EP0036222A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Focus servo system and focussing method
Assignee: Discovision Associates
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Filing: 1979-03-27
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Granted: —
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Expires: 1999-03-27
Abstract
Abstract An optical apparatus is described for use with a video disc (7) having frequency modulated video information (9) recorded thereon in the form of a plurality of concentric circles or a single spiral. The information track comprises successively positioned light reflective and light non-reflective regions (10,11). A focussed light beam (4) is caused to be positioned over the centre of an information track and the light reflected from the information track is gathered by an objective lens (17) for application to electronic circuitry (30) for recovering the recorded frequency modulated video signals. Lens focussing means are described for positioning the objective lens at the optimum focussed position above the information track for gathering the maximum amount of reflected lightfrom the information track.
Inventors
- 👤 Ludwig Ceshkovsky
- 👤 Wayne Ray Dakin
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 03:33
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/12; G11B19/00; G11B19/20; G11B19/28; G11B21/00; G11B21/02; G11B21/10; G11B7/004; G11B7/005; G11B7/08; G11B7/085; G11B7/08505; G11B7/08511; G11B7/09; G11B7/0941; G11B7/0908
Claims Analysis
Total Claims: 33
Claim 1
Independent Claim
121 words
A focus servo system for use in a player apparatus for deriving information recorded on an information bearing surface, the player apparatus comprising optical means (2) for focussing a source beam (4) of radiation on the information bearing surface (7), and signal recovery means (30) for receiving the source beam after modulation by the information bearing surface and for developing an electrical output signal representing the recorded information, characterised by control means coupled between the optical means and the signal recovery means for driving an objective lens means (17) of the optical means (2) to establish optimum focus of the beam on the surface in response to a signal derived from the output signal and representing the degree of focussing achieved.
Claim 2
Dependent Claim
121 words
A focus servo system for use in a player apparatus for deriving information recorded on an information bearing surface, the player apparatus comprising optical means (2) for focussing a source beam (4) of radiation on the information bearing surface (7), and signal recovery means (30) for receiving the source beam after modulation by the information bearing surface and for developing an electrical output signal representing the recorded information, characterised by control means coupled between the optical means and the signal recovery means for driving an objective lens means (17) of the optical means (2) to establish optimum focus of the beam on the surface in response to a signal derived from the output signal and representing the degree of focussing achieved.
Claim 3
Dependent Claim
96 words
A system as claimed in Claim 1, wherein the control means comprises focus error detection means for detecting the position of the objective lens means relative to the information bearing surface, lens driver means for moving said objective lens means relative to the information bearing surface along the path of the source beam,toward the.optimum focussing position, and focus acquisition signal means responsive to the focus error detection means for selectively generating an output to the lens driver means in a focus acquisition mode, for disabling the lens driver means upon detection of the optimum focussing position.
Claim 4
Dependent Claim
38 words
A system as claimed in Claim 2, which further includes restart means for restarting the focus acquisition mode of the focus acquisition signal means if the lens driver means is disabled without the optimum focussing position being detected.
Claim 5
Dependent Claim
66 words
A system as claimed in Claim 2 or Claim 3 wherein the focus acquisition signal means includes focus servo switching means for selectively establishing open and closed loop modes of operation, the switching means disconnecting the lens driver means from the focus error detection means.in the open loop mode and connecting the lens driver means to the focus error detection means in the closed loop mode.
Claim 6
Dependent Claim
25 words
A system as claimed in Claim 4, wherein the focus servo switching means establishes the open loop mode of operation during the focus acquisition mode.
Claim 7
Independent Claim
48 words
A system as claimed in any of Claims 2-5 wherein the focus error detection means includes information detection means for detecting the information as the objective lens means reaches the optimum focussing position and for disabling the focus acquisition signal means in response to detection of the information.
Claim 8
Dependent Claim
56 words
The focus servo system as claimed in Claim 6, and Claim 3, wherein the restart means is responsive to the information detection means to restart the focus acquisition mode, even after once disabling the focus acquisition signalmeans in response to detection of the information, if the information detection means does not continue to detect the information.
