Scanning range finder

• US 10,024,964 B2
• Filed: 10/31/2014
• Issued: 07/17/2018
• Est. Priority Date: 11/01/2013
• Status: Active Grant

• Current Assignee: iRobot Corporation
• Original Assignee: iRobot Corporation
• Inventors: Pierce, Travis, Milliken, Jamie, Wilga, Marc
• Primary Examiner(s): Ratcliffe, Luke D
• Application Number:
  US14/529,815
• Publication Number:
  US 20150124242A1
• Time in Patent Office: 1,355 Days
• CPC Class Codes: A01D 34/008 for automated or remotely controlled operation
• CPC Class Codes: G01S 17/06 Systems determining position data of a target
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 7/4816 of receivers alone
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: Y10S 901/47 Optical

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.

Claims

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 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 of the mowing robot 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.

20. 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; and

reducing power applied to a laser diode of the rotating laser range finder to avoid reflection from diffuse targets at ranges closer than one of the at least two retro-reflective beacons, the diffuse targets having known signal strengths.

21. The method of claim 20, wherein the rotating laser range finder comprises:

a non-imaging optical element arranged to receive distinct optical signals at an entrance aperture thereof responsive to pulsing the rotating laser range finder and to direct the optical signals to an output aperture thereof; and

collection optics that are arranged to direct the optical signals to the non-imaging optical element responsive to rotation of the laser range finder during the planar sweep.

22. The method of claim 20, wherein the retro-reflective beacons are encoded with unique identification markers and distances between the retro-reflective beacons are known, or wherein coordinates of the retro-reflective beacons relative to the predetermined boundary are known.

23. The method of claim 20, wherein the amplitude of the RSSI is indicative of a reflectivity of respective targets in the bounded area, and further comprising:

dynamically increasing or decreasing the power applied to the laser diode of the laser range finder based on the amplitude of the RSSI relative to a threshold.

24. The method of claim 20, further comprising:

performing a subsequent planar sweep over the planar sweep angle responsive to identification of the planar sweep angle, wherein a rotational frequency of the rotating laser range finder for the subsequent planar sweep is reduced relative to the planar sweep.

25. The method of claim 24, further comprising:

dynamically increasing the power applied to the laser diode at the locations of the at least two retro-reflective beacons during the subsequent planar sweep.

26. 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; and

dynamically increasing or decreasing power applied to a laser diode of the rotating 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.

27. The method of claim 26, wherein the rotating laser range finder comprises:

a non-imaging optical element arranged to receive distinct optical signals at an entrance aperture thereof responsive to pulsing the rotating laser range finder and to direct the optical signals to an output aperture thereof; and

collection optics that are arranged to direct the optical signals to the non-imaging optical element responsive to rotation of the laser range finder during the planar sweep.

28. The method of claim 26, wherein the retro-reflective beacons are encoded with unique identification markers and distances between the retro-reflective beacons are known, or wherein coordinates of the retro-reflective beacons relative to the predetermined boundary are known.

29. The method of claim 26, further comprising:

reducing the power applied to the laser diode of the rotating 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.

30. The method of claim 26, further comprising:

performing a subsequent planar sweep over the planar sweep angle responsive to identification of the planar sweep angle, wherein a rotational frequency of the rotating laser range finder for the subsequent planar sweep is reduced relative to the planar sweep.

31. The method of claim 30, further comprising:

dynamically increasing the power applied to the laser diode at the locations of the at least two retro-reflective beacons during the subsequent planar sweep.

32. A method of mowing an area with an autonomous mowing robot, the method comprising:

performing a planar sweep on initial power-up of the mowing robot in the area to verify boundaries and/or to compare detected boundaries to stored boundaries from a previous sweep, wherein the area is bounded by a predetermined boundary;

controlling the mowing robot to autonomously traverse the bounded area, 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;

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 the 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; 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.

33. The method of claim 32, wherein the rotating laser range finder comprises:

a non-imaging optical element arranged to receive distinct optical signals at an entrance aperture thereof responsive to pulsing the rotating laser range finder and to direct the optical signals to an output aperture thereof; and

collection optics that are arranged to direct the optical signals to the non-imaging optical element responsive to rotation of the laser range finder during the planar sweep.

34. The method of claim 32, wherein the retro-reflective beacons are encoded with unique identification markers and distances between the retro-reflective beacons are known, or wherein coordinates of the retro-reflective beacons relative to the predetermined boundary are known.

35. The method of claim 32, wherein the amplitude of the RSSI is indicative of a reflectivity of respective targets in the bounded area, and further comprising:

dynamically increasing or decreasing power applied to the laser diode of the laser range finder based on the amplitude of the RSSI relative to a threshold.

36. The method of claim 32, further comprising:

reducing power applied to the laser diode of the rotating 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.

37. The method of claim 32, further comprising:

dynamically increasing power applied to the laser diode at the locations of the at least two retro-reflective beacons during the subsequent planar sweep.