Laser beam emitting unit

[0002] 1. Field of the Invention

[0003] The present invention relates to a laser beam emitting unit which serves as a fundamental component of a scanning optical system incorporated in, e.g., a laser printer.

[0004] 2. Description of the Related Art

[0005] A laser beam emitting unit which serves as a fundamental component of a scanning optical system incorporated in, e.g., a laser printer is known in the art. Such a laser beam emitting unit is provided with a base plate to which a laser diode is fixed, and a lens holder which is fixed to the base plate and holds a collimating lens which collimates a laser beam emitted from the laser diode.

[0006] Formerly, the lens holder is fixed to the base plate so that through holes formed on the lens holder and corresponding through holes formed on the base plate are aligned and so that set screws are screwed into these aligned through holes.

[0007] According to such a conventional fixing manner, since the relative position between the lens holder and the base plate is determined by bringing the through holes of the lens holder into alignment with the through holes of the base plate, all the through holes must be formed with an extremely high degree of precision. This is a troublesome task. In addition, the necessity of the set screws for fixing the lens holder to the base plate increases assembling costs.

[0008] An object of the present invention is to provide a laser beam emitting unit which is characterized in that the lens holder and the base plate can be fixed to each other while being precisely positioned relative to each other with a high degree of precision and with easy of assembly.

[0009] To achieve the object mentioned above, according to an aspect of the present invention, a laser beam emitting unit is provided, including a laser diode, a collimating lens upon which a laser beam emitted by the laser diode is incident, a base plate to which the laser diode is fixed, a lens holder which holds the collimating lens, and a holder support plate via which the lens holder is fixed to the base plate. The holder support plate includes a flat portion which faces the base plate with a gap between the flat portion and the base plate, and at least two leg portions which extend from the flat portion to the base plate in a direction substantially perpendicular to the flat portion. Each of the at least two leg portions includes a claw portion which is deformed to be fixed to the base plate, wherein the gap is maintained between the flat portion and the base plate.

[0010] Preferably, the base plate includes at least two receiving portions which receive the at least two leg portions, respectively.

[0011] Preferably, the at least two receiving portions include at least two recessed portions in which the at least two leg portions are respectively fitted.

[0012] Preferably, each of the at least two leg portions includes an engaging member having a contacting surface which is in contact with the base plate, and a projecting portion which extends from the engaging member to be fitted in corresponding one of the at least two recessed portions, the claw portion being formed on the projecting portion.

[0013] Preferably, the base plate has a substantially rectangular shape, the at least two receiving portions including at least one pair of receiving portions respectively formed on opposite sides of the base plate to be opposed to each other.

[0014] Preferably, the projecting portion has a substantially U-shape, and includes a projecting base, the claw portion, and a recessed portion formed between the projecting base and the claw portion, and wherein the lens holder is fixed to the base plate by bending the claw portion along a surface of the base plate so that the engaging member and the projecting base hold a portion of the base plate therebetween.

[0015] Preferably, the following condition is satisfied:

[0016] Ze<Z₅<Zt; wherein “Z₅” represents a thickness of the base plate; “Zt” represents a distance from a plane including the contacting surface to a first point on a surface of the claw portion in the vicinity of a tip of the claw portion, in the direction substantially perpendicular to the flat portion; and “Ze” represents a distance from the plane to a second point on a surface of the claw portion in the vicinity of the root of the claw portion, in the direction substantially perpendicular to the flat portion.

[0017] Preferably, the holder support plate is made of a metal.

[0018] Preferably, the projecting base is fitted in corresponding one of the at least two recessed portions with a minimum clearance.

[0019] Preferably, the claw portion includes an inclined engaging surface provided on the claw portion opposing the projecting base, the lens holder being fixed to the base plate with the engaging surface in contact with the surface of the base plate.

[0020] Preferably, the lens holder is fixed to the holder support plate via at least two set screws, a through hole being formed on the base plate so that a screw driver is accessible to one of the at least two set screws through the through hole.

