Browse Prior Art Database

Use curve fit to reduce/remove position errors

IP.com Disclosure Number: IPCOM000032338D
Publication Date: 2004-Nov-01
Document File: 3 page(s) / 105K

Publishing Venue

The IP.com Prior Art Database

Abstract

ID692505

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 54% of the total text.

Page 1 of 3

ID692505

Use curve fit to reduce/remove position errors

    In optical systems curve fit (second order polynomial regression) is used to find an optimum setting for a parameter in order to obtain good optical signals. At this moment curve fit is used to compensate for spread between discs and positions on the disc.

    Now curve fit will also be used to reduce/remove position errors due to adjustment errors and tolerances on mechanical reference positions.

    Due to mechanical position errors of a certain item (for example alpha tilt) the quality of the optical signals will not be optimal. Curve fit will increase the signal quality by reducing/removing position errors.

    In principle curve fit can be generally used in optical systems to reduce/remove position errors.

    In this invention disclosure curve fit (second order polynomial regression) for the alpha tilt correction in the Blu-ray disc engine is described.

    Alpha tilt (also called tangential tilt) correction is needed because the optimum alpha tilt is different for DVD and BD discs. In other words: the angle in tangential direction between the disc and OPU is different for DVD and BD discs.

    Alpha tilt correction is achieved by vertically moving one side of the OPU. This movement is the resulting vertical movement of a rotating crankshaft, see figure 1. This system is non linear. The alpha tilt control range is ± 10 mrad.

Figure 1: alpha tilt correction mechanism

    The crankshaft is driven by a stepper motor. To get to the optimum position for BD or DVD discs the crankshaft must rotated against a mechanical stop (called reference position) at least one time. From this reference position the crankshaft is rotated to the optimum position for BD or DVD discs.

    The OPU department measures the optimum positions (angle between disc and OPU). When assembling the Blu-ray disc engine the alpha tilt between turntable motor plane (disc) and OPU will be adjusted to the optimum BD value with the crankshaft set in the middle position.

    However due to mechanical tolerances on the reference position, adjustment errors and possible back stepping of the stepper motor when rotating against the reference position the actual alpha tilt will differ from the optimum value. The error can be up to 1.5 mrad alpha tilt.

    To remove this position error a calibration will be done. Curve fit (second order ...