Abstract:
A plurality of connecting rods are attached to an injection device located opposite a stationary platen on a base structure of an injection molding machine. The stationary platen is provided with a magnetism generating unit formed of a permanent magnet, and the connecting rods are provided with a magnetic body. As the magnetism generating unit and the magnetic body are attracted to each other by magnetism, a nozzle of an injection unit is brought into contact with a mold. By this structure, the stationary platen can be prevented from inclining during nozzle touch operation.

Description:
RELATED APPLICATIONS 
     The present application claims priority to Japanese Application Number 2012-270689, filed Dec. 11, 2012, 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 a nozzle touch mechanism of an injection molding machine, configured to prevent a stationary platen from inclining during nozzle touch operation. 
     2. Description of the Related Art 
     In a mold clamping mechanism section of an injection molding machine, a stationary platen and a rear platen are connected to each other by a plurality of tie-bars, and a movable platen is disposed between these platens for movement along the tie-bars. Further, stationary and movable mold halves of a mold are attached individually to facing machined surfaces of the stationary and movable platens, whereby mold clamping and opening operations are performed. 
     Furthermore, an injection unit is advanced and retracted relative to the stationary platen on a machine base, and a nozzle on the distal end of an injection cylinder of the injection unit is brought into close contact with a resin injection port of the stationary platen. In this state, a resin is introduced into the mold through the injection cylinder. A nozzle touch mechanism is provided to bring the nozzle into close contact with or separate it from the resin injection port of the stationary platen. The nozzle on the distal end of the injection cylinder is configured to be pressed against the resin injection port of the stationary platen by the nozzle touch mechanism during continuous molding operation. 
       FIGS. 11 and 12  are views showing the entire configuration of an injection molding machine comprising a nozzle touch mechanism section.  FIGS. 11 and 12  show states where the nozzle is untouched and touched, respectively. 
     The injection molding machine comprises a mold clamping section Mc and an injection section Mi on a machine base (not shown). The injection section Mi serves to melt a resin material (pellets) by heating and inject the molten resin material into a cavity of a mold  40  (comprising movable and stationary mold halves  40   a  and  40   b ). The mold clamping section Mc serves mainly to open and close the mold  40 . 
     The injection section Mi will be described first. A nozzle  2  is attached to the distal end of an injection cylinder  1 , and a screw  3  is inserted in the injection cylinder  1 . The screw  3  is provided with a resin pressure sensor  5 , such as a load cell, configured to detect the resin pressure based on a pressure on the screw  3 . 
     The screw  3  is rotated by a screw-rotation servomotor through a transmission mechanism  6  comprising pulleys, belt, etc. Further, the screw  3  is axially moved by an injection device advancing/retracting mechanism  8 . Reference numeral  4  denotes a hopper that supplies the resin to the injection cylinder  1 . 
     The following is a description of the mold clamping section Mc. The mold clamping section Mc comprises a rear platen  31 , movable platen  30 , tie-bars  32 , stationary platen  33  secured on a base structure  9 , crosshead  34 , and ejector mechanism  35 . The rear platen  31  and the stationary platen  33  are connected to each other by the tie-bars  32 , and the movable platen  30  is located so as to be guided by the tie-bars  32 . The movable and stationary mold halves  40   a  and  40   b  are attached to the movable and stationary platens  30  and  33 , respectively. If the crosshead  34  is advanced or moved to the right in  FIGS. 11 and 12 , the movable platen  30  is advanced to close the mold. 
     The following is a description of the molding operation by means of the injection molding machine. If a movable platen advancing/retracting motor (not shown) is rotated forward, a ball screw shaft  38  is rotated forward. Thereupon, the crosshead  34  threadedly engaged with the ball screw shaft  38  is advanced (to the right in  FIG. 1 ), so that the movable platen  30  is also advanced. 
