SE2250247A1

SE2250247A1 - Improved navigation for a robotic work tool system

Info

Publication number: SE2250247A1
Application number: SE2250247A
Authority: SE
Inventors: Claes Johannesson; Johan Rogö; Jonas Holgersson; Marcus Liljedahl; Martin Joelsson; ULF äRLIG
Original assignee: Husqvarna Ab
Priority date: 2022-02-24
Filing date: 2022-02-24
Publication date: 2023-08-25
Also published as: DE102023103689A1

Abstract

A method for use in a robotic working tool system comprising a robotic work tool (100) arranged to operate in an operating area and a boundary wire for demarking the operating area, wherein the operating area comprises a narrow passage, and wherein the robotic work tool (100) comprises at least one navigation sensor (180, 185) and a first and a second magnetic sensor (170-1, 170-2), wherein the robotic work tool (100) is configured to operate in a first navigation mode based on the at least one navigation sensor (180, 185), wherein a position is determined and compared to a map, and to operate in a second navigation mode based on the a first and a second magnetic sensor (170-1, 170-2), wherein a position in the narrow passage is determined based on signal levels of magnetic signals received via the a first and a second magnetic sensor (170-1, 170-2), wherein the method comprises navigating in the first navigation mode, determining that a narrow passage is entered and in response thereto navigating the narrow passage based on the second navigation mode.

Description

IMPROVED NAVIGATION FOR A ROBOTIC WORK TOOL SYSTEM TECHNICAL FIELD This application relates to a robotic Work tool and in particular to a system and a method for providing an improved navigation for robotic Work tools, such as laWnmoWers or ﬂoor grinders, in such a system.

BACKGROUND Automated or robotic Work tools such as robotic laWnmoWers are becoming increasingly more advanced and so is the need for proper mapping of an operational area (Work area). At the same time, the operational areas are growing in size and comprise more and more features, such as trees, hedges, rocks, houses, structures and also different Work areas Within the operational area Which can only be reached through narroW passages from one another.

Navigation in operational areas is commonly done by navigating based on a magnetic signal emanating from a boundary Wire enclosing the operational area - or parts thereof. Another common manner of navigating an operational area is based on satellite navigation (such as GPS navigation) Where a (virtual) boundary is stored as a set of coordinates Which the robotic Work tool is configured to compare its determined position to and keep inside. HoWever, satellite navigation is relatively expensive, requires a lot of user interaction When defining the coordinates for the boundary and also suffers from areas Where satellite reception is insufficient for enabling an accurate navigation, that it so-called GPS shadoWs.

The international patent application published as WO202l209277Al discloses a manner of navigating Where a map is built based on a combination of input from satellite navigation sensor, the magnetic field and other sensor input (such as odometers and/or accelerometers) and then navigated accordingly along determined paths. The publication discloses a robotic Work tool system for defining a Working area, i.e. an operational area or part of an operational area, in Which at least one robotic Work tool subsequently is intended to operate. The system comprises at least one controller being configured to receive sensor data for pose estimation and event data relating to a plurality of events of at least one robotic Work tool moving Within the Working area. The received sensor and event data are associated With each other in time. The controller is configured to deterrnine positions for the events based on the received sensor data associated With the respective event data and to determine features reflecting the Working area by relating positions associated With corresponding events With each other. The controller is configured to adjust the determined positions based on the determined features by, for each feature, comparing the respective deterrnined positions With each other; and deterrnine, based on the adjusted positions, a map defining the Working area.

HoWever, this system, as Well as other satellite-based navigation systems, suffer from that in narroW passages, the position detern1ined based on the satellite navigation may not be accurate enough for navigating through the narroW passage. Especially in two circumstances; i) When multiple robotic Work tools are to navigate the same narroW passage as accurate navigation becomes more important to avoid collisions or deadlocks, and ii) Where the narroW passage eXtends at least partially through a GPS-shadow, Which is highly likely as a narroW passage is usually in a narroW area surrounded by high structures or other objects.

Thus, there is a need for an improved manner of navigating an operational area With narroW passages.

SUMMARY It is therefore an object of the teachings of this application to overcome or at least reduce those problems by providing by providing a robotic Working tool system comprising a robotic Work tool arranged to operate in an operating area and a boundary Wire for demarking the operating area, Wherein the operating area comprises a narroW passage, and Wherein the robotic Work tool comprises a controller, at least one navigation sensor and a first and a second magnetic sensor, Wherein the robotic Work tool is configured to operate in a first navigation mode based on the at least one navigation sensor, Wherein a position is deterrnined and compared to a map, and to operate in a second navigation mode based on the a first and a second magnetic sensor, Wherein a position in the narroW passage is determined based on signal levels of magnetic signals received via the a first and a second magnetic sensor, Wherein the controller of the robotic Work tool is configured to navigate in the first navigation mode, determine that a narroW passage is entered and in response thereto navigate the narroW passage based on the second navigation mode.

