Patent Description:
A robotic work tool is an autonomous robot apparatus that is used to perform certain tasks, for example for cutting lawn grass. A robotic work tool is generally controlled by defining an area, in which the robotic work tool is intended to operate. The work area is defined by a perimeter enclosing the work area. The perimeter includes borders, or boundaries, which the robotic work tool is not intended to cross. The robotic work tool is typically configured to work in a random pattern inside the work area.

When larger areas are to be mowed, these are generally divided into subareas, i.e. smaller defined areas with boundaries. An example of such a large area may be a sports area, which comprises several football fields. In such sports area, the robotic work tool typically has to transport between a charging station and the football fields, or subareas, and between the different football fields. Generally, there is a desired path which the robotic work tool should take in order to avoid obstacles, disturbances of other areas etc. The robotic work tool is typically guided along a travel path between these subareas and charging station. The travel path is thereafter repeatedly used by the robotic work tool for transport between the subareas and the charging station.

However, even if there are many advantages with a specified travel path for transporting the robotic work tool between different locations such that obstacles may be avoided and such that the robotic work tool may operate autonomously, without an operator, the inventors have realized that there may arise problems when such travel path is used by multiple robotic work tools and/or when it is used repeatedly. Thus, there is a need for an improved way of transporting a robotic work tool between different locations.

<CIT> was cited during the prosecution before the European Patent Office. This patent application later issued into a patent, i.e. <CIT>, which is assigned to Husqvarna AB. This patent discloses a method and system for guiding a robotic garden tool. The robotic garden tool may include at least two sensing means. The robotic garden tool is equipped to follow along a guiding wire on a lawn. While the robotic garden tool moves along the guiding wire, the sensing means may detect a magnetic field strength generated from current carrying guiding wire. The method and the system is equipped to provide instructions to the robotic garden tool to follow the guiding wire based on the difference of magnetic field strength sensed by at least two sensing means.

<CIT>, which was also cited during the prosecution before the European Patent Office, discusses robotic mowing of separated lawn areas. In this disclosure, a method of mowing multiple areas includes training a robotic mower to mow at least two areas separated by a space, including moving the robotic mower about the areas while storing data indicative of location of boundaries of each area relative to boundary markers, training the robotic mower to move across the space separating the areas, and initiating a mowing operation. Training the robotic mower to move across the space separating the areas includes moving the robotic mower to a traversal launch point of a first of the areas and moving the robotic mower to a traversal landing point of a second of the areas. The mowing operation causes the robotic mower to move to the traversal launch point, move from the traversal launch point across the space to the traversal landing point, and then mow the second of the areas.

The inventors of the various embodiments have realized, after inventive and insightful reasoning, that when a defined travel path between different locations is used repeatedly and/or by multiple robotic work tools, the travel path eventually gets permanent marks, or trails, from the wheels of the robotic work tools. This is usually undesirable as it may destroy the area where the travel path is located. It may be perceived as unattractive, but more importantly, it may make the travel path difficult to travel for the robotic work tools. Thus, there is a need for a solution which allows at least one robotic work tool to travel between different locations repeatedly but which still allows the at least one robotic work tool to travel autonomously, without a manual operator, and which still allows the at least one robotic work tool to avoid obstacles.

In view of the above, it is therefore a general object of the aspects and embodiments described throughout this disclosure to provide a solution for an improved way of transporting at least one robotic work tool between different locations.

This general object has been addressed by the appended independent claims. Advantageous embodiments are defined in the appended dependent claims.

According to a first aspect, there is provided a robotic work tool system for avoiding trails from at least one robotic work tool in a transit zone. The transit zone is an area in which the at least one robotic work tool is allowed to travel from a start point to a goal point along a travel path. In addition, the transit zone is an area connecting a first work area with a second work area.

In one exemplary embodiment, the robotic work tool system comprises at least one memory configured to store information about the transit zone and at least one robotic work tool configured to travel along the travel path within the transit zone. The robotic work tool system further comprises at least one controller for controlling operation of the at least one robotic work tool. The at least one controller is configured to receive, from the at least one memory, information about the transit zone; and to generate, based on the determined transit zone, the travel path for the at least one robotic work tool from the start point to the goal point. The generated travel path is configured to differ from previously generated travel paths within the transit zone.

Furthermore, the robotic work tool system further comprises at least one input device configured to receive transit data associated with the start point and the goal point. The at least one controller is further configured to determine the transit zone based on the transit data received from the at least one input device.

In one embodiment, the at least one input device comprises a user interface configured to receive user input from a user during the user's operation and interaction with said user interface.

