OPTICAL DEVICE

An optical device according to an embodiment includes a lens mirror array and a holder. The lens mirror array is opposed to a light emitting section. The lens mirror array includes a plurality of optical elements. The optical elements include incident-side lens surfaces, emission-side lens surfaces that emit incident light, and reflection surfaces that reflect incident light. A cross section orthogonal to a first direction of the lens mirror array has a constricted shape. The holder includes a slit having width smaller than width of both the ends in the cross section of the lens mirror array and larger than width of the center in the cross section and extending in the first direction. The holder holds the lens mirror array in a state in which a constricted portion in the center in the cross section of the lens mirror array is disposed in the slit.

FIELD

Embodiments described herein relate generally to an optical device including a lens mirror array, and an image forming apparatus containing the optical device.

BACKGROUND

A printer or a multifunction peripheral includes, for example, as an exposure device for forming an electrostatic latent image on a photoconductive drum, a solid-state head including a light emitting element such as an LED. The solid-state head includes, for example, a substrate on which a plurality of light emitting elements are arrayed and mounted, a SELFOC lens array (SLA) disposed to be opposed to the plurality of light emitting elements, and a holder that positions and holds the substrate and the SLA. The SLA has structure in which a plurality of micro rod lenses are arrayed and embedded in resin. The solid-state head has approximately the same length as the length of the photoconductive drum.

Since the SLA is made of long resin, the SLA is easily bent by an external force. If the SLA is bent, defocus occurs. Therefore, the rigidity of the holder that holds the SLA needs to be set as high as possible. Since the SLA has a short focal length and a small depth of field, the solid-state head needs to be disposed close to the photoconductive drum. Therefore, the solid-state head is desirably made as thin as possible. However, if the size of the holder is increased or a reinforcement member is attached to the holder to increase the rigidity of the holder, the width of the holder also increases to make it difficult to dispose the solid-state head close to the photoconductive drum.

DETAILED DESCRIPTION

An optical device according to an embodiment includes a lens mirror array and a holder. The lens mirror array is opposed to a light emitting section extending in a first direction. The lens mirror array includes a plurality of optical elements side by side in the first direction. The optical elements include incident-side lens surfaces on which light emitted from the light emitting section is made incident, emission-side lens surfaces that emit the incident light, and reflection surfaces that reflect the light made incident from the incident-side lens surfaces toward the emission-side lens surfaces. A cross section orthogonal to the first direction of the lens mirror array has a constricted shape, a center of which is narrower than both ends thereof that are along an optical path on which the light emitted from the light emitting section passes. The holder includes a slit having width smaller than width of both the ends in the cross section of the lens mirror array and larger than width of the center in the cross section and extending in the first direction. The holder holds the lens mirror array in a state in which constricted portion in the center in the cross section of the lens mirror array is disposed in the slit.

The embodiment is explained below with reference to the drawings.

An image forming apparatus100illustrated inFIG.1is a so-called multifunction peripheral including, for example, a print function, a copy function, and a scan function. The image forming apparatus100includes a housing2. A transparent original table glass3, on which an original is set, is present on the upper surface of the housing2. The original table glass3and a reading glass5disposed in parallel to the original table glass3are present on the upper surface of the housing2. The original table glass3and the reading glass5are disposed side by side in the left-right direction inFIG.1(a sub-scanning direction) . An auto document feeder (ADF)4is present on the original table glass3. The ADF4is capable of opening and closing the original table glass3. The ADF4functions as an original cover for pressing the original placed on the original table glass3and has a function of feeding the original through the reading glass5.

An original reading device10is present in the housing2under the original table glass3. The original reading device10is an example of the optical device described in the claims of the present application. The original reading device10is movable in the sub-scanning direction along the original table glass3by a not-illustrated driving mechanism and can be fixed under the reading glass5(in a position illustrated inFIG.1) . The original reading device10extends in a main scanning direction (the first direction) orthogonal to the paper surface ofFIG.1and causes a not-illustrated image sensor to form an erected image of an original.

