JP2009220531A - Light exposure system and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a high printing speed in a printing apparatus by always shortening a time required for charging a pixel circuit with electricity regardless of height of gradation of image data. <P>SOLUTION: A light exposure system is equipped with a light emitting element array in which a plurality of pixels with light emitting elements are aligned in a line, and performs light exposure in accordance with the image data. In the light exposure system, the light emitting element array is divided into a plurality of pixel groups with a specified number of the pixels, and respective pixels in respective pixel groups are driven by time sharing. A plurality of driving signal lines Idrva-f for feeding driving signals based on the image data for driving the light emitting elements to respective pixel groups, and a plurality of selective signal lines Select 1-4 provided in accordance with respective pixels in respective pixel groups and for feeding selective signals writing the driving signals by making respective pixels as selecting conditions, are equipped. The time for one line performing a light exposure assigned on respective pixel groups is divided into two divided periods, and divided image data prepared by dividing the image data in accordance with the duty ratio of respective divided periods, are formed. On respective divided periods, respective pixels are driven by the divided image data, and exposed in accordance with the image data. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic exposure apparatus and an image forming apparatus including the exposure apparatus.

An electrophotographic image forming apparatus (printer apparatus) has an exposure apparatus for image formation. In recent years, various attempts have been made to use a light emitting element such as an organic EL element as a light source of the exposure apparatus. In an image display device using such a light emitting element for each pixel, a plurality of transistors for selecting the pixel and supplying a driving current for the light emitting element to the light emitting element, a holding capacitor for holding the driving current, etc. Is provided for each pixel. For example, Patent Document 1 discloses a display device having such a configuration. (Patent Document 1)
An outline of a specific operation in this type of display circuit will be described. During the period selected by the selection transistor, the drive current corresponding to the gray level of the image data flows between the drain and source of the drive transistor, thereby driving the holding capacitor connected between the gate and source of the drive transistor. Gradation data corresponding to the current is written. Since the signal charge corresponding to the gradation of the image data is written in the holding capacitor after the selection transistor is turned off, the current corresponding to the signal charge is driven by holding it during the display period. The pixel transistor is supplied to the pixel display element to light up, and display with a desired display luminance is executed.
JP 2003-043995 A

  In the current drive type display circuit described above, a charge corresponding to the gradation of the image data is charged in a charge holding capacitor in the pixel circuit by a current drive output. For this reason, particularly when the drive current has a small current value at a low gradation, the time required for charging the charge holding capacitor with the charge corresponding to the drive current becomes long. For this reason, when such a display circuit is used in an image forming apparatus, the charging time at a low gradation becomes longer than that at the time of lighting at a high gradation, which results in the optical exposure of the printing apparatus. This is one of the factors that lower the printing speed as an apparatus.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to always shorten the time required for charging the pixel circuit regardless of the gradation of image data to be printed. It is an object of the present invention to provide an exposure apparatus capable of realizing a high printing speed and an image forming apparatus including the exposure apparatus.

  According to the first aspect of the present invention, there is provided an exposure apparatus for performing exposure according to image data on a photosensitive drum, wherein a plurality of pixels having light emitting elements are arranged in a line shape, and the photosensitive drum is adapted to the image data. A light emitting element array that performs the exposure, and one line time that exposes one line on the photosensitive drum by the light emitting element array is divided into a plurality of divided periods in which lighting times of the light emitting elements of the light emitting element array are different, Based on the image data, an image data processing unit that generates a plurality of divided image data corresponding to a duty ratio composed of a ratio of the lighting time to the one line time corresponding to each of the divided periods; A drive signal generation circuit that generates a plurality of drive signals corresponding to the image data and supplies the drive signals to the corresponding light emitting element arrays in each of the divided periods. Exposure apparatus according to claim.

  According to a second aspect of the present invention, in the first aspect of the invention, the plurality of pixels in the light emitting element array are divided into a plurality of pixel groups having a predetermined number, and the pixels of the pixel groups are time-divided. It is characterized by being driven by.

