Injection apparatus

Abstract: A stationary plate (34) is fixed to a rear end of a cylinder section (12). A movable plate (36) is disposed such that it can be advanced and retracted relative to the stationary plate (34). An injection member (22) is disposed within the cylinder section (12) such that it can be advanced and retracted. The rear end of the injection member (22) is rotatably supported by the movable plate (36). A drive unit generates rotation when driven. Conversion units (52) disposed between the stationary plate (34) and the movable plate (36) and are adapted to convert a rotational force to a thrust force. A transmission unit is disposed between the drive unit and one of the conversion units (52) and is adapted to transmit a rotation generated by the drive unit (78) to the conversion unit (52). A synchronization unit is provided in order to synchronize the rotation of the one of the conversion units with rotations of the remaining conversion units. In this case, rotation generated by the drive unit (78) is transmitted via the transmission unit to one of the conversion units (52), and the rotation of the one conversion unit is synchronized with rotation of the remaining conversion units (52).

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to an injection apparatus. Description of the related art: Conventionally, in an injection molding machine, resin heated and melted in a heating cylinder is injected into a cavity of a mold apparatus under high pressure so that the cavity is filled with the resin. The molten resin is then cooled and solidified within the cavity so as to obtain a molded product. The injection molding machine includes a mold clamping apparatus and an injection apparatus. The mold clamping apparatus is provided with a stationary platen and a movable platen. The movable platen is advanced and retracted by a mold clamping cylinder, to thereby perform mold closing, mold clamping, and mold opening. The injection apparatus includes a heating cylinder for heating and melting resin supplied from a hopper, and an injection nozzle for injecting the molten resin. Further, a screw is disposed within the heating cylinder such that the screw can be rotated and can be advanced and retracted. When the screw is advanced by a drive section disposed at the rear end of the screw, the resin is injected from the injection nozzle, and when the screw is retracted by the drive section, the resin is metered. The drive section comprises a front plate for supporting the heating cylinder; a rear plate disposed a predetermined distance away from the front plate; guide bars disposed between and supported by the front plate and the rear plate; and a movable plate disposed to be slidable along the guide bars. The above-described screw is rotatably supported by the movable plate. A ball screw shaft and a ball nut are disposed between the front plate and the movable plate. When an injection motor is driven to rotate the ball screw shaft or the ball nut, the movable plate is advanced or retracted. FIG. 1 is a fragmentary sectional view of a drive section of a conventional injection apparatus; FIG. 2 is a side view of the drive section of the conventional injection apparatus; and FIG. 3 is a schematic diagram showing the concept of the drive section of the conventional injection apparatus. In these drawings, reference numeral 12 denotes a heating cylinder, 22 denotes a screw, 31 denotes a slide table slidably disposed on an unillustrated frame, and 34 denotes a stationary plate fixed to the slide table 31. The rear end (right end in FIG. 1) of the heating cylinder 12 is fixed to the stationary plate 34. Further, a movable plate 36 is disposed such that the movable plate 36 can be advanced and retracted relative to the stationary plate 34. A screw support shaft 38 is disposed at the approximate center of the movable plate 36 and is rotatably supported thereby via bearings 41 and 42. The rear end of the screw 22 is fixed to the screw support shaft 38, and a driven pulley 43 is fixed to the rear end of the screw support shaft 38. An unillustrated metering motor is attached to one side surface S1 of the movable plate 36, and an unillustrated drive pulley is attached to the output shaft of the metering motor. An unillustrated timing belt extends between and is wound, under tension, around the drive pulley and the driven pulley 43. The bearing 42 assumes the form of a thrust bearing in order to bear injection force that acts on the screw 22 upon injection. Parallel ball screw shafts 45 are disposed at a plurality of positions, for example, at two positions in the vicinity of the circumferential edge of the movable plate 36 and are rotatably supported by the movable plate 36 via bearings 