Patent Publication Number: US-10782705-B2

Title: Obstacle detection for a robotic working tool

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 15/105,013, filed Jun. 16, 2016, which is a U.S. National Stage Entry of PCT/SE2013/051574 filed Dec. 19, 2013, the entire contents of both are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This application relates to a method and a robotic work tool system for an improved navigation for a robotic work tool. And in particular to an improved detection of obstacles. 
     BACKGROUND 
     Contemporary robotic work tools are becoming more and more advanced and are able to perform more and more advanced tasks such as executing advanced operation patterns. In the example of lawnmower robots the advanced working pattern may be a complicated mowing pattern based on the layout of a garden including bushes, garden islands and other structures. To successfully navigate such complicated areas some contemporary robotic work tools employ various navigation techniques three of the main being deduced reckoning (also known as dead reckoning), satellite navigation or using boundary wires. 
     One factor that complicates the working pattern is the presence of different obstacles or structures inside a working area. For the example of the robotic work tool being a lawnmower robot and the work area being a garden, the obstacles may be bushes and trees and the structures may be a porch or a shed. 
     Such structures are usually fixed or permanent and will not change over time and can thus be marked with a boundary marker such as a boundary wire that transmits an electric current that is detected by the robotic work tool. Alternatively they can be marked in a map of the work area and the robotic work tool includes the coordinates of such structures in its operating pattern so that the structures are avoided. Such technologies are well known in the art. 
     However, obstacles may change over time and may also not always be present. For example, a user may dig a hole in his garden for example to service some pipes and this hole would not be a permanent feature of the garden. Furthermore, the user may want that one area should not be serviced at a specific time such as when a child is playing in one corner of the garden. Such areas will hereafter be referred to as temporary or virtual obstacles. 
     To mark such obstacles with prior art technologies is cumbersome as it requires that boundary wires are dug down or that the map is reprogrammed. Something which can be cumbersome to a user, especially if the obstacle will only be present for a short time. 
     The international patent application WO99/59042A discloses a robotic system for systematically moving about an area to be covered. The system includes at least one boundary marker located along the outer edge of the area to be covered, a robot with a navigation system and a sensor unit. The navigation system navigates the robot in generally straight, parallel lines from an initial location and turns the robot when the robot encounters one of the boundary markers, thereby to systematically move about the area to be covered. The sensor unit senses proximity to one of the at least one boundary marker. The system may further comprise obstacle markers that are also sensed by the robot. 
     The disclosure teaches on page 7; lines 17 to 20 that obstacles that are above ground may be detected by mere collision detection, whereby the obstacle itself is the obstacle marker and the sensing is the collision detection. This will increase the wear and tear of a robotic work tool as it will be subjected to numerous collisions. Furthermore, such detection is highly unsuitable for virtual obstacles. 
     The disclosure also teaches on page 9 that the obstacle markers are wires and a manner of differentiating between obstacle markers and boundary markers is given. As has been discussed above, such wires need to be dug down in the ground and as such require much work to be done which may be especially cumbersome if it is only for a temporary marker. 
     The disclosure further teaches on page 10 that the obstacle markers may be a post having a bar code written on it which is detected through a bar code reader. Such barcodes must therefore be visually detected which limits the placement, the distance/size of the (virtual) obstacle and the arrangement is also sensitive to debris blocking the barcode reader&#39;s lens. 
     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. 
     There is thus a need for a manner of enabling indicating obstacles, that is easy to install, is not sensitive to debris or waste, and does not increase the wear and tear of a robotic work tool. 
     SUMMARY 
     It is 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 and a beacon marker, said robotic work tool comprising a beacon sensor configured to sense a signal being transmitted by the beacon marker, said beacon marker marking an area around an obstacle in a work area in which said robotic work tool is arranged to operate, wherein said robotic work tool is configured to determine a proximity to a beacon marker and to adapt its operation accordingly. 
     In one embodiment the robotic work tool is a farming equipment, a vacuum cleaner, a floor cleaner, a street sweeper, a snow removal tool, a golf ball retriever robot, a cleaner robot, a leaves blower robot, a leaves collector robot, snow thrower robot or a mine clearance robot. 
     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 system comprising a robotic work tool and a beacon marker, said robotic work tool comprising a beacon sensor configured to sense a signal being transmitted by the beacon marker, said beacon marker marking an area around an obstacle in a work area in which said robotic work tool is arranged to operate, said method comprising determining a proximity to a beacon marker and adapt an operation of the robotic work tool accordingly. 
     The inventors of the present invention have realized, after inventive and insightful reasoning that by arranging a beacon (radio frequency or ultrasonic) to be placed on an or close to obstacle, a simple and effective manner of marking an obstacle is achieved. The obstacle marker will uniformly mark most objects, especially such that occur in everyday scenarios and especially with regards to temporary obstacles, and enable a radius to be effectively set by a user by setting the strength of the signal transmitted by the beacon. 
