Patent Description:
A cutting tool often has one or more laterally extending, straight or curvilinear cutting edges along which pressure is applied to make a cut. The cutting edge is often defined along the intersection of opposing surfaces (bevels) that intersect along a line that lies along the cutting edge.

In some cutting tools, such as many types of conventional kitchen knives, the opposing surfaces are generally symmetric; other cutting tools, such as many types of scissors and chisels, have a first opposing surface that extends in a substantially normal direction, and a second opposing surface that is skewed with respect to the first surface.

Complex blade geometries can be used, such as multiple sets of bevels at different respective angles that taper to the cutting edge. Scallops or other discontinuous features can also be provided along the cutting edge, such as in the case of serrated knives.

Cutting tools can become dull over time after extended use, and thus it can be desirable to subject a dulled cutting tool to a sharpening operation to restore the cutting edge to a greater level of sharpness. A variety of sharpening techniques are known in the art, including the use of grinding wheels, whet stones, abrasive cloths, abrasive belts, etc..

<CIT> discloses a knife sharpening machine, using an endless abrasive belt, comprises a pair of guide pulleys around which the belt extends to provide an operative run, with one of the pulleys movable to tauten the belt. A slotted guide in a casing of the machine enables a knife to be presented to the operative run of the belt at a correct angle. The belt and pulleys, as well as an optional resilient support for the operative run of the belt, may all be provided in a removable cartridge.

<CIT> discloses a spring tension grinding machine.

<CIT> discloses a n apparatus arranged for grinding, polishing, etc. with a closed loop of grinding, polishing, etc. belt mounted on the output shaft of a motor and driven by a rotating drive wheel. This loop belt is intended to be applied against a workpiece which is to be machined by means of the loop belt, said closed loop having loop portions differing from one another in running direction. The loop is steered by steering members to adopt an essential L-shape and comprising at least two loop portions, of which the loop portion which is arranged to make contact with said workpiece is preferably selected shorter than the other loop portion. Said drive wheel for driving of the belt is arranged displaceable relative to a foundation by a guide steered by the foundation and turnable by means of guide members arranged on the guide. An angle existing between the L-shaped coil portions of the loop is resettable, for instance by means of resetting members and is lockable by means of locking members.

Various embodiments of the present disclosure are generally directed to a sharpener for sharpening a cutting tool having a blade portion with a cutting edge, such as but not limited to a kitchen knife.

In some embodiments, the sharpener has first and second rollers, with the first roller rotatable about a first roller axis and the second roller rotatable about a second roller axis parallel to the first roller axis. An endless abrasive belt is arranged along a belt path that passes over the first and second rollers to define a planar segment that lies along a neutral plane from the first roller to the second roller. A guide assembly adjacent the planar segment of the belt is configured to contactingly engage the cutting edge of the cutting tool and apply a non-uniform surface pressure to a side of the cutting tool adjacent the cutting edge across a width of the belt.

In some embodiments, the non-uniform surface pressure is established by inducing tilt in the cutting edge relative to the belt. In other embodiments, the non-uniform surface pressure is established by inducing skew in the cutting edge relative to the belt. In yet further embodiments, the non-uniform surface pressure is established by using a support member which supports the belt in a position near the application of the cutting tool to the belt, the support member inducing localized skew of the belt.

These and other features and advantages of various embodiments can be understood with a review of the following detailed description in conjunction with the accompanying drawings.

Generally, so-called slack belt sharpening techniques can be used to sharpen the cutting edge of a cutting tool, such as a knife, using a power-driven endless abrasive belt. One non-limiting example of a slack belt powered sharpener is provided in <CIT>, assigned to the assignee of the present application.

As discussed more fully in the '<NUM> patent, slack belt sharpening generally involves using an unsupported expanse of abrasive belt to contactingly engage a cutting edge of a knife or other cutting tool at an appropriate presentation (bevel) angle to deform a portion of the belt out of a neutral plane (e.g., a planar extent of the belt extending between a pair of belt supports, such as rollers). The deflection of the belt generally induces a small twisting effect in relation to curvilinear changes in the cutting edge along the length of the knife.

In this way, a user can draw the cutting edge across the moving belt and the belt will automatically adjust to follow the contour of the cutting edge as it removes material along the blade portion of the knife. By applying respective sharpening operations to opposing sides of the blade, a sharpened cutting edge can be efficiently produced.

While operable, one limitation that has been found with these and other forms of slack-belt sharpeners is a non-uniform amount of material removal along the length of the blade (e.g., so called material take off, or MTO rate). Certain types of cutting tools, such as kitchen ("chef") knives, tend to have a curvilinearly extending cutting edge with relatively small amounts of curvature near a handle of the knife and increasingly greater amounts of curvilinearity near the tip of the blade. In such knives, it has been found that the unsupported segment of the belt can tend to remove too little material at the base of the blade near the handle, and too much material near the tip. One factor that induces this variation is the amount of deflection (twist) induced in the belt; generally, the greater the deflection, the higher the localized surface pressure and higher the corresponding MTO rate.