  According to a third aspect of the invention, in the first or second aspect of the invention, the drive signal generation circuit generates a drive current having a current value corresponding to the divided image data as the drive signal. To do.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the image data processing unit is configured such that the light emitting element has a luminance corresponding to the divided image data corresponding to each divided period. The sum of the light energy supplied to the photosensitive drum when the lamp is lit for a time corresponding to the corresponding duty ratio within the one line time is set to a value at which the light energy corresponding to the image data is obtained. Features.

  According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, the image data processing unit performs the first division in which the one line time is set to the first value. The divided image data is divided into a period and a second divided period in which the duty ratio is set to a second value smaller than the first value, and the divided image data is a first divided image corresponding to the first divided period. Data and second divided image data corresponding to the second divided period, and the first divided image data is obtained when the gradation value of the image data is lower than a predetermined first gradation value. It is set to zero, and the second divided image data is set to zero when the gradation value of the image data is higher than a predetermined second gradation value.

  A sixth aspect of the invention is characterized in that, in the fifth aspect of the invention, at least one of the first divided image data and the second divided image data is set to zero.

  According to a seventh aspect of the present invention, there is provided an image forming apparatus for performing printing according to image data, wherein a photosensitive drum and a plurality of pixels having light emitting elements are arranged in a line, and the image data is recorded on the photosensitive drum. The light emitting element array that performs the corresponding exposure and one line time in which one line is exposed to the photosensitive drum by the light emitting element array are divided into a plurality of divided periods having different lighting times of the light emitting elements of the light emitting element array. An image data processing unit that generates a plurality of divided image data corresponding to a duty ratio that is a ratio of the lighting time to the one line time corresponding to each of the divided periods, based on the image data; A drive signal generation circuit that generates a plurality of drive signals according to the divided image data and supplies the drive signals to the corresponding light emitting element arrays in each of the corresponding divided periods. The features.

  The invention according to claim 8 is the invention according to claim 7, wherein the drive signal generation circuit generates a drive current having a current value corresponding to the divided image data as the drive signal. .

  According to a ninth aspect of the invention, in the invention of the seventh or eighth aspect, the image data processing unit corresponds to the luminance of the light emitting element corresponding to the divided image data corresponding to each divided period. The sum of the light energy supplied to the photosensitive drum when the lamp is lit for a time corresponding to the duty ratio is set to a value that provides light energy corresponding to the image data. To do.

  According to a tenth aspect of the present invention, in the invention according to any one of the seventh to ninth aspects, the image data processing unit performs the first division in which the one line time is set to the first value. The divided image data is divided into a period and a second divided period in which the duty ratio is set to a second value smaller than the first value, and the divided image data is a first divided image corresponding to the first divided period. Data and second divided image data corresponding to the second divided period, and the first divided image data is obtained when the gradation value of the image data is lower than a predetermined first gradation value. It is set to zero, and the second divided image data is set to zero when the gradation value of the image data is higher than a predetermined second gradation value.

  The invention described in claim 11 is characterized in that, in the invention described in claim 10, at least one of the first divided image data and the second divided image data is set to zero.

  According to the present invention, it is possible to always shorten the time required for charging the pixel circuit regardless of the gradation of the image data to be printed, and to realize a high printing speed in the printing apparatus.

An exposure apparatus and an image forming apparatus (printing apparatus) according to an embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus using the exposure apparatus according to the present embodiment. In the figure, the image forming apparatus includes a photosensitive drum 1, an exposure device 2 integrally provided with a case portion 2A and a rod lens array portion 2B, a charging roller 3, an eraser light source photosensitive member 4, a cleaning member 5, and a developing roller 6a. The image forming (printing) is carried out by an electrophotographic method, including a developing device 6 including a transfer roller 8, a transfer roller 8, a fixing roller 9, and a conveying belt 11. Note that reference numeral 7 denotes the printing paper 7.