The at least one controller is further configured to determine the transit zone by determining virtual boundaries which define a corridor between the start point and the goal point.

The at least one input device comprises a recording device. The recording device is configured to record a transit path of the at least one robotic work tool while the at least one robotic work tool is moved from the start point to the goal point. The at least one controller is configured to determine the virtual boundaries by expanding the recorded transit path sideway, wherein the transit zone is determined as the area between the recorded transit path and the sideway expanded transit path.

Alternatively, in a non-claimed embodiment, the at least one controller may be configured to determine the virtual boundaries by expanding the recorded transit path sideway on both sides of the recorded transit path, wherein the transit zone is determined as the area between the sideways expanded transit paths.

In one embodiment, the transit path is expanded by a distance that is configurable by the at least one input device.

In one embodiment, the recording device is configured to record transit paths of the at least one robotic work tool while the at least one robotic work tool is moved from the start point to the goal point, and from the goal point back to the start point. The at least one controller is configured to determine the transit zone to be the area between the two recorded transit paths.

In one embodiment, the at least one controller is configured to randomly generate the travel path. In another embodiment, the at least one controller is configured to systematically generate the travel path.

In one embodiment, the previously generated travel paths are the travel paths that have been used by the at least one robotic work tool for the last <NUM> days. In another embodiment, the previously generated travel paths are the <NUM> previous generated travel paths.

In one embodiment, at least one of the at least one robotic work tool is a robotic lawn mower.

According to a second aspect, there is provided a method implemented by the robotic work tool system according to the first aspect.

In one exemplary implementation, the method is performed by a robotic work tool system for avoiding trails from at least one robotic work tool in a transit zone. The transit zone is an area wherein the at least one robotic work tool is allowed to travel from a start point to a goal point along a travel path. In addition, the transit zone is an area connecting a first work area with a second work area. The robotic work tool system comprises at least one memory configured to store information about the transit zone and at least one robotic work tool configured to travel along the travel path within the transit zone. The robotic work tool system further comprises at least one controller for controlling operation of the at least one robotic work tool. The method comprises receiving, from the at least one memory, information about the transit zone, determining the transit zone by determining virtual boundaries which define a corridor between the start point and the goal point, and generating, based on the determined transit zone, the travel path for the at least one robotic work tool from the start point to the goal point. The generated travel path is configured to differ from previously generated travel paths within the transit zone.

The robotic work tool system further comprises at least one input device. The method further comprises receiving, by the at least one input device, transit data associated with the start point and the goal point; recording, by the at least one input device a transit path of one of the at least one robotic work tool while the robotic work tool is moved from the start point to the goal point; and determining, by the at least one controller, the transit zone based on the transit data received from the at least one input device; and further determining, by the at least one controller, the virtual boundaries by expanding the recorded transit path sideway, wherein the transit zone is determined as the area between the recorded transit path and the sideway expanded transit path. Some of the above embodiments eliminate or at least reduce the problems discussed above. By generating a transit zone wherein the at least one robotic work tool may be transported between a start point and a goal point along different travel paths, it may be assured that the same travel path is not used repeatedly. Thereby, it may be possible to avoid that trails are generated. Thus, a robotic work tool system and method are provided that improve the way of transporting a robotic work tool between different areas.

These and other aspects, features and advantages will be apparent and elucidated from the following description of various embodiments, reference being made to the accompanying drawings, in which:.

The disclosed embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the robotic work tool system are shown. This robotic work tool system may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the robotic work tool system to those skilled in the art.

In one of its aspects, the disclosure presented herein concerns a robotic work tool system for avoiding trails from at least one robotic work tool in a transit zone. A transit zone is an area in which the at least one robotic work tool is allowed to travel from a start point to a goal point along a travel path. The transit zone is a corridor within which the at least one robotic work tool may take different travel paths in order to reach the goal point when starting at the start point.

The robotic work tool system comprises at least one robotic work tool. The at least one robotic work tool may be realised in many different ways. While the present disclosure will mainly be described in general terms of an autonomous robot designed for mowing grass, it should be understood that the robotic work tool described herein may be implemented into any type of autonomous machine that may travel between different work areas. Examples of such types of autonomous machines include, without limitation, cleaning robotic work tools, polishing work tools, repair work tools, surface-processing work tools (for indoors and/or outdoors), garbage handling work tools, transportation work tools and/or demolition work tools or the like.

