Navigation for a robotic work tool

• US 10,598,793 B2
• Filed: 11/26/2015
• Issued: 03/24/2020
• Est. Priority Date: 12/24/2014
• Status: Active Grant

• Current Assignee: Husqvarna AB (HUSQVARNA)
• Original Assignee: Husqvarna AB (HUSQVARNA)
• Inventors: Ohrlund, Magnus, Reigo, Peter
• Primary Examiner(s): Liu, Harry K
• Application Number:
  US15/539,356
• Publication Number:
  US 20170357006A1
• Time in Patent Office: 1,580 Days
• Field of Search: 34235752
• CPC Class Codes: A01D 34/008 for automated or remotely controlled operation
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01S 19/14 specially adapted for specific applications
• CPC Class Codes: G01S 19/49 whereby the further system is an inertial position system, e.g. loosely-coupled
• CPC Class Codes: G05D 1/0219 ensuring the processing of the whole working surface
• 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: G05D 1/0272 comprising means for registering the travel distance, e.g. revolutions of wheels measuring distance traversed on the ground by vehicles, e.g. using odometers G01C22/00
• CPC Class Codes: G05D 1/0278 using satellite positioning signals, e.g. GPS
• CPC Class Codes: G05D 1/028 using a RF signal

Abstract

A robotic work tool system, comprising a robotic work tool, said robotic work tool comprising a position determining device for determining a current position and at least one deduced reckoning (also known as dead reckoning) navigation sensor, the robotic work tool being configured to determine that a reliable and accurate current position is possible to determine and in response thereto determine an expected navigation parameter, compare the expected navigation parameter to a current navigation parameter to determine a navigation error, determine if the navigation error is negligible, and if the navigation error is not negligible, cause the robotic work tool to change its trajectory to accommodate for the navigation error. Wherein the robotic work tool (100) is further configured to change the trajectory by aligning the trajectory with an expected trajectory, wherein the expected trajectory is determined as an expected direction originating from an expected position and wherein the robotic work tool (100) is configured to change the trajectory by returning to a position that should have been visited and aligning the trajectory with the expected direction originating from the expected position, said position that should have been visited being aligned with the expected direction originating from the expected position.

Claims

1. A robotic work tool comprising a Global Navigation Satellite System (GNSS) device for determining a current position of the robotic work tool and at least one deduced reckoning navigation sensor, the deduced reckoning navigation sensor being configured to provide signals for deduced reckoning navigation,

wherein the robotic work tool is configured to:

in response to the GNSS device determining the current position, operate based on the current position,

in response to the GNSS device no longer being able to determine the current position, continue operating using the deduced reckoning navigation,

determine that the GNSS device is again able to determine the current position and in response thereto determine an expected navigation parameter based on control data for the deduced reckoning navigation, the expected navigation parameter comprising an expected position and an expected direction of the robotic work tool,

compare the expected navigation parameter to a current navigation parameter to determine a navigation error, the current navigation parameter comprising the current position and a current direction of the robotic work tool,

determine if the navigation error is negligible,

in response to the navigation error not being negligible, cause the robotic work tool to change a trajectory to accommodate for the navigation error,

by aligning the trajectory with an expected trajectory of the robotic work tool, wherein the expected trajectory is determined as being along the expected direction originating from the expected position of the robotic work tool, and

wherein the robotic work tool is further configured to;

perform the change of the trajectory by returning to a position that has been passed and should have been visited and aligning the trajectory with the expected direction originating from the expected position, said position that should have been visited being aligned with the expected direction originating from the expected position and not coinciding with the expected position, and

wherein the position that should have been visited is determined to be a point in an area in which the GNSS navigation is not possible or the position that should have been visited is a position where a GNSS signal could have been received again but along the expected trajectory.

2. The robotic work tool according to claim 1, wherein the expected position is a position being determined based on the control data for the deduced reckoning navigation used when no GNSS signal was received.

3. The robotic work tool according to claim 1, wherein the robotic work tool is configured to determine the position that should have been visited by extrapolating positions known to have GNSS signal reception.

4. The robotic work tool according to claim 1, wherein the robotic work tool is configured to calibrate the deduced reckoning navigation sensor based on the determined navigation error.

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

6. A method for operating a robotic work tool, said robotic work tool comprising a Global Navigation Satellite System (GNSS) device for determining a current position of the robotic work tool and at least one deduced reckoning navigation sensor, the deduced reckoning navigation sensor configured to provide signals for deduced reckoning navigation, the method comprising:

in response to the GNSS device determining the current position of the robotic work tool, causing the robotic work tool to operate based on the current position retrieved from the GNSS device;

in response to the GNSS device no longer being able to determine the current position, causing the robotic work tool to continue operating using the deduced reckoning navigation;

determining that the GNSS device is again able to determine the current position and in response thereto determining an expected navigation parameter based on control data for the deduced reckoning navigation, the expected navigation parameter comprising an expected position and an expected direction of the robotic work tool;

comparing the expected navigation parameter to a current navigation parameter to determine a navigation error, the current navigation parameter comprising the current position and a current direction of the robotic work tool;

determining if the navigation error is negligible;

in response to the navigation error not being negligible, causing the robotic work tool to change a trajectory to accommodate for the navigation error by aligning the trajectory with an expected trajectory, wherein the expected trajectory is determined as being along the expected direction originating from the expected position of the robotic work tool; and

performing the change of the trajectory by returning to a position that has been passed and that should have been visited and aligning the trajectory with the expected direction originating from the expected position of the robotic work tool, the position that should have been visited being aligned with the expected direction originating from the expected position and not coinciding with the expected position, wherein the position that should have been visited is determined to be a point in an area in which the GNSS navigation is not possible, or the position that should have been visited is a position where a GNSS signal could have been received again but along the expected trajectory.