GB2123323A - Blade sharpener - Google Patents

Abstract

An electric blade sharpener, in which an abrasive grinding wheel (W) is arranged to be rotated at high speed by an electric motor (M) to sharpen the edge of a blade (a) brought into contact with a side face of the wheel (W) by drawing the blade through a guide slot (V) in the upper wall of the casing (H) of the sharpener. An opening is provided in the bottom wall of the casing below the grinding wheel (W) in a position to collect much of the grinding debris produced during operation of the sharpener, the opening normally being closed by a closure member (C) which can be removed or otherwise opened to remove the debris from the casing (H). Preferably the closure member (C) is provided with a heat-resistant inner surface (Ca). <IMAGE>

Description

SPECIFICATION Blade sharpener The present invention generally relates to blade sharpening devices, and more particularly to electrically driven blade sharpeners for sharpening the cutting edges of knives and other bladed tools by bringing the edge to be sharpened into contact with a side face of an abrasive member, such as a grinding wheel, rotating at high speed.

In blade sharpeners of this type, it is common for the grinding operation to produce a large amount of debris in the form of particles, both from the grinding wheel and from the blade itself. The debris is scattered within the casing of the sharpener, and is usually removed by turning the casing upside down and shaking the particles outthroughablade inserting guide slots in the top of the casing. However, not only is this method of removing the ground particles not sufficiently effective, but the particles are further scattered within the casing, which can lead to troubles due, for example, to clogging or adhesion of such particles to rotating parts or to electrical components of the sharpener.Moreover, since the particles are produced at considerably high temperatures, due to frictional heat during grinding, inner wall portions of the casing which are contacted by the scattered particles can be locally deformed if the casing is moulded from an ordinary plastics material, and thus the casing cannot withstand the sharpener being used for long periods. Furthermore, when ground particles at high temperatures accumulate on the inside of a casing made of ordinary plastics material, smoke may be generated, which may alarm the user. However, avoiding these disadvantages by forming the whole casing from a heat-resistant plastics material or the like is not practical from a cost viewpoint.

Investigations made by the inventors into the scattering of the ground particles during an edge grinding operation have revealed that the particles are generally produced at the side face or grinding surface of the rotating abrasive wheel and are deflected downwards from the grinding position after striking against the side face of the blade being sharpened, the particles mainly accumulating on the wall surfaces in the lower region of the casing below the grinding position without being directed out of the blade inserting guide slots of the casing.

As a result, according to the present invention, an electrically driven blade sharpener comprises a casing, an electric motor mounted in the casing, a main on/off switch for turning the motor on and off, an abrasive member mounted on the driving shaft of the electric motor so that the abrasive member is rotated when the electric motor is turned on, a blade insertion guide slot located in an upper wall of the casing so that insertion of a blade to be sharpened into the slot brings the edge of the blade into contact with a side face of the abrasive member, an opening located in a lower wall of the casing below the abrasive member in a position where grinding debris would tend to collect when the abrasive member is rotated to sharpen the edge of a blade in contact therewith, and a closure member selectively operable to open or close the opening in the lower wall of the casing.

With this arrangement, grinding debris collects on the closure member and can be removed from the casing efficiently and easily, simply by opening the closure member. Preferably the closure member is completely detachable from the casing to facilitate removal of the debris.

Furthermore, it is perfectly satisfactory for the main casing of the sharpener to be made from an ordinary inexpensive plastics material, since the hot grinding debris collects mainly on the closure member. Consequently, preferably at least a portion of the inner surface of the closure member is made of heat-resistant material.

Also, the closure member may be provided with a magnet for the purpose of attracting iron particles (from the blade) contained in the grinding debris, which may otherwise be attracted by the motor.

Preferably the sharpener is provided with an auxiliary on/off switch which is automatically closed when the opening in the lower wall of the casing is closed by the closure member, and which is automatically opened to immobilise the motor when the closure member is opened. This forms a safety mechanism for the protection of a user against accidents during cleaning.

Blade sharpeners in accordance with the invention may be made which are simple in construction, stable and reliable in operation, and can be manufactured readily on a large scale and at low cost.

Several examples of blade sharpeners in accordance with the invention will now be described with reference to the accompanying drawings, in which Figure 1 is a perspective view of a preferred example showing its closure member removed for the purpose of cleaning; Figure 2 is an exploded perspective view showing the components forming the casing of the sharpener shown in Figure 1; Figure 3 is an exploded perspective view of a portion of the sharpener of Figure 1, showing the mounting arrangement for the electric motor of the sharpener; Figure 4 is a side elevation of the sharpener of Figure 1 in an operative condition; Figure 5 is a view similar to that of Figure 4, but showing the sharpener in an inoperative condition; Figure 6 is a top plan view of the sharpener in the operative condition;; Figure 76aJ is a horizontal section through the sharpener in the operative condition; Figures 7(b) and 7(c) show an electrical circuit diagram of the sharpener when it is on and when it is off respectively; Figure 8 is a longitudinal vertical section through a portion of the sharpener; Figure 9 is a transverse vertical section through the sharpener; Figure 10 is a view similar to that of Figure 9 but taken at a slightly different position and illustrating the scattering of ground particles during operation of the sharpener; Figure 11 is a diagram explanatory of the way in which a blade contacts an abrasive wheel of the sharpener during operation; Figure 12 is a fragmentary perspective view of the underside of the sharpener and showing the closure member removed;; Figure 13 is a perspective view showing the construction of a modified form of closure member for use in the sharpener; Figure 14 is a cross section, on an enlarged scale, through a portion of another modified form of closure member; Figure 15 is a perspective view of a further modified form of the closure member; Figure 16 is a fragmentary perspective view showing the casing and closure member of another modified form of the sharpener; Figure 17 is a fragmentary sectional view, on an enlarged scale, of the arrangement shown in Figure 16; Figure 18 is a perspective view similar to that of Figure 12, but showing a different example including a safety switch in conjunction with the closure member; Figure 19 is an electrical circuit diagram of the example shown in Figure 18;; Figures 20 and 21 are fragmentary perspective views showing alternative constructions for the example of Figures 18 and 19; Figure 22 is a part elevational, part sectional, fragmentary view showing an arrangement for fixing an abrasive grinding wheel on the driving shaft of the electric motor of the sharpener of Figure 1; Figure 23 is a fragmentary cross section, on an enlarged scale, showing the fixing of Figure 22 in more detail; and, Figure 24 is a view similar to that of Figure 23, but showing an alternative fixing arrangement.

