Electrical appliance for performing a cutting action on hairs as present on an area of skin

Abstract

An electrical appliance for performing a cutting action on hairs present on an area of skin (7) comprises at least one assembly of a driven internal cutting member (5) for cutting off the hairs and an external cutting member (6) which serves for contacting the area of skin (7) and also for covering and contacting the internal cutting member (5). The cutting members (5, 6) are designed such that friction between them is related to their condition of wear in a predetermined way. Information relating to an actual condition of wear of the cutting members (5, 6) is determined by measuring a parameter related to the friction between the cutting members (5, 6) and processing the parameter, and such information is indicated to a user of the appliance.

Claims

1. An electrical appliance for performing a cutting action on hairs present on an area of skin, the electrical appliance comprising: a functional head having at least one movably arranged internal cutting member for cutting off the hairs, and further having an external cutting member for contacting the area of skin, wherein the external cutting member is arranged in the functional head to cover and contact the internal cutting member, wherein the external cutting member is provided with hair-entry apertures for allowing the hairs to penetrate the external cutting member and thereby encounter the internal cutting member, and wherein the internal cutting member and the external cutting member are designed such that a friction between the internal cutting member and the external cutting member is related to a condition of wear of at least one of the internal cutting member and the external cutting member according to a predetermined relation between the friction and the wear; a motor for driving the internal cutting member of the functional head; measuring means for performing a measurement of a parameter related to the friction between the internal cutting member and the external cutting member; processing means for processing the measured parameter and thereby determining an actual condition of wear of one of the internal cutting member and the external cutting member on the basis of the measured parameter; and indicating means for providing a user, of the electrical appliance with information relating to the actual condition of wear of the one of the internal cutting member and the external cutting member; wherein the internal cutting member is rotatably arranged in the functional head, wherein the internal cutting member includes a pin which is arranged on a side of the internal cutting member facing the external cutting member and which extends in a direction towards the external cutting member, and wherein a length of the pin corresponds to a distance which, when present between the internal cutting member and the external cutting member, is predetermined to be a worn-away condition of at least one of the internal cutting member and the external cutting member.

2. The electrical appliance according to claim 1, wherein, according to the predetermined relation, the parameter has a predetermined property when the condition of wear is at a predetermined level corresponding to a required replacement of at least one of the internal cutting member and the external cutting member; and wherein the indicating means indicate the required replacement of the at least one of the internal cutting member and the external cutting member when the measured parameter has the predetermined property.

3. The electrical appliance according to claim 1, wherein the internal cutting member and the external cutting member are designed such that the friction between them is at a first level during a first period of operation following initial use and an initial running-in period of the internal cutting member and the external cutting member, the friction changes during a second period of operation following the first period of operation, and the friction is at a second level, which is different from the first level, during a third period of operation following the second period of operation.

4. The electrical appliance according to claim 3, wherein the internal cutting member and the external cutting member are furthermore designed to cause the friction to change during a fourth period of operation following the third period of operation, and the friction to be at a third level which is different from both the first level and the second level during a fifth period of operation following the fourth period of operation.

5. The electrical appliance according to claim 1, wherein the measuring means are adapted to perform a measurement of a parameter related to operation of the motor during idle running of the functional head.

6. The electrical appliance according to claim 1, wherein the processing means are adapted to determine a difference between a value of an actual measurement of the parameter and at least one reference value of the parameter, and to determine the information to be indicated to the user on the basis of the difference.

7. The electrical appliance according to claim 6, wherein the processing means are adapted to determine an end of an initial running-in period after the electrical appliance has been activated for the very first time, and to determine the at least one reference value of the parameter on the basis of a value of a measurement performed at the end of the running-in period.

8. The electrical appliance according to claim 1, wherein the internal cutting member and the external cutting member are designed to cause a change of at least one of: types of material in a contact area between the internal cutting member and the external cutting member; and a size and/or a position of the contact area between the internal cutting member and the external cutting member at a predetermined degree of wear.

