JP2002331705A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus in which an image having high image quality is formed by suppressing variation of beam profile. SOLUTION: Two print heads 14A and 14B for irradiating a photosensitive drum, respectively, with a light beam and forming a latent image are provided while arranging identical lens arrays 24A and 24B in the same direction. When viewed from the direction of the optical axis of a rod lens 32, the light emitting elements 32 of the print head 14A are offset from the center line 36 of the lens array 24A in the direction Z1 (subscanning direction) and the light emitting elements 32 of the print head 14B are offset in the direction Z2. Variation in the beam diameter formed on the photosensitive drum by both print heads 14A and 14B is thereby repeated in units of the pitch of lens diameter but since the beam diameters are shifted mutually by one half of the wavelength (the pitch of lens radius), sum of the diameter of beams projected frpm respective print heads 14A and 14B to the same position on the photosensitive drum 10 approaches a constant value and a good image is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus suitable for a printer head or a dot array printer using an LED (light emitting diode) or an LCD (liquid crystal display element).

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, an LED array in which LED light emitting elements (hereinafter referred to as light emitting elements) are arranged in one row in a main scanning direction has a lens in the main scanning direction. An LED print head that forms a latent image on a photosensitive drum via a lens array arranged in rows or two rows is used.

When a print head is used in an image forming apparatus, there is a great problem that unevenness in the amount of light from the light emitting elements and unevenness in density occur in an image formed due to the characteristics of the lens array. I have.

In general, when the LED light emitting elements are arranged in one row in the main scanning direction with respect to a lens array in which the lenses are arranged in two stages in the sub-scanning direction, the diameter of the beam irradiated on the photosensitive drum becomes smaller than the lens array. Fluctuates in units of the lens diameter pitch. Therefore, if the fluctuation width is large, a streak occurs in the image at the lens radius pitch.

To cope with the above problem, a method of uniformly correcting the light amount of the light emitting element, a method of designing a lens so as to reduce the periodic unevenness due to the lens, and the like have been studied.

Japanese Patent Application Laid-Open No. 2000-71508 (hereinafter referred to as Conventional Example 1) discloses a method for preventing the occurrence of streaks in an image by using two sets of LED print heads and manufacturing errors. Discloses a configuration in which the fluctuation state of the beam profiles is shifted to reduce the fluctuation.

Japanese Patent Application Laid-Open No. 2000-37903 (hereinafter referred to as Conventional Example 2) discloses that, in a color image forming apparatus, when a plurality of colors are overlapped by changing the position of a lens in the main scanning direction for each color. A configuration for canceling the fluctuation of the beam profile and performing good image formation is disclosed.

[0008]

However, the prior art 1 is a method of avoiding an image defect based on a manufacturing error of the LED print head, so that the occurrence of the streak can be avoided in some cases. Is not something that can be reliably avoided.

Further, the conventional example 2 has a disadvantage in that it is impossible to avoid streaks in an image unless each color is superimposed, and there is an inconvenience that use of a single color is not effective. In addition, there is a drawback that the image cannot be used unless a so-called tandem method of superimposing images is used.

Further, in an LED print head provided with a lens array in which lenses are arranged in one or two rows in the sub-scanning direction, since a light beam emitted from the LED light-emitting element is diffused to the lens array, it becomes large in the sub-scanning direction. It is shielded from light and loss of light quantity is large. Therefore, this L
In an image forming apparatus provided with an ED print head, it is difficult to increase the process speed to 150 mm / s or more.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has as its object to provide an image forming apparatus which suppresses fluctuation of a beam profile and improves image quality. It is another object of the present invention to provide an image forming apparatus that achieves high-speed image formation.

[0012]

In order to achieve the above object, according to the first aspect of the present invention, a light source in which a plurality of light emitting elements are arranged in one line in a main scanning direction, and a condensing lens are arranged in a sub scanning direction. A converging lens array that is arranged in a two-tiered stack, and forms a light beam emitted from the light source on the object to be scanned, and the sub-scanning direction as viewed from the optical axis direction of the condensing lens. A first print head and a second print head each having a light emitting element arranged offset from a center line of the condenser lens array in the sub scanning direction, and a first print head arranged along the sub scanning direction of the object to be scanned. In the second print head, the same condensing lens array is arranged in the same direction in the sub-scanning direction, and the condensing lenses are arranged in the same position in the main scanning direction. Wherein the set direction, each of the heating elements so that the opposite direction is arranged.

