SE2250836A1

SE2250836A1 - Cutting blade for a lawn mower

Info

Publication number: SE2250836A1
Application number: SE2250836A
Authority: SE
Inventors: Michael Kistler; Thomas Renner
Original assignee: Husqvarna Ab
Priority date: 2022-07-04
Filing date: 2022-07-04
Publication date: 2024-01-05
Also published as: DE102023117460A1

Abstract

A grass cutting blade (5) for a lawn mower is elongate with two longitudinal sides and comprises at least one cutting edge (12) on at least one of its longitudinal sides. The cutting blade (5) has an attachment opening (8) with a mounting portion (11) and at least one working portion (9). The width of the mounting portion (11) is larger than the width of the working portion (9).In a combination of at least one cutting blade (5) and a protection plate (7), the cutting blade (5) and the protection plate (7) are mounted on a cutting disk (4). The cutting blade (5) is held in place by the protection plate (7) while being rotatable.

Description

Field of the invention The present invention relates to a grass cutting blade for a lawn mower, the cutting blade being elongate with two Iongitudinal sides and comprising at least one cutting edge on at least one of the Iongitudinal sides of the cutting blade and an attachment opening in an area between the Iongitudinal sides.

The invention also relates to a combination of at least one cutting blade, according to any of the preceding claims, and a protection plate.

Finally, the invention relates to a robotic lawn mower.

Background EP4000366A1 is one document which discloses a cutting blade with a Iongitudinal slit, through which a pivot pin on a cutting disk extends. The pin is typically an attachment device, such as a screw. The cutting blade is kept from falling off the cutting disk by the head of the screw, which is unable to pass through the slit. When the cutting disk rotates at a high speed, the blades may extend radially outwards from the pins on the cutting disk. On impact with obstacles, the blades may yield. Also, the rotational direction of the cutting disk is arbitrary and may change occasionally. Then the cutting action may be performed by the cutting edge on the opposite Iongitudinal side of the blade.

An additional feature of the disclosed blades is that they may turn on impact, so that the pin comes into contact mainly with an opposite end of the slit. The opposite cutting edge of the respective blade then faces forward in the direction of rotation, and the cutting ability of the blade is still intact. Blades that turn in this manner around pins have the advantage of an extended lifetime, since all side edges of the blades may come into use, thereby distributing the wear over a larger surface. Also, the blades may or may not turn, if the direction of rotation of the cutting disk is reversed.

Regardless of whether a cutting blade turns entirely around its pivot pin or if it just yields, the mounting and dismounting thereof may be equally time consuming. 1 Each screw serving as a pin must be unscrewed and then screwed back in place, when a blade is exchange for a new one. There are usually at least three blades on a cutting disk, and in many cases, there is also a skid plate that has to be removed as well, before the screws are accessible. The procedure is time-consuming and requires at least one screwdriver with a driver suited to the head of the screws. The needed tools may not always be available, thereby delaying the process of exchanging the cutting blades.

Summary lt 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 attachment opening has a mounting portion and at least one working portion, wherein a width of the mounting portion, in a direction transversal to the longitudinal sides, is larger than a width of the working portion in the direction transversal to the longitudinal sides.

Hereby the cutting blade may be removed from an attachment device without the use of tools. The blade may be slid to a position where an attachment device extends through the mounting portion of the attachment opening. Since the mounting portion is designed to be wide enough to let an upper part of the attachment device pass therethrough, the blade may in this position be lifted off the attachment device. A new cutting blade may be easily installed by the reverse procedure. The new blade is hence positioned with the mounting portion of its attachment opening above the attachment device, and thereafter lowered, so that the upper part of the attachment device may pass through the mounting portion. The cutting blade may then be slid in its plane of extension, until the attachment device is positioned in a working portion.

Each of the at least one working portions has one open end and one closed end. The number of working portions may be different in different embodiments of the cutting blade, but there are usually one or two working portions. The open end of each working portion is open into the mounting portion, so that the cutting blade may be slid from a position with the attachment device in the mounting portion to a position in a working portion and vice versa. ln an embodiment, both longitudinal sides of the blade are provided with cutting edges.

