FIELD OF THE DISCLOSURE

The present disclosure relates to knife sharpeners, more particularly to knife sharpeners of the type having rotating grinding drums.

BACKGROUND OF THE DISCLOSURE

Traditionally, knife sharpening has been done by grinding the edge of the knife against a grinding stone one side at a time. This procedure creates a burr which is removed by altering side and using finer grit grinding stones. To remove any residual burr and to create optimal sharpness a leather sharpening strop is often used for as a final stage. The traditional sharpening process requires a very specific set of skills and is generally perceived as cumbersome. To this end, commercial knife sharpeners have been provided, in which the knife is fed along a pair of sharpening elements, which grind both sides of the knife’s edge at a set angle. While this simplifies the sharpening process, problems may still arise as the tip or heel of the knife may slip from the grinding elements. This problem is particularly prominent when a pair of driven grinding drums are used as the grinding elements, because the blade of a slipped knife may hit parts of the grinding drum other the actual grinding surface, which, in turn, may damage the blade of the knife and I or the knife sharpener.

For example, documents JP H0816943, US 3484997, US3758993 and US 1184517 disclose sharpeners according to the prior art.

BRIEF DESCRIPTION OF THE DISCLOSURE

An object of the present disclosure is to provide a knife sharpener having a simple structure, providing good sharpening results and minimising the risk of user error during operation.

The object of the disclosure is achieved by a knife sharpener which is characterized by what is stated in the independent claims. The preferred embodiments of the disclosure are disclosed in the dependent claims.

The disclosure is based on the idea of providing a pair grinding drums each equipped with a grinding portion radially protruding from their respective cylindrical bodies. The grinding portions are arranged axially staggered and radially overlapping with each other. Each of the griding drums is also equipped with a gear arranged at or adjacent to an axial end of their respective cylindrical bodies, thereby rotationally coupling the grinding drums. Particularly, the grinding portions of the grinding drums have an outer diameter exceeding that of their respective gears.

Rotationally coupling the grinding drums to each other with gears provides for a simple, reliable structure of the knife sharpener which can be fitted in compactly. Moreover, providing the grinding portions as radially protruding from the cylindrical bodies of the grinding drums and having a diameter exceeding that of their respective gears minimizes the risk of a knife (particularly the tip or heel of the blade’s edge) slipping and hitting the gears as it passed along the grinding portion of the grinding drum.

According to the present disclosure, a knife sharpener comprising a first grinding drum and a second grinding drum is provided.

The first grinding drum comprises a first cylindrical body and a first grinding portion arranged on the first cylindrical body radially protruding therefrom. The first grinding portion extends axially along and circumferentially around the first cylindrical body. The first grinding drum further comprises a first gear arranged at or adjacent to an axial end of the first cylindrical body.

The second grinding drum comprises a second cylindrical body and a second grinding portion arranged on the second cylindrical body radially protruding therefrom. The second grinding portion extends axially along and radially around the second cylindrical body. The second grinding drum further comprises a second gear arranged at or adjacent to an axial end of the second cylindrical body.

The knife sharpener further comprises a motor arranged to rotationally drive either or both of the first grinding drum and the second grinding drum. Advantageously, a belt drive, such as a toothed belt and associated pulleys, can be arranged between the motor and either one of the first and second grinding drums. Moreover, the first gear and the second gear are arranged mutually engaged with each other, thereby rotationally coupling the first grinding drum and the second grinding drum. Suitably, the first and second gears are directly coupled to each other, thereby resulting in the first and second grinding drum rotating in opposite directions.

Moreover, the first grinding portion and the second grinding portion are arranged axially staggered with respect to each other and to radially overlap each other. Most suitably, the first and second grinding portions are provided with a suitable, wear resistant abrasive coating, suitably electroplated fine grinding grits, e.g., a carbide grits, ceramic grits, diamond grits, or CBN (cubic boron nitride) -grits. The remainder of the grinding portion, and suitably the grinding wheel, may be made of a different material, such as steel. Particularly, the first grinding portion and the first gear are arranged concentrically with the first cylindrical body, such that the first grinding portion has an outer diameter greater than that of the first gear. In a similar manner, the second grinding portion and the second gear are arranged concentrically with the second cylindrical body, such that the second grinding portion has an outer diameter greater than that of the second gear.

