Abstract:
A sharpening device operable to maintain a stable angle of a cutting edge during sharpening is disclosed. A sharpening member reciprocates parallel to a first direction. The sharpening member comprises a sharpening surface comprising at least one groove along the first direction. Reciprocation can reduce a presence of a sharpening residue on the sharpening surface while maintaining a stable sharpening angle of a cutting edge.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2009-077088, filed on Mar. 26, 2009, entitled SHARPENER, Japanese Patent Application No. 2009-268245, filed on Nov. 26, 2009, entitled SHARPENER, and Japanese Patent Application No. 2010-015205, filed on Jan. 27, 2010, entitled SHARPENER, each of which is incorporated by reference herein in its entirety. 
     FIELD 
     An embodiment of the present disclosure relates generally to a sharpener, and more particularly to a sharpener that sharpens a cutting edge of a cutting device. 
     BACKGROUND 
     A sharpening device generally modifies a cutting edge of a cutting device to an appropriate shape. The sharpening device generally operates by grinding or abrading away material on the cutting edge with an abrasive substance harder than the material of the cutting edge. A polishing process may also be applied to the cutting edge to increase smoothness and correct for possible deformations. 
     A manual sharpener generally comprises a sharpening stone comprising a sharpening surface with abrasive grains and a surface without abrasive grains, the surface without abrasive grains comprises a groove. The groove generally extends along a direction substantially perpendicular to a sharpening direction. With the manual sharpener, a sharpening residue generated by sharpening with the sharpening stone may remain on the sharpening surface, and may reduce an effectiveness of the sharpening surface. 
     An electric knife sharpener generally comprises a rotational sharpening member coupled to an output shaft of an electric motor. The rotational sharpening member rotates and contacts the cutting edge of the cutting device, thereby sharpening the cutting edge of the cutting device. In the electric knife sharpener, the cutting edge to be sharpened may be repelled by the rotational sharpening member. If the cutting edge is repelled, an angle at which the cutting edge is sharpened may not be stable, thereby reducing a cutting quality of the cutting edge. 
     Therefore, there is a need for a sharpener that maintains a stable angle of the cutting edge during sharpening. 
     SUMMARY 
     A sharpening device operable to maintain a stable angle of a cutting edge during sharpening is disclosed. A sharpening member reciprocates parallel to a first direction. The sharpening member comprises a sharpening surface comprising at least one groove along the first direction. Reciprocation can reduce a presence of a sharpening residue on the sharpening surface while maintaining a stable sharpening angle of a cutting edge. 
     A first embodiment comprises a sharpener. The sharpener comprises a sharpening member reciprocating in a first direction and comprising a sharpening surface with a groove along the first direction. 
     A second embodiment comprises a sharpener. The sharpener comprises sharpening means operable to reciprocate in a first direction and comprising a sharpening surface with a groove along the first direction. 
     A third embodiment comprises a method of sharpening. The method comprises reciprocating a sharpening member in a first direction, the sharpening member comprising a sharpening surface with a groove along the first direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present disclosure are hereinafter described in conjunction with the following figures, wherein like numerals denote like elements. The figures are provided for illustration and depict exemplary embodiments of the present disclosure. The figures are provided to facilitate understanding of the present disclosure without limiting the breadth, scope, scale, or applicability of the present disclosure. The drawings are not necessarily made to scale. 
         FIG. 1  is an illustration of a perspective view of an exemplary sharpener according to an embodiment of the present disclosure. 
         FIG. 2  is an illustration of a top view of the sharpener shown in  FIG. 1 . 
         FIG. 3  is an illustration of a side view of the sharpener shown in  FIG. 2 . 
         FIG. 4  is an illustration of a perspective view of an exemplary sharpening member according to an embodiment of the present disclosure. 
         FIG. 5  is an illustration of a front view of the sharpening member shown in  FIG. 4 . 
         FIG. 6  is an illustration of a top view of the sharpening member shown in  FIG. 4 . 
         FIG. 7  is an illustration of a side view of the sharpening member shown in  FIG. 4 . 
         FIG. 8  is an illustration of a fragmentary sectional view taken along line A-A of the sharpening member shown in  FIG. 7 . 
         FIG. 9A  is an illustration of an enlarged schematic view of a sharpening surface according to an embodiment of the present disclosure, showing a state of the sharpening surface with insufficient open pores. 
         FIG. 9B  is an illustration of a state of a sharpening surface with insufficient open pores. 
         FIG. 9C  is an illustration of a state of a sharpening surface with excessive open pores. 
         FIG. 10  is an illustration of a plan view of an exemplary sharpening member according to an embodiment of the present disclosure. 
         FIG. 11A  is an illustration of a sectional view taken along line X-X of the sharpening member shown in  FIG. 10 . 
         FIG. 11B  is an illustration of a sectional view taken along line Y-Y of the sharpening member shown in  FIG. 10 . 
         FIG. 11C  is an illustration of a front view of the sharpening member shown in  FIG. 10  when viewed in a direction indicated by arrow B. 
         FIG. 12  is an illustration of a perspective view of an exemplary sharpener according to an embodiment of the present disclosure. 
         FIG. 13  is an illustration of a top view of the sharpener shown in  FIG. 12 . 
         FIG. 14  is an illustration of a side view of the sharpener shown in  FIG. 12 . 
         FIG. 15  is an illustration of a perspective view of an exemplary sharpener according to an embodiment of the present disclosure. 
         FIG. 16  is an illustration of a top view of the sharpener shown in  FIG. 15 . 
         FIG. 17  is an illustration of a side view of the sharpener shown in  FIG. 15 . 
         FIG. 18  is an illustration of an enlarged sectional view taken along line Z-Z in  FIG. 15 ,  FIG. 18  illustrating the relationship between a partition structure of a guide plate and a sharpening member. 
         FIG. 19A  is an illustration of a side view briefly showing a sharpening state when a portion near a first end of the sharpener shown in  FIG. 15  is used. 
         FIG. 19B  is an illustration of a side view briefly showing a sharpening state when a portion near a second end of the sharpener shown in  FIG. 15  is used. 
