JP2023184025A - Lens unit, led head, exposure device, image forming apparatus, reading head, and image reading device - Google Patents

Abstract

To solve the problem in which in a lens unit of an exposure device, a light beam incident on an outer peripheral part of a lens cannot be formed into an image at one point, which causes flare and deteriorates print quality.SOLUTION: A lens unit has: a first lens plate 106 in which a plurality of first lenses 106a are arranged in an arrangement direction substantially orthogonal to an optical axis 106b; a second lens plate 108 in which a plurality of second lenses 108d are arranged in an arrangement direction substantially orthogonal to an optical axis 108e; and a mask 105 and a shield 107 in which a plurality of openings 105a, 107a through which the optical axis 106b and the optical axis 108e pass are arranged in the arrangement direction. The first lens plate 106 and the second lens plate having substantially the same shape are arranged opposite to each other so that the optical axis 106b and the optical axis 108e match each other. The lens plates are arranged so that a distance Lc1 between an intermediate image to be formed and the first lens plate 106 is larger than a distance Lc2 between the intermediate image and the second lens plate 108.SELECTED DRAWING: Figure 10

Description

The present invention relates to a lens unit, an exposure device, a reading head, an image forming device, and an image reading device.

When two lenses are used to form an erect, same-magnification image, the first lens forms an inverted reduced image as an intermediate image, while the second lens forms an inverted enlarged image. This is achieved by At this time, an inverted reduced image as an intermediate image is formed at a position approximately equidistant from the two lenses (see, for example, Patent Document 1).

JP 2020-34795 (Page 9, Figure 6)

However, in the conventional method, there was a problem in that the light rays incident on the outer periphery of the lens could not be focused on a single point, causing flare and deteriorating printing quality.

A lens unit according to the present invention includes a first lens array in which a plurality of first lens elements are arranged in a row in an arrangement direction substantially perpendicular to a first optical axis, and a plurality of second lens elements. a second lens array arranged in a row in the arrangement direction substantially perpendicular to the second optical axis; and a plurality of apertures through which the first optical axis and the second optical axis pass. A lens unit having light shielding members arranged in rows in the arrangement direction,
The first lens array and the second lens array having substantially the same shape are arranged to face each other so that the first optical axis and the second optical axis coincide, and the first lens array The present invention is characterized in that the distance between the intermediate image to be formed and the first lens array is greater than the distance between the intermediate image and the second lens array.

According to the present invention, since the area of light incident on the second lens element can be narrowed, it is possible to prevent light rays from entering the outer periphery of the lens, which causes flare, and reduce flare. The resolution of the optical system as a whole is improved, and printing quality can be improved.

1 is a diagram schematically showing a main part configuration of an image forming apparatus according to a first embodiment of the present invention, which includes an LED head according to the present invention; FIG. It is an external perspective view of an LED head. FIG. 3 is a stacked exploded view showing the stacked components of the LED head shown in FIG. 2 in an exploded manner. Regarding the light source board and the mask, (a) is an explanation of the engagement relationship near the left end in the longitudinal direction, (b) is in the center part in the longitudinal direction, and (c) is near the right end in the longitudinal direction. It is a diagram. Description of each engagement relationship between the mask and the first lens plate: (a) near the left end in the longitudinal direction, (b) near the center in the longitudinal direction, and (c) near the right end in the longitudinal direction FIG. Description of each engagement relationship between the shield and the second lens plate: (a) near the left end in the longitudinal direction, (b) near the center in the longitudinal direction, and (c) near the right end in the longitudinal direction. FIG. This is a diagram for explaining the engagement relationship between the head holder and the second lens plate, and (a), (b), and (c) are the vicinity of the left end, the center, and the right end of the second lens plate in the longitudinal direction, respectively. FIG. 3D is a perspective view of the vicinity of the head holder as seen diagonally from below, and FIG. FIG. 2 is a perspective view of the area around a section cut at the center in the longitudinal direction of an LED head configured by a head holder and members laminated therein, as seen diagonally from above. (a) is a configuration diagram of the mask viewed from below, (b) is a configuration diagram of the first lens plate viewed from below, (c) is a configuration diagram of the shield viewed from below, and (d ) is a configuration diagram of the second lens plate viewed from below. FIG. 2 is a cross-sectional view schematically showing a cross section of the lens unit taken along a plane that includes the optical axis of the first lens of the first lens plate and is parallel to the ZY plane. 3 is a graph showing simulation results, in which (a) shows a change in the average value of MTF, and (b) shows a change in MTF dispersion. FIG. 3 is a perspective view showing an image reading device according to a second embodiment. 7 is a cross-sectional view showing the configuration of a reading head in Embodiment 2. FIG.

