TECHNICAL FIELD

The present disclosure relates to a self-propelled robotic lawnmower comprising a caster wheel.

BACKGROUND

A self-propelled robotic lawnmower is a lawnmower capable of cutting grass in areas in an autonomous manner, i.e. without the intervention or direct control of a user. Some robotic lawnmowers require a user to set up a border wire around a lawn that defines the area to be mowed. Such robotic lawnmowers use a sensor to locate the wire and thereby the boundary of the area to be trimmed. As an alternative, or in addition, robotic lawnmowers may comprise other types of positioning units and sensors, for example sensors for detecting an event, such as a collision with an object within the area. The robotic lawnmower may move in a systematic and/or random pattern to ensure that the area is completely cut. A robotic lawnmower usually comprises one or more batteries and one or more electrically driven cutting units being powered by the one or more batteries. In some cases, the robotic lawnmower uses the wire to locate a recharging dock used to recharge the one or more batteries.

A self-propelled robotic lawnmower usually comprises two drive wheels and one or more support wheels configured to support the robotic lawnmower during operation thereof. Many areas comprise more or less slopes which may pose problems for the traction and navigability of the robotic lawnmower. That is, slopes, as well as objects on a ground surface, irregularities of a ground surface, and the like, may cause unwanted changes in travel direction of a robotic lawnmower. Such unwanted changes of travel direction of the robotic lawnmower may result in that some parts of the area are operated more frequently, and some other parts of the area are operated less frequently. Moreover, unwanted changes of travel direction of a robotic lawnmower may result in wear and unwanted marks in an area operated due to wheel slip of one or more drive wheels of the robotic lawnmower.

Furthermore, generally, on today’s consumer market, it is an advantage if products, such as robotic lawnmowers and associated components, systems, and arrangements, have conditions and/or characteristics suitable for being manufactured and assembled in a cost- efficient manner.

SUMMARY It is an object of the present invention to overcome, or at least alleviate, at least some of the above-mentioned problems and drawbacks.

According to a first aspect of the invention, the object is achieved by a self-propelled robotic lawnmower comprising a lawnmower body and at least one caster wheel pivotally attached to the lawnmower body about a swivel joint. The caster wheel is configured to support the lawnmower body by abutting against a ground surface during operation of the lawnmower. The lawnmower further comprises a locking assembly configured to at least partially lock the caster wheel from pivoting about the swivel joint.

Since the robotic lawnmower comprises a locking assembly configured to at least partially lock the caster wheel from pivoting about the swivel joint, a robotic lawnmower is provided having a reduced probability of unwanted changes in travel direction while having conditions and/or characteristics suitable for being manufactured and assembled in a cost-efficient manner.

That is, a caster wheel is a simple and low cost solution for supporting a lawnmower body and for allowing turning and steering of a robotic lawnmower. However, normally, a caster wheel has some drawbacks, especially when it comes to stability of travel direction of a robotic lawnmower.

As an example, if a robotic lawnmower is travelling sideways along a slope, a caster wheel normally does not provide any support in a lateral direction of the robotic lawnmower. Therefore, a rear wheel driven robotic lawnmower comprising one or more caster wheels supporting a front of the robotic lawnmower tends to turn down the slope. Likewise, a front wheel driven robotic lawnmower comprising one or more caster wheels supporting a rear of the robotic lawnmower tends to turn up the slope. However, since the robotic lawnmower according to the embodiments herein comprises a locking assembly configured to at least partially lock the caster wheel from pivoting about the swivel joint, a robotic lawnmower is provided having an improved ability to travel along slopes without unwanted changes in travel direction. As a further result thereof, a robotic lawnmower is provided having conditions for an improved coverage of an area operated by a robotic lawnmower. Moreover, a robotic lawnmower is provided having conditions for reducing wear and unwanted marks in an area operated.

Moreover, a further problem associated with caster wheels is that the force between the cutting unit of the robotic lawnmower and vegetation may apply a turning force onto the robotic lawnmower. Such a turning force may cause a robotic lawnmower comprising one or more caster wheels to travel in a curved path during cutting, especially when cutting vegetation having great length and/or density. However, since the robotic lawnmower according to the embodiments herein comprises the locking assembly configured to at least partially lock the caster wheel from pivoting about the swivel joint, a robotic lawnmower is provided having an improved ability to travel along a predetermined path. Thus, also for this reason, a robotic lawnmower is provided having conditions for an improved coverage of an area operated by a robotic lawnmower.

Also, a further problem associated with caster wheels is that it may rotate freely around the swivel joint when the wheel loses ground engaging contact. That is, many lawns are not perfectly flat and when a caster wheel is lifted from the ground surface it may rotate to an angle other than the travel direction of the robotic lawnmower. When the caster wheel regains ground engaging contact, it may cause a quick change in travel direction of the robotic lawnmower. However, since the robotic lawnmower according to the embodiments herein comprises the locking assembly configured to at least partially lock the caster wheel from pivoting about the swivel joint, such quick changes in travel direction can be avoided. Thus, also for this reason, a robotic lawnmower is provided having conditions for an improved coverage of an area operated by a robotic lawnmower.

Accordingly, a robotic lawnmower is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

Optionally, the locking assembly is configured to at least partially lock the caster wheel from pivoting about the swivel joint when the caster wheel is at a first predetermined angle relative to the lawnmower body. Thereby, a robotic lawnmower is provided capable of obtaining an improved directional stability when travelling in a predetermined travel direction in a simple and efficient manner.

Optionally, the caster wheel is free to pivot about the swivel joint until the caster wheel reaches a first predetermined angle relative to the lawnmower body. Thereby, a robotic lawnmower is provided having conditions for turning and steering in an efficient manner while obtaining an improved directional stability when travelling in a predetermined travel direction.

Optionally, a rolling direction of the caster wheel coincides with a forward direction of travel of the lawnmower when the caster wheel is at the first predetermined angle relative to the lawnmower body. Thereby, a robotic lawnmower is provided capable of obtaining an improved directional stability when travelling in the forward direction of travel of the robotic lawnmower. As a further result thereof, a robotic lawnmower is provided having conditions for an improved coverage of an area operated by a robotic lawnmower.

Optionally, the locking assembly is configured to at least partially lock the caster wheel from pivoting about the swivel joint when the caster wheel is at a second predetermined angle relative to the lawnmower body. Thereby, a robotic lawnmower is provided capable of obtaining an improved directional stability when travelling in a second predetermined travel direction in a simple and efficient manner.

Optionally, a rolling direction of the caster wheel coincides with a reverse direction of travel of the lawnmower when the caster wheel is at the second predetermined angle relative to the lawnmower body. Thereby, a robotic lawnmower is provided capable of obtaining an improved directional stability when travelling in the reverse direction of travel in a simple and efficient manner. As a further result thereof, a robotic lawnmower is provided having conditions for an improved coverage of an area operated by a robotic lawnmower.

Optionally, the locking assembly is configured to unlock the caster wheel when a torque is applied onto the caster wheel around the swivel joint exceeding a threshold torque. Thereby, a robotic lawnmower is provided capable of obtaining an improved directional stability when travelling in one or more predetermined travel directions while being capable of turning and steering in an efficient manner simply by applying a torque onto the caster wheel around the swivel joint exceeding the threshold torque.

Optionally, the lawnmower comprises a control arrangement configured to navigate the lawnmower, and wherein the control arrangement is configured to selectively perform a control operation of the lawnmower in which a torque is applied onto the caster wheel around the swivel joint exceeding the threshold torque. Thereby, a robotic lawnmower is provided capable of obtaining an improved directional stability when travelling in one or more predetermined travel directions while having conditions for turning from the travel direction in a predetermined and efficient manner.

Optionally, the control operation comprises a turning of the lawnmower. Thereby, a robotic lawnmower is provided capable of obtaining an improved directional stability when travelling in one or more predetermined travel directions while having conditions for turning from the travel direction in a predetermined and efficient manner. Optionally, the control operation comprises stopping the lawnmower before initiating the turning of the lawnmower. Thereby, a robotic lawnmower is provided having an improved ability to pivot the caster wheel from a predetermined angle relative to the lawnmower body so as to turn the robotic lawnmower from a predetermined travel direction.

Optionally, the locking assembly comprises two elements configured to at least partially lock the caster wheel from pivoting about the swivel joint by an abutting contact between the two elements. Thereby, a simple, efficient, and reliable lock of the caster wheel can be provided.

