# US 11,112,505 B2 · Navigation for a robotic work tool

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- Number: US 11,112,505 B2
- Document ID: US11112505B2
- Status: Granted
- Kind: B2
- Application number: 16/803,276
- Filed: 2020-02-27
- Published: 2020-06-18
- Granted: 2021-09-07
- Earliest claimed: 2014-12-24
- Assignees: Husqvarna AB
- Applicants: Husqvarna AB
- Inventors: Magnus Öhrlund; Peter Reigo
- Web page: https://patentgrep.com/patent/US11112505B2

## CPC

- G01S 19/14: specially adapted for specific applications
- A01D 34/008: {for automated or remotely controlled operation}
- G01C 21/165: {combined with non-inertial navigation instruments}
- G01S 19/49: whereby the further system is an inertial position system, e.g. loosely-coupled
- G05D 1/0219: {ensuring the processing of the whole working surface}
- G05D 1/0265: {using buried wires}
- 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)}
- 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)}
- G05D 1/0278: {using satellite positioning signals, e.g. GPS}
- G05D 1/028: {using a RF signal}
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- A01D: HARVESTING; MOWING
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)
- G05D: SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES

## 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

### Claim 1

A robotic work tool comprising:
a position determining device configured to determine a current position of the robotic work tool; and
at least one deduced reckoning navigation sensor configured to provide signals for deduced reckoning navigation;
wherein the robotic work tool is configured to:
in response to the position determining device no longer being able to determine the current position, operate based on the deduced reckoning navigation via the at least one deduced reckoning navigation sensor,
subsequently determine that the position determining device is able to determine the current position of the robotic work tool, and in response thereto, determine an expected navigation parameter based on control data for the deduced reckoning navigation sensor, the expected navigation parameter comprising an expected position and an expected direction of travel 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 as indicated by the position determining device and a current direction of travel of the robotic work tool as determined from the position determining tool,
determine if the navigation error exceeds a navigation error threshold,
in response to the navigation error exceeding the navigation error threshold, 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
perform the change of the trajectory by returning to a position and align the trajectory while at that position with the expected direction originating from the expected position of the robotic work tool, the position not coinciding with the expected position, and
wherein the position is determined to be a point in an area in which navigation from the position determining device is not possible or the position is a point along the expected trajectory.

### Claim 2 (depends on 1)

The robotic lawnmower work tool according to claim 1, wherein the expected position is determined based on the control data for the deduced reckoning navigation sensor used when no signal from the position determining device was received.

### Claim 3 (depends on 1)

The robotic work tool according to claim 1, wherein the robotic work tool is configured to determine the position by extrapolating positions known to have signal reception.

### Claim 4 (depends on 1)

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.

### Claim 5 (depends on 1)

The robotic work tool according to claim 1, wherein the position determining device is an optical position determining device.

### Claim 6 (depends on 1)

The robotic work tool according to claim 1, wherein the position determining device is a radio frequency position determining device.

### Claim 7 (depends on 1)

The robotic work tool according to claim 1, wherein the position determining device is an ultrawideband beacon.

### Claim 8

A method for operating a robotic work tool, said robotic work tool comprising a position determining device configured to determine a current position of the robotic work tool and at least one deduced reckoning navigation sensor configured to provide signals for deduced reckoning navigation, the method comprising:
in response to the position determining device no longer being able to determine the current position, operating the robotic work tool based on the deduced reckoning navigation via the at least one deduced reckoning navigation sensor;
subsequently determining that the position determining device is able to determine the current position of the robotic work tool, and in response thereto, determining an expected navigation parameter based on control data for the deduced reckoning navigation sensor, the expected navigation parameter comprising an expected position and an expected direction of travel 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 as indicated by the position determining device and a current direction of travel of the robotic work tool as determined from the position determining tool;
determining if the navigation error exceeds a navigation error threshold;
in response to the navigation error exceeding the navigation error threshold, causing 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
performing the change of the trajectory by returning to a position and aligning the trajectory while at that position with the expected direction originating from the expected position of the robotic work tool, the position not coinciding with the expected position;
wherein the position is determined to be a point in an area in which navigation via the position determining device is not possible, or the position is a point along the expected trajectory.

### Claim 9 (depends on 8)

The method according to claim 8, wherein the expected position is determined based on the control data for the deduced reckoning navigation sensor used when no signal from the position determining device was received.

### Claim 10 (depends on 8)

The method according to claim 8, wherein the method further comprises determining the position by extrapolating positions known to have signal reception.

### Claim 11 (depends on 8)

The method according to claim 8, wherein the method further comprises calibrating the deduced reckoning navigation sensor based on the determined navigation error.

### Claim 12 (depends on 8)

The method according to claim 8, wherein the position determining device is an optical position determining device.

### Claim 13 (depends on 8)

The method according to claim 8, wherein the position determining device is a radio frequency position determining device.

### Claim 14 (depends on 8)

The method according to claim 8, wherein the position determining device is an ultrawideband beacon.