Embodiment 1.
FIG. 1 is a diagram schematically showing the configuration of main parts of an image forming apparatus 11 according to a first embodiment, which includes an LED head 15 as an exposure device according to the present invention.

The image forming apparatus 11 has, for example, a configuration as an electrophotographic color printer, and includes four independent image forming units 12K, 12Y, 12M, and 12C that constitute an image forming section (if there is no particular need to distinguish, it is simply an image forming unit). Forming units 12 (sometimes referred to as forming units 12) are arranged in order from the upstream side along the conveyance direction (direction of arrow A) of recording paper 40 as a recording medium.

The image forming unit 12K forms a black (K) image, the image forming unit 12Y forms a yellow (Y) image, the image forming unit 12M forms a magenta (M) image, and the image forming unit 12C forms a magenta (M) image. A cyan (C) image is formed. In addition to the recording paper 40, OHP paper, envelopes, copy paper, special paper, etc. can be used as the recording medium.

Since each of the image forming units 12K, 12Y, 12M, and 12C has the same configuration except for the color of the developer used, the configuration of the image forming unit 12K will be described here as a representative.

The image forming unit 12K includes a photoreceptor drum 13K, a charging roller 14K that uniformly charges the surface of the photoreceptor drum 13K, and a charging roller 14K that charges the electrostatic latent image formed on the surface of the photoreceptor drum 13K. A developing roller 16K to which a developer (for example, toner, not shown) is attached to form a visible toner image, and a toner supply roller 18K in pressure contact with the developing roller 16K. A cleaning blade 27K is provided to remove residual toner.

The toner supply roller 18K is a roller that supplies toner supplied from a corresponding toner cartridge 20K that is detachably attached to the image forming unit main body to the developing roller 16K. A developing blade 19K is pressed against the developing roller 16K. The developing blade 19 forms a thin layer of toner supplied from the toner supply roller 18K on the developing roller 16K. Here, the toner cartridge 20K is detachably attached to the main body of the image forming unit 12K, but it may be integrally formed.

Note that each component of the image forming unit 12K has a (K) suffixed with the reference numeral, but each of the corresponding components of the image forming unit 12Y, image forming unit 12M, and image forming unit 12C has a (Y), respectively. (M) and (C) are added to distinguish them, but they are not added if this distinction is not particularly required.

Above the photoreceptor drums 13K, 13Y, 13M, 13C in each image forming unit 12K, 12Y, 12M, 12C are the corresponding LED heads 15K, 15Y, 15M, 15C (if there is no particular need to distinguish, simply An LED head 15 (sometimes referred to as an LED head 15) is disposed at a position facing the photoreceptor drums 13K, 13Y, 13M, and 13C. Each LED head 15 is a device that exposes the photoreceptor drum 13 to light according to image data of a corresponding color to form an electrostatic latent image. Note that the LED head 15 will be explained in detail later.

A transfer unit 21 is arranged below each photosensitive drum 13 of the four image forming units 12. The transfer unit 21 is configured to be tensioned by transfer rollers 17K, 17Y, 17M, and 17C (sometimes simply referred to as the transfer roller 17 if there is no need to distinguish between them), a transfer belt drive roller 21a, and a transfer belt driven roller 21b. The transfer belt 26 is provided so as to be able to run in the direction of arrow A in FIG. 1 in this state. Each transfer roller 17 is placed in pressure contact with the corresponding photoconductor drum 13 via the transfer belt 26, and charges the recording paper 40 to the opposite polarity to the toner at this nip portion, and charges the recording paper 40 with the polarity opposite to that of the toner. The formed toner images of each color are sequentially transferred onto the recording paper 40 in an overlapping manner.

