Abstract:
A robotic work tool system ( 200 ) comprising a robotic work tool ( 100 ) comprising a collision detection sensor ( 190 ), said collision detection sensor ( 190 ) comprising a first sensor element ( 191 ) and a plurality of second sensor elements ( 192 ), wherein said first sensor element ( 191 ) is movably arranged with respect to said plurality of second sensor elements ( 192 ), wherein said robotic work tool ( 100 ) is configured to detect that said first sensor element ( 191 ) is proximate a peripheral second sensor element ( 192 ) and in response thereto determine that a collision has been detected, and detect that said first sensor element ( 191 ) is not proximate any peripheral second sensor element ( 192 ) and in response thereto determine that a lift has been detected.

Description:
TECHNICAL FIELD 
       [0001]    This application relates to a method, a robotic work tool system, a robotic work tool and a computer-readable medium for an improved handling of slopes and hills. 
       BACKGROUND 
       [0002]    As most contemporary robotic work tools are designed to operate in areas with obstacles and in rough terrain it is important to maintain good control of its movement, allowing it to turn accurately. The steering control of a robotic work tool may be impaired or reduced when going down hill (as will also be explained below with reference to  FIG. 3 ) as the gravitational forces will then be shifted to put extra load on the front wheels. The reduction n traction and control may cause the robotic work tool to start sliding or otherwise be unable to steer accurately. 
         [0003]    Even though the problems above have been discussed for lawnmower robotic work tools, the same or similar problems exist also for other robotic work tools. 
         [0004]    There is thus a need for a manner of maintaining accurate control of the steering of a robotic work tool when going downhill. 
       SUMMARY 
       [0005]    It is an object of the teachings of this application to overcome the problems listed above by providing a robotic work tool comprising at least two rear wheels, at least one front wheel and a controller for controlling the propulsion of the robotic work tool and a level detection device, wherein the robotic work tool is configured to detect a downwards slope and then turn and reverse down the downwards slope. 
         [0006]    In one embodiment the robotic work tool is a lawnmower robot. 
         [0007]    It is also an object of the teachings of this application to overcome the problems listed above by providing a robotic work tool system comprising a robotic work tool according to any claim above and a charging station. 
         [0008]    It is also an object of the teachings of this application to overcome the problems listed above by providing a method for use in a robotic work tool comprising at least two rear wheels, at least one front wheel, the method comprising detecting a downwards slope and then turn and reverse down the downwards slope. 
         [0009]    It is also an object of the teachings of this application to overcome the problems listed above by providing a computer readable storage medium encoded with instructions that, when executed on a processor, performs the method according to herein. 
         [0010]    The inventors of the present invention have realized, after inventive and insightful reasoning that by reversing down a slope, full advantage may be taken of the gravitational force to provide better traction and steering control. 
         [0011]    Other features and advantages of the disclosed embodiments will appear from the following detailed disclosure, from the attached dependent claims as well as from the drawings. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the [element, device, component, means, step, etc]” are to be interpreted openly as referring to at least one instance of the element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]    The invention will be described in further detail under reference to the accompanying drawings in which: 
           [0013]      FIG. 1  shows a schematic overview of a robotic work tool according to one embodiment of the teachings of this application; 
           [0014]      FIG. 2  shows a schematic view of a robotic working tool system according to one embodiment of the teachings of this application; 
           [0015]      FIG. 3  shows a schematic view of a robotic working tool system in operation according to one embodiment of the teachings of this application; 
           [0016]      FIG. 4  shows a schematic side view of a robotic working tool; 
           [0017]      FIG. 5  shows a schematic side view of a robotic working tool; 
           [0018]      FIG. 6  shows a schematic side view of a robotic working tool according to herein; 
           [0019]      FIG. 7  shows a flowchart for a general method according to herein; and 
           [0020]      FIG. 8  shows a schematic view of a computer-readable medium according to herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The disclosed embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention 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 invention to those skilled in the art. Like numbers refer to like elements throughout. 
         [0022]      FIG. 1  shows a schematic overview of a robotic work tool  100  having a body  140  and a plurality of wheels  130 . In the exemplary embodiment of  FIG. 1  the robotic work tool  100  has four wheels  130 , two front wheels  130 ′ and two rear wheels  130 ″. It should be noted that the robotic work tool  100  may also be arranged with only one front wheel  130 ′. At least some of the wheels  130  are drivably connected to at least an electric motor  150 . It should be noted that even if the description herein is focussed on electric motors, combustion engines may alternatively or additionally be used possibly in combination with an electric motor. 
         [0023]    In the example of  FIG. 1 , the rear wheels  130 ″ are connected to each an electric motor  150 . This allows for driving the rear wheels  130 ″ independently of one another which, for example, enables steep turning. The front wheel(s)  130 ′ may be arranged to pivot to enable the robotic work tool  100  to execute steep turns more easily and without adding to the complexity of the robotic work tool  100 , such as through advanced steering of the front wheel(s)  130 ′. 
