Abstract:
A depilating device ( 14 ) for depilating hair ( 12 ) from a surface ( 10 ) of a skin ( 11 ) comprises a housing ( 16 ) and a depilating member ( 18 ) arranged in said housing. In operation, said depilating member has an effective depilating action when positioned within a predetermined range of angular positions ( 5 ) relative to the surface of the skin. The depilating device further comprises a detector for detecting an actual angular position ( 28 ) of the depilating member relative to the surface of the skin, and feedback means cooperating with said detector for providing a feedback signal when said actual angular position exceeds said predetermined range of angular positions. According to a specific embodiment, the detector comprises a skin contact member ( 34 ) arranged adjacent to the depilating member ( 18 ) and being pivotable relative to the housing ( 16 ) about a pivot axis ( 54 ) extending parallel to a skin contact surface of the depilating member.

Description:
FIELD OF THE INVENTION 
     The invention relates to a depilating device for depilating hair from a surface of a skin, comprising a housing and a depilating member arranged in said housing, wherein, in operation, said depilating member has an effective depilating action when positioned within a predetermined range of angular positions relative to the surface of the skin. 
     BACKGROUND OF THE INVENTION 
     Depilating devices such as epilators, shavers, and hair clippers must often be placed in a certain angular position on the surface of the skin in order to obtain an optimal result. More specifically, the application angle, defined as the angle between a reference axis (longitudinal axis) of the depilating device and the surface of the skin, should lie within a certain optimal range. For disc-type epilators with closing tweezers, for example, the optimal application angle is about 90° plus/minus 15°. A depilating device typically comprises a depilating member for extracting or cutting hairs, and a body comprising a motor and providing a grip for holding the device. The depilating member comprises, for example, tweezers or cutting blades. The inclination of the depilating member relative to the surface of the skin is generally determined by the inclination of the body relative to the surface of the skin. In order to achieve an effective depilating action, the depilating member has to come into contact with the hair and/or the skin surface in a position which lies within a predetermined range of angular positions relative to the surface of the skin. If the depilating device is applied to the skin at an angular position which exceeds substantially from said predetermined range of angular positions, the depilating action may be insufficient. Furthermore the treatment may cause injuries, skin irritations, pain, or broken hairs resulting in ingrowing hair. This can pose problems to inexperienced users who have difficulties in positioning the depilating device at the optimal application angle relative to the skin. It is therefore an object of the invention to provide a depilating device having means for increasing the probability that the depilating device is being held at an optimal application angle relative to the surface of the skin. 
     This object is achieved by the features of the independent claim. Further specifications and preferred embodiments of the invention are outlined in the dependent claims. 
     SUMMARY OF THE INVENTION 
     According to the invention, the depilating device further comprises a detector for detecting an actual angular position (application angle) of the depilating member relative to the surface of the skin, and feedback means cooperating with said detector for providing a feedback signal when said actual angular position exceeds said predetermined range of angular positions. Thus the depilating device is capable of delivering a feedback signal to the user when the application angle passes from a predefined first range and to an adjoining predefined second range. The first range may be optimal in the sense that the depilating device has a characteristic which is a function of the application angle and which is optimal for an optimal application angle, the optimal application angle being in the first range. The characteristic may for example be one of the following characteristics: depilation efficiency, depilation quality, percentage of remaining hairs after a single passing of the depilating member over the skin, average length of cut hairs, uniformness of the length of the hair after cutting, noise, collection of removed hairs inside the depilating device, wearing-down of the depilating member, and skin irritation. The characteristic which defines the optimum application angle may also be a combination of two or more of the above-mentioned characteristics, in which case the optimum application angle may be a compromise. The second range may be suboptimal in the sense that the characteristic is not optimal for any application angle in the second range. In this case depilation may however still be possible at least for a subrange of the suboptimal second range. The first range may, for example, comprise the range of 75° to 105°, an application angle of 90° corresponding to the case in which the depilating device is held perpendicular relative to the surface of the skin. The second range may then, for example, comprise all angles larger than 105°. The term “range” as used herein is synonymous with the mathematical term “interval”. Generating a feedback signal as a function of the variation of the application angle allows alerting the user as soon as the application angle exceeds the predetermined range of angular positions. According to a preferred embodiment, the longitudinal axis of the depilating device is pivotable relative to the skin only about an axis which is oriented parallel to the skin and perpendicular to a moving direction of the depilating device. Indeed most existing types of depilating devices are designed for being moved on the skin in a moving direction defined by the orientation of the depilating member, and for being tilted about an axis parallel to the skin and perpendicular to the moving direction. In most depilating devices the direction opposite the moving direction is also an allowed moving direction. The depilating device then has at least two opposite moving directions. The longitudinal axis may be fixed relative to a body for holding the depilating device. Alternatively the longitudinal axis may be fixed relative to the depilating member. According to a specific embodiment, the feedback mechanism generates a feedback signal also when the application angle passes from the first range to a third range while the depilating member is applied to the skin, the first range lying between the second range and the third range. Herein the third range is defined analogously to the second range. The first range, the second range, and the third range may, for example, be the following ranges: 75° to 105°, less than 75°, and larger than 105°, respectively. Of course, the most suitable division of the total allowed range of application angles into a first, second, and third range may depend strongly on the specific type of depilating device. The depilating device may be such that it is in a first state when the application angle is in the first range and in a second state when the application angle is in the second range. Thus the feedback signal may be generated by the depilating device passing from the first state to the second state. Each state may be characterized by a certain mechanical state and/or, in the case where the depilating device includes an electronic control unit, a logical state. In this context, the second state may be energetically higher than the first state. Thus, in order to tilt the depilating device out of the first range, the user needs to supply energy to the depilating device, for example by overcoming a mechanical load inside the depilating device. This mechanical effort will be experienced by the user as a tactile feedback signal. If the second state is energetically higher than the first state, the second state may be metastable. That is, it has a finite “lifetime”, so that if no external force is exerted on the depilating device, the device will automatically return from its metastable second state to its energetically lower first state after a certain delay. The depilating device may be arranged such that a feedback signal is provided as long as the application angle lies in the second range. Thus the user may be informed on tilting the depilating device in a suboptimal manner not only at the moment at which the device is being tilted out of the first range, but as long as the application angle is outside the first range. Alternatively a feedback signal may be provided only each time the application angle crosses the border between the first range and the second range. Thereby a possible irritation of the user is avoided, especially when the user has deliberately decided to apply the depilating device at an application angle outside the first range, e.g. when treating parts of the skin at which applying the depilating device at an optimal application angle is more difficult, such as in armpits. 
