Patent EP0127845A2 successfully refreshed from Google Patents.
EP0127845A2
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EP
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System for focusing a light beam on a light reflecting surface
Assignee: Toshiba Corp
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Filing: 1984-05-23
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Granted: —
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Expires: 2004-05-23
Abstract
Abstract In a system provided with an optical head, laser beam produced from a laser unit 30 is converged by an objective lens 42 and reflected from a light reflecting layer 14 of an optical disk 2. The reflected laser beam is converged by a projection lens 62 and is projected to photo sensitive regions of a photodetector 48. The photosensitive regions have an area smaller than a portion of a beam spot which is formed outside the regions when the objective lens 42 reaches a predetermined defocusing state. Photo signals generated from the photodetector 48 are added and processed by a focusing signal generator 68. A focus signal generated from the focusing signal generator 68 is supplied to a voice coil driver 72 so that the objective lens 42 is moved to a position which is in just focusing state by a voice coil 44 which is driven by the voice coil driver72. When the objective lens 42 reaches the predetermined defocusing state and the level of the added photosignal falls within a predetermined level, a CPU 74 generates a off-signal to open a switching circuit 70 so that connection between the focusing signal generator 68 and the voice coil driver 72 is disconnected.
Inventors
- 👤 Hideo C/O Patent Division Ando
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-26 16:07
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/12; G11B7/135; G11B7/1381; G11B7/08; G11B7/09; G11B7/0908; G11B7/0916; G11B7/0945
Claims Analysis
Total Claims: 31
Claim 1
Independent Claim
147 words
A system for focusing light beam on a light reflecting surface (12, 14) of an optical disk (2) comprising: means (30) for generating a light beam; means (36, 38, 40) for transferring the light beam; an objective lens (42) which converts the transferred light beam into a convergent light beam with a beam waist, projects the light beam on the light-reflecting surface (14) and transmits the light beam reflected from the light-reflecting surface (14); and a photodetector (48, 52) having photo sensitive regions (48-1, 48-2, 52-1, 52-2) to which the light beam is directed and which generates photo signals, characterized in that an area of said regions (48-1, 48-2, 58-1, 58-2) of said photodetector (48, 52) is smaller than a portion of the beam spot which is formed outside said regions (48-1, 48-2, 58-1, 58-2) of said photodetector when said objective lens reaches a predetermined defocusing state.
Claim 2
Independent Claim
147 words
A system for focusing light beam on a light reflecting surface (12, 14) of an optical disk (2) comprising: means (30) for generating a light beam; means (36, 38, 40) for transferring the light beam; an objective lens (42) which converts the transferred light beam into a convergent light beam with a beam waist, projects the light beam on the light-reflecting surface (14) and transmits the light beam reflected from the light-reflecting surface (14); and a photodetector (48, 52) having photo sensitive regions (48-1, 48-2, 52-1, 52-2) to which the light beam is directed and which generates photo signals, characterized in that an area of said regions (48-1, 48-2, 58-1, 58-2) of said photodetector (48, 52) is smaller than a portion of the beam spot which is formed outside said regions (48-1, 48-2, 58-1, 58-2) of said photodetector when said objective lens reaches a predetermined defocusing state.
Claim 3
Dependent Claim
29 words
A system according to claim 1, characterized by further comprising: means (44, 72) for fine moving said objective lens along its optical axis within a predetermined working distance WD.
Claim 4
Dependent Claim
45 words
A system according to claim 2, further comprising: deflecting means (58), arranged between said photodetector (48, 52) and said objective lens (42), for deflecting the reflected light beam in accordance with a distance between said objective lens (42) and said light reflecting layer (12, 14).
Claim 5
Dependent Claim
50 words
A system according to claim 2, characterized in that a first undefocusing state outside the defocusing allowance is defined by a position assumed by said objective lens (42) after moving toward said light reflecting layer (12, 14) by a distance WD/2 from a position corresponding to the just in-focusing state.