9. The electrical appliance according to claim 1, wherein at least an area of the pin for contacting the external cutting member in the worn-away condition of the at least one of the internal cutting member and the external cutting member includes material for causing a change of friction between the internal cutting member and the external cutting member when, during operation, the area of the pin comes into contact with the external cutting member.

10. The electrical appliance according to claim 1, wherein the internal cutting member includes at least one bump/rib which is arranged on a side of the internal cutting member facing the external cutting member, and wherein the bumps/ribs of the internal cutting member are arranged for contacting the external cutting member when a predetermined degree of wear of the at least one of the internal cutting member and the external cutting member is reached and hence when the internal cutting member and the external cutting member have moved closer towards one another.

11. The electrical appliance according to claim 1, wherein one of the internal cutting member and the external cutting member includes a layered structure of at least two different materials in an area for contacting the other one of the internal cutting member and the external cutting member.

12. The electrical appliance according to claim 1, wherein a surface of one of the internal cutting member and the external cutting member facing the other one of the internal cutting member and the external cutting member includes an elevated surface portion intended to wear away as a result of contact with the other one of the internal cutting member and the external cutting member.

13. The electrical appliance according to claim 1, wherein a surface of one of the internal cutting member and the external cutting member facing the other one of the internal cutting member and the external cutting member is provided with at least one projection, and wherein a surface of the other one of the internal cutting member and the external cutting member is provided with at least one recessed portion at a similar position.

14. An electrical appliance for performing a cutting action on hairs present on an area of skin, the electrical appliance comprising: a functional head having at least one movably arranged internal cutting member for cutting off the hairs, and further having an external cutting member for contacting the area of skin, wherein the external cutting member is arranged in the functional head to cover and contact the internal cutting member, wherein the external cutting member is provided with hair-entry apertures for allowing the hairs to penetrate the external cutting member and thereby encounter the internal cutting member, and wherein the internal cutting member and the external cutting member are designed such that a friction between the internal cutting member and the external cutting member is related to a condition of wear of at least one of the internal cutting member and the external cutting member according to a predetermined relation between the friction and the wear; a motor for driving the internal cutting member of the functional head; measuring means for performing a measurement of a parameter related to the friction between the internal cutting member and the external cutting member; processing means for processing the measured parameter and thereby determining an actual condition of wear of one of the internal cutting member and the external cutting member on the basis of the measured parameter; and indicating means for providing a user, of the electrical appliance with information relating to the actual condition of wear of the one of the internal cutting member and the external cutting member; wherein the external cutting member is rotatably arranged in the functional head, wherein the external cutting member includes a pin which is arranged on a side of the external cutting member facing the internal cutting member and which extends in a direction towards the internal cutting member, and wherein a length of the pin corresponds to a distance which, when present between the internal cutting member and the external cutting member, is predetermined to be a worn-away condition of at least one of the internal cutting member and the external cutting member.

15. The electrical appliance according to claim 14, wherein at least an area of the pin for contacting the internal cutting member in the worn-away condition of the at least one of the internal cutting member and the external cutting member includes material for causing a change of friction between the internal cutting member and the external cutting member when, during operation, the area of the pin comes into contact with the internal cutting member.

16. The electrical appliance according to claim 15 wherein the external cutting member includes at least one bump/rib which is arranged on a side of the external cutting member facing the internal cutting member, and wherein the bumps/ribs of the external cutting member are arranged for contacting the internal cutting member when a predetermined degree of wear of the at least one of the internal cutting member and the external cutting member is reached and hence when the internal cutting member and the external cutting member have moved closer towards one another.