As mentioned, this results in a simple structure for rotating the grinding drums, while ensuring that the contact line of a knife being sharpened (i.e., the line at which the first grinding portion intersects with the second grinding portion) is radially spaced apart from the first and second gears, thereby minimizing the risk of the knife contacting said gears.

In an embodiment according to the present disclosure, the first grinding drum comprises a first flange at and axial end thereof, such that the first flange has an outer diameter equal to that of the first grinding portion. Correspondingly, the second grinding drum comprises a second flange at and axial end thereof, wherein the second flange has an outer diameter equal to that of the second grinding portion. Particularly the first flange and second flange radially overlap each other and are axially spaced apart from each other.

Providing an additional support point (i.e., the flanges) at an axial end of the grinding drum minimisers the risk of user error during operation by preventing the edge of the knife from slipping off the grinding portion at an axial end thereof as the knife is advanced along the grinding portions.

Additionally, or alternatively, the first grinding drum may comprise a first flange at and axial end thereof, such that the first gear is situated axially between the first grinding portion and the first flange. Particularly, the first flange has an outer diameter greater than that of the first gear and equal to that of the first grinding portion. Correspondingly, the second grinding drum may comprise a second flange at and axial end thereof, such that the second gear is situated axially between the second grinding portion and the second flange. Particularly, the second flange has an outer diameter greater than that of the second gear and equal to that of the second grinding portion. In such a case, the first flange and second flange radially overlap each other and are axially spaced apart from each other.

Providing an additional support point (i.e., the flanges) at an axial end of the grinding drum such that the respective gears reside between the flanges and the grinding portion minimisers the risk of user error during operation by preventing the edge of the knife from slipping off the grinding portion at an axial end thereof and hitting the respective gear as the knife is advanced along the grinding portions. Preferably, but not necessarily, the first grinding drum may comprise a first flange at both opposing axial ends thereof, and the second grinding drum comprises a second flange at each opposing axial end thereof.

Moreover, any such flanges may be coated in similar manner as the grinding portions.

In an embodiment according to the present disclosure, a first central axis of the first cylindrical body is coplanar with a second central axis of the second cylindrical body.

Preferably, but not necessarily, a distance between the first central axis and the second central axis at first axial ends thereof differs from the distance between the first central axis and the second central axis at second axial ends thereof, wherein said second axial ends being opposite to the first axial ends.

This allows the sharpening angle to differ between the axial ends of the grinding drums, allowing a faster sharpening process in addition to improved sharpness.

Suitably, at the first axial ends, a first inclination between a first tangent line of the first grinding portion and a second tangent line of the second grinding portion at a cross- sectional intersection point of the first grinding portion and the second grinding portion, as seen along the first central axis and the second central axis, is between 26 - 32 deg. Preferably, the first inclination may be between 27 - 31 deg, and more preferably between 28 - 30 deg.

Suitably, at the second axial ends, a second inclination between a first tangent line of the first grinding portion and a second tangent line of the second grinding portion at a cross- sectional intersection point of the first grinding portion and the second grinding portion, as seen along the first central axis and the second central axis, is between 33 - 39 deg. Preferably the second inclination may be between 34 - 38 deg, and more preferably between 35 - 37 deg.

Such a configuration has been considered to provide a combination of most efficient sharpening and best results for obtained sharpness. Particularly, when the knife to be sharpened is introduced between the grinding drums at the first axial ends (corresponding to an inlet side of the knife sharpener) and passed along therethrough towards the second axial ends (corresponding to an outlet side of the knife sharpener), a convex sharpening profile of the knife’s blade is obtained, which also improves the longevity of sharpness.

