JP2020082398A - Exposure device and image formation apparatus - Google Patents

Abstract

To reduce deformation due to heat generation of a substrate formed with a light source.SOLUTION: An exposure device includes: a substrate assembly 210 in which a plurality of substrates including a plurality of light sources arrayed in one direction are fixed to each other so as to be superimposed in the optical axis direction of the plurality of light sources; and a holder 301 which supports the substrate assembly 210 on at least three support spots in a support substrate 201 of the plurality of substrates 201, 202. The substrate assembly 210 is fixed to the holder 301 on a single fixation spot other than the two support spots being both ends in one direction out of at least three support spots, and is configured so that the heat expansion amount of the support substrate 201 becomes smaller than the heat expansion amount of other substrates.SELECTED DRAWING: Figure 4

Description

The present invention relates to an exposure apparatus and an image forming apparatus, and more particularly to an exposure apparatus in which a plurality of light sources are arranged along a main scanning direction and an image forming apparatus including the exposure apparatus.

In recent years, a print head using an OLED (Organic Light-Emitting Diode) as a light source is known. This line head forms an electrostatic latent image on the photosensitive drum by irradiating the photosensitive drum as an image carrier with light emitted from a plurality of light sources. Further, in order to improve the resolution, a line head in which a plurality of light sources are arranged at different positions in the sub scanning direction is known.

For example, Japanese Patent Laid-Open No. 2008-36850 describes an image forming apparatus that simultaneously forms images of a plurality of colors on an image carrier using a plurality of line heads corresponding to the respective colors.

Since the print head has a plurality of light sources arranged on the glass substrate along the main scanning direction, it has a long shape in the main scanning direction. Then, when the temperature of the glass substrate partially rises because the plurality of light sources generate heat, there is a problem that the glass substrate is thermally expanded and deformed. Due to the deformation of the glass substrate, the distance between the light source and the optical element provided between the light source and the photosensitive drum may change, and the focus position may shift.

JP 2008-36850 A

The present invention has been made to solve the above-mentioned problems, and one of the objects of the present invention is to provide an exposure apparatus in which deformation of a substrate on which a light source is formed due to heat generation is reduced.

Another object of the present invention is to provide an image forming apparatus with improved image quality.

According to an aspect of the present invention, an exposure apparatus includes a substrate assembly in which a first substrate and a second substrate each including a plurality of light sources arranged in one direction are fixed to each other while overlapping in the optical axis direction of the plurality of light sources. And a holder for supporting the substrate assembly at at least three supporting points of the first substrate, wherein the substrate assembly has a single supporting point other than the two supporting points at both ends in one direction among the at least three supporting points. The thermal expansion amount of the first substrate is fixed to the holder at the fixing portion so that the thermal expansion amount of the first substrate is smaller than the thermal expansion amount of the second substrate.

According to this aspect, in the substrate assembly in which the first substrate and the second substrate are overlapped and fixed to each other, the thermal expansion amount of the first substrate is smaller than the thermal expansion amount of the second substrate, and the substrate assembly is the first The substrate is fixed to the holder at a single fixing position other than the two supporting positions at both ends in one direction among at least three supporting positions of the substrate. Therefore, the amount of distortion of the substrate assembly on the side of the first substrate due to thermal expansion can be reduced. As a result, it is possible to provide an exposure apparatus in which the deformation of the substrate on which the light source is formed due to heat generation is reduced.

Preferably, the first substrate has a smaller linear expansion coefficient than the second substrate.

According to this aspect, the thermal expansion amount of the first substrate can be made smaller than the thermal expansion amount of the second substrate.

Preferably, the first substrate has a higher thermal conductivity than the second substrate.

According to this aspect, the temperature of the first substrate becomes lower than the temperature of the second substrate, so that the thermal expansion amount of the first substrate can be made smaller than the thermal expansion amount of the second substrate.

Preferably, the holder has a higher thermal conductivity than the first substrate.

According to this aspect, since the heat of the first substrate is conducted to the holder, the temperature of the first substrate can be made lower than the temperature of the second substrate.

Preferably, it further comprises an elastic member for fixing the substrate assembly to the holder at a sub-fixing point different from the fixing point.

