ROBOTIC LAWN MOWER WITH ENHANCED CUTTING PROPERTIES

The present disclosure relates to a robotic lawn mower (100) comprising a body (140), at least two drive wheels (130a, 130b) arranged along a drive wheel axis (145) with a center (146) that is positioned between the drive wheels (130a, 130b). The robotic lawn mower (100) further comprises a control unit (110) and at least a first rotatable grass cutting disc (160). When the robotic lawn mower (100) is approaching a boundary (220) of an operation area (610), the control unit (110) is adapted to          position the robotic lawn mower (100a) such that there is a shortest distance (ds) between the center (146) and the boundary (220), and to     control the drive wheels (130a, 130b) to turn in mutually different directions such that the second end portion (102) of the robotic lawn mower (100a, 100b, 100c) performs an arcuate movement along a cutting arc (210), enabling the first cutting disc (160) to cut grass within the cutting arc (210).       The boundary (220) is positioned between a border (139) and the operation area (610), and where the shortest distance (ds) admits the cutting arc (210) to have a closest arc portion (211) that is closest to the border (139) without passing the border (139).

TECHNICAL FIELD

The present disclosure relates to a robotic lawn mower that is adapted to operate within a certain operation area. The robotic lawn mower comprises a body, at least two drive wheels, at least one swivelable wheel, a control unit adapted to control the operation of the robotic lawn mower, and a first rotatable grass cutting disc having a rotation axis.

BACKGROUND

Robotic lawn mowers such as for example robotic lawn mowers are becoming increasingly more popular. A robotic lawn mower is usually battery-powered by means of a rechargeable battery and is adapted to cut grass on a user's lawn automatically. The robotic lawn mower can be charged automatically without intervention of the user, and does not need to be manually managed after being set once.

In a typical deployment a work area, such as a garden, park, sports field, golf court and the like, the work area is enclosed by a boundary that can be in the form of a boundary wire with the purpose of keeping the robotic lawn mower 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 working tool is typically arranged with one or more sensors adapted to sense the control signal.

Alternatively, or as a supplement, the robotic lawn mower can be equipped with a navigation system that is adapted for satellite navigation by means of GPS (Global Positioning System) or some other Global Navigation Satellite System (GNSS) system, for example using Real Time Kinematic (RTK). A boundary does in this case not be defined by a physical wire, but by an imaginary boundary.

A problem associated with robotic lawn mowers is that they normally have a limited ability to cut grass close to objects and borders that may lie outside a cutting area boundary that may be defined by means of a boundary wire. That is, normally, the cutting unit is arranged at an underside of a lawn mower body of the robotic lawn mower and portions of the lawn mower body, and/or wheels attached thereto, may hinder the cutting unit from reaching grass close to objects and borders. If so, the cutting result is impaired because there will be uncut grass close to object such as trees, stones, furniture, building walls, and the like. At the same time, cutting outside a lawn edge should be prevented, irrespective of angle of approach towards a border.

SUMMARY

The object of the present disclosure is to provide means and a method for cutting grass close to objects and borders, while preventing cutting outside a border such as a lawn edge, irrespective of angle of approach towards a cutting area boundary.

This object is achieved by means of a robotic lawn mower comprising a body, at least two drive wheels that form a pair of drive wheels arranged along a drive wheel axis with a center, the center being positioned between the drive wheels in the pair. The robotic lawn mower further comprises at least one swivelable wheel, a control unit adapted to control the operation of the robotic lawn mower, at least a first rotatable grass cutting disc having a rotation axis. A first end portion is facing a forward travelling direction and a second end portion is facing a reverse travelling direction. When the robotic lawn mower, during grass cutting in an operation area, is approaching a boundary of the operation area, the control unit is adapted to position the robotic lawn mower such that there is a shortest distance between the center and the boundary, and to control the drive wheels to turn in mutually different directions such that the second end portion of the robotic lawn mower performs an arcuate movement along a cutting arc, enabling the first cutting disc to cut grass within the cutting arc.

The boundary is positioned between a border and the operation area, where the shortest distance admits the cutting arc to have a closest arc portion that is closest to the border without passing the border.

In this way, cutting the grass relatively close to a border is enabled without cutting outside the border irrespective of angle of approach for the robotic lawn mower.

According to some aspects, the control unit is adapted to position the robotic lawn mower such that there is a shortest distance between the center and the boundary by furthermore being arranged to control the robotic lawn mower to move towards the boundary such that the first end portion at least partly passes the boundary, where the boundary is determined to have a certain straight extension where the first end portion has crossed the boundary, and to determine a smallest angle between the forward travelling direction and the extension. If the smallest angle exceeds a certain threshold value, the control unit is adapted to control the robotic lawn mower to move back a certain rearward distance towards the operation area such there is a shortest distance between the center and the boundary.

This means that the robotic lawn mower can be positioned such that there is a shortest distance between the center and the boundary if a boundary wire is used for defining the boundary.

