Controlled flight of a multicopter experiencing a failure affecting an effector

Patent metadata

Field	Value
Publication number	US-9856016-B2
Application number	US-201414893874-A
Country	US
Kind code	B2
Filing date	Jun 5, 2014
Priority date	Jun 9, 2013
Publication date	Jan 2, 2018
Grant date	Jan 2, 2018

Abstract

According to a first aspect of the invention, there is provided a method for operating a multicopter experiencing a failure during flight, the multicopter comprising a body, and at least four effectors attached to the body, each operable to produce both a torque and a thrust force which can cause the multicopter to fly when not experiencing said failure. The method may comprise the step of identifying a failure wherein the failure affects the torque and/or thrust force produced by an effector, and in response to identifying a failure carrying out the following steps, (1) computing an estimate of the orientation of a primary axis of said body with respect to a predefined reference frame, wherein said primary axis is an axis about which said multicopter rotates when flying, (2) computing an estimate of the angular velocity of said multicopter, (3) controlling one or more of said at least four effectors based on said estimate of the orientation of the primary axis of said body with respect to said predefined reference frame and said estimate of the angular velocity of the multicopter. The step of controlling one or more of said at least four effectors may be performed such that (a) said one or more effectors collectively produce a torque along said primary axis and a torque perpendicular to said primary axis, wherein (i) the torque along said primary axis causes said multicopter to rotate about said primary axis, and (ii) the torque perpendicular to said primary axis causes said multicopter to move such that the orientation of said primary axis converges to a target orientation with respect to said predefined reference frame, and (b) such that said one or more effectors individually produce a thrust force along said primary axis.

First claim

The invention claimed is:

1. A method for operating a multicopter experiencing a failure during flight, the multicopter comprising,
a body; and
at least four effectors attached to the body, each configured to produce both a torque and a thrust force which can cause the multicopter to fly when not experiencing said failure,
the method comprising the step of,
identifying, using an evaluation unit, a failure wherein the failure affects the torque and/or the thrust force produced by an effector;
in response to said identifying of said failure, using a control unit to carry out the steps of,
computing an estimate of the orientation of a primary axis of said body with respect predefined reference frame, wherein said primary axis is an axis about which said multicopter rotates when flying;
computing an estimate of the angular velocity of said multicopter;
controlling one or more of said at least four effectors which are without a failure, based on said estimate of the orientation of the primary axis of said body with respect to said predefined reference frame and said estimate of the angular velocity of the multicopter,
such that said one or more effectors collectively produce, a torque along said primary axis and a torque perpendicular to said primary axis, wherein
the torque along said primary axis causes said multicopter to rotate about said primary axis, and
the torque perpendicular to said primary axis causes said multicopter to move such that the orientation of said primary axis converges to a target orientation with respect to said predefined reference frame,
and such that each of said one or more effectors individually produces a thrust force along said primary axis.

2. The method according to claim 1 , wherein
said step of controlling one or more of said at least four effectors which are without a failure, comprises, controlling one or more of said at least four effectors which are without a failure based on said estimate of the orientation of the primary axis of said body with respect to the predefined reference frame and said estimate of the angular velocity of the multicopter, such that said thrust force produced along said primary axis by each of said one or more effectors which are without a failure is at least 20% of the thrust collectively produced by said one or more effectors which are without a failure when the orientation of said primary axis has converged to said target orientation.

3. The method according to claim 1 , wherein the step of identifying a failure affecting the torque and/or the thrust force produced by an effector, comprises
identifying a failure, wherein said failure causes the torque and/or the thrust force produced by at least one of said effectors to decrease by an amount greater than 20%.

4. The according to claim 1 , wherein
said torque along said primary axis causes said multicopter to rotate about said primary axis at a speed greater than 0.5 revolutions per second.

5. The method according to claim 1 , further comprising the steps of
defining a target acceleration for said multicopter, and
using said target acceleration to compute said target orientation of said primary axis for said multicopter,
and wherein said controlling one or more of said at least four effectors which are without a failure additionally comprises the step of controlling said one or more effectors so that the thrust collectively produced by said one or more effectors accelerates said multicopter at said target acceleration.

6. The method according to claim 5 , wherein the step of computing said target orientation of said primary axis using said target acceleration of said multicopter comprises the step of,
computing said target orientation using the equation

n
~

=

a
-
g



a
-
g



wherein the vector a represents said target acceleration and the vector g represents the gravitation acceleration, and the vector ñ represents said target orientation, and ∥.∥ represents the Euclidean norm of a vector.

7. The method according to claim 1 , comprising the additional step of
defining a target thrust force magnitude, and wherein
said step of controlling one or more of said at least four effectors which are without a failure based on said estimate of the orientation of the primary axis of said body with respect to the predefined reference frame and said estimate of the angular velocity of the multicopter, comprises controlling said one or more effectors which are without a failure such that the magnitude of the sum of each of said thrust forces produced individually by said one or more effectors along said primary axis averaged over a predefined time period equals said target thrust force magnitude.

8. The method according to claim 7 , wherein
said step of controlling one or more of said at least four effectors which are without a failure comprises, controlling each of said one or more of said at least four effectors so that they each contribute at least 20% to the target thrust force magnitude when the orientation of said primary axis has converged to said target orientation.

9. The method according to claim 5 , wherein the step of computing said target thrust force magnitude using said target acceleration of said multicopter comprises the steps of,
defining said target acceleration,
computing said target thrust force magnitude as
f des =m∥a−g∥

wherein f des represents the target thrust force magnitude, ∥.∥ represents the Euclidean norm of a vector, a represents the said target acceleration, g represents the acceleration due to gravity and m represents the mass of said multicopter.

10. The method according to claim 7 , further comprising the steps of,
defining a target translational velocity of said multicopter,
defining a target position of said multicopter,
estimating the current translational velocity of said multicopter,
estimating the current position of said multicopter,
using at least one of said target translational velocity, said target position, said current translational velocity, and said current position of said multicopter to compute said target acceleration.

11. The method according to claim 1 , wherein
said multicopter is a quadrocopter.

12. The method according to claim 1 , wherein said controlling comprises controlling at most the of said at least four effectors.

13. The method according to claim 1 , wherein said controlling comprises controlling at most two of said at least four effectors.

14. A multicopter comprising,
a body,
at least four effectors attached to the body, each configured to produce both a torque and a thrust force which can cause the multicopter to fly when not experiencing a failure,
a flight module configured such that it can carry out the method comprising tae steps of,
identifying a failure wherein the failure affects the torque and/or the thrust force produced by an effector;
in response to said identifying of said failure, carrying out the steps of,
computing an estimate of the orientation of a primary axis of said body with respect to a predefined reference frame, wherein said primary axis is an axis about which said multicopter rotates when flying;
c

Assignees

• Eth Zuerich

Inventors

• Mueller Mark W
• Lupashin Sergei
• D'Andrea Raffaello
• Waibel Markus

Classifications

• B64U2201/10

  autonomous, i.e. by navigating independently from ground or air stations, e.g. by using inertial navigation systems [INS] · CPC title

• B64U2201/20

  Remote controls · CPC title

• B64U2101/30

  for imaging, photography or videography · CPC title

• B64C13/24 Primary

  Transmitting means · CPC title

• B64C2203/00

  Flying model aircraft, flying toy aircraft · CPC title