         FIG. 20A  is an illustration of a top view of  FIG. 19A . 
         FIG. 20B  is an illustration of a top view of  FIG. 19B . 
         FIGS. 21A to 21C  are illustrations of sectional views briefly illustrating protruding amounts of sharpening members when the sharpening members are rotated according to an embodiment of the present disclosure. 
         FIG. 22A  is an illustration of an exploded perspective view of an exemplary sharpener according to an embodiment of the present disclosure. 
         FIG. 22B  is an illustration of an exploded perspective view of a grip of the sharpener shown in  FIG. 22A . 
         FIG. 23  is an illustration of a front view of an exemplary sharpener according to an embodiment of the present disclosure. 
         FIG. 24A  is an illustration of a plan view of an exemplary sharpening member according to an embodiment of the present disclosure. 
         FIG. 24B  is an illustration of a plan view of an exemplary sharpening member according to an embodiment of the present disclosure 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description is presented to enable a person of ordinary skill in the art to make and use the embodiments of the disclosure. The following detailed description is exemplary in nature and is not intended to limit the disclosure or the application and uses of the embodiments of the disclosure. Descriptions of specific devices, techniques, and applications are provided only as examples. Modifications to the examples described herein will be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the disclosure. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. The present disclosure should be accorded scope consistent with the claims, and not limited to the examples described and shown herein. 
     Embodiments of the disclosure are described herein in the context of one practical non-limiting application, namely, a knife sharpener. Embodiments of the disclosure, however, are not limited to such sharpeners, and the techniques described herein may also be utilized in other applications. For example, embodiments may be applicable to broach sharpeners, pencil sharpeners, and the like. 
     As would be apparent to one of ordinary skill in the art after reading this description, these are merely examples and the embodiments of the disclosure are not limited to operating in accordance with these examples. Other embodiments may be utilized and structural changes may be made without departing from the scope of the exemplary embodiments of the present disclosure. 
       FIG. 1  is an illustration of a perspective view showing an exemplary sharpener  8  according to an embodiment of the present disclosure.  FIG. 2  is a top view of the sharpener  8 .  FIG. 3  is a side view of the sharpener  8 . 
     The sharpener  8  comprises a grip  2  and a sharpening member  3 . The sharpening member  3  is coupled to an output shaft  1   a  extending from the grip  2  to the outside. The sharpening member  3  reciprocates in a first direction  5 . 
       FIG. 4  is an illustration of a perspective view of the exemplary sharpening member  3 .  FIG. 5  is an illustration of a front view of the sharpening member  3 .  FIG. 6  is an illustration of a top view of the sharpening member  3 .  FIG. 7  is an illustration of a side view of the sharpening member  3 .  FIG. 8  is an illustration of a fragmentary sectional view taken along line A-A in  FIG. 7 . 
     Referring to  FIGS. 4 and 5 , the sharpening member  3  is a columnar member, and comprises a flat portion  3   b  and a curved portion  3   c . Referring to  FIGS. 6 and 7 , the flat portion  3   b  and the curved portion  3   c  each comprise a sharpening surface  3   d  and a plurality of the grooves  3   a.    
     The sharpening surface  3   d  sharpens a cutter  15 . The sharpening surface  3   d  is substantially parallel to the first direction  5  of the sharpening member  3 . 
     The plurality of the grooves  3   a  extends along the first direction  5 , specifically. Specifically, the grooves  3   a  extend substantially in parallel to the first direction  5  of the sharpening member  3 . Referring to  FIG. 8 , the grooves  3   a  have a uniform width W 1 . The grooves  3   a  are arranged substantially in parallel to one another at a uniform interval P. Hence, a portion of the sharpening surface  3   d  between the adjacent two grooves  3   a  has a substantially uniform width W 2 . 
     Each of the grooves  3   a  of the sharpening member  3  may have a width W 1  ranging from about 0.4 to about 0.5 mm, and a depth D 1  ranging from about 0.1 to about 0.3 mm. Accordingly, sharpening residue  16  can be easily removed to the outside of the sharpening member  3 . 
     Referring to  FIG. 8 , if the sharpening surface  3   d  is a flat surface, the width W 1  of each of the grooves  3   a  may be a substantially maximum dimension of the groove  3   a , a dimension which is parallel to the sharpening surface  3   d , and the depth D 1  of the groove may be a substantially maximum dimension of the groove  3   a , a dimension which is perpendicular to the sharpening surface  3   d.    
     Referring to  FIGS. 6 and 7 , in a process of sharpening the cutter  15  with the sharpening member  3 , sharpening residue  16  is generated at a position near the center of the sharpening member  3 . Part of the generated sharpening residue  16  may enter the grooves  3   a . The sharpening residue  16  moves from the center toward both ends of the grooves  3   a  by swinging due to the reciprocation of the sharpening member  3  in the first direction  5 , and is removed to the outside of the sharpening member  3 . 
     That is, the reciprocation of the sharpening member  3  causes the sharpening residue  16  to be vibrated. Accordingly, the sharpening residue  16  in the grooves  3   a  of the sharpening member  3  is easily removed without being clogged in the grooves  3   a.    
     Accordingly, the amount of sharpening residue  16  staying in the sharpening surface of the sharpening member  3  is decreased, and likelihood of appearance of spots on a cutting edge  15   a  is decreased, and smooth sharpening is provided. 
     In other words, since the sharpening member  3  comprising the grooves  3   a  reciprocates, the sharpening residue  16 , which deeply enters the grooves  3   a  and hence is hardly removed merely by a centrifugal force, can be easily removed. The sharpening residue  16  can be more smoothly removed to the outside as the sharpening member  3  reciprocates more frequently. For example, if the motion of the sharpening member  3  is like supersonic oscillation, the sharpening residue  16  can be easily removed to the outside of the sharpening member  3 . 
     As the reciprocation of the sharpening member  3  becomes more frequent, a variation in angle θ (described below) defined by the cutter  15  and the sharpening member  3  can be reduced during sharpening. 
     The reciprocation of the sharpening member  3  may be provided by, for example, an electric motor. In particular, the sharpening member  3  may reciprocate in the first direction  5  by rotation of the electric motor. 
