Optical scanning device and image forming device provided with optical scanning device

An optical scanning device provided with a casing, a plurality of light sources, a deflection scanning unit that deflects and scans light beams from the plurality of light sources onto a plurality of bodies to be scanned, and a plurality of optical units arranged between the deflection scanning unit and the bodies to be scanned, in which optical unit supporting members that support the optical units are provided, the optical unit supporting members support the plurality of optical units arranged at predetermined intervals, and a thermal expansion coefficient of the optical unit supporting members is lower than a thermal expansion coefficient of the casing.

TECHNICAL FIELD

This invention relates to an optical scanning device that forms electrostatic latent images with the surfaces of photoreceptor drums in a charged state being irradiated with laser light that corresponds to image information composed of digital signals, and an image forming device provided with the optical scanning device, in an image forming device such as a printer, a copying machine, or a facsimile.

BACKGROUND ART

Conventionally, in an image forming device, an image is formed with images of a plurality of colors being superposed by an optical scanning device (laser scanning unit: LSU), and therefore a problem that is referred to as color deviation sometimes occurs.

For example, image forming devices having configurations such as the following are known. A light beam such as a laser is scanned on the surfaces of a plurality of latent image carriers (also referred to as drum-shaped photoreceptor units or photoreceptor drums, for example) that correspond to each color of yellow, magenta, and cyan, and respective latent images are thereby written to each latent image carrier. Those latent images are then developed for images of each color to be formed on each latent image carrier, the images of each color are transferred from each latent image carrier to an image carrier (transfer belt), and the images of each color are superposed and formed on the image carrier. In addition, the images of each color are transferred from the image carrier to a printing sheet for an image to be formed on the printing sheet. In an image forming device of this kind of configuration, the images of each color sometimes deviate when transferred from each latent image carrier to the image carrier, color deviation occurs, and image quality deteriorates.

In particular, when an image forming device is being driven, the temperature inside the casing of the image forming device rises, the casing of the optical scanning device thermally expands, and as a result the positions of optical components such as Fθ second lenses fluctuate and color deviation sometimes occurs.

To prevent this kind of color deviation caused by thermal expansion, conventionally, a method is known in which a temperature sensor such as a thermistor is provided inside the optical scanning device, and color deviation is corrected according to the temperature inside and peripheral to the optical scanning device (see PTL 1, for example).

According to this method, the positions of the images of each color are corrected by controlling the latent image writing timing with reference to a table indicating characteristics of the color deviation amounts for each color for the image carrier with respect to temperature changes in the temperature inside and peripheral to the optical scanning device.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, there is a problem in that as the casing of the optical scanning device becomes larger, the amount of color deviation caused by thermal expansion also increases, and the precision of the color deviation correction consequently decreases.

Meanwhile, a method is also known in which thermal expansion of the casing is reduced by using a material having a low thermal expansion coefficient as the material for the casing of the optical scanning device. However, a material having a low thermal expansion coefficient is expensive compared to an ordinary material, and therefore is there is a problem in that manufacturing costs increase.

This invention has been devised in light of such problems, and a purpose thereof is to provide an optical scanning device that reduces the amount of color deviation caused by thermal expansion of a casing, even in a case where a material having a high thermal expansion coefficient is used.

Solution to Problem

This invention provides an optical scanning device provided with a casing, a plurality of light sources, a deflection scanning unit that deflects and scans light beams from the plurality of light sources onto a plurality of bodies to be scanned, and a plurality of optical units arranged between the deflection scanning unit and the bodies to be scanned, in which optical unit supporting members that support the optical units are provided, the optical unit supporting members support the plurality of optical units arranged at predetermined intervals, and a thermal expansion coefficient of the optical unit supporting members is lower than a thermal expansion coefficient of the casing. Furthermore, this invention provides an image forming device provided with the optical scanning device.

Advantageous Effects of Invention

This invention is able to realize an optical scanning device that reduces the amount of color deviation caused by thermal expansion of a casing, even in a case where a material having a high thermal expansion coefficient is used for the casing.

DESCRIPTION OF EMBODIMENTS

(1) An optical scanning device of this invention is provided with a casing, a plurality of light sources, a deflection scanning unit that deflects and scans light beams from the plurality of light sources onto a plurality of bodies to be scanned, and a plurality of optical units arranged between the deflection scanning unit and the bodies to be scanned, in which an optical unit supporting member that supports the optical units is provided, the optical unit supporting member supports the plurality of optical units arranged at predetermined intervals, and a thermal expansion coefficient of the optical unit supporting member is lower than a thermal expansion coefficient of the casing.

Furthermore, the optical scanning device of this invention is an image forming device that is provided with the optical scanning device.

In this invention, the “optical scanning device” is a device that forms electrostatic latent images with the surfaces of photoreceptor drums in a charged state being irradiated with laser light that corresponds to image information composed of digital signals, in an image forming device such as a copying machine or a facsimile.

The “thermal expansion coefficient” is a proportion by which the volume of the casing or a lens supporting unit thermally expands due to a temperature increase. Furthermore, a linear expansion coefficient (proportion by which a length changes) in a sub-scanning direction may be used instead of the thermal expansion coefficient.

The “plurality of light sources” of this invention are light sources corresponding to yellow (Y), magenta (M), cyan (C), and black (K), for example, and are realized by a first semiconductor laser44a, a second semiconductor laser44b, a third semiconductor laser44c, and a fourth semiconductor laser44d.

Furthermore, the “bodies to be scanned” of this invention are realized by photoreceptor drums13Y,13M,13C, and13K.

Furthermore, the “deflection scanning unit” of this invention is realized by a polygon mirror42and a polygon motor43or the like.

Furthermore, the “optical units” of this invention are realized by Fθ second lenses63b1to63b4and Fθ second lens holding units65b1to65b4or the like.

Furthermore, the “optical unit supporting member” of this invention is realized by Fθ second lens supporting units71and72.

Furthermore, the “image forming device” of this invention is a device that forms and outputs an image, such as a copying machine that has a copying function like a printer, or an MFP (multifunction peripheral) that includes functions other than copying.

Furthermore, the optical scanning device of this invention may have the configurations described hereinafter, or these may be combined as appropriate.

(2) The optical unit supporting member may support the plurality of optical units at both end sections thereof in a first direction in which the light beams scan the bodies to be scanned.

Thus, by means of a low cost and simple structure, it is possible to realize an optical scanning device that reduces the effect of elongation from thermal expansion of the casing without obstructing the paths of the light beams.

The “first direction in which the light beams scan the bodies to be scanned” is a direction in which the light beams scan the photoreceptor drums, and corresponds to a main scanning direction X in the embodiments of this invention.

(3) The casing may displace relative to the optical unit supporting member.

Thus, by providing the optical unit supporting member in the casing in such a way that the casing displaces relative to the optical unit supporting member, it is possible to realize an optical scanning device that reduces the amount of color deviation caused by thermal expansion of the casing.

(4) There may be further provided: a fixing unit that fixes a predetermined first portion of the optical unit supporting member to the casing; and an engaging unit that engages a predetermined second portion of the optical unit supporting member to the casing in such a way that displacement is possible relative to a second direction in which the plurality of optical units are arranged.

Thus, by providing a fixing unit that fixes the optical unit supporting member to the casing, and an engaging unit that engages the optical unit supporting member to the casing in such a way that displacement is possible relative to the direction in which the plurality of optical units are arranged, it is possible to realize an optical scanning device that reduces the amount of color deviation caused by thermal expansion of the casing.

An example of the “second direction in which the plurality of optical units are arranged” is a direction orthogonal to the direction in which the light beams scan the photoreceptor drums (first direction), and corresponds to a sub-scanning direction Y in the embodiments of this invention.

(5) The fixing unit may be provided nearer to the plurality of light sources than the engaging unit.

Thus, by providing the fixing unit nearer to the plurality of light sources than the engaging unit, it is possible to realize an optical scanning device that reduces the amount of color deviation caused by thermal expansion of the casing.

(6) The fixing unit may be configured by inserting a first screw into a first screw hole provided in the casing, via a first insertion section provided in the first portion of the optical unit supporting member.

