NASA Infrared Telescope Facility Author: Morgan Bonnet ...

2/16/2016 1NASA Infrared Telescope Facility

Institute for AstronomyUniversity of Hawaii

Author:Morgan Bonnet

IRTF Upgrades

2/16/2016 2

- Dome drive system- Refurbishing of the dome rail- Primary mirror re-aluminization- HVAC system- Shutter drive (Alimak)- TCS upgrades- MIM re-inforcement- Telescope Balancing- Dome re-painting (not started, contracting ongoing)- Instrumentation

Primary Mirror Re-aluminization

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Dome Drive System: Description

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- 12 bogie wheels at ~30 deg - Including 3 drives- 1 circular rail made of 12 sections- 24 guide rollers (Guide roller lip in

rail groove => earthquake)

Dome Drive System: Section View

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Guide Roller

Spring Plate

Bogie Wheel

Bull Gear

Dome Rail

Root Causes: Ishikawa Diagram

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Main Root Causes

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“Loose” Spring Plates / uneven Rail bottom surface:

=> Improper tracking = Dome becomes off-centered rapidly=> heavy loads on Guide Rollers (Bogie Wheel or/and Rail)

=> “wedge effect”

Shortened Rail:

=> Contact between top of Guide Roller with top of Rail groove

Worn down Bogie Wheel (due to contact with guide roller)

=> Contact between bogie wheel and spring plate

Insufficient Motor Torque / inefficient Motor Control:

=> Dome can’t pass hard spots, especially at low speed (insufficient Momemtum)=> Improper tracking

Accelerated Wear (vicious circle)

Action Items (1/4)

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General Maintenance / Complete Check‐up:

- To insure that issues aren’t simply originating from a damaged bearing or lack of grease (no issue found)

Bogie Wheels and Guide Rollers Tuning:

- To insure wheels are tangent to the Rail - To insure that guide rollers aren’t allowing the wheels totouch the spring plates(Remark: action is being repeated as needed)

Damaged Bogie Wheel replacement:

- Reduce sideways movement range of wheel

Action Items (2/4)

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Spring Plates retightening and readjustment:

- To insure proper tracking and to help keepingthe dome centered

(Remark: the dome needs tobe supported from the concreteground to work on the springplates )

Dome Height Adjustment:

- To re-center the guide roller’s lip in the middle of the rail groove- On the non-drive wheels: by raising the wheel height using the stud shaft adjustment nut - On the drive wheels: since the drive wheels can’t be raised any further due to their bull gear, by placing shims under their spring plate and replacing the guide rollers with newly designed ones (lowered lip)

Action Items (3/4)

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Dome Drive Motors Upgrade:

- 2x more torque and across full speed range(Cont. Stall Torque: 10 ft-lb / Peak Torque: 31 ft-lb.) - Improved Control Strategy: speed based control with anti torque runaway function instead of torque based.

Action Items (4/4)

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Rail Resurfacing: (Remark: Cold flown rail debris buildup was already grinded down)

- Rail tracking improvement- Elimination of the dips (constant rail height) In-situ machining needed. Required a special custom setup. A Request for Proposal was written and several vendors were identified. A local machine shop was chosen for the contract. Very long and complicated process which took over a year.

Dome Drive Improvements: Rail ResurfacingSetup:

Grinder

Motor

Attachment to Dome

Station Pier

Hydraulic System to adjust grinder height

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After 1st

Roughing Pass

After 0.19” of Material Removed. Most of the rail was cleaned up.

Worst/Last spot after 0.23” of Material Removed.

Finish Pass Quality

Worst/Last spot after 0.247” of Material Removed.

Dome Drive Improvements: Rail Resurfacing

Dome Drive Improvements: Rail Resurfacing

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Servo Motor Currents BEFORE resurfacing:

• Servo Motor Currents AFTER resurfacing:

AMP

AMP

AMP

AMP

(Histogram showing the current distribution)

• Rail Resurfacing reduced the needed current by about 50%• Most of the current values are now under 11.4 amps, well within the

rated current for the motors.

MULTIPLE INSTRUMENT MOUNT (MIM)

In preparation to adding a new instrument (ISHELL) to the facility, we needed to insure that the current structure could support it.

Quartus Engineering was selected with a RFP to perform a structural analysis of the MIM:

• Goal: ‐ verify that the addition of iSHELL can be supported by the existing

system. ‐ if calculated strengths are below safety margins, identify components

to be re‐enforced or re‐designed.