According to this aspect, since the substrate assembly is fixed to the holder by the elastic member at the sub-fixing portion, the substrate assembly can be prevented from receiving an external force in the main scanning direction.

Preferably, the holder has a Young's modulus larger than that of the first substrate.

According to this aspect, it is possible to reduce the amount of distortion of the substrate assembly on the side of the first substrate due to thermal expansion.

Preferably, the first substrate and the second substrate are fixed to each other in a state where the plurality of light sources do not emit light.

According to another aspect of the present invention, an image forming apparatus includes the exposure device described above. According to this aspect, it is possible to provide an image forming apparatus with improved image quality.

FIG. 3 is a perspective view showing an external appearance of the MFP according to one of the embodiments of the present invention. FIG. 3 is a schematic cross-sectional view showing the internal configuration of the MFP. It is a perspective view which shows an example of an internal structure of an exposure apparatus. It is a 1st sectional view of a part of exposure apparatus in this Embodiment. It is a 1st figure which shows an example of a difference of the thermal expansion amount of a 1st light source board and a 2nd light source board. It is a 2nd figure which shows an example of a difference of the thermal expansion amount of a 1st light source board and a 2nd light source board. FIG. 6 is a second cross-sectional view of a part of the exposure apparatus in the present embodiment. It is a sectional view of a part of exposure apparatus in the 2nd modification.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

FIG. 1 is a perspective view showing the external appearance of an MFP according to one of the embodiments of the present invention. Referring to FIG. 1, an MFP (Multi Function Peripheral) 100 is an example of an image forming apparatus, and includes a document reading unit 130 for reading a document and an automatic document feeding device for feeding the document to the document reading unit 130. 120, an image forming unit 140 for forming an image on a sheet based on image data, a sheet feeding unit 150 for feeding the sheet to the image forming unit 140, and an operation panel 160 as a user interface.

The automatic document feeder 120 automatically conveys a plurality of documents set on the document tray 125 one by one to the document reading position of the document reading unit 130, and the image formed on the document by the document reading unit 130 is displayed. The read document is discharged onto the document discharge tray 127.

The document reading unit 130 has a rectangular reading surface for reading a document. The reading surface is formed of, for example, platen glass. The automatic document feeder 120 is rotatably connected to the main body of the MFP 100 and can be opened and closed around an axis parallel to one side of the reading surface. A document reading unit 130 is arranged below the automatic document feeder 120, and the reading surface of the document reading unit 130 is exposed in an open state in which the automatic document feeder 120 is rotated and opened. Therefore, the user can place the original on the reading surface of the original reading unit 130. The automatic document feeder 120 can change its state between an open state in which the reading surface of the document reading unit 130 is exposed and a closed state in which the reading surface is covered.

The image forming unit 140 forms an image on a sheet conveyed by the sheet feeding unit 150 by a well-known electrophotographic method. The sheet on which the image is formed is discharged to the discharge tray 159.

Operation panel 160 is provided on the top of MFP 100. The operation panel 160 includes a display unit 161 and an operation unit 163. The display unit 161 is, for example, a liquid crystal display device (LCD), and displays an instruction menu for the user, information regarding acquired image data, and the like. Instead of the LCD, an organic EL (electroluminescence) display can be used as long as it is an apparatus that displays an image.

The operation unit 163 includes a touch panel and hard keys. The hard key is, for example, a contact switch. The touch panel detects a position designated by the user on the display surface of the display unit 161.

FIG. 2 is a schematic cross-sectional view showing the internal configuration of the MFP. Referring to FIG. 2, automatic document feeder 120 separates one or more documents placed on document tray 125 and conveys them one by one to document reading unit 130. The document reading unit 130 exposes the image of the document set on the document glass 11 by the automatic document feeder 120 with the exposure lamp 13 attached to the slider 12 that moves below the image. The reflected light from the document is guided to the lens 16 by the mirror 14 and the two reflecting mirrors 15 and 15A, and forms an image on a CCD (Charge Coupled Devices) sensor 18. The exposure lamp 13 and the mirror 14 are attached to the slider 12, and the slider 12 is moved by the scanner motor 17 in the arrow direction (sub-scanning direction) shown in FIG. 2 at a speed V according to the copy magnification. As a result, the original set on the original glass 11 can be scanned over the entire surface. Further, with the movement of the exposure lamp 13 and the mirror 14, the two reflecting mirrors 15 and 15A move in the direction of the arrow in FIG. 2 at a speed V/2. As a result, the optical path length from the light emitted from the exposure lamp 13 to the document to the image formed on the CCD sensor 18 after being reflected by the document is always constant. The document reading unit 130 executes shading correction as an initialization process and moves the slider 12 to a predetermined position when the operation mode is switched from the power saving mode to the normal mode.

