18/13/2015alex delacroix ngao laser guide star mechanical pdr

104/19/23 Alex Delacroix

NGAOLaser Guide Star

Mechanical

PDR


1) LGS Asterism Arrangements

2) LGS Fixed Asterisms

2.1) LGS, Lower Fixed Asterism, Design Overview

2.2) LGS Fixed Asterism Probe Arm Design

2.3) LGS Fixed Asterism Gimbal Design

2.4) LGS Fixed Asterism Camera Assembly Adjustment Design

2.5) LGS, Central Fixed Asterism, Design Overview

3) LGS Patrolling Asterisms

3.1) LGS, Patrolling Asterism, Design Overview

3.2) LGS, Patrolling Asterism, Pick Off Arm Design

3.2.1) LGS, Probe Assembly Optical Design

3.2.1.1) LGS, Probe Assembly Optical Path

3.2.1.2) Static Load on the Lever Motor

3.2.1.3) Static Load on the Crank Motor

3.2.1.4) Probe position accuracy

3.2.1.5) Probe position repeatability


Mechanical


3.2.2) LGS, Probe Assembly Mechanical Design

3.2.2.1) LGS, Probe Assembly Limit Switch Mechanical Design

3.2.2.2) LGS, Probe Tip Design

3.2.2.3) LGS, Probe Tip Deflection

3.2.2.4) LGS, Probe Tip Frequency Analysis

3.2.3) LGS, Patrolling Asterism, Lever Assembly Design

3.2.4) LGS, Patrolling Asterism, Crank Assembly Design

3.3) LGS, Patrolling Asterism, Camera Assembly Design

4) LGS, Structure Design Overview

4.1) LGS, Plate Structure Assembly

4.2) LGS, Beam Support Assembly

4.3) LGS, Legs Assembly


Mechanical


1) LGS Asterisms arrangementThe Lgs is composed of 3 patrolling asterisms and 4 fixed asterisms, equally spaced around the central Field of view.

Fixed Asterism, lateral upper

Fixed Asterism, lateral, lower, left Fixed Asterism, lateral, lower, right

Patrolling Asterism, upper, left Patrolling Asterism, upper, right

Patrolling Asterism, lower

Fixed Asterism, center

LGS arrangementCurrent Mass Estimate: 80 Kg


2) LGS Fixed AsterismThe Lgs fixed asterism is composed of three lateral probes pointing toward the center of the science field within a diameter of 14.5mm (20”) (FR-2360) and one central Channel. Each Channels are installed thru a three point kinematic mount, shimmed as required.

Fixed Asterism arrangement

Fixed Asterism Field of View

Fixed Asterism, lateral, upper

Fixed Asterism, lateral, lower, left

Fixed Asterism, lateral, lower, right

Fixed Asterism, center

Kinematic mount

Current Mass Estimate: 55 Kg


2.1) LGS, Lower Fixed Asterism, Design OverviewThe fixed asterisms is adjustable in pitch and yaw about its focus point.The camera assembly is mounted on a gimbal, holding the fold mirror , is bolted on the probe body that also receives the collimator lens

Lateral Fixed Asterism design

Probe (Fold mirror holder)

Focus Lens holderAdjustable 0.25mm per rev.Thorlabs ST1XY-A

Probe Body(Collimator lens holder)Probe Bracket

Tip TiltPI S330-2

Tip Tilt Bracket

Mounting base

Post 1in diaThorlabs RS2 2837-EOW

Field stop(FR-2397)

Collimator Lens holder

Lenslet holder

Relay Lens holder

CCD

Gimbal Assembly

Adjustment KnobNewport AJS100-0.5

Mounting Bolts


2.2) LGS Fixed Asterism Probe Arm DesignThe Fold mirror is bonded at the extremity of a tubular probe design, bolted to the body, sandwitching the Collimator lens thru a soft o-ring, compressed to hold the lens in place against a machined receptacle.

