NAVIGATION FOR A ROBOTIC LAWNMOWER SYSTEM

A method for use in a robotic lawnmower system comprising a robotic lawnmower arranged to operate in an operational area based on the satellite navigation sensor, determining that the robotic lawnmower is in a satellite shadowed area and in response thereto querying the map application for a reference object, and navigate to the reference object based on the deduced reckoning sensor, determining that the reference object has been reached based on the object sensor and, if so, confirming a new position of the robotic lawnmower, determining that the robotic lawnmower is not in the satellite shadowed area and in response thereto again operate based on the satellite navigation sensor.

TECHNICAL FIELD

This application relates to a robotic lawnmower and in particular to a system and a method for providing an improved navigation for robotic lawnmowers in such a system.

BACKGROUND

Automated or robotic lawnmowers are becoming increasingly more popular and so is the use of the robotic lawnmower in various types of operational areas. Furthermore, there is also a trend for satellite navigation and virtual borders for such robotic lawnmowers and specifically for performing (sophisticated) patterns in the grass or other work that requires high accuracy. However, sometimes the robotic lawnmowers are not able to properly navigate the pattern, especially in areas where there are many structures or foliage.

Thus, there is a need for an improved manner of navigating with high accuracy, especially in areas where there are many structures or foliage.

SUMMARY

The inventors are proposing to achieve this by maneuvering the robotic lawnmower to reference objects having known positions and there (re) confirm the robotic lawnmower's position and allow to it continue operating based on the confirmed position.

a. It is therefore an object of the teachings of this application to overcome or at least reduce those problems by providing a robotic lawnmower system comprising a robotic lawnmower arranged to operate in an operational area, the robotic lawnmower comprising a satellite navigation sensor, a deduced reckoning sensor, an object sensor, a memory storing a memory application, and a controller configured for causing the robotic lawnmower to operate in the operational area based on the satellite navigation sensor, determining that the robotic lawnmower is in a satellite shadowed area and in response thereto querying the map application for a reference object, causing the robotic lawnmower to navigate to the reference object based on the deduced reckoning sensor, determining that the reference object has been reached based on the object sensor and, if so, confirming a new position of the robotic lawnmower, determining that the robotic lawnmower is not in the satellite shadowed area and in response thereto causing the robotic lawnmower to again operate in the operational area based on the satellite navigation sensor.

This has the benefit that the robotic lawnmower is enabled to navigate also in satellite shadowed areas with a high accuracy, as the position is again and again confirmed.

Further embodiments are as in the following detailed description and as per the appended patent claims.

It is also an object of the teachings of this application to overcome the problems by providing a method for use in robotic lawnmower system comprising a robotic lawnmower arranged to operate in an operational area, the robotic lawnmower comprising a satellite navigation sensor, a deduced reckoning sensor, an object sensor, and a memory storing a memory application, wherein the method comprises causing the robotic lawnmower to operate in the operational area based on the satellite navigation sensor, determining that the robotic lawnmower is in a satellite shadowed area and in response thereto querying the map application for a reference object, causing the robotic lawnmower to navigate to the reference object based on the deduced reckoning sensor, determining that the reference object has been reached based on the object sensor and, if so, confirming a new position of the robotic lawnmower, determining that the robotic lawnmower is not in the satellite shadowed area and in response thereto causing the robotic lawnmower to again operate in the operational area based on the satellite navigation sensor.

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.

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.

FIG.1shows a schematic overview of a robotic lawnmower100. The robotic lawnmower100may be a multi-chassis type or a mono-chassis type (as inFIG.1). 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 1 meter for large robots arranged to service for example airfields.

It should also be noted that the robotic lawnmower is a self-propelled robotic lawnmower, capable of autonomous navigation within a work area, where the robotic lawnmower propels itself across or around the work area in a pattern (random or predetermined).

The robotic lawnmower100has a main body part140, possibly comprising a chassis140and an outer shell140A, and a plurality of wheels130(in this example four wheels130, but other number of wheels are also possible, such as three or six).