The reflected light imaged on the CCD sensor 18 is converted into image data as an electric signal in the CCD sensor 18. The image data is converted into printing data of cyan (C), magenta (M), yellow (Y), and black (K), and output to the image forming unit 140.

The image forming unit 140 includes yellow, magenta, cyan, and black image forming units 20Y, 20M, 20C, and 20K. Here, “Y”, “M”, “C” and “K” represent yellow, magenta, cyan and black, respectively. An image is formed by driving at least one of the image forming units 20Y, 20M, 20C, and 20K. When all the image forming units 20Y, 20M, 20C and 20K are driven, a full color image is formed. To the image forming units 20Y, 20M, 20C and 20K, yellow, magenta, cyan and black printing data are input, respectively. Since the image forming units 20Y, 20M, 20C, and 20K are different only in the color of the toner they handle, the image forming unit 20Y for forming a yellow image will be described here.

The image forming unit 20Y includes an exposure device 21Y to which yellow printing data is input, a photosensitive drum 23Y that is an image carrier of the exposure device 21Y, a charger 22Y, a developing device 24Y, and a transfer charger 25Y. And a toner bottle 41Y. The toner bottle 41Y stores yellow toner.

The exposure device 21Y emits light according to the printing data (electrical signal) to expose the photoconductor drum 23Y, which is a subject. The photoconductor drum 23Y is charged by the charger 22Y and then irradiated with the laser light emitted by the exposure device 21Y. As a result, an electrostatic latent image is formed on the photoconductor drum 23Y. Subsequently, the developing device 24Y places the toner supplied from the toner bottle 41Y on the electrostatic latent image to form a toner image. The toner image formed on the photoconductor drum 23Y is transferred onto the intermediate transfer belt 30 by the transfer charger 25Y.

On the other hand, the intermediate transfer belt 30 is suspended by the drive roller 33C and the roller 33A so as not to loosen. When the drive roller 33C rotates counterclockwise in FIG. 2, the intermediate transfer belt 30 rotates counterclockwise in the figure at a predetermined speed. With the rotation of the intermediate transfer belt 30, the roller 33A rotates counterclockwise.

As a result, the image forming units 20Y, 20M, 20C, 20K sequentially transfer the toner images onto the intermediate transfer belt 30. The timing at which each of the image forming units 20Y, 20M, 20C, and 20K transfers the toner image onto the intermediate transfer belt 30 is adjusted by detecting the reference mark attached to the intermediate transfer belt 30. As a result, the yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 30.

The toner image formed on the intermediate transfer belt 30 is transferred onto a sheet by the transfer roller 26. The sheet on which the toner image is transferred is conveyed to the fixing roller pair 32 and heated by the fixing roller pair 32. As a result, the toner is melted and fixed on the paper. After that, the paper is discharged to the paper discharge tray 159.

A registration sensor 39 for reading a part of the toner image transferred to the intermediate transfer belt 30 is provided between the image forming unit 20K and the transfer roller 26. The registration sensor 39 includes a light projecting unit that emits light toward the intermediate transfer belt 30 and a light receiving unit that receives the light reflected by the intermediate transfer belt 30, and outputs a signal indicating the amount of light received by the light receiving unit. Output. Since the registration sensor 39 is provided between the image forming unit 20K and the transfer roller 26, it is possible to read the toner image formed on the intermediate transfer belt 30 by each of the image forming units 20Y, 20M, 20C and 20K. .. The registration sensor 39 is capable of detecting toner images of yellow, magenta, cyan, and black.

A removing device 28 is provided upstream of the image forming unit 20Y on the intermediate transfer belt 30. The removing device 28 removes the toner remaining on the intermediate transfer belt 30.

