PRODUCT EJECTING APPARATUS FOR INJECTION MOLDING MACHINES

Abstract: Product ejector for an injection moulding machine in which a movable platen is driven by a ball nut and screw system comprises an ejection rod which passes axially through and is in splined engagement with the movable platen, an ejection plate which is fixed to the rear end of the ejection rod and has a round depression in its centre, a spring urging the ejection rod and plate rearwards, and a pusher rod which is screwed into a bore portion in the front end of the movable platent drive ball screw and has a rounded front end which can contact the round depression in the ejection plate. The pusher rod moves integrally with the ball screw and its effective length can be adjusted by screwing it to different positions in the ball screw and retaining it by a retainer nut.

Description: The present invention relates to product ejectors for use in injection molding machines and, particularly, to a product ejector in a direct-acting type mold clamping system in which a ball screw is driven by a servomotor to move a moving platen fixedly mounted to a ball nut threadedly engaged with the ball screw, thereby carrying out mold clamping. In an injection molding machine, there is known a product ejector for removing a product from a mold, which is of such a type that, during rearward movement of a moving platen toward a rear platen, a rod fixed to the rear platen pushes an ejector plate, short of a point of time mold opening is completed, to project a product ejector bar fixedly mounted to the ejector plate, toward the mold mounted on the moving platen, thereby ejections a product from the mold. A product ejector is also known, which is of such a type that a driving source separate from a driving source for a mold clamping system is employed to drive a product ejector bar to project the same, thereby removing a product from a mold. A direct-acting type mold clamping system has been developed, in which a ball screw is rotated by a servomotor, to move a moving platen which is movable together with a ball nut threadedly engaged with the ball screw, to thereby carry out mold closing, mold clamping and mold opening. It is required for the above direct-acting type mold clamping system to set a length of the ball screw supported by a rear platen, in a considerably large value corresponding to a moving stroke of the moving platen. It is also necessary to prevent the ball screw and the platen from interfering with each other at a position where mold opening is completed. As a result, the spacing between the rear platen and the moving platen becomes long. For this reason, if the rod for pushing the product ejector bar mounted on the side of the moving platen is fixed to the rear platen, the rod must also be long, so that deflection might occur or a problem might arise as to strength of the rod. On the other hand, if an attempt is made to carry out driving of the product ejector bar without the use of such a long rod, a separate driving source for ejection of the product is required, making the injection molding machine expensive. JP-U-59 24311 discloses a product ejector in a direct-acting-type mold clamping system having the features of the preamble of accompanying claim 1. An ejector bar is acted on by a bar penetrating through the length of a movable ball screw, and is provided with an adjusting means for setting an amount of projection of the ejector bar. EP-A-0 090 863 discloses a mold clamping system for an injection molding apparatus corresponding to that of JP-U-59 24311. According to the present invention, there is provided a product ejector in a direct-acting-type mold clamping system for an injection molding machine, in which a motor is arranged to move a moving platen via a ball screw and ball nut mechanism, wherein a ball nut is threadedly mounted to a ball screw, thereby carrying out mold clamping, comprising:- a rod; an ejector bar arranged within a bore provided in said moving platen such that the ejector bar extends through the bore and is slidable; an ejector plate fixedly mounted to an end of said ejector bar on the side of the rod and arranged to be engageable with said rod; and a spring arranged between said ejector plate and said moving platen, for biasing said ejector bar toward said ball screw; characterised in that:- said moving platen is fixedly mounted to said ball nut; said rod is mounted to a forward end of said ball screw on the side of the moving platen; one of a forward end of said rod on the side of said ejector plate and a face of said ejector plate on the side of said rod is formed into a spherically convex shape, and the other is formed therein with a spherical recess engageable with and disengageable from said spherically convex shape; and engaging means in the form of one or more projections is provided on said moving platen and/or said ejector bar, arranged to engage with a corresponding groove or grooves on said ejector bar and/or said moving platen, respectively, so as to allow sliding but to prevent rotation of said ejector bar relative to said moving platen. An embodiment of the present invention may provide a product ejector in a motor-driven, direct-acting-type mold clamping system for an injection molding machine, in which a product can be ejected without the necessity of an additional driving source and with a simple structure, and by which it is possible to reduce a length of a rod for transmitting driving force to an ejector bar. As described above, the arrangement of the invention is such that the rod mounted to the forward end of the ball screw extending to a position near the moving platen pushes the ejector bar toward a mold just before