     The depilating member may comprise clamping members which are rotatable relative to the housing about a rotational axis, wherein said predetermined range is associated with an angular effective operating zone of said clamping members relative to said rotational axis. The clamping members are typically but not necessarily disc-shaped. The angular effective operating zone is typically the stationary (non-rotating) zone where adjacent clamping members cooperate in a tweezer-like manner for gripping and extracting hairs from the skin. 
     The detector may comprise a skin contact member arranged adjacent to the depilating member and being pivotable relative to the housing about a pivot axis extending parallel to a skin contact surface of the depilating member. When the depilating device is applied to the skin in a prescribed manner such that a skin contact surface of the skin contact member contacts the skin, the application angle is thus translated into an internal angle of the depilating device, namely, into a pivot angle of the pivotable skin contact relative to the housing. According to a particular embodiment, the application angle and the pivot angle coincide as long as the application angle is in the first range or in the adjoining second range. Thus the orientation of the skin contact member relative to the skin remains unchanged when the application angle passes from the first range to the second range. Thus the skin contact member may remain in firm contact with the skin for both the first range and the second range of the application angle, thereby further increasing the stability of the position and/or orientation of the depilating device relative to the skin. In particular, it is avoided that the skin contact member lifts off from the skin when the application angle passes from the first range to the second range. It is only when the application angle leaves the second range and enters a non-working range that the skin contact member will be tilted over its edge, in which case the application angle and the pivot angle will no longer coincide. 
     The pivot axis of the skin contact member may extend parallel to the rotational axis of the clamping members. 
     The skin contact member may be spring-biased to a rest position in which a pivot angle of the skin contact member relative to the skin contact surface is 90°. Thereby the user of the depilating device is encouraged to hold the device at a right application angle relative to the skin. 
     The feedback means may be adapted to provide at least one of the following feedback signals to the user: a tactile feedback signal, an acoustic feedback signal, and an optical feedback signal. A tactile feedback signal involves a mechanical stimulus on the skin of the user or any other effect experienced by the skin, by the device-holding hand or by other sensitive body regions of the user. An acoustic feedback signal involves the emission of audible sound. An optical feedback signal involves the emission of visible light. 
     For providing an acoustic feedback signal the feedback means may comprise an elastic member arranged such that it is elastically deformed when the skin contact member is pivoted. The elastic member may, for example, be a spring, in particular a metal leaf spring. 
     The elastic member may notably be arranged so as to be able to assume a stable or metastable first shape and a stable or metastable second shape, wherein the shape of the elastic member changes from the first shape to the second shape under production of a clicking sound. Such an arrangement may be familiar from metal toy clickers (so-called frog clickers). The toy clicker arrangement typically comprises a metal leaf that produces a click sound when it bends (or is forced to bend) from a first stable or metastable shape to a second stable or metastable shape. 
     According to a specific embodiment, the feedback means comprise a spring and a carrier coupled to the skin contact member, the carrier comprising a first bearing and a second bearing such that when said actual angular position is in said predetermined range of angular positions the spring engages with the first bearing and when said actual angular position exceeds said predetermined range of angular positions the spring engages with the second bearing. This mechanism ensures that, depending on the actual angular position, the spring assumes either a first or a second position, shape, or orientation. Thus the feedback signal is associated with the spring disengaging from the first bearing and engaging with the second bearing. The first bearing may for example be provided by a first notch in the carrier, and the second bearing may be provided by a second notch in the carrier. 
     In this context, the feedback means may be designed such that the spring automatically returns from the second bearing to the first bearing if no external force is exerted on the depilating device. Thus, if the depilating device is taken off the skin while the application angle is in the second range, the skin contact member will automatically pivot relative to the housing of the depilating device such that the pivot angle returns from the second range to the first range. The spring may automatically return from the second bearing to the first bearing either immediately or after a delay. 
     The feedback means may also be such that when the actual angular position is in the predetermined range of angular positions the skin contact member does not couple to the depilating member or a driving member thereof, whereas when the actual angular position exceeds the predetermined range of angular positions the skin contact member couples to the depilating member or the driving member. Hence, when the actual angular position exceeds the predetermined range of angular positions, the skin contact member is vibrated or otherwise moved by the depilating member or by its driving member, thereby providing a tactile and/or acoustic feedback signal. In particular, a rattling sound may be produced. 
     The skin contact member may comprise a coupling member for contacting the depilating member or the driving member when the actual angular position exceeds the predetermined range of angular positions. The coupling member may form a single piece with the skin contact member. The coupling member contacting the depilating member or the driving member may produce vibrations of the skin contact member and/or noise, thus providing a tactile and/or acoustic feedback signal. 