Claim 6
Dependent Claim
67 words
A system according to claim 4, characterized in that said photo sensitive regions (48-1, 48-2, 52-1, 52-2) are defined within a circle of an area substantially half that of the portion of the beam spot formed on said photodetector (48, 52) when said objective lens (42) is moved toward said light reflecting layer (14) by the distance WD/2 from the position corresponding to the just in-focusing state.
Claim 7
Dependent Claim
66 words
A system according to claim 5, characterized in that said photo sensitive regions (48-1, 48-2) are defined within a circle having a radius ra given by: where Rl is a radius of the beam spot formed on said photodetector (48) when said objective lens (42) is moved by the distance WD/2 toward said light reflecting layer (14) from the position corresponding to the just in-focusing state.
Claim 8
Dependent Claim
19 words
A system according to claim 6, characterized by further comprising means (54, 62) for converging the retlected light beam.
Claim 9
Dependent Claim
52 words
A system according to claim 6, characterized in that said photo sensitive regions (48-1, 48-2) are located in a plane in which an image of a light reflecting surface (14) is formed by said objective lens (42) and said converging means when said objective lens (42) is in the just in-focusing state.
Claim 10
Dependent Claim
66 words
A system according to claim 8, characterized in that the radius Rl of the beam spot is given by: where F is a distance between a principal point of said objective lens (42) and a focal point thereof, A is a radius of an exit pupil of said objective lens (42), and m is a transverse magnification factor of an imaging system of said photodetector (48).
Claim 11
Dependent Claim
57 words
A system according to claim 7, characterized in that said photo sensitive regions are located slightly shifted by a distance A from a plane in which an image of a light reflecting surface is formed by said objective lens and said converging lens when said objective lens is at the position corresponding to the just in-focusing state.
Claim 12
Dependent Claim
61 words
A system according to claim 10, characterized in that the radius Rl is given by: where F is a distance between a principal point of said objective lens (42) and a focal point thereof, A is a radius of an exit pupil of said objective lens (42), and m is a transverse magnification of an imaging system of said photodetector (48).
Claim 13
Dependent Claim
49 words
A system according to claim 3, characterized in that a predetermined defocusing state outside the defocusing allowance is defined by a position assumed by said objective lens (42) upon moving toward said light reflecting layer (14) by a distance WD/4 from the position corresponding to the just in-focusing state.
Claim 14
Dependent Claim
65 words
A system according to claim 12, characterized in that said photo sensitive regions (48-1, 48-2) are defined within a circle of an area substantially a quarter that of the portion of the beam spot formed on said photodetector (48) when said objective lens (42) is moved toward said light reflecting layer (14,) by the distance WD/4 from the position corresponding to the just in-focusing state.
Claim 15
Dependent Claim
66 words
A system according to claim 13, characterized in that said photo sensitive regions (48-1, 48-2) are defined within a circle having a radius ra given by: where R2 is a radius of the beam spot formed on said photodetector (48) when said objective lens (42) is moved by the distance WD/4 toward said light reflecting layer (14) from the position corresponding to the just in-focusing state.
Claim 16
Dependent Claim
53 words
A system according to claim 14, characterized in that said photo sensitive regions (48-1, 48-2) are located in a plane in which an image of said light reflecting layer (14) is formed by said objective lens (42) and said converging means (62) when said objective lens (42) is in the just in-focusing state.
Claim 17
Dependent Claim
66 words
A system according to claim 15, characterized in that the radius R2 of the beam spot is given by: where F is a distance between a principal point of said objective lens (42) and a focal point thereof, A is a radius of an exit pupil of said objective lens (42), and m is a transverse magnification factor of an imaging system of said photodetector (48).
Claim 18
Dependent Claim
62 words
A system according to claim 14, characterized in that said photo sensitive regions (48-1, 48-2) are located slightly shifted by a distance A from a plane in which an image of a light reflecting surface (14) is formed by said objective lens (42) and said converging means (62) when said objective lens is at the position corresponding to the just in-focusing state.
Claim 19
Dependent Claim
61 words
A system according to claim 17, characterized in that the radius R2 is given by: where F is a distance between a principal point of said objective lens (42) and a focal point thereof, A is a radius of an exit pupil of said objective lens (42), and m is a transverse magnification of an imaging system of said photodetector (48).
Claim 20
Dependent Claim
50 words
A system according to claim 3, characterized in that a second undefocusing state outside the defocusing allowance is defined by a position which is assumed by said objective lens (42) upon moving toward the photodetector (48, 52) by a distance F/10 from the position corresponding to the just in-focusing state.
Claim 21
Dependent Claim
56 words
A system according to claim 19, characterized in that said photo sensitive regions of said photodetector are defined within a circle having a raidus ra given by: where A is a radius of an exit pupil of said objective lens (42) and m is a transverse magnification factor of an imaging system of said photodetector (42).
Claim 22
Dependent Claim
15 words
A system according to claim 2, characterized by further comprising a projection lens (54, 62).
Claim 23
Dependent Claim
58 words
A system according to claim 21, characterized in that said projection lens (54, 62) has an effective aperture which is smaller than a region through which the light beam projected to said regions of said photodetector (48, 52) is passed when said objective lens (42) reaches a position corresponding to a predetermined defocusing state outside the defocusing allowance.
Claim 24
Dependent Claim
49 words
A system according to claim 22, characterized in that a first defocusing state outside the defocusing allowance is defined by a position assumed by said objective lens (42) after moving toward said light reflecting layer (14) by a distance WD/2 from a position corresponding to the just in-focusing state.
Claim 25
Dependent Claim
66 words
A system according to claim 23, characterized in that said projection lens (54, 62) has an effective aperture of 2rp where rp is given by: where A is a radius of an expit pupil of said objective lens (42), f0 is a focal length of said projection lens (54, 62), and L is a distance between said objective lens (42) and said projection lens (54, 62).
Claim 26
Dependent Claim
66 words
A system according to claim 23, characterized in that said projection lens (54, 62) has an effective aperture of 2rp where rp is qiven by: where A is a radius of an expit pupil of said objective lens (42), f0 is a focal length of said projection lens (54, 62), and L is a distance between said objective lens (42) and said projection lens (54, 62).
Claim 27
Dependent Claim
46 words
A system according to claim 23, characterized by further comprising: deflecting means (58), arranged between said photodetector (48, 52) and said objective lens (42), for deflecting the reflected light beam in accordance with a distance between said objective lens (42) and said light reflecting layer (14).
Claim 28
Dependent Claim
60 words
A system according to claim 26, characterized in that said projection lens (54, 62) has an effective aperture of 2rp where rp is given by: where A is a radius of an expit pupil of said objective lens, f0 is a focal length of said projection lens, and L is a distance between said objective lens and said projection lens.
Claim 29
Dependent Claim
64 words
A system according to claim 26, characterized in that said projection lens has an effective aperture of 2rp where rp is given by: where A is a radius of an expit pupil of said objective lens (42), fO is a focal length of said projection lens (54, 62), and L is a distance between said objective lens (42) and said projection lens (54, 62).
Claim 30
Dependent Claim
60 words
A system according to claim 1, characterized by further comprising: means (84, 94) for adding the photo signals generated from the photo sensitive regions (48-1, 48-2, 52-1, 52-2); and means (74) for comparing the level of the added signal with a predetermined level and generating an alarm signal when the level of the added signal smaller than the predetermined level.
Claim 31
Dependent Claim
78 words
A system according to claim 29, characterized by further comprising means (68) processing the photo signals to generate a focus signal depending on the distance between the objective lens (42) and the light reflecting (14); means (44, 72) for fire moving the objective lens (42) in accordance with the focus signal; and means (70) for connecting the processing means (68) and the moving means (44, 72) and opening therebetween when the connecting means (70) receives the alarm signal.
References Cited (Backward Citations)
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