Patent Application
20140292101
The present invention relates to power supplies and more particularly to wireless power supplies capable of supplying power to portable heating devices.
Wireless power supplies can transfer electrical energy to portable devices without mechanical connection. A typical wireless power supply drives an alternating current through a primary coil to create a time-varying electromagnetic field. One or more portable devices can each include an inductive element. When the inductive element is placed in proximity to the electromagnetic field, the field induces a time-varying voltage in the inductive element, thereby transferring power from the wireless power supply to the portable device.
Wireless power supplies have been proposed for a number of applications, including applications involving portable heating devices. As the name suggests, portable heating devices differ apart from other portable devices in that a substantial portion of the power induced in the inductive element is directly or indirectly converted to heat. In the case of a clothes iron, for example, a substantial portion of the power received by the portable heating device is converted to heat in the iron's soleplate. That is, eddy currents are induced in the soleplate as a direct result of the electromagnetic field and generate heat at a rate proportional to the soleplate's electrical resistance.
In many instances it can be desirable to provide power to the portable heating device across multiple positions with respect to the primary coil. For example, a primary coil array can provide power to the cordless clothes iron at multiple locations along the ironing board. However, the primary coil array can generate a magnetic field directed only partially toward the inductive element, and away from the inductive element in equal or greater measure. As a result, stray electromagnetic field lines can cause undesirable heating in nearby metal objects, while also reducing the efficiency of the wireless power supply.
Accordingly, there remains a continued need for an improved wireless power supply to provide power to one or more portable heating devices. In addition, there remains a continued need for a low-cost wireless power supply to provide power to one or more portable heating devices across multiple positions relative to the primary coil while minimizing stray electromagnetic emissions that might otherwise impede efficient operation of the wireless power supply and potentially harm nearby objects.
The present invention provides a wireless power supply system including a wireless power supply and a portable heating device. The wireless power supply includes an electromagnetic shield and the portable heating device includes a magnetic field source. Placement of the magnetic field source proximate the electromagnetic shield can create a local “flux window” in the electromagnetic shield. The resulting transfer of electromagnetic flux through the local flux window energizes the portable heating device, and stray electromagnetic field lines are reduced at other regions of the electromagnetic shield.
In one embodiment, the wireless power supply can include one or more primary coils and a power transfer surface adapted to supportably receive the portable heating device. The electromagnetic shield can be interposed between the one or more primary coils and the power transfer surface to reduce the effect of the electromagnetic flux outside of the wireless power supply. Optionally, the electromagnetic shield is a flux guide and concentrates the electromagnetic field lines within the electromagnetic shield.
In another embodiment, the wireless power supply includes power supply circuitry to drive the one or more primary coils with a time-varying current or voltage. The power supply circuitry can include a controller to vary a characteristic of power in the one or more primary coils. For example, the controller can be responsive to changes in the current, voltage or phase in the one or more primary coils. Alternatively, or in addition, the controller can be responsive to active or passive communications from the portable heating device.
In still another embodiment, the portable heating device includes a heating element that is directly or indirectly energized by the wireless power supply. For example, the heating element can include a conductive ferromagnetic material. When exposed to a time-varying electromagnetic field, eddy currents are induced in the material, and the resistance of the material dissipates energy in the form of heat. Also by example, the heating element can increase in temperature when subject to a suitable electrical current from a power source within the portable heating device. For example, a battery within the device or a rectified current from a secondary coil can power a heating element. In these configurations, the ferromagnetic material and/or the secondary coil can form an electromagnetic coupling with the primary coil through the localized flux window, providing energy to the heating element either directly from the primary coil through coupling, or indirectly by powering the secondary coil, or both.
In even another embodiment, the magnetic field source includes any device or material adapted to generate a persistent magnetic field, including for example a permanent magnet or an electromagnet. The magnetic field source can include multiple permanent magnets and/or multiple electromagnets to create flux windows of various sizes and shapes. For example, multiple permanent magnets and/or multiple electromagnets can be positioned radially outward of the heating element, or adjacent a major surface of the heating element. The portable heating device optionally includes a permanently magnetized conductive material that functions as both the magnetic field source and the heating element.
In yet another embodiment, the wireless power supply includes a primary coil array and an electromagnetic shield contained within an ironing board, and the portable heating device includes a heating element and a magnetic field source contained within a cordless clothes iron. The electromagnetic shield can encompass at least a substantial portion of the primary coil array to reduce the emission of stray electromagnetic field lines from the ironing board. As the user runs the cordless iron along the ironing board, a localized flux window moves in real time with the cordless iron. As a result, the heating element receives wireless power through the localized flux window, and the effectiveness of the electromagnetic shield is maintained elsewhere along the ironing board. Other portable heating devices can include curling irons, hair straighteners, heating pads, heated beverage containers and items of cookware.