46. Each of the ball screw shafts 45 has a screw portion 48 and a shaft portion 49 projecting from the rear end (right end in FIG. 1) of the screw portion 48. The shaft portion 49 penetrates a hole 36a formed in the movable plate 36 and extends rearward (rightward in FIG. 1), and a driven pulley 51 is attached to the rear end of the shaft portion 49. The screw portion 48 penetrates a hole 34a formed in the stationary plate 34 and extends forward (leftward in FIG. 1) to be screw-engaged with a ball nut 52 attached to the stationary plate 34. The ball nut 52 has a flange portion 53 at its front end (left end in FIG. 1) and is fixed to the stationary plate 34 by use of unillustrated bolts that penetrate the flange portion 53. Reference numeral 55 denotes a press plate for pressing the bearing 46. An injection motor 75 is attached to the approximate center of the other side surface S2 of the movable plate 36. A drive pulley 76 is attached to the output shaft 75a of the injection motor 75, and a timing belt 77 extends between and is wound, under tension, around the drive pulley 76 and the driven pulley 51. Next, operation of the injection apparatus having the above-described structure will be described. In a metering stage, when the screw 22 is rotated through driving of the metering motor, resin falls from an unillustrated hopper, enters the heating cylinder 12, and is advanced (moved to leftward in FIG. 1) within the heating cylinder 12. At this time, the screw 22 is retracted (moved to rightward in FIG. 1) while being rotated. An unillustrated heater is disposed to surround the heating cylinder 12 and is adapted to heat the heating cylinder 12 to thereby melt the resin within the heating cylinder 12. Therefore, when the screw 22 is retracted by a predetermined amount, while being rotated, molten resin for one shot is accumulated on the front side of an unillustrated screw head. In a subsequent injection stage, when the screw 22 is advanced through driving of the injection motor 75, the resin accumulated on the front side of the screw head is injected from an unillustrated injection nozzle attached to the front end of the heating cylinder 12 and is charged into a cavity of an unillustrated mold apparatus. In such a conventional injection apparatus, since the two ball screw shafts 45 are rotated at the same circumferential speed through driving of the single injection motor 75, the diameters of the respective driven pulleys 51 must be made equal to each other in order to make their reduction ratios equal. When the diameters of the driven pulleys 51 are increased in order to increase their reduction ratios, their inertia increases, with the result that the performance of the injection apparatus is lowered. Further, the timing belt 77 must have a longer length. When 1 represents an effective angle of engagement of the drive pulley 76 which establishes meshing engagement for transmitting rotation from the injection motor 75 to the timing belt 77, and 2 and 3 respectively represent effective angles of engagement of the driven pulleys 51 which establish meshing engagements for transmitting rotation from the timing belt 77 to the respective ball screw shafts 45, the following equation is satisfied. 1 + 2 + 3 = 360° When the drive-side effective angle 1 is small, as shown in FIG. 3, the rotation transmitted from the injection motor 75 cannot be transmitted to the timing belt 77 in a reliable manner. Therefore, rotation cannot be transmitted to the ball screw shafts 45 in a stable manner, resulting in a deterioration in the performance of the injection apparatus. The inter-axis distance L1 between the drive pulley 76 and the driven pulleys 51 or the widths of the driven pulleys 51, the drive pulley 76, and the timing belt 77 may be increased in order to increase the drive-side effective angle 1. However, when the inter-axis distance L1 is increased, the size of the injection apparatus increases, because the width of the movable plate 36 or the depth of the drive section must be increased. When the widths of the driven pulleys 51, the drive pulley 76, and the timing belt 77 are increased, noise generated when the injection motor 75 is driven at high speed increases. EP-A-0 427 866 discloses a two-plate type injection device provided to the injection molding machine, which is light in weight and low in manufacturing cost. This injection device is provided with an injection screw spline-connected to the screw sleeve rotatably supported by a pusher plate movable toward or away from a front plate, and the screw is connected, through a transmission mechanism, to a measuring motor fixed to the upper surface of the pusher plate so that the motor proper may be positioned between both plates. First and second