SE544910C2 - Improved navigation for a robotic work tool - Google Patents

Improved navigation for a robotic work tool

Info

Publication number
SE544910C2
SE544910C2 SE2150161A SE2150161A SE544910C2 SE 544910 C2 SE544910 C2 SE 544910C2 SE 2150161 A SE2150161 A SE 2150161A SE 2150161 A SE2150161 A SE 2150161A SE 544910 C2 SE544910 C2 SE 544910C2
Authority
SE
Sweden
Prior art keywords
work tool
robotic
robotic work
reached
distance
Prior art date
Application number
SE2150161A
Other languages
Swedish (sv)
Other versions
SE2150161A1 (en
Inventor
Jonas Holgersson
Original Assignee
Husqvarna Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Husqvarna Ab filed Critical Husqvarna Ab
Priority to SE2150161A priority Critical patent/SE544910C2/en
Priority to EP22704604.2A priority patent/EP4291013A1/en
Priority to PCT/SE2022/050106 priority patent/WO2022173343A1/en
Publication of SE2150161A1 publication Critical patent/SE2150161A1/en
Publication of SE544910C2 publication Critical patent/SE544910C2/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/50—Systems of measurement based on relative movement of target
    • G01S13/52—Discriminating between fixed and moving objects or between objects moving at different speeds
    • G01S13/56—Discriminating between fixed and moving objects or between objects moving at different speeds for presence detection
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01D—HARVESTING; MOWING
    • A01D34/00—Mowers; Mowing apparatus of harvesters
    • A01D34/006—Control or measuring arrangements
    • A01D34/008—Control or measuring arrangements for automated or remotely controlled operation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
    • G01S1/70—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using electromagnetic waves other than radio waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/86—Combinations of radar systems with non-radar systems, e.g. sonar, direction finder
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/881—Radar or analogous systems specially adapted for specific applications for robotics
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G01S15/06—Systems determining the position data of a target
    • G01S15/08—Systems for measuring distance only
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/02—Control of position or course in two dimensions
    • G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
    • G05D1/0259—Control of position or course in two dimensions specially adapted to land vehicles using magnetic or electromagnetic means
    • G05D1/0265—Control of position or course in two dimensions specially adapted to land vehicles using magnetic or electromagnetic means using buried wires
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/02—Control of position or course in two dimensions
    • G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
    • G05D1/0276—Control of position or course in two dimensions specially adapted to land vehicles using signals provided by a source external to the vehicle
    • G05D1/0278—Control of position or course in two dimensions specially adapted to land vehicles using signals provided by a source external to the vehicle using satellite positioning signals, e.g. GPS
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/20—Control system inputs
    • G05D1/24—Arrangements for determining position or orientation
    • G05D1/247—Arrangements for determining position or orientation using signals provided by artificial sources external to the vehicle, e.g. navigation beacons
    • G05D1/248—Arrangements for determining position or orientation using signals provided by artificial sources external to the vehicle, e.g. navigation beacons generated by satellites, e.g. GPS
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S901/00—Robots
    • Y10S901/01—Mobile robot

Landscapes

  • Engineering & Computer Science (AREA)
  • Remote Sensing (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Automation & Control Theory (AREA)
  • Electromagnetism (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Acoustics & Sound (AREA)
  • Robotics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Environmental Sciences (AREA)
  • Control Of Position, Course, Altitude, Or Attitude Of Moving Bodies (AREA)
  • Manipulator (AREA)

Abstract

A robotic work tool (100) configured to operate in a work area (205), the robotic work tool (100) comprising a controller (110) configured to cause the robotic work tool to follow (410) a first side (SI) of the work area (205) at a distance for the first side (SI); determine (420) that an end (EP1, EP2) has been reached and in response thereto cause the robotic work tool to make a turn (430) and follow (440) the first side (SI) of the work area (205) at a next distance; determine that a middle (M) has been reached (450) and in response thereto cause the robotic work tool to proceed to a second side (S2) and follow (470) the second side (S2) of the work area (205) at a first distance for the second side (S2); determine that an end (EP1, EP2) has been reached and in response thereto cause the robotic work tool to make a turn and follow (480) the second side (S2) of the work area (205) at a next distance.