Probe Arm Assembly (Cross Section)

Probe Mirror(bonded)

Probe Body

Collimator lens

Soft O-ring(Shore A: 50, Buna-N )

Probe Bracket


2.3) LGS Fixed Asterism Gimbal DesignThe Camera assembly is mounted on an aluminium gimbal thru shoulder screws and bronze bushings. The necessary gap and relative position of the gimbal is controlled using shoulder shim stocks.

Gimbal Assembly (Cross Section)

Probe Body

Mounting Base

Shoulder Screw , Stainless SteelØ1/2” x ¾” Lg

Mc Master 94035a503

Gimbal

Sleeve Bearing, flanged, bronzeØ 5/8” OD x Ø 1/2” ID x ½” LgMc Master 7815K29

Shoulder Screw , Stainless SteelØ3/4” x 1-1/4” Lg

Mc Master 90298a837

Sleeve Bearing, flanged, bronzeØ 1” OD x Ø 3/4” ID x 1” LgMc Master 7815K49

Camera Assembly

Shim Stock , Stainless SteelID .501 x .005” +/-.0005” Thk

Mc Master 94773A616

Shim Stock, Stainless SteelID .751” x .020” +/-.0025”

Mc Master 94773A720


2.4) LGS Fixed Asterism Camera Assembly Adjustment DesignThe Camera Assembly pitch and yaw adjustments are located 250mm away from the axis.The 1 inch travel adjustment knobs with a 0.7µm resolution gives the system a 0.57” angular resolution.(tan α = 0.7 E-6 / 250 E-3 = 28 E-7 , α= 160E-6 deg = 0.57 “)

Camera Assembly Adjustment(Cross Section) Mounting Base

Rod, threaded TBD

Camera Assembly

Compression Spring TBD

Adjustment KnobNewport AJS100-0.5

Steel plate


2.5) LGS, Central Fixed Asterism, Design OverviewThe Central fixed asterism differs in design only by the absence of a probe, rendered unnecessary by it’s central location in the sensor.

Central Fixed AsterismMounting base

Camera Assy

Gimbal Assembly

Fold Mirror


3) LGS, Patrolling Asterism, Design OverviewPatrolling asterisms are located 120 degrees apart from each other and are pointing the probes toward the 120” FoV

Patrolling Asterism

Patrolling Asterism, upper, left Patrolling Asterism, upper, right

Patrolling Asterism, lower

120” FoV(FR-2362)



3.1) LGS, Patrolling Asterism, Design OverviewThe Patrolling Asterism is composed of two distinct sub assemblies: The Pick off arm Assembly and the Camera Assembly.

Patrolling Asterism

Camera Assembly

Pick off Arm Assembly



3.2) LGS, Patrolling Asterism, Pick Off Arm DesignThe Pick off arm Assembly is composed of three distinct sub assemblies: - The Probe Assembly- The Lever Assembly- The Crank Assembly-The Course limiter pattern is a single part installed at the LGS Assembly level.

Pick off Assembly

Probe Assembly

Lever Assembly

Crank Assembly

Course limiter pattern

3.2.1) LGS, Probe Assembly Optical Design

14

a b c d

AO Focus

Collimator Lens (L1)

TT

L2

PO Focus

a1 a2

Probe(FM1)

Lever Arm

OSM# a1 a2= a - a1 a = b = a1 + a2

Arm = b + a2

I 10 110 120 230

II -5 125 120 245

III -20 140 120 260


Table 1

The Pick off arm Assembly is designed to answer the optical equation: a = b & c = d with a + b = x (c + d) and a = a1 + a2

Lever Arm length = b + a2 Solving for a2 2a2 = Lever Arm length - a1 a2 = (Lever Arm length - a1 )/2, so, with a = b = 120


The Patrolling Asterism is composed of two distinct sub assemblies: The Pick off arm Assembly and the Camera Assembly.

