NL1023634C2 - Injection molding machine, has grooved drive shaft cooperating with ribbed transmission rolls and screw threaded transmission casings - Google Patents

Abstract

The drive shaft (7) contains circular grooves for cooperating with ribbed rolls in two transmissions. The inside of the transmission casing has screw threading which cooperates with ribs. The casings are rotated using two drive units (8,9), the rotation direction and speed of which care regulated so that the drive shaft and screw can be rotated and/or displaced in axial direction. An injection-molding machine (1) has a screw extending into a cylinder (3) with a feed opening (4) and injection nozzle (5). The screw is connected to a drive shaft housed inside a drive casing (6) and connected in turn to a first and second electric drive unit. The drive shaft has a series of parallel circular grooves for engaging with two transmissions, each one comprising a number of rolls with peripheral grooves defined by ribs. The drive shaft extends through the transmission casing housing the rolls and the ribs engage with the grooves in the shaft. The inner mantle surface of the casing has a screw threading which cooperates with the ribs and the pitch direction for the threading inside one casing differs from that for the threading inside the other casing. The casing for the first transmission can be rotated by the first drive unit and the casing for the second transmission can be rotated by the second drive unit. The machine has a control system for regulating the rotation direction and speed of the two drive units so that the drive shaft and screw can be rotated and/or displaced in the axial direction. The power for axial displacement and rotation is provided by both drive units An independent claim is also included for an injection-molding process using this machine, in which the rotation direction and speed of the two drive units is varied so that the screw is rotated and/or axially displaced according to a chosen pattern and/or a desired axial force is generated.

Description

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Title: Injection molding device and method for using such an injection molding device.

The invention relates to an injection-molding device provided with a screw extending in a cylinder, which cylinder is provided with a filling opening and with a nozzle, the screw being connected to a drive shaft accommodated in a drive housing, which drive shaft is in driving connection with a first and a second electric drive unit.

The invention also relates to a method for manufacturing an injection-molded product using such an injection-molding device.

Such an injection-molding device is known from EP-A-0 882 564. With the known injection-molding device, the first electric drive unit serves for the rotation of the screw spindle. The second electric drive unit serves for the translation of the screw spindle.

In connection with the required injection speed, the most commonly used drive for the axial movement of the screw is a hydraulic drive. However, hydraulic drives have a number of disadvantages including the following: - the rigidity of a hydraulic drive system is much lower than that of an electric drive system.

Oil pressure pulsations often occur in the system, which does not improve the axial positioning accuracy; - a hydraulic drive is much dirtier than an electric drive; the static losses of a hydraulic drive are much greater than with electric drives; hydraulic pressure must also be supplied when the propeller is stationary, which requires energy; These problems have been solved with the injection molding apparatus according to EP-A-0 882 564. However, the known electrically driven injection molding apparatus I has a number of disadvantages, among which the following: for the axial movement, the total power must be supplied by the one drive unit, the drive unit in question must therefore have a considerable power; I - for the rotational movement, the total power I must be supplied by the other drive unit, the respective drive unit I must therefore have a considerable power; When the axial movement is started, the drive unit serving for that movement must be brought into rotation from standstill; this leads to transition in the frictional resistance I (static frictional resistance to dynamic frictional resistance) of the bearing and transfer of the relevant drive unit; such a transition in frictional resistance makes accurate force feedback via motor current measurement impossible; - between the drive units, the drive shaft and the drive housing there are a number of complicated force transfer mechanisms I (D1, D2, D3, £ 1) which convert the rotation into either exclusively an axial movement, or exclusively a rotation movement, or a combination of I an axial and a rotational movement of the screw; such transmission mechanisms lead to a loss of accuracy and H also consume power; The heavy engines and the associated transmissions lead to a considerable mass that must be set in motion each time; The mass inertia is therefore high and the dynamic behavior, in particular I the control speed of the known device, therefore leaves something to be desired.

These problems are essentially solved by the proposal from the European patent application EP-A-1 083 036 and the European patent application EP-A-1 215 029. In those known injection molding machines, the drive shaft is provided with two sections of thread with a reverse rush. A drive nut engages each section, which drive nuts are each independently driven by an electric drive motor.

