CA1109560A - Apparatus for reading a radiation-reflecting record carrier - Google Patents
Apparatus for reading a radiation-reflecting record carrierInfo
- Publication number
- CA1109560A CA1109560A CA298,999A CA298999A CA1109560A CA 1109560 A CA1109560 A CA 1109560A CA 298999 A CA298999 A CA 298999A CA 1109560 A CA1109560 A CA 1109560A
- Authority
- CA
- Canada
- Prior art keywords
- radiation
- focussing
- record carrier
- astigmatic
- detectors
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
- G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
- G11B7/0909—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only by astigmatic methods
Landscapes
- Optical Recording Or Reproduction (AREA)
- Optical Head (AREA)
- Automatic Focus Adjustment (AREA)
Abstract
ABSTRACT:
An apparatus is described for reading a record carrier with an optical information structure, which apparatus comprises an astigmatic focussing error detection system, said detection system com-prising an astigmatic element and a radiation-sensi-tive detector which comprises four sub-detectors.
By arranging the dividing lines between the sub-detectors parallel to and perpendicularly to the effective track direction respectively and at an angle of 45 with the astigmatic focal lines, it can be avoided that the focussing error signal is affected by a movement of the radiation spot formed on the record carrier in n direction transverse to the track direction.
An apparatus is described for reading a record carrier with an optical information structure, which apparatus comprises an astigmatic focussing error detection system, said detection system com-prising an astigmatic element and a radiation-sensi-tive detector which comprises four sub-detectors.
By arranging the dividing lines between the sub-detectors parallel to and perpendicularly to the effective track direction respectively and at an angle of 45 with the astigmatic focal lines, it can be avoided that the focussing error signal is affected by a movement of the radiation spot formed on the record carrier in n direction transverse to the track direction.
Description
PIIN. 8721.
VMI/1~JM/COBB.
24-4-1977.
Apparatus for reading a radiation-reflecting record carrier.
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The invention relates to an apparatus for reading a radiation-reflecting record c~rrier on which information is stored in an opticall-y readable track-~; wise arranged information structure, which apparatus comprises a radiation source which prod~lces a r2ad beam, an objective system for passing the read beam to a rad.iation-sensitive de-tection system vla the record carrier, which system converts the read 'beam which has been rnodulated by the information structure into an electri.cal signal, and an opto-elec-tronic focussing-~'~ ' error detection system for determining a deviation between the desired and the actual position of the plane of focussing of the objective system, which focllssirlg-error detection system comprises an astigmatic elem~ent ;~ 15 and a radiation-sensitive detector9 which detector compr.ises for sub-detectors which are dispos~d in ~our different quadrants of an imaginary X-Y coordinate system, the X and th~ Y-a~'is being di.sposed at an angle of 45 ~ith the astigrnatic focal lines of the astigmatic 20 ` el~me~t.
Such apparatus is described in Gerrnan Patent Application No. 2,501,124 which has been laid open for public inspection. I`his apparatus ls for example .
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5~ 01 PHN. 8721.
VMI/1~JM/COBB.
24-4-1977.
Apparatus for reading a radiation-reflecting record carrier.
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,~ .
The invention relates to an apparatus for reading a radiation-reflecting record c~rrier on which information is stored in an opticall-y readable track-~; wise arranged information structure, which apparatus comprises a radiation source which prod~lces a r2ad beam, an objective system for passing the read beam to a rad.iation-sensitive de-tection system vla the record carrier, which system converts the read 'beam which has been rnodulated by the information structure into an electri.cal signal, and an opto-elec-tronic focussing-~'~ ' error detection system for determining a deviation between the desired and the actual position of the plane of focussing of the objective system, which focllssirlg-error detection system comprises an astigmatic elem~ent ;~ 15 and a radiation-sensitive detector9 which detector compr.ises for sub-detectors which are dispos~d in ~our different quadrants of an imaginary X-Y coordinate system, the X and th~ Y-a~'is being di.sposed at an angle of 45 ~ith the astigrnatic focal lines of the astigmatic 20 ` el~me~t.
Such apparatus is described in Gerrnan Patent Application No. 2,501,124 which has been laid open for public inspection. I`his apparatus ls for example .
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5~ 01 PHN. 8721.
