Air assist for AC ionizers

[0001] This application claims the benefit of U.S. provisional application 60/726,874 filed Oct. 13, 2005 and entitled “Orifice Assist for Ionizers with Airflow Nozzles”, and U.S. provisional application 60/778,755, filed Mar. 3, 2006 and entitled “Fringe Field Ion Extraction for Ionization Systems”.

[0002] 1. Field of the Invention

[0003] The present invention relates to an alternating current (AC) ionizer that removes or minimizes static charge from a charged object selected for static charge removal. More particularly, the present invention relates to an AC ionizer that uses at least one flowing gas to enhance the static neutralization of the charged object.

[0004] 2. Description of Related Art

[0005] It is generally known that AC ionizers, sometimes referred to as “AC static neutralizers”, remove static charge by ionizing gas molecules, and delivering these ionized gas molecules, named gas ions, to a charged object. These gas ions are typically created by applying a high voltage to ionizing electrodes, by releasing nuclear sub-atomic particles, or by ionizing photon radiation. The location in which these gas ions are created is referred to as an ionizing source. Positive gas ions neutralize negative static charges, and negative gas ions neutralize positive static charges.

[0006] Delivering gas ions to a charged object is a factor in the static charge removal effectiveness of an AC ionizer because only the gas ions that reach the charged object produce useful charge removal, hereinafter “useful gas ions”. Static charge removal is also sometimes referred to as “static charge neutralization”. There are at least two mechanisms responsible for gas ion loss: recombination and grounding. Both recombination and grounding losses are more probable when gas ions are held to the ionizer by strong electrostatic forces.

[0007] One approach for reducing the effects of recombination and grounding includes using at least one nozzle with flowing air or gas with an AC ionizer, such as described in U.S. Pat. No. 6,807,044. Recombination is minimized because the flowing gas exiting a nozzle dilutes the gas ions before the positive ions and negative ions are mixed. Upon mixing, the lower gas ion density results in a lower recombination rate. In addition, the flowing gas from the nozzle propels the gas ions toward a charged object targeted for neutralization, which reduces the transport time and conserves the ions. Additionally, a nozzle can be oriented to direct generated gas ions toward the charged object, reducing the number of gas ions lost from grounding. Finally, some air nozzle geometries protect the ionizing electrodes from impurities in the environment.

[0008] For example, one type of AC ionizer places an ionizing electrode inside a nozzle. High purity air, nitrogen, or other non-reactive gas flows through each nozzle and along the ionizing electrode. This combination of nozzle and flowing gas partially protects the ionizing electrode from impurities in the environment, which reduces the cleaning frequency of ionizing electrodes, reducing the cost of maintenance and ownership. Moreover, ion balance is maximized because less buildup occurs on the ionizing electrode tips.

[0009] Although combining nozzles with an AC ionizer enhances the neutralization efficiency of the AC ionizer, nozzles alone miss the opportunity for even better AC ionizer performance. Consequently, a need exists for enhancing the performance of an AC static neutralizer that employs at least one nozzle.

[0020] While the invention has been described in conjunction with a specific best mode, it is to be understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the following description. The use of these alternatives, modifications and variations in or with the various embodiments of the invention shown below would not require undue experimentation or further invention.

[0021] The various embodiments of the present invention described herein are generally directed to the improvement of AC ionizers that utilize nozzles by adding at least one orifice within a placement zone between adjacent ionizing electrodes. Although AC ionizers that utilize nozzles are known, such as the AC ionizer disclosed in U.S. Pat. No. 6,807,044, hereinafter the “Patent” and which is incorporated by reference as if fully set forth herein, it is not intended that the various embodiments of the present invention be limited to existing AC ionizer designs.

[0022] Although a gas is delivered through both nozzles and orifices, nozzles and orifices are different. The term “nozzle” includes a structure with a hollow inner portion. One example is a cylinder having an inner and outer diameter. An ionizing electrode is positioned within that hollow inner portion. Gas flows through that hollow inner portion, and past the ionizing electrode. The term “orifice” includes an opening through which air or gas may exit. An air orifice does not possess or contain an ionizing electrode.

