Electric shaver with a rotatable external cutting member having a V-shaped hair entry opening

Abstract

The electric shaver 1 comprises at least one hair-cutting unit 9a, 9b, 9c having a central axis 11, an external cutting member 13 with a hair entry opening 61 and an internal cutting member 15. The internal and external cutting members are each rotated about the central axis in a first rotation direction R1 at a first rotation speed ω1 and in a second rotation direction R2 opposite to the first rotation direction at a second rotation speed ω2 lower than the first rotation speed. The hair entry opening has a V-shaped opening 63 facing away from the second rotation direction R2. The tangential speed VT of the external cutting member relative to the central axis 11, measured at a radial position RC of a central origin 65 of the V-shaped opening, is in the range between 7.5 cm / s and 50 cm / s.

Description

[Technical field]

[0001] The present invention relates to an electric shaver, comprising: at least one hair-cutting unit having a central axis, an outer cutting member having a hair entry opening in an annular shaving area concentrically arranged about the central axis, and an inner cutting member surrounded by the outer cutting member and having an annular array of cutting elements concentrically arranged about the central axis; and a drive system configured to rotate the internal cutting member of each hair-cutting unit about a central axis of the hair-cutting unit in a first rotational direction at a first rotational speed, and to rotate the external cutting member of each hair-cutting unit about the central axis of the hair-cutting unit in a second rotational direction opposite to the first rotational direction at a second rotational speed lower than the first rotational speed. [Background technology]

[0002] Electric shavers are well known, comprising at least one hair-cutting unit having a central axis, an external cutting member having a hair entry opening in an annular shaving area arranged concentrically around the central axis, an internal cutting member covered by the external cutting member and having an annular array of cutting elements arranged concentrically around the central axis, and a drive system configured to rotate the internal cutting member of each hair-cutting unit relative to the external cutting member around the central axis of the hair-cutting unit. Such electric shavers usually have a shaving unit with two or more such hair-cutting units supported by a support structure of the shaving unit. Electric shavers usually have a main housing that houses an electric motor. The shaving unit can be coupled to the main housing in a permanent or releasable manner. When the shaving unit is coupled to the main housing, the motor is coupled to the internal cutting member of the hair-cutting unit via a transmission system, which enables the motor to rotate the internal cutting member relative to the external cutting member. During rotation of the internal cutting member, hair enters the external cutting member through the hair entry opening of the external cutting member and is cut by interaction of a cutting edge provided on the cutting element of the rotating internal cutting member with a counter-cutting edge provided at the hair entry opening of the external cutting member. Summary of the Invention [Problem to be solved by the invention]

[0003] An important characteristic of the hair-cutting unit of such an electric shaver is the hair capture efficiency, i.e. the extent to which hair can enter the hair entry opening of the external cutting member while the electric shaver moves over the user's skin with the annular shaving area of ​​the external cutting member in contact with the skin. A high hair capture efficiency is desirable because it reduces the time of the shaving process required to obtain a desired shaving result, for example in terms of the average remaining hair length after the shaving process. The higher the hair capture efficiency, the more hairs enter the hair entry opening of the external cutting member and are cut by the hair-cutting unit, for example during a single moving stroke of the electric shaver over a specific area of ​​the skin, and the smaller the average remaining hair length after the shaving process. In order to improve the hair capture efficiency, it is also proposed to rotate the external cutting member of the hair-cutting unit around the central axis of the hair-cutting unit. In particular, for this purpose it is proposed to rotate the external cutting member in a rotational direction opposite to that of the internal cutting member at a rotational speed (number of revolutions per unit time) significantly lower than that of the internal cutting member. For this purpose, known electric shavers have a drive system configured to rotate the internal cutting member of each hair-cutting unit in a first rotational direction and at a first rotational speed around a central axis of the hair-cutting unit and to rotate the external cutting member of each hair-cutting unit in a second rotational direction opposite to the first rotational direction and at a second rotational speed lower than the first rotational speed around the central axis of the hair-cutting unit. Examples of such known electric shavers are disclosed in the following prior art documents:

[0004] US 2,283,834 discloses an electric shaver with a hair-cutting unit having an external cutting member with a slit-like hair entry opening extending substantially radially with respect to a central axis of the hair-cutting unit. The hair-cutting unit has an internal cutting member which is rotated at a relatively high speed, for example 6,000-15,000 rpm. The external cutting member is rotated in a direction opposite to the direction of rotation of the internal cutting member at a significantly lower speed in the range of 40-120 rpm, preferably about 80 rpm. According to this patent, the relatively slow and continuous rotation of the external cutting member results in oblique hairs growing in various directions being captured in the slit-like hair entry opening better and more regularly than is possible with a circular manual movement of a shaver with a stationary external cutting member.

[0005] US10,195,751B2 discloses an electric shaver with a shaving unit having three hair-cutting units. Each hair-cutting unit has an internal cutting member and an external cutting member with a slit-shaped hair entry opening, a circular hair entry opening, or a combination of a circular and a slit shape extending radially with respect to the central axis of the hair-cutting unit. The internal cutting member and the external cutting member of each hair-cutting unit are driven to rotate in opposite directions around the central axis of the hair-cutting unit. According to this patent, the rotation of the external cutting member has the advantageous effect of improving the user's action to raise and capture hair, thereby providing a more pleasant feel on the skin. In one example, the shaver has a gear transmission mechanism configured to convert a motor rotation speed of 8,000 rpm to a rotation speed of the external cutting member of about 10 rpm.

