Search

In this paper, we propose a new control scheme, position and velocity profile tracking control for new generation servo track writing (STW). While conventional servo track writers need controllers that perform fast positioning control with fast track seek and regulation, spiral servo track writers require accurate position and velocity profile tracking control for high quality servo patterns on the media disk. Since STW timing eventually renders geometrically accurate servo patterns, in constant velocity region both position and and velocity error signals should be regulated within small bounds. It is known that regulation via integral sliding mode controller (SMC) provides a good tracking performance, but using a high switching gain is not appropriate for a system having resonance modes. In this paper, thus we apply sliding mode control with disturbance observer to STW. To verify utility of the proposed position/velocity profile track control, we conducted some experiments using a state-of-the-art STW system. Comparative study with the conventional control method was made. The performance of proposed method was experimentally validated.

Archival demands for digital tape storage systems require smaller spacing between data tracks on the magnetic tape to allow for more data storage on a single cartridge. Increasing track density while maintaining track following provides a challenge for the servo control of the tape drive. In particular, interchangeable tape cartridges and time-varying tape reel diameters during operation cause variable disturbances during servo control. In this paper we show how a tape servo control algorithm can be regulated to handle changes in disturbance dynamics during servo operation of the tape drive. The approach is based on adaptive regulation by exploiting a Youla-Kucera parameterization of the servo controller and an explicit minimization of the Position Error Signal (PES) during servo operation in real-time. Theoretical results on the stability of the feedback system and real-time application results on an Linear Tape-Open (LTO) drive are included in the paper. The result show a significant reduction of the variance of the PES over different tape cartridges and a constant PES variance during a complete reel-in operation of the tape drive.

The positioning accuracy achievable by track-follow servo for flexible tape media is investigated using advanced concepts for several elements of the system. First, the servo pattern geometry in the timing-based servo system is designed in conjunction with a digital synchronous servo channel to minimize the measurement error in the position-error signal. Second, a flangeless tape path is introduced to mitigate high-frequency components of the lateral tape motion. Finally, a track-follow controller is designed based on the H ∞ approach, taking into account the disturbance and noise characteristics of tape path and servo-channel and the measured plant transfer function. Combining these elements with a new high SNR magnetic tape based on perpendicularly-oriented BaFe particles, we demonstrate a closed-loop track-follow performance with a standard deviation of the position-error signal of less than 15 nm.

In a tape drive, the head assembly, which hosts servo readers and data writers/readers, must initially be moved to a target position, so that information can be written to or read from the desired tracks. The positioning of a servo reader over a servo band, from which the position-error signal for steady-state track-following operation is obtained, has to be fast, because of the moving-target nature of the problem. This is especially true in the presence of non-negligible lateral tape motion, as found in tape paths with flangeless rollers. In this paper, a method is proposed whereby not only the servo readers but also the data readers in a drive are used to detect the presence of a valid servo signal. If a servo reader is not positioned over a servo band, the distance between servo reader and servo band is continuously estimated by identifying the data reader detecting the presence of a servo signal. This information is then provided to a control element, which determines a trajectory for the actuator and outputs a control signal so that the servo reader rapidly lands over the servo band with optimum control effort. A realization of the proposed method is illustrated by simulation as well as experimental results.

Generally, tracking control for optical disk system is accomplished by the feedback control designed by using PID control, repetitive control and so on. However, it is difficult to reduce the tracking error on condition of high disk rotation speed. In the near future, the disk rotation speed of the optical disk system becomes higher than 10000[rpm]. Therefore, the tracking servo system for optical disk system must have the new structure and highly performance. This paper proposes a new free parameter and desgin method of feedback servo system, which suppresses the high speed periodic disturbance. It has the widebandwidth and high gaim margin. Moreover, in order to suppress this periodic disturbance, this paper proposes a new control structure of robust feedforward servo system, which includes the prediction of tracking error, a new design method of disturbance observer and the zero error phase tracking control. The experimental results point out that the proposed system well regulates the high precision tracking servo control on condition of the disk rotation speed 8000[rpm], which is equal to CD system of 40 X speed.

This paper presents a digital servo driver that realizes a novel multirate feedback controller based on position, velocity and acceleration feedback. The velocity and acceleration signals are firstly estimated by state observer using optical encoder information, and the estimated velocity is fed into discrete disturbance observer (DDOB) to estimate and compensate the external disturbance. In this scheme, controller with acceleration feedback can be realized by replacing the current loop with acceleration loop. When the DC servo motor is controlled by the proposed acceleration feedback control with disturbance compensation, the total servo system from acceleration to position becomes the acceleration controlled system which is fixed to a nominal double integral dynamics in the presence of parameter variation and torque disturbance. Hence, the fast and precise position control can be carried out easily. The proposed acceleration feedback controller and PD position feedback controller are evaluated experimentally on a DSP, which is implemented multirate control scheme, controlled DC servo motor positioning system. The experimental results show that this digital servo system is robust and remarkably sustains the same performance compared to the single fast rate control scheme.

To achieve frequency separation between actuators of a dual-stage servo actuator system in a hard disk drive, the PQ control design method can be used. In the PQ method, the servo controller is designed by focusing on structural interference of the actuators. This paper provides a specific parametrization for fixed order feedback controllers used in the PQ-method for which the structural interference between actuators can be minimized. The proposed control design method is applied to a dual-stage instrumented suspension, where the additional sensor of the instrumented suspension is used to attenuate high frequency disturbance caused by windage turbulence in a hard disk drive.

This paper proposes a modification in the decoupled master-slave dual-stage hard disk drive (HDD) servo control configuration to enhance its stability when the secondary actuator is saturated. This method utilizes the special structure of the decoupled master-slave dual-stage control design and uses a nonlinear secondary actuator model instead of the usual linear one to predict its output and decouple the dual-actuator loop. This technique relaxes the displacement range requirements on the secondary actuator, and also greatly improves the stability of the servo system during the actuator saturation.

This paper proposes a new design method of the type-1 deadbeat servo system, in which the output settles to a command signal in a finite number of control steps, for linear digital systems. By using a virtual command signal in the period of the transient response, new degree of freedom is induced. Even when the integrator is added to the controlled system, the minimum settling time does not increase. Furthermore, two theorems are induced to obtain the general form of the type-1 deadbeat servo system.

An important aspect of linear controller design is to clarify whether the design reaches the performance limit. Based on an industrial project-a high precision three-axis gyro test table (servo system), a paradigm is presented to demonstrate that the performance limit of the disturbance attenuation design of the servo system can be reached in a systematic way by using the μ -synthesis. Moreover, this paper reveals that the performance limit is determined by the bandwidth. This finding will help the designer to judge whether any given performance specification is achievable.

As optical disks are removable and have some distortions, servo systems of optical disk drives must be robust, especially at low frequency. We proposed the high-gain servo controller with complex zeros, which is the same 2nd order controller as conventional controllers, and realizes a much higher gain at low frequency. Decrease of servo error was confirmed, but the controller increased overshoot of initial value responses. We also proposed applying the initial value compensation to suppress the overshoot.