Patent Description:
This invention pertains to the field of drying a load of clothes using dielectric heating.

Dielectric heating involves the heating of materials by dielectric loss. A changing electric field across the dielectric material (in this case, a load of clothes) causes energy to be dissipated as the molecules attempt to line up with the continuously changing electric field, creating friction. This changing electric field may be caused by an electromagnetic wave propagating in free space as in a microwave oven, or it may be caused by a rapidly alternating electric field inside a capacitor, as in the present invention. In the latter case, there is no freely propagating electromagnetic wave. This changing electric field may be seen as analogous to the electrical component of an antenna near field.

Frequencies in the RF range of <NUM> to <NUM> have been used to cause efficient dielectric heating in some materials, especially liquid solutions with polar salts dissolved. These relatively low frequencies can have significantly better heating effects than higher, e.g., microwave frequencies, due to the physical heating mechanisms. For example, in conductive liquids such as salt water, "ion drag" from using lower RF frequencies causes heating, as charged ions are "dragged" more slowly back and forth in the liquid under influence of the electric field, striking liquid molecules in the process and transferring kinetic energy to them, which is eventually translated into molecular vibrations, and thus into thermal energy.

Dielectric heating at these low frequencies, as a near-field effect, requires a distance from the radiator to the absorber of less than about <NUM>/16th of a wavelength (λ) of the source frequency. It is thus a contact process or near-contact process, since it usually sandwiches the material to be heated (usually a non-metal) between metal plates that set up to form what is effectively a very large capacitor, with the material to be heated acting as a dielectric inside the capacitor. Actual electrical contact between the capacitor plates and the dielectric material is not necessary, as the electrical fields that form inside the plates are what cause the heating of the dielectric material. However, the efficient transfer of the RF heating energy to the load is greatly improved as the air gap that may arise between the capacitor plates and the load is minimized.

At higher frequencies, e.g., microwave frequencies ><NUM>, the wavelength of the electromagnetic field becomes closer to the distance between the metal walls of the heating cavity, or to the dimensions of the walls themselves. This is the case inside the cavity of a microwave oven. In such cases, conventional far-field electromagnetic (EM) waves form; and the enclosure no longer acts as a pure capacitor, but rather as a resonant cavity. The EM waves are absorbed into the load to cause heating. The dipole-rotation mechanism of induced heat generation remains the same as in the case of capacitive electrical coupling.

However, microwave induced ion rotation is not as efficient at causing the heating effects as the lower RF frequency fields that depend on slower molecular motion, such as those caused by ion drag.

Novel applications of RF dielectric heating to the drying of clothes have been patented in commonly owned <CIT> and <CIT> (a family member of <CIT>), where rotary RF heating capacitive structures are disclosed.

These patented inventions require the introduction of specialized connections to both anodes inside the dryer drum and to the drum surface acting as a cathode.

A clothes dryer apparatus (<NUM>) comprising an electrically conductive, grounded, generally cylindrical rotatable drum (<NUM>) having a hollow interior adapted to contain a load (<NUM>) of wet clothes to be dried. The drum's (<NUM>) exterior surface (<NUM>) is partially indented to form one or more integral, generally ring-shaped insulated notches (<NUM>). An electrically conductive, generally flat arcuate anode (<NUM>) is positioned within each notch (<NUM>), with no physical contact between an anode (<NUM>) and its corresponding notch (<NUM>). Each anode (<NUM>) is spatially fixed with respect to the rotatable drum (<NUM>), and is electrically isolated from conductive portions of the drum (<NUM>). A source (<NUM>) of RF power (<NUM>), operating at a single fixed frequency, is coupled to each anode (<NUM>).

These and other more detailed and specific objects and features of the present invention are more fully disclosed in the following specification, reference being had to the accompanying drawings, in which:.

This invention comprises a rotating drum <NUM> that acts as a cathode of a large capacitor, with simplified connections to the one or more anodes <NUM> that produce an electric field inside the drum <NUM>. The anodes <NUM> are spatially fixed, are mounted outside the hollow interior of the drum <NUM>, and protrude into one or more notches <NUM> that are fabricated as indentations as part of the drum periphery <NUM>. Anodes <NUM> maintain the necessary electric field contact with a load <NUM> of clothes inside the rotating drum <NUM>, to effect optimum RF capacitive coupling. The minimization of parasitic capacitance from the anode <NUM> (where RF is applied) to the cathode drum <NUM> (which is grounded) is important for energy conversion efficiency when using the present invention's relatively low RF frequency. For this reason, it is desirable for the clothes <NUM> to be close to both the cathode <NUM> and to the anode(s) <NUM>. In this patent application, parasitic capacitance is defined as any capacitance between the anode(s) <NUM> and cathode drum <NUM> not associated with the capacitance of the load <NUM> itself.