[0023] The term “placement zone” is defined as the optimal location or area for placing at least one orifice between adjacent nozzles that are disposed on an AC ionizer and that each have an ionizing electrode contained generally within their inner portion. This placement zone area is not an additional hardware structure. It is a geometrical projection onto the face or surface of a portion of an AC ionizer that contains nozzles. In accordance with one embodiment of the present invention, the placement zone has a shape in cross-section that is commonly referred to as a diamond shape.

[0024] AC ionizers differ from DC ionizers. With an AC ionizer, typically all ionizing electrodes are connected to the same voltage source. Unlike DC ionizers, the strongest attractive electrostatic field forces for AC ionizers are found between the ionizing electrodes and ground. And, unlike DC ionizers, electrostatic field forces between adjacent ionizing electrodes are repulsive. Gas ions produced by one ionizing electrode are repelled by an adjacent ionizing electrode because they have the same polarity. As a consequence, the optimal placement of orifices is different for an AC ionizer than it is for a DC ionizer, and gas ion delivery efficiency for AC ionizers can be improved by adding at least one orifice between adjacent nozzles that each contains an ionizing electrode.

[0025] For an AC ionizer, the placement zone between adjacent nozzles is particularly useful for two reasons. First, gas ions that would normally be lost to grounding are present in the placement zone in moderately high concentration. Recovery of these gas ions is functionally equivalent to creating more gas ions. Second, gas ions in the placement zone are not held tightly to the AC ionizer by strong electrostatic fields.

[0026] In addition, AC ionizer discharge times commonly achieved by using nozzles alone can be reduced by placing at least one orifice between adjacent ionizing electrodes within a placement zone. It has been further observed that this decrease in discharge times is achieved even when the total gas consumption from the nozzles and the orifice(s) does not exceed the consumption from the nozzles alone.

[0027] Referring now to the drawings, FIGS. 1 and 2 depict examples of AC ionizer portions 2a and 2b that use nozzles 4a and 4b and ionizing electrodes 6a and 6b, respectively. Gas ions are created by corona discharge when a high voltage is applied to ionizing electrodes 6a and 6b. In FIG. 1, gas enters nozzle 4a from a pressurized supply (not shown) through a jet 8 located besides ionizing electrode 6a, while in FIG. 2, gas enters nozzle 4b through a concentric opening 10. After exiting jet 8 or concentric opening 10, the gas flows around and past ionizing electrodes 6a or 6b, respectively.

[0028] The term “gas” is intended to include a gas or a combination of gases, such as air. This gas is supplied to nozzles 4a and 4b through tubing or through a common plenum, which is not shown to avoid overcomplicating FIGS. 1 and 2.

[0029] Utilizing nozzles help protect ionizing electrodes from impurities since relatively pure or clean gas may be forced to flow past and generally along the ionizing electrode. Impurities from air within the operating environment of the ionizer are thus largely excluded from contacting the ionizing electrodes, minimizing particle buildup on the ionizing electrodes. Moreover, balance and discharge time remain constant for long time periods, and the frequency of cleaning is reduced.

[0030] Nozzles, such as nozzles 4a and 4b, also direct gas ions toward a charged object (not shown), reducing the gas ion density required for neutralizing the charged object. Also, the ion movement transit time to the object is reduced by the gas nozzle flow, which decreases ion recombination.

[0031] FIG. 3 illustrates a configuration of an ionizing electrode 12 within a nozzle 14 from an AC ionizer portion 16. Nozzle 14 receives gas from a plenum 15 and is disposed through a cut-out 18 formed on a bottom surface 20. Plenum 15 provides a supply of pressurized gas or gases, such as air, to nozzle 14. Bottom surface 20 includes a conductive surface 22 that receives a reference potential, such as ground. When used in this manner, conductive surface 22 may be referred to as a non-ionizing electrode or as a reference electrode.

