JP2003312051A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus employing a plurality of light sources in which a clear image can be outputted by preventing deterioration of the image, due to difference in the quantity of light among the plurality of light sources or deformation of the dot diameter of a latent image. <P>SOLUTION: The imaging apparatus comprises a plurality of light emitting sources, a light emitting source driving section having a current setting means for determining the emission quantity and a switching means for turning the light emitting source on/off, and a section for scanning a photosensitive body with a rotary deflected writing light. The current setting means sets an input gray scale range by selecting two points which can be approximated linearly (approximation curve 2) by the I/O gray scale characteristics of at least one light emitting source as maximum and minimum gray scale points. The switching means sets the ratio Tp/Tw of the emission time (Tp) and the emission period (Tw) at an arbitrary gray scale point between the maximum and minimum gray scale points at 0.75 or less, and sets the emission timing of adjacent light emitting sources to be different. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus that forms an image by irradiating a photoconductor with light beams from a plurality of light emitting sources.

[0002]

2. Description of the Related Art Generally, an image forming apparatus such as a printer or a copying machine using an electrophotographic system uniformly charges the surface of a photosensitive member by a charging device, and an optical writing unit generates an optical signal corresponding to externally recorded data. A beam is irradiated onto the surface of the photoconductor to form an electrostatic latent image. In the optical writing means,
The light beam for irradiating the surface of the photoconductor collects parallel light rays emitted by a laser diode or the like, and scans the surface of the photoconductor by the rotating and deflecting means. Further, the optical writing means of the laser scanning optical system needs a synchronization signal that defines the writing start timing, and this signal is generated by the synchronization detection means provided at an arbitrary position of the optical writing means.

As a method of forming an electrostatic latent image, a so-called binary recording method in which a light beam is turned on / off on the surface of a photoconductor has become popular. In the binary recording method, image processing such as a dither method and an error diffusion method is performed on a recording signal to realize halftone reproduction. In the image forming apparatus, an image visualization agent is attached to the electrostatic latent image formed on the photoconductor surface as described above by the developing means to obtain a visualized image visualized on the photoconductor surface and transfer it. The image visualized image is transferred to a recording medium by means, and the image transferred to the transfer material is heated and pressed by the fixing means and fixed on the recording medium. In recent years, demands for higher pixel density and higher speed have been increasing in image forming apparatuses. Therefore, as a method of increasing the speed of the image forming apparatus, a plurality of light beams are simultaneously emitted onto a photosensitive member surface by using a multiple beam laser capable of emitting a plurality of light beams at the same time or a laser array element including a plurality of laser diodes. A method of irradiating and forming an electrostatic latent image is used. In the above binary recording method, in order to achieve both stable resolution and gradation reproducibility, 1000 values / m
It is known that it is necessary to perform area gradation with m ² .
To meet this condition, a recording density of 600 × 1200 dpi
In the above image formation, the latent image dots formed on the photoconductor need to be accurately formed in the latent image position and the latent image dot diameter, and the fluctuation of the exposure amount for forming the latent image needs to be small. It is said that However, in an image forming apparatus using a plurality of laser beams, when performing image formation by exposing a plurality of lines at the same time by scanning with a plurality of laser beams, there is a concern about image deterioration due to a difference in light amount of the plurality of lasers. It That is, the gradation characteristics are reversed due to the difference in the light amount of a plurality of lasers, and the gradation characteristics and sharpness are affected.

Various solutions have been proposed for such problems. For example, in Japanese Patent Application Laid-Open No. 07-319086, the light quantity distribution of emitted light of each laser diode is detected using a light quantity distribution measuring means, and the effective lower limit of the beam of each laser diode is detected based on the detected quantity. A method of controlling the exposure amount of each laser diode so that the width of the light amount distribution curve in the exposure amount becomes equal, or measuring the density of the toner image visualized by the toner on the latent image formed by each laser beam, and measuring it A method using a density measuring means for controlling the exposure amount of each laser diode based on the value is shown.

However, in the invention of the above-mentioned item, the profile of the output gradation characteristic showing the relationship of the output gradation to the input gradation of the image data is, according to the experiment by the present inventor, the light quantity of the laser diode itself due to the influence of temperature. Due to fluctuations or fluctuations in the circuit multiplier of multiple circuits of the laser diode drive circuit, non-linear characteristics are shown in the low gradation part and the high gradation part of the gradation profile, forming an unstable region. As a result, it has been found that it is difficult to make the gradation profile characteristics of a plurality of beams have the same gradient, since the gradation characteristics of the middle portion show linearity. However, conversely, by using the gradation region having this linearity, it is possible to reduce the difference in the light amount of a plurality of lasers and prevent image deterioration.