     If the movable mold half  40   a  attached to the movable platen  30  contacts the stationary mold half  40   b  attached to the stationary platen  33  (or if the mold is closed), a mold clamping process is started. In the mold clamping process, a mold clamping force is generated in the mold  40  by further driving the movable platen advancing/retracting motor forward. Further, the cavity in the mold  40  is filled with the molten resin as a geared motor M 1  for injection device advance and retraction of the injection device advancing/retracting mechanism  8 , attached to the injection section Mi, is driven so that the screw  3  advances axially. 
     In a mold opening process, if the movable platen advancing/retracting motor is driven in the reverse direction, the ball screw shaft  38  is rotated in the reverse direction. As this is done, the crosshead  34  is retracted, a toggle mechanism is operated to bend, and the movable platen  30  is retracted toward the rear platen  31 . When the mold opening process is completed, an ejector pin (not shown) is pushed out of the movable mold half  40   a , whereby a molded article is ejected from the movable mold half  40   a.    
     If the nozzle touch mechanism in the state of  FIG. 11  is shifted to the state of  FIG. 12  so that a nozzle touch occurs, a moment equivalent to the product of a nozzle touch force and the distance from the lower surface of the stationary platen to the nozzle center is generated, possibly causing the stationary platen to tilt or overturn. 
     Japanese Patent Application Laid-Open No. 9-277306 discloses a nozzle touch mechanism configured so that a pair of rotation/linear motion conversion mechanisms are arranged axially symmetrically with respect to the center of an injection unit. In this configuration, the points of action of the respective screw shafts of the rotation/linear motion conversion mechanisms on the stationary platen are made axially symmetrical with respect to the point of action of a nozzle of an injection cylinder, so that the stationary platen can be prevented from being inclined or overturned by a nozzle touch. 
     In the nozzle touch mechanism described above, the stationary platen can be prevented from inclining or overturning as the point of action of a nozzle of an injection cylinder is made axially symmetrical with respect to the points of action of the respective screw shafts of the rotation/linear motion conversion mechanisms on the stationary platen, but connecting rods may hinder the maintenance of a swivel of the injection unit or the nozzle tip. Since a nozzle touch mechanism section is located near a front plate of an injection molding machine, moreover, the maintenance of a screw joint is not easy. 
     Furthermore, Japanese Patent Application Laid-Open No. 2001-315157 discloses a nozzle touch mechanism of an injection molding machine, which uses an electromagnet to bring a nozzle into contact with a sprue bushing of a mold by pressure bonding with a predetermined force. 
     Since this nozzle touch mechanism uses the electromagnet, electric current must always be kept flowing while the force is being generated. If electric power consumption increases or power failure occurs when generation of the force is required, the pressing force of the nozzle becomes so small that a resin inevitably flows out. 
     SUMMARY OF THE INVENTION 
     Accordingly, the object of the present invention is to provide a nozzle touch mechanism of an injection molding machine, capable of economically performing reliable nozzle touch operation while preventing a stationary platen from inclining or overturning. 
     The present invention relates to a nozzle touch mechanism of an injection molding machine, configured to press a nozzle on a distal end of a cylinder against a mold attached to a stationary platen with a predetermined nozzle touch force. The stationary platen is secured to a base structure of the injection molding machine such that a front plate of an injection device is located opposite the stationary platen and the cylinder is secured to the front plate. 
     A first aspect of the nozzle touch mechanism of an injection molding machine comprises an injection device advancing/retracting unit configured to advance and retract the injection device and a plurality of connecting members arranged at the sides of the cylinder and provided to the injection device. Further, one of the stationary platen and the connecting members is provided with a magnetism generating unit comprising a permanent magnet, and the other with a magnetic body. The magnetism generating unit is configured to generate magnetism to attract the magnetic body, thereby bringing the nozzle into contact with the mold. 
     A second aspect of the nozzle touch mechanism of an injection molding machine comprises an injection device advancing/retracting unit configured to advance and retract the injection device, a plurality of magnetic connecting members arranged at the sides of the cylinder and supported at one ends thereof by a proximal portion of the cylinder, and a magnetism generating unit comprising a permanent magnet provided on that part of the stationary platen which faces the other ends of the magnetic connecting members. The magnetism generating unit is configured to generate magnetism to attract the magnetic connecting members, thereby bringing the nozzle into contact with the mold. 
