kinematic mounting scheme of miniature precision elements for mission survivability against...

THEORETICAL ANALYSIS AND AN EXPERIMENTAL CHARACTERIZATION OF A HEAT PIPE

Kinematic Mounting Scheme of Miniature Precision Elements for Mission Survivability against Externally Imposed Environmental ConditionsPREPARED BY :ANKITKUMAR P. SARVAIYAM.TECH (CAD/CAM)09CAD14GANPAT UNIVERSITYGUIDED BY:PROF. D. M. PATELMECHANICAL ENGG. DEPT.,U.V.PATEL COLEEGE OF ENGG., GANPAT UNIVERSITY, KHERVA

GUIDED BY:MR. J. T. DESAISCI /ENGG, HEAD, LPMDOPMG,MESA,SACISROAHMEDABAD

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Presentation Outline

Introduction Literature ReviewDesign of Kinematic MountActual Testing and RealizationConclusion Future WorkReferences

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1. IntroductionSpace craft

A spacecraft is designed to leave Earth's atmosphere and operate beyond the surface of the Earth in outer space. Spacecrafts are designed for a variety of missions which may include communications, earth observations, navigation, planetary explorations, scientific research, and so on.Spacecraft Typical Subsystems like Attitude control, Payloads, Launch vehicle etc.

Payload

The payload is dependent upon the mission of the spacecraft, Typical payloads could include scientific instruments (cameras, telescopes, or particle detectors, etc.).

Remote sensing payload

The remote sensing component of the programme, in particular, has successfully achieved global acceptance. Operational satellites have been indigenously built and launched, which cater to land and ocean applications.There are numbers of elements for imaging, sensing etc. in remote sensing payload.

Telescope

A telescope is an instrument designed for the observation of remote objects.

Camera Structure

Filters:

To have single collecting optics for all 4 bands and use appropriate spectral separation system for band selection.To use separate collecting optics for each band

Types of FiltersLow Pass Filter- Passes low-frequency signals but attenuates signals.High Pass Filter- Passes high frequencies well but attenuates frequencies lower than the filter's cutoff frequency.Band Pass Filter- Band pass filter are uses to pass these 4 bands, every band has a specific spectrum.

Kinematic mount

Kinematic Mount are widely used to minimize the deformation of optical elements caused by Kinematic mount induced stresses. Kinematic mount uses the principle of kinematic theory.

Theory of Kinematics

A rigid body in space has 6-DOF, three translations and three rotations. Kinematic theory assumes that perfectly rigid bodies contact only at infinitesimal points.The application of kinematic theory consists of selecting no more than six contact points to provide the type of support or motion required.

Flexure:

Definition of Flexure:

Flexure is usually considered to be a mechanism of a series of rigid bodies conducted by compliant elements that is designed to produced a geometrical well defined motion upon application of forceOr Flexure is an elastic element which provides controlled motion

2. Literature Review

Advantages:

It must exert low force on the optical element to minimize optical surface distortion.The mount must be such that a thermal changes in temperature must not degrade the optical surface or change the position of the optical element.It must maintain the position of the optical element throughout its assigned life time.Mounting fabrication and material cost should be as low as possible.

Flexure Elements:

Flexure device consist of compliant elements that connect rigid bodies to from a mechanism.Types of Flexure Elements

Types of Notch JointsCompliant JointCompliant Notch Universal JointCruciform Joint

Material Selection:

Compliance of an individual flexure depends of the shape and flexure material.Stability of flexure material with respect to time so its important for maintaining alignment of optical element.Dimensional stability of flexure is controlled by choice of material.Another consideration, thermal properties of flexure material- good matching between CTE of flexure and optical element.

Test on Vibration Shaker:

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Sinusoidal Vibration Test

Sine vibration testing is used to find out natural frequencies, peak value of acceleration.

Random Vibration Test

Many vibration environment are not related to a specific deriving frequency and may have input from multiple sources which may not be harmonically related. Unlike Sine vibration, acceleration, velocity & displacement are not directly related by any specific frequency. Primary concern in Random testing is the complete spectral content of the vibration being measured.