In a laser diode array having a plurality of light sources, the distance between the light emitting sources is generally as small as several tens of microns. When each light source of such a laser diode array is driven individually, a thermal difference occurs between the light sources, and the influence of driving one light emitting source affects adjacent light emitting sources as a light amount variation, so-called thermal crosstalk. Is known to occur. Various methods have been proposed in order to reduce the fluctuation of the light amount due to the thermal crosstalk. For example, the invention of JP-A-5-226786 discloses that a temperature change is detected and the temperature of the laser chip is kept constant by a thermoelectric cooling element. However, there is a problem that the configuration of the present invention is complicated to be applied to an actual device.

[0007]

SUMMARY OF THE INVENTION Therefore, the present invention has been made in view of the above problems, and it is possible to prevent image deterioration due to the difference in the light amount between the light sources or the deformation of the latent image dot diameter even if a plurality of light sources are used. The purpose is to provide a device.

[0008]

According to a first aspect of the present invention, a plurality of light emitting sources, a switching means for turning on / off each light emitting source in a predetermined light emitting cycle according to an input image signal, and driving for each light emitting source. It has a current setting means for supplying a current to set a desired light emission amount, generates an output gradation value for an input gradation value based on the input image signal, and drives each light emitting source to generate a plurality of writing lights. Has a light source drive unit and an optical system,
In an image forming apparatus for forming an image, which comprises a rotary deflecting unit for simultaneously deflecting the plurality of writing lights and scanning each on the surface of the photoconductor, the current setting unit has a maximum value that the output gradation value can take. At least 1 between an absolute maximum value and an absolute minimum value that is the minimum value that can be taken.
Two points at which the input / output gradation characteristics of the two light emitting sources can be linearly approximated are selected as the gradation maximum point and the gradation minimum point, and
The switching unit has a function of setting the range of the input gradation according to the input gradation value determined by the point, and the switching unit is configured to emit light at an arbitrary gradation point between the maximum gradation point and the minimum gradation point. T
p) and the light emission period (Tw) (light emission ratio) is Tp /
Tw ≦ 0.75 is set, and when the plurality of light emitting sources emit light in the same light emitting cycle, the light emitting timings of adjacent light emitting sources are different from each other. . With such a configuration, the range in which the output / input gradation characteristics of a plurality of light emitting sources can be approximated to linearity is selected, so that the difference in the light emitting amount of each light emitting source can be reduced, and the light emitting ratio and the light emitting timing can be adjusted. By reducing the degree of interference, it is possible to reduce fluctuations in the amount of light due to thermal crosstalk and prevent image quality deterioration.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the output gradation values of the plurality of light emitting sources are the same at the input gradation value that determines the gradation maximum point. It is characterized in that the current setting means sets and the switching means sets such that the respective light emission ratios become the same. The image forming gradation is set within the range defined by the approximate straight line by setting the output levels of the plurality of beams to be the same at the input gradation value that gives the maximum point of the gradation and the emission ratios of the beams to be the same. By using the region, it is possible to reduce the light amount difference between the plurality of beams, and it is possible to prevent image quality deterioration due to the light amount variation.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, one point within the range between the maximum gradation point and the minimum gradation point is selected as a high gradation point, and the high gradation point is selected. A function in which the current setting means sets the output grayscale values of the plurality of light emitting sources to be the same at a predetermined input grayscale value, and the switching means sets the light emission ratios of the plurality of light emission sources to be the same. It is characterized by having. The image forming gradations in the range defined by the approximate straight line are set so that the plurality of beam outputs at the input gradation values that give the above-mentioned higher gradation points are the same, and the respective light emission ratios are the same. By using the region, it is possible to reduce the light amount difference between the plurality of beams, and it is possible to prevent image quality deterioration due to the light amount variation.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the gradation minimum point is a lower gradation point, and one or more intermediate points are provided between the high gradation point and the lower gradation point. It is characterized in that gradation points are provided and an image is formed using the high gradation points, the intermediate gradation points, and the low gradation points. By using a so-called low-value image forming method in which an image is formed by selectively combining a plurality of gradation points with such a configuration to obtain a larger number of gradations than a binary image, a light amount difference between a plurality of beams can be reduced. It is possible to improve the image quality by preventing the deterioration of the image quality due to the fluctuation of the light amount and increasing the number of gradations.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, in the light emission of the plurality of light emitting sources at the input gradation value that determines the high gradation point, the switching unit emits light of all light emitting sources. Constant, and the current setting means variably sets the drive current of each light emitting source, and the switching means performs all light emission of the plurality of light emitting sources at the input gradation value that determines the lower gradation point. The light emission ratio of the light emitting sources is made constant, and the current setting means variably sets the drive current of each light emitting source, and the plurality of light emitting sources at the input gradation value that determines the one or more intermediate gradation points. The light emission is characterized in that the switching means variably sets the light emission ratio. The light emission ratios of the plurality of light sources corresponding to the high gradation points are set to be constant for all light sources, and the drive currents are set to be variable, and the light emission ratios of the plurality of light sources corresponding to lower gradation points are set to be constant for all light sources. The current is variably set, and the light emission output corresponding to one or more intermediate gradation points is set by variably setting the light emission ratio of each light source. Since the number of tones can be set to be the same and the slope of the approximate linear function can be approximately approximated among a plurality of beams, the difference in light amount at the above-mentioned intermediate gradation points can be reduced and the deterioration of image quality due to light amount fluctuation can be prevented.

