0045]     Preferably, the power transmission member is a group of balls or rollers.  
         [0046]     In this case, since a sufficient quantity of lubrication oil is supplied to the peripheral surfaces of the balls or rollers, a lubrication oil film does not break, and therefore, the contact surfaces of the respective portions of the feed mechanism do not wear.  
         [0047]     Preferably, at least a portion of the screw shaft is immersed in the lubrication oil.  
         [0048]     Preferably, at least a portion of the screw shaft is covered by a storage member to an extent such that the portion is immersed in the lubrication oil.  
         [0049]     Alternatively, at least a lower portion of a return tube of the screw nut is immersed in the lubrication oil.  
         [0050]     Preferably, at least a portion of the return tube of the screw nut is covered by storage member to an extent such that the portion is immersed in the lubrication oil.  
         [0051]     Preferably, impurities contained in the lubrication oil are removed by filter means disposed in the lubrication oil circulation pipe.  
         [0052]     In this case, since impurities, such as iron particles and dust, contained in the lubrication oil are removed by the filter means, the contact surfaces of the feed mechanism are not worn away by the impurities, such as iron particles and dust, contained in the lubrication oil.  
         [0053]     Preferably, the lubrication oil is cooled by a cooling unit disposed in the lubrication oil circulation pipe.  
         [0054]     In this case, since the respective portions of the feed mechanism are cooled by means of cooled lubrication oil, wear of the feed mechanism can be prevented.  
         [0055]     Preferably, iron content of the lubrication oil is measured by use of an iron-content measurement unit disposed in the lubrication oil circulation pipe.  
         [0056]     Preferably, the forming machine is controlled by use of control means and on the basis of the iron content measured by the iron-content measurement unit.  
         [0057]     Preferably, the service life of the conversion mechanism is calculated by use of the control means and on the basis of the measured iron content.  
         [0058]     Preferably, the control means produces a warning for prompting exchange of the lubrication oil or the conversion mechanism when the measured iron content exceeds a predetermined level. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0059]     The structure and features of the apparatus and method for lubricating a feed mechanism of a forming machine according to the present invention will be readily appreciated as the same becomes better understood by reference to the drawings, in which:  
         [0060]      FIG. 1  is a cross-sectional view of a drive section of a conventional mold clamping apparatus;  
         [0061]      FIG. 2  is a schematic view of a mold clamping apparatus of an injection molding machine according to a first embodiment of the present invention;  
         [0062]      FIG. 3  is a cross-sectional view of a lubrication apparatus for a feed mechanism according to the first embodiment of the present invention;  
         [0063]      FIG. 4  is a cross-sectional view showing a first example structure of the feed mechanism according to the first embodiment of the present invention;  
         [0064]      FIG. 5  is a cross-sectional view showing a second example structure of the feed mechanism according to the first embodiment of the present invention;  
         [0065]      FIG. 6  is a schematic view showing a third example structure of the feed mechanism according to the first embodiment of the present invention;  
         [0066]      FIG. 7  is a cross-sectional view showing a fourth example structure of the feed mechanism according to the first embodiment of the present invention;  
         [0067]      FIG. 8  is a cross-sectional view as viewed in the direction of arrow A in  FIG. 3 ;  
         [0068]      FIG. 9  is a cross-sectional view of a lubrication apparatus for a feed mechanism according to a second embodiment of the present invention;  
         [0069]      FIG. 10  is a cross-sectional view as viewed in the direction of arrow B in  FIG. 9 ;  
         [0070]      FIG. 11  is a partial cross-sectional view showing the lubrication conditions of the feed mechanism according to the second embodiment of the present invention;  
         [0071]      FIG. 12  is a cross-sectional view as viewed in the direction of arrow A in  FIG. 3  showing a third embodiment of the present invention;  
         [0072]      FIG. 13  is a cross-sectional view as viewed in the direction of arrow B in  FIG. 9  showing the third embodiment of the present invention; and  
         [0073]      FIG. 14  is a diagram showing the configuration of an iron-content measurement unit used in the third embodiment of the present invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0074]     Embodiments of the present invention will next be described in detail with reference to the drawings. Although the apparatus and method for lubricating a feed mechanism of a forming machine according to the present invention can be applied to various forming machines, such as extrusion molding machines, laminators, transfer molding machines, die casting machines, and IJ encapsulation presses, here, a case in which the present invention is applied to an injection molding machine will be described.  
         [0075]      FIG. 2  is a schematic view of a mold clamping apparatus of an injection molding machine according to a first embodiment of the present invention.  
