Folded Pendulum Compression Joints for Low Resonance

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Solution Overview

Problem

Existing low-frequency seismic sensors face limitations in achieving low resonance frequencies below 100 mHz due to mechanical dissymmetries and low mechanical quality factors, leading to large and complex systems, and traditional folded pendulum designs are constrained by joint stress and robustness issues.

Innovation Solution

A folded pendulum design featuring elliptic joints working in compression, rather than tension, and a monolithic block construction with electro-erosion cutting, allowing for reduced resonance frequency and enhanced mechanical quality factor, with the joints' thickness optimized for minimal deformation and maximum robustness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional folded pendulum designs with joints in tension are used, then the system can be assembled, but the mechanical quality factor remains low and the resonance frequency cannot be lowered below around 100 mHz

Engineering Contradiction:

Improvemechanical quality factorVSAvoidjoint stress and robustness issues

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent inverts the traditional design by having joints work in compression rather than tension. This fundamental reversal allows the joints to function as load-bearing compression members, significantly improving mechanical quality factor and enabling resonance frequencies below 100 mHz while maintaining structural robustness

Inventive Principle:

Principle #13The other way round (Inversion)

2Volume of moving object

If simple pendulum dimensions are reduced to achieve compact size, then the device becomes transportable, but the resonance frequency increases above desired low-frequency range

Engineering Contradiction:

Improvesensor dimensionsVSAvoidresonance frequency

Core Design Contradiction:

Volume of moving objectVSSpeed

Solution Approach 1:

The patent employs a dynamically adjustable resonance frequency through variable stiffness joints. The stiffness can be modified to tune the resonance frequency, allowing compact dimensions to be maintained while achieving low resonance frequencies below 100 mHz through optimal stiffness selection rather than requiring large physical dimensions

Inventive Principle:

Principle #15Dynamics

3Reliability

If joints are made thinner to reduce deformation, then the mechanical quality factor improves, but the joint robustness and resistance to breaking decrease

Engineering Contradiction:

Improvemechanical quality factorVSAvoidjoint robustness

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent employs composite construction with a monolithic aluminum block for the pendulum mass and steel components for the joints and frame. This material combination allows joints to be thin enough for high mechanical quality factor while maintaining sufficient robustness through the use of high-strength steel materials

Inventive Principle:

Principle #40Composite materials

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

The design achieves a mechanical quality factor improvement of at least an order of magnitude compared to traditional systems, maintaining robustness and reliability, and extends the range of measurable frequencies, including low-frequency seismic applications with compact and transportable sensors.

Implementation Method 1

each joint system relevant to the inverted pendulum comprises one or more joints in compression

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

the folded pendulum being able to guarantee a highest mechanical quality factor

Methodology Applied

Scientific EffectMechanical quality factor: Resonance

Implementation Method 3

a folded pendulum, in particular a monoblock pendulum, that, thanks to its particular conformation is able to guarantee a highest mechanical quality factor

Methodology Applied

Scientific EffectPendulum oscillation: Pendulum

Implementation Method 4

such a combination of classical pendulum and inverted pendulum, which allows, instead, to attain very low frequencies keeping at the same time dimensions relatively reduced

Methodology Applied

Scientific EffectResonance frequency: Resonance

Implementation Method 5

The folded pendulum is formed by a monolithic block of a suitable machined material

Methodology Applied

Scientific EffectMonolithic structure:

Implementation Method 6

the monolithic block is cut-machined by electro-erosion

Methodology Applied

Scientific EffectElectro-erosion: Electrical Discharge Machining

Data Source

PatentUS8950263B2Low frequency folded pendulum with high mechanical quality factor, and seismic sensor utilizing such a folded pendulum

Publication Date: 2015.02.10 UNIVERSITA DEGLI STUDI DI SALERNO

AI summary

The invention concerns a folded pendulum, comprising:a support (F);a test mass (PM);a simple pendulum (SP);an inverted pendulum (IP);the simple pendulum and the inverted pendulum being connected at one of their ends to the test mass (PM) and at the other end to the support (F) by means of 4 corresponding joint systems (G), the test mass being not connected to the support (F) and being therefore free to oscillate, each joint system (G) relevant to the simple pendulum (PS) comprising one or more joints in tension,the folded pendulum being characterized in that:each of the joint systems (G) relevant to the inverted pendulum (IP) comprises one or more joints in compression.The invention further concern a seismic sensor utilizing the folded pendulum according to the invention.