High-voltage cable with multiple conductors

Abstract

The invention relates to a high-voltage cable (6), in particular for the electrostatic charging of a coating in a coating system for coating motor vehicle body components (14) with a coating. The high-voltage cable (6) according to the invention has a first conductor (7) extending longitudinally and being electrically conductive. According to the invention, the high-voltage cable (6) additionally has a second conductor (9) extending longitudinally and being electrically conductive, wherein the second conductor (9) is electrically insulated from the first conductor (7). Furthermore, the invention also includes a coating system with such a high-voltage cable (6) and the novel use of such a high-voltage cable (6) in a coating system.

Description

Technical field of the invention

[0001] The invention relates to a high-voltage cable, in particular for the electrostatic charging of a coating material (e.g., paint) in a coating system (e.g., a paint shop) for painting components (e.g., automotive body parts). Furthermore, the invention relates to a coating system (e.g., a paint shop) with electrostatic charging of the coating material and the high-voltage cable according to the invention. Finally, the invention also relates to the novel use of a high-voltage cable according to the invention in a coating system. Background of the invention

[0002] In modern paint shops for painting vehicle body components, the paint to be applied is usually atomized by a rotary atomizer and then deposited on the vehicle body component to be coated.

[0003] To increase the application efficiency and thus avoid disruptive overspray, an electrostatic coating agent is charged; that is, the paint to be applied is electrostatically charged to a high voltage in the range of 20 kV to 100 kV, while the vehicle body component to be painted is electrically grounded, so that the sprayed and electrostatically charged paint is electrostatically attracted to the electrically grounded vehicle body component and is therefore deposited almost completely on the vehicle body component with a high application efficiency and correspondingly little overspray.

[0004] The high voltage required for this electrostatic charging of the paint is generated by a high-voltage source and conducted via a high-voltage cable to a high-voltage electrode to electrostatically charge the paint. This high-voltage electrode can, for example, be an external electrode that electrostatically charges the sprayed paint stream. Alternatively, a direct charging method (contact charging) is also possible, in which the bell-shaped disc of the rotary atomizer itself is electrically charged and therefore electrostatically charges the paint to be applied before atomization due to the contact between the paint and the bell-shaped disc.

[0005] A problem with this type of electrostatic paint charging is that the high-voltage source, the high-voltage cable, and the rotary atomizer all form an electrical capacitance with respect to ground (earth). The high-voltage cable accounts for the largest share of this total capacitance, depending on its length and how it is laid. The capacitance of the high-voltage cable is associated with various problems, which are briefly described below.

[0006] Firstly, the high-voltage cable stores electrical energy during operation, according to its capacity. In the event of an unintentional release through spark discharge against the electrically grounded vehicle body, this energy could ignite the explosive atmosphere in the paint booth or endanger people.

[0007] On the other hand, the capacitance of the high-voltage cable also leads to inertia in the high-voltage supply, meaning that regulating the high voltage is made more difficult by the inertia of the high-voltage supply. This is particularly true when the desired voltage value has to be reduced due to process requirements. Because of this disruptive inertia of the high-voltage supply, switching it off also takes longer the higher the capacitance of the high-voltage cable. Consequently, the cycle time increases when the high voltage has to be switched off for process reasons, for example, during the automatic cleaning of the rotary atomizer.

[0008] Furthermore, the capacitance of the high-voltage cable can also lead to problems during a safety shutdown. Normally, the high voltage is automatically switched off if the rotary atomizer gets too close to the electrically grounded vehicle body component. However, with a high capacitance of the high-voltage supply, and especially the high-voltage cable, a spark discharge can occur despite timely detection and shutdown of the power supply. This is because, during a safety shutdown, the painting robot must first decelerate its movement and can thereby move closer to the vehicle body component. During this deceleration, the distance between the high-voltage electrode and the electrically grounded vehicle body component can decrease further, allowing the energy stored in the high-voltage cable to be released.

[0009] To avoid the problems described above caused by the electrical energy stored in the high-voltage cable, the high-voltage cable is usually kept as short as possible in order to achieve the lowest possible capacitance of the high-voltage cable.

[0010] Furthermore, it should be noted that during operation, electrical connections in high-voltage cables can become faulty. This can occur, for example, if connectors become loose due to movement or vibration of the cable. Depending on the severity of the fault, such contact defects often go undetected because the high voltage of several tens of kilovolts present during operation is easily capable of bridging even small gaps of just a few millimeters. Nevertheless, this can pose a risk, as, for example, after the high-voltage power supply is switched off, a residual voltage of several kilovolts remains in the system, and this residual voltage then falls below the value required to bridge the gap. For this reason, technical standards mandate regular inspection of cable connections in such high-voltage power supplies.