Description

TECHNICAL FIELD This application relates to robotic Work tools and in particular to a system and a method for providing an improved navigation for a robotic Work tool, such as a laWnmoWer.
BACKGROUND Automated or robotic Work tools such as robotic laWnmoWers are becoming increasingly more popular. In a typical deployment a Work area, such as a garden, the Work area is enclosed by a boundary Wire With the purpose of keeping the robotic laWnmoWer inside the Work area.
An electric control signal may be transmitted through the boundary Wire thereby generating an (electro-) magnetic field emanating from the boundary Wire. The robotic Work tool is typically arranged With one or more (electro-) magnetic sensors adapted to sense the control signal.
The Work areas, such as gardens may comprise passages that are narroW compared to the size of the robotic laWnmoWer, Which introduces a risk of the robotic Work tool getting stuck in the passage or at least not being able to navigate properly and therefor unable to properly or sufficiently operate in the passage in a manner that services the Whole area of the passage properly.
Thus, there is a need for an improved manner of enabling a reliable operation of a robotic Work tool, such as a robotic laWnmoWer, even in areas that are difficult to maneuver in.
SUMMARY It is therefore an object of the teachings of this application to overcome or at least reduce those problems by providing a robotic Work tool configured to operate in a Work area, the robotic Work tool comprising a controller configured to cause the robotic Work tool to follow a first side of the Work area at a distance for the first side; determine that an end has been reached and in response thereto cause the robotic work tool to make a turn and follow the first side of the work area at a next distance; determine that a middle has been reached and in response thereto cause the robotic work tool to proceed to a second side and follow the second side of the work area at a first distance for the second side; determine that an end has been reached and in response thereto cause the robotic work tool to make a turn and follow the second side of the work area at a next distance = In one embodiment the controller is further configured to cause the robotic work tool to proceed to second side after it is deterrnined that an end is reached.
In one embodiment the controller is further configured to repeat following the first side and/or the second side at a next distance until it is deterrnined that the middle is reached.
In one embodiment the controller is further configured to perform an additional lap as the middle is reached.
In one embodiment the controller is further configured to perform an additional lap as the middle is reached from the first side.
In one embodiment the controller is further configured to perform an additional lap as the middle is reached from the second side.
In one embodiment the controller is further configured to determine whether to perform the additional lap or not based on a shape of the first side and/or a shape of the second side.
In one embodiment the robotic work tool comprises a satellite navigation sensor, wherein the controller is further configured to determine that the end is reached based on the satellite navigation sensor.
In one embodiment the robotic work tool comprises a deduced reckoning navigation sensor, wherein the controller is further configured to detern1ine that the end is reached based on the deduced reckoning navigation sensor.
In one embodiment the first distances are smaller than the next distances.
In one embodiment the first distances are the same.
In one embodiment the first distance is larger than a zone where a signal strength is reduced due to a polarity change.
In one embodiment the next distance is increased by an amount smaller than or equal to the width of a work tool comprised in the robotic Working tool.
In one embodiment the work area comprises terrain that is of varying altitude; obstacles that are not easily discemed from the ground; and/or obstacles that are overhanging.
In some embodiments the robotic work tool is a robotic lawnmower.
In one embodiment the first side and/or second side is a side of a passage comprised in the work area.
It is also an object of the teachings of this application to overcome the problems by providing a method for use in a robotic work tool configured to operate in a work area, the method comprising following a first side of a work area at a distance for the first side; determining that an end has been reached and in response thereto making a turn and following the first side of the work area at a next distance; determining that a middle has been reached and in response thereto proceeding to a second side and following the second side of the work area at a first distance for the second side; determining that an end has been reached and in response thereto make a turn and follow the second side of the work area at a next distanceflggå.
