OPTICAL SKIN SENSOR USING OPTIMAL SPECTRAL BANDS TO MINIMIZE THE EFFECT OF PROBE PRESSURE

Abstract

The invention provides a system (1) comprising a sensor (100) for measuring a skin parameter, the sensor (100) comprising a plurality of spatially separated light sources (110) configured to provide light source light (111), and one or more detectors (120) configured at a first distance (d1) from each of the light sources (110), wherein the first distance (d1) is selected from the range of 5-80 mm, wherein the sensor (100) is configured to provide the light source light (111) with optical axes (OL) under an angle (a) relative to an optical axis (O2) of the one or more detectors (120) selected from the range of 10-80, wherein the sensor (100) comprises at least three light sources (110), wherein the light sources (110) are configured to provide unpolarized light source light (111), wherein the system (1) further comprises an analysis system (2) wherein the analysis system (2) is configured to generate a corresponding skin sensor value on the basis of a detector response of the one or more detectors (120) at one or more wavelengths selected from a spectral range of 350-780 nm.

Claims

1. A system comprising a sensor for measuring a skin parameter, the sensor comprising a plurality of spatially separated light sources configured to provide light source light, and one or more detectors configured at a first distance from the light sources, wherein the first distance is selected from the range of 5-80 mm, wherein the sensor is configured to provide the light source light with optical axes under an angle relative to an optical axis of the sensor selected from the range of 10-80, wherein the sensor comprises at least three light sources, wherein the light sources are configured to provide unpolarized light source light, wherein the system further comprises an analysis system wherein the analysis system is configured to generate a corresponding skin sensor value on the basis of a detector response of the one or more detectors at one or more wavelengths selected from a spectral range of 350-780 nm.

2. The system according to claim 1, wherein the analysis system is configured to generate a corresponding skin sensor value on the basis of one or more of a detector response of the one or more detectors in the entire wavelength range of 370-740 nm, a detector response of the one or more detectors at one or more wavelengths selected from the spectral range of 370-420 nm, and a detector response of the one or more detectors at one or more wavelengths selected from the spectral range of 600-650 nm.

3. The system according to claim 1, wherein the analysis system is configured to generate a corresponding skin sensor value on the basis of a detector response of the one or more detectors at one or more wavelengths selected from the spectral range of 370-420 nm, and a detector response of the one or more detectors at one or more wavelengths selected from the spectral range of 600-650 nm.

4. The system according to claim 3, wherein the light sources are configured to provide light source light only at one or more wavelengths selected from the spectral range of 370-420 nm, and at one or more wavelengths selected from the spectral range of 600-650 nm.

5. The system according to claim 1, wherein the analysis system is configured to generate a corresponding skin sensor value on the basis of the detector response of the one or more detectors in the entire wavelength range of 370-740 nm, the detector response of the one or more detectors at one or more wavelengths selected from the spectral range of 370-420 nm, and the detector response of the one or more detectors at one or more wavelengths selected from the spectral range of 600-650 nm.

6. The system according to claim 1, wherein the analysis system is configured to generate a corresponding skin sensor value on the basis of a detector response of the one or more detectors in the entire wavelength range of 350-780 nm excluding the wavelength ranges 440-620 nm and 640-740 nm.

7. The system according to claim 1, wherein one or more detectors are configured for detection of a part of the wavelength range of 350-780 nm.

8. The system according to claim 1, wherein the analysis system is configured to determine the type of skin for measuring the skin parameter, and wherein on the basis of the type of skin, the analysis system is configured to select the one or more wavelengths for generating the corresponding skin sensor value.

9. The system according to claim 1, wherein the sensor further comprises a sensor opening downstream of the light sources and downstream of the detector for propagation of the light source light out of the sensor and for entrance of reflected sensor light into the sensor, and wherein the sensor opening has a circular shape.

10. The system according to claim 1, wherein the detector has a field of view with an equivalent diameter at the sensor opening, wherein the sensor opening has an opening diameter selected from the range of 0.9d5/D21.1, and wherein the opening diameter is at maximum 15 mm.

