WO2017167733A1

WO2017167733A1 - A hair cutting device

Info

Publication number: WO2017167733A1
Application number: PCT/EP2017/057286
Authority: WO
Inventors: Kiran Kumar THUMMA; Rieko Verhagen; Yannyk Parulian Julian BOURQUIN; Bastiaan Wilhelmus Maria Moeskops
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2016-03-29
Filing date: 2017-03-28
Publication date: 2017-10-05
Anticipated expiration: 2018-09-29

Abstract

There is provided a hair cutting device for cutting hair on a body of a subject, the hair cutting device comprising a light source for generating laser light at one or more specific wavelengths corresponding to wavelengths absorbed by one or more chromophores in hair; a cutting element that comprises an optical waveguide that is coupled to the light source to receive laser light, wherein a portion of a sidewall of the optical waveguide forms a cutting face for contacting hair, wherein the cutting face has a coupling liquid applied thereto for improving the coupling of laser light from the optical waveguide to hair that contacts the cutting face. The coupling liquid forms a meniscus between the optical waveguide and hair that contacts the cutting face.

Description

A HAIR CUTTING DEVICE

FIELD OF THE INVENTION

The invention relates to a hair cutting device for cutting (e.g. shaving) hair on a body of a subject, and in particular relates to a hair cutting device that uses laser light to cut or shave hair.

BACKGROUND OF THE INVENTION

Shaving devices for cutting or shaving hair on a body of a subject typically make use of one or more blades that cut hairs as the blade is moved across the skin of the subject. The blades can be static within the device, for example as in a wet razor, whereas in other types of devices, for example electric shavers, one or more blade elements can be actuated (e.g. rotated or oscillated) in order to produce a cutting action.

However, an alternative type of shaving device has been proposed in WO 2014/143670 that makes use of laser light. In particular a laser light source is provided that is configured to generate laser light having a wavelength selected to target a predetermined chromophore to effectively cut a hair shaft. A fiber optic is located on a shaving portion of the device that is positioned to receive the laser light from the laser light source at a proximal end, conduct the laser light from the proximal end toward a distal end, and emit the light out of a cutting region of the fiber optic and toward hair when the cutting region is brought in contact with the hair.

SUMMARY OF THE INVENTION

To achieve good shaving performance, the volume of hair that is heated by the light should be minimised, and the intensity of the light should be high enough to effectively melt/burn/cut the hair.

A normal bare core optic fibre has an evanescent field but the intensity is typically not sufficient to cut or melt hairs. When the hair is in contact with the core, total internal reflection is violated and light is coupled from the core to the hair. However, the out coupling of light is still not sufficient to cut/melt hairs. One of the reasons for this is due to poor contact between the core and the hair. Therefore there is a need for a hair cutting device in which the coupling of light from the fibre to the hair is improved in order to provide a better cutting (melting) action.

Therefore, according to a first aspect, there is provided a hair cutting device for cutting hair on a body of a subject, the hair cutting device comprising a light source for generating laser light at one or more specific wavelengths corresponding to wavelengths absorbed by one or more chromophores in hair; a cutting element that comprises an optical waveguide that is coupled to the light source to receive laser light, wherein a portion of a sidewall of the optical waveguide forms a cutting face for contacting hair, wherein the cutting face has a coupling liquid applied thereto for improving the coupling of laser light from the optical waveguide to hair that contacts the cutting face. In other words: the cutting face is coated with the coupling liquid to improve the out coupling of light from the optical waveguide. The coupling liquid forms a meniscus between the optical waveguide and hair that contacts the cutting face.

In some embodiments, the coupling liquid has a refractive index that is selected to enable laser light to couple from the optical waveguide to the hair.

In some embodiments, the coupling liquid has a refractive index that is the same as the refractive index of hair.

In alternative embodiments, the coupling liquid has a refractive index that is equal to or between the refractive index of the optical waveguide and the refractive index of hair.