     As shown in  FIGS. 6 and 7 , the shape of each of the grooves  3   a  in plan view is linear. However, the shape of the groove  3   a  is not limited thereto. The grooves  3   a  are disposed on the sharpening surface  3   d  so as to extend along the first direction  5 . 
     The expression “the groove extends along the first direction” can be referred to include both cases as described below. First case is in which an auxiliary line is arranged along the first direction when the auxiliary line is a line connecting the center points in the widths of the groove, the widths correspond to each width of the groove at some arbitrary points in the first direction. The second case is in which the maximum difference between the center points in the direction perpendicular to the first direction is less than the maximum width of the groove. Therefore, the shape of the groove  3   a  may be, for example but without limitation, curved in plan view, and the like. In addition, a single groove  3   a  may be split in midcourse into a plurality of grooves  3   a , or the grooves  3   a  may be joined in midcourse, depending on the type of the cutter  15 . 
       FIGS. 24A and 24B  illustrate other exemplary shapes of the groove  3   a  according to an embodiment to the present disclosure. Specifically,  FIGS. 24A and 24B  illustrate the fist and the second case described above respectively. In  FIG. 24A , the auxiliary line described above is shown as a dashed line and arranged along the first direction  5 . In  FIG. 24B , the maximum difference between the center points in the direction perpendicular to the first direction is shown as P and the maximum width of the groove is shown as W max . the P is less than the W max . In both of the cases, the groove  3  has the meander shape. Both cases also can remove the sharpening residue  16  smoothly to the outside of the sharpening member  3 . 
     As described above, the grooves  3   a  are substantially parallel to the first direction  5 . Accordingly, the sharpening residue  16  can be easily removed. In this manner, since the cutting edge  15   a  is arranged substantially perpendicularly to the first direction  5  during sharpening, occurrence of a phenomenon, in which the cutting edge  15   a  is stacked in the groove  3   a  and hence the cutting edge  15   a  is nicked, can be reduced. 
     As described above, the grooves  3   a  are substantially parallel to the first direction  5 . The arrangement of the grooves  3   a  is not limited thereto. For example, but without limitation, part of the grooves  3   a  may be inclined to the first direction  5  in plan view, and the like. 
     A number of the grooves  3   a  may be one or more. If the number of the grooves  3   a  is more than one, the interval P between the adjacent grooves  3   a  and the width W 1  of the grooves  3   a  each do not have to be uniform. For example, the interval P between the adjacent grooves  3   a  and the width W 1  of the grooves  3   a  each may have different values. 
     Referring to  FIG. 8 , the interval P between the adjacent grooves  3   a  is larger than the width W 1  of the grooves  3   a . Accordingly, the area of the sharpening surface  3   d  is sufficiently provided in the sharpening member  3 , and hence a sharpening speed can be substantially maintained at or above a set speed. 
     Referring to  FIGS. 6 and 7 , the grooves  3   a  are continuously arranged from a first end  31  to a second end  32  of the sharpening member  3  along the first direction  5 . Accordingly, the sharpening residue  16  can be efficiently removed to the outside. The grooves  3   a  may be partly intermittent. 
     Also, as described above, the sharpening member  3  is a columnar member, and comprises the flat portion  3   b  and the curved portion  3   c . Thus, the sharpening member  3  comprises a flat sharpening surface  3   d   1  that is a flat surface along the first direction  5 , and a curved sharpening surface  3   d   2  that is a convex surface along the first direction  5 . 
     Owing to this, the sharpening surface  3   d  of the sharpening member  3  can be desirably properly used in accordance with the shape of the cutting edge  15   a . Likelihood of appearance of spots on the cutting edge  15   a  is decreased, and smooth sharpening is provided. 
     In particular, by selecting the sharpening surface for sharpening from the flat sharpening surface  3   d   1  and the curved sharpening surface  3   d   2 , the pressure exerted by the sharpening surface  3   d , which is in contact with the cutter  15  can be adjusted, and sharpening can be performed in accordance with a fine and complex shape of the cutting edge  15   a.    
     Accordingly, likelihood of appearance of spots on the cutting edge  15   a  of the cutter  15  is decreased, and smooth sharpening is provided. 
     As shown  FIGS. 4 and 5 , the sharpening surface  3   d  comprises the flat sharpening surface  3   d   1  and the curved sharpening surface  3   d   2 . However, the sharpening surface  3   d  is not limited thereto. The sharpening surface  3   d  may comprise a plurality of curved sharpening surfaces with different curvature radiuses. 
     Material of the sharpening member  3  may be any material as long as the material can be used as a sharpening stone. The sharpening member  3  may be made from, for example but without limitation, alumina ceramic, silicon nitride, or the like. Accordingly, the sharpening member  3  can have a higher hardness than that of a metal knife, and have good wear resistance. Thus, the life of the sharpening subject as a sharpening stone can be increased. In this example embodiment, the sharpening member  3  may comprise a base made of alumina or silicon nitride and diamond abrasive grains adhering on the surface of the base. Accordingly, the sharpening member  3  can be used for sharpening a ceramic knife. 
       FIGS. 9A to 9C  schematically illustrate in an enlarged view of sharpening surfaces.  FIG. 9A  is an illustration of a state of the sharpening surface  3   d  of the sharpening member  3  according to an embodiment of the present disclosure. Referring to the  FIG. 9A , a sharpening surface  3   d  comprises open pores  17 . If a number of times an arbitrary line in the sharpening surface  3   d  intersects with an edge portion of the open pore  17 , hereinafter referred to as N, is larger, the sharpening speed becomes higher. 
     The N can be determined by observation of the sharpening surface  3   d  with an X-ray microanalyser. A secondary electron image magnified 100 times of any area on the sharpening surface  3   d  is observed to count the N. The N can be counted in a region 1 mm by 2 mm of the sharpening surface  3   d .  FIG. 9A  is the secondary electron image of the region 1 mm by 2 mm of the sharpening surface  3   d . As shown in  FIG. 9A , the arbitrary line shown as a dashed line has a length of about 2 mm in the region and the N may be from about 9 to about 11. In addition, the radius of the pore may be about 0.05 mm. In this case, the sharpening speed can be reached sufficient value. Accordingly, the sharpening member  3  can provide good sharpening performance. 
