Source: http://www.google.com/patents/US6771300?dq=6948823
Timestamp: 2017-04-25 11:42:02
Document Index: 665040225

Matched Legal Cases: ['art.\n21', 'art.\n44', 'art 18', 'art 18', 'art 18', 'art 18', 'art 18', 'art 18', 'application No. 2001']

Patent US6771300 - Multi-beam scanning device - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsA light-source unit includes two LD arrays, each comprising four light-emitting points, a corresponding two coupling lenses coupling laser beams emitted from the two LD arrays, and a holding member integrally holding these LD arrays and coupling lenses rotatably approximately about optical axes on the...http://www.google.com/patents/US6771300?utm_source=gb-gplus-sharePatent US6771300 - Multi-beam scanning deviceAdvanced Patent SearchTry the new Google Patents, with machine-classified Google Scholar results, and Japanese and South Korean patents.Publication numberUS6771300 B2Publication typeGrantApplication numberUS 10/090,824Publication dateAug 3, 2004Filing dateMar 6, 2002Priority dateMar 7, 2001Fee statusPaidAlso published asUS20020149666Publication number090824, 10090824, US 6771300 B2, US 6771300B2, US-B2-6771300, US6771300 B2, US6771300B2InventorsTaku Amada, Naoki MiyatakeOriginal AssigneeRicoh Company, Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (3), Non-Patent Citations (9), Referenced by (43), Classifications (10), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetMulti-beam scanning device
US 6771300 B2Abstract
What is claimed is: 1. A multi-beam scanning device, scanning a to-be-scanned surface with a plurality of laser beams simultaneously, comprising:
a light-source unit comprising a plurality of laser arrays, each comprising a plurality of light-emitting points, a corresponding plurality of coupling lenses coupling laser beams emitted from said plurality of laser arrays, respectively and a holding member integrally holding said plurality of laser arrays and plurality of coupling lenses rotatably approximately about optical axes of said laser arrays; and a scanning optical system deflecting the laser beams emitted from said light-source unit and imaging them onto the to-be-scanned surface, wherein said light-source unit and scanning optical system are configured so that the following equation be satisfied: AY=|q×cos φ×mY×(n−1)/(2×fcol×tan θ×cos γ×mZ)|≦0.1 where:
n denotes the number of light-emitting points on each laser array; q denotes an interval between each adjacent ones of the light-emitting points on each laser array; φ denotes an inclination angle of each laser array with respect to a sub-scanning direction; mY denotes a magnification of said scanning optical system on main scanning direction; mZ denotes a-magnification of said scanning optical system on sub-scanning direction; fcol denotes the focal length of each coupling lens; θ denotes half a crossing angle at which the laser beams emitted from said plurality of laser arrays cross therebetween; γ denotes a maximum required rotational angle of said light-source unit in case of adjustment. 2. The multi-beam scanning device as claimed in claim 1, wherein the number of laser arrays on said light-source unit is two.
3. The multi-beam scanning device as claimed in claim 1, wherein the inclination angle of each laser array can be adjusted individually.
4. The multi-beam scanning device as claimed in claim 1, wherein each laser array is rotatably held by said holding member.
5. The multi-beam scanning device as claimed in claim 1, wherein said light-source unit and scanning optical system are configured such that a ratio A0 between a main-scanning-directional component and a sub-scanning-direction component of a change in beam-spot interval on the to-be-scanned surface occurring according to change in the inclination angle of each laser array satisfies the following equation:
⅓≦A 0≦3 where
A0=|(mY/mZ)×tan φ|
mY denotes a magnification of said scanning optical system on main scanning direction; and mZ denotes a magnification of said scanning optical system on sub-scanning direction. 6. An image formation apparatus comprising the multi-beam scanning device as claimed in claim 1.
a plurality of photoconductor members to provide to-be-scanned surfaces; and the multi-beam scanning device claimed in claim 1 scanning at least one of said to-be-scanned surfaces. 8. A multi-beam scanning device, scanning a to-be-scanned surface with a plurality of laser beams simultaneously, comprising:
a light-source unit comprising a plurality of laser arrays, each comprising a plurality of light-emitting points, a corresponding plurality of coupling lenses coupling laser beams emitted from said plurality of laser arrays, and a holding member integrally holding said plurality of laser arrays and plurality of coupling lenses rotatably approximately about optical axes of said laser arrays; and a scanning optical system deflecting the laser beams emitted from said light-source unit and imaging them onto the to-be-scanned surface, wherein said light-source unit and scanning optical system are configured so that the following equation be satisfied: AZ=|q×sine φ×(n−1)/(2×fcol×tan θ×cos γ)|≦0.1 where:
n denotes the number of light-emitting points on each laser array; q denotes an interval between each adjacent ones of the light-emitting points on each laser array; φ denotes an inclination angle of each laser array with respect to a sub-scanning direction; fcol denotes the focal length of each coupling lens; θ denotes half a crossing angle at which the laser beams emitted from said plurality of laser arrays cross therebetween; and γ denotes a maximum required rotational angle of said light-emitting unit in case of adjustment. 9. The multi-beam scanning device as claimed in claim 8, wherein the number of laser arrays on said light-source unit is two.