Claim 9
Dependent Claim
38 words
A system as claimed in Claim 7 wherein the restart means includes means for preventing restart of the fo-cus acquisition mode, if the information detection means detects loss of information for less than a predetermined amount of time.
Claim 10
Dependent Claim
121 words
A system as claimed in Claim 4 or Claim 5, wherein the focus acquisition signal means selectively drives the objective lens means in a first . direction through a predetermined range of travel that includes an optimum focussing position located at a predescribed distance from the information bearing surface, and the focus servo system includes kickback signal means, responsive to the focus error detection means, for providing an additional output to the lens driver means to intermittently drive the objective lens in a direction opposite to the first direction, whereby the objective lens means scans back and forth past the optimum focussing position as the focus acquisition signal means tends to drive the objective lens means through a range of travel.
Claim 11
Dependent Claim
40 words
A system as claimed in Claim 9, wherein the kickback signal means includes differentiation means for differentiating the signal applied to the lens driver means from the kickback signal means to convert the signal to a more practically usable form.
Claim 12
Dependent Claim
44 words
A system as claimed in Claim 9 or Claim 10, and further including information detection means for detecting the information as the objective lens means reaches the optimum focussing position and for disabling the focus acquisition signal means in.response to detection of the information.
Claim 13
Dependent Claim
43 words
A system as claimed in Claim 11, and further including restart means for restarting the focus acquisition mode if the focus acquisition signal means drives the objective lens means through the predetermined range of travel without the information detection means detecting the information.
Claim 14
Dependent Claim
52 words
A system as claimed in Claim 12, and further including delay means for delaying the restart means for a predetermined period of time in the event the information detection means does not continue to detect the information, after previously disabling the focus acquisition signal means in response to detection of the information.
Claim 15
Independent Claim
80 words
A system as claimed in any of Claims 2-13, for use in apparatus including a spindle for rotating a disc with an information bearing surface at a predetermined angular rate of rotation, the focus servo system including spindle lock detector means, responsive to the spindle, for detecting the angular rate of rotation of the disc, the spindle lock detector means inhibiting the focus acquisition signal means if the rotation rate of the disc is less than a predetermined rotation rate.
Claim 16
Independent Claim
85 words
A system as claimed in any of Claims 2-14, wherein the lens driver means is responsive to the focus error detection means in co-operation with the focus acquisition signal means for maintaining the objective lens in an optimum focussing range of travel relative to the information bearing surface, the objective lens means, the focus error detection means, the focus acquisition signal means, and the lens driver means forming a closed loop focus servo control system for maintaining the objective lens in the optimum focussing range.
Claim 17
Independent Claim
67 words
A system as claimed in any of Claims 2-15, wherein the focus error detection means includes transducer means for producing a focus error signal responsive to the positioning of the objective lens means at other than the optimum focussing position, the focus error signal being applied through the focus acquisition signal means to the lens driver means for maintaining the lens means at said optimum focussing position.
Claim 18
Dependent Claim
66 words
A system as claimed in Claim 16, wherein the transducer means comprises a pair of spaced transducers each receiving a portion of the reflected beam of radiation; the focus error detection means includes a differential amplifier responsive to the outputs of the pair of transducers; and the focus error signal is comprised at least in part of the differential focus error signal from the differential amplifier.
Claim 19
Dependent Claim
64 words
A system as claimed in Claim 16 or Claim 17, wherein the transducer means includes means for producing a signal representing detection of the information; and the focus acquisition signal means disables the lens driver only upon detection by the focus error detection means that optimum focussing position has been reached and upon detection by the transducer means that the information has been detected.
Claim 20
Independent Claim
91 words
A system as claimed in any of Claims 2-18, wherein the objective lens means is movable by the lens driver means between a retracted position away from the surface and an extended position closer to the surface, the optimum focussing position being located between the retracted and extended.positions, and the focus acquisition signal means includes a ramp signal generator for generating a ramp signal to cause the lens driver means to drive the lens in a ramp fashion toward the information bearing surface from the retracted position to the extended position.
