Patent Application
20180191139
The present invention relates to an antistatic device for reducing electrostatic charges on moving material webs. The invention also relates to a method for operating such an antistatic device.
Electrostatic charges are created when dielectric materials are moved relative to each other or to other materials. Electrostatic charges are critical particularly in applications involving fast moving, thin sheets of material, such as paper or foils. If these electrostatic charges are not reduced or neutralised, they can lead to uncontrolled discharges. Discharges of such kind can injure people, damage materials and cause sparks, fire and explosions. In addition, downstream processes such as coating, printing and finishing are impaired. This can also affect product quality significantly, even to the point of complete destruction of the product or material.
An active electrode assembly comprising a plurality of active needle-shaped individual electrodes that are electrically connected to a high voltage source and supplied with alternating current when an antistatic device is in operation is known from DE 1 197 1 342 A1. In this case, the electrode assembly is arranged in a bar-shaped electrode carrier in which a ground conductor is also integrated.
From U.S. Pat. No. 6,674,630 B1, antistatic devices are known in which either two active electrode assemblies with the same polarity are arranged consecutively in the direction of movement of a material web, or in which two pairs of electrode assemblies are arranged consecutively in the direction of movement of a material web, each pair comprising a positive electrode assembly and a negative electrode assembly that are arranged consecutively in the direction of movement of the material web. In these known antistatic devices, the neutralisation current flowing at the active electrode assemblies is measured and evaluated. The neutralisation efficiency and the residual charge remaining on the material web is calculated on the basis of the detected current. The speed of advance of the material web can then be adjusted depending on this residual charge.
A further antistatic device in which an active positive electrode assembly and an active negative electrode assembly are arranged consecutively in the direction of movement of the material web and wherein the neutralisation efficiency can be measured with the aid of the measured neutralisation currents of the active electrode assemblies is known from U.S. Pat. No. 6,259,591.
Such systems, in which both positive and negative electrodes are active during operation, can also be described as bipolar systems.
Active electrode assemblies differ from passive electrode assemblies in that the active electrode assemblies are connected to a high voltage source, whereas passive electrode assemblies are connected to a grounding element, particularly an earthing conductor. For the purposes of the present, high voltage is considered to be at least 1 kV.
For an active electrode assembly of such kind, it is generally possible to actuate the associated high voltage sources in order to generate an alternating current or a pulsed DC current, and in the case of pulsed DC current it is advantageous to actuate both high-voltage sources of a positive electrode assembly and a negative electrode assembly deliberately so that positive voltage pulses at the positive electrode assembly alternate with negative voltage pulses at the negative electrode assembly, thereby creating a virtual AC so to speak, if the two electrodes are considered as a single unit. However, the “zebra effect” is observed with alternating current and pulsed direct current. An unnecessary half-wave and half-polarity exist between each of two positive or negative voltage pulses, and neutralisation does not take place here because this half-wave has exactly the same polarity as the web and is therefore not available for discharging the material web and thereby avoiding personal injury, material damage, sparks, fire and explosions. Moreover, the voltage requires a certain time at the beginning of each voltage pulse until the ionisation voltage is built up. The ionisation voltage is the voltage level at which the ionisation of the surrounding air molecules begins at a charged peak. This ionisation phase based on a certain minimum voltage is absolutely necessary in order for the neutralisation to take place. The neutralising effect of the respective electrode assembly is reduced or even cancelled out entirely during these temporally delayed build-up and decay phases of the respective voltage pulse and during the unnecessary half-waves and polarities. Then, neutralised and non-neutralised or incompletely neutralised sections of the web may occur consecutively like zebra stripes depending on the speed of movement of the material web. The distances between these stripes, that is to say the bars of the zebra stripes, are correlated to the pulse frequency of the ionisation and the speed of the web.
The present invention addresses the problem of providing an improved embodiment of an antistatic device of the type described in the introduction, and an associated operating method, which is characterized in particular by the absence of web sections that are not neutralised or not completely neutralised, and at the same time consumes less energy.
This problem is solved with the present invention in particular by the subject matter of the independent claim. Advantageous embodiments are the subject matter of the dependent claims.