17. An electrical appliance for performing a cutting action on hairs present on an area of skin, the electrical appliance comprising: a head having at least one movably arranged internal cutting member for cutting the hairs, and further having an external cutting member for contacting the area of skin, wherein the external cutting member is arranged in the head to cover and contact the internal cutting member, wherein the external cutting member is provided with hair-entry apertures for allowing the hairs to enter the external cutting member and thereby encounter the internal cutting member, and wherein the internal cutting member and the external cutting member are designed such that a friction between the internal cutting member and the external cutting member is related to a condition of wear of at least one of the internal cutting member and the external cutting member according to a predetermined relation between the friction and the wear; a motor for driving the internal cutting member of the head; measuring means for performing a measurement of a parameter related to the friction between the internal cutting member and the external cutting member; processing means for processing the measured parameter and thereby determining an actual condition of wear of one of the internal cutting member and the external cutting member on the basis of the measured parameter; and indicating means for providing a user of the electrical appliance with information relating to the actual condition of wear of the one of the internal cutting member and the external cutting member; wherein the internal cutting member is rotatably arranged in the head, wherein the internal cutting member includes a pin which is arranged on a side of the internal cutting member facing the external cutting member and which extends in a direction towards the external cutting member, and wherein a length of the pin corresponds to a distance which is determinative of the condition of wear of at least one of the internal cutting member and the external cutting member and the condition of wear indicates the required replacement of at least one of the cutting members.

18. The electrical appliance according to claim 17, wherein the internal cutting member and the external cutting member are designed such that the friction between them is at a first level during a first period of operation following initial use and an initial running-in period of the internal cutting member and the external cutting member, the friction changes during a second period of operation following the first period of operation, and the friction is at a second level, which is different from the first level, during a third period of operation following the second period of operation.

19. The electrical appliance according to claim 17, wherein the processing means are adapted to determine a difference between a value of an actual measurement of the parameter and at least one reference value of the parameter, and to determine the information to be indicated to the user on the basis of the difference.

20. The electrical appliance according to claim 17, wherein one of the internal cutting member and the external cutting member includes a layered structure of at least two different materials in an area for contacting the other one of the internal cutting member and the external cutting member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained in greater detail with reference to the figures, in which equal or similar parts are indicated by the same reference signs, and in which:

(2) FIG. 1 diagrammatically shows a sectional view of a known configuration of a rotatably arranged internal cutting member, an external cutting member and a portion of skin;

(3) FIGS. 2 and 3 diagrammatically show a sectional view of a first embodiment according to the invention of a rotatably arranged internal cutting member, an external cutting member and a portion of skin, in two different conditions of wear of the cutting members;

(4) FIGS. 4 and 5 diagrammatically show a sectional view of a second embodiment according to the invention of a rotatably arranged internal cutting member, an external cutting member and a portion of skin, in two different conditions of wear of the cutting members, wherein it is noted that only a relevant portion of the cutting members is shown;

(5) FIG. 6 diagrammatically shows a sectional view of a third embodiment according to the invention of a rotatably arranged internal cutting member, an external cutting member and a portion of skin, wherein it is noted that only a relevant portion of the cutting members is shown;

(6) FIG. 7 diagrammatically shows a sectional view of a fourth embodiment according to the invention of a rotatably arranged internal cutting member;

(7) FIGS. 8 and 9 diagrammatically show a sectional view of a fifth embodiment according to the invention of a rotatably arranged internal cutting member, an external cutting member and a portion of skin, in two different conditions of wear of the cutting members, wherein it is noted that only a relevant portion of the cutting members is shown; and

(8) FIG. 10 illustrates how a device in communication with a shaving appliance can be used for indicating a condition of wear of the cutting members of the functional head of the appliance to a user of the appliance.

(9) These figures are only intended to provide a diagrammatic representation of aspects of the invention. In particular, the various components shown in the figures are not drawn to scale.

