MR fluid damper

This High Intelligence Prosthesis for the knee uses an MR fluid damper to provide motion that closely duplicates the naturai movement of the knee joint. 

An example of a simple valve-mode device is the RD-1005-3 linear damper by Lord Corporation shown in Fig. 6.77 [152]. As in the vast majority of all commercial MR fluid dampers, these dampers have an internal, axi-symmetric valve with an annular flow path. In this case the damper is a single-ended, mono-tube style having an internal rod volmne accumulator pressurized with nitrogen. As indicated in the Fig. 6.77, downward motion of the piston causes MR fluid to flow up through the annular flow channel. Application of current to the coil creates a magnetic field that interacts with the MR fluid in two regions where the magnetic flux crosses the flow channel. 

The range of force control that is possible with a valve-mode MR fluid damper is illustrated in Fig. 6.78. Here the force/velocity character that is typical of a passive hydraulic damper is compared to the range of forces possible with a MR damper. With appropriate control based on displacement, velocity or acceleration, any force profile between the upper and lower bounds can be realized. Unlike passive viscous dampers, with the MR damper it is easy to achieve large force at very low speed. 

Fig. 6.77. Basic MR fluid damper with axi-symmetric valve geometry Force...

Fig. 6.78. Controllable force range possible with MR fluid damper Direct-Shear Mode...

In another civil engineering application, MR fluid dampers have been used to mitigate potentially damaging wind-induced cable vibrations in a cable-... 

Fig. 6.89. MR fluid dampers used control wind-induced cable vibrations on Dong ting Lake cable-stayed bridge in central China...

Fig. 6.91. Above-knee prosthesis with real-time control provided MR fluid damper...

Fig. 6.93. Algorithm for controlling the MR fluid damper in the artiflcial knee...

Magnetorheological fluid production levels in 2005 are of the order of hundreds of metric tons per year (or tens of thousands of liters) such that commercial applications on several automotive platforms are supported. A factor of ten or more increase in volume over the next decade is anticipated. It is estimated that there are presently more than one hundred thousand MR dampers, shock absorbers, brakes and clutches in use worldwide. This number is expected to rise into the millions as more automotive platforms adopt smart MR fluid suspensions and clutch systems. 

Virtually all devices that use controllable MR fluids operate in a valvemode, direct-shear mode, or a combination of these two modes. Diagrams of the basic valve and direct-shear modes are shown in Fig. 6.76. Examples of valve-mode devices include dampers, and shock absorbers. Examples of direct shear-mode devices include clutches, brakes, chucking and locking devices, and some dampers. 

As a final example of a MR fluid controlled adaptronic system, the smart prosthesis knee developed by Biedermann Motech GmbH [178-181] is presented. This system shown in Fig. 6.91 is a complete artificial knee that automatically adapts and responds in real-time to changing conditions to provide the most natural gait possible for above-knee amputees. The heart of this system is a small magnetorheological fluid damper that is used to semi-actively control the motion of the knee based on inputs from a group... 

Numerous dampers have been developed to release seismic forces such as soft steel damper, friction damper, magneto-rheological (MR) damper, viscous fluid damper, etc. In this study, the relative mature viscous fluid damper is applied. The force of damper varying with the relative velocity can be formed as ... 

The discovery of both ER and MR fluids dates back to the late 1940s (Winslow 1947). ER fluid dampers have been developed, modeled, and tested for civil engineering applications (Erhrogott and Marsi 1992, 1993 Makris et al. 1995). Work on MR devices have been done by Spencer et al. (1997), Soong and Spencer (2002), Spencer and Nagarajaiah (2003), Carlson et al. (1995), and Dyke et al. (1996c-f). 

In semi-active control, the control actuator does not directly apply force to the structure (as in the case of active control), but instead it is used to control the properties of a passive energy (Fig. Id). Within the class of semi-active control, the use of controllable electrorheological (ER) and magnetorheological (MR) fluids in dampers has found ground in the recent years, with applications mostly on the stay cables of cable-stayed bridges. 

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