Abstract:
A shaving unit for an electric shaver which comprises an outer cutter and an inner cutter associated to that outer cutter. The cutters are mounted so as to be movable relative to each other and adapted to be set in a relative motion by a drive mechanism. The inner cutter provides a plurality of cutting edges and abuts with its outer face on the inner face of the outer cutter. The outer cutter provides a plurality of teeth equipped with cutting edges. The outer cutter provides two comb elements which are disposed opposite one another and which extend according to the direction of the relative motion. The two comb elements are aligned with respect to one another such that the tips of the teeth of the first comb element are facing the tips of the teeth of the second comb element, the tips of the teeth spaced from one another.

Description:
FIELD OF THE INVENTION 
     This invention relates to a shaver unit for an electric shaver according to the generic part of claim  1 . Shaving units of this kind are designated to be used in electric shavers, beard trimmers and hair cutters. They can be arranged as a sole cutting element or in combination with other cutting elements—often they are used as so-called center trimmers and arranged between two shaving foils. 
     BACKGROUND OF THE INVENTION 
     Shaving units of the type initially referred to are known for example from EP 0693988 B1. This document discloses an electric dry shaver where a center trimmer is arranged between two foil type shaving elements. The upper cutter of this center trimmer is provided with hair feeding means consisting of projecting teeth which are directed outwardly. Those center trimmers in general are rather effective in cutting the hairs to a very short remaining length of hair. With respect to hairs which are resting flat against the skin the performance of the known cutting system is not optimal since such hairs—especially if they are located on skin areas with flexible skin—tend to escape from the feeding area formed between two teeth of the comb-shaped feeding means. 
     From the EP 1930135 A1 there is known a shaving head with a center trimmer which comprises a multiplicity of bars arranged at a small distance to each other, so as to form small slits between the bars. Such kinds of center trimmers are a more open construction without a center bar arranged along the longitudinal axis of the trimmer. Cutting units of this type have proven to be mechanically stable even with a small thickness of the outer cutter. The drawback of this kind of shaving units is the risk to cause skin irritations. 
     SUMMARY OF THE INVENTION 
     It is an objective of the present invention to provide an improved shaving unit for electric shavers of the type initially referred to such to ensure an optimal feeding of hairs as well as to avoid skin irritation during the shave. 
     This objective is accomplished by the combination of features as indicated in claim  1 . 
     According to the invention, the outer cutter provides two comb elements each directed inwardly. This inventive solution enables a high mechanical stability in combination with providing extremely thin comb elements, which consequently ensure an optimal lifting of hairs that are lying flat to the skin. A thin outer cutter additionally enhances a close shave because the cutting area between the inner and the outer cutter can be placed extremely narrow to the skin. The central area of the upper cutter between the inwardly directed teeth of the comb elements provides a high likelihood for hairs to be lifted from the skin. 
     In an embodiment of the present invention increasing the probability of catching as well as lifting hairs, the teeth of the first comb element are arranged offset in relation to the teeth of the second comb element along a direction of the relative motion. In a particularly advantageous embodiment of the invention the pitch of the teeth of the two comb elements is equal and the teeth of the first comb element are provided offset in relation to the second comb element by half of the pitch. This enables a longer free distance in front of the tips and helps feeding the hairs to be cut. 
     Another embodiment of the invention that helps both to completely avoid skin irritation during and after shaving and to capture flat hairs is characterized in that the teeth of the first and of the second comb element are designed such that their surfaces which contact the skin during the shaver lie in one plane. Another embodiment that is characterized by a superior performance of feeding hairs resting flat against the skin may be realized in a way that the teeth of the first and second comb elements each lie in planes that extend at an angle of 180-120 degrees to each other. Especially a difference in height of up to a maximum of 250 μm between the tips of the teeth and the respective opposite ends of the teeth—which means that the tips are upwardly elevated—is an optimal compromise which guarantees both extremely effective feeding performance with respect to hairs which are lying flat to the skin and avoidance of irritation of the skin. This is because during the shaving strokes this geometry leads to a deformation of the skin also in that range of 250 μm. This, in turn, makes it highly likely for the prong-shaped teeth to under slide and to then lift stubbles of a length of some 100 μm. 
     It has turned out that a distance between facing teeth tips of approximately 0.7 to 1.6 millimeters assures high shaving comfort as well as excellent feeding of hairs, even in case of a beard having grown for several days. 