ball screws rotatably supported by the front plate mesh with first and second ball nuts fixed to the pusher plate, respectively, and the motor proper is positioned between the front plate and pusher plate and connected to an injection motor fixed to the front plate, through transmission mechanisms, so as not to interfere with the proper measuring of the motor. EP-A-0 247 208 discloses an injection-molding machine which performs injection by driving a screw by means of servomotors, one or more ball screws, used to drive a screw in the axial direction, are driven by means of a plurality of servomotors, a position detector for detecting the screw position is provided only for one servomotor, and the servomotors are provided individually with power amplifiers, which are controlled by means of one control circuit so that the individual servomotors are controlled in synchronism with one another. EP-A-0 188 622 discloses a screw-rotating/injection mechanism of an injection molding machine comprising a screw shaft having a rear portion thereof connected to a drive shaft which is rotatably fixed to a pressure plate. A nut which is spline-coupled to a spline shaft constituting a rear portion of the drive shaft is driven by a screw rotating motor through a first transmission unit to rotate the screw shaft. A ball screw threadedly engaged with a ball nut, fixed to the pressure plate, is driven by an injection servo motor through a second transmission unit to move the screw shaft forward, thereby performing injection. EP-A-0 627 289 discloses a injection molding unit for use in an injection molding machine for processing synthetic material including a driving unit provided for axially displacing the injection molding unit in a direction of an injection axis. An injection unit, symmetrically arranged with respect to the injection axis, is provided for axially driving a rotatable feed screw placed inside a plasticizing cylinder. The injection unit is connected with an injection bridge. Since the driving unit is also arranged symmetrically with respect to the injection axis and is integrated in the injection molding unit, it is possible to realize a moment free nozzle contact point and a compact injection molding unit in a simple constructional way. The present invention is directed to overcoming one or more of the problems associated with the above prior art. The present invention is an injection apparatus and a method of operating the same as set forth in claims 1 and 15, respectively. Preferred embodiments of the present invention may be gathered from the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS: The structure and features of the injection apparatus 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 fragmentary sectional view of a drive section of a conventional injection apparatus; FIG. 2 is a side view of the drive section of the conventional injection apparatus; FIG. 3 is a schematic diagram showing the concept of the drive section of the conventional injection apparatus; FIG. 4 is a fragmentary sectional view of a drive section of an injection apparatus according to an embodiment of the present invention; FIG. 5 is a sectional view of a main portion of the injection apparatus according to the embodiment of the present invention; and FIG. 6 is a side view of the drive section of the injection apparatus 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. 4 is a fragmentary sectional view of a drive section of an injection apparatus according to an embodiment of the present invention; FIG. 5 is a sectional view of a main portion of the injection apparatus according to the embodiment of the present invention; and FIG. 6 is a side view of the drive section of the injection apparatus according to the embodiment of the present invention. In FIG. 5, reference numeral 12 denotes a heating cylinder serving as the cylinder section, and an injection nozzle 12a is attached to the front end (left end in FIG. 5) of the heating cylinder 12. A screw 22 serving as the injection member is disposed within the heating cylinder 12 such that the screw 22 can be rotated and can be advanced and retracted. The screw 22 has a screw head 22a at its front end, and extends rearward (rightward in FIG. 5) within the heating cylinder 12. The rear end (right end in FIG. 5) of the screw 22 is connected to a drive section, which will be described later. Also, a spiral flight 23 is formed on the peripheral surface of the screw 22, thereby forming a groove 26. A resin supply port 29 is formed at a predetermined position on the heating cylinder 12, and a hopper 30 is fixed to the resin supply port 29. Thus, resin 33 accommodated within the hopper 30 can be supplied to the resin supply port 29. The resin supply