JPH11334140A - Image output unit and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reduce a size variation of image dots written by light spots by setting an emission quantity of light of each LED so that an integral value within a predetermined width smaller than a diameter of the light spots becomes substantially common among the light spots. SOLUTION: A slit with an appropriately set aperture width (w) is arranged. LEDs are turned on one by one. A predetermined width smaller than a diameter of a light spot (integral value within (w)) in an arrangement direction of light spots is obtained from an output of a photodetecting element 70. A light emission quantity is corrected for each LED, so that an integral value for all LEDs is accommodated within a permissible range. An image output unit having a light emission power adjusted individually for LEDs as above is incorporated in an image formation apparatus. Whether or not a problem due to an irregularity in size of image dots is brought about is checked by driving the apparatus actually. The aperture width (w) at the slit is changed and the process is repeated, whereby the aperture width which decreases the irregularity problem best is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image output unit and an image forming apparatus. The present invention is applicable to digital copiers, page printers, digital facsimile machines, and the like.

[0002]

2. Description of the Related Art A light beam from a light source whose light emission amount is modulated by a digital signal is condensed as a light spot on a photoreceptor to write an image and form an electrostatic latent image corresponding to a recorded image. Embedded recording is widely used as an optical scanning device for an image forming apparatus such as a digital copying machine. Although the optical scanning device can realize extremely high quality image formation, it is difficult to make the image forming device compact because of the size of the optical scanning device, and the scanning image forming optical system for imaging the deflected light beam is difficult. Since it is difficult to increase the angle of view to a certain degree or more, it is difficult to write a large area image. Recently, an LED array light source in which light-emitting diodes or “LEDs” are closely arranged in an array is used, and a light beam from each LED of the LED array light source is condensed as a light spot on a photoconductor by an “imaging element using a lens array”. One line is written at a time by the LED array light source (main scanning), and the “LED array light source and imaging element” and the photoconductor are relatively moved in a direction orthogonal to the LED arrangement direction to perform sub-scanning. It is intended to commercialize a writing method for performing writing in one direction, that is, a so-called “solid-state scanning writing method”.

The solid-state scanning writing method does not require a "mechanical driving part" such as a rotary polygon mirror, and can shorten the optical path length from the light source to the photosensitive member, so that the image forming apparatus can be made compact. , LED in LED array light source
By increasing the length of the array and the length of the lens array in the imaging element, image writing in a large area can be easily realized. However, on the other hand, since there are many LEDs for writing one line, and since the imaging element is composed of an array of a plurality of lenses, the following problems occur. That is, LE
Variation in the amount of light emitted by each LED in the D array light source,
Due to the variation in the optical characteristics of the individual lenses constituting the lens array, the size of the "image dot" written by the light spot of each LED varies. In recent years, with the demand for higher density of recorded images, the diameter of a light spot has been required to be reduced, and realization of a light spot having a small diameter and having no variation has been demanded.

[0004] Recently, LED array light sources commercially available include:
Generally, a current value to be supplied to each LED is determined by, for example, 4-bit data, and the light amount can be corrected for each LED so that the light amount can be changed. By doing so, it is conceivable to reduce the variation of the light spot. For example, a method of adjusting the total amount of light emitted from each LED and transmitted through the imaging element to be equal to all the LEDs can be considered. However, in the exposure of the photoconductive photoconductor with a light spot, Since the "light spot around the light spot with low light intensity does not contribute to the formation of image dots", if the adjustment is made with the total amount of light transmitted through the imaging element, the amount of light required for image dot formation will vary, and The variation in the size is not so much improved.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to effectively reduce variations in the size of image dots written by light spots in an image forming apparatus that performs writing using an LED array light source.

Another object of the present invention is to realize an image output unit capable of effectively reducing the variation in the size of image dots.

[0007]

An image output unit according to the present invention comprises a light emitting diode (LED) having a plurality of light emitting diodes arranged in a line.
In an image forming apparatus of a method of forming an electrostatic latent image according to a recorded image by forming a light beam from each light emitting diode of an ED array light source on a photosensitive member by an imaging element, an LED array light source; An image output unit comprising a lens array and an imaging element as a unit,
The features are as follows. That is, the integration of the light intensity distribution of the light spot corresponding to each LED on the light spot formation surface of the imaging element within a predetermined width smaller than the light spot diameter in the light spot arrangement direction and / or the light spot arrangement orthogonal direction. That is, the emission standard of each LED is set so that the value becomes a value substantially common to each light spot. The “LED array light source” has a “control circuit” for arranging a plurality of LEDs in an array and controlling blinking of each LED independently and independently. The “control circuit” is an individual L
The current value to be supplied to the ED is determined by, for example, 4-bit data, and the light emission amount can be changed for each LED. Assuming that the current value is determined by 4-bit data, each LED can change the light emission amount in 16 steps. However, since the light emission characteristics of the individual LEDs vary, for example, even if the LED: A and the LED: B emit light at the maximum light emission amount (the light emission amount at the top of the 16 steps), A, The light emission amounts of B are not always the same. Even if the light emission amounts of the LEDs A and B are equal to each other, if there is a difference in characteristics between the lenses in the lens array forming the imaging element, the light amounts of the light spots formed on the photoreceptor are mutually different. It will be different.

In the present invention, as described above, the light intensity distribution of the light spot corresponding to each LED on the light spot forming surface by the imaging element in the light spot arrangement direction and / or the light spot arrangement orthogonal direction. The light emission amount of each LED is set such that an integrated value within a predetermined width smaller than the light spot diameter becomes a value substantially common to each light spot. That is, the amount of light for forming image dots of the same size is made common to all light spots. The “light spot forming surface” is a surface corresponding to the photoconductor surface (exposure surface) when the image output unit is mounted on the image forming apparatus. Considering a state in which a light beam emitted from an arbitrary LED in the LED array light source forms a light spot on a light spot forming surface by the action of an image forming element, the light spot array direction (main scanning direction) is X, and is orthogonal to this. Let the direction (sub-scanning direction) be Y, and consider the light intensity distribution of the light spot: P (X, Y). Light intensity distribution: P
The range on the X axis of (X, Y) is ab and the range on the Y axis is c
To d. That is, the light intensity distribution: P (X, Y) is 0 outside the range: a to b, c to d. As described above, it is assumed that the light emission amount of each LED can be changed in 16 steps with 4-bit data, and that the light intensity distribution at the i-th step is Pi (X, Y), and the a, b, c, and Since d also changes depending on the parameter: i, if these maximum values are changed to a, b, c, and d, the LED becomes i-th.
When the light was emitted at the step light emission amount, the total light amount of the light spot corresponding to this LED: Ri was integrated: ∫∫Pi (X, Y) dXdY was performed in the integration ranges: ab, cd. Become something. L
Assuming that the total number of LEDs in the ED array light source is N, each L
Number the ED from 1 to n to N, and LE for the number: n
Assuming that Pi and Ri with respect to D are Pin and Rin, respectively, Pin and Rin are LED numbers according to differences in the light emission characteristics of individual LEDs and variations in the characteristics of the imaging element:
It will be different depending on n. The above-described method of “adjusting so that the total light amount transmitted through the imaging element is equal to all the LEDs” is a method of adjusting the parameter: i in each LED such that the total light amount: Rn is equal to each other. is there. Since the parameter: i can be changed only in 16 steps in the case of 4-bit value data, for example, Rn
Even itself can be changed only in 16 ways. Therefore, even if it is said that the total light amount: Rn is equal to all the LEDs, in reality, the adjustment is performed so that the variation of Rn is included in a certain allowable range. It is natural. This point
The same applies to the present invention.

In the present invention, the total light quantity: Rn
Instead of making it equal to the ED, the light spot in the light spot array direction and / or the light spot array orthogonal direction of the light intensity distribution of the light spot corresponding to each LED on the light spot formation surface by the imaging element. The light emission amount of each LED is set so that the integrated value within a predetermined width smaller than the diameter becomes a value substantially common to each light spot. For example, if the integral value within a predetermined width in the light spot array direction (X direction) is to be a value common to each light spot, the upper and lower limits of the width are set to e and f (| e− When f | <| ab |, the integral is: Lin = ∫∫Pi (X, Y) dXdY (the integral area is X
For e to f, for Y from c to d)
Is within the tolerance for all n
Is nothing more than adjusting the parameter i.
It is easily understood that the larger the value of the parameter: i, the narrower the allowable range can be. A photoreceptor exposed by a light spot has a “sensitivity threshold”. Since the light spot usually has a light intensity distribution such that the light intensity monotonously decreases from the center to the peripheral portion, the “portion having a light intensity distribution smaller than the sensitivity threshold” in the peripheral portion is an image. Does not contribute to dot formation. According to the present invention, the “integral value within a predetermined width smaller than the light spot diameter” of the light intensity distribution of the light spot corresponding to each LED on the light spot formation surface in the light spot arrangement direction and / or the light spot arrangement orthogonal direction is obtained. Since the light emission standard of each LED is set so as to have a value substantially common to each light spot, it effectively contributes to the formation of image dots instead of the light amount of the peripheral portion which does not contribute to the formation of image dots. The light intensity of each LED is within the range of the digital correction data.
, It is possible to effectively reduce the variation in the size of the image dots.

