Multi-beam light source unit, multi-beam scanner and image forming apparatus

Abstract: A multi-beam light source unit is provided with a light source emitting a plurality of light beams from corresponding light emitting points arranged in an array at equal intervals, a collimator lens forming the plurality of light beams into parallel bundle of rays, and an adjusting mechanism adjusting relative positions of the light source and the collimator lens so that a central part between the light emitting points at both ends of the light source matches an optical axis of the collimator lens. The collimator lens is rotatable about the optical axis of the collimator lens.

Description: The present invention generally relates to multi-beam light source units, multi-beam scanners and image forming apparatuses, and more particularly to a multi-beam light source unit which generates a plurality of beams in one optical scan, a multi-beam scanner which uses such a multi-beam light source unit to make the optical scan, and an image forming apparatus such as a laser printer, a digital copying machine and a facsimile machine which forms an image by use of such a multi-beam scanner. Recently, in image forming apparatuses such as laser printers and digital copying machines, a multi-beam scanner is employed to meet demands to realize a high recording speed and a high recording density. The multi-beam scanner simultaneously scans a scanning surface of a photoconductive body by a plurality of laser beams. The multi-beam scanner collimates light beams from a plurality of semiconductor laser diodes, and composes the light beams with a minute mutual angular deviation along a sub scanning direction. The composed light beams are passed through a deflecting means and are imaged on the scanning surface by an imaging optical system in the form of a plurality of light spots, so as to scan a plurality of lines at one time. A semiconductor laser array having a plurality of light emitting points arranged in an array on a single substrate, is used as a light source of the plurality of laser beams. For example, Japanese Laid-Open Patent Application No.8-136841 proposes a technique which adjusts a first optical path of a 2-beam laser diode array to a rotary axis of a rotary member, and rotates a second optical path about the first optical path. On the other hand, Japanese Laid-Open Patent Application No.9-26550 proposes a technique which arranges a desired spot position within an inconsistency range in a depth direction of a plurality of light beams from a laser diode array. Furthermore, Japanese Laid-Open Patent Application No.56-42248 proposes a technique which makes a light source having a plurality of light emitting parts rotatable about an optical axis of an optical lens, so as to adjust a beam pitch. However, according to the system proposed in the Japanese Laid-Open Patent Application No.8-136841, the first laser optical path is matched to the center of rotation of the rotary member, and the second laser optical path is rotated by turning the rotary member so as to adjust first and second scanning pitches (pixel density pitches). But because of the construction of this proposed system, the second laser optical path becomes arranged further away from a collimator lens than the first laser optical path. As a result, first and second beam waist positions on the scanning surface become different, thereby making it difficult to obtain a desired beam diameter. In addition, in the semiconductor laser array having two or more light emitting points, it becomes even more difficult to obtain a desired beam diameter, and it is impossible to cope with the further improvement of the high-speed recording and the high-density recording. On the other hand, by rotating the collimator lens about the optical axis of the collimator lens, it is possible to obtain a uniform beam pitch and a uniform beam shape with respect to each of the laser beams on an imaging surface side. But in this case, it becomes necessary to increase the precision of the dimensions of the constituent parts so as to match the optical axis of the collimator lens, and the cost of the parts increases. Moreover, when the number of constituent parts of the rotary member becomes large, an accumulation of the errors also becomes large. Consequently, the beam position on the scanning surface deviates from a desired position when the accumulated error is large and the rotary member is turned, and the cost of the system further increases because of the need to adjust and correct the beam position. JP 10-01-04 47A discloses a multi-beam light source unit according to the preamble of claim 1 or 2. The multi-beam light source unit comprises a light source emitting a plurality of light beams from corresponding light emitting points arranged in an array at equal intervals. A collimator lens is provided as well as an adjusting mechanism suitable for adjusting relative positions of the light source and the collimator lens so that a centre between outermost light-emitting points of the light source matches an optical axis of the collimator lens, said collimator lens being rotatable about the optical axis of the collimator lens. The adjusting mechanism comprises a support for supporting the light source, a first base and a second base, wherein said support is mountable to said first base, said first base is rotatable about the optical axis relative to said second base and wherein the collimator lens is accommodated within a pipe that is received in a fitting hole of a sleeve shaft of the first base and wherein the sleeve shaft