Optionally, the lawnmower comprises an actuator operably connected to one element of the two elements. Thereby, conditions are provided for utilizing a greater locking force of the caster wheel relative to the lawnmower body at one or more predetermined angles of the caster wheel relative to the lawnmower body. As a further result thereof, a robotic lawnmower is provided having conditions for obtaining a further improved directional stability when travelling in one or more predetermined travel directions. In addition, since lawnmower comprises an actuator, conditions are provided for unlocking the locking assembly so as to initiate a turn from a predetermined travel direction in a simple and efficient manner.

Optionally, one element of the two elements is rod-shaped and the other element of the two elements comprises a groove. Thereby, a simple and efficient locking assembly is provided having conditions for obtaining a predetermined locking force in a simple and efficient manner. Moreover, conditions are provided for forcing the caster wheel to assume a predetermined angle relative to the lawnmower body when the caster wheel is in a region of the predetermined angle relative to the lawnmower body.

Optionally, the two elements are biased against each other by the force of a spring element. Thereby, a simple and efficient locking assembly is provided having conditions for obtaining a predetermined locking force in a simple and efficient manner. Moreover, conditions are provided for forcing the caster wheel to assume a predetermined angle relative to the lawnmower body, using the force of the spring element, when the caster wheel is in a region of the predetermined angle relative to the lawnmower body.

Optionally, the spring element form part of a suspension assembly configured to bias the caster wheel against a ground surface during operation of the lawnmower. Thereby, a simple and efficient locking assembly is provided having conditions for obtaining a predetermined locking force of the caster wheel in a simple and efficient manner. In addition, a robotic lawnmower is provided in which the spring element serves two purposes, namely obtaining a predetermined locking force of the caster wheel and supporting the lawnmower body against a ground surface during operation of the lawnmower. Thus, due to these features, a robotic lawnmower is provided conditions and/or characteristics suitable for being manufactured and assembled in a cost-efficient manner.

Optionally, the lawnmower comprises a sensor configured to provide data representative of a current angle of the caster wheel relative to the lawnmower body. Thereby, a robotic lawnmower is provided having conditions for supplying data to a control arrangement of the robotic lawnmower, wherein the data is representative of a current angle of the caster wheel. Thereby, conditions are provided for controlling the navigation of the robotic lawnmower, and/or an actuator of the locking assembly, based on the data representative of a current angle of the caster wheel relative to the lawnmower body. Thereby, a robotic lawnmower is provided having conditions for a further improved navigational abilities.

Optionally, the locking assembly comprises one or more magnets configured to partially lock the caster wheel from pivoting about the swivel joint. Thereby, a simple, efficient, and reliable locking assembly is provided having conditions for locking the caster wheel from pivoting with an accurate predetermined locking force. In addition, conditions are provided for forcing the caster wheel to assume a predetermined angle relative to the lawnmower body, using the magnetic force of the one or more magnets, when the caster wheel is in a region of the predetermined angle relative to the lawnmower body.

Optionally, the locking assembly comprises an electromagnet configured to partially lock the caster wheel from pivoting about the swivel joint. Thereby, a simple, efficient, and reliable locking assembly is provided having conditions for locking the caster wheel from pivoting with an accurate predetermined locking force. In addition, a controllable locking assembly is provided capable of locking the caster wheel from pivoting by activating the electromagnet and capable of unlock the caster wheel by deactivating the caster wheel. Thereby, a robotic lawnmower is provided having conditions for improved directional stability when travelling in one or more predetermined travel directions while being capable of turning and steering in an efficient manner simply by deactivating the electromagnet.

Furthermore, conditions are provided for forcing the caster wheel to assume a predetermined angle relative to the lawnmower body, using the magnetic force of the electromagnet, when the caster wheel is in a region of the predetermined angle relative to the lawnmower body. Still further, conditions are provided for forcing the caster wheel from a predetermined angle relative to the lawnmower body by reversing a current flow through the electromagnet.

Optionally, the lawnmower comprises a control arrangement connected to the electromagnet, and wherein the control arrangement is configured to estimate a current angle of the caster wheel relative to the lawnmower body by monitoring electrical data of the electromagnet. Thereby, an estimation of the current angle of the caster wheel is provided a simple, efficient, and reliable manner.

Optionally, the locking assembly is controllable between a locked state, in which the locking assembly at least partially locks the caster wheel from pivoting about the swivel joint, and an unlocked state, in which the caster wheel is free to pivot about the swivel joint. Thereby, a controllable locking assembly is provided capable of locking the caster wheel from pivoting so as to improve directional stability of the robotic lawnmower and capable of unlocking the locking assembly so as to allow for an efficient turning and steering of the robotic lawnmower.

Moreover, conditions are provided for utilizing a greater locking force of the caster wheel relative to the lawnmower body at one or more predetermined angles of the caster wheel relative to the lawnmower body. As a further result thereof, a robotic lawnmower is provided having conditions for obtaining a further improved directional stability when travelling in one or more predetermined travel directions.

Optionally, the locked state constitutes a state in which the caster wheel is free to pivot about the swivel joint until the caster wheel reaches a predetermined angle relative to the lawnmower body. Thereby, conditions are provided for a simple and efficient locking assembly. This because the locking assembly can be controlled to the locked state when the caster wheel is at any angle relative to the lawnmower body and the caster wheel becomes locked from pivoting relative to the lawnmower body when reaching the predetermined angle relative to the lawnmower body.

Optionally, the locking assembly is configured to force the caster wheel to assume a predetermined angle relative to the lawnmower body when the locking assembly is transferred to the locked state. Thereby, a locking assembly is provided capable of steering the robotic lawnmower towards one or more predetermined travel directions. Optionally, the locking assembly is controllable to a third state and wherein the locking assembly is configured to force the caster wheel from a predetermined angle relative to the lawnmower body if the caster wheel is at the predetermined angle relative to the lawnmower body and the locking assembly is controlled to the third state. Thereby, a robotic lawnmower is provided in which turning of the robotic lawnmower can be initiated in a more efficient and reliable manner.

Optionally, the lawnmower comprises a control arrangement configured to control the locking assembly between the locked state and the unlocked state based on input data. Thereby, a robotic lawnmower is provided having conditions for further improved navigational abilities.

Optionally, the input data is representative of at least one of a current or impending slope inclination at the location of the lawnmower, a current or impending inclination angle of the lawnmower, traction conditions at the location of the lawnmower, weather conditions at the location of the lawnmower, and humidity at the location of the lawnmower. Thereby, a robotic lawnmower is provided having conditions for further improved navigational abilities.

Moreover, a robotic lawnmower is provided having conditions for reducing wear and unwanted marks in an area operated.

Optionally, the lawnmower comprises a control arrangement configured to navigate the lawnmower in a manner being adapted to one or more predetermined angles of the caster wheel relative to the lawnmower body at which the locking assembly is configured to at least partially lock the caster wheel from pivoting about the swivel joint. Thereby, a robotic lawnmower is provided having conditions for further improved navigational abilities. In addition, a robotic lawnmower is provided having conditions for operating in systematic patterns with higher accuracy even when operating undulated areas. Moreover, a robotic lawnmower is provided having conditions for reducing wear and unwanted marks in an area operated.

Optionally, the lawnmower comprises two drive wheels, and wherein the lawnmower comprises a control arrangement configured to navigate the lawnmower by controlling rotation of the drive wheels. Thereby, a robotic lawnmower is provided capable of obtaining an improved directional stability when travelling in one or more predetermined travel directions in a simple and efficient manner while having conditions for obtaining an efficient steering of the robotic lawnmower simply by controlling rotation of the drive wheels. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the invention, including its particular features and advantages, will be readily understood from the example embodiments discussed in the following detailed description and the accompanying drawings, in which:

Fig. 1 illustrates a perspective view of a self-propelled robotic lawnmower, according to some embodiments,

Fig. 2 illustrates a first side view of the self-propelled robotic lawnmower illustrated in Fig. 1 , Fig. 3 illustrates a second side view of the robotic lawnmower according to the embodiments illustrated in Fig. 1 and Fig. 2,

Fig. 4 illustrates a perspective view of a caster wheel assembly according to some embodiments of the robotic lawnmower illustrated in Fig. 1 - Fig. 3,

Fig. 5 illustrates a top view of the caster wheel assembly according to the embodiments illustrated in Fig. 4,

Fig. 6 illustrates the caster wheel assembly illustrated in Fig. 5 in which a locking assembly has been transferred to an unlocked state,

Fig. 7 illustrates a top view of a caster wheel assembly according to some further embodiments,

Fig. 8 illustrates the caster wheel assembly illustrated in Fig. 7 in which a caster wheel has pivoted from a predetermined angle relative to a lawnmower body,

Fig. 9 illustrates a top view of a caster wheel assembly according to some further embodiments,

Fig. 10 illustrates a top view of a caster wheel assembly according to some further embodiments,

Fig. 11 illustrates a top view of a caster wheel assembly according to some further embodiments,

Fig. 12 illustrates a caster wheel assembly, according to some further embodiments, in a disassembled state, and

Fig. 13 illustrates the caster wheel assembly according to the embodiments illustrated in Fig. 12 in an assembled state.

