Patent Publication Number: US-2023144894-A1

Title: Razor comprising a hair-severing member having a plurality of sawing teeth

Description:
FIELD OF THE INVENTION 
     The invention relates to a razor comprising a support, a skin engagement member, and a hair-severing member having a plurality of sawing teeth arranged along a hair-severing edge of the hair-severing member, wherein the hair-severing member is mounted to the support in a position relative to the skin engagement surface such that the hair-severing edge is exposed to a user&#39;s skin for sawing through hairs present on the skin by means of the sawing teeth, and wherein the hair-severing member is suspended relative to the support for allowing movement of the sawing teeth in a local direction of extension of the hair-severing edge at the position of the sawing teeth. 
     The invention further relates to a method of shaving hairs projecting from a skin surface by means of a razor as described here before. 
     BACKGROUND OF THE INVENTION 
     Blade shaving allows achieving a very close shave. However, an inconvenience of blade shaving (also commonly referred to as ‘wet shaving’) is the need of moistening the skin and the hairs, e.g. by applying water thereto and by lubricating the skin and the hairs, e.g. by applying a shaving foam. After shaving, residues of the lubricating agent need to be removed and lubricating agent is easily spoilt onto clothing, furniture or the floor. Accordingly, blade shaving has to be carried out in a bathroom-like surrounding and, even then, involves cumbersome handling of water and shaving foam. Without water and foam, hairs remain too hard, leading to high hair-cutting forces, high and painful drag forces, and fast destruction of the blade cutting edge. 
     Another disadvantage of blade shaving is the relatively high cost of replacing worn shaving blades, in particular if high quality blades are used. 
     Many attempts have been made to make shaving blades lasting longer and to improve the shaving process by reducing the hair-cutting and drag forces. One approach is to cause the cutting edge to reciprocally move in the (longitudinal) direction of extension thereof, in analogy to movement of a knife or saw during cutting. An example of a blade razor with a shaving blade having a straight cutting edge using this principle is described in U.S. Pat. No. 1,394,827. Another approach is to use a razor comprising a saw-like hair-severing member having a plurality of sawing teeth arranged in a row, wherein the sawing teeth are reciprocally driven in the direction of extension of the row. An example of a razor with a saw-like hair-severing member using this principle is described in U.S. Pat. No. 1,158,741. 
     In practice, such solutions have not been successful. In particular since the introduction of PTFE coated razor blades, drag occurring during hair cutting is much less of an issue, so the solutions based on movement of the cutting edge in its direction of extension became less relevant. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a razor of the type as described here before in the section “Field of the Invention” that allows the cutting of hairs close to the skin with relatively low hair-cutting forces, while generating very little friction, and with a saw-like hair-severing member having a relatively long life span. 
     According to the invention, this object is achieved by providing a razor according to claim  1 . The invention can also be embodied in a method according to claim  14 . 
     Using a razor and a method according to the invention, at each cutting instance, small amounts of hair tissue are sequentially removed from a hair by the moving tooth tips of the sawing teeth engaging that hair. Thus, the top and bottom portions of the hair are severed from each other by a number of subsequent cuts, each machining away a thin layer of the hair tissue. Since only little hair tissue is removed per passage of a sawing tooth through the hair, and since the hair does not have to be split in two at once, cutting forces exerted onto the hair and, accordingly, counter forces causing drag forces are much smaller than when the hairs are each cut by a single cut, such as by means of a non-reciprocating razor blade having a straight cutting edge. In particular, the present invention defines a number of operational and dimensional parameters of the hair-severing member, including the average velocity of the sawing teeth in the local direction of extension of the hair-severing edge and the spacing between the tooth tips, that result in effective shaving with reduced drag allowing shaving without wetting and/or lubricating the skin and without suffering from uncomfortable levels of drag on the hairs being shaved. Because the hairs are severed by sawing rather than by cutting each hair at once, the hair-severing edge of the razor according to the invention does not need to be as sharp as the cutting edge in a conventional blade razor. And because reduced drag results in slower wear of the hair-severing edge, useful shaving performance of the hair-severing member is maintained over a larger number of shaving sessions. 