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3. Design of Kinematic MountIntroductionDesign StepsCAD modelsStructural Analysis of Assembly

IntroductionKinematic mount is monolithic part. The mount needs to be designed to perform satisfactorily without losing its alignment. The mount itself has to avoid deformation of the mounted optics. Kinematic mount is to be made by incorporating different types of flexures in this design.Kinematic mount following the cantilever principle, a large mount allows finer control than a smaller one.

Design Steps

1) Identification of NeedFilters need to be housed in mechanical assembly to give them support as well as to maintain separation between different optical elements under the application of loads. Need arises to design to this mechanical element.

2) Definition of ProblemTo design mechanical support for supporting optical elements like band pass filter in such a way that it will sustain different loads and the optical elements will perform satisfactorily under this load.

Goals:

Supporting optical element and maintaining its position relative to other optical elements in an optical system.Design has to be such a way that to sustain gravity loads and changing temperature conditions in space, sine and random vibrations.

Loads and boundary conditions :Loads

Inertial load: 100g, 200g (gravity load) individually in all axes as per requirement.Temperature: 40c excursion load.Sine loads, Random loads as per below table

Qualification Levels(ii) Sine Vibration loads(iii) Random Vibration loadsDirectionIn PlaneOut of PlaneDirectionIn PlaneOut of PlaneFrequency(Hz)Amplitude at Qualification LevelAmplitude at Qualification LevelFrequency (Hz)Qualification LevelQualification Level5 164.85 mm9.7 mm20 100+3 dB/Oct+3 dB/Oct16 505 g10 g100 - 7000.1g2 / Hz0.2 g2 / Hz50 803 g6 g700 2000- 3 dB/ Oct- 6 dB/ Oct80 - 1003g3 gOverall g rms11.89 rms14.8 rmsRate & Duration2 Oct/min2 Oct/minDuration2 minutes2 minutes

Boundary conditions:

Mount should have 2 fixing holes at the end.

Specifications:

Mount design to hold optical elements having sizes: 85x10x2, 30x20x1and 30x20x3 mm3.Filter material: NBK-7, fused silica (glass material).Mount should be made with optimum size (approaching close to filter size) and minimum mass as possible.

3) SynthesisThis is the most important step in the designing. Here are various schemes for designing of kinematic mount. Kinematic mount is made by using different types of thin sections. These thin sections are called flexures. Cross strip,Notch joints (Square, Circular, Elliptical), Cruciform flexure etc.

Material selection for mount:

Sufficient flexibility of mount should be made up from material which has low stiffness.Difference between CTE (co-efficient of thermal expansion) of filter material and mount material should be as minimum as possible.Mount material should have sufficient strength so that it should not fail under the action of different loads.The mount material should be dimensionally stable over a period of time.Flexures will be having complicated geometry and the material should have good machinability.

4) Analysis and OptimizationAnalysis of the mount gives the results in frequencies, stress, acceleration and displacement. Here , Two types of analysisStatic Analysis

Dynamic Analysis

Natural FrequencyAnalysisFrequency ResponseAnalysisRandom ResponseAnalysisDynamic AnalysisStatic AnalysisInertial loadTemperature load

6) PresentationEvaluation is the final proof of a successful design and usually involves the testing of a prototype.

5) EvaluationA brief summary is presented which involves different steps in the process as well as final results obtained from the analysis and testing.

Option-1

CAD Models (Different options for mount design)

For Filter size:- 85x10x2



Option-2


Assembly view



Option-3




Option-4


Assembly view

Structural Analysis of AssemblyAnalysis means examination of the different components or elements that make up an assembly, to discover their interrelationships and relative importance in the realization of its goals or purpose.

Basically in analysis three steps are involved1) Pre Processing2) Processing3) Post Processing

Pre-Processing:

Meshing:Meshing is performed to discretize the geometry created into small pieces called elements.

FE model of Mount:Option -2

Option -4

Loads and Boundary Condition:Loads: Inertial, temperature, sine & random vibration loads

Boundary conditions:

Fixing point

Processing:

Import the model for processing which is exported from Pre-processor.

