AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Innovation Patent Applicant: Brand Developers Aust Pty Ltd Invention Title: BLADE SHARPENER The following statement is a full description of this invention, including the best method for performing it known to me/us: -2 BLADE SHARPENER TECHNICAL FIELD The present disclosure relates to a sharpening apparatus for cutting blades, 5 particularly although not exclusively, to an apparatus facilitating single-hand sharpening of bladed hand tools such as a knife or a pair of scissors. BACKGROUND ART Some blade sharpeners present a risk to users in that often a bladed hand tool is 10 held in one hand, whilst another hand is employed to operate or restrain a sharpening apparatus, such as a sharpening stone, steel or ceramic. Other blade sharpeners provide blade sharpening assemblies that suffer from loosening after extended and/or continuous use. US Pat. No. 7,153,200 describes a blade grinding tool including a main base, a 15 sucker mounted on the main base and attached to a surface, and a grinding unit mounted on the main base for grinding a blade of a cutting tool. The blade grinding tool is attached to a surface, so that a user need not hold the blade grinding tool when grinding the blade of the cutting tool to thereby protecting the user's safety. However, the grind stones of the grinding unit are not adequately supported by the main base nor by a cover 20 provided on the mounting base. Australian Patent No. 2010101072 describes a knife sharpening tool including a main base a sucker mounted on the main base, and a grinding unit mounted on the main base for grinding a blade of a cutting tool. The grinding unit includes two grind stones juxtaposed to each other to form a grinding space to receive the blade of a cutting tool. 25 A cover mounted to the base includes limit plates and a ramp which extends beyond the grinding space in a blade sharpening direction relative to the cover. However, the grind stones are again inadequately supported by the base and/or cover protuberances. The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in 30 the art. The above references are also not intended to limit the application of the knife sharpener as disclosed herein. 3719848_1 (GHMatters) P91283.AU 26/09/12 -3 SUMMARY OF THE DISCLOSURE In a first aspect there is disclosed a blade sharpener for manually maintaining an edge of a bladed hand tool, said blade sharpener comprising: a base carrying a selectively operable retaining mechanism having an 5 attachment device for releaseably retaining the blade sharpener on a surface; a blade sharpening assembly located in the base and including at least two sharpening heads disposed adjacent to one another in overlapping relation to form a generally "V" shaped configuration; a cover removably fastened to the base, the cover including a slotted opening 10 through which the heads of the blade sharpening assembly protrude and including at least two head support portions disposed at the slotted opening for supporting respective sharpening heads; wherein each sharpening head support portion is positioned adjacent to a respective sharpening head and offset from an opposing sharpening head support 15 portion, which head support portions extend laterally of a blade sharpening direction. The blade sharpener can provide improved security and strength for retention of the blade sharpening assembly, including in relation to positioning and supporting the sharpening heads of said assembly. In one embodiment the blade sharpening direction may be defined by a channel 20 provided in the cover, which channel extends from the slotted opening towards a periphery of the cover. The channel on the cover can provide a visual guide for use of the blade sharpener. In another embodiment, the base may further include a blade attachment structure having wells for retaining elements of the blade sharpening structure therein 25 and a thickened wall portion integrally formed on the base and bordering the wells. The thickened wall portion bordering wells for reception of the blade sharpening elements can add additional structural rigidity to the blade sharpener. In a further embodiment of the blade sharpener, the cover may include a depending post member which engages a complementary socket provided on the base 30 for supporting a periphery of the cover. Support for the cover can facilitate the operation of the retaining mechanism for attaching the blade sharpener to a surface. 3719848_1 (GHMatters) P91283.AU2so9/12 In a second aspect, there is disclosed a method for assembling a blade sharpener including a base, a selectively operable retaining mechanism, a blade sharpening assembly including two elements having sharpening heads, and a cover including a slotted opening and at least two head support portions disposed at the slotted opening, 5 the method including the steps of: housing the selectively operable retaining mechanism in a cavity of the base; disposing the two elements of the blade sharpening assembly in a blade attachment structure of the base such that the two sharpening heads are adjacent to one another in overlapping relation to form a generally "V" shaped configuration; 1o fastening the cover to the base such that the heads of the blade sharpening assembly protrude the slotted opening therein and whereby each of said at least two head support portions support a respective sharpening head; wherein upon assembly each sharpening head support portion is positioned adjacent to a respective sharpening head and offset from an opposing sharpening head 15 support portion, which head support portions extend laterally of a blade sharpening direction. In one embodiment the assembly method may include providing a channel in the cover to define a blade sharpening direction, which channel extends from the slotted opening towards a periphery of the cover. 