The original reading device10includes a lens mirror array20and a holder54having substantially the same structure as the structure of a solid-state head504explained below. Accordingly, the lens mirror array20and the holder54are explained in detail below in explanation of the solid-state head504. Explanation of the lens mirror array20and the holder54of the original reading device10is omitted.

If an original is read, for example, the original reading device10is fixed under the reading glass5(a state illustrated inFIG.1), the original is fed by the ADF4, and the original is irradiated with illumination light via the reading glass5. The lens mirror array20guides reflected light reflected from the original and forms an image on the image sensor. A surface extending in the main scanning direction on which the original receives the illumination light is a surface that reflects the light and is an example of the light emitting section described in the claims of the present application. The original reading device10photoelectrically converts the reflected light reflected from the original and received by the image sensor and outputs the reflected light as an image signal.

At this time, the original reading device10reads, line by line in the main scanning direction, an erected image of the original passing on the reading glass5according to the operation of the ADF4. If the original passes on the reading glass5in the sub-scanning direction, the original reading device10can acquire an image of the entire original (for a plurality of lines). Alternatively, if the original is set on the original table glass3and the original reading device10is moved in the sub-scanning direction along the original table glass3, similarly, the original reading device10can read, line by line in the main scanning direction, an erected image of the original formed on the image sensor via the lens mirror array20and acquire an image of the entire original.

The image forming apparatus100includes an image forming section30substantially in the center in the housing2. The image forming section30includes a yellow unit301, a magenta unit302, a cyan unit303, and a black unit304in a traveling direction of an intermediate transfer belt40. Since the color units301,302,303, and304of the image forming section30have substantially the same structure, the black unit304is representatively explained herein. Detailed explanation about the other color units301,302, and303is omitted.

As illustrated inFIG.2, the black unit304includes, for example, a photoconductive drum314, an electrifying charger324, a solid-state head504, a developing device334, a primary transfer roller344, a cleaner354, and a blade364. Solid-state heads501,502,503, and504of the color units301,302,303, and304are examples of the optical device described in the claims of the present application. The intermediate transfer belt40is wound around a plurality of rollers and extended endlessly and travels in the counterclockwise direction inFIG.2.

The photoconductive drum314has a rotation axis extending in the main scanning direction. The photoconductive drum314rotates in a state in which the outer circumferential surface thereof is set in contact with the surface of the intermediate transfer belt40. The primary transfer roller344is present on the inner side of the intermediate transfer belt40opposed to the photoconductive drum314. The photoconductive drum314is rotated by a not-illustrated driving mechanism in an illustrated arrow direction (the clockwise direction) at the same peripheral speed as the peripheral speed of the intermediate transfer belt40.

The electrifying charger324uniformly charges the surface of the photoconductive drum314. The solid-state head504irradiates the surface of the photoconductive drum314with exposure light based on an image signal for color-separated black and forms an electrostatic latent image based on the image signal for black on the surface of the photoconductive drum314. The developing device334supplies black toner to the electrostatic latent image formed on the surface of the photoconductive drum314and forms a black toner image on the surface of the photoconductive drum314.

The primary transfer roller344transfers the black toner image formed on the surface of the photoconductive drum314to be superimposed on toner images of the other colors. The cleaner354and the blade364remove toner remaining on the surface of the photoconductive drum314. The color toner images transferred to be superimposed one another on the surface of the intermediate transfer belt40move according to the traveling of the intermediate transfer belt40.

A transfer roller pair37for transferring, onto paper P, the color toner images transferred to be superimposed one another on the surface of the intermediate transfer belt40is present on a downstream side of the black unit304in the traveling direction of the intermediate transfer belt40. One transfer roller371is present on the inner side of the intermediate transfer belt40. The intermediate transfer belt40is supported by the one transfer roller371. The other transfer roller372is opposed to the one transfer roller371across the intermediate transfer belt40.