The invention is based on the general idea for an antistatic device comprising at least one positive electrode assembly and at least one negative electrode assembly of deactivating the electrode assembly that is not required depending on the polarity of the material web that is to be neutralised and only keeping the single electrode assembly that is required active in unipolar mode.
The antistatic device according to the invention preferably comprises only one positive electrode assembly and only one negative electrode assembly. It is further preferred that the respective active electrode array comprises only one row of needle-shaped electrodes arranged side by side and transversely to the direction of movement of the material web, so that a maximum of two rows of needles or two rows of electrodes are provided to make up both active electrode assemblies. According to a particularly advantageous embodiment, the needle-shaped electrodes of the positive electrode assembly and the negative electrode assembly may be arranged side by side in the same row transversely to the direction of movement of the material web, so that in extreme cases both active electrode assemblies may be constituted by a single row of electrodes or needles.
In particular, in the context of the invention the controller can activate or leave activated the negative high voltage source and deactivate or leave deactivated the positive high voltage source for a positive neutralisation current, and activate or leave activated the positive high voltage source for a negative neutralisation current. In this context, the invention makes use of the discovery that the polarity set up on a material web during a production process remains constant as long as the process parameters do not change. However, this polarity cannot be predicted. Based on the check of the polarity set up on the material web as suggested according to the invention, the active electrode assembly that is not required can be deactivated in each case, since it is essentially unable to contribute to the neutralisation of the electrostatic charge on the material web. Compared with other systems, this system then continues working in unipolar, not bipolar mode. The deactivation of the unused electrode enables the energy consumed by the antistatic device to be reduced significantly, since it is not necessary to apply a high voltage to the electrode assembly that is not needed. The antistatic device according to the invention operates in unipolar DC mode with the unnecessary electrode assembly deactivated, which significantly reduces the energy consumption of the antistatic device. The inventive unipolar DC mode of the antistatic device is preferably non-pulsed so that the required neutralisation current is constant and constantly present, which significantly reduces the control and regulation effort.
In an advantageous embodiment, it may be provided that the controller is configured and/or programmed such that it is switchable between at least a learning phase and a working phase. In the learning phase, both the positive high voltage source and the negative high voltage source are activated, while in the working phase only one of the high voltage sources, the high voltage source required for neutralising the material web, is activated. The sensor system may now advantageously be configured and/or programmed in such manner that during the learning phase it monitors the currents leaving each high voltage source, that is to say the neutralisation currents from the active electrode assemblies, to detect the polarity of the neutralisation current of ach high-voltage source. Inevitably, the current flow is markedly greater at one of the high voltage sources than at the other, from which it is possible to deduce the polarity of the charge of the material web and the polarity of the neutralisation current.
Alternatively, in another embodiment it may be provided that a passive sensor electrode assembly comprising a plurality of needle-shaped individual sensor electrodes is provided in addition to the two electrode assemblies, and is electrically connected to a grounding element when the antistatic device is operating. By virtue of it connection to the grounding element, the sensor electrode assembly becomes a passive electrode assembly. Moreover, the sensor assembly may now be programmed and/or configured in such manner that it monitors the current flowing away from the sensor electrode assembly, that is to say the neutralisation current of the sensor electrode assembly, to detect the polarity of the neutralisation current.
In this case, the invention is thus based on the general idea of providing at least one sensor electrode assembly in an antistatic device comprising at least one positive electrode assembly and at least one negative electrode assembly, which may be used to help detect the polarity of a neutralisation current of the sensor electrode assembly, so that the respective unnecessary electrode assembly may be deactivated according to the polarity determined, and only the electrode assembly that is needed may be actively operated. In particular, to this end the controller may activate or leave active the negative high voltage source and deactivate or leave deactivated the positive high voltage source in the case of a positive neutralisation current, and deactivate or leave deactivated the negative high voltage source and activate or leave activated the positive high voltage source in the case of a negative neutralisation current. In this context, the invention makes use of the discovery that the polarity set up on a material web during a production process remains constant as long as the process parameters do not change. However, this polarity cannot be predicted. Based on the check of the polarity set up on the material web as suggested according to the invention, the active electrode assembly that is not required can be deactivated in each case, since it is essentially unable to contribute to the neutralisation of the electrostatic charge on the material web. The deactivation of the unused electrode enables the energy consumed by the antistatic device to be reduced significantly, since it is not necessary to apply a high voltage to the electrode assembly that is not needed.
