SE2250557A1

SE2250557A1 - Navigation for a robotic work tool system

Info

Publication number: SE2250557A1
Application number: SE2250557A
Authority: SE
Inventors: Gustaf Lagercrantz; Mikael Alexiusson
Original assignee: Husqvarna Ab
Priority date: 2022-05-09
Filing date: 2022-05-09
Publication date: 2023-11-10

Abstract

A method for use a robotic work tool (100) wherein the method comprises: selecting (410) a following distance at which to follow a wire (225, 225A, 225B); following (415) the wire at the selected follow distance (fd); determining (420) that an obstacle (S, H) is reached by determining (421) that a noted wire distance (wd) for the wire (225, 225A, 225B) being followed is reached; determining (425) a corresponding noted following distance (fd) for the noted wire distance for the wire (225, 225A, 225B) being followed; and following (440) the wire (225, 225A, 225B) being followed at the noted following distance.

Description

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, in such a system.

BACKGROUND Automated or robotic work tools such as robotic lawnmowers are becoming increasingly more popular and so is the use of the robotic Working tool(s) in more and more complicated operational areas. This has led to that unless the user is diligent and careful in installing boundary and guide wires, the robotic work tool may appear to behave erratically as it tries to follow a wire as there are many factors that the robotic work tool must take into account, especially as regards not leaving tracks. This may result in that the robotic work tool is unable to follow the wire properly.

Thus, there is a need for an improved manner of following a wire.

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 work tool system comprising one or more wires and a robotic work tool, wherein the one or more wires comprises a boundary wire, and wherein the robotic work tool is arranged to operate in an operational area bounded by the boundary wire and wherein the robotic work tool comprises a controller, wherein the controller is configured to: select a following distance at which to follow one of the one or more wires; follow the wire to be followed at the selected follow distance (fd); determine that an obstacle (S, H) is reached by deterrnining that a noted wire distance (wd) for the wire being followed is reached; determine a corresponding noted following distance (fd) for the noted wire distance for the wire being followed; and follow the wire being followed at the noted following distance.

In some embodiments the controller is further configured to determine that the obstacle (S, H) is reached by deterrnining that the obstacle is approached, and in response thereto note the wire distance (wd) at which the obstacle is approached and note the following distance (fd) as corresponding to the wire distance (wd).

In some embodiments the controller is further configured to determine that the obstacle has been passed, and in response thereto follow the wire to be followed at the selected follow distance (fd).

In some embodiments the controller is further configured to determine that the following of the wire was unsuccessful.

In some embodiments the controller is further configured to determine that the following of the wire was successful.

In some embodiments the controller is further configured to utilize machine leaming and train the machine leaming based on successful and unsuccessful followings of the wire based on selected following distances.

In some embodiments the controller is further configured to utilize machine leaming to determine that the obstacle (S, H) is reached and adapting the following distance (fd) for the wire being followed.

In some embodiments the controller is further configured to determine that a noted follow distance is marked as successful and if so determine that the noted follow distance is longer than the selected follow distance and in response thereto follow the wire at the selected distance.

In some embodiments the controller is further configured to determine that a noted follow distance is marked as unsuccessful and if so determine that the noted follow distance is shorter than the selected follow distance and in response thereto decrease the follow distance and follow the wire at the decreased follow distance.

In some embodiments the controller is further configured to note the wire distance and the corresponding follow distance in a record.

In some embodiments the robotic work tool system further comprises a memory wherein the controller is further configured to store the record in the memory.

In some embodiments the the controller is further conf1gured to select the wire to be followed to be the boundary wire In some embodiments the one or more wires comprises one or more guide wires and wherein the controller is further conf1gured to select the wire to be followed to be one of the one or more guide wires.

It is also an object of the teachings of this application to overcome the problems by providing a method for use in a method for use in a robotic work tool system comprising one or more wires and a robotic work tool, wherein the one or more wires comprises a boundary wire, and wherein the robotic work tool is arranged to operate in an operational area bounded by the boundary wire, wherein the method comprises the robotic work tool following one of the one or more wires one or more wires at a first follow distance and deterrnining that a wire distance has been reached, and in response thereto, following the wire at a second follow distance.

In some embodiments the first follow distance is a selected follow distance, wherein the method further comprises selecting the selected follow distance differently from time to time to reduce the formation of tracks.

In some embodiments the second follow distance is a noted follow distance and wherein the method comprises following the wire at the noted follow distance.

In some embodiments the method comprises selecting the second follow distance to be equal to or less than a noted follow distance.

In some embodiments the method comprises selecting the second follow distance differently from time to time to reduce the formation of tracks.

In some embodiments the method comprises utilizing machine leaming for deterrnining the wire distance and the second follow distance.

In some embodiments the wire distance is a distance along the wire and is predeterrnined.

In some embodiments the method further comprises: selecting a following distance at which to follow one of the one or more wires; following the wire to be followed at the selected follow distance (fd); deterrnining that an obstacle (S, H) is reached by deterrnining that a noted wire distance (wd) for the wire being followed is reached; deterrnining a corresponding noted following distance (fd) for the noted wire distance for the wire being followed; and following the wire being followed at the noted following distance.

In some embodiments the robotic work tool is a robotic lawnmower.

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 l 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 2A shows a schematic view of a robotic work tool system according to some example embodiments of the teachings herein; Figure 2B shows a schematic view of a robotic work tool system according to some example embodiments of the teachings herein; Figure 2C shows a schematic view of a robotic work tool system according to some example embodiments of the teachings herein; Figure 2D shows a schematic view of a robotic work tool system according to some example embodiments of the teachings herein; Figure 2E shows a schematic view of a robotic work tool system according to some example embodiments of the teachings herein; Figure 3A shows a schematic view of a record to be used in a robotic work tool system according to some example embodiments of the teachings herein; Figure 3B shows a schematic view of a record to be used in a robotic work tool system according to some example embodiments of the teachings herein; Figure 3C shows a schematic view of a record to be used in a robotic work tool system according to some example embodiments of the teachings herein; Figure 4A shows a corresponding ﬂowchart for a method according to some example embodiments of the teachings herein; Figure 4B shows a corresponding ﬂowchart for a method according to some example embodiments of the teachings herein; and Figure 4C 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 farrning equipment, or other robotic work tools.

