METHOD FOR OPERATING A MANUFACTURING PLANT

Description

[0001] The invention relates to a method for operating a production plant, wherein the production plant comprises at least one plastics processing machine and a power supply, wherein the plastics processing machine and / or an additional unit cooperating therewith comprises at least one motor which is designed to drive a component of the plastics processing machine or to drive the additional unit and for generator operation in the event of braking of a movement of the component or the additional unit, wherein the plastics processing machine further comprises at least one heating element for heating plastic material, wherein the power supply comprises an alternating current network which is connected to a direct current network via a power converter, and a direct current source which is connected to the direct current network,wherein the plastics processing machine is connected to the direct current network for supplying electrical energy, wherein a control element detects whether the at least one motor and / or the auxiliary unit generates energy by generator, wherein, in the event that the motor and / or the auxiliary unit generates energy by generator, the control element controls a semiconductor switching element in order to supply the energy generated by generator to the heating element, wherein the energy generated by generator from the motor and / or the auxiliary unit is fed into a direct current intermediate circuit of the plastics processing machine, which can be connected to the direct current network and wherein at least one storage element for electrical energy, in particular a capacitor, is electrically connected to the direct current intermediate circuit.

[0002] A generic method is described in DE 10 2009 033 228 A1. Similar and further solutions are shown in DE 10 2006 036 267 A1. , DE 10 2013 104 814 A1 , DE 101 52 198 A1 , DE 103 24 516 A1 and US 6 333 611 B1 . JP 2000 202886 A discloses an injection molding machine in which a photovoltaic system is used for energy supply.

[0003] The efficient supply of energy to plastics processing machines, and especially injection molding machines, is a relevant challenge, particularly from the perspective of environmental compatibility. Such machines often have variable-speed drives. The machines are designed for connection to alternating current networks. The alternating current network feeds a direct current intermediate circuit via a power converter (i.e., rectifier), from which the machine is then supplied with energy. Such a solution is known from the aforementioned DE 10 2009 033 228 A1.

[0004] In principle, it is also possible for the plastics processing machine to be operated as a generator. This means that when a machine movement is decelerated, the braking process is used to recover energy via the drive motor, which then acts as a generator. The recovered energy is then instantly fed into the electrical grid (if an AC regenerative unit is installed).

[0005] If a direct current (DC) network is used to supply the machine with energy, the direct current obtained from the kinetic energy is fed directly into the DC network.

[0006] However, this has the following disadvantage: If no other consumer is requesting energy within the plastics processing machine at the time the recuperation energy is generated, the recuperation energy must be transported to other consumers via long cables, which may incur losses. If the instantaneous energy demand is below the level provided by the direct current grid, the recuperation energy must be transformed, with losses, and fed into an alternating current grid, provided there is no more capacity in storage batteries. In some cases, it may even be necessary to thermally dissipate the recovered energy using braking resistors, which is very disadvantageous. In DC grids with multiple recuperation-capable consumers (motors), severe fluctuations can also occur if recuperation energy peaks coincide unfavorably, which can lead to problems.

[0007] The invention is based on the Task The aim is to propose a method by which a production plant with a plastics processing machine, in particular an injection molding machine, can be operated in such a way that an improved and environmentally friendly energy supply is possible. The recuperative recovery of energy from the plastics processing machine or from units working in conjunction with it should ensure that this energy can be used with minimal loss. This should also minimize disruption to the power grid.

[0008] The solution to this problem by the invention is characterized in that a photovoltaic system is used as the direct current source, wherein energy is transferred from the direct current network into an energy storage device in the form of a battery or withdrawn from it, wherein electrical energy is transferred between the direct current network and the direct current intermediate circuit via a connection module and wherein the method comprises the steps: a) Determining the sum of the currently available recuperation energy supplied by all generator-operating motors and / or additional units; b) Determining the sum of the energy taken from the DC link required by all consumers connected to the DC link; c) Determining the difference between the sum of the recuperation energy according to step a) and the sum of the energy taken according to step b); d) Initiating the feeding of energy into the heating element by the control element and the semiconductor switching element, whereby the difference in energy determined according to step c) is supplied to the heating element.

[0009] This enables the recuperation energy to be used as optimally as possible and prevents it from being fed back into the direct current grid.

[0010] This approach allows the heating element to be used specifically to dissipate the energy generated by the generator, thereby minimizing the load on the electrical grid. In particular, the conversion of the energy generated by the generator into an AC grid can be avoided, enabling low-loss energy management.

[0011] According to the invention, energy is transferred from the DC grid to or withdrawn from an energy storage device (battery). This is particularly important when the available recuperation energy within the machine exceeds the demand in the heating element, so that electrical energy then flows from the DC link into the DC grid and on to the energy storage device.