In an embodiment according to the present disclosure, either or both of the first grinding drum or the second grinding drum are adjustably supported such that the distance between the first central axis and the second central axis is adjustable at either or both of the first axial ends and the second axial end. Such an arrangement allows the sharpening angles to be optimized for different types of knives.

For example, an adjustable support element may be provided at an axial end of the first grinding drum, such that the distance between the first central axis and the second central axis at said axial end is adjustable by moving said adjustable support element.

Alternatively, or in addition, an adjustable support element may be provided at an axial end of the second grinding drum, such that the distance between the second central axis and the first central axis at said axial end is adjustable by moving said adjustable support element.

Suitably, the first and second gears of the first and second grinding drums, respectively, are arranged at the first axial ends, while the first and second grinding drums are adjustably supported at the second axial ends so as to allow adjustment of the distance between the first central axis and the second central axis at the second axial ends. Such an arrangement allows adjustment of the sharpening angle at the second axial ends while maintaining sufficient alignment of the first and second gears.

Suitably, at least the distance between the first central axis and the second central axis is adjustable at the second axial ends between a first position and a second position, such that a second inclination in the second position exceeds that in the first position by 2 - 7 degrees, preferably by 3-6 degrees and more preferably by 4-5 degrees. Particularly, the second inclination is defined between a first tangent line of the first grinding portion and a second tangent line of the second grinding portion at a cross-sectional intersection point of the first grinding portion and the second grinding portion at the second axial ends, as seen along the first central axis and the second central axis.

Such an arrangement is considered advantageous, as an increased second inclination (corresponding to the sharpening angle at an outlet side of the knife sharpener) during a final sharpening pass of the knife helps remove any residual burrs caused by slight misalignment of the knife during previous passes and results in improved sharpness.

Naturally, the second inclination in the second position could exceed that the second inclination at the first position by even further, e.g., by 10 degrees, which would be advantageous for adjusting the sharpening angle for different types of knifes.

In an embodiment according to the present disclosure, the first gear and second gear are involute gears. Involute gears are considered to be most resistant to slight misalignment of the gears due to possible adjustment of distance between the first central axis and the second central axis. In an embodiment according to the present disclosure, the first grinding portion extends helically around and along the first cylindrical body, and the second grinding portion extends helically around and along the second cylindrical body. Such a helical arrangement of the grinding portions ensures a uniform sharpening along the length of the knife’s blade, as the grinding portions are constantly in relative movement with respect to the knife’s edge along the length thereof.

In an embodiment according to the present disclosure, the knife sharpener further comprises a frame for supporting the remaining knife sharpener on a surface. Most suitably, at least the first grinding drum and the second grinding drum are supported on a cradle pivotable with respect to the frame, so as to allow a limited mutual tilting motion of the first central axis and the second central axis with respect to the surface, on which the knife sharpener is supported on. This allows the grinding drums to align with the edge of the knife, and thereby prevent misalignment thereof.

It should be noted that the present disclosure encompasses any combination of two or more embodiments, or variants thereof, as discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Fig. 1 schematically illustrates a grinding drum arrangement of a knife sharpener according to an embodiment of the present disclosure, as seen from above.

Fig. 2 schematically illustrates a portion of a knife sharpener according to an embodiment of the present disclosure in an uncovered configuration, as seen as a perspective view;

Fig. 3 schematically illustrates a knife sharpener according to an embodiment of the present disclosure in a covered configuration, as seen as a perspective view.