Figure l shows a schematic overview of a robotic work tool l00, here exemplified by a robotic lawnmower l00. The robotic work tool l00 may be a multi- chassis type or a mono-chassis type (as in figure l). 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 even more than l meter for large robots arranged to service for example airf1elds.

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 Watering tools, robotic golfball collectors, and robotic mulchers to mention a few examples.

In some embodiments, and as Will be discussed below, the robotic Work tool is a semi-controlled or at least supervised autonomous Work tool, such as farrning equipment or large laWnmoWers, for example riders or comprising tractors being autonomously controlled.

It should also be noted that the robotic Work tool is a self-propelled robotic Work tool, capable of autonomous navigation Within a Work area, Where the robotic Work tool propels itself across or around the Work area in a pattem (random or predeterrnined).

The robotic Work tool 100, exemplified as a robotic laWnmoWer 100, has a main body part 140 and a plurality of Wheels 130 (in this example four Wheels 130, but other number of Wheels are also possible, such as three or six).

The main body part 140 substantially houses all components of the robotic laWnmoWer 100. At least some of the Wheels 130 are drivably connected to at least one electric motor 155 powered by a battery 150. 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. In the example of figure 1, each of the Wheels 130 is connected to a common or to a respective electric motor 155 for driving the Wheels 130 to navigate the robotic laWnmoWer 100 in different manners. The Wheels, the motor 155 and possibly the battery 150 are thus examples of components making up a propulsion device. By controlling the motors 155, the propulsion device may be controlled to propel the robotic laWnmoWer 100 in a desired manner, and the propulsion device Will therefore be seen as synonymous With the motor(s) 150.

It should be noted that Wheels 130 driven by electric motors is only one example of a propulsion system and other variants are possible such as caterpillar tracks.

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.

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.

The robotic laWnmoWer 100 is further arranged With a Wireless communication interface 115 for communicating With other devices, such as a server, a personal computer, a smartphone, the charging station, and/ or other robotic Work tools. Examples of such Wireless communication devices are Bluetooth®, WiFi® (IEEE802.11b), Global System Mobile (GSM) and LTE (Long Term Evolution), to name a feW. The robotic laWnmoWer 100 may be arranged to communicate With a user equipment (referenced 250 in figure 2A, as an example of a connected device) as discussed in relation to figure 2A below for providing information regarding status, location, and progress of operation to the user equipment as Well as receiving commands or settings from the user equipment. Altematively or additionally, the robotic laWnmoWer 100 may be arranged to communicate With a server (referenced 240 in figure 2A) for providing information regarding status, location, and progress of operation as Well as receiving commands or settings.

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 Work tool 100. In embodiments Where the robotic Work tool 100 is exemplified as an automatic grinder, the Work tool 160 is a rotating grinding disc.

The robotic laWnmoWer 100 may further comprise at least one signal navigation sensor 185 configured to provide navigational information (such as position) based on receiving one or more signals. In some embodiments the signal navigation sensor is an optical navigation sensor, such as a camera-based sensor and/or a laser-based sensor. In some embodiments the navigation sensor is a beacon navigation sensor, such as a Radio Frequency receiver, such as an Ultra Wide Band (UWB) receiver or sensor, configured to receive signals from a Radio Frequency beacon, such as a UWB beacon. Altematively or additionally, the beacon navigation sensor may be an optical receiver configured to receive signals from an optical beacon. In some embodiments the navigation sensor is a satellite navigation sensor such as a GPS (Global Positioning System) device or other Global Navigation Satellite System (GNSS) device. In some embodiments the navigation sensor is a combination of one or more of the examples given above.

The robotic laWnmoWer 100 may also or altematively comprise deduced reckoning sensors 180. The deduced reckoning sensors may be odometers, accelerometer or other deduced reckoning sensors. In some embodiments, the deduced reckoning sensors are comprised in the propulsion device, Wherein a deduced reckoning navigation may be provided by knowing the current supplied to a 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 Wire, such as a boundary Wire or guide Wire, emitting a magnetic field caused by a control signal (referenced 210A in figure 2A) transmitted through the Wire, the robotic laWnmoWer 100 is configured to have at least one magnetic field sensor 170 arranged to detect the magnetic field and for detecting the Wire and/or for receiving (and possibly also sending) information to/ from a signal generator (Will be discussed With reference to figure 2A). 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 Wire. This enables the controller 110 to determine Whether the robotic 1aWnmoWer 100 is close to or Crossing the boundary Wire, or inside or outside an area enclosed by the boundary Wire.

The robotic 1aWnmoWer 100 is in some embodiments arranged to operate according to a map application representing one or more Work areas (and possibly the surroundings of the Work area(s)) stored in the memory 120 of the robotic 1aWnmoWer 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.

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 2A). 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.

The robotic Working tool 100 may also comprise additional sensors 190 for enabling operation of the robotic Working tool 100, such as visual sensors (for example a camera) for enabling camera-based navigation and/or for enabling object detection, ranging sensors for enabling SLAM-based navigation (Simultaneous Localization and Mapping), moisture sensors, collision sensors, distance detecting sensors (for example camera, laser or radar), Wheel load sensors to mention a feW examples of sensors.

Figure 2A 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 2A is simplified for illustrative purposes.

