SE543943C2

SE543943C2 - Automower fender and robotic work tool including a fender

Info

Publication number: SE543943C2
Application number: SE2050454A
Authority: SE
Inventors: Anders Hjalmarsson; Anders Sjögren; Hanna Reingård; Mats Svensson; Petrus Ekbladh
Original assignee: Husqvarna Ab
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2021-09-28
Also published as: SE2050454A1; SE2050765A1

Abstract

A robotic tool fender (7), for a work tool (1) comprises an outer, main body (3), movably suspended on a chassis (2). The fender (7) has a longitudinal attachment section (8), attachable to the lower edge (6) of the main body (3), a longitudinal contact section (10) for contact with objects (12) on the ground and a longitudinal bending section (9) between the attachment section (8) and the contact section (10). The fender (7) is arranged to bend around a bending axis extending along the bending section (9) when the objects (12) are contacted.A robotic work tool (1) includes a fender (7) as above. The robotic work tool (1) comprises an outer main body (3), movably suspended on a chassis (2), with a collision sensor and a lift sensor. The fender (7) is attached to a front region of the main body (3) for activating the collision sensor and the lift sensor, when an object (12) lower than the distance between the main body (3) and the ground isencountered.

Description

AUTOMOWER FENDER AND ROBOTIC WORK TOOL INCLUDING AFENDER Field of the invention The present invention relates to a robotic tool fender, for a work toolcomprising an outer, main body, which is movably suspended on a chassis.

The invention also relates to a robotic work tool including a fender as above,and the robotic work tool comprising an outer main body, movably suspended on a chassis, with a collision sensor and a lift sensor.

Background US5204814A discloses a bumper including a hose of a flexible material. Thehose deforms on impact with an object. Contact switches inside and under thebumper will signal that an obstacle has been encountered. This construction requiresa number of dedicated contact switches, which require a separate wiring, and hence this bumper is difficult to mount on pre-existing robotic work tools.

SE540823C2 discloses a robotic work tool wherein collision and lift sensorsare arranged for detection of collisions with obstacles or whether the robotic work toolis lifted by the outer main body. Such safety features work well when larger objectsare encountered, but smaller objects, such as hoglets may still be run over and injured by the robotic work tool.

There are also work tools on the market where a circumferential rubber screenis arranged below the lower edge of the outer main body. Although it may keep smallanimals etc. outside of the work tool in many cases, there is still a risk that animals may be trapped inside the screen.

Summagy lt is an object of the present invention to solve, or at least mitigate, parts or all of the above-mentioned problems. To this end, there is provided a fender, which has a longitudinal attachment section, attachable to the lower edge of the main body, alongitudinal contact section for contact with objects on the ground and a longitudinalbending section between the attachment section and the contact section, and thefender is arranged to bend around a bending axis extending along the bendingsection when the objects are contacted.

Hereby the fender efficiently may activate a co||ision sensor and/or a liftsensor which are included as safety features in many robotic work tools. The co||isionsensor is arranged to sense movements of the outer main body in relation to thechassis in an approximately horizontal direction, i. e. it is activated when the roboticwork tool contacts objects sideways. The co||ision sensor may be activated byobjects that would othen/vise pass under the lower edge of the main body, if thefender had not been arranged thereon. On activation of the co||ision sensor, therobotic work tool will move in the reverse direction. The lift sensor is arranged tosense movements of the outer, main body in relation to the chassis in anapproximately vertical direction, i. e. it is activated when the robotic work toolcontacts objects from below, or when it is lifted by the outer, main body. On activationof the lift sensor, any cutting etc. will stop immediately, and the robotic work tool willreverse. With the fender attached, the lift sensor will lift the main body even for lowobjects, and the lifting thereof will be more distinct, since the lower contact section ofthe bent fender will add to the height of the contacted object and expedite the lifting. ln one embodiment the contact section is deformable.

Hereby any living creatures contacted by the fender will be very gentlyimpacted and will not be injured. Also, the deformed fender locally takes on a shapewhich is complementary to the outer contour of the creature and may slide along itsbody, to be positioned on its top. Hence the lifting of the main body will also beexpedited. ln a further embodiment the contact section comprises a hollow cross-section with flexible exterior walls.

Hence the deformation may easily take place, while a customary, durable, andcost-efficient material is used in the fender. ln even further embodiments the exterior walls have a thickness in the rangeof 1 to 3 mm, preferably approximately 2 mm. ln some embodiments the contact section has an oval or round cross-section.

