Patent Application
20210185911
The present invention relates to various aspects of a robotic lawnmower cutting arrangement to be carried by a robotic lawnmower.
Robotic lawnmowers, used for garden or lawn maintenance, are well known in the art. Typically, a robotic mower includes multiple cutting blades detachably connected to a rotating blade carrier disc, acting as blade or knife holder. The blade carrier, usually a circular disc, is arranged to rotate about a vertical axis, perpendicular to the grass surface, and is powered by an electric motor of the robotic lawnmower to rotate the cutting blades.
Generally, during cutting the robotic lawnmower uses energy for cutting grass, and to propel itself across the lawn. In a battery powered electric robotic lawnmower, the robotic lawnmower has to return to its charging station after its energy resources have been consumed. Besides performing the actual grass cutting, the robotic lawnmower also consumes energy through its control logic, sensors and communication system. Even the return trip to the charging station to recharge batteries contributes to energy being spent. Typical robotic lawnmowers navigate randomly, and thereby operate on already-cut grass multiple times. For some robotic mowers, several cuts on each particular area may anyhow be required before the desired cutting quality is reached, including aesthetical evenness of the grass surface.
Battery powered robotic mowers are limited by their battery capacity and energy efficiency for cutting grass. Energy efficiency depends on the power train efficiency of its electronic control logic, electric motors, wheels, transmission and cutting efficiency, besides environmental conditions such as grass properties, ground properties, obstacles, and proper maintenance of the robotic lawnmower. To cut grass at a high cutting height of the grass blades usually requires less energy than cutting deeper into the grass, with short cut grass length as a result. As a consequence, cutting very short grass is more challenging and energy demanding than cutting grass at a higher cutting height. Another issue of some of today's robotic lawnmowers is a tendency to get stuck, for example by beaching on bumps in uneven terrain. When this happens, energy such as battery power is also spent when the robotic lawnmower is trying to free itself. EP0808096 B1 suggests the use of a free-rotating shielding lower plate between the grass surface and the rotating blade carrier disc. In order to save energy, the blade carrier disc's rotation axis has a forward inclination of 7 degrees, such that the cutting blades will not touch again the grass at the rear of the cutting head. There is however still a need for a robotic lawnmower which is capable of covering a larger area, and/or provides improved cutting result, and/or is less prone to get stuck on terrain features.
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, according to a first aspect, provided a robotic lawnmower cutting arrangement comprising a blade carrier configured to be rotated by a cutting motor about a blade carrier rotation axis, the blade carrier extending radially away from the blade carrier rotation axis and comprising a blade attachment interface radially offset from the blade carrier rotation axis, the blade attachment interface being configured to pivotally hold a cutting blade; and a cutting blade comprising a substantially flat cutting portion provided with a cutting edge, and a blade carrier interface pivotally connected to the blade attachment interface of the blade carrier, the pivotal connection thereby allowing the cutting blade to pivot relative to the blade carrier about a blade pivot axis offset from the blade carrier rotation axis such that, when the blade carrier is rotated about the blade carrier rotation axis, the blade carrier interface of the cutting blade follows a circular path in a blade carrier interface rotation plane perpendicular to the blade carrier rotation axis, and the cutting portion follows a circular path in a cutting plane, wherein the cutting edge extends within the cutting plane and the cutting plane is axially, with respect to the carrier rotation axis, offset from the blade carrier interface rotation plane by a cutting plane offset distance. Such a robotic lawnmower cutting arrangement allows raising the blade carrier above the grass, which reduces friction against the grass and thereby reduces power consumption. Such a friction reduction may be obtained with a cutting arrangement which is free from, i.e. not provided with, a free-rotating lower plate, such as that of EP0808096B1, between the grass surface and the rotating blade carrier. At the same time, the blade design permits cutting the grass to a low cutting height. In particular, compared to the cutting arrangement of EP0808096B1, the friction between the lower plate and the grass may be avoided. The increased ground clearance thereby obtainable may also reduce the risk of getting stuck. The expression “axially, with respect to the carrier rotations axis, offset” is to be construed as offset in the direction of the carrier rotation axis. The blade pivot axis may be offset from the blade carrier rotation axis by a pivot axis radial offset defined as the radial distance from the blade carrier rotation axis to the point where the pivot axis passes through a plane, which plane passes through the blade carrier interface, and which plane is perpendicular to the blade carrier rotation axis. According to an embodiment, the cutting portion and the blade carrier interface may be interconnected by an offset portion extending in a direction transversal to a plane defined by the cutting portion. Preferably, the cutting arrangement is configured to be oriented, when in use, such that the cutting plane is below the blade carrier interface rotation plane.