[0006] US 6,901,662 B1 discloses an electric shaver with a shaving unit having three hair-cutting units. Each hair-cutting unit has an internal cutting member and an external cutting member with a hair entry opening in the form of a slot or hole perforation. The internal and external cutting members of each hair-cutting unit are rotated in opposite directions to each other around the central axis of the hair-cutting unit. Furthermore, the three hair-cutting units are mounted on a common support frame that is rotated around the central axis of the shaving unit relative to a stationary shaver body. According to this patent, the rotation of the external cutting members around the central axis of the hair-cutting units combined with the rotation of the hair-cutting units around the central axis of the shaving unit results in all hair tips being erected and forced into the slot or hole perforations of the external cutting members. The rotation speed of the external cutting members is approximately twice the rotation speed of the common support frame to which the hair-cutting units are mounted. In particular, the rotational speed of the outer cutting member is in the range of 2-10 revolutions per second (120-600 rpm) and the rotational speed of the common support frame is in the range of 1-5 revolutions per second (60-300 rpm). However, the combined rotation of the inner and outer cutting members about the central axis of the hair-cutting unit and the hair-cutting unit about the central axis of the shaving unit requires a complex and bulky drive system. [Means for solving the problem]

[0007] The object of the present invention is to provide an electric shaver of the kind previously described in the section "Technical Field", which however has a significantly improved hair capturing efficiency compared to the electric shavers known at least from US 2,283,834 and US 10,195,751 and does not require an additional rotational movement of the hair-cutting unit around the central axis of the shaving unit as proposed by US 6,901,662 B1.

[0008] In order to achieve the above object, the present invention provides an electric shaver, comprising: at least one hair-cutting unit having a central axis, an outer cutting member having a hair entry opening in an annular shaving area concentrically arranged about the central axis, and an inner cutting member surrounded by the outer cutting member and having an annular array of cutting elements concentrically arranged about the central axis; a drive system configured to rotate the internal cutting member of each hair-cutting unit about a central axis of the hair-cutting unit in a first rotational direction at a first rotational speed and to rotate the external cutting member of each hair-cutting unit about the central axis of the hair-cutting unit in a second rotational direction opposite to the first rotational direction at a second rotational speed lower than the first rotational speed; a hair entry opening of the outer cutting member of each hair-cutting unit having a V-shaped opening facing towards the first rotational direction of the inner cutting member; The second rotational speed of the external cutting member of each hair-cutting unit is configured such that the tangential speed of the external cutting member relative to the central axis, measured at the radial position of the central origin of the V-shaped opening relative to the central axis, is in the range between 7.5 cm / s and 50 cm / s.

[0009] Thus, in the electric shaver according to the invention, the internal and external cutting members of each hair-cutting unit are rotated by the drive system in opposite directions around the central axis of the hair-cutting unit, where the second rotation speed (number of rotations per unit time) of the external cutting member is lower than the first rotation speed (number of rotations per unit time) of the internal cutting member. In particular, according to the invention, the hair entry opening of the external cutting member has a V-shaped opening facing in the opposite direction to the first rotation direction of the internal cutting member, i.e. the second rotation direction of the external cutting member. Furthermore, the second rotation speed of the external cutting member is configured such that the tangential speed of the external cutting member relative to the central axis, measured at the radial position of the central origin of the V-shaped opening relative to the central axis, is in the range between 7.5 cm / s and 50 cm / s. With respect to the V-shaped opening, the term "central origin" refers to the point where the two legs of the V-shaped opening connect to each other.

[0010] Experiments carried out by the inventors of the present invention have revealed that for a prior art hair-cutting unit having an external cutting member with a hair entry opening in the form of a straight slot extending substantially radially relative to the central axis of the hair-cutting unit, by rotating the external cutting member in a direction opposite to the rotation direction of the internal cutting member, an improvement in hair capture efficiency and, as a result, a reduction in the average remaining hair length after a shaving process is realized. However, it has been found that the improvement in hair capture efficiency and, as a result, a reduction in the average remaining hair length are relatively small and not even perceptible to the user. Experiments have further shown that for a hair-cutting unit having an external cutting member with a hair entry opening with a V-shaped opening facing a first rotation direction of the internal cutting member, by rotating the external cutting member in a direction opposite to the rotation direction of the internal cutting member at a second rotation speed such that the tangential speed of the external cutting member relative to the central axis is in the range between 7.5 cm / s and 50 cm / s, a very significant improvement in hair capture efficiency and, as a result, a very significant user-perceptible reduction in the average remaining hair length after a shaving process is realized. In particular, it has surprisingly been found that the relative increase in hair capture efficiency and the relative decrease in average remaining hair length as a result of rotation of the external cutting member relative to the hair capture efficiency and average remaining hair length achieved with a stationary external cutting member is significantly higher for an electric shaver according to the invention than for an electric shaver having an external cutting member with linear radially extending hair entry openings.

[0011] In an embodiment of the electric shaver according to the invention, the second rotation speed of the external cutting member of each hair-cutting unit is configured such that said tangential speed of the external cutting member relative to the central axis is in the range between 11.25 cm / s and 30.0 cm / s. In this embodiment, the previously mentioned significantly improved hair capture efficiency and the resulting noticeable and user-perceptible reduction in the average remaining hair length after the shaving process are achieved with a minimal degree of additional skin friction caused by the rotation of the external cutting member.

[0012] In a further embodiment of the electric shaver according to the invention, the hair entry opening of the external cutting member of each hair-cutting unit further comprises a radially inner linear opening connected to the V-shaped opening at a first end of the V-shaped opening facing the central axis of the hair-cutting unit and a radially outer linear opening connected to the V-shaped opening at a second end of the V-shaped opening facing away from the central axis of the hair-cutting unit, said radially inner and outer linear openings each having a main direction extending radially with respect to the central axis of said hair-cutting unit. In this embodiment, the radially inner linear opening and the radially outer linear opening of the hair entry opening provide a relatively high hair capture efficiency for hair approaching the hair entry opening of the external cutting member via the inner peripheral region of the annular shaving zone and the outer peripheral region of the annular shaving zone, respectively. The V-shaped opening of the hair entry opening provides a relatively high hair capture efficiency for hair approaching the hair entry opening via the central region of the annular shaving zone.

