Meindert L. Norg

Advanced Motion Control: An Industrial Perspective*

Industrial feedback motion controllers are tuned using manual loopshaping, according to certain design rules. This controller tuning serves as a benchmark for robust control research as applied to optical and magnetic disk drive storage systems. The design and implementation of robust controllers for the focus servo of a compact disk and the tracking servo of a hard disk mechanism is investigated. The design objective is to achieve good track-following performance in the presence of disk disturbances. H∞ robust control is used to systematically include disturbance and specification models in the standard plant framework. The control design iteration is based on disturbance identification, including implementation within the design cycle. The industrial relevance of robust control is discussed and areas for academic research in robust control are indicated, as feedback from industry.

Experimental demonstration of reset control design

Abstract Using the describing function method, engineers in the 1950s and 1960s conceived of novel nonlinear compensators in an attempt to overcome performance limitations inherent in linear time-invariant (LTI) control systems. This paper is concerned with a subset of such devices called “reset controllers”, which are LTI systems equipped with mechanisms and laws to reset their states to zero. This paper reports on a design procedure and a laboratory experiment, the first to be reported in the literature, in which the resulting reset controller provides better design tradeoffs than LTI compensation. Specifically, it is shown that reset control increases the level of sensor-noise suppression without sacrificing either disturbance-rejection performance or gain/phase margins.

Suppressing non-periodically repeating disturbances in mechanical servo systems

Non-periodically repeating (NPR) disturbances are fixed-shape disturbances that occur randomly in time. We can provide a control system with the capability to suppress this type of disturbance by adding in parallel to the input of the nominal feedback controller a learning look-up-table based feedforward controller that is activated using an NPR-disturbance detector.

A System Analysis for High- and Very High-Speed CD-ROM Drives

Abstract This paper presents an overview of the specific design issues related to the high- and very high-speed CD-ROM drives. The general architecture and key specifications of a CD-ROM system are briefly introduced and various aspects regarding the improvement of these specifications are considered. The strategies employed to control the turntable motor as well as to position the optical head(s) are discussed. The described control techniques and algorithms are specifically aimed to boost the performance of the CD-ROM drives, namely to increase their data throughput and decrease their access time.

Feed Forward control to enhance CD skip performance

This paper considers the design, implementation and validation of FeedForwardControl for a Compact Disk mechanism. The design objective is to increase the ability of the CD mechanism to withstand external mechanical disturbances. For the research described an accelerometer has been used to measure the base-acceleration. This signal is filtered and added to the focus servo loop. The reduction of the servo error signal has been used to indicate the effectiveness of the feedforward.