Daniel Y. Abramovitch

REJECTING ROTATIONAL DISTURBANCES ON SMALL DISK DRIVES USING ROTATIONAL ACCELEROMETERS

Abstract Small disk drives are inherently designed for portable applications and thus must be able to reject external shock and vibration. This paper expands on previous efforts at using the signal from a rotational accelerometer to minimize the the effects of these disturbances by dealing with several issues that come up; accelerometer beam resonances, low sample rate of the embedded servo on the disk drive, and widely varying accelerometer gains. The resulting algorithm is both simple and effective, making it practical for in drive use. Experimental data is provided.

Disk drive pivot nonlinearity modeling. I. Frequency domain

This paper describes studies done at HP Labs on the actuator pivot bearing nonlinearity of a small disk drive. The nonlinear frictional behavior of the pivot bearing varies with actuator position, from drive to drive, and with time and temperature. This nonlinear behavior has made the traditional linear disk drive models inadequate. The paper shows how the swept-sine/describing function method was used to develop a nonlinear model of the pivot. This model departs from the classical friction models, but does a good job of matching laboratory frequency domain measurements.

On the stability of adaptive pole-placement controllers with a saturating actuator

The authors examine how existing pole-placement algorithms work in the case of a saturating input. The stability of such algorithms and the modifications needed to make them work in the case of saturation are examined. The net result is that the analysis of G.C. Goodwin and K.S. Sin (1984) can be slightly modified to prove the stability of adaptive pole-placement, but only for the case where the plant is stable. It is shown that, for unstable plants, it is possible to push the plant into a state from which it cannot be returned to the origin (with a saturating input). Thus, it is fairly easy to generate examples of instability in the adaptive control system that would not exist with unbounded control authority. >

An overview of the PES Pareto Method for decomposing baseline noise sources in hard disk position error signals

This paper gives an overview of the PES Pareto Method, a useful tool for identifying and eliminating key contributors to uncertainty in the Position Error Signal (PES) of a magnetic disk drive servo system. Once identified and ranked according to their overall effect on PES, the top-ranking sources can be worked on first, either by finding ways to reduce their magnitude or by altering system components to reduce sensitivity to the contributors. The PES Pareto Method is based on three ideas: (1) an understanding of how Bodes Integral Theorem applies to servo system noise measurements, (2) a measurement methodology that allows for the isolation of individual noise sources, and (3) a system model that allows these sources to be recombined to simulate the drives Position Error Signal. The method requires the measurement of frequency response functions and output power spectra for each servo system element. Each input noise spectrum can then be inferred and applied to the closed loop model to determine its effect on PES uncertainty. The PES Pareto Method is illustrated by decomposing PES signals that were obtained from a hard disk drive manufactured by Hewlett-Packard Company. In this disk drive, it is discovered that the two most significant contributors to PES baseline noise are the turbulent wind flow generated by the spinning disks (Windage) and the noise involved in the actual readback of the Position Error Signal (Position Sensing Noise).

Lyapunov redesign of analog phase-lock loops

In general, the design of phase-lock loops has been done by a combination of linear analysis, phase plane plots, rule of thumb, and simulation. Very few analytical tools have been used to determine the stability of the nonlinear models used for these devices. A method from the control literature known as Lyapunov redesign[1] has recently been used to design a third order phase-lock loop whose nonlinear model is guaranteed to be stable [2]. In this paper, this technique is demonstrated to be an effective stability analysis and design technique for many analog phase-lock loops. The ability of loops designed using these techniques to track a phase step is also proven.

Disk drive pivot nonlinearity modeling. II. Time domain

For pt. I see ibid. p.2600-3. This paper describes studies done at HP Labs on the actuator pivot bearing nonlinearity of a small disk drive. It presents several models and discusses a time-domain approach, comparing simulated and lab measured torque versus displacement hysteresis curves. Using the measured and simulated time and frequency responses as a guide, the designer can iteratively improve the model of the system and verify the correctness of the measurements.

The PES Pareto method: uncovering the strata of position error signals in disk drives

Describes a method of breaking down the position error signal (PES) of a magnetic disk drive to its contributing components. Once these components are identified, they can be ranked in terms of their overall effect on PES and thus the most critical ones can be worked on first. This method is based on three things: an understanding of how Bodes integral theorem ties into noise measurements, a measurement methodology that allows for the isolation of individual noise sources, and a system model that allows these sources to be recombined to form the drives position error signal. We have found this method to be dramatically useful in identifying the key contributors to PES noise.

Decomposition of baseline noise sources in hard disk position error signals using the PES Pareto method

This paper uses the position error signal (PES) Pareto method and measurement techniques for isolating noise sources to decompose the PES of a Lynx II hard disk drive manufactured by Hewlett-Packard. This accomplishes three things: it demonstrates the utility of the PES Pareto method in a practical example, it allows us to discover which noise sources are insignificant to PES, and it identifies which noise sources are significant to PES. In this particular hard disk drive, it is discovered that the two most significant sources of baseline noise at the disks position error signal are the turbulent wind flow generated by the spinning disks (windage) and the noise involved in the actual readback of the Position Error Signal (position sensing noise).

Some crisp thoughts on fuzzy logic

The author believes that there are some fundamental pieces of information not provided in most fuzzy logic control papers. When one realizes what those pieces of information are, one gets a different opinion about how and when fuzzy logic control works and when it is more practical than conventional control. He first states some opinions on fuzzy logic and tries to justify them. He then returns to some of the articles written by proponents of fuzzy logic and use the previous understanding to shed some light on what is really responsible for the improved system performance.

Rejecting Rotational Disturbances on Small Disk Drives Using Rotational Accelerometers

Abstract Small disk drives are inherently designed for portable applications and thus must be able to reject external shock and vibration. This paper expands on previous efforts at using the signal from a rotational accelerometer to minimize the the effects of these disturbances by dealing with several issues that come up; accelerometer beam resonances, low sample rate of the embedded servo on the disk drive, and widely varying accelerometer gains. The resulting algorithm is both simple and effective, making it practical for in drive use. Experimental data is provided.