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 lA shows an example of a robotic lawnmower according to some embodiments of the teachings herein; Figure lB shows a schematic view of the components of an example of a robotic work tool being a robotic lawnmower according to an example embodiment of the teachings herein; Figure lC shows a schematic view of a work tool of an example of a robotic work tool being a robotic lawnmower according to an example embodiment of the teachings herein; Figure 2 shows an example of a robotic work tool system being a robotic lawnmower system according to an example embodiment of the teachings herein; Figure 3 shows a schematic view of a subsection of a work area where a robotic work tool is configured to operate according to an example embodiment of the teachings herein; Figure 4 shows a corresponding flowchart for a method according to an example embodiment of the teachings herein; Figure 5A and figure 5B shows a schematic view of an alternative subsection of a work area where a robotic work tool is configured to operate according to an example embodiment of the teachings herein; and Figure 6A and figure 6B each shows a schematic illustration of zones in a subsection of a work area according to an example embodiment 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 farn1ing equipment, or other robotic work tools where passages or narrow areas may have to be traversed.
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.
The robotic lawnmower 100 may comprise charging skids for contacting contact plates (not shown in figure 1) when docking into a charging station (not shown in figure 1, but referenced 210 in figure 2) for receiving a charging current through, and possibly also for transferring information by means of electrical communication between the charging station and the robotic lawnmower 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 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 lB, each of the wheels 130 is connected to a respective electric motor. This allows for driving the wheels 130 independently of one another which, for example, enables steep turning and rotating around a geometrical center for the robotic lawnmower 100. It should be noted though that not all wheels need be connected to each a motor, but the robotic lawnmower 100 may be arranged to be navigated in different manners, for example by sharing one or several motors 150. In an embodiment where motors are shared, a gearing system may be used for providing the power to the respective Wheels and for rotating the wheels in different directions. In some embodiments, one or several wheels may be uncontrolled and thus simply react to the movement of the robotic lawnmower The robotic lawnmower 100 also comprises a grass cutting unit 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. The robotic lawnmower 100 also has (at least) one battery 155 for providing power to the motor(s) 150 and/or the cutter motor 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 of the robotic lawnmower. 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, RAM, SRAM, DRAM, FLASH, DDR, SDRAM or some other memory technology.
The robotic lawnmower 100 may further be arranged with a wireless com- munication interface 115 for communicating with other devices, such as a server, a personal computer or smartphone, the charging station, and/or other robotic work tools. Examples of such wireless communication devices are Bluetooth®, WiFi® (IEEE802. 1 lb), Global System Mobile (GSM) and LTE (Long Term Evolution), to name a few.
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 (not shown) and for detecting the boundary wire and/or for receiving (and possibly also sending) information to/from a signal generator (will be discussed with reference to figure 2). 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 some embodiments, the robotic lawnmower 100 may further comprise at least one navigation sensor, such as a beacon navigation sensor and/or a satellite navigation sensor 180. The beacon navigation sensor may be a Radio Frequency receiver, such as an Ultra Wide Band (UWB) receiver or sensor, configured to receive signals from a Radio Frequency beacon, such as a UWB beacon. Altematively or additionally, the beacon navigation sensor may be an optical receiver configured to receive signals from an optical beacon. The satellite navigation sensor may be a GPS (Global Positioning System) device or other Global Navigation Satellite System (GNSS) device.
In some embodiments, the robotic lawnmower 100 may further comprise at least one deduced reckoning navigation sensor 190, such as an accelerometer and/or an odometer to mention a few examples. Utilizing the deduced reckoning navigation sensor 190, the robotic work tool 100 is able to navigate at some accuracy through complicated mowing patterns even when no satellite reception is reliably received.
Figure 1C shows a schematic view of a work tool of an example of a robotic work tool being a robotic lawnmower according to an example embodiment of the teachings herein.