         [0076]     In  FIG. 2 , reference numeral  15  denotes a frame;  13  denotes a stationary platen, which is fixed to the frame  15 ;  23  denotes a toggle support, serving as a base plate, which is movably disposed on the frame  15  and is separated a predetermined distance from the stationary platen  13 ;  14  denotes tie bars which are disposed to extend between the stationary platen  13  and the toggle support  23 ; and  12  denotes a movable platen which is disposed to face the stationary platen  13  and is reciprocatable (can be moved leftward and rightward in  FIG. 2 ) along the tie bars  14 . An unillustrated stationary mold is attached to a surface of the stationary platen  13 , which surface faces the movable platen  12 . An unillustrated movable mold is attached to a surface of the movable platen  12 , which surface faces the stationary platen  13 .  
         [0077]     A dive unit  10  is attached to the rear end (left-hand end in  FIG. 2 ) of the movable platen  12 . The drive unit  10  includes a motor  11  serving as a drive source and adapted to advance and retract (move leftward and rightward in  FIG. 2 ) an ejector rod  24 , which is a member to be moved. The advancement and retraction of the ejector rod  24  causes advancement and retraction motions of an unillustrated ejector pin which projects into the cavity of the movable mold of the mold apparatus, to thereby eject a molded product. The motor  11  may be any type of motor; however, a servomotor is preferably used as the motor  11 .  
         [0078]     A toggle mechanism  18  is disposed between the movable platen  12  and the toggle support  23 . A drive unit  10 ′ serving as a drive means for mold clamping operation of the injection molding machine is attached to the rear end (left-hand end in  FIG. 2 ) of the toggle support  23 . The drive unit  10 ′ includes a motor  11 ′ serving as a drive source and adapted to advance and retract a cross head  17 , which is a member to be moved, to thereby operate the toggle mechanism  18 . Thus, the movable platen  12  is advanced (moved rightward in  FIG. 2 ) to thereby perform mold closing. Further, a clamping force, which is the product of a thrust force generated by the motor  11 ′ and a toggle magnification ratio, is generated in order to perform mold clamping with the clamping force. In the present embodiment, the clamping force is generated through operation of the toggle mechanism  18 . However, the thrust force generated by the motor  11 ′ can be transmitted directly to the movable platen  12  as a clamping force, without use of the toggle mechanism  18 .  
         [0079]     The toggle mechanism  18  includes toggle levers  21  swingably supported by the cross head  17 ; toggle levers  22  swingably supported by the toggle support  23 ; and toggle arms  16  swingably supported by the movable platen  12 . The toggle levers  21  are linked with the toggle levers  22 . The toggle levers  22  are linked with the toggle arms  16 .  
         [0080]     Next, a lubrication apparatus for a feed mechanism of the drive unit  10  will be described.  
         [0081]      FIG. 4  is a cross-sectional view showing a first example structure of the feed mechanism according to the first embodiment of the present invention;  FIG. 5  is a cross-sectional view showing a second example structure of the feed mechanism according to the first embodiment of the present invention;  FIG. 6  is a cross-sectional view showing a third example structure of the feed mechanism according to the first embodiment of the present invention; and  FIG. 7  is a cross-sectional view showing a fourth example structure of the feed mechanism according to the first embodiment of the present invention.  
         [0082]     In  FIG. 4 , reference numeral  25  denotes a screw nut, and  26  denotes a screw shaft. The screw shaft  26  and the screw nut  25  have spiral grooves, respectively, which are formed at the same pitch. A plurality of balls  29   a , collectively serving as a power transmission member, are disposed between the spiral groove of the screw shaft  26  and the spiral groove of the screw nut  25 . A return tube  25   a  is attached to the screw nut  25  by means of a return-tube attachment member  25   b . This configuration enables the balls  29   a  to circulate, while rolling, through the space between the spiral groove of the screw shaft  26  and the spiral groove of the screw nut  25 , as well as through the interior of the return tube  25   a.    
         [0083]     In the feed mechanism, the plurality of balls  29   a  transmit power between the screw shaft  26  and the screw nut  25 , while rolling. Therefore, no friction is generated between the screw shaft  26  and the screw nut  25 , and power is smoothly transmitted therebetween. Therefore, rotational motion of the screw shaft  26  is efficiently converted to rectilinear motion of the screw nut  25 . Alternatively, rotational motion of the screw nut  25  is efficiently converted to rectilinear motion of the screw shaft  26 .  