[0021] According to another aspect of the present invention, a laser beam emitting unit is provided, including a laser diode, a collimating lens upon which a laser beam emitted by the laser diode is incident, a base plate to which the laser diode is fixed, and a holder support plate which is fixed to the base plate and supports the collimating lens. The base plate includes at least two recessed portions which define a fixing position of the holder support plate relative to the base plate. The holder support plate includes a flat portion which faces a front surface of the base plate with a gap between the flat portion and the base plate, and at least two leg portions which extend from the flat portion to the base plate in a direction substantially perpendicular to the flat portion to be associated with the at least two recessed portions. Each of the at least two leg portions includes an engaging member which is in contact with the front surface of the base plate, and a projecting portion which extends from the engaging member to be fitted in corresponding one of the at least two recessed portions, a claw portion being formed on the projecting portion, the claw portion being deformed to be fixed to a rear surface of the base plate with the gap being maintained between the flat portion and the base plate.

[0022] According to another aspect of the present invention, a laser beam emitting unit is provided, including a base plate to which a laser diode is fixed, a lens holder which holds a collimating lens through which a laser beam emitted by the laser diode is collimated, and a holder support plate positioned between the base plate and the lens holder to fix the lens holder to the base plate via the holder support plate. The holder support plate includes a flat portion which faces the base plate with a gap between the flat portion and the base plate, and a pair of leg portions which extend from the flat portion in a direction substantially perpendicular to the flat portion to be engaged with the base plate. Each of the pair of two leg portions includes a claw portion which is deformed to be fixed to the base plate.

[0023] The present disclosure relates to subject matter contained in Japanese Patent Application No.2000-321396 (filed on Oct. 20, 2000) which is expressly incorporated herein by reference in its entirety.

[0024] The present invention will be described below in detail with reference to the accompanying drawings in which:

[0025] FIG. 1 is a schematic plan view of a scanning optical system incorporated in a laser printer which is provided with an embodiment of a laser beam emitting unit according to the present invention;

[0026] FIG. 2 is a side elevational view of the laser beam emitting unit shown in FIG. 1;

[0027] FIG. 3 is a schematic plan view of a base plate of said laser beam emitting unit;

[0028] FIG. 4 is a top plan view of a holder support plate of the laser beam emitting unit shown in FIG. 1;

[0029] FIG. 5 is a side elevational view of the holder support plate shown in FIG. 4;

[0030] FIG. 6 is a side elevational view of the holder support plate shown in FIG. 4;

[0031] FIG. 7 is an enlarged side elevational view of a fundamental portion of the holder support plate and an associated fundamental portion of the base plate;

[0032] FIG. 8 is a perspective view of the laser beam emitting unit in a state after the holder support plate has been fixed to the base plate;

[0033] FIG. 9 is an exploded perspective view of the laser beam emitting unit, showing a state before the holder support plate is fixed to the base plate; and

[0034] FIG. 10 is a plan view of the laser beam emitting unit shown in FIG. 8.

[0035] FIG. 1 shows a scanning optical system 100 having an embodiment of a laser beam emitting unit 10 according to the present invention. The scanning optical system 100 is incorporated in a laser printer. The scanning optical system 100 is provided with a cylindrical lens 20, a rotary polygon mirror (light-beam deflector) 30, an fθ lens group 40, a reflecting mirror 50, and a laser-beam detector (photo-detector) 60, in that order in an optical path of the scanning optical system 100 from the laser beam emitting unit 10 side.

[0036] A collimated laser beam emitted from the laser beam emitting unit 10 is incident on the polygon mirror 30 after passing through the cylindrical lens 20. The polygon mirror 30 is driven to rotate at a constant rotational speed by a motor (not shown), so that the laser beam incident on the polygon mirror 30 is deflected in the main scanning direction to scan a surface (photoconductive surface) of a photoconductive drum D in the main scanning direction (the horizontal direction shown by an arrow S in FIG. 1) via the fθ lens group 40. The laser beam deflected by the polygon mirror 30 is initially incident on the reflecting mirror 50, before being incident on the photoconductive drum D, to be received by the laser-beam detector 60. The scanning starting point of a spot of the scanning laser beam on the photoconductive surface of the drum D is controlled by a controller (not shown) in accordance with the detection of the scanning laser beam with the laser-beam detector 30.

