SYSTEM FOR NEUTRALIZING SURFACE CHARGES AND METHOD FOR MONITORING THE FUNCTIONAL SAFETY OF SUCH A SYSTEM

Abstract

System (1) for neutralizing surface charges, wherein the system (1) comprises the following: - at least one passive discharge electrode (2) for neutralizing surface charges along an ionization region formed between the at least one passive discharge electrode (2) and the surface charges; - an earthing conductor (3) via which the at least one passive discharge electrode (2) is galvanically connected to a reference potential (4), in particular ground potential; and - a reference potential resistance monitoring device (5) for monitoring the functional safety of at least one discharge electrode (2), wherein the reference potential resistance monitoring device (5) is designed to monitor the functional reliability of the at least one discharge electrode (2), regardless of whether or not surface charges flow to the reference potential (4) via the at least one discharge electrode (2), and wherein the reference potential resistance monitoring device (5) is associated with a measuring circuit or wherein the reference potential resistance monitoring device (5) is part of a measuring circuit, wherein the measuring circuit is formed by the earthing conductor (3) and a measuring or return line (6) with a defined electrical resistance (10), wherein the measuring or return line (6) and the earthing conductor (3) are galvanically connected together with the reference potential (4) and the reference potential resistance monitoring device (5) is preferably integrated in the measuring or return line (6).

Description

[0001] The present invention is generally in the field of passive electrode arrangements which are used as discharge electrodes in a wide variety of applications.

[0002] In particular, the invention relates to a method and a device for monitoring the functional reliability of at least one passive electrode for neutralizing surface charges, in particular charges on web materials. The invention further relates to a corresponding system for neutralizing such surface charges.

[0003] The document DE 10 2011 078 603 A1 relates to a method and a device for monitoring the functional reliability of at least one passive electrode for neutralizing surface charges, in particular charges on web materials, along an ionization region formed between the at least one passive electrode and the surface charges.

[0004] The document DE 698 30 609 T2 relates to a device and a method for providing positive and negative ions for controlling a surface charge, for example on stationary objects and on continuously moving webs of non-conductive material.

[0005] The processing of a wide variety of materials, especially materials in web form such as paper or plastic webs, requires the presence of web areas that are largely free of static electricity, particularly static charges resting on the surface of the web materials. In many cases, such a charge-free state is generally desirable, for example, to prevent unwanted adhesion of layers of this material that are layered or are to be layered on top of each other. In other applications, it may be useful to first create a web surface free of charges and then apply a specific amount of charge in a targeted manner.Such a procedure is particularly useful if a targeted atesional force of the various web layers is to be created by the amount of surface charges or if the web surfaces of a paper web, for example, are to be prepared accordingly in preparation for an electrostatically assisted printing process.

[0006] It is known to use so-called active discharge electrodes for such discharge processes. These electrodes are based on the principle of targeted ionization of the air molecules located between the active discharge electrode, which is arranged a short distance from the web surface, and the web surface, sufficient to dissipate all surface charges within a given time. Particularly when such active discharge systems or active discharge electrodes are to be used in potentially explosive atmospheres, the high voltage required to achieve sufficient ionization, which must be applied to these passive electrodes, is a disadvantage, as under certain conditions this can easily lead to unwanted, ignitable spark penetration. Furthermore, the high voltages required for these active discharge electrodes are disadvantageous if personal contact protection cannot be effectively guaranteed in an area of ​​use.Nevertheless, such active discharge electrodes are predominantly used in today's technology because monitoring the ionization current discharged through them is relatively easy. A current flowing through the deliberately induced ionization path serves as an indicator that the active discharge electrode is functioning properly. If no current flow is detected, the ionization path essential for discharging the surface charges is not formed, which then indicates that the active discharge electrode is not functioning properly.

[0007] To circumvent the aforementioned disadvantages of active discharge systems or active discharge electrodes, it is also known to use so-called passive discharge electrodes, which do not rely on the principle of an actively and artificially created ionization gap. Such passive discharge electrodes are usually cord- or wire-like structures, for example, cords with carbon fibers, grounding tabs, brushes, or so-called "tinsle bars." These passive discharge electrodes are arranged at a short distance from the material surface to be discharged and are connected to a reference or ground potential.Due to their mostly pointed shape, the electric field lines emanating from the surface charges are concentrated at the ends of the individual elements extending in the direction of the surface to be discharged, so that the resulting high electric field strength ensures that these surface charges flow away via the small gap between the electrode elements and the surface, even if this gap is not additionally ionized by actively applying an ionization voltage.