The present invention's dielectric heating of a load <NUM> of clothes by a single frequency RF-generated electric current <NUM> in a rotating cathode drum <NUM> using at least one spatially fixed, non-rotating, radial anode <NUM>, by creating an AC current flow through the semiconductive (wet) load <NUM> of clothes in a capacitive electrical circuit, is in stark contrast to other RF heaters that are based on exciting an electromagnetic field within a microwave cavity.

A rotating connection to an anode is not required or used in the present invention. The benefits of this include: a simpler, more reliable connection between the RF power <NUM> and the anode(s) <NUM>, lower cost, and lower parasitic anode <NUM> capacitance compared with prior art devices. The grounded cathode connection <NUM>, <NUM> to the rotating drum <NUM> can be capacitive <NUM> or mechanical <NUM>. The cathode (conductive drum <NUM>) has a large contact surface <NUM> area with no parasitic capacitance issues when the drum surface <NUM> is connected <NUM> directly to ground.

Each fixed anode <NUM> can be fabricated of bare metal or insulated metal. The insulation may be painted on the anode <NUM>.

The clothes drying process of the present invention may include forcing room temperature or heated air <NUM> to flow inside the drum <NUM>, to facilitate the removal of moisture from the load <NUM> of clothes, and for other reasons as described below.

<FIG> is a side view of rotating electrically conductive drum <NUM> showing two insulated radial notches <NUM>. The drum <NUM> can be made of a conducting material, i.e., metal, or an insulating material that is coated with a conductive layer. Drum <NUM> is free to rotate in both clockwise and counterclockwise directions about a single axis of rotation <NUM>. Two radial anode rings <NUM> are positioned in corresponding notches <NUM>. Anodes <NUM> couple the applied RF electric power <NUM> into the load <NUM> of clothes. Load <NUM> is located between the fixed anode plates <NUM> and the rotating conductive drum <NUM>.

Two <NUM>-degree generally flat anode rings <NUM> are shown in <FIG>, but one or more rings <NUM> can be shortened to any percentage circumference of <NUM> degrees. These anode rings <NUM> are connected in a low-loss manner to an RF power source <NUM>. The rotating conductive drum <NUM> is shown connected to ground by a direct rotary or capacitive coupling connection <NUM>. Connection <NUM> can be selectively activated, e.g., only when the RF power <NUM> is applied, or, alternatively, connection <NUM> can be continuously connected, e.g., using a "brush" type connection between connection point or strip <NUM> and a fixed ground mass.

Because the use of spatially fixed radial anode rings <NUM> eliminates the need for a moving RF anode contact, the single frequency RF power <NUM> can be easily applied to the anode(s) <NUM> with low loss, when drum <NUM> is rotating, when drum <NUM> is stationary, or when drum <NUM> is both rotating and stationary. The rotation can have a variable speed, including zero speed (stopped), and can be in either rotational direction.

<FIG> is a side center-line cutaway view of the rotating conductive drum <NUM> of <FIG>. The two insulated radial notches <NUM> are positioned with clearance from (i.e., without touching) the fixed anode plates <NUM>, to allow free rotation of the drum <NUM> in either direction. These insulated notches <NUM> can be fabricated in a continuous physical structure with surfaces of drum <NUM>.

<FIG> is a detailed view of a bottom area of drum <NUM> while drum <NUM> is in a stationary position. Notches <NUM> allow the electric field <NUM> from the fixed anodes <NUM> to electrically penetrate into the hollow interior of drum <NUM>. RF power <NUM> flows through anode ring <NUM>, through insulated notch <NUM>, and through the load <NUM> of clothes; and finally returns to the conductive surface <NUM> of grounded cathode drum <NUM>. RF power <NUM> can be applied when the load <NUM> of clothes is tumbling, stationary, or when it is both tumbling and stationary. The anode rings <NUM> are sized to fit the particular application, e.g., their widths and percentages of circular arc can be varied as desired.

<FIG> is a detailed view of an area around an insulated notch <NUM> in an embodiment in which air flow <NUM> is used. The notches <NUM> rotate with drum <NUM>, and can be integrally fabricated as part of drum <NUM>. Air flow <NUM> is forced through holes <NUM> in notch <NUM> and thus into the hollow interior of drum <NUM>. The primary purpose of the air flow <NUM> is to remove from the interior of the drum <NUM> the water that was evaporated from the load <NUM> by the application of the RF power <NUM>. Air flow <NUM> can also remove additional moisture from the load <NUM> by induced direct evaporation, help to cool the anodes <NUM>, and help to cool variable tuning inductor <NUM> (see <FIG>). In embodiments in which air flow <NUM> is used, a drip pan <NUM> is positioned beneath the drum <NUM> to catch any water that escapes out of the drum <NUM> through holes <NUM>.

