Intelligent and Robust Control of Dual Stage Actuator Arm using GA based Fixed Structure Robust Loop Shaping Control

Since the aerial density of Hard Disk Drive (HDD) is increasing at very impressive rate, conventional techniques for controlling HDD servo system can no longer meet the necessary tracking performance and robustness; a new class of servo controller will be required to address this issue. H∞ robust controller is one of the most popular techniques for designing a robust controller and it provides necessary robustness and performance even under perturbed plant conditions. However, the order of controller designed by this technique is usually higher than that of the plant, making it difficult to implement practically. To overcome this problem, this paper proposes a new technique for designing a robust controller for HDD with Voice Coil motor (VCM) and micro actuator called dual stage actualtor. The proposed technique does not only solve the problem of complicated and high order controller but also still retains the robust performance of conventional H∞ control technique. Simulation results show the effectiveness of our proposed techniqu

CHALLENGES OF CONTROL DESIGN FOR PRECISION SERVO SYSTEM WITH APPLICATION ON HARD DISK DRIVE

Ph.DDOCTOR OF PHILOSOPH

Robust vibration suppression control profile generation

Scope and Method of Study:The control of flexible structures has been extensively studied in recent years. Flexible structures such as high-speed disk drive actuators require extremely precise positioning under very tight time constraints. Whenever a fast motion is commanded, residual vibration in the flexible structure is induced, which increases the settling time. One solution is to design a closed-loop control to damp out vibrations caused by the command inputs and disturbances to the plant. However, the resulting closed-loop response may still be too slow to provide an acceptable settling time. Also, the closed-loop control is not able to compensate for high frequency residual vibration which occurs beyond the closed-loop bandwidth. An alternative approach is to develop an appropriate reference trajectory that is able to minimize the excitation energy imparted to the system at its natural frequencies.Findings and Conclusions:A robust vibration suppression control profile is generated which suppresses all the high frequency vibrations in a flexible dynamic system. This robust control profile is the shifted time-limited version of the functions that optimally achieve the energy concentration property. The robust control profile is designed by considering the first resonance frequency. In practical system, a lower resonance frequency mode may exist which is located far from the high frequency resonance modes. In this case, a robust control profile is generated which suppresses one specific resonant mode in a flexible dynamic system. This robust control profile is a smooth function which can be used as a robust velocity profile, or as a robust shape filter to an arbitrary control command. The robustness can be arbitrarily improved, which brings about a smoother profile. Combination of high frequency vibration suppression control profile and low frequency vibration suppression control profile generates a robust vibration suppression control profile that is able to suppress all the resonant dynamics in a flexible dynamic system. The technique can be applied to both open-loop and closed-loop systems

On the robust controller design for Hard Disk Drive servo systems with time delays

Due to the existence of various sources of delays, the dynamical model of HDD (Hard Disk Drive) servo systems is actually infinite dimensional, although most of the control algorithms simplified the model with Padé expansions or other finite dimensional approximations. In this paper, a robust loop shaping algorithm is developed for the HDD model with delays by using an h ∞ synthesis approach for infinite dimensional systems. The h∞ controller is derived with a structure of an internal feedback loop including an FIR (Finite Impulse Response) filter and an IIR (Infinite Impulse Response) filter, which facilitates non-fragile implementations. Comparisons to other robust control methods are given and the advantages of this approach are demonstrated in terms of improvement of TMR (track misregistration) and tracking TPI (Track-per-Inch) capability. © 2013 EUCA

'Constant in gain Lead in phase' element - Application in precision motion control

This work presents a novel 'Constant in gain Lead in phase' (CgLp) element using nonlinear reset technique. PID is the industrial workhorse even to this day in high-tech precision positioning applications. However, Bode's gain phase relationship and waterbed effect fundamentally limit performance of PID and other linear controllers. This paper presents CgLp as a controlled nonlinear element which can be introduced within the framework of PID allowing for wide applicability and overcoming linear control limitations. Design of CgLp with generalized first order reset element (GFORE) and generalized second order reset element (GSORE) (introduced in this work) is presented using describing function analysis. A more detailed analysis of reset elements in frequency domain compared to existing literature is first carried out for this purpose. Finally, CgLp is integrated with PID and tested on one of the DOFs of a planar precision positioning stage. Performance improvement is shown in terms of tracking, steady-state precision and bandwidth

Randomized algorithms for control of uncertain systems with application to hand disk drives

Ph.DDOCTOR OF PHILOSOPH

Advance Servo Control for Hard Disk Drive in Mobile Application

Ph.DDOCTOR OF PHILOSOPH