The robotic Work tool system 200 further comprises a station 210 possibly at a station location. A station location may altematively 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.

The robotic Work tool system comprises a boundary 220 that is electro mechanical, but may also be may be virtual. An example of an electro mechanical boundary is a magnetic field generated by a control signal 210A being transmitted through a boundary wire 225, and which magnetic ﬁeld is sensed by sensor in the robotic work tool 100. In some embodiments the control signal 210A is generated by a signal generator comprised in the station 210. An example of a Virtual boundary is a set of coordinates representing or defining a geofence that can be naVigated using the signal navigation sensor 180.

In addition to a boundary wire 225, the robotic work tool system may also, in some embodiments, comprise one or more guide wires 225A, 225B for guiding the robotic work tool 100 to a specific portion of the operational area, such as to and/or from the charging station 210 (as for guide wire 225A in figure 2A) or to/ from a specific portion of the operational area, such as between work areas 205A, 205B, possibly through transport areas TA )as for guide wire 205B in figure 2A). As is known a second control signal, or a part of the control signal 210A, is transmitted through the guide wire for enabling the robotic work tool 100 to recognize and differentiate the guide wire 225A,B from the boundary wire 225.

It should be noted though that some embodiments utilize electro mechanical boundaries and some embodiments utilize both Virtual and electro mechanical boundaries. In embodiments where an electro mechanical boundary is used, the signal navigation sensor 180 is optional.

As with figure 1, the robotic work tool(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 a work 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 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 adj acent for easy transition between the work areas, or connected by one or more transport paths or areas, also referred to as corridors. ll 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 an airfield. As discussed above, the garden may contain a number of obstacles, for example a number of trees, stones, slopes and houses or other structures.

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 determine an angle between a sensor mounted on the robotic Work tool and the ground. The robotic Work tool is also or altematively arranged or conf1gured to traverse and operate in a Work area that contains obstacles that are not easily discemed 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 Work area 205 exemplified With referenced to figure 2A, may thus be such a non- uniforrn Work area as disclosed in this paragraph that the robotic Work tool is arranged to traverse and/or operate in.

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, direct from a user equipment 250, indirect from the robotic Working tool l00 via the service station 2l0, and/or indirect from the robotic Working tool 100 via the user equipment 250.

A skilled person Would understand that a server, a cloud server or a cloud service may be implemented in a number of Ways utilizing one or more controllers 12 240A and one or more memories 240B that may be grouped in the same server or over a plurality of servers.

The user equipment 250 may be a smartphone, a tablet computer or a remote control panel, and comprises one or more controllers 240A and one or more memories 240B for storing instructions that when executed by the controller l50A controls the operation of the user equipment. The user equipment 250 also comprises a user interface for receiving commands from a user, such as buttons or Virtual keys 25 0C.

In the below, several embodiments of how the robotic work tool 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.

Figure 2B shows a simpliﬁed view of a robotic work tool system 200 as in figure 2A, where a manner of following a wire is shown in the lower right-hand comer of the operational area 205. In order to avoid causing tracks in a lawn, or other substrate, robotic work tools may be arranged to follow a wire at different distances from time to time. In some embodiments, the distance may be changed each time, and in some embodiments, the distance may be changed less frequently. In figure 2B a robotic work tool 100 is shown at two time instances T1, T2 where at the first time instance T1 the robotic work tool 100 is following the boundary wire 225 at a first distance (in this example it is adj acent the boundary wire 225), and where at the second time instance T2 the robotic work tool 100 is following the boundary wire 225 at a second distance d, (in this example further away from the boundary wire 225).

The inventors have realized that when the robotic work tool 100 is operating in operational areas 205 comprising objects or other obstacles (as in the operational area 205 exemplified in figures 2A and 2B), or simply where the guide wire(s) 225A,B is laid close to the boundary wire 225, this manner of following the wire may lead to collisions with objects, borders of transport corridors or with the boundary wire 225 which will obstruct the propulsion of the robotic work tool 100, and may cause the robotic work tool 100 to tum away from the followed wire, be stuck behind an obstacle, or be unable to enter a transport corridor. Such instances are considered to be obstructed or unsuccessful attempts at following the wire. It should be noted that in some embodiments, an attempt may be obstructed even if the robotic work tool 100 manages 13 to eventually navigate around or through an obstacle and be able to follow the wire, as such evasive manoeuvring costs time and power.

In figure 2B the robotic work tool 100 is also shown at two further time instances TS and T4 where at the third time instance TS the robotic work tool 100 is attempting to follow the first guide wire 225A at a distance d from the charging station 210, but collides with the stone (referenced S), and where at the fourth time instance T4 the robotic work tool 100 is attempting to follow the second guide wire 225 at a distance d to the second work area (shown and referenced 205B in figure 2A), but collides with the house (referenced H).

It should be noted that even though the distance d is referenced the same for all instances, the distance may be the same or different in each or some of the instances.

In order to overcome such obstructed attempts to follow the wire, a complete map of the operational area 205 could be built comprising all the obstacles and their exact locations, which can be deterrnined using a signal navigation device, such as a GPS sensor. Such a map can be used for the navigation whereby the robotic work tool could maneuver to avoid any collisions.

As discussed, such a map requires a high-accuracy position deterrnining sensor, such as a GPS sensor, which increases the cost of the robotic work tool 100. Furthermore, as the operational area 205 comprises obstacles, such as trees (referenced T) and houses H, there may be areas where even such high-accuracy position sensors does not operate accurately enough. In areas where there are signal shadows (i.e. areas where signal reception from a GPS satellite may be blocked), the accuracy may be less than 1 or 2 meters (meaning that the position error may be larger than 1 or 2 meters), which is not accurate enough for avoiding obstacles in most operational areas 205, such as common gardens.