Thus, by configuring the fixing unit using the first insertion section, the first screw hole, and the screw, it is possible to realize an optical scanning device that reduces the amount of color deviation caused by thermal expansion of the casing.

The “fixing unit” is not restricted to a screw, and, for example, a columnar-shaped boss may be provided on the casing, that boss may be inserted into a hole in sheet metal, and the sheet metal may be prevented from separating by means of an E-ring.

(7) The engaging unit may be configured by inserting a second screw into a second screw hole provided in the casing, via a second insertion section provided in the second portion of the optical unit supporting member, and the second screw may have a spring that presses the second portion of the optical unit supporting member when the second screw is inserted into the second screw hole via the second insertion section.

Thus, by configuring the engaging unit using the second insertion section, the second screw hole, and a spring or a hook, it is possible to realize an optical scanning device that reduces the amount of color deviation caused by thermal expansion of the casing.

(8) The engaging unit may have a hook that engages with the casing, via the second insertion section provided in the second portion of the optical unit supporting member.

Thus, it is possible to realize an optical scanning device that reduces the amount of color deviation caused by thermal expansion of the casing, by means of a simple configuration.

(9) The second insertion section may have an elongated hole or a notch that extends in the second direction.

Thus, it is possible to realize an optical scanning device that reduces the amount of color deviation caused by thermal expansion of the casing, by means of engagement between the second insertion section having an elongated hole or a notch that extends in the second direction, and the screw or the hook.

(10) The optical units may be composed of a lens and a lens holding member that holds the lens, the optical unit supporting member may have an insertion hole into which a protrusion provided on the casing is inserted, and, when one end in the first direction in which the light beams scan the bodies to be scanned, of the optical units is arranged on the optical unit supporting member, a lower surface of the lens holding member may make contact with a tip end of the protrusion inserted into the insertion hole.

Thus, since the lower surface of the lens holding member makes contact with the tip end of the protrusion inserted into the insertion hole, it is possible to realize an optical scanning device in which the lens holding member can be mounted easily and precisely by adjusting the tip end of the protrusion.

(11) The optical unit supporting member may have mounted thereon an adjustment unit that adjusts a position in the second direction in which the plurality of optical units are arranged, of one end in the first direction in which the light beams scan the bodies to be scanned, of the optical units when the one end of the optical units is arranged on the optical unit supporting member.

Thus, it is possible to realize an optical scanning device in which the optical unit supporting member has mounted thereon an adjustment unit that reduces the effect caused by thermal expansion of the casing.

(12) A driving unit that drives the adjustment unit may be mounted on the optical unit supporting member.

Thus, it is possible to realize an optical scanning device in which the optical unit supporting member has mounted thereon a driving unit that drives the adjustment unit while the effect caused by thermal expansion of the casing is reduced.

The “driving unit that drives the adjustment unit” is a motor, for example. Furthermore, the driving unit may be a manually driven type.

(13) The optical unit supporting member may support the optical units for black, cyan, and magenta, or the optical units for black, cyan, magenta, and yellow, from among the plurality of optical units.

Thus, by supporting the optical units for black, cyan, and magenta, or the optical units for black, cyan, magenta, and yellow, using the optical unit supporting member, it is possible to realize an optical scanning device that reduces the amount of color deviation for black, cyan, and magenta, or for black, cyan, magenta, and yellow, caused by thermal expansion of the casing.

(14) The lens supporting units may be composed of a metal material, and the casing may be composed of a resin material.

Thus, it is possible to realize an optical scanning device that reduces the effect of color deviation caused by thermal expansion of the casing with low cost.

An example of the “metal material” is SECC, and an example of the “resin material” is a PC/ABS alloy.

Hereinafter, this invention will be described in greater detail using the drawings. It should be noted that the description hereinafter is exemplary in all respects, and shall not be construed as restricting this invention.

First, the differences between a conventional optical scanning device11cand an optical scanning device11of this invention will be described based onFIG. 1.

FIG. 1(A)is an explanatory diagram depicting a deviation in the positions of Fθ second lenses63b1,63b2,63b3, and63b4caused by thermal expansion of a casing41of the conventional optical scanning device11c. Furthermore,FIG. 1(B)is an explanatory diagram depicting a mechanism that suppresses a deviation in the positions of Fθ second lenses63b1,63b2,63b3, and63b4caused by thermal expansion of a casing41of the optical scanning device11of this invention.

As depicted inFIG. 1(A), in the conventional optical scanning device11c, the Fθ second lenses63b1,63b2,63b3, and63b4are fixed directly to the casing41.

Thus, in a case where the casing41has thermally expanded in the sub-scanning direction Y, based on an end section (basis for thermal expansion) of the casing41in the opposite direction to the sub-scanning direction Y (hereinafter, the −Y direction; the same is also true for the X direction and the Z direction), positional deviation occurs in the sub-scanning direction Y for each Fθ second lens63b1,63b2,63b3, and63b4, and color deviation consequently occurs.

To resolve this kind of problem, in this invention, rather than being provided directly on the casing41, the Fθ second lenses63b1,63b2,63b3, and63b4are provided on the casing41having arranged therebetween Fθ second lens supporting units71and72that are composed of a material having a lower thermal (linear) expansion coefficient than the casing41, as depicted inFIG. 1(B).

At such time, in the Fθ second lens supporting units71and72, only −Y direction end sections71aand72aare fixed to the casing41, and end sections71band72bat the sub-scanning direction Y side are not fixed to the casing41, so that the Fθ second lens supporting units71and72are not pulled by the expansion of the casing41.

By doing so, in the casing41, the Fθ second lens supporting units71and72expand independently, and therefore the Fθ second lenses63b1,63b2,63b3, and63b4provided on the Fθ second lens supporting units71and72are not affected by the thermal expansion of casing41, and consequently color deviation caused by thermal expansion of the casing41is suppressed.

<Configuration of Image Forming Device100>

Next, a configuration of an image forming device100provided with the optical scanning device11according to embodiment 1 of this invention will be described based onFIGS. 2 and 3.

FIG. 2is a cross-sectional view depicting a schematic configuration of the image forming device100provided with the optical scanning device11of this invention. Furthermore,FIG. 3is a block diagram depicting a schematic configuration of a control system of the image forming device100depicted inFIG. 2.

<<Configuration of Image Forming Device100>>

In this image forming device100, an image that uses each color of black (K), cyan (C), magenta (M), and yellow (Y) is printed on a printing sheet. Alternatively, a monochrome image that uses a single color (black, for example) is printed on a printing sheet. Therefore, four of each of a developing device12, a photoreceptor drum13, a drum cleaning device14, and a charger15or the like are provided. These are respectively associated with black, cyan, magenta, and yellow, and four image forming stations Pa, Pb, Pc, and Pd are configured, in order to form four kinds of toner images corresponding to each color.

In any of the image forming stations Pa, Pb, Pc, and Pd, a toner image is formed as follows. The drum cleaning devices14remove and recover remaining toner on the surfaces of the photoreceptor drums13Y,13M,13C, and13K. Thereafter, the surfaces of the photoreceptor drums13Y,13M,13C, and13K are uniformly charged to a prescribed potential by the chargers15. The charged surfaces are then exposed by the optical scanning device11and electrostatic latent images are formed on the surfaces. Thereafter, the electrostatic latent images are developed by the developing devices12. Toner images of each color are thereby formed on the surfaces of the photoreceptor drums13Y,13M,13C, and13K.

Furthermore, an intermediate transfer belt21moves in a circular manner in the direction of an arrow C. A belt cleaning device22removes and recovers remaining toner on the intermediate transfer belt21moving in a circular manner. Then, the toner images of each color on the surfaces of the photoreceptor drums13Y,13M,13C, and13K are sequentially transferred and superposed on the intermediate transfer belt21. In this way, toner images of each color are formed on the intermediate transfer belt21.