fits into a fitting hole of a second base. Each time the multi-beam light source unit is replaced, the rotary position thereof must be adjusted again. This is cumbersome and may cause inaccuracies during image forming, e.g. in an image forming apparatus. Accordingly, it is an object of the present invention to improve the multi-beam light source unit according to the preamble of claim 1 or 2 in that a replacement of the multi-beam light source unit may be performed at high accuracy while preserving image forming characteristics of the multi-beam light source unit. The above problem is solved by a multi-beam light source unit comprising the features of claim 1 or 2. Further advantageous embodiments are the subject matter of the dependent claims. It is another object of the present invention to provide a multi-beam scanner comprising an improved multi-beam light source unit as well as an image forming apparatus comprising such a multi-beam scanner. These further objects are obtained by a multi-beam scanner comprising the features of claims 6 or 7 and by an image forming apparatus comprising the features of claim 8. According to the present invention there is provided a multi-beam light source unit which uses as a light source a semiconductor laser array having a plurality of light emitting points arranged at equal intervals, wherein an adjustment is made to match a center or an apprwoximatel center between the outermost light emitting points of the light source to an optical axis of a collimator lens, and the semiconductor laser array is rotatable about the optical axis of the collimator lens, so that it is possible to obtain a uniform beam pitch and a uniform beam shape can be obtained with respect to each of laser beams on an imaging surface side. In the multi-beam light source unit a lens outer sleeve of a collimator lens is used as a fit-and-slide part of a rotary member, so as to reduce the number of constituent parts and to turn the rotary member with a high accuracy. A multi-beam scanner which uses the multi-beam light source unit described above is capable of obtaining a desired scanning pitch (pixel density pitch) on the scanning surface and obtaining a uniform and desired beam diameter with respect to each of the laser beams. An image forming apparatus which uses the multi-beam scanner described above is capable of further improving the high-speed recording and the high-density recording without deteriorating the picture quality. The multi-beam light source unit according to the present invention comprises a light source emitting a plurality of light beams from corresponding light emitting points arranged in an array at equal intervals, a collimator lens forming the plurality of light beams into a parallel bundle of rays, and an adjusting mechanism adjusting relative positions of the light source and the collimator lens so that a central part between the outermost light emitting points of the light source matches an optical axis of the collimator lens, where the collimator lens is rotatable about the optical axis of the collimator lens. According to the present invention the adjusting mechanism adjusts a position of the collimator lens relative to the light source, and comprises a mirror pipe accommodating therein the collimator lens, and a base having a hole which receives the mirror pipe so that the mirror pipe is rotatable about the optical axis of the collimator lens. According to the present invention the multi-beam scanner comprises a multi-beam light source unit emitting a plurality of light beams, a scanning section scanning a scanning surface by the plurality of light beams from the multi-beam light source unit, and an imaging section imaging the plurality of light beams from the scanning section on the scanning surface, where the multi-beam light source unit comprises a light source emitting a plurality of light beams from corresponding light emitting points arranged in an array at equal intervals, a collimator lens forming the plurality of light beams into a parallel bundle of rays, and an adjusting mechanism adjusting relative positions of the light source and the collimator lens so that a central part between the outermost light emitting points of the light source matches an optical axis of the collimator lens, and the collimator lens is rotatable about the optical axis of the collimator lens. According to the present invention the image forming apparatus comprises a multi-beam scanner, and an image transfer system developing an image formed by the multi-beam scanner and transferring the image onto a recording medium, where the multi-beam scanner comprises a multi-beam light source unit emitting a plurality of light beams, a scanning section scanning a scanning surface by the plurality of light beams from the multi-beam light source unit, and an imaging section imaging the plurality of light beams from the scanning section on the scanning surface, the multi-beam light source unit comprises a light source emitting a plurality of light beams from corresponding light emitting points arranged in an array at equal intervals, a collimator lens forming the plurality of light beams into a parallel bundle of rays, and an adjusting mechanism adjusting relative positions of the light source and the collimator lens so that a central part between the outermost light emitting points of the light source matches an optical axis of the collimator lens, and the collimator lens is rotatable about the optical axis of the collimator lens. Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings. FIG. 1 is a perspective view generally showing the construction of an embodiment of a multi-beam scanner according to the present invention; FIG. 2 is a perspective view showing the construction of a first embodiment of a multi-beam light source unit according to the present invention; FIG. 3 is a diagram showing a relationship of a semiconductor laser array and a collimator lens; FIGS. 4A and 4B respectively are diagrams for explaining positions of beam spots in a vertical direction (sub scanning direction or pixel density pitch direction) at imaging positions; FIG. 5 is a perspective view showing the construction of a second embodiment of the multi-beam light source unit according to the present invention; and FIG. 6 is a system block diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 1 generally shows the construction of an embodiment of a multi-beam scanner according to the present invention. The multi-beam scanner shown in FIG. 1 generally includes a semiconductor laser array (semiconductor laser diode array) 30 having a plurality of light sources arranged in an array, a collimator lens 35 which forms a plurality of light beams from the semiconductor laser array 30 into a parallel or substantially parallel bundle of rays, a cylindrical lens 31 having power in a sub scanning direction, a rotary polygonal mirror 32 which forms a deflecting and scanning means with respect to the light beams, a f lens system 33, a toroidal lens 34, a reflecting mirror 38, a photoconductive drum 36 which forms an image bearing body, and a photodetector 37 which detects a scan start timing of each main scan and outputs a synchronizing signal. The plurality of laser beams emitted from the semiconductor laser array 30 are formed into the parallel or substantially parallel bundle of rays by the collimator lens 35, and pass to the deflecting and scanning means which is formed by the rotary polygonal mirror 32 via the cylindrical lens 31. By rotating this rotary polygonal mirror 32 by a known means, the laser beams repeatedly scan in a main scanning direction. The laser beams reflected by the rotary polygonal mirror 32 are formed into converging light beams by the f lens system 33 and the toroidal lens 34 which form an imaging system. The converging light beams are reflected by the reflecting mirror 38 and are projected onto a scanning surface 39, such as the photoconductive drum 36 which is arranged at an imaging position, that is, a beam waist position, in the form of light spots. If four laser beams exist, for example, four scanning lines are simultaneously written in one scan, where the four scanning lines are arranged at a pixel density pitch P in the sub scanning direction which is perpendicular to the main scanning direction. For example, if the pixel density is 600 dpi, the pixel density pitch P becomes P = 1 inch/600 ≒ 42.3 µm. In addition, the photodetector 37 is provided at a position outside a region of an effective scanning width, and synchronization is achieved by detecting the laser beams at the scan start timing of each main scan. FIG. 2 shows the construction of a first embodiment of a multi-beam light source unit according to the present invention. In FIG. 2, the semiconductor laser array 30 is press-fit or adhered on a support body 2. Alternatively, it is possible to fix the semiconductor laser array 30 on the support body 2 by screws or the like using another member (not shown). The support body 2 is connected to a back surface 3a of a rotary base 3 by screws. Holes in the support body 2 permit play with respect to the screws, so that it is possible to adjust the position of the semiconductor laser array 30 in upward, downward, rightward and leftward directions with respect to an optical axis A of the collimator lens 35. The collimator lens 35 (not visible in FIG. 2) is accommodated within a mirror pipe 6. This mirror pipe 6 is fitted into a fitting hole 3b of the rotary base 3 and is bonded to the rotary base 3 by matching the position in the direction of the optical axis A with respect to the semiconductor laser array 30. Alternatively, it is possible to fix the mirror pipe 6 on the rotary base 3 by screws or the like. A sleeve shaft 3e of the rotary base 3 is provided concentrically to the fitting hole 3b. This sleeve shaft 3e fits into a fitting hole 10a of a base 10, and the rotary base 3 is rotatable about the sleeve shaft 3e. In other words, the center of rotation of the rotary base 3 matches or substantially matches the optical axis A of the collimator lens 35. The rotary base 3 is fixed to the base 10 by screws 11 after adjustment of the multi-beam light source unit. A substrate 7 including a driving circuit for the semiconductor laser array 30 is fixed on bosses 3d of the rotary base 3 by screws 8. The multi-beam light source unit is mounted on an optical housing 12 of the multi-beam scanner via positioning pins 12a and 12b which fit into corresponding positioning holes 10b and 10c of the base 10, so that the multi-beam light source unit is mounted with a spatial distance determined by a mounting surface 12c. FIG. 3 shows a relationship of the semiconductor laser array 30 and the collimator lens 35. In addition, FIGS. 4A and 4B respectively show positions of beam spots in a vertical direction (sub scanning direction or pixel density pitch direction) at imaging positions. In explaining an adjusting method hereunder, it is assumed for the sake of convenience that the semiconductor laser array 30 has four light sources 101, 102, 103 and 104. The position of the support body 2 is adjusted in the upward, downward, rightward and leftward directions so that the