DETAILED DESCRIPTION OF EMBODIMENTS

(10) As mentioned in the foregoing, examples of the invention, as will be discussed in the following, are in the context of a shaving appliance of the rotary type. With reference to FIG. 10, it is noted that, in general, such a shaving appliance 1 is a hand-held appliance comprising a handle 2, which is intended to be taken hold of by a user 3, and a functional head 4 which is intended to be placed against the user's skin to be subjected to a shaving action. With reference to FIG. 1, it is furthermore noted that, in general, the functional head 4 comprises at least one assembly of an internal cutting member 5 and an external cutting member 6. The internal cutting member 5 is rotatably arranged and comprises a disc-shaped base 51 having a circular periphery and legs 52 extending from the periphery of the base 51 towards the external cutting member 6, the legs 52 having cutters at their free ends for cutting through the hairs to be removed from the skin 7. In the diagrammatic sectional view of FIG. 1, only two legs 52 are shown. It is known for the legs 52 to be distributed along the periphery of the base 51 and to be provided in a number which is considerably larger than two, e.g. twelve. In FIG. 1, an axis of rotation of the internal cutting member 5 is depicted as a dash-dot line and indicated by reference numeral 53. The external cutting member 6 is arranged such as to cover the internal cutting member 5, thereby preventing the internal cutting member 5 from contacting the skin 7, and comprises hair-entry apertures (not shown in FIG. 1) for allowing the hairs to penetrate the external cutting member 6 and hence encounter the internal cutting member 5. The shaving appliance 1 comprises a motor (not shown in any of the figures) for driving the internal cutting member 5 during operation of the appliance 1.

(11) In the shown examples, the external cutting member 6 is in contact with the internal cutting member 5 in a ring-shaped or torus-shaped area, which will hereinafter be referred to as shaving area 61, wherein contact between the cutting members 5, 6 is maintained under the influence of a force acting on the internal cutting member 5 in the direction of the external cutting member 6. Generally, the hair-entry apertures are present in the shaving area 61 and comprise a plurality of slits, dividing the shaving area 61 into lamellas 62. For the sake of completeness, it is noted that the slits may be radially oriented, but that other orientations are also possible. Also, besides the slits, more or less circular holes may be present in the external cutting member 6. Furthermore, it is noted that the thickness of the lamellas 62 is exaggerated in FIG. 1. In reality, the lamellas 62 are made to very accurate thickness dimensions in order to control a balance between skin irritation and shaving results. A practical thickness of the lamellas 62 is 80 microns with an accuracy of +/5 or 6 microns. Wear of the lamellas 62 taking place over time under the influence of contact with the rotating internal cutting member 5 may cause the thickness of the lamellas 62 to be reduced to 70 microns. When the thickness is reduced even further, to 60 microns or 50 microns, skin irritation will increase. However, this is usually not taken as a signal that at least the external cutting member 6 should be replaced by the user 3 of the shaving appliance 1, due to the gradual nature of the increase. This is a risk in the use of the appliance 1, because the shaving performance and the balance between skin irritation and smoothness of the shaving results can be restored only by timely replacing the external cutting member 6, and, in addition, the risk of breakage of the external cutting member 6 will be reduced to a minimum again.

(12) The invention provides a way of indicating to a user 3 an appropriate moment for replacing the cutting members 5, 6. In the following, various embodiments of the invention will be explained on the basis of FIGS. 2-10.

(13) In FIGS. 2 and 3, it is shown how the internal cutting member 5 can be equipped with a centrally arranged pin 10 on the side 54 of the internal cutting member 5 facing the external cutting member 6. In particular, in the shown example, the pin 10 has a central position in which a longitudinal axis 11 of the pin 10 coincides with the axis of rotation 53 of the internal cutting member 5. Furthermore, in the shown example, the pin 10 is shaped like a hollow cylinder having a ring-shaped end surface, wherein the radius of the pin 10 is smaller than the radius of the shaving area 61 of the external cutting member 6.

(14) In FIG. 2, an initial situation is illustrated, i.e. a situation in which the external cutting member 6 is free from wear. The length of the pin 10 is such that, in this situation, contact between the internal cutting member 5 and the external cutting member 6 occurs at the shaving area 61 of the external cutting member 6 only. In other words, the length of the pin 10 is shorter than the distance between the cutting members 5, 6 at the position of the pin 10 in the initial situation. FIG. 3 depicts a situation in which the thickness of the shaving area 61 has decreased with respect to the initial thickness due to wear, and in which contact between the internal cutting member 5 and the external cutting member 6 takes place at the shaving area 61 of the external cutting member 6 as well as at the end surface of the pin 10. In this situation, in view of the fact that the ring-shaped end surface of the pin 10 is considerably larger than the total of the surfaces of the cutters at the end of the legs 52 of the internal cutting member 5, most of the friction forces prevailing between the cutting members 5, 6 cover a considerably smaller diameter than in the initial situation, as a consequence of which the torque needed for the friction forces is considerably smaller.