Hereby the cutting blade may cut the grass regardless of the direction of rotation of the cutting disk, and regardless of the orientation of the cutting blade, as long as it extends outside the cutting disk. ln other embodiments there is one single working portion and one single mounting portion in the attachment opening.

Hereby a blade with an attachment opening shaped generally as a keyhole may result. The mounted blade on the cutting disk should extend outwards by action of the centrifugal force, but it may yield in case of contact with obstacles, such as twigs or branches, that are too thick to be cut, or rocks etc. on the ground. A yielding blade reduces the risk of damages to the cutting blade as well as to the cutting disk or other parts of the lawn mower. ln some embodiments the working portion of the attachment opening of the cutting blade is partially surrounded by a band of material of an approximately uniform width, adjacent to the opening.

Hereby the cutting blade may be configured to pivot around its attachment device in a predictable motion. The outer edge of the cutting blade, adjacent to the opening, may pivot freely without a demand for much space around the attachment device. ln further embodiments the outer edge of the band of material comprises two, or more, line segments, forming a transversal, polygonal outer edge of the blade.

Hereby a cutting blade, which is particularly well adapted to automatic manufacture, may be attained. ln some other embodiments the outer edge of the band of material has the shape of a circle segment, forming a transversal, rounded outer edge of the blade.

Hereby the demand for space around the blade is minimized. Also, the consumption of material for the cutting blade is minimized. ln even further embodiments, the working portion is concentric with the rounded outer edge.

Hereby the weight distribution of the blade is optimised for keeping the blade in an optimal working position. By the influence of the centrifugal force, the cutting blade tends to align itself in an approximately radial direction, when the cutting disk rotates. This effect is more pronounced if the mass center of the cutting blade is located as far out from the pivot axis as possible, while other demands on the cutting blade are also accommodated, e. g. total length, limiting material consumption, shape and angle of the cutting edges. By reducing the amount of material, and hence the weight in the area around the pivot axis, the mass center may be localized further away therefrom. ln further embodiments a second transversal edge, opposite the first transversal outer edge, at least partly has a shape which is complementary to that of the first transversal, outer edge.

Hereby an automated manufacture, wherein one end of the cutting blade, or a blank therefor, is at least partly nestable with the other end of an adjacent cutting blade. A large number of cutting blades may be cut from a large piece of raw material without unnecessary waste or scrap. ln some embodiments the working portion of the attachment opening is closer than the mounting portion to a nearest transversal side edge.

Hereby an orientation of the attachment opening is defined, where the working portion is closest to a transversal edge. Hereby this end may be the inner end of the cutting blade, when the cutting disk rotates. ln other embodiments there are two working portions and one mounting portion in the attachment opening.

After yielding to obstacles, or if the direction of rotation changes, the blade may turn in such a way that other parts of its cutting edges extend radially outwards from the cutting disk than previously. ln this way more of its side edges may be utilized for cutting before the blade is worn out and needs to be exchanged. This feature saves resources and money. ln further embodiments the mounting portion is arranged at the longitudinal center of the cutting blade.

Hereby an advantageous configuration is obtained, wherein the cutting blade may be symmetrical around both a Iongitudinal as well as a transversal axis. The blade may turn either side outwards with approximately equal probability. The utilization of the blade may be further enhanced. ln even further embodiments, the working portions of the attachment opening are arranged opposite one another with the mounting portion between them.

Hereby the symmetrical properties of the cutting blade are further enhanced. A maximum utilization of the cutting edges may be obtained. ln still further embodiments, the mounting portion of the attachment opening has e|ongated sides extending along the Iongitudinal sides of the blade.

Hereby all possible positions of the attachment device in the mounting portion are unstable positions. That means that the blade may not remain in any of these positions when the cutting disk is rotated. lnstead, the blade tends to move to a position wherein the attachment is positioned in a working portion, and positions where the blade may be in an inefficient position, transversal to the radial direction of the cutting disk, may be avoided. ln further embodiments the mounting portion of the attachment opening is approximately rectangular.

