Rotor Speed Avoidance Band for Resonant Vibration Control

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Solution Overview

Problem

Unmanned vehicles with rotors driven by actuators face issues due to vibratory forces that come into resonance with rotor natural frequencies, leading to increased loads and reduced component lifespan, as well as restricted flight operations.

Innovation Solution

Implementing a system that determines and biases rotational speeds to avoid resonance frequencies by adjusting the commands for pairs of rotors, ensuring they operate outside a defined avoid band, thereby reducing dwell times at resonant speeds and minimizing net effect on vehicle control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If variable-speed actuators are used to modulate rotor thrust for flight control, then flight control capability is improved, but rotor loads are amplified when harmonic vibratory forces come into resonance with rotor natural frequencies

Engineering Contradiction:

Improveflight control capabilityVSAvoid rotor load capacity

Core Design Contradiction:

Ease of operationVSStrength

Solution Approach 1:

The system dynamically adjusts rotor speeds in real-time to avoid resonant conditions. The control system continuously monitors rotor speed and modifies actuator commands to keep operational speeds outside the avoid band, allowing full utilization of variable-speed capability while preventing resonance-induced load amplification.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent implements an avoid band of rotor speeds that excludes resonant frequencies. By changing the operational parameters (rotor speeds) to stay outside this band, the system maintains flight control capability while preventing the harmful resonance effect that amplifies rotor loads.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If rotor speeds are varied through the vehicle's flight envelope, then flight envelope utilization is improved, but component usable life is reduced due to resonance-induced load amplification

Engineering Contradiction:

Improveflight envelope utilizationVSAvoidcomponent usable life

Core Design Contradiction:

Adaptability or versatilityVSDuration of action of stationary object

Solution Approach 1:

The system skips over the harmful resonant speed range by implementing an avoid band. When rotor speeds approach the avoid band during flight envelope expansion, the control system adjusts speeds to bypass the resonant region, allowing broad flight envelope utilization while protecting components from resonance-induced fatigue that would reduce usable life.

Inventive Principle:

Principle #21Skipping (Rushing through)

3Force

If resonance occurs at critical rotor speeds, then vibratory forces are amplified, but structural weight increases if components are designed to carry the amplified load

Engineering Contradiction:

Improvevibratory force magnitudeVSAvoidairframe structural weight

Core Design Contradiction:

ForceVSWeight of moving object

Solution Approach 1:

Instead of designing structures to withstand harmful resonance-induced loads (which would increase weight), the system converts the problem into a control solution. By actively managing rotor speeds to avoid resonance, the harmful vibratory forces are prevented from occurring in the first place, allowing lightweight结构设计 without compromising safety.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

4Reliability

If resonance amplifies rotor loads, then actuator and airframe component durability is reduced, but flight operations become restricted to avoid the issue

Engineering Contradiction:

Improvecomponent durabilityVSAvoidflight operation freedom

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system implements continuous feedback monitoring of rotor speeds and uses this information to adjust actuator commands in real-time. This closed-loop control ensures rotor speeds remain outside the avoid band, protecting component durability while maintaining full flight operation freedom without restrictions.

Inventive Principle:

Principle #23Feedback

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach reduces the time spent at resonant speeds, minimizing load amplification and extending component lifespan while maintaining flight path control, thus enhancing the operational reliability and longevity of unmanned vehicles.

Implementation Method 1

harmonic vibratory forces generated by the rotor may come into resonance with rotor natural frequencies. This resonance, occurring at some critical rotor speed, may amplify rotor loads

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS11884413B2Operating a vehicle with rotors while avoiding a band of rotor rotational speed

Publication Date: 2024.01.30 THE BOEING CO

AI summary

A method is provided for operating a vehicle that includes rotors driven by actuators to cause the vehicle to move. The method includes determining rotational speeds at which to drive the rotors to achieve a controlled movement of the vehicle. The rotational speeds include a rotational speed for a rotor of a pair of the rotors driven by a pair of the actuators. The method includes monitoring the rotational speed to detect that the rotational speed has approached or reached a defined avoid band of rotational speeds, and biasing the rotational speed to produce at least one biased rotational speed for respective rotors of the pair that is outside the defined avoid band. The method includes generating commands for the actuators based on the rotational speeds, and modifying the commands including those of the commands for the pair of the actuators based on the at least one biased rotational speed.