The drawback of the devices described from EP-A1 083 036 and EP-A-1 215 029 5 is that the production of the drive shaft is particularly critical since the quality and the mutual position of the two thread sections are very close. The known drive shafts of EP-A-1 083 036 and EP-A-1 215 029 are therefore particularly expensive. A further drawback of the known devices is that the drive nuts are provided with internal screw thread which engages the screw thread sections of the drive shaft. For a certain length of linear displacement, therefore, a corresponding thread length on the drive shaft is required, plus the required outflow of the thread. This therefore leads to the disadvantage that the known drive units must have a longer length than strictly necessary for the required axial stroke.

It is an object of the invention to provide an electric injection molding apparatus without the above-described disadvantages of the known electric injection molding apparatus while maintaining the advantages thereof. The invention also contemplates a method for using such an injection molding device

To this end, the injection molding apparatus of the type described in the preamble is characterized according to the invention in that the drive shaft is provided with a series of circular, parallel circumferential grooves, wherein two transmissions engage on the parallel circumferential grooves, which transmissions are each provided with a number of cylindrical rollers which are provided with circumferential grooves bounded by ridges, said rollers being enclosed in a cylindrical chamber of a transmission housing through which the drive shaft extends and wherein the backs of the rollers engage on the parallel circumferential grooves of the drive shaft, wherein 4 λ λ λ λο ni 4 the inner jacket surface of the housing is provided with a screw thread, the backs of the rollers in the assembled state also engaging the respective screw thread of the housing, the direction of the thread of the housing of the one transmission deviating from the urgent direction of the thread of the housing of the other transmission, wherein the housing of the one transmission is rotatably drivable by the first drive unit and wherein the housing of the other transmission is rotatably drivable by the second drive unit, wherein the injection-molding device is provided with a control adapted to 10 controlling the direction of rotation and the speed of rotation of the first and the second drive unit, such that the drive shaft and hence the screw spindle can be rotated in use and / or translated in the axial direction, the power required for translation being provided by both drive units being and wherein the power required for rotation is supplied by both drive units.

With such a device the drive shaft can be made much simpler in that it only needs to be provided with a number of parallel concentric grooves. As a result, the shaft is much less expensive and the tolerances of the shaft are less critical. Moreover, the drive shaft may be shorter in length than in the known devices in that I does not require a spout for thread. The drive shaft with drive units and transmissions can therefore be made more compact.

According to a further elaboration of the invention, the housing of each transmission can be provided with two parts which are adjustable relative to each other in the axial direction, so that the rollers can be accommodated in the axial direction without play between the drive shaft and the housing. As a result of such a shared structure of the housing of a transmission, the accuracy of the parallel grooves on the drive shaft can remain limited, which benefits the cost price of the drive shaft.

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The circumferential grooves of the rollers may be parallel grooves extending substantially perpendicular to the longitudinal axis of the rollers with ridges located therebetween. In that embodiment, however, it is preferable for the rollers to be provided with at least one gear wheel which engages a gear wheel mounted on the drive shaft in order to positively transfer rotation of the rollers to the drive shaft.

In an alternative embodiment, the circumferential grooves of the rollers may be in the form of a thread. In such an embodiment, the gear wheels on the rollers and the drive shaft can be dispensed with.

In the method of the type described in the preamble, according to the invention, the direction of rotation and the speed of rotation of the first and second drive units are varied such that the drive shaft and hence the screw are rotated in use and / or translated in the axial direction according to the invention. a desired pattern and / or while exerting a desired axial force, wherein the power required for axial translation is supplied by both drive units and wherein the power required for rotation is supplied by both drive units.

With such a device and method, the force required for the axial movement is supplied by two drive units. The force for the rotational movement is also supplied by these two drive units. If only an axial displacement of the screw is desired without rotation, both drive units rotate in opposite directions at the same speed, at least when the pitch of the thread in the housing of the one transmission is directed equally and in the opposite direction to the pitch of the thread in the home of the other shipment. If only a rotation of the screw is desired, the two drive units rotate in the same direction at the same speed. Axial displacement in combination with rotation of the screw is obtained by suitably combining the direction of rotation and the rotational speeds of 1 to 36 34 I 6 I with the two drive units. The sum of the torque of the two drive units provides the output torque and the difference of the torque of the two drive units provides the axial force via the transmission to the drive shaft.

