Abstract:
An injection apparatus is disposed to be movable relative to the frame. A driver advances and retracts the injection apparatus. An energy absorption element is disposed between the driver and the frame and adapted to absorb mechanical energy relating to the nozzle touch force. A buffer member may also be disposed between the injection apparatus and the driver. In this case, variation in nozzle touch force due to overload can be adjusted by the action of the buffer member. Accordingly, when the buffer member is adjusted so as to reduce the variation in nozzle touch force due to overload, an excessively large nozzle touch force is not generated, so that breakage of the mold apparatus and the nozzle can be prevented. Further, resin is prevented from leaking from any clearance between the injection nozzle and the molding apparatus.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a nozzle touch apparatus for an injection molding machine. 
     2. Description of the Related Art 
     Conventionally, an injection molding machine comprises an injection apparatus and a mold apparatus. The injection apparatus is constructed such that resin heated and melted in a heating cylinder is injected from an injection nozzle. The injected resin is charged into a cavity of the mold apparatus. The molten resin is then cooled and solidified, and the mold apparatus is opened so as to permit removal of a molded article from the mold apparatus. 
     FIG. 1 is a conceptual diagram of a conventional injection molding machine, and FIG. 2 is a nozzle touch characteristic chart of the conventional injection molding machine. In FIG. 2, the horizontal axis represents an amount of deformation x, and the vertical axis represents a nozzle touch force f. 
     In FIG. 1, numeral  10  denotes an injection apparatus, numeral  11  denotes a heating cylinder, and numeral  13  denotes an injection nozzle provided at the front end (the left end in FIG. 1) of the heating cylinder  11 . An unillustrated screw is disposed within the heating cylinder  11  such that the screw can be rotated and can be advanced and retracted by a drive section  12 . 
     The screw extends rearwardly (rightward in FIG. 1) within the heating cylinder  11 , and the rear end (the right end in FIG. 1) of the screw is connected to the drive section  12 . The screw has a screw head at the front end thereof and a spiral flute formed on the peripheral surface of a metering portion of the screw, so that the flute defines a groove. 
     In the injection apparatus  10  having the above-described structure, during a metering stage, the drive section  12  is driven in order to retract the screw (rightward in FIG.  1 ), while rotating the screw in a forward direction. Consequently, pellet-shaped resin within an unillustrated hopper flows into the heating cylinder  11 , and is caused to advance (move leftward in FIG. 1) along the groove of the screw. At this time, the resin is heated and melted by an unillustrated heater and accumulated on the front side of the screw head. 
     Further, during an injection stage, the drive section  12  is driven in order to advance the screw, so that the resin accumulated at the front side of the screw head is injected from the injection nozzle  13  and is charged into an unillustrated cavity of a mold apparatus  14 . The mold apparatus  14  is composed of a stationary mold  15  and a movable mold  16 . The movable mold  16  is advanced and retracted by an unillustrated mold clamping apparatus in order to bring the movable mold  16  into contact with the stationary mold  15  and separate the movable mold  16  from the stationary mold  15 . Thus, mold closing, mold clamping, and mold opening are performed. 
     Subsequently, when the charging of resin into the cavity is completed, cooling water is caused to flow through an unillustrated cooling passage formed within the molding apparatus  14 , so that the resin is cooled. After the resin is solidified, the molding apparatus is opened so as to permit removal of a molded product. 
     In the injection molding machine, resin may leak from a clearance between the injection nozzle  13  and the stationary mold  15  while the resin is being charge into the cavity, unless the injection nozzle  13  is in contact with the stationary mold  15  with a predetermined pressing force or nozzle touch force. 
     In order to solve the above-described drawback, a nozzle touch apparatus is provided. The nozzle touch apparatus advances the injection apparatus  10  such that the injection nozzle  13  comes in contact with the stationary mold  15  with a predetermined nozzle touch force. Thus, a nozzle touch operation is completed. 
     In order to perform the nozzle touch operation, a support member  22  and a motor  25  serving as drive means are fixed to a frame  21  of the injection molding machine; a ball screw shaft  23  is rotatably supported by the support member  22 ; and a ball nut  24  is in screw-engagement with the ball screw shaft  23 . Further, the ball screw shaft  23  is connected to an output shaft  25   a  of the motor  25 , and the ball nut  24  is connected to the injection apparatus  10  via a spring  26 . A sensor  28  is disposed to face the spring  26 . The sensor  28  senses a displacement of a certain portion of the spring  26  due to deformation of the spring  26  (hereinafter referred to as a “deforming position”) to thereby detect an amount of deformation. 