10. The multi-beam scanning device as claimed in claim 8, wherein the inclination angle of each laser array can be adjusted individually.
11. The multi-beam scanning device as claimed in claim 8, wherein each laser array is rotatably held by said holding member.
12. The multi-beam scanning device as claimed in claim 8, wherein said light-source unit and scanning optical system are configured such that a ratio A0 between a main-scanning-directional component and a sub-scanning-direction component of a change in beam-spot interval on the to-be-scanned surface occurring according to change in the inclination angle of each laser array satisfies the following equation:
⅓≦A0≦3 where
mY denotes a magnification of said scanning optical system on main scanning direction; and mZ denotes a magnification of said scanning optical system on sub-scanning direction. 13. An image formation apparatus comprising the multi-beam scanning device as claimed in claim 8.
a plurality of photoconductor members to provide to-be-scanned surfaces; and the multi-beam scanning device claimed in claim 8 scanning at least one of said to-be-scanned surfaces. 15. A multi-beam scanning device, scanning a to-be-scanned surface with a plurality of laser beams simultaneously, comprising:
a light-source unit comprising a plurality of laser arrays, each comprising a plurality of light-emitting points, a corresponding plurality of coupling lenses coupling laser beams emitted from said plurality of laser arrays, respectively, and a holding member integrally holding said plurality of laser arrays and plurality of coupling lenses rotatably approximately about optical axes of said laser arrays; a scanning optical system deflecting the laser beams emitted from said light-source unit and imaging them onto the to-be-scanned surface; and a part switching a scanning density on the to-be-scanned surface by rotating said light-source unit approximately about the optical axes of said laser arrays. 16. The multi-beam scanning unit as claimed in claim 15, further comprising a detecting part detecting a synchronization signal for determining a scanning start timing,
wherein: said detecting part obtains the synchronization signal from a laser beam emitted from one of the light-emitting points of each of the laser arrays; and scanning start timings on the other light-emitting points are determined as a result of shifting by specific delay times from the synchronization signal thus obtained. 17. The multi-beam scanning device as claimed in claim 15, wherein the number of the laser arrays provided is two.
18. The multi-beam scanning device as claimed in claim 15, wherein said light-source unit and scanning optical system are configured so that the following formula be satisfied:
ΔRY=|{(n−1)×(2n−1)/2}×{(q×cos φ×mY×d)/(fcol×tan θ×mZ)}|≦d/4 where:
d denotes a scanning line interval on the to-be-scanned surface; n denotes the number of light-emitting points on each laser array; q denotes an interval between each adjacent ones of the light-emitting points one each laser array; φ denotes an inclination angle of each laser array with respect to a sub-scanning direction; mY denotes a magnification of said scanning optical system on main-scanning direction; mZ denotes a magnification of said scanning optical system on sub-scanning direction; fcol denotes the focal length of each coupling lens; θ denotes half a crossing angle at which the laser beams emitted from said plurality of laser arrays cross therebetween; and ΔRY denotes the main-scanning-directional component of beam-spot interval between both ends of beam spots on the to-be-scanned surface for each laser array. 19. The multi-beam scanning device as claimed in claim 15, wherein said light-source unit and scanning optical system are configured so that the following formula be satisfied:
ΔRZ=|{(n−1)×(2n−1)/2}×{(q×sin φ×d)/(fcol×tan θ)}|≦d/4 where:
d denotes a scanning line interval on the to-be-scanned surface; n denotes the number of light-emitting points on each laser array; q denotes an interval between each adjacent ones of the light-emitting points on each laser array; φ denotes an inclination angle of each laser array with respect to a sub-scanning direction; fcol denotes the focal length of each coupling lens; θ denotes half a crossing angle at which the laser beams emitted from said plurality of laser arrays cross therebetween; and ΔRZ denotes the sub-scanning-directional component of beam-spot interval between both ends of beam spots on the to-be-scanned surface for each laser array. 20. The multi-beam scanning device as claimed in claim 15, wherein delay times applied on the respective beam spots for scanning start timing are determined such that scanning start timing is optimum in case where a higher scanning density is applied through said switching part.
21. The multi-beam scanning device as claimed in claim 15, wherein delay times applied on the respective beam spots for scanning start timing are variable according to the scanning density switched.
22. An image formation apparatus comprising the multi-beam scanning device as claimed in claim 15.
a plurality of photoconductor members to provide to-be-scanned surfaces; and the multi-beam scanning device claimed in claim 15 scanning at least one of said to-be-scanned surfaces. 24. A multi-beam scanning device, scanning a to-be-scanned surface with a plurality of laser beams simultaneously, comprising:
light-source unit comprising a plurality of laser means, each comprising a plurality of light-emitting points, a corresponding plurality of coupling means for coupling laser beams emitted from said plurality of laser arrays, and a holding means for integrally holding said plurality of laser means and plurality of coupling means rotatably approximately about optical axes on the laser means; and a scanning optical system deflecting the laser beams emitted from said light-source unit and imaging them onto the to-be-scanned surface, wherein said light-source unit and scanning optical system are configured so that the following equation be satisfied: AY=|q×cos φ×mY×(n−1)/(2×fcol×tan θ×cos γ×mZ)|≦0.1 where:
n denotes the number of light-emitting points on each laser means; q denotes an interval between each adjacent ones of the light-emitting points on each laser means; φ denotes an inclination angle of each laser means with respect-to a sub-scanning direction; mY denotes a magnification of said scanning optical system on main scanning direction; mZ denotes a magnification of said scanning optical system on sub-scanning direction; fcol denotes the focal length of each coupling means; θ denotes half a crossing angle at which the laser beams emitted from said plurality of laser means cross therebetween; and γ denotes a maximum required rotational angle of said light-emitting unit in case of adjustment. 25. The multi-beam scanning device as claimed in claim 24, wherein the number of laser means on said light-source unit is two.
