Heating Unit for Rollers Employing Magnetic Inductance

Abstract

Heating units for heating hair rollers are provided, as well as rollers for use therewith. An exemplary heating unit includes a housing having a lid and a lower portion, with a first magnetic core disposed within the lower portion and a second magnetic core disposed within the lid. The first magnetic core includes two parallel legs, and a plurality of conductive windings wound around one of the two legs. When the housing is closed the first and second magnetic cores together form a square closed core. When energized, the windings generate a magnetic field within the square closed core that induces an electric current in a roller disposed around the second of the two legs. An exemplary roller for use with the heating unit comprises a conductive cylinder, such as aluminum, having a diameter of at least two inches and including bristles protruding perpendicular to the exterior surface.

Claims

1. A heating unit for rollers, comprising: a housing comprising a lid and a lower portion; a first magnetic core disposed within the lower portion and a second magnetic core disposed within the lid, wherein when the lid is engaged with the lower portion the first and second magnetic cores together form a square closed core, and wherein the first magnetic core includes two parallel legs; a plurality of conductive windings wound around one of the two legs, wherein a second of the two legs is configure to receive a roller.

2. The heating unit of claim 1 wherein the lid and the lower portion are connected by a hinge.

3. The heating unit of claim 1 wherein the first magnetic core comprises a U-shape or a C-shape.

4. The heating unit of claim 1 wherein the first magnetic core comprises an E-shape.

5. The heating unit of claim 1 wherein the first and second magnetic cores comprise grain-oriented laminated silicon steel.

6. The heating unit of claim 1 wherein the plurality of conductive windings includes 350 turns of 12GA enameled copper wire.

7. The heating unit of claim 1 further comprising a thermal sensor disposed proximate to the second leg and configured to produce an analog signal in response to a temperature of the roller.

8. The heating unit of claim 7 further comprising a microcontroller configured to control the flow of alternating current to the windings and to turn off the alternating current in response to the thermal sensor.

9. The heating unit of claim 1 further comprising the roller disposed on the second of the two legs.

10. A roller for use in conjunction with a heating unit, the roller comprising: a cylinder of an electrically conductive material having an inside diameter of at least two inches and including a plurality of bristles protruding perpendicular to the exterior surface.

11. The roller of claim 10 wherein the electrically conductive material comprises aluminum.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0010] FIG. 1 is a cross-sectional view of an exemplary heating unit according to various embodiments.

[0011] FIG. 2 is a cross-sectional view of an exemplary heating unit with an open lid, including rollers, according to various embodiments.

[0012] FIG. 3 schematically illustrates the magnetic fields within an exemplary magnetic core, according to various embodiments.

[0013] FIG. 4 is a top view of a four-station heating unit with no lid to show a roller in each station, according to various embodiments.

[0014] FIG. 5 is an electrical diagram of an exemplary heating unit, according to various embodiments.

DETAILED DESCRIPTION

[0015] Reference will now be made in detail to some specific examples including the best modes contemplated by the inventors. Examples of these specific embodiments are illustrated in the accompanying drawings. While the present disclosure is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In addition, although many of the components and processes are described below in the singular for convenience, it will be appreciated by one of skill in the art that multiple components and repeated processes can also be used to practice the techniques of the present disclosure.

[0016] FIG. 1 shows a cross-sectional view of an exemplary heating unit 100 including a housing 110, a magnetic core 120, and windings 130. The housing 110 can be opened to provide access to the inside of the heating unit 100, as shown in FIG. 2, to insert and remove rollers, also known as hair curlers. FIG. 2 shows a side view of the heating unit 100 with a lid 200 partially open and two rollers 210 inserted into the heating unit 100. While FIG. 1 is a simple cross-sectional view, FIG. 2 presents a cross-sectional view overlaid with side views of two rollers 210.

[0017] The housing 110 is a protective and cosmetic shell designed to provide structure to the internal components, protect users from electrical contact, help position rollers 210 via bosses or other features, and provide a cosmetic cover. The housing 110 can be fabricated from a variety of materials including injection molded plastic such as polycarbonate or ABS plastic. In the case of a metallic or otherwise electrically conductive housing 110, electromagnetic shielding may be employed between the magnetic core 120 and the housing 110 to prevent unwanted heating of the housing 110.

