Abstract:
A rotary electric shaver includes an outer cutter which has an upper surface with annular shaving faces, in which many hair-entry apertures are formed, and an inner cutter having small blades, which rotate in sliding contact with the lower surface of the outer cutter from below the shaving faces. The outer cutter ( 10 ) has a plurality of concentric annular shaving faces ( 16, 18 ), which are integrally formed therewith. The density of the hair-entry apertures ( 65 ) is varied in the circumferential direction of the plurality of annular shaving faces ( 16, 18 ). The rotary electric shaver increases the shaving area of the outer cutter to improve shaving efficiency and also restrains excessively close shaving thereby to protect skin even when the contact pressure of an area near the center of the outer cutter against skin increases.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a rotary electric shaver and, more particularly, to a rotary electric shaver having an outer cutter, which has annular shaving sections or faces with many hair-entry apertures formed therein, and an inner cutter having small blades which rotate in sliding contact with the outer cutter from below the shaving faces. 
         [0003]    2. Description of the Related Art 
         [0004]    This type of rotary electric shaver is required to be capable of enabling an approximately disc-shaped outer cutter thereof to minutely trace the fine irregularities of skin surface according to the characteristics of beard, which differ from user to user, so as to smoothly shave the beard without leaving any unshaved places. For example, there is a problem in that chances of leaving unshaved areas tend to increase in a markedly uneven skin surface, such as an area under the jaw of a user or a wrinkled skin. Further, pressing the outer cutter excessively firmly against the skin surface could result in excessively close shaving, damaging the skin. 
         [0005]    JP 2000-509628(A) (corresponding to WO 98/35794 and US 2001/0039734A1) discloses a shaving apparatus having a plurality of outer cutters, each of which has a single annular shaving face (also referred to as a single track). The patent discloses outer cutters having different densities of apertures serving as hair-entry apertures in the annular shaving faces thereof (an aperture ratio, which is the ratio of the aperture area with respect to a shaving area, i.e., (aperture area)/(shaving area)). In one type, the aperture density decreases toward the center (in the vicinity of a portion wherein the plurality of outer cutters is close to each other) of a cutter frame (outer cutter frame), while in another type, the aperture density increases toward the center. More specifically, the outer cutters have different types of hair-entry apertures (hair input apertures), including a type for cutting long hair and another type for cutting short hair, the same type of shaving faces of different outer cutters being disposed at positions where they face each other. 
         [0006]    JP 2006-510430(A) (corresponding to WO 2004/056539 and U.S. Pat. No. 7,269,902B and EP 1578567A1) discloses shaving apparatuses in which each of the plurality of outer cutters in JP 2000-509628(A) is made rotative and the outer cutters rotate such that the hair-entry apertures of the same type in different outer cutters are disposed in positions where they face each other (adjacently to the center of the cutter frame). More specifically, the outer cutters are rotatively moved by a frictional force produced when inner cutters rotate, and projections provided on the outer peripheries of the outer cutters are abutted against control members, thereby fixing the positions thereof in the direction of rotation of the outer cutters. In this case, the control members are engaged with or disengaged from the projections to change the rotating positions of the outer cutters. 
         [0007]    JP 2004-515283(A) (corresponding to WO 02/45920A1 and U.S. Pat. No. 6,868,611B) discloses a shaving apparatus in which the upper surface of a decorative cover (a skin support area) installed at the center adjacent to the inner periphery of an annular outer cutter shaving face is provided with ridges in a partial angular area in the peripheral direction close to the inner periphery of the outer cutter shaving face. The ridges reduce the contact pressure of the shaving face against skin, thereby protecting skin. More specifically, the ridges push the skin that comes in contact the ridges in a direction away from the shaving face to reduce the contact pressure of the shaving face close to the outer side of the ridges. 
