Patent ID: 12256822

In the figures, like elements are indicated by like reference numerals throughout.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present embodiments represent the best ways known to the Applicant of putting the invention into practice. However, they are not the only ways in which this can be achieved.

Overview

FIGS.1and2show, in perspective and cross-sectional views respectively, an assembly10that may form part of a hair styling appliance such as a curling tong (e.g. as illustrated inFIG.3), a curling wand, or a hot iron brush. The assembly10comprises an elongate barrel12that, in use, may be used to heat and style hair. The barrel12has a curved external surface14and an integral internal heater-mounting surface16. The assembly10further comprises one or more heater elements20mounted on the heater-mounting surface16. As illustrated, the heater element(s)20are typically elongate, planar, and relatively thin in form (i.e. having a thin rectangular cross-sectional shape), although other geometries are also possible.

In the illustrated embodiment a spring clip18is inserted within the barrel12to hold the heater element(s)20in place against the heater-mounting surface16. However, in alternative embodiments other means for securing the heater element(s)20in place may be used instead.

Barrel with Integral Heater-Mounting Surface

The barrel12, with external surface14and integral heater-mounting surface16, is preferably formed as a single extruded metal component. The external surface14may, in cross-section, be any desired shape. In our presently-preferred embodiments the external surface14has a circular or elliptical cross-sectional shape, although other cross-sectional shapes are also possible.

When viewed in cross section, the integral heater-mounting surface16extends as a chord across the inside of the barrel12, from one side to the other. Thus, the heater-mounting surface16is integrally attached to the external surface14in two opposing places. In our presently-preferred embodiments the integral heater-mounting surface16is situated along (or close to) a diameter of the barrel12—i.e. passing through or near to the centre of the barrel12when viewed in cross-section. However, in alternative embodiments the integral heater-mounting surface16may be positioned further away from the diameter of the barrel12(for example if the or each heater element20is relatively bulky such that more than half the internal cross-sectional area of the barrel12is required to accommodate it).

Whilst, in the illustrated embodiment, the integral heater-mounting surface16is a flat surface on which the or each heater element20is mounted, in alternative embodiments the heater-mounting surface16may incorporate a longitudinal recess in which the heater element(s)20can be located. Such a longitudinal recess may be readily incorporated in the cross-sectional shape of the extruded metal.

In manufacture, the barrel12may be cut from a long or continuous length of extruded metal having a cross-sectional profile that includes the external surface14and the integral heater-mounting surface16. As a consequence of being formed as a single extruded metal component, manufacture of the barrel12is facilitated, giving rise to lower production costs. Furthermore, by using an extruded component, this enables the barrel12to be any desired length, or for a range of barrel lengths to be readily produced.

Any suitable metal may be extruded to form the barrel12. For example, the metal may be aluminium, which is relatively inexpensive, has a relatively low density (enabling the resulting product to be relatively light weight), and is easy to extrude.

Thermal Transfer Considerations

The integral heater-mounting surface16also serves as an internal feature for the conduction and/or radiation of heat from the heater element(s)20to the external surface14of the barrel12.

As shown inFIG.2, heat transfer from the one or more heater elements20is provided by the heater element(s)20thermally engaging an adjacent internal surface of the barrel (point A), on the heater-mounting surface16. Heat is efficiently transmitted from the or each heater element20to the external surface14(point C) by means of the heater-mounting surface16serving as an integral internal feature for the conduction of heat (e.g. via point B) and/or radiation of heat.

With the presently-preferred embodiments, improved efficiency can be achieved by the heater-mounting surface16having a thickness (e.g. at point A) that is twice the thickness of the outer external surface14(e.g. at point C).

With such a geometry, improved thermal performance has been achieved, as the design and thickness of the integral internal conducting/radiating features (i.e. the heater-mounting surface16) relative to the thickness of the external surface14provides effective heat transfer with minimal temperature difference from the heater element20to the external “working” surface14.