In some embodiments, the refractive index of the coupling liquid is equal to or around 1.56, optionally equal to or around 1.55, optionally equal to or around 1.54.

In some embodiments, the refractive index of the optical waveguide at the cutting face is equal to or lower than 1.56, optionally equal to or lower than 1.55, optionally equal to or lower than 1.54.

In some embodiments, the refractive index of the optical waveguide at the cutting face is equal to or higher than 1.48, optionally equal to or higher than 1.51, optionally equal to or higher than 1.53 or optionally equal to or higher than 1.54.

In some embodiments, the coupling liquid is, or comprises, Ethyl Cinnamate.

In some embodiments, the coupling liquid is transparent or substantially transparent to light at the one or more specific wavelengths.

In some embodiments, the coupling liquid has a viscosity in the range of 0.1 Centipoise to 50000 Centipoise. In some embodiments, the coupling liquid has a thickness that is less than 50 microns. In some embodiments, the coupling liquid has a thickness that is less than 25 microns, or less than 5 microns.

In some embodiments, the optical waveguide comprises a core, and wherein the cutting face is a portion of the side wall of the core.

In some embodiments, the optical waveguide is an optical fibre.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

Fig. 1 is a block diagram of a hair cutting device according to an embodiment of the invention;

Fig. 2 is a pair of schematic drawings showing different views of an exemplary hair cutting device according to an embodiment of the invention;

Fig. 3 is a graph illustrating the refractive index of hair;

Fig. 4 is an illustration of an optical fibre cutting element having a coating or coupling liquid according to a specific embodiment; and

Fig. 5 is an illustration of a meniscus formation of coupling liquid around a hair.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As noted above, the present invention provides an improvement in coupling of light to hair in a laser light-based shaving device, for example as described in WO

2014/143670. In particular, it has been recognised that by applying a coating or coupling liquid to the optic fibre cutting element (and in particular to a part of the optic fibre that forms a cutting face), the coupling of laser light from the optic fibre to hair that contacts the optic fibre can be improved. It will be appreciated that the invention is applicable to shaving devices (e.g. razors or electric shavers), and any other type of device that is used to cut hair (e.g. hair clippers), even if those devices do not necessary aim to provide a 'clean shave' (i.e. to remove hair at the level of the skin). Fig. 1 is a block diagram of a hair cutting device 2 according to an

embodiment of the invention. Fig. 2 shows a hair cutting device 2 in the form of a handheld razor according to an exemplary embodiment of the invention. The hair cutting device 2 is for cutting (e.g. shaving) hair on a body of a subject. The subject may be a person or an animal. The hair may be facial hair (i.e. hair on the subject's face), or hair on the subject's head or other part of their body (legs, chest, etc.).

The hair cutting device 2 comprises a cutting element 4 that enables hair to be cut as the hair cutting device 2 is moved over the skin of a subject. The cutting element 4 is an optical waveguide 4 that is arranged on the hair cutting device 2 so that the optical axis of the optical waveguide 4 (i.e. the line along which light typically propagates through the optical waveguide 4) is generally perpendicular to the direction in which the hair cutting device 2 is moved so that hairs contact the side wall of the optical waveguide 4 (the side wall corresponding to the long edge of the optical waveguide 4) as the hair cutting device 2 is moved across the skin of the subject. In some embodiments, the optical waveguide 4 is an optical fibre, although those skilled in the art will be aware of other types of optical waveguide that can be used according to the invention, such as a slab waveguide, a strip waveguide or a photonic crystal waveguide. An optical fibre comprises a core, and in some embodiments also comprises a cladding, which may or may not fully encompass the core (e.g. part of the core may be exposed).

A light source 6 is provided in the hair cutting device 2 that generates laser light at one or more specific wavelengths. The light source 6 is optically coupled to the optical waveguide 4 so that the laser light generated by the light source 6 is coupled into the optical waveguide 4 (and specifically coupled into an end of the optical waveguide 4 so that the laser light propagates through the optical waveguide 4).