Papers of different sizes are set in the paper feed cassettes 35, 35A, 35B. The paper stored in each of the paper feed cassettes 35, 35A, 35B is supplied to the conveyance path by the take-out rollers 36, 36A, 36B attached to the paper feed cassettes 35, 35A, 35B, and by the paper feed roller 37. It is sent to the timing roller 31.

The MFP 100 drives all the image forming units 20Y, 20M, 20C, 20K when forming a full-color image, but when forming a monochrome image, any one of the image forming units 20Y, 20M, 20C, 20K is formed. Drive one. Further, an image can be formed by combining two or more of the image forming units 20Y, 20M, 20C and 20K. Here, a tandem-type MFP 100 including image forming units 20Y, 20M, 20C, and 20K that form toners of four colors on a sheet will be described. It may be a 4-cycle type MFP that transfers the image to the.

Next, the exposure devices 21Y, 21M, 21C and 21K will be described. Since the exposure apparatuses 21Y, 21M, 21C, and 21K are all the same, the exposure apparatus 21Y will be described here as an example.

FIG. 3 is a perspective view showing an example of the internal configuration of the exposure apparatus. Referring to FIG. 3, exposure apparatus 21Y includes a substrate assembly 210 and a microlens array 240. The microlens array 240 includes a plurality of optical elements 245. The substrate assembly 210 includes a first light source substrate 201 and a second light source substrate 202. A plurality of light sources 200 are formed on each of the first light source substrate 201 and the second light source substrate 202. The first light source substrate 201 and the second light source substrate 202 overlap with each other in the optical axis direction of the plurality of light sources 200 and are fixed to each other. With the first light source substrate 201 and the second light source substrate 202 fixed to each other, the plurality of light sources 200 formed on the first light source substrate 201 and the plurality of light sources 200 formed on the second light source substrate 202 are The position in the sub-scanning direction is different. The second light source substrate 202 overlaps the upper side of the first light source substrate 201. Part of the lower surface of the second light source substrate 202 and part of the upper surface of the first light source substrate 201 overlap.

The first light source substrate 201 and the second light source substrate 202 are made of glass. The first light source substrate 201 and the second light source substrate are fixed to each other in the overlapping portion. For example, the first light source substrate 201 and the second light source substrate 202 are adhered by an adhesive on the entire surfaces where they overlap in a normal temperature state in which the plurality of light sources 200 formed on each of them do not emit light. Therefore, the surfaces of the first light source substrate 201 and the second light source substrate on which the plurality of light sources 200 are formed are parallel at room temperature.

The formation region of the first light source substrate 201 where the light source 200 is formed does not overlap with the second light source substrate 202. Therefore, the light emitted from the plurality of light sources 200 formed on the first light source substrate 201 is emitted to the optical element 245 provided on the microlens array 240 without being emitted to the second light source substrate 202. .. In addition, the light emitted from the plurality of light sources 200 formed on the second light source substrate 202 is emitted to the optical element 245 provided on the microlens array 240 without being emitted to the first light source substrate 201. ..

FIG. 4 is a sectional view of a part of the exposure apparatus in this embodiment. FIG. 4 shows a cross section of a part of the exposure device 21Y taken along a plane parallel to the sub-scanning direction at a portion where the first light source substrate 201 and the second light source substrate 202 overlap. Referring to FIG. 4, in exposure apparatus 21Y, substrate assembly 210 is arranged on the bottom of holder 301.

A first protrusion 303 and two second protrusions 305A and 305B are formed side by side in the main scanning direction on the bottom of the holder 301. The first protrusion 303 is located between the two second protrusions 305A and 305B. Two first protrusions 305A and 305B of the first protrusion 303 and the two second protrusions 305A and 305B are located at both ends.

Each of the first protrusion 303 and the two second protrusions 305A and 305B has an upper surface. The substrate assembly 210 abuts the first protrusion 303 and the two second protrusions 305A and 305B, respectively. The bottom surface of the first light source substrate 201 of the substrate assembly 210 contacts the top surfaces of the first protrusion 303 and the two second protrusions 305A and 305B. A region on the bottom surface of the first light source substrate 201 that contacts the upper surface of the first protrusion 303 and a region that contacts the upper surface of each of the two second protrusions 305A and 305B are called support points. Further, of the three support locations, the area that comes into contact with the upper surface of the first protrusion 303 is also referred to as a fixed location.