A paper feeding mechanism for feeding recording paper 40 to transfer belt 26 is disposed at the lower part of image forming apparatus 11 . The paper feeding mechanism includes a hopping roller 43, a pair of registration rollers 45, a paper storage cassette 24, and the like.

Further, a fixing device 28 is provided on the side where the recording paper 40 is discharged by the transfer belt 26. The fixing device 28 has a heating roller 29 and a backup roller 30, and is a device that fixes the toner transferred onto the recording paper 40 by applying pressure and heating. A pair of conveyance rollers 46, a pair of ejection rollers 47, a paper stacker section 48, and the like are provided.

The printing operation in the image forming apparatus 11 configured as described above will be briefly described. First, the recording paper 40 in the paper storage cassette 24 is fed out to the paper guide 41 by the hopping roller 43, sent to a pair of registration rollers 45 to correct the skew, and then sent from the pair of registration rollers 45 to the transfer belt 26. As the transfer belt 26 runs, it is sequentially conveyed to the image forming units 12K, 12Y, 12M, and 12C.

On the other hand, in each image forming unit 12, the surface of the photoreceptor drum 13 is charged by a charging roller 14 and then exposed to light by a corresponding LED head 15, and an electrostatic latent image is formed on the surface by this exposure. A thin layer of toner is electrostatically adhered to the area where the electrostatic latent image is formed on the developing roller 16, thereby forming a toner image of the corresponding color. The toner images formed on each photosensitive drum 13 are sequentially transferred onto the recording paper 40 by the corresponding transfer rollers 17 in an overlapping manner to form a color toner image on the recording paper 40 . After the transfer, the toner remaining on each photoreceptor drum 13 is removed by a cleaning blade 27, respectively.

The recording paper 40 on which the color toner image has been formed is sent to the fixing device 28. In this fixing device 28, the color toner image is fixed onto the recording paper 40 to form a color image. The recording paper 40 on which the color image has been formed is transported along the paper guide 42 by a pair of transport rollers 46, and is ejected to a paper stacker section 48 by a pair of ejection rollers 47. Through the process described above, a color image is formed on the recording paper 40. Note that residual toner adhering to the transfer belt 26 is contained in a belt cleaner container 35 by a belt cleaning blade 34.

Note that the X, Y, and Z directions in FIG. The direction of the rotational axes of 13K, 13Y, 13M, and 13C is the Y direction, and the direction perpendicular to these axes is the Z direction. Furthermore, when X, Y, and Z directions are shown in other figures (up to FIG. 10) to be described later, these directions are assumed to indicate a common direction. That is, the XYZ directions in each figure indicate the directions in which the depicted portions in each figure are arranged when constructing the image forming apparatus 11 shown in FIG. 1. Further, here, it is assumed that the Z direction is arranged to be substantially vertical.

FIG. 2 is an external perspective view of the LED head 15, and FIG. 3 is an exploded view showing the laminated components of the LED head 15 shown in FIG. 2. Note that when viewed from the direction of arrow A, the left and right, up and down, and front and back directions of the LED head 15 may be specified.

As shown in these figures, the LED head 15 includes a head holder 110, a second lens plate 108 as a second lens array arranged on the exit side having the same shape, and a first lens arranged on the entrance side. There are a first lens plate 106 as an array, a shield 107 and a mask 105 as light shielding members, and a light source and a light source board 104 and a control board 101 that control the light source.

These members are stacked and mounted in the inside 110a of the head holder 110 in the order of the second lens plate 108, the shield 107, the first lens plate 106, the mask 105, and the light source substrate 104 from the bottom. At this time, the lower end of the second lens plate 108 is placed on a pair of mounting members 110e (FIG. 8) extending in the longitudinal direction at the bottom 110c (FIG. 8) of the head holder 110, as described later. They are placed in contact with each other.

Each of these members is fitted from the outside through a plurality of through holes 110b formed in the side wall of the head holder 110 and protrudes inward while being biased in the -Z direction by a jig (not shown). The upper surface of the light source substrate 104 is regulated by a plurality of fixing members 109 disposed in the substrate, and is clamped in the Z direction and fixed in the interior 110a. After that, the insulating film 103 and the control board 101 are attached, and then sealed with silicone rubber 102 as a sealing member.

