Differential phase detection (DPD) and push-pull methods are widely used to generate tracking error signals in reading and writing high-density digital disks. Radial and tangential tilts, which will deteriorate the performance of the servo system, occur while the disk is spinning. Such influences vary with different tracking error generating methods and physical parameters of the disk. An analytic description of the disk diffraction model is obtained by diffraction theory. Disk radial tilt effects on tracking error signal and cross talk of read only and rewriteable disks are simulated and analyzed. A tracking error signal offset caused by radial tilt is 0.06 µm/deg on a DVD-ROM disk using the DPD method, 0.15 µm/deg using the push-pull method, and 0.12 µm/deg (0.10 pitch/deg) using the DPD method on a DVD-RAM disk. The DPD method exhibits better performance than the push-pull method when the disk is tilted on a DVD-RAM disk. The relationship between the tracking error signal offset and the groove depth is obtained in advance. The intertrack cross talk is also analyzed when disk tilt occurs.
A model of the compound pendulum used for measurement of micro impulses is presented. The effects of pivot friction, air friction and vibration of the stand are simulated through numerical method. To improve the measurement accuracy, it is concluded through the simulation results that the natural period of the compound pendulum should be greater than twenty times the time duration of action of the force being measured. And the moment of inertia of the compound pendulum and the pivot friction should be properly decreased to get a better sensitivity.
In this paper, the pupil energy distribution is calculated with parameters of digital versatile disk and by using the scalar diffraction theory. In view of radial tilt, a radial tilt angle in pit model is added, and consequently, a simulation of push-pull tracking error is given when a radial tilt error occurs. Furthermore, the influence of radial tilt is analyzed by using push-pull tracking servo method.
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