Tracking learning feedforward control for high speed CD-ROM

The periodic disturbances caused by the inherent eccentricity and unbalancing in compact disc systems is one of the prominent radial tracking problems in high-speed and high density optical storage systems. To compensate these periodic disturbances, a learning feedforward compensation (LFF) method is presented and investigated. Computer simulations and experimental evaluation on the high speed CD-ROM product show that the proposed LFF provides a effective way to improve the radial tracking performance by reducing the radial error by 85%

Look-ahead seek correction in high-performance CD-Rom drives

As the performance of CD-ROM drives continues to increase, special attention should be paid to any element in the system that disturbs the desired specifications. When very low access times are considered, it is mandatory to reach the target track within only one seek action, i.e. without any consequent retry or correction seek. Many CD-ROM drives count the tracks crossed during seeking and, by comparing this count with the pre-calculated seek length, the exact target location can be detected. This paper considers the error that affects the track-counting mechanism due to the rotating disc spiral. It is shown that, for a given seek length, the number of crossed tracks differs between outside- and inside-oriented seeks. The involved equations are derived and an algorithm proposed for determining the correct number of tracks to be crossed during a seek action. The proposed algorithm, which is optimized for microprocessor implementation, relies on two look-up tables and a learning scheme that allows look-ahead seek correction for both spiral rotation and system tolerance

Switching control in blu-ray disk drives

To improve the nominal PID-controlled servo performances of a blu-ray disk drive, a switching observer is studied. Switching is done using a deadzone switching gain having the following properties: large-magnitude signals induce extra gain, small-amplitude signals do not. Additionally the observer part assures that large-magnitude signals induce extra low-pass filtering. As a result the design has low-frequency disturbance rejection properties resulting from high-gain feedback but with a favorable high-frequency noise response related to the properties of low-gain feedback. Robust stability is guaranteed using a Lyapunov characterization of input-to-state stability, whereas improved performances under vibrations and disk surface defects are demonstrated using two blu-ray disk drive setups

A cost-effective scheme to improve radial tracking performance for higher-speed optical disk drives

The periodic disturbances caused by the inherent eccentricity and unbalancing in compact disc systems is one of the prominent radial-tracking problems in high-speed and high-density optical storage systems. To compensate these periodic disturbances, an adaptive feedforward compensation technique is presented and investigated with the aim to have cost-effective optical disc drive manufacturing. Computer simulations and experimental evaluation on a high speed CD-ROM product show that the proposed adaptive feedforward compensator is very effective and provides a way to significantly improve the radial tracking performance by reducing the radial error by 85%

Tracking learning feedforward control for high speed CD-ROM

The periodic disturbances caused by the inherent eccentricity and unbalancing in compact disc systems is one of the prominent radial tracking problems in high-speed and high density optical storage systems. To compensate these periodic disturbances, a learning feedforward compensation (LFF) method is presented and investigated. Computer simulations and experimental evaluation on the high speed CD-ROM product show that the proposed LFF provides a effective way to improve the radial tracking performance by reducing the radial error by 85%

Look-ahead seek correction in high-performance CD-Rom drives

As the performance of CD-ROM drives continues to increase, special attention should be paid to any element in the system that disturbs the desired specifications. When very low access times are considered, it is mandatory to reach the target track within only one seek action, i.e. without any consequent retry or correction seek. Many CD-ROM drives count the tracks crossed during seeking and, by comparing this count with the pre-calculated seek length, the exact target location can be detected. This paper considers the error that affects the track-counting mechanism due to the rotating disc spiral. It is shown that, for a given seek length, the number of crossed tracks differs between outside- and inside-oriented seeks. The involved equations are derived and an algorithm proposed for determining the correct number of tracks to be crossed during a seek action. The proposed algorithm, which is optimized for microprocessor implementation, relies on two look-up tables and a learning scheme that allows look-ahead seek correction for both spiral rotation and system tolerance

Disc defect classification for optical disc drives

Optical disc drives are subject to various disturbances and faults. A special type of fault is the so-called disc defect. In this paper we present an approach for disc defect classification. It is based on hierarchical clustering of measured signals that are affected by disc defects. The timeseriesare mapped into a feature space after which the feature vectors are clustered in a hierarchical fashion. Finally, signals are fitted onto the clusters to obtain single representations for each fault class. The resulting class descriptions can then be used for (on-line) classification ofnew disc defects. The approach is evaluated by applying it to a set of test data

Improved noise sensitivity under high-gain feedback in nano-positioning motion systems

To avoid an increased noise response under high-gain feedback in nano-positioning motion systems, a nonlinear (N-PID) control design is proposed. The design is of particular interest in the wafer scanning industry where nano-accuracy should be achieved under high-speed motion. In a variable gain controller setting, the N-PID control design has an observer structure with state-dependent low-pass filter characteristics. Under high-gain feedback and being induced by sufficiently large servo error signals, the nonlinear observer acts as a low-pass filter with a significantly smaller cut-off frequency as compared to the case of low-gain feedback. As a result, the high-frequency noise response that usually increases under high-gain feedback is kept limited. For a validated wafer stage model, the effectiveness of the control approach in dealing with position-dependent behavior is assessed through simulation

Data-based spatial feedforward for over-actuated motion systems

For advanced motion systems there is an increasing demand for higher production throughput and accuracy. Traditionally, such systems are designed using a rigid-body design paradigm, which aims at designs with high stiffness. The alternative is to design a lightweight system and deal with the resulting flexibilities by over-actuation and over-sensing. This paper presents a data-based spatial feedforward method based on previous task trials, which aims at reducing the vibrations over the complete structure during motion. The proposed method is experimentally validated on an industrial prototype and compared to standard mass feedforward using rigid-body decoupling

Reading of Cracked Optical Discs Using Iterative Learning Control

Optical discs, including Compact Discs (CDs), Digital Versatile Discs (DVDs), and Blu-ray Discs (BDs), can get cracked during storage and usage. Such cracks commonly lead to discontinuities in the data track, potentially preventing reading of the data on the disc. The aim of the present paper is to improve tracking performance of the optical disc drive in the presence of cracks. A Hankel Iterative Learning Control (ILC) algorithm is presented that can perfectly steer the lens during the crack towards the beginning of the track immediately after the crack, i.e., the actuator is steered appropriately during the crack crossing to compensate for the discontinuity in the data track. Experimental results confirm improved reading capabilities of cracked discs. The presented approach potentially enables the recovery of data from cracked discs that were previously considered as unreadable