# US 11,661,204 B2 · Rotor noise reduction using signal processing

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- Number: US 11,661,204 B2
- Document ID: US11661204B2
- Status: Granted
- Kind: B2
- Application number: 17/323,750
- Filed: 2021-05-18
- Published: 2022-02-24
- Granted: 2023-05-30
- Earliest claimed: 2020-08-20
- Assignees: Kitty Hawk Corporation
- Applicants: Kitty Hawk Corporation
- Inventors: Cameron Robertson
- Web page: https://patentgrep.com/patent/US11661204B2

## CPC

- B64C 29/0025: {the propellers being fixed relative to the fuselage}
- B64D 31/06: actuated automatically
- G10K 11/175: using interference effects; Masking sound
- G10K 11/1752: {Masking}
- H02P 5/52: additionally providing control of relative angular displacement
- H02P 5/74: controlling two or more AC dynamo-electric motors (H02P5/46, H02P5/60 take precedence)
- H02P 23/06: Controlling the motor in four quadrants
- B64C 2220/00: Active noise reduction systems
- G10K 2210/123: Synchrophasors or other applications where multiple noise sources are driven with a particular phase relationship
- B64C: AEROPLANES; HELICOPTERS
- B64D: EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
- G10K: SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS

## Abstract

A takeoff location and a landing location are received for an autonomous vertical takeoff and landing (VTOL) vehicle that includes a plurality of rotors. An autonomous and noise-reduced flight trajectory for the autonomous VTOL vehicle is determined based at least in part on the takeoff location, the landing location, a jerk function, and a noise function, including by minimizing the jerk function and minimizing the noise function. A set of one or more desired forces or moments is determined for the autonomous VTOL vehicle based at least in part on autonomous and noise-reduced flight trajectory. A plurality of motor control signals is determined for the plurality of rotors based at least in part on the set of one or more desired forces or moments.

## Claims

### Claim 1

A system, comprising:
a memory; and
a processor coupled to the memory and configured to:
receive a takeoff location and a landing location for an autonomous vertical takeoff and landing (VTOL) vehicle that includes a plurality of rotors;
determine an autonomous and noise-reduced flight trajectory for the autonomous VTOL vehicle based at least in part on the takeoff location, the landing location, a jerk function, and a noise function, including by minimizing the jerk function and minimizing the noise function;
determine a set of one or more desired forces or moments for the autonomous VTOL vehicle based at least in part on autonomous and noise-reduced flight trajectory; and
determine a plurality of motor control signals for the plurality of rotors based at least in part on the set of one or more desired forces or moments, wherein:
the plurality of rotors includes a first rotor and a second rotor;
the first rotor includes one of a first center inboard rotor and a second center inboard rotor;
the second rotor includes another of the first center inboard rotor and the second center inboard rotor; and
the determining of the plurality of motor control signals for the plurality of rotors includes to:
determine a first deconflicted motor control signal for the first rotor, wherein the first deconflicted motor control signal rotates the first rotor at a slower frequency than the second rotor; and
determine a second deconflicted motor control signal for the second rotor, the second deconflicted motor control signal rotating the second rotor at a faster frequency than the first rotor, and the first deconflicted motor control signal and the second deconflicted motor control signal causing the first rotor and the second rotor to respectively rotate at a frequency difference that exceeds a threshold.

### Claim 2 (depends on 1)

The system recited in claim 1, wherein:
the autonomous VTOL vehicle includes an overwater vehicle that includes a float having a top surface;
the plurality of rotors includes an inboard rotor that is disposed on the top surface of the float; and
the plurality of rotors includes an outboard rotor that is disposed on a distal end of a boom that extends outward from a fuselage.

### Claim 3 (depends on 1)

The system recited in claim 1, wherein the autonomous and noise-reduced flight trajectory has one or more of the following properties compared to an autonomous flight trajectory that is determined without using the noise function: a longer trajectory, a longer flight duration, a lower maximum speed, or a higher cruising altitude.

