WO2013006348A1

WO2013006348A1 - Method for monitoring the operational reliability of at least one passive electrode and apparatus for monitoring the operational reliability of at least one passive electrode

Info

Publication number: WO2013006348A1
Application number: PCT/US2012/044460
Authority: WO
Inventors: Joachim HISAM; Udo Schmidt; Thomas Vinnay
Original assignee: Illinois Tool Works Inc.
Priority date: 2011-07-04
Filing date: 2012-06-27
Publication date: 2013-01-10
Also published as: EP2730150A1; DE102011078603A1; DE102011078603B4

Abstract

A method is specified for monitoring the operational reliability of at least one passive electrode for the purpose of neutralizing surface charges. In order to ensure an effective explosion protection and personal protection, the inventive method provides the use of at least one measuring electrode to apply a measuring electric field strength to an ionization region, and to detect an ionization current flow through this ionization region.

Description

METHOD FOR MONITORING THE OPERATIONAL RELIABILITY OF AT

LEAST ONE PASSIVE ELECTRODE AND APPARATUS FOR MONITORING THE OPERATIONAL RELIABILITY OF AT LEAST ONE

PASSIVE ELECTRODE

Description

The present invention relates to a method and an apparatus for monitoring the operational reliability of at least one passive electrode for the purpose of neutralizing surface charges, in particular charges on sheet materials, along an ionization region formed between the at least one passive electrode and the surface charges .

The processing of the most varied materials, in particular materials in sheet form such as, for example, paper sheets or plastic sheets, reguires the occurrence of sheet regions that is as far as possible free from static electricity, in particular static charges resting on the surface of the sheet materials. In many cases, such a freedom from charge is generally to be desired in order, for example, to prevent an undesirable mutual adherence of sheets of this material that are stacked on one another or can be stacked on one another. In other applications, it can be advisable firstly to create a sheet surface free from charges in order, subseguently, deliberately to apply an entirely specific charge guantity. Such a procedure is particularly advisable when the aim is to produce an adhering force, determined by the guantity of the surface charges, of the various sheet layers, or else when, in order to prepare an electrostatically supported printing process, the sheet surfaces of a paper sheet, for example, are to be appropriately prepared .

It is known to make use for such discharging processes of so-called active discharge electrodes that are based on the active principle of a targeted ionization, sufficient to discharge all the surface charges in a given time, of the air molecules located between the active discharge electrode, arranged at a short distance from the sheet surface, and the sheet surface. Particularly when such active discharge systems or active discharge electrodes are to be used in potentially explosive regions, the high voltage that is necessary for adeguate ionization and is to be applied to these passive electrodes is disadvantageous, because this can easily lead to an undesired spark discharge, and thus to explosion. Furthermore, the reguired high voltages of these active discharge electrodes are disadvantageous when the personal shock protection in an area of use cannot be effectively ensured. Nevertheless, such active discharge electrodes are favored for use in current technology, since it is relatively easy to monitor the ionization current they discharge. Such a current flowing via the ionization path deliberately brought about serves here as an indicator that the functionality of the active discharge electrode is ensured. In the case when no current flow is detected, the ionization path absolutely necessary for discharging the surface charges is not formed, from which it can then be concluded that the functionality of the active discharge electrode is not ensured.

In order to circumvent the abovenamed disadvantages of active discharge systems or active discharge electrodes, it is, furthermore, known to use passive discharge electrodes, which are not based on the active principle of an actively and artificially formed ionization path. Such passive discharge electrodes are mostly bodies shaped in cord-like or wire-like fashion, for example cords with carbon fibers, grounding tongues, brushes or so-called tinsle bars. These passive discharge electrodes are arranged at a short distance from the material sheet surface or material surface to be discharged, and connected to a reference or ground potential. Owing to their mostly pointed shape, at the ends of the individual elements extending in the direction of the surface to be discharged, the electric field lines emanating from the surface charges are concentrated, and so the resulting high electric field strength ensures that these surface charges flow off via the small interspace between the electrode elements and the surface even when this interspace is not additionally ionized by active application of an ionization voltage.