2~ -10~7.
employed for reading a record carrier ~n which a (colour) television programme is stored. The information structure then consists of a multitude of areas alter-nating wlth intermediate areas arranged in a spiral track, which areas and intermediate areas influence a read beam in different manners. The information is for exan.ple contained in the lengths of the areas and those of the intermediate areas. In order to obtain a sufficiently long playing time with a record carrier of limited size, the details of the informa-tion struct-`; ure have to be very small. For e~ample, if a 30-minute television programme is stored on one side of a disc-shaped round record carrier in an annular area with an outer radius of approx~mately 15 cm and an inner radius of approximately 6 cm, the width o~ the tracks will be approx. 0.5 /um and the average length of the areas and o~ the intermediate areas will be approx. I /um.~
In order to enable these minute details to be read an objective system with a fairly large numerical aperture is to be used. Howe~er, the depth of focus of such an objective system is small. ~s in the read apparatus the distance between the plane of the information structure and the objective system ma-y var~
by an amount greater than the depth of focus~ provisions must be made so as to enable these variations -to be detected and the focussing to be corrected.
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PHN. 8721.
24-4-1977.
In accordance with the said German Patent Application for this purpose a beam of radiation which has been reflected by -the record carrier is made astig-matic, in that a cyliIldrical lens is arranged in the path of this beam behind the obJective system. Between the focal lines of the astigmatic system constituted by the objective system ancl the cylindrical lens a radiation-sensitive detector which consists of four sub-detectors is disposed. When the posi-tion of the plane of the information struc-ture relative to the objective system changes, the shape of the image formed on the sub-detectors also changesO This change in shape ~ can be detected by combining the output signals of the ;~ ~ sub-detectors in a suitable manner.
15~ ~ ~ When the known read apparatus is used practical problems may arise. The radiation distribution across the composite detector also depends on the dif-fraction of the radia-tion beam by the details of the nform~tion structure. ~irst of all~ diffraction is ob-20 ~ talned in the longltudlnal direction~of a track to be read,~owing to the sequence of areas and intermediate ; areas. The variations in the radiation distribution :
across the composite detector owing to this dlffraction havc a high frequcncy relative to the focussing errors~
` Z5 .so that the influence of this diffractio~ on the focus-si~g control signal can be eliminated electronically.
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PHN. 8721.
2l~ -1977 Furthermore, diffraction occurs in a d:irection transverse to the track direction. This diffraction depends on the position of the radiation spot formed on the record carrier relative to the centre of a track to be read. During assembly of the read apparatus the focussing-error detection system will have to be adjusted so that when the centre of the radiation spot coincides with the centre of a track to be read and the focussing is correct, the focussing error signal is zero. However, if during read-out of the record carrier the read spot moves from the centre of a track to be read towards its edge, the radiation distribu-tion across the composite detector will change ; ~ independen-tly of the focussing. This gives rise to an erroneous focussing error signal, 50 that the focussing of the objective system is adjusted incorrectly.
The read apparatus may also comprise a posltlonal-error detection system for determing a deviation between the centr0 of a radiation spo t formed on the record carrler and the centre of a track to be read, and a servo-syst0m for correct:lng the position of the centre of` the read spot. Th~ positional error ;~ ~ si~nal also depends on the focussing of th0 obJ0cti~e syste~n. If the focussing LS incorr0ct th0 position of the radiation spot will also b0 adjusted incorr~ctly~
As a result of this the~ focussing error in its turn ,~ _ ..
PHN. o721.
24-Ll-1977.
increases again. It may then happen that both the ; servo-system for focussing and the servo-system for correcting the position of the radiation spot relative to a track to be read become deranged.
When the optical rsad unit, on its way to a specific passage in the programme stored, is moved radially across the record carrier with a high speed, the edges of each track which is traversed will give rise to a change in the focussing error signal. The servo-system .for the focussing then intervenes unneces-sarily and with a high frequencyO When the focussing of tha objective system is corrected to moving said system, the high-frequency control signals which are ~pplied to the drive means of the objective system, give rise to an annoying acoustic "rattling". Moreover, the drive means than consumes additi.onal power.
As the width of a track is smaller than the distance between the tracks the radiation spot will on the average be shorter at the tracks than hetween the tracks, when the read unit is rapidly moved trans-versely to the track direction. As a resul-t of this -the average focussing error signal will neither be zero in the case o.f a correct focussing. Consequently, the ~ focussing will be adjusted incorrectly on the averag~c.
The influence of the diffraction o~ the radiation beam transverse to the track di.rec-ti.on becomes ~ 6 --.
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PHN. 8721.
24~ 1977-in particular apparent when a track portion -to be read which is projected on the surface of the sub-detectors, - hereinafter to be referred to as -the "effective track direction~, makes an angle of 45 with the X and the Y-axis of the composite detector.
