Abstract:
Ions for neutralizing electrostatic charge on an object are generated and delivered in a stream of gas flowing through a dielectric channel that surrounds a loop of conductive filament which forms an ionizing electrode. The loop is formed within a single plane, or within multiple planes, and is supported within the channel with a plane of the loop substantially aligned with flow of gas through the channel. A region of minimum field intensity within the bounded region of the loop electrode is oriented in alignment with substantially maximum velocity of gas flow through a cross section of the dielectric channel.

Description:
RELATED APPLICATION  
       [0001]     This application claims benefit under 35 U.S.C. § 120 as a continuation-in-part of application Ser. No. 10/459,865, filed on Jun. 11, 2003 by P. Gefter et al, which application is incorporated herein in the entirety by this reference thereto. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to air or gas ionizing electrodes and more particularly to apparatus for neutralizing electrostatic charge on an object by efficiently generating and collecting ions for delivery to the object in a flowing gas stream and in a low-maintenance manner.  
       BACKGROUND OF THE INVENTION  
       [0003]     Electrode structures for generating ions of one or other polarity commonly rely upon sharp pointed electrodes or small diameter stretched filaments for creating a corona discharge in response to an applied high ionizing voltage.  
         [0004]     However, ions generated in this manner are strongly influenced by a high intensity electrical field near the electrode surface that controls ion movement and reduces the effectiveness of a flowing gas stream to capture, collect and deliver ions to the charged object.  
         [0005]     Moreover, pointed electrodes and filament electrodes are prone to deposit on the electrode surfaces byproducts of corona discharge in the gas stream. These deposits of byproducts create instability of corona discharge, reduce ion generation and disrupt ion balance in the gas stream.  
       SUMMARY OF THE INVENTION  
       [0006]     In accordance with one embodiment of the present invention, a conductive filament is formed as a loop that is supported within a nozzle for a stream of flowing gas and that is connected to a source of high ionizing voltage.  
         [0007]     The filament is formed from electrically conductive material, for example, such as tungsten or hastelloy alloy. The diameter of the filament ranges from about 10 to about 100 microns, and preferably is about 30-60 microns. The filament may have surface coating of corrosion-resistant materials in one or more layers that may be electrically conductive or non-conductive. For example, the surface coating may be glass or ceramic or metal or metal alloy.  
         [0008]     The loop electrode may be formed in a flat two-dimensional or three-dimensional configuration and may have round or elliptical or semi-elliptical shape with various ratios of major and minor axes.  
         [0009]     The loop electrode may be positioned in close proximity to a non-ionizing electrode and may be disposed in a flowing gas stream to move the generated ions and slow down the formation of corona byproducts. The gas may be an inert gas such as argon, or a low-moisture gas such as nitrogen or clean dry air (CDA).  
         [0010]     Various configurations of the loop electrode, the support structure and the non-ionizing electrode are arranged to maximize interaction between generated ions and the flowing gas stream to enhance ions collection for delivery to a charged object.  