In some embodiments the at least one navigation sensor comprises a GNSS sensor deterrnining a position based on the GNSS sensor and compare the position to the map.

In some embodiments the at least one navigation sensor comprises a deduced reckoning sensor and Wherein robotic Work tool is configured to navigate in the first navigation mode by determining a position based on the deduced reckoning sensor and compare the position to the map.

In some embodiments the robotic Work tool is configured to navigate in the first navigation mode by receive sensor data for pose estimation and event data relating to a plurality of events of at least one robotic Work tool moving Within the Working area, Wherein the received sensor data and event data are associated With each other in time; determine positions for the plurality of events based on the received sensor data associated With the respective event data; determine features reﬂecting the Working area by relating positions associated With corresponding events With each other; adjust the deterrnined positions based on the deterrnined features by, for each deterrnined feature, comparing the respective determined positions With each other; and detern1ine, based on the adjusted positions of the deterrnined features, a map defining the Working area.

In some embodiments the map comprises information indicating a predefined narroW passage, Wherein the controller is further configured to detect that the robotic Work tool is entering the narroW passage (NP) by comparing coordinates deterrnined in the first navigation mode With the coordinates stored in the map for the narroW passage.

In some embodiments the controller is further configured to detect that the robotic Work tool is entering the narroW passage (NP) based on signal levels of magnetic signals received via a first and a second magnetic sensor. In some such embodiments the controller is further configured to detect that the narroW passage is entered causing the robotic Work tool to move sideWays towards lower signal levels and noting an increase in signal level of one magnetic sensor.

In some such embodiments the controller is further configured to note the increase in signal level Within a travelled distance.

In some embodiments the robotic Work tool is configured to operate in the second navigation mode by deterrnining a first signal level for the first magnetic sensor and a second signal level for the second magnetic sensor and determining in Which zone of the narroW passage (NP) the robotic Work tool is by comparing the first and second signal levels.

In some such embodiments the robotic Work tool is further configured to determine an orientation of the robotic Work tool and to determine in Which zone of the narroW passage (NP) the robotic Work tool is further based on the orientation.

In some embodiments the robotic Work tool is a robotic laWnmoWer.

In some embodiments the robotic Work tool is a robotic ﬂoor grinder.

It is also an object of the teachings of this application to overcome the problems by providing a method for use in a robotic Working tool system comprising a robotic Work tool arranged to operate in an operating area and a boundary Wire for demarking the operating area, Wherein the operating area comprises a narroW passage, and Wherein the robotic Work tool comprises at least one navigation sensor and a first and a second magnetic sensor, Wherein the robotic Work tool is configured to operate in a first navigation mode based on the at least one navigation sensor, Wherein a position is deterrnined and compared to a map, and to operate in a second navigation mode based on the a first and a second magnetic sensor, Wherein a position in the narroW passage is deterrnined based on signal levels of magnetic signals received via the a first and a second magnetic sensor, Wherein the method comprises navigating in the first navigation mode, deterrnining that a narroW passage is entered and in response thereto navigating the narroW passage based on the second navigation mode.

Further embodiments and aspects are as in the attached patent claims and as discussed in the detailed description.

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 interpreted according to their ordinary meaning in the technical field, unless eXplicitly defined otherwise 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 of any 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 work tool being a robotic lawnmower according to some embodiments of the teachings herein; Figure 1B shows a schematic view of the components of an example of a robotic work tool being a robotic lawnmower according to some example embodiments of the teachings herein; Figure 2 shows a schematic view of a robotic work tool system according to some example embodiments of the teachings herein; Figure 3 shows a schematic view of a robotic work tool system according to some example embodiments of the teachings herein; Figures 4A and 4B each shows a schematic illustration of zones in a narrow passage of a work area according to an example embodiment of the teachings herein; and Figure 5 shows a corresponding ﬂowchart for a method according to some example embodiments of the teachings herein.

DETAILED DESCRIPTION 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. This invention may, however, be embodied in many different forms 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 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 a work tool is to be safeguarded against from accidentally extending beyond or too close to the edge of the robotic work tool.

Figure 1A shows a perspective view of a robotic work tool 100, here exemplified by a robotic lawnmower 100, having a body 140 and a plurality of wheels 130 (only one side is shown). The robotic work tool 100 may be a multi-chassis type or a mono-chassis type (as in figure 1A). A multi-chassis type comprises more than one main body parts that are movable with respect to one another. A mono-chassis type comprises only one main body part.