DETAILED DESCRIPTION Aspects of the present invention will now be described more fully. Like numbers refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

Fig. 1 illustrates a perspective view of a self-propelled robotic lawnmower 1, according to some embodiments. The self-propelled robotic lawnmower 1 is a self-propelled autonomous robotic lawnmower 1 capable of cutting grass in an area in an autonomous manner, i.e. without the intervention or direct control of a user. According to the illustrated embodiments, the robotic lawnmower 1 is configured to be used to cut grass in areas used for aesthetic and recreational purposes, such as gardens, parks, city parks, sports fields, lawns around houses, apartments, commercial buildings, offices, and the like. For the reason of brevity and clarity, the self-propelled robotic lawnmower 1 is in some places herein referred to as “the robotic lawnmower 1”, or simply “the lawnmower 1”.

The robotic lawnmower 1 comprises a lawnmower body 3 and wheels 4, 5 configured to support the lawnmower body 3 by abutting against a ground surface 22 during operation of the lawnmower 1. According to the illustrated embodiments, the robotic lawnmower 1 comprises a first and a second drive wheel 4. The drive wheels 4 may also be referred to as propulsion wheels 4. In Fig. 1, only one of the two drive wheels 4 is visible. Moreover, according to the embodiments illustrated in Fig. 1, the robotic lawnmower 1 comprises two caster wheels 5 each configured to abut against a ground surface 22 during operation of the robotic lawnmower 1. The caster wheels 5 are non-driven wheels each configured to support the robotic lawnmower 1 during operation thereof. Moreover, according to the illustrated embodiments, the two caster wheels 5 constitute front wheels and the first and second drive wheels 4 constitute rear wheels of the robotic lawnmower 1. The first and second drive wheels 4 are driven by a respective propulsion motor which may be powered by electricity from a battery comprised in the robotic lawnmower 1. These propulsion motors and the battery are not illustrated in Fig. 1 for the reason of brevity and clarity.

According to the embodiments illustrated in Fig. 1, the robotic lawnmower 1 comprises four wheels and may be referred to as a four-wheeled rear wheel driven robotic lawnmower 1.

The robotic lawnmower 1 may be provided with another number of wheels 5, 4 and another configuration of driven and non-driven wheels than depicted in Fig. 1.

The robotic lawnmower 1 comprises a control arrangement 21. The control arrangement 21 is configured to steer, turn, and navigate the robotic lawnmower 1 by controlling rotation of the first and second drive wheels 4. The control arrangement 21 may also be referred to as a “propulsion control arrangement 21”. The control arrangement 21 is configured to control rotation of the first and second drive wheels 4 by controlling the power and direction of the respective propulsion motor.

Fig. 2 illustrates a first side view of the self-propelled robotic lawnmower 1 illustrated in Fig.

1. In Fig. 2, the robotic lawnmower 1 is illustrated as positioned on a flat ground surface 22. The robotic lawnmower 1 has longitudinal axis la. The longitudinal axis la of the robotic lawnmower 1 is parallel to a first plane p1 extending through ground engaging portions of the wheels 5, 4 of the robotic lawnmower 1. Accordingly, the longitudinal axis la of the robotic lawnmower 1 is parallel to the ground surface 22 in case the robotic lawnmower 1 is positioned onto a flat and planar ground surface 22. The robotic lawnmower 1 has a yaw axis ya that crosses the longitudinal axis la and is perpendicular to the longitudinal axis la and to the first plane p1. In Fig. 2, a forward direction fd of travel of the lawnmower 1 is indicated. The forward direction fd of travel of the robotic lawnmower 1 may also be referred to as a forward direction of the robotic lawnmower 1 and is a direction in which the robotic lawnmower 1 mainly may operate during operation of an area. The forward direction fd of travel of the robotic lawnmower 1 coincides with the longitudinal axis la of the robotic lawnmower 1. Also, in Fig. 2, a reverse direction rd of travel of the lawnmower 1 is indicated. The reverse direction rd of travel of the lawnmower 1 is opposite to the forward direction fd of travel and also coincides with the longitudinal axis la of the robotic lawnmower 1.

In Fig. 2, one of the caster wheels 5 of the robotic lawnmower 1 is visible. According to the illustrated embodiments, each caster wheel 5 comprises the same features and functions as the other of the caster wheels 5. Therefore, below, reference is made to one of the caster wheels 5, if not indicated otherwise. As indicated in Fig. 2, the caster wheel 5 is pivotally attached to the lawnmower body 3 about a swivel joint 7. The robotic lawnmower 1 comprises a caster arm 10, wherein the caster wheel 5 and the wheel axis wa of the caster wheel 5 is arranged at one end of the caster arm 10 and the other end of the caster arm 10 is pivotally attached about the swivel joint 7. In this manner, the caster wheel 5 can pivot, i.e. rotate, around a pivot axis pa at the swivel joint 7, to change its rolling direction dr relative the lawnmower body 3. The pivot axis pa is substantially perpendicular to the first plane p1, i.e. perpendicular to the ground surface 22 in case the robotic lawnmower 1 is positioned onto a flat and planar ground surface 22. As seen in Fig. 2, the caster arm 10 is arranged such that the wheel axis wa of the caster wheel 5 is at a distance from the pivot axis pa measured in a direction parallel to the first plane p1. The caster wheel 5 may be free to pivot around the pivot axis pa such that the rolling direction rd of the caster wheel 5 can follow a travel direction of the robotic tool 3. The caster wheel 5, as referred to herein, may also be referred to as a “swivel caster wheel 5”. The rolling direction rd of the caster wheel 5 is perpendicular to the wheel axle aw of the caster wheel 5. The swivel joint 7, the caster arm 10 and the caster wheel 5 are comprised in a caster wheel assembly 50 of the robotic lawnmower 1 , as is further explained herein.

In Fig. 2, the robotic lawnmower 1 is illustrated as travelling in the forward direction fd of travel of the robotic lawnmower 1. As can be seen in Fig. 2, when travelling in the forward direction fd of travel, the rolling direction rd of the caster wheel 5 is parallel to the longitudinal axis la of the robotic lawnmower 1 and the wheel axle aw of the caster wheel 5 is located behind the pivot axis pa seen in the forward direction fd of travel. Moreover, as seen in Fig.

2, the rolling direction dr of the caster wheel 5 coincides with the forward direction fd of travel of the lawnmower 1 when the robotic lawnmower 1 is travelling in the forward direction fd. This angle a1 between the caster wheel 5 and the lawnmower body 3 is in some places herein referred to as a first predetermined angle a1 of the caster wheel 5 relative to the lawnmower body 3.

Fig. 3 illustrates a second side view of the robotic lawnmower 1 according to the embodiments illustrated in Fig. 1 and Fig. 2. In Fig. 3, the robotic lawnmower 1 is illustrated as travelling in the reverse direction rd of travel of the robotic lawnmower 1. As can be seen in Fig. 3, when travelling in the reverse direction rd of travel of the robotic lawnmower 1, the rolling direction rd of the caster wheel 5 is parallel to the longitudinal axis la of the robotic lawnmower 1 and the wheel axle aw of the caster wheel 5 is located in front of the pivot axis pa seen in the forward direction fd of travel of the robotic lawnmower 1. Thus, in relation to Fig. 2, the caster wheel 5 has rotated 180 degrees from the first predetermined angle a1 relative to the lawnmower body 3 to a second angle a2 relative to the lawnmower body 3.

This second angle a2 between the caster wheel 5 and the lawnmower body 3 is in some places herein referred to as a second predetermined angle a2 of the caster wheel 5 relative to the lawnmower body 3. As seen in Fig. 3, the rolling direction dr of the caster wheel 5 coincides with a reverse direction rd of travel of the lawnmower 1 when the caster wheel 5 is at the second predetermined angle a2 relative to the lawnmower body 3.