         [0011]     In accordance with one embodiment of the present invention, two ionizing electrodes are each configured as a loop that is immersed in a flowing gas stream and is connected individually to one of positive and negative high voltage power supplies for optimized ion generation and ion collection. In accordance with one embodiment of the present invention the ionizing electrode is configured as a loop that is immersed in a flowing gas stream and is connected to AC high voltage power supply operating at a voltage and frequency that are preset to optimize ion generation and ion collection. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1A  is a plan view of one embodiment of the ionizing electrode according to the present invention in which a round loop is supported by a ceramic tube and is conductively connected to a high voltage terminal;  
         [0013]      FIG. 1B  is a plan view of one embodiment of the ionizing electrode according to the present invention in which an elliptical two-dimensional loop is supported by a ceramic tube and is conductively connected to a high voltage terminal;  
         [0014]      FIG. 1C  is a plan view of one embodiment of the ionizing electrode according to the present invention in which a semi-elliptical loop is supported by a conductive tube for connection to a high voltage terminal;  
         [0015]      FIG. 2A  is a pictorial view of a typical pattern of electrical field lines associated with a conventional pointed electrode positioned inside a dielectric tube;  
         [0016]      FIG. 2B  is a simplified graph of electrostatic field intensity distribution for the conventional pointed electrode of  FIG. 2A ;  
         [0017]      FIG. 2C  is a simplified graph of gas velocity distribution through a cross section of the dielectric tube of  FIG. 2A ;  
         [0018]      FIG. 3A  is a pictorial view of electrical field lines for one embodiment of the present invention in which the filament loop electrode is positioned inside a dielectric tube that confines gas flow therethrough;  
         [0019]      FIG. 3B  is a simplified graph of electrostatic field intensity distribution for the filament loop electrode positioned inside the dielectric tube in the embodiment of  FIG. 3A ;  
         [0020]      FIG. 3C  is a simplified graph of gas velocity distribution inside the dielectric tube of  FIG. 3A ;  
         [0021]      FIG. 4A  is a plan view illustrating different angular orientations of one embodiment of an ionizing electrode according to the present invention in which an elliptical three-dimensional loop electrode is supported by a glass bead for conductive connection to a high voltage terminal;  
         [0022]      FIG. 4B  is a plan view of one embodiment of the ionizing electrode according to the present invention in which an elliptical three-dimensional loop is supported on a conductive tube for connection to a high voltage terminal;  
         [0023]      FIG. 5A  is a sectional view of one embodiment of the ionizing electrode according to the present invention in which an elliptical two-dimensional loop electrode is positioned inside a dielectric tube and non-ionizing electrodes are positioned parallel to the plane of the loop electrode;  
         [0024]      FIG. 5B  is a sectional view of one embodiment of the ionizing electrode according to the present invention in which an elliptical two-dimensional loop electrode is positioned inside a dielectric tube and non-ionizing electrodes are positioned perpendicular to the plane of the loop electrode;  
         [0025]      FIG. 6A  is a sectional view of one embodiment of the ionizing electrode according to the present invention in which an elliptical flat loop electrode is positioned inside two concentric tubes and non-ionizing electrode are disposed parallel to the plane of the loop electrode;  
         [0026]      FIG. 6B  is a sectional view of one embodiment of the ionizing electrode according to the present invention in which a flat elliptical loop electrode is positioned inside two concentric tubes and non-ionizing electrodes are positioned perpendicular to the plane of the loop electrode;  
         [0027]      FIG. 6C  is a sectional view of one embodiment of the ionizing electrode according to the present invention in which a flat elliptical loop electrode is positioned inside two concentric tubes and in which the outer tube is a conductive, non-ionizing electrode;  
         [0028]      FIG. 7A  is a sectional view of one embodiment of the ionizing electrode according to the present invention in which a two-dimensional elliptical loop electrode is connected to receive AC ionizing voltage and is positioned inside a dielectric tube with non-ionizing electrodes positioned perpendicular to the loop electrode; and  
         [0029]      FIG. 7B  is a sectional view of one embodiment of apparatus according to the present invention in which an ionizing bar includes two elliptical two-dimensional loop electrodes positioned inside dielectric tubes and are connected separately to sources of positive and negative ionizing voltage.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]     Referring now to  FIG. 1A , there is shown a plan view of one embodiment of the present invention in which ionizing electrode  1  includes a conductive filament  2  in the form of a flat, round loop  3  having radius R. The loop radius may be in the range 0.1-50 mm, preferably, in the range 0.5-10 mm.  
         [0031]     The loop  3  is supported by a dielectric structure, for example, ceramic tube  4  and is connected through a conductor in the dielectric structure to terminal  5  that forms an appropriate support and connection to socket  5   a  that is connected to a supply of high ionizing voltage.  
         [0032]     Similarly, in the embodiment of  FIG. 1B  the filament  2  is formed as an elliptical two-dimensional loop lying within a plane. The elliptical configuration of the loop  13  is a suitable form for an ionizing electrode  1  positioned inside a confined space such as a tube or channel for confining a stream of flowing gas.  
         [0033]     In the embodiment of  FIG. 1C  the filament  2  is configured as a semi-elliptical flat loop  18  as a suitable shape for an ionizing electrode  1  supported by a conductive structure  14  inside a confined space such as an outlet nozzle for release of gas under pressure above ambient.  