     During a continuous shaving stroke the skin remains tensioned and stretched in the area of the gap between the facing teeth tips. However, when reversing the direction of the stroke the skin tends to penetrate into the gap due to the fact that skin folds may occur caused by peaks of the contact pressure between skin and shaver. Therefore, it is advantageous that the inner cutter is provided with a recess in its area between the tips of the teeth of the outer cutter. It is additionally beneficial to avoid sharp edges on the inner cutter in said area. 
     The inventive shaving unit may be incorporated in both linear/translational oscillating and rotatory shaving systems. This means that the relative motion of the inner and outer cutter may be a translational oscillating motion along the longitudinal axis of the shaving unit or a rotatory motion around the perpendicular axis of an annular-shaped shaving unit. 
     If at least one of the two comb elements is provided with a bar arranged opposite the tips of the teeth, the possibility of catching skin in a slit between two teeth is drastically reduced. Furthermore, if a hair lying flat, i.e. nearly parallel to the skin is fed between two teeth and then during the shaving stroke is pressed with its free end against this bar, there is a certain likelihood of leveraging the hair away from the skin and moving it deeper into the shaving unit to cut it. 
     The invention also concerns a shaving head whereby at least one shaving unit as described above is arranged, especially in combination with additional shaving units of the same type or of other types. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be further elucidated by detailed explanation of exemplary embodiments and by reference to figures. In the figures 
         FIG. 1  is a perspective illustration of an exemplary embodiment of the invention, 
         FIG. 2  shows detail D 1  of  FIG. 1  in a larger scale, 
         FIG. 3  is another perspective illustration of an embodiment of the invention, 
         FIG. 4  shows a cross-section along the longitudinal axis of a shaving unit according to  FIG. 3 , 
         FIG. 5  is a cross-section along the lateral axis through an embodiment of the invention according to  FIG. 2 , 
         FIG. 6  depicts Detail D 2  of  FIG. 5  in a larger scale with omission of some details which are not important for the invention, 
         FIG. 7  shows an upper cutter according to the invention to be used in shavers of the rotating type and 
         FIG. 8  is a cross-section through the embodiment according to  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an embodiment of a shaving unit  1  according to the invention, having a longitudinal axis X, a lateral axis Y and vertical axis Z. In the enlarged view, as depicted in  FIG. 2 , there is shown the outer cutter  5  which consists essentially of the first comb element  2 , the second comb element  3  and the sidewalls  4  which parts all together compose the U-shaped form of the outer cutter  5 . In the embodiment according to  FIG. 2 , the two comb elements  2  and  3  are arranged in a way that they run towards each other at an angle, whereby top faces of the comb elements which contact the skin during shaving increase in height from their outer borders  8  going inwards to shape a roof-form with an elevated middle part. For identical parts or parts which accord each other the same reference numbers are used in the description. 
     As can be taken best from  FIGS. 1-3 , the two comb elements  2 ,  3  are integrally formed and comprise a multiplicity of teeth  6  arranged at regular intervals. The respective pitch P is 0.9 mm. The teeth  6  extend inwardly in parallel to the lateral axis Y and have a length of 1.2 mm measured from the tooth root surface  9  to the tip  10 . The distance from the outer border  8  to the tip  10  is 2.25 mm. Every tooth has a width W measured along the longitudinal axis X of around 0.5 mm (500 μm) which—under calculating with the pitch P value of 0.9 mm—gives a value of the slit  7  between two teeth  6  of around 0.4 mm. The overall width of the shaving unit  1  (along lateral axis Y) is 5.5 mm and its length along the longitudinal axis X is 41 mm. The two end sections  11  of the shaving unit  1  which delimit the section where the teeth  6  are arranged have a plane surface without any tooth. The two end sections  11  may be provided with a relief-like structure for interacting with the user&#39;s skin or it may be perforated. The perforation of the end sections  11  positively impacts the process of bending the integrally formed two comb elements  2 ,  3  along the common symmetry line  12  parallel to the longitudinal axis X. This bending is for providing an obtuse angle A between the two comb elements  2 ,  3 . This topic and the advantages associated therewith will be described below, especially in connection with  FIGS. 5 and 6 . 
     The outer cutter  5  encompasses the inner cutter  13  which also is U-shaped. It is composed of two side walls  14  which are interconnected by a plurality of bars  15  whereby the single bars are arranged displaced from each other by a distance to form a plurality of slots  16  between two adjacent bars  15  (see  FIG. 4 ). The bars  15  are arranged at regular intervals. The respective pitch is 1.5 mm. The bars have a width along the longitudinal axis X of around 0.7 mm which leads to a slot width of 0.8 mm. A leave spring  17  is arranged preloaded between the inner and the outer cutter  13 ,  5  to bias both parts against each other in a way that is known per se. The inner cutter  13  comprises coupling means  18  to be coupled in a known manner with an oscillating drive, which drive is not shown in the drawing. The outer cutter  5  is preferably fixed to a shaver head or a housing of an electric shaver, but might in a further embodiment of the invention (not shown) also be driven by a drive mechanism. 
