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THE GONIOMETERS

Yury Gavrikov25/03/2009

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Looking back

1 year ago… I met with two very nice g…oniometers

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Because we decided to adapt their for a new experiment

The idea of mechanicsLinear movement

Gear boxBelt drive + “virtual”

screw

Engine DC-servo motor

Carriage slides on the 2 guides

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Linear motion

(full range = 90mm)(full range = 90mm)

Inside of beam

Outside of beam

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The idea of mechanics Angular

movement

1mm~

63m

m

AxisAxis

PusherPusher

Angle Stepper motor

&Belt driveMicroscrew

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ModernizationUnificated solution for angular & linear

motion:

• Stepper motor for driving

• LVDT for position measurement

• Common Control system for all devices

It was needed the mashining of original parts

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Mechanical revision

After modernization during last month before installation :

- 4 revisions and full disassembling- A lot of motion tests and measurements- Fixing of sources of the problems

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Measurement & Calibration

Angle measurement Digital Autocollimator specially

designed for the experiment

Range: ~ 8000 mrad (horizontal)~ 6500 mrad (vertical)

Resolution: < 0.5mrad10

Angle measurement

The general Idea of angle measurement

Mirror

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Angle calibration The Idea of crystal angle calibration

Reference mirror

Crystal

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Angle calibration Angle vs. LVDT position

-50000 0 50000

-7500

-5000

-2500

0

2500

5000

7500

An

gle

, u

rad

LVDT, uV

Goniometer 2Goniometer 1

-50000 0 50000

-7500

-5000

-2500

0

2500

5000

7500

Ang

le, u

rad

LVDT, uV

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Nonlinearity of goniometers

Periodical structure corresponds to the motor revolutionNonlinearity : about +/- 50mrad

-30000 -20000 -10000 0 10000 20000 30000-50

-40

-30

-20

-10

0

10

20

30

40

Non

linea

rity,

ura

d

LVDT, V

-30000 -20000 -10000 0 10000 20000-60

-50

-40

-30

-20

-10

0

10

20

30

No

nlin

ear

ity,

rad

LVDT, V

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Stability

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The goniometers are very SENSITIVE to any mechanical disturbance

The design is SOFT. “Don’t touch” should be placed everywhere

We can move it only in work direction to avoid all gaps

Mechanical stability

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Stability Stability of LVDT during 14 hours looks quite good (*)

Gonio2, LVDT

3-5 mrad

(*) with averaging to reduce the noise

Repeatability Preliminary estimation for angular motion

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-30000 -20000 -10000 0 10000 20000 30000

-70-60-50-40-30-20-10

0102030405060708090

No

nlin

ea

rity

, ra

d

LVDT, V

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Alignment system

Crystal align andAngle measurement on the tank

T ank

D i g i tal Auto c o l l i m ato r

P e ntapr i zm 1

P e ntapr i zm 2

C r ys tal 1 C r ys tal 2

R e fe r e nc e m i r r o r

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Crystal 1

Crystal 2

Ref. mirror

Photos of alignment system

Digital autocollimator

Reference mirror

Laser

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Penta prizm

Viewport

Sources of uncertainty• Initial orientation of the alignment rail to

the tank geometry +/- 350mrad• Nonlinearity of goniometers +/- 50 mrad

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Conclusions

We can use this goniometers with some magic gestures right now

BUT

To reach better results in the future we have to develop a new goniometer

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