Electric shaver with a rotationally adjustable external cutting element having a rotationally adjustable rotation speed - Patents.com

Abstract

The electric shaver comprises at least one hair cutting unit having a central axis, an external cutting element having a hair entry opening, and an internal cutting element. The internal and external cutting elements are rotated at a first rotational speed (ω1) and a second rotational speed (ω2) respectively around the central axis, and the internal and external cutting elements are rotated relative to each other. The electric shaver further comprises a detection system for measuring at least one user-related parameter related to the skin or hair of the user of the electric shaver or related to the operation of the electric shaver by the user on the user's body. The electric shaver further comprises a processor for controlling the second rotational speed (ω2) of the external cutting element in response to at least one measured user-related parameter.

Description

[Technical Field]

[0001] The present invention provides at least one hair-cutting unit having a central axis, an outer cutting element having a hair entry opening in an annular shaving area concentrically disposed about the central axis, and an inner cutting element surrounded by the outer cutting element and having an annular array of cutting elements concentrically disposed about the central axis; a drive system configured to rotate the inner cutting element of each hair-cutting unit about the central axis of the hair-cutting unit at a first rotational speed and the outer cutting element of each hair-cutting unit about the central axis of the hair-cutting unit at a second rotational speed, such that the inner and outer cutting elements of each hair-cutting unit are rotated relative to one another about the central axis of the hair-cutting unit; The present invention relates to an electric shaver having: [Background technology]

[0002] Electric shavers are known that include at least one hair-cutting unit having a central axis, an outer cutting element having a hair entry opening in an annular shaving area concentrically arranged around the central axis, and an inner cutting element covered by the outer cutting element and having an annular array of cutting elements concentrically arranged around the central axis, and further include a drive system configured to rotate the inner cutting element of each hair-cutting unit relative to the outer cutting element around the central axis of the hair-cutting unit. Such electric shavers typically include a shaving unit having two or more such hair-cutting units supported by a support structure of the shaving unit. Electric shavers typically include a main housing that houses an electric motor. The shaving unit may be permanently or releasably coupled to the main housing. When the shaving unit is coupled to the main housing, the motor is coupled to the inner cutting element of the hair-cutting unit via a transmission system that allows the motor to rotate the inner cutting element relative to the outer cutting element. During rotation of the internal cutting element, hair enters the external cutting element through the hair entry opening of the external cutting element and is cut by interaction of a cutting edge on the rotating internal cutting element with an opposing cutting edge on the hair entry opening of the external cutting element.

[0003] An important characteristic of the hair-cutting unit of such an electric shaver is its hair-trapping efficiency, i.e., the degree to which hair can penetrate the hair entry opening of the external cutting element during movement of the electric shaver over the user's skin with the annular shaving area of ​​the external cutting element in contact with the skin. High hair-trapping efficiency is desirable because it reduces the shaving time required to achieve a desired shaving result, for example, in terms of the average remaining hair length after the shaving process. The higher the hair-trapping efficiency, the more hair penetrates the hair entry opening of the external cutting element and is cut by the hair-cutting unit, for example, during a single stroke of the electric shaver over a specific area of ​​skin, and the smaller the average remaining hair length obtained after the shaving process. To improve hair-trapping efficiency, it has also been proposed to rotate the external cutting element of the hair-cutting unit around the central axis of the hair-cutting unit. To this end, known electric shavers have a drive system configured to rotate the internal cutting element of each hair-cutting unit about the central axis of the hair-cutting unit at a first rotational speed (revolutions per unit time), to rotate the external cutting element of each hair-cutting unit about the central axis of the hair-cutting unit at a second rotational speed (revolutions per unit time), and to rotate the internal and external cutting elements of each hair-cutting unit relative to each other about the central axis of the hair-cutting unit.

[0004] U.S. Patent Application Publication No. 2,283,834 discloses an electric shaver with a hair-cutting unit having an external cutting element with a slit-shaped hair entry opening extending substantially radially relative to the central axis of the hair-cutting unit. The hair-cutting unit has an internal cutting element that is rotated at a relatively high speed, e.g., 6,000 to 15,000 revolutions per minute (rpm). The external cutting element is rotated in a direction opposite to the rotation of the internal cutting element at a significantly lower speed, in the range of 40 to 120 rpm, preferably about 80 rpm. According to this patent, the relatively slow, continuous rotation of the external cutting element allows oblique hairs growing in various directions to be captured better and more regularly in the slit-shaped hair entry opening than can be achieved by circular manual movement of a shaver with a stationary external cutting element.

[0005] US 10,195,751 B2 discloses an electric shaver with a shaving unit having three hair-cutting units. Each hair-cutting unit has an internal cutting element and an external cutting element with a slit-shaped hair entry opening extending radially relative to the central axis of the hair-cutting unit, a round hair entry opening, or a combination of a round and slit-shaped hair entry opening. The internal and external cutting elements of each hair-cutting unit are rotatably driven in the same direction or in opposite directions around the central axis of the hair-cutting unit. According to this patent, the rotation of the external cutting elements improves the hair-raising and catching action of the user's hair, thereby providing a beneficial effect of a better sensation on the skin. In one example, the shaver has a gear transmission mechanism configured to convert a motor rotation speed of 8,000 rpm into a rotation speed of the external cutting elements of approximately 10 rpm.

[0006] A drawback of these known electric shavers is that the rotation speed of the external cutting element may not be optimal under all circumstances of use or operation of the shaver by the user, and generally may not be optimal for all users of the shaver. In particular, although the hair capture efficiency of the shaver is improved by the rotation of the external cutting element, this may vary depending on the specific use or operation of the shaver by the user, or on the specific characteristics of the user's hair, and may therefore not be optimal under all usage circumstances or for all users. In addition, the rotation of the external cutting element may be experienced as unpleasant by some users under certain circumstances, for example, depending on the specific characteristics of the user's skin.

[0007] Japanese Patent Application Laid-Open Publication No. 2010227225 discloses an electric shaver having a main body or handle and a shaving unit or head disposed above the handle. The head includes three hair-cutting units or blade blocks, each having an outer cutting element or blade and an inner cutting element or blade. The outer blades of the blade blocks extend parallel to each other in the longitudinal direction of the head. The head includes an electric inner blade drive unit for reciprocatingly swinging the inner blades of each blade block parallel to the longitudinal direction relative to the outer blades of the blade block. The head also includes an electric head drive unit for reciprocating the entire head in the longitudinal direction and / or in the lateral direction of the head, which extends perpendicular to the longitudinal direction, and for swinging and reciprocating the entire head around a central rotation axis of the head, which extends perpendicular to the longitudinal direction and / or the lateral direction. According to this patent application, as a result of at least one of the longitudinal vibration, lateral vibration, and oscillating vibration of the head unit described above, the introduction of hair into the outer blades of the blade block is improved, resulting in improved shaving performance of the electric shaver. The shaver also includes a detection means for detecting the operating state of the shaver and a control means for controlling the head drive device based on the detection signal from the detection means. As a result, even when the operating state of the shaver differs, the rate of hair introduction into the outer blades of the blade block and shaving performance are stable. Examples of the operating state that can be measured are the movement speed or movement acceleration of the head unit and the contact pressure that the outer blades receive from the user's skin. The control means can control the frequency, amplitude, speed, or acceleration of the longitudinal vibration, lateral vibration, and / or oscillating vibration of the entire head. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide an electric shaver of the type described hereinabove, which does not have the drawbacks described hereinabove in relation to the electric shavers known from US Pat. No. 2,283,834 and US Pat. No. 10,195,751. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides: at least one hair-cutting unit having a central axis, an outer cutting element having a hair entry opening in an annular shaving area concentrically disposed about the central axis, and an inner cutting element surrounded by the outer cutting element and having an annular array of cutting elements concentrically disposed about the central axis; a drive system configured to rotate the inner cutting element of each hair-cutting unit about the central axis of the hair-cutting unit at a first rotational speed and the outer cutting element of each hair-cutting unit about the central axis of the hair-cutting unit at a second rotational speed, such that the inner and outer cutting elements of each hair-cutting unit are rotated relative to one another about the central axis of the hair-cutting unit; An electric shaver having The electric shaver further comprises: a detection system constructed and arranged to measure at least one user-related parameter related to the skin or hair of a user of the electric shaver or related to the operation of the electric shaver by the user relative to the body of the user; a processor constructed and arranged to control the drive system such that the second rotational speed at which the drive system rotates the external cutting element about a central axis of the hair-cutting unit is dependent on the at least one measured user-related parameter; an electric shaver having to provide.

[0010] Thus, in the electric shaver according to the present invention, the internal cutting element of each hair-cutting unit is rotated by the drive system at a first rotational speed (number of revolutions per unit time) about the central axis of the hair-cutting unit, and the external cutting element of each hair-cutting unit is rotated by the drive system at a second rotational speed (number of revolutions per unit time) about the central axis of the hair-cutting unit. The internal and external cutting elements may have the same or opposite rotational directions about the central axis. The first and second rotational speeds and rotational directions of the internal and external cutting elements should achieve a relative rotation between the internal and external cutting elements to a degree sufficient to achieve an effective hair-cutting process, as is known in the art.