According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, a storage unit is further provided, and an input gradation value based on the image data is stored in the storage unit for each of the plurality of light emitting sources. It is characterized by According to a seventh aspect of the invention, in the image forming apparatus according to the sixth aspect, the stored input gradation value can be arbitrarily changed. According to an eighth aspect of the invention, in the image forming apparatus according to the seventh aspect, the stored input gradation value is changed with reference to image output. The generation of the drive signal can refer to the conversion data table for each of a plurality of beams, or the values of the conversion data table can be stored in advance, or the modulation signal setting data for setting the modulation of the signal stored in the storage means is Can be changed arbitrarily,
Alternatively, the modulation signal setting data is changed by referring to the image output to set the image forming gradation area and the input / output gradation characteristic in a range in which a plurality of beams are defined by the same approximate curve for each image forming apparatus. This makes it possible to reduce the difference in image quality between devices.

According to a ninth aspect of the present invention, in the image forming apparatus according to the first aspect, the current value setting data set by the current setting unit is stored in the storage unit for each of the plurality of light emitting sources. And The invention of claim 10 is
The image forming apparatus according to claim 9 is characterized in that the stored current value setting data can be arbitrarily changed. The current setting means stores current value setting data for determining a driving current for driving a plurality of beams in each storage means for each plurality of beams, or the modulation signal setting data stored in the storage means can be arbitrarily changed. As a result, the difference in image quality between devices can be reduced.

An eleventh aspect of the present invention is the image forming apparatus according to the first aspect, wherein an electrophotographic system is used as the image forming apparatus. Even in the image forming apparatus using the conventional electrophotographic method, it is possible to reduce the fluctuation of the light amount due to thermal crosstalk and prevent the deterioration of the image quality. The invention of claim 12 is
In the image forming apparatus according to claim 1, a digital electrophotographic system is used as the image forming apparatus. Even in the image forming apparatus using the conventional digital electrophotographic method, it is possible to reduce the fluctuation of the light amount due to thermal crosstalk and prevent the deterioration of the image quality. According to a thirteenth aspect of the present invention, in the image forming apparatus according to the twelfth aspect, the digital writing pixel density is 120.
It is characterized by being 0 dpi.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) This embodiment will be described below with reference to the drawings. FIG. 1 is a perspective view showing an outline of an image forming apparatus according to an embodiment of the present invention. The multiple light sources depicted in FIG. 1 are described herein as being laser light. The plurality of laser beams emitted from the plurality of laser light sources 10 are collected by the condenser lens 11
The parallel beam is converted into parallel light by means of the aperture 12, which has a slit portion corresponding to the size of the dot, so that only the required beam diameter is extracted, and the cylinder lens 13 forms an appropriate beam diameter. , And is scanned in the main scanning direction which is the major axis direction of the photoconductor 21. On the optical path, conversion fθ lenses 17 and 18 for converting an equal-angle scan into a constant-speed scan, an optical path changing mirror 19, and a cylinder lens 20 for converging light in the rotation direction of the photoconductor are arranged. The minute laser beam spot 22 is imaged on the top. Further, the beam returned by the synchronization detection mirror 23 is applied to the optical sensor 25 to generate a synchronization signal. Here, the image forming apparatus is, for example, a combination of a beam spot diameter of 35 μm and a photoconductor film thickness of 30 μm, and the light intensity on the photoconductor surface is aimed at an integrated light quantity value of 45 μW.