         [0034]     Referring to the pictorial view of  FIG. 2A  there is shown as conventional pointed ionizing electrode positioned inside a dielectric tube  6  of radius r that confines a flowing gas. Also shown is a simplified picture of electrostatic field lines distributed between the pointed electrode and the reference electrode  7 .  
         [0035]     Referring to  FIG. 2B  there is shown a plot of electrical field intensity E distribution in cross section A-A of  FIG. 2A . High voltage applied to the pointed electrode creates maximum field intensity E max near the tip or point of the electrode that is positioned in the middle of dielectric tube  6  and that is surrounded by reference electrode  7 . The tube confines a gas stream for moving ions away from the pointed electrode. As illustrated in  FIG. 2C  which is a plot of flowing gas velocity across the diameter of tube  6  at cross section A-A, the maximum of the field intensity E coincides with the maximum flowing gas velocity U max in the central region of the tube. Ion generation is concentrated in the small volume around the tip of the electrode and such generated ions are trapped in a strong electrical field around that location. These conditions promote inefficient collection and delivery of generated ions within the stream of flowing gas.  
         [0036]     Referring now to  FIG. 3A  there is shown one embodiment of the present invention in which an elliptical loop  13  forming ionizing electrode  1  is positioned inside a dielectric tube  6  that confines a flowing gas stream  8 . Also in  FIG. 3B  there is shown a simplified picture of electrostatic field lines between the filament loop electrode  13  inside the dielectric tube  6  and the non-ionizing electrode  7  disposed outside the dielectric tube  6 .  
         [0037]     According to Gauss&#39;s law, electric field intensity E is primarily concentrated about the outer dimensions of the loop conductor  2  (see  FIG. 3A ) operating at high voltage, as shown in the plot of  FIG. 3B , with minimal electric field intensity Emin distributed within the bounds of the loop  13 . As illustrated in  FIG. 3C  which is a plot of flowing gas velocity across the diameter of tube  6  at cross section A-A, the maximum gas velocity near the center of tube  6  coincides with location of minimum field intensity Emin. The near-maximum gas velocities about the center of tube  6  coincide with locations of maximum field intensities. Thus, ions generated about the looped filament conductor  2  are able to migrate toward the interior volume of loop  13  that exhibits low field intensity, and are maximally generated about the loop conductor  2 , all in locations of maximum or near-maximum gas flow velocity within dielectric tube  6 . These conditions promote highly efficient capture or collection and delivery of generated ions within the flowing gas stream (for example, toward a charged object to be neutralized, not shown).  
         [0038]     The loop electrode embodiment of the present invention as illustrated in  FIG. 3A  thus effectively establishes large surface area for the generation and collection of ions within a stream of gas flowing past the loop electrode. Ions may diffuse or otherwise migrate toward the central region of low field intensity within the bounds of the loop electrode  2  for efficient collection and delivery within the central region of the gas stream that exhibits maximum flow velocity. And, the large emitting area of the loop electrode promotes lower current density per unit length along the loop conductor  2  with concomitant reduction in erosion of the conductor  2 .  
         [0039]     Referring now to  FIG. 4A , there are shown separate angular orientations about a central axis of a looped filament electrode  9  that is configured as a three-dimensional loop with portions disposed in separate, skewed planes. This configuration exposes large surface areas of the loop filament  9  to a gas stream flowing past the conductor  9 . The loop filament  9  is connected to a supporting electrical terminal  5  and is spaced therefrom by dielectric bead  10 . Alternatively, as shown in  FIG. 4B , the loop filament  9  may be directly attached to and supported by the conductive terminal  5  that also serves as a high voltage electrode.  
         [0040]     Referring now to  FIG. 5A  there is shown a sectional view of one embodiment in which ionizing electrode  2  is configured as the elliptical, two-dimensional loop that is positioned within a dielectric tube  6  which confines a flowing stream of air or gas  8 . Non-ionizing planar reference electrodes  7  are positioned outside the tube  6  and are oriented, for example, parallel to the plane of the loop electrode  2 .  
         [0041]     Ions generated by the loop ionizing electrode  2  are collected by flowing gas  8  passing through orifices  8  for delivery to a charged object (not shown). The gas  8  may be low-moisture dry clean air (CDA), nitrogen or a mix of gases for reducing formation of corona byproducts on the loop electrode  2 .  