[0011] In particular, according to the present invention, the second rotation speed at which the drive system rotates the external cutting element depends on at least one user-related parameter measured by the detection system. In particular, the at least one user-related parameter is related to the skin or hair of a user of the electric shaver or related to the user's operation of the electric shaver relative to the user's body. Thus, the processor can automatically adapt the second rotation speed of the external cutting element to, for example, the specific user-specific way in which the user operates the electric shaver relative to the user's body, which affects hair-capturing efficiency, the user-specific hair characteristics, which affect hair-capturing efficiency, or the user-specific skin characteristics, which affect how the user experiences the rotation of the external cutting element. In particular, the processor can adjust the second rotation speed so that the hair-capturing efficiency remains at an optimal or at least desired level, independent of or less dependent on the specific way in which the user operates the electric shaver or the user-specific hair characteristics, or so that the rotation of the external cutting element is independent of or less dependent on the user-specific skin characteristics. Examples of such user-related parameters and methods for controlling the second rotation speed of the external cutting element in response to such user-related parameters are described below with reference to embodiments of the present invention.

[0012] In one embodiment of the electric shaver according to the present invention, the at least one user-related parameter includes at least one of the following: a position of the electric shaver on the user's body; an amount of time the electric shaver has accumulated shaving different areas of the user's body during a shaving session; a speed of movement with which the user moves the electric shaver on the user's body; a pressure or force with which the user presses the electric shaver against the body; a parameter related to the user's skin characteristics; and a parameter related to the user's hair characteristics. The detection system may be configured and arranged to measure only one of the user-related parameters or to measure two or more of the user-related parameters. Accordingly, the processor may be configured and arranged to control the second rotation speed of the external cutting element in response to only one of the user-related parameters or in response to two or more of the user-related parameters.

[0013] In one embodiment of the electric shaver according to the present invention, the at least one user-related parameter includes the position of the electric shaver on the user's body. That is, as a first example of a user-related parameter related to the user's operation of the electric shaver relative to the user's body, the detection system includes a detector configured and arranged to measure the position of the electric shaver on the user's body. In such an embodiment, the processor may be configured to reduce the second rotation speed of the external cutting element when it detects, for example, that the detector is moving from a position on the user's body known to have relatively low sensitivity, such as the cheek region of the face, to a position on the user's body known to have relatively high sensitivity, such as the neck region, or vice versa. In this way, the user can experience an acceptable rotation of the external cutting element independently of, or depending on, the position where the electric shaver is actually being shaved.

[0014] In one embodiment of the electric shaver according to the present invention, the at least one user-related parameter includes a cumulative shaving time of the electric shaver for multiple different areas of the user's body during a shaving session. In other words, as a second example of a user-related parameter related to the user's operation of the electric shaver on the user's body, the detection system includes a detector configured and arranged to measure the position of the electric shaver on the user's body, and the processor is configured to measure the cumulative shaving time of the electric shaver for each of multiple different areas of the user's body based on the position of the electric shaver measured by the detector and a timing output provided by the timer. When a user shaves for a longer period of time on the same skin area, even on the cheek area, skin irritation may increase. The increase in skin irritation may be limited, for example, by automatically reducing the second rotational speed of the external cutting element when the cumulative amount of shaving time on a specific skin area exceeds a predetermined threshold. To this end, the processor may be configured to reduce the second rotational speed of the external cutting element when the measured cumulative shaving time for a specific one of the multiple different areas of the user's body exceeds a predetermined threshold and the position of the electric shaver measured by the detector is within the specific one of the multiple different areas of the user's body.

[0015] In an embodiment of the electric shaver according to the present invention, the at least one user-related parameter includes a speed at which the user moves the electric shaver on the user's body. As a third example of a user-related parameter related to the user's operation of the electric shaver relative to the user's body, the detection system includes a detector configured and arranged to measure the speed at which the user moves the electric shaver on the user's body. A known problem with electric shavers is that as the user increases the speed at which the electric shaver moves on the user's body, the hair-capturing efficiency of the hair-cutting unit decreases. The hair-capturing efficiency can be increased by increasing the second rotational speed of the external cutting element, at least within a predetermined range of the second rotational speed, which depends on the detailed specific design of the external cutting element and the design of its hair entry slot. Thus, in this embodiment, the processor can be configured to increase the second rotational speed of the external cutting element when the measured speed of movement increases.

[0016] In an embodiment of the electric shaver, the at least one user-related parameter includes a pressure or force with which the user presses the electric shaver against the main body, i.e., as a fourth example of a user-related parameter related to the operation of the electric shaver against the user's body, the detection system is configured and arranged to measure the pressure or force with which the electric shaver is pressed against the main body. As the pressure or force increases, the degree of skin doming into the hair entry opening of the external cutting element increases, resulting in a potential increase in skin irritation. Because increasing the second rotational speed of the external cutting element can reduce the degree of skin doming into the hair entry opening, in this embodiment, when the processor is configured to increase the second rotational speed of the external cutting element when the measured pressure or force increases, it is possible to prevent or limit the increase in skin irritation caused by the increase in pressure.

[0017] In one embodiment of the electric shaver according to the present invention, the at least one user-related parameter includes a parameter related to a user's skin characteristic, and the detection system includes a detector configured and arranged to measure the parameter related to the user's skin characteristic. A known skin characteristic affected by the shaving process is, for example, skin redness, which may be an indicator of the degree of skin irritation caused by the shaving process. In this example, the processor may be configured to reduce the second rotational speed of the external cutting element when the detector measures an increase in skin redness. The second rotational speed of the external cutting element may also be controlled by the processor depending on another skin characteristic, particularly when such a skin characteristic affects hair capture efficiency.

[0018] In one embodiment of the electric shaver according to the present invention, the at least one user-related parameter includes a parameter related to the user's hair characteristics, and the detection system includes a detector configured and arranged to measure the parameter related to the user's hair characteristics. Preferably, the hair characteristics are hair characteristics that can affect the hair-capturing efficiency of the hair-cutting unit, such as hair length, hair thickness, or hair density on the skin. For example, when hair length is measured by the detector, the processor may be configured to increase the second rotational speed of the external cutting element when the detector measures an increase in hair length, thereby improving hair-capturing efficiency for longer hairs.

[0019] In one embodiment of the electric shaver according to the present invention, the drive system includes a single motor configured and arranged to rotate both the inner cutting element of each hair-cutting unit and the outer cutting element of each hair-cutting unit about the central axis of the hair-cutting unit via a transmission system, and the processor is configured and arranged to control the single motor so that the second rotational speed of the outer cutting element depends on the measured user-related parameter. The use of a single motor in this embodiment results in a relatively simple structure of the electric shaver. In this embodiment, adjustment of the second rotational speed of the outer cutting element by the processor generally also results in a proportional adjustment of the first rotational speed of the inner cutting element. However, such adjustment of the first rotational speed of the inner cutting element may be acceptable in many practical applications as long as the first rotational speed remains within the range required for effective haircutting.

[0020] In a preferred embodiment of the electric shaver according to the present invention, the drive system includes a first motor configured and arranged to rotate the internal cutting elements of each hair-cutting unit about a central axis of the hair-cutting unit and a second motor configured and arranged to rotate the external cutting elements of each hair-cutting unit about a central axis of the hair-cutting unit, and the processor is configured and arranged to control the second motor so that the second rotational speed of the external cutting elements depends on the measured user-related parameter. In this embodiment, the second rotational speed of the external cutting elements can be adjusted independently of the first rotational speed of the internal cutting elements. For example, the first motor can maintain the first rotational speed of the internal cutting elements at a constant value optimal for hair cutting, while the second motor can adjust the second rotational speed of the external cutting elements to maintain the hair-capturing efficiency of the hair-cutting unit at an optimal level as the measured user-related parameter changes. Independent control of the rotation of the external cutting element in this embodiment further enables the provision of a user input element, for example, by means of which the user can turn the rotation of the external cutting element on or off, or select between several predetermined speed ranges for the external cutting element based on user preference.

[0021] In a further embodiment of the electric shaver according to the present invention, the drive system is configured to rotate the internal cutting element of each hair-cutting unit in a first rotational direction about the central axis of the hair-cutting unit and to rotate the external cutting element of each hair-cutting unit in a second rotational direction opposite to the first rotational direction about the central axis of the hair-cutting unit, the second rotational speed of the external cutting element being lower than the first rotational speed of the internal cutting element. By rotating the internal and external cutting elements of each hair-cutting unit in opposite directions, the rotational speed of the internal cutting element relative to the external cutting element, which primarily determines the hair-cutting efficiency of the internal cutting element, can be reduced compared to embodiments in which the internal and external cutting elements rotate in the same direction. Furthermore, it has been found that the optimal value or range (number of rotations per unit time) of the second rotational speed of the external cutting element, which primarily determines the hair-capturing efficiency of the external cutting element, is generally lower than the optimal value or range (number of rotations per unit time) of the first rotational speed of the internal cutting element required for an optimal haircut.

[0022] In one embodiment of the electric shaver according to the invention, the drive system is configured to rotate the inner and outer cutting elements of each hair-cutting unit in opposite directions as described above, the hair entry opening of the outer cutting element of each hair-cutting unit may have a V-shaped opening pointing in the first direction of rotation of the inner cutting element, and the second rotational speed of the outer cutting element of each hair-cutting unit may be such that the tangential speed of the outer cutting element relative to the central axis, measured at a radius of the center point of the V-shaped opening relative to the central axis, is in the range of 7.5 to 50 cm / s. In this embodiment, 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.

