WO2009033926A1

WO2009033926A1 - Method for operating an injection device for an injection moulding machine, an injection device and an injection moulding machine with such an injection device

Info

Publication number: WO2009033926A1
Application number: PCT/EP2008/060947
Authority: WO
Inventors: Thomas Budde; Ingo Geier; Klaus Oberndorfer
Original assignee: Siemens Aktiengesellschaft
Priority date: 2007-09-07
Filing date: 2008-08-21
Publication date: 2009-03-19
Also published as: DE102007042643A1

Abstract

A method is provided for operating an injection device (2) for an injection moulding machine (1), which has an extruder screw (9) that can be driven by means of a rotating machine (23). According to the invention, a linear motor (24) is provided for moving the extruder screw (9) along. A motor current or values derived therefrom and/or acceleration values and/or values dependent on an operating point of the linear motor (24) are used to calculate an injection pressure and/or a back pressure.

Description

description

Method for operating an injection device for an injection molding machine, injection device and injection molding machine with such an injection device

The invention relates to a method for operating an injection device for an injection molding machine, which has an extruder screw drivable by means of a rotating machine, wherein a linear motor is provided for moving the extruder screw.

The invention further relates to an injection device corresponding to the method for an injection molding machine.

Finally, the invention relates to an injection molding machine with such an injection device.

German Offenlegungsschrift DE 198 47 298 A1 discloses an injection molding machine with a plurality of modular drive groups on the injection molding side and on the positive-locking side. At least one of the drive groups is connected to the injection molding machine via at least one multifunctional element, which as an interface optionally enables the connection of different types of drive, such as, for example, an injection molding machine. As electromechanical drives, hydraulic drives, pneumatic drives, linear motors or electromagnetic drives as a drive group with otherwise unchanged injection molding machine allows. In a local embodiment, a linear motor is used for linear displacement of the extruder screw.

Known injection devices for injection molding machines have an extruder screw drivable by means of an electric machine, a screw cylinder and a heater. Typically, in an injection molding process, plastic granules are fed via a hopper of a screw, which is also referred to as an extruder screw. By a rotary movement of the screw the plasticgrain Nulat transported forward towards the top of the snail. Approximately to the extent that the plastic granulate, which has been converted into a molten mass, is transported forwards to the tip of the screw, the screw deviates backwards, ie in the opposite direction. Due to the power loss resulting from the promotion and by means of the electric heater, which is provided on a worm cylinder, it melts the Kunststoffgranu- lats. The plastic granulate melt collects in front of the screw tip in a so-called worm entrance and pushes the worm back. Since the generated shear heat depends on the pressure of the screw on the material, this pressure must be specified as a pressure / displacement profile and controlled or controlled. Once enough molten material has been metered into the screw antechamber, the screw is pressed as a kind of piston in the direction of the screw tip. In this way, the melt of the plastic granules can be injected into a closed mold. The closed mold is a mold, which consists for example of two moldings. The speed of the screw, in particular in the function of a piston, is regulated in such a way that a defined limiting pressure is not exceeded. The limiting pressure affects, for example, the pressure in front of the screw tip.

Now, if the mold is filled with the melt of the plastic granules, the pressure in the mold increases rapidly, since it comes now to a compression of the plastic melt material. In this phase, for example, is switched from a speed control of the screw to a pressure control. It is of great importance here that the switching of this type is carried out in a reproducible and exact manner. For switching a switching criterion is used. The switchover criterion is a transitional criterion between two control types, one control type being, for example, the speed control and a second control type being the pressure control. Instead of the speed control, a speed control can also be used. Likewise, a pressure control is also used instead of the pressure control. settable. The transition criterion then relates to two types of control. The switching criterion is, for example, a position of the screw, a melt pressure or an in-mold pressure within the mold. The change-over represents a changeover from, for example, a speed control to a pressure control. It is to be avoided that pressure drops or pressure peaks occur which adversely affect the quality of injection molded parts. In order to always obtain a reproducible and exact, in particular with respect to a Umstellkriteriums precise conversion to the pressure control, for example, the shortest possible sampling times for the control and / or the control can be used. A possible sampling time is for example in the range of 100 μs.

