Beam Wire Scanner: Optical position sensor assembly and performance tests

BWS Design meetingJose Luis Sirvent

PhD. StudentXX/03/2014

ResolverX Axis: Optical position sensor

Y Axis: Diamond Detector

Position Sensors and Secondary Particle Shower Acquisition

X Axis Optical position sensor measurements

Y Ax

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1. Optical Position SensorWorking Principle• Primary Electronics: Control LD power and adapt PD signal to be acquired by ADC.• Optical Circulator: Directs the light form the LD to the sensor system and the reflected signal to the PD.• Optical Feedthrough: Overcomes the vacuum barrier.• Lens system: Focuses the light from ~9um (fibre core) to ~20um (reading spot) and collects reflections.• Encoder disc: Made of Soda-lime glass with high reflectivity Cr. Tracks.

• Characteristics: All optic sensor system (in tunnel) working with SMF 9/125um @ 1310nm

Photodiode Signal

1. Assembly Tests:Focusers Housings and Caps

• We have 4 sets:• 2 x Schaffter + Kirrchoff• 2 x Thorlabs + Asphericon

• Focusers fixation system:• Schaffter + Kirrchoff : 2 Screws @ 180 deg.• Thorlabs + Asphericon: 2 Screws + Pressure

1. Assembly Tests:Disc Holder

• The disc holder consist of two pieces:• A) Shaft attachment• B) Compressing Ring

• There was an small problem in the compressing ring:• Manufacturing drawings: Step to fit disc Diam. ~ 39.9 mm• Physical piece: Step to fit disc Diam. ~ 40.9 mm• Solved modifying the piece Thanks William!

• To Consider:1. Materials dilatation: Different design

2. Amount of pressure on screws: Special tool for fixation

3. Mounting references: The disk should always be mounted in the same angular position. Key in disk?. If calibration is always performed alignment by eye is OK.

1. Assembly Tests:Adjustment tools and Caps

Good:• The micrometric screws took some time to arrive• The pieces fit perfectly

To Consider:• The caps are very thick and for the focuser clamping with the screw quite

a lot of strength is needed. The screw could be damaged or what is worse, the focusers housing while fixed in the crown.

• We’ll perform a small modification on the caps making a slit after the adjusting screw

1. Assembly Tests:The whole system in the Crown

SMF UHVFeedthroughs

SMF UHV High TempPatchcords

Good:• The focuser systems (housing and adjusting elements) fits perfectly and slides softly• The micrometric screws adjusting range is correct• The space for mounting the SMF and the slits are not forcing the fibre to bend

To consider:• The fixing screws are not the best ones

(not flat and scratch the focusers housing)

• Too much strength needed to fix/release the cap to the focuser housing, if adjusted and dismounted the adjustment could be lost.

• The fibres are quite rigid and need free space to bend (We’ll have space enough to not force them?)

1. Assembly Tests:Complete system mounted and fibre routing

Good:• The Focusers are perfectly aligned with the disc (90 degrees) and in the correct track (I cannot verify if completely in the centre…)

To consider:• The fibre routing is not trivial, it’s quite rigid and we should avoid force it to bend too much.• The use of a flexible tube to route the fibre would be a good idea (protection & routing)• We are using now 1m of special UHV SMF for High Temp (Too long, we’d need a loop inside)

2. Performance Tests:The Set-Up used

CH_1

CH_2

2. Performance Tests:The Software used

Matlab-Based Script with user interface for quick tests:• Standalone operation• Analyses the two channels independently• Extracts position information • Checks that every pulse has been correctly detected• Extracts disc eccentricity (position error)• Applies calibration curves, corrected positions• Checks the calibration reliability/repetitivity• Extracts errors after calibration

• Available on-line with demo files and user guide:https://issues.cern.ch/browse/BIWS-483

2. Performance Tests:Channel 1: Pulses detected correctly & 10um Track in good conditions

Scan Region

Complete Revolution

Revolution - Scan Region

2. Performance Tests:Channel 2: Pulses detected correctly & 10um Track in good conditions

2. Performance Tests:Disc Eccentricity Detected & Calibration curves: Prototype

Scan Region

Complete Revolution

Revolution - Scan Region

5e-4 Rad

2. Performance Tests:Disc Eccentricity Detected & Calibration curves: Prototype

Scan Region

Complete Revolution

Revolution - Scan Region

5e-4 Rad

Projected Error Eccentricity Fork 10cm (P.E.):P.E= 2.5e-4 * 0.1m = 25mm

Disc centre offset (e):2.5e-4 = e / 0.5DD = 136.5 e = 17mm

2. Performance Tests:Disc Eccentricity Detected & Calibration curves: Lab. Test-Bench

2e-3 RadP.E. = 100mm

e = 68mm

2. Performance Tests:Disc Eccentricity Correction (1x Scan region): Prototype

P.E. = 0.601mm

2. Performance Tests:Disc Eccentricity Correction (4 x Scan region): Prototype

P.E. = 1.1mm

2. Performance Tests:Disc Eccentricity Correction (1x Revolution – Scan Region): Prototype

P.E. = 1.501mm

2. Performance Tests:Disc Eccentricity Correction (3x Revolution – Scan Region): Prototype

P.E. = 1.8mm