     Particular elaborations and embodiments of the invention are set forth in the dependent claims. 
     Further features, effects and details of the invention appear from the detailed description and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a first example of a razor according to the invention; 
         FIG.  2    is a schematic perspective view of a drive of the razor shown in  FIG.  1   ; 
         FIG.  3    is a cross-sectional side view of a portion of the razor shown in  FIGS.  1  and  2   , while in use; 
         FIG.  4    is a schematic cross-sectional view of a hair-severing edge of the razor shown in  FIGS.  1 - 3    and thin and thick beard hairs to be severed; 
         FIG.  5    is a schematic perspective view of a section of the hair-severing edge of the razor shown in  FIGS.  1 - 3    in an operating position relative to a skin surface; 
         FIG.  6    is a schematic perspective view of a portion of the section shown in  FIG.  5    cut-off through a sawing tooth along a plane perpendicular to a local direction of extension of the hair-severing edge at the shown sawing tooth; 
         FIG.  7    is a schematic cross-sectional view of a hair-severing edge of a hair-severing member of a second example of a razor according to the invention; 
         FIG.  8    is a perspective view of a third example of a razor according to the invention; 
         FIG.  9    is a perspective view of a fourth example of a razor according to the invention; and 
         FIG.  10    is an enlarged view of a portion X of the razor indicated in  FIG.  9   . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIGS.  1 - 6    show a first example of a razor  1  according to the invention. The razor  1  has a support  2  and skin engagement surfaces  3 - 6 . For severing hairs  7  projecting from a user&#39;s skin close to the level of the skin surface  8 , a hair-severing member  9  having a hair-severing edge  10  is provided. The razor  1  further has a stem-shaped handle  11  for holding the razor  1  by hand. The hair-severing member  9  is mounted to the support  2  in a position relative to the skin engagement surfaces  3 - 6  such that the hair-severing edge  10  is exposed to the user&#39;s skin surface  8  for sawing through hairs  7  present on the skin when the skin engagement surfaces  3 - 6  are in contact with the skin. The hair-severing member  9  is suspended relative to the support  2  for allowing movement of the hair-severing member  9  in a direction of extension  12  of the hair-severing edge  10 . In operation, the hair-severing edge  10  moves along the skin surface  8  while only slightly contacting the skin as in conventional blade shaving. In this example, the hair-severing edge  10  is straight, so the hair-severing edge  10  has a local direction of extension which remains constant along the entire length of the hair-severing edge  10 . As will be illustrated by further examples, the local direction of extension of the hair-severing edge may also vary along the length of the hair-severing edge. Where, in the discussion of effects, reference is made to the ‘direction of extension of the hair-severing edge’, this has to be read as the ‘local direction of extension of the hair-severing edge at the position of the respective sawing tooth or sawing teeth’ for embodiments in which the direction of extension of the hair-severing edge varies along the length of the hair-severing edge. 
     The hair-severing edge  10  has a plurality of sawing teeth  14  (preferably evenly) arranged along the hair-severing edge  10  of the hair-severing member  9 . In the present example, as shown in detail in  FIGS.  4  and  5   , the sawing teeth  14  each have two tooth tips  16  connected by a concavely shaped front tooth edge  15 . The front tooth edge  15  of each sawing tooth  14  is connected to a respective one of two upper side tooth edges  29  of the sawing tooth  14  and to a respective one of two lower side tooth edges  36  of the sawing tooth  14  via a respective one of the two tooth tips  16 . Each sawing tooth  14  is arranged along the hair-severing edge  10  for sawing through hairs  7  by movement in the direction of extension  12  of the hair-severing edge  10 . In  FIG.  5   , orientations  8   x  and  8   y  of the skin surface  8  are shown in the direction of extension  12  of the hair-severing edge  10  ( 8   x ) and in a direction along the skin surface  8  perpendicular to the direction of extension  12  of the hair-severing edge ( 8   y ). Each lower side tooth edge  36  connects to a side edge  39  of a skin contacting surface  40  of the sawing tooth  14  which, as shown in  FIG.  5   , extends at a wedge angle  41  relative to the associated upper side tooth edge  29  which is smaller than a first tip angle  38  of the tooth tip  16  enclosed by the upper side tooth edge  29  and the lower side tooth edge  36 . The wedge angle  41  between the side edge  39  of the skin contacting surface  40  and the associated upper side tooth edge  29  is preferably between 10 and 20°, so that, when the razor  1  is being used, the skin contacting surface  40  is approximately in a same plane as the skin surface  8  (in  FIG.  5    defined by the directions  8   x  and  8   y ). 
