Field of the Invention

The present invention relates to an apparatus and method for styling hair. The invention has particular although not exclusive relevance to parts of such hair styling apparatus, such as the mechanism by which the arms of such an apparatus can be opened and closed.

Background to the Invention

There exist a variety of apparatus for styling hair, which use heat to effect a change in the shape of hair. The hair styling apparatus heat the hair to above its glass transition temperature, where the hair becomes mouldable. The hair is styled at a temperature above the glass transition temperature; once it has cooled, it generally remains styled until it next becomes wet.

One example of such a hair styler is a hair straightener, which usually comprises a pair of arms hinged at one end and each arm comprising one or more heaters. Each heater comprises a heating element and one or more heating plates. The hair can be sandwiched and clamped between the plates and heated from both sides. Placing hair between two plates can improve styling as heat is applied more evenly to both sides of a tress of hair. In the case of hair straighteners, the hair contacting surfaces of the plates are flat and style the hair in a ‘straight’ configuration while at the elevated temperature. If the surface of the heating plate is corrugated then the styler can crimp the user’s hair. Another example of a device that can be used to style hair is a hair curler (also known as a curling tong) which typically has one or more curved heating surfaces.

Styling with hair straighteners or similar is most effective if only small sections or tresses of hair are applied to the device each time. In order to style a whole head of hair, this means the user must clamp and open the arms many times while moving around the head, which can become tiring for the user - particularly if the force required to close the arms is excessive. However, if the force required to close the arms is too small, then the arms are able to open and close quite easily which can give the user the perception that the apparatus is of low quality.

Summary of the Invention

Accordingly, according to one aspect, the present invention seeks to provide an improved mechanism for the opening and closing mechanism of the apparatus.

The present disclosure also describes an illumination device that can help a computer device determine the orientation of the hair styling apparatus within captured images of the hair styling apparatus as it is being used by the user. This is beneficial as it allows a computer system to track motion of the hair styling apparatus as it is being used - which motion can then be stored and shared with other users or used to control feedback to the user to control the way the user uses the hair styling apparatus.

According to a first aspect of the invention, there is provided a hair styling device comprising: a shoulder; first and second arms, wherein at least the first arm is pivotally coupled to the shoulder such that it is moveable between an open position and a closed position; and spring means with a first end acting on the first arm and a second end acting on the second arm for biasing the arms in the open position.

In some implementations, the spring means comprises a torsion spring. The spring means may comprise one or more springs, such as torsion springs. Torsion springs are advantageously durable and compact.

The torsion spring may also preferably comprise at least one leg configured to act on the first arm and one leg configured to act on the second arm. The torsion spring can therefore act on both the first arm and second arm, to bias them in the open position.

The first arm preferably comprises a cam surface and the spring means acts on the cam surface. This can allow the spring means to slip relative to the cam surface at a particular force and/or displacement, such that the force remains constant after a set displacement.

Preferably, the spring means acts on the cam surface such that the force required to move the arms from the open position to the closed position is regularised over the majority of the displacement between the open and closed positions.

According to a further aspect of the invention, there is provided a hair styling device comprising: a shoulder; first and second arms, wherein at least the first arm is pivotally coupled to the shoulder, such that the arms are moveable between an open position in which hair can be introduced between the arms and a closed position in which the hair is clamped between the arms, at least one of the arms having a heater for heating hair that contacts a hair contacting surface of the heater; and spring means configured to bias the arms into the open position; wherein the spring means acts on a cam surface of the first arm such that an actuation force required to move the arms from the open position to the closed position is regularised between the open and closed positions.

The regularisation of the actuation force required between the open and closed positions can help to improve the ease of use by a user, aiding in the prevention of fatigue.

Preferably the spring means comprises a torsion spring. The torsion spring may comprise at least one leg configured to act on the cam surface of the first arm. This can allow the spring to slip relative to the cam surface.

Preferably the spring means is configured to slip on the cam surface. This can advantageously regularise the actuation force required to move between the open and closed positions. In preferable implementations, the first arm pivots about a pivot axis and the cam surface is located at a distance from the pivot axis, such that the cam surface rotates around the axis. This arrangement can facilitate relative movement between the cam surface and the spring means.

The cam surface may be curved, and preferably the cam surface is convex. This configuration can allow the spring means to remain generally stable as the arms rotate, facilitating slipping of the spring means on the cam surface.

In some implementations, the second arm is configured to pivot relative to the shoulder about a second pivot axis. The two arms in this manner may have independent pivot axes. A twin pivot arrangement can require less hand movement distance to move the arms between the open and closed positions, which can reduce the stretch required by a user.