As understood from the above, the caster wheels 5 of the robotic lawnmower 1 are allowed to pivot around a respective swivel joint 7 such that the rolling directions dr of the caster wheels 5 can follow a current travelling direction of the robotic lawnmower 1. Caster wheels 5 are an efficient means for supporting a lawnmower body 3 while allowing steering and turning of the robotic lawnmower 1 around a yaw axis ya of a robotic lawnmower 1 by controlling rotation of a first and a second drive wheel 4. However, caster wheels 5 are associated with some drawbacks such as a lack of lateral support. The lack of lateral support, i.e. the lack of support in a lateral direction of the robotic lawnmower 1 being perpendicular to the longitudinal axis la and parallel to the first plane p1 , may lead to unwanted changes in travelling direction of the robotic lawnmower 1 for example when travelling sideways along a slope. Moreover, the lack of lateral support provided by the caster wheels 5 may cause the robotic lawnmower 1 to travel in a curved path due to a reaction force between a cutting unit of the robotic lawnmower 1 and vegetation.

According to embodiments herein, robotic lawnmower 1 comprises a locking assembly 9.

The locking assembly 9 is configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7. In this manner, unwanted changes in travel direction of the robotic lawnmower 1 can be avoided in a simple and efficient manner. Moreover, unwanted pivoting of a caster wheel 5 as a result of lack of ground engaging contact can be avoided. In Fig. 3, the locking assembly 9 of the robotic lawnmower 1 is schematically indicated.

According to the illustrated embodiments, the locking assembly 9 is configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7 when the caster wheel 5 is at the first predetermined angle a1 relative to the lawnmower body 3. In this manner, an improved directional stability is provided when the robotic lawnmower 1 is travelling in the forward direction fd of travel of the robotic lawnmower 1 as indicated in Fig. 2. Moreover, according to the illustrated embodiments, the locking assembly 9 is configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7 when the caster wheel 5 is at the second predetermined angle a2 relative to the lawnmower body 3. In this manner, an improved directional stability is provided when travelling in the reverse direction rd of travel of the robotic lawnmower 1 as indicated in Fig. 3. According to some embodiments, the caster wheel 5 may be free to pivot about the swivel joint 7 until the caster wheel 5 reaches a predetermined angle a1, a2 relative to the lawnmower body 3, as is further explained herein.

As understood from the above, according to the illustrated embodiments, the locking assembly 9 is configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7 at two predetermined angles a1 , a2 between the caster wheel 5 and the lawnmower body 3. However, according to some embodiments, the locking assembly 9 may be configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7 only at one predetermined angle a1 , a2 between the caster wheel 5 and the lawnmower body 3, such as an angle a1 in which the rolling direction dr of the caster wheel 5 coincides with the forward direction fd of travel of the robotic lawnmower 1 or an angle a2 in which the rolling direction dr of the caster wheel 5 coincides with the reverse direction rd of travel of the robotic lawnmower 1. Furthermore, according to some embodiments, the locking assembly 9 may be configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7 at three or more predetermined angles a1, a2 between the caster wheel 5 and the lawnmower body 3. Such three or more predetermined angles a1 , a2 between the caster wheel 5 and the lawnmower body 3 may include one or more angles of the caster wheel 5 relative to the lawnmower body 3 in which a turning of the robotic lawnmower 1 is obtained, as is further explained herein.

Moreover, according to some embodiments of the present disclosure, the locking assembly 9 is controllable between a locked state, in which the locking assembly 9 at least partially locks the caster wheel 5 from pivoting about the swivel joint 7, and an unlocked state, in which the caster wheel 5 is free to pivot about the swivel joint 7. The control arrangement 21 of the robotic lawnmower 1 may be configured to control the locking assembly 9 between the locked state and the unlocked state based on input data, as is further explained herein. The locked state may constitute a state in which the caster wheel 5 is free to pivot about the swivel joint 7 until the caster wheel 5 reaches a predetermined angle a1, a2 relative to the lawnmower body 3.

Fig. 4 illustrates a perspective view of a caster wheel assembly 50 according to some embodiments, of the robotic lawnmower 1 illustrated in Fig. 1 - Fig. 3. The caster wheel assembly 50 comprises a chassis portion 3’. The chassis portion 3’ may be rigidly attached to the lawnmower body 3 of the robotic lawnmower 1 illustrated in Fig. 1 - Fig. 3 or may form part of the lawnmower body 3 of the robotic lawnmower 1 illustrated in Fig. 1 - Fig. 3. Therefore, in the following, the chassis portion 3’ of the caster wheel assembly 50 is referred to as the lawnmower body 3’. In Fig. 4, the caster wheel 5 is illustrated at the first predetermined angle a1 relative to the lawnmower body 3’ referred to above, i.e. at an angle a1 in which the rolling direction dr of the caster wheel 5 coincides with the forward direction fd of travel of the robotic lawnmower 1.

According to the embodiments illustrated in Fig. 4, the locking assembly 9 is a mechanical locking assembly 9 comprising two elements 11, 12 configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7 by an abutting contact between the two elements 11, 12. Moreover, as seen in Fig. 4, the locking assembly 9 comprises an actuator 13 operably connected to one element 11 of the two elements 11, 12. In more detail, according to the embodiments illustrated in Fig. 4, the locking assembly 9 comprises a first element 11 connected to the actuator 13 and a second element 12 attached to the caster arm 10. The second element 12 is rotationally locked to the caster arm 10 and is thus configured to pivot, i.e. rotate, with the caster arm 10 upon pivoting of the caster wheel 5 around the pivot axis pa. According to the illustrated embodiments, the second element 12 comprises a first dent 31 and a second dent 32. Each of the first and second dents 31 , 32 may also be referred to as a groove, a cam surface, or the like.

Fig. 5 illustrates a top view of the caster wheel assembly 50 according to the embodiments illustrated in Fig. 4. In Fig. 5, the caster wheel assembly 50 is illustrated as seen in a direction coinciding with the pivot axis pa. Also in Fig. 5, the caster wheel 5 is illustrated at the first predetermined angle a1 relative to the lawnmower body 3’. According to the embodiments illustrated in Fig. 4 and Fig. 5, the locking assembly 9 is controllable between a locked state, in which the locking assembly 9 at least partially locks the caster wheel 5 from pivoting about the swivel joint 7, and an unlocked state, in which the caster wheel 5 is free to pivot about the swivel joint 7. In Fig. 4 and Fig. 5, the locking assembly 9 is illustrated in the locked state. According to these embodiments, the actuator 13 moves the first element 11 towards the second element 12 upon transition to the locked state. As seen in Fig. 4 and Fig. 5, the first element 11 is positioned in the first dent 31 of the second element 12. In this manner, the locking assembly 9 locks the caster wheel 5 from pivoting about the swivel joint 7. The locking of the locking assembly 9 may be a full lock or a partial lock which becomes unlocked if a torque is applied onto the caster wheel 5 around the swivel joint 7 exceeding a threshold torque. According to the embodiments illustrated in Fig. 4 and Fig. 5, the actuator 13 comprises a solenoid. According to further embodiments, the actuator 13 may comprise another type of actuator. The control arrangement 21 of the robotic lawnmower 1 , indicated in Fig. 1 - Fig. 3, may be operably connected to the actuator 13 of the locking assembly 9. The control arrangement 21 may be configured to control the locking assembly 9 between the locked state and the unlocked state based on input data, as is further explained herein.

Fig. 6 illustrates the caster wheel assembly 50 illustrated in Fig. 5 in which the locking assembly 9 has been transferred to the unlocked state. In the unlocked state, the caster wheel 5 is free to pivot about the swivel joint 7. As seen in Fig. 6, the actuator 13 has moved the first element 11 in a direction away from the second element 12. Upon transfer of the locking assembly 9 from the locked state, illustrated in Fig. 5, to the unlocked state illustrated in Fig. 6, the actuator 13 moves the first element 11 out of the first dent 31 of the second element 12. As a result thereof, the second element 12 and the caster wheel 5, which is rotationally locked to the second element 12, is free to pivot around the pivot axis pa. As can be seen in Fig. 6, the caster wheel 5 has pivoted from the first predetermined angle relative to the lawnmower body 3’ to a third angle a3 relative to the lawnmower body 3’. Accordingly the caster wheel 5 can pivot around the pivot axis pa, for example by a turning of the robotic lawnmower 1 around a yaw axis ya of the robotic lawnmower 1 by controlling rotation of the first and second drive wheels 4 illustrated in Fig. 2 and Fig. 3.