Next, the mutual engagement relationship of the stacked members will be explained.

FIG. 4 shows the light source substrate 104 and the mask 105 in the vicinity of the left end in the longitudinal direction (arrow Y direction) in FIG. 4(a), in the center in the longitudinal direction, and in FIG. FIG. 6 is a diagram for explaining each engagement relationship in the vicinity of the right end in the longitudinal direction.

As shown in these figures, cylindrical positioning protrusions 115L and 115R that protrude upward are formed at both left and right ends of the mask 105, and cylindrical positioning protrusions 115L and 115R are formed at both left and right ends of the light source board 104, facing the positioning protrusions 115L and 115R. U-shaped grooves 114L and 114R extending in the longitudinal direction are formed at the positions. Therefore, the mask 105 and the light source board 104 are relatively connected in the lateral direction (arrow X direction).

Further, a cylindrical positioning protrusion 125 is formed in the longitudinal center of the mask 105 and protrudes upward at the front end in the transverse direction, and a positioning protrusion 125 is formed in the longitudinal center of the light source board 104. A U-shaped groove 124 extending in the lateral direction is formed at a position facing the . Therefore, by fitting the positioning protrusion 125 into the U-shaped groove 124 and joining them, the mask 105 and the light source substrate 104 are relatively positioned in the longitudinal direction.

With the above configuration, since the longitudinal direction is regulated at one point, even if a difference in expansion/contraction occurs in the longitudinal direction due to a difference in the coefficient of linear expansion of each member, the deviation at that time can be corrected by the U-shaped groove 114L, 114R.

FIG. 5 shows the mask 105 and the first lens plate 106 in the vicinity of the left end in the longitudinal direction (arrow Y direction) in the same figure (a), in the central part in the longitudinal direction, and in the same figure ( c) is a diagram for explaining each engagement relationship in the vicinity of the right end in the longitudinal direction.

As shown in these figures, a plurality of rectangular positioning protrusions 135 (only the front end side is shown) projecting downward are formed at approximately equal intervals in the longitudinal direction at both front and rear ends of the mask 105 in the width direction. A plurality of long grooves 116 extending in the longitudinal direction are formed at both front and rear ends of the first lens plate 106 in the lateral direction at positions facing each positioning protrusion 135 . Therefore, the mask 105 and the first lens plate 106 are relatively positioned in the X direction by joining each positioning protrusion 135 so as to fit into the opposing long groove 116.

In addition, a pair of concave grooves 126 are formed in the longitudinal center of the first lens plate 106 and extend in the same direction at both ends in the transverse direction, and each concave groove 126 is formed in the longitudinal center of the mask 105. A pair of positioning protrusions (not shown) are formed at positions opposite to 126. Therefore, the mask 105 and the first lens plate 106 are relatively positioned in the longitudinal direction by being joined so that the positioning protrusion fits into the concave groove 126.

With the above configuration, since the longitudinal direction is regulated at one point, even if a difference in expansion/contraction occurs in the longitudinal direction due to a difference in the coefficient of linear expansion of each member, the deviation at that time can be tolerated by the long groove 116. I can do it.

6A and 6B show the shield 107 and the second lens plate 108 in the vicinity of the left end in the longitudinal direction (arrow Y direction) in the same figure (a), in the central part in the longitudinal direction in the same figure (b), and in the same figure ( c) is a diagram for explaining each engagement relationship in the vicinity of the right end in the longitudinal direction.

As shown in these figures, a plurality of rectangular positioning protrusions 117 (only the front end side shown) projecting downward are formed at approximately equal intervals in the longitudinal direction at both the front and rear ends of the shield 107 in the transverse direction. A plurality of long grooves 118 extending in the longitudinal direction are formed at both front and rear ends of the second lens plate 108 in the lateral direction at positions facing each positioning protrusion 117 . Therefore, the shield 107 and the second lens plate 108 are relatively positioned in the X direction by joining each positioning protrusion 117 so as to fit into the opposing long groove 118.

A pair of cylindrical positioning protrusions 128 that protrude upward are formed at the longitudinal center of the second lens plate 108, and a position opposite to the positioning protrusions 128 is formed at the longitudinal center of the shield 107. A pair of U-shaped grooves 127 extending in the lateral direction are formed in the lateral direction. Therefore, by fitting the positioning protrusion 128 into the U-shaped groove 127 and joining them, the shield 107 and the second lens plate 108 are relatively positioned in the longitudinal direction.

