WO2005102201A1

WO2005102201A1 - A hair removing device

Info

Publication number: WO2005102201A1
Application number: PCT/IB2005/051235
Authority: WO
Inventors: Robbert A. M. Van Hal; Erik Houbolt; Jasper Zuidervaart; Antonius M. Nuijs; Mathijs Niehaus; Paul A. J. Ackermans; Rieko Verhagen
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-04-26
Filing date: 2005-04-15
Publication date: 2005-11-03

Abstract

The present invention relates to a hair-removing device (1) in which a beam (14) of radiation is focused to a spot (18) for treating hairs to be removed. The focus (18) may be scanned over a part of a skin (20) to be treated by means of a manipulator means (32). The distance between the focus (18) and a window (24) through which the beam exits is held constant. In order to provide optimum skin-window contact and to prevent wrinkles in the skin to be treated, the window (24) is curved in at least one direction. The distance between the focus (18) and the window (24) may be adjusted. The device may provide a more constant focal intensity distribution with a simpler optical system.

Description

A hair removing device

The present invention relates to a hair-removing device having a housing provided with a source of optical radiation and a window transparent to said optical radiation, wherein the device comprises an optical system for projecting said optical radiation through said window as a focused beam with a focus, wherein the device comprises at least one manipulator means for manipulating the direction of the focused beam within a predetermined solid angle, and wherein a distance between the focus and an outer surface of the window is substantially the same for all directions within said solid angle.