         [0008]    All the shaving apparatuses disclosed in the three patents described above has a single annular shaving face or section in the outer cutter thereof, posing a problem of significant limitation in increasing the shaving area with resultant limited improvement in shaving efficiency. The shaving area could be increased by providing double (multiple) annular shaving faces. In this case, however, since a skin surface normally bulges out, vertically pressing the upper surface of the outer cutter against the skin would cause the portion near the center of the outer cutter, that is, the inner annular shaving face, to be firmly applied to the skin. Hence, especially when the contact pressure of the outer cutter is increased, a problem could arise in that the inner annular shaving face leads to excessively close shaving, damaging the skin. 
         [0009]    According to the one disclosed in JP 2000-509628(A), the hair-entry apertures of the same type in the plurality of outer cutters are disposed in opposing positions. If multiple shaving faces are formed in each of the outer cutters, then the contact pressure in the vicinity of the center of each outer cutter will increase, leaving the aforesaid problem unsolved. 
         [0010]    According to the one disclosed in JP 2006-510430(A), the plurality of outer cutters could be rotated simultaneously and control could be carried out such that the shaving faces of the same type of the outer cutters oppose each other. However, firmly pressing the plurality of outer cutters vertically against flat skin at the same time would cause an increase in the contact pressure in the vicinity of the center of each outer cutter, leading to the same problem as that described in the JP 2000-509628(A). According to the JP 2004-515283(A), the ridges provided on the central decorative cover (the skin support area) limit the increase of the shaving area, thus limiting the improvement in the shaving efficiency. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention has been made with a view of the background described above, and it is an object of the invention to provide a rotary electric shaver capable of increasing the shaving area of an outer cutter to improve shaving efficiency and preventing excessively close shaving thereby to protect skin surface even if the contact pressure applied to the skin from the vicinity of the center of an outer cutter increases when the outer cutter is firmly pressed vertically against the skin. 
         [0012]    According to the present invention, the object is fulfilled by a rotary electric shaver including an outer cutter, an upper surface of which has annular shaving faces with a plurality of hair-entry apertures formed therein, and an inner cutter having a small blade which rotates in sliding contact with a lower surface of the outer cutter from below the shaving face, wherein the outer cutter has a plurality of concentric annular shaving faces integrally formed, and the density of the hair-entry apertures varies in the circumferential direction of the plurality of annular shaving faces. 
         [0013]    According to the present invention, the plurality of concentric annular shaving faces or sections are formed on the upper surface of the outer cutter, so that the shaving area is increased to permit improved shaving efficiency. An electric shaver is usually used by moving it in contact with skin (slid on the surface of skin), so that slightly moving the outer cutter will cause shaving faces of different aperture densities to come in contact with the same area of skin in sequence or repeatedly. At this time, the aperture densities of the plurality of shaving faces vary in the circumferential direction, so that the shaving faces of different aperture densities will come in contact with the same place of the skin in sequence or repeatedly by slightly moving the outer cutter relative to the skin or slightly rotating a grip or a main unit about the outer cutter to move the position of the contact of the outer cutter on the surface of the skin. Thus, even when the outer cutter is brought into firm contact with the outer cutter, the chances of damaging the skin due to excessively close shaving will be minimized, because the area in which the aperture density is high will not be in constant contact. 
         [0014]    The annular shaving faces or sections formed in the outer cutter may be arranged in two concentric circles or three or more concentric circles. To change the aperture density in the circumferential direction, two or more areas wherein the density of the hair-entry apertures is minimal may be provided at equiangular intervals around the annular shaving face. The portions with the minimum aperture density may be formed of smooth metal surfaces (blanks) free of apertures. In this case, the blanks are provided at two or more locations at equidistant intervals in the circumferential direction. In place of the blanks, areas with an extremely low aperture density may be provided. The blanks or the areas with an extremely low aperture density allow highly smooth slide on a skin surface. Hence, excessively close shaving will be restrained, thus maximizing the advantages of the present invention by moving the outer cutter. 
