An electric shaver having a rotatable external cutting element with a rotatable speed that can be adjusted

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 relates to at least one hair cutting unit having a central axis, an external cutting element having a hair entry opening provided in an annular shaving region arranged concentrically around the central axis, and an internal cutting element having an annular array of cutting elements covered by the external cutting element and arranged concentrically around the central axis, a drive system configured to rotate the internal cutting element of each hair cutting unit at a first rotational speed around the central axis of the hair cutting unit, rotate the external cutting element of each hair cutting unit at a second rotational speed around the central axis of the hair cutting unit, and rotate the internal and external cutting elements of each hair cutting unit relative to each other around the central axis of the hair cutting unit and an electric shaver having the same.

Background Art

[0002] An electric shaver is well-known that comprises at least one hair-cutting unit having a central axis, an external cutting element having a hair entry opening provided in an annular shaving area arranged concentrically around the central axis, and an internal cutting element having an annular array of cutting elements covered by the external cutting element and arranged concentrically around the central axis, and further comprises a drive system configured to rotate the internal cutting element of each hair-cutting unit relative to the external cutting element around the central axis of the hair-cutting unit. Such an electric shaver typically includes a shaving unit having two or more such hair-cutting units supported by a support structure of the shaving unit. The electric shaver typically comprises a main housing that houses an electric motor. The shaving unit may be coupled to the main housing in a permanent manner or in a releasable manner. When the shaving unit is coupled to the main housing, the motor is coupled to the internal cutting element of the hair-cutting unit via a transmission system that enables the motor to rotate the internal cutting element relative to the external cutting element. During rotation of the internal cutting element, hairs enter the external cutting element through the hair entry opening of the external cutting element and are cut by the interaction between a cutting edge provided on the cutting elements of the rotating internal cutting element and an opposing cutting edge provided at the hair entry opening of the external cutting element.

[0003] An important characteristic of the hair-cutting unit of such an electric shaver is the hair capture efficiency, i.e., the degree to which hair can penetrate into the hair entry opening of the external cutting element during the movement of the electric shaver on the user's skin while the annular shaving area of the external cutting element is in contact with the skin. A high hair capture efficiency is desirable because it reduces the shaving time required to achieve the desired shaving result, for example, with respect to the average remaining hair length after the shaving process. The higher the hair capture efficiency, the more hair penetrates into the hair entry opening of the external cutting element and is better cut, for example, during a single movement stroke of the electric shaver over a specific area of the skin by the hair-cutting unit, and the average remaining hair length obtained after the shaving process is smaller. To improve the hair capture 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. For this purpose, a known electric shaver has 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 (number of rotations per unit time), rotate the external cutting element of each hair-cutting unit about the central axis of the hair-cutting unit at a second rotational speed (number of rotations per unit time), and rotate the internal cutting element and the external cutting element 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 comprising a hair cutting unit having an external cutting element with a slit-shaped hair entry opening extending substantially radially with respect 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, for example, 6,000 to 15,000 revolutions per minute (rpm). The external cutting element is rotated in a direction opposite to the direction of 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 and continuous rotation of the external cutting element causes the slit-shaped hair entry opening to capture diagonal hairs growing in various directions better and more regularly than is achieved by the circular manual movement of a shaver having a stationary external cutting element.

[0005] US 10,195,751 B2 discloses an electric shaver comprising 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 with respect to the central axis of the hair cutting unit, a round hair entry opening, or a hair entry opening combining a round and a slit shape. The internal and external cutting elements of each hair cutting unit are driven to be rotatable about the central axis of the hair cutting unit in the same direction or in opposite directions. According to this patent, the rotation of the external cutting element improves the lifting and snagging action of the user's hair, resulting in an advantageous effect of a better feel against the skin. In one example, the shaver has a gear transmission mechanism configured to convert a motor rotation speed of 8,000 rpm to a rotation speed of the external cutting element of about 10 rpm.

[0006] The drawbacks of these known electric shavers are that the rotational speed of the external cutting element may not be optimal in all situations of use or operation of the shaver by the user, and generally may not be optimal for all users of the shaver. In particular, the hair capture efficiency of the shaver is improved by the rotation of the external cutting element, but may vary depending on the particular manner of use or operation of the shaver by the user, or depending on the particular characteristics of the user's hair, whereby it may not be optimal in all usage situations or for all users. Additionally, the rotation of the external cutting element may be experienced as uncomfortable by some users under certain circumstances, for example, depending on the particular characteristics of the user's skin.

[0007] Japanese Patent Application Laid-Open No. 2010-227225 discloses an electric shaver having a main body or a gripping portion and a shaving unit or a head portion disposed above the gripping portion. The head portion includes three hair cutting units or blade blocks, and each blade block has an external cutting element or an external blade and an internal cutting element or an internal blade. The outer blades of the blade blocks extend parallel to each other in the longitudinal direction of the head portion. In the head portion, an electric inner blade driving device is disposed for reciprocatingly swinging the inner blade of each blade block parallel to the longitudinal direction with respect to the outer blade of the blade block. Further, in the head portion, there is provided an electric head driving device for reciprocatingly moving the entire head portion in the longitudinal direction and / or in the lateral direction perpendicular to the longitudinal direction of the head portion, and for swinging and reciprocatingly moving the entire head portion about the central rotation axis of the head portion extending 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 swinging vibration of the head portion described above, the introduction of beard hairs into the outer blade of the blade block is improved, and as a result, the shaving performance of the electric shaver is improved. Further, it includes detection means for detecting the operating state of the shaver, and control means for controlling the head driving device based on the detection signal from the detection means. As a result, even when the operating state of the shaver is different, the introduction rate of beard hairs into the outer blade of the blade block and the shaving performance are stabilized. Examples of the measured operating states are the moving speed or moving acceleration of the head portion, and the contact pressure received by the outer blade from the user's skin. The control means can control the frequency, amplitude, speed, or acceleration of the longitudinal vibration and / or lateral vibration and / or swinging vibration of the entire head. Summary of the Invention Problems to be Solved by the Invention

[0008] An object of the present invention is to provide an electric shaver of the type described above in this specification that does not have the drawbacks described above in this specification, in relation to the electric shavers known from U.S. Patent Application Publication Nos. 2,283,834 and 10,195,751.

Means for Solving the Problem

[0009] To achieve the above object, the present invention provides at least one hair cutting unit having a central axis, an external cutting element having a hair entry opening provided in an annular shaving region arranged concentrically around the central axis, and an internal cutting element having an annular array of cutting elements covered by the external cutting element and arranged concentrically around the central axis; a drive system configured to rotate the internal cutting element of each hair cutting unit at a first rotational speed around the central axis of the hair cutting unit, rotate the external cutting element of each hair cutting unit at a second rotational speed around the central axis of the hair cutting unit, and rotate the internal cutting element and the external cutting element of each hair cutting unit relative to each other around the central axis of the hair cutting unit; an electric shaver having wherein the electric shaver further comprises a detection system configured and arranged to measure 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; a processor configured and arranged to control the drive system such that the second rotational speed at which the drive system rotates the external cutting element around the central axis of the hair cutting unit depends on the at least one measured user-related parameter; an electric shaver having is provided.