Fig. 4 schematically illustrates a grinding drum arrangement of a knife sharpener according to the present disclosure, as seen from a side of first axial ends of the grinding drums, and

Fig. 5 schematically illustrates a grinding drum arrangement of a knife sharpener according to the present disclosure, as seen from a side of second axial ends of the grinding drums. DETAILED DESCRIPTION OF THE DISCLOSURE

Fig. 1 schematically illustrates a grinding drum arrangement of a knife sharpener 1 according to an embodiment of the present disclosure, as seen from above. A first grinding drum 2 is shown comprising a first cylindrical body 3, and a first grinding portion 4 arranged thereon. The first grinding portion 4 extends radially from, axially along and circumferentially around the first cylindrical body 3. Particularly, the first grinding portion 4 extends helically around the first cylindrical body 3. A first flange 6 is arranged at a first axial end 3a of the first cylindrical body and a first gear 5 is arranged adjacent to the first axial end 3a of the first cylindrical body 3, such that the first gear 5 is axially situated between the first grinding portion 4 and the first flange 6. A further first flange 6’ is provided at a second, opposite axial end 3a’ of the first cylindrical body 3. The first flange 6 has an outer diameter greater than that of the first gear 5 and equal to that of the first grinding portion 4, whereas an outer diameter of the further first flange 6’ is suitably dimensioned identically with that of the first flange 6.

In a similar manner, a second grinding drum 7 is shown comprising a second cylindrical body 8, and a second grinding portion 9 arranged thereon. The second grinding portion 9 extends radially from, axially along and circumferentially around the second cylindrical body 8. Particularly, the second grinding portion 9 extends helically around the cylindrical first body 8. A second flange 11 is arranged at first axial end 8a of the second cylindrical body 8 and a second gear 10 is arranged adjacent to the first axial end 8a of the second cylindrical body 8, such that the second gear 10 is axially situated between the second grinding portion 9 and the second flange 11 . A further second flange 1 T is provided at a second, opposite axial end 8a’ of the second cylindrical body 8. The second flange 11 has an outer diameter greater than that of the second gear 10 and equal to that of the second grinding portion 9, whereas an outer diameter of the further first flange 11 ’ is suitably dimensioned identically with that of the second flange 11 .

Particularly, the first gear 5 and the second gear 10 are arranged mutually engaged with each other, thereby rotationally coupling the first grinding drum 2 and the second grinding drum 7. Moreover, the first grinding portion 4 and the second grinding portion 9 are arranged axially staggered with respect to each other and to radially overlap each other. Also, the pitches of the helical grinding portion 4, 9 is configured so as to maintain the staggering and overlapping as the grinding drum 3, 8 are rotated.

Moreover, a distance d1 between a first central axis 3b of the first cylindrical body 3 and a second central axis 8b of the second cylindrical body 8 at the first axial ends 3a, 8a is different than the distance d2 between said first central axis 3b and said second central axis 8b at the opposing, second axial ends 3a, 8a.

Although not indicated in Fig. 1 , the outer diameter of the first grinding portion 4 exceeds that of the first gear 5, and respectively, the outer diameter of the second grinding portion 9 exceeds that of the second gear 10.

Fig. 2 schematically illustrates a portion of a knife sharpener, including the grinding drum arrangement of Fig.1 , according to an embodiment of the present disclosure in an uncovered configuration, as seen as a perspective view. Particularly, the configuration of Fig. 2 illustrates the knife sharpener 1 without a frame 14 (illustrated in Fig. 3). Particularly, the first grinding drum 2 and the second grinding drum 7 are rotatably supported on a cradle 15. The second grinding drum 7 is rotationally coupled to a motor 13, which is also supported on the cradle 15. The motor 13 is powered by an electrical power supply, provided as a battery 16, which too, is supported on the cradle 15. It should be noted that the knife sharpener could equally well be mains powered. An axial end of the first griding drum 2 is attached to the cradle 15 by an adjustable support element 12, which allows for adjustment of the distance d2 between the first central axis 3b of the first cylindrical body 3 and the second central axis 8b of the second cylindrical body 8, and thereby, the sharpening angle.

Moreover, the cradle 15 is provided with opposing lugs, which allow it to be supported on a frame 14 such that the cradle 15 is pivotable with respect to the frame 14. This, in turn, allows a limited mutual tilting motion of the first central axis 3b and the second central axis 8b with respect to the surface, on which the knife sharpener 1 is supported on.