It is an obJect of the present invention to provide an embodiment of the known read apparatus in which the ~if~raction in a direction transverse to the track direction has no influence on the focussing error signal. For this the apparatus in accordallce with the invention is characterized in that one of the a~es : .
of the co-ordinate system in whose quad~ants the sub-- detectors are disposed, is parallel to the effective track direction, and that the astigmatic focal lines are disposed at an angle of 45 relativ~ to the effect-ive track direction.
The invention will now be described in more detail with reference to the drawing, in which Fig. 1 shows the read apparatus in accord-20 ~ ance with the invention, and ~igs 2a, 2b and 2c show how the shape of the spot imaged on the detector varies as a function o~
the focussing.
In the apparatus of Fig. 1 a round disc-2~ shaped reco*d carrier is designated 1. The :inf'ormatiorl structure is fo-r example a phase structure and compI1i ses ~ 7 -~:
PHN. 8721.
24-LI-1977.
a multitude of concentric or quasi^concentric tracks 7, which tracks consist of a sequence of areas ~ and intermediate areas t. The areas may for example be dis-posed a-t an other level in the record carrier -than the intermediate areas, The information may for example be a (colour) television programme, but alternatively other in~ormation such as a multitude of different imagss, or digital information.
The record carrier is illuminated by a read beam 3 which is obtained from a radiation source 4,~or example a c.w.-laser. An objective system, which for simplicity is represented by a single lens 5, focusses the read beam to a read spot V on the plane of' the tracks 2. The focal length of the auxiliary lens 6 has been se1ected so that the pupil of the objective s~stem is adequately filled. The read beam is reflect-ed by the record carrier and is then modulated in ac cordance with the information ~stored in a track portion to be read. ~or separating the incident (unmodulated) and the reflected (modulated) read beam the radiation path includes a beam splitter 8, for example in the form of a partly -transparent mirror. The beam splitter directs the modulated read beam towards a radiation-sensitive detector 9. This detector is cOnnected to an electronic circuit 10 which derives a high frequeney information signal~Si and, as wlll be explained herei.n-.
.
- P~N. g721, 24-LI-1977.
after, a focussing error signal S~ of lower frequency.
In order to enable focussing errors to be detected the radiation path behind the beam splitter 8 includes an astigmatic element 11. This element, as is shown in ~ig. 1, may be a cylindrical lens. It is also possible to obtain astigmatism in a different manner~ for example with a plane transparent plate which is obliquely disposed in the beam or with a lens which is tilted relative to the beam~ Instead o~ one focus point an astigmatic system has two astigmatic focal lines which, viewed in an axial direction, oc-cupies different positions and ~hich are perpendicular - to each other. Thus~ the objective system and the cy-lindrical lens add two focal lines 12 and 13 to the read spot V~ The radiation-sensitive detector 9 is now ar-ranged in a plane which viewed along the optical axis is disposed between the lines 12 and 13, preferably at the location where the dimensions, in two mutua:l]y perpendicular direc-tions, of the image spot added to the read spot V are equal to the highest possib~e degree in the case of correct focussingO
In order to enable the shape of the spot V' and thus the degree of focussing, to be detectcd, the detector 9 comprises four sub-detectors which are ~ disposed in the four q~adrants of an X-Y co-ordinate ~ system. Fig~res 2a, 2b and 2c show arl elevation Or -the ; 9 _ ., ~
, PHN. 872l.
Zl~ _ 1 977.
four sub-detectors ~, B, C and D in accordance w:ith the line 2, 2' in ~ig. 1, with the various shapes of the spot V~ projected on them for different values of the distance between the objective system and the plane of the tracks. The X and the Y-axis make an angle of 45 with the axis 15 of the cylindrical lens, i.e.
with the astigmatic focal lines 12 and 13, whilst the X-axis is now parallel to the effective track direction.
Fig. 2a represents the situation that the distance between the objective system and the plane of the tracks is correct. If this distance is too ~reat, the focal lines 12 and 13 are nearer the cylindrical lens 11. The de-tector 9 is -then nearer the focal line 13 than near the focal line 12. The spot V' then has a shape as is shown in ~g. 2b. If the distance between the objec-tive system and the plane of the tracks is too small, the focal lines 12 and 13 are farther from the cylindrical lens, and the focal line 12 is nearer the detector 9 than the focal line 13. The spot V~ then has a shape as shown in Fig. 2c.
