Patent Description:
Conventional handheld hairdryers, that incorporate an electrically-powered motorised fan to blow a current of cool or hot air in order to dry a person's hair, are well known. The fan draws ambient air into the body of the hairdryer and blows the current of air towards the hair to be dried. When hot air is to be blown, typically an electric heating element, incorporated within the body of the hairdryer, is used to heat the current of air before it leaves the hairdryer. Optionally, the hairdryer may be equipped with a concentrator nozzle attachment to intensify and direct the current of air, or a diffuser attachment to deliver the air more gently.

However, conventional hairdryers can often be noisy, heavy and bulky. Moreover, they can be awkward to use, and it can be difficult for a user (in particular a domestic user attending to their own hair) to achieve desired results, particularly in respect of styling the hair whilst drying it. For instance, a hairdryer will often be used simultaneously with a hairbrush or comb, or another piece of styling equipment, to style the hair during drying. The styling process may be, for example, to straighten the hair, or to provide "body and volume" to the hair (if necessary, preceded or succeeded by the application of styling products such as mousse, gel, wax, hairspray, etc.). Simultaneously manoeuvring a hairdryer and a brush (or a comb, etc.) around the head can be awkward for the user, and often requires a degree of skill to achieve the desired results.

Thus, whilst using a conventional hairdryer is the fastest method to dry hair, it can be very difficult and/or time-consuming to create a desired end result in respect of styling. To do this the user has to use a brush and/or additional hair styling tools.

As an alternative to conventional hairdryers, some people may use products such as hot air brushes or hot air paddle bushes when styling their hair. However, such products, whilst being easy to use, are slow in drying the hair.

A further category of products, that are both quick and easy to use, are so-called "wet to straight" hair straighteners. These are used to both dry and straighten hair, by drawing wet hair between a pair of heated plates mounted on opposing arms of the device. These devices tend to use conductive heating at high temperatures on wet hair (typically <NUM>-<NUM>) but can be damaging to hair, and/or may be perceived to be damaging to hair, due to sounds of cavitation (sizzle) or the use of elevated temperatures around the denaturation temperature of wet hair.

Background art is provided in <CIT>, which discloses a hair styling and drying apparatus having a pair of pivotally connected arms, styling surfaces on the arms, air suction and discharge orifices in the styling surfaces, and a blower for blowing air through the air orifices and recycling air between the arms. At least some suction orifices of one styling surface can align with at least some discharge orifices of the other styling surface. The blowers blow air out the discharge orifices and suck air into the suction orifices, thereby recycling much of the blown air. The apparatus can include heaters for heating the blown air and for heating the styling surfaces.

The present invention aims to provide alternative apparatus and methods to those of conventional handheld hairdryers in order to dry hair, by combining the functionality and benefits of a conventional hairdryer with those of a hair straightener, within one grip-sized device. Thus, advantageously, embodiments of the present invention provide, as a single handheld device, means for both drying and styling the hair, which is simple to use, and less awkward than manoeuvring a conventional hairdryer around the head simultaneously with a brush, comb or other piece of styling equipment.

More particularly, the present invention provides apparatus as defined in Claim <NUM> of the appended claims, for drying and styling hair. Details of certain embodiments are set out in the dependent claims. Also provided is a method of drying hair using such apparatus, as defined in Claim <NUM>.

According to a first aspect of the present invention there is provided apparatus for drying and styling hair, comprising:.

The term "chamber" as used herein should be interpreted broadly, to encompass chambers that are partially open on at least one side, as well as those that are enclosed.

By virtue of the configuration of the present apparatus, including the at least one airflow conduit and the inter-arm chamber formed by the arms when in the closed configuration, this enhances the delivery of air to the hair, enabling the hair to be dried/styled in a quick and easy manner, and also enabling improved energy efficiency to be achieved.

One or both of the arms further comprises an airflow guide structure arranged to receive the flow of air from the respective conduit and to direct the flow of air from a first direction that is substantially parallel to the length of the respective arm, to a second direction that is from the respective arm towards the opposing arm, into the inter-arm chamber. The provision of such an airflow guide structure further enhances the delivery of air to the hair, further facilitating the drying/styling process, and enabling a further improvement in energy efficiency to be achieved.

Moreover, according to the invention, first and second plates are disposed on the first arm, and respective opposing first and second plates are disposed on the second arm, wherein the opposing plates disposed on the first and second arms are arranged to come together when the first and second arms are in the closed configuration. Moreover, according to the invention, the inter-arm chamber is located between the first and second plates of the first and second arms when the arms are in the closed configuration and at least one of said plates comprises means for applying heat to said length of hair in use, when the first and second arms are in the closed configuration.

In a particular embodiment each of the first and second arms comprises a respective conduit and a respective airflow guide structure, and the means for delivering the flow of air is arranged to deliver the air along the conduit in each of the first and second arms and thence through the respective airflow guide structure and into the inter-arm chamber. This enables air to be delivered to the hair in the device simultaneously from above and below, enhancing the drying/styling process.

Each airflow guide structure may be offset from an imaginary centreline midway between the first and second arms when in the closed configuration. Such an offset advantageously creates an airflow restriction between the air and hair in use, to increase the speed of the airflow around the hair, to increase drying. In a particular embodiment the offset of each airflow guide structure from the imaginary centreline is about <NUM> (i.e. the airflow guide structures are separated from one another by a distance of about <NUM>).

The conduit in the or each arm may advantageously act as a plenum chamber through which the air flows into the respective airflow guide structure and thence into the inter-arm chamber. This promotes uniformity of airflow from the or each arm through the respective airflow guide structure and into the inter-arm chamber.

Preferably the airflow guide structure in the or each arm comprises a cellular structure configured to direct the flow of air from the first direction to the second direction, the cellular structure comprising a plurality of cell walls which extend along the second direction into the respective plenum chamber.

The depth of the cells into the respective plenum chamber may progressively increase with distance along the respective arm. Such a configuration advantageously causes the incoming airflow in the first direction to turn and exit from the plenum chamber in the second direction and enter the inter-arm chamber with uniform airspeed.

Alternatively, or in addition, the diameter of the cells of the airflow guide structure in the or each arm may progressively decrease with distance along the respective arm. Such a configuration has been found to provide a more even distribution of airflow along the airflow guide structure.

In presently-preferred embodiments the cellular structure has a hexagonal (honeycomb) structure. The inventors have found this to be beneficial in maximising the open area through the guide structure whilst minimising the area occupied by the cell walls, and thereby minimising airflow resistance due to the cell walls.

The or each airflow guide structure may further comprise a plurality of airflow redirecting channels configured to convey the flow of air from the second direction to third and fourth directions that are outward from the apparatus, substantially perpendicular to the length of the arms. By expelling air in these third and fourth directions, this enables air to be easily directed towards the roots of the hair, to dry the roots and enable root lift to be created.

In presently-preferred embodiments the airflow redirecting channels extend between longitudinal edges and corresponding longitudinal sides of the airflow guide structure.

Airflow conduits may be provided that extend behind the first and second plates of the respective arm, to receive air from said airflow redirecting channels and to direct airflow behind the first plate and outward through vents along the edge of the apparatus in substantially the third direction, and to direct airflow behind the second plate and outward through vents along the edge of the apparatus in substantially the fourth direction.

