JP2001205845A - Led printer head, rod lens array, and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an easy-to-regulate high resolution LED printer head having a large depth of focus. SOLUTION: Outgoing light from an LED array 2 passes through a micro lens array 6 impinge on a rod lens array 20. diverging angle of the outgoing light from an LED 4 decreases when it passes through a micro lens 12. A light beam passed through the micro lens array 6 further passes through a first prism 40, the rod lens array 20, a space filter 60, and a second prism 42 to focus an image 122 corresponding to each LED 4 on a photosensitive material 120.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an LED printer head using an LED (light emitting diode) array as a light source,
The present invention relates to a rod lens array used for the LED printer head and an image forming apparatus including such an LED printer head.

[0002]

2. Description of the Related Art In order to guide a light beam from an LED array to a photoreceptor, a microlens is provided for each LED of the LED array, and a light beam condensed by the microlens is applied to a photoreceptor drum. An LED printer head configured and an LED printer configured to guide light from individual LEDs to microlenses via respective waveguides and to irradiate a light beam condensed by these microlenses to a photosensitive drum The head is disclosed in
Conventionally known as described in 156320 and the like.

[0003]

Since the divergence angle of the light beam emitted from the LED is large, in order to obtain high resolution in the above-mentioned conventional LED printer head, the LED array and the microlens must be arranged close to each other. It is necessary to make the light emitting area of each LED sufficiently small.

[0004] However, it is difficult to fabricate a minute LED, and even if it is fabricated, the amount of light emitted from the minute LED is so small that it may not be possible to use it as an LED printer head. Further, in the conventional LED printer head, since the divergence angle of the light emitted from the LED is large, the depth of focus is small. Therefore, it is necessary to align the photoconductor and the printer head with each other with high precision. There is also a problem that is difficult. LE
There is also known a configuration in which such a problem is mitigated by providing a waveguide between D and the microlens, but in this case, another problem occurs in that the structure of the LED printer head becomes complicated. The present invention has been made to solve such a problem, and an object of the present invention is to increase the depth of focus of an LED printer head and to facilitate adjustment during assembly.

[0005]

Means for Solving the Problems In order to solve the above problems,
The LED printer head according to the present invention includes a light source array composed of a plurality of LEDs arranged in an array and a plurality of rod lenses arranged in an array, and forms light from each LED on a predetermined surface. Erect imaging rod lens array; and means for reducing the divergence angle of light rays from each LED incident on the erect imaging rod lens array to be smaller than the numerical aperture of the erect imaging rod lens array. It is characterized by having.

According to this, since the spread angle of the light beam from each LED incident on the erect image forming rod lens array is small, the resolution is improved, and the depth of focus on the photoreceptor surface is increased. The positioning accuracy with respect to the photoreceptor is relaxed, a high-quality image without defocus can be formed, and the assembly of the apparatus becomes easy.

In this case, it is preferable that the spread angle of the light beam from each LED incident on the erecting image-forming rod lens array is in the range of 1.35 ° to 5.5 ° in half angle. In this range, the beam diameter of the light beam does not increase due to the diffraction of the lens, and the effect of improving the resolution is great.

As a rod lens array used in the LED printer head, a first optical member and a second optical member are provided on a light incident end face and a light exit end face of a rod lens array composed of a plurality of rod lenses arranged in an array. Are respectively disposed, the first optical member and the second optical member,
It has such a refractive index that the position of the apparent light emitting point of the light beam emitted from one light source and transmitted through the first optical member is shifted from the position of the light source in a direction perpendicular to the longitudinal direction of the rod lens array. It is preferable to use a rod lens array characterized by the above.

According to this, the incident angle of the light beam incident on the light incident end face of the rod lens array is small, and the resolution can be improved. The first and second optical members can be composed of triangular prisms.

Instead of this rod lens array, in a rod lens array composed of a plurality of rod lenses arranged in an array, when one period length of a light beam propagating in the rod lens is P, the rod lens array At least one of the light incident end face and the light emitting end face of
A spatial filter in which a periodic light transmission pattern is formed is disposed at a position of length P / 4 from the end face in the rod lens array, and the periodic light transmission pattern of the spatial filter is
The light is emitted from a plurality of light emitting sources arranged periodically, is incident on a light incident end face of the rod lens array, and simulates a periodic image pattern formed at the position of the spatial filter. Rod lens array can be used.

In this rod lens array, the image blurred due to the lens aberration is corrected by a spatial filter having the same pattern as the periodic spatial pattern of the image, and formed into an image. Can be

[0012] The LED printer head of the present invention including the light source array composed of a plurality of LEDs arranged in an array and the rod lens array of the present invention has a structure in which each LED has a width larger than the width of the light source array extending in the longitudinal direction. Preferably, it is formed so that the length extending in a direction perpendicular to the longitudinal direction is longer.

By doing so, the divergence angle of the light beam incident on the rod lens array is small, so that the light emitting area of the LED can be increased and the light emission amount of the light source can be increased without lowering the resolution.

The image forming apparatus according to the present invention is the image forming apparatus according to the present invention.
An ED printer head, and a photoreceptor on which an image is formed by exposing with a light beam from the LED printer head;
And a developing device for developing an image formed on the photoreceptor. In this case, when a plurality of photoconductors, LED printer heads, and developing units are provided for each color to form a plurality of images of different colors, the developing units are connected to the image forming apparatus to facilitate removal of the developing units. Are preferably arranged in the height direction.