Hereby a particularly soft but efficient shape of the fender may be obtained. Afender with such a profile is typically efficiently manufactured by extrusion e. g. in an elastomeric material such as rubber. ln some embodiments the contact section extends 25 to 45 mm, preferably 35 mm, downwards, as seen in the mounted position. ln some embodiments the contact section has a cross-section with a width of15 to 25 mm, preferably 20 mm.

Hereby, when the fender contacts an animal or a small object, it may fold, andthe width of the contact section may add to the distance that the outer main sectionwill be lifted, and the lift sensor may be activated sooner and more efficiently. ln further embodiments the attachment section has an approximately U- shaped cross-section with lugs on the inner sides thereof.

Hereby the fender will be easily attachable on the lower edge of a main bodyof a robotic work tool without the use of glue or mechanical attachment devices, such as clips or screws. ln further embodiments the lugs extend obliquely towards the bottom of the U-shaped cross-section.

Hereby the fender will be easily attachable on the lower edge of the main bodyof the robotic work tool and will stay in place during extended periods of use. ln even further embodiments, the width of the opening of the U-shaped cross-section is in the range of 4-10 mm, preferably approximately 6 mm.

Hereby the fender may be suitable for arrangement on the lower edge of theouter, main body of most robotic work tools. ln some embodiments the cross-section of the bending section has a widthwhich is equal to or less than the smallest width of the cross-sections of the contact section and the attachment section.

Hereby there may be an efficient transition from the deformable, highly flexiblecontact section to the attachment section, which is intended to have as firm a grip aspossible on the lower edge of the main body. ln still further embodiments the fender is bendable to fit a curved lower edge ofthe work tool with a radius of curvature of 15 cm or higher. ln even further embodiments, the length of the fender is in the range of 25 to50 cm.

Hereby the length of the fender corresponds to most distances between thewheels of the robotic work tool, where the knives, cutting discs, and other sharpobjects performing the work of the robotic work tool may be arranged. ln many embodiments the fender is extruded in an elastomeric material such as rubber.

According to the second aspect, parts or all of the above mentioned problemsare solved, or at least mitigated, by a robotic work tool where the fender is attachedto a front region of the main body for activating the collision sensor and the liftsensor, when an object lower than the distance between the main body and the ground is encountered.

Hereby the robotic work tool is prevented, by the use of the disclosed fender,from injuring small animals or from damaging toys or other forgotten objects present in the work area. ln one embodiment the fender is arranged to bend backwards below the mainbody on impact with the object, for activation of the lift sensor.

Hereby the lift sensor is more easily activated than without the fender, sincethe lower edge of the fender is lower than the lower edge of the main body. Also, thelower section, i. e. the contact section, of the fender is bent on contact with the encountered object and will add to the perceived height thereof. The protection of encountered creatures or objects is improved. ln further embodiments the fender is at least as long as than the distancebetween a set of wheels on the robotic work tool.

Knives, cutting discs, and other sharp objects performing the work of therobotic work tool are arranged between the wheels. Since the robotic work toolprimarily moves in a fon/vard direction, entrance into the critical zone, where smallanimals may be injured, may mainly take place at the front end in a regioncorresponding to the width between the wheels. This region should preferably becovered by the fender. ln even further embodiments, the fender extends, at the fon/vard lower edge ofthe robotic work tool, mainly in a direction transversal to the main direction of movement thereof.

Hence the lateral sides and the back side of the robotic tool will be open belowthe main body. lt is unlikely that entrance into the critical zone would take place fromthe sides of the robotic work tool or from behind. lnstead there will be open spaceswherethrough an animal may escape, when the robotic work tool is reversed and themain body thereof is lifted on activation of the lift and collision sensors. ln some embodiments the fender is attached directly to the edge of the outermain body.

Hereby the fender may be easily applied to many models of robotic work tools,provided that the lower edge of the main body is compatible with the profile of the attachment section of the fender. ln other embodiments the fender is attached to a dedicated plate, which isattached to the edge of the main body.

Hereby an alternative way of attaching the fender is proposed. lt may be usedin cases where it is not possible to attach the fender directly to the main body. Henceoptions for most new and used robotic work tools are proposed. ln further embodiments the fender is arranged with a lower edge thereofarranged 10-30 mm above the ground, preferably 15-25 mm above the ground.

