# Presentation: 775475

## Pixel Support tube Supports

**October 17, 2001**
**E Anderssen, LBNL**

## Interface to SCT Interlink

**Pixel Support Tube is supported by Interface Blocks which are mounted to the SCT**
**All Interface Blocks have identical interface to SCT**
- Need to define interface holes, but in principle agreed
- Brief modification of the end of the interlink to accommodate
**Mounting Pixel Support Tube Should be independent of SCT mount hardware**

## SCT to Interlink Interface

**Absolute accuracy of Holes in SCT Barrel 3 is 20******
**Implies that the twist in the free state is limited to 20******
**Pixel Support Tube will be of same order, but hesitate to claim better than 75******

## Mount Scheme Goals

**Benefit from the stiffness of the SCT across the Diameter, but minimize extraneous loads:**
**Minimize loads induced due to misalignment of mount features**
- Each mount is potentially constrained in 6-Degrees of Freedom
- Use pins to locate but let bolts float until all pins are aligned
**Minimize Internal load on SCT/Pixel**
- CTE mis-match of very stiff objects leads to potentially high forces
- Use of Flexures to minimize induced tension in the SCT.
**Minimize External Load on ID Barrel**
- Mis-match of Cryostat and Support tube yields potentially high strains
- Use of larger flexures at Forward End Support to minimize load

## Support Condition of Pixel Support Tube

- SCT

- TRT

- Support condition of Pixel Support Tube intends to couple in stiffness across diameter

- Fixed XYZ

- Fixed YZ (N/A)

- Fixed XY

- Fixed Y

- _ID Vee Rail_
- (float Z/dogged Z)
- (constrained XY)

- _ID Flat Rail_
- (float XZ)
- (constrained Y)

- +Z

- +X

- _Side C_

- _Side A_

- +Y Vertical

- _SCT Vee Rail_
- (float Z/dogged Z)
- (constrained XY)

- _SCT Flat Rail_
- (float XZ)
- (constrained Y)

- View from top—all
- Tube Supports are
- Horizontal and Co-planar

- Properties TBD

- Constraint TBD

## How Much Float is needed

**Fixed Point to End of SCT yields an internal stress**
- Due to CTE mismatch on the order of 1-2ppm/C
- It is likely near Zero
**Fixed point to end of Cryostat yields an External load on the ID Barrel via the SCT**
- There is potentially a large CTE mismatch between Cryostat and the Pixel Support Tube
- Case where Cryostat raised 10C above no-power condition, and where Support tube CTE is unusually high (>1ppm/C)
**Flexures need to assure minimal loads at these extensions yet remain stiff in the orthogonal directions**

- fixed

- 1.6m
- ___120___

- 4.25m @ +1ppm/C

- 2.65m @ +1ppm/C

- 4.25m @ +23ppm/C
- ___1.2mm_

- 2.65m @ +23ppm/C
-  700

- -20C

- -20C

- +30C

## Analysis of Mounts

**Several Criteria were used to assess the acceptability of mount designs—in this order**
- Fits in Envelope/Vertical Displacement (equal in standing)
- Flexure Force at expected Travel/Peak Stress
- Overall mass
**Designs were iterated until all criteria were acceptable**
- Deflections on order of those anticipated for structures (meaning do not detract from frequency appreciably)
- Flexure Stiffnesses were reduced to provide loads under half that estimated for a friction/sliding coupling
**With more space, vertical deflection can be reduced as can the flexure force**
- Case in point—Forward end support Flexure as compared to Barrel support Flexure

## Supports Fixed or Float in Z

- Pixel Support tube

- SCT Barrel Interlinks

- SCT Interlink to barrel interface

- Z Flexure

- Pixel Support Tube interface

- Inside bore of SCT Barrel

- Can rotate parallel to mount face of Z-flexure, but rotation and vertical travel of Z-flexure are coupled
**Rotate mount orientation on Z-flexure to accommodate this**

## Floating Mount Design Study

- Torsion

- Bending
- & Shear

- Lever Arm

- 50g

- 85g

- 108g80g (target)

