Page 145 - Servo Motors and Industrial Control Theory

140 8 Actuators Based on Electro-Rheological Fluid

40

t **
e
30

Current, i (mA) 20

10

t **
e
0
0 1 2 3
Time, t (ms)
Fig. 8.16 Step input response of the current for ER fluid in shear mode

ship is nonlinear and rotating speed has little influence on this characteristic. It
should be noted that the driven side was kept stationary in this experiment. There-
fore, it can be concluded that the nonlinear resistance also applies in shear mode.
The values of R may be different from that of identified from the ER fluid in flow
mode. This can be set as a project to investigate.
The other interesting property is the transient current response of ER fluid to a
sudden step change in voltage. This is shown in Fig. 8.16. It can be seen that the
current rises rapidly to a large value and then decays exponentially to its steady state
values. The time delay shown by t e is so small that it can be ignored and may be
*
due to instrumentations error. The current response shows that there is a charging
phenomenon. Therefore, the electrical model identified for ER fluid in flow made is
valid for ER fluid in shear mode. The values of R and C may be different to that of
the ER fluid in flow made. This subject has not yet been studied in detail. This can
be set as a PhD project. For this, the sinusoidal excitation superimposed on various
base voltages must be used. At each frequency by knowing the amplitude of current
and voltage and phase angle, the values of R and C may be identified. Or alterna-
tively the identification technique may be used to identify more accurate values of
R and C for the ER fluid in shear mode. The values of R and C cannot be identified
from step input of voltage response because their values are function of voltage.
The nonlinear characteristic, that is, the undershoot in the current response can be
explained by nonlinear model for R and C. This behavior has been investigated by
the author and it shows that nonlinear behavior explains the undershoot of the cur-
rent response. The interested readers are referred to paper publications.
The next interesting phenomena are the response of torque to a step input of volt-
age. The high speed torque transducer was unavailable and a torque transducer with