Page 136 - Servo Motors and Industrial Control Theory -

Chapter 8
Actuators Based on Electro-Rheological Fluid

8.1 Introduction

Electro-Rheological (ER) fluids are special fluids made of base hydraulic fluids
with chargeable particles suspended in the fluids. The important properties of ER
fluid is that when it is put between two plates with gap h (typical of less than 1 mm)
and a voltage is applied on the two plates, the fluid becomes stiffer with shear stress
2
of typical 2 kN/m has been reported. This is shown in Fig. 8.1. The range of the
applied voltage is 4 kV/mm. The current drawn is very small and it is the range of
a few milliamps.
When the gap is filled with ER fluid, and the voltage is applied on the plates, the
fluid becomes stiff and the plate subjected to force F, a resistance is observed. The
amount of resistance is the function of gap sizes and the applied voltage and the type
of ER fluid is used. There are several types of ER fluid available in the market with
different values of maximum shear stress for a given gap and applied voltage. The
voltage cannot be increased very large because there may be spark flashing through
the gap. The maximum force applied to the plates depends on the gap size and the
fluid. It has been shown that the voltage does not change the fluid viscosity but the
particles suspended in the fluid forms a chain that prevents the fluid from flowing.
In this form, ER fluid has many potential applications such as valves, clutches, and
variable dampers. At present because of sensitivity to temperature and low overall
yield stress have limited its application to only laboratory test equipments. Some
practical applications may emerge in the near future. This chapter provides up to
date information about the characteristic behavior of ER fluid in shear and valve
modes. The author has been involved in both processing the data from flow and
shear modes of experimentation. The information provided in this chapter is the
result of identification technique and data processing technique. The technique used
will be described briefly but only the results are presented in this chapter.

R. Firoozian, Servo Motors and Industrial Control Theory, Mechanical Engineering Series, 131
DOI 10.1007/978-3-319-07275-3_8, © Springer International Publishing Switzerland 2014