It follows that some belt sharpening operations can result in a rounding of the tip of the blade rather than retaining the tip as a sharp, well defined point, as well as incomplete sharpening of the cutting edge immediately adjacent the handle. While the user may be able to mitigate these and other effects through controlled presentation and withdrawal of the blade across the belt, various embodiments of the present disclosure present a number of operative features that can promote easier, more consistent abrasive belt sharpening that reduces such variations in surface pressure and corresponding MTO rates during a sharpening operation.

As explained below, such features include the use of what is collectively and/or variously referred to herein as "tilted angle abrasive belt sharpening. " Generally, tilted angle abrasive belt sharpening, also referred to as "modified slack belt sharpening," refers to a novel sharpener configuration and methodology that purposefully induces a selected non-orthogonal alignment between the cutting edge of the knife or other cutting tool with respect to the abrasive belt in order to better control surface pressures and corresponding MTO rates across the width of the belt. A variety of different approaches can be used to achieve this tilted sharpening effect.

In some embodiments, a presentation angle of the knife or other cutting tool is fixed at a selected non-orthogonal angle with respect to the axis of one or more rollers along which the endless abrasive belt is driven. This may be carried out by tilting the belt path in a "backward" direction so that the top of the belt path is moved in a direction away from the user and using a substantially horizontal set of edge guides to support the presentation of the tool. Another way in which the non-orthogonal angle can be established is by skewing the presentation angle of the knife inwardly with respect to the belt. Yet another way the non-orthogonal angle can be established is through the use of a backing support member the supports the belt in the vicinity of the contact zone. These respective approaches can be combined or used individually.

In each of these cases, surface pressures and corresponding MTO rates are controlled to enhance the sharpening process. Depending on the configuration, greater surface pressures and higher MTO rates can be supplied to the front edge of the belt (e.g., closer to the user or adjacent a proximal end of the tool) and lower surface pressures and lower MTO rates can be supplied to the rear edge of the belt (e.g., farther from the user or adjacent a distal end of the tool).

These and other features and advantages of various embodiments of the present disclosure can be understood beginning with a review of <FIG> which shows a functional block diagram of a tilted angle abrasive belt sharpener <NUM>. An initial overview of various operative elements of the sharpener <NUM> will enhance an understanding of various sharpening geometries established by the sharpener which will be discussed below. It will be appreciated that sharpeners constructed and operated in accordance with various embodiments can take various forms so that the particular elements represented in <FIG> are merely for illustrative purposes and are not limiting.

The exemplary sharpener <NUM> is configured as a powered sharpener designed to rest on an underlying horizontal base surface, such as a table top, and to be powered by a source of electrical power such as residential or commercial alternating current (AC) voltage, a direct current (DC) battery pack, etc. Other forms of tilted angle abrasive belt sharpeners can be implemented, including handheld sharpeners, non-powered sharpeners, etc. that employ the various features disclosed herein.

The sharpener <NUM> includes a rigid housing <NUM> that may be formed of a suitable rigid material such as but not limited to injection molded plastic. A user switch and power control module <NUM> includes one or more user operable switches (e.g., power, speed control, etc.) and power conversion circuitry to transfer electrical power to an electrical motor <NUM>.

The motor <NUM> induces rotation of a shaft or other coupling member linked to a power transfer assembly (PTA) <NUM>, which may include various mechanical elements such as gears, linkages, etc. which, in turn, impart rotation to one or more drive rollers <NUM>. It is contemplated albeit not necessarily required that the drive roller <NUM> will rotate at a steady state rotational velocity during powered operation of the sharpener.

An endless abrasive belt <NUM> extends about the drive roller <NUM> and at least one additional idler roller <NUM>. In some cases, multiple rollers may be employed by the sharpener, such as three or more rollers to define a segmented belt path. A tensioner <NUM> may impart a bias force to the idler roller <NUM> to supply a selected amount of tension to the belt. A guide assembly <NUM> is configured to enable a user to present a cutting tool such as a knife against a segment of the belt <NUM> between the respective rollers <NUM>, <NUM> along a desired presentation orientation, as discussed below.

A schematic representation of the belt path is provided in <FIG> in accordance with some embodiments. A generally triangular path is established for the belt <NUM> through the use of three rollers: the drive roller <NUM> in the lower left corner, the idler roller <NUM> at the top of the belt path, and a third roller <NUM> which may also be an idler roller. It will be appreciated that any number of belt paths can be established using any suitable corresponding numbers and sizes of rollers as desired so that a triangular path is used in some embodiments, but not others. The tensioner <NUM> (<FIG>) is represented as a coiled spring operable upon the idler roller <NUM> in a direction away from the remaining rollers <NUM>, <NUM>. Other tensioner arrangements can be used including, but not limited to, a tensioner that applies the tension force to lower idler roller <NUM>.

