ACCELERATING & ENABLING DESIGN EXCELLENCE
Importance & Application of
ETS MET-Series Shaker System
Prepared By Mel Tan
ETS Solutions Asia PteLtd
60 Kaki Bukit Place, Eunos Techpark, #08-14, Singapore 415979
Tel : +65-63401036 Fax : +65-63401037
[email protected]
www.etssolution-asia.com
Copyright©2014ETSSolutions. All rights reserved.
This document and translations of it may be copied and furnished to others, and derivative works that comment on
or otherwise explain it or assist in its implementation may be prepared, copied, published, and distributed, in whole
or in part, without restriction of any kind, provided that the above copyright notice and this section are included on all
such copies and derivative works. However, this documents itself may not be modified in anyway, including by
removing the copyright notice or references to ETS Solutions, without the permission of the copyright owners.
This document and the information contained herein is provided on an "ASIS" basis and ETS Solutions DISCLAIMS
ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE
USE OF THE INFORMATION HEREIN W ILL NOT INFRINGE ANY OWNERSHIP RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANT ABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright©2014ETSSolutions. All rights reserved.
This document and translations of it may be copied and furnished to others, and derivative works that comment on or
otherwise explain it or assist in its implementation may be prepared, copied, published, and distributed, in whole or in
part, without restriction of any kind, provided that the above copyright notice and this section are included on all such
copies and derivative works. However, this document itself may not be modified in anyway, including by removing
the copyright notice or references to ETS Solutions, except as needed for the purpose of developing any document
or deliverable produced by ETS Technical Team (in which case the rules applicable to copyrights, asset forth in the
ETS Policy, must be followed) or as required to translate it into languages other than English. The limited
permissions granted above are perpetual and will not be revoked by ETS Solutions or its successors or assigns.
This document and the information contained herein is provided on an "ASIS" basis and ETS Solutions DISCLAIMS
ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY W ARRANTY THAT THE
USE OF THE INFORMATION HEREIN W ILL NOT INFRINGE ANY OWNERSHIP RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANT ABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
All brands, and product names, other than those owned by ETS Solutions, are used for identification purposes only
and may be trademarks that are the sole property of their respective owners.
Any comments relating to the material contained in this document may be submitted to:
ETS Solutions Asia Pte Ltd
60 Kaki Bukit Place, Eunos Techpark, #08-14, Singapore 415979
Tel : +65–63401036 Fax : +65–63401037
[email protected]
www.etssolution-asia.com
2
Table of Contents
Topic
PageNo.
Acknowledgements.................................................................................................................................... 4
Introduction to “Vibration” & Need for Vibration Testing............................................................................5
Basics of Vibration Testing........................................................................................................................ 6
Benefits of Vibration Testing……………………………………………………………………………………. 6
Limitations of Single Axis Vibration Testing Systems…………………………………………………………7
Typical Construction of Single Axis Shaker System……………………………………………………….… 9
Multi Axis Shaker System …………………………………………………………………………………........ 10
Construction of Multi Axis Shaker System ………………………………………………………………........11
Conventional Adapter…………………………………………………………………………….…………….. 12
Hydrostatic Spherical Adapter……………………………………………………………………………….…..13
Auto Centering System……………………................................................................................................. 14
Auto Centering System (cont’d)................................................................................................................. 15
Unibase Mounting.......................................................................................................................................16
Applications................................................................................................................................................ 17
Applications (contd.).................................................................................................................................. 18
Example of MIL-STD-810G Test Profile…………………………………..………………………................ 19
ETS 3 x 50 kN Performance Test – Sine Sweep………………………..………………………................ 20
ETS 3 x 50 kN Performance Test – Random…..………………………..………………………................ 21
ETS 3 x 50 kN Performance Test – Shock……...………………………..………………………................ 22
Partial Shaker References........................................................................................................................ 23
3
Acknowledgements
We would like to thank the following individuals for their participation and contribution to the development
of this document:
Mel Tan
Mauro Berno
Rohit Bansal
M.T. Utama
Graham Carmichel
Richard Chen
Q. S. Zhang
G. H. Zhang
Z. X. Wang
Jenny Yue
ETS Solutions, Singapore
ETS Solutions, Singapore
ETS Solutions, Singapore
ETS Solutions, Singapore
ETS Solutions, USA
ETS Solutions, China
ETS Solutions, China
ETS Solutions, China
ETS Solutions, China
ETS Solutions, China
This joint document from ETS Solutions Pte Ltd. is written to help companies and technical community at
large to navigate the myriad of overlapping technical products in vibration testing industry, produced by
various organizations.