A nip area is formed between the intermediate transfer belt21and a transfer roller23aof a secondary transfer device23. A printing sheet that has been conveyed through an S-shaped sheet conveyance path R1has the toner images of each color on the surface of the intermediate transfer belt21transferred thereto while being sandwiched and conveyed in that nip area. The printing sheet having passed through the nip area is inserted between a heating roller24and a pressurizing roller25of a fixing device17to have heat and pressure applied thereto, and the toner images of each color are fixed on the printing sheet.

The printing sheet is extracted from a feed tray18by a pickup roller33and conveyed via the sheet conveyance path R1. The printing sheet then passes through the secondary transfer device23and the fixing device17, and is taken out to a discharge tray39via a discharge roller36. A resist roller34that momentarily stops the printing sheet and aligns the tip end of the printing sheet is arranged on this sheet conveyance path R1. The resist roller34, after having momentarily stopped the printing sheet, conveys the printing sheet in accordance with a transfer timing for the toner images in the nip area between the intermediate transfer belt21and the transfer roller23a. Furthermore, a conveying roller35or the like that prompts conveying of the printing sheet is arranged on the sheet conveyance path R1.

<<Configuration of Control System>>

InFIG. 3, a control unit101integrally controls the image forming device100, and is composed of a CPU, a RAM, a ROM, various types of interfaces, and the like.

A printing unit102prints a print image on the printing sheet by means of an electrophotographic method. The printing unit102is configured including the optical scanning device11, the developing devices12, the photoreceptor drums13Y,13M,13C, and13K, the drum cleaning devices14, and the chargers15inFIG. 2. In addition, the printing unit102is configured including the intermediate transfer belt21, the fixing device17, the sheet conveyance path R1, the feed tray18, and the discharge tray39or the like.

Furthermore, an input operation unit103is composed of a plurality of input keys and a liquid crystal display device, for example.

A memory104is a nonvolatile storage means such as a hard disk device (HDD) or a flash memory, for example, and stores various data and programs.

For example, the control unit101controls an image reading device111and a document conveying device112for a document to be conveyed by the document conveying device112. An image of the document is then read by the image reading device111, and image data indicating the image of the document is stored in the memory104. In addition, the printing unit102is controlled for the image of the document indicated by the image data within the memory104to be printed on a printing sheet by the printing unit102.

Incidentally, in the image forming stations Pa, Pb, Pc, and Pd, images of the respective colors are formed on the photoreceptor drums13Y,13M,13C, and13K, and then the images on the photoreceptor drums13Y,13M,13C, and13K are sequentially transferred in such a way as to be superposed onto the intermediate transfer belt21. Thus, the transfer positions (image positions) deviate among the images of each color on the intermediate transfer belt21, color deviation occurs, and the image quality sometimes deteriorates.

A device that reduces this color deviation as follows is conventionally known.

Specifically, the memory104has stored therein data of a temperature characteristics table for color deviation amounts obtained by detecting the temperature inside and/or peripheral to the optical scanning device11by means of a thermistor and measuring the amount of color deviation for each color of yellow, magenta, cyan, and black in the main scanning direction X (hereinafter, the X direction) and the sub-scanning direction Y (hereinafter, the Y direction) at each temperature.

Next, the control unit101causes the thermistor to detect the temperature inside and/or peripheral to the optical scanning device11, and, on the basis of the detected temperature, corrects the positions of the images of each color formed on the photoreceptor drums13Y,13M,13C, and13K with reference to the temperature characteristics table for color deviation amounts.

In this way, control is performed in such a way that the images on the photoreceptor drums13Y,13M,13C, and13K are accurately superposed, transferred, and formed on the intermediate transfer belt21, and color deviation is prevented.

The correction of image positions on the photoreceptor drums13Y,13M,13C, and13K is ordinarily carried out by controlling, for example, the timing for writing electrostatic latent images onto the photoreceptor drums13Y,13M,13C, and13K by means of scanning beams that are emitted from laser diodes of the optical scanning device11. Furthermore, the Y direction image position is corrected by adjusting the Y direction position of a main scanning line on the photoreceptor drums13Y,13M,13C, and13K. Furthermore, the X direction image position is corrected by adjusting the length and X direction position of the main scanning line on the photoreceptor drums13Y,13M,13C, and13K.

Next, a detailed configuration of the optical scanning device11of the image forming device100according to the first embodiment of this invention will be described based onFIGS. 4 to 6.

FIG. 4is a perspective view of the interior of the casing41, with an upper lid having been removed, of the optical scanning device11according to this invention. Furthermore,FIG. 5is a plan view of the optical scanning device11depicted inFIG. 4. Furthermore,FIG. 6(A)is a cross-sectional view along arrow A-A of the optical scanning device11depicted inFIG. 5. Furthermore,FIG. 6(B)is a cross-sectional view along arrow B-B of the optical scanning device11depicted inFIG. 5.

It should be noted that a direction orthogonal to the X direction is taken as the Y direction, and a direction orthogonal to the X direction and the Y direction (the longitudinal direction of the rotation axis of the polygon motor43) is taken as the height direction Z.

The casing41has a rectangular base plate41aand four side plates41band41cthat surround the base plate41a.

Furthermore, the polygon motor43(not depicted) is fixed to the base plate41a, the center of rotation of the polygon mirror42, which is polygonal in a plan view, is connected and fixed to a rotary shaft of the polygon motor43in a position that is slightly displaced in the −Y direction from the center of the base plate41a, and the polygon mirror42rotates by means of the polygon motor43.

The optical scanning device11is provided with first to fourth incident optical systems that guide light beams L1to L4of the first to fourth semiconductor lasers44ato44dto the polygon mirror42.

The first incident optical system is composed of a collimator lens53a, an aperture54a, a mirror55aarranged at the same height as the first semiconductor laser44a, and a cylindrical lens56, or the like.

The second incident optical system is composed of a collimator lens53b, an aperture54b, a mirror55barranged at the same height as the second semiconductor laser44b, and the cylindrical lens56, or the like.

The third incident optical system is composed of a collimator lens53c, an aperture54c, a mirror55carranged at the same height as the third semiconductor laser44c, and the cylindrical lens56, or the like.

The fourth incident optical system is composed of a collimator lens53d, an aperture54d, a mirror55darranged at the same height as the fourth semiconductor laser44d, and the cylindrical lens56, or the like.

In addition, first to fourth imaging optical systems are provided.

The first imaging optical system guides the light beam L1of the first semiconductor laser44areflected by the polygon mirror42, to the photoreceptor drum13Y corresponding to yellow.

The second imaging optical system guides the light beam L2of the second semiconductor laser44breflected by the polygon mirror42, to the photoreceptor drum13M corresponding to magenta.

The third imaging optical system guides the light beam L3of the third semiconductor laser44creflected by the polygon mirror42, to the photoreceptor drum13C corresponding to cyan.

The fourth imaging optical system guides the light beam L4of the fourth semiconductor laser44dreflected by the polygon mirror42, to the photoreceptor drum13K corresponding to black.

The first imaging optical system is composed of the Fθ second lens63b1and two reflective mirrors64a1and64a2or the like.

The second imaging optical system is composed of the Fθ second lens63b2and two reflective mirrors64b1and64b2or the like.

The third imaging optical system is composed of the Fθ second lens63b3and two reflective mirrors64c1and64c2or the like.

The fourth imaging optical system is composed of the Fθ second lens63b4and a reflective mirror64dor the like.

Next, a description will be given regarding the optical paths along which the light beams L1to L4of the semiconductor lasers44ato44dare incident on the scanning surfaces of the respective photoreceptor drums13Y,13M,13C, and13K.

First, in the first incident optical system, the light beam L1of the first semiconductor laser44apasses through the collimator lens53aand is formed into parallel light, has the amount of light thereof reduced by the aperture54a, is incident on and reflected by the mirror55a, and passes through the cylindrical lens56and is incident on a reflective surface42aof the polygon mirror42.

Furthermore, in the second incident optical system, the light beam L2of the second semiconductor laser44bpasses through the collimator lens53band is formed into parallel light, has the amount of light thereof reduced by the aperture54b, is incident on and reflected by the mirror55b, and passes through the cylindrical lens56and is incident on a reflective surface42aof the polygon mirror42.

