Lawn mower cutting blade

Abstract

A robotic lawn mower cutting blade (1, 1a) with a longitudinal extent and two longitudinal side borders (3, 3a) comprises cutting edges (2, 2a) and an attachment portion. The attachment portion comprises an aperture (4, 4a) for a fastening device (8, 8a) and is arranged in a recess (6, 6a). The bottom of the recess (6, 6a) is arranged separate from a border plane defined by the longitudinal side borders (3, 3a). A cutting disk for a robotic lawn mower is configured to be rotatably arranged on a cutting shaft and comprises at least one cutting blade (1, 1a), which is pivotably arranged at a pivot (8, 8a), offset from the cutting shaft. A method of mounting the cutting blade (1, 1a) on a cutting disk of a robotic lawn mower, comprises the steps of arranging a fastening device (8, 8a) to extend through the aperture (4, 4a) in the recess (6, 6a), such that a head (9, 9a) of the fastening device (8, 8a) is arranged inside the recess (6, 6a); and tightening the fastening device (8, 8a) on the cutting disk.

Description

[0001] LAWN MOWER CUTTING BLADE

[0002] Field of the invention

[0003] The present invention relates to a robotic lawn mower cutting blade, having a longitudinal extent and two longitudinal side borders comprising cutting edges and an attachment portion comprising an aperture for a fastening device.

[0004] The invention also relates to a cutting disk for a robotic lawn mower, configured to be rotatably arranged on a cutting shaft.

[0005] The invention further relates to a method of mounting a cutting blade.

[0006] W02020011524A1 discloses a cutting blade for a robotic lawn mower. The cutting blade comprises an aperture for a fastening element on a cutting disk in the robotic lawn mower. The aperture is elongate and permits a pivoting motion of the cutting blade relative to the cutting disk. Since the cutting edges of the cutting blade are offset from the aperture, the cutting height may be very low.

[0007] A cutting blade with a similar configuration is disclosed in US3643409A.

[0008] However, in these disclosures the effective length of the cutting edges as compared with the total length of the blade is not very long, and a fairly large amount of raw material has to be used to provide an efficient length of the cutting edge. Also, the fastening element holding the cutting blade on the cutting disk is exposed to dirt and wear during the mowing. There is a need for a blade with improved durability and efficient use of raw material.

[0009] It is an object of the present invention to solve, or at least mitigate, parts or all of the above-mentioned problems. To this end, there is provided a cutting blade wherein the aperture is arranged in a recess, such that the bottom of the recess is arranged separate from a border plane defined by the longitudinal side borders, as seen in a section extending through the aperture perpendicular to the longitudinal extent.

[0010] Hereby a fastening, or attachment, device, such as a screw, which extends through the aperture, may be countersunk and its head may extend only in the space of the recess. It does not extend past the border plane, whereas the cutting edges extend in the border plane. The screw may hereby not contact the ground below the cutting blade during the mowing procedure, and the risk of damage to the fastening device or sensitive lawn surfaces is reduced. In particular, the cutting blade is manufactured such that the offset bottom of the recess and the border plane are provided in a single, contiguous piece. The manufacture of the cutting blade may take place by one or more of previously known manufacturing methods, such as punching, stamping, pressing, cupping, drawing, etc. The offset of the recess from the border plane is thus preferably large enough to contain the head of the fastening device. At the same time, the fastening device is arranged to allow a pivoting motion of the cutting blade around the fastening device.

[0011] In one embodiment the aperture is at least partly surrounded by a wall extending from the aperture to the border plane.

[0012] Hereby the lawn to be mowed is further protected from damages from the fastening device. Also, the head of the fastening device may be protected from wear and corrosion, and the risk that the fastening device may be difficult to release when needed may be reduced.

[0013] In a further embodiment, the wall encloses the aperture.

[0014] Hereby the recess may be sealed off, since it may be surrounded by an edge portion in the border plane. Also, a completely surrounding wall reduces the risk that the head of the fastening device gets caught in anything, and the risk of damages to the lawn is further reduced.

[0015] In some further embodiments, a section of the wall, taken along a plane parallel to the border plane, is circular.