Referring back toFIG.1, a paper feeding cassette61in which a plurality of pieces of paper P of a predetermined size are stacked and stored is present near the lower end in the housing2of the image forming apparatus100. The paper feeding cassette61can be, for example, drawn out and received from the front surface of the housing2. A pickup roller62that picks up a piece of paper P at the upper end in a stacking direction among the pieces of paper P stored in the paper feeding cassette61is present at an illustrated right upper end of the paper feeding cassette61. The pickup roller62rotates with the circumferential surface thereof set in contact with the paper P to pick up the pieces of paper P one by one.

A paper discharge tray63is present in an upper part in the housing2. The paper discharge tray63is present between the original table glass3and the image forming section30and discharges the paper P, on which an image is formed, into the body of the image forming apparatus100. A conveying path64for conveying the paper P picked up from the paper feeding cassette61in the longitudinal direction toward the paper discharge tray63is present between the pickup roller62and the paper discharge tray63. The conveying path64extends through a nip of the transfer roller pair37and includes a plurality of conveying roller pairs641and a not-illustrated conveyance guide. A paper discharge roller pair631for discharging the paper P to the paper discharge tray63is present at the terminal end of the conveying path64. The paper discharge roller pair631is rotatable in both of forward and backward directions.

A fixing roller pair65is present on the conveying path64on the downstream side of the transfer roller pair37(the illustrated upper side) . The fixing roller pair65heats and pressurizes the paper P conveyed via the conveying path64and fixes, on the surface of the paper P, a toner image transferred onto the surface of the paper P.

The image forming apparatus100includes a reverse conveying path66for reversing the paper P, on one surface of which an image is formed, and feeding the paper P into the nip of the transfer roller pair37. The reverse conveying path66includes a plurality of conveying roller pairs661that nip the paper P and rotates to convey the paper P and a not-illustrated conveyance guide. A gate67that switches a conveyance destination of the paper P between the conveying path64and the reverse conveying path66is present on an upstream side of the paper discharge roller pair631.

If an image is formed on the paper P, the image forming apparatus100rotates the pickup roller62to pick up the paper P from the paper feeding cassette61and conveys, with the plurality of conveying roller pairs641, the paper P toward the paper discharge tray63via the conveying path64. At this time, the image forming apparatus100feeds the color toner images transferred and formed on the surface of the intermediate transfer belt40into the nip of the transfer roller pair37to be timed to coincide with conveyance timing of the paper p, gives a transfer voltage to the color toner images with the transfer roller pair37, and transfers the color toner images onto the surface of the paper P.

The image forming apparatus100conveys the paper P, onto which the toner images are transferred through the fixing roller pair65, to heat and pressurize the paper P, melts the toner images and presses the toner images against the surface of the paper P, and fixes the toner images on the paper P. The image forming apparatus100discharges the paper P, on which an image is formed in this way, to the paper discharge tray63via the paper discharge roller pair631.

At this time, if a duplex mode for forming an image on the rear surface of the paper P as well is selected, the image forming apparatus100switches the gate67to the reverse conveying path66at timing immediately before the trailing end in a discharging direction of the paper P being discharged toward the paper discharge tray63passes through the nip of the paper discharge roller pair631, reverses the paper discharge roller pair631, and switches back and conveys the paper P. Consequently, the image forming apparatus100directs the trailing end of the paper P to the reverse conveying path66and reverses the paper P to feed the paper P into the nip of the transfer roller pair37.

The image forming apparatus100forms, on the surface of the intermediate transfer belt40, toner images based on image data formed on the rear surface of the paper P, causes the intermediate transfer belt40holding color toner images to travel, and feeds the color toner images into the nip of the transfer roller pair37. Further, the image forming apparatus100transfers and fixes the toner images on the rear surface of the reversed paper P, and discharges the paper P to the paper discharge tray63via the paper discharge roller pair631.