Two types of analysis has been carried out

1) Static analysis

2) Dynamic analysis

Post- Processing:

After completion of analysis solver generates result files.

Viewing and Interpretation of Results:

Before looking the results the terms Von-Mises and Max. Principal are as follows.

Von-Mises Stress: Ductile material fails at a plane inclined 45 to axis of loading. Normal stress not act on this plane so this theory is best for ductile material.

Max.Principal:Failure of brittle material subjected to uniaxial test is along a plane to perpendicular to axis of loading. So this theory is best for brittle material.

Case-1 : Inertial Load of 100g & 200g

Inertial loading analysis is done to analyses strength of the structure during its flight.

Stresses due to Inertial Load

Option-2Band Pass Filter assemblyComponent Stress (MPa) value at 200 g Inertial loadFilter ( Max Principal)9.22.293.23Mount (Von Mises)39.613.050.9Adhesive14.73.0911.5

Stress on filter ( Max. Principal)Stress on Mount ( Von Mises)Stress CountersThis results shown only Yaw axis results because yaw axis is critical axis for analysis

Option-4Band Pass Filter assemblyComponent Stress (MPa) value at 100 g Inertial loadFilter ( Max Principal)2.881.440.84Mount (Von Mises)8.648.162.96Adhesive2.481.590.76

Stress Counters

Stress on filter ( Max. Principal)

Stress on Mount ( Von Mises)

This results shown only Yaw axis results because yaw axis is critical axis for analysis

Case-2 : Temperature Load (T= 40c)

Temperature loading analysis is done to measure the strength of structure under temperature difference. During in-orbit operation of payload, some faces see the sun side and experiences radiation from the sun.

Stresses due to Temperature Load

Option-2Band Pass Filter assemblyComponent Stress (MPa) on Temperature changeT=40C Filter ( Max Principal)4.35Mount (Von Mises)51.3Adhesive5.75

Stress Counters

Stress on filter ( Max. Principal)Stress on Mount ( Von Mises)

Option-4Band Pass Filter assemblyComponent Stress (MPa) on Temperature changeT=40C Filter ( Max Principal)13.2Mount (Von Mises)36Adhesive12.4

Stress Counters

Stress on Mount ( Von Mises)Stress on filter ( Max. Principal)

Case-3 : Normal Mode Analysis

Normal mode analysis is done for finding out normal mode shapes and frequencies for final configured models to be tested on vibration shaker. It determines the natural (resonant) frequency and mode shapes of the structure.

Results of Normal Modes:

Only flexure modes are important because its shows the behavior of mount and shows the acceleration of filter also.

Normal Mode AnalysisOption-2

First mode: 885.1 HzFilter has translation in out of plane. Flexure worked as a cantilever beam.

Frequency (Hz)ModeNastran ( Theoretical )First mode885.1Second mode1597.2Flexure in plane mode2141

Second mode: 1597.2 HzFlexure will flex in plane direction

Third mode: 2141 Hz

Option-4

First mode: 885.1 HzFilter has translation in out of plane. Flexure worked as a cantilever beam.

Frequency (Hz)ModeNastran ( Theoretical )First mode985.27Local mode of mount1519.5Second mode2030Flexure in plane mode2036

Local mode of mount: 1519.5 Hz

Second mode: 2030 Hz

Flexure in plane mode: 2036Hz

Case-4: Frequency Response

Frequency response analysis is done to simulate the response at different locations of the job for given acceleration Critical damping factor is most unpredicted term of the frequency response analysis.Critical damping factor is most unpredicted term. It depends on many parameters like material, shape, no. of joints in the structure etc). It is difficult to evaluate damping factor theoretically. Hence, to determine damping factor, low level Sine test of Band Pass filter assembly was carried out. Damping factor is calculated by half power bandwidth method

Damping factor () = 1/2*Dynamic magnification factor (Q)

Derived dynamic magnification factor (Q) for BP filter mount assembly are shown in following.