<FIG> shows a schematic overview of a robotic working tool <NUM>, which may be exemplified by a robotic lawnmower <NUM>, having a front carriage <NUM>' and a rear carriage <NUM>". It is appreciated that the present disclosure is not limited to a robotic work tool <NUM> having separate front and rear carriages <NUM>', <NUM>". Rather, the robotic work tool <NUM> may also be of a type that comprises one single integral body.

The robotic working tool <NUM> comprises a plurality of wheels <NUM>. In the exemplary embodiment of <FIG>, the robotic working tool <NUM> comprises two pair of wheels <NUM>. One pair of front wheels <NUM> is arranged in the front carriage <NUM>' and one pair of rear wheels <NUM> is arranged in the rear carriage <NUM>". However, it may be appreciated that the numbers and locations of the plurality of wheels <NUM> of the robotic work tool <NUM> in the present disclosure is not limited to any number and/or location of the plurality of wheels <NUM>. At least some of the wheels <NUM> are drivably connected to at least one electric motor <NUM>. It is appreciated that combustion engines may alternatively be used, possibly in combination with an electric motor.

With reference to the <FIG>, a first embodiment according to the first aspect will now be described. <FIG> shows a schematic view of a robotic work tool system <NUM> according to one embodiment. As will be appreciated, the schematic view is not to scale.

As illustrated in <FIG>, the robotic work tool system <NUM> comprises at least one robotic work tool <NUM>, at least one controller <NUM>, <NUM> and at least one memory <NUM>, <NUM>. The at least one robotic work tool <NUM> is configured to travel along a travel path <NUM>.

The at least one memory <NUM>, <NUM> is configured to store information about the transit zone <NUM>. The transit zone <NUM> may be exemplified in many different ways, but <FIG> illustrates one example of such transit zone <NUM>. The transit zone may be, for example, a zone, or an area, connecting a work area with a charging station located outside the work area, such that the start, or goal, point is located at the border of the work area and the goal, or start, point is located at the charging station. According to another example, the transit zone may be an area connecting a first work area with a second working area, such that the start point is at the border of the first work area and the goal point at the border of the second work area.

As understood from <FIG>, the at least one memory <NUM>,<NUM> may be the internal memory <NUM> of the at least one robotic work tool <NUM>, and/or the at least one memory <NUM>, <NUM> may be a memory <NUM> located remote from the at least one robotic work tool <NUM>, e.g. remotely in a cloud-based solution. The at least one memory <NUM>, <NUM> may be implemented using any commonly known technology for computer-readable memories such as ROM, RAM, SRAM, DRAM, FLASH, DDR, SDRAM or some other memory technology. In embodiments where the robotic work tool system <NUM> comprises a plurality of robotic work tools <NUM>, it may be appreciated that the at least one memory <NUM>, <NUM> may be shared between the plurality of robotic work tools <NUM>. In these embodiments, the at least one memory may be a memory <NUM> located remote from the plurality of robotic work tools <NUM>, e.g. remotely in a cloud-based solution or in a central server. Alternatively, the at least one memory may be the internal memories <NUM> of the plurality of robotic work tools <NUM> and shared between the robotic work tools <NUM>.

The at least one controller <NUM>, <NUM> is configured to control the operation of the at least one robotic work tool <NUM>. The controller <NUM>, <NUM> is configured to read instructions from the at least one memory <NUM>, <NUM> and execute these instructions to control the operation of the at least one robotic work tool <NUM>. In one embodiment, the at least one controller <NUM> is embodied as software, e.g. remotely in a cloud-based solution. In another embodiment, the at least one controller <NUM>, <NUM> may be embodied as a hardware controller. The at least one controller <NUM>, <NUM> may be implemented using any suitable, publicly available processor or Programmable Logic Circuit (PLC).

The at least one controller <NUM>, <NUM> may, for example, be the controller <NUM> located in the at least one robotic work tool <NUM>. According to another example, the at least one controller <NUM> may be located in a device that is separate from the robotic work tool <NUM>. When the at least one controller <NUM> is located in another device than in the at least one robotic work tool <NUM>, the separate device is communicatively coupled to the at least one robotic work tool <NUM>. They may be communicatively coupled to each other by a wireless communication interface. Additionally, or alternatively, the wireless communication interface may be used to communicate with other devices, such as servers, personal computers or smartphones, charging stations, remote controls, other robotic work tools or any remote device, which comprises a wireless communication interface and a controller. Examples of such wireless communication are Bluetooth®, Global System Mobile (GSM) and LTE (Long Term Evolution), <NUM> New Radio, to name a few.

