This paper deals with the measurement of the frequency response of the mechanical part of a drive for the parameter identification of a plant. The system is stimulated by pseudorandom binary signals. The measurement of the frequency response is part of a system identification procedure being carried out during an automatic commissioning of the drive. For the calculation of the frequency response of the mechanics, the Welch-method is applied for spectral analysis. The Welch-method is known from the fields of communications and measurement engineering. This paper addresses the application of this powerful method for the identification of electrical drives. Investigations have pointed out that the pure utilization of conventional identification strategies does not yield satisfying experimental results. Experimental results presented in this paper point out clearly the efficiency and flexibility of the proposed Welch-method. This paper contains many practical aspects and realization details that are important for their implementation on industrial systems. Although in principle, commercial software tools can be utilized for identifying the parameters of the plant, this paper addresses the implementation of the necessary identification algorithms on the embedded control electronics of the drives. The utilization of the Levenberg-Marquardt-algorithm yields excellent results for the identified parameters on the basis of the measured frequency response data.

Application of the Welch-Method for the Identification of Two- and Three-Mass-Systems

In this paper, novel repetitive controllers are proposed based on perfect tracking control (PTC) in order to reject high-order repeatable runout (RRO) of hard disk drives. First, the feedback approach of the repetitive PTC (RPTC) is developed with internal model of periodic disturbance. Although this method has performance robustness against small plant variation, the internal model worsens the stability robustness for big modeling error. Then, the feedforward (FF) approach of RPTC is introduced with switching mechanism such that the high-order RRO can be rejected without any sacrifice of the closed-loop characteristics. In both approaches, multirate FF control is utilized to overcome the unstable zero problem of discrete-time plant. Finally, the advantages and disadvantages are demonstrated through simulations and experiments.

RRO Compensation of Hard Disk Drives With Multirate Repetitive Perfect Tracking Control

http://www.nt.ntnu.no/users/skoge/prost/proceedings/ifac2008/data/papers/0448.pdf

Disturbance suppression beyond Nyquist frequency in hard disk drives

This paper presents a novel deadbeat feedforward compensation in the fast and precise positioning control for mechatronic systems. The proposed compensator is designed considering the frequency shaping in control input to suppress the residual vibration, under the constraint of specified step number in position reference. A 2-degree-of-freedom positioning controller with the deadbeat feedforward compensation can ensure the required settling performance with the specified steps regardless of the positioning amplitude in reference. The effectiveness of the proposed approach has been verified by numerical simulations and experiments using a prototype of Galvano scanner.

Deadbeat feedforward compensation with frequency shaping in fast and precise positioning

The aim of this paper is to put forward a novel design of a nonlinear PID controller type based on carefully choosing nonlinear gains to enable reducing the settling time, minimizing the overshoot and improving the required control effort during the functions of the read/write (R/W) head positioning servomechanism in hard disk drives. The controller is capable of adjusting a driving force, a damping effect and an integral action according to the position of the actual system output with respect to the desired output. This is carried out by utilizing the three actions of the PID controller which are tuned by different nonlinear functions to provide the system with the needed level of a driving force, a damping and a steady-state error correction action. Simulation results, including step function response, control signal history, and a disturbance rejection capability are presented to show the efficiency of the proposed controller.

A nonlinear PID control scheme for hard disk drive servosystems

This paper is concerned with a mechanical resonant mode compensation problem for hard disk drives. Conventional notch filters must have deep and wide enough frequency characteristics in order to accommodate all possible resonant mode characteristic perturbations, which result in deterioration in positioning accuracy and residual vibration after seeking. This paper proposes an easy-to-implement adaptive notch filter of which the center frequency follows the resonant frequency change. The basic idea of this adaptive filter is to balance two kinds of frequency weighted variances of the control input signal.

T. Hara

Papers

Adaptive resonant mode compensation for hard disk drives