         [0084]     In the present embodiment, the power transmission member may be rollers. In this case, as shown in  FIG. 5 , a plurality of rollers  29   b , collectively serving as a power transmission member, are disposed between the spiral groove of the screw shaft  26  and the spiral groove of the screw nut  25 . Notably, the spiral groove of the screw shaft  26  and the spiral groove of the screw nut  25  have the same pitch. In this case, two return tubes  25   a - 1  and  25   a - 2  are provided. Rollers  29   b  which pass through the return tube  25   a - 1  and rollers  29   b  which pass through the return tube  25   a - 2  are inclined in opposite directions. Notably, rollers  29   b  inclined in one direction and rollers  29   b  inclined in the opposite direction may be disposed alternately, as shown in  FIG. 6 .  
         [0085]     In this case, the direction of inclination of the rollers  29   b  is determined in consideration of the axial direction in which the feed mechanism receives a load. Thus, the feed mechanism can bear a heavier load, and can efficiently convert rotational motion to rectilinear motion.  
         [0086]     In the present embodiment, the power transmission member may be a planetary roller. In this case, as shown in  FIG. 7 , a plurality of planetary rollers  29   c , collectively serving as a power transmission member, are disposed between the spiral groove of the screw shaft  26  and a spiral groove formed on a screw-groove formation member  25   c  of the screw nut  25 . Notably, the spiral groove of the screw shaft  26  and the spiral groove of the screw-groove formation member  25   c  of the screw nut  25  have the same pitch. Further, a spiral thread is formed on the perimeter of each of the planetary rollers  29   c  at the same pitch as the spiral grooves. The spiral threads of the planetary rollers  29   c  are in screw-engagement with the spiral groove of the screw shaft  26  and the spiral groove of the screw-groove formation member  25   c  of the screw nut  25 . Notably, the screw nut  25  and the screw-groove formation member  25   c  may be formed as a single member.  
         [0087]     The planetary rollers  29   c  are disposed around the screw shaft  26  in such manner that the center axes of the planetary rollers  29   c  become parallel to the axis of the screw shaft  26 . The opposite ends of the planetary rollers  29   c  are rotatably supported by guide rings  25   d  secured to the screw-groove formation member  25   c . This configuration enables the planetary rollers  29   c  to transmit power between the screw shaft  26  and the screw nut  25  while rotating.  
         [0088]     In this case, since the backlash between the screw shaft  26  and the planetary rollers  22   c  and the backlash between the screw-groove formation member  25   c  and the planetary rollers  29   c  are extremely small, rotational motion can be converted to rectilinear motion with high accuracy.  
         [0089]     In the present embodiment, the feed mechanism may have any one of the above-described configurations. Here, a case in which balls are used as the power transmission member will be described.  
         [0090]      FIG. 3  is a cross-sectional view of a lubrication apparatus for the feed mechanism according to the first embodiment of the present invention; and  FIG. 8  is a cross-sectional view as viewed in the direction of arrow A in  FIG. 3 .  
         [0091]     In  FIG. 3 , the screw nut  25  of the feed mechanism is fixed to a nut support member  31  by use of, for example, bolts.  
         [0092]     The nut support member  31  may be a stationary member such as the toggle support  23 , or a movable member such as the cross head  17 . The screw shaft  26 , which has a spiral groove on the perimeter thereof, is in screw-engagement with the screw nut  25 . The right-hand end (in  FIG. 3 ) of the screw shaft  26  is connected directly, or indirectly, to an unillustrated drive source, such as the above-described motor  11 . The screw shaft  26  is rotated by the drive source.  
         [0093]     A portion of the screw shaft  26  in which no groove is formed is attached to a screw-shaft support member  41  via bearings  42 . The screw shaft  26  has an integrally formed flange portion  26   a . The screw shaft  26  is fixed to the inner rings of the bearings  42  by means of the flange portion  26   a  and a fixing member  43 , such as a lock nut, fixed to the screw shaft  26 . Thus, the screw shaft  26  and the screw-shaft support member  41  are coupled to each other in such a manner that they can rotate relative to each other but cannot move relative to each other along the axial direction.  
         [0094]     When rotation of the screw-shaft support member  41  is prohibited by a member such as a guide member, only the reciprocative motion; i.e., axial rectilinear motion, of the screw shaft  26  is transmitted to the screw-shaft support member  41 .  
         [0095]     When relative rotation occurs between the screw nut  25  and the screw shaft  26 , the screw nut  25  axially moves relative to the screw shaft  26 . Therefore, when the nut support member  31  is a stationary member, the screw-shaft support member  41  is a movable member such as the cross head  17 ; and when the nut support member  31  is a movable member, the screw-shaft support member  41  is a stationary member such as the toggle support  23 .  
         [0096]     A nut cover member  32  (storage member) for covering the perimeter of the screw nut  25  is fixed to the nut support member  31  by use of, for example, bolts. The nut cover member  32  assumes a cylindrical shape and has an open end and a closed bottom, which has a circular hole formed therein. The open end of the nut cover member  32  is attached to the nut support member  31 . The screw shaft  26  passes through the circular hole formed in the bottom wall.  