Patrolling Asterism(Cross Section)

Tip Tilt

Collimator Lens

Fold Mirror

Periscope

Focus Lens

3.2.1.1) LGS, Probe Assembly Optical Path

Total Mass: 1,240 grams ( 12.2N )

CG located at the Axis of rotation, 38 mm above the Lever motor Interface.

Torque at the Lever Rotation Stage Interface: 0.038 X 12.2 = 0.46 Nm Well below the manufacturer recommendation of 3 Nm

This gives a Factor of Safety of 3 / 0.46 = 6.5

16

½ in dia Collimator Lens1 gram

Tip TiltOIM100

340 grams

Limit Switch Assembly50 grams

CG Location Lever Arm454 grams


Fig. 11

3.2.1.2) Static Load on the Lever Motor

Probe30 gramsCounterweight

300 grams

Total Mass: 3,525 grams (35N)

CG located at the Crank Axis of rotation, 60 mm above the Lever motor Interface.

Torque at the Crank Rotation Stage Interface: 0.060 X 35 = 2.1 Nm Well below the manufacturer recommendation of 6 Nm

This gives a Factor of Safety of 6 / 2.1 = 2.8

17

Lever Arm Assembly1,240 grams

Lever Adaptor455 grams

CG Location

Lever MotorPI M-037.DG

650 grams

Crank Adaptor435 grams

Counterweight700 gramsPeriscope Assy

60 grams


3.2.1.3) Static Load on the Crank Motor

18

Position Accuracy at the longest probe: OSM #3, a1 = -20

Lever Arm Length: 260mmCrank arm Length: 41.8mm

Lever Stage M-037.DG Design resolution: 0.000034°Crank Stage M-038.DG1 Design resolution : 0.000035°

Lever arm position accuracy: 250mm X tan 0.000034° = 0.00015mm

Crank arm position accuracy: 290mm X tan 0.000035° = 0.00018mm __________

= 0.00033mm = 0.00045”


Fig. 13

Resulting position accuracy at the tip of the probe = 0.00033mm = 0.45 mas

3.2.1.5) Probe Position RepeatabilityPosition Repeatability at the longest probe: OSM #3, a1 = -20

Lever Arm Length: 260mmCrank arm Length: 41.8mm

Lever Stage M-037.DG Design repeatability: 30 μrad = 0.0017°Crank Stage M-038.DG1 Design repeatability : 20 μrad = 0.0011°

Lever arm position repeatability: 250mm X tan 0.0017° = 0.007mmCrank arm position accuracy: 290mm X tan 0.0011° = 0.005mm __________

Resulting Repeatability = 0.012mm = .016” = 16 mas

3.2.1.4) Probe Position Accuracy

FR-2391: Patrolling LGS acquisition accuracy due to absolute positioing accuracy of the OSM shall be better than 100 milliarcseconds


The Collimator lens, installed inside the Probe body, is held in place by a Soft o-ring installed inside the collimator lens spacer, that is held by the Probe.The Fold mirror is bonded at the tip of the probe.The Probe Assembly needs to be balanced about its axis of rotation to avoit placing uncontrolled loadings on the Lever Rotation Stage.

Probe Arm Assembly(Cross Section)

Limit Switch Assembly

Fold Mirror

Probe

1 inch dia Tip Tilt Optics In Motion 100

3.2.2) LGS, Probe Assembly Mechanical Design

Collimator Lens

Collimator Lens spacer

Probe Body

Soft O-ring(Shore A: 50, Buna-N )


This device is a wobbler limit switch that gives direction indication.

The wobbler is composed of a Ball Bearing Track Roller (Mc Master 3668K2), a steel shaft mounted on three compression springs, resting on 3 load cells.The load cells give direction and distance measurements.

Operation:Shortly after the arm deviates from its allowed path, the roller will contact the custom track, forcing the spring mounted wobbler base to exercise a pressure on a one or two of the load cells, signaling a trajectory error.Retraction can then be safely done by rotating the crank motor in any direction and rotating the Lever arm in accordance with load cells signals.