[0016] Hereby a recess of a cylindrical or conical shape may be provided. Such a shape may be particularly easy to attain in a manufacture of large series of cutting blades.

[0017] In some even further embodiments, the wall at least partly coincides with a mantle surface of a cylinder.

[0018] Hereby the transversal, surrounding wall may extend smoothly around the aperture. The surrounding wall may form a suitable contact surface for a plug-shaped insert, which may be introduced into the recess.

[0019] In some embodiments the bottom of the recess is circular.

[0020] Hereby the surrounding wall may be smooth, and a fastening device, such as a screw extending through the aperture and the blade may be mutually rotated without risking an interference between the screw and the surrounding wall. In an alternative embodiment, the wall may be intermittent. Also, a plug-shaped insert may be easily insertable in the circular recess. Further the recess may be formed in a single step with the aperture during the manufacture of the cutting blade.

[0021] In some embodiments the thickness of the blade is uniform along said section.

[0022] Hereby the manufacture of the cutting blade may be relatively easy and costefficient. In some embodiments, a large number of cutting blades may be cut and formed in series from a band-shaped steel material.

[0023] In some embodiments the recess is arranged at one of the ends of the cutting blade as seen in the longitudinal direction of the cutting blade.

[0024] Hereby the cutting blade may be rotatably arranged on a fastening device, which in its turn is arranged on a cutting disk. The cutting blade may easily arrange itself in a position extending radially outwards from the center of the cutting disk, as the cutting disk is spinning.

[0025] In some embodiments the cutting blade comprises a detachable fastener cover mating with the recess.

[0026] Hereby, when a fastening device is arranged in the recess, the insert may cover the head of the insert and provide a smooth outer surface, which is arranged to face the lawn, during the operation of the lawn mower. The insert has a low profile facing the lawn and protects the lawn from any sharp parts of the fastening device.

[0027] In a further embodiment, the fastener cover is manufactured from a plastic material.

[0028] Hereby the insert may have a low surface friction facing the lawn and may not impede the rotation of the cutting disk close to the lawn.

[0029] In still further embodiments, the fastener cover comprises cylindrical walls and an end surface configured to be level with the border plane of the cutting blade.

[0030] Hereby the fastening device may be protected from any dirt or grass clippings entering the recess. The cutting blade may rotate smoothly on its fastening device, and neither the fastening device nor the cutting blade may be subject to excessive wear, and their respective lifetimes may be prolonged.

[0031] In some embodiments a wall next to the aperture extends approximately parallel to at least one tangent of the aperture.

[0032] Hereby the manufacture of the cutting blade from a band-shaped material may be facilitated, while still preventing the head of the fastening device from coming into contact with the lawn.

[0033] In some further embodiments the recess is elongate and extends in the longitudinal direction of the cutting blade. Hereby the manufacture may be facilitated, as mentioned previously, in particular from a band-shaped material. Another advantage is that the cutting blade with this shape may be very strong and may be used also for comparatively powerful mowers, often in the range of 300-900W. Also, the elongate recess may easily accommodate an elongate aperture.

[0034] In some even further embodiments, the aperture is elongate and extends in the longitudinal direction of the cutting blade.

[0035] Hereby a cutting blade which is not only rotatable, but also translatable to a certain extent, is attained. By an elongate aperture, the cutting blade may perform a longitudinal motion such that the fastening device may come into contact with either of the two ends of the aperture and the cutting blade is pivotable around the fastening device in either of these end positions. The translative motion of the cutting blade serves to distribute the wear on the cutting edges and thereby to prolong the life of the cutting blade. No manual action need be taken to reverse the cutting blade, in order to distribute the wear on all sides of the edges.

[0036] In some embodiments the cutting blade is integrally formed of metal.

[0037] Hereby the manufacturing process may be simplified, since no separate parts, of different materials need to be assembled.

[0038] According to a second aspect, parts or all of the above-mentioned problems are solved, or at least mitigated, by a cutting disk comprising at least one cutting blade a described above, pivotably arranged at a pivot, which is offset from the cutting shaft.

[0039] Hereby the cutting disk may be particularly useful for mowing areas where a very low cutting height is desired, without damage to the lawn or ground.