[0032] When conductive surface 22 is used as a reference electrode and when a sufficient voltage from a high voltage power supply (not shown) is applied to ionizing electrode 12, electrostatic field lines 24 originating at ionizing electrode 12 are grounded at the edge of the cut-out 18. Because electrostatic field lines 24 are strong in a region 26, gas exiting from jet 27 and flowing out of nozzle 14 is marginally effective for harvesting or displacing gas ions (not shown) created within region 26. Most of these gas ions will follow electrostatic field lines 24 to conductive surface 22, grounding gas ions that would have been useful for static charge neutralization, reducing the efficiency of the AC ionizer.

[0033] FIG. 4 includes a graph 28 that illustrates the relationship between the strength of electrostatic field forces and the distance from the source of the electrostatic field. Graph 28 shows that electrostatic field forces on gas ions increase as the distance from an ionizing electrode decreases.

[0034] In accordance with one embodiment of the present invention, FIG. 5 illustrates the use of at least one orifice, such as orifice 30, in combination with an AC ionizer to enhance ionizer efficiency in harvesting gas ions for use in the static neutralization of a charged object (not shown). The embodiment shown includes orifice 30 disposed within a placement zone 34 that is located between adjacent nozzles 36a and 36b of AC ionizer portion 32. Nozzles 36a and 36b respectively include ionizing electrodes 38a and 38b disposed in their respective inner hollow portions 39a and 39b. Nozzles 36a and 36b utilize forced or compressed gas, which exit from jets 37a and 37b, to harvest gas ions near or at the tips of ionizing electrodes 38a and 38b.

[0035] In the embodiment in FIG. 5, orifice 30 is nominally placed midway between ionizing electrodes 38a and 38b, which enables compressed gas exiting orifice 30 to harvest gas ions trapped under the electrostatic field generated when a high voltage is applied to ionizing electrodes 38a and 38b. Further, since orifice 30 and nozzles 36a and 36b each provide an exit from which the gas may flow, an optimal allocation of the gas is obtained, resulting in a relatively low gas ion discharge time. Orifice 30 is coupled to or form on a surface 45 of a plenum 41 and located within placement zone 34. A cut-out 40 is formed on conductive surface 42, permitting a pressurized gas to flow past conductive surface 42.

[0036] Nozzles 36a and 36b are also coupled to surface 45 of plenum 41. Cut-outs 48a and 48b are formed on conductive surface 42, permitting nozzles 36a and 36b to protrude past conductive surface 42. Conductive surface 42 is used as a non-ionizing electrode and when coupled to a reference voltage, such as ground, functions as a reference electrode. Conductive surface 42 may be located on the same side of AC ionizer portion 32 on which nozzles 36a and 36b are located. In the embodiment shown in FIG. 5, conductive surface 42 is composed of a thin relatively rigid material having electrically conductive properties, such as thin metal. The use of thin metal is not intended to be limiting. For example, conductive surface 42 may be composed of a non-metallic and electrically insulating material that has a conductive coating that faces in the same general direction as the gas flow provided by nozzles 36a and 36b.

[0037] The term “cut-out” is intended to be interpreted broadly and includes any hole or aperture that is formed on a surface, such as conductive surface 42, that will permit the use of a nozzle, an orifice or both in accordance with the embodiment described with reference to FIG. 5. Those of ordinary skill in the art after receiving the benefit of this disclosure would readily recognize that using a separate plenum and conductive surfaces, such as plenum and conductive surfaces 45 and 42, respectively, is not intended to limit the present invention. For example, a conductive plating material (not shown) may be formed on surface 45 of plenum 41. This conductive plating material would have voids that are similar in diameter and location as cut-outs 40 and 48.