     As shown in  FIG.  2   , the razor  1  comprises a drive  13  which is coupled to the hair-severing member  9  for driving the movement of the hair-severing member  9  relative to the support  2  such that the sawing teeth  14  move in the direction of extension  12  of the hair-severing edge  10  with an average velocity larger than or equal to 10 m/s. In this example, the movement of the sawing teeth  14  is a reciprocal movement in the direction of extension  12  with said average velocity. 
     The thicknesses of beard hairs  7  are typically in a range from about 50 μm, for a thin beard hair, up to about 300 μm for a thick beard hair. Thus, at least the thinnest beard hairs  7 B would fit in an intermediate space  30  between two successive sawing teeth  14  (a sawing tooth and the first next or previous sawing tooth) if a spacing  17  (see  FIG.  5   ) between two successive sawing teeth  14  is larger than 50 μm. It has been found that, if beard hairs  7  are entirely caught in the intermediate space  30  between the sawing teeth, the beard hairs tend to be just reciprocally moved by the sawing teeth instead of being chipped. To avoid that thin beard hairs are just reciprocally moved and less effectively chipped, a depth  18  of the intermediate space  30  between two (preferably each pair of) successive sawing teeth  14 , in a direction perpendicular to the direction of extension  12  of the hair-severing edge  10 , is preferably smaller than or equal to 25 μm when the spacing  17  between the tooth tips  16  of two successive sawing teeth  14  is larger than 50 μm. The depth  18  between two successive sawing teeth  14  can be considered up to a straight bottom  19  of the intermediate space  30  as shown in  FIG.  5   , but the effective depth can also be determined (limited) by one or more small ridges or other projections between successive sawing teeth  14 . As is shown in  FIG.  4   , a spacing  17  between successive sawing teeth  14  smaller than or equal to 50 μm can also prevent thin hairs  7 B from fully entering the intermediate space  30  between successive sawing teeth  14 , even if the depth  18  would be large enough to entirely accommodate at least thin hairs  7 B. 
     The spacing  17  between the tooth tips  16  of two successive sawing teeth  14  is at most 150 μm, so that, for hairs with an average hair diameter, during movement of the severing edge  10  along a hair  7 A or  7 B, before a sawing tooth  14  leaves the hair  7 , a next sawing tooth  14  already enters a groove in the hair  7  which the previous sawing tooth  14  has cut therein. For effective sawing of thin hairs  7 B, it is advantageous if the spacing  17  between the tooth tips  16  of two successive sawing teeth  14  is very small, but it has also been found that, if the spacing  17  between the tooth tips  16  of two successive sawing teeth  14  is very small, debris obtained during cutting tends to remain stuck in the intermediate spaces  30  between the sawing teeth  14 . Therefore, the spacing  17  is 20 μm or larger. Also, when a large number of sawing teeth  14  is simultaneously in engagement with a hair  7 , the advantage of reduced cutting forces may be offset by the large sum of the cutting forces of the individual sawing teeth  14  in engagement with the hair  7 . The sum of the cutting forces should preferably not exceed 0.007 N to prevent drag. This is another reason why the spacing  17  is at least 20 μm. 