Now, if the tool is filled with injected material, the cooling of the material leads to the shrinkage of the material. This shrinkage is advantageously compensated by the piston continues to press material into the tool after the injection process via a pressure / time profile.

For this purpose, in all such pressure control and monitoring tasks so far the detection of the actual pressure, ie the injection pressure or the dynamic pressure, imperative. The injection pressure is the pressure during the injection process. The dynamic pressure is the pressure to be maintained during the dosing process.

The detection of the injection or dynamic pressure is usually carried out by pressure sensors. These may be sensors which detect the melt pressure directly in the screw antechamber or else also strain gauges or load cells which detect the bearing forces resulting from the dynamic pressure at a suitable point in the mechanics. Both methods are associated with high costs.

The object of the present invention is now to provide a method for operating an injection device of an injection molding machine, with which it is possible to apply to hitherto necessary ge pressure sensors or corresponding measuring devices to determine the injection pressure or the back pressure to dispense.

It is a further object of the invention to specify an injection device for an injection molding machine corresponding to the method and a suitable injection molding machine with such an injection device.

The object of the invention is achieved with a method for operating an injection device for an injection molding machine having the features of claim 1. Advantageous process variants are mentioned in the dependent claims 2 to 6. In claim 7, an injection device for an injection molding machine is specified. In the dependent claims 8 to 12 advantageous embodiments of the injector are called. In claim 13, an injection molding machine is provided which has such an injection device.

According to the invention, a motor current or values derived therefrom and / or acceleration values and / or values dependent on an operating point of the linear motor are used to calculate an injection pressure and / or a dynamic pressure.

This has the advantage that it is possible to dispense with a sensor for pressure detection. For the calculation, not only a force-generating current of the linear motor is used as a calculation value, but also other values which use values dependent on an acceleration value and / or on an operating point of the linear motor. The acceleration value is, for example, a derivation of the travel speed of the linear motor or of the extruder screw according to time, or else a linear acceleration of the extruder screw in the direction of the mold. By including the acceleration value occurring acceleration forces are taken into account in the calculation of the injection pressure or the back pressure. The consideration The acceleration forces in the calculation of the injection pressure or the dynamic pressure is based on the dynamic basic law, after the sum of all forces including the inertia forces is always in equilibrium.

A further advantage is that, in contrast to the ball-and-socket spindle drives customary in injection molding machines, the force of the linear motor acts directly on the injection molding process. The force is thus not dependent on the efficiency of the ball screw and different influences such as lubrication, contamination or aging of the ball screw. Therefore, in the case of a linear motor, the resulting pressure in the screw cylinder, in particular in the screw antechamber, can be directly deduced from the force-generating current to the resulting force and via the force in conjunction with the known cross-sectional geometry of the worm cylinder.

By including operating point-dependent values of the linear motor, operating point-dependent ratios of the power generating current to the resulting force are taken into account in the pressure calculation.

According to one embodiment, a force constant or a so-called kF factor of the linear motor is used as a value dependent on the operating point of the linear motor. The force constant of the linear motor can be considered as the description value of the linear motor. It indicates the direct relationship between the force-generating current and the resulting, linear-acting force. The resulting pressure can be determined as follows:

Pschnecke = F / (R-screw * Tl) r

where F is the thrust force of the linear motor, with a screw the pressure in the screw antechamber, Rs _c nn _ec k _e the worm radius and π the circle number. Advantageously, the operating point dependence of the kF factor is taken into account. For this purpose, for example, a measurement of the linear motor and the storage of the kF factors. This takes place, for example, in the production facility of the linear motor. The kF factors are advantageously stored in a memory device on the linear motor, wherein the stored values can be read by a control and / or control device. The control and / or control device is provided, for example, for the travel speed control and / or current control of the linear motor. The memory device is, for example, a motor electronics or an encoder electronics of a transmitter for the linear motor, which is provided for moving the extruder screw. Typically, the force constant kF varies over both the travel speed and the thrust force (see FIG. 9). In addition, due to production reasons, the force constant spreads from linear motor to linear motor. By individually recording the respective characteristic curves for a specific linear motor, the respective kF factor can be used as a function of the current travel speed and the current motor speed

Current can be determined. This can be used e.g. Transfer machine parameters from one linear motor to another.