[0015]

FIG. 1 is a perspective view of an optical system according to an embodiment of the LED printer head of the present invention. The emitted light from the LED array 2 which is the light source array
4 through the microlens array 6 having the microlenses 12 corresponding one-to-one to the rod lens array 20.
Incident on. The rod lens array 20 is formed by arranging a plurality of rod lenses 30 each having a refractive index distribution formed symmetrically with respect to the center. It is an image. The spread angle of the light emitted from the LED 4 is reduced by transmitting the light through the microlens 12. As described above, the microlens array 12 functions as an optical member that reduces the spread angle of the light emitted from the LED 4. A first prism 40 and a second prism 42 are provided on the light entrance surface and the light exit surface of the rod lens array 20, respectively. In addition, rod lens array 2
A spatial filter 60 in which the light transmittance changes depending on the position is provided in 0. The light transmitted through the microlens array 6 is reflected by the first prism 40 and the rod lens array 2
0, the light passes through the spatial filter 60, and the second prism 42, and an image 122 corresponding to each LED 4 is formed on the photoconductor 120.

Next, the configuration and function of each part of the optical system will be described in detail.

First, the LED array 2 and the microlens array 6 will be described with reference to FIGS. FIG. 2 is a sectional view of the LED array 2 and the microlens array 6. A microlens array 6 composed of a plurality of microlenses 12 formed in advance on a glass substrate 16 at the same interval as the LEDs 4 is adjusted so that the LEDs 4 come to the center of the microlenses 12, and is adhered and fixed on the LED array 2. I do. The LED array 2 and the microlens array 6 constitute an LED array head. When the distance from the surface of the microlens 12 to the LED 4 is L, it is desirable that the first focal length f of the microlens 12 be selected such that f> L (1). By doing so, L
The spread angle of the light beam from the ED 4 is reduced by the micro lens 12. Assuming that the cycle of the LED 4 in the LED array 2 is a, if the beam divergence angle α (half angle) from the LED 4 is L · tan α> a / 2 (2), the light beam from the LED 4 is transmitted to the adjacent microlens 12. Light enters and becomes stray light. In order to suppress this stray light, the microlens array 6 is provided with a black shielding portion 14. Light rays having a large divergence angle among the light rays emitted from the LED 4 are absorbed by the shielding portion 14 and do not go out. However, light rays incident on lenses other than the opposing microlenses 12 have a large divergence angle, and even if they enter the rod lens array, they are absorbed in the rod lens array and hardly pass through the rod lens. In the case where the above problem does not occur, it is not necessary to provide the shielding portion 14. When the microlens array 6 is made thinner and closer to the LED array 2, the light beam having a large divergence angle is totally reflected on the surface of the microlens 12 and does not come out. Therefore, it is not necessary to provide the shielding portion 14. FIG. 3 shows the relationship between the divergence angle of the light beam incident on the rod lens array 20 and the MTF of the rod lens array 20 when a test line pattern having a period of 1/24 mm is collected. A line pattern having a period of 1/24 mm corresponds to a resolution of approximately 1200 dpi. The rod lens array 20 used here has an aperture angle of 11.8 °, a lens element diameter of 1.1 mm, and a lens length of 1
6.3 mm, two lens rows. The first prism 40, the second prism 42, and the spatial filter 60 in FIG. 1 are not provided. MTF of rod lens array 6
Is the maximum value of the light intensity on the light-converging surface is Imax, and the minimum value is Imax.
min

[0018]

(Equation 1) Which indicates the resolution of the lens. It can be seen that the MTF once decreases as the beam divergence angle is reduced, but the MTF increases when the beam divergence angle is further reduced to 5.5 ° or less, thereby improving the resolution. That is, by setting the beam divergence angle from the LED 4 to 5.5 ° or less using the microlens array 6, the resolution can be improved as compared with the case where the microlens array 6 is not used. However, when the divergence angle of the beam is further reduced, the beam diameter of the condensing portion increases due to the diffraction effect of the lens even when the lens has no aberration. When a beam from a point light source having a wavelength λ is condensed at an angle α by a lens, the beam diameter at the light condensing portion becomes approximately λ / sin α due to diffraction. Therefore, in order to separate the LED 4 and form an image using the rod lens array 20, the beam divergence angle β
Assuming that the period of the array 2 is a, it is necessary to satisfy λ / sin β <a (4). Period a (mm) of LED array 2
And the resolution N (dpi: dot per inch), there is a relationship of a = 25.4 / N (5), so that the resolution can be increased at a wavelength of about 750 nm generally used in the OPC photoconductor. 1200d
In order to obtain pi, the beam spread angle β needs to be 2 ° or more. According to equation (4), if the wavelength is short, the LED
Can be made smaller. For example, at a wavelength near 500 nm where the sensitivity is high with an amorphous silicon photoreceptor, the beam spread angle β may be set to 1.35 ° or more. From the above, the beam divergence angle is 1.35 ° to 5.5.
°, preferably in the range of 2 ° to 5.5 °. Here, the beam divergence angle is a value at a half angle, and is defined as an angle at which the intensity becomes 1 / e ² with respect to the maximum light intensity.

