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METHODICAL DESIGN OF RELIABLE ENERGY AUTONOMOUS SMART SENSOR NETWORKS FOR HEALTH AND USAGE MONITORING

EpoSS Technical Forum 2014, Turin, Italy

September 25, 2014

Thilo Bein, Dirk Mayer, Michael Koch, Thomas Pfeiffer, Enrico Janssen, Jürgen Nuffer Fraunhofer-Institute for Structural Durability and System Reliability LBF www.lbf.fraunhofer.de

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OVERVIEW

Introduction and Motivation

Design issues for self-powered sensor node

Tunable Vibration absorbers

Design-to-reliability approach

Conclusion and outlook

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Introduction and motivation Application scenario: self-powered sensor networks for freight trains

Supply of a sensor for temperature monitoring of the bearing (hotbox detector)

Prevention of bearing failures, derailments

Prevention of fire due to overheating

Energy Harvester

Energy Storage Sensor Node

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Self-powered sensor node

Goal

Analyse and transmit data under restrictions of limited energy supply

Size and weight of energy harvesting system versus amount of generated energy.

Energy consumption for on-board data reduction versus power for wireless data transmission

Energy Management, adaption of task scheduling to available energy

Design-to-reliability of the overall system at early development stages

Energy Harvester

Energy Storage

Sensor Node

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Hardware-in-the-loop testing HIL testing approach for methodical design of self-powered sensor node

Energy Harvester

Energy Storage

Sensor Node

Excitation

+ - Auxiliary

power

Real time emulation (dSpace)

Temperature sensor (on board)

By prototype hardware (Libelium WaspMote)

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Power measurement probe

Real time analysis of consumed electrical power

Power balance analysis to decide if hardware realization make sense.

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Energy harvester

Design process and simulation

HIL testing real time (rt)

Laboratory test Field test

Energy Harvester Simulated Simulated (rt) Hardware Hardware Energy Harvester

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Mechanical vibration absorber consisting of bending beam with tip mass, tuned to frequency with maximal excitation.

Integration of electromechanical transducers (e.g. piezo elements).

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Tunable vibration absorber

The resonance frequency is tunable by moving the mass by means of the spindle

Excitation in accordance to the later application conditions

Excitation at single frequency near the vibration absorber frequency

Aim: design-to-reliability at early development stages

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Different vibration absorbers developed at LBF

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Development according to V-Model

Testing device

Functional demonstra

tor

Pilot series

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Design-to-Reliability approach Interdisciplinary team is

involved consisting of experts in

Electronics

Mechanics

Control

Manufacturing

Reliability

Integration of reliability aspects at the early stage of the design process

Integration of the results into the design process

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Design-to-Reliability approach Example: Excerpt from the

“re-design phase”

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Example for iteration process: Experimental tests

Vibration absorber attached to a electrodynamic shaker

Measuring points for accelerometer:

baseplate

E-motor

mass

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Results for the first version of the vibration absorber

Excitation of the baseplate close to zero

Sinusodial excitation of the mass

High excitation of attached parts

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Design advices for the next design iteration step The vibration absorber must be designed for the frequency range greater

than its resonance frequency

Loose fittings lead to wide vibration excitation of the whole structure

All fittings have to be redesigned

Mountings have to be designed for a wide vibration range

The mounting of the e-motor has to be redesigned

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Results for the optimized version

Excitation of the baseplate close to zero

Reduced excitation of attached parts

Vibration of the mass is enhanced

Smoother excitation

Reduced stress on the attachments

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V-Model during development time

Reliability engineering

Reliability engineering

Demonstrator Gen. 1 Demo. Gen. 2 Reliable

demonstrator

Reliable demonstrator

Design to reliability

Development time

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Conclusion and outlook

Tunable vibration absorbers are promising devices for applications showing broad range frequency excitation

Design-to-reliability process for 2 different tunable absorber concepts was introduced

By considering the system reliability at an early stage of the design process, it was possible to reduce the total development time.

The time consuming reliability tests were be performed in parallel to the iteration steps of the design process.

Next step: enhancing the work to all subdomains (e.g. electronics)