According to some aspects, if the smallest angle falls below the threshold value, the control unit is adapted to position the robotic lawn mower such that there is a shortest distance between the center and the boundary by furthermore being arranged to control the robotic lawn mower to move back towards the operation area. When the robotic lawn mower has moved a certain extended rearward distance that exceeds the rearward distance, there is a shortest distance between the center and the boundary.

In this way, if the smallest angle falls below the threshold value, cutting the grass relatively close to a border is enabled anyway without cutting outside the border by increasing the rearward distance to an extended rearward distance.

According to some aspects, if the smallest angle falls below the threshold value, the control unit is adapted to position the robotic lawn mower such that there is a shortest distance between the center and the boundary by furthermore being arranged to control the robotic lawn mower to move back towards the operation area such that the smallest angle between the forward travelling direction and the extension, when the first end portion passes the boundary, exceeds the threshold value, such that there is a shortest distance between the center and the boundary.

This means that the robotic lawn mower is controlled to move back towards the operation area in such a way that the smallest angle now exceeds the threshold value. Moving back in such a manner can be accomplished in many ways

According to some aspects, a center of the cutting arc is positioned along the drive wheel axis. According to some further aspects, a center of the cutting arc is positioned in the center of the drive wheel axis.

This is the case when the drive wheels are driven in different rotation directions and at the same rotation velocities by the first electric motor arrangement.

According to some aspects, the cutting arc has an angular extension that exceeds 180°, where the control unit is adapted to control the robotic lawn mower to continue moving when a second end center, constituting a rearmost point, that has followed the extension of the cutting arc has reached an end of the cutting arc.

This means that the robotic lawn mower will continue moving at an angle to the original angle of approach, away from the boundary. This in turn enables the robotic lawn mower to repeat the above procedure, performing arcuate movements, such that a continuous grass edge close to the boundary is cut. This can be performed in combination with cutting the rest of the grass on the lawn.

According to some aspects, when the robotic lawn mower has moved back towards the operation area such that there is a shortest distance between the center and the boundary, the center is positioned within the operation area.

This means that that before the robotic lawn mower performs an arcuate movement along a cutting arc, it has moved such that the center is positioned within the operation area.

According to some aspects, the control unit is adapted to position the robotic lawn mower such that there is a predetermined shortest distance between the center and the boundary. According to some further aspects, the control unit is adapted to position the robotic lawn mower by means of input derived from a navigation sensor arrangement comprised in the robotic lawn mower.

This means that the robotic lawn mower can be positioned for performing an arcuate movement along a cutting arc according to the above directly, without first having to detect a boundary wire and then move back to the position.

According to some aspects, the navigation sensor arrangement comprises at least one of satellite signal navigation sensor; and deduced reckoning sensors.

According to some aspects, the navigation sensor arrangement comprises deduced reckoning sensors that include visual sensors for Simultaneous Localization And Mapping (SLAM) navigation.

According to some aspects, the navigation sensor arrangement is adapted for navigation by means of active local radio beacons using Ultra Wide Band (UWB).

According to some aspects, the robotic lawn mower comprises at least two electric motor arrangements, where at least two drive wheels have a drive wheel axis with a center and are drivably connected to a first electric motor arrangement. At least one swivelable wheel has a corresponding swivel axis, where a swivel attachment axis, running through at least one swivel axis and being parallel to the drive wheel axis, is positioned between the second end portion and the drive wheel axis. The first cutting disc is drivably connected to a second electric motor arrangement, where the first cutting disc at least partly is positioned between the swivel attachment axis and the second end portion.

In this way, the first cutting disc is positioned such that it can move laterally in an arcuate manner when the drive wheels are driven in different rotation directions by the first electric motor arrangement. This enables the first cutting disc to reach relatively close to a border.

According to some aspects, the rotation axis is positioned between the swivel attachment axis and the second end portion when the rotation axis passes through the cutting disc.

In this manner, the cutting disc can easily follow the movement of the second end portion, in particular when the drive wheels are driven in different rotation directions by the first electric motor arrangement.

According to some aspects, the robotic lawn mower further comprises a first arcuate protective wall that at least partly runs along the second end portion, and at least one further arcuate protective wall. The protective walls extend from the body towards the ground during normal running, the protective walls being radially separated.

According to some aspects, the protective walls are partly positioned between the first cutting disc and the ground during normal running.

This means that the protective walls confer an injury protection for humans and animals that come close to the second end portion during normal running.

According to some aspects, the protective walls at least mainly follow respective protective wall arcs, where all protective wall arcs have a common center.

In this way, when the arcuate movement is performed, the grass will not be bent when moving between the protective walls.

According to some aspects, the common center is the center of a drive wheel axis.

The present disclosure also relates to methods, control unit arrangements and computer program products that are associated with above advantages.