T~ the signals supplied by the sub~detectors A, B. C and D are represented by S~, S~, Sc and SD, the fOCUssiIIg error signal Sf, is given by;
Sf = (S~ + SCj - (SB ~ SD).
2S~ It is evident that in the situation of Fig. 2a ~ S~ + Sc~ SB + SD~ so that S~ . 0. For the situation of :~ :
5~
PliN. 8721.
2ll-4-1~77.
Fig. 2b and ~ig. 2c Sf is negative and positive respect-ively. By adding the signals SA and Sc -to each other, as well as the signals SB and SD9 and subtracting the - sum signals thus obtained from each o-ther, an unambi-- 5 guous focussing error signal is obtained. This signal can be processed electronically, in a manner known ~
se, to a ~ocussing control signal ~ith which the focus-sing of the objective system can be corrected~ for e~ample by moving the objective system relative to the plane of the tracks ~ith the aid of an electromagnetic coil.
When the radiation spot V is moved in a direction transverse to the track direction, the amount of radiatlon on for example the detectors A and B may increase, relative to that on the detectors C and D, independently o~ the focussing. Ilowever, as the focus~
, slng error slgnal Sf is derived by subtracting the sig--nals S~ and S~ from each other, the influence of said movement on the signal Sf is negligible.
~ Finally, it is to be noted that the beam b may also be used for reading the information on the record carrier. The in~ormation signal Si can be obtain-ed by for example adding the signals of the four sub-detectors to each other. The variations i.n the radiat'lon distribution across the'sub-detectors as a result of a ~ mo:~ement of the radiation spot V in a direction trans--~ ~ verse to the track dLrection then have a substantlall~
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P~IN. 8721.
24-4-1977.
lower frequency than the variations in the radiation distribution as a result of the sequence of areas and intermediate areas in a track. By passing the sum sig-nal SA ~ S~ ~ Sc ~ SD through a high-pass filter the influence of this movement trans-verse to the track direction on -the signal Si can be eliminated.
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employed for reading a record carrier ~n which a (colour) television programme is stored. The information structure then consists of a multitude of areas alter-nating wlth intermediate areas arranged in a spiral track, which areas and intermediate areas influence a read beam in different manners. The information is for exan.ple contained in the lengths of the areas and those of the intermediate areas. In order to obtain a sufficiently long playing time with a record carrier of limited size, the details of the informa-tion struct-`; ure have to be very small. For e~ample, if a 30-minute television programme is stored on one side of a disc-shaped round record carrier in an annular area with an outer radius of approx~mately 15 cm and an inner radius of approximately 6 cm, the width o~ the tracks will be approx. 0.5 /um and the average length of the areas and o~ the intermediate areas will be approx. I /um.~
In order to enable these minute details to be read an objective system with a fairly large numerical aperture is to be used. Howe~er, the depth of focus of such an objective system is small. ~s in the read apparatus the distance between the plane of the information structure and the objective system ma-y var~
by an amount greater than the depth of focus~ provisions must be made so as to enable these variations -to be detected and the focussing to be corrected.
_ 3 _ :
:
`
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.
: ` ` ~:
9~
PHN. 8721.
24-4-1977.
In accordance with the said German Patent Application for this purpose a beam of radiation which has been reflected by -the record carrier is made astig-matic, in that a cyliIldrical lens is arranged in the path of this beam behind the obJective system. Between the focal lines of the astigmatic system constituted by the objective system ancl the cylindrical lens a radiation-sensitive detector which consists of four sub-detectors is disposed. When the posi-tion of the plane of the information struc-ture relative to the objective system changes, the shape of the image formed on the sub-detectors also changesO This change in shape ~ can be detected by combining the output signals of the ;~ ~ sub-detectors in a suitable manner.
15~ ~ ~ When the known read apparatus is used practical problems may arise. The radiation distribution across the composite detector also depends on the dif-fraction of the radia-tion beam by the details of the nform~tion structure. ~irst of all~ diffraction is ob-20 ~ talned in the longltudlnal direction~of a track to be read,~owing to the sequence of areas and intermediate ; areas. The variations in the radiation distribution :
across the composite detector owing to this dlffraction havc a high frequcncy relative to the focussing errors~
` Z5 .so that the influence of this diffractio~ on the focus-si~g control signal can be eliminated electronically.
.
_ 4 _ : ::
.
~:
56~
PHN. 8721.
