Stationary cutting blade for a hair clipping device

Abstract

A stationary cutting blade for a hair clipping device has a base body and a coined cutting teeth. The coined cutting teeth are spaced apart from each other, arranged on a front side of the base body, and each extend parallel to a longitudinal axis of the stationary cutting blade. A thickness ratio between the thickness of the base body and the thickness of the cutting teeth is larger than 1.1. Each cutting tooth has a substantially wedge-shaped cross-section with a scissor angle and a wedge angle, where the sum of the scissor angle and the wedge angle is smaller than 70?.

Claims

1. A stationary cutting blade for a hair clipping device, comprising: a base body defining a body longitudinal axis and a transverse axis perpendicular to the body longitudinal axis; and a plurality of spaced apart cutting teeth arranged on a front side of the base body, wherein each of the cutting teeth has at least one cutting edge and defines a tooth longitudinal axis which is parallel to the body longitudinal axis; wherein the stationary cutting blade is a metal cutting blade and the base body has a first thickness, said first thickness being measured between a top side and a bottom side of the base body along the transverse axis, wherein the cutting teeth have a second thickness measured parallel to the transverse axis, wherein a thickness ratio between the first thickness and the second thickness is larger than 1.1, wherein each of the cutting teeth has a substantially wedge-shaped cross-section with a top face, a bottom face and two opposing lateral faces running in between the top and the bottom face, each of the two opposing lateral faces having a first sharp bend between an upper section and an intermediate section which is inclined with respect to the upper section, and a second sharp bend between the intermediate section and a lower section which is inclined with respect to the intermediate section, wherein the at least one cutting edge is defined at an intersection between the top face and the upper section of one of the two opposing lateral faces and has a scissor angle and a wedge angle, the scissor angle being defined between the at least one cutting edge and the tooth longitudinal axis, and the wedge angle being defined between said upper section of the one of the lateral faces and the top face, and wherein a sum of the scissor angle and the wedge angle is smaller than 70?.

2. The stationary cutting blade according to claim 1, wherein the scissor angle is smaller than 25?.

3. The stationary cutting blade according to claim 1, wherein the wedge angle is smaller than 55?.

4. The stationary cutting blade according to claim 1, wherein the scissor angle is between 5? and 25?.

5. The stationary cutting blade according to claim 1, wherein the wedge angle is between 40? and 55?.

6. The stationary cutting blade according to claim 1, wherein the first thickness is larger than 1.3 mm.

7. The stationary cutting blade according to claim 1, wherein the at least one cutting edge is exactly two cutting edges and wherein each of the two cutting edges is substantially straight.

8. The stationary cutting blade according to claim 1, wherein each of the plurality of cutting teeth is symmetrical, wherein a distance between a portion of two of the upper sections of the two opposing lateral faces of the each of the cutting teeth near the top face is larger than a distance between two of the lower sections of the two opposing lateral faces near the bottom face.

9. The stationary cutting blade according to claim 8, wherein an angle between the bottom face and each of the two lower sections of the two opposing lateral faces is larger than the wedge angle .

10. A cutting assembly for a hair clipping device, comprising: a stationary cutting blade according to claim 1; and a moveable cutting blade that is resiliently biased against the stationary cutting blade by a spring.

11. A hair clipping device comprising a cutting assembly having stationary cutting blade and a moveable cutting blade, and an actuator for moving the moveable cutting blade relative to the stationary cutting blade in a reciprocal manner, where the stationary cutting blade comprises: a base body defining a body longitudinal axis and a transverse axis perpendicular to the body longitudinal axis; and a plurality of spaced apart cutting teeth with arranged on a front side of the base body, wherein each tooth of the cutting teeth has at least one cutting edge and defines a tooth longitudinal axis, and extends along the tooth longitudinal axis which is parallel to the body longitudinal axis of the stationary cutting blade; wherein the stationary cutting blade is a metal cutting blade and the base body has a first thickness, said first thickness being measured between a top side and a bottom side of the base body along the transverse axis, wherein the cutting teeth have a second thickness measured parallel to the transverse axis, wherein a thickness ratio between the first thickness and the second thickness is larger than 1.1, wherein each of the cutting teeth has a substantially wedge-shaped cross-section with a top face, a bottom face and two opposing lateral faces running in between the top and the bottom face, each of the two opposing lateral faces having a first sharp bend between an upper section and an intermediate section which is inclined with respect to the upper section, and a second sharp bend between the intermediate section and a lower section which is inclined with respect to the intermediate section, wherein the at least one cutting edge is defined at an intersection between the top face and the upper section of one of the two opposing lateral faces and has a scissor angle and a wedge angle, the scissor angle being defined between the at least one cutting edge and the tooth longitudinal axis, and the wedge angle being defined between said upper section of the one of the lateral faces and the top face, and wherein a sum of the scissor angle and the wedge angle is smaller than 70?.

12. A process for manufacturing a stationary cutting blade or a hair clipping device, comprising acts of: providing a piece of metal having a first thickness that serves as raw material; creating a tapered shape into the piece of metal in order to create a rough shape of a tip of the stationary cutting blade; stamping a preliminary teeth geometry into the tip to create a plurality of spaced-apart cutting teeth having a second thickness measured in parallel to the first thickness, such that a thickness ratio between the first and the second thickness is larger than 1.1; and coining a final teeth geometry by means of a coining die to provide each tooth of the plurality of spaced-apart cutting teeth with a substantially wedge-shaped cross-section, a top face, a bottom face and two opposing lateral faces running in between the top and the bottom face and having inclined sections, and to simultaneously form a cutting edge at the intersection between the top face and one of an upper section of one of the lateral faces, wherein at the cutting edge a scissor angle is created, which is defined between the cutting edge and a longitudinal axis of the stationary cutting blade, and a wedge angle is created, which is defined between said upper section of the one of the lateral faces and the top face; wherein the inclined sections of the two opposing lateral faces include a first sharp bend between the upper section and an intermediate section which is inclined with respect to the upper section, and a second sharp bend between the intermediate section and a lower section which is inclined with respect to the intermediate section, and wherein a sum of the scissor angle and the wedge angle is smaller than 70?.

13. The manufacturing process according to claim 12, wherein, before the coining act, the process further comprises an act of stamping into said piece of metal at a position where the tip of the stationary cutting blade is to be created.

14. The manufacturing process according to claim 12, wherein during the coining act a scissor angle of between 5? and 25? is formed.

15. The manufacturing process according to claim 12, wherein during the coining act a wedge angle between 40? and 55? is formed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. In the following drawings

(2) FIG. 1 shows a sectional view of parts of a hair clipping device with a stationary cutting blade according to the present invention;

(3) FIG. 2 shows a perspective view of an embodiment of a cutting unit according to the present invention;

(4) FIGS. 3A and 3B show perspective and sectional views of an embodiment of the stationary cutting blade according to the present invention;

(5) FIG. 4 shows an enlarged view of the teeth of the stationary cutting blade according to the present invention;

(6) FIG. 5 shows a top view of the teeth of the stationary cutting blade according to the present invention;

(7) FIG. 6 shows a schematic cross section of a tooth of the stationary cutting blade according to the present invention;

(8) FIGS. 7A-7D show schematically illustrate a manufacturing process of the stationary cutting blade according to the present invention;

(9) FIGS. 8A and 8B show a first example of a stationary cutting blade according to the prior art; and

(10) FIGS. 9A and 9B show a second example of a stationary cutting blade according to the prior art.

DETAILED DESCRIPTION OF THE INVENTION

(11) FIGS. 1 and 2 schematically illustrate an example of a hair clipping device and a cutting unit in which a stationary cutting blade according to the present invention may be used. The hair clipping device is therein in its entirety denoted with reference numeral 100.

(12) The hair clipping device 100 usually comprises a housing (not explicitly shown) in which all remaining parts are usually integrated. The housing also serves as a holder for a cutting assembly 10 (see FIG. 2). The housing usually has an elongated body, wherein the cutting assembly 10 is releasably fixed to a front end of said housing. The cutting assembly 10 may of course also be permanently fixed to the front end of the housing. The housing may further comprise a handle at its rear end (not shown).

(13) The cutting assembly 10 includes a stationary cutting blade 12 and a movable cutting blade 14. The movable cutting blade 14 is displaceably mounted on a top side 16 of the stationary cutting blade 12, which top side 16 faces substantially towards the inner side of the housing. By the help of a spring 18, the movable cutting blade 14 is resiliently biased against the stationary cutting blade 12. The spring 18 may be realized as a mechanical spring that comprises two spring levers 20. These spring levers 20 exert a spring force onto the movable cutting blade 14 in order to keep the two cutting blades 12, 14 close together.

(14) The stationary cutting blade 12 comprises a plurality of cutting teeth 22 at its free front end. In this example the movable cutting blade 14 also comprises an array of cutting teeth 24. However, it could generally also comprise a continuous sharp edge instead of the array of cutting teeth 24. During operation haircutting is performed by the interaction of the stationary cutting blade 12 and the movable cutting blade 14 that reciprocates on the stationary cutting blade 12, as this is known from other conventional hair clipping devices.

(15) A drive arrangement including a motor 26 is adapted to drive the movable cutting blade 14 in an oscillatory manner in an opposing movement direction 28. The motor 26 thereto comprises a rotary driven shaft 30 that is forced into rotation. An eccentric transmission element 32 including an eccentric pin 34 protruding therefrom is arranged on said rotary-driven shaft 30. The eccentric transmission element 32 may be clamped onto the shaft 30 or coupled to it in another way. However, the shaft 30 and the eccentric transmission element 32 may also be realized as one integrated part. The motor 26 may, for example, be realized as an electric motor that is either powered by main supplied electricity or battery-driven.

(16) The rotary movement of the eccentric transmission element 32 is translated into the translatory movement of the movable cutting blade 14 via a coupling element 36. The coupling element 36 is also called driving bridge.

(17) The stationary cutting blade 12 is usually designed to be thicker than the movable cutting blade 14. Said stationary cutting blade 12 is also denoted as guard. The guard 12 is according to the present invention realized as a full metal guard (fully made of metal). It comprises a base body 48, wherein the cutting teeth 22 are arranged at a front part (also referred to as tip) of the base body 48 (see FIG. 3). The thickness t.sub.1 of the base body 48 is preferably chosen to be larger than 1.3 mm. Such thick guards 12 serve for an optimal mechanical stability. Thick metal guards 12 like these also have a very good heat dissipation behavior, which is quite important, since the guard 12 should not heat up too much in order to reduce the risk for a user to get burned.

(18) Such thick full metal guards 12 are, however, more difficult to manufacture. Especially the teeth geometry is very difficult to manufacture. Common thick full metal guards are manufactured exclusively with a process wherein the cutting teeth are grinded. This grinding process is quite time-consuming and therefore costly. Apart from that, grinding also has some geometrical limitations. Teeth geometries that may be established with the state of the art grinding process are quite limited. It is hardly possible to create specific combinations of scissor angles ? and wedge angles ? within the teeth. Only certain combinations are possible. The reason for that is the dressing of the grinding wheel that follows a fixed geometrical logic. Grinding the cutting teeth therefore usually results in a fixed dependency between the so-called scissor and wedge angle (see below).

(19) The inventors of the present invention have now found that the teeth geometry of the stationary cutting blade 12 may also be manufactured in a coining process even if it is a thick full metal guard with a base body 48 that might have a thickness t.sub.1 of more than one millimeter. The front part of the stationary cutting blade 12 is thereto designed to be thinner than the base body 48. A ratio between the thickness t.sub.1 of the base body 48 and the thickness t.sub.2 of the cutting teeth 22 is chosen to be larger than 1.1. The reduced thickness t.sub.2 of the cutting teeth 22 allows to manufacture the teeth geometry in a very accurate coining process. With the coining process there is no longer a limit in creating scissor angles ? in combination with any desired sharp wedge angle ?. It is therefore possible to create new and unique teeth geometries which would not be possible with the common grinding technique.

(20) It shall be understood that the thickness t.sub.2 of the cutting teeth 22 denotes the dimension of the cutting teeth 22 measured in parallel to the transverse axis 42 of the stationary cutting blade 12 at the thickest point (rear end) of the cutting teeth 22.

(21) FIGS. 3 to 6 show the new design of the stationary cutting blade 12, wherein the focus is on the new geometry of the cutting teeth 22.

(22) FIG. 3A shows a perspective view of the stationary cutting blade 12 and FIG. 3B shows a sectional view of the stationary cutting blade 12 according to the present invention. It shall be noted that the stationary cutting blade 12 is in these figures shown with its bottom side 37 facing upwards. When fixed in the cutting assembly 10, it is compared to these figures turned round.

(23) The base body 48 of the stationary cutting blade 12 comprises a top side 16 that is usually pressed against the lower side of the movable cutting blade 14. The bottom side 37 runs substantially parallel thereto. The plurality of coined cutting teeth 22 are arranged on the front side 38 of the stationary cutting blade 12. A longitudinal axis of each cutting teeth 22 extends parallel to a longitudinal axis 40 of the stationary cutting blade 12.

(24) The teeth geometry of the cutting teeth 22 may be best seen in FIGS. 4 to 6. Each cutting tooth 22 has a substantially wedge-shaped cross section with a top face 44, a bottom face 46 and two opposing lateral faces 50, 50 running in between the top and the bottom face 44, 46. Each cutting tooth 22 comprises two cutting edges 52, 52 that are arranged at the intersection between the top face 44 and an upper section 54, 54 of one of the lateral faces 50, 50. Each lateral face 50, 50 also comprises a lower section 56, 56 which is inclined with respect to the upper section 54, 54 of the respective lateral face 50, 50. Each lateral face 50, 50 therefore has sharp bend(s) in it, a kind of step form or echelon form. Such a shape would hardly be possible with the state of the art grinding process. With the presented new coining process it is however easy to manufacture. As shown in FIGS. 4 and 6, the front of a tooth has a kind of a 2-step form while the back of the tooth has a kind of a 3-step form (FIG. 4), including the lower section 56, the upper section 54 and an intermediate section 55 between the lower and upper sections 56, 54.

(25) By coining the cutting teeth 22 it is possible to freely design the scissor angle ? and the wedge angle ? independent from each other. As shown in FIG. 5, the scissor angle ? is defined between each cutting edge 52, 52 and an imaginary plane 41 that is parallel to the longitudinal axis 40 of the stationary cutting blade 12. That is, the scissor angle ? is defined between a cutting edge 52 and the longitudinal tooth axis, which is parallel to the imaginary plane 41. Said scissor angle ? is important for the ability of the teeth 22 to limit the amount of simultaneous cutting of hair in order to prevent an overload under heavy load conditions. Compared to completely straight teeth with a scissor angle of 0? (as e.g. in the prior art example shown in FIG. 8) slightly inclined teeth 22 show a better cutting performance.

(26) According to the present invention, this scissor angle ? is preferably chosen to be smaller than 25?. More preferably, it is chosen to be between 5? and 25?. Most preferably, the scissor angle ? is around or equal to 12?.

(27) As best shown in FIG. 6, the coining process at the same time allows to create fairly sharp cutting edges 52, 52 by having a comparatively small wedge angle ?. The smaller this wedge angle ? is, the sharper the cutting edge 52, 52 gets. However, a too small wedge angle ? would result in a mechanically instable and too sensitive cutting edge 52, 52. It has therefore been found by experiments of the applicant that an optimal range for the wedge angle ? is between 40? and 55?. Most preferably, this wedge angle ? is around or equal to 45?. Again it shall be noted that the cross section as shown in FIG. 6 would not be possible with the regular grinding technique. A combination of a scissor angle ? around 12? combined with a wedge angle ? around 45? is therefore unique. Hair cut tests of the applicant have shown that hair clipping devices equipped with the stationary cutting blade 12 according to the present invention show a very good hair cutting performance. Especially under extreme tight and thick hairs the new stationary cutting blade 12 with the new teeth geometry showed an almost perfect cutting behavior, wherein there is almost no risk for the unwanted pulling effect.

(28) FIG. 7 schematically illustrates the manufacturing process of the stationary cutting blade 12 according to the present invention. In a first step (see FIG. 7A) a metal coil having a thickness t.sub.1 of more than one millimeter is trimmed in order to receive separate metal pieces from which the guard 12 may be manufactured. This is usually done by stamping a recess into the metal coil material at a position where the tip 23 of the cutting teeth 22 shall be created. In the next step (see FIG. 7B), a tapered shape will be created at the tip of the guard. This may be done either by removing the metal material or by deforming it. Several techniques are thereto generally conceivable, e.g. milling, grinding, forging, abrading, etc. According to a preferred embodiment, this is done by coining using a coining wedge that is schematically illustrated in FIG. 7B and indicated by reference numeral 58. This process step is used to create a rough shape of the tip of the stationary cutting blade 12.A further benefit of this step is that the thickness of the metal is decreased to t.sub.2 at the position where the cutting teeth will be created. This facilitates the following coining process that is used to create the final teeth geometry.

(29) In the third step (see FIG. 7C) the teeth geometry including the excess material from the wedge cold forming process will be stamped out. In this step, the preliminary teeth geometry will be stamped into the tip to create a plurality of spaced-apart cutting teeth. Finally, in a fourth third step (see FIG. 7D), the teeth geometry will be cold formed with a coining process by means of a coining die 60. This is usually done for all cutting teeth in parallel. The coining die 60 thereto has the negative of the teeth geometry that shall be created. In this process step the above-mentioned angles ? and ? are created.

(30) In order to receive a completely flat top side 16 of the guard 12, the top side 16 may be finally polished or flat-grinded (not shown).

(31) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 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.

(32) 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 element or other unit may fulfill the functions of several items recited in the claims. 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.

(33) Any reference signs in the claims should not be construed as limiting the scope.