[0010] The image forming element combined with the LED array light source is a "lens array". As a specific form, "micro lenses are arranged so as to correspond to each LED in the LED array light source in a one-to-one correspondence. Microlens array "(claim 2),
A "lens array in which small-diameter lens systems each corresponding to a plurality of LEDs are arranged" may be used (claim 3). The lens array according to the third aspect includes a well-known “roof mirror lens array” and “selfoc lens array”. An image forming apparatus according to the present invention is configured such that “an LED array light source in which a plurality of light emitting diodes are arranged in a line, a light beam from each light emitting diode is condensed as a light spot on a photosensitive member by an imaging element to write an image. And forming an electrostatic latent image corresponding to the recorded image, and developing the electrostatic latent image to obtain a visible image corresponding to the recorded image. An image output unit according to claim 1 or 2 or 3 is used (claim 4).

[0011]

FIG. 1 schematically shows only an essential part of an image forming apparatus according to an embodiment of the present invention.
This image forming apparatus is a digital copying apparatus. A portion indicated by reference numeral 10 in the drawing is a document reading section, and a document glass 17 is provided.
The document 0 placed flat on the surface is illuminated and scanned by the known illumination scanning means 11, and the reflected light flux from the document 0 is imaged on the solid-state imaging device 15 by the imaging lens 13 to read the document image. . The read signal is sent to the image processing unit 20, processed into an image signal suitable for image writing, and sent to the image output unit 30. The image processing unit 20 can also process external information, which is a "signal from reproducing an output from an external computer or image information recorded on a floppy disk", into an image signal suitable for image writing. The photoconductive photoconductor 40 is formed in a cylindrical shape, rotates at a constant speed in the direction of the arrow, and is rotated by a charging means 42 (an example of a corona charger is shown, but a contact charging type such as a charging roller may be used). The surface is uniformly charged, and image writing is performed by light by the image output unit 30,
An electrostatic latent image corresponding to the recorded image is formed. The formed electrostatic latent image is developed by the developing device 44 to become a visible image, and is transferred onto a transfer belt 50 as an intermediate transfer medium by a transfer unit 5.
2, and further transferred from the transfer belt 50 to a recording sheet S (transfer paper or paper for an overhead projector, etc.) by a transfer roller 54 (transfer voltage is applied from a voltage application unit (not shown)). The transferred visible image of the recording sheet S is fixed by the fixing device 60 and is discharged out of the device.

As will be described later, the image output unit 30 is composed of an image forming element formed by a lens array and an LED array light source as a unit, and a light spot corresponding to each LED on a light spot forming surface formed by the image forming element. The individual LEDs are so arranged that the integrated value within a predetermined width smaller than the light spot diameter in the light spot array direction and / or the light spot array orthogonal direction of the light intensity distribution is a value substantially common to each light spot. The amount of light emission is set "(claim 1). Therefore, the digital copying apparatus of the embodiment shown in FIG. 1 is described as “a light beam from each light-emitting diode of an LED array light source in which a plurality of light-emitting diodes are arranged in a row as a light spot on the photoreceptor 40 by an imaging element. In the image forming apparatus of the type in which the condensed light is written to form an electrostatic latent image corresponding to the recorded image and the electrostatic latent image is developed to obtain a visible image corresponding to the recorded image, An image forming apparatus using the image output unit according to claim 1 as the output unit 30 (claim 4).

FIG. 2A shows the image output unit shown in FIG. The LED array light source body denoted by reference numeral 31 has a large number of LEDs closely arranged in a line in the left-right direction in the figure, and each LED can be independently controlled to blink by a control circuit 33. The image signal from the image processing unit 20 is input to the control circuit 33, and the control circuit 33
D blink control is performed. The imaging element 35 is a lens array formed by arranging small-diameter lens systems, each of which is an “erecting equal-magnification imaging system”. The distance between the imaging element 35 and the LED array light source main body 31 is adjusted to a predetermined distance by a spacer 36. Are unitized by being integrated by the connecting means 37. Each of the small-diameter lens systems corresponds to a plurality of LEDs (claim 3). In FIG. 2A, reference numeral 3
Reference numeral 9 denotes a “light spot forming surface”, which is matched with the surface of the photoconductor 40 in FIG.

