SE544293C2 - Method of operating a robotic work tool based on a charge level and an estimated distance value for a plurality of work areas - Google Patents

Abstract

A method of processing a work area using a robotic work tool (1) comprising a chargeable battery, in a work area (2) comprising a charging station (4), comprises: estimating, for a work area portion (2a, 2b, 2c, 2d), a distance value representing a distance from said work area portion (2a, 2b, 2c, 2d) to the charging station (4); and operating the robotic work tool (1) based on an estimated amount of charge needed to transit from said work area portion (2a, 2b, 2c, 2d) to the charging station (4).

Description

METHOD OF OPERATING A ROBOTIC WORK TOOL BASED ON ACHARGE LEVEL AND AN ESTIMATED DISTANCE VALUE FOR APLURALITY OF WORK AREAS Field of the invention The present invention relates to a method of processing a work area using arobotic work tool comprising a chargeable battery, in a work area comprising acharging station.

The invention also relates to a robotic work tool comprising a battery and acontroller for controlling the operation of the robotic working tool.

The invention further relates to a robotic work tool system.

Background EP140614O discloses a method and a system for performing work using arobotic work tool. A work area is divided into a number of different cells, and therobotic work tool is directed along a work path which is as energy efficient aspossible.

However, there is a need for enabling an even more efficient use of the batteryof a robotic work tool, such that larger areas may be covered.

Summary lt is an object of the present disclosure to solve, or at least mitigate, parts or all of the above mentioned problem. To this end, there is provided a methodcomprising estimating, for a work area portion, a distance value representing adistance from said work area portion to the charging station; and operating therobotic work tool based on an estimated amount of charge needed to transit fromsaid work area portion to the charging station.

According to the prior art, robotic work tools, such as robotic lawnmowers,decide to go back to the charging station based on the measured voltage level fallingbelow a limit voltage, and not based on the actual distance between the robotic worktool and the charging station. The robotic work tool could for example decide to go back to the charging station in suboptimal places and make it unnecessarily difficultfor it to find a way back. The method defined above, on the other hand, permitsenabling the robotic work tool to return to the charging station before the remainingcharge is fully depleted. Also, the method improves the ability of the robotic work toolto operate hard-to-reach areas, by enabling a matching between different work areaportions and charge levels required to reach the charging station. ln an embodiment, the method further comprises that said estimating of adistance value comprises estimating a distance value for each of a plurality of areaportions, each estimated distance value representing a distance from the respectivework area portion to the charging station, the method further comprising determininga current charge level of the battery; and selecting a target work area portion of thework area of said plurality of area portions based on the current charge level.

The advantage of selecting the work area to the charge level of the battery inthe robotic work tool is that a high degree of utilization of its potential may be reachedat each given point in time. At the same time, the risk is reduced that the robotic work tool will run out of charge at a point far away from the charging station. ln an embodiment the method comprises: directing the robotic work tooltowards the selected target portion of the work area; and operating the robotic worktool within the target portion of the work area.

This has the effect of enabling the robotic work tool to find and start working inthe selected target portion. While doing so, its level of charge may gradually bedepleted. ln a further embodiment the method comprises: directing the robotic work tooltowards the charging station when the current charge level is below a limit charge level.

The technical effect is that the robotic work tool may remain working as longas its charge is sufficient for a return trip to the charging station. When a limit chargeis reached, the return trip may take place. ln anembodiment the limit charge level is set based on the estimated distancevalue.

This has the effect of enabling a dynamic limit charge level, i. e. that the limitcharge level may be different depending on the current work area, the work areaportions wherein the robotic work tool has recently been working, and/or the workarea portions which have been selected for further work. ln yet an embodiment of the method, the limit charge level is based on anestimated charge for reaching the charging station multiplied by a factor F, which isequal to or larger than 1.