Hereby most small animals, such as hoglets, will be protected by the disclosedfender. At the same time the robotic work tool will be able to work in most work areas without unnecessary stops.ln many embodiments the robotic work tool is a lawn mower.

Application of the disclosure on a lawn mower will have the effect of protectingany young animals, in particular hoglets, since the birth of young animals take placeat virtually the same time as the season for lawn mowing, and lawn mowers are equipped with sharp knives or cutting discs. 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 vice versa.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 sectional view in from the side of a robotic work tool with a fender according to the present disclosure; Fig. 2 is a perspective view from below of the robotic work tool disclosed in Fig. 1; Fig. 3 is a perspective view of the robotic work tool about to encounter a hoglet; Fig. 4 is a view similar to that of Fig. 3 of the robotic work tool and the hoglet on impact;Fig. 5 is a partial sectional view from the side of the impact; Fig. 6a-6c are sectional views of different embodiments of the disclosed fender; and Fig. 7 is a view corresponding to that of Fig. 1 of another embodiment of the disclosure.

All the figures are schematic, not necessarily to scale, and generally only showparts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted.Detailed description of the exemplary embodiments Fig. 1 discloses a robotic work tool 1, more particularly a robotic lawn mower.Robotic lawn mowers are at the focus of the disclosure, but there may be many other applications for the disclosure.

The robotic work tool 1 comprises a chassis 2 and an outer main body 3,which is movably suspended on the chassis 2. Front wheels 4a and rear wheels 4bare arranged to allow the robotic work tool 1 to move around in a work area. A cuttingsystem, typically including a cutting disc 5 or cutting knives, is arranged on thebottom side of the robotic work tool 1. Other devices may be disposed on the bottomside of the robotic work tool 1, depending on the intended field of use for the tool,such as leaf raking, snow blowing or golf ball collection etc. A common denominatorfor the different robotic work tools 1 is that they work without immediate supervisionby an operator, and that the devices on the bottom side are often sharp and/or fast moving and may cause injuries in contact with humans or animals. ln order to protect humans and animals from injuries, and to a certain extentprevent damages to the work tool 1 and objects in the work area, robotic work tools 1are often provided with various safety features. One such feature is a collisionsensor, which detects a relative motion, mainly in a horizontal direction, between thechassis 2 and the outer main body 3. Whenever the robotic work tool 1 comes into contact with an external object, such as a tree, a rock, or even a human in the workarea, the impact will result in a motion of the main body 3, in relation to the chassis 2.The sensor will register the motion, and the robotic work tool 1 will be caused tomove in the reverse direction, in order to back away from the object which has beenimpacted.

Another common safety feature is a lift sensor, which senses relative motionsin the vertical direction. lf a robotic work tool 1 were to be lifted upwards by the mainbody 3, there would be such a relative motion, already before the robotic work tool 1has lost contact with the ground, and the cutting device 5 etc. on the bottom side ofthe work tool 1 is exposed. Also, if a hand or a foot extends into the area under themain body 3, it is likely that the lower edge of the main body 3 will be contacted tosuch an extent that there is a vertical motion component for the main body 3, and thelift sensor may be activated.

According to safety standards prevailing in many regions of the world, thedistance between a lower edge 6 of the main body 3 has been set fairly low, in orderto protect humans and most animals from injuries caused by accidental access tocutting discs 5 etc. at the bottom of robotic work tools 1. At the same time, the roboticwork tool 1 needs the position of the lower edge to be high enough to allow uninterrupted work in most terrains.

While the present robotic work tools 1 with collision and lift sensors work wellfor protecting humans and most animals, there are problems with small animaloffspring, such as chipmunk pups and hoglets. They often reside in or in the vicinityof grass, and they are small enough to be run over by robotic work tools 1 withouttriggering any of the collision or lift sensors. Moreover, they are considered asdelicate and fetching, and many people would be upset by harming themaccidentally.

The disclosed robotic work tool 1 further comprises a fender 7 arranged at thefront part of the lower edge 6 of the main body 3, as seen in the intended maindirection of motion M. The fender 7 is long enough to extend across the front of thelower edge 6 a distance corresponding to the axle track of the robotic work tool 1.