[0013] A particularly significant improvement in hair capture efficiency is achieved in an embodiment of the electric shaver according to the invention, in which the hair entry opening extends radially over a first radial distance relative to a central axis of the hair-cutting unit and the V-shaped opening of the hair entry opening extends radially over a second radial distance, the second radial distance being at least 50% of the first radial distance.

[0014] In a preferred embodiment of the electric shaver according to the invention, the V-angle of the V-shaped opening of the hair entry opening is in the range of 60° to 135°. In this embodiment, the V-angle is defined for the V-shaped opening as the angle enclosed by the two legs of the V-shaped opening. A V-angle in the range of 60° to 135° provides a stretching effect on the skin in two mutually divergent directions, which results in a reduced doming of the skin towards the hair entry opening, thereby resulting in a reduced skin irritation caused by the shaving process.

[0015] In a further embodiment of the electric shaver according to the invention, the cutting elements of the internal cutting members of each hair-cutting unit have cutting edges with a V-shaped cutting edge facing in the second rotation direction of the external cutting member, said V-shaped cutting edge and said V-shaped opening of the hair entry opening of said external cutting member being aligned in a tangential direction with respect to the central axis of said hair-cutting unit. Thus, in this embodiment, the V-shaped opening of the hair entry opening of the external cutting member and the V-shaped cutting edge of the cutting elements of the internal cutting member face in opposite directions. In this embodiment, due to the interaction of the V-shaped opening of the hair entry opening of the external cutting member and the V-shaped cutting edge of the cutting elements of the internal cutting member, the hairs captured at the hair entry opening are cut mainly in the central area of ​​the V-shaped opening, and as a result of the fact that the degree of doming of the skin into the hair entry opening is minimal, skin irritation caused by the shaving process is further reduced. It is noted that in this embodiment of the electric shaver according to the invention, the advantages of the invention in terms of improved hair capture efficiency are effectively combined with the advantages of improved shaving comfort, i.e. reduced skin irritation, provided by the shaving unit known from the Applicant's WO 2013 / 104965 A1. However, the invention also covers embodiments in which the cutting edges of the cutting elements have a more conventional shape, such as a substantially straight or slightly curved shape, each with a main direction extending radially.

[0016] As long as the first rotational speed of the internal cutting member is within the normal range applied to rotary electric shavers, the effect of this first rotational speed on the hair capturing efficiency of the hair-cutting unit is limited, so that the first rotational speed of the internal cutting member with respect to the central axis, measured at a radial distance from the central axis equal to the radial distance from the central axis at which the radial position of the central origin of the V-shaped opening is located, is in the range between 70 cm / s and 375 cm / s, more preferably in the range between 140 cm / s and 250 cm / s.

[0017] In an embodiment of the electric shaver according to the invention, the drive system comprises a single motor constructed and arranged to rotate both the internal cutting member of each hair-cutting unit and the external cutting member of each hair-cutting unit around a central axis of each hair-cutting unit via a transmission system. The use of a single motor simplifies the construction of the electric shaver. The motor can be arranged in a main housing of the shaver, and at least one hair-cutting unit is arranged in a shaving unit of the shaver coupled to the main housing, and the transmission system is arranged partly in the main housing and partly in the shaving unit. Instead of a single motor, the drive system can have a first motor for rotating the internal cutting member of each hair-cutting unit and a second motor for rotating the external cutting member of each hair-cutting unit independently of the rotation of the internal cutting member. In this alternative embodiment, the electric shaver can have, for example, a user input member, by means of which a user can select a second rotation speed of the external cutting member independent of the first rotation speed of the internal cutting member, or can switch on or off the rotation of the external cutting member independently of the rotation of the internal cutting member.

[0018] The above-mentioned and other aspects of the invention will become apparent from and will be elucidated with reference to the following detailed description of embodiments of an electric shaver according to the invention. [Brief description of the drawings]

[0019] [Figure 1] 1 shows a schematic diagram of an electric shaver according to the present invention; [Diagram 2] 2 is a schematic cross-sectional view of the hair-cutting unit of the electric shaver taken along line II-II in FIG. 1. [Diagram 3] FIG. 2 is a diagram illustrating a schematic diagram of a drive system of the electric shaver of FIG. [Figure 4a] FIG. 2 is a top view of the shaving unit of the electric shaver of FIG. 1. [Figure 4b] FIG. 4 shows a part of the drive system of FIG. 3. [Diagram 5]FIG. 3 is a top view of the external cutting member of the hair-cutting unit of FIG. 2; [Figure 6A] FIG. 13 is a graph showing the hair capture efficiency of an external cutting member with a straight hair entry opening as a function of the rotational speed of the external cutting member. [Figure 6B] 6 is a graph illustrating the hair capture efficiency of the external cutting member of FIG. 5 as a function of rotational speed of the external cutting member. [Figure 7a] FIG. 2 shows a graph of the shaving efficiency of a hair-cutting unit having an external cutting member with a straight hair entry opening as a function of the rotational speed of the external cutting member of the hair-cutting unit. [Figure 7b] FIG. 3 shows a graph of the shaving efficiency of the hair-cutting unit of FIG. 2 as a function of the rotational speed of the external cutting member of the hair-cutting unit. [Figure 8] FIG. 3 shows an internal cutting member of the hair-cutting unit of FIG. 2; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The invention will now be explained in more detail with reference to the figures, in which equivalent or similar features are designated with the same reference numbers.

