DE10051101A1 - Drive system for the injection screw of a plastics injection molding machine has separate electromotors and gearing for the rotary and axial movements with a rack and pinion transmission - Google Patents

Abstract

The drive for the injection screw (4), for a plastics injection molding machine, has separate electromotors (A1,A2) for the rotary and axial screw movements. A rack overdrive has at least one double rack for the axial movements of the injection screw. The rotary and axial movements are combined in a drive unit (100). The drive for the injection screw at an injection molding machine can have two double racks as the overdrive, spaced apart and parallel to the rotary axis of the injection screw. The rack overdrive has angled teeth, on both sides of each double rack, pitched against each other in a mirror image to equalize the tooth forces and the inertia. The teeth profiles of the double racks and the toothed pinions are on a common plane. The pinions can be adjusted to equalize the forces in the direction of their rotary axes. The gearing for the rotary and axial movements are integrated into a single component group. The rotating and sliding mechanisms form a compact group, moving in a guide tube coaxial to the injection axis (41). The racks, at the drive side, are mounted at the bearing bushes of the screw coupling, which has two axial radial bearings and the bearing bush slides through a guide tube. The racks are linked to a guide strip by a closure flange, at the ends away from the injection screw, to pass through the guide tube. The racks have their teeth aligned outwards, so that the common working line of the rack drive is an extension of the injection screw. The rack drive motor has a gearing (45) with two outputs, or it is operated by two motors with vertically upright drive axes in relation to the injection screw drive. The rotary drive is through a wedge projection and a splined shaft for a sliding mounting linked to the drive motor. The splined shaft is mounted with a gearing (40) at the drive side, and rides with the wedge projection for the stroke length to transmit the rotary movement through a sleeve with the screw coupling. The wedge projection with a sleeve extends over the rack length when retracted. The splined shaft is flush with the screw shaft axis, with symmetrical or coaxial racks and sleeve. The racks are at a quadrilateral profile with teeth on two sides. At least one rack drive is used for the axial movements of the injection screw, as a twin-axis gearing. The working axis of the rack matches the rotary drive axis to rotate the injection screw in an advance action. The gearing for the rotary and axial movements of the injection screw have their own gear housings. The rotary drive gearing has the wedge projection and the splined shaft. The rack of the double-rack overdrive is mounted to the gear housing at the drive take-off side for the rotary movement. The gear housing, for the axial movement, is bonded to a frame of the injection assembly and the rotary drive gearing has additionally a sliding movement in relation to the injection unit. The rotary and axial drive gearing are on a powered injection unit with a sliding movement in relation to the machine columns, with a third drive (A3). The electromotor (A1) for the rotary movement is an asynchronous servo motor or a hollow motor. The electromotor (A2) for the axial movement is an alternating current synchronous servo motor, with electronic power control.

Description

The invention relates to an injection screw drive for a plastic injection molding machine, with one axis each for the rotary and for the axial movement of the Injection screw.

A number of successive processes are distinguished in plastic injection molding. Plastic is fed into the injection cylinder through a filling funnel. The rotating injection screw captures the raw material through the screw flights and moves it forward in the heated injection cylinder. The rotary movement of the screw flights continues to convey the plastic to the tip of the injection screw. Primarily through the geometry of the screw or through appropriate shear heat, the raw material is melted and arrives as a melt in a collecting area directly in front of the nozzle. Approximate values are that the heat of fusion is largely generated by mechanical work between the injection screw and the cylinder wall and the rest by the jacket heating. The melt builds up as the screw continues to rotate in the collecting space and pushes the injection screw backwards in its axial direction by increasing the volume in the collecting space. When the amount of liquid plastic required for a shot is ready in the collecting area, the worm drive is stopped. The non-return valve at the top of the screw is closed by the forward movement. The injection screw now takes on the function of an injection piston. In the classic state of the art, a hydraulic system, which is also referred to as a piston drive in the following, is used to inject the plastic compound into the mold. The piston drive pushes the entire worm forward as a pure axial movement. The injection screw, now acting as a pure piston, injects the melt through the nozzle into the cavities of the mold. The injection itself takes place in two phases. The first phase is the actual filling. The required pressure can rise towards the end of the filling phase up to the range of 2000 bar. After filling, the post-pressure phase follows, while the final pressure of the filling phase is maintained. To ensure the processes described for plastic injection molding, two fundamentally different drive types are required:

• - The axial drive of the plasticizing screw in the sense of a piston
• - The rotary drive of the plasticizing screw in the sense of a screw conveyor.