[0040] In a third aspect, the problems of the prior art may be solved by mounting a cutting blade as described above on a cutting disk of a robotic lawn mower, comprising the steps of: arranging a fastening device to extend through the aperture in the recess, such that a head of the fastening device is arranged inside the recess, and tightening the fastening device on the cutting disk.

[0041] Hereby a cutting disk with a very low cutting height may be attained.

[0042] In a further embodiment of the third aspect, the method further comprises the step of arranging a fastener cover in the recess to cover the head of the fastening device.

[0043] Hereby a particularly gentle mowing may be attained. It is noted that embodiments of the invention may be embodied by all possible combinations of features recited in the claims. Further, it will be appreciated that the various embodiments described for the device are all combinable with the method as defined in accordance with the second aspect of the present invention, and vice versa.

[0044] Brief description of the drawings

[0045] The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and nonlimiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:

[0046] Fig. 1 is a diagrammatic view in perspective of one embodiment of the disclosed cutting blade;

[0047] Fig. 2 is a sectional view of the cutting blade of Fig. 1 with a fastening device;

[0048] Fig. 3 is a view according to Fig. 2, including a fastener cover;

[0049] Fig. 4 is a perspective view of the cutting blade of Fig. 3, with the fastening device and fastener cover;

[0050] Fig. 5 is a perspective view of a second embodiment of the disclosed cutting blade with a fastening device; and

[0051] Fig. 6 is a sectional view of the cutting blade and fastening device of Fig. 5.

[0052] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted.

[0053] Detailed description of the exemplary embodiments

[0054] Fig. 1 illustrates one embodiment of a cutting blade 1 , which comprises two sharp cutting edges 2 along its longitudinal borders 3. The longitudinal borders 3 define a plane between them, in which plane the main part of the cutting blade 1 extends.

[0055] The cutting blade 1 has an aperture 4 for a fastening element, such as a screw, bolt, etc., for rotatable attachment of the cutting blade 1 to a cutting disk of a robotic lawnmower. The aperture 4 is arranged offset, in the longitudinal direction of the cutting blade 1 , from the mass center of the cutting blade 1 . The greater part of the mass is arranged in the area between the cutting edges 2. Hence the attached cutting blade 1 may take on an orientation with its cutting edges aligned radially outwards form the center of the rotating cutting disk, while yielding on encountering objects that are too hard to be cut. Since the direction of rotation of the cutting disk may reverse, both cutting edges 2 may be subjected to an equivalent amount of wear.

[0056] The area 5 around the aperture 4 is offset from the plane of extent defined by the longitudinal borders 3. A recess 6 is hereby formed, and the aperture 4 is located at the bottom of the recess 6, i. e. the area 5 around the aperture 4 forms the bottom of the recess 6. Although the plane of the area 5 around the aperture 4 is offset from the plane of extent as defined by the borders 3, the area 5 is still manufactured contiguously with the rest of the cutting blade 1 , extending between the borders 3. Typically, the recess 6 may be cup-shaped or trough-shaped. The offset between the area 5 around the aperture 4 and the plane of extent between the longitudinal borders 3 is preferably at least as large as the height of the head of the fastening device.

[0057] The side wall 7 of the recess 6 extend along a cylindrical or frustoconical shape, with the transitions to the bottom of the recess 6 and to the plane of extent defined by the borders 3, respectively, having smooth edges with a radius of 0.1 to 3 mm. The side wall 7 may surround the area 5 around the aperture 4 completely, as shown in Fig. 1 , but embodiments where there are apertures in the side wall 7 are also conceivable.

[0058] In Fig. 1 the bottom of the recess 6 is approximately circular, thereby affecting the shape of the surrounding side wall 7. In some embodiments, the aperture 4 may be elongate, and the area 5 around the aperture 4, as well as the surrounding side wall 7, may be adapted thereto.

[0059] The depth of the recess 6, i. e. the distance between the plane defined by the longitudinal side borders 3 and the offset area 5, is preferably corresponding to at least the height of the head 9 of a fastening element 8, as seen in Fig. 2. The height of the head 9 is measured in the longitudinal direction of the fastening element 8. The transverse dimension of the recess 6 is sufficient to accommodate the transverse dimension, typically the largest diameter, of the head 9 of the fastening element 8. Since the head 9 of the fastening element 8 is accommodated in the recess 6, the head 9 may be less subjected to wear and damages from dirt and contact with the ground than in constructions according to the prior art. At the same time, the cutting edges 2 may operate extremely close to the ground, without the impediment of the head 9 of the fastening element 8 touching the ground. A further advantage is that the risk that the head 9 of the fastening element 8 damages the lawn is greatly reduced.