Fig. 1C schematically illustrates a cutting unit 160 according to some embodiments of the cutting assembly 1 according to the present disclosure. The cutting unit 160 comprises a cutting disc 161 and a cutting member 162 arranged at a periphery of the cutting disc 161. For reasons of brevity and clarity, the cutting unit 160 in Fig. 16 is illustrated as comprising only one cutting member 162. However, the cutting unit 160 may comprise more than one cutting member 162, such as two, three, four, five, or six cutting members 162. The kinetic energy of each cutting member 162 of the cutting unit 160 as described herein may be determined by means of the following formula: Ek=1/2*mv^where Ek is the kinetic energy, in J oules; m is the mass, of reckonable length L of the cutting member 162, in kilograms, wherein the reckonable length L of the cutting member 162 may be the length L between the pivot axis 166 of the cutting member 162 and the radially outer portion 163 of a cutting member 162; V is the maximum attainable Velocity of the point z which is halfway along the reckonable length L of the cutting member 162, in metres per second.
Therefore v=0,1047n[r-L/2] where n is the maximum rotational speed, in revolutions per minute; r is the distance from the rotational axis Ax of the cutting unit 160 to the radially outer portion 163 of a cutting member 162, in metres; Lis the reckonable length of the cutting member 162, in metres.
The pivot axis 166 of a cutting member 162 coincides with a centre line of a hole 164 configured for attachment of the cutting member According to some embodiments of the cutting arrangement, the distance r from the rotational axis Ax of the cutting unit 160 to the radially outer portion 163 of a cutting member 162 is within the range of 160 cm to 20 cm, or is within the range of 6 cm to 12 cm, or is approximately 8.5 cm.
According to some embodiments of the cutting unit 3, the reckonable length L of the cutting member 162 is within the range of 1 cm to 9 cm, or is within the range of 1.7 cm to 6 cm, or is approximately 3.4 cm.
According to some embodiments of the cutting unit 160, the mass m, of reckonable length L of the cutting member 162, is Within the range of 1 to 25 grams, or is Within the range of 1.7 to 6.5 grams, or is approximately 3.4 grams.
According to some embodiments, the thickness of the cutting member 162, i.e. the thickness of the cutting member 162 measured in a direction perpendicular to the rotational plane of the cutting member 162, is Within the range of 0.2 mm to 3.5 mm, or is Within the range of 0.32 mm to 1.2 mm, or is approximately 0.63 mm.
According to some embodiments, the height h of the cutting member 162 of the cutting unit 160 is Within the range of 0.7 cm to 6 cm, or is Within the range of 1 cm to 2.9 cm, or is approximately 1.9 cm.
According to some embodiments of the cutting arrangement, the diameter of the cutting disc 161 of the cutting unit 160 is Within the range of 5 cm to 39 cm, or is Within the range of 8 cm to 20 cm, or is approximately 14.3 cm.
According to some embodiments, the maximum attainable Velocity V of the point z Which is half Way along the reckonable length L of the cutting member 162 is Within the range of 10 to 80 metres per second, or is Within the range of 15 to 50 metres per second, or is approximately 34 metres per second.
According to some embodiments, the maximum rotational speed of the cutting unit 160 is Within the range of 1 000 to 8 500 revolutions per minute, or is Within the range of 2 400 to 7 200 revolutions per minute, or is approximately 4 800 revolutions per minute.
Figure 2 shows a schematic view of a robotic Work tool system 200 in some embodiments. The schematic view is not to scale. The robotic Work tool system 200 comprises a robotic Work tool 100. As With figures 1A and lB, the robotic Work tool is exemplified by a robotic laWnmoWer, Whereby the robotic Work tool system may be a robotic laWnmoWer system or a system comprising a combinations of robotic Work tools, one being a robotic laWnmoWer, but the teachings herein may also be applied to other robotic Work tools adapted to operate Within a Work area.
The robotic Work tool system 200 may also comprises charging station 210 Which in some embodiments is arranged With a signal generator 215 and a boundary Wire The signal generator is arranged to generate a control signal 225 to be transn1itted through the boundary wire 220. To perform this, the signal generator is arranged with a controller and memory module. The controller and memory module operates and functions in the same manner as the controller ll0 and memory l20 of the robotic work tool l00. The controller and memory module may also be the controller and memory module of the charging station, hereafter simply referred to as the controller 2l In one alternative or additional embodiment the controller and memory module may also comprise or be connected to a communication interface (not shown eXplicitly but considered to be part of the controller and memory module). The communication interface is enabled for communicating with other devices, such as a server, a personal computer or smartphone, a robotic work tool l00, another signal generator 2l5 and/or another charging station 2l0 using a wireless communication standard. EXamples of such wireless communication standards are Bluetooth®, WiFi® (lEEE802. l lb), Global System Mobile (GSM) and LTE (Long Term Evolution), to name a few.