[0018] The housing 110 comprises two pieces, a lower portion 220 and an upper portion forming the lid 200. In the embodiment shown in FIG. 2 the lid 200 is hinged to the lower portion 220, but in other embodiments the lid 200 lifts straight off the lower portion 220 to completely detach therefrom. In still further embodiments, the lid 200 is configured to slide longitudinally relative to the lower portion 220, such as through the use of tracks.

[0019] The magnetic core 120 comprises, in some embodiments, a square closed core comprising a U-shaped or C-shaped core disposed within the lower portion 220, and a straight core disposed in the lid 200 and arranged such that when the lid is closed, the straight core is brought together with the C- or U-shaped core to complete the square closed core. In the embodiments illustrated by FIGS. 1 and 2 the magnetic core 120 comprises a combination of an E-shaped core 140 and a straight core 150 to create two magnetic loops 300, 310 that both pass through the windings 130, as shown in FIG. 3. It will be appreciated that more complex magnetic cores can be made to accommodate additional rollers 210.

[0020] Each of the parallel arms of the C- or U-shaped core or E-shaped core 140 will be referred to herein as legs. In embodiments in which a C- or U-shaped core is employed, the windings 130 are disposed around one leg, while a roller 210 fits over the other leg. In embodiments in which an E-shaped core 140 is employed, the windings 130 are disposed around the center leg of the three legs, and rollers 210 can be positioned over the outer two legs. Various embodiments include more than two legs, to accommodate more than two rollers 210, symmetrically arranged around a central hub leg around which the windings 130 are disposed.

[0021] In various embodiments, the magnetic core 120 comprises laminated silicon steel with a high relative magnetic permeability (a unitless value) of at least 5000. Individual layers of silicon steel for lamination can be produced, for instance, by plasma cutting, laser cutting, manual shearing, or stamping from sheets of the silicon steel. In various embodiments the steel comprises grain-oriented silicon steel. An exemplary commercially available material known by the industry designation EI150 is suitable for making magnetic cores 120. Individual lamination layers can be between 0.01 to 0.035 thick, with a thickness in one embodiment of 0.02. Individual laminations are coated so that the layers of silicon steel are electrically insulated from one another.

[0022] In other embodiments, the magnetic core 120 comprises a ferrite core such as for higher frequency applications above 500 Hz. Here, the frequency refers to that of the alternating current from an AC power supply. Below 500 Hz silicon steel is preferred. In some embodiments, an oscillating tank circuit can be employed to produce a frequency of 3-10 kHz, or 200-400 kHz, for example. These frequency ranges are within the induction heating band and within the allowable FCC EM spectrum. Hysteresis losses for silicon steel increase due to eddy currents with increasing frequency.

[0023] The windings 130 can be fabricated from enameled copper wire, for example, but can also be made from any conductive material that is electrically isolated from the magnetic core 120 and that allows adjacent windings to be insulated from each other. In one embodiment, the windings 130 comprise 350 turns of 12GA enameled copper wire. Other embodiments may contain any number of turns, wire gauges, and supply currents. Wall heating units 100 of the disclosure draw power from the public power grid at 120V and 60 Hz, the voltage and frequency can be varied from this to be delivered to the windings 130 to meet design requirements such as to limit current draw as well as to avoid core saturation.

[0024] Rollers 210 suitable for use with embodiments of the heating unit 100 comprise cylinders of an electrically conductive material with a diameter of 2 inches or more and including bristles protruding from the exterior surface. Rollers 210 are sized to fit over the legs of the magnetic core 120, to allow the magnetic field to pass though with few losses either through air or another material. In one embodiment, the roller 210 is made from 6061 aluminum. Low density materials such as aluminum are heated more quickly through magnetic induction. In other embodiments the rollers 210 can utilize any number of other electrically conductive materials with or without specialty coatings, including 304 stainless steel and titanium. An example of such a specialty coating is titanium nitride. As illustrated, embodiments of rollers 210 are bristled, and therefore they require no additional clips to secure them to the hair, thus avoiding dragging hair downward across the scalp which has the effect of flattening roots. In some embodiments the bristles are made of silicone to protect the hair and prevent tangling.