The inventors have realized a simple and ingenious manner of enabling a robotic work tool 100 to follow a wire successfully without being obstructed, without requiring expensive high-accuracy position sensors. It should be noted that even if high-accuracy position sensors are not required, they may be utilized in some embodiments to supplement the navigation. 14 The inventors are proposing to simply keep a track of a distance along the wire being followed and each time an obstruction is detected, make a note of the distance along the wire (hereafter referred to as the wire distance, referenced wd) and the distance to the wire (hereafter referred to as the following distance, referenced fd).

Similarly, each time the wire is followed successfully, or without being obstructed, the following distance is noted. In some embodiments the robotic work tool l00 is conf1gured to noting the following distance also when the wire is partially followed successfully. In some embodiments following the wire partially includes following the wire after an obstruction has been detected, but later cleared (noting the following distance at which the obstruction was cleared). In some altemative or additional embodiments following the wire partially includes following the wire for a segment of the wire successfully.

An obstruction may be colliding with an obstacle, colliding with another wire, and/or colliding with a Virtual border (shown as dashed lines in figure 2A), such as of a transport area (referenced TA in figure 2A), obstructing the robotic work tool from entering the transport area - or other area marked by the Virtual border 225. In some embodiments colliding includes actually colliding with or coming into close contact with the object in question.

Figure 2C shows a simplified View of a robotic work tool system 200 as in figures 2A and 2B, where four time instances are shown Tl, T2, TS and T4 are shown. At the first time instance Tl, the robotic work tool 100 has detected an obstruction (by colliding with the stone S) and notes the wire distance wdl and the following distance fdl. At the second time instance T2, the robotic work tool l00 has detected that it has successfully followed the wire (partially or fully, and in this example fully) as it has reached the boundary wire 225 and notes the following distance fd2. In situations where the wire has been successfully followed partially, the wire distance wd2 is also noted.

At the third time instance T3, the robotic work tool 100 has detected an obstruction (by colliding with the house H) and notes the wire distance wd3 and the following distance fd3. At the fourth time instance T4, the robotic work tool l00 has managed to navigate around the house and has detected that it has successfully followed the wire (partially or fully, and in this example partially) and notes the following distance fd4 and the wire distance wd4. In some embodiments, the robotic work tool 100 is conf1gured to determine that an obstacle is cleared by noting that it is able to again follow the wire for a distance (for example 1, 2, 5 or 10 meters or any range covering these distances) and/or a time (for example 10, 20, 30, 60 or 120 seconds or any range covering these times). IN some embodiments the wire distance of a cleared obstacle, is taken as the wire distance of the detected obstacle. In the example of figure 2C the wire distance at the fourth time instance is thus set as the wire distance at the third time instance T3; wd4=wd3.

For a fully successful following, the wire distance may be noted implicitly as the whole length of the followed wire is successfully noted, the wire distance thus being all distance points along the wire 225.

It should be noted that even if the wire distances wd are shown as being on the wire 225, it should be noted that they are measured as the distance traVelled by the robotic work tool 100 along the wire being followed (possibly at the corresponding following distance).

In some embodiments the robotic work tool 100 is configured to note a wire distance, a following distance and/or an obstruction by keeping a record of such distances. In some embodiments, a record is kept for one wire 225, 225A,B and in some embodiments a record is kept for some or all wires 225.

Noting a wire distance for a successful following includes, in some embodiments, noting the following distance fd for the successful following for all the wire distances already noted that is within the successfully followed wire segment.

Figure 2C also shows an example of a record 125. In some embodiments the record is stored in the memory 120 of the robotic work tool 100, and is therefore referenced 125.

As the record only comprises Very small data points (two distances for each obstruction) and Very few data points (the obstructions of which there are only a few, say 2 or 3, in a normal operating area) the record will be Very small and will thus require only a Very small storage space making it highly suitable for local storage in the memory 120 of the robotic work tool 100. However, in some embodiments the record is 16 stored in the memory 240B of the server 240, where its small size makes it easy to quickly transfer back and forth (fully or partially).

The record 125 is shown as a table, where one column indicates a wire distance and one column indicates a following distance that was successful.

To enable the following of more than one wire, there may be one record for each wire, or there may be a column indicating the wire.

As a skilled person would understand, there exist many Variations and possibilities of how the record is stored and the given example of storing it as a table is only for illustrative purposes.

In some embodiments a successfully followed distance fd may also be noted as being successful along with an indication of the wire segment (full or partial) along which the following distance lead to a successful following.

Figure 3A shows a schematic View of a record 125 and how it is updated according to one example sequence of the time instances of figure 2C. In this example it will be assumed that the record is empty as we start (time instance T0, not shown in figure 2C). At time instance T1 where the obstruction is noted at wire distance wd1 and at the following distance fd1 along the first guide wire 225A, the record 125 is updated by noting these distances. The following distance is also marked as unsuccessful, which is illustrated by the "-" sign.

In embodiments where multiple wires are to be followed, an indication of the corresponding wire is also noted. In this example an "A" is noted to represent the first guide wire 225A. At time instance T2 where the wire is successfully followed at the following distance fd2 along the first guide wire 225A, the record 125 is updated by noting the following distance as successful. As is shown in figure 3A, this may be done by replacing all following distances that are noted as unsuccessful for wire distances falling within the successful wire distance. In the example of figure 3A fd2 thus replaces fd1 and is marked as successful indicated by the "+° sign.

In some embodiments, the following distance for a successful following is also noted for the successful segment. In this example the successful segment is the full length of the first guide wire 225 and the successful following distance is thus indicated for the wire (shown as the fd2 in parenthesis). 17 Similarly, at the third time instance T3 the obstruction is detected and the record 125 is updated accordingly as in ﬁgure 3A, where "B° references the second guide wire 225B. And as the obstacle is successfully maneuvered at time instance T4, possibly being at the same attempt to follow or at a later attempt to follow the second guide wire 225B, the record 125 is updated as in figure 3A. As no further obstacles exist along the second guide wire 225B, the record will indicate that the following distance f4 is successful for the wire in this example.