Before the description of the examples proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings.

Referring now to the drawings, there is shown in Figures 1 and 2, a sharpener for edged tools according to one preferred embodiment of the present invention, which generally includes a main casing H of a rectangular box-like configuration made of a plastic material such as ABS resin or the like and having an upper casing H1 and a lower casing H2 which are combined with each other, for example, by set screws (not particularly shown) to provide a grinding chamber G at the right side and a battery chamber B at the left side in Figures 1 and 2, a protective cover member P slidably applied onto the upper casing H1 for movement between an operative position (F2) at the left side and an inoperative position (F1 ) at the right side (Figures 4 and 5), grinding or abrasive wheels W1 for rough grinding and W2 for finishing grinding driven for rotation by a motor M and accommodated in said grinding chamber G, and a pushbotton switch SW provided in the battery chamber B accommodating batteries or cells b therein, so as to control functionings of said motor M, with a light emitting diode LED being provided in one side wall of the upper casing H1 for indication of state of functionings of the sharpener as described later with reference to Figures 7(b) and 7(c).

Referring also to Figure 3, each of the abrasive wheels W1 and W2 for the rough grinding and finishing grinding is generally formed into a disc-like configuration, and each side face Ws thereof is tapered from a central portion towards its peripheral surface Wp as shown at Wt, while opposite ends of a rotary shaft Ms of the motor M are respectively fitted into central openings Wo of the abrasive wheels W1 and W2 for rigid connection therewith, for example, in a manner as described later with reference to Figures 22 to 24.

For mounting the motor M, there is provided a motor holder Mh which includes a motor mounting base Mh1 and a pair of opposite spaced side walls Mh3 extending downwardly from opposite side edges of the motor mounting base Mh1. Each of said side walls Mh3 is formed, at the same edge thereof, with a recess or notch Mhn for engagement with a bearing boss portion Mb axially extending outwardly out of each of opposite side faces of the electric motor M, with an elastically deformable retaining pressure piece Mhp being provided to project from the motor mounting surface of said motor mounting base Mh1 in a position confronting said recesses Mhn of the side walls Mh3.

For mounting the electric motor M onto the motor holder Mh, the motor M is fitted into between the opposed spaced side walls Mh3 to be placed on the mounting base Mh1, by causing the retaining pressure piece Mhp to resiliently contact the outer peripheral surface of the motor M so as to depress the bearing boss portions Mb of the motor M into said recesses Mhn of the side walls Mh3 for fixing the motor M on said motor holder Mh through contact of the retaining pressure piece Mhp with said electric motor. By the above arrangement, the electric motor M may be rigidly mounted on the motor holder Mh by one stroke without requiring set screws or the like, while for detaching the motor M from the motor holder Mh, the motor M may be pulled out slantwise towards the end portion of the retaining pressure piece Mhp.

The motor holder Mh is arranged to be movably suspended from the inner surface of the upper wall Hla of the upper casing H1 in a manner as described hereinbelow.

More specifically, as is seen in Figure 3, as a sliding movement guiding mechanism S for movement of the motor holder Mh in the axial direction of the casing H, suspension projections Mhw are provided at four corners on the upper surface of the mounting base Mh 1 of the motor holder Mh so as to be supported on the upper surfaces of support plates Mhs secured to the inner surface of the upper casing H1, for example, by screws, while steel balls Mhb are disposed between the respective suspension projections Mhw and the support plates Mhs for free movement of the motor holder Mh with respect to the support plates Mhs in the axial direction of the casing H. On the upper face of the mounting base Mh1, guide pins Mhg are erected, and corresponding guide ribs Hg are provided on the inner wall of the upper casing H1 for engagement with said guide pins Mhg. Furthermore, between the inner wall of the upper casing H1 and the mounting base Mh1, there are provided steel balls Mhf for preventing the motor holder Mh from rising and also for smooth movement of said motor holder Mh.On the inner wall of the upper casing H1, a pair of plate springs Sp are disposed through initial deformation so as to be close to each other at free ends thereof, with a guide pin Mh2 projecting from the upper surface of the mounting base Mh1 being engaged between said plate springs Sp, so that the motor holder Mh is normally held in a central or neutral position between the moving range thereof in the axial direction of the main casing H and is adapted to be movable against the plate springs Spin said axial direction. In the normal state, the abrasive wheels W1 and W2 are exposed from guide grooves V to a large extent, and upon insertion of the edged tool a into the guide groove V, the abrasive wheels W1 and W2 are resiliently depressed thereby for retreatment together with the motor M and the motor holder Mh.

Accordingly, when the edged tool, for example, a knife a (Figure 1) is inserted into one of the guide grooves V to be described later, along the side face Ws of the abrasive wheel W, said wheel W is displaced to the left or right side against the urging force of the plate springs Sp so as to be brought into contact with the blade of the edged tool a to be ground under a constant pressure.