     The detector may comprise circuitry for emitting sound and/or light and/or triggering a tactile signal. The circuitry may comprise a power circuit for energizing a lamp and/or a sound output device and/or a vibrator. The sound output device may, for example, be capable of emitting a beep sound. The circuitry may further comprise a relay for controlling the power transmitted through the power circuit. 
     The detector may comprise circuitry for detecting whether the actual angular position exceeds said predetermined range of angular positions of the depilating member. The circuitry may, for example, comprise two complementary conductors which either contact each other or are separated depending on whether the pivot angle corresponds to the predetermined range of angular positions (first range). 
     In this context, the detector may detect a pivot angle of a skin contact member arranged adjacent to the depilating member and being pivotable relative to the housing about a pivot axis extending parallel to a skin contact surface of the depilating device. 
     The feedback means may alternatively be mechanical feedback means. Thus the feedback signal may be generated mechanically, without making use of circuitry. 
     The mechanical feedback means may in particular comprise mechanical indication means for providing an optical feedback signal. The mechanical indication means may, for example, comprise a slide indicator exhibiting either a first portion colored in a first color (e.g. green), or a second portion colored in a second color (e.g. red). 
     These and other aspects of the invention will be apparent from and elucidated further with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified side view of a generic depilating device. 
         FIG. 2  is a simplified front view of the device shown in  FIG. 1 . 
         FIG. 3  is a simplified side view of a depilating device having a pivotable skin contact member, for an application angle of 60°. 
         FIG. 4  is a simplified side view of the depilating device shown in  FIG. 3 , for an application angle of 90°. 
         FIG. 5  is a simplified side view of the depilating device shown in  FIG. 3 , for an application angle of 120°. 
         FIGS. 6-9  schematically illustrate a depilating device having a skin contact member, for different application angles. 
         FIG. 10  schematically illustrates a first state and a second state of a depilating device. 
         FIG. 11  schematically illustrates a first state, a second state, and a third state of a depilating device. 
         FIG. 12  is a simplified bottom view of a depilating device having a skin contact member, according to a first embodiment. 
         FIG. 13  is a simplified bottom view of two carriers and two springs of the depilating device shown in  FIG. 12 , for an optimal first range of application angles. 
         FIG. 14  is a simplified bottom view of the carriers and springs shown in  FIG. 13 , for a suboptimal second range of application angles. 
         FIG. 15  is a simplified bottom view of the carriers and springs shown in  FIG. 13 , for a suboptimal third range of application angles. 
         FIG. 16  is a simplified side view of one of the carriers and the associated spring shown in  FIGS. 13 to 15 , for an application angle of 60°. 
         FIG. 17  is a simplified side view of the carrier and spring shown in  FIG. 16 , for an application angle of 90°. 
         FIG. 18  is a simplified side view of the carrier and spring shown in  FIG. 16 , for an application angle of 120°. 
         FIG. 19  is a simplified side view of a depilating device according to a second embodiment. 
         FIG. 20  is a simplified side view of a depilating device according to a third embodiment. 
         FIG. 21  is a partial front view of a depilating device according to a fourth embodiment, for an application angle of 90°. 
         FIG. 22  is a partial side view of the depilating device shown in  FIG. 21 . 
         FIG. 23  is a partial front view of the depilating device shown in  FIG. 21 , for an application angle of 84°. 
         FIG. 24  is a partial side view of the depilating device shown in  FIG. 23 . 
         FIG. 25  is a schematic side view of an inclination detector comprising electric contact pads, for an application angle of 90°. 
         FIG. 26  is a schematic side view of the inclination detector shown in  FIG. 33 , for an application angle of 130°. 
         FIG. 27  represents a flow chart illustrating a method of operating a depilating device. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the drawings, similar or analogous features appearing in different Figures are designated using the same reference numerals and are not necessarily described more than once. 
       FIG. 1  schematically illustrates an example of a generic depilating device  14  applied to skin  11  by a user (not shown). The depilating device  14  comprises a depilating member  18  contacting the skin  11  at a skin contact surface  20 , and a body  16  for being held by the user. The body  16  may, for example, include a housing enclosing a motor (not shown) coupled to the depilating member  18  for driving the depilating member  18 . The depilating member  18  is designed for removing or cutting hairs  12  on the skin  11  when brought into contact with the hairs  12 . The depilating member  18  may be of any type known in the art. The depilating member  18  may, for example, comprise rotatable clamping discs for extracting hairs  12  from the skin  11 , or cutter teeth, or a shaving foil for cutting the hairs  12 . The depilating device  14  is designed for being moved by the user across the skin  11  in either the moving direction  30  or in the moving direction  32 , the moving directions  30  and  32  being opposite to each other. The body  16  has a longitudinal axis  24  which in the illustrated case coincides with the intersection of a first symmetry plane and a second symmetry plane of the body  16 , the first symmetry plane being parallel to the Figure and the second symmetry plane being perpendicular to it, wherein the outer shape of the body  16  is essentially symmetric under reflections by the first symmetry plane and under reflections by the second symmetry plane. The longitudinal axis  24  defines an angle  28  relative to the surface  10  of the skin  11 . The angle  28  thus defined is referred to as the application angle (α)  28 . The application angle  28  is thus defined as the inclination of the body  16  relative to the surface  10  of the skin  11 . Alternatively, the application angle could be defined relative to a normal axis  22  perpendicular to the surface  10  of the skin  11 , the normal axis  22  intersecting the surface  10  of the skin  11  at point  40 . In the Figure, the application angle  28  is 60°. Accordingly the angle  26  between the normal axis  22  and the longitudinal axis  24  is 30°. In the example shown, the total allowed range for the application angle  28  is approximately 15° to 165°. The total allowed range is understood to be that range of application angles in which depilation by the depilating device  14  is possible. However the depilating device  14  behaves unsatisfactorily or at least not in an optimal manner if the application angle  28  is not within a certain sub range of the total allowed range. In other words, the depilating device  14  has an operational characteristic which depends on the application angle  28  and which is optimum only for a certain value of the application angle  28  or for a sub range of application angles  28 , the sub range being substantially smaller than the total allowed range of application angles. The operational characteristic may, for example, be the effectiveness in removing hairs  12  from the skin  11 , or, in the case where the depilating member  18  is designed for cutting hair, the average length of the remaining stubs of hair. The overall performance of the depilating device  14  may be optimum when the depilating device is applied at a right angle to the skin  11 , i.e. for an application angle  28  of about 90°, in which case the normal axis  22  coincides with the longitudinal axis  24 . The range of application angles  28  for which the depilating device  14  functions properly typically covers about 30° and is centered on an optimum application angle. The optimum application angle is typically 90°, but this is not necessarily the case. Depending on the device design, for some devices the optimum application angle may, for example, be about 60°. Furthermore some depilating devices may have two optimum application angles, such as 60° and −60°, or even more. 