[0010] Therefore, in the electric shaver according to the present invention, the internal cutting element of each hair cutting unit is rotated by a drive system around the central axis of the hair cutting unit at a first rotational speed (number of rotations per unit time), and the external cutting element of each hair cutting unit is rotated by the drive system around the central axis of the hair cutting unit at a second rotational speed (number of rotations per unit time). The internal cutting element and the external cutting element may have the same rotational direction around the central axis or rotational directions opposite to each other. Depending on the first and second rotational speeds and rotational directions of the internal cutting element and the external cutting element, the relative rotation between the internal cutting element and the external cutting element should be achieved to such an extent that an effective hair cutting process is achieved, as is known in the art.

[0011] In particular, according to the present invention, the second rotational speed at which the drive system rotates the external cutting element depends on at least one user-related parameter measured by a detection system. In particular, the at least one user-related parameter is related to the skin or hair of the user of the electric shaver or to the operation of the electric shaver by the user on the user's body. Thus, the processor can automatically adapt the second rotational speed of the external cutting element, for example, to a particular user-specific way in which the user operates the electric shaver on the user's body that affects hair capture efficiency, to user-specific hair characteristics that affect hair capture efficiency, or to user-specific skin characteristics that affect the way the user experiences the rotation of the external cutting element. In particular, the processor causes the hair capture efficiency to remain at an optimal level or at least a desired level that is independent of or not very dependent on a particular way in which the user operates the electric shaver or user-specific hair characteristics, or is independent of or not very dependent on user-specific skin characteristics, or the rotation of the external cutting element is independent of or not very dependent on user-specific skin characteristics. Examples of such user-related parameters and methods of controlling the second rotational speed of the external cutting element in response to such user-related parameters will be described below with reference to embodiments of the present invention.

[0012] In one embodiment of an electric shaver according to the present invention, at least one user-related parameter includes at least one of the position of the electric shaver on the user's body, the amount of cumulative shaving time of the electric shaver for a plurality of different regions of the user's body during a shaving session, the movement speed at which the user moves the electric shaver on the user's body, the 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 can 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 can be configured and arranged to control a second rotational 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 an electric shaver according to the present invention, 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 operation of the electric shaver by the user with respect 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 can be configured to reduce the second rotational speed of the external cutting element when, for example, the detector detects that the electric shaver is moved from a position on the user's body that is known to have a relatively low sensitivity, such as the cheek region of the face, to a position on the user's body that is known to have a relatively high sensitivity, such as the neck region, and vice versa. In this way, the user can experience the rotation of the external cutting element in an acceptable manner, independently of or depending on the position where the electric shaver is actually shaving.

[0014] In one embodiment of the electric shaver according to the present invention, at least one user-related parameter includes the cumulative shaving time of the electric shaver for a plurality of different regions of the user's body during a shaving session, that is, as a second example of a user-related parameter regarding the operation of the electric shaver by the user 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 a plurality of different regions of the user's body based on the position of the electric shaver measured by the detector and the timing output provided by the timer. When the user shaves for a longer time on the same skin region, even on the cheek region, skin irritation can increase. The increase in skin irritation can be limited, for example, by automatically reducing the second rotational speed of the external cutting element when the cumulative amount of shaving time in a specific skin region exceeds a predetermined threshold. For this purpose, the processor is configured to reduce the second rotational speed of the external cutting element when the measured cumulative shaving time exceeds a predetermined threshold for a specific one of a plurality of different regions of the user's body and the position of the electric shaver measured by the detector is within the specific one of the plurality of different regions of the user's body.

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

[0016] The at least one user-related parameter includes the pressure or force with which the user presses the electric shaver against the body. That is, in an embodiment of the electric shaver, as a fourth example of the user-related parameter regarding the operation of the electric shaver with respect to the user's body, the electric shaver is provided with a detector configured and arranged to measure the pressure or force of the electric shaver, and the detection system is configured and arranged to measure the pressure or force with which the electric shaver is pressed against the body. When 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. By increasing the second rotational speed of the external cutting element, the degree of skin doming into the hair entry opening can be reduced. Therefore, in this embodiment, when the measured pressure or force by the processor increases and the processor is configured to increase the second rotational speed of the external cutting element, the increase in skin irritation caused by the increase in the pressure can be prevented or limited.

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

[0018] In one embodiment of the electric shaver according to the present invention, 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 capture efficiency of the hair cutting unit, such as hair length, hair thickness, or hair density on the skin. For example, when the hair length is measured by the detector, the processor can be configured to increase the second rotational speed of the external cutting element when the detector measures an increase in hair length. Thereby, the hair capture efficiency for longer hair can be enhanced.

[0019] In one embodiment of an electric shaver according to the present invention, a drive system is configured and arranged via a transmission system to rotate both an internal cutting element and an external cutting element of each hair cutting unit around a central axis of the hair cutting unit by a single motor, and a processor is configured and arranged to control the single motor such that a second rotational speed of the external cutting element depends on user-related parameters measured. 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 external cutting element by the processor generally also results in a proportional adjustment of the first rotational speed of the internal cutting element. However, such an adjustment of the first rotational speed of the internal cutting element can be acceptable in many practical applications as long as the first rotational speed remains within the range required for an effective hair cut.

[0020] In a preferred embodiment of an electric shaver according to the present invention, a 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 a central axis of the hair cutting unit, and a processor is configured and arranged to control the second motor such that a second rotational speed of the external cutting element depends on user-related parameters measured. In this embodiment, the second rotational speed of the external cutting element can be adjusted independently of the first rotational speed of the internal cutting element. For example, the first motor can maintain the first rotational speed of the internal cutting element at a constant value optimal for hair cutting, while the second motor can adjust the second rotational speed of the external cutting element to maintain the hair capturing efficiency of the hair cutting unit at an optimal level when the measured user-related parameters change. The independent control of the rotation of the external cutting element in this embodiment further enables, for example, the provision of a user input element by means of which a user can switch the rotation of the external cutting element on and off, or select between several predetermined speed ranges for the external cutting element based on the user's preference.

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

[0022] In one embodiment of the electric shaver according to the invention, the drive system is configured to rotate the internal cutting element and the external cutting element of each hair cutting unit in opposite directions to each other as described above. The hair entry opening of the external cutting element of each hair cutting unit can be provided with a V-shaped opening pointing in the first rotational direction of the internal cutting element. The second rotational speed of the external cutting element of each hair cutting unit can be such that the tangential speed of the external cutting element with respect to the central axis, measured at the radius position of the center point of the V-shaped opening with respect 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 base point" refers to the point where the two legs of the V-shaped opening are connected to each other.