FIG. 4 shows light emission patterns when the microlens array 6 is used and when it is not used in the above optical system. By using the microlens array 6, the beam divergence angle is 4 °. By using the microlens array 6, light rays are collected in the center direction, and the center intensity is improved. The aperture angle of the rod lens array 20 is usually in the range of 4 to 20 °, and the improvement of the central strength as described above allows the rod lens array 20 having a small numerical aperture to be formed.
In, the amount of light transmitted through the rod lens array 20 can be improved as compared with the case where the microlens array 6 is not used.

FIG. 5 shows the relationship between the defocus amount (deviation from the in-focus position) on the photoconductor side and the MTF when the LED array 2 is imaged by the rod lens array 20 at this time. The used LED array 2 is for 1200 dpi (L
(ED interval: 21.2 μm) and the size of the light emitting portion is 12 μm.
m × 12 μm. This MTF is a non-lit one L
This is a case where two adjacent LEDs on both sides of the ED are turned on. By using the microlens array 6, both resolution and depth of focus are improved. MTF is 0.
Assuming that the range of 5 or more is the depth of focus, the depth of focus is increased about 1.6 times by using the microlens array 6. By increasing the depth of focus in this way, the LED array 2 and the rod lens array 6, and the rod lens array 6 and the electrophotographic photosensitive member 120 which is an image-receiving member
Alignment with the other is facilitated.

Table 1 shows the unevenness in the amount of light in the lens array direction of the rod lens array 20 and the spatial variation of the resolution when the microlens array 6 is used and when it is not used. As shown in Table 1, it can be seen that reducing the beam divergence angle using the microlens array 6 also has the effect of reducing unevenness in light quantity and variation in resolution.

[0022]

[Table 1] In the above optical system, since the distance between the LED array 2 and the micro lens array 6 is short, the apparent position of the light emitting point of the LED 4 with respect to the rod lens array 20 hardly changes. Further, since the distance between the rod lens array 20 and the photoconductor is short, even if the positional relationship between the LED 4 and the microlens 12 is slightly shifted, the light condensing position on the photoconductor hardly changes. Therefore, the LED 4 and the micro lens 12
The accuracy of the positioning is not strict and adjustment is easy.
In the above optical system, the LED array 2 and the microlens array 6 which were separately manufactured were attached.
The microlens array 6 may be formed directly on the array 2 using an ultraviolet curable resin or the like.

In the above optical system, the beam divergence angle from the LED 4 is reduced by using the microlens array 6. However, when the light amount of the LED 4 is sufficient, an opening is provided instead of the microlens array 6 to reduce the divergence angle. You may make it restrict. In addition, a surface emitting laser (VCSE)
A light source array having a small divergence angle such as L) can also be used. In the VCSEL, a divergence angle of 3 to 5.5 ° (half angle) is realized, and a microlens array is not required and can be used as it is.

The improvement of the resolution and the depth of focus of the LED printer head due to the reduction of the beam divergence angle, which is an advantage of the above optical system, can also be obtained by using a conventional rod lens array conventionally used for the rod lens array 20. It is. The advantages of the above optical system such as improvement in resolution and depth of focus are as follows.
Can be obtained at any resolution, but especially at 1200 dpi
The effect is great when applied to the above printer. By reducing the beam divergence angle as in the above optical system,
Even if a lens having a small take-in angle is used, the light transmission efficiency can be increased, so that the distance from the LED array to the photoconductor can be increased. Further, the lens that forms an image of light from the LED array need not be limited to the rod lens array, but may be any lens that can form an object at the main plane position on the incident side on the main plane on the emission side at the same magnification as the erect. For example, a lens in which two lens arrays are opposed to each other may be used.

In the above optical system, a combination of an LED array head and a rod lens array is used as an LED printer head. However, the present invention is not limited to a printer. Can also be applied.

Next, a first example of the rod lens array of the present invention will be described.
Will be described with reference to FIGS. 6 to 10. FIG. FIG. 6 is a perspective view of the rod lens array 20 according to the first embodiment. A first prism 40 and a second prism 42 each having a triangular prism are attached to the light incident surface 26 and the light exit surface 28 of the rod lens array 20, respectively.

The function and shape of the prism will be described with reference to FIG. FIG. 7 shows the rod lens array 20 and the
FIG. 3 is a cross-sectional view illustrating a positional relationship between one prism 40 and an LED 4. The light emitted from the LED 4 is transmitted to the first prism 40
The light is refracted by the inclined surface 44 and enters the rod lens array 20. The light beam emitted from the light source position O and incident on the rod lens array 20 has the original light source position O in the x-axis direction.
, But a virtual light source O ′ in the y-axis direction.
Can be regarded as light rays emitted from.