It should be noted that even if the examples herein indicate that old paths are deleted, the old paths may be saved, for example for use as showing already tried paths that need not be repeated. The old paths may also be stored to provide altematives if a path without obstructions is not possible, whereby the best of the old paths may be selected.

Figure 3B shows a schematic view of a record 125 and how it is updated according to another example sequence of the time instances of figure 2C. In this example it will be assumed that the record is empty as we start (time instance T0, not shown in figure 2C). In this example time instance T2 takes place before time instance T1 and time instance T4 takes place before time instance T3.

At time instance T2 where the wire is successfully followed at the following distance fd2 along the first guide wire 225A, the record 125 is updated by noting the following distance as successful.

At time instance Tl where the obstruction is noted at wire distance wdl and at the following distance fdl along the first guide wire 225A, the record 125 is updated by noting these distances. As there is a successful following distance noted for the segment in which wdl falls within (in this example the whole wire) the following distance marked as successful for that segment is noted for the wire distance. In this example fd2 is noted for wdl, and noted as successful as it has previously been successfully navigated.

Similarly, at the fourth time instance T4 the obstacle is successfully maneuvered and the record 125 is updated as in figure 3B. In this example it is assumed that the obstacle is maneuvered at a first attempt to follow the second guide wire 225B. 18 At the third time instance T3 the obstruction is detected While following the wire at the following distance fd3. As the obstruction is detected at that following distance and for the wire distance wd3 the record 125 is updated accordingly as in figure 3B, by noting the obstruction at wire distance wd3 and the already noted successful following distance fd4, which is now also noted for the specific wire distance.

As can be seen in figures 3A and 3B, the end record l25 is the same in both examples.

The operation of the robotic work tool l00 will now be described in relation to figure 2D, figures 3A and 3B (specifically the record l25 at the end of the corresponding examples) and figure 4 showing a general ﬂowchart for a method according to herein.

The robotic work tool l00 is configured to select 4l0 a following distance to be used for following a wire and starts to follow 4l5 the wire at the following distance, see time instance T5 in figure 2D. In this example, the second guide wire 225B is followed at a following distance fd5.

The robotic work tool l00 is also configured to determine 420 that an obstacle is reached. In some embodiments it is deterrnined that a noted obstacle has been reached by deterrnining 42l that a noted wire distance is reached. The deterrnination whether a noted wire distance is reached may be done in different manners.

In some embodiments, the robotic work tool l00 is configured to determine that a noted wire distance for the wire to be followed is reached by deterrnining if there is a noted wire distance(s) for the selected wire. This may be done by polling or querying the record l25. As it is deterrnined that there is a noted wire distance, the robotic work tool l00 may determine that the noted wire distance has been reached by deterrnining a traVelled distance along the wire and determine that the traVelled distance matches the noted wire distance.

In some embodiments, the robotic work tool l00 is configured to determine that a noted wire distance is reached by deterrnining a travelled distance and polling the record l25 to determine if there is a noted wire distance that matches the traVelled distance. By polling the record l25, it can be assured that any updates made by another robotic work tool l00 is taken into account. 19 It should be noted that the record 125 is, in some embodiments, stored locally in the memory or, in some embodiments, stored remotely in the server 240. It should be noted that in some embodiments, where the record 125 is stored remotely in the server 240, the record 125 may be retrieved from the server 240 as the wire to be followed is selected and thereafter be stored locally in the memory 120, possibly temporarily and later be uploaded again to the server 240.

In the example of figure 2D the record 125 indicates that there is a noted wire distance for the second guide wire 225B, namely wd3 which has a corresponding noted following distance fd4.

As it has been deterrnined that a noted wire distance is reached, the robotic work tool deterrnines 425 a noted following distance fd corresponding to the noted wire distance wd. In some embodiments it is further deterrnined 430 if the noted following distance fd is indicated as successful or not.

In the example of figure 2D time instance T6 indicates that the noted wire distance wd3 has been reached and as can be seen in figures 3A and 3B, the corresponding noted following distance fd4 is successful.

In some embodiments, if the noted following distance is successful, it is further deterrnined 435 if the noted following distance is shorter than the currently used following distance, i.e. the selected following distance, and if so follow 440 the wire at the noted following distance.

In the example of figure 2D the corresponding noted following distance fd4 is shorter than the selected following distance fd5 and the robotic work tool 100 accordingly follows the second guide wire 225B at the noted following distance fd4, as can be seen at time instance T7.

In some embodiments, it is deterrnined 445 that the noted obstacle has been passed, and in response thereto, the robotic work tool follows 450 the wire again at the selected following distance. By retuming to the selected following distance reduces the formation of tracks behind an obstacle. In some embodiments it is deterrnined 445 that the noted obstacle has been passed by travelling to a wire distance marked as safe in the record 125. In some embodiments it is deterrnined 445 that the noted obstacle has been passed by travelling a safety distance indicated in the record 125. In some such embodiments the safety distance is a length of the corresponding obstacle. The robotic work tool 100 is thus in some embodiments configured to store a distance or length (i.e the safety distance) of the obstacle corresponding to the noted wire distance in the record 125. In some alternative such embodiments the safety distance is a default distance, for example 1, 2, 5, 10, 15 or 20 meters or any range there in between, or possibly longer. In some altemative such embodiments the safety distance is a default time distance, for example, 5, 10, 15, 20, 30 or 60 seconds or any range there in between, or possibly longer.

