SE543941C2 - Boundary system with two work areas for robotic working tool - Google Patents

Abstract

A robotic working tool system (200) for providing an aggregated work area (205) comprising a first work area (205-1) and a second work area (205-2) in which a robotic working tool (100) may operate, the robotic working tool system (200) comprising a signal generator (215-2) and a boundary cable (230-2) arranged to delimit, the second work area (205-2), wherein the signal generator (215-2) is configured to: determine signal characteristics of a first control signal (235-1) for being transmitted through a first boundary cable delimiting the first work area (205-1); generate a supplemental control signal (235-2) based on the signal characteristics of the first control signal (235-1); and to transmit the supplemental control signal (235-2) through the second boundary cable thereby cancelling the first control signal (235-1) at least along a portion of the first boundary cable (230-1) where at least a portion of the second boundary cable is laid adjacent to the first boundary cable (230-1), thereby providing said aggregated work area (205).

Description

TECHNICAL FIELD This application relates to robotic working tools and in particular to asystem and a method for providing an improved boundary for a work area for 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, thework area is enclosed by a boundary cable with the purpose of keeping the roboticlawnmower inside the work area.

An electric control signal may be transmitted through the boundary cablethereby generating an electromagnetic field emanating from the boundary cable. Therobotic working tool is typically arranged with one or more electromagnetic sensorsadapted to sense the control signal.

Due to electrical characteristics of the control signals most commonly used,the boundary cables and the fact that the boundary cables are often laid onto or buried inthe ground, the maximum length of a boundary cable is limited. Commonly the maximumlength of a boundary cable is 800 m.

Furthermore, in order to not cause too much interference to the neighbouringenvironment, the energy allowed to be transmitted through the cable is limited. This limitsthe range of the robotic Working tools further as a robotic Working tool must always beable to sense its control signal or it must suspend its operation until a control signal isfound as required by safety standards such as the Intemational and European safetystandards for robotic lawnmowers IEC 60335-2-107 and EN 50636-2-107 respectively.According to these standards a robotic lawnmower must seize operation if a control signal is lost. For robotic lawnmowers utilizing a more complex control signal, such as a CDMA (Code Division Multiple Access) coded signal, the standards apply to situations whensynchronization with the signal is lost.

As mentioned above, this limits the range of the robotic working tool in thatthe robotic working tool may never be too far away from a boundary cable or the controlsignal may no longer be properly or reliably detected. Commonly a robotic working toolcan operate at a maximum distance of 35 m from a boundary cable. The maximum widthof a work area is in such systems therefore effectively limited to a maximum width of 70m (=2x35 m).

As most gardens include multiple objects or features, such as bushes, stones,trees, sand pits and so on, it is common practice to lay the boundary cable so that suchfeatures are excluded from the work area in order to provide for reliable operation of therobotic working tool. This requires that more cable length is used and a boundary cableof 800 m is often not enough for large and or complicated gardens.

Contemporary robotic working tool systems are designed to use satellite orbeacon navigation for navigation where a virtual boundary cable may be generated todelimit a work area. However, as a garden often contains or is located close to high treesor other structures that may block satellite signals, only using such navigation methods isnot always allowed by the safety standards.

Thus, there is a need for an improved manner of delimiting a work area using a boundary cable for a robotic working tool, such as a robotic lawnmower.

SUMMARY As will be disclosed in detail in the detailed description, the inventors haverealized that a system where two signal generators are arranged to provide two controlsignals to two boundary cables, where one control signal cancels out the other controlsignal in an area where the two boundary cables are laid adjacent one another may beused to both provide a much larger work area, without exceeding the maximum length of800 m for each boundary cable. The two work areas delimited by each a boundary cablethen forms an aggregated work area. And, in such a system a standard robotic workingtool may be used as the control signals must be highly similar to be able to cancel each other out, whereby the robotic working tool can operate in an aggregate work area without requiring any modification and possibly not even be aware of the fact that it is operatingin an aggregated Work area.