WO 95/03089 discloses a hair-removing device of the kind mentioned in the opening paragraph. The known device is a laser treatment system for e.g. epilation, comprising a laser source, a telecentric optical system and a transparent contact plate. The telecentric optical system comprises a number of mirrors and lenses such that the central ray of the laser beam always goes through the focus of said lens, and the focal point of the laser beam always has the same distance to the contact plate. The laser treatment system may be used for providing optical energy in the focal point of the laser beam to a root of a hair. By providing sufficient energy, the root will die and the hair may be removed. A disadvantage of the known hair-removing device is that difficulties may be encountered when applying the device to the skin. Because many parts of e.g. a human subject to be depilated are not flat, at least a part of the skin will be deformed or compressed. The contact between the skin and the contact plate will be difficult to control. Especially in the case of optical hair removal, this is however important, since the position of the hairs on the skin, or alternatively the roots of the hairs, should be well defined with respect to the focal point of the applied radiation. In practice, this corresponds to a well-defined position with respect to the contact plate, or window. Another difficulty would be that folds in the skin cause an irregular distance between hairs and contact plate. These difficulties limit the performance of the known hair-removing device. It is an object of the invention to provide a hair-removing device of the kind mentioned in the opening paragraph, with which a more reliable and efficient performance may be achieved. In particular, a well-defined distance between hairs and the contact plate may be obtained more reliably. To achieve this object, a hair-removing device according to the invention is characterized in that the outer surface of the window is at least locally curved in at least one direction. Due to the curved outer surface of the window, the skin is much better able to contact the window. Hence the distance between the skin and the window will be much better defined, and may be controlled over a larger area. Therefore, the window may also be made larger. Furthermore, wrinkles in the skin may be avoided, and the pressure pattern of the skin on the window is much more regular. Local spots where blood is contained in the skin, e.g. due to wrinkles in the skin, can be avoided. Hence a more regular absorption of the skin results, leading to an improved performance of the hair-removing device. Another advantage is that a curved surface of the window may also decrease an irregular distribution of blood in the skin. By compressing the skin, a part of the blood will be expelled from the tissue. Since blood is generally a good absorber of the applied radiation, removal of such blood will influence the performance of the hair-removing device. Hence, since the skin is better able to follow a curved surface, irregular compression can be prevented. It is noted that the telecentric lens system of the known device is limited to a ^■ flat focal plane, and hence does not provide the advantages according to the present invention. In the present context, the words "locally curved" should be interpreted as indicating a local radius of curvature of at most 300 mm in at least one direction, as opposed to substantially flat, indicating an infinite radius of curvature. In practice, the radius of curvature may be smaller, such as between about 25 mm and 100 mm. The window need not have a constant radius of curvature over its surface. For example, a part may be flat, while other parts may be curved, rounded etc. An example would be a window which is flat in the center, and rounded near its edge. Other curvatures are of course possible. The window will advantageously be convex, i.e. outwardly curved. Concave windows are contemplated, and may e.g. be useful when the skin is sucked towards the window by means of a vacuum device. Combinations of a convex part, a concave part and/or a flat part are also possible. Furthermore, the expression "substantially the same distance" should be interpreted to indicate that the difference between the focus and the outer surface of the window varies at most 0.2 mm, and preferably less than 0.1 mm. This relates to variations between all the possible positions of the focus or directions of the corresponding beam, for a certain setting of the focus distance, i.e. the average distance between the focus and the outer surface of the window. Especially when the device is used for shaving, it is advantageous to provide a well-defined shaving depth. Allowing large differences in shaving depth over the surface of the skin to be treated would cause the regrowing hairs to appear irregularly on the skin, which is not desirable. In the case of e.g. epilation by damaging hair roots, variations in the distance between focus and outer surface is sometimes less important, although good knowledge thereof is advantageous here as well. The expression "solid angle" is intended to encompass a collection of directions that need not emanate from only one apex point. It rather relates to the collection of directions that the focused beam may have in its focus. For example, in the case of a stationary focused beam which is manipulated by means of a tip-tilt mirror which is moved around the spot where the beam strikes the mirror surface, the directions are comprised in a cone, while when the beam is manipulated by means of e.g. a parabolic mirror which is rotatable around as well as displaceable along an axis parallel to its axis of symmetry, different directions need not emanate from one point. However, in all cases the focus will describe a surface for every set focus distance, and the solid angle relates to the collection of directions that allow a focus to lie in that surface. Another important aspect of the invention is the possibility of the use of an optical system that allows a focus property to be kept substantially constant for all directions of the above- mentioned solid angle. In particular, the energy intensity in the focus may be kept constant when using an appropriate optical system, contrary to the case of a telecentric lens system. In many cases it is sufficient when the convergence of the focused beam in its focus is substantially constant. For example, in the known telecentric optical system, the beam will be incident at a varying distance from the optical centre of the lens, which will cause the focus to vary in shape, and hence in intensity. Furthermore, such telecentric lens systems are rather complex and expensive in order to provide a predetermined precision, while the numerical aperture is often