It should be noted that robotic lawnmower may be of different sizes, where the size ranges from merely a few decimetres for small garden robots, to more than 1, 1.5 5 or even over 2 meters for large robots arranged to service for example sports fields or airfields.

It should be noted that even though the description herein is focussed on the example of a robotic lawnmower, the teachings may equally be applied to other types of robotic work tools, such as robotic ﬂoor grinders, robotic watering tools, robotic golfball collectors, and robotic mulchers to mention a few examples.

It should also be noted that even though the detailed description herein is focussed on outdoor robotic work tools, and especially gardening work tools, the teachings may equally be applied to other types of robotic work tools, such as indoor robotic work tools or construction robotic work tools, such as robotic ﬂoor grinders.

It should also be noted that more than one robotic working tool may be set to operate in a same operational area, and that all of these robotic working tools need not be of the same type.

It should also be noted that the robotic work tool is a self-propelled robotic work tool, capable of autonomous navigation within an operational area, where the robotic work tool propels itself across or around the work area in a pattern (random or predeterrnined) without user control (except, of course, possibly for a start and/or stop command).

Figure 1B shows a schematic overview of the robotic work tool 100, also exemplified here by a robotic lawnmower 100. In this example embodiment the robotic lawnmower 100 is of a mono-chassis type, having a main body part 140. The main body part 140 substantially houses all components of the robotic lawnmower 100. The robotic lawnmower 100 has a plurality of wheels 130. In the exemplary embodiment of figure 1B 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 155 powered by a battery 150, for driving the wheels 130 to navigate the robotic lawnmower 100 in different manners. It should be noted that even if the description herein is focused on electric motors, combustion engines may altematively be used, possibly in combination with an electric motor.

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 one example of a work tool 160 for a robotic work tool 100. A grinding tool is another example of a work tool 160 for use in a robotic ﬂoor grinder.

The robotic lawnmower 100 also comprises a controller 110 and a computer readable storage medium or memory 120. The controller 110 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 120 to be executed by such a processor. The controller 110 is configured to read instructions from the memory 120 and execute these instructions to control the operation of the robotic lawnmower 100 including, but not being limited to, the propulsion and navigation of the robotic lawnmower.

The controller 110 in combination with the electric motor 155 and the wheels 130 forms the base of a navigation system (possibly comprising further components) for the robotic lawnmower, enabling it to be self-propelled as discussed under figure 1A, The controller 110 may be implemented using any suitable, available processor or Programmable Logic Circuit (PLC). The memory 120 may be implemented using any commonly known technology for computer-readable memories such as ROM, FLASH, DDR, or some other memory technology.

In some embodiments, the robotic laWnmoWer 100 is further arranged With a Wireless communication interface 115 for communicating With a server, and in some embodiments, also With other devices, such as a personal computer, a smartphone, the charging station, and/or other robotic Work tools. Examples of such Wireless communication devices are B1uetooth®, WiFi® (IEEE802.11b), Global System Mobile (GSM) and LTE (Long Term Evolution), to name a few. The robotic laWnmoWer 100 is thus arranged to communicate With a server (referenced 240 in figure 2) for providing information regarding status, location, and/or progress of operation as Well as receiving commands or settings from the server.

The robotic laWnmoWer 100 further comprises a satellite navigation sensor 185. The satellite navigation sensor may be a GPS (Global Positioning System), RTK (Real- Time Kinetic) device or other Global Navigation Satellite System (GNSS) device.

In some embodiments, the robotic laWnmoWer 100 also or alternatively comprises navigation sensors based on deduced reckoning sensors 180. The deduced reckoning sensors may be odometers, accelerometers, inertial measuring units or other deduced reckoning sensors. In some embodiments a deduced reckoning navigation may be provided by knowing the current supplied to a 150 motor and the time the current is supplied, Which Will give an indication of the speed and thereby distance for the corresponding Wheel.

