Pixel Detector Supports

1
Pixel Detector Supports

• T Loew, N Hartman, E Anderssen
• ID Engineering, Session 4
• October, 2001

2
Requirements Goals
3
Partial Concepts List

• Rolling, sliding or toothed elements.
• Linear, torsion and other springs in diverse
  configurations.
• Torsion and bending elements as springs
  themselves.
• Rollers and ramps with either positive or
  negative V grooved features.
• Dual stacked rollers either self contacting or
  separate.
• Roller with housing that initiates sliding
  contact with an overhead spring.
• Stationary PST-mounted supports that catch and
  hold frame on linear slides.
• Long screwdriver-type tool to set/release preload
  condition.

4
Preload Beam/Roller Schematic
Beam spring achieves 75N preload with less than
1Nm moment transfer to the Pixel Frame.
An applied force of 75N deflects the beam tip
2.5mm
Pixel Frame
PST
Ø7mm axle fits within space envelope and
satisfies overall deflection criteria
5
Rollers and Preload Beam Operation
Preload Beam Roller
Load Bearing Roller
6
Pixel Support Locations
7
Support Constraints Locations
Fixed Y
Fixed X,Y
z
Fixed X,Y,Z
Fixed Y
x
y
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PST Support Envelope
Support Dimensions
Envelope Requirement
Fit Within Requirement
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PST Support Upper Profile Development
Movement of load bearing and preloading rollers
along lower ramp contour defines centerline
trajectory and neutral path of upper contour.
Neutral path boundary along which no preload
force is generated.
Centerlines
Lower ramp contour
Deviation from this path governs the
correlation between the magnitude of preload
and axial position within PST.
10
Dimensioned Path
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Insertion and Preload Forces

• Insertion force due to services and rail sliding
  friction is a constant 130 N from insertion until
  the frame meets the supports. There is no
  preload in this region.
• Fi 130 N
• P 0 N
• If z represents axial position in mm starting
  at the first contact with supports, then
  insertion and preload forces are predicted to be
  as follows
• Fi(z) 0.5z 90.1 N
• P(z) 5.0z N

0 lt z lt 20
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PST Supports Deflection

• Deflections due to Bending and Shear

75N
75N


11.1 µm
53.2mm
5.8 µm
5.3 µm
This conservative first order determination is
already larger than the 10 µm total budget
allows, but it is of the right order of
magnitude and will shrink by about half with
reduced span length.
13
Axle Strength Stiffness
Back to back angular contact bearings.
75N
75N
For Ø7mm Ti axle with 10mm bearing spacing, end
deflection can be limited to 3µm.
14
Axle Strength Stiffness
Maximum moment of 1.1Nm on Ø7mm Ti axle
s M?/I
smax 314 MPa

• For the titanium alloy Ti6Al4V, a safety
  factor gt 2 can be
• achieved against yield onset.
• Due to the nature of the requirements, the
  axles
• frequency response (stiffness) drives the
• design instead of strength.