FIG. 2 is a block diagram of a drive circuit for driving a plurality of laser light sources according to the embodiment of the present invention.
FIG. 3 is a block diagram illustrating the operation of the driving unit according to the embodiment of the present invention. Looking at the flow of image data, the data input from the image data I / F 76 is converted into a pulse drive signal by the data conversion unit 75, and the drive control unit 74a.
The drive signal time is generated at ~ 74d, and the LD drive unit 73a is generated.
Is input to ~ 73d. The LD drive unit 73 generates a laser diode drive current by combining the drive current setting level generated by the LD drive current setting unit 77 (FIG. 3) and the laser diode drive time generated by the drive control unit 74. To do.

FIG. 4 is a graph showing the relationship between the input gradation and the light emission amount (output gradation). Using the circuits shown in FIGS. 2 and 3, the relationship between the light emission amounts of the laser diodes corresponding to the input grayscale data of a plurality of beams becomes the graph shown in FIG. FIG. 4 is a graph showing the relationship between the input gradation and the light emission amount (output gradation) of the image forming apparatus according to the embodiment of the present invention. FIG. 4 shows the input / output gradation characteristics of the beams of four channels, and as shown in the figure, a difference in the emitted light amount occurs between the beams (ch1 to ch4). FIG. 5 is a graph showing the relationship between the input gradation and the light emission amount (output gradation) of the image forming apparatus according to the embodiment of the present invention. As a method of reducing the difference in the amount of light emission between the beams, when an approximate curve is obtained between the inflection points of interest from the profile of the graph, three approximate curves (straight lines) are obtained for one channel as shown in FIG. That is, three approximate curves 1 to 3 shown in FIG. 5 are obtained. Now, one beam channel for four beams (in this case CH
It is represented by the profile of 3).

In this case, an approximate straight line is actually obtained.
Of the approximate curves of this book, focusing on the gradient (derivative) f ′ (x) = a of the approximate curve function f (x) = ax + b shown by the approximate curve (straight line) 2, 4 shown in FIG. It can be considered that the inclinations of the beam approximation curves are substantially the same. From this, in the figure, the area that can be approximated by the approximation curve (straight line) 2 is
It is determined by the maximum gradation point and the minimum gradation point. That is, the maximum gradation point is determined at the intersection of the approximate curves 1 and 2 in the figure, and the minimum gradation point is determined at the intersection of the approximate curves 3 and 2 in the figure.
Then, in the profile of the output gradation characteristic showing the relationship of the output gradation to the input gradation of the image data, the above-mentioned two points of the entire gradation region, that is, the image forming floor in the range where the gradation characteristic is approximated by a linear expression. By using the adjustment area, the gradients of gradation increase / decrease among a plurality of beams become substantially the same, and the difference in the light emission amount between the beams can be reduced.

FIG. 6 is a perspective view showing a laser diode array used in the embodiment of the present invention. In a laser diode array having a plurality of light sources, the distance between adjacent light emitting sources is generally as small as several tens of microns as shown in FIG. When each light source of such a laser diode array is driven individually, a thermal difference occurs between the light sources,
It is known that the influence of driving one light emitting source causes so-called thermal crosstalk that affects the light emitting source adjacent to it as a light amount variation.

FIG. 7 is a timing chart showing the light emission drive timing of a plurality of laser diodes according to the conventional example. Although FIG. 7 shows an example of four channels, all channels are driven to emit light at the same timing.

FIG. 8 is a timing chart showing the light emission drive timing of the plurality of laser diodes according to the embodiment of the present invention. Here, the light emission ratio is 75%, and by shifting the light emission timings between the adjacent light sources, the adjacent light sources have the same timing for 2/3 of the mutual light emission time. Compared to the conventional example shown in FIG. 7, mutual thermal interference is reduced. In this way, by controlling the light emission time ratio of the plurality of light sources within the light emission cycle so that the light emission ratio is smaller than 100%, the degree of thermal interference between adjacent light emission sources can be reduced. Further, when the light emission ratio is set to 50%, the light emission time does not overlap with each other between the adjacent light emission sources,
The degree of thermal interference can be further reduced. In this way, by shifting the light emission timing of the adjacent light emitting sources, it is possible to reduce the fluctuation of the light amount due to thermal crosstalk between the adjacent light emitting sources (claim 1).