Option-2

Option-4

Yaw axisFrequency (Hz)Q92918

Yaw axisFrequency (Hz)Q101019.61570116

Results of Frequency Response Analysis

Option-2 Input level of 1mm/s2 for 10Hz-2000Hz

TheoreticalExperimentalFrequency (Hz)885929Response (g/g)30.4627.11

Sine Response at middle of the filter

Acceleration V/s Frequency

Theoretical value of stress

At 1st freq stress is 0.00127 x 10-5 MPa for input of 1 mm/s2Calculation: 0.00127 x 10-5 *9810*0.5= 0.622 MPaExperimental value of stress

Strain is 15.4 x 10-6Stress = E* = (0.82x105) x (8.35 x 10-6) = 0.684 MPa

TheoreticalExperimentalFrequency (Hz)885929Stress (MPa)0.6220.684

Stress middle of filter

Stress vs. Frequency

Option-4Input level of 1mm/s2 for 10Hz-2000Hz


Sine Response at middle of the filter

Acceleration V/s Frequency

Theoretical value of stress

At 1st freq stress is 9.3 x 10-5 MPa for input of 1 mm/s2Calculation: 9.3 x 10-5 *9810*0.5= 0.456 MPaExperimental value of stress

Strain is 6.78 x 10-6Stress = E* = (0.73x105) x (6.78 x 10-6) = 0.495 MPa

TheoreticalExperimentalFrequency (Hz)9851010Stress (MPa)0.4560.495

Stress middle of filter

Case-5: Random Response

Random response analysis is the same analysis that performed as the random vibration test on vibration shaker. This is the most effective step towards the measurement of vibration characteristics. This analysis takes input from the result of frequency response analysis. So it's a dependable analysis. Along with above input, this analysis requires power spectral density (PSD) level for the frequency range to be tested.

Results of Random Response Analysis

Option-2

TheoreticalExperimentalInput level(gRMS) at mounting I/P14.814.8Response at middle of filter (gRMS)96.3164.83

Random Response at middle of Filter due to Random Qualification load

Response (g2/Hz) V/s Frequency

TheoreticalExperimentalFilter (Max. Prin.) MPa2.9439.86*10-6*0.82*105 = 3.28Mount (Von Mises) MPa8.5-Adhesive MPa3.31-

Stress (rms) at middle of filter due to Random Qualification load

Response (stress2/Hz) V/s Frequency

Stress counter for stress (rms) due to Random Qualification loadStress on filter 2.94 MPaStress on Mount 8.5 MPa

Option-4

TheoreticalExperimentalInput level(gRMS) at mounting I/P14.814.8Response at middle of filter (gRMS)71.863.93

Random Response at middle of Filter due to Random Qualification load

Response (g2/Hz) V/s Frequency

TheoreticalExperimentalFilter (Max. Prin.) MPa2.9345.07*10-6*0.73*105 = 3.29Mount (Von Mises) MPa2.56-Adhesive MPa1.2-

Stress (rms) at middle of filter due to Random Qualification load

Response (stress2/Hz) V/s Frequency

Stress counter for stress (rms) due to Random Qualification load

Stress on filter 2.93 MPaStress on Mount 2.56 MPa

4. Actual Testing and RealizationActual test is performed by vibration testing of band pass filter assembly on vibration shaker.

Purpose of Testing

This test has basic purpose of evaluating the behavior of filter assembly to the actual launch environment that is simulated during testing.

The set up consists of Shaker Fixture BP filter assembly Spacer Accelerometers Strain gauges

Test Configuration

Requirements to measure Acceleration and StrainAccelerometerIt is a piezoelectric transducer used to convert the kinetic energy into an electrical signal. One accelerometer is used in the test. Its mass was 1 gram.Strain GaugeA strain gauge is used to measure the strain of an object. The gauge is attached to the object by a suitable adhesive. Strain gauge measure the strain of filter in terms of mst (micro strain). One strain gauge is used in the test.