For enabling the robotic laWnmoWer 100 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 100 is, further configured to have at least one magnetic field sensor 170 arranged to detect the magnetic field 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 figure 1). In some embodiments, the sensors 170 may be connected to the controller 110, possibly via filters and an amplifier, and the controller 110 may be configured to process and evaluate any signals received from the sensors 170. The sensor signals are caused by the magnetic field being generated by the control signal being transmitted through the boundary Wire. This enables the controller 110 to determine Whether the robotic laWnmoWer 100 is close to or crossing the boundary Wire, or inside or outside an area enclosed by the boundary Wire. In the discussion herein, examples Will be discussed With reference to two magnetic sensors, a left (first) sensor 170-1 and a right (second) sensor 170-2 As mentioned above, in some embodiments, the robotic laWnmoWer 100 is in some embodiments arranged to operate according to a map application representing one or more operational areas (and possibly the surroundings of the operational area(s)) stored in the memory 120 of the robotic laWnmoWer 100. The map application may be generated or supplemented as the robotic laWnmoWer 100 operates or otherwise moves around in the Work area 205. In some embodiments, the map application includes one or more start regions and one or more goal regions for each Work area. In some embodiments, the map application also includes one or more transport areas between areas of the operational area.

In some embodiments the map of the operational area (or a part thereof) and/or any path to be navigated therein is generated as disclosed in the international patent application published as WO2021209277A1.

As discussed in the above, the map application is in some embodiments stored in the memory 120 of the robotic Working tool(s) 100. In some embodiments the map application is stored in the server (referenced 240 in figure 2). In some embodiments maps are stored both in the memory 120 of the robotic Working tool(s) 100 and in the server, Wherein the maps may be the same maps or shoW subsets of features of the area.

As discussed in the above, the robotic Work tool is eXemplified mainly as an autonomous robotic Work tool. HoWever, the teachings herein may also be applied to remote-controlled robotic Work tools 100.

Figure 2 shoWs a robotic Work tool system 200 in some embodiments. The schematic vieW is not to scale. The robotic Work tool system 200 comprises one or more robotic Work tools 100 according to the teachings herein. It should be noted that the operational area 205 shoWn in figure 2 is simplified for illustrative purposes. The robotic Work tool system comprises a boundary generated by a magnetic field generated by a control signal 225 being transmitted through a boundary Wire 220, and Which magnetic field is sensed by sensors 170 in the robotic Work tool 100. In the map, the boundary is further stored as a virtual border defined by coordinates and navigated using a location-based navigation system, such as a GPS (or RTK) system.

The robotic work tool system 200 further comprises a station 210 possibly at a station location. A station location may alternatively or additionally indicate a service station, a parking area, a charging station or a safe area where the robotic work tool may remain for a time period between or during operation session.

As with figures 1A and 1B, the robotic work too1(s) 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 the operational area. ln embodiments, where the operational area is outdoors, the robotic work tool system is an outdoor robotic work tool system.

However, in some embodiments, where at least parts of the operational area is indoors, the robotic work tool system may be in some embodiments, an indoor robotic work tool system, such as comprising a robotic ﬂoor grinder. Naturally a robotic work tool system may be both an indoor and an outdoor system, depending on the operational area.

The one or more robotic Working tools 100 of the robotic work tool system 200 are arranged to operate in an operational area 205, which in this illustrative example comprises a first work area 205A and a second work area 205B connected by a transport area TA.

However, it should be noted that an operational area may comprise a single work area or one or more work areas, possibly arranged adjacent for easy transition between the work areas, or connected by one or more transport paths or areas, also referred to as corridors. In the following work areas and operational areas will be referred to interchangeably, unless specifically indicated.

The operational area 205 is in this application exemplified as a garden, but can also be other work areas as would be understood, such as a (part of a) neighbourhood, or a sports field to mention a few examples. A garden and a (part of a) neighbourhood are both examples of domestic areas.

As discussed above, the garden may contain a number of obstacles and/or objects, for example a number of trees, stones, slopes and houses or other structures. ll In some embodiments the robotic work tool is arranged or configured to traverse and operate in work areas that are not essentially ﬂat, but contain 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 deterrnine an angle between a sensor mounted on the robotic work tool and the ground. The robotic work tool is also or altematively 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 altematively 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 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 operational area or any of its work areas 205 eXemplified with referenced to figure 2, may thus be such a non-uniforrn area as disclosed in this paragraph that the robotic work tool is arranged to traverse and/or operate in.

For the purpose of the teachings herein an object in an operational area is taken to be any obstacle or object discussed herein. And, in some embodiments, an object may be any area that is not a grass area, such as a gravel area, a sand area, a walkway, a road, a path or any other area that is not covered by grass.

The robotic working tool system 200 may altematively or additionally comprise or be arranged to be connected to a server 240, such as a cloud service, a cloud server application or a dedicated server 240. The connection to the server 240 may be direct from the robotic working tool l00, indirect from the robotic working tool l00 via the service station 2l0, and/or indirect from the robotic working tool l00 via user equipment (not shown).

