INJECTION MOULDING MACHINE WITH ELECTRIC SWITCHING UNITS AND METHOD FOR SYNCHRONISING THE CURRENTS OF ELECTRIC SWITCHING UNITS

Abstract

The invention relates to an injection moulding machine having: an electric machine; multiple switching units electrically connected in parallel, wherein each switching unit has at least one electrical output and at least one electrical switch associated with the output, wherein corresponding outputs of the switching units are electrically connected in parallel with a common output; at least one primary open-loop and/or closed-loop controller which is designed to control the switching units with control signals in order to operate the electric machine; a measuring device for measuring output currents at the outputs; and at least one correction controller which is designed to adjust a corresponding control signal in the event of a deviation between a measured output current at an output and a target value.

Claims

1. Injection moulding machine, comprising: at least one electrical machine; multiple electrically parallel-connected switching units, which are designed to drive the electrical machine, wherein each switching unit having at least one electrical output and at least one electrical switch associated with the output, which can be switched according to a switching pattern, wherein corresponding outputs of the switching units are electrically connected in parallel to a common output, which is connected to the electrical machine; at least one primary open-loop and/or closed-loop control, which is designed to actuate the switching units with control signals, in order to operate the electrical machine; a measuring device for measuring output currents at the outputs of the switching units; and at least one correction controller, which is designed to adjust a corresponding control signal in the event of a deviation between a measured output current at an output and a target value for an output current, such that switching times, which are predetermined by the switching pattern, of at least one switch, which is associated with the relevant output, are shifted forwards or backwards in time and thereby the deviation between the target value and the output current is reduced, wherein the at least one correction controller is adjusted to synchronise switching times of switches, which are associated with corresponding outputs, such that these switch simultaneously, wherein, corresponding outputs of the switching units are connected to the respective common outputs via connecting lines, wherein, in order to smooth the output currents, each connecting line is guided through a smoothing inductance element in opposite directions at least once together with the connecting line of another corresponding output.

2. Injection moulding machine according to claim 1, wherein, n switching units are provided and each output of at least n?1 switching units is associated with a respective correction controller, which adjusts a corresponding control signal when the measured output current at the output deviates from the target value.

3. Injection moulding machine according to claim 1, wherein the at least one correction controller is designed to apply an offset signal value to the control signal in order to adjust the control signal.

4. Injection moulding machine according to claim 3, wherein a memory, including a non-volatile memory, is provided, in which the offset signal value or a temporal average value thereof can be stored.

5. Injection moulding machine according to claim 1, wherein the switching units are configured as inverter units and each have at least two electrical outputs.

6. Injection moulding machine according to claim 1, wherein n switching units are provided and one of the switching units represents a reference switching unit and all outputs of the other n?1 switching units are each associated with a correction controller, wherein the correction controllers are designed in each case to adjust a control signal of the n?1 switching units in such a way that the output currents of the other n?1 switching units correspond to the respective corresponding output currents of the reference switching unit.

7. Injection moulding machine according to claim 1, wherein a correction controller is associated in each case with all outputs of all switching units, wherein the correction controllers are designed in each case to adjust a control signal of the switching units in such a way that the output currents of the switching units each correspond to an averaged total current from the respective output current and all corresponding output currents.

8. Injection moulding machine according to claim 1, wherein the connecting lines of corresponding outputs of the switching units are guided through a common mode choke or a self-contained, annular, magnetic core element as smoothing inductance element.

9. (canceled)

10. (canceled)

11. Method for synchronising output currents of electrically parallel-connected switching units, which are connected to an electrical machine of an injection moulding machine, wherein each switching unit has at least one electrical output and at least one electrical switch associated with the output, which is switched according to a switching pattern, wherein corresponding outputs of the switching units are electrically connected in parallel to a common output for the electrical machine and the method has the following steps: outputting control signals to the switching units; measuring output currents at the outputs of the switching units; comparing measured output currents with a target value for each output current; adjusting a corresponding control signal by at least one correction controller in the event of a deviation between a measured output current at an output and a target value, such that switching times, which are predetermined by the switching pattern, of the at least one switch, which is associated with the relevant output, are shifted forwards or backwards in time and thereby reducing the deviation between the target value and the output current, wherein the at least one correction controller synchronises switching times of switches, which are associated with corresponding outputs, such that these switch simultaneously, wherein, corresponding outputs of the switching units are connected to the respective common outputs via connecting lines, wherein in order to smooth the output currents each connecting line is guided through a smoothing inductance element in opposite directions at least once together with the connecting line of another corresponding output.