According to the embodiments illustrated in Fig. 4 - Fig. 6, the locking assembly 9 can lock the caster wheel 5 at the second predetermined angle a2, referred to above, by moving the first element 11 of the locking assembly 9 into the second dent 32 of the second element 12 of the locking assembly 9. The third angle a3 illustrated in Fig. 6 is thus an angle a3 between the first and second predetermined angles a1, a2. The second element 12 of the locking assembly 9 may comprise one or more further surfaces 33 or structures against which the first element 11 can abut so as to lock pivoting of the caster wheel 5 at one or more angels between the first and second predetermined angles a1, a2. In this manner, the caster wheel 5 can for example be locked at an angle causing a turning motion of the robotic lawnmower 1.

Moreover, according to some embodiments herein, the locking assembly 9 may be configured to force the caster wheel 5 to assume a predetermined angle a1 , a2 relative to the lawnmower body 3 when the locking assembly 9 is transferred to the locked state. According to the embodiments illustrated in Fig. 4 - Fig. 6, this is achieved by the design of the first and second elements 11, 12. That is, as is best seen in Fig. 5 and Fig. 6, each of the first and second elements 11, 12 has a curved profile in a plane perpendicular to the pivot axis pa. Thereby, when the caster wheel 5 and the second element 12 is in a position close to the first or second predetermined angle a1, a2, the caster wheel 5 is forced towards the first or second predetermined angle a1 , a2 when the first element 11 is forced against the second element 12.

Furthermore, according to some embodiments herein, the lawnmower 1 comprises a sensor 14 configured to provide data representative of a current angle a1 , a2, a3 of the caster wheel 5 relative to the lawnmower body 3. According to the embodiments illustrated in Fig. 4 - Fig. 6, the locking assembly 9 comprises a sensor 14 configured to provide data representative of a current position of the first element 11 relative to the second element 12. In this manner, a control arrangement of the robotic lawnmower 1 can obtain data indicative of whether the caster wheel 5 is at the first or second predetermined angles a1 , a2 when the locking assembly 9 is in the locked state. This because according to the illustrated embodiments, the first element 11 is allowed to move a shorter distance towards the pivot axis pa when the caster wheel 5 is at the first or second predetermined angles a1 , a2 than when the caster wheel 5 is at an angle between the first and second predetermined angles a1 , a2, such as an angle a3 illustrated in Fig. 6. Fig. 7 illustrates a top view of a caster wheel assembly 50 according to some further embodiments. In Fig. 7, the caster wheel assembly 50 is illustrated as seen in a direction coinciding with the pivot axis pa. The caster wheel assembly 50 according to the embodiments illustrated in Fig. 7 may comprise the same features, functions, and advantages as the caster wheel assembly 50 explained with reference to Fig. 4 - Fig. 6 with some differences explained below. Also in the embodiments illustrated in Fig. 7, the locking assembly 9 is a mechanical locking assembly 9 comprising two elements 1 T, 12 configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7 by an abutting contact between the two elements 1T, 12. However, according to the embodiments illustrated in Fig. 7, the first element 1T is a portion of a spring element 28 comprised in the locking assembly 9. Accordingly, in these embodiments, the two elements 1T, 12 are biased against each other by the force of the spring element 28. According to the embodiments illustrated in Fig. 7, the spring element 28 is a leaf spring. According to further embodiments, the spring element 28 may be another type of spring element, such as a rubber element or a coil spring.

According to the embodiments illustrated in Fig. 7, the second element 12 of the locking assembly 9 is of corresponding design as the second element 12 of the locking assembly 9 of the caster wheel assembly 50 explained with reference to Fig. 4 - Fig. 6. That is, also in the embodiments illustrated in Fig. 7, the second element 12 is rotationally locked to the caster arm 10 and is thus configured to pivot, i.e. rotate, with the caster arm 10 upon pivoting of the caster wheel 5 around the pivot axis pa. Moreover, the second element 12 comprises a first dent 31 and a second dent 32.

In Fig. 7, the caster wheel 5 is illustrated at the first predetermined angle a1 relative to the lawnmower body 3’ referred to above, i.e. at an angle a1 in which the rolling direction dr of the caster wheel 5 coincides with the forward direction fd of travel of the robotic lawnmower 1. As can be seen in Fig. 7, the first element 11’, i.e. the portion 1T of the spring element 28, is positioned in the first dent 31 of the second element 12 when the caster wheel 5 is at the first predetermined angle a1 relative to the lawnmower body 3’. Due to the biasing force of the spring element 28, a certain torque is required onto the caster wheel 5 around the swivel joint 7 so as to pivot the caster wheel 5 from the first predetermined angle a1. Thus, according to the embodiments illustrated in Fig. 7, the locking assembly 9 is configured to unlock the caster wheel 5 when a torque is applied onto the caster wheel 5 around the swivel joint 7 exceeding a threshold torque. In these embodiments, the threshold torque is determined by the biasing force of the spring element 28 and the shape of the first and second elements 11’, 12.

Fig. 8 illustrates the caster wheel assembly 50 illustrated in Fig. 7 in which the caster wheel 5 has pivoted from the first predetermined angle a1 relative to the lawnmower body 3’ to a third angle a3 relative to the lawnmower body 3’. Thus, in relation to Fig. 7, a torque has been applied onto the caster wheel 5 around the pivot axis pa exceeding the threshold torque. Moreover, as seen in Fig. 8, the first element 1 T has been displaced out from the first dent 31 of the second element 12 upon the pivoting of the caster wheel 5 from the first predetermined angle a1.

The solution according to the embodiments illustrated in Fig. 7 and Fig. 8 is a cost-efficient solution since it requires no active control and electronic components. Still, the solution according to these embodiments can provide a rigid lock of the caster wheel 5 in one or more predetermined angles to provide improved directional stability of the robotic lawnmower 1.

Fig. 9 illustrates a top view of a caster wheel assembly 50 according to some further embodiments. In Fig. 9, the caster wheel assembly 50 is illustrated as seen in a direction coinciding with the pivot axis pa. The caster wheel assembly 50 according to the embodiments illustrated in Fig. 9 may comprise the same features, functions, and advantages as the caster wheel assembly 50 explained with reference to Fig. 4 - Fig. 8 with some differences explained below. The locking assembly 9 of the caster wheel assembly 50 according to the embodiments illustrated in Fig. 9 comprises a spring element 28 as explained with reference to Fig. 7 and Fig. 8 combined with an actuator 13 explained with reference to Fig. 4 - Fig. 6. Thereby, both an active and a passive control of locking assembly 9 can be provided.

Fig. 10 illustrates a top view of a caster wheel assembly 50 according to some further embodiments. In Fig. 10, the caster wheel assembly 50 is illustrated as seen in a direction coinciding with the pivot axis pa. The caster wheel assembly 50 according to the embodiments illustrated in Fig. 10 may comprise the same features, functions, and advantages as the caster wheel assembly 50 explained with reference to Fig. 4 - Fig. 9 with some differences explained below.

According to the embodiments illustrated in Fig. 10, the locking assembly 9 comprises a set of permanent magnets 15, 15’, 16 configured to partially lock the caster wheel 5 from pivoting about the swivel joint 7. In more detail, the locking assembly 9 comprises two first permanent magnets 15, 15’ attached to an element 23. The element 23 is rotationally locked to the caster arm 10 and is thus configured to pivot, i.e. rotate, with the caster arm 10 upon pivoting of the caster wheel 5 around the pivot axis pa. Moreover, the locking assembly 9 comprises a second permanent magnet 16 attached to a portion of the caster wheel assembly 50 being stationary relative to the lawnmower chassis 3’. In Fig. 10, the caster wheel 5 is illustrated at the first predetermined angle a1 relative to the lawnmower body 3’, i.e. at an angle a1 in which the rolling direction dr of the caster wheel 5 coincides with the forward direction fd of travel of the robotic lawnmower 1.

As seen in Fig. 10, one of the first magnets 15 faces the second magnet 16 when the caster wheel 5 is at the first predetermined angle a1 relative to the lawnmower body 3’. The other of the first magnets 15’ faces the second magnet 16 when the caster wheel 5 is at the second predetermined angle a2 relative to the lawnmower body 3’. Thereby, the magnetic force between the first and second magnets 15, 15’, 16 provides a partial lock of the caster wheel 5 around the swivel joint 7. Accordingly, a certain torque is required onto the caster wheel 5 around the swivel joint 7 so as to pivot the caster wheel 5 from the first or second predetermined angles a1, a2. Thus, according to the embodiments illustrated in Fig. 10, the locking assembly 9 is configured to unlock the caster wheel 5 when a torque is applied onto the caster wheel 5 around the swivel joint 7 exceeding a threshold torque. In these embodiments, the threshold torque is determined by the magnetic strength of the first and second magnets 15, 15’, 16 and the relative distance between the first and second magnets 15, 15’, 16 when the caster wheel 5 is at the first or second predetermined angle a1, a2 relative to the lawnmower body 3’.