The image forming apparatus100includes a control section70that controls operations of the mechanisms explained above. The control section70includes a processor such as a CPU and a memory. The processor executes a program stored in the memory, whereby the control section70realizes various processing functions. The control section70controls the original reading device10to thereby acquire an image from an original. The control section70controls the image forming section30to thereby form an image on the surface of the paper P. For example, the control section70inputs image data read by the original reading device10to the image forming section30. The control section70controls operations of the pluralities of conveying roller pairs641and661to convey the paper P through the conveying path64and the reverse conveying path66.

The solid-state head504of the black unit304is explained below with reference toFIGS.2to5. Detailed explanation of the solid-state heads501,502, and503of the other color units301,302, and303is omitted because the solid-state heads501,502, and503have the same structure as the structure of the solid-state head504.

As illustrated inFIG.2, the solid-state head504is separated from and opposed to the photoconductive drum314below the photoconductive drum314inFIG.2. The solid-state head504includes the lens mirror array20, a light source unit52, and the holder54. The components20,52, and54of the solid-state head504extend in the main scanning direction orthogonal to the paper surface parallel to the rotation axis of the photoconductive drum314and have substantially the same length as the length of the photoconductive drum314.

The holder54holds the lens mirror array20. The holder54and the lens mirror array20of the solid-state head504have the same structures as the structures of the holder54and the lens mirror array20of the original reading device10explained above. The lens mirror array20of the solid-state head504is attached in a direction vertically reversed from the direction of the lens mirror array20of the original reading device10. The holder54of the solid-state head504fixes the light source unit52. The holder54fixes the light source unit52and the lens mirror array20in a state in which the light source unit52and the lens mirror array20are alighted with each other.

As illustrated inFIGS.2to4, the lens mirror array20has structure in which a plurality of transparent optical elements21having the same shape are disposed side by side in the main scanning direction and integrated.FIG.2enlarges and illustrates a cross section of the lens mirror array20taken along a surface orthogonal to the main scanning direction between two optical elements21adjacent to each other. In this embodiment, the lens mirror array20is formed by integrally molding transparent resin. The lens mirror array20may be formed by transparent glass.

The optical elements21of the lens mirror array20guide diffused light diffused from an object point o to form an image at an image forming point F. One optical element21causes lights from a plurality of object points O arranged in the main scanning direction to form images on an image surface. For example, the one optical element21causes light from the object points O arranged in width twice or three times as large as a pitch in the main scanning direction of the optical element21to form images on the image surface. The optical element21reflects, on two reflection surfaces23and24, light made incident on an incident-side lens surface22and emits the light via an emission-side lens surface25to form an erected image of the object point O at the image forming point F.

In the solid-state head504, the object point O is present on a light emission surface of a light emitting element521explained below of the light source unit52and the image forming point F is present on the surface of the photoconductive drum314. That is, the lens mirror array20of the solid-state head504guides lights emitted from a plurality of light emitting elements521disposed side by side in the main scanning direction and forms an image on the surface of the photoconductive drum314. Since the lens mirror array20includes the plurality of optical elements21side by side in the main scanning direction, the lens mirror array20forms an elongated image in the main scanning direction. In contrast, for example, in the original reading device10illustrated inFIG.1, the object point O is present on an original surface and the image forming point F is present on a light receiving surface of the image sensor. That is, the lens mirror array20of the original reading device10guides light reflected on the original surface and forms an image on the light receiving surface of the image sensor.

The optical element21includes, on the surface thereof, an incident-side lens surface22, an upstream-side reflection surface23, a downstream-side reflection surface24, and an emission-side lens surface25. The incident-side lens surface22, the downstream-side reflection surface24, and the emission-side lens surface25are curved surfaces convex to the outer side. The upstream-side reflection surface23is a flat surface. The upstream-side reflection surface23is an example of the first reflection surface described in the claims of the present application. The downstream-side reflection surface24is an example of the second reflection surface described in the claims of the present application.

