JP2002120395A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that does not narrow a gradation representation region in terms of the image forming apparatus utilizing a multi-element laser array having a relatively large beam with respect to a scanning pitch in the case where an image is formed by using a laser beam. SOLUTION: This image forming apparatus utilizes the multi-element laser device having a relatively large beam diameter with respect to the scanning pitch. A contingent of the operation is applied to each of the elements and then the emission of each of the elements is controlled according to input image information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a laser printer,
In an image forming apparatus for exposing and forming an image such as an electrostatic latent image using a light beam on an image carrier of a digital xerography apparatus such as a digital copying machine or a facsimile apparatus, particularly, light emitting elements are arranged in an array. The present invention relates to an image forming apparatus capable of achieving both gradation and edge position accuracy when a semiconductor laser array is used as a light source.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus,
A semiconductor laser is used as a light source for exposure because of its high response, and the semiconductor laser beam is optically stopped down.
By scanning and exposing a beam with a polygon mirror, a high-speed, high-resolution image forming apparatus is realized.

[0003] In recent years, demands for higher speed and higher resolution have been met by increasing the rotation speed of the video signal and the polygon mirror. However, the speed of the polygon mirror has almost reached its limit, and further higher speeds have been achieved. For higher resolution and higher resolution, for example, as disclosed in Japanese Patent Application Laid-Open No. 5-294005, an image forming apparatus has been proposed in which a plurality of lasers or a laser array are used to increase the number of beams and perform exposure. 25). Further, a laser array having multiple elements as shown in FIG. 26A has been proposed.

On the other hand, there is a limit to the improvement of the beam diameter by an optical system, and in a scanning system using a polygon mirror,
It is very difficult to reduce the beam diameter.

For this reason, even if the scanning line density is increased by increasing the number of beams, the beam diameter remains large. In an image forming apparatus using the laser array, the image forming apparatus uses a photosensitive member as an image carrier in a sub-scanning direction. The exposure beam is shown in FIG.
Exposure with a large overlapping portion is obtained as shown in FIG. Therefore, a latent image is formed differently from the conventional low-resolution image forming apparatus shown in FIG.

That is, in the conventional image forming apparatus having a scanning line density of 600 dpi, the beam diameter in the sub-scanning direction is about 60 μm with respect to the scanning line pitch (resolution) of 42 μm. As shown, the average value of the combined exposure and the peak intensity of each laser beam are almost equal.

On the other hand, in an image forming apparatus having a scanning line density of 2400 dpi using the laser array, the beam diameter in the sub-scanning direction is not changed to about 60 μm, and is relatively smaller than the scanning line pitch of 10 μm. Beam diameter is large.

Therefore, as shown in FIG. 29, even if the exposure amount of each laser beam is small, the combined exposure amount is large. Is possible.

In general, in an electrophotographic image forming apparatus using a laser, the potential of a charged photoreceptor is exposed by turning on / off a laser beam for each pixel in accordance with input image data. An image is formed by lowering the body potential, but when reproducing the gradation, pulse width modulation is performed.

[0010] Pulse width modulation is a method in which the lighting time of a laser in a tone reproduction pixel is changed in accordance with the image density to control the ratio of the toner adhering area (area tone control). It is changed to perform gradation expression.

As a method of realization, a pulse is generated by converting image data supplied as multi-valued data usually expressed by 8 bits into an analog value and comparing it with a reference wave (triangular wave). The analog screen method that sets the pulse width based on the cross point of the image) and the digital screen method that controls the area ratio by changing the number of lighting of the fine pixels contained in the image in units of halftone dots It has been known.

In the analog screen system, fine gradation expression can be performed for each scanning line. However, since the pulse width is determined by an analog circuit, the configuration is complicated and the circuit scale becomes large.

Further, it is difficult to transmit a high-speed analog signal, and the circuit is disposed immediately before the laser driving circuit. For this reason, a data line corresponding to the number of elements × 8 bits is required, and the circuit scale for transmission and reception is increased. Therefore, it is not practical when the number of elements is large.

On the other hand, the digital screen system is a system in which an area ratio is determined by turning on / off fine pixels included in an area according to a desired screen to reproduce a gradation.

FIG. 30 is a schematic diagram when pulse width modulation is performed by a conventional image forming apparatus having a scanning line density of 600 dpi.

The horizontal axis represents the position in the main scanning direction where the laser beam is moved and scanned, and the vertical axis represents the exposure energy.

The area on the photoreceptor that is not exposed is maintained at the surface potential VH charged by the charger. 1 on the vertical axis is the exposure energy required for stable development.

The exposure of this energy changes the surface potential on the photoreceptor to VL. The dotted line of the exposure energy 0.4 shown in FIG. 30 is the minimum energy level (threshold) necessary for development.

[0019]

FIG. 30 shows that as the exposure width is gradually increased, the exposure profile changes in height as well as in width. The following can be said from these graphs. In the low density portion (highlight portion, FIGS. 30A and 30B), the toner does not adhere because the threshold value of the exposure profile has not been reached. In the high density portion (shadow portion, FIG. 30G), the entire exposure profile exceeds the threshold value, and the output density does not change even when the input density is changed (the output density is saturated).

Therefore, as shown in FIG. 31, in the gradation image of the pulse width modulation, the gradation reproduction is not started up to a certain input density in the highlight portion, and the input density is 1 in the shadow portion.
The output density is saturated before reaching 00%.