Location of Accelerometer and Strain gauge

Location of Accelerometer (Tri axial)Location of strain gaugeActual locations of Accelerometer and Strain gauge for testing (option-4)

Test Sequence

Low Level Sine test (LLS) Sine qualification test (SQ)Post SQ LLSLow Level Random (LLR)Random Qualification test (RQ) Post RQ LLS

Test Results ( option-4)Yaw axisYaw axis Test Set up

Yaw axis Test Results Band pass filter assemblyPre SQ LLS(I/P= 0.5g)Freq (Hz)10101570g/g19.915Micro strain6.788.43Post SQ LLS(I/P = 0.5 g)Freq (Hz)10101570g/g19.514.6Micro strain6.538.16LLRI/P=1.48ggRMS5.79Micro Strain RMS4.135RAI/P= 10.52ggRMS42.9Micro Strain RMS30.31RQ(Qualification)I/P=14.8 ggRMS63.93Micro Strain RMS45.07Post RQ LLR(I/P= 0.5g )g/g10301570Micro strain16.613Freq (Hz)5.586.97

Roll axisRoll axis Test Set up

Roll axis Test Results Band pass filter assemblyPre SQ LLS(I/P= 0.5g )Freq9541460g/g9.8612.8LLR (I/P=1.17g)gRMS4.285gRQ(Qualification)(I/P 11.77 gRMS)gRMS46.11gPost RQ LLR(I/P= 0.5g )Freq9541460g/g10.915.1

Pitch axisPitch axis Test Set up

Pitch axis Test Results Band pass filter assemblyPre SQ LLS(I/P= 0.5g )Freq16401530g/g3.741.76LLR (I/P 1.17 gRMS)gRMS1.502g1.34gRQ(Qualification)(I/P 11.77 gRMS)gRMS14.9g13.45gPost RQ LLS(I/P= 0.5g )Freq16501530g/g3.781.72

Comparison of Theoretical and Experimental data of Band Pass Filter AssemblyIn actual test, accelerometer & strain gauge are present; hence their masses are considered. So in theoretical analysis, I have to add those masses and so my analysis is done with consideration of these masses. In theoretical analysis, accelerometer has been simulated as a lumped mass.

Low level Sine Response

Comparison of Frequency Response during LLS

Sine Response at middle of Filter TheoreticalExperimentalFrequency (Hz)9851010Response (g/g)24.120.55

Comparison of Stress during Low Level Sine Test

Stress at middle of Filter TheoreticalExperimentalFrequency (Hz)9851010Stress (MPa)0.4560.495

Low Level Random Response

Comparison of Random Vibration Qualification Response

Random Response at middle of Filter due to Random Qualification LoadTheoreticalExperimentalInput level (gRMS) at mounting I/P14.814.8Response at middle of filter (gRMS)71.863.93

Comparison of Stress during Random Vibration Qualification

Stress (rms) at middle of filter due to Random Qualification LoadComponentTheoreticalExperimentalFilter (Max. prin.) MPa2.933.29

Testing of Option-2

Yaw axis test set up

Yaw axis test dataBand pass filter assemblyPre SQ LLS(I/P= 0.5g)Freq (Hz)929g/g27Micro strain8.35Post SQ LLS(I/P = 0.5 g)Freq (Hz)929g/g26.1Micro strain8.04LLRI/P=1.48ggRMS929Micro Strain RMS4.347RAI/P= 10.52ggRMS932Micro Strain RMS28.45RQ(Qualification)I/P=14.8 ggRMS932Micro Strain RMS39.86Post RQ LLR(I/P= 0.5g )g/g28.3Micro strain8.84Freq (Hz)929

Comparison of Theoretical and Experimental data of Band Pass Filter Assembly Low level Sine Response


Sine response at the middle of the Filter

Comparison of Frequency Response during LLS

Comparison of Stress during Low Level Sine Test

Stress at middle of Filter TheoreticalExperimentalFrequency (Hz)885929Stress (MPa)*0.6220.684

Low Level Random Response

Comparison of Random Vibration Qualification Response

Random Response at middle of Filter due to Random Qualification LoadTheoreticalExperimentalInput level (gRMS) at mounting I/F14.814.8Response at middle of filter (gRMS)96.3164.83

Comparison of Stress during Random Vibration Qualification

Stress (rms) at middle of filter due to Random Qualification LoadComponentTheoreticalExperimentalFilter (Max. Prin.) MPa2.943.28

5. ConclusionThe dissertation establishes a need to develop an accurate mechanical structure that corrects the deficiencies of the alignment problem during launching and it's throughout operational life in orbit. Different types of flexure geometries are evaluated for making a kinematic mount.

