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Mark Tillack, Lane Carlson,Jon Spalding
Laboratory Demonstration of In-chamber Target Engagement
HAPL Project MeetingRochester, NY
8-9 November 2005
Dan Goodin, Graham Flint, Ron Petzoldt, Neil Alexander
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We are attempting to demonstrate the “pessimistic” version in-situ target
engagement system proposed by Flint 3/05 (Gen II)
Key Requirements:
•20 m accuracy in (x,y,z)
•1 ms response time
Goals:
Full integration of all key elements of target engagement
Benchtop demo first: identify and solve problems before investment in full-scale, high-performance demonstration
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Glint system: beamlet fine adjustmentto compensate drift
The system consists of Poisson spot detection, Doppler fringe counting, a
simulated driver with steering, and a glint-based alignment
The driver beam is simulated with a HeNe laser
Doppler fringe counting provides z and timing (v)
Poisson spot system measures (x,y)
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Initial Poisson spot results were reported at the previous HAPL
meeting*
We demonstrated Poisson spot detection with 5 µm accuracy in <1 ms using a translation stage and an ex-situ centroiding algorithm
* L. Carlson, M. Tillack, D. Goodin, G. Flint, “R&D Plan for Demonstrating Elements of a Target Engagement System”
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To perform real-time target engagement on the benchtop, we needed a target transport
method
CMOS camera
illumination laser
PSD
4-mm SS sphere
We are using various translation stages and rail systems
We’re still working on a more prototypical surrogate transport method
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Our in-line benchtop centroiding system now runs continuously at <20 ms per
measurement
– this allows us to begin real-time feedback to beam steering
– higher speed will require real-time OS and a faster camera
– 1 cm/s target speed over 1 m travel
– 100 fps Basler camera
– Labview running on Windows XP
Approximate Time (ms)
Image Processing Initialize/setup visualization subvi's 0.5 Acquire image from 100 fps CMOS camera via firewire 6 Search image and match Poisson spot pattern with memory 9 Set coordinate system to center of matched pattern 0.5 Find circular edge of the Poisson spot 0.5 Output centroid coordinates, convert pixels to distance 1
Total 17.5
Breakdown of times
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Integration of Poisson spot detection with a “fast” steering mirror was
implemented
We passed a pseudo driver beam through a 10x beam expander to magnify the range of motion of FSM (±1.5 mm)
Determining the location of the driver on the target is difficult – the accuracy of engagement is confirmed with an offset PSD as a surrogate target
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QuickTime™ and aMPEG-4 Video decompressor
are needed to see this picture.
Open loop Poisson spot tracking: The Movie
±3 mm CMOS±1.5 mm PSD
white dot:Poisson spot
yellow dot:PSD
1. At t=0, PSD initialized at (0,0)
2. Start train moving
3. Measure Poisson spot (x,y)
4. Move FSM to follow sphere
5. Measure accuracy using PSD
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Engagement is performed in 23.5 ms, but dynamic errors are too
large
Sources of errors: • rocking of PSD & target• speed limitations in PC hardware/
software • overly simplistic gain curves • FSM quality
Approximate Time (ms)
Image Processing Same steps itemized above 17.5
Read DAQ Channels Read DAQ channels for PSD voltages, 2 convert to distance, graph, display
PID Control Apply PID algorithm to X and Y axies, 2 apply gain, graph, display
Write DAQ Channels Output voltages to FSM controller 2
Total 23.5
Breakdown of timesx-axis comparison of PS and PSD readings
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higher performance will require a better FSM
Beam deflection is nonlinear with drive voltage and exhibits
severe resonant behavior
595 Hz 617 Hz
1 ms
We characterized the Thorlabs piezo cage mirror mount using a signal generator
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Work has begun on Doppler fringe counting
• Restrictions on laser power limit the use of a metal sphere, so we’re using an n=2 sphere and flat mirror
• Single-wavelength (632.8 nm)
• Errors due to translation stage, vibration, air flow
Repeatability demo using micrometer: travel of 5 mm with 10 m increments
An N=2 ball lens is a retroreflector:
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We performed a fast tracking demo at 1000 Hz using a high-speed pellet and post-shot centroid analysis
1000 fps, 10 ms per frame video sequence of surrogate target coming into, then out of the camera’s FOV, at 150 m/s (Photron camera)
Curvature in the target trajectory allows us to avoid a shutter mirror for a range of velocities
Speed of gun is too fast, speed of tracking too slow:
work on the benchtop
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Next Steps: more integration and more
prototypical
Poisson system:Acquire a faster camera and real-time OS
Doppler system:
Demonstrate counting on metal spheres with longer pathsImplement dual-wavelength counting
Integration of Doppler and Poisson:On-axis demonstration (pseudo-integration)Off-axis demonstration (true integration)
Integration of Poisson and FSM:Improve control of the environment, acquire a high-end
FSM
Glint system Install glint laser and coincidence sensor, align 2 beamlets