Hereby a critical area is covered, since any critical equipment, that may be dangerous to a small animal is arranged under the robotic work tool 1 between thewheels. The assumption is made that the robotic work tool 1 primarily risksencountering a small animal when it is driving in its fon/vard direction M and theanimal is still. Due to the construction of the wheels 4a, 4b, the robotic work tool 1 willnot move straight sideways, and it is assumed that the small animals will not enterthe area under the robotic work tool 1 from the side while it is running. When therobotic work tool 1 is in reverse, it is unlikely that it will encounter any animals, sinceit has almost always just passed the area behind it, while driving in a fonivarddirection.

The fender 7 extends downwards from the lower edge 6 of the main body 3,when it is mounted on the robotic work tool 1. The distance between the lower edgeof the fender 7 and the ground is approximately 20 mm, since that distance issufficient to allow an uninterrupted working in most work areas, without any major inclinations.

The fender 7, which will be shown in a larger scale in Fig. 6a-6c, preferablycomprises three main sections. The attachment section 8 may in the presentdisclosure be U-shaped to fit on the lower edge 6 of the main body 3. The fit may beimproved by the provision of flanges, lugs 13 etc. (not shown in Fig. 1) on the insideof the U-shaped section 8.

The bending section 9 may be provided as a transition between the upperattachment section 8 and a lower contact section 10. The bending section 9 mayhave a cross-section which is more narrow in its transversal direction than theattachment 8 and contact 10 sections respectively. The narrow section may have thefunction of a hinge, and if the contact section 10 is subjected to a force, e. g. from the impact with an animal or an object, bending of the fender 7 willprimarily take place at the bending section 9. Another factor that concentrates thebending locally to the bending section 9 is that its narrow cross-section will give roomfor some displacement of the contact section 10, without the immediate need fordeformation thereof.

The contact section 10 may have a hollow cross-section, as seen in theembodiment of Fig. 1. lts outer walls are thin in relation to the outer measurements of the contact section 10, which will enable a deformation in case of contact with ananimal or an object. ln the disclosed embodiment, there is also a partitioning wall 11,which divides the inner space of the contact section 10 into two separate chambers.The partitioning wall 11 will keep the stability of the contact section 10 at a desired level. ln fig. 2, the robotic work tool 1 of Fig. 1 is shown in a perspective view frombelow, so that the function of the disclosure may be better understood. From thefigure it may be seen that the cutting disc 5 is arranged in an area, whereof the outerlimits are defined by the wheels 4a, 4b. The length of the fender 7, as seen in itslongitudinal direction, corresponds to the distance between the wheels 4a, 4b, i. e.the axle track. Preferably the length of the fender 7 corresponds to the widest of thetwo axle tracks, in case they are mutually different. When the robotic work tool 1moves in its main, fon/vard direction M, the fender 7 may contact any animals orinanimate objects, that the robotic work tool 1 may encounter, and may block them from entering the high risk zone between the wheels 4a, 4b.

Fig. 3 discloses a robotic work tool 1 moving fon/vard and about to impact witha hoglet 12 that has appeared in its intended work path, as defined by the direction ofmovement M and the width of the fender 7. At this point in time neither the robotic work tool 1 nor the hoglet 12 are forewarned of the impact. ln Fig. 4 the impact between the hoglet 12 and the robotic work tool 1 is taking place. The impact situation is also shown in the partial section of Fig. 5. The contactsection 10 of the fender 7 may contact the hoglet 12 at a level of 20 mm aboveground level. The fender 7 may bend inwards to some extent, opposite the directionof movement M, primarily along the bending section 9. At the same time, the softcontact section 10 may undergo a local deformation where it contacts the hoglet 12,making the impact therewith gentle, so that the hoglet 12 may not be injured. lt willadapt to the outer contour of the back of the hoglet 12.

Since the material of the fender 7 preferably is an elastomeric material, suchas rubber, there will in most cases be a fairly high friction between the contact section10 of the fender 7 and the back of the hoglet 12. Rather than sliding over the hoglet12, with a simple bending at the bending section 9, the contact section 10 may be displaced a distance upwards, and hereby the lift sensor of the robotic work tool 1may be triggered. The height and/or width of the contact section 10, will be added tothe height of the hoglet 12, and the upward movement of the front of the main body3, triggering the lift sensor may be distinct, so that the robotic work tool 1 will stop itswork an move to the rear as quickly as possible after an impact with the hoglet 12 orsome other object. The cutting disc 5 etc. under the robotic work tool 1 will, in such a case be immediately stopped, and the work tool 1 will move in a reverse direction.