As shown in Figures 1 and 2, the pair of guide grooves V for insertion of the edged tool are provided in the upper wall H1a ofthe upper casing H1 in positions corresponding to the opposite side faces Ws of each of the abrasive wheels W1 and W2, and in the side wall Hle of the upper casing H1 whereat each pair of the guide grooves V intersect each other, a blade receiving block Vb is detachably fitted, so that as shown in Figure 10, upon insertion of the edged tool a into the guide groove V, with a blade a1 thereof directed downwards, the side face a2 of the edged tool a supported by the guide groove V is restricted in its contact angle with respect to the abrasive wheel W, while the blade a1 thereof supported on the block Vb is restricted in the contacting height with respect to the abrasive wheel W.

Still referring to Figure 3, one line L1 for feeding electric power to the motor M is connected to one corresponding electrode El provided in the battery chamber B (Figure 6), while the other line L2 is coupled to the other corresponding electrode E2 in said battery chamber B through the pushbutton switch SW, and thus, in association with the on/off operation of said pushbutton switch SW, power feeding from the cells b to the motor M is controlled as desired.

In Figures 3 and 6, the arrangement for the pushbutton switch SW includes a switch opening SWh of a generally rectangular shape formed in the side wall Hic of the upper casing H1 in a position corresponding to the battery chamber B adjacent to the grinding chamber G, a switch piece SW1 fitted into the switch opening SWh, and a switch plate SWp in the form of a plate spring suitably disposed at the reverse face side of the switch piece SW1 so as to outwardly urge said switch piece SW1, while a contact terminal E2t is arranged to project from the electrode E2 disposed in a position confronting the switch plate SWp, so that upon depression of the switch piece SW1, the switch plate SWp is deflected to contact the contact terminal E2t for closing the circuit.

Referring back to Figure 2, the lower casing H2 to be combined with the upper casing H1 of the casing H for closing the lower portions of the grinding chamber G and the battery chamber B, is formed to have strip portions of a reduced thickness in the vicinity of open end sides of front and rear side walls H2w thereof so as to provide sliding grooves g in the longitudinal direction of the casing H2 along the mating edges of the upper and lower casings H1 and H2 upon combination of said casings.

Meanwhile, as shown in Figure 2, the protective cover member P made, for example, of a semitransparent plastic material, has a generally Ushaped cross section open at its opposite sides and lower portion, and is formed with opposed protrusions P2 extending along the lower edges P1 of front and rear side walls Ps thereof. By fitting the protrusions P2 into the sliding grooves g of the lower casing H2 described earlier, the protective cover member P may be slid, for example, by a finger tip between an advanced or inoperative position (F1 ) for closing or covering the blade inserting guide grooves V and a retreated or operative position (F2) for opening or exposing said grooves Vto use the sharpener (Figures 4 and 5).In approximately a central portion of each sliding groove g of the lower casing H2, a roller R having a size not protruding out of said groove g is rotatably provided around a vertical pin Rs, while a pair of spaced notches Pv are formed in each of the protrusions P2 of the protective cover member P so as to confront to each other for providing a detent positioning means for positioning of the protective cover member P at the positions (F1 ) and (F2) through contact between the rollers R and the notches Pv.

The protective cover member P is further formed with a switch operating opening Po of a rectangular shape in a position which overlaps the switch piece SW1 of the pushbutton switch SW when said cover member P is located in the operative position (F2).

One side edge Po2 of the opening Po is arranged to inwardly descend or taper more gently than in the other side edge Pol thereof, so that, during retreatment of the cover member P towards the position (F2) for exposing the guide grooves V, upon insertion of a thumb hi into the opening Po after fixing the cover member P to the casing H by holding said cover member P, for example, by the left hand h as shown in Figure 6, the switch SW may be efficiently turned on without any hindrance by the side edge Po2 so as to efficiently drive the abrasive wheels W.

Moreover, the protective cover member P is provided with a rib Pr formed widthwise at the right side edge on the upper face Pu thereof, and also, a plurality of ribs Pt formed on one side wall Ps thereof for facilitation of sliding movement of the cover member P by a finger tip. Furthermore, a clearance tc is provided between the entire peripheral surface of the casing H and the corresponding inner surface of the protective cover member P as shown in Figures 9 and 10 so as to prevent scratches and the like possibly formed on the surface of the casing H by ground particles produced during grinding and entering between the cover member P and the casing H.

Incidentally, in the conventional sharpeners for edged tools of this kind, mass of each abrasive wheel is sufficiently increased in general so as to impart an inertia force thereto for reduction of deviations in the state of grinding due to irregular rotation. However, in the known practice as described above, since the abrasive wheels continue to rotate for some time, even upon shutting down of the motor after use, there has been such a disadvantage that those who are not accustomed to operations of the sharpener tend to feel uneasy, while it is dangerous because the abrasive wheels can not be stopped immediately upon occurrence of unexpected accidents such as chipping of the abrasive wheels, etc. during grinding.

In order to overcome the disadvantages as described above, there may be considered such countermeasures as forcible stopping of the abrasive wheels by bringing a frictional braking means such as a brake shoe into pressure contact therewith, but such an arrangement is not fully suitable for practical application, since the construction is undesirably complicated, with a simultaneous generation of frictional heat which may adversely affect various parts of the sharpener.

For elimination of such inconvenience as described above, according to the present invention, circuit constructions as described hereinbelow with reference to Figures 7(b) and 7(c) may be employed.

As shown in Figures 7(b) and 7(c), the circuit generally comprises a main circuit la including the motor M connected in series with the power source, i.e. cells b through the switch SW, and a parallel circuit Ib connected in parallel with said main circuit la and including the light emitting diode LED and a resistor r connected to the opposite ends of the motor M through the switch SW, so that said circuits la and Ib may be selected as desired by changing over the switch SW between switch contacts p and q.