With the above configuration, since the longitudinal direction is regulated at one point, even if a difference in expansion/contraction occurs in the longitudinal direction due to a difference in the coefficient of linear expansion of each member, the long groove 118 allows the deviation at that time. I can do it.

The engagement relationship between the first lens plate 106 and the shield 107 is symmetrical in the vertical direction with the engagement relationship between the second lens plate 108 and the shield 107, so a description thereof will be omitted here. .

FIG. 7 is a diagram for explaining the engagement relationship between the head holder 110 and the second lens plate 108. FIGS. It is a perspective view of the vicinity of the end, the center, and the right end as seen diagonally from below, and FIG. .

As shown in these figures, U-shaped grooves 138L and 138R extending in the longitudinal direction are formed on the lower surface of both left and right ends of the second lens plate 108, and U-shaped grooves 138R are formed on both left and right ends of the head holder 110. A positioning protrusion (not shown) that protrudes upward is formed at a position facing 138L and 138R. Therefore, the head holder 110 and the second lens plate 108 are relatively positioned in the lateral direction (direction of the arrow Ru.

Further, a recessed groove 108c is formed at the front end of the central portion in the longitudinal direction of the second lens plate 108, and is sandwiched between a pair of convex portions 108a and 108b that protrude in the lateral direction. A positioning protrusion 110d that protrudes in the lateral direction is formed in the center at a position facing the recessed groove 108c. Therefore, the head holder 110 and the second lens plate are relatively positioned in the longitudinal direction by being joined so that the positioning protrusion 110d is fitted into the recessed groove 108c.

With the above configuration, since the longitudinal direction is regulated at one point, even if a difference in expansion/contraction occurs in the longitudinal direction due to a difference in the linear expansion coefficient of each member, the U-shaped groove 138L, 138R.

FIG. 8 is a perspective view of the periphery of a section cut at the center in the longitudinal direction of the LED head 15, which is configured by the head holder 110 and each member stacked in the interior 110a thereof, as seen diagonally from above. .

As shown in the figure, the light source substrate 104, the mask 105, the first lens plate 106, the shield 107, and the second lens plate 108 each have a contact convex portion formed on each member disposed above and below them. It is provided with an abutting convex portion that abuts, and each of these abutting portions is held in an abutting state. A long hole 110f is formed in the bottom portion 110c of the head holder 110 over the entire length thereof. Convergent light is output from this elongated hole 110f, as will be described later.

Therefore, the lens unit 140 consisting of the mask 105, the first lens plate 106, the shield 107, and the second lens plate 108 is held between the bottom 110c of the head holder 110 and the light source substrate 104, and is held in the interior 110a of the head holder 110. It is settled in.

Next, an opening 105a as an aperture formed in the mask 105 of the LED head 15, a first lens 106a as a first lens element formed in the first lens plate 106, and an aperture formed in the shield 107 as an aperture. The positional relationship between the opening 107a and the second lens 108d as a second lens element formed in the second lens plate 108 will be explained.

FIG. 9A is a configuration diagram of the mask 105 viewed from below. The arrangement of the opening 105a in the XY plane corresponds to the arrangement of the first lens 106a, which will be described next. The opening 105a has a truncated cone shape centered on the optical axis 106b (extending in the Z direction) as the first optical axis of the first lens 106a. The radius of the opening 105a on the imaging plane side (-Z direction) is larger than the radius on the light source side.

FIG. 9(b) is a configuration diagram of the first lens plate 106 viewed from below. The first lenses 106a are arranged in two rows in a staggered manner on the XY plane. The distance between the optical axes of the first lens 106a in the X direction is PX, and the distance between the optical axes of the first lens 106a in the Y direction is PY.

FIG. 9(c) is a configuration diagram of the shield 107 viewed from below. The arrangement of the opening 107a in the XY plane corresponds to the arrangement of the first lens 106a of the first lens plate 106. The opening 107a has a cylindrical shape centered on the optical axis 106b of the first lens 106a.