The belt <NUM> has an outer abrasive surface denoted generally at <NUM> and an inner backing layer denoted generally at <NUM> that supports the abrasive surface. These layers are shown more fully in <FIG>. The relative thicknesses of these respective layers can vary. The abrasive surface <NUM> includes a suitable abrasive material operative to remove material from the knife during a sharpening operation. The backing layer <NUM> provides mechanical support and other characteristic features for the belt such as belt stiffness, overall thickness, belt width, etc. The backing layer <NUM> is configured to contactingly engage the respective rollers <NUM>, <NUM> and <NUM> during powered rotation of the belt along the belt path.

The exemplary arrangement of <FIG> establishes two respective, elongated planar segments <NUM>, <NUM> of the belt <NUM> against which the knife or other cutting tool can be presented for sharpening operations on alternate sides thereof. Segment <NUM> substantially extends from roller <NUM> to roller <NUM>, and segment <NUM> substantially extends from roller <NUM> to roller <NUM>. Each of the segments <NUM>, <NUM> normally lies along a neutral plane that is orthogonal to respective rotational axes 110A, 114A and 120A of the rollers <NUM>, <NUM> and <NUM>.

Each segment <NUM>, <NUM> is unsupported by a corresponding restrictive backing support member against the backing layer <NUM>. This allows the respective segments to remain aligned along the respective neutral planes in an unloaded state and to be rotationally deflected ("twisted") out of the neutral plane during a sharpening operation through contact with the knife. It is contemplated that one or more support members can be applied to the backing layer <NUM> in the vicinity of the segments <NUM>, <NUM>, such as in the form of a leaf spring, etc., so long as the support member(s) still enable the respective segments to be rotationally deflected away from the neutral plane during the modified slack-belt sharpening operation. A specially configured support member that provides controlled support to less than the full width of the belt will be discussed below.

<FIG> shows aspects of the exemplary sharpener <NUM> in accordance with some embodiments. A cutting tool <NUM>, in the form of a kitchen (or chef) knife, is presented against the segment <NUM> of the belt <NUM> between rollers <NUM>, <NUM>. The knife <NUM> includes a user handle <NUM> and a blade <NUM> with a curvilinearly extending cutting edge <NUM>. The cutting edge <NUM> extends to a distal tip <NUM> and is formed along the intersection of opposing sides (not numerically denoted) of the blade <NUM> which taper to a line. Removal, honing and/or alignment of material from the respective sides of the blade <NUM> operate to produce a sharpened cutting edge <NUM> along the entire length of the blade.

An abrasive belt axis is represented by broken line <NUM> and indicates a direction of travel and alignment of the belt <NUM> during operation. The abrasive belt axis <NUM> is nominally orthogonal to the respective roller axes 110A, 114A of rollers <NUM>, <NUM> (identified in the drawing as Roller Axes <NUM> and <NUM>).

A pair of edge guide rollers are represented at <NUM>, <NUM>. The edge guide rollers form a portion of the aforementioned guide assembly <NUM> (see <FIG>), and can be made of any suitable material designed to support portions of the cutting edge <NUM>. Other forms of edge guides can be used, including stationary edge guides as discussed below.

Generally, the edge guide rollers <NUM>, <NUM> provide a retraction path <NUM> for the blade <NUM> as the user draws the cutting edge across the belt <NUM> via the handle <NUM>. The retraction path <NUM> is non-orthogonal to the abrasive belt axis <NUM>. The intervening angle between lines <NUM> and <NUM> is referred to herein as a tilt angle, and is denoted in <FIG> as angle A.

A second angle, referred to herein as a bevel angle, is represented as angle B in <FIG>. Generally, the bevel angle B represents the intervening angle between the abrasive belt axis <NUM> and a lateral centerline of the blade <NUM>, denoted at <NUM>. The tilt angle can be thought of as the relative angle of the cutting edge <NUM> "across" the belt (see <FIG>) and the bevel angle can be thought of as the relative angle of the blade <NUM> "along" the belt (see <FIG>).

The magnitude of the tilt angle A can vary. In some embodiments, the tilt angle A as defined in <FIG> is selected to be less than <NUM> degrees, such as but not limited to the range of from about <NUM> degrees to about <NUM> degrees. This is in contrast to other belt sharpeners, such as but not limited to the sharpener disclosed in the '<NUM> patent mentioned above, which provides a presentation angle of nominally <NUM> degrees. At this point it will be noted that other formulations for the tilt angle can be used as desired. For example, a review of <FIG> shows that the tilt angle can alternatively be defined as the non-orthogonal angle between the presentation line <NUM> and the respective roller axes 110A, 114A (e.g.. , the complementary angle to angle A). Using this alternative formulation, the tilt angle may be on the order of from about <NUM> degree to about <NUM> degrees.