However, such passive discharge electrodes have the disadvantage of not ensuring a simple function monitoring, that is to say a monitoring which enables the electrode to discharge charges. 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 discharging performance.

It is therefore the object of the present invention to specify an option for monitoring the operational reliability of such passive discharge electrodes for the purpose of neutralizing surface charges, the aim being for the function monitoring to be uncomplicated, employ simple means, and be reliable and cost effective .

For a method for monitoring the operational reliability of at least one passive electrode for the purpose of neutralizing surface charges of the type mentioned at the beginning, this object is achieved by virtue of the fact that at least one measuring electrode is provided for applying a measuring electric field strength to the ionization region formed between the at least one passive electrode and the surface charges, the at least one passive electrode being connected via a current measurement device to a reference potential, and the method providing that a measurement voltage is applied to the at least one measuring electrode, that a current flow is detected by means of the current measurement device, that the detection result is compared with a reference value, and that the operational reliability is assessed with the aid of this comparison.

The inventive solution has an entire series of important advantages over the known methods for neutralizing surface charges by means of passive charge electrodes. In particular, the inventive method can be used for reliable monitoring of the operational reliability not only for active discharge systems, but also for passive discharge electrodes. Because the voltage for generating the measuring electric field strength along the ionization region is small in relation to an ionization voltage for comparable active discharge systems, protection against explosion, in particular, continues to be ensured during use in potentially explosive environments. Furthermore, shock protection, and thus personal protection, are effectively ensured by the low level of this measurement voltage .

As a rule, after an appropriate electric voltage has been applied to the measuring electrode in order to apply a measuring electric field strength to the ionization region with the current measurement device, it is detected whether an electric current is flowing through the passive electrode. If the detection result indicates that an electric current is flowing, this demonstrates that the region between the passive discharge electrode and the material surface can be ionized, and that, in principle, charges, and thus, in particular, surface charges as well, can flow off via the passive electrode to the reference potential, that is to say to the ground potential, in particular. Since, by contrast with active discharge systems, it is possible in this case to use a substantially smaller measurement voltage, the disadvantages of an active discharge system - such as lack of explosion protection and personal protection - are, however, effectively prevented in the case of the inventive solution.

Advantageous developments of the invention are specified in the subclaims .

Thus, for example, it is provided that detecting the current flow includes measuring the current strength. In this case, the reference value constitutes a reference current strength, and the detected current flow, that is to say the measured current strength, is compared with this reference current strength in order to assess the operational reliability with the aid of this comparison. Owing to this development, it is, in particular, no longer only possible to assess the operational reliability qualitatively. Rather, it is also possible to make a quantitative assessment of how far the discharging performance of the passive discharge system or the passive discharge electrode deviates from the desired discharging performance, and whether this possibly reduced discharging performance is still adequate to ensure operational reliability of the at least one passive electrode.

Furthermore, it can be provided to apply a continuous measurement voltage to the at least one measuring electrode in order to apply the measuring electric field strength to the ionization region. The advantage of a continuous measurement voltage is that it can be continuously assessed whether the at least one passive discharge electrode is still capable in principle of removing surface charges from the material sheet or the other type of material. This is advantageous, in particular, when the number of surface discharges on the material sheet fluctuates over time. Even when there are absolutely no surface charges present on the material sheet at a specific instant, the low ionization by means of the measurement voltage ensures, nevertheless, that a minimum ionization current always flows in the ionization region and indicates the basic functionality of the passive discharge electrode. By contrast with active discharge systems, however, it is possible here to use substantially lower voltages.

Egually well, however, it can also be provided to apply a pulsed measuring electrode instead of the continuous measurement voltage to the at least one measuring electrode. Here, "pulsed" comprises uniform pulses as well as sporadic switching on and off of the measurement voltage. By way of example, it is possible hereby to monitor the passive electrode only when this is also necessary in the operational seguence. Not least, such a pulsed application of the measurement voltage in the operational seguence can save energy.

