IMPROVED ROBOTIC WORKING TOOL

• US 20150373906A1
• Filed: 02/21/2013
• Published: 12/31/2015
• Est. Priority Date: 02/21/2013
• Status: Active Grant

• Current Assignee: Husqvarna AB (HUSQVARNA)
• Original Assignee: Husqvarna AB (HUSQVARNA)
• Inventors: JGENSTEDT, Patrik, KAMFORS, Mattias
• Granted Patent: US 9,713,303 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A01D 34/008 for automated or remotely controlled operation
• 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: G05D 1/0225 involving docking at a fixed facility, e.g. base station or loading bay parking aids B62D15/027
• CPC Class Codes: G05D 1/0259 using magnetic or electromagnetic means
• CPC Class Codes: G05D 1/0265 using buried wires
• 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

Disclosed is a robotic work tool (100) for use with at least one guiding wire (250; 260) adapted to conduct electric current to generate a magnetic field around the guiding wire. The robotic work tool has a sensing system (510) adapted to detect a strength of the magnetic field, a steering system (540), a controller (530) configured to control the steering system in response to output from the sensing system by means of a feedback control loop (532) so as to cause movement of the robotic work tool along the guiding wire. The controller is configured to determine a measure indicative of a distance between the robotic work tool and the guiding wire, and adjust at least one parameter of the feedback control loop in response to the determined distance measure.

Claims

1. A robotic work tool for use with at least one guiding wire adapted to conduct electric current to generate a magnetic field around the guiding wire, the robotic work tool comprising:

a sensing system adapted to detect a strength of the magnetic field;

a steering system; and

a controller configured to control said steering system in response to output from said sensing system by means of a feedback control loop so as to cause movement of said robotic work tool along said guiding wire, wherein the controller is configured to;

determine a measure indicative of a distance between the robotic work tool and the guiding wire; and

adjust at least one parameter of the feedback control loop in response to the determined distance measure.

2. The robotic work tool according to claim 1, wherein the distance measure is determined as a particular distance range, in a set of distance ranges, in which an estimated distance between the robotic work tool and the guiding wire falls.

3. The robotic work tool according to claim 2, further comprising a memory configured to store a set of predefined feedback control loop parameter values for respective distance ranges in said set of distance ranges, wherein the controller is configured to use the predefined feedback control loop parameter values for the determined particular distance range when adjusting the at least one parameter of the feedback control loop.

4. The robotic work tool according to claim 3, wherein:

the feedback control loop is a PID control loop,

the predefined feedback control loop parameter values represent possible values of the proportional gain, the integral gain and the derivative gain of said PID control loop for different distance ranges in said set of distance ranges, and

the adjusted at least one parameter of the feedback control loop is at least one of the present proportional gain, the present integral gain and the present derivative gain of said PID control loop.

5. The robotic work tool according to claim 2- 4, wherein the set of distance ranges includes:

a first distance range representing estimated distances larger than a threshold distance at one side of the guiding wire; and

a second distance range representing estimated distances closer than the threshold distance at said one side of the guiding wire.

6. The robotic work tool according to claim 5, wherein the guiding wire is a boundary wire, and said one side is the inside of an area demarcated by the boundary wire.

7. The robotic work tool according to claim 5, wherein the set of distance ranges further includes:

a first intermediate distance range representing estimated distances between the first and second distance ranges at said one side of the guiding wire.

8. The robotic work tool according to claim 7, wherein the second distance range is considerably narrower than the first distance range, and the first intermediate distance range is considerably narrower than the second distance range.

9. The robotic work tool according to claim 8, wherein the set of distance ranges further includes:

a third distance range representing estimated distances closer than the threshold distance at an opposite side of the guiding wire,

a fourth distance range representing estimated distances larger than a threshold distance at said opposite side of the guiding wire, and

a second intermediate distance range representing estimated distances between the third and fourth distance ranges at said opposite side of the guiding wire.

10. The robotic work tool according to claim 1, wherein the sensing system comprises a first magnetic field sensor and a second magnetic field sensor, the second sensor being positioned at an offset with respect to the first sensor, and wherein the controller is configured to:

read a first sensor signal value from the first sensor,

read a second sensor signal value from the second sensor, obtained simultaneously with the sensor first signal value, and

determine the distance measure by assessing;

1) the first sensor signal value, and

2) a relation between the first and second sensor signal values.

11. The robotic work tool according to claim 10, wherein determining the distance measure involves:

estimating a present distance value by cross-referencing a predefined mapping between sensor signal value and distance using the first sensor signal value as index, and

in case multiple possible present distance values are found by the cross-referencing, using the relation between the first and second sensor signal values to uniquely determine a present distance value.

12. The robotic work tool according to claims 5, wherein the controller is configured to:

generate a virtual sensor signal value as;

the first sensor signal value, when the determined present distance value is within the second distance range,

the first sensor signal value plus the absolute value of a difference between a top signal value of the first sensor signal and the first sensor signal value, when the determined present distance value is within the first distance range; and

use the virtual sensor signal value as process variable in the feedback control loop for controlling the steering system.

13. The robotic work tool according to claim 10, wherein the first magnetic field sensor and the second magnetic field sensor are placed at a front section of the robotic work tool, along an axis transversal to a longitudinal center axis of the robotic work tool'"'"'s propulsion direction.

14. The robotic work tool according to claim 13, wherein the first magnetic field sensor is placed on the longitudinal center axis and the second magnetic field sensor is placed at a transversal offset from the longitudinal center axis.

15. The robotic work tool according to claim 10, wherein the first magnetic field sensor and the second magnetic field sensor are placed at a front section of the robotic work tool, along respective parallel axes which are transversal to a longitudinal center axis of the robotic work tool'"'"'s propulsion direction, wherein the second magnetic field sensor is placed at a transversal offset and a longitudinal offset from the first magnetic field sensor.

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

17. A robotic work tool system, comprising a charging station, a guiding wire, a signal generator for generating and transmitting an electric signal through said guiding wire to generate a magnetic field around the guiding wire, and a robotic work tool, the robotic work tool comprising:

a sensing system configured to detect a strength of the magnetic field;

a steering system; and

a controller configured to control said steering system in response to output from said sensing system by means of a feedback control loop so as to cause movement of said robotic work tool along said guiding wire, wherein the controller is configured to;

determine a measure indicative of a distance between the robotic work tool and the guiding wire; and

adjust at least one parameter of the feedback control loop in response to the determined distance measure.

18. A method of controlling a robotic work tool to follow along a guiding wire adapted to conduct electric current and generate a magnetic field around the guiding wire, the method comprising:

controlling a steering system of the robotic work tool by means of a feedback control loop based on a detected magnetic field strength;

determining a measure indicative of a distance between the robotic work tool and the guiding wire; and

adjusting at least one parameter of the feedback control loop in response to the determined distance measure.