The magnitude of the bevel angle B can also vary. In some embodiments, the bevel angle B is selected to be in the range of from about <NUM> to about <NUM> degrees. The bevel angle generally determines the side geometry of the blade adjacent the cutting edge. For clarity, it will be appreciated that the conformal nature of the belt <NUM> will tend to impart a convex curvilinear shape to the side of the cutting edge rather than a flat "bevel" shape. Nevertheless, the term "bevel" is useful in generally denoting the relative orientation between the belt extent <NUM> and the blade <NUM>.

The non-orthogonal tilt angle A is selected to reduce the deflection of the rear edge of the belt (e.g., that portion of the belt farthest from the handle) and to increase the deflection of the front edge of the belt (e.g., that portion of the belt closest to the handle). Tilting the belt with respect to the blade such as exemplified in <FIG> provides a more uniform average surface pressure across the length of the cutting edge <NUM> from the handle <NUM> to the tip <NUM>.

Referring again to <FIG>, it will be noted that the edge guide rollers <NUM>, <NUM> define the presentation line <NUM> so as to be nominally horizontal (e.g., along the X-Y plane), and the belt is tilted forward so that the respective roller axes 110A, 114A are skewed with respect to the horizontal direction. This allows the user to present the knife <NUM> in a substantially horizontal fashion as the knife is drawn across the belt. This arrangement is merely illustrative and is not limiting. In other embodiments, these respective elements may be rotated such that the belt <NUM> is vertical (e.g., roller axes <NUM>10A and <NUM>14A are horizontally disposed and the belt extends along the X-Z plane), and the edge guide rollers <NUM>, <NUM> are adjusted so that the presentation line <NUM> extends upwardly in a non-horizontal fashion. In this latter case, the user may draw the knife across the belt such that the handle <NUM> is relatively lower and the tip <NUM> is relatively higher above a horizontal base surface on which the sharpener rests. Other arrangements may be used as well.

<FIG> is an isometric depiction of another knife <NUM> adjacent the belt <NUM>. The knife <NUM> is similar to the knife <NUM> discussed above and includes a handle <NUM>, blade <NUM> and cutting edge <NUM>. During sharpening, the cutting edge <NUM> is drawn across the belt <NUM> in direction <NUM>. Respective front and rear edges of the belt are denoted with respect to this direction. It will be recalled that the front edge of belt is that portion of the width of the belt closest to the handle <NUM>, and the rear edge is that portion of the width of the belt farthest away from the handle.

<FIG> is a cross-sectional representational view of the rear edge deflection encountered by the belt. <FIG> shows a corresponding cross-sectional representational view of the front edge deflection encountered by the belt. Dotted line <NUM> represents the neutral plane along which the belt <NUM> normally lies in the absence of the knife <NUM> or other cutting tool.

From <FIG> it can be seen that a larger amount of deflection (twist) is incurred at the front edge of the belt as compared to the rear edge. The tilt angle and the width of the belt will influence the difference between the front and rear deflection. This difference can be optimized for a specific belt/abrasive combination as well as for the shape of the blade being sharpened. Generally, decreasing the tilt angle A (see <FIG>) and/or increasing the belt width will tend to increase the difference between the front and rear deflection amounts. This in turn will adjust the relative surface pressure and MTO rates at the front and rear edges.

The particular configuration of the sharpener <NUM> (see <FIG>) can be arranged to achieve the desired tilt and bevel angles. As noted above, the belt and rollers can be "canted" within the interior of the housing <NUM> so that a user presents the knife (or other cutting tool) via the guide assembly <NUM> in a substantially horizontal orientation, as generally depicted in <FIG>. In other embodiments, the belt and rollers can be nominally vertically aligned within the housing <NUM> and the user can present the knife against the guide assembly <NUM> at an elevated, non-horizontal orientation. These and other considerations are well within the ability of the skilled artisan to implement depending on the requirements of a given application.

<FIG> illustrate aspects of the sharpener <NUM> of <FIG> in accordance with further embodiments. A knife <NUM> includes a handle <NUM>, blade <NUM> and cutting edge <NUM> which tapers to a point <NUM>. The aforementioned guide assembly <NUM> includes a guide member <NUM> which provides a guide surface in facing relation to the belt <NUM> to facilitate alignment of the blade <NUM> thereagainst. A stationary edge support surface <NUM> allows the user to support a portion of the cutting edge <NUM> as the user withdraws the blade across the belt <NUM> in direction <NUM>. It will be noted that a single edge guide surface <NUM> can be used as illustrated in <FIG>, or multiple edge guide surfaces 170A, 170B can be utilized as illustrated in <FIG>.

The relative tilt angle A between the guide <NUM> and the belt <NUM> is contemplated as extending from about <NUM> degrees to about <NUM> degrees, as indicated in <FIG>. Other angles can be used so long as the tilt angle is nominally non-orthogonal to an axis associated with the belt path (e.g., belt axis, roller axis).