In the above circuit arrangement, to rotate the abrasive wheels W1 and W2 for use, the switch SW is connected to the contact Pat the side of the main circuit la for conduction between the cells b and the motor M as in Figure 7(a), and thus, the motor M is rotated at high speeds for driving the abrasive wheels W1 and W2 ready to use. Subsequently, upon switching over the switch 5W to the switch contact q at the side of the parallel circuit Ib, the cells b are cut off, while the motor M continues to rotate by the inertia force of the abrasive wheels W1 and W2.In this case, however, since the motor M acts as a generator, said motor M is brought into a state of overload in the generating action, i.e. an electromotive force produced by the rotation of the motor M acts conversely to brake the motor M for forcibly stopping the motor M. In the above state, the light emitting diode LED connected in the parallel circuit Ib and partially exposed from the main casing H for observation from outside of said casing as shown in Figures 1 and 2, is energized by the electro-motive force resulting from the generating action of the motor M so as to be illuminated until the motor M is perfectly stopped.

Accordingly, when it becomes necessary to stop rotation of the abrasive wheels W1 and W2 after use or upon occurrence of unexpected accidents such as chipping of the abrasive wheels, the motor M is braked for stopping by switching over the switch SW to the switch contact q, i.e. into the off state so as to stop the abrasive wheels at once, while the light emitting diode LED is illuminated by the electromotive force from the motor M rotating through the inertia force of the abrasive wheels for informing the user that the stopping function is accurately effected.

Moreover, in the above embodiment, in the state where the switch SW is in the off state, since said switch SW is automatically connected to the switch contact q at the side of the parallel circuit Ib, with the motor M being held under the state of overload so as to be normally braked, it is possible to prevent the abrasive wheels W1 and W2 from unnecessary rotation during transit or transportation, etc.

It is needless to say that the light emitting diode LED described as employed in the above embodi mentforthe indication means or reporting means may be replaced by other light emitting elements or a sound producing means such as a buzzer and the like.

It should be noted here that the present invention is particularly characterized in that, in the sharpener for edged tools as described above, openings H20 are formed in the lower wall H2b of the grinding chamber G, i.e. the lower casing H2 for selective opening or closing of said openings H20 by a lid member C for efficient removal of ground particles in a manner as described hereinbelow.

More specifically, as shown in Figures 2 and 12, in the lower or bottom wall H2b of the lower casing H2 at two positions corresponding to the peripheral faces Wp of the abrasive wheels W7 for the rough grinding and W2 for the finishing grinding, there are formed the openings H2o so as to be selectively closed or opened by the lid member C, which includes a pair of lid pieces Ca each having a size sufficient to close the opening H2o, an operating piece Cb connecting base ends of said lid pieces Ca to each other, and stopper pieces Cs respectively provided at end portions of the lid pieces Ca and the operating piece Cb, thus presenting a generally U-shape on the whole. Meanwhile, inserting grooves H2g are respectively formed at corresponding positions in the edge of the openings H20 in the bottom wall H2b of the lower casing H2 for engagement with the stopper pieces Cs of the lid member C.

In the above arrangement, as shown in Figures 10 and 11, when the edged tool a is ground, while being moved towards a user (not shown), with the blade al being pressed slantwise against the side face Ws of the abrasive wheel W rotating in the counterclockwise direction, a grinding point X is located in a position somewhat behind the rotating center 0, and therefore, ground particles f are mostly concentrated upon a position prior to the rotating enter 0 (i.e. towards the left side beyond the rotating center 0 in Figure 10) by a centrifugal force.Accordingly, the openings H20 are not required to be provided over the entire area below the abrasive wheels W1 and W2, but may fully serve the purpose, if provided at the positions prior to the rotating center 0 of the abrasive wheels W1 and W2 to extend up to the front side wall H2w of the lower casing H2.

The lid member C is formed, in the surfaces of the lid pieces Ca thereof confronting the peripheral faces Wp of the abrasive wheels W1 and W2, with dish-like recesses Cu (Figure 2) either by forming concave portions thereat or by providing ribs (not shown) therearound, so that, when the lid member C is to be detached from the openings H20 by pushing the lid member C outwardly through application of a finger tip to a concave groove Cg (Figure 12) formed in the under surface of the operating piece Cb, the ground particles f accumulated on the lid pieces Ca may not be spilt out of the lid member C.

It should be noted here that the embodiment of the present invention described so far may further be modified in various ways within the scope. For example, the lid member C may be so modified that its base portion Cb is pivotally connected to the casing H without being completely detached therefrom as in the foregoing embodiment. Moreover, even when the number of the adhesive wheels are decreased to be only one or increased to be more than three pieces, the present invention is readily effected by merely decreasing or increasing the number of the lid pieces Ca accordingly.Furthermore, if the lid member C is entirely or partly formed by a transparent resinous material or the like, the amount of accumulated ground particles may be readily ensured, and particularly, if the operating piece Cb of the lid member C is elongated and provided with a transparency, the state of accumulation of the ground particles may be confirmed from the side portion of the casing, even when the casing H is placed as it is.

As is seen from the foregoing description, in the sharpener according to the present invention, since it is so arranged that the bottom wall H2b of the lower casing H2 for the main casing H is opened at positions confronting the abrasive wheels W for selective closing or opening by the lid member C, the ground particles produced during grinding are most ly accumulated on the lid member, and therefore, after completion of grinding, the ground particles are readily removed for cleaning by merely detaching the lid member C, without necessity for turning over the main casing H.