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, apparatus, component, means, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, 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. Further features of, and advantages with, the present disclosure will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present disclosure may be combined to create embodiments other than those described in the following, without departing from the scope of the present disclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings. The different devices, systems, computer programs and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

FIG.1shows a top view of a robotic lawn mower100,FIG.2shows a bottom view of the robotic lawn mower100, andFIG.3shows a side perspective bottom view of the robotic lawn mower. The robotic lawn mower100has a first end portion101and a second end portion102, is adapted for a forward travelling direction F and a reverse travelling direction R. The first end portion101is facing the forward travelling direction F and the second end portion102is facing the reverse travelling direction R. The robotic lawn mower100comprises a body140, at least two drive wheels130a,130b,

that form a pair of drive wheels arranged along a drive wheel axis145with a center146, the center146being positioned between the drive wheels130a,130bin the pair. The robotic lawn mower100further comprises at least one swivelable wheel131a,131b, a control unit110adapted to control the operation of the robotic lawn mower100, at least a first rotatable grass cutting disc160having a rotation axis152. According to some aspects, least one swivelable wheel has a corresponding swivel axis153,154. The drive wheel axis145is an imaginary axis, not being constituted by a physical axle that connects the drive wheels.

According to some aspects, as illustrated in this example, the robotic lawn mower100comprises four wheels, two larger drive wheels130a,130band two smaller swivelable wheels131a,131bthat are in form of castor wheels and are arranged to swivel around a corresponding swivel axis153,154when the robotic lawn mower100is turning. For this purpose, the swivelable wheels131a,131bare connected to the body140by means of corresponding swivel wheel holders158a,158b, where, according to some aspects, it is the swivel wheel holders158a,158bthat swivel in relation to the body and are fixed in relation to the swivelable wheels131a,131b. The opposite is of course conceivable.

The robotic lawn mower100may be a multi-chassis type or a mono-chassis type. A multi-chassis type comprises more than one body parts that are movable with respect to one another. A mono-chassis type comprises only one main body part. In this example embodiment, the robotic lawn mower100is of a mono-chassis type, having a main body part140. The main body part140substantially houses all components of the robotic lawn mower100.

According to some aspects, the robotic lawn mower100also comprises at least two electric motor arrangements150,165(only schematically indicated inFIG.2) and at least one rechargeable electric power source such as a battery155(only schematically indicated inFIG.1) for providing power to the electric motor arrangements150,165. The battery155is arranged to be charged by means of received charging current from a charging station, received through charging skids156or other suitable charging connectors. Inductive charging without galvanic contact, only by means of electric contact, is also conceivable. The battery is generally constituted by a rechargeable electric power source155that comprises one or more batteries that can be separately arranged or be arranged in an integrated manner to form a combined battery.

The drive wheels130a,130b, having a drive wheel axis145with a center146and are drivably connected to a first electric motor arrangement150. The first electric motor arrangement150is adapted to drive the drive wheels130a,130bin the same rotation direction, or in different rotation directions, and at different rotational speeds. According to some aspects, the first electric motor arrangement150comprises two separate electrical motors, and according to some further aspects each such electric motor is mounted to a corresponding drive wheel130a,130b, for example in a corresponding drive wheel hub.

According to some aspects, the first cutting disc160is drivably connected to a second electric motor arrangement165that in this example is in the form of a cutter motor. According to some aspects, the first cutting disc160comprises a plurality of cutting knives157, in this example three cutting knives157are shown (only one indicated inFIG.2). The cutting disc160is at least partly positioned between the swivel attachment axis151and the second end portion102. This means that at least some part of the cutting disc160is positioned closer to the second end portion102than any part of the swivel attachment axis151.

In this way, the cutting disc160is positioned such that it can move laterally in an arcuate manner when the drive wheels130a,130bare driven in different rotation directions by the first electric motor arrangement150.

According to some aspects, the rotation axis152is positioned between the swivel attachment axis151and the second end portion102when the rotation axis152passes through the cutting disc160. In this manner, the cutting disc160can easily follow the movement of the second end portion102, in particular when the drive wheels130a,130bare driven in different rotation directions by the first electric motor arrangement150.

According to the present disclosure, with reference toFIG.6andFIG.9, when the robotic lawn mower100, during grass cutting in an operation area610, is approaching a boundary220of the operation area610, the control unit110is adapted to position the robotic lawn mower100asuch that there is a shortest distance dsbetween the center146and the boundary220. The control unit110is further adapted to control the drive wheels130a,130bto turn in mutually different directions such that the second end portion102of the robotic lawn mower100a,100b,100cperforms an arcuate movement along a cutting arc210, enabling the first cutting disc160to cut grass within the cutting arc210. The boundary220is positioned between a border139and the operation area610, and where the shortest distance dsadmits the cutting arc210to have a closest arc portion211that is closest to the border139without passing the border139.

In this context, the term shortest distance refers to a certain distance that runs the shortest way between the center146and the boundary220. The shortest distance has such properties that the cutting arc210has a closest arc portion211that is closest to the border139without passing the border139. According to some aspects, the shortest distance can be a predetermined distance, for example given a certain angle of approach towards the boundary220, alternatively the shortest distance can be an otherwise deduced distance, for example given a certain angle of approach towards the boundary220.