• Method: static, seismic and fatigue FEA analysis

MULTIPLE INSTRUMENT MOUNT (MIM) UPGRADE

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• Components that are explicitly modeled include:– Mirror Cell Plates (8X)– Interface Boxes w/ Shims (4X)– MIM Quadmount Weldment– North Rail Assembly– North Truck– Cabinet Support Weldments (4X)

• Components that are modeled as concentrated masses attached via rigid elements include:– West, South, and East Rail Assemblies and

Trucks– Coolracks Cabinets & Electronics (4X)– Coolracks Coolers (2X)– Instruments (4X)

Mirror Cell Plate

I/F Box

MIM Weldment

North Rail Assembly

North Truck

Cabinet Support

Weldment

Instrument iSHELL Instrument

Cooler

Cabinet and Electronics

MIM STRUCTURAL ANALYSIS

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MIM SEISMIC ANALYSIS: OVERVIEW Structure analyzed in 3 different orientations:

Zenith: DEC = 19° N; RA = 0° Horizon East: DEC = 19° N; RA = 60° E Horizon Southeast: DEC = ‐31° S; RA = 60° E

Seismic loads of 0.95G Horizontal and 1.14G Vertical are applied to the structure in each orientation: Load levels and directions calculated using ASME code

9 load cases total analyzed: 3 telescope orientations X 3 earthquake horizontal directions

Von Mises Stresses are recovered from shell elements

Forces are recovered from weld lines, fasteners, and truck wheels

Weld material strengths receive a knockdown factor of 0.6

Safety factors used for margin of safety calculations are defined in AISC: Safety factor of = 1.67 used for:

Material Von Mises yield Safety factor of = 2.0 used for:

Material Von Mises ultimate & bearing stress Weld tensile & shear stress Fastener stress (tensile yield, tensile ultimate, shear ultimate) Fastener gapping and slipping Truck wheel axial & radial loads

MIM SEISMIC ANALYSISMaterial Stress Summary

Conclusion: Mirror Cell Plates, Interface Boxes and Rail Support need to be re‐enforced

Rail was later verified as being hardened, so margin are actually positive. No change needed.

Fasteners size to be increased at the Interface Box / Shim junction.

MIM SEISMIC ANALYSISMaterial Stress Details (Negative Margins)

MIRROR CELL PLATE:

Min. Margin of Safety: ‐0.26 yield; ‐0.01 ultimate Max. Stress = 29.2 ksi (Horizon East) Occurs on upper interface to mirror cell around the top bolt

Bolted joint takes 6150 lb of shear load

Negative margins show in all 3 telescope orientations Always located around 3rd bolt on mirror cells

INTERFACE BOXES:• Min. Margin of Safety: ‐0.43 yield; ‐0.23 ultimate

– Max. Stress = 37.7 ksi (Horizon East)– Occurs on upper interface to mirror cell at junction of 3 welded plates

• Major load path for center bolt to MIM as well as outer bolt to shim

• Three negative margin locations exist in I/F boxes:– Welded plates 3‐way junction (37.7 ksi)

– Bolted joints to mirror cell (27 ksi) – Bolted joints to shim (37 ksi)

MIM SEISMIC ANALYSISMaterial Stress Details (Negative Margins)

RAIL SUPPORT ASSEMBLY:• Min. Margin of Safety: ‐0.48 yield; ‐0.30 ultimate

– Max. Stress = 41.3 ksi (Horizon East)– Occurs on rail mount aligned near center of truck– Peak stress is driven by bending in rail mount flange

• Negative margins show in all 3 telescope orientations

• Positive stress margins in all otherrail support assembly material

Bolt size = 3/8”-16• Max axial force = 7821 lb• Max shear force = 4012 lb

FASTENERS (Interface Box to Shim)

Negative gapping and stress margins exist in bolts from interface boxes to shims

Gapping margin = ‐0.41 Shear ultimate stress margin = ‐0.08 Tensile yield stress margin = ‐0.26 Tensile ultimate stress margin = ‐0.15

These smaller bolts react a large portion of the moment induced by the MIM

Wide rectangular pattern forces them to take more load than the central 3/4”‐10 bolt to the MIM

Structure analyzed in two telescope orientations Horizon Southeast: DEC = ‐31° S; RA = 60° E Horizon Northwest: DEC = 59° N; RA = 60°W

Fatigue load of 1G applied in the gravity direction

Fatigue analysis performed for 90,000 cycles (10 cycles/night, 300 nights/year, 30 year lifespan)

For steel components (including welds), AISC gives a variety of fatigue strengths based on the location of the material (bolted joint, welded joint, etc)

Stress ranges are determined for the maximum to minimum stresses that the structure sees as it moves from Horizon Southeast to Horizon Northwest orientation

Forces are recovered from weld lines and truck wheels

No safety factors are used for fatigue analysis as specified in AISC

Bolted joints will not fatigue as long as joint does not gap

MIM FATIGUE ANALYSIS: OVERVIEW

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MIM FATIGUE ANALYSIS Material Stress Summary

Same conclusion as for the Seismic Analysis.