rather limited. Contrarily, for example, a focused beam that is incident on a tip-tilt mirror, at its swivel point, will describe part of a sphere, as will the window. The skin will always be subjected to the same focus shape and intensity. Furthermore, it is much easier to provide such a system with a relatively high numerical aperture, especially when the focussing is brought about by a stationary or movable mirror, or by a fixed lens, and combined with a separate beam manipulator. Avoiding the constraint of a telecentric lens system thus offers not only a simpler and cheaper construction, with a higher possible numerical aperture, but also with a more constant focal intensity distribution. Put more generally, the hair-removing device according to the invention and according to the preamble may be characterized by an optical system that provides a focus with a substantially constant intensity distribution for said solid angle. For various embodiments described below, details as to this aspect will be given. It is noted that the hair-removing device according to this aspect of the invention need not have a curved window, since for example an optical system wherein the source and a focusing lens are movable as a whole in a predetermined plane may also provide a focus with constant intensity distribution. Returning now to the first mentioned aspect of the invention, and keeping in mind that most of the advantageous features mentioned in the description below will also hold for the second aspect, it is found that, advantageously, said outer surface has at least locally a first radius of curvature in a first direction and a second radius of curvature in a second direction perpendicular to the first direction, wherein said first radius of curvature is at most 300 mm, while the second radius of curvature is at least as large as the first radius of curvature. Such local radii of curvature need not be constant over the surface of the window. For example, a flat or relatively flat central part of the window may be combined with a more rounded off peripheral part. Note that the second radius of curvature may be made very large, in principal any value between 300 mm and infinite. The latter value would indicate an outer surface which is curved in only one direction. By providing an outer surface which is curved in two directions, the advantages of the surface being curved are even more pronounced. Notably, the shape of the window may be adapted to a body part of which the skin is to be treated, such that the skin will even better follow the outer surface of the window. In an advantageous embodiment of the invention, the outer surface is a part of a cylinder or a part of a sphere. These are two extreme cases of the embodiment above, the sphere indicating equal radius of curvature in every direction, while the cylinder indicates an infinite radius of curvature in one direction. Such shapes are relatively easy to manufacture from very many materials. Furthermore, their shapes allow relatively simple manipulation of the radiation. This will be elucidated further on. Note, however, that other combinations of radii of curvature in different directions are also allowed. Advantageously, the window is displaceable in at least one of the directions in said solid angle. This offers a very simple way to adjust the distance between the focus and the outer surface of the window. In other words, the working depths, such as a shaving depth, may be set as desired. For example, the focus may be positioned at a distance between 0 mm and e.g. 3 mm. This means that, when the hair-removing device contacts the skin, the focus is located in a position between 0 mm and 3 mm below the surface of the skin. Specially adapted means may be provided for displacing the window. An example is a window actuator such as an electromotor; other means may comprise manually adjustable mechanical means such as a settable stop spring or thread. In another advantageous embodiment, at least one of the source of optical radiation and/or at least a part of the optical system and/or at least a part of the at least one manipulator means are adjustable, such that the distance between the focus and the window is adjustable. This also offers the possibility of adjusting the distance between the focus and the outer surface of the window, but it has the additional advantage that the window need not be displaceable. In other words, the device need not comprise any moveable part at its outer surface. This is advantageous for making the device dustproof, waterproof etc. It is also possible to provide the device as a whole with a smooth outer surface, which may prevent possible injury. An example of an adjustable source comprises a source of which the divergence may be adjusted, such as a light source with built-in optical system: Alternatively, the source of optical radiation may be displaceable with respect to a focusing element of the optical system and/or manipulator means. This may cause a shift in the position of the focus, and hence an adjustment of the distance between the focus and the outer surface of the window. Alternatively, or additionally, the optical system, or a part thereof, may be adjustable, such as displaceable. For example, if the optical system comprises a zoom lens, changing the focal length of the zoom lens may also cause a change of the mentioned distance. Simply displacing a lens of the optical system has a similar effect. Displacing another optical element, such as a mirror behind a lens, or a focusing mirror, etc., may also bring about the desired change of the distance between the focus and the window. Similar considerations also apply in the case of at least a part of the at least one manipulator means being adjustable, such as a rotatable mirror being displaceable also with respect to the light source. For example, if a focused beam is reflected by a rotatable mirror, then the displacement of said rotatable mirror may bring about a change in the position of the focus after reflection. Note that in many of the above cases the focal intensity will be substantially constant in the predetermined solid angle, as the skilled person will readily see. For example, if, within the predetermined solid angle, the distance of the beam to the optical axis of the focusing element(s), and its orientation with respect thereto, remain constant, then in general said focal intensity distribution will be a constant. It is remarked here, that it may sometimes be required to adjust the control of the source of optical radiation and/or the optical system and/or the manipulator means in order to ensure that, for a certain setting of the device, the distance between the focus and the outer surface of the window is still substantially a constant for every direction in the predetermined