[0038] Gas ions found between electrodes that receive the same polarity are not tightly held to AC ionizer portion 32. Orifice 30 permits gas to exit from it, providing a high velocity flow of gas that displaces gas ions within the vicinity of orifice 30 away from AC ionizer portion 32 and towards a charged object (not shown) selected for static neutralization. This discharge flow of gas from orifice 30 creates a low pressure area and entrains additional airflow within an air entrainment zone 50. Air entrainment zone 50 covers portions of cut-outs 48a and 48b and cut-out 40, where electrostatic fields created by ionizing electrodes 38 during operation are weak.

[0039] It is contemplated that orifice 30 and jets 37a and 37b have diameters of approximately within the range of 0.010 and 0.016 inches, providing a volume of gas discharge of approximately within the range of 0.5 and 5 liters per minute, respectively, when a supply of gas at a pressure approximately between 5 and 60 psi is provided in plenum 41. These ranges are not intended to be limiting and will vary depending on the physical characteristics and design of portion 32, including the diameters selected for the nozzle and orifices, number of nozzles and orifices used, and the like.

[0040] As shown in FIG. 6, a graph 52 illustrates that an AC ionizer having nozzles and ionizing electrodes configured with orifices in a manner similar to that described in FIG. 5 can provide the same level of performance as an AC ionizer with roughly twice the number of nozzles and ionizing electrodes but without orifices. The values on graph 52 include measurements of time needed to reduce an electrical charge on a plate from a charge plate monitor from 1000V to 100V. These time measurements are obtained for each polarity and then averaged. Assuming all other factors constant, the ion discharge time achieved will be shorter than that of an AC ionizer that does not employ the improvement taught by the embodiment described in FIG. 5.

[0041] In accordance with another embodiment of the present invention, the embodiment disclosed in FIG. 5 may be further improved by using at least one non-ionizing electrode having the features described with reference to FIG. 7. FIG. 7 illustrates an AC ionizer portion 54 that includes at least two nozzles 56a and 56b with ionizing electrodes 58a and 58b and jets 59a and 59b, at least one orifice 60 located within a placement zone 62, and a non-ionizing electrode 66 that is used as a reference electrode. However, unlike the embodiment in FIG. 5, the example in FIG. 7 does not require cut-outs on a conductive surface since the conductive surface used as a non-ionizing electrode, such as non-ionizing electrode 66, is positioned approximately parallel to an imaginary line 68 that intersects ionizing electrodes 56a and 56b and consequently, does not impede the formation or placement of nozzles 56a and 56b and orifice 60 onto plenum surface 61. Plenum surface 61 is part of plenum 63, and plenum 63 functions as a channel or passage way through which a pressurized supply of gas may be routed to nozzles 56a and 56b and orifice 60.

[0042] Non-ionizing electrode 66 is intended to be used as a reference electrode and is thus, coupled to a reference voltage, such as ground. It is contemplated that non-ionizing electrode 66 has a shape approximately in the form of a strip. Those of ordinary skill in the art will readily recognize that the aspect ratio of the strip-like shape of non-ionizing electrode 66 is not intended to be limiting. The shape of non-ionizing electrode 66 may vary as long as non-ionizing electrode 66 does not intersect line 68. Nozzles 56a and 56b, ionizing electrodes 58a and 58b, jets 59a and 59b, orifice 60, plenum surface 61, placement zone 62, and plenum 63 may have substantially the structure and function as nozzles 36a and 36b, ionizing electrodes 38a and 38b, jets 37a and 37b, orifice 30, orifice 30, plenum surface 45, placement zone 44 and plenum 41, respectively, in FIG. 5.

[0043] In accordance with yet another embodiment of the present invention and as disclosed in FIG. 8, the embodiment disclosed in FIG. 7 may be further improved by using at least two non-ionizing electrodes. FIG. 8 illustrates an AC ionizer portion 70 that includes at least two nozzles 70a and 70b with ionizing electrodes 72a and 72b and jets 73a and 73b, at least one orifice 74 located within a placement zone 76, two non-ionizing electrodes 80a and 80b that are used as reference electrodes, a plenum surface 77 and a plenum 78. Nozzles 70a and 70b, ionizing electrodes 72a and 72b, jets 73a and 73b, orifice 74, placement zone 76, plenum surface 77 and plenum 78 may respectively have substantially the same function and structure as nozzles 56a and 56b, ionizing electrodes 58a and 58b, jets 59a and 59b, orifice 60, placement zone 62, plenum surface 61 and plenum 63, disclosed in FIG. 7.