[0037] As shown in FIGS. 2, 8, 9 and 10, the laser beam emitting unit 10 is provided with a laser diode (LD) 1, a collimating lens 2, a lens holder 3, a holder support plate 4 and a base plate 5. The laser diode 1 is provided with three legs la (see FIG. 8) which are respectively inserted into three through holes 5h(see FIG. 3) formed on the base plate 5. The three legs 1arespectively inserted into the three through holes 5hare soldered to the base plate 5 to fix the laser diode 1 to the base plate 5. As shown in FIG. 9, the lens holder 3 that holds the collimating lens 2 is fixed to the holder support plate 4 by two set screws 3ato be integral with the holder support plate 4. The structures of the collimating lens 2 and the lens holder 3 are not limited solely to the particular structures shown in the drawings.

[0038] As shown in FIG. 3, the base plate 5 has a substantially rectangular shape. The lateral direction (the horizontal direction as viewed in FIG. 3) of the base plate 5, the longitudinal direction (the vertical direction as viewed in FIG. 3) of the base plate 5, and the direction normal to both the lateral and longitudinal directions (i.e., the direction normal to the drawing surface of FIG. 3) are herein defined as X-direction, Y-direction and Z-direction, respectively. The Z-direction corresponds to the direction of the optical axis of the collimating lens 2. The base plate 5 is provided, on the opposite sides thereof in the vicinity of one end (the left end as viewed in FIG. 3) of the base plate 5, with a pair of recessed portions 5awhich have the same shape and size. The pair of recessed portions 5aare formed on the base plate 5 on the opposite sides thereof to be opposed to each other. The positions of the pair of recessed portions 5adefine the fixing position of the holder support plate 4 and the lens holder 3 relative to the base plate 5.

[0039] FIGS. 4 through 6 show the shape of the holder support plate 4. As shown in FIGS. 4 through 6, the holder support plate 4 is made of a single plate, and is provided with a flat portion 11 having a substantially octagonal shape, and a pair of leg portions 12. The flat portion 11 is provided at the center thereof with a circular through hole 11hin which a head portion of the laser diode 1 is fitted. The flat portion 11 is provided on opposite sides of the circular through hole 11hwith two through holes 11ain which two set screws 3aare inserted, respectively. The pair of leg portions 12 are formed on the holder support plate 4 in a manner such that each of opposite end portions (upper and lower end portions as viewed in FIG. 4) of the flat portion 11 is bent by approximately 90 degrees in a direction opposite to the surface of the flat portion 11 to which the lens holder 3 is mounted (see FIGS. 6 and 9). The holder support plate 4 is made of a metal such as an aluminum alloy to efficiently dissipate heat generated by the laser diode Each of the pair of leg portions 12 is provided with a spacer portion 13 which extends substantially perpendicular to the flat portion 11, and a projecting portion 14 which extends from the spacer portion 13 from a substantially center thereof. Each spacer portion 13 extends parallel the X-direction, and is provided with a contacting surface 13awhich is positioned apart from the flat portion 11 of the holder support plate 4 in the Z-direction by a predetermined distance. Each projecting portion 14 has a substantially U-shape, and is provided with a projecting base 14a, a claw portion 14band a recessed portion 14cformed between the projecting base 14aand the claw portion 14b. The projecting base 14ais fitted in the corresponding one of the pair of recessed portions 5awith a minimum clearance.

[0040] FIG. 7 shows one of the two leg portions 12, the projecting portion 14 of which is fitted in the corresponding recessed portion 5aof the base plate 5. As shown in FIG. 7, an engaging surface (upper surface as viewed in FIG. 7) of the claw portion 14bbetween the projecting base 14aand the claw portion 14bis formed as an inclined surface α which is inclined to the X-direction. Accordingly, the following condition is satisfied:

[0041] Ze<Z₅<Zt

[0042] wherein “Z₅” represents the thickness of the base plate 5,

[0043] “Zt” represents the distance from a plane P (shown by one-dot chain line in FIG. 7) including the contacting surface 13aof the spacer portion 13 to a point on the inclined surface a in the vicinity of the tip of the claw portion 14bin the Z-direction; and

[0044] “Ze” represents the distance from the plane P to a point on the inclined surface a in the vicinity of the root of the claw portion 14bin the Z-direction.

[0045] The width X_5a(see FIG. 3) of each recessed portion 5ain the X-direction corresponds to the width X₁₄(see FIG. 5) of each projecting portion 14 in the X-direction, while the space Y₅(see FIG. 3) between the pair of recessed portions 5acorresponds to the space Y₄(see FIG. 6) between the pair of leg portions 12, so that the two projecting bases 14aof the two projecting portions 14 are respectively fitted in the two recessed portions 5awith a minimum clearance. In this state, a gap (space) X is formed between the flat portion 11 of the holder support plate 4 and the base plate 5 (see FIGS. 2 and 6).