2l~ -1977 Furthermore, diffraction occurs in a d:irection transverse to the track direction. This diffraction depends on the position of the radiation spot formed on the record carrier relative to the centre of a track to be read. During assembly of the read apparatus the focussing-error detection system will have to be adjusted so that when the centre of the radiation spot coincides with the centre of a track to be read and the focussing is correct, the focussing error signal is zero. However, if during read-out of the record carrier the read spot moves from the centre of a track to be read towards its edge, the radiation distribu-tion across the composite detector will change ; ~ independen-tly of the focussing. This gives rise to an erroneous focussing error signal, 50 that the focussing of the objective system is adjusted incorrectly.
The read apparatus may also comprise a posltlonal-error detection system for determing a deviation between the centr0 of a radiation spo t formed on the record carrler and the centre of a track to be read, and a servo-syst0m for correct:lng the position of the centre of` the read spot. Th~ positional error ;~ ~ si~nal also depends on the focussing of th0 obJ0cti~e syste~n. If the focussing LS incorr0ct th0 position of the radiation spot will also b0 adjusted incorr~ctly~
As a result of this the~ focussing error in its turn ,~ _ ..
PHN. o721.
24-Ll-1977.
increases again. It may then happen that both the ; servo-system for focussing and the servo-system for correcting the position of the radiation spot relative to a track to be read become deranged.
When the optical rsad unit, on its way to a specific passage in the programme stored, is moved radially across the record carrier with a high speed, the edges of each track which is traversed will give rise to a change in the focussing error signal. The servo-system .for the focussing then intervenes unneces-sarily and with a high frequencyO When the focussing of tha objective system is corrected to moving said system, the high-frequency control signals which are ~pplied to the drive means of the objective system, give rise to an annoying acoustic "rattling". Moreover, the drive means than consumes additi.onal power.
As the width of a track is smaller than the distance between the tracks the radiation spot will on the average be shorter at the tracks than hetween the tracks, when the read unit is rapidly moved trans-versely to the track direction. As a resul-t of this -the average focussing error signal will neither be zero in the case o.f a correct focussing. Consequently, the ~ focussing will be adjusted incorrectly on the averag~c.
The influence of the diffraction o~ the radiation beam transverse to the track di.rec-ti.on becomes ~ 6 --.
' ' ~
PHN. 8721.
24~ 1977-in particular apparent when a track portion -to be read which is projected on the surface of the sub-detectors, - hereinafter to be referred to as -the "effective track direction~, makes an angle of 45 with the X and the Y-axis of the composite detector.
It is an obJect of the present invention to provide an embodiment of the known read apparatus in which the ~if~raction in a direction transverse to the track direction has no influence on the focussing error signal. For this the apparatus in accordallce with the invention is characterized in that one of the a~es : .
of the co-ordinate system in whose quad~ants the sub-- detectors are disposed, is parallel to the effective track direction, and that the astigmatic focal lines are disposed at an angle of 45 relativ~ to the effect-ive track direction.
The invention will now be described in more detail with reference to the drawing, in which Fig. 1 shows the read apparatus in accord-20 ~ ance with the invention, and ~igs 2a, 2b and 2c show how the shape of the spot imaged on the detector varies as a function o~
the focussing.
In the apparatus of Fig. 1 a round disc-2~ shaped reco*d carrier is designated 1. The :inf'ormatiorl structure is fo-r example a phase structure and compI1i ses ~ 7 -~:
PHN. 8721.
24-LI-1977.
a multitude of concentric or quasi^concentric tracks 7, which tracks consist of a sequence of areas ~ and intermediate areas t. The areas may for example be dis-posed a-t an other level in the record carrier -than the intermediate areas, The information may for example be a (colour) television programme, but alternatively other in~ormation such as a multitude of different imagss, or digital information.
The record carrier is illuminated by a read beam 3 which is obtained from a radiation source 4,~or example a c.w.-laser. An objective system, which for simplicity is represented by a single lens 5, focusses the read beam to a read spot V on the plane of' the tracks 2. The focal length of the auxiliary lens 6 has been se1ected so that the pupil of the objective s~stem is adequately filled. The read beam is reflect-ed by the record carrier and is then modulated in ac cordance with the information ~stored in a track portion to be read. ~or separating the incident (unmodulated) and the reflected (modulated) read beam the radiation path includes a beam splitter 8, for example in the form of a partly -transparent mirror. The beam splitter directs the modulated read beam towards a radiation-sensitive detector 9. This detector is cOnnected to an electronic circuit 10 which derives a high frequeney information signal~Si and, as wlll be explained herei.n-.