The first light source substrate 201 is attached to the upper surface of the first protrusion 303 with an adhesive at a fixed position. Therefore, the substrate assembly 210 is fixed to the holder 301 by the first protrusion 303. In order to increase the adhesive force between the first light source substrate 201 and the first protrusion 303, the length of the fixed portion in the sub-scanning direction is set to be the same as the length of the first light source substrate 201 in the sub-scanning direction. It is preferable that the length of the upper surface of 303 in the sub scanning direction is equal to or longer than the length of the first light source substrate 201 in the sub scanning direction.

The first light source substrate 201 is not fixed to the two second protrusions 305A and 305B. Therefore, the movement of the first light source substrate 201 toward the two second protrusions 305A and 305B is restricted in the two support regions that are in contact with the two second protrusions 305A and 305B, respectively, but the other direction is restricted. Movement is not regulated.

The substrate assembly 210 is configured such that the thermal expansion amount of the first light source substrate 201 is smaller than the thermal expansion amount of the second light source substrate 202. Specifically, the first light source substrate 201 has a smaller linear expansion coefficient than the second light source substrate 202. The holder 301 is a material having a Young's modulus larger than that of the substrate assembly 210. Here, the holder 301 is made of aluminum or stainless steel (SUS).

The plurality of light sources 200 formed on each of the first light source substrate 201 and the second light source substrate 202 generate heat when emitting light. Further, a plurality of drive circuits for driving the plurality of light sources 200 are formed on each of the first light source substrate 201 and the second light source substrate 202. Each of the plurality of drive circuits may generate heat when the light source 200 emits light.

FIG. 5 is a first diagram showing an example of a difference in thermal expansion amount between the first light source substrate and the second light source substrate. Referring to FIG. 5, the linear expansion coefficient of first light source substrate 201 is smaller than the linear expansion coefficient of second light source substrate 202. The item of temperature indicates the temperature of each of the first light source substrate 201 and the second light source substrate 202. The item of elongation indicates the amount of elongation from the length of 330 mm at room temperature. Here, the normal temperature is 25 degrees Celsius. The second light source substrate 202 has an extension amount of 49.5 μm at 50 degrees Celsius, whereas the first light source substrate 201 has an extension amount of 39.6 μm at 60 degrees Celsius. For this reason, since the extension amount of the first light source substrate 201 is smaller than the extension amount of the second light source substrate 202, the substrate assembly 210 is distorted in the direction from the second light source substrate 202 toward the first light source substrate 201.

Returning to FIG. 4, the linear expansion coefficient of the first light source substrate 201 is smaller than the expansion coefficient of the second light source substrate 202, and the Young's modulus of the holder 301 is large in the Young's modulus of the substrate assembly 210. Therefore, when the light sources 200 of the first light source substrate 201 and the second light source substrate 202 emit light and generate heat, the substrate assembly 210 moves toward the first protrusion 303 at a portion where the first light source substrate 201 contacts the first protrusion 303. The external force in the direction is applied from the first protrusion 303, and the external force in the direction in which the first light source substrate 201 is in contact with the second protrusions 305A and 305B causes the second external force in the direction away from the second protrusions 305A and 305B. It is added from each of the protrusions 305A and 305B. Therefore, the amount of distortion of the substrate assembly 210 in the direction from the second light source substrate 202 to the first light source substrate 201 can be reduced.

Further, the fixing portion of the substrate assembly 210 where the first light source substrate 201 contacts the first protrusion 303 is fixed to the first protrusion 303 with an adhesive, and the first light source substrate 201 of the substrate assembly 210 has the second protrusion 305A. The supporting portions that come into contact with the respective 305B are not fixed to the second protrusions 305A and 305B. Therefore, even if the temperature of the substrate assembly 210 rises and the substrate assembly 210 expands in the main scanning direction, the substrate assembly 210 can be prevented from receiving an external force in the main scanning direction.