optical axis A of the collimator lens 35 matches a center between the outermost light sources 101 and 104 of the semiconductor laser array 30 among the four light sources 101 through 104 which are arranged at equal intervals, as shown in FIG. 3. As a result, a distance X1 from the light source 101 to the collimator lens 35, a distance X2 from the light source 102 to the collimator lens 35, a distance X3 from the light source 103 to the collimator lens 35, and a distance X4 from the light source 104 to the collimator lens 35 become substantially the same. A pitch p of the light sources 101 through 104 is extremely small and is on the order of several tens of µm. For this reason, all of the laser beams from the light source 101 through 104 pass a vicinity of the optical axis A, and a pixel density pitch P and a beam diameter D become approximately uniform at the imaging position for each of the laser beams, as shown in FIG. 4A. When the rotary base 3 is turned in this state, a rotation takes place substantially about the optical axis A, and the pixel density pitch P decreases to a pixel density pitch P' as shown in FIG. 4B. Hence, it is possible to easily obtain a desired pixel density pitch by determining a sub scan magnification of an imaging system so that the pixel density pitch P is greater than the desired pixel density pitch. Since the rotation takes place in the vicinity of the center of the light sources, the beam position will not greatly deviate due to the rotation. The beam position is thus extremely stable, and is adjustable with a high accuracy. It is possible to maintain compatibility among independent multi-beam light source units by adjusting a rotary position of the multi-beam light source unit by an adjusting tool when adjusting the pixel density pitch P' by this rotation. The positioning of the rotary position of the multi-beam light source unit is achieved by the positioning holes 10b and 10c provided in the base 10, and the corresponding positioning pins 12a and 12b of the housing 12 which fit into these positioning holes 10b and 10c, as shown in FIG. 2. In other words, the base 10 is positioned by the optical housing 12 and the adjusting tool, so that the base 10 is arranged at the same position as the imaging position of the laser beams. Accordingly, even if it becomes necessary to replace the multi-beam light source unit, it becomes possible to mount a new multi-beam light source unit without adjusting the rotary position thereof. In this embodiment, the position of the semiconductor laser array 30 is adjusted. However, it is of course possible to adjust the position of the collimator lens 35. Next, a description will be given of a second embodiment of the multi-beam light source unit according to the present invention. FIG. 5 shows the construction of the second embodiment of the multi-beam light source unit. In FIG. 5, those parts which are the same as those corresponding parts in FIG. 2 are designated by the same reference numerals, and a description thereof will be omitted. As shown in FIG. 5, the collimator lens 35 is bonded or press-fit within a mirror pipe 60. In addition, the mirror pipe 60 is bonded within the fitting hole 3b of the rotary base 3, by matching the position with respect to the semiconductor laser array 30 in the direction of the optical axis A. Alternatively, the mirror pipe 60 is fixed within the fitting hole 3b of the rotary base 3 by screws (not shown) or the like. The mirror pipe 60 which is fixed to the rotary base 3 fits into the fitting hole 10a of the base 10, and the mirror pipe 60 is rotatable about an outer diameter 60a of the mirror pipe 60. In general, an outer diameter of a lens and an optical axis of the lens can be formed at a high precision with respect to each other, and eccentricity thereof can be suppressed. In addition, the outer diameter 60a of the mirror pipe 60 and an inner fitting part 60b of the mirror pipe 60 into which the collimator lens 35 fits can be formed by a common process, thereby guaranteeing coaxial accuracy of the outer diameter 60a and the inner fitting part 60b. Therefore, the center of the outer diameter 60a of the mirror pipe 60 and the optical axis A of the collimator lens 35 accurately match. FIG. 6 shows an embodiment of an image forming apparatus according to the present invention. In this embodiment of the image forming apparatus, the present invention is applied to any image forming apparatus which uses a multi-beam scanner, such as a laser printer, a digital copying machine, a facsimile machine, and a composite machine which has the functions of two or more of the laser printer, the copying machine and the facsimile machine. An image forming apparatus 80 shown in FIG. 6 generally includes a multi-beam scanner 81 provided with a multi-beam light source unit 82, an image transfer system 83 which develops an image formed on the photoconductive drum within the multi-beam scanner 81 and transfers the developed image on a recording medium such as paper, and a paper supply system 84 which supplies the paper. The multi-beam scanner 81 has a construction shown in FIG. 1, for example. Further, the multi-beam light source unit 82 has a construction shown in FIG. 2 or 5, for example. In this embodiment of the image forming apparatus, the multi-beam light source unit 82 is constructed so that constituent elements thereof are provided within a single package. The image transfer system 83 and the paper supply system 84 may have known constructions employed by known image forming apparatuses. Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention.