20 In another embodiment, the blade attachment structure of the base may further have wells for retaining individual elements of the blade sharpening structure therein and a thickened wall portion integrally formed on the base and bordering the wells. In a further embodiment of the assembly method, the cover may include a depending post member whereby fastening of the cover to the base may further involve 25 engagement of the depending post with a complementary socket provided on the base for supporting a periphery of the cover. BRIEF DESCRIPTION OF THE DRAWINGS Notwithstanding any other forms which may fall within the scope of the 30 apparatus and method as set forth in the summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: 3719848_1 (GHMatters) P91283.AU26/09/12 -5 Figure 1 shows a front view of a first embodiment in the form of a blade sharpener, with a handle section in up upright position; Figure 2 shows a top plan view of the embodiment as shown in Fig. 1; Figure 3 shows a side view of the embodiment of the blade sharpener, 5 with a handle section in a declined position; Figure 4 shows a front perspective view of the embodiment as shown in Fig. 3; Figure 5 shows an exploded rear perspective view of the embodiment of Fig. 1; 10 Figure 6 shows a rear perspective view of a base section of the embodiment of Fig. 1; Figure 7 shows a front view of the base section of Fig. 6; Figure 8 shows a sectional side view on B-B of the base section shown in Fig. 7; 15 Figure 8A shows an enlarged fragmentary sectional view of the base section shown in Fig. 8; Figure 9 shows an enlarged front perspective view of a cover section of the embodiment of Fig. 1; Figure 10 shows a reduced front perspective view of the embodiment of 20 the blade sharpener, with the handle section removed for clarity; and Figure 1OA is an enlarged fragmentary front perspective view of the embodiment as shown in Fig. 10. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 25 Referring firstly to Figures 1 to 5, there are shown several views of a first embodiment of an apparatus for maintaining an edge on a bladed hand tool in the form of a knife sharpener 10. As most easily recognized from the exploded view on Fig. 5, the knife sharpener 10 of the embodiment includes a handle section 12, a cover section 14, a base section 16, and a retaining mechanism 18. For ease of understanding, only 30 those structural elements of the knife sharpener 10 that are clearly visible will be labelled in the respective (non-exploded) views. 3719848_1 (GHMatters) P91283.AU 2609/12 The handle section 12 includes a grip portion 20 and a cam portion 22, which handle is shown in the "rest" position in Figs. 1 and 2 and in the alternative "locked" position in Figs. 3 and 4. The cam portion 22 interoperates with an attachment structure of the retaining section 18, as described further below. 5 The cover section 14 includes an outer surface 24 which is provided with a channel 26, a pair of apertures 28 and a support structure 30. The support structure in turn includes a first support portion 32 and an opposing second support portion 34 which is laterally offset from the first support portion, as apparent from the plan view of the cover section 14 in Fig. 2. The cover section 14 also includes a depending post 10 portion 36 adjacent an exit of the channel 26, which post portion has a spigot end 38 (see Fig. 9) for mounting the cover section 14 on the base section 16. The cover section 14 further includes a skirt portion 40 and, at an entry of the channel 26, a slotted opening 42 for receiving upper end portions or "heads" 52, 54 of a blade sharpening assembly 50 (see Fig. 1 OA). It will also be apparent from Fig. 2 that channel 26 extends is from the opening 42 outwardly to a periphery of the cover 14, thereby defining a "blade-sharpening" direction. The base section 16 includes a body 44 having a stepped structure (see profile in Fig. 3) with a cylindrical wall terminating at a lower shoulder 46. The cover section 14 is fixed to an upper step of the body 44 by fasteners 48, here in the form of screws (see 20 Fig 5), which pass through the apertures 28 and into the body 44 (see Fig 4). The base section 16 also includes, on a lower step of body 44, a follower plate 56 located by ribs 58 and an upstanding post portion 57 provided for receiving the spigot end 38 of depending post portion 36 of cover section (see Fig. 1). The base section further includes, on an upper step of body 44, an attachment structure 60 for the blade 25 sharpening assembly 50. The attachment structure 60 will be further described below in relation to Figs. 6 to 8A. The retaining mechanism 18 includes a releasable attachment device, here in the form of a suction pad 62, having an upstanding central actuator shaft 64 and a bias in the form of a tapered coil spring 66 disposed over the central actuator shaft. Both the 30 lower step of the base body 44 and the follower plate 56 include an aperture which, in use, are aligned for receiving an upper end of the actuator shaft 64, which upper end includes a transverse bore 68 for receiving a pivot pin 69. When assembled, outer ends 3719848_1 (GHMatters) P91283.AU 26/09/12 -7 of the pivot pin 69 also engage in a corresponding bore provided in the cam portion 22 of handle section 12 (see Fig. 3), which cam potion is bifurcated to allow reception of the upper end of the actuator shaft 54. Referring now to Figs 6 to 8A, where like reference numerals are used to denote 5 similar or like parts, details of the attachment structure 60 for the blade sharpening assembly (not shown) of the base section 16 are illustrated. The cylindrical body 44 of the base includes an internal cavity 70 for housing the suction pad 62 