[0021] FIG. 1 shows a schematic representation of an embodiment of an electric shaver 1 according to the invention. The electric shaver 1 comprises a main housing 3 designed to be held in the hand of a user during operation. The shaving device 1 further comprises a shaving unit 5 coupled to the main housing 3. The shaving unit 5 comprises a support structure 7 and three hair-cutting units 9a, 9b, 9c supported by the support structure 7. The support structure 7 may comprise a coupling structure, not shown in FIG. 1, of a type well known to a person skilled in the art, for releasably coupling the shaving unit 5 to the main housing 3. Alternatively, the shaving unit 5 may be permanently connected to the main housing 3. It is noted that the shaving unit of an electric shaver according to the invention may comprise a different number of hair-cutting units, for example one, two or more than two hair-cutting units. It is further noted that FIG. 1 merely shows a general layout of an electric shaver in a schematic manner and is not intended to limit the scope of the invention to the specific detailed design of the electric shaver as shown. For example, the present invention also covers embodiments of electric shavers in which the shaving unit is coupled to the main housing via a relatively narrow, centrally located coupling structure, where there is an open space between the shaving unit and the main housing around the periphery of said coupling structure, as is well known in the art.

[0022] Figure 2 is a schematic cross-sectional view of the hair-cutting unit 9c along line II-II in Figure 1. The hair-cutting units 9a and 9b are similar to the hair-cutting unit 9c. The hair-cutting unit 9c has a central axis 11, an external cutting member 13 and an internal cutting member 15. The external cutting member 13 has an annular shaving area 17 arranged concentrically around the central axis 11. The annular shaving area 17 is configured to contact the skin of a user of the electric shaver 1 and has hair entry openings (not visible in Figure 2) which will be described in more detail below. The hair entry openings are separated from each other by bridges 19 provided in the annular shaving area 17. The internal cutting member 15 is covered by the external cutting member 13 and has an annular arrangement of cutting elements 21 arranged concentrically around the central axis 11. The electric shaver 1 comprises a drive system, described in more detail below, configured to rotate the internal cutting member 15 and the external cutting member 13 relative to one another about a central axis 11 during operation of the electric shaver 1. As a result of the mutual rotation of the internal cutting member 15 and the external cutting member 13, hair on the user's skin entering a hair entry opening present in the annular shaving zone 17 is cut by interaction of a cutting edge 23 present in the cutting element 21 of the internal cutting member 15 with a counter-cutting edge 25 present in the bridge portion 19 of the external cutting member 13. It is noted that an electric shaver according to the invention may have two or more annular shaving zones arranged concentrically around a central axis, as is known in the art.

[0023] The drive system of the electric shaver 1 described above is shown diagrammatically in Fig. 3 and referenced with the reference number 27. In the embodiment shown in Fig. 3, the drive system 27 comprises a single motor 29 arranged in the main housing 3. According to the invention, the drive system 27 is configured to rotate the internal cutting member 15 of each hair-cutting unit 9a, 9b, 9c around the central axis 11 of the hair-cutting unit 9a, 9b, 9c in a first rotational direction R1 (shown in Fig. 2) at a first rotational speed ω1 and to rotate the external cutting member 13 of each hair-cutting unit 9a, 9b, 9c around the central axis 11 of the hair-cutting unit 9a, 9b, 9c in a second rotational direction R2 (shown in Fig. 2) opposite to the first rotational direction R1 at a second rotational speed ω2 lower than the first rotational speed ω1. For this purpose, the drive system 27 comprises a transmission system 31, via which the motor 29 can rotate both the internal cutting member 15 and the external cutting member 13 of each hair-cutting unit 9a, 9b, 9c. Here, the transmission system 31 is arranged partly in the main housing 3 and partly in the shaving unit 5. It should be noted that for the sake of simplicity, FIG. 3 shows in detail only one of the hair-cutting units 9c. In the following, the driving of the other hair-cutting units 9a, 9b by the drive system 27 will be described. It should further be noted that for the sake of simplicity, FIG. 3 shows only partly the support structure 7 of the shaving unit 5.

[0024] As shown in Fig. 3, the transmission system 31 comprises a first primary gear wheel 33 and a second primary gear wheel 35, each mounted on a motor shaft 37 of the motor 29. The transmission system 31 further comprises three secondary gear wheels 39, each mounted on a respective one of the three drive spindles 41, which are each coupled to a respective one of the three internal cutting members 15 of the hair-cutting units 9a, 9b, 9c and rotatably journalled relative to the support structure 7 of the shaving unit 5. Each of the three secondary gear wheels 39 engages with the first primary gear wheel 33. It should be noted that Fig. 3 shows only one of the secondary gear wheels 39 and one of the drive spindles 41 coupled to the internal cutting member 15 of the hair-cutting unit 9c, and that the secondary gear wheels and drive spindles associated with the internal cutting members 15 of the hair-cutting units 9a, 9b are arranged in a corresponding manner.