solid angle. It may for example be that the surface described by the focus when the manipulating means change the direction of the focused beam, would no longer more or less follow the outer surface of the window. In that case, it is advantageously ensured through appropriate control of the source and/or the optical system and/or the manipulator means that said distance is still substantially a constant as a function of the direction in the predetermined solid angle. In an exemplary embodiment a control unit adjusts the focal length of a zoom lens in the optical system as a function of the position of a displaceable manipulating means. In a special embodiment of the device according to the invention, at least one manipulator means comprises a moveable mirror. A moveable mirror offers very simple control over the reflected beam while the properties of the focus may be maintained, notably its focal intensity distribution. Furthermore, a mirror makes it possible to scan the focus over a relatively large surface while the mirror itself may have very small dimensions, and may hence be controlled with high speed. Nevertheless, other manipulator means are also conceivable, such as moveable or deformable lenses. For example, when a lens is moved in a direction perpendicular to the direction of a parallel beam, the focus will remain in the same position with respect to the lens, and will hence travel along with the movement of the lens. Note that in this case the focal intensity distribution will generally not be a constant over the predetermined solid angle. Other alternatives will occur to the skilled person without difficulty. In a special embodiment, said moveable mirror comprises a mirror surface that is a part of a paraboloid, the moveable mirror being rotatable around an axis parallel to but not coincident with a symmetry axis of the paraboloid. Note that in this case the moveable mirror is a focusing element. This is one of the examples where a manipulator means is also part of the optical system for projecting. In other words, one physical part of the device according to the invention may have several functions. In this embodiment, the mirror surface is a part of a paraboloid. When such a mirror is irradiated by a parallel beam, that beam is focused in the focus of the paraboloid. When the symmetry axis of the paraboloid lies outside the mirror, in other words the top of the paraboloid is not a part of the mirror surface, then the focus will lie outside the incident beam. When this mirror is rotated around an axis which is parallel to but does not coincide with the symmetry axis of the paraboloid, the focus will describe a circle. The center of the circle, and hence the axis of rotation, preferably coincides with the same as the center of curvature of the window when measured in the same plane. Furthermore, in order to ensure that a large part and preferably all of the incident beam is reflected, the axis of rotation and the central ray of the incident beam may be selected to be parallel and as close to each other as possible. It is noted that in most of such cases the focal intensity distribution will be a constant. It is however possible to irradiate a different part of the mirror, if desired. Advantageously, the moveable mirror is displaceable in the direction of the symmetry axis of the paraboloid. When the moveable mirror (e.g. paraboloid) is displaced in the direction of its symmetry axis, the focus will describe a line parallel to said symmetry axis. When said displacement is combined with a rotation around an axis parallel to said symmetry axis, the focus may describe a part of a cylinder surface. In other words, every position on a part of a cylinder may be irradiated by the focused beam by appropriately displacing and rotating the moveable paraboloid mirror. The window will then also be a part of a cylinder, with a radius of curvature of its outer surface which is equal to or slightly smaller than the radius of curvature of the cylinder described by the focus. In the case of equal radii of curvature, the distance between the focus and the outer surface of the window is zero, and there will be zero depth in the skin. In other words, in the case of a shaver, the hairs will be cut flush with the skin. In the case where the radius of curvature of the cylinder described by the focus is slightly larger than the radius of curvature of the window, there is a positive focal depth, or distance between the focus and the outer surface. In this case it is possible to position the focus inside the skin, in order to cut a hair below the surface of the skin, or to perform any other desired action with said focus below the skin surface. In an alternative embodiment, the moveable mirror comprises a plane mirror which is rotatable around a non-perpendicular first axis. Rotating the moveable mirror around said first axis will cause the focus of an incident beam to describe a circle around said first axis. If, furthermore, the plane mirror is displaceable along a direction of the incident beam, then in principle the focus will describe a part of a conical surface. Note that the term non- perpendicular relates to the first axis not being perpendicular to the plane of the mirror, since in that case rotating the mirror may not cause any visible effect. In that case other means are required to focus the beam, e.g. a lens. In order for the focus to describe a cylinder, or part thereof, it may be required to displace the focusing element(s) together with the plane mirror, such that the combined effect of the focusing element and the rotatable plane mirror adds up to a cylinder shape. Note that for a plane mirror manipulator means, the focal intensity distribution will generally be a constant in the predetermined solid angle. As an alternative embodiment, said moveable mirror is independently rotatable around a second axis which is parallel to the mirror surface and transverse to the first axis. Such a mirror, which is moveable in two independent directions, will cause the focus to describe a sphere or part thereof. It is advantageous to ensure that at least one, and preferably both, of the first axis and the second axis lie in the mirror surface, because in that case the largest part of the incident beam will be reflectable in most of the possible positions of the rotatable mirror. Note, however, that it is not necessary to provide one or both of said first and said second axis in the mirror surface. Rotation around two different axes may be obtained by providing two of said axes, shafts etc. as well as corresponding actuators. A similar control over the movement of the moveable mirror may be obtained by making the moveable mirror pivotable around a swivel point in two directions. A general term for such a mirror would be a tip-tilt