In this way, cutting the grass relatively close to a border139is enabled without cutting outside the border139irrespective of angle of approach for the robotic lawn mower100. In this context, a boundary is a cutting area boundary that according to some aspects is defined by means of a boundary wire, and a border139is in the form of an object or a lawn edge139, and these should not be passed by any part of the robotic lawn mower100. The cutting arc210has a closest arc portion211that is closest to the border139without passing the border139.

There is a border distance dB between the border139and the boundary220, the border distance dB for example being between 20 cm and 40 cm. Other values for the border distance dB are of course conceivable, and the distance dB may vary along the boundary220. The border139can thus be in many forms and still allow a relatively close cutting of the grass by means of robotic lawn mower100performing the arcuate movement according to the above.

According to some aspects, the control unit110is adapted to position the robotic lawn mower100asuch that there is a shortest distance dsbetween the center146and the boundary220by furthermore being arranged to control the robotic lawn mower100ato move towards the boundary220such that the first end portion101at least partly passes the boundary220, where the boundary220is determined to have a certain straight extension E where the first end portion101has crossed the boundary220. According some aspects, the control unit110is adapted to stop the robotic lawn mower100at this position.

The control unit110is further adapted to determine a smallest angle φA, φBbetween the forward travelling direction F and the extension E. This means that the robotic lawn mower100is approaching the boundary with a certain angle of incidence, inFIG.6a first angle of incidence, which corresponds to the smallest angle φA, and inFIG.9a second angle of incidence, which corresponds to the smallest angle φB.

According to some aspects, the boundary is in the form of a boundary wire220defining the operation area610for the robotic lawn mower100, where the robotic lawn mower100comprises at least two boundary wire sensors173A,173B,173C, three boundary wire sensors173A,173B,173C are schematically indicated inFIG.1. By means of the boundary wire sensors173A,173B,173C, the smallest angle φA, φBbetween the forward travelling direction F and the extension E can be determined by having knowledge of the robotic lawn mower's velocity and the time that passes between when different boundary wire sensors173A,173B,173C pass and detect the boundary wire220. This means that the boundary220is conferred a determined straight extension E at least where the boundary wire sensors173A,173B,173C pass the boundary wire220.

This means that the robotic lawn mower100acan be positioned such that there is a shortest distance dsbetween the center146and the boundary220for the case with a boundary wire defining the boundary.

According to some aspects, with reference also toFIG.7andFIG.8, if the smallest angle φAexceeds a certain threshold value, the control unit110is adapted to control the robotic lawn mower100ato move back a certain rearward distance drtowards the operation area610such there is a shortest distance dsbetween the center146and the boundary220. The robotic lawn mower100ais then in position, and the control unit110is adapted to control the drive wheels130a,130bto turn in mutually different directions such that the second end portion102of the robotic lawn mower100a,100b,100cperforms an arcuate movement along a cutting arc210, enabling the first cutting disc160to cut grass within the cutting arc210.FIG.7thus illustrates the robotic lawn mower100moving back according to a first example.

The wire sensors173A,173B,173C are adapted to sense a boundary wire control signal and/or at least one environment detection device170,171adapted to detect objects. In this example, radar transceivers170,171are provided and adapted to transmit signals and to receive reflected signals that have been reflected by an object. Other environment detection devices such as camera devices, ultrasonic devices and Lidar devices are of curse also conceivable, as alternatives or in any suitable combination.

The control unit110is adapted to control the environment detection device170,171and to control the speed and direction of the robotic lawn mower100in dependence of information acquired by means of the of the environment detection devices170,171and/or said wire sensor173A,173B,173C when the robotic lawn mower100is moving.

According to some aspects, with reference toFIG.9andFIG.10, if the smallest angle φB falls below the threshold value, the control unit110is adapted to control the robotic lawn mower100a′ to move back towards the operation area610. When the robotic lawn mower100a′ has moved a certain extended rearward distance drethat exceeds the rearward distance dr, there is a shortest distance ds′ between the center146and the boundary220, the robotic lawn mower100a′ is then in position and the control unit110is then adapted to control the drive wheels130a,130bto turn in mutually different directions such that the second end portion102of the robotic lawn mower100a,100b,100cperforms an arcuate movement along a cutting arc210, enabling the first cutting disc160to cut grass within the cutting arc210.FIG.10thus illustrates the robotic lawn mower100moving back according to a second example.

In this way, if the smallest angle φBfalls below the threshold value, cutting the grass relatively close to a border139is enabled anyway without cutting outside the border139by increasing the rearward distance drto an extended rearward distance dre.

According to some aspects, with reference toFIG.9,FIG.11,FIG.12,FIG.13andFIG.14, if the smallest angle φBfalls below the threshold value, the control unit110is adapted to control the robotic lawn mower100to move back towards the operation area610such that the smallest angle φC, φDbetween the forward travelling direction F and the extension E, when the first end portion101passes the boundary220, exceeds the threshold value, such that there is a shortest distance ds″, ds′″ between the center146and the boundary220.