[0025] The transmission system 31 further comprises a second shaft 43 arranged parallel to the motor shaft 37. The upper part of the second shaft 43 is arranged between the two secondary gear wheels 39, but this arrangement is not visible in FIG. 3. The second shaft 43 carries a third primary gear wheel 45 which engages with the second primary gear wheel 35 via a number of intermediate gear wheels 47, and a fourth primary gear wheel 49. The transmission system 31 further comprises a third shaft 51 arranged in line with the motor shaft 37 and rotatably journalled with respect to the support structure 7 of the shaving unit 5. The third shaft 51 carries a fifth primary gear wheel 53 which engages with the fourth primary gear wheel 49, and a sixth primary gear wheel 55. Each of the external cutting members 13 of the hair-cutting units 9a, 9b, 9c has a secondary gear wheel 57 which engages with the sixth primary gear wheel 55 which is centrally arranged between the secondary gear wheels 57 of the external cutting member 13. It should be noted that Fig. 3 only shows the secondary gear wheel 57 of the external cutting member 13 of the hair-cutting unit 9c, and that the secondary gear wheels 57 of the external cutting members 13 of the hair-cutting units 9a and 9b are arranged in a corresponding manner. For clarity, the arrangement of the secondary gear wheels 57 of the external cutting members 13 of all three hair-cutting units 9a, 9b, 9c is shown in Fig. 4b. Fig. 4a shows that the external cutting members 13 are surrounded by skin support members 59a, 59b, 59c of each individual hair-cutting unit 9a, 9b, 9c. The skin support members 59a, 59b, 59c provide a rotational bearing for each individual external cutting member 13 and also cover the secondary gear wheel 57 of each individual external cutting member 13.

[0026] It should be noted that the drive system 27 described here above is only one example of how a drive system in an electric shaver according to the invention can be embodied. A person skilled in the art will be able to design alternative embodiments of the drive system. With this drive system, according to the invention, the internal cutting member 15 and the external cutting member 13 of each hair-cutting unit 9a, 9b, 9c can be rotated in mutually opposite directions R1, R2 around a central axis, where the second rotation speed ω2 of the external cutting member 13 is lower than the first rotation speed ω1 of the internal cutting member 15. Instead of a single motor 29, the drive system 27 can have a first motor for rotating the internal cutting member 15 of each hair-cutting unit 9a, 9b, 9c and a second motor for rotating the external cutting member 13 of each hair-cutting unit 9a, 9b, 9c independently of the rotation of the internal cutting member 15. In this alternative embodiment, the electric shaver 1 can have, for example, a user input member. Using the user input member, the user can select the second rotational speed ω2 of the external cutting member 13 independent of the first rotational speed ω1 of the internal cutting member 15, or can switch the rotation of the external cutting member 13 on or off independent of the rotation of the internal cutting member 15.

[0027] From electric shavers of the prior art it is known that the hair capturing efficiency of the hair-cutting units 9a, 9b, 9c is improved by rotating the external cutting member 13 of each hair-cutting unit 9a, 9b, 9c in a rotation direction R2 opposite to the rotation direction R1 of the internal cutting member 15 and at a rotation speed ω2 lower than the rotation speed ω1 of the internal cutting member 15. The hair capturing efficiency is the extent to which hair can enter the hair entry opening of the external cutting member 13 while the electric shaver 1 moves over the skin of the user with the annular shaving area 17 of the external cutting member 13 in contact with the skin. The higher the hair capturing efficiency, the better the hair will enter the hair entry opening of the external cutting member 13 and be cut by the hair-cutting units 9a, 9b, 9c, for example during one moving stroke of the electric shaver 1 over a particular area of ​​the skin, resulting in a smaller average remaining hair length after one moving stroke.

[0028] In order to further improve the hair capture efficiency of the hair-cutting units 9a, 9b, 9c, according to the present invention, the external cutting member 13 of each hair-cutting unit 9a, 9b, 9c of the electric shaver 1 has a hair entry opening 61 with a V-shaped opening 63 facing in a direction opposite to the first rotation direction R1 of the internal cutting member 15, i.e. the second rotation direction R2 of the external cutting member 13, as shown in Fig. 5. Furthermore, according to the present invention, the second rotation speed ω2 of the external cutting member 13 of each hair-cutting unit 9a, 9b, 9c is configured such that the tangential speed VT of the external cutting member 13 relative to the central axis 11 of the hair-cutting unit 9a, 9b, 9c is in the range between 7.5 cm / s and 50 cm / s. In this respect, said tangential speed VT is measured at a radial position RC of the central origin 65 of the V-shaped opening 63 relative to the central axis 11, as shown in Fig. 5. The central origin 65 is the point of the V-shaped opening 63 where the two legs 67a, 67b of the V-shaped opening 63 join each other, as also shown in Fig. 5. Therefore, VT = 2π × RC × ω2 and ω2 = VT / (2π × RC). The inventors of the present invention carried out experiments in the form of numerical simulations using a mathematical model of human skin with hair, a mathematical model of a hair-cutting unit with an external cutting member with a straight slot-like hair entry opening extending substantially radially to the central axis of the hair-cutting unit, and a mathematical model of the hair-cutting units 9a, 9b, 9c. Figs. 6a and 6b respectively show graphs of the hair capture efficiency of the external cutting member with a straight hair entry opening and the external cutting member 13 as a function of the second rotation speed ω2 (in rpm). In these figures, the hair capture efficiency is expressed as the average penetration depth APD (mm) of the hair into the hair entry opening of the individual external cutting members. The simulations were performed for a uniform hair length of 1 mm and for multiple single strokes of the individual external cutting members over a particular skin area with stroke speeds between 10 cm / s and 30 cm / s. For the external cutting member 13, the radial position RC of the central origin 65 of the V-shaped opening 63 relative to the central axis 11 is 9 mm. For the external cutting member with a straight hair entry opening, the radial position of the radial centre point of the straight hair entry opening is also 9 mm. Thus, the value of ω2=500 rpm in the graph corresponds to VT=47 cm / s.The graph shows that the hair capture efficiency (APD) of the external cutting member with a straight hair entry opening is comparable to that of the external cutting member 13 without rotational movement of the external cutting member (ω2=0). With rotation of the external cutting member, the hair capture efficiency (APD) of the external cutting member with a straight hair entry opening is increased slightly, and as shown in FIG. 6a, the optimum hair capture efficiency is achieved at a rotation speed ω2 of about 200 rpm. With rotation of the external cutting member 13 of the electric shaver 1 according to the present invention, as shown in FIG. 6b, the hair capture efficiency (APD) of the external cutting member 13 is increased to a significantly greater extent compared to the external cutting member with a straight hair entry opening. As shown in FIG. 6b, the optimum hair capture efficiency is achieved for the external cutting member 13 at a second rotation speed ω2 of about 300 rpm. In particular, as is evident from Figures 6a and 6b, it has been found that the relative increase in hair capture efficiency (APD) as a result of rotation of the external cutting member, i.e. the ratio of the average penetration depth (APD) of the hair into the hair entry opening with and without rotation of the external cutting member, is significantly higher for the external cutting member 13 of the electric shaver 1 according to the present invention than for an external cutting member having a linear radially extending hair entry opening.