In yet another embodiment, a wireless power receiver using electromagnets to saturate the interposed electromagnetic shield can control the amount of power received by adjusting the intensity of the induced DC magnetic field, thus adjusting the saturation level of the interposed magnetic shield. As a result, the transmitter can provide a more constant voltage/current and reduce reliance on communication between the transmitter and receiver. If the receiver is using multiple electromagnets spaced along the bottom of the device, the receiver can adjust the temperature of multiple points within the receiver, controlling where the device is heated.
In yet another embodiment, the portable heating device includes a magnetic field source including a specifically tuned Curie temperature (Tc). In this embodiment, the magnetic field source can saturate the interposed electromagnetic shield to allow inductive power transfer to the portable heating device. As the heating element is heated, the magnetic field source is also heated. As the temperature of the magnetic field source approaches Tc, its magnetic field strength decreases. This reduces the saturation of the electromagnetic shield, reducing the amount of power transferred to the portable heating device. In this embodiment, equilibrium can be reached where the magnetic field source is heated to a temperature less than Tc. If the wireless power supply heats the magnetic field source to Tc, the interposed electromagnetic shield is no longer saturated, and transfer of wireless power therethrough is stopped or slowed. The magnetic field source can be formed by combining a soft magnetic material such as iron with a resin, and curing the mixture in the presence of a magnetic field, creating a weak magnet. As the weak magnet is heated once again, the molecules lose their combined magnetic dipole moment as they near Tc.
In yet another embodiment, a wireless power receiver includes an electromagnetic shield that can be saturated to open an aperture allowing magnetic flux to pass through to a secondary coil. In this embodiment, the wireless power receiver controls when the shield is saturated (and to what level) using an electromagnet, or a wireless power supply may use a permanent magnet or an electromagnet to saturate the shield. This feature allows the wireless power circuitry in the receiver to be protected when the electromagnetic field is strong enough to damage the wireless power circuitry. For example, the wireless power receiver may be constructed to handle small amounts of power and communication. If such a receiver is placed next to a high-power wireless power supply capable of providing large amounts of magnetic flux energy, the electromagnetic field may damage the power circuitry in the receiver. To prevent this, the receiver may saturate the shield on both the remote device and the transmitter in the area of the low power coil and circuitry, begin communications and provide information about the portable device and its power requirements, then remove the DC magnetic bias in the area of the secondary coil. The system then saturates the shielding in the area between the area of the receiver requiring high power and the wireless power supply. Thus, the wireless power receiver can accept high power amounts in one area while protecting the low power areas. In this embodiment, the transmitter will typically provide high power for a period of time, and then reduce the power to allow the receiver to provide communications and power control. Additionally, the material may be heated until it reaches its Curie temperature, resulting in a saturation of the material (its relative permeability approaches ambient space). Once saturation is reached, the material may be cooled back below its Curie temperature using a heatsink or a peltier junction.
These and other advantages and features of the present invention will be more fully understood and appreciated in view of the description of the current embodiments and the drawings.
The current embodiments relate to systems and methods for providing a source of wireless power to a portable heating device. The systems generally include a wireless power supply having an electromagnetic shield and a portable heating device having a magnetic field source. Placement of the magnetic field source proximate the electromagnetic shield creates a localized flux window in the electromagnetic shield. The effectiveness of the electromagnetic shield is generally maintained apart from the flux window, and the electromagnetic shield reduces stray flux that might otherwise cause an undesired electromagnetic coupling with the wireless power supply.