(15) By applying the pin 10, it is possible to find the exact moment in time when the condition of wear of the cutting members 5, 6 is such that replacement is appropriate. This can be attributed to the fact that the length of the pin 10 can be chosen such that it is ensured that the pin 10 comes into contact with the external cutting member 6 when the thickness of the lamellas 62 has decreased to a predetermined extent. For example, if it is advisable to replace the external cutting member 6 when the thickness of the lamellas 62 has decreased by 15 microns, the length of the pin 10 is chosen such as to equal the distance between the cutting members 5, 6 at the position of the pin 10 in the initial situation minus 15 microns and the associated wear of the internal cutting member 5, which may exceed 15 microns in practical cases.

(16) On the basis of the fact that motor power is directly related to the torque provided by the motor, it is a practical possibility to measure the power which is consumed by the motor for operating the appliance 1 when it has just been switched on but not yet been placed against the user's skin 7, and to compare the actual value as found to a reference value associated with a situation of acceptable wear in order to determine whether the pin 10 is in contact with the external cutting member or not. As soon as it is found that the actual value differs too much from the reference value, for example, by 30% or 40%, it is safe to assume that the large difference is caused by contact of the pin 10, so that a reliable indication can be given to the user 3 that it is time to replace the external cutting member 6, and possibly also the internal cutting member 5.

(17) The reference value of the motor power can be determined in any possible way. For example, it is an option to log the initial motor power over time and conclude that the pin 10 is in contact with the external cutting member 6 when the power changes to a considerable extent.

(18) It is noted that it is alternatively possible to measure the motor power during a shaving action in order to assess the condition of wear of the cutting members 5, 6. However, in such a case, power is not only needed to overcome friction, but also to perform a cutting process. As a consequence, it is hard to distinguish the friction power from the cutting power. That is the reason why it is preferred to perform the measurement of the motor power for the purpose of determining the condition of wear of the cutting members 5, 6 before a shaving action is actually started, i.e. the time which is available between the moment that the user 3 switches on the appliance 1 and places the functional head 4 against the skin 7 to be subjected to the shaving action.

(19) In FIGS. 4 and 5, another option for obtaining a reliable indication of the condition of wear of the cutting members 5, 6 is illustrated. According to this option, which is applicable to both rotary systems and linear systems, the lamellas 62 of the external cutting member 6 comprise an elevated surface portion 63 on the side 64 facing the internal cutting member 5. In general, in the friction regime of shaving, friction is proportional to the contact area between the cutting members 5, 6 due to a viscous component of the friction forces. In particular, skin grease between the internal cutting member 5 and the lamellas 62 of the external cutting member 6 shears when the internal cutting member 5 moves with respect to the external cutting member 6, and it is this shearing of grease which leads to shear forces which are proportional to the shearing/contact area. Hence, it is possible to have different outcomes of measurements of the motor power or another suitable parameter and to link those outcomes to different dimensions of contact surfaces.

(20) In particular, in the shown example, initial contact between the cutting members 5, 6 is established through the elevated surface portion 63 of the lamellas 62 of the external cutting member 6. With use and time, the elevated surface portion 63 of the appliance 1 gets worn away. As a result, at a certain point in time, there is a change of the nature of the contact between the cutting members 5, 6, wherein the contact changes from contact through the elevated surface portion 63 of the lamellas 62, which has relatively small dimensions with respect to the total dimensions of the lamellas 62, to contact through a major portion of the lamellas 62. This change can be detected because it involves an increase of friction forces and a related increase of motor power needed during idle running. By choosing an appropriate height of the elevated surface portion 63 of the lamellas 62, the change of the motor power can be relied upon for obtaining an indication that the cutting members 5, 6 are in a worn-away condition. It will be clear to a person skilled in the art that it is equally well possible to apply elevated surface portions on the internal cutting member 5 for obtaining the above-described change of the dimensions of the contact area between the cutting members 5, 6 at a predetermined degree of wear of the cutting members 5, 6.

