Patent Publication Number: US-2007103842-A1

Title: AC Ionizer with Enhanced Ion Balance

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of Provisional Application 60/733,418, filed Nov. 3, 2005 and entitled “Diode Balanced AC Ionization System”. 
    
    
     BACKGROUND  
      (1) Technical Field  
      This invention relates to ionizers, which are designed to remove or minimize static charge accumulation from an item selected for static charge neutralization.  
      (2) Background Art  
      Ionizers remove static charge by generating ions and delivering those ions to a charged target. One type of ionizer, named “AC ionizer”, uses an AC voltage to produce ions. One type of AC ionizer that is isolated from ground can produce equal numbers of positive and negative ions and will normally appear to have a positive ion balance because negative ions have greater mobility than positive ions. These negative ions are grounded, and thus, lost at a faster rate than positive ions. Downstream from the source of the ions, the remaining ion mixture usually has more positive than negative ions.  
      Electrical grounds close to the ionizing sources, such as emitter tips or emitting wires, also change the ion balance. For example, a grounded object that is closer to the positive emitter than to the negative emitter will result in a negative ion because the positive ions have a shorter path to ground. Alternately, a grounded object that is closer to the negative emitter than to the positive emitter will result in a positive ion balance when measured downstream from the ionizer.  
      Ion balance requirements for electro-static sensitive components are important considerations when manufacturing and handling these components. Consequently, a need exists for an improved AC ionizer that provides an enhanced ion balance.  
     BRIEF SUMMARY OF THE INVENTION  
      The present invention relates to an improved ionizer that provides an enhanced ion balance. The ionizer may include a first ion emitter and a second ion emitter; at least one reference electrode coupled to ground; and a power supply for providing an AC voltage to the first and second ion emitter. This power supply is DC isolated from ground. In addition, the present invention includes a first rectifier coupled in series between the first ion emitter and the power supply, a second rectifier coupled in series between the second ion emitter and the power supply. The first and second rectifiers cause a DC bipolar voltage to be created from the first and second ion emitters during operation of the ionizer.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram showing an ionizer having enhanced ion balance in accordance with one embodiment of the present invention.  
       FIG. 2  is a block diagram showing a power supply that is DC isolated from ground and that may be used with an ionizer having enhanced ion balance in accordance with another embodiment of the present invention.  
       FIG. 3  is a block diagram showing an ionizer having enhanced ion balance in accordance with yet another embodiment of the present invention.  
       FIG. 4  is a block diagram showing an ionizer having enhanced ion balance in accordance with another embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION  
      In the following detailed description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the various embodiments of the present invention. Those of ordinary skill in the art will realize that these various embodiments of the present invention are illustrative only and are not intended to be limiting in any way. Other embodiments of the present invention will readily suggest themselves to such skilled persons having benefit of the herein disclosure.  
      In addition, for clarity purposes, not all of the routine features of the embodiments described herein are shown or described. It is appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals. These specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine engineering undertaking for those of ordinary skill in the art having the benefit of the herein disclosure.  
      Referring now to  FIG. 1 , a block diagram illustration of an ionizer  100  having enhanced ion balance is shown in accordance with one embodiment of the present invention. Ionizer  100  includes a first ion emitter  102  and a second ion emitter  104 ; at least one reference electrode  106  coupled to ground; and a power supply  108  for providing an AC voltage to the first and second ion emitters  102  and  104 . The term ion emitter is intended to include an electrode that emits ions by corona discharge upon receiving a sufficient voltage. In the embodiment shown, this AC voltage has a voltage magnitude sufficient to cause a corona discharge when the voltage is applied to an ion emitter, such as emitters  102  and  104 . An ion emitter may be implemented in the form of a conductive cylinder having a sharp point at one end, a wire, a loop and the like. Ion emitters, sometimes referred to as ionizing electrodes, are commonly known by those of ordinary skill in the art.  
      Power supply  108  is DC isolated from a source  110  having a ground potential, named “ground”  110 . The term DC isolated is defined as a configuration in which any DC component from ground  110  is electrically decoupled from power supply  108 , precluding DC from flowing to power supply  108  from ground  110 . The term DC is sometimes referred to as direct current.  
