Digital/Analog Hybrid Magnetization of Magnetorheological Fluids for Expansion of Their Controllable Viscosity Range

This paper proposes a mechanism for controlling the viscosity of magnetorheological (MR) fluids from the viewpoint of expanding their controllable viscosity range. An MR fluid changes its viscosity according to the intensity of the applied external magnetic field. Electromagnets are generally used as the source of the applied external magnetic field. For applying the magnetic field effectively to an MR fluid, typical magnetic poles are made to form a pair of plates facing each other. To increase the intensity of the magnetic field, the distance between the magnetic poles must be small. However, from the viewpoint of expanding the controllable viscosity range, the distance must be large in order to reduce the fluid viscosity resistance of the nonmagnetized MR fluid. This study develops a new magnetizing device that can cope with these two conflicting requirements. This device uses a combination of the digital/analog magnetizing method and a modified pulse code modulation. The evaluation of the control performance of the MR fluid´s viscosity by the proposed device is reported, which confirms that this magnetizing device can continuously control the MR fluid´s viscosity and is very effective in expanding its controllable range.