  The rod lens array unit 2B constituting the exposure apparatus 2 is, for example, a lens array in which SELFOC (registered trademark) lenses are arranged in one row or in a plurality of rows. 1 is a lens unit that forms an image on 1;

  The photosensitive drum 1 is a negatively charged OPC (Organic Photo Conductor) photosensitive member (organic photosensitive member), and the charging roller 3 is a negative charger correspondingly. The exposure apparatus 2 includes a light emitting element array in which a plurality of light emitting elements are arranged in an array, which will be described in detail later.

  In the image forming apparatus shown in FIG. 1, printing is generally performed by the following steps. First, when the charging roller 3 comes into contact with the surface of the rotating photosensitive drum 1, the contacted surface of the photosensitive drum 1 is uniformly charged with a negative potential.

  Subsequently, the exposure device 2 irradiates the photosensitive drum 1 with light, and an electrostatic latent image is formed on the photosensitive drum 1. Thereafter, toner is attached to the electrostatic latent image by the developing device 6. Then, the toner attached to the electrostatic latent image is transferred to the printing paper 7 by the transfer roller 8.

Hereinafter, such a printing process will be described in detail.
First, a negative high voltage supplied from a charging power source (not shown) is applied to the photosensitive drum 1 by the charging roller 3. As a result, the peripheral surface of the photosensitive drum 1 is uniformly negatively charged, and is in an initialized charged state that is initialized in terms of potential.

  Then, optical writing (exposure) according to the printing information is performed by the exposure device 2 on the photosensitive drum 1 whose peripheral surface is in an initialized charged state. As a result, an electrostatic latent image composed of a negative high potential portion due to initialization charging and a negative low potential portion of about −50 [V] due to exposure is formed on the peripheral surface of the photosensitive drum 1.

  Here, the toner charged in the developing unit 6 and charged to a weak negative potential is rotated and conveyed by the developing roller 6a to the facing portion between the developing roller 6a and the photosensitive drum 1. At this time, a developing bias voltage of about −250 [V], for example, is applied to the developing roller 6a from a power source (not shown).

  Accordingly, between the developing roller 6a to which the developing bias voltage of −250 [V] is applied and the minus low potential portion of about −50 [V] of the electrostatic latent image on the photosensitive drum 1 is about 200 [V]. Is formed.

  Due to the potential difference from the developing voltage in these electrostatic latent images, the negatively charged potential portion in the electrostatic latent image that has a positive polarity relative to the developing roller 6a has a negatively charged toner. Is transferred to form a toner image. The toner image is conveyed to a transfer portion where the photosensitive drum 1 and the transfer roller 8 are opposed to each other by the rotation of the photosensitive drum 1.

  Note that the toner adhesion amount in the toner image formed as described above, that is, the density of the developed image, depends on the exposure amount of the photosensitive drum 1 by the light emitting element of the exposure device 2. It is determined by the amount of potential attenuation on the circumferential surface.

  Next, as described above, when the toner image is conveyed to the transfer unit, the printing paper 7 is conveyed to the transfer unit by the conveyance belt 11. In the transfer portion, the toner image is transferred onto the printing paper 7 by the transfer roller 8.

  The printing paper 7 onto which the toner image has been transferred in this manner is conveyed further downstream by the conveying belt 11, and after the toner image is thermally fixed by the fixing roller 9, the printing paper 7 is discharged to the outside of the image forming apparatus. The

  Further, after the toner image is transferred onto the printing paper 7, the residual toner is removed from the peripheral surface of the photosensitive drum 1 by the cleaning member 5, and is further uniformly 0 (zero) [V] by the eraser light source photosensitive member 4. To be charged for the charging roller 3.

  In the exposure unit 2, the case portion 2 </ b> A emits light composed of organic EL elements along the axial direction of the photosensitive drum 1, which is the main scanning direction of exposure scanning on the photosensitive drum 1 shown in FIG. 1. A light emitting element array in which a large number of pixels having elements is arranged in a line is provided.