         [0097]     A first seal member  36  such as a packing is disposed between the nut cover member  32  and the nut support member  31  in order to establish a fluid-tight condition to thereby prevent leakage of lubrication oil  35 . Further, a second seal member  37  such as an oil seal is disposed between the inner circumferential surface of the circular hole and the outer circumferential surface of the screw shaft  26  in order to establish a fluid-tight condition to thereby prevent leakage of the lubrication oil  35 . An oil pan  44  is attached to a side surface (left side surface in  FIG. 3 ) of the screw-shaft support member  41 , which surface faces the screw nut  25 , and extends to a point below the nut cover member  32 . Therefore, when the lubrication oil  35  leaks from the clearance between the inner circumferential surface of the circular hole and the outer circumferential surface of the screw shaft  26 , the leaked lubrication oil  35  is received by the oil pan  44  without dripping further downward.  
         [0098]     A screw-shaft cover member  33  (storage member) is attached to the side of the nut support member  31  opposite the nut cover member  32  by use of, for example, bolts. The screw-shaft cover member  33  covers the perimeter of an end portion of the screw shaft  26  which projects from the screw nut  25  toward the side opposite the nut cover member  32 . The screw-shaft cover member  33  assumes a cylindrical shape and has an open end and a closed end; i.e., a closed bottom. The open end of the screw-shaft cover member  33  is attached to the nut support member  31 . A first seal member  36  such as a packing is disposed between the screw-shaft cover member  33  and the nut support member  31  in order to establish a fluid-tight condition to thereby prevent leakage of the lubrication oil  35 .  
         [0099]     As shown in  FIG. 8 , a lubrication oil supply pipe  34  and a lubrication oil discharge pipe  38 , serving as a lubrication oil circulation pipe, and an air bleeder pipe  39  are connected to the screw-shaft cover member  33 . One end of the lubrication oil supply pipe  34  is connected to a top portion of the screw-shaft cover member  33 , and the other end of the lubrication oil supply pipe  34  is connected to a lubrication oil supply pump  47 . A suction pipe  45 , serving as a lubrication oil circulation pipe, is attached to the lubrication oil supply pump  47 , and filter means  46  is attached to the lower end of the suction pipe  45 . The lubrication oil  35 , which the lubrication oil supply pump  47  pumps from a lubrication oil tank  49  via the suction pipe  45  and the filter means  46 , is supplied to the interior of the screw-shaft cover member  33  via the lubrication oil supply pipe  34 . The lubrication oil supply pump  47  is driven by a pump drive source  48  such as an electric motor.  
         [0100]     As shown in  FIG. 8 , one end of the lubrication oil discharge pipe  38  is connected to a lower side portion of the screw-shaft cover member  33 , and the other end of the lubrication oil discharge pipe  38  is connected to the lubrication oil tank  49 . By virtue of this configuration, the quantity of the lubrication oil  35  stored inside the screw-shaft cover member  33  is controlled in such a manner that the oil level does not exceed the point at which the lubrication oil discharge pipe  38  is connected to the screw-shaft cover member  33 . As a result, only a bottom portion of the screw shaft  26  is immersed in the lubrication oil  35 . As shown in  FIG. 8 , one end of the air bleeder pipe  39  is connected to a upper side portion of the screw-shaft cover member  33 , and the other end of the air bleeder pipe  39  is connected to the vicinity of the lubrication oil tank  49 . The air bleeder pipe  39  introduces air into the interior of the sealed screw-shaft cover member  33  to thereby enable the lubrication oil  35  to be discharged smoothly from the lubrication oil discharge pipe  38 .  
         [0101]     The filter means  46  attached to the lower end of the suction pipe  45  is immersed in the lubrication oil  35  stored in the lubrication oil tank  49 . When the lubrication oil supply pump  47  pumps the lubrication oil  35  from the lubrication oil tank  49 , the lubrication oil  35  is caused to pass through the filter means  46 . Therefore, impurities such as iron particles and dust contained in the lubrication oil  35  are filtered out. Preferably, the filter means  46  is removably attached to the suction pipe  45 . Further, preferably, the filter means  46  has a filtering material, such as filter paper or wire mesh; i.e., a filter element in a removable form such as a cassette. In this case, the filter element can be exchanged with ease when a large quantity of impurities such as iron particles and dust have accumulated in the filter element due to use over a long period of time.  
         [0102]     Next, operation of the lubrication apparatus having the above-described configuration will be described.  