12. Method of claim 11, wherein the at least one correction controller applies an offset signal value to the control signal to adjust the control signal.

13. Method according to claim 11, wherein the offset signal value or a temporal average value thereof is stored in a memory, including a non-volatile memory, so that the offset signal value or its temporal average value is available when the method is used again.

14. Method according to claim 10, wherein n switching units are provided and one of the switching units represents a reference switching unit, wherein each output of the other n?1 switching units is associated with a correction controller and the target values of all output currents of the other n?1 switching units are formed by the output currents of the reference switching unit corresponding to the respective output currents of the other n?1 switching units.

15. Method according to claim 10, wherein a correction controller is associated with each output and for each output current an averaged total current of the respective output current and all corresponding output currents is used as target value.

16. Injection moulding machine according to claim 1, the injection moulding machine for producing plastic parts, wherein the at least one electric machine is a synchronous motor, and the multiple electrically parallel-connected switching units are inverter units.

Description

[0037] The invention is described below with the help of figures to which it is not intended to be limited. It shows:

[0038] FIG. 1 a schematic side view of an all-electric injection moulding machine from the state of the art;

[0039] FIG. 2 an electrical block diagram of the invention in accordance with a first embodiment;

[0040] FIG. 3 an electrical block diagram of the invention in accordance with a second embodiment;

[0041] FIG. 4A-D respective interconnections of connecting lines between switching units connected in parallel and common outputs with smoothing inductance elements;

[0042] FIG. 5 a switching unit; and

[0043] FIG. 6 multiple switching units.

[0044] FIG. 1 shows a schematic side view of an all-electric injection moulding machine 1 from the state of the art. The injection moulding machine 1 has multiple electrical machines 2, each of which is operated by individual inverter units 3. The electrical machine 2a drives an injection piston 4 for introducing material into a mould 5. The electrical machine 2b operates a plasticising unit 6 for preparing raw material. The electrical machine 2c operates a clamping unit 7 to open and close the mould 5.

[0045] Injection moulding machines 1 exist in different sizes and designs. Electrical machines 2 of different power and design are used. The powers of the associated inverter units 3 must be adjusted to the powers of the electrical machines 2, i.e. they must be able to output currents and voltages in the corresponding order of magnitude. However, the higher the powers, the more expensive and larger the inverter units become 3.

[0046] According to the invention, it is therefore intended to operate the electrical machines 2 each on switching units 8 electrically connected in parallel, as shown for example in FIG. 2. If higher powers are required, more switching units 8 are connected in parallel, which facilitates scalability. Advantageously, the individual powers of the switching units 8 can be lower than the power of the connected electrical machine 2. FIG. 5 shows an exemplary switching unit 8 in more detail.

[0047] FIG. 2 shows an electrical block diagram in accordance with a first embodiment of the invention. In FIG. 2, three (n=3) switching units 8 configured as inverter units 3 are electrically connected in parallel. The switching units 8 each have three outputs 9, which are associated with the outer conductors (phases) U, V and W. Corresponding outputs 9 of the switching units 8, i.e., outputs 9 of the same outer conductors U, V and W, are electrically connected to each other via connecting lines 11 into common outputs 10. Each common output 10 is associated with an outer conductor U, V or W. The electrical machine 2 is connected to the common outputs 10 via motor connection lines 12. PWM-modulated output voltages are output at the outputs 9.