         [0024]    The robotic work tool  100  also comprises a controller  110 . The controller  110  may be implemented using instructions that enable hardware functionality, for example, by using executable computer program instructions in a general-purpose or special-purpose processor that may be stored on a computer readable storage medium (disk, memory etc)  120  to be executed by such a processor. The controller  110  is configured to read instructions from the memory  120  and execute these instructions to control the operation of the robotic work tool  100 . The controller  110  may be implemented using any suitable, publically available processor or Programmable Logic Circuit (PLC). The memory  120  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. 
         [0025]    The robotic work tool  100  further may have at least one sensor  170 , in the example of  FIG. 1  there are two sensors  170 , arranged to detect a magnetic field (not shown). The sensors are connected to the controller  110  and the controller  110  is configured to process any signals received from the sensors  170 . The sensor signals may be caused by the magnetic field caused by a control signal being transmitted through a boundary wire (for more details on charging stations, control signals and boundary wires, see the description below with reference to  FIG. 2 ). This enables the controller  110  to determine whether the robotic work tool  100  is inside or outside an area enclosed by a boundary wire. 
         [0026]    It should be noted that the teachings herein may also be used for a robotic work tool  100  that is configured to operate in a work area, where the work area is not bounded by a boundary wire. Examples of such robotic work tools  100  are tools arranged to physically detect a boundary by collision detection, or a robotic work tool  100  that uses a position determination system (such as GNSS) to maintain a position within the work area, which work area is specified by coordinates. 
         [0027]    The controller  110  is connected to the motors  150  for controlling the propulsion of the robotic work tool  100  which enables the robotic work tool  100  to service an enclosed area without leaving the area. 
         [0028]    The robotic work tool  100  also comprises a work tool  160 , which may be a grass cutting device, such as a rotating blade  160  driven by a cutter motor  165 . The cutter motor  165  is connected to the controller  110  which enables the controller  110  to control the operation of the cutter motor  165 . The controller  110  is also configured to determine the load exerted on the rotating blade, by for example measure the power delivered to the cutter motor  165  or by measuring the axle torque exerted by the rotating blade. The robotic work tool  100  is, in one embodiment, a lawnmower robot. 
         [0029]    In one embodiment the robotic work tool  100  is a farming equipment. In one embodiment the robotic work tool  100  is a golf ball collecting tool. The robotic work tool  100  may also be a vacuum cleaner, a floor cleaner, a street sweeper, a snow removal tool, a mine clearance robot or any other robotic work tool that is required to operate in a work area in a methodical and systematic or position oriented manner. 
         [0030]    The robotic work tool  100  also has (at least) one battery  180  for providing power to the motors  150  and the cutter motor  165 . Alternatively or additionally the robotic work tool may have a fuel tank  180  for supplying fuel to any other type of engine  150 . 
         [0031]    The robotic work tool  100  also comprises at least one level detection sensor  190 , which is configured to detect if the robotic work tool  100  is currently at an angle, that is, not horizontal. The level detection sensor  190  may be arranged to detect the level using a gyroscope. The level detection sensor  190  may also or alternatively be arranged to detect the level by monitoring the load on the rear wheels  130 ″ and on the front wheels  130 ′. If the load on the rear wheels  130 ″ is higher than the load on the front wheels  130 ′, the robotic work tool  100  is most likely going up a slope or a hill. If the load on the rear wheels  130 ″ is lower than the load on the front wheels  130 ′, the robotic work tool  100  is most likely going down a slope or a hill. 
         [0032]      FIG. 2  shows a schematic view of a robotic work tool system  200  comprising a charging station  210  and a boundary wire  250  arranged to enclose a working area  205 , the working area  205  not necessarily being a part of the robotic work tool system  200 , in which the robotic work tool  100  is supposed to service. As stated above, the robotic work tool  100  may be arranged to operate solely using the position determining device in which case no boundary wire  250  nor signal generator (to be disclosed) is part of the robotic work tool system  200 . The charging station  210  has a charger  220  coupled to, in this embodiment, two charging plates  230 . The charging plates  230  are arranged to co-operate with corresponding charging plates (not shown) of the robotic work tool  100  for charging the battery  180  of the robotic work tool  100 . The charging station  210  also has, or may be coupled to, a signal generator  240  for providing a control signal (not shown) to be transmitted through the boundary wire  250 . Optionally, the charging station  210  also has a guide cable  260  for enabling the robotic work tool to find the entrance of the charging station  210 . 