In certain embodiments the airflow guide structure including the cellular structure and the airflow redirecting channels, and the outward vents in the third and fourth directions, may be formed as a unitary structure (e.g. by 3D printing).

Advantageously the outward vents may be oriented at an angle of about <NUM>° relative to the plane of said plates, to enhance the degree of root lift created.

The device may further comprise an airflow splitter arranged to divide airflow into the conduits in the first and second arms in the first direction. Optionally the airflow splitter may comprise a flexible member.

The means for delivering the flow of air may comprise a fan. The fan may advantageously incorporate a brushless motor designed to operate at high speeds (e.g. over <NUM>,<NUM> revolutions per minute) and low power (e.g. <NUM> W maximum, <NUM> W during normal operation), and may driven by a DC power supply. Such high-speed low-power parameters of the fan have been found to provide excellent drying performance, drying hair as quickly as a <NUM> W conventional hairdryer, but using significantly less power.

Presently-preferred embodiments further comprise means for heating said airflow, such as one or more heating elements or electrical heating coils, for example.

Advantageously, the apparatus may further comprise an airflow splitter arranged to direct incoming airflow towards said heating coils, thereby enhancing the efficiency of heat transfer from the coils to the incoming airflow during use. For example, the airflow splitter may be tapered or conical in shape.

Moreover, the apparatus may further comprise means for performing pulse width modulation in respect of electrical power applied to said means for heating said airflow. This can advantageously be used to regulate the thermal output of the means for heating, irrespective of variations in the power supply voltage (e.g. due to local variations in mains voltage around the world).

To promote a generally uniform air temperature profile across the air stream, the apparatus may further comprise means for causing turbulence in the heated airflow (such as one or more baffles within the airflow, or a conical or tapered airflow mixing member) prior to the airflow reaching the inter-arm chamber. Alternatively, the means for heating said airflow may comprise the airflow guide structure, the airflow guide structure being formed of a material that generates heat on application of an electric current thereto.

Optionally the apparatus may further comprise one or more sets of flexible bristles on the first and/or second arms, outside or within the inter-arm chamber, arranged to promote the application of uniform tension to the hair passing across the inter-arm chamber in use.

Advantageously, to prevent the escape of air past the end of each of the first and second arms, the apparatus may further comprise mutually-opposing spring-loaded sealing elements at the distal tip of said arms.

Moreover, the apparatus may further comprise at least one airflow deflector on the outer surface of at least one of said arms, shaped and positioned to deflect any rearward-flowing escaping air away from the user's hand. Such an airflow deflector may advantageously be ramp-shaped.

According to a second aspect of the present invention there is provided a method of drying hair using the apparatus of the first aspect.

The method may further comprise using the apparatus to style the hair substantially simultaneously with drying the hair.

Embodiments of the invention will now be described, by way of example only, and with reference to the drawings in which:.

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

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

<FIG> is a perspective overview of a combined hair dryer/styler device <NUM> according to a first embodiment, with arms <NUM>, <NUM> in an open configuration, and <FIG> shows the same device with the arms <NUM>, <NUM> closed (as in use, e.g. as shown in <FIG>). <FIG> show further views of parts of the device <NUM>, with <FIG> showing parts of the device in use.

Referring initially to <FIG> and <FIG>, the device <NUM> is an all-in-one handheld device that can be used to dry hair in a quick and easy manner, whilst also enabling styling of the hair (e.g. to straighten the hair, or to add "body and volume" to it).

The device <NUM> comprises a body part <NUM>, and first and second mutually-opposing arms <NUM>, <NUM> arranged in a broadly similar manner to the arms of a handheld hair styler. The first and second arms <NUM>, <NUM> are adapted for movement between an open configuration (as shown in <FIG>) for receiving a length of wet hair therebetween, and a closed configuration (as shown in <FIG>) adjacent the hair, to create tension in the hair, such that, in use, when the arms <NUM>, <NUM> are in the closed configuration they form an inter-arm plenum chamber (<NUM>, <FIG>) across which the hair passes.

Turning briefly to <FIG>, a first airflow conduit <NUM> is provided within and along the first arm <NUM>, and a second airflow conduit <NUM> is provided within and along the second arm <NUM>. In alternative embodiments (e.g. as illustrated in <FIG>, <FIG> and <FIG>) only one of the arms may incorporate such an airflow conduit.

Referring to <FIG>, the device further comprises a fan assembly <NUM> within the body part <NUM>, for delivering a flow of air along the first and second conduits <NUM>, <NUM> in the first and second arms <NUM>, <NUM>. The fan assembly <NUM> has an impeller and is typically also provided with a filter.

As shown for example in <FIG>, <FIG>, <FIG>, <FIG> and <FIG>, each of the first and second arms <NUM>, <NUM> further comprises a respective airflow guide structure <NUM> arranged to receive the flow of air from the respective first or second conduit <NUM>, <NUM> and to direct (i.e. steer) the flow of air from a first direction (D1, <FIG>) that is substantially parallel to the length of the respective arm (i.e. incoming air, lengthways along the device), to a second direction (D2, <FIG>) that is from the respective arm towards the opposing arm, i.e. inwards into the inter-arm plenum chamber <NUM> formed by the arms <NUM>, <NUM> in the closed position. In alternative embodiments, only one of the arms <NUM>, <NUM> may be provided with such an airflow guide structure <NUM>, if only one of the arms incorporates an airflow conduit. The configuration and function of the airflow guide structure <NUM> are described in greater detail below. In yet other variants, the airflow guide structure(s) <NUM> may be omitted altogether.

As illustrated for example in <FIG>, the first arm <NUM> is a continuation of the body part <NUM>, and the second arm <NUM> is coupled to the body part <NUM> by means of a hinge <NUM>, by virtue of which the first and second arms <NUM>, <NUM> are movable relative to one other (in the illustrated embodiment, by moving the second arm <NUM> towards the first arm <NUM>). Thus, the first and second arms <NUM>, <NUM> can be brought together, into the closed configuration (as shown in <FIG>), or moved apart, into the open configuration (as shown in <FIG>), by a user in use. In the illustrated embodiment, each of the arms <NUM>, <NUM> widens relative to the body part <NUM> to form a "head" of the device <NUM>, distal from the body part <NUM>, although other embodiments are possible in which the head does not widen in the illustrated manner.

The hinge <NUM> can incorporate any suitable means for allowing the first and second arms <NUM>, <NUM> to be moved relative to one other.

Preferably the hinge <NUM> also incorporates spring means configured to bias the first and second arms <NUM>, <NUM> into the open configuration, such that the user is required to apply pressure to the arms to close them together (overcoming the effect of the spring means), and such that the arms <NUM>, <NUM> automatically open, under the effect of the spring means, once the pressure is removed. For example, the hinge <NUM> may incorporate a leaf spring or a coiled spring.

The hinge <NUM> and the spring means can be one and the same. For example, the spring means itself can be used to couple the second arm <NUM> to the body part <NUM>, thereby avoiding the need to provide a separate mechanical hinge and simplifying the overall construction of the device.