[0012] The at least one motor of the plastics processing machine is preferably designed as a variable speed drive.

[0013] The semiconductor switching element is preferably designed as an insulated gate bipolar transistor (IGBT).

[0014] The temperature in a component heated by the heating element is preferably maintained at a predetermined temperature in a closed control loop, particularly by means of the control element. Thus, the input of recuperative energy into the heating element has no negative impact on the quality of temperature control.

[0015] According to a preferred embodiment of the invention, the plastics processing machine is an injection molding machine. In this case, the heating element is preferably the cylinder heater of a plasticizing unit of the injection molding machine.

[0016] The additional unit is preferably a robot that interacts with the plastics processing machine.

[0017] Furthermore, it can be provided that a control circuit is electrically connected to the DC link via a switched-mode power supply, whereby the electrical loads of the plastics processing machine are supplied with power from the DC link and controlled by the control circuit. The electrical load is, for example, a machine control unit (CPU), a control unit (MMI), a control section of a servo converter, a sensor, an indicator lamp, a contactor, a switch, a valve, a magnet, or a fan.

[0018] Regarding the further possible embodiment of the invention, reference is expressly made to the above-mentioned DE 10 2009 033 228 A1.

[0019] Accordingly, the present invention provides for the detection of recuperative energy (braking energy from the plastics processing) generated by a load that also operates as a generator (in particular, a motor). If recuperative energy is available, the energy is fed to the heating element, in particular to the cylinder heater of a plasticizing unit of an injection molding machine, by means of a fast-switching semiconductor switching element.

[0020] The recuperation energy fed into the heating element is preferably taken into account by a temperature controller so that the quality of the temperature control is not reduced.

[0021] This advantageously makes a significant contribution to stabilizing the DC grid by utilizing the recuperation energy within the machine (in the exemplary embodiment described below, the energy flow is represented either with unidirectional energy direction arrows or double arrows, depending on whether current flows in only one direction or can flow in both directions).

[0022] Furthermore, the line losses during the exchange of recuperation energy can be minimized.

[0023] Another advantage is that conversion losses (DC to AC) can be avoided. It is particularly advantageous if the proposed method can prevent energy dissipation in braking resistors.

[0024] As explained, additional units, particularly in the form of robots (e.g., removal robots for removing workpieces from the machine), can also be integrated into the use of generator-operated drives of the plastics processing machine. Here, too, braking energy can be recovered during operation of the additional unit and fed to the heating element in the manner described.

[0025] The invention thus allows for effective use of the potential of direct current (DC) technology and provides an industrial direct current network for power supply, which is fed with renewable energy.

[0026] The DC intermediate circuit of the plastics processing machine is connected to the DC network without loss by a connection module, preferably including a charging circuit and EMC filter.

[0027] The drawing illustrates an embodiment of the invention. The single figure shows a schematic electrical circuit diagram of a production system comprising a power supply and an injection molding machine.

[0028] The figure shows an electrical circuit diagram showing a production plant 1 comprising an injection molding machine 2 which is supplied with electrical energy via a power supply 3.

[0029] The energy supply 3 comprises two components: The first component is an alternating current network 4 (three phases L1, L2, and L3 are indicated), which feeds electrical energy into a direct current network 6 via a power converter 5 (rectifier). The second component is a direct current source 7 together with an (optional) energy storage device 8, which feeds electrical energy into the direct current network 6. The direct current source 7 is designed here as a photovoltaic system that generates direct current from solar energy. The energy storage device 8 is a battery in which excess energy can be stored and retrieved when needed.

[0030] The injection molding machine 2 has a DC intermediate circuit 23 (DC+ / DC-) that can be electrically connected to the DC network 6 via a connection module 9 (the connection module 9 also includes a charging circuit, a bypass relay, and an EMC filter). A main switch HS for switching on the machine is also indicated.

[0031] The injection molding machine in the present case is designed as a purely electric injection molding machine. Accordingly, all of the machine's drives are electrical, preferably with servo motors. Three motors 16, 17 and 18 are shown, with which the required adjustment movements of the machine are carried out. Motor 16 serves to drive the clamping unit of the injection molding machine. Motor 17 serves to drive the injection unit. Motor 18 in the present case serves to drive a further axis, which can be that of an ejector, for example. The motors 16, 17, 18 are also designed to be operated as generators, i.e. to generate electrical energy from kinetic energy. Therefore, if a movement of the injection molding machine needs to be slowed down, the motor is used as the braking element, generating electrical energy and feeding it back into the DC intermediate circuit 23 orfurther into the direct current network 6, which is connected to the electrical intermediate circuit 23 via the connection module 9.