     A third aspect of the nozzle touch mechanism of an injection molding machine comprises an injection device advancing/retracting unit configured to advance and retract the injection device, a plurality of connecting members arranged at the sides of the cylinder and supported at one ends thereof by a proximal portion of the cylinder, a magnetic detachably-attaching plate detachably attached to the other ends of the connecting members, and a magnetism generating unit comprising a permanent magnet provided on that part of the stationary platen which faces the other ends of the connecting members. The magnetism generating unit is configured to generate magnetism to attract the magnetic detachably-attaching plate, thereby bringing the nozzle into contact with the mold. 
     A fourth aspect of the nozzle touch mechanism of an injection molding machine comprises an injection device advancing/retracting unit configured to advance and retract the injection device, a plurality of connecting members arranged at the sides of the cylinder and supported at one ends thereof by a proximal portion of the cylinder, a magnetism generating unit comprising a permanent magnet provided on the other ends of the connecting members, and a magnetic body provided on that part of the stationary platen which faces the other ends of the connecting members. The magnetism generating unit is configured to generate magnetism to attract the magnetic body, thereby bringing the nozzle into contact with the mold. 
     Each of the connecting members may comprise a connecting rod and a connecting rod adjusting member, and the length of the connecting member may be adjusted by the connecting rod adjusting member. 
     Each of the connecting members may be slidably supported by a base secured to the proximal portion of the cylinder, and be secured to a pressing plate by a spring. 
     The magnetism generating unit may comprise a variable-polarity magnet, a polarity switching coil arranged around the variable-polarity magnet and configured to change the polarity of the variable-polarity magnet, and a fixed-polarity magnet, and the permanent magnet may comprise the variable-polarity magnet and the fixed-polarity magnet. 
     According to the present invention, there can be provided a nozzle touch mechanism of an injection molding machine, capable of economically performing reliable nozzle touch operation while preventing a stationary platen from inclining or overturning. 
    
    
     
       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 perspective view illustrating Embodiment 1 of a nozzle touch mechanism of an injection molding machine according to the present invention; 
         FIG. 2  is a perspective view of the nozzle touch mechanism of  FIG. 1  taken from a different angle from that of  FIG. 1 ; 
         FIG. 3  is a perspective view illustrating Embodiment 2 of the nozzle touch mechanism of the injection molding machine according to the invention; 
         FIG. 4  is a perspective view illustrating Embodiment 3 of the nozzle touch mechanism of the injection molding machine according to the invention; 
         FIG. 5  is a diagram illustrating the magnetism generating unit of the nozzle touch mechanism of  FIG. 1  in a magnetized state; 
         FIG. 6  is a diagram illustrating the magnetism generating unit of the nozzle touch mechanism of  FIG. 1  in a demagnetized state; 
         FIG. 7  is an enlarged diagram showing a portion surrounded by broken line H in  FIG. 5 ; 
         FIG. 8  is an enlarged view showing a first example of a connecting rod adjusting member in the nozzle touch mechanism of  FIG. 3  and its surroundings; 
         FIG. 9  is an enlarged view showing a second example of the connecting rod adjusting member in the nozzle touch mechanism of  FIG. 3  and its surroundings; 
         FIG. 10  is an enlarged view showing a spring used in the nozzle touch mechanism of  FIG. 2  and its surroundings; 
         FIG. 11  is a view showing the entire configuration of an injection molding machine not in a nozzle touch state; and 
         FIG. 12  is a view showing the entire configuration of the injection molding machine in the nozzle touch state. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following is a description of some embodiments of a nozzle touch mechanism of an injection molding machine. An outline of the configuration of the injection molding machine is similar to that of the prior art example shown in  FIGS. 11 and 12 . 
     (Embodiment 1) 
     Embodiment 1 of the nozzle touch mechanism of the injection molding machine according to the present invention will be described with reference to  FIGS. 1 and 2 . 
