THE NEED FOR CONTROLLED SHOCKS A NEW TYPE OF … · SPEKTRA Schwingungstechnik und Akustik GmbH Dresden THE NEED FOR CONTROLLED SHOCKS -A NEW TYPE OF SHOCK EXCITER ALLOWS TO APPLY

1IMEKO XIX World Congress 2009

SPEKTRA Schwingungstechnik und Akustik GmbH Dresden

THE NEED FOR CONTROLLED SHOCKS

-

A NEW TYPE OF SHOCK EXCITER ALLOWS TO

APPLY WELL DEFINED MECHANICAL SHOCKS

IMEKO XIX World Congress, Lisbon, September 2009

Dr. Holger Nicklich, Martin Brucke, Michael Mende

SPEKTRA Sound & Vibration

Calibration Systems • Special Equipment • DKD Laboratory • Environmental Testing

Author: Dr. Holger Nicklich, Martin Brucke, Michael Mende


Introduction

Shock Exciters


What do you expect from a

perfect shock exciter?

• precise shock amplitude control

• very good repeatability

• no transverse motion

• pulse width / amplitude independent

• arbitrary shape of shock

• easy and convenient to operate

• allow primary shock calibration

• no wear parts (longterm stability) * patent pending DE 10 2008 025 866,

international PCT application planned



Introduction

Shock Exciters


CS18 LS Low Shock system

• 100 m/s2 to 2,000 m/s2

• up to 8 ms pulse width

CS18 LMS Low-Medium Shock

system

• 100 m/s2 to 150,000 m/s2

• pulse width 0.1 ms … 5 ms

CS18 HS High Shock system

• 10,000 m/s² to 1,000,000 m/s²

• typical 50 µs pulse width



Introduction

Shock Exciters


CS18 LS Low Shock system

• 100 m/s2 to 2,000 m/s2

• up to 8 ms pulse width

CS18 LMS Low-Medium Shock

system

• 100 m/s2 to 150,000 m/s2

• pulse width 0.1 ms … 5 ms

CS18 HS High Shock system

• 10,000 m/s² to 1,000,000 m/s²

• typical 50 µs pulse width

p +/-

Barrel

Projectile(Hammer)

Adjustable Stop

Anvil

Back-to-BackReference Sensor

DUT

Authors: Dr. Holger Nicklich, Martin Brucke, Michael Mende


Hammer-Anvil Shock Exciters

Amplitude and Pulse Width Control


Hammer - Anvil Shock Exciters

do not allow a very precise control

of the shock amplitude!

• insufficient control of hammer

(kinetic energy )

• Hammer – Anvil impact is not

completely elastically

• wear problems in the contact zone






Hammer - Anvil Shock Exciters do not allow to control

shock amplitude and pulse width independently!

• nonlinear stiffness in contact zone

( according to Hertz)

• additional nonlinear stiffness from an elastomer layer or

other mitigator on the anvil surface

the higher the amplitude, the shorter the pulse width

Anvil

Stiffness






A Hopkinson-bar shows even a stronger dependency of

shock amplitude and pulse width!

• the force pulse input causes a longitudinal compression wave

in the bar

• the relationship between force input and acceleration output is

c0 = speed of sound A = sectional area of bar

E = Young’s modulus

• Hopkinson–bar works like a ‘shock amplifier’

the time derivative makes things even worse

F

t

a

t

Displacement u(x,t)

MP1 MP2 MPn



The HOP-MS Shock Exciter

Design goals


Development of a shock exciter that

is closer to an ideal exciter

• easy and precise control

• very good repeatability of shocks

• shock amplitudes up to some 1,000 gn

• convenient to operate

• primary and secondary calibration

• no wear parts

• low transverse motion

SAVIAC Conference October 2009 9

Overview Shock Exciter

Hopkinson-Bars cover a broad amplitude range

10 100 1000 10000

20

200

2000

20000

200000

2000000

20000000

Impulse Duration [µs]

Accele

ration

[m/s

²]A

ccele

rati

on

[m/s

²]

Pneumatic Shock Exciter

e.g. SPEKTRA SE-201 PN-LMS

Shock Pendulum

e.g. SPEKTRA SE-210 SP-LSNEW !

