Biomedical Engineering Reference
In-Depth Information
system. Future efforts to model beam motion more accurately by modifying the
method used to model the forcing moment, by expanding the model to predict the
performance of beams of all dimensions, and by validating model performance
against actual beam motion were recommended
7.4.6
F
EEDBACK
C
ONTROL
IN
B
ENDING
R
ESPONSE
OF
IPMNC
A
CTUATORS
One of the disadvantages of ionic polymer materials is that their rather slow time
constant limits the actuation bandwidth. A feedback controller has been developed
by Mallavarapu and colleagues (Mallavarapu and Leo, 2001) in order to reduce the
open-loop response time of cantilevered actuators from 4 to 10 sec to closed-loop
response time from 0.1 to 1.5 sec using linear quadratic regulator (LQR) control.
Figure 7.32 shows an open-loop response for a 40-
0.2-mm IPMNC
actuator for an unsupported length of 30 mm. The inset in figure 7.29 shows the
resonant modes on closer observation of the open-loop step response. Figure 7.33
shows the control of a 10-
×
10-
×
0.2-mm IPMNC actuator polymer.
This section demonstrates the use of feedback control to overcome these reso-
nance modes. An empirical control model was developed after measuring the open
loop step response of a 40-
×
20-
×
0.2-mm IPMNC actuator in a cantilever config-
uration. A compensator was designed using a linear observer-estimator in state space.
The design objectives were to constrain the control voltage to less than 2 V and
minimize the settling time by using feedback control. The controller was designed
using LQR techniques, which reduced the number of design parameters to one
variable. This LQR parameter was varied and simulations were performed, which
reduced the settling time for the closed loop. The controller was later used in
experimentation to check simulations. Results obtained were consistent to a high
degree. The electromechanical impedance of five sample actuators was measured.
×
10-
×
Tip displacement for 10 mm
×
40 mm
×
0.2 mm
IPMC actuator
3500
3000
2500
2000
1500
1000
500
0
−
500
0
10
20
Time (sec)
30
40
FIGURE 7.32
Tip displacement of IPMNC actuator for 1 V.
