SE1850379A1 - Improved navigation for a robotic working tool - Google Patents

Abstract

A robotic working tool system (200) comprising at least one beacon (220) arranged to at least partially delimit work area (205) and a robotic working tool (100) configured to operate within said work area, the robotic working tool (100) being configured to: determine an expected position; determine a current position relative at least one of the at least one beacon (220); determine if there is an error in the determined current position compared to the expected position, and, if so, determine that the at least one of the at least one beacon (220) has moved.

Description

IMPROVED NAVIGATION FOR A ROBOTIC WORKING TOOL TECHNICAL FIELDThis application relates to robotic working tools and in particular to asystem and a method for performing improved navigation of work to be performed by a robotic working tool, such as a lawnmower.

BACKGROUND Automated or robotic power tools such as robotic lawnmowers are becomingincreasingly more popular. In a typical deployment, a work area, such as a garden, isenclosed by a boundary cable with the purpose of keeping the robotic lawnmower insidethe work area. The robotic lawnmower is typically configured to work in a random patteminside the work area. As such, it does not take into account features of the work area.Also, the boundary cable may be difficult and cumbersome to install in the work area ina proper manner.

Therefore, prior art mo dels have been proposed where the robotic lawnmowersystem is designed to use beacons to mark the boundaries and/or obstacles of the workarea. Placing beacons requires significantly less work from the user (or operator) and alsoenables the marking of specific obstacles or other features in the work area.

However, as will be discussed in the below, the inventors have realizedproblems with these traditional manners of navigating a robotic lawnmower.

Thus, there is a need for improved navigation of a robotic lawnmower.

SUMMARY The inventors have realized that at least one problem exists with prior artbeacon-based navigation systems, in that if a beacon is lost, or especially if it is movedas the user may not be aware of this, the robotic lawnmower will not be able to navigatecorrectly any longer. As the beacon may only have moved slightly it may be difficultfor a user to identify the cause of the erroneous behavior of the robotic lawnmower. As robotic lawnmowers in most contemporary deployments are operating according to spatial requirements measuring only centimeters, the accuracy of the navigation systemis delicate and even slight movements of a beacon, such as by centimeters, may havedetrimental effects to the navigation, but may be difficult for a human user to see orobserve. A slight movement is thus a movement that is difficult for a human user todetect Without performing accurate measurements. Such movements may be of a few(less than l0) centimeters. Depending on the size of the Work area, such movementmay even be measure in meters. Generally, a distance of less than 5 % of the Workarea°s extension Will be difficult to observe by a human user Without specificmeasurements.

As the inventors have realized, the detection of Whether a beacon has movedor not is a completely different situation and also one overlooked so far..

As a moved beacon may result in improper navigation, the inventors haverealized that there is also a safety-aspect to realize that a beacon has been moved, also ifonly slightly. The teachings herein may thus also be used beneficially to detect Whetherbeacons have been tampered With, such as being moved.

As Will be disclosed in detail in the detailed description, the inventors haverealized that the traditional manner of navigating a robotic laWnmoWer brings aboutproblems With regard to detecting that a beacon is missing and especially With regard torealizing that a beacon has moved. It is therefore an object of the teachings of thisapplication to overcome or at least reduce those problems by providing an altemativefor detecting a missing beacon and a manner of detecting a moved beacon by providinga robotic Working tool system comprising at least one beacon arranged to at leastpartially delimit Work area and a robotic Working tool configured to operate Within saidWork area, the robotic Working tool being configured to: determine an expectedposition; determine a current position relative at least one of the at least one beacon;determine if there is an error in the deterrnined current position compared to theexpected position, and, if so, determine that the at least one of the at least one beaconhas moved.

In one embodiment, the robotic Working tool is further configured todetermine the current position by deterrnining a current distance to the at least one of the at least one bacon, and determine if there is an error in the deterrnined current position compared to the expected position by deterrnining an expected distance to theat least one of the at least one beacon; and determine if there is an error in thedeterrnined distance compared to the expected distance.

According to an aspect which may form the basis of a divisional application,a robotic lawnmower system is provided, wherein the robotic working tool isconfigured to determine that a distance is not possible to be deterrnined to the at leastone of the at least one beacon, and in response thereto determine that the at least one ofthe at least one beacon is missing. Such a robotic lawnmower system is combinablewith any of the features of all embodiments disclo sed herein.