The boundary wire 220 is arranged to enclose a work area 205, in which the robotic lawnmower l00 is supposed to serve. The control signal 225 transmitted through the boundary wire 220 causes a magnetic field (not shown) to be emitted.
In some embodiments the control signal 225 is a sinusoid periodic current signal. In some embodiments the control signal 225 is a pulsed current signal comprising a periodic train of pulses. In some embodiments the control signal 225 is a coded signal, such as a CDMA signal.
As an electrical signal is transmitted through a wire, such as the control signal 225 being transmitted through the boundary wire 220, a magnetic field is generated. The magnetic field may be detected using field sensors, such as Hall sensors. A sensor - in its simplest form -is a coil surrounding a conductive core, such as a ferrite core. The amplitude of the sensed magnetic field is proportional to the derivate of the control signal. A large variation (fast and/or of great magnitude) results in a high amplitude for the sensed magnetic field. ll The Variations are sensed and compared to a reference signal or pattern of Variations in order to identify and thereby reliably sense the control signal.
The robotic work tool system 200 may also optionally comprise at least one beacon (not shown) to enable the robotic lawnmower to navigate the work area using the beacon navigation sensor(s) 180 or in combination with the satellite navigation sensor 180. As systems such as RTK systems are widely known the beacon sensor and the satellite sensor will hereafter be discussed as being the same sensor.
The work area 205 is in this application eXemplified as a garden, but can also be other work areas as would be understood. The garden contains a number of obstacles (O), exemplified herein by a number (3) of trees (T), a rock (R), a slope (S) and a house structure (H). The trees are marked both with respect to their trunks (filled lines) and the extension of their foliage (dashed lines).
As can be seen in figure 2, the boundary wire 220 has been laid so that so- called islands are formed around the trees" trunks and the house (H). This requires that more boundary wire is used, than if the work area was without such obstacles. It should be noted that any distances between wires are greatly eXaggerated in this application in order to make the distances visible in the drawings. In a real-life installations the boundary wire is usually laid so that there is not distance between the wire going out and the wire coming back (distance = 0). This allows the robotic work tool l00 to cross any such sections as the magnetic field emitted by the wire going out cancels out the magnetic field emitted by the wire coming back.
The work area 205 is in this application eXemplified as a garden, but can also be other work areas as would be understood. The garden contains a number of obstacles (O), eXemplified herein by a slope (S), a rock (R), a number (3) of trees (T) and a house structure (H). The trees are marked both with respect to their trunks (filled lines) and the extension of their foliage (dashed lines).
In some embodiments the robotic work tool is arranged or configured to traverse and operate in a work area that is not essentially flat, but contains terrain that is of varying altitude, such as undulating, comprising hills or slopes or such. The ground of such terrain is not flat and it is not straightforward how to determine an angle between a sensor mounted on the robotic work tool and the ground. The robotic worktool is also or alternatively arranged or configured 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 alternatively arranged or configured to traverse and operate in a work area that contains obstacles that are overhanging, i.e. obstacles that may not be detectable from the ground up, such as low hanging branches of trees (T) or bushes. Such a garden is thus not simply a flat lawn to be mowed or similar, but a work area of unpredictable structure and characteristics. The work area 205 eXemplified with referenced to figure 2, may thus be such a non-uniform work area as disclosed in this paragraph that the robotic work tool is arranged to traverse and/or operate in. This is an example of a work area or garden where some robotic lawnmowers are configured to work within.
The work area may also comprise a passage P that leads from one area of the work are 205 to another area. The passage need not be a specific corridor, or path, but can be any part of the work area that is narrow compared to the width of the robotic work tool. The passage is shown in figure 3 as having straight and parallel sides, but it should be noted that the sides of the passage may have any shape or form.