[0008] However, such passive discharge electrodes have the disadvantage that simple functional monitoring, i.e. monitoring that the electrode can discharge charges, is not guaranteed.

[0009] Furthermore, such passive discharge elements do not have current-limiting components, which means that under certain conditions, an ignitable spark can occur between the surface to be discharged and a single protruding fiber. This can even occur within such a passive discharge electrode (discharge cord, grounding tab, brush, tinsle bars, etc.), since surface charges on a track are rarely homogeneous; instead, they exhibit a multitude of charge regions with different charge levels and signs.

[0010] In particular, the distance between the individual discharge tips of the individual elements of such a passive discharge electrode can influence the formation of the described electric field during operation and thus reduce the discharge performance. The goal is to achieve an optimal balance between tip spacing and achievable field concentration, aiming for the lowest possible residual charge at a fixed distance from the surface to be discharged.

[0011] Based on this problem, the invention is therefore based on the object of providing a possibility for monitoring the functional reliability of such passive discharge electrodes for neutralizing surface charges, wherein the functional monitoring should be uncomplicated, with simple means, reliable and cost-effective.

[0012] This object is achieved on the one hand by a system for neutralizing surface charges according to independent patent claim 1 and on the other hand by a method for monitoring the functional reliability of at least one passive electrode according to the subject matter of the independent patent claim 6, wherein advantageous developments of the system according to the invention or of the method according to the invention are specified in the corresponding dependent claims.

[0013] Accordingly, the invention relates in particular to a system for neutralizing surface charges, wherein the system comprises at least one passive electrode for neutralizing surface charges along an ionization region formed between the at least one passive electrode and the surface charges, and a grounding conductor via which the at least one passive electrode is galvanically connected to a reference potential, in particular to the ground or earth potential. To monitor the functional reliability of the at least one passive electrode, the system is further provided with a reference potential resistance monitoring device configured to determine a reference potential resistance of the grounding conductor (either directly or indirectly).The reference potential resistance of the earthing conductor is in particular the electrical resistance of the earthing conductor which is galvanically connected on the one hand to the at least one passive electrode and on the other hand to the reference potential and in particular to the ground or earthing potential.

[0014] With regard to the method according to the invention, it is particularly provided that the at least one passive electrode, which serves to neutralize surface charges and in particular to neutralize charges on web materials, is connected to a reference potential, in particular to the ground or earth potential, via a grounding conductor. To monitor the functional reliability of the at least one passive electrode, the electrical resistance of the grounding conductor is monitored via the measuring circuit comprising the grounding conductor, a defined electrical resistance, a return line, and an evaluation unit. This monitoring of the resistance of the grounding conductor with the aid of the measuring circuit can be implemented, in particular, independently of whether or not charges are dissipating via the discharge electrode.

[0015] The solution according to the invention offers a whole series of significant advantages over known methods and systems for neutralizing surface charges using passive charging electrodes. In particular, the method according to the invention and the system according to the invention make it possible to reliably monitor functional reliability not only in active discharge systems, but also in passive discharge electrodes. In particular, no additional measuring voltage is generated in the ionization region between the at least one passive electrode and the surface charges to monitor functional reliability. Therefore, no voltage is required to generate an electric measuring field strength along the ionization region, thus fully ensuring explosion protection when used in potentially explosive environments.Furthermore, by avoiding an additional measuring voltage, contact protection and thus personal protection are effectively ensured.

[0016] Rather, the invention provides that the galvanic contact between the earth or reference potential and the passive discharge electrode is detected continuously, as needed or cyclically by checking the specified resistance in the measuring circuit and evaluated accordingly.