mirror. Advantageously, the swivel point is located in the mirror surface, and most preferably, said swivel point is located at the intersection of the central ray of the incident beam and the mirror surface. In this case, too, it is possible to ensure that in as many positions as possible, as large a part as possible of the incident beam is reflectable by the moveable mirror. In any case, for a plane mirror, the focal intensity distribution will be substantially constant. As another alternative embodiment, the manipulator means comprises two moveable mirrors, one of which is rotatable around a first axis, while a second mirror is rotatable around a second axis, which is non-parallel to the first axis. Note that, if desired, more than two mirrors may be provided. By providing mirrors that are rotatable around two different axes, a laser beam that is reflected by the first mirror, and subsequently by the second mirror, may be scanned over a surface. A set-up like this is known per se, and is for example described in WO 95/03089. There, a special embodiment is shown, in which the first mirror is rotatable around an axis which is not part of the mirror surface, such that the reflected beam always crosses the second mirror in approximately the same spot. This ensures that scanning in the first direction is more or less independent of scanning in the second direction. However, other embodiments of two or more mirrors may be used as alternatives. In principle, when using two or more plane mirrors, the focal intensity distribution may be kept constant in the predetermined solid angle. In an advantageous embodiment of the hair-removing device according to the invention, the optical system comprises at least one lens or focusing mirror. Note that the lens is either a single positive lens, or a combination of lenses with a net focusing action. A combination of transparent optical elements and reflective optical elements that as a whole focus incident radiation is also possible. Since optical properties of various possible combinations of material and shapes may readily be calculated, it will not be difficult for a skilled person to devise a combination of such mentioned optical elements that are other than simple lenses or (paraboloid) mirrors in themselves. It is advantageous to locate such a lens or focusing mirror, or other focusing optical element, between the source of optical radiation and the first of the moveable manipulator means. Note that the expression "the first" in this case does not relate to there being present more than one moveable manipulator means, which is however not excluded, but to the position along the optical path of the beam. In other words, when radiation travels from the source, through the optical system and manipulator means towards the focus, it will preferably first pass at least one lens or focusing mirror before reaching any moveable manipulator means. This has the advantage that it is easily ensured that the focus properties remain constant for many if not all positions of the focus. It is however not excluded to reverse this order, for example in the case where the optical elements are designed to limit the variations of the focused properties to a minimum. Alternatively, as described above, the moveable manipulator means may itself be a lens. In an advantageous embodiment, the source of radiation comprises a laser. A laser has the advantage that its radiation may be focused in a very small focus spot. In principle, it would be possible to focus a laser beam to a spot with a diameter of a few micrometers, although this would generate an extremely high energy density. Even with very- simple and cheap lenses, it is possible to focus a laser beam to a focus diameter of about 0.1 mm, which is a very useful dimension for e.g. cutting, or otherwise affecting or influencing, a hair without damaging surrounding tissue. Laser sources may be made very compact, e.g. in the form of a laser diode. Alternatively, an external laser source may be used, the radiation of which may be coupled into the hair-removing device by a light guiding device, such as an optical fiber. In this case, the source of optical radiation is external to the housing, although the light emitting surface of the optical fiber or other light guiding means may be considered to be the source of optical radiation. It is noted that it is not necessary to use a laser as the source of optical radiation. Any light source that is focusable down to a focus diameter of around a few tenths of a mm may be used. Examples are a high-power LED and a short-arc gas discharge lamp, which offers high power density. An alternative method is to use fiber optics, since the light emitting end of an optical fiber may be considered to be a small source, which may be easily focused down to the desired diameter. Note that, in principle, the power density will not be increased by simply using a fiber, but it offers the possibility to use a high power radiation source at a distance away from the skin to be treated. Note that in the present context, optical radiation is considered to comprise visible electromagnetic radiation, as well as the contiguous near-infrared and near-ultraviolet ranges of the spectrum. Visible radiation is preferred, e.g. because of absorption properties of notably melanin in many hairs. The present hair-removing device according to the invention advantageously further comprises a hair-imaging system. Such a hair- imaging system visualizes a hair on the skin, on the basis of which visualization a control unit may control the position of the focus. The hair- imaging system may thus ensure that the radiation is only directed to the desired target, and not to surrounding hairless skin, which would only induce heating up of the skin, with possible damage or discomfort as a consequence. A hair-imaging system is known per se, and will not be elaborated in great detail here. Advantageously, the hair- imaging system is adjustable as a function of the distance between the focus and the window. This offers the possibility to use a hair-imaging system with a limited depth-of- field. By this adjustability, the hair-imaging system may select the field at a distance where the actual focus is located. Note however that a hair- imaging system which is not adjustable, but simply images the skin as it is pressed against the window is also useable. Furthermore, it is to be noted that the hair- imaging system as a whole is also purely optional, since the focus may also scan the part of the skin to be treated continuously, e.g. using a larger focus diameter and radiation which is absorbed by hairs but much less by skin or other surrounding tissue. It is however to be expected that the performance of such a device is either worse or more painful for the subject to be treated.