Referring further to Figure 13, there is shown a modification of the lid member C described so far with reference to Figures 1 through 12.

In the modified lid member CB of Figure 13, it is intended to impart heat-resistance particularly to the lid pieces Ca thereof confronting the peripheral faces Wp of the abrasive wheels W1 and W2.

More specifically, two heat-resistant metallic sheets Ch made, for example, of aluminum sheets applied with an adhesive on the reverse faces thereof are prepared, and releasably applied or stuck onto generally entire surfaces of the upper faces of the respective lid pieces Ca so as to receive thereon the ground particles at high temperatures scattering thereover during grinding. Each of the metallic sheets Ch may thus be readily replaced with new one depending on necessity.

It should be noted here that, in order to avoid such an inconvenience that, upon application of the metallic sheets Ch onto the lid pieces Ca, steps are formed by a difference in height between the surfaces of the metallic sheets Ch and the inner surface of the bottom wall H2b of the lower casing H2, resulting in spilling of the ground particles accumulated on the surfaces of the metallic sheets Ch during detaching of the lid member C, projecting walls Cp should preferably be formed generally on entire peripheral edges of each of the lid pieces Ca so as to apply the heat-resistant metallic sheets Ch into the thus formed recesses Cu' in a sunk state as shown in the modified lid member CC in Figure 14.

Furthermore, for imparting heat-resistance to the inner surfaces of the lid pieces Ca, such inner surfaces may be formed by a heat-resistant plastic material, in which case, it is conceived to form a series of heat-resistant walls of the heat-resistant plastic material over the respective inner surfaces of the lid pieces Ca confronting the corresponding abrasive wheels W1 and W2.

As is seen from the above description, in the modification of Figure 13, the heat-resistance is imparted only to the inner surfaces of the lid pieces Ca confronting the abrasive wheels W, while the main casing H may be constituted by an inexpensive plastic material, and therefore, not only the sharpener can be produced at low cost, but the inner surfaces of the lid pieces Ca of the lid member C are advantageously protected against damages or deformation by melting, even when ground particles at high temperatures fall to impinge upon such inner surfaces during grinding, thus providing a superior durability of the sharpener on the whole.

Incidentally, ground particles produced during grinding as described above include grains from abrasive wheels and iron particles from edged tools to be ground, in which the iron particles tend to be attracted onto the motor by magnetic induction, thus resulting in troubles of the motor in some cases, especially when the motor is provided in the grinding chamber together with the abrasive wheels.

Particularly, if the iron particles are attracted onto brushes or commutators of the motor, short-circuit may result, making it impossible to operate the sharpener in the worst case. Moreover, such iron particles attracted onto the motor and the like are very difficult to remove, requiring troublesome procedures for cleaning.

Referring to Figures 15 to 17, there are shown further modifications of the lid member particularly intended to efficiently remove ground particles, especially, iron particles as described above.

In the modified lid member CD in Figure 15, the heat-resistant metallic sheets ch described as applied onto the inner surfaces of the lid pieces Ca in the lid member CB of Figure 13 are replaced by permanent magnets Cm in the form of sheets or plates applied onto the lid pieces Ca. It is needless to say that such permanent magnets Cm may be applied onto the inner surfaces of the lid pieces Ca in the sunk state as in the modified lid member CC described with reference to Figure 14.

By the arrangement of Figure 15, the ground particles, especially, the iron particles therein produced during grinding of edged tools, are directed onto the permanent magnets Cm by the centrifugal action resulting from rotation of the abrasive wheels W1 and W2so as to be attracted onto the surfaces of said permanent magnets Cm, without being scattered between the motor shaft and the abrasive wheels or attracted onto the motor. Accordingly, for cleaning of the interior of the main casing, the ground particles accumulated on the lid member CD or scattered in the interior of the main casing may be readily removed by a brush or the like upon detaching the lid member, while the iron particles attracted onto the permanent magnets on the lid member CD can also be easily removed by brushing and the like.

Meanwhile, in the further modification in Figures 16 and 17, the lid member CE includes a base plate CE1 having a rear portion CE 1 a folded, for example, into a U-shaped cross section, an iron plate CE2 extending over the inner surface of the base plate CE1 except for the forward edge of said base plate CE1 where stopper pieces CEs are provided, and a permanent magnet CEm having, for example, a rectangular cross section and disposed on the iron plate CE2 within the rear portion CEl a of the base plate CE1, with said iron plate CE2 being magnetized by the permanent magnet CEm.Meanwhile, in the lower casing H2, at a position adjacent to and along the upper edge of the opening H20' formed therein, an iron plate H2p is provided through an angular fixing plate H2f suitably secured to said upper edge so as to receive the lid member CE as shown.

In the arrangement of Figures 16 and 17, the lid member CE is attached to the casing H by the magnetic attraction of the permanent magnet CEm with respect to the iron plate H2p and by the engagement of the stopper pieces CEs thereof with the corresponding edge of the opening H20'. Upon attaching of the lid member CE, since the iron plate H2p is also magnetized by the permanent magnet CEm, iron particles n in the ground particles produced by the grinding of an edged tool are advantageously attracted onto the iron plate CE2 of the lid member CE and the iron plate H2p at the side of the casing H.Upon detaching of the lid member CE from the lower casing H2, the iron plate H2p at the side of the casing H2 is de-magnetized, with the iron particles n attracted onto the iron plate H2p spontaneously falling out of the casing H2, while the iron particles attracted onto the iron plate CE2 of the lid member CE can also be readily removed by a brush orthe like.