This means that the robotic lawn mower100is controlled to move back towards the operation area610in such a way that the smallest angle φC, φDnow exceeds the threshold value. Moving back in such a manner can be accomplished in many ways, a few examples are disclosed below.

As illustrated inFIG.11andFIG.12, the robotic lawn mower100,100a″ is controlled to move in the reverse travelling direction R in an arcuate manner such that the smallest angle changes to a larger value φCthan the value φBat the original approach such that there is a shortest distance ds″ between the center146and the boundary220.FIG.11andFIG.12thus illustrate the robotic lawn mower100moving back according to a third example.

As illustrated inFIG.13andFIG.14, the robotic lawn mower100,100a′″ is controlled to first make a turn T and then move in the reverse travelling direction R in a straight manner such that the smallest angle changes to al larger value φDthan the value φBat the original approach such that there is a shortest distance ds′″ between the center146and the boundary220.FIG.13andFIG.14thus illustrate the robotic lawn mower100moving back according to a fourth example.

When the robotic lawn mower100a″,100a′″ has moved back such that there is a shortest distance ds″, ds′″ between the center146and the boundary220, the robotic lawn mower100a″,100a′″ is in position. The control unit110is then adapted to control the drive wheels130a,130bto turn in mutually different directions such that the second end portion102of the robotic lawn mower100a,100b,100cperforms an arcuate movement along a cutting arc210, enabling the first cutting disc160to cut grass within the cutting arc210.

In this way, if the smallest angle φBfalls below the threshold value, cutting the grass relatively close to a border139is enabled anyway without cutting outside the border139by increasing the rearward distance drto an extended rearward distance dre.

According to some aspects, a center159of the cutting arc210is positioned along the drive wheel axis145. According to some further aspects, the center159of the cutting arc210is positioned in the center146of the drive wheel axis145. This is the case when the drive wheels130a,130bare driven in different rotation directions and at the same rotation velocities by the first electric motor arrangement150. Of course, this should not be interpreted literally, since small deviations can occur due to motor inaccuracies, uneven ground, uneven ground contact and uneven ground friction. The velocities being the same and the center159of the cutting arc210being positioned in the center146of the drive wheel axis145should be interpreted according to what is intended and practically achievable, not to be mathematically exact.

According to some aspects, the cutting arc210has an angular extension φ that exceeds 180°, where the control unit110is adapted to control the robotic lawn mower100dto continue moving forward when a second end center106, according to some aspects constituting a rearmost point, that has followed the extension of the cutting arc210has reached an end212of the cutting arc210. This means that the robotic lawn mower100dwill continue moving at an angle to the original angle of approach, away from the boundary182,220. This in turn enables the robotic lawn mower100to repeat the above procedure, performing arcuate movements, such that a continuous grass edge close to the boundary182,220is cut. This can be performed in combination with cutting the rest of the grass on the lawn.

According to some aspects, the lawn mower100can be adapted to be set in a mode where only a continuous grass edge close to the boundary182,220is cut, the rest of the lawn not being cut during that time. This mode could be selected by a user.

According to some aspects, when the robotic lawn mower100has moved back towards the operation area610such that there is a shortest distance ds, ds′, ds″, ds′″ between the center146and the boundary220, the center146is positioned within the operation area610. This means that that before the robotic lawn mower100aperforms an arcuate movement along a cutting arc210, it has moved such that the center146is positioned within the operation area610.

According to some aspects, the control unit110is adapted to position the robotic lawn mower100aby means of input derived from a navigation sensor arrangement175comprised in the robotic lawn mower100.

This means that the robotic lawn mower100acan be positioned for performing an arcuate movement along a cutting arc210according to the above directly, without first having to detect a boundary wire and then move back to the position100a.

In some embodiments, the navigation sensor arrangement175comprises a satellite signal navigation sensor175aconfigured to provide navigational information, such as position, based on receiving one or more signals from a satellite. According to some aspects, the navigation sensor arrangement175is adapted for navigation by means of active local radio beacons using Ultra Wide Band (UWB). According to some aspects, the signal navigation sensor175amay be combined with receiving a signal from a base station or a charging station which can provide active local radio beacons, for example using UWB.

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 sensor175is a RTK (Real Time Kinetics) sensor. This enables the robotic lawn mower100to operate in the operation area610bounded by a virtual boundary, not shown explicitly inFIG.8but deemed to be included in the boundary220.

In some embodiments, alone or as a complement to the satellite signal navigation sensor175a, the navigation sensor arrangement175also comprises deduced reckoning sensors175b. The deduced reckoning sensors175bmay be odometers, accelerometers or other deduced reckoning sensors. In some embodiments the deduced reckoning sensors175binclude visual sensors, such as for Simultaneous Localization And Mapping, SLAM, navigation or other visual navigation. In such embodiments the boundary may be bounded by reference objects, not shown explicitly in any Figure, but deemed to be included in the boundary220.

