Fast Seek Servo Method Using Two-Degree-of-Freedom Control for Magneto-Optical Disk Drives

The seek speed of magneto-optical disk drives is greater than that of other optical disk drives. To design a high-speed seek servo system that will be an improvement over the traditional system, we must achieve following two goals. One is to drive the coarse-positioning actuator as fast as possible. The other is to restrain shift and vibration of the lens during the seek. We propose to apply two-degree-of-freedom (2-DOF) seek-velocity control and lens-shift restriction control. The 2-DOF seek-velocity control uses acceleration feedforward of the lens motion as well as target velocity signal of the lens velocity. This method can work the coarse actuator quickly. Further, the lens-shift restriction control uses the controlling input to cancel the inertial force that acts on the lens during the seek. By simulating this method, we discovered that such control systems provide the prospect of average seek time shorter than 19 ms.