Leica Absolute Distance Meter Technology Days at NASA/MSFC May - - PowerPoint PPT Presentation

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Leica Absolute Distance Meter Technology Days at NASA/MSFC May - - PowerPoint PPT Presentation

Dec 27, 2023 151 likes •437 views

Leica Absolute Distance Meter Technology Days at NASA/MSFC May 22-23, 2002 Ron Eng NASA/MSFC 256-544-3603 ron.eng@msfc.nasa.gov Leica Disto-Pro ranging device Used during SBMD and NMSD tests for radius of curvature measurements.

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SLIDE 1

Leica Absolute Distance Meter

Technology Days at NASA/MSFC May 22-23, 2002 Ron Eng NASA/MSFC 256-544-3603 ron.eng@msfc.nasa.gov

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2

Leica Disto-Pro ranging device

  • Used during SBMD and NMSD tests for radius of

curvature measurements.

  • Time of flight ranging device.
  • +/- 2mm accuracy.
  • 1.5 to 50 meters range.
  • Works best with diffuse targets.
  • Compact.
  • Inexpensive.
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Requirements for measuring AMSD radius of curvature

  • Remote measurement device to be located at or near

ROC.

  • Absolute distance measurement or ranging device.
  • 1 micron measurement resolution.
  • Better than 25 microns measurement accuracy.
  • Better than 25 microns measurement repeatability.
  • Greater than 50 meters range.
  • Specular surface and corner cube.
  • Fast sample rate.
  • Compact.
  • Easy to use.
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4

Leica laser tracker

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5

CPU, power supply, and ADM

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6

ADM on hexapod

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Ranging system principle Distance D, is determined by measuring the phase angle between the transmitted sine wave and the received sine wave. The relationship between phase angle φr ,time delay tr ,and modulation frequency f0 ,is:

tr = φr /2π f0 D = C tr / 2 = C φr / 4π f0 D0 = N0C / 2f0

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ADM description

IR laser diode 780nm (1mW max output) Visible laser diode for pointing Polarization modulation External modulation with LiTaO3 crystal @700-900 MHz Differential signal detection Detection of the same signal (same phase position) Frequency Shift ==> 0° Phase Minimal measurement distance 1.5 m due to minimum bandwidth of 150 MHz Maximum measurement range 50 m Distance measurement resolution 1 µm Distance measurement accuracy better than 50 µm. 400 x 120 x 40 mm (L x H x T) 2 kg

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ADM schematic

Laser

  • pt.

Isolator pol. Beam- splitter Modulator Light- detector Controller Sythesizer Lock-In Amplifier, A\D - Converter Wobbler Data- Connection Laser – pointer Quarz, /4-Plate Crystal 10 9 8 7 6 5 4 3 2 1 Optics Reflector

  • r

Mirror 11 12 Beam Splitter

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π / 4 π / 2 3π / 4 π 5π / 4 5π / 2 7π / 4 2 π Modulation Wave

X Y Z X Y Z E EX EX EY EY EY EX Example for a π/2 shift of light beam (circular polarization)

External modulation with LiTaO3 crystal

  • not directly influencing the laser
  • using non linearity effects
  • beam velocity is different at different

axis EX and EY

Polarization Modulation systematical change of the beam shift by an electronic oscillation circuit high frequency 700 - 900 MHz

ADM - Modulation methods

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11

ADM - Beam Pass and Phase Control

polarization beam splitter with an angle of 45° to the crystal works like an analyzer linear polarized light beam (ne, no) Crystal λ / 4 - plate Reflector zero current no light on the Receiver Diode

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Overview - Major Functionality Blocks Modulator HF - Circuit Digital synthesizer Differential signal detection CPU

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Modulator - High Frequency Circuit

E C B

Back - Coupling (same phase) Transistor

"Connected"

Measuring Pin High Frequeny Circuit Wobble - Frequency Overlay

UEB UCB

Systematical influencing of the refraction indices ne and no of the crystal High frequency with enough power Optimized modulation voltage ==> enough modulation strength

Crystal Plate Box Spring

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Digital synthesizer Synthesizer for flexible and defined frequency movement Very short reaction time Very small frequency steps (system resolution)

Oszillator 10 MHz Phase compare 3.6 MHz to 4 MHz Amplifier NCO VCO

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ADM - Differential Signal Detection

Difference (Int_1-Int_2) = Int Set frequency f Intensity Int_1 of

  • 1. sampling

f+∆f

if Int >0, measured frequency f is higher than frequency at minimum position

Int>0

Intensity Int_2

  • f 2. sampling

f-∆f

180° -phase difference

  • 2. Sample

measurement [*]

  • 1. Sample

measurement [*] Sample Int_1 Sample Int_2

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ADM - Differential Signal Detection