In some embodiments, the deduced reckoning sensors175bare 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 deduced reckoning sensors175b, especially in combination with the visual odometry sensor, enables the root to operate according to a map of the operational area. In some such embodiments, the navigation is based on SLAM, and in some embodiments, where a visual odometry sensor, such as a camera, is utilized, the navigation is based on V-SLAM.

The robotic lawn mower100is in some embodiments arranged to operate according to a map application representing one or more operational areas, and possibly the surroundings of the operational area(s) as well as features of the operational area(s) stored in the memory120of the robotic lawn mower100. In some embodiments, the map is also or alternatively stored in the memory of a remote server243. The map application may be generated or supplemented as the robotic lawn mower100operates or otherwise moves around in the operational area. In some embodiments, the map application is downloaded, possibly from the server. In some embodiments, the map application also includes one or more transport areas. The robotic lawn mower100is arranged to navigate according to the map based on the navigation sensor arrangement175.

According to some aspects, there is a swivel attachment axis151, running through at least one swivel axis153,154and being parallel to the drive wheel axis145, is positioned between the second end portion102and the drive wheel axis145. This means that a largest first axis distance d1between the swivel attachment axis151and the second end portion102falls below a largest second axis distance d2between the drive wheel axis145and the second end portion102. The first cutting disc160is at least partly is positioned between the swivel attachment axis151and the second end portion102.

In this way, the first cutting disc160is positioned such that it can move laterally in an arcuate manner when the drive wheels130a,130bare driven in different rotation directions by the first electric motor arrangement150. This enables the first cutting disc160to reach relatively close to a border139.

According to some aspects, with reference toFIG.2,FIG.3andFIG.4, the robotic lawn mower100further comprises a first arcuate protective wall141that at least partly runs along the second end portion102, and at least one further arcuate protective wall142,143,144, the protective walls141,142,143,144extending from the body140towards the ground G during normal running, the protective walls141,142,143,144being radially separated.

In this examples, there are four protective walls141,142,143,144; the first protective wall141, a second protective wall142, a third protective walls14, and a fourth protective wall144. Since the cutting disc160is at least partly positioned between the swivel attachment axis151and the second end portion102, and, according to some aspects, the rotation axis152is positioned between the swivel attachment axis151and the second end portion102when the rotation axis152passes through the cutting disc160, the protective walls141,142,143,144confer an injury protection for humans and animals that come close to the second end portion102during normal running.

There is a first distance h1between the first protective wall141and the ground G, where the first distance h1of course varies slightly during running. There is a second distance h2between the first end portion101and the ground G, where the second distance h2of course also varies slightly during running. In this example, the first distance h1falls below the second distance h2, and in the case of the first end portion101is facing the forward travelling direction F, this means that relatively high grass can enter between the robotic lawn mower100and the ground G without being bent, or only being slightly bent, before reaching the cutting disc160. A spring-back effect for bent grass can need an additional distance and thus also an additional time to bend back.

This is advantageous since this provides a more efficient cut of the grass, and is enabled by having the cutting disc160positioned relatively close to the second end portion102where the cutting disc160is protected by means of the protective walls141,142,143,144.

According to some aspects, the protective walls141,142,143,144are partly positioned between the cutting disc160and the ground G during normal running. In this manner, the cutting disc160can reach the second end portion102while humans and animals that come close to the second end portion102during normal running still are protected from injury.

According to some aspects, the protective walls141,142,143,144at least mainly follow respective protective wall arcs141a,142a,143a,144a, where all protective wall arcs141a,142a,143a,144ahave a common center146. According to some aspects, the common center146is the center of the drive wheel axis145. In this way, when the arcuate movement is performed, the grass will not be bent when moving between the protective walls141,142,143,144. According to some aspects, the radial separation of the protective walls141,142,143,144relates to the common center.

According to some aspects, an arcuate extension of at least one protective wall141,142,143, at least mainly following a respective protective wall arc, comprises tapered end portions147,148,149. In this example, this is the case for the first three protective walls141,142,143, and enables the grass to be easily divided between the protective walls141,142,143,144when the arcuate movement is performed.

It is to be noted that, according to some aspects, the rotation axis152can be tilted with a cutting disc angle of incidence, constituting an angle of approach a as illustrated inFIG.5, towards the ground G. Such a tilt improves the cutting result, the cutting disc160being closer to the ground G where the cutting disc160faces the forward travelling direction F. In the case where the first end portion101is facing the forward travelling direction F and the second end portion102is facing the reverse travelling direction R, there is an advantage since the first distance h1between the first protective wall141and the ground G can be increased.

It is to be noted that all position references to the rotation axis152are intended to be considered when the rotation axis152passes through the cutting disc160

According to some aspects, the second electric motor arrangement165is positioned closer to the drive wheel axis145than to the rotation axis152. In this way, the weight of the cutter motor165is positioned closer to the drive wheels130a,130bwhich will confer an enhanced traction. Some power transfer means is needed in this case for transferring rotational power from the cutter motor165to the cutting disc160. Such power transfer means can for example be in the form of a drive belt, a drive chain or a geared transmission.