Hereby the tendency of the blade to move to a position wherein the attachment is positioned in a working portion is enhanced. ln some embodiments the mounting portion ofthe attachment opening is approximately square.

Hereby the tendency of the blade to move to a position wherein the attachment is positioned in a working portion is also enhanced. ln some embodiments the attachment opening is symmetric about a lateral center line of the cutting blade.

Hereby the symmetrical properties of the cutting blade are further enhanced. A maximum utilization of the cutting edges may also be obtained. ln some embodiments the attachment opening has a longitudinal axis which forms an angle to a |atera| center line of the cutting blade.

Hereby the cutting performance, as well as the yielding performance of the cutting blade, may be altered, since the centrifugal force may cause the blade to assume an angle to the radius of the cutting disk, when the cutting disk is rotating at its cutting speed. ln further embodiments the cutting blade includes at least two attachment openings.

Hereby the operator may have a higher influence on the distribution of the wear on the blades. A manual change of the attachment opening through which the attachment device extends may lead to a shift of the distribution of the wear. The attachment openings may be arranged at an angle to the |atera| center line of the cutting blade, or they may be symmetrically arranged thereabout. ln a second aspect of the disclosure, parts or all of the above-mentioned problems are solved, or at least mitigated, by the cutting blade and a protection plate being mounted on a cutting disk, and the cutting blade is held in place by the protection plate in a direction across its plane of extension, while being rotatable in its plane of extension.

Hereby a construction may be attained, wherein a dismounting or exchange of the cutting blade may take place without the use of tools. ln further embodiments the protection plate is provided with accommodation spaces, evenly spaced around a peripheral zone of the plate, for accommodating attachment means holding each cutting blade in its position in its plane of extension.

Hereby the movements of the cutting blade out of its working plane may be limited, while there is still room for the attachment means. ln even further embodiments, the protection plate is pretensioned by contact with the attachment device holding each cutting blade.

Hereby the blade is not restricted in its movements in its intended working plane. ln still further embodiments, each attachment device is accessible by a bending of an adjacent edge portion of the protection plate away from the cutting disk.

Hereby, the cutting blade is also easily accessible, and may be demounted without the use of tools, since it may be removed by sliding the blade to a position where the mounting portion of the attachment opening may pass over the head of the attachment device. ln a third aspect of the disclosure, a robotic lawn mower includes a blade as described above. ln some embodiments even the combination described above is included. lt 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 VGFSG.

Brief description of the drawinqs The above, as well as additional objects, features and advantages of the present disclosure, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments thereof, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein: Fig. 1 is a schematic view from above of a robotic lawn mower; Fig. 2 is an exploded view of a cutting disk and a protection plate included in the mower according to Fig. 1; Fig.

Fig.

Fig. 3a 3b 3c 4a 4b 4c 6 is a sectional view of the cutting disk and the protection plate of Fig. 2; is an enlargement of a portion of Fig. 3a; is a perspective view of a cutting blade included in the cutting disk of Figs. 3a and 3b; is a sectional view in perspective of the cutting disk and the protection plate of Figs. 3a-b, with another embodiment of the cutting blade; is an enlargement of a portion of Fig. 4a; is a perspective view of the cutting blade included in the cutting disk of Figs. 4a and 4b; is a sectional view from the side of the cutting disk and the protection plate of Fig. 2; is an enlargement of a portion of Fig. 5a; and is a perspective view of a further embodiment of a cutting blade according to the disclosure.

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.

Detailed description of the exemplarv embodiments Fig. 1 illustrates a typical robotic lawnmower 1, which may include the invention. The robotic lawnmower 1 includes a chassis 2 and a number of wheels 3.

At the bottom side of the chassis 2, a rotatable cutting disk 4 is arranged. A number of cutting blades 5 are evenly spaced around the periphery of the cutting disk 4. The cutting blades 5 extend some distance outside the cutting disk 4. When the cutting disk 4 is rotated, the forward edge of the respective blades, as seen in the direction of rotation, may cut the grass. lf a blade 5 encounters something that has too high a resistance to be cut, the blade 5 may yield and pivot around an attachment device 6, with which it is attached to the cutting disk 4. As the direction of rotation of the cutting disk 4 is arbitrary, the cutting blades 5 are preferably provided with cutting edges 12 on both longitudinal sides of the blades 5 (see Figs. 3c and 4c).