More specifically, and with reference to
The primary coil or coils 32 can form part of a primary tank circuit 36. In the illustrated embodiment, the primary tank circuit 36 includes a series resonant capacitor 38, and the primary tank circuit 36 is positioned proximate to or subjacent the electromagnetic shield 34. The wireless power supply 30 can further include power supply circuitry to drive the primary tank circuit 36 with a time-varying current or voltage. For example, the power supply circuitry can include a mains rectifier 40, a DC to DC converter 42, an inverter 44 and a current sensor 46. The mains rectifier 40 can convert a mains voltage into a DC voltage, and can include a full bridge rectifier, a half bridge rectifier, or other rectifier having a DC output. The DC to DC converter 42 is electrically connected to the output of the mains rectifier 40 and provides a conditioned output to the inverter 44. The inverter 44 in turn generates a time-varying current or voltage in the primary tank circuit 36 under the control of a controller 48. The controller 48 can selectively vary one or more characteristics of power in the primary tank circuit 36 to improve the transfer of power from the wireless power supply 30 to the portable heating device 50. For example, the controller 48 can vary the operating frequency, duty cycle, pulse width, waveform, amplitude and/or phase in the primary tank circuit 36, as well as other parameters including the resonant frequency and/or the impedance of the primary tank circuit. In some embodiments the controller 48 is responsive to changes in a characteristic of power in the primary tank circuit 36, including for example current, voltage or phase. The controller 48 can additionally or alternatively be responsive to transmissions from a dedicated communications unit 52 associated with the portable heating device 50 as generally depicted in
As noted above, the portable heating device 50 includes a magnetic field source 54 and a heating element 56 that is directly or indirectly energized in response to a time-varying electromagnetic field generated by the wireless power supply 30. The magnetic field source 54 can include any device adapted to generate a persistent magnetic field, including for example a permanent magnet or an electromagnet. Exemplary permanent magnets include single bonded NdFeB magnets (also known as a neodymium, NIB, rare earth, or Neo magnets), ferrite magnets, sintered NdFeB magnets, sintered SmCo magnets or Alnico magnets. The desired magnetic field source 54 can be selected to have a sufficient magnetic flux density, also referred to as the magnetic field strength, to generate a localized flux window in the electromagnetic shield 34. The magnetic field source 54 can be oriented within the portable heating device 50 to generate a flux window by magnetically saturating a localized portion of the electromagnetic shield 34. For example, the magnetic field source 54 can include multiple permanent magnets and/or electromagnets oriented such that a common magnetic pole is closest to the electromagnetic shield 34. The magnetic field source 54 can also include multiple permanent magnets and/or electromagnets to create flux windows of various sizes and shapes. As shown in
The heating element 56 is directly or indirectly energized in response to the time-varying electromagnetic field or flux directed through the flux window in the electromagnetic shield 34. For example,
The electromagnetic shield 34 can be formed of any material exhibiting a suitably high magnetic permeability (p). For example, the shielding material can exhibit a magnetic permeability at least ten times the magnetic permeability of free space, or μ/μ0>10. The electromagnetic shield 34 can also be formed of a material exhibiting a suitably low resistance to magnetic saturation. For example, the shielding material can be readily saturated to the point that the localized permeability approaches that of free space in the presence of the magnetic field source 54. The electromagnetic shield 34 can also be formed of a material having a sufficiently low conductivity to minimize the accumulation of eddy currents therein. Suitable shielding materials can include soft metallic materials such as sheet steel, silicon steel, cast steel, tungsten steel, magnet steel, cast iron, nickel, cobalt and magnetite. Other materials can include a flexible composite ferrite, such as FLEXIELD IRJ09, and/or a pre-fractured ferrite, such as FLEXIELD IBF20, both available by TDK Corporation of Garden City, N.Y. In addition, the thickness of the shielding material may also play a role in the amount of the magnetic field required to saturate the shield. For example, a thinner shield will typically be more easily saturated than a thicker shield. The electromagnetic shield of the present invention may sometimes be referred to by names that reflect its ability to function as a flow path for electromagnetic field lines, such as a flux guide, a flux concentrator or a magnetic flux concentrator.
The heating element 56 can also be preheated. For example, an energy storage element can be used to pre-heat the heating element 56, and/or a charging station 106 can be used to pre-heat the heating element 56. This may be accomplished using an inductive heating element, or by passing current directly through the heating element from a battery or other power source. Once the heating element 56 has reached a sufficient pre-heat temperature, as optionally measured by a temperature sensor 62, the portable heating device 50 can generate an alert, for example an audible alert, a luminescent alert, or a mechanical vibration. The remote device is then placed atop a power transfer surface. Heat from the heating element 56 heats the electromagnetic shield 34 and reduces its electromagnetic permeability in the region of a localized flux window. As the electromagnetic permeability decreases, the coupling between primary coil 32 and the portable heating device 50 increases. This increase in coupling is depicted in
To reiterate, the localized flux window can be generated by directly or indirectly heating the electromagnetic shield, independent of whether the electromagnetic shield is also saturated with a nearby magnet. Heating of the electromagnetic shield can decrease its effectiveness as a flux guide, thereby increasing the magnetic flux through the electromagnetic shield. A pre-heated article in the vicinity of the electromagnetic field, and opposite of the primary coil, can receive wireless power more readily than a room-temperature article. In this regard, the electromagnetic coupling between pre-heated article and the primary coil is likely greater than the electro-magnetic coupling between the room-temperature article and the primary coil. This difference in coupling coefficients is functionally a safeguard against inadvertently energizing a nearby room-temperature article. In addition, as the pre-heated article is positioned over or moved along the wireless power supply power transfer surface, the electromagnetic coupling maintains the elevated temperature of the heating element 56, which in turn maintains the elevated temperature of the electromagnetic shield.
