[Univ of Cambridge] [Dept of Engineering]

 Deployable structures with self-locking hinges

Alan M Watt


This dissertation considers the design of hinges for rigid body hinged deployable structures for small satellites.

A review of current deployable structures, the features required of hinges within them and the ability of current hinge designs to meet these requirements is made.  Hinges based on tape-springs (curved elastic strips as found in tape-measures) are found to be the most suitable as they are lightweight, simple to manufacture, low-friction, self-locking, self-deploying and give good latching accuracy.

Analytical predictions of the end-moments required to buckle an offset tape-spring hinge with two or more tape-springs are made. These are then compared to finite element predictions and experimental results.

Tape-spring Rolamite hinges, which include a Rolamite hinge connected to a tape-spring hinge, offer the same advantages as tape-spring hinges whilst improving the unlatched stiffness of the tape-spring hinge and giving a definite kinematic opening path. These improvements simplify the modelling of the dynamics and ground-based testing of any deployable structure made from the hinges. A new design of tape-spring Rolamite hinge is presented, which incorporates wires rather than bands, and weighs less than a tenth of previous designs. Analyses of the deployment moment, buckling moment and
stiffness are made and then compared to experimental tests.

The deployment dynamics of a two panel system with one moving panel connected by tape-spring Rolamite hinges are investigated. When the effects of air resistance and the elasticity of the panels were taken into account, the rigid-body dynamic model showed good agreement with results
measured from experimental tests. A review of damping methods used in deployable structures and their applicability to structures with tape-spring Rolamite hinges is presented. The effectiveness of some of these damping methods in controlling the deployment rate and latching shock is tested.

The design and manufacture of a conical tape-spring Rolamite hinge is presented. This hinge uses conical rolling surfaces in place of the cylindrical surfaces
commonly used in rolamite hinges. Such a hinge functions as two hinge lines held at a constant angle to each other with the rotations of each hinge line constrained to be equal.  Initial analytical design guidelines and the integration of finite element models of tape-springs and three-dimensional computer aided design are used to overcome the issues raised by the complex folding geometry of the tape-springs in such a hinge. Rapid prototyping is used
to create the complex geometry of the hinge.

Finally, a number of deployable structures which include hinges based on tape-springs are analysed, built and tested. Close attention is paid to the analysis of the number of mechanisms present within these structures.


[Cambridge University | CUED | Structures Group | Geotechnical Group]

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