According to an advantageous embodiment of the method, a force constant which is at the same time dependent on a temperature of the linear motor is used as a value dependent on the operating point of the linear motor. By taking into account the temperature dependence of the kF factor, ie the kF value, the accuracy of the pressure calculation can be increased. Thus, in addition, the dependence of the kF factor on the temperature of the magnetic material of the linear motor primary part can be compensated by detecting the motor temperature. When using common neodymium-iron-boron permanent magnets, for example, the drop of the magnetization is 12% when the primary part is heated by 100 K. The operating-point-dependent value used in the calculation of the pressure can be read from a memory or can also be estimated. The estimation is carried out in a so-called kF estimator, where for the estimation current detected EMF values are used. The estimation is preferably carried out by calculating the force factor using a motor model.

In a further advantageous embodiment of the method, a control and / or control device is used to calculate the injection pressure and / or the back pressure, in which a current controller and / or a Verfahrgeschwin- digkeitsregler of the linear motor is integrated. As a result, dead times, which would arise when using a separate control and / or control device, reduce. This also applies to the case that not only the calculation of the pressure in the control and / or control device, in which the current controller and / or the Verfahrgeschwindigkeitsregler the linear motor is integrated, takes place, but also further control and / or control functions of the injector or the injection molding machine. Thus, if the control and / or control device for the current or traversing speed controller of the drive has sufficient computing power, both a force calculation and / or a pressure calculation can already be carried out in a subordinate manner. This results in further advantages in terms of the controller design, since then e.g. Filtering of the values can already be carried out in the subordinate controller.

The object of the invention is further achieved with an injection device for an injection molding machine, wherein the injection device can be driven by means of a rotating electrical machine extruder screw and a

Linear motor for moving the extruder screw has. The rotating electrical machine and the linear motor may be formed, for example, as a unit.

According to the invention, the injection device to a control and / or control device in which a current / power controller and / or Verfahrgeschwindigkeitsregler the linear motor is integrated. They are working point dependent Values stored for a force constant of the linear motor. For calculating an injection pressure and / or dynamic pressure, acceleration values and / or values dependent on an operating point of the linear motor are provided. This has the advantage that it is possible to dispense with a sensor for detecting the injection pressure and / or the dynamic pressure.

In particular, an encoder for detecting the travel of the linear motor is present. The acceleration values for calculating the injection pressure and / or back pressure can be determined from a time derivative of the change in the detected travel path. The encoder can e.g. be attached to the primary part of the linear motor and detect along the travel rail of the linear motor mounted markings. The encoder can be based for example on an optical or magnetic principle.

Preferably, a temperature sensor for detecting a temperature of the linear motor, in particular for detecting the temperature of the permanent magnets in the primary part of the linear motor, is present. The corresponding temperature values are provided for calculating the injection pressure and / or dynamic pressure by the control and / or control device.

According to a further embodiment of the injection device, operating point and temperature-dependent values for a force constant of the linear motor are also stored. Preferably, these values are stored in a non-volatile memory of the control and / or control device.

In one embodiment of the injection device, the regulating and / or control device of the injection device has a kF estimator for estimating the injection pressure and / or the dynamic pressure on the basis of the detected travel speed and the determined operating point of the linear motor. The kF estimator preferably has means for calculating the force constant with the aid of a motor model. Finally, the object of the invention is achieved by injection molding machine, which has an injection device according to the invention. Such an injection molding machine is cheaper to produce by the elimination of pressure sensors. It is also maintenance-free.

The invention and advantageous embodiments of the invention will be described in more detail below with reference to the following figures. Show it

FIG 1-3 phases of an injection process,

4 shows a belt drive device for a linear movement of an extruder screw of a injection device according to the prior art,

FIG. 5 shows a linear motor for moving a prior art rotating electrical machine driving the extruder screw, FIG.