[0023] Experiments conducted by the inventors have confirmed that for a hair-cutting unit having an outer cutting element with a straight, slot-shaped hair entry opening extending substantially radially relative to the central axis of the hair-cutting unit, an increase in hair capture efficiency, and consequently a reduction in the average remaining hair length after a shaving process, can be achieved by rotating the outer cutting element in a direction opposite to the rotation direction of the inner cutting element. The experiments have further demonstrated that for a hair-cutting unit having an outer cutting element with a hair entry opening with a V-shaped opening oriented in a first rotation direction of the inner cutting element, a very significant increase in hair capture efficiency, and consequently a very significant and user-perceptible reduction in the average remaining hair length after a shaving process, can be achieved by rotating the outer cutting element in a direction opposite to the rotation direction of the inner cutting element at a second rotation speed such that the tangential velocity of the outer cutting element relative to the central axis is in the range of 7.5 to 50 cm / s. In particular, it has been surprisingly found that the relative increase in hair capture efficiency and the relative decrease in average remaining hair length as a result of the rotation of the external cutting elements, i.e., relative to the hair capture efficiency and the average remaining hair length achieved with a fixed external cutting element, are significantly higher in an electric shaver according to an embodiment of the present invention than in an electric shaver having external cutting elements with hair entry openings extending in a straight radial direction. In this embodiment, when the second rotation speed of the external cutting elements of each hair-cutting unit is such that the tangential speed of the external cutting elements relative to the central axis is in the more preferred range of between 11.25 and 30.0 cm / s, a significant increase in hair capture efficiency, and consequently a significant and user-perceptible decrease in the average remaining hair length after the shaving process as described above, is achieved with a minimal degree of additional skin friction caused by the rotation of the external cutting elements.

[0024] A particularly significant improvement in hair capture efficiency is achieved in an embodiment of the electric shaver according to the invention, wherein the hair entry opening extends radially relative to a central axis of the hair-cutting unit over a first radial distance, and the V-shaped opening of the hair entry opening extends radially over a second radial distance, said second radial distance being at least 50% of said first radial distance.

[0025] In a further embodiment of the electric shaver according to the invention, The hair entry opening of the outer cutting element 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, the radially inner and outer linear openings each having a main direction extending radially relative to the central axis of the hair-cutting unit. In this embodiment, the radially inner linear opening and the radially outer linear opening of the hair entry opening provide relatively high hair capture efficiency for hairs approaching the hair entry opening of the outer cutting element through 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 relatively high hair capture efficiency for hairs approaching the hair entry opening through the central region of the annular shaving zone.

[0026] 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 degrees to 135 degrees. In this embodiment, with respect to the V-shaped opening, the V-angle is defined as the angle enclosed by the two legs of the V-shaped opening. A V-angle in the range of 60 degrees to 135 degrees provides a stretching effect on the skin in two mutually divergent directions, which results in reduced skin doming towards the hair entry opening and thereby reduced skin irritation caused by the shaving process.

[0027] These and other aspects of the invention will be apparent from and will be elucidated with reference to the following detailed description of embodiments of an electric shaver according to the invention.

[0028] The invention will now be described in more detail with reference to the drawings, in which like or similar features are designated by like reference numerals. [Brief explanation of the drawings]

[0029] [Figure 1] 1 shows a schematic representation of an electric shaver according to the invention; [Figure 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. [Figure 3] 2 shows a schematic diagram of a drive system of the electric shaver of FIG. 1. [Figure 4a] FIG. 2 is a top view of the shaver unit of the electric shaver of FIG. 1. [Figure 4b] 4 shows a portion of the drive system of FIG. 3. [Figure 5] FIG. 3 is a top view of the external cutting element of the hair-cutting unit of FIG. 2. [Figure 6a] 1 shows a graph of the external cutting element having a straight hair entry opening as a function of rotational speed of the external cutting element. [Figure 6b] 6 shows a graph of the hair capture efficiency of the external cutting element of FIG. 5 as a function of the rotational speed of the external cutting element. [Figure 7a] 1 shows a graph of shaving efficiency of a hair-cutting unit having an outer cutting element with a straight hair entry opening as a function of rotational speed of the outer cutting element of the hair-cutting unit. [Figure 7b] 2 shows a graph of the shaving efficiency of the hair-cutting unit as a function of the rotational speed of the outer cutting element of the hair-cutting unit. [Figure 8] 3 shows the internal cutting elements of the hair-cutting unit of FIG. 2; [Figure 9] 2 shows a schematic diagram of a detection system, a processor and a drive system of the electric shaver of FIG. 1; [Figure 10a] 10A and 10B show schematic diagrams of different embodiments of the detection system shown in FIG. [Figure 10b] 10A and 10B show schematic diagrams of different embodiments of the detection system shown in FIG. [Figure 10c] 10A and 10B show schematic diagrams of different embodiments of the detection system shown in FIG. [Figure 10d] 10A and 10B show schematic diagrams of different embodiments of the detection system shown in FIG. [Figure 10e] 10A and 10B show schematic diagrams of different embodiments of the detection system shown in FIG. [Figure 10f] 10A and 10B show schematic diagrams of different embodiments of the detection system shown in FIG. [Figure 11] 2 shows a schematic diagram of an alternative embodiment of the drive system of the electric shaver of FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0030] FIG. 1 schematically illustrates an embodiment of an electric shaver 1 according to the present invention. The electric shaver 1 comprises a main housing 3 designed to be held by a user's hand 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, and 9c supported by the support structure 7. The support structure 7 may comprise a coupling structure, not shown in FIG. 1 , known to those skilled in the art, by which the shaving unit 5 is releasably coupled to the main housing 3. Alternatively, the shaving unit 5 may be permanently connected to the main housing 3. It should be noted that the shaving unit of an electric shaver according to the present invention may include a different number of hair-cutting units, for example, one, two, or more than two hair-cutting units. It should be further noted that FIG. 1 merely schematically illustrates the general layout of an electric shaver and is not intended to limit the scope of the present invention to the specific detailed design of the electric shaver shown. For example, the present invention also covers an embodiment of an electric shaver in which the shaving unit is coupled to the main housing via a relatively narrow, centrally located coupling structure, with an open space between the shaving unit and the main housing around the coupling structure, as is known in the art.

[0031] FIG. 2 is a schematic cross-sectional view of the hair-cutting unit 9c taken along line II-II in FIG. 1. The hair-cutting sections 9a and 9b are similar to the hair-cutting section 9c. The hair-cutting unit 9c comprises a central axis 11, an outer cutting element 13, and an inner cutting element 15. The outer cutting element 13 has an annular shaving region 17 arranged concentrically around the central axis 11. The annular shaving region 17 is positioned to contact the skin of a user of the electric shaver 1 and includes a hair entry opening (not visible in FIG. 2), which will be described in detail below. The hair entry openings are separated from each other by a bridge portion 19 provided in the annular shaving region 17. The inner cutting element 15 is covered by the outer cutting element 13 and includes an annular array of cutting elements 21 arranged concentrically around the central axis 11. The electric shaver 1 comprises a drive system, described in detail hereinafter, configured to rotate the inner cutting element 15 and the outer cutting element 13 relative to each other about the central axis 11 during operation of the electric shaver 1. As a result of the mutual rotation of the internal cutting element 15 and the external cutting element 13, hair on the user's skin that penetrates into the hair entry opening present in the annular shaving zone 17 is cut by the interaction of the cutting edge 23 present on the cutting element 21 of the internal cutting element 15 with the opposing cutting edge 25 present on the bridge portion 19 of the external cutting element 13. It should be noted that an electric shaver according to the present invention may have two or more annular shaving zones arranged concentrically around a central axis, as is known in the art.

[0032] The drive system of the electric shaver 1 described hereinabove is shown schematically in Figure 3 and is referenced by the reference numeral 27. In the embodiment shown in Figure 3, the drive system 27 comprises a single motor 29 arranged within the main housing 3. Furthermore, in this embodiment, the drive system 27 is configured to rotate the internal cutting elements 15 of each hair-cutting unit 9a, 9b, 9c about the central axis 11 of the hair-cutting units 9a, 9b, 9c in a first rotational direction R1 (shown in Figure 2) and at a first rotational speed ω1, and to rotate the external cutting elements 13 of each hair-cutting unit 9a, 9b, 9c about the central axis 11 of the hair-cutting units 9a, 9b, 9c in a second rotational direction R2 (shown in Figure 2) opposite to the first rotational direction R1 and at a second rotational speed ω2 lower than the first rotational speed ω1. To this end, the drive system 27 comprises a transmission system 31 enabling the motor 29 to rotate both the internal cutting element 15 and the external cutting element 13 of each hair-cutting unit 9a, 9b, 9c, the transmission system 31 being arranged partly within the main housing 3 and partly within the shaving unit 5. It should be noted that, for simplicity's sake, Figure 3 shows in detail only one of the hair-cutting units 9c. The drive of the other hair-cutting units 9a, 9b by the drive system 27 will be described below. It should also be noted that, for simplicity's sake, Figure 3 only partly shows the support structure 7 of the shaving unit 5.