This document explains and positions the ETS MET Series shaker system in view of the modern day
industry requirements and existing competitive products in market. This document is intended to serve as
a guide to the reader to help differentiate and select specifications appropriate to their needs.
This document outlines where the works are similar and helps users of the technical products produced by
ETS Solutions to understand the strengths of each body of work and select the technical products most
appropriate for their needs, consistent with where they are today, and where they plan to head on their
journeys.
A secondary goal was to establish collaboration between the existing testing procedures and practices to
encourage consistency across the testing standards. It is anticipated that future products and solutions by
ETS Solutions Pte Ltd. Will consider the relative positioning described here to reduce overlaps and gaps
between related standards and practices.
4
Introduction to “Vibration” and Need for Vibration Testing
Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The oscillations may be
periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.
There are three main reasons for which we require vibration testing:
- To ensure reliability, functionality and structural integrity
You want the equipment to be reliable, to continue to function correctly and – to put it bluntly – you don’t want it to fall
apart.
Even equipment that is permanently fixed in one place needs to withstand vibration during its lifecycle. In fact, there are
four specific stages in the lifecycle of a product when it might have to withstand vibration:
Assembly:
While the equipment is being manufactured, circuit boards and other components are often subject to shock and
vibration – for example when a PC Bus being put into its housing and may be dropped on the assembly bench.
Packaged transportation:
When the equipment is being transported, must withstand vibration, shocks and drops. For some types of equipment
– e.g. telecoms systems – packaged transportation is the time when the equipment is subjected to the greatest
mechanical stresses.
Installation:
Equipment that must be installed needs to withstand manual handling.
Service environment:
The environment in which the equipment must operate, the challenges can range from track vibrations and the shock of
shunting in rail applications, engine and gearbox induced vibration on road vehicles and aircraft, as well as the need to
survive handling and drops in the case of portable consumer electronics.
Consumers expect and demand products of high quality and reliability. To fulfill these requirements we must consider
vibration, since at some time in its life the product will be subjected to vibration. Poor mechanical design will result in
mechanical failure and customer dissatisfaction which will add cost and reduce credibility.
COST
Product Failure
CREDIBILITY
5
Basics of Vibration Testing
The most common types of vibration testing services conducted by vibration test labs are Sinusoidal and Random.
Sine (one-frequency-at-a-time) tests are performed to survey the structural response of the device under test
(DUT).
A random (all frequencies at once) test is generally considered to more closely replicate a real world environment,
such as road inputs to a moving automobile.
Most vibration testing is conducted in a 'single DUT axis' at a time, even though most real – world vibration occurs
in various axes simultaneously. MIL-STD-810G, released in late 2008, Test Method 527, calls for multiple exciter
testing. The vibration test fixture which is used to attach the DUT to the shaker table must be designed for the
frequency range of the vibration test spectrum. Generally for smaller fixtures and lower frequency ranges, the
designer targets a fixture design which is free of resonances in the test frequency range. This becomes more
difficult as the DUT gets larger and as the test frequency increases, and in these cases multi-point control
strategies can be employed to mitigate some of the resonances which may be present in the future.