Fig. 2 shows a cutting disk 4 according to the present disclosure. The cutting disk 4 has a protection plate 7 mounted on the side which faces downwards in a normal working position of the lawnmower 1. Hereby the cutting disk 4, the cutting blades 5, as well as their attachment devices 6 may be more or less protected from dirt and grass clippings. The protection plate 7 is preferably fixed to the cutting disk 4 at a central portion thereof, with screws or similar fixation devices 16. The protection plate 7 is preferably slightly smaller than the cutting disk 4 and does not extend outside the peripheral edge thereof. ln the areas corresponding to the positions of the cutting blades 5, the protection plate 7 is provided with spaces for accommodation of the attachment devices 6, that are holding the blades 5. ln Fig. 2 the attachment openings 8 in the cutting blades 5 may be discerned, or at least that they extend further, in the Iongitudinal direction of each cutting blade 5, than the width of the upper part, or head 10, of the attachment device 6. By the centrifugal force, the blade 5 may be extended as far out as possible from the pin or stem 13 of the attachment device 6, when the cutting disk 4 is rotated at its cutting speed. This means that the stem 13 of the attachment device 6 is located in the inner part of the attachment opening 8 during rotation.

Fig. 3a is a section of the cutting disk 4 with the mounted protection plate 7. ln this figure it may be noted that the center of the cutting disk 4, and also of the attached protection plate 7, are offset in an axial direction from the plane of the cutting blades 5. Hereby the protection plate 7 may be somewhat biased against the attachment devices 6. The bias may be useful in keeping the cutting blades 5 in their respective places, while they are still pivotable around the attachment devices 6.

Fig. 3b, which is an enlarged view of the area including one of the cutting blades 5, shows the cutting blade 5 and the attachment device 6 more clearly. The attachment device 6 extends through a working portion 9, i. e. a narrow end portion, of the attachment opening 8, and the blade 5 may pivot therearound. Although the attachment opening 8 has a fairly long extent in the Iongitudinal direction, the cutting blade 5 is not prone to wobbling out of its plane of extent, since the protection plate 7 defines a narrow slit wherein the cutting blade 5 may pivot. However, the protection plate 7 contacts the upper end, or head 10 of the attachment device 6, and does not exert a force on the cutting blade 5 in its normal, pivotable position.

Fig. 3c shows one embodiment of the cutting blade 5 only. The disclosed cutting blade 5 has a rectangular outer contour, with two Iongitudinal sides and two transversal sides. There are cutting edges 12 along the longitudinal sides of the cutting blade 5. Preferably both Iongitudinal sides of the cutting blade 5 are provided with cutting edges 12, so that a cutting may be performed regardless of the direction of rotation of the cutting disk 4. Also, the mounting of the cutting blade 5 may be simplified, since no account needs to be taken of which side of the cutting blade 5 is facing upwards. ln a central portion of the cutting blade 5, the attachment opening 8 is arranged symmetrically about both a Iongitudinal and a transversal axis. A wide middle portion of the attachment opening 8 forms a mounting portion 11, which enables a mounting and a demounting of the cutting blade 5 on the attachment device 6 without a demounting thereof. The mounting portion 11 is wide enough to pass over the upper part or head 10 of the attachment device 6. The narrow working portions 9 at two sides of the mounting portion 11 has the same width as the stem 13 of the attachment device 6 or slightly wider, so that the cutting blade 5 may pivot around the stem, when the stem 13 is positioned in either of the working portions 9.