Furthermore, in the third incident optical system, the light beam L3of the third semiconductor laser44cpasses through the collimator lens53cand is formed into parallel light, has the amount of light thereof reduced by the aperture54c, is incident on and reflected by the mirror55c, and passes through the cylindrical lens56and is incident on a reflective surface42aof the polygon mirror42.

Furthermore, in the fourth incident optical system, the light beam L4of the fourth semiconductor laser44dpasses through the collimator lens53dand is formed into parallel light, has the amount of light thereof reduced by the aperture54d, is incident on and reflected by the mirror55d, and passes through the cylindrical lens56and is incident on a reflective surface42aof the polygon mirror42.

The cylindrical lens56concentrates the light beams L1to L4in such a way as be substantially converged in a direction corresponding to the Y direction and forms a linear image, thereby correcting a deviation in a dot pitch in the Y direction of the scanning surfaces of the photoreceptor drums13Y,13M,13C, and13K generated by a processing error of the mirror surfaces of the polygon mirror42or an inclination error (plane inclination) of the reflective surfaces42acaused by inclining or the like of the rotary shaft of the polygon motor43.

The light beams L1, L2, L3, and L4reflected by the reflective surfaces42aof the polygon mirror42pass through an Fθ first lens63aand are thereby respectively incident on the reflective mirrors64a1,64b1,64c1, and64dwhile the main scanning and sub-scanning light beam widths converge.

Next, in the first imaging optical system, the light beam L1is reflected in an obliquely upward direction by a reflective surface42aof the polygon mirror42, is then reflected by the reflective mirrors64a1and64a2, passes through the Fθ second lens63b1, and is incident on the photoreceptor drum13Y on which a yellow toner image is formed.

Furthermore, in the second imaging optical system, the light beam L2is reflected in an obliquely downward direction by a reflective surface42aof the polygon mirror42, is then reflected by the reflective mirrors64b1and64b2, passes through the Fθ second lens63b2, and is incident on the photoreceptor drum13M on which a magenta toner image is formed.

Furthermore, in the third imaging optical system, the light beam L3is reflected in an obliquely downward direction by a reflective surface42aof the polygon mirror42, is then reflected by the reflective mirrors64c1and64c2, passes through the Fθ second lens63b3, and is incident on the photoreceptor drum13C on which a cyan toner image is formed.

Furthermore, in the fourth imaging optical system, the light beam L4is reflected in an obliquely upward direction by a reflective surface42aof the polygon mirror42, is then reflected by the reflective mirrors64d, passes through the Fθ second lens63b4, and is incident on the photoreceptor drum13K on which a black toner image is formed.

The polygon mirror42is a rotary polygon mirror that has a polygonal columnar shape such as a hexagonal column or an octagonal column, is provided with mirrors on side surfaces, and rotates about the central axis of a polygonal column. The polygon mirror42rotates at a constant angular velocity by means of the polygon motor43, sequentially reflects the light beams L1to L4by means of the reflective surfaces42a, and repeatedly deflects the light beams L1to L4in the X direction at the constant angular velocity.

Thus, the scanning surfaces of the photoreceptor drums13Y,13M,13C, and13K are scanned in the X direction, and dot-like electrostatic latent images are formed at equal pitches.

The Fθ second lenses63b1,63b2,63b3, and63b4adjust focal length in such a way that the light beams L1to L4reflected by the reflective surfaces42aof the polygon mirror42form images on the scanning surfaces of the photoreceptor drums13Y,13M,13C, and13K respectively.

Furthermore, the Fθ second lenses63b1,63b2,63b3, and63b4convert the light beams L1to L4in such a way as to move at a constant linear velocity along the main scanning line on the respective photoreceptor drums13Y,13M,13C, and13K with regard to both the X direction and the Y direction.

Thus, the light beams L1to L4repeatedly scan the surfaces of the respective photoreceptor drums13Y,13M,13C, and13K in the X direction.

Meanwhile, the photoreceptor drums13Y,13M,13C, and13K on which yellow, magenta, cyan, and black toner images are formed are rotationally driven, two-dimensional surfaces (peripheral surfaces) of the photoreceptor drums13Y,13M,13C, and13K are scanned by the light beams L1to L4, and respective electrostatic images are formed on the surfaces of the photoreceptor drums13Y,13M,13C, and13K.

<<Configuration of Fθ Second Lens Supporting Units71and72>>

Next, a configuration of the Fθ second lens supporting units71and72of this invention will be described based onFIGS. 4 to 8.

FIG. 7(A)is a perspective view of the Fθ second lens supporting unit71depicted inFIG. 4. Furthermore,FIG. 7(B)is a plan view of the Fθ second lens supporting unit71depicted inFIG. 4. Furthermore,FIG. 7(C)is a side view of the Fθ second lens supporting unit71depicted inFIG. 4. Furthermore,FIG. 8(A)is a perspective view of the Fθ second lens supporting unit72depicted inFIG. 4. Furthermore,FIG. 8(B)is a plan view of the Fθ second lens supporting unit72depicted inFIG. 4. Furthermore,FIG. 8(C)is a side view of the Fθ second lens supporting unit72depicted inFIG. 4.

When the casing41of the optical scanning device11has thermally expanded, the casing41thermally expands equally in the X, Y, and Z directions; however, the effect of a fluctuation in the optical paths of the light beams L1to L4appears most in thermal expansion in the Y direction. Thus, in order to reduce the amount of color deviation, it is necessary to suppress the effect of thermal expansion exerted in the Y direction.

Furthermore, when based on the Fθ second lens63b1in the position nearest to a laser light source, the elongation from thermal expansion of the casing41appears more as the distance from the Fθ second lens63b1increases in the Y direction.

Thus, the elongation from thermal expansion appears more in the order of the Fθ second lens63b4, the Fθ second lens63b3, the Fθ second lens63b2, and the Fθ second lens63b1, and therefore the amount of color deviation increases in the order of yellow, magenta, cyan, and black that respectively correspond to the Fθ second lens63b1, the Fθ second lens63b2, the Fθ second lens63b3, and the Fθ second lens63b4.

Thus, rather than providing the Fθ second lenses63b2and63b3and the Fθ second lens63b4, which are likely to be affected by thermal expansion of the casing41, directly on the casing41, these are provided on the Fθ second lens supporting units71and72, which are composed of a material having a lower thermal expansion coefficient (or linear expansion coefficient) than the casing41, as depicted inFIGS. 4 to 6.

InFIGS. 4 to 6, the Fθ second lens supporting units71and72are respectively provided on level differences41dand41ethat are provided on inner side portions of the side plates41bon both sides of the casing41of the optical scanning device11.

The Fθ second lens supporting units71and72are composed of a material having a lower thermal expansion coefficient (or linear expansion coefficient) than the casing41of the optical scanning device11. For example, in a case where a PC/ABS alloy (linear expansion coefficient of approximately 7.8 to 8×10−5[cm/cm/° C.]), which is a resin material, is used for the casing41, SECC (electrogalvanized steel sheet having a linear expansion coefficient of approximately 11.7×10−6[cm/cm/° C.]), which is a metal material and has a lower linear expansion coefficient than a PC/ABS alloy, is used for the Fθ second lens supporting units71and72.

Generally, with [×10−6/° C.] as a unit, the thermal expansion coefficients of resin materials are 70 to 80 for PC resin material, 80 to 110 for ABS resin, 70 for PET resin material, and so forth, the thermal expansion coefficients of alloys are 23 for aluminum, 11.7 for iron, and 16.6 for copper, and the thermal expansion coefficients of alloys are 17 to 18 for stainless steel, 10 to 12 for cast iron, 5 to 6 for cemented carbide, and so forth. Thus, in a case where a casing41composed of a resin material having a thermal expansion coefficient of 70 to 110 [10−6/° C.] is used, it is desirable to use Fθ second lens supporting units71and72composed of a metal material or an alloy material of 5 to 23 [10−6/° C.].

Furthermore, as the material of the Fθ second lens supporting units71and72, other than SECC, a material having a low linear expansion coefficient such as SUS may be used.

As depicted inFIGS. 7(A)to (C), the Fθ second lens supporting unit71has formed therein notch sections71b2,71b3, and71b4to allow for bosses66a2,66a3, and66a4provided on the level difference41eof the casing41.

