SDL. Control of the UltraLITE Precision Deployable Test Article Using Adaptive Spatio-Temporal Filtering Based Control

Transcription

1 Control of the UltraLITE Precision Deployable Test Article Using Adaptive Spatio-Temporal Filtering Based Control Albert B. Bosse Thomas D. Sharp Stuart J. Shelley Sheet Dynamics, Ltd. Cincinnati, OH Keith K. Denoyer R. Scott Irwin Air Force Research Laboratory Kirtland Air Force Base 3/3/99, Page SDL-1

2 Overview UltraLITE Deployable Optical Telescope program DOT test beds Mirror Mass Simulator PDOS DOT BGD Active structural control issues Spatio-Temporal Filtering (STF) STF based structural control PDOS test experience 3/3/99, Page SDL-2

3 Acnowledgements Phase II SBIR award from Ballistic Missile Defense Organization (BMDO) Contract managed by and technical collaboration with Air Force Research Lab - Kirtland AFB 3/3/99, Page SDL-3

4 Air Force Research Laboratory Deployable Space Telescope Concept Large aperature/resolution through deployable, sparse, optical array Deployable primary mirrors Golay 6 configuration Telescoping seconday tower 3/3/99, Page SDL-4

5 Deployable Optics Concepts Evaluation Experimental Test Beds Mirror Mass Simulator (MMS) Precision Deployable Optics Structure (PDOS) Deployable Optical Telescope Brassboard Ground Demonstration (BGD) 3/3/99, Page SDL-5

6 Preliminary DOT Evaluation - Mirror Mass Simulator Mirror Mass Simulator mounted to optics bench 3 interferometer displacement sensors 3 piezo stac actuators Electromagnetic disturbance shaer 3/3/99, Page SDL-6

7 Precision Deployable Optical Structure Actuation Subsystem Optical Subsystem & Truth Sensor Mirror Simulator Interface Deployable Boom Granite Slab 3/3/99, Page SDL-7

8 Deployable Optical Telescope Brassboard Ground Demonstration 1.5m Deployable Telescope Secondary Mirror 3m Deployable Secondary Tower Test Tower Optical Test Bench: Finite Conjugate Scene Center of Curvature Sensor Laser Metrology Composite/Glass Hybrid Mirrors Deployable Reaction Plate Precision Mechanisms Optical Bench Aft Optics Adaptive Optics Wavefront Sensors Deployable Telescope Integrated Technology in Simulated Space/Ops Environment Supporting SBL, Global Virtual Presence, and Tactical Imaging Missions 3/3/99, Page SDL-8

9 Requirements SDL s primary mission is to provide a Vibration Control System that will assist the Optical Control System in meeting the DOT mirror positioning requirements Precision Deployable Optical Structure (PDOS): Achieve 30 nanometers or less RMS value for relative displacement between the granite slab and the mirror mass simulator Deployable Optical Telescope (DOT) (1) Maintain the position of the primary mirror segments within: Piston: ± 14 nanometers error per segment Tilt: ± 95 nanoradians error per segment (2) Maintain the position of the secondary mirror within: Decenter ±50 microns Piston: ± 4 microns Tilt: ± 20 microradians 3/3/99, Page SDL-9

10 Deployable Optics - Jitter Requirements Disturbances torque wheel actuators slewing space based laser Vibration Control isolation passive vibration control high bandwidth position control active vibration control 3/3/99, Page SDL-10

11 Active Structural Vibration Control Issues Modeling - accurate and complete dynamic models of complex real-world systems are difficult to obtain. Time Variance - Often, by the time you ve got the model the system has changed - It s a moving target. System dynamics - temperature, load, wear, damage Discrete failures - sensors, actuators, signal conditioning Computational burden 3/3/99, Page SDL-11

12 Spatio-Temporal Filter Based Control Uncontrolled Response Controlled Response Uncontrolled Modal Responses Extracted with STF Controlled Modal Responses 3/3/99, Page SDL-12

13 Modal Coordinate Transformation Uncouples System into SDOF Modes Mx + Cx + Kx = f Modal Coordinate Transformation L NM O QP L NM O QP T m η + c η + η= Φ f L NM b g N b g b g r= 1 xt = φrηr t = Φη t O QP 3/3/99, Page SDL-13

14 STF Origin - Modal or Spatial Filtering Spatial filter vector ψ Extract single mode response from measured response ψ φ i T r = 0 i r = 1 i = r T T ψ xt () = ψ φ η () t i i i N r= 1 T = ψ i φη i = η () t i r () t r 3/3/99, Page SDL-14

15 Spatio-Temporal Filtering Spatial filter estimate of time η at Spatio-Temporal filter estimate of η at time η = η ψ = T x ψ T R S T x x x 1 Nt U V W 3/3/99, Page SDL-15