According to embodiments, the cutting plane offset distance may exceed 5 mm, 10 mm, 15 mm, or 20 mm. Alternatively or additionally, the cutting plane offset distance may be less than 50 mm, less than 35 mm, or less than 25 mm.
According to a second aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a robotic lawnmower cutting arrangement comprising a blade carrier configured to be rotated by a cutting motor about a blade carrier rotation axis, the blade carrier extending radially away from the blade carrier rotation axis and comprising a blade attachment interface radially offset from the blade carrier rotation axis, the blade attachment interface being configured to pivotally hold a cutting blade; and a cutting blade comprising a substantially flat cutting portion extending along a cutting portion plane, the cutting portion being provided with a cutting edge, and a blade carrier interface pivotally connected to the blade attachment interface of the blade carrier, the pivotal connection thereby allowing the cutting blade to pivot relative to the blade carrier about a blade pivot axis, wherein the cutting blade further comprises an offset portion interconnecting the cutting portion and the blade carrier interface and extending in a direction transversal to the cutting portion plane, such that the cutting portion plane is axially, with respect to the carrier rotation axis, offset from the blade carrier interface, at least at the blade carrier interface. Such a robotic lawnmower cutting arrangement allows raising the blade carrier above the grass, which reduces friction against the grass and thereby reduces power consumption. At the same time, the blade design permits cutting the grass to a low cutting height. Optionally, also the offset portion may be provided with a cutting edge.
According to embodiments of any of the robotic lawnmower cutting arrangements defined above, the pivotal connection between the blade carrier interface of the cutting blade and the blade attachment interface of the blade carrier is configured to allow free, i.e. unbiased, pivoting of the cutting blade about the blade pivot axis. Thereby, the impact energy when striking an object will be low, which provides a long lifetime along with a high level of safety. According to examples, the cutting blade may be allowed to freely pivot about the blade pivot axis over a pivoting angle range of more than 90 degrees, over more than 120 degrees, over more than 150 degrees, over more than 180 degrees, or over more than 210 degrees. The cutting blade may also be allowed to rotate freely, to complete full turns about the blade pivot axis.
According to an embodiment, the blade pivot axis may be inclined in relation to the blade carrier rotation axis. The inclination may be oriented such that when the blade carrier is rotated about the blade carrier axis, the path of the blade pivot axis defines a cone having its apex pointing downwards. Thereby, when hitting an uncuttable object, the cutting blade may pivot about the pivot axis to a raised position, higher above the ground. By way of example, the blade pivot axis may form an angle of between 3 degrees and 20 degrees with the blade carrier rotation axis. Moreover, the blade pivot axis may lie in a plane along which the blade carrier rotation axis extends. Thereby, the same impact behaviour may be obtained regardless of in which direction the blade carrier is rotated.
According to embodiments of any of the robotic lawnmower cutting arrangements defined above, the blade carrier interface may be integrally formed with the cutting portion. This may result in a strong and inexpensive blade. According to embodiments, the cutting blade may be integrally formed of a sheet material. The sheet material may, by way of example, be sheet metal, such as steel sheet. A maximum thickness of the sheet material of the cutting portion may, for example, be less than 2 mm, or less than 1.25 mm. By using a thin, and thereby also low-weight blade, the power consumption may be even further reduced. At the same time, a sufficient strength for cutting the grass of a typical lawn is desired. A particularly suitable thickness of the sheet material may be, for example, between 0.4 mm and 0.8 mm.
According to some embodiments, the cutting portion plane may coincide with the cutting plane. According to other embodiments, the cutting portion plane may be inclined relative to the cutting plane. The cutting portion plane may, for example, be inclined relative to the cutting plane by an inclination angle of between one and five degrees, as seen in a vertical section comprising the blade carrier rotation axis and the blade carrier interface.
According to embodiments, the blade carrier interface may be made of a sheet material extending in a blade carrier interface plane, wherein the blade carrier interface plane is substantially parallel to at least one of the cutting plane and the cutting portion plane, and optionally, both. Such a cutting arrangement is particularly well suited for a situation wherein the blade pivot axis is parallel to the blade carrier rotation axis. According to embodiments, the blade carrier interface plane may form an angle with the at least one of the cutting plane and the cutting portion plane of less than ten degrees, or of less than five degrees.