<First Modification>
In the MFP 100 according to the first modified example, the substrate assembly 210 is configured such that the thermal conductivity of the first light source substrate 201 is higher than the thermal conductivity of the second light source substrate 202. The linear expansion coefficient of the first light source substrate 201 is the same as or smaller than the linear expansion coefficient of the second light source substrate 202. Here, a case where the linear expansion coefficient of the first light source substrate 201 and the linear expansion coefficient of the second light source substrate 202 are the same will be described as an example.

In the first modification, when the temperatures of the first light source substrate 201 and the second light source substrate 202 rise, the thermal conductivity of the first light source substrate 201 is higher than the thermal conductivity of the second light source substrate 202. The heat radiation amount of the light source substrate 201 becomes larger than the heat radiation amount of the second light source substrate 202. Therefore, the temperature of the first light source substrate 201 becomes lower than the temperature of the second light source substrate 202.

FIG. 6 is a second diagram showing an example of a difference in thermal expansion amount between the first light source substrate and the second light source substrate. Referring to FIG. 6, the linear expansion coefficient of first light source substrate 201 is the same as the linear expansion coefficient of second light source substrate 202. The item of temperature indicates the temperature of each of the first light source substrate 201 and the second light source substrate 202. The item of elongation indicates the amount of elongation from the length of 330 mm at room temperature. Here, the room temperature is set to 30 degrees Celsius. An example is shown in which the first light source substrate 201 radiates heat to 50 degrees Celsius when the second light source substrate 202 is 60 degrees Celsius. The second light source substrate 202 has an extension amount of 59.4 μm at 60 degrees Celsius, whereas the first light source substrate 201 has an extension amount of 50° C. at 49.5 μm. Since the extension amount of the first light source substrate 201 is smaller than the extension amount of the second light source substrate 202, the substrate assembly 210 is distorted in the direction from the second light source substrate 202 toward the first light source substrate 201.

Although the linear expansion coefficient of the first light source substrate 201 is the same as that of the second light source substrate 202 in FIG. 6, the linear expansion coefficient of the first light source substrate 201 is the linear expansion coefficient of the second light source substrate 202. When the coefficient is smaller than the coefficient, the elongation amount of the second light source substrate 202 at 60 degrees Celsius becomes smaller than 59.4 μm.

Referring again to FIG. 4, since the thermal conductivity of the first light source substrate 201 is higher than the thermal conductivity of the second light source substrate 202, the light sources 200 of the first light source substrate 201 and the second light source substrate 202 emit light. When the heat is generated, the temperature of the first light source substrate 201 becomes lower than the temperature of the second light source substrate 202. Therefore, in the substrate assembly 210, an external force in a direction toward the first protrusion 303 is applied to a portion in contact with the first protrusion 303 from the first protrusion 303, and a portion in which the substrate assembly 210 contacts each of the second protrusions 305A and 305B. In addition, external force in a direction away from each of the second protrusions 305A and 305B is applied from each of the second protrusions 305A and 305B. Therefore, the amount of distortion of the substrate assembly 210 in the direction from the second light source substrate 202 to the first light source substrate 201 can be reduced.

Further, as shown in FIG. 7, a heat conducting member 311 may be arranged between the first light source substrate 201 and the holder 301. The thermal conductivity of the thermal conductive member 311 is higher than that of the first light source substrate 201. Thereby, the heat generated in the first light source substrate 201 is conducted to the heat conducting member 311 and the holder 301, so that the heat radiation amount of the first light source substrate 201 can be increased. Therefore, the temperature difference between the first light source substrate 201 and the second light source substrate 202 can be increased. Further, it is preferable that the thermal conductivity of the holder 301 be larger than that of the first light source substrate 201.

<Second Modification>
The substrate assembly 210 may be fixed to the holder 301 at a sub-fixing point different from the fixing point.

FIG. 8 is a sectional view of a part of the exposure apparatus in the second modified example. Referring to FIG. 8, a point different from FIG. 4 is that a fixing member 309 is added. The board assembly 210 is fixed to the holder 301 by a fixing member 309 near each of the second protrusions 305A and 305B. An area on the bottom surface of the first light source substrate 201, which is in contact with the fixing member 309, is a sub fixing portion.

The fixing member 309 has elasticity. Therefore, even if the temperature of the substrate assembly 210 rises and the substrate assembly 210 expands in the main scanning direction, the external force in the main scanning direction that the substrate assembly 210 receives from the fixing member 309 can be reduced.