By the friction there may also be a gentle resistance against the fon/vardmovement of the robotic work tool 1, and its collision sensor may also be triggered,so that the robotic work tool 1 will start a reverse movement.

A further effect of the friction between the fender 7 and the hoglet 12 etc. isthat the hoglet 12 may topple over and be drawn into the area behind the fender 7.However, as the robotic work tool 1 is designed to stop its work and reverse, therewill be no immediate danger for the hoglet 12. Since the fender 7 is arranged only atthe front of the lower edge 6 of the main frame 3, the hoglet 12 may easily escapeand will not be trapped. When the robotic work tool 1 is in motion, it moves in afon/vard direction, where the fender 7 may serve as protection for small animals.Although the open space below the lower edge 6 of the main body 3 is larger at thesides and the back of the work tool 1, it is highly unlikely that animals may activelyenter the area under the work tool 1 in those directions.

Fig. 6a to 6c disclose cross-sections of a couple of embodiments, with nolimitation thereto, of the fender 7 according to the disclosure. ln all the disclosedembodiments, the attachment section 8 has a cross-section resembling a U, asmentioned above. The shape may allow the easy mounting of the fender 7 on thelower edge 6 of the main body 3 without any tools, glue or fastening devices. Themounting will be possible on many pre-existing robotic work tools 1, so that thefender 7 may be sold separately. lt may also be factory mounted on new robotic worktools 1. ln both cases there is no need for separate wiring or contacts, since thefender 7 utilizes the existing systems for detection of collisions and lifting. lnside the U-shape of the attachment section 8, there are a number oflongitudinal flanges or lugs 13, which are arranged to improve the engagement of the attachment section 8 on the main body 3. The lugs 13 may be arranged to slantdownwards towards the bottom of the U-shape. The slanting shape may facilitate themounting on the lower edge 6 of the main body 3, since they may bend and give waywhen the fender 7 is pressed on to the lower edge 6. A movement of the fender 7 inthe other direction, i. e. removal of the fender 7 by accident during use, may becounteracted, since the lugs 13 would have to be bent upwards to allow such amotion. Another advantage of the slanted lugs 13 may be that they provide for agood fit on a range of outer dimensions of the lower edge 6.

The bending section 9 has the appearance of a neck, as seen in the cross-sectional views of Fig. 6a to 6c, since it is one of the most narrow parts of the fender7. As mentioned above, bending of the fender 7 may take place in this section, as itmay act like a hinge, and the adjacent regions of the contact section 10 need not bedeformed to allow for the bending.

The contact section 10 is hollow and relatively thin-walled in comparison to itsouter dimensions. Hereby the desired deformation to decrease an impact and adaptto the outer contours of e. g. a hoglet 12 are facilitated. The bulkiness of the contactportion 10 serves to enhance the motion upwards of the main body 3, so that the liftsensor may be activated.

Although a gentle impact with small animals is desired, and hence adeformation of at least the lower parts of the contact portion 10, there maysimultaneously be a need for a certain retention of the shape of the contact portion10. Hereby may be attained that the contact section 10 does not compresscompletely and flex away from the hoglet 12 etc. without causing the lift or collisionsensors to be activated. The embodiment of Fig. 6b comprises a partitioning wall 11,which divides the contact section 10 into two separate cavities 14a, 14b andcontributes to holding the walls of the contact section 10 at a certain distance fromone another, so that it does not collapse completely on impact. The contact section10, although it undergoes a deformation to some extent, may still be able to transfera motion, resulting from the impact, large enough to trigger the collision and lift SGHSOFS.

The embodiment of fig. 6c comprises only a small cavity 15 at the lower edgeof the contact section 10, in order to provide the flexibility and deformation properties,whereas there is a solid section 16 closer to the bending section 9. Hereby motionsfrom the impact with a hoglet 12 etc. may be transferred to the lift and collision sensors of the robotic work tool 1.

An embodiment of the invention, disclosing the use of a plate 17, is shown inFig. 7. The plate 17 is provided with the purpose of acting as an adapter between thefender 7 and the lower edge 6 of the main body 3. This may be useful for caseswhere the shape of the lower edge 6 is not compatible with the shape of theattachment section 8 of the fender 7. Retrofitting of a fender 7 on some existing robotic work tools 1 may be such a situation where a plate 17 is useful.