     The sharpening member  3  may have a porosity ranging from about 10% to about 30%. 
     If the porosity is within the range, edge portions of the open pores  17  intersecting with the arbitrary line, that is, effectively making a contribution to sharpening performance can be sufficiently provided, the sharpening speed can be maintained, and stable cutting quality can be provided. In the case shown in FIG. A 9 , the porosity may be around 20%. 
     Alternatively, the porosity may range from about 0.2% to about 2%. In this case, the sharpening member  3  can have a predetermined hardness. Accordingly, wear of the sharpening member  3  can be decreased. The sharpening member  3  having such a porosity may be fabricated by, for example but without limitation, press molding. 
     The porosity can be measured as an apparent porosity complying with a testing method (e.g., JIS C2141-1992) by using a tablet with a diameter of about 17 mm. 
       FIG. 10  is an illustration of a top view of an exemplary sharpening member  20  according to an embodiment of the present disclosure.  FIG. 11A  is an illustration of a sectional view taken along line X-X in  FIG. 10 .  FIG. 11B  is an illustration of a sectional view taken along line Y-Y in  FIG. 10 . Embodiments shown in  FIGS. 10-11B  may have functions, material, and structures that are similar to the embodiments shown in  FIGS. 4-8 . Therefore common features, functions, and elements may not be redundantly described here. 
     The sharpening member  20  has grooves  3   a . Regarding the width W 1  of the grooves  3   a , widths w 21  and w 22  at first and second ends  21  and  22  are larger than a width w 23  at a center  23  (w 21 &gt;w 23 , w 22 &gt;w 23 ). 
     Thus, sharpening residue  16  deeply entering the grooves  3   a  can be easily removed as shown in  FIG. 10 . The amount of the sharpening residue  16  staying in the grooves  3   a  can be decreased. As a result, a stable sharpening speed and a stable sharpening angle can be obtained. For example, the widths w 21  and w 22  of the grooves  3   a  may be twice to fourfold the width w 23  of the grooves  3   a.    
     Referring to  FIG. 10 , the sharpening member  20  comprises a first portion  41 , a center portion  42 , and a second portion  43  in that order from the first end  21 . In the first portion  41 , the width W 1  of the grooves  3   a  increases toward the first end  21 . In the center portion  42 , the width W 1  of the grooves  3   a  is uniform. In the second portion  43 , the width W 1  of the grooves  3   a  increases toward the second end  22 . 
     That is, the center portion  42  of the sharpening member  20  has the region in which the width W 1  of the grooves  3   a  is uniform. Accordingly, since a contact area between a cutting edge  15   a  and the sharpening surface  3   d  of the sharpening member  20  can be sufficiently provided, the sharpening speed is decreased less. 
     Further, referring to  FIG. 11A , regarding the depth D 1  of the grooves  3   a , depths d 21  and d 22  at the first and second ends  21  and  22  of the sharpening member  20  are larger than a depth d 23  at the center  23  of the sharpening member  20  (d 21 &gt;d 23 , d 22 &gt;d 23 ). 
     Accordingly, the sharpening residue  16  in the grooves  3   a  can be easily removed, and the amount of sharpening residue  16  staying in the grooves  3   a  can be decreased. As a result, a stable sharpening speed and a stable sharpening angle can be obtained. For example, the depths d 21  and d 22  of the grooves  3   a  may be twice to fourfold the depth d 23  of the grooves  3   a.    
     To be more specific, in the first portion  41 , the depth D 1  of the grooves  3   a  increases toward the first end  21 . In the center portion  42 , the depth D 1  of the grooves  3   a  is uniform. In the second portion  43 , the depth D 1  of the grooves  3   a  increases toward the second end  22 . 
     That is, the center portion  42  of the sharpening member  20  has the region in which the width W 1  and the depth D 1  of the grooves  3   a  are uniform. 
     Further, referring to  FIG. 11B , the grooves  3   a  comprise curved bottom portions in sectional view perpendicular to the first direction  5 . 
     Accordingly, the sharpening residue  16  in the grooves  3   a  can be easily removed without being hooked in midcourse. The sharpening residue  16  does not stay in the grooves  3   a , and a stable sharpening speed and a stable sharpening angle can be obtained. 
     Referring to  FIGS. 11B and 11C , the bottom portions of the grooves  3   a  are curved at both of the first end  21  and the center portion  42 . Also at the second end  22 , the bottom portions of the grooves  3   a  are curved. That is, the bottom portions are curved anywhere in the first direction  5 . The shape of the bottom portions of the grooves  3   a  is not limited thereto. For example, the bottom portions of the grooves  3   a  may be, for example but without limitation, at least curved at both ends (the first end  21 , the second end  22 ) of the sharpening member  20 , and the like. 
     The grooves  3   a  comprising such bottom portions may be fabricated by, for example but without limitation, cutting, processing with a die or a laser, and the like. Processing with a die or a laser easily performs processing of the grooves  3   a  comprising such bottom portions. 
       FIG. 12  is an illustration of a perspective view showing an exemplary sharpener  40  according to an embodiment of the present disclosure.  FIG. 13  is an illustration of a top view of the sharpener  40 .  FIG. 14  is an illustration of a side view of the sharpener  40 . Embodiments shown in  FIGS. 12-14  may have functions, material, and structures that are similar to the embodiments shown in  FIGS. 4-8 . Therefore common features, functions, and elements may not be redundantly described here. 
     The sharpener  40  comprises a sharpening member  3  and a protector  4  surrounding the sharpening member  3 . The protector  4  comprises an opening  4   a . Part of the sharpening surface  3   d  of the sharpening member  3  is exposed to the outside through the opening  4   a.    
     Thus, a cutting edge  15   a  can contact a predetermined portion of the sharpening surface  3   d  in the sharpening member  3 . That is, the cutting edge  15   a  can selectively contact the sharpening surface  3   d  exposed through the opening  4   a . Likelihood of appearance of spots on the cutting edge  15   a  is decreased, and smooth sharpening is provided. 
     Since the predetermined portion of the sharpening surface  3   d  of the sharpening member  3  is exposed through the opening  4   a , the positional relationship between the cutting edge  15   a  and the sharpening surface  3   d  can become stable. Accordingly, the predetermined portion of the sharpening surface  3   d  of the sharpening member  3  can be used for sharpening. 