     From  FIG. 3  it can be taken that the first and second comb elements  2 ,  3  are providing the same pitch P of 0.9 mm. However, the two comb elements are parallel shifted by 0.45 mm—which is half of that pitch—against each other. Consequently the tips  10  of the first comb element  2  are located opposite the slits  6  of the second comb element  3 . 
       FIGS. 5 and 6  are showing a cross-section along the lateral axis through an embodiment of the invention according to  FIG. 2  and are clearly demonstrating the obtuse angle A between the two comb elements  2  and  3 . This angle A leads to a difference in height H between the outer border  8  and the tip  10  by an amount of 250 μm. The obtuse angle A between the two comb elements is produced by simply bending around the symmetry line  12  in the area of the end sections  11 . Consequently the teeth  6  of the comb elements  2 ,  3  are brought into the angled position without getting touched by a bending tool. 
     The free gap G between the tips  10  of the first comb element  2  and their respective counterparts of the second comb element  3  is around 1.00 mm. The tooth length L—which is the distance from tip  10  to the tooth root surface  9 —is 1.2 mm. The height of the teeth in dimension Z is 150 μm in the area of the tips  10  and increases linearly along the length L in direction to the tooth root surface  9  up to 400 μm. Since the distance from the outer border  8  to the tip  10  is 2.25 mm, the conjunction bar  19  has width of 1.05 mm. By this, a bending stiffness of the teeth  6  is achieved which is optimally adapted to the teeth&#39;s capacity to cope with pressure. In this way, it will be possible to realize extremely thin comb tips  10  by nevertheless maintaining the stability of the teeth  6 . A tapering of the teeth  6  thickness towards the tips  10  is achieved by the removal of material at the underside of the teeth. It is true that there is an enhanced risk of skin irritations with extremely thin teeth, but the comb tips facing each other allow an optimal stretching of the skin, thus compensating for this risk. 
     The elevation of the tips  10  relative to the outer conjunction bars  19  causes a deformation of the skin in areas of flexible skin which helps lifting up flat lying hairs and directing them in a optimal alignment to then feed them into the cutting gaps defined by the slits  7  of the outer cutter  5  and the slots  16  of the inner cutter  13 . The teeth  6  are—as known per se—equipped with cutting edges  22  at their lower side and the bars  15  provide cutting edges  23  at their upper side. 
     To avoid skin contact with the driven inner cutter  13  in case the skin during shaving is pressed into the free gap G the bar  15  is providing a recess  20  at the top surface of its middle section. Whereas the height of the bars  15  at the boundary area is about 0.3 mm the height at the recessed middle area  20  is only about 0.2 mm. In addition to this 0.1 mm recess, the middle area  20  of the bar  15  is provided with a concave top surface which delivers an additional free space in the vertical of about 0.1 mm in the center. The recess  20  extends over a total width R of 1.7 mm along the axis Y. Due to free gap G of 1.00 mm the undercut U (the extent from the tip  10  to the respective bound of the recess  20 ) is 0.35 mm. This undercut U in conjunction with the recess ensures the avoidance of skin irritations during the shave. 
     Due to the fact that the outer cutter  5  as well as the inner cutter  13  posses U-form profiles the shaving unit  1  is distinguished by a superior mechanical stability even though using parts of only minor material thickness. 
       FIG. 7  shows an outer cutter  5  of a shaving unit according to the invention to be used in shavers of the rotating type with a rotating inner cutter of a type known per se and not shown in the drawing. Also this outer cutter  5  provides inwardly directed teeth  6  of two comb elements  2  and  3 . The first comb element  2  shows the form of a circle and the second comb element  3  has a ring-form and is arranged concentrically around the first comb element  2 . The geometry and the dimensions as well as the function, the effects and the advantages of this embodiment of the invention are analog to the linear version depicted above and shown in the  FIGS. 1 to 6 . 
     As can be taken from the cross section in  FIG. 8  the teeth  6  are bent to an angle in a manner that the tips  10  are elevated about a height H of 250 μm relative to the level of the outer border  8  and the inner border  21 . The free gap G between two opposite tips  10  is around 1.00 mm 
     The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.” 
     Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.