It is therefore an object of the teachings of this application to overcome orat least reduce those problems by providing a robotic Working tool system roboticWorking tool system for providing an aggregated Work area comprising a first Work areaand a second Work area in Which a robotic Working tool may operate, the roboticWorking tool system comprising a signal generator and a boundary cable arranged todelimit the second Work area, Wherein the signal generator is configured to: determinesignal characteristics of a first control signal for being transmitted through a firstboundary cable delimiting the first Work area; generate a supplemental control signalbased on the signal characteristics of the first control signal; and to transmit thesupplemental control signal through the second boundary cable thereby cancelling thefirst control signal at least along a portion of the first boundary cable Where at least aportion of the second boundary cable is laid adj acent to the first boundary cable, therebyproviding said aggregated Work area.

In one embodiment the robotic Working tool is a robotic laWnmoWer.

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 arobotic Working tool comprising for providing an aggregated Work area comprising afirst Work area and a second Work area in Which a robotic Working tool may operate, therobotic Working tool system comprising a signal generator and a boundary cablearranged to delimit the second Work area, the method comprising: deterrnining signalcharacteristics of a first control signal for being transmitted through a first boundarycable delimiting the first Work area; generating a supplemental control signal based onthe signal characteristics of the first control signal; and transmitting the supplementalcontrol signal through the second boundary cable thereby cancelling the first controlsignal at least along a portion of the first boundary cable Where at least a portion of thesecond boundary cable is laid adjacent to the first boundary cable, thereby providingsaid aggregated Work area.

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. 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 theaccompanying 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 working tool being a robotic lawnmower according to an example embodimentof the teachings herein; Figure 2 shows an example of a robotic working tool system being a roboticlawnmower system according to an example embodiment of the teachings herein; Figure 3 shows a schematic View of a cable and a magnetic field and howthe direction of the magnetic field depends on the direction of a signal as it istransmitted through the cable; Figure 4 shows a graph of the amplitude of the magnetic field as it dependson the distance to the cable; Figure 5A shows a schematic view of a robotic working tool systemaccording to an example embodiment of the teachings herein and Figure 5B shows a corresponding time graph of a first control signal and asupplemental control signal in such a robotic working tool system according to anexample embodiment of the teachings herein; Figure 6A shows a schematic view of a robotic working tool system according to an example embodiment of the teachings herein and Figure 6B shows a corresponding time graph of a first control signal and asupplemental control signal in such a robotic working tool system according to anexample embodiment of the teachings herein; and Figure 7 shows a corresponding flowchart for a method according to an example embodiment of the teachings herein.

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.

Like reference 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, roboticball collectors, robotic mine sweepers, robotic farrning equipment, or other roboticworking tools where lift detection is used and where the robotic working tool issusceptible to dust, dirt or other debris.

Figure 1A shows a perspective view of a robotic working tool 100, hereexemplified 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 figure 1) when docking into a charging station(not shown in figure 1, but referenced 210 in figure 2) for receiving a charging currentthrough, 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, alsoexemplified here by a robotic lawnmower 100. In this example embodiment the roboticlawnmower 100 is of a mono-chassis type, having a main body part 140. The main bodypart 140 substantially houses all components of the robotic lawnmower 100. The roboticlawnmower 100 has a plurality of wheels 130. In the exemplary embodiment of figure1B the robotic lawnmower 100 has four wheels 130, two front wheels and two rear wheels. At least some of the wheels 130 are drivably connected to at least one electric motor 150. It should be noted that even if the description herein is focused on electricmotors, combustion engines may altematively be used, possibly in combination with anelectric motor. In the example of figure 1B, each of the wheels 130 is connected to arespective electric motor. This allows for driving the wheels 130 independently of oneanother which, for example, enables steep tuming and rotating around a geometricalcenter for the robotic lawnmower 100. It should be noted though that not all wheelsneed be connected to each a motor, but the robotic lawnmower 100 may be arranged tobe navigated in different manners, for example by sharing one or several motors 150. Inan embodiment where motors are shared, a gearing system may be used for providingthe power to the respective wheels and for rotating the wheels in different directions. Insome embodiments, one or several wheels may be uncontrolled and thus simply react tothe movement of the robotic lawnmower 100.

The robotic lawnmower 100 also comprises a grass cutting device 160, suchas a rotating blade 160 driven by a cutter motor 165. The grass cutting device being anexample of a work tool 160 for a robotic working tool 100. The robotic lawnmower 100also has (at least) one battery 155 for providing power to the motor(s) 150 and/or thecutter motor 165.