The locking assembly 9 of the caster wheel assembly 50 according to the embodiments illustrated in Fig. 10 may comprise another number of first magnets 15, 15’ than two, such as a number between one and eight. In this manner, a partial lock if the caster wheel 5 can be provided at one or more angles between the first and second predetermined angles a1, a2, as explained herein. In addition, according to some embodiments, one of the first magnet/magnets 15, 15’ and the second magnet 16 may comprise a ferromagnetic material, such as iron, whereas the other of the first magnet/magnets 15, 15’ and the second magnet 16 comprises a permanent magnet.

Fig. 11 illustrates a top view of a caster wheel assembly 50 according to some further embodiments. In Fig. 11, the caster wheel assembly 50 is illustrated as seen in a direction coinciding with the pivot axis pa. The caster wheel assembly 50 according to the embodiments illustrated in Fig. 11 may comprise the same features, functions, and advantages as the caster wheel assembly 50 explained with reference to Fig. 4 - Fig. 10 with some differences explained below.

According to the embodiments illustrated in Fig. 11, the locking assembly 9 comprises an electromagnet 19 configured to partially lock the caster wheel 5 from pivoting about the swivel joint 7. In more detail, the locking assembly 9 comprises two magnetic units 15, 15’ attached to an element 23. The element 23 is rotationally locked to the caster arm 10 and is thus configured to pivot, i.e. rotate, with the caster arm 10 upon pivoting of the caster wheel 5 around the pivot axis pa. Moreover, the electromagnet 19 is attached to a portion of the caster wheel assembly 50 being stationary relative to the lawnmower chassis 3’. In Fig. 11 , the caster wheel 5 is illustrated at the first predetermined angle a1 relative to the lawnmower body 3’, i.e. at an angle a1 in which the rolling direction dr of the caster wheel 5 coincides with the forward direction fd of travel of the robotic lawnmower 1.

As seen in Fig. 11, one of magnetic units 15 faces the electromagnet 19 when the caster wheel 5 is at the first predetermined angle a1 relative to the lawnmower body 3’. The other of the magnetic units 15’ faces the electromagnet 19 when the caster wheel 5 is at the second predetermined angle a2 relative to the lawnmower body 3’. Thereby, by actuating the electromagnet 19, the magnetic force between electromagnet 19 and a magnetic units 15’ provides a partial lock of the caster wheel 5 around the swivel joint 7.

As indicated in Fig. 11, the locking assembly 9 may comprise one or more further magnetic units 15”, so as to partially lock the caster wheel 5 at another angle relative to the lawnmower body 3’ than the first and second predetermined angle a1, a2 explained herein. A magnetic unit 15, 15’, 15” may comprise a permanent magnet, and/or a ferromagnetic material, such as iron.

According to the embodiments illustrated in Fig. 11, a certain torque is required onto the caster wheel 5 around the swivel joint 7 so as to pivot the caster wheel 5 from the first or second predetermined angles a1, a2 when the electromagnet is activated. Thus, according to the embodiments illustrated in Fig. 10, the locking assembly 9 is configured to unlock the caster wheel 5 when a torque is applied onto the caster wheel 5 around the swivel joint 7 exceeding a threshold torque. In these embodiments, the threshold torque is determined by the magnetic strength between the electromagnet 19 and a magnetic unit 15, 15’, 15” and the relative distance between the electromagnet 19 and a magnetic unit 15, 15’, 15”. According to the embodiments illustrated in Fig. 11, the control arrangement 21 of the robotic lawnmower 1 is operably connected to the electromagnet 19. The control arrangement 21 may transfer the locking assembly 9 to the locked state by activating the electromagnet 19. Likewise, the control arrangement 21 may transfer the locking assembly 9 to the unlocked state by deactivating the electromagnet 19. The control arrangement 21 may activate and deactivate the electromagnet based on input data, as is further explained herein. Moreover, according to some embodiments, the control arrangement 21 may be configured to estimate a current angle a1 , a2, a3 of the caster wheel 5 relative to the lawnmower body 3 by monitoring electrical data of the electromagnet 19. In this manner, the electromagnet 19 can be utilized as a sensor 19 configured to provide data representative of a current angle a1 , a2, a3 of the caster wheel 5 relative to the lawnmower body 3.

Furthermore, according to some embodiments of the present disclosure, the locking assembly 9 is controllable to a third state. According to some embodiments, the locking assembly 9 is configured to force the caster wheel 5 from a predetermined angle a1 , a2 relative to the lawnmower body 3 if the caster wheel 5 is at the predetermined angle a1 , a2 relative to the lawnmower body 3 and if the locking assembly 9 is controlled to the third state. According to the embodiments illustrated in Fig. 11, this may be achieved by reversing a current flow through the electromagnet 19 such that a polarity of the electromagnet 19 is opposite to when the electromagnet is in the locked state, referred to above. Thereby, the caster wheel 5 is forced from the first predetermined angle a1 relative to the lawnmower body 3’ illustrated in Fig. 11 and turning of the robotic lawnmower can thereby be initiated in a more efficient and reliable manner. The feature that the locking assembly 9 is configured to force the caster wheel 5 from a predetermined angle a1, a2 relative to the lawnmower body 3 may encompass that the locking assembly 9 is configured to force the caster wheel 5 towards another angle than the predetermined angle a1, a2.

Fig. 12 illustrates a caster wheel assembly 50, according to some further embodiments, in a disassembled state. The caster wheel assembly 50 comprises a chassis portion 3’. In Fig.

12, the chassis portion 3’ is illustrated as cut in half to improve understanding of the working principle of the caster wheel assembly 50. The chassis portion 3’ may be rigidly attached to the lawnmower body 3 of the robotic lawnmower 1 illustrated in Fig. 1 - Fig. 3 or may form part of the lawnmower body 3 of the robotic lawnmower 1 illustrated in Fig. 1 - Fig. 3. Therefore, in some places below, the chassis portion 3’ of the caster wheel assembly 50 is referred to as the lawnmower body 3’. The caster wheel assembly 50 comprises a caster arm 10 and a caster wheel 5 attached to the caster arm 10. Moreover the caster wheel assembly 50 comprises two slide bearings 35, 35’ forming the swivel joint 7. A vertical portion 10’ of the caster arm 10 is slidably received in the chassis portion 3’ via the two slide bearings 35, 35’ when the caster wheel assembly 50 is in an assembled state, as is further explained herein.

According to the embodiments illustrated in Fig. 12, the locking assembly 9 is a mechanical locking assembly 9 comprising two elements 11”, 12” configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7 by an abutting contact between the two elements 11”, 12”. According to these embodiments, a first element 11” of the two elements 11”, 12” is rod-shaped and a second element 12” of the two elements 11”, 12” comprises a groove 18. The groove 18 of the second element 12” is not visible in Fig. 12. The vertical portion 10’ of the caster arm 10 comprises a through hole 37. The first rod-shaped element 11” is configured to be received in the through hole 37 when the caster wheel assembly 50 is in an assembled state. The first rod-shaped element 11” may also be referred to as a pin 11

Fig. 13 illustrates the caster wheel assembly 50 according to the embodiments illustrated in Fig. 12 in an assembled state. Also in Fig. 12, the chassis portion 3’ is illustrated as cut in half to improve understanding of the working principle of the caster wheel assembly 50. As seen in Fig. 12, the vertical portion 10’ of the caster arm 10 is slidably received in the chassis portion 3’ via the two slide bearings 35, 35’ when the caster wheel assembly 50 is in the assembled state. In this manner, the caster wheel 5 can pivot, i.e. rotate, around the pivot axis pa of the swivel joint 7 to follow a travelling direction of a robotic lawnmower 1 comprising the caster wheel assembly 50. Moreover, according to the embodiments illustrated in Fig. 12 and Fig. 13, the caster wheel 5 is allowed to move in vertical directions vd since the vertical portion 10’ of the caster arm 10 is slidably received in the chassis portion 3’ via the two slide bearings 35, 35’. Vertical directions vd coincides with the direction of the pivot axis pa.