     For avoiding the occurrence of too much drag while allowing to effectively sever hairs  7 , the average velocity of the sawing teeth  14  in the direction of extension  12  of the hair-severing edge  10  is larger than or equal to 10 m/s. Each saw tooth  14  can be regarded as a small chisel which, given a certain contact stress at the hair and a lateral motion, will chip away hair tissue from the hair. It has been found that, for effectively sawing through hairs, a ratio between the velocity of the hair-severing edge  10  in its direction of extension and the velocity at which the depth of the sawing slit in the hair is increased should at least be about 100. Therefore, to be able to shave at acceptable shaving velocities, i.e. velocities in the shaving direction of the razor  1  of at least 100 mm/s, the minimal velocity of the hair-severing edge  10  in its direction of extension  12  should be larger than 100×100 mm/s=10 m/s. 
     The hair-severing edge  10  is preferably made of tool grade steel, but the material of the hair-severing edge  10  is not limited to tool grade steel. There are several ways for manufacturing the sawing blades, such as by chemical etching and laser ablation. However other methods, like growing nickel and a combination of processes like wire spark erosion with mechanical or chemical polishing, are also conceivable. 
     The front tooth edge  15  and each of the upper side tooth edges  29  of each of the sawing teeth  14  preferably enclose a second tip angle  20 , as shown in  FIG.  5   , smaller than 80° at the tooth tip  16  to assure sufficient contact stress at the tooth tip  16 . Thus, the second tip angles  20  of the tooth tips  16  between the front tooth edge  15  and each of the upper side tooth edges  29  are preferably each smaller than 80°. The first tip angles  38  of the tooth tips  16  between the upper side tooth edge  29  and the lower side tooth edges  36  of each sawing tooth  14  are preferably smaller than 80° and more preferably smaller than 60°. For sufficient sharpness of the tooth tips  16 , a tip radius R TIP  (see  FIG.  5   ) of the tooth tips  16  is preferably equal to or smaller than 5 μm. The tip radius R TIP  of the tooth tips  16  is schematically shown in  FIG.  5   . For effective sawing, the tooth edges  15 ,  29 ,  36  preferably have an edge radius R EDGE  of 5 μm or smaller. Thus, seen in cross-section along a plane perpendicular to the tooth edge  15 ,  29 , each tooth edge  15 ,  29  preferably has an edge radius R EDGE  equal to or smaller than 5 μm. The tooth edges  15 ,  29 ,  36  preferably have such an edge radius R EDGE  at least at the position of the tooth tips  16  and, preferably, up to a distance from the tooth tips  16 . Said distance may be, for example, 25%, 50% or even 100% of the depth  18  of the intermediate space  30 . The edge radius R EDGE  of the front tooth edge  15  is shown in detail in  FIG.  6   . 
     To avoid abrasion of the skin and dragging along of the skin with the movement of the sawing teeth  14 , the side edges  39  of the skin contacting surface  40 , and preferably also portions of the lower side tooth edges  36  adjacent to the respective side edges  39  of the skin contacting surface  40 , are preferably rounded or chamfered, for example to an edge radius larger than 5 μm and preferably larger than 10 μm. Outer ends of the side edges  39  of the skin contacting surface  40  may each be curved so as to provide smooth transitions to the lower side tooth edge  36  and a lower tooth edge  42  contiguous with that side edge  39  of the skin contacting surface  40 . 