According to embodiments, the cutting blade may be detachably connected to the blade carrier. In particular, the cutting blade may be tool-less detachable from the blade carrier.
According to embodiments, the engagement between the blade carrier interface of the cutting blade and the blade attachment interface of the blade carrier may have a radial play, with respect to the blade pivot axis, of at least 5 mm. Thereby, the blade may automatically be thrown radially inwards upon impact with an uncuttable object, which reduces damage to the blade and the uncuttable object. According to embodiments, the radial play may exceed 10 mm, 15 mm, or 20 mm. Alternatively or additionally, the radial play may be less than 50 mm, less than 35 mm, or less than 25 mm. The radial play may be configured to allow moving the cutting blade relative to the blade attachment interface in a direction along a longitudinal axis of the blade. In a transversal direction perpendicular to the longitudinal axis and the blade pivot axis, the engagement between the blade carrier interface of the cutting blade and the blade attachment interface of the blade carrier may have a tighter fit, such that the cutting blade is not allowed to substantially move relative to the blade attachment interface in said transversal direction. Such an arrangement may be obtained by, for example, configuring one of the blade carrier interface of the cutting blade and the blade attachment interface of the blade carrier as an elongate hole or slot having an axis of elongation extending, when in use, in a direction radially away from the blade carrier rotation axis, and pivotally and slidably connecting the other of the blade carrier interface of the cutting blade and the blade attachment interface of the blade carrier to the elongate hole, in a manner to allow it to slide along said elongate hole in said direction of elongation.
According to embodiments, the engagement between the blade carrier interface and the blade attachment interface may have an axial play, with respect to the blade pivot axis, of at least 0.2 mm or, according to other embodiments, of at least 0.5 mm. When combined with a cutting portion axially separated from the carrier interface, the axial play reduces the risk that the pivotal connection at the blade carrier interface jams during operation due to centrifugal forces striving to tilt the cutting blade.
According to embodiments, the engagement between the blade carrier interface and the blade attachment interface allows tilting the blade about a blade tilt axis extending through the blade attachment interface in the direction of travel of the blade attachment interface during rotation of the blade carrier, i.e. in a tangential direction with respect to the blade carrier rotation axis. Thereby, the blade may, upon rotation, automatically assume an optimal tilt for cutting. According to embodiments, the blade may be tiltable within a tilt play of between 1 degree and 30 degrees, or within a tilt play of between 5 degrees and 15 degrees. When combined with a cutting portion axially separated from the blade carrier interface, the tilt play reduces the risk that the pivotal connection at the blade carrier interface jams during operation due to centrifugal forces striving to tilt the cutting blade.
According to embodiments, the cutting edge may be substantially straight. The robotic lawnmower cutting arrangement may be devised in such a manner that, when the blade carrier is rotated, the cutting blade automatically, in response to centrifugal forces, assumes a position in which the cutting edge extends substantially radially away from the blade carrier rotation axis. According to embodiments, the cutting edge forms an angle of less than ten degrees, or of less than five degrees, with said radial direction. According to embodiments the blade may, in addition to the straight cutting edge of the cutting portion, comprise auxiliary cutting edges which may be non-straight, and which may optionally extend along e.g. any offset portion between the blade carrier interface and the cutting portion.
According to embodiments, the cutting blade may comprise a first cutting edge extending along a first side edge of the cutting blade, and a second cutting edge extending along a second side edge of the cutting blade, the second side edge being opposite to the first side edge. Thereby, the cutting arrangement may be operated by rotating in either rotation direction about the blade carrier rotation axis, or by rotating alternatingly in the two opposite rotation directions. In particular, the cutting blade may be symmetric about a symmetry axis passing through the blade carrier interface, such that the first and second cutting edges extend along the symmetry axis on either sides thereof. Thereby, the exact same behaviour may be obtained regardless of the direction of rotation of the cutting arrangement.
According to embodiments, the cutting blade may be elongate and have a cutting blade length along its direction of elongation, wherein the cutting portion has a cutting portion length along said direction of elongation of at least 20% of the cutting blade length. The cutting portion length may, according to embodiments, exceed 25%, 30%, or 35% of the cutting blade length. Alternatively or additionally, the cutting portion length may be shorter than 70%, or shorter than 50%, of the cutting blade length.