     The definition of the application angle  28  depends on how the longitudinal axis  24  is defined relative to the depilating device  14 . It is also noted that depilating devices are known or may be conceived in which the depilating member  18  can be inclined relative to the body  16  by a variable angle. In this case, it may be convenient to define the longitudinal axis relative to the depilating member  18  rather than to the body  16 . 
     It has been mentioned above that the user does not necessarily apply the depilating device  14  at an optimal application angle  28 , in particular if the user is not aware of the correct application angle. For example, if the optimum application angle is 90° with a tolerance of 15°, the user may tilt the depilating device beyond the optimal range of application angles of 75° to 105°. In the particular case of a depilating device  14  having a depilating member  18  that comprises tweezers for extracting hairs, an optimal depilation result may then not be achieved because the tweezers lift up relative to the skin  11 . 
       FIG. 2  is a simplified front view of the depilating device  14  discussed above with reference to  FIG. 1 , as seen when looking in the moving direction  30 . The depilating member  18  contacts the skin  11  via the elongated skin contact surface  20  perpendicular to the moving directions  30 ,  32  shown in  FIG. 1 . Depending on the design of the depilating member  18 , the elongated skin contact surface  20  may be continuous, for example, in the case where the depilating member  18  comprises a flexible shaving foil, or discontinuous, for example in the case where the depilating member  18  comprises a plurality of clamping discs (not shown), each clamping disc contacting the surface  10  of the skin  11  on a segment of its circumference. 
     Referring now to  FIG. 3 , there is shown in a simplified manner a depilating device  14  comprising a depilating member  18  for removing hair  12  from skin  11 , and a feedback mechanism for generating a tactile and/or acoustic and/or optical feedback signal when the application angle  28  (i.e. the angle  28  between the longitudinal axis  24  of the depilating device  14  and the skin  11 ) passes from a predefined first range to a predefined second range while the depilating member  18  is applied to the skin  11 . The second range adjoins the first range and depilation is possible both when the application angle  28  is in the first range and when the application angle  28  is in the second range. The depilating device  14  has a characteristic which is a function of the application angle  28  and which is optimum for an optimum application angle, the optimum application angle being in the first range. In the example shown, the first range lies between the second range and a third range, the first, second and third range comprising application angles between 75° and 105°, less than 75°, and more than 105°, respectively. The feedback signal will alert a user (not shown) of the device  14  when the application angle  28  passes from the first range to the second range of application angles, e.g. from 76° to 74°. The feedback mechanism generates a tactile and/or acoustic and/or optical feedback signal also when the application angle  28  passes from the first range to the third range (e.g. from 104° to 106° while the depilating member  18  is applied to the skin  11 . The longitudinal axis  24  is fixed relative to the body  16  for holding the depilating device  14 . The skin contact member  34  is attached to the body  16  of the depilating device  14  by means of an axle  38 . The axle  38  defines a pivot axis  54  about which the skin contact member  34  is pivotable relative to the body  16 . The pivot axis  54  defined by the axle  38  extends parallel to the skin contact surface  36  and perpendicularly to the moving directions  30  and  32  and, when the depilating device  14  is applied to the skin  11 , the pivot axis  54  is also parallel to the surface  10  of the skin  11 . In the example shown, the axle  38  is offset relative to the surface of the skin  10  on an axis  78  perpendicular to the skin  11 . The application angle  28  may be varied by pivoting the body  16  relative to the skin contact member  34  about the pivot axis  54 , the skin contact member  34  remaining fixed relative to the skin  11 , at least as long the application angle  28  is within the first, second, or third range. It is noted that pivoting the body  16  about the pivot axis  54  implies shifting the intersection point  40  parallel to the surface of the skin  11 . The skin contact member  34  has an essentially plane skin contact surface  36  for contacting the skin  11 . When the depilating device  14  is applied to the skin  11 , as shown in the Figure, the skin contact surface  36  is parallel to the surface  10  of the skin  11 . Thus the pivot angle  29  defined as the angle between the longitudinal axis  24  and the skin contact surface  36  coincides with the application angle  28 . In fact a primary purpose of the skin contact member  34  is to translate the application angle  28  into an internal angle, namely the pivot angle  29 , of the depilating device  14 . Thus the feedback signal is delivered when the pivot angle  29  passes from the predefined first range to the predefined second range. The feedback mechanism thus involves triggering the feedback signal as a function of the variation of the pivot angle  29 . In the Figure, the application angle (α)  28  and hence the pivot angle  29  equal 60°. 