Below, simultaneous reference is made to Fig. 12 and Fig. 13. According to these embodiments, the second element 12” of the locking assembly 9 is formed as a follower 12” slidably arranged in the chassis portion 3’ in directions coinciding with the direction of the pivot axis pa, i.e. in vertical directions vd referred to above. Therefore, below, the second element 12” of the locking assembly 9 is in some places referred to as the follower 12”. The first rod-shaped element 11” is configured to abut against the follower 12” when the caster wheel assembly 50 is in the assembled state. Moreover, the caster wheel assembly 50 comprises a spring element 20. According to the illustrated embodiments, the spring element 20 is a coil spring 20 arranged around the vertical portion 10’ of the caster arm 10. According to further embodiments, the spring element 20 may be another type of spring element, such as a rubber element or a leaf spring. The two elements 11”, 12” of the locking assembly 9 are biased against each other by the force of the spring element 20.

In more detail, according to the illustrated embodiments, the spring element 20 biases the follower 12” towards the rod-shaped element 11”. As seen in Fig. 13, the follower 12” comprises a groove 18. According to the illustrated embodiments, the groove 18 has a diameter substantially corresponding to the diameter of the rod-shaped element 11”. The rod-shaped element 11” is rotationally locked to the caster arm 10 since the rod-shaped element 11” extends through the through hole 37 indicated in Fig. 12. The follower 12” is rotationally locked to the chassis portion 3’ via protrusions 39 of the follower 12” being slidably arranged in elongated grooves 41 of the chassis portion 3’. The protrusions 39 of the follower 12” and the elongated grooves 41 of the chassis portion 3’ are indicated in Fig. 12.

Due to these features, when the caster wheel 5 is pivoted around the pivot axis pa of the swivel joint 7 to a certain angle relative to the chassis portion 3’, the rod-shaped element 11” is displaced into the groove 18 of the follower 12”. In this manner, the locking assembly 9 partially locks the caster wheel 5 from pivoting about the swivel joint 7. Due to the biasing force of the spring element 20, a certain torque is required onto the caster wheel 5 around the swivel joint 7 so as to pivot the caster wheel 5 from this position. Thus, according to the embodiments illustrated in Fig. 12 and Fig. 13, the locking assembly 9 is configured to unlock the caster wheel 5 when a torque is applied onto the caster wheel 5 around the swivel joint 7 exceeding a threshold torque. In these embodiments, the threshold torque is determined by the biasing force of the spring element 20 and the shape of the rod-shaped element 11” and the groove 18 of the follower 12”.

The caster wheel assembly 50 may be designed such that the rod-shaped element 11” is positioned in the groove 18 when the caster wheel 5 is at the first predetermined angle a1 relative to the chassis portion 3’ in which a rolling direction dr of the caster wheel 5 coincides with the forward direction fd of travel indicated in Fig. 2. As an alternative, or in addition, the caster wheel assembly 50 may be designed such that the rod-shaped element 11” is positioned in the groove 18 when the caster wheel 5 is at the second predetermined angle a2 relative to the chassis portion 3’ in which a rolling direction dr of the caster wheel 5 coincides with the reverse direction rd of travel indicated in Fig. 3.

According to the embodiments illustrated in Fig. 12 and Fig. 13, the spring element 20 of the locking assembly 9 form part of a suspension assembly 24 configured to bias the caster wheel 5 against a ground surface 22 during operation of the lawnmower 1. In more detail, upon movement of the caster wheel 5 in the vertical direction vd indicated in Fig. 13, the rod shaped element 11” presses the follower 12” in the vertical direction vd which compresses the spring element 20. Thus, according to the embodiments illustrated in Fig. 12 and Fig. 13, the spring element 20 serves two purposes, namely obtaining a predetermined locking force of the caster wheel 5 and supporting the lawnmower body against a ground surface 22 during operation of the lawnmower.

Below simultaneous reference is made to Fig. 1 - Fig. 13. As mentioned, the lawnmower 1 comprises two drive wheels 4, wherein the lawnmower 1 comprises a control arrangement 21 configured to navigate the lawnmower 1 by controlling rotation of the drive wheels 4. According to some embodiments herein, the locking assembly 9 is controllable between a locked state, in which the locking assembly 9 at least partially locks the caster wheel 5 from pivoting about the swivel joint 7, and an unlocked state, in which the caster wheel 5 is free to pivot about the swivel joint 7. Moreover, according to some embodiments herein, the lawnmower 1 comprises a sensor 14, 19 configured to provide data representative of a current angle a1 , a2, a3 of the caster wheel 5 relative to the lawnmower body 3. The sensor 14, 19 may be a sensor 14 as described with reference to Fig. 4 - Fig. 6, or a sensor 19 described with reference to Fig. 11. According to further embodiments, the robotic lawnmower 1 may comprise a Hall effect sensor configured to provide data representative of a current angle a1 , a2, a3 of the caster wheel 5 relative to the lawnmower body 3.

According to some embodiments of the present disclosure, the control arrangement 21 is configured to control the locking assembly 9 between the locked state and the unlocked state based on input data. The input data may representative of at least one of a current or impending slope inclination at the location of the lawnmower 1 , a current or impending inclination angle of the lawnmower 1, traction conditions at the location of the lawnmower 1, weather conditions at the location of the lawnmower 1 , and humidity at the location of the lawnmower 1. As an alternative, or in addition, the input data may be representative of a current angle a1, a2, a3 of the caster wheel 5 relative to the lawnmower body 3 inputted from a sensor 14, 19 configured to provide such data.

The control arrangement 21 may be configured to receive the input data from a sensor 51 arranged on the lawnmower 1 and/or may be configured to receive the input data from an external communication unit 61. The sensor 51 arranged on the lawnmower 1 may be configured to sense a current inclination angle of the lawnmower 1 relative to a horizontal plane at the location of the lawnmower 1. The sensor 51 may be configured to sense the orientation of the lawnmower 1 relative the gravitational field at the location of the lawnmower 1. According to such embodiments, the sensor 51 may comprise an accelerometer.

As an alternative, or in addition, the sensor 51 may be configured to sense angular displacements of the lawnmower 1. According to such embodiments, the sensor 51 may comprise a gyroscope. Moreover, the control arrangement 21 may be arranged to obtain reference values at one or more predetermined locations, such as at a charging dock. According to such embodiments, the sensor 51 may obtain the current inclination angle by monitoring changes in inclination angle, for example by sensing changes in inclination angle of the lawnmower 1 and comparing such changes with one or more reference values. According to still further embodiments, the control arrangement 21 may be configured to obtain a current or impending slope inclination at the location of the lawnmower 1, and/or a current or impending inclination angle of the lawnmower 1, by receiving such data from an external source 61, and/or by comparing the current position of the lawnmower 1 and map data comprising data indicative of slope inclination angles at the area. The inclination angle of the lawnmower 1, as referred to herein, may be a lateral inclination angle of the robotic lawnmower 1, i.e. an angle between a lateral axis of the robotic lawnmower 1 the horizontal plane at the location of the lawnmower 1.

The control arrangement 21 may be configured to control the locking assembly 9 to the locked state when a current or impending slope inclination at the location of the lawnmower 1 , and/or a current or impending inclination angle of the lawnmower 1 , exceeds a threshold value. In this manner, an improved directional stability of the robotic lawnmower 1 can be obtained which reduces the risk of unwanted changes in travel direction in an efficient manner.

Input data representative of traction conditions at the location of the lawnmower 1 , weather conditions at the location of the lawnmower 1 , and/or humidity at the location of the lawnmower 1 may be inputted from a sensor 51 arranged on the lawnmower 1, and/or may be inputted from an external communication unit 61. As an alternative, or in addition, traction conditions at the location of the lawnmower 1 may be estimated by the control arrangement 21 by monitoring rotation of the drive wheels 4 so as to detect presence of wheel slip of the drive wheels 4. The control arrangement 21 may be configured to control the locking assembly 9 to the locked state more frequently, and/or during longer time periods, when traction conditions, weather conditions, and/or humidity at the location of the lawnmower 1 indicates a higher probability of wheel slip. In this manner, an improved directional stability of the robotic lawnmower 1 can be obtained under such circumstances which reduces the risk of unwanted changes in travel direction in an efficient manner.