An imaginary boundary surface (the cross section illustrated inFIG.2) between two optical elements21adjacent to each other in the main scanning direction is a surface orthogonal to the main scanning direction and is a surface generally orthogonal to the surfaces22,23,24, and25explained above. The cross section is an example of the cross section described in the claims of the present application but may be a cross section of the optical element21taken along an imaginary surface orthogonal to the main scanning direction in any position in the main scanning direction. In the lens mirror array20in which the plurality of optical elements21are integrally connected in the main scanning direction, the surfaces22,23,24, and25of the optical elements21are respectively continuous surfaces connected in the main scanning direction.

Light made incident on the incident-side lens surface22of the optical element21is diverging light. The incident-side lens surface22converges the diverging light and directs the diverging light toward the upstream-side reflection surface23. Light reflected on the upstream-side reflection surface23and the downstream-side reflection surface24converges once and changes to diffused light thereafter and is emitted via the emission-side lens surface25. The emission-side lens surface25converges and emits the light reflected on the downstream-side reflection surface24. An optical path of light passing the center in the main scanning direction of the optical element21and passing the cross section orthogonal to the main scanning direction is indicated by a broken line. An optical path of light transmitted through the optical element21is reflected twice and bent. The width in the cross section of the optical path of the light transmitted through the optical element21is smaller in the center than both ends that are along the optical path. Therefore, the lens mirror array20includes a constricted portion201narrow in the center that is along the optical path.

The lens mirror array20of the solid-state head504needs to cause light emitted from the light emitting element521to form an image on the surface of the photoconductive drum314without deviation such that deviation and distortion do not occur in an electrostatic latent image formed on the surface of the photoconductive drum314. That is, in order to form a high-quality image in the image forming apparatus100in this embodiment, the lens mirror array20having extremely high dimension accuracy without deviation and distortion is necessary. Since the lens mirror array20easily bends, the holder54that holds the lens mirror array20desirably has high rigidity not to cause a bend in the lens mirror array20. The optical element21of the lens mirror20has a small focal length and a small depth of field. Therefore, the solid-state head504needs to be disposed close to the photoconductive drum314.

As illustrated inFIG.5, the holder54integrally includes a top wall541and two sidewalls542,542. The top wall541and the two sidewalls542,542of the holder54can be formed by, for example, bending one piece of rectangular sheet metal in two parts along the main scanning direction. Therefore, a cross section of the holder54taken along any plane orthogonal to the main scanning direction has a U shape. A ridge portion between the top wall541and the sidewall542has a gently curving shape. The top wall541is a long and flat plate shape extending in the main scanning direction and is opposed to the surface of the photoconductive drum314. Since the solid-state head504is disposed close to the surface of the photoconductive drum314, it is desirable to reduce the width in the sub-scanning direction of the top wall541of the holder54as much as possible. The holder54can be formed by machining sheet metal such as stainless steel or iron or can be formed by resin or the like.

The top wall541includes, in the center in the sub-scanning direction, a slit5411with a fixed width extending in the main scanning direction. The slit5411pierces through the top wall541. Both ends in the longitudinal direction of the slit5411respectively terminate in positions separated from both end portions in the longitudinal direction of the top wall541. Besides, the holder54includes two end walls543disposed at both ends in the main scanning direction. The outer circumferential portions of the end walls543, the end portion of the top wall541, and the end portion of the sidewall542are joined by welding or the like. The holder54has higher bending strength and is less easily deformed than the lens mirror array20. In other words, the lens mirror array20has lower bending strength and more easily bends than the holder54.

The width in the sub-scanning direction of the slit5411is slightly larger than the width in the sub-scanning direction of the constricted portion201in the cross section of the lens mirror array20illustrated inFIG.2. The constricted portion201is, in the cross section orthogonal to the main scanning direction of the lens mirror array20, a portion narrower in the center than both ends that are along an optical path on which light emitted from the light emitting element521passes the lens mirror array20. The constricted portion201of the lens mirror array20indicates all portions of the lens mirror array20that can be disposed in the slit5411.