The electromagnetic shield 56 may optionally be cooled with a heat sink or a peltier junction to cool the shielding material below Tc, and optionally to room temperature, optionally when the portable heating device 50 is no longer on the surface of the wireless power supply 30. Although the electromagnetic shield 34 prevents much of the electromagnetic flux from passing through the power transfer surface, some flux may still pass through to the portable heating device 50. This field may be used by the portable heating device 50 to heat the heating element 56 substantially as set forth above.
In some embodiments it can be desirable to incorporate an electromagnetic shield 34 into the portable heating device 50. For example, it can be desirable to provide a portable heating device 50 that is generally shielded from certain external electromagnetic fields. In this configuration, the wireless power supply 30 will generally include a magnetic field source, such as one or more permanent magnets or electromagnets. When the portable heating device 50 is placed adjacent to the wireless power supply 30, the magnetic field source will generate a localized flux window in the electromagnetic shield. Electromagnetic field lines from within the wireless power supply 30 can more readily penetrate the electromagnetic shield at the localized flux window to provide power to the portable heating device 50 in the manner set forth above.
To reiterate, the electromagnetic shield 34 can reduce the effect of electromagnetic field lines originating within the wireless power supply on external objects or devices. The electromagnetic shield 34 can also be selectively saturated by the magnetic field source 54. In a non-saturated state, the shield 34 has a high magnetic permeability relative to free space, and therefore draws much of the electromagnetic field into itself. In a saturated state, the shield 34 has a greatly reduced magnetic permeability relative to free space, and therefore enhances the electromagnetic coupling of the primary coil 32 with external objects or devices. It should be noted that “saturation” as used herein refers to substantial saturation and is not limited to complete saturation.
Embodiments of the invention can be utilized in connection with a wide variety of portable heating devices 50, including for example cordless clothes irons, curling irons, hair straighteners, heating pads, heated beverage containers and cookware. In these embodiments, the wireless power supply 30 can be self-contained within any of a variety of surfaces, including for example ironing boards, wall-mounted holding racks, bathroom or kitchen countertops, stovetops and portable charging pads. As illustrated in
Referring again to
The cordless iron 84 includes a heating element 96 and a magnetic field source 98. The magnetic field source 98 optionally includes multiple magnets embedded within the heating surface 96. As shown in
Operation of the cordless clothes iron can be understood with reference to
At decision step 120, the wireless power supply determines whether the cordless iron is stationary. This can indicate the cordless iron is seated within the charging cradle or otherwise stationary along the ironing board working surface, despite the cordless iron being ready for use. If at decision step 120 the cordless iron is determined not to be stationary—optionally with the aid of one or more accelerometers—the wireless power supply maintains the soleplate at the desired temperature at step 114 with feedback from step 116. As the user moves the cordless iron over the ironing board, the magnetic field source creates a localized flux window in the electromagnetic shield. The resulting transfer of electromagnetic flux through the local flux window directly or indirectly heats the soleplate, while maintaining reduced stray electromagnetic emissions at other regions along the ironing board working surface. If however the cordless iron is determined at step 120 to be stationary, an internal timer initiates a standby period at step 122 in which the cordless iron remains on and heated. At decision step 124 and after the standby period, the cordless iron is deactivated at step 126 or remains on at step 114, optionally in response to detected movement of the cordless iron. If deactivated, the above process repeats itself at step 110.
The cordless iron can therefore receive wireless power through a localized flux window that moves in real time with the cordless iron. As the user runs the cordless iron along the ironing board working surface, the flux window essentially shadows the cordless iron at all locations along the ironing board. Because the flux window is localized, the effectiveness of the electromagnetic shield is maintained elsewhere along the ironing board. This can be of notable concern in instances where parasitic metal objects might otherwise intersect with a leaked electromagnetic field. Instead, electromagnetic losses are minimized, and the risk of inadvertently heating nearby metallic objects is also minimized.