6 shows by way of example drive devices,

7 shows a current / force characteristic of an exemplary linear motor,

8 shows the course of a corresponding force constant of the linear motor as a function of the exciter current according to FIG. 7 and FIG

9 shows by way of example a function diagram for the regulation and / or control of the injection device according to the invention with the aid of a kF estimator.

1 to 3 show phases of an injection process. The representations according to FIG. 1 to FIG. 3 show three steps 3, 5, 7 of an injection molding process in an injection molding machine 1 shown only in rudimentary form, which has an injection device 2. The first step according to FIG. 1 is concerned the plasticizing and metering, the second step according to FIG 2 relates to the injection and Nachdrücken and the third step of FIG 3 relates to the cooling and demolding.

The injection molding process relates to an injection molding machine 1. The injection molding machine 1 has an extruder screw 9. The worm 9 is located in a worm cylinder 11. The injection molding machine 1 also has a funnel 13. The funnel 13 can be loaded with plastic granulate 15. By a rotary movement 17 of the screw 9, the plastic granules 15 can be transported in a screw antechamber 19. During transport, the plastic granules are heated to a melt by friction or by means of an electric heater 21. The melt collects by a rotary movement 17 in the screw antechamber 19, which adjoins a screw tip 10. The rotational movement 17 can be achieved, for example, by means of a rotating electric machine 23, that is to say by means of an electric motor.

The electric machine 23 is coupled to an axis 22 and regulated or controllable, for example, by means of a control and / or control device 25. Due to the fact that melt accumulates in the screw antechamber 19, the screw 9 is pushed away by a nozzle 27. The nozzle 27 is provided for discharging the melt. It can have a corresponding activatable sealing mechanism for the melt. The entire injection device 2 can be brought to the molding tool 29, 31. The mold 29, 31 has two moldings. The first mold part 29 and the second mold part 31 are joined together to form a mold.

The first step of the casting process according to FIG. 1 includes plasticization and metering of the melt material. The second step of the casting process according to FIG. 2 relates to the injection of the melt or the pressing of it. To inject the melt, the screw 9 is moved in the direction of the nozzle 27. As a result, melt penetrates into the mold 29, 31 a. At the end of the injection process a reprint is applied.

In a third step of the casting process according to FIG. 3, cooling and demoulding take place. The worm cylinder 11 is separated from the mold 29, 31. The two parts of the molding tool 29 and 31 are separated, so that a sprayed 33 is released. After this step, again follows the first step 3 of the casting process, namely the plasticizing and dosing.

4 shows a belt drive device 47 for a linear movement of an extruder screw 9 of an injection device 2 according to the prior art.

The illustration according to FIG 4 shows a belt drive device 47. It is by means of a belt 37, the rotary movement of an electric machine 23, which has a transmitter 35, transferable. The electric machine 23 is connected to a drive device 45, wherein the drive device 45 has, for example, a power converter and a control and / or control device. By means of a spindle 39, the rotating movement in a linear movement 41 is changeable. The linear movement 41 serves the linear movement of the worm 9, which is advantageously located in the same axis 43 as the spindle 39.

FIG. 5 shows a linear motor 24 for moving a prior art rotating electrical machine 23 that drives the extruder screw 9. The reference numeral 26 denotes a primary part of the linear motor 24. It typically includes a field winding and permanent magnets. Reference numeral 28 denotes a secondary part of the linear motor 24 or a travel rail or carrier. The primary part 26 moves with appropriate electrical control in the sense of a carriage along the secondary part 28. The rotating electric machine 23 is fixedly connected to the primary part 26. Linear movement 41 as well as turning movement 17 of the extruder screw 9 are therefore decoupled from each other. For detecting the travel of the linear motor 24, an encoder is present. Acceleration values can be determined from the time derivation of the change in the detected travel path in order to be able to calculate the injection pressure and / or the back pressure in the extruder screw 9 of the injection device 2 according to the invention.

