Instrumented Screw with Conical Hole Strain Gauges

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Solution Overview

Problem

Conventional screws with integrated stress measurement gauges face challenges such as complexity, damage from tightening tools, limited measurement precision, and inability to accurately measure both tensile and shearing stresses due to parasitic deformations and accessibility issues.

Innovation Solution

A screw design featuring strain gauges arranged within a conical hole on the screw head, oriented to measure both tensile and shearing stresses, connected via a Wheatstone bridge for reliable deformation amplification and protected from damage, with optional wireless communication for easy stress monitoring.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If strain gauges are arranged on the lateral wall of the screw head, then the tightening stress can be measured, but the gauges can be damaged by tightening tools and are difficult to access for periodic checks

Engineering Contradiction:

Improvetightening stress measurementVSAvoidgauge protection and accessibility

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The strain gauges are nested within a conical hole in the screw head, placing them inside a protective cavity. This nesting arrangement shields the gauges from external damage by tightening tools while allowing access through the conical hole opening for periodic measurements

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The conical hole acts as an intermediary structure that provides both protection and access. It serves as a mediator between the need to protect the gauges from damage and the need to access them for periodic stress measurements

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If strain gauges are arranged in an annular groove on the lower face of the screw head, then the gauges can transmit measured values, but they are trapped between the screw and parts making wireless communication difficult and are easily damaged by tightening pressure

Engineering Contradiction:

Improvestress value transmissionVSAvoidgauge protection and communication

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

Instead of placing gauges on the lower face where they are trapped and damaged, the gauges are inverted to the upper face within a conical hole. This reversal of position eliminates the trapping problem and exposes the gauges to a controlled environment where they are protected yet accessible

Inventive Principle:

Principle #13The other way round (Inversion)

3Ease of manufacture

If conventional tightening tools with dynamometers are used, then the tightening torque can be precisely controlled, but the torque does not necessarily correspond to the actual tightening obtained due to friction and material variations

Engineering Contradiction:

Improvetorque controlVSAvoidactual tightening measurement

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The strain gauges provide direct feedback on the actual tightening stress within the screw body. This feedback mechanism allows verification and adjustment of the tightening process to ensure the desired clamping force is achieved, compensating for friction and material variations that make torque-only control insufficient

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

Enhances measurement reliability and accessibility of tensile and shearing stresses, reducing the risk of gauge damage and providing accurate stress monitoring over time without parasitic measurements.

Implementation Method 1

screw head (2), provided with strain gauges (12a-12d, 14a-14h) arranged so as to be deformed together with the deformation of the screw head (2), in order to measure a stress within the screw (1)

Methodology Applied

Scientific EffectStrain gauge measurement: Piezoresistive Effect

Implementation Method 2

said gauges being connected by a Wheatstone bridge (13) connected or able to be connected to a power supply and to determination means (8c, 13c-13d) for determining a value of at least one stress within the screw (1)

Methodology Applied

Scientific EffectWheatstone bridge: Wheatstone Bridge

Data Source

PatentUS10731693B2Screw instrumented with extensometric strain gauges to measure the tensile and/or shear strain experienced by the screw

Publication Date: 2020.08.04 TEXYS INT

AI summary

Screw having a head and a threaded cylindrical body, the head being provided with strain gauges arranged so as to be deformed in order to measure a stress within the screw, the gauges being connected or able to be connected to a power supply and to a determination unit for determining the value of at least one inner stress from the deformations of the gauges. The head has, on the upper face thereof, a conical hole having a revolution axis that is aligned with the revolution axis of the cylindrical body. The gauges are arranged on the wall of the conical hole so as to be deformed together with the conical hole and are oriented to measure at least one type of inner stress selected among the tension and the shearing.