     Referring to  FIG. 12 , the shape of the opening  4   a  is based on the profile of the sharpening member  3  in plan view. That is, a profile of the sharpening member  3  is similar to a profile of the opening  4   a.    
     Accordingly, a gap between the sharpening member  3  and the opening  4   a  can be decreased. Occurrence of a phenomenon, in which the edge of the cutter  15  enters the gap, can be decreased. 
     To be more specific, the opening  4   a  may have dimensions of approximately about 20 to about 30 mm (vertical)× about 12 to about 16 mm (horizontal). 
     Referring to  FIG. 14 , the protector  4  is coupled to a grip  2  such that the sharpening surface  3   d  protrudes from the opening  4   a . That is, the sharpening surface  3   d  is arranged separately from the virtual plane of the opening  4   a  by a protruding amount T. 
     Accordingly, the cutter  15  can contact the predetermined portion (the flat portion  3   b  and the curved portion  3   c ) of the sharpening surface  3   d  first. In this manner, a likelihood of appearance of spots on the cutting edge  15   a  is decreased, and smooth sharpening is provided. This is because a variation in pressure between the cutter  15  and the sharpening member  3  due to instantaneous contact between the cutter  15  and the protector  4  during sharpening can be decreased. 
     The protruding amount T of the sharpening member  3  may range from about 0.5 to about 1 mm in view of workability. 
       FIG. 15  is an illustration of a perspective view showing an exemplary sharpener  60  according to an embodiment of the present disclosure.  FIG. 16  is an illustration of a top view of the sharpener  60 .  FIG. 17  is a side view of the sharpener  60 .  FIG. 18  is a sectional view taken along line Z-Z in  FIG. 15 .  FIGS. 19A ,  19 B,  20 A, and  20 B briefly illustrate sharpening states when a sharpener  60  is used.  FIG. 19A  is a side view in a direction indicated by arrow C in  FIG. 15 .  FIG. 19B  is a side view in a direction indicated by arrow D in  FIG. 15 .  FIGS. 20A and 20B  are top views of the sharpener  60  respectively corresponding to  FIGS. 19A and 19B . Embodiments shown in  FIGS. 15-20B  may have functions, material, and structures that are similar to the embodiments shown in  FIGS. 1-3  and  12 - 14 . Therefore common features, functions, and elements may not be redundantly described here. 
     Referring to  FIGS. 15 to 17 , the sharpener  60  comprises a guide plate  4   b . The guide plate  4   b  comprises a plate portion  9  facing the opening  4   a  and a support member  4   c  supporting the plate portion  9 . A gap separates the plate portion  9  from the opening  4   a . Referring to  FIGS. 16 ,  19 A and  19 B, the plate portion  9  comprises a bottom portion  91  and flap portions  92  on both sides of the bottom portion  91 . The bottom portion  91  is located above the opening  4   a  and faces the sharpening surface  3   d . The support member  4   c  is located on the protector  4 , and supports the bottom portion  91  of the guide plate  4   b.    
     Referring to  FIGS. 17 to 19B , the support member  4   c  divides the sharpening surface  3   d  of the sharpening member  3  exposed through the opening  4   a  into two regions in the first direction  5 . A cutter  15  contacts one of the two regions of the sharpening surface  3   d  divided by the support member  4   c  from a first end  31  or a second end  32  of the sharpening member  3 . In other words, the support member  4   c  comprises a partition structure that divides the opening  4   a  into a portion near the first end  31  and a portion near the second end  32 . Specifically, referring to  FIGS. 16 to 19B , the support member  4   c  comprises two parts located on both sides of the opening  3   a  in the direction perpendicular to the first direction  5 . The two parts of the support member  4  each have columnar shape and are arranged perpendicular to the first direction  5 . 
     Accordingly, the two parts of the support member  4   c  guide the cutting edge  15   a  stably to the arrangement substantially perpendicular to the first direction  5 . Therefore, occurrence of a phenomenon, in which the cutting edge  15   a  is stacked in the groove  3   a  and hence the cutting edge  15   a  is nicked, can be reduced as well as the sharpening residue  16  can be removed easily during sharpening. In addition, a direction in which the cutter  15  contacts the sharpening member  3 , and a pressure of the cutter  15  to the sharpening member  3  can become stable. In this manner, likelihood of appearance of spots on the cutting edge  15   a  is decreased, and smooth sharpening is provided. 
     Since the cutter  15  is guided to a position between the sharpening member  3  and the guide plate  4   b , the motion of the cutter  15  can be easily restricted within a proper range. That is, the cutting edge  15   a  of the cutter  15  is guided by the guide plate  4   b  including the support member  4   c , and hence, the cutting edge  15   a  can stably contact the sharpening surface  3   d  of the sharpening member  3 . 
     The gap W 3  between the guide plate  4   b  and the opening  4   a  may range from about 1 to about 2 mm. Referring to  FIGS. 19A and 19B , the gap W 3  may be narrowed toward the support member  4   c . For example, a gap w 91  between the bottom portion  91  and the protector  4  may be uniform, and a gap w 92  between the flap portions  92  and the protector  4  may be narrowed toward the support member  4   c.    
     Further, as described above, the guide plate  4   b  comprises the support member  4   c  that divides the sharpening surface  3   d  exposed through the opening  4   a  into the portion near the first end  31  and the portion near the second end  32 . 
     When one face of the cutting edge  15   a  is sharpened at the side of the first end  31 , the cutting edge  15   a  is directed to the second end  32  as shown in  FIG. 20A . When the other face of the cutting edge  15   a  is sharpened at the side of the second end  32 , the cutting edge  15   a  is directed to the first end  31  as shown in  FIG. 20B . Accordingly, both faces of the cutter  15  can be easily sharpened while a user uses a dominant hand. The cutting edge  15   a  is hardly moved beyond the support member  4   c.    
     A size of the gap W 3  between the guide plate  4   b  and the opening  4   a  may be adjustable. 
     Accordingly, likelihood of appearance of spots on the cutting edge  15   a  is decreased for the cutter  15  having any of various shapes, and smooth sharpening is provided. This is because the angle θ defined by the center line of the cutter  15  and the sharpening surface  3   d  of the sharpening member  3  can be adjusted through adjustment for the gap W 3 , for example, by replacing the guide plate  4   b  with another one. 
     In the viewpoint of durability of the cutting quality, the angle θ defined by the center line and the sharpening surface  3   d  in sectional view of the cutter  15  may range from about 10° to about 20°. When the cutter  15  to be sharpened comprises two types of edges including a large blade and a small blade, the guide plate  4   b  may be selected accordingly. A guide plate  4   b  for the large edge may have an angle θ ranging from about 5° to about 10°, and a guide plate  4   b  for the small edge may have an angle θ ranging from about 20° to about 30°. 