[0046] The holder support plate 4 and the base plate 5 are fixed to each other, and the relative position therebetween is determined in such a manner in the following descriptions.

[0047] Firstly, the two projecting bases 14aof the two projecting portions 14 are respectively fitted in the two recessed portions 5aof the base plate 5 to bring the contacting surface 13ainto contact with a surface of the base plate 5. This determines the position of the lens holder 3 relative to the base plate 5 in the X-direction via the spacer portion 13 and the projecting portion 14. At the same time, the position of the lens holder 3 relative to the base plate 5 in the Z-direction is determined by the contact of the contacting surface 13awith a surface of the base plate 5 since each spacer portion 13 extends parallel the X-direction.

[0048] In a state where the contacting surface 13ais in contact with the base plate 5, the aforementioned gap X (see FIGS. 2 and 6) is formed between the base plate 5 and the flat portion 11. With this structure, one or more parts can be disposed in the gap X and the base plate 5 can be made smaller, while the heat generated by the laser diode 1 can be dissipated efficiently via the gap X.

[0049] In a state where the pair of leg portions 12 are respectively inserted into the pair of recessed portions 5a, bending each of the two claw portions 14binwardly, toward the three through holes 5h, in the Y-direction along a surface of the base plate 5 causes the inclined surface α of each claw portion 14bto come into firm contact with the base plate 5, so that each claw portion 14band the corresponding projecting base 14ahold a portion of the base plate 5 therebetween in the vicinity of the associated recessed portion 5a. Namely, bending each of the two claw portions 14binwardly causes the holder support plate 4 to be fixed to the base plate 5 firmly. FIG. 8 shows such a state after the holder support plate 4 has been firmly fixed to the base plate 5 with the two claw portions 14bbent inwardly. The base plate 5 is provided with a through hole 5bthrough which a screw driver is accessible to one of the set screws 3a(the left set screw 3aas viewed in FIG. 10). The lens holder 3 that holds the collimating lens 2 is fixed to the holder support plate 4 via the two set screws 3ato be integral therewith as described above, so that the lens holder 3 can be freely mounted to and dismounted from the holder support plate 4 either before or after the holder support plate 4 is fixed to the base plate 5.

[0050] Although the flat portion 11 of the holder support plate 4 has a substantially octagonal shape in the above described embodiment of the laser beam emitting unit 10, the shape of the flat portion 11 is not limited solely to a particular shape.

[0051] Although the holder support plate 4 is made of a single metal plate as described above, the holder support plate 4 is not limited solely to such particular material or plate. For instance, the flat portion 11 can be made of a single metal plate while two metal plates which respectively constitute the pair of leg portions 12 can be welded to the flat portion 11.

[0052] Although the holder support plate 4 is fixed to the base plate 5 at two points via the two set screws 3a, the holder support plate 4 can be fixed to the base plate 5 at more than two points if it is desired to fix the holder support plate 4 to the base plate 5 more firmly.

[0053] Although the base plate 5 has a substantially rectangular shape in the above described embodiment of the laser beam emitting unit 10, the shape of the base plate 5 is not limited solely to a particular shape. Although each of the pair of recessed portions 5ais formed by cutting out a part of the base plate 5 in the above described embodiment of the laser beam emitting unit 10, each of the pair of recessed portions 5acan be formed by forming projecting portions on an edge of base plate 5 at predetermined intervals. The pair of recessed portions 5acan be replaced by a pair of through slots formed on the base plate 5 into which the pair of projecting portions 14 can be inserted.

[0054] As can be understood from the above descriptions, according to a laser beam emitting unit to which the present invention is applied, since the holder support plate includes a flat portion (11) which faces the base plate with a gap (X) between the flat portion and the base plate, and at least two leg portions (12) which extend from the flat portion to the base plate in a direction substantially perpendicular to the flat portion, and each of the two leg portions includes a claw portion (14b) which is deformed to be fixed to the base plate with the gap being maintained between the flat portion and the base plate, the holder and the base plate can be fixed to each other while being precisely positioned relative to each other with a high degree of precision and with ease of assembly.

[0055] Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.