[0048] The switching units 8 are controlled via control signals 13. The control signals 13 are illustrated by U.sub.1*, V.sub.1* and W.sub.1*. Each output 9 of each switching unit 8 is controlled via its own control signal 13. The control signals 13 are given by a primary closed-loop control 14, which is intended to control the output currents I.sub.U1-I.sub.W3 of the outputs 9 in the connection lines 11 and thus consequently the outer conductor currents I.sub.U, I.sub.V, I.sub.W in the motor connection lines 12. Sizes relating to the switching units 8 are provided with numbered indices in this disclosure of invention. In the embodiment shown, all output currents I.sub.U1-I.sub.W3 of the switching units 8 are measured with the aid of current measuring sensors 15a of a measuring device 15 and made available to the primary closed-loop control 14. For the sake of clarity, however, this is only shown for the outer conductor U. However, the statements apply analogously to the other outer conductors V and W. As shown in the embodiment, corresponding output currents I.sub.U1-I.sub.W3 are added in a sum block 16 to obtain the outer conductor currents I.sub.U, I.sub.V, I.sub.W (represented by total currents I.sub.U_sum, etc.) in the motor connection lines 12. This is only shown for the outer conductor U, the explanations for the other outer conductors V and W apply analogously. In an alternative embodiment, it can also be assumed for simplification that corresponding output currents I.sub.U1-I.sub.W3 of the outer conductors U, V, W are identical, such that only one output current I.sub.U1-I.sub.W3 of each outer conductor U, V, W must be fed back and multiplied by the number of switching units 8 to obtain the corresponding outer conductor current I.sub.U, I.sub.V, I.sub.W. The outer conductor currents I.sub.U, I.sub.V, I.sub.W determined by summation and fed back are guided through a first coordinate transformation block 18 and transformed from the string size representation into a two-axis dq-coordinate system of the space vector representation such that transformed currents I.sub.d, I.sub.q are obtained in the dq-coordinate system. The transformed currents I.sub.d, I.sub.q are compared with a current specification I.sub.d_soll, I.sub.q_soll as a reference variable, which is also specified in space vector representation in the dq-coordinate system. The deviation resulting from the comparison is fed to a current controller 19 which, on the basis of the deviation between the current specification I.sub.d_soll, I.sub.q_soll and the transformed currents I.sub.d, I.sub.q specifies manipulated variables 20 which are fed to a second coordinate transformation block 21 in order to obtain the manipulated variables 20 in string size representation for the outer conductors U, V, W. The transformed manipulated variables 22 are output to the switching units 8 connected in parallel. These may each have one or more modulators 23 to generate the (PWM) switching pattern for the switches 30. The modulators 23 can of course also be arranged in front of the switching units 8. The control signals 13 reach the switching units via control signal lines 50. This is fully shown for the outer conductor U. The control for the outer conductors V and W is analogous. The control signal lines 50 as well as the other blocks, such as the sum block 16, the modulator 23, the coordinate transformation blocks 18, 21 and the current controller 19, do not have to be physical lines or blocks. These can also be implemented in software, just like the correction controllers 24, which will be described in more detail.

[0049] If switching units 8 are connected in parallel, the corresponding output currents I.sub.U1-I.sub.W3, for example the output currents I.sub.U1, I.sub.U2 and I.sub.U3, can deviate from each other despite the similar construction of the switching units 8 due to different switching times of the switches contained in the switching units 8, different impedances in the current paths of the output currents I.sub.U1-I.sub.W3 and different signal propagation times of the control signals 13. In order to reduce the deviations and current peaks caused by non-synchronised switching operations, large chokes with high inductance are used in the state of the art. However, such chokes take up a lot of space and are expensive.

[0050] According to the invention, at least one correction controller 24 is therefore provided, which is design to adjust a corresponding control signal 13 in the event of a deviation between a measured output current I.sub.U1-I.sub.W3 at an output 9 of a switching unit 8 and a target value S. By adjusting the control signal 13, the switching times of the at least one switch associated with the relevant output 9, which are predetermined by the switching pattern, are shifted forward or backward in time, thereby reducing the deviation between the target value S and the output current I.sub.U1-I.sub.W3. The output currents I.sub.U1-I.sub.W3 of the switching units 8 are kept equal by the at least one correction controller 24 and thus the switching times of corresponding switches 30 are also indirectly synchronised.