[0025] When the windings 130 are energized with an alternating current, they produce an oscillating magnetic field around the windings 130. The windings 130 can be produced by winding a conductive wire around a bobbin to produce a solenoid which can then be placed over a leg of the magnetic core 120. Since the relative permeability of the magnetic core 120 is significantly less than that of the surrounding air, the magnetic field produced by the windings 130 is channeled through the transformer core 120 thereby completing a magnetic loop through the windings 130 as shown in FIG. 3. The use of an E-shaped core 140 together with a straight core 150 to produce a square closed core (sometimes called an EI core) provides a balanced return path for the magnetic field. Since the rollers 210 are electrically conductive and form continuous loops, the magnetic field passing through their centers induces an opposing magnetic field that in turn causes an internal electrical current to circulate within the rollers 210. The rollers 210 serve as an electrical load, essentially becoming shorted single-turn secondary windings. The circulating current within each roller 210 is characterized by a high current at a low voltage. Because of the internal electrical resistance of the rollers 210, the electrical current causes the rollers 210 to heat.

[0026] FIG. 4 provides a top view of an exemplary four-station heating unit 400, with the lid 200 removed. In the embodiment of FIG. 4, the heating unit 400 includes two magnetic cores 120, each comprising an E-shaped core 140, each magnetic core 120 configured to heat two rollers 210.

[0027] FIG. 5 is a circuit diagram 500 for an exemplary four-station heating unit such as the four-station heating unit 400. Each of the magnetic cores 120 is represented as a transformer. In operation, a microcontroller 505 receives input from a user interface 510 for example to heat two rollers 210 in positions 1 and 2. The microcontroller 505 signals a solid state relay 515 to close in order to allow alternating current supplied by an AC power supply 520 to flow through windings 130 to cause the rollers 210 to heat. A thermal sensor 525 disposed proximate to a roller 210, or disposed in contact with the roller 210, creates a changing analog signal in response to the changing temperature of the roller 210. An analog to digital converter 530 changes the analog signal into a digital one, which is received by the microcontroller 505. The microcontroller 505 controls the solid state relay 515 to open once the digital signal reaches a threshold indicating that the roller 210 is sufficiently hot. The microcontroller 505 can additionally provide a signal to the user through the user interface 510, such as a sound, an indicator light, or by providing text (e.g. Ready) on a display, or any combination of these.

[0028] The microcontroller 505 is powered by direct current supplied by a DC-DC converter 535 that in turn receives direct current from a full wave bridge rectifier 540 in electrical communication with the AC power supply 520. More specifically, the alternating current produced by the power supply 520 is split into three paths, where one path goes to one relay 515 and one transformer, a second path goes to the second relay 515 and second transformer, while the third goes to the bridge rectifier 540. The direct current voltage from the bridge rectifier 540 can be adjusted as appropriate for the microcontroller 505, thermal sensors 525, and for triggering the relays 515.

[0029] The thermal sensor 525 can be, for instance, a K-type thermocouple, while in other embodiments the thermal sensor 525 comprises an infrared sensor. The thermal sensor 525 can be located in the housing 110 near or touching each roller 210. In those embodiments that employ an infrared sensor, the thermal sensor 525 does not contact the roller 210.

[0030] While the present disclosure has been particularly shown and described with reference to specific embodiments thereof, it will be understood by those skilled in the art that changes in the form and details of the disclosed embodiments may be made without departing from the spirit or scope of the invention. Specifically, there are many alternative ways of implementing the processes, systems, and apparatuses described. It is therefore intended that the invention be interpreted to include all variations and equivalents that fall within the true spirit and scope of the present invention. Moreover, although particular features have been described as part of each example, any combination of these features or additions of other features are intended to be included within the scope of this disclosure. Accordingly, the embodiments described herein are to be considered as illustrative and not restrictive.