As a skilled person would understand a server, a cloud server or a cloud service may be implemented in a number of ways utilizing one or more controllers 240A and one or more memories 240B that may be grouped in the same server or over a plurality of servers. 12 Returning to the Work areas and the transport path, as shown in figure 2, the robotic Working tool(s) 100 is arranged to navigate in one or more Work areas 205A, 205B, possibly connected by a transport area TA. The transport area is one example of a narroW passage NP that the robotic Work tool l00 Will need to traverse When following some paths to reach all sections of the operational area.

It should be noted that the one or more Work areas may be defined as a same Work area and Where the transport area is simply a narroW passage in a Work area.

As discussed in the above, a map of the operational area and/or any path to be travelled, is in some embodiments generated as disclosed in the international patent application published as WO202l209277Al, Where a method and variants of the method are disclosed for how to define an operational area or Work area as referred to therein. The method may be performed by a robotic Work tool system for defining a Working area in Which at least one robotic Work tool subsequently is intended to operate. The method starts With receiving sensor data for pose estimation and event data relating to a plurality of events of at least one robotic Work tool moving Within the Working area. The received sensor data and event data are associated With each other in time. The received sensor data may comprise at least one of position data, IMU data and odometer data. The event data relating to the events of the at least one robotic Work tool may comprise loop events, timer events and state events.

The method continues With deterrnining positions for the plurality of events based on the received sensor data associated With the respective event data. Thereafter, the method continues With deterrnining features reﬂecting the Working area by relating positions associated With corresponding events With each other. This may further comprise categorizing, based on the received event data, the deterrnined positions into different categories, and, for each category, adding the deterrnined positions into a feature map. The feature map may correspond to the respective feature.

After features reﬂecting the Working area has been deterrnined, the method continues With adjusting the positions of the determined features by, for each deterrnined feature, comparing the respective deterrnined positions With each other. The adjusting the positions of the determined features may further comprise finding outliers of the detern1ined positions and removing the found outliers from the deterrnined 13 positions of the deterrnined feature. Additionally, or alternatively, the method may further comprise performing a bias estimation. According to some embodiments, the method further comprises deterrnining updated features reﬂecting the Working area by relating the adjusted positions With each other based on the associated event data and adjusting the positions of the determined features by, for each determined feature, comparing the respective determined positions With each other. These two steps may, according to some embodiments, be repeated a plurality of times.

When the positions of the detern1ined features have been adjusted, the method continues With determining, based on the adjusted positions of the deterrnined features, a map defining the Working area. According to some embodiments, the method may further comprise controlling, based on the determined map, an operation of at least one robotic Work tool operating Within the Working area. The controlling an operation of at least one robotic Work tool may, for example, comprise deterrnining, based on the deterrnined map defining the Working area, a travel path Within the Working area Which the at least one robotic Work tool is intended to follow When operating Within the Working area.

In some embodiments, the method may further comprise transrnitting the deterrnined map and/or the travel path to at least one of the robotic Work tool and a visualization unit.

With the proposed method it may be possible to determine a map, Which accurately defines a Working area in a reliable and cost efficient Way. The method makes it possible to determine the map defining the Working area based solely on sensor data and event data related to at least one robotic Work tool moving Within the Working area to be defined. Thus, the provided method may determine an accurate map of a Working area, based on relatively simple data.

For more details reference is given to the international patent application published as WO202l209277Al.

HoWever, it should also be noted that the teachings herein may also be applied to as has been discussed in the above to other navigation methods or methods of generating a map based on a combination of magnetic boundary signals and satellite navigation. 14 In the below several embodiments of how the robotic work tool 100 may be adapted will be disclosed. It should be noted that all embodiments may be combined in any combination providing a combined adaptation of the robotic work tool.

It should be noted that for the teachings herein an operational area 205 may, in some embodiments, be thought of as any of its sub areas.

Figure 3 shows a schematic view of an example operating area 205, possibly one such as discussed in relation to figure 2, for use with a robotic work tool system 200 as discussed in relation to figure 2. A robotic work tool l00 is set to navigate the operational area 205.

The robotic work tool l00 is set to follow a transport path (referenced TP) and in the illustrated example, the transport path goes through a narrow passage (referenced NP). As discussed in the above, the narrow passage may be a transport path between work areas, a transport path inside a work area or simply a narrow part of a work area.

As can also be seen in the illustrated example, the narrow passage may be close to shadowing structures, such as trees (referenced T) and/or a house (referenced H). Such shadowing structures may give rise to areas, commonly referred to as GPS shadows, where satellite reception is not receivable at a quality level sufficient to sustain or enable accurate satellite-based navigation. In some situations, the number of satellite signals received is not sufficient. In some situations, the quality (as in signal level) of the received signals is not sufficient. As would be apparent to a skilled reader, such GPS shadows are commonly known and need no further explanation or details.