26. The multi-beam scanning device as claimed in claim 24, wherein the inclination angle of each laser means can be adjusted individually.
27. The multi-beam scanning device as claimed in claim 24, wherein each laser means is rotatably held by said holding means.
28. The multi-beam scanning device as claimed in claim 24, wherein said light-source unit and scanning optical system are configured such that a ratio A0 between a main-scanning-directional component and a sub-scanning-direction component of a change in beam-spot interval on the to-be-scanned surface occurring according to change in the inclination angle of each laser means satisfies the following equation:
mY denotes a magnification of said scanning optical system on main scanning direction; and mZ denotes a magnification of said scanning optical system on sub-scanning direction. 29. An image formation apparatus comprising the multi-beam scanning device as claimed in claim 24.
30. An image formation apparatus comprising:
a plurality of photoconductor members to provide to-be-scanned surfaces; and the multi-beam scanning device claimed in claim 24 scanning at least one of said to-be-scanned surfaces. 31. A multi-beam scanning device, scanning a to-be-scanned surface with a plurality of laser beams simultaneously, comprising:
a light-source unit comprising a plurality of laser means, each comprising a plurality of light-emitting points, a corresponding plurality of coupling means for coupling laser beams emitted from said plurality of laser means, and holding means for integrally holding said plurality of laser means and plurality of coupling means rotatably approximately about optical axes on the laser means; and a scanning optical system deflecting the laser beams emitted from said light-source unit and imaging them onto the to-be-scanned surface, wherein said light-source unit and scanning optical system are configured so that the following equation be satisfied: AZ=|q×sine φ×(n−1)/(2×fcol×tan θ×cos γ)|≦0.1 where:
n denotes the number of light-emitting points on each laser means; q denotes an interval between each adjacent ones of the light-emitting points on each laser means; φ denotes an inclination angle of each laser means with respect to a sub-scanning direction; fcol denotes the focal length of each coupling means; θ denotes half a crossing angle at which the laser beams emitted from said plurality of laser means cross therebetween; and γ denotes a maximum required rotational angle of said light-source unit in case of adjustment. 32. The multi-beam scanning device as claimed in claim 31, wherein the number of laser means on said light-source unit is two.
33. The multi-beam scanning device as claimed in claim 31, wherein the inclination angle of each laser means can be adjusted individually.
34. The multi-beam scanning device as claimed in claim 31, wherein each laser means is rotatably held by said holding means.
35. The multi-beam scanning device as claimed in claim 31, wherein said light-source unit and scanning optical system are configured such that a ratio A0 between a main-scanning-directional component and a sub-scanning-direction component of a change in beam-spot interval on the to-be-scanned surface occurring according to change in the inclination angle of each laser means satisfies the following equation;
mY denotes a magnification of said scanning optical system on main scanning direction; and mZ denotes a magnification of said scanning optical system on sub-scanning direction. 36. An image formation apparatus comprising the multi-beam scanning device as claimed in claim 31.
37. An image formation apparatus comprising:
a plurality of photoconductor members to provide to-be-scanned surfaces; and the multi-beam scanning device claimed in claim 31 scanning at least one of said to-be-scanned surfaces. 38. A multi-beam scanning device, scanning a to-be-scanned surface with a plurality of laser beams simultaneously, comprising:
a light-source unit comprising a plurality of laser means, each comprising a plurality of light-emitting points, a corresponding plurality of coupling means coupling laser beams emitted from said plurality of laser means, and holding means integrally holding said plurality of laser means and plurality of coupling means rotatably approximately about optical axes on the laser means; a scanning optical system deflecting the laser beams emitted from said light-source unit and imaging them onto the to-be-scanned surface; and means for switching a scanning density on the to-be-scanned surface by rotating said light-source unit approximately about the optical axes of the laser means. 39. The multi-beam scanning unit as claimed in claim 38, further comprising detecting means for detecting a synchronization signal for determining a scanning start timing,
wherein: said detecting means obtains the synchronization signal from a laser beam emitted from one of the light-emitting points of each laser means; and scanning start timings on the other light-emitting points are determined as a result of shifting by specific delay times from the synchronization signal thus obtained. 40. The multi-beam scanning device as claimed in claim 38, wherein the number of laser means provided is two.
