Patent Description:
Lawn striping is a technique for creating patterns on lawns by flattening one row of grass in one direction and an adjacent row of grass in another direction. Typically, lawn striping is applied on sports fields such as football- or baseball fields in which the grass on the entire field is striped in parallel rows of grass that is flattened in opposite directions.

Conventionally, striping of lawns is performed by flattening the grass with a rubber mat that is attached to a ride-on lawn mower or a tractor that is driven by a person.

Robotic lawn mowers are increasingly used for maintaining lawns and sports fields. Robotic lawn mowers are advantageous for these tasks since they operate autonomous and thus reduce the need and cost for personnel operating lawn mowers.

However, it has shown that when robotic lawn mowers are equipped with striper mats, the striper mat may impede the maneuvering of the robotic lawn mower. For example, the striper mat may impede the robotic lawn mower when the robotic lawn mower changes driving direction from forward to reverse.

<FIG> shows schematically a situation where a robotic lawn mower <NUM> with a striper mat <NUM> reverses driving direction from forward to backwards. During this maneuver, friction between the edge of the striper mat <NUM> and the ground <NUM> causes the striper mat <NUM> to transit from a convex bent shape to a concave bent shape. During this transition, the striper mat <NUM> exerts a counter force onto the robotic lawn mower <NUM> which impedes the rearward motion of robotic lawn mower and results in that the robotic lawn mower is lifted from the ground by the striper mat.

Striper arrangements are e.g. known from <CIT> and <CIT>.

There is a need for an improved lawn striping arrangement for robotic work tools, such as robotic lawn mowers.

It is therefore an object of the present disclosure to provide a striper arrangement for striping a lawn configured to be arranged on a robotic work tool that solves or at least mitigates one of the problems of the prior-art. It is an object of the present disclosure to provide a striper arrangement that allows for smooth maneuvering of the robotic work tool that comprises the striper arrangement. A further object of the present disclosure is to provide a striper arrangement that is robust and of simple construction. Yet a further object of the present disclosure is the provide a striper arrangement that may be realized at low cost.

Yet a further object of the present invention is to provide a robotic lawnmower, comprising a striper arrangement for striping a lawn.

According to the invention at least one of the aforementioned objects is solved by a robotic lawnmower comprising a striper arrangement for striping a lawn; wherein the striper arrangement comprises a striper mat and a holding arrangement for holding the striper mat in contact with a surface of a lawn, wherein the holding arrangement is configured to be joined to, or be a part of, the robotic work tool, wherein the holding arrangement is configured such that:.

The striper arrangement according to the invention provides an advantage when the robotic work tool changes between forward driving direction and reverse, for example, during a backward turn. According to the present disclosure, the striper mat is movable in upwards/downwards direction but biased downwards so that the striper mat applies a sufficient pressure onto the lawn. Therefore, when the striper mat transits from a convex bent shape to a concave bent shape during the backward turn, the striper mat moves upwards as soon as the counter force from the striper mat exceeds the biasing force the striper arrangement. This allows the bent striper mat to straighten out, which in turn allows the striper mat to smoothly transit from convex to concave bent shape. Thus, the striper arrangement of the present disclosure, allows free maneuverability of the robotic work tool between forward and rearward driving direction without impediment from the striper mat or that the striper mat lifts the robotic work tool.

The holding arrangement comprises a striper mat holder that is joined to the striper mat and a striper mat holder attachment configured to be joined to, or be a part of, the robotic work tool. The striper mat holder is thereby connected to the striper mat holder attachment such that the striper mat holder is movable in upwards/downwards direction. Preferably, the striper mat holder is pivotally coupled to the striper mat holder attachment such that the striper mat holder may pivot in upwards/downwards direction relative the striper mat holder attachment. In summary, this holding arrangement is simple, yet robust and reliable.

In detail, the striper mat holder attachment may comprise at least one elongate attachment part which is configured to, in use, extend from the robotic work tool. The striper mat holder may thereby comprise a central elongated portion which is joined to an upper edge of the striper mat and at least one elongated extension part which extends from the central portion and that is pivotally attached to the striper mat holder attachment by a pivot shaft.

The striper arrangement comprises a biasing element configured to provide the biasing force (BF) onto the striper mat. Typically, the biasing element is a spring element. The biasing element is preferably coupled to the striper mat holder and to the striper mat holder attachment. Spring elements are preferred since they are available in many forms and therefore may be easily integrated into the construction of the striper arrangement. Spring elements may readily be selected in dependency of their spring characteristics to fit various types of robotic work tools, striper mats and operating conditions.

Typically, the counterforce (CF) is the force exerted by the striper mat onto the holding arrangement when the striper mat transits from a convex bent shape to a concave bent shape or vice versa. The counter force (CF) may be determined by practical trials and used as basis for selecting a biasing element that provides a suitable biasing force (BF).