Embodiments of a hair-removing device in accordance with the invention will be described in detail in the following, with reference to the accompanying Figures, in which: Fig. 1 diagrammatically shows a hair-removing device according to the invention; Fig. 2 diagrammatically shows a detail of the device according to Figure 1; Fig. 3 diagrammatically shows a second embodiment of a detail of the hair- removing device according to Figure 1; and Fig. 4 diagrammatically shows the operation of the hair-removing device according to Figure 1.

Figure 1 diagrammatically shows an embodiment of the hair-removing device according to the invention. Therein, 10 denotes a housing with a chamber 11. 12 denotes a laser source, which emits a laser beam 14 which is focused into a focused beam 16 ending in a focus spot 18 in the skin 20. On the skin 20, hairs 22 are present, which are pressed against the skin 20 by transparent window 24. The window 24 is moveable in the direction of arrow A along an optional ruler 26, by means of a window actuator 28. The beam 14 is focused by a mirror 30, which is actuatable by a mirror actuator 32 along and around an axis 34. 36 denotes an imaging sensor, and 38 denotes a beam of imaging radiation, while 40 denotes an imaging control unit. 42 denotes a general control unit. The laser source 12 emits a laser beam 14. Not shown is an optional optical system for shaping the laser beam 14. For example, said optional optical system may change the beam diameter, optimize the beam divergence, etc. However, in many cases, the inherent properties of an emitted laser beam 14 may suffice. Alternative sources of radiation are not excluded. However, in order to be able to focus the emitted radiation into a focus spot 18 having dimensions comparable to or smaller than the diameter of a hair, i.e. around 0.1 mm, special sources or additional measures may be required. Optional alternative radiation sources are short-arc gas discharge lamps or certain fiber optic lighting systems. However, for e.g. epilation, a larger spot diameter may be useful, such as 1 cm or more. The wavelength of the laser beam 14 is for example such that the radiation is readily absorbed by a hair 22, in particular by melanin present therein. Most visible radiation fulfils this requirement. Nevertheless, other radiation may also be used, such as e.g. a 337 nm N₂ laser beam. Since more constituents of hair than only melanin absorb this radiation, the melanin dependence may be decreased, although sometimes mechanisms other than simply heating and burning a hair are employed. The laser beam 14 is focused and directed by means of a mirror 30, actuatable by mirror actuator 32. Preferably, the mirror has the shape of a part of a paraboloid. More in particular, the surface of the mirror 30 does not comprise the axis of symmetry of the paraboloid. This ensures that the focused spot 18 is not present in the laser beam 14. Note that in Figure 1, the reflection of the laser beam 14 and the shape of mirror 30 are indicated only diagrammatically. The mirror 30 is rotatable around an axis 34 by means of mirror actuator 32. This causes the focused spot 18 to describe a circle around the axis 34, or at least a part thereof, depending on the range of rotation angles. Furthermore, the mirror 30 is displaceable along the axis 34 in the direction of arrow B. The combined rotation and displacement cause the focused spot 18 to describe a part of a cylinder. The focused beam 16 exits the housing 10 via transparent window 24. The material of the window 24 may be any material which is sufficiently transparent to the radiation from the laser beam 14, such as glass, sapphire, many plastics etc. The shape of the window 24 will be discussed in connection with the following Figure. The position of the window 24 may be adjusted along ruler 26 by means of window actuator 28. The window actuator 28 may be a simple motor. Note that the window actuator 28 is entirely optional, as an operating person could also manually adjust the window 24 with respect to the housing 10. For this purpose, the window could be accommodated slidingly in the housing 10, or e.g. with a thread, such that rotating the window 24 moves the latter in the direction of arrow A. Any other means of ensuring displaceability of the window 24 is also possible. These possibilities may depend on the shape of the window 24. For example, the ruler 26 and the window actuator 28 may be replaced by a belt-driven motor, a chain gear, or the like. The axis 34 runs parallel to the direction of the laser beam 14, and preferably in the optical centre thereof. The imaging sensor 36 may e.g. be a CCD-camera or other optical sensor able to form an image of the piece of skin 20 that is being treated. To this end, imaging radiation is received by the imaging sensor 36. A separate radiation source (not shown) may be provided for supplying radiation in the direction of the skin 20, which after reflection at the skin forms the beam of imaging radiation 38. It is also possible that the imaging sensor 36 itself comprises a source of radiation which after reflection at the skin 20 forms the beam of imaging radiation 38. The image as formed in the imaging sensor 36 may be processed by imaging control unit 40. For this purpose, the imaging control unit 40 may comprise circuitry or a programme for determining the presence of e.g. a hair 22 in the image. By means of measures which are known per se, such as a frame grabber and hair recognition software such as a LabNiew application, the position and orientation of a hair 22 on the skin 22 may be determined. The general control unit 42 may be provided either as a separate unit or built into one of the other parts mentioned, such as the imaging control unit 40. The general control unit 42 is connected to at least the imaging control unit 40 and the mirror actuator 32, and preferably also to at least one of the laser source 12 and the window actuator 28. On the basis of the determined position and/or orientation of a hair 22, the general control unit 42 may control the mirror actuator 32 to adjust the position of the mirror 30, such that the focused spot 18 is directed to an intended target. Such intended target may be e.g. a root of a hair 22 or a desired position for cutting said hair 22. In principle, the laser source 12 may continuously emit a laser beam 14. Preferably, however, the laser source 12 emits a laser beam 14 only when the mirror 30 is in a desired position. For this purpose, either a shutter or the like (not shown) may be provided or e.g. the laser source 12 is switchable by means of the general control unit 42. After having emitted a desired amount of laser energy onto a first desired target, e.g. in order to cut a hair, the general control unit 42 may readjust the mirror 30 by means of mirror actuator 32 in order to position a focused spot 18 on a new target position, etc. It is possible to adjust the distance between the focused spot 18 and an outer surface of the window 24 by moving the window 24 with respect to the housing 10. To achieve this, window actuator 28 may displace the window 24 in a direction parallel to an optical axis of the focused beam 16, or more generally, in a transverse direction with respect to the part of the skin 20 being treated. Said