       FIGS. 21A to 21C  are illustrations of sectional views briefly showing sharpening members  80 ,  81 , and  82  according to an embodiment of the present disclosure. Embodiments shown in  FIGS. 21A-21C  may have functions, material, and structures that are similar to the embodiments shown in  FIGS. 2-8  and  12 - 14 . Therefore common features, functions, and elements may not be redundantly described here. 
     The sharpening members  80 ,  81 , and  82  are rotational members each comprising a plurality of flat surfaces at a plurality of distances from a corresponding central axis  14 . The flat surfaces are used for sharpening. 
     The central axis  14  is substantially parallel to the first direction  5 . A protruding amount T of each of the sharpening members  80 ,  81 , and  82  can be adjusted when each of the sharpening members  80 ,  81 , and  82  is rotated around the corresponding central axis  14  as the axis as shown in  FIGS. 21A to 21C . The protruding amount T is the amount by which a corresponding sharpening surface  3   d  protrudes from the virtual plane of the opening  4   a . In  FIGS. 21A to 21C , the virtual plane of the opening  4   a  is indicated by a dotted line. 
     By adjusting the protruding amount T, by which the sharpening member  3  protrudes from the virtual plane of the opening  4   a , the angle θ can be adjusted. 
     Further, the plurality of flat surfaces of each of the sharpening members  80 ,  81 , and  82  may comprise at least two types of the sharpening surfaces  3   d  with different porosities. In particular, the sharpening members  80 ,  81 , and  82  may be columnar members each including a plurality of the sharpening surfaces  3   d  with different porosities extending along the first direction  5 . 
     Accordingly, by rotating each of the sharpening members  80 ,  81 , and  82  around the corresponding central axis  14 , the sharpening surfaces  3   d  of each sharpening member can be selectively used for rough sharpening and fine sharpening. 
       FIG. 22A  is an illustration of an exploded perspective view of an exemplary sharpener  8 .  FIG. 22B  is an illustration of an exploded perspective view showing the inside of a grip  2  of the sharpener  8 . 
     The sharpener  8  comprises an electric motor  1 , a gear  10 , an elliptic cam  11 , a shaft  12 , and a sleeve  13 . Rotation of the electric motor  1  is converted into linear reciprocation by the gear  10  and the elliptic cam  11 . The shaft  12  is connected to the elliptic cam  11 . The shaft  12  is connected to a sharpening member  3  through the sleeve  13 . 
     The motion substantially perpendicular to the first direction  5  of the shaft  12  is restricted by the sleeve  13 . The shaft  12  can cause the sharpening member  3  to reciprocate while the sharpening member  3  is stably held. Accordingly, a sharpening force can be generated. 
     Further, the frequency of the reciprocation of the sharpening member  3  may be adjusted by changing a ratio of rotation of the elliptic cam  11  to rotation of the gear  10 . 
     Accordingly, the sharpening speed can be selected depending on the situation for rough sharpening or for fine sharpening. 
     The frequency of the reciprocation of the sharpening member  3  may range from about 20 to about 300 Hz. Accordingly, the resonation of the cutter  15  can be decreased, and sonic oscillation that allows sharpening residue  16  to be smoothly removed can be obtained. Also, the cutting edge  15   a  is less hooked to the sharpening member  3  during sharpening. Appearance of sharpening unevenness of the cutting edge  15   a  can be decreased. 
     The amplitude of the reciprocation of the sharpening member  3  may be, for example but without limitation, about 0.5 mm, and the like. Accordingly, the removing performance for the sharpening residue  16  is increased, and decrease in life of the sharpening member  3  due to wear can be decreased. 
       FIG. 23  is an illustration of a perspective view showing an exemplary sharpener  90  according to an embodiment of the present disclosure. The sharpener  90  comprises a sharpening member  50 . The sharpening member  50  comprises a plurality of sharpening surfaces  5   d . Referring to  FIG. 23 , the sharpening member  50  is a rotational member that is rotatable around an axis along the first direction  5 . 
     Accordingly, an unused sharpening surface  5   d  can be used if the sharpening member  50  is rotated. A stable sharpening speed and a stable sharpening angle can be obtained. 
     Furthermore, the sharpening member  50  rotates freely around the first direction  5  as the axis. 
     Accordingly, the sharpening member  3  rotates freely as a user moves the cutting edge. A phenomenon, in which only a certain part of the sharpening surface  5   d  of the sharpening member  50  sharpens the cutter  15 , less frequently occurs. A stable sharpening speed and a stable sharpening angle can be obtained. 
     The sharpening member  50  rotates freely in the example embodiment shown herein. However, rotation of the sharpening member  50  may be controlled automatically around the first direction  5  as the axis. 
     In this case, the sharpening member  50  is rotated even if the cutting edge is not moved. A phenomenon, in which only a certain part of the sharpening surface  5   d  of the sharpening member  50  sharpens the cutter  15 , less frequently occurs. A stable sharpening speed and a stable sharpening angle can be obtained. 
     Such an automatic rotational mechanism may use a mechanism that allows automatic rotation to be performed in addition to the reciprocation of the output shaft  1   a . For example, a rotational roller is brought into contact with the output shaft  1   a  and the output shaft  1   a  is automatically rotated, so that the sharpening member  50  is automatically rotated. 
     The grooves  3   a  may be formed in advance when the sharpening member  3  is molded with a die. Alternatively, the grooves  3   a  may be formed by NC microfabrication. 
     The grip  2  and the protector  4  may be made from, for example but without limitation, acrylonitrile butadiene styrene (ABS) resin, polypropylene (PP), or polystyrene (PS), and the like. 
     EXAMPLES 
     Example 1 
     Sample Fabrication 
     Sharpeners with different conditions were fabricated as samples. The conditions of each sample comprised the presence of the grooves  3   a  of a sharpening member  3 , the presence of the flat portion  3   b  and the curved portion  3   c , the presence of a protector  4  comprising the opening  4   a , a protruding amount T of the sharpening member  3  from the opening  4   a , the presence of a guide plate  4   b , and the presence of a support member  4   c . Table 1 shows the conditions for the sharpeners. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                   
                   