[0033] As shown in Figure 3, the transmission system 31 comprises a first primary gear 33 and a second primary gear 35, each mounted on a motor shaft 37 of the motor 29. The transmission system 31 further comprises three secondary gears 39, each mounted on a respective one of the three drive spindles 41, each coupled to a respective one of the three internal cutting elements 15 of the hair-cutting units 9a, 9b, 9c, and each rotatably journalled relative to the support structure 7 of the shaving unit 5. Each of the three secondary gears 39 engages with the first primary gear 33. It should be noted that Figure 3 only shows one of the secondary gears 39 and one of the drive spindles 41 coupled to the internal cutting element 15 of the hair-cutting unit 9c, and that the secondary gears and drive spindles associated with the internal cutting elements 15 of the hair-cutting units 9a and 9b are arranged in a corresponding manner.

[0034] The transmission system 31 further includes a secondary shaft 43 arranged parallel to the motor shaft 37. The upper portion of the secondary shaft 43 is positioned between two of the secondary gears 39, although this arrangement is not visible in FIG. 3 . The secondary shaft 43 carries a third primary gear 45 that engages with the second primary gear 35 via a plurality of intermediate gears 47, and a fourth primary gear 49. The transmission system 31 further includes a third shaft 51 that is aligned with the motor shaft 37 and rotatably journaled relative to the support structure 7 of the shaving unit 5. The third shaft 51 carries a fifth primary gear wheel 53 that engages with the fourth primary gear wheel 49, and a sixth primary gear wheel 55. Each of the external cutting elements 13 of the hair-cutting units 9a, 9b, and 9c includes a secondary gear 57 that engages with the sixth primary gear 55, which is centrally positioned between the secondary gears 57 of the external cutting elements 13. It should be noted that Figure 3 only shows the secondary gear 57 of the external cutting element 13 of hair-cutting unit 9c, while the secondary gears 57 of the external cutting elements 13 of hair-cutting units 9a and 9b are arranged in a corresponding manner. For clarity, the arrangement of the secondary gears 57 of the external cutting elements 13 of all three hair-cutting units 9a, 9b, and 9c is shown in Figure 4b. Figure 4a shows that the external cutting elements 13 are surrounded by skin support elements 59a, 59b, and 59c of each hair-cutting unit 9a, 9b, and 9c, respectively. Each skin support element 59a, 59b, and 59c provides a rotational bearing for the respective external cutting element 13 and also covers the secondary gear 57 of the respective external cutting element 13.

[0035] It is known from prior art electric shavers that the hair-catching efficiency of the hair-cutting units 9a, 9b, 9c can be improved by rotating the outer cutting element 13 of each hair-cutting unit 9a, 9b, 9c around the central axis 11 of the hair-cutting unit 9a, 9b, 9c. The hair-catching efficiency is the degree to which hair can penetrate into the hair entry opening of the outer cutting element 13 while the electric shaver 1 is moved over the user's skin, with the annular shaving area 17 of the outer cutting element 13 in contact with the skin. The higher the hair-catching efficiency, the more hair penetrates into the hair entry opening of the outer cutting element 13 and is cut by the hair-cutting units 9a, 9b, 9c, for example, during a single moving stroke of the electric shaver 1 over a particular area of ​​skin, and the smaller the average remaining hair length obtained after a single moving stroke. To improve hair capture efficiency, the rotation direction R2 of the outer cutting elements 13 of each hair-cutting unit 9a, 9b, 9c may be opposite to the rotation direction R1 of the inner cutting elements 15, as in the embodiment shown in the figures, or the inner cutting elements 15 and outer cutting elements 13 of each hair-cutting unit 9a, 9b, 9c may have the same rotation direction. In the latter case, the rotation speeds ω1 and ω2 of the inner cutting elements 15 and outer cutting elements 13 should be sufficiently different from each other so that relative rotation between the inner cutting elements 15 and outer cutting elements 13 is achieved to a degree sufficient to achieve an effective hair-cutting process, as known to those skilled in the art. Therefore, the present invention is not limited to embodiments in which the inner cutting elements 15 and outer cutting elements 13 of the hair-cutting units 9a, 9b, 9c have mutually opposite rotation directions R1, R2, as in the embodiment shown in the figures.

[0036] In the embodiment of the invention shown in the figures, a particularly significant improvement in the hair capture efficiency of the hair-cutting units 9a, 9b, 9c is achieved by providing the outer cutting element 13 of each hair-cutting unit 9a, 9b, 9c of the electric shaver 1 with a hair entry opening 61 having a V-shaped opening 63 pointing in the first rotation direction R1 of the inner cutting element 15, i.e., pointing in a direction opposite to the second rotation direction R2 of the outer cutting element 13, as shown in Fig. 5. Furthermore, in this embodiment, the second rotation speed ω2 of the outer cutting element 13 of each hair-cutting unit 9a, 9b, 9c is lower than the first rotation speed ω1 of the inner cutting element 15. In particular, the second rotation speed ω2 is such that the tangential speed Vt of the outer cutting element 13 relative to the central axis 11 of the hair-cutting unit 9a, 9b, 9c is in the range of 7.5 to 50 cm / s. In this regard, the tangential velocity VT is measured at the 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 connect to each other, as also shown in FIG. 5. Therefore, VT = 2π × RC × ω2, and ω2 = VT / (2π × RC). It should be noted that the present invention is not limited to electric shavers in which the hair entry opening of the rotating external cutting element has a V-shaped opening, as in the illustrated embodiment. The external cutting element may have, for example, a more conventional straight or slightly curved hair entry slot extending primarily radially relative to the central axis of the hair-cutting unit, or other known hair entry opening shapes.

[0037] The inventors of the present invention conducted experiments in the form of numerical simulations using a mathematical model of human skin with hair, a mathematical model of a hair-cutting unit having an external cutting element with a straight, slot-shaped hair entry opening extending substantially radially relative to the central axis of the hair-cutting unit, and a mathematical model of embodiments of hair-cutting units 9a, 9b, and 9c. Figures 6a and 6b are graphs showing the hair capture efficiency of an external cutting element with a straight hair entry opening and external cutting element 13, respectively, as a function of second rotational speed ω2 (in rpm). In these figures, hair capture efficiency is expressed as the average penetration depth APD (in mm) of hair into the hair entry opening of each external cutting element. Simulations were performed for a uniform hair length of 1 mm and multiple single strokes of each external cutting element over a specific skin area at stroke speeds ranging from 10 cm / s to 30 cm / s. The external cutting element 13 has a radial position RC of the central origin 65 of the V-shaped opening 63 relative to the central axis 11 of 9 mm. For the external cutting element with a straight hair entry opening, the radial position of the central radial point of the straight hair entry opening is also 9 mm. Therefore, the value ω2 = 500 rpm in the graph corresponds to a value VT = 47 cm / s. The graph shows comparable hair capture efficiencies (APD) of the external cutting element with a straight hair entry opening and the external cutting element 13 when there is no rotational movement of the external cutting element (ω2 = 0). As the external cutting element rotates, the hair capture efficiency (APD) of the external cutting element with a straight hair entry opening increases slightly, with optimal hair capture efficiency being achieved for a rotational speed ω2 of approximately 200 rpm, as shown in FIG. 6a. As shown in FIG. 6b, as the external cutting element 13 of the electric shaver 1 according to this embodiment of the present invention rotates, the hair capture efficiency (APD) of the external cutting element 13 increases to a significantly greater extent than that of the external cutting element with a straight hair entry opening. As shown in Figure 6b, for the external cutting element 13, optimum hair capture efficiency is achieved for a second rotation speed ω2 of about 300 rpm.In particular, as is evident from Figures 6a and 6b, the relative increase in hair capture efficiency (APD) as a result of rotation of the external cutting element, i.e. the ratio between the average penetration depth (APD) of a hair into the hair entry opening with and without rotation of the external cutting element, was found to be significantly higher for the external cutting element 13 of the electric shaver 1 according to this embodiment of the invention than for an external cutting element having a hair entry opening extending in a straight radial direction.

[0038] 7a and 7b show graphs of the shaving efficiency of hair-cutting units 9a, 9b, and 9c, respectively, with an external cutting element having a straight hair entry opening, as a function of the second rotational speed ω2 (rpm). In these figures, the shaving efficiency is expressed as the average hair length reduction ALR (mm) achieved by each hair-cutting unit. Simulations were performed for a uniform hair length of 1 mm and multiple single strokes of each hair-cutting unit over a specific skin area at stroke speeds ranging from 10 cm / s to 30 cm / s. For the external cutting element 13 of hair-cutting units 9a, 9b, and 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 hair-cutting units with external cutting elements having a straight hair entry opening, the radial position of the central radial point of the straight hair entry opening is also 9 mm. Thus, the value ω2 = 500 rpm in the graph corresponds to a value VT = 47 cm / s. The graph shows that, without rotational movement of the external cutting elements (ω2 = 0), the shaving efficiency (in terms of ALR) of the hair-cutting units 9a, 9b, 9c is approximately 25% higher than the shaving efficiency of a hair-cutting unit having an external cutting element with a straight hair entry opening. With rotation of the external cutting elements, the shaving efficiency (ALR) of the hair-cutting unit having an external cutting element with a straight hair entry opening increases slightly, with an optimal shaving efficiency being achieved for a rotation speed ω2 of approximately 120 rpm, as shown in Figure 7a. With rotation of the external cutting elements 13 of the hair-cutting units 9a, 9b, 9c of the electric shaver 1 according to this embodiment of the present invention, the shaving efficiency (ALR) of the hair-cutting units 9a, 9b, 9c is increased to a significantly greater extent compared to a hair-cutting unit having an external cutting element with a straight hair entry opening, as shown in Figure 7b. As shown in Figure 7b, for the hair-cutting units 9a, 9b, 9c, an optimum shaving efficiency is achieved for 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 element, i.e. the ratio between the average hair length reduction (ALR) with and without rotation of the external cutting element, is significantly higher for the hair-cutting units 9a, 9b, 9c of the electric shaver 1 according to this embodiment of the invention than for hair-cutting units having external cutting elements with straight radially extending hair entry openings.

