Analysis of open-loop characteristics on SISO sampled-data positioning control system

Abstract

In the sampled-data positioning control system of mechatronic products, it is hard to analyze the effect of mechanical resonances above the Nyquist frequency after the control systems were assembled. However, unexpected variations of mechanical characteristics often happen in actual mechatronic systems. To solve such a problem, this paper proposed two analysis methods with measurable open-loop characteristics in single-input/single-output (SISO) sampled-data positioning control systems. These methods use frequency responses of the controlled object and the digital controller for calculating the measurable open-loop characteristics without complicated calculations involving state-space representations of a controlled object, or integrations of matrix exponentials. The proposed methods indicate that we can analyze the performance of the sampled-data control system beyond the Nyquist frequency by using these measurable open-loop characteristics. To show the validity of the proposed methods, this study conducted simulation analyses on the sampled-data positioning control system of a magnetic headpositioning control system in a hard disk drive. These results show that proposed open-loop characteristics are good approximated solutions in order to analyze the control system performance of the sampled-data positioning control system beyond the Nyquist frequency.

Two-degree-of-freedom control scheme for flying-height and tracking-position controls with thermal actuators in HDDs

“…This means that the control system for the magnetic head position is a sampled-data control system which should control not only sampled position but also intersampling position. Therefore, we have to evaluate performances of the control system by using continuous-time signals instead of measurable discrete-time signals (Atsumi and Messner, 2013;Atsumi and Messner, 2014;Atsumi, 2016;Atsumi, 2017a). Atsumi, Journal of Advanced Mechanical Design, Systems, and Manufacturing, Vol.12, No.1 (2018) 2.1.…”

“…24, dot-dashed lines indicate the results without the flying-height control, solid lines indicate the results with the feedforward control only for the flying-height control, and dashed lines indicate that results with the proposed TDOF control for the flying-height control. Note that these figures and table showed the results of continuous-time signals y cFH that include intersampling oscillations for the sampled-data control system (Atsumi and Messner, 2012;Atsumi and Messner, 2013;Atsumi and Messner, 2014;Atsumi, 2016). From these simulation results, we can see that, when the control system doesn't have plant perturbations, the flyingheight fluctuations with the feedforward and the TDOF controls are almost same because the feedforward control can compensate for almost all of the flying-height fluctuations in discrete-time signal y dFH and the feedback controller doesn't need to work for the flying-height fluctuations.…”

Magnetic-head positioning control of HDDs with improved <i>H</i>_∞ controller by Robust Controller Bode (RCBode) plot

“…The HDD is comprised of disks, a spindle motor, magnetic heads, and a voice coil motor (VCM). In the magnetic-head positioning control systems of the HDD, the control input is an input command value to a VCM driver, and the observed output is the magnetic-head position (Atsumi, 2016b). Note that we can use many second-order filters for the magnetic-head position control system (Atsumi et al, 2007).…”

Flying-height and tracking-position controls with thermal-positioning actuator in hard disk drives

“…magnetic-head-position signal is generated from embedded information in servo sectors located at regular intervals on the disks. The magnetic-head-position signal therefore is only available as a discrete-time signal at a sampling time determined by the rotation rate of the spindle and the number of servo sectors (Atsumi and Messner, 2012a;Atsumi and Messner, 2013;Atsumi and Messner, 2014;Atsumi, 2016a;Atsumi, 2017a;Atsumi, 2017b). Figure 2 shows a magnetic head which includes thermal actuators for the TFC and TPC systems.…”