[0044] Non-ionizing electrodes 80a and 80b are each similar in function and in shape to non-ionizing reference electrode 66. Non-ionizing electrodes 80a and 80b are oriented so that they do not intersect an imaginary line 82 that intersects ionizing electrodes 72a and 72b. In addition, non-ionizing electrodes 80a and 80b are disposed on opposite sides of nozzles 70a and 70b, as shown.

[0045] The embodiments disclosed in FIGS. 7 and 8 achieve even less discharge time when compared to the embodiment disclosed in FIG. 5. The embodiment in FIG. 8 takes advantage of weak field extraction of gas ions because no grounds exist between ionizing electrodes 72a and 72b, and the distances between ionizing electrodes 72a and 72 and an available reference potential, such as ground, provided by non-ionizing electrodes 80a and 80b are increased on average. Thus, proportionately more gas ions are bound with weak electrostatic forces using an AC ionizer modified according to the embodiment disclosed in FIG. 8. These gas ions are also be entrained by the action of the orifice(s) used, such as orifice 74. Further, the size of the non-ionizing electrodes that are used as reference electrodes, such as non-ionizing electrodes 80a and 80b, may be reduced which lowers overall capacitance and capacitance losses. One practical consequence of lower high voltage power losses is the capability to build AC ionizers with more ionizing electrodes without using larger power supplies.

[0046] With reference to FIG. 9, the term “placement zone”, such as placement zone 85, may be defined as a location on an AC ionizer portion 83 that is defined by two first opposite corners 82a and 82b situated respectively between two adjacent ionizing electrodes 88a and 88b. Nozzles 84a and 84b have inner hollow portions 86a and 86b that contain all or part of ionizing electrodes 88a and 88b, respectively. Inner hollow portions 86a and 86b also house jets 87a and 87b, respectively. Nozzles 84a and 84b and ionizing electrodes 88a and 88b may have respectively the same function and structure as nozzles 36a and 36b and ionizing electrodes 38a and 38b disclosed in FIG. 5; nozzles 56a and 56b and ionizing electrodes 58a and 58b disclosed in FIG. 7; or nozzles 70a and 70b and ionizing electrodes 72a and 72b disclosed in FIG. 8. First opposite corners 82a and 82b respectively have first corner angles 90a and 90b that are less than or equal to 30 degrees. An imaginary straight line 92 drawn between ionizing electrodes contained within adjacent nozzles, such as ionizing electrodes 88a and 88b, bisects first corner angles 90a and 90b.

[0047] In addition, placement zone 85 may also be defined to include two second opposite corners 94a and 94b situated respectively between two adjacent ionizing electrodes, such as electrodes 88a and 88b. Second opposite corners 94a and 94b are formed by the intersection of lines 96a and 96b, and 97a and 97b, respectively. Lines 96a and 97a originate from first opposite corner 82a, while lines 96b and 97b originate from first opposite corner 82b. Second opposite corners 94a and 94b also include second corner angles 99a and 99b, respectively, which are each equal to or greater than 150 degrees. By using these descriptions with reference to FIG. 9, placement zone 85 may be said to be a geometric projection on AC ionizer portion 83 that has a “diamond-like” shape.

