Importance & Application of ETS MET-Series Shaker System

Transcription

1 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 Tel : Fax : sales@etssolution-asia.com

2 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 Tel : Fax : sales@etssolution-asia.com 2

3 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 Construction of Multi Axis Shaker System...11 Conventional Adapter Hydrostatic Spherical Adapter...13 Auto Centering System Auto Centering System (cont d) Unibase Mounting...16 Applications Applications (contd.) Example of MIL-STD-810G Test Profile ETS 3 x 50 kn Performance Test Sine Sweep ETS 3 x 50 kn Performance Test Random ETS 3 x 50 kn Performance Test Shock Partial Shaker References

4 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

5 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

6 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

7 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

8 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

9 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

10 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

11 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

12 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

13 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

14 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

15 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

16 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

17 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

18 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 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 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

19 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

20 EXAMPLE OF MIL-STD-810G TEST PROFILE 20

21 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

22 b. 3 Axis Random 22

23 c. Shock Test 23

24 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