Benefits of Vibration Testing
Some key benefits of vibration testing are:
•
Reduce product development time
•
Ensure new products are fit for purpose
•
Reduce in-plant rework due to QA rejection
•
Reduce damage in transit and subsequent rejection by the customer
•
Reduce marginal or non-performance rejection under Warranty
•
Reduce legal costs and damage claims due to incorrect operation of the product
•
Maintain a good reputation for the company and its products
•
Maintain profit margins
6
Limitations of Single Axis Vibration Testing System
Single Axis (Uniaxial) Vibration Shaker is the
common vibration testing system used for vibration
test. Historically, this is the method which is firstly
developed to perform vibration test and to bring in
the end user environment into the laboratory scale
test.
In fact, the actual end user environment shows that
the product delivered to customer is subjected to
vibration on all directions simultaneously. In order
to fulfill the requirement of applying the load as
close as possible to the actual environmental load
condition, the method of sequentially applying
uniaxial excitation has been introduced. This
method is implemented by using a uniaxial shaker
and applying the load along three orthogonal axes
by rotating the test article after each test
There are two common test approaches that have been used, the first one is by performing statistical calculation in
order to obtain the characteristic of actual field condition. Standards and practical recommendation such as MILSTD-167 have been produced to provide common approach for specific environment. The second approach is to
perform such stress screen vibration testing, which is product dependent, not environment dependent. This approach
is more for detecting the failure mode which might occur rather than applying the load similar to actual environmental
condition.
Although the single axis shaker is still widely used for vibration testing, there are some conditions which is not
appropriate to be simulated by this equipment. Below are some examples:

A product which is subjected to more than one load, at different locations, but need to be performed
simultaneously,

A product which is subjected to load at one position, at more than one direction simultaneously,

Testing of large test article which requires forcer higher than force available from the shaker.
7
Type of Tests
Test Description
Application
Performance under Multi-Axis Vibration Loading
Automotive Body Mounted
Components
Audio Video Quality under Multi-Axis Vibration Loading
Automotive Audio Video
Entertainment System
Performance Vibration Mounting under Multi Axis
Vibration Loading
Components with Vibration
Mounting
Response Time Performance
Air Bag Sensors
Acoustic Noise under Multi Axis Vibration Loading
Automotive Cabin Mounted
Components
Human Body Vibration Response
Drivers and Passengers Seat
Durability Tests
Strength Durability under Multi-Axis Random Vibration
Loading
Automotive Body Mounted
Components
Transportation
Tests
Strength Durability of Packaging under Multi-Axis
Random Vibration Loading
Electronics, Computers, Home
Appliances, etc.
Field Data
Replication
Multi Axis Field Data Replication,
Multi-Axis Earthquake Simulation
Automotive, Electronics,
Home Appliances
Calibration of
Transducers
Transverse Sensitivity Calibration
Accelerometer, Load Cell
Functionality
Tests
Comfort Ability
Tests
8
Typical Construction of the Single Axis Shaker System
A shaker is an electromechanical transducer that converts electrical current into mechanical force for vibration
testing. To accomplish this, the shaker uses the characteristics of current flow crossing a magnetic field.
9
ETS “MET” Series Vibration Testing System
The ETS MET Series shaker system is a Multi Excitation Testing System which is developed to overcome the
further challenge of vibration testing, which is to provide simultaneous multi-dimensional excitation, which cannot
be performed by conventional Single Axis Shaker System. It is designed to meet the test requirement of wide
frequency range, long stroke and high acceleration of Sine, Random, and Shock Test. It is able to perform the
Multi Excitation Testing based on military and international standards, such as MIL-STD-810G Method 527.
The MET Series Multi-Axis vibration testing system consists of 3 single axis vibration test system specially
engineered to function as one system. The MET Series system redefines how standard tests can be performed.
True replication of the actual environmental vibration condition in the laboratory can now be carried out to
stimulate the real failure mode. It can effectively avoid over-testing or under-testing problems caused by singleaxis vibration test, and thus increase products reliability and adaptability to actual environment.
