Abstract:
An adjustment mechanism for a movable platen of an injection molding machine is provided with a push bolt, configured to apply a force to push up the movable platen against a gravitational force, and a pull bolt, configured to apply a force to draw in the movable platen in the direction of gravity. The movable platen is adjusted by regulating its height above a base of the molding machine in a plurality of positions at different distances from a fixed platen.

Description:
RELATED APPLICATIONS 
     The present application claims priority to Japanese Application No. 2013-209066, filed Oct. 4, 2013, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1 . Field of the Invention 
     The present invention relates to an adjustment mechanism for a movable platen used in an injection molding machine. 
     2 . Description of the Related Art 
       FIG. 1  is a view showing a mold clamping unit of an injection molding machine. The mold clamping unit comprises a movable platen  30 , rear platen  31 , toggles  32 , fixed platen  33 , crosshead  34 , and ball screw shaft  38 . The rear platen  31  and the fixed platen  33  are connected by a plurality of tie-bars  41 , and the movable platen  30  can be advanced (to the right in  FIG. 1 ) toward and retracted (to the left in  FIG. 1 ) from the fixed platen  33  by the toggles  32 . 
     A mold  40  is mounted on the movable platen  30 . The position of the movable platen  30  can be changed by advancing or retracting the crosshead  34  on the ball screw shaft  38 . If the crosshead  34  is advanced (to the right in  FIG. 1 ), in this case, the movable platen  30  is advanced to close the mold. 
     In precision molding such as lens molding, the parallelism between the fixed and movable platens greatly affects the quality of molded products. The parallelism in the vertical direction is conventionally adjusted by changing the slant or inclination of the movable platen. In general, the inclination of the movable platen is changed by changing the respective heights of the fixed-platen-side end portion of a support portion between the movable platen and the base frame and the opposite end portion. The heights of the two opposite end portions of the support portion are typically changed by a method using wedges, shims, or bolts. 
     Japanese Patent Application Laid-Open No. 2009-262514 discloses a technique related to an inclination adjustment method for a movable platen using a bolt-and-wedge assembly. Bolts are used as adjustment elements for adjusting the height of the movable platen above a base of a molding machine. The distal ends of the respective threaded portions of the bolts contact the fixed-platen-side end portion of a support block, which is inserted below the movable platen, and the end portion opposite thereto. Thus, the level of the movable platen in the vertical direction above the base of the molding machine in a position corresponding to each of the bolts can be adjusted by means of a wedge-shaped portion of the support block by rotating the bolts. 
     In the technique disclosed in Japanese Patent Application Laid-Open No. 2009-262514 described above, a front or rear inclination of the movable platen toward a fixed platen can be adjusted by regulating the vertical positions of the movable platen on the fixed-platen side and the opposite side by means of the wedge-shaped portion of the support block by rotating the bolts. Normally, in this case, the movable platen is designed so that its center of gravity is located at an intermediate point between the positions of contact of the bolts, and the degrees to which the positions are raised are adjusted by the weight of the movable platen. If a mold is mounted on the movable platen, however, the position of the center of gravity may be sometimes changed and shifted from between the positions of contact of the bolts. If the bolts are adjusted in this case, the entire movable platen only moves up and down and its inclination cannot be adjusted, in some cases. 
     SUMMARY OF THE INVENTION 
     Accordingly, the object of the present invention is to provide an adjustment mechanism for a movable platen, capable of adjusting the inclination of a movable platen used in an injection molding machine without regard to the position of the center of gravity of the movable platen. 
     The present invention relates to an adjustment mechanism for a movable platen used in a mold clamping unit of an injection molding machine. The mold clamping unit comprises a fixed platen fixed on a base and a movable platen placed substantially parallel to the fixed platen on the base. The adjustment mechanism for the movable platen includes: a push bolt configured to apply a force to push up the movable platen against a gravitational force; and a pull bolt configured to apply a force to draw in the movable platen in the direction of gravity. The height of the movable platen above the base of the injection molding machine in a plurality of positions at different distances from the fixed platen is adjusted using the push bolt and the pull bolt so that the height and inclination of the movable platen with respect to the fixed platen are adjusted. 
     The push bolt and the pull bolt may be arranged so that the head portion of the push bolt and the head portion of the pull bolt extend in one direction. 
     The adjustment mechanism may further include a fixing bolt configured to secure the base and the movable platen to each other, wherein the fixing bolt extends perpendicular to the push bolt and the pull bolt. 
     The base may include a support portion for the movable platen, the fixing bolt may penetrate the support portion and is secured to the movable platen, and an interval between the support portion and the fixing bolt secured to the movable platen may be set as an adjustable range of the height of the movable platen above the base of the injection molding machine and the inclination of the movable platen with respect to the fixed platen. 
     According to the present invention, the inclination of a movable platen used in an injection molding machine can be adjusted without regard to the position of the center of gravity of the movable platen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and features of the present invention will be obvious from the ensuing description of embodiments with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic view of a mold clamping unit of an injection molding machine incorporating a first embodiment of an adjustment mechanism for a movable platen according to the present invention; 
         FIG. 2  is a schematic view of a mold clamping unit of an injection molding machine incorporating a second embodiment of the adjustment mechanism for a movable platen according to the present invention; 
         FIG. 3  is a sectional view taken along line A-A′ of  FIG. 2 ; and 
         FIG. 4  is an enlarged view of a portion B in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A mold clamping unit of an injection molding machine incorporating a first embodiment of an adjustment mechanism for a movable platen according to the present invention will first be described with reference to  FIG. 1 . 