As indicated inFIG.8, according to some aspects, the control unit110may be adapted to be in contact, suitably by means of wireless communication241, with external units, for example a communication system240. This may, e.g., be a third generation partnership program (3GPP) defined access network like the fourth generation (4G) or the fifth generation (5G) access networks or a satellite system such as GPS. The access network may provide access to remote networks and other resources such as, e.g., the Internet.

It is also appreciated that some processing functions may be performed by resources in a remote network242, such as a remote server243.

The control unit110may be constituted by one or more control unit parts that can be separate from each other. Some or all control unit parts may be comprised in a control unit arrangement110and/or a remote server243.

InFIG.16it is schematically illustrated, in terms of a number of functional units, the components of the control unit110according to embodiments of the discussions herein. Processing circuitry115is provided using any combination of one or more of a suitable central processing unit CPU, multiprocessor, microcontroller, digital signal processor DSP, etc., capable of executing software instructions stored in a computer program product, e.g. in the form of a storage medium120. The processing circuitry115may further be provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA. The processing circuitry thus comprises a plurality of digital logic components.

Particularly, the processing circuitry115is configured to cause the control unit110to perform a set of operations, or steps to control the operation of the robotic lawn mower100including, but not being limited to, controlling the radar transceivers170, processing measurements results received via the radar transceivers170, and the propulsion of the robotic lawn mower100. For example, the storage medium120may store the set of operations, and the processing circuitry115may be configured to retrieve the set of operations from the storage medium120to cause the control unit110to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry115is thereby arranged to execute at least parts of the methods as herein disclosed.

According to some aspects, the control unit110further comprises an interface112for communications with at least one external device such as a user terminal, the remote server243and/or a charging station. As such the interface112may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of ports for wireline communication. The interface112can be adapted for communication with other devices, such as the remote server243, a charging station, and/or other robotic working 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. This means that, according to some aspects, other units such as the remote server243are adapted to partly execute the methods as herein disclosed.

Generally, the present disclosure relates to a control unit arrangement110is adapted to execute any of the methods disclosed herein.

FIG.17shows a computer program product400comprising computer executable instructions410stored on media420to execute any of the methods disclosed herein.

With reference toFIG.18, the present disclosure also relates to a method for controlling a robotic lawn mower100having a body140, at least two drive wheels130a,130bthat form a pair of drive wheels arranged along a drive wheel axis145with a center146, the center146being positioned between the drive wheels130a,130bin the pair. A first end portion101is facing a forward travelling direction F and a second end portion102is facing a reverse travelling direction R. When the robotic lawn mower100, during grass cutting in an operation area610, is approaching a boundary220of the operation area610, the method comprises positioning S100the robotic lawn mower100asuch that there is a shortest distance dsbetween the center146and the boundary220, and controlling S200the drive wheels130a,130bto turn in mutually different directions such that the second end portion102of the robotic lawn mower100a,100b,100cperforms an arcuate movement along a cutting arc210, enabling the first cutting disc160to cut grass within the cutting arc210.

where the boundary220is positioned between a border139and the operation area610, and where the shortest distance dsadmits the cutting arc210to have a closest arc portion211that is closest to the border139without passing the border139.

According to some aspects, positioning S100the robotic lawn mower100asuch that there is a shortest distance dsbetween the center146and the boundary220comprisescontrolling S110the robotic lawn mower100to move towards the boundary220such that the first end portion101at least partly passes the boundary220, where the boundary220is determined to have a certain straight extension E where the first end portion101has crossed the boundary220, and determining S120a smallest angle φA, φBbetween the forward travelling direction F and the extension E. If T100the smallest angle φAexceeds a certain threshold value, the method comprises controlling S130the robotic lawn mower100ato move back a certain rearward distance drtowards the operation area610such there is a shortest distance dsbetween the center146and the boundary220.

According to some aspects, if T100the smallest angle φBfalls below the threshold value, the method comprises controlling S140the robotic lawn mower100a′ to move back towards the operation area610, and, when the robotic lawn mower100a′ has moved a certain extended rearward distance drethat exceeds the rearward distance dr, there is a shortest distance ds′ between the center146and the boundary220.

According to some aspects, if T100the smallest angle φBfalls below the threshold value, the method comprises controlling S150the robotic lawn mower100to move back towards the operation area610such that the smallest angle φC, φDbetween the forward travelling direction F and the extension E, when the first end portion101passes the boundary220, exceeds the threshold value, such that there is a shortest distance ds″, ds′″ between the center146and the boundary220.

According to some aspects, the boundary is in the form of a boundary wire220defining the operation area610for the robotic lawn mower100, where the robotic lawn mower100comprises at least two boundary wire sensors173A,173B,173C.

According to some aspects, a center159of the cutting arc210is positioned along the drive wheel axis145.

According to some aspects, a center159of the cutting arc210is positioned in the center146of the drive wheel axis145.

According to some aspects, the cutting arc210has an angular extension φ that exceeds 180°, where the control unit110is adapted to control the robotic lawn mower100dto continue moving when a second end center106, constituting a rearmost point, that has followed the extension of the cutting arc210has reached an end212of the cutting arc210.

