Biomedical Engineering Reference
In-Depth Information
The notation
D
is the overall diffusion coefficient of ions within PAN fibers.
The implication of the preceding equation is that the contraction or elongation
kinetics must be faster than that which we had observed in this study. In fact, a
proper approximation of physical properties provides a time constant of
L
/
L
5%/sec
or less for both contraction and elongation. Therefore, it was decided to change the
activation scheme into a much more compact form. One successful way was to deal
with individual fibers rather than strands made with 2,000 fibers.
≈
4.6.10.4
PAN Actuator System Design and Fabrication
Figure 4.88 shows the newly fabricated PAN actuator system. The new linear contractile
PAN actuator system consisted of a much more flexible electrochemical cell membrane
electrode (bellows-type rubber boots) than that of the previous system. In this new
configuration, a softer membrane (rubber boots) than that of the previous system was
also adopted. As a result, the spring constant of these bellows-type rubber boots includ-
ing the electrode was measured at
k
s
= 0.01 kgf/mm and turned out to be 0.004 kgf/mm
less than the previously fabricated system. The PAN fiber length was also changed from
115 to 145 mm (a 26% increase). Detailed dimensions are provided in figure 4.88.
In order to address the problem associated with the erosion and corrosion of the
electrode (on the anode side), an erosion/corrosion-resistive beryllium copper springs
(Small Parts Inc.) and a wire diameter of 0.0508 in. (1.29 mm) were chosen to serve
as the anode that was also gold-plated (fig. 4.89). By doing this, it was anticipated
that the electrodes would have long-term operation even under the action of elec-
trochemical reactions caused by the imposed electric field. The operating voltage
was lowered from 10 to 5 V so as to prevent the quick temperature rise of the
solution. The initial testing proceeded for 27 min and produced a 5-mm displacement
(producing 50 gf) (fig. 4.90). It was noted that even after 27 min, the PAN muscle
∅
38 mm
FIGURE 4.88
Previous (left) and new (right) PAN actuating systems.