[0048] Referring now to FIG. 10, a portion 98 of an AC ionizer is shown with a placement zone 100 in accordance with yet another embodiment of the present invention. Portion 98 is part of an ionizing bar, sometimes referred to as a module, that has a plurality of nozzles containing ionizing electrodes, such as nozzles 102a and 102b and ionizing electrodes 104a and 104b, and modified to have a protrusion 114 having an orifice 106 placed within placement zone 100. Other orifices may be placed within other placement zones although in FIG. 10 only orifice 108 is shown to avoid overcomplicating the figure. Portion 98 also includes two reference electrodes 110a and 110b that each have a strip-like shape and that are orientated approximately parallel to imaginary line 112. Nozzles 102a and 102b, as well as protrusion 114 are coupled to plenum surface 116. The manner of coupling nozzles 102a and 102b and protrusion 114 to plenum surface 116 is not intended to be limiting in any way. Plenum surface 116 is part of plenum 117. Nozzles 102a and 102b, ionizing electrodes 104a and 104b, orifice 106, reference electrodes 110a and 110b imaginary line 112 plenum surface 116 and plenum 117 may have approximately the same function as similarly named elements described previously above with respect to FIG. 7 or 8 above.

[0049] In accordance, with another embodiment of the present invention, the placement zones described in FIG. 5 and FIGS. 7 through 10 may be further modified by excluding sections of the placement zone that overlap areas occupied by each nozzle and ionizing electrode. Excluding these sections as part of the placement zone, avoids placing an orifice near a nozzle, and hence, an ionizing electrode. For example, these excluded sections may include areas 118a and 118b, 120a and 120b, 122a and 122b, 124a and 124b and 126a and 126b in FIGS. 5 and 7 through 10, respectively.

[0050] As disclosed in the various embodiments of the present invention, placing an orifice, such as orifice 98, within placement zone 85 of an AC ionizer having nozzles and ionizing electrodes, such as nozzles 84a and 84b and ionizing electrodes 88a and 88b, reduces gas ion discharge times, enhances gas ion harvesting or both. However, placing an orifice within placement zone 85 or using a location that has a diamond-like shape is not intended to limit the scope of various embodiments disclosed herein. One of ordinary skill in the art would readily recognize that other locations or location shapes may be used to reduce discharge times and/or enhance gas ion harvesting through any or all of the following mechanisms.

[0051] The first mechanism is breakup of the turbulence in the vicinity of an AC ionizer portion that employs nozzles. Ions trapped in turbulence are vulnerable to recombination and grounding. Orifices prevent a stable turbulent vortex from forming beneath the ionizer portion, and propel gas ions within the vortex toward a charged object targeted for static charge removal.

[0052] The second mechanism is generation of supplemental air flow due to air entrainment (air amplification) by the high velocity air, which is delivered through the orifices. This supplemental air flow helps to remove gas ions which are trapped between the nozzles.

[0053] The third mechanism is weak electrostatic field gas ion extraction. The ionizing electrodes of an AC ionizer are connected to a common electrical bus with adjacent ionizing electrodes receiving the same polarity and voltage at any given time, which creates repellant electrostatic fields between adjacent ionizing electrodes, and the weakest electrostatic field is located between adjacent ionizing electrodes or between adjacent nozzles if such ionizing electrodes are placed within the adjacent nozzles. An orifice located between adjacent ionizing electrodes is optimally positioned for removing gas ions from the AC ionizer.

[0054] Gas from an orifice within a placement zone blows perpendicular to the electric field lines in the region of weakest electrostatic field constraint, and this gas has a high probability of removing gas ions that are constrained by an electrostatic field. The removed gas ions are, hence, available to remove static charge from the charged object.

[0055] The forth mechanism is relocation of high turbulence away from the tip of an ionizing electrode where the recombination rate is potentially the highest.

[0056] The fifth mechanism is redistribution of forced or compressed gas to achieve maximum ion output. As disclosed in the various embodiments of the present invention above, nozzles utilize forced or compressed gas to harvest gas ions near or at an ionizing electrode tip, while orifices utilize compressed gas to harvest gas ions trapped under the electrostatic field generated by the ion generation process. The optimal allocation of compressed gas results in a relatively low discharge time.

[0057] While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments. Rather, the present invention should be construed according to the claims below.