Nozzle touch apparatus for injection molding machine

Abstract: A nozzle touch apparatus for an injection molding machine comprises a frame; an injection apparatus having an injection nozzle, the injection apparatus being disposed to be movable relative to the frame; drive means for advancing and retracting the injection apparatus; conversion means for converting rotational force generated by the drive means to thrust force and for transmitting the thrust force to the injection apparatus; accumulation means disposed between the conversion means and the frame and adapted to accumulate nozzle touch force; and a buffer member disposed between the injection apparatus and the conversion means. 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 can be prevented. Further, in the case where a reaction force acting on the injection nozzle increases due to resin pressure during injection, when the buffer member is adjusted such that the nozzle touch force changes to a large extent, it becomes possible to prevent leakage of resin from the clearance between the injection nozzle and the mold apparatus.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a nozzle touch apparatus for an injection molding machine. 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 product 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 a deformation amount 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 rearward (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. Also, a spiral flight is formed on the peripheral surface of a metering portion of the screw, so that the flight forms 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. 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 mold apparatus 14, so that the resin is cooled. After the resin is solidified, the mold apparatus 14 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 charged 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. Before injection is started the nozzle touch apparatus advances the injection apparatus 10 such that the injection nozzle 13 presses 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 25a 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 by use of the sensor 28. When the deformation amount x reaches a preset value x1 and thus a proper nozzle touch force f equal to a target nozzle touch force f1 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 mold 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 f1 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. When the spring 26 is expanded, the nozzle touch force f becomes excessively small, resulting in leakage of resin 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. Attention is drawn to US-A-4676730 which describes a nozzle touch mechanism for urging a nozzle of an injection unit against a mold. The threaded portion of a ball screw of the mechanism is engaged with a ball nut fixed to a pressure plate for moving the injection unit through springs. When a predetermined flexure of the springs is generated to urge the nozzle against the mold with an appropriate urging force, the threaded portion is disengaged from the ball nut at that point. The threaded portion holds the injection unit at this position and urges and holds the nozzle against the mold by the flexure of the springs. Further, US-A-4299791 is mentioned which describes a method for the prevention of drooling from a plastic injection molding mold and injection nozzles. The method comprises the steps of varying a volume of a sprue in injection molding mold by movement of a plunger in a nozzle touch member inserted into the sprue, automatically returning the plunger previously moved by the nozzle touch force to its original position as the nozzle touch force decreases when the nozzle moves away after injection molding has been carried out, and increasing the sprue volume equal to an amount of movement thereof more than when injection is made to reduce the residual pressure to the extent that no drooling is introduced while maintaining said nozzle in contact with said nozzle receiver. According to the present invention, a nozzle touch apparatus for an injection molding machine as set forth in claim 1 is provided. Preferred embodiments are recited in the dependent claims. 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, and 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 which facilitates work for maintenance and management of the injection molding machine. To achieve the above object, a nozzle touch apparatus for an injection molding machine according to the present invention comprises a frame; an injection apparatus having an injection nozzle, the injection apparatus being disposed to be movable relative to the frame; drive means for advancing and retracting the injection apparatus; conversion means for converting rotational force generated by the drive means to thrust force and for transmitting the thrust force to the injection apparatus; accumulation means disposed between the conversion means and the frame and adapted to accumulate nozzle touch force; and a buffer member disposed between the injection apparatus and the conversion means. 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 can be prevented. Further, in the case where a reaction force acting on the injection nozzle increases due to resin pressure during injection, when the buffer member is adjusted such that the nozzle touch force changes to a large extent, it becomes possible to prevent leakage of resin from the clearance between the injection nozzle and the molding apparatus. In addition, since the accumulation means can be positioned outside the casing of the injection apparatus, work for maintenance and management of the injection molding machine are facilitated. Further, the buffer member can be adjusted in accordance with conditions during movement of the injection apparatus to thereby adjust variation in nozzle touch force. In another nozzle touch apparatus for an injection molding machine according to the present invention, the accumulation means comprises urging means for generating an urging force for changing the nozzle touch force, and restriction means for restricting the stroke of the urging means. In this case, even when the urging means expands or contracts due to an external force applied to the injection apparatus, the amount of expansion and contraction is restricted, so that the external force is absorbed by the buffer member. Accordingly, there can be reduced the possibility that the sensor for detecting the nozzle touch force causes erroneous detection, so that the nozzle touch force can be accurately detected. Consequently, a proper nozzle touch force can be generated. In still another nozzle touch apparatus for an injection molding machine according to the present invention, there are further provided nozzle touch force detection means for detecting the nozzle touch force; and drive stop means for stopping the drive means when the nozzle touch force reaches a target value. BRIEF DESCRIPTION OF THE DRAWINGS The structure and features of the nozzle touch apparatus for an injection molding machine according to the present invention will be 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 an injection molding machine according to an embodiment of the present invention; and FIG. 4 is a nozzle touch characteristic chart of the injection molding machine according to the embodiment of the present invention. 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 an injection molding machine according to an embodiment of the present invention; and FIG. 4 is a nozzle touch characteristic chart of the injection molding machine according to the embodiment of the present invention. In FIG. 4, the horizontal axis represents a deformation amount x, and the vertical axis represents a nozzle touch force f. 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. Also, a spiral flight is formed on the peripheral surface of a metering portion of the screw, so that a groove is formed along the flight. 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 mold apparatus 14, so that the resin is cooled. After the resin is solidified, the mold apparatus 14 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 charged 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, before injection is started, advances the injection apparatus 10 such that the injection nozzle 13 presses 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 (restricting means) 31 fixed to the frame 21, a spring (urging means) 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 25a 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 contracting or deforming 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 in a state in which the injection nozzle 13 is in contact with the stationary mold 15, the support member 33 and the motor 25 are retracted against the urging force of the spring 32, because advancement of the injection apparatus 10 is prevented. 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 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, 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 x1, as shown in FIG. 4, and thus a proper nozzle touch force f equal to a target nozzle touch force (a target value) f1 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 x1, the deformation of the spring 32 is 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 displace even when the nozzle touch force f is applied to the buffer member 36 as a compression force. When an external force is applied to the injection apparatus 10 due to impact caused by, for example, closing or opening of the mold 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. In FIG. 4, line L1 represents urging force generated due to deformation of the spring 32, and line L2 represents buffering force generated due to displacement of the buffer member 36. When the buffering force is represented by fa and the urging force is represented by fb, the nozzle touch force f can be expressed as follows. f = fa + fb Therefore, at the time of overload, a relationship as shown in FIG. 4 exists between the deformation amount x and the nozzle touch force f. The rate of change of the buffering force fa; i.e., the inclination of line L2, can be changed as needed. Therefore, the nozzle touch force f at the time of overload can be changed within a region between line L3 indicating a maximum value and line L4 indicating a minimum value. 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 fa 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 L2 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 L2. As described above, the nozzle touch force f can be adjusted through adjustment of the buffer member 36 performed in accordance with operation conditions. 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, there can be reduced the possibility that the sensor 28 erroneously detects the deformation amount x due to expansion or contraction of the spring 32. 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 10. Therefore, work for maintenance and management of the injection molding machine can be facilitated. The present invention is not limited to the above-described embodiments. Numerous modifications and variations of the present invention are possible, and they are not excluded from the scope of the present invention.