According to embodiments, the blade carrier interface may comprise a through-hole having an elongate shape along a plane perpendicular to the blade pivot axis. The elongate shape may have a direction of elongation extending, when in use, in the radial direction, with respect to the blade carrier rotation axis. According to an embodiment, the through-hole may be oval.
According to embodiments, the cutting blade may extend between a proximal end, which is provided with said blade carrier interface, and a distal end, which is provided with said cutting portion. The proximal end may be chamfered between short and long side edges of the cutting blade, in order to facilitate pivoting about the blade pivot axis. In an alternative configuration, the cutting blade may have both a cutting portion and a blade carrier interface at each longitudinal end. Such a cutting blade may be alternatingly connected to the blade carrier via either of the blade carrier interfaces for extended service life.
According to embodiments, the blade carrier may be made of plastic, and may optionally have the shape of a circular disc.
According to embodiments, the blade carrier may pivotally carry a plurality of cutting blades, in the manner defined hereinabove, distributed about its periphery. A suitable number of blades may be, for example, two, three, four, or five. According to a typical example, the cutting assembly comprises at least four cutting blades distributed about the periphery of the blade carrier.
According to a third aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a robotic lawnmower cutting blade comprising a substantially flat cutting portion extending along a cutting portion plane, the cutting portion being provided with a cutting edge; a blade carrier interface; and an offset portion interconnecting the cutting portion and the blade carrier interface and extending in a direction transversal to the cutting portion plane, thereby holding the blade carrier interface at a position offset from the cutting portion plane. Such a cutting blade may be used as the cutting blade in a robotic lawnmower cutting arrangement as defined above. Additional optional features of the robotic lawnmower cutting blade are apparent from the above defined exemplary robotic lawnmower cutting arrangements.
According to a fourth aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a robotic lawnmower comprising a robotic lawnmower cutting arrangement or a robotic lawnmower cutting blade as defined hereinabove.
According to embodiments, the blade carrier rotation axis may be substantially vertical, e.g. forming an angle of less than three degrees with a vertical line, when the robotic lawnmower is positioned in normal operating position on a horizontal surface. At least one of a cutting plane and a cutting portion plane may be substantially horizontal, e.g. forming a maximum angle with a horizontal plane of less than three degrees. By having a substantially horizontal cutting plane, the grass may be cut at any position around the periphery of the rotating carrier disc, and not only at the front position as suggested in EP0808096B1. Thereby, cutting efficiency and cutting quality is increased. By having a horizontal cutting portion plane, all grass leaves will receive a horizontal cut at the same height, even if the robotic lawnmower transits over the parcel at a relatively high speed. This also improves the visual quality of the cut. For example, a drawback of an inclined cutting arrangement such as that of EP0808096 B1 is that it tends to give a non-horizontal cut of the grass leaves and, when moving across the lawn at a high speed while cutting, also tends to result in a striped upper envelope of the grass leaves of the lawn. Thereby, multiple re-cuts of each spot of the lawn are required for obtaining an even cut, which consumes energy. As path planning and precision guiding of systematic cutting robotic mowers are reaching better precision, is particularly beneficial to just have to cut each spot once, with minimal overlap, to reach the desired lawn surface evenness quality expected. Hence, according to embodiments, the cutting arrangement is carried by a robotic lawnmower configured for systematic navigation, as opposed to the typical random navigation generally used in present-day robotic lawnmowers.
According to embodiments, the robotic lawnmower may further comprise a controller and a cutting motor, wherein the controller is configured to operate the cutting motor below a limit RPM adapted to give the cutting portion of said cutting blade a maximum impact energy of less than 5 joules, and preferably of less than 2 joules. Those limits may be safeguarded e.g. by operating the cutting motor at an RPM adapted to give said cutting portion a total kinetic energy of less than 5 joules or 2 joules, respectively.
According to embodiments, the cutting motor may be an electric motor configured to be operated at an output power of less than 200 watt. Such power levels are typical of robotic lawnmowers. According to embodiments, the cutting motor may be configured to be operated at an output power of less than 50 watt, or less than 20 watt. Such power levels may be particularly suitable for low-power robotic lawnmowers for domestic and garden use.
