Shaving head with doming control

Abstract

A cutter unit (1) for a rotary shaver is formed by an outer cutting element or cap (2) which interacts with a rotating inner cutting element or cutter (4) to trap and cut hairs. The cap has an annular shaving track (8) of domed cross-section having slots (30) through which the hairs may protrude. The cutter has a convex upper face (22) to engage the shaving track and a concave forward face (26).

Claims

1. A rotary shaver, comprising: a cap comprising one or more annular shaving tracks, the one or more annular shaving tracks comprising a plurality of slots, each slot oriented at an angle () to a radial direction with respect to the axis of rotation, each track having a domed shaped upper surface and a curved shaped lower surface, a cutter unit, comprising a support member having an axis of rotation and carrying a plurality of cutting elements each cutting element comprising: a leg portion, and a distal portion adjacent the leg portion, wherein the distal portion comprises: an upper face that is convex having a partial circular cylindrical shape and partially flat in a circumferential direction in a plane perpendicular to a direction of movement, said upper face terminating in a cutting edge lying in a radial plane and wherein said upper face and said cutting edge have a first radius of curvature R, a forward face, having a slightly concave shape angled at a cutter angle () with respect to a direction of movement of the leg portion relative to the axis of rotation of the support member, wherein the cutter angle () is between 40 and 50, said forward face having a second radius of curvature r, wherein said upper face intersects the forward face in said cutting edge forming a straight line when viewed in a vertical direction at least over a portion intended to contact the shaving track formed in the cap, thus allowing a constant shearing angle over over the radial extent of the cutter by ensuring that R=r.Math.cos(), wherein the second radius of curvature r depends on the cutter angle () such that R=r cos() such that the cutting edge will be located at an intersection of the forward face and the upper face.

2. The rotary shaver of claim 1, wherein the curved lower surface has a different profile to the upper surface.

3. The rotary shaver of claim 1, wherein the cutting edge and a cutting surface of at least one of the slots are angled with respect to each other at a shearing angle () and the shearing angle is constant over a radial extent of said at least one of the slots.

4. The rotary shaver according to claim 1, comprising at least two cutter units, each of said at least two cutter units comprising a drive unit to cause rotation of the cutter(s) of the at least two cutter units.

5. The rotary shaver according to claim 1, comprising three cutter units arranged at the vertices of an equilateral triangle.

6. A cutter unit, comprising: a support member having an axis of rotation and carrying a plurality of cutting elements each cutting element comprising: a leg portion, and a distal portion adjacent the leg portion, wherein the distal portion comprises: an upper face that is convex having a partial circular cylindrical shape and partially flat in a circumferential direction in a plane perpendicular to a direction of movement, said upper face terminating in a cutting edge lying in a radial plane and wherein said upper face and said cutting edge have a first radius of curvature R, a forward face, having a slightly concave shape angled at a cutter angle () with respect to a direction of movement of the leg portion relative to the axis of rotation of the support member, wherein the cutter angle () is between 40 and 50, said forward face having a second radius of curvature r, wherein said upper face intersects the forward face in said cutting edge forming a straight line when viewed in a vertical direction at least over a portion intended to contact the shaving track formed in the cap, thus allowing a constant shearing angle over over the radial extent of the cutter by ensuring that R=r.Math.cos(), wherein the second radius of curvature r depends on the cutter angle () such that R=r cos() such that the cutting edge will be located at an intersection of the forward face and the upper face.

7. The cutter unit according to claim 6, wherein the cutting edge and a cutting surface of at least one of the slots are angled with respect to each other at a shearing angle () and the shearing angle is constant over a radial extent of said at least one of a plurality of slots of a cap having one or more annular shaving tracks comprising a plurality of slots.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features and advantages of the invention will be appreciated upon reference to the following drawings of a number of exemplary embodiments, in which:

(2) FIG. 1 is a perspective view of an electric shaver incorporating the invention;

(3) FIG. 2 is a partial cross sectional view of FIG. 1, taken along line II-II;

(4) FIG. 3 shows a perspective view of a cutter according to the invention;

(5) FIGS. 4A to 4C show orthogonal views of the distal portion of a cutter according to an embodiment of the invention;

(6) FIG. 4D shows a view taken in the direction of arrow IV in FIG. 4B;

(7) FIG. 5 shows one of the cutter units of FIG. 1 taken in plan view;

(8) FIG. 5A shows a detail of FIG. 5;

(9) FIGS. 6A to 6C show orthogonal views of the distal portion of a conventional cutter;

(10) FIG. 7 shows a view of a cutter unit incorporating the conventional cutter of FIGS. 6A to 6C; and

(11) FIG. 7A shows a detail of FIG. 7.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(12) FIG. 1 is a perspective view of an electric shaver 100 according to the present invention. The shaver 100 has a handle 102 and a head 104. The head is provided with three cutter units 1 arranged in a triangular shape.

(13) FIG. 2 shows a cross sectional view through one of the cutter units 1 of FIG. 1, taken along line II. Cutter unit 1 comprises a cap 2 and a cutter 4 which can rotate about an axis X-X. The cap 2 has a shaving track 8 having a domed upper surface 10 and a curved lower surface 12. The cutter 4 comprises a support member or cutter disk 14 having a plurality of upstanding legs 16, each terminating in a distal portion 18 as will be described in further detail below. The distal portions 18 are arranged and shaped to follow the shaving track 8 as the cutter rotates around the axis X-X.

(14) FIG. 3 shows a perspective view of the cutter 4 of FIG. 2. As can be seen, each leg 16 extends upwards from the periphery of the cutter disk 14 to a distal portion 18. The distal portion 18 has a convex or cylinder shaped upper face 22 which terminates in a cutting edge 24. The distal portion 18 also has a forward face 26 which intersects with the upper face 22 at the cutting edge 24. The leg 16 and the forward face 26 are angled with respect to a direction of movement Y. This angle is the cutter angle which in the example is 45. The cutting edge 24 thus forms a leading edge as the cutter disk 14 rotates. At the centre of the cutter disk 14 a key 28 is provided for interaction with a drive spindle of a drive unit (not shown) of the shaver which may be otherwise conventional.

(15) According to the invention, and as can be seen in FIG. 3, the forward face 26 is slightly concave. This is better seen in FIGS. 4A to 4D which show three views of the distal portion 18 in orthogonal projection and an additional view 4D taken in the direction D at the cutter angle . Noticeable is that when viewed in the vertical direction FIG. 4A shows the cutting edge 24 to be a straight line. It is also noted in FIG. 4A that the cutting edge is radial in orientation or in fact lies in a radial plane. This can also be seen in the side view according to FIG. 4B. Viewed in FIG. 4C contrary to the direction of motion, the cutting edge 24 and the upper face 22 appear as a curved line having the same curvature as the lower surface of the cap. The radius of curvature is R which may have a value of around 4 mm. In FIG. 4D, the curvature of the concave forward face 26 is shown to be r. By ensuring that R is equal to r Cos , the two faces will intersect at a cutting edge 24 which lies in the vertical plane.

(16) FIGS. 5 and 5A show in detail one of the cutter units 1 of FIG. 1 taken in plan view in the direction of the axis X-X. As can be seen, the cap 2 and the shaving track 8 are provided with slots 30 which extend across the shaving track 8. The slots 30 are oriented at a slight angle to the radial direction. The distal portions 18 can be seen through the slots 30 and have their cutting edges 24 aligned radially whereby a shearing angle is defined between a cutting edge 24 and a cutting surface 32 of a slot 30. It is noted that in this example, the cutter distal portion 18 rotates in a clockwise direction when viewed towards the shaver head. This results in cutting taking place in a shearing motion from an outer edge of the shaving track 8 inwards. It will be understood that the opposite direction of shearing is also possible if desired.

(17) As a consequence of the configuration of the cutting edge 24, a constant shearing angle is achieved over the full length of the slot 30.

(18) A conventional distal portion 50 is shown for comparison in FIGS. 6A to 6C which show the distal portion in orthogonal projections. As can be seen in the front view of FIG. 6C, this distal portion 50 has a convex upper face 52. Side view FIG. 6B shows the substantially flat forward face 54, angled at the cutter angle . Seen in plan view from above in FIG. 6A, the cutting edge 56 thus forms a curved line lying in the plane of the forward face 54.

(19) FIGS. 7 and 7A shows similar views to FIGS. 5 and 5A of the cap 2 in operation with the conventional distal portion 50 of FIG. 6. As can be seen, the curved cutting edge 56 causes a variation in the shearing angle between an inner part of the slot 30 and the outer part. This variation in shearing angle means that hairs will not be equally cut at all positions and may be dragged sideways along the slot 30 causing snagging and discomfort.

(20) Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. In particular, for other, irregular shaped shaving tracks a similar irregular, concave shaped front surface can be made to create a straight cutting edge. The shaving track torus shape can be projected onto the cutter front surfaces with a scaling factor of the cosine of the cutter angle. In this way a concave front surface can be determined that can accommodate for any convex or domed shaving track shape.

(21) Many modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention as defined by the appended claims.