EP0190439A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Focus servo loop correction
Assignee: International Business Machines Corp
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Filing: 1985-12-10
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Granted: —
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Expires: 2005-12-10
Abstract
Abstract Error correction in a feedback servo system. The feedback servo loop in, for example, a head positioning circuit in an optical disk data recording and retrieval system is provided with means for forcing the feedback signal to zero when the head is positioned at best focus as determined by a peak in the laser monitoring diode. The head in such a system must be dynamically maintained at a best focus position but, through use and transporting, the alignment of the head position error detecting system can be disturbed. In some cases, the loop circuit parameters may drift from their original values. To correct for errors introduced from such causes, the head is positioned at best focus and the focus error (head position error) signal is sensed. A correction system forces the sensed value to zero, e.g., by adjusting the gain of amplifiers used in the feedback loop.
Inventors
- 👤 Keith Allen Bates
- 👤 Russell Alan Budd
- 👤 Millard Alvin Habegger
- 👤 Mark Len Rhoades
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 06:05
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/12; G11B7/125; G11B7/08; G11B7/09; G11B7/094; G11B7/0945; G11B7/0908; G11B7/0909
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
193 words
System for storing information on a reflective medium, the information values being represented by variations in reflectivity of said medium, said system including: source means for supplying a beam of radiant energy, said source means including means for supplying a monitor signal to maintain said beam of radiant energy at a predetermined energy level; detection means for supplying signals representative of energy reflected from said medium, said detection means including means for supplying a focus error signal; lens means for focusing said beam onto an information-bearing surface of said medium and for directing energy reflected from said surface to said detection means, said lens means including actuating means responsive to a focus signal for varying the focus of said beam onto said surface; means responsive to said focus error signal for supplying a focus signal to said actuating means; the sdaid said being characterized in that it further comprises : means responsive to said monitor signal for determining when the lens means is at position of best focus; and means responsive to said determining means for reducing said focus error signal to zero while said lens means is at its best focus position.
Claim 2
Dependent Claim
193 words
System for storing information on a reflective medium, the information values being represented by variations in reflectivity of said medium, said system including: source means for supplying a beam of radiant energy, said source means including means for supplying a monitor signal to maintain said beam of radiant energy at a predetermined energy level; detection means for supplying signals representative of energy reflected from said medium, said detection means including means for supplying a focus error signal; lens means for focusing said beam onto an information-bearing surface of said medium and for directing energy reflected from said surface to said detection means, said lens means including actuating means responsive to a focus signal for varying the focus of said beam onto said surface; means responsive to said focus error signal for supplying a focus signal to said actuating means; the sdaid said being characterized in that it further comprises : means responsive to said monitor signal for determining when the lens means is at position of best focus; and means responsive to said determining means for reducing said focus error signal to zero while said lens means is at its best focus position.
Claim 3
Dependent Claim
71 words
The system according to claim 1 wherein : said means responsive to said monitor signal includes peak detector means for supplying an output signal when said monitor signal attains a peak value; and the means responsive to said determining means includes controller means comprising: means for sensing said focus error signal; and means for supplying a correction signal to said detection means to cause said focus error signal to become zero.
Claim 4
Dependent Claim
94 words
The system according to claim 2, wherein said detection means includes quadrature diode means for supplying diode signals and means responsive to said diode signals for supplying a focus error signal, further comprising: adjustable gain preamplifier means for coupling said diode signals to said means responsive to said diode signals; means in said controller means for sensing output signals from said preamplifier means; and said means for supplying a correction signal includes means for varying the gain of said preamplifier means to cause the output signal from said preamplifier to assume a given value.
Claim 5
Dependent Claim
33 words
The system according to claim 3 further including in said controller means: averaging means for deriving the average value of said diode signals and for supplying said average value as said given value.
Claim 6
Dependent Claim
213 words
Information storage and retrieval system including: a beam of radiant energy; recording means for storing information having values manifested by variations in reflectivity; focusing means for controlling the convergence of said beam onto said recording means in a plane at which said information is manifested; focus control means responsive to a portion of radiant energy reflected from said recording means for providing a control signal to said focusing means to keep said beam converged on said recording means; means responsive to reflected radiant energy for supplying a feedback signal which attains a maximum value when said beam of radiant energy converges at said recording means; and means responsive to said feedback signal for maintaining the energy level of said beam substantially constant at a predetermined level; said system being characterized in that it further includes : means for decoupling said control signal from said focusing means; means coupled to said focusing means for driving said focusing means from one limit to the other; means responsive to said feedback signal for supplying a peak indicating signal when a peak is detected in said feedback signal; means responsive to said control signal and said peak indicating signal for varying said feedback signal to zero; and means for coupling said control signal to said focusing means.
Claim 7
Dependent Claim
213 words
Information storage and retrieval system including: a beam of radiant energy; recording means for storing information having values manifested by variations in reflectivity; focusing means for controlling the convergence of said beam onto said recording means in a plane at which said information is manifested; focus control means responsive to a portion of radiant energy reflected from said recording means for providing a control signal to said focusing means to keep said beam converged on said recording means; means responsive to reflected radiant energy for supplying a feedback signal which attains a maximum value when said beam of radiant energy converges at said recording means; and means responsive to said feedback signal for maintaining the energy level of said beam substantially constant at a predetermined level; said system being characterized in that it further includes : means for decoupling said control signal from said focusing means; means coupled to said focusing means for driving said focusing means from one limit to the other; means responsive to said feedback signal for supplying a peak indicating signal when a peak is detected in said feedback signal; means responsive to said control signal and said peak indicating signal for varying said feedback signal to zero; and means for coupling said control signal to said focusing means.
References Cited (Backward Citations)
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