FIG. 9(d) is a configuration diagram of the second lens plate 108 viewed from below. The arrangement of the second lens 108d in the XY plane corresponds to the arrangement of the first lens 106a of the first lens plate 106. That is, the optical axis 108e as the second optical axis of the second lens 108d coincides with the optical axis 106b of the first lens 106a. The second lenses 108d are arranged in two rows in a staggered manner, and the distance between the optical axes of the second lenses 108d in the X direction is PX, and the distance between the optical axes of the second lenses 108d in the Y direction is PY. .

Here, the second lens plate 108 is the same as the first lens plate 106, but is inverted around the axis in the X direction. Therefore, the exit side surface of the first lens plate 106 and the entrance side surface of the second lens plate 108 have the same shape, and the entrance side surface of the first lens plate 106 and the exit side surface of the second lens plate 108 have the same shape. have the same shape.

Note that the mask 105 and the shield 107 are made of resin such as polycarbonate. Further, the first lens plate 106 and the second lens plate 108 are made of resin such as cycloolefin polymer. The light source board 104 is a glass epoxy resin board on which wiring is formed.

FIG. 10 is a cross-sectional view schematically showing a cross section of the lens unit 140 taken along a plane parallel to the ZY plane and including the optical axis 106b of the first lens 106a of the first lens plate 106 in FIG. 8, for example. It shows the path of light emitted from the output surface of the LED element 150 as a light source disposed on the substrate 104 until it forms an image on the surface of the photoreceptor drum 13. Note that the lens unit 140 shown in FIG. 10 is upside down compared to the lens unit 140 shown in FIG. 8.

As shown in FIG. 10, here, the LED element 150 is arranged so that the distance Lc2 to the second lens plate 108 is smaller than the distance Lc1 to the first lens plate 106, based on the imaging position of the intermediate image. The distance Lo between the exit surface and the first lens plate 106, the focal length f of the first lens 106a and the second lens 108d, and the distance L (Lc1+Lc2) between the first lens plate 106 and the second lens plate 108 are set. There is.

here,
1/Lo+1/Lc1=1/f
Because it is,
Lc1=f・Lo/(Lo−f)
becomes.
Therefore, the inequality f・Lo/(Lo−f)>L/2 (1)
By satisfying
Lc1>Lc2
is obtained.

The position of the intermediate image that satisfies the above inequality (1) can be obtained by adjusting the focal length f, the distance L, and the distance Lo, and it is particularly desirable to adjust the distance Lo. Modifying the focal length f involves modifying the lens surface, which requires high precision, which takes time and cost.Adjusting the distance L requires adjusting the distance because the intermediate image is an n-reduced image with a magnification of m. This is because the sensitivity increases by 1/m times with respect to the adjustment of Lo.

During exposure using the LED head 15, the LED element 150 emits light at a predetermined timing. When the light beam from the LED element 150 enters the first lens plate 106, the role of the mask 105 as an aperture stop is to restrict the light from entering outside the lens surface of the first lens 106a. The light beam passing through the first lens 106a of the first lens plate 106 forms a reduced image with a magnification m between the first lens 106a and the second lens 108d of the second lens plate 108.

At this time, the role of the shield 107 as a field diaphragm is to block light incident at a high angle of view with large aberrations. The second lens plate 108 forms an enlarged standing image of this reduced standing image on the photoreceptor drum 13 . Since the second lens plate 108 is a member having the same shape as the first lens plate 106 but inverted in the vertical direction, its magnification is 1/m. In this way, the lens unit 140 forms an erect, same-size image of the light source array in which the LED elements 150 are arranged in the longitudinal direction (Y direction) on the light source substrate 104 on the surface of the photoreceptor drum 13, and operates as an exposure device.

Here, since the structure is configured to satisfy inequality (1), the distance between the intermediate image and the second lens plate 108 is small, and the light rays on the lens surface of the second lens 108d of the second lens plate 108 are The incident range can be narrowed.

Next, a case will be described in which the position of the intermediate image is adjusted by changing the distance Lo by an offset distance x (-Z direction is +) in the arrangement shown in FIG. For example, if the distance Lc1 is set to (L/2),
1/(Lo+x)+1/(L/2)=1/f
Then,
x=f・L/(L-2f)-Lo
becomes.

