FIELD OF THE INVENTION
This invention relates to apparatus and method for producing an air stream containing substantially balanced quantities of positive and negative air ions for neutralizing static charge on a charged object.
BACKGROUND OF THE INVENTION
Certain known static-charge neutralizers commonly operate on alternating current (AC) applied to a step-up transformer for producing high ionizing voltages applied to sharp-tipped electrodes. Ideally, operation of such a neutralizer should produce a moving air stream of electrically balanced quantities of positive and negative ions that can be directed toward a proximate object having an undesirable static electrical charge that must be neutralized.
Various electrical circuits are known for substantially balancing the quantity of positive and negative ions transported in a moving air stream using biased control grids, floating power supplies, and the like. However, such conventional balancing circuits commonly include bulky transformers and lack capability for manual balancing or offsetting adjustments.
In addition, conventional ionizers exhibit low efficiency of ion generation and erosion of the emitter electrodes attributable to high current densities at electrode tips, with concomitant particulate contamination attributed to eroded electrode tips. Electrodes formed of titanium or silicon may reduce the rates of electrode erosions that contribute to reductions in ion-generating efficiencies with time, but eventual replacements of eroded electrodes in complex installations promote prohibitively expensive maintenance requirements.
Accordingly, it is desirable to efficiently produce balanced quantities of air ions in a flowing air stream with low-maintenance equipment that can be readily serviced as well as conveniently adjusted for offset control and manual balancing.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, an ionizing module operates on applied AC to efficiently produce a substantially balanced flowing stream of positive and negative air ions that can be directed toward a statically-charged object, or into an environment of unbalanced air ions that is to be neutralized. An ionizing electrode includes a thin wire shaped as a closed figure within regions of an air stream of maximum flow velocity, and reference electrodes are disposed at generally different distances upstream and downstream of the ionizing electrode to enhance ion-generation efficiency and balance control. A high-voltage power supply circuit is connected to the ionizing electrode and is tapped for low voltage to supply as bias to the down-stream reference electrode. An outlet structure of insulating material is disposed within the flowing air stream to aid in balancing the positive and negative ions flowing in the air stream.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a pictorial side illustration of apparatus and circuitry in accordance with one embodiment of the present invention;
FIG. 2 is a pictorial side illustration of an ionizer cell in accordance with another embodiment of the present invention;
FIG. 3 is a graph illustrating ion-flow offset voltages in the outlet air stream as a function of bias voltage applied to a downstream reference electrode;
FIGS. 4A, 4B are frontal pictorial illustrations of various embodiments of ionizing electrodes in accordance with the present invention; and
FIG. 5 is a graph illustrating regions of an air stream from a radial fan at which flow velocities are greatest for use in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the pictorial side illustration of FIG. 1, there is shown a fan 11 disposed to rotate the fan blades about a longitudinal axis that substantially aligns between input and output ports 13, 15 of a supporting housing 17. An ionizing electrode 19, as described in detail later herein, is supported within the insulating housing 17 at a location downstream of the fan 11. A pair of reference electrodes 21, 23 are supported within the insulating housing 17 generally at different distances upstream and downstream relative to the ionizing electrode 19. An insulating grid structure 25 is disposed across the outlet port 15 to pass a flowing air stream containing positive and negative ions therethrough toward a charged object 20 to be neutralized of static charges.
A high-voltage power supply 27 includes a step-up transformer 29 having one terminal of a secondary winding connected to the ionizing electrode 19 through a capacitor 31, and having another terminal of the secondary winding connected to ground through an adjustable voltage divider, or potentiometer 33. An adjustable AC voltage derived from the voltage divider 33 is rectified 35 and applied as a DC bias voltage to the downstream reference electrode 23. Of course, a power supply that switches recurringly between high ionizing voltages of one polarity and opposite polarity may alternatively energize the ionization electrode 19. The electrodes 19, 21, 23 are all electrically insulated from ground as supported within the insulating housing 17.