The robotic lawnmower 100 also comprises a controller 110 and a computerreadable storage medium or memory 120. The controller 110 may be implementedusing instructions that enable hardware functionality, for example, by using executablecomputer program instructions in a general-purpose or special-purpose processor thatmay be stored on the memory 120 to be executed by such a processor. The controller110 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, available processor or Programmable Logic Circuit(PLC). The memory 120 may be implemented using any commonly known technologyfor 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, a personal computer or smartphone, or the charging station. Examples of such wirelesscommunication devices are B1uetooth®, WiFi® (IEEE802.l lb), Global System Mobile(GSM) and LTE (Long Term Evolution), to name a few.

For enabling the robotic lawnmower l00 to navigate with reference to aboundary cable emitting a magnetic field caused by a control signal transmitted throughthe boundary cable, the robotic lawnmower l00 is further configured to have at leastone magnetic field sensor l70 arranged to detect the magnetic field (not shown) and fordetecting the boundary cable and/or for receiving (and possibly also sending)information to/ from a signal generator (will be discussed with reference to figure 2). Insome embodiments, the sensors l70 may be connected to the controller ll0, possiblyvia filters and an amplifier, and the controller ll0 may be configured to process andevaluate any signals received from the sensors l70. The sensor signals are caused by themagnetic field being generated by the control signal being transmitted through theboundary cable. This enables the controller ll0 to determine whether the roboticlawnmower l00 is close to or crossing the boundary cable, or inside or outside an areaenclosed by the boundary cable.

In one embodiment, the robotic lawnmower l00 may further comprise atleast one beacon navigation sensor and/or a satellite navigation device 175. The beaconnavigation device may be a Radio Frequency receiver, such as an Ultra Wide Band(UWB) receiver or sensor, configured to receive signals from a Radio Frequencybeacon, such as a UWB beacon. The beacon navigation device may be an opticalreceiver configured to receive signals from an optical beacon. The satellite navigationdevice may be a GPS (Global Positioning System) device.

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 2l0 having a signal generator 2l5 and a roboticworking tool l00. As with figures lA and lB, the robotic working tool is exemplifiedby a robotic lawnmower, whereby the robotic working tool system may be a roboticlawnmower system or a system comprising a combinations of robotic working tools,one being a robotic lawnmower, but the teachings herein may also be applied to other robotic working tools adapted to operate within a work area.

The signal generator is arranged to generate a control signal 235. Toperform this, the supplemental signal generator is arranged with a controller andmemory module 216. The controller and memory module 216 operates and functions inthe same manner as the controller 110 and memory 120 of the robotic working tool 100.

The robotic working tool system 220 also comprises a boundary cable 230arranged to enclose a work area 205, in which the robotic lawnmower 100 is supposedto serve. The control signal 235 is transmitted through the boundary cable 230 causing amagnetic field (not shown) to be emitted.

In one embodiment the control signal 235 is a sinusoid periodic currentsignal. In one embodiment the control signal 235 is a pulsed current signal comprising aperiodic train of pulses. In one embodiment the control signal 235 is a coded signal,such as a CDMA signal.

The robotic Working tool system 220 may also optionally comprise at leastone beacon 220 to enable the robotic lawnmower to navigate the work area using thebeacon navigation sensor(s) 175.

The work area 205 is in this application exemplified as a garden, but canalso be other work areas as would be understood. The garden contains a number ofobstacles (O), exemplified herein by a number (3) of trees (T) and a house structure (H).The trees are marked both with respect to their trunks (filled lines) and the extension oftheir foliage (dashed lines).

As can be seen in figure 2, the boundary cable 230 has been laid so that so-called islands are formed around the trees” trunks and the house (H). This requires thatmore boundary cable is used, than if the work area was without such obstacles. It shouldbe noted that any distances between cables are greatly exaggerated in this application inorder to make the distances Visible in the drawings. In a real-life installations theboundary cable is usually laid so that there is not distance between the cable going outand the cable coming back (distance = 0).

As an electrical signal that Varies in time is transmitted through a cable,such as the control signal 235 being transmitted through the boundary cable 230, amagnetic field is generated. The amplitude of the 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 for the magnetic field. The polarity of the magnetic field depends onthe direction of the control signal. Figure 3 shows a schematic view of a cable C and amagnetic field M and how the direction of the magnetic field M depends on thedirection of the control signal as it is transmitted through the cable C. In the upper partof figure 3, the control signal is transmitted through the cable C out of the figure(towards the viewer). In the lower part of figure 3, the control signal is transmittedthrough the cable C in to the figure (away from the Viewer). The resulting magneticfield is directed anti-clock wise in the upper part of figure 3, and clockwise in the lowerpart of figure 3 as is indicated by the arrows.