The spring means may act on a second cam surface of the second arm such that an actuation force required to move the arms from the open position to the closed position is regularised between the open and closed positions.

The spring means may comprise a torsion spring having a first leg acting on the cam surface of the first arm and a second leg acting on the cam surface of the second arm. In this manner, the same spring means can act on both cam surfaces.

The spring means may comprise a second torsion spring. The provision of two torsion springs can improve the symmetry and stability of the arrangement. Further to this aim, preferably the torsion springs are positioned symmetrically with respect to a central axis of the device.

In preferable arrangements of the hair styling device, each torsion spring comprises two legs and one leg of each torsion spring acts on a cam surface of the first arm, and the other leg of each torsion spring acts on a cam surface of the second arm. This arrangement can improve the stability as each spring acts on both arms, and each arm is acted upon at two locations either side. Any irregularity of force is less likely to disrupt the pivoting motion to a large extent.

Preferably, the spring means is in tension when the arms are in the open position. This keeps the arms in an open configuration when the user does not exert a force on the arms.

In preferable implementations, the force required to move the arms from the open position to the closed position is regularised between 1.5N and 1.9N, preferably between 1.6N and 1.8N, more preferably at approximately 1.7N.

The shoulder may comprise one or more stop formations configured to limit movement of the first and/or second arms. This can aid in preventing over-rotation of the arms. The hair styling device may further comprise a pivot pin via which the first arm is pivotally coupled to the shoulder. Preferably, the hair styling device may further comprise a second pivot pin via which the second arm is pivotally coupled to the shoulder. These provide the two pivot axes about which the arms rotate.

Preferably, the hair styling device further comprises a rigid housing. This can protect the components, such as heating components and electronics.

In preferable implementations, the first arm and the second arm each comprise a heater for heating hair that contacts a hair contacting surface of the heater. The heater can be used to style hair.

The hair styling device may further comprise a printed circuit board (PCB) comprising light emitting diodes (LEDs). These can be used for general illumination and/or to convey information.

Preferably, the PCB comprises LEDs of more than one colour. This can aid in conveying information; this may include tracking movements of the hair styling device.

The hair styling device may further comprise a light guide configured to transmit light emitted from the LEDs to a rim on an external surface of the device. This can aid in transmitting and diffusing the light, to provide more uniform illumination.

According to a further aspect of the invention, there is provided an illumination apparatus for a hair styling device comprising: a plurality of light sources; a light guide having a first end adjacent to the light sources and a second end on an external surface of the hair styling device; and a controller configured to control the light sources; wherein the light sources, the controller and the light guide are arranged so that different portions of the second end of the light guide are illuminated in different ways.

The light sources can convey information via the different ways in which they illuminate the different portions. For example, this may facilitate a computer vision system identifying and tracking the orientation of the hair styling device. The different ways may include different light patterns, for example frequency of intermittent illumination and/or brightness. It may comprise different colours.

The light sources may be of more than one colour, and wherein the different portions of the second end are illuminated in different colours. This can allow the different portions to be distinguished.

The controller may be configured to control the light sources to generate light having a different brightness in the different portions or light that varies in time in a different manner in the different portions. Preferably, the light sources are Light Emitting Diodes, LEDs. These are light, compact and energy efficient.

In preferable implementations, the light guide comprises a plurality of portions, each comprising a respective first end adjacent one or more light sources and a respective second end corresponding to a different one of said portions. The portions of the light guide may transmit different light arrangements.

The second end preferably comprises a rim which forms an external surface of the hair styling device. This can display the illumination.

The different portions may form a rim that extends round a handle of the hair styling device. This can facilitate tracking of the movement of the handle, when a user is styling with the device. Preferably, the different portions comprise a first half of the rim and a second half of the rim.

The rim is preferably a diffuser that diffuses the light from the light sources. This can spread the light over a greater area.

The hair styling device may comprise a cable connector that extends through the rim.

The light guide may comprise a plurality of ridges that mesh with ridges on the cable connector to secure the cable connector to the rim. This improves the stability of the connection, and can hinder or prevent relative rotation.

Preferably, the controller and the light sources are located in a housing, and the light guide extends from inside the housing to outside of the housing. This arrangement can allow the light sources to be protected within the housing, while the light is still displayed on the outside of the housing.

In preferable implementations, the first end of the light guide is configured to engage with a feature within the housing to secure the light guide to the housing. This can improve the stability of the arrangement.