[0011] Therefore, monitoring systems capable of detecting such faulty contact points are already known in the art. However, these systems also have disadvantages, such as additional costs due to extra components, increased complexity, and consequently, a higher susceptibility to system failure. A particularly significant drawback of such monitoring systems is the requirement for a second high-voltage cable to connect the monitoring unit to the applicator (e.g., rotary atomizer). This second high-voltage cable is often even longer than the high-voltage cable required for the electrostatic paint charging process, especially when space constraints necessitate mounting the monitoring unit further away from the applicator (e.g., rotary atomizer).This quickly increases the capacity of the high-voltage supply by a factor of two or even more. Accordingly, the safety gain achieved through monitoring comes at the cost of a further increase in the interfering capacity and additional effort.

[0012] When designing paint systems with electrostatic paint charging, a conflict of objectives arises. On the one hand, contact faults in the high-voltage cable should be detected by the monitoring system described above. On the other hand, this safety monitoring actually leads to an increase in the interfering capacitance. Description of the invention

[0013] The invention is therefore based on the objective of resolving the conflict of objectives described above.

[0014] This problem is solved by a high-voltage cable according to the invention, a corresponding coating system (e.g., a painting system) with such a high-voltage cable, and the novel use of the high-voltage cable according to the invention in a coating system (e.g., a painting system).

[0015] The high-voltage cable according to the invention is preferably designed for use in electrostatic coating agent charging in a coating system (e.g., a paint shop). However, the invention is not limited to use in electrostatic coating agent charging with regard to the field of application of the high-voltage cable according to the invention, but can also be used in other ways.

[0016] In accordance with known high-voltage cables (e.g., DE 10 2014 010 777 A1), the high-voltage cable according to the invention also initially comprises a first conductor running longitudinally along the cable and being electrically conductive, which can, for example, be made of copper or a resistive material. Within the scope of the invention, it is therefore not necessary for the conductors in the high-voltage cable to be made of a material with very good electrical conductivity, such as copper or aluminum. Rather, the conductors can also be made of a resistive material, provided that the electrical conductivity of the resistive material is sufficiently high to supply the high-voltage electrode (e.g., outer electrodes of an external charging ring) with the required high voltage for electrostatic coating charging.

[0017] The high-voltage cable according to the invention is characterized by an additional second conductor running lengthwise along the cable and electrically insulated from the first conductor. The high-voltage cable according to the invention thus has at least two electrically insulated conductors and therefore offers redundancy in the connection. For example, if a connector on one of the two conductors should be faulty, the connector on the other conductor is still sufficient to correctly transmit the high voltage. Because of this redundancy, the safety monitoring described above, with its associated disadvantages, can potentially be dispensed with.

[0018] In a simple version of the invention, the two conductors run side by side in the high-voltage cable.

[0019] However, it is particularly advantageous if the two conductors in the high-voltage cable are arranged coaxially, with the second conductor surrounding the first conductor.

[0020] In such a coaxial arrangement of the two conductors, an inner first insulator is preferably arranged between the two conductors, which electrically isolates the two conductors from each other. Furthermore, in such a coaxial arrangement, an outer second insulator is preferably provided, which surrounds the outer second conductor.

[0021] The inner first insulator between the two conductors can have a relatively small radial thickness because the two conductors are normally at the same electrical potential during operation, meaning that only a correspondingly short insulation distance is sufficient to isolate the two conductors from each other. Therefore, the inner first insulator preferably has a smaller radial thickness than the outer second insulator.

[0022] For example, the inner first insulator between the two conductors can have a radial layer thickness that is less than 10 mm, 5 mm, 2 mm, 1 mm or 0.5 mm.

[0023] The dielectric strength of the inner first insulator between the two conductors can therefore be relatively low and be less than 50 kV, 20 kV, 15 kV, 12 kV, 10 kV, 5 kV, 2 kV or 1 kV.

[0024] Otherwise, the high-voltage cable according to the invention can be constructed in a conventional manner. For example, the high-voltage cable according to the invention can have a field smoother extending longitudinally along the cable, which is arranged between the outer second conductor and the outer second insulator. Such field smoothers are known, for example, from the aforementioned patent application DE 10 2014 010 777 A1 and therefore do not need to be described in more detail.