FIG. 2B is a diagram for explaining the formation of a light spot on the imaging element by each small-diameter lens system 35. The symbol Lk indicates the k-th small-diameter lens system in the lens array. The small-diameter lens system Lk is an erecting equal-magnification system, and corresponds to a plurality of LEDs. In the figure, light emitted from two of the plurality of LEDs Di, Dj is converted into a corresponding light spot Sp by a small-diameter lens system Lk.
A state where an image is formed as i, Spj is shown. Of course, as the lens array of the imaging element, a microlens array in which each microlens corresponds to each LED in a one-to-one relationship can be used (claim 2), or a self-occurring lens such as a selfoc lens. A refractive index distribution type rod-shaped lens arranged in two rows in close proximity to a staggered arrangement (in this case, LRD
The arrangement is arranged to be located in the middle of two rows).

Now, the image output unit 30 is provided with each LED on the light spot forming surface 39 by the imaging element 31.
Of the light intensity distribution of the light spot corresponding to the light spot arrangement direction and / or the orthogonal direction of the light spot arrangement within a predetermined width smaller than the light spot diameter becomes a value substantially common to each light spot. Thus, the light emission amount of each LED is set, and this point will be described below. FIG.
In (a), reference numeral 30 denotes an image output unit, and reference numeral S
T indicates a slit, and reference numeral 70 indicates a light receiving element. FIG.
In (b) to (e), the symbol SP indicates a light spot on the light spot formation surface, and the horizontal direction in the drawing is the main scanning direction (LED arrangement direction), and the vertical direction is the sub-scanning direction.
In FIG. 3A, the slit ST is provided so as to match the light spot forming surface, and the image output unit 30 is provided with an LED.
Can be displaced in the direction of the arrow by the array pitch. 3 (b) to 3 (e), the solid rectangular shapes indicate four forms of the opening shape of the slit ST. The opening width in each opening shape is “w” in the main scanning direction and “z” in the sub-scanning direction. FIG. 3B shows a case where the opening width: w is smaller than the diameter of the light spot SP in the main scanning direction and the opening width: z is larger than the diameter of the light spot SP in the sub-scanning direction. The received light amount is “an integral value within a predetermined width: w smaller than the light spot diameter in the light spot arrangement direction (main scanning direction)”. FIG. 3C shows that the opening width w is larger than the diameter of the light spot SP in the main scanning direction.
In this case, the aperture width: z is smaller than the diameter of the light spot SP in the sub-scanning direction. In this case, the light amount received by the light receiving element 70 is “a predetermined width smaller than the light spot diameter in the light spot array orthogonal direction (sub-scanning direction)”. : Integral value in z ”.
FIG. 3D shows that the light spot S has both the aperture widths: w and z.
In this case, the amount of light received by the light receiving element 70 is “light spot in the light spot array direction (main scanning direction) and in the light spot array orthogonal direction (sub scanning direction)”. Predetermined width smaller than diameter:
integral value in w and z ". FIG. 3E shows the opening width:
In this case, w and z are both larger than the diameter of the light spot SP in the main and sub-scanning directions. In this case, the amount of light received by the light receiving element 70 is the “integral value of the entire light spot”.

In the case of FIG. 3B as an example, each LED
The adjustment of the light emission amount will be described. First, a slit ST having an appropriately set opening width: w is used and arranged as shown in FIG. The LEDs are turned on one by one, and the output of the light receiving element 70 indicates that “in the light spot arrangement direction (main scanning direction),
Predetermined width smaller than the light spot diameter: integral value within w ". Then, for each LED, the light emission amount (in digital value)
Correction is performed so that the integrated value for all LEDs is within the allowable range. The image output unit in which the light emission power is individually adjusted by the LED is incorporated in the image forming apparatus shown in FIG. 1, and the apparatus is actually operated, and the problem due to the unevenness of the size of the image dots (the In the example, since irregularities in the size of image dots appear in the main scanning direction, for example, when all the LEDs are turned on and a certain area is exposed as a `` solid portion '', in a small portion of the image dots, (A “linear black streak in the sub-scanning direction” occurs) is checked.

When the problem actually occurs, the slit ST
Above, and the above steps are repeated. Thus repeated attempts, the image dot size (in the example in the description corresponding to the main scanning direction size) problem due to the variation of best mitigated opening width when: Request w _0. Then, the “integral value within a predetermined width w ₀ smaller than the light spot diameter in the light spot arrangement direction (main scanning direction) in the light spot arrangement direction (main scanning direction)” falls within the allowable range for all the LEDs by the slit having the opening width w _0. An arbitrary image output unit whose light emission amount is adjusted as described above realizes image writing in a state in which variations in the size of image dots in the sub-scanning direction are effectively corrected by simply incorporating the image output unit in the image forming apparatus of FIG. can do. Thus, once the opening width: If Motomare is w _0, opening width: slit of w _0, the light emission amount adjustment to equalize the integral values, for any image output unit, a separate image forming apparatus main body It is only necessary to incorporate the image output unit whose light emission amount has been adjusted in this way into the image forming apparatus main body.
There is no need to individually adjust the light emission of the ED.