In the example illustrated in figure 3, the two work areas and the narrow passage are all bounded by a boundary wire 220 demarking the work areas for the robotic work tool to successfully navigating therein.

Figure 4A shows a schematic illustration of a narrow passage NP having two sides, Sl and S2, where the two sides are made up of sections of the boundary wire 220. In figure 4A four zones Zl-Z4 are indicated by dashed lines. Figure 4B shows a graph of the received signal strength P as a graph based on location in the narrow passage, where the two sides Sl, S2 are specifically indicated.

Utilizing the first magnetic sensor l70-l and the second magnetic sensor l70-2, the robotic work tool is enabled to determine where in the narrow passage with regards to the zones that the robotic work tool is currently positioned. This may be done by knowing the orientation of the robotic work tool, which is known from the past movement history if nothing else as the robotic work tool knows in which orientation it enters the narrow passage, and then deterrnining a first signal level for the first magnetic sensor l70-l and a second signal level for the second magnetic sensor l70-2 and deterrnining in which zone by comparing the first and second signal levels.

This provides for a very accurate determination of at least which zone the robotic work tool is currently in.

As is known to a skilled person the received signal undergoes a polarity shift as a sensor passes a wire emitting the signal. To be able to do this a drastic drop in signal strength is perceived close to the wire. The outerrnost zones, Zl, Z4 indicate an area close to the side (or rather boundary wire) where the received signal strength starts to drop to enable for the polarity shift that is at the boundary wire.

And in this area, the received signal is unreliable. The robotic work tool is therefore configured in some embodiments to stay out of the outermost zones, or at least not to follow the boundary in those zones (unless following the wire by straddling the wire).

Therefore, the smallest (first) distance d at which the robotic work tool 100 follows a side, should be larger than the width (as in indicating a distance falling outside) of the outerrnost zones Zl, Z4. In one embodiment, the first distance d at which the robotic work tool l00 follows a side is 20, 30 or 40 cm. Alternatively the first distance d at which the robotic work tool l00 follows a side is 0 (straddling the wire). In some embodiments the successive or next distances are increased by 20, 30, 40 or 50 cm.

The innerrnost zones Z2 and Z3 indicate an area on each side of the middle of the passage where the received signal strength is relatively stable. It should be reminded that the received signal strength is the sum of the signal emitted from the first side Sl and the signal emitted from the second side S2. Where the power line crosses the horizontal aXis indicates the position of the two sides/boundary wires S l, S2.

As discussed above, the robotic work tool is able to detect in which of zone Z2 and Z3 the robotic work tool is by determining which of the first signal levels is the 16 higher, based on the orientation of the robotic work tool. If the robotic work tool is oriented as in figure 4A, the first signal level will be higher than the second signal level if the robotic work tool 100 is in the second zone, Z2.

By deterrnining the magnitude of either signals, it can be deterrnined if the robotic work tool l00 is in the outerrnost zones as the signal therein increases to its maximum and then drops of quickly towards 0.

The robotic work tool is also enabled to detect a passage from zone 2 Z2 to zone 3 Z3, by detecting a shift in the received signal strength of two sensors placed at different distances from the side(s). If for example a first sensor l70-l is placed closer to the first side Sl, than a second sensor l70-2 is, which in tum is placed closer to the second side S2, and the robotic work tool is in zone 2 Z2, the robotic work tool will be able to determine that the middle has been reached or rather crossed by determining that the signal strength received by the first sensor is no longer larger than the signal strength received by the second sensor. The robotic work tool is thus able to determine that the robotic work tool has crossed into zone 3.

This thus provide for an accurate determination of a position within the narrow passage NP and as the inventors have realized after insightful and inventive reasoning, may be used as a supplement to other navigation techniques, such as satellite-based navigation, for example as disclosed in the international patent application published as WO202l209277Al, or even other navigation methods such as deduced reckoning navigation methods.

Figure 5 shows a general ﬂowchart according to a method of the teachings herein for use in a robotic working tool system for navigating an operating area having a boundary and a narrow passage, the robotic work tool system comprising a robotic work tool configured to navigate based on a first navigation mode and a second navigation mode.

In some embodiments the first navigation mode is based on determining a location relative a map, such as in a satellite-based navigation system and/or deduced reckoning-based navigation system. In some such embodiments the first navigation mode is as disclosed in the international patent application published as WO202l209277Al. 17 In some embodiments the second navigation mode is based on determining where in a narrow passage the robotic work tool is based on receiving a first and a second signal from a first and second magnetic sensor, such as discussed in relation to figures 4A and 4B above. In some such embodiments, the second navigation method is to determine in which zone of the narrow passage the robotic work tool is as discussed in relation to figures 4A and 4B above.