Here, we performed a simulation assuming a vertical stripe pattern (90° MTF) and a horizontal stripe pattern (0° MTF) regarding changes in MTF (Modulation Transfer Function), which evaluates lens performance when the offset distance x is changed. . FIG. 11 is a graph showing the results of this simulation, in which (a) shows changes in the average value of MTF, and (b) shows changes in variation in MTF. The horizontal axis of each graph represents the offset distance x, which is the offset amount of the distance Lo, and the value of the focal length f of the lens 106a and the second lens 108d here is 1.16 [mm].

As is clear from the graph in the same figure, as the distance Lo between the output surface of the LED element 150 and the first lens plate 106 is reduced, the average value of MTF (MTF Average) increases, and the variation in MTF (MTF Average) increases. Peak to Valley)) decreases, but beyond a certain range, both the average value and the dispersion worsen.

Therefore, here, the range in which the distance Lo between the output surface of the LED element 150 and the first lens plate 106 is shorter than the condition that the intermediate image is formed at the center between the lenses is set to approximately x = -0.12 [mm]. That is, it was set to 10% of the focal length f (1.16 [mm]). This is because if it is brought closer than that, even if the above inequality (1) can be satisfied, the original imaging state may deteriorate too much. Therefore, in addition to the above inequality (1), the following inequality f・L/(L-2f)-Lo<f/10...(2)
It is desirable to satisfy the following.

As described above, according to the image forming apparatus of the first embodiment, the second lens plate 108 can prevent light rays from entering the outer periphery of the lens, which causes flare, thereby reducing flare and printing. Quality can be improved.

Embodiment 2.
Next, an image reading device 200 including a reading head 210 according to the present invention will be described.

FIG. 12 is a perspective view showing the image reading device 200. The image reading device 200 is, for example, a flatbed type image scanner. The image reading device 200 includes a housing 202 , a document table 203 provided on the top surface of the case 202 , a reading head 210 (contact image sensor head) placed below the document table 203 , and a document table 203 provided on the top surface of the document table 203 . A lid 204 covering the upper side is provided. The document table 203 is made of a material such as glass that transmits visible light, and a document to be read (an object to be read) is placed on the surface thereof.

In order to guide the reading head 210 in the sub-scanning direction, a pair of guides 205 are provided along the document table 203 and extending in the same direction. The reading head 210 is also connected to a drive belt 206, which in turn is connected to a stepping motor 207. Further, the reading head 210 is connected to the control circuit 201 via a flexible flat cable 208.

FIG. 13 is a cross-sectional view showing the configuration of the reading head 210. The reading head 210 includes a light receiving element substrate 212 having a plurality of light receiving elements 211 instead of the light source board 104 (FIG. 8) having the LED element 150 which is a light emitting element. The reading head 210 has the same main structure as the LED head 15 except that the light source substrate 104 is replaced with a light receiving element substrate 212. Note that the reading head 210 shown in FIG. 13 is drawn upside down with respect to the LED head 15 shown in FIG. 8 and with respect to the reading head 210 shown in FIG. 12.

That is, the reading head 210 includes a head holder 110, a cover member 215, a first lens plate 106, a shield 107, a second lens plate 108, a mask 105, and a light receiving element substrate 212.

The reading head 210 is arranged so that the output side (that is, the cover member 215 side) faces the light receiving element substrate 212. Light from the original 220 placed on the original table 203 is transmitted through the opening 105a of the mask 105, the first lens 106a of the first lens plate 106, the opening 107a of the shield 107, and the second lens 108d of the second lens plate 108. The light passes through and is focused on the light receiving element 211.

The basic operation of the image reading device 200 is as follows. When an original to be read is placed on the original table 203 and a switch such as a scan button is pressed, a light source (not shown) attached to the reading head 210 is turned on to illuminate the original to be read. The reading head 210 is moved in the sub-scanning direction by a drive belt 206 driven by a stepping motor 207, and captures light reflected from the surface of the original to be read. The reading head 210 converts the received optical signal into an electrical signal.

Also here, since the lens unit 140 is configured to satisfy the above-mentioned inequality (1), the distance between the intermediate image and the second lens plate 108 becomes small, so that the second lens 108d of the second lens plate 108 The range of incidence of light rays on the lens surface can be narrowed.