         [0015]    To vary the aperture density in the circumferential direction, a full annular shaving face may be circumferentially divided into two or more equal segments and the aperture density within the angular range of each of the equal segments may be continuously changed in a fixed rotational direction. This is ideal for a user who has a habit of rotating a shaver while laterally swinging the grip with the outer cutter thereof applied to his skin surface. More specifically, such a habit causes the aperture density of the portion that comes in contact with a shaving portion of skin to constantly change in continuity as the outer cutter is moved, so that excessively close shaving is restrained while maintaining smooth shaving, thus permitting protection of the skin. 
         [0016]    Arranging changes in the density of the hair-entry apertures, which are provided in an outer periphery annular shaving face and an inner periphery annular shaving face, in the circumferential direction automatically arranges changes in the aperture densities on the outer peripheral side and the inner peripheral side in a radial direction, thus further maximizing the advantages. For example, arranging the blank areas on the outer peripheral side and the inner peripheral side in the radial direction leads to smoother slide of the outer cutter, so that chances of excessively close shaving can be minimized, resulting further improved protection of skin. 
         [0017]    The density of the hair-entry apertures formed in the shaving face on the outer peripheral side is preferably higher than the density of the hair-entry apertures formed in the shaving face on the inner peripheral side. This is because the danger of excessively close shaving or damaging skin by the hair-entry apertures on the outer peripheral side is reduced even if the contact pressure on the inner peripheral side increases when the outer cutter is pressed against a convex portion of skin. 
         [0018]    The hair-entry apertures in the shaving faces of the outer cutter may be in the form of slits. The slits can be efficiently formed in all the annular shaving faces in a single step by moving a rotary disk grindstone, which rotates about a horizontal axis, in the radial direction of the outer cutter (the annular shaving faces) or by moving it while slightly tilting it in the radial direction (substantially in the radial direction) when machining the outer cutter, which will be discussed hereinafter. The directions of the slits do not necessarily have to be precisely the radial direction of the outer cutter, and may be at an angle relative to the radius, which will be referred to also as the radial direction. 
         [0019]    Setting the angles of the slit intervals in the circumferential direction in the shaving face on the outer peripheral side to be smaller than those of the slit intervals in the shaving face on the inner peripheral side makes it possible to set the density of the hair-entry apertures formed in the shaving face on the outer peripheral side to be higher than the density of the hair-entry apertures formed in the shaving face on the inner peripheral side. 
         [0020]    For example, the aperture density of the shaving face on the outer peripheral side can be increased by providing common hair-entry slits positioned on a common straight line and formed on the inner periphery shaving face and the outer periphery shaving face, respectively, and a non-common hair-entry slit on the outer peripheral side that is formed in the outer periphery shaving face and positioned between the common hair-entry slits. In this case, using the same opening width of the slits allows the same machining tool (e.g., a rotary disk grindstone) to be conveniently used. Alternatively, however, the opening width of the slits may be varied. 
         [0021]    Setting the shaving face on the outer peripheral side and the shaving face on the inner peripheral side to have different heights in the direction of the rotational axis of the inner cutter makes it possible to obtain a proper pressure of contact with skin. For example, setting the shaving face on the inner peripheral side to be higher than the shaving face on the outer peripheral side in the direction of the rotational axis of the inner cutter makes it possible to increase the skin contact pressure of the shaving face on the inner peripheral side, and smooth slide is ensured because of the lower aperture density of the shaving face on the inner peripheral side. Thus, excessively close shaving can be restrained to protect skin. Conversely, if the shaving face on the inner peripheral side is set to be lower than or substantially the same height as the shaving face on the outer peripheral side in the direction of the rotational axis of the inner cutter, then proper contact with a convex portion of skin can be accomplished. 