Here, it is desirable to set the light emission amounts of a plurality of beams at the gradation point A shown in FIG. 5 (here, the highest gradation point is taken) to the same amount (claim 2). In the area of the input gradation approximated by the approximation curve 2 shown in FIG.
As shown in, multiple beams can be approximated by approximately the same linear equation. That is, in the range of the input gradation that defines the maximum gradation point and the minimum gradation point, if the light emission amount of each light emitting source corresponding to the input gradation at the maximum gradation point is set to be the same, the The difference in the amount of emitted light can be reduced. A graph in which the characteristics are set in this way is shown in FIG.

FIG. 9 is a graph showing input / output gradation characteristics of a plurality of light emitting sources of the image forming apparatus according to this embodiment.
The relationship of the light emission amount of the laser diodes of a plurality of beams with respect to the input gradation is shown. Here, the respective light emission amounts are set to be the same at the input gradation point that gives the maximum gradation point. In this range, by setting the light emission amounts corresponding to the input gradation to be the same at one point, the difference in the light emission amount between a plurality of beams can be reduced.

Further, a light emission amount (output gradation value) suitable for the actual image density is set as a high gradation point at any one point of the image forming gradation region, and light emission of a plurality of beams is made at the high gradation point. It is desirable that the amounts are set to be the same, and that the light emission ratios of the plurality of light emission sources are the same at the high gradation point (claim 3). That is, as described above, a high gradation point is determined at a point equal to or lower than the maximum gradation point determined, and a setting procedure (light amount adjustment) is performed so that the above-mentioned light emission amounts become the same amount. By doing so, an approximate expression of the same gradation characteristic that determines the light emission amount between a plurality of beams in the actually used image forming gradation region is derived with high accuracy. However, as the high gradation point, the maximum gradation point may be selected.

FIG. 10 is a graph in which the light amount is adjusted based on the high gradation points for the plurality of beams obtained from FIG. Here, the high gradation point is set below the maximum gradation point. At any two points in the entire gradation area, one point in the above-mentioned image forming gradation area determined in a range in which the gradation characteristic between the two points is approximated by the linear expression f (x) = ax + b It is newly set so that the light emission amounts of a plurality of beams corresponding to the input gradation value that gives the higher gradation point are selected to be the same amount. FIG. 11 is a light emission timing chart of a plurality of light emission sources of the image forming apparatus according to the embodiment of the present invention. As shown in FIG. 11, by making the light emission ratio to be 50% to emit light and shifting the light emission timing of the adjacent light emitting sources, it is possible to prevent the adjacent light emitting sources from emitting light at the same time. The light amount variation due to thermal crosstalk between the light sources can be reduced, the light amount difference between the plurality of beams can be further reduced, and the image quality deterioration due to the light amount variation can be prevented. FIG. 12 is a graph showing input / output gradation characteristics of a plurality of light emitting sources of the image forming apparatus according to this embodiment. As shown in the figure, the lower gradation point may be a gradation zero point having a gradation of 0, or a gradation minimum point.

Here, a plurality of high gradation points, lower gradation points lower than that, and one or more intermediate gradation points between the high and low gradation points are selectively combined to form a plurality of gradation points. Image formation may be performed using gradation points (claim 4).
This is a so-called multi-valued image forming method. 12 and 13 are graphs showing input / output gradation characteristics of a plurality of light emitting sources of the image forming apparatus according to the present embodiment. As shown in FIG. 13, using the high gradation points, as described above, one or more gradation points obtained by subtracting a constant gradation from the high gradation points are set as intermediate gradation points. Then, one or more intermediate gradation points, for example, two intermediate gradation points 1 and 2 are set. Further, a portion without an image, that is, a so-called background gradation point, that is, a zero emission amount point (output gradation zero point) is given by an input gradation value “0”, and if this is used, the above-mentioned gradation number is so-called. It will have four gradation levels. As described above, since the light emission amount of each beam is already set to the same amount at the maximum gradation point or the high gradation point, the light emission amounts of a plurality of beams are substantially the same at each gradation point, that is, the difference in light emission amount is small. can do. Here, the lower gradation point may not be the zero point.