According to a fifth aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a method of operating a robotic lawnmower, the method comprising: rotating a blade carrier interface of a cutting blade about a blade carrier rotation axis in a blade carrier interface rotation plane; and rotating a cutting portion of said cutting blade, the cutting portion having a cutting edge facing in the tangential direction of travel of the cutting blade, wherein the cutting edge is rotated in a cutting plane below said blade carrier interface rotation plane. The cutting edge may extend within the cutting plane. By way of example, the cutting edge may extend in a direction which is radial to the blade carrier rotation axis. Moreover, the cutting edge may extend in a direction which is perpendicular to the blade carrier rotation axis. Additional optional features of the method are apparent from the above defined exemplary robotic lawnmower cutting arrangements.
According to a sixth aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by the use of a robotic lawnmower cutting arrangement, robotic lawnmower cutting blade, robotic lawnmower, or method as defined herein for cutting the grass of a golf court fairway at a cutting height of less than 15 mm. The robotic lawnmower cutting arrangement, robotic lawnmower cutting blade, and robotic lawnmower as defined above are particularly well suited for cutting very short grass with very high accuracy, e.g. for golf courts and football fields.
According to a seventh aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by the use of a robotic lawnmower cutting arrangement, robotic lawnmower cutting blade, robotic lawnmower, or method as defined herein for cutting the grass of a golf court green at a cutting height of less than 5 mm. According to embodiments, the cutting height may be lower than 4 mm, or even lower than 3 mm. The robotic lawnmower cutting arrangement, robotic lawnmower cutting blade, and robotic lawnmower as defined above may be suited for cutting grass at a cutting height as low as a couple of mm. For golf greens, it may be beneficial to provide the robotic lawnmower with a suction arrangement and grass collection chamber, for vacuuming grass clippings from the golf green.
According to an eighth aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a method of producing a robotic lawnmower cutting blade, the method comprising: bending a sheet metal blank to form a substantially flat cutting portion, a substantially flat blade carrier interface portion, and an offset portion separating the cutting portion from the blade carrier interface portion in a direction transversal to the plane of the cutting portion; and grinding a cutting edge; and optionally, after grinding the cutting edge, locally treating the cutting edge to change the material properties thereof. By locally treating only the cutting edge, and leaving other portions of the cutting blade untreated, the blade may remain sharp for a long time, while the untreated body portion of the cutting blade may allow it to withstand impact with uncuttable objects without breaking. Optionally, a through-hole may be punched in the blade carrier interface portion to form a blade carrier interface.
According to a ninth aspect, parts or all of the above mentioned problems are solved, or at least mitigated, by a method of producing a robotic lawnmower cutting blade, the method comprising: bending a sheet metal blank to form a substantially flat cutting portion, a substantially flat blade carrier interface portion, and an offset portion separating the cutting portion from the blade carrier interface portion in a direction transversal to the plane of the cutting portion; and attaching a cutting edge to the cutting portion. Using the method, a hardened cutting edge may be attached to an unhardened cutting portion. The cutting edge may be attached by e.g. soldering, welding, press-fitting or gluing.
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 devices according to some aspects are all combinable with the embodiments of the devices according to other aspects, as well as with the methods according to still other aspects, and vice versa.
The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting 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:
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.
A wireless data transceiver 32 is connected to the controller 26, and allows the controller 26 to communicate with the charging station 16 or any other device, such as a remote control or a smart phone (not shown).
The robotic lawnmower 10 further comprises a navigation system 34. In the illustrated example, the navigation system 34 comprises an inertial navigation device 36, such as an accelerometer or a gyroscope, and a magnetic field sensor 38 configured to detect a magnetic field emitted by the boundary wire 11 (
The controller 26 also controls the propulsion motors 24, thereby controlling the propulsion of the robotic lawnmower 10 within the area 12 to be treated. The propulsion motors 24 may be stepper motors, allowing the controller 26 to keep track of the respective numbers of turns of the motors 24, and thereby also the distance travelled by the robotic lawnmower 10, as well as any turning angle of the robotic lawnmower 10 when the motors 24 are operated at different speeds or in reverse directions. In this respect, the propulsion motors 24 may operate as odometers. Alternatively, the wheels 20 may be provided with odometer indexers configured to provide feedback to the controller 26 as regards the number of turns of each motor 24. The navigation system 34 further comprises a GNSS (Global Navigation Satellite System) receiver 42 Navigation information from the navigation system 34 and the motors 24 is fused in the controller 26 to provide an accurate position indication, in order to enable e.g. a systematic movement pattern of the robotic lawnmower 10, wherein the robotic lawnmower 10 traverses the lawn 2 along parallel, adjacent mowing tracks.
The controller 26, navigation system 34, transceiver 32, and electric motors 24, 30 are powered by a battery 40. The robotic lawnmower 10 is configured to navigate to the charging station 16 on a regular basis, and/or whenever the battery charge is running low, in order to dock with the charging station 16 for recharging the battery 40. The charging station 16 may be connected to receive power from the electric power grid.
Battery powered robotic mowers are limited by their battery capacity and energy efficiency for cutting grass. If energy consumption can be reduced, cutting coverage, cutting quality and cutting speed can be gained, while reducing wear and tear of the robotic mower machinery.
The cutting blade 400 comprises, at a distal 424 end thereof, a substantially flat cutting portion 401 extending along a cutting portion plane 410 which is horizontal, i.e. parallel to the surface of the lawn to be cut. The cutting portion 401 is provided with a cutting edge 403 facing in a tangential direction with respect to the blade carrier rotation axis 201. A blade carrier interface 404 is arranged at a proximal end 422 of the cutting blade 400. The blade carrier interface 404 pivotally connects the cutting blade 400 to the blade attachment interface 202 of the blade carrier 200 via a cutting blade attachment screw 418, which operates as a pivot pin and thereby defines the blade pivot axis 405. The blade pivot axis 405 may be vertical, as is illustrated by the blade 400 attached to the blade carrier 200. According to other embodiments, however, the blade pivot axis 405 may be inclined radially inwards by an inwards inclination angle 407, or radially outwards by an outwards inclination angle 409, as is illustrated by the alternative positions 413′, 413″ of the cutting blade 400 and cutting blade attachment screw 418 relative to respective blade pivot axes 405′, 405″. The blade pivot axis 405 is radially separated from the blade carrier rotation axis 201 by a pivot axis radial offset 102, defined as the radial distance from the blade carrier rotation axis 201 to the point where the pivot axis 405 passes through a plane 415, which plane 415 passes through the blade carrier interface 404, and which plane 415 is perpendicular to the blade carrier rotation axis 201. A typical pivot axis radial offset 102 may be between 50 and 500 mm; and more typically, between 100 and 300 mm.
Between the cutting portion 401 and the blade carrier interface 404, the cutting blade 400 has an offset portion 406 which extends in a direction transversal to the cutting portion plane 410, and thereby defines an axial, with respect to the blade carrier rotation axis 201 as well as the blade pivot axis 405, cutting plane offset 408 between the cutting portion 401 and the blade carrier interface 404. The cutting plane offset distance 408 may be, by way of example, about 15 mm.
When operating the robotic lawnmower cutting arrangement 100, the blade carrier 200 is rotated about the blade carrier rotation axis 201 such that the blade 400 orbits the blade carrier rotation axis 201. Thereby, the blade carrier interface 404 of the cutting blade 400 follows a circular path in a blade carrier interface rotation plane 415 perpendicular to the blade carrier rotation axis 201, and the cutting portion 401 follows a circular path in a cutting plane 402, which planes 402, 415 are vertically offset from each other by the cutting plane offset distance 408.
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Thanks to the ability of reaching very close to the ground with high precision and low friction, the methods and devices herein are suitable for cutting very short grass, in applications such as golf court fairways and golf court greens.
The cutting blade described above may be produced following a production method illustrated in the flow chart of
1101: providing a sheet metal blank;
1102: bending the sheet metal blank to form a substantially flat cutting portion 401 (
1103: grinding a cutting edge 403; and
1104: after grinding the cutting edge, locally treating the cutting edge to change the material properties thereof, for example to change its hardness.
In an alternative embodiment, steps 1103 and 1104 may be replaced by the step 1105: attaching a cutting edge 403 to the cutting portion 401. Also, the order of steps 1102 and 1105 may be reversed.
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. For example, a vertical a blade carrier rotation axis has been illustrated. However, also a robotic lawnmower cutting arrangement having a blade carrier rotation axis which is tilted relative to a vertical axis may benefit from the teachings disclosed herein. Hence, even though less preferred for cutting very short grass, such an arrangement is also intended to be within the scope of the claims. Similarly, a blade carrier without any free-rotating lower protection plate, such as that of EP0808096 B1, has been illustrated. However, also a robotic lawnmower cutting arrangement having a free-rotating lower protection plate may benefit from the teachings disclosed herein. Hence, even though less preferred for cutting very short grass, such an arrangement is also intended to be within the scope of the claims. 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1850895.2 | Jul 2018 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/066787 | 6/25/2019 | WO | 00 |