When the above is applied to the above-described exposure using the laser array, the light amount of each laser beam becomes 0.266, which is about 1 / 3.76 of the conventional example, so that pulse width modulation is similarly applied. Even when scanning with a single element, the threshold value is not exceeded.

In order to exceed the threshold value, it is necessary to turn on the laser continuously in the sub-scanning direction.

That is, when a low-density image is formed, the amount of light is insufficient, so that the contrast of the latent image cannot be obtained and the reproduction start point of the image is shifted to the high-density side.

Similarly, on the high density side, even if non-illuminated pixels are present, the exposure amount per pixel is small, so that the contrast of the latent image cannot be secured. There has been a problem that the image density is saturated and the image reproduction area is narrowed. Further, if the light amount is simply increased to compensate for the light amount shortage, when the pixels are connected in the sub-scanning direction or the oblique direction, the light amount becomes excessive or the output image quality is deteriorated.

In addition, since a multi-element laser array is used as a light source, if even one of the elements in the array has a defect, the corresponding scanning line is not formed and the image quality is impaired. Further, in addition to the fact that the laser array is more expensive than a single laser element, there is a problem that it takes a long time to exchange and to make adjustments due to the exchange because it is multi-element.

Further, the large number of light emitting elements causes a huge amount of data to be handled. By adopting a digital screen, only one bit of data can be transmitted per element. However, since the number of elements is very large, the amount of data to be handled at the same time is also large, and high-speed transmission of data at a resolution of 2400 dpi is required. Compatible IC
Or require a large capacity line buffer,
As a result, there is a problem that the apparatus becomes expensive.

In consideration of the above facts, the present invention provides an image forming apparatus using a multi-element laser array having a beam relatively large with respect to the scanning pitch without reducing the gradation reproduction area. The purpose is to get.

Another object of the present invention is to provide an image forming apparatus which does not easily affect the image quality even if a defect occurs in the element.

Further, in addition to the above-mentioned object, it is another object of the present invention to obtain an inexpensive image forming apparatus having a relatively simple apparatus configuration even when transmitting high-resolution data at a high speed.

[0030]

According to a first aspect of the present invention, there is provided an array-like light source comprising a plurality of light emitting elements arranged at a predetermined density and light emission control means for controlling light emission of the light emitting elements. The light beam emitted from the array light source is main-scanned in one direction, and the light beam and the image carrier are relatively moved in a sub-scanning direction substantially orthogonal to the light beam scanning direction. In an image forming apparatus that forms an image according to an image signal, a dividing unit that divides the light emitting elements of the array light source into a plurality of groups, and a basic image is recorded on a plurality of light emitting elements included in the group Role sharing means for setting a main beam having a plurality of intensity levels to perform the auxiliary exposure and an auxiliary beam having one intensity level for performing the auxiliary exposure;
Multi-beam laser drive control means for performing exposure / modulation control for each group according to the image signal.

Further, the present invention is characterized in that a main beam included in one group of the light-emitting elements has an auxiliary beam function according to image data.

Further, a beam diameter of the light beam on the image carrier is substantially twice or more as large as an interval between the plurality of light beams.

[0033] Further, the apparatus further comprises a detecting means for detecting an abnormality of the light emitting element, and a transmitting means for transmitting an abnormality to a higher-level control device when an abnormality is found by the detecting means. When the element is a main beam, the group is changed to a group in which an image defect does not occur in the main beam at the time of division by the division unit. .

Further, the image data is a pattern number code representing a bit image of an image block composed of an array of a plurality of pixels.

Further, the multi-beam driving means uses the input pattern number code, the group information from the dividing means, and the role assignment information from the role assignment means to assign the pattern number code to a bit of a pixel block. The image processing apparatus is characterized in that it comprises a restoration unit for restoring an image, and a decoding unit for outputting light emission information according to the group and the role assignment.

According to the first aspect of the invention, the light emitting elements of the array light source are divided into a plurality of groups, and a main beam for recording a basic image and an auxiliary beam for performing auxiliary exposure are provided on the plurality of elements included in the group. By having a multi-beam laser drive circuit that performs exposure / modulation control for each group according to the image signal, switching between lighting pixels and intensity levels according to image data for each group Can be done.

Further, by providing the main beam of the group with the same function as the auxiliary beam, it is possible to more flexibly cope with the image data.

Further, when the beam diameter of the array light source is at least about twice the interval between the plurality of light beams, the gradation reproduction area can be improved.

In addition, when a defect occurs in the array light source, the role distribution of the laser is switched so that a decrease in gradation and a decrease in edge reproducibility due to the defect can be reduced.

Furthermore, since the data can be coded by dividing the image data into blocks, the amount of image data to be transmitted can be reduced.

Further, the provision of the data code means makes it possible to easily generate a laser lighting control signal based on the pattern number code, the group information, and the role assignment information.

[0042]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG.
1 shows an image forming apparatus 10 according to a first embodiment of the present invention.

A photoconductor 12 is provided inside the image forming apparatus 10. A charger 14 is provided so as to face the image forming surface of the photoconductor. Thereby, the photosensitive member 12
Can be charged.

An optical scanning device 16 is provided inside the image forming apparatus 10. The optical scanning device 16 uses a multi-element laser array composed of 36 elements arranged in a parallelogram as a light source, and emits one laser beam from each element of the multi-element laser array, for a total of 36 laser beams. Can be simultaneously and independently scanned and exposed. Thereby, an electrostatic latent image can be formed on the surface of the photoconductor 12.

