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

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

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)

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”

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

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

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

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

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

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

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:

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

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