As shown in <FIG>, and in close-up in <FIG>, in the illustrated embodiment the inner surface of the first arm <NUM> incorporates first and second elongate heater plates 20a, 20b, parallel to each other and to the length of the arm <NUM>. The second arm <NUM> also incorporates first and second elongate heater plates 22a, 22b (not visible in <FIG> and <FIG>, but shown for example in <FIG> and <FIG>) in corresponding positions to heater plates 20a and 20b. Each of the heater plates is provided with a respective electrical heating element, operable to cause the respective heater plates to heat up. In the illustrated embodiment the operating temperature of the heater plates is typically around <NUM>-<NUM>.

The first and second arms <NUM>, <NUM> and the first and second heater plates on each arm are arranged such that, when the device <NUM> is in the closed configuration, the first and second heater plates 20a, 20b of the first arm <NUM> come into contact with the first and second heater plates 22a, 22b of the second arm <NUM>. Preferably the heater plates 20a, 20b, 20c, 20d are made of a material having relatively high thermal conductivity, and are preferably provided with one or more temperature sensors (e.g. a temperature sensor for each plate, or one or more temperature sensors that each serves a plurality of heater plates).

Optionally, flexible bristles may be provided alongside the heater plates 20a, 20b, 20c, 20d. More particularly, flexible bristles may be positioned on either or both sides of the first arm <NUM>, and/or on either or both sides of the second arm <NUM>, adjacent to the inlet/outlet of the hair to/from the heater plates 20a, 20b, 20c, 20d. Alternatively, or in addition, flexible bristles may be provided within or around the airflow guide structure <NUM>, between the heater plates. Such bristles enable more uniform tension to be applied to the hair fibres within a section of hair passing through the chamber <NUM> formed by the arms <NUM>, <NUM> in the closed position.

As shown in <FIG>, a control button or switch <NUM> may be provided on the device <NUM>, to enable it to be turned on or off, together with an indicator light to show whether the power is on. A sound can also be played by a sound generator (not illustrated) when the device <NUM> is switched on and ready to use.

As shown in the cross-sectional views in <FIG>, a fan assembly <NUM> is mounted towards an end of the body part <NUM>, distal from the first arm <NUM>. The fan <NUM>, driven by an electric motor, is operable to draw in air from the surrounding environment and to deliver a flow of air along the inside of the body part <NUM>; and then into and along the conduits <NUM>, <NUM> in the arms <NUM>, <NUM>; and then into and through the inter-arm plenum chamber <NUM> formed by the arms <NUM>, <NUM> in the closed position, around and through the hair to be dried.

Advantageously the fan <NUM> may incorporate a brushless motor designed to operate at high speeds (e.g. over <NUM>,<NUM> revolutions per minute) and low power (e.g. <NUM> W maximum, <NUM> W during normal operation), and may driven by a DC power supply. Such high-speed low-power parameters of the fan have been found to provide excellent drying performance, drying hair as quickly as a <NUM> W conventional hairdryer, but using significantly less power.

An electrically-powered heating coil (or other electrical heating elements), operable to heat the air drawn in by the fan <NUM>, is provided in part <NUM>, towards the end of the body part <NUM> proximal to the first arm <NUM>.

The heater plates 20a, 20b, 22a, 22b serve a number of purposes during use of the device <NUM>. Firstly, with the user having sandwiched a length of wet hair between opposing plates 20a and 22a, and between opposing plates 20b and 22b (i.e. transversely across the plenum chamber <NUM> formed by the first and second arms <NUM>, <NUM> in the closed configuration), and by drawing the device along the length of wet hair, the heater plates 20a, 20b, 22a, 22b subject the wet hair to a squeegeeing effect, removing excess unbound water, and also heat the hair to promote subsequent evaporation of the water. Secondly, the heating provided by the heater plates 20a, 20b, 22a, 22b causes the walls of the plenum chamber <NUM> to be heated (via thermal conduction), and also helps maintain the temperature of the airflow delivered through the plenum chamber <NUM> by the fan <NUM>. Thirdly, the heater plates 20a, 20b, 22a, 22b can be used to style the hair, as an integral part of the drying process.

The heater plates 20a, 20b, 22a, 22b are preferably configured as ceramic float plates with springs having a low spring rate or stiffness, thereby giving good control of hair tension.

Allowing for the airflow heating coil (or other heater elements) and the heater plates 20a, 20b, 22a, 22b, as well as the fan <NUM>, the overall power consumption of the device <NUM> is around <NUM>-<NUM> W, which is significantly less than a <NUM> W conventional hairdryer.

As shown in <FIG>, the electrical and electronic circuitry of the device <NUM> is housed within the body part <NUM> and the first and second arms <NUM>, <NUM> (although predominately within the body part <NUM> and the first arm <NUM>). In the example illustrated, a printed circuit board assembly <NUM> is provided within the body part <NUM>. Electrical power is provided to the device <NUM> by means of a power supply located at the end of the body part <NUM> distal from the first arm <NUM>. In the illustrated embodiment the power supply is an AC mains power supply. However, in an alternative embodiment the power supply may comprise one or more DC batteries or cells (which may be rechargeable, e.g. from the mains or a DC supply via a charging lead), thereby enabling the device <NUM> to be a cordless product.

Amongst other things, the circuit board assembly <NUM> includes four TRIACs <NUM>, each for powering a respective one of the heater plates 20a, 20b, 22a, 22b.

The device <NUM> incorporates a number of features that guide the airflow from the fan <NUM> to the user's hair <NUM> so as to enable the hair to be both dried and styled. These features will now be described in detail with particular reference to <FIG>.

As mentioned above, and as shown for example in <FIG>, in the illustrated embodiment each of the first and second arms <NUM>, <NUM> (at the head of the device <NUM> distal from the body part <NUM>) comprises a cellular airflow guide structure <NUM> in airflow communication with a respective first or second conduit <NUM>, <NUM>. The first and second conduits <NUM>, <NUM> act as plenum chambers to supply air through the guide structure <NUM> of each of the first and second arms <NUM>, <NUM>.

Air is supplied to the first and second conduits <NUM>, <NUM> by the action of the fan <NUM>, via cylindrical part <NUM>. Part <NUM> includes a heating element to heat the air, and, as shown in close-up in <FIG>, a set of elongate baffles <NUM> (at a plurality of angles, essentially star-shaped in cross-section), an airflow splitter <NUM>, and a diffuser grille <NUM>.

The elongate baffles <NUM> are arranged to mix the air, to reduce hotspots from the heater in the region between the inlet of the air heater and the outlet from the cellular airflow guide structure <NUM>. This is of importance to achieve uniform air temperatures at the outlet of the cellular airflow guide structure <NUM>, thereby achieving uniform drying across the hair section within the chamber <NUM>. It also prevents the formation of hot spots in the air, which could damage the hair. Accordingly, without such baffles it may be necessary to reduce the hair heating power and therefore reduce the drying speed of the device.

The airflow splitter <NUM>, which is aligned across the diameter of the cylindrical part <NUM>, is arranged to split the incoming airflow into separate upper and lower airflows, which feed directly into the first and second conduits <NUM>, <NUM>. Advantageously, the shape of the airflow splitter <NUM> is such as to guide the air into the first and second conduits <NUM>, <NUM> without causing whistling from the air, thereby providing acoustic benefits.