If the first prism 40 is not provided, light rays incident on the rod lens 30 are off-axis rays with respect to the rod lens 30, so that the rod lens 30 causes aberration. In the case of the rod lens array arranged in two rows, the virtual light source position O ′ in the case where the first prism 40 is provided is set in or near the plane including the center of each rod lens row, so that each rod lens 30 Can be relaxed, and the aberration caused by the rod lens 30 can be reduced. The diameter of the rod lens 30 is D,
When the refractive index of the prism is n and the working distance of the rod lens array 20 is z, the angle θ between the inclined surface and the bottom surface of the first prism 40 is

[0029]

(Equation 2) By setting so as to satisfy the condition, the virtual light source O ′ can be present in a plane including the center of each rod lens row. When the first prism 40 having a refractive index of 1.5 is used for the rod lens array 20 with D = 1.1 mm and z = 7.8 mm, the virtual light source is set by setting the angle θ to 6.9 °. O ′ may be present in a plane including the center of each rod lens row. Rod lens array 20
The range of L desirable for relaxing the angle of the ray incident on the lens and reducing the aberration is indicated by a letter.

[0030]

(Equation 3) By providing the second prism 42 having the same shape as the first prism 40 on the emission side of the rod lens array 20, the astigmatism of the x-axis and the y-axis caused by the first prism 40 is eliminated, and the light is emitted from the rod lens array 20. The beam that is
Light is condensed on an image point corresponding to the light source position O.

In the LED array row shown in FIG.
The width of D4 is W and the length is L. FIG. 9 shows the change of the MTF when the length L of the LED 4 is changed for the image of the LED array condensed by the rod lens array with a prism. The LED array is for 1200 dpi and LED4
Is 21.2 μm. Also, the width W of the LED 4
Is 12 μm.

FIG. 9 shows an MTF when two LEDs 4 adjacent to both sides of one non-lighted LED of the LED array are lighted. When the length L of the LED 4 is 12 μm or more, it is understood that the use of a prism improves the resolution. If the length L of the LED 4 is within 28 μm, the resolution does not decrease and is substantially constant. Therefore, it is desirable that the length of the LED 4 is 28 μm or less. As described above, the rod lens array having a prism is
If it is used when the length of 4 is large, it is effective in terms of resolution. Increasing the area of the light emitting part of LED4
When it is possible to increase the amount of light emission of
It is possible to increase the amount of light by lengthening the ED4.
In the above embodiment, by using a light refracting member such as a prism, the LED length can be increased to 2.3 times the LED width. Since the amount of light emitted from the LED is proportional to the area of the light emitting portion of the LED, the amount of light emitted can be increased by 1.5 times if the length of the LED is 1.5 times the width of the LED. In the printer head for 1200 dpi, when the LED width is 12 μm when the prism is not used, the length of the LED is reduced to 18 μm by using the prism.
m or more.

In the first embodiment of the rod lens array, the astigmatism generated in the first prism 40 is corrected by the second prism 42, but cannot be completely removed. Causes astigmatism in which the focal position is slightly different. This astigmatism can be corrected by using a concave cylindrical lens 48 between the rod lens array 20 and the LED 4 as shown in FIG.
Alternatively, instead of the concave cylindrical lens 48, y
Astigmatism can also be corrected by using a parallel flat glass plate inclined in the axial direction between the rod lens array 20 and the LED 4.

Next, a second embodiment of the rod lens array will be described with reference to FIG. FIG. 11 is a cross-sectional view of the rod lens array 20 according to the second embodiment. Second
In this embodiment, the prism is divided into a plurality of parts to form a sheet-like divided prism 46. The angle of the inclined surface of the split prism 46 may be in the same range as the angle of the prism of the first embodiment. Further, it is desirable that the width of the split prism 46 be wide enough to prevent diffraction. Alternatively, it is desirable to adjust the interval between the prisms so that the angle of diffraction and the angle of refraction are substantially equal. A split prism having the same shape is also provided on the exit side of the rod lens array 20. In the first embodiment of the rod lens array, the astigmatism generated in the prism cannot be completely removed, and the focal positions are different between the x-axis and the y-axis, and the improvement in resolution is not so large. However, in the second embodiment, since the prism can be made thinner by using the split prism 48, this astigmatism can be reduced, and the resolution can be greatly improved.

Next, a third embodiment of the rod lens array will be described with reference to FIGS. FIG. 12 shows the third
It is sectional drawing of the rod lens array 20 which concerns on embodiment. In the third embodiment, the rod lens array 20 is divided into a first rod lens array 22 and a second rod lens array 24, and a spatial filter 60 is provided between the first rod lens array 22 and the second rod lens array 24. Have been placed. Light rays from the LED array 2 enter the first rod lens array 22, pass through the spatial filter 60, and are collected by the second rod lens array 24. The length of the second rod lens array 24 is one of the rod lenses 20.
When the cycle length is P, P / 4 is set.
The one-period length P of the rod lens 20 is represented by the following equation, where A is the refractive index distribution constant of the rod lens.

[0036]

(Equation 4) Next, the function of the spatial filter 60 will be described. In the rod lens array 20, a Fourier image is formed at the position at a distance P / 4 from the light incident surface 26 of the rod lens array 20 by performing a Fourier transform on the intensity distribution of the object. LED array 2
Since the LEDs 4 are arranged periodically, a Fourier image when all the LEDs 4 are turned on is also formed as a periodic image. Similarly, the rod lens array 2 is located at a distance P / 4 from the light exit surface 28 of the rod lens array 24 toward the light source.
A Fourier image of the image 122 formed at 0 is formed. L
In the ED printer head, the image of the LED array 2 is erect and formed one-to-one by using the rod lens array 20. Therefore, the light incident surface 26 of the rod lens array 20 is theoretically used.
, And the same Fourier image is formed at a position at a distance P / 4 from the light exit surface 28.

