Multi-rate short track-seeking control of hard disk drives for computation saving

This paper is concerned with multi-rate shortseeking control for a dual-actuator hard disk drive (HDD). Multi-rate control has been proposed to reduce the real time computation in HDD servos, and it has been shown that in track following control of HDDs, computation can be saved greatly without performance degradation by using multi-rate controllers. In this paper, we propose a novel short-seeking control method for dual-actuator HDDs based on multi-rate track following control and initial value adjustment. This method, which utilizes the same multi-rate controllers and same servo structure as track following, adjusts the initial values of the track-following controller for short seeking. Real time computation is greatly saved in two ways: (1) computation is saved by multi-rate scheme; (2) initial value adjustment of the feedback controller makes the use of the feedforward controller and reference trajectory unnecessary, which implies no real time computation for feedforward control is needed. Simulation and experimental results verify the effectiveness of the proposed method.

The mode switching control (MSC) is a kind of variable-structure control system with switching in only one direction. When the mode is switched from the fast-movement servo mode to the precise-positioning servo mode, the switching time is the initial time when the precise-positioning mode begins. As a result, initial value compensation (IVC), a method that takes into account the initial state values, can be applied. We (1996) previously proposed the design of IVC and showed its effectiveness in disk drive servo controls. In this paper, a design method for determining the optimal combination of initial states for mode switching is proposed. Here, the H/sub 2/ norm of the transfer function between the initial values and the control input is defined as the performance index of the transient response after mode switching. By combining the IVC method with this method of determining the optimal switching conditions, the issues of mode switching are resolved. Several experimental results show the effectiveness of these methods.

A mode-switching controller with initial value compensation for hard disk drive servo control

Proposes a state-space approach to deadbeat servomechanism design using multirate input control. The focus is on the advantage of multirate control over conventional single-rate control. Multirate controllers can achieve required settling time with less frequent sampling of measurement. The multirate input mechanism can yield shorter settling time than single-rate control using the same frequency of sampling. In general, multirate control exhibits intersample ripple. Nevertheless, the paper demonstrates that the negative effect of multirate input on the steady-state response can be removed completely to accomplish ripple-free deadbeat, keeping the settling time short using the multirate mechanism at the same time. In addition, the paper presents a design method for multirate ripple-free deadbeat control which guarantees robustness against continuous-time disturbance and model uncertainty.

In a communication network, transmission control protocol (TCP) is used to avoid congestion through which the sources with small round trip time (RTT) allocate the bottleneck link unfairly. On the other hand, the bottleneck link capacity is time-varying in wireless access networks due to the fading effects and errors in the acknowledgment packets. Therefore, queue management is more sophisticated in wireless networks than that in wired ones. Also, when the number of the sources changes, the network acts as a switched system in which non-zero initial values cause the response not to converge to the desired value. The main contribution of this paper is to design a switched rate-based robust queue management (SRRQM) to control the congestion contemporary with weighted fairness and maximum utilization compatible with wireless access networks. Moreover, a procedure called initial value compensation (IVC) is designed to overcome the non-zero initial value effects. Two degree of freedom multi-loop internal model (TDF-MIM) method is used for robust congestion control. The utilization factors are designated proportionally to user's RTT values to ensure weighted fairness and maximum utilization. To the authors' knowledge, this is the first time that a SRRQM is designed for a wireless access network with the advantages of weighted fairness, maximum utilization and robustness against capacity variation, PER and changing in the number of the sources. Analytical and simulation results demonstrate the efficacy of the proposed procedure.

To meet an increasing demand for high performance and large-capacity in magnetic hard disk drives, both fast response and precise positioning are strongly required for the head positioning control. A mode switching control (MSC) system, which includes a track seeking controller, a track following controller, and a switching function, is widely used to meet this requirement. The issue for MSC is to confirm a design method of servo mode switching. This paper proposes the initial value compensation method (IVC). The IVC inputs certain initial values in the controller state variables at mode switching in order to improve the transient response after switching. There are two approaches to determine the values: (1) minimizing a linear-quadratic function of the plant state variables; and (2) cancelling the unfavorable poles of the transfer function between initial values and head position by relocating zeros. Some experimental results are shown to be effective.