16 Spatio-Temporal vs. Modal Filtering FIR or all-zero filter on each channel Pole-zero cancellation & preferential pass filter fewer sensors required Inherent estimation of modal velocity Compensation for filter delays, sensor & signal conditioning dynamics Non-homogeneous sensor suites - piezo patches, accelerometers, etc. 3/3/99, Page SDL-16

17 Adaptive Calculation of STF Coefficients using Reference Model Approach Know only poles of controlled modes Don t now mode shapes modal scaling factors (modal mass) modal participation vectors anything about uncontrolled modes (not even poles) 3/3/99, Page SDL-17

18 Adaptive Calculation of STF Coefficients using Reference Model Approach SDOF (Single Mode) Reference Model η bg r bg = λ η r T z l f η η bg bg bg r = z η + r λ brn g i rn N zλη i f i + 1 = b g + b g f + η bg r = = l l T T R S T η η η r b bg r1 rn i g U V W 3/3/99, Page SDL-18

19 3/3/99, Page SDL-19 SDL Adaptive Calculation of STF Coefficients using Reference Model Approach e l x x x l x x r T r T Nto T Nto r = = R S T U V W = R S T U VW R S T U V W η η η ψ ψ η bg 1

20 STF Based Modal Velocity Feedbac Control Control Command Vector for i th mode f c f c bg bg bg bg bg i i i i = η α i i i i = η α bg bgbg l v Modal Coordinate Velocity Estimate Force Vector Scalar Feedbac Gain Estimated Modal Participation Vector is Ideal Force Vector 3/3/99, Page SDL-20

21 Initial Mirror Mass Simulator Control Experiments STF based velocity feedbac 3 inputs, 3 outputs, 5 controlled modes Random disturbance excitation 1 1/2 days to implement familiarization with test bed all system ID control implementation and testing 3/3/99, Page SDL-21

22 Implementation of STF Based Control l η dspace System Controller ADC's ψ l e + η η bg r Ref. Model Random Excitation Control Command Control/Excitation Command DAC's Signal Cond Sensors Structure Actuators Amplifiers 3/3/99, Page SDL-22

23 Preliminary DOT Evaluation - Mirror Mass Simulator Mirror Mass Simulator mounted to optics bench 3 interferometer displacement sensors 3 piezo stac actuators Electromagnetic disturbance shaer 3/3/99, Page SDL-23

24 Initial Mirror Mass Simulator Control Experiments Amplitude - Displacement/Force Interferometer 1 versus Disturbance Force Frequency - Hertz 3/3/99, Page SDL-24

25 Initial Mirror Mass Simulator Control Experiments 10 1 Interferometer 2 versus Disturbance Force Amplitude Displacement/Force Frequency - Hertz 3/3/99, Page SDL-25

26 Initial Mirror Mass Simulator Control Experiments Amplitude - Displacement/Force Interferometer 3 versus Disturbance Force Frequency - Hertz 3/3/99, Page SDL-26

27 Bac-Up Structure Precision Deployable Optical Structure Gravity Off-Load Mirror Inertial Simulator Reference Bench Composite Boom Proved Deployment, Acquisition, Maintenance and Control System for a 2m Optical Segment 3/3/99, Page SDL-27

28 Precision Deployable Optical Structure 3/3/99, Page SDL-28

29 Precision Deployable Optical Structure 3/3/99, Page SDL-29

30 PDOS Frequency Response Function Interferometer 1 / PZT 2 FRF 5 Hertz boom mode only mode in low frequency range 1.6 Hertz slab mode not apparent - must treat as a disturbance TEST MODEL /3/99, Page SDL-30

31 STF Control PDOS 5 Hz Boom Mode OPEN LOOP CLOSED LOOP /3/99, Page SDL-31

32 Open and Closed Loop Interferometer PSD s OPEN LOOP CLOSED LOOP MAG (db) FREQUENCY (Hz) 3/3/99, Page SDL-32

33 PDOS Ambient Vibration RMS Vibration, Hz Int 1: nm Int 2: nm Int 2: nm Resonant and forced vibration 10 7 ch 1 ch 2 ch Resonant Frequencies /3/99, Page SDL-33

34 Interferometer RMS Value Versus Frequency Band 10 3 ch 1 ch 2 ch 3 RMS DISPLACEMENT (nm) FREQ (Hz) 3/3/99, Page SDL-34

35 PDOS Low Frequency Control RMS Vibration, Hz Assuming 50x reduction 0-13 Hz. Int 1: nm Int 2: nm Int 3: nm ch 1 ch 2 ch Note the control objective is 30 nm RMS vibration levels 3/3/99, Page SDL-35

36 Conclusions Resonant control alone is not sufficient to meet PDOS/DOT optical jitter control requirements High bandwidth position control in conjunction with resonant mode control required STF based modal control is practical approach for resonant mode control; Implement effective MIMO control on complex, realworld structures with little nowledge of dynamics Adapts to sensor/actuator failure Accommodates filter/signal conditioning dynamics Easily updated to accommodate changing system dynamics (only update poles of controlled modes) 3/3/99, Page SDL-36