Robust feedforward control system considering sudden disturbance for optical disk recording system

In optical recording system, the tracking servo system must follow the track of optical disk against the influence of the track eccentricity and the force disturbance. In tracking servo system, the influence of the track eccentricity becomes a periodic disturbance. The influence of force disturbance is a sudden disturbance. This work proposes a new robust tracking servo system for an optical disk recording system with feedforward controller and sudden disturbance observer. In order to suppress the periodic disturbance, This work designs the feedforward control system with the prediction of tracking error. For suppressing the sudden disturbance, This work proposes the sudden disturbance observer by using the predictive tracking error. The experimental results point out that the proposed tracking servo system has a precise tracking response against both periodic disturbance and sudden disturbance.

This paper proposes a new high speed robust control system based on both zero phase error tracking (ZPET) control system and disturbance observer for an optical disk recording system. In optical disk recording systems (for example CD-R), the servo system must have a precise response whose error is less than 0.1 [/spl mu/m] for a reference input signal with an amplitude of 100 [/spl mu/m]. Moreover, the servo system can detect only the error, i.e. the position difference between the optical spot and the track to be followed. For this purpose, the servo system proposed in this paper estimates the reference input signal from the error, and realizes the high speed robust control based on ZPET control. Numerical simulation results point out that the proposed system has a quick and robust response.

ROBUST FOLLOWING CONTROL OF OPTICAL DISK RECORDING SYSTEM BASED ON ZPET CONTROL AND SUDDEN DISTURBANCE OBSERVER

Recently, the size of digital content has continued to increase. In order to cope, manufacturers of digital storage media have tried to increase capacity by narrowing the track pitch of these digital storage media. In addition, recent advancements in technology have resulted in a new optical disk has a rotation speed of over 15,000 rpm. Considering all these factors, we believe that a high-precision tracking control system is needed for optical disks. Consequently, this paper proposes a new robust double feedforward control (RDFFC) system for high-precision control. The proposed system is constructed by using two error prediction-based zero phase error tracking (ZPET) control systems, and includes an error-based disturbance observer (EDOB) that uses notch filter to suppress non-periodic disturbances. The proposed control system is designed for DDU-1000 for DVD. The experimental results confirm that our proposed system is practicable and effective.

The increasing demand for high-density and high-speed digital optical recording systems has made the development of advanced coding and signal processing techniques for fast and reliable data recovery increasingly important. In recent years, the parity-check (PC)-code-based reception technique has been widely studied for magnetic recording systems, and it is projected to be highly promising for high-density optical recording. The PC code is an inner error correction code (ECC), which can detect dominant short error events of the system, using only a few parity bits. This reduces the loss in error correction capability of the outer ECC due to random short errors and results in a simple and efficient solution to improve the overall performance. This thesis is dedicated to the design and analysis of PCcode- based recording systems to achieve higher recording capacity with low implementation complexity, for high-density blue laser disc systems. In particular, most of the key components of the PC-code-based optical recording system have been designed and optimized for different recording densities, and different proportions of white noise and media noise. During the development of advanced coding and detection techniques, it becomes necessary to investigate the system’s performance with different coding schemes and recording densities. In Chapter 2 of the thesis, we propose a generalized Braat-Hopkins model for optical recording channels, which provides a fair basis for the performance comparison of detection schemes over different coding schemes and recording densities, for channels with additive, white Gaussian noise (AWGN) and media noise. Various basic issues associated with the PC-code-based systems are investigated in Chapter 3. These include bounds for bit error rates and error event probabilities, the dominant error events at channel detector output, different PC codes, simple and efficient post-processors, the impact of error events that are split across data block boundaries and the corresponding remedy, as well as the effects of code rates and recording densities. Simulation results show that a 4-bit PC code achieves the best performance. The corresponding bit error rates (BERs) are very close to the performance bounds, at both nominal and high densities. Constrained codes, which serve as a key component in the read-write channel of data storage systems, are desired to have a high code rate with low-complexity encoder/decoder. In Chapter 4, we investigate the design of certain capacity-approaching constrained codes for optical recording systems. In particular, we derive analytically the relationship between the number of encoder states and the maximum size of these codes. We identify the minimum number of encoder states that maximizes the code rate, for any desired codeword length. The design of constrained PC codes is key to the development of PCcode- based systems, and the systematic design of efficient constrained PC codes remains a challenging problem. In Chapter 5, we propose a general and systematic code design technique for constructing capacity-approaching constrained PC codes, which can detect any type of error events of the system, with the minimum code rate loss. Compared to the rate 2/3 code without parity, the newly designed constrained 4-bit PC code achieves a performance gain of 2 dB at nominal density, and 1.5 dB at high density, at BER = 10-5. As the dominant noise for high-density optical recording systems, media noise severely degrades the performance of channel detectors and postprocessors that are designed for AWGN. In Chapter 6, we propose two novel modifications to the bit detector to combat media noise. We further develop a data-dependent post-processing scheme for error correction. Compared to the system designed without considering media noise and without PC codes, the overall performance gain of the developed scheme can be more than 11 dB at high media noise levels. In data storage systems, the ECC failure rate (EFR) serves as the ultimate measure of the data recovery performance. In Chapter 7, we develop semi-analytical approaches for estimating the EFR, and analyze EFRs for the developed PC-code-based systems, for the cases without and with interleaving. Our analysis shows that with the optimum interleaving degrees, compared to the rate 9/13 code without parity, the 2-bit PC code achieves a gain of around 0.5 dB, and the 4-bit PC code gains 0.6 dB, at high record ing density and EFR = 10-16. The thesis concludes in Chapter 8 with some suggestions for further work.