The main body part140substantially houses all components of the robotic lawnmower100. At least some of the wheels130are drivably connected to at least one electric motor155powered by a battery150. It should be noted that even if the description herein is focused on electric motors, combustion engines may alternatively be used, possibly in combination with an electric motor. In the example ofFIG.1, each of the wheels130is connected to a common or to a respective electric motor155for driving the wheels130to navigate the robotic lawnmower100in different manners. The wheels, the motor155and possibly the battery150are thus examples of components making up a propulsion device. By controlling the motors155, the propulsion device may be controlled to propel the robotic lawnmower100in a desired manner, and the propulsion device will therefore be seen as synonymous with the motor(s)150.

It should be noted that wheels130driven by electric motors is only one example of a propulsion system and other variants are possible such as caterpillar tracks.

The robotic lawnmower100also comprises a controller110and a computer readable storage medium or memory120. The controller110may 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 memory120to be executed by such a processor. The controller110is configured to read instructions from the memory120and execute these instructions to control the operation of the robotic lawnmower100including, but not being limited to, the propulsion and navigation of the robotic lawnmower.

The controller110in combination with the electric motor155and the wheels130forms the base of a navigation system (possibly comprising further components) for the robotic lawnmower, enabling it to be self-propelled as discussed.

The controller110may be implemented using any suitable, available processor or Programmable Logic Circuit (PLC). The memory120may be implemented using any commonly known technology for computer-readable memories such as ROM, FLASH, DDR, or some other memory technology.

The robotic lawnmower100is further arranged with a wireless communication interface115for communicating with other devices, such as a server, a personal computer, a smartphone, the charging station, and/or other robotic lawnmowers. 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 lawnmower100also comprises a grass cutting device160, such as a rotating blade160/2driven by a cutter motor160/1.

The robotic lawnmower100further comprises at least one satellite signal navigation sensor175configured to provide navigational information (such as position) based on receiving one or more signals from a satellite-possibly in combination with receiving a signal from a beacon. In some embodiments the satellite navigation sensor is a GPS (Global Positioning System) device or other Global Navigation Satellite System (GNSS) device. In some embodiments the satellite navigation sensor is a RTK sensor.

The robotic lawnmower100may also or alternatively comprise deduced reckoning sensors180. 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.

The robotic lawnmower100is 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 memory120of the robotic lawnmower100. The map application may be generated or supplemented as the robotic lawnmower100operates or otherwise moves around in the work area205. 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. The robotic lawnmower100is in some embodiments arranged to navigate according to the map based on the satellite navigation sensor175and/or the deduced reckoning sensors180.

For F enabling the robotic lawnmower100to navigate with reference to a boundary wire (referenced220inFIG.2) emitting a magnetic field caused by a control signal transmitted through the wire, the robotic lawnmower100is in some embodiments configured to have at least one magnetic field sensor170arranged to detect the magnetic field and for detecting the wire and/or for receiving (and possibly also sending) information to/from a signal generator.

The robotic lawnmower100also comprises one or more than one object sensors185. In some embodiments the object sensor185is a collision sensor which is configured to detect a collision (possibly through a change in geometry of the housing of the robotic lawnmower100or by detecting a deceleration pattern specific to collisions through the use of a gyro or other inertial measurement unit (IMU))) with an object. Collision sensors are generally known and no further details will be given. In some alternative or additional embodiments the object sensor185is a visual sensor, such as an image sensor which is configured to detect an object by capturing one or more images and performing image analysis on these images. Such image sensors are generally known and no further details will be given. In some alternative or additional embodiments the object sensor185is a distance sensor, such as laser or radar, which is configured to detect an object by detecting that the distance to something in front of the robotic lawnmower is below a threshold distance. Such distance sensors are generally known and no further details will be given.

FIG.2shows a robotic lawnmower system200in some embodiments. The schematic view is not to scale. The robotic lawnmower system200comprises one or more robotic lawnmowers100according to the teachings herein. It should be noted that the operational area205shown inFIG.2is simplified for illustrative purposes. The schematic view ofFIG.2also illustrates a graphic representation of a map application120A stored in the memory of the robotic lawnmower100as discussed in the above.