[0017] According to the invention with regard to the system, it is further provided that the reference potential resistance monitoring device has a measuring or return conductor that is galvanically connected, on the one hand, to the grounding conductor via a resistor and, on the other hand, to the reference potential (grounding or mass potential). The reference potential resistance monitoring device is designed to detect and appropriately evaluate a current flowing through the measuring or return conductor to the reference potential when neutralizing surface charges. In this case, it is fundamentally conceivable for the grounding conductor, together with the measuring or return conductor, to be designed, at least in part, as a coaxial conductor or as a two-wire cable.

[0018] This design offers significant advantages in terms of functional reliability. In particular, it enables electrical connection monitoring, i.e., electrical monitoring of the reference potential connection (ground or earth connection), in an easy-to-implement yet effective manner. This connection monitoring ensures the early and continuous detection of potential damage to connecting elements or the earthing conductor during operation of the passive discharge electrode. This provides the user of the system or the passive discharge electrode with significant added value in terms of safety and performance.

[0019] In particular, the reference potential resistance monitoring device can have an evaluation device configured to determine an electrical resistance of the grounding conductor or to draw a conclusion about an electrical resistance of the grounding conductor based on the detected current flow through the measuring or return conductor and / or through the grounding conductor. In particular, the evaluation device is configured to detect functionally reliable grounding of the at least one passive discharge electrode based on the detected current flow.

[0020] For example, the evaluation device is designed to output a corresponding signal depending on a result of a comparison of the determined electrical resistance of the earthing conductor with at least one predetermined or definable value and / or depending on the detected current flow.

[0021] According to advantageous implementations of the evaluation device, it has a warning device for outputting a warning signal, wherein the warning device is designed to output the warning signal when the determined electrical resistance of the measuring section (i.e. of the measuring circuit with the fixed electrical resistance integrated therein) deviates from a fixed or definable resistance value, in particular with a possibly provided tolerance. The pre-determined or definable resistance value can, for example, correspond to an empirically determined or calculated resistance value. According to embodiments of the invention, the pre-determined or definable resistance value corresponds to a resistance value at which functional reliability of the system is no longer guaranteed.

[0022] By integrating the reference potential resistance monitoring device within the system for neutralizing surface charges, an external evaluation unit is always able to monitor the correct electrical connection of at least one passive discharge electrode. The signal generated by the external connection monitoring can be used for further processing. This provides the system user with information about the correct electrical connection of the passive discharge electrodes. This signal can also be used to activate additional functions. This connection monitoring ensures the early and continuous detection of possible damage to connecting elements or the grounding conductor during operation of the system or of the at least one passive discharge electrode.

[0023] An exemplary embodiment of the solution according to the invention is described in more detail below with reference to the accompanying drawing.

[0024] It shows: Fig. 1 schematically shows a schematic diagram of an exemplary embodiment of the system according to the invention for neutralizing surface charges.

[0025] In Fig. 1 shows a schematic diagram of an embodiment of the system 1 according to the invention for neutralizing surface charges.

[0026] In this embodiment, a plurality of passive electrodes 2 are arranged on an electrode housing 8, extending toward a web material to be discharged, which carries surface charges. The individual passive electrodes 2 are each galvanically connected to a grounding line 3 via a high-voltage resistor 9, with the grounding line 3 in turn being connected to a reference potential 4, such as ground potential.

[0027] A reference potential resistance monitoring device 5 is used to monitor the ground connection of the grounding line 3. In the Fig. In the embodiment shown schematically in Figure 1, the reference potential resistance monitoring device 5 has a measuring or return conductor 6, which is galvanically connected via a coding resistor 10 to the earthing conductor 3 on the one hand and to the reference potential 4 (ground potential) on the other hand.

[0028] When neutralizing surface charges via the passive discharge electrodes 2, a discharge current flows via the grounding conductor 3 to the reference potential 4 (ground potential). A portion of this discharge current flows via the coding resistor 10 and the measuring or return line 6 via an evaluation device of the reference potential resistance monitoring device 5, also to the reference potential 4 or ground potential. Fig. In the exemplary embodiment shown in Figure 1, at least in some areas, the grounding conductor 3 and the measuring or return conductor 6 are designed as coaxial cables 7; however, this embodiment is by no means to be considered restrictive; rather, it is also conceivable, for example, to use separate cables or a two-core cable for both conductors (grounding conductor 3 and measuring or return conductor 6).