[0051] FIG. 2 shows a first embodiment of the invention. One of the n=3 switching units 8 is configured as the reference switching unit 8a. The control signals 13 of the other n?1 switching units 8 are to be adjusted in this embodiment in such a way that their output currents I.sub.U2, I.sub.U3, I.sub.V2, I.sub.V3, I.sub.W2 and I.sub.W3 correspond to the respective output currents I.sub.U1, I.sub.V1 und I.sub.W1 of the reference switching unit 8a. For this purpose, correction controllers 24 are associated with all outputs 9 for the output currents I.sub.U2, I.sub.U3, I.sub.V2, I.sub.V3, I.sub.W2 and I.sub.W3 of the other n?1 switching units 8. In FIG. 2, only the correction controllers 24 for the outputs 9 or output currents I.sub.U2, I.sub.U3 associated with the outer conductor U are shown for the purpose of clarity. The output currents I.sub.U2 and I.sub.U3 should correspond to the output current I.sub.U1 with the aid of the correction controllers 24 shown (the same applies to the output currents of the outer conductors V and W). The correction controllers 24 are therefore designed to adjust corresponding control signals 13 for the other n?1 switching units 8 in such a way that the output currents I.sub.U2 and I.sub.U3 are changed in the event of a deviation from the output current I.sub.U1. For this purpose, the output current I.sub.U1 is selected as the target value S for the correction controllers 24 shown. The deviation between an output current and a target value S can be determined by means of subtraction in a subtraction block 25. In the event of a deviation between one of the output currents I.sub.U2 und I.sub.U3 of the other n?1 switching units 8 and the corresponding output current I.sub.U1 of the reference switching unit 8a, the correction controllers 24 shown apply a positive or negative offset signal value R to the corresponding control signals 13 in order to reduce or increase the PWM-modulated output voltage of the other n?1 switching units 8. The correction controller outputs 26 of the correction controllers 24 are connected to the control signal lines 50 via a summing block 27 for this purpose, such that the offset signal values R can be applied to the control signals 13. As already mentioned, the control signal line 50 does not have to be physically present but can be implemented in software. If the output currents I.sub.U2 und I.sub.U3 deviate from the output current I.sub.U1 during operation, the correction controllers 24 shown detect these deviations and generate an offset signal value R such that the control signals 13 are adjusted accordingly and the deviations are thereby reduced. Preferably, the correction controllers 24 are configured as P, PI or PID correction controllers. The at least one correction controller 24 and the primary closed-loop control 14 may be implemented in one or more microprocessors in a discrete-time manner. The correction controllers for the outputs 9 associated with the output currents I.sub.V2, I.sub.V3, I.sub.W2 and I.sub.W3 are not shown in FIG. 2 for the sake of clarity; however, the statements about the correction controllers 24 shown also apply accordingly to these correction controllers. The correction controllers, which are not shown, thus also adjust corresponding control signals 13 by applying offset signal values R, such that the output currents I.sub.V2 und I.sub.V3 are adjusted to the output current I.sub.V1 and the output currents I.sub.W2 and I.sub.W3 are adjusted to the output current Iwi of the reference switching unit 8a.

[0052] The offset signal values R or temporal averages thereof can be stored in particular in non-volatile memories (not shown). In this way, the settling times of the correction controllers 24 can be reduced when the method is used again or when the motor 2 is restarted. The offset signal values R can already be determined during the production of the switching units 8. In the case of PI controllers in particular, it can be provided that the integral components (I-components) of the correction controllers 24 are stored in a memory, in particular a non-volatile memory.

[0053] In the embodiment of FIG. 2, it is thus provided in summary that one of the switching units 8 represents a reference switching unit 8a and a respective correction controller 24 is associated with all outputs 9 of the other n?1 switching units 8, the correction controllers 24 being designed to adjust a respective control signal 13 of the other n?1 switching units 8 in such a way that the output currents I.sub.U2-I.sub.W3 of the other n?1 switching units 8 correspond to the respective corresponding output currents I.sub.U1-I.sub.W1 of the reference switching unit 8a.

[0054] FIG. 3 shows an alternative embodiment of the invention. Since the basic structure of the embodiment in accordance with FIG. 3 essentially corresponds to the structure of FIG. 2, only the differences will be discussed below. In FIG. 3, each output 9 of each switching unit 8 and thus each output current I.sub.U1-I.sub.W3 is assigned its own correction controller 24. For the sake of an overview, only the correction controllers 24 for the outputs 9 of the switching units 8 that are associated with the outer conductor U are shown. In contrast to the embodiment in accordance with FIG. 2, the embodiment in accordance with FIG. 3 does not have a reference switching unit 8a. The target value S for a correction controller 24 is formed by an averaged total current I.sub.U_sum from all corresponding output currents I.sub.U1-I.sub.U3. The same applies to the correction controllers of the other outputs 9 of the switching units 8, which are not shown. Total currents can be averaged by adding the corresponding measured output currents I.sub.U1-I.sub.W3 and then dividing by the number of corresponding output currents. In FIG. 3 this is done by the division block 51. In FIG. 3, n=3 switching units are provided. In other words, in the embodiment of FIG. 3, the correction controllers 24 (shown and not shown) are each designed to adjust a control signal 13 of the switching units 8 in such a way that the output currents I.sub.U1-I.sub.uw3 of the switching units 8 each correspond to an averaged total current from the respective output current I.sub.U1-I.sub.W3 and all corresponding output currents I.sub.U1-I.sub.W3.