10
CONSTRUCTION OF ETS MET SHAKER SYSTEM
Trunnion
Trunnion Support
Air Bag
Armature
Base Plate
Shaker body
Head Expander
Rotation Locking
Bolts
Blower Duct Joint
Unibase Mounting
Hydrostatic
Spherical Adapter
11
Conventional Adapter
The biggest problem in Multi Excitation Testing is how to attach the shaker to the test article, or to the head
expander. If these connections are not designed properly, it will produce a large moment to the test article and/or to
the shaker armature. If these connections do not allow angular deflection, severe damage may occur.
Historically, combination of spherical roller bearing and universal joint is used to provide enough angular deflection
allowance. It can be done theoretically, but the clearances in the mechanical system may lead to the low test
accuracy since force reversal cause an impact loading. At low frequency, the displacement of test article is relatively
large. But in higher frequency, the displacement will become very small and almost similar to the mechanical system
clearances.
In order to solve this problem, the preload on the mechanical bearing and joints are increased. However, this higher
value of preload will increase the stiffness of the joints which will influence also the total characteristic of the vibration
system. And also, long test duration will require high maintenance requirement, since clearances will increase due to
repeated loading.
Spherical Roller
Bearing
Universal Joint
12
ETS MET Series Hydrostatic Spherical Adapter
Spherical adapter is the mechanical decoupling device
between electro-dynamic shaker table and working
platform. It is the essential part of the multi-axis vibration
system. This spherical adapter has high axial stiffness
and is simple and easy to install. It can transfer high
frequency vibration and has no restriction for three axis
rotations and other two axis translations. It is mostly
applied in the multi-axis vibration system and transfers
the shaker vibration to the specimen without distortion.
Hydrostatic spherical adapter is a spherical coupler with two joints and it is comprised of spherical hydrostatic
bearings. There could be rotation and lateral translation at the adapter end. The angular and lateral displacements
are different with various adapter structures. It applies high pressure oil film to lubricate and assures very low friction
moment during relative movements. This high pressure oil film is of extremely high stiffness, which assures the
adapter’s usable frequency up to 2,000 Hz.
The spherical bearing configuration in the MET Series
vibration system is specially configured to optimize the
cross axial restraint on the roll, yaw and pitch achieving the
optimal respective 3 axes vibration response.
13
AUTO CENTERING SYSTEM
The auto-centering system is also named as photo-electric
auto controlling device. It is used to adjust the armature
position automatically and keep at the equilibrium position. It
applies
the
diffuse
reflection
photo-electric
sensor
technology and operational amplifier circuit to monitor the
inlet/outlet solenoid valves. It has the advantages of short
response time, reliable operation and anti-interference
ability. The dynamic frequency response is as low as 1 Hz. It
is also easy to operate manually and applicable for various
electro-dynamic shakers.
There are two digital photo-electric switches to get the
system input signals, which are simple and can also
prevent mal-operation. The auto-centering system also
has stable static centering function. The object black/white
strip reflects the light from photo-electric switches. The
reflection signals are transferred by photo-electric sensors
and output into the centering system. After some isolation,
magnifying and integral calculations, the control signals
are input into the valve to keep the armature at the
equilibrium position.
14
AUTO CENTERING SYSTEM
The armature is guided by upper flexures and lower hydraulic bearings inside the shaker. The load support
suspension is controlled by SCC. The SCC system is a self-control unit regulating the amount of air to the load
support to maintain the armature at its center position. The load support suspension is to be re-adjusted each time
for each test to ensure the armature is in its center position with respect to the field coil and shaker mechanical
structure.
The shaker is integrated with SCC unit to vertically center the armature in the middle of its peak-to-peak
displacement. The SCC consists of a dual-proximity sensor and a reflector plate, display lights, and an adjustable
air bag system.
.
15
UNIBASE MOUNTING
The three sets of electro-dynamic shakers of the multi-axis vibration system are all mounted on the unibase. The
unibase design plays an important part in the system stability and resonant damping. The unibase should have
sufficient stiffness to damp the counterforce from the shaker during tests and avoid unnecessary resonance.