It should be noted that even though the teachings herein will be mainly eXemplified and discussed as relating to traversing a passage, they may also be applied to general traversal of a part of a work area, especially work areas with uneven or irregular sides, or even a whole work area.
Figure 3 shows a schematic view of a passage P of a general work area 205. As mentioned above, the passage P may represent any part of a work area. The passage has two sides Sl, S2 and two ends EPl and EP The robotic work tool l00 is configured to follow a side at a given distance d utilizing the magnetic sensors l70. This is achieved by comparing the signal strength received by two or more sensors l70 as is known to a skilled person. This provides for an accurate deterrnination of the distance d to the boundary wire 230 assumingly being laid in or close to the corresponding side. In one embodiment the boundary wire is laid at the distance from the side, whereby the robotic work tool following the side t the distance is actually following the boundary wire at a 0 distance.Figure 4 shows a flowchart of a general method according to the teachings herein. A manner of operating a robotic work tool 100 according to the teachings herein Will be described with simultaneous reference to figures 3 and In figure 3 a novel and beneficial operating path is indicated by the dashed arrows. The robotic work tool l00 is configured to traverse through and operate within a passage P (also applicable to other parts of the work area) by following 4l0 a first side at a first distance. And, as the robotic work tool l00 deterrnines 420 that an end EPl/EP2 of the passage P has been reached, the robotic work tool tums around 430 and follows 440 the first side Sl at a second or next distance d (a next distance indicating a lap where the robotic work tool follows the side farther away from the side than the previous distance). It should be noted that only the second distance d is specifically marked in the figure to not clutter the illustration, but it would be clear to a skilled person that the other distances are clearly illustrated even if not being specifically referenced.
This is repeated at next distances until the robotic work tool l00 deterrnines 450 that it is at or in a middle M of the passage P. The middle M may be defined as a line or as an area. More details on this will be discussed in the below. As it is deterrnined 450 that the robotic work tool l00 is in the middle and it is deterrnined 455 that an end EPl, EP2 of the passage P is reached, the robotic work tool tums around, proceeds 460 to the other or second side S2 of the passage P and follows 470 the second side S2 at the first distance and then at a next distance 480, which procedure is repeated until the robotic work tool reaches the middle M again 485 upon which time the robotic work tool l00 optionally leaves 490 the passage P or performs another task.
Such a systematic traversal of the passage (or other work area) has the benefits that it ensures a sufficient and proper operation in the area, as all of it is covered, without risking that the robotic work tool l00 is not able to perform any tums (as the tums are made in the open areas at the ends of the passage).
As a skilled person would notice when observing figure 3, there may be some overlap of a work tool, such as a cutting blade, in the middle which area may be serviced twice or doubly. In some embodiments the robotic work tool l00 is thus configured to operate at least partially overlapping in the middle of the passage toensure that the middle is properly covered. In figure 3 this is specifically illustrated by the schematic representations of two cutting discs" circumference referenced Cl and C As can be seen, the two circumferences (may) overlap in the middle. Likewise, by increasing the distances d by an amount smaller than or equal to a circumference of a work tool, such as a cutting disc, a sufficient operation in the area can be ensured, such as through an overlap between passings (laps of following a side).
As discussed in the above, the robotic work tool 100 may be configured to determine that an end of a passage has been reached in different manners. The use of magnetic sensors may not give enough of an indication as they basically only give a distance to a boundary wire. However, the robotic work tool 100 may utilize a deduced reckoning navigation sensor 180, a beacon navigation sensor 190, a satellite navigation sensor 190 possibly in combination with a beacon navigation sensor to determine a location relative an end point. As such sensors may not be as accurate as the magnetic sensors when it comes to deterrnining an exact location or distance, they may beneficially be used in combination with the magnetic sensors, where the magnetic sensors 170 are used to ensure that an accurate distance to the side is maintained (either alone or supplementing the navigation sensors) while the navigation sensors 180/ 190 (alone or in combination) are used to determine that an end of the passage P is reached possibly in combination with a map application stored in the memory 120 of the robotic work tool 100. As this does not require the same accuracy the navigation sensors may be used beneficially even if not being able to provide a high accuracy.