In some embodiments it is deterrnined 445 that the noted obstacle has not been passed as an obstacle has been approached. This may be a new - previously unknown obstacle.

If it is deterrnined that the noted following distance is unsuccessful the robotic work tool deterrnines 450 if the noted following distance is shorter than the selected following distance, and if so deterrnines a new selected following distance by decreasing 455 the noted following distance and attempts 460 to follow the wire at the now selected following distance being the decreased noted following distance.

The noted following distance may be decreased by a default amount (for example 10, 20, 50 or 100 cm) or by a relative amount (for example 10, 15, 20, 25 or 50 %). A decreased following distance resulting in a negative value may in some embodiments indicate following the wire on the other side of the wire. It should be noted that the record is updated for the new follow distance whether marking it as successful or unsuccessful based on the attempt to follow the wire at the decreased distance.

If it is deterrnined that the noted follow distance is unsuccessful (referenced NO in 430) and that the noted following distance is shorter than, i.e. not longer than, the selected following distance (referenced NO in 450), the robotic work tool 100 attempts 460 to follow the wire at the selected following distance.

If it is deterrnined that the noted follow distance is successful and that the noted following distance is longer than, i.e. not shorter than, the selected following distance (referenced NO in 435), the robotic work tool 100 attempts 460 to follow the wire at the selected following distance. 21 If the attempt is successful, then the obstacle will have been passed 445 without any obstructions. If the attempt is unsuccessful, the robotic work tool 100 has approached an obstacle 422. In some embodiments, the noted following distance may be adapted based on the success of the attempt. If attempt is successful, replace the noted following distance and mark it as successful. And, if not successful, replace the noted following distance and mark it as unsuccessful.

The robotic work tool is in some embodiments configured to keep track of the shortest unsuccessful following distance and the longest successful following distance to enable exploration of the distances between these noted following distances. In such embodiments and as discussed in some embodiments above, the robotic work tool may determine if the selected following distance is between the longest successful following distance and the shortest unsuccessful following distance and if so, the robotic work tool attempts the selected following distance.

In some embodiments the robotic work tool 100 is configured to follow the wire at the noted following distance by selecting a following distance that is shorter or equal to the noted following distance. This further reduces the formation of tracks even around the noted obstacles.

Retuming to deterrnining that an obstacle has been reached, the robotic work tool is in some embodiments configured to deterrnining that an obstacle is reached or approached 422 by detecting an obstruction and noting the wire distance.

The obstacle may be detected by detecting a collision with the obstacle.

Altematively or additionally, the obstacle may be detected by detecting that the robotic work tool is approaching the obstacle for example by detecting that a distance to the obstacle is below a threshold distance, for example 10, 20, or 50 cm. Such a distance can be detected or deterrnined utilizing visual sensors, such as a camera providing images that are processed buy the controller, or through the use of range finding sensors such as laser or radar sensors 190.

As the robotic work tool 100 deterrnines that an obstacle is approached, the robotic work tool 100 notes the travelled distance along the wire to be followed and the distance at which the wire is (currently) followed. This distance may be the follow distance, a decreased follow distance or a selected following distance. 22 The robotic work tool 100 notes 423 the travelled distance as a wire distance in the record, thereby noting an obstruction in the record 125. The record 125 may therefore be considered as an obstruction map.

If there already is a noted wire distance matching the travelled distance, the robotic work tool 100 compares the current following distance to the noted following distance. If the noted following distance is longer than the current following distance, the current following distance, being unsuccessful, is noted 424 in the record 125. If there is a noted successful following distance for the currently travelled segment, such as the wire, and the noted successful following distance is shorter than the current following distance, the noted successful following distance is noted 424 for the wire distance as a successful distance. In some embodiments also the current following distance, being unsuccessful is, recorded for the wire distance.

The recording of wire distances and follow distances have been discussed in relation to figures 2A, 2B and 2C and apply also to the discussion herein.

In some embodiments the travelled distance is measured using the deduced navigation sensors 185. In some embodiments utilizing an odometer, counting the wheel tums and thus measuring the distance travelled by the robotic work tool 100 (as wheel tums, or the actual distance if the wheel diameter is known). In some altemative or additional embodiments utilizing an inertial measurement unit (IMU), an accelerometer or a gyro for measuring accelerations of the robotic work tool 100 and thereby the speed and thus the distance travelled by the robotic work tool 100.

In some embodiments the travelled distance is measured as the time travelled. If the robotic work tool 100 is arranged to travel at a specific speed, the time travelled will implicitly provide the distance travelled. In some embodiments the travelled distance is measured as the time travelled at a given speed, possibly noting one time for different speeds if more than one speed is utilized. In some such embodiments, the speed may be the actual speed (possibly deterrnined by wheel tums per time unit), and in some embodiments the speed may be represented by the strength of the current delivered to the motor(s) 150, as a given current level will cause a proportional speed - at least for known surfaces. 23 As discussed in relation to figure 1, the robotic work tool 100 may comprise further magnetic sensors 170, and additionally, the magnetic sensors 170 may also pick up other magnetic fields, such as from other wires and/or form other magnetic sources. The robotic work tool 100 may also comprise other sensors 190, deduced reckoning sensors 185 and signal navigation sensors 180. The input from these sensors may also be stored for providing an indication of a wire distance, or rather allocation for an obstacle.

Such further sensor data may make it easier for the robotic work tool 100 to determine a wire distance also when retuming along a wire being followed. Retuming to figures 2A, 2B and 2C it is easy to determine a travelled distance to be compared with the wire distance when the starting point is known, such as in the charging station. However, if a wire is started to be followed at a random point, such as when receiving an indication that it is time to retum to a charging station for recharging the batteries, it may be more difficult to determine the travelled distance along the wire. However, by comparing to other sensor data, a location that shows some significant features, such as a sensor data value exceeding a threshold or a combination of sensor data values appearing, may be identified and used as a reference point along the wire to be followed.