         [0103]     When the motor  11  serving as a drive source is operated, the screw shaft  26  is rotated. Since the screw shaft  26  is in screw-engagement with the screw nut  25  fixedly attached to the nut support member  31 , upon rotation of the screw shaft  26 , the screw shaft  26  and the screw nut  25  move (i.e., advance or retract) relative to each other in the axial direction. Notably, whether the screw shaft  26  and the screw nut  25  advance or retract relative to each other is determined by the direction of the screw thread and the rotational direction of the screw shaft  26 .  
         [0104]     As result, the screw-shaft support member  41  and the nut support member  31  move relative to each other in the axial direction. For example, when the nut support member  31  is a stationary member such as the toggle support  23  and the screw-shaft support member  41  is a movable member such as the cross head  17 , the screw-shaft support member  41  is advanced or retracted along the axis of the screw shaft  26 .  
         [0105]     As described above, the lubrication oil  35  is stored within the screw-shaft cover member  33 ; and, as shown in  FIGS. 3 and 8 , the oil level is set slightly higher than the lowest point of the screw shaft  26 . In other words, a lower portion of the screw shaft  26  is immersed in the lubrication oil  35 . Therefore, when the screw shaft  26  rotates, the lubrication oil  35  comes to cover the entire surface of the portion of the screw shaft  26  located within the screw-shaft cover member  33 . In addition, the lubrication oil  35  flows along the spiral groove formed on the perimeter of the screw shaft  26  and enters the space between the screw nut  25  and the screw shaft  26 . Since the screw shaft  26  axially moves relative to the screw nut  25  and the screw-shaft cover member  33 , the lubrication oil  35  is sufficiently supplied to the inner circumferential surface (i.e., the spiral groove) of the screw nut  25  and a portion of the screw shaft  26  which projects rightward from the screw nut  25  in  FIG. 3 .  
         [0106]     By virtue of sufficient supply of the lubrication oil  35 , a film of the lubrication oil  35  is formed on the surface of the spiral groove of the screw shaft  26 , the surfaces of the balls  29   a  held within the screw nut  25 , and the surface of the spiral groove of the screw nut  25 , thereby improving the lubrication conditions at the ball screw portion. As a result, the movement of the ball screw becomes smooth, and wear of the ball screw can be prevented, whereby the service life of the ball screw can be prolonged.  
         [0107]     A portion of the lubrication oil  35  flows along the spiral groove formed on the perimeter of the screw shaft  26  to thereby move rightward in  FIG. 3  beyond the screw nut  25 . However, since the second seal member  37  such as an oil seal is disposed between the inner circumferential surface of the circular hole of the nut cover member  32  and the outer circumferential surface of the screw shaft  26 , the lubrication oil  35  hardly leaks to the outside of the nut cover member  32 . Even when the lubrication oil  35  leaks outside along the spiral groove of the screw shaft  26 , the lubrication oil  35  leaks in a very small amount; i.e. oozes out. Since such an oozing portion of the lubrication oil  35  is received by the oil pan  44 , the lubrication oil  35  does not drip down.  
         [0108]     The pump drive source  48  is operated periodically in order to drive the lubrication oil supply pump  47 . As a result, the lubrication oil  35  stored in the lubrication oil tank  49  is pumped via the filter means  46  and the suction pipe  45  and is supplied to the interior of the screw-shaft cover member  33  via the lubrication oil supply pipe  34 . Thus, the oil level within the screw-shaft cover member  33  rises, and an excessive portion of the lubrication oil  35  is discharged from the lubrication oil discharge pipe  38  and is caused to return to the lubrication oil tank  49 . When the lubrication oil  35  is caused to circulate in the above-described manner, impurities, such as iron particles and dust, contained in the portion of the lubrication oil  35  stored in the screw-shaft cover member  33  are removed by the filter means  46 , thereby cleaning the lubrication oil  35 .  
         [0109]     The operation for driving the lubrication oil supply pump  47  by operating the pump drive source  48  may be performed, for example, once every week, once every day, or once every hour. Alternatively, the lubrication oil supply pump  47  may be operated continuously in order to circulate the lubrication oil  35  at all times. The filter element, which may be loaded with impurities such as iron particles and dust, may be replaced at predetermined time intervals or whenever the operation time of the injection molding machine reaches a predetermined time.  
         [0110]     When the feed mechanism is used over a long period of time due to long-term operation of the injection molding machine, the lubrication oil  35  may contain impurities, such as iron particles and dust, which are generated due to wear of the ball screw. If lubrication is performed by use of the lubrication oil  35  containing impurities, such as iron particles and dust, the contact surfaces may be worn away by the impurities. Therefore, the impurities, such as iron particles and dust, must be removed from the lubrication oil  35 . In the present embodiment, the lubrication oil  35  is circulated periodically or continuously in order to remove impurities, such as iron particles and dust, from the lubrication oil  35  by use of the filter means  46 . Therefore, the contact surfaces of the feed mechanism are not worn away by the impurities, such as iron particles and dust.  