The operation of the first aspect of the present invention will be described.

When a plurality of heating elements are arranged in a single row in the main scanning direction with respect to a lens array arranged in two stages in the sub-scanning direction, the beam profile is changed by a lens diameter pitch unit in the main scanning. It has been confirmed that the variation state is shifted by a half wavelength by changing the offset direction of the heating element with respect to the center line in the sub-scanning direction of the lens array.

Therefore, the first lens having the same lens array
The print head and the second print head are arranged along the sub-scanning direction of the object to be scanned, the lens array is arranged in the same direction in the sub-scanning direction, and the condenser lens of each print head is arranged in the main scanning direction. By disposing them at the same position and making the offset direction of the light emitting element with respect to the center line in the sub-scanning direction of the lens array opposite to the optical axis direction of the condenser lens, the main scanning is performed by each print head and formed on the object to be scanned. The fluctuation of the beam profile to be performed is shifted by half (half wavelength) of the lens diameter pitch in the main scanning direction. Therefore, the sum of the beam profiles of the respective print heads that irradiate the same position on the object to be scanned approaches a constant, and the fluctuation of the beam profile in the main scanning direction is suppressed, so that good image formation can be performed.

Further, since the object to be scanned is exposed from the two print heads, a sufficient amount of light is secured, and the speed of image formation can be increased.

According to a second aspect of the present invention, there is provided a light source in which a plurality of light emitting elements are arranged in one line in a main scanning direction, and a condensing lens is arranged in a two-stage stack in a sub scanning direction. A light-collecting lens array for forming an image of the light beam on the object to be scanned, and the light-emitting element is moved from a center line in the sub-scanning direction of the condensing lens array in the sub-scanning direction when viewed from the optical axis direction of the condensing lens. A first print head and a second print head that are arranged offset, and the first print head and the second print head that are arranged along the sub-scanning direction of the object to be scanned have the same condensing lens array. In the main scanning direction, the condensing lenses are arranged at the same position while being arranged in the opposite direction in the sub-scanning direction, and the offset direction with respect to the sub-scanning direction center line is in the same direction. Wherein the heating element is disposed.

The operation of the second aspect of the invention will be described.

When a plurality of heating elements are arranged in a single row in the main scanning direction with respect to a lens array arranged in two rows in the sub-scanning direction, the beam profile is changed by a lens diameter pitch unit in the main scanning. It has been confirmed that the variation state is shifted by a half wavelength by changing the offset direction of the heating element with respect to the center line in the sub-scanning direction of the lens array.

Accordingly, the first lens having the same lens array
The print head and the second print head are arranged along the sub-scanning direction of the object to be scanned, and the lens arrays are arranged in the sub-scanning direction so as to face in opposite directions. Arranged at the same position, and by making the offset direction of the light emitting element with respect to the center line in the sub-scanning direction of the lens array in the same direction as viewed from the optical axis direction of the condenser lens, the main scan is performed by each print head and the scan is performed on the object to be scanned. The fluctuation of the formed beam profile is shifted by half of the lens diameter pitch (half wavelength) in the main scanning direction. Therefore, the sum of the beam profiles of the respective print heads that irradiate the same position on the object to be scanned approaches a constant, and the fluctuation of the beam profile in the main scanning direction is suppressed, so that good image formation can be performed.

Further, since the object to be scanned is exposed from the two print heads, a sufficient amount of light is secured, and the speed of image formation can be increased.

The invention according to claim 3 is the invention according to claim 1 or 2
In the invention described above, in the first print head and the second print head, an offset from a center line in the sub-scanning direction of the lens array to the light-emitting element in a sub-scanning direction when viewed from an optical axis direction of the condenser lens. It is characterized by equal amounts.

The operation of the third aspect of the invention will be described.

If the offset amounts are equal, the fluctuation waveform of the beam profile formed on the object to be scanned by each print head becomes an equal waveform shifted by a half wavelength.
Therefore, the sum of the beam profiles at the same position on the scanned object becomes more constant, and good image formation can be performed.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the distance by which the heating element is offset from the center line in the sub-scanning direction of the lens array in the sub-scanning direction is: 0.10mm ~ 0.30
mm.