In actuality, the LED array 2 is changed due to the transmission characteristics of the rod lens array 20 with respect to the spatial frequency, aberrations, and the like.
An image is formed which is more deteriorated than the Fourier image described above, but this deterioration is particularly large on the exit side of the rod lens array 20. Therefore, in order to obtain a high-resolution image of the LED array 2, the distance P from the light exit surface 28 of the rod lens array 20.
A spatial filter 60 created using a mask having the same period as that of the LED array 2 is installed at the position of / 4. Since the image blurred by the aberration of the rod lens array 20 is corrected and formed by the spatial filter 60, an image with high resolution can be obtained.

Hereinafter, a method for manufacturing the spatial filter 60 will be described with reference to FIGS. FIG. 13 is a diagram showing an arrangement of a mask and a photosensitive member for producing a spatial filter. Second rod lens array 2 of length P / 4
The mask 68 is arranged at a position separated from the reference numeral 4 by the working distance of the rod lens array 20. The mask 68 has a pattern having a period equal to the period of the LED array. A photosensitive member 74 is arranged on the surface of the second rod lens array 24 opposite to the mask 68. Irradiate light from behind the mask 68,
The photosensitive member 74 is exposed through the second rod lens array 24. After the exposure, development and fixing are performed as needed in accordance with the characteristics of the photosensitive member 74.

The wavelength of the light source for exposure needs to be a wavelength at which the photosensitive member 74 is exposed, but is preferably close to the wavelength of the LED array used. Instead of using the mask 68, exposure can be performed using a laser array or the like. In addition, as the photosensitive member 74, a photographic film, a resist, or the like can be used. In the case of a photographic film, after being exposed to the second rod lens array 24 and exposed, the film is developed and fixed while being attached to the second rod lens array 24. In the case of a photographic film, the density of the Fourier image of the mask 68 can be recorded, and the Fourier transform image of the mask can be recorded more faithfully. After forming the spatial filter 60,
One rod lens array 22 and second rod lens array 2
Adjust the position of 4 and paste.

When a light refracting member such as a prism is used as in the first embodiment of the rod lens array, the spatial filter 60 may be manufactured using the light refracting member. When attaching a separately manufactured spatial filter to the rod lens array, it is necessary to align the spatial filter and the rod lens array with very high accuracy. Here, the second rod lens used for the rod lens array 20 is used. Since the photosensitive member 74 is exposed through the array 24 to form the spatial filter 60, no alignment between the spatial filter 60 and the second rod lens array 24 is required.

Next, a method of manufacturing a spatial filter using a resist will be described with reference to FIG. FIG. 14 (a)
Shows a cross section of the mask 68 when the spatial filter 60 is manufactured. As shown in FIG. 14B, a resist 62 is formed on the surface of the second rod lens array 24 opposite to the mask 68.
Is applied and exposed through a mask 68. Here, a negative resist 62 is used, and as shown in FIG. 14C, the exposed portion 64 of the resist 62 remains after development. Subsequently, as shown in FIG.
As shown in (e), the exposed portion 64 of the resist 62 is removed to form a spatial filter 60.

When the negative type resist 62 is used,
The portion irradiated with the light from the mask 68 is the spatial filter 6.
It becomes a light transmitting portion of 0. When the light irradiating part from the mask becomes the light transmitting part of the spatial filter 60 as described above, in order to record a Fourier image that forms a high-resolution image by the spatial filter 60, FIG. It is desirable that the width d of the light transmitting portion 70 of the mask 68 is smaller than the width s of the light shielding portion 72. When using a positive resist,
The relationship between the width d of the transmitting part 70 and the width s of the light shielding part 72 may be reversed. When the resist does not transmit the light of the wavelength of the LED array and blocks the light by the resist itself without using the light blocking member, the relationship between the width d of the transmitting portion 70 and the width s of the light blocking portion 72 is also reversed. Good.

In the above embodiment, the spatial filter 6
0 is the distance P from the light exit surface 26 of the rod lens array 20.
The resolution is further improved by providing the spatial filters 60 at two positions, which are P / 4 from the light incident surface 24 and P / 4 from the light exit surface 26. In addition, even if the spatial filter 60 is used only on the light incident side, the effect is small compared with the case where the spatial filter 60 is used on the light emitting side, but the effect of high resolution can be obtained.

Next, the structure of the LED printer head of the present invention will be described with reference to FIG. FIG. 15 shows the LE of the present invention.
LED using D array head and rod lens array
FIG. 3 is a perspective view of a printer head. LED array 2 and LE
The driver circuit 100 for driving the D array 2 is mounted on the wiring board 102. This driver circuit is
In order to make the light emission luminance of D uniform, a circuit for correcting the variation of the light emission luminance of each LED is provided. It is also possible to provide a circuit capable of outputting gradation. LED
Each LED of the array 2 and the driver circuit 100 are electrically connected through a wiring board 102. In addition, the driver circuit 100 receives L from the outside through the wiring board 102.
A signal for driving the ED array is input. The wiring board 102 is fixed to the base 104, and the heat generated by the LED array 2 is released to the outside by the radiation fins 106 of the base 104. The rod lens array 20 is fixed to a lens holder 108, and the lens holder 108 is fixed to a base 104. The rod lens array 20 is adjusted so as to be at a predetermined position and distance from the LED array head 130.
08.