Furthermore, hole sections711a4and712a4of the Fθ second lens supporting unit71are relief holes to allow for protrusions411e4and412e4provided on the level difference41eof the casing41.

The hole sections711a4and712a4have a shape that extends in the Y direction in such a way that the protrusions411e4and412e4can displace relatively in the Y direction when the casing41expands.

The same is also true for hole sections711a3and712a3and hole sections711a2and712a2of the Fθ second lens supporting unit71.

Furthermore, the Fθ second lens supporting unit71has screw holes71c2,71c3, and71c4for fixing an adjustment member for adjusting bending (inclination) of a sub-scanning line to the Fθ second lens supporting unit71, and has protrusions71d2,71d3, and71d4for positioning an adjustment member for adjusting inclination on the Fθ second lens supporting unit71.

Furthermore, the Fθ second lens supporting unit71has screw holes71e2,71e3, and71e4for fixing an adjustment member for adjusting inclination to the Fθ second lens supporting unit71, and has protrusions71f2,71f3, and71f4for positioning an adjustment member for adjusting inclination on the Fθ second lens supporting unit71.

Furthermore, the Fθ second lens supporting unit71has a hole section712a1for fixing one end section71aby means of a screw67aor the like, and has a notch section71b1for inserting a spring screw69bat an end section71bat the opposite side.

Furthermore, a boss (protrusion) that positions the Fθ second lens supporting unit71is provided on the level difference41eof the casing41, and the Fθ second lens supporting unit71is positioned by inserting the boss (protrusion) inside a hole section711a1.

As depicted inFIGS. 8(A)to (C), the Fθ second lens supporting unit72has formed therein notch sections72b2,72b3, and72b4to allow for bosses66b2,66b3, and66b4provided on the level difference41dof the casing41.

Hole sections721a4and722a4of the Fθ second lens supporting unit72are relief holes to respectively allow for protrusions411d4and412d4provided on the level difference41dof the casing41.

Furthermore, a hole section723a4is a hole section for positioning a protrusion provided on the lower surface of the Fθ second lens holding unit65b4.

The same is also true for hole sections721a3,722a3, and723a3and hole sections721a2,722a2, and723a2of the Fθ second lens supporting unit72.

Furthermore, the Fθ second lens supporting unit72has a hole section72a5to allow for a protrusion72b5provided on the level difference41dof the casing41. The Fθ second lens supporting unit72is screwed to the protrusion72b5by means of a spring screw69bbthat is not depicted, and thereby engages with the casing41.

The hole section72a5is formed in an elliptical shape in such a way that the protrusion72b5can slide in the Y direction inside the hole section72a5when the casing41expands. In other words, the casing41displaces relative to the Fθ second lens supporting unit72.

Furthermore, the Fθ second lens supporting unit72has a hole section722a1for fixing the −Y direction end section72aby means of a screw67bor the like, and has a notch section72b1for inserting the spring screw69bat the end section72bat the opposite side.

Furthermore, a boss (protrusion) that positions the Fθ second lens supporting unit72is provided on the level difference41dof the casing41, and the Fθ second lens supporting unit72is positioned by inserting the boss (protrusion) inside a hole section721a1.

Furthermore, the Fθ second lens supporting unit72has three level differences72c2,72c3, and72c4.

These level differences72c2,72c3, and72c4are intentionally inclined for there to be sufficient engagement between the stops for positioning the Fθ second lens holding units65b1,65b2, and65b3and the positioning holes of the Fθ second lens supporting unit72.

FIG. 9is a partial enlarged view of the optical scanning device11depicted inFIG. 4.

As depicted inFIG. 9, the spring screw69bis inserted into the notch section72b1of the Fθ second lens supporting unit72.

Furthermore, a plate spring63c4is a member that supports the Fθ second lens63b4on the Fθ second lens holding unit65b4.

In other words, the plate spring63c4is fixed to the boss66b4by means of a screw67b4, an end section of the Fθ second lens63b4is pressed in the −Z direction by the plate spring63c4, and the Fθ second lens63b4is thereby supported on the Fθ second lens holding unit65b4.

Furthermore, also for the end section at the opposite side of the Fθ second lens63b4, a plate spring63d4is fixed to the boss66a4by means of a screw67a4, the end section at the opposite side of the Fθ second lens63a4is pressed in the −Z direction by the plate spring63d4, and the end section at the opposite side of the Fθ second lens63a4is fixed on an Fθ second lens holding unit65a4.

Furthermore, the same is also true for both end sections of the Fθ second lenses63b1to63b3.

<Configuration of Spring Screw69b>

Next, the spring screw69bof this invention will be described based onFIGS. 10(A)and (B).

FIG. 10(A)is a partial enlarged view of the optical scanning device11depicted inFIG. 4. Furthermore,FIG. 10(B)is a cross-sectional schematic view of the spring screw69bofFIG. 10(A)seen from the Y direction.

As depicted inFIGS. 10(A)and (B), the spring screw69bis configured from a protruding section691bformed on the level difference41dof the casing41, a torsion spring (kick spring692b) screwed to the protruding section691b, a washer693bthat is provided on the top surface of the protruding section691band presses and compresses the kick spring692bfrom above, and a screw694bthat fixes the washer693bto the top surface of the protruding section691b.

The spring screw69b, due to the urging force of the kick spring692b, urges the end section72bof the Fθ second lens supporting unit72in the −Z direction and presses on the level difference41dof the casing41, thereby preventing the Fθ second lens supporting unit72from separating from the casing41.

According to a configuration such as the aforementioned, it becomes possible for the spring screw69bto slide freely inside the notch section72b1, even if the spring screw69b, which is fixed to the casing41, has moved in the Y direction due to thermal expansion. The casing41displaces relative to the Fθ second lens supporting units71and72. In other words, the spring screw69bcorresponds to an engaging unit.

<Configuration of Spring Screw69c>

Next, a hook69cserving as a modified example of the spring screw69bof this invention will be described based onFIGS. 11(A)and (B).

FIG. 11(A)is a partial enlarged view in which the spring screw69bof the optical scanning device11depicted inFIG. 5has been replaced with the hook69c. Furthermore,FIG. 11(B)is a schematic view of the hook69cofFIG. 11(A)seen from the Y direction.

As depicted inFIGS. 11(A)and (B), the hook69cis configured from a protruding section691cformed on the level difference41dof the casing41, and a plate section692cthat is provided near the lower end of the protruding section691cand having a slight gap from the end section72bin such a way that the end section72bof the Fθ second lens supporting unit72does not separate from the casing41.

The hook69cengages in such a way as to prevent the Fθ second lens supporting unit72from separating from the casing41, by means of the plate section692c. In other words, the hook69ccorresponds to an engaging unit.

FIG. 12is a schematic plan view of after thermal expansion of the optical scanning device11depicted inFIG. 5.

As depicted inFIG. 12, even if the casing41has thermally expanded with respect to the Fθ second lens supporting unit72, the Fθ second lens supporting unit72thermally expands regardless of the casing41in the Y direction, and therefore the effect of color deviation caused by thermal expansion of the casing41can be reduced.

Furthermore, the same is also true for the Fθ second lens supporting unit71.

InFIG. 12, since laser light is radiated from the −Y direction end section of the casing41, a basis for the thermal expansion of the casing41is a baseline BL that corresponds to a main body fixing unit (fastening unit) of the optical scanning device11.

It should be noted that the baseline BL is a line that serves as a basis for where the optical scanning device11is mounted on the image forming device100, specifically, a main body frame of the image forming device100.

The amount of deviation caused by thermal expansion of the casing41increases as the distance from the baseline BL increases, and it is therefore thought that the Fθ second lens63b1provided at the −Y direction end section is least affected by the thermal expansion.

Consequently, due to the Fθ second lenses63b2,63b3, and63b4other than the Fθ second lens63b1being provided with the Fθ second lens supporting units71and72interposed, thermal fluctuation of the Fθ second lenses63b2,63b3, and63b4can be effectively reduced, and the amount of color deviation caused by thermal expansion of the casing41can be greatly reduced.