An example of such a geometry is given inFIG.2, in which possible dimensions are provided by way of example only. In this example, the heater-mounting surface16(serving as an internal feature for the conduction and/or radiation of heat) has a thickness (e.g. at point A) of 2 mm, whereas the external surface14(e.g. at point C) has a uniform thickness of 1 mm. In passing, it may be noted that, in this example, the barrel12has an external diameter of 30 mm (+/−5 mm).

It will of course be appreciated that other geometries are possible in which the thickness of the heater-mounting surface16is twice the thickness of the external surface14. For example, the thickness of the heater-mounting surface16may be 3 mm and the thickness of the external surface14may be 1.5 mm, or alternatively, the thickness of the heater-mounting surface16may be 1.5 mm and the thickness of the external surface14may be 0.75 mm.

Spring clip (or other securing means) In the illustrated embodiment the spring clip18positions the heater element(s)20adjacent to the heater-mounting surface16and provides sufficient force to hold the heater element(s)20in close contact with the heater-mounting surface16, thereby enabling effective thermal transfer to take place through the heater-mounting surface16and thence to the external surface14of the barrel12.

However, as mentioned above, in alternative embodiments other means for securing the heater element(s)20in place against the heater-mounting surface16may be used instead.

Example Hair Styling Appliance

FIG.3illustrates an example of a hair styling appliance—in this case, a curling tong30—which incorporates a barrel assembly10as described above (i.e. an extruded barrel12with an integral heater-mounting surface16on which one or more heater elements20are mounted). The curling tong30includes a main body32that is grasped by a user during use. The main body32incorporates an electrical power supply (e.g. a mains electricity supply cable38, or conceivably a rechargeable battery). The barrel12is attached to the main body32and wired such that electrical power can be provided to the heater element20within the barrel12(e.g. under the control of a control circuit within the main body32) and thereby cause the barrel12to heat.

A clamp member34, having a curved profile to complement the external surface14of the barrel12, is pivotally mounted adjacent to the barrel12by means of a pivot mechanism35and a user-pressable lever36. As will be familiar to those skilled in the art, the clamp member34is spring-biased into a closed position in which the clamp member34presses against the barrel12. With the clamp member34in the closed position and the barrel12heated, the curling tong30can be used to style hair that has been introduced between the clamp member34and the barrel12. However, upon the user pressing on the lever36, the clamp member34pivots about the pivot mechanism35and thereby opens, for example to allow hair to be introduced between the barrel12and the clamp member34for styling, or to release hair once the desired styling operation has been completed.

Improved Heater Architecture

To improve the thermal response of a hair styling appliance (e.g. curling tong) such as those described above, we have found that it is advantageous not to use a temperature sensor that is separate from the heater element. Rather, as shown inFIG.4, a temperature sensor may be embedded in the heater element20as a secondary layer of resistive track, such that the heater element20includes two layers: a heater track layer26and a temperature sensor layer24. In the illustrated embodiment, both the heater track and the temperature sensor are embedded within a ceramic substrate22(for example made of aluminium oxide).

The resistive track forming the temperature sensor may have either a positive or a negative temperature coefficient, such that as the temperature is changed the resistance of the track changes, which can then be detected by a control circuit, and hence the temperature can be calculated (once the change in track resistance has been calibrated against temperature). In turn, depending on the calculated temperature, the electrical power supplied to the heater track can be controlled, thereby regulating the temperature of the heater element20. The benefits of using an embedded temperature sensor track are twofold: the temperature can be sensed over an area, not just a point, and the track can advantageously be molecularly bonded to the heater, thus removing any need for thermal paste (which is difficult in manufacture and thermally resistive, such that it would reduce performance).

The use of such an integrated heater and sensor construction is by no means limited to a hair styling appliance as described above (i.e. one having a barrel12formed as a single extruded metal component, with an external surface14and an integral heater-mounting surface16). Indeed, such an integrated heater and sensor construction is more broadly applicable, and can for example be used in other pieces of hair styling equipment, such as hair straighteners, as well as on tri-zone heaters.