According to the present disclosure, the at least one controller <NUM>, <NUM> is configured to receive, from the at least one memory <NUM>, <NUM>, information about the transit zone <NUM>. The at least one controller <NUM>, <NUM> is further configured to generate, based on the transit zone <NUM>, the travel path <NUM> for the at least one robotic work tool <NUM> from the start point <NUM> to the goal point <NUM>. The generated travel path <NUM> is configured to differ from previously generated travel paths within the transit zone <NUM>. As understood from e.g. <FIG>, the travel path <NUM> is generated based on the transit zone <NUM> such that it is generated to be located within the transit zone <NUM>. Thus, the transit zone <NUM> limits where the travel path <NUM> may be located. However, within the transit zone <NUM>, there are no boundaries and the at least one controller <NUM>, <NUM> may generate the travel path <NUM> in any way as long as the travel path <NUM> is located within the transit zone <NUM> and the travel path <NUM> differs from previously generated travel paths <NUM>.

The provided robotic work tool system <NUM> improves the way of transporting at least one robotic work tool <NUM> between different areas. By allowing the at least one controller <NUM>, <NUM> to generate travel paths at any place inside the entire transit zone <NUM>, it may be assured that the at least one robotic work tool <NUM> does not have to repeatedly be transported along the same travel path to reach the goal point. The provided robotic work tool system <NUM> may assure that the generated travel path <NUM> for the at least one robotic work tool <NUM> is not the same as previously generated and used travel paths. Accordingly, the same travel path is not used repeatedly and thereby, it is avoided that marks, or trails, from the at least one robotic work tool <NUM> are generated. This may be advantageous as trails usually are undesirable as they may destroy the area where the travel path <NUM> is located. Trails may be perceived as unattractive, but more importantly, they may make the travel path difficult to travel for the robotic work tools <NUM>. Furthermore, as the at least one robotic work tool <NUM> is limited to the transport within the transit zone <NUM>, an improved way of transporting the at least one robotic work tool <NUM> between different locations may also be achieved. The transit zone <NUM> will assure that the at least one robotic work tool <NUM> does not travel along any travel path, it may only travel along the generated travel paths <NUM> within the transit zone <NUM>.

As previously described, the at least one controller <NUM>, <NUM> is configured to control the operation of the at least one robotic work tool <NUM>. Thus, the at least one controller <NUM>, <NUM> may control the at least one robotic work tool <NUM> such that the at least one robotic work tool <NUM> travels according to the generated travel path <NUM> when the at least one robotic work tool <NUM> is going to transport from the start point <NUM> to the goal point <NUM>. The at least one controller <NUM>, <NUM> may control the at least one motor <NUM> of the at least one robotic work tool <NUM> such that the at least one robotic work tool <NUM> travels in accordance with the direction of the generated travel path <NUM>.

In one embodiment, the robotic work tool system <NUM> may further comprise at least one input device <NUM>, <NUM>. The input device <NUM>, <NUM> may be configured to receive transit data associated with the start point <NUM> and the goal point <NUM>. The at least one controller <NUM>, <NUM> may further be configured to determine the transit zone <NUM> based on the transit data received from the at least one input device <NUM>, <NUM>. Accordingly, the at least one input device <NUM>, <NUM> may be configured to receive data related to the start point <NUM> and the goal point <NUM> and based on this data, the at least one controller <NUM>, <NUM> may determine the corridor in which the at least one robotic work tool <NUM> is allowed to travel in order to reach the goal point <NUM> from the start point <NUM>. The information about the determined transit zone <NUM> may be stored in the at least one memory <NUM>, <NUM>, and the travel path <NUM> for the robotic work tool <NUM>, from the start point <NUM> to the goal point <NUM>, may be generated based on the determined transit zone <NUM>.

The at least one input device <NUM>, <NUM> may be located in the at least one robotic work tool <NUM>, or the at least one input device <NUM>, <NUM> may be located in a device that is separate from the at least one robotic work tool <NUM>. When the at least one input device <NUM>, <NUM> is located in another device than in the at least one robotic work tool <NUM>, the separate device is communicatively coupled to the at least one robotic work tool <NUM> by a wireless communication interface arranged with the robotic work tool <NUM>.

Accordingly, by including at least one input device <NUM>, <NUM> in the robotic work tool system <NUM>, it may be possible to influence the transit zone <NUM>. It may be possible to determine the transit zone <NUM> based on additional data received from the at least one input device <NUM>, <NUM>. Thus, a more precise transit zone <NUM> may be provided as additional data may be considered when determining the transit zone <NUM>.

In some embodiments, the at least one input device <NUM>, <NUM> may comprise a user interface <NUM> configured to receive user input from a user during the user's operation and interaction with said user interface <NUM>. The user interface <NUM> may be configured to receive input related to, and associated with, the transit zone <NUM>. The user interface <NUM> may be, for example, a touch user interface. The user interface <NUM> is preferably separated from the robotic work tool <NUM> as illustrated in <FIG>. However, in some embodiments, the user interface <NUM> may be located at the at least one robotic work tool <NUM>.

By providing a user interface <NUM> that may receive transit data, a more precise transit zone <NUM> may be achieved. For example, in some embodiments, the user, or operator, may input transit data that reflect certain requirements desired by the operator and may thereby the influence the transit zone <NUM>. Thus, a flexible way of providing a more accurate transit zone <NUM> may be achieved. Furthermore, by providing a user interface <NUM> a more flexible robotic work tool system <NUM> may be achieved as the operator may input transit data.

In some embodiments, the at least one controller <NUM>, <NUM> may further be configured to determine the transit zone <NUM> by determining virtual boundaries <NUM> which define a corridor between the start point <NUM> and the goal point <NUM>. By determining the virtual boundaries <NUM> of the transit zone <NUM> in which the at least one robotic work tool <NUM> is allowed to travel between different locations, it may also be assured that hindrance and obstacles are avoided. For example, if a goal point <NUM> is difficult to access, e.g. because it may be located behind a flowerbed, the transit zone may assure that the at least one robotic work tool <NUM> is not allowed to pass over the flowerbed. This may be achieved by determining the transit zone <NUM> such that it is guided around the flowerbed. Accordingly, the proposed robotic work tool system <NUM> provides an improved way of transporting at least one robotic work tool <NUM> between different locations.

In some embodiments, the at least one input device <NUM>, <NUM> may comprise a recording device. The recording device may register a distance and/or a force with which the robotic work tool <NUM> is moved along a travel route. The recording device may use odometry to estimate the change in position over time. The recording device may, for example, be an encoder. The encoder may be configured to record the travel route of the at least robotic work tool <NUM> by tracking rotation of the at least one wheel <NUM>. Pulses noted by the encoder may be transformed into distances per time units. By realizing the recording device by an encoder, a relatively simple but accurate input device is provided.

In some embodiments, the recording device may be configured to record a transit path of the at least one robotic work tool <NUM> while the at least one robotic work tool <NUM> is moved from the start point <NUM> to the goal point <NUM>. In some embodiments, the at least one controller <NUM>,<NUM> may be configured to determine the virtual boundaries <NUM> by expanding the recorded transit path sideway. The transit zone <NUM> may then be determined as the area between the recorded transit path and the sideway expanded transit path. In other embodiments, the at least one controller <NUM>,<NUM> may be configured to determine the virtual boundaries <NUM> by expanding the recorded transit path sideway on both sides of the recorded transit path. Thereafter, the transit zone <NUM> may be determined as the area between the sideways-expanded transit paths. The transit path may expanded by a distance that is configurable by the at least one input device <NUM>.

Accordingly, by using a recording device to record at least one transit path when the at least one robotic work tool <NUM> is moved from the start to the goal point and thereafter use this recorded transit path to determine the transit zone <NUM>, it may be easy to assure that the transit zone <NUM> is located where it is desired. Furthermore, it may be easy to assure that no objects or obstacles are within the way of the at least one robotic work tool <NUM>.

In other embodiments, the recording device may be configured to record transit paths of the at least one robotic work tool <NUM> while the at least one robotic work tool <NUM> is moved from the start point <NUM> to the goal point <NUM>, and from the goal point <NUM> back to the start point <NUM>. The at least one controller <NUM>,<NUM> may be configured to determine the transit zone <NUM> to be the area between the two recorded transit paths. Thus, it may be easy to define where the transit zone <NUM> is located as both boundaries <NUM> are driven by the at least one robotic work tool <NUM>.

In some embodiments, the at least one controller <NUM>,<NUM> may be configured to randomly generate the travel path <NUM>. Thereby, the risk of the same travel path <NUM> being generated several times is minimized. In other embodiments, the at least one controller <NUM>, <NUM> may be configured to systematically generate the travel path <NUM>. In one embodiment, the travel path <NUM> may generated as a polygonal chain comprising of a connected series of line segments. Each line segment may be generated independently. Each line segment may be generated either randomly or systematically. When they are generated independently, each line segment may be generated such that the generated line segment differ from previously generated corresponding line segments. Furthermore, by generating the travel path <NUM> as a polygonal chain it may be possible to set different levels of sensitivity for the different line segments. For example, if the first line segment extend over asphalt, that line segment may not be so critical for being used repeatedly, while if the second line segment may extend over grass, that line segment may be really sensitive for repeated use. Thus, the generated travel paths for the first line segment may more often be similar to each other than the generated travel paths for the second line segment.

The travel paths <NUM> may be pre-generated and assigned to the at least one robot work tool <NUM> at the moment when it is going to transport between the start point <NUM> and the goal point <NUM> in the transit zone <NUM>. Alternatively, the travel paths <NUM> may be pre-generated and saved within the at least memory <NUM> within the robotic work tool <NUM>. In case the robotic work tool system <NUM> comprises multiple robotic work tools <NUM>, each of the at least one robotic work tool <NUM> may then be assigned different pre-generated travel paths <NUM>.

The previously generated travel paths may, for example, be the travel paths that have been used by the at least one robotic work tool <NUM> for the last <NUM> days. Accordingly, within <NUM> days, the same travel path should not be generated again. Alternatively, the previously generated travel paths <NUM> may be the <NUM> previous generated travel paths <NUM>. In this scenario, it is not until the eleventh time that any of the at least one robotic work tools <NUM> may be transported along the same travel paths <NUM> within the transit zone <NUM>. In some embodiments, the criteria for previous generated travel paths may be set differently depending on the ground of the transit zone, as also discussed above. For example, a transit zone <NUM> which comprises grass may be more sensitive to repeatedly used travel paths <NUM> than a transit zone <NUM> which comprises of gravel. Thus, the previously generated travel paths <NUM> may, for example, be the <NUM> previous generated travel paths <NUM> for a transit zone <NUM> of gravel, while it may be the <NUM> previous generated paths <NUM> for a transit zone <NUM> of grass. However, it may be appreciated that the criteria for the previous generated travel paths also may depend on how frequently the transit zone <NUM> is used.

<FIG> illustrates an example embodiment implementing the proposed robotic work system <NUM>. The robotic work tool system <NUM> has received information about a transit zone <NUM>. As previously described, the transit zone <NUM> is the area in which the at least one robotic work tool <NUM> is allowed to travel from a start point <NUM> to a goal point <NUM> along a travel path <NUM>. The two solid lines <NUM> beside the robotic work tools <NUM> in <FIG> represents the boundaries of the transit zone <NUM>. The at least one controller <NUM>, <NUM> will not generate a travel path <NUM> that crosses these boundaries <NUM> or a travel path <NUM> that is located outside this transit zone <NUM>. The dotted line <NUM> in front of the robotic work tools <NUM> in <FIG> represents the generated travel path <NUM>. As seen in <FIG>, there are two robotic work tools <NUM> within the transit zone <NUM>. The number of robotic work tools <NUM> may also be larger. Alternatively, there may only be one robotic work tool <NUM>. According to this example embodiment, the two robotic work tools <NUM> are located within the transit zone <NUM> at approximately the same time. However, it may be appreciated that there may be more than the one robotic work tool <NUM>, but that they may not transport within the transit zone <NUM> at the same time. Furthermore, it may be appreciated that the travel paths <NUM> within the transit zone <NUM> may be directed in different directions. When one of the at least one robotic work tool <NUM> may be transporting from a start point to a goal point, another robotic work tool <NUM> may transport in the other direction, i.e. from the first robotic work tool's <NUM> goal point to its start point. However, regardless of the number of robotic work tools <NUM> and the directions they are travelling, the at least one robotic work tool <NUM> travels along different travel paths <NUM> in order to avoid trails from the wheels <NUM> of the robotic work tools <NUM>.

As has been described above, when the robotic work tool system <NUM> comprises a plurality of robotic work tools <NUM>, the plurality of robotic work tools <NUM> may share the same memory <NUM>, <NUM>. By sharing the memory <NUM>, <NUM>, it may be assured that the generated travel paths <NUM> are configured to differ also from the previously generated travel paths <NUM> within the transit zone <NUM> for the other robotic work tools <NUM>. The plurality of robotic work tools <NUM> thus have access to the same transit zone <NUM> and the same history of previously generated travel paths <NUM>. Accordingly, the generated travel paths <NUM> are configured such that they not only differ from the travel paths <NUM> generated for a specific robotic work tool <NUM>, but for all robotic work tools <NUM> comprised in the robotic work tool system <NUM>.