<Configuration of Lens Adjustment Members68a2to68a4>

Next, lens adjustment members68a2to68a4that adjust the Y direction inclination of the Fθ second lenses63b2to63b4of this invention will be described based onFIGS. 13to17.

FIG. 13is a main-part enlarged perspective view depicting mainly a portion from which the Fθ second lens63b2, the Fθ second lens holding unit65b2, and the lens adjustment member68a2have been removed from the optical scanning device11depicted inFIG. 4. Furthermore,FIG. 14is an explanatory diagram of when a mechanism of part of the lens adjustment mechanism68a2that adjusts the Fθ second lens holding unit65b2has been provided in the portion depicted inFIG. 13. Furthermore,FIG. 15is an explanatory diagram of when the lens adjustment unit68a2has been provided in the portion depicted inFIG. 13. Furthermore,FIG. 16is an explanatory diagram of when the Fθ second lens holding unit65b2, which has the Fθ second lens63b2, and the lens adjustment unit68a2have been provided in the portion depicted inFIG. 13. Furthermore,FIG. 17(A)is a perspective view in which a cover680a2is seen from the upper side. Furthermore,FIG. 17(B)is a perspective view in which the cover680a2is seen from the lower side.

Hereinafter, the lens adjustment member68a2will be described as an example; however, the same is also true for the other lens adjustment members68a3and68a4.

As depicted inFIG. 13, the Fθ second lens supporting unit71has formed therein the notch section71b2and the hole sections711a2and712a2to respectively allow for the boss66a2and the protrusions411e2and412e2provided on the level difference41eof the casing41.

The protrusions411e2and412e2have a columnar shape, and, when respectively inserted into the hole sections711a2and712a2of the Fθ 2nd lens supporting unit71, the upper surfaces thereof are in positions higher than the upper surface of the Fθ second lens supporting unit71.

As depicted inFIG. 14, the lower surface of the Fθ second lens holding unit65b2holding the Fθ second lens63b2is placed on the upper surfaces of the columnar-shaped protrusions411e2and412e2provided on the level difference41eof the casing41.

The lower surface of the Fθ second lens holding unit65b2makes contact with the upper surfaces of the protrusions411e2and412e2at positions higher than the upper surface of the Fθ second lens supporting unit71, thereby defining the height of the Fθ second lens holding unit65b2, in other words, the Fθ second lens63b2.

Thus, the Fθ second lens holding unit65b2and the Fθ second lens supporting unit71do not make contact.

However, the Fθ second lens supporting unit71supports the Fθ second lens holding units65b2,65b3, and65b4, in other words, the Fθ second lenses63b2,63b3, and63b4, with the lens adjustment members68a2,68a3, and68a4interposed.

Furthermore, the Fθ second lens holding unit65b2is constantly pressed by an urging member (spring) such as a spring683a2ofFIG. 16, and the Fθ second lens holding unit65b2, in other words, the Fθ second lens63b2, is thereby supported.

The same is also true for the Fθ second lens holding units65b3and65b4, in other words, the Fθ second lenses63b3and63b4.

It should be noted that the Fθ second lens supporting unit71may support the Fθ second lenses63b2,63b3, and63b4by making direct contact with the Fθ second lens holding units65b2,65b3, and65b4.

Furthermore, an end section of the Fθ second lens63b2on the Fθ second lens holding unit65b2is pressed in the −Z direction by a plate spring63d2.

Furthermore, as depicted inFIG. 14, a cam682a2is provided at a side section of the Fθ second lens holding unit65b2.

As depicted inFIGS. 14 and 15, a shaft section681a2and the cam682a2are provided inside the cover680a2, and a tip end of the shaft section681a2abuts one X direction end of the cam682a2.

The shaft section681a2has an end section that can manually rotate about a shaft, and a male screw and a female screw are formed between the shaft section681a2and the cover680a2in such a way that the shaft section681a2advances in the −X direction when the end section is rotated clockwise.

The cam682a2, which is pressed in the −X direction by the tip end of the shaft section681a2, rotates clockwise about a Z direction shaft, and presses the side section of the Fθ second lens holding unit65b2in the Y direction.

The shaft section681a2can be inserted via a hole section41b2formed in the side plates41bof the casing41, and be rotated by a driver from outside of the casing41.

The shaft section681a2and the cam682a2are provided inside the cover680a2, and the lens adjustment member68a2is constituted.

The lens adjustment member68a2is fixed to the Fθ second lens supporting unit71by a screw73c2.

As depicted inFIG. 16, the spring683a2is provided between the lens adjustment member68a2and the side section of the Fθ second lens holding unit65b2. InFIG. 16, the Fθ second lens holding unit65b2is constantly urged in the −Y direction by the spring683a2, and enters a state of constantly abutting the cam682a2ofFIG. 14, and therefore rattling in the ±Y direction of the Fθ second lens holding unit65b2is prevented. Thus, the position adjusted by the shaft section681a2can be ensured.

As depicted inFIGS. 17(A)and (B), the cover680a2has a hole section6801a2for inserting the shaft section681a2, a notch section6802a2and a hole section6803a2into which the protrusions71d2and71e2provided on the level difference41dof the casing41are respectively fitted, and a hole section6804a2for inserting the screw73c2.

FIG. 18is a main-part enlarged perspective view depicting mainly a portion from which the Fθ second lens supporting unit72has been removed from the optical scanning device11depicted inFIG. 4. Furthermore,FIG. 19is a main-part enlarged perspective view depicting a portion of the Fθ second lens supporting unit72that corresponds toFIG. 18. Furthermore,FIG. 20is an explanatory diagram of when the portion of the Fθ second lens supporting unit72ofFIG. 19has been provided in the portion depicted inFIG. 18.

As illustrated inFIG. 8, the hole sections721a2and722a2of the Fθ second lens supporting unit72are relief holes to respectively allow for protrusions411d2and412d2provided on the level difference41dof the casing41.

The protrusions411d2and412d2have a columnar shape, and have upper surfaces in positions higher than the upper surface of the Fθ second lens supporting unit72. Furthermore, in accordance with the inclination of the Fθ second lens supporting unit72, the upper surface of the protrusion411d2is in a position higher than the upper surface of the protrusion412d2.

FIG. 21(A)is a main-part enlarged perspective view in which the Fθ second lens holding unit65b2depicted inFIG. 4is seen from the upper side.FIG. 21(B)is a main-part enlarged perspective view in which the Fθ second lens holding unit65b2depicted inFIG. 4is seen from the lower side.

As depicted inFIGS. 21(A)and (B), the lower surface of the Fθ second lens holding unit65b2having a projecting section653b3provided thereon makes contact with the upper surfaces of the protrusions411d2and412d2that are in positions higher than the upper surface of the Fθ second lens supporting unit72, thereby defining the height of the Fθ second lens holding unit65b2, in other words, the Fθ second lens63b2. Thus, the Fθ second lens holding unit65b2and the Fθ second lens supporting unit72do not make contact.

However, a projecting section653b2is provided on the −Z direction surface of the Fθ second lens holding unit65b2, and the hole section723a2in the Fθ second lens supporting unit72is a hole section for positioning a projecting section723b2.

Thus, the Fθ second lens supporting unit72supports the Fθ second lens holding unit65b2, in other words, the Fθ second lens63b2.

The same is also true for the hole sections721a3,722a3, and723a3and the hole sections721a2,722a2, and723a2of the Fθ second lens supporting unit72.

<<Example of Comparison with Prior Art>>

Next, an example of a comparison with the prior art will be described based onFIG. 22.

FIGS. 22(A)and (B) are graphs of experiment results indicating the amount of color deviation for each color of cyan, magenta, and yellow in the Y direction respectively for the optical scanning device11of the prior art and the optical scanning device11according to embodiment 1 of this invention.

These graphs indicate the amount of color deviation (μm/deg.) at the rear, center, and front of the optical scanning device11in the Y direction for each color of cyan (Cy), magenta (Mg), and yellow (Ye) from the left side of the horizontal axis.