The above-described LED printer head uses at least one of the LED array head and the rod lens array of the present invention, and can constitute a high-resolution LED printer head. When an LED array head using a microlens array is used as the LED array 2, the depth of focus of the rod lens array 20 is increased, so that the position adjustment between the LED array 2 and the rod lens array 20 becomes easy. In addition, rod lens array 2
Since the unevenness of the light amount and the fluctuation of the resolution in the lens row direction of 0 become small, the range of the luminance correction of each pixel in the driver circuit becomes narrow, and the adjustment becomes easy, and in some cases it becomes unnecessary. In addition, when the rod lens array of the present invention is used, a high-resolution image can be formed on the photoreceptor by using a conventional LED array.

Next, an embodiment of an image forming apparatus using the LED printer head of the present invention will be described with reference to FIG. FIG. 16 is a schematic sectional view of the color image forming apparatus. The main body includes four photoconductors 201a, 201b, 201c, and 2 corresponding to four color toners of yellow, magenta, cyan, and black necessary for forming a color image.
01d are arranged vertically. Further, the intermediate transfer belt 202 stretched vertically is moved to the photosensitive members 201a and 201.
b, 201c and 201d. Each photoconductor 20
1a, 201b, 201c, and 201d, opposite to the intermediate transfer belt 202, the photosensitive members 201a, 201b, and 2
Exposure devices 204a, 204b, 204c, and 204d for exposing the surfaces of 01c and 201d to form electrostatic latent images, and developing devices 205a and 205 for visualizing the electrostatic latent images with toner
b, 205c, and 205d are vertically stacked. The LED printer head of the present invention is used as the exposure device 204.

Each photoconductor 201a (201b, 201c,
201d), a charger (not shown) for charging the photoconductor 201, and an exposing device 204a (204b, 204c)
204d), developing units 205a (205b, 205c, 2
05d), the intermediate transfer belt 202, and the photoconductor 201a (2
01b, 201c, 201d) are provided with an erase lamp (not shown) for removing electricity from the surface and a photoreceptor cleaner (not shown) for cleaning residual toner. On the outer periphery of the intermediate transfer belt 202, an image sensor 211 for detecting a displacement of the toner image of each color, a toner charger 212 for charging the toner, a transfer unit 213 for transferring the toner image on the intermediate transfer belt 202 to a sheet, and a sheet To the intermediate transfer belt 202
Paper remover 214 and intermediate transfer belt 202 that separate from paper
An intermediate transfer belt cleaner 215 for cleaning the upper toner is provided. Furthermore, on the paper transport path,
A paper cassette 216, a paper feeding mechanism 217, and a fixing device 219 are arranged. In the above image forming apparatus, the exposure device 2
Since the LED printer head of the present invention is used as 04, a small and high-resolution exposure unit 204 can be configured.

In an image forming apparatus using an optical scanning optical system,
In order to scan light by the paper width, it is necessary to keep a distance from the polygon mirror to the photoconductor, and the thickness of the exposure unit is required due to the height of the polygon motor that rotates the polygon mirror and the height of the fθ lens. Miniaturization has its limits. On the other hand, an image forming apparatus using an LED printer head does not require a large lens such as an fθ lens or an optical scanning mechanism and has a short optical path length, so that the size of the exposure device can be significantly reduced. Therefore, the size of the image forming apparatus using the exposure device can be reduced.

In the above-described image forming apparatus, since the elements around the photosensitive member are arranged in a concentrated manner below the center of the photosensitive member, the exposing unit 4 is arranged away from the photosensitive member, and each process around the photosensitive member is performed. It is desirable to increase the layout allowance. To this end, it is effective to increase the lens length of the LED array exposure device or to increase the working distance of the lens. In an LED printer head using an LED array head with a small beam divergence angle, a sufficient light quantity and resolution can be obtained even if a rod lens array with a small aperture angle is used, so that the working distance of the rod lens array can be increased. .

As described above, by using the LED printer head of the present invention, a color image forming apparatus using a plurality of photoconductors can be downsized. In particular, in the configuration in which the developing devices are arranged in the height direction and the exposing devices are arranged corresponding to the respective developing devices as in the above-described device, the size of the device, particularly, the height of the device can be reduced. .

Next, a printing sequence of the image forming apparatus will be described. When a print command is first sent to a controller (not shown), driving and charging of the intermediate transfer belt 202 and the photoconductors 201a, 201b, 201c, and 201d are started. Subsequently, the photoconductor 201a that is in contact with the intermediate transfer belt 202 at the most upstream portion is image-exposed by the exposure device 204a, the electrostatic latent image is developed by the developing device 205a, and the toner image is transferred onto the intermediate transfer belt 202. Almost at the same time, image exposure is performed on the photoconductor 201b immediately below, and development and transfer are performed. In the exposure of the photoconductor 201b, an image formed on the photoconductor 201b is first exposed to the photoconductor 20b.
The process is started at a timing that exactly overlaps with the image formed in 1a. In this process, an image in which two color toner images are superimposed on the intermediate transfer belt 202 is formed. Similarly, exposure, development, and transfer are performed on the photoconductors 201c and 201d for the third color and the fourth color, and a full-color image in which toner images of respective colors are superimposed on the intermediate transfer belt 202 is formed. The full-color image on the intermediate transfer belt 202 is transferred to a recording medium such as a sheet by a transfer unit 213 and fixed by a fixing unit 219.