### Claim 4

A system, comprising:
a memory; and
a processor coupled to the memory and configured to:
receive a takeoff location and a landing location for an autonomous vertical takeoff and landing (VTOL) vehicle that includes a plurality of rotors;
determine an autonomous and noise-reduced flight trajectory for the autonomous VTOL vehicle based at least in part on the takeoff location, the landing location, a jerk function, and a noise function, including by minimizing the jerk function and minimizing the noise function;
determine a set of one or more desired forces or moments for the autonomous VTOL vehicle based at least in part on autonomous and noise-reduced flight trajectory; and
determine a plurality of motor control signals for the plurality of rotors based at least in part on the set of one or more desired forces or moments, wherein:
the plurality of rotors includes a first rotor and a second rotor; and
determining the plurality of motor control signals for the plurality of rotors includes determining a first deconflicted motor control signal for the first rotor and a second deconflicted motor control signal for the second rotor, wherein:
the first deconflicted motor control signal and the second deconflicted motor control signal cause the first rotor and the second rotor to respectively rotate at a frequency difference that exceeds a threshold; and
determining the first deconflicted motor control signal for the first rotor and the second deconflicted motor control signal for the second rotor includes:
receiving a first raw motor control signal for the first rotor and a second raw motor control signal for the second rotor;
comparing the first raw motor control signal and the second raw motor control signal; and
adjusting at least one of the first raw motor control signal or the second raw motor control signal for a second of the first raw motor control signal and the second raw motor control signal where the first rotor and the second rotor would not respectively rotate at a frequency difference that exceeds the threshold.

### Claim 5 (depends on 1)

The system recited in claim 1, wherein:
the plurality of rotors includes a first phase-locked rotor and a second phase-locked rotor; and
determining the plurality of motor control signals for the plurality of rotors includes determining a first phase-locked motor control signal for the first phase-locked rotor and a second phase-locked motor control signal for the second phase-locked rotor, wherein the first phase-locked motor control signal and the second phase-locked motor control signal cause the first phase-locked rotor and the second phase-locked rotor to respectively rotate at a fixed phase difference.

### Claim 6 (depends on 1)

The system recited in claim 1, wherein:
the plurality of rotors includes a first phase-locked rotor and a second phase-locked rotor;
determining the plurality of motor control signals for the plurality of rotors includes determining a first phase-locked motor control signal for the first phase-locked rotor and a second phase-locked motor control signal for the second phase-locked rotor, wherein the first phase-locked motor control signal and the second phase-locked motor control signal cause the first phase-locked rotor and the second phase-locked rotor to rotate at a fixed phase difference; and
the first phase-locked rotor and the second phase-locked rotor include a first center inboard rotor and a second center inboard rotor.

### Claim 7 (depends on 1)

The system recited in claim 1, wherein determining the plurality of motor control signals for the plurality of rotors includes:
determining whether a control margin exceeds a threshold;
in the event it is determined that the control margin exceeds the threshold, determining at least one noise-reduced motor control signal for the plurality of rotors; and
in the event it is determined that the control margin does not exceed the threshold, determining a non-noise-reduced motor control signal for each of the plurality of rotors.

### Claim 8 (depends on 1)

The system recited in claim 1, wherein determining the plurality of motor control signals for the plurality of rotors includes:
determining whether a moving window of past motor control signals satisfies a steady state criteria;
in the event it is determined that the moving window of past motor control signals satisfies the steady state criteria, determining at least one noise-reduced motor control signal for the plurality of rotors; and
in the event it is determined that the moving window of past motor control signals does not satisfy the steady state criteria, determining a non-noise-reduced motor control signal for each of the plurality of rotors.

### Claim 9

A method, comprising:
receiving a takeoff location and a landing location for an autonomous vertical takeoff and landing (VTOL) vehicle that includes a plurality of rotors;
determining an autonomous and noise-reduced flight trajectory for the autonomous VTOL vehicle based at least in part on the takeoff location, the landing location, a jerk function, and a noise function, including by minimizing the jerk function and minimizing the noise function;
determining a set of one or more desired forces or moments for the autonomous VTOL vehicle based at least in part on autonomous and noise-reduced flight trajectory; and
determining a plurality of motor control signals for the plurality of rotors based at least in part on the set of one or more desired forces or moments, wherein:
the plurality of rotors includes a first rotor and a second rotor;
the first rotor includes one of a first center inboard rotor and a second center inboard rotor;
the second rotor includes another of the first center inboard rotor and the second center inboard rotor; and
the determining of the plurality of motor control signals for the plurality of rotors includes:
determining a first deconflicted motor control signal for the first rotor, wherein the first deconflicted motor control signal rotates the first rotor at a slower frequency than the second rotor; and
determining a second deconflicted motor control signal for the second rotor, the second deconflicted motor control signal rotating the second rotor at a faster frequency than the first rotor, and the first deconflicted motor control signal and the second deconflicted motor control signal causing the first rotor and the second rotor to respectively rotate at a frequency difference that exceeds a threshold.