      In addition, ionizer  100  further includes a first rectifier  112  coupled in series between first ion emitter  102  and power supply  108 , a second rectifier  114  coupled in series between second ion emitter  104  and power supply  108 . First and second rectifiers  112  and  114  cause a bipolar voltage to be created from first and second ion emitters during operation of the ionizer. First and second rectifiers may be implemented using any device that can limit the flow of current in one direction, such as a diode, transistor, a Zener diode or their respective equivalents.  
      In the example shown in  FIG. 1 , rectifiers  112  and  114  are implemented in the form of diodes  116  and  118 , respectively. Diode  116  includes a cathode coupled to first ion emitter  102  and an anode for receiving a voltage potential sourced from power supply  108 , while diode  118  includes an anode coupled to second ion emitter  104  and a cathode for receiving a voltage potential sourced from power supply  108 .  
      Ionizer  100  is also shown configured with at least one gas moving device  120  for moving gas across first and second ion emitters  102  and  104  and generally towards the selected item. The use, type, placement and structure of this device are not intended to limit the embodiment of the present invention disclosed in  FIG. 1 . Device  120  may be omitted if another means for moving gas across emitters  102  and  104  is provided. For example, a gas provided by a pressurized source may be used.  
      The balance of positive and negative ions produced by ionizer  100  may be enhanced at the point of neutralization or at a location downstream from the ion emitters  102  and  104  by selecting a DC bipolar voltage. This DC bipolar voltage may be established by placing ion emitters  102  and  104  at a selected distance from each other. A downstream ion balance of approximately zero volts may then be obtained by varying the distance between an ion emitter that generates positive ions, such as ion emitter  102 , and a reference electrode that is nearby or nearest to ion emitter  102 , such as reference electrode  106 . For example, an enhanced ion balance that may be achieved with the example in  FIG. 1  may be less than a +/−10 volt difference between negative and positive ions when measured collectively at or near an item (not shown) selected for neutralization.  
       FIG. 2  illustrates one example of a power supply  130  that is DC isolated from ground and that may be used to implement power supply  108  in  FIG. 1 . Power supply  130  includes a high voltage transformer  132  and a DC decoupling element  134 . DC decoupling element may be implemented by using a device that electrically decouples power supply  130  from direct current that can flow from ground  136 , precluding this direct current from flowing to power supply  130 . DC decoupling element  134  may include a capacitor  138  as shown although the use of capacitor  138  is not intended to limit the scope and spirit of embodiment disclosed in  FIG. 2 . In  FIG. 2 , DC decoupling element  134  is coupled in series between power supply output  140  and high voltage terminal  142  of transformer  132 . However, in an alternative embodiment, which is not shown in  FIG. 2 , DC decoupling element  134  may be coupled in series between ground  136  and low voltage terminal  144  of transformer  132 .  
      In addition, implementing a power supply  130  in the manner shown is not intended to be limiting in any way. Any power supply that is DC isolated from a selected potential, such as ground, may be utilized. For example, a power supply that uses a piezo-electric AC generator provides DC isolation from ground.  
       FIGS. 3 and 4  are two additional embodiments of novel ionizers with air movers  21  that have been modified with capacitors  7  and diodes  8 . The ionizers also include reference electrodes  11  and  12 . Inclusion of a resistor  20  in series with the capacitor  7  is useful, but not essential. The diodes  8  provide a DC bipolar voltage between the emitters  9  in addition to the AC voltage.  
       FIGS. 3 and 4  show that the capacitor  7  is placed between the diodes  8  and the high voltage terminal of the transformer  1 .  FIG. 2  and  FIG. 3  also show that the low voltage terminal of the transformer is grounded.  
      The amplitude of the bipolar DC voltage depends upon an inherent capacitance  30  between the emitters  9 . In turn, the inherent capacitance  30  between the emitters  9  depends on how close each emitter  9  is to ground  6 .  