It should be noted that even though the discussion herein has been made with reference to following a guide wire, the teachings herein may also be applied to follow the boundary wire, the boundary wire then acting as a guide wire.

Even if such sensor data adds to the data stored in the record, the record may still be kept small by simply storing such reference points.

The robotic work tool is thus configured to also gather sensor data from other sensors, as exemplified herein, and recording reference points in the record 125 or in connection to the record 125.

Even though the description herein has been highly detailed as to which deterrninations are made and in what order, it should be noted that many variations exist and that some deterrninations may be left out, combined, replaced or altered. It should also be noted that the inventors have realized that by applying machine leaming the essence of the invention may be carried out by an artificial intelligence system that over 24 time records which followings of a wire are successful and which are not and notes common traits between the successful ones, thereby leaming which wire should be followed at which distance from the wire at which locations or segments along the wire.

The use of machine leaming is especially beneficial as to noting the wire distance as the wire distance may depend on many factors and actually vary. Examples of factors that may affect the wire distance are rain and moisture sensors as this may cause slip of the wheels whereby the deterrnination of the travelled distance will include an error. The rain sensor, moisture sensor and any slip sensor are thus examples of sensors that may affect a wire distance, or its deterrnination.

The machine leaming is effected by noting successful attempts, i.e. those without any obstructions, and training the robotic work tool l00 based on these.

Figure 4B shows an altemative ﬂowchart for a general method according to herein. The method is for use in a robotic work tool as in figure l in a manner as discussed above in relation to figures 2A to 2D and also as discussed in relation to figure 4A. The method of figure 4B is a simplified version of the method of figure 4A, where some deterrninations have been omitted as they may be performed utilizing machine leaming. The method comprises selecting 400 a wire to follow and selecting 410 a distance to follow the wire at, whereby the wire is followed 415 at the selected distance. As it is deterrnined that an obstacle is reached 420, either that the known obstacle is reached at a known distance which may be deterrnined based on a reached distance 42l, or that an obstacle is detected 422, the robotic work tool l00 reacts accordingly.

If the object is known the following distance is potentially adapted 426 as per previous training and the wire is followed 426 at an adapted follow distance until the obstacle is passed 445. If the obstacle is passed successfully, the following is marked as successful 427. If the object is approached at a previously unknown distance or the object is unknown, the following is recorded 425 as unsuccessful. The robotic work tool l00 is possibly trained 428 accordingly if in a training phase.

As noted, many of the deterrninations of the method of figure 4A will be made implicitly by a machine leaming algorithm as in figure 4B, and the two figures thus show different aspects of similar methods.

As discussed herein, the inventors are thus proposing a robotic work tool that is configured to follow a wire at a selected distance, and in order to avoid being obstructed, the robotic work tool is further configured to switch to another (shorter or at an opposite side of the wire(being a negative distance)) distance at a predeterrnined distance from a start point of the (following of the) wire, such as where the wire connects to another wire, the border of a work area or a charging (or other service) station 210 to mention a few examples.

The switching of distance to follow at is thus only based on the distance along the wire, the wire distance, and not a map position such as coordinates.

As discussed above, the wire distance at which to switch the following distance may be specific to a previously detected obstacle, but it may also relate to a segment of the wire.

Figure 2E shows a simplified view of a robotic work tool system 200 as in figures 2A, 2B, 2C, or 2D. Figure 2E shows an example of where a robotic work tool 100 starts to travel along the wire 205B at a selected following distance referenced fds as is shown at time instance Tl. As the robotic work tool 100 reaches a predeterrnined wire distance wda, the robotic work tool 100 switches to a follow distance noted for that wire distance, in this example the follow distance referenced fda. As is shown at time instance T2, the robotic work tool 100 then follows the wire 225B at the noted follow distance fda.

Later as the robotic work tool 100 reaches a second noted wire distance, wdb, the robotic work tool again switches to a further follow distance and follows the wire now at the further follow distance. The further follow distance is in some examples and/or embodiments the selected distance fds, and in some examples and/or embodiments a follow distance noted for the second noted wire distance.

As discussed in the above, a wire distance may be specific to a detected obstacle or it may relate to a segment, such as the end of one segment and start of another. In some such embodiments, segments are of varying length, and in some such embodiments segments are of fixed length. One example of such an embodiment is where a follow distance is noted for each segment distance, a segment distance being 5, or 20 meters. 26 Figure 3C shows a schematic View of a record to be used in a robotic work tool system according to some example embodiments of the teachings herein. As can be seen in figure SC, the record is only a collection of follow distances for segments. As can be seen in figure 3C, the follow distance specified for a segment or wire distance may be the selected follow distance, referenced fds, which indicates that the follow distance may be freely selected.

Figure 4C shows a ﬂowchart for a general method according to herein, which is aimed to disclose the Very core of the teachings herein, namely that a robotic work tool follows 415 a wire at a first follow distance and as the robotic work tool reaches a predeterrnined wire distance 421, the robotic work tool switches and follows the wire at a second (adapted) follow distance 426.

The first follow distance is in some examples and embodiments a selected follow distance, which is selected differently from time to time to reduce the formation of tracks.

The second follow distance is in some examples and embodiments a noted follow distance that has been experienced to allow for an unobstructed following of the wire. In some such embodiments the second follow distance is the noted follow distance and in some such embodiments is selected differently from time to time to reduce the formation of tracks, but selected to be equal to or less than the noted follow distance.

In some embodiments the method is implemented utilizing machine leaming for deterrnining the wire distance(s) and the corresponding noted following distance(s).

It should be noted that the wire distances wd that the robotic work tool 100 switches the follow distance are distances along the wire and are predeterrnined.