As described above, according to some embodiments herein, the locking assembly 9 is configured to unlock the caster wheel 5 when a torque is applied onto the caster wheel 5 around the swivel joint 7 exceeding a threshold torque. According to such embodiments, the control arrangement 21 may configured to selectively perform a control operation of the lawnmower 1 in which a torque is applied onto the caster wheel 5 around the swivel joint 7 exceeding the threshold torque. Such control operation may comprise a turning of the lawnmower 1. In this manner, the contact between the ground surface 22 and the caster wheel 5 can apply a torque onto the caster wheel 5 around the swivel joint 7 exceeding the threshold torque so as to unlock the caster wheel 5. According to some embodiments, the control operation may comprise stopping the lawnmower 1 before initiating the turning of the robotic lawnmower 1. That is, according to such embodiments, the control arrangement 21 may stop the robotic lawnmower 1 and then initiate a turning of the robotic lawnmower 1 so as to apply a torque onto the caster wheel 5 around the swivel joint 7 exceeding the threshold torque. Thereby, the caster wheel 5 can be unlocked with higher certainty.

According to some embodiments herein, the control arrangement 21 may be configured to navigate the robotic lawnmower 1 in a manner being adapted to one or more predetermined angles a1 , a2 of the caster wheel 5 relative to the lawnmower body 3 at which the locking assembly 9 is configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7. Such adaptation may comprise an adaptation of a systematic or random pattern in which the control arrangement 21 navigates the robotic lawnmower 1. Since the robotic lawnmower 1 according to embodiments herein comprises the locking assembly 9 capable of providing improved directional stability of the robotic lawnmower 1 and a reduced risk of unwanted changes in travel direction, this can be utilized by the control arrangement 21 in a navigational control of the robotic lawnmower 1. As an example, the control arrangement 21 can navigate the robotic lawnmower 1 in a systematic manner along a navigation path comprising adjacent mowing strokes. Due to the improved directional stability of the robotic lawnmower 1, the robotic lawnmower 1 can operate in such patterns with higher accuracy even when operating undulated areas.

The robotic lawnmower 1 may comprise another type of locking assembly being configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7, then what is illustrated in the illustrated embodiments. As an example, the locking assembly may comprise a piezo-electric element configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7. Such a piezo-electric element may be controlled by the control arrangement 21 of the robotic lawnmower 1. As another example, the locking assembly may comprise a fluid having controllable viscosity, such as a ferromagnetic fluid. According to such embodiments, the viscosity can be increased, for example by control of the control arrangement 21 of the robotic lawnmower 1 , so as to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7

One skilled in the art will appreciate the control performed by the control arrangement 21 described herein may be implemented by programmed instructions. These programmed instructions are typically constituted by a computer program, which, when it is executed in the control arrangement 21, ensures that the control arrangement 21 carries out the desired control. The computer program is usually part of a computer program product which comprises a suitable digital storage medium on which the computer program is stored.

The control arrangement 21 may comprise a calculation unit which may take the form of substantially any suitable type of processor circuit or microcomputer, e.g. a circuit for digital signal processing (digital signal processor, DSP), a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The herein utilised expression “calculation unit” may represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above.

The control arrangement 21 may further comprise a memory unit, wherein the calculation unit may be connected to the memory unit, which may provide the calculation unit with, for example, stored program code and/or stored data which the calculation unit may need to enable it to do calculations. The calculation unit may also be adapted to store partial or final results of calculations in the memory unit. The memory unit may comprise a physical device utilised to store data or programs, i.e. , sequences of instructions, on a temporary or permanent basis. According to some embodiments, the memory unit may comprise integrated circuits comprising silicon-based transistors. The memory unit may comprise e.g. a memory card, a flash memory, a USB memory, a hard disc, or another similar volatile or non-volatile storage unit for storing data such as e.g. ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), etc. in different embodiments. The control arrangement 21 is connected to components of the lawnmower 1 for receiving and/or sending input and output signals. These input and output signals may comprise waveforms, pulses, or other attributes which the input signal receiving devices can detect as information and which can be converted to signals processable by the control arrangement 21. These signals may then be supplied to the calculation unit. One or more output signal sending devices may be arranged to convert calculation results from the calculation unit to output signals for conveying to other parts of the control system and/or the component or components for which the signals are intended. Each of the connections to the respective components of the lawnmower 1 for receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, e.g. a CAN (controller area network) bus, or some other bus configuration, or a wireless connection.

In the embodiments illustrated, the lawnmower 1 comprises a control arrangement 21 but might alternatively be implemented wholly or partly in two or more control arrangements or two or more control units.

The computer program product may be provided for instance in the form of a data carrier carrying computer program code for performing the desired control when being loaded into one or more calculation units of the control arrangement 21. The data carrier may be, e.g. a CD ROM disc, or a ROM (read-only memory), a PROM (programable read-only memory), an EPROM (erasable PROM), a flash memory, an EEPROM (electrically erasable PROM), a hard disc, a memory stick, an optical storage device, a magnetic storage device or any other appropriate medium such as a disk or tape that may hold machine readable data in a non- transitory manner. The computer program product may furthermore be provided as computer program code on a server and may be downloaded to the control arrangement 21 remotely, e.g., over an Internet or an intranet connection, or via other wired or wireless communication systems.

The control arrangement 21 may be configured to control propulsion of the lawnmower 1, and steer the lawnmower 1, so as to navigate the lawnmower 1 in an area to be operated. The lawnmower 1 may further comprise one or more sensors arranged to sense a magnetic field of a wire, and/or one or more positioning units, and/or one or more sensors arranged to detect an impending or ongoing collision event with an object. The one or more positioning units may comprise a space based satellite navigation system such as a Global Positioning System (GPS), The Russian GLObal NAvigation Satellite System (GLONASS), European Union Galileo positioning system, Chinese Compass navigation system, or Indian Regional Navigational Satellite System. As an alternative, or in addition, the control arrangement 21 may be configured to obtain data from, or may comprise, one or more positioning units utilizing a local reference source, such as a local sender and/or a wire, to estimate or verify a current position of the lawnmower 1.

In addition, the lawnmower 1 may comprise a communication unit connected to the control arrangement 21. The communication unit may be configured to communicate with a remote communication unit 61 to receive instructions therefrom and/or to send information thereto. The communication may be performed wirelessly over a wireless connection such as the internet, or a wireless local area network (WLAN), or a wireless connection for exchanging data over short distances using short-wavelength, i.e. ultra-high frequency (UHF) radio waves in the industrial, scientific, and medical (ISM) band from 2.4 to 2.485 GHz.

The control arrangement 21 may be configured to control propulsion of the lawnmower 1, and steer the lawnmower 1, so as to navigate the lawnmower 1 in a systematic and/or random pattern to ensure that an area is completely covered, using input from one or more of the above described sensors and/or units. Furthermore, the lawnmower 1 may comprise one or more batteries arranged to supply electricity to components of the lawnmower 1. As an example, the one or more batteries may be arranged to supply electricity to propulsion motors of the lawnmower 1 by an amount controlled by the control arrangement 21.

Moreover, the one or more batteries may be arranged to supply electricity a motor configured to power a cutting unit of the robotic lawnmower 1.

As explained above, the locking performed by the locking assembly 9 may be a full lock or a partial lock, wherein the partial lock may become unlocked if a torque is applied onto the caster wheel 5 around the swivel joint 7 exceeding a threshold torque. That is, the feature that the locking assembly 9 is configured to at least partially lock the caster wheel 5 from pivoting about the swivel joint 7 may encompass that the locking assembly 9 is configured to lock the caster wheel 5 from pivoting about the swivel joint 7 and/or partially lock the caster wheel 5 from pivoting about the swivel joint 7. As understood from the herein described, a partial lock is a partial fixation of the caster wheel 5 about the swivel joint 7 which partial lock may become unlocked/unfixed if a torque is applied onto the caster wheel 5 around the swivel joint 7 exceeding a threshold torque. A partial lock can be equated with a hindrance of movement. The hindrance of movement may be obtained by applying a counter torque to the caster wheel 5 around the swivel joint 7 if a torque is applied onto the caster wheel 5 around the swivel joint 7. Therefore, throughout this disclosure, the wording “at least partially lock the caster wheel 5 from pivoting” may be replaced with the wording “at least partially hinder the caster wheel 5 from pivoting”, or “hinder the caster wheel 5 from pivoting”, or “at least partially preventing the caster wheel 5 from pivoting”, or “prevent the caster wheel 5 from pivoting”.

It is to be understood that the foregoing is illustrative of various example embodiments and that the invention is defined only by the appended claims. A person skilled in the art will realize that the example embodiments may be modified, and that different features of the example embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the present invention, as defined by the appended claims.

As used herein, the term "comprising" or "comprises" is open-ended, and includes one or more stated features, elements, steps, components, or functions but does not preclude the presence or addition of one or more other features, elements, steps, components, functions, or groups thereof.