It should be noted here that the arrangements described so far with reference to Figures 15 to 17 may further be modified in various ways within the scope, for example, in such a mannerthatthe lid member CD or CE is pivotally mounted to the casing, or that permanent magnets are employed for the stopper pieces Cs or CEs, or that the permanent magnet CEm is provided at the side of the casing H, or further that such permanent magnet CEm is replaced by an electro-magnetforfacilitation of removal of iron particles through de-energization of an exciting coil for the electro-magnet.

As is seen from the above description, in the arrangement of Figures 15 to 17, since the magnets are provided on the inner surface of the lid member disposed close to the abrasive wheels, iron particles in the ground particles may be quite readily removed, and troubles such as faulty rotation of the motor due to attraction of the iron particles thereto, or clogging of spaces between the motor shaft and bearing portions by the iron particles, etc. may be positively prevented, with a simultaneous improvement of cleaning efficiency.

Meanwhile, in the case of a sharpener of this kind, particularly one provided with a pushbutton switch as referred to earlier, there is a possibility that, during cleaning of ground particles, with the lid member detached, the pushbutton switch SW is accidentally pushed for unexpected driving of the abrasive wheels for rotation, thus resulting in accidents such as injuring fingertips by the abrasive wheels rotating at high speeds or hurting eyes by the scattering ground particles, etc.

In the still further modifications to be described hereinbelow with reference to Figures 18 to 21, for elimination of the inconvenience as described above, it is so arranged that, upon detaching of the lid member for cleaning the interior of the main casing, an electrical circuit to drive the motor for the abrasive wheels is automatically opened so as to prevent unexpected rotation of the abrasive wheels.

More specifically, in the modification of Figures 18 and 19, the modified lid member CF having a construction generally similar to that of the lid member C in Figures 1 and 2, is further provided with an electrically conductive contact piece CFc mounted on the central stopper piece Cs, while a pair of spaced contacts j are provided on the lower casing H2 at the stepped portion H2s connecting the openings H20 and corresponding in position to the contact piece CFc when the lid member CF is applied onto the casing H2.

As shown in Figure 19, the safety switch means as described above including the contacts j and the contact piece CFc for selectively closing or opening said contacts j is inserted in series with respect to the power source cells b, the motor M and the push but ton switch SW.

In the arrangement of Figures 18 and 19, upon detachment of the lid member CF from the casing H2, the contact piece CFc is kept off from the contacts j to open the circuit for driving the motor M.

Accordingly, the abrasive wheels are not rotated by the motor, even when the pushbutton switch SW is accidentally actuated during cleaning, and thus, cleaning may be effected very safely, while in the state where the lid member is attached, the driving circuit can of course be driven at any time.

The safety switch device as described above with reference to Figures 18 and 19 may further be modified as in the arrangements shown in Figures 20 and 21.

In the modified lid member CG of Figure 20, the contact piece CFc described as employed in the lid member CF of Figure 18 is replaced by a hook member kformed on the central stopper piece CGs of the lid member CG, while the contacts j in Figure 18 are replaced by a pair of spaced resilient terminal plates tl and t2 provided in the casing H2 in positions corresponding to the hook k of the lid member CG.

In the arrangement of Figure 20, when the lid member CG is kept mounted on the casing H2, one terminal plate tl is held in contact with the other terminal plate t2 to close the circuit, since the terminal plate tl is depressed by the hook k, while, upon detachment of the lid member CG, the terminal plate tl is spaced from the terminal plate t2 by its own resiliency, and thus, the driving circuit is opened.

Meanwhile, in the modification of Figure 21, the hook CGs of the lid member CG in Figure 20 is replaced by a claw CHs for the lid member CH, while the terminal plates tl and t2 are also replaced by a microswitch MSW connected in series with the driving circuit and provided on the casing H2 in position similar to that for the terminal plates tl and t2 in Figure 20 for selective opening or closing of the driving circuit by the disengagement or engagement of the claw CHs with respect to the contactor MSW-1 of the microswitch MSW.

It should be noted here that the above arrangements in Figures 20 and 21 may further be modified within the scope, for example, in such a manner that, the switch device is replaced by a lead switch or the like so as to selectively close or open the driving circuit by contact or spacing of a magnet means mounted on the lid member, although such arrangement is not particularly shown.

On the other hand, in the sharpeners for edged tools of the above described type, it is required to drive the abrasive wheels for rotation at high speeds generally in the range of 5,000 to 8,000 r.p.m. so as to bring the blade of an edged tool into contact with the grinding surface of the abrasive wheel at a predetermined position, and thus, there are prob lems related to fixing of the abrasive wheels onto the rotary shaft of the motor.For example, in the conventional arrangement in which a resilient bush member having a blind cylindrical bore extending straight from an open and to a bottom portion thereof is fitted into a circular axial through-hole formed in an abrasive wheel, and the motor shaft having a diameter larger than that of the blind cylindrical bore, is forced into said cylindrical bore of the bush member, an enclosed space is formed between the end face of the motor shaft and the bottom portion of the blind cylindrical bore to obstruct smooth insertion of the motor shaft, and thus, the motor shaft tends to come out of the abrasive wheel due to air pressure in such enclosed space.There has also conventionally been proposed another arrangement in which an air vent is formed in the bottom portion of the blind cylindrical bore of the bush member in order to eliminate the disadvantage as described above, but in this arrangement, the motor shaft tends to be eccentrically fitted into the blind cylindrical bore in some cases, although the motor shaft is readily forced into said cylindrical bore, thus resulting in another inconvenience that the abrasive wheel goes off-center during rotation.

In both of the above known arrangements, a fit-in margin is provided between the motor shaft end portion and the blind cylindrical bore of the bush member, but such fit-in margin tends to be deviated in size during manufacture, and moreover, since the abrasive wheel is weak against tension, if such fit-in margin is not fully absorbed by the compressive deformation of the bush member, a strong tensile stress is applied between grains of the abrasive wheels, thus giving rise to formation of cracks or damages to the abrasive wheels.