The robotic work tool 100 is in some embodiments further arranged to determine that it is at or in the middle M of the passage utilizing the navigation sensors possibly in combination with a map application stored in the memory 120 of the robotic work tool 100. IN an alternative or supplemental embodiment the robotic work tool 100 is arranged to determine that it is at or in the middle M of the passage utilizing the magnetic sensors 170. If two (or more) sensors are arranged at different distances to a boundary wire, such as the two front sensors 170-1, 170-2 of the robotic work tool 100 in figure 1B will be when following the side as in figure 3, the two sensors will receive signals from the boundary wire 220 at both sides S1, S2 at the same time, but at different signal levels. As the sides S1, S2 are comparatively close to one another (compared to the speed of light), the two signals will be seen as the same signal by a magnetic sensor 170. However, - in the example of figure 3 and Where the robotic work tool 100 is in the first illustrated location L1, the magnetic sensor closest to the first side S1 (i.e sensor 170-1 in figure lB), will receive a higher signal strength than the other sensor (i.e sensor 170-2 in figure 1B). Whereas at the second location indicated L2 the opposite signal strengths will be received, where sensor 1702 in figure 1B will receive a higher signal strength than sensor 170-1. By comparing a first signal strength received by a first sensor (for example 170-1 in this illustrative descriptive example) with a second signal strength received by a second sensor (for example 170-2) it is possible to determine which side of the middle the robotic work tool 100 is. As the relationship changes, the robotic work tool has crossed the middle M.
As the robotic work tool may tum and have a different sensor closer to the seide than before the turn, the robotic work tool need keep track of which side of the robotic work tool is closest to the side at any given time, such as through a turn, or at least when following a side, to know how to differentiate between a turning and a crossing of the middle, as the relationship between received signal strengths will change in both instances. The robotic work tool 100 is thus configured in some embodiments to adapt the determination or comparison of received signal strengths based on which sensor is closest to the side being followed. In some embodiments, the adaptation is done at each turn. In some embodiments the adaptation is based on the deduced reckoning navigation sensor Figure 5A shows an alternative passage, where the sides S1, S2 are not parallel. In the example of figure 5A the sides are not even the same. As can be seen, the robotic work tool is still able to cover the whole area without missing any portions by first following one side, from the side and in towards the middle M, and then following the other side, from the side and in towards the middle M by successively increasing the distance the side S1, S2 is followed at.
In the example of figure 5A there will be a portion in the middle where operation may not be effectively provided (as indicated by the circumferences Cl, Cnot overlapping). To avoid such situations the robotic work tool 100 is, in someembodiments, configured to provide an additional following or lap in the middle. This is illustrated in figure SB where the additional lap is marked by a thicker line.
In some embodiments, the robotic work tool 100 is configured to perform an additional lap at the end of the second traversal as in figure SB. In some embodiments, the robotic work tool l00 is configured to perform an additional lap at the end of the first traversal. And, in some embodiments, the robotic work tool l00 is configured to perform an additional lap both at the end of the first traversal and at the end of the second traversal.
The robotic work tool l00 is in some embodiments configured to determine to make an additional lap based on the shape of the side. If the side is irregularly shape (such as having a sideways extension and/or a total tuming radius (accumulated turnings) eXceeding a threshold level, an additional lap is performed. The determination may be made at the end of each traversal (i.e as it is determined that the middle M is reached), at the end of the first traversal, or at the end of the last traversal.
A traversal here being the laps performed up until it is determined that the middle has been reached, possibly including the last lap.
Figure 6A shows a schematic illustration of a passage having two sides, Sl and S2, where four zones Zl-Z4 are indicated by dashed lines. Figure 6B shows a graph of the received signal strength P as a graph based on distance from a side. The outerrnost zones, Zl, Z4 indicate an area close to the side or rather boundary wire where the received signal strength starts to drop. 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 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 perform the laps (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 l00 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. Altematively the first distance d atWhich the robotic work tool 100 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, S As discussed above, the robotic work tool is able to detect a passage from zone 2 Z2 to zone 3 Z3 that is a crossing of the middle M, 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 turn 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.