     In this case, when the ball screw shaft  23  is rotated through drive of the motor  25 , the ball nut  24  is advanced from a retracted position, so that the injection apparatus  10  is advanced. Thus, the injection apparatus  10  reaches a nozzle touch position, and the injection nozzle  13  comes into contact with the stationary mold  15 . Subsequently, when the motor  25  is further driven in a state in which the injection nozzle  13  is in contact with the stationary mold  15 , the ball nut  24  is advanced against the urging force of the spring  26 , so that the spring  26  contracts by an amount corresponding to the distance advanced by the ball nut  24 . At this time, the injection nozzle  13  presses the stationary mold  15  with a force corresponding to the amount of deformation of the spring  26 . When the deformation amount of the spring  26  is represented by x, and a pressing force that the injection nozzle  13  exerts on the stationary mold  15  or a nozzle touch force is represented by f, a relationship as shown in FIG. 2 exists between the deformation amount x and the nozzle touch force f. Accordingly, the nozzle touch force f can be detected through detection of the deforming position of the spring  26 . When the deformation amount x reaches a preset value x 1  and thus a proper nozzle touch force f equal to a target nozzle touch force f 1  is generated, the motor  25  is stopped. 
     In the nozzle touch apparatus of the conventional injection molding machine, the injection apparatus  10  is connected to the ball nut  24  via the spring  26 . Therefore, if an external force is applied to the injection apparatus  10  due to impact caused by, for example, closing or opening of the molding apparatus  14  or injection of resin, the spring  26  is expanded or contracted, so that the deformation amount x varies. 
     Therefore, even when the ball nut  24  is accurately positioned, the sensor  28  may erroneously detect the deformation amount x due to expansion or contraction of the spring  26  caused by an external force. In this case, the nozzle touch force f is not accurately detected, with the result that a proper nozzle touch force f equal to the target nozzle touch force f 1  cannot be generated. For example, when the spring  26  is contracted, the nozzle touch force f becomes excessively large, resulting in breakage of the mold apparatus  14  and/or nozzle  13 . When the spring  26  is expanded, the nozzle touch force f becomes excessively small, resulting in resin leaking from the clearance between the injection nozzle  13  and the stationary mold  15 . 
     Since the spring  26  and the sensor  28  are attached to the injection apparatus  10 , the spring  26  and the sensor  28  are accommodated within an unillustrated casing of the injection apparatus  10 , which deteriorates ease of maintenance and management of the injection molding machine. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the above-mentioned problems in the conventional nozzle touch apparatus for an injection molding machine, to provide a nozzle touch apparatus for an injection molding machine which can accurately detect nozzle touch force, which can generate a proper nozzle touch force, and/or which facilitates work for maintenance and management of the injection molding machine. 
     A nozzle touch apparatus for an injection molding machine according to one example of the present invention comprises: a frame; an injection apparatus having an injection nozzle, said injection apparatus being disposed to be movable relative to said frame, moving means for moving said injection nozzle of said injection apparatus towards and away from a mold, said injection nozzle thus being movable to abut said mold with a nozzle touch force, and first energy absorption means disposed between said moving means and said frame for absorbing mechanical energy relating to the nozzle touch force. 
     Other aspects of the invention and their advantages will become apparent with reference to the following description of one detailed example of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The structure and features of the detailed example of a nozzle touch apparatus for an injection molding machine according to the present invention will be more readily appreciated as the same becomes better understood by reference to the accompanying drawings, in which: 
     FIG. 1 is a conceptual diagram of a conventional injection molding machine; 
     FIG. 2 is a nozzle touch characteristic chart of the conventional injection molding machine; 
     FIG. 3 is a conceptual diagram of a detailed example of an injection molding machine according to an embodiment of the present invention; and 
     FIGS. 4A and 4B are nozzle touch characteristic charts. 
     FIG. 5 illustrates one example of a tubular holding member and spring. 
     FIG. 6 illustrates one example of a buffer member. 
     FIG. 7 illustrates another example of a tubular holding member and spring. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     An embodiment of the present invention will next be described in detail with reference to the drawings. 
     FIG. 3 is a conceptual diagram of one example of an injection molding machine according to an embodiment of the present invention. 
     In FIG. 3, numeral  10  denotes an injection apparatus which is disposed to be movable relative to a frame  21  of the injection molding machine; numeral  11  denotes a heating cylinder (cylinder member); numeral  13  denotes an injection nozzle provided at the front end (the left end in FIG. 3) of the heating cylinder  11 ; and numeral  25  denotes a motor (drive means) for advancing and retracting (leftward and rightward in FIG. 3) the injection apparatus  10 . 