The light source 6 is configured to generate laser light at one or more specific wavelengths that can be used to cut or burn through hair. In particular, each wavelength corresponds to the wavelength of light absorbed by a chromophore that is found in hair. As is known, a chromophore is the part of a molecule that provides the molecule with its colour. Thus, the laser light will be absorbed by the chromophore and converted into heat which will melt or burn the hair or otherwise destroy the bonds in the molecules of the hair, and it is this melting or burning that provides the cutting action of the hair cutting device 2.

Suitable chromophores that can be targeted by the laser light generated by the light source 6 include, but are not limited to, melanin, keratin and water. Suitable

wavelengths of laser light that can be used include, but are not limited to, wavelengths selected from the range 380 nm (nanometers) to 500 nm and 2500 nm to 3500 nm. Those skilled in the art will be aware of the wavelengths of light that are absorbed by these chromophores, and thus also the specific wavelengths of light that the light source 6 should generate for this purpose, and further details are not provided herein.

In some embodiments the light source 6 can be configured to generate laser light at a plurality of wavelengths (either simultaneously or sequentially), with each wavelength being selected to target a different type of chromophore. This can improve the cutting action of the optical waveguide 4 since multiple types of molecules in the hair may be burnt using the laser light. Alternatively multiple light sources 6 can be provided that each generate laser light at a respective wavelength, and each light source 6 can be coupled to a respective optical waveguide 4 to provide multiple cutting elements 4 in the device 2.

The hair cutting device 2 also comprises a control unit 8 that controls the operation of the hair cutting device 2, and in particular is connected to the light source 6 to control the activation and deactivation of the light source 6 (and in some embodiments control the wavelength and/or intensity of the light generated by the light source 6). The control unit 8 may activate and deactivate the light source 6 in response to an input from a user of the hair cutting device 2. The control unit 8 can comprise one or more processors, processing units, multi-core processors or modules that are configured or programmed to control the hair cutting device 2.

As noted above, Fig. 2 shows a hair cutting device 2 that is in the form of a handheld wet razor. Fig. 2 shows a side view and a bottom view of the razor 2. The razor 2 comprises a handle 10 for the subject (or other user of the device 2) to hold, and a head portion 12 that includes the cutting element 4 (optical waveguide/fibre). As shown, the optical waveguide 4 is arranged along an edge of the head portion, and a part of the optical waveguide 14 forms (or corresponds to) a cutting face 14. The cutting face 14 is the part of the optical waveguide 14 that is intended to come into contact with hair as the hair cutting device 2 is moved across the skin of the subject. A light source 6 and control unit 8 are shown as being incorporated into the head portion 12 and handle 10 respectively, but it will be appreciated that the positions of these components in the hair cutting device 2 as shown in Fig. 2 is not limiting. Likewise it will be appreciated that the embodiment shown in Fig. 2 is merely an example, and the invention can be incorporated or used in any type of hair cutting device 2 that conventionally comprises a blade for physically cutting or slicing hair (whether the blade is static or actuated in order to achieve a cutting action). The graph in Fig. 3 illustrates the refractive index of hair, which can be found in a paper by M. D. Greenwell, A. Willner, Paul L. Kirk: Human Hair Studies: III. Refractive Index of Crown Hair, 31 Am. Inst. Crim. L. & Criminology 746 (1940-1941). Curve 1 is a composite line, curve 2 is a line representing the refractive index for Caucasian people, and curve 3 is a line representing the refractive index for non-Caucasian people. Thus, it can be seen that the refractive index of hair is between (approximately) 1.545 and 1.555, although there will be variation between individuals. For example the above paper also recognises that the refractive index of hair can depend on the sex of the subject, e.g. the refractive index of hair on a female is generally higher than the refractive index of hair on a male.