WobblerAssembly

3.2.2.1) LGS, Probe Assembly Limit Switch Mechanical Design

Ball Bearing Track RollerMc Master 3668K2

Threaded Steel Shaft

Spring Mounted base

Compression Spring Load cellHoneywell BL912A

Load cellsHoneywell BL912A

http://content.honeywell.com/sensing/sensotec/pdf_catalog08/008649_2_EN_Model_D.pdf





3.2.2.2) LGS, Probe Tip Design

FM1

Probe Tip

Light from Focus

Light to L1

Ellipse Minor Diameter: d = d at Focus Plan + (a1 / f#) = 5 X 0.727 + (20 / 13.66) = 3.635 + 1.464d = 5.10 mm

Ellipse Major Diameter: D = d√2 = 5.1√2 D = 7.21 mm

Ellipse Minor Diameter: d = d at Focus Plan + (a1 / f#) = 5 X 0.727 + (5 / 13.66) = 3.635 + .366d = 4.00 mm

Ellipse Major Diameter: D = d√2 = 4√2 D = 5.66 mm

Ellipse Minor Diameter: d = d at Focus Plan + (a1 / f#) = 5 X 0.727 + (10 / 13.66) = 3.635 + .732d = 4.37 mm

Ellipse Major Diameter: D = d√2 = 4.37√2 D = 6.18 mm

The Field of View at the Focal Plane is Ø 5” (3.635mm)The Field of View at the probe is defined by it’s distance from the Focal Plane / f#The probe Fold Mirror intercept the light beam at a 45 degree angle creating an elliptical projection at a distance a1 from the Focal plane. (See Fig. 4)The minimum diameter of the mirror needs to be larger than the Ellipse Major Diameter.The Larger Fold mirror will be at the furthest distance from the Focal plane OSM #1 (a1 = -20)The Patrolling Asterism LGS WFS channels shall be able to measure wavefronts from two LGS beacons separated by 10 arcseconds. FR-3430

Probe is sized to 8mm Diameter for commonality

22

-Mass of the probe w = mg = 0.01 Kg x 9.81 ms-2 = 0.098N

-Moment of Inertia: I = bh3/12 = 4.57 x 7.643/12 = 169.8 mm4

-6061-T6 Module of Elasticity: E = 68,800 N/mm2

-Max Deflection: ν = wL3 / 8EI

ν =0.098 X 1003 / (8 X 68,800 X 169.8)

ν = 98000/ 93457920

ν = 0.001mm

Probe Deflection

Max Probe Deflection, at rest, under it’s own weight: 1µm

• Deflection analyzed on the longest Inclined probe (OSM #2)

Probe Length


3.2.2.3) LGS, Probe Tip Deflection

23

OSM #1

OSM #2

OSM #3

3.2.2.4) LGS, Probe Tip Frequency Analysis

Lowest Frequency


3.2.3) LGS, Patrolling Asterism, Lever Assembly DesignThe Lever Assembly needs to be balanced about its axis of rotation to avoid uncontrolled loadings on the Crank motor.However, to compensate for undesired backlash of the Lever rotation stage, a slight, almost constant load is applied to the Probe Arm by the Backlash compensating spring system.

Lever Assembly(Cross Section)

Cable WrapEnergy Chain Z045

Backlash compensating spring

Crank Adaptor

Rotation StagePI M-037.DG

Cable Boom

Lever Assembly

Rotation Axis

Lever Adaptor

Periscope


3.2.4) LGS, Patrolling Asterism, Crank Assembly DesignThe Crank Assembly holds the Crank Rotation Stage, the focus Lens and the Crank Backlash compensating spring system.

Backlash compensating spring

Crank Bracket

Rotation StagePI M-038.DG Folded

Crank Assembly

Focus Lens holder


3.3) LGS, Patrolling Asterism, Camera Assembly DesignThe Patrolling Asterism Camera Assembly is made of a ¾ in thick Aluminum Honeycomb panel potted with aluminum inserts.It receives the Sensor optical mounts and the Pick off arm assembly.The panel is installed on the LGS Structure through shim stocks for tip tilt adjustment.

