Detecting robot stasis
A coverage robot includes a drive configured to maneuver the robot as directed by a controller, a stasis indication wheel rotatable about a first axis perpendicular to a direction of forward travel, and a suspension supporting the wheel. The stasis indication wheel defines a first reflective portion and a second reflective portion. The second reflective portion is substantially less reflective than the first reflective portion. The suspension permits movement of the wheel in a direction other than rotation about the first axis. A signal emitter is disposed remotely from the wheel and positioned to direct a signal that sequentially is intercepted by the first and second reflective portions of the wheel. A signal receiver is positioned to receive the reflected signal by the rotating wheel. Communication between the emitter and the receiver is affected by rolling transitions between the first and second reflective portions during permitted movement of the wheel.
1. A coverage robot comprising:
a drive configured to maneuver the robot as directed by a controller in communication with the drive;
a swivel caster assembly coupled to the drive and comprising:
a stasis indication wheel freely rotatable about a horizontal axis parallel to a traveling surface, the stasis indication wheel defining a first reflective portion and a second reflective portion, the second reflective portion being substantially less reflective than the first reflective portion;
a wheel housing mounted on a freely rotatable shaft positioned at an angle relative to the horizontal axis, the wheel housing supporting the wheel such that rotation of the shaft causes the wheel to swivel on the traveling surface; and
a suspension supporting the wheel housing and permitting movement of the wheel in a direction other than rotation about the horizontal axis and swiveling on the traveling surface;
a signal emitter disposed remotely from the wheel and positioned to direct a signal that sequentially is intercepted by the first and second reflective portions of the wheel; and
a signal receiver co-located adjacent the signal emitter to receive the signal as reflected by the first and second reflective portions of the wheel as the wheel freely rotates about the horizontal axis as the wheel swivels on the traveling surface, and as the wheel moves in the direction permitted by the suspension,
wherein the strength of the reflected signal received by the receiver changes based at least in part on rolling transitions between the first reflective portion and the second reflective portion of the wheel in multiple swivel positions and along the movement permitted by the suspension.
2. The coverage robot of claim 1 wherein the permitted direction of wheel movement by the suspension comprises vertical displacement of the wheel.
3. The coverage robot of claim 2 further comprising a wheel drop sensor arranged to detect vertical displacement of the wheel.
4. The coverage robot of claim 1 wherein the permitted direction of wheel movement by the suspension comprises tilting away from a vertical axis.
5. The coverage robot of claim 1 wherein the permitted direction of wheel movement by the suspension comprises translation parallel to an underside of the robot.
6. The coverage robot of claim 1 wherein the wheel housing shrouds the wheel and defines an aperture exposing the wheel to the signal emitter and the signal receiver.
7. The coverage robot of claim 6 wherein the wheel housing is configured to minimize an entry of ambient light into the aperture of.
8. The coverage robot of claim 1 wherein the first reflective portion of the wheel reflects light of a first infrared wavelength and the second reflective portion reflects light of a second infrared wavelength different from the first wavelength.
9. The coverage robot of claim 1 wherein the emitter and receiver are arranged above the wheel, the emitter emitting the signal onto a top portion of the wheel, and the receiver responsive to reflected emissions.
10. The coverage robot of claim 1 further comprising a cliff signal emitter and a cliff signal receiver, the cliff signal emitter aligned to emit a cliff detection signal onto the traveling surface, the cliff signal receiver configured to receive the cliff detection signal reflected from the traveling surface;
wherein the cliff signal emitter and cliff signal receiver are arranged with respect to the traveling surface such that communication between the cliff signal emitter and the cliff signal receiver is affected by vertical movement of the traveling surface with respect to the robot.
11. The coverage robot of claim 1 wherein the controller monitors a drive current of the drive to determine a presence of a stasis condition.
12. The coverage robot of claim 1 wherein the stasis indication wheel is disposed adjacent a drive wheel.
13. A coverage robot comprising:
a drive configured to maneuver the robot as directed by a controller in communication with the drive;
a stasis indication wheel freely rotatable about a horizontal axis parallel to a traveling surface and freely rotatable about a vertical axis perpendicular to a direction of forward travel and disposed adjacent the drive, the wheel comprising a hub and multiple spokes extending outwardly from the hub, the wheel defining a first reflective portion and a second reflective portion, the second reflective portion being substantially less reflective than the first reflective portion;
a signal emitter disposed remotely from the wheel and positioned to direct a signal that sequentially is intercepted by the first and second reflective portions of the wheel; and
a signal receiver positioned to receive the signal as reflected by the first and second reflective portions of the wheel as the wheel freely rotates about the horizontal and vertical axes, and as a suspension permits movement of the wheel in a direction other than rotation about the vertical axis,
wherein the strength of the reflected signal received by the receiver changes based at least in part on rolling transitions between the first reflective portion and the second reflective portion of the wheel in multiple positions about the vertical axis and along permitted movement in a direction other than rotation about the vertical axis.
14. The coverage robot of claim 13 wherein the spokes of the stasis indication wheel spiral outwardly from the hub.
15. The coverage robot of claim 13 wherein the spokes of the stasis indication wheel are compliant.
16. The coverage robot of claim 13 wherein the stasis indication wheel includes a magnet disposed on one of the spokes, the magnet interacts with a reed switch in communication with the controller.
17. The coverage robot of claim 13 wherein the first reflective portion of the wheel reflects light of a first infrared wavelength and the second reflective portion reflects light of a second infrared wavelength different from the first wavelength.
18. The coverage robot of claim 13 wherein the emitter and receiver are arranged above the wheel, the emitter emitting the signal onto a top portion of the wheel, and the receiver responsive to reflected emissions.
19. The coverage robot of claim 13 wherein the controller monitors a drive current of the drive to determine a presence of a stasis condition.
20. The coverage robot of claim 1 wherein the shaft is freely rotatable within a predetermined angular range as wide as the field of detection of the signal receiver, such that the signal receiver receives the reflected signal irrespective of a swivel position of the wheel on the traveling surface.
21. The coverage robot of claim 1 wherein the signal receiver is a first signal receiver, and further comprising a second signal receiver, the first and second signal receivers having a sufficient aggregate field of detection to receive the reflected signal throughout 360 degrees of rotation by the shaft.