With the antistatic device according to the invention it is advantageous for the sensor electrode assembly to be connected to a grounding element, particularly an earth conductor, particularly via a measuring resistor. In this way, the sensor electrode assembly also functions as a passive neutralisation electrode assembly that is directly capable of neutralising a large part of the electrostatic charge in the material web. As a consequence of this passive neutralisation at the sensor electrode assembly, a neutralisation current is generated at the sensor electrode assembly that may be measured using a corresponding measuring resistor, for example. At the same time, the effect of the sensor electrode assembly as a passive neutralising electrode assembly also makes it possible to reduce the power at the respective active electrode assembly or to achieve a better neutralising effect with the same power, or to set a greater distance between the electrode assembly and the material web.
In particular, with the sensor system it is possible to measure the level of the neutralisation current in order to adjust or fine tune the power at the respectively required ionisation electrode assembly depending on the measured current level.
According to another advantageous embodiment, provision may be made to actuate the currently activated high voltage source in such manner that it delivers a non-pulsed, preferably constant positive or negative DC voltage. By using a non-pulsed direct current it is possible to draw the charge off from the material web continuously and thus to neutralise the charge thereon. By using non-pulsed DC voltage, it is possible to prevent the zebra effect to a large extent, and particularly completely, so that a particularly high-quality, constant and continuous neutralisation of the material web can be achieved to a large degree and particularly entirely without a residual charge.
According to another advantageous embodiment, provision may be made to actuate the high voltage sources for generating a pulsed DC voltage at the respective active electrode assembly during a learning phase, so that a pulsed DC voltage is present at both the positive electrode assembly and the negative electrode. Here too, it may be advantageously provided to actuate the high voltage sources in such manner that the pulsed DC voltages are present at the positive electrode assembly and the negative electrode assembly alternately. In other words, a positive voltage pulse at the positive electrode assembly occurs simultaneously with a voltage gap at the negative-electrode assembly, and a voltage gap at the positive electrode assembly coincides with a negative voltage pulse at the negative electrode assembly.
The polarity of the neutralisation current of the sensor electrode assembly is determined during this learning phase. As soon as it is established that a given polarity is present and steady, the switch is made to a working phase, during which the electrode assembly and the high voltage source therefor are switched off, while the electrode assembly that is still needed remains active, and the high voltage source associated therewith is actuated to generate a non-pulsed DC voltage. This embodiment assumes that during the learning phase, which can be initiated for example by a change in the process parameters of a production process connected to the material web, such as changing the web, it is initially unclear which polarity will be set up on the web. During this learning phase, both active electrode assemblies, that is to say both the positive electrode assembly and the negative electrode assembly, are then activated in order to ensure effective neutralisation even during the learning phase. During said learning phase, both active electrode assemblies are supplied with pulsed DC voltage. However, as soon as the polarity becomes stable and is identified during the learning phase, the system switches to the working phase, in which only one of the active electrode assemblies is activated, and this assembly is supplied with non-pulsed DC voltage. Here too, the non-pulsed DC voltage is preferably constant.
It is also possible for both high voltage sources to be deactivated during the learning phase, and in the working phase only the high voltage source for the required electrode assembly is activated. This is particularly advantageous when the controller is able to activate the required electrode assembly rapidly on the basis of the detected polarity of the material web.
In another embodiment, a neutralisation current of the respective activated active electrode assembly may be measured with the sensor system, using a current measuring device, for example. With this arrangement, the neutralisation current of the respective activated active electrode assembly will also be monitored during the working phase. Then it becomes possible to switch between two operating modes of the antistatic device depending on the measured neutralisation current of the active electrode assembly. For example, a distinction can be made between a primary operating mode or primary operation and a fallback operating mode or fallback operation. In primary operation, only one of the two high voltage sources is active, in particular to supply the associated electrode assembly with non-pulsed direct current. This primary operation thus corresponds in particular to the desired operating state for the working phase. On the other hand, the particular characteristic of the fallback mode may be that both high voltage sources are active, and preferably in such manner that both electrode assemblies are supplied with pulsed DC voltage, particularly in an alternating sequence. The fallback operating mode may thus correspond in particular to the learning phase with active ionisation electrodes. In general therefore, such an embodiment may also be created in such manner that a switch can be made from the learning phase to the working phase depending on the neutralisation current of the sensor electrode assembly, yet it is still possible for the system to be switched back to the learning phase depending on the neutralisation current of the electrode assembly that is activated during the working phase. For example, if the neutralisation current at the active electrode assembly becomes too weak, this may be an indication that a process parameter has been changed, so the polarity on the material web has also changed. Accordingly, a new learning phase may then be initiated by the monitoring system for the neutralisation current of the active electrode assembly, for example.