41. The multi-beam scanning device as claimed in claim 38, wherein said light-source unit and scanning optical system are configured so that the following formula be satisfied:
d denotes a scanning line interval on the to-be-scanned surface; n denotes the number of light-emitting points on each laser means; q denotes an interval between each adjacent ones of the light-emitting points on each laser means; φ denotes an inclination angle of each laser means with respect to a sub-scanning direction; mY denotes a magnification of said scanning optical system on main scanning direction; mZ denotes a magnification of said scanning optical system on sub-scanning direction; fcol denotes the focal length of each coupling means; θ denotes half a crossing angle at which the laser beams emitted from said plurality of laser means cross therebetween; and ΔRY denotes the main-scanning-directional component of beam-spot interval between both ends of beam spots on the to-be-scanned surface for each laser means. 42. The multi-beam scanning device as claimed in claim 38, wherein said light-source unit and scanning optical system are configured so that the following formula be satisfied:
d denotes a scanning line interval on the to-be-scanned surface; n denotes the number of light-emitting points on each laser means; q denotes an interval between each adjacent ones of the light-emitting points on each laser means; φ denotes an inclination angle of each laser means with respect to a sub-scanning direction; mZ denotes a magnification of said scanning optical system on sub-scanning direction; fcol denotes the focal length of each coupling means; θ denotes half a crossing angle at which the laser beams emitted from said plurality of laser means cross therebetween; and ΔRZ denotes the sub-scanning-directional component of beam-spot interval between both ends of beam spots on the to-be-scanned surface from each laser means. 43. The multi-beam scanning device as claimed in claim 38, wherein delay times applied on the respective beam spots for scanning start timing are determined such that scanning start timing is optimum in case where a higher scanning density is applied through said switching part.
44. The multi-beam scanning device as claimed in claim 38, wherein delay times applied on the respective beam spots for scanning start timing are variable according to the scanning density switched.
45. An image formation apparatus comprising the multi-beam scanning device as claimed in claim 38.
a plurality of photoconductor members to provide to-be-scanned surfaces; and the multi-beam scanning device claimed in claim 38 scanning at least one of said to-be-scanned surfaces.
AY=|q×cos φ×mY×(n−1)/(2×fcol×tan θ×cos γ×mZ)|≦0.1 where:
AZ=|q×sine φ×(n−1)/(2×fcol×tan θ×cos γ)|≦0.1 Thereby, even in case, an error in scanning line interval occurring due to optical-axis manufacture/assembling error or so between the plurality of laser arrays should be corrected by rotating (γ rotation) the holding unit in an adjustment work, a newly occurring scanning line interval error along the sub-scanning direction and/or beam spot interval error along the main scanning direction due to the above-mentioned adjustment work can be controlled to be made within a permissible range.
FIG. 1 illustrates a multi-beam scanning device in a first embodiment of the present invention;
FIG. 2 shows a perspective view of parts/components located in and near a light source unit in the configuration shown in FIG. 1;
FIG. 3 shows a perspective view of an LD base shown in FIG. 2 viewed from the rear side;
FIG. 4 illustrates a state of crossing of laser beams on a deflection reflective surface of a polygon mirror in the configuration shown in FIG. 1;
FIGS. 5A and 5B illustrate a state where an LD array is inclined with respect to a sub-scanning direction in the configuration shown in FIG. 1;
FIGS. 6, 7 and 8 illustrate adjustment of a beam spot arrangement on the to-be-scanned surface in the configuration shown in FIG. 1;
FIGS. 9A, 9B, 9C, 10A, 10B and 10C illustrate how to derive conditional formulas according to the present invention on the configuration shown in FIG. 1;
FIGS. 11 and 12 illustrate different examples in adjustment of beam spot arrangement according to the first embodiment of the present invention;
FIGS. 13A, 13B and 14 illustrate how to derive conditional formulas according to the present invention on the configuration shown in FIG. 1;
FIGS. 15A and 15B illustrate a configuration of a comparison example for the first embodiment of the present invention;
FIGS. 16A and 16B illustrate an arrangement on an LD array and an arrangement on a to-be-scanned surface in the configuration shown in FIGS. 15A and 15B;
FIGS. 17 and 18 illustrate a light-source unit according to a second embodiment of the present invention (FIG. 17 shows a main scanning section while FIG. 18 shows a sub-scanning section);
FIG. 19 shows a conceptual perspective view of a multi-beam scanning device according to a third embodiment of the present invention;
FIGS. 20A and 20B illustrate exploded perspective views of a holding mechanism for LD array and a light-source rotating mechanism, applicable to the third embodiment of the present invention;
FIG. 21 shows a perspective view of another configuration example of a light-source device applicable to the third embodiment;
FIGS. 22A and 22B illustrate an arrangement angle (inclination angle) of light-emitting points on an LD array with respect to a sub-scanning direction (A), and the same of beam spots on a to-be-scanned surface (B) in the third embodiment;
FIGS. 23A and 23B illustrate a scanning density switching operation through γ rotation according to the third embodiment of the present invention;
FIG. 24 illustrates change in beam spot arrangement on the to-be-scanned surface occurring due to the γ rotation of the light-source device (light-source unit) in the configuration of the third embodiment;
FIG. 25 shows a specification of the third embodiment of the present invention;
FIG. 26 show s a specification of a fourth embodiment of the present invention; and
FIGS. 27A, 27B, 27C and 27D illustrate configuration examples of image formation apparatuses each applying any one of the embodiments of the present invention.