[0039] As can be seen from Figure 7b, a significant increase in shaving efficiency (ALR) of about 10% can already be achieved when the second rotation speed ω2 of the external cutting element 13 is about 80 rpm, corresponding to a value of V T of about 7.5 cm / s. As is clear from Figure 7a, such a significant relative increase in shaving efficiency (ALR) cannot be achieved by rotating an external cutting element with a straight hair entry opening. Furthermore, the line L in Figures 7(a) and 7(b) th represents an increase in shaving efficiency (ALR) that is considered particularly perceptible by a user of the electric shaver 1. For the external cutting element 13, such a particularly perceptible increase in shaving efficiency (ALR) is achieved when the second rotational speed ω2 is between about 120 rpm (corresponding to VT = 11.25 cm / s) and about 550 rpm (corresponding to VT = 50 cm / s). Values ​​of VT greater than 50 cm / s may be undesirable in view of the relatively high skin friction caused by the rotation of the external cutting element 13. Therefore, in this embodiment of the invention, the second rotational speed ω2 of the external cutting element 13 is such that the tangential velocity VT of the external cutting element 13, measured at a radial position RC of the central origin 65 of the V-shaped opening 63 of the hair entry opening 61, is in the range of 7.5 cm / s to 50 cm / s, while a more preferred range of values ​​of VT is in the range of 11.25 cm / s to 50 cm / s.

[0040] 7b, the relative increase in shaving efficiency (ALR) for a range of ω2 values ​​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) for a range of ω2 values ​​between about 300 rpm (VT = 28.3 cm / s) and about 550 rpm (VT = 50 cm / s). Because skin friction caused by rotation of the external cutting element 13 is lower at lower values ​​of VT, in accordance with a further 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 significant increases in hair capture efficiency and shaving efficiency as previously described herein with minimal additional skin friction caused by rotation of the external cutting element 13.

[0041] Similar experiments conducted on hair-cutting units having external cutting elements in which the hair entry opening, particularly its V-shaped opening, is positioned at a greater or lesser radial distance from the central axis than the radial distance R of the external cutting element 13 as described above have shown that the advantages of this embodiment of the present invention as described above are achieved regardless of the radial distance. In other words, in this embodiment of the present invention, the V-shaped opening 63 of the hair entry opening 61 is positioned at a greater or lesser radial distance R from the central axis 11, and the second rotational speed ω2 of the external cutting element 13 should be reduced in proportion to the radial distance R to achieve equivalent results in terms of improved hair capture and shaving efficiency. For example, if the second rotational speed ω2 is approximately 300 rpm (RC = 9 mm), equivalent results are achieved with a second rotational speed ω2 of approximately 225 rpm in an embodiment in which RC = 12 mm, and with a second rotational speed ω2 of approximately 450 rpm in an embodiment in which RC = 6 mm.

[0042] As shown in FIG. 5 , the hair entry openings 61 of the external cutting elements 13 each extend a first radial distance RD1 radially relative to the central axis 11. The V-shaped openings 63 of the hair entry openings 61 extend a second radial distance RD2 radially relative to the central axis 11. In the embodiment shown in FIG. 5 , the ratio RD2 / RD1 is approximately 0.75. Particularly significant improvements in hair capture and shaving efficiency are achieved in electric shaver embodiments in which the ratio RD2 / RD1 is at least 0.5. However, improvements in hair capture and shaving efficiency may also be achieved for smaller values ​​of the ratio, particularly when the first radial distance RD1 over which the hair entry openings 61 extend is relatively large.

[0043] 5, the hair entry opening 61 of the external cutting element 13 further comprises a radially inner straight opening 69a and a radially outer straight opening 69b. The radially inner straight 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 the central axis 11. The radially outer straight opening 69b is connected to the V-shaped opening 63 at a second end 71b of the V-shaped opening 63 opposite the central axis 11. The radially inner and outer straight openings 69a, 69b each have a primary extension direction radially relative to the central axis 11. In this embodiment, the radially inner straight opening 69a provides a relatively high hair capture efficiency for hairs approaching the hair entry opening 61 of the external cutting element 13 through the inner peripheral region 73 of the annular shaving region 17 while the hair-cutting units 9a, 9b, 9c move randomly over the user's skin. During such random movement, the radially outer straight openings 69b provide 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 relatively high hair capture efficiency for hairs approaching the hair entry opening 61 through the central region of the annular shaving area 17.

[0044] 5 further illustrates the V-angle α of the V-shaped opening 63 of the hair entry opening 61, defined as the angle enclosed by the two legs 67a, 67b of the V-shaped opening 63. In the embodiment illustrated in FIG. 5, the V-angle α is approximately 115 degrees. A preferred range for the V-angle α is between 60 and 135 degrees. With values ​​of the V-angle α in this preferred range, the V-shaped opening 63 provides a stretching effect on the skin in two mutually divergent directions during rotation of the external cutting element 13 in the second rotational direction R2, in addition to improved hair capture and shaving efficiency. The skin stretching effect results in reduced skin doming toward the hair entry opening 61, thereby reducing skin irritation caused by the shaving process.

[0045] FIG. 8 illustrates the internal cutting elements 15 of the hair-cutting units 9a, 9b, and 9c, the first rotational direction R1 of the internal cutting elements 15 about the central axis 11 of the hair-cutting units 9a, 9b, and 9c, and the second rotational direction R2 of the external cutting elements 13. Each cutting element 21 in the annular array of cutting elements 21 is connected to the carrier 77 of the internal cutting element 15 via a flexural connecting element 79. The carrier 77, cutting element 21, and flexural connecting element 79 may be integrally formed from a single metal plate in a manner known to those skilled in the art. The cutting edge 23 of each cutting element 21 is provided on the leading or front edge (relative to the first rotational direction R1) of the upper surface 81 of the cutting element 21. The carrier 77 is coupled to one of three drive spindles 41 of the drive system 27 described hereinabove in a manner known to those skilled in the art. Therefore, the coupling between the drive spindle 41 and the carrier 77 is not shown in FIG. 8.

[0046] In the embodiment shown in FIG. 8 , each cutting edge 23 of the cutting elements 21 of the internal cutting element 15 includes a V-shaped cutting edge portion 83 that points in the second rotational direction R2 of the external cutting element 13, i.e., points in a direction opposite to the first rotational direction R1 of the internal cutting element 15, and that is opposite to the direction pointed by the V-shaped opening 63 of the hair entry opening 61 of the external cutting element 13. 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 portions 83 of the cutting edges 23 of the internal cutting element 15 and the V-shaped openings 63 of the hair entry openings 61 of the external cutting element 13 are aligned tangentially with respect to the central axis 11. This alignment means that the central origin 85 of each V-shaped cutting edge portion 83 is disposed at a radial distance RCC from the central axis 11 that is 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 between the V-shaped opening 63 of the hair entry opening 61 of the outer cutting element 13 and the V-shaped cutting edge 83 of the cutting element 21 of the inner cutting element 15 causes hair caught in the hair entry opening 61 to be cut primarily in the central region of the V-shaped opening 63 where skin doming into the hair entry opening 61 is minimized, thereby reducing skin irritation during the shaving process. However, it should be noted that the present invention also covers embodiments in which the cutting edges 23 of the cutting elements 21 of the inner cutting element 15 have more conventional shapes, such as substantially straight or slightly curved shapes, each having a primary radial direction of extension.

[0047] The first rotational speed ω1 of the internal cutting element 15 has a limited effect on the hair-capturing efficiency of the hair-cutting units 9a, 9b, 9c. Therefore, the first rotational speed ω1 can be selected primarily based on the required hair-cutting efficiency of the cutting elements 21 of the rotating internal cutting element 15, as known to those skilled in the art. In the embodiment of FIG. 8, a preferred range of first rotational speeds ω1 is such that the tangential velocity VTT of the cutting elements 21 of the internal cutting element 15 relative to the central axis 11, as measured at the radial distance RCC from the central axis 11 shown in FIG. 8, is in the range of 70 to 375 cm / s, more preferably in the range of 140 to 250 cm / s. In the present embodiment, where RCC = 9 mm, the ranges of the tangential velocity VTT correspond to first rotational speed ω1 ranges of approximately 750 to 4000 rpm and approximately 1500 to 2700 rpm, respectively.