         [0022]    As described above, further versatile shaving features can be obtained by changing the aperture densities on the outer peripheral side and the inner peripheral side in addition to using different aperture densities in the circumferential direction on the inner peripheral side and the outer peripheral side of the outer cutter, or combining the different heights of the outer periphery annular shaving face and the inner periphery annular shaving face, respectively. This enables the shaver to be adapted more properly to user&#39;s preferences and other characteristics, including the type of his beard. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a perspective view illustrating the appearance of a rotary electric shaver according to an embodiment of the present invention; 
           [0024]      FIG. 2  is a diagram illustrating a layout example of hair-entry apertures of an outer cutter of the electric shaver in  FIG. 1 ; 
           [0025]      FIG. 3  is a sectional view of a cutter assembly of the electric shaver in  FIG. 1 ; 
           [0026]      FIG. 4  is a partial enlarged sectional view of the outer cutter shown in  FIG. 3  and illustrates the machining method of slits; 
           [0027]      FIG. 5  is a sectional view illustrating the grinding/abrading method of an outer cutter according to the embodiment of the present invention; 
           [0028]      FIG. 6  is a sectional view illustrating the grinding/abrading method of an inner cutter according to the embodiment of the present invention; and 
           [0029]      FIG. 7  is a diagram illustrating the layout of hair-entry apertures of an outer cutter of a rotary electric shaver according to another embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment  
       [0030]    Referring to  FIG. 1 , a main body  50  has a case  54  formed by curving an upper portion of a grip  52 , which is approximately columnar, diagonally upward to the front. The case  54 , which can be split into a front counterpart and a back counterpart, houses a chargeable battery, an electric motor, a control circuit board and the like (not shown). A power switch  56  is attached to the front surface of the case  54 . A display (not shown) composed of LED lamps indicating the amount of remaining charge of the battery, an operation status and the like is located under the switch  56 . The display can be seen from outside through a translucent portion  54 A of the case  54 . 
         [0031]    A head unit  58  is openably and detachably attached to an upper portion of the case  54 . The head unit  58  is inclined relative to the grip  52  of the case  54  such that the shaving faces (the upper surface of a cutter frame  60 , which will be discussed later) are directed diagonally upward to the front. The electric motor has its rotation output shaft protruded from the upper surface of the case  54  into the head unit  58 , rotatively drives an inner cutter  12 , which will be discussed later, and elastically pushes up the inner cutter  12  upward thereby to properly maintain the contact pressure of small blades  22  and  24  against the lower surfaces of shaving faces  16  and  18 . 
         [0032]    The head unit  58  has the cutter frame (outer cutter frame)  60  openably attached to the upper face of the case  54 , and three sets of cutter assemblies  62  are installed to the cutter frame  60 . The cutter frame  60  is approximately triangular in a planar view, the peripheral edge thereof being gently curved downwards. The cutter frame  60  has three circular mounting ports in which the cutter assemblies  62  are movably retained such that they may be tilted and also exhibit the habit of returning upwards. 
         [0033]    More specifically, each of the cutter assemblies  62  includes an outer cutter  10  which has a substantially discoid shape and the periphery of which is bent downwards, an outer cutter rim  64  in which the outer periphery of the outer cutter  10  is fitted ( FIG. 1 ), and an inner cutter  12  which is in sliding contact with the outer cutter  10  from below ( FIG. 3 ). The inner cutter  12  is rotatively retained on the cutter assembly  62  such that it does not come off downwards and is rotatively driven by the electric motor, as described above. 
         [0034]    The upper surface of the outer cutter  10  has an annular groove  14  formed concentrically with a central axis  20  and two annular shaving sections or faces  16  and  18  formed on an outer side and an inner side of the annular groove  14 , as illustrated in  FIGS. 2 and 3 . Referring to the two annular shaving faces  16  and  18 , the inner periphery shaving face  18  is taller than the outer periphery shaving face  16  along the central axis  20 , and these shaving faces  16  and  18  are positioned on planes horizontal to the central axis  20 . In other words, these shaving faces  16  and  18  are positioned on horizontal planes which have different heights along the central axis  20 . 
