HAIR-CUTTING UNIT FOR A SHAVING DEVICE

Abstract

A hair-cutting unit with rotatable cutting elements for use in a shaving device has hair entry slits of which at least a side surface facing in a direction generally opposite to a direction of rotation of the cutting elements, has a relatively flat and oblique intermediate segment between an upper segment forming a curved transition to the outer surface of the annular wall and a lower segment which serves for catching hairs and urging these into an upright position for achieving a close shave. Within a relatively broad range of shaving pressures, the pleat of skin bulging into a hair-cutting slit contacts a portion or at most all of the intermediate segment. Because the intermediate segment is relatively flat, changes in the extent of skin penetration in response to changes in shaving pressure are significantly reduced.

Claims

1. A hair-cutting unit for use in a shaving device, said hair-cutting unit comprising an external cutting member and an internal cutting member which is rotatable relative to the external cutting member in a rotational direction about an axis of rotation, wherein: the internal cutting member comprises a plurality of cutting elements, each having a cutting edge with a respective main directional component of extension in a radial direction relative to the axis of rotation and located on a side of said cutting element leading in said direction of rotation; the external cutting member comprises an annular wall having an outer surface facing away from the internal cutting member and a plurality of hair-entry slits which are mutually separated by hair-guiding strip portions of the annular wall, each hair-entry slit and each hair-guiding strip portion being elongated and having a respective main directional component of longitudinal extension in a radial direction relative to the axis of rotation, and each hair-guiding strip portion having a counter-cutting edge for co-operation with the cutting edges of the internal cutting member during rotation of the internal cutting member in said rotational direction; each hair-guiding strip portion has an inward surface facing the internal cutting member, an outward surface being part of said outer surface, a first side surface facing in the rotational direction, and a second side surface facing in a direction opposite to the rotational direction, wherein said inward surface and said second side surface mutually connect at the counter-cutting edge of the respective hair-guiding strip portion; and wherein, as seen in a cross-section taken perpendicularly to the radial direction at least within a range of radial positions relative to the axis of rotation: a maximum depth D of a respective hair-entry slit is defined as a length of a maximum axial extension of a hair-guiding strip portion adjacent to the respective hair-entry slit in an axial direction parallel to the axis of rotation; a depth y is defined as a depth within the respective hair-entry slit as measured from said outer surface and along the axial direction, wherein 0≤y≤D; first normal vectors at a respective first side surface and second normal vectors at a respective second side surface are each defined in a direction facing away from the corresponding hair-guiding strip portion; if said first normal vector has a non-zero component in said axial direction facing away from the internal cutting member, a first angle α1 between the first normal vector and said axial direction is defined in the acute angular range 0°<α1<90°, and if said first normal vector has no component in said axial direction or a non-zero component in said axial direction facing towards the internal cutting member, said first angle α1 is defined in the obtuse angular range 90°≤α1<180°, wherein α1(y) is a value of the first angle α1 in a position on the first side surface at the depth y; if said second normal vector has a non-zero component in said axial direction facing away from the internal cutting member, a second angle α2 between the second normal vector and said axial direction is defined in the acute angular range 0°<α2<90°, and if said second normal vector has no component in said axial direction or a non-zero component in said axial direction facing towards the internal cutting member, said second angle α2 is defined in the obtuse angular range 90°≤α2<180°, wherein α2(y) is a value of the second angle α2 in a position on the second side surface at the depth y; said first side surface has an upper segment extending from the outer surface until a depth y1 and a lower segment extending from a depth y2 in a direction away from the upper segment, wherein y2≥y1, y1≤0.2*D and y2≤0.6*D; said second side surface has an upper segment extending from the outer surface until a depth y3, an intermediate segment extending from the depth y3 until a depth y4>y3, and a lower segment extending from the depth y4 in a direction away from the intermediate segment, wherein y3≤0.2*D, y4≤0.6*D and y4−y3≥0.2*D; an average angle of normal vectors of said intermediate segment of said second side surface α2AV=0.5*{α2(y3)+α2(y4)}; α2(y3)=α2AV+/−α2δ and α2(y4)=α2AV+/−α2δ; α2AV is in a range from 20° until 50°; α2δ is in a range from 0° to 10°; in each position on the upper segment of said first side surface α1≤α1(y1) and dα1(y)/dy≥0; in each position on the lower segment of said first side surface 70°≤α1≤110°; in each position on the upper segment of said second side surface α2≤α2(y3) and dα(y)/dy≥0; and in each position on the lower segment of said second side surface 70°≤α2≤110°.

2. A hair-cutting unit as claimed in claim 1, wherein: said first side surface further has an intermediate segment extending from the depth y1 until the depth y2>y1 and y2−y1≥0.2*D; and an average angle of normal vectors of said intermediate segment of said first side surface α1AV=0.5*{α1(y1)+α1(y2)}; α1(y1)=α1AV+/−α1δ and α1(y2)=α1AV+/−α1b; α1AV is in a range from 20° until 50°; α1δ is in a range from 0° to 10°.

3. A hair-cutting unit as claimed in claim 2, wherein in any cross-section, taken perpendicularly to the radial direction, within said range of radial positions, y1=y3 and/or y2=y4.

4. A hair-cutting unit as claimed in claim 2, wherein in any cross-section, taken perpendicularly to the radial direction, within said range of radial positions, α1AV=α2AV.

5. A hair-cutting unit as claimed in claim 2, wherein in any cross-section, taken perpendicularly to the radial direction, within said range of radial positions, α1δ=α2δ.

6. A hair-cutting unit as claimed in claim 2, wherein in any cross-section, taken perpendicularly to the radial direction, within said range of radial positions y2−y1≥0.3*D.

7. A hair-cutting unit as claimed in claim 1, wherein in any cross-section, taken perpendicularly to the radial direction, within said range of radial positions, y4−y3≥0.3*D.

8. A hair-cutting unit as claimed in claim 1, wherein in any cross-section, taken perpendicularly to the radial direction, within said range of radial positions, α2δ=0 and a2=α2AV in each position on the intermediate segment of said second side surface.

9. A hair-cutting unit as claimed in claim 2, wherein α1δ=0 and α1=α1AV in each position on the intermediate segment of said first side surface.

10. A hair-cutting unit as claimed in claim 1, wherein y2≤0.5*D and/or y4≤0.5*D.

11. A hair-cutting unit as claimed in claim 1, wherein in any cross-section, taken perpendicularly to the radial direction, within said range of radial positions: in each position on the lower segment of said second side surface for which y≤0.8*D, 70°≤α2≤110°; and/or in each position on the lower segment of said first side surface for which y≤0.8*D, 70°≤α1≤110°.

12. A hair-cutting unit as claimed in claim 11, wherein in each position on the lower segment of said second side surface for which y≤0.9*D, 70°≤α2≤110°.

13. A hair-cutting unit as claimed in claim 1, wherein, in any cross-section taken perpendicularly to the radial direction, said first side surface has a rounded shape connecting the lower segment of said first side surface to an adjacent portion of said inward surface.

14. A hair-cutting unit as claimed in claim 1, wherein, in any cross-section taken perpendicularly to the radial direction within said range of radial positions, a width W of each hair-entry slit has a value in the range 0.24 mm≤W≤0.36 mm, and said maximum depth D of each hair-entry slit has a value in the range 0.19*W≤D≤0.42*W.

15. A hair-cutting unit as claimed in claim 1, wherein rotary paths of the cutting edges of the internal cutting member along an inward surface of said annular wall extend from a radially inward cutting zone boundary at a first radial diameter relative to the axis of rotation until a radially outward cutting zone boundary at a second radial diameter relative to the axis of rotation, and wherein, for each of said hair-entry slits, said range of radial positions extends at least radially outwardly from a radially outermost one of said first radial diameter and a radially inward radial end of said hair-entry slit to a radially innermost one of said second radial diameter and a radially outward radial end of said hair-entry slit.

16. A shaving unit for use in a shaving device, said shaving unit comprising a supporting member and at least two hair-cutting units according to claim 1.

17. A shaving device comprising a shaving unit according to claim 16 and a main body accommodating a motor and a drive system, wherein the shaving unit is coupled to the main body such that the internal cutting members of the hair-cutting units are rotatable by means of the motor via the drive system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 shows, in a perspective view, a first example of a shaving device according to the invention.

[0034] FIG. 2 is a perspective view of an example of one of three hair-cutting units according to the invention of the shaving device of FIG. 1, wherein an internal cutting member and an external cutting member of the hair-cutting unit are shown as an exploded view.

[0035] FIG. 3 is a more detailed top plan view in a direction parallel to an axis of rotation of the hair-cutting unit of a portion of the hair-cutting unit of FIG. 2,

[0036] FIG. 4 is a schematic cross-sectional view along line IV-IV in FIG. 3,

[0037] FIG. 5 is a view according to FIG. 4 of a second, different example of a hair-cutting unit according to the invention, and

[0038] FIG. 6 is a view according to FIGS. 4 and 5 of a third, different example of a hair-cutting unit according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] As can be seen in FIGS. 1 and 2 a shaving device 1 according to the shown example has a main body 2, a shaving unit 3 coupled to the main body via a supporting member 4. The shaving unit 3 has three hair-cutting units 5. Each of the hair-cutting units 5 has an external cutting member 6 with an annular wall 12 and an internal cutting member 7 rotationally suspended and drivable for rotation in a direction (sense) of rotation 8 about an axis 9, such that cutting elements 10 of the internal cutting member 7 slide along an inward facing surface 18 of the annular wall 12. The annular wall is provided with slits 15 alternating in circumferential sense with strip portions 16 of the annular wall 12. The cutting elements 10 are (preferably evenly) distributed in circumferential sense around the axis of rotation 9 and each have a cutting edge 11 arranged for co-operation with counter cutting edges 17 that are located where second side walls 21 facing in a direction opposite to the sense of rotation 8 meet the inward surface 18 of the annular wall 12.

[0040] The cutting edges 11 each have a main directional component of extension in a radial direction 13 relative to the axis of rotation 9 and are each located on a side of the associated cutting element 10 that is leading in the direction of rotation 8. FIG. 3 shows one of these cutting elements 10 with its cutting edge 11 having, in a radial direction 13, an inward cutting edge end 31 and an outward cutting edge end 32.

[0041] The annular wall 12 further has an outer surface 14 facing away from the internal cutting member 7. Each hair-entry slit 15 and each hair-guiding strip portion 16 is elongated and has a respective main directional component of longitudinal extension in a radial direction 13 relative to the axis of rotation 9. In general, the length of the slits is preferably at least four times, and more preferably at least eight times the width of the slits. Portions of the inward facing surface 18 of the annular wall 12 are located on each hair-guiding strip portion 16 and face the internal cutting member 7. Each slit 15 has a first side surface 19 facing generally in the rotational direction 8 and a second side surface 21 facing generally in a direction opposite to the rotational direction 8.

[0042] As best seen in FIG. 4, in a cross-section taken perpendicularly to the radial direction 13 at least within a range of radial positions relative to the axis of rotation 9 a maximum depth D of a respective hair-entry slit 15 is defined as a length of a maximum axial extension of a hair-guiding strip portion 16 adjacent to the respective hair-entry slit 15 in an axial direction parallel to the axis of rotation 9. Furthermore, a depth y is defined as a depth within the respective hair-entry slit 15 as measured from a level defined by the outer surface 14 and along the axial direction 9, wherein 0≤y≤D. First normal vectors 20 at a respective first side surface ′19 and second normal vectors 22 at a respective second side surface 21 are each defined in a direction facing away from the corresponding hair-guiding strip portion 16.

[0043] For normal vectors 20 projecting from different positions along the first side surface 19 the following applies: α1(y) is a value of a first angle α1 in a position on the first side surface 19 at the depth y, while if the first normal vector 20 has a non-zero component in the axial direction 9 facing away from the internal cutting member 7, a first angle α1 between the first normal vector 20 and the axial direction 9 is defined in the acute angular range 0°<α1<90° and if the first normal vector 20 has no component in the axial direction 9 or a non-zero component in the axial direction 9 facing towards the internal cutting member 7, the first angle α1 is defined in the obtuse angular range 90°≤α1<180°.

[0044] For normal vectors 22 projecting from different positions along the second side surface 21 the following applies: α2(y) is a value of a second angle α2 in a position on the second side surface 21 at the depth y, while if the second normal vector 22 has a non-zero component in the axial direction 9 facing away from the internal cutting member 7, a second angle α2 between the second normal vector 22 and the axial direction 9 is defined in the acute angular range 0°<α2<90°, and if the second normal vector 22 has no component in the axial direction 9 or a non-zero component in the axial direction 9 facing towards the internal cutting member 7, the second angle α2 is defined in the obtuse angular range 90°≤α2≤180°.

[0045] The first side surface 19 has an upper segment 33 extending from the outer surface 14 until a depth y1 and a lower segment 35 extending from a depth y2 in a direction away from the upper segment 33. The depth y1 where a lower end of the upper segment 33 is located is smaller than or equal to 0.2*D, so that the upper segment 33 occupies only a small portion of the depth D. y2 is smaller than or equal to 0.6*D, so that the depth of the lower segment 35 is larger than 0.4*D.

[0046] The second side surface 21 has an upper segment 36 extending from the outer surface 14 until a depth y3 and a lower segment 38 extending from a depth y4 in a direction away from the upper segment 36. y3 is smaller than or equal to 0.2*D, so that the upper segment 36 extends over only a small portion of the depth D. The depth y4 where a lower end of the upper segment 33 is located is smaller than or equal to 0.6*D, so that the depth of the segment 38 is larger than 0.4*D. The second side surface 21 moreover has an intermediate segment 37 extending from the depth y3 until a depth y4>y3. Furthermore, y4−y3≥0.2*D, so that the intermediate segment extends over at least one fifth of the depth D of the slit 15.

[0047] An average angle of normal vectors 22 of the intermediate segment 37 of the second side surface 21 (α2AV) is the average of the angle α2 at depth y3 and the angle α2 at depth y4. Furthermore the angles α2 at depth y3 and the angle α2 at depth y4 differ from the average angle by less than α2δ. The value of the average angle of the normal vectors 22 of the intermediate segment 37 of the second side surface 21 is in a range from 20° until 50° and at the depths y3 and y4, the deviation α2δ of that angle α2(y3) and α2(y4) from the average angle (α2AV) is in a range from 0° to 10°.

[0048] In each position on the upper segment 33 of the first side surface 19 α1≤α1 (y1) and dα1(y)/dy≥0 and in each position on the upper segment 36 of the second side surface 21 α2≤α2(y3) and dα(y)/dy≥0, so that the upper segments 33 and 36 are flat, convex or partially flat and partially convex. In the present example, the upper segments 33 and 36 are both convex, which is preferred to achieve a smooth transition from the outward surfaces 14 to each of the intermediate segments 33 and 36.

[0049] In each position on the lower segment 35 of the first side surface 19 70°≤α1≤110° and in each position on the lower segment 38 of the second side surface 21 70°≤α2≤110°, so that the lower segments 35 and 38 are oriented sufficiently transverse to the outward surface 14 to catch and upright hairs if the hair-cutting unit 5 is moved over a skin 23.

[0050] Without being bound to theory, the effect of the invention appears to be that variations in the direction of friction force F.sub.F exerted on the skin 23 by the side surface of the hair-guiding strip portion 16 facing in generally the direction of movement 39 of the hair-cutting unit 5 over the skin 23 depending on the extent to which the skin 23 bulges into the hair-cutting slit 15 are at least significantly reduced. In FIG. 4, this is illustrated by friction forces F.sub.F and normal forces F.sub.N exerted on two portions of skin 23. The portion of skin 23 shown on the right bulges further into the hair-entry slit 15 than the portion of skin 23 shown on the left. Such a difference is typically caused by a difference in pressure with which the hair-cutting unit 5 is pressed against the skin 23, but may also be caused or influenced by differences in skin tension and/or local skin flexibility.

[0051] As can be seen in FIG. 4, the directions in which the friction forces F.sub.F, the normal forces F.sub.N and the total forces F are oriented are the same regardless whether the skin 23 bulges into the hair-entry slit 15 far, as in the example shown at the right, or bulges into the hair-entry slit 15 to a smaller extent, as in the example shown at the left. More in particular, the angle β.sub.h between the direction of the total force F at high shaving pressure and the axial direction 9 is essentially identical to the angle β.sub.l between the direction of the total force F at low shaving pressure and the axial direction 9. Because the intermediate segment 37 is flat, the direction of frictional forces and normal forces does not change when the skin bulges further into the hair-entry slit 15 and also contacts lower portions of intermediate segment 37. Accordingly, there is no change in direction of the forces exerted onto the skin 23 near the pleat that bulges onto the hair-entry-slit 15 and accordingly, the extent to which the pleat of skin is pushed into the hair-cutting slit is not increased by a change of direction of forces exerted thereon near the pleat that bulges onto the hair-entry-slit 15.

[0052] The effect of an increased variation of skin penetration in accordance with variation of shaving pressure, is particularly relevant on the side of the second side surface 21, which faces in the rotational sense of movement 8 of the cutting elements 10. In particular when the cutting elements 10 touch the skin 23 close to the side surface 21 facing in a direction opposite to the rotational sense of movement 8 of the cutting elements 10, skin irritation is often caused.

[0053] In the hair-cutting unit according to the present example, such effects are at least significantly mitigated, because the second side surface 21 has a flat and oblique intermediate segment 37 between the upper segment 36 forming a curved transition to the outer surface 14 of the annular wall 12 and the lower segment 38 which serves for catching hairs and urging these into an upright position for achieving a close shave.

[0054] For a particularly effective reduction of the variation in depth of skin penetration into the hair-entry slit 15 in response to variation of shaving pressure while the shaving unit is moved over the skin in a direction generally opposite to the direction 39 shown in FIG. 4, it is preferred that, as in the example shown in FIG. 4, also the side surface 19 facing generally in the direction of rotation 8 of the cutting elements 10 are provided with an oblique, relatively flat intermediate segment 34 with a geometry as described for the intermediate segment 37 of the side surface 21 facing in generally a direction opposite to the direction of rotation of the cutting elements 10.

[0055] In FIG. 5, a portion of an annular wall 112 of an alternative example of a cutting head according to the invention is shown. In this example, the strip portions 116 of the annular wall 112 have side surfaces with upper segments 133, 136, intermediate segments 134, 137 and lower segments 135, 138. The intermediate segments 136 and 137 are each mainly shaped with a concave radius R.sub.102. To the extent that the skin can follow the concave shape of the intermediate segments 136 and 136, the normal force FN and the frictional force FF are caused to become more horizontal as the skin bulges further into the hair-entry slit and is contacted by portions of the intermediate segment 134 or 137 closer to the lower end of the respective intermediate surface 134 or 137 of the side surface facing in generally the direction of movement over the skin. Thus, the angle βh between the direction of the total force F at high shaving pressure and the axial direction 9 is smaller than the angle βl between the direction of the total force F at low shaving pressure and the axial direction 9. Accordingly, a higher shaving pressure causes reaction forces exerted onto the skin near the pleat of skin bulging into the hair-entry opening 15 to be oriented more outwardly, which counteracts the tendency of the skin bulging further into the hair-entry opening as shaving pressure is increased.

[0056] In FIG. 6, a portion of an annular wall 212 of an alternative example of a cutting head according to the invention is shown. In this example, the strip portions 216 of the annular wall 212 have side surfaces with upper segments 233, 236, intermediate segments 234, 237 and lower segments 235, 238. The intermediate segments 236 and 237 are each mainly shaped with a convex radius R.sub.202. In this example, the normal force F.sub.N and the frictional force F.sub.F are caused to rotate towards an axial direction 9 to the inside of the annular wall as the skin bulges further into the hair-entry slit and is contacted by portions of the intermediate segment 234 or 237 closer to the lower end of the respective intermediate surface 234 or 237 of the side surface facing in generally the direction of movement over the skin. Thus, the angle β.sub.h between the direction of the total force F at high shaving pressure and the axial direction 9 is larger than the angle β.sub.l between the direction of the total force F at low shaving pressure and the axial direction 9. Accordingly, a higher shaving pressure causes reaction forces exerted onto the skin near the pleat of skin bulging into the hair-entry opening 15 to be oriented more inwardly, but less so than if the side surface has no oblique intermediate segment between the upper segment and the lower segment with a substantially larger radius of curvature R.sub.202 than the radius of curvature of the upper segment. Thus, also in a cutting head according to this example the intermediate segments 234, 237 are relatively flat, so that changes in the surface portion of the intermediate segment that is contacted by the pleat of skin bulging into the hair-cutting slit only relatively small changes in the direction in which forces are exerted on the skin when the hair-cutting unit is moved over the skin generally in a direction in which the side surface is facing. Thus, a contribution to changes in the extent of skin penetration in response to changes in shaving pressure by a change of the direction in which forces are exerted onto the skin by the side surface facing in generally the direction of movement over the skin is significantly reduced.

[0057] If the angle α is constant or increases from the upper border of the intermediate segment to the lower border of the intermediate segment (i.e. α1(y1)≤α1(y2) or α2(y3)≤α2(y4), so the intermediate segment is convex and/or flat, it is preferred that in each position on the intermediate segment dα(y)/dy≥0 and, if the angle α is constant or decreases from the upper border of the intermediate segment to the lower border of the intermediate segment (i.e. α1(y1)≥α1(y2) or α2(y3)≤α2(y4), so the intermediate segment is concave and/or flat, it is preferred that in each position on the intermediate segment dα(y)/dy≤0. Thus, the intermediate segment is preferably either flat, concave, convex, partially convex and partially flat or partially concave and partially flat. The absence of transitions from a convex shape to a concave shape are advantageous for allowing smooth sliding of the skin over the intermediate surface.

[0058] While the invention has been described and illustrated in detail in the foregoing description and in the drawing figures, such description and illustration are to be considered exemplary and/or illustrative and not restrictive; the invention is not limited to the disclosed embodiments.

[0059] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. For the purpose of clarity and a concise description, features are disclosed herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features disclosed. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0060] The reference signs used in the figures refer to examples of the above-mentioned parts and aspects of the invention, as well as to related parts and aspects, in the following manner: [0061] 1 shaving device [0062] 2 main body [0063] 3 shaving unit [0064] 4 supporting member [0065] 5 hair-cutting unit [0066] 6 external cutting member [0067] 7 internal cutting member [0068] 8 rotational direction [0069] 9 axis of rotation [0070] 10 cutting element [0071] 11 cutting edge [0072] 12 annular wall portion [0073] 13 radial direction [0074] 14 outer surface [0075] 15 hair-entry slit [0076] 16, 116, 216 hair-guiding strip portion [0077] 17 counter-cutting edge [0078] 18 inner surface [0079] 19 first side surface [0080] 20 normal vector at first side surface [0081] 21 second side surface [0082] 22 normal vector at second side surface [0083] 23 skin [0084] 31 radially inward cutting edge end [0085] 32 radially outward cutting edge end [0086] 33, 133, 233 upper segment of first side surface [0087] 36, 136, 236 upper segment of second side surface [0088] 34, 134, 234 intermediate segment of first side surface [0089] 37, 137, 237 intermediate segment of second side surface [0090] 35, 135, 235 intermediate segment of first side surface [0091] 38, 138, 238 intermediate segment of second side surface [0092] y1-y4 axial distances to outer surface [0093] FN Normal force [0094] FF Frictional force [0095] F Total resultant force [0096] α1 angle between axial direction and normal vector at first side surface [0097] α2 angle between axial direction and normal vector at second side surface [0098] βl angle between axial direction and direction of exerted force at low pressure [0099] βh angle between axial direction and direction of exerted force at high pressure [0100] R1 radius of curvature of upper segment seen in cross-section [0101] R102 radius of curvature of intermediate segment seen in cross-section [0102] R202 radius of curvature of intermediate segment seen in cross-section [0103] W distance between first and second surface=width of hair-entry slit

[0104] In some instances the same reference signs have been used for mutually identical parts and portion of different examples shown.