<FIG> is a cut-away end view of the drum <NUM> showing a fixed radial anode ring <NUM> positioned within an insulated notch <NUM>. The radial fixed anode rings <NUM> are shaped in form, length, and width to maximize capacitive coupling to load <NUM> and to minimize parasitic, non-load coupled, capacitance to ground <NUM>, <NUM>. Although the anode <NUM> that is illustrated in <FIG> is a full <NUM> degree ring, the anode rings <NUM> can be any percentage of <NUM> degrees of circumference.

Drum <NUM> can rotate at any speed, including zero speed (stopped), and can rotate in either rotational direction about axis <NUM>. One or more mechanical impellers <NUM> can be placed inside the hollow interior of drum <NUM>, to stir the heated load <NUM> of clothes during rotation. This tends to inhibit bunching of the load <NUM>, and speeds the drying process. The impellers <NUM> are fixedly mounted to the inside of surface <NUM> of drum <NUM>, and rotate with drum <NUM>. Drum <NUM> can rotate, i.e., load <NUM> can be stirred, when the RF power <NUM> is applied to anode(s) <NUM>, or when it is not applied, or when it is both applied and not applied.

<FIG> is an electrical circuit model of the load <NUM> inside the drum <NUM>. The load <NUM> can be represented, electrically, as a lossy capacitor. The radial anode(s) <NUM> and drum (cathode) <NUM> are optimized in form and materials to maximize the RF electrical power <NUM> coupling to the load <NUM>, and to minimize the parasitic drum <NUM> capacitance.

<FIG> is a center cut, end view of a typical cathode (ground) connection <NUM> to the drum <NUM> using capacitive coupling <NUM>. An exterior electrically conductive ring <NUM> envelops the drum <NUM>, is stationary, and is grounded to complete the RF circuit. The conductive outer surface <NUM> of the drum <NUM> is grounded to ground ring <NUM> capacitively via air gap <NUM>.

<FIG> is a side center line cut view of a cathode capacitive coupling <NUM> arrangement in which three spatially fixed cylindrical ground rings <NUM> are used. Each ring <NUM> is capacitively coupled to outer metallic surface <NUM> of the metallic dryer drum <NUM> via capacitive air gap <NUM>.

In an alternative embodiment, as shown in <FIG>, a single rotating "brush type" ground connection <NUM> is used to ground drum <NUM>. This ground connection <NUM> can be an electrically conductive small area or elongated strip that is fabricated as part of electrically conductive surface <NUM> of drum <NUM>, and rotates with drum <NUM>. During rotation, ground connection <NUM> is in continuous electrical connection with a spatially fixed ground mass, ensuring continuous grounding of drum <NUM>.

Even when the maximum dimension of drum <NUM> is only a small percentage of the total wavelength dimension at the operating frequency of the applied RF power <NUM>, there can be a far field (electro-magnetic) cavity effect set up within the periphery of the drum <NUM> as it rotates or sits in its overall enclosure <NUM> (see <FIG>). This far field effect in turn causes a distortion of the desired uniform electric field within drum <NUM>, resulting in lower dielectric heating uniformity and overall heating efficiency. For example, a <NUM>-foot diameter by <NUM>-foot long cylindrical cathode drum <NUM> at <NUM> has a wavelength of only about <NUM> degrees (<NUM> degrees = <NUM> feet). A single point (small area) or strip ground connection <NUM>, as shown in <FIG>, can improve RF to heat transfer efficiency by up to <NUM>% compared to the wide area connection <NUM> shown in <FIG> and <FIG>. Another way to minimize this far field parasitic effect is to use the lowest practicable frequency in the selected range to power the anodes <NUM>, given constraints such as component size and cost. The tradeoff is that component size and cost increase as the frequency decreases.

The ground connection <NUM>, <NUM> can be continuously activated during movement of the drum <NUM>; or grounding can be activated selectively, such as only when drum <NUM> is not rotating or when it is rotating.