[0048] The inventors of the present invention have recognized that for electric shavers in which the external cutting element of the hair-cutting unit rotates around the central axis of the hair-cutting unit to increase hair-capturing efficiency, the hair-capturing efficiency may depend on parameters other than the second rotational speed of the external cutting element. In particular, the inventors have recognized that the hair-capturing efficiency may depend on the specific user's manner of operating the electric shaver relative to the user's body and the specific hair characteristics of the specific user. The inventors have also recognized that different users may experience the rotation of the external cutting element differently depending on their specific skin characteristics. Therefore, without further measures, the second rotational speed of the external cutting element may not be optimal under all circumstances of the user's use or operation of the electric shaver, and may not be optimal for all users of electric shavers in general.

[0049] To prevent or at least mitigate this problem, in the electric shaver 1 according to the invention the second rotation speed ω2 of the external cutting elements 13 of the hair-cutting units 9a, 9b, 9c is automatically adapted so that the hair capture efficiency is maintained at an optimum or at least a desired level independent of the particular way in which the user operates the electric shaver 1 and / or independent of the user's specific hair characteristics and / or independent of the user's specific hair characteristics and / or independent of the user's specific skin characteristics and / or so that the user experiences the rotation of the external cutting elements as acceptable. To this end, as shown schematically in Figure 9, according to the invention the electric shaver 1 comprises a detection system 87 constructed and arranged to measure at least one user-related parameter, said user-related parameter being related to the skin or hair of a user of the electric shaver 1 or related to the operation of the electric shaver 1 by the user relative to the user's body. Further, according to the present invention, the electric shaver 1 includes a processor 89 configured and arranged to control the drive system 27 such that the second rotational speed ω2 at which the drive system 27 rotates the external cutting element 13 about the central axis 11 of the hair-cutting units 9a, 9b, 9c depends on the at least one measured user-related parameter. As shown in FIG. 9 , during use, the detection system 87 can generate an output signal URP representative of the value of the measured user-related parameter. The output signal URP can be received by the processor 89, which can generate an output signal Ω2 representative of the second rotational speed ω2 of the external cutting element 13 achieved by the drive system 27. The drive system 27 can include a power control module 91 connected to a battery 93 and configured to supply power to the motor 29 based on the output signal Ω2, so that the drive system 27 achieves the second rotational speed ω2 of the external cutting element 13. To this end, the power control module 91 can include feedback speed control known to those skilled in the art and will therefore not be described in detail.

[0050] The locations of the processor 89, the power control module 91 and the battery 93 in the main housing 3 of the electric shaver 1 are shown, by way of example, schematically in Figure 3. Examples of user-related parameters, detection systems for measuring the user-related parameters and specific methods for controlling the second rotational speed ω2 of the external cutting element 13 in response to the user-related parameters will be described below with reference to further embodiments of the present invention.

[0051] It should be noted that the present invention also covers embodiments in which the processor and / or detection system are located in a separate electronic device, such as a smartphone, separate from the main housing 3 and the shaving unit 5. In such embodiments, the term "electric shaver" should be understood as a "shaving system" that includes such a separate electronic device.

[0052] Examples of user-related parameters that can be measured by the detection system 87 include the position of the electric shaver 1 on the user's body, the amount of accumulated shaving time of the electric shaver 1 on different areas of the user's body during a shaving session, the speed of movement of the electric shaver 1 on the user's body, the pressure or force with which the user presses the electric shaver 1 against the body, parameters related to the user's skin characteristics, and parameters related to the user's hair characteristics. The position of the electric shaver 1, the accumulated shaving time, the speed of movement, and the pressure are each examples of user-related parameters related to the user's operation of the electric shaver 1 relative to the user's body. In other words, in these examples, the value of the user-related parameter depends on how the user operates the electric shaver 1 relative to the user's body, for example, whether the user positions, moves, or pushes it. The detection system 87 can be configured and arranged to measure only one user-related parameter or to measure two or more user-related parameters. Accordingly, the processor 89 can be configured and arranged to control the second rotational speed ω2 of the external cutting element 13 in response to only one user-related parameter or in response to two or more user-related parameters.

[0053] In an embodiment of the electric shaver 1 according to the present invention, the user-related parameters include the position of the electric shaver 1 on the user's body, and the detection system 87 is constructed and arranged to measure the position of the electric shaver 1 on the user's body. To this end, the detection system 87 may include any suitable detector known to those skilled in the art. By way of example, the detection system 87 may comprise a system for determining the position of a device on the surface of a target body part, as disclosed in WO 2020 / 182698 A1 in the name of the applicant. In such an example, as shown schematically in FIG. 10a, the detection system 87 comprises an orientation sensor 95, such as an inertial measurement unit (IMU) sensor, arranged in the main housing 3 (as shown schematically in FIG. 3) or in the shaving unit 5 of the electric shaver 1, for measuring a series of 3D orientations of the electric shaver 1 during use and generating a corresponding output signal 3D0. In this example, the detection system 87 further comprises a processing unit 97 configured to compare the sequence of 3D orientations of the electric shaver 1 with normal vectors on a 3D representation of the user's body or body part, for example the face and neck area, stored in the processing unit 97. From said comparison, the processing unit 97 is further configured to determine the position of the electric shaver 1 on the body or body part based on the position of the normal vector on the 3D representation, and to generate a corresponding output signal LS, which is supplied to the processor 89, as an embodiment of the output signal URP shown in Figure 9. Further details of this detection system are disclosed in WO 2020 / 182698 A1. In this embodiment, the processor 89 may be configured, for example, to apply a relatively low second rotational speed ω2 of the external cutting element 13 when the detection system 87 detects that the electric shaver 1 is present in an area of ​​the user's body where the skin is known to have relatively high sensitivity, such as the neck area, and to apply a relatively high second rotational speed ω2 of the external cutting element 13 when the detection system 87 detects that the electric shaver 1 is present in an area of ​​the user's body where the skin is known to have relatively low sensitivity, such as the cheek area.In this way, the user can experience an acceptable rotation of the external cutting element 13 independently of, or depending on, the position at which the electric shaver 1 is actually shaving. Alternatively, the processor 89 may adapt the second rotation speed ω2 depending on the detected position of the electric shaver 1 based on different position-dependent characteristics, for example based on average user hair characteristics in different areas of the body. The processing unit 97 of the detection system 87 may be part of the processor 89, as shown in Figure 10a, or may be separate from the processor 89.

[0054] In a further embodiment of the electric shaver 1 according to the invention, the user-related parameters include an accumulated amount of shaving time of the electric shaver 1 for a plurality of different areas of the user's body during a shaving session. In this further embodiment, as shown in Fig. 10b, the detection system 87 comprises an orientation sensor 95 and a processing unit 97 for measuring the position of the electric shaver 1 on the user's body and generating a corresponding output signal LS, as described earlier in this specification with reference to the embodiment of Fig. 10a. In this embodiment, the detection system 87 further comprises a timer 99 configured to output a timing signal TS. The detection system 87 comprises a further processing unit 101 configured to determine the accumulated shaving time of the electric shaver 1 for each of the plurality of different areas of the user's body based on the output signal LS of the further processing unit 97 and the timing signal TS of the timer 99. The further processing unit 101 generates an output signal LCST, which is supplied to the processor 89 as an embodiment of the output signal URP shown in Fig. 9 and represents the accumulated amount of shaving time for the area of ​​the user's body that is actually being shaved by the electric shaver 1. In this embodiment, the processor 89 may be configured, for example, to reduce the second rotation speed ω2 of the external cutting element 13 when the output signal LCST of the further processing unit 101 indicates that the accumulated amount of shaving time for the area of ​​the user's body that the electric shaver 1 is actually shaving exceeds a predetermined time threshold. In this way, increased skin irritation due to the rotation of the external cutting element 13, which may occur when the user shaves for too long on the same skin area, is limited or prevented. The processing unit 97, timer 99 and further processing unit 101 of the detection system 87 may be part of the processor 89, as shown in FIG. 10b, or may be separate from the processor 89.

[0055] In a further embodiment of the electric shaver 1 according to the invention, the user-related parameter comprises a speed at which the user moves the electric shaver 1 over the user's body. In this further embodiment, as shown in FIG. 10c, the detection system 87 may comprise an orientation sensor 95 and a processing unit 103, as previously described herein with reference to the embodiment of FIGS. 10a and 10b. In this embodiment, the orientation sensor 95 is an IMU sensor, as previously described. The processing unit 103 is configured to receive an output signal ACC generated by the IMU sensor and representing a measured acceleration of the electric shaver 1. The processing unit 103 is configured to determine from the measured acceleration a speed at which the electric shaver 1 moves over the user's body, and to generate a corresponding output signal MS, as one embodiment of the output signal URP shown in FIG. 9 that is supplied to the processor 89. The processing unit 103 of the detection system 87 may be part of the processor 89, as shown in FIG. 10c, or may be separate from the processor 89. Instead of an IMU sensor, the detection system 87 may comprise a displacement sensor 105 arranged in the shaving unit 5 as shown schematically in Figure 4A, such as an optical displacement sensor known to those skilled in the art. In such a case, the processing unit 103 is configured to determine the speed of movement of the electric shaver 1 from the displacement measured by the displacement sensor 105.