In another advantageous embodiment it may be provided that for example an eroded and/or contaminated electrode may be detected by monitoring the quiescent current of at least one of the active electrode assemblies and/or of the sensor electrode assembly. Thus, a diagnosis of the antistatic device can be performed by monitoring the quiescent current. A quiescent current of such kind occurs particularly when the material web has practically no electrostatic charge and/or when the web is idling or only moving very slowly. In this case, for example, the positive ions of the positive-electrode assembly can migrate through the air to the negative electrode assembly and create a current flow, the quiescent current described in the preceding. In the same way, ions from the positive electrode assembly and ions from the negative electrode assembly can also migrate through the air to the sensor electrode assembly, which is electrically connected to the ground, so a quiescent current can arise in this direction too. Such a quiescent current can also be measured advantageously during a diagnostic phase of the antistatic device, which is characterised by a low electrostatic charge of the material web. For example, the electrostatic charge initially builds up gradually on the material web when the web begins moving, so it is particularly useful to make provision for such a diagnostic phase when the material web is beginning to move or at a standstill.
For example, a drop in the quiescent current, for example below 50% or 40% of a reference current may be indicative of electrically non-conductive contamination of the electrodes concerned. In this context, the reference current in question represents the 100% value. Alternatively, for example, an increase in the quiescent current to more than 150% or more than 160% of a reference current for example, may be indicative of electrically conductive contamination of the electrodes concerned. In this context, the reference current in question represents the 100% value. Therefore, if electrode contamination is detected by analysing the quiescent current of the active electrode assemblies and/or of the sensor electrode assembly, a corresponding contamination alert can be generated on a corresponding monitoring means. Optionally, it may also be indicated whether the contamination is electrically conductive or electrically non-conductive, so that appropriate countermeasures can be taken.
It is further possible that, starting from a base reference current that is present with new electrodes, a new reference current is established each time after the electrodes are cleaned. Inevitably, the new reference current will be lower than the base reference current. The constantly revised reference current decreases steadily over time. The decrease in the reference current correlates with the erosion of the electrodes. A monitoring device can then detect a cleaning process of the electrodes automatically, since cleaning the electrodes causes the quiescent current to change abruptly in the direction of the respective preceding reference current. When a predetermined degree of electrode erosion is reached relative to the base reference current, an appropriate maintenance signal can be generated again.
Accordingly, the quiescent current and the diagnostic phase is preferably present when the material web is not charged and/or when it is at a standstill. In contrast, the learning phase and a neutralisation current of the sensor electrode assembly is present in particular when the material web speeds up and already carries a certain charge that can be passively drawn off. In the working phase, the material web moves at the normal working speed and carries the charge that it collects, so that a neutralisation current flows at each active ionisation electrode assembly.
Since the antistatic device according to the invention only works with one active electrode assembly when it is operating, that is to say during the working phase, no particularly great distance must be maintained between the electrode assemblies in the direction of movement of the material web. For example, the two active electrode assemblies may be at a distance from one another in the direction of movement of the material web that is smaller than the length of the antistatic device transversely to the material web, or smaller than a distance between a first and a last electrode of an electrode group comprising 10 or 5 electrodes arranged one after the other or side by side within one of the electrode assemblies. To this extent, the antistatic device according to the invention has a relatively compact construction.