The light guide preferably comprises one or more recesses or slots that mesh with one or more ridges inside the housing to prevent the light guide from rotating within the housing. This may be important so that the different ways of illumination are correctly aligned with the portions.

The illumination apparatus may form part of the hair styling device as described above.

According to a further aspect of the invention, there is provided a hinge joint comprising: a shoulder; first and second arms, wherein at least the first arm is pivotally coupled to the shoulder such that it is moveable between an open position and a closed position; and spring means with a first end acting on the first arm and a second end acting on the second arm for biasing the arms in the open position. The provision of a spring with two ends acting on each of the arms can reduce the hand movement distance required by a user to move the arms from the open position to the closed position, minimising hand movement and stretch, and the likelihood of fatigue.

The hinge joint may be provided in a hair styling device as described above.

Brief Description of the Drawings

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

Figure 1a illustrates a hair styler;

Figure 1 b illustrates a user using the hair styler on their hair;

Figure 2a is a perspective view of the hair styler in an open configuration;

Figure 2b is a perspective view of the hair styler in a closed configuration;

Figure 3 is an exploded view of the hair styler shown in Figure 1 ;

Figure 4a is an exploded view of a connector cable and shoulder casing of the hair styler shown in Figure 1 ;

Figure 4b is a perspective view of the connector cable and shoulder casing in an assembled state;

Figure 4c is a further perspective view of the connector cable and shoulder casing in the assembled state;

Figure 4d is a front view of the connector cable and shoulder casing in the assembled state;

Figure 5a is an exploded view of a shoulder assembly that is housed within the shoulder casing illustrated in Figure 4;

Figure 5b is a perspective view of the shoulder assembly shown in Figure 5a, in an assembled state;

Figure 6a is a perspective view of the shoulder assembly mounted within the shoulder casing;

Figure 6b is an exploded view of the assembled shoulder assembly and shoulder casing illustrating how the shoulder assembly is mounted within the shoulder casing;

Figure 7 is an exploded view of the arms and a pivot mechanism that is used to hingedly couple the proximal end of each arm to the shoulder casing;

Figure 8 is a perspective view of the arms when coupled to the shoulder casing (shown in phantom) and illustrating the action of springs between the arms and the biasing mechanism to bias the arms in the open configuration; Figure 9a is an exploded view of the shoulder casing, shoulder assembly and proximal ends of the arms;

Figure 9b is a partially assembled view showing an interaction between the ends of a pair of springs and cam surfaces on the proximal ends of the two arms;

Figure 10a is a partial cross-section view of the styler in an open configuration;

Figure 10b is a partial cross-section view of the styler in a closed configuration;

Figure 11 is a force-displacement plot for the hair styler shown in Figure 1 ; and

Figure 12 is a force-displacement plot for a prior art hair styler.

Detailed Description of Preferred Embodiments

The embodiments described below 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.

Overview of hair styler

Figure 1 a illustrates a hair styler 1 . The hair styler 1 includes a first movable arm 4a and a second movable arm 4b, which are hingedly coupled at proximal ends thereof to a shoulder 2. The first and second movable arms 4a, 4b oppose one another and are movable relative to one other by virtue of the hinged connection to the shoulder 2. Thus, the first and second arms 4a, 4b can be brought together, into a closed configuration, or moved apart, into an open configuration, by a user during use. Figure 2a shows the hair styler 1 in the open configuration, and Figure 2b shows the hair styler 1 in the closed configuration.

The first arm 4a bears a first heating plate 6a at its distal end, and the second arm 4b bears a second heating plate 6b at its distal end. The first and second heating plates 6a, 6b oppose one another and are brought together as the first and second arms 4a, 4b are moved from the open configuration to the closed configuration. They are also separated as the first and second arms 4a, 4b are moved from the closed configuration to the open configuration. Hair can be clamped between the heating plates 6a, 6b when the arms 4a, 4b are brought together - as illustrated in Figure 1 b.

As will be described in more detail below, the shoulder 2 includes spring means configured to bias the first and second arms 4a, 4b into the open configuration, such that the user is required to apply pressure to the arms 4a, 4b to close them together, and such that the arms 4a, 4b automatically open once the pressure is removed. This means that hair is automatically released from the plates 6a, 6b when the user is not actively applying pressure, which can provide more control to the user and assist in preventing accidental damage to the hair. The electrical and electronic circuitry of the hair sty ler 1 is housed in the first arm 4a. The electrical and electronic circuitry of the hair styler 1 could instead be housed in the second arm 4b, or could be split between the arms 4a and 4b.

A switch 8 may be provided on the first arm to enable the styler 1 to be turned on and off. A user interface may also be provided. The user interface may include a light to indicate whether the power is on. A sound can also be played by a sound generator when the styler 1 is switched on and ready to use. In alternative embodiments the user interface may include additional components (such as, for example, a display means, to provide the user with more information on the operational status of the styler and/or a user input means to allow the user to set, for example a desired operating temperature). The hair styler 1 may be battery powered, although in this embodiment is powered by mains electricity, typically 110V or 230V, and is connected to the mains supply by means of an electrical cable 3. Electrical power from the battery or the mains supply is used to heat the heating plates 6a, 6b for styling the user’s hair.

Figure 1 b illustrates the styler in use: the hair is clamped between the two heating plates 6a, 6b and then the styler is moved such that the hair is pulled through the styler 1 between the first and second heating plates 6a, 6b. Heat passes from hair contacting surfaces of the heating plates 6a, 6b into the hair to allow the styling of the user’s hair using the device. The hair is heated above its glass transition temperature, after which the shape of the hair can be manipulated. By passing and clamping the hair between two plates 6a, 6b which have flat faces, the hair can be ‘straightened’. Alternatively, hair can be wrapped around the arms 4a, 4b of the styler and clamped between the plates 6a, 6b, such that when the styler is pulled downwards through the hair, the hair can be ‘curled’. Alternatively, the styling device may have corrugated plates, in which case the hair is ‘crimped’ when clamped between the two plates or curved plates to create waves. The hair styler 1 may comprise a barrel-shaped ‘tong’ or ‘wand’ around which hair can be wrapped, and a corresponding clamp configured to fit around the ‘tong’ and clamp the hair around it. In this manner, the hair can be styled in curls or waves.

Shoulder overview

Figure 3 shows an exploded view of the shoulder 2, the arms 4a, 4b and cable connector 36 used in a preferred embodiment. The shoulder 2 comprises a shoulder casing 32, pivot pins 30a, 30b, printed circuit board (PCB) 28, light guide 34 (in two parts 34a, 34b), collar 26, springs 20-1 , 20-2, frame 24, and inner casing 22.

Figures 4a to 4d show the shoulder portion of the hinge mechanism in detail. The shoulder casing 32 is a generally Y-shaped or ‘wishbone’-shaped component. The shoulder casing has a generally arcuate shape to fit between the two arms 4a, 4b, this arcuate shape forming the top portion of the ‘Y’ shape. At the base of the ‘Y’, the shoulder casing 32 curves into a generally circular aperture 320, through which a cable can be passed to provide power to electronic elements of the device such as the heating elements and the PCB 28. On each branch of the ‘Y’, the inner surface of the shoulder casing 32 comprises a plurality of inwardly extending tabs - including the pairs of inner tabs 326a and 326b and the pairs of outer tabs 324a, 324b. As will be described in more detail below, the inner tabs 326a, 326b are positioned to define stops that limit the range of motion of the arms in the closed configuration whilst the outer tabs 324a, 324b provide a coupling point for coupling the arms 4a, 4b to the shoulder 2. As shown in Figure 4, the outer tabs 324a, 324b comprise holes 3242a, 3242b through which a pivot pin 30a, 30b can be extended. The shoulder casing 32 is preferably formed of a rigid plastic, ceramic or metallic material; it may be formed of a plastic or ceramic material with a metallic coating. The rigidity of the shoulder casing 32 helps to protect the elements enclosed within.

In the illustrated embodiment, a cable connector 36 is used to provide electrical power to the hair styler 1. The cable connector 36 comprises an electrical connector head 360 which ends in a connector pin 368 extending from the connector body 366. The connector pin 368 acts as an electrical connector and is configured to sit within a socket (not shown) of the device. Extending from the connector body 366 in a different orientation is an electrical cable 362 which joins the connector 36 to a plug (not shown) for connecting to an electric socket. At the point of connection between the connector body 366 and the cable 362, the cable is wrapped in a cable protector 364.

A light guide 34 is formed of two parts 34a and 34b of transparent or translucent rigid plastic material, which fit together to form a generally cylindrical shell configured to fit around the electrical connector head 360. The light guide 34a, 34b is configured to carry light from LEDs 284 that are mounted on the PCB 28. The light guide 34a, 34b preferably comprises slots 342 configured to receive or accommodate ridges 322 which are located on the inner surface of the shoulder casing 32 adjacent to the generally circular aperture 320. The respective orientations of the slots 342 and ridges 322 locates the light guide 34a, 34b, and thereby the connector 36, within the shoulder casing 32. This arrangement prevents the light guide 34 and the shoulder casing 32 rotating with respect to one another once assembled. As an alternative to slots (which comprise completely cut-out portions), grooves (regions in which the wall has reduced thickness) could be provided on the light guide 34a, 34b to achieve the same purpose.

At the proximal end of the light guide 34 closest to the connector body 366, the inner surface comprises a pattern of ridges and grooves 340 which interleave with corresponding ridges and grooves on the connector head 360 to secure the connector 36 to the shoulder casing 32.

The light guide 34 further comprise a thicker edge 344 at its distal end (furthest from the connector 36) which provides a larger surface area to collect light emitted by the LEDs 284 on the PCB 28. At the proximal end, the light guide 34 comprises a further rim 346, which protrudes radially outwards from the surface. When assembled, the rim 346 sits between the shoulder casing 32 and the connector 36 - as shown in Figure 4b. The light guide 34 guides light emitted from the LEDs 284 on the PCB 28 to the outer rim 346, where the light diffuses and can be seen by the user. The assembled state of the shoulder casing 32, light guide 34 and connector 36 is shown in Figures 4b and 4c. In order to assemble these components, the two parts of the light guide 34a, 34b are placed around the connector head 360. The corresponding ridges and grooves on the inner surface of the light guide 34 and the outer surface of the connector head 360 prevent axial movement of the connector head 360 relative to the light guide 34. Once the connector head 360 is encased, the arrangement is placed within the shoulder casing 32. The ridges 322 on the inner surface of the shoulder casing 32 fit within the slots 342 of the light guide 34 as the connector head 360 assembly is slid into the shoulder casing 32. The raised edge 344 of the light guide 34 interlocks with a lip 325 on the inside of the shoulder casing 32 (as can be seen in Figures 4c and 4d) - in order to secure the light guide 34 and connector 36 to the shoulder 2.

Shoulder assembly

Figures 5a and 5b show the components of a shoulder assembly 200 of the hair sty ler 1 , in an exploded view and an assembled view, respectively. The shoulder assembly 200 comprises two helical torsion springs 20-1 , 20-2, a frame 24, a collar 26 and printed circuit board (PCB) 28. Figures 6a and 6b illustrate how the shoulder assembly 200 is mounted within the shoulder casing 32.

As illustrated in Figure 5a, torsion spring 20-1 comprises a continuous metal wire formed into a central coil 202-1 and two legs 204-1 a, 204-1 b at either end of the coil 202-1. In an unbiased configuration, the angle between the two legs 204-1 a, 204-1 b is between about 50 and 90 degrees, preferably at 60 to 70 degrees, more preferably at 65 to 67 degrees, and most preferably at 66 degrees. Each leg 204-1 a, 204-1 b has a smooth and flat end so that it can interact with the arms (in the manner discussed below). This can be provided, as is illustrated, by a ‘folded’ (or ‘bent’) arrangement to minimise the weight. The bends on each leg 204-1 a, 204-1 b of one torsion spring 20-1 are preferably mirrored reflections of one another so that any asymmetry of shear forces is also mirrored.

The frame 24 comprises a central body 244, which has a general ring shape. Fingers 242a, 242b extend from opposite sides of the central body 244 such that they form a gently curving ‘U’ shape, with the ring of the central body 244 forming the lower portion of the ‘U’.

Extending parallel to the axis of the ring of the body 244 is a shank 246 on one side, and a neck 248 on the opposite side. The shank 246 extends into the space created by the ‘U’ of the fingers 242a, 242b, while the collar extends in the other direction. The shank comprises protrusions 2462 which extend perpendicular to the plane formed between the fingers 242a, 242b, which are configured to hold the torsion springs 20-1 , 20-2. The protrusions 2462 comprise a recess to accommodate the torsion springs 20-1 , 20-2 and clips 2464 to secure them. The neck 248 comprises a ring-shaped collar from which extends a first formation 2482 adjacent one finger 242a and a second formation 2484 adjacent the other finger 242b, configured to engage with the other components of the shoulder assembly.

The collar 26 has a ring-shaped body 260 comprising a flange 264 configured to sit adjacent to a face 2444 of the frame 24 and be secured by a lip 2446 which surrounds it. The collar 26 further comprises components to secure the engagement with the frame 24. In the illustrated embodiment it comprises a ledge 262 which extends perpendicular from the plane of the ring-shaped body 260, for engagement with a recess 2442 on the frame 24.

The PCB 28 is formed as a generally ring-shaped component configured to fit within the collar 26. It comprises a body 280 which is formed as a flat ring, and comprises formations configured to engage with the collar 26 and the frame 24 for securement. In the illustrated embodiment, a pin 286 is configured to align with and fit within the recess 2442 on the frame 24.

Figure 5b illustrates the torsion springs 20-1 , 20-2, frame 24, collar 26 and PCB 28 in an assembled configuration. The torsion springs 20-1 , 20-2 fit over the protrusions 2462 on the shank 246 and are held in place by the clips 2464. The flange 264 of the collar 26 fits around neck 248 of the frame 24 and sits flush against the face 2444. The PCB 28 sits within the collar 26 flush against the flange 264, also surrounding the neck 248 of the frame 24. The connector pin 286 of the PCB 28 sits on top of the ledge 262 of the collar, which itself fits within the recess 2442 of the frame.

Illuminated Rim

The PCB 28 comprises a plurality of light sources (such as Light Emitting Diodes, LEDs) 284 located around the ring-shaped body 280. The PCB 28 may also comprise a controller 288 (such as a microprocessor or CPU) for controlling the operation of the LEDs 284, although the controller 288 may be mounted on a main control board elsewhere in the hair styler 1. In the illustrated embodiment, the PCB 28 comprises four LEDs 284-1 to 284-4 whose positions are aligned with the four thicker edges 344 of the light guide 34 so that light emitted from the LEDs 284 will be guided by the light guide 34 to the rim 346 of the light guide 34. Preferably, there are at least two LEDs 284 on the PCB 28, although there could of course be many more. The LEDs 284 may be monochromatic LEDs or multi-colour LEDs. The controller 288 controls the LEDs 284 so that they emit light in different manners. This may comprise the light being emitted in different patterns, intermittently at different frequencies, or may comprise emitting light having at least two different colours. In the preferred embodiment, LEDs 284-1 and 284- 2 are configured to produce light of a first colour (red for example) and LEDs 284-3 and 284-4 are configured to produce light of a second colour (green for example). The light from LEDs 284-1 and 284-2 couples into the upper light guide 34b and the light from LEDs 284-3 and 284-4 couples into the lower light guide 34a. Thus, when the LEDs are illuminated, the rim 346 of the light guide 34 will have its upper half illuminated in one colour of light and will have the lower half illuminated in a second different colour. This arrangement is particularly useful for helping a computer vision system (not shown) identify and track the orientation of the hair styler 1 as the user is using it to style their hair.

More specifically, the applicant has described in an earlier patent application (WO2019/122838 - the contents of which are hereby incorporated by reference) the benefit of being able to track the user’s use of the hair styler - for the purposes of teaching the user how to use the hair styler to achieve a desired style. That system can employ a camera to capture images of the user as they use the hair styler. Whilst it is possible to process the images to identify the arms of the styler and from that, work out the orientation of the hair styler, having an illuminated rim 346 with multiple different patterns of light at known locations or portions of the rim 346 makes it easier for the computer system to process each captured image to work out the orientation of the hair styler in the captured image. As those skilled in the art will appreciate, having a rim 346 with two halves in different colours allows the computer system to be able to determine the orientation of the styler to a certain level of accuracy. As you increase the number of colours or zones around the rim 346, it is possible to make a more accurate determination of the orientation of the styler. In addition to being useful for determining the orientation of the hair styler, the illuminated ring 346 can also be used to present different information to the user. For example, if all the LEDs are multicolour LEDs, then the controller can control the LEDs so that the rim 346 can be illuminated in red when the device is powered but the heating plates are not up to the desired temperature, and then changed to green when the plates are at the desired temperature for use.

Pivot arrangement

Figure 7 shows an overview of the pivot arrangement of the hair styler 1 that is used to couple each arm 4 to the shoulder 2. Specifically, each arm 4a, 4b of the styler 1 is connected to the shoulder 2 (in the exemplary embodiment to the shoulder casing 32) via a pivot pin 30a, 30b. The pivot pins 30a, 30b extend through holes 40a, 40b on the arms 4 and holes 3242a, 3242b (shown in Figure 4) on the pairs of outer tabs 324a, 324b on the shoulder casing 32. The holes 40a, 40b and 3242a, 3242b are aligned with one another in a direction perpendicular to the length of each arm 4a, 4b such that they define a pivot axis for each arm 4a, 4b.

Figure 7 shows an enlarged (detailed) view of a section at the proximal end of the upper arm 4b. Although not shown in detail the proximal end of the lower arm 4a has a corresponding (mirror) configuration. As shown in Figure 7, the proximal end of arm 4b forms a connector 42b comprising two fingers 420b, 430b. On the external face of each finger 420b, 430b (the side facing away from the axis of the pivot) is a cam surface 422b, 424b. In the illustrated embodiment, each cam surface 422b, 424b has a curved portion 4222 over which the upper legs 204-1 b, 204-2b of the torsion springs 20-1 , 20-2 slide when the arm 4b pivots around the pivot pin 30b. Specifically, as the arm 4b moves from the open configuration to the closed configuration, the upper legs 204-1 b, 204-2b of the torsion springs slip down the curved cam surface 4222 and as the arm 4b moves from the closed configuration to the open configuration, the upper legs 204-1 b, 204-2b of the torsion springs slip up the curved surface 4222. A similar sliding motion happens between the lower legs 204-1 a, 204-2a of the torsion springs 20-1 , 20-2 and the corresponding curved cam surfaces 422a, 424a on the lower arm 4a. In order to achieve the same function, it is sufficient for each cam surface 422b, 424b to comprise at least a single point of contact with the legs 204-1 b, 204-2b of the torsion springs, for example at least a single edge. It is simply required that the legs 204-1 b, 204-2b can move in relation to the cam surface 422b, 424b, as the arm 4b moves from the closed configuration to the open configuration.

On the inner side of each cam surface 422b, 424b there is a wall 426b, that helps to prevent the upper legs 204-1 b, 204-2b of the torsion springs 20-1 , 20-2 from slipping off the cam surfaces 422b, 424b laterally.

An inner casing 22 is provided for the shoulder. The inner casing 22 is formed as a U shape and is configured to form the middle of the ‘Y’ or ‘wishbone’ shape of the shoulder casing 32. Ensuring that the mechanism and electrical elements is enclosed within the casing helps to protect the component parts and improves the aesthetics of the hair sty ler 1 .

Assembled hinge mechanism

Figures 8, 9a and 9b illustrate the assembled hinge connection of the shoulder 2 (with the shoulder casing 32 shown in phantom in Figures 8 and 9b). Considering only arm 4b, pivot pin 30b extends through the holes 40b (only one is visible) on the arm 4b and through the holes 3242b on the outer tabs 324 of the shoulder casing 32. One finger 242b of the frame 24 fits between the two fingers 420b, 430b of the connector 42b of the arm 4b. This helps to provide structural rigidity to the hair styler 1 by preventing rotation and yaw motions of the arm 4b relative to the shoulder 2. The other arm 4a is assembled in a corresponding manner.

The extent to which the arms 4a and 4b are able to move away from one another (in the open direction, in which they are biased) is limited by the shank 246 of the frame 24 acting as a stop. Specifically, the limit of rotation is reached when an end surface of the fingers 420a, 430a, 420a, 420b hits with an adjacent face of the shank 246 of the frame 24. The extent to which the arms 4a, 4b are able to move inwardly towards the closed position is limited by the pairs of inner tabs 326a, 326b on the shoulder casing 32 acting as stops. Specifically, the upper surface of the two walls 426b on the fingers 420b, 430b of the upper arm 4b will come into contact with the surface of the inner tabs 326b, preventing further rotation of the arm 4b about the pivot 30b (and similarly for the lower arm 4a). In the preferred embodiment, each arm 4a, 4b can rotate a short distance beyond the central line (as indicated by line ‘X’ in Figures 10a and 10b); for example, 3 degrees past the central line, X.

Movement of styler arms

Figures 10a and 10b show the hair styler 1 in an open configuration and a closed configuration, respectively. As each arm 4a, 4b rotates around its own pivot pin 30a, 30b, with the movement of each of the arms being independent of the shoulder 2. The shoulder 2 remains in the same configuration and the arms 4a, 4b rotate relative to it.

The torsion springs 20-1 , 20-2 act on the proximal ends of the connectors 42a, 42b of the arms 4a, 4b to bias the arms in the open configuration. When the arms 4a, 4b are in their open configuration, the torsion springs 20-1 , 20-2 are already in tension. When a user presses the arms 4a, 4b together to bring together the plates 6a, 6b, the user’s force overcomes the bias provided by the torsion springs 20-1 , 20-2 and the arms 4a, 4b rotate around the pivot pins 30a, 30b relative to the shoulder 2. However, as a result of the ends 204-1 a, 204-1 b, 204-2a, 204-2b of the torsion springs 20-1 , 20-2 sliding over the curved cam surfaces 4222 on the proximal ends of the fingers 420a, 420b, 420a, 430b, the angle between the legs of the torsion springs, 204-1 a and 204-1 b, and204-2a and 204-2b, remain at approximately the same angle with respect to one another and therefore the force required by the user to close the arms 4a and 4b remains substantially constant over the length of travel from the open configuration to the closed configuration.

Figure 11 is a force displacement plot showing the variation in the force felt by the user when moving the arms from their open configuration to their closed configuration and from their closed configuration back to their open configuration. The plot starts in the lower left corner - with zero force and zero displacement. As the user starts to apply force to the arms 4, there is an initial part of the plot where the applied force overcomes the biasing force of the tension springs and then the arms begin to move towards their closed configuration. As the ends of the torsion springs start to slide over the curved cam surfaces on the proximal ends of the two arms, the closing force remains substantially constant (A) over the majority of the displacement until the arms are closed at which point the force plot increases sharply as the user squeezes the arms together. When the user starts to release their force on the arms 4a, 4b, the plot drops back down to force B, over the majority of the displacement between the arms being in their closed configuration and their open configuration. As the arms 4 reach their fully open position, the force drops again to zero. The opening force, A, is higher than the closing force, B, due to energy lost to friction (the system exhibits hysteresis). The difference between the closing force A and opening force B is indicated as C in Figure 11 .

Figure 12 shows a similar force displacement plot for a prior art styler comprising a leaf spring between the shoulder and each arm. As can be seen in Figure 12, the force required to move the arm between the open and closed configurations increases substantially linearly over the range of motion. The gradient of the force-displacement plot is determined by the spring constants of the leaf springs. If a low spring constant is chosen, the force required by a user to close the plates completely is manageable, but the arms are susceptible to a lot of unwanted movement in the arms when in open configuration - which can give the impression that the styler is poor quality. If, on the other hand, a large spring constant is chosen, the arms are more stable, but a much greater force is required to close the arms - which can lead to fatigue for the user. In contrast, the styler described above has a force-displacement plot which has a steeper gradient initially, due to the pre-tensioning of the torsion springs 20-1 , 20-2. This ensures the arms remain stable when in the open configuration, giving the impression of good quality. When the closing force A is reached, the force required to close the arms then remains approximately constant over the majority of the range of motion between the open and closed configurations. As discussed above, this is achieved by providing the curved cam surfaces 422a, 424a, 422b, 424b over which the ends of the torsion springs 20-1 , 20-2 can slide.

The force required to move the arms 4a, 4b from an open configuration to a closed configuration (closing force A) is preferably between 1.5N and 1.9N, more preferably between 1.6N and 1.8N, and most preferably approximately 1.7N. If the device is battery powered, then the closing force, A, may be greater than this due to the additional mass of the arm with the battery.

The force difference between the closing and opening actions, indicated by C, is typically in the region of 0.7N. This is larger than for the prior art system, indicated by Cx in Figure 12. This is because the invention of the present invention exhibits greater hysteresis as energy is lost to frictional forces as the torsion springs 20-1 , 20-2 slide over the cam surfaces 422a, 424a, 422b, 424b. By contrast, in the prior art system, the user does work predominately against the leaf springs and the frictional losses are smaller as the springs do not slide against a surface of the arms.

Modifications and Alternatives

As those skilled in the art will appreciate, various modifications and alternatives can be made to the above described control system and method.

In the above embodiment, two torsional springs were provided acting between the two arms. In an alternative embodiment, a single torsion spring may act between the two arms. In another embodiment, one torsional spring may act between the shoulder and one arm and another torsional spring may act between the shoulder and the other arm.

In the above embodiment, the pivot mechanism included a pivot pin that extended through holes in the end of the arms and holes in tabs of the shoulder. In alternative embodiments, there may be no pivot pins. Instead, the shoulder may comprise stubs which engage with corresponding recesses (or holes) on the arms; or, the arms may comprise stubs which engage with corresponding recesses (or holes) in the shoulder. The stubs and recesses (or holes) would be aligned on the same pivot axis (corresponding to the location of the pivot pins of main embodiment described above).

Furthermore, the hinge mechanism described above can be implemented in other devices employing at least two arms, such as devices for ironing and/or steaming clothes. Similarly, the illuminated rim described above can be provided on other hair styling devices - including those having a single styling arm. No doubt many other effective alternatives will occur to the skilled person. It will 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.

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.