In the image formation gradation area defined by the maximum gradation point and the minimum gradation point, the light emission amount at the maximum gradation point is set so that a plurality of beams are the same, or the high gradation point is set. A case where the light emission amounts of a plurality of beams are set to be the same will be described with reference to the laser drive circuits shown in FIGS. 2 and 3. FIG. 2 is a block diagram of a drive circuit for a multiple laser emission source. FIG. 3 is a block diagram of a drive circuit of one circuit portion. The image data input from the image data I / F 76 of FIG. 2 is converted into a pulse width modulation PWM signal by the data conversion unit 75, the PWM control unit 73 generates a drive signal time, and the LD signal is input to the LD drive unit 73. It The LD drive unit 73 is the LD drive current setting means 7
7 (FIG. 3) and the drive current setting level and the PW
The laser diode drive time is generated in combination with the laser diode drive time generated by the M control unit 74. FIG. 14 is a graph showing the relationship between the drive current set value and the drive current of the image forming apparatus according to the embodiment of the present invention. The current driven by the LD drive current setting means 77 is shown in FIG.
Shown in. The drive current setting input specifies the drive current flowing through the laser diode.

FIG. 15 is a light emission timing chart of a plurality of light emission sources of the image forming apparatus according to the present invention. As shown in FIG. 15, the pulse width modulation PWM is performed by the data conversion unit 75.
The drive signal time converted into a signal and generated by the PWM control unit is variable in the range of 0 to 100%. In FIG. 15, the drive time is 100%, 50%, and 25%.
The case of is shown. In this way, the laser diode drive current is generated by combining the drive current and the drive time.

As a method for obtaining the light emission amount at the maximum gradation point or the high gradation point, first, the driving time of all the beams of a plurality of beams is set to be the same at an arbitrary time, and then each beam is set. The light amount of the LD drive current setting means 7
A predetermined value is set by 7 so that the light emission amounts of all the beams are equal. The same applies to the gradation minimum point. First, the driving time of all the beams of the plurality of beams is set to be the same at an arbitrary time, and thereafter, the light amount of each beam is set to a predetermined value by the LD drive current setting means 77. It can be set so that the light emission amounts of all beams are equal.

By doing so, as shown in FIG.
The light emission amount is set so that the plurality of beams are the same at a certain point described above, so that the plurality of beams can be image-formed by using the image formation gradation region in the range defined by the same approximate curve. By doing so, an image having no difference in light emission amount between the beams can be obtained. As a result, an image with a small difference in the amount of emitted light between the beams can be obtained. Further, it is desirable that the light emission output value corresponding to the intermediate gray scale between the two gray scale maximum points and the gray scale minimum points variably sets the drive time of each of the plurality of beams. By doing so, as shown in FIG. 13, the light emission amount of the intermediate gradation is set so that the plurality of beams are the same, and the plurality of beams are imaged using the image formation gradation region in the range defined by the same approximate curve. By being formed, a multi-valued image with a small difference in the amount of light emitted between the beams can be obtained.

Looking back at FIG. 2, the image data I /
The data input from F76 is converted into a pulse width modulation PWM signal by the data conversion unit 75, the PWM control unit 74 generates a drive signal time, and is input to the LD drive unit 73,
The image data is converted into a pulse width modulation PWM signal, and P
The generation of the drive signal time in the WM control unit 74 can be performed by referring to the conversion data table for each of a plurality of beams. Further, the values of the conversion data table can be stored in the data control unit 75 in advance. Further, the modulation signal setting data stored in the above-mentioned storing means can be arbitrarily changed so that the modulation signal setting data can be changed by referring to the image output. Items 6 to 8). In this way, by the configuration of the image forming apparatus having the function of storing the modulation signal time setting data of a plurality of beams in each storage unit for a plurality of light beams, the plurality of beams are defined by the same approximate curve for each image forming apparatus. It is possible to set the image formation gradation area in the range described above, and it is possible to obtain an image with little difference between apparatuses.

The drive current setting means 77 shown in FIG. 3 preferably stores the current value setting data for determining the drive current for driving the plurality of beams in each storage means for each of the plurality of beams. Further, for each image forming apparatus, it is possible to set an image forming gradation area within a range in which a plurality of beams are defined by the same approximate curve, and further it is possible to arbitrarily change the modulation signal setting data stored in the storage means. In such a configuration, the modulation signal setting data can be changed by referring to the image output, so that an image with little difference between the devices can be obtained (claims 9 and 10). Further, it is desirable that the stored current value setting data is changed with reference to image output.