[0055] FIGS. 4A-C show the circuitry of the connection lines 11 to common outputs 10 in more detail. The circuitry can be made in a block 52 (see FIG. 2 and FIG. 3). With the correction controllers 24 described, it is possible to reduce deviations between the output currents I.sub.U1-I.sub.W3. In order to compensate for minor remaining deviations between the output currents and to smooth the output currents I.sub.U1-I.sub.W3 the connecting lines 11 may have smoothing inductance elements 28. FIG. 4A shows the situation with n=2 switching units 8. Two corresponding connection lines 11 are guided through a common smoothing inductance element 28, preferably in opposite directions. The smoothing inductance element 28 in FIG. 4A may, for example, be formed by a common mode choke (also referred to as a current compensated choke). A common mode choke has the advantage of compensating for magnetic fluxes due to the output currents flowing in opposite directions, such that the common mode chokes can be kept small in size. Common mode interference is suppressed.

[0056] FIG. 4B shows that two corresponding connection lines 11 are guided in opposite directions through a common smoothing inductance element 28 in the form of a preferably ring-shaped magnetic core element 29. They can be coherent ferrite rings. By passing the connecting lines 11 through a magnetic core element 29 in opposite directions, the magnetic fields cancel each other out as in a common mode choke. For example, a magnetic core element 29 can be a ferrite core element. Of course, other materials are also conceivable, such as, for example, magnetic core elements made of metal, in particular iron or iron powder. The magnetic core elements 29 do not saturate due to the cancellation of the magnetic fields generated. Common mode interference is suppressed.

[0057] FIG. 4C shows the situation for n=3 switching units. It can be seen that each connection line 11 is guided at least once together with the connection line 11 of each other corresponding output 9 through a smoothing inductance element 28, for example a common mode choke, wherein the connection lines 11 are preferably guided in opposite directions through the smoothing inductance elements 28.

[0058] FIG. 4D illustrates the situation with n=4 switching units. In order to save smoothing inductance elements 28, the number of smoothing inductance elements 28 is reduced compared to FIG. 4C. In this embodiment, each connection line 11 is guided with a further connection line 11 through a smoothing inductance element 28, for example a common mode choke. k?1 connection lines 11 being thereby routed with only exactly one further connection line 11 through a smoothing inductance element 28. Exactly one connection line 11, as shown here the k* connection line 11 of the output 9 with the designation U1, is however connected to two further connection lines 11, namely those of the outputs 9 with the designations U1 and U4, by a smoothing inductance element 28.

[0059] The arrangements of smoothing inductance elements 28 shown in FIGS. 4A-D may also be referred to as a smoothing inductance matrix.

[0060] FIG. 5 shows a simplified schematic of a switching unit 8, which is configured as an inverter unit 3. The inverter unit 3 has three outputs 9, wherein two switches 30 are associated with each output 9. The switches can be, for example, field-effect transistors or IGBTs (Insulated-Gate Bipolar Transistor).

[0061] The switching units 8 can be arranged on a common printed circuit board 31, as shown in FIG. 6. The connecting lines 11 and the smoothing inductance elements 28 may also be arranged on the common printed circuit board 31. The smoothing inductance elements 28 may be integrated into a terminal block with terminals (not shown) for the machine 2. The parallel connection of switching units 8 allows electrical machines 2 to be operated with higher power compared to the power of the individual switching units 8. If an electrical machine 2 has a lower output, it may be sufficient to connect fewer switching units 8 in parallel than those arranged on the common printed circuit board 31. If, for example, three switching units 8 are arranged on a printed circuit board 31, but only the parallel connection of two switching units 8 is required to operate an electrical machine 2, the third switching unit 8 can be used to operate a further electrical machine 2. This is in line with the universal applicability and scalability mentioned at the beginning, since only minor adjustments are necessary for such an operation, which is shown in FIG. 6. Thus, a common printed circuit board 31 with multiple switching units 8 can be manufactured in large numbers. Depending on the requirements, the circuitry of the printed circuit board 31 can then be easily adjusted.