It should be noted that these amounts of color deviation indicate relative differences in the amount of color deviation from the amount of color deviation for black (K).

As is clear from these graphs, the amount of color deviation in the Y direction in the optical scanning device11of embodiment 1 of this invention has been reduced by approximately 80% from the amount of color deviation in the Y direction in the optical scanning device11of the prior art.

In this way, by using the Fθ second lens supporting units71and72, the amount of color deviation is greatly reduced, and therefore it becomes easy to increase the precision of electronic correction for color deviation.

Thus, even in a case where size of the casing41is large or a case where a heater for condensation prevention is provided, an optical scanning device11having high precision for color deviation correction can be realized.

Next, an optical scanning device11according to embodiment 2 of this invention will be described based onFIG. 23.

FIG. 23is a schematic plan view of after thermal expansion of the optical scanning device11according to embodiment 2 of this invention.

The optical scanning device11according to embodiment 2 is different from the optical scanning device11according to embodiment 1 in that not only the Fθ second lenses63b2,63b3, and63b4but also the Fθ second lens63b1is provided on the Fθ second lens supporting units71and72.

Thus, the Fθ second lenses63b1,63b2,63b3, and63b4are all provided on the Fθ second lens supporting units71and72, and therefore positioning becomes easy, and it becomes easy to predict the amount of color deviation caused by thermal expansion.

Next, an optical scanning device11according to embodiment 3 of this invention will be described based onFIG. 24.

FIG. 24is a schematic plan view of after thermal expansion of the optical scanning device11according to embodiment 3 of this invention.

The optical scanning device11according to embodiment 3 is different from the optical scanning devices11according to embodiment 1 and embodiment 2 in that the Fθ second lenses63b1,63b2, and63b3are provided on the Fθ second lens supporting units71and72, and the Fθ second lens63b4is not provided on the Fθ second lens supporting units71and72.

The problem of color deviation when printing a color image that does not use black is caused by color deviation of each color of yellow, magenta, and cyan, which are three primary colors that make up the image, and therefore, by providing the Fθ second lens63b1,63b2, and63b3corresponding to these colors on the Fθ second lens supporting units71and72, color deviation caused by thermal expansion of the casing41can be reduced.

Furthermore, the Fθ second lens63b1that is closest to the baseline BL and is least affected by thermal expansion of the casing41may be excluded, and only the two Fθ second lenses63b2and63b3may be provided on the Fθ second lens supporting units71and72.

Thus, the lengths of the Fθ second lenses63b2and63b3can be shortened compared to the optical scanning devices11according to embodiments 1 and 2 while reducing the effect of color deviation caused by thermal expansion, and therefore cost can be further suppressed.

Next, an optical scanning device11according to embodiment 5 of this invention will be described based onFIG. 25.

FIG. 25is a schematic plan view of after thermal expansion of the optical scanning device11according to embodiment 5 of this invention.

As depicted inFIG. 25, the optical scanning device11according to embodiment 5 is different from the optical scanning device11according to embodiment 1 in that the Fθ second lens supporting units71and72are connected at the −Y direction end sections71aand72a.

Thus, it is possible to realize an optical scanning device11that is unlikely to be affected even in a case where the degree of elongation from thermal expansion in the Y direction of the casing41is different at both sides of the Fθ second lens supporting units71and72.

Next, an example of a sliding (the casing41displaces relative to the Fθ second lens supporting unit71) mechanism of the Fθ second lens supporting unit71of the optical scanning device11according to embodiment 6 of this invention will be described based onFIG. 26.

FIG. 26(A)is an explanatory diagram depicting an example of the sliding (the casing41displaces relative to the Fθ second lens supporting unit71) mechanism of the Fθ second lens supporting unit71of the optical scanning device11according to embodiment 1 of this invention. Furthermore,FIG. 26(B)is an explanatory diagram depicting an example of a sliding (the casing41displaces relative to the Fθ second lens supporting unit71) mechanism of the Fθ second lens supporting unit71of the optical scanning device11according to embodiment 6 of this invention.

As depicted inFIG. 26(A), a notch section71b1that extends in the Y direction is provided at the end section71bof the Fθ second lens supporting unit71, and a spring screw69ais inserted into the casing41through the notch section71b1, and it thereby becomes possible for the Fθ second lens supporting unit71to slide in the Y direction (the casing41displaces relative to the Fθ second lens supporting unit71) during thermal expansion of the casing41inside the notch section71b1that extends in the Y direction.

Furthermore, as depicted inFIG. 26(B), an elongated hole section71c1having an elliptical shape that extends in the Y direction is provided in a portion of the Fθ second lens supporting unit71, and the spring screw69ais inserted into the casing41through the elongated hole section71c1, and it thereby becomes possible for the Fθ second lens supporting unit71to slide in the Y direction (the casing41displaces relative to the Fθ second lens supporting unit71) during thermal expansion of the casing41inside the elongated hole section that extends in the Y direction.

Thus, deviation in the Y direction of the Fθ second lens supporting unit71when the casing41thermally expands can be prevented by means of a low cost and simple structure, and it is therefore possible to realize an optical scanning device11that reduces the amount of color deviation caused by thermal expansion of the casing41.

Next, an optical scanning device11according to embodiment 7 of this invention will be described based onFIGS. 27 to 31.

FIG. 27is a perspective view of the interior of the casing41, with an upper lid having been removed, of the optical scanning device11according to embodiment 7 of this invention. Furthermore,FIG. 28is a plan view of the optical scanning device11depicted inFIG. 27. Furthermore,FIG. 29is a perspective view of the Fθ second lens supporting unit71depicted inFIG. 27. Furthermore,FIG. 30is a perspective view of the Fθ second lens supporting unit72depicted inFIG. 27.

The optical scanning device11according to embodiment 7 is different from the optical scanning device11according to embodiment 1 in that the four Fθ second lens holding units65b1to65b4are all provided on the Fθ second lens supporting units71and72.

Furthermore, as depicted inFIGS. 27 to 31, the Fθ second lens supporting unit71is provided with three spring screws69a2,69a3, and69a4near the Y direction end section and the center, which is different from the optical scanning device11according to embodiment 1. The same is also true for the Fθ second lens supporting unit72.

By providing the spring screws69a2and69a3also in positions other than the Y direction end section in this way, it is possible to prevent the Fθ second lens supporting unit71from separating from the level difference41eof the casing41.

Furthermore, the lower surface of the Fθ second lens holding unit65b1makes contact with the upper surfaces of protrusions411e1and412e1, which are not depicted, at positions higher than the upper surface of the Fθ second lens supporting unit71, thereby defining the height of the Fθ second lens holding unit65b1, in other words, the Fθ second lens63b1. The same is also true for the Fθ second lens holding units65b2to65b4.

However, the Fθ second lens supporting unit71supports each of the Fθ second lens holding units65b1to65b4, in other words, the Fθ second lenses63b1to63b4, with the lens adjustment members68a1to68a4interposed.

It should be noted that the Fθ second lens supporting unit71may support the Fθ second lenses63b1to63b4by making direct contact with the Fθ second lens holding units65b1to65b4.

As depicted inFIG. 29, the four lens adjustment members68a1to68a4that respectively adjust the Y direction inclination of the Fθ second lens holding units65b1to65b4are provided on the Fθ second lens supporting unit71.

Furthermore, as depicted inFIG. 30, the Fθ second lens supporting unit72has a hole section721a0for fixing a screw to the −Y direction end section72a.

Furthermore, a boss (protrusion) that positions the Fθ second lens supporting unit is provided on the level difference41dof the casing41, and the Fθ second lens supporting unit72is positioned by inserting the boss (protrusion) inside a hole section722a0.

The hole sections721a1and722a1of the Fθ second lens supporting unit72are relief holes to respectively allow for protrusions411d1and412d1provided on the level difference41dof the casing41.

Furthermore, a hole section723a1is a hole section for positioning a protrusion provided on the lower surface of the Fθ second lens holding unit65b1. Due to this positioning, the Fθ second lens holding unit65b1is supported by the Fθ second lens supporting unit72.

The same is also true for the hole sections721a2to721a4and722a2to722a4and the hole sections723a2to723a4of the Fθ second lens supporting unit72.