port 29 is formed at a position such that the resin supply port 29 faces the rear end portion (right-side end in FIG. 5) of the groove 26 when the screw 22 is positioned at a foremost position (leftward in FIG. 5) within the heating cylinder 12. Next, the drive section will be described. In FIG. 4, reference numeral 12 denotes the heating cylinder, 22 denotes the screw, 31 denotes a slide table slidably disposed on an unillustrated frame, and 34 denotes a stationary plate fixed to the slide table 31. The rear end (right end in FIG. 4) of the heating cylinder 12 is fixed to the stationary plate 34. Further, a movable plate 36 is disposed such that the movable plate 36 can be advanced and retracted relative to the stationary plate 34. A screw support shaft 38 is disposed at the approximate center of the movable plate 36 and is rotatably supported thereby via bearings 41 and 42. The rear end of the screw 22 is fixed to the screw support shaft 38, and an unillustrated driven pulley is fixed to the rear end of the screw support shaft 38. The bearing 42 assumes the form of a thrust bearing in order to bear injection force that acts on the screw 22 upon injection. An unillustrated metering motor serving as the first drive means is attached to one side surface S1 of the movable plate 36, and an unillustrated drive pulley is attached to the output shaft of the metering motor. A timing belt extends between and is wound, under tension, around the drive pulley and the driven pulley. Each of the drive pulley, the driven pulley, and the timing belt is of a toothed type. Parallel ball screw shafts 45 are disposed at a plurality of positions, for example, at two positions in the vicinity of the circumferential edge of the movable plate 36 and are rotatably supported by the movable plate 36 via bearings 46. Each of the ball screw shafts 45 has a screw portion 48 and a shaft portion 49 projecting from the rear end (right end in FIG. 4) of the screw portion 48. The shaft portion 49 penetrates a hole 36a formed in the movable plate 36 and extends rearward (rightward in FIG. 4), and a synchronization pulley 80 is attached to the rear end of the shaft portion 49. In the upper ball screw shaft 45, a driven pulley 81 is attached to the front end (left end in FIG. 4) of the shaft portion 49. Reference numeral 55 denotes a press plate for pressing the bearing 46. The screw portion 48 of each ball screw shaft 45 penetrates a hole 34a formed in the stationary plate 34 and extends forward (leftward in FIG. 4) to be screw-engaged with a ball nut 52 attached to the stationary plate 34. The ball nut 52 has a flange portion 53 at its front end (left end in FIG. 4) and is fixed to the stationary plate 34 by use of unillustrated bolts that penetrate the flange portion 53. A ball screw composed of the ball screw shaft 45 and the ball nut 52 serving as the conversion means is disposed between the stationary plate 34 and the movable plate 36 and is adapted to covert rotational force to thrust force. An injection motor 78 serving as the second drive means is attached to the top surface S3 of the movable plate 36. A drive pulley 79 is attached to the output shaft 78a of the injection motor 78, and a timing belt 82 extends between and is wound, under tension, around the drive pulley 79 and the driven pulley 81. The drive pulley 79, the driven pulley 81, and the timing belt 82 constitute the transmission means. Further, a tension roller 85 is rotatably disposed on the rear end surface S4 of the movable plate 36, and a timing belt 83 extends between and is wound, under tension, around the synchronization pulley 80 and the tension roller 85. The tension roller 85 is movably disposed, and tension is applied to the timing belt 83 in the direction of an arrow in FIG. 6. In the present embodiment, the tension roller 85 is disposed on the back-face-side of the timing belt 83 in order to apply tension to the timing belt 83 in the direction indicated by the arrow. However, a tension roller may be disposed on the front-face-side of the timing belt 83 in order to apply tension to the timing belt 83 in the direction opposite that indicated by the arrow. In this case, a toothed tension roller is not used for the tension roller 85. The synchronization pulley 80, the timing belt 83, and the tension roller 85 constitute the synchronization means for synchronizing rotation of one ball screw with rotation of the remaining ball screw(s). Each of the drive pulley 79, the synchronization pulley 80, the driven pulley 81, the timing belts 82 and 83, and the tension roller 85 is of a toothed type. Next, operation of the injection apparatus having the above-described structure will be described. In a metering stage, when the screw 22 is rotated through