The operation of the fourth aspect of the present invention will be described.

In the sub-scanning direction, the light emitting element is 0.10 mm to 0.3 mm with respect to the center line of the lens array in the sub-scanning direction.
If it is offset by 0 mm, the fluctuation waveform of the beam profile in the main scanning direction approaches a sine curve,
The sum with the beam profile shifted by a half wavelength in the main scanning direction becomes closer to a constant, and the fluctuation of the beam profile is favorably suppressed.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. The image forming apparatus is a well-known electrophotographic image forming apparatus, and the main part of the present invention is a light source portion that forms a latent image on the photosensitive drum by irradiating the photosensitive drum with light. Since there are features, only the relevant portions will be described.

As shown in FIG. 2, the image forming apparatus includes a charger 12 around a photosensitive drum 10 along a rotational direction.
A light source 14, a developing unit 16, a transfer roller 18, and a cleaner 20 for removing toner remaining on the photosensitive drum 10 are arranged. With this configuration, a latent image is formed on the surface of the photosensitive drum 10 charged by the charger 12 by irradiating light from the light source 14, the latent image is formed into a toner image by the developing device 16, and the toner image is formed by the transfer roller 18. In this configuration, an image is formed by transferring an image to a sheet.

Here, a configuration in which the image is directly transferred to a sheet has been described. However, it is also possible to form a color image by transferring the image to a transfer belt and superimposing images of four colors.

As shown in FIG. 2, the light source 14 is composed of two print heads 14A and 14B arranged along the outer peripheral surface of the photosensitive drum 10. As shown in FIG. 1, the print head 14 </ b> A extends in the rotation axis direction (main scanning direction, arrow X direction) of the photosensitive drum 10 so as to face the outer peripheral surface of the photosensitive drum 10. Array 22A that emits a light beam for image formation with respect to
And a lens array 24A that forms a light beam emitted from the LED array 22A on the photosensitive drum 10, respectively.

Each of the LED arrays 22A is
The LED chips 28 are arranged in one line in the main scanning direction on the end surface 26A of the LED chip 6.
128 light-emitting points (light-emitting elements) 30 are arranged in one line in the main scanning direction at intervals of 0 dpi. Therefore,
On the end face 26A, the light emitting elements 30 are arranged in one line in the main scanning direction. This light emitting element 30 is a self-scanning LED
(SLED), a driver can be externally attached, and the number of electrodes required for each LED chip 28 can be formed with a simple configuration of four or five places.

On the other hand, in the lens array 24A, a refractive index distribution type rod lens (for example, a SELFOC lens (manufactured by Nippon Sheet Glass Co., Ltd.)) 32 has two rows in the rotation direction (sub-scanning direction) of the photosensitive drum 10. The light beams emitted from the light emitting elements 30 of the LED array 22 are imaged on the photosensitive drum 10.

The structure of the print head 14B is substantially the same as that of the print head 14A, and a detailed description thereof will be omitted.

The print heads 14A, 14B have lens arrays 24A, 24A,
Only the relative positional relationship between the LED array 4B and the LED arrays 22A and 22B is different.

Hereinafter, the relative positional relationship between the LED arrays 22A and 22B and the lens arrays 24A and 24B will be described.
This will be described with reference to FIG. 3 as viewed from the optical axis direction of the rod lens 32 (arrow Y direction).

The lens arrays 24A and 24B, which are formed identically, are arranged in the same direction in the sub-scanning direction (arrow Z direction), and the rod lenses 32 are positioned at the same position in the main scanning direction (arrow X direction). It is arranged in.

The print head 14A is such that the light-emitting element 30 is arranged above the center line 36A passing through the center of the lens array 24A in the sub-scanning direction and offset by a distance d (hereinafter, referred to as an arrow Z1 direction). It is.

On the other hand, the print head 14B is arranged such that the light emitting element 30 is offset by a distance d below (hereinafter referred to as an arrow Z2 direction) a center line 36B passing through the center of the lens array 24B in the sub-scanning direction. It was done.