The has the effect of providing another option for dynamically setting the limitcharge level for returning to the charging station. ln a further embodiment of the method, the factor F is in the range of 1-3.This is yet an option for dynamically setting the limit charge level. ln a still further embodiment the method comprises: determining a current charge level of the battery; determining a current position of the robotic work tool;wherein said estimating, for a work area portion, a distance value representing adistance from a work area portion to the charging station comprises estimating, forthe present position, a distance value representing a distance from the presentposition to the charging station.

The technical effect is that the estimated distance value is available to be usedas a basis for further calculations and decisions on how the robotic work tool is toproceed. By way of example, the distance value may form a basis for detemining alimit charge value as defined above. ln a still further embodiment the method comprises that the estimated distancevalue is based on an estimated driving distance from said work area portion to thecharging station.

This has the technical advantage that the robotic work tool may have asufficient charge for returning to the charging station, regardless of where it isworking, while at the same time permitting a high degree of battery depletion whenoperating close to the charging station. The limit charge level may be higher whenthe robotic work tool is working in an area which is far away from the charging stationor in an area which is complicated to reach. 3 ln a further embodiment of the method, the estimated distance value is based on any of an elevation difference between said work area portion and the chargingstation, estimated terrain conditions between said work area portion and the chargingstation, a drive path complexity between said work area portion and the chargingstation, a set of stored obstacles between said work area portion and the chargingstation, and an estimated slope inclination between said work area portion and thecharging station.

The technical effect is a further consideration of the ground conditions in thework area and of the complexity of a return path to the charging station, which mayhave an effect on the amount of battery power required for returning to the chargingstation. ln an even further embodiment of the method, the steps of the method arerepeatedly iterated during the operation of the robotic work tool.

This allows that the charge level may be periodically, though not necessarilyregularly, monitored, as well as the distance value representing the distance to thecharging station. Also, the selected target portion of the work area may bereevaluated periodically, as the robotic work tool is working in the area, and therobotic work tool may gradually select work area portions closer to the chargingstation as the battery gets more and more discharged. ln a second aspect there is disclosed a robotic work tool comprising a batteryand a controller for controlling the operation of the robotic work tool, wherein thecontroller further is configured to operate the robotic work tool according to themethod described above. ln an embodiment of the second aspect, the robotic work tool is a roboticoutdoor tool. ln a further embodiment of the second aspect, the robotic work tool is a roboticgarden tool, in a particular embodiment a robotic lawn mower. ln a third aspect of the disclosure a robotic work tool system comprising arobotic work tool as described above and a charging station is disclosed. lt is noted that embodiments of the invention may be embodied by all possiblecombinations of features recited in the claims. Further, it will be appreciated that thevarious embodiments described for the device are all combinable with the method asdefined in accordance with the second aspect of the present invention, and viceversa.

Brief description of the drawingg The above, as well as additional objects, features and advantages of thepresent invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, withreference to the appended drawings, where the same reference numerals will be used for similar elements, wherein: Fig. 1 is a schematic view in perspective of a robotic work tool at work in awork area; Fig. 2 is a schematic plan view of a work area.Fig. 3 is a flow chart outlining the steps of the method; and Fig. 4 is a flow chart outlining the steps of an advantageous embodiment ofthe method.

All the figures are schematic, not necessarily to scale, and generally only showparts which are necessary in order to elucidate the embodiments, wherein other partsmay be omitted.

Detailed description of the exemplarv embodiments Fig. 1 illustrates a robotic work tool 1 at work in a work area 2. The work area2 has an outer boundary 3 and may be demarcated with an electric cable, withphysical means, such as a wall or a fence, or with virtual means, such as GPSreferences.

The robotic work tool 1 may be any of a number of different types of tools,such as a lawn mower, a snow blower, a golf ball collector etc., which are all designed to work independently in a certain, limited area. The robotic work tool 1 is equipped with a rechargeable battery, which needs to be recharged periodically,depending on the amount of work performed by the robotic work tool 1.