In some embodiments, a central controller <NUM> generates the travel paths <NUM> for each robotic work tool <NUM>. In other embodiments, the travel paths <NUM> for each robotic work tool <NUM> are generated locally in each robotic work tool <NUM> by the robotic work tools' local controllers <NUM>. In these embodiments, all the robotic work tools <NUM> within the robotic work tool system <NUM> share the same history of generated travel paths <NUM>, i.e. have information of all generated travel paths <NUM> within the transit zone <NUM> for all the robotic work tools <NUM>, but the generation of the travel paths <NUM> is decentralized. When a travel path <NUM> has been generated within a robotic work tool <NUM>, this information is thereafter stored in the shared memory <NUM>, <NUM>, such that subsequent generation of travel paths <NUM> may also take this travel path <NUM> into account when a new travel path <NUM> is generated.

In some embodiments, when the robotic work tool system <NUM> comprises a plurality of robotic work tools <NUM>, each generated travel path <NUM> may be generated for a specific robotic work tool <NUM>. In such embodiments, each generated travel path <NUM> may be generated with regard to the properties of the specific robotic work tool <NUM>. Example of such properties that may be taken into account when generating the travel path may be, for example, the weight of the robotic work tool <NUM>, the wheels of the robotic work tool <NUM> and the tools of the robotic work tool <NUM>. In other embodiments, a plurality of travel paths <NUM> are generated and divided among the plurality of robotic work tools <NUM> without regard to a specific robotic work tool <NUM>.

In some embodiments, the at least one robotic work tool <NUM> comprises at least one sensor unit. The at least one sensor unit may detect when the at least one robotic work tool <NUM> crosses the virtual boundaries <NUM> of the transit zone <NUM>. Accordingly, the at least one sensor may transmit signals to the at least one controller <NUM>, <NUM> of the robotic work tool system <NUM>, informing it of that the at least one robotic work tool <NUM> have entered, or exited, the transit zone <NUM>. The at least one controller <NUM>,<NUM> may thus warn, or inform, an operator of the robotic work tool system <NUM> about that the at least one robotic work tool <NUM> has crossed the virtual boundaries of the transit zone <NUM>. The operator of the robotic work tool system <NUM> may, for example, be informed via the user interface <NUM> or via a sound signal.

The at least one sensor unit may, for example, be a position sensor <NUM>. A robotic work tool <NUM> comprising a position sensor <NUM> is illustrated in <FIG>. The position sensor <NUM> may be configured to detect a position of the robotic work tool <NUM> when the robotic work tool <NUM> is moving. The position sensor <NUM> may comprises a satellite signal receiver <NUM>. The satellite signal receiver <NUM> may be a Global Navigation Satellite System (GNSS) satellite signal receiver, such as a Global Positioning System (GPS) satellite signal receiver. The position sensor <NUM> may be connected to the controller <NUM>, <NUM> for enabling the controller <NUM>, <NUM> to determine current positions for the robotic work tool <NUM> using the position sensor <NUM>.

By introducing the above proposed robotic work tool system <NUM>, the previously described disadvantages are eliminated or at least reduced. It may be possible to avoid trails from at least one robotic work tool <NUM> within a transit zone <NUM> by guiding the at least one robotic work tool <NUM> along different travel paths <NUM> within the transit zone <NUM> each time the robotic work tool <NUM> has to transport between the start and goal points. Furthermore, with the proposed robotic work tool system <NUM>, it may be possible to define in which areas a robotic work tool <NUM> is allowed to travel when transporting between different locations. Accordingly, obstacles and objects on the robotic work tool's <NUM> way to the goal point <NUM> may be avoided by defining the transit zone around such obstacles. Thus, a robotic work tool system <NUM> is provided that improve the way of transporting a robotic work tool between different areas.

According to a second aspect, there is provided a method <NUM> performed by the robotic work tool system <NUM> according to the first aspect for avoiding trails from at least one robotic work tool <NUM> in a transit zone <NUM>. The transit zone <NUM> is an area wherein the at least one robotic work tool <NUM> is allowed to travel from a start point <NUM> to a goal point <NUM> along a travel path. The method <NUM> will be described with reference to <FIG>.

In one embodiment, the robotic work tool system <NUM> comprises at least one memory <NUM>,<NUM> configured to store information about the transit zone <NUM> and at least one robotic work tool <NUM> configured to travel along the travel path <NUM> within the transit zone <NUM>. The robotic work tool system <NUM> further comprises at least one controller <NUM>, <NUM> for controlling operation of the at least one robotic work tool <NUM>. The method <NUM> comprises step <NUM> of receiving, from the at least one memory <NUM>, <NUM>, information about, or related to, the transit zone <NUM>. Thereafter, the method <NUM> comprises step <NUM> of generating, based on the determined transit zone <NUM>, the travel path <NUM> for the at least one robotic work tool <NUM> from the start point <NUM> to the goal point <NUM>. The generated travel path is configured to differ from previously generated travel paths within the transit zone <NUM>.

In some embodiments, the method <NUM> may further comprise step <NUM> of receiving transit data. The transit data may be associated with the start point <NUM> and the goal point <NUM>. The transit data may be received by at least one input device comprised within the robotic work tool system <NUM>. The method may further comprise step <NUM> of determining the transit zone <NUM> based on the transit data.

By introducing the above proposed method <NUM>, it may be possible to avoid trails from the at least one robotic work tool <NUM> within a transit zone <NUM>. The proposed method <NUM> may provide an improved way of transporting the robotic work tool <NUM> between different locations.

Figure <NUM> shows a schematic view of a computer-readable medium as described in the above. The computer-readable medium <NUM> is in this embodiment a data disc <NUM>. In one embodiment, the data disc <NUM> is a magnetic data storage disc. The data disc <NUM> is configured to carry instructions <NUM> that when loaded into a controller, such as a processor, execute a method or procedure according to the embodiments disclosed above. The data disc <NUM> is arranged to be connected to and read by a reading device <NUM>, for loading the instructions into the controller. One such example of a reading device <NUM> in combination with one (or several) data disc(s) <NUM> is a hard drive. It should be noted that the computer-readable medium can also be other mediums such as compact discs, digital video discs, flash memories or other memory technologies commonly used. In such an embodiment, the data disc <NUM> is one type of a tangible computer-readable medium <NUM>.

The instructions <NUM> may also be downloaded to a computer data reading device <NUM>, such as the controller <NUM>, <NUM> or other device capable of reading computer coded data on a computer-readable medium, by comprising the instructions <NUM> in a computer-readable signal <NUM> which is transmitted via a wireless (or wired) interface (for example via the Internet) to the computer data reading device <NUM> for loading the instructions <NUM> into a controller. In such an embodiment, the computer-readable signal <NUM> is one type of a non-tangible computer-readable medium <NUM>.

The instructions may be stored in a memory (not shown explicitly in Figure <NUM>, but referenced <NUM>, <NUM> in <FIG>) of the computer data reading device <NUM>.

Claim 1:
A robotic work tool system (<NUM>) configured to avoid trails from a robotic work tool (<NUM>) in a transit zone (<NUM>), the transit zone (<NUM>) being an area connecting a first work area with a second work area and an area in which the robotic work tool (<NUM>) is allowed to travel from a start point (<NUM>) to a goal point (<NUM>) along a travel path (<NUM>), wherein the robotic work tool system (<NUM>) comprises:
at least one memory (<NUM>,<NUM>) configured to store information about the transit zone (<NUM>);
at least one robotic work tool (<NUM>) configured to travel along the travel path (<NUM>) within the transit zone (<NUM>); and
at least one controller (<NUM>,<NUM>) for controlling operation of the at least one robotic work tool (<NUM>), the at least one controller (<NUM>,<NUM>) being configured to:
receive, from the at least one memory (<NUM>,<NUM>), information about the transit zone (<NUM>);
determine the transit zone (<NUM>) by determining virtual boundaries (<NUM>) which define a corridor between the start point (<NUM>) and the goal point (<NUM>); and
generate, based on the determined transit zone (<NUM>), the travel path (<NUM>) for the robotic work tool (<NUM>) from the start point (<NUM>) to the goal point (<NUM>), wherein the generated travel path (<NUM>) is configured to differ from previously generated travel paths within the transit zone (<NUM>) characterized in that
the robotic work tool system (<NUM>) further comprises at least one input device (<NUM>,<NUM>) configured to receive transit data associated with the start point (<NUM>) and the goal point (<NUM>); and wherein the at least one controller (<NUM>,<NUM>) is further configured to determine the transit zone (<NUM>) based on the transit data received from the at least one input device (<NUM>); and in that
the at least one input device (<NUM>,<NUM>) comprises a recording device, wherein the recording device is configured to record a transit path of one of the at least one robotic work tool (<NUM>) while the robotic work tool (<NUM>) is moved from the start point (<NUM>) to the goal point (<NUM>); and further in that
the at least one controller (<NUM>, <NUM>) is configured to determine the virtual boundaries (<NUM>) by expanding the recorded transit path sideway, wherein the transit zone (<NUM>) is determined as the area between the recorded transit path and the sideway expanded transit path.