According to a particularly advantageous embodiment, the two active electrode assemblies may be arranged in or on a common bar-shaped electrode carrier, which make installation of the antistatic device considerably easier. If the above-mentioned sensor electrode assembly is also present, it can also be arranged in or on said common electrode carrier to good effect. Such an electrode carrier may be suitably equipped with connections for the high voltage sources and the sensor system to enable the positive electrode assembly to be connected electrically to the positive high voltage source, the negative electrode assembly to the negative high voltage source and optionally the sensor electrode assembly to the sensor system.
The electrode carrier may comprise a partition wall extending between the active electrode assemblies on the one side and the sensor electrode assembly on the other. The partition wall may particularly be electrically insulating. The partition wall may thus reduce the risk of a short circuit between the active electrodes and the sensor electrodes via the direct air route, since it forces an alignment of the ion movement toward the material web. This alignment of the ion movement toward the material web may be improved for example if the partition wall protrudes beyond the electrodes or the electrode tips thereof in the direction of the material web.
In another embodiment, the electrode carrier may comprise at least one high voltage conductor, which is electrically connected to the respective high voltage connection. The present of the high voltage conductor makes it particularly easy to connect the individual electrodes of each electrode assembly to the respective high voltage source. According to a particularly advantageous embodiment, the respective high voltage conductor may be made from a carbon fibre composite element, which may serve at the same time to stiffen the electrode carrier. In particular, the high voltage conductor and the carbon fibre composite element is flat or in the form of a strip, and particularly configured with a rectangular profile.
The sensor electrodes are advantageously arranged side by side in a straight row of sensor electrodes. The positive electrodes may also be arranged side by side in a straight row of positive electrodes. Additionally, the negative electrodes may also be arranged side by side in a straight row of negative electrodes. According to a particularly useful embodiment, the positive and negative electrodes may be arranged in alternating sequence side by side in a common straight row of electrodes. This results in a particularly compact construction of the antistatic device and the electrode carrier.
In particular, the antistatic device may then comprise two rows of electrodes, which are arranged one behind the other relative to the direction of movement of the material web, wherein one row of electrodes contains the sensor electrodes while the other contains the positive and negative electrodes. In another embodiment it may be provided that the sensor electrodes, the positive and negative electrodes are arranged in alternating sequence side by side in a common straight row of electrodes. Thus, only one row of electrodes is discernible, and it contains positive electrodes, negative electrodes and sensor electrodes in an appropriately alternating sequence. In this way, the construction of the antistatic device and the electrode carrier is particularly compact.
For practical purposes, the sensor electrode assembly is arranged before the active electrode assemblies in the direction of movement of the material web when the antistatic device is in operation. In this way, the sensor electrode assembly is able to measure the polarity of the material web before the web reaches the active electrode assemblies. Surprisingly, however, it has been found that positioning the sensor electrode assembly before or after the active electrode assemblies is of little importance for the antistatic device according to the invention, which means that an embodiment is also possible in which the sensor electrode assembly is positioned after the active electrode assemblies in the direction of movement of the material web.
According to an advantageous embodiment, it may be provided that each positive electrode is disposed on a separate carrier foil on which an associated series resistor of the positive electrode is imprinted. It may further be provided that a plurality of positive electrodes is disposed on a shared carrier foil, on which a corresponding number of series resistors for the positive electrodes is imprinted. It is further possible to arrange all of the positive electrodes on a shared carrier foil, on which all of the series resistors associated with the positive electrodes are imprinted. The same also applies for the negative electrodes and the sensor electrodes. Thus, a separate carrier foil with corresponding series resistor may be provided for each negative electrode. Likewise, a plurality of carrier foils may be provided, on which a plurality of negative electrodes is disposed and which include a plurality of series resistors for the negative electrodes. A shared carrier foil may also be provided for all negative electrodes, which foil is furnished with all of the series resistors for the negative electrode. A carrier foil for each sensor electrode, each of which is imprinted with a series resistor for the respective sensor electrode is also conceivable. Likewise, a plurality of carrier foils may be provided on which a plurality of sensor electrodes are arranged and on which a plurality of series resistors are imprinted for the sensor electrodes. Finally, an embodiment is conceivable in this respect too, in which a single carrier foil is provided, on which all sensor electrodes are disposed and which bears all of the series resistors for the sensor electrodes in the form of imprinted resistors.