It is also an object of the teachings of this application to overcome theproblems by providing a method for use in a robotic working tool system comprising atleast one beacon arranged to at least partially delimit work area and a robotic Workingtool configured to operate within said work area, the method comprising: deterrniningan expected position; deterrnining a current position relative at least one of the at leastone beacondeterrnining if there is an error in the deterrnined position compared to theexpected position, and, if so, deterrnining that the at least one of the at least one beacon has moved.

Other features and advantages of the disclosed embodiments will appearfrom the following detailed disclo sure, from the attached dependent claims as well asfrom the drawings. Generally, all terms used in the claims are to be interpretedaccording to their ordinary meaning in the technical field, unless explicitly definedotherwise herein. 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 steps ofany method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in further detail under reference to the accompanying drawings in which: Figure 1A shows an example of a robotic lawnmower according to oneembodiment of the teachings herein; Figure 1B shows a schematic view of the components of an example of arobotic lawnmower according to one embodiment of the teachings herein; Figure 2 shows an example of a robotic lawnmower system according to theteachings herein; Figure 3 shows a schematic overview of a robotic lawnmower system, suchas that in figure 2, in which a robotic lawnmower is conf1gured to detect a missingand/or moved beacon; and Figure 4 shows a corresponding flowchart for a method according to an example embodiment.

DETAILED DESCRIPTION The disclosed embodiments will now be described more fully hereinafterwith reference to the accompanying drawings, in which certain embodiments of theinvention are shown. This invention may, however, be embodied in many differentforms and should not be construed as limited to the embodiments set forth herein;rather, these embodiments are provided by way of example so that this disclosure willbe thorough and complete, and will fully convey the scope of the invention to thoseskilled in the art. Like numbers refer to like elements throughout.

It should be noted that even though the description given herein will befocused on robotic lawnmowers, the teachings herein may also be applied to roboticcleaners such as robotic vacuum cleaners and/or robotic floor cleaners, robotic ballcollectors, robotic mine sweepers, robotic farrning equipment, or other robotic workingtools to be employed in a work area defined by a boundary.

Figure 1A shows a perspective view of a robotic working tool 100, hereexemplif1ed by a robotic lawnmower 100, having a body 140 and a plurality of wheels130 (only one shown). The robotic lawnmower 100 may comprise charging skids forcontacting contact plates (not shown in f1gure 1) when docking into a charging station (not shown in f1gure 1, but referenced 210 in f1gure 2) for receiving a charging current through, and possibly also for transferring information by means of electricalcommunication between the charging station and the robotic lawnmower 100.

Figure 1B shows a schematic overview of the robotic working tool 100,also exemplified here by a robotic lawnmower 100, having a body 140 and a plurality ofwheels 130. In the exemplary embodiment of figure 1B the robotic lawnmower 100 has4 wheels 130, two front wheels 130" and the rear wheels 130". At least some of thewheels 130 are drivably connected to at least one electric motor 150. It should be notedthat even if the description herein is focused on electric motors, combustion enginesmay altematively be used possibly in combination with an electric motor. In theexample of figure 1B, each of the rear wheels 130" is connected to a respective electricmotor 150. This allows for driving the rear wheels 130" independently of one anotherwhich, for example, enables steep tuming.

The robotic lawnmower 100 also comprises a controller 110. Thecontroller 110 may be implemented using instructions that enable hardwarefunctionality, for example, by using executable computer program instructions in ageneral-purpose or special-purpose processor that may be stored on a computer readablestorage medium (disk, memory etc) 120 to be executed by such a processor. Thecontroller 110 is conf1gured to read instructions from the memory 120 and execute theseinstructions to control the operation of the robotic lawnmower 100 including, but notbeing limited to, the propulsion of the robotic lawnmower. The controller 110 may beimplemented using any suitable, publically available processor or Programmable LogicCircuit (PLC). The memory 120 may be implemented using any commonly knowntechnology for computer-readable memories such as ROM, RAM, SRAM, DRAM,FLASH, DDR, SDRAM or some other memory technology.

The robotic lawnmower 100 may further be arranged with a wireless com-munication interface 115 for communicating with other devices, such as a server, apersonal computer or smartphone, or the charging station. Examples of such wirelesscommunication devices are BluetoothTM, Global System Mobile (GSM) and LTE (LongTerm Evolution), to name a few.