Portions at both the ends along the optical path in the cross section of the lens mirror array20are all portions that are wider than the slit5411and cannot be disposed in the slit5411. The portions indicate an emission-side portion202further on the emission-side lens surface25side than the constricted portion201and an incident-side portion203further on the incident-side lens surface22side than the constricted portion201. The emission-side portion202projecting to the outer side of the holder54via the slit5411is an example of the projecting portion described in the claims of the present application.

The emission-side portion202of the lens mirror array20is located on the outer side of the holder54via the slit5411. The incident-side portion203of the lens mirror array20is located on the inner side of the holder54(the light source unit52side) . The constricted portion201of the lens mirror array20is located in the slit5411and located on the inner side of the holder54. That is, the end portion on the emission-side portion202side of the constricted portion201of the lens mirror array20is located in the slit5411. In other words, a portion between the downstream-side reflection surface24and the emission-side lens surface25of the lens mirror array20is located in the slit5411. If the constricted portion201is disposed in the slit5411and the lens mirror array20is attached to the holder54in this way, it is possible to reduce the width of the slit5411and maintain high rigidity of the holder54.

A widened portion5412where the width of the slit5411is increased is present at one end of the slit5411. The widened portion5412is a hole piercing through the top wall541of the holder54. The width in the sub-scanning direction of the widened portion5412is larger than the width in the sub-scanning direction of the incident-side portion203of the lens mirror array20. The widened portion5412only has to have a size and a shape for enabling the incident-side portion203of the lens mirror array20to be inserted through the widened portion5412and can be formed in any shape.

For example, if the lens mirror array20illustrated inFIGS.3and4is attached to the holder54illustrated inFIG.5, the lens mirror array20is bent, the incident-side portion203of the lens mirror array20is inserted into the widened portion5412of the holder54from the one end in the longitudinal direction, and the constricted portion201of the lens mirror array20is disposed in the slit5411while being slid. The length in the main scanning direction of the widened portion5412is length with which the lens mirror array20does not interfere with the top wall541of the holder54if the lens mirror array20is bent and the constricted portion201is inserted through and disposed in the slit5411.

After the constricted portion201of the lens mirror array20is disposed in the slit5411of the holder54, the lens mirror array20is positioned with respect to the holder54and the lens mirror array20is fixed to the holder54. The lens mirror array20is fixed to the holder54using, for example, an adhesive S. The lens mirror array20brings a positioning surface2021of the emission-side portion202into surface-contact with an outer surface5413of the holder54to position the positioning surface2021with respect to the holder54.

The outer surface5413of the top wall541of the holder54and the surface of the lens mirror array20are fixed by the adhesive S. In a state in which the lens mirror array20is positioned with respect to the holder54, the inner surface of one sidewall542of the holder54and the surface of the lens mirror array20are fixed by the adhesive S. Fixing parts by the adhesive S are a plurality of parts separated in the main scanning direction and are positions not interfering with the incident-side lens surface22, the upstream-side reflection surface23, the downstream-side reflection surface and the emission-side lens surface25of the lens mirror array20.

If the positioning surface2021of the emission-side portion202of the lens mirror array20is brought into surface-contact with the outer surface5413of the holder54as explained above, a positioning surface2031of the incident-side portion203of the lens mirror array20comes into surface-contact with the inner surface of one sidewall542of the holder54. In other words, the holder54has a shape in which the positioning surface2031of the lens mirror array20is in surface-contact with the inner surface of one sidewall542of the holder54in a state in which the positioning surface2021of the lens mirror array20is in surface-contact with the outer surface5413of the holder54.