A control unit 18 is connected to the optical scanning device 16. The control unit 18 receives an image signal from a computer or the like, generates a modulation signal based on the image signal, and transmits the modulated signal to the optical scanning device 16.

Further, a developing device 20 is provided so as to face the photoconductor 12. The developing device 20 can visualize the electrostatic latent image by attaching toner to the electrostatic latent image formed on the surface of the photoconductor 12.

The electrostatic latent image formed on the surface of the photoreceptor 12 to which the toner has adhered is transferred to a sheet or the like by a transfer unit (not shown) at an image transfer position.

Further, an erase lamp 22 is provided so as to face the photoconductor 12. The eraser 22 removes the charge of the charged photoreceptor 12 so that an image can be formed again.

FIG. 3 shows the optical scanning device 16.

The 36 laser beams emitted from the multi-element laser array 24 are converted by the collimator lens 26 into parallel light.

The laser beam converted into parallel light by the collimator lens 26 is applied to a cylinder lens 28
, And is guided to the polygon mirror 30.

A part of the laser beam converted into a parallel light by the collimator lens 26 is guided by a half mirror (not shown) or the like and enters a light quantity detection sensor for detecting the light quantity of the laser beam. The amount of light is detected.

The polygon mirror 30 is rotated by a scanner motor (not shown) and scans the laser beam on the photosensitive member 12 in a polarized manner.

The Fθ lenses 32 and 34 keep the scanning speed of the laser beam on the photosensitive member 12 uniform, and
The laser beam is imaged on 2.

FIG. 4 schematically shows the setting of the potential on the surface of the photoconductor 12.

The potential on the surface of the photosensitive member 12 is set to VH, VL,
Each parameter of Vbias is set.

VH is the highest potential on the photosensitive member 12, VL
Is the lowest potential on the photoconductor 12 on which an image is formed by laser exposure, and Vbias is a threshold potential applied to the surface potential of the photoconductor 12 set between VH and VL. VH, VL, and Vbias are set so that the toner adheres to the exposed photosensitive portion so that the potential on the photoconductor 12 becomes lower than Vbias (VH, VL).
And Vbias are all absolute values. ).

The potential difference between VH and Vbias is represented by Vcln.
(The value of Vcln is an absolute value.) VH is Vb
ias is set to an optimum value having a sufficient potential difference Vcln so that the toner of the opposite polarity does not adhere to the surface of the photoconductor 12 and the toner does not adhere to the background portion.

The potential difference between Vbias and VL is represented by Vc
ont. VL is Vbias relative to photoconductor 12
An optimal value having a sufficient potential difference Vcont is set so that an appropriate amount of toner is stably attached to the portion where the image is formed above.

The intensity of the laser is obtained as an intensity for obtaining VL at an average potential when exposure is performed when the input density is 100%, and the intensity of each element is determined by its lighting conditions.

FIG. 5 shows the outline of the multi-element laser array 24 used in the image forming apparatus of the present invention and the block configuration of the elements in the multi-element laser array 24.

The multi-element laser array 24 has a light emitting point L _XY (X corresponds to the main scanning direction and Y corresponds to the sub-scanning direction) on a two-dimensional plane. )
Simultaneous emission of a large number of laser beams such as spots is possible.

In the multi-element laser array 24, each light emitting point is located at each vertex of a parallelogram. By tilting the multi-element laser array 24 at an appropriate angle, the photosensitive member 12
A scanning line of 2400 dpi can be formed thereon.
This scanning line pitch is 1 corresponding to a resolution of 2400 dpi.
The pitch is 0 μm, and the beam diameter is 5 in the main scanning direction.
5 μm, and the sub-scanning direction is 60 μm.

In order to prevent the image forming position in the main scanning direction from being shifted, the control unit 18 performs delay control on the modulation signal of each laser, and 36 laser beams are simultaneously and independently adjoined on the signal. Can be scanned.

The multi-element laser array 24 is divided into blocks each having four elements forming continuous scanning lines. Of the four elements in the block, the central two elements take off three levels of laser intensity of OFF, intensity level 1 and intensity level 2, and the two elements surrounding the central two elements are OFF and intensity level 1 binary. The laser intensity can be controlled so as to take it. In addition, the assignment of the intensity to the laser element is common to each block. In the laser array of 36 elements in the present embodiment, 9 blocks can be configured.

Hereinafter, an element capable of obtaining ternary laser intensity is referred to as a main element, and an element capable of obtaining binary laser intensity is referred to as a sub-element.

In this embodiment, the image data is 2
Supplied as binary (ON / OFF) data of 400 dpi.

Next, the driving conditions of this embodiment will be described.

In the exposure in which the light amounts are evenly distributed, the exposure profile when all the elements are turned on is as shown in the center of FIG. 29 as described in the section of the prior art. Assuming that (PVL) is 1, the intensity of each light emitting point is 0.266, which is about 1 / 3.76 of that.

On the other hand, in the present invention, the illuminated pixels and their intensities are changed according to the image data of four pixels that are continuous in the sub-scanning direction.

FIG. 6 shows the correspondence between the image data in the block and the lighting states of the elements in the block.

The lighting state of each element and the laser intensity of each element are determined by image data corresponding to each block. When the image data in the block contains 0, the laser corresponding to each image data has the intensity level 1
When the light is turned on at (P1) and the data of all the pixels in the block is 1, the lighting state is switched so that the main element (the central two elements in the block) is turned on at the intensity level 2 (P2) and the sub-element (the above-described element). The two elements at the end of the two central elements are turned off (O
FF).