completion of mold opening motion of the moving platen, to eject a product from the mold. By virtue of such an arrangement, the product can be ejected and removed without the use of a special driving source for ejection of the product and with a simple structure, and the rod can be reduced in length so that no particular consideration has to be given to deflection and strength of the rod. Reference will now be made, by way of example, to the single Figure which is a partially cross-sectional view of a principal portion of a product ejector according to an embodiment of the invention. In the Figure, the reference numeral 1 denotes a moving platen, and the reference numeral 2 designates a rear platen which is fixedly mounted to a base (not shown) of an injection molding machine. One of a pair of molds (not shown) is mounted on the moving platen 1, and the other mold is mounted on a stationary platen (not shown) which is fixedly secured to the base of the injection molding machine. Both edge portions of the moving platen have respective bores (not shown) formed therein. Tie bars 3 extending between the rear platen 2 and the stationary platen are inserted respectively through the bores in the moving platen 1 so that the moving platen 1 is supported for movement along the tie bars 3 to the right and left as viewed in the figure. The reference numeral 4 denotes a ball screw having an end portion, on the side of the rear platen 2, which is supported by the latter for rotation, but against axial movement. The end portion of the ball screw 4 is connected to a servomotor (not shown) mounted to the rear platen 2. The reference numeral 5 denotes a ball nut threadedly engaged with the ball screw 4. The ball nut 5 has a forward end which is fixedly attached to a rear end of a nut attachment 6 by means of bolts 16. The nut attachment 6 has a forward end which is fixedly mounted to a rear side of the moving platen 1 by means of bolts 16′. The nut attachment 6 has a cylindrical shape, and is formed such that an end of the nut attachement to which the ball nut 5 is attached is small in diameter, while an end of the nut attachment on the side of the moving platen is large in diameter. The nut attachment 6 is formed therein with a bore 7 through which the ball screw 4 passes and which extends along an axis of the nut attachment 6. A large space 8 is provided in the nut attachment 6 on the side of the moving platen. A product ejector bar 10 has a rearward end which projects into the space 8. The product ejector bar 10 slidably extends through a bore 9 provided in the moving platen 1 and is arranged in coaxial relation to the ball screw 4. An ejector plate 11 is fixedly mounted to the rearward end of the ejector bar. A spring 12 is arranged between the ejector plate 11 and the moving platen 1, for biasing the ejector plate 11 and the ejector bar 10 toward the ball screw 4. A splined section 10a is provided on an outer peripheral surface of a rearward half portion of the ejector bar 10, for preventing rotation of the ejector bar 10 and for guiding axial movement thereof. A spline nut 13 in slidable engagement with the splined section 10a is fixedly mounted to the moving platen 1. On the other hand, a threaded bore 14 is formed in the forward end portion of the ball screw 4 and extends along an axis thereof. A stroke adjusting rod 15 has a threaded section 15a which is threadedly engaged with the threaded bore 14. Alteration of the threadedly engaging position between the rod 15 and the ball screw 4 enables adjustment of an amount of projection (effective length) of the stroke adjusting rod 15 from the forward end face of the ball screw 4, in turn, an ejection stroke of the ejector bar 10. The stroke adjusting rod 15 has a forward end 15b which is formed into a spherically convex shape. On the other hand, a spherical recess 11a is formed in a portion of the above-mentioned ejector plate 11, which is confronted with the forward end portion 15b. The arrangement is such that when the moving platen 1 is moved rearwardly (to the left as viewed in the figure) to a predetermined position at mold opening, the spherically convex forward end 15b and the spherical recess 11a are brought into engagement with each other. Additionally, the reference numeral 17 denotes a nut for preventing loosening of the stroke adjusting rod 15. The operation of the ejector according to the embodiment will next be described. When mold closing and mold clamping are carried out, the servomotor, not shown, is driven rotatively in the normal direction to move the moving platen 1 in the right-hand direction in the figure. On the other hand, when mold opening is carried out, the motor is rotated in the reverse direction to move the moving platen 1 in the left-hand direction in the figure. That is, as the servomotor is driven rotatively in the reverse direction to rotate the ball screw 4 in the reverse direction, the ball nut 5 threadedly engaged with the ball screw 4 is moved in the left-hand direction in the figure along the axis of the ball screw 4. The moving platen 1 is also moved in the left-hand direction in the figure, through the nut attachment 6 fixedly mounted to the ball nut 5, thereby carrying out opening of the mold. Short of completion of the mold opening, the spherically convex forward end 15b of the stroke adjusting rod 15 is abutted against the spherical recess 11a in the ejector plate 11. As the moving platen 1 is further moved in the left-hand direction in the figure toward a position where the mold opening is completed, the forward end 15b of the stroke adjusting rod 15 pushes the ejector plate 11 to move the ejector plate 11 and the ejector bar 10 in the right-hand