[0025] Preferably, the field smoother rests directly on the outer second conductor without an intermediate layer. The field smoother can be made of plastic, for example, polyolefin. Furthermore, it should be noted that the field smoother can be made of a material with a specific electrical resistance that is lower than that of the inner first insulator and the outer second insulator, but higher than that of the inner first conductor and the outer second conductor.

[0026] Furthermore, the high-voltage cable according to the invention can have an outer cable sheath to protect the high-voltage cable from mechanical or chemical influences. For example, this high-voltage cable can be made of plastic (e.g., polyurethane). It should be noted that the cable sheath preferably has greater abrasion resistance, is less flammable, and / or more acid-resistant than the outer second insulator.

[0027] It has already been mentioned above that the invention enables a redundant high-voltage supply, since the high-voltage cable according to the invention contains several separate conductors. This redundancy should also exist in the electrical contacting of the high-voltage cable according to the invention. Preferably, the high-voltage cable according to the invention therefore has multi-pole electrical connectors (e.g., plug connectors) at its ends, which enable a multi-pole electrical connection between the high-voltage cable according to the invention on the one hand and another device (e.g., high-voltage source) or cable on the other. Each conductor of the high-voltage cable is assigned a pole (e.g., contact pin) of the electrical connector. In the event of a contact fault (e.g.,If there is a loose connection at one of the poles of the electrical connector, the high voltage can still be transmitted via the other pole of the electrical connector, so that the electrical connector is also redundant.

[0028] It should be noted that, generally speaking, the inner first conductor and / or the outer second conductor can be made of copper or aluminum or of a resistive material.

[0029] In contrast, the inner first conductor and the outer second conductor preferably consist of a material with a lower specific electrical resistance than the inner first insulator and the outer second insulator.

[0030] Furthermore, it should be noted that the high-voltage cable according to the invention is preferably high-voltage resistant up to a high voltage of at least 1 kV, 2 kV, 5 kV, 10 kV, 20 kV, 50 kV, 100 kV or 150 kV.

[0031] Furthermore, it should be mentioned that the high-voltage cable according to the invention preferably has an electrical resistance which, based on its length, is at least 1 kΩ / m, 2 kΩ / m, 5 kΩ / m, 10 kΩ / m and / or at most 1 MΩ / m, 500 kΩ / m, 200 kΩ / m, 100 kΩ / m, 50 kΩ / m or 20 kΩ / m.

[0032] The high-voltage cable according to the invention preferably has an electrical capacitance that, based on its length, is at least 1 pF / m, 10 pF / m, 20 pF / m, 50 pF / m, 70 pF / m and / or at most 1000 pF / m, 500 pF / m, 250 pF / m, 100 pF / m.

[0033] It should also be mentioned that the inner first insulator and / or the outer second insulator can be made of plastic, especially polyolefin.

[0034] In the preferred embodiment of the invention, the inner first conductor, the outer second conductor, the inner first insulator, the outer second insulator, the field smoother and / or the cable sheath are arranged coaxially.

[0035] In such a coaxial arrangement, the inner first conductor is preferably cylindrical or hollow cylindrical, while the outer second conductor, the inner first insulator, the outer second insulator, the field smoother and / or the cable sheath are each hollow cylindrical.

[0036] It has been described above that the high-voltage cable according to the invention offers redundancy due to the use of two conductors. However, the invention is not limited to high-voltage cables with exactly two conductors. Rather, within the scope of the invention, it is also possible for the high-voltage cable to have more than two conductors that are electrically insulated from each other, for example, three, four, five, or six conductors, to name just a few examples.

[0037] Furthermore, it should be mentioned that the invention does not only claim protection for the high-voltage cable according to the invention as a single component. Rather, the invention also claims protection for a coating system (e.g., a paint system) for coating components (e.g., automotive body components) with a coating agent (e.g., paint).

[0038] The coating system according to the invention initially comprises a high voltage source to generate the high voltage required for electrostatic charging of the coating material, as is known in the prior art.

[0039] Furthermore, the coating system according to the invention, in accordance with the prior art, also includes at least one high-voltage electrode for electrostatically charging the coating material (e.g., paint). For example, the high-voltage electrode can be an external electrode, such as one mounted in an external charging ring on a rotary atomizer, which electrostatically charges the sprayed coating material. Alternatively, so-called direct charging (contact charging) is also possible, in which, for example, the bell-shaped plate of the rotary atomizer is charged and therefore electrostatically charges the coating material during spraying. The invention is thus not limited to a specific type of electrostatic charging of the coating material (external charging or direct / contact charging).

[0040] Furthermore, the coating system according to the invention also has a high-voltage cable that connects the high-voltage source to the high-voltage electrode.