This means that the polarity of the magnetic field M will differ dependingon which side of the cable C an observer or sensor is. For example, a sensor 170-1 onthe left side of the cable C in the upper part of the figure will sense a magnetic field Mhaving a negative polarity, whereas a sensor 170-2 on the right side of the cable C in theupper part of figure 3, will sense the same magnetic field M but as having a positivepolarity. This polarity change enables a robotic lawnmower to deterrnine which side ofthe cable C a sensor 170 is.

Figure 4 shows a graph of the amplitude of the magnetic field M (measuredin the unit Henry H) as it depends on the distance (D) to the cable. As a magnetic fieldsensor comes close to the center of the cable, the magnetic field will make a polarityshift, which results in an abrupt change in amplitude of the magnetic signal M. Close tothe boundary cable, the magnetic field will thus be close to zero (0) H and thus bedifficult to detect, at least to reliably detect. This area is referred to as the polarityreversal area, indicated S in figure 4.

Figure 5A shows a schematic view of an example embodiment of a roboticworking tool system 200. The work area 205 of the robotic working tool system 200 offigure 5A is an aggregated work are comprising more than one work areas. In thisexample embodiment, the aggregated work area 205 comprises two work areas 205-1and 205-2. As can be seen in this example a second signal generator 215-2 has beenutilized to provide a second control signal 235-2 that is transmitted through a secondboundary cable 23 0-2 for delimiting the second work area 205-2, while the first signalgenerator 215-1 and the first boundary cable 23 0-1 is utilized to delimit the first work area 205-1. The second boundary cable 230-2 is laid so that it is adjacent the firstboundary cable 230-1 at least along a portion of its length. It should be noted that aboundary cable need not consist of a single cable, but may comprise several cablesspliced or otherwise joined together to forrn one longer cable.

The second signal generator 215-2, Which may also be called asupplemental signal generator 215-2 as it supplements the first signal generator inenabling the establishment of a larger Work area, is arranged to deterrnine the firstcontrol signal 235-1 being transmitted through the first boundary cable 23 0-1. Toperforrn this, the supplemental signal generator is arranged With a controller andmemory module 216. The controller and memory module 216 operates and functions inthe same manner as the controller 110 and memory 120 of the robotic Working tool 100.

In one embodiment, the supplemental signal generator 215-2 is arrangedWith a signal pickup or sensor 270. The sensor 270 is an electromagnetic sensor andfunctions in the same general manner as the sensor 170 of the robotic Working tool 100.The first control signal may then be deterrnined by a controller of the signal generatorby integrating the sensed magnetic field over time. A pulsed signal Will be easilydetected by sensing the electromagnetic spikes corresponding to the flanks of the pulsesof the control signal. The sensor 270 may be extemal and connectable to thesupplemental signal generator 215-2, as in the example embodiment of figure 5A. In analtemative embodiment, the sensor 270 may be intemal to the supplemental signalgenerator 215-2. In an altemative embodiment, the sensor 270 may be intemal to thesupplemental signal generator 215-2, but arranged to be extended from the supplementalsignal generator.

An intemal sensor has the benefit that installation is simplified. An extemalsensor has the benefit of being easier to place so that a reliable reading of the firstcontrol signal is provided.

In one embodiment, the supplemental signal generator 215-2 may bearranged With more than one sensor 270 for sensing several magnetic fields emanatingfrom different cables.

In one altemative or additional embodiment the controller and memory module 216 may also comprise or be connected to a communication interface (not shown explicitly but considered to be part of the controller and memory module). Thecommunication interface is enabled for communicating With other devices, such as aserver, a personal computer or smartphone, a robotic Working tool 100, a signalgenerator 215 or a charging station 210 using a Wireless communication standard.Examples of such Wireless communication standards are Bluetooth®, WiFi®(IEEE802. 1 lb), Global System Mobile (GSM) and LTE (Long Term Evolution), toname a few.

