US-12627248-B2 - Injection moulding machine with electric switching units and method for synchronising the currents of electric switching units

US12627248B2US 12627248 B2US12627248 B2US 12627248B2US-12627248-B2

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.

Inventors

Tomas Kalender
Klaus BERGKIRCHNER
Christoph Friedrich

Assignees

WITTMANN TECHNOLOGY GMBH

Dates

Publication Date: 20260512
Application Date: 20220520
Priority Date: 20210521

Claims (14)

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 synchronize 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 1 , wherein the switching units are configured as inverter units and each have at least two electrical outputs.
5 . 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.
6 . 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.
7 . 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.
8 . 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.
9 . 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.
10 . Method for synchronizing 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 synchronizes 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.
11 . Method of claim 10 , wherein the at least one correction controller applies an offset signal value to the control signal to adjust the control signal.
12 . Method according to claim 10 , 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.
13 . 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.
14 . 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.

Description

The invention relates to an injection moulding machine with at least one electrical machine, in particular a rotating field machine, and at least one switching unit, in particular an inverter unit. Furthermore, the invention relates to the method for synchronising output currents of switching units electrically connected in parallel, in particular inverter units, in an injection moulding machine. Injection moulding machines for the production of parts made of plastic or other materials exist in different sizes and variants. When developing such machines, manufacturers strive to design components that can be used as universally as possible, function reliably and are at the same time inexpensive. Ideally, the parts produced should be scalable to meet different requirements and require only minor adjustments to use at different points on an injection moulding machine. Injection moulding machines usually have multiple electrical machines for actuating various components and units. For example, there may be a motor for a clamping unit, a motor for an injection piston and a motor for a plasticising unit. Electric switching units, in particular inverter units, are used to drive the motors. The electrical power of the switching units must be adjusted to the electrical power of the electrical machine. However, the higher the required power, the larger and more expensive the switching units become. It would therefore be desirable to have universally applicable switching units available that are scalable and at the same time inexpensive. It is known from the state of the art that switching units can be connected in parallel, thereby dividing the energy flows among the individual switching units. This allows an electrical machine of high power to be operated with multiple switching units of lower power. Depending on the demand for electrical power, the number of switching units connected in parallel can be increased or decreased. This is in line with the above-mentioned desire for standardisation and scalability. However, since the currents output by switching units connected in parallel sometimes deviate considerably during operation, correspondingly large chokes with high inductance must be used at the outputs of the switching units to compensate for these differences and the current pulse peaks that occur during switching. However, large chokes are expensive and take up a lot of space. In addition, downstream chokes have the disadvantage that they can limit the bandwidth of any current control. Chokes with high inductance limit the bandwidth more. From U.S. Pat. No. 7,138,773 B2 inverter units connected in parallel with high power ratings for controlling asynchronous motors in vehicles are known. Using a complicated algorithm based on multiple parameters and input variables, the switching times of switches in the inverters that switch too early are delayed in order to synchronise the switches contained in the inverter units. The switches of U.S. Pat. No. 7,138,773 B2 are configured as IGBTs or GTOs and are designed for high currents. For this reason, the switches of U.S. Pat. No. 7,138,773 B2 switch very slowly compared to other types of switches. As a drawback, the actual switching of the switches must be monitored, and the output voltage measured in order to execute the algorithm. This requires precise and complex monitoring of the switching edges. Another disadvantage is that the system of U.S. Pat. No. 7,138,773 B2 is designed for vehicles and the used switches switch comparatively slowly due to their design for high currents. This means that it is not possible to achieve such high precision and dynamics in the control of electrical machines as is required for injection moulding machines. It is therefore the object of the present invention to eliminate or at least partially alleviate the disadvantages of the state of the art. It is preferably the object of the present invention to provide an injection moulding machine with switching units for controlling electrical machines, in which the chokes for compensating differences in the output currents of the switching units connected in parallel can be kept as small as possible in size or can even be omitted altogether. This object is first solved by an injection moulding machine according as described herein. An injection moulding machine according to the invention therefore comprises: at least one electrical machine, in particular a synchronous motor;multiple switching units electrically connected in parallel, in particular inverter units, which are designed to drive the electrical machine, wherein each switching unit has at least one electrical output and at least one electrical switch which is associated with the output and can be switched in accordance with 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 a