Biomedical Engineering Reference
In-Depth Information
'
simset
' function. The simulation is performed using a fixed-step fifth-order method to
100 seconds.
When the simulation is completed, the variables and
t
out
,
x
out
and
y
out
are now in the
current workspace (that is, the workspace of '
tracklsq
'). The '
Outport
' block in the block
diagram model puts
y
out
into the current workspace at the end of the simulation. When
you run '
runtracklsq
', the optimization gives the solution for the proportional, integral,
and derivative (
K
p
,
K
i
,and
K
d
) gains of the controller after 20 function evaluations as
K
p
0.9236,
K
i
= 0.1654, and
K
d
=
−
0.0095.
11.7 Processing Software
The processing software which was developed in the LabVIEW environment, receives the
feedback signals from an FSR and a linear potentiometer (Figure 11.16). After filtering
these signals and removing 60 Hz noise, the force (
F
) and shaft position (
X
r
) are calculated
in separate modules using relationships 11.3 and 11.4. Then the calculated force is used
to find the strain for the simulated material, which is saved in a lookup table (LUT).
After acquiring the dimensions of the material to be simulated, the stress is transformed
to compression displacement (
X
d
) and then the shaft position, and the desired compression
displacement (
X
r
and
X
d
), are fed to the PID controller. The output of the controller is
finally transmitted to the output.
Figure 11.17 shows these parameters, which are plotted in LabVIEW. The force, shaft
displacement, desired displacement, displacement error, and the output are sketched in real
time. Figure 11.18 shows the programming environment and block diagram of the system.
11.8 Experiments
The following materials and elastomers: A2 (
3
/
4
inch thick), EVA (
1
/
2
inch), ICF400
(1 inch), A2-FR (
3
/
4
inch), and B1 (
3
/
4
inch), and a hard material (Plexiglas), were
DAQ
input
60Hz
filter
Vs
,
V
+
Vr
,
V
+
Shaft position
measurement
Force
measurement
F
LUT
PID
controller
Xr
Xd
DAQ
output
Figure 11.16
The flowchart of the processing software