Furthermore, it can be provided that the at least one passive electrode and the at least one measuring electrode are designed as a common electrode. The passive electrode in this case simultaneously takes over the function of the measuring electrode, and this enables a particularly simple design. In order to apply the measuring electric field strength to the ionization region, a voltage source is then provided directly between the at least one passive electrode and the current measurement device. The low internal resistance of the voltage source always ensures that the surface charges flow off through the current measurement device in the direction of the reference potential. The minimum measurement voltage, which is adeguate for ionization, however, simultaneously ensures that a minimum ionization current always flows and that the functionality of the at least one passive electrode can thereby be monitored at any time .

However, it is also equally possible to provide that the at least one passive electrode and the at least one measuring electrode are designed as separate electrodes. In this case, the at least one measuring electrode is arranged at a spacing from the at least one passive electrode along the ionization region. This ensures that the measurement current flows from one electrode to the opposite electrode over an ionized path in each case. It is possible hereby to ensure that the interspace between the electrodes can be ionized in each case. In particular, this excludes the current flow detected by means of the current measurement device from, for example, taking place via a conductive contamination on the electrode housing of the at least one passive electrode.

Furthermore, an additional warning device can be provided, the method then additionally providing that a warning signal is output by means of the warning device when the assessment is that operational reliability is lacking. In such a case, it is easily possible to detect an unreliable discharging situation, and to initiate appropriate countermeasures - in automated fashion, as the case may be. Such countermeasures can consist, for example, of stoppage or maintenance of the machines in use, or the like.

In addition to the inventive method described, an apparatus is provided for carrying out the inventive method, the apparatus having at least one passive electrode for the purpose of neutralizing surface charges along an ionization region formed between the at least one passive electrode and the surface charges, at least one measuring electrode for applying a measuring electric field strength to the ionization region, a current measurement device via which the at least one passive electrode is connected to a reference potential, in particular ground potential, and at least one voltage source for applying a measurement voltage to the at least one measuring electrode.

Such an inventive apparatus enables effective and reliable monitoring of the operational reliability of the passive electrode for the purpose of neutralizing surface charges .

Two preferred exemplary embodiments of an apparatus for carrying out the inventive method are explained below in more detail with the aid of a drawing.

In the drawing: figure 1 shows a schematic sectional view of a first exemplary embodiment of an apparatus for carrying out the inventive method, the passive electrode and the measuring electrode being of common design; and figure 2 shows a schematic sectional view of a second exemplary embodiment of an apparatus for carrying out the inventive method in a way similar to figure 1, although the passive electrode and the measuring electrode are of separate design.

Figure 1 shows a schematic sectional view of a first exemplary embodiment of an apparatus for carrying out the inventive method. Arranged on an electrode housing 100 is a multiplicity of passive electrodes 110 that extend in the direction of a sheet material 140 that is to be discharged and carries surface charges. The individual passive electrodes 110 in this case simultaneously constitute measuring electrodes 120 and, at their end on the housing side, are interconnected and connected as a whole to the positive pole of a voltage source 135 designed to be of low resistance. The negative pole of the voltage source 135 is, in turn, connected to a current measurement device 130 which, for its part, ensures contact with a reference potential 132. The current measurement device 130 includes a measuring shunt 131 and is designed to output a measured value of the current strength 134 for the purpose of comparison and assessment to an assessment device (not illustrated) .

The measurement voltage 136 output by means of the voltage source 135 to the multiplicity of measuring electrodes 120 ensures that a minimum ionization of the ionization region 150 between the sheet material and the electrodes 110 or 120 is always maintained. At the same time, the measurement voltage 136 of the voltage source 135 is so low that shock protection of the measuring electrodes 120 is ensured at any time. At the same time, the measurement voltage 136 is intrinsically safe, that is to say is not adeguately high in potentially explosive regions to ignite the solvent/air mixture .

Conseguently, owing to the applied measurement voltage 136 it is possible to deliberately generate a minimum ionization current even when no surface charges are present on the surface of the sheet material 140 at a specific operating instant. It is then hereby possible to detect that the functionality of the passive electrodes 110 is fundamentally still ensured.