[0060] In order to further protect the head 9 of the fastening element 8 from dirt, wear, and damages, a fastener cover 10 may be applied in the recess 6, covering the head 9 of the fastening element 8, as seen in Figs. 3 and 4. The fastener cover 10 comprises an approximately flat, rounded lid part 11 and a hollow, approximately cylindrical insert 12.

[0061] The material of the fastener cover 10 is preferably slightly deformable, and the outer circumference of the insert 12 is equal to or slightly larger than the inner circumference of the recess 6. Hereby a tight fit between the insert 12 and the side wall 7 of the recess 6 may be attained. In some advantageous embodiments, the surface friction of the outside of the insert 12 is high, such that the insert 12 may remain in its position in the recess 6, once inserted.

[0062] When the insert 12 of the fastener cover 10 is inserted in the recess 6, the rounded lid part 11 extends only a very short distance over the plane defined by the longitudinal borders 3 of the cutting blade 1 , as seen in both Figs 3 and 4. Hence the cutting blade 1 may still operate at a very low cutting height. The outer circumferential edge 13 of the lid part 11 of the fastener cover 10 is rounded, such that the cutting blade 1 with the fastener cover 10 may smoothly pass over the lawn to be mowed without any damage thereto. Also, the risk that the fastener cover 10 gets caught on the lawn or the ground and is ripped out of the recess 6 is very low. In some embodiments, the outer surface of the lid part 11 has a low friction vis-a-vis the lawn, such that the resistance during the mowing is minimized.

[0063] In Fig. 5, another embodiment of the disclosed cutting blade 1 a is shown. The cutting blade 1 a has two cutting edges 2a along its two longitudinal borders 3a. A recess 6a extends in a longitudinal direction of the cutting blade 1 a. An aperture 4a is arranged at the bottom of the recess 6a. In the embodiment disclosed in Fig. 5, the aperture 4a is elongate, but embodiments wherein the aperture 4a is of another shape, e. g. circular, are also conceivable. A fastening element 8a is arranged in the aperture 4a, and the cutting blade is slidably and pivotably arranged thereon. The fastening elements 8a are arranged on a cutting disk (not shown in the figures) near the outer circumference thereof, offset a distance from the cutting shaft of the mower. The elongate aperture 4a may enable the cutting blade 1 a to shift its position relative to the fastening element 8a. When the cutting disk, whereon the cutting blade 1a is arranged, is rotated with a high velocity around the cutting shaft of the mower, the cutting blade 1 a may align itself to extend radially from the center of the cutting disk. When the cutting blade 1 a encounters an obstacle, it may temporarily yield and sometimes also shift its position on the fastening element 8a. On continued rotation of the cutting disk, it will resume a position in approximate alignment with the radius of the cutting disk. Either end of the cutting blade 1 a may extend outwards, provided that the mass distribution is approximately the same at both ends of the longitudinal aperture 4a. Over time the arrangement with an elongate aperture 4a may entail an evenly distributed wear on the cutting edges 2a, if both ends of the cutting blade 1a are turned outwards with approximately the same probability.

[0064] Since the recess 6a extends from one transversal border 14 to the opposite, the aperture 4a is not enclosed on all its sides by the side walls 7a. However, since the bottom of the recess 6a is offset from the plane of the longitudinal borders 3a, the head 9a of the fastening element 8a is protected from direct contact with the ground, and hereby protected from most of the wear and dirt from the lawn and the ground. Also, the lawn and the ground are protected from damages that may be caused by contact with the head 9a of the fastening element 8a rotating near the edge of the cutting disk of a lawnmower. Only that plane of the cutting blade 1a which is defined by the longitudinal borders 3a comes typically into contact with the lawn and the ground.