The image forming apparatus employs a simultaneous printing method in which an image is simultaneously formed using four photosensitive members corresponding to yellow, magenta, cyan, and black toners. Furthermore, since the color toner images formed by the photoconductors 201 are superimposed on the intermediate transfer belt 202 and then collectively transferred to a final recording medium such as paper, the entire apparatus can be downsized.

In the above image forming apparatus, the process speed, which is the moving speed of the photosensitive member, the intermediate transfer belt, and the recording medium, is set to 10
0 mm / s, and the printing density was 1200 dpi (dot / dot).
Inches). Assuming that the process speed is 100 mm / s, the printing speed is about 16 PPM and about 24 PPM when A4 size paper is passed vertically and horizontally, respectively. In addition, by setting the printing density to 1200 dpi, a high-quality image can be obtained. In particular, a high-quality image can be obtained when printing a photograph.

In order to realize a process speed of 100 mm / s and a print density of 1200 dpi in an image forming apparatus using an optical scanning optical system, the reference frequency for modulating a semiconductor laser as a light source is 100 MHz or more. further,
In the case of a six-plane polygon mirror generally used in a monochrome printer, the number of rotations of the polygon mirror is 48,000. It is very difficult to use a reference frequency of 100 MHz or more. Usually, a multi-beam system is used in which a plurality of laser beams are used to lower the reference frequency. In order to rotate the polygon mirror stably at a high speed such as 48,000 rotations, it is necessary to use a large polygon motor. The number of rotations of the polygon mirror can be reduced by increasing the number of faces of the polygon mirror, but the optical path length needs to be increased. As described above, if an image forming apparatus using an optical scanning optical system is to achieve high speed, high resolution, and wider paper, the size of the exposure device will be increased. Therefore, if an LED printer head is used for realizing high speed, high resolution, and wider paper, the effect of reducing the size of the image forming apparatus is great. In particular,
At a printing density of 1200 dpi or more, the process speed is 40
mm / s, the reference frequency in an exposure device using an optical scanning optical system becomes 50 MHz or more, and the difficulty increases. Therefore, a great effect can be obtained particularly when the LED printer head is used in this range.

In the above apparatus, a plurality of photoconductors 201a, 201b, 201c, 20 on which toner images of respective colors are formed are formed.
1d is made into a unit, and the entire unit is replaced. In this way, by adjusting the accuracy of the photoconductor unit at the time of manufacturing, each of the photoconductors 201a, 201b, 201
The intervals and parallelism between c and 201d can be arranged with high accuracy, and the accuracy can be maintained. Furthermore, even when the user replaces the photoconductor, each photoconductor 201a, 20
Since the photoconductor units 1b, 201c, and 201d are exchanged as an integrated photoconductor unit, the spacing and parallelism between the photoconductors can be stabilized.

The positioning of the toner of each color image described above is performed with respect to each of the photosensitive members 201a, 201b, 201c,
Exposure devices 204a, 204b, 204 for exposing 201d
The placement accuracy of c and 204d is also important. In the image forming apparatus, each of the exposure units 204a, 204b, 204c, 20
4d is fixedly arranged on the main body housing. Each of the exposure devices 204a, 204b, 204
c and 204d can be precisely arranged, and variations can be reduced. In particular, since a small LED printer head is used for the exposure device, the displacement due to vibration and impact after assembly is small.

Further, in the above-described image forming apparatus, the developing units 205a, 205b, 205c, and 205d of the respective colors are arranged at the horizontal positions with respect to the photosensitive members 201a, 201b, 201c, and 201d, and are slid in the horizontal direction to be detached. And In the apparatus shown in FIG. 16, each of the exposure units 204a, 204b, 204c,
The developing devices 205a, 205b,
05c and 205d, and the photoconductor 201 inside
Although a, 201b, 201c, and 201d are developed, replacement is easy with the above configuration.

The above-described image forming apparatus is capable of recording high-quality color images such as photographs, has a high speed capable of printing a large amount of business documents in a short time, and has a size and a price that can be easily installed in an office environment. That is, the replacement of consumables is easy at the same time as being small in size and low in price.

Although the embodiment of the electrophotographic printer has been described as an image forming apparatus, the present invention can be applied to various image forming apparatuses for optically forming and recording an image, such as a plate making apparatus for a printing press.

[0060]

According to the present invention, an LED printer head having a large depth of focus and easy adjustment can be provided. According to the present invention, an LED printer head with high resolution and a rod lens array suitable for such an LED printer head are also provided. According to the present invention, there is further provided a small high-resolution image forming apparatus provided with such an LED print head.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an optical system of an LED printer head according to the present invention.

FIG. 2 is a sectional view of an LED array and a microlens array of the LED printer head of the present invention.

FIG. 3 is a diagram showing a relationship between a divergence angle of a light beam incident on a rod lens array of the LED printer head of the present invention and an MTF when a test line pattern is imaged.