In operation, air flows into the housing 17 through the inlet port 13 in response to rotation of the fan 11 about the rotational axis that is substantially aligned between the inlet and outlet ports 13, 15. As illustrated in the graph of FIG. 5, maximum flow velocity 37 of air established by the radial blades of fan 11 occurs at a selected displacement radially from the rotational axis of the fan 11. Accordingly, the ionizing electrode 19 is disposed as a substantially continuous thin conductive filament within the region of maximum airflow velocity, as shown in FIGS. 4A, 4B. The thin filament or wire 19 is formed of tungsten or stainless steel or a gold-plated composite structure including such materials, with a diameter in the range of about 20–200 microns, and preferably in the range of about 50–60 microns to provide sufficient mechanical strength while promoting high ionizing electric field intensity along the entire length of the ionizing electrode 19. The ionizing electrode 19 is supported within the insulating housing 17 on a plurality of insulating mounts 39 that form the ionizing electrode in a substantially closed figure, or polygon, with the enclosed area thereof disposed substantially normal to the direction of air flow between inlet and outlet ports 13, 15.
In the embodiment illustrated in FIG. 4B, the mounts 39 support the ionizing electrode wire 19 in a 15-sided polygon configuration approximating a circle at a ‘diameter’ 37 that closely approximates the diameter at which maximum air flow velocity occurs. In the embodiment illustrated in FIG. 4A, the ionizing electrode wire 19 is supported on fewer (5) mounts 39 to form a distinctive pentagon that is disposed substantially within the region of maximum air flow velocity from fan 11. About 5–7 mounts 39 are preferred for fabrication simplicity and adequate support for the ionizing electrode wire 19 in a substantially closed polygon configuration. In the embodiment illustrated in FIG. 4A, a spring 41 disposed between ends of the electrode wire 19 maintains the electrode wire in tension about substantially rigid mounts 39, and in the embodiment illustrated in FIG. 4B, one or more resilient mounts 39 maintain tension in a loop of the electrode wire 19 that is supported thereby.
Referring again to FIG. 1, there is shown a set of reference electrodes 21, 23 disposed upstream and downstream of the ionizing electrode 19. Each of these reference electrodes 21, 23 may include one or more conductive rings 45, 47 that are mounted concentrically about the axis of rotation of the fan 11, within the region of maximum air velocity produced thereby. Thus, as illustrated in the graph of FIG. 5, the concentric ring electrodes 45, 47 may be supported at about the radii 49, 51 from the axis of rotation of the fan 11, within and about the region of maximum air flow velocity produced thereby.
It should be noted from the illustrated circuitry of FIG. 1 that the upstream reference electrode 21 is not connected (i.e., is at ‘floating’ potential) and is only loosely capacitively coupled to the nearest electrode 19 via distributed capacitance therebetween. Additionally, the one or more conductive rings 45, 47 in the upstream and downstream reference electrodes 21, 23 are formed of conductors of much thicker diameter, for example, 10 to 100 times the diameter of the ionization electrode wire 19 to assure no ionization from the reference electrodes 45, 47. In addition, the upstream reference electrode 21 is positioned closer to the ionization electrode 19 than the downstream reference electrode 23. This promotes an intense or highly dense flow of generated ions in a direction opposite the air flow through the upstream reference electrode 21 and the ionization electrode 19 for enhanced capture of the generated ions within the flowing air stream. Ions of one polarity that are generated during one half cycle of the AC high voltage applied to the ionization electrode 19 migrate toward the floating reference electrode 21 to charge that electrode 21 toward a static voltage of one polarity. However, ions of the opposite polarity that are generated during the alternate half cycle of the applied AC high voltage migrate toward the floating reference electrode 21 to discharge that electrode 21 and charge that electrode toward a static voltage of opposite polarity.
In steady-state operation, high ion current densities flow between the upstream reference electrode 21 and the ionization electrode 19 for capture within the air stream from fan 11 flowing in the opposite direction, and the potential on reference electrode 21 settles toward approximately zero volts. The spacing of the upstream reference electrode 21 from the ionization electrode 19 is set at a closer distance, L1, than the distance, L2, at which the downstream reference electrode 23 is set from the ionization electrode 19 for enhanced ion current flow within the spacing L1 and improved efficiency of entrainment of the generated ions within the flowing air stream.
