High stiffness control of direct-drive motor system by a homogeneous ER fluid

Since a direct-drive (DD) motor system does not have the reduction gear, its structure is simple and has stiffness. In the DD motor system, the disturbance torque directly influences the control accuracy. The high servo stiffness is effective and important for reducing the influence of the disturbance torque. However, the high servo control often makes the system vibratory or unstable. Therefore, the servo gain must be lowered for assuring stability, and the influence of the disturbance becomes serious. In this study, the DD motor system using an electro-rheological (ER) fluid damper is developed. By applying the ER damper to the DD motor system, the gain margin of the control system is improved, so it is possible to realize the high servo control. Finally, it is experimentally shown that the proposed system is effective for high-speed and high-precision control