Referring to FIG. 4, the horizontal axis in the figure indicates the light spot imaging plane in the main scanning direction, and the vertical axis indicates the light intensity. In FIG. 4 (a), the curve 4-1 and 4-2, the slit width: light spots corresponding to two LED when the integrated value of the light intensity is adjusted so that the acceptable range in the w ₀ It is a light intensity distribution. On the other hand, curves 4-3 and 4-4 in FIG. 4B indicate that the slit widths w and z are larger than the size of the light spot (in the case of FIG. This is an intensity distribution of light spots corresponding to two LEDs when the amount of light (integral value) falls within the allowable amount range in each LED. In the case of FIG. 4 (a), the width of the curve 4-1 and 4-2: The integration value of the w ₀ are equal, width: within w _0, the shape of the curve 4-1 and 4-2 are close. For this reason, for example, assuming that the threshold value of the light intensity required for exposing the image dots is T, the width of the image dots formed by each light spot in the main scanning direction is represented by a curve 4-4 as shown in FIG.
Dm1 and Dm2 for 1,4-2, respectively.
On the other hand, curves 4-3 and 4-4 in FIG. 4B when the total light amount of the light spot is made equal.
Has a shape in which the light intensity distribution is thicker horizontally in the curve 4-4. For this reason, the width of the image dot formed by each light spot in the main scanning direction is equal to the width of the curve 4-
Dm3 and Dm4 respectively for 3, 4-4.
If the magnitude relationship between Dm1 and Dm2 is compared with the magnitude relationship between Dm3 and Dm4, the relationship between FIG. 4B and FIG.
It will be understood that in the case (a), the range of the variation in the size of the image dots can be reduced. If desired
By using the slit shape shown in FIG. 3C, it is possible to effectively reduce the variation in the size of the image dots in the sub-scanning direction, and to use the slit shape shown in FIG. Variations in the size in the sub-scanning direction can be effectively reduced.

[0019]

As described above, according to the present invention, a novel image output unit and image forming apparatus can be realized. The image output unit of the present invention can adjust the light emission amount of each LED so as to effectively reduce the variation in the size of the image dots separately from the image forming apparatus main body incorporating the image output unit. Only by incorporating, it is possible to realize image writing in which variation in the size of image dots is effectively reduced. In addition, the image forming apparatus of the present invention incorporates an image output unit in which the amount of light emitted from each LED is adjusted so as to effectively reduce variations in the size of image dots. Good image formation can be realized without troublesome adjustment.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a diagram for explaining an image output unit in the embodiment of FIG.

FIG. 3 is a diagram for explaining light emission amount adjustment in the image forming unit.

FIG. 4 is a diagram for explaining that the variation in the size of image dots can be reduced by the image output unit of the present invention.

[Explanation of symbols]

 Reference Signs List 30 Image output unit 35 Imaging element using lens array ST Slit 70 Light receiving element w, z Opening width of slit ST

Claims (4)

[Claims] An image is written by converging a light beam from each light emitting diode as a light spot on a photoreceptor by an image forming element in an LED array light source in which a plurality of light emitting diodes are arranged in a line, and writing a recorded image. An image forming apparatus for forming an electrostatic latent image according to the following: An image output unit in which an image forming element using a lens array and a LED array light source are unitized, and a light spot forming surface using the image forming element Each L above
The integrated value of the light intensity distribution of the light spot according to the ED within a predetermined width smaller than the light spot diameter in the light spot array direction and / or the light spot array orthogonal direction is a value substantially common to each light spot. So that each L
An image output unit characterized in that an ED light emission amount is set. 2. The image output unit according to claim 1, wherein the imaging element is a microlens array in which microlenses are arranged in a one-to-one correspondence with the LEDs in the LED array light source. Image output unit. 3. The image output unit according to claim 1, wherein each of the imaging elements is a lens array in which a small-diameter lens system corresponding to a plurality of LEDs is arranged. 4. An image writing method in which a light beam from each light emitting diode of an LED array light source in which a plurality of light emitting diodes are arranged in a line is condensed as a light spot on a photosensitive member by an image forming element, and an image is written. 4. An image forming apparatus according to claim 1, wherein an electrostatic latent image corresponding to the image is formed, and the electrostatic latent image is developed to obtain a visible image corresponding to the recorded image. An image forming apparatus using the image output unit described above.