FIG. 1 illustrates a general configuration of a multi-beam scanning device in a first embodiment of the present invention, FIG. 2 shows a perspective view of a part including a light source unit of this device, and FIG. 3 shows a perspective view of FIG. 2 viewed from the reverse side. This multi-beam scanning device 1 is provided in a color laser printer, and has a function of scanning on a surface (to-be-scanned surface) 16 a of a photoconductor 16 of the color laser printer with laser beams, thereby, according to a well-known electrostatic photographic scheme, an electrostatic latent image being formed on the photoconductor surface.
Generally, the LD array 11 a (having the intervals q between adjacent light emitting points) is disposed to have an inclination angle φ with respect to the sub-scanning direction (vertical direction on the figure) as shown in FIG. 5A. In this case., on the to-be-scanned surface 16 a, as shown in FIG. 6, as a result of being magnified by magnification (mY along the main scanning direction and mZ along the sub-scanning direction) of the optical system, the resulting interval of adjacent beam spots is expressed as QY and QZ on the to-be-scanned surface 16 a. Moreover, in FIG. 5B, the light-emitting points on the LD array 11 a are expressed as r1, r2, . . . , rn, while the beam spots on the to-be-scanned surface 16 a corresponding to the above-mentioned light-emitting point are expressed with R1, R2, . . . , Rn in FIG. 6, respectively. There, ‘n’ shows the number of the light-emitting points on each of the LD arrays 11 a and 11 b. By rotating (rotation angle: γ) the light source unit 18 approximately about the optical axes, as shown in FIG. 8, the sub-scanning direction component PZ of the distance (pitch between adjacent centers) between center positions Ca and Cb of beam spots from the respective LD arrays 11 a and 11 b on the to-be-scanned surface 16 a can be set to be a predetermined value according to the following formula (1). There, in the formula (1), fcol denotes the focal length of the coupling lens 12 a (12 b), and mZ denotes the imaging magnification along the sub-scanning direction of the entire optical system (multi-beam scanning device).
PZ=2×fcol×tan θ×sin γ×mZ (1) How to derive the above-mentioned formula (1) will now be described with reference to FIGS. 9A-9C and FIGS. 10A-10C. As shown in FIG. 9A, unit vectors of the laser beams coming from the respective LD array 11 a and 11 b are assumed as a1 and a2 (i.e., directions of the optical axes of the respective LD arrays), respectively, and, also, as shown in FIGS. 9B and 9C, the vectors of the laser beams obtained when the LD arrays 11 a and 11 b are rotated by an angle γ about the X-axis (γ rotation) is assumed as α1 and α2, respectively. Then, 2 sin θ sine γ is obtained as the sub-scanning component of (α1-α2). Then, as shown in FIG. 10A, the angle β0 which is the angle (sub-scanning direction component) between the laser beams obtained through the γ rotation is expressed as follows:
Z 0=fcol×tan θ×sin γ×mZ Then as shown in FIG. 10C, the formula (1) for the sub-scanning direction component PZ of the distance between adjacent centers of the LD arrays 11 a and 11 b (Z direction), i.e., the distance between the center positions Ca and Cb of the beam spots from the respective LD arrays on the to-be-scanned surface 16 a (pitch between centers) is obtained.
QY=q×sin φ×mY (4) Sub-scanning direction:
QZ=q×cos φ×mZ (5) How to derive these formulas (4) and formula (5) will now be described based on FIGS. 13A and 13B. In case the LD array 11 a in the state shown in FIG. 13A is inclined by the angle φ as shown in FIG. 13B, the interval between the light-emitting points on the LD array 11 a is obtained as qY=q sin φ along the main scanning direction while the interval along the sub-scanning direction is obtained as qZ=q cos φ. Thereby, the formula (4) for the interval QY along the main scanning direction between beam spots on the to-be-scanned surface 16 a (image surface) and the formula (5) for the interval QZ along the sub-scanning direction are obtained.
ΔQY=q×cos φ×mY×Δφ (6) Sub-scanning direction:
ΔQZ=−q×sin φ×mZ×Δφ (7) Furthermore, an amount of deviation ΔPZ on the sub-scanning direction component PZ of the pitch between centers Ca and Cb is expressed by the following formula (10) from the formula (1).
ΔPZ=2×fcol×tan θ×cos γ×mZ (10) Position adjustment on the coupling lens 12 a (12 b) corresponding to the LD array 11 a (11 b) is made such that a desired collimate characteristic and light-emitting direction (optical axis) may be achieved. Generally, such assembly adjustment is called “optical axis/collimate adjustment”. It is assumed that optical axis adjustment accuracy (possible angle error along the sub-scanning direction on the laser beam) is iZ (rad). In case the angle errors on the two LD arrays 11 a and 11 b occur oppositely one another (maximum: 2×iZ), the amount E deviation (adjustment error) on the center positions Ca and Cb of the beam spots on the to-be-scanned surface 16 a is obtained, as shown in FIG. 14, by the following formula (2):
E=2×fcol×tan(iZ)×mZ (2) The rotation angle γE of the light source unit 18 required to correct this amount E of derivation (maximum possible error) is obtained by the following formula (3) from the formula (1).