As noted above, an alternative way to define the non-orthogonal tilt angle A is to state that the retraction path line <NUM> is non-parallel with the associated roller axes that support the segment of belt against which the knife is drawn (see e.g., roller axes 110A, 114A in <FIG>). Using this latter formulation, the tilt angle range of <NUM>-<NUM> degrees between lines <NUM>, <NUM> would correspond to the complementary angle range of from about <NUM> to about <NUM> degrees between line <NUM> and the roller axes 110A, 114A (see e.g., <FIG>).

<FIG> shows the use of two guides <NUM> on opposing sides of the topmost roller <NUM> to enable double sided sharpening operations. <FIG> shows a top plan view of a portion of one of the guides <NUM>, and <FIG> shows a corresponding elevational view of the guide from <FIG>. The guide <NUM> includes a substantially vertically extending outward portion 168A, a substantially horizontally extending base portion 168B and a substantially vertically extending inward portion 168C.

The aforementioned edge surface <NUM> extends along the top of portion 168B. An inwardly facing guide surface <NUM> extends along portion 168A, and an outwardly facing guide surface <NUM> extends along portion 168C. Surfaces <NUM>, <NUM> and <NUM> form a generally u-shaped channel, or guide slot, to accommodate the knife <NUM>. The edge guide surface contactingly supports the cutting edge <NUM>, and the opposing side surfaces can contactingly support the opposing sides of the blade <NUM>. The relative elevation and orientation of the surfaces <NUM>, <NUM> and <NUM> are selected with respect to the central axis <NUM> of the belt <NUM> (see <FIG>) to provide the desired tilt angle. It will be noted that the guide surfaces <NUM>, <NUM> lie along associated planes each parallel to each of the roller axes <NUM>10A, 114A and 120A.

<FIG> shows an alternative construction for the guide <NUM>. The respective interior guide surfaces <NUM>, <NUM> and <NUM> taper to provide narrowed, substantially v-shaped guide slot. The guide elements 168A-168C may be formed of a suitable non-abrasive cuttable or non-cuttable material to support the cutting tool.

<FIG> show another embodiment for the sharpener <NUM> of <FIG>. Similar elements are identified by like reference numerals from <FIG>. <FIG> shows the knife <NUM> to be aligned in the guide member <NUM> with the stationary edge guide surface <NUM> from <FIG>. In this case, the retraction path line <NUM> is nominally orthogonal to the belt axis <NUM> (e.g., nominally <NUM> degrees), as shown by <FIG>.

However, as further shown by the top plan view of <FIG>, the guide <NUM> and edge support surface <NUM> are skewed with respect to the central axis 114A of the top roller <NUM> (see <FIG>) by a skew angle C. Unlike in <FIG> where the tilt angle A is generally along the X-Z plane, the skew angle C in <FIG> is along the X-Y plane. The skew angle C between the axis 114A and the line <NUM> is on the order of about <NUM> to about <NUM> degrees. Other ranges of angles can be used as required.

Further amounts of non-orthogonality can be supplied by combining the arrangement of <FIG> with that of <FIG>; for example, the guide member <NUM> can be aligned so as to be nonparallel with the axis 114A as in <FIG> as well as non-orthogonal to the belt axis <NUM> as in <FIG>. Stated another way, both some measure of tilt angle A and skew angle C can be concurrently imparted by the guide member <NUM>. As before, the guide <NUM> can use a single edge guide surface <NUM> (see, e.g., <FIG>) or a pair of edge guide surfaces (see e.g., guide surfaces 170A and 170B in <FIG>).

While the tilt belt arrangement of <FIG> can provide similar benefits as an arrangement such as shown in <FIG>, it will be noted by those skilled in the art that arrangements such as depicted in <FIG> may enable better sharpening at the base of the blade adjacent the handle since larger features (e.g., thumb guards, etc.) proximate the juncture between handle and blade can be more readily accommodated. It is noted that the skewed guides in <FIG> can take the general configurations shown in <FIG> except that the respective guides are skewed. For example, the respective guide surfaces <NUM>, <NUM> would lie along respective planes that intersect (e.g., are non-parallel with) the roller axes <NUM>10A, 114A and 120A.

<FIG> show another configuration of the tilted belt abrasive sharpener <NUM> of <FIG> in accordance with further embodiments. A localized support member <NUM> is supported by a stationary, rigid base (shown schematically at <NUM>) behind the belt <NUM>. The support member <NUM> is arranged to contactingly engage and support the backing layer <NUM> as the belt <NUM> moves in direction of travel <NUM>. The support member <NUM> is represented as a cylindrically shaped, tapered pin for clarity of illustration, although any number of different configurations can be used as required.

A suitable low wear material may be used for stationary support members such as <NUM>. Any number of contact shapes can be used (e.g., circular, oval, rectangular, etc). It is contemplated that the support member <NUM> and base <NUM> may be incorporated as a portion of the guide assembly used to support the cutting tool (see e.g., guide <NUM> in <FIG>).

