Patent Description:
Automated or robotic power tools such as robotic lawnmowers are becoming increasingly more popular. In a typical deployment a work area, such as a garden, the work area is enclosed by a boundary wire with the purpose of keeping the robotic lawnmower inside the work area.

The work area usually also has a number of obstacles inside it, such as rocks, trees, walls and so on. In order to avoid colliding with such objects, many robotic work tools are equipped with proximity sensors that enable the robotic work tool to detect an obstacle before reaching it and take evasive action before colliding with the obstacle. If the obstacle is not inside the work area (such as a rock just outside the boundary or a bush having its stem outside the boundary, but with branches hanging in over the boundary and into the work area), this operation results in that a part of the work area is not serviced even though no collision with the object outside the work area would ever happen.

The patent document published as <CIT> discloses an automatic travelling work vehicle configured to execute work travel along a travel route is provided, the automatic travelling work vehicle includes a work travel control section configured to control work travel, work travel state detection sensors configured to detect a work travel state, at least one obstruction sensor configured to detect an obstruction disturbing travel, an obstruction detection section configured to detect an obstruction positioned within an obstruction detection area in accordance with a sensor signal from the obstruction sensor, and an obstruction detection area determination section configured to determine the obstruction detection area in accordance with the work travel state detected by the work travel state detection sensors. Further, a method for executing work travel of an automatic travelling work vehicle along a travel route is provided.

The patent document published as <CIT> discloses a method of establishing an area of confinement and an autonomous robot for performing a task within the area of confinement. In one aspect, the invention can be a method of defining an area of confinement for an autonomous robot comprising: a) positioning the autonomous robot at a first location point P1, the autonomous robot comprising a location tracking unit, and recording the first location point P1 within a memory device; b) moving the autonomous robot from the first location point P1 to a plurality of location points P2-N and recording each of the plurality of location points P2-N within the memory device; and c) defining, with a central processing unit, a first closed-geometry comprising the first location point P1 and the plurality of location points P2-N as a perimeter of the area of confinement within the memory device.

Thus, there is a need for an improved manner of enabling a reliable navigation for a robotic work tool, such as a robotic lawnmower.

As will be disclosed in detail in the detailed description, the inventors have realized that a system where the robotic work tool deactivates the proximity sensors (or the input received therefrom) when being close to the boundary, the problems discussed above, may be solved.

It is therefore an object of the teachings of this application to overcome or at least reduce those problems by providing a robotic work tool system comprising a boundary enclosing a work area and a robotic work tool comprising a proximity sensor arranged to sense an obstacle, the robotic work tool being arranged to operate within the work area and the robotic work tool being configured to determine a sensed obstacle; determine a distance d to the boundary, wherein the determined distance is the distance from the sensed obstacle to the boundary; determine whether the distance d is inside a threshold distance D, and if so disregard the proximity sensor; and, if not, take evasive action to avoid the sensed obstacle as per the appended claims.

One benefit is that objects just outside the work area does not result in that parts of the work area are unnecessarily skipped, especially since the accuracy of a proximity sensor may be leading to patches of grass not being serviced by the robotic lawnmower turning prematurely. Another benefit is that false positives of detecting obstacles, such as obstacles hanging over the work area is avoided.

In one embodiment the robotic work tool system further comprises a signal generator arranged to generate a control signal, wherein the work area is enclosed by a boundary wire through which the control signal is being transmitted thereby generating a magnetic field and wherein the robotic work tool further comprises at least one magnetic field sensor for detecting the magnetic field, wherein the robotic work tool is further configured to receive magnetic sensor input from the magnetic field sensor; and determine a magnetic field magnitude based on the magnetic sensor input for determining a relative position of the robotic work tool with regards to the boundary wire, and wherein the threshold distance D is based on a threshold magnetic field magnitude.

In one embodiment the robotic work tool is further configured to reduce its speed when it is determined that the distance d is inside the distance D. In one such embodiment the robotic work tool is further configured to reduce its speed if it is determined that an object is sensed.

In one embodiment the robotic work tool further comprises a memory configured to store map data indicating a boundary for the work area and a navigation sensor, wherein the robotic work tool is further configured to receive position input from the navigation sensor; determine a position of the robotic work tool based on the position input; and wherein the threshold distance D is based on the map data. In one such embodiment the navigation sensor comprises a satellite navigation sensor.