As illustrated inFIG.2, the light source unit52of the solid-state head504includes a substrate522on which the plurality of light emitting elements521are mounted side by side in the main scanning direction. The light source unit52is an example of the light emitting section described in the claims of the present application. The light emitting elements521may be disposed in one row or a plurality of rows extending in the main scanning direction. A driving circuit523is mounted on the surface of the substrate522on which the light emitting elements521are mounted. A connector524for power feed is fixed on the opposite surface of the surface of the substrate522on which the light emitting elements521are mounted. The substrate522is fixed to the inner surface of the sidewall542of the holder54by the adhesive S in a state in which the substrate522is positioned with respect to the holder54.

The positioning of the substrate522with respect to the holder54is implemented by incorporating the substrate522in the holder54in which the lens mirror array20is positioned and fixed, causing the light emitting elements521to emit lights, detecting, with a camera, an image formed on an image surface via the lens mirror array20, and disposing the substrate522in a position where deviation does not occur in the image. After the substrate522is positioned with respect to the holder54in this way, the holder54and the substrate522are fixed using the adhesive S in a state in which a positional relation between the substrate522and the holder54is maintained.

The plurality of light emitting elements521emit lights based on image data (an image signal) for black obtained by color-separating image data acquired by the original reading device10or image data acquired via external equipment such as a not-illustrated personal computer. The plurality of light emitting elements521are, for example, LEDs or OLEDs that emit lights or extinguish lights based on image data.

The lights emitted from the plurality of light emitting elements521are made incident on the lens mirror array20. The lens mirror array20reflects and condenses the lights emitted from the light emitting elements521and emits light. The light emitted from the lens mirror array20is condensed on the surface of the rotating photoconductive drum314. At this time, an electrostatic latent image is written line by line in the main scanning direction on the surface of the photoconductive drum314according to the rotation of the photoconductive drum314. If the photoconductive drum314rotates a fixed amount, an electrostatic latent image for black obtained by color separation corresponding to an entire image of an original is formed on the surface of the photoconductive drum314.

The holder54may be a holder56in which an opening section5414connected to one end of the slit5411is provided in one end wall543as illustrated inFIG.6instead of the widened portion5412provided at one end of the slit5411. In this case, the one end of the slit5411provided in the top wall541needs to be extended to the end wall543in which the opening section5414is provided. The opening section5414of the end wall543has a size and a shape for enabling the incident-side portion203of the lens mirror array20to be inserted through the opening section5414. In order to keep high rigidity of the holder56, the opening section5414is desirably closed by not-illustrated sheet metal or the like after the lens mirror array20is fixed to the holder56.

If the lens mirror array20is attached to the holder56illustrated inFIG.6, one end in the longitudinal direction of the lens mirror array20is inserted through the opening section5414of the holder56and the constricted portion201of the lens mirror array20is disposed in the slit5411of the top wall541. At this time, the lens mirror array20only has to be slid in the longitudinal direction and does not need to be bent. Positioning of the lens mirror array20with respect to the holder56and bonding and fixing of the lens mirror20to the holder56and positioning and bonding and fixing of the substrate522of the light source unit52only have to be implemented in the same manner as in the embodiment explained above.

A bending test for a solid-state head explained below was implemented in order to check a relation between the rigidity of the holder54(56) and the width of the slit5411.

First, three test specimens of the solid-state head were prepared. A first test specimen A is the solid-state head504illustrated inFIG.2in which the lens mirror array20illustrated inFIGS.3and4is fixed to the holder54illustrated inFIG.5. A second test specimen B is a solid-state head in which the lens mirror array20illustrated inFIGS.3and4is fixed to the holder56illustrated inFIG.6. A third test specimen C is, as a comparative example, a solid-state head in which the SELFOC lens array of the related art is fixed to a slit of a holder. The holders of the third test specimen C include relatively wide slits that hold the SELFOC lens array.

The three test specimens A, B, and C were formed by pieces of sheet metal having width of the top wall of 10 mm, length of the top wall of 340 mm, and height of the sidewall of 12 mm and having the same thickness. The width of slits of the test specimens A and B was small width for allowing the constricted portion201of the lens mirror array20to pass and was set to 20% of the width of the top wall. In contrast, the width of the slit of the test specimen C was large width for allowing the SELFOC lens array to pass and was set to 40% of the width of the top wall. That is, the width of the slit of the test specimen C was set to a double of the width of the slits of the test specimens A and B.