Ball-screw-driven stages are often used as feed systems of machine tools. Precise control of the stage is desired; however, rolling friction degrades tracking accuracy and causes a large tracking error called a quadrant glitch. Although model-based feedforward friction compensation effectively suppresses the tracking error, the compensation often results in a negative quadrant glitch, which is the tracking error in the direction opposite to the quadrant glitch. This study aims to present a suppression method of the negative quadrant glitch. In this study, initial value compensation with additional input is exploited. The approach is evaluated through simulations and experiments.

The head-positioning control system of a magnetic disk drive must enable precise positioning and high-speed access. To meet these control requirements, a Mode-Switching Control (MSC) system composed of two or three control modes and a mode-switching function has been used widely in current head-positioning control systems. One of the issues concerning MSC is to improve the transient response after it switches the mode. Although the mode switching is a non-linear action, the transient response can be improved if the control system considers the initial state response after mode switching. Initial-Value Compensation (IVC), which is based on this condition, can improve the transient response after mode switching. In the current study, we applied IVC to reduce acoustic noise during the seek operation of the head-positioning control system. Furthermore, we developed a new method for the mode switching condition; this method considers a trade-off between the peak value of operation current (which is an important factor in the reduction of acoustic noise during seek), the overshoot of displacement response, and the settling-time after mode switching. Acoustic noise during seek was experimentally found to be significantly reduced by IVC and the new switching method.

This paper presents an analytic design of multirate controllers to guarantee stable haptic interaction and high fidelity. When the reflective force is computed by using slowly simulated virtual model, the control frequency of the conventional controller becomes low. This increases the zero-order-hold effect, and makes the system unstable. We propose a multirate control method to reduce the zero-order-hold effect. The multirate controller is implemented by adding a high frequency controller to the conventional controller. The high-frequency controller is designed to compensate the energy generated by the conventional controller. The stability analysis of the multirate haptic control system shows that the stiffness of the virtual model can be increased while maintaining the stability. A nonlinear virtual coupling is designed using this multirate control scheme. The multirate controller is evaluated by mathematical analysis and experiments.

This paper deals with multirate tracking control of linear time-invariant systems with two sampling-rates: a slower one for the output and a faster one for the input. It is known that intersample ripples often arise in the outputs of the closed-loop multirate systems although multirate control has interesting advantages. There are some papers which discuss this problem, but only few studies which confirm the validity of the control design methods through experiments. In this paper, a ripple-suppressed multirate control scheme is presented arid applied to a position servo experimental system with an ultrasonic sensor. Experimental results show the effectiveness of the algorithm.

The high gain servo controller with complex zeros was proposed[1]. The controller can realize a much higher gain with the same servo bandwidth. We applied the controller to Blu-ray disc drives, and confirmed decrease of servo error and improvement of a resistance to vibration. On the other hand, we observed the controller increased an overshoot of an initial value response. We applied the initial value compensation [2], and confirmed suppression of the overshoot.

Frequency steer limits are important aspects that influence the overall response and design of a robust control system. We study the effects that frequency steer limits have on the response of a control system when underlying components of the system have undergone nonstochastic perturbations. Examples of the disturbances include environmental changes and hardware anomalies. Additionally, we attempt to find a balance between the performance of the control system and the robustness of maintaining parameter limits in the presence of outlying events. Performance of design strategies are evaluated utilizing both simulated and archived measured data.

This paper presents a new design method for multirate output feedback control (MROFC) using a multirate state estimator. The proposed method is computationally efficient since filtering the estimator at every measurement instant is not required. The MROFC system is shown to be less sensitive to measurement noise than single-rate control system. The proposed MROFC is applied to a galvanometer servo system. Experimental results show improved settling and tracking performances over the conventional single-rate control.

For information devices such as hard disk drives, actuators must be controlled as quickly and precisely as possible. The design of the feedforward input is very important in satisfying these requirements. Therefore, we have proposed design methods based on final-state control so as to reduce its spectrum at the desired frequency points. Furthermore, the final-state control method has been extended to generate the feedforward input using a polynomial. By using a polynomial, the required memory size can be drastically reduced because only the coefficients of the polynomial must be stored. However, when the step number of the input increases, the method may not produce a correct solution because of a numerically ill-posed problem. In this paper, we propose a design method for the final-state control based on a time-symmetric polynomial input. The simulation results show that the proposed method contributes to the improvement of not only the numerically ill-posed problem but also the performance.

A Design Method of Bilateral Control of Teleoperators with Uncertain Communication Time-Delay