FIG. 8 shows intensity level assignment to each element in the present embodiment.

The intensity levels that can be taken by the elements in the block thus determined are as shown in the graph, and it is possible to appropriately control input image data expressed in binary.

That is, when the input image density is 100%,
In the input image data, all four pixels in the block become 1, and of the four pixels, the main element (central two pixels) is turned on at the intensity level 2 and the sub-element (central two pixels at the end 2).
Pixel) is an exposure condition that does not light.

FIG. 7 shows a beam combining profile of intensity level 2 (see FIG. 6) in the present embodiment.

The exposure state in this case is as shown in the graph. If the intensity PVL for obtaining VL is 1, the intensity of the intensity level 2 of the lit pixel is about 0.53.

Further, when the image data of at least one of the four pixels in the image data is 0, the pixel corresponding to the image data of 1 is turned on at the intensity level 1. At this time, the emission intensity at the intensity level 1 is set to 0.3 in consideration of the positional accuracy of the edge.

Here, comparing the exposure profiles in the sub-scanning direction when all the pixels shown in FIG. 28 (prior art) are uniformly lit, the exposure profile in FIG. 29 has a large beam overlap and the composite exposure profile is flat. On the other hand, in FIG. 9 (this embodiment), the composite exposure profile has a distribution, similarly to the conventional low-resolution (600 dpi) exposure.

The intensity level 1 is P1 and the intensity level 2 is P
2. The normal strength per element when allocated equally is P
N, P1V, the strength for obtaining the VL pass-through is PVL
When L = 1 is replaced, each intensity becomes PVL = 1 P1 = 0.3 P2 = 0.53 PN = 0.27.

In the setting of the respective intensities in the present embodiment, the intensity of the intensity level 1 and the intensity of the intensity level 2 are both set higher than in the conventional case where the intensities of the respective light emitting elements are equalized. Exposure can be performed more stably than conventional exposure.

Next, reproduction of gradation will be described. Below P
The value of VL is treated as 1.

For reproduction of gradation, a digital screen system is used. Halftone dots are formed by the digital screen, and gradation is reproduced by the area occupancy of the halftone dots.

In the conventional exposure, since the intensity assigned to each element is low, the intensity of the peak of the exposure profile becomes insufficient unless continuous lighting is performed in the sub-scanning direction. For example, at the peak of intensity when four pixels continue, the intensity stops at 0.82.

On the other hand, in the present invention, when four pixels are continuous, the central two elements in the block are lit at intensity level 2, so that the combined intensity is 1, and stable exposure can be performed. When four pixels continue between blocks, each element (both the main element and the sub-element) is lit at intensity level 1, but even in this case, the combined intensity is 0.
93, which makes it possible to perform more stable exposure than before.

Further, in the conventional exposure mode, the intensity of each element is small, and the intensity of the peak is insufficient even if the halftone pixels continue in the main scanning direction. In the embodiment, since the strength of each element is large, the restriction on the halftone dot growth is relaxed.

FIG. 1 shows the configuration of the halftone dots and the lighting state.

The center of the halftone dot is a continuous four dots in the sub-scanning direction.
Since all the image data of the pixels are 1, the pixels are replaced with the lighting pixels of the intensity level 2.

FIG. 10 shows an example of a lighting state in highlight and a profile in the main scanning direction.

FIG. 11 shows an example of the lighting state of the shadow portion and the profile in the main scanning direction.

Although the input image data of the line screen system is shown here, the profile in the main scanning direction is the same in the main scanning direction regardless of the position in the sub-scanning direction in the exposure by the conventional technique. However, in the present embodiment, there is a lighting / non-lighting element, so that an exposure profile at a position in the sub-scanning direction is different. Since the profile A & A 'for normal exposure is located between the profiles A and A' in the present embodiment, a large contrast can be obtained at the position in the sub-scanning direction corresponding to the non-lighted element. Thus, it is possible to expand the gradation reproduction area.

Next, the reproduction of the edge will be described.

When the laser intensities are evenly allocated by the conventional technique, the position of the edge can be controlled in units of 10 μm by turning on / off the pixels at the edge. Similarly, the center position accuracy of the image can be controlled in units of 10 μm. However,
In the case of a thin line or the like, since the intensity per element is small, the stability of image reproduction is reduced.

FIGS. 12 to 16 show the sub-scanning direction 4 with the pitch in the sub-scanning direction of 10 μm in this embodiment.
The change of the position of the edge of the ８8 dot line is shown.

Since the lighting state of the element differs depending on the image data, the positional accuracy of the edge slightly decreases. The right edge position in the figure is based on the position in FIG.
16 to 0, +10 μm, +20 μm, +33
μm and +40 μm. In recent years, the demand for image quality has increased, and the position accuracy of the edge is 2400d.
Although pi is required, the effect of stably reproducible fine lines is large due to the high laser intensity, and the error of the edge position does not cause a significant problem with respect to the effect.

Next, a case where a certain element cannot be turned on due to a defect in the laser element will be described.

FIG. 32 shows a profile in the sub-scanning direction at the time of occurrence of a defect in exposure according to the conventional technique.