       FIGS. 4 and 5  further illustrate the depilating device  14  discussed above with reference to  FIG. 3 , for different values of the application angle (α)  28 . In  FIG. 4  the application angle  28  equals 90°, the longitudinal axis  24  being perpendicular to the surface  10  of the skin  11 . In  FIG. 5 , the application angle  28  is 120°. 
     In  FIGS. 6 to 9 , there is schematically illustrated a depilating device  14  comprising a body  16  and a skin contact member  34  having a skin contact surface  36 . The body  16  is pivotable relative to the skin contact member  34  about a pivot axis  54 . The pivot axis  54  is perpendicular to the longitudinal axis  24  of the body  16  and extends parallel to the skin contact surface  36  and also parallel to the surface  10  of the skin  11  as long as the depilating device  14  is applied to the skin  11  in an operational position. An operational position is understood to be a position of the depilating device  14  relative to the skin  11  to be treated, such that the depilating device  14  is able to depilate the skin  11  in an optimal or in a suboptimal manner. The longitudinal axis  24  of the body  16  defines an application angle  28  relative to the skin  11 . The longitudinal axis  24  further defines a pivot angle  29  relative to the skin contact surface  36 . The application angle  28  and the pivot angle  29  coincide as long as the skin contact surface  36  is parallel to the surface  10  of the skin  11 . The total possible range for the application angle  28  comprises an optimal first range  5 , a suboptimal second range  3 , a suboptimal third range  7 , and suboptimal non-working ranges  1  and  9 . The non-working range  1 , the suboptimal second range  3 , the optimal first range  5 , the suboptimal third range  7 , and the non-working range  9  are adjoining and are separated by borders  2 ,  4 ,  6 , and  8 , respectively. In the example shown, the border  2  between the non-working range  1  and the suboptimal second range  3  is at 60°; the border  4  between the suboptimal second range  3  and the optimal first range  5  is at 75°; the border  6  between the optimal first range  5  and the suboptimal third range  7  is at 105°; and the border  8  between the suboptimal third range  7  and the non-working range  9  is at 120°. By changing the inclination of the body  16  relative to the skin, a user of the depilating device  14  may vary the value of the application angle  28  in a continuous manner. In the example shown, the application angle  28  may thus assume any value between around 0° and 180°, although depilation is impossible for application angles smaller than about 60° or larger than about 120°. In line with the invention, the depilating device  14  generates a feedback signal when the application angle  28  passes from the optimal first range  5  to the suboptimal second range  3  as the application angle  28  crosses the border  4  between the first range  5  and the second range  3 . The depilating device  14  also generates a feedback signal when the application angle  28  passes from the optimal first range  5  to the suboptimal third range  7  as the application angle  28  crosses the border  6  between the first range  5  and the third range  3 . Additionally, feedback signals may be provided for the contrary sense of movement, that is, when the application angle  28  enters the optimal first range  5  either from the suboptimal second range  3  or from the suboptimal third range  7 . 
     In  FIG. 6 , the depilating device  14  is applied to the skin  11  at an application angle  28  of 90°, i.e. the longitudinal axis  24  of the body  16  is perpendicular to the surface  10  of the skin  11 . From the direction of the longitudinal axis  24 , the application angle  28  is seen to lie in the optimal first range  5 . In the present example, the application angle  28  of 90° is an optimal application angle, in the sense that depilation by the depilating device  14  is most efficient for this particular value of the application angle  28 . 
     In  FIG. 7 , the depilating device  14  is applied to the skin  11  at an application angle  28  of 82°. From the direction of the longitudinal axis  24 , the application angle  28  is seen to lie still in the optimal first range  5 . 
     In  FIG. 8 , the depilating device  14  is applied to the skin  11  at an application angle  28  of 67°. From the direction of the longitudinal axis  24 , the application angle  28  is seen to lie in the suboptimal second range  3 . It is noted that when the application angle  28  is within any of the optimal first range  5 , the suboptimal second range  3 , and the suboptimal third range  7 , the pivot angle  29  coincides with the application angle  28 , the skin contact surface  36  of the skin contact member  34  then being parallel to the surface  10  of the skin  11 . 
     In  FIG. 9 , the depilating device  14  is applied to the skin  11  at an application angle  28  of only 50°. From the direction of the longitudinal axis  24 , the application angle  28  is seen to lie in the non-working second range  1 . The pivot angle  29  now differs from the application angle  28 . The reason is that in the embodiment shown, the pivot angle  29  is restricted to the range consisting of the optimal first range  5 , the suboptimal second range  3 , and the suboptimal third range  7 . When the pivot angle  29  reaches the minimum allowed value of 60°, a part of the body  16  contacts another part of the skin contact member  34  such that pivoting the body  16  any further relative to the skin contact member  34  is mechanically impossible. Thus, when the application angle  28  is in any of the non-working ranges  1  and  9 , the skin contact member  34  partially lifts off the skin  11  such that the skin contact surface  36  is no longer parallel to the surface  10  of the skin  11 . The skin contact surface  36  being not parallel to the skin  11 , the application angle  28  and the pivot angle  29  differ. It is pointed out, however, that the pivotable skin contact member may alternatively be designed such that its pivot angle coincides with the application angle for all possible values of the application angle. 