The robotic lawnmower 100 also comprises a grass cutting device 160, such as a rotating blade 160 driven by a cutter motor 165. The grass cutting device being an example of a Work tool 160 for a robotic Working tool 100. The roboticlaWnmoWer 100 also has (at least) one battery 180 for providing power to the motors150 and the cutter motor 165.

The robotic laWnmoWer 100 may be further configured to have at least onemagnetic sensor 170 arranged to detect a magnetic field (not shoWn) and for detecting aboundary cable and/or for receiving (and possibly also sending) information from asignal generator (Will be discussed With reference to figure 2). In some embodiments,the sensors 170 may be connected to the controller 110, and the controller 110 may beconfigured to process and evaluate any signals received from the sensor pairs 170, 170".The sensor signals may be caused by the magnetic field being generated by a controlsignal being transmitted through a boundary cable. This enables the controller 110 todetermine Whether the robotic laWnmoWer 100 is close to or crossing a boundary cable,or inside or outside an area enclosed by the boundary cable. This also enables therobotic laWnmoWer 100 to receive (and possibly send) information from the controlsignal.

It should be noted that the magnetic sensor(s) 170 as Well as the boundarycable (referenced 230 in figure 2) and any signal generator(s) are optional as is indicatedby the dashed line of the boundary cable (230) in figure 2. The boundary cable maysimply be used as an additional safety measure. The boundary cable may altemativelybe used as the main perimeter marker and any other navigation sensors (see below) areused for more detailed or advanced operation, or for marking temporary obstacles.

The robotic laWnmoWer 100 further comprises at least one beaconnavigation sensor 175, such as a Ultra Wide Band (UWB) sensor, configured to receivesignals from a beacon (referenced 220 in figure 2), such as a UWB beacon (referenced220 in figure 2). Other altematives include, but are not limited to: Ultrasound, Infrared,radio frequency, light, to mention a feW.

The beacon navigation sensor 175 may be arranged as a transceiver, thusbeing able to both receive and transmit beacon signals, in this example UWB signals.This alloWs the beacon navigation sensor 175 to communicate With the beacon (220).To determine a distance to a beacon (220), the beacon navigation sensor 175 may transmit a signal that the beacon (220) reflects, either by receiving and transmitting a response signal (possible the same signal) or by simply reflecting the signal. As theresponse signal is received, the beacon navigation sensor 175 may deterrnine (on itsown or through the controller 110) the distance, by knowing the time from transmittingthe signal to receiving the reflection, the speed of course being the speed of light.Possibly a known time delay for the beacon to process the signal and transmit theresponse has to be subtracted from the transmission time.

By placing such beacons 220 at various positions, they can be used todefine a perimeter or boundary of the Working area. They may also be used to marktemporary or fixed obstacles so that the robotic lawnmower 100 may avoid colliding orrunning into such obstacles, something that is highly useful for marking frail or fragileobstacles (such as flower beds) or for marking areas that the robotic lawnmower 100may have difficulties exiting from, such as holes or sand pits. In some embodiments, thebeacons may thus be placed or arranged out of (physical) reach for the roboticlawnmower.

The robotic lawnmower 100 may further comprise at least onesupplemental navigation sensor 195, such as a deduced reckoning navigation sensor forproviding signals for deduced reckoning navigation, also referred to as dead reckoning.Examples of such deduced reckoning navigation sensor(s) 195 are odometers andcompasses. The supplemental navigation sensor may also or altematively beimplemented as a vision navigation system to mention one example. The supplementalsensor 195 will hereafter be exemplified through the deduced reckoning sensor.

The robotic lawnmower 100 may also or altematively comprise a satellitenavigation sensor, such as a Global Positioning System (GPS) device 190, or aGLONASS device. In the example of figure 1B, the robotic lawnmower 100 is arrangedwith two GPS sensors, a first GPS sensor 190" and a second GPS sensor 190". The twoGPS sensors 190°, 190" are arranged at a known distance to one another.

Using any combination of the navigation sensors 175, 190, 195, therobotic lawnmower may be configured to navigate the work area using storedcoordinates. The coordinates for the work area (referenced 205 in figure 2), may bestored in the form of a map of the work area. Such a map may include information on obstacles (referenced O in figure 2). The robotic lawnmower may thus be arranged to navigate the work area in a precise manner using any combination of the navigationsensors 175, 190, 195 and the map, thereby also being able to service different portionsof the work area.

One combination of navigation sensors being the deduced reckoningsensors 195 in combination with the beacon navigation sensor(s) 175.

One combination of navigation sensors being the deduced reckoningsensors 195 in combination with the beacon navigation sensor(s) 175 combination withthe GPS sensor(s) 190.

One combination of navigation sensors being in combination with thebeacon navigation sensor(s) 175 and the GPS sensor(s) 190.

As has been indicated above, in one embodiment, the robotic lawnmoweris conf1gured to navigate the work area based on any combination of the navigationsensors 175, 190, 195 without utilizing a boundary cable, or using the boundary cableonly as an emergency fall back, should the other navigation sensors fail. The boundarycable is as such not an essential part of the robotic lawnmower system.

Figure 2 shows a schematic view of a robotic Working tool system 200 inone embodiment. The schematic view is not to scale. The robotic working tool system200 comprises a charging station 210, a robotic working tool 100 and at least onebeacon 220. As discussed above, the beacon(s) 220 may be used to mark a perimeter ofthe work area or an obstacle/ area in the work area 205. As with figures 1A and 1B, therobotic working tool is exemplified by a robotic lawnmower, but the teachings hereinmay also be applied to other robotic working tools adapted to operate within a workarea.

The robotic working tool system 220 may also optionally comprise aboundary cable 230 arranged to enclose a work area 205, in which the roboticlawnmower 100 is supposed to serve.

For its operation within the work area 205, in the embodiment of figure 2,the robotic lawnmower 100 may additionally use the satellite navigation device 190,possibly supported by the deduced reckoning navigation sensor 195 to navigate the work area 205.

The work area 205 is in this application exemplif1ed as a garden, but canalso be other work areas as would be understood. The garden contains a number ofobstacles (O), exemplified herein by a house (O:HOUSE) and a garage (O:GARAGE)that are surrounded by a lawn. In front of the garage there is a drive way and a smallpath leads to the house from the driveway. There are also other obstacles in the gardenrepresented by a number (3) of trees (T). The trees are marked both with respect to theirtrunks (filled lines) and the extension of their fo liage (dashed lines).

In this example there are six beacons 220. The beacons 220 are hereexemplified as being UWB beacons. The beacons operate by either transmitting orreceiving and reflecting (possibly after processing) UWB signals to a beacon navigationsensor 175 on a robotic lawnmower 100.

The beacons 220 may also be configured to transmit signals to anotherbeacon, whereas the beacons may exchange information to one another, regarding theirpositions. This can be used for detecting that a beacon has changed its position. Thedetection may be based on a change in time of flight for a reflected signal to anotherbeacon. If the time changes, the position of either or both beacons has changed.

As would be understood, the number of beacons necessary depends on theshape of the work area to be defined by the beacons 220. The beacons 220 may beplaced to indicate a comer or edge of the work area 205. The beacons may also beplaced to indicate a reference point for the robotic lawnmower 100 to use whennavigating according to stored (map) coordinates. The beacons may also be paced toindicate an obstacle or an area not to be entered. The beacons may be placed astemporary beacons to mark a temporary obstacle and/or as a more or less permanentbeacon to mark a more or less temporary obstacle. As a skilled person wouldunderstand, no obstacle is permanent in a garden as all gardens may change over timeand permanent obstacles will be understood herein to be obstacles that are presently notplanned to be moved, such as houses or flower beds to mention a few examples.Whereas temporary obstacles will be understood to be objects that are planned to bemoved/removed, such as holes, flowers to be planted to mention a few obstacles.

As a general rule, the more complicated the garden structure, the more beacons are needed. As a parallel rule, the more advanced the programming of the map of the robotic lawnmower 100, the fewer beacons are needed. For a simple garden, witha detailed map, it may even suff1ce with a single beacon working as a reference point,although three beacons 220 would provide a more reliable deterrnination of the positionof the robotic lawnmower 100. The number of beacons used in the examples hereinshould be understood to be for exemplifying reasons and any number of beacons maybe used. For example a single beacon may suff1ce in some systems, whereas othersystems may use two beacons. Some systems may use more than two beacons. Insystems where at least three beacons are used, and being detectable by the roboticlawnmower, the at least three beacons may be used to provide angle or directioninformation by triangulation or similar method. The beacons are thus used to at leastpartially delimit the work area. This can be done by marking the perimeter of the workarea or an obstacle within the work area.

A robotic lawnmower 100 according to herein may determine its positionrelative a beacon 220 and thus also navigate in the work area 205 by for exampledeterrnining each a distance to at least three beacons and triangulate its position basedon the distances to the three beacons.

However, it should be noted that the robotic lawnmower 100 may alsooperate herein in combination with GPS sensors 190. The robotic lawnmower 100 mayalso operate herein in combination with deduced reckoning sensors 195. As asupplement, in one embodiment the robotic lawnmower 100 is thus conf1gured to utilizethe supplemental navigation sensor 195, exemplified as dead reckoning sensors(odometer and/or compass), to aid in deterrnining its position and also to maintain trackof its position as the robotic lawnmower traverses the work area, especially in casereception from one or more beacons is (temporarily) blocked or where the informationretrieved from the beacons alone (as regards the distance to them) is insufficient toprovide a deterrnination of the robotic lawnmower°s position.

The robotic lawnmower 100 is also configured to for at least one positionstore identifiers for the beacons that the position is relative to. The robotic lawnmower100 may thus compare the distance deterrnined based on the transmission time to thebeacon(s) and the latest recorded or noted position and determine if the deterrnined distance(s) matches the distances according to the stored data (i.e. is the relative ll position correct with regards to distance). From this is it possible to deterrnine apositional error (even at startup or during operation) by comparing the deterrninedcurrent distance to an expected distance based on the stored relative position. Thepositions may be stored in or as a map of the work area.

In one embodiment the robotic lawnmower is configured to operate usinga particle filter, as would be understood by a skilled person in robotic navigation. Usinga particle filter as understood in the field of robotic navigation, the robotic lawnmower100 will travel for a short distance relying on its supplemental navigation device 195and then "guess" or estimate a plurality of estimated locations based on the datareceived from the supplemental sensor 195. At regular intervals, or at least repeatedly,the robotic lawnmower 100 will confirm an estimation by deterrnining distance(s) tosurrounding beacon(s) and comparing the estimated locations to the one that matchesthe deterrnined distance(s) to the beacon(s) best.

It should be noted that navigation using a particle filter is but one mannerof navigating a robotic lawnmower and many altematives exist. Examples of othermanners are manners for identifying inliers and outliers possibly through utilization ofRANSAC or singular -value decomposition (SVD) techniques. The teachings hereinrelate to any such manner of navigating where a position needs to be recalibrated.

Based on its knowledge of the beacon(s) position(s) and thus also theexpected distance(s) to the beacon(s), the robotic lawnmower 100 may be configured todeterrnine if there is an error in the closest estimation regarding one or more distances toa beacon or several beacons.

The knowledge of the beacon(s) position(s) may be retrieved from thestored map, comprising relative distances to the beacon(s).

If there is an error, the robotic lawnmower 100 is configured to comparethe error to a moved beacon threshold value and if the error exceeds the moved beaconthreshold value, the robotic lawnmower 100 is configured to adapt the map accordinglyassuming that the beacon has been moved. This will be explained in more detail below.

Also, if there is an error, the robotic lawnmower 100 may also be configured to compare the error to a calibration threshold value and if the error exceeds 12 the threshold value, the robotic lawnmower 100 is conf1gured to calibrate the beaconnavigation sensor 175 accordingly.

The robotic lawnmower may be conf1gured to recalibrate the navigationby deterrnining a new position of the moved beacon, e.g. using a set of unmovedbeacons as navigation reference, and/or any kind of auxiliary navigation system.

The robotic lawnmower may be conf1gured to recalibrate the navigationby noting the moved beacon as being unreliable and disregarding it during furthernavigation.

As the beacons are probably mounted on stick or similar support pillars,they may accidentally be moved slightly or moved completely, such as when a ball hitsit (slight movement) and the stick possibly falls over and is raised again, but in adifferent position. The robotic lawnmower 100 according to herein is enabled fordetecting that a beacon is missing or has been moved and take appropriate action byutilizing the teachings herein, thereby avoiding that a navigation error grows and leadsto the robotic lawnmower escaping the work area.