As further illustrated in <FIG>, the support member <NUM> is offset with respect to a centerline <NUM> of the belt <NUM> so as to provide contacting support to the backing layer <NUM> on only a single side of the centerline, e.g., on the side closest to the handle of the tool (e.g., the front edge of the belt; see <FIG>). A contact region <NUM> generally represents that portion of the belt <NUM> that will nominally contact the side of the tool during the sharpening operation. The location of tool contact is offset (e.g., above) the pin <NUM>. The side of the belt farthest from the handle of the tool (e.g., the rear edge of the belt) remains unsupported.

As the belt serpentines over the pin and adjacent the tool, a greater surface pressure and a higher MTO rate are applied closer to the handle (front edge of the belt or to the right of centerline <NUM> in <FIG>), and a lower surface pressure and a lower MTO rate are applied farther from the handle (rear edge of the belt or to the left of centerline <NUM> in <FIG>).

The relative presentation angle of the tool (see e.g., line <NUM> in <FIG>) can be any suitable angle, including orthogonal or non-orthogonal to the belt centerline <NUM>. The support member <NUM> can thus be used in a stand-alone fashion, or can be added to any of the previous embodiments utilized above.

<FIG> show yet another embodiment for the tilt angle abrasive belt sharpener <NUM> of <FIG> that is similar to the embodiment of <FIG>, except that the embodiment of <FIG> uses a rotatable support member <NUM> ("support roller") that is arranged to rotate about a rotatable roller axis 200A to provide variable surface pressure and MTO rates across the width of the belt <NUM>.

<FIG> show the sharpener in an unloaded condition. <FIG> show corresponding views of the sharpener in a loaded condition (e.g., with the presentation of a knife blade <NUM>).

As shown by <FIG>, two (<NUM>) rotatable support rollers <NUM> are used to provide double sided sharpening configurations in opposing guide slots (not separately shown) in a triangular belt path arrangement similar to that discussed above in <FIG>. Each of the rotatable support members <NUM> is characterized as a cylindrically shaped roller, although other configurations can be used.

For example, in an alternative embodiment, each support member <NUM> has a tapered (e.g., frusto-conical) shape so that the support varies in a direction toward the rear edge of the belt. Other shapes can be used such as crowned rollers, etc. While the support rollers <NUM> extend across the full width of the belt <NUM>, this is merely exemplary and is not limiting. In other embodiments, the support rollers <NUM> may extend less than a full width across the belt.

The roller axes 200A of the support rollers <NUM> are skewed inwardly from the front edge to the rear edge of the belt so as to be non-parallel with the roller axes 110A, 114A and 120A of the belt rollers <NUM>, <NUM> and <NUM>. The amount of skew of the support roller axes 200A can vary, but may be on the order of from about <NUM>-<NUM> degrees with respect to the belt roller axes 110A, 114A and 120A. This induces a localized increase in the surface pressure of the belt <NUM> upon each roller <NUM> toward the front edge, as depicted by force vectors <NUM> in <FIG>.

The force vectors <NUM> in <FIG> represent a variable force that is applied across the width of the belt <NUM><NUM>, from a largest amount of force being applied adjacent the front edge and successively smaller amounts of force being applied in a direction away from the front edge and toward the rear edge. The actual extent and rate of change of the applied force in a given system will depend on a number of factors relating to the belt, tensioner, radius and location of the support roller, skew angle of the support roller, etc. For purposes of clarity, it will be noted that the view provided in <FIG> is generally a top down view of the left-side support roller <NUM> (see <FIG>) with the belt in cross section at the point of contact against the support roller.

<FIG> shows the loaded (e.g., sharpening) condition of <FIG> in greater detail. Placing the support roller <NUM> adjacent and below the contact location for the cutting edge of the knife blade <NUM> against the belt <NUM> induces a localized, generally S-shaped serpentine path (indicated generally by path <NUM>) for the belt.

More specifically, this serpentine path <NUM> is caused by passage of the belt <NUM> over the skewed support roller <NUM>, which induces a small amount of twist in the belt, with less belt deflection adjacent the front edge of the belt and greater belt deflection adjacent the rear edge of the belt. The belt continues to pass upwardly until the belt encounters the inward side of the knife blade <NUM>. The belt contactingly engages this inward side to perform a sharpening operation upon a cutting edge of the blade. The blade then continues to pass upwardly to upper roller 114A (see <FIG>).

As the belt <NUM> engages the side of the knife blade <NUM>, the belt induces a variable surface pressure as generally represented by force vectors <NUM> in <FIG>. As before, greater amounts of surface pressure and MTO rate are experienced along the front edge of the belt <NUM>, and these values are reduced across the width of the belt toward the rear edge.