When, in the present disclosure, reference is made to directions such as "upwards" or "downwards" it is intended that these directions are in relation to the ground surface that the robotic work tool is operating on. Thus, "upwards" is in direction substantially away from the ground surface and "downwards" is in direction substantially towards the ground surface.

The robotic work tool according to the present disclosure will now be described more fully hereinafter. The robotic work tool according to the present disclosure may however be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Same reference numbers refer to same elements throughout the description.

<FIG> shows schematically a robotic work tool <NUM>, embodied as a robotic lawn mower. The robotic work tool <NUM> is positioned on the surface of a lawn <NUM> and has a front <NUM> and a rear and comprises a pair of rear wheels <NUM>, which may be propelled by a motor (not shown) a pair of front wheels <NUM> and a housing <NUM> which protects components of the robotic work tool such as motor, cutting tool, sensors and the controller for controlling the robotic work tool with e.g. regards to maneuvering performance. These parts will be described hereinafter with regards to <FIG>. In <FIG>, the robotic work tool is moving in a forward driving direction indicated by arrow <NUM>. That is, the front <NUM> of the robotic work tool <NUM> is facing in the driving direction.

The robotic work tool <NUM> comprises a striper arrangement <NUM> for striping the lawn <NUM>. The striper arrangement <NUM> comprises a striper mat <NUM> and a holding arrangement <NUM> for holding the striper mat <NUM> in contact with the lawn <NUM>. The holding arrangement <NUM> is arranged at the rear <NUM> of the robotic work tool <NUM>, however alternatively it may be arranged at the front <NUM> of the robotic work tool. The striper mat is manufactured of flexible material such as a rubber material. For example, textile reinforced rubber. The striper mat may have an arbitrary width, for example <NUM> to create sufficiently wide stripes on the lawn. The thickness of the striper mat may be <NUM>. The length of the striper mat depends on dimensions of the robotic work tool and the position of the holder arrangement <NUM> on the robotic work tool. However, the length is adapted such that the striper mat <NUM> is bent into a concave/convex shape when striping the lawn <NUM>. In <FIG>, the striper mat <NUM> is trailed behind the robotic work tool <NUM>. The grass <NUM> behind the striper mat <NUM> is thus flattened by and the grass <NUM> in front of striper mat <NUM> is un-flattened.

<FIG> shows the striper arrangement <NUM> in detail. Thus, the holding arrangement <NUM> is configured such that the striper mat <NUM> is movable in upwards- and downwards direction. In the embodiment shown in <FIG>, the holding arrangement <NUM> thereby comprises a striper mat holder <NUM> which comprises a central elongated portion <NUM> which is joined to the upper edge <NUM> of the striper mat <NUM> and a first and a second elongated extension part <NUM> that extends, e.g. orthogonally, from the central elongated portion <NUM>. The striper mat holder may for example be manufactured by metal profiles having a square or rectangular cross-section. For example, steel or aluminum profiles. The width of the striper mat holder <NUM>, i.e. the length of the central elongated portion <NUM> may correspond to the width of the striper mat <NUM>. It is possible that the striper mat holder <NUM> comprises only one, or more than two, elongate extension parts <NUM> that extends from the central elongate portion <NUM>.

The holding arrangement <NUM> further comprises a striper mat holder arrangement <NUM> which comprises a first and a second elongate attachment part <NUM> which is are configured to extend, i.e. protrude, from the robotic work tool <NUM>. For example, from the rear <NUM> of the robotic work tool. Also, the first and the second elongate attachment part <NUM> may be manufactured of profiles of a suitable length and cross-section. For example, steel or aluminum profiles having a square or rectangular cross-section. The striper mat holder arrangement <NUM> may comprise a central elongated portion <NUM>. The first and the second elongate attachment part <NUM> may thereby extend, e.g. orthogonally from opposite ends of the central elongated portion <NUM>. The striper mat holder arrangement <NUM>, may be attached to the robotic work tool <NUM> by e.g. bolts (not shown). In correspondence with the striper mat holder <NUM> it is possible that also the striper mat holder arrangement <NUM> comprises only one, or more than two elongate attachment parts <NUM> that may extend from the central elongate portion <NUM>.

The striper mat holder <NUM> is movable connected to the striper mat holder attachment <NUM> such that the striper mat holder <NUM>, and thus the striper mat <NUM>, is movable in upwards-, downwards direction. In the embodiment shown in <FIG> the striper mat holder <NUM> is pivotally connected, i.e. pivotally coupled, to the striper mat holder attachment <NUM>. The first and second elongated extension portions <NUM> of the striper mat holder <NUM> are thereby pivotally coupled to a respective one of the first and the second elongated attachment part <NUM> of the striper mat holder attachment <NUM>. The pivotal coupling of the striper mat holder <NUM> and the striper mat holder attachment <NUM> may be achieved by a pivot shaft <NUM> that extends through openings in the first and second elongated extension portions <NUM> of the striper mat holder <NUM> and through openings in the first and the second elongated attachment parts <NUM> of the striper mat holder attachment <NUM>. Alternatively (not shown), one pivot shaft <NUM> may connect the first elongated extension portion <NUM> with the first elongated attachment part <NUM> and a second pivot shaft <NUM> may connect the second elongated extension portion <NUM> with the second elongated attachment part <NUM>.

It is obvious that the striper mat holder <NUM> may be movable connected to the striper mat holder attachment <NUM> in other ways than described above. For example, the striper mat holder <NUM> may be arranged to translate vertically in the striper mat holder attachment <NUM>. An example of such an arrangement is shown in <FIG> in which the first elongated extension portion <NUM> of the striper mat holder <NUM> is movable attached to a slot <NUM> that extends vertically in the first elongated attachment part <NUM> of the striper mat holder attachment <NUM>.

The holding arrangement <NUM> is further configured to bias the striper mat bias the striper mat <NUM> in downwards direction by a biasing force (BF). The holder arrangement <NUM> thereby comprises a biasing element, <NUM> such as a spring element which is coupled to the striper mat holder attachment <NUM> and to the striper mat holder <NUM> such that the striper mat holder <NUM>, and thus the striper mat <NUM>, is biased downwards. By "biased" is thereby meant that a force is permanently applied onto the striper mat holder <NUM> and forces, i.e. presses the striper mat holder <NUM> downwards.

In <FIG>, the biasing element <NUM> is a torsion spring. The torsion spring is manufactured of steel wire and comprises a coiled middle section <NUM> and a first leg <NUM> and a second leg <NUM>. The coiled middle section <NUM> is arranged around the pivot shaft <NUM> and the first leg <NUM> is attached to the first elongated attachment part <NUM> of the striper mat holder attachment <NUM>. The other leg <NUM> of the torsion spring <NUM> is attached to the first elongated extension portion <NUM> of the striper mat holder <NUM>. The torsion spring <NUM> is arranged such that the legs <NUM>, <NUM> strive apart from each other and create a downwards directed biasing force on the striper mat holder <NUM>.

It is obvious that the biasing force may be achieved in other ways. For example, the biasing element <NUM> may be a pressure spring, or a pneumatic spring or a piece of compressed rubber. The biasing element <NUM> may also be attached directly to the robotic work tool and coupled to the striper mat holder <NUM>, or alternatively to the striper mat.

The biasing force (BF) restricts movement of the striper mat <NUM> in upwards direction until a counter force (CF) exerted by the striper mat <NUM> onto the holding arrangement <NUM> exceeds the biasing force (BF).

<FIG> shows the holding arrangement <NUM> in a situation in which the striper mat holder <NUM> is pivoted upwards by a counter force (CF) that is applied onto the striper mat. In <FIG>, the counter force (CF) exceeds the biasing force (BF) from the biasing element <NUM> and forces the striper mat holder <NUM> upwards.

Preferably, the biasing force BF is selected such that it is substantially equal to a counter force (CF) exerted by the striper mat <NUM> when the striper mat <NUM> transits from a convex bent shape to a concave bent shape, or vice versa.

This feature is in the following described with reference to <FIG>.

<FIG> shows a situation in which the robotic work tool <NUM> described under <FIG> has changed driving direction from forward to reverse to make a backward turn. In this situation, friction between the lower edge <NUM> of the concavely bent striper mat <NUM> and the surface of the lawn <NUM> prevents the striper mat <NUM> from sliding over the surface of the lawn. Since the slider mat <NUM> does not follow the rearward movement of the robotic work tool <NUM>, a counter force (CF) starts immediately to build up in the flexible striper mat <NUM> as the striper mat <NUM> strives to transit from a concave bent shape into a convex bent shape. The counter force (CF) is exerted onto the holder arrangement <NUM>, i.e. onto the striper mat holder <NUM> (see <FIG>) and exceeds the biasing force (BF). The striper mat holder <NUM> and thus the striper mat <NUM> is therefore allowed to move upwards which allows the striper mat <NUM> to smoothly transit, without any lifting of the robotic work tool <NUM>, into a concave bent shape as shown in <FIG>. In this situation, the counter force (CF) decreases and the biasing force (BF) prevails and forces the striper mat <NUM> downwards to the state shown in <FIG>. The robotic work tool <NUM> may now complete the backwards turn. The procedure described above is repeated in inverted order when the robotic work tool <NUM> reverses driving direction from the rearward direction as shown in <FIG> to forward direction.

The counter force (CF) from the striper mat <NUM> may vary in dependency of e. dimension and material of the striper mat or operating conditions. However, the counter force (CF) produced during the transit between convex and concave shape of the striper mat <NUM> may be determined by practical trials. It may, for example, be measured with a potentiometer. It is then possible to use such measurements for providing a suitable biasing force, for example selecting a biasing element with appropriate spring characteristics.

Following is a description of further parts of the robotic work tool.

<FIG> shows a schematic overview of the robotic work tool <NUM>, which is exemplified by a robotic lawnmower <NUM>. The housing <NUM> has been omitted in order to not obscure other parts of the robotic work tool.

Thus, the robotic work tool <NUM> comprises a chassis <NUM> and pair of wheels. One pair of front wheels <NUM> is arranged in the front of the chassis <NUM> and one pair of rear wheels <NUM> is arranged in the rear of the chassis <NUM>. At least some of the wheels <NUM>, <NUM> are drivably connected to at least one electric motor <NUM>. It is appreciated that while the description herein is focused on electric motors, combustion engines may alternatively be used possibly in combination with an electric motor. A striper arrangement <NUM> according to the present disclosure is arranged at the rear of the robotic lawn mower <NUM>.

In the example of <FIG>, each of the rear wheels <NUM> is connected to a respective electric motor <NUM>. This allows for driving the rear wheels <NUM> independently of one another which, for example, enables steep turning.

The robotic work tool <NUM> also comprises a controller <NUM>. The controller <NUM> may be implemented using instructions that enable hardware functionality, for example, by using executable computer program instructions in a general-purpose or special-purpose processor that may be stored on a computer readable storage medium (disk, memory etc.) <NUM> to be executed by such a processor. The controller <NUM> is configured to read instructions from the memory <NUM> and execute these instructions to control the operation of the robotic work tool <NUM> including, but not being limited to, the propulsion of the robotic work tool. The controller <NUM> may be implemented using any suitable processor or Programmable Logic Circuit (PLC). The memory <NUM> may be implemented using any technology for computer-readable memories such as ROM, RAM, SRAM, DRAM, FLASH, DDR, SDRAM or some other memory technology.

The robotic work tool <NUM>, may comprise a grass cutting device <NUM>, such as a rotating blade driven by a cutter motor <NUM>. In the embodiment of <FIG> the grass cutting device <NUM> and the cutter motor <NUM> are arranged in the front carriage <NUM>. The cutter motor <NUM> is connected to the controller <NUM> which enables the controller <NUM> to control the operation of the cutter motor <NUM>. The controller <NUM> may also be configured to determine the load exerted on the rotating blade, by for example measure the power delivered to the cutter motor <NUM> or by measuring the axle torque exerted by the rotating blade. The robotic work tool <NUM> also has (at least) one battery <NUM> for providing power to the motors <NUM> and the cutter motor <NUM>. The robotic work tool may further have a satellite navigation device <NUM>, such as a GPS-device, which may be used by the robotic lawn work tool <NUM> to navigate within a work area.

Claim 1:
A robotic lawnmower (<NUM>) characterized in comprising a striper arrangement (<NUM>) for striping a lawn (<NUM>), wherein the striper arrangement (<NUM>) comprises a striper mat (<NUM>), a biasing element (<NUM>) configured to provide a biasing force (BF) onto the striper mat (<NUM>), and a holding arrangement (<NUM>) for holding the striper mat (<NUM>) in contact with a surface of a lawn (<NUM>), wherein the holding arrangement (<NUM>) is configured such that:
the striper mat (<NUM>) is movable in upwards and downwards direction; and further configured to
bias the striper mat (<NUM>) in a downwards direction by the biasing force (BF), such that movement of the striper mat (<NUM>) in upwards direction is restricted until a counter force (CF) exerted by the striper mat (<NUM>) onto the holding arrangement (<NUM>) exceeds the biasing force (BF), wherein
the holding arrangement (<NUM>) comprises a striper mat holder (<NUM>) joined to the striper mat (<NUM>) and a striper mat holder attachment (<NUM>) of the robotic lawnmower (<NUM>), wherein
the striper mat holder (<NUM>) is connected to the striper mat holder attachment (<NUM>) such that the striper mat holder (<NUM>) is movable in upwards/downwards direction, upwards movement allowing the striper mat (<NUM>) to straighten out when the robotic lawnmower (<NUM>) changes between forward direction and reverse and the resulting counter force (CF) forces the striper mat holder (<NUM>) upwards, thereby enabling smooth transit between convex and concave bent shape of the striper mat (<NUM>).