Patent Application
20080078295
As illustrated in
First electrode 10 preferably comprises a thin wire, about 0.2 millimeters (mm) in diameter, but wires or other thin, elongated structures between about 0.1 and 0.3 mm in diameter or width may be suitable. For example, a razor-thin strip or ribbon may be suitable. Second electrodes 12 are blade-like or paddle-like in that they have broad, substantially similar opposing surfaces. Although the opposing surfaces are flat or planar and parallel to each other in the illustrated embodiment of the invention, in other embodiments they can be curved, cambered, contoured, etc., can have surface features, or any other suitable blade-like shape. Nevertheless, smooth, featureless surfaces are believed to minimize undesirable corona. To further minimize corona, one or both edges of second electrodes has a blunt, rounded shape, preferably with a radius of curvature greater than about 1 mm. Electrodes 10 and 12 can be made of any suitable conductive material, though a material that resists corrosion and is easily cleanable, such as stainless steel, is preferred.
The above-described elements can be housed in a suitable housing 20 and retained in suitable mechanical assemblies (not shown for purposes of clarity), for example, as described in U.S. Pat. No. 6,946,103, entitled “AIR PURIFIER WITH ELECTRODE ASSEMBLY INSERTION LOCK,” the specification of which is incorporated herein in its entirety by this reference. With reference to a desired direction of air flow through housing 20, indicated by the arrow 22, an upstream side of housing 20 has grill-like or louver-like intake apertures 24, and a downstream side of housing 20 has similar exhaust apertures 26. When the indicated electrical potential is applied between first electrode 10 and second electrodes 12, the resulting electro-kinetic effect causes air to enter housing 20 through intake apertures 24, flow through housing 20 past electrodes 10 and 12, and exit the housing 20 through exhaust apertures 26. Particulate matter entrained in the air is electrostatically attracted to the surfaces of electrodes 12 and collects upon the surfaces.
Note that in the exemplary embodiment illustrated in
The amount of kinetic energy imparted to the air through the electro-kinetic effect increases with an increase in power consumed by the circuit defined by first and second electrodes 10 and 12. Thus, to maximize air flow velocity, it may at first glance seem optimal to maximize power. However, high electrode current can result in the corona effect generating undesirable amounts of ozone and nitrogen oxides. Rather than maximizing current, as power is the mathematical product of voltage and current, the present invention maximizes voltage (within what are believed to be safe and otherwise desirable limits for a consumer product) and controls electrode current.
Although power supply 14 is described in further detail below, it can be noted here that in the exemplary embodiment it provides an electrical potential between first electrode 10 and each of second electrodes 12 of about 23-50 kilovolts (kV). Still more preferably, it provides a potential of about 30 kV. With a potential of about 23-50 kV, the electrode current is generally less than about 500 microamperes (μA). To avoid applying excessive voltage to any one electrode (with respect to ground), the potential can be divided equally or at least approximately equally between first electrode 10 and each second electrode 12. Thus, for example, in an embodiment in which power supply 14 provides a potential of 30 kV between first electrode 10 and each of second electrodes 12, power supply 14 can provide a potential of +15 kV with respect to ground to first electrode 10 and a potential of −15 kV with respect to ground to each of second electrodes 12. Nevertheless, in other embodiments the reference ground can be omitted.
The optimal distance or spacing between first electrode 10 and the closest point on any of second electrodes 12 depends upon the electrical potential between them. A higher potential militates a greater distance or spacing to minimize corona. A portion of the axis 28 shown in
Although in this embodiment of the invention, axis 28 is parallel to the direction of air flow (arrow 22), in other embodiments the axis extending between respective closest electrode points may be oriented in any other suitable manner. Similarly, although in this embodiment second electrodes 12 are parallel to the direction of air flow, parallel to each other, and parallel to first electrode 10, in other embodiments they can be oriented in any other suitable manner. Nevertheless, orienting electrodes 12 in the manner shown in
As illustrated in
Electrodes 32, 34 and 36 are as described above with regard to the embodiment illustrated in
The manner in which a first electrode (e.g., electrode 10 in
Note that the end 60 of retainer 54 extends to a location between the ends of first electrode 10, approximately even or level with the end of 62 of tubular portion 62. It has been found that the electrical field can be unevenly distributed because first electrode 10 and second electrode 12 have unequal lengths, which can result in electrical discharge noise emanating primarily from the areas where the ends of electrode 10 are retained. To adjust the distribution of the electric field and thereby maintain quiet operation, semi-tubular extension 50 extends a distance 64 beyond this location. Preferably, distance 64 is at least 5 mm. Although this double-wall shielding arrangement with tubular portion 62 and extension 50 is suitable, in other embodiments guard 46 can be structured differently. For example, tubular portion 62 can be longer, extending approximately distance 64 beyond the end 60 of retainer 54.
As illustrated in
The power supply circuit primarily comprises a microcontroller 66, a pulse-width modulation (PWM) signal generator 68, a line filter 70, a low voltage power supply 72, a rectifier 74, a MOSFET 76, a transformer 78, and a high voltage multiplier 80. As controlled by a main power switch 81, line filter 70 receives and filters household utility power (e.g., 120 VAC). Low voltage power supply 72 receives the filtered utility power and provides the digital voltage (e.g., 5 VDC) required to power microcontroller 66. Rectifier 74 converts the AC power to DC, and transformer 78 steps up the voltage. High voltage multiplier 80 similarly multiplies the stepped-up voltage to the (e.g., +15 and −15 kV) electrode voltages. The circuit through the primary side of transformer 78 is coupled to ground through the drain terminal of MOSFET 76 and a resistor 82. This circuit also provides a feedback signal, representative of electrode current, to microcontroller 66. A peak voltage rectifier 84 tapping into the output of transformer 78 allows microcontroller 66 to monitor peak voltage. A reset switch 86 and two control switches 88 and 90 allow a user to control the operation of the power supply (e.g., “on”, “off”, etc.) and thus of the air purifier as a unit. Microcontroller 66 also controls a number of status indicator LED's 92.
Microcontroller 66 digitizes the feedback signal and, in response to the corresponding digital value, adjusts the digital signal it provides to PWM signal generator 68. The pulse train output by PWM signal generator 68 controls MOSFET 76. Changes in the duty cycle and frequency of the pulse train cause MOSFET 76 to adjust the output voltage (indicated by “+” and “−” at the output of high voltage multiplier 80) accordingly. If the circuit senses an increase in electrode current above a predetermined normal operational value (e.g., 300 μA), the circuit responds by lowering the output voltage by an amount needed to maintain essentially constant power. In addition, if microcontroller 66 senses an electrode current that is beyond normal operational range by a predetermined amount, it responds by shutting off power to avoid potentially harmful conditions.
It will be apparent to those skilled in the art that various modifications and variations can be made to this invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided that they come within the scope of any claims and their equivalents. With regard to the claims, no claim is intended to invoke the sixth paragraph of 35 U.S.C. Section 112 unless it includes the term “means for” followed by a participle.