When the pixels are not lit when the intensity is evenly allocated, the main scanning line is not formed. When the input image density is 100%, the exposure distribution is disturbed and the latent image is not formed. The stability against In the case of a low-density image, the peak value of the intensity of the combined exposure profile decreases, and the stability of image reproduction decreases.

On the other hand, in this embodiment, since the lighting state of the elements is controlled according to the image data arrangement, it is possible to reduce the influence of defective elements on the image quality (details will be described later). By arranging the defective element so as to be a sub-element, the influence of the defective element on the image quality is reduced. Since the defective element becomes a sub-element, the input image density becomes 100%.
In the case of%, only the main element is turned on, so that the defective element has no effect on the image quality.

The influence of the defective element becoming a sub-element is at the time of edge reproduction and half-tone reproduction. In this embodiment, however, the influence at that time is reduced.

FIG. 17 shows the results obtained when the element has a defect.
The dot line profile is shown.

Taking a 4-dot line of 2400 dpi in the sub-scanning direction as an example and comparing the case of the prior art with the uniform allocation and the case of the present embodiment, when a defective element occurs, The combined exposure profiles near the element are as shown in FIGS.

As shown in FIG. 33, the exposure is performed by the conventional technique, and a defective element is included in the line.
When the defective element corresponds to the edge, the position of the edge does not change in the defective element.

On the other hand, as shown in FIG. 17, in this embodiment, the edge moves even in the defective element portion,
In addition, since the laser intensity is ensured as compared with the conventional technology at the time of uniform allocation, a decrease in line reproducibility due to a defective element is reduced.

In some cases, the edge position does not change due to a defective element in this embodiment depending on conditions.
In this embodiment, since the laser intensity is secured, it is apparent that the influence of the defective element is greatly reduced as compared with the case of the equal allocation according to the conventional technique. This also affects the generation of halftone dots for reproducing halftones in the present embodiment. In the equal-distribution exposure according to the conventional technique, the continuity of gradation is lost in a portion including a condition in which a defective element emits light. On the other hand, in the present embodiment, defective elements are assigned to sub-elements,
When the halftone dot is generated, the lighting is switched to the lighting by the main element due to the continuous image data. As a result, the probability that the element that must be turned on is a defective element is greatly reduced, and even if there is a defective element, the edge position changes, thereby suppressing a decrease in gradation reproducibility due to the occurrence of the defective element. Can be done.

In this embodiment, the lighting conditions for the input image data are defined as shown in FIG. 7. However, according to the arrangement of the data in the block, the lighting state of the peripheral blocks, or objects such as characters, line drawings, and halftones. By switching the lighting intensity level, the stability of image reproduction can be further improved.

Although the description is omitted, the allocation of the intensity to the main element is made into four values, and the intensity is subdivided or expanded to arrange the data in the block, the lighting state of peripheral blocks, characters, line drawings, and the like. It is possible to set more appropriate lighting conditions according to an object such as a halftone. In addition, by storing a plurality of conversion conditions for the main element and the sub element in a table format, the lighting conditions can be easily switched in response to a change in the conditions.

Note that the assignment of the main element and the sub element to the laser element is not fixedly assigned. For example, when fixedly assigned, the element assigned to the main has a higher lighting time and lighting intensity than the element assigned to the sub, so that the life is shortened. In order to avoid this, the assignment of main and sub may be switched so that the life of each element becomes equal.

In the case of constructing a system for forming a color image, the assignment of elements may be changed so that the registration of each color is matched.

In the present embodiment, the basic scanning line is constituted by treating four pixels continuous in the sub-scanning direction as one unit and lighting the main element at intensity level 2, but the beam diameter which can be realized by the optical system By changing the number of pixels to be handled and the assignment to the main elements and sub-elements according to the above, the same effect can be obtained with respect to the configuration of the basic scanning line and the edge reproduction.

(Second Embodiment) A second embodiment of the present invention will be described.

In this embodiment, a description will be given of a case where a defective element occurs.

A multi-element laser array composed of 6 × 6 (36 in total) elements is used as a light source, and each element is numbered from 1 to 36 so as to correspond to 36 continuous scanning lines. .

FIG. 18 shows a multi-element laser array 24 according to the present embodiment.

The element 10 of the multi-element laser array 24
1, 102, 135 and 136 are allocated as spare pixels, and a total of three elements 103 to 134 are used for actual image formation.
Two pixels are used. Further, a block is configured as a unit of four pixels continuous in the sub-scanning direction. The lighting conditions in the block are the same as in the first embodiment of the present invention.

In order to judge a defective element, it is necessary to separately provide a light amount detection sensor since the light amount by the back beam cannot be detected with the multi-elements like the edge emitting laser.

On the other hand, since the number of laser elements is large, the system is close to multiple exposure, but the light quantity (intensity) of each laser element is relatively smaller than that of an exposure system using an edge emitting laser. .

Therefore, in an image forming apparatus using a multi-element light source, a method is adopted in which a part of the beam after collimating the beam from the light source is extracted and its light amount is detected. However, when the above method is adopted, it is difficult to emit light one element at a time and detect it because the light amount of each beam is small. Also, since the number of elements is very large, it is difficult to individually detect and control. Since it takes a long time, a method is employed in which a plurality or all of the lights are simultaneously turned on to perform detection.

It is assumed that the intensity of all lasers has been adjusted at the time of initial adjustment in the case of employing this method.

In this embodiment, when a defect occurs in a laser element, the laser element is assigned to a sub-pixel.

