Page 146 - Servo Motors and Industrial Control Theory -

8.5 Conclusion 141

1200 1.8
voltage V
1000 1.5

800 t m * 1.2
Voltage (v) 600 T e torque 0.9 Torque (Nm)

400 T Σ 0.6

200 T oF 0.3

0 0
95 100 105 110 115 120
Time (ms)
Fig. 8.17 Torque response from step input of voltage extracted from the data collected from the
torque transducer

known dynamic characteristic was used. The data from this torque transducer was
then processed to extract the torque response. The data processing technique will
not be explained here since it is beyond the scope of this book and only the result
will be presented here. The torque transducer data processed for step input of volt-
age is shown in Fig. 8.17.
It can be seen that the response is similar to that of pressure in flow mode. There
is a slight transport lag and then a sudden rise of torque. It seems that the second or-
der characteristic of ER fluid is also present in the torque response. There is low fre-
quency oscillation that as of yet has not explained. This is probably due to the static
friction. This is because the particle chains continuously are broken and repeatedly
are formed and broken. The ER fluid in shear mode obeys the law of plastic flow
and, therefore, this oscillation is not present.
However, there is room for research to investigate the properties the properties
of ER fluid in both shear and flow mode.

8.5 Conclusion

In this chapter, some properties of ER fluids were discussed and some obvious ap-
plications of ER fluid were presented. By knowing the maximum yield stress, vari-
ous ER devices can be designed. Some ER fluids are available in the market with
different yield stress capability. There is an intensive ongoing research to develop
ER fluids with higher yield stress capability. The interested reader should visit pub-
lications on various properties of ER fluids.