Figure 3 shows a situation when a robotic lawnmower 100 moves from afirst point P1 to a second point P2 and deterrnines at least one estimated position EP(only one is shown to keep the illustration clear) possibly based on the supplementalnavigation sensor 195. Altematively or additionally, the estimated position may bedeterrnined using a particle filter. Altematively or additionally, the estimated positionmay be deterrnined using a GPS sensor 190. The robotic lawnmower 100 may alsodetermine the estimated position to be the current position upon startup, i.e. beforemoving. The estimated position EP is associated with (at least) one expected distanceED to (at least) one beacon 220. The robotic lawnmower 100 also deterrnines a distanceD to (at least) one beacon 220. The expected distance ED is then compared to thedeterrnined distance D. If there is an error (i.e a difference) in the estimated distance EDand the deterrnined distance D, the robotic lawnmower 100 is conf1gured to determinethat the beacon has moved and that the second point P2 is actually the current point, thatis EP is corrected to be P2, by reconfiguring the stored values for the beacon 220.

As the robotic lawnmower 100 most commonly is able to receive signals from more than one beacon sensor, the procedure herein may be repeated for more than 13 one beacon as is indicated. In such an embodiment or situation Where more than beaconis used, the robotic laWnmoWer 100 may also be configured to determine an angle(referenced ot or ß in figure 3) or direction, such as a bearing, to the beacon (throughinverted triangulation, especially if more than three beacons are used) and compare it toan expected direction and also use the direction in deterrnining if the estimated positionequals the second position and if not, correct the position and the stored readings for theassociated beacon.

In one embodiment, Where the beacon 220 is enabled to transferinformation on the angle to the robotic laWnmoWer 100, the robotic laWnmoWer 100may also be configured to determine an angle (referenced ot or ß in figure 3) ordirection to the beacon based on the direction information and compare it to an expecteddirection and also use the direction in deterrnining if the estimated position equals thesecond position and if not, correct the position and the stored readings for the associatedbeacon.

In one embodiment the robotic laWnmoWer is configured to determine thatthe beacon has moved by deterrnining that the error in distance exceeds a thresholdvalue.

In one embodiment the robotic laWnmoWer is configured to determine thatthe beacon has moved by deterrnining that the error in direction exceeds a thresholdvalue.

The inventors have realized that contrary to a moved beacon, a deducednavigation sensor 195 has a tendency to drift thereby not showing a sudden shift,Whereas a moved beacon Will be detectable as a sudden difference in distance.Therefore, the inventors are also proposing to determine the error in distance (and/ordirection) as a beacon is first sensed. The robotic laWnmoWer 100 may favorablyperform such deterrninations When a beacon 220 is first sensed, as in this instance, thereading is most true not exhibiting a build-up of sequential errors. In this context, abeacon first being sensed may be When it is first sensed reliably, i.e. When the receivedsignal from it is of a significant (over a threshold) amplitude and/or When the quality is significant (over a threshold). 14 Altematively, the inventors are also proposing to determine the error indistance (and/or direction) over time to see if it changes in a predictable manner, or ofthe change indicates a drift in the sensor. This may be achieved by assuming the currentposition P2 to be the correct position and moving to a new estimated position. An errorin the distance indicating a moved beacon Will then not appear again (at least not if threeor more beacons 220 are used), Whereas a drift Will still produce an error, Whereuponthe robotic laWnmoWer l00 is conf1gured to indicate that a calibration of the sensors isneeded, and possibly perform such a calibration.

As an error has been deterrnined to be significant enough to indicate amoved beacon, the current position (P2) is deterrnined, possibly through making a bestmatch using a particle filter or comparing to a map using readings from additionalsensors, and the current position is set stored along With the current readings for thebeacon(s) used.

Should a robotic laWnmoWer determine that it is unable to determine adistance to a beacon 220, it may determine that the beacon is no longer present i.e.missing, and adapt the stored values accordingly, thus adapting the map of the Workarea accordingly.