  FIG. 2 shows a configuration of an exposure head portion provided in the case portion 2A. In the drawing, for the sake of simplicity, the light emitting element array on the exposure head substrate is assumed to be composed of all 24 pixels. However, as described above, the actual exposure head substrate has a print resolution of, for example, 1200 [dpi]. ], The printing apparatus corresponding to A4 paper (long side 297 [mm]) has a configuration of about 14,000 pixels.

  In the drawing, in the case unit 2A of the exposure apparatus 2, a data analysis / timing control unit (image data processing unit) 20 to which image data to be printed is given, a data driver (drive signal generation circuit) 21, and a selection generation unit 22 are provided. , An exposure head substrate 23 and an anode generator 24 are provided. A total of six pixel groups a1 to a4, b1 to b4,..., F1 to f4 divided by four adjacent pixels are arranged on the exposure head substrate 23.

  When performing exposure in accordance with image data, the data analysis / timing control unit 20 receives image data from a raster image processor (not shown), a horizontal control signal HSYNC that matches the paper size and transport speed, and a vertical control signal. Then, data is transferred to the data driver 21 in accordance with these control signals.

  The data driver 21 generates a plurality of drive currents Idrva to Idrvf having current values based on gradation signals corresponding to on / off of each pixel and image data in accordance with data transmission from the data analysis / timing control unit 20 and exposure. Supply to the head substrate 23.

  The select generation unit 22 generates a plurality of selection signals (Select1 to Select4) for selecting the pixels in accordance with the control signal from the data analysis / timing control unit 20 and supplies the selection signals to the exposure head substrate 23. .

On the other hand, the anode generation unit 24 also generates a plurality of holding signals (Anode1 to Anode4) for turning on the pixels in accordance with the control signal from the data analysis / timing control unit 20 and supplies them to the exposure head substrate 23.
Further, the data analysis / timing control unit 20 generates and sends a reset signal to each pixel of the exposure head substrate 23 as will be described later.

FIG. 3 is an equivalent circuit of the exposure head substrate 23 shown in FIG. FIG. 4 is a drive timing chart as a comparison target for explaining the effect of the present invention.
FIG. 3 shows a pixel group a consisting of four pixels a1 to a4 and a part of a pixel group b consisting of four pixels b1 to b4 among the pixel groups a to f on the exposure head substrate 23 shown in FIG. (Pixels b1, b2).

  Each pixel is composed of, for example, a thin film transistor, and includes a selection transistor 33 as a pixel selection switch, an organic EL element 34 as a light emitting element, and a driving transistor 31 for driving the organic EL element 34, which is composed of a thin film transistor. And a holding transistor 30 formed of a thin film transistor and a holding capacitor 32 for holding a signal charge corresponding to the display luminance of the pixel.

  In the exposure head substrate 23 shown in FIG. 3, a plurality of driving signal lines to which each driving current is applied, a plurality of selection signal lines to which each selection signal is applied, and a plurality of holding signals to which each holding signal is applied. With lines.

  During the pixel selection period in which the selection signal applied to each selection signal line is at a high level, the drive currents Idrva to Idrvf having a current value based on the grayscale signal are supplied from the data driver 21 to each drive signal line and selected. The charge corresponding to the current that flows to the drive transistor 31 through the transistor 33 and flows through the current path of the drive transistor 31 is accumulated in the holding capacitor 32.

  Then, during the holding period in which the selection signal is set to the low level and the holding signal applied to the holding signal line is set to the high level, a current corresponding to the charge accumulated in the holding capacitor 32 is supplied from the driving transistor 31 to the organic EL element 34. And the organic EL element 34 is lit with a luminance corresponding to the current value of the current.

  In addition, reset transistors 35 and 36 are provided in each drive signal line, and the reset transistors 35 and 36 are turned on at the initial stage of the selection period to discharge the charge charged in the holding capacitor 32.