.
- P~N. g721, 24-LI-1977.
after, a focussing error signal S~ of lower frequency.
In order to enable focussing errors to be detected the radiation path behind the beam splitter 8 includes an astigmatic element 11. This element, as is shown in ~ig. 1, may be a cylindrical lens. It is also possible to obtain astigmatism in a different manner~ for example with a plane transparent plate which is obliquely disposed in the beam or with a lens which is tilted relative to the beam~ Instead o~ one focus point an astigmatic system has two astigmatic focal lines which, viewed in an axial direction, oc-cupies different positions and ~hich are perpendicular - to each other. Thus~ the objective system and the cy-lindrical lens add two focal lines 12 and 13 to the read spot V~ The radiation-sensitive detector 9 is now ar-ranged in a plane which viewed along the optical axis is disposed between the lines 12 and 13, preferably at the location where the dimensions, in two mutua:l]y perpendicular direc-tions, of the image spot added to the read spot V are equal to the highest possib~e degree in the case of correct focussingO
In order to enable the shape of the spot V' and thus the degree of focussing, to be detectcd, the detector 9 comprises four sub-detectors which are ~ disposed in the four q~adrants of an X-Y co-ordinate ~ system. Fig~res 2a, 2b and 2c show arl elevation Or -the ; 9 _ ., ~
, PHN. 872l.
Zl~ _ 1 977.
four sub-detectors ~, B, C and D in accordance w:ith the line 2, 2' in ~ig. 1, with the various shapes of the spot V~ projected on them for different values of the distance between the objective system and the plane of the tracks. The X and the Y-axis make an angle of 45 with the axis 15 of the cylindrical lens, i.e.
with the astigmatic focal lines 12 and 13, whilst the X-axis is now parallel to the effective track direction.
Fig. 2a represents the situation that the distance between the objective system and the plane of the tracks is correct. If this distance is too ~reat, the focal lines 12 and 13 are nearer the cylindrical lens 11. The de-tector 9 is -then nearer the focal line 13 than near the focal line 12. The spot V' then has a shape as is shown in ~g. 2b. If the distance between the objec-tive system and the plane of the tracks is too small, the focal lines 12 and 13 are farther from the cylindrical lens, and the focal line 12 is nearer the detector 9 than the focal line 13. The spot V~ then has a shape as shown in Fig. 2c.
T~ the signals supplied by the sub~detectors A, B. C and D are represented by S~, S~, Sc and SD, the fOCUssiIIg error signal Sf, is given by;
Sf = (S~ + SCj - (SB ~ SD).
2S~ It is evident that in the situation of Fig. 2a ~ S~ + Sc~ SB + SD~ so that S~ . 0. For the situation of :~ :
5~
PliN. 8721.
2ll-4-1~77.
Fig. 2b and ~ig. 2c Sf is negative and positive respect-ively. By adding the signals SA and Sc -to each other, as well as the signals SB and SD9 and subtracting the - sum signals thus obtained from each o-ther, an unambi-- 5 guous focussing error signal is obtained. This signal can be processed electronically, in a manner known ~
se, to a ~ocussing control signal ~ith which the focus-sing of the objective system can be corrected~ for e~ample by moving the objective system relative to the plane of the tracks ~ith the aid of an electromagnetic coil.
When the radiation spot V is moved in a direction transverse to the track direction, the amount of radiatlon on for example the detectors A and B may increase, relative to that on the detectors C and D, independently o~ the focussing. Ilowever, as the focus~
, slng error slgnal Sf is derived by subtracting the sig--nals S~ and S~ from each other, the influence of said movement on the signal Sf is negligible.
~ Finally, it is to be noted that the beam b may also be used for reading the information on the record carrier. The in~ormation signal Si can be obtain-ed by for example adding the signals of the four sub-detectors to each other. The variations i.n the radiat'lon distribution across the'sub-detectors as a result of a ~ mo:~ement of the radiation spot V in a direction trans--~ ~ verse to the track dLrection then have a substantlall~
.~:
P~IN. 8721.
24-4-1977.
lower frequency than the variations in the radiation distribution as a result of the sequence of areas and intermediate areas in a track. By passing the sum sig-nal SA ~ S~ ~ Sc ~ SD through a high-pass filter the influence of this movement trans-verse to the track direction on -the signal Si can be eliminated.