In one such embodiment Where the supplemental signal generator 215-2 isarranged With a communication interface, the supplemental signal generator 215-2 isconfigured to establish contact With the robotic Working tool 100 and query the roboticWorking tool 100 for details, such as signal characteristics, on the control signal beingused. As Would be apparent to a skilled person, the manner of establishing such aconnection differs depending on the Radio Access Technology or Wirelesscommunication standard used but generally includes the steps of sensing a presence ofthe robotic Working tool, sending an identifying signal, requesting a connection to beestablished, establishing the connection, sending a query and receiving a response. Insuch an embodiment, the supplemental signal generator 215-2 is thus configured tosimply query the robotic Working tool for details on the used control signal. HoWever,this requires that a specially adapted robotic Working tool 100 is utilized.

In an altemative or additional such embodiment Where the supplementalsignal generator 215-2 is arranged With a communication interface, the supplementalsignal generator 215-2 is configured to establish contact With the first signal generator215-1, possibly through the first charging station 210, and query first signal generator215-1 for details on the control signal being used. HoWever, this requires that aspecially adapted first signal generator 215-1 is utilized.

In an altemative or additional such embodiment Where the supplementalsignal generator 215-2 is arranged With a communication interface, the supplementalsignal generator 215-2 is conf1gured to establish contact With an extemal server, such asthrough a cloud service, and query the extemal server for details on the control signal being used.

The supplemental signal generator 215-1 may be arranged in a chargingstation 210-2 as is indicated in figure 5A by the dashed box, Wherein two roboticWorking tool systems may be used to provide an aggregated Work area 205.

In one embodiment, the supplemental signal generator 215-2 is not housedin a charging station, Which enables for an aggregated Work area to be forrned by simplyproviding only a signal generator 215-2. The installation of such a supplemental systemis very easy and aggregated Work areas may be easily constructed Without having to buya complete second system.

As the supplemental signal generator 215-2 has detected or deterrnined thefirst control signal 23 5-1 , the supplemental signal generator 215-2 provides andtransmits a second or supplemental control signal 235-2 in order to cancel out themagnetic field caused by the first control signal 235-1. Figure 5B shoWs a time graph ofan example of a first control signal 235-1 and a supplemental control signal 235-2 andhoW the control signals interact. It should be noted that the time graph of figure 5B isonly for exemplifying and illustrative purposes Whereby no units are given. It can alsobe noted that as the magnetic field is caused by variations in the electrical signal, thelevel of the signal is not important. It is thus also not important that the signals shoWn infigure 5B are illustrated as lying on different levels. Only the timing and extent ofchanges is of importance.

In the upper part of figure 5B the first control signal 235-1 is shown, in thisexample being a pulsed signal comprising a pulse train that reoccurs regularly at timeperiod P. In the middle part of figure 5B the supplemental control signal 235-2 isshoWn, in this example being a pulsed signal comprising a pulse train that reoccursregularly at time period P. For illustrative purposes, the supplemental control signal235-2 has been shoWn as being the negative of the first control signal 235-1. As Wouldbe clear to the skilled person, depending on how the second boundary cable 230-2 islaid in relation to the first boundary cable 23 0-1 , the supplemental control signal 235-2may be identical to the first control signal 235-1 or the negative of the first controlsignal 235-1. If the boundary cables are laid in the same manner so that the electricsignal is transmitted in the same general direction (clockWise/anti-clockwise), the supplemental control signal Would be identical to the first control signal to cancel it out.

If the boundary cables are laid in the same manner so that the electric signal istransmitted in the same general direction (clockwise/anti-clockwise), the supplementalcontrol signal would be the negative of the first control signal to cancel it out.

The supplemental control signal 235-2 is thus generated so that any changein the first control signal 235-1 has a corresponding change in the opposite direction(depending on how the boundary cables are laid).

In an embodiment, where the supplemental signal generator comprises asensor 270, the supplemental signal generator 215-2 is configured to deterrnine theorientation of the second boundary cable 23 0-2 with respect to the first boundary cable230-1. In one such embodiment, the supplemental signal generator 215-2 is configuredto do this by transmitting a test signal and receive a sensing of the magnetic fieldgenerated by the test signal from the sensor 270. The supplemental signal generator215-2 is configured to deterrnine whether the supplemental control signal 235-2 shouldbe the negative of the first control signal based on the sensing of the test signal. If thesensing signal returns a polarity equalling the sensing of the first control signal, thesupplemental control signal 235-2 should be of reverse polarity, and vice-versa.

Continuing with the example of figure 5B, as the supplemental controlsignal 235-2 is generated to cancel out the first control signal 235-1, the sum of theireffect corresponds to a DC current (shown in the lower part of figure 5B and referenced235-3) which does not give rise to any magnetic field.

As the robotic working tool 100 comes close to the area where the firstboundary cable 230-1 and the second boundary cable 230-2 are laid adjacent oneanother, it will thus not be able to sense either boundary cable and would traverse fromone work area 205-1 freely to the other 205-2 thereby effectively having access to alarger aggregated work area 205 in which to operate.

Key features that the supplemental signal generator 215-2 deterrnines for thecontrol signal are any periodicity of the control signal and where and to what extent achange happens. For a pulsed signal this includes the flanks of the pulses and theamplitude of the pulses.

Contemporary robotic working tool systems sometimes utilizes an identifier that is included or appended to the control signal 235. By utilizing identifiers and assigning a different identifier to the second Work area 205-2 than to the first Work area235-1, different zones may be generated in the aggregated Work area 205.

Figure 6A shows a schematic vieW of a robotic Working tool system Wherean aggregated Work area is comprised of two Work areas 205-l, 205-2 each beingassociated With a different identity. Figure 6B shoWs a time graph of an example of afirst control signal 235-l and a supplemental control signal 235-2 and hoW the controlsignals interact. It should be noted that the time graph of figure 6B is only forexemplifying and illustrative purposes. Even if figure 6B only the electrical signals andnot the resulting magnetic fields, a skilled person Would understand the generalprinciple.

As illustrated in both figure 6A and figure 6B, the first control signal 235-lcomprises a first identifier IDl and the supplemental control signal 235-2 comprises asecond identifier ID2. The identifier may be coded into the control signal or it may beappended to or transmitted subsequent to the control signal.

In the example embodiments of figure 6A and figure 6B the first identifierIDl does not match the second identifier ID2 Which leads to that the supplementalcontrol signal 235-2 does not completely cancel out the first control signal 235-l. Theresulting magnetic field, Will, however, as is illustrated in figure 6B by thecorresponding signal 235-3, not resemble a control signal and Will thus be disregardedby the robotic Working tool l00.

HoWever, as the distance increases from the boundary cables 230-1, 230-1that are laid adj acent one another, one control signal Will dominate the other one, andthe robotic Working tool Will determine that the dominating control signal is the one tofolloW. The robotic Working tool l00 Will then be able to identify Which Work area ofthe aggregated Work area it is currently in, based on the identifier of the dominatingcontrol signal.

This enables the robotic Working tool l00 to perform a scheduled operationtaking different zones into account, Where the schedule may indicate that a zone is notto be entered, that a zone is not to be exited, or that a zone is to be traversed. The schedule may be time dependent for enabling one zone to be treated at a given time and/or for a given time period to ensure a smooth and even treatment of the aggregatedWork area.

As a skilled person Would realize, the magnetic field sensed in any one pointin a Work area, does not result only from the magnetic field of one portion of theboundary cable. For example a robotic Working tool 100 that is located close to forexample the lower edge of a Work area, Will not only sense the magnetic field emanatingfrom the portion of the boundary closest to the robotic Working tool, but from allportions of the boundary cable Within a distance from the sensor 170, for example of upto 35 m. This leads to that there is no clear-cut line Where the robotic Working tool 100senses one signal over another, but there is an area in Which one signal graduallyovertakes the other signal. As this is gradual and Will vary With extemal factors, there isless risk of Wheel tracks forrning close to the boundary cable 230. The area is indicatedby the dashed oval in figure 6A.

In an embodiment Where the supplemental signal generator 211-2 isarranged With a communication interface, the supplemental signal generator 215-2 isarranged to establish a connection With the robotic Working tool 100 to receiveinformation on possible identifiers to be used for the second Work area 205-2.

In an altemative or additional embodiment Where the supplemental signalgenerator 211-2 is arranged With a communication interface, the supplemental signalgenerator 215-2 is arranged to establish a connection With the charging station or thefirst signal generator 215-1 to receive information on possible identifiers to be used forthe second Work area 205-2.

