SPM을 사용한 정보저장시스템을 위한 수정된 슬라이딩 모드 PTOS

Abstract

Scanning Probe Microscope (SPM)-based Data Storage (SDS) 시스템의 저장 용량이 높아짐에 따라 트랙 탐색 제어와 트랙 추종 제어의 성능이 중요시된다. 트랙 탐색 제어의 빠른 정착 시간을 위해 SDS 시스템에 적합한 Proximate Time-Optimal Servomechanism (PTOS)가 제안되어 왔지만, 빠른 정착 시간은 큰 overshoot을 야기하며, 트랙 탐색 거리에 따른 overshoot 특성이 나빠질 수 있다. 본 논문은 Modified-Sliding Mode Proximate Time-Optimal Servomechanism (MSMPTOS) 제어기를 제안하여 PTOS의 단점인 overshoot가 트랙 탐색 거리에 따라 크게 발생하는 것을 최소화하고, 또한 Time-Optimal (TO) 제어기의 deceleration 구간을 충분히 사용하지 못하는 특성을 개선시켜, overshoot 없이 정착 시간을 줄여줌으로써 트랙 탐색 제어의 응답 속도를 빠르게 설계하였다. MSMPTOS 제어기를 적용하여 기존 PTOS의 overshoot을 제거하고, SMPTOS보다 정착 시간을 모든 트랙 탐색 구간에 대해 감소하는 것을 모의 실험을 통해 확인하였다. 이를 통해 SDS 시스템의 데이터 처리 속도를 최적화할 수 있는 제어기를 설계할 수 있음을 확인하였다.; The growth rate of data storage density of Scanning Probe Microscope (SPM)-based Data Storage (SDS) system has been increased. Thus, access time is one of the key parameters characterizing SDS systems. It is always desirable to minimize the seek time. Basically, track seeking is a time optimal problem and its optimal solution is the so-called bang-bang control law in Hard Disk Drive. However, the bang-bang controller is extremely sensitive to disturbances, unmodelled dynamics, and parameter variations. The Proximate Time Optimal Servomechanism (PTOS) was proposed by Workman to reduce chattering problem. The PTOS is robust to model uncertainties, but has slow settling time more than time optimal control. To eliminate the common chattering and overshoot problem, variable structure control with sliding mode control, such as Sliding Mode PTOS (SMPTOS) for double integrator system and discrete-time sliding mode control, is proposed. In SDS system, recently, the Proximate Time Optimal Servomechanism (PTOS) for damped harmonic oscillator model is proposed by IBM. However, this method is difficult to obtain some parameters within an acceptable overshoot margin both short and long strokes. In this thesis, we propose a discrete-time Mmodified-Sliding Mode Proximate Time-Optimal Servomechanism (MSMPTOS). In the proposed method, convergence rate factor, θ, affects settling time. Fast settling time cause large overshoot, so there is a trade-off between settling time and overshoot in sliding mode control. The proposed algorithm uses variable θ which is a nonlinear function of position error. The θ, depending on position error determines the width of unsaturation region. As we use a θ varying to position error, the system has a fast settling time with no overshoot. As we use a MSMPTOS instead of PTOS and SMPTOS, overshoot does not happen and settling time is decreased. Simulation results are included to show the effectiveness of proposed method.