driving of the metering motor, the resin 33 falls from the hopper 30, enters the heating cylinder 12, and is advanced (moved leftward in FIG. 5) within the heating cylinder 12. At this time, the screw 22 is retracted (moved rightward in FIG. 5) while being rotated. An unillustrated heater is disposed to surround the heating cylinder 12 and is adapted to heat the heating cylinder 12 to thereby melt the resin 33 within the heating cylinder 12. Therefore, when the screw 22 is retracted by a predetermined amount, while being rotated, the molten resin 33, in an amount required for one shot, is accumulated on the front side of the screw head 22a. In a subsequent injection stage, the injection motor 78 is driven. The rotation of the injection motor 78 is transmitted to one of the ball screw shafts 45 via the drive pulley 79, the timing belt 82, and the driven pulley 81. The rotations transmitted to the respective ball screw shafts 45 are synchronized with each other via the timing belt 83 and the synchronization pulleys 80. Accordingly, as the ball screw shafts 45 rotate, the respective ball nuts 52 are advanced, so that the screw 22 is advanced via the movable plate 36. As a result, the resin 33 accumulated on the front side of the screw head 22a is injected from the injection nozzle 12a and is charged into a cavity of an unillustrated mold apparatus. In the injection apparatus having the above-described structure, in order to rotate the two ball screw shafts 45 through driving of the single injection motor 78, the timing belt 82 extends between and is wound around the drive pulley 79 and the driven pulley 81, and the timing belt 83 extends between and is wound around the synchronization pulleys 80 and the tension roller 85. Therefore, each of the timing belts 82 and 83 travels along a track of a substantially oval shape. In this case, an effective angle 11 of the drive pulley 79 which contributes to transmission of rotation from the injection motor 78 to the timing belt 82 is 180° or approximately 180 ° , and an effective angle 12 of the driven pulley 81 which contributes to transmission of rotation from the timing belt 82 to the corresponding ball screw shaft 45 is 180° or approximately 180 ° An effective angle 13 of each synchronization pulley 80 which contributes to synchronization of rotation transmitted from the shaft portion 49 becomes approximately 180 ° . Since the respective effective angles 11 - 13 are increased sufficiently, the rotation transmitted from the injection motor 78 can be reliably transmitted to the timing belt 83, and the rotations transmitted to the respective synchronization pulleys 80 can be synchronized in a reliable manner. As a result, the rotation can be transmitted to the ball screw shafts 45 in a stabilized manner, so that the performance of the injection apparatus can be improved. Since the output shaft 78a of the injection motor 78 is not required to be disposed at a location away from the movable plate 36, the size of the injection apparatus can be decreased. Since the widths of the drive pulley 79, the synchronization pulleys 80, the driven pulley 81, and the timing belts 82 and 83 are not required to be increased, noise generated when the injection motor 78 is driven at high speed can be decreased. Further, since the drive pulley 79, the driven pulley 81, and the timing belt 82 are disposed independent of the synchronization pulleys 80 and the timing belt 83, the specifications of the drive pulley 79, the driven pulley 81, and the timing belt 82 can be set to differ from those of the synchronization pulleys 80 and the timing belt 83. Therefore, the size of, for example, the driven pulley 81 can be decreased, and the corresponding inertia can be decreased. In the above described embodiment, the synchronization means is constituted by the synchronization pulleys 80, the timing belt 83, and the tension roller 85. However, the synchronization means may be constituted by a gear mechanism. In this case, a synchronization gear is attached to the rear end of each shaft portion 49, and an idle gear is disposed between the synchronization gears in order to transmit rotation. The idle gear is disposed such that all of the synchronization gears rotate in the same direction. It is emphasized that the present invention is not limited to the above-described embodiments. Numerous modifications and variations of these embodiments are possible in light of the spirit of the present invention, and they are not excluded from the scope of the present invention. Many advantages of the various aspects of the above described embodiments will be apparent to those skilled in the art. However, the scope of the invention is intended to be defined only by the following claims.