In one embodiment the robotic work tool is further configured to receive input indicating whether the function of disregarding the proximity sensor based on a determined distance d should be enabled or disabled.

In one embodiment the robotic work tool is further configured to receive input indicating the threshold distance D.

In one embodiment the robotic work tool is a robotic lawnmower.

It is also an object of the teachings of this application to overcome the problems by providing a method for use in a robotic work tool system comprising a boundary enclosing a work area and a robotic work tool comprising a proximity sensor arranged to sense an obstacle, the robotic work tool being arranged to operate within the work area, and the method comprising: determining a sensed obstacle; determining a distance d to the boundary; determining whether the distance d is inside a threshold distance D, and if so disregarding the proximity sensor; and, if not, taking evasive action to avoid the sensed obstacle as per the appended claims.

Other features and advantages of the disclosed embodiments will appear from the following detailed disclosure, from the attached dependent claims as well as from the drawings. All references to "a/an/the [element, device, component, means, step, etc.]" are to be interpreted openly as referring to at least one instance of the element, device, component, means, step, etc., unless explicitly stated otherwise.

The invention will be described in further detail under reference to the accompanying drawings in which:.

The disclosed embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. Like reference numbers refer to like elements throughout.

It should be noted that even though the description given herein will be focused on robotic lawnmowers, the teachings herein may also be applied to, robotic ball collectors, robotic mine sweepers, robotic farming equipment, or other robotic work tools where lift detection is used and where the robotic work tool is susceptible to dust, dirt or other debris.

<FIG> shows a perspective view of a robotic work tool <NUM>, here exemplified by a robotic lawnmower <NUM>, having a body <NUM> and a plurality of wheels <NUM> (only one pair is shown). The robotic work tool <NUM> may be a multi-chassis type or a mono-chassis type (as in <FIG>). A multi-chassis type comprises more than one body parts that are movable with respect to one another. A mono-chassis type comprises only one main body part.

The robotic lawnmower <NUM> may comprise charging skids for contacting contact plates (not shown in <FIG>) when docking into a charging station (not shown in <FIG>, but referenced <NUM> in <FIG>) for receiving a charging current through, and possibly also for transferring information by means of electrical communication between the charging station and the robotic lawnmower <NUM>.

<FIG> shows a schematic overview of the robotic work tool <NUM>, also exemplified here by a robotic lawnmower <NUM>. In this example embodiment the robotic lawnmower <NUM> is of a mono-chassis type, having a main body part <NUM>. The main body part <NUM> substantially houses all components of the robotic lawnmower <NUM>. The robotic lawnmower <NUM> has a plurality of wheels <NUM>. In the exemplary embodiment of <FIG> the robotic lawnmower <NUM> has four wheels <NUM>, two front wheels and two rear wheels. At least some of the wheels <NUM> are drivably connected to at least one electric motor <NUM>. It should be noted that even if the description herein is focused on electric motors, combustion engines may alternatively be used, possibly in combination with an electric motor. In the example of <FIG>, each of the wheels <NUM> is connected to a respective electric motor. This allows for driving the wheels <NUM> independently of one another which, for example, enables steep turning and rotating around a geometrical center for the robotic lawnmower <NUM>. It should be noted though that not all wheels need be connected to each a motor, but the robotic lawnmower <NUM> may be arranged to be navigated in different manners, for example by sharing one or several motors <NUM>. In an embodiment where motors are shared, a gearing system may be used for providing the power to the respective wheels and for rotating the wheels in different directions. In some embodiments, one or several wheels may be uncontrolled and thus simply react to the movement of the robotic lawnmower <NUM>.

The robotic lawnmower <NUM> also comprises a grass cutting device <NUM>, such as a rotating blade <NUM> driven by a cutter motor <NUM>. The grass cutting device being an example of a work tool <NUM> for a robotic work tool <NUM>. The robotic lawnmower <NUM> also has (at least) one battery <NUM> for providing power to the motor(s) <NUM> and/or the cutter motor <NUM>.

The robotic lawnmower <NUM> also comprises a controller <NUM> and a computer readable storage medium or memory <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 the memory <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 lawnmower <NUM> including, but not being limited to, the propulsion of the robotic lawnmower. The controller <NUM> may be implemented using any suitable, available processor or Programmable Logic Circuit (PLC). The memory <NUM> may be implemented using any commonly known technology for computer-readable memories such as ROM, RAM, SRAM, DRAM, FLASH, DDR, SDRAM or some other memory technology.

The robotic lawnmower <NUM> may further be arranged with a wireless communication interface <NUM> for communicating with other devices, such as a server, a personal computer or smartphone, the charging station, and/or other robotic work tools. Examples of such wireless communication devices are Bluetooth®, WiFi® (IEEE802.11b), Global System Mobile (GSM) and LTE (Long Term Evolution), to name a few.

For enabling the robotic lawnmower <NUM> to navigate with reference to a boundary wire emitting a magnetic field caused by a control signal transmitted through the boundary wire, the robotic lawnmower <NUM> is further configured to have at least one magnetic field sensor <NUM> arranged to detect the magnetic field (not shown) and for detecting the boundary wire and/or for receiving (and possibly also sending) information to/from a signal generator (will be discussed with reference to <FIG>). In some embodiments, the sensors <NUM> may be connected to the controller <NUM>, possibly via filters and an amplifier, and the controller <NUM> may be configured to process and evaluate any signals received from the sensors <NUM>. The sensor signals are caused by the magnetic field being generated by the control signal being transmitted through the boundary wire. The magnitude of the magnetic field varies with the distance to the boundary wire. In principle, the magnitude decrease as the distance to the boundary wire increases. This enables the controller <NUM> to determine whether the robotic lawnmower <NUM> is close to the boundary wire and approximately how close the robotic lawnmower is to the boundary wire. As the magnetic field has a different polarity depending on which side of the boundary it is sensed, the magnitude of the magnetic field changes abruptly in the immediate vicinity of the boundary, going from the strongest magnitude in one polarity (for example positive) to the strongest polarity in the other polarity (for example negative) as the boundary wire is crossed. This enables the controller <NUM> to determine whether the robotic lawnmower <NUM> is crossing the boundary wire by sensing a change in polarity, or inside or outside an area enclosed by the boundary wire by sensing the polarity.

The robotic lawnmower <NUM> also comprises one or more proximity detectors <NUM>. In the example of <FIG>, the robotic lawnmower <NUM> comprises one proximity sensor facing forwards for detecting proximity of objects in front of the robotic lawnmower. The robotic lawnmower <NUM> may also comprise one proximity sensor facing backwards for detecting proximity of objects behind the robotic lawnmower, which is especially useful when reversing. As a proximity sensor enables the robotic lawnmower to detect objects before colliding with them, it increases the longevity of the robotic lawnmower (by reducing the wear and tear inflicted by collisions) and also decrease the risk of getting stuck on any object, as the object is detected beforehand and the robotic lawnmower may take action to avoid colliding with the object. A proximity sensor <NUM> is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. A proximity sensor <NUM> may be implemented as an optical proximity sensor, such as a camera utilizing image analysis, a laser range finder, infrared sensor, or as an audio sensor such as sonar, ultrasonic sensor, or as a radio frequency based sensor such as radar.

The robotic lawnmower <NUM> may also comprise one or more collision detectors <NUM>. In the example of <FIG>, the robotic lawnmower <NUM> comprises a front collision detector <NUM>-<NUM>, enabling the robotic lawnmower <NUM> to detect a collision while moving in a forwards direction, i.e. a forwards collision, and a rear collision detector <NUM>-<NUM>, enabling the robotic lawnmower <NUM> to detect a collision while moving in a reverse direction, i.e. a reverse collision.

In some embodiments, the robotic lawnmower <NUM> further comprises one or more sensors for deduced navigation <NUM>. Examples of sensors for deduced reckoning are odometers, accelerometers, gyroscopes, and compasses to mention a few examples. In the example of <FIG>, the robotic lawnmower <NUM> may comprise two odometers, being wheel turn counters, enabling the robotic lawnmower <NUM> to count the number of wheel turns executed by two opposite wheels and thereby both determine a distance travelled (equalling number of wheel turns multiplied with the diameter of the wheel), and also any directional changes (by noting differences in wheel turns between the two wheels). In the example of <FIG>, the robotic lawnmower <NUM> may further comprise an accelerometer enabling the robotic lawnmower <NUM> to not only determine directional changes, but also changes in altitude and current inclination.

In one embodiment, the robotic lawnmower <NUM> may further comprise at least one navigation sensor, such as a beacon navigation sensor and/or a satellite navigation sensor <NUM>. The beacon navigation sensor may be a Radio Frequency receiver, such as an Ultra Wide Band (UWB) receiver or sensor, configured to receive signals from a Radio Frequency beacon, such as a UWB beacon. Alternatively or additionally, the beacon navigation sensor may be an optical receiver configured to receive signals from an optical beacon. The satellite navigation sensor may be a GPS (Global Positioning System) device, a RTK (Real-Time Kinematic) device or other Global Navigation Satellite System (GNSS) device.

In embodiments, where the robotic lawnmower <NUM> is arranged with a navigation sensor, the magnetic sensors <NUM> are optional. In such systems, and also other systems utilizing a boundary wire, the robotic lawnmower may be arranged to determine a distance to the boundary of the work area by comparing a current location determined through the navigation sensor, to a stored location of the boundary. In such systems the boundary is virtual and corresponds to positions or locations stored in the memory <NUM> of the robotic lawnmower <NUM>.

<FIG> shows a schematic view of a robotic work tool system <NUM> in one embodiment. The schematic view is not to scale. The robotic work tool system <NUM> comprises a robotic work tool <NUM>. As with <FIG>, the robotic work tool is exemplified by a robotic lawnmower, whereby the robotic work tool system may be a robotic lawnmower system or a system comprising a combinations of robotic work tools, one being a robotic lawnmower, but the teachings herein may also be applied to other robotic work tools adapted to operate within a work area.

The robotic work tool system <NUM> may also comprises charging station <NUM> which in some embodiments is arranged with a signal generator <NUM> and a boundary wire <NUM>.

The signal generator is arranged to generate a control signal <NUM> to be transmitted through the boundary wire <NUM>. To perform this, the signal generator is arranged with a controller and memory module. The controller and memory module may also be the controller and memory module of the charging station.

The boundary wire <NUM> is arranged to enclose a work area <NUM>, in which the robotic lawnmower <NUM> is supposed to serve. The control signal <NUM> transmitted through the boundary wire <NUM> causes a magnetic field (not shown) to be emitted.

In one embodiment the control signal <NUM> is a sinusoid periodic current signal. In one embodiment the control signal <NUM> is a pulsed current signal comprising a periodic train of pulses. In one embodiment the control signal <NUM> is a coded signal, such as a CDMA signal.

As an electrical signal is transmitted through a wire, such as the control signal <NUM> being transmitted through the boundary wire <NUM>, a magnetic field is generated. The magnetic field may be detected using field sensors, such as Hall sensors. A sensor - in its simplest form - is a coil surrounding a conductive core, such as a ferrite core. The amplitude of the sensed magnetic field is proportional to the derivate of the control signal. A large variation (fast and/or of great magnitude) results in a high amplitude or magnitude for the sensed magnetic field. As discussed above, the magnitude of the magnetic field varies with the distance to the boundary wire <NUM>. The variations are sensed and compared to a reference signal or pattern of variations in order to identify and thereby reliably sense the control signal.

The work area <NUM> is in this application exemplified as a garden, but can also be other work areas as would be understood. The garden contains a number of obstacles (O), exemplified herein by a slope (S), a rock (R), a number (<NUM>) of trees (T) and a house structure (H). The trees are marked both with respect to their trunks (filled lines) and the extension of their foliage (dashed lines).

In one embodiment the robotic work tool is arranged or configured to traverse and operate in a work area that is not essentially flat, but contains terrain that is of varying altitude, such as undulating, comprising hills or slopes or such. The ground of such terrain is not flat and it is not straightforward how to determine an angle between a sensor mounted on the robotic work tool and the ground. The robotic work tool is also or alternatively arranged or configured to traverse and operate in a work area that contains obstacles that are not easily discerned from the ground. Examples of such are grass or moss covered rocks, roots or other obstacles that are close to ground and of a similar colour or texture as the ground. The robotic work tool is also or alternatively arranged or configured to traverse and operate in a work area that contains obstacles that are overhanging, i.e. obstacles that may not be detectable from the ground up, such as low hanging branches of trees (T) or bushes. Such a garden is thus not simply a flat lawn to be mowed or similar, but a work area of unpredictable structure and characteristics. The work area <NUM> exemplified with referenced to <FIG>, may thus be such a non-uniform work area as disclosed in this paragraph that the robotic work tool is arranged to traverse and/or operate in.

As can be seen in <FIG>, the boundary wire <NUM> has been laid so that so-called islands are formed around the trees' trunks and the house (H). This requires that more boundary wire is used, than if the work area was without such obstacles. It should be noted that any distances between wires are greatly exaggerated in this application in order to make the distances visible in the drawings. In a real-life installations the boundary wire is usually laid so that there is not distance between the wire going out and the wire coming back (distance = <NUM>). This allows the robotic work tool <NUM> to cross any such sections (indicated by the dashed arrow in <FIG>) as the magnetic field emitted by the wire going out cancels out the magnetic field emitted by the wire coming back.

<FIG> shows a schematic view of a robotic work tool system <NUM> in one embodiment illustrating various problem situations that may occur with prior art systems. The schematic view is not to scale. In this view, the work area <NUM> comprises different obstacles than the work area <NUM> of <FIG> shows two stones, one stone S1 inside the work area <NUM> and close to the boundary wire <NUM>, and one stone S2 outside the work area. <FIG> also shows a bush B along the edge of the boundary wire <NUM>. As is indicated the bush is actually located outside the work area but has branches hanging in over the work area <NUM>.

As the robotic lawnmower approaches the first stone, that is inside the work area and close to the boundary wire <NUM>, the proximity sensor <NUM> senses an imaginary or sensed location il1 for the first stone S1 (indicated by a dotted representation of the stone S1). As the robotic lawnmower <NUM> approaches the imaginary location il1 as determined by the proximity sensor <NUM>, the robotic lawnmower <NUM> will take evasive action and turn away to avoid a collision as indicated by the dashed line. This will result in that the lawn is not cut in proximity to the stone S1. A similar example is illustrated with reference to the second stone S2. However, in this example the robotic lawnmower <NUM> will take evasive action as it approaches an imaginary location il2 for the second stone S2 as determined by the proximity sensor <NUM> even though the second stone is not inside the work area <NUM> resulting in that a part of the work area is not being serviced. In both cases, the result is that the robotic lawnmower <NUM> does not cut as close to an object as possible resulting in parts of the work area not being serviced. A similar problem to the problem of the second stone S2 arises when the robotic lawnmower <NUM> approaches the bush B. as the bush has branches hanging over the boundary wire <NUM>, the bush may be determined as being inside the boundary wire, when in fact it is outside the boundary wire, resulting in that a part of the work area <NUM> is not being serviced completely unnecessarily as the robotic lawnmower <NUM> will take evasive action before reaching the boundary wire even though a collision with the second stone would never happen.

In <FIG> a further object O is also shown and as the robotic lawnmower <NUM> approaches an imaginary or sensed location il3 of the object, the robotic lawnmower <NUM> will take evasive action.

<FIG> shows a schematic view of a robotic work tool system <NUM> in one embodiment illustrating how the problem situations that may occur with prior art systems as shown by <FIG> may be overcome with a robotic work tool system <NUM> as per the present teachings. The schematic view is not to scale. In this view, a threshold signal level <NUM> of the magnitude of the sensed magnetic field indicating a distance D to the boundary wire <NUM> is illustrated by a dashed line. In the embodiments disclosed in <FIG>, the robotic lawnmower <NUM> is configured to determine a distance to the boundary wire <NUM> and determine whether the distance d is below (or within) the distance D corresponding to the threshold signal level of the magnitude of the sensed magnetic field. If so, the robotic lawnmower <NUM> is configured to disregard the input from the proximity sensor <NUM> and thus the imaginary locations and simply rely on the magnetic sensors <NUM>. The magnetic sensors <NUM> have a higher accuracy and are also not affected by branches hanging over the boundary wire <NUM>. As such, the robotic lawnmower <NUM> will proceed up to the boundary wire <NUM> in the case of approaching the second stone S2 thereby preventing that a part of the work area <NUM> is not serviced and thus solving the problem as discussed in relation to <FIG>.

As can be seen in <FIG>, there is no longer any sensing of the stone S1 received from the proximity sensor, which would lead the robotic lawnmower <NUM> to collide with the stone S1. In order to reduce the impact of such a collision the robotic lawnmower <NUM> is configured to reduce its speed when it is determined that the distance d is below (or within) the distance D corresponding to the threshold signal level of the magnitude of the sensed magnetic field. This will not prevent a collision, but will reduce the effect of such a collision thereby also reducing the wear and tear of the robotic lawnmower <NUM> leading to an increased lifetime of the robotic lawnmower.

In one such embodiment, the robotic lawnmower is configured to ignore the proximity sensor only in the aspect that the robotic lawnmower will not take evasive action (such as turn away) based on the input from the proximity sensor. The robotic lawnmower may, however, be configured to reduce its speed based on the proximity sensor, so that the speed is only reduced when the input received from the proximity sensor actually indicates that there is something to collide with. This also reduces the wear and tear of the robotic lawnmower but maintains most of the efficiency of the robotic lawnmower by not slowing down unnecessarily.

As is also shown in <FIG>, the robotic lawnmower <NUM> is configured to determine the imaginary or sensed location il3 of the object O as determined by receiving input from the proximity sensor <NUM>, as the distance d determined would be over or outside the distance D corresponding to the threshold signal level of the magnitude of the sensed magnetic field. In case the imaginary or sensed location il3 of the object O does not correspond accurately to the actual location of the object, it may result in that a part of the work area <NUM> is not serviced. However, in this case, it will be in order to avoid a collision, and thus not unnecessarily.

In one embodiment, the distance determined d is the distance of the robotic lawnmower to the boundary wire <NUM>, as in the example of <FIG>.

In one such embodiment, the distance determined d is determined based on the magnitude of the magnetic field sensed by a magnetic field sensor <NUM>. In one alternative or additional such embodiment, the distance determined d is determined based on determining a location of the robotic lawnmower <NUM> and comparing the location determined to a stored location of the boundary using alternative navigation sensors.

In one embodiment, the distance determined d is the sensed distance from the obstacle to the boundary <NUM>. In one such embodiment, the distance determined d is determined based on input received from the proximity sensor <NUM>. This enables the robotic lawnmower <NUM> to determine that the sensed object is too close to the boundary wire for trusting the accuracy of the proximity sensor <NUM> and instead relying on the magnetic sensor <NUM> for avoiding that apart is unnecessarily not serviced.

In one embodiment the distance is a two-fold distance being a combination of both the distance from the robotic work tool to the boundary <NUM> and from the sensed object to the boundary <NUM>, wherein it is determined if any or both of the distances falls within a respective threshold distance D.

<FIG> shows a more detailed view of the problem situation that may occur with prior art systems in relation to the bush B of <FIG>. As the robotic lawnmower <NUM> approaches the bush B, it will determine an imaginary or sensed location ilB for the bush, and take evasive action prematurely and unnecessarily as discussed in relation to <FIG> resulting in that the part indicated A is left unserved. Even though the robotic lawnmower <NUM> would have been able to navigate under the hanging branches of the bush B.

<FIG> shows a more detailed view of how the problem situation is solved as discussed above in relation to the bush B of <FIG>. The robotic lawnmower <NUM> determines a distance d and compares it to the distance D indicating the signal level corresponding to a threshold distance to the boundary wire <NUM> (the threshold distance D). As the determined distance d is below or within the threshold distance D, the robotic lawnmower <NUM> deactivates the proximity sensor <NUM> or ignores the input received from the proximity sensor <NUM> (as indicated by the proximity sensor <NUM> being crossed out in <FIG>) and instead relies on the magnetic sensor <NUM> for determining how far to go, and possibly the collision sensor <NUM>-<NUM> to avoid getting stuck due to a collision.

As indicated in <FIG> by the dashed representation of the robotic lawnmower <NUM>, the robotic lawnmower <NUM> is thereby enabled to also service the part A of the work area, thereby solving the problem discussed herein and as shown in <FIG> and more precisely in <FIG>.

In one embodiment, the robotic lawnmower <NUM> is configured to receive input indicating whether the function of deactivating the proximity sensor based on a determined distance should be enabled or disabled. The input may be received from a user through a user interface, not shown explicitly but considered to be part of the communication interface <NUM> as it enables communication with external entities.

In one such embodiment, the input is received internally due to a determination that the robotic lawnmower is in a specific area. The specific area may be seen as being inside the threshold distance to the boundary wire. The specific area may also or alternatively be a user-defined area (either in the map or by laying the boundary wire) indicating for example an area with lots of bushes or low hanging trees.

In such embodiments, the robotic lawnmower <NUM> is further configured to determine that it is within a specific area and in response thereto either enable or disable the function of deactivating the proximity sensor based on a determined distance.

In one embodiment, the robotic lawnmower <NUM> is configured to receive input indicating the size or extent of the area where the proximity sensor possibly should be disabled, i.e. input indicating the distance D. The input may be received from a user through a user interface, not shown explicitly but considered to be part of the communication interface <NUM> as it enables communication with external entities.

In one such embodiment, the area is indicated by receiving a setting for the distance D. In one alternative or additional embodiment, the area is indicated by receiving input corresponding to or defining the actual borders of the area, for example through the use of a map application in the user interface or in the user interface of a cooperating device.

<FIG> shows a flowchart of a general method according to the teachings herein. As discussed above, the robotic lawnmower <NUM> is configured to determine <NUM> a sensed or imaginary location il1, il2, il3, ilB of an obstacle S1, S2, O, B. It should be noted that it is not essential to determine the exact location of a sensed object, and that it may suffice to determine a distance to, i.e. the presence of, the sensed object. The robotic work tool <NUM> is also configured to determine <NUM> a distance d and to determine <NUM> whether the distance d is inside a threshold distance D. If it is determined that the determined distance d is within the threshold distance D, then the robotic work tool <NUM> is configured to disregard <NUM> the proximity sensor <NUM> and the sensed location il1, il2, il3, ilB. The proximity sensor <NUM> may be disregarded by being deactivated thereby not determining the sensed location or the proximity sensor may be disregarded by not utilizing the sensed location.

If it is determined that the determined distance d is outside the threshold distance D, then the robotic work tool <NUM> is configured to take <NUM> evasive action as the robotic lawnmower <NUM> approaches the sensed location il1, il2, il3, ilB. In one embodiment the sensed location is determined only if it is determined that the proximity sensor is not to be disregarded.

In one embodiment the determined distance d is the distance from the robotic lawnmower <NUM> to the boundary wire <NUM>. In an alternative or additional embodiment the determined distance d is the distance from the sensed location il1, il2, il3, ilB, i.e. from the sensed object, to the boundary wire <NUM>.

In an embodiment where the robotic lawnmower system <NUM> comprises a signal generator <NUM> arranged to generate a control signal <NUM>, wherein the work area <NUM> is enclosed by a boundary wire <NUM> through which the control signal <NUM> is being transmitted thereby generating a magnetic field, the threshold distance D is based on a threshold magnetic field magnitude corresponding to a distance from the boundary wire <NUM>. And the robotic lawnmower <NUM> is further configured to receive magnetic sensor input from the magnetic field sensor <NUM>; and determine a magnetic field magnitude based on the magnetic sensor input for determining a relative position of the robotic lawnmower <NUM> with regards to the boundary wire <NUM> for enabling the robotic lawnmower <NUM> to navigate in relation to the boundary wire <NUM>. The magnetic field magnitude sensed may also be utilized to determine a distance of the robotic lawnmower <NUM> to the boundary wire to be used as the determined distance d.

In an alternative or additional embodiment wherein the robotic lawnmower <NUM> further comprises a navigation sensor <NUM>, <NUM> and a memory <NUM> configured to store map data representing the work area <NUM> and especially indicating a boundary <NUM> for the work area <NUM>, the robotic lawnmower <NUM> is configured to navigate in relation to the boundary by determining a position based on navigation sensor input and comparing this to the stored map data. In such an embodiment the threshold distance D is based on the map data and represents a distance to the boundary. In one such embodiment the navigation sensor comprises a satellite navigation sensor <NUM> as discussed in relation to <FIG>.

Claim 1:
A robotic work tool system (<NUM>) comprising a boundary (<NUM>) enclosing a work area (<NUM>) and a robotic work tool (<NUM>) comprising a proximity sensor (<NUM>) arranged to sense an obstacle (S1, S2, O, B), the robotic work tool (<NUM>) being arranged to operate within the work area (<NUM>) and the robotic work tool (<NUM>) being configured to
determine (<NUM>) a sensed obstacle (S1, S2, O, B)
determine (<NUM>) a distance (d) to the boundary (<NUM>);
determine (<NUM>) whether the distance (d) is inside a threshold distance (D), and if so
disregard (<NUM>) the proximity sensor (<NUM>) and not take (<NUM>) evasive action to avoid the sensed obstacle (S1, S2, O, B); and, if not,
take (<NUM>) evasive action to avoid the sensed obstacle (S1, S2, O, B), characterized in that the determined distance (d) is the distance from the sensed obstacle (S1, S2, O, B) to the boundary (<NUM>).