[0032] Also shown is a heating element 10, which in this case is the cylinder heater of a plasticizing unit. The heating element 10 is suitable for high voltages, in particular for voltages greater than or equal to 900 VDC. Furthermore, the heating element 10 is suitable for absorbing high, but only short-term, power peaks, in particular of at least 30 kW over a period of at least 250 ms.

[0033] The motors and the heating element are all electrically connected to the DC link 23.

[0034] An energy exchange can take place via this DC link connection if, for example, a drive 16, 17, 18 is decelerated (braked), thereby operating as a generator and feeding energy into the DC link 23, which can be taken from another consumer.

[0035] For this purpose, the invention provides that a control element 12 detects whether one of the motors 16, 17, 18 is generating energy, wherein in the event that at least one of the motors 16, 17, 18 is generating energy, a semiconductor switching element 11 is controlled by the control element 12 in order to supply the energy generated by the generator to the heating element 10.

[0036] For this purpose, the control element 12 is connected to the motors 16, 17, 18 (or their control element "CPU") via respective data lines 19, 20, 21, so that it can be detected when one of the motors is operating as a generator and consequently feeds energy into the DC link 23.

[0037] In order to enable the most optimal use of recuperation energy and prevent it from being fed back into the DC grid, it can be specifically planned to calculate the current recuperation energy value minus the current total energy demand of all motors and other consumers and to control the heating element 10 in such a way that precisely this excess energy is fed into the heating element 10. In this respect, reference is made to the above-mentioned procedure with steps a) to d).

[0038] In the given case, i.e. when generator energy is generated, the control element 12 controls the semiconductor switching element 11 via a data line 22, so that the latter draws energy from the DC intermediate circuit 23 to operate the heating element 10.

[0039] In this way, the stability of the electrical supply in power supply 3 is improved.

[0040] In this case, an upper limit value can be specified for the control element 12, in particular for the current temperature T of the heating element 10, above which no further energy transfer into the heating element 10 takes place in order to prevent it from overheating.

[0041] The DC intermediate circuit 23 is electrically connected to an electrical storage element 13 (energy storage) in the form of a high-capacity capacitor. During braking, if excess energy is available, the capacitor 13 can be charged, which can provide further advantages in the recuperative operating mode.

[0042] A control circuit 14 required for the operation of the injection molding machine 2 is supplied with electrical energy from the DC link 23 via a switching power supply 15 to generate a control voltage (e.g., 24 VDC). The control circuit 14 supplies a variety of electrical consumers, such as machine controls (CPU; control or processing unit), an operating unit (MMI; screen, input unit), a control section of a servo converter (CPU), sensors, indicator lamps, contactors, switches, valves, magnets, etc. These electrical consumers represent a certain proportion of the total energy consumption (e.g., 500 W).

[0043] In the exemplary embodiment, the semiconductor switching element 11 is an insulated-gate bipolar transistor (IGBT). This is a semiconductor component used in power electronics because it combines the advantages of a bipolar transistor (good conductivity, high blocking voltage, robustness) with the advantages of a field-effect transistor (virtually powerless control). A certain degree of robustness against short circuits is also advantageous, since the IGBT limits the load current.

[0044] The heating element 10 is designed in such a way that it is suitable for the high or highest permissible voltage of the DC intermediate circuit (e.g. 900 VDC), can absorb high power peaks (e.g. 30 kW) for a short time (e.g. for 250 ms) and can thereby fulfill its actual purpose (in this case: heating a zone of the plasticizing cylinder) with regard to the rated power.

[0045] The heating element 10 is therefore specifically available if energy reduction in the DC intermediate circuit 23 is required by recovering recuperative energy from the motors 16, 17, 18, namely, during braking phases, particularly when other elements (drives 16, 17, 18, energy storage device 13, control circuit 14) do not draw sufficient energy from the DC intermediate circuit 23 to prevent the intermediate circuit voltage from rising above a maximum permissible value. Furthermore, the heating element 10 naturally fulfills its original purpose, in this case, heating a zone of the plasticizing unit.

[0046] The semiconductor switching element 11 can be controlled by a corresponding controller (in a closed control loop) depending on the temperature T of the heating element 10 in order to maintain a target temperature; for this purpose, a corresponding temperature sensor must be provided on the heating element 10 to detect the actual temperature T actual . For the exact procedure in this regard, reference is expressly made to EP 2 276 165 B1.