The fender 7, i. e. any model thereof, may be attached to a lower edge of theplate 17, which is shaped and dimensioned so as to correspond to the shape andsize of the attachment section 8 of the fender 7. The plate 17 is attached to the lower edge 6 of the main body 3 with fastening elements 18, such as screws or rivets.

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 of the invention, as defined by the appended patent claims. ln 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

1. Robotic tool fender (7), for a work tool (1) comprising an outer, main body (3), which is movably suspended on a chassis (2), the fender (7) has a Iongitudinal attachment section (8), attachable to thelower edge (6) of the main body (3), a Iongitudinal contact section (10) forcontact with objects (12) on the ground and a Iongitudinal bending section (9)between the attachment section (8) and the contact section (10), and thefender (7) is arranged to bend around a bending axis extending along thebending section (9) when the objects (12) are contacted.

2. Robotic tool fender (7) according to claim 1 wherein the contact section (10) is deformable.

3. Robotic tool fender (7) according to claim 2, wherein the contact section (10) comprises a hollow cross-section with flexible exterior walls.

4. Robotic tool fender (7) according to claim 3, wherein the exterior walls have a thickness in the range of 1 to 3 mm, preferably approximately 2 mm.

5. Robotic tool fender (7) according to any of the preceding claims, wherein the contact section (10) has an oval or round cross-section.

6. Robotic tool fender (7) according to any of the preceding claims, wherein the contact section (10) extends 25 to 45 mm, preferably 35 mm, downwardsjïg: as seen in the mounted position.

7. Robotic tool fender (7) according to any of the preceding claims, wherein the contact section (10) has a cross-section with a width of 15 to 25 mm, preferably 20 mm.

8. Robotic tool fender (7) according to any of the preceding claims, wherein the attachment section (8) has an approximately U-shaped cross-section withlugs (13) on the inner sides thereof.

9. Robotic tool fender (7) according to claim 8, wherein the lugs (13) extend obliquely towards the bottom of the U-shaped cross-section.

10. Robotic tool fender (7) according to claim 8 or claim 9, wherein the width ofthe opening of the U-shaped cross-section is in the range of 4-10 mm,preferably approximately 6 mm.

11.Robotic tool fender (7) according to any of the preceding claims, wherein thecross-section of the bending section (9) has a width which is equal to or lessthan the smallest width of the cross-sections of the contact section (10) andthe attachment section (8).

12. Robotic tool fender (7) according to any of the preceding claims, wherein thefender (7) is bendable to fit a curved lower edge (6) of the work tool (1) with aradius of curvature of 15 cm or higher.

13. Robotic tool fender (7) according to any of the preceding claims, wherein thelength of the fender (7) is in the range of 25 to 50 cm.

14. Robotic tool fender (7) according to any of the preceding claims, wherein thefender (7) is extruded in an elastomeric material such as rubber.

15. Robotic work tool (1) including a fender (7) according to any of the precedingclaims, and the robotic work tool (1) comprising an outer main body (3), movably suspended on a chassis (2), with a collision sensor and a lift sensor, fender (7) is attached to a front region of themain body (3) for activating the collision sensor and the lift sensor, when anobject (12) lower than the distance between the main body (3) and the ground is encountered.

16. Robotic work tool (1) according to claim 15, wherein the fender (7) is arrangedto bend backwards below the main body (3). on impact with the object (12), for activation of the lift sensor.

17. Robotic work tool (1) according to claim 15 or claim 16, wherein the fender (7)is at least as long as than the distance between a set of wheels (4a, 4b) onthe robotic work tool (1 ).

18. Robotic work tool (1) according to any of claims 15 to 17, wherein the fender(7) extends, at the forward lower edge (6) of the robotic work tool (1 ), mainly in a direction transversai to the main direction of movement (M) thereof.

19. Robotic work tool (1) according to any of claims 15 to 18, wherein the fender(7) is attached directly to the edge (6) of the outer main body (3).

20. Robotic work tool (1) according to any of claims 15 to 18, wherein the fender(7) is attached to a dedicated plate (17), which is attached to the edge (6) ofthe main body (3).

21. _ Robotic work tool (1) according to any of claims 15 to 20, wherein the fender(7) is arranged with a lower edge thereof arranged 10-30 mm above theground, preferably 15-25 mm above the ground.

22. Robotic work tool (1) according to any of claims 15 to 21, wherein the robotic work tool (1) is a lawn mower.