     To further limit movement of the skin induced by movement of the hair-severing member  9  contacting the skin surface  8  during use, the razor  1  according to the present example is equipped with a skin-shielding member  5 , as show in  FIG.  3   , arranged in a stationary position relative to the support  2  at a side of the hair-severing member  9  facing the skin during use. As a result, during use the hair-severing member  9  is exposed to the skin only in an exposure area  32  between the hair-severing edge  10  and an edge  33  of the skin-shielding member  5 . The exposure area  32  has a depth d between 100 and 500 μm, preferably between 250 and 350 μm, in a direction perpendicular to the direction of extension  12  of the hair-severing edge  10 . Movement of the skin induced by the movement of the hair-severing member  9  reduces the effectiveness of the sawing process and is limited as much as possible by exposing the hair-severing member  9  to the skin only in the relatively small exposure area  32  that includes the hair-severing edge  10 . The selected depth d of the exposure area  32  safeguards sufficient exposure of the hair-severing edge  10  to the skin and, thereby, sufficient effectivity of the sawing process of the moving hair-severing edge  10 . The skin-shielding member  5  also limits skin irritation caused by contact between the moving hair-severing edge  10  and the skin, because the skin-shielding member  5  reduces the pressure at which the hair-severing edge  10  contacts the skin. The skin-facing surface  34  of the skin-shielding member  5  may be provided with a friction-reducing coating to reduce skin friction. 
     As shown in  FIG.  5   , the sawing teeth  14  each have a width  21  in the direction of extension  12  of the hair-severing edge  10  smaller than 75 μm, so that a large number of tooth tips  16  can be provided leaving a given minimum spacing  17  between each pair of successive tooth tips  16 . For a double-edged (twin tip) sawing tooth  14 , a width  21  of 20 μm is preferred for optimizing performance while maintaining sufficient tooth strength. 
     Instead of a single hair-severing member  9 , one or more further hair-severing members may be provided in a razor according to the invention, wherein all hair-severing members may be coupled to the same drive arranged for driving the movement of each hair-severing member relative to the support in the direction of extension of its hair-severing edge with the average velocity larger than or equal to 10 m/s. 
     As mentioned here before, in the razor  1  according to the present example, the movement of the sawing teeth  14  in the direction  12  of extension of the hair-severing edge  10  is a reciprocal movement. 
     For high shaving performance, the sawing teeth  14  each have two tooth tips  16 , so that the sawing teeth  14  cut in the two movement directions parallel to the direction  12  of extension of the hair-severing edge  10 . Moreover, the second tip angle  20  of the tooth tips  16  can be smaller than 80°. Furthermore, in the present example the front tooth edges  15 , that mutually connect the two tooth tips  16  of the sawing teeth  14 , are concavely shaped. As a result of the concave shape of the front tooth edges  15 , a hair temporarily present between the top of a sawing tooth  14  and the skin  8  does not cause the sawing tooth  14  to be lifted from the skin  8  so far that shaving performance is significantly compromised. This is the more relevant the thicker the sawing teeth  14  are. 
     In  FIG.  7    a hair-severing edge  60  of a hair-severing member of a second example of a razor according to the invention is shown, which is also configured for shaving with the hair-severing edge  60  reciprocally moving in its direction of extension  12 . The sawing teeth  64  each have a single tooth tip  66  at the location where the two tooth edges  79  are mutually connected. The tip angle  70  of the sawing teeth  64  is preferably smaller than 60° to keep the negative cutting (rake) angle  72  as small as possible to achieve a sufficiently high initial contact stress with the hair  7  to create an initial notch. For obtaining sufficient strength of the sawing teeth  64 , the sawing teeth  64  preferably have a base width  73  of at least 20 μm. 
     For the sawing teeth  14  to move in the direction of extension  12  of the hair-severing edge at an average speed of at least 10 m/s, the reciprocal movement of the sawing teeth  14  preferably has a stroke length between 1 and 30 mm, and the reciprocal movement preferably has a frequency equal to or larger than 330 Hz. The combination of said stroke length and said frequency results in the required average speed of at least 10 m/s. 
