Scanning range finder

Patent metadata

Field	Value
Publication number	US-10024964-B2
Application number	US-201414529815-A
Country	US
Kind code	B2
Filing date	Oct 31, 2014
Priority date	Nov 1, 2013
Publication date	Jul 17, 2018
Grant date	Jul 17, 2018

Abstract

A scanning optical range finder in a mobile robot includes an optical emitter circuit, a non-imaging optical element, an optical detector circuit, and a ranging circuit. The non-imaging optical element is arranged to receive optical signals at an entrance aperture thereof responsive to operation of the optical emitter circuit, and to direct the optical signals to an output aperture thereof. The optical detector circuit is configured to receive the optical signals from the output aperture of the non-imaging optical element, and to generate detection signals based on respective phase differences of the optical signals relative to corresponding outputs of the optical emitter circuit. The ranging circuit is configured to calculate a range of a target from the phase differences indicated by the detection signals. Related devices and methods of operation are also discussed.

First claim

The invention claimed is:

1. A method of mowing an area with an autonomous mowing robot, the method comprising:
controlling the mowing robot to autonomously traverse the area bounded by a predetermined boundary, including altering direction of the mowing robot at or near the predetermined boundary so as to redirect the mowing robot back into the bounded area; and
determining a pose of the mowing robot relative to locations of at least two retro-reflective beacons within the bounded area, wherein determining the pose of the mowing robot relative to the locations of the at least two retro-reflective beacons comprises:
pulsing a rotating laser range finder during a planar sweep about an axis of rotation;
monitoring an amplitude of a received signal strength (RSSI) responsive to the pulsing;
identifying a planar sweep angle at which the RSSI sharply transitions from a low level state to a high level state thereby indicating a presence of one of the at least two retro-reflective beacons; and
calculating a heading from the mowing robot to the at least two retro-reflective beacons,
wherein the at least two retro-reflective beacons comprises three retro-reflective beacons, and wherein determining the pose further comprises performing triangulation to the three retro-reflective beacons to calculate the pose within the bounded area.

2. The method of claim 1 , wherein the laser range finder fires 256 pulses of a laser diode with about 1 degree of synchronization during a rotational sweep.

3. The method of claim 1 , wherein the laser range finder rotates at at least 10 Hz.

4. The method of claim 1 , wherein the laser range finder alters a frequency or power of a laser diode output during the planar sweep.

5. The method of claim 1 , wherein the laser range finder comprises:
an optical emitter circuit;
a non-imaging optical element arranged to receive distinct optical signals at an entrance aperture thereof responsive to operation of the optical emitter circuit and to direct the optical signals to an output aperture thereof;
an optical detector circuit configured to receive the optical signals from the output aperture of the non-imaging optical element and to generate respective detection signals based on respective phase differences of the optical signals relative to corresponding outputs of the optical emitter circuit; and
a ranging circuit coupled to the optical detector circuit and configured to calculate a plurality of distances from the phase differences indicated by the detection signals, and to identify one of the plurality of distances as a range of a target.

6. The method of claim 5 , wherein the non-imaging optical element comprises a compound parabolic collector element, and further comprising:
operating a rotatable turret to rotate about the axis of rotation, the rotatable turret comprising collection optics that are arranged to direct the optical signals to the compound parabolic collector element responsive to rotation of the turret during the planar sweep.

7. The method of claim 6 , wherein the compound parabolic collector element comprises:
a parabolic surface defining the entrance and output apertures at opposing ends thereof; and
a flange extending around a periphery of the parabolic surface adjacent the entrance aperture thereof, the flange having a greater diameter than the entrance aperture and defining a lip protruding from the parabolic surface.

8. The method of claim 1 , further comprising changing a rotational frequency of the laser range finder, wherein, during a subsequent sweep, power to a laser diode from an optical emitter circuit of the laser range finder is configured to be dynamically increased at the locations of the at least two retro-reflective beacons, thereby increasing the amplitude of the RSSI based on identifying the locations of the at least two retro-reflective beacons in an initial sweep at a higher rotational frequency than the subsequent sweep.

9. The method of claim 1 , further comprising reducing power to a laser diode of the laser range finder to avoid reflection from diffuse targets at ranges closer than one of the retro-reflective beacons, the diffuse targets having known signal strengths.

10. The method of claim 1 , wherein the retro-reflective beacons are encoded with unique identification markers and distances between the retro-reflective beacons are known.

11. The method of claim 1 , wherein coordinates of the retro-reflective beacons relative to the predetermined boundary are known and determining the pose based on the retro-reflective beacons further comprises determining the pose relative to the predetermined boundary of the area.

12. The method of claim 1 , further comprising:
dynamically increasing or decreasing power to a laser diode of the laser range finder based on the amplitude of the RSSI relative to a threshold, wherein the amplitude of the RSSI is indicative of a reflectivity of respective targets in the bounded area.

13. The method of claim 5 , wherein the respective optical signals have different frequencies, and further comprising:
operating the ranging circuit to identify one of the plurality of distances as the range of the target by comparing the plurality of distances indicated by the respective detection signals.

14. The method of claim 13 , wherein the respective detection signals represent average voltages based on the respective phase differences, and wherein the comparing comprises:
calculating, for the respective detection signals, the plurality of distances from the average voltages thereof; and
identifying the one of the plurality of distances as the range of the target based on a least common multiple thereof.

15. The method of claim 14 , further comprising:
sequentially switching between the different frequencies to transmit respective ranging signals from the optical emitter circuit.

16. The method of claim 1 , wherein determining the pose further comprises:
determining a time delay between transmission of respective outputs from an optical emitter circuit of the laser range finder responsive to the pulsing and arrival of a corresponding one of respective optical signals at an optical detector circuit of the laser range finder responsive to the monitoring; and
identifying a range of the one of the at least two retro-reflective beacons based on the time delay.

17. The method of claim 16 , further comprising:
determining a time of the arrival of the one of the respective optical signals based on the amplitude of the RSSI thereof exceeding a threshold.

18. The method of claim 1 , further comprising:
performing the planar sweep on initial power-up of the mowing robot in the bounded area to verify boundaries and/or to compare detected boundaries to stored boundaries from a previous sweep; and
performing a subsequent planar sweep over the planar sweep angle responsive to identification thereof, wherein a rotational frequency of the rotating laser range finder for the subsequent planar sweep is reduced relative to the planar sweep.

19. A mowing robot, comprising:
a controller; and
a memory comprising computer program code stored therein, which, when executed by the controller, directs the controller to perform operations comprising:
controlling the mowing robot to autonomously traverse an area that is bounded by a predetermined boundary, including altering direction of the mowing robot at or near the predetermined boundary so as to redirect the mowing robot back into the bounded area; and
determining a pose of the mowing robot relat

Assignees

• Irobot Corp

Inventors

• Pierce Travis
• Milliken Jamie
• Wilga Marc

Classifications

• G01S7/4817

  relating to scanning · CPC title

• Y10S901/47

  Optical · CPC title

• G01S17/10

  using transmission of interrupted, pulse-modulated waves (determination of distance by phase measurements G01S17/32) · CPC title

• G01S7/4816

  of receivers alone · CPC title

• G01S17/42

  Simultaneous measurement of distance and other co-ordinates (indirect measurement G01S17/46) · CPC title