[0056] A known problem with electric shavers is that the hair-capturing efficiency of the hair-cutting units decreases as the user increases the movement speed of the electric shaver on their body. To alleviate this problem, in this embodiment, the processor 89 is configured to increase the second rotational speed ω2 of the external cutting elements 13 of the hair-cutting units 9a, 9b, and 9c as the movement speed of the electric shaver 1 measured by the detection system 87 increases. By increasing the second rotational speed ω2, i.e., for the embodiment of the external cutting element 13 shown in FIG. 6b, at least within a predetermined range of the second rotational speed ω2 depending on the detailed design of the external cutting element 13, such as a range of 0 to 300 rpm, the increase in hair-capturing efficiency achieved by increasing the second rotational speed ω2 can partially or even completely compensate for the decrease in hair-capturing efficiency caused by increasing the movement speed of the electric shaver 1. The processor 89 can be configured to gradually increase the second rotational speed ω2 as the measured movement speed increases. Alternatively, processor 89 may be configured to incrementally increase second rotational speed ω2 at certain thresholds of the measured movement speed. In another example, second rotational speed ω2 may be set to a first predetermined value when the measured movement speed is below a first threshold, set to a second predetermined value higher than the first predetermined value when the measured movement speed is above the first threshold, or set to a value between the first and second predetermined values ​​in proportion to values ​​of the measured movement speed between the first and second thresholds.

[0057] With respect to this embodiment, the inventors have also found that in order to achieve an optimal improvement in hair capture efficiency, the processor 89 must set the second rotational speed ω2 of the external cutting element 13 of the hair-cutting unit 9a, 9b, 9c such that the tangential speed V of the external cutting element 13 relative to the central axis 11 of the hair-cutting unit 9a, 9b, 9c as defined earlier in this specification is higher than the movement speed measured by the detection system 87. It has been found that the majority of electric shaver users move the shaver over their body at a speed between 10 cm / s and 30 cm / s. In an embodiment of the external cutting element 13, it has been found that a tangential speed V of about 14 cm / s (corresponding to ω2 = 150 rpm) provides optimal hair capture efficiency for a movement speed of 10 cm / s. For movement speeds of 20 cm / s and 30 cm / s, the optimum values ​​of the tangential velocity V of the external cutting element 13 were found to be approximately 28 cm / s (corresponding to ω2 = 300 rpm) and approximately 38 cm / s (corresponding to ω2 = 400 rpm), respectively.

[0058] In one embodiment of the electric shaver 1 in which the user-related parameter includes the pressure or force with which the user presses the electric shaver 1 against their body, the detection system 87 is constructed and arranged to measure said pressure or force. For this purpose, the detection system 87 may include any suitable detector known to those skilled in the art. By way of example, the detection system 87 may include a pressure-sensing system such as that disclosed in International Publication No. WO 2020 / 212276 A1 in the name of the applicant. The main parts of this known pressure-sensing system are shown schematically in FIG. 3 , in which the support structure 7 of the shaving unit 5 includes a pair of blade springs 107 resiliently suspended relative to the main housing 3 in an orientation parallel to the central axis 109 of the shaving unit 5, a permanent magnet 111 attached to the support structure 7, and a Hall sensor 113 attached to the main housing 3 in a position close to the magnet 111. As a result of the use of the blade springs 107, the distance between the permanent magnet 111 and the Hall sensor 113, which is parallel to the central axis 109 of the shaving unit 5, depends on the pressure applied to the shaving unit 5 parallel to the central axis 109 of the shaving unit 5. As shown schematically in FIG. 10d, in this embodiment, the Hall sensor 113 generates an output signal HS representative of the magnetic field strength of the magnet 111 measured at the location of the Hall sensor 113, which depends on the distance between the magnet 111 and the Hall sensor 113 and, therefore, the pressure with which the shaving unit 5 is pressed against the body. As shown schematically in FIG. 10d, in this embodiment, the detection system 87 further comprises a processing unit 115 configured to determine the pressure or force with which the shaving unit 5 is pressed against the body from the output signal HS of the Hall sensor 113, the known magnetic properties of the permanent magnet 111 and the Hall sensor 113, and the known elastic properties of the blade spring 107. The processing unit 115 generates an output signal PF representative of the determined pressure or force as one embodiment of the output signal URP shown in FIG. 9, which is supplied to the processor 89. As shown in FIG. 10d, the processing unit 115 of the detection system 87 may be part of the processor 89 or may be separate from the processor 89.Further details of the pressure sensing system are disclosed in WO 2020 / 212276 A1. It should be noted that instead of the pressure sensing system described hereinabove, the detection system 87 may comprise a different type of pressure sensor, for example one or more mechanical pressure sensors 117 of a type known to those skilled in the art, which may be arranged on the shaving unit 5, as shown diagrammatically in FIG. 4a.

[0059] As the pressure or force increases, the degree of skin doming into the hair entry opening 61 of the external cutting element 13 increases, which may result in increased skin irritation experienced by the user. It has been found that the degree of skin doming into the hair entry opening 61 can be reduced by increasing the second rotational speed ω2 of the external cutting element 13. Thus, as a first example relevant to this embodiment, the processor 89 is configured to increase the second rotational speed ω2 when the detection system 87 detects an increase in pressure or force exerted on the shaving unit 5. This can prevent or limit an increase in skin doming and associated skin irritation due to the increase in pressure or force.

[0060] An increase in the pressure or force increases the friction between the skin and the rotating external cutting element 13, which may also result in increased skin irritation experienced by the user. Since the skin friction can be reduced by reducing the second rotation speed ω2 of the external cutting element 13, in a second example related to this embodiment, the processor 89 is configured to reduce the second rotation speed ω2 when the detection system 87 detects an increase in the pressure or force applied to the shaving unit 5. This can prevent or limit an increase in skin friction and associated skin irritation due to the increase in pressure or force. In this embodiment, the electric shaver 1 can include a user interface that allows the user to select a preferred way for the processor 89 to adapt the second rotation speed ω2 depending on the measured pressure, i.e., to control skin doming to the hair entry 61 according to the first example described above, or to control skin friction according to the second example described above.

[0061] In an embodiment of the electric shaver 1 according to the present invention, the user-related parameters include parameters related to the user's skin characteristics, and the detection system 87 is configured and arranged to measure the parameters related to the user's skin characteristics. In one example, the skin-characteristic-related parameter is skin redness, which is a known skin characteristic that is affected by the shaving process. The degree of skin redness is considered to be an indicator of the degree of skin irritation caused by the shaving process. In this example, the detection system 87 may include an optical color sensor 119 disposed within the shaving unit 5 and configured to detect the degree of skin redness, as shown schematically in FIG. 4a. Alternatively, as shown schematically in FIG. 10e, the detection system 87 may include a camera 121, which may be disposed separately from the main housing 3 and the shaving unit 5, for example, in a smartphone. The camera 121 is configured to generate an output signal IMG representing an image of the user's skin. The detection system 87 further includes a processing unit 123 configured to analyze the image generated by the camera 121, determine the degree of skin redness based on the analysis, and generate a corresponding output signal SR, which is provided to the processor 89 as an embodiment of the output signal URP shown in FIG. 9. In this example, processor 89 may be configured to reduce second rotational speed ω2 of external cutting element 13 when detection system 87 measures an increase in skin redness. As shown in FIG. 10e, processing unit 123 of detection system 87 may be part of processor 89 or may be separate from processor 89. Instead of skin redness, processor 89 may control second rotational speed ω2 of external cutting element 13 in response to another type of skin characteristic, particularly when such skin characteristic is affected by second rotational speed ω2 of external cutting element 13 and / or when such skin characteristic affects the hair-capturing efficiency of external cutting element 13.

[0062] In an embodiment of the electric shaver 1 according to the present invention, the user-related parameters include parameters related to the user's hair characteristics, and the detection system 87 is configured and arranged to measure the parameters related to the user's hair characteristics. In one example, the hair characteristics are hair characteristics that may affect the hair-capturing efficiency of the external cutting elements 13 of the hair-cutting units 9a, 9b, 9c. Examples of such hair characteristics include hair length, hair thickness, or hair density on the skin. As shown schematically in FIG. 10f, similar to the embodiment shown in FIG. 10e, the detection system 87 can include a camera 121 configured to generate an output signal IMG representing an image of the user's skin. The detection system 87 further includes a processing unit 125 configured to analyze the image generated by the camera 121, determine hair characteristics based on the analysis, and generate a corresponding output signal HP as an embodiment of the output signal URP shown in FIG. 9, which is supplied to the processor 89. For example, if the hair characteristic is hair length or hair density on the skin, the processor 89 may be configured to increase the second rotational speed ω2 of the external cutting element 13 when the detection system 87 measures an increase in hair length or hair density. This may increase hair capture efficiency for longer hairs or higher hair densities. As shown in Figure 10f, the processing unit 125 of the detection system 87 may be part of the processor 89 or may be separate from the processor 89.

[0063] As mentioned above, in the embodiment shown in FIG. 3 , the drive system 27 of the electric shaver 1 comprises a single motor 29 and a transmission system 31 that enables the motor 29 to rotate both the internal cutting element 15 and the external cutting element 13 of each hair-cutting unit 9 a, 9 b, 9 c. The use of a single motor 29 in this embodiment results in a relatively simple structure of the electric shaver 1. In this embodiment, adjustment of the second rotational speed ω2 of the external cutting element 13 by the processor 89 also results in a proportional adjustment of the first rotational speed ω1 of the internal cutting element 15. Such adjustment of the first rotational speed ω1 may be acceptable in many practical applications, as long as the first rotational speed ω1 remains within the range required for effective haircutting by the rotating internal cutting element 15. FIG. 11 schematically illustrates an alternative embodiment of a drive system 127 for an electric shaver 1 according to the present invention, which allows the second rotational speed ω2 of the external cutting element 13 to be adjusted independently of the first rotational speed ω1 of the internal cutting element 15. Parts of the alternative embodiment of the drive system 127 and electric shaver 1 shown in Figure 11 correspond to parts of the embodiment of the drive system 27 and electric shaver 1 shown in Figure 3 and are indicated in Figure 11 by corresponding reference numerals.