[0029] 7a and 7b show graphs of the shaving efficiency of the hair-cutting unit with an external cutting member with a straight hair entry opening and the hair-cutting units 9a, 9b, 9c, respectively, as a function of the second rotation speed ω2 (units: rpm). In these figures, the shaving efficiency is expressed as the average hair length reduction ALR (mm) achieved by the individual hair-cutting units. The simulations were performed for a uniform hair length of 1 mm and for multiple single strokes of the individual external cutting members over a specific skin area with stroke speeds between 10 cm / s and 30 cm / s. For the external cutting members 13 of the hair-cutting units 9a, 9b, 9c, the radial position RC of the central origin 65 of the V-shaped opening 63 relative to the central axis 11 is 9 mm. For the hair-cutting units with an external cutting member with a straight hair entry opening, the radial position of the radial center point of the straight hair entry opening is also 9 mm. Thus, the value of ω2=500 rpm in the graph corresponds to VT=47 cm / s. The graph shows that in the absence of a rotational movement of the external cutting member (ω2=0), the shaving efficiency (ALR) of the hair-cutting units 9a, 9b, 9c is about 25% higher than the shaving efficiency of the hair-cutting unit with an external cutting member with a straight hair entry opening. With the rotation of the external cutting member, the shaving efficiency (ALR) of the hair-cutting unit with an external cutting member with a straight hair entry opening is slightly increased, and an optimal shaving efficiency is achieved for a rotation speed ω2 of about 120 rpm, as shown in FIG. 7a. With the rotation of the external cutting member 13 of the hair-cutting units 9a, 9b, 9c of the electric shaver 1 according to the invention, the shaving efficiency (ALR) of the hair-cutting units 9a, 9b, 9c is increased to a significantly greater extent compared to the hair-cutting unit with an external cutting member with a straight hair entry opening, as shown in FIG. 7b. As shown in FIG. 7b, for the hair-cutting units 9a, 9b, 9c, optimal shaving efficiency is achieved at a second rotation speed ω2 of about 300 rpm.In particular, as is evident from Figures 7a and 7b, it has been found that the relative increase in shaving efficiency (ALR) as a result of rotation of the external cutting member, i.e. the ratio of the average hair length reduction (ALR) with and without rotation of the external cutting member, is significantly higher for the hair-cutting units 9a, 9b, 9c of the electric shaver 1 according to the invention than for hair-cutting units having external cutting members with linear radially extending hair entry openings.

[0030] As can be seen from Fig. 7b, a significant increase in the shaving efficiency (ALR) of about 10% can already be achieved when the second rotation speed ω2 of the external cutting member 13 is about 80 rpm, corresponding to a value of VT of about 7.5 cm / s. As is evident from Fig. 7a, such a significant relative increase in the shaving efficiency (ALR) cannot be achieved with the rotation of an external cutting member with a straight hair entry opening. Moreover, the line Lth in Fig. 7a and Fig. 7b represents an increase in the shaving efficiency (ALR) that is considered to be particularly perceptible by the user of the electric shaver 1. For the external cutting member 13, such a particularly user-perceptible increase in the shaving efficiency (ALR) is achieved when the second rotation speed ω2 is between about 120 rpm (corresponding to VT = 11.25 cm / s) and about 550 rpm (corresponding to VT = 50 cm / s). In view of the relatively high skin friction caused by the rotation of the external cutting member 13, a value of VT exceeding 50 cm / s may not be favorable. Thus, according to the invention, the second rotational speed ω2 of the external cutting member 13 is configured such that said tangential speed VT of the external cutting member 13, measured at the radial position RC of the central origin 65 of the V-shaped opening 63 of the hair entry opening 61, is in the range between 7.5 cm / s and 50 cm / s, while a more preferred range of values ​​of VT is between 11.25 cm / s and 50 cm / s.

[0031] 7b, the relative increase in shaving efficiency (ALR) in the range for values ​​of ω2 between about 120 rpm (VT=11.25 cm / s) and about 300 rpm (VT=28.3 cm / s) is comparable to the relative increase in shaving efficiency (ALR) in the range for values ​​of ω2 between about 300 rpm (VT=28.3 cm / s) and about 550 rpm (VT=50 cm / s). Since the skin friction caused by the rotation of the external cutting member 13 is smaller at lower values ​​of VT, in accordance with an embodiment of the present invention, a range of VT values ​​between 11.25 cm / s and 30.0 cm / s provides a favorable combination of significantly improved hair capture efficiency and shaving efficiency as described hereinabove with a minimal degree of additional skin friction caused by the rotation of the external cutting member 13.