Furthermore, the Fθ second lens supporting unit72has a hole section72a2that allows for the protruding section691bofFIG. 10(B)provided on the level difference41dof the casing41. The Fθ second lens supporting unit72is screwed to the protruding section691bby means of the spring screw69bofFIGS. 10(A) and 10(B), and thereby engages with the casing41.

The hole section72a2is formed in an elliptical shape in such a way that the protrusion72b2can slide (the casing41displaces relative to the Fθ second lens supporting unit72) in the Y direction inside the hole section72a2when the casing41expands. The same is also true for other hole sections72a3and72a4.

It should be noted that the remaining structure of the Fθ second lens supporting units71and72is similar to the Fθ second lens supporting units71and72according to embodiment 1 and are therefore not described.

FIG. 31(A)is a partial enlarged view of the lens adjustment member68a1depicted inFIG. 27. Furthermore,FIG. 31(B)is a partial enlarged view of the lens adjustment member68a1depicted inFIG. 27.

As depicted inFIGS. 31(A)and (B), when a first shaft section681a1is manually rotated clockwise in the −X direction, a second gear685a1which is engaged with a first gear684a1that is coupled with the first shaft section681a1rotates clockwise in the −Y direction.

At such time, a second shaft section686a1advances in the −Y direction and presses a side section of the Fθ second lens holding unit65b1with a linking member687a1interposed, and the Fθ second lens holding unit65b1is thereby inclined in the Y direction.

It should be noted that the lens adjustment method of the lens adjustment member68a3is similar to that in embodiment 1 and is therefore omitted.

The linking member687a1is in an adjusted position, and constantly abuts the side section of the Fθ second lens holding unit65b1. In other words, the Fθ second lens holding unit65b1is constantly pressed by the linking member687a1due to an urging member (spring) such as the spring683a2ofFIG. 16, for example, which is not depicted.

However, if the lens adjustment member68a1is provided directly on the casing41, the entire lens adjustment member68a1including the linking member687a1moves when the casing41thermally expands, and sometimes the adjustment deviates.

In embodiment 7, in order to avoid this kind of problem, lens adjustment members68a1to68a4are provided on the Fθ second lens supporting unit71. Specifically, as inFIGS. 31(A)and (B), a shaft section holding plate689a1is fixed to the Fθ second lens supporting unit71by a screw672a1.

After the adjustment of the Fθ 2nd lenses63b1to63b4by the lens adjustment members68a1to68a4, even if the temperature of the optical scanning device11has risen, the positions of the lens adjustment members68a1to68a4do not change, and therefore naturally the positions of the Fθ second lenses63b1to63b4also do not change.

Consequently, compared to when provided directly on the casing41, it becomes unlikely that thermal expansion will have an effect.

Next, an optical scanning device11according to embodiment 7 of this invention will be described based onFIGS. 32 to 38.

FIG. 32is a perspective view of the interior of the casing41, with an upper lid having been removed, of the optical scanning device11according to embodiment 8 of this invention. Furthermore,FIG. 33is a plan view of the optical scanning device11depicted inFIG. 32. Furthermore,FIG. 34is a cross-sectional view along arrow C-C of the optical scanning device11depicted inFIG. 33. Furthermore,FIG. 35is a perspective view in which the optical scanning device11depicted inFIG. 32is seen from the lower side.

In the optical scanning device11according to embodiment 8, the lens adjustment members68a1to68a4that adjust the Y direction inclination of the Fθ second lens holding units65b1to65b4are provided on the Fθ second lens supporting unit71.

FIG. 36is a perspective view of the Fθ second lens supporting unit71depicted inFIG. 32. Furthermore,FIG. 37is a perspective view of the Fθ second lens supporting unit71depicted inFIG. 32. Furthermore,FIG. 38(A)is a partial enlarged view of the lens adjustment member68a2depicted inFIG. 33. Furthermore,FIG. 38(B)is a partial enlarged view of the lens adjustment member68a2depicted inFIG. 36.

Furthermore, the lower surface of the Fθ second lens holding unit65b1makes contact with the upper surfaces of the protrusions411e1and412e1, which are not depicted, at positions higher than the upper surface of the Fθ second lens supporting unit71, thereby defining the height of the Fθ second lens holding unit65b1, in other words, the Fθ second lens63b1.

The same is also true for the Fθ second lens holding units65b2to65b4.

However, the Fθ second lens supporting unit71supports each of the Fθ second lens holding units65b1to65b4, in other words, the Fθ second lenses63b1to63b4, with the lens adjustment members68a1to68a4interposed.

It should be noted that the Fθ second lens supporting unit71may support the Fθ second lenses63bto63b4by making direct contact with the Fθ second lens holding units65b1to65b4.

InFIG. 37, the hole sections721a1and722a1of the Fθ second lens supporting unit72are relief holes to respectively allow for the protrusions411d1and412d1provided on the level difference41dof the casing41.

Furthermore, the hole section723a1is a hole section for positioning a protrusion, which is not depicted, provided on the lower surface of the Fθ second lens holding unit65b1. Due to this positioning, the Fθ second lens holding unit65b1is supported by the Fθ second lens supporting unit72.

The same is also true for the hole sections721a2to721a4and722a2to722a4and the hole sections723a2to723a4of the Fθ second lens supporting unit72.

Furthermore, the lower surface of the Fθ second lens holding unit65b2makes contact with the upper surfaces of the protrusions411d2and412d2, which are not depicted, at positions higher than the upper surface of the Fθ second lens supporting unit72, thereby defining the height of the Fθ second lens holding unit65b2, in other words, the Fθ second lens63b2.

It should be noted that the remaining structure of the Fθ second lens supporting units71and72is similar to the Fθ second lens supporting units71and72according to embodiment 7 and are therefore not described.

As depicted inFIGS. 34 to 37andFIG. 38(B), the lens adjustment members68a1to68a4have driving units (motors)688a1to688a4outside the casing41, which is different from the optical scanning device11according to embodiment 7 that is manually powered.

As depicted inFIG. 38(B), when a first gear684a2is rotated clockwise in the Z direction by the driving unit688a2, a second gear685a2that is engaged with the first gear684a2rotates clockwise in the −Y direction.

At such time, a second shaft section686a2advances in the −Y direction and presses the side section of the Fθ second lens holding unit65b2, and the Fθ second lens holding unit65b2is thereby inclined in the Y direction.

As depicted inFIG. 38(B), the lens adjustment member68a2is provided on the Fθ second lens supporting unit71including also the driving unit688a2, and is not provided on the casing41.

The same is also true for the lens adjustment members68a1,68a3, and68a4.

In this way, the lens adjustment members68a1to68a4are provided on the Fθ second lens supporting unit71. Specifically, as inFIGS. 38(A)and (B), the driving unit (motor)688a2and a shaft section holding plate689a2are fixed to the Fθ second lens supporting unit72by a screw671a2.

The linking plate689a2is in an adjusted position, and the second shaft section686a2of the linking plate689a2constantly abuts the side section of the Fθ second lens holding unit65b2. In other words, the Fθ second lens holding unit65b2is constantly pressed by the second shaft section686a2of the linking plate689a2due to an urging member (spring) such as the spring683a2ofFIG. 16, for example, which is not depicted.

After the adjustment of the Fθ second lenses63b1to63b4by the lens adjustment members68a1to68a4, even if the temperature of the optical scanning device11has risen, the positions of the lens adjustment members68a1to68a4do not change, and therefore naturally the positions of the Fθ second lenses63b1to63b4also do not change.

In addition, the distance between the first gears684a1and684a2of a driving unit (motor) also do not change, and therefore the backlash between the first gears684a1and684a2does not become large.

Consequently, compared to when provided directly on the casing41, it becomes unlikely that thermal expansion will have an effect.

Preferred aspects of this invention also include combinations of any of the aforementioned plurality of aspects.

Other than the aforementioned embodiments, various modified examples are possible in relation to this invention.

Those modified examples shall not be construed as not belonging to the scope of this invention. All modifications within the meaning and the range of equivalency of the claims shall be included in this invention.

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