Since the cutting blades 5 are pivotally arranged on the attachment devices 6, they may yield when they encounter objects that are not easily cut or that cannot be cut at all by the lawnmower 1. After yielding, they are returned to their respective cutting positions by the centrifugal force. Sometimes, the impact of the cutting blade 5 with an object has been so hard, that the attachment device 6 loses contact with the working portion 9 of the attachment opening 8. The cutting blade 5 moves so that the attachment device 6 is temporarily located in the mounting portion 11 of the attachment opening. The mounting portion 11 is shaped and positioned such that the cutting blade 5 may not remain in a stable position, while the attachment device 6 is located therein. lnstead, the centrifugal force may bring the blade 5 into a position wherein the attachment device 6 is located in either of the working portions 9. ln preferred embodiments, the mounting portion 11 is rectanguiar or even square.

This means that the cutting blade 5 may pivot into a position which is approximately 180 degrees opposite to the position previously occupied. The same movement of the blades 5 may also take place if the direction of rotation of the cutting disk 4 is reversed. Both ends of the respective cutting blades 5 may hence alternately be directed radially outwards. ln a lifetime perspective, this is an advantage, as the wear on the cutting edges 12 may be more evenly distributed.

Figs. 4a and 4b correspond to Figs. 3a and 3b, with the exception that another embodiment of the cutting blade 5a is included therein. This embodiment is shown in Fig. 4c. This cutting blade 5a has two longitudinal sides with cutting edges 12a. There is one transversal side 15 which has the form of a straight line. At the opposite end of the cutting blade 5a, the outer edge 14 is rounded, preferably having the shape of a circle segment, possibly even a semicircle. The attachment opening 8a is arranged in that half of the cutting blade 5a which is closest to the rounded outer edge 14.

The attachment opening 8a has one single working portion 9a, the end of which may be concentric with the rounded outer edge 14. Next to the working portion 9a, and connected therewith, is a mounting portion 11a. The mass center of the cutting blade 5a is located in the area between the attachment opening 8a and the straight transversal side 15. The provision of rounded outer edge 14 means not only that the pivoting of the cutting blade 5a around an attachment device 6 is unimpeded by any parts of the cutting disk 4 or the protection plate 7. lt also leads to a shifting of the mass center towards the straight transversal side 15, as compared with an embodiment where both transversal sides had been straight, but with the same arrangement of the attachment opening 8a. Most of the material, e. g. steel, is arranged in that half of the cutting blade 5a, closest to the straight transversal side 15, whereas a large part of the other half comprises the attachment opening 8a. Hereby the reliable positioning of the cutting blade 5a in a radial direction outwards from the cutting disk 4 may be obtained under the influence of the centrifugal force. At the same time, the yielding of the cutting blade 5a by pivoting around the attachment device 6 may be attained. 11 Fig. 5a shows the cutting disk 4 with a mounted cutting blade 5 in a section, and Fig. 5b is an enlargement of the area including the cutting blade 5 and its attachment device 6. The section is made straight through one of several accommodation spaces 17 of the protection plate 7. lt is visible that the head 10 of the accommodation device 6 is in contact with the inside of the accommodation space 17. Hereby the protection plate 7 may be biased away from the cutting disk 4 in this area, such that there may be a small gap between the cutting disk 4 and the protection plate 7, allowing the cutting blade 5 to pivot around the attachment device 6 but keeping the blade 5 from being unintentionally dismounted.

Fig. 6 discloses another embodiment of the cutting blade 5b according to the disclosure. As compared to the embodiment disclosed in Fig. 4c, a main visible feature is that two corners near the attachment opening 8a are chamfered. The outer edge 14a is hence polygonal, i. e. it comprises a number of line segments; three line segments in the drawing. Other numbers of line segments in the outer edge may easily be envisaged.

Yet further embodiments of the cutting blades 5c, 5d are disclosed in Figs. 7a and 7b. The disclosed blades 5c, 5d are each provided with an attachment opening 8a as described above. They also have longitudinal cutting edges 12 as described above. Further the blades 5c, 5d each have a rounded outer edge 14 at one transversal side near the attachment opening 8a. An opposite transversal edge 18 has a shape, which is complementary to at least a portion of the rounded outer edge 14. Hereby it may be possible to manufacture a large number of blades efficiently with a minimum amount of scrap.