[0041] The coating system according to the invention is now characterized in that the high-voltage cable is designed in the manner described above according to the invention.

[0042] Preferably, all conductors of the high-voltage cable are connected to the high-voltage source or the high-voltage electrode and are therefore at the same electrical potential, thus creating a redundant high-voltage supply. In the event of a break in one of the conductors, the correct connection via the other conductor is then sufficient.

[0043] The high-voltage cable according to the invention preferably has a very low electrical capacitance to ground in order to achieve the lowest possible inertia when switching off the high-voltage source and when regulating the high voltage. The electrical capacitance of the high-voltage cable is preferably so low that the voltage at the high-voltage electrode drops with a time constant of at most 2 s, 1 s, 500 ms, 250 ms, 100 ms, 50 ms, 25 ms, 10 ms, or 5 ms when the high-voltage source is switched off abruptly.

[0044] Furthermore, the high-voltage cable should also have a very low electrical capacitance to ground so that the electrical energy stored in the high-voltage cable is less than the energy required to endanger people or to ignite a spark. Preferably, the electrical energy stored in the high-voltage cable is therefore less than 10 J, 5 J, 2 J, 1 J, 500 mJ, 350 mJ, or 250 mJ at operating voltage.

[0045] The high-voltage cable according to the invention can therefore be relatively long and have a length of more than 2 m, 5 m, 10 m or even more than 20 m.

[0046] Finally, it should be mentioned that the invention not only claims protection for the high-voltage cable according to the invention and a coating system according to the invention with such a high-voltage cable. Rather, the invention also claims protection for the novel use of the high-voltage cable according to the invention for supplying voltage to an electrostatic coating agent charging system in a coating system (e.g., a paint shop).

[0047] Other advantageous embodiments of the invention are characterized in the dependent claims or are explained in more detail below together with the description of the preferred embodiments of the invention with reference to the figures. Brief description of the drawings Fig. Figure 1 shows a cross-sectional view of a conventional high-voltage cable according to the state of the art. Fig. Figure 2 shows a cross-sectional view of a high-voltage cable according to the invention with a coaxial arrangement of two separate conductors. Fig. Figure 3 shows a cross-sectional view of another embodiment of a high-voltage cable according to the invention with two conductors arranged side by side. Fig. Figure 4 shows a schematic representation of a painting system according to the invention for painting motor vehicle body components. Fig. Figure 5 shows a simplified schematic representation of a high-voltage cable according to the invention with plug connections at both ends. Detailed description of the drawings

[0048] The following section will first show the cross-sectional view according to... Fig. Figure 1 shows a conventional high-voltage cable 1 according to the state of the art.

[0049] This high-voltage cable 1 is characterized by a coaxial structure and has a conductor 2 made of copper in the middle, which is surrounded by a field smoother 3 made of plastic (e.g. polyolefin), an insulator 4 and a cable sheath 5 made of plastic (e.g. polyurethane), as is known from the prior art.

[0050] High-voltage cable 1 therefore only has conductor 2 as its single conductor. This can lead to the problems described at the beginning, for example at the plug connections of high-voltage cable 1, if there are contact problems.

[0051] The embodiment according to the invention will now be described in the following example. Fig. 2 described. Thus, it shows Fig. 2 also a high-voltage cable 6 with a coaxial arrangement with an inner conductor 7, which is surrounded by an insulator 8 and another conductor 9. The conductor 9 is in turn surrounded by a field smoother 10 made of plastic (e.g., polyolefin). A further insulator 11 and finally a cable sheath 12 made of plastic (e.g., polyurethane) are attached to the outside of the field smoother 10.

[0052] The high-voltage cable therefore has two conductors, 7 and 9, which allows for redundancy. If, for example, the connector on conductor 7 is defective, the high voltage can still be transmitted via the other conductor 9.

[0053] Furthermore, it should be noted that the two conductors 7 and 9 are at the same electrical potential during operation. The inner insulator 8 between the two conductors 7 and 9 can therefore have a significantly smaller radial thickness than the outer insulator 11, since the dielectric strength of the inner insulator 8 only needs to be a few kilovolts.

[0054] Furthermore, the larger diameter of the outer conductor 9, which is effective for the field strength, reduces the load on the outer insulator 11, which serves as the main insulating layer, allowing it to be somewhat thinner and thus compensate for the increased space requirement of the inner core.

[0055] The high-voltage cable 1 according to the invention, with its coaxial construction, can be considered capacitively in the same way as a conventional high-voltage cable with only one – somewhat thicker – conductor. Nevertheless, it makes it possible to equip even longer connection distances with a redundant connection and thus increase reliability.

