Negative Torsional Stiffness Spring via Preloaded Spokes

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing mechanical designs for negative torsional stiffness elements often rely on conversion mechanisms that add mass and are prone to wear, necessitating a solution that does not require rotational-to-translational motion conversion.

Innovation Solution

A negative stiffness torsional spring composed of a hub, an outer cylinder assembly, and a plurality of spokes preloaded in compression, where the spokes are secured to both the hub and the outer cylinder, providing negative torsional stiffness without the need for conversion mechanisms.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conversion mechanism (rack and pinion) is used to convert rotational motion to translational motion, then negative torsional stiffness can be achieved, but mass increases and wear occurs

Engineering Contradiction:

Improvenegative torsional stiffnessVSAvoidmass

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent removes the conversion mechanism (rack and pinion) from the system entirely. Instead of converting rotational motion to translational motion through separate components, the invention directly creates negative torsional stiffness through pre-compressed spokes that remain in compression throughout the rotation range, thereby reducing mass while maintaining the desired mechanical property

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Rather than using a mechanism that converts rotation to translation (the conventional approach), the invention inverts the approach by having elements that remain in compression during rotation and directly provide negative torsional stiffness. The spokes are pre-compressed and configured to maintain compression throughout the rotational range, eliminating the need for motion conversion

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If a conversion mechanism (rack and pinion) is used to convert rotational motion to translational motion, then negative torsional stiffness can be achieved, but wear increases due to moving contacts

Engineering Contradiction:

Improvenegative torsional stiffnessVSAvoidwear

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention replaces the mechanical conversion system (rack and pinion with moving contacts) with a direct mechanical structure where pre-compressed spokes provide negative torsional stiffness without requiring motion conversion. This substitution eliminates the wear-prone moving contacts while achieving the same functional outcome

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If spokes are preloaded in compression, then negative torsional stiffness is achieved over a range of angles, but manufacturing precision requirements increase

Engineering Contradiction:

Improvenegative torsional stiffnessVSAvoidpreload accuracy

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The spokes are pre-compressed during assembly using a preliminary action (radially inward force applied to the outer cylinder). This preliminary compression establishes the negative torsional stiffness property before the device enters service. The pre-compression can be achieved through various methods including interference fits, hydraulic pressing, or mechanical compression devices that apply radial forces during assembly

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention merges the hub, outer cylinder, and spokes into an integrated assembly where the pre-compression of spokes is combined with the structural integrity of the entire device. The outer cylinder and hub work together to maintain the pre-compressed state of the spokes, creating a unified structure where the negative torsional stiffness is an inherent property of the combined assembly rather than a separate adjustment

Inventive Principle:

Principle #5Merging (Combining)

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 design achieves negative torsional stiffness over a range of angles, enabling applications such as drive shaft isolators and bi-stable hinges with reduced mass and wear, while allowing for efficient energy storage and release, preventing damage to the components.

Implementation Method 1

a plurality of spokes, having a compressional preload, the plurality of spokes being secured to the hub and secured to the outer cylinder assembly

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS10030731B1Assembly with negative torsional stiffness

Publication Date: 2018.07.24 HRL LAB

AI summary

A negative stiffness torsional spring. A plurality of spokes secured between a hub and an outer cylinder assembly are preloaded in compression. As the hub is rotated, the stiffness of the torsional spring is negative over a range of angles.