     An unillustrated screw (injection member) is disposed within the heating cylinder  11  such that the screw can be rotated and can be advanced and retracted by a drive section  12 . 
     The screw extends rearward (rightward in FIG. 3) within the heating cylinder  11 , and the rear end (the right end in FIG. 3) of the screw is connected to the drive section  12 . The screw has a screw head at the front end thereof and a spiral flute is formed on the peripheral surface of a metering portion of the screw, so that a groove is formed along the flute. 
     In the injection apparatus  10  having the above-described structure, during a metering stage, the drive section  12  is driven in order to retract the screw (rightward in FIG.  3 ), while rotating the screw in a forward direction. Consequently, pellet-shaped resin within an unillustrated hopper flows into the heating cylinder  11 , and is caused to advance (move leftward in FIG. 3) along the groove. At this time, the resin is heated and melted by an unillustrated heater and accumulated on the front side of the screw head. 
     Further, during an injection stage, the drive section  12  is driven in order to advance the screw, so that the resin accumulated at the front side of the screw head is injected from the injection nozzle  13  and is charged into an unillustrated cavity of a mold apparatus  14 . The mold apparatus  14  is composed of a stationary mold  15  and a movable mold  16 . The movable mold  16  is advanced and retracted by an unillustrated mold clamping apparatus in order to bring the movable mold  16  into contact with the stationary mold  15  and separate the movable mold  16  from the stationary mold  15 . Thus, mold closing, mold clamping, and mold opening are performed. 
     Subsequently, when the charging of resin into the cavity is completed, cooling water is caused to flow through an unillustrated cooling passage formed within the molding apparatus  14 , so that the resin is cooled. After the resin is solidified, the molding apparatus is opened so as to permit removal of a molded product. 
     In the injection molding machine, resin may leak from a clearance between the injection nozzle  13  and the stationary mold  15  while the resin is being charge into the cavity, unless the injection nozzle  13  is in contact with the stationary mold  15  with a predetermined nozzle touch force. 
     In order to solve the above-described drawback, the nozzle touch apparatus advances the injection apparatus  10  such that the injection nozzle  13  comes in contact with the stationary mold  15  with the predetermined nozzle touch force. Thus, a nozzle touch operation is completed. 
     In order to perform the nozzle touch operation, the nozzle touch apparatus has the following structure. A support unit  30  is disposed on the frame  21 . The support unit  30  includes a tubular holding member  31  fixed to the frame  21 , a spring  32  whose rear end is fixed to the holding member  31 , and a support member  33  fixed to the front end of the spring  32 . The holding member  31  restricts expansion and contraction of the spring  32 . The holding member  31  and the spring  32  are disposed between the frame  21 , and a ball screw shaft  23  and a ball nut  24  and serve as accumulation means for accumulating nozzle touch force f. 
     The support member  33  is provided with an unillustrated bearing and rotatably supports the ball screw shaft  23 . The ball nut  24  is in screw-engagement with the ball screw shaft  23 . The ball nut  24  and the ball screw shaft  23  constitute conversion means for converting rotational force to thrust force. Accordingly, rotational force generated by the motor  25  is converted to thrust force by the ball nut  24  and the ball screw shaft  23 , and the thrust force is transmitted to the injection apparatus  10 . Further, the ball screw shaft  23  is connected to an output shaft  25   a  of the motor  25 , and the ball nut  24  is connected to the injection apparatus  10  via a buffer member  36  such as a damper. 
     A sensor (deformation amount detection means)  28  is disposed adjacent to the spring  32 . The sensor  28  senses the deforming position of the spring  32  to thereby detect a deformation amount x. The sensor  28  supplies a detection signal to an unillustrated controller. The holding member  31  functions as a stopper that restricts the stroke of the spring  32  and the displacement of the support member  33  in order to prevent the spring  32  from deforming (e.g., contacting) by an amount greater than a preset amount. 
     When the ball screw shaft  23  is rotated through drive of the motor  25 , the ball nut  24  is advanced from a retracted position, so that the injection apparatus  10  is advanced. During this period, the spring  32  is prevented from deforming. For this purpose, a pre-load is applied to the spring  32  such that the spring  32  does not contract even when a compression force acts on the spring  32  due to friction resistance between the ball screw shaft  23  and the ball nut  24  or friction resistance of an unillustrated support mechanism that movably supports the injection apparatus  10 . 