     Furthermore, such beacon markers may be easily arranged on for example a pole or stick which can easily be driven into the ground to mark a virtual obstacle or a hole. 
     A problem that exists in using radio Frequency Identification technology (RFID) is that an RFID tag can not be used to set a radius easily. Furthermore, the RFID tag is only arranged to operate at short distances without requiring that a sensor on a robot is used at high power, which of course would severely limit the operation of the robotic work tool. 
     Furthermore, this would result in an increased interference in a work area, which can be very disturbing in for example a residential neighbourhood. 
     Also, RFID tags can not indicate a distance, such as by reflecting a transmitted signal. Using RFID technology thus provide a more complicated solution that requires that more power is used, increases the interference and can not provide all the functionality of using a beacon based system as disclosed herein. 
     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 
       The invention will be described in further detail under reference to the accompanying drawings in which: 
         FIG. 1  shows a schematic overview of a robotic work tool according to one embodiment of the teachings of this application; 
         FIG. 2  shows a schematic view of a robotic working tool system according to one embodiment of the teachings of this application; 
         FIG. 3  shows a schematic view of a robotic working tool system in operation according to one embodiment of the teachings of this application; and 
         FIG. 4  shows a schematic view of a beacon marker according to one embodiment of the teachings of this application. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
       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 4 wheels  130 , two front wheels  130 ′ and the rear wheels  130 ″. At least some of the wheels  130  are drivably connected to at least one 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. 
     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 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. 
     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. 
     It should be noted that the teachings herein may also be used for a robotic work tool 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 are tools arranged to physically detect a boundary by collision detection, or a robotic work tool that uses a position determination system (such as GNSS) to maintain a position within the work area, which work area is specified by coordinates. 
     The robotic work tool  100  may also or alternatively be arranged with a position determining device  190 , such as a GNSS (Global Navigation Satellite System) device  190 . In one embodiment the GNSS device is a GPS (Global Positioning Service) device  190 . The GNSS device  190  is connected to the controller  110  for enabling the controller  110  to determine a current position for the robotic work tool  100  using the GNSS device and to control the movements of the robotic work tool  100  based on the position. 
     Alternatively, the robotic work tool  100  may be arranged to operate within the work area solely or mainly based on the position determining device  190 . A user may then establish a work area through coordinates and the robotic work tool will ensure that it stays within those coordinates based on the signals received by the position determining device  190 . 
     Other examples of position determining devices  190  include optical (such as laser) position determining devices, other radio frequency position determining systems, such as ultrawideband (UWB) beacons and receivers. 
     The robotic work tool  100  may further be arranged with at least one sensor  195  for providing signals for deduced reckoning navigation. Examples of such deduced reckoning navigation sensors  195  are odometers, accelerometers, gyroscopes and compasses. 
     The deduced reckoning sensor(s) may be used to navigate in areas where satellite reception is not possible, i.e. areas hereafter referred to as shadowed areas. 
     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. 
     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 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. 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. 
     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 . In one embodiment the robotic work tool is arranged with solar panel for supplying power to the battery  180 . 
       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 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 . As is known in the art, the control signal will generate a magnetic field around the boundary wire  250  which the sensors  170  of the robotic work tool  100  will detect. As the robotic work tool  100  (or more accurately, the sensor  170 ) crosses the boundary wire  250  the direction of the magnetic field will change. The robotic work tool  100  will thus be able to determine that the boundary wire has been crossed. The use of more than one sensor  170  enables the controller  110  of the robotic work tool  100  to determine how the robotic work tool  100  is aligned with relation to the boundary wire  250  by comparing the sensor signals received from each sensor  170 . This enables the robotic work tool to follow the boundary wire  250 , for example when returning to the charging station  210  for charging. 
     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 . In one embodiment the guide cable  260  is formed by a loop of the boundary wire  250 . In one embodiment the guide wire  260  is used to generate a magnetic field for enabling the robotic work tool  100  to find the charging station without following a guide cable  260 . 
       FIG. 3  shows another schematic view of a robotic work tool system  200  according to the teachings herein, such as the robotic work tool system  200  of  FIG. 2 , being depicted here at a larger scale. 
     The work area  205  is shown here to include two obstacles  260  and being delimited by a boundary  250 . It should be noted that there may be more or less than two obstacles  260 . 
     The boundary  250  may be effected through navigation coordinates or a boundary wire or other suitable means for defining a boundary for a work area for robotic work tools. 
