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

Because a direct-drive (DD) motor system does not use a reduction gear unit, the drive system can be made constructively simple and stiff. However, the disturbance torque directly influences the motor shaft. High gain feedback control is effective for reducing the influence of the disturbance torque. The high servo gain makes the control system vibratory or unstable. Therefore, the servo gain must be low for stability, and the influence of the disturbance become large. In this study, the DD motor system using an electrorheological (ER) fluid damper is discussed. By applying the ER damper to the DD motor system, the gain margin of the system becomes large and the servo gain can become high. Finally, it is shown that the proposed DD motor system is effective in improving the servo gain