The robotic lawnmower100is also or alternatively arranged to operate according to a virtual boundary referenced220specified in the map application120A based on the satellite navigation sensor(s)175, and/or the deduced reckoning sensors180.

The example ofFIG.2also shows a satellite to represent the various satellites referenced S necessary for establishing or determining a position using satellite navigation. Also, the satellite ofFIG.2is taken to also represent various types of beacons that may be utilized in order to increase the accuracy and/or coverage of a satellite navigation system, such as in Real Time Kinetic (RTK) systems.

The robotic lawnmower system comprises, in some embodiments, a boundary wire also referenced220through which a control signal is transmitted thereby generating a magnetic field, and which magnetic field is sensed by sensor(s) (170) in the robotic lawnmower100. In some embodiments the control signal is generated by a signal generator comprised in a station. The boundary may thus in some embodiments act as a supplement to the virtual boundary.

As withFIG.1, the robotic lawnmower(s) is exemplified by a robotic lawnmower, whereby the robotic lawnmower system may be a robotic lawnmower system or a system comprising a combination of robotic lawnmowers, one being a robotic lawnmower, but the teachings herein may also be applied to other robotic lawnmowers adapted to operate within a work area.

In some embodiments the robotic lawnmower 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 lawnmower and the ground. The robotic lawnmower is also or alternatively arranged or configured to traverse and operate in a work area that contains obstacles that are not easily discerned from the ground. Examples of such are grass or moss-covered rocks, roots or other obstacles that are close to ground and of a similar colour or texture as the ground. The robotic lawnmower 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 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 area205exemplified with referenced toFIG.2, may thus be such a non-uniform work area as disclosed in this paragraph that the robotic lawnmower is arranged to traverse and/or operate in.

As is shown inFIG.2there may be obstacles such as houses (referenced H), structures, trees (referenced T), rocks (referenced R) to mention a few examples that block signal reception in certain areas, hereafter referred to as shadowed areas. InFIG.2such obstacles are indicated and referenced H (as in house). Additionally the boundary may comprise one or more than one such obstacles, for example a wall referenced W or fence.

Returning to the map application, the map application is in some embodiments configured to store the location of one, some or all of these obstacles. The map application120thus contain one or more than one stored or known obstacles and the robotic lawnmower100thus has knowledge of the position of one or more than one of the obstacles in the operational area, be it trees, stones, structures or walls. In some embodiments the boundary wire is also a known obstacle.

FIG.3is a schematic view of a robotic lawnmower system200as inFIG.2, the robotic lawnmower system200comprising one or more robotic lawnmower(s)100as discussed in relation toFIGS.1and2.

As is illustrated inFIG.3, there may be areas where the satellite reception is insufficient to determine a position of the robotic lawnmower100accurately. As a skilled person would understand determining a position utilizing satellite navigation (including possibly beacon-based systems) requires the reception of several reference signals transmitted from the satellites and/or beacons. For example, to establish a position in three dimensions requires 4 signals. However, in order to accurately determine such a position requires many more signals, and most contemporary satellite navigation systems utilize many more satellites, for example 12 or 16 signals. As a skilled person would also understand there may be areas where one or more of the satellites (and/or beacons) are blocked by for example structures or foliage. In such areas, the received signals are not of a sufficiently high quality—as regards the number of signals received and/or the signal level that the signals are received at. Such an area will hereafter be defined as an area where the received satellite signals (including any beacon signals) are received at a signal quality level falling under a threshold acceptance level and be referred to as a satellite shadowed area. The robotic lawnmower100is in some embodiments configured to determine that the robotic lawnmower100is in such an area by determining that the number of reference (satellite or beacon) signals received fall under an acceptance number and/or by determining that the quality of received reference (satellite or beacon) signals fall under an acceptance level.