Upgrades needed for the same components.

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MIM RE-ENFORCEMENT

‐ Increased Plates thickness‐ Increased weld filets width‐ Increased fasteners size‐ Added 4 side braces‐ All fasteners minimum Grade 8

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MIM RE-ENFORCEMENT WORK SCHEDULE• Re-design + Drawings • Fabrication • Preparation: Cable labeling, remove un-

scheduled instruments, …

Telescope Shutdown: OCT 19th – 29th 2015

• Preparation work: (4 days)- Remove Electronic cabinets, chillers, instrument- Lower MIM onto platform- Prep welding area- Protect Primary mirror

• Welding work: (4 days)- Cut-out old interface plates (x4)- Weld new interface plates (x4)

• Telescope Re-assembly: (3 days)

• Other parallel tasks:- Chillers Fans upgrade (6 days max)- SpeX work (8 days max)

Note: Contingency built-in within different TasksOct 30th = engineering = add’l day of contingency

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TELESCOPE BALANCING SYSTEM

Movable Counterweights

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Movable Counterweight locations

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Fixed Counterweights

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• Goal: - verify that the existing system can still be balanced after the addition of ISHELL- optimize the location and amount of the static counterweights- predict optimal location of the movable counterweights

• Method: - calculate sum of moments on the RA and DEC axis. Run theoretical balancing routine to find the smallest possible moments by moving the movable counterweights.

TELESCOPE BALANCING MODEL AND OPTIMIZATION TOOL

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1) Model Inputs: • Fixed values:

- Masses: calculated/estimated from CAD model or measured- Center of Gravity: calculated/estimated from CAD model

• Parameters:- Instruments CoG: stowed and operation- Movable Counterweight: range and orientation vector

• Existing balanced configurations:- to determine / estimate unknown weights- Allocate Dummy Weights to compensate for approximations

2) Model Outputs:• DEC and RA Moments (are they small enough to allow for stable telescope

tracking?)• Movable counterweights positions (and corresponding voltages)


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3) Model Calculations:

Moments are calculated for each component Assume movable CWs are centered

DEC axis moments Zenith pointing

M = W*y

90° South pointing M = W*z

RA axis moments Zenith pointing

M = W*x

19° South, 90° East pointing (DEC and RA axes are perpendicular to each other) For components on CS: M = W*(z+7.992) For components on YK: M = W*(‐y*sin(19°)+z*cos(19°)+7.992)

Sum moments for each axis in both orientations (4 moment sums total) DEC axis only sums components on CS RA axis sums components on CS and YK

Use movable counterweights to try and zero moment balances

M = moment [in*lb]W = weight [lb][x,y,z] = [x,y,z]-direction coordinate of CoG [in]


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4) Balancing steps:

Step 1: DEC 90° South Pointing (Tube Top/Bottom Balance)

Step 2: DEC Zenith Pointing (North/South Balance)

Step 3: RA 19° South, 90° East Pointing (Yoke Top/Bottom Balance)

Step 4: RA Zenith Pointing (East/West Balance)

Tube Vertical SW Tube Vertical NW Tube Vertical SE Tube Vertical NE

Tube Horizontal Bottom Tube Horizontal Top

Yoke Vertical W Yoke Vertical E

Yoke Horizontal Center Yoke Horizontal S Bottom Yoke Horizontal S Top

Calculate optimal position for the following Movable CounterweightCalculate optimal position for the following Movable Counterweight

Calculate optimal position for the following Movable Counterweight



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TELESCOPE BALANCING METHOD Model is missing too much data (weight, CoG) or estimates are too far off to

determinate the dummy weight accurately. Optimization of the static CW locations can still be done by “hand” For each instrument configuration, the movable CWs which are maxed out

indicate where the unbalance resides. (Yoke or Tube Top/Bottom, North/South, East/West)

Then, static CWs are added/removed to compensate. The telescope balancing procedure is run again to find new movable CWs

locations Repeat until none of the configurations have maxed out movable CWs. Model equations can be used to predict the amount of static CWs to be

added/removed.

NASA Infrared Telescope Facility Author: Morgan Bonnet ...

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