The work area 2 may be a lawn, a yard, a driveway, a driving range etc., whichare all areas possible to demarcate by any means, mentioned above or otherwise. Aboundary cable may be buried in the ground but could also be placed and securedon the surface of the ground.

When an electric cable is used for demarcation, there is an electric current,which emits a magnetic field, in the cable. The magnetic field is registered by sensorsin the robotic work tool 1, which is programmed to remain in the work area 2, insideof the outer boundary 3. The boundary cable may also be connected to a chargingstation 4, to which the robotic work tool 1 returns for charging. Depending on how therobotic work tool 1 is programmed to keep track of its position, the boundary cablemay be utilized for guiding the robotic work tool 1 to the charging station 4. Therobotic tool may also, alternatively or additionally, be provided with other navigationsystems, such as a Global Navigation Satellite System, GNSS, receiver, or a set ofsensors configured to perceive the local environment for navigating based on a mapof the work area.

The robotic tool 1 is configured to process the surface of the work area; byway of example, in the case of a lawnmower 1, the lawnmower 1 is configured tomow the lawn of the work area 2. The robotic work tool 1 may according to the priorart operate in the work area 2 along a random path, along a pre-programmed path,along a path that is guided by pre-programmed principles, or any combinationthereof. However, in the present disclosure the robotic work tool 1 operates mainlyaccording to pre-programmed principles, which will be described in the following. ln figure 2 the work area 2 is shown divided into smaller portions 2a, 2b, 2c,2d. The subdivision into smaller portions may be partly based on the distance to thecharging station 4. However, in order to take account of the local ground conditions,local obstacles, such as stones or steep inclines, etc., a distance value may beestimated for the distance from each work area portion to the charging station.

For each work area portion 2a, 2b, 2c, 2d the approximate distance the roboticwork tool 1 would have to travel back to the charging station 4 is estimated as a 6 distance value. The estimated distance value is primarily based on an estimate of thegeometric driving distance, but may optionally also be adjusted to compensate fortraction conditions along the route, altitude differences, and other aspects having animpact on the effort required for reaching the charging station 4. The correspondingcharge needed for the robotic work tool 1 to travel this distance is also estimated.The robotic work tool 1 is operated based on the estimated distance value andestimated charge needed to head back to the charging station 4, for the respectivework area portion 2a, 2b, 2c, 2d wherein it is currently working. This means that therobotic work tool 1 will be directed to head back to the charging station 4 when itscharge is at a level needed to cover the distance back to the charging station 4 orlower. lt is pointed out that the coarse division of the work area 2 into the work areaportions 2a, 2b, 2c, 2d illustrated in Fig. 2 is merely an example; in anotherimplementation, there could be a much finer division into a much higher number ofsmaller work area portions.

Starting out from the charging station 4 with a full battery, the robotic work toolmay, based on the battery charge and the distance values estimated for each of thework area portions 2a, 2b, 2c, 2d, select to start with a remote work area 2d, andgradually work its way back to the charging station while processing the work areaalong the way. ln each work area portion 2a, 2b, 2c, 2d, possible positions 5a, 5b, 5c, 5d ofthe robotic work tool 1 have been indicated. When the robotic work tool 1 has startedto travel back to the charging station 4, it may reach a position 5a, 5b, 5c in a workarea portion 2a, 2b, 2c, which is closer to the charging station 4. The estimateddistance value and the estimated charge needed will typically be lower in this workarea portion 2a, 2b, 2c than in the work area portion 2b, 2c, 2d, where the roboticwork tool 1 previously worked. Hence there may be a reason to interrupt the journeyback to the charging station 4, and direct the robotic work tool 1 to work in the newwork area portion 2a, 2b, 2c until the charge level is so low that the robotic work tool1 will once again be directed to head back to the charging station 4, thereby possiblyreaching other possible positions 5a, 5b in another work area portion 2a, 2b, which iseven closer to the charging station.