Returning toFIG.3, in such satellite shadowed areas, the robotic lawnmower100may be unable to determine its position adequately. In some prior art systems, the robotic lawnmower100is then configured to supplement the navigation based on for example deduced reckoning. However, deduced reckoning suffers from a number of drawbacks and can thus not be relied upon and the prior art systems therefore propose to leave the satellite shadowed area as soon as possible and then to reconfirm the position of the robotic lawnmower100and continue operation, possibly after calibrating the deduced reckoning sensors. However, the inventors have proposed an alternative to such systems which enables for a better servicing of the satellite shadowed areas that does not require the robotic lawnmower100to (hurriedly) leave the satellite shadowed area.

InFIG.3there is such a satellite shadowed area exemplified behind the house H and indicated by the dotted area and referenced SSA, where it is illustrated how a signal from the satellite S is blocked by the house. Any robotic lawnmower100operating in the satellite shadowed area will thus suffer from a reduced accuracy when operating according to a prior art system.

FIG.4Ais a schematic view of a robotic lawnmower system200as inFIG.2, the robotic lawnmower system200comprising one or more robotic lawnmower(s)100as discussed in relation toFIGS.1and2, wherein the robotic lawnmower100is configured to operate as per the teachings herein.

As the robotic lawnmower100determines that the accuracy for determining a location is reduced, such as by determining that robotic lawnmower is in a satellite shadowed area, the robotic lawnmower100notes its position. In some embodiments the position is the last accurately determined position. In some embodiments the position is the current position. In some embodiments the robotic lawnmower100also notes a budget distance. In some embodiments the budget distance is determined based on the length of the robotic lawnmower100, for example 1 or 2 times the length of the robotic lawnmower. In some embodiments the budget distance is determined based on the accuracy of the satellite navigation, for example 1, 5 or 10 meters or any range there inbetween.

The robotic lawnmower100then queries the map application for a known obstacle. In some embodiments the robotic lawnmower100queries the map application120A for a known obstacle within the budget distance. In some embodiments the robotic lawnmower100queries the map application120A for a known obstacle within for example 1 or 2 times the length of the robotic lawnmower. In some embodiments the robotic lawnmower100queries the map application120A for a known obstacle within for example 1, 5 or 10 meters or any range there inbetween. In some embodiments the robotic lawnmower100queries the map application120A for the known obstacle being closest to the robotic lawnmower100. In some embodiments the robotic lawnmower100queries the map application120A for the known obstacle being closest to the robotic lawnmower100in the direction of travel (+/−90 degrees) for the robotic lawnmower100. the known obstacle being closest to the robotic lawnmower100in the direction or path of an intended operating pattern.

The queried obstacle is then used or selected as a reference object for the robotic lawnmower100, and the robotic lawnmower100continues to operate for a distance or time. In some embodiments the operating distance is equal to or less than the budget distance. In some embodiments the operating distance is equal to or less than for example 1 or 2 times the length of the robotic lawnmower. In some embodiments the operating distance is equal to or less than for example 1, 5 or 10 meters or any range there inbetween. No matter what the operating distance is, the operating distance includes the distance required to travel to the reference object. The robotic lawnmower100is thus enabled to continue operating (for a distance) even in the satellite shadowed area. Unless the satellite reception becomes reliable again (i.e. that the robotic lawnmower100determines that it is no longer operating in a satellite shadowed area), the robotic lawnmower100moves to the reference object.

In the example ofFIG.4Athe obstacle closest to the robotic lawnmower100is the house H, and is assumed to be the reference object selected. The robotic lawnmower100ofFIG.4Ais thus enabled to continue operating in its intended direction for a distance and is then controlled to navigate to the reference object as is indicated by the arrow inFIG.4A.

During this continued navigation the robotic lawnmower100is in some embodiments configured to operate according to the deduced reckoning sensors180.

As the robotic lawnmower100approaches or reaches the reference object the robotic lawnmower100determines that the reference object has been reached through the use of the object sensor185. How the robotic lawnmower100determines that the reference object has been reached depends on the type of obstacle sensor used. As an example, if the obstacle sensor185is a collision sensor, the robotic lawnmower100determines that the reference object has been reached by detecting a collision. As another example, if the obstacle sensor185is an image sensor, the robotic lawnmower100determines that the reference object has been reached by identifying the reference object through image processing. As another example, if the obstacle sensor185is a distance sensor, the robotic lawnmower100determines that the reference object has been reached by detecting that the distance to any object in front of the robotic lawnmower100has fallen under a detection distance, for example 10, 20 or 50 cm.