According to some aspects, when the robotic lawn mower100has moved back towards the operation area610such that there is a shortest distance ds, ds′, ds″, ds′″ between the center146and the boundary220, the center146is positioned within the operation area610.

According to some aspects, the method comprises positioning S100the robotic lawn mower100asuch that there is a predetermined shortest distance dsbetween the center146and the boundary220.

According to some aspects, the method comprises positioning S100the robotic lawn mower100ausing S160input derived from a navigation sensor arrangement175comprised in the robotic lawn mower100.

According to some aspects, the navigation sensor arrangement175uses at least one ofsatellite signal navigation sensor175a; anddeduced reckoning sensors175b

According to some aspects, the navigation sensor arrangement175uses deduced reckoning sensors175bthat include visual sensors for Simultaneous Localization And Mapping, SLAM, navigation.

According to some aspects, the navigation sensor arrangement175is used for navigation by means of active local radio beacons using Ultra Wide Band, UWB.

The present disclosure is not limited to the above, but may vary freely within the scope of the appended claims. For example, the first end portion101can be facing the reverse travelling direction R and the second end portion102can be facing the forward travelling direction F.

The end portions101,102are shown as arcuate portions facing a forward travelling direction F or rearward travelling direction R where, according to some aspects, the first arcuate protective wall141constitutes the second end portion102. According to some aspects, an end portion101,102can be defined as a rearmost of foremost point at the robotic lawn mower100. According to some aspects, the first end portion101is opposite the second end portion102, each end portion facing a travelling direction.

According to some aspects, the swivel attachment axis151runs via the points where the swivelable wheels131a,131bare connected to the body140by means of corresponding swivel wheel holders158a,158b.

According to some aspects and with reference toFIG.2, there is a further cutting disc180(only schematically indicated) having a rotational axle181positioned between the swivel attachment axis151and the drive wheel axis145. This further cutting disc180can constitute a main cutting disc180that is operative during normal cutting, the cutting disc160possibly being disengaged. When the robotic lawn mower100is controlled to cut grass relatively close to a boundary, for example by performing the previously described arcuate movement along a cutting arc, the main cutting disc180may be disengaged and the cutting disc160is engaged into operation.

According to some aspects, the main cutting disc180has a larger diameter, and thus cutting width, than the cutting disc160. By only using the cutting disc160when cutting grass relatively close to a boundary and using the main cutting disc180otherwise, energy may be saved and efficiency increased. According to some aspects, the main cutting disc180is adjustable with respect to grass cutting height, manually or automatically in previous known manners. This means that the main cutting disc180is displaceable such that a distance between the main cutting disc180and the ground G can be adjusted,

According to some aspects, in particular for the case where there is a boundary wire that defines a boundary for an operation are116, there is a robotic lawn mower100comprising a body140, at least two drive wheels130a,130bthat form a pair of drive wheels arranged along a drive wheel axis145with a center146, the center146being positioned between the drive wheels130a,130bin the pair. The robotic lawn mower100further comprises at least one swivelable wheel131a,131b, a control unit110adapted to control the operation of the robotic lawn mower100, at least a first rotatable grass cutting disc160having a rotation axis152. A first end portion101is facing a forward travelling direction F and a second end portion102is facing a reverse travelling direction R. When the robotic lawn mower100, during grass cutting in an operation area610, is approaching a boundary220of the operation area610, the control unit110is adapted to control the robotic lawn mower100to move towards the boundary220such that the first end portion101at least partly passes the boundary220, where the boundary220is determined to have a certain straight extension E where the first end portion101has crossed the boundary220, and to determine a smallest angle φA, φBbetween the forward travelling direction F and the extension E.

If the smallest angle φAexceeds a certain threshold value, the control unit110is adapted to control the robotic lawn mower100ato move back a certain rearward distance drtowards the operation area610such there is a shortest distance dsbetween the center146and the boundary220, and to control the drive wheels130a,130bto turn in mutually different directions such that the second end portion102of the robotic lawn mower100a,100b,100cperforms an arcuate movement along a cutting arc210, enabling the first cutting disc160to cut grass within the cutting arc210,

According to some aspects, the boundary220is positioned between a border139and the operation area610, and where the shortest distance dsadmits the cutting arc210to have a closest arc portion211that is closest to the border139without passing the border139.

According to some aspects, with reference toFIG.9andFIG.15, for the above example, if the smallest angle φBfalls below the threshold value, the control unit110is adapted to control the robotic lawn mower1001,1002,1003to move towards the operation area610, and then to continue cutting the lawn. This can be performed by continuing a forward movement in arcuate manner as illustrated inFIG.15, or by reversing, as illustrated inFIG.10, and then continuing cutting the lawn in an ordinary forward movement.FIG.15thus illustrates the robotic lawn mower100moving back to the operation area610according to a fifth example.

In this way, the smallest angle φBis considered to be too small to admit cutting the grass relatively close to a border139in the manner described above.