As is known, the optical waveguide 4 acts as a waveguide for the light coupled from the light source 6 through the occurrence of total internal reflection, since the refractive index of air is lower than that of the optical waveguide 4. However, if an object that has a refractive index higher than the optical waveguide 4 is put into contact with the optical waveguide 4, then the total internal reflection is 'frustrated' and light can couple from the optical waveguide 4 into that object. Thus, in order for light to be coupled into a hair from the optical waveguide 4 (to provide the cutting action according to the invention), the optical waveguide 4 must have the same or a lower refractive index than hair at the point at which the hair contacts the optical waveguide 4. Thus, the optical waveguide 4 must have the same or a lower refractive index than hair at least at the cutting face 14 portion of the optical waveguide 4. Preferably the refractive index of the optical waveguide 4 at the cutting face 14 is the same as that of hair since that provides the best coupling of light from the optical waveguide 4 to the hair.

Thus, in some embodiments, the refractive index of the optical waveguide 4 at least at the cutting face 14 is equal to or lower than 1.56. More preferably the refractive index of the optical waveguide 4 at least at the cutting face 14 is equal to or lower than 1.55. Even more preferably, the refractive index of the optical waveguide 14 at least at the cutting face 14 is equal to or lower than 1.54, since this refractive index is below the refractive indices identified in Fig. 3. In some embodiments, a lower bound for the refractive index of the optical waveguide 4 at the cutting face 14 can be 1.48, 1.51, 1.53 or 1.54.

A range of values from which the refractive index of the optical waveguide 4 is selected can be formed from any combination of the upper and lower refractive index bounds set out in the preceding paragraphs. The optical waveguide/fibre 4 can be made from any suitable material or combination of materials. For example optical waveguides/fibres can be composed of or comprise silica, fluoride glass, phosphate glass, chalcogenide glass, and/or crown glass (such as BK7).

As noted above a normal bare core optic fibre or waveguide has an evanescent field but the intensity is typically not sufficient to cut or melt hairs. When the hair is in contact with the core, total internal reflection is violated and light is coupled from the core to the hair. However, the out coupling of light is still not sufficient to cut/melt hairs. Therefore, it has been recognised that a coating or coupling liquid on the optical waveguide 4 (and particularly on the cutting face 14) can improve the coupling of laser light from the optical waveguide 4 to hair that contacts the optical waveguide.

Fig. 4 illustrates an exemplary embodiment of the cutting element 4 (optical waveguide 4) according to the invention. In Fig. 4, only the optical waveguide 4 part of the hair cutting device 2 is shown, and the optical waveguide 4 is shown side on (i.e. looking down the optical axis of the optical waveguide 4), and no support structure for the optical waveguide 4 is shown.

In Fig. 4, an optical waveguide 4 is shown that has a core 16. In this illustrated embodiment, the optical waveguide 4 does not include any cladding around the core 16. However it will be appreciated that in some embodiments the optical waveguide 4 can comprise cladding around the core 16, although preferably no cladding is present along the cutting face 14 (and indeed, in some embodiments the cutting face 14 can correspond to those parts of the optical waveguide 4 where there is no cladding).

The optical waveguide 4 is shown in contact with a hair 18 and the skin 20. The portion of the side wall of the core 16/optical waveguide 4 that is intended to contact hairs during use forms the cutting face 14. As described above, the refractive index of the core 16 is the same or lower than the refractive index of hair.

The core 16 may have a uniform refractive index (i.e. the same refractive index throughout the core 16), or it may be a graded index fibre, which means that the refractive index decreases with increasing distance from the optical axis.

A coating or coupling liquid 22 is applied to the core/optical waveguide 4, at least on a part of the cutting face 14, so that hair 18 is in contact with the optical waveguide 4 via the coating or coupling liquid 22. The coating or coupling liquid 22 is provided to improve the coupling of laser light from the optical waveguide 4 to hair 18. Preferably, the refractive index of the coating or coupling liquid is selected to enable laser light to couple from the optical waveguide 4 to the hair 18. In some embodiments, the coating or coupling liquid 22 has a refractive index that is the same as or similar to the refractive index of hair. In some embodiments the coating or coupling liquid 22 has a refractive index that is the same as or just above the refractive index of the optical waveguide 4, or that is between the refractive index of the optical waveguide 4 and the refractive index of hair 18.