A new tracking method for an optical tape recording system is described. Since it is difficult to form pits or grooves on tape media, we have employed crosstalk signals to detect tracking error. On the 2 tracks adjacent to the one that the focused spot must follow, pilot signals at 2 different frequencies are recorded respectively. When reading the track, the pilot signals from the 2 adjacent tracks are derived from the readout signal. The tracking error signal is generated by differential detection of their amplitudes. We carried out fundamental experiments using a rotating optical head and a magneto-optical recording medium sputtered on a flat glass substrate. A 5 micrometers mark length was available to detect the tracking error for a 2 micrometers track pitch. A total residual tracking error of less than 0.1 micrometers was obtained when the medium was displaced in a 2 micrometers peak to peak range.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We propose a robust control system which has robustness for disturbance and can deal with a nonlinear system with partially unknown structure by fusing reinforcement learning and robust control theory. First, we solved an optimal control problem without using unknown part of functions of the system, using neural network and the repetition learning of reinforcement learning algorithm. Second, we built the robust reinforcement learning control system which permits uncertainty and has robustness for disturbance by fusing the idea of H infinity control theory with above system.

This paper proposes a new force sensorless robust tracking servo system, which detects and suppresses both the periodic disturbance and the sudden disturbance without force sensor. The proposed system estimates both the periodic disturbance and the sudden disturbance and the sudden disturbance by using a new sudden disturbance observer and the memory of tracking error. In the proposed system, the influence of sudden disturbance is suppressed by the proposed sudden disturbance observer. On the other hand, the influence of periodic disturbance is suppressed by means of ZPET feed‐forward servo system. The experimental results point out that the proposed tracking servo system has a precise tracking response against both the periodic disturbance and the sudden disturbance. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(1): 82–90, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20614

This paper discusses an application of Robust Model Matching (RMM) to the spill position control of a fuel injection pump. Since the fuel injection servo mechanism is soaked in fuel oil, the parameters of the plant vary due to differences in the viscosity coefficient caused by wide changes in temperature. The invariable fuel injection characteristic is required to meet the demands of the drivability, exhaust emissions and fuel consumption, even though the parameters change. The RMM is an idea which makes up a robust control system against parameter uncertainties.In this paper, we design a robust discrete-time control system based on the RMM: (1) For the low sensitivity, to make small pulse transfer functions from equivalent disturbances to controlled variables. (2) For the robust stability, to increase the margin of pulse transfer functions from conceptual inputs to control variables. The experimental results show that this robust compensator makes up a robust control system against the parameter variations due to the change in temperature. And it is confirmed that the idea of the RMM is effective for the fuel injection pump which includes the variations, identification errors, friction, hysteresis and delay time of the calculation.

The antilock braking systems are designed to maximize wheel traction by preventing the wheels from locking during braking, while also maintaining adequate vehicle steerability; however, the performance is often degraded under harsh road conditions. In this study, a robust hybrid control system is developed for the antilock braking systems. In this design method, the robust hybrid control system is comprised of a hybrid controller and a robust controller to achieve a desired H/sup /spl infin// control performance. The hybrid controller containing a fuzzy uncertainty observer is the principal controller, and the robust controller is designed to achieve the desired H/sup /spl infin// tracking performance. Finally, simulations are performed to demonstrate the effectiveness of the proposed robust hybrid control system for antilock braking control under various road conditions.