With a desired maximum axial force, the drive units in the device according to the invention can therefore have substantially half the power of the drive unit for axial displacement in the known device. This I also applies to the rotation. So it comes down to the fact that the drive units in the device according to the invention can be substantially half as heavy as the device known from the aforementioned European publication. This also implies that the thermal load of the drive as a whole is better distributed over the housing. A simple convective cooling or a very small-sized water cooling can therefore suffice. That cooling is a problem appears from the aforementioned European publication EP-A-0882564. Furthermore, the distribution of the load over two drive units has the consequence that I mass inertia in relation to the torque to be realized by the I drive units of the device according to the invention is considerably more favorable than that of the known device. The axial displacement, which I must in particular take place during the high-speed injection, can therefore take place faster with the device according to the invention and requires less energy. Moreover, fewer deceleration and acceleration forces occur, so that a better control is obtained on the load of drive units for the purpose of generating the injection force and the plasticizing force. Since, during the injection, the I drive units rotate in opposite directions, at least when the first and the second threads have an opposite pitch direction, both motors have an opposite reaction torque. As a result, there is little or no external reaction torque, so that the suspension of the drive housing relative to the outside world can be made relatively light. An additional advantage is that the same drive units can be used, which is advantageous for maintenance, stock and therefore also for cost reasons.

According to a further elaboration of the invention, the control is adapted to make the injection molding apparatus go through a plasticizing phase, an injection phase and optionally an emphasis phase.

In the plasticizing phase, the screw is rotated and moved away from the nozzle in the axial direction. When sufficient liquid plastic is available, the injection phase follows in which the screw passes through a fast axial movement in the direction of the nozzle. During the injection phase, the mold to which the nozzle of the cylinder is connected is filled. Then, during the hardening of the plastic in the mold, the possible emphasis phase is completed. This compensates for shrinkage that occurs in the mold during curing because, if necessary, refilling of the mold with plastic takes place as a result of the fact that a certain pressure is maintained in the cylinder at the nozzle location.

According to a further elaboration of the invention, the control of the first and the second drive unit in the plasticizing phase and the optional emphasis phase is based on force feedback, wherein the control of the first and the second drive unit in the injection phase is based on position feedback.

During the injection phase, accurate dosing of a certain volume in the mold is of the utmost importance. Particularly in the case of injection molding of CDs and DVDs, in which use is made of molds that are not completely closed and in which the filling pressure is not a measure of whether the mold is completely filled, such a position-controlled injection phase is of great advantage. Incidentally, other products are also conceivable in which a partially opened mold is used, which therefore requires dosing. 8 volume is particularly critical. During the plasticization phase and the emphasis phase, it is precisely the maintenance of a certain pressure on the liquid plastic that is important. Because the control combines both control principles with each other, an injection-molding device is obtained which has the desired control behavior in all the 5 phases mentioned.

The control for control on the basis of force feedback as an input signal can herein measure the electric current consumed by the first drive unit and the electric current consumed by the second drive unit 10, the control being adapted to controlling the filling pressure according to a desired pattern on the basis thereof.

According to a second, alternative further elaboration of the invention, the injection-molding device can be provided with force sensors, such as for example piezo-electric elements or strain gauges, which measure a force exerted by the screw, the force sensors being connected to the control for force feedback, wherein the control is adapted to control the filling pressure according to a desired pattern on the basis thereof.

In the first variant in particular, it is important that there is a relatively direct coupling between the motor current required by the drive units and the force supplied by the screw. That is, the number of transmissions between the drive units and the screw should be minimal. With the injection molding apparatus according to the present invention, this can be realized by firmly connecting the housing of the transmission to the rotor of the relevant drive unit.

According to a further elaboration of the variant in which the force feedback takes place on the basis of motor current measurement, it is particularly favorable if the pitch of the first and second threads in the transmissions is such that the axial force experienced by the 9 screw spindle in use can be accurate. are derived from the drive current consumed by the first and the second drive unit.

In the plasticizing phase, the direction of rotation is constant and the drive units rotate continuously. As a result, there are no transitions from static to dynamic frictional resistance in the system and such a transition therefore does not contribute to the hysteresis in the motor current-driven power feedback. Because of this and because the pitch of the drive shaft is large, it is possible to very accurately derive the plastic pressure from the differential currents of both motors in order to subsequently only adjust the rotational speed of the two motors in order to achieve the correct thrust for plasticization.

