JP3667989B2 - Image output unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image output unit. The present invention can be applied to a digital copying machine, a page printer, a digital facsimile, and the like.
[0002]
[Prior art]
Optical writing recording, in which an image is written by condensing a light beam from a light source whose light emission is modulated by a digital signal as a light spot on a photoconductor, and forming an electrostatic latent image corresponding to a recorded image, is digital Widely used as an optical scanning device for an image forming apparatus such as a copying machine.
Although the optical scanning device can realize extremely high quality image formation, it is difficult to make the image forming device compact due to the size of the optical scanning device, and the scanning imaging optical system for imaging the deflected light beam is difficult. Since it is difficult to widen the angle of view to some extent, there is a problem that it is difficult to write a large area image.
Recently, an LED array light source in which light-emitting diodes or “LEDs” are closely arrayed is used, and light beams from each LED of the LED array light source are condensed as a light spot on a photoconductor by a “lens array imaging element”. The LED array light source writes one line at a time (main scanning), and the “LED array light source and imaging element” and the photosensitive member are moved relative to each other in the direction perpendicular to the LED arrangement direction to perform sub scanning. It is intended to put to practical use a writing method for writing in a direction, that is, a so-called “solid-state scanning writing method”.
[0003]
The solid-state scanning writing method does not require "mechanical drive parts" like a rotating polygon mirror, and the optical path length from the light source to the photosensitive member can be shortened, so that the image forming apparatus can be made compact, and the LED array Large area image writing can be easily realized by increasing the array length of the LEDs in the light source and the length of the lens array in the imaging element.
However, since there are a large number of LEDs for writing one line and the imaging element is composed of an array of a plurality of lenses, the following problems arise.
That is, the size of the “image dot” written in the light spot by each LED is caused by the variation in the light emission amount of each LED in the LED array light source and the variation in the optical characteristics of the individual lenses constituting the lens array. It is scattered.
Recently, along with a demand for higher density of recorded images, it is required to reduce the diameter of the light spot, and it is required to realize a light spot having a small diameter and no variation.
[0004]
Recently, LED array light sources that are commercially available are those that can determine the current value supplied to each LED, for example, using 4-bit data, and can change the amount of light emitted for each LED. It is conceivable to reduce variations in the light spot by correcting the light emission amount in units of LEDs.
For example, “a method of adjusting the total amount of light emitted from each LED and transmitted through the imaging element so as to be equal to all LEDs” can be considered, but in exposure of a photoconductive photoconductor by a light spot, “The periphery of the light spot with low light intensity does not contribute to the formation of image dots.” Therefore, if the adjustment is made with the total amount of light transmitted through the imaging element, the amount of light necessary to form the image dots will vary, and the image dots The variation in size is not improved so much.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to effectively reduce variation in the size of image dots written by a light spot in an image forming apparatus that performs writing using an LED array light source.
[0006]
Another object of the present invention is to realize an image output unit that can effectively reduce variations in the size of image dots.
[0007]
[Means for Solving the Problems]
The image output unit according to the present invention is "corresponding to a recorded image by forming an image of a light beam from each light emitting diode of a LED array light source formed by arranging a plurality of light emitting diodes in a line on a photosensitive member by an imaging element. The image forming apparatus of the type that forms an electrostatic latent image is an “image output unit that includes an LED array light source and an imaging element by a lens array as a unit”, and is characterized by the following points.
That is, the integral of the light intensity distribution of the light spot corresponding to each LED on the light spot forming surface by the imaging element within a predetermined width smaller than the light spot diameter in the light spot array direction and / or the light spot array orthogonal direction. That is, the light emission reference of each LED is set so that the value becomes a value substantially common to each light spot.
The integrated value is determined by the light receiving element through an opening portion of a slit having a predetermined opening width that can effectively correct the variation in the size of the image dot and is provided to match the light spot forming surface. Ru obtained as the integral value to be received.
Upper Symbol "LED array light source" includes a plurality of LED to the array sequence, the "control circuit" blinking controlled independently of each LED.
The “control circuit” can determine a current value to be supplied to each LED based on, for example, 4-bit data, and change the light emission amount for each LED.
If the current value is determined by 4-bit value data, each LED can change the light emission amount to 16 levels. However, since individual LEDs have variations in light emission characteristics, for example, even if LED: A and LED: B are caused to emit light at the maximum light emission amount (the uppermost light emission amount of the above 16 steps), A, The light emission amount of B is not always the same. Further, 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 constituting the imaging element, the light amounts of the light spots formed on the photoconductor are mutually different. It will be different.
[0008]
In the present invention, as described above, the light spot in the light spot array direction and / or the light spot array orthogonal direction of the light spot distribution according to each LED on the light spot forming 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. That is, the amount of light for forming image dots of the same size is made common to all the light spots.
The “light spot forming surface” is a surface corresponding to the surface of the photoreceptor (exposure surface) when the image output unit is mounted on the image forming apparatus. Considering a state where a light beam emitted from an arbitrary LED in the LED array light source forms a light spot on the light spot forming surface by the action of the imaging element, the light spot array direction (main scanning direction) is X, and is orthogonal to this. Consider the light intensity distribution of the light spot: P (X, Y) where Y is the direction (sub-scanning direction). Light intensity distribution: The range on the X axis of P (X, Y) is a to b, and the range on the Y axis is c to d. That is, the light intensity distribution: P (X, Y) is 0 outside the ranges: ab, cd.
As described above, assuming that the light emission amount of each LED can be changed in 16 steps with 4-bit value data, and the light intensity distribution in the i-th step is Pi (X, Y), a, b, c, Since d varies depending on the parameter: i, if these maximum values are changed to a, b, c, d, the light spot corresponding to this LED when the LED emits light at the i-th emission amount. The total amount of light: Ri is integral:
∫∫Pi (X, Y) dXdY
In the integration range: ab, cd. If the total number of LEDs in the LED array light source is N, each LED is numbered as 1 to n to N, and Pi and Ri for the LED of number: n are Pin and Rin, respectively, and the light emission characteristics of each LED Pin and Rin are different depending on the LED number: n according to the difference in characteristics and the variation in characteristics of the imaging element.
The above-described method of “adjusting the total amount of light transmitted through the imaging element to be equal to all LEDs” is a parameter for each LED so that the total amount of light: Rn (n = 1 to N) is equal to each other. : A method of adjusting i. For example, in the case of 4-bit value data, the parameter: i can only be changed in 16 steps. Therefore, Rn itself can only be changed in 16 ways. Therefore, the total light amount: Rn is the same for all LEDs. However, it is natural that the adjustment is such that the variation in Rn is included in a certain allowable range. This also applies to the present invention.
[0009]
In the present invention, the total light amount: Rn is not made equal to all the LEDs, but the light intensity distribution of the light spot corresponding to each LED on the light spot forming surface by the imaging element, In other words, the light emission amounts of the individual LEDs are set so that the integrated value within a predetermined width smaller than the light spot diameter in the direction orthogonal to the light spot array is a value that is substantially common to each light spot.
For example, if the integral value within a predetermined width in the light spot arrangement direction (X direction) is a value common to each light spot, the upper and lower limits of the width are set to e, f (| e− f | <| a−b |), integral:
Parameters for each LED such that Lin = ∫∫Pi (X, Y) dXdY (integration region from e to f for X and c to d for Y) is within the acceptable range for all n: It is none other than adjusting i. It will be easily understood that the allowable range can be narrowed as the size of the parameter i increases.
A photoreceptor exposed by a light spot has a “sensitivity threshold”. Since the light spot usually has a light intensity distribution in which the light intensity decreases monotonously from the central part to the peripheral part, the above "peripheral part having a light intensity distribution smaller than the sensitivity threshold" is an image. Does not contribute to dot formation. In the present invention, the “integral 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 of the light spot corresponding to each LED on the light spot forming surface is Since the light emission reference of each LED is set so as to have a value that is substantially common to each light spot, it contributes effectively to the formation of image dots, not the amount of light at the peripheral portion that does not contribute to the formation of image dots. Since the light quantity of the portion is made uniform for each LED within the range allowed by the digital correction data, it is possible to effectively reduce the variation in the size of the image dots.
[0010]
The imaging element combined with the LED array light source is a “lens array”, and a specific form thereof is “a microlens in which microlenses are arranged to correspond to each LED in the LED array light source 1: 1. (Claim 2) or "lens array in which small-diameter lens systems each corresponding to a plurality of LEDs" are arranged (Claim 3). The lens array described in claim 3 includes a well-known “roof mirror lens array” and “selfoc lens array”.
“An LED array light source in which a plurality of light-emitting diodes are arranged in a line, the light flux from each light-emitting diode is condensed as a light spot on the photosensitive member by the imaging element, and image writing is performed. 4. The image forming apparatus according to claim 1, wherein the electrostatic latent image is formed and the electrostatic latent image is developed to obtain a visible image corresponding to the recorded image. An output unit can be used.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 schematically shows only a portion necessary for the description of an embodiment of an image forming apparatus according to the present invention. This image forming apparatus is a digital copying apparatus.
A portion indicated by reference numeral 10 in the drawing is an original reading unit, and the original 0 placed on the original glass 17 is illuminated and scanned by a known illumination scanning means 11 to form a reflected light beam from the original 0. An image is formed on the solid-state image pickup device 15 by the lens 13 to read an original 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 obtained by reproducing image information recorded on an output from an external computer or a floppy disk” into an image signal suitable for image writing.
The photoconductive photoreceptor 40 is formed in a cylindrical shape and rotates at a constant speed in the direction of the arrow, and is surrounded by a charging means 42 (a corona charger is shown as an example, but a contact charging type such as a charging roller may be used). The surface is uniformly charged, and image writing by light is performed by the image output unit 30 to form an electrostatic latent image corresponding to the recorded image. The formed electrostatic latent image is developed by the developing device 44 to become a visible image, transferred onto the transfer belt 50 as an intermediate transfer medium by the transfer means 52, and further from the transfer belt 50 to the recording sheet S (transfer paper or overhead). The image is transferred onto a projector sheet or the like by a transfer roller 54 (a transfer voltage is applied from a voltage application unit (not shown)). On the recording sheet S, the transferred visible image is fixed by the fixing device 60 and discharged outside the device.
[0012]
As will be described later, the image output unit 30 is formed by unitizing an imaging element by a lens array and an LED array light source, and a light intensity distribution of a light spot corresponding to each LED on a light spot forming surface by the imaging element. The light emission amount of each LED so 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 becomes a value substantially common to each light spot. Is set "(claim 1). This point will be described in detail later.
Accordingly, in the digital copying apparatus shown in FIG. 1, the light beam from each light emitting diode of the LED array light source formed by arranging a plurality of light emitting diodes in a line is formed as a light spot on the photosensitive member 40 by the imaging element. In an image forming apparatus of a type that collects images and writes an image, forms an electrostatic latent image corresponding to a recorded image, and develops the electrostatic latent image 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 .
[0013]
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 controlled to blink independently by the control circuit 33. The image signal from the image processing unit 20 is input to the control circuit 33, and the control circuit 33 performs blinking control of the LED.
The imaging element 35 is a lens array in which small-diameter lens systems, each of which is an “erecting equal-magnification imaging system”, are arranged. The distance from the LED array light source body 31 is adjusted to a predetermined distance by a spacer 36. These 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 39 denotes a “light spot forming surface”, which is matched with the surface of the photoreceptor 40 in FIG.
[0014]
FIG. 2B is a diagram for explaining the formation of a light spot by each small-diameter lens system 35 in the imaging element.
Symbol Lk indicates the kth 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. The figure shows a state in which light emitted from two Di and Dj of the plurality of LEDs forms an image as corresponding light spots Spi and Spj by the small-diameter lens system Lk.
Of course, as the lens array of the imaging element, a microlens array in which each microlens corresponds to each LED 1: 1 can be used (Claim 2), or a lens lens such as a SELFOC lens. It is also possible to use a refractive index distribution type rod-shaped lens in which two rows are arranged in close proximity to the staggered arrangement (in this case, the LRD arrangement is arranged so as to be positioned in the middle of the two rows).
[0015]
Now, the image output unit 30 has a light spot in the light spot arrangement direction and / or the light spot arrangement orthogonal direction of the light intensity distribution of the light spot corresponding to each LED on the light spot forming surface 39 by the imaging element 31. 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. This point will be described below.
In FIG. 3A, reference numeral 30 denotes an image output unit, reference numeral ST denotes a slit, and reference numeral 70 denotes a light receiving element. 3B to 3E, the symbol SP indicates a light spot on the light spot forming surface, the horizontal direction in the figure is the main scanning direction (LED arrangement direction), and the vertical direction is the sub-scanning direction. In FIG. 3A, the slits ST are arranged so as to coincide with the light spot forming surface, and the image output unit 30 can be displaced in the arrow direction by the arrangement pitch of the LEDs.
In FIGS. 3B to 3E, the solid rectangular shape shows four modes 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 aperture width: w is smaller than the diameter of the light spot SP in the main scanning direction and the aperture width: z is larger than the diameter of the light spot SP in the sub-scanning direction. The amount of light received is “a predetermined width smaller than the light spot diameter in the light spot arrangement direction (main scanning direction): an integral value within w”.
FIG. 3C shows a case where the aperture width: w is larger than the diameter of the light spot SP in the main scanning direction, and the aperture width: z is smaller than the diameter of the light spot SP in the sub-scanning direction. The amount of light received is “a predetermined width smaller than the light spot diameter in the direction orthogonal to the light spot array (sub-scanning direction): an integral value in z”.
FIG. 3D shows a case where the aperture widths: w and z are both smaller than the main / sub-scanning direction diameter of the light spot SP. In this case, the amount of light received by the light receiving element 70 is “light spot arrangement direction (main spot direction (main spot)”. Scanning direction) and light spot array orthogonal direction (sub-scanning direction) in a predetermined width smaller than the light spot diameter: integral value in w, z ”.
FIG. 3E shows a case where the aperture widths: w and z are both larger than the diameter of the light spot SP in the main / sub scanning direction. In this case, the amount of light received by the light receiving element 70 is “the integrated value of the entire light spot”. Is.
[0016]
Taking the case of FIG. 3B as an example, adjustment of the light emission amount of each LED will be described.
First, a slit ST with an appropriately determined opening width: w is provided as shown in FIG. The LEDs are turned on one by one, and “the predetermined value smaller than the light spot diameter in the light spot arrangement direction (main scanning direction): integral value within w” is obtained from the output of the light receiving element 70. For each LED, the light emission amount is corrected (by a digital value) so that the integrated value for all the LEDs is within the allowable range.
The image output unit in which the luminous power is individually adjusted in this way is incorporated into the image forming apparatus shown in FIG. 1, and the apparatus is actually operated to cause a problem due to the uneven size of the image dots (in the description) In the example, unevenness in the size of the image dots appears in the main scanning direction.For example, when it is necessary to turn on all the LEDs and expose a certain area area as a “solid portion”, in a small portion of the image dots, It is checked whether or not “a linear black stripe in the sub-scanning direction” occurs.
[0017]
When the problem actually occurs, the opening width: w in the slit ST is changed and the above steps are repeated. In this way, the trial is repeated, and the aperture width: w ₀ when the problem due to the variation in the size of the image dot (the size in the main scanning correspondence direction in the example in the explanation) is best reduced is obtained. Then, the slit having the aperture width: w ₀ makes “the integrated value within a predetermined width: w ₀ smaller than the light spot diameter in the light spot arrangement direction (main scanning direction)” within the allowable range for all LEDs. Any image output unit whose light emission amount is adjusted in this way can be incorporated into the image forming apparatus shown in FIG. 1 and image writing can be performed in a state where the variation in the size of the image dots in the sub-scanning direction is effectively corrected. can do.
Therefore, once the aperture width: w ₀ is obtained, the light emission amount adjustment for making the integrated value uniform can be performed separately for the image output apparatus main body with respect to an arbitrary image output unit by the slit having the aperture width: w _0. The image output unit having the light emission amount adjusted in this way only needs to be incorporated into the image forming apparatus main body, and after the image output unit is incorporated into the image forming apparatus as in the prior art, the LED of the image output unit is adjusted. There is no need to individually adjust the light emission.
2. The image output unit according to claim 1, wherein “light in the light spot arrangement direction and / or the light spot arrangement orthogonal direction of the light intensity distribution of the light spot corresponding to each LED on the light spot forming surface by the imaging element”. The “predetermined width” in the “integrated value within a predetermined width smaller than the spot diameter” is most likely to be caused by variations in the size of the image dot (in the example in the description, the size in the main scanning correspondence direction). Opening width when reduced: w ₀ (in this case, a predetermined width in the light spot arrangement direction) ”.
[0018]
Referring to FIG. 4, the horizontal axis in the figure represents the light spot imaging plane in the main scanning direction, and the vertical axis represents the light intensity.
In FIG. 4A, curves 4-1 and 4-2 indicate the light spots corresponding to the two LEDs when adjusted so that the integrated value of the light intensity within the slit width: w _{0 is} within the allowable range. Light intensity distribution.
On the other hand, in curves 4-3 and 4-4 in FIG. 4B, the slit width: w, z is made larger than the size of the light spot (in the case of FIG. 3E), and the entire light spot is obtained. It is an intensity distribution of light spots corresponding to two LEDs when the amount of light (integrated value) falls within the allowable range of 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, if the threshold value of the light intensity necessary for the exposure of the image dots is T, the width in the main scanning direction of the image dots formed by the respective light spots is curves 4-1, 4-2 as shown in the figure. Are Dm1 and Dm2, respectively.
On the other hand, curves 4-3 and 4-4 in FIG. 4B in the case where the total amount of light of the light spots is made equal have a shape in which the light intensity distribution is thick horizontally in the curve 4-4. ing. For this reason, the width of the image dot formed by each light spot in the main scanning direction is Dm3 and Dm4 with respect to the curves 4-3 and 4-4, respectively, as shown in the figure.
If the magnitude relationship between Dm1 and Dm2 is compared with the magnitude relationship between Dm3 and Dm4, the variation in image dot size is greater in the case of FIG. 4A than in the case of FIG. It will be appreciated that the range can be reduced.
If desired, the slit shape shown in FIG. 3C can be used to effectively reduce the variation in the size of the image dots in the sub-scanning direction. The slit shape shown in FIG. The variation in the size in the main / sub-scanning direction can be effectively reduced.
[0019]
【The invention's effect】
As described above, according to the present invention, a novel image output unit can be realized.
The image output unit of the present invention can adjust the light emission amount of each LED separately from the image forming apparatus main body in which the image output unit is incorporated so that the variation in the size of the image dots can be effectively reduced. Only by incorporating, it is possible to realize image writing in which variation in image dot size is effectively reduced. In addition, since the image forming apparatus of the present invention incorporates an image output unit in which the light emission amount of each LED is adjusted in advance so that the variation in the size of the image dots can be effectively reduced, No troublesome adjustment is required, and good image formation can be realized.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining an embodiment of an image forming apparatus using an image output unit of the present invention.
FIG. 2 is a diagram for explaining an image output unit in the embodiment of FIG. 1;
FIG. 3 is a diagram for explaining light emission amount adjustment in the image forming unit.
FIG. 4 is a diagram for explaining that variation in image dot size can be reduced by the image output unit of the present invention.
[Explanation of symbols]
30 Image output unit 35 Imaging element ST by lens array Slit 70 Light receiving element w, z Opening width of slit ST

Claims (3)

An LED array light source composed of a plurality of light emitting diodes arranged in a row, the light flux from each light emitting diode is condensed as a light spot on the photosensitive member by the imaging element, and image writing is performed, and electrostatics corresponding to the recorded image are recorded. In an image forming apparatus that forms a latent image,
An image output unit formed by unitizing an imaging element by a lens array and an LED array light source,
An 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 of the light spot corresponding to each LED on the light spot forming surface by the imaging element. a light receiving element through the opening in the slit provided consistent with the light spot forming surface with an opening width of the predetermined width that can be effectively correcting variation in size of the image dots An image output unit characterized in that the light emission amount of each LED is set so that the integrated value obtained as an integrated value for receiving light is a value substantially common to each light spot. The image output unit according to claim 1.
The image forming element is a microlens array in which microlenses are arranged so as to correspond to each LED in the LED array light source 1: 1. The image output unit according to claim 1.
Each of the imaging elements is a lens array in which small-diameter lens systems corresponding to a plurality of LEDs are arranged.

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