11. The system according to claim 1, wherein the first distance is selected from the range of 4-20 mm, preferably 8-14 mm, and wherein the angle is selected from the range of 20-60, wherein the detector is configured to detect polarized light, wherein the sensor comprises a polarizer configured upstream of the one or more detectors, and wherein the polarizer comprises one or more of a segmented polarizer and a spatially varying polarizer, wherein the detector comprises a 2D camera, wherein the sensor further comprises a focusing lens configured downstream of the one or more detectors, and an aperture configured downstream of the one or more detectors and upstream of the focusing lens, wherein the aperture has a diameter selected from the range of 0.1-0.8 mm, and wherein the light sources are configured to provide unpolarized white light source light.

12. The system according to claim 1, wherein the device comprises a sensing mode, wherein the light sources are configured to sequentially provide the light source light, wherein the detector is configured to sequentially detect reflected light source light, and configured to generate corresponding detector signals, wherein the analysis system is configured to generate a corresponding skin sensor value in dependence of a sensor signal of the sensor, wherein the skin sensor value is based on an average of respective detector signals, wherein the sensor has a sensor optical axis, and wherein the light sources are configured rotationally symmetric around the sensor optical axis.

13. A method of sensing a skin parameter, the method comprises providing light source light with the system according to claim 1 to a skin and sensing with the system the reflected light source light reflected at the skin.

14. A data carrier having stored thereon program instructions, which when executed by the system causes the system to execute the method according to claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0090] FIGS. 1a-1b schematically depict some aspects of the system;

[0091] FIG. 2 shows an example of the reflectance spectra measured using spectrometer (probe diameter of 6 mm) on Caucasian skin (here skin type II) for different applied pressure; L indicates low pressure, M indicates medium pressure, and H indicates high pressure;

[0092] FIG. 3: shows an example of the changes in the reflectance spectra with respect to the base-line (no or low pressure) measured using a spectrometer on Caucasian skin for medium and high pressure. We have used two probes with inner diameter of 6 and 12 mm for the measurements; L, M, and H are as indicated above, the values 6 and 12 refer to the inner diameter;

[0093] FIG. 4: shows the percentage of changes in the spectral reflectance characteristics with respect to the baseline (no or low-pressure) for different spectral bands. Spectral measurements were performed on Caucasian skin using a spectrometer with a probe diameter of 12 mm; on the y-axis, the % of change in reflectance spectra with respect to a baseline is indicated; the x-axis indicate a number of different spectral bands.

[0094] FIG. 5: shows an example of the reflectance spectra measured using a spectrometer (probe diameter of 6 mm) on skin type II and skin type VI for different applied pressure; L, M and H are again as indicated above; on the y-axis the relative spectral reflectance in arbitrary units is indicated;

[0095] FIG. 6 shows the changes in the number of pixels above a threshold measured using different caps for different applied pressure; here, the pressure is indicated in relative values 100, 200, 300, and 600; on the y-axis the number of counted of pixels is indicated. The closer the values are for different pressures, the more reliable the system is;

[0096] FIG. 7: shows skin doming measured using different caps for different pressures. Caps with internal diameter of 13 and 15 mm results in skin doming less than 2 mm and lower variation in skin doming for different applied pressures; SD refers to the skin doming (in mm); and

[0097] FIG. 8: shows the maximum skin doming measured as a function of the inner diameter of the opening. The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0098] FIG. 1a schematically depicts a system 1 comprising a sensor 100 for measuring a skin parameter (selected from one or more of the group consisting of skin gloss and skin oiliness). The sensor 100 comprises a plurality of spatially separated light sources 110 configured to provide light source light 111, and a detector 120 configured at a first distance d1 from each of the light sources 110. The sensor 100 is configured to provide the light source light 111 with optical axes OL under an angle of incidence a selected from the range of 10-80 with the skin at a third distance d3 and to detect reflected light source light 111. The sensor 100 may especially comprise at least three light sources 110 here, only two are depicted for the sake of understanding, wherein the light sources 110 are configured to provide unpolarized (visible) light source light 111. The first distance d1 may e.g. be selected from the range of 10-80 mm, and wherein the detector 120 is configured to detect polarized light. The dashed line S indicates the skin. Reference 150 indicates a sensor window and reference 151 indicates the sensor window material. The sensor window 150 has a sensor window thickness d4, e.g. selected from the range of 0.1-20 mm. Window 150 is optional.