As in the case of starting the image forming apparatus,
When there is enough time, and the detection control of the individual laser light amount is possible, a laser element that cannot be turned on can be specified in the detection control, and the assignment of the laser element is changed based on the information. At the same time, by setting a flag of the failure of the laser element, it is easy to cope with the maintenance.

In a state where the amount of light of each laser cannot be detected, such as during printing, the laser element is set to # 4.
n, 4n-1, 4n-2, 4n-3} (n = 1, 2,...
.., 8), and illuminate each set to detect the amount of light. The amount of light is adjusted when the image forming apparatus is started up, and if there is no defect, the amount of light in each group is almost the same. Therefore, it is possible to identify the group in which the defect has occurred from the difference in the amount of light when the defect occurs. Become. If the determination is difficult, each set may be further divided into two sets to increase the rate of change of the detected light amount when a defect occurs, thereby improving the detection accuracy.

In the present embodiment, a multi-element arranged in 6 elements × 6 elements is used. However, in a multi-element arranged in 4 elements × 4 elements or 8 elements × 4 elements, for example, a column unit is used. By illuminating with, a defective element can be detected.

As another detecting means, a synchronous sensor may be used, or a method of arranging a light amount detecting sensor outside the image area on the scanning line as in the case of the synchronous sensor. However, since the scanning beam based on the image data is incident on the sensor arranged as described above, not all the elements emit light at the same time. For this reason, not all beams can be detected simultaneously.

From this, a method of detecting elements that can be simultaneously incident on the sensor in groups is considered. For example, since the multi-element light-emitting elements are arranged as shown in FIG. 18, the scanned beams are simultaneously incident on the synchronous sensor in units of columns. Therefore, by illuminating the laser elements in columns so that the beam is incident on the synchronous sensor, it is also possible to detect the light quantity in columns. Further, in the present embodiment, since the function of the main element / sub-element is assigned to each element, a group consisting of four elements continuous in the sub-scanning direction is further divided into groups according to functions, and the judgment is performed. Thus, the beam may be detected.

For example, laser element numbers 101 and 113
And 125 as one set, and 107, 119 and 131 as one set, it is possible to detect the light quantity of the elements having the same function, and it is possible to determine the defect of the elements. Become. If the arrangement of the elements of the multi-element laser array is such as an arrangement of 4 elements × 4 elements or 8 elements × 4 elements, the detection may be performed in units of columns.

When a defect is found in an element of the multi-element laser array by such a detecting means, if a defect is found, it is assumed that {4n,
n-1, 4n-2, 4n-3} (n = 1, 2,...,
It is required to determine which of the elements in 8) has a defect, and the function of the main element / sub element is assigned to the laser element again.

The switching method will be described in the third embodiment.

(Third Embodiment) Hereinafter, a third embodiment of the present invention will be described.
An embodiment will be described.

In this embodiment, the optical scanning device 16 of the first embodiment can be used as it is, but in order to further simplify the description, a 4 × 4 16-element multi-element laser array is used. . In addition, since the configuration of the control unit 18 changes, that part will be described.

FIG. 19 shows an image forming apparatus according to the third embodiment.

The image forming apparatus comprises an image processing apparatus 200 and an image forming apparatus 10. The image processing apparatus 200 includes a plurality of client computers 202A, 202B,
... a group of client computers 202 comprising
Other device group 204 including server computer 204A and image processing device 204 # (hereinafter collectively referred to as device group)
And are connected via a network 206.

In the present embodiment, the image processing device 20
Although the case where the image processing apparatus 200 and the image forming apparatus 10 are configured as separate blocks as separate blocks has been described, an apparatus in which the image processing apparatus 200 and the image forming apparatus 10 are integrally configured may be used.

Information sent from the client computer group 202 or the other device group 204 to the image processing device 200 is analyzed by a communication protocol analysis, PDL (Page Desert).
(cliption Language: page description language) Performs command analysis, data expansion processing, code conversion processing, and the like, temporarily stores the image data in a buffer memory (not shown), and synchronizes the image data with the image forming apparatus 10 while synchronizing the image data with the image forming apparatus 10. Output to

The image data written in the buffer memory of the image processing apparatus 200 is read out in synchronization with a control signal sent from the image forming apparatus 10, passed to the image processing unit 208 in the image forming apparatus 10, and A modulation signal is generated and supplied to the image exposure unit 210. When the image data written in the buffer memory is compressed, the image data is read out while performing the decompression processing at the same time.

FIG. 20 is a schematic diagram of the image processing unit 208.

The image processing section 208 is provided with a line buffer 212 for temporarily storing coded 8-bit image data.

A decoder 214 for converting the 8-bit image data transmitted from the line buffer 212 into an exposure image and determining the exposure light amount of each pixel is connected to the line buffer 212.

The decoder 214 has a selector 216.
Is connected.

The selector 216 includes the LD driver 2
18 are connected.

A laser diode array 220 is connected to the LD driver 218.

The sensor 222 monitors the lighting state of the laser diode array 220.

The image processing unit 210 includes a line buffer 212, a decoder 214, a selector 216, and a PCL.
A buffer, a delay circuit, a data latch, and the like (not shown) for synchronizing with K are included.

The details of each component will be described below with reference to the drawings.

The image data read from the image processing device 200 is input to the image processing unit 208. As shown in FIG. 21 or 22, image information is sent to the input image data as a pattern number and the processing is executed.

The image data read from the image processing device 200 is input to the line buffer 212 of the image processing unit 208.

FIG. 20 shows an LD driver 218, a laser diode array 220, and a sensor 222 for explanation.

FIG. 21 is a schematic diagram showing the operation of the line buffer 212 in the image processing section 210.

In the line buffer 212, 8-bit image data is read by one pulse of PCLK. In the present embodiment, the image data is bitmap data of 4 × 4 pixels of 16 pixels and is coded data of 8 bits. Therefore, the image data can be read by one pulse of PCLK, that is, PCLK of 1/4 speed. . Further, the image data width may be set to 4 bits and read with two pulses of PCLK, that is, PCLK at a half speed, or the image data width may be set to 2 bits and read with four pulses of PCLK.

Further, since the capacity of the line buffer 212 is obtained by converting data of 16 bits into coded data of 8 bits, the capacity of the line buffer 212 may be half that of one line in the main scanning.

On the other hand, FIG. 34 shows an image processing section of a conventional image processing apparatus. In this image processing unit, one data line is required for one laser diode, and one pulse of PCLK is required for one pixel in order to directly read the bitmap data. Further, the line buffer 212 needs a capacity for one main scanning line.

FIGS. 22 and 23 are schematic diagrams showing the operation of the decoder 214 in the image processing unit 208 shown in FIG.

The decoder 214, as shown in FIG.
It mainly comprises an LUT (Look Up Table) and a modulation circuit. The LUT is 4 pixels × 4 Level based on predetermined data from 8-bit image data.
Pattern data for 16 pixels to which intensity information of 1 (2 bits) × 4 columns is added is output.

At this time, the image data may be converted into a pattern shape different from the original Bitmap pattern assumed.

For example, when coded image data of 0x06 is input as shown in FIG. 22A, the original patterns are 1111, 1111, 1110, 1
100, but the pattern output from the LUT is 02
20, 0220, 1110, 1100, and 1111
Is converted to 0220, and the intensity information is added simultaneously with the conversion of the pixels to be turned ON / OFF.

In the case of FIG. 22B, the image data is 0x1E, and the original pattern is 0000, 0110, 0110, 0000 in order from the upper left to the lower.
The pattern output from the UT is 0000,0300,0
030,0000 and 0110 is 0300 or 0
030, and the intensity information is added simultaneously with the conversion of the pixels to be turned ON / OFF.

In the present embodiment, only one type of LUT is provided, but a plurality of LUTs are provided for switching or
Processing such as arbitrarily replacing data previously stored in the LUT may be added. Furthermore, the pattern to be output may be changed by inputting data to be input to the LUT together with data around the target pixel.

On the other hand, as shown in FIG.
1 with laser intensity information output from LUT
Pulse Gen according to the pattern data for 6 pixels
Select and output the Plus waveform generated by the errator. For example, as the data 2210 of the Y row, a waveform of two pixels of the Plus waveform corresponding to the level of 2, a pixel of the Plus waveform corresponding to the level of 1 and a waveform of one pixel turned off corresponding to the level of 0 are output. With this, LU
The laser intensity information output from T is converted into a pulse-width modulated signal, which becomes a laser lighting signal. That is, the pulse width modulation makes it possible to control the exposure energy integrated by multiplying the exposure time by the laser intensity.

Next, an outline of the operation of the selector will be described.

FIG. 24 shows the image processing unit 20 shown in FIG.
8 shows an operation schematic diagram of the selector 216 in FIG.

FIG. 24 shows an outline of the operation of the selector. To make the explanation easier, here
A multi-element laser array including ten laser elements will be described.

The selector is mainly a Matrix S
It consists of a switch and a control circuit.
Depending on the state of the laser detected by or, the roles of the main element and the sub element can be assigned to the elements (LDs) in each group, and the roles can be further changed. For example, it is assumed that each LD is allocated as shown in FIG. That is, it is assumed that the LD numbers 300 to 309 are allocated to the spare element, the sub element, the main element, the main element, the sub element, the sub element, the main element, the main element, the sub element, and the spare element, respectively. Now, assuming that the LD with the LD number 303 assigned to the main element has failed, the control circuit detects the failure, sets a flag and operates matrix switch, and the LD with the failed LD number 303 becomes the LD of the sub element. Is re-assigned. The LD assigned to the sub-element
Assuming that the LD of No. 301 has failed, the control circuit detects the failure and sets a flag. However, since the LD is a sub-element, no reallocation is performed.

[0163]

As described above, according to the present invention, even in an image forming apparatus using a multi-element laser having a beam diameter relatively large with respect to the scanning pitch, each element is assigned a role. By controlling the light emission of each element according to the input image information, there is an effect that it is possible to provide an image forming apparatus without narrowing the gradation reproduction area of the image.

Further, by switching the role assignment given to each element at the time of a failure, there is an effect that an image forming apparatus which does not easily affect the image quality as an image defect when a failure occurs in the element can be provided.

Further, the data transfer speed can be increased by using the input image information as a pattern number code representing a bit image of a pixel block composed of an array of a plurality of pixels. Since the amount of memory to be used can be reduced, a relatively inexpensive device can be provided even when transmitting high-resolution data at high speed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating generation of halftone dots in the present invention.

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

FIG. 3 is a top view of the optical scanning device according to the present invention.

FIG. 4 is a schematic diagram of setting a potential on the surface of a photoconductor in the present invention.

FIG. 5 is a schematic view of a multi-element laser array according to the present invention.