     The drive  13  may for instance be a driven resonant system which brings and maintains a mass-spring system in a resonating movement relative to a main body. An example of such a driven resonant system is schematically shown in  FIG.  2    and can be accommodated in a housing portion  24  of the handle  11 . The hair-severing member  9  is movably guided in the direction of extension  12  relative to the support  2  by means of a plurality of guiding members  35  and is attached to a first end of a leaf spring  25  of which an opposite second end is fixedly connected to the support  2 . The leaf spring  25  has a stiffness such that, in combination with the mass of the hair-severing member  9  connected thereto, it is ‘resonant’ in an Eigen frequency that matches the desired frequency of the reciprocal movement of the hair severing member  9  in its direction of extension  12 , for instance 7700 Hz at a stroke length of 1.3 mm. To drive movement at such a high frequency without using a motor revolving at the same rpm or a very high frequency linear electric motor, a rotatable driven drum  37  carrying multiple alternately polarized magnets  26 ,  27  and a counter magnet  28  attached to the leaf spring  25  can be used. In operation, the counter magnet  28  is attracted or pushed away by a passing magnet  26 ,  27  during rotation of the drum  37 . In this example the excitation frequency of the leaf spring  25  is six times the number of rotations per unit of time of the drum  37 . Such a multiplication of the excitation frequency allows use of a standard electric motor for achieving a high excitation frequency. Moreover, the excitation frequency can be an undertone of the Eigen frequency of the mass-spring system formed by the leaf spring  25  and the hair-severing member  9 . 
     In  FIG.  8    a third example of a razor  101  according to the invention is shown. In this example, the hair-severing edges  110  of the hair-severing members  109  have a local direction of extension which varies along the hair-severing edges  110 . Accordingly, the direction of movement of the sawing teeth of the hair-severing edges  110  varies along the hair-severing edges  110 . In particular, each sawing tooth moves in the local direction of extension  112  of the associated hair-severing edge  110  at the position of the sawing tooth. In particular, in this example the sawing teeth of the hair-severing edges  110  move in the respective local directions of extension of the hair-severing edges according to a rotational movement in a single direction. For this purpose, the hair-severing members  109  are provided in the form of circular saw blades having circular hair-severing edges  110 . However, other ways to create a continuous motion in a single direction are also conceivable, such as a band saw and a chain saw system. In all such systems, the hair-severing edges can in principle also be driven so as to move in a reciprocating fashion. 
     To obtain sufficiently long operative sections of the hair-severing edges  110  in a construction that is sufficiently compact for daily use and can easily be taken along when travelling, the hair-severing edges  110  of the hair-severing members  109  preferably have a diameter between 5 and 75 mm. 
     The drive for rotationally driving the hair-severing members  109  is preferably arranged for rotating the hair-severing members  109  about an axis of rotation at speeds of at least 2500 rpm. Such speeds in combination with the diameter of the hair-severing edges  110  as described here before are suitable to achieve the required average velocity of the sawing teeth of at least 10 m/s. 
     In  FIGS.  9  and  10   , a fourth example of a razor  151  according to the invention is shown, in which the movement of the sawing teeth (not individually visible in  FIGS.  9  and  10   ) of the hair-severing edge  160  of the hair-severing member  159  in the local direction of extension  162  of the hair-severing edge  160  is a continuous rotational movement in a single direction. The rotational movement can be along any rotational trajectory, for instance as in a chain-saw or a flexible band-saw. In this example, the hair-severing member  159  is provided in the form of a single circular saw blade to achieve the rotational movement of the hair-severing edge  160 . For protecting the skin from being damaged or irritated by the rotating hair-severing member  159 , a skin-shielding member  178  is provided, which has comb teeth  175  with a skin engagement surface  155  contacting the skin during shaving. Between these comb teeth  175 , open spaces  176  are present into which the skin can bulge into a position close to or slightly in contact with the hair-severing edge  160 . 
     As in the other examples, the hair-severing effect is achieved by sawing through the hairs at or in close proximity to the skin surface. In particular, the sawing teeth of the hair-severing edge  160  do not interact with the comb teeth  175  of the skin shielding member  178  to act as a pair of co-operating hair-cutting teeth as in conventional electrical shaver and trimmers with a moving cutting member moving relative to and co-operating with a stationary cutting member. 
     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. 
     Several features have been described as part of the same or separate embodiments. However, it will be appreciated that the scope of the invention also includes embodiments having combinations of all or some of these features other than the specific combinations of features embodied in the examples. 
     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.