                 Flat surface and 
                 Protector and 
                 Protruding 
                   
                 Partition 
               
               
                 Sample 
                 Groove 
                 curved surface 
                 opening 
                 amount 
                 Guide plate 
                 structure 
               
             
          
           
               
                 No. 
                 Included 
                 Lacking 
                 Included 
                 Lacking 
                 Included 
                 Lacking 
                 (mm) 
                 Included 
                 Lacking 
                 Included 
                 Lacking 
               
               
                   
               
             
          
           
               
                 1 
                 ∘ 
                   
                 ∘ 
                   
                 ∘ 
                   
                 2 
                 ∘ 
                   
                 ∘ 
                   
               
               
                 2 
                   
                 ∘ 
                 ∘ 
                   
                 ∘ 
                   
                 2 
                 ∘ 
                   
                 ∘ 
               
               
                 3 
                 ∘ 
                   
                   
                 ∘ 
                 ∘ 
                   
                 2 
                 ∘ 
                   
                 ∘ 
               
               
                 4 
                 ∘ 
                   
                 ∘ 
                   
                   
                 ∘ 
                 — 
                   
                 ∘ 
                   
                 ∘ 
               
               
                 5 
                 ∘ 
                   
                 ∘ 
                   
                 ∘ 
                   
                 1 
                 ∘ 
                   
                 ∘ 
               
               
                 6 
                 ∘ 
                   
                 ∘ 
                   
                 ∘ 
                   
                 0 
                 ∘ 
                   
                 ∘ 
               
               
                 7 
                 ∘ 
                   
                 ∘ 
                   
                 ∘ 
                   
                 −1 
                 ∘ 
                   
                 ∘ 
               
               
                 8 
                 ∘ 
                   
                 ∘ 
                   
                 ∘ 
                   
                 2 
                   
                 ∘ 
                   
                 ∘ 
               
               
                 9 
                 ∘ 
                   
                 ∘ 
                   
                 ∘ 
                   
                 2 
                 ∘ 
                   
                   
                 ∘ 
               
               
                 10 
                   
                 ∘ 
                   
                 ∘ 
                   
                 ∘ 
                 — 
                   
                 ∘ 
                   
                 ∘ 
               
               
                   
               
             
          
         
       
     
     A sample  3  did not comprise the curved portion  3   c , but comprised the flat portion  3   b.    
     A sample  9  comprised the guide plate  4   b , but did not comprise the support member  4   c . Thus, the sample  9  was used for sharpening from one side. 
     A sample  10  corresponded to an existing grinder, that is, a sharpener like a rotational sharpening stone. 
     Evaluation Method 
     The sharpeners under the conditions described in Table 1 were used to sharpen cutting edges  15   a  of metal knifes made of stainless steel. 
     A sharpening condition was that each of edges of a metal knife was sharpened for 10 seconds. After sharpening, cutting qualities of the metal knifes were compared with one another by the Honda-method cutting tester. 
     Conditions for the Honda-method cutting test were that a measurement environment was in a hothouse, test paper was good quality paper, a paper shape was 0.038-mm-thick and 8-mm-wide, the number of sheets comprised in a bundle was 400, an application load was about 800 g, and a sliding speed was 20 mm/g. Under the conditions, the test paper was fixed, and the bundle of sheets reciprocates once. Then, the number of cut sheets was measured. Table 2 shows the results. 
     
       
         
               
               
             
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Cutting quality 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Sample 1 
                 ◯ 
               
               
                   
                 Sample 2 
                 X 
               
               
                   
                 Sample 3 
                 ◯ 
               
               
                   
                 Sample 4 
                 Δ 
               
               
                   
                 Sample 5 
                 ◯ 
               
               
                   
                 Sample 6 
                 Δ 
               
               
                   
                 Sample 7 
                 — 
               
               
                   
                 Sample 8 
                 Δ 
               
               
                   
                 Sample 9 
                 ◯ 
               
               
                   
                 Sample 10 
                 X 
               
               
                   
                   
               
             
          
         
       
     
     In Table 2, respective reference signs indicate the numbers of cut sheets, ◯ (circle) indicating 100 or more sheets, Δ (triangle) indicating 50 to 99 sheets, X (cross) indicating fewer than 50 sheets. 
     A sample  1  had the grooves  3   a  in the surface of a sharpening member  3 , and the sharpening surface  3   d  at a flat portion  3   b  and a curved portion  3   c . The sample  1  comprised a protector  4  comprising the opening  4   a , and had a sufficient value (2 mm) for a protruding amount T of the sharpening member  3 . Also, the sample  1  comprised a guide plate  4   b  for holding a cutting edge  15   a  at a predetermined angle θ, and comprised a support member  4   c  capable of adjusting an insertion amount of the cutting edge  15   a  to a position between the guide plate  4   b  and the sharpening member  3 . Thus, the sample  1  provided good cutting quality. 
     A sample  5  comprising a protruding amount T of 1 mm provided good cutting quality in a similar manner to the sample  1  comprising the protruding amount T of 2 mm in a similar manner to the sample  1  with the protruding amount T of 2 mm. 
     A sample  9  did not comprise a support member  4   c . A user could not use a dominant hand for one face of the cutter  15 , and hence sharpening took a time. However, the sample  9  provided good cutting quality. 
     In a sample  7 , a sharpening member  3  did not protrude. Hence, the sample  7  could not sharpen the entire cutting edge  15   a . However, the sample  7  could sharpen a tip portion of the cutter  15 . 
     In the sample  7 , since a sharpening surface  3   d  did not protrude from the plane of an opening  4   a , the above-described test for cutting quality was not performed. 
     Example 2 
     Table 3 shows the evaluation results of Example 2 which was carried out on the basis of Example 1. 
     
       
         
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                 Both 
                 Both 
                   
                   
                   
                   
                   
                   
               
               
                 Sample 
                 Reciprocation 
                 end 
                 end 
                 Groove 
                 Free 
                 Automatic 
                 Frequency 
                 Cutting 
               
               
                 No. 
                 direction 
                 width 
                 depth 
                 shape 
                 rotation 
                 rotation 
                 (Hz) 
                 quality 
                 Life 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 11 
                 Perpendicular 
                 Large 
                 Large 
                 Parabolic 
                 None 
                 None 
                 150 
                 ∘ 
                 Δ 
               
               
                 12 
                 Parallel 
                 Large 
                 Large 
                 Parabolic 
                 None 
                 None 
                 150 
                 Δ 
                 Δ 
               
               
                 13 
                 Perpendicular 
                 Same 
                 Large 
                 Parabolic 
                 None 
                 None 
                 150 
                 Δ 
                 Δ 
               
               
                 14 
                 Perpendicular 
                 Large 
                 Same 
                 Parabolic 
                 None 
                 None 
                 150 
                 Δ 
                 Δ 
               
               
                 15 
                 Perpendicular 
                 Large 
                 Large 
                 Rectangular 
                 None 
                 None 
                 150 
                 Δ 
                 Δ 
               