Patrolling Asterism, Camera Assembly

Aluminum HoneyComb Panel ¾ in thick

Tip TiltPI S330-2

Collimator Lens holder

Lenslet holder

Relay Lens holder

CCD

Fold Mirror

Three point mount5/16 Bolts and Shim stock


4) LGS, Structure Design OverviewThe Structure is composed of:- The Plate Structure assembly- The Beam Support Assembly- The Legs Assembly

Pole Assembly

Plate Structure Assembly

Structure Design

Beam Support Assembly

Degree of freedom Criterion Tolerance required

x, y ~ 0.1 arcsec on sky 65 micronsz ~0.1 arcsec spot deflection at

outer subaperture2 mm

qx, qy 15 cm subap / 10 110 micro radiansqz ~0.1 arcsec at 10 arcsec off-

axis radius10 milliradian

X

Y


4.1) LGS, Plate Structure AssemblyThe Structure, made of 1 inch and ¾ inch Thick bolted Aluminum plates, is rigidly holding each Asterisms. Each channel can be moved individually and locked in place thru a three point mount scheme.Three Hoist Rings are provided for lifting the Assembly with a Crane.

Plate Structure Assembly

Hoist rings

875 mm

616 mm

860 mm

Current Mass Estimate: 90Kg

5/16 Bolts x 1.5in Lg

¼ in Dia Shear pin(Match drilled in place after

assembly and inspection)


4.2) LGS, Beam Support AssemblyOne side of the Beam Support Assembly carries the LGS Translation mechanism, composed of two Deltron Slide bearings and a motorized stage (FR-2378 ). The other side of the Beam Support Assembly carries the LGS Kinematic Mount Scheme Composed of three receptacles: A Cone, a groove and a Flat. Three Hoist rings are also provided to tie-down the Structure to the telescope Nasmyth.The Beam Support Assembly is made of standard Aluminum IPN and plates Welded.The alignment of the structure relative to the Bench can be done by shimming between this assembly and the Structure assembly.The LGS WFS support structure shall be aligned to the required optical bench interface point to better than 1 mm. FR-2375The LGS WFS support structure shall be aligned to the required optical bench interface optical axis direction to better than 2 arcminutes (physical angle at the interface point) FR-2376

Beam Support Assembly

High Precision Series Crossed Roller Slides10 inches Travel, accuracy .00004 in/in Deltron HPRS 5-10


Translation StageNewport MTM250CC

0.1 µm resolution

Tie down Hoist rings

Cone

Groove

Flat


4.3) LGS, Legs AssemblyThe Legs are the link between the Telescope Nasmyth platform and the LGS structure.They are made of three different materials to compensate for dome temperature variations in conformity with the stability requirement. The LGS WFS support structure shall be stable to a level better than (x,y,z,thetax,thethay,thethaz) = (TBD, TBD, TBD, TBD, TBD, TBD) with respect to the telescope coordinate system. FR-2377

Legs Assembly Current Mass Estimate: 65 Kg

Legs

LGS

Leg Assembly(Cross Section)

Leg Outer shellStainless SteelCTE 14 µm/m/°C

Leg Inner shellAluminiumCTE 25 µm/m/°C

Leg CoreTitaniumCTE 8 µm/m/°C

860 mm

18-8 SS Alu Ti Total Outer Shell Inner Shell Core

Delta T (°C) 40 40 40 Length (m) 0.826 0.775 0.808

CTE (µm/m/°C) 0.000014 0.000025 0.000008 Variation (mm) 0.46256 -0.775 0.25856 -0.05

18/13/2015alex delacroix ngao laser guide star mechanical pdr

Documents

lgs asterism arrangements

lgs fixed asterisms

lower fixed asterism

central fixed asterism

lateral upper fixed

lgs patrolling asterisms

leftpatrolling asterism

right patrolling asterism