Developing prosthetic artificial muscle actuator using dielectric elastomers
The loss of an upper limb can impair the ability to do even the simplest daily tasks. Robust prosthetic devices need to replicate the smooth movement, while maintaining the relatively high forces typical of the original limb. Dielectric elastomers (DEs) are potential candidates for actuating such...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2016
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/67069/1/FK%202016%20157IR.pdf |
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| Summary: | The loss of an upper limb can impair the ability to do even the simplest daily tasks.
Robust prosthetic devices need to replicate the smooth movement, while maintaining
the relatively high forces typical of the original limb. Dielectric elastomers (DEs) are
potential candidates for actuating such prosthetic devices, however, DE materials are
associated with material failure which limits their use as actuators. They also have been
reported to generate low output force. This has limited DEs from being used for
prosthetic devices that mainly require high output forces. This thesis proposes a
conceptual design for a prosthetic arm, where the actuator is the DE material arranged
in a suggested mechanism to generate high output force.
A two-bar mechanism was assumed to represent the human arm. The flexion action of
the elbow was achieved by a slider-crank mechanism connecting the two bars actuated
by DEs membranes. The DE actuator mechanism comprised of the arrangement of
1000 parallel planar linear DE membranes in parallel to maintain high output force and
reduce the tensile stress. An Analytic model was developed to analyze the output force
of the designed mechanism for a range of input electric fields. An electrical model was
developed to model electrodes resistance and DE membrane leakage current resistance.
Material and mechanism‟s dimensions and parameters were mathematically optimized
to produce the highest possible output force while maintaining the tensile stress and the
input electric field below material failure points. An open loop system was designed to
control the angular position of the arm. Mechanical and electrical power consumption
calculations were carried out and the efficiency of the actuator and major energy
dissipations were determined.
The actuator‟s generated force counteracts a compressive mechanical force of 97 N
which is higher than reported actuator designs for arm prosthetics and is comparable to
human muscle output force for arm flexion estimated between 40 N to 116 N. The
1000 DE membranes arrangement led to a reduction of the compressive stress over the
material to be (30 kPa) which is well below the break point of 690kPa. The stimulant
input electric field that is below the dielectric strength of the material which is
40MV/m. The critical input electric field at which electromechanical instability failure occurs has been increased by 2.05 times the critical input of voltage induced strain
only. A high input electric field of range of 31.287 MV/m to 33.837 MV/m, yet with a
power consumption of 248 mW per membrane is convenient for use in prosthetic
devices. The electromechanical efficiency is 55.7% and the loss is mainly due to
viscous energy dissipation and current leakage. The 1000 DE membrane arrangement
led to the generation of high output force with lower input electric fields and lower
stress over the material. Therefore, this actuator‟s design could be used as a prosthetic
arm actuator replacing conventional actuators provided that further steps of realization
are taken. |
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