[0099] The detector 120 may e.g. comprise a 2D camera 101. Further, the sensor 100 may comprise a focusing lens 1O2 configured downstream of the detector 120, and an aperture 103 configured downstream of the detector 120 and upstream of the focusing lens 1O2. The aperture 103 has a diameter D1 selected from the range of 0.1-0.8 mm. The focusing lens may e.g. be an f 5-15 mm, like 10 mm lens. Further, the system may include a second focusing lens, the combination of this lens with the first lens may provide a desired field of view and depth of focus for the overall system (see e.g. FIG. 1A). The light sources 110 are configured to provide unpolarized white light source light 111.

[0100] As indicated in FIG. 1a, the system 1 may further comprise an analysis system 2 wherein the analysis system 2 is configured to generate a corresponding skin sensor value in dependence of a sensor signal of the sensor 100.

[0101] The analysis system 2 may be comprised by a device that also comprise the sensor 100 (see also FIG. 1b), or may be comprised by a separated device. FIG. 1a also schematically depicts such embodiment, wherein the system 1 comprises the a skin care device 3, wherein the skin care device 3 comprises the sensor 100, and a second device 200 functionally coupled to the skin care device 3, wherein the second device 200 comprises the analysis system 2.

[0102] The sensor 100 includes an opening 107. This opening may especially be flat, i.e. its circumference may have an edge that is essentially flat. In this way, the sensor may be configured flat on the skin. The opening 107 may have a diameter D2 or equivalent diameter D2 which may be in the range of about 1-30 mm.

[0103] The opening 107 is available in a housing. The housing comprises the sensor 100.

[0104] D2 especially refers to an inner diameter, as the opening may be formed by a protruding ridge, which may have a larger (equivalent) diameter.

[0105] Reference O2 refers to the optical axis of the sensor 100. When the sensor 100 is configured on the skin, this axis may essentially coincide with a normal to the skin. As the system, more especially the sensor also has an opening 107, the optical axis may be perpendicular to a virtual plane through the opening 107, and penetrate through the center of such virtual plane. Note that the optical axis O2 here also essentially coincides with an optical axis of the detector 120.

[0106] Reference TS indicates a top surface of the sensor. This may be a planar surface. Reference LB indicates a direct light blocker, configured to prevent that light of the light sources may reach the detector without a single reflection and/or which may reduce light reaching the detector 120 that has not been reflected by the skin but by other internal surfaces of the sensor. Reference 104 refers to a polarizer.

[0107] FIG. 1b schematically depicts an embodiment of the system 1, wherein the system 1 comprises a skin care device 3, such as skin cleansing device, skin rejuvenation device, wherein the skin care device 3 comprises the sensor 100 and the analysis system 2. The skin care device 3 may comprise an indication unit IU and/or also a user interface UI. Reference FA indicates a functional area, such as an area that may be used for massaging or exfoliating the skin.

[0108] Experiments were performed on skin type II and skin type VI for different probe pressures (low (L), medium (M), high (H)) using a spectrometer with two caps of inner diameter 6 and 12 mm respectively. Spectral reflectance measurements are obtained while varying the contact pressure of the probe of the spectrometer. It was observed that probe pressure is a variable that affects the local optical properties of the tissue and the spectral reflectance from the skin and the effect of pressure on spectral reflectance is different for different spectral bands. The amount of probe pressure applied on the skin affects the amount of blood and reflectance spectrum in a predictable manner.