[0032] Similar experiments carried out on hair-cutting units having external cutting members in which the hair entry openings, in particular the V-shaped openings thereof, are located at a greater or lesser radial distance from the central axis compared to the radial distance RC of the external cutting member 13 described above, have shown that the range of values ​​of VT according to the invention described above, in which the advantages of the invention as described above are achieved, is independent of said radial distance. In other words, in embodiments of the invention in which the V-shaped openings 63 of the hair entry openings 61 are located at a greater or lesser radial distance RC from the central axis 11, the second rotation speed ω2 of the external cutting member 13 should be decreased or increased in proportion to said radial distance RC in order to achieve comparable results in terms of improved hair capture efficiency and shaving efficiency. For example, while in the previously described embodiment the second rotation speed ω2 is about 300 rpm (RC=9 mm), comparable results are achieved in an embodiment in which RC=12 mm with a second rotation speed ω2 of about 225 rpm and in an embodiment in which RC=6 mm with a second rotation speed ω2 of about 450 rpm.

[0033] As shown in Fig. 5, each hair entry opening 61 of the external cutting member 13 extends over a first radial distance RD1 radially relative to the central axis 11. Each V-shaped opening 63 of the hair entry opening 61 extends over a second radial distance RD2 radially relative to the central axis 11. In the embodiment shown in Fig. 5, the ratio RD2 / RD1 is about 0.75. A particularly significant improvement in hair capture efficiency and shaving efficiency is achieved in embodiments of the electric shaver in which the ratio RD2 / RD1 is at least 0.5. However, improvements in hair capture efficiency and shaving efficiency can also be achieved for smaller values ​​of the ratio, in particular when the first radial distance RD1 over which the hair entry openings 61 extend is relatively large.

[0034] In the embodiment shown in Fig. 5, the hair entry opening 61 of the external cutting member 13 further comprises a radially inner linear opening 69a and a radially outer linear opening 69b. The radially inner linear opening 69a is connected to the V-shaped opening 63 of the hair entry opening 61 at a first end 71a of the V-shaped opening 63 facing towards the central axis 11. The radially outer linear opening 69b is connected to the V-shaped opening 63 at a second end 71b of the V-shaped opening 63 facing away from the central axis 11. The radially inner and outer linear opening portions 69a, 69b each have a main direction extending radially with respect to the central axis 11. In this embodiment, the radially inner linear openings 69a provide a relatively high hair capture efficiency for hairs approaching the hair entry opening 61 of the external cutting member 13 through the inner peripheral region 73 of the annular shaving area 17 during random movement of the hair-cutting units 9a, 9b, 9c across the user's skin. During such random movement, the radially outer linear openings 69b provide a relatively high hair capture efficiency for hairs approaching the hair entry opening 61 through the outer peripheral region 75 of the annular shaving area 17, while the V-shaped openings 63 provide a relatively high hair capture efficiency for hairs approaching the hair entry opening 61 through the central region of the annular shaving area 17.

[0035] Furthermore, FIG. 5 shows the V-angle α of the V-shaped opening 63 of the hair entry opening 61, which is defined as the angle enclosed by the two legs 67a, 67b of the V-shaped opening 63. In the embodiment shown in FIG. 5, the V-angle α is about 115°. A preferred range for the V-angle α is between 60° and 135°. With the value of the V-angle α in this preferred range, the V-shaped opening 63 provides a stretching effect on the skin in two divergent directions during the rotation of the external cutting member 13 in the second rotation direction R2, in addition to improved hair capture efficiency and shaving efficiency. Said skin stretching effect results in a reduced doming of the skin to the hair entry opening 61, thereby reducing skin irritation caused by the shaving process.

[0036] FIG. 8 shows the internal cutting member 15 of the hair-cutting units 9a, 9b, 9c, the first direction of rotation R1 of the internal cutting member 15 around the central axis 11 of the hair-cutting units 9a, 9b, 9c, and the second direction of rotation R2 of the external cutting member 13. Each cutting element 21 of the annular array of cutting elements 21 is connected to the carrier 77 of the internal cutting member 15 via a bent connecting element 79. The carrier 77, the cutting elements 21 and the bent connecting element 79 can be integrally formed from a single metal sheet in a manner known to those skilled in the art. The cutting edge 23 of each cutting element 21 is provided on a leading or front edge (with respect to the first direction of rotation R1) of the upper surface 81 of the cutting element 21. The carrier 77 is coupled to one of the three drive spindles 41 of the drive system 27 mentioned above in a manner well known to those skilled in the art. The coupling between the drive spindle 41 and the carrier 77 is therefore omitted in FIG. 8.

[0037] In the embodiment shown in FIG. 8, each cutting edge 23 of the cutting element 21 of the internal cutting member 15 has a V-shaped cutting edge portion 83 facing in the second direction of rotation R2 of the external cutting member 13, i.e. in a direction opposite to the first direction of rotation R2 of the internal cutting member 15 and opposite to the direction in which the V-shaped opening 63 of the hair entry opening 61 of the external cutting member 13 faces. In the embodiment shown in FIG. 8, each V-shaped cutting edge portion 83 extends over the entire extension of the cutting edge 23. The V-shaped cutting edge portion 83 of the cutting edge 23 of the internal cutting member 15 and the V-shaped opening 63 of the hair entry opening 61 of the external cutting member 13 are aligned tangentially with respect to the central axis 11. Said alignment means that the central origin 85 of each V-shaped cutting edge portion 83 is located at a radial distance RCC from the central axis 11 substantially equal to the radial position RC of the central origin 65 of the V-shaped opening 63 with respect to the central axis 11. In this embodiment, the interaction of the V-shaped opening 63 of the hair entry opening 61 of the external cutting member 13 with the V-shaped cutting edge 83 of the cutting element 21 of the internal cutting member 15 further reduces skin irritation caused by the shaving process as a result of the fact that the hairs captured by the hair entry opening 61 are primarily cut in the central region of the V-shaped opening 63, where there is a minimum level of doming of the skin into the hair entry opening 61. It is noted, however, that the present invention also covers embodiments in which the cutting edges 23 of the cutting elements 21 of the internal cutting member 15 have more conventional shapes, such as a substantially straight or slightly curved shape, each with a main direction extending in a radial direction.