More particularly, part <NUM> has a circular cross-section, the lower half of which (beneath the airflow splitter <NUM>) corresponds with the cross-sectional geometry of the first conduit <NUM>. The upper half of part <NUM> (above the airflow splitter <NUM>) corresponds with the cross-sectional geometry of the second conduit <NUM>. As shown in cross-section in <FIG>, as the second arm <NUM> is brought into the closed position the second conduit <NUM> fits snugly around the upper half of part <NUM>, so that airflow can pass through the part <NUM>, below and above the airflow splitter <NUM>, into the first and second conduits <NUM>, <NUM>, without leaking.

Thus, as shown in <FIG>, the air enters the first and second conduits <NUM>, <NUM> in a first direction D1 that is substantially parallel to the length of each of the first and second arms <NUM>, <NUM>.

As also shown in <FIG>, and in perspective longitudinal cross-section in <FIG>, the airflow guide structure <NUM> in each of the first and second arms <NUM>, <NUM> includes a cellular structure comprising a plurality of cell walls. In the illustrated embodiment the cellular structure has a hexagonal (honeycomb) structure, although such a geometry is not essential and other geometries (for example as illustrated in <FIG>) may be used instead. However, a hexagonal (honeycomb) structure has been found to be beneficial in maximising the open area through the guide structure <NUM> whilst minimising the area occupied by the cell walls, and thereby minimising airflow resistance due to the cell walls. In the illustrated embodiment the cell width is about one tenth the cell length.

It should be noted that the depth of the cells of the airflow guide structure <NUM> into the respective conduit/plenum chamber <NUM>, <NUM> progressively increases with distance along the respective arm <NUM>, <NUM>, in the direction away from the hinge <NUM>, towards the distal tip of the device. By virtue of this arrangement, incoming air in the first direction D1 is steered from the first direction D1 to a second direction D2 that is substantially perpendicular to the first direction D1, inwardly towards the inter-arm chamber <NUM> that is formed by the arms <NUM>, <NUM> in the closed position.

More particularly, the gradual change in the depth of the cells of the airflow guide structure <NUM> into the respective plenum chamber <NUM>, <NUM> advantageously causes the incoming airflow in direction D1 to turn and exit from the plenum chamber in direction D2 and enter the inter-arm chamber <NUM> with uniform airspeed.

<FIG> also shows that, when the arms <NUM>, <NUM> are in the closed position, the inner face of each airflow guide structure <NUM> is offset from an imaginary centreline midway between the first and second arms <NUM>, <NUM> by a distance of <NUM> - <NUM> (preferably about <NUM>). The position of the imaginary centreline is where hair <NUM> under tension will span the inter-arm chamber <NUM> in use (e.g. as shown in <FIG>). This offset of each airflow guide structure <NUM> from this imaginary centreline creates an airflow restriction between the air and hair in use, to increase the speed of the airflow around the hair, to increase drying.

The airflow guide structure <NUM> also includes a plurality of airflow redirecting channels <NUM>, which extend between longitudinal edges and corresponding longitudinal sides of the airflow guide structure <NUM>, as shown most clearly in <FIG>. These channels <NUM> are configured to convey the flow of air from the second direction D2 to third and fourth directions D3, D4 that are outward from the apparatus, substantially perpendicular to the length of the arms <NUM>, <NUM>, the fourth direction D4 being opposite to the third direction D3. <FIG> also illustrates airflow directions D3 and D4. Incidentally, as shown in <FIG>, the airflow guide structure <NUM> including the cellular (e.g. honeycomb) structure and the airflow redirecting channels <NUM>, along with the outward vents <NUM> in the third and fourth directions D3, D4, may be integrally formed as a unitary structure, e.g. by 3D printing.

Turning now to <FIG>, this illustrates further directions of airflow though the arms <NUM>, <NUM> of the device <NUM> when viewed in transverse cross-section, facing towards the body part <NUM> of the device.

Starting in the centre of <FIG>, the air flowing in direction D2 can be seen entering the inter-arm chamber <NUM> from the plenum chambers <NUM>, <NUM> via the cells of the airflow guide structures <NUM>.

The air is then spread sideways and enters the airflow redirecting channels <NUM>, from which the air then passes along airflow conduits 19a, 19b, 21a and 21b to leave the device via vents <NUM> in opposing directions D3 (via conduits 19a and 21a) and D4 (via conduits 19b and 21b). As shown in <FIG>, airflow conduits 19a, 19b, 21a and 21b respectively extend behind the heater plates 20a, 20b, 22a and 22b that are mounted on the first and second arms <NUM>, <NUM>.

For completeness, it should be noted that, although the directions of the airflow D3 and D4 upon leaving vents <NUM> may be said to be "substantially perpendicular" to the length of the arms <NUM>, <NUM>, the overall path followed by the air as it passes through the airflow redirecting channels <NUM> and along airflow conduits 19a, 19b, 21a and 21b, and then through the vents <NUM>, is not linear.

Advantageously, the vents <NUM> direct the outgoing air towards the roots of the hair, to dry the roots and create root lift.

<FIG> is a transverse cross-sectional view corresponding to that of <FIG>, through the arms <NUM>, <NUM> of the device <NUM> in the closed configuration (around hair <NUM>) and facing towards the body part <NUM> of the device. Looking along channels <NUM> and <NUM> in the direction of the body part <NUM>, features of the cylindrical part <NUM> can be seen, including the diffuser grille <NUM> and the elongate baffles <NUM> end-on. Other features of <FIG> correspond to those identified in <FIG> and described above.

<FIG> and <FIG> illustrate (in perspective longitudinal and transverse cross-sectional views respectively) airflow directional changes due to the airflow guide structure <NUM> and other features in each of the arms <NUM>, <NUM> of the device <NUM>.

As noted above, the first airflow direction D1 is substantially parallel to the length of each of the first and second arms <NUM>, <NUM>, as the air passes the baffles <NUM> and enters the first and second conduits (plenum chambers) <NUM>, <NUM> in the respective first and second arms <NUM>, <NUM>. Then the cellular airflow guide structure <NUM> directs (i.e. steers) the flow of air from the first direction D1 to the second direction D2 inwards into the inter-arm chamber <NUM> that is formed by the arms <NUM>, <NUM> in the closed position, through which the hair <NUM> passes in use.

The air is then spread sideways and enters the airflow redirecting channels <NUM>, from which the air then passes along airflow conduits 19a, 19b, 21a and 21b behind the heater plates to leave the device via vents <NUM> in opposing directions D3 and D4.

The expressions "to dry hair", "drying hair" and the like, as used herein, should be taken to refer primarily to the removal of "unbound" water that exists on the outside of hair when wet. Such "unbound" water should be contrasted with "bound" water, which exists inside individual hairs, and which can be interacted with when heat styling hair. There is no requirement to remove this "bound" water when drying hair in the context of the present invention, although removal of some bound water may occur during the drying process. Further removal of bound water usually occurs during the styling process.

<FIG> is a graph of hair sample temperature against drying time, useful for understanding the technical principles associated with the present work. As the temperature of the hair is increased, the hair goes through a warming-up period and then first and second drying periods, as set out below. The first drying period relates primarily to the removal of unbound water, and the second drying period relates primarily to the removal of bound water.

In the present work the inventors have considered the following problems (amongst others) and have provided the following solutions thereto:.

