Robotic work tool configured for improved turning in a slope, a robotic work tool system, and a method for use in the robot work tool

• US 10,149,430 B2
• Filed: 02/20/2013
• Issued: 12/11/2018
• Est. Priority Date: 02/20/2013
• Status: Active Grant

• Current Assignee: Husqvarna AB (HUSQVARNA)
• Original Assignee: Husqvarna AB (HUSQVARNA)
• Inventors: Bergstrom, Jonas, Klackensjo, Fredrik, Markusson, Olle
• Primary Examiner(s): Heinle, Courtney D
• Assistant Examiner(s): Martinez Borrero, Luis A
• Application Number:
  US14/767,122
• Publication Number:
  US 20150366130A1
• Time in Patent Office: 2,120 Days
• Field of Search: 701 23, 701 50, 701 25, 701 36, 701 2, 701 22, 901 1, 901 28, 901 41, 901 46, 901 5, 901 6, 901 9
• CPC Class Codes: A01D 34/008 for automated or remotely controlled operation
• CPC Class Codes: A01D 75/28 Control mechanisms for harvesters or mowers when moving on slopes; Devices preventing lateral pull
• CPC Class Codes: B60L 1/003 to auxiliary motors, e.g. for pumps, compressors
• CPC Class Codes: B60L 15/20 for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed
• CPC Class Codes: B60L 2200/40 Working vehicles
• CPC Class Codes: B60L 2240/36 Temperature of vehicle components or parts
• CPC Class Codes: B60L 2240/421 Speed
• CPC Class Codes: B60L 2260/32 Auto pilot mode
• CPC Class Codes: B60L 3/0061 relating to electrical machines
• CPC Class Codes: B60L 50/52 characterised by DC-motors
• CPC Class Codes: B60L 50/66 Arrangements of batteries
• CPC Class Codes: B60L 53/16 Connectors, e.g. plugs or sockets, specially adapted for charging electric vehicles
• CPC Class Codes: B60L 8/003 Converting light into electric energy, e.g. by using photo-voltaic systems
• CPC Class Codes: B62D 11/001 control systems B62D11/183 takes precedence
• CPC Class Codes: G05D 1/0212 with means for defining a desired trajectory involving a plurality of land vehicles G05D1/0287
• CPC Class Codes: G05D 1/0259 using magnetic or electromagnetic means
• CPC Class Codes: G05D 1/0265 using buried wires
• CPC Class Codes: G05D 1/027 comprising intertial navigation means, e.g. azimuth detector inertial navigation G01C21/16; inertial navigation combined with non-inertial navigation instruments G01C21/165
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 10/7072 : Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
• CPC Class Codes: Y02T 10/72 : Electric energy management in electromobility
• CPC Class Codes: Y02T 90/14 : Plug-in electric vehicles
• CPC Class Codes: Y10S 901/01 : Mobile robot

Abstract

Robotic work tool (100) configured for improved turning in a slope (S), said robotic work tool comprising a slope detector (190), at least one magnetic field sensor (170), a controller (110), and at least two driving wheels (130″), the robotic work tool (100) being configured to detect a boundary wire (250) and in response thereto determine if the robotic work tool (100) is in a slope (S), and if so, perform a turn by rotating each wheel (130″) at a different speed thereby reducing a risk of the robotic work tool (100) getting stuck.

Claims

1. A robotic work tool configured for improved turning, said robotic work tool comprising:

a slope detector,

at least one magnetic field sensor,

a controller, and

at least two driving wheels,

wherein the robotic work tool is configured, via the controller, to;

determine that the robotic work tool is on a slope via the slope detector;

in response to determining that the robotic work tool is on the slope, change a magnetic field detection threshold for initiating a turn to a modified magnetic field detection threshold;

detect, via the at least one magnetic field sensor, that a magnetic field from a boundary wire exceeds the modified magnetic field detection threshold; and

in response to detecting that the magnetic field from the boundary wire exceeds the modified magnetic field detection threshold, instruct the robotic work tool to perform a turn based on the slope by rotating at least one driving wheel at a speed different from a speed of rotation of another driving wheel.

2. The robotic work tool according to claim 1, wherein the robotic work tool is further configured to determine that the robotic work tool is on the slope by using data from said slope detector, the slope detector being at least one inclinometer, the slope detector indicating that the robotic work tool is on the slope by indicating an inclination exceeding a certain threshold value.

3. The robotic work tool according to claim 1, wherein the robotic work tool is further configured to avoid wheel slip during the turn on the slope by:

determining a wheel slip or risk of wheel slip by using data from said slope detector, the slope detector being at least one accelerometer;

comparing measured acceleration data with data expected for a certain shift of rotational speed of one of the driving wheels; and

reducing the rotational speed of the driving wheel indicating a wheel slip or risk of wheel slip which is indicated by a mismatch between the measured acceleration data and the expected acceleration data.

4. The robotic work tool according to claim 1, wherein the robotic work tool is further configured to reverse a rotational direction of one driving wheel and reduce rotational speed of the driving wheel having a least expected grip.