In another embodiment as shown in
The portable heating device 50 can also control the amount of power transferred by adjusting the saturation level of the interposed electromagnetic shield 34. When the portable heating device 50 utilizes magnetic field sources 54 at least partially composed of electromagnets to provide a DC magnetic field to saturate the electromagnetic shielding 34, the secondary controller 66 can adjust the amount of current flowing through the electromagnets 54, or the number of turns of the electromagnet. By reducing the current or number of turns, the magnetic flux density of the electromagnets 54 are reduced, reducing the saturation level of the electromagnetic shield 34. This in turn reduces the amount of field coupled into the portable heating device 50.
Additionally, if the portable heating device 50 utilizes magnetic field sources 54 at least partially composed of permanent magnetic materials, the controller 66 may utilize the Curie temperature of the magnetic materials to control the temperature of the heating element 56. For example, if the temperature of the heating element 56 nears the Curie temperature of the nearby magnetized material 54, the magnetized material begins to lose some of its magnetism. This reduces the field strength of the magnet, reducing the saturation level of the electromagnetic shield 34. If the saturation level of the electromagnetic shield 34 is reduced enough, the permeability of the shield 34 begins to rise, reducing the amount of flux coupled into the portable heating device coil 58 and/or the induction material 56. If heat energy is drawn off from the portable heating device 50 at the same rate as it is added from the coupled energy, the portable heating device 50 will maintain an equilibrium temperature. If more heat energy is coupled into the portable heating device 50 than what is removed, the temperature will continue to increase, making the temperature of the magnetized material 54 rise closer to its Curie temperature, further reducing its magnetism. If the Curie temperature of the magnetized material 54 is reached, or if the amount of heat energy being removed from the portable heating device 50 is greater than what is being added, the portable heating device 50 will begin to cool.
A method for controlling the transfer of power from the wireless power supply 30 to the portable heating device 50 is illustrated in
The wireless power supply 30 can also be utilized to directly and indirectly power a heating element. Referring again to
An example of this relationship is illustrated in
In another embodiment as shown in
As optionally shown in
The portable heating device 50 can therefore generate a first flux window proximate the heating element 56 and a second flux window proximate the secondary coil 58. For example, a first plurality of electromagnets 54 can facilitate wireless power transfer through the shielding layer 34 and a second plurality of electromagnets 55 can facilitate communications through the shielding layer 34. A flow chart illustrating this feature is shown in
As noted above in connection with step 152, a portion of the electromagnetic flux from the primary coil array 32 penetrates the shielding layer 34 when in a non-saturated state. This is perhaps best shown in
In another embodiment as shown in
Though described above in connection with a portable heating device, embodiments of the wireless power supply system can also be utilized in conjunction with a remote device not having a heating element. Exemplary remote devices include, for example, laptop computers, tablet computers, desktop computers, smartphones, mobile telephones, e-book readers, personal digital assistants, portable gaming systems, console gaming systems, and other electronic devices, whether now known or hereinafter developed. Embodiments can also be used in conjunction with one or more wireless power supplies and/or remote devices set forth in U.S. patent application Ser. No. 13/241,521, entitled “Selectively Controllable Electromagnetic Shielding” by Baarman et al, published as U.S. Patent Application Publication 2012/0112552, the disclosure of which is hereby incorporated by reference in its entirety.
As the term is used herein, a primary coil includes any inductive element adapted to generate an electromagnetic field when driven with a current or voltage. Further by example, a primary coil includes any inductive element adapted to induce eddy currents in a nearby conductive material, and/or adapted to induce an electrical current or voltage in a nearby secondary coil. A secondary coil, as the term is used herein, can include any inductive element adapted to experience a current or voltage when subject to an electromagnetic field. Primary and secondary coils can include, for example, a wound inductive element (e.g., a spirally, helically or toroidally wound inductor), a printed inductive element, and/or an etched inductive element, each including one, less than one, or greater than one “loops” of an electrically conductive material.
The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. For example, and without limitation, any individual element(s) of the described invention may be replaced by alternative elements that provide substantially similar functionality or otherwise provide adequate operation. This includes, for example, presently known alternative elements, such as those that might be currently known to one skilled in the art, and alternative elements that may be developed in the future, such as those that one skilled in the art might, upon development, recognize as an alternative. Further, the disclosed embodiments include a plurality of features that are described in concert and that might cooperatively provide a collection of benefits. The present invention is not limited to only those embodiments that include all of these features or that provide all of the stated benefits, except to the extent otherwise expressly set forth in the issued claims. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2012/068059 | 12/6/2012 | WO | 00 | 4/30/2014 |
| Number | Date | Country | |
|---|---|---|---|
| 61567224 | Dec 2011 | US |