         [0042]     Alternatively, as shown in the sectional view of  FIG. 5B , the planar, non-ionizing reference electrodes  7  are positioned outside the tube  6  perpendicular to the plane of the loop electrode  2 . Of course, the reference electrode  7  in each of the described embodiments may also be configured as a ring, or portions thereof, disposed about the outer periphery of dielectric tube  6 .  
         [0043]     Referring now to  FIG. 6A , there is shown a sectional view of one embodiment of the ionizing electrode  1  in which an elliptical flat loop electrode  13  is positioned inside a gas nozzle  6  comprising two concentric tubes  6   a  and  6   b . A non-ionizing or reference electrode  7  is positioned parallel to the plane of the loop electrode  13 . Gas  8  flowing in tube  6   a  may be different from gas flowing in tube  6   b . For example, gas in tube  6   a  may be nitrogen  8   a  and gas flowing in tube  6   b  may be clean dry air  8   b . Gas velocity and gas consumption in tube  6   a  and in tube  6   b  may be different. In this embodiment, the consumption of more expensive gas  8   a  may be minimized.  
         [0044]     Alternatively, as shown in the sectional view of  FIG. 6B , the ionizing loop electrode  13  is positioned inside the nozzle  6  and the non-ionizing electrode  7  is disposed perpendicular the plane of the loop electrode  13 . Of course, the reference electrode  7  may also be configured as a ring, or portions thereof, disposed about the outer periphery of outer tube  6   b.    
         [0045]     Referring now to  FIG. 6C , there is shown a sectional view of one embodiment of the ionizing electrode  1  in which the flat elliptical loop electrode  13  is positioned inside two concentric tubes  6   a  and  6   b  of different materials. The outer tube  6   b  is conductive and serves as a non-ionizing reference electrode  7   a , and the inner tube  6   a  is formed of dielectric material.  
         [0046]     Referring now to  FIG. 7A  there is shown a sectional view of one embodiment of the ionizing loop electrode in which the two-dimensional elliptical loop electrode  13  is connected to high AC ionizing voltage source  111  and is positioned inside dielectric tube  6  that confines a flowing gas  8 . The planar non-ionizing electrode  7  is disposed outside the dielectric tube  6  perpendicular to the plane of the loop electrode  13 . Of course, the reference electrode may be configured as a ring, or portions thereof, disposed about the outer periphery of tube  6 .  
         [0047]     The distal edge of the filament loop  13  is recessed L eg  relative to the orifice or distal end of the nozzle  6 , or is recessed L c  between the center of the loop  13  and the orifice of the nozzle. The recess L eg  may be in the range (+)5-(−) 10 mm, preferably (+)1-(−)5 mm. “Positive recess” as used herein means that the distal edge of the loop  13  protrudes or is positioned outside the nozzle  6  and may be exposed to ambient air or gas. “Negative recess” as used herein means that the distal edge of the loop  13  is retracted or is positioned inside the nozzle  6 .  
         [0048]     Referring now to  FIG. 7B  there is shown a sectional view of one embodiment of ionizing electrodes according to the present invention assembled in apparatus such as an ionizing bar  12  comprising at least two elliptical loop electrodes  13   a  and  13   b  separately connected to positive and negative high voltage power supplies  14 ,  15 , with each electrode positioned inside a dielectric nozzle  6   a ,  6   b  that confines a flowing gas  8   a  and  8   b . The recesses L eg  of the loop electrodes  13   a  and  13   b  may be different. For example, the recess L eg  for negative-voltage electrode  13   b  may be smaller than the recess L eg  for positive-voltage loop electrode  13   a . Also, the gas  8   b  flowing in the nozzle  6   b  may be different from gas  8   a  flowing in the nozzle  6   a , or may flow at a different velocity. For example, the gas  8   a  may be clean dry air and gas  8   b  may be nitrogen. Generation of negative ions in nitrogen is more efficient with small recess L eg . In this way, a desirable ion balance between generation of positive and negative ions can be achieved through combinations of two different recesses and compositions of two different gases flowing in the separate nozzles at different velocities.  
         [0049]     Therefore, the ionizing electrodes of the present invention promote efficient generation of ions that can be readily captured in a stream of flowing gas for delivery to a charged object to be neutralized of static charge.