### Claim 10 (depends on 9)

The method recited in claim 9, wherein:
the autonomous VTOL vehicle includes an overwater vehicle that includes a float having a top surface;
the plurality of rotors includes an inboard rotor that is disposed on the top surface of the float; and
the plurality of rotors includes an outboard rotor that is disposed on a distal end of a boom that extends outward from a fuselage.

### Claim 11 (depends on 9)

The method recited in claim 9, wherein the autonomous and noise-reduced flight trajectory has one or more of the following properties compared to an autonomous flight trajectory that is determined without using the noise function: a longer trajectory, a longer flight duration, a lower maximum speed, or a higher cruising altitude.

### Claim 12

A method, comprising:
receiving a takeoff location and a landing location for an autonomous vertical takeoff and landing (VTOL) vehicle that includes a plurality of rotors;
determining an autonomous and noise-reduced flight trajectory for the autonomous VTOL vehicle based at least in part on the takeoff location, the landing location, a jerk function, and a noise function, including by minimizing the jerk function and minimizing the noise function;
determining a set of one or more desired forces or moments for the autonomous VTOL vehicle based at least in part on autonomous and noise-reduced flight trajectory; and
determining a plurality of motor control signals for the plurality of rotors based at least in part on the set of one or more desired forces or moments, wherein:
the plurality of rotors includes a first rotor and a second rotor; and
determining the plurality of motor control signals for the plurality of rotors includes determining a first deconflicted motor control signal for the first rotor and a second deconflicted motor control signal for the second rotor, wherein:
the first deconflicted motor control signal and the second deconflicted motor control signal cause the first rotor and the second rotor to respectively rotate at a frequency difference that exceeds a threshold; and
determining the first deconflicted motor control signal for the first rotor and the second deconflicted motor control signal for the second rotor includes:
receiving a first raw motor control signal for the first rotor and a second raw motor control signal for the second rotor;
comparing the first raw motor control signal and the second raw motor control signal; and
adjusting at least one of the first raw motor control signal or the second raw motor control signal for a second of the first raw motor control signal and the second raw motor control signal where the first rotor and the second rotor would not respectively rotate at a frequency difference that exceeds the threshold.

### Claim 13 (depends on 9)

The method recited in claim 9, wherein:
the plurality of rotors includes a first phase-locked rotor and a second phase-locked rotor; and
determining the plurality of motor control signals for the plurality of rotors includes determining a first phase-locked motor control signal for the first phase-locked rotor and a second phase-locked motor control signal for the second phase-locked rotor, wherein the first phase-locked motor control signal and the second phase-locked motor control signal cause the first phase-locked rotor and the second phase-locked rotor to respectively rotate at a fixed phase difference.

### Claim 14 (depends on 9)

The method recited in claim 9, wherein:
the plurality of rotors includes a first phase-locked rotor and a second phase-locked rotor;
determining the plurality of motor control signals for the plurality of rotors includes determining a first phase-locked motor control signal for the first phase-locked rotor and a second phase-locked motor control signal for the second phase-locked rotor, wherein the first phase-locked motor control signal and the second phase-locked motor control signal cause the first phase-locked rotor and the second phase-locked rotor to rotate at a fixed phase difference; and
the first phase-locked rotor and the second phase-locked rotor include a first center inboard rotor and a second center inboard rotor.

### Claim 15 (depends on 9)

The method recited in claim 9, wherein determining the plurality of motor control signals for the plurality of rotors includes:
determining whether a control margin exceeds a threshold;
in the event it is determined that the control margin exceeds the threshold, determining at least one noise-reduced motor control signal for the plurality of rotors; and
in the event it is determined that the control margin does not exceed the threshold, determining a non-noise-reduced motor control signal for each of the plurality of rotors.

### Claim 16 (depends on 9)

The method recited in claim 9, wherein determining the plurality of motor control signals for the plurality of rotors includes:
determining whether a moving window of past motor control signals satisfies a steady state criteria;
in the event it is determined that the moving window of past motor control signals satisfies the steady state criteria, determining at least one noise-reduced motor control signal for the plurality of rotors; and
in the event it is determined that the moving window of past motor control signals does not satisfy the steady state criteria, determining a non-noise-reduced motor control signal for each of the plurality of rotors.