Hasse A (2011)
Publication Language: English
Publication Type: Thesis
Publication year: 2011
Publisher: Eidgenössische Technische Hochschule ETH Zürich
City/Town: Zürich
In many technical problems, e.g. the shape adaptation of wings or rotor
blades, it is desired that the changing of the structure's shape is smooth in
order to operate as eciently as possible. Even where loads are not exactly
predictable, a defined shape is required. Nevertheless, the complexity of
the actuator system and of the mechanics should be as low as possible.
It is within this context that this thesis presents the concept and the
synthesis of compliant mechanisms with selective compliance.
In contrast to classical mechanisms, which realize their motion through
classical joints (e.g. bearings), compliant mechanisms use the deformability
of the material to produce a particular movement. They therefore
present several advantages, ranging from the absence of wear and
backlash, to lower noise levels, clean operation, easier maintenance and
reduced manufacturing eort. In addition, the deformation is not constrained
to the joint areas, as in the case of a classical mechanism, rather
it can be distributed continuously over the structure - this is advantageous
in terms of a smooth shape adaptation. However, the kinematic
behavior of compliant mechanisms is mostly load-dependent, i.e. a large
number of possible deformation patterns can be obtained by altering the
load acting on the system. This is not the case with classical mechanisms,
as they usually have a defined number of kinematic degrees of freedom.
The compliant mechanisms with selective compliance presented in this
thesis combine both of these advantages: their kinematics may include a
distributed deformation and they are virtually constrained to a defined
number of kinematic degrees of freedom.
The aim of this study is to develop an automated design method for
compliant mechanisms with selective compliance. In this context, the design
requirements are identified and classified. A design criterion based
on eigenvalues and eigenvectors is presented after a modal analysis of various
compliant structures. In order to be able to determine the compliant
mechanism by means of numerical structural optimization, a modal objective
function is introduced, the minimization of which leads to a structure
that meets the design criterion. The modal objective function is validated
by dierent design tasks. A force-inverter problem is taken from literature
and is subjected to the developed methods. In addition, structures
are presented which have complex kinematics, including smooth surface
deformations.
Since the dawn of aviation, engineers have tried to design shape adaptive
wings in order to improve the eciency of aircrafts at different flight
conditions. Concepts using conventional mechanics turned out to be too
heavy and too complex. The belt-rib concept is a new approach: the classical
ribs, which define the shape of the wing, are replaced by so-called
"belt ribs". These are compliant mechanisms with selective compliance,
consisting of an outer belt and an inner stiening structure, which are
virtually limited to one kinematic degree of freedom. The kinematics depicted
by a belt rib show a defined profile change. So far, the realizable
profile changes have been limited, due to the chosen inner stiening structure
and the synthesis methods available. With the findings of this thesis,
it is now possible to design belt ribs describing an arbitrary profile change.
In this thesis, an example of this is given in the form of a rib belt whose
profile can be adapted from a NACA 0012 to a NACA 2412.
APA:
Hasse, A. (2011). Synthesis of planar compliant mechanisms with selective compliance for shape adaptation (Dissertation).
MLA:
Hasse, Alexander. Synthesis of planar compliant mechanisms with selective compliance for shape adaptation. Dissertation, Zürich: Eidgenössische Technische Hochschule ETH Zürich, 2011.
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