Intensity Int_1 of

  • 1. sampling

Intensity Int_2

  • f 2. sampling

Sample Int_1 Sample Int_2 Difference (Int_1-Int_2) = Int

Int=0

set frequency f if Int = 0, frequency f is set to minimum position

f+∆f f-∆f

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ADM - Differential Signal Detection

f+∆f f-∆f

Intensity Int_1 of

  • 1. sampling

Intensity Int_2

  • f 2. sampling

Sample Int_1 Sample Int_2 Difference (Int_1-Int_2) = Int set frequency f if Int < 0, measured frequency f is smaller than frequency at minimum position

Int<0

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Sampling along a Minimum Position

5 0 10 0 15 0 20 0

  • 50
  • 10 0
  • 15 0
  • 2 00

F re que ncy m ovem en t [in N S ] Inte nsity va lue s [in A /D con ve rter un its] 50 10 0 1 50 20 0

  • 5 0
  • 10 0
  • 15 0
  • 2 00

m ea sured in te nsity fu nctio n (83 5.5 M H z)

Using difference method to sample along a minimum position, the intensity values will follow a line

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Micro - Controller Functionality

CPU data - interfaces hardware- switches measuring - display Power Supply- Reset Data- and program memory

  • scillator

configurable memory (Parameter) bus select synthesizer controlling and data transfer wobble-frequency control measuring- and high frequency (VCO) signals Laser ON / OFF Data bus

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Measurement flow and distance calculation

start measurement yes no yes no begin with starting actions search next minimum position

enough minimum positions?

further measurements? start fine measurement distance calculation result display

minimum frequency f0 minimum position f0+1 search minimum by defined frequency movement set frequency at low boarder of modulation band search exactly next minimum position

1

f f f − = ∆

+

f f

N

∆

=

  • r

f f

N

∆

=

1

1

2 f c N

D

⋅ ⋅

=

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Atmospheric Influence

Accuracy depends on refractive index of air between the ADM and the target. Refractive Index

  • T = air temperature in degrees Celsius
  • P = pressure in millimeters of Mercury
  • R = relative humidity in percent

N P P T T R

Gr T T

= ⋅ ⋅ + ⋅ ⋅ − ⋅ + ⋅         − ⋅ ⋅ ⋅

− − ⋅ + +

03889479 1 10 0817 00133 1 00036610 55668 10 10

6 6 7 5 237 3 0 6609

. ( . . ) . .

. . .

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Shortest Distance

Limitations are related to: Bandwidth of the modulator of 150 MHz Modulation frequency

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ADM measurement output

ADM Measurement Refraction = 1.00027529886 A = -49849.000000

  • Dist. [m]

C K [um] P [um] f [Hz] M [m] SD [um] 20.465532 124

  • 3

2 840019528 20.465532 0.000000000 20.465532 124 1 840019472 20.465532 0.000000000 20.465534 125

  • 1

2 840019472 20.465532 1.168007728 20.465534 124

  • 1

2 840019472 20.465533 1.168007728 20.465534 124

  • 1

2 840019472 20.465533 1.118282261 20.465532 123

  • 3

2 840019528 20.465533 1.087356019 20.465532 123

  • 3

2 840019528 20.465532 1.066240300 20.465534 124 2 840019416 20.465533 1.081365031 20.465534 123

  • 1

1 840019472 20.465533 1.092571186 20.465534 124 2 840019416 20.465533 1.054326627 20.465534 124 2 840019416 20.465533 1.000222061 20.465534 124 2 840019416 20.465533 0.996080337

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Acceptance test methods

Repeatability test S.D. of 30 measurements to a corner cube <25 um S.D. of 30 measurements to a mirror <50 um Relative accuracy test 20 distance measurements to a corner cube, compare distance with LTD500, deviation ∆D <25 um 20 distance measurements to a mirror, compare distance with LTD500, deviation ∆D <50 um

measure ∆D

ADM LTD500 or DMI

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Acceptance test methods (continue)

D1 D3 D2

ADM offset determination (LTD500 required) 3 distances to be measured from both directions with LTD500 3 distances to be measured from both directions with ADM Deviation between (D1 + D2) and D3 < 35 um

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Acceptance test methods (continue)

Absolute distance accuracy test (LTD500 required) Measure 3 distances between 3 points with LTD500 Measure 3 distances between 3 points with ADM Deviation between (D1 + D2) and D3 < 35 um

= corner cube positions

NASA-ADM

O1 O2 O3 3 Mounting support

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Acceptance test results

< 36 < 21 ∆D < 35 um Absolute distance accuracy < 35 < 19 ∆D < 50 um Relative accuracy to mirror < 1.8 < 1.1 ∆D < 25 um Relative accuracy to corner cube < 2.7 < 3.5 S.D. < 50 um Repeatability to mirror < 1.8 < 1.3 S.D. < 25 um Repeatability to corner cube ADM s/n 406 ADM s/n 166 Requirements

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Conclusions

ADM measurements are very accurate and repeatable for corner cubes. Performed cryo deformation test of Gr-Ep reaction structure with ADM. Software interface is easy to use. May have problem measuring to Be mirror due to polarization properties or scatter. Currently have no method to calibrate the ADM in house. Demo is available on Friday during tour at XRCF. Demonstrate relative accuracy with a HP DMI.