The illustration in accordance with FIG. 6 shows a structure with different drive devices 46. The drive devices 46 are each assigned to a rotating electric machine 23 and a linear motor 24 and connected thereto. The rotating electrical machines 23 can, for example, drive the extruder screw 9. You can, for example, drive the ejector, the clasp or the injector. The feed of the drive devices 46 takes place via a common feed device 49. The drive devices 46 are designed such that they are connected to a common control and / or control device 25. In particular, the speed control or the travel speed control of the connected drive devices 46 is performed in this control and / or regulating device 25. This function can also be integrated in a single drive device, which is not shown in FIG. Optionally, the control and / or regulating device 25 is connected to the electrical machines 23, 24 via a drive bus system 51. In the example of FIG. 6, the electrical machines 23, 24 have an encoder interface with an electronic nameplate 53. There, for example, kF values are stored for the shown linear motor 24 or other electrical parameters of the respective electric machine 23, 24, such as e.g. Polzahl, rated currents and the like.

7 shows a current / force characteristic 58 of an exemplary linear motor. There is a thrust force F of the primary part of the linear motor via an effective force-generating current I, which flows through the exciter winding of the primary part. carried. It can be seen that the current / characteristic curve 58 is no longer linear for higher current values in the range from 20 to 30 A _e ff. In other words, the efficiency of conversion of excitation current I to thrust F decreases with increasing current values.

FIG. 8 shows the course of a corresponding force constant kF of the linear motor as a function of the exciter current I according to FIG. 7. The force constant kF describes the effectivity of the conversion from the exciter current I to the thrust force F. It is calculated from the quotient of the thrust force F and the corresponding excitation current I formed. As FIG. 8 shows, the force constant kF decreases for current values from approximately 20 A _eff from approximately 0.97 to approximately 0.88. Alternatively, the force constant kF can be normalized to a 100% value, which results for small excitation currents greater than 0 A _e ff.

According to the invention, the force constant kF of the linear motor 24 is used as a value dependent on the operating point of the linear motor 24. In other words, the force-dependent force constant kF dependent on the excitation current I serves to correct the transmission ratio of the exciter current I to the resultant thrust force F. Preferably, a force constant kF dependent on a temperature of the linear motor 24 is also considered to be dependent on the operating point of the linear motor 24 Value used. Above all, this temperature is the primary part temperature of the linear motor 24 and in particular the temperature of the local permanent magnets whose magnetization decreases with increasing temperature.

Preferably, the operating point-dependent and temperature-dependent values for the force constant kF are stored in a corresponding two-dimensional matrix, so that the control and / or regulating device 25 of the linear motor 24 can read out the respectively suitable force constant value. The matrix can be determined, for example, during the factory final test of the linear motor 24. Since the force constant kF from linear motor 24 to linear motor 24 is typically due to production. can vary by up to 8%, it is advantageous for each linear motor 24 to create such a matrix. As a result, the corresponding thrust force F of the linear motor 24 and, taking into account the worm radius of the extruder worm 9 and the efficiency of the extruder worm 9, can ultimately be determined by the injection and / or ram pressure of the injection device 2 according to the invention with very high accuracy via the detected exciter current I of the linear motor 24 be determined .

Alternatively, the respective current force constant value can be derived from a suitable mathematical interpolation function with the function parameters excitation current I and primary part temperature.

Preferably, the values for the force constant kF that depend on the operating point of the linear motor 24 and optionally on the temperature of the linear motor 24 are read from a memory or estimated. The memory is preferably a non-volatile memory such as e.g. an EEPROM memory. It is typically present in the control and / or regulating device 25, in which preferably also a current regulator and / or Verfahrgeschwindigkeitsregler the linear motor 24 is integrated.

FIG. 9 shows, by way of example, a functional diagram for controlling and / or controlling the injection device 2 according to the invention with the aid of a kF estimator 61.