displacement may be a continuous displacement, or a step-like displacement. Alternatively, the displacement may be brought about manually, either continuously or as a discrete displacement. The distance between the focused spot 18 and the outer surface of the window 24, also called focus depth, is a useful parameter for adjusting a shaving depth. It is e.g. possible to set the shaving depth at around 0 mm, i.e. substantially flush with the outer surface of the window 24 and hence substantially flush with the skin resting against said outer surface. After shaving, by cutting the hairs flush with the skin, the skin will be smooth. However, the regrowing hairs will protrude relatively quickly. By setting a larger shaving depth, such as 1 mm, the hairs may be cut within the skin. It will then take a longer time before the regrowing hairs protrude above the skin. Setting such a larger shaving depth may be achieved by displacing the window 24 towards the mirror 30 over the desired distance. Figure 2 diagrammatically shows a detail of the hair-removing device according to the invention. Herein, as well as throughout the drawings, similar parts are denoted by the same reference numerals. Hence, 14 is a laser beam, which becomes a focused laser beam 16 upon reflection at parabolic mirror 30. The focused spot 18 is located a distance d away from the window 24. The window 24 is accommodated in a holder 44, having e.g. a thread for displacement in the direction of arrow A. The mirror 30 may be moved along axis 34 in the direction of arrow B, as well as around that axis 34. In this way, the focused spot 18 may describe a part of a cylinder surface around the axis 34. The mirror 30 is e.g. a part of a parabolic mirror, such that its focus is outside the incident beam 14. In Figure 2, the incident laser beam 14 makes a right angle with the optical axis of the focused beam 16. This angle between incident and reflected beam is dependent on the specific shape of the mirror. Other parts of a parabolic mirror may also be used in order to obtain a different angle between the incoming beam and the reflected beam. Furthermore, the mirror 30 is shown as a solid block. However, it is also possible to construct mirror 30 as a thin layer of e.g. metal, plastics with a mirror coating etc., which has been formed in the desired shape. The focused spot 18 is located at a distance d in front of the window 24. By displacing the window 24 with respect to the housing (not shown) in the direction of arrow A, said distance d may be set. The distance d may be used to obtain the desired shaving depth or the like. Note that it is possible to cut a hair at a position under the surface of the skin without sustaining substantial damage to the skin, because the radiation is focused substantially onto the focused position. Away from the focused position, the intensity decreases rapidly, and injury may be prevented. Figure 3 diagrammatically shows a second embodiment of a detail of the hair- removing device according to the invention. Herein, 14 denotes a laser beam, which is focused by lens 50, and reflected by plane mirror 30'. The focused beam 16 passes window 24. Note that the laser beam 14 is focused before the thus focused beam 16 strikes the surface of the mirror 30'. This ensures that the properties of the focus point remain substantially the same under all practical tip and tilt angles of the mirror 30'. The mirror 30' is tiltable and/or rotatable around a swivel point 52, around axis C in the plane of the drawing, as well as around axis D, which is here perpendicular to axis C and in the plane of the mirror 30'. Note that other orientations of the axes of rotation or swivel may be possible, as long as the focused spot 18 is able to describe a desired surface. Alternatively, it is possible to use two separate axes/shafts instead of a single swivel point 52. A general name for the construction shown in Figure 3 with respect to the mirror 30' is a tip/tilt mirror. Although beam 14 is depicted as a collimated laser beam, which is focused by means of lens 50, which may also be a complex optical system, it is alternatively possible to use a divergent beam, which is made convergent by means of an appropriate lens at the position of lens 50. It is also conceivable to devise an optical system comprising one or more lenses, and at least one mirror. The mirror may be a plane mirror or a mirror having a curved surface, such that the beam is adjustable by the moveable mirror of said at least one mirror system, while no lens is present between said moveable mirror and the focused spot. Said optical system will still ensure that the optical properties of the focused spot remain constant over the various positions it may be positioned in, while the combined working of the optical system and the at least one mirror may be selected to provide sufficient focusing action. In other words, it is not necessary to focus the beam either by a parabolic mirror or by a lens, but a combined action will also suffice, provided that no lens is present in the optical path behind a moveable mirror therein. It is explicitly noted here that it is of course also conceivable to position at least one lens behind such moveable mirror part, in cases where it is not important to have optimum control over the properties of the focus. Figure 4 diagrammatically shows the operation of the hair-removing device according to the invention. A mirror 30' is shown in a first position (solid line) and a second position (dashed line). An incident beam 14 is reflected by the mirror 30' into a reflected and focused beam 16, again in a first position indicated by a solid line and a second position indicated by a dashed line. Furthermore, 24 denotes a transparent window, shown in a first position in solid lines and a second position in a dotted line. Note that the two positions do not relate to the two positions of the mirror 30'. Although only 2 reflected beams 16 are shown, it will be clear that a focused spot 18 will describe a continuous service surface when the mirror 30' is moved through its range of possible rotations etc. When the transparent window 24 is in its first position, i.e. as shown in the solid line, the distance between the focused spot 18 and an outer surface of the transparent window 24 is a constant. However, if the transparent window 24 is displaced, e.g. to the second position in the dotted line, said distance will no longer be exactly the same for all positions of the mirror 30'. However, the difference can be made very small. Furthermore, it may be ensured that the deviation from the optimum shape of the transparent window 24 is symmetrical with respect to the surface 60. Note that the surface 60 is the focal plane of the optical system of the hair-removing device. Such deviations from the ideal shape may be minimized when the outer surface of the window 24 is designed such that it has the correct shape in about the middle of the range of the desired displacement. Furthermore, when the distance between the focused spot 18 and the adjustable beam manipulator, e.g. mirror 30', is much larger than the desired range of shaving depths, cf. d in Fig. 2, then said deviations will often be negligible, at least with respect to the desired precision for setting the shaving depth.