Figure 2 shows a second exemplary embodiment of an apparatus for carrying out the inventive method, in this case a measuring electrode 120 being designed separately from the passive electrodes 110, and being arranged at a spacing from the passive electrodes 110. Again, a measurement voltage 136 is applied to the measuring electrode 120 by means of a voltage source 135. In the case of the second exemplary embodiment, however, the ionization region 150 is located between the measuring electrode and the multiplicity of passive electrodes. This ensures that conductive contaminations that may be present on the electrode housing 100 and can form a creepage path to the reference potential 132 do not constitute a bypass path for the ionization current to be detected. Owing to the mutually spaced- apart arrangement of the passive electrodes 110 and the measuring electrode 120 with the inclusion of the ionization region 150, it is absolutely ensured that the interspace between the electrodes is ionized, or at least ionizable, in each case given a current flow detected by means of the current measurement device 130. This results in a yet higher reliability in the carrying out of the inventive method.

List of reference numerals

100 Electrode housing

110 Passive electrode

120 Measuring electrode

130 Current measurement device

131 Measuring shunt

132 Reference potential

134 Current strength

135 Voltage source

136 Measurement voltage

140 Sheet material

150 Ionization region

Claims

"Method for monitoring the operational reliability of at least one passive electrode and apparatus for monitoring the operational reliability of at least one passive electrode" Patent Claims

1. A method for monitoring the operational reliability of at least one passive electrode (110) for the purpose of neutralizing surface charges, in particular charges on sheet materials, along an ionization region (150) formed between the at least one passive electrode and the surface charges, at least one measuring electrode (120) being provided for applying a measuring electric field strength to the ionization region (150), the at least one passive electrode (110) being connected via a current measurement device (130) to a reference potential (132), in particular ground potential, the method having the following method steps :

- applying a measurement voltage (136) to the at least one measuring electrode (120);

- detecting a current flow by means of the current measurement device (130);

- comparing the detection result with a reference value; and

- assessing the operational reliability with the aid of the comparison.

2. The method as claimed in claim 1, in which detecting the current flow includes measuring the current strength (134), and in which the reference value is a reference current strength.

3. The method as claimed in either of claims 1 and 2, in which a continuous measurement voltage (136) is applied to the at least one measuring electrode (120) in order to apply the measuring electric field strength to the ionization region (150) .

4. The method as claimed in claim 1 or 2, in which a pulsed measurement voltage (136) is applied to the at least one measuring electrode (120) in order to apply the measuring electric field strength to the ionization region ( 150 ) .

5. The method as claimed in one of claims 1 to 4, in which the at least one passive electrode (110) and the at least one measuring electrode (120) are designed as a common electrode (110, 120) .

6. The method as claimed in one of claims 1 to 4, in which the at least one passive electrode (110) and the at least one measuring electrode (120) are designed as separate electrodes, and in which the at least one measuring electrode (120) is arranged at a spacing from the at least one passive electrode (110) along the ionization region (150).

7. The method as claimed in one of the preceding claims, in which a warning device is provided in addition, and in which the method additionally has the following method step:

- outputting a warning signal by means of the warning device when the assessment is that operational reliability is lacking.

8. An apparatus for carrying out the method as claimed in one of claims 1 to 7, in which the apparatus has the following:

at least one passive electrode (110) for the purpose of neutralizing surface charges along an ionization region (150) formed between the at least one passive electrode (110) and the surface charges ; - at least one measuring electrode (120) for applying a measuring electric field strength to the ionization region (150);

- a current measurement device (130) via which the at least one passive electrode (110) is connected to a reference potential (132), in particular ground potential; and

- at least one voltage source (135) for applying a measurement voltage (136) to the at least one measuring electrode .

9. The apparatus as claimed in claim 8, in which the at least one voltage source (135) is designed to output a continuous measurement voltage (136).

10. The apparatus as claimed in claim 8, in which the at least one voltage source (135) is designed to output a pulsed measurement voltage (136).

11. The apparatus as claimed in one of claims 8 to 10, in which the apparatus further has a warning device for outputting a warning signal, the warning device being designed to output the warning signal when the assessment is that operational reliability is lacking.