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Claims
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS
Apparatus for reading a radiation-reflect-ing record carrier on which information is stored in an optically readable track-wise arranged information structure, which apparatus comprises a radiation source which produces a read beam, an objective system for passing the read beam to a radiation-sensitive detect-ion system via the record carrier, which system con-verts the read beam which has been modulated by the information structure into an electrical signal, and an opto-electronic focussing-error detection system for determining a deviation between the desired and the actual position of the plane of focussing of the objective system, which focussing-error detection system comprises an astigmatic element, and a radiation sensitive detector, which detector comprises four sub-detectors which are disposed i four different quadrants of an imaginary X-Y coordinate system, the X and the Y-axis being disposed at an angle of 45° with the astigmatic focal lines of the astigmatic element, characterized in that one of the axes of the co-ordinate system in whose quadrants the sub-detectors are disposed, is parallel to the effective track direction, and that the astigmatic focal lines are disposed at an angle of 45° with the effective track direction.
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS
Apparatus for reading a radiation-reflect-ing record carrier on which information is stored in an optically readable track-wise arranged information structure, which apparatus comprises a radiation source which produces a read beam, an objective system for passing the read beam to a radiation-sensitive detect-ion system via the record carrier, which system con-verts the read beam which has been modulated by the information structure into an electrical signal, and an opto-electronic focussing-error detection system for determining a deviation between the desired and the actual position of the plane of focussing of the objective system, which focussing-error detection system comprises an astigmatic element, and a radiation sensitive detector, which detector comprises four sub-detectors which are disposed i four different quadrants of an imaginary X-Y coordinate system, the X and the Y-axis being disposed at an angle of 45° with the astigmatic focal lines of the astigmatic element, characterized in that one of the axes of the co-ordinate system in whose quadrants the sub-detectors are disposed, is parallel to the effective track direction, and that the astigmatic focal lines are disposed at an angle of 45° with the effective track direction.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7703076 | 1977-03-22 | ||
| NL7703076A NL7703076A (en) | 1977-03-22 | 1977-03-22 | DEVICE FOR READING A RADIATION-REFLECTING RECORD CARRIER. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1109560A true CA1109560A (en) | 1981-09-22 |
Family
ID=19828205
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA298,999A Expired CA1109560A (en) | 1977-03-22 | 1978-03-15 | Apparatus for reading a radiation-reflecting record carrier |
Country Status (20)
| Country | Link |
|---|---|
| JP (1) | JPS53117403A (en) |
| AR (1) | AR214353A1 (en) |
| AT (1) | AT369580B (en) |
| AU (1) | AU510218B2 (en) |
| BE (1) | BE865083A (en) |
| BR (1) | BR7801690A (en) |
| CA (1) | CA1109560A (en) |
| CH (1) | CH627016A5 (en) |
| DE (1) | DE2810616A1 (en) |
| DK (1) | DK145868C (en) |
| ES (1) | ES468055A1 (en) |
| FR (1) | FR2385171A1 (en) |
| IT (1) | IT1093316B (en) |
| MX (1) | MX143603A (en) |
| NL (1) | NL7703076A (en) |
| NZ (1) | NZ186732A (en) |
| PL (1) | PL113996B1 (en) |
| SE (1) | SE424676B (en) |
| YU (1) | YU39193B (en) |
| ZA (1) | ZA78216B (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1131361A (en) * | 1977-05-11 | 1982-09-07 | Fumitaka Kotaka | Focus servo device for use in optical read-out device of information |
| FR2460022B1 (en) * | 1979-06-25 | 1987-09-11 | Hitachi Ltd | OPTICAL INFORMATION REPRODUCING SYSTEM |
| NL7907216A (en) * | 1979-09-28 | 1981-03-31 | Philips Nv | OPTICAL FOCUS ERROR DETECTION SYSTEM. |
| JPS59125727U (en) * | 1983-02-15 | 1984-08-24 | パイオニア株式会社 | Optical information pickup device |
| NL8400674A (en) * | 1984-03-02 | 1985-10-01 | Philips Nv | DEVICE FOR REGISTERING AND / OR READING INFORMATION IN A TRACK OF A REFLECTIVE RECORD CARRIER WITH A FOCUS CONTROL WITH REDUCED SPOT OFFSET SENSITIVITY. |
| JPS6139942A (en) * | 1984-08-01 | 1986-02-26 | Matsushita Electric Ind Co Ltd | Optical pickup |
| US4609813A (en) * | 1985-03-18 | 1986-09-02 | International Business Machines Corporation | Optical systems employing ovate light beams |
| JPS6310326A (en) * | 1986-07-01 | 1988-01-16 | Sanyo Electric Co Ltd | Optical pickup device |
| DE3828146A1 (en) * | 1988-08-19 | 1990-02-22 | Philips Patentverwaltung | ELECTRODYNAMIC ACTUATOR FOR AN OPTICAL WRITE-IN AND READ-OUT UNIT |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2271590B1 (en) * | 1974-01-15 | 1978-12-01 | Thomson Brandt | |
| NL182990C (en) * | 1975-07-07 | 1988-06-16 | Philips Nv | DEVICE FOR READING A RADIATION-REFLECTING RECORD CARRIER. |
| FR2325987A1 (en) * | 1975-09-29 | 1977-04-22 | Thomson Brandt | OPTICAL READING DEVICE FOR A RECORDING |
| GB1532345A (en) * | 1976-06-25 | 1978-11-15 | Hitachi Ltd | Information play-back apparatus |
| JPS5337722A (en) * | 1976-09-20 | 1978-04-07 | Ebata Shiyouji Kk | Method of producing concrete piles |
| NL7703077A (en) * | 1977-03-22 | 1978-09-26 | Philips Nv | DEVICE FOR READING A RADIATION-REFLECTING RECORD CARRIER. |
-
1977
- 1977-03-22 NL NL7703076A patent/NL7703076A/en not_active Application Discontinuation
-
1978
- 1978-01-12 ZA ZA00780216A patent/ZA78216B/en unknown
- 1978-02-06 AR AR270983A patent/AR214353A1/en active
- 1978-03-11 DE DE19782810616 patent/DE2810616A1/en active Pending
- 1978-03-15 CA CA298,999A patent/CA1109560A/en not_active Expired
- 1978-03-17 MX MX172816A patent/MX143603A/en unknown
- 1978-03-17 IT IT21340/78A patent/IT1093316B/en active
- 1978-03-17 DK DK120578A patent/DK145868C/en not_active IP Right Cessation
- 1978-03-20 AU AU34294/78A patent/AU510218B2/en not_active Expired
- 1978-03-20 NZ NZ186732A patent/NZ186732A/en unknown
- 1978-03-20 PL PL1978205453A patent/PL113996B1/en unknown
- 1978-03-20 AT AT0196578A patent/AT369580B/en not_active IP Right Cessation
- 1978-03-20 BR BR7801690A patent/BR7801690A/en unknown
- 1978-03-20 BE BE186087A patent/BE865083A/en not_active IP Right Cessation
- 1978-03-20 SE SE7803138A patent/SE424676B/en not_active IP Right Cessation
- 1978-03-20 CH CH302678A patent/CH627016A5/en not_active IP Right Cessation
- 1978-03-20 ES ES468055A patent/ES468055A1/en not_active Expired
- 1978-03-21 YU YU00673/78A patent/YU39193B/en unknown
- 1978-03-22 JP JP3182778A patent/JPS53117403A/en active Pending
- 1978-03-22 FR FR7808294A patent/FR2385171A1/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| SE7803138L (en) | 1978-09-23 |
| IT7821340A0 (en) | 1978-03-17 |
| NZ186732A (en) | 1981-02-11 |
| AT369580B (en) | 1983-01-10 |
| MX143603A (en) | 1981-06-05 |
| DK120578A (en) | 1978-09-23 |
| AU510218B2 (en) | 1980-06-12 |
| ATA196578A (en) | 1982-05-15 |
| ZA78216B (en) | 1979-08-29 |
| PL113996B1 (en) | 1981-01-31 |
| AU3429478A (en) | 1979-09-27 |
| FR2385171A1 (en) | 1978-10-20 |
| IT1093316B (en) | 1985-07-19 |
| YU67378A (en) | 1982-06-30 |
| DK145868C (en) | 1983-09-12 |
| CH627016A5 (en) | 1981-12-15 |
| ES468055A1 (en) | 1978-11-16 |
| SE424676B (en) | 1982-08-02 |
| AR214353A1 (en) | 1979-05-31 |
| JPS53117403A (en) | 1978-10-13 |
| YU39193B (en) | 1984-08-31 |
| DK145868B (en) | 1983-03-21 |
| BR7801690A (en) | 1979-01-02 |
| NL7703076A (en) | 1978-09-26 |
| BE865083A (en) | 1978-09-20 |
| PL205453A1 (en) | 1978-12-18 |
| DE2810616A1 (en) | 1978-09-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |