# US 6,246,041 B1 · Apparatus and method for measuring focusing characteristics of optical pickup and/or optical disc and apparatus and method for recording and/or reproducing optical disc > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,246,041 B1 - Document ID: US6246041B1 - Status: Granted - Kind: B1 - Application number: 09/182,845 - Filed: 1998-10-29 - Granted: 2001-06-12 - Earliest claimed: 1997-10-31 - Assignees: Sony Precision Engineering Center (Singapore) PTE Ltd.; Disk Ware Co. Ltd. - Inventors: Akihito Nakayama; Kenji Shintani; Shunsuke Kohama; Yukari Hashimoto - Web page: https://patentgrep.com/patent/US6246041B1 ## CPC - G11B 7/094: {Methods and circuits for servo offset compensation} - G11B 7/0945: {Methods for initialising servos, start-up sequences} - G11B 2007/0006: {adapted for scanning different types of carrier, e.g. CD & DVD} - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract A device for measuring focusing characteristics of an optical pickup and/or an optical disc capable of measuring characteristics of focusing states with high accuracy by a simplified circuit. An arithmetic-logic unit 12d controls an offset supplying circuit 23 for applying an offset voltage to a focusing servo control signal. This arithmetic-logic unit 12d detects an error rate of the playback data in such a state in which the focusing position of the laser light is deviated by a pre-set offset amount. The arithmetic-logic unit 12d sequentially varies the offset voltage to repeat the above processing for detecting the error rate. The arithmetic-logic unit 12d approximates the relationship of the error rate to the offset amount by a quadratic curve based on detected data. The offset amount which minimizes the error rate is found from this equation of approximation. ## Claims ### Claim 1 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 said reproducing means; and measurement means for imparting a pre-set offset amount to a control amount of said focusing servo control means for varying the focusing position of the laser light, getting from said 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. ### Claim 2 (depends on 1) The apparatus for measuring focusing characteristics of an optical pickup and/or an optical disc as claimed in claim 1 wherein said measurement means finds 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. ### Claim 3 (depends on 2) The apparatus for measuring focusing characteristics of an optical pickup and/or an optical disc as claimed in claim 2 wherein said measurement means sets said pre-set setting range which is not higher than an error rate at a focusing position of the laser light enabling focusing servo control and which is not less than an error rate which occurs without dependency on the focusing position of the laser light. ### Claim 4 (depends on 2) The apparatus for measuring focusing characteristics of an optical pickup and/or an optical disc as claimed in claim 2 wherein said measurement means finds the quadratic curve equation of approximation of the error rate from data of the error rates in said 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. ### Claim 5 (depends on 1) The apparatus for measuring focusing characteristics of an optical pickup and/or an optical disc as claimed in claim 1 wherein said measurement means imparts 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. ### Claim 6 (depends on 1) The apparatus for measuring focusing characteristics of an optical pickup and/or an optical disc as claimed in claim 1 further comprising: 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. ### Claim 7 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. ### Claim 8 (depends on 7) The method for measuring focusing characteristics of an optical pickup and/or an optical disc as claimed in claim 7 further comprising: 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. ### Claim 9 (depends on 8) The method for measuring focusing characteristics of an optical pickup and/or an optical disc as claimed in claim 8 wherein the setting range is 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 is found using an error rate within this setting range. ### Claim 10 (depends on 8) The method for measuring focusing characteristics of an optical pickup and/or an optical disc as claimed in claim 8 wherein the quadratic curve equation of approximation of the error rate is found from data of the error rates in said 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. ### Claim 11 (depends on 7) The method for measuring focusing characteristics of an optical pickup and/or an optical disc as claimed in claim 7 wherein an offset amount corresponding to the focusing position of the laser light with the least error rate is imparted to the control amount of focusing servo control for measuring the pre-set characteristic values of the optical pickup and/or the optical disc. ### Claim 12 (depends on 7) The method for measuring focusing characteristics of an optical pickup and/or an optical disc as claimed in claim 7 wherein focusing characteristics of the optical pickup are adjusted based on the focusing position of the laser light corresponding to the least error rate as found from the equation of approximation of the error rate relative to each focusing position of the laser light. ### Claim 13 An apparatus for recording/reproducing 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 said reproducing means; and adjustment means for imparting a pre-set offset amount to a control amount of said focusing servo control means for varying the focusing position of the laser light beam, getting from said error rate detection means an error rate of reproduced data when the focusing position of the laser light is varied, 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 beam and for imparting to a control amount of the focusing servo control means an offset amount corresponding to the focusing position of the laser light with the least error rate. ### Claim 14 (depends on 13) The apparatus for recording and/or reproducing an optical pickup and/or an optical disc as claimed in claim 13 wherein said adjustment means finds 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 with the least error rate based on this quadratic curve equation of approximation. ### Claim 15 (depends on 14) The apparatus for recording and/or reproducing an optical pickup and/or an optical disc as claimed in claim 14 wherein said adjustment means sets said pre-set setting range which is not higher than an error rate at a focusing position of the laser light enabling focusing servo control and which is not lower than an error rate which occurs without dependency on the focusing position of the laser light. ### Claim 16 (depends on 13) The apparatus for recording and/or reproducing an optical pickup and/or an optical disc as claimed in claim 13 further comprising: an optical pickup for detecting a signal from plural optical discs using plural objective lenses of different characteristics; said focusing servo control means controlling the focusing position of the laser light illuminated on the optical disc responsive to each optical disc for focusing the laser light on the recording surface of the optical disc. ### Claim 17 A method for recording and/or reproducing 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; finding a focusing position of the laser light with the least error rate based on the equation of approximation for the error rate for each focusing position of the laser light; and imparting to the control amount of focusing servo control an offset amount corresponding to the focusing position of the laser light with the least error rate. ### Claim 18 (depends on 17) The method for recording and/or reproducing an optical pickup and/or an optical disc as claimed in claim 17 further comprising: finding a 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. ### Claim 19 (depends on 18) The method for recording and/or reproducing an optical pickup and/or an optical disc as claimed in claim 18 wherein the setting range is 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. ### Claim 20 (depends on 17) The method for recording and/or reproducing an optical pickup and/or an optical disc as claimed in claim 17 further comprising: detecting signals from plural optical discs of different sorts using plural objective lenses of different characteristics; and controlling the focusing position of the laser light illuminated on the optical disc depending on each optical disc for focusing the laser light on the recording surface of the optical disc.