FIG.5is a schematic illustration of a control circuit40suitable for use with (and shown connected to) the heater element20ofFIG.4. The control circuit40includes a current drive unit42operable to supply electrical current to the heater track layer26of the heater element20, and a resistance sensing unit44operable to generate a signal representative of (or dependent on) the resistance of the resistive track of the temperature sensor layer24. The current drive unit42and the resistance sensing unit44are both connected to a control unit46(e.g. a suitably programmed microprocessor).

In use, the control unit46causes the current drive unit42to supply electrical current to the heater track layer26, thus causing the heater element20to heat up. In parallel with the operation of the current drive unit42, the resistance sensing unit44generates a signal representative of (or dependent on) the resistance of the resistive track of the temperature sensor layer24, and supplies this signal to the control unit46(i.e. in a feedback manner). The signal generated by the resistance sensing unit44may be processed by the control unit46to determine the temperature of the heater element20(e.g. by employing a calibration relationship), and in turn the control unit46is configured to adjust the electrical current supplied to the heater track layer26, to thereby regulate the temperature of the heater element20—specifically, such that the heater element20reaches and maintains a desired temperature.

A user-adjustable control knob or other user interface (e.g. electronic buttons) may be provided, coupled to the control unit46, to enable the user to specify the temperature to be attained by the heater element20. In a first variant the control knob or user interface may enable the user to specify the actual temperature required (e.g. in ° C.). In a second variant the control knob or user interface may enable the user to select whether the temperature is to be “high”, “medium” or “low”, for example, such settings corresponding to respective predetermined temperatures. In a third variant the control knob or user interface may enable the user to specify the type of hair and/or styling operation to be carried out, upon which the control unit46determines (from effectively an internal look-up table) an appropriate temperature to which the heater element20is to be heated.

FIG.6illustrates another heater element having an integral temperature sensor, similar to that ofFIG.4, with possible dimensions by way of example only. In this case the heater element20comprises a ceramic substrate22(for example aluminium oxide) having an embedded temperature sensor layer24and a heater track layer26. As discussed in greater detail below, the heater element20may be formed from three constituent layers that are joined together.

With reference to the exemplary dimensions given inFIG.6, the resistive heater track (of layer26) may be 0.6 mm above the undersurface of the heater element20(i.e. the surface which is adjacent to the heater-mounting surface16in the case of the assembly illustrated inFIGS.1and2). The resistive track of the temperature sensor (of layer24) may be 0.2 mm above the resistive heater track, and 0.2 mm beneath the upper surface of the heater element20.

Further, the resistive track of the temperature sensor (of layer24) and the resistive heater track (of layer26) may both be at least 0.6 mm inward of the outer edges of the heater element20, to prevent undesirable external effects such as short-circuiting or arcing with the heater-mounting surface, or flashover. To explain this in more detail, it will be appreciated that the heater element20may operate at a high voltage (e.g. ˜240V AC), and the heater-mounting surface may be a metal plate. Hence, there needs to be sufficient insulation between the heater track and the heater-mounting surface to stop electricity jumping between the two, as this could otherwise cause electrocution of the user. Although air is an insulator, it is not a particularly good or reliable one, due to variation in water content (which is especially the case in the context of hair styling). Accordingly, in order to comply with the relevant safety provisions, at least a 0.6 mm gap is provided between the live track (of layer26) and the heater-mounting surface (e.g. metal plate), to ensure there can be no conduction of electricity between the two.

The overall substrate22of the heater element20may be formed from three ceramic layers that are fired together (or otherwise joined together). The overall substrate22may for example be formed of aluminium oxide, by virtue of the constituent layers also being formed of aluminium oxide.

FIG.7illustrates examples of such layers, namely a top layer23, a temperature sensor layer24, and a heater track layer26.

When taken separately, the heater track layer26(lowermost in the cross-sectional view ofFIG.6) has its own ceramic substrate22c(e.g. aluminium oxide) on which the resistive heater track27is deposited. The resistive heater track27preferably has a minimal temperature coefficient (be it positive or negative) to allow for fast heat-up.