(21) FIG. 6 illustrates how the sides 54, 64 of the cutting members 5, 6 facing each other can be provided with a special shape in order to obtain a reliable indication of the condition of wear of the cutting members 5, 6. In the shown example, which is applicable to both rotary systems and linear systems, the sides 54, 64 of said cutting members 5, 6 are not flat, but comprise a pattern of projections 55, 65 and recesses 56, 66. When the cutting members 5, 6 move closer towards each other due to wear, the force needed to move the internal cutting member 5 with respect to the external cutting member 6 increases, as during the movement increasingly higher obstacles are encountered at the positions of the transitions of the recesses 56, 66 to the projections 55, 65, each time a cutter of the internal cutting member 5 moves over a lamella 62 of the external cutting member 6. For the sake of completeness, it is noted that in FIG. 6 a number of lamellas 62 is shown, wherein the hair-entry apertures which are present between the lamellas 62 are indicated by reference numeral 8.

(22) As explained in the foregoing, a time-varying level of force needed to move the internal cutting member 5 can be used in a process of determining the condition of wear of the cutting members 5, 6. In the case illustrated in FIG. 6, a considerable increase of the force is directly related to a worn-away condition of the cutting members 5, 6. Furthermore, as explained in the following, measuring a motor power parameter, such as the torque, every time that the appliance 1 is switched on is a practical option for monitoring the variation of the force level.

(23) FIG. 7 illustrates how it is possible to obtain an extremely reliable indication of different levels of wear when a pin 10 is used, such as shown in FIGS. 2 and 3. As explained in the foregoing, it is possible to use the pin 10 for indicating a condition of wear, based on the fact that as soon as the pin 10 contacts the external cutting member 6, the radius of contact between the cutting members 5, 6 decreases, which causes a reduction of the friction torque. By choosing an appropriate length of the pin 10, the moment of the reduction of the friction torque can be made to correspond to the moment that the condition of wear of the cutting members 5, 6 can be denoted as being a worn-away condition.

(24) According to the option illustrated in FIG. 7, two bumps 12, 13 are disposed at the ring-shaped end surface of the pin 10, in a diametrical positioning, wherein one bump 13 is higher than the other bump 12. The external cutting member 6 is also provided with at least one bump or rib on the side 64 facing the internal cutting member 5. (This is not illustrated in FIG. 7.) The use of the highest bump 13 on the pin 10 and, at a later stage, the lowest bump 12, involves a change in the shape of the signal representing the friction-related parameter during one rotation of the internal cutting member 5. For example, the highest bump 13 can be made so as to come into contact with the bump/rib of the external cutting member 6 after a first amount of wear of 15 microns. In that case, every rotation involves a peak in the signal. Eventually, as a result of continued operation of the appliance 1 over time, the highest bump 13 wears down and the cutting members 5, 6 move closer. At a certain point, after a second amount of wear, which may also be 15 microns, for example, the height of the highest bump 13 is reduced to such an extent that it resembles the height of the lowest bump 12, so that both bumps 12, 13 contact the bump/rib of the external cutting member 6 during one rotation, which results in a signal having two peaks per rotation. The bumps 12, 13 may be made from plastic, for example, in order to have bumps 12, 13 which are subject to wear in an appropriate way.

