Optical Pickup Tracking Servo Stability for Eccentric Discs
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Solution Overview
Problem
Optical disc apparatuses with optical pickups face instability in tracking servo control due to optical discs with offset or eccentric centers of gravity, leading to vibrations that disrupt the objective lens and prevent the acquisition of appropriate tracking error signals, causing unstable tracking servo control and failure in tracking pull-in.
Innovation Solution
An optical pickup with a microprocessor that performs preliminary tracking servo control by equally dividing the photodetector's light receiving sections and adjusting the objective lens in the radial direction to equalize DC components of electrical signals, ensuring stable tracking pull-in even with discs having offset centers of gravity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the optical pickup is used with optical discs having offset or eccentric centers of gravity, then the optical disc rotates and vibrates strongly at high speed, but the vibrations are transmitted to the objective lens causing displacement in tracking direction, which disrupts the photodetector signal and prevents stable tracking servo control
Solution Approach 1:
The patent applies preliminary action by performing preliminary tracking servo control before normal tracking operation. The microprocessor moves the objective lens in the radial direction to equalize the DC components of signals from the first and second light receiving sections before starting conventional tracking servo control. This preliminary positioning compensates for vibrations caused by offset center of gravity, enabling stable tracking pull-in even when the optical disc rotates at high speed
Solution Approach 2:
The patent uses feedback by continuously monitoring the signals from the first and second light receiving sections and adjusting the objective lens position accordingly. The microprocessor compares the DC components of the signals and moves the objective lens to equalize them, creating a closed-loop control system that compensates for vibrations and maintains stable tracking during high-speed rotation
2Illumination intensity
If the objective lens is vibrated strongly due to disc vibrations, then the light beam irradiation to the optical disc is disrupted, but the photodetector cannot receive stable reflected light, resulting in inability to obtain appropriate tracking error signal
Solution Approach 1:
The patent applies preliminary action by performing preliminary tracking servo control to position the objective lens correctly before normal operation begins. The microprocessor moves the objective lens in the radial direction to equalize DC components of signals from the first and second light receiving sections, ensuring the laser beam is properly irradiated onto the optical disc track before conventional tracking servo control starts, thus enabling accurate tracking error signal acquisition
3Device complexity
If conventional tracking servo control is used without preliminary positioning, then the tracking control is simpler, but the tracking pull-in fails when optical disc has offset center of gravity
Solution Approach 1:
The patent applies preliminary action by adding a preliminary tracking servo control stage before conventional tracking servo control. The microprocessor performs preliminary positioning by moving the objective lens in the radial direction to equalize DC components of signals from the first and second light receiving sections. This additional preliminary stage increases complexity slightly but ensures reliable tracking pull-in even when the optical disc has offset center of gravity, making the system more robust
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the acquisition of appropriate tracking error signals and achieves stable tracking pull-in by maintaining the objective lens in a constant position relative to the photodiode, effectively compensating for disc vibrations and ensuring accurate tracking control.
Implementation Method 1
a photodetector for receiving a beam reflected by the recording surface of the optical disc and converting it to an electrical signal
Implementation Method 2
an objective lens for collecting the laser beam on a recording surface of the optical disc
Implementation Method 3
a light emitting element for emitting a laser beam
Data Source
AI summary
A microprocessor performs preliminary tracking servo control of an objecting lens by moving the objective lens in a radial direction of an optical disc so as to allow a laser beam reflected by the optical disc to be equally divided and received by first and second light receiving sections PD1, PD2 of the photodiode PD before the microprocessor starts tracking servo control of the objective lens. This makes it possible to perform preliminary tracking servo control of the objective lens before tracking pull-in, and thereby to obtain an appropriate tracking error signal for performing stable tracking pull-in, even when an optical disc with an offset center of gravity is mounted on an optical disc apparatus.