     Thus, the injection apparatus  10  reaches a nozzle touch position, and the injection nozzle  13  comes into contact with the stationary mold  15 . Subsequently, when the motor  25  is further driven the support member  33  and the motor  25  are retracted (moved to the right in FIG. 3) against the urging force of the spring  32 , because advancement of the injection apparatus  10  is prevented because the injection nozzle  13  is in contact with the stationary mold  15 . 
     Accordingly, the spring  32  contracts by an amount corresponding to the retracted distance of the support member  33  and the motor  25 , and the urging force of the spring  32  (corresponding to the nozzle touch force of the injection nozzle  13  against the mold  15 ) increases by an amount corresponding to the deformation amount x of the spring  32 . Therefore, the nozzle touch force f can be detected through detection of the deformation amount x of the spring  32  by use of the sensor  28 . In order to detect the nozzle touch force f, an unillustrated nozzle touch force detection means is provided in the controller. Upon receipt of a detection signal from the sensor  28 , the nozzle touch force detection means detects the nozzle touch force f on the basis of the detection signal. When the deformation amount x reaches a preset value x 1 , as shown in FIG. 4, and thus a proper nozzle touch force f equal to a target nozzle touch force f 1  is generated, unillustrated drive stop means provided in the controller stops the motor  25 . 
     When the deformation amount x of the spring  32  reaches the preset value x 1 , the deformation of the spring  32  may be restricted by the holding member  31 , so that the spring  32  does not deform further. 
     During this period, the buffer member  36  is prevented from displacing. For this purpose, a pre-load is applied to the buffer member  36  such that the buffer member  36  does not contract even when the nozzle touch force f is applied to the buffer member  36  as a compression force. When an additional force is applied to the injection apparatus  10 , such as an external force due to impact caused by, for example, closing or opening of the molding apparatus  14  or injection of resin and the amount of movement of the injection apparatus  10  increases, the buffer member  36  displaces in order to absorb impact force. 
     FIG. 5 illustrates one example of tubular holding member  31  and spring  32 . In this example, spring  32  is a coiled wire disposed within tubular holding member  31 . The length of the tubular holding member is shorter than the length of spring  32  in its relaxed state so that spring  32  is compressed within tubular holding member  32  to apply a preload to spring  32 . Tubular holding member  31  may be positioned next to the support member  33  at a distance less than the length of the tubular holding member  31  so that the tubular holding member will abut support member  33  prior to spring  32  being fully compressed. In this example, spring  32  is prevented from deforming by an amount greater than a preset amount x 1 . The preset amount x 1  of deformation may correspond to the proper nozzle touch force. Any forces applied to the nozzle greater than the proper nozzle touch force may be absorbed by buffer member  36 . 
     FIG. 6 illustrates one example of buffer member  36 . A piston  60  is disposed within a cylinder  62  containing gas or fluid to create pneumatic cylinder or a hydraulic cylinder, respectively. In this example, the piston  60  is connected to drive section  12  and the hydraulic cylinder is connected to nut  24 . The gas or fluid within the cylinder  62  can exit piston  60  via outlet  64  to a pressure source/accumulator  66 . The piston  60  moves to an equilibrium position where the pressure exerted against the piston from one side is substantially equal to the force exerted from drive section  12 . By changing the initial pressure in the pressure source/accumulator  66 , a spring constant associated with the buffer member  36  can be changed as desired. 
     In FIG. 4A, line L 1  represents an urging force generated due to deformation of spring  32 . In FIG. 4B, line L 2  represents a buffering force generated due to deformation of buffer member  36 . Line L 3  represents a maximum value and line L 4  represents a minimum value of a range through which the inclination of line L 2  can be changed (the rate of change of the buffering force corresponding to a spring constant associated with the buffering member). 
     In this example, the position of the tubular holding member  31  is set to contact support member  33  at position x 1  which corresponds to a nozzle touch force of f 1 . Also, the preload applied to buffer member is set to the nozzle touch force of f 1 . In FIG. 4A, x 0  represents a deformation of spring  32  corresponding to a preload applied to spring  32 . In this example, the nozzle touch force f corresponds to deformations applied to spring  32  and buffer member  36 . That is, when spring  32  is deformed past x 0 : 
     
       
           f =( x )· k   32 +( y−y   0 )· k   36   
       
     
     where x is the deformation amount of spring  32 , k 32  is the spring constant of spring  32 , y is the deformation amount of buffer member  36 , y 0  is the deformation amount corresponding to the preload applied to buffer member  36  and k 36  is the spring constant associated with buffer member  36 . 