[0065] Another advantage of the longitudinally extending recess 6a and side walls 7a is that the stiffness and resistance to bending of the cutting blade 1a, as seen in a direction transverse to the longitudinal direction, is increased. Hereby a stronger and more durable cutting blade 1 a results, without the use of excessive amounts of raw material, i. e. metal. An embodiment which may be easy to manufacture in large quantities is integrally formed by punching, cutting and / or bending of a single material, e. g. a metal band or a metal sheet in only one or a few operations.

[0066] The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

[0067] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Claims

Claims1 . A robotic lawn mower cutting blade (1 , 1 a), having a longitudinal extent and two longitudinal side borders (3, 3a) comprising cutting edges (2, 2a) and an attachment portion comprising an aperture (4, 4a) for a fastening device (8, 8a), wherein the aperture (4, 4a) is arranged in a recess (6, 6a), such that the bottom of the recess (6, 6a) is arranged separate from a border plane defined by the longitudinal side borders (3, 3a), as seen in a section extending through the aperture (4, 4a) perpendicular to the longitudinal extent.

2. The cutting blade (1 , 1a) according to claim 1 , wherein the aperture (4, 4a) is at least partly surrounded by a wall (7, 7a) extending from the aperture (4, 4a) to the border plane.

3. The cutting blade (1 , 1a) according to claim 2, wherein the wall (7, 7a) encloses the aperture (4, 4a).

4. The cutting blade (1 , 1a) according to claim 2 or claim 3, wherein a section of the wall (7, 7a), taken along a plane parallel to the border plane, is circular.

5. The cutting blade (1 , 1a) according to any of claims 2 to 4, wherein the wall (7, 7a) at least partly coincides with a mantle surface of a cylinder.

6. The cutting blade (1 , 1a) according to any of the preceding claims, wherein the bottom of the recess (6, 6a) is circular.

7. The cutting blade (1 , 1a) according to any of the preceding claims, wherein the thickness of the blade (2, 2a) is uniform along said section.

8. The cutting blade (1 , 1a) according to any of the preceding claims, wherein the recess (6, 6a) is arranged at one of the ends of the cutting blade (1 , 1 a) as seen in the longitudinal direction of the cutting blade (1 , 1 a).

9. The cutting blade (1 ) according to any of the preceding claims, comprising a detachable fastener cover (10) mating with the recess (6).

10. The cutting blade (1 ) according to claim 9, wherein the fastener cover (10) is manufactured from a plastic material.1 1 . The cutting blade (1 ) according to claim 9 or claim 10, wherein the fastener cover (10) comprises cylindrical walls (12) and an end surface (11 ) configured to be level with the border plane of the cutting blade (1 ).

12. The cutting blade (1 , 1 a) according to any of claims 1 or claim 2, wherein a wall (7, 7a) next to the aperture (4, 4a) extends approximately parallel to at least one tangent of the aperture (4, 4a).

13. The cutting blade (1 , 1 a) according to any of claims 1 , 2, or 12, wherein the recess (6, 6a) is elongate and extends in the longitudinal direction of the cutting blade (1 , 1 a).

14. The cutting blade (1 , 1 a) according to any of claims 1 , 2, 12, or 13, wherein the aperture (4, 4a) is elongate and extends in the longitudinal direction of the cutting blade (1 , 1 a).

15. The cutting blade (1 , 1 a) according to any of the preceding claims, wherein the cutting blade (1 , 1 a) is integrally formed of metal.

16. A cutting disk for a robotic lawn mower, configured to be rotatably arranged on a cutting shaft and comprising at least one cutting blade (1 , 1 a) according to any of claims 1 to 15, pivotably arranged at a pivot (8, 8a), which is offset from the cutting shaft.

17. A method of mounting a cutting blade (1 , 1 a) according to any of claims 1 to 15 on a cutting disk of a robotic lawn mower, comprising the steps of:- arranging a fastening device (8, 8a) to extend through the aperture (4, 4a) in the recess (6, 6a), such that a head (9, 9a) of the fastening device (8, 8a) is arranged inside the recess (6, 6a); and- tightening the fastening device (8, 8a) on the cutting disk.

18. The method according to claim 17, further comprising the step of arranging a fastener cover (10) in the recess (6) to cover the head (9) of the fastening device (8).

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