Tape-Spring Rolling Hinges

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Tape-Spring Rolling Hinges

• Alan M. Watt

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Outline of Talk

• Why build new hinges.
• What is a tape-spring rolling hinge.
• Previous designs.
• Conceptual design.
• Stiffness of hinge.
• Moment - rotation properties.
• Damping.
• Wire Effects.
• Applications of hinges.

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Why build new hinges
Present designs rely on motors or complex hinge
assemblies to drive mechanisms.

• Heavy.
• Stiff (large, heavy) support frames required.
• Unreliable

• Complex.
• Require power.

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What is a Tape-Spring Rolling Hinge

• Benefits of tape-springs
• Deployment moment.
• Locking moment.
• Very light weight and simple.
• Good pointing accuracy.
• Problem
• - No constraint when undeployed.

Two arrangements of tape-springs.

• Benefits of rolling hinges
• Very low friction (rolling contact only).
• No lubrication required.
• Constrained deployment.

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Aerospatiale Adele Hinge

• Very complex.
• Wide.
• Locking mechanism required.
• Complex band tightening mechanism.
• Heavy 1.1 kG

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Astro / JPL Nasa Hinge

• Simpler than Aerospatiale hinge.
• Tightening mechanism simpler.
• Still very wide.
• Small locking moment, as tape-springs almost
  co-planar.

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Hinge Design Parameters
Rradius of curvature of tape-spring
Assuming standard tape-springs, there are four
variable parameters

• S spacing
• d offset

• r radius
• L - Length

Three main constraints

• S-d lt r
• d gt s/2

• L gt 2pR

Can lead to hinge that operates in one direction
only.
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Calculation of Mmax
Considering Local buckling at point 2.
Stress in eccentrically loaded strut shell
buckling stress.
Comparison to FE Calculation
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Deployed Stiffness of Hinge
Deployed stiffness required for natural frequency
analysis and dynamic simulations.
Generally require high deployed stiffness and low
stowed stiffness.

• 3 linear stiffnesses
• Extensional, in-plane shear (Y), out of plane
  shear (Z).
• 3 torsional stiffnesses
• Torsional, in-plane bending (about Z), out of
  plane bending (about Y).
• Each can be found for tape or rolling hinge on
  their own as well as the combination.

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Extensional Stiffness of Tape-Spring

• Dead band caused by play in test set-up now
  fixed although no results.
• Predictions made using FE and beam models. Poor
  correlation between prediction and experiment. 10
  kN/mm to 3 kN/mm respectively.

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Extensional Stiffness of Rolling Hinge
Stiffness predicted using FE model made in
Pro/Mechanica with 2940 tetra elements and
contact surface at join of hinge.
Analysis is only true as long as wires are kept
under sufficient tension to maintain compressive
contact.
Stiffness results compare reasonably with
practical results 1530 N/mm 1040 N/mm.
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Extensional Stiffness of Rolling Hinge (cntd)
For faster analysis equivalent bar model using
hertzian contact theory was developed.
Hertz theory gives approach (d) of bodies as
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Shear Stiffnesses
Out-of-Plane hinge stiffness
Predictions found from finite element analysis
and beam bending theory. Good match found for
rolling hinge part of hinge but tape-spring
results high.
Stiffness predominantly arises from tape-spring
for out-of-plane direction and rolling hinge for
in-plane direction.
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Torsional Stiffness
Experimental measurements taken with FSH testing
machine with rotating head.
Experiments matched predictions reasonably well.
Rolling hinge and tape both contribute to
stiffness.
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Bending Stiffnesses
Predictions found from FE analysis and beam
theory. Poor match between predictions and
experimental results.
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Summary of Results
Practical Results Practical Results Practical Results Predictions Predictions Predictions
Direction Tape Rolamite Total Tape Rolamite Total Units
Kxx 3660 1530 4414 10363 1040 11402 N/mm
Kyy 200 31.9 216 425 40 465 N/mm
Kzz 9.66 115 134 23 160 183 N/mm
Txx 29 40 75 31 70 101 kNmm/rad
Tyy 114 0 240 426 0 900 kNmm/rad
Tzz 102 86 210 451 735 1186 kNmm/rad
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Moment - Rotation Properties

• Manual data capture.
• Hard to capture peak moment.
• Results match FE model well.
• Redesign of hinge based on data.
• New automated set-up to be used to obtain peak
  moment and test hinges of different sizes.

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Damping

• Two types of Damping
• During deployment, to slow the hinge deployment
  time.
• At locking, to lower shock transmitted to
  structure and prevent re-buckling of tape-springs.

A number of damping schemes were considered.
There are few that apply true damping without
adding greatly to the complexity of the hinge.
Constrained layer damping added to tape-springs.
Aluminium layer with damping material underneath.
Preliminary tests suggest that constrained layer
damping is relatively ineffective and that there
is a large amount of natural damping in the hinge
at locking.
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Analysis of Wire Effects
For a given configuration, a straight section of
wire tangentially links two points on either side
of the hinge. From this the position of the wire
can be found for any hinge configuration.
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Analysis of Wire Effects (cntd)
Moment - rotation can be found from a number of
analytical methods

• Virtual WorkMqFe
• M2F(L2-L1)
• MRd

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Tensioning Hinge
A set-up such as this, with the wire transferring
from a large radius to a small one provides a
moment (due to tensioning of wires) proportional
to rotation.
Can be applied to current hinge design simply by
cutting some of the grooves deeper than others,
to increase the moment provided by the hinge.
Moment is still proportional to rotation and work
is ongoing to find layout to give near linear
moment.
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Dynamic Modelling

• Model made for Pro/Mechanica simulation of
  deployments.
• Hinge acts as two pin joints separated by a
  constant distance.
• Joint angles forced to be equal or gear pair
  added.

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Dynamic Modelling (Cntd)
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Applications of New Hinges

• Deployable solar panels with cold mirrors for
  QinetiQ (formerly DERA).
• Deployable Synthetic Aperture Radar for QinetiQ.
• Deployable Synthetic Aperture Radar for Astrium
  (formerly Matra Marconi Space).
• Deployable Radiator for Astrium.