Abstract:
A rotary electric shaver includes an outer cutter having an upper surface with annular shaving sections, formed with hair entry apertures, and an inner cutter having small blades, which rotate in sliding contact with the outer cutter from below the shaving sections. The outer cutter has a plurality of concentric annular shaving sections. The shaving section adjacent to an outer periphery is lower than the shaving section adjacent to a center. The shaving sections are formed on a plane horizontal to a central axis. This makes it possible to increase a shaving area, to precisely trace the curved surface of a concave portion of skin and to come in contact with the skin with a proper contact pressure, thus permitting smooth shaving of the concave portion. The shaver has a simple structure with a smaller number of components, featuring easier assembly and easier removal of hair bits.

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 faces or sections 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 section. The present invention also relates to a manufacturing method of the outer cutter and the inner cutter used with the rotary electric shaver. 
         [0003]    2. Description of the Related Art 
         [0004]    This type of rotary electric shaver is required to be capable of enabling approximately disc-shaped outer cutters to minutely trace the fine irregularities in the skin surface to smoothly shave 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 below the jaw of a user or a wrinkled skin. As a solution to the problem, it is conveniently performed that the areas of the shaving faces or sections have been increased. 
         [0005]      FIG. 6  illustrates two annular shaving sections concentrically formed to increase the shaving area so as to decrease the chances of leaving unshaved portions. Referring to  FIG. 6 , reference numeral  10  denotes an outer cutter and reference numeral  12  denotes an inner cutter. The upper surface (shaving section) of the outer cutter  10  has an annular outside shaving section  16  and an annular inner periphery (adjacent to the center) shaving section  18 , which are concentrically formed around a central axis  20  (the rotational axis of the inner cutter  12 ), an annular groove  14  being provided therebetween. The inner cutter  12  has small blades  22  and  24 , which are in sliding contact with the outer and the inner shaving sections  16  and  18  from below the lower surface thereof and which are integrally formed with the same metal sheet. 
         [0006]    In the unit illustrated in  FIG. 6 , the inner and the outer shaving sections  16  and  18  are positioned on the same plane on which the central axis (the rotational axis)  20  is vertical (on a plane horizontal relative to the central axis  20 ) thereby to permit easy machining of the outer cutter  10  and the inner cutter  12 . In this case, however, when shaving a portion where skin surface concavely curves, as with the portion below a jaw (reference numeral  26  in  FIG. 6  denoting the skin curved surface under the jaw), the annular shaving section  18  adjacent to the center moves away from the skin surface, posing a problem in that the shaving area does not increase as expected. 
         [0007]    To solve the aforesaid problem, according to the one illustrated in  FIG. 7 , an outer annular shaving section  16   a  and an inner periphery annular shaving section  18   a  adjacent to the center are bent into gently curved surfaces along a skin curved surface  26 . In this case, however, the machining of the upper surface of an outer cutter  10   a , i.e., the machining of the two annular shaving sections  16   a  and  18   a , is complicated, and the tips (the top edges) of small blades  22   a  and  24   a  formed on the inner cutter  12   a  have to be curved accordingly. This poses a problem of poor machining efficiency with consequent lower productivity. 
         [0008]    According to the rotary electric shaver illustrated in JP 2008-517696 (A) (corresponding to US 2009-025227A1 and WO 2006/048799), an outer cutter has three concentric annular shaving sections to provide a still larger shaving area than the one illustrated in  FIG. 6  described above. However, the three shaving sections are positioned on the same plane, presenting the same problem as that illustrated in  FIG. 6  (refer to  FIG. 1  and paragraph [0018] (corresponding to paragraph 0021 of US 2009-025227A1)). 
         [0009]    According to the outer cutters disclosed in JP 2008-99770 (A) (corresponding to U.S. Pat. No. 7,845,078B and EP 1914045A) and JP 2001-000755 (A) (corresponding to U.S. Pat. No. 6,460,252B and EP 1063033A1), an outer ring with an outer shaving section formed therein and an inner ring with an inner shaving section formed therein are provided separately, and the inner ring is engaged with the outer ring from below, allowing them to independently move in the vertical direction. The shaving section of each ring is set to be horizontal relative to the central axis so as to permit easy machining thereof. 
         [0010]    As described above, the rotary electric shaver according to the JP 2008-517696 (A) provides a larger area of the shaving sections of the outer cutter, but the upper faces (the shaving section faces) of the outer cutters are on the same plane, so that the innermost or a middle shaving section cannot be brought into close contact with skin surface with a proper contact pressure, as with the example illustrated in  FIG. 6 , presenting the problem of an insufficiently increased substantial shaving area. 
