Isokinetic Exercise Machine Using High Performance MR Fluid Brake and Iso-Contraction Exercise - Biomechatronics in Medicine and Healthcare - page 155

11.3 EXPERIMENTAL SETUP
11.3.1 MR Fluid Brake
Fluids whose properties vary with changes in external fields, called functional
fluids, include electrorheological (ER) fluid) (Kikuchi, 2003), whose apparent
viscosity changes in different electrical fields, and magnetorheological (MR) fluid
(Carlson, 2000), whose viscosity changes in different magnetic fields. ER and MR
fluid viscosity changes rapidly and reversibly, enabling application to clutches
requiring rapid, highly accurate torque control (Furusho, 1999; Takesue, 2004).
The basic MR fluid brake structure, as shown in Fig. 11.3 , involves MR fluid
filled around a rotating disc. MR fluid viscosity varies with the magnetic field
generated by the magnet coil, used as brake torque. Brake torque is rapidly
reversibly controlled by supplying electricity to the magnet coil.
We use an MR fluid brake in which the rotational input of an MR clutch is
fixed mechanically. Such an MR fluid brake with rapidly changing fluid viscosity
should also respond rapidly as brake torque: its response time constant — the
time until 63% of the constant is reached - is 3 to 5 milliseconds in both first and
last transitions (Kikuchi, 2006).
Figure. 11.4 s hows an experimental setup to determine the relationship
between torque of the MR brake, in which MRF-132DG (Lord Inc., US) is used,
Figure 11.3 Basic structure of MR Fluid Break.
Figure 11.4 Experimental setup for MR Fluid Break.