         [0111]     Notably, since the quality of the lubrication oil  35  deteriorates with heat or with time, the lubrication oil  35  is desirably exchanged with fresh lubrication oil  35  at predetermined time intervals.  
         [0112]     The feed mechanism is cooled by means of the lubrication oil  35 . Therefore, when the feed mechanism generates excessive heat due to severe use conditions, the heat generation of the feed mechanism can be suppressed through an increase in the quantity of the lubrication oil  35  stored in the screw-shaft cover member  33  or an increase in the circulation rate of the lubrication oil  35 .  
         [0113]     Wear of the feed mechanism can be prevented through employment of a cooling unit which is disposed in the lubrication oil supply pipe  34  in order to cool the lubrication oil  35  to thereby cool the screw shaft  26 , the return tube  25   a , and the balls  29   a . Further, the lubrication oil  35  stored in the lubrication oil tank  49  may be cooled through employment of a cooling unit connected to the lubrication oil tank  49 .  
         [0114]     As described above, in the present embodiment, the perimeters of the screw shaft  26  and the screw nut  25  are covered by the nut cover member  32  and the screw-shaft cover member  33 , respectively; and the lubrication oil  35  is stored in the screw-shaft cover member  33  in an amount such that a lower portion of the screw shaft  26  is immersed in the lubrication oil  35  to thereby lubricate the feed mechanism by means of the lubrication oil  35 .  
         [0115]     Accordingly, a uniform film of the lubrication oil  35  can be maintained on the contact surfaces of the screw shaft  26  and the screw nut  25  through which they come into contact with the balls  29   a  serving as the power transmission member. Thus, the service lives of the respective portions of the feed mechanism can be extended. Further, the respective portions of the feed mechanism are cooled by the lubrication oil  35 . Therefore, wear of the respective portions of the feed mechanism can be prevented in order to extend the service life of the feed mechanism.  
         [0116]     Further, impurities, such as iron particles and dust, contained in the lubrication oil  35  are removed by use of the filter means  46 , whereby the lubrication oil  35  is cleaned. Therefore, wear of the respective portions of the feed mechanism due to impurities, such as iron particles and dust, can be prevented in order to extend the service life of the feed mechanism.  
         [0117]     Next, a second embodiment of the present invention will be described. Repeated descriptions of structural features and operation which are the same as those of the first embodiment will be omitted.  
         [0118]      FIG. 9  is a cross-sectional view of a lubrication apparatus for a feed mechanism according to the second embodiment of the present invention;  FIG. 10  is a cross-sectional view as viewed in the direction of arrow B in  FIG. 9 ; and  FIG. 11  is a partial cross-sectional view showing the lubrication conditions of the feed mechanism according to the second embodiment of the present invention.  
         [0119]     As shown in  FIG. 10 , in the present embodiment, the lubrication oil supply pipe  34  and the lubrication oil discharge pipe  38  are connected not to the screw-shaft cover member  33  but to the nut cover member  32 . One end of the lubrication oil supply pipe  34  is connected to a top portion of the nut cover member  32 , and the other end of the lubrication oil supply pipe  34  is connected to the lubrication oil supply pump  47 . The lubrication oil  35 , which the lubrication oil supply pump  47  pumps from the lubrication oil tank  49  via the suction pipe  45  and the filter means  46 , is supplied to the interior of the nut cover member  32  via the lubrication oil supply pipe  34 . Although the air bleeder pipe  39  is omitted, the air bleeder pipe  39  may be provided in a manner similar to that in the first embodiment.  
         [0120]     As shown in  FIG. 10 , one end of the lubrication oil discharge pipe  38  is connected to a lower side portion of the nut cover member  32 , and the other end of the lubrication oil discharge pipe  38  is connected to the lubrication oil tank  49 . By virtue of this configuration, the quantity of the lubrication oil  35  stored inside the nut cover member  32  is controlled in such a manner that the oil level does not exceed the point where the lubrication oil discharge pipe  38  is connected to the nut cover member  32 .  