In the past, it was obvious that the piston drive was hydraulic and the Rotary drive to be carried out by an electric motor. The specific advantages of the two different forms of output can be optimally used. At hydraulic cylinders becomes the largest possible linear for a linear movement Displacement force generated without deformation. With electric motor drives on the other hand, generates a rotating force and stands as such with a corresponding Gear reduction available.

Figs. 1 and 2 show two typical solutions of the prior art. Fig. 1 shows a hydraulically / electrically combined, and Fig. 2 shows a so-called electrical solution. In Fig. 1, the axial movement of a hydraulic piston and the rotation is actuated by the axis of rotation of an engine.

Another route was taken with EP 451 294. For the injection movement of the Snail becomes a pure crank drive with a crank or toggle system in between a stationary plate, and one that can be moved to and from this Plate suggested. One crank is provided to implement a forward and a reverse rotation of the drive axle in a reciprocating motion of the Injection conveyor screw. The drive or overdrive for the axial movement of the Injection screw is used as an impact force between the fixed plate and the Auger used. The applicant is not aware of a solution according to EP 451 294 (corresponds to DE 69 01 8063) has been put into practice. The Print is aimed exclusively at the special use of a Crank drive for the injection screw conveyor. It was recognized that it can be difficult if a crank is operated near zero. The zero or Dead center is said to be in the proposed application for injection screws be avoided.

EP 427 438 shows as a further possibility the combination of a toggle lever system with a rack and pinion drive for the mold movement. A corresponding commitment for the axial drive of the injection screw is not known. Interesting is however, the proposal of an actual rack and pinion gearbox with a flange Drive motor. As in the technical colloquial language, is subsequently a single motor drive understood as a single "axis" in the sense of the motor axis. Accordingly, EP 427 438 suggests one axis of the form movement  Rack drive before. Such rack and pinion gearboxes have one in practice found considerable spread for the drive of the movable form.

The invention was based on the object, an advantageous concept for the axial and to develop a rotary drive for the injection screw. The goal was to get out of the Many of the known solutions are the best components for an economical one Manufacturing to combine for two the injector movements to create a structurally optimal drive concept.

The injection screw drive according to the invention is characterized in that it has at least one toothed rail overdrive for the axial movement, and as Double-axis gear is formed, the effective axis of the toothed rail overdrive coincides with the rotary drive axis for the rotary movement of the injection screw Right.

The new solution proposes two main things:

• - A rack drive in the frame
• - a double-axle transmission.

As will be explained in the following, the new solution allows two differences execution methods. Common to both is the direct assignment of two different gears, one drive being designed as a toothed rail overdrive and the effective axes of the two with the axis of the injection screws or one Extension of the same coincide.

The injection screw drive according to the first very inexpensive Solution is characterized in that the gear for the rotary movement and the gear for the axial movement each have their own gear housing, which preferably each form its own assembly. The huge advantage is that on the one hand two special gears are required, but on the other hand each for can be structurally optimally configured according to its own function. Both can be inexpensive or economical in the sense of a separate assembly produce advantageously without the one on the function of the other has negative repercussions. Because of the force transmission in both cases is also completely aligned with the axis of the injection screw an ideal introduction of force and an ideal force action and reaction game.  

The gear housing is preferred for the rotary movement and the Gearbox for axial movement on one opposite the machine stand displaceable and with a third axis drivable injection unit, wherein the gear housing for the rotary movement in addition to the injection unit is movable.

The toothed rail of the toothed rail overdrive is advantageously on the output side firmly with the gear housing for the rotary movement and the gear housing for the axial movement is firmly connected to a base frame of the injection unit. The whole injection unit bears in addition to the means for the own moving three subassemblies, namely the fixed ones Injection cylinder, together with the drive housing for the rotary movement relatively displaceable injection screw, as well as the drive housing for the axial Movement of the screw conveyor, which is preferably fixed on the injection unit is arranged. This solution is particularly suitable for module production with individual standard subassemblies.

The toothed rail overdrive has two toothed rails, each at a distance and parallel to the axis of rotation of the injection screw, and preferably with the tooth profile directed towards the outside in such a way that the line of action of the toothed drive is an extension the axis of rotation of the injection screw. The toothed rails are advantageous designed as a square profile with double-sided toothing and fixed on the drive side flanged the housing for the rotary movement.

A second embodiment is characterized in that the gear for rotative movement and the gear for the axial movement integrated in one common assembly are high. As will be shown, the second allows Solution an unexpected compactness, precisely because two drive axes one individual gears can be assigned, at least in the usual industrial Practice is not very common. Rather, a transmission is expected to be one motor drive or an axis one or many drives are provided. The The injection screw drive requires the two completely different drive types (axial and rotary). The surprising positive effects are now shown on the basis of particularly advantageous embodiments explained. The rack is spaced and parallel to an imaginary extension of the axis of rotation of the injection screw arranged, preferably two toothed rails symmetrically each at a distance and parallel to the axis of rotation of the injection screw and with the tooth profile to be arranged outside.  

EP 427 438 was, as it were, tainted with the idea of using a round rod or bumper. With that, however, the use for the spray side could could not be recognized or was blocked because it was at least mentally difficult it is conceivable to pierce the rack to drive another through the To provide rod through. In the preferred embodiment of the new solution the rotatably driven worm shaft between the two toothed rails carried out. The two toothed rails can be incorporated in a larger profile , or else the two are meaningfully connected in such a way that the There is room for the rotary exaggeration.

Advantageously, the turning and sliding mechanism is a compact assembly formed and in a guide tube aligned with the injection screw axis guided. The toothed rails are connected on the output side via a fixed connection Housing of the worm clutch part mounted. The worm clutch part of his On the drive side, each has an axial and radial bearing, the housing over one, two or more guide bands are mounted in the guide tube. The rotative Drive takes place via a spline hub and a spline shaft, which on the one hand interlock slidably and on the other hand connected to a motor transmission. The spline shaft is on the drive side in the gearbox and for the required stroke length in one Wedge hub slidably guided. The spline hub is fixed on the other side via a sleeve connected to the worm clutch. The spline extends with the sleeve in the essentially over the usable length of the tooth splints. The spline shaft is in itself aligned with the worm shaft axis. The sleeve and the racks are included arranged coaxially. The basic function of the injection screw requires a longitudinal ver shift or one to be determined depending on the size of the part to be sprayed Hubes, for a larger machine from e.g. B. 20 cm. By interlocking the two drives, the toothed rail as well as the spline shaft, only a minimum Overall length required. The second approach is therefore very short. The dental splints are on the end facing away from the injection screw via a End flange with a guide band in the guide tube. With the The configurations described can be combined extremely compact Push it into a piece of pipe, as it were, with central lubrication and against all sides Lubricant leakage can be easily sealed, and gives with a view Clean room technology is an ideal requirement. The two are preferred Toothed rails as double toothed rails, each with its own drive pinion, gear and Drive motor, in particular AC servo motors. The drive motors a computer or a corresponding power electronics  Control means associated with the movement, in particular the drive torques completely compensate.

The drive motors are with their axes in relation to the single-screw drive preferably mounted at the top. This allows the whole machine short and compact to build, at least as far as the injection unit is concerned. The As is known per se, the entire injection unit rests on guide rails, on the machine stand. For the movement of the whole unit preferably another drive concept is provided.

The invention will now be compared with the prior art and some embodiments explained with further details. Show it:

Fig. 1 and 2 two embodiments of the prior art;

FIGS. 3a and 3b are perspective view of an inventive Doppelachsantriebes with a; or two drive motors for the axial movement;

Fig. 4 is a longitudinal section IV-IV of Fig. 3a;

Figures 5a and 5b the stroke or axial movement based on a rack rail engine.

Fig. 6 is a section VI-VI of Fig. 4;

FIG. 7a is a solution having each a gear housing for axial and rotative movement of the injection screw;

Fig. 7b schematically shows a rack and pinion drive.

Fig. 1 shows schematically as prior art, as it were, a school example for the injection side of an injection molding machine. The centerpiece is an injection cylinder 1 into which raw material 3 , mostly in granular form, is fed via a filling funnel 2 . In the injection cylinder 1 there is a screw conveyor or injection screw 4 , which is mounted on the right side in a bearing 5 . The rotary movement of the injection screw is replaced by the axis A1 via a gearwheel 6 , and the axial injection movement (axis A2) is generated by a hydraulic piston 7 , which is movable in an hydraulic cylinder 8 by an axial displacement. The axial displacement is based on the desired shot quantity for the injection of a part, or the corresponding amount for multiple molds. On the far left, the injection cylinder 1 ends with a nozzle 10 , through which the molten plastic mass 11 is injected into the cavities 38 of the two mold halves 36 , 37 . The injection cylinder 1 is surrounded by heating packages 12 . The selectable spray stroke is shown with the dimension SpH, SptHmax. means the maximum spray stroke. The technology of the spraying process is assumed to be known. The “periphery” required for the hydraulics is only indicated by reference number 9 . The reference number 13 marks a pressure sensor (P) and the reference number 14 a speed sensor (VE). The piston 7 is controlled via a servo or proportional valve 15 . The required control pulses are output by a controller 16 or a machine control 17 . The rotary movement of the injection screw 4 is actuated by a drive motor 18 (referred to as axis A1). The axial movement is triggered by the hydraulic piston 7 or the piston rod 19 (axis A2). It can be seen that the two axes A1 and A2 are completely independent of one another, but have only the same output in common on the coupling piece 20 for the injection screw 4 .

The basic structure of the injection cylinder 1 is, as far as it concerns the area of the screw conveyor for Fig. 1 and Fig. 2 identical. The solution of FIG. 2 schematically shows an example of a purely electrical solution, the entire injection unit for feeding and removing the nozzle 10 from the injection mold being additionally moved with a motor 21 . The motor 18 (axis A1) drives the gearwheels 6 ′ for the rotary movement of the screw conveyor, and the motor 22 drives the gearwheels 23 and 24 for the piston movement or the axial movement of the injection screw 4 . The motion transmission can e.g. B. via a shaft 25 and ball screw 26 .

FIGS. 3a and 3b show in perspective two examples of the new solution. A double-axis gear 30 is attached to a base plate 31 . The entire injection unit 34 is slidably arranged on rails 32 on the machine stand 33 via an axis A3, for the nozzle infeed to the mold 36 arranged on a fixed mold carrier plate 35 analogously to FIG. 1. The mold 36 not shown in FIGS . 3a and 3b forms, together with a movable mold 37, the cavities 38 for the plastic mold to be injection molded. The striking in Fig. 3a are in addition to the double-axis gear 30 , the axes A1 and A2. Two motors A2.1 and A2.2 are provided for axis A2. A2 corresponds to the drive motor 18 of FIGS. 1 and 2. The drive motor 18 is flanged to the gear housing 42 via a gear 40 with an output, in alignment with the screw axis 41 . As axis A2, two identical drive motors 43 and 44 are also flanged to the gear housing 42 via a gear 45 . All three motors 18 , 43 and 44 each have a vertical motor shaft and therefore allow a very short design. The injection cylinder 1 is connected to the base plate 31 via a housing block 46 , so that the screw conveyor 4 can be driven both axially and rotatively by the double-axis gear via the coupling piece 20 which is freely accessible from the outside. The action or reaction forces are primarily closed via the base plate 31 .

The Fig. 3b has only one drive motor 44 with a gear 45 'to drive two toothed rails 65. The gear 45 'has two outlets accordingly.

FIGS. 4 and 5a and 5b show an example of a Doppelachsgetriebe in section IV-IV of Fig. 3a. In Figs. 4 and 5a, the rear position of the injection screw is shown in an extreme position, eg. B. as a service position or out of service position, or for the maximum possible screw reverse position or for the theoretically largest possible molded part, with maximum injection of the amount of plastic 11 according to SpH.max ( Fig. 1). Fig. 5b shows the other extreme position, at the end of each injection operation and in the phase of the dwell pressure. The worm clutch 20 is firmly screwed via a collar 50 and a shaft end 51 , a support collar 52 and a screw connection 53 to a sleeve 54 and is connected at the opposite end via a spline hub 55 to a spline shaft 56 , and the gear 40 for the rotary movement. The torque on the screw conveyor or injection screw 4 is thus transmitted directly from the spline hub 55 via sleeve 54 to the coupling piece 20 , regardless of the position of the spline hub 55 (with the length l) with respect to the spline shaft, as shown in FIGS. 5a and 5b can be seen. The stub shaft 51 is mounted in a bearing bush 59 via two strong radial / axial roller bearings 57 and 58 . The inner rings of the two bearings 57 , 58 are held between the shoulders 61 and 62 via support rings 60 , 60 ', with the clamping force generated by the sleeve 54 and thread 53 . The outer rings of the two bearings 57/58 are held in bores in the bearing bushing 59 with respective shoulders 63, 64, such that the axial force flow from the injection screw 4 directly over the greater bearing 57 and the bearing bush is guided on the toothed rail 65 59th The toothed rail 65 is rigidly connected to the bearing bush 59 by means of locking screws 66 , and is held at the opposite end by means of a fixation ring 67 and the inner bearing ring of the bearing 57 . The axial movement of the screw conveyor or the corresponding action and reaction forces are based on the two motors 43 , 44 , the gear 45 and two pinions 70 , 70 'via the two toothed rails 65 , 65 ', the bearing bush 59 , the bearings 57 and transmit the coupling piece 20 . The coupling piece 20 and stub shaft 51 are thus driven by the two axes A1 and A2 (or A2.1 / A2.2). The two main transmission elements, spline shaft overdrive 72 and toothed rail overdrive 71 , allow the two types of movement (axial, rotary) to be controlled independently and are combined in a gear block 72 , which is installed in a cylindrical bore 73 . In order to achieve complete power symmetry, the A2 axis is designed in two ways, with two coordinated motors, two gears, two pinions and two toothed rails. The toothed rails are, as indicated by XX, each arranged parallel and at the same distance from the screw axis 41 . The designation double-axis gearbox refers to the respective axes A1 and A2 for the rotary and the axial movements of the injection screw.

Fig. 6 shows schematically a cross section through the double-axis transmission. The Fig. 6 clearly shows the symmetry of all drives or power transmissions. The entire gear block 72 is guided via guide bands 74 in the bore 73 ( FIG. 4) and has a wiper 75 so that any leakage of lubricating oil from the interior of the gear is prevented. According to FIG. 6 the axes 76 perpendicular to the two toothed pinion, which has advantages in terms of use of space. The two axes should be parallel to each other, but can be inclined or horizontal. If there is enough space to the rear in the direction of the screw axis 41 , a motor 18 with a horizontal axis can also be arranged.

FIGS. 7a and 7b show a further very advantageous embodiment with two separate gears, a gear 80-screw for the rotative movement of the injection and a transmission 81 for the axial movement of the injection screw. The gear 81 is a rack and pinion gear with a gear housing 82 . With A2 the axis of the drive motor for the rack and pinion gear is designated. Two identical toothed pinions 83 , 84 drive a toothed rail 85 . The toothed rail is formed on a square profile and is held on the drive side by means of the two pinions 83 and 84 and on the drive side via a flange 86 on the housing 87 of the transmission 80 .

The example according to FIG. 7a shows a solution in which the toothed rail 85 is part of the gear 80 , which can be displaced relative to the base plate 31 via guide rails 88 , corresponding to the linear movement of the toothed rack 85 . The gear 81 , however, is firmly connected to the base plate 31 by means of screws 89 . It is important that both effective axes coincide with the axis of rotation 41 of the injection screw, both for the rotary and for the axial movement. The toothed rail gearbox, like the gearbox for the rotary movement, is designed as a completely independent gearbox, each with its own drive motor. The toothed rail 85 transmits the linear displacement force either directly via the housing 87 or via corresponding bearing parts of the drive wheel, with a corresponding configuration of the bearing.

Claims (12)

1. Injection screw drive for a plastic injection molding machine, each with an axis for the rotary and for the axial movement of the injection screw, characterized in that it has at least one toothed rail overdrive for the axial movement of the injection screw and is designed as a double-axis gear, the effective axis of the toothed rail overdrive with the Rotary drive axis for the rotary movement of the injection screw coincides. 2. Injection screw drive according to claim 1, characterized, that the gear for the rotary movement and the gear for the axial Have movement of the injection screw each with its own gear housing. 3. Injection screw drive according to claim 1 or 2, characterized, that the gear housing for the rotary movement and the gear housing for the axial movement on a movable with respect to the machine stand and a third axis drivable injection unit are arranged, the Gearbox for the rotary movement in addition to the injection unit is movable. 4. Injection screw drive according to claim 3, characterized that the toothed rail of the toothed rail overdrive is firmly connected to the Gearbox for the rotary movement the gearbox for the axial Movement is firmly connected to a frame of the injection unit.   5. Injection screw drive according to one of claims 1 to 4, characterized, that the toothed rail exaggeration two toothed rails, each at a distance and parallel to the Rotation axis of the injection screw and preferably with the tooth profile facing outwards directed, such that the line of action of the toothed drive is an extension of the The axis of rotation of the injection screw forms. 6. Injection screw drive according to one of claims 1 to 5, characterized, that the toothed rails on a square profile with double-sided toothing is formed, which is firmly on the output side to the housing for the rotary movement is flanged. 7. Injection screw drive according to claim 1, characterized, that the gear for the rotary movement and the gear for the axial Movement are integrated into a common assembly. 8. Injection screw drive according to claim 7, characterized, that the rotating and sliding mechanism is designed as a compact assembly and in a guide tube aligned coaxially to the injection screw axis is guided, the toothed rails on the output side via a fixed connection to the Bearing bush of the worm clutch part are stored. 9. Injection screw drive according to claim 7 or 8, characterized, that the rotary drive takes place via a spline hub and a spline shaft, which with are connected to a motor gearbox that the spline shaft on the drive side in the gearbox stored and guided at least for the required stroke length in a spline and which for transmission of the torque the splined hub with a fixed sleeve Worm clutch is connected, the splined hub with sleeve in the rear Position extends essentially over the length of the toothed rails, the spline is aligned with the worm shaft axis and the sleeve and the toothed rail are arranged coaxially or symmetrically thereto.   10. Injection screw drive according to one of claims 1 to 9, characterized, that the toothed rails on the end side facing away from the injection screw an end flange with a guide band is guided into the guide tube. 11. Injection screw drive according to claim 7, characterized, that the toothed rails from a drive motor with a gearbox with two Outlets, or can be driven by two drive motors, the Drive motors with their axes perpendicular to the injection screw drive are attached at the top. 12. Injection screw drive according to claim 1 or 7, characterized, that the injection screw is part of an injection unit with the injection cylinder Guide rails and slidable on the other drive axis Stand of the plastic injection molding machine is arranged.