Furthermore, it is also possible to arrange the positive and negative electrodes on a shared carrier foil on which the series resistors of the positive and negative electrodes are imprinted. An embodiment is also conceivable in which the sensor electrodes and the positive and/or negative electrodes are all arranged on a common carrier foil on which the series resistors of the sensor electrodes and the series resistors of the positive and/or negative electrodes are imprinted. The use of such carrier foils with imprinted resistors results in a particularly inexpensive construction of the respective electrode arrangement, and ultimately of the antistatic device. Furthermore, when such carrier foils are used the electrode support can be constructed with a particularly flat design.
Optionally, it may also be provided that the carrier foil with the electrodes and the series resistors is provided as a continuous strip, which greatly simplifies component collection for the electrode assemblies and renders their manufacture relatively inexpensive. In addition or alternatively thereto, it may be provided that the carrier foil is imprinted with series resistors on both sides. This enables an extremely compact design, in that for example both positive and negative electrodes can be attached to different sides of the carrier foil together with their associated series resistors. Additionally or alternatively thereto, it may be provided that the carrier foil is made of a flexible material, which facilitates handling of the carrier foil.
The present invention is also represented by an operating method in which an antistatic device comprising an active positive electrode assembly and an active negative electrode assembly is operated in such manner that the polarity of the material web is determined initially, and thereafter only the ionisation electrode assembly required is activated or left in the active state, whereas the ionisation electrode assembly that is not needed in each case is deactivated or left in the deactivated state.
In this context, a particularly advantageous embodiment is one in which the polarity of the material web is determined during a learning phase, and in a subsequent working phase the required active ionisation of the electrode assembly is carried out with a non-pulsed DC voltage.
During the learning phase, both ionisation electrode assemblies can be operated in alternating sequence with pulsed DC voltage in order to be able to deionise or neutralise the web to a certain degree during the learning phase. However, in principle it is also possible to leave both ionisation electrode assemblies deactivated during the learning phase, so that only the required ionisation electrode assembly is activated for the working phase.
During the working phase, a neutralisation current of the active ionisation electrode assembly may be monitored, and can then be switched to another mode automatically, particularly to the learning phase, depending on the calculated neutralisation current.
In another embodiment, it is also possible to measure a quiescent current of at least one of the two ionising electrode assemblies and/or the sensor electrode assembly, particularly during a diagnosis phase. The current state of the antistatic device can be evaluated depending on the measured quiescent current. For example, electrode consumption and/or electrode contamination can be detected on the basis of the measured quiescent current.
A particularly advantageous embodiment of the operating method is one in which the two active electrode assemblies are operated with a pulsed DC voltage during a learning phase in such manner that positive current pulses of the positive electrode arrangement are alternated with negative current pulses of the negative electrode assembly, and in which the active electrode assembly that is not needed is deactivated during a working phase, while only the required active electrode assembly is activated and is operated with non-pulsed DC voltage. To this extent, therefore, a bipolar pulsed DC mode (DC operation) is set in order to determine the polarity of the material web, and a unipolar non-pulsed DC mode is set for the actual neutralising operation. Since the learning phase is typically tiny compared with the working phase, the antistatic device presented here functions with significantly lower power consumption than conventional bipolar DC systems.
In this context, it may be practically provided that during the learning phase the two active electrode assemblies are initially operated with a predetermined initial pulse width ratio of positive to negative current pulses. In this case, a particularly advantageous embodiment is one in which, after the polarity of the material web has been determined during the learning phase, both active electrode assemblies are operated with at least one transition pulse width ratio of positive current pulses to negative current pulses, wherein for this at least one transition pulse width ratio the current pulses required to neutralise the material web are made longer than the initial pulse width ratio, and the current pulses that are not needed are made correspondingly shorter. This procedure may be used to verify the previously determined polarity again during the learning phase, before the high voltage source that is not needed is deactivated. This provides a greater degree of operational reliability. For example, the output pulse width ratio may be 50:50, so that the positive current pulses are the same length as the negative current pulses. If the material web has a negative polarity, then initially a transition pulse width ratio of 75:25 can be set, for example, in which the positive current pulses are therefore made longer in time, while the negative current pulses are made shorter. In the working phase, the high voltage source that is not needed, for example the negative high voltage source, is then deactivated, the system also switched from pulsed mode to non-pulsed mode, which in the example given finally results in a working pulse width ratio of 100:0.