Claims

CLAIMS:

1. A hair-removing device (1) having a housing (10) provided with a source (12) of optical radiation and a window (24) transparent to said optical radiation, wherein the device comprises an optical system (50) for projecting said optical radiation through said window as a focused beam (16) with a focus (18), wherein the device comprises at least one manipulator means (30; 30') for manipulating the direction of the focused beam within a predetermined solid angle, and wherein a distance between the focus (18) and an outer surface of the window (24) is substantially the same for all directions within said solid angle, characterized in that the outer surface of the window (24) is at least locally curved in at least one direction.

2. A hair-removing device according to claim 1, characterized in that said outer surface has at least locally a first radius of curvature in a first direction and a second radius of curvature in a second direction perpendicular to the first direction, wherein said first radius of curvature is at most 300 mm, while the second radius of curvature is at least as large as the first radius of curvature. ;

3. A hair-removing device according to claim 1, characterized in that the outer surface is a part of a cylinder or a part of a sphere.

4. A hair removing device according to claim 1 , characterized in that the window

(24) is displaceable in at least one of the directions in said solid angle.

5. A hair-removing device according to claim 1, characterized in that at least one of the source (12) of optical radiation and/or at least a part of the optical system (30; 50) and or at least a part of the at least one manipulator (32; 30') means are adjustable, such that the distance between the focus (18) and the window (24) is adjustable.

6. A hair-removing device according to claim 1, characterized in that at least one manipulator means comprises a moveable mirror (32; 30').

7. A hair-removing device according to claim 6, characterized in that said moveable mirror (32) comprises a mirror surface (30) that is a part of a paraboloid, the moveable mirror being rotatable around an axis (34) parallel to but not coincident with a symmetry axis of the paraboloid.

8. A hair-removing device according to claim 6, characterized in that the moveable mirror (32) is displaceable in the direction of the symmetry axis of the paraboloid.

9. A hair-removing device according to claim 6, characterized in that the moveable mirror (30') comprises a plane mirror which is rotatable around a non- perpendicular first axis.

10. A hair-removing device according to claim 9, characterized in that said moveable mirror (30') is independently rotatable around a second axis which is parallel to the mirror surface and transverse to the first axis.

11. A hair-removing device according to claim 1, characterized in that the optical system comprises at least one lens (50) or focusing mirror (30).

12. A hair-removing device according to claim 1, characterized in that the source of radiation comprises a laser (12).

13. A hair-removing device according to claim 1, characterized in that the hair- removing device further comprises a hair-imaging system (36, 40).

14. A hair-removing device according to claim 13, characterized in that the hair- imaging system (36, 40) is adjustable as a function of the distance between the focus (18) and the window (24).