While the serpentine path <NUM> in <FIG> is shown to be traveling generally upwardly in <FIG>, it will be appreciated that the same general forces represented in <FIG> will be experienced if the direction of belt travel is reversed, such as for a sharpening operation applied to the second support roller <NUM> on the right side of the system diagram in <FIG>.

<FIG> show another tilt angle abrasive belt sharpener <NUM> in accordance with some embodiments. The sharpener <NUM> is similar to the sharpener <NUM> discussed above. <FIG> is an isometric view of the sharpener <NUM>. <FIG> provides a top plan view, <FIG> is a front (user) side view, and <FIG> is a rear side view.

The sharpener <NUM> is a powered combination sharpener configured to rest on a horizontal base surface <NUM> during operation. As explained below, the sharpener <NUM> includes an endless abrasive belt that is driven along three rollers in a manner as discussed above in <FIG> to provide a triangular belt path. The roller axes are parallel and are each tilted forward in a manner similar to that shown in <FIG>, so that the belt cants forward at a selected non-orthogonal angle A on the order of about <NUM> degrees (see e.g., <FIG>).

An internal motor rotates the belt along the belt path. The motor may be mounted at the same tilt angle so that an output drive shaft of the motor is parallel to the roller axes and non-parallel to the horizontal direction. Alternatively, an internal linkage system can be used to link a horizontally disposed motor drive shaft to the non-horizontal roller axes. The sharpener further utilizes stationary guide slots with edge guide surfaces that are arranged in a horizontal fashion, as generally depicted in <FIG>.

Referring now specifically to <FIG>, the sharpener <NUM> has a rigid housing <NUM> formed of a suitable material, such as injection molded plastic, and encloses various elements of interest such as the motor, transfer assembly, rollers, control electronics, etc. The housing <NUM> includes a plurality of spaced apart base support contact features (e.g., pads) <NUM> configured to provide stable support of the housing on the underlying horizontal base surface <NUM>. A user activated power on/off switch is shown at <NUM>.

An endless abrasive belt <NUM> is partially enclosed by the housing <NUM>. Linear extents <NUM>, <NUM> of the belt are exposed adjacent corresponding guide slots <NUM>, <NUM> (best viewed in <FIG>). The guide slots <NUM>, <NUM> are substantially v-shaped in a manner similar to that shown above in <FIG> and include horizontally aligned, bottom edge surfaces <NUM>, <NUM> in each of the guide slots <NUM>, <NUM>. The belt <NUM> is tilted forward approximately <NUM> degrees with respect to the horizontal base surface <NUM>; stated another way, the roller axes of the rollers disposed within the housing <NUM> and about which the belt <NUM> passes are skewed (nonparallel) with the horizontal plane established by the support contact features <NUM> by about <NUM> degrees.

To sharpen a cutting tool such as a kitchen knife, the user activates the sharpener <NUM> using the switch <NUM>. While facing the front side of the sharpener (e.g., <FIG>), the user grasps the handle of the knife, places the blade into a selected guide slot (e.g., slot <NUM>) so that the cutting edge rests on the bottom edge surface (e.g., edge surface <NUM>) and the side of the blade contacts the belt <NUM> (e.g., belt extent <NUM>) nearest the handle. The configuration of the guide slot will ensure the desired tilt and bevel angles are maintained. The user withdraws the knife across the belt while maintaining contact with the edge surface. To the extent that the knife has a curvilinear cutting edge, the user may raise the handle during this backward stroke to maintain contact between the cutting edge and the edge guide surfaces <NUM>.

The foregoing process may be repeated a suitable number of times, such as <NUM>-<NUM> times. This applies a primary sharpening operation to one side of the knife. The user then places the knife in the other slot (e.g., slot <NUM>) and repeats. This completes the primary sharpening operation to the other side of the knife, producing a sharpened cutting edge. The tilt angle configuration of the sharpener will provide enhanced surface pressure and MTO control, and tip rounding will be avoided.

Continuing with <FIG>, a leg portion of the housing <NUM> is generally represented at <NUM>. This leg portion <NUM> extends from the main body of the housing to support a secondary abrasive member <NUM>. The secondary abrasive member <NUM> is comprises a stationary ceramic abrasive rod, although other forms of abrasive members can be used. The abrasive rod <NUM> is tapered and is disposed at a selected angle with respect to horizontal (in this case, about <NUM> degrees). Guide surfaces <NUM>, <NUM> are disposed at each end of the rod <NUM>. The tapered shape allows large or small serrations to be individually sharpened as desired.

In some cases, the user may elect to perform a secondary sharpening operation upon the knife using the abrasive rod. This is carried out by placing the side of the blade against a selected one of the guide surfaces (such as the surface <NUM>) to establish a desired orientation angle of the blade with respect to the rod <NUM>. Once oriented, the user advances the blade along the rod while retracting the cutting edge thereacross, maintaining the angular orientation established by the guide surface. This can be repeated a number of times, such as <NUM>-<NUM> times, after which the process may be repeated using the other guide surface (e.g., surface <NUM>). This applies a secondary honing operation to further sharpen the knife. In this way, the sharpening applied against the rod <NUM> is similar to sharpening applied using a steel-type sharpener.