Further embodiments of the cutting blades 5, 5a, 5b, 5c, 5d may be envisioned, even though they are not illustrated in the drawings. One example is a cutting blade with chamfered corners, like that of Fig. 6, but where an opposite transversal edge has a complementary polygonal shape. Further examples include cutting blades which comprise different combinations of shape, number and position of the attachment openings, and the shapes of the transversal edges. ln order to intentionally demount a cutting blade 5, 5a according to the disclosure, the protection plate 7 may have to be removed, at least from the area of 12 the cutting blade 5, 5a to be demounted. Preferably the protection plate 7 is sufficiently flexible to be bent away from the cutting disk 4 at its edge to an extent that the cutting blade 5, 5a is exposed, and the operator may easily access the cutting blade 5, 5a. Othervvise, the protection plate 7 may be removed by unfastening the central fixation devices 16.

When the cutting blade 5, 5a is accessible in either way, it may be slid approximately in its plane of extension, such that the wide mounting portion 11, 11a is aligned with the head 10 of the attachment device 6. From this position the mounting portion 11, 11a may easily pass the head 10 of the attachment device 6. The attachment device 6 need preferably not be loosened or otherwise manipulated. Hence the cutting blade 5, 5a may be quickly removed without the use of any tools (except for tools that might exceptionally be needed for removal of the protection plate 7).

When a new (or possibly a renovated) cutting blade 5, 5a is to be mounted, the procedure is reversed. The mounting portion 11, 11a is passed over the head 10 of the attachment device 6, which remains in its mounted position on the cutting disk 4. Thereafter, the cutting blade 5, 5a is slid in its plane of extension, such that the stem 13 of the attachment device 6 in introduced into a narrow working portion 9, 9a of the attachment opening 8, 8a. Finally the protection plate 7 is brought back into its original position on the cutting disk 4, preferably by releasing it from a bent-up position, but possibly by refastening the central fixation devices 16.

Further embodiments of the cutting blades 5, 5a, which do not appear in the drawings, but which may be readily understood, may be envisaged. For example, the configurations of attachment openings 8, 8a shown in the drawings may be arranged differently in the cutting blades 5, 5a. The longitudinal axis of the attachment openings 5, 5a may be arranged at an angle to the lateral center line of the cutting blades. The angled attachment opening 8, 8a may result in various effects on the cutting result and on the yielding capabilities of the cutting blades 5, 5a. An optimal size of the angle for each cutting application may be decided experimentally by the skilled person. 13 Other embodiments of this disclosure may be attained if more than one attachment opening 8, 8a is provided in each cutting blade 5, 5a. Hereby a change of which attachment opening 8, 8a is currently used may chance what parts of the cutting edges 12 will be most worn. The operator will then have a wider influence of the wear-depending cutting abilities of the blades. When the operator deems it suitable, the blades may be repositioned, and unworn parts of the cutting edges may come into use, without an exchange of the blades. The attachment openings may be of any type previously described, and they may be angled relative to the center line or not.

Even further embodiments may be envisaged, e. g. that the transversal edges have complementary shapes. As an example, the blade of Fig. 4c may be varied such that the outer edge 15 farthest from the attachment opening is rounded inwards into the blade. Hereby its shape is complementary to the shape of the other end of the blade. During manufacture, this shape may be advantageous, since the blanks of the blades may be positioned end to end in a sheet of raw material without any scrap or waste. A corresponding complimentary shaping of the ends14a, 15 of the cutting blade 5b of Fig. 6 may likewise be easily envisaged.

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. ln 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

1._ A grass cutting blade (5, 5a) for a lawn mower, the cutting blade (5, 5a) being elongate with two Iongitudinal sides and comprising at least one cutting edge (12) on at least one of the Iongitudinal sides of the cutting blade (5, 5a) and an attachment opening (8, 8a) in an area between the Iongitudinal sides, wherein the attachment opening (8, 8a) has a mounting portion (11, 11a) and at least one working portion (9, 9a), wherein a width of the mounting portion (11, 11a), in a direction transversa| to the Iongitudinal sides, is larger than a width of the working portion (9, 9a) in the direction transversa| to the Iongitudinal sides.

2._ The cutting blade (5, 5a) according to claim 1, wherein both Iongitudinal sides of the blade (5, 5a) are provided with cutting edges (12).