     In  FIGS. 1 and 2 , reference numeral  1  denotes an injection cylinder  1 ;  10 , magnetism generating unit;  21 , connecting rods;  22 , detachably-attaching plates;  33 , stationary platen;  51 , front plate;  52 , plate;  53 , water jacket;  54 , base;  55 , spring; and  56 , guide. 
     The connecting rods  21  and the detachably-attaching plates  22  are symmetrically disposed in pairs on the left and right sides of the injection cylinder  1 . As in the conventional case, a nozzle touch mechanism section is advanced and retracted by utilizing torque fluctuation of a geared motor or servomotor or using a proximity switch. As the nozzle touch mechanism section is advanced, the injection cylinder  1 , along with the connecting rods  21  and the detachably-attaching plates  22 , moves (or advances) toward the stationary platen  33 . As the magnetism generating unit  10  and the detachably-attaching plates  22  are magnetically connected, a nozzle touch on the tip of a nozzle is made and a nozzle touch state is maintained. The configuration of the magnetism generating unit  10  will be described later. 
     In the nozzle touch state, the detachably-attaching plate  22  is pressurized by the spring  55  ( FIG. 2 ), besides being magnetically connected to the magnetism generating unit  10 . Thus, the nozzle tip can be reliably brought into close contact with a mold even if the length of the nozzle or cylinder is changed due to temperature expansion or the reaction force of a resin pressure. 
     The spring  55  used in the nozzle touch mechanism of  FIG. 2  and its surroundings will be described with reference to the enlarged view of  FIG. 10 . 
     In  FIG. 10 , reference numeral  21  denotes a connecting rod;  54 , base;  55 , spring;  56 , guides;  57  and  59 , bushes;  58 , nut;  60 , bolts; and  61 , pressing plate. One end of the connecting rod  21  is secured to the pressing plate  61  and slidably supported by the base  54  (forming a part of the injection cylinder  1 ), which is secured to the water jacket  53  or the front plate  51 . The spring  55  is wound around that part of the connecting rod  21  which is located between the base  54  and the pressing plate  61 . 
     Further, one end of the guide  56  on the side of the pressing plate  61  is larger in diameter than the other part, so that the pressing plate  61  is kept from moving toward the front plate  51 . 
       FIGS. 5 and 6  are diagrams illustrating the magnetism generating unit of the nozzle touch mechanism of  FIG. 1  in magnetized and demagnetized states, respectively. 
     In  FIGS. 5 and 6 , reference numeral  11  denotes electromagnetic coils;  12 , alnico magnets;  13 , neodymium magnets;  14 , magnetic cores;  21 , connecting rod; and  22 , detachably-attaching plate. 
     The alnico magnets  12  are disposed between the electromagnetic coils  11 . As shown in the enlarged diagram of  FIG. 7  corresponding to a portion surrounded by broken line H in  FIG. 5 , the electromagnetic coils  11  are configured so that coil wires  15  are wound around shafts that extend from the alnico magnets  12  toward the neodymium magnets  13 . In each two adjacent electromagnetic coils  11  in a pair, their respective coil wires  15  are oppositely wound. 
     The polarity of each alnico magnet  12  changes each time the electromagnetic coils  11  are energized. If the electromagnetic coils  11  in the demagnetized state are energized, the magnetized state shown in  FIG. 5  is established. In this state, the alnico and neodymium magnets  12  and  13  are made homopolar so that lines of magnetic force  16  are formed as indicated by broken lines in  FIG. 5 . Thereupon, the magnetic cores  14  become strong magnets to be connected to the detachably-attaching plates  22 . 
     The demagnetized state shown in  FIG. 6  is established as the electromagnetic coils  11  in the magnetized state are energized. If the demagnetized state is established, the lines of magnetic force  16  cease to appear on the surfaces of the magnetic cores  14 , as indicated by broken lines in  FIG. 6 . Thus, the detachably-attaching plates  22  are separated from the magnetism generating unit  10 . 
     (Embodiment 2) 
     Embodiment 2 of the nozzle touch mechanism according to the present invention will be described with reference to  FIG. 3 . 