Returning to figure 3, with simultaneous reference to figure 5, the robotic work tool 100 is configured to operate 510 in a first navigation mode and to determine 520 that a narrow passage is to be entered, and in response thereto navigate 530 through the narrow passage based on the second navigation mode.

In some embodiments the map stored in the memory of the robotic work tool (or the server 240) comprise information indicating a predefined narrow passage, such as the coordinates for the narrow passage. This is indicated in figure 3, by a dotted rectangle encompassing the narrow passage. In some such embodiments the robotic work tool 100 is configured to detect that it is entering 520 the narrow passage NP by comparing coordinates received from the first navigation mode with coordinates stored in the map application for the narrow passage(s).

In some embodiments the robotic work tool 100 is configured to detect that it is entering 520 the narrow passage by receiving and comparing the first and second signal values of the magnetic fields. In some such embodiments, the narrow passage may be detected to be entered by moving the robotic work tool away from a side towards another side and thereby noting an increase in signal level of the outerrnost magnetic sensor, instead of a decline as if not in a narrow passage. The robotic work tool is thus configured to move sideways (or to a side) away from a side. Which way is a way can easily be determined by determining which of the magnetic sensors receives the lower signal value of the two and move in the direction of that sensor. In some such embodiments, the increase in signal level is to be noted within a travelled distance not exceeding a threshold distance, or the robotic work tool determines that there is no narrow passage. In some such embodiments, the travelled threshold distance is based on the width of the robotic work tool, and is 1, 2 or 3 widths of the robotic work tool. In some altemative or additional such embodiments, the travelled threshold distance is 18 0.25, 0.5, 0.75 or 1 meter or any range or value thereinbetween. In some alternative or additional such embodiments, the travelled threshold distance is 1, 1.5, 2 or 3 meter or any range or value thereinbetween.

It should be noted that in some embodiments, the navigation mode is switched irrespective of whether the robotic work tool is in a GPS shadow or not which allows for reducing the risk of losing the satellite navigation accuracy.

As the robotic work tool determines 540 that the narrow passage is exited, the robotic work tool switches 550 back to operating in the first navigation mode.

It should be noted that the robotic work tool may determine that the narrow passage is exited in a corresponding manner to as how the robotic work tool deterrnined that the narrow passage was entered, as would be apparent to a skilled person.

It should be noted that the first navigation mode may include navigating based on the electromagnetic sensors 170. One particular such case is as disclosed in the intemational patent application published as WO2021209277A1.

A robotic work tool system may thus in some embodiments be configured to perform the method according to figure 5 as discussed above for example in relation to figures 3, 4A and 4B.

In some further embodiments where the robotic work tool is configured to operate as in the international patent application published as WO2021209277A1, for example such as when the robotic work tools system comprise a guide wire, being one example of a wire 220, the robotic work tool may operate in different manners. As a boundary wire can also act as a guide wire, no specific guide wire is shown, but it should be noted that a skilled person is well-aware of systems where boundary wires acts as guide wires as well as systems having specific guide wires not being the boundary wire, and no further details on this are needed for a skilled person.

In some embodiments the robotic work tool is configured to follow the guide until last narrow passage have been passed, then switch to follow a path according to the first navigation mode. This may be used for example when leaving a charging station. Similarly, when moving to a charging station, the robotic work tool is in some embodiments configured to navigate in the first operating mode and to follow a path to 19 a narrow passage, then switch to follow the wire and follow it all the way to the charging station.

In some embodiments, the robotic work tool is configured to prioritize the wire. For example, when going from a first position to a second position on opposite ends of a narrow passage, the robotic work tool may pre-prepare a path so that the path goes along a short path to a guide close to the first position, then follow the wire through the narrow passage and continue as close as possible to the second position, and then switch to follow path. In such embodiments, the robotic work tool is thus configured to determine that the narrow passage has been entered and eXited already (or as late as) when reaching a wire to follow.

In some embodiments the robotic work tool is configured to handle errors. In some such embodiments, the robotic work tool is configured to try to follow the path all the way, and to detect that a wire is being crossed, such as the boundary wire, and in response thereto determine that the navigation according to the first navigation mode is not accurate enough and thereby switch to a navigation mode where the boundary control signal is followed.

