ELFT HÍRADÓ

[Gyorgy Karolyi <karolyi AT tas.me.bme.hu>]

MEGHÍVÓ 

Greschik Gyula 

(Center for Aerospace Structures, Univ. of Colorado) 

The Marionette Paradigm -- the Ultimate in Passive Gravity Compensation 

2004. december 17. péntek, 12.30 óra

Az előadás helye:
BME Tartószerkezetek Mechanikája Tanszék

K épület magasföldszint 35, könyvtár

Az előadás tartalma:  
Proposed is a novel gravity compensation paradigm whereby virtually all
tribological imperfections (damping and stiffness interference with
specimen dynamics) of classic approaches are eliminated or minimized.  
In this concept, the specimen is suspended by a cascaded set of force
distribution elements (fly beams) integrated into a single hierarchy
(whiffle tree), suspended from one external location.  By virtue of
the application of a single (as opposed to multiple) external
supports, the specimen is subjected to a one dimensional mechanical
constraint.  Namely, the center of gravity (the ever-current geometric
location of the c.g. in the full ideal sense) is maintained
stationary in space.  This condition is equivalent to weightlessness
(full gravity compensation) with a fidelity (resolution) defined by
the geometry of the suspending system hierarchy.

This concept is in stark contrast to previous applications of whiffle
trees and fly beams in gravity compensation, wherein such elements
traditionally have secondary load distribution roles and the combined
specimen-offloading system is externally supported at more than one
location.  Such systems constrain the specimen kinematics in more than
one way (no rigid body rotation in space is typically permitted).  No
such constraints are imposed by the Marionette system, within the limits
of small to moderate displacements and rotations.  Further, the
Marionette system has no frictional components or elastically adaptive parts.
Accordingly, it imposes neither damping nor deleterious stiffness
on the specimen.  While inertial pollution (the flybeam hierarchy mass)
cannot be entirely eliminated, this effect is deterministic and can be
conveniently minimized.

With minimally affecting structural response, Marionette
suspension enables the direct testing even of structural damping and
of free vibration without prior knowledge of modal characteristics,
impossible with traditional means.

The concept can also conform to the extreme deploying geometry of even
complex space systems, at the cost of replacing (some) fly beams with
scissor elements.  While scissor elements are not friction-free (in
contrary to the rest of the system), their tribological pollution
(a) can be well minimized and (b) does not interfere with lateral
specimen kinematics.  A possible means to entirely eliminate scissor
element friction has also been conceptually identified.

The Marionette suspension scheme offers an effective yet
simple means to directly study deploying and deployed system
kinematics and dynamics (in the full imperfect context) for many
space structural systems.

The presentation discusses the concept and illustrates its
key features with hardware models.  The results of a design optimization
parametric study are also presented, enabling the rapid assessment of
system overhead and application scope.