(Second Embodiment) As the above-mentioned image forming apparatus, an image forming apparatus using a conventional electrophotographic process system can be constructed. This can be constituted by a conventional method, but a toner formed by forming an OPC film on a photosensitive layer and using a resin as an image visualization agent is used for a photoreceptor. Even in such a conventional electrophotographic process system, an image forming apparatus capable of outputting an image with good sharpness and gradation by forming an image using an image forming gradation region defined by the approximate curve of the present invention. Can be provided (Claim 11).

(Third Embodiment) Furthermore, a laser beam digital electrophotographic image forming apparatus using a laser diode as a plurality of writing lights of an optical writing means is provided.
It can be constructed by a conventional method. Also in this case, it is possible to provide an image forming apparatus capable of outputting an image having good sharpness and gradation by forming an image using the image forming gradation region defined by the approximate curve of the present invention ( Claim 1
2). Here, the digital writing pixel density is 1200d
In the image forming apparatus having a high pixel density of pi, an image having good sharpness and gradation can be obtained by forming an image using the image forming gradation area in the range defined by the above-mentioned approximate curve according to the embodiment of the present invention. It is possible to provide an image forming apparatus capable of outputting (claim 13).

[0036]

According to the first aspect of the present invention, it is possible to provide an image forming apparatus capable of reducing the difference in light amount between beams by a plurality of light emitting sources, reducing the influence of thermal crosstalk, and preventing image quality deterioration due to light amount fluctuation. . According to the invention of claim 6, in addition to the effect of the invention of claim 1, input / output gradation characteristics from a plurality of light emitting sources can be set and stored for each image forming apparatus. It is possible to provide an image forming apparatus with a small difference. According to the invention of claim 9, in addition to the effect of the invention of claim 1, current setting data for determining the light emission amount can be set and stored for each image forming apparatus, so that there is little difference in images between the apparatuses. An image forming apparatus can be provided. According to the eleventh aspect of the present invention, it is possible to provide an image forming apparatus using an electrophotographic method, which can reduce a light amount variation due to thermal crosstalk and prevent image quality deterioration. According to the twelfth aspect of the present invention, it is possible to provide an image forming apparatus using a digital electrophotographic system that can reduce fluctuations in light amount due to thermal crosstalk and prevent image quality deterioration.

[Brief description of drawings]

FIG. 1 is a perspective view showing an outline of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of a drive circuit that drives a plurality of laser light sources according to an embodiment of the present invention.

FIG. 3 is a block diagram illustrating an operation of the driving unit according to the embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the input gradation and the light emission amount (output gradation) of the image forming apparatus according to the embodiment of the present invention.

FIG. 5 is a graph showing the relationship between the input gradation and the light emission amount (output gradation) of the image forming apparatus according to the embodiment of the present invention.

FIG. 6 is a perspective view showing a laser diode array used in the embodiment of the present invention.

FIG. 7 is a timing chart showing a light emission drive timing of a plurality of laser diodes according to a conventional example.

FIG. 8 is a timing chart showing light emission drive timings of a plurality of laser diodes according to the embodiment of the present invention.

FIG. 9 is a graph showing input / output gradation characteristics of a plurality of light emitting sources of the image forming apparatus according to the present embodiment.

FIG. 10 is a graph in which the light amount is adjusted with reference to the high gradation point for a plurality of beams obtained from FIG.

FIG. 11 is a light emission timing chart of a plurality of light emission sources of the image forming apparatus according to the embodiment of the present invention.

FIG. 12 is a graph showing input / output gradation characteristics of a plurality of light emitting sources of the image forming apparatus according to the present embodiment.

FIG. 13 is a graph showing input / output gradation characteristics of a plurality of light emitting sources of the image forming apparatus according to the present embodiment.

FIG. 14 is a graph showing a relationship between a drive current set value and a drive current of the image forming apparatus according to the embodiment of the present invention.

FIG. 15 is a light emission timing chart of a plurality of light emission sources of the image forming apparatus according to the embodiment of the present invention.