For eliminating disadvantages as described above, in the arrangement of Figures 22 to 24 according to the present invention, it is so arranged that a blind axial bore is formed in a resilient bush member provided in the central axis of the abrasive wheel, and either one of the blind axial bore or the motor shaft end portion is formed to have a circular cross section, while the other is formed to have a polygonal cross section contacting internally or externally said circular cross section, and thus, the motor shaft is smoothly fitted into the blind axial bore of the bush member even when a fit-in margin for sufficient pressure contacttherebetween is provided, while air within the blind axial bore may be discharged through gaps formed during the fitting for positive fixing of the abrasive wheels onto the motor shaft, without deviation in center or disengagement therebetween.

More specifically, in the fixing arrangement between the abrasive wheel and motor shaft in Figures 22 and 23, the abrasive wheel W produced by bonding grinding grains with a bonding material so as to have a disc-like configuration is formed, at its central axis, with a circular through bore Wh, into which a bush member U is fitted so as to be secured thereat, with the blade grinding side faces Ws of the abrasive wheel W are formed into conical convex shape for contact of the blade of an edged tool therewith at the optimum angle. The bush member U made of a resilient material, for example, synthetic resin such as polyacetal, nylon or the like, or hard rubber, etc., and molded into a circular cylindrical configuration, is formed, at its central axis, with a blind axial bore Uh open at the side of the motor shaft Ms of the motor M. The blind axial bore Uh is formed, between the open end Ue and the bottom portion Uf thereof with inner peripheral walls Uw having, for example, a regular hexagonal cross section and arranged, in respective side faces thereof, to be parallel to each other in the axial direction.

On the other hand, the motor shaft Ms of solid metallic material has its end portion Ms-1 formed into a circular cross section concentric with the rotary axis of the motor M, while the diameter D of the motor shaft Ms is made larger than a distanced between confronting peripheral side faces of the walls Uw in the blind axial bore Uh by the amount equivalent to the fit-in margin, with the distal end face Ms-2 of the motor shaft Ms being chamfered for facilitation of fitting thereof into the blind axial bore Uh of the bush member U.

By the above arrangement, for securing the abrasive wheel W onto the motor shafts Ms, the end portion Ms-1 of the motor shaft Ms is forced into the blind axial bore Uh of the bush member U. As the end portion Ms-l is inserted into the bore Uh, air remaining in a space Uo formed between the bottom portion Uf of the bore Uh and the end face Ms-2 of the motor shaft Ms is discharged externally through gaps Us formed between the peripheral walls Uw of the bore Uh and the peripheral face at the end portion Ms-1 of the motor shaft Ms, and upon completion of the fitting therebetween, the end face Ms-2 of the motor shaft Ms is brought into close contact with the bottom portion Uf of the bore Uh.In Figure 23, the peripheral walls Uw of the bore Uh of the bush member U contact the peripheral surface of the motor shaft Ms at six positions, i.e. at positions corresponding to respective normal lines of the peripheral walls Uw passing through the motor axis, and the peripheral walls Uw at such contact portions are deformed into arcuate shape along the peripheral surface of the end portion Ms-1 of the motor shaft Ms, and the portion of the peripheral walls Uw at opposite sides of the above portions deformed into the arcuate shape, are further deformed generally in tangential direction from said opposite sides, with the result that lines for the respective side faces of the peripheral walls Uw of the bore Uh are, on the whole, in wordly drawn in the axial direction, as compared with the initial state surrounded by twodotted line in Figure 23, thus preventing the bush member U from being deformed through expansion towards the side of the abrasive wheel W.

Referring to Figure 24, there is shown a modification of the arrangement of Figures 22 and 23.

In the modification of Figure 24, the end portion Ms-1 ' of the motor shaft Ms' is formed into a regular hexagonal shape, while the blind axial bore Uh' of the bush member U' is formed into a circular cross section, with the length D' of the diagonal line passing through the central axis of the motor shaft Ms' being made larger than the diameter d' of the axial bore Uh'.In this case also, upon insertion of the end portion Ms-l' into the bore Uh', air remaining in the space between the end face Ms-2' of the motor shaft Ms' and the bottom portion Uf' of the bore Uh' is externally discharged through the gaps Us' between peripheral surface of the end portion Ms-l' of the motor shaft Ms' and the inner peripheral walls Uw' of the bore Uh', and in this case, the arcuate portions between the respective contact portions of the circular perpheral wall Uw' pressed against the respective side faces of the motor shaft end portion Ms-1 ' having the hexagonal cross section are subjected to tension to have an increased radius of curvature as compared with the stage prior to the insertion surrounded by two-dotted lines in Figure 24, so as to be drawn, on the while, in the axial direction.

It should be noted here that in the arrangement of Figures 22 through 24, although the blind axial bore Uh of the bush member U or the end portion Ms-1 of the motor shaft Ms is described as formed into the regular hexagonal cross section, the cross sectional configuration is not limited to the above, but may be modified, for example, into a polygonal shape in which the respective peripheral wall surfaces or respective side faces are all held in pressure contact with an inscribed circle or an circumscribed circle to achieve the same effect as above.