               
                 16 
                 Perpendicular 
                 Large 
                 Large 
                 Parabolic 
                 Applied 
                 None 
                 150 
                 ∘ 
                 ∘ 
               
               
                 17 
                 Perpendicular 
                 Large 
                 Large 
                 Parabolic 
                 None 
                 Applied 
                 150 
                 ∘ 
                 ∘ 
               
               
                 18 
                 Perpendicular 
                 Large 
                 Large 
                 Parabolic 
                 None 
                 None 
                 10 
                 Δ 
                 ∘ 
               
               
                 19 
                 Perpendicular 
                 Large 
                 Large 
                 Parabolic 
                 None 
                 None 
                 20 
                 ∘ 
                 ∘ 
               
               
                 20 
                 Perpendicular 
                 Large 
                 Large 
                 Parabolic 
                 None 
                 None 
                 300 
                 ∘ 
                 ∘ 
               
               
                 21 
                 Perpendicular 
                 Large 
                 Large 
                 Parabolic 
                 None 
                 None 
                 400 
                 ∘ 
                 Δ 
               
               
                   
               
             
          
         
       
     
     In particular, in Example 2, on the basis of Example 1 (standard conditions), conditions for samples were changed, and cutting quality and life of the samples were evaluated. The conditions in Table 3 comprised a relationship between the groove  3   a  and a reciprocation direction of a sharpening member  3 , a width W 1  at both ends of the groove  3   a , a depth D 1  at both ends of the groove  3   a , a shape of a bottom portion of the groove  3   a , availability of free rotation of the sharpening member  3  around a first direction  5  as the rotation axis, availability of automatic rotation of the sharpening member  3 , and a frequency of the reciprocation of the sharpening member  3 . 
     When a sample  11 , in which a first direction  5  was perpendicular to a cutting edge  15   a  during sharpening, was compared with a sample  12 , in which a first direction  5  was parallel to a cutting edge  15   a , the sample  11  had better cutting quality than that of the sample  12 . 
     When a sample  13 , in which the groove  3   a  had a width W 1  uniform in a first direction  5  of a sharpening member  3 , was compared with the sample  11 , in which the groove  3   a  had a width W 1  increased from a center portion toward both ends in a first direction  5 , the sample  11  had better cutting quality and removed sharpening residue  16  more smoothly. 
     When a sample  14 , in which the groove  3   a  had a depth D 1  uniform in a first direction  5  of a sharpening member  3 , was compared with the sample  11 , in which the groove  3   a  had a depth D 1  increased from a center portion toward both ends in a first direction  5 , the sample  11  had better cutting quality and removed sharpening residue  16  more smoothly. 
     When a sample  15 , in which the groove  3   a  had a rectangular shape in a cross section perpendicular to a first direction  5 , was compared with the sample  11 , in which the groove  3   a  had a parabolic shape protruding downward, the sample  11  had better cutting quality. 
     When a sample  16 , in which a sharpening member  3  was freely rotated around a first direction  5  as the axis, was compared with the sample  11 , in which the sharpening member  3  was fixed to a grip  2 , the life of the sharpening member  3  in the sample  16  was longer. 
     When a sample  17 , in which a sharpening member  3  was automatically rotated around a first direction  5  as the axis, was compared with the sample  11 , in which the sharpening member  3  was fixed to the grip  2 , the life of the sharpening member  3  in the sample  17  was longer. 
     The embodiment, in which a frequency of reciprocation was in a range from 20 to 300 Hz, provided good cutting quality because decrease in removal stress for sharpening residue  16  was reduced. Thus, the life of a sharpening member  3  was longer. 
     Example 3 
     Alumina and silicon nitride were prepared for the materials of sharpening members  3  for samples. The sharpening members  3  with porosities ranging from 9% to 40% were fabricated, and cutting quality was evaluated. 
     Table 4 shows the results. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Material 
                 Porosity (%) 
                 Cutting quality 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Sample 22 
                 Alumina 
                 9 
                 Δ 
               
               
                   
                 Sample 23 
                 Alumina 
                 10 
                 ◯ 
               
               
                   
                 Sample 24 
                 Alumina 
                 30 
                 ◯ 
               
               
                   
                 Sample 25 
                 Alumina 
                 40 
                 Δ 
               
               
                   
                 Sample 26 
                 Silicon nitride 
                 9 
                 Δ 
               
               
                   
                 Sample 27 
                 Silicon nitride 
                 10 
                 ◯ 
               
               
                   
                 Sample 28 
                 Silicon nitride 
                 30 
                 ◯ 
               
               
                   
                 Sample 29 
                 Silicon nitride 
                 40 
                 Δ 
               
               
                   
                   
               
             
          
         
       
     
     Regarding samples  22  to  29 , in samples  23 ,  24 ,  27 , and  28 , edge portions of the pores that make a contribution to sharpening could be provided by sufficient amounts. Hence, sharpening at a good sharpening speed could be provided. Accordingly, efficient sharpening could be provided, and cutting quality was good. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, the present disclosure is not limited to the above-described embodiment or embodiments. Variations may be apparent to those skilled in the art. In carrying out the present disclosure, various modifications, combinations, sub-combinations and alterations may occur in regard to the elements of the above-described embodiment insofar as they are within the technical scope of the present disclosure or the equivalents thereof. The exemplary embodiment or exemplary embodiments are examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a template for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof. Furthermore, although embodiments of the present disclosure have been described with reference to the accompanying drawings, it is to be noted that changes and modifications may be apparent to those skilled in the art. Such changes and modifications are to be understood as being comprised within the scope of the present disclosure as defined by the claims. 
     Terms and phrases used in this document, and variations hereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term “including” should be read as mean “including, without limitation” or the like; the term “example” is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; and adjectives such as “conventional,” “traditional,” “normal,” “standard,” “known” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, a group of items linked with the conjunction “and” should not be read as requiring that each and every one of those items be present in the grouping, but rather should be read as “and/or” unless expressly stated otherwise. Similarly, a group of items linked with the conjunction “or” should not be read as requiring mutual exclusivity among that group, but rather should also be read as “and/or” unless expressly stated otherwise. Furthermore, although items, elements or components of the disclosure may be described or claimed in the singular, the plural is contemplated to be within the scope thereof unless limitation to the singular is explicitly stated. The presence of broadening words and phrases such as “one or more,” “at least,” “but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent. The term “about” when referring to a numerical value or range is intended to encompass values resulting from experimental error that can occur when taking measurements.