5. The robotic work tool according to claim 1, wherein the robotic work tool is further configured to:

detect that the robotic work tool is approaching the boundary wire substantially head on, and in response thereto,

reduce rotational speed of either of the driving wheels such that the robotic work tool performs a U-turn.

6. The robotic work tool according to claim 5, wherein the robotic work tool is configured to detect that the robotic work tool is approaching the boundary wire substantially head on by comparing sensor signals from at least one front magnetic field sensor to sensor signals from another front magnetic field sensor, and if the sensor signals are substantially equal for the front magnetic field sensors, determine that the robotic work tool is approaching the boundary wire substantially head on.

7. The robotic work tool according to claim 1, wherein the robotic work tool is further configured to:

detect that the robotic work tool is approaching the boundary wire at an angle, and in response thereto,

reduce rotational speed of either of the driving wheels such that the robotic work tool performs an L-turn.

8. The robotic work tool according to claim 7, wherein the robotic work tool is configured to detect that the robotic work tool is approaching the boundary wire at an angle by comparing sensor signals from at least one magnetic field sensor disposed on a front portion of the robotic work tool to sensor signals from another magnetic field sensor disposed on the front portion of the robotic work tool, and if the sensor signals for the magnetic field sensors disposed on the front portion of the robotic work tool differ by more than a threshold value, determine that the robotic work tool is approaching the boundary wire at an angle.

9. The robotic work tool according to claim 3, wherein the at least one accelerometer is two accelerometers, the two accelerometers being positioned such that each of the accelerometers can measure an acceleration imparted by a change of rotational speed or direction of a corresponding driving wheel.

10. The robotic work tool according to claim 2, wherein the at least one inclinometer measures at least the sideways inclination of the robotic work tool.

11. The robotic work tool according to claim 10, wherein the sideways inclination of the robotic work tool is used to determine which driving wheel has a least load and consequently a least grip.

12. The robotic work tool according to claim 11, wherein a reduction of rotational speed of the driving wheel having the least load is proportional to a measured inclination.

13. The robotic work tool according to claim 12, wherein the rotational speed of the driving wheel having the least load is zero when the sideways inclination has reached a predetermined threshold value.

14. The robotic work tool according to claim 13, wherein the predetermined threshold value is determined by a maximum slope of the ground to be serviced.

15. The robotic work tool according to claim 13, wherein the predetermined threshold value is 35 degrees.

16. The robotic work tool according to claim 1, wherein the robotic work tool is a robotic lawnmower.

17. The robotic work tool according to claim 1, wherein the controller is configured to change the magnetic field detection to the modified magnetic field detection threshold, the modified magnetic field detection threshold being reduced such that the robotic work tool starts to turn earlier than when the robotic work tool starts to turn on flat ground.

18. The robotic work tool according to claim 1, wherein the at least one magnetic field sensor comprises a first magnetic field sensor and a second magnetic field sensor;

wherein the robotic work tool is further configured, via the controller, to determine a difference between magnetic field readings from the first magnetic field sensor and the second magnetic field sensor; and

wherein the robotic work tool is further configured to, in response to detecting the magnetic field form the boundary wire exceeds the modified magnetic field detection threshold, instruct the robotic work tool to perform the turn based on the slope and the difference between magnetic field readings from the first magnetic field sensor and the second magnetic field sensor.

19. A robotic work tool system comprising:

a robotic work tool; and

a boundary wire demarcating a work area;

wherein the robotic work tool comprises;

a slope detector,

at least one magnetic field sensor,

a controller, and

at least two driving wheels,

wherein the robotic work tool is configured, via the controller, to;

determine that the robotic work tool is on a slope via the slope detector;

in response to determining that the robotic work tool is on the slope, change a magnetic field detection threshold for initiating a turn to a modified magnetic field detection threshold;

detect, via the at least one magnetic field sensor, that a magnetic field from a boundary wire exceeds the modified magnetic field detection threshold; and

in response to detecting that the magnetic field from the boundary wire exceeds the modified magnetic field detection threshold, instruct the robotic work tool to perform a turn based on the slope by rotating at least one driving wheel at a speed different from a speed of rotation of another driving wheel.

20. A method for operating a robotic work tool for improved turning, said robotic work tool comprising a slope detector, at least one magnetic field sensor, a controller, and at least two driving wheels, the method, executed by the controller, comprising:

determining that the robotic work tool is on a slope via the slope detector;

in response to determining that the robotic work tool is on the slope, changing a magnetic field detection threshold for initiating a turn to a modified magnetic field detection threshold;

detecting, via the at least one magnetic field sensor, that a magnetic field from a boundary wire exceeds the modified magnetic field detection threshold; and

in response to detecting that the magnetic field from the boundary wire exceeds the modified magnetic field detection threshold, instructing the robotic work tool to perform a turn based on the slope by rotating at least one driving wheel at a speed different from a speed of rotation of another driving wheel.