[0023] In an experiment conducted by the inventors, for a hair cutting unit having an external cutting element with a straight slot-shaped hair entry opening that extends substantially radially with respect to the central axis of the hair cutting unit, an increase in hair capture efficiency and, as a result, a decrease in the average remaining hair length after shaving are achieved by rotating the external cutting element in a direction opposite to the rotational direction of the internal cutting element. The experiment was conducted on a hair cutting unit having an external cutting element with a hair entry opening having a V-shaped opening facing the first rotational direction of the internal cutting element, and a very significant increase in hair capture efficiency and, as a result, a very significant and user-perceivable decrease in the average remaining hair length after shaving are achieved by rotating the external cutting element in a direction opposite to the rotational direction of the internal cutting element such that the tangential speed of the external cutting element with respect to the central axis is in the range of 7.5 to 50 cm / s. In particular, surprisingly, 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 element, i.e., with respect to the hair capture efficiency and the average remaining hair length achieved by a fixed external cutting element, are found to be significantly higher in the electric shaver according to an embodiment of the present invention than in an electric shaver having an external cutting element with a straight radially extending hair entry opening. In this embodiment, when the second rotational speed of the external cutting element of each hair cutting unit is such that the tangential speed of the external cutting element with respect to the central axis is in the more preferred range between 11.25 and 30.0 cm / s, a significant increase in hair capture efficiency and, as a result, a significant and user-perceivable decrease in the average remaining hair length after shaving as described above are achieved by the minimum degree of additional skin friction caused by the rotation of the external cutting element.

[0024] In an embodiment of the electric shaver according to the present invention, a particularly remarkable improvement in hair capture efficiency is achieved. The hair entry opening extends over a first radial distance in the radial direction with respect to the central axis of the hair cutting unit. The V-shaped opening of the hair entry opening extends over a second radial distance in the radial direction, and the second radial distance is at least 50% of the first radial distance.

[0025] In a further embodiment of the electric shaver according to the present invention, The hair entry opening of the outer cutting element of each hair cutting unit further includes a radially inner straight 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 straight 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 straight openings each have a main direction extending in the radial direction with respect to the central axis of the hair cutting unit. In this embodiment, the straight opening radially inside and the straight opening radially outside of the hair entry opening provide a relatively high hair capture efficiency for the hair approaching the hair entry opening of the outer cutting element through the inner peripheral region of the annular shaving region and the outer peripheral region of the annular shaving region, respectively. The V-shaped opening of the hair entry opening provides a relatively high hair capture efficiency for the hair approaching the hair entry opening through the central region of the annular shaving region.

[0026] In a preferred embodiment of the electric shaver according to the present invention, the V-shaped angle of the V-shaped opening of the hair inlet opening is in the range of 60 degrees to 135 degrees. In this embodiment, with respect to the V-shaped opening, the V-shaped angle is defined as the angle surrounded by the two leg portions of the V-shaped opening. The V-shaped 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 a reduction of skin doming towards the hair entry opening, thereby resulting in a reduction of skin irritation caused by the shaving process.

[0027] The above and other aspects of the present invention will become apparent from the following detailed description of embodiments of the electric shaver according to the present invention, which will be described with reference thereto.

[0028] The present invention will be described in more detail with reference to the drawings, in which the same or similar features are denoted by the same reference numerals.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4a

Figure 4b

Figure 5

Figure 6a

Figure 6b

Figure 7a

Figure 7b

Figure 8

Figure 9

Figure 10a

Figure 10b

Figure 10c

Figure 10d

Figure 10e

Figure 10f

Figure 11

DETAILED DESCRIPTION OF THE INVENTION

[0030] Figure 1 schematically shows 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, 9c supported by the support structure 7. The support structure 7 may comprise a coupling structure well-known to those skilled in the art, not shown in Figure 1, 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 the electric shaver according to the present invention can include a different number of hair cutting units, for example, one, two, or three or more hair cutting units. It should be further noted that Figure 1 only schematically shows a general layout of the electric shaver and is not intended to limit the scope of the present invention to the specific detailed design of the shown electric shaver. For example, the present invention also covers embodiments of an electric shaver, where the shaving unit is coupled to the main housing via a coupling structure arranged in a relatively narrow center, and there is a space open around the coupling structure between the shaving unit and the main housing, as is well-known in the art.

[0031] Figure 2 is a schematic cross-sectional view of the hair cutting unit 9c along line II-II of Figure 1. The hair cutting parts 9a and 9b are the same as the hair cutting unit 9c. The hair cutting unit 9c includes a central axis 11, an external cutting element 13, and an internal cutting element 15. The external cutting element 13 has an annular shaving area 17 arranged concentrically around the central axis 11. The annular shaving area 17 is arranged to contact the skin of the user of the electric shaver 1 and has a hair entry opening (not visible in Figure 2) which will be described in detail below. The hair entry openings are separated from each other by a bridge part 19 provided in the annular shaving area 17. The internal cutting element 15 is covered by the external cutting element 13 and has an annular array of cutting elements 21 arranged concentrically around the central axis 11. The electric shaver 1 includes a drive system, which will be described in detail later in this specification, configured to rotate the internal cutting element 15 and the external cutting element 13 relative to each other about the central axis 11 during the operation of the electric shaver 1. As a result of the relative rotation between the internal cutting element 15 and the external cutting element 13, the hairs on the skin of the user that penetrate into the hair entry openings present in the annular shaving area 17 are cut by the interaction between the cutting edges 23 present on the cutting elements 21 of the internal cutting element 15 and the opposing cutting edges 25 present on the bridge part 19 of the external cutting element 13. It should be noted that the electric shaver according to the present invention can have two or more annular shaving areas arranged concentrically around the central axis, as is known in the art.

[0032] The drive system of the electric shaver 1 described above is schematically shown in FIG. 3 and is referenced by reference numeral 27. In the embodiment shown in FIG. 3, the drive system 27 comprises a single motor 29 disposed within the main housing 3. Further, in this embodiment, the drive system 27 rotates the inner cutting elements 15 of each of the hair cutting units 9a, 9b, 9c about the central axis 11 of the hair cutting units 9a, 9b, 9c in a first rotational direction R1 (shown in FIG. 2) and at a first rotational speed ω1, and rotates the outer cutting elements 13 of each of the hair cutting units 9a, 9b, 9c about the central axis 11 of the hair cutting units 9a, 9b, 9c in a second rotational direction R2 (shown in FIG. 2) opposite to the first rotational direction R1 and at a second rotational speed ω2 lower than the first rotational speed ω1. For this purpose, the drive system 27 comprises a transmission system 31 by which the motor 29 can rotate both the inner cutting elements 15 and the outer cutting elements 13 of each of the hair cutting units 9a, 9b, 9c, the transmission system 31 being partially disposed within the main housing 3 and partially within the shaving unit 5. It should be noted that, for simplicity, FIG. 3 shows in detail only one of the hair cutting units 9c. The driving of the other hair cutting units 9a, 9b by the drive system 27 will be described below. Further, it should be noted that, for simplicity, FIG. 3 shows only partially the support structure 7 of the shaving unit 5.

[0033] As shown in FIG. 3, the transmission system 31 includes a first primary gear 33 and a second primary gear 35, each attached to the motor shaft 37 of the motor 29. The transmission system 31 further includes three secondary gears 39, each attached to one of the three drive spindles 41 and coupled to one of the three internal cutting elements 15 of the hair cutting units 9a, 9b, 9c, and each pivotally supported for rotation relative to the support structure 7 of the shaving unit 5. The three secondary gears 39 each engage the first primary gear 33. FIG. 3 shows only one of the secondary gears 39 coupled to the internal cutting element 15 of the hair cutting unit 9c and one of the drive spindles 41, and it should be noted 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 part of the secondary shaft 43 is arranged between two of the secondary gears 39, but 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 arranged in line with the motor shaft 37 and rotatably supported with respect 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. The external cutting elements 13 of the hair cutting units 9a, 9b, 9c each include a secondary gear 57 that engages with a sixth primary gear 55 arranged at the center between the secondary gears 57 of the external cutting element 13. FIG. 3 shows only the secondary gear 57 of the external cutting element 13 of the hair cutting unit 9c. It should be noted that the secondary gears 57 of the external cutting elements 13 of the hair cutting units 9a and 9b are arranged in a corresponding manner. For clarity, the arrangement of the secondary gears 57 of all the external cutting elements 13 of the three hair cutting units 9a, 9b, 9c is shown in FIG. 4b. FIG. 4a shows that the external cutting elements 13 are each surrounded by the skin support elements 59a, 59b, 59c of their respective hair cutting units 9a, 9b, 9c. The skin support elements 59a, 59b, 59c each provide a rotary bearing for their respective external cutting element 13 and also cover the secondary gear 57 of their respective external cutting element 13.

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

[0036] In the embodiment of the present invention shown in the figure, a particularly significant improvement in the hair capture efficiency of the hair cutting units 9a, 9b, 9c is achieved by providing a hair entry opening 61 in the outer cutting element 13 of each hair cutting unit 9a, 9b, 9c of the electric shaver 1, which indicates the first rotation direction R1 of the inner cutting element 15, that is, a V-shaped opening 63 that indicates a direction opposite to the second rotation direction R2 of the outer cutting element 13, as shown in FIG. 5. Further, 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 with respect to the central axis 11 of the hair cutting units 9a, 9b, 9c is in the range of 7.5 to 50 cm / s. In this regard, as shown in FIG. 5, the tangential speed VT is measured at the radius position RC of the central base point 65 of the V-shaped opening 63 with respect to the central axis 11. The central base point 65 is the point of the V-shaped opening 63 where the two legs 67a, 67b of the V-shaped opening 63 are connected 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 an electric shaver in which the hair entry opening of the rotating outer cutting element has a V-shaped opening, as in the embodiment shown in the figure. The outer cutting element may have, for example, a more conventional linear or slightly curved hair entry slot that extends mainly in the radial direction with respect to the central axis of the hair cutting unit, or other known hair entry opening shapes.

[0037] The inventors of the present invention used a mathematical model of the skin of a human having hair, a mathematical model of a haircut unit having an external cutting element with a straight slot-shaped hair entry opening that extends substantially radially with respect to the central axis of the haircut unit, and a mathematical model of embodiments of haircut units 9a, 9b, 9c to conduct experiments in the form of numerical simulations. FIGS. 6a and 6b are graphs showing the hair capture efficiency of an external cutting element having a linear hair entry opening and the external cutting element 13, respectively, as a function of the second rotational speed ω2 (in rpm). In these figures, the hair capture efficiency is represented as the average penetration depth APD (in mm) of the hair into the hair entry opening of each external cutting element. The simulations were performed for a plurality of single strokes of each external cutting element over a specific skin area at a uniform hair length of 1 mm and a stroke speed of 10 cm / s to 30 cm / s. The external cutting element 13 has a radial position RC of 9 mm with respect to the central axis 11 of the central base point 65 of the V-shaped opening 63. In the case of the external cutting element 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 the value VT = 47 cm / s. The graph shows the equivalent hair capture efficiency (APD) of the external cutting element having a straight hair entry opening and the external cutting element 13 when there is no rotational movement of the external cutting element (ω2 = 0). With the rotation of the external cutting element, the hair capture efficiency (APD) of the external cutting element having a straight hair entry opening increases slightly, and as shown in FIG. 6a, an optimal hair capture efficiency is achieved for a rotational speed ω2 of about 200 rpm. As shown in FIG. 6b, with the rotation of the external cutting element 13 of the electric shaver 1 according to this embodiment of the present invention, the hair capture efficiency (APD) of the external cutting element 13 increases to a significantly greater extent compared to the external cutting element having a straight hair entry opening. As shown in FIG. 6b, for the external cutting element 13, an optimal hair capture efficiency is achieved for a second rotational speed ω2 of about 300 rpm.In particular, as is apparent from FIGS. 6a and 6b, the relative increase in hair capture efficiency (APD) as a result of the rotation of the external cutting element, i.e., the ratio between the average penetration depth (APD) of the hair into the hair entry opening with or without the rotation of the external cutting element, is significantly higher for the external cutting element 13 of the electric shaver 1 according to this embodiment of the present invention than for an external cutting element having a straight radially extending hair entry opening.

[0038] Figures 7a and 7b respectively show graphs of shaving efficiency of a hair cutting unit having an external cutting element with a straight hair entry opening and of hair cutting units 9a, 9b, 9c as a function of the second rotational speed ω2 (rpm). In these figures, the shaving efficiency is represented as the average hair length reduction ALR (mm) achieved by each hair cutting unit. The simulations were performed for a plurality of single strokes of each hair cutting unit over a specific skin area with a uniform hair length of 1 mm and a stroke speed of 10 cm / s to 30 cm / s. For the external cutting elements 13 of the hair cutting units 9a, 9b, 9c, the radial position RC of the central base point 65 of the V-shaped opening 63 with respect to the central axis 11 is 9 mm. In the case of a hair cutting unit having an 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. Thus, the value ω2 = 500 rpm in the graph corresponds to the value VT = 47 cm / s. The graph shows that when there is no rotational movement of the external cutting element (ω2 = 0), the shaving efficiency (with respect to ALR) of the hair cutting units 9a, 9b, 9c is approximately 25% higher than that of a hair cutting unit having an external cutting element with a straight hair insertion opening. With the rotation of the external cutting element, the shaving efficiency (ALR) of the hair cutting unit having an external cutting element with a straight hair entry opening increases slightly, and as shown in Figure 7a, an optimal shaving efficiency is achieved for a rotational speed ω2 of approximately 120 rpm. As shown in Figure 7b, with the 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 increases 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, for the hair cutting units 9a, 9b, 9c, an optimal shaving efficiency is achieved for a second rotational speed ω2 of approximately 300 rpm.In particular, as is apparent from FIGS. 7a and 7b, the relative increase in shaving efficiency (ALR) as a result of the 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 a hair cutting unit having an external cutting element with a straight radially extending hair entry opening.

[0039] As can be seen from FIG. 7b, a significant increase in shaving efficiency (ALR) of about 10% can already be achieved when the second rotational speed ω2 of the external cutting element 13 is about 80 rpm and corresponds to a value of VT of about 7.5 cm / s. As is apparent from FIG. 7a, such a significant relative increase in shaving efficiency (ALR) cannot be achieved by the rotation of an external cutting element having a straight hair entry opening. Further, the line L in FIGS. 7(a) and 7(b) th represents an increase in shaver efficiency (ALR) that is considered to be particularly perceptible to the user of the electric shaver 1. For the external cutting element 13, such a particularly user-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 above 50 cm / s may be undesirable considering the relatively high skin friction caused by the rotation of the external cutting element 13. Thus, in this embodiment of the invention, the second rotational speed ω2 of the external cutting element 13 is such that the tangential speed VT of the external cutting element 13 is measured at the radial position RC of the center base point 65 of the V-shaped opening 63 of the hair entry opening 61 and 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] Furthermore, as shown in Figure 7b, the relative increase in shaving efficiency (ALR) in the range of values of ω2 between about 120 rpm (VT = 11.25 cm / s) and about 300 rpm (VT = 28.3 cm / s) is equivalent to the relative increase in shaving efficiency (ALR) in the range of values of ω2 between about 300 rpm (VT = 28.3 cm / s) and about 550 rpm (VT = 50 cm / s). Since the skin friction caused by the rotation of the external cutting element 13 is lower at lower values of VT, according to a further embodiment of the present invention, the range of values of VT between 11.25 cm / s and 30.0 cm / s provides a favorable combination of a significant increase in hair capture efficiency and shaving efficiency as previously described herein and minimal additional skin friction caused by the rotation of the external cutting element 13.

[0041] Similar experiments conducted on a hair cutting unit having a hair entry opening, particularly a V-shaped opening thereof, disposed at a radial distance from the central axis that is greater or smaller compared to the radial distance RC of the external cutting element 13 as previously described herein, indicate that the range of values of VT in this embodiment of the present invention as previously described herein is independent of the radial distance and that the advantages of this embodiment of the present invention as previously described herein are achieved. In other words, in an embodiment of the present invention, the V-shaped opening 63 of the hair entry opening 61 is disposed at a greater, respectively smaller, radial distance RC from the central axis 11, and the second rotational speed ω2 of the external cutting element 13 should be decreased proportionally to the radial distance RC in order to achieve equivalent results with respect to improved hair capture and shaving efficiency. For example, when the second rotational speed ω2 is about 300 rpm (RC = 9 mm), in an embodiment with RC = 12 mm, the second rotational speed ω2 is about 225 rpm, and in an embodiment with RC = 6 mm, the second rotational speed ω2 is about 450 rpm, and equivalent results are achieved.

[0042] As shown in FIG. 5, the hair entry openings 61 of the outer cutting element 13 each extend radially with respect to the central axis 11 over a first radial distance RD1. The V-shaped opening 63 of the hair entry opening 61 extends radially with respect to the central axis 11 over a second radial distance RD2. In the embodiment shown in FIG. 5, the ratio RD2 / RD1 is about 0.75. A particularly significant improvement in hair capture and shaving efficiency is achieved in embodiments of an electric shaver in which the ratio RD2 / RD1 is at least 0.5. However, particularly when the first radial distance RD1 over which the hair entry opening 61 extends is relatively large, an improvement in hair capture and shaving efficiency can also be achieved for smaller values of said ratio.

[0043] In the embodiment shown in FIG. 5, the hair entry opening 61 of the outer 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 the 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 the 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 main extension direction radially with respect to the central axis 11. In this embodiment, the straight opening 69a on the radially inner side provides a relatively high hair capture efficiency for the hair approaching the hair entry opening 61 of the outer 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 on the user's skin. During such random movement, the radially outer straight opening 69b provides a relatively high hair capture efficiency for the hair approaching the hair entry opening 61 through the outer peripheral region 75 of the annular shaving region 17, while the V-shaped opening 63 provides a relatively high hair capture efficiency for the hair approaching the hair entry opening 61 through the central region of the annular shaving region 17.

[0044] Furthermore, FIG. 5 shows the V-shaped angle α of the V-shaped opening 63 of the hair entry opening 61, which is defined as the angle surrounded by the two legs 67a, 67b of the V-shaped opening 63. In the embodiment shown in FIG. 5, the V-shaped angle α is about 115 degrees. The preferred range of the V-shaped angle α is in the range of 60 degrees to 135 degrees. At the values of the V-shaped angle α within this preferred range, in addition to the improved hair capture and shaving efficiency of the V-shaped opening 63, during the rotation of the outer cutting element 13 in the second rotation direction R2, a stretching effect on the skin in two mutually diverging directions is provided. The skin stretching effect results in a reduction of skin doming towards the hair entry opening 61, thereby resulting in a reduction of skin irritation caused by the shaving process.

[0045] FIG. 8 shows the inner cutting element 15 of the hair cutting units 9a, 9b, 9c, the first rotation direction R1 of the inner cutting element 15 about the central axis 11 of the hair cutting units 9a, 9b, 9c, and the second rotation direction R2 of the outer cutting element 13. Each cutting element 21 of the annular array of cutting elements 21 is connected to the carrier 77 of the inner cutting element 15 via a flexure connection element 79. The carrier 77, the cutting element 21, and the flexure connection element 79 can 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 at the leading edge or front edge (with respect to the first rotation direction R1) of the upper surface 81 of the cutting element 21. The carrier 77 is coupled to one of the three drive spindles 41 of the drive system 27 described above herein in a manner well known to those skilled in the art. Accordingly, the connection between the drive spindle 41 and the carrier 77 is not shown in FIG. 8.

[0046] In the embodiment shown in FIG. 8, the cutting edges 23 of the cutting elements 21 of the internal cutting element 15 each point in the second rotational direction R2 of the external cutting element 13, that is, in a direction opposite to the first rotational direction R1 of the internal cutting element 15, and include a V-shaped cutting edge portion 83 on the side opposite to the direction indicated 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, the V-shaped cutting edge portions 83 each extend 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 base points 85 of the respective V-shaped cutting edge portions 83 are arranged at a radial distance RCC from the central axis 11 that is substantially equal to the radial position RC of the central base point 65 of the V-shaped opening 63 with respect to the central axis 11. In the present embodiment, due to the interaction between the V-shaped opening 63 of the hair entry opening 61 of the external cutting element 13 and the V-shaped cutting edge portion 83 of the cutting element 21 of the internal cutting element 15, the hair caught in the hair entry opening 61 is mainly cut in the central region of the V-shaped opening 63 where the degree of skin doming into the hair entry opening 61 is minimized, and as a result, skin irritation caused by the shaving process is reduced. However, it should be noted that the present invention also targets embodiments having a more conventional shape, such as a substantially linear shape or a slightly curved shape, in which the cutting edges 23 of the cutting elements 21 of the internal cutting element 15 each have a main radial extension direction.

[0047] The influence of the first rotational speed ω1 of the internal cutting element 15 on the hair capturing efficiency of the hair cutting units 9a, 9b, 9c is limited. Therefore, the first rotational speed ω1 can be mainly selected based on the required hair cutting efficiency of the cutting element 21 of the rotating internal cutting element 15, as is known to those skilled in the art. In the embodiment of FIG. 8, the preferred range of the first rotational speed ω1 is such that the tangential velocity VTT of the cutting element 21 of the internal cutting element 15 with respect to the central axis 11, measured by 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 this embodiment where RCC = 9 mm, the said ranges of the tangential velocity VTT respectively correspond to ranges of the first rotational speed ω1 of about 750 to 4000 rpm and about 1500 to 2700 rpm.

[0048] The inventors of the present invention recognized that for an electric shaver that rotates an external cutting element of a hair cutting unit around the central axis of the hair cutting unit to enhance hair capturing efficiency, the hair capturing efficiency may depend on other parameters than the second rotational speed of the external cutting element. In particular, the inventors recognized that the hair capturing efficiency may depend on a specific user-specific way in which the user operates the electric shaver against the user's body, and specific user-specific hair characteristics. The inventors also recognized that different users may experience the rotation of the external cutting element differently depending on specific skin characteristics. Therefore, in the absence of further means, the second rotational speed of the external cutting element may not be optimal under all circumstances of use or operation of the electric shaver by the user, and generally may not be optimal for all users of the electric shaver.

[0049] To prevent or at least mitigate this problem, in the electric shaver 1 according to the invention, the second rotational speed ω2 of the external cutting element 13 of the hair cutting units 9a, 9b, 9c is such that the hair capture efficiency is independent of the specific way in which the user operates the electric shaver 1 and / or independent of user-specific hair characteristics and / or independent of and / or independent of user-specific hair characteristics and / or independent of user-specific skin characteristics and / or such that the rotation of the external cutting element is experienced by the user as acceptable and is automatically adapted to be maintained at an optimal or at least desired level. For this purpose, according to the invention, as schematically shown in FIG. 9, the electric shaver 1 comprises a detection system 87 configured and arranged to measure at least one user-related parameter, said user-related parameter being related to the skin or hair of the user of the electric shaver 1 or related to the operation of the electric shaver 1 by the user with respect to the user's body. Further, according to the invention, the electric shaver 1 comprises 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 around 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, in use, the detection system 87 can generate an output signal URP representing the value of the measured user-related parameter. The output signal URP can be received by a processor 89 that can generate an output signal Ω2 representing the second rotational speed ω2 of the external cutting element 13 realized by the drive system 27. The drive system 27 can be connected to a battery 93 and comprise a power control module 91 configured to supply power to the motor 29 based on the output signal Ω2, and the drive system 27 realizes the second rotational speed ω2 of the external cutting element 13. For this purpose, the power control module 91 can include a feedback speed control known to those skilled in the art and will not be described in detail accordingly.

[0050] The positions of the processor 89, the power control module 91, and the battery 93 in the main housing 3 of the electric shaver 1 are schematically shown in FIG. 3 as an example. Examples of user-related parameters, a detection system for measuring the user-related parameters, and a specific method for controlling the second rotational speed ω2 of the external cutting element 13 according 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 encompasses embodiments in which the processor and / or the detection system are arranged separately from the main housing 3 and the shaving unit 5, for example, within a separate electronic device such as a smartphone. 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 cumulative shaving time of the electric shaver 1 for a plurality of different regions of the user's body during a shaving session, the movement speed at which the user moves 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 above-mentioned position of the electric shaver 1, the above-mentioned cumulative shaving time, the above-mentioned movement speed, and the above-mentioned pressure are each an example of a user-related parameter related to the user's operation of the electric shaver 1 with respect 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 with respect to the user's body, for example, places it, moves it, or presses 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 according to only one user-related parameter or according to two or more user-related parameters.

[0053] In an embodiment of the electric shaver 1 according to the present invention, the user-related parameter includes the position of the electric shaver 1 on the user's body, and the detection system 87 is configured and arranged to measure the position of the electric shaver 1 on the user's body. For this purpose, the detection system 87 can include any suitable detector known to those skilled in the art. As an example, the detection system 87 may comprise a system for determining the position of the device on the surface of the body part of interest, as disclosed by International Publication No. WO 2020 / 182698 A1 in the name of the applicant. In such an example, as schematically shown in FIG. 10a, the detection system 87 measures a series of 3D orientations of the electric shaver 1 during use and is arranged within the main housing 3 (as schematically shown in FIG. 3) or the shaving unit 5 of the electric shaver 1 to generate a corresponding output signal 3DO, and includes an orientation sensor 95, such as an inertial measurement unit (IMU) sensor. In this example, the detection system 87 further comprises a processing unit 97, which is configured to compare the sequence of 3D orientations of the electric shaver 1 with the normal vectors on the 3D representation of the user's body or body part, such as the face and neck region, stored in the processing unit 97. Based on the comparison, the processing unit 97 determines the position of the electric shaver 1 on the body or body part based on the position of the normal vectors on the 3D representation, and is further configured to generate a corresponding output signal LS as an embodiment of the output signal URP shown in FIG. 9, which is supplied to the processor 89. Further details of this detection system are disclosed in WO 2020 / 182698 A1. In this embodiment, the processor 89, for example, applies 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 a region of the user's body where the skin is known to have a relatively high sensitivity, such as the neck region, and applies 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 a region of the user's body where the skin is known to have a relatively low sensitivity, such as the cheek region.In this way, the user can experience the rotation of the external cutting element 13 in an acceptable manner, regardless of or in response to the position where the electric shaver 1 is actually shaving. Alternatively, the processor 89 may adapt the second rotational speed ω2 according to the detected position of the electric shaver 1 based on different position-dependent characteristics, for example, based on the average user hair characteristics in different regions of the body. The processing unit 97 of the detection system 87 may be part of the processor 89 or separate from the processor 89, as shown in FIG. 10a.

[0054] In a further embodiment of the electric shaver 1 according to the present invention, the user-related parameters include the cumulative amount of shaving time of the electric shaver 1 for a plurality of different regions of the user's body during a shaving session. In this further embodiment, as shown in FIG. 10b, the detection system 87 measures the position of the electric shaver 1 on the user's body and generates a corresponding output signal LS, as previously described herein with reference to the embodiment of FIG. 10a, and comprises an orientation sensor 95 and a processing unit 97. 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 cumulative shaving time of the electric shaver 1 for each of a plurality of different regions 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 cumulative amount of shaving time of the region of the user's body on which the electric shaver 1 is actually shaving. In this embodiment, the processor 89 may be configured, for example, to reduce the second rotational speed ω2 of the external cutting element 13 when the output signal LCST of the further processing unit 101 indicates that the cumulative amount of shaving time for the region of the user's body on which the electric shaver 1 is actually shaving exceeds a predetermined time threshold. In this way, an increase in 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, the timer 99, and the further processing unit 101 of the detection system 87 may be part of the processor 89 or separate from the processor 89, as shown in FIG. 10b.

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

[0056] A known problem with electric shavers is that when the user increases the movement speed of the electric shaver on the body, the hair capture efficiency of the hair cutting unit decreases. To mitigate this problem, in the present embodiment, when the movement speed of the electric shaver 1 measured by the detection system 87 increases, 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, 9c. By increasing the second rotational speed ω2, that is, in the case of the embodiment of the external cutting elements 13 as shown in FIG. 6b, at least within a predetermined range of the second rotational speed ω2 that depends on the detailed design of the external cutting elements 13, such as in the range of 0 to 300 rpm, the hair capture efficiency can be increased. The increase in hair capture efficiency achieved by increasing the second rotational speed ω2 can partially or even completely compensate for the decrease in hair capture efficiency caused by the increase in 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, the processor 89 may be configured to incrementally increase the second rotational speed ω2 at a specific threshold of the measured movement speed. In another example, the second rotational speed ω2 is 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, and set to a value between the first and second predetermined values in proportion to the value of the measured movement speed between the first and second thresholds.

[0057] Regarding this embodiment, the inventors also found that, in order to achieve an optimal improvement in hair capture efficiency, the processor 89 sets the second rotational speed ω2 of the outer cutting elements 13 of the hair cutting units 9a, 9b, 9c such that the tangential speed VT of the outer cutting elements 13 with respect to the central axis 11 of the hair cutting units 9a, 9b, 9c defined previously herein is higher than the motion speed measured by the detection system 87. The majority of users of electric shavers were found to move the shaver on the body at a speed of 10 cm / s to 30 cm / s. In the embodiment of the outer cutting elements 13, a tangential speed VT of about 14 cm / s (corresponding to ω2 = 150 rpm) was found to provide optimal hair capture efficiency for a motion speed of 10 cm / s. For motion speeds of 20 cm / s and 30 cm / s, the optimal values of the tangential speed VT of the outer cutting elements 13 were found to be about 28 cm / s (corresponding to ω2 = 300 rpm) and about 38 cm / s (corresponding to ω2 = 400 rpm), respectively.

[0058] In one embodiment of the electric shaver 1, where the user-related parameter includes the pressure or force with which the user presses the electric shaver 1 against the body, the detection system 87 is configured and arranged to measure the pressure or force. For this purpose, the detection system 87 can include any suitable detector known to those skilled in the art. As an example, the detection system 87 can include a pressure sensing system as disclosed in International Publication No. WO 2020 / 212276 A1 in the name of the applicant. The main part of this known pressure sensing system is schematically shown in FIG. 3, and the support structure 7 of the shaving unit 5 is elastically suspended from the main housing 3 in a direction parallel to the central axis 109 of the shaving unit 5 by a pair of blade springs 107, 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 in parallel with the central axis 109 of the shaving unit 5 depends on the pressure applied to the shaving unit 5 in parallel with the central axis 109 of the shaving unit 5. As schematically shown in FIG. 10d, in this embodiment, the hall sensor 113 generates an output signal HS representing the magnetic field strength of the magnet 111 measured at the position of the hall sensor 113, which depends on the distance between the magnet 111 and the hall sensor 113, and thus the pressure with which the shaving unit 5 is pressed against the body. As schematically shown in FIG. 10d, in this embodiment, the detection system 87 further includes 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 characteristics of the permanent magnet 111 and the hall sensor 113, and the known elastic characteristics of the blade springs 107. The processing unit 115 generates an output signal PF representing the determined pressure or force as an embodiment of the output signal URP shown in FIG. 9 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 by the pamphlet of International Publication No. WO 2020 / 212276 A1. Instead of the pressure sensing system described above, it should be noted that the detection system 87 can have different types of pressure sensors, for example, one or more mechanical pressure sensors 117 of the type known to those skilled in the art, arranged on the shaving unit 5 as schematically shown 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 can result in an increase in skin irritation experienced by the user. It has been found that by increasing the second rotational speed ω2 of the external cutting element 13, the degree of skin doming into the hair entry opening 61 can be reduced. Thus, as a first example related to this embodiment, the processor 89 is configured to increase the second rotational speed ω2 when the detection system 87 detects an increase in the pressure or force exerted on the shaving unit 5. Thereby, an increase in skin doming and the associated increase in skin irritation due to the increase in the pressure or force can be prevented or limited.

[0060] When the pressure or force increases, the friction between the skin and the rotating external cutting element 13 increases, which can also result in an increase in skin irritation experienced by the user. Since the skin friction can be reduced by decreasing the second rotational speed ω2 of the external cutting element 13, in a second example related to this embodiment, when the processor 89 detects an increase in the pressure or force applied to the shaving unit 5 by the detection system 87, it is configured to decrease the second rotational speed ω2. Thereby, the increase in skin friction and the associated increase in skin irritation due to the increase in the pressure or force can be prevented or limited. In this embodiment, the electric shaver 1 can comprise a user interface by which the user can select a suitable method for the processor 89 to adapt the second rotational speed ω2 depending on the measured pressure, i.e., to control skin doming to the hair entry 61 according to the first embodiment described above, or to control skin friction according to the second embodiment 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 the redness of the skin, which is a known skin characteristic affected by the shaving process. The degree of skin redness is considered an indicator of the degree of skin irritation caused by the shaving process. In this example, the detection system 87 can have an optical color sensor 119 arranged within the shaving unit 5 and configured to detect the degree of skin redness, as schematically shown in FIG. 4a. Alternatively, as schematically shown in FIG. 10e, the detection system 87 can have a camera 121 that can be arranged 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 an output signal SR corresponding to an output signal URP shown in FIG. 9 that is supplied to the processor 89. In this example, the processor 89 can be configured to reduce the second rotational speed ω2 of the external cutting element 13 when the detection system 87 measures an increase in skin redness. As shown in FIG. 10e, the processing unit 123 of the detection system 87 can be part of the processor 89 or separate from the processor 89. Instead of skin redness, the processor 89 can control the second rotational speed ω2 of the external cutting element 13 according to another type of skin characteristic, particularly when such skin characteristics are affected by the second rotational speed ω2 of the external cutting element 13 and / or when such skin characteristics affect the hair capture efficiency of the 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 can affect the hair capture efficiency of the external cutting elements 13 of the haircut units 9a, 9b, 9c. Examples of such hair characteristics include hair length, hair thickness, or hair density on the skin. As schematically shown in FIG. 10f, similar to the embodiment shown in FIG. 10e, the detection system 87 can have a camera 121 configured to generate an output signal IMG representing an image of the user's skin. The detection system 87 analyzes the image generated by the camera 121, determines the hair characteristics based on the analysis, and further includes a processing unit 125 configured to generate an output signal HP corresponding to an embodiment of the output signal URP shown in FIG. 9 supplied to the processor 89. For example, when the hair characteristic is the 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 the hair length or hair density. Thereby, the hair capture efficiency for longer hair or higher hair density can be increased. As shown in FIG. 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 described above, in the embodiment shown in FIG. 3, the drive system 27 of the electric shaver 1 includes 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 elements 13 of each of the hair cutting units 9a, 9b, 9c. The use of a single motor 29 in this embodiment results in a relatively simple structure of the electric shaver 1. In this embodiment, the 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 an adjustment of the first rotational speed ω1 can be acceptable in many practical applications as long as the first rotational speed ω1 remains within the range required for an effective hair cut by the internal cutting element 15 rotating at the first rotational speed ω1. FIG. 11 schematically shows an alternative embodiment of the drive system 127 of the electric shaver 1 according to the present invention that enables 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. A part of the alternative embodiment of the drive system 127 and the electric shaver 1 shown in FIG. 11 corresponds to a part of the embodiment of the drive system 27 and the electric shaver 1 shown in FIG. 3 and is shown in FIG. 11 by corresponding reference numerals.

[0064] As shown in FIG. 11, in the alternative embodiment, the drive system 127 includes a first motor 129 configured and arranged to rotate the internal cutting elements 15 of each of the hair cutting units 9a, 9b, 9c about the central axis 11 of the hair cutting units 9a, 9b, 9c via a first transmission system 131, and a second motor 133 configured and arranged to rotate the external cutting elements 13 of each of the hair cutting units 9a, 9b, 9c about the central axis 11 of the hair cutting units 9a, 9b, 9c via a second transmission system 135. The first transmission system 131 includes a main shaft 137 that supports the first main gear 33 as described above with reference to the drive system 27 shown in FIG. 3. The shaft 137 is rotatably supported with respect to the main housing 3 and the support structure 7 of the shaving unit 5, and is arranged to be driven by the first motor 129 via an intermediate gear 139 attached to the motor shaft 141 of the first motor 129 and an intermediate gear 143 attached to the shaft 137. The first primary gear 33 is connected to each of the three internal cutting elements 15 via the three secondary gears 39 and the three drive spindles 41 as described 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 the motor shaft 147 of the second motor 133. The second primary gear 145 engages with the third primary gear 45 as described above with reference to the drive system 27 shown in FIG. 3. Thus, the second primary gear 145 is connected 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 as described above 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 configured and arranged to control the second motor 133 of the drive system 127 such that the second rotational speed ω2 of the external cutting element 13 depends on the measured user-related parameters, for example, according to the example previously discussed with reference to FIGS. 10a to 10f. In particular, the processor 89 can control the second rotational speed ω2 independently of the first rotational speed ω1 of the internal 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 optimal for hair cutting by the rotating internal cutting element 15, and the processor 89 can control the second motor 133 to adjust the second rotational speed ω2 to maintain the hair capture efficiency of the external cutting element 13 at an optimal level when the measured user-related parameters change. For this purpose, as will be apparent to those skilled in the art, the power control module 91 can be configured to supply power to the first motor 129 and the second motor 133 independently, based on the first output signal of the processor 89 related to the first rotational speed ω1 realized by the first motor 129 and the second output signal of the processor 89 related to the second rotational speed ω2 realized by the second motor 133, respectively. The independent control of the rotation of the external cutting element 13 in this alternative embodiment of the drive system 127 further enables, for example, the provision of a user input element by means of which the user can switch the rotation of the external cutting element 13 on and off, or select between several predetermined ranges for the second rotational speed ω2 based on the user's preference.

[0066] It will be apparent to those skilled in the art that the scope of the present invention is not limited to the foregoing embodiments, and that some modifications and variations can be made without departing from the scope of the invention as defined in the appended claims. The present invention is intended to cover all such modifications and variations as long as they are within the scope of the claims or the scope of their equivalents. Although the present invention has been illustrated and described in detail in the figures and description, such illustrations and descriptions should be considered as exemplary or illustrative only and not limiting. The present invention is not limited to the disclosed embodiments. The drawings are schematic and details that are not necessary for understanding the present invention may be omitted and they may not necessarily be to scale.

[0067] Modifications to the disclosed embodiments can be understood and achieved by those skilled in the art when implementing 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] For a particular embodiment, or for elements and aspects discussed in relation to a particular embodiment, they can be appropriately combined with elements and aspects of other embodiments unless otherwise explicitly stated. Thus, the mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used advantageously.

Claims

1. At least one hair cutting unit having a central axis, an external cutting element having a hair entry opening provided in an annular shaving region arranged concentrically around the central axis, and an internal cutting element covered by the external cutting element and having an annular array of cutting elements arranged concentrically around the central axis, a drive system configured such that the internal cutting element of each hair cutting unit is rotated at a first rotational speed around the central axis of the hair cutting unit, the external cutting element of each hair cutting unit is rotated at a second rotational speed around the central axis of the hair cutting unit, and the internal and external cutting elements of each hair cutting unit are rotated relative to each other around the central axis of the hair cutting unit, wherein the electric shaver has, the electric shaver further comprising, a detection system configured and arranged to measure 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, a processor configured and arranged to control the drive system such that the second rotational speed at which the drive system rotates the external cutting element around the central axis of the hair cutting unit depends 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 user's body, the cumulative shaving time of the electric shaver on a plurality of different regions of the user's body during a shaving session, the movement speed at which the user moves the electric shaver on the user's body, the pressure or force with which the user presses the electric shaver against the body, a parameter related to the skin characteristics of the user, and a parameter related to the hair characteristics of the user The electric shaver according to claim 1, having at least one of.

3. The at least one user-related parameter has the position of the electric shaver on the user's body, The detection system has a detector configured and arranged to measure the position of the electric shaver on the user's body, The electric shaver according to claim 2.

4. The at least one user-related parameter comprises the cumulative shaving time of the electric shaver for a plurality of different regions of the user's body during a shaving session, The detection system comprises a detector configured and arranged to measure the position of the electric shaver on the user's body, The processor is configured to measure the cumulative shaving time of the electric shaver for each of a plurality of different regions of the user's body based on the position of the electric shaver measured by the detector and the timing output provided by a timer, The electric shaver according to claim 2.

5. The at least one user-related parameter has a movement speed at which the user moves the electric shaver over the user's body, The detection system has a detector configured and arranged to measure the movement speed at which the user moves the electric shaver over the user's body, The electric shaver according to claim 2.

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

7. The at least one user-related parameter has a parameter related to the skin characteristics of the user, The detection system has a detector configured and arranged to measure a parameter related to the skin characteristics of the user, The electric shaver according to claim 2.

8. The at least one user-related parameter has a parameter related to the hair characteristics of the user, The detection system has a detector configured and arranged to measure a parameter related to the hair characteristics of the user, The electric shaver according to claim 2.

9. The drive system is configured and arranged with a single motor to rotate both the internal cutting element of each haircut unit and the external cutting element of each haircut unit around the central axis of the haircut unit via a transmission system, and the processor is configured and arranged to control the single motor such that a second rotational speed of the external cutting element depends on the measured user-related parameter. The electric shaver according to any one of claims 1 to 8.

10. The drive system comprises a first motor configured and arranged to rotate the internal cutting element of each haircut unit around the central axis of the haircut unit, and a second motor configured and arranged to rotate the external cutting element of each haircut unit around the central axis of the haircut unit, and the processor is 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. The electric shaver according to any one of claims 1 to 8.

11. The drive system is configured to rotate the internal cutting element of each haircut unit in a first rotational direction around the central axis of the haircut unit, and to rotate the external cutting element of each haircut unit in a second rotational direction opposite to the first rotational direction around the central axis of the haircut unit, and the second rotational speed of the external cutting element is lower than the first rotational speed of the internal cutting element. The electric shaver according to any one of claims 1 to 10.

12. The hair entry opening of the external cutting element of each haircut unit comprises a V-shaped opening pointing in the first rotational direction of the internal cutting element, and the second rotational speed of the external cutting element of each haircut unit is measured at the radial position of the central base point of the V-shaped opening with respect to the central axis, and is configured such that the tangential speed of the external cutting element with respect to the central axis is within the range between 7.5 cm / s and 50 cm / s, more preferably within the range between 11.25 cm / s and 30.0 cm / s. The electric shaver according to claim 11.

13. The hair entry opening extends over a first radial distance in the radial direction with respect to the central axis of the hair cutting unit, the V-shaped opening of the hair entry opening extends over a second radial distance in the radial direction, and the second radial distance is at least 50% of the first radial distance. The electric shaver according to claim 12.

14. The hair entry opening of the outer cutting element of each hair cutting unit further includes a radially inner straight 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 straight 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 straight openings each have a main direction extending in the radial direction with respect to the central axis of the hair cutting unit. The electric shaver according to claim 12 or 13.

15. The V-shaped angle of the V-shaped opening of the hair entry opening is in the range of 60 degrees to 135 degrees. The electric shaver according to any one of claims 12 to 14.

Images