CONTROLLED FLIGHT OF A MULTICOPTER EXPERIENCING A FAILURE AFFECTING AN EFFECTOR

• US 20160107751A1
• Filed: 06/05/2014
• Published: 04/21/2016
• Est. Priority Date: 06/09/2013
• Status: Active Grant

• Current Assignee: ETH Zurich
• Original Assignee: ETH Zurich
• Inventors: WAIBEL, Markus, D'ANDREA, Raffaello, LUPASHIN, Sergei, MUELLER, Mark W.
• Granted Patent: US 9,856,016 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B64C 13/24 Transmitting means
• CPC Class Codes: B64C 2203/00 Flying model aircraft, flying toy aircraft
• CPC Class Codes: B64C 27/08 with two or more rotors
• CPC Class Codes: B64C 27/20 Rotorcraft characterised by having shrouded rotors, e.g. flying platforms
• CPC Class Codes: B64C 27/32 Rotors
• CPC Class Codes: B64C 39/024 of the remote controlled vehicle type, i.e. RPV
• CPC Class Codes: B64D 45/00 Aircraft indicators or protectors not otherwise provided for camouflage F41H3/00
• CPC Class Codes: B64U 10/10 Rotorcrafts
• CPC Class Codes: B64U 10/13 Flying platforms
• CPC Class Codes: B64U 2101/30 for imaging, photography or videography
• CPC Class Codes: B64U 2201/10 autonomous, i.e. by navigating independently from ground or air stations, e.g. by using inertial navigation systems [INS]
• CPC Class Codes: B64U 2201/20 Remote controls
• CPC Class Codes: B64U 30/20 Rotors; Rotor supports
• CPC Class Codes: B64U 40/10 for adjusting control surfaces or rotors
• CPC Class Codes: B64U 50/19 using electrically powered motors
• CPC Class Codes: G05D 1/0072 to counteract a motor failure

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.

Claims

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 operable 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 a failure wherein the failure affects the torque and/or thrust force produced by an effector;

in response to said identifying of said failure carrying out the following steps,

a) 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;

b) computing an estimate of the angular velocity of said multicopter;

c) 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,

i. such that said one or more effectors collectively produce, a torque along said primary axis and a torque perpendicular to said primary axis, wherein

A. the torque along said primary axis causes said multicopter to rotate about said primary axis, and

B. 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,

ii. and such that each of said one or more effectors individually produces a thrust force along said primary axis.

2. A method according to claim 1, wherein

said step of controlling one or more of said at least four effectors comprises 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 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.

4. A method according to claim 1, wherein the step of identifying a failure affecting the torque and/or thrust force produced by an effector, comprises

identifying a failure, wherein said failure causes the torque and/or thrust force produced by at least one of said effectors to decrease by an amount greater than 20%.

8. A method 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.

10. A method according to claim 1, further comprising the steps of

a) defining a target acceleration for said multicopter, and

b) 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 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.

11. A method according to claim 10, 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

13. A 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 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 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.

14. A method according to claim 13, 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.

15. A method according to claim 10, 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.

16. A method according to claim 13, further comprising the steps of,

a) defining a target translational velocity of said multicopter,

b) defining a target position of said multicopter,

c) estimating the current translational velocity of said multicopter,

d) estimating the current position of said multicopter,

e) 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.

17. A method according to claim 1, wherein

said multicopter is a quadrocopter.

20. A method according to claim 1, wherein said controlling comprises controlling at most three of said at least lour effectors.

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

22. A multicopter comprising,

a) a body,

b) 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 a failure,

c) a flight module configured such that it can carry out the method according to claim 1.

23. A multicopter according to the claim 22, wherein the flight module comprises,

a) an input unit for receiving data from sensors and/or users,

b) a sensing unit for measuring data representative of the motion of said multicopter and/or the operation of at least one of said effectors,

c) an evaluation unit operationally connected to said sensing unit and/or input unit for identifying a failure affecting the torque and/or thrust force produced by one or more of said effectors, and

d) a control unit configured to be operationally connected to said evaluation unit, and configured

i. to compute 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 under the control of said control unit;

ii. to send control signals to one or more of said effectors so that,

A. 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

B. each of said one or more effectors individually produces a thrust force along said primary axis.

24. A multicopter according to claim 22, wherein

a) said evaluation unit is configured to provide data representative of the motion of said multicopter, and is operationally connected to said control unit to provide said data, and

b) said control unit is configured to perform controlling of said one or more effectors based on said data of said evaluation unit.

33. The multicopter according to claim 22, wherein said control unit is further configured to compute said target orientation of said primary axis using said target acceleration of said multicopter by computing said target orientation using the equation

37. The multicopter of claim 22, said multicopter further comprising a sensor which is operationally connected to said sensing unit and configured

to detect the motion of the multicopter, and

to provide data representative of the detected motion of the multicopter to said sensing unit.

39. The multicopter according to claim 23, wherein said control unit is mechanically independent of said body and said at least four effectors, and is operationally connected to the multicopter via a wireless connection.

40. The multicopter according to claim 39, wherein said mechanically independent control unit is contained in a housing configured to be held in the hand of a user and configured to receive input from said user via a user interface usable to control one or more of said at least four effectors of said multicopter via said wireless connection.

3. (canceled)

5-7. -7. (canceled)

9. (canceled)

12. (canceled)

18-19. -19. (canceled)

25-32. -32. (canceled)

34-36. -36. (canceled)

38. (canceled)

41-45. -45. (canceled)