     Referring now to  FIG. 10 , there are schematically represented two internal states  44  and  48  of a depilating device comprising a feedback mechanism for generating a tactile and/or acoustic and/or optical feedback signal when the application angle, defined as the angle between the skin surface and a longitudinal axis of the depilating device, passes from a predefined first range to a predefined second range while the depilating device is applied to the skin. An internal state is understood to be a state of the device which depends only on the depilating device itself but not on any relation between the device and its surroundings. In particular the position or inclination of the device relative to the skin is not an internal state of the device. An internal state may, for example, be characterized by the mutual positions of members of the depilating device. The depilating device may be designed such that when the application angle is in the first range the depilating device is in the first state  44  and when the application angle is in the second range the depilating device is in the second state  48 . The second state  48  is energetically higher than the first state  44 . Furthermore the first state  44  is coupled to the second state  48  as symbolized by the dashed line  46 . Thus, if the depilating device is left isolated, it may automatically return from the second state  48  to the first state  44 , wherein the energy difference between the first state  44  and the second state  48  may be dissipated, for example by friction. The second state  48  being energetically higher than the first state  44  means that a user of the device needs to supply energy in order to make the application angle pass from the first range to the second range. In particular the user may need to apply a certain force, hence a certain amount of energy, to cause a transition from the first state  44  to the second state  48 . Thus, when tilting the depilating device such that the application angle passes from the first to the second range, the user may experience a mechanical resistance of the depilating device, the resistance constituting a tactile feedback signal. 
     Schematically represented in  FIG. 11  are three internal states of a depilating device having a feedback mechanism for generating a tactile and/or acoustic and/or optical feedback signal when the application angle passes from a predefined first range to a predefined second range or from the predefined first range to a predefined third range while the depilating device is applied to the skin. When the application angle is in the first range, the depilating device is in its first internal state  44 . When the application angle is in the second or third range, the depilating device is in the second internal state  48  or in the third internal state  52 , respectively. Both the second internal state  48  and the third internal state  52  are higher in energy compared to the first internal state  44 . In the example shown, the second internal state  48  and the third internal state  52  are equal in energy. A physical coupling  46  exists between the first internal state  44  and the second internal state  48 . Similarly a physical coupling  50  exists between the first internal state  44  and the third internal state  52 . Due to the couplings  46  and  50 , the depilating device may return automatically from the second internal state  48  and from the third internal state  52  to the first internal state  44 . 
     Referring now to  FIG. 12 , there is shown in a schematic and simplified manner a bottom view of a depilating device  14  of the type discussed above with reference to  FIGS. 3 to 5 . The skin contact member  34  has the skin contact surface  36  and forms a frame surrounding a treatment window through which the depilating member  18  may contact the skin (not shown). The pivot axis  54  is defined by the axle  38  (not shown) by means of which the body  16  (not shown) may be pivoted relative to the skin contact member  34 . Rigidly attached to opposite inner side walls  57  and  59  are a carrier  58  for engaging with a spring  62  and a carrier  56  for engaging with another spring  60 . Each of the carriers  58  and  60  has two bearings, as will be illustrated in greater detail with reference to  FIGS. 13 to 18 . The spring  60  is mobile relative to the carrier  56  in the sense that it may engage with either of the two bearings of the carrier  56 , depending on whether the pivot angle  29  (not shown) is in a predefined first range or in a predefined second range. In the Figure, the pivot angle is assumed to be within the first range. For the sake of clarity, the first range is assumed here and with reference to  FIGS. 13 to 18  to be the angular range from 75° to 105°. 
       FIGS. 13 ,  14 , and  15  provide more detailed bottom views of the carriers  56  and  58  introduced above with reference to  FIG. 12 . The carrier  56  comprises a bearing  72  for engaging with the spring  60  when the pivot angle  29  (see  FIGS. 3 to 5  and  12  to  14 ) is larger than 75°. The carrier  56  also comprises a bearing  64  for engaging with the spring  60  when the pivot angle is less than 75°. Similarly, the carrier  58  comprises a bearing  74  for engaging with the spring  62  when the pivot angle is less than 105°, and a bearing  66  for engaging with the spring  62  when the application angle is larger than 105°. Each of the bearings  64 ,  66 ,  72  and  74  is provided by a notch traversing the carrier  56  respectively the carrier  58  in a direction perpendicular to the skin contact surface  36  shown in  FIGS. 3 ,  4 ,  5 , and  8 . The notch providing the bearing  64  and the notch providing the bearing  72  of the carrier  56  are separated by a barrier  68  preventing a transition of the spring  60  from the bearing  72  to the bearing  64  and vice-versa if no force is exerted on the spring  60  or by the spring  60  itself. The bearings  66  and  74  of the carrier  58  are arranged similarly to those of the carrier  56 . 
       FIGS. 16 ,  17 , and  18  are simplified side views of the carrier  58  and the spring  62  discussed above with reference to  FIGS. 12 to 15 , for three different values of the application angle  28 . The depilating device  14  being applied to the skin  11 , the pivot angle  29  defined by the orientation of the skin contact member  34  (shown in  FIG. 12 ) relative to the longitudinal axis  24  is identical to the application angle  28 . In each of  FIGS. 16 ,  17 , and  18 , the carrier  58  and the spring  62  are shown relative to the skin  11  and the moving directions  30 ,  32 . Also indicated is the pivot axis  54  of the skin contact member  34 . A support  76  is rigidly attached to a housing  16  (not shown) of the depilating device  14 . To facilitate the understanding of the Figures, the skin  11 , the carrier  58  and the pivot axis  54  may be assumed immobile, whereas the support  76  may be pivoted about the pivot axis  54 . The spring  62  may for example be a thin metal rod or leaf. An upper end of the spring  62  is maintained by the support  76  while a lower end of the spring  62  engages with either the bearing  66  or the bearing  74 . The relative position of the support  76  and the carrier  58  determines the shape of the spring  62  and also the bearing  74  or  66  the spring  62  engages with. The support  76  holds the spring  62  by means of a notch oriented along the longitudinal axis  24  such that the spring  62  would extend along the longitudinal axis  24  from the support  76  toward the intersection point  40  of the longitudinal axis  24  and the skin surface  10  if the spring&#39;s lower end were free. The support  58  forces the lower end of the spring to point along an axis  78  defined by the bearing  74  or along an axis  80  defined by the bearing  66 , depending on whether the spring  62  engages with the bearing  74  or with the bearing  66 . 