Similarly, when taken separately, the temperature sensor layer24has its own ceramic substrate22b(e.g. aluminium oxide) on which the resistive track25of the temperature sensor is deposited. As mentioned above, the resistive track25of the temperature sensor may have either a positive or a negative temperature coefficient, to allow the temperature of the heater to be measured. As illustrated, the pattern of the resistive track25of the temperature sensor may correspond with, and be in alignment with, the pattern of the resistive heater track27, although variants are possible in which this need not be the case.

Similarly, when taken separately, the top layer23comprises a ceramic substrate22a(e.g. aluminium oxide).

At one end, the top layer23further comprises a series of four through-thickness solder pads21for electrical connection to associated circuitry—e.g. to a current drive unit42and a resistance sensing unit44as illustrated inFIG.4.

As illustrated, the temperature sensor layer24also has a corresponding series of through-thickness solder pads21, two of which are connected to the resistive track25of the temperature sensor.

The heater track layer26also has a corresponding series of solder pads21(not through-thickness, so as to avoid making electrical contact with the underlying heater-mounting surface16in use), two of which are connected to the resistive heater track27.

The positions of the solder pads21on the three layers23,24,26are in mutual alignment. When the three layers23,24,26are joined together (e.g. by being fired together), on top of one another, the solder pads21on each of the layers23,24,26come into contact with one another. Moreover, the individual ceramic substrates22a,22b,22cjoin to form one overall substrate22.

Subsequently, the solder pads21on the top layer23are connected to the associated circuitry (e.g. units42and44as mentioned above). More particularly, the current drive unit42is connected to the specific solder pads on the top layer23whose positions correspond to the specific solder pads of the heater track layer26to which the resistive heater track27is connected (i.e. the middle two solder pads as illustrated). Likewise, the resistance sensing unit44is connected to the specific solder pads on the top layer23whose positions correspond to the specific solder pads of the temperature sensor layer24to which the resistive sensor track25is connected (i.e. the outermost two solder pads as illustrated).

In an alternative embodiment, the solder pads are not through thickness, but rather the specific solder pads of each layer24,26that are directly connected to a respective track25,27are exposed on the respective layer, to allow electrical connections to be made directly to the respective solder pads. This may be achieved by shaping the ceramic layers such that the solder pads of an underlying ceramic layer's track are not covered by an overlying ceramic layer.

Possible Modifications and Alternatives

Detailed embodiments and some possible alternatives have been described above. As those skilled in the art will appreciate, a number of modifications and further alternatives can be made to the above embodiments whilst still benefiting from the inventions embodied therein. It will therefore be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the scope of the claims appended hereto.

For example, in the above embodiments the heater-mounting surface16extends across the inside of the barrel, from one side to the other. However, in alternative embodiments the heater-mounting surface may be formed as a more enclosed channel in which the heater element(s) may be inserted. For example, the heater-mounting surface may have a “U”-shaped cross-section, integrally formed with the external surface by extrusion, and the heater element(s) may be slotted into the inside of the “U”.

In the above embodiments a single heater-mounting surface16extends across the inside of the barrel. However, in alternative embodiments more than one heater-mounting surface may be provided across the inside of the barrel, from one side to the other. For example, two (or more) separate heater-mounting surfaces may be provided as two (or more) parallel chords extending across the inside of the barrel, integrally formed with the external surface by extrusion. A separate heater element may then be mounted on each of the heater-mounting surfaces, e.g. using respective spring clips or alternative securing means.

In the above embodiments a single heater element20is mounted on a single heater-mounting surface16. However, in alternative embodiments one heater element20may be mounted on one side of a heater-mounting surface and another heater element may be mounted on the opposite side of the same heater-mounting surface, e.g. using a respective spring clip on each side, or alternative securing means. In such a manner the heat provided to a given heater-mounting surface may be increased (potentially doubled).

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “containing”, means “including but not limited to”, and is not intended to (and does not) exclude other components, integers or steps.