[0056] Fig. Figure 3 shows a modification of the embodiment of the invention described above according to the invention. Fig. 2, so that, to avoid repetition, reference is made to the preceding description, using the same reference numerals for relevant details.

[0057] A special feature of this embodiment is that the high-voltage cable 6 does not have a coaxial structure. Rather, the two conductors 7, 9 are arranged side by side in the high-voltage cable 6.

[0058] The following section will describe the in Fig. Figure 4 shows a schematic representation of a painting system 13 according to the invention, wherein the painting system 13 serves for painting motor vehicle body components 14, which are electrically grounded during painting and are only symbolically represented in the drawing.

[0059] Firstly, the painting system 13 according to the invention has a high voltage source 15, which can be designed in a conventional manner and generates the high voltage required for electrostatic paint charging, wherein the high voltage can be, for example, in the range of 20 kV to 100 kV.

[0060] Furthermore, the paint system 13 has a rotary atomizer 16 as an application device, which atomizes the paint by means of a rotating bell plate 17 and releases a spray jet 18 of the paint onto the motor vehicle body component 14 to be painted.

[0061] The rotary atomizer 16 has an external charging ring 19 with external electrodes 20, as is known from the prior art. The external electrodes 20 are connected to the high-voltage source 15 via a high-voltage cable 21.

[0062] However, it should be noted that direct charging (contact charging) is the more important application in this case. With external charging, the energy storage device is decoupled due to the resistance between the electrode and the high-voltage supply. This reduces the energy output and the risk of electric shock.

[0063] The high-voltage cable 21 is designed in the manner described above and has several conductors, which enables redundancy in the high-voltage supply.

[0064] Finally, it shows Fig.5 a simplified schematic representation of a high-voltage cable 22 according to the invention with two coaxially arranged and electrically insulated conductors 23, 24, wherein the high-voltage cable 22 can otherwise be constructed in the manner described above, so that reference is made to the preceding description to avoid repetition.

[0065] At both ends, the high-voltage cable 22 has a connector 25, 26, with connector 25 having two contact pins 27, 28, and connector 26 having two corresponding contact sockets 29, 30. Contact pin 27 and contact socket 29 are connected to the outer conductor 23, while contact pin 28 and contact socket 30 are connected to the inner conductor 24, as shown schematically in the drawing. The high-voltage cable 22 thus also has separate contacts at the two connectors 25, 26, thereby creating redundancy. Therefore, if, for example, contact pin 27 has a loose connection, the high voltage can still be transmitted via the other contact pin 28.

[0066] The invention is not limited to the preferred embodiments described above. Rather, the invention also claims protection for modifications and further developments of the invention that likewise make use of the initiating concept and therefore fall within the scope of protection. In particular, the invention also claims protection for the subject matter and features of the claims independently of the respective referenced claims and especially without the features of the main claim. The invention thus comprises various aspects of the invention that enjoy independent protection. Advantages of the invention

[0067] The invention offers, among other things, the following advantages: • The high-voltage supply with the high-voltage cable according to the invention is redundant due to the multiple conductors in the high-voltage cable, thereby improving safety and system availability. • The electrical capacitance of the high-voltage cable according to the invention is not increased by the design according to the invention, so that the inertia of the high-voltage supply does not worsen in the event of dynamic changes in the high voltage (e.g. when switching off or when setpoint changes). • Despite the advantageous redundancy provided by the multiple conductors, only a single high-voltage cable is still required. • The high-voltage cable according to the invention can optionally be implemented with conductors made of copper or of resistance material. • The high-voltage cable according to the invention can be realized with a similar or the same outer diameter as high-voltage cables in existing installations, so that the high-voltage cable according to the invention can also be used in existing installations. Reference symbol list 1 High-voltage cable in accordance with the state of the art 2 conductors 3 field trowels 4 Insulator 5 cable sheath 6 high-voltage cables according to the invention 7 ladders 8 Insulator 9 ladders 10 field trowels 11 Insulator 12 cable sheath 13 Paint shop 14 Motor vehicle body component 15 High-voltage source 16 rotary atomizers 17 bell plates 18 Spray jet of paint 19 External charging ring on the rotary atomizer 20 external electrodes on the external charging ring 21 high-voltage cables according to the invention 22 high-voltage cables according to the invention 23, 24 ladder 25, 26 connectors 27, 28 contact pins 29, 30 contact sockets QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2014 010 777 A1 [0016, 0024]

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