<FIG> shows a typical RF power source <NUM> used in conjunction with the present invention. The conductive dryer drum <NUM> is connected to single fixed frequency solid state power source <NUM> by an RF tuner <NUM> that, in conjunction with controller <NUM>, measures and determines appropriate power, dryness, load size, and drying end time settings to perform the drying process. In the apparatus according to the present invention, the operating frequency of the RF power source <NUM> is in the range of <NUM> to <NUM>.

In one method embodiment, initially the RF power <NUM> is applied for a set amount of time to the load <NUM> with the drum <NUM> in a stationary position, with the clothes <NUM> forced to the bottom of the drum <NUM> by gravity. This ensures a continuous close contact of the load <NUM> to both the insulated notch <NUM> areas adjacent to the anodes <NUM> and to the conductive drum <NUM>. Then the drum <NUM> is rotated, with continuous air flow <NUM>, to fluff the clothes <NUM> and to facilitate the removal of the evaporated water, again for a preset amount of time. The process is repeated until the desired level of load <NUM> dryness is obtained. The dryness can be measured by RF sensors coupled to controller <NUM>, to automatically terminate the drying cycle when the preselected dryness level is reached.

<FIG> is a partly schematic, partly block diagram showing an embodiment of the present invention in which unified, high efficiency, energy conserving dryer power and control is achieved. AC to RF power source <NUM> and controller <NUM> are integrated into a single power and control module <NUM> comprising impedance (Z) measuring module <NUM>, and a power supply <NUM> adapted to receive AC from input <NUM> and to output 300V DC to driver <NUM>, which is coupled to power amplifier <NUM>. Power supply <NUM> also passes the input AC and 15V DC to serial port <NUM> for providing power to the motors <NUM> controlling drum <NUM> and air blower <NUM>. Module <NUM> can also comprise an integral heat sink <NUM> to assist in cooling the components within module <NUM>.

Tuner <NUM> comprises a variable inductor <NUM> and a variable capacitor <NUM>. In this embodiment, air flow <NUM> is used as previously described, and also serves to cool variable tuning inductor <NUM>.

The introduced forced air <NUM> can be room temperature air, heated air, or a combination of both. It is also possible to recover heat from power and control module <NUM> by blowing air <NUM> across integral heat sink <NUM>, and subsequently through variable inductor <NUM>, and then to funnel this heated air back into the drum <NUM> to assist in drying the load <NUM>.

Serial port <NUM> can be used to change parameters within controller <NUM> via an outboard computer, or a Graphical User Interface (not illustrated). These parameters can include the preselected degree of dryness that will cause controller <NUM> to shut down the application of power from RF source <NUM> in order to end the drying process.

Motors <NUM> are used to control the tuning of inductor <NUM> and capacitor <NUM>; the drum rotation speed and direction of rotation of drum <NUM>; and the operation of air blower <NUM>. In the case of variable inductor <NUM>, a clockwise sensor <NUM> and a counterclockwise sensor <NUM> feed signals to the corresponding motor <NUM>, indicating the position of the variable tuning mechanism of inductor <NUM>. In the case of capacitor <NUM>, a clockwise sensor <NUM> and a counterclockwise sensor <NUM> feed signals to the corresponding motor <NUM> indicating the position of the tuning mechanism of variable capacitor <NUM>.

Sensors <NUM> and a Door switch/lock <NUM> are coupled to controller <NUM>. Sensors <NUM> measure the load <NUM> temperature, and parameters of the air flow <NUM> within drum <NUM>. Switch/lock <NUM> is adapted to send a signal to controller <NUM> informing controller <NUM> whether the door to the drying drum <NUM> is open or closed, and, if it is closed, whether the door is locked or unlocked. Additionally, controller <NUM> is adapted to send a control signal to switch/lock <NUM> to selectively open and close the door, and, if the door is closed, to selectively lock and unlock it. The purpose of the door is, of course, to place clothes <NUM> into, and to remove them from, the hollow interior of drum <NUM>. For purposes of simplicity, <FIG> does not show the (front-loaded) door. The door has a grounded screen to ground <NUM>, <NUM> to confine possible stray fields inside the drum <NUM>.

In an embodiment, anode rings <NUM> are limited to short semi-circular generally planar arcs (for instance, less than +/-<NUM> degrees). This enables controller <NUM> to measure load <NUM> impedance Z as a function of anode ring <NUM> angular displacement, as the load <NUM> is rocked back and forth along the bottom of the drum <NUM>. In this embodiment, the efficiency of the RF power <NUM> coupling to the load <NUM> varies as a function of anode ring <NUM> angular displacement. Knowing this displacement, and measuring the varying impedance Z of the load <NUM> as a function of ring <NUM> angular displacement, controller <NUM> can determine load <NUM> size and density. This information may be then used by controller <NUM> to further automate the drying process, as now the wet load <NUM> can be introduced into the drum <NUM>, and by a combination of rocking the drum <NUM>, coupled with measuring the impedance and power efficiency variation, drying power and time settings can be adroitly determined by controller <NUM>.