Hence the robotic work tool 1 will tend not to return to the charging station 4until the battery charge is about to be depleted. On the other hand, the risk that the 7 robotic work tool 1 will run out of battery charge before it has reached the chargingstation 4 is minimized. lf such an unlikely event still takes place, the robotic work tool1 will likely have been operated in such a way as to direct it towards the chargingstation 4, and it will not have to be transported very far manually to the chargingstation 4.

All in all, the robotic work tool 1 with a full charge will, according to thedisclosed method, select a target portion 2a, 2b, 2c, 2d of the work area 2 as faraway from the charging station 4 as possible and may then work its way backgradually to the charging station 4. lt preferably moves to target portions 2a, 2b, 2ccloser to the charging station 4 at suitable places, thereby avoiding unnecessarilydifficult paths back to the charging station 4. The operation is ideally more efficientand the path that the robotic work tool 1 travels is optimized, while the risk of runningout of charge is minimized. ln an embodiment of this disclosure, outlined in the flow chart of Fig. 3, the distance value for each work area portion 2a, 2b, 2c 2d is estimated in step 6, as wellas the estimated charge needed to return from the respective work area portion. Thecharge level of the battery in the robotic work tool 1 is determined in step 7. Based onthe determined charge level, a suitable work area portion 2a, 2b, 2c, 2d is selected.Assuming that the battery has a fairly high charge, the work area portion 2a, 2b, 2c,2d that is selected may or may not be farther away from the charging station 4 thanthe work area portion 2a, 2b, 2c, 2d where the robotic work tool 1 is currentlyworking. When a different work area portion 2a, 2b, 2c, 2d than the current one hasbeen selected, the robotic work tool 1 is directed towards that work area portion 2a,2b, 2c, 2d and directed to work therein in step 8 of the method. ln step 9 of themethod, the current voltage is checked, and if it is below a limit voltage, the roboticwork tool 1 will be directed back to the charging station 4, or to another work area forcontinued work closer to the charging station 4, in step 10.

An advantageous feature of the disclosure is shown in Fig. 4. Determining thecurrent position 5a, 5b, 5c, 5d of the robotic work tool 1 and calculating an estimateddistance value representing an estimated effort to go back to the charging station 4takes place in step 11. The estimated distance value need not represent a straightline, since the ground conditions etc. may be taken into account. A limit charge levelfor initiating the return trip to the charging station 4 may be set based on the 8 estimated distance value in step 12, regardless of whether the estimated distancevalue is based on the shortest possible distance between the current position and thecharging station 4.

A particularly advantageous feature of the disclosure is that the remainingcharge is compared to the estimated limit charge in step 13. lf the remaining chargehas reached below the limit charge, the robotic work tool 1 is directed to head back tothe charging station 4 in step 14, and if not, the robotic work tool 1 keeps on working,and iterates back to step 11. The limit charge is based on the charge needed for areturn trip to the charging station, but preferably with a certain safety margin. Such asafety margin may be a fixed value added to the estimated charge needed. The limitcharge level may also be a value calculated by multiplying the estimated chargeneeded with a factor F, which is 1 or more, preferably in the range of 1 to 3.

Hence the estimated distance value need not be one single value, whichunconditionally directs the robotic work tool 1 back towards the charging station 4,but rather a dynamic value, so that the robotic work tool 1 is directed back when it isin a suitable place, based on e.g. the estimated driving distance back, with a certainsafety margin. ln this way a situation is avoided where the robotic work tool 1 is in asuitable position for a return trip but has not quite reached the limit charge forreturning and is directed into a position from which the estimated driving distancewould be unnecessarily long or complex.