Fig. 3 illustrates the knife sharpener 1 of Fig. 2 with the frame 14 in place, i.e. covering the cradle 15 and the components supported thereon.

Fig. 4 schematically illustrates a grinding drum arrangement of a knife sharpener 1 according to the present disclosure, as seen from a side of first axial ends 3a, 8a of the grinding drums 2, 7, whereas Fig. 5 schematically illustrates a grinding drum arrangement of a knife sharpener 1 according to the present disclosure, as seen from a side of opposing second axial ends 3a’, 8a’ of the grinding drums 2, 7.

Particularly, Fig. 4 illustrates a configuration in which the central axis 3b of the first grinding drum 2 is at a distance d1 form the central axis 8b of the second grinding drum 7. In such a case, a first inclination A1 is defined between a first tangent line t1 of the first grinding portion 4 and a second tangent line t2 of the second grinding portion 9 at a cross-sectional intersection point x1 . Correspondingly, Fig. 5 illustrates a configuration in which the central axis 3b of the first grinding drum 2 is at a distance d2 form the central axis 8b of the second grinding drum 7. In such a case, a second inclination A2 is defined between a second tangent line t1 ’ of the first grinding portion 4 and a second tangent line t2’ of the second grinding portion 9 at a cross-sectional intersection point x2.

In an exemplary arrangement, the grinding portions 4, 9 have an outer diameter of 32 mm, and the gears 5, 10 have been dimensioned to an outer diameter of 31 ,8 mm to 31 ,9 mm, which has been found to be suitable to prevent collision between the blade of the knife being ground and the teeth of the gears 5, 10. Moreover, this allows the gears 5, 10 to dimensioned to have 62 teeth with a modulus of 0,5, thereby resulting in a pitch circle of 31 mm. The pitch circle also corresponds to the distance d1 between the central axis 3b of the first grinding drum and the central axis 8b of the second grinding drum 7 at the first axial ends 3a, 8a thereof. Consequently, such an arrangement results in a first inclination A1 of 28,8 degrees, which has been considered a suitable sharpening angle for an inlet side of the knife sharpener, i.e., a side from which the knife is introduced into the sharpener.

Furthermore, the distance d2 between the central axis 3b of the first grinding drum 2 and the central axis 8b of the second grinding drum 7, at the second axial ends 3a’, 8a’ thereof, is set at 30,4 mm. This, in turn, results in a second inclination A2 of 36,4 degrees, which is considered a suitable sharpening angle for an outlet side of the knife sharpener, i.e., a side opposing the inlet side. Providing a greater inclination angle A2 at the outlet end than the inclination angle A1 at the inlet end of the knife sharpener 1 results in a convex sharpening profile, which provides a more efficient sharpening process and improved longevity of the sharpened edge. With the exemplary arrangement described above, a rotation speed of the grinding drums 2, 7 of 2000 to 3000 rpm has been considered advantageous, i.e. providing fast sharpening, while minimising the risk of excessive heating of the knife’s blade and annealing of the steel.

LIST OF REFERENCE NUMERALS

1 knife sharpener

2 first grinding drum

3 first cylindrical body

3a first axial end of first cylindrical body

3a’ second axial end of first cylindrical body 3b first central axis

4 first grinding portion

5 first gear

6, 6’ first flange

7 second grinding drum

8 second cylindrical body

8a first axial end of second cylindrical body

8a’ second axial end of second cylindrical body

8b first central axis

9 second grinding portion

10 second gear

11 second flange

12 adjustable support element

13 motor

14 frame

15 cradle

16 battery

A1 first inclination

A2 second inclination d1 distance between the first and second central axes at first axial ends d2 distance between the first and second central axes at second axial ends t1 first tangent line at first axial end t1 ’ first tangent line at second axial end t2 second tangent line at first axial end t2’ second tangent line at second axial end x1 cross sectional intersection point at first axial ends x2 cross sectional intersection point at second axial ends