         [0121]     In the present embodiment, the screw nut  25  is attached to the nut support member  31  in such a manner that the return tube  25   a  is located on the lower side of the screw nut  25 , and, as shown in  FIG. 11 , the oil level is set such that a lower portion of the return tube  25   a  is immersed in the lubrication oil  35 . One or a plurality of fine holes (not shown) are formed in the return tube  25   a . Therefore, the lubrication oil  35  is supplied to the interior of the return tube  25   a  via the hole(s), so that the surfaces of the balls  29   a  are covered with the lubrication oil  35 . Further, since the lubrication oil  35  is supplied to the balls  29   a , which circulate along the spiral grooves of the screw shaft  26  and the screw nut  25 , an oil film is formed on the surfaces of the spiral grooves.  
         [0122]     Further, as shown in  FIG. 9 , the oil level of the lubrication oil  35  is set such that the oil level does not reach the height of the second seal member  37 , disposed between the inner circumferential surface of the circular hole of the nut cover member  32  and the outer circumferential surface of the screw shaft  26 . Therefore, the lubrication oil  35  hardly leaks from the clearance between the inner circumferential surface of the circular hole and the outer circumferential surface of the screw shaft  26 . Moreover, an oil pan  44  is attached to a side surface (left side surface in  FIG. 9 ) of the screw-shaft support member  41 , which surface faces the screw nut  25 , and extends to a point below the nut cover member  32 . Therefore, when the lubrication oil  35  leaks from the clearance between the inner circumferential surface of the circular hole and the outer circumferential surface of the screw shaft  26 , the leaked lubrication oil  35  is received by the oil pan  44  without dripping further downward.  
         [0123]     Notably, a cooling unit may be disposed in the lubrication oil supply pipe  34  in order to cool the lubrication oil  35  to thereby cool the screw shaft  26 , the return tube  25   a , and the balls  29   a  for the purpose of preventing wear of the feed mechanism. Further, the lubrication oil  35  stored in the lubrication oil tank  49  may be cooled through employment of a cooling unit connected to the lubrication oil tank  49 .  
         [0124]     As described above, in the present embodiment, the perimeters of the screw shaft  26  and the screw nut  25  are covered by the nut cover member  32  and the screw-shaft cover member  33 , respectively; and the lubrication oil  35  is stored in the nut cover member  32  in an amount such that a lower portion of the return tube  25   a  is immersed in the lubrication oil  35 , which is thus supplied to the interior of the return tube  25   a.    
         [0125]     Since the surfaces of the balls  29   a , serving as the power transmission member, are covered with the lubrication oil  35 , a uniform film of the lubrication oil  35  can be maintained on the contact surfaces of the screw shaft  26  and the screw nut  25  through which they come into contact with the balls  29   a . Thus, the service life of the feed mechanism can be extended.  
         [0126]     Next, a third embodiment of the present invention will be described. Repeated descriptions of structural features and operation which are the same as those of the first and second embodiments will be omitted.  
         [0127]      FIG. 12  is a cross-sectional view as viewed in the direction of arrow A in  FIG. 3  showing the third embodiment of the present invention; and  FIG. 13  is a cross-sectional view as viewed in the direction of arrow B in  FIG. 9  showing the third embodiment of the present invention.  
         [0128]     In the present embodiment, an iron-content measurement unit  71  for measuring quantity of iron contained in the lubrication oil  35  is disposed in the lubrication oil supply pipe  34 . In the present embodiment, the lubrication oil supply pipe  34  and the lubrication oil discharge pipe  38  may be connected to the screw-shaft cover member  33 , as shown in  FIG. 12 , or to the nut cover member  32 , as shown in  FIG. 13 . Further, the iron-content measurement unit  71  may be disposed in the lubrication oil discharge pipe  38 .  
         [0129]     The iron-content measurement unit  71  is communicatably connected to a controller  72 , which serves as control means for controlling the operation of the molding machine, and transmits to the controller  72  a measurement signal indicative of a measured iron content. The controller  72  displays the measured iron content; calculates the service life of the feed mechanism on the basis of the iron content and displays the same; and, when the iron content is in excess of a preset value, warns an operator that the service life of the feed mechanism has been reached.  
         [0130]     Next, the configuration of the iron-content measurement unit  71  will be described in detail.  
         [0131]      FIG. 14  is a diagram showing the configuration of the iron-content measurement unit used in the third embodiment of the present invention.  
         [0132]     In  FIG. 14 , reference numeral  74  denotes a first excitation coil, which is disposed in such a manner that the lubrication oil supply pipe  34  passes through the center thereof. Reference numeral  75  denotes a second excitation coil, which is disposed to face the first excitation coil  74 . However, the lubrication oil supply pipe  34  does not pass through the center of the second excitation coil  75 . A detection coil  77  is disposed at the midpoint between the first excitation coil  74  and the second excitation coil  75 . The first excitation coil  74  and the second excitation coil  75  have the same configuration and are excited by the same current output from an oscillation circuit  76 . Therefore, the first excitation coil  74  and the second excitation coil  75  generate magnetic fields of the same intensity in the same direction.  
