Optical Disk Focus Control Gain Adjustment
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Solution Overview
Problem
Existing optical disk apparatuses require expensive equipment and increased installation space and costs to measure open-loop gains for focus servo control, leading to instability and oscillation during focus control between land and groove due to differing gain sensitivities.
Innovation Solution
An optical disk apparatus that quickly sets focus control gains by comparing focus offsets and amplitude variations between recess and protrusion signals, using a controller to adjust gains without the need for a frequency characteristic analyzer, and sets adjustment step sizes based on relative optical gains for stable focus control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If open-loop gain measurement is performed using a frequency characteristic analyzer, then focus control stability is improved, but device complexity and installation space increase
Solution Approach 1:
The optical disk apparatus performs self-diagnosis and self-adjustment by measuring its own open-loop gain characteristics during normal operation. The controller uses the optical pickup unit to read test patterns from the optical disk, processes the returned signals through the servo circuit, and automatically determines gain values without external measurement equipment.
Solution Approach 2:
The patent extracts only the essential measurement function from the complex frequency characteristic analyzer. Instead of using a complete external analysis system, the invention isolates and implements just the gain measurement capability within the apparatus itself, using existing components (optical pickup, servo circuit, controller) to perform the measurement.
2Measurement precision
If different focus control gains are set for land and groove, then focus control precision is improved, but device complexity increases
Solution Approach 1:
The patent applies different focus control gains specifically to land and groove regions based on their different optical characteristics. The controller identifies whether the current position is land or groove and automatically selects the appropriate gain value from predetermined settings, optimizing focus control for each region's specific properties without requiring manual configuration.
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 method stabilizes focus control by simplifying the process of setting focus control gains, reducing open-loop gain differences between land and groove, and enabling optimal focus position learning without additional equipment, thus improving focus servo control efficiency and reducing costs.
Implementation Method 1
light emitted from a laser, which serves as a light source installed on laser diode unit
Implementation Method 2
The linearly polarized light from polarization hologram 104 is then converted into circularly polarized light by quarter-wave plate 105
Implementation Method 3
focused on optical disk 101 by objective lens 106 driven by actuator 107
Implementation Method 4
the light is received by a photodetector serving as a light-receiving element on LDU 102. The photodetector outputs to pre-amplifier 121 a detection signal of the incident light thereon
Implementation Method 5
the light is diffracted by polarization hologram 104 and then passes through collimating lens 103
Data Source
AI summary
An optical disk apparatus includes: an optical pickup unit for reading out information recorded on an optical disk; a demodulation circuit for demodulating digital data from an output signal of the optical pickup unit; and a controller for performing a servo control based on the output signal of the optical pickup unit. When performing a focus/tracking control in a recess and a protrusion of a guide groove of the optical disk, the controller obtains a focus control gain difference between the recess and the protrusion by comparing focus offsets with respect to variations in amplitudes of signals from the optical disk for the recess and the protrusion, respectively.