Therefore, while in contact with the hair 18 at cutting face 14, the laser light is coupled through the cutting face 14 and coating or coupling liquid 22 into the hair 18 as the refractive index of the core 16 at cutting face 14 is smaller than the refractive index of the coating or coupling liquid 22 and the hair 18.

In some embodiments, the coating or coupling liquid 22 has a refractive index that is or is around 1.56 (e.g. between 1.555 and 1.565). In some embodiments, the coating or coupling liquid 22 has a refractive index that is or is around 1.55 (e.g. between 1.545 and 1.555). In some embodiments, the coating or coupling liquid 22 has a refractive index that is or is around 1.54 (e.g. between 1.535 and 1.545). In some embodiments, the coating or coupling liquid 22 has a refractive index that is between 1.52 and 1.56.

When the hair 18 is in contact with the coating or coupling liquid 22 and optical waveguide 4, the coating or coupling liquid 22 creates and acts like a liquid 'bridge' between the waveguide 4 and the hair 18, and thus the out-coupling of light into the hair 18 is increased compared to a bare waveguide 4.

Fig. 5 is an illustration of the formation of a light bridge by a coating or a coupling liquid 22 when an optical waveguide 4 having a coating or coupling liquid 22 on the cutting face 14 is in contact with hair 18. In particular it can be seen that due to the capillary effect and surface tension, the coating or coupling liquid 22 forms a meniscus 24 between the waveguide 4 and the hair 18. This meniscus 24 has the effect of increasing the surface area of the contact between the hair 18 and waveguide 4, thereby increasing the amount of light that can couple into the hair 18.

In some embodiments, the coupling liquid 22 is, or comprises, one or more of an oil, aqueous liquid, emulsion, paste or gel. The coating 22 can comprise or be based on any one or more of the following types of material: Teflon, hydrogel, artificial sebum, fat, a cream, Vaseline, silicone rubber or glycerol. In preferred embodiments the coating or coupling liquid 22 is, or comprises, Cinnamate oil, otherwise known and Ethyl Cinnamate. Other examples of suitable liquids 22 include Refractive Index liquids produced by Cargille (http://www.cargille.com/refractivestandards.shtml). The coating or coupling liquid 22 preferably has a viscosity that is high enough cause the coating or coupling liquid 22 to ' stick' to the hair 18 and optical waveguide 4 and form the meniscus 24, but also low enough to allow the coating or coupling liquid 22 to flow around the hair to form the meniscus 24. The viscosity of the coating or coupling liquid 22 should also be such that coating or coupling liquid 22 re-establishes itself by flow when hair is no longer in contact with the coating or coupling liquid 22. The viscosity of the coating or coupling liquid 22 can be in the range of 0.1 Centipoise (cps) to 50000 cps at room temperature (e.g. ~20°C).

It has been found that an optical waveguide contacting a hair without a coating or coupling liquid results in the hair being heated to around 50°C from the coupling of light (of intensity 1 Watt at a wavelength of 462 nm) from the waveguide to the hair, which is not sufficient to melt the hair. However, with a coating or coupling liquid 22 on the cutting face 14 (and light at the same wavelength and intensity), the improved coupling contact results in the hair being heated to above 150°C, and the hair 18 was observed to be molten.

The coating or coupling liquid 22 is preferably formed as a thin layer on the cutting face 14. The thickness of the coating or coupling liquid 22 should be sufficient to enable initiation of the melting of hair. A minimum thickness for the layer is of the order of the wavelength of the light, e.g. 1 micron. The thickness of the coating or coupling liquid 22 should also be significantly less than the thickness of hair 18, since the hair should 'indent' the coating or coupling liquid 22 and not be immersed in it. The maximum thickness of the coating or coupling liquid 22 can therefore be 50 microns, or preferably 25 microns, or more preferably 5 microns.

Since the hair 18 can be heated to a high temperature (e.g. above 150°C), it will be appreciated that the coating or coupling liquid 22 should have an evaporation point that is above the expected temperature of the hair 18 to avoid the coating or coupling liquid 22 from evaporating during use of the cutting device 2.

In addition, the coating or coupling liquid 22 should be transparent or sufficiently transparent to the wavelength of light in the optical waveguide 4 to allow the light to pass through the coating or coupling liquid 22 and into the hair. The absorption of the light by the coating or coupling liquid 22 should therefore preferably be less than 0.1% over 50 microns of the coating or coupling liquid 22, more preferably less than 0.01% over 50 microns, which corresponds to less than 0.02/centimetre. It will be appreciated that the amount of the coating or coupling liquid 22 present on the cutting face 14 can be depleted over time (for example if some of the coating or coupling liquid 22 is retained on a hair 18 after the waveguide 4 is moved across the hair 18). Therefore, the amount of coating or coupling liquid 22 on the waveguide 4 can be replenished by applying additional coating or coupling liquid 22 to the optical waveguide 4, for example by dipping the waveguide 4 in a reservoir of the coating or coupling liquid 22 or by brushing or otherwise applying coating or coupling liquid 22 to the waveguide 4.

There is therefore provided a hair cutting device in which the coupling of light from the fibre to the hair is improved in order to provide a better cutting (melting) action.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A hair cutting device for cutting hair on a body of a subject, the hair cutting device comprising:

a light source for generating laser light at one or more specific wavelengths corresponding to wavelengths absorbed by one or more chromophores in hair;

a cutting element that comprises an optical waveguide that is coupled to the light source to receive laser light, wherein a portion of a sidewall of the optical waveguide forms a cutting face for contacting hair,

wherein the cutting face has a coupling liquid applied thereto for improving the coupling of laser light from the optical waveguide to hair that contacts the cutting face;

wherein the coupling liquid forms a meniscus between the optical waveguide and hair that contacts the cutting face.

2. A hair cutting device as claimed in claim 1, wherein the coupling liquid has a refractive index that is selected to enable laser light to couple from the optical waveguide to the hair.

3. A hair cutting device as claimed in claim 1 or 2, wherein the coupling liquid has a refractive index that is the same as the refractive index of hair.

4. A hair cutting device as claimed in claim 1 or 2, wherein the coupling liquid has a refractive index that is equal to or between the refractive index of the optical waveguide and the refractive index of hair.

5. A hair cutting device as claimed in any of claims 1 -4, wherein the refractive index of the coupling liquid is equal to or around 1.56, optionally equal to or around 1.55, optionally equal to or around 1.54.

6. A hair cutting device as claimed in any of claims 1 -5, wherein the refractive index of the optical waveguide at the cutting face is equal to or lower than 1.56, optionally equal to or lower than 1.55, optionally equal to or lower than 1.54.

7. A hair cutting device as claimed in any of claims 1 -6, wherein the refractive index of the optical waveguide at the cutting face is equal to or higher than 1.48, optionally equal to or higher than 1.51, optionally equal to or higher than 1.53 or optionally equal to or higher than 1.54.

8. A hair cutting device as claimed in any of claims 1 -7, wherein the coupling liquid is, or comprises, Ethyl Cinnamate.

9. A hair cutting device as claimed in any of claims 1 -8, wherein the coupling liquid is transparent or substantially transparent to light at the one or more specific wavelengths.

10. A hair cutting device as claimed in any of claims 1 -9, wherein the coupling liquid has a viscosity in the range of 0.1 Centipoise to 50000 Centipoise.

1 1. A hair cutting device as claimed in any of claims 1 -10, wherein the coupling liquid has a thickness that is less than 50 microns.

12. A hair cutting device as claimed in any of claims 1 -1 1, wherein the optical waveguide comprises a core, and wherein the cutting face is a portion of the side wall of the core.

13. A hair cutting device as claimed in any of claims 1 -12, wherein the optical waveguide is an optical fibre.