     In  FIG. 16 , the application angle is 60°. The spring  62  engages with the bearing  74  so as to minimize its energy, since, if the spring  62  engaged with the bearing  66 , it would have to bend more and would thus possess more energy as compared to the configuration shown. In other words, the spring  62  “chooses” the bearing  74  or  66  so as to minimize its deviation from a straight line. 
     In  FIG. 17 , the application angle  28  is 90°. The spring  62  accordingly engages with the bearing  74  of the carrier  58  so as to minimize its energy. 
     In  FIG. 18 , the application angle  28  is 120°. The spring  62  engages with the bearing  66  of the carrier  58  so as to minimize its energy. If it engaged with the bearing  74 , it would have to bend more and would thus have more energy. 
     Comparing  FIGS. 17 and 18 , it is noted that the spring  62  performs a transition from the bearing  74  to the bearing  66  as the application angle  28  passes from 90° to 120°. The bearings  74  and  66  and the barrier  70  separating them are shaped such that the spring&#39;s  62  transition from the bearing  74  to the bearing  66  happens abruptly at a predetermined value of the pivot angle  29 , for example at 105°. The abrupt transition produces, via the skin contact member  34 , a palpable effect on the skin  11 . Furthermore it produces a click sound. The spring&#39;s  62  transition from the bearing  74  to the bearing  66  (and possibly also its back transition from the bearing  66  to the bearing  74  when the pivot angle  29  passes from 120° to) 90°) thus produces a tactile and/or acoustic feedback signal. 
     Referring now to  FIG. 19 , there is illustrated in a schematic and simplified manner a depilating device  14  comprising a pivotable skin contact member  34  for contacting the skin  11 , wherein the pivot angle  29  of the skin contact member  34  relative to the longitudinal axis  24  coincides with the application angle  28  when the depilating device  14  is applied to the skin  11 , at least as long as the application angle  28  is within an optimal first range or a suboptimal second range. It is recalled that the application angle  28  is the angle between the surface  10  of the skin  11  and the longitudinal axis  24  defined by the body  16 . Mounted to the body  16  of the depilating device  14  is an epilation cylinder  82  for driving clamping discs or other hair removing means (not shown). The epilation cylinder  82  is mounted to the body  16  by means of an axle  84  extending parallel to the surface  10  of the skin  11  and perpendicular to the moving directions  30  and  32 . Tilting the body  16  relative to the skin  11  is equivalent to pivoting the body  16  about the pivot axis  54 , thereby changing the application angle  28 . For application angles in the optimal first range of between 75° and 105° the epilation cylinder  82  rotates without contacting the skin contact member  34 . However, when the application angle assumes values of about 75° or 105°, the epilation cylinder  82  comes into contact with a rib  90  or a rib  92 , respectively, of the skin contact member  34 . Arranged on the circumference  88  of the epilation cylinder  82  are regularly spaced protrusions or knobs  86 . The rib  90  or the rib  92  contacting the epilation cylinder  82  while the latter is being rotated about the axle  84  creates a rattling sound and induces vibrations of the skin contact member  34 , whereby an acoustic and tactile feedback signal is given to the user. The body  16  is coupled to the skin contact member  34  by means of springs  94 ,  96 . This ensures that the pivot angle  29  will automatically return to its equilibrium value of about 90° if no external torque relative to the pivot axis  54  is applied on the body  16 , e.g. when the user releases the depilating device  14 . In other words, the skin contact member  34  will automatically rotate back to its equilibrium position relative to the body  16  when the depilating device  14  is taken off the skin  11 . 
     Shown in  FIG. 20  is an embodiment similar to the one discussed above with reference to  FIG. 15 . The depilating device  14  comprises a first skin contact member  34  having a skin contact surface  36 , and a second skin contact member  35  having a skin contact surface  37 . The first skin contact member  34  and the second skin contact member  35  are mobile relative to each other so that they may adapt themselves, at least to a certain degree, to a curved skin surface  10 . The skin contact surface  37  of the second skin contact member  35  defines a second pivot angle  29  relative to the body  16  of the depilating device, while the skin contact surface  36  of the first skin contact member  34  analogously defines a first pivot angle (not indicated) relative to the body  16 . A rib  90  of the first skin contact member  34  contacts the epilation cylinder  82  when the first pivot angle deviates from its equilibrium value of 90° by more than about 15°, to create a rattling sound and vibrations of the first skin contact member  34 . Similarly, a rib  92  of the second skin contact member  35  contacts the epilation cylinder  82  when the second pivot angle  29  deviates form its equilibrium value of about 90° by more than about 15°, to create a rattling sound and vibrations of the skin contact member  35 . 