[0047] In the figure, the arrows indicate the direction in which energy flows. Accordingly, the direct current source 7 can only supply energy, while the energy storage device 8 can both output and absorb energy. Excess energy, particularly from recuperation or, in the case of surplus energy, from the photovoltaic system, can also be fed into the alternating current grid 4. However, in light of the above explanations, this is not intended in order to minimize losses.

[0048] The AC network 4 typically has a voltage of 400 VAC. In the DC network 6, for example, voltages of approximately 600 VDC are desired. The control circuit 14 is usually operated with 24 VDC.

[0049] It should be mentioned in passing that several plastics processing machines, in particular injection molding machines, can of course also be connected to the DC network 6. It is also possible to connect other consumers, in particular the aforementioned auxiliary units (robots). List of reference symbols:

[0050] 1Production plant 2Plastics processing machine (injection molding machine) 3Power supply 4Alternating current network (AC network) 5Power converter 6Direct current network (DC network) 7Direct current source (photovoltaic system) 8Energy storage (battery) 9Connection module 10Heating element 11Semiconductor switching element (IGBT) 12Control element 13Storage element (capacitor) 14Control circuit 15Switched power supply 16Motor 17Motor 18Motor 19Data line 20Data line 21Data line 22Data line 23DC intermediate circuit

Claims

1. Method for operating a production arrangement (1), wherein the production arrangement (1) comprises at least one plastic processing machine (2) and an energy supply (3), wherein the plastic processing machine (2) and / or an auxiliary unit interacting with it comprises at least one motor (16, 17, 18) which is designed to drive a component of the plastic processing machine (2) or to drive the auxiliary unit, and also to operate as a generator in the event of deceleration of a movement of the component or of the auxiliary unit, wherein the plastic processing machine (2) further comprises at least one heating element (10) for heating plastic material, wherein the energy supply (3) comprises an alternating current network (4) which is connected to a direct current network (6) via a power converter (5), and comprises a direct current source (7) which is connected to the direct current network (6), wherein the plastic processing machine (2) is connected to the direct current network (6) for the supply of electrical energy, wherein a control element (12) detects whether the at least one motor (16, 17, 18) and / or the auxiliary unit generates energy in a generator mode, wherein, if energy is generated in a generator mode by the motor (16, 17, 18) and / or by the auxiliary unit, the control element (12) activates a semiconductor switching element (11) in order to feed the energy generated by the generator to the heating element (10), wherein the generator-generated energy is fed from the motor (16, 17, 18) and / or from the auxiliary unit into a direct current intermediate circuit (23) of the plastic processing machine (2), which can be connected to the direct current network (6), and wherein at least one storage element (13) for electrical energy, in particular a capacitor, is electrically connected to the direct current intermediate circuit (23), wherein a photovoltaic system is used as the direct current source (7), wherein energy is transferred from the direct current network (6) to an energy storage device (8) in the form of a battery or withdrawn therefrom, wherein electrical energy is transferred between the direct current network (6) and the direct current intermediate circuit (23) via a connection module (9), and wherein the method comprises the steps: a) Determination of the sum of recuperation energy currently available, which is supplied by all motors (16, 17, 18) operating as generators and / or auxiliary units; b) Determination of the sum of the energy taken from the direct current intermediate circuit (23) that is required by all consumers connected to the direct current intermediate circuit (23); c) Determination of the difference between the sum of the recuperation energy according to step a) and the sum of the extracted energy according to step b); d) Initiating the supply of energy to the heating element (10) by means of the control element (12) and the semiconductor switching element (11), wherein the difference in energy determined in step c) is supplied to the heating element (10).

2. Method according to claim 1, characterised in that the at least one motor (16, 17, 18) of the plastic processing machine (2) is designed as a variable-speed drive.

3. Method according to claim 1 or 2, characterised in that the semiconductor switching element (11) is designed as an insulated gate bipolar transistor (IGBT).

4. Method according to one of claims 1 to 3, characterised in that the temperature (Tist) in a component heated by the heating element (10) is maintained at a predetermined temperature (T) in a closed control loop, in particular by means of the control element (12).

5. Method according to one of claims 1 to 4, characterised in that the plastic processing machine (2) is an injection moulding machine.

6. Method according to claim 5, characterised in that the heating element (10) is the cylinder heater of a plasticising unit of the injection moulding machine.

7. Method according to one of claims 1 to 6, characterised in that the auxiliary unit is a robot that interacts with the plastic processing machine (2).

8. Method according to one of claims 1 to 7, characterised in that a control circuit (14) is electrically connected to the direct current intermediate circuit (23) via a switching power supply (15), wherein the electrical consumers of the plastic processing machine (2) are supplied with energy from the direct current intermediate circuit (23) and are controlled from the control circuit (14).