Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1998-10-29
2001-06-12
Kim, Robert H. (Department: 2877)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C369S044250
Reexamination Certificate
active
06246041
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an apparatus and a method for measuring focusing characteristics of an optical pickup and/or an optical disc. The invention also relates to an apparatus and a method for adjusting focusing characteristics of an optical pickup or an optical disc for recording and/or reproducing the optical disc.
DESCRIPTION OF THE RELATED ART
There has so far been known a device for inspecting characteristics of an optical pickup used in an optical disc drive. The device for inspecting characteristics of an optical pickup is used for example for inspection for shipment or reception of an optical pickup in connection with whether or not the optical pickup satisfies the prescribed specifications.
Among inspection items of the device for inspecting characteristics of an optical pickup, there is in general the inspection of so-called defocusing characteristics of the optical pickup.
In a reproducing device for an optical disc, focusing servo is carried out so that the laser light radiated from the optical pickup will produce a minimum-sized spot on a recording track. In an optical disc device, for example, the reflected light from the optical disc is detected by an optical pickup and the reflected light as detected is converted by an photoelectric converting device into electrical signals from which focusing error signals are produced. With the optical disc device, the objective lens of the optical pickup is controlled so that the focusing error signals will be reduced to zero. There are occasions wherein, due to adjustment errors of a semiconductor laser or an objective lens, characteristics thereof or to lack in precision of the photoelectric converting device, the minimum-sized spot of the laser light radiated from the optical pickup is not produced on the recording track of the optical disc even although the focusing error signals are reduced to zero. This error of the optical pickup is termed so-called defocusing. The device for inspecting characteristics of the optical pickup measures the defocusing characteristics of the optical pickup for carrying out shipment or acceptance inspection of the optical pickup.
With a conventional characteristics inspection device of the optical pickup, jitter components of the playback signals of an optical disc are detected for measuring defocusing characteristics of the optical pickup.
However, the conventional characteristics inspection device of the optical pickup necessitates a complicated circuit structure for detecting the jitter components and an extremely costly circuit for detecting data of higher accuracy. Moreover, if the defocusing characteristics are measured in the conventional characteristics inspection device of the optical pickup based on the jitter components, it has been difficult to achieve measurement of characteristics of high accuracy.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an apparatus for measuring focusing characteristics of an optical pickup and/or an optical disc comprising:
focusing servo control means for controlling a focal point position of a laser light beam illuminated on the optical disc, based on an output of a photoelectric converting unit of the optical pickup, for focusing the laser light beam on a recording surface of the optical disc;
reproducing means for reproducing data recorded on the optical disc based on an output of the photoelectric converting unit of the optical pickup;
error rate detection means for detecting an error rate of data reproduced by the reproducing means; and
measurement means for imparting a pre-set offset amount to a control amount of the focusing servo control means for varying the focusing position of the laser light, getting from the error rate detection means an error rate of reproduced data when the focusing position of the laser light is varied and for finding the focusing position of the laser light corresponding to the minimum error rate in accordance with an equation of approximation of the error rate corresponding to each focusing position of the laser light.
The measurement means may find the equation of approximation of a quadratic curve for error rates for respective focusing positions of the laser light using an error rate within a pre-set setting range in order to find the focusing position of the laser light corresponding to the least error rate based on this quadratic curve equation of approximation.
The measurement means may set the pre-set setting range which preferably is not higher than an error rate at a focusing position of the laser light enabling focusing servo control and which preferably is not less than an error rate which occurs without dependency on the focusing position of the laser light.
The measurement means may find the quadratic curve equation of approximation of the error rate from data of the error rates in the pre-set setting range from the focusing position with the high error rate to the focusing position directly before or in the vicinity of the error rate first exceeding the lower setting range limit.
The measurement means may impart an offset amount corresponding to the focusing position of the laser light with the least error rate to the control amount of the focusing servo control means for measuring the pre-set characteristic values of the optical pickup and/or the optical disc.
The apparatus for measuring focusing characteristics of an optical pickup and/or an optical disc may further comprise:
adjustment means for adjusting focusing characteristics of the optical pickup based on the focusing position of the laser light corresponding to the least error rate.
According to another aspect of the invention, there is provided a method for measuring focusing characteristics of an optical pickup and/or an optical disc comprising:
controlling the focusing position of the laser light illuminated on the optical disc based on an output of a photoelectric converting unit of the optical pickup for focusing the laser light on the recording surface of the optical disc;
reproducing data recorded on the optical disc based on an output of the photoelectric converting unit of the optical pickup;
detecting an error rate of the reproduced data;
imparting a pre-set offset amount to a control amount of the focusing servo control for varying the focusing position of the laser light;
finding an equation of approximation for the error rate for each focusing position from an error rate of data reproduced on varying the focusing position of the laser light; and
finding a focusing position of the laser light corresponding to the least error rate based on the equation of approximation for the error rate for each focusing position of the laser light.
The method for measuring focusing characteristics of an optical pickup and/or an optical disc may further comprise:
finding the quadratic curve equation of approximation of the error rate for each focusing position of the laser light using error rates within a pre-set setting range; and
finding the focusing position of the laser light corresponding to the least error rate based on this quadratic curve equation of approximation.
The setting range may be set so as to be not more than an error rate at a focusing position of the laser light enabling focusing servo control and so as to be not less than an error rate occurring without dependency on the focusing position of the laser light and wherein the quadratic curve equation of approximation for each focusing position of the laser light may be found using an error rate within this setting range.
The quadratic curve equation of approximation of the error rate may be found from data of the error rates in the pre-set setting range from the focusing position with the high error rate to the focusing position directly before or in the vicinity of the error rate first exceeding the lower setting range limit.
An offset amount corresponding to the focusing position of the laser light with the least error rate may be imparted to the control amount of focusing servo control for measuring the pre-set charact
Hashimoto Yukari
Kohama Shunsuke
Nakayama Akihito
Shintani Kenji
Frommer William S.
Frommer Lawrence & Haug LLP.
Kim Robert H.
Polito Bruno
Smith Zandra
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