         [0035]    As illustrated in  FIGS. 1 and 2 , formed in the outer cutter  10  in the radial direction are many slits  65  ( 65 A and  65 B), which provide hair-entry apertures, the upper surface of the outer cutter  10  projecting out beyond the outer cutter rim  64 . The slits  65  are formed by a rotary disk grindstone  66 , as illustrated in  FIG. 4 . More specifically, a metal sheet (metal material) that is to be turned into the outer cutter  10  is pressed to form the two annular shaving faces  16  ( 16 A) and  18  ( 18 A) and the annular groove  14  positioned therebetween, and then the rotary disk grindstone  66  cuts in the portions of the pressed metal material which are to be formed into the annular shaving faces  16 A and  18 A, from above, leaving the annular groove  14  intact. At this time, the rotary disk grindstone  66  is moved substantially in the radial direction while being rotated with the outer periphery thereof set vertically. The rotary disk grindstone  66  is a thin disc-shaped tool made by dispersing wear-resistant particles, such as diamond abrasive grains, in the abrasive grains, which are then hardened. 
         [0036]    First, the rotary disk grindstone  66  forms the two annular shaving faces  16  and  18  at the same time to a depth along a first machining line  68  in  FIG. 4 . More specifically, a center of rotation A of the rotary disk grindstone  66  is moved substantially in the radial direction (in the direction of a movement line  68   a  in  FIG. 4 ) such that the outer periphery (cutting edge) of the rotary disk grindstone  66  moves along a first machining line  68 . To form only the slits  65  ( 65 B) in the outer peripheral annular shaving face  16  selectively deeply, the center of rotation A is moved to position B so as to cause the outer periphery of the rotary disk grindstone  66  to move along a second machining line  70  shown in  FIG. 4 , and then the center B is moved substantially in the radial direction along a movement line  70   a  parallel to the second machining line  70 . 
         [0037]    In the present embodiment, the aperture density (aperture ratio) of the annular shaving face  18  ( 18 A) on the inner peripheral side is lower than the aperture density of the annular shaving face on the outer peripheral side. More specifically, the slits  65 A,  65 A on the inner peripheral side and the slit  65 A on the outer peripheral side are formed as common linear slots (common hair-introduction slits) on a common straight line  67 A ( FIG. 2 ) by machining along the first machining line  68  in  FIG. 4 , and non-common linear slits (non-common hair-introduction slits)  65 B are formed along the second machining line  70  on non-common straight lines  67 B only in the outer periphery shaving face  16 . In this case, the same rotary disk grindstone  66  can be used for machining the slits  65 A and  65 B, which share the same aperture width. 
         [0038]    If the non-common linear slits  65 B are formed one each between the common linear slits  65 A, then the number of the slits in the outer periphery shaving face  16  will be double the number of the slits in the inner periphery shaving face ( 18 A), provided that there are an even number of the common linear slits  65 A. Thus, the aperture density on the outer peripheral side can be made higher than the aperture density on the inner peripheral side. 
         [0039]    In this state, the portions which are to be formed into the annular shaving faces  16 A and  18 A have the thickness of the metal sheet of the outer cutter  10 , and will be machined to sufficiently thin annular shaving faces  16 A and  18 A ( FIG. 5 ) by grinding the portions corresponding to the annular shaving faces  16 A and  18 A in the next step or by polishing the portions thereafter. The upper surfaces of the shaving sections  16 A and  18 A can be machined by rotating a grinding tool, such as a turning tool, or a abrasive tool (referring also to a grinding/abrasive tool to include both)  72 , such as a grindstone, about the central axis  20 . The tool  72  has a step corresponding to the difference in height between the annular shaving faces  16 A and  18 A, as illustrated in  FIG. 5 . 