Claims (16)

1. 1. A robotic work tool (100) configured to operate in a work area (205), the robotic work tool (100) comprising Mjgšpa controller (110) configured to š v: I cause the robotic work tool to follow (410) a first side (S1) of the work area (205) at a distance for the first side (S1); determine (420) that an end (EP1, EP2) has been reached and in response thereto cause the robotic work tool to make a turn (430) and follow (440) the first side (S1) of the work area (205) at a next distance; deterrnine that a middle (M) has been reached (450) and in response thereto cause the robotic work tool to proceed to a second side (S2) and follow (470) the second side (S2) of the work area (205) at a first distance for the second side (S2); deterrnine that an end (EP1, EP2) has been reached and in response thereto cause the robotic work tool to make a turn and follow (480) the second side (S2) of the work area (205) at a next distance, wherein the first distances are smaller than the next
2. The robotic work tool (100) according to claim 1, wherein the controller (110) is further configured to cause the robotic work tool to proceed to second side (S2) after it is deterrnined (455) that an end is reached. The robotic Work tool (100) according to any preceding claim, Wherein the controller (110) is further configured to repeat following the first side (S1) and/or the second side (S2) at a next distance until it is determined that the middle (M) is reached. The robotic Work tool (100) according to any preceding claim, Wherein the controller (110) is further configured to perform an additional lap as the middle (M) is reached. The robotic Work tool (100) according to claim Wherein the controller (110) is further configured to perform an additional lap as the middle (M) is reached from the first side (S 1). The robotic Work tool (100) according to claim or Wherein the controller (110) is further configured to perform an additional lap as the middle (M) is reached from the second side (S2). The robotic Work tool (100) according to claim or Wherein the controller (110) is further configured to determine Whether to perform the additional lap or not based on a shape of the first side (S1) and/or a shape of the second side (S2). The robotic Work tool (100) according to any preceding claim comprising a satellite navigation sensor (190), Wherein the controller (110) is further configured to determine that the end is reached based on the satellite navigation sensor (190). The robotic Work tool (100) according to any preceding claim comprising a deduced reckoning navigation sensor (180), Wherein the controller (110) is further configured to determine that the end is reached based on the deduced reckoning navigation sensor (180). The robotic Work tool (100) according to any preceding claim, Wherein the first distances are the same. The robotic Work tool (l00) according to any preceding claim, Wherein the first distance is larger than a zone Where a signal strength is reduced due to a polarity change (Zl, Z4). The robotic Work tool (l00) according to any preceding claim, Wherein the next distance is increased by an amount smaller than or equal to the Width of a Work tool comprised in the robotic Working tool (l00). The robotic Work tool (l00) according to any preceding claim, Wherein the Work area (205) comprises terrain that is of varying altitude; obstacles that are not easily discerned from the ground; and/or obstacles that are overhanging. The robotic Work tool (l00) according to any preceding claim, Wherein the robotic Work tool (l00) is a robotic laWnmoWer: The robotic Work tool (l00) according to any preceding claim, Wherein the first side (Sl) and/or second side (S2) is a side of a passage (P) comprised in the Work area (205). A method for use in a robotic Work tool (l00) configured to operate in a Work area (205), the method comprising following (4l0) a first side (Sl) of a Work area (205) at a distance for the first side (Sl);determining (420) that an end (EPl, EP2) has been reached and in response thereto making a turn (430) and following (440) the first side (Sl) of the Work area (205) at a next distance; determining that a rr1iddle (M) has been reached (450) and in response 5 thereto proceeding to a second side (S2) and following (470) the second side (S2) of the Work area (205) at a first distance for the second side (S2); determining that an end (EPl, EP2) has been reached and in response thereto make a turn and follow (480) the second side (S2) of the Work area (205) at a next distance, Wherein the first distances are smaller than the next distances,__ l0
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