     Illustrated in  FIGS. 21 to 24  is a depilating device  14  according to a fourth embodiment. The depilating device  14  comprises a body  16  and a depilating member  18  comprising a plurality of rotatable clamping discs. A skin contact member  34  mounted to the body  16  is pivotable about a pivot axis  54 . Integrated in the body  16  are an ON/OFF button  98  for starting and stopping a motor (not shown) in the body, and a lamp  100  for emitting either red or green light. The depilating device  14  further comprises an inclination detector (not shown) for measuring the pivot angle  29  between the longitudinal axis  24  of the depilating device  14  and the skin contact member  34 . The inclination detector is arranged so as to deliver an electric voltage when the pivot angle  29  is outside a predefined first range (e.g. 75° to 105° and to deliver no voltage when the pivot angle  29  is within the first range. The inclination detector&#39;s output is fed to an electronic microcontroller (not shown) coupled to the lamp  100 . When the depilating device  14  is ON (its motor running), then as long as the pivot angle  29  is within the first range the lamp  100  emits green light, indicating to the user that the depilating device  14  is being applied to the skin at a good application angle. When the application angle and thus the pivot angle  29  leave the first range, the inclination detector no longer delivers a voltage to the microcontroller. The microcontroller accordingly causes the lamp  100  to emit red light. The lamp&#39;s color changing from green to red constitutes an optical feedback signal for the user. The lamp may, for example, comprise a red and a green light-emitting diode (LED), or a bicolor LED. 
     In a related embodiment, the lamp  100  is a single-color lamp coupled to the skin contact member  34  such that when the pivot angle  29  is in the optimal first range the lamp  100  is off, whereas when the pivot angle  29  is outside the optimal first range the lamp  100  emits light, for example red light. The lamp  100  may in particular be a red LED. 
     In another related embodiment (not shown), the skin contact member  34  is coupled mechanically to a mechanical slide indicator arranged on the body  16 . The slide indicator is advantageously arranged close to the skin contact member  34 , as this allows for a particularly simple coupling mechanism between the indicator and the skin contact plate  34 . The slide indicator is of the type commonly used for indicating whether a door is locked or unlocked. It comprises a slidable or pivotable indicator plate having a first portion which is red while a second portion is green. The indicator plate is coupled to the skin contact member  34  and the body  16  of the depilating device  14  such that when the pivot angle  29  is in the optimal first range, only the green portion of the indicator plate is visible, the red portion being hidden by the body  16 . In contrast, when the pivot angle  29  is outside the optimal first range, only the red portion of the indicator plate is visible. The visible portion changing from green to red (or from red to green) then constitutes an optical feedback signal for the user. Of course, arbitrary color combinations may be used instead of the conventional pair of colors green and red. 
     Referring to  FIGS. 25 and 26 , there is illustrated in a simplified manner a mechanism for generating in a depilating device  14  an electric or electronic signal as a function of the application angle  28 . The depilating device  14  comprises a body (not shown) defining a longitudinal axis  24 . The depilating device  14  further comprises a pivotable skin contact member (not shown), the skin contact member being of the type discussed above with reference to  FIGS. 3 to 5  and defining a pivot angle  29  that is identical to the application angle  28  when the depilating device  14  is applied to the skin  11 , provided that the application angle is within an optimal first range or a suboptimal second range. The skin contact member is mounted to the body by means of an axle  38  extending parallel to the pivot axis  54 , that is, perpendicular to the plane of the Figures. The axle  38  is rigidly coupled to the body and is coated on its end surface visible in the Figures by a first conductor segment  102  covering the angular range between directions  110  and  112 , the directions  110  and  112  being fixed relative to the body and hence to the longitudinal axis  24 . The skin contact member comprises a second conductor segment  104  covering the angular range between directions  114  and  116 . The position of the first conductor segment  102  relative to the second conductor segment  104  depends on the value of the pivot angle  29  and hence on the application angle  28 . As seen in  FIG. 25 , when the application angle  28  is within a first range, the first conductor segment  102  and the second conductor segment  104  are separated by gaps  106  and  108 . When the application angle  28  is outside the first range, as illustrated in an exemplary manner in  FIG. 26 , the first conductor segment  102  comes to lie below the second conductor segment  104 . The conductor segments  102  and  104  are spring-biased toward each other so that they contact each other when they come to lie below each other. The conductor segments  102  and  104  thus contact each other when the application angle  28  is outside the first range. Both conductor segments  102  and  104  form part of an electric or electronic circuit coupled, for example, to a lamp arranged on the body of the depilating device  14  such that when the conductor segments  102  and  104  do not contact each other the lamp emits green light whereas when the conductor segments  102  and  104  contact each other the lamp emits red light. 
     Referring now to  FIG. 27 , there is represented in a schematic and simplified manner a method of operating a depilating device as described above with reference to  FIGS. 1 and 2 . The method starts in step  200 . In a subsequent step  201  the depilating device is applied to the skin with an application angle belonging to an optimal range of application angles. In a subsequent step  202 , it is determined whether the application angle is still in the optimal range. If the application angle is found to be in the optimal range, the process returns to step  202 . Otherwise a tactile and/or acoustic and/or optical feedback signal is generated (step  203 ). In a subsequent step  204 , it is again determined whether the application angle is in the optimal range. If the application angle is found to be in the optimal range, the process returns to step  202 . Otherwise the process returns to step  204 . The process may be terminated at any time, e.g. by removing the depilating device from the skin. 
     While the invention has been illustrated and described in detail in the drawings and in the foregoing description, the drawings and the description are to be considered exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Equivalents, combinations, and modifications not described above may also be realized without departing from the scope of the invention. 
     The verb “to comprise” and its derivatives do not exclude the presence of other steps or elements in the matter the “comprise” refers to. The indefinite article “a” or “an” does not exclude a plurality of the subjects the article refers to. It is also noted that a single unit may provide the functions of several means mentioned in the claims. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.