[0064] 11, in the alternative embodiment, the drive system 127 comprises a first motor 129 configured and arranged to rotate the inner cutting elements 15 of each hair-cutting unit 9a, 9b, 9c about the central axis 11 of the hair-cutting unit 9a, 9b, 9c via a first transmission system 131, and a second motor 133 configured and arranged to rotate the outer cutting elements 13 of each hair-cutting unit 9a, 9b, 9c about the central axis 11 of the hair-cutting unit 9a, 9b, 9c via a second transmission system 135. The first transmission system 131 comprises a main shaft 137 supporting the first main gear 33 as previously described herein with reference to the drive system 27 shown in FIG. The shaft 137 is rotatably journaled relative to the support structure 7 of the main housing 3 and the shaving unit 5 and is arranged to be driven by the first motor 129 via an intermediate gear 139 attached to a motor shaft 141 of the first motor 129 and an intermediate gear 143 attached to the shaft 137. The first primary gear 33 is coupled to each of the three internal cutting elements 15 via three secondary gears 39 and three drive spindles 41 described herein above with reference to the drive system 27 shown in FIG. 3. The second transmission system 135 includes a second primary gear 145 attached to a motor shaft 147 of the second motor 133. The second primary gear 145 engages with the third primary gear 45 described herein above with reference to the drive system 27 shown in FIG. 3. Thus, the second primary gear 145 is coupled to each of the three external cutting elements 13 via the third primary gear 45, the secondary shaft 43, the fourth primary gear 49, the fifth primary gear 53, the third shaft 51, the sixth primary gear 55, and the three secondary gears 57, with reference to the drive system 27 shown in FIG. 3 .

[0065] When the electric shaver 1 includes an alternative embodiment of the drive system 127, the processor 89 is constructed and arranged to control the second motor 133 of the drive system 127 so that the second rotational speed ω2 of the outer cutting element 13 depends on the measured user-related parameter, for example, according to the examples discussed above with reference to Figures 10a to 10f. In particular, the processor 89 can control the second rotational speed ω2 independently of the first rotational speed ω1 of the inner cutting element 15. For example, the processor 89 can control the first motor 129 to maintain the first rotational speed ω1 at a constant value that is optimal for cutting hair with the rotating inner cutting element 15, and the processor 89 can control the second motor 133 to adjust the second rotational speed ω2 as the measured user-related parameter changes so as to maintain the hair-capturing efficiency of the outer cutting element 13 at an optimal level. To this end, as will be apparent to those skilled in the art, the power control module 91 may be configured to independently power the first motor 129 and the second motor 133 based on a first output signal of the processor 89 related to the first rotational speed ω1 achieved by the first motor 129 and a second output signal of the processor 89 related to the second rotational speed ω2 achieved by the second motor 133, respectively. Independent control of the rotation of the external cutting element 13 in this alternative embodiment of the drivetrain 127 further enables the provision of a user input element, for example, by means of which the user can turn the rotation of the external cutting element 13 on or off or select between several predetermined ranges for the second rotational speed ω2 based on user preference.

[0066] It will be apparent to those skilled in the art that the scope of the present invention is not limited to the above-described examples, but that several modifications and variations thereof are possible without departing from the scope of the present invention as defined in the appended claims. It is intended that the present invention be construed as including all such modifications and variations insofar as they come within the scope of the claims or their equivalents. While the present invention has been illustrated and described in detail in the drawings and description, such illustration and description should be considered as exemplary or illustrative only and not restrictive. The present invention is not limited to the disclosed embodiments. The drawings are schematic and may omit details not necessary for understanding the invention and may not necessarily be to scale.

[0067] 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 drawings, 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.

[0068] Elements and features discussed with respect to or in connection with a particular embodiment may be combined with elements and features of other embodiments as appropriate, unless expressly stated otherwise. 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. at least one hair-cutting unit having a central axis, an outer cutting element having a hair entry opening in an annular shaving area concentrically disposed about the central axis, and an inner cutting element surrounded by the outer cutting element and having an annular array of cutting elements concentrically disposed about the central axis; a drive system configured to rotate the inner cutting element of each hair-cutting unit about the central axis of the hair-cutting unit at a first rotational speed and the outer cutting element of each hair-cutting unit about the central axis of the hair-cutting unit at a second rotational speed, such that the inner and outer cutting elements of each hair-cutting unit are rotated relative to one another about the central axis of the hair-cutting unit; An electric shaver having The electric shaver further comprises: a detection system constructed and arranged to measure at least one user-related parameter related to the skin or hair of a user of the electric shaver or related to the operation of the electric shaver by the user relative to the body of the user; a processor constructed and arranged to control the drive system such that the second rotational speed at which the drive system rotates the external cutting element about a central axis of the hair-cutting unit is dependent on the at least one measured user-related parameter; An electric shaver having

2. The at least one user-related parameter is: the position of the electric shaver on the body of the user; a cumulative shaving time of the electric shaver on a plurality of different areas of the user's body during a shaving session; the speed at which the user moves the electric shaver over the user's body; the pressure or force with which the user presses the electric shaver against the body; parameters related to the user's skin characteristics; and parameters relating to the user's hair characteristics; The electric shaver according to claim 1 , further comprising at least one of:

3. the at least one user-related parameter comprises a position of an electric shaver on the body of the user; the detection system comprises a detector constructed and arranged to measure the position of the electric shaver on the body of the user; 3. The electric shaver according to claim 2.

4. the at least one user-related parameter comprises a cumulative shaving time of the electric shaver on a plurality of different areas of the user's body during a shaving session; the detection system comprises a detector constructed and arranged to measure a position of an electric shaver on the body of the user; the processor is configured to measure a cumulative shaving time of the electric shaver for each of a plurality of different areas of the user's body based on the position of the electric shaver measured by the detector and a timing output provided by a timer.

3. The electric shaver according to claim 2.

5. the at least one user-related parameter comprises a speed of movement at which the user moves the electric shaver over the user's body; the detection system includes a detector constructed and arranged to measure a speed at which the user moves the electric shaver over the user's body.

3. The electric shaver according to claim 2.

6. the at least one user-related parameter comprises a pressure or force with which the user presses the electric shaver against the body; the detection system comprises a detector constructed and arranged to measure the pressure or force with which the user presses the electric shaver against the body; 3. The electric shaver according to claim 2.

7. the at least one user-related parameter comprises a parameter related to a skin characteristic of the user; the detection system includes a detector constructed and arranged to measure a parameter related to a skin characteristic of the user; 3. The electric shaver according to claim 2.

8. the at least one user-related parameter comprises a parameter related to a hair characteristic of the user; the detection system comprising a detector constructed and arranged to measure a parameter related to a hair characteristic of the user; 3. The electric shaver according to claim 2.

9. 9. The electric shaver of claim 1, wherein the drive system comprises a single motor configured and arranged to rotate both the inner cutting element of each hair-cutting unit and the outer cutting element of each hair-cutting unit about a central axis of the hair-cutting unit via a transmission system, and the processor configured and arranged to control the single motor such that a second rotational speed of the outer cutting element depends on the measured user-related parameter.

10. 9. The electric shaver of claim 1, wherein the drive system comprises a first motor configured and arranged to rotate an internal cutting element of each hair-cutting unit about a central axis of the hair-cutting unit, and a second motor configured and arranged to rotate an external cutting element of each hair-cutting unit about the central axis of the hair-cutting unit, and the processor configured and arranged to control the second motor such that a second rotational speed of the external cutting element depends on the measured user-related parameter.

11. 9. The electric shaver of claim 1, wherein the drive system is configured to rotate the internal cutting element of each hair-cutting unit in a first rotational direction about a central axis of the hair-cutting unit and to rotate the external cutting element of each hair-cutting unit in a second rotational direction opposite to the first rotational direction about the central axis of the hair-cutting unit, the second rotational speed of the external cutting elements being lower than the first rotational speed of the internal cutting elements.

12. 12. The electric shaver of claim 11, wherein the hair entry opening of the outer cutting element of each hair-cutting unit comprises a V-shaped opening pointing in the first rotation direction of the inner cutting element, and wherein the second rotation speed of the outer cutting element of each hair-cutting unit is configured such that a tangential speed of the outer cutting element 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, more preferably in the range of between 11.25 cm / s and 30.0 cm / s.

13. 13. The electric shaver of claim 12, wherein the hair entry opening extends 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 a second radial distance in the radial direction, the second radial distance being at least 50% of the first radial distance.

14. 13. The electric shaver of claim 12, wherein the hair entry opening of the outer cutting element 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 toward 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, the radially inner and outer linear openings each having a main direction extending radially relative to the central axis of the hair-cutting unit.

15. 13. The electric shaver of claim 12, wherein the V-shaped opening of the hair entry opening has a V-angle in the range of 60 degrees to 135 degrees.

Images