Sin γE=tan(iZ)/tan θ (3) By rotating the light source unit 18 by the above-mentioned angle γE, the LD arrays 11 a and 11 b revolve by the angle γE (relative positional change) and also each rotates by the same angle alone. Accordingly, as the change amount on the arrangement angle of the LD array 11 a (11 b) alone occurring thereby can be expressed by Δφ=γE. Thereby, as the deviation amount E on the center positions is corrected, the amount of change ΔQY along the main scanning direction of the beam spot arrangement and the amount of change ΔQZ along the sub-scanning direction of the same occurring thereby can be expressed by the following formulas (8) and (9) from the formulas (6) and (7):
ΔQY =q×cos φ×mY×γE (8) Sub-scanning direction:
ΔQZ=−q×sin φ×mZ×γE (9) With reference to FIGS. 15A, 15B, 16A and 16B, previously, a reason why, in an 8 beam scanning device in which laser beams emitted by two semiconductor laser arrays 51 a and 51 b each of which has four light-emitting points are used, beam spot arrangement on a to-be-scanned surface 56 a is difficult, will now be described for a comparison example shown in the figures. A configuration of an optical system of the comparison example shown in the figures is almost the same as that shown in the figures with which how to derive the above-mentioned formulas has been described above. However, as shown FIG. 15B, a light source unit 58 is used there in which beams are combined by using a beam combining prism 57. Further, coupling lenses 52 a and 52 b, a cylindrical lens 53, and a scanning optical system 55 are provided there.
ΔQY/Δγ=q×cos φ×mY (11) ΔPZ/Δγ=2×fcol×tan θ×cos γ×mZ (12) When the value of the formula (11) is fully small as compared with the value of the formula (12), the influence of rotation (Δγ) of the light source unit 18 exerted on ΔQZ can also be made sufficiently small. The formula (11) is a formula concerning the arrangement between adjacent beam spots. With regard to the beam spot arrangement (relation between R1 and Rn in FIG. 6) between the light-emitting points at both ends on each LD array 11 a (11 b), a formula is obtained as a result of the formula (11) being multiplied by (n−1). Accordingly, the absolute value AY of the ratio of formula (11)×(n−1) and the formula (12) is given by the following formula (13):
AY=|(ΔQY/Δγ)×(n−1)/(ΔPZ/Δγ)|=|(q×cos φ×mY)×(n−1)/(2×fcol×tan θ×cos γ×mZ)| (13) According to the first embodiment of the present invention, q=14 μm (light-emitting point interval on each LD array 11 a (11 b)); n=4 (the number of light-emitting points on each LD array 11 a (11 b)), φ=60° (arrangement angle of LD array 11 a (11 b); fcol=15 mm (focal length of coupling lens 12 a (12 b)); θ=1.5° (half the crossing angle of the laser beams emitted from the LD arrays 11 a and 11 b near the deflection reflective surface 14 a; mY=10 times (imaging magnification on the main scanning direction); mZ=3 times (imaging magnification on the sub-scanning direction).
n×(scan-line interval)=4×21=84 (μm) Further, the relative positional shift (along the sub-scanning direction) between the two LD arrays 11 a and 11 b and the coupling lenses 12 a and 12 b should be set as 14 μm in the mutual opposite direction. Then, it is assumed that the positional accuracy error between the LD arrays 11 a and 11 b and the coupling lenses 12 a and 12 b causes the optical-axis shift along the sub-scanning direction of
iZ=0.6 (mrad) In this case, same as in the above-described case of comparison example, from the formula (2), the amount of change of E=0.054 (mm) occurs in the pitch between centers Ca and Cb along the sub-scanning direction, the rotation angle γE of the light source unit 18 needed for correcting this change is as follows:
For example, deviation occurring in the center-to-center distance up to 100 μm can be corrected in case the permissible value of the amount of change in beam spot arrangement along the main scanning direction is set as 10 μm (≈21 (μm)/2), i.e., ½ dot in writing density of 1200 dpi, determined according to an image output experiment result. In other words, even when such a correction is made on the center-to-center distance ΔPZ, the change ΔQY in the main-scanning-direction beam spot arrangement can be controlled to be within the above-mentioned permissible value.
AZ=|(ΔQZ/Δγ)×(n−1)/(ΔPZ/Δγ)|=|(q×sin φ×(n−1))/(2×fcol×tan θ×cos γ)| (15) By controlling this absolute value AZ by configuring the scanning device 1 such that the coefficient C2 included in the following formula (16) be not more than {fraction (1/10)}, the center-to-center deviation E (along the sub-scanning direction) caused by the optical axis adjustment error can be easily corrected.
ΔQZ=AZ×E=0.05×54=2.5 μm occurring in correcting the center-to-center deviation E=54 μm caused by the optical axis deviation iZ=0.6 (mrad). As this value is sufficiently small, the influence on an output image by the image formation apparatus using this scanning device can be controlled to be sufficiently small, and can prevent generation of an unusual/degraded image.