Claims: A multi-beam light source unit arranged to be mounted on a housing (12) of a multi-beam scanner, said light source unit comprising: a light source (30) for emitting a plurality of light beams from corresponding light emitting points (101 - 104) arranged in an array at equal intervals; a collimator lens (35) for forming the plurality of light beams into a parallel bundle of rays; and an adjusting mechanism (2, 3, 10) for adjusting relative positions of the light source (30) and the collimator lens (35) so that a center between outermost light emitting points (101, 104) of the light source matches an optical axis (A) of the collimator lens, said collimator lens and said light source being simultaneously rotatable about the optical axis of the collimator lens and said adjusting mechanism comprising a support (2) for supporting said light source (30), a first base (3) and a second base (10), wherein said support (2) is mountable to said first base (3), said first base (3) is rotatable about said optical axis (A) relative to said second base (10) and said collimator lens (35) is accommodated within a pipe (6) that is received in a fitting hole (3b) of a sleeve shaft (3e) of said first base (3), said sleeve shaft (3e) fitting into a fitting hole (10a) of said second base (10), characterized in that said second base (10) is not integral with said housing (12), and in that said second base (10) is provided with positioning holes (10a, 10b) and said housing (12) is provided with corresponding positioning pins (12a, 12b) adapted to fit into said positioning holes (10a, 10b) thereby positioning the second base (10) with respect to the housing (12). A multi-beam light source unit arranged to be mounted on a housing (12) of a multi-beam scanner, said light source unit comprising: a light source (30) for emitting a plurality of light beams from corresponding light emitting points (101 - 104) arranged in an array at equal intervals; a collimator lens (35) for forming the plurality of light beams into a parallel bundle of rays; and an adjusting mechanism (2, 3, 10) for adjusting relative positions of the light source (30) and the collimator lens (35) so that a center between outermost light emitting points (101, 104) of the light source matches an optical axis (A) of the collimator lens, said collimator lens and said light source being simultaneously rotatable about the optical axis of the collimator lens and said adjusting mechanism comprising a support (2) for supporting said light source (30), a first base (3) and a second base (10), wherein said support (2) is mountable to said first base (3), said first base (3) is rotatable about said optical axis (A) relative to said second base (10) and said collimator lens (35) is accommodated within a pipe (60) that is fixed within a fitting hole (3b) of said first base (3), characterized in that said pipe (60) fits into a fitting hole (10a) of said second base (10) and in that said second base (10) is not integral with said housing (12), and in that said second base (10) is provided with positioning holes (10a, 10b) and said housing (12) is provided with corresponding positioning pins (12a, 12b) adapted to fit into said positioning holes (10a, 10b) thereby positioning the second base (10) with respect to the housing (12). The multi-beam light source unit as claimed in claim 1 or 2, wherein said adjusting mechanism is configured for adjusting a position of the light source relative to the collimator lens. The multi-beam light source unit as claimed in claim 1 or 2, wherein said adjusting mechanism is configured for adjusting a position of the collimator lens relative to the light source. The multi-beam light source unit as claimed in any of claims 1 to 4, wherein the light source (30), the collimator lens (35) and the adjusting mechanism (2, 3, 10) are provided within a single package. A multi-beam scanner comprising: a multi-beam light source unit according to any of the proceeding claims for emitting a plurality of light beams; a scanning section (32) for scanning a scanning surface (36) by the plurality of light beams emitted from the multi-beam light source unit; and an imaging section (33, 34, 38) for imaging the plurality of light beams emerging from the scanning section on the scanning surface. The multi-beam scanner according to claim 6, wherein said multi-beam light source unit is mounted on said optical housing (12) of said multi-beam scanner via said positioning pins (12a, 12b) which fit into the corresponding positioning holes (10b, 10c) of said second base (10), so that said multi-beam light source unit is mounted with a spatial distance determined by a mounting surface (12c) of said housing (12). An image forming apparatus comprising: a multi-beam scanner (81) according to claim 6 or 7; and an image transfer system (83) for developing an image formed by the multi-beam scanner and transferring the image onto a recording medium.

Inventors: MAKINO HIDEYO, MAKINO, HIDEYO
Applicants: RICOH KK, RICOH COMPANY, LTD.
Application year: 1999
Main classification: H04N1
IPC codes: H04N1, G02B26, B41J2