The invention has mainly been described above with reference to a fewembodiments. However, as is readily appreciated by a person skilled in the art, otherembodiments than the ones disclosed above are equally possible within the scope ofthe invention, as defined by the appended patent claims. For example, the work areadoes not need to be divided into predefined work area portions 2a-2d as describedhereinabove. instead, work area portions may be defined “on the go”, e.g. as apreferred interval of a working distance from the charging station which maygradually decrease with a gradually decreasing battery charge level, or similar.Moreover, the robotic work tool need not be bound to operate at a certain distancefrom the charging station based on the level of charge. instead, the controller may beset to have a preference or statistical inclination towards operating at said certaindistance.

In the claims, the word "comprising" does not exclude other elements or steps,and the indefinite article "a" or "an" does not exclude a plurality.

Claims (15)

1. A method of processing a work area using a robotic work tool (1) comprising achargeable battery, in a work area (2) comprising a charging station (4), themethod comprising: estimating, for a work area portion (2a, 2b, 2c, 2d), a distance value representinga distance from said work area portion (2a, 2b, 2c, 2d) to the charging station (4);and operating the robotic work tool (1) based on an estimated amount of chargeneeded to transit from said work area portion (2a, 2b, 2c, 2d) to the chargingstation (4), wherein said estimating of a distance value comprises estimating a distancevalue for each of a plurality of area portions, each estimated distance valuerepresenting a distance from the respective work area portion (2a, 2b, 2c, 2d) tothe charging station (4), the method further comprising: determining a current charge level of the battery; and selecting a target work area portion (2a, 2b, 2c, 2d) of the work area (2) of saidplurality of area portions (2a, 2b, 2c, 2d), based on the current charge level and the estimated distance value.

2. The method of claim 1, further comprisingdirecting the robotic work tool (1) towards the selected target portion (2a, 2b, 2c,2d) of the work area (2); and operating the robotic work tool (1) within the target portion (2a, 2b, 2c, 2d) of thework area (2).

3. The method of claim 1 or claim 2, further including directing the robotic work tool(1) towards the charging station (4) when a current charge level is below a limitcharge level.

4. The method of claim 3, wherein said limit charge level is set based on theestimated distance value.

5. The method of claim 3 or claim 4, wherein the limit charge level is based on an estimated charge for reaching the charging station multiplied by a factor F, whichis equal to or larger than 1.

6. The method of claim 5, wherein the factor F is in the range of 1-3.

7. The method of any of the claims 1-6, further comprising: determining a current charge level of the battery; anddetermining a current position of the robotic work tool (1 ); wherein said estimating, for a work area portion (2a, 2b, 2c, 2d), a distance valuerepresenting a distance from a work area portion (2a, 2b, 2c, 2d) to the chargingstation comprises estimating, for the present position, a distance valuerepresenting a distance from the present position to the charging station.

8. The method according to any of the preceding claims, wherein the estimated distance value is based on an estimated driving distance from said work areaportion to the charging station.

9. The method according to any of the preceding claims, wherein the estimated distance value is based on any of an elevation difference between said work area portion and the chargingstation, estimated terrain conditions between said work area portion and the chargingstation, a drive path complexity between said work area portion and the chargingstation, a set of stored obstacles between said work area portion and the chargingstation, and an estimated slope inclination between said work area portion and thecharging station.

10.The method of any of the preceding claims, wherein the steps of the method arerepeatedly iterated during the operation of the robotic work tool.

11.A robotic work tool comprising a battery and a controller for controlling theoperation of the robotic work tool (1 ), the controller further being configured tooperate the robotic work tool (1) according to the method according to any ofclaims 1 to 10.

12.A robotic work tool according to claim 11, wherein the robotic work tool (1) is arobotic outdoor tool.

13.A robotic work tool according to claim 11 or claim 12, wherein the robotic worktool (1) is a robotic garden tool.

14.A robotic work tool according to claim 13, wherein the robotic garden tool is arobotic lawn mower.

15.A robotic work tool system comprising a robotic work tool (1) according to any ofclaims 11 to 14 and a charging station (4).