The horizontal control signal HSYNC shown in FIG. 4 is a synchronization signal in the main scanning direction of the printing apparatus, and the dot formation processing time (one line time) that is allowed for one line to be exposed on the photosensitive drum 1 in the active to active period. ) For example, if the printing resolution is 1200 [dpi] in both the main scanning direction and the conveyance direction, the printing speed is 40 [sheets / minute], and the distance between sheets is 50 [mm], an A4 horizontal size light source unit is used.
((25.4mm / 1200dpi) / (210mm x 40 sheets + 50mm x 40 sheets)) / 60
≈122 [μ seconds].

  The light-emitting element array in the exposure apparatus 2 has various forms such as a structure in which a plurality of light-emitting elements are arranged in a row, a structure in which a plurality of light-emitting elements are arranged in a staggered manner in two or more rows, and the like. Correspondingly, the shape exposed on the photosensitive drum 1 by the light emitting element array also has a shape corresponding to the arrangement of the plurality of light emitting elements in the light emitting element array, and one line exposed on the photosensitive drum 1 is: In addition to the exposed dots arranged in a line, for example, the exposed dots are arranged in a staggered pattern, but include those that appear to be one line in appearance.

  The data driver 21 is configured so that light energy necessary for exposing the photosensitive drum 1 to form a latent image can be obtained during a period (one line time) when the horizontal control signal HSYNC is active to active. The pixel is driven to emit light for a predetermined time.

  If the light emission time is sufficiently short with respect to one line time, it is possible to cause each pixel to emit light a plurality of times during one line time, and it is cost-effective to implement the arranged pixels in a time division manner. Desirable from the above viewpoint.

  In that case, as shown in FIG. 2 and FIG. 3, the selection signals Select 1 to Select 4 are connected to the anodes of the plurality of pixels 34 by the output from one data driver 21, and the cathode side is generated by the selection generation unit 22. Shift within one line time.

  In FIG. 2, as an example, the data driver 21 drives the four pixels a1 to a4 of the pixel group a with one drive signal line Idrva, and the supply lines to the exposure head substrate 23 are a total of six lines Idrva to Idrvf. However, the present invention is not limited to this.

  Similarly, the selection signal lines Select1 to Select4 from the select generation unit 22 to the exposure head substrate 23 and the holding signal lines Anode1 to Anode4 from the anode generation unit 24 to the exposure head substrate 23 are also for four pixels of each pixel group. Although four lines are output at a time, the present invention is not limited to this.

  Therefore, in the exposure head substrate 23, 24 (= 4 × 6) pixels are formed in a row in the horizontal direction (scanning direction). In the exposure head substrate 23 using an actual organic EL, pixel elements corresponding to the paper size are formed in one or a plurality of columns.

  FIG. 4 shows a control timing when the circuit configuration as described above is controlled by a general driving method. In the period in which the selection signal Select1 is at "H" level, the signal charges are retained by the current of Idrva to Idrvf = Ia1 to If1 corresponding to the gradation data in the circuits of the pixels a1, b1,. 32 is written. The current corresponding to the signal charge written in the holding capacitor 32 is supplied from the drive transistor 31 to the organic EL element 34, so that the organic EL element 34 is turned on during the period in which the holding signal Anode1 is at "H" level. To do.

  Similarly, the pixels a2, b2,..., F2 in each pixel group when the selection signal Select2 is “H” level, and the pixels a3, b3 in each pixel group when the selection signal Select3 is “H” level. ,..., F3 are output from the data driver 21 in accordance with the grayscale data of the pixels a4, b4,..., F4 in each pixel group during the period in which the selection signal Select4 is at "H" level. Then, during the period in which the subsequent holding signals Anode2 to 4 are at “H” level, the corresponding pixels are lit.