Additionally, the robotic laWnmoWer l00 may be configured to determineWhether enough beacons are detectable to make a reliable localization, and if notdiscontinue operation and/or inforrn a user, for example through an output errormessage. In one embodiment, the robotic laWnmoWer l00 may be configured todetermine that the number of beacons that are detectable are less than three, and if sodetermine that there are not enough beacons detectable for making a reliablelocalization. In one embodiment, the robotic laWnmoWer l00 may be configured todetermine that the number signals reliably received from beacons that are detectable areless than three, and if so determine that there are not enough beacons detectable formaking a reliable localization. A signal may be deemed reliably received if the signalstrength is above a threshold value and/or if the signal quality is above a threshold valueor a combination of the two.

For example, if a beacon is deterrnined to be missing or having been moved signif1cantly so that it is no longer in certain positions to perform successful and reliable triangulations or other position deterrnining means, the robotic laWnmoWer maydetermine that it is no longer possible to navigate reliably in the surrounding area.

The robotic laWnmoWer 100 may stay away from such an area or interruptits operation.

As the robotic laWnmoWer 100 deterrnines that a beacon 220 is missing,the robotic laWnmoWer 100 may report that the beacon is missing to a user possiblythrough a controlling application or through a user interface of the robotic laWnmoWer100. A user or operator (or a controlling application) may then take necessary actions toreplace the beacon 220 or to recalibrate the robotic laWnmoWer 100.

If the robotic laWnmoWer 100 deterrnines that a beacon 220 has beenmoved (or other circumstance has resulted in) that the beacon 220 can no longer be usedreliably, the robotic laWnmoWer 100 may report that the beacon is no longer reliable to auser possibly through a controlling application or through a user interface of the roboticlaWnmoWer 100. A user or operator (or a controlling application) may then takenecessary actions to ensure that the beacon 220 is rendered reliable again or torecalibrate the robotic laWnmoWer 100.

As discussed above, the robotic laWnmoWer 100 may also or altemativelyrecalibrate based on the moved beacon 220.

In one embodiment, a second robotic laWnmoWer 100 may be arranged toact as a beacon. In such an embodiment, the robotic laWnmoWer beacon may provide itscurrent position to the robotic laWnmoWer 100 for improving the accuracy of thenavigation system.

Altematively or additionally, if the robotic laWnmoWer deterrnines that abeacon has moved, and that navigation based on beacons is no longer reliable, therobotic laWnmoWer may shift over to rely more on another manner of navigating, forexample by relying on deduced reckoning for example. In such an embodiment, therobotic laWnmoWer may continue operating using a second navigation sensor, such asthe GPS sensor 190 or the deduced reckoning sensor 195 or the magnetic sensor 170.

To determine that a beacon has moved, and that it is not the position ofrobotic laWnmoWer that is incorrect, possibly resulting from an incorrect navigation sensor, the robotic laWnmoWer may be configured to compare the location deterrnined 16 based on the beacons with a location deterrnined utilizing another navigation sensor. Inone such embodiment, the other navigation sensor may be a GPS sensor 190. In onesuch embodiment, the other navigation sensor may be a deduced reckoning sensor 195.In one such embodiment, the other navigation sensor may be a magnetic field sensor170. In one such embodiment, the other navigation sensor may be any combination of aGPS sensor 190, a deduced reckoning sensor 195 and/or a magnetic field sensor 170.

In one embodiment the robotic lawnmower may be configured to halt (orstop) for a time period of 1, 2, 5, 10, 20, 30 or 60 seconds, and determine a newlocation, possibly as the robotic lawnmower starts moving again. If the new locationdoes not correspond to the previous location, there is an error in the localization. Bychecking the other navigation sensors and asserting that they are Working correctly, itmay be deterrnined that it is the beacon that has been moved. The procedure may beinitiated every time the robotic lawnmower starts operating.

Figure 4 shows a flowchart for a general method according to herein,wherein a robotic lawnmower 100 deterrnines 410 an expected position. The expectedposition may correspond to a position moved to, or a position that the roboticlawnmower is currently in (such as when starting up). The robotic lawnmower thendeterrnines 420 a position relative at least one of the beacons that it can sense (i.e.is inrange of), by deterrnining a direction to at least one of the beacons that it can sense(i.e.is in range of). The robotic lawnmower also or altematively determine 430 anexpected direction to the beacon to which the direction was deterrnined for.Altematively, the robotic lawnmower 100 deterrnines 430 an expected direction for abeacon 220 and then deterrnines 420 the actual direction to that beacon 220. The roboticlawnmower 100 then deterrnines 440 if there is an error in the deterrnined distancecompared to the expected distance. If there is a significant error or difference (such as inexceeding a threshold or otherwise significant as discussed herein), the robotic lawnmower 100 then deterrnines 450 that the beacon (220) has moved.

Claims (16)

1. A robotic Working tool system (200) comprising at least one beacon (220)arranged to at least partially delimit Work area (205) and a robotic Working tool (100)conf1gured to operate Within said Work area, the robotic Working tool (100) beingconfigured to: determine an expected position; deterrnine a current position relative at least one of the at least one beacon(220); deterrnine if there is an error in the deterrnined current position compared tothe expected position, and, if so, deterrnine that the at least one of the at least one beacon (220) has moved.

2. The robotic laWnmoWer system according to claim 1, Wherein the robotic Working tool is further configured to deterrnine the current position by deterrnining acurrent distance to the at least one of the at least one bacon (220), and deterrnine if thereis an error in the deterrnined current position compared to the expected position bydeterrnining an expected distance to the at least one of the at least one beacon (220); anddeterrnine if there is an error in the deterrnined distance compared to the expected distance.

3. The robotic laWnmoWer system according to claim 2, Wherein the roboticWorking tool is further configured to store the deterrnined position for the at least one of the at least one beacon (220) along With the current position.

4. The robotic laWnmoWer system according to claim 1, 2 or 3, Wherein therobotic Working tool is further configured to: deterrnine the current position by deterrnining a direction to at least one ofthe at least one beacon (220); deterrnine an expected direction to the at least one of the at least one beacon (220); 18 determine if there is an error in the deterrnined direction compared to theexpected direction, and, if so, deterrnine that the at least one of the at least one beacon (220) has moved.

5. The robotic laWnmoWer system according to any previous claim, Whereinthe robotic Working tool is further configured to deterrnine the distance to a beacon as the beacon is first sensed by the robotic Working tool (100).

6. The robotic laWnmoWer system according to any previous claim, Whereinthe robotic Working tool is further conf1gured to move to a second expected position; deterrnine a second current position relative to the at least one of the at least one beacon (220); deterrnine if there is an error in the deterrnined position compared to theexpected second position, and, if so, deterrnine that a navigation sensor needs to be calibrated.

7. The robotic laWnmoWer system according to any previous claim, Whereinthe robotic Working tool is further conf1gured to deterrnine that a distance is not possibleto be deterrnined to the at least one of the at least one beacon (220) and in response thereto deterrnine that the at least one of the at least one beacon (220) is missing.

8. The robotic laWnmoWer system according to any previous claim, Whereinthe robotic Working tool is further conf1gured to recalibrate its navigation based on the beacon (220) having been moved.

9. The robotic laWnmoWer system according to claim 8, Wherein the roboticWorking tool is further conf1gured to recalibrate the navigation by deterrnining a neW position of the moved beacon. 19

10. The robotic laWnmoWer system according to claim 8, Wherein therobotic Working tool is further conf1gured to recalibrate the navigation by noting the moved beacon as being unreliable and disregarding it during further navigation.

11. The robotic laWnmoWer system according to any previous claim,Wherein the robotic Working tool is further conf1gured to interrupt its operation based on having deterrnined that a beacon (220) has been moved.

12. The robotic laWnmoWer system according to any previous claim,Wherein the robotic Working tool is further conf1gured to utilize a second navigationsensor (170, 190, 195) based on having deterrnined that a beacon (220) has been moved.

13. The robotic laWnmoWer system according to any previous claim, Wherein the robotic Working tool is a robotic laWnmoWer (100).

14. The robotic laWnmoWer system according to any previous claim, Wherein at least one of the at least one beacon (220) is an Ultra Wide Band beacon.

15. The robotic laWnmoWer system according to any previous claim,Wherein at least one of the at least one beacon (220) is arranged out of reach for the robotic Working tool (100).

16. A method for use in a robotic Working tool system (200) comprising atleast one beacon (220) arranged to at least partially delimit Work area (205) and arobotic Working tool (100) conf1gured to operate Within said Work area, the methodcomprising: deterrnining an expected position; deterrnining a current position relative at least one of the at least one beacon (220); deterrnining if there is an error in the deterrnined position compared to theexpected position, and, if so, deterrnining that the at least one of the at least one beacon (220) has moved.