Medium Shock Hopkinson-Bar

SPEKTRA SE-220 HOP-MS

High Shock Hopkinson-Bar

e.g. SPEKTRA SE-221/222 HOP-HS/VHS




Operating principle


Hopkinson-Bar

Piezoelectric ActuatorReaction Mass Laservibrometer

(reference standard)

DUTF –Reaction Force F – Input Force




Operating principle





Control


The HOP-MS shock exciter can be

precisely controlled!

• force generation due to elongation

of a piezo actuator simply controlled

by an electrical signal

• simple two-mass oscillator model

fits well with measurements

• a transfer function H(f) [N/V] for the

force input can be determined

• the transfer behavior of the

Hopkinson-bar is also well known

shock output can be controlled

in amplitude and wave form




Amplitude Control


Wide amplitude range and

good repeatability!

•lowest possible shock amplitude just

limited by noise (actuator, measurement chain)

•20 m/s2 in current type

•maximum shock amplitude limited bymaximum force of actuator and

pulse width, due to a(t) ~ dF(t) / dt

geometry and material of the bar

•40,000 m/s2 in current type

•amplitude repeatability < 0.3%

(conventional Hopkinson-bar 8% -10 %)




Pulse Width Control


Pulse width and shock amplitude

can be controlled independently!

• maximum pulse width is limited by

length of the bar

• current 2m bar -> 400 µs

• at high shock amplitudes the

exciter is also limited by the

maximum force amplitude of the

actuator (see a(t) ~ dF(t) / dt)

F

t

a

t

Displacement u(x,t)

MP1 MP2 MPn



Shock Calibration

ISO 16063-22 – Signal Processing


0 1 2 3 4 5 6

Accele

rato

r S

ign

al U

[V

]

Time [ms]

Halfsine Shock

Reference DUT

URef

UDUT



Shock Calibration

ISO 16063-22 – Dependency on Shock Input


0 10000 20000 30000 40000

Sen

siti

vity

Acc

ele

rati

on

Frequency

Spectrum Shock Short Spectrum Shock Long Accelerometer Sensitivity

Datenreihen4




Shock Shaping


The HOP-MS Exciter allows to shape the

acceleration output in a wide range!

• the electrically controlled piezo actuator

allows a nearly arbitrary force input signal

• the transfer function of the exciter can be

determined

• apply controlled pre-distortion to the input

signal taking the transfer function into

account

controlled acceleration output with

nearly arbitrary shape is possible




Shock Shaping


time domain frequency domain




Shock Shaping


time domain frequency domain





Conclusions

The HOP-MS is a really new type of

shock exciter !

• it brings a new quality to shock

excitation and measurement

• the simple electrical control allows

an all automated operation

• it makes shock calibration and

amplitude linearity checks

quick, convenient and cost saving

• the exact and independent control

of shock amplitude and shape

opens new application ranges (e.g. MEMS testing)



Acknowledgements


I like to thank all authors for their work on

this project especially

Martin Brucke, who developed the HOP-MS

shock exciter and wrote his doctoral thesis

about this development.

Matthias Woog who spend a lot of work in

the development of the software that controls

this shock exciter and who performed many

experiments that showed its impressive

range of applications.



Gostritzer Straße 61 - 63

D - 01217 Dresden

phone +49 351 400 24 0

fax +49 351 400 24 99

[email protected]

www.spektra-dresden.com

Calibration Systems • Special Equipment • DKD Laboratory • Environmental Testing

Documents

THE NEED FOR CONTROLLED SHOCKS A NEW TYPE OF … · SPEKTRA Schwingungstechnik und Akustik GmbH Dresden THE NEED FOR CONTROLLED SHOCKS -A NEW TYPE OF SHOCK EXCITER ALLOWS TO APPLY