[0038] The first rotation speed ω1 of the internal cutting member 15 has a limited effect on the hair capture efficiency of the hair-cutting units 9a, 9b, 9c. Therefore, the first rotation speed ω1 can be selected mainly based on the required hair-cutting efficiency of the cutting elements 21 of the rotating internal cutting member 15, as known to those skilled in the art. In the embodiment of Fig. 8, the preferred range of the first rotation speed ω1 is configured such that the tangential speed VTT of the cutting elements 21 of the internal cutting member 15 relative to the central axis 11, measured at the radial distance RCC from the central axis 11, is in the range between 70 cm / s and 375 cm / s, more preferably in the range between 140 cm / s and 250 cm / s, as shown in Fig. 8. In the present embodiment with RCC = 9 mm, the above ranges of the above tangential speeds VTT correspond to the ranges of the first rotation speed ω1 between about 750 rpm and about 4000 rpm and between about 1500 rpm and about 2700 rpm, respectively.

[0039] The scope of the present invention is not limited to the above examples, and it will be apparent to those skilled in the art that some modifications and changes can be made thereto without departing from the scope of the present invention defined in the appended claims. It is intended that the present invention be construed as including all such modifications and changes insofar as they are within the scope of the claims or their equivalents. Although the present invention has been illustrated and described in detail in the drawings and description, such illustrations and descriptions are merely explanatory or exemplary and not restrictive. The present invention is not limited to the disclosed embodiments. The drawings are schematic, in which details that are not necessary for understanding the present invention may be omitted and are not necessarily drawn to scale.

[0040] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the figures, the description, and the appended 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. Any reference signs in the claims should not be construed as limiting the scope of the invention.

[0041] Elements and aspects discussed for or in connection with a particular embodiment can be combined with elements and aspects of other embodiments as appropriate, unless otherwise expressly stated. Thus, 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.

Claims

1. An electric shaver, at least one hair-cutting unit including a central axis, an outer cutting member having a hair entry opening in an annular shaving area concentrically disposed about the central axis, and an inner cutting member surrounded by the outer cutting member and having an annular array of cutting elements concentrically disposed about the central axis; a drive system for rotating the internal cutting member of each hair-cutting unit about a central axis of the hair-cutting unit in a first rotational direction at a first rotational speed and for rotating the external cutting member of each hair-cutting unit about a central axis of the hair-cutting unit in a second rotational direction opposite to the first rotational direction at a second rotational speed lower than the first rotational speed, the hair entry opening of the external cutting member of each hair-cutting unit has a V-shaped opening facing the first rotational direction of the internal cutting member; an electric shaver, wherein the second rotational speed of the external cutting member of each hair-cutting unit is configured such that a tangential speed of the external cutting member relative to the central axis, measured at a radial position of a central origin of the V-shaped opening relative to the central axis, is in the range of between 7.5 cm / s and 50 cm / s.

2. 2. The electric shaver of claim 1, wherein the second rotational speed of the external cutting member of each hair-cutting unit is configured such that the tangential speed of the external cutting member relative to the central axis is in the range between 11.25 cm / s and 30.0 cm / s.

3. 3. An electric shaver as claimed in claim 1 or 2, wherein the hair entry opening of the external cutting member of each hair-cutting unit further comprises a radially inner linear opening connected to the V-shaped opening at a first end of the V-shaped opening facing a central axis of the hair-cutting unit and a radially outer linear opening connected to the V-shaped opening at a second end of the V-shaped opening facing away from the central axis of the hair-cutting unit, the radially inner and outer linear openings each having a main direction extending radially with respect to the central axis of the hair-cutting unit.

4. 4. An electric shaver according to claim 1, wherein the hair entry opening extends over a first radial distance in a radial direction relative to a central axis of the hair-cutting unit, and the V-shaped opening of the hair entry opening extends over a second radial distance in the radial direction, the second radial distance being at least 50% of the first radial distance.

5. 5. An electric shaver according to claim 1, wherein the V-angle of the V-shaped opening of the hair entry opening is in the range of 60[deg.] to 135[deg.].

6. 6. An electric shaver as claimed in any one of claims 1 to 5, wherein the cutting elements of the internal cutting member of each hair-cutting unit have cutting edges with a V-shaped cutting edge portion facing in the second rotational direction of the external cutting member, the V-shaped cutting edge portion and a V-shaped opening of a hair entry opening of the external cutting member being aligned tangentially to a central axis of the hair-cutting unit.

7. 7. An electric shaver as claimed in any preceding claim, wherein the first rotational speed of the internal cutting member of each hair-cutting unit is configured such that a tangential speed of the internal cutting member relative to the central axis, measured at a radial distance from the central axis equal to the radial distance from the central axis at which the radial position of the central origin of the V-shaped opening is located, is in the range between 70 cm / s and 375 cm / s, more preferably in the range between 140 cm / s and 250 cm / s.

8. 8. The electric shaver according to claim 1, wherein the drive system comprises a single motor which rotates, via a transmission system, both the internal cutting member of each hair-cutting unit and the external cutting member of each hair-cutting unit about a central axis of the hair-cutting unit.

9. 9. The electric shaver of claim 8, wherein the motor is disposed within a main housing of the shaver, the at least one hair-cutting unit is disposed within a shaving unit of the shaver coupled to the main housing, and the transmission system is disposed partially in the main housing and partially in the shaving unit.

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