The inventors have determined that, in general, drying hair with heated air is an inefficient use of energy, although traditional hair dryer technology is efficient at converting electrical energy to a high temperature airflow. Moreover, using heated air alone to dry hair is very inefficient, with most of the energy being lost in hot air to the atmosphere. To dry hair faster, traditional hair dryers have used higher air pressures and large volume flow rates by employing increasingly high speed motor and fan technologies with air heating to increase drying rates. However, this leads to reduced energy inefficiency, increased unit costs and increased noise levels.

On the other hand, using conductive heating plates is a very efficient way of heating water and hair to dry, helping to increase a quick-drying, compact and quiet product. However over temperatures of ~<NUM>-<NUM> (nominally) liquid water in contact with the metal plates causes an audible sound of cavitation (sizzle), which causes a perception of damage. Hair temperatures over <NUM> can lead to the denaturation of hair.

A possible solution to this would be to combine heated air blowing though conductive heater plates, but this would present an additional challenge by creating very high airflow resistance. This would require inefficient high-speed motor technologies to achieve the airflow pressures needed to pass hair through the hair and plates).

The solution provided by the present work is to enclose hair within a heated air plenum chamber <NUM> between conductive heater plates 20a, 20b, 22a, 22b. This enables the hair to be efficiently heated to evaporate more quickly toward the phase change temperatures of water with plate temperatures of ~<NUM>-<NUM> (nominally <NUM>) to avoid cavitation and damage. Moreover, heated plenum temperatures of <NUM>-<NUM> (nominally <NUM>) enables us to efficiently support and maintain phase change and evaporation without cavitation.

The inventors have determined that hair, and wet hair in particular, has a large variation in airflow resistance, depending on the size and water content of the section. A solution is therefore needed to avoid excessive temperature rise (hair damage) and large variations in air heater power and fan pressure requirements.

The solution provided by the present work is that the plenum chamber <NUM> enclosed around the hair enables heated air to pass around the hair (not just through the hair section), reducing the range of airflow resistance of the system. This helps to reduce the heater power and range in power requirements to regulate the air temperature, thereby increasing energy efficiency and reducing product size and cost.

By reducing the range of resistance in the airflow requirements of the system this also in turn enables lower speed motors/fans to be used, helping to increase the energy efficiency of the fan, and to reduce sound and cost.

Moreover, by designing system resistance to accurately meet the airflow and temperature requirements to dry hair when closed, this enables the product's air temperature when open to be cooler, thereby helping to improve the drying experience to the user and reducing losses of energy, and reducing the physical size of the air heater which would otherwise make the product bigger and less easy to use.

The inventors have determined that achieving uniform air temperature and speed across the hair-to-air interface is beneficial to maintain drying efficiency. However to achieve this within the context of the present product form requires a method to turn the air, with uniform air speed and pressure at the hair-to-air interface.

The solution provided by the present work is the provision of an airflow path that incorporates various features for guiding or steering the airflow, as follows:.

The inventors have determined that achieving uniform air temperature across the air stream can be difficult if air heater windings are placed on the outer perimeter of an air duct (as is conventional practice). This causes the air temperature to be higher on the outer perimeter of the air stream relative to the centre of the air stream, giving a non-uniform distribution of heat across the air stream.

The solution provided by the present work is to place features in the air stream on the outside of the ring of the heater outlet, or inside the airflow, such as the baffles <NUM>, to cause turbulence in the heated airflow and promote better mixing of air in the air stream before passing the airflow splitter <NUM>. As a result, a more uniform air temperature profile across the air stream can be achieved.

The inventors have determined that it is desirable to dry hair at the roots, e.g. with a view to creating root lift.

The solution provided by the present work is to provide air outlet vents <NUM> at the side and/or rear of the conductive heater plates 20a, 20b, 22a, 22b. These vents <NUM> direct the outgoing air towards the roots of the hair, to dry the roots and create root lift.

The inventors have determined that plate cavitation (sizzle) with very wet hair over around <NUM>-<NUM> is a limitation to drying speed.

The solution provided by the present work is based on the realisation that as the unbound water on the hair evaporates, the plate temperature can be elevated to higher temperatures, to heat and dry hair faster and more efficiently.

Accordingly, a method is provided to measure the level of unbound water on the hair (moisture sensing), to enable the plate and/or air temperatures to be increased to accelerate the drying rate further. This may be done by providing temperature sensors in the device <NUM>, for example in the following locations:.

A very large temperature difference between these sensors will indicate the arms <NUM>, <NUM> are open, as the air will not be channelled past location B. The state of the arms <NUM>, <NUM> being open can also be sensed by measuring the electrical power needed to elevate the air temperature, as the airflow system resistance will also change between the states of being open, closed, and closed with hair in.

The thermal loading of the plates in location C will indicate that hair is in the product (from power and/or temperature sensing).

A high temperature difference between the sensors will indicate water is evaporating (drying hair) and thus the hair is wet. On the other hand, a low temperature difference between the plates will indicate minimal phase change is occurring, so the hair is "dry".

As noted above, the inventors have determined that increasing the heater plate temperature in response to the presence of unbound water in hair enables faster drying. However if the user moves the device to a wetter section of hair the product's plates will ideally need to cool very quickly to prevent cavitation (sizzle) and or hair damage.

The present work provides a solution to this problem based on actively cooling the heater plates with air (from the fan) that passes over the plates. This enables accelerated cooling of the plates back down to <NUM>-<NUM>. The air temperature can be controlled for example using an NTC (negative temperature coefficient) device and TRIAC control of the air heater.

A PTC (positive temperature coefficient) heater may also be beneficial to enabling a simple and compact conductive heater with an air heat sink.

The inventors have determined that it can be advantageous to regulate the maximum temperature rise to hair when the air outlet is restricted with hair during loading, to prevent hair damage, and/or to minimise energy losses to the atmosphere, to deliver cooler feeling air to the user. It is also desirable to regulate the air temperature to achieve fast drying and minimal hair damage.

The present work provides a solution to this problem by placing a NTC (negative temperature coefficient) device at the air heater outlet, between the air heater and hair contact surface, with a preferred location closest to the hair interface at the outlet nozzle. This enables the NTC to respond to changes in airflow resistance caused by hair restriction or increased temperature differences caused by increased airflow resistance when the arms are open. TRIAC control can be used to regulate the power to the air heater if an upper temperature limit is reached.

The inventors have determined that users may wish to get a freshly washed and blow dry feeling to their hair on days when they do not have the time, ability or inclination to wash and dry their hair.

The present work provides a solution to this problem by enabling a fragrance to be emitted into the air stream generated by the device <NUM>, to give the hair a fresh smell. To achieve this, a user-replaceable piezo-atomiser and/or a simpler fragrance reservoir and wick may be used to enable phase exchange (liquid to gas) into the air stream and thence onto the user's hair.

The inventors have determined that mains powered electrical air heaters are typically heated wire resistors formed to maximise the heated surface area in the air stream. This also adds complexity, size and cost, due to the requirement for a thermal fuse.

The present work provides a solution to this problem by recognising that a PTC (positive temperature coefficient) heater can enable a new form of air heater that merges the cellular (e.g. honeycomb) airflow guide structure <NUM> with an air heater, as a single product part. Thus, this merges the functionally of the two parts, making the overall product smaller and more compact. Moreover, because of the PTC effect, this can also negate the need for an additional thermal fuse (and the associated cost).