- Initial Concept
- Low Mass
- Only preliminary sizing

- Rotation of Mount Feature
- Realistic Sizing
- Developed Figures of Merit

_**Final Concept**_
- Acceptable Deflection
- Acceptable Flex Force
- Need to Optimize Mass

- Increased Inertias, Rotated Mounts

- Flex Force

- _Figures of Merit_

- Acceptable Force and Deflection

## Motivation for Changes

- Deflection is primarily Torsion about mount section—want to reduce Lever-arm and increase Sectional Inertia

- All of these are Free deflections, real constraints restrict some of these motions yielding 30-50% reductions in deflections

## Barrel Flexure Final Concept

- High local/
- Low average
- STRESS

- Results	50N force at full potential travel (115)
- 	Highest Stress <35% Yield Ti6Al4V
- 	14.5 Vertical Deflection relative to SCT

## Thin Flexure armatures

- Yields same deflection and stiffness—lower peak stress
- But—higher vertical deflection ~factor 2

## Half width Flexure

- Flexure width is 6mm (half of the other)  Z-stiffness cut in half
- Vertical deflection increases by ~50%

## Narrow Flexure, Big Gap

- Extending the support arm increases the flexure vertical
- Deflection negligibly

## Forward Flexure Final Concept

- Results	37.5N load at full 1.24mm travel (this is an external load)
- 	Stress is high-ish in the 65% yield range—not worrisome
- 	Vertical displacement limited to 5
- 	It is unclear if 1.2mm is needed, but flexure length is easily
- 	modified

- 80

## Comparison of Performance to Req.

**Fixed Support**
- Small rotation—less than 10mmN moment
- Vertical Deflection less than 5
**Barrel Z Flexure**
- Full Z-Travel of 120—force less than 50N
- Vertical Deflection of 14.5
- Would like to reduce both if practical
**Forward End Support**
- Full Z-Travel on Side A of 1200—force less than 38N (31.25N/mm)—external force on ID Barrel
- Vertical deflection of less than 5
**Internal Tension Load on SCT in Z of up to 100N (two flexures)**
- Requires Full Temperature excursion of –40C is seen and 2ppm/C CTE mis-match
- Compared with 30Kg mass load, 2X preload on contact and friction coefficient of 0.3 (30X9.81X2X.3)=175N Stiction load
**Potential External Z Load on ID Barrel of 30N**
- Side A strain is large, but partially cancelled by Side C which is shorter
- Side A=(2X37.5N) Side C=-(2X22.5)
- Requires Both 10C raise in Cryostat Temp (+1mm) and positive 1ppm/C support Tube @ negative 20C (anything less is smaller strain)

## Flange Envelope

- Pixel Support Tube (Barrel Region)

- Pixel Support Tube (forward)

- 240

- 261

- 242

- 260

**Dimensions**** from 1:1 ID Layout May ‘01**

- 775**780**

- 765

- 785**792**

- 796**800**

- 795**799**

- 245**246**

- 257**259.5**

- 248

- 811

- 251

- May change
- By ~5mm to
- 806new structure added

- 700

- SCT BARREL 3

- Barrel Mount Flange

- Interlink

- SCT Forward Envelope

- 806

- requested
- Changes

- 244

## Flange Envelope

- Pixel Support Tube (Barrel Region)

- Pixel Support Tube (forward)

- 240

- 261

- 242

- 260

**New Proposed Envelopes—not yet agreed**

- 780

- 765

- 792

- 800

- 799

- 252

- 811

- 251

- 700

- SCT BARREL 3

- Barrel Mount Flange

- Interlink

- SCT Forward Envelope

- 806

- 244

- shim

- shim

- 255

- 254

- 246

## Z-Flexure (Side A)

- Support Tube Mount Pad M55J

- View
- Direction

- Cut Plane

- Insulator (G10) or Al203

- Access hole
- Thru
- Service Rail

- Gap filled
- After
- picture

- Dowel pins have line fit

- Metal Insert Bonded in

- Thermal Barrier squeezed in here

## Flexure Mount Access Hole