Claims

1. A robotic Working tool system comprising a robotic Work tool (100) arranged to operate in an Operating area and a boundary Wire for demarking the operating area, Wherein the operating area comprises a narroW passage, and Wherein the robotic Work too1 (100) comprises a contro11er (110), at 1east one navigation sensor (180, 185) and a first and a second magnetic sensor (170-1, 170-2), Wherein the robotic Work too1 (100) is configured to operate in a first navigation mode based on the at 1east one navigation sensor (180, 185), Wherein a position is deterrnined and compared to a map, and to operate in a second navigation mode based on the a first and a second magnetic sensor (170-1, 170-2), Wherein a position in the narroW passage is deterrnined based on signa1 1eve1s of magnetic signa1s received via the a first and a second magnetic sensor (170-1, 170-2), Wherein the contro11er (110) of the robotic Work too1 (100) is configured to navigate in the first navigation mode, determine that a narroW passage is entered and in response thereto navigate the narroW passage based on the second navigation mode.

2. The system according to c1aim 1, Wherein the at 1east one navigation sensor (185) comprises a GNSS sensor deterrnining a position based on the GNSS sensor (185) and compare the position to the map.

3. The system according to c1aim 1 or 2, Wherein the at 1east one navigation sensor (180) comprises a deduced reckoning sensor and Wherein robotic Work too1 is configured to navigate in the first navigation mode by determining a position based on the deduced reckoning sensor (180) and compare the position to the map.

4. The system according to any preceding c1aim, Wherein the robotic Work too1 is configured to navigate in the first navigation mode by receive sensor data for pose estimation and event data re1ating to a p1ura1ity of events of at 1east one robotic Worktool (100) moving Within the Working area (205), Wherein the received sensor data and event data are associated With each other in time; deterrnine positions for the p1ura1ity of events based on the received sensor data associated With the respective event data; deterrnine features reﬂecting the Working area (205) by re1ating positions associated With corresponding events With each other; adjust the determined positions based on the deterrnined features by, for each determined feature, comparing the respective deterrnined positions With each other; and determine, based on the adjusted positions of the deterrnined features, a map defining the Working area (205).

5. The system according to any preceding c1aim, Wherein the map comprises information indicating a predefined narroW passage, Wherein the controller (110) is further configured to detect that the robotic Work too1 (100) is entering the narroW passage (NP) by comparing coordinates determined in the first navigation mode With the coordinates stored in the map for the narroW passage.

6. The system according to any preceding c1aim, Wherein the contro11er (110) is further configured to detect that the robotic Work too1 (100) is entering the narroW passage (NP) based on signa1 1eve1s of magnetic signa1s received via the a first and a second magnetic sensor (170-1, 170-2).

7. The system according to c1aim 6, Wherein the contro11er (110) is further configured to detect that the narroW passage is entered causing the robotic Work too1 (100) to move sideWays towards 1oWer signa1 1eve1s and noting an increase in signa1eve1 of one magnetic sensor.

8. The system according to c1aim 7, Wherein the contro11er (110) is further configured to note the increase in signa1 1eve1 Within a trave11ed distance.

9. The system according to any preceding c1aim, Wherein the robotic Work too1 is configured to operate in the second navigation mode bydetermining a first signal level for the first magnetic sensor (170-1) and a second signal level for the second magnetic sensor (170-2) and determining in Which zone of the narroW passage (NP) the robotic Work tool (100) is by comparing the first and second signal levels.

10. The system according to claim 9, Wherein the robotic Work tool is further configured to determine an orientation of the robotic Work tool and to determine in Which zone of the narroW passage (NP) the robotic Work tool (100) is further based on the orientation.

11. The system according to any preceding claim, Wherein the robotic Work tool is a robotic laWnmoWer.

12. The system according to any of claims 1 to 10, Wherein the robotic Work tool is a robotic ﬂoor grinder.

13. A method for use in a robotic Working tool system comprising a robotic Work tool (100) arranged to operate in an operating area and a boundary Wire for demarking the operating area, Wherein the operating area comprises a narroW passage, and Wherein the robotic Work tool (100) comprises at least one navigation sensor (180, 185) and a first and a second magnetic sensor (170-1, 170-2), Wherein the robotic Work tool (100) is configured to operate in a first navigation mode based on the at least one navigation sensor (180, 185), Wherein a position is deterrnined and compared to a map, and to operate in a second navigation mode based on the a first and a second magnetic sensor (170-1, 170-2), Wherein a position in the narroW passage is determined based on signal levels of magnetic signals received via the a first and a second magnetic sensor (170-1, 170-2), Wherein the method comprises navigating in the first navigation mode, deterrr1ining that a narroW passage is entered and in response thereto navigating the narroW passage based on the second navigation mode.