Hereinafter, a problem in the general driving method shown in FIG. 4 will be described.
When the content of the image data is low gradation, the drive current from the data driver 21 to each pixel circuit has a smaller current value than the current value of the drive current at high gradation. Therefore, the time until the signal charge written in the holding capacitor 32 reaches a value corresponding to the driving current at the time of the low gradation becomes longer than that in the case of the high gradation. Therefore, in order to make the signal charge written to the holding capacitor 32 accurately correspond to the gradation of the image data even at the low gradation, the one line time is set to a relatively long time. This causes a problem that the overall throughput is reduced.

  Alternatively, when priority is given to throughput, in the set one line time, the writing time to the holding capacitor 32 becomes shorter than the time necessary for writing the signal charge corresponding to the low gradation at the time of low gradation. For this reason, the signal charge corresponding to the gradation of the image data cannot be written, and there may be a problem that printing corresponding to the gradation of the image data cannot be performed accurately.

A driving method according to the present invention that solves the above-described problems will be described below.
FIG. 5 shows control timing when the circuit configuration shown in FIGS. 2 and 3 is controlled by the driving method according to the embodiment of the present invention.
Here, the data analysis / timing control unit 20 divides lighting at one pixel into a plurality of divided periods within one line time in order to obtain light energy necessary for a latent image formed by exposing the photosensitive drum 1. Drive control. That is, the original image data is set so that the data transferred to the data driver 21 with the lighting luminance and lighting time of the organic EL element 34 becomes a driving current according to the ratio of the duty ratio described later in each divided period. It is assumed that it has a function of calculating and generating divided image data obtained by dividing the image data corresponding to each divided period. FIG. 5 shows an example in which one line time is divided into two parts before and after, the first half being a first period (first divided period), and the second half being a second period (second divided period).

FIG. 6 shows, as a reference example, a light source corresponding to an A4 horizontal size with a print resolution of 1200 [dpi] in the main scanning direction and the transport direction, a printing speed of 40 [sheets / minute], and a sheet spacing of 50 [mm]. The unit is exposed for the purpose of forming an image on the surface of the photosensitive drum 1 with a photosensitivity of the photosensitive drum 1 of 0.3 [μJ / cm ² ] and an efficiency of the organic EL element 34 of 2.2 [cd / A]. Driving current required for pixel formation with respect to the gradation level by the conventional general driving method when the light transmission degree of the lens array provided in the unit is 6 [%] and the gradation level of the pixel is 9 gradations Are shown for three types of duty ratios of 5%, 20%, and 40%, which are ratios of lighting times with respect to one line time.

  As shown in the figure, the drive current at the time of low gradation becomes smaller as the duty ratio value is higher (40%), that is, as the light emission time within one line time is longer. Further, as the duty ratio value is lower (5%), that is, the light emission time within one line time is shorter, the current value at the time of high gradation becomes larger.

  On the other hand, FIG. 7 shows an example of the relationship of the drive current to the gradation level in the present embodiment. As shown in FIG. 5, one line time is divided into a first period and a second period, and the ratio of the lighting time (duty ratio) in the same period is set to be different between the first period and the second period. Thus, the drive current has a relatively large current value even at the time of low gradation.

  FIG. 7A shows the relationship of the drive current to the gradation level when the duty ratio in the first period is 20 [%] and the duty ratio in the second period is 5 [%]. The setting shown in FIG. 7A is such that at least one of the driving currents in the first period and the second period is 0 (zero) [μA], and lighting driving is performed only in one divided period. It is.

  In this case, in the 0 [%] (0/8) gradation, the drive current is 0 (zero) [μA] in both the first period and the second period. Next, from the 12.50 [%] (1/8) gradation to the 37.5 [%] (3/8) gradation having a low gradation value, the drive current in the first period with a large duty ratio is 0 (zero). ) [ΜA], and the drive current in the second period with a small duty ratio is changed in the range of 26 [μA] to 78 [μA].

  On the other hand, from 50 [%] (4/8) gradation to 100 [%] (8/8) gradation having a relatively high gradation value, the drive current in the second period with a small duty ratio is 0 (zero). [ΜA], and the drive current in the first period with a large duty ratio is changed in the range of 26 [μA] to 52 [μA].