         [0011]    The rotary electric shavers according to the aforesaid JP 2008-99770 (A) and JP 2001-000755 (A) pose problems of complicated structures, a considerably large number of parts, and cumbersome assembly processes, resulting in low production efficiency. In addition, hair debris caught between parts are hard to remove, making the cleaning difficult. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention has been made with a view of the background described above, and it is a first object of the invention to provide a rotary electric shaver which is capable of increasing a shaving area, precisely tracing the curved surface of a concave portion of skin, and coming in contact with the skin with a proper contact pressure to smoothly shave the concave portion, which has a simple structure with a smaller number of components, and which permits easy assembling and also easy removal of hair bits. 
         [0013]    A second object of the invention is to provide a manufacturing method of an outer cutter used with the electric shaver. Further, a third object of the invention is to provide a manufacturing method of an inner cutter used with the electric shaver. 
         [0014]    According to the present invention, the first object is achieved by a rotary electric shaver including an outer cutter, an upper surface of which has annular shaving sections with a plurality of hair entry apertures formed therein, and an inner cutter having a small blade which rotates in sliding contact with the outer cutter from below the shaving section, wherein the outer cutter has a plurality of concentric annular shaving sections integrally formed, a shaving section adjacent to an outer periphery of the outer cutter is lower than a shaving section adjacent to a center of the outer cutter, and these shaving sections are formed on a plane horizontal relative to a central axis of the outer cutter. 
         [0015]    The second object is achieved by a manufacturing method of an outer cutter used with the rotary electric shaver according to claim  1 , including steps of: 
         [0016]    concentrically forming a plurality of annular shaving sections and an annular groove positioned thereamong in a substantially disc-shaped metal material; 
         [0017]    forming slits, which provide hair entry apertures, by a rotary disc-shaped grindstone, which rotates about a horizontal axis while moving across the annular shaving sections substantially in a radial direction, in a plurality of annular shaving sections at the same time; 
         [0018]    grinding/abrading the upper surfaces of the plurality of the annular shaving sections by a grinding/abrasive tool which relatively rotates concentrically with a central axis and which has steps of different heights; and 
         [0019]    grinding/abrading the lower surfaces of the plurality of annular shaving sections by a stepped grinding/abrasive tool which relatively rotates concentrically with the central axis. 
         [0020]    The third object is fulfilled by a manufacturing method of an inner cutter used in the rotary electric shaver according to claim  1 , wherein small blades which slidably contact with a plurality of annular shaving sections from below are integrally formed on a metal plate constituting an inner cutter, and the upper edges of the small blades are ground/abraded by a grinding/abrasive tool which relatively rotates concentrically with the central axis and which has steps, the heights of which vary toward the central axis. 
         [0021]    According to the first aspect of the present invention, the plurality of concentric annular shaving sections or faces is formed on the upper surface of the outer cutter, so that the shaving area is increased to permit improved shaving efficiency. Further, the outer annular shaving section (adjacent to the outer periphery) is low, while the inner annular shaving section (adjacent to the center) is high. This allows all the annular shaving sections to precisely trace the curved surface of a concave portion of skin and to come in contact with the skin surface with an optimum contact pressure, thus making it possible to smoothly shave the concave portion. 
         [0022]    A flat or convex portion of the skin can be smoothly shaved by applying mainly the inner annular shaving section thereto or tilting the entire electric shaver so as to tilt the upper surface (shaving section) thereof with respect to the skin. Further, the respective annular shaving sections are positioned on planes which are horizontal relative to the central axis and the heights of which differ toward the central axis. This simplifies the structures of the outer cutters and the inner cutters, reduces the number of components, and ensures easy assembling. Moreover, hair debris can be easily removed. 
         [0023]    According to the second aspect of the present invention, the plurality of the annular shaving sections and the annular groove thereamong are formed in the metal sheet, which serves as the outer cutter, and the grinding/abrading tool with steps is relatively rotated concentrically with central axis of the outer cutter to grind/abrade the upper and lower surfaces of the outer cutter, thus making the machining easier. 
         [0024]    According to the third aspect of the invention, the small blades that slidably contact with the plurality of annular shaving sections from below are integrally formed on the metal sheet constituting the inner cutter, and the upper edges of the small blades are ground/abraded by the grinding/abrasive tool which rotates concentrically with the central axis and which has steps having heights that differ toward the central axis. This permits easy machining of the inner cutter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a perspective view illustrating the appearance of an embodiment of the present invention; 
           [0026]      FIG. 2  is a sectional view of a cutter assembly as seen in  FIG. 1 ; 
           [0027]      FIG. 3  is an enlarged partial sectional view of an outer cutter according to the embodiment of the present invention, illustrating the machining method of slits; 
           [0028]      FIG. 4  is a sectional view illustrating the grinding/abrading method of an outer cutter according to an embodiment of the present invention; 
           [0029]      FIG. 5  is another sectional view illustrating the grinding/abrading method of an inner cutter according to an embodiment of the present invention; 
           [0030]      FIG. 6  is a sectional view of a conventional cutter assembly; and 
           [0031]      FIG. 7  is a sectional view of another conventional cutter assembly. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    The annular shaving sections in the outer cutter may be arranged in two concentric circles or three or more concentric circles. The hair entry apertures formed in the shaving sections of the outer cutter may be in the form of slits. The slits can be efficiently formed in all the shaving sections in a single step by moving a rotary disc grindstone, which rotates about a horizontal axis, in the radial direction thereof 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 later. 
         [0033]    In the inner cutter, the plurality of the small blades having different radii of rotation corresponding to all the annular shaving sections may be cut and raised to be integrally formed on the same metal plate, thus simplifying the structure of the inner cutter. In this case, as the rotary disc grindstone moves, the center of rotation thereof is moved vertically (in parallel to the central axis of the outer cutter) to form slits only in the annular shaving sections without cutting the annular groove. The annular groove is not to be cut, because it functions to support and reinforce adjoining annular shaving sections. 
       First Embodiment 
       [0034]    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 . 
         [0035]    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 sections (the upper surface of a cutter frame  60 , which will hereinafter be described in detail) 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 A, which will be described hereinafter, and elastically pushes up the inner cutter  12 A upward thereby to properly maintain the contact pressure of small blades  22 A and  24 A against the lower surfaces of shaving sections  16 A and  18 A. 
         [0036]    The head unit  58  has a 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. 
         [0037]    More specifically, each of the cutter assemblies  62  includes an outer cutter  10 A 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 A is fitted ( FIG. 1 ), and an inner cutter  12 A which is in sliding contact with the outer cutter  10 A from below ( FIG. 2 ). The inner cutter  12 A 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. 
         [0038]    The upper surface of the outer cutter  10 A has two annular shaving sections  16 A and  18 A formed concentrically with a central axis  20 A, and an annular groove  14 A formed therebetween, as illustrated in  FIG. 2 . Referring to the two annular shaving sections  16 A and  18 A, the inner shaving section  18 A is above the level of the outer shaving section  16 A along the central axis  20 A, and these shaving sections  16 A and  18 A are positioned on horizontal planes orthogonal to the central axis  20 A. In other words, these shaving sections  16 A and  18 A are positioned on horizontal planes which have different heights along the central axis  20 A. Reference numeral  26 A in  FIG. 2  denotes a curved surface of skin which is concavely recessed. 
         [0039]    As illustrated in  FIG. 1 , formed in the outer cutter  10 A in the radial direction are many slits  65  which provide hair entry apertures, and the upper surface of the outer cutter  10 A projects out beyond the outer cutter rim  64 . The slits  65  are formed by a rotary disk grindstone  66 , as illustrated in  FIG. 3 . More specifically, a metal sheet (metal material) that is to be turned into the outer cutter  10 A is pressed to form the two shaving sections  16 A and  18 A and the annular groove  14 A 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 sections  16 A and  18 A, from above, leaving the annular groove  14 A intact. 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. 
         [0040]    The rotary disk grindstone  66  first forms the two annular shaving sections  16 A and  18 A simultaneously to a depth along a first machining line  68  in  FIG. 3 . 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. 3 ) 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  in the outer annular shaving section  16 A 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. 3 , 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 . 
         [0041]    In this state, the portions which are to be formed into the annular shaving sections  16 A and  18 A have the thickness of the metal sheet of the outer cutter  10 A, and will be machined to sufficiently thin annular shaving sections  16 A and  18 A by grinding the portions corresponding to the annular shaving sections  16 A and  18 A in the next step or by abrading the portions after the next step. 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 A. The tool  72  has a step corresponding to the difference in height between the annular shaving sections  16 A and  18 A, thereby machining the upper surface, as illustrated in  FIG. 4 . 
         [0042]    Further, the lower surfaces of the annular shaving sections  16 A and  18 A can be machined by rotating a grinding/abrading  74 , which has a step corresponding to the difference in height therebetween, about the central axis  20 A in the same manner as described above. Referring to  FIG. 4 , the dashed lines  16 A and  18 A denote the upper surfaces of the shaving sections (the surfaces to come in contact with skin) and the dashed lines  16 B and  18 B denote the lower surfaces of the shaving sections (the surfaces against which the small blades  22 A and  24 A of the inner cutter  12 A slide, that is, the sliding surfaces of the inner cutter). It is needless to say that the outer cutter  10 A may be rotated instead or together when the grinding/abrasive tool  72  or  74  is rotated. 
         [0043]    Referring to  FIG. 5 , in the inner cutter  12 A, the small blades  22 A and  24 A, which slidably contact with the lower surfaces (the inner cutter sliding surfaces)  16 B and  18 B of the shaving sections  16 A and  18 A, are integrally formed on a same metal plate  12 B. The upper edges of the small blades  22 A and  24 A 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. For this purpose, the metal plate  12 B, which is to be formed into the inner cutter, can be machined by relatively rotating a grinding/abrasive tool  76 , which has a step corresponding to the height difference, about the central axis  20 A. Dashed lines  22 B and  24 B in  FIG. 5  indicate the upper edges (blade surfaces) machined by the grinding/abrasive tool  76 .