(25) The capability of distinguishing various predetermined levels of wear of the cutting members 5, 6 makes it possible to provide more detailed information to the user 3, disclosing the gradual change in the shaving appliance 1. In such a case, it may be desirable to use devices or services connected to the shaving appliance 1 for communicating the information to the user 3, as illustrated in FIG. 10. For example, the shaving appliance 1 with the wear-indicating functionality may be adapted to transmit information regarding the condition of wear of the cutting members 5, 6 to a mobile phone 9 through Bluetooth. That does not alter the fact that the hand-held appliance 1 may comprise a display or other suitable means for indicating a condition of wear. In any case, the shaving appliance 1 may be equipped with an internal or external controller (not shown) for controlling the process of measuring the motor power parameter at the appropriate time and determining the type of information to be indicated to the user 3 regarding the condition of wear of the cutting members 5, 6. In general, in case one or more external components are used with the shaving appliance 1, for example, components which serve as processing means and/or indicating means, the total arrangement comprising both the shaving appliance 1 and the relevant components is to be understood to make up the electrical appliance as defined in the claims.

(26) FIGS. 8 and 9 illustrate an option comprising at least one groove 67 in the side 64 of the external cutting member 6 facing the internal cutting member 5, said groove(s) extending in the direction of movement of the internal cutting member 5. Therefore, in a rotary system, the groove 67 has a generally ring-shaped appearance. In the sectional views of FIGS. 8 and 9, only one sectional half of the external cutting member 6 and a free end of one leg 52 of the internal cutting member 5 are shown. The basic concept applied in this embodiment is that a pin or rib has more friction when moving through a V-shaped groove than when moving on a flat surface. The outmost portion of the free end of the leg 52 is beveled, such that the portion has angled sides 57. In the initial situation, as shown in FIG. 8, the contact between the cutting members 5, 6 is only through a bottom 58 of the outmost portion of the leg 52 of the internal cutting member 5. After wear, contact is also through the angled sides 57, as shown in FIG. 9. In that situation, vertical forces acting on the internal cutting member 5 are partly transmitted through the angled sides 57. This leads to a high normal force on the sides 57, invoking high friction forces in the direction of movement perpendicular to the external cutting member 6. Hence, in the situation after wear, the friction is higher than in the initial situation. The increase in friction depends on the angle of the angled sides 57. By measuring a friction-related parameter, such as a motor power parameter, and determining whether the parameter has increased to such an extent that a worn-away condition of the cutting members 5, 6 has been reached, a useful indication of the condition of wear can be given to the user 3.

(27) It is possible to have more than one groove 67 in the external cutting member 6 and more than one portion having angled sides 57 at a corresponding position on the internal cutting member 5. In known embodiments of a rotary shaver, the shaving area 61 mentioned hereinbefore is present in the external cutting member 6, which almost has a suitable shape for acting as the groove 67 described in the foregoing. Thus, in such embodiments, it is preferred to have only one groove 67 in order to minimize adaptations to the design of the external cutting member 6.

(28) It will be clear to a person skilled in the art that the scope of the invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the invention as defined in the attached claims. While the invention has been illustrated and described in detail in the figures and the description, such illustration and description are to be considered illustrative or exemplary only, and not restrictive. The invention is not limited to the disclosed embodiments.

(29) Variations to the disclosed embodiments can be understood and effected by a person skilled in the art in practicing the claimed invention, from a study of the figures, the description and the attached claims. In the claims, the word comprising does not exclude other steps or elements, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the invention.

(30) In addition to the embodiments of the invention shown in the figures, or as an alternative, a concept comprising multiple layers of material of at least one of the cutting members 5, 6 at the contact position between the cutting members 5, 6, wherein a top layer may be worn away over time so that an underlying layer is exposed, and wherein a change of friction is obtained on the basis of a change of material, can be applied to arrive at a useful indication of the condition of wear of the cutting members 5, 6.

(31) In short, the invention relates to an electrical appliance 1 for performing a cutting action on hairs present on an area of skin 7, comprising at least one assembly of a driven internal cutting member 5 for cutting off the hairs and an external cutting member 6 for contacting the area of skin 7 and also for covering and contacting the internal cutting member 5. The cutting members 5, 6 are designed such that friction between them is related to their condition of wear in a predetermined way. Information relating to an actual condition of wear of the cutting members 5, 6 is determined by measuring a parameter related to the friction between the cutting members 5, 6 and processing the parameter, and such information is indicated to a user 3 of the appliance 1.