     The nozzle touch mechanism shown in  FIG. 3  differs from the nozzle touch mechanism of Embodiment 1 ( FIG. 2 ) in that a connecting rod adjusting member  23  is provided between a connecting rod  21  and a detachably-attaching plate  22 . While an injection cylinder  1  and a nozzle  2  vary in length, the connecting rod adjusting member  23  serves to adjust the length of the connecting rod  21  so that the tip of the nozzle  2  can appropriately contact a stationary platen  33  of a mold. 
       FIGS. 8 and 9  are enlarged views showing the connecting rod adjusting member  23  in the nozzle touch mechanism of  FIG. 3  and its surroundings. 
     In the example of  FIG. 8 , the connecting rod  21 , detachably-attaching plate  22 , and connecting rod adjusting member  23  are penetrated individually by holes, and a thread groove is formed on the inner surface of the hole in the connecting rod  21 . A screw  24  having its proximal end portion secured to the detachably-attaching plate  22  penetrates the hole in the connecting rod  21 , and an external thread formed on the tip end of the screw  24  is threadedly engaged with the thread groove of the hole in the rod  21 . Thus, the length of a combination of the connecting rod  21 , detachably-attaching plate  22  and connecting rod adjusting member  23  can be adjusted by rotating the detachably-attaching plate  22  relative to the connecting rod  21  and the connecting rod adjusting member  23 . 
     In the example of  FIG. 9 , the distal end of the connecting rod adjusting member  23  is shaped so that it can be fitted into the connecting rod  21  in such a manner that an external thread formed thereon engages with an internal thread formed inside the connecting rod  21 . Further, the screw  24  having one end portion secured to the detachably-attaching plate  22  penetrates holes that penetrate the detachably-attaching plate  22  and the connecting rod adjusting member  23 . Also in the example of  FIG. 9 , the combination of the connecting rod  21 , detachably-attaching plate  22 , and connecting rod adjusting member  23  can be adjusted, although the range of the length adjustment is somewhat smaller than in the example of  FIG. 8 . 
     (Embodiment 3) 
     Embodiment 3 of the nozzle touch mechanism according to the present invention will be described with reference to  FIG. 4 . 
     The nozzle touch mechanism shown in  FIG. 4  differs from the nozzle touch mechanism of Embodiment 1 ( FIG. 2 ) in that the detachably-attaching plates  22  of Embodiment 1 are omitted and connecting rods  21  are magnetic members. Thus, according to this embodiment, the nozzle touch mechanism is not provided with the detachably-attaching plates  22 , so that the parts count can be reduced. 
     In the embodiments of the nozzle touch mechanism according to the present invention, the magnetism generating unit  10  is provided on the side of the stationary platen  33 , the magnetic detachably-attaching plates  22  are provided on the side of the connecting rods  21 , or the connecting rods  21  are provided as magnetic members. Alternatively, however, a magnetic member, e.g., a magnetic body, and the magnetism generating unit  10  may be provided, for example, on the sides of the stationary platen  33  and the connecting rods  21 , respectively, only if the magnetism generating unit  10  and the detachably-attaching plates  22  (or the connecting rods  21 , in the case where the detachably-attaching plates  22  is not used) are magnetically connected. 
     Although the neodymium and alnico magnets are used for the permanent magnet in the embodiments of the nozzle touch mechanism according to the present invention, moreover, they may be replaced with magnets of other types. In the present embodiment, furthermore, the magnetized and demagnetized states are switched in such a manner that the polarity of the alnico magnets is inverted by energizing the electromagnetic coils disposed around the alnico magnets. However, the polarity may also be changed by other means. 
     In the embodiments of the nozzle touch mechanism according to the present invention, moreover, the length adjustment of the connecting rod  21  in each connecting rod adjusting member  23  is performed by means of the screw  24  that penetrate the detachably-attaching plate  22 , adjusting member  23 , and connecting rod  21  or the screw that penetrates the detachably-attaching plate  22  and the adjusting member  23 . However, other means may be used for the length adjustment.