and spring 66 of the retaining mechanism 16. A central polygonal aperture 72, here hexagonal to restrain rotational movement of the base relative to the retainer 18, is provided in the 10 lower step of body 44 and dimensioned to receive the actuator shaft 64 as best seen in Fig. 8. The attachment structure 60 takes the form of two wells 74, 76 opening into the upper step of the base body 44 and bordered by a thickened wall portion 78 of the wall delineating the lower step of the body 44. Two reinforcements 80, 82 extend way from the thickened wall portion on the upper step and adjacent to the wells 74, 76 which are is provided to receive and locate respective elements of the blade sharpening assembly 50. The upper step of the base also includes two threaded holes or captive nut formations 84 for reception of the fasteners 48. During assembly, two blade sharpening elements are inserted into the wells 74, 76, such that when the cover section 14 is positioned on the base 16 whereby the 20 apertures 28 are aligned with the nut formations 84, the two sharpening heads 52, 54 of the elements protrude through the slot 42 (see Fig. 9) so as to contact a respective support portion 32, 34 of the cover. As the head ends 52, 54 of the blade sharpening elements are tapered, the slot 42 is suitably dimensioned to also secure the elements in respective wells of the base when the fastening screws are fully engaged in the nut 25 formations 84 (see Fig. 10). The arrangement of thickened wall portion 78, which is integrally formed with the base body 44 and anchored by the reinforcements 80, 82, tends to resist the force applied to the base through the sharpening assembly during use (as described further below). The cover section 14 is also positioned with the aid of the spigot end 38 of depending post 36, which engages with the socket provided by 30 upstanding post portion 57 on the base 16. With reference to the enlarged view in Fig. 1 OA, it can be seen that the first sharpening head 52 is in contact with first support portion 32 and also located directly 3719848_1 (GHMatters) P91283.AU 26/09/12 -8 opposite to the second support portion 34. Conversely, the second sharpening head 54 is in contact with the second support portion 34 and located directly opposite to the first support portion 32. Thus it will be appreciated from Fig. 2 that the support portions 32, 34 being longitudinally aligned with the heads 54, 52 of the opposing sharpening 5 elements, the overlap of the sharpening elements results in the support portions being (also) laterally offset with respect to one another. A complementary support formation (not shown) may be provided on the underside of the cover section 14, including but not limited to depending wall portions arranged for inter-engagement with the ribs 80, 82 provided on the upper step of base 10 body 44 at respective ends of the wells 74, 76. As best appreciated from Fig. 1, the two heads 52, 54 formed by the tapered ends of the blade sharpening elements are disposed in overlapping adjacent relation so as to form a "V", wherein the internal vertex of the V is configured to receive a blade edge for sharpening. 15 The knife sharpener 10 of the embodiment is arranged for attachment to a clean, smooth surface, such as provided by a laminated bench top, glass, marble, granite or fibreglass. In order to effect attachment to such a surface, the base section 16 of the sharpener 10 may be held on the surface with one hand, the handle section 12 commencing in the rest position as shown in Figs. 1 and 2. Another hand can employ 20 the grip portion 20 to move the handle section 12 into the locked position as shown in Figs. 3 and 4. Movement of the handle 12 causes the cam portion 22 of handle 12 to engage the follower plate 56 of the base 16 and draw the central actuator shaft 64 of suction pad 62 upwardly, whilst an out edge of the pad is held against the surface by the should 46 of base body 44. This action should result in attachment of the sharpener 10 25 to the surface. In order to sharpen (including possible grinding or honing actions) a bladed hand tool such as a knife, the knife blade is placed with a handle end of the blade edge in the V of the sharpening assembly 50 formed by the overlapping sharpening heads 52, 54. The knife blade is then slowly drawn back through the V of the sharpening heads in 30 the direction of the channel 26. This is suitably repeated a number of times (such as 3 or 4), without ever pushing the knife forward in the V which might otherwise damage the edge. 3719848_1 (GHMatters) P91283.AU 26/0912 Whilst a number of specific embodiments have been described, it should be appreciated that the apparatus and method may be embodied in many other forms. In the claims which follow, and in the preceding description, except where the 5 context requires otherwise due to express language or necessary implication, the word "comprise" and variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein. 3719848_1 (GHMatters) P91283.AU 26/0912 - 10 LIST OF REFERENCE NUMERALS 10 knife sharpener 68 bore 12 handle section 69 pivot pin 14 cover section 70 cavity 16 base section 72 polygonal aperture 18 retaining mechanism 74 first well 20 grip portion 76 second well 22 cam portion 78 thickened wall portion 24 outer surface 80 first reinforcement 26 channel 82 second reinforcement 28 apertures 84 nut formation 30 support structure 32 first support portion 34 second support portion 36 post portion 38 spigot end 40 skirt portion 42 slotted opening 44 base body 46 base shoulder 48 fasteners 50 blade sharpening assembly 52 first sharpening head 54 second sharpening head 56 follower plate 57 post portion 58 ribs 60 attachment structure 62 suction pad 64 central actuator shaft 66 tapered spring 37198481 (GHMatters) P91283.AU 26/09/12