3._ The cutting blade (5, 5a) according to claim 1 or claim 2, wherein there is one single working portion (9a) and one single mounting portion (11a) in the attachment opening (8a).

4._ The cutting blade (5, 5a) according to any of claims 1 to 3, wherein the working portion of the attachment opening (8, 8a) of the cutting blade (5, 5a) is partially surrounded by a band of material of an approximately uniform width, adjacent to the opening (8, 8a).

5._ The cutting blade according to claim 4, wherein the outer edge (14a) of the band of material comprises two, or more, line segments, forming a first transversa|, polygonal outer edge (14a) of the blade (5, 5a, 5b)_

6._ The cutting blade (5, 5a) according to claim 4, wherein the outer edge (14) of the band of material has the shape of a circle segment, forming a first transversa|, rounded outer edge (14) of the blade (5, 5a).

7._ The cutting blade (5, 5a) according to claim 6, wherein the working portion (9a) is concentric with the first transversa|, rounded outer edge (14).

8._ The cutting blade (5, 5a, 5b) according to claims 5 to 7, wherein a second transversa| edge (18), opposite the first transversa| outer edge (14, 14a), at least partly has a shape which is complementary to that of the first transversa|, outer edge (14, 14a)_

9. The cutting blade (5, 5a) according to any of claims 1 to 8, wherein the working portion (9a) of the attachment opening (8a) is closer than the mounting portion (11a) to a nearest transversal side edge.

10.The cutting blade (5, 5a) according to claim 1 or claim 2, wherein there are two working portions (9) and one mounting portion (11) in the attachment opening (s).

11.The cutting blade (5, 5a) according to claim 10 wherein the mounting portion (11, 11a) is arranged at the |ongitudina| center of the cutting blade (5, 5a).

12.The cutting blade (5, 5a) according to claim 10 or claim 11, wherein the working portions (9) of the attachment opening (8) are arranged opposite one another with the mounting portion (11) between them.

13.The cutting blade (5, 5a) according to any of claims 10 to 12, wherein the mounting portion (1 1) of the attachment opening (8) has elongated sides extending along the |ongitudina| sides of the blade (5, 5a).

14.The cutting blade (5, 5a) according to any of claims 10 to 13, wherein the mounting portion (11) of the attachment opening (8) is approximately rectangular.

15.The cutting blade (5, 5a) according to any of claims 10 to 14, wherein the mounting portion (11) of the attachment opening (8) is approximately square.

16.The cutting blade (5, 5a) according to any of the preceding claims, wherein the attachment opening (8, 8a) is symmetric about a lateral center line of the cutting blade (5, 5a).

17.The cutting blade (5, 5a) according to any of the preceding claims, wherein the attachment opening (8, 8a) has a |ongitudina| axis which forms an angle to a lateral center line of the cutting blade (5, 5a).

18.The cutting blade (5, 5a) according to any of the preceding claims, wherein the cutting blade includes at least two attachment openings (8, 8a).

19.Combination of at least one cutting blade (5, 5a), according to any of the preceding claims, and a protection plate (7), wherein the cutting blade(5, 5a)and the protection plate (7) are mounted on a cutting disk (4), and the cutting blade (5, 5a) is held in place by the protection plate (7) in a direction across its plane of extension, while being rotatable in its plane of extension.

20.Combination according to claim 19, wherein the protection plate (7) is provided with accommodation spaces (17), evenly spaced around a peripheral zone of the plate (7), for accommodating attachment devices (6) holding each cutting blade (5, 5a) in its position in its plane of extension.

21.Combination according to claim 20, wherein the protection plate (7) is pretensioned by contact with the attachment device (6) holding each cutting blade (5, 5a).

22.Combination according to any of claims 19 to 21, wherein each attachment device (6) is accessible by a bending of an adjacent edge portion of the protection plate (7) away from the cutting disk (4).

23. Robotic lawn mower (1) including a cutting blade (5, 5a) according to any of claims 1 to

24. Robotic lawn mower (1) according to claim 23, further including the combination of any of claims 19 to 17