That is, the offset direction of the light emitting element 30 with respect to the center lines 36A and 36B of the lens arrays 24A and 24B is opposite. The center lines 36A, 36
B means each lens array 24A, 2B in the sub-scanning direction.
A line drawn at a position equidistant (= a) from the upper and lower ends of 4B.

The operation of the image forming apparatus thus configured will be described.

First, an LED array in which light-emitting elements are arranged in one line in the main scanning direction, and a rod lens in the sub-scanning direction
When a print head having a lens array stacked in a stack is used, the positional relationship between the center line of the lens array and the light emitting element in the sub-scanning direction, as viewed from the optical axis direction of the lens, and the photoconductor when main scanning is performed The relationship between the fluctuations of the beam diameter on the drum will be described.

That is, when the photosensitive drum is main-scanned using a print head in which the offset amount between the light emitting element and the center line of the lens array in the sub-scanning direction is set as d, the beam diameter on the photosensitive drum is reduced. The fluctuation state is shown in FIGS. 4 (A) to 4 (J).

Here, the horizontal axis represents the position (mm) in the main scanning direction on the photosensitive drum, and the vertical axis represents the beam diameter (μm). The value of d attached to each figure indicates an offset d (mm) from the center line of the lens array in each light source.
The lens diameter D of the rod lens used in this test was 0.845 mm, and the lens radius r was 0.422.
5 mm.

As shown in FIGS. 4A to 4J, the diameter of the beam formed on the photosensitive drum in accordance with the offset d between the light emitting element and the center line of the lens array in the sub-scanning direction. It can be confirmed that the fluctuation state is different.

Here, as shown schematically in FIG. 5, when the offset direction of the light emitting element 30 with respect to the center line 36 is reversed, the fluctuation waveform of the beam diameter is shifted by a half wavelength. Therefore, if the fluctuation waveform of the beam diameter (see FIG. 5A) is close to a sine wave, the fluctuation waveform of the beam diameter shifted by a half wavelength (see FIG. 5B) is superimposed (the sum of the two). As a result, the amplitude of the fluctuation waveform of the beam diameter is greatly suppressed (see FIG. 5C).

Here, in order for the sum of the beam diameters of the two to approach a constant, it is desirable that the fluctuation waveform of the beam diameter approximates a sine curve.
4 mm to 0.30 mm (see FIGS. 4F to 4J), and more preferably 0.15 mm to 0.20 mm.

Therefore, the lens arrays 24A and 24B
The main scanning of the photosensitive drum 10 is performed by the print heads 14A and 14B in which the photosensitive drum 1 and the LED arrays 22A and 22B are arranged in the above-described relative positional relationship.
The fluctuation waveform in the main scanning direction of the beam diameter imaged on zero shifts by half a wavelength. Therefore, print head 1
The sum of the diameters of the beams irradiated from 4A and 14B onto the photoreceptor drum 10 approaches a constant value, the fluctuation of the beam diameter in the main scanning direction is suppressed, and good image formation is achieved.

Even in the arrangement described below, the fluctuation waveform of the beam diameter by the print heads 14A and 14B is shifted by a half wavelength, and the fluctuation of the beam diameter on the photosensitive drum 10 can be suppressed.

That is, as shown in FIG. 6, when the lens arrays 24A and 24B are arranged to face the same direction in the sub-scanning direction, the LED array 2
The light emitting element 30 of the LED array 22B is offset from the center line 36A in the Z2 direction.
0 may be offset from the center line 36B in the Z1 direction.

Further, as shown in FIGS. 7 and 8, when the lens arrays 24A and 24B are arranged to face in the opposite direction in the sub-scanning direction, the LED arrays 22A and
The 2B light emitting element 30 may be arranged so as to be offset in the same direction (Z2 direction or Z1 direction) with respect to the center lines 36A and 36B.

In this embodiment, the print head 1
Since the offset amount d in 4A and 14B is the same, the fluctuation state (amplitude) of the beam diameter becomes the same,
The sum of the beam diameters becomes closer to a constant, and the fluctuation of the beam diameter in the main scanning direction can be suppressed. However, the offset amounts d need not be the same.

Further, the two print heads 14A, 1
Since the latent image is formed by exposing the photosensitive drum 10 using 4B, a sufficient amount of light reaches the photosensitive drum 10 and the process speed of the image forming apparatus can be improved.