As described above, according to the image reading device of the second embodiment, the second lens plate 108 can prevent light rays from entering the outer peripheral portion of the lens, which causes flare, thereby reducing flare and reading. Accuracy can be improved.

Note that instead of moving the reading head 210 as described above, an ADF (Automatic Document Feeder) transports the original to be read so as to pass a predetermined reading position on the document table 203, and the reading head stops at the reading position. In step 210, the image of the read document may be read.

Although the preferred embodiments of the present invention have been specifically described above, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the gist of the present invention. be able to.

In addition, in the claims and the description of the embodiments described above, words such as "upper", "lower", "left", "right", "front", and "rear" are used for convenience. However, the absolute positional relationship in the state in which the devices are arranged is not limited.

Examples of image forming devices include printers, copying machines, facsimile machines, and multifunction devices. Examples of image reading devices include scanners and multifunction peripherals.

11 image forming apparatus, 12 image forming unit, 13 photosensitive drum, 14 charging roller, 15 LED head, 16 developing roller, 17 transfer roller, 18 toner supply roller, 19 developing blade, 20 toner cartridge, 21 transfer unit, 21a transfer belt drive roller, 21b transfer belt driven roller, 24 paper storage cassette, 26 transfer belt, 27 cleaning blade, 28 fixing device, 29 heating roller, 30 backup roller, 34 belt cleaning blade, 35 belt cleaner container, 40 recording paper, 41 paper guide, 42 paper guide, 43 hopping roller, 45 registration roller pair, 46 transport roller pair, 47 discharge roller pair, 48 paper stacker section, 101 control board, 102 silicone rubber, 103 insulating film, 104 light source board, 105 mask , 105a opening, 106 first lens plate, 106a first lens, 106b optical axis, 107 shield, 107a opening, 108 second lens plate, 108a convex part, 108b convex part, 108c concave groove, 108d second lens, 108e optical axis, 109 fixing member, 110 head holder, 110a inside, 110b through hole, 110c bottom, 110d positioning protrusion, 110e mounting member, 110f long hole, 114L U-shaped groove, 114R U-shaped groove, 115L positioning protrusion, 115R Positioning projection, 116 Long groove, 117 Positioning projection, 118 Long groove, 124 U-shaped groove, 125 Positioning projection, 126 Concave groove, 127 U-shaped groove, 128 Positioning projection, 135 Positioning projection, 138L U-shaped groove, 138R U-shaped groove, 140 Lens unit, 150 LED element, 200 Image reading device, 201 Control circuit, 202 Housing, 203 Document table, 204 Lid, 205 Guide, 206 Drive belt, 207 Stepping motor, 208 Flexible flat cable, 210 Reading head, 211 Light receiving element , 212 light receiving element substrate, 215 cover member, 220 manuscript.

Claims (7)

a first lens array in which a plurality of first lens elements are arranged in a row in an arrangement direction substantially perpendicular to a first optical axis;
a second lens array in which a plurality of second lens elements are arranged in a row in the arrangement direction substantially perpendicular to the second optical axis;
A lens unit including a light shielding member in which a plurality of apertures through which the first optical axis and the second optical axis pass are arranged in a row in the arrangement direction,
The first lens array and the second lens array having substantially the same shape are arranged to face each other so that the first optical axis and the second optical axis coincide,
The lens array is arranged such that the distance between the intermediate image formed by the first lens array and the first lens array is greater than the distance between the intermediate image and the second lens array. lens unit. In the lens unit, in the distance Lo between the first lens array and the light source, the focal length f of the first lens element, and the distance L between the first lens array and the second lens array, an inequality f is satisfied.・Lo/(Lo-f)>L/2
And the inequality f・L/(L-2f)-Lo<f/10
The lens unit according to claim 1, wherein the lens unit satisfies the following. An LED head comprising the lens unit according to claim 1 or 2 and an LED element. An exposure apparatus comprising the lens unit according to claim 1 or 2 and a light emitting element. An image forming apparatus comprising the lens unit according to claim 1 or 2. A reading head comprising the lens unit according to claim 1 or 2 and a light receiving element. An image reading device comprising the reading head according to claim 6.

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