Other important features and advantages of the invention will be apparent from the dependent claims, the drawings and the associated description of the drawings with reference to the figures.
Of course, the above-mentioned features and the features that will be explained in the following can be used not only in the combination presented for each, but also in other combinations or alone without departing from the scope of the present invention.
Preferred embodiments of the invention are illustrated in the drawings and will be explained in greater detail in the following description, wherein like reference signs refer to identical or similar or functionally equivalent components.
The diagrammatic drawings show:
As shown in
As shown in
A controller 18 cooperates with a sensor system 20, which may be used to determine a polarity of a neutralisation current of sensor electrode assembly 9 during the operation of antistatic device 4. Controller 18 serves to actuate high voltage sources 12, 15 and is suitably coupled to sensor system 20. In the example, sensor system 20 is integrated with controller 18. In order to evaluate the signals detected with the aid of sensor system 20 and actuate high voltage sources 12, 15, controller 18 may contain a corresponding microprocessor 21.
In this way, the polarity of the charge of material web 3 may be detected through sensor system 20 in conjunction with sensor electrode assembly 9 from the polarity of the neutralisation current of sensor electrode assembly 9. Since sensor electrodes 16 are connected to grounding element 19 via their series resistors 17 and measuring resistor 22, sensor electrode assembly 9 functions as a passive neutralising electrode assembly, through which a neutralisation current flows when material web 2 carries a corresponding charge. The polarity of the charge on material web 2 may be detected by determining the polarity of the neutralisation current. If sensor electrode assembly 9 is not present, the polarity of material web 2 may also be determined with reference to the neutralisation currents that drain off from active electrode assemblies 7, 8, and are detectable by sensor system 18. For example, if a relatively large neutralisation current is flowing at positive electrode assembly 7, it may be assumed that material web 2 is negatively polarised. In this case, both active electrode assemblies 7, 8 are activated while the polarisation of material web 2 is being determined.
Controller 18 can now disable the active electrode assembly 7, 8 that is not needed depending on the polarity determined. For example, the polarity of the neutralisation current of sensor electrode assembly 9 may be negative, which indicates a negative charge of material web 2. Subsequently, controller 18 activates positive high voltage source 12 and therewith positive electrode assembly 7. At the same time, negative high voltage source 15 and therewith negative electrode assembly 8 is deactivated. On the other hand, if it is determined that the neutralising current of sensor electrode assembly 9 is positive, this indicates that the charge carried by material web 2 is positive. Accordingly, controller 18 causes positive high voltage source 12 to be deactivated, and therewith deactivates positive electrode assembly 7, while simultaneously activating negative high voltage source 15 and negative electrode assembly 8.
Controller 18 preferably actuates the currently activated high voltage source 12 or 15 at least during a working phase in such manner that a non-pulsed DC voltage is present at the respective active electrode assembly 7, 8, and this voltage is preferably also constant.
A particularly advantageous approach, which can be implemented with the aid of controller 18, is explained in detail with reference to
In another embodiment, it may be provided that both ionisation electrode assemblies 7, 8 are deactivated during learning phase 24. As soon as a neutralising current with stable polarity is detected via sensor electrode assembly 9, controller 18 causes the respective required ionisation electrode assembly 7, 8 to be activated.
During this working phase 25, the neutralisation current of the respective active electrode assembly 7, 8 may be monitored constantly, for example. Thus, in the example of
Additionally or alternatively thereto, a degree of electrode abrasion and/or a degree of electrode contamination may also be monitored by measuring a quiescent current of the respective active electrode assembly 7, 8 and/or the sensor electrode assembly 9.
The quiescent current is expediently monitored during a diagnostic phase, which is active or switched on for example whenever material web 2 is started up, for example after the material web has been changed. When material web 2 is started up or at a standstill, there is little or no build-up of static charge, so that particularly no ions flow from one of the ionisation electrodes 7, 8 to the material web. The same is also true for passive sensor electrode assembly 9. On the other hand, ions flow through the air between negative electrode assembly 8 and positive electrode assembly 7, and between sensor electrode assembly 9 and at least one of the ionisation electrode assemblies 7, 8. These quiescent currents vary significantly according to the degree of contamination, and also correlate with the abrasion of electrodes 10, 13, 16, and with the erosion of electrode tips 10, 13, 16.