The drive units preferably each comprise a servomotor, the control being adapted to position-control the servomotors. Modern servomotors are equipped with motor angle encoders, which motor angle encoders can be used for position control of the screw during, for example, the injection phase. As a result of the particularly direct transmission between the servomotors and the drive shaft, an axial position control with a very high resolution is still obtained using the motor angle encoders. Moreover, with such servomotors, use can be made of standard "high performance servo controllers" which have excellent control behavior and in which the occurrence of control deviations is practically excluded.

In order to obtain a compact injection-molding device, it is preferred that the first and the second drive unit are arranged coaxially. Moreover, as a result of this, during the injection phase the external torque supplied by the two motors is canceled out against each other if the pitch of both screws is opposite, so that the resulting external torque is nil.

In order to be able to move the nozzle away from the cylinder of the injection mold, the drive housing is, according to a further elaboration of the invention, mounted on a carriage which is provided with a, preferably I electric drive for displacing the I in axial direction. 5 drive housing and the associated cylinder.

Further elaborations of the invention are described in the subclaims and will be further explained below with reference to the drawing.

Figure 1 shows a side view of an injection molding apparatus according to the state of the art, more in particular according to EP-A-1083 036; Figure 2 shows a cross-sectional view of the drive unit for an injection-molding device according to the state of the art, more particularly I according to EP-A-1 215 029; Figure 3 shows a side view of the drive unit of an exemplary embodiment of an injection molding apparatus according to the invention; Figure 4 shows a sectional view along line IV-IV from Figure 3; Figure 5 shows a partial sectional view of a first exemplary embodiment of a transmission with drive shaft of an injection molding apparatus according to the invention; Figure 6 shows a second exemplary embodiment of a transmission with drive shaft of an injection molding apparatus according to the invention; and figure 7 shows a cross-sectional view along line VII-VH of figure 6.

For an exhaustive description of Figures 1 and 2, reference is made to EP-A-1083 036 and EP-A-1215 029, respectively. For both known I devices, the drive shaft is provided with two sections with I threads, the pitch direction of the thread in one section I is opposite to the pitch direction of the thread from the other I section. Such a drive shaft is particularly expensive to manufacture because of the high tolerances that the relevant thread sections 11 have to meet. Moreover, the known drive shafts are relatively long because of the required outflow of the thread for the drive nuts engaging on the thread.

The exemplary embodiment shown in figures 3 and 4 shows an injection molding apparatus 1 provided with a screw 2 extending in a cylinder 3. The cylinder 3 is provided with a filling opening 4 for feeding in plastic granulate and with a nozzle 5 which can be connected to an injection mold. The now liquid plastic from the cylinder 3 is pressed into the mold via the nozzle 5. The screw 2 is connected to a drive shaft 7 accommodated in a drive housing 6. The drive shaft 7 is in driving communication with a first and a second electric drive unit 8 and 9. For the manner in which the rotation of the drive units 7 and 8 is transmitted reference is made to figures 5 and 6 on the drive shaft 7.

Figure 2 schematically shows a control 14 which is adapted to control the direction of rotation and the speed of rotation of the first and second drive unit 8 and 9, respectively, such that the drive shaft 7 and thus the screw 2 can be rotated in use and / or can be translated in the axial direction. The power required for axial translation is supplied by both drive units 8, 9. The power required for the rotation is also supplied by both drive units 8, 9.

The drive housing 6 is mounted on a schematically shown slide 16 which is provided with a, preferably electric drive 17 for displacing the drive housing 6 and the associated cylinder 3 in axial direction. Thus, the nozzle 5 can be moved away from an injection mold. and moved there.

In order to keep the screw 2 and the drive shaft 7 manageable during manufacture, in the present embodiment these parts are designed as separate parts which are mutually connected

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I 12 I connected by means of a coupling 18. The coupling 18 I is designed as a breaking coupling. This offers the advantage that the risk of damage to the screw 2 is reduced. After all, when the forces exerted on the screw by the drive shaft 7 become too great, the breaking coupling 18 breaks and no more forces are exerted on the screw 2 and / or drive shaft 7. It is noted that the invention also comprises a drive shaft 7 and screw 2 which are designed as a one-piece, integral part.