[0109] The intensity of the reflected light is decreased at wavelengths lower than 600 nm and is increased at wavelengths higher than 600 nm in comparison with the spectra corresponding to non-pressure against the skin. FIG. 3 shows the percentage of changes in the reflectance spectrum for different spectral bands. The results show that by selecting the optimal spectral bands such as 360-740 nm, 360-420 nm, 600-650 nm it would be possible to reduce the spectral variability in reflectance measurements to less than 1% and thereby the sensitivity and specificity for measuring skin characteristics such as skin oiliness and gloss can be increased.

[0110] Deoxyhemoglobin exhibits absorption maxima at 550 nm and 760 nm, and oxyhemoglobin shows maxima at 548 nm and 576 nm. The spectra shown in FIGS. 2-3 shows the characteristic minima around 540 and 578 nm (W pattern) corresponding to the absorption spectrum of oxy-hemoglobin. The W pattern in the diffuse reflectance spectra is more pronounced in light skin volunteers (FIGS. 3 and 5) than in dark skin ones (FIG. 5) at all the probe pressures applied. We observe that there is no remarkable difference in diffuse reflectance spectra at different pressures in the spectral band around 420 nm due to oxyhemoglobin absorption spectra.

[0111] Several types of caps were investigated, with different dimension and differently shaped openings:

TABLE-US-00001 CAP Area Pressure type Shape (mm.sup.2) (gram) Gram/mm.sup.2 A Small round 77 0, 150, 300 0, 2, 4 B Large round 77 0, 150, 300 0, 2, 4 C Small rectangular 77 0, 150, 300 0, 2, 4 D Large rectangular 77 0, 150, 300 0, 2, 4 11 Small rectangular 344 0, 150, 300, 0, 0.44, but larger surface 600 0.87, 1.74 12 Large rectangular 608 0, 150, 300, 0, 0.25, and larger surface 600 0.49, 0.99

[0112] FIG. 6 shows the changes in the number of pixels above a threshold measured using different caps for different applied pressure. The larger the differences between the number of pixels as function of the pressure, the less desirable the cap is. The phrase Small rectangular but larger surface and similar phrases refer to the opening and the surrounding area (relatively large surface of the surrounding area and the opening is rectangular).

[0113] Experiments were performed for different pressure (low, medium, high) using different cap dimensions. The diameters of the cap were varied from 15 mm to 30 mm. The skin doming was measured using a sensor. Skin doming was measured was calculated as the difference in the profile measured on skin and the profile measured on a flat surface. The maximum skin doming increases with increase in internal beam diameter and was less dependent on other parameters of the contact window such as skin contact area, outer diameter. The depth of focus is desirably to be less than 2 mm. Based on the in-vivo experiments done for different pressures, we conclude that an exit window diameter of less than 15 mm results in a skin doming that is less than 2 mm (FIGS. 7-8). Possible selection criteria for the optimal cap configuration that minimize the effect of pressure is as follows: the maximum doming is less than 2 mm and the minimum variation in skin doming for low, medium and high pressure.

[0114] Hence, herein e.g. skin gloss and oiliness measurement systems and methods using circular exit window with an inner diameter less than 15 mm to minimize the dependence of skin gloss and oiliness value on the applied pressure are herein provided.

[0115] The term substantially herein, such as in substantially consists, will be understood by the person skilled in the art. The term substantially may also include embodiments with entirely, completely, all, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term substantially may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term comprise includes also embodiments wherein the term comprises means consists of. The term and/or especially relates to one or more of the items mentioned before and after and/or. For instance, a phrase item 1 and/or item 2 and similar phrases may relate to one or more of item 1 and item 2. The term comprising may in an embodiment refer to consisting of but may in another embodiment also refer to containing at least the defined species and optionally one or more other species.

[0116] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0117] The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

[0118] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb to comprise and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words comprise, comprising, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of including, but not limited to. The article a or an preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. 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.

[0119] The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

[0120] The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.