Claims: A nozzle touch apparatus for an injection molding machine comprising: (a) a frame (21); (b) an injection apparatus (10) having an injection nozzle (13), said injection apparatus (10) being disposed to be movable relative to said frame (21); (c) drive means (25) for advancing and retracting said injection apparatus (10); (d) conversion means (23, 24) for converting rotational force generated by said drive means (25) to thrust force and for transmitting the thrust force to said injection apparatus (10); said nozzle touch apparatus for an injection molding machine being characterized in further comprising: (e) accumulation means (31, 32) disposed between said conversion means (23, 24) and said frame (21) and adapted to accumulate nozzle touch force; and (f) a buffer member (36) disposed between said injection apparatus (10) and said conversion means (23, 24). A nozzle touch apparatus for an injection molding machine according to Claim 1, wherein said accumulation means comprises urging means (32) for generating an urging force for changing the nozzle touch force, and restriction means (31) for restricting the stroke of said urging means. A nozzle touch apparatus for an injection molding machine according to Claim 1 or 2, further comprising nozzle touch force detection means (28) for detecting the nozzle touch force; and drive stop means for stopping said drive means (25) when the nozzle touch force reaches a target value.

Inventors: EMOTO ATSUSHI, EMOTO, ATSUSHI
Applicants: SUMITOMO HEAVY INDUSTRIES, SUMITOMO HEAVY INDUSTRIES, LTD.
Application year: 1999
Main classification: B29C45
IPC codes: B29C45