Therefore, in the image forming apparatus according to the present embodiment, a high-quality image without streaks can be formed at a process speed of 200 mm / s by the action of suppressing the fluctuation amount of the beam diameter.

In the present embodiment, the photosensitive drum 10
Print head 14 at a different position in the rotation direction of
Although the exposure is performed from A and 14B, as shown in FIG. 9, the exposure may be performed at the same position in the rotation direction.

[0056]

As described above, according to the present invention,
By suppressing the fluctuation of the beam profile, it is possible to form a high-quality image. Further, high-speed image formation can be performed.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part of a light source according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a positional relationship between an LED array and a lens array according to an embodiment of the present invention.

FIGS. 4A to 4J show L for a lens array.
FIG. 9 is a diagram illustrating a state of fluctuation of a beam diameter due to main scanning when the positional relationship of the ED array in the sub-scanning direction is different.

FIGS. 5A to 5C are schematic diagrams illustrating an operation of suppressing the fluctuation width of the beam diameter when the fluctuation state of the beam diameter is shifted by half a wavelength.

FIG. 6 is an explanatory diagram showing a positional relationship between an LED array and a lens array according to another example of the present invention.

FIG. 7 is an explanatory diagram showing a positional relationship between an LED array and a lens array according to another example of the present invention.

FIG. 8 is an explanatory diagram showing a positional relationship between an LED array and a lens array according to another example of the present invention.

FIG. 9 is a schematic configuration diagram of an image forming apparatus according to another example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Photoconductor drum (subject to be scanned) 22 ... LED array 24 ... Lens array 28 ... LED chip (chip) 30 ... Light emitting element 32 ... Rod lens (light collecting lens) 36 ... Center line (center line in the sub-scanning direction)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H04N 1/19 F term (Reference) 2C162 AE28 AE47 AF06 FA04 FA17 FA45 FA50 FA68 5C051 AA02 CA08 DA03 DA06 DB02 DB22 DB29 DC04 DC05 5C072 AA03 BA03 BA17 DA03 DA25 HA01 HA06 HA20 XA04 5F041 AA39 DA13 EE12

Claims (4)

[Claims] 1. A light source in which a plurality of light-emitting elements are arranged in one line in a main scanning direction, and a condensing lens are arranged in a two-stage stack in a sub-scanning direction, and a light beam emitted from the light source is scanned by a light source. A light-collecting lens array that forms an image on the light-emitting element, and the light-emitting element is arranged offset from the center line in the sub-scanning direction of the light-collecting lens array in the sub-scanning direction when viewed from the optical axis direction of the light-collecting lens. A first print head and a second print head, wherein the first print head and the second print head arranged along the sub-scanning direction of the object to be scanned have the same condensing lens array in the same direction in the sub-scanning direction. In addition, the condenser lenses are arranged at the same position in the main scanning direction, and the respective heating elements are arranged so that the offset direction with respect to the sub-scanning direction center line is in the opposite direction. Image forming apparatus characterized by there. 2. A light source in which a plurality of light-emitting elements are arranged in one line in a main scanning direction, and a condensing lens are arranged in a two-stage stack in a sub-scanning direction. A light-collecting lens array that forms an image on the light-emitting element, and the light-emitting element is arranged offset from the center line in the sub-scanning direction of the light-collecting lens array in the sub-scanning direction when viewed from the optical axis direction of the light-collecting lens. A first print head and a second print head, wherein the first print head and the second print head arranged along the sub-scanning direction of the object to be scanned have the same condensing lens array in opposite directions in the sub-scanning direction. And the condenser elements are arranged at the same position in the main scanning direction, and the respective heating elements are arranged so that the offset direction with respect to the sub-scanning direction center line is in the same direction. Image forming apparatus characterized by there. 3. In the first print head and the second print head, when viewed from an optical axis direction of the condenser lens,
3. The image forming apparatus according to claim 1, wherein an offset amount from the center line of the lens array in the sub-scanning direction to the light emitting element is equal in the sub-scanning direction. 4. The apparatus according to claim 1, wherein a distance in which the heating element is offset from a center line in the sub-scanning direction of the lens array in the sub-scanning direction is 0.10 mm to 0.30 mm. The image forming apparatus according to claim 1.