The inventors have determined that consumers desire products that are suitable for "on the go" use, e.g. away from home, or in any event away from plug sockets (e.g. in the bathroom).

By virtue of the above-described energy savings, the present work enables a low voltage (LV) device <NUM> to be used for safe operation in the bathroom, and/or enables the device <NUM> to be used cordlessly (e.g. with a rechargeable battery) and/or a compact isolated power supply.

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.

In the embodiments described above, each of the first and second arms <NUM>, <NUM> contains a respective airflow conduit <NUM>, <NUM> and is provided with a respective airflow guide structure <NUM>. However, in alternative embodiments, only one of the arms <NUM>, <NUM> may be provided with an airflow conduit and airflow guide structure <NUM>. Examples of such variants will be described below and are illustrated by way of example in <FIG>, <FIG> and <FIG>. In yet other variants, the airflow guide structure(s) <NUM> may be omitted altogether.

In the embodiments described above, heater plates are provided symmetrically on either side of each arm <NUM>, <NUM>. However, as those skilled in the art will appreciate, it is not necessary that both these plates be heated, and in alternative embodiments only one plate may be heated, or neither of the plates may be heated. The squeegeeing effect of the plates may be sufficient in some circumstances to dry the hair in combination with the airflow, without either or both the plates being heated. Furthermore, unheated plates may be used to apply tension to the hair to provide a degree of styling. However, having at least one heater plate is preferred as it helps with the drying/styling process. Moreover, using a pair of heater plates, as in the embodiments described above, advantageously allows for bidirectional/ambidextrous use of the device.

In the embodiments described above, the airflow guide structure <NUM> in each of the first and second arms <NUM>, <NUM> comprises a cellular structure having hexagonal (honeycomb) cells, configured to direct the flow of air from the first direction D1 to the second direction D2. However, in alternative embodiments, the cells of the airflow guide structure may be different shapes. For example, <FIG> shows an perspective longitudinal cross-sectional view of an alternative cellular airflow guide structure 24a, in this case having rectangular cells in one linear dimension (with the depth of the cells progressively increasing with distance along the structure, in the same manner as the hexagonal cells described above). As another example, <FIG> shows a perspective longitudinal cross-sectional view of another alternative cellular airflow guide structure 24b, in this case having rectangular cells in two linear dimensions (again with the depth of the cells progressively increasing with distance along the structure).

In the embodiments described above, the airflow is heated, e.g. by a heater element in the body <NUM> of the device, downstream of the fan <NUM>. However, in alternative embodiments the means for heating the airflow may comprise the airflow guide structure <NUM> itself, the airflow guide structure being formed of a material that generates heat on application of an electric current thereto. In other alternative embodiments the device may not heat the air, relying instead on delivering air at a sufficiently high flow rate to dry the hair.

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.

Further alternative features in relation to the embodiments described above have been developed to address particular additional problems or to provide particular additional functionality. These further alternative features (and, as applicable, the particular problems they address or the additional functionality they provide) will now be described in detail.

To begin with, in order to achieve rapid drying but also a high quality of styling (i.e. high levels of shine, colour retention and style longevity), hair tresses passing through the active styling area (i.e. the head of the styler) should be subjected to even drying and heating across the width of the tress. To do this well, the following five considerations have been found to be important:.

Safety and quality of the product are also extremely important, of course, and hence the following issues have also been considered and addressed:.

The above points (<NUM>) to (<NUM>) have been addressed through the following further features, as follows:.

In the embodiments described above, the design of the cellular airflow guide structure <NUM> seeks to provide even airflow by using a honeycomb (or other cellular) structure in which the depth of the cells progressively increases towards the distal tip of the device, to effectively "scoop up" more air as it progresses down the length of the head in a direction perpendicular to the depth direction of the cells. While this technique is helpful, with the above-described cellular airflow guide structure <NUM> it has nevertheless been found that a disproportionate amount of the airflow is still emitted near the distal tip of the device.

To illustrate this, <FIG> shows the above-described cellular airflow guide structure <NUM> of the lower arm <NUM> of the device, in which the hexagonal cells are equal in diameter. Aligned with <FIG> illustrates the airflow distribution along the length of the airflow guide structure <NUM> - i.e. the average emitted air velocity at each longitudinal position along the airflow guide structure <NUM>, from the tip end to the handle end along the head of the device. From <FIG> it can indeed be seen that a disproportionate amount of the airflow leaves the airflow guide structure <NUM> near to the distal tip of the device, due to a build-up of airflow towards the tip of the device. This is not conducive to even styling, and will lead to less shine on the hair, and individual strands of hair being blown in unwanted directions (so-called "fly away" hair strands), especially near the tip of the device, due to the greater velocity of the emitted air in that location.

To resolve this issue, and with reference now to <FIG>, in an alternative (improved) airflow guide structure <NUM> the diameter of the honeycomb cells is progressively reduced towards the distal tip of the device, to restrict the airflow. The depth of the cells also progressively increases towards the distal tip of the device, as described above. <FIG> shows the resulting airflow distribution along the length of the airflow guide structure <NUM>, from which it can be seen that a more even distribution of airflow is achieved, with a peak in airflow located around the midpoint of the airflow guide structure <NUM>, i.e. midway between the tip end and the handle end of the head of the device. Such an airflow distribution leads to more even styling, more shine on the hair, and fewer occurrences of individual strands of hair being blown in unwanted directions.

<FIG> provides exemplary dimensions of the hexagonal cells of this alternative airflow guide structure <NUM>. It can be seen that the cells proximal to the handle of the styler have a diameter of <NUM>, the cells around the midpoint of the airflow guide structure <NUM> have a diameter of <NUM>, and the cells near to the distal tip of the device have a diameter of <NUM>. These dimensions are by way of example only, and may be different in other implementations (whilst still progressively reducing the diameter of the cells towards the distal tip of the device). For the sake of completeness, it should be noted that the progressive reduction in the diameter of the cells need not be continuous along the length of the airflow guide structure <NUM>, but may decrease in a stepwise manner, i.e. in discrete stages.

The temperature of the air being passed through the head of the styler should be as even as possible to ensure that drying is even across the tress, to result in better hair fibre alignment and improved shine and style longevity. The above-described structure (e.g. with reference to <FIG>) whereby air passes from part <NUM> into the first airflow conduit <NUM> (provided within and along the first arm <NUM>) and into the second airflow conduit <NUM> (provided within and along the second arm <NUM>) has been found to not provide as even a temperature distribution as would be desirable. This is due to the manner in which the airflow into the conduits <NUM>, <NUM> is created, and the design of the heater - particularly the annular configuration of the heating element which leads to a cooler centre core of the airflow.

The result of this issue is that a difference of over <NUM> in the temperature of the emitted air may be observed from one end of the airflow guide structure <NUM> to the other. For instance, in representative experimental tests, an emitted air temperature of <NUM> was measured near to the proximal end of the airflow guide structure <NUM> (i.e. close to the handle), a temperature of <NUM> was measured around the midpoint of the airflow guide structure <NUM>, and a temperature of <NUM> was measured near to the distal end of the airflow guide structure <NUM>, near to the tip of the device.