<Third Modification>
In the above embodiment, the example in which the holder 301 has the first protrusion 303 and the two second protrusions 305A and 305B has been shown, but the first protrusion 303 and the two second protrusions 305A and 305B may be omitted. Good.

In the third modification, the holder 301 has a fixing region at the same position as the first protrusion 303, and the fixing portion on the bottom surface of the first light source substrate 201 and the fixing region of the holder 301 are bonded with an adhesive material.

In addition, in the above-described embodiment, the substrate assembly 210 has a configuration in which the first light source substrate 201 and the second light source substrate 202 are stacked, but there may be a plurality of second light source substrates 202. For example, the substrate assembly 210 may include a third light source substrate in addition to the first light source substrate 201 and the second light source substrate 202. In this case, the third light source substrate is made of glass and the plurality of light sources 200 are formed. The second light source substrate 202 overlaps the upper side of the first light source substrate 201, and the third light source substrate overlaps the upper side of the second light source substrate 202. Part of the lower surface of the third light source substrate and part of the upper surface of the second light source substrate 202 overlap. The second light source substrate 202 and the third light source substrate are overlapped and fixed to each other in the optical axis direction of the plurality of light sources 200. The plurality of light sources 200 formed on the first light source substrate 201 with the first light source substrate 201 and the second light source substrate 202 fixed to each other and the second light source substrate 202 and the third light source substrate 202 fixed to each other. The plurality of light sources 200 formed on the second light source substrate 202 and the plurality of light sources 200 formed on the third light source substrate have different positions in the sub-scanning direction.

As described above, MFP 100 in the present embodiment functions as an image forming apparatus. In each of the exposure devices 21Y, 21M, 21C, and 21K included in the MFP 100, the first light source substrate 201 and the second light source substrate 202 each including a plurality of light sources arranged in the main scanning direction are the optical axes of the plurality of light sources 200. The substrate assembly 210 is overlapped with each other and fixed to each other, and the holder 301 that supports the substrate assembly 210 by the first protrusion 303 and the two second protrusions 305A and 305B. The substrate assembly 210 is fixed to the holder 301 at a fixing position where the first light source substrate 201 contacts the first protrusion 303 and the two second protrusions 305A and 305B, respectively. The thermal expansion amount of the light source substrate 201 is smaller than the thermal expansion amount of the second light source substrate 202. Therefore, the amount by which the substrate assembly 210 is distorted in the direction from the second light source substrate 202 toward the first light source substrate 201 due to thermal expansion can be reduced.

The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

100 MFP, 21Y, 21M, 21C, 21K exposure device, 200 light source, 210 substrate assembly, 201 first light source substrate, 202 second light source substrate, 240 microlens array, 245 optical element, 301 holder, 303 first protrusion, 305A , 305B 2nd protrusion, 309 fixing member, 311 heat conduction member.

Claims (8)

A substrate assembly in which a first substrate and a second substrate each including a plurality of light sources arranged in one direction overlap with each other in the optical axis direction of the plurality of light sources and are fixed to each other,
A holder that supports the substrate assembly at at least three support points of the first substrate,
The substrate assembly is fixed to the holder at a single fixing point other than the two supporting points at both ends of the at least three supporting points in the one direction.
An exposure apparatus configured such that the thermal expansion amount of the first substrate is smaller than the thermal expansion amount of the second substrate. The exposure apparatus according to claim 1, wherein the first substrate has a smaller linear expansion coefficient than the second substrate. The exposure apparatus according to claim 1, wherein the first substrate has a higher thermal conductivity than the second substrate. The exposure apparatus according to claim 3, wherein the holder has a thermal conductivity higher than that of the first substrate. The exposure apparatus according to claim 1, further comprising an elastic member that fixes the substrate assembly to the holder at a sub-fixing location different from the fixing location. The exposure apparatus according to claim 1, wherein the holder has a Young's modulus larger than that of the first substrate. The exposure apparatus according to claim 1, wherein the first substrate and the second substrate are fixed to each other in a state where the plurality of light sources do not emit light. An image forming apparatus comprising the exposure device according to claim 1.

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