After considering four options, it is realized that option 2 and option 4 are practically suitable as per the requirements cited.Further, option 4 is better in comparison to option 2 since it has satisfies all the design requirements and it has a very good match of analytical results with its experimental results.Hence, option 4 can be used for future space projects which are having similar design criterion.

6. Future WorkPresent work has excluded Opto-mechanical analysis like finding surface deformations due to different mechanical loading conditions. This sort of work can be undertaken in future during integrated payload development.

This design philosophy of the filter mount assembly can also be applied to other mechanical components holding different optical elements.

Though the design is made for different mounts having different materials, actual testing is done only for mounts made from Aluminum and Invar due to scarcity of time. Mounts from other materials like titanium, composite materials can be made and can be tested to know their behavior.

Experimentation of the filter mount assembly can be done by putting them in thermo-vacuum chamber and subjecting it to designed temperature excursion loads to know their practical suitability.

7. ReferencesDr. Jinjun Shan, Assistant Professor of Space Engineering, ENG 4360 - Payload Design, 1.2 Introduction to Space Missions.Dr. Jinjun Shan, Assistant Professor of Space Engineering, ENG 4360 - Payload Design, 2.1 Payload Design and Sizing.Dr. Jinjun Shan, Assistant Professor of Space Engineering, ENG 4360 - Payload Design, 4.2 Space Craft Sensors- Introduction to Sensors.George Joseph and P.D. Bhavsar, Activities at Indian Space Research Organization (ISRO) on development of space borne remote sensing sensors.Daniel Vukobratovich and Ralph M. Richard, Flexure Mount for High Resolution Element, Proc. of SPIE Vol. 0959, Opto-mechanical and Electro-Optical Design of Industrial Systems, ed. R J Bieringer, K G Harding (Jan 1988) Copyright SPIE.Daniel Vukobratovich, Opto-Mechanical Design Principal, 1999 CRC Press, http://www.engnetbase.comStuart T. Smith. Flexure: Elements of Elastic Mechanisms. New York, (2000).Brian Trease, Flexures: lecture summary. Compliant System Design Laboratory The University of Michigan, April 30 (2004).Chirag Kalariya, M Tech. thesis, Design, Development and Analysis of Payload Fixation Device for Space Optical Payload. Department of Mechanical Engineering, Nirma University, Ahmedabad, May 2010.

http://enpub.fulton.asu.edu/imtl/HTML/Manuals/MC105_Cantilever_Flexure.htm, accessed on 21st May 2011.Rechard G. Budynas and J. Keith Nisbett, Shigleys Mechanical Engineering Design, Eighth Edition (2008).Y. Tian, B. Shirinzadeh, D. Zhang, Y. Zhong, Three Flexure Hinges for Compliant Mechanism Design based on Dimensionless Graph Analysis, Science Direct, Precision engineering 34(2010)92-100.3M Scotch Weld Epoxy Adhesive 2216B/A, Technical Data, December 2009.http://www.colorado.edu/engineering/cas/courses.d/IFEM.d/IFEM.Ch06.d/IFEM.Ch06.pdf, chapter 6 FEM Modeling: Introduction.Nitin S. Gokhale, Sanjay S. Deshpande, Sanjeev V Bedekar, Anand N Thite, Practical Finite Element Analysis, First Edition.Naimesh Patel, J.B.Rami, A.P.Vora, C.P.Dewan, D.Subrahmanayam, Derived vibration spectrum based qualification of opto-mechanical subassembly, SSME (Space Society of Mechanical engineers) Journal of Mechanical Engineering ,Vol.8 No.1 ,June, 2010, Page 43-47.

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