         [0033]      FIG. 3  shows a schematic side view of the robotic work tool  100  according to  FIGS. 1 and 2 . As the rear wheels  130 ″ are connected to the motor(s)  150  and the battery  180  (or fuel tank) is connected to the motor(s)  150  and therefore most likely arranged close to the motor(s)  150 , the center of gravity C for the robotic work tool  100  is offset towards the rear of the robotic work tool  100  as is shown in  FIG. 3 . The center of gravity can be moved towards the center of the robotic work tool  100  by rearranging the components, but then additional space around the cutting tool  165  has to be provided. As the center of gravity C is closer to the rear wheels  130 ″, the rear wheels will in most cases provide for better traction, as the gravity force F helps push down on the rear wheels  130 ″. Also, the rear wheels  130 ″ usually have a larger diameter than the front wheels  130 ′ and are provided with tread patterns for providing better traction, as the robotic work tool  100  is designed to provide god traction while being able to do steep turns. 
         [0034]      FIG. 4  shows a schematic view of a robotic work tool  100  going down a slope or hill. As can be seen the gravitational force F is now partially directed forwards in relation to the direction of the robotic work tool  100 . This puts a higher load on the front wheels  130 ′ and a lower load on the rear wheels  130 ″. As the robotic work tool  100  is designed to use the rear wheels  130 ″ for steering the robotic work tool  100 , whereby the front wheels  130 ′ only pivot, the control of the steering of the robotic work tool  100  may be impaired when going down hill. However, when the robotic work tool  100  is going up a hill or a slope, see  FIG. 5  which shows a side view of a robotic work tool  100  going up a hill, the gravitational force F is now even closer to the rear wheels  130 ″ thereby providing additional traction and control. 
         [0035]    The inventors have realized that by going against normal views on directions of movement and instead of driving the robotic work tool  100  forwards down a hill, the robotic work tool  100  can be driven backwards down a hill whereby the robotic work tool  100  gains additional traction and control by utilizing its weight distribution and the incline of the slope or hill. 
         [0036]      FIG. 6  shows a schematic side view of a robotic work tool  100  according to the teachings herein and  FIG. 7  shows a flowchart for a general method according to the teachings herein. The robotic work tool  100  is configured to detect that it is embarking on a downwards trajectory or coming upon a downwards slope. This may be detected by sensing an increased load on the front wheel(s)  130 ′ and/or through a gyroscope or other level detection devices  190 . As it is determined that the robotic work tool  100  is heading downwards, the robotic work tool  100  is configured to turn  720  around approximately 180 degrees and reverse down the slope. The robotic work tool  100  may be configured to detect the direction of the slope and turn to so that its rear faces the same direction. The direction of the slope may be determined through consulting a map stored in the memory  120  of the robotic work tool  100 . Or by moving in a scanning pattern, sensing in which direction the incline is the slope is the greatest. 
         [0037]    The robotic work tool  100  may be configured to turn around 180 degrees as the downward trajectory is detected. The robotic work tool  100  may also or alternatively be configured to reverse until it is on substantially level ground  722 , or at least until the incline is reduced and then turn around 180 degrees  724 . This enables the robotic work tool  100  to do the turn with full traction on the rear wheels  130 ″ thereby increasing the accuracy of the turning and also preventing any sliding to occur as the robotic work tool  100  is turning. 
         [0038]    The robotic work tool  100  is further configured to detect that the downwards slope ends  730  and then turn to move in a forwards direction again  740 . The end of the slope may be determined in a manner similar to detecting the start of the slope. 
         [0039]      FIG. 8  shows a schematic view of a computer-readable medium as described in the above. The computer-readable medium  80  is in this embodiment a data disc  80 . In one embodiment the data disc  80  is a magnetic data storage disc. The data disc  80  is configured to carry instructions  81  that when loaded into a controller, such as a processor, executes a method or procedure according to the embodiments disclosed above. The data disc  80  is arranged to be connected to or within and read by a reading device  82 , for loading the instructions into the controller. One such example of a reading device  82  in combination with one (or several) data disc(s)  80  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  80  is one type of a tangible computer-readable medium  80 . 
         [0040]    The instructions  81  may also be downloaded to a computer data reading device  84 , such as the controller  110  or other device capable of reading computer coded data on a computer-readable medium, by comprising the instructions  81  in a computer-readable signal  83  which is transmitted via a wireless (or wired) interface (for example via the Internet) to the computer data reading device  84  for loading the instructions  81  into a controller. In such an embodiment the computer-readable signal  83  is one type of a non-tangible computer-readable medium  80 . 
         [0041]    The instructions may be stored in a memory (not shown explicitly in  FIG. 8 , but referenced  120  in  FIG. 1 ) of the computer data reading device  84 . 
         [0042]    References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc. 
         [0043]    As the teachings herein do not necessarily require any additional hardware (as many robotic work tools  100  are configured with gyroscopes or load detectors  190  through their collision and/or lift detection systems, a robotic work tool  100  may be configured according to the teachings herein through a simple software update wherein instructions for executing a method according to herein may be downloaded to the memory  120  of the robotic work tool. 
         [0044]    The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.