A similar situation is illustrated in <FIG>, in which heated air is emitted near the distal end of the airflow guide structure <NUM>, and cool air is emitted at the proximal end of the airflow guide structure <NUM>. This is due to the annular configuration of the heating element <NUM> (within a heater assembly <NUM>) which causes regions of heated air to be generated adjacent to the heating element <NUM>, and a cooler central core of air to be generated between the heated regions.

In passing, it should also be noted that <FIG> (and subsequently <FIG>, <FIG> and <FIG>) show a variant of the first arm <NUM> in which all the incoming airflow is directed along the first airflow conduit <NUM>, and thence through the airflow guide structure <NUM>. That is to say, in this example, the second arm <NUM> does not comprise a second airflow conduit for delivering air to the head of the styler (but may nevertheless comprise an airflow guide structure in communication with the inter-arm chamber <NUM>, for receiving the air emitted from the first arm <NUM>). Conversely, in another variant, all the incoming airflow may be directed along the second airflow conduit <NUM>, within the second arm <NUM>, and none along the first arm <NUM>. Such variants may enable easier manufacture of the overall device, and may also improve airflow performance, as they avoid having opposing airflows from the first and second conduits <NUM>, <NUM> coming into conflict with one another and causing turbulence within the inter-arm chamber <NUM>, and moreover provide a well-defined "escape route" for moisture-laden air.

With reference to <FIG>, the above issue of uneven temperature distribution may be addressed by providing an airflow mixer <NUM>, in this case in the form of an airflow diverter or splitter, near to the end of the heater assembly <NUM>, before the airflow conduit <NUM>. The airflow mixer <NUM> causes the heated air (from adjacent to the heating element) to mix with the cooler central core of air, to provide a more evenly heated flow of air along the airflow guide structure <NUM>. The airflow mixer <NUM> may be generally tapered or conical in shape, as illustrated, or some other shape so as to cause turbulence and mixing of the air within the airstream.

By virtue of the airflow mixer <NUM> removing or reducing the cool core of air, the temperature difference of the emitted air from one end of the airflow guide structure <NUM> to the other can be considerably reduced. For instance, in comparative experimental tests in which the airflow mixer <NUM> was present, an emitted air temperature of <NUM> was measured near to the proximal end of the airflow guide structure <NUM> (i.e. close to the handle), a temperature of <NUM> was measured around the midpoint of the airflow guide structure <NUM>, and a temperature of <NUM> was measured near to the distal end of the airflow guide structure <NUM>, near to the tip of the device. Accordingly, in this case, the difference in temperature from one end of the airflow guide structure <NUM> to the other was only <NUM>.

<FIG> is a perspective view of the heater assembly <NUM> as present within <FIG>, showing the airflow mixer <NUM> in the centre. Similarly, <FIG> is a transverse plan view of the heater assembly <NUM> of <FIG>, and also showing a representation of the heating coils <NUM>.

In the embodiments described above and as illustrated in <FIG>, for example, the root lifting vents <NUM> are located along either side of the head of the styler head and extend parallel to the plane of the heater plates 20a, 20b, 22a, 22b.

However, with reference now to <FIG>, further development work has found that improved lifting of the roots of the hair may be achieved if the air leaves the vents <NUM> at around <NUM>° to the plane of the heater plates 20a, 20b, 22a, 22b, in directions D3' and D4', rather than parallel to the plane of the heater plates. This means the air flow direction D4' is not opposite to D3' on either side of the styler head (unlike directions D3 and D4 shown in <FIG>). Rather, the air flow directions D3' and D4' are at around <NUM>° to each other, on either side of the styler head. Other angles between the air flow directions D3' and D4', emitted from the roof lifting vents, are also possible.

Having the root lifting vents <NUM> oriented at an angle that is not parallel to the plane of the heater plates 20a, 20b, 22a, 22b has been found to be beneficial, as when the root lifting air flow is parallel to the heater plates, it has been found to create "fly away" hair strands and reduces alignment of the hair fibres, thus reducing the end result of shine and style longevity. It has therefore been found that an angle of around <NUM>° reduces the creation of "fly away" hair strands, while still providing an angle of flow which makes it easy for the user to create root lift. If the angle is substantially larger than <NUM>°, creating root lift becomes more difficult.

From the cross-sectional illustration of <FIG>, it should also be noted that, in this variant of the head of the styler, the incoming airflow is only along the first airflow conduit <NUM>, from which it passes (in direction D2) through the airflow guide structure <NUM> and into the inter-arm chamber <NUM>. Thus, in this variant, the second arm <NUM> does not comprise a second airflow conduit for delivering air to the head of the styler, but nevertheless includes airflow redirecting channels <NUM> for receiving some of the air emitted from the first arm <NUM> and delivered via the airflow guide structure <NUM> through the inter-arm chamber <NUM>.

From the inter-arm chamber <NUM>, the air is then spread sideways (e.g. by means of angled surfaces <NUM> incorporated within the second arm <NUM>) and enters the airflow redirecting channels <NUM>, from which the air then passes along airflow conduits 19a, 19b, 21a and 21b to leave the device via vents <NUM> in <NUM>° directions D3' (via conduits 19a and 21a) and D4' (via conduits 19b and 21b). As shown in <FIG>, airflow conduits 19a, 19b, 21a and 21b respectively extend behind the heater plates 20a, 20b, 22a and 22b that are mounted on the first and second arms <NUM>, <NUM>.

In the embodiments described above, it has been found that, when the styler is closed with hair between the heater plates, it is possible for air to escape from the distal end of the styler, particularly at the end of the heater plates. This has been found to reduce the drying rate, since less air passes through the hair tress, and also to lead to fibre alignment issues.

However, with reference now to <FIG>, following further development work this issue of escaped air from the distal tip of the styler has been resolved by providing mutually-opposing spring-loaded non-thermally-conductive (e.g. plastic) sealing elements <NUM> on both the top and bottom styler arms <NUM>, <NUM>, at the distal tip of the device. The sealing element <NUM> is flat and also stands proud of the adjacent heater plates (e.g. 20a, 20b) to ensure that, when the heater plates are loaded with hair, the top and bottom sealing elements <NUM> come together to create a seal which prevents air escaping from the tip of the styler along the heater plates. A spring, by means of which each sealing element <NUM> is mounted, allows for varying amounts of hair to be placed between the heater plates and for a seal to still be maintained.

It is desirable that the styler product should have substantially the same performance wherever it is used around the world, even though mains voltages may vary from country to country. Mains voltage variation particularly impacts the temperature of the heated air within the device, since the air is heated using a standard resistive wire heater, and the electrical power consumed by such a heater and converted to heat is a function of voltage. It is therefore desirable to ensure that the energy transferred to the air is the same, regardless of the location of the device around the world, to ensure that the drying rate is the same and the product does not damage the hair fibre.

Control of energy transfer to the air can be achieved in various ways - for example, by varying the fan speed (which is undesirable since it affects the amount of airflow), or by using a variable resistor in the heater (which is also undesirable). Another option, which we have found to work well, is to control the temperature of the heater by means of an electrical switching technique, whilst keeping the fan speed constant. For instance, the number of mains cycles across the heater per second may be controlled using a standard zero-crossing switching technique employing triacs, essentially performing pulse width modulation of the electrical power supplied to the heater. In such a manner the thermal output of the heater element, and the device more generally, can be controlled irrespective of variations in local mains voltage.