  For example, the drive current in the second period at the lowest 12.50 [%] (1/8) gradation is lower than the drive current 52 [μA] in the first period at 100 [%] (8/8) gradation. Is a sufficiently large value of 26 [μA], and it can be easily understood that the time required for writing to the holding capacitor 32 can be sufficiently shortened.

  As a result, the throughput in the image forming apparatus can be improved, and good printing can be performed that accurately corresponds to the gradation of the image data.

  In addition, the maximum driving current is 78 [μA] in the second period at 37.5 [%] (3/8) gradation, and this current value is in the general driving method shown in FIG. The power consumption of the exposure head substrate 23 can be suppressed as compared with the case where the duty ratio is sufficiently smaller than the maximum current (208 [μA]) when the duty ratio is 5% and the duty ratio is only 5%.

  Next, FIG. 7B shows the relationship of the drive current to the gradation level when the duty of the first period is 40 [%] and the duty of the second period is 20 [%]. The setting in FIG. 7B is such that a driving current is allowed to flow in both the first period and the second period in some gradations.

  In this case, in the 0 [%] (0/8) gradation, the drive current is 0 (zero) [μA] in both the first period and the second period. Next, the driving current in the second period with a small duty ratio is 6.5 [μA] from the 12.50 [%] (1/8) gradation having the low gradation value to the 50 [%] (4/8) gradation. ] To 9.75 [μA].

  On the other hand, from the 25 [%] (2/8) gradation to the 100 [%] (8/8) gradation having a relatively high gradation value, the driving current in the first period with a large duty ratio is 3.25 [ [μA] to 26 [μA].

  That is, at three gradation levels from 25 [%] (2/8) gradation to 50 [%] (4/8) gradation, a drive current is allowed to flow in both the first period and the second period. . In this case, the current value of the driving current at the time of the low gradation is smaller than that in the configuration shown in FIG. 7A, but compared with the general driving method shown in FIG. The time required for writing to the holding capacitor 32 can be shortened.

  Further, in the configuration in FIG. 7B, the maximum drive current is 26 [μA], which can be made smaller than 78 [μA] in the configuration of FIG. 7A. In addition, an increase in power consumption of the exposure head substrate 23 can be suppressed.

  As described above, FIGS. 7A and 7B show an example of the relationship with the drive current when the ratio of the lighting time in the first period and the second period is set to be different. The values are not limited.

Accordingly, in FIG. 5, as shown in FIG. 7A or FIG. 7B, an example of the duty of the lighting time and the drive current value, the selection signal Select1 becomes the “H” level during the first period. In the period, signal charges corresponding to the first gradation data (first divided image data) are given from the data driver 21 to the circuits of the pixels a1, b1,..., F1 in each pixel group.
Idrva to Idrvf = Ia′1 to If′1
The signal charge is written with the current of, and the current corresponding to the signal charge is supplied from the drive transistor 31 to the organic EL element 34, so that during the period in which the holding signal Anode1 is at the “H” level, The organic EL element 34 is turned on.

  Similarly, during this first period, the pixels a2, b2,..., F2 in each pixel group when the selection signal Select2 is at “H” level, and each pixel group when the selection signal Select3 is at “H” level. .., F3 of the pixels a4, b4,..., F4 in each pixel group during the period when the selection signal Select4 is at the “H” level, The current corresponding to the divided image data) is output from the data driver 21, and the corresponding pixels are turned on during the period in which the subsequent holding signals Anode2 to 4 are at "H" level.

After that, in the second period following the first period, the second gradation data (second gradation) is supplied to the circuits of the pixels a1, b1,..., F1 in each pixel group in a period in which the selection signal Select1 becomes “H” level. Signal charges corresponding to the divided image data) are given from the data driver 21;
Idrva to Idrvf = Ia "1 to If" 1
The signal charge is written with the current of, and the current corresponding to the signal charge is then supplied from the drive transistor 31 to the organic EL element 34, so that the corresponