Shape
Memory Alloy Based Micro/Meso Manipulator (mMM)
(NSF)
The
push toward miniaturization and the emerging trends toward the
development of microfactories of the future necessitate the availability
of reliable, robust and accurate micro/meso-scale manipulators. These
are devices that are capable of manipulating micro/meso-scale objects
(from several microns to several millimeters) that are, at the same
time, of commensurate dimensions. Hitherto, the major problem was to
develop a manipulator with a high force output, minimum degradation in
repeatability and high positioning accuracy for the realization of
microfactories and in support of the rapidly emerging field of nano/micro-manufacturing.
The
underlying hypothesis in this project is that the above-mentioned needs
might be plausibly met by a Shape Memory Alloy (SMA) based 3-DOF
micro/meso-manipulator (mMM) that integrates structural, actuation and
sensing functions in a single monolithic component. The realization of
this concept necessities the consideration of four (4) distinct
problems: (1) development of Selective Laser Sintering (SLS) and Direct
Material Deposition (DMD) rapid prototyping technology based processes
for the cost-effective manufacture of the monolithic mMMs, (2) SMA
property characterization as a function of the manufacturing process,
(3) theoretical and experimental investigation of the self-sensing
concept, (4) formulation of control algorithms, and (5) the mathematical
modeling of the system’s behavior.
Theoretical
modeling and experimental verification of the feasibility and
manufacturability of our preliminary designs by DMD have been completed.
Work in progress is focused on model verification experiments for
exploring position control and integral position feedback (self-sensing)
concepts by using mid-point positioning of connected SMA accordion-type
springs shown below.
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| Conceptual design of an mMM
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Individual actuators manufactured
by
DMD from NiTi powder
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Actuator
made from a DMD deposited ingot by EDM
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Video
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Differential
Scanning Calorimetry (DSC) of the annealed NiTi accordion spring showing
the phase transformation temperatures (TTRs)
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The
property of SMAs to change their electrical resistance when heated is
used to control the motion of the SMA based actuators. The use of the
electrical resistance as the feedback control signal for motion control
is referred to as the “self-sensing” principle.
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(a)
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(b)
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Experimentally
obtained characteristics confirming the feasibility of the
“self-sensing” method: (a) sensitivity of the method, (b) resolution
of the method
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A
1-DOF experimental setup is being used to verify the feasibility of an
agonistic-antagonistic human-muscle like controller being developed for
the mMM. The controller is partly based on a newly formulated kinetic
transformation model of the SMA actuators of the mMM.