The downstream reference electrode 23 is set at a greater distance L2 from the ionization electrode 19 and may include one or more ring-shaped conductors 45, 47 of thick dimension, for example 10 to 100 times the diameter of the ionization electrode wire 19 to avoid high ionizing electrostatic field intensities and resultant ion generation. Instead, the downstream reference electrode 23 is connected to a DC bias supply including the voltage divider 33 connected in the secondary circuit of transformer 29, and rectifier 35. In this way, a DC bias voltage of one polarity (typically, negative) is supplied to the downstream reference electrode 23 to repel an excess of ions of the one polarity (typically, negative due to a greater mobility of negative air ions). In addition, because the voltage divider 33 is connected to conduct current flowing in the secondary winding of transformer 29, higher bias voltage is supplied to the downstream reference electrode 23 on higher current flowing in the secondary winding attributable to higher ion generation in each half cycle of AC high ionizing voltage applied to the ionization electrode 19. In steady-state operation, the DC bias voltage supplied to the downstream reference electrode 23 approximates the voltage (typically of negative polarity) at which balanced quantities of positive and negative ions flow in the air stream through the downstream reference electrode 23. As illustrated in the graph of FIG. 3, such bias voltage may be about −230 volts to establish zero offset or balanced flow of positive and negative ions. As illustrated by the graph of FIG. 3, a substantial positive offset voltage results from operating the downstream reference electrode 23 at zero applied bias. Thus, for balanced flow of generated positive and negative ions through the downstream reference electrode 23, spaced a distance L2 from the ionization electrode 19, a negative DC bias of about −230 volts may be applied to the reference electrode 23 in the illustrated embodiment of the present invention. However, DC bias voltage provided by the voltage divider 33 may be adjusted to provide a wide range of outlet ion flow offset voltages, as desired, approximated by the curve 46 in the graph of FIG. 3. One or more ring-shaped conductors 45, 47, preferably 2–6 conductors in concentric array as shown in FIGS. 2, 3, are disposed within the region of greatest velocity of the flowing air stream. The number of conductors 45, 47 of selected diameter, lying within a substantially common plane at a distance L2 from the ionization electrode 19, relative to the distance L1 of the upstream reference electrode 21 from the ionization electrode 19, affect the bias level required on the downstream reference electrode 23 to establish balanced flow of generated positive and negative ions in the flowing air stream from fan 11. Ideally, the bias supply including rectifier 35 and voltage divider 33 exhibit low output impedance to ground to serve as an electrostatic screen against high ionizing voltage and radiation emission outside of housing 17.
In one embodiment of the present invention, the upstream reference electrode 21 is positioned about 0.2–1.5 inches, and preferably about 0.5 inches, from the ionization electrode 19, and the downstream reference electrode 23 is positioned about 0.3–2 inches, and preferably 0.6–0.75 inches, from the ionization electrode 19, for a ratio of L2/L1 in the range of about 1.01–1.5, and preferably about 1.15.
Referring now to FIG. 2, there is shown a side pictorial view of the air ionizing module, substantially as shown in FIG. 1 without fan 11. Multiple ones of such modules may be accumulated and positioned within flowing air to distribute generated ions into an environment, for example, associated with a static-free workstation. Such module includes components similar to counterpart components as described herein with reference to FIG. 1 using similar legend numbers. The downstream reference electrode 23 may include additional concentric ring conductors 48, and the high voltage and bias power supplies 27, 35 may be conveniently packaged for installation with each such module. A screen grid 54 formed of insulating material is disposed across the outlet port 15 as a mechanical barrier against inadvertent penetration by external objects into the interior components and structure of the module. Such screen grid of electrically-insulating material may accumulate surface charge of one polarity that then repels and attracts ions of the one and opposite polarities to promote self-balancing of the outlet flow of generated ions.
Therefore, the air ionizing module, or ion generating apparatus, and generation method according to the present invention creates an intense ion flow in a direction opposite to airflow for enhanced efficiency of ion transfer to the air stream. Convenient biasing circuitry adjusts the offset voltage of the outlet ion flow over a range that includes ion balance and ion imbalance of either polarity. Ions are generated along a fine wire electrode instead of at a sharp-tip electrode, for distribution throughout regions of greatest airflow velocity in the flowing air stream. For operation with a fan having radial fan blades rotating about an axis, the fine-wire ionization electrode may be configured as a closed-area polygon or circle supported substantially within a plane oriented normal to the rotational axis of the fan blades for enhanced ion generation and ion transfer to the flowing air stream.
Patent Grant
7212393