     Two obstacles  260 A and  260 B are shown in the example embodiment of  FIG. 3 , one obstacle being a virtual obstacle  260 A and one being an actual obstacle  260 B. An obstacle marker in the form of a beacon marker  280  is arranged on or in each obstacle  260 . The beacon markers  280  emit each a signal that marks an area  270  around the obstacle  260 . As can be seen in  FIG. 3 , the areas  270  may be of different size/radius. The area  270 A for the virtual obstacle  260 A being larger than the area  270 B for the physical obstacle  260 B. It should be noted that the area  270  of a beacon marker  280  may be regulated and possibly user settable by increasing or decreasing the signal power, or by programming the robotic work tool to detect a signal at a certain strength. The size relationship of the areas  270  in  FIG. 3  are only examples and any internal relationship of sizes is possible and within the scope of this application. 
     As a robotic work tool  100  comes close to a beacon marker  280  it will detect a signal transmitted by the beacon marker  280  through a beacon sensor  175  arranged in the robotic work tool (see  FIG. 1 ). The beacon sensor  175  is coupled to the controller  110  for determining the proximity to the beacon marker  280 . Alternatively the beacon sensor  175  is arranged to determine the proximity to the beacon marker  280  by itself and signal that a beacon marker is close by to the controller as the proximity of a beacon marker  280  is determined. 
     In one embodiment the robotic work tool  100  is configured to determine the proximity to a beacon marker by comparing the signal strength (SSI) of the beacon signal, or a radio signal strength indicator (RSSI) of the beacon signal. 
     In one embodiment the robotic work tool  100  is configured to determine the proximity to a beacon marker as a state close or not close by comparing the signal strength of the beacon signal to a threshold value. If the signal strength is above the threshold value, the beacon is close, and, if not, it is not close. 
     In one embodiment the robotic work tool  100  is configured to determine the proximity to a beacon marker by comparing the signal strength of the beacon signal to a model of signal declination. In this embodiment the robotic work tool  100  is configured to know at what signal strengths the beacon signal is transmitted. This enables for determining a more precise distance to the beacon marker  280  and the robotic work tool  100  may take different actions depending on the actual distance. Such different actions may be to slow down or make a turn less than 180 degrees depending on the distance. For example, the robotic work tool may be configured to slow down if the distance is 5 m, to turn 90 degrees if the distance is 2 m, and to turn 180 degrees if the distance is less than 1 m. 
     In one embodiment the robotic work tool  100  is configured to determine the proximity to a beacon marker by sending a signal to the beacon and measure the two-way response time or alternatively phrased to measure the time of arrival (TOA). 
     In one embodiment the robotic work tool  100  is configured to determine the proximity to a beacon marker as a state close or not close by comparing the two-way response to a threshold value. If the two-way response is above the threshold value, the beacon is close, and, if not, it is not close. 
     In one embodiment the robotic work tool  100  is configured to determine a more precise distance to the beacon marker  280  based on the two-way response. This enables for determining a more precise distance to the beacon marker  280  and the robotic work tool  100  may take different actions depending on the actual distance. Such different actions may be to slow down or make a turn less than 180 degrees depending on the distance. For example, the robotic work tool may be configured to slow down if the distance is 5 m, to turn 90 degrees if the distance is 2 m, and to turn 180 degrees if the distance is less than 1 m. 
     In one embodiment the beacon marker  280  and the beacon sensor  175  are synchronized wherein the robotic work tool  100  need not transmit a signal to the beacon marker  280 , but merely measures the time of arrival from a known last transmission time. Such an embodiment may operate in a manner similar to measure the two-way response time. 
       FIG. 4  shows a schematic view of a beacon marker  280 . The beacon marker  280  is arranged to be fastened to an obstacle or a pole  260 ′ (indicated with dashed lines). The beacon marker  280  may be fastened through various fastening means  281 , such as, but not limited to, straps, belts, adhesive tape, Velcro™ to name a few examples. 
     In one embodiment the beacon marker  280  is a radio frequency beacon emitting a radio frequency signal and the beacon sensor  175  is a radio frequency receiver (or transceiver). 
     In one embodiment the beacon marker  280  is an ultrasonic beacon emitting an ultrasonic signal and the beacon sensor  175  is an ultrasonic receiver (or transceiver). 
     This has one benefit in that an obstacle  260  is simple to mark by simply arranging a beacon marker on or adjacent to the obstacle  260 . This is especially so for virtual obstacles  260 A. 
     This finds particular use in setting up temporary working areas, something of importance for robotic work tools  100  such as mine clearing robots. It is also useful in sensitive areas or areas having many holes and other hazards. 
     This also has the benefit of that it is easy to mark obstacles that are above ground at its outer perimeter, such as sun chairs. Robotic work tools  100  may otherwise become stuck under such obstacles if collision detection is used. 
     As has been stated above, collision detection increases the wear and tear of the robotic work tool  100 , alternatively, the collision detection systems may be highly sensitive to dirt and debris and may become blocked rendering the collision detection inefficient. 
     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.