The prepared test specimens A, B, and C were disposed in a horizontal posture in which the outer surfaces of the top walls face upward, spacers were disposed on the upper surfaces of both ends of the top walls of the test specimens A, B, and C, and reference surfaces parallel to the top walls of the test specimens A, B, and C were disposed above the top walls across these two spacers. In this state, the longitudinal direction center portions of the test specimens A, B, and C were pushed up toward the reference surfaces and amounts of the center portions of the test specimens A, B, and C approaching the reference surfaces were measured as bending amounts. Pressing forces for pushing up the centers of the test specimens A, B, and C gradually increased from 0 g. Bending amounts of the test specimens A, B, and C at a point in time when a load of 500 g was further applied from a state in which the spacers at both the ends were in contact with the reference surface (a state in which the loads of the test specimens were supported) were measured. The bending amounts were evaluated by lengths in which the distances between the centers of the test specimens and the reference surfaces changed before and after of the bending.

As a result of the measurement, the bending amount of the test specimen A was 100 μm, the bending amount of the test specimen B was 140 μm, and the bending amount of the test specimen C was 200 μm. From this result, it was found that the test specimen A has the highest rigidity and the test specimen C has the lowest rigidity. That is, it was found that the rigidity of the solid-state head can be increased by reducing the width of the slit provided in the top wall of the holder.

As explained above, with the solid-state head504in this embodiment, since the lens mirror array20is fixed to the holder54(56) in a state in which the constricted portion201of the lens mirror array20is disposed in the slit5411of the holder56(56), it is possible to reduce the width of the slit5411as much as possible and maintain high rigidity of the holder54and increase the rigidity of the solid-state head504. It is possible to prevent a deficiency in which a bend occurs in the lens mirror array20.

In the holder54of the solid-state head504in this embodiment, since the ridge portion between the top wall541and the sidewall542is bent, the width in the sub-scanning direction of the flat outer surface5413of the top wall541in surface-contact with the positioning surface2021of the lens mirror array20is smaller than the width between the outer surfaces of the two sidewalls542(that is, the width of the holder54) . By providing the slit5411in the top wall541, the flat outer surface5413of the top wall541that can come into surface-contact with the positioning surface2021is further narrowed. Therefore, as in this embodiment, it is effective to reduce the width of the slit5411as much as possible. It is possible to, without increasing the width of the holder54, sufficiently secure the width of the flat outer surface5413of the top wall541that comes into surface-contact with the positioning surface of the lens mirror array20.

According to this embodiment, it is possible to, without increasing the size of the holder54(56) and without separately pasting a reinforcement member, increase the rigidity of the holder54(56) by reducing the width of the slit5411. It is possible to form the solid-state head504in a compact size. Therefore, according to this embodiment, it is possible to dispose the solid-state head504having high rigidity near the photoconductive drum314.

According to this embodiment, if the lens mirror array20is attached to the holder54(56) , the constricted portion201of the lens mirror array20comes into slide-contact with the slit5411of the holder54(56) . However, since the constricted portion201between the downstream-side reflection surface24and the emission-side lens surface25of the lens mirror array20is disposed in the slit5411, it is possible to prevent a change in an optical characteristic due to friction.

In the solid-state head504in this embodiment, if the emission-side lens surface25disposed on the outside of the holder54is stained, the emission-side lens surface25is wiped by a brush or cloth. At this time, it is conceivable that an external force is likely to be applied to a projecting portion projecting from the slit5411of the holder54to damage the lens mirror array20. Accordingly, as in this embodiment, it is effective to dispose, in the slit5411, the constricted portion201between the downstream-side reflection surface24and the emission-side lens surface25of the lens mirror array20and reduce the size of a portion projecting to the outside of the holder54as much as possible.