As shown in
In the embodiment shown in
In the embodiment shown in
Since the antistatic device 4 shown here only works with one active electrode assembly 7 or 8 when operating, that is to say during working phase 25, it is not necessary to maintain an especially large distance between electrode assemblies 7, 8, even relative to direction of movement 3 of material web 2. For example, as shown in
As shown in
Since a plastic is used as carrier material 44, it is also possible to implement relatively thin support materials 44, having a thickness less than 1 mm or less than 1.0 mm. In this case, it is also possible to create a flexible carrier material 44 depending on the plastic material used. In particular, substrate 41 may be constructed as a carrier foil. Said carrier will also be designated with reference sign 41 in the following.
Contact zones 47 can be used to attach said electrode 10, 13, 16 to one side of carrier foil 41, and an electrical connection to the other side. The respective terminal and the respective electrode 10, 13, 16 may be soldered to the respective contact zone 47, for example. It is also possible to crimp the terminals or electrodes 10, 13, 16 with contact zones 47. Alternatively, electrical contacts may also be produced by applying a coating or adhesive layer using an electrically conductive adhesive or an electrically conductive varnish. A plug connection or clamping connection is also conceivable. Foil carrier 41 may also be provided with a protective layer 48 made from a plastic, which is designed to be electrically insulating and is applied to carrier foil 41 in such manner as to cover at least the resistive paste 46 or resistor track 45. More particularly, the entire carrier material 44 may be coated with said electrically insulating protective layer 48, preferably leaving recesses for electrical contact zones 47.
In order to manufacture the carrier foil 41 presented here, the electrical contact zones 47 may first be imprinted on carrier material 44. Then, contact zones 47 may be burned in. Contact zones 47, may be burned in in a temperature range from about 150° C. to 220° C. inclusive. Electrical contact zones 47 may be made from conductive silver for example, which may preferably be prepared on a polymer epoxy resin. After electrical contact zones 47 are burned in, the respective resistor track 45 can be imprinted on carrier material 44. After resistor track 45 has been imprinted, said resistor track 45 is also burned in. The burning in process for resistor track 45 may be carried out in a temperature range from about 150° C. to about 240° C. inclusive. After the respective resistor track 45 has been burned in, an injection moulding process may also be carried out, by means of which the insulation layer 48 is applied. Insulation layer 48 covers at least resistor track 45. Depending on whether electrical terminals and electrodes 10, 13, 16 have already been attached to contact zones 47, insulation layer 48 may also cover contact zones 47. The injection moulding process for applying insulating layer 48 is preferably designed as a low-temperature spraying process, which is carried out at a temperature below 200° C. Contact zone 47 and/or resistance track 45 is/are expediently applied in a screen printing process. The use of a polymer paste as a resistance paste 46 makes it possible to burn in resistor track 45 at relatively low temperatures, so that a plastic material may be used for carrier material 44. In this way, carrier foil 41 is extremely inexpensive. The manufacturing process is also relatively inexpensive, since only relatively low firing temperatures have to be implemented, so the energy requirements for obtaining the firing temperatures and carrying out the burning in processes are comparatively low. An embodiment of the process in which a plurality of carrier foils 41 is produced on a sheet of carrier material 44 at the same time, and are then separated by cutting or punching is particularly convenient. In this way, the time for producing single carrier foils 41 can be significantly reduced by printing a plurality of contact zones 47 and/or a plurality of resistor tracks 45 at the same time.
The carrier foil 41 shown in
As shown in
In another advantageous embodiment, it may be provided for the carrier foil 41 to be usable on both sides. For example, positive electrode assembly 7 may be created on the front of carrier foil 41, facing the viewer in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 007 136.9 | Apr 2011 | DE | national |
This application claims priority to German Patent Application No. 10 2011 007 136.9 filed Apr. 11, 2011, and International Patent Application No. PCT/EP2012/056414 filed Apr. 10, 2012, both of which are hereby incorporated by reference in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/056414 | 4/10/2012 | WO | 00 | 3/8/2018 |