9 shows an example of an adaptation of the force constant kF in a linear motor 24. Here, a kF estimator 61 is used. Also, a temperature adaptation 63 is provided (see the upper part of FIG 9). With the designations Pxxx, such as P121 for a primary part resistance, input parameters are designated. With rxxx, such as rO88, read-out parameters are designated. The adaptation of the force constant kF serves to improve the absolute thrust force accuracy in the control of the linear motor 24. Due to manufacturing tolerances, temperature fluctuations and saturation effects, the magnetization of the permanent magnets varies. The function "kF estimator" 61 adjusts the force constant kF [N / A _e ff] in the control to the instantaneous magnetization. The kF estimator 61 needs as accurate as possible values of the motor parameters of the linear motor 24 in order to achieve high thrust. Therefore, prior to the use of the kF estimator 61, a motor identification with activated kF estimator 61 must be performed, in which the values for primary part resistance, leakage inductance and voltage mapping error are determined. The line resistance must be entered in a corresponding manner before the motor identification. The linear motor 24 should have room temperature for identification. The compensation of the voltage imaging errors must be activated. The engine temperature, in particular the primary part temperature, should be detected by a so-called KTY sensor. The engine temperature is needed by estimator 61 to track the temperature dependent quantities. If no motor temperature sensor is connected, the accuracy is severely limited. The kF estimator 61 is activated only after a certain travel speed v, the so-called application speed. The terminal voltage of the drive inverter is always associated with small errors caused by voltage drops across the semiconductors, etc. The lower the travel speed v and thus the output voltage, the more small voltage errors can disturb the estimation. Therefore, the estimation below a certain operating speed is deactivated. The estimated value is preferably smoothed with a predefinable time constant. In rO88 the current kF nominal value is displayed, in rO88 the kF actual value is displayed.

Claims

claims

1. A method for operating an injection device (2) for an injection molding machine (1), which by means of a rotating machine (23) drivable extruder screw (9) and wherein a linear motor (24) for moving the extruder screw (9) is provided , characterized in that a motor current or values derived therefrom and / or acceleration values and / or values dependent on an operating point of the linear motor (24) are used for calculating an injection pressure and / or a dynamic pressure.

2. A method according to claim 1, wherein a force constant (kF) of the linear motor (24) is additionally used as a value dependent on the operating point of the linear motor (24).

3. The method according to claim 1 or 2, wherein a force constant dependent on a temperature of the linear motor is used as a value dependent on the operating point of the linear motor.

4. Method according to one of the preceding claims, characterized in that the values for the force constant (kF) which are dependent on the operating point of the linear motor (24) and optionally on the temperature of the linear motor (24) are read from a memory or estimated.

5. The method according to claim 4, characterized in that the estimation is carried out by calculation of the force constant (kF) with the aid of a motor model.

6. The method according to any one of the preceding claims, characterized in that for the calculation of the injection pressure and / or the back pressure, a control and / or control device (25) is used, in which a current / force controller and / or a Verfahrge- speed controller of the linear motor (24) is integrated.

7. Injection device for an injection molding machine (1), wherein the injection device comprises an extruder screw (9) which can be driven by means of a rotating electric machine (23) and a linear motor (24) for moving the extruder screw (9), d a d u c h e c e n e c e n e,

- That the injection device comprises a control and / or control device (25) in which a current / force controller and / or Verfahrgeschwindigkeitsregler the linear motor (24) is integrated,

- that operating point-dependent values for a force constant

(kF) of the linear motor (24) are stored, and - that a motor current or values derived therefrom and / or acceleration values and / or values dependent on an operating point of the linear motor (24) are provided for calculating an injection pressure and / or dynamic pressure.

8. Injection device according to claim 7, characterized in that a sensor for detecting the travel of the linear motor (24) is present and that the acceleration values for calculating the injection pressure and / or back pressure from a time derivative of the change of the detected travel can be determined.

9. Injection device according to claim 7 or 8, characterized in that at least one temperature sensor for detecting a temperature of the linear motor (24) is present and that corresponding temperature values for calculating the injection pressure and / or congestion pressure by the control and / or control device (25) are provided.

10. Injection device according to claim 9, characterized in that at the same time operating point and temperature-dependent values for a force constant (kF) of the linear motor (24) are stored.

11. Injection device according to one of claims 7 to 10, characterized in that the control and / or control means (25) of the injection device a kF estimator (61) for estimating the injection pressure and / or the back pressure based on the detected travel speed (v) and the determined operating point of the linear motor (24).

12. Injection device according to claim 11, characterized in that the kF estimator (61) has means for calculating the force constant (kF) with the aid of a motor model.

13. Injection molding machine with an injection device (2) according to one of claims 7 to 12.