It should be noted that the ﬂowcharts of figures 4A, 4B and 4C are intended to show aspects of the same general teaching and embodiments discussed with relation to one ﬂowchart may be used with another ﬂowchart.

It should also be noted that a segment or section may be a partial segment or section and the robotic work tool may thus be configured to travel along the wire at different distances, both shorter and longer distances.

Claims

1. A robotic work tool system (200) comprising one or more wires (225, 225A, 225B) and a robotic work tool (100), wherein the one or more wires (225, 225A, 225B) comprises a boundary wire (225), and wherein the robotic work tool (100) is arranged to operate in an operational area bounded by the boundary wire (225) and wherein the robotic work tool (100) comprises a controller (110), wherein the controller (110) is configured to: select (410) a following distance at which to follow one of the one or more wires (225, 225A, 225B); follow (415) the wire to be followed at the selected follow distance (fd); deterrnine (420) that an obstacle (S, H) is reached by deterrnining (421) that a noted wire distance (wd) for the wire (225, 225A, 225B) being followed is reached; deterrnine (425) a corresponding noted following distance (fd) for the noted wire distance for the wire (225, 225A, 225B) being followed; and follow (440) the wire (225, 225A, 225B) being followed at the noted following distance.

2. The robotic work tool system (200) according to claim 1, wherein the controller (110) is further configured to deterrnine (420) that the obstacle (S, H) is reached by deterrnining (422) that the obstacle is approached, and in response thereto note (423) the wire distance (wd) at which the obstacle is approached and note (424) the following distance (fd) as corresponding to the wire distance (wd).

3. The robotic work tool system (200) according to claim 1 or 2, wherein the controller (110) is further configured to deterrnine that the obstacle has been passed (445), and in response thereto follow (415) the wire to be followed at the selected follow distance (fd).

4. The robotic work tool system (200) according to claim 2, wherein the controller (110) is further conf1gured to deterrnine that the following of the wire was unsuccessful.

5. The robotic work tool system (200) according to claim 3, wherein the controller (110) is further conf1gured to deterrnine that the following of the wire was successful.

6. The robotic work tool system (200) according to claim 4 and 5, wherein the controller (110) is further conf1gured to utilize machine leaming and train the machine leaming based on successful and unsuccessful followings of the wire based on selected following distances.

7. The robotic work tool system (200) according to claim 6, wherein the controller (110) is further conf1gured to utilize machine leaming to deterrnine (420) that the obstacle (S, H) is reached and adapting the following distance (fd) for the wire (225, 225A, 225B) being followed.

8. The robotic work tool system (200) according to any preceding claim, wherein the controller (110) is further conf1gured to deterrnine that a noted follow distance is marked as successful and if so deterrnine that the noted follow distance is longer than the selected follow distance and in response thereto follow the wire at the selected distance.

9. The robotic work tool system (200) according to any preceding claim, wherein the controller (110) is further conf1gured to deterrnine that a noted follow distance is marked as unsuccessful and if so deterrnine that the noted follow distance is shorter than the selected follow distance and in response thereto decrease the follow distance and follow the wire at the decreased follow distance.

10. The robotic work tool system (200) according to any preceding claim, wherein the controller (110) is further configured to note the wire distance and the corresponding follow distance in a record (125).

11. The robotic work tool system (200) according to claim 10, further comprising a memory (120) wherein the controller (110) is further configured to store the record (125) in the memory (120).

12. The robotic work tool system (200) according to any preceding claim, wherein the controller (110) is further configured to select the wire to be followed to be the boundary wire

13. The robotic work tool system (200) according to any preceding claim, wherein the one or more wires comprises one or more guide wires (225A, 225B) and wherein the controller (110) is further configured to select the wire to be followed to be one of the one or more guide wires.

14. The robotic work tool system (200) according to any preceding claim, wherein the robotic work tool (100) is a robotic lawnmower.

15. A method for use in a robotic work tool system (200) comprising one or more wires (225, 225A, 225B) and a robotic work tool (100), wherein the one or more wires (225, 225A, 225B) comprises a boundary wire (225), and wherein the robotic work tool (100) is arranged to operate in an operational area bounded by the boundary wire (225), wherein the method comprises the robotic work tool (100) following (415) one of the one or more wires one or more wires (225, 225A, 225B) at a first follow distance and deterrnining that a wire distance has been reached (421), and in response thereto, following the wire at a second follow distance (426).

16. The method according to claim 15 wherein the first follow distance is a selected follow distance, wherein the method further comprises selecting the selected follow distance differently from time to time to reduce the formation of tracks.

17. The method according to claim 15 or 16, wherein the second follow distance is a noted follow distance and wherein the method comprises following the wire at the noted follow distance.

18. The method according to claim 15 or 16, wherein the method comprises selecting the second follow distance to be equal to or less than a noted follow distance.

19. The method according to claim 18 wherein the method comprises selecting the second follow distance differently from time to time to reduce the formation of tracks.

20. The method according to any of claims 15 to 19, wherein the method comprises utilizing machine leaming for deterrnining the wire distance and the second follow distance.

21. The method according to any of claims 15 to 20, wherein the wire distance is a distance along the wire and is predeterrnined.

22. The method according to any of claims 15 to 21, wherein the method further comprises: selecting (410) a following distance at which to follow one of the one or more wires (225, 225A, 225B); following (415) the wire to be followed at the selected follow distance (fd); deterrnining (420) that an obstacle (S, H) is reached by deterrnining (421) that a noted wire distance (wd) for the wire (225, 225A, 225B) being followed is reached; deterrnining (425) a corresponding noted following distance (fd) for the noted wire distance for the wire (225, 225A, 225B) being followed; andfollowing (440) the Wire (225, 225A, 225B) being followed at the noted following distance.