In some cases, the primary sharpening angle applied to the blade by the belt <NUM> may be a first value, such as nominally <NUM> degrees, and the secondary sharpening angle applied to the blade by the rod <NUM> may be a second value, such as nominally <NUM> degrees. This allows the blade to be configured with a micro-beveled geometry to enhance sharpness and durability. Touch up sharpening may be applied using just the ceramic rod <NUM> as desired. Sharpening may be applied by the belt without the use of the ceramic rod.

<FIG> show yet another tilt angle abrasive belt sharpener <NUM> in accordance with some embodiments. The sharpener <NUM> is similar to the sharpener <NUM> discussed above. <FIG> is an isometric view of the sharpener <NUM> from one vantage point, and <FIG> is an isometric view of the sharpener <NUM> from another vantage point and is partially cutaway to show selected interior components of interest.

As with the sharpener <NUM>, the sharpener <NUM> is a powered sharpener configured to rest on a horizontal base surface <NUM> during operation. Generally, an endless abrasive belt is driven along a triangular belt path over three internally disposed rollers that are parallel with each other and are each tilted forward at a selected non-orthogonal angle with respect to the horizontal direction. An internal motor rotates the belt along the belt path, and includes an output drive shaft that is parallel to the roller axes and non-parallel to the horizontal direction. Guide slots are arranged with stationary, horizontal edge guide surfaces to provide non-orthogonal angles with respect to the belt roller axes.

With reference now to <FIG>, a rigid housing <NUM> encloses various elements of interest such as the motor, transfer assembly, rollers, control electronics, etc. Base support contact features (e.g., pads) <NUM> extend from the housing <NUM> and are aligned along a horizontal plane to rest on the base surface <NUM>.

An endless abrasive belt <NUM> is routed along a plurality of rollers, including rollers <NUM>, <NUM>. Opposing guide slots <NUM>, <NUM> operate as before to enable a user to carry out modified slack-belt sharpening on opposing distal extents of the belt. An interior motor drive shaft <NUM> transfers rotational power to the drive roller <NUM> via a drive belt <NUM>.

It will now be appreciated that the various embodiments presented herein can provide a number of benefits over the prior art. By providing a non-orthogonal alignment angle such as but not limited to those shown in <FIG>, a differential deflection can be induced across the width of the belt with respect to the blade being sharpened. This provides a more uniform surface pressure and MTO rate against the side of the blade along the length thereof and tends to reduce increases of surface pressure at points along the cutting edge that experience relatively large amounts of variation of curvature, such as points adjacent the tip of the blade. As noted above, this non-orthogonal "tilt angle" belt sharpening can be carried out by enacting one or more of a tilt angle B (see e.g., <FIG> and <FIG>), a skew angle C (see e.g., <FIG>), and/or an offset/skewed support member (see e.g., <FIG>; <FIG>; and <FIG>).

Claim 1:
A sharpener (<NUM>, <NUM>, <NUM>) for sharpening a cutting tool (<NUM>, <NUM>, <NUM>) having a blade portion (<NUM>, <NUM>, <NUM>, <NUM>) with a cutting edge (<NUM>, <NUM>, <NUM>) affixed to a user handle (<NUM>, <NUM>, <NUM>), the sharpener comprising:
- first and second rollers (<NUM>, <NUM>, <NUM>), the first roller rotatable about a first roller axis (110A, 114A, 120A), the second roller rotatable about a second roller axis (110A, 114A, 120A) parallel to the first roller axis;
- an endless abrasive belt (<NUM>, <NUM>, <NUM>) arranged along a belt path that passes over the first and second rollers to define a planar segment (<NUM>, <NUM>) that lies along a neutral plane from the first roller to the second roller, the belt having a belt axis (<NUM>); and
- a guide assembly (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) arranged adjacent the planar segment of the belt, the guide assembly (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising edge guide rollers (<NUM>, <NUM>) or a side guide member (<NUM>), the edge guide rollers (<NUM>, <NUM>) or the side guide member (<NUM>) defining a retraction path line (<NUM>) along which the blade is retracted during a sharpening procedure, wherein the retraction path line (<NUM>) and the belt axis (<NUM>) are oriented at a non-orthogonal tilt angle relative to one another or the side guide member (<NUM>) and the first roller axis are non-parallel to one another, so as to cause the belt to apply a non-uniform surface pressure to the side of the blade of the cutting tool adjacent the cutting edge across a width of the belt so that a greater amount of surface pressure is applied by a portion of the belt adjacent a proximal end of the blade portion adjacent the user handle of the cutting tool and a lesser amount of surface pressure is applied by a portion of the belt adjacent a distal end of the blade portion opposite the user handle.