[0029] To monitor the functional reliability of the passive discharge electrodes 2, the connection is monitored via the measuring circuit consisting of the grounding conductor 3, the fixed coding resistor 10, the measuring or return line 6, and the evaluation unit 5. This also occurs regardless of whether charges are flowing through the discharge electrodes 2.

[0030] Advantageously, the evaluation device comprises a warning device configured to output a warning signal, wherein the warning signal is output in particular when the (indirectly) determined electrical resistance of the grounding conductor 3 exceeds a predetermined or definable resistance value. This predetermined or definable resistance value is preferably selected such that it corresponds to a resistance value at which functional reliability of the system 1 is just still ensured.

[0031] The invention is not limited to the embodiment shown in the drawing, but results from a combination of all features disclosed herein.

[0032] In particular, it is conceivable in this context that several measuring circuits are provided, wherein each individual measuring circuit is assigned to a predetermined group of discharge electrodes 2 in order to monitor the functional reliability of this group of discharge electrodes 2 accordingly.

Claims

[1] System (1) for neutralising surface charges, the system (1) comprising: - at least one passive discharge electrode (2) for neutralizing surface charges along an ionization region formed between the at least one passive discharge electrode (2) and the surface charges; - an earthing conductor (3) via which the at least one passive discharge electrode (2) is galvanically connected to a reference potential (4), in particular ground potential; and - a reference potential resistance monitoring device (5) for monitoring the functional reliability of the at least one discharge electrode (2), wherein the reference potential resistance monitoring device (5) is designed to monitor the functional reliability of the at least one discharge electrode (2), regardless of whether or not surface charges flow via the at least one discharge electrode (2) to the reference potential (4), and wherein the reference potential resistance monitoring device (5) is assigned a measuring current circuit or wherein the reference potential resistance monitoring device (5) is part of a measuring current circuit, wherein the measuring current circuit is formed by the earthing conductor (3) and a measuring or return line (6) with a fixed electrical resistance (10), wherein the measuring or return line (6) and the earthing conductor (3) are jointly galvanically connected to the reference potential (4) and the reference potential resistance monitoring device (5) is preferably integrated in the measuring or return line (6). [2] System (1) according to claim 1, wherein the earthing conductor (3) together with the measuring or return line (6) are designed at least in regions as a coaxial conductor (7) or as a two- or multi-core cable. [3] System (1) according to claim 1 or 2, wherein the reference potential resistance monitoring device (5) has an evaluation device which is designed to determine an electrical resistance in a measuring circuit on the basis of a detected current flow, wherein the measuring circuit is formed by the earthing conductor (3) and the measuring or return line (6) with the specified electrical resistance (10). [4] System (1) according to claim 3, wherein the evaluation device is designed to output a corresponding signal depending on a result of a comparison of the determined electrical resistance with at least one predetermined or definable value and / or depending on the detected current flow. [5] System (1) according to claim 3 or 4, wherein the evaluation device comprises a warning device for outputting a warning signal, wherein the warning device is designed to output the warning signal when the determined electrical resistance and / or the detected current flow deviates from a predetermined or definable value. [6] Method for monitoring the functional reliability of at least one passive discharge electrode (2) for neutralising surface charges, in particular charges on web materials, wherein the at least one passive discharge electrode (2) is connected to a reference potential (4), in particular ground potential, via an earthing conductor (3), and wherein the method comprises the following method steps: - the electrical resistance of a measuring circuit is determined, the measuring circuit being formed by the earthing conductor (3) and a measuring or return line (6) with a fixed electrical resistance (10), the measuring or return line (6) and the earthing conductor (3) being galvanically connected together to the reference potential (4); and - the determined electrical resistance of the measuring circuit is compared with a predetermined or definable resistance value and, if the predetermined or definable resistance value is exceeded, a warning signal is emitted which indicates that the functional reliability of the at least one passive discharge electrode (2) is no longer guaranteed. [7] Method according to claim 6, wherein the electrical resistance of the measuring circuit is determined independently of whether or not surface charges are discharged by means of the at least one passive discharge electrode (2).

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