The unibase is made of structural steels and channel sections. The hollow body is filled with silver sand to
decrease the center of gravity and increase the damping. The bottom is welded with channel sections. There are
four lifting points for installation and transportation.
The unibase applies eight air springs to suspend the unibase and shakers. There are optional dampers mounted
with the air springs as required. As resonance is intend to occur during long stroke tests at low frequency, it is
preferable to use the dampers to quickly absorb the counterforce from shakers, which increases the whole system
stability.
16
Based on MIL-STD-810G Method 527 ETS MET Series Shaker System is suitable for applications where it
is involving:
1.
Fatigue, cracking and rupture sensitive to multi-axis excitation
2.
Deformation of material structure, e.g. protruding parts
3.
Loosening of seals and connections
4.
Chafing of surfaces with single-axis design
5.
Contact, short-circuiting or degradation of electrical components
6.
Misalignment of material components (e.g., optical)
The system is suitable to comply with the widely accepted MIL-STD-810G standard.
A Brief Introduction to MIL-STD-810 Standard:
MIL-STD-810, Environmental Engineering Considerations and Laboratory Tests is a United States Military Standard
that emphasizes tailoring equipment’s environmental design and test limits to the conditions that it will experience
throughout its service life, and establishing chamber test methods that replicate the effects of environments on the
equipment rather than imitating the environments themselves. The MIL-STD-810 test series are approved for use by
all departments and agencies of the United States Department of Defense (DoD). Although prepared specifically for
military applications, the standard is often used for commercial products as well.
The MIL-STD-810 test series originally addressed generic laboratory environmental testing. The first edition of MILSTD-810 in 1962 included only a single sentence allowing users to modify tests to reflect environmental conditions.
Subsequent editions contained essentially the same phrase, but did not elaborate on the subject until MIL-STD-810D
was issued marking one of the more significant revisions of the standard with its focus more on shock and vibration
tests that closely mirrored real-world operating environments. MIL-STD-810F further defined test methods while
continuing the concept of creating test chambers that simulate conditions likely to been countered during a product's
useful life rather than simply replicating the actual environments. More recently, MIL-STD-810G implements Test
Method 527 calling for the use of multiple vibration exciters to perform multi-axis shaking that simultaneously excites
all test article resonances and simulates real-world vibrations. This approach replaces the legacy approach of three
distinct tests, i.e., shaking a load first in its x axis, then its y axis, and finally in its z axis.
Various types of tests that can be performed are as follows:
1. Development Test:
Development testing is used to determine characteristics of material, to uncover design and construction
deficiencies, and to evaluate corrective actions. Begin as early as practical in the development, and continue as the
design matures. The ultimate purpose is to assure developed material is compatible with the environmental lifecycle,
and that formal testing does not result in failure. The tests have a variety of specific objectives. Therefore, allow
considerable freedom in selecting test vibration levels, excitation, frequency ranges, and durations. Typical programs
17
might include modal analysis to verify analytical mode shapes and frequencies, and sine dwell, swept sine, transient,
or random excitation transient vibration to evaluate function, fatigue life, or wear life. The test types, levels, and
f r eq ue nc i es ar e s e l e c t e d to a c c o m p l i s h specific t e s t o b j e c t i v e s . Levels m a y be l o w e r t h a n
l i f e c yc l e environments to avoid damage to a prototype, higher to verify structural integrity, or raised in steps to
evaluate performance variations and fragility.
2. Qualification Test:
Qualification testing is conducted to determine compliance of a material with specific environmental requirements.
Such tests are commonly a contractual requirement and will include specific test specifications. Qualification tests
should be conducted using an excitation that has the same basic characteristics as the anticipated service
environment. For most items, this consists of a functional test and an endurance test (sometimes combined). The
functional test represents the worst case vibration (or envelope of worst case conditions) of the environmental
lifecycle. The endurance test is a fatigue test representing an entire lifecycle. Often, vibration can be combined with
other environmental stresses.
2.1. Functional Test:
Functional testing is conducted to verify that the material is functioning as required while exposed to worst case
operational vibration. Full function verification is performed at the beginning, middle and end of each test segment.
