Tape-Spring Rolling Hinges
Alan M. Watt
Outline of Talk
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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.
Why build new hinges
Present designs rely on motors or complex hinge assemblies to drive
mechanisms.
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Heavy.
Stiff (large, heavy) support frames
required.
Unreliable
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Complex.
Require power.
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.
Aerospatiale “Adele” Hinge
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Very complex.
Wide.
Locking mechanism required.
Complex band tightening mechanism.
Heavy – 1.1 kG
Astro / JPL Nasa Hinge
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Simpler than Aerospatiale hinge.
Tightening mechanism simpler.
Still very wide.
Small locking moment, as tape-springs almost co-planar.
Hinge Design Parameters
R=radius of
curvature of
tape-spring
Assuming standard tape-springs, there are four variable parameters:
• S – spacing
• d – offset
Three main constraints:
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S-d < r
d > s/2
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r – radius
L - Length
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L > 2pR
Can lead to hinge that operates in one direction only.
Calculation of Mmax
Considering Local buckling at point 2.
Stress in eccentrically loaded strut = shell
buckling stress.
Solve for
and substitute into
Comparison to FE Calculation
Deployed Stiffness of Hinge
Deployed stiffness required for
natural frequency analysis and
dynamic simulations.
Generally require high deployed
stiffness and low stowed stiffness.
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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.
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.
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.
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:
with
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.
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.
Bending Stiffnesses
Predictions found from FE analysis and beam
theory. Poor match between predictions and
experimental results.
Summary of Results
Practical Results
Direction Tape Rolamite Total
Predictions
Tape
4414 10363
216
425
134
23
75
31
Rolamite
1040
40
160
70
Total
Units
Kxx
Kyy
Kzz
Txx
3660
200
9.66
29
1530
31.9
115
40
11402
N/mm
465
N/mm
183
N/mm
101 kNmm/rad
Tyy
114
0
240
426
0
900
kNmm/rad
Tzz
102
86
210
451
735
1186
kNmm/rad
Moment - Rotation Properties
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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.
Damping
Two types of Damping:
1)
During deployment, to slow the hinge deployment time.
2)
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.
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.
Analysis of Wire Effects (cntd)
Moment - rotation can be found
from a number of analytical
methods:
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Virtual Work–Mq=Fe
M=2F(L2-L1)
M=Rd
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.
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.
Dynamic Modelling (Cntd)
Applications of New Hinges
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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.