      By varying the distance between the positive and negative emitters  9  and their respective nearby ground(s)  6 , enhanced or near zero ion balance can be obtained at the point of neutralization or at a location downstream from the emitters.  
      Note that the diodes  8  are necessary for the creation of a DC bipolar voltage, and are a central component of this inventive concept. In one embodiment, a positive directed diode is placed in series with a first ionizing electrode, such as a first wire or group of shafts with sharp tips, while a negative directed diode is placed in series with a second ionizing electrode, such as a second wire or group of shafts with sharp tips. A positive directed diode is defined as a diode that passes positive current, while a negative directed diode is defined as a diode that passes negative (electron) current.  
      In  FIG. 4 , wires are used for emitters  9 . One wire is attached to each terminal of the transformer&#39;s  1  output. Since the view of  FIG. 4  is along the length of the wires, the wires are shown as points. The wires are placed parallel to each other, and parallel to the long dimension of the ionizer. By rotating the wires along the long dimension, or by balancing the wires between two grounded items (such as blowers, heaters or metal guards), the relative position of each emitter wire to grounds is changed. Hence, one ion polarity is selectively closer to ground, and workstation balance is changed.  
      In  FIG. 3 , the emitters  9  comprise shafts with sharp tips. Multiple shafts with sharp tips are typically used. Since the view of  FIG. 3  is along the length of the ionizer, only one pair of emitters is shown. One group of shafts with sharp tips is attached to each terminal of the transformer&#39;s  1  output.  
      The balance of this ionizer is shifted by bringing the mean distance of one group of shafts with sharp tips closer to ground than the mean distance of the second group of shafts with sharp tips. This can be accomplished by rotation, angling or translation of the emitter groups. Combined rotation, angling or translation may be appropriate.  
      For example, two wire emitters  9  may be used, and both wires are contained in a single plane. Ion balance is achieved by positioning the first wire closer to ground than the second wire. After positioning the emitter, the emitters may either be configured in a fixed position or movable wire attachment connectors may be used to allow each wire to be moved separately while maintaining both wires in the same plane.  
      In another example, two wire emitters  9  are employed, and both wires are contained in a single plane. Ion balance is achieved by rotating a mechanism which holds both wires in a parallel plane. Rotation brings one of the two wires closer to ground.  
      In yet another example, a group of shafts with sharp tips may be used and the shafts forms a plane. One plane is moved closer to ground  6  than the second plane to adjust balance.  
      Ion balance may also be achieved by holding the ion emitters stationary, and moving the reference electrodes, such as reference electrodes  11  and  12  shown in  FIGS. 3 and 4 .  
      Relative distances between emitter planes and their respective grounds are selected for optimal performance. This is true regardless of whether shafts with sharp tips are used or wires are used for emitters  9 .  
      Optimal relative distances between components vary with the specific AC ionizer design. In one specific case, the optimal distance between the first emitter plane and ground is more than 4 times the distance between the second emitter plane and ground. In a second specific case, the optimal distance between the first emitter plane and ground is 2 to 4 times the distance between the second emitter plane and ground. In a third specific case, the optimal distance between the first emitter plane and ground is 1.2 to 2 times the distance between the second emitter plane and ground.  
      The distance between emitter planes can also be optimized. In an operating prototype, the distance from the first emitter plane to ground is 0.5 to 5 times the distance between the first and second emitter planes. And the distance from the second emitter plane to ground is 3 to 8 times the distance between the first and second emitter planes. In this prototype, the first emitter plane is in series with the positive directed diode, and the second emitter plane is in series with the negative directed diode.  
      When wires are used for emitters in the prototype, the distance between wires is approximately between an eight of inch (⅛) and three (3) inches and achieves an enhanced or near zero ion balance of at least less than +/−10 volts.  
      Emitters  9  may be placed upwind or downwind from the air mover  21 . Since air must flow through the grounded reference electrodes  11  and  12 . Reference electrodes  11  and  12  may be configured to have porosity greater than 70%, where porosity is defined as the ratio of open area to the total area of reference electrodes  11  and  12 . Reference electrodes  11  and  12  may have varying shapes and sizes.  
      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.