For the sake of safety and comfort, air should not be able to flow back onto the user's hand, given that the temperature of the air can be in excess of <NUM>°. In internal tests using an early prototype of the styler, it was found that, when styling, it was possible for hot air to escape from the end of the heater plates closest to the handle/hinge, and that this risked causing discomfort to the user.

To address this issue, and with reference to <FIG> and <FIG>, a ramp-like airflow deflector feature <NUM> (also shown in <FIG>) has been developed for inclusion at the proximal end (i.e. handle end) of each of a pair of heater plates, i.e. either plates 20a and 20b, or plates 22a and 22b, to prevent hot air from escaping backwards towards the user's hand. The ramp-like shape of the deflector <NUM> is important for two reasons: it stops the air from passing backwards, and does not trap the user's hair during styling. In comparison, a standard "block" form would risk creating pinch points that would pull and trap the user's hair. The ramp design of deflector <NUM> prevents this from happening, and also redirects the back-flowing air (that would otherwise escape towards the user) towards the opposing arm of the device, to prevent discomfort to the user's hand.

For safety reasons, the styler device will ordinarily contain a thermostat and a thermal fuse, either of which will cause the device to stop working when tripped (or, in the case of the thermal fuse, when blown). The thermostat is resettable and is designed to protect against accidental blockage of the air inlet to the device, or lack of filter cleaning. If the thermostat is tripped, the device can be used again once it has cooled back down.

However, the thermal fuse blowing is a more permanent issue (requiring the fuse to be replaced), and is designed to protect the device against an uncontrollable catastrophic failure, such as a commutation failure in the triacs driving the air heater. The thermal fuse failing would render the product unusable until the fuse is replaced. Hence, it is not desirable for the fuse to fail during normal and safe use.

In internal tests using an early prototype of the styler, it was found that, when the unit is switched from on to off (i.e. at the end of a period of use) and the internal fan consequently stops, the temperature of the air heating components in the area of the thermostat and thermal fuse could peak to high temperatures. After a number of cycles of operation and an extended period of time, such temperature peaks could cause either the thermostat to trip or the thermal fuse to blow, particularly in the extreme case of blocked filters. (Also both components have a high variance in activation temperature from the nominal activation temperature, and degrade with age. ) Such tripping of the thermostat or blowing of the thermal fuse would cause an undesirable fail in a safe device that is otherwise working normally.

One way of addressing this is to cause the internal fan to continue to operate in a so-called "ramp-down" mode when the device is switched from on to off. Accordingly, the fan would continue to run for a short period of time to reduce the residual heat in the heating components and associated electronics. That is to say, the fan in ramp-down mode would remove the residual heat from the system by causing the passage of a flow of air over said components.

However, it was found that, should someone unplug the device rather than simply switch off the product using its on/off switch, the temperature would peak as previously, since the fan would not enter its ramp-down mode.

With reference to <FIG>, this issue has been resolved by providing an initial airflow splitter <NUM> at the entrance to the heater assembly <NUM>. The airflow splitter <NUM> has a generally tapered or conical shape, to direct incoming airflow from the fan towards the heating coils <NUM> (rather than simply passing along the centre of the heater assembly <NUM>). By specifically directing the incoming airflow over the heating coils <NUM> in this manner, this provides more efficient transfer of heat from the coils <NUM> to the incoming airflow during use. Moreover, since the coils <NUM> are run more efficiently, with more of the heat being transferred from the coils to the incoming airflow, there is less build-up of heat in the coils (and associated electronics) themselves, thus keeping them generally cooler. As a consequence, when the device is switched from on to off, there is less residual heat in the heating system. Accordingly, even if the fan is suddenly turned off, components such as the thermostat and thermal fuse are exposed to less severe peaks in temperature, such that they do not trip or blow.

To illustrate this further, <FIG> shows plots of internal air temperature over time, in the region of the thermostat (lower line) and the thermal fuse (upper line) within a styler device having an airflow splitter <NUM>. The plots span the point when the device is switched from on to off and the internal fan stops. It can be seen that, at the point when the device is switched off and the fan stops, a modest thermal spike of about <NUM> is experienced in the vicinity of the thermostat and thermal fuse, reaching a maximum temperature of about <NUM>. This thermal spike is within the permitted operating temperatures of those components and causes neither component to trip or blow.

By way of comparison, <FIG> shows corresponding plots of internal air temperature over time, in the region of the thermostat (lower line) and the thermal fuse (upper line) within a test styler device that does not have an airflow splitter <NUM>. Again, the plots span the point when the device is switched from on to off and the internal fan stops. It can be seen that, at the point when the device is switched off and the fan stops, a more pronounced thermal spike of about <NUM> is experienced in the vicinity of the thermostat and thermal fuse. A maximum temperature of about <NUM> is reached in the vicinity of the thermal fuse, which may in some cases be sufficient to cause this component to blow. Accordingly, such an issue is prevented by the provision of the airflow splitter <NUM>.

<FIG> also shows the airflow mixer <NUM> from Figures <NUM>-<NUM>, although the airflow mixer <NUM> and the airflow splitter <NUM> need not necessarily both be present. However, synergistic advantages can be realised if the airflow mixer <NUM> and the airflow splitter <NUM> are both present - i.e. in respect of more efficiently heating the incoming air, and delivering the heated air more evenly to the user's hair.

Claim 1:
Apparatus (<NUM>) for drying and styling hair, comprising:
first and second mutually-opposing arms (<NUM>, <NUM>) adapted for movement between an open configuration for receiving a length of wet hair therebetween and a closed configuration adjacent the hair, such that, in use, when the arms are in the closed configuration they form an inter-arm chamber (<NUM>) across which the hair passes, and wherein an airflow conduit (<NUM>, <NUM>) is provided within and along at least one of the first and second arms (<NUM>, <NUM>);
means (<NUM>) for delivering a flow of air along the conduit (<NUM>, <NUM>) in the at least one of the first and second arms (<NUM>, <NUM>), and subsequently into the inter-arm chamber (<NUM>); and
first and second plates (20a, 20b) disposed on the first arm (<NUM>), and respective opposing first and second plates (22a, 22b) disposed on the second arm (<NUM>), wherein the opposing plates (20a, 20b, 22a, 22b) disposed on the first and second arms (<NUM>, <NUM>) are arranged to come together when the first and second arms (<NUM>, <NUM>) are in the closed configuration;
wherein the inter-arm chamber (<NUM>) is located between the first and second plates (20a, 20b, 22a, 22b) of the first and second arms (<NUM>, <NUM>) when the arms are in the closed configuration;
wherein at least one of said plates (20a, 20b, 22a, 22b) comprises means for applying heat to said length of hair in use, when the first and second arms (<NUM>, <NUM>) are in the closed configuration; and
wherein one or both of the arms (<NUM>, <NUM>) further comprises an airflow guide structure (<NUM>) arranged to receive the flow of air from the respective conduit (<NUM>, <NUM>) and to direct the flow of air from a first direction (D1) that is substantially parallel to the length of the respective arm (<NUM>, <NUM>), to a second direction (D2) that is from the respective arm (<NUM>, <NUM>) towards the opposing arm (<NUM>, <NUM>), into the inter-arm chamber (<NUM>).