Claims: An injection apparatus comprising: a cylinder section; a stationary plate fixed to a rear end of said cylinder section; a movable plate movable relative to said stationary plate; an injection member disposed within said cylinder section such that said injection member can be advanced and retracted, a rear end of said injection member being rotatably supported by said movable plate; drive means for generating a rotation; and a plurality of conversion means each disposed between said stationary plate and said movable plate and adapted to convert a rotational force to a thrust force; characterized by : transmission means disposed between said drive means and only a first conversion means of said plurality of conversion means for transmitting the rotation generated by said drive means to said first conversion means; and synchronization means for synchronizing rotation of said first conversion means with rotation of the remaining conversion means, for transmitting a force between said conversion means and the remaining conversion means. An injection apparatus according to Claim 1, wherein said synchronization means comprises a plurality of synchronization pulleys and a timing belt extending between and wound around said synchronization pulleys. An injection apparatus according to Claim 2, wherein said timing belt contacts approximately 180° of a rim of each of said synchronization pulleys. An injection apparatus according to Claim 1, wherein said synchronization means comprises a plurality of synchronization gears and an idle gear disposed between said synchronization gears. An injection apparatus according to Claim 1, wherein said transmission means is disposed on said movable plate. An injection apparatus according to Claim 1, wherein said synchronization means is disposed on said movable plate. The injection apparatus according to Claim 1, wherein said transmission means includes a driving pulley connected to said drive means, a driven pulley connected to said first conversion means and a timing belt wound around said driving pulley and said driven pulley. The injection apparatus according to Claim 6, wherein said timing belt contacts approximately 180° of a rim of said driving pulley and said timing belt contacts approximately 180 ° of a rim of said driven pulley. An injection apparatus according to claim 1, wherein said cylinder section is a cylinder fixed to said stationary plate; said injection member is a screw, rotatably connected to said movable plate, disposed within said cylinder; said conversion means is at least first and second ball and screw mechanisms connecting said stationary plate to said movable plate, operable to move said movable plate relative to said stationary plate; said drive means is a motor having a rotatable output shaft; said transmission means transmitting a rotation of the output shaft of the motor to only said first ball and screw mechanism; and said synchronization means transmitting a rotation of the first ball and screw mechanism to at least said second ball and screw mechanism. The injection apparatus of Claim 9, wherein said transmission means includes a driving pulley connected to the output shaft of the motor, a driven pulley connected to a screw of the first ball and screw mechanism, and a belt wound around said driving pulley and said driven pulley. The injection apparatus of Claim 10, wherein said belt contacts approximately 180° of a rim of said driving pulley and contacts approximately 180° of a rim of said driven pulley. The injection apparatus of Claim 9, wherein said synchronization means includes a first pulley connected to a screw of the first ball and screw mechanism, a second pulley connected to a screw of the second ball and screw mechanism and a belt wound around said first pulley and said second pulley. The injection apparatus of Claim 12, wherein said belt contacts about 180° of a rim of said first pulley and contacts approximately 180° of a rim of said second pulley. The injection apparatus of Claim 9, wherein said synchronization means includes a plurality of synchronization gears and an idle gear disposed between said synchronization gears. A method of operating an injection apparatus including a cylinder fixed to a first support and a metering screw rotatable connected to a second support and disposed within said cylinder, the method comprising: (a) rotating a driving pulley with a motor; (b) rotating a first screw through a belt connection from said driving pulley to a driven pulley fixed to said first screw; characterized by : (c) rotating at least a second screw through a transmission connected between said first screw and said second screw at a different axial position with said belt connection; and (d) moving said first support relative to said second support via forces exerted by said first and second screws respectively on first and second nuts disposed about said first and second screws. The method of Claim 15, wherein step (c) includes rotating at least said second screw through a belt connection between a first synchronization pulley connected to said first screw and a second synchronization pulley connected to said second screw. The method of Claim 16, wherein step (c) includes rotating at least said second screw through a belt connection which winds around approximately 180 ° of a rim of said first synchronization pulley and which winds around approximately 180° of a rim of said second synchronization pulley. The method of Claim 15, wherein step (b) includes rotating said first screw through a belt connection which winds around approximately 180 ° of a rim of said driving pulley and which winds around approximately 180° of a rim of said driven pulley.

Inventors: HIRAGA NORITSUGU, NISHIO OKITO, HIRAGA, NORITSUGU, NISHIO, OKITO
Applicants: SUMITOMO HEAVY INDUSTRIES, SUMITOMO HEAVY INDUSTRIES, LTD.
Application year: 1999
Main classification: B29C45
IPC codes: B22D17, B29C45