Vacuum deposited gold thin layer on a ultraviolet (UV) light pre-exposed polysilanc film undergoes colloidal gold formation by heating. This process was found to accompany the degradation of polysilane by catalytic oxidation due to the colloidal gold formed. Incorporating a titanyl phthalocyanine (TiOPc) pigment layer as a photon-thermal energy conversion layer in-between polysilane film and substrate, we have succeeded in demonstrating experimentally the possible application of such phenomenon to a new optical recording system.

Signal processing and coding technology for digital magnetic recording is the core technology of the channel electronics module in a hard disk drive (HDD) that processes signals read from magnetic media. In this historical review I focus on what is now widely known as partial-response, maximum-likelihood (PRML) technology, which takes advantage of the inherent redundancy that exists in signals read out of magnetic media; its theoretical foundation goes back to 1970, and it capitalizes on the analogy between high-speed data transmission and high-density digital recording, and that between a convolutional code and a partial-response signal. The first PRML-based product was introduced by IBM in 1990, and PRML technology soon became the industry standard for all digital magnetic recording products, ranging from computers' HDDs and tape drives to micro hard discs used in PCs, mobile phones, and MP3 players; use of the PRML principle has recently been extended to optical recording products such as CDs and DVDs. Its improved version, called NPML (noise-predictive, maximum-likelihood), and variants have been adopted by the HDD industry since 2000. Today, a large number of communication and information theory researchers are investigating use of advanced techniques such as turbo coding/decoding to further improve the density and reliability of both magnetic and optical recording systems.

In this paper, a new scheme based on an optical zero phase error tracking controller (ZPETC) and zero phase error notch filter (ZPNF) is proposed. ZPETC is a method of feed-forward controller with effects that tracking speed of a position servo accelerated and system stability guaranteed. As the bandwidth of system includes the characteristic of gain and phase, ZPETC improves phase bandwidth greatly but the performance of gain bandwidth deteriorates slightly. So that a gain correction controller (GC)was introduce ahead of ZPETC to compensate the deterioration of the gain. Generally, ZPNF is adopted in two-mass system. ZPNF is a method of non-casual filter with effects of vibration eliminating for position servo on its load end and has less phase lag when compared with a normal notch filter. In proposed scheme, ZPETC and ZPNF are cascaded ahead of the position control loop. Simulation results on a two-mass PMSM system indicates that, a combination ZPETC and ZPNF improves both the tracking and positioning performance for a position servo system.

The issues of expediency of using adaptation tools in robust control systems are discussed. It is stated that purely robust systems without the use of adaptation tools, in principle, cannot provide high efficiency and versatility in solving practical problems. Robust control systems were originally conceived as non-adaptive systems (passive adaptive systems). In view of the emerging problems in solving practical problems, then a mutation occurred and works appeared under the name "Adaptive-robust systems", "Combined robust systems", etc., partially using adaptation algorithms. Setting the problem of control synthesis under conditions of uncertainty without elements of adaptation is figuratively speaking similar to "search for a black cat in a dark room, especially if it is not there" (Confucius). The most adequate from the point of view of compliance with the fundamental principles of the theory of automatic control is an approach based on an increase in the gain of an open loop. Nevertheless, here too a problem arises — an increase in the gain violates the stability of a closed system. All known research is concentrated around the solution of this problem. An integrated gain self-tuning algorithm and the corresponding circuitry and Simulink implementation scheme have been developed. The reliability of theoretical reasoning was verified by simulating a limiting robust system with self-tuning and a parametrically indeterminate object — "peak gyroscope (parametric pendulum)". Computer studies have made it possible to draw a number of positive conclusions that are of great practical importance.

Rotorcraft flight control systems present design challenges which often exceed those associated with fixed-wing aircraft. First, large variations in the response characteristics of rotorcraft result from the wide range of airspeeds of typical operation (hover to over 100 kts). Second, the assumption of vehicle rigidity often employed in the design of fixed-wing flight control systems is rarely justified in rotorcraft where rotor degrees of freedom can have a significant impact on the system performance and stability. Proposed herein is a methodology for the design of robust rotorcraft flight control systems utilizing Quantitative Feedback Theory (QFI'), a technique which accounts for variability in the dynamic response of the controlled element in the design of robust control systems. It was developed to address a Multiple-Input-Single-Output (MISO) design problem, but was extended to the address the Multiple-Input-Multiple-Output (MIMO) flight control system (FCS) design problem of a UH-60 Black Hawk Helicopter. Inherent conservatism in this design technique leads to limitations in its utility. A modified QFI' approach proved a viable method for designing robust MIMO flight control systems. An analysis of the two flight control system design methodologies is presented.