In an altemative or additional embodiment Where the supplemental signalgenerator 211-2 is arranged With a communication interface, the supplemental signalgenerator 215-2 is arranged to establish a connection With an extemal server, such asthrough a cloud service, to receive information on possible identifiers to be used for thesecond Work area 205-2.

Figure 7 shows a flowchart of a general method according to the teachingsherein. 10. A signal generator 215-2 deterrnines 710 signal characteristics of a firstcontrol signal 235-1 for being transmitted through a first boundary cable delimiting the first Work area 205-1. The signal generator 215-2 generates 720 a supplemental control signal 235-2 based on the signal Characteristics of the first control signal 235-1 and transniits 730 the suppleniental control signal 235-2 through the second boundary cable.

The second control signal thereby cancels 740 the first control signal 235-1 at leastalong a portion of the first boundary cable 23 0-1 Where at least a portion of the secondboundary cable is laid adjacent to the first boundary cable 230-1, and an aggregatedWork area 205 is provided 750.

Claims (10)

1. A robotic Working tool system (200) for providing an aggregated Workarea (205) comprising a first Work area (205-1) and a second Work area (205-2) inWhich a robotic Working tool (100) may operate, the robotic Working tool system (200)comprising a signal generator (215-2) and a boundary cable (230-2) arranged to delimitthe second Work area (205-2), Wherein the signal generator (215-2) is configured to: determine signal Characteristics of a first control signal (235-1) for beingtransmitted through a first boundary cable delimiting the first Work area (205-l); generate a supplemental control signal (235-2) based on the signalCharacteristics of the first control signal (235-l); and to transmit the supplemental control signal (235-2) through the secondboundary cable thereby cancelling the first control signal (235-1) at least along a portionof the first boundary cable (230-1) Where at least a portion of the second boundary cableis laid adjacent to the first boundary cable (230-1), thereby providing said aggregatedwork area (205).

2. The robotic Working tool system (200) according to claim 1, Where therobotic Working tool system (200) further comprises a magnetic sensor (270) connectedto or comprised in the signal generator (215-2), Wherein the signal generator (215-2) isconfigured to receive readings of the magnetic field generated by the first control signal and based on the received readings determine said signal characteristics.

3. The robotic Working tool system (200) according to claim 2, Wherein thesignal generator (215-2) is configured to determine the orientation of the secondboundary cable (230-2) relative the first boundary cable (230-1) by transmitting a test signal.

4. The robotic Working tool system (200) according to any preceding claim,Wherein the signal generator (215-2) further comprises a communication interface (216), Wherein the signal generator (215-2) is configured to determine the signal characteristics by establishing a connection through the communication interface and query the signal Characteristics.

5. The robotic Working tool system (200) according to any preceding claim,Wherein the first control signal (235-1) is associated With a first identifier (IDl) andWherein the signal generator (215-2) is further configured to generate the supplementalcontrol signal (235-2) as being associated With a second identifier (ID2) for enabling therobotic Working tool (100) to identify Which Work area, the robotic Working tool (100) is currently operating Within.

6. The robotic Working tool system (200) according to any preceding claimfurther comprising a first signal generator (215-1) to generate the first control signal (235-1) and the robotic Working tool (100).

7. The robotic Working tool system (200) according to any preceding claim Wherein the robotic Working tool (100) is a robotic lawnmower.

8. The robotic Working tool system (200) according to any preceding claimWherein the signal characteristics comprise at least one of a time period, a location and a magnitude of a change in the control signal.

9. The robotic Working tool system (200) according to any preceding claim Wherein the signal generator (215-2) is comprised in a charging station.

10. l0. A method for use in a robotic Working tool system (200) for providingan aggregated Work area (205) comprising a first Work area (205-l) and a second Workarea (205-2) in Which a robotic Working tool (100) may operate, the robotic workingtool system (200) comprising a signal generator (215-2) and a boundary cable (230-2)arranged to delimit the second Work area (205-2), the method comprising: determining signal characteristics of a first control signal (235-1) for being transmitted through a first boundary cable delimiting the first Work area (205-1); generating a supplemental control signal (235-2) based on the signalCharacteristics of the first control signal (235-l); and transmitting the supplemental control signal (235-2) through the secondboundary cable thereby cancelling the first control signal (235-1) at least along a portionof the first boundary cable (230-1) Where at least a portion of the second boundary cableis laid adjacent to the first boundary cable (230-1), thereby providing said aggregatedWork area (205).