FIG. 4 is a diagram showing a light emission pattern in the LED printer head of the present invention.

FIG. 5 is a diagram showing the relationship between the defocus amount on the photoconductor side of the LED printer head of the present invention and the MTF when an image of the LED array is formed by the rod lens array.

FIG. 6 is a perspective view showing a first embodiment of the rod lens array of the present invention.

FIG. 7 is a diagram illustrating the function and shape of a prism in the rod lens array according to the first embodiment of the present invention.

FIG. 8 is a diagram showing dimensions of an LED array.

FIG. 9 is a diagram showing a change in MTF when the length of the LED is changed in the first embodiment of the rod lens array of the present invention.

FIG. 10 is a sectional view showing an optical system for correcting astigmatism according to the first embodiment of the rod lens array of the present invention.

FIG. 11 is a sectional view of a rod lens array according to a second embodiment of the present invention.

FIG. 12 is a sectional view of a rod lens array according to a third embodiment of the present invention.

FIG. 13 is a diagram showing an arrangement of a mask and a photosensitive member when producing a spatial filter used in a rod lens array according to a third embodiment of the present invention.

FIG. 14 is a diagram illustrating a method of manufacturing a spatial filter according to a third embodiment of the rod lens array of the present invention.

FIG. 15 is a perspective view showing an embodiment of the LED printer head of the present invention.

FIG. 16 is a cross-sectional view illustrating an embodiment of the image forming apparatus of the present invention.

[Explanation of symbols]

2 LED array 4 LED 6 Micro lens array 12 Micro lens 14 Shielding part 16 Glass substrate 20 Rod lens array 22 First rod lens array 24 Second rod lens array 26 Light incident surface 28 Light emitting surface 30 Rod lens 40 First prism 42 Second prism 44 Slope 46 Dividing prism 48 Concave cylindrical lens 60 Spatial filter 62 Resist 64 Photosensitive part 66 Light shield 68 Mask 70 Opening 72 Light shield 74 Photosensitive member 100 Driver circuit 102 Wiring board 104 Base 106 Heat radiating fin 108 Lens holder 120 Electrophotographic photoreceptor 122 LED image 201a, 201b, 201c, 201d Photoreceptor 202 Intermediate transfer belt 204a, 204b, 204c, 204d Exposure device 205a, 205b, 20 5c, 205d Developing units 210a, 210b, 210c, 210d Belt stretching roller 211 Image sensor 212 Toner charger 213 Transfer unit 214 Paper erasing device 215 Intermediate transfer belt cleaner 216 Paper cassette 217 Paper feed mechanism 219 Fixing device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C162 AE28 AE47 FA17 FA45 FA49 FA50 5C051 AA02 CA08 DA03 DB02 DB21 DB22 DB23 DC04 DC05 DC07

Claims (9)

[Claims] 1. A light source array comprising a plurality of LEDs arranged in an array, and an erecting arrangement comprising a plurality of rod lenses arranged in an array and forming light beams from the LEDs on a predetermined surface. An imageable rod lens array, and means for reducing the spread angle of light rays from each LED incident on the erectable imageable rod lens array to be smaller than the aperture angle of the erectable imageable rod lens array. LED printer head. 2. An LED according to claim 1, wherein said means adjusts a divergence angle of a light beam from each LED incident on the erecting image-forming rod lens array to a half angle of 1.35 ° to 5.5 °. Printer head. 3. A first optical member and a second optical member are respectively disposed on a light incident end face and a light output end face of a rod lens array composed of a plurality of rod lenses arranged in an array, and The optical member and the second optical member are arranged such that the position of an apparent light emitting point of a light beam emitted from one light source and transmitted through the first optical member is perpendicular to the longitudinal direction of the rod lens array from the position of the light source. Rod lens array having a refractive index that shifts in various directions. 4. The rod lens array according to claim 3, wherein said first and second optical members are triangular prisms. 5. In a rod lens array composed of a plurality of rod lenses arranged in an array, when one period length of a light beam propagating in the rod lens is P, the light incident end face of the rod lens array and the light beam A spatial filter having a periodic light transmission pattern formed at a position of length P / 4 from the end surface in the rod lens array on at least one of the emission end surfaces, and a periodic light transmission pattern of the spatial filter is provided. Is a rod simulating a periodic image pattern formed at a position of the spatial filter, which is emitted from a plurality of light emitting sources arranged periodically, is incident on a light incident end face of the rod lens array, and Lens array. 6. An LED printer head comprising: a light source array comprising a plurality of LEDs arranged in an array; and the rod lens array according to claim 3. 7. A light source array comprising a plurality of LEDs arranged in an array and the rod lens array according to claim 3, wherein each LED extends in a longitudinal direction of the light source array. An LED printer head formed so that a length extending in a direction perpendicular to the longitudinal direction is larger than a width. 8. The LED printer head according to claim 1, a photoconductor on which an image is formed by exposing with a light beam from the LED printer head, and a photoconductor. An image forming apparatus comprising: a developing device that develops a formed image. 9. The image forming apparatus according to claim 8, further comprising: a plurality of photoconductors, an LED printer head, and a developing device for each color for forming a plurality of images of different colors. An image forming apparatus arranged in a matrix.