ΔQZ/Δγ=−q×sin φ×mZ (17) The absolute value of the ratio of the value of this formula (17) and the value of the formula (11) is expressed by A0, by the following formula (18):
A0=|(ΔQY/Δγ)/(ΔQZ/Δγ)|=|(mY/mZ)×tan φ| (18) This formula (18) expresses the ratio of the main scanning direction component and the sub-scanning direction component of the beam spot arrangement change occurring when the rotation γ approximately about the optical axes of the light source unit 18 is made, i.e., change of the arrangement angle φ of the LD arrays 11 a and 11 b. The allowable range of the absolute value A0 of this ratio is shown in the following formula (19):
⅓≦A0≦3 (19) By making the range of an absolute value A0 into the range according to the formula (19), the main scanning direction component and sub-scanning direction component of the change in the beam spot arrangement can be made to have an appropriate balance. As for this formula (18), in the case of the above-mentioned comparison example, A0=0, while A0=1.7 in the first embodiment according to the present invention. Accordingly, according to the first embodiment of the present invention, the main scanning direction component and the sub-scanning direction component of the change in beam spot arrangement have an appropriate balance therebetween in comparison with the comparison example.
FIG. 17 is a sectional view taken along the main scanning direction of-a light source unit in the second embodiment of the present invention, and FIG. 18 is a sectional view taken along the sub-scanning direction of the same light source. The configuration according to the second embodiment for illustrating an aspect of the present invention will now be descried with reference to FIGS. 17 and 18. As shown in FIG. 17, the light source unit 18 has a first light source part 18 a and a second light source part 18 b. In the first light source part 18 a, the LD array 11 a is fixed onto an LD base 41 a, a coupling lens 12 a is adhered thereonto with adjustment, and, thus, adjustment is made on the collimate characteristics and optical axis directions of laser beams emitted from the LD array 11 a according to the characteristics of subsequent scanning optical system. Similarly, on the second light source part 18 b, appropriate adjustment is performed. The first light source part 18 a and second light source part 18 b are rotatably held onto a common flange 42, respectively. This light source unit 18 is rotatably held by an optical housing 31 at an insertion hole 32 (see FIG. 2) thereof.
In the description below, 111 a, 111 b denote semiconductor laser arrays (LD array); 112 a, 112 b denote coupling lenses; 113 denotes cylindrical lens, 114 denotes a polygon mirror; 115 denotes a scanning optical system; 116 denotes a photoconductor drum (providing a to-be-scanned surface); 117 denotes a beam combining prism; 118 denotes a light source device (light-source unit); 119 denotes a part of detecting synchronization signals; a1 through a4 denote beam spots from the LD array 111 a formed on the to-be-scanned surface 116; b1 through b4 denotes beam spots from the LD array 111 b formed on the to-be-scanned surface; Ca and Cb denote the center positions of the beam spots from the LD arrays 111 a and 111 b, respectively; QY, QZ denote the interval between beam spots on the same LD array on the to-be-scanned surface 116; PY, PZ denote the interval (center-to-center pitch) between the center positions Ca and Cb; and subscripts Y, Z denote the main and sub-scanning directions, respectively.
FIG. 20B shows an exploded perspective view of a mechanism for performing the γ rotation of the light source device shown in FIG. 20A also disclosed by Japanese laid-open patent application No. 2001-4941. As shown in the figure, the mechanism rotates the light-source device 1211 with respect to the housing 1212 of the multi-beam scanning device, and, includes a sliding member 1213, a motor bracket 1214, the pressing plate 1215, the spring 1218, the sprint pressing plate 1219, a stepper motor 1220, guides 1221 and a switch 1226.
QY=q×sin φ×mY QZ=q×cos φ×mZ Therefore, the interval (RY, RZ) of the farthest beam spots on each LD array is expressed as follows:
RY=(n−1)QY=(n−1)×q×sin φ×mY RZ=(n−1)QZ=(n−1)×q×cos φ×mZ Generally speaking, it is difficult to change the magnification (and focal length) of a scanning optical system in case a multi-beam scanning device employs an existing scanning optical system (the optical system subsequent to the deflector is used as it is). However, desired magnification (mY and mZ) can be obtained by setting appropriately the focal length of an optical system (i.e., coupling lens and cylindrical lens) before the deflector relatively easier.
FIGS. 23A and 23B illustrate methods of placing beam spots on the to-be-scanned surface 116.
FIG. 23A shows a way of arranging alternately the beam spots of first LD array 111 a, and the beam spots of the second LD array 111 b. The sub-scanning direction component PZ of the distance (referred to as a center-to-center distance) between the central positions Ca and Cb of the beam spot arrangement of the first LD array 111 a and second LD array 111 b corresponds to one scanning line interval (d). Thus, the center-to-center distance at a time of 1200 dpi is set as P1200=d.
FIG. 23B shows a way of arranging the beam spots of the first LD array 111 a, and the beam spots of the second LD array 111 b, in series. The sub-scanning direction component PZ of the center-to-center distance between centers Ca and Cb of the respective beam spot arrangements of the LD arrays 111 a and 111 b corresponds to 2n·d.
P=2×fcol×tan θ×sin γ×mZ (20) Then, this formula (20) is differentiated with respect to (as Δφ=Δγ),
ΔP/Δφ=2×fcol×tan θ×cos γ×mZ (21) Now, γ≈0. Then, it is assumed cos γ=1. Accordingly, from the formula (21),
Δφ=ΔP/(2×fcol×tan θ×mZ) (22) Further, Δ   P =  P600 - P1200 =  2  n · d - d = ( 2  n - 1 ) · d ( 23 ) Accordingly, by substituting the formula (23) for the formula (22), Δ   φ =  ( 2   n - 1 ) · d / ( 2 × fcol × tan   θ × m   z ) =  { ( 2  n - 1 ) / 2 } × { d / ( fcol × tan   θ × m   z ) } ( 24 ) Then, as mentioned above,
RY=(n−1)×q×sin φ×mY and this formula is differentiated with respect to φ, then, the absolute value thereof is obtained, i.e.,
ΔRY=|(n−1)×q×cos φ×mY×Δφ| (25) Then, the formula (24) is substituted for the formula (25), thus, Δ   R =   ( n - 1 ) × q × cos   φ × m   Y × { ( 2   n - 1 ) / 2 } × { d / ( fcol × tan   θ × m   z ) }  =   ( n - 1 ) × ( 2   n - 1 ) / 2 } × { ( q × cos   φ × m   Y × d ) / ( fcol × tan   θ × m   z ) }  Similarly,
RZ=(n−1)×q×cos φ×mY is differentiated with respect to φ, the absolute value thereof is obtained, and then
ΔRZ=|(n−1)×q×sin φ×mY×Δφ| Thus, the formula (24) is substituted therefor, and, thus,
QY′=QY+ΔQY RY′=RY+ΔRY QZ′=QZ−ΔQZ RZ′=RZ−ΔRZ. Assuming the specification of the above-mentioned third embodiment as shown in FIG. 25,
Δφ=0.7(°) ΔRY=2.8 (μm) ΔRZ=4.5 (μm) Then, assuming that the multi-beam scanning device in the third embodiment is used as a multi-beam scanning device in an image formation apparatus using an electronic photograph process, it is assumed that permissible value of change amount in the beam spot arrangement (in case of scanning density switching) as ¼ the scanning line interval (=d/4). Then,
d/4=5.3 (μm) Thus, for the main scanning direction (ΔRY) and for the sub-scanning direction (ΔRZ), the above-mentioned change amount on the beam spot arrangement falls within the permissible range. Accordingly, by satisfying the following requirements:
ΔRZ=|(n−1)×(2n−1)/2}×{(q×sin φ×d)/(fcol×tan θ)}|=d/4 (II) an output image by the image formation apparatus which uses the multi-beam scanning device in which the above conditional formulas (I) and (II) are satisfied can be a quality image.
QY=q×sin(φ)×mY=0.197 (mm) And, thus, as this distance is very small, the synchronization signal may not be able to be individually detected for each of the four laser beams on each LD array depending on the scanning speed. Therefore, it may be that, the synchronization signal is detected only for one light-emitting point of the four as mentioned above, a specific time (delay time) is shifted from the synchronization signal in sequence for the other respective light-emitting points for setting up the scanning start timing therefor. On the other hand, the main scanning direction component PY of the center-to-center distance between the center positions Ca and Cb of the beam spot arrangements between the two LD arrays 111 a and 111 b is expressed as:
PY=FY×(2θ)=225×(5°×2π/360°)=19.6 (mm) Thereby, as this value is relatively large, it is easy to detect the synchronization signals for the both LD arrays, respectively.
ΔRY=39.3 (μm) ΔRZ=0.3 (μm) Thus, the main scanning direction component ΔRY=39.3 μm of the amount of change in the beam spot arrangement exceeds the above-mentioned permissible amount d/4=5.3 μm. On the other hand, as to the sub-scanning direction, no problem occurs as ΔRZ=0.3 μm is sufficiently smaller than the above-mentioned permissible value 5.3 μm.
ΔT=T600−T1200=ΔQY/Vs. Since
ΔQY=ΔRY/(n−1)=39.3/(4−1)=13.1 (μm) In case Vs=500 (m/s), for example,
ΔT=26.2 (ns) Moreover, by providing a measure of detecting at least the main scanning direction component of the spot interval in the beam spot arrangement, it becomes possible to-determine the delay time to be applied more precisely according to the detection result.
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2010May 12, 2011Naoki MiyatakeOptical scanning device and image forming apparatus* Cited by examinerClassifications U.S. Classification347/241International ClassificationG02B26/10, H04N1/113, B41J2/47, B41J2/44, G02B26/12Cooperative ClassificationG02B26/123, B41J2/473European ClassificationG02B26/12D, B41J2/47B1Legal EventsDateCodeEventDescriptionMay 8, 2002ASAssignmentOwner name: RICOH COMPANY, LTD., JAPANFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:AMADA, TAKU;MIYATAKE, NAOKI;REEL/FRAME:012878/0568Effective date: 20020405Jan 11, 2008FPAYFee paymentYear of fee payment: 4Feb 1, 2012FPAYFee paymentYear of fee payment: 8Jan 25, 2016FPAYFee paymentYear of fee payment: 12RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services