Under very exceptional circumstances it may happen that, as a result of a malfunction in the control, the drive shaft is undesirably moved at high speed in an axial direction. Damage to the injection molding apparatus could occur. In order to prevent this, the exemplary embodiment shown is provided with an axial brake 19 which is mounted on the drive shaft 7 and which comes into effect in the event of undesired axial displacements of the drive shaft 7 due to control errors. The brake 19 shown is provided of a ball 20 mounted on the drive shaft 7 which is slidable relative to the shaft 7 over the permitted length of the axial stroke of the drive shaft 7. The slidability is limited by two stops 21, 22.

The ball 20 is accommodated in a bush 23 which is fixedly connected to the drive housing 6. The ball 20 can only move in the bush 23 under plastic deformation of the bush 23. Thus a certain braking distance I is realized which is short enough to prevent damage due to collision and the resulting delay forces.

In the present exemplary embodiment, the control 14 is adapted to cause the injection molding apparatus 1 to pass through a plasticizing phase, an injection phase and an emphasis phase. In the plasticizing phase I a portion of plastic is made sufficiently liquid by rotating the screw 2 and at the same time slowly moving it away from the nozzle 5.

When the required amount of liquid plastic is available, the liquid is rapidly injected into the mold via the nozzle 5 in the injection phase by moving the screw 2 at a high speed in the direction of the nozzle 5. When the mold is filled with the desired volume of liquid plastic, the emphasis phase follows in which the liquid plastic in the mold is kept under pressure, so that shrinkage occurring in the mold is compensated by refilling. To this end, in the present exemplary embodiment, the control 14 of the first and the second drive unit 8, 9 in the plasticizing phase and the emphasis phase is based on force feedback. In the injection phase, the control 14 of the first and the second drive unit 8, 9 is based on position feedback.

It is preferable for the control on the basis of force feedback to have the control determine as input signal the electric current consumed by the first drive unit 8 and the electric current consumed by the second drive unit 9. Based on the motor flow measurement 15, the controller 14 can control the filling pressure according to a desired pattern.

On the other hand, it is also possible for the injection-molding device 1 to be provided with at least one force sensor 15, such as, for example, a piezo-electric element or a number of strain gauges, which measures a force exerted by the screw 2. The force sensor 15 is connected to the controller 14 for the purpose of force feedback. The controller 14 is adapted to control the filling pressure according to a desired pattern on the basis thereof.

In the present exemplary embodiment, the drive units 8, 9 are each designed as a servo motor 8, 9 which are arranged coaxially. The servomotors are each provided with a stator 8a, 9a and a rotor 8b, 9b. The rotors 8b, 9b are each fixedly connected to a housing of a transmission, which will be explained in more detail below. The control 14 is arranged for position-controlled control of the servomotors 8, 9. As already indicated above, the control 14 is also arranged for force-controlled control of the servomotors 8, 9.

Figure 5 shows schematically a part of the drive shaft of a first exemplary embodiment according to the invention. For the sake of clarity, only one transmission is shown, although, as may be seen from the above, two such transmissions must be present. The drive shaft 7 clearly visible on its circumference is provided with parallel circumferential grooves 10 which extend in planes which are substantially perpendicular to the axis of the drive shaft 7. A portion of a transmission housing 11 of the transmission is also shown.

As can be seen clearly from Figure 7, the transmission housing 11 comprises a cylindrical chamber 12 through which the drive shaft 7 extends. Between the inner casing surface of the transmission housing 11, which defines the cylindrical chamber 12, there are a number of substantially cylindrical rollers 13. In the exemplary embodiment of Figure 5, these cylindrical rollers 13 are provided with substantially parallel circumferential grooves 26 extending in planes perpendicular to the longitudinal axis of the respective roller 13. In the exemplary embodiment of Fig. 5, the rollers are further provided with at least one gear wheel 24 which is in engagement with a gear wheel 25 on the drive shaft 7. This gear wheel transmission 24.25 serves for the rotary drive of the drive shaft 7. The axial displacement is effected by the said circumferential grooves 26 and those circumferential grooves defining ridges 27 on the rollers 13 which on the one hand engage inner thread 28 which is arranged on the inner jacket surface of the transmission housing 11 and, on the other hand, to the parallel circumferential grooves 10 of drive shaft 7. Each I transmission housing 11 is fixedly connected to or forms part of the rotor I 8b, 9b of the drive unit 8, resp. 9 and are therefore rotatably driven by the respective drive units 8, 9.