[Explanation of symbols]

1, 2, 3 ... Approximate curve (straight line) 10 ... Laser light source 11 ... Condensing lens 12 ... Aperture 13 ... Cylinder lens 15 ... Polygon mirror 17, 18 ... fθ lens 19: Optical path changing mirror 20 …… Cylinder lens 21 ... Photoconductor 22 …… Small laser beam spot 23 ... Synchronous detection mirror 25 ... Optical sensor 70 ... Laser diode array 71a-71d ... Laser diode (LD) 72 ... Photo detector 73a-73d ... Laser diode drive unit 74a to 74d ... Drive control unit 75 ... Data converter 76 ... Image data I / F 77: LD drive current setting means ch1 to ch4 ... Laser diode array number

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/14 B41J 3/00 D 5C072 H04N 1/036 H04N 1/04 104A 1/113 G03G 21/00 372 F-term (reference) 2C362 AA07 AA16 AA26 AA32 AA55 AA61 CA02 2H027 DA09 EA02 EC03 HA07 2H045 BA22 CB33 CB42 2H076 AB06 AB09 AB12 DA17 DA19 DA21 EA24 5C051 A02 HA02 HA06B02 HA02A06 HA02B06 HA02A06 HA02A02 HAC02 DA02 DEA 5C072

Claims (13)

[Claims] 1. A plurality of light emitting sources and each light emitting source is turned on at a predetermined light emitting cycle according to an input image signal.
It has a switching means for turning on / off and a current setting means for supplying a drive current to each light emitting source to set a desired light emission amount, and generates an output gradation value for an input gradation value based on the input image signal to generate each output gradation value. An image is provided that includes a light source drive unit that drives a light emission source to generate a plurality of writing lights, and a rotation deflection unit that has an optical system and that simultaneously deflects the plurality of writing lights and scans them on the surface of the photoconductor. In the image forming apparatus to be formed, the current setting unit is arranged so that, between the absolute maximum value which is the maximum value that the output gradation value can take and the absolute minimum value which is the minimum value, the at least one light emitting source It has a function of selecting two points where the input / output gradation characteristics can be linearly approximated as the gradation maximum point and the gradation minimum point, and setting the range of the input gradation according to the input gradation value determined by the two points. The switch The ratio of the light emission time (Tp) to the light emission period (Tw) (light emission ratio) is Tp / Tw ≦ 0 at any gray scale point between the gray scale maximum point and the gray scale minimum point. .75
The image forming apparatus has a function of setting so that when the plurality of light emitting sources emit light within the same light emitting period, the light emitting timings of the light emitting sources adjacent to each other are different from each other. 2. The current setting means sets the input gradation value that determines the gradation maximum point so that the output gradation values of the plurality of light emitting sources are the same, and The image forming apparatus according to claim 1, wherein the switching unit has a function of setting the same. 3. One point within the range between the maximum gradation point and the minimum gradation point is selected as a high gradation point, and at each of the input gradation values that define the high gradation point, each of the plurality of light emitting sources is selected. The current setting means sets so that the output gradation values are the same,
The image forming apparatus according to claim 1, further comprising a function of setting the switching unit so that the respective light emission ratios are the same. 4. The minimum gradation point is defined as a lower gradation point, and one or more intermediate gradation points are provided between the higher gradation point and the lower gradation point to obtain the high gradation point and the intermediate gradation point. The image forming apparatus according to claim 3, wherein an image is formed using the gradation points and the lower gradation points. 5. The light emission of the plurality of light emitting sources at the input gradation value that determines the high gradation point, the switching unit keeps the light emission ratio of all the light emitting sources constant, and the current setting unit emits each light. The drive current of the light sources is variably set, and the light emission of the plurality of light emission sources at the input grayscale value that defines the lower grayscale point is such that the switching means makes the light emission ratio of all the light emission sources constant, and the current setting Means variably sets drive currents of the respective light emitting sources, and the light emitting sources of the plurality of light emitting sources at an input gradation value defining one or more intermediate gradation points are made variable by the switching means. The image forming apparatus according to claim 4, which is set. 6. The image forming apparatus according to claim 1, further comprising a storage unit, wherein input gradation values based on the image data are stored in the storage unit for each of the plurality of light emitting sources. apparatus. 7. The image forming apparatus according to claim 6, wherein the stored input gradation value can be arbitrarily changed. 8. The image forming apparatus according to claim 7, wherein the stored input gradation value is changed with reference to image output. 9. The image forming apparatus according to claim 1, wherein the current value setting data set by the current setting unit is stored in the storage unit for each of the plurality of light emitting sources. 10. The stored current value setting data is:
The image forming apparatus according to claim 9, which can be arbitrarily changed. 11. The image forming apparatus according to claim 1, wherein an electrophotographic system is used as the image forming apparatus. 12. The image forming apparatus according to claim 1, wherein a digital electrophotographic system is used as the image forming apparatus. 13. The digital writing pixel density is 1200.
The image forming apparatus according to claim 12, wherein the image forming apparatus is a dpi.