         [0133]     Therefore, at the midpoint between the first excitation coil  74  and the second excitation coil  75 , the magnetic field generated by the first excitation coil  74  and that generated by the second excitation coil  75  are cancelled out, so that no electromotive force is induced; i.e., no voltage is generated in the detection coil  77  disposed at the midpoint.  
         [0134]     However, when the lubrication oil  35  flowing inside the lubrication oil supply pipe  34 , which passes through the center of the first excitation coil  74 , contains iron particles  73 , the intensity of the magnetic field formed by the first excitation coil  74  increases, upsetting the balance of magnetic fields at the midpoint. Therefore, an electromotive force or voltage is generated in the detection coil  77 . The thus-generated voltage is amplified by means of an amplification circuit  78  and is sent to the controller  72  as a measurement signal. Since the amplitude of the voltage changes in proportion to the quantity of the iron particles  73  contained in the lubrication oil  35 , the quantity of the iron particles  73  can be measured on the basis of the amplitude of the measurement signal.  
         [0135]     When the lubrication oil  35  circulates, the iron particles  73  contained in the portion of the lubrication oil  35  located inside the screw-shaft cover member  33  circulate together with the lubrication oil  35 . Therefore, the quantity of the iron particles  73  contained in the lubrication oil  35  can be measured by use of the iron-content measurement unit  71  disposed in the lubrication oil supply pipe  34 . Notably, the quantity of the iron particles  73  may be measured at all times, or intermittently at intervals corresponding to a frequency at which the lubrication oil supply pump  47  is operated.  
         [0136]     When the iron-content measurement unit  71  is operated, the oscillation circuit  76  starts its operation, whereby magnetic fields are generated by the first excitation coil  74  and the second excitation coil  75 . When the lubrication oil  35  contains no iron particles  73 , the magnetic field generated by the first excitation coil  74  and that generated by the second excitation coil  75  have the same intensity, so that no voltage is generated in the detection coil  77 . However, when the lubrication oil  35  flowing inside the lubrication oil supply pipe  34  contains iron particles  73 , the intensity of the magnetic field generated by the first excitation coil  74  increases, so that a voltage is generated in the detection coil  77 . Since the intensity of the magnetic field generated by the first excitation coil  74  increases in proportion to the quantity of the iron particles  73 , the amplitude of the voltage generated by the detection coil  77  also increases in proportion to the quantity of the iron particles  73 . Therefore, the quantity of the iron particles  73  can be measured on the basis of the voltage generated by the detection coil  77 .  
         [0137]     When the measurement signal is sent from the iron-content measurement unit  71  to the controller  72 , the controller  72  calculates the service life of the feed mechanism. When the quantity of the iron particles  73  contained in the lubrication oil  35  is in excess of a preset value, the controller  72  provides a warning to the operator. For example, when the iron content of the lubrication oil  35  has exceeded 0.1%, the controller  72  warns the operator to change the lubrication oil  35 ; and when the iron content of the lubrication oil  35  has exceeded 1.0%, the controller  72  warns the operator to change the feed mechanism, while commenting that the degree of wear of the feed mechanism has reached the allowable limit. The above-described values and contents of warning may be changed freely.  
         [0138]     The controller may be configured to continuously display the iron content on a display or meter of the controller. Further, the controller may be configured to stop the molding machine when the controller determines that the feed mechanism has come into an anomalous condition due to excessively high iron content. Alternatively, the controller may be configured to display a predicted service life of the feed mechanism by means of a message reporting, for example, that one month remains before the time for exchange, or that the feed mechanism must be exchanged within one week. In this case, the operator can grasp the timing for exchange, and therefor can make complete preparation for exchange of the feed mechanism.  
         [0139]     As described above, in the present embodiment, the iron content of the lubrication oil  35  is measured by use of the iron-content measurement unit  71 ; and the controller  72  calculates the service life of the feed mechanism on the basis of the measured iron content and warns the operator to replace the lubrication oil  35  or the feed mechanism. Therefore, the service life of the feed mechanism can be predicted accurately, thereby enabling replacement of components at proper timings.  
         [0140]     In the above-described embodiments, a horizontal-type injection molding machine in which the movable platen moves in the horizontal direction has been described. However, the apparatus and method for lubricating a feed mechanism of a forming machine can be applied to a vertical-type injection molding machine in which the movable platen moves in the vertical direction. Further, the apparatus and method for lubricating a feed mechanism of a forming machine according to the present invention can be applied not only to injection molding machines, but also to other forming machines, such as die casting machines and IJ encapsulation presses.  
         [0141]     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.