         [0040]    Further, the lower surfaces of the annular shaving faces  16  and  18  can be machined by rotating a grinding/abrasive tool  74 , which has a step corresponding to the difference in height therebetween, about the central axis  20  in the same manner as described above. Referring to  FIG. 5 , the dashed lines  16 A and  18 A denote the upper surfaces of the shaving faces (the surfaces to come in contact with skin) and the dashed lines  16 B and  18 B denote the lower surfaces of the shaving faces (the surfaces against which the small blades  22  and  24  of the inner cutter  12  slide, that is, the sliding surfaces of the inner cutter). It is needless to say that the outer cutter  10  may be rotated instead or together when the grinding/abrasive tool  72  or  74  is rotated. 
         [0041]    Referring to  FIG. 3 , in the inner cutter  12 , the small blades  22  and  24 , which slidably contact with the lower surfaces (the inner cutter sliding surfaces)  16 B and  18 B of the shaving faces  16 A and  18 A, are integrally formed on a same metal plate  12 A. The upper edges of the small blades  22  and  24  slidably contact with the lower surfaces  16 B and  18 B, which are the inner cutter sliding surfaces, to cut the hair that enters the slits  65 . It is necessary, therefore, to match the heights of the upper edges with the heights of the inner cutter sliding surfaces  16 B and  18 B and also to abrade them so as to improve their sharpness beforehand. For this purpose, the metal plate  12 A, which is to be formed into the inner cutter, can be machined by relatively rotating a grinding/abrasive tool  76  ( FIG. 6 ), which has a step corresponding to the height difference, about the central axis  20 . Dashed lines  22 A and  24 A in  FIG. 6  indicate the upper edges (blade surfaces) machined by the grinding/abrasive tool  76 . 
         [0042]    In the present embodiment, the slits  65  are laid out unevenly in the circumferential direction. As illustrated in  FIG. 2 , the outer periphery shaving face  16  and the inner periphery shaving face  18  have areas with a lower aperture density, such as smooth areas free of slits (blanks or areas  16 C and  18 C with an extremely low slit density), provided at eight locations at predetermined intervals in the circumferential direction of the shaving faces  16  and  18 . The outer periphery blank areas  16 C and the inner periphery blank areas  18 C are radially arranged in the circumferential direction. Hence, the blank areas  16 C and  18 C do not cause deteriorated smoothness on skin, permitting improved shaving smoothness especially when moving the outer cutter  10  parallel to skin. 
         [0043]    In areas  10 A between the blanks  16 C and  18 C, the densities of the slits  65  in the circumferential direction are fixed. Further, the number of the slits  65  on the inner peripheral side is smaller than the number of the slits  65  on the outer peripheral side (the former is half the latter in the embodiment illustrated in  FIG. 2 ), thus minimizing the danger of causing damage to skin even if the pressure of contact with skin increases because of the inner shaving face ( 18 A) being higher than the outer shaving face  16  ( 16 A). 
       Second Embodiment  
       [0044]      FIG. 7  illustrates a second embodiment, in which shaving faces  16  and  18  of each of outer cutters  10  are divided into four segments  10 B in the circumferential direction. In each of the areas  10 B, the density of slits  65  ( 65 A and  65 B) is gradually changed in the circumferential direction. In this embodiment, the slit density has been gradually changed from high to low in the circumferential direction. Further, in an inner periphery shaving face  18  and an outer periphery shaving face  16 , areas with low slit densities (smooth blank areas free of slits)  16 C and  18 C are radially arranged in the circumferential direction. In  FIG. 7 , the same components as those shown in  FIG. 2  are assigned the same reference numerals, and the descriptions thereof will not be repeated. 
         [0045]    According to the present embodiment, at the time of shaving by shuttling each of the outer cutters  10  in the direction of rotation about a central axis  20  within the range of the divided area  10 B, the density of the slits that come in contact with skin changes, thereby obviating the danger of damage to the skin. In addition, the number of the slits  65  on the inner peripheral side is smaller than the number of the slits  65  on the outer peripheral side (the former is half the latter in the embodiment illustrated in  FIG. 7 ), thus minimizing the danger of causing damage to skin even if the pressure of contact with skin increases because of the inner shaving face  18  being higher than the outer shaving face  16 .