direction in the figure against the spring 13. As a result, the ejector bar 10 projects into the mold to eject a product therefrom. Meanwhile, although the stroke adjusting rod 15 rotates with rotation of the ball screw 4, the rotation of the stroke adjusting rod 15 is not transmitted to the ejector plate 11. In addition, since the ejector bar 10 is engaged with the spline nut fixedly mounted to the moving platen 1, through the splined section 10a, the ejector bar 10 is prevented from rotating. Accordingly, the ejector bar 10 does not also rotate. Thus, the ejector bar 10 does not mar a molded article at ejection. Further, if runout occurs on the ball screw 4 with respect to its axis during rotation of the ball screw, or it the stroke adjusting rod 15 is not correctly arranged in coaxial relation to the ball screw 4, the forward end 15b of the rod 15 would move while describing an eccentric circle. However, even if the forward end 15b moves while describing an eccentric circle, engagement of the rod 15 and the ejector plate 11 with each other through the spherically convex forward end 15b and the spherical recess 11a ensures that the ejector plate 11 and the ejector rod 10 are pushed axially by the rod 15 to eject a product. Additionally, the ejection amount of the ejector bar 10, that is, the ejection stroke is adjusted in such a manner that the threadedly engaging position of the stroke adjusting rod 15 with respect to the ball screw 4 is adjusted to alter the ejection amount of the stroke adjusting rod 15 from the end face of the ball screw 4. Subsequently, as the moving platen 1 is driven to move in the mold closing direction, the ejector plate 11 leaves the rod 15, so that the ejector plate 11 is returned to the initial position under the spring force of the spring 12. The above embodiment has been described as utilizing the spline engagement for prevention of rotation of the ejector bar 10 and for guide of movement of the same. In place of the spline engagement, however, either one of the moving platen 1 and the ejector bar 10 may be provided thereon with an elongated projection or projections, and the other may be provided therein with a groove or grooves with which the projection or projections are engaged. Further, the forward end of the rod 15 and the opposed face of the ejector plate 11 have been described as being formed respectively into the spherically convex and concave shapes, but, in contrast with this, may be formed respectively into concave and convex shapes.

Claims: 1. A product ejector in a direct-acting-type mold clamping system for an injection molding machine, in which a motor is arranged to move a moving platen (1) via a ball screw and ball nut mechanism, wherein a ball nut (5) is threadedly mounted to a ball screw (4), thereby carrying out mold clamping, comprising:- a rod (15); an ejector bar (10) arranged within a bore provided in said moving platen (1) such that the ejector bar (10) extends through the bore and is slidable; an ejector plate (11) fixedly mounted to an end of said ejector bar (10) on the side of the rod (15) and arranged to be engageable with said rod (15); and a spring (12) arranged between said ejector plate (11) and said moving platen (1), for biasing said ejector bar (10) toward said ball screw (4); characterised in that:- said moving platen (1) is fixedly mounted to said ball nut (5); said rod (15) is mounted to a forward end of said ball screw (4) on the side of the moving platen (1); one of a forward end of said rod (15) on the side of said ejector plate (11) and a face of said ejector plate (11) on the side of said rod (15) is formed into a spherically convex shape (15b), and the other is formed therein with a spherical recess (11a) engageable with and disengageable from said spherically convex shape; and engaging means (13) in the form of one or more projections are provided on said moving platen (1) and/or said ejector bar (10), arranged to engage with a corresponding groove or grooves on said ejector bar (10) and/or said moving platen (1), respectively, so as to allow sliding but to prevent rotation of said ejector bar (10) relative to said moving platen (1). 2. A product ejector for an injection molding machine according to claim 1, wherein said forward end of said ball screw (4) is formed with a threaded bore (14), and said rod (15) has a threaded section (15a) threadedly engaged with said threaded bore (14), so that a threadedly engaging position between said rod (15) and said threaded bore (14) is adjustable. 3. A product ejector for an injection molding machine according to claim 1 or 2, wherein said motor is a servomotor. 4. A product ejector for an injection molding machine according to claim 3, wherein said rod (15) projects from the front end of said ball screw (4) toward said ejector plate (11) by a predetermined length which is set to a value sufficient to bring said rod (15) in engagement with said ejector plate (11) when said moving platen (1) reaches a position short of completion of mold opening. 5. A product ejector for an injection molding machine according to claim 4, wherein said predetermined length of said rod (15) is of short enough length to eliminate any substantial deflection of said rod (15) during operation. 6. A product ejector for an injection molding machine according to any preceding claim, wherein said engaging means comprises a spline nut (13) fixedly mounted to said moving platen (1), and wherein said ejector bar (10) has on its outer peripheral surface, a splined section (10a) engaged with said spline nut (13).

Inventors: INABA, YOSHIHARU, TOKUNAGA, SHIGEO
Applicants: FANUC LTD.
Application year: 1987
Main classification: B29C45
IPC codes: B29C45