Claim 21
Dependent Claim
52 words
A system as claimed in Claim 19 wherein the focus acquisition signal means includes restart means, and wherein, if the optimum focussing position is not acquired, the restart means automatically causes the lens driver means to drive the lens back to its retracted position and commence ramping again toward the extended position.
Claim 22
Dependent Claim
66 words
A system as claimed in Claim 19 or Claim 20, including signal recovery means for developing an electrical signal representing the information carried by the information bearing surface, and wherein the focus acquisition signal means combines the electrical signal and the ramp signal for controlling the lens driver means to disable the lens driver only upon detection of the electrical signal from the signal recovery means.
Claim 23
Independent Claim
61 words
A system as claimed in any of Claims 19-21, wherein the focus acquisition signal means includes a kickback generator for generating an oscillatory waveform: and means for superimposing the oscillatory waveform on the ramp signal to cuase the lens driver means to driver the lens means a reciprocating movement about the optimum focussing position during the period of each ramp signal.
Claim 24
Dependent Claim
27 words
A system as claimed in Claim 22, wherein the kickback generator includes means for triggering said oscillatory waveform a fixed time after initiation of the ramp signal.
Claim 25
Dependent Claim
49 words
A system as claimed in Claim 22 or Claim 23, wherein the focus error detection means includes information detection means for detecting the information as said lens means reaches the optimum focussing position; and the kickback generator includes means for triggering the oscillatory waveform upon detection of the information.
Claim 26
Independent Claim
60 words
A system as claimed in any preceding claim including upper and lower limit switches, operated by movement of the objective lens means to its extreme retracted and extended positions, for halting movement of the objective lens means in the direction of retraction and extension, respectively, the optimum focussing position lying within the range of lens movement between the limit switches.
Claim 27
Dependent Claim
33 words
A system as claimed in Claim 25, wherein the limit switches, when operated, halt movement of the objective lens means in its direction of movement and initiates movement thereof in the opposite direction.
Claim 28
Dependent Claim
88 words
A system as claimed in Claim 2, wherein the control means further includes a ramp signal generator for generating a ramp signal for driving said objective lens means in a ramp fashion toward said information bearing surface from a retracted position, said control means further including a kickback generator fcr generating an oscillatory waveform for driving said objective lens means in a reciprocating movement about said optimum focussing position, said oscillatory waveform commencing at a fixed time after initiation of said ramp signal by said ramp signal generator.
Claim 29
Dependent Claim
95 words
A focussing method for use in a player apparatus for deriving information from an information bearing surface, the player apparatus including optical means for directing a source beam of radiation along a prescribed optical path to the surface, the method comprising the steps of directing the source beam through an objective lens means onto the information bearing surface, detecting the position of the objective lens means relative to the information bearing surface, driving the objective lens means toward an optimum focussing position, and halting the objective lens means as the optimum focussing position is detected.
Claim 30
Dependent Claim
95 words
A focussing method for use in a player apparatus for deriving information from an information bearing surface, the player apparatus including optical means for directing a source beam of radiation along a prescribed optical path to the surface, the method comprising the steps of directing the source beam through an objective lens means onto the information bearing surface, detecting the position of the objective lens means relative to the information bearing surface, driving the objective lens means toward an optimum focussing position, and halting the objective lens means as the optimum focussing position is detected.
Claim 31
Dependent Claim
35 words
29, A method as claimed in Claim 28, including the step of restarting the drive step if the objective lens means is driven past said optimum focussing position without the optimum focussing position being detected.
Claim 32
Dependent Claim
62 words
A method according to Claim 28 or Claim 29, including the steps of driving the objective lens means in a first direction through a predetermined range of travel that includes the optimum focussing position, and intermittently driving the objective lens in a direction opposite to the first direction, whereby the lens driver means scans back and forth past the optimum focussing position.
Claim 33
Independent Claim
41 words
The method according to any of Claims 28-30, including the further step of detecting the information as the objective lens means passes through the optimum focussing position and for halting the objective lens means in response- to detection of said information.
References Cited (Backward Citations)
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