As is clear from the above description, in the arrangements for fixing the abrasive wheels on the motor shaft of Figures 22 to 24, since either one of the blind axial bore Uh of the bush member U or the end portion Ms-1 of the motor shaft M is formed into a circular cross section, while the other is formed to have a polygonal cross section internally or externally contacting said circular cross section, air remaining in the space Uo between the bottom Uf of the axial bore Uh of the bush member U and the end face Ms-2 of the motor shaft Ms is externally discharged during insertion of the motor shaft Ms into the bore Uh, through air gaps Us formed between the peripheral surfaces of said bore Uh and motor shaft Ms, and thus, the motor shaft Ms can be readily fitted into the axial bore Uh, with axes thereof being aligned, so as to positively prevent any deviation in center of the abrasive wheels. Owing to the fact that no air under high pressure remains within the axial bore Uh after completion of the fitting, there is no possibility that the abrasive wheel unexpectedly comes off the motor shaft Ms.

Moreover, although the bush member U is deformed during insertion of the motor shaft Ms thereinto, by the amount equivalent to the fit-in margin, such strain due to the deformation is absorved by the narrowed inwardly in the direction of axis, and thus, almost no tension is applied to the abrasive wheel itself, and therefore, formation of cracks or damages to the abrasive wheels may be effectively prevented.

It should be noted here that in the foregoing embodiment, although the present invention has been mainly described with reference to the sharpener for edged tools provided with two abrasive wheels, the concept of the present invention is not limited in its application to the above embodiment alone, but may readily be applied to a sharpener for edged tools having one abrasive wheel or more than three abrasive wheels by merely changing the configuration of the openings and the lid member accordingly.

Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as included therein.

Claims (16)

1. An electrically driven blade sharpener comprising a casing, an electric motor mounted in the casing, a main on/off switch for turning the motor on and off, an abrasive member mounted on the driving shaft of the electric motor so that the abrasive member is rotated when the electric motor is turned on, a blade insertion guide slot located in an upper wall of the casing so that insertion of a blade to be sharpened into the slot brings the edge of the blade into contact with a side face of the abrasive member, an opening located in a lower wall of the casing below the abrasive member in a position where grinding debris would tend to collect when the abrasive member is rotated to sharpen the edge of a blade in contact therewith, and a closure member selectively operable to open or close the opening in the lower wall of the casing.

2. A blade sharpener according to claim 1 in which at least a portion of the inner surface of the closure member is made of heat-resistant material.

3. A blade sharpener according to claim 1 or claim 2, in which the closure member is provided with a magnet.

4. A blade sharpener according to any one of claims 1 to 3, comprising an auxiliary on/off switch which is automatically closed when the opening in the lower wall of the casing is closed by the closure member, and which is automatically opened to immobilisethe motor when the closure member is opened.

5. A blade sharpener according to any one of the preceding claims, comprising a protective cover which is mounted on the coasing so that the cover is movable between a protective position covering the blade insertion guide slot and an operating position in which the slot is exposed.

6. A blade sharpener according to claim 5, in which the protective cover is mounted on the casing to slide btween the protective and operating positions, and is arranged to cover both the blade insertion guide slot and the main on/off switch when in the protecting position, and to expose both the slot and the switch when in the operating position.

7. A blade sharpener according to any one of the preceeding claims, in which the electric meter is supended from the upper wall of the casing in a motor holder which is mounted to be movable towards and away from the blade insertion slot, and which is biassed by spring means engaging a guide pin on the motor holder to hold the motor and hence the abrasive member in a neutral position when the sharpener is not in use and to press the abrasive member against the edge to be sharpened when a blade is inserted in the blade guide slot.

8. A blade sharpener according to claim 7, in which the motor holder comprises a motor mounting base, a pair of similar side walls which extend from opposite side edges of the motor mounting base and which are each provided, in the same edge as each other, with a recess receiving a bearing boss axially extending from the corresponding end of the electric motor, and a resiliently deformable retaining pressure piece projecting from the motor mounting base and engaging the outer peripheral surface of the electric motor so as to press the bearing boss portions into the recesses and thereby hold the motor in the motor holder.

9. A blade sharpener according to any one of the preceding claims, in which the abrasive member is mounted on the driving shaft of the electric motor by means of an interference press fit of the end of the driving shaft in a blind axial bore in a central bush of resilient material fixed in the abrasive member, either the end of the driving shaft or the blind axial bore having a circular cross section while the other has a polygonal cross section.

10. A blade sharpener according to any one of the preceding claims, in which the electric motor is arranged to be short-circuited across its poles when the main on/off switch is turned off.

11. A blade sharpener according to any one of claims 1 to 9, in which the main on/off switch is connected in a power circuit for driving the motor when the switch is turned on, and is also connected in a braking circuit in parallel with the power circuit so that the braking circuit is open when the switch is on, and is closed to short-circuit the motor when the switch is off.

12. A blade sharpener according to claim 11, in which the braking circuit is connected across the electric motor through an indicator device which operates while the motor is still rotating following turning off of the main switch.

13. A blade sharpener according to any one of the preceding claims, in which the closure member is completely detachable from the casing.

14. A blade sharpener according to any one of the preceding claims, in which there are two blade insertion guide slots in the upper wall of the casing located so that insertion of a blade into one of the slots brings the edge on one side of the blade into contact with one side face of the abrasive member, and insertion of the blade into the other slot brings the edge on the other side of the blade into contact with the other side face of the abrasive member.

15. A blade sharpener according to any one of the preceding claims, in which there are more than one abrasive member mounted on the driving shaft of the motor for rotation thereby, each abrasive member having associated therewith at least one blade insertion guide slot in the upper wall of the casing and an opening in the lower wall which is normally closed by a closure member selectively operable to open or close the opening.

16. A blade sharpener according to claim 1, substantially as described with reference to Figures 1 to 12 and Figures 22 and 23, or as modified with reference to any one of Figures 13 to 15, or Figures 16 and 17, or Figures 18 and 19, or any one of Figures 20, 21 and 24 of the accompanying drawings.