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In an alternative embodiment of the transmission shown in Fig. 6, the rollers 13 are provided with thread 29 instead of parallel circumferential grooves 26 and ridges 27 defining these grooves. This thread 29 is on the one hand in engagement with the parallel grooves 10 on the drive shaft 7 and on the other hand with the internal thread 28 of the relevant transmission housing 11 on the other. In this embodiment, both the axial displacement and the rotational displacement of the drive shaft 7 can be effected by rotation of the transmission housings 11. Optionally, a transmission casing 11 can still consist of two axially adjacent parts which are mutually adjustable in the axial direction. A play-free confinement in the axial direction of the rollers 13 relative to the transmission housing 11 can thus be realized.

Preferably the pitch of the internal thread of one transmission housing 11 is on the left and of the other transmission housing (not shown) on the right or vice versa. It is furthermore preferred here that the pitch of the left-hand and right-hand thread is such that the axial force experienced by the screw 2 in use can be accurately derived from the drive unit current consumed by the first and second drive units 8, 20 and 9, respectively. .

It will be clear that the invention is not limited to the exemplary embodiment described, but that various modifications are possible within the scope of the invention as defined by the claims.

For example, all phases within a cycle can only be realized on the basis of position feedback, so that the movement of the screw is position-controlled not only in the injection phase but also in the plasticizing phase and the emphasis phase. When using a left-hand and right-hand thread in the gear housing, the pitch angles of those threads need not be the same.

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Claims (24)