Uniform heating of the load <NUM> can often be better achieved when the load <NUM> is in a semi-stationary position, when back and forth drum <NUM> rocking about axis of rotation <NUM> occurs.

The rate of drum <NUM> rotation can be tracked by controller <NUM> to help determine optimum power tuning during the drying cycle as water gradually evaporates from the load <NUM>. The controller <NUM> can adapt, via software, to the varying impedance Z that the load <NUM> presents to the applied RF power <NUM> as the load <NUM> rocks. As before, when the power <NUM> is applied to the load <NUM> for a set amount of time, the drum <NUM> is rotated, preferably with air flow <NUM>. The air flow <NUM> can be continuous throughout both heated drying and unpowered tumble cycles. Alternatively, the air flow <NUM> can be controlled on and off for treatment of specialized loads <NUM>, such as when the clothes <NUM> contain wrinkles. Again, the air flow <NUM> can be applied for a preset time, to fluff the clothes <NUM> and to remove some of the evaporated water.

Controller <NUM> can perform one or more of the following functions:
Real-time tuning for optimum energy transfer to load <NUM> using at least one of measured RF power <NUM> applied to the load <NUM>, changes in the level of RF power <NUM>, the load impedance Z, RF reflection coefficient, VSWR, etc. Controller <NUM> then uses these measurements to determine type, size, and wetness of the load, as well as an optimum time for terminating the drying process.

Determination of real-time water weight and density, along with user parameters derived from test runs and calculations that allow a more accurate prediction, compared to a conventional clothes dryer, of when to stop the drying process.

Because the evaporation of water from the clothes <NUM> with applied power <NUM> is usually a well behaved function of time, controller <NUM> can develop a graph or table taking into account known observed and calculated parameters, such as amount of water present in the clothes <NUM> to be evaporated, and how much heat is required to evaporate <NUM> gram of water (heat of vaporization). An algorithm can then be used to enable controller <NUM> to forecast total load <NUM> energy levels applied, and with this information, predict how long the drying cycle should last, as it is continuously observed by controller <NUM> and correlated to changes in the load impedance/VSWR. This same process can be used to accurately send notification signals or messages to the user, both before drying begins and when the drying process is completed. These messages can be in the form of text messages sent to the user's cell phone, using the SMS protocol, for example.

In another embodiment, dryer operation can be speeded up by presetting variable RF tuning inductor <NUM>, upon initial dryer startup or restart, to a value that will produce a measurable null in the load <NUM> RF return loss for all load <NUM> type ranges, then using RF variable capacitor <NUM> to scan the impedance/VSWR of the load <NUM> when it is in the dryer <NUM>. This can be done without any user input regarding the size of the load <NUM>. This speeds up the tuning convergence.

Also, starting the tuning process, after a load <NUM> mixing tumble cycle, at the previous RF heat cycle end tuner element <NUM>, <NUM> settings can advantageously speed up the tuning process. Varying RF heating levels, drum load stir rotation cycle length and speed, RF heating cycle length, and air flow <NUM> can be used to optimize drying performance.

<FIG> is a perspective view showing an implementation of the fixed radial anode rotary drum <NUM> in a clothes dryer enclosure <NUM>. Rotating drum <NUM>, rotating ground connection <NUM>, insulated notch <NUM>, air holes <NUM>, air blower <NUM>, drip pan <NUM>, power and control module <NUM>, and tuner <NUM> are shown. All of these items are housed inside the dryer enclosure <NUM>. The fixed anode ring <NUM> dimensions are limited to an arc of <NUM> degrees, less than a full circumference.

Claim 1:
A clothes dryer apparatus comprising:
an electrically conductive, grounded, generally cylindrical rotatable drum (<NUM>) having a hollow interior adapted to contain a load (<NUM>) of wet clothes to be dried;
characterized in that:
said drum (<NUM>) has a partially indented exterior surface in which at least one generally ring-shaped insulated notch (<NUM>) has been formed;
positioned within each notch (<NUM>) is an electrically conductive anode (<NUM>),
coupled to each anode (<NUM>) is a RF power source (<NUM>) operating at a single fixed frequency in a frequency range between <NUM> and <NUM>;
the RF power source (<NUM>) being configured to produce an electrical field between the anode(s) (<NUM>) and the conductive drum (<NUM>) acting as a cathode.