     The mold clamping unit of the injection molding machine shown in  FIG. 1  operates in the same manner as in the prior art. 
     In the present embodiment, a support portion  20  is provided on a base frame to which a fixed platen  33  is secured, and one or more push bolts  12  ( 12   a  and  12   b ) and one or more pull bolts  14  ( 14   a  and  14   b ) are arranged between the base  20  and the movable platen  30 . 
     The push bolts  12  are screwed into the movable platen  30  and are configured so that their distal end portions contact the upper surface of the support portion  20 . If the push bolts  12  are screwed in, their distal end portions press the upper surface part of the support portion  20 , thereby pushing up the movable platen  30 . Thus, that part of the movable platen  30  corresponding to the push bolts  12  is raised by a distance equal to the lift. 
     On the other hand, the pull bolts  14  are screwed into both the movable platen  30  and the support portion  20 . If the pull bolts  14  are screwed in, their head portions push down the movable platen  30 , thereby drawing in the movable platen  30  in the direction of gravity. Thus, that part of the movable platen  30  corresponding to the pull bolts  14  is lowered by a distance equal to the depression. 
     According to the example of  FIG. 1 , one ( 12   b ) of the two push bolts  12  is located closest to the fixed platen  33 , while the other ( 12   a ) is located farthest from the fixed platen  33 . The two pull bolts  14   a  and  14   b  are arranged between the two push bolts  12   a  and  12   b.    
     Conventionally, only the push bolts  12  are used to push up the movable platen  30 . If a mold is mounted on the movable platen  30  so that the center of gravity of the movable platen  30  is shifted from between the push bolts  12 , for example, the entire movable platen  30  only moves up and down and its inclination cannot be adjusted even though the push bolts  12  are adjusted. If the pull bolts  14  are also provided, as in the present embodiment, however, the inclination of the movable platen  30  can be adjusted without regard to the position of the center of gravity of the movable platen  30 . 
     In the present embodiment, the push bolts  12  and the pull bolts  14  are respectively provided in pairs. However, the number of these bolts can be suitably set as far as at least on push bolt  12  and at least one pull bolt  14  are provided. Therefore, the positions where the push bolts  12  are to be screwed into the movable platen  30  need not always be the two positions closest to and farthest from the fixed platen  33 . Further, the positions where the pull bolts  14  are to be screwed into both the movable platen  30  and the support portion  20  need not always be intermediate between the two push bolts  12   a  and  12   b  , either. 
     In the present embodiment, furthermore, the support portion  20  is provided on a guide between the movable platen  30  and the base frame, and the movable platen  30  is disposed on the support portion  20 . Alternatively, however, the movable platen  30  may be disposed directly on the guide without the use of the support portion  20 . 
     A mold clamping unit of an injection molding machine incorporating a second embodiment of the adjustment mechanism for a movable platen according to the present invention will now be described with reference to  FIG. 2 . 
     The present embodiment differs from the first embodiment in that two fixing bolts  16  ( 16   a  and  16   b ) are arranged horizontally (at right angles to the axes of tie-bars  41 ) on a support portion  20  on a base frame. As shown in  FIG. 3 , the fixing bolts  16  are passed individually through through-holes in each support portion  20  and their distal ends are threadedly engaged with a movable platen  30 . The support portion  20  is firmly secured to the movable platen  30  by the fixing bolts  16 . 
     Further, the fixing bolts  16  extend perpendicular to push bolts  12  and pull bolts  14  and horizontally connect each support portion  20  to the movable platen  30 . Thus, the inclination of the movable platen  30  can be adjusted by the push and pull bolts  12  and  14  with the fixing bolts  16  loosened. Even if the fixing bolts  16  are tightened after the inclination of the movable platen is adjusted, the tightening does not affect the result of the adjustment by the bolts  12  and  14 , since the tightening direction of the fixing bolts  16  is perpendicular to the extending direction of the bolts  12  and  14 . 
     The fixing bolts  16  are passed individually through the through-holes ( FIG. 3 ) in each support portion  20  and their distal ends are threadedly engaged with the movable platen  30 . Since the inner diameter of each through-hole in the support portion  20  is larger than the outer diameter of each fixing bolt  16 , as shown in the enlarged view of  FIG. 4 , a gap  22  is formed between each through-hole of the support portion  20  and the fixing bolt  16  that penetrates the through-hole. In the present embodiment, the size of the gap  22  determines a range in which the inclination of the movable platen  30  is adjustable. It is unnecessary, therefore, to separately provide a mechanism for restricting the adjustable range for the inclination of the movable platen  30 , so that the number of parts used can be reduced. 
     In the present embodiment, the push bolts  12  and the pull bolts  14  are respectively provided in pairs, as in the first embodiment shown in  FIG. 1 , and the fixing bolts  16  are provided in a pair. However, the number of these bolts  12 ,  14  and  16  can also be suitably set. Further, the movable platen  30  and the tie-bars  41  may or may not be provided with a sliding portion each. Furthermore, a linear guide or slide guide can be used as the guide between the movable platen  30  and the base frame. In the case where the linear guide is used, it is bound in all other directions than the direction in which it normally moves back and forth. Thus, even if a pulling-up force is generated by the pull bolts  14 , it does not affect the guide function. Also in the case where the slide guide is used, it is only necessary to provide a lift prevention mechanism for preventing the pull bolts  14  from causing a lift.