FIG. 6 is a diagram showing correspondence between image data in a block and lighting states of elements in the block according to the present invention.

FIG. 7 is a beam synthesis profile of intensity level 2 in the present invention.

FIG. 8 is a diagram showing intensity level assignment to each element in the present invention.

FIG. 9 is an exposure profile in the sub-scanning direction corresponding to an input density of 100% in the present invention.

FIG. 10 shows a lighting state and a profile in a main scanning direction in a highlight according to the present invention.

FIG. 11 shows a lighting state of a shadow portion and a profile in a main scanning direction.

FIG. 12 is a diagram showing the accuracy of an edge position in the present invention.

FIG. 13 is a diagram showing the accuracy of an edge position in the present invention.

FIG. 14 is a diagram showing the accuracy of an edge position according to the present invention.

FIG. 15 is a diagram showing the accuracy of an edge position according to the present invention.

FIG. 16 is a diagram showing the accuracy of an edge position in the present invention.

FIG. 17 is a 4-dot line profile when a defect occurs in the present invention.

FIG. 18 is a schematic view of a multi-element laser array according to the present invention.

FIG. 19 is a schematic view of an image forming apparatus according to the present invention.

FIG. 20 is a schematic diagram of an image processing unit according to the present invention.

FIG. 21 is an operation schematic diagram of a line buffer in the image processing unit according to the present invention.

FIG. 22 is a schematic diagram (1) of the operation of the decoder according to the present invention.

FIG. 23 is an operation outline diagram (2) of the decoder in the present invention.

FIG. 24 is an operation schematic diagram of a selector in the present invention.

FIG. 25 is a configuration diagram of an image forming apparatus according to a conventional technique.

FIG. 26A shows a laser array according to a conventional technique, and FIG. 26B shows an exposure profile in a sub-scanning direction on a photoconductor surface.

FIG. 27 is a low-resolution sub-scanning direction exposure profile according to the related art.

FIG. 28 shows an exposure profile and a composite exposure profile of each element of a low-resolution image forming apparatus according to a conventional technique.

FIG. 29 shows an exposure profile and a combined exposure profile of each element in a multi-element laser array according to a conventional technique.

FIG. 30 is a diagram showing a relationship between an input density and an exposure profile in pulse width modulation when the input density is changed in the conventional technique.

FIG. 31 is a diagram showing a relationship between an input density and an output density in a conventional technique.

FIG. 32 shows a profile in the sub-scanning direction when a defect occurs in exposure in the related art.

FIG. 33 is a 4-dot line profile at the time of occurrence of a defect in the related art.

FIG. 34 is a configuration diagram of an image processing unit of an image forming apparatus according to a conventional technique.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 image forming apparatus 12 photoreceptor 16 optical scanning device 18 control unit 24 multi-element laser array 26 collimator lens 28 cylinder lens 30 polygon mirror 32 Fθ lens 34 Fθ lens 200 image processing device 208 image processing unit 210 image exposure unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) H04N 1/23 103 H04N 1/04 104A 5C074 F term (reference) 2C362 AA16 AA22 AA75 BA60 BA67 CA09 CA10 CA11 CA12 CA14 CB19 CB29 CB74 EA04 EA07 2H045 AA01 BA23 BA32 DA28 2H076 AB05 AB06 AB09 AB41 AB75 AB85 EA21 2H110 AA19 AA21 CD17 5C072 AA03 BA03 BA04 BA15 BA20 HA02 HA06 HA13 XA05 5C074 AA05 AA07 BB02 GG02 DD03

Claims (6)

[Claims] 1. A light beam emitted from an array light source comprising a plurality of light emitting elements arranged at a predetermined density and light emission control means for controlling light emission of the light emitting elements. The main scanning is performed in one direction, the light beam and the image carrier are relatively moved in a sub-scanning direction substantially orthogonal to the light beam scanning direction, and an image is formed on the image carrier according to an image signal. In the forming apparatus, a dividing unit that divides the light emitting elements of the array light source into a plurality of groups, a plurality of light emitting elements included in the group, a main beam having a plurality of intensity levels for recording a basic image, Role setting means for setting an auxiliary beam having one intensity level for performing auxiliary exposure, and multi-beam laser drive control means for performing exposure / modulation control for each group according to the image signal. Image forming device. 2. The image forming apparatus according to claim 1, wherein a main beam included in one group of the light emitting elements has an auxiliary beam function according to image data. 3. The image forming apparatus according to claim 1, wherein a beam diameter of the light beam on the image carrier is at least twice as large as an interval between the plurality of light beams. Image forming device. 4. A light emitting device that further comprises: detecting means for detecting an abnormality of the light emitting element; and transmitting means for transmitting an abnormality to a higher-level control device when the detecting means detects the abnormality. 4. The image forming apparatus according to claim 1, wherein when the element is a main beam, the group is changed to a group in which an image defect does not occur in the main beam at the time of division by the division unit. 5. apparatus. 5. The image processing apparatus according to claim 1, wherein the image data is a pattern number code representing a bit image of an image block composed of an array of a plurality of pixels. Image forming device. 6. The multi-beam driving means, based on an input pattern number code, group information from the division means, and role assignment information from the role assignment means, assigns the pattern number code to a bit of a pixel block. 6. The image forming apparatus according to claim 5, further comprising a restoration unit for restoring an image, and a decoding unit for outputting light emission information according to the group and the role assignment.