Injection molding device (1) provided with a screw (2) extending into a cylinder (3), which cylinder is provided with a filling opening I (4) and with a nozzle (5), the screw (2) being connected to a drive shaft (7) received in a drive housing (6), which drive shaft (7) is in driving connection with a first and a second electric drive unit (8 and 9, respectively), characterized in that the drive shaft I provided with a series of circular, parallel circumferential grooves, two transmissions engaging the parallel circumferential grooves, which transmissions are each provided with a number of cylindrical rollers which are provided with circumferential grooves bounded by ridges, which rollers are enclosed in a cylindrical chamber of a transmission housing through which the drive shaft extends and wherein backs of the rollers I engage on the parallel circumferential grooves of the drive shaft, the inner jacket surface k of the housing is provided with a screw thread, the backs of the rollers in the mounted state also engaging the respective screw thread of the housing, wherein the pitch direction of the thread of the housing of the one transmission deviates from the pitch direction of the thread of the housing of the other transmission, wherein the housing of one transmission is rotatably drivable by the first drive unit and wherein the housing of the other transmission is rotatably drivable by the second drive unit, wherein the injection molding device ( 1) is provided with a control (14) which is arranged for controlling the direction of rotation and the speed of rotation of the first and the second drive unit (8 and 9, respectively) such that the drive shaft 25 (7) and hence the screw ( 2) can be rotated in use and / or translated in the axial direction, the power required for the axial translation by r both drive units (8, 9) are supplied and with the power required for rotation being supplied by both drive units (8, 9). Injection-molding device according to claim 1, wherein the housing of each transmission is provided with two parts which are adjustable in axial direction relative to each other, so that the rollers can be accommodated play-free between the drive shaft and the housing. 3. Injection-molding device as claimed in claim 1 or 2, wherein the circumferential grooves of the rollers are parallel grooves extending substantially perpendicular to the longitudinal axis of the rollers, with ridges between them. Injection molding apparatus according to claim 1 or 2, wherein the circumferential grooves of the rollers are designed as screw threads. 5. Injection-molding device as claimed in any of the foregoing claims, wherein the rollers are provided with at least one gear wheel which engages on a gear wheel arranged on the drive shaft to transfer rotation of the rollers positively to the drive shaft. Injection-molding device according to any one of claims 1-5, wherein the control (14) is adapted to cause the injection-molding device (1) to pass through a plasticizing phase, an injection phase and optionally an emphasis phase. Injection molding apparatus according to claim 6, wherein the control (14) of the first and the second drive unit (8, 9) in the plasticizing phase and the optional emphasis phase is based on force feedback, wherein the control (14) of the first and the second drive unit (8, 9) in the injection phase is based on position feedback. Injection-molding device according to one of the preceding claims, wherein the control (14) for the purpose of control on the basis of force feedback as input signal the electric current consumed by the first drive unit (8) and the electric current consumed by the second drive unit (9) measuring, wherein the I 18 controller (14) is adapted to control the filling pressure I on the basis thereof according to a desired pattern. An injection molding apparatus according to any one of claims 1-8, wherein the injection molding apparatus (1) is provided with at least one force sensor (15), such as for example piezo-electric elements or strain gauges, which is a force exerted by the screw (2) measuring, wherein the at least one I force sensor (15) is connected to the control (14) for the purpose of force feedback, the control (14) being adapted to control the filling pressure according to a desired pattern on the basis thereof. I 10 An injection molding apparatus according to any one of the preceding claims, wherein the drive units (8, 9) each comprise a servo motor (8, 9), the I control (14) being arranged for position-controlled control of the I servo motors (8, 9) . 11. Injection molding apparatus according to claim 8, wherein the pitch of the screw thread in the housing of the first and the second transmission is so large that the axial force experienced by the screw (2) in use can be accurately derived from the drive current consumed by the first and second drive units (8 and 9, respectively). 12. Injection-molding device according to one of the preceding claims, wherein the first and the second drive unit (8, 9) are arranged coaxially. An injection molding apparatus as claimed in any one of the preceding claims, wherein the drive housing (6) is mounted on a carriage (16) which is provided with a, preferably electric drive (17) for displacing the drive housing in axial I direction ( 6) and the cylinder (3) connected thereto. An injection molding apparatus according to any one of the preceding claims, wherein I first and second electric drive unit (8, 9) directly drive the first and second housing (11, 13) of the transmission, respectively. 15. Injection-molding device according to one of the preceding claims, wherein a coupling (18) is provided between the drive shaft (7) and the screw (2). The injection molding apparatus of claim 15, wherein the coupling (18) is a break coupling. 17. Injection molding apparatus according to any one of the preceding claims, wherein an axial brake (19) is arranged on the drive shaft (7) which comes into operation in the event of undesired axial displacements of the drive shaft (7) due to control errors. The injection molding apparatus of claim 17, wherein the axial brake (19) comprises a ball (20) mounted on the drive shaft (7), the ball (20) being slidable with respect to the shaft (7) over the permitted length of the Axial stroke of the drive shaft (7), the slidability being limited by two stops (21, 22), the ball (20) being received in a bush (23) fixedly connected to the drive housing (6), wherein the ball (20) can only move in the bush (23) under plastic deformation of the bush (23). A method for manufacturing an injection molded product using an injection molding apparatus according to any one of the preceding claims, wherein the direction of rotation and the speed of rotation of the first and second drive units (8, 9, respectively) are varied such that the drive shaft (7) and thereby the screw (2) is rotated in use and / or is translated in axial direction according to a desired pattern and / or under the application of a desired axial force, the power required for the axial translation by both drive units (8, 9) is supplied and wherein the power required for rotation is supplied by both drive units (8, 9). The method of claim 19, wherein the injection molding apparatus passes through a plasticizing phase, an injection phase and optionally a stress phase in one cycle. 21. Method according to claim 20, wherein the control (14) of the first and the second drive unit (8, 9) is controlled in the plasticizing phase and the possible emphasis phase on the basis of force feedback, wherein the control (14) of the first and the second drive unit (8, 9) in the injection phase is controlled on the basis of position feedback. 22. Method as claimed in claim 21, wherein for the purpose of the control on the basis of force feedback the control (14) as input signal the electric I current consumed by the first drive unit (8) and the electric I consumed by the second drive unit (9) obtains current, the controller (14) regulating the filling pressure I on the basis of a desired pattern. 23. Method as claimed in claim 21, wherein for the purpose of control on the basis of force feedback the control (14) receives as I input signal the I force measurement signals detected by force sensors (15) on the screw, the control (14) on the basis thereof regulates filling pressure according to a desired pattern. A method according to claim 21, wherein the drive units (8, 9) each comprise a servomotor (8, 9), wherein the control (14) the servomotors (8, 9) in at least one of the phases of an injection cycle I position-driven control.