     Alternatively, the nozzle touch force may be expressed as: 
     f=x·k 32  when spring  32  is deformed between x 0  and x 1 , and 
     f=y·k 36  when spring  32  is deformed to position x 1 . It is emphasized that the above expressions for the nozzle touch force are only exemplary; preloads do not need to be applied, nor does the stopping by stopping member  31  need to correspond to the preload applied to buffer member  36  (spring  32  and buffer member  36  can both be deformed at the same time, or the preload of the buffer member can exceed x·k 32 ). However, it is emphasized that it is preferable to have the preload of the buffer member exceed the x·k 32 . 
     The nozzle touch force f can be adjusted through adjustment of the buffer member  36  performed in accordance with operation conditions. The inclination of line L 2  can be changed as needed. FIG. 4B illustrates a maximum value L 3  and a minimum value L 4  between which the slope of line L 2  may be varied. 
     For example, when the amount of movement of the injection apparatus  10  increases due to opening or closing of the mold apparatus  14 , the buffering force increases accordingly, with the result that the nozzle touch force f increases by an amount corresponding to the increase in the buffering force fa. In order to solve this problem, when the amount of movement of the injection apparatus  10  is large, the buffering member  36  is adjusted so as to reduce the slope of line L 2  to thereby prevent increase of the nozzle touch force f. 
     By contrast, when the hole diameter of the injection nozzle  13  is large, the pressure receipt area through which resin pressure is received increases, so that a large reaction force is applied to the injection nozzle  13  during injection. In this case, resin leaks from the clearance between the injection nozzle  13  and the stationary die  15  unless the buffering force fa is increased in accordance with the amount of movement of the injection apparatus  10 . In this case, the buffer member  36  is adjusted to increase the slope of line L 2 . 
     FIG. 7 illustrates another example of tubular holding member  31  and spring  32 . If this example were to be utilized with the example described in connection with FIG. 3, the tubular holding member  31  and the spring  32  should be positioned on the left side of support member  33  in FIG. 33 to thereby exert a pulling force on support member  33  rather than a pushing force. In the example of FIG. 6, a spring  32  is disposed within tubular holding member  32 . The spring extends from one end of the tubular holding member to a nut  40  positioned on a screw part  42  of fixing element  44 . Fixing element  44  extends through tubular holding member  31  and is fixed to frame  21 . A stopping member  46  is fixed onto fixing element  44  outside the tubular holding member  31 . 
     The position of nut  40  on screw element  42  is adjustable, thereby adjusting the maximum distance the spring  32  can expand and thus the preload applied to spring  32 . 
     It is emphasized that the structure of the spring  32  and buffering member  36  shown in FIGS. 5-7 are merely exemplary. Those skilled in the art will recognize that other types of springs, buffer members and other structure can be used in conjunction with this invention. The term “spring” as used in this application is considered to mean any elastic device which regains its original shape after being compressed or extended and should not be considered as merely a coil of wire. It is noted, therefore, that the example of the structure of buffer member  36  shown in FIG. 6 is also considered a spring. 
     Even when an external force is applied to the injection apparatus  10  with a resultant expansion or contraction of the spring  32 , the amount of expansion or contraction of the spring  32  is restricted by the holding member  31  and absorbed by the buffer member  36 . Accordingly, when an external force is applied to the injection apparatus  10  (e.g., due to moving a mold or an injecting of resin) the deformation amount x is unlikely to significantly change and the likelihood of improper control of the motor  25  is reduced. Thus, the nozzle touch force f can be accurately detected, and consequently, a proper nozzle touch force f can be generated. 
     In addition, since the sensor  28 , the spring  32 , and the holding member  31  are attached to the frame  21 , these components are located outside an unillustrated casing of the injection apparatus. Therefore, maintenance and management of the injection molding machine can be facilitated. 
     The present invention is not limited to the above-described embodiment. This embodiment is only intended to set forth only one detailed example. Numerous modifications and variations of this example are possible in light of the spirit of the present invention, and they are not excluded from the scope of the present invention. For example, spring  32  is described as accumulating a nozzle touch force by compression. It is apparent however, that fixing spring  32  at a position leftward with respect to support  22  would allow accumulation of a nozzle touch force by expansion of spring  32 . Further, many advantages of different aspects of the invention will be apparent to those skilled in the art. However, not all of these aspects are intended to be a required part of the invention as broadly defined. The scope and spirit of the invention are intended to be defined by the appended claims.