2.2. Endurance Test:
Endurance testing is conducted to reveal time-dependent failures. In many cases the test is accelerated in order to
produce the same damage as the entire duration of the required service life. Generally, it is not required to have an
item powered-up during the endurance phase of test. We define the test time at maximum service levels (function all
levels) that is equivalent to a vibration lifetime (levels vary throughout each mission). Use the equivalent time as the
functional test duration, thereby combining functional and endurance tests. There may be cases when this test
duration is too long to be compatible with program restraints. In these cases, use as long of a test duration as is
practical and use the fatigue relationship to define the test level. While this approach does not completely eliminate
non linearity questions, it does limit levels to more realistic maximums. Generally, the test item will not be in a
powered-upstate during the endurance (“non-operating”) phase of testing; particularly in a situation in which the test
levels have been exaggerated beyond maximum measured values in order to significantly compress the test
duration.
3. Durability Test:
Durability testing is a real-time (non-exaggerated) simulation of the environmental life cycle to a high degree of
accuracy. A durability analysis precedes the test and is used to determine which environmental factors (vibration,
temperature, altitude, humidity, etc.) must be included in the test to achieve realistic results. Although the test is
intended to be a real time simulation of the lifecycle, it may be shortened by truncation if feasible. Truncation is the
elimination of time segments that are shown by the durability analysis to be benign with regard to material function
and life. Durability analysis should use fatigue and fracture data applicable to each material.
18
4. Reliability Test:
Reliability testing is accomplished to obtain statistical definitions of material failure rates. These tests may be
development tests or qualification tests. The accuracy of the resulting data is improved by improving realism of the
environmental simulation. Test requirements are developed by engineers responsible for material reliability.
5. Worthiness Test:
When unqualified material is to be evaluated in the field, verification that the material will function satisfactorily is
normally required for safety and/or test efficiency reasons. This is accomplished by environmental worthiness
test. The worthiness test is identical to a qualification test except that it covers only the lifecycle of the field
evaluation. Levels are usually typical operating levels unless safety is involved; then maximum operating levels are
necessary. Durations are either equivalent to a complete system/subsystem test, long enough to check materiel
function, or an arbitrary short time (5 or 10 minutes). For safety driven worthiness test, the test item is considered to
be consumed by the test (the test item may not be used in the field). An identical item of hardware is used in the field
evaluation. When safety is not an issue, an item may be subjected to a minimum time functional test and then used
in the field evaluation. When it is required to evaluate the cumulative environmental effects of vibration and
environments such as temperature, altitude, humidity, leakage, or EMI/EMC, a single test item should be exposed to
all environmental conditions. For air worthiness testing, a three step approach may be required. For example, this
could include conducting an initial laboratory vibration test, followed by experimental flight testing to acquire the
actual exposure levels, and ending with a qualification test based on the measured field data.
19
EXAMPLE OF MIL-STD-810G TEST PROFILE
20
ETS MET SERIES PERFORMANCE CURVE
Following are the Performance Test Result from an ETS Multi Excitation Testing System which consists of 3 x 50 kN
single axis vibration shaker. There were three tasks which were performed: Sine Sweep, Random, and Shock.
a. 3 Axis Sine Sweep
21
b. 3 Axis Random
22
c.
Shock Test
23
It has been mentioned at the MIL-STD-810G:
1. In some cases, especially fatigue and crack cases, the single axis vibration testing is not appropriate to represent
the actual field condition.
2. Based on MIL-STD-810G test profile, the frequency range that needs to be delivered is up to 2 kHz.
ETS MET Series Vibration Testing System with Hydrostatic Spherical Adapter system that can deliver frequency
range up to 2 kHz is able to perform the test profile mentioned by MIL-STD-810G Method 527 about Multi Exciter
Testing.
Partial Shaker References
MET-5000 Shaker References:
ATE Detroit, MI
ETL Dallas, TX
PTS Orlando, FL