In some embodiments the robotic lawnmower100is further configured to determine that the reference object was reached by determining that the reference object is at an expected position. In some such embodiments the robotic lawnmower100is configured to determine that the reference object is at the expected position by determining the current position of the robotic lawnmower100(based on the deduced reckoning sensors180) and comparing to the stored position for the reference object as per the map application120A. In some alternative or additional such embodiments, the robotic lawnmower100is configured to determine that the reference object is at the expected position by determining a travelled distance and comparing this to a determined expected distance to be travelled to reach the reference object, i.e. the distance from the previous position of the robotic lawnmower100to the reference object (along an intended path to the reference object).

As the robotic lawnmower determines that the reference object has been reached, the robotic lawnmower100determines its (new) position and queries the map application for a further reference object based on its new position. The new position can be confirmed or determined more accurately as the robotic lawnmower100knows that the new position is adjacent the reference object.FIG.4Bshows an example where the robotic lawnmower100has reached the reference object (the house) and confirmed its position. As the position has been confirmed the operating distance (in some embodiments the budget distance) is renewed and the robotic lawnmower100continues operating seeking out the further reference object as for navigating to the (first) reference object discussed above.

In the example ofFIG.4Bthe robotic lawnmower100reaches the end of the satellite shadowed area and continues operation along the intended operating pattern (without the reference object).

If the reference object is determined to not be at the expected position, the robotic lawnmower100halts operating and possibly issues an error message in some embodiments. In some alternative embodiments, where the robotic lawnmower100determines that the robotic lawnmower100still is allowed to navigate a remainder of the operating distance, the robotic lawnmower100is configured to query the map application for a further reference object and attempt to navigate to the further reference object.FIG.4Cshows an example where the robotic lawnmower100encounters or reaches an object (in this example a rock R) at an unexpected position. In this example, and in some embodiments the robotic lawnmower100is configured to determine that the path to the reference object is unsuccessful and query the map application for a further reference object.FIG.4Dshows the example where the robotic lawnmower100is attempting to reach the other known obstacle, the wall W, being a further reference object.

In some alternative embodiments the robotic lawnmower100is configured to determine a new path to the reference object and attempt the new path.FIG.4Eshows the example where the robotic lawnmower100is attempting to reach the reference object through an alternative path.

FIG.5shows a flowchart for a general method according to herein. The method is for use in a robotic lawnmower as inFIG.1in a manner as discussed above in relation toFIGS.4A,4B,4C,4D and4E. The method comprises the robotic lawnmower100operating510in the operational area205possibly according to an intended pattern. As the robotic lawnmower100determines520that the robotic lawnmower100is in a satellite shadowed area, the robotic lawnmower100queries530the map application for a reference object as discussed above. The robotic lawnmower then navigates540to the reference object for an (allowed) operating distance. The robotic lawnmower100then determines550that the reference object has been reached and if so, confirms560the position of the robotic lawnmower100. In some embodiments the deduced reckoning sensors are also calibrated based on the confirmed new position as part of the confirmation of the position.

In some embodiments the allowed distance is renewed (as in increased)565as the position is confirmed. In some embodiments the allowed distance is increased by being set as discussed above. In some embodiments the allowed distance is increased by being increased by the distance travelled since the last confirmed position (i.e. the distance travelled to reach the reference object).

As the reference object has been reached, the robotic lawnmower100queries540for a further reference object and continues as per above and as indicated by the arrow inFIG.5.

In some embodiments, and if the robotic lawnmower determines that the reference object has not been reached at the expected position (arrow referenced NO inFIG.5), the robotic lawnmower queries for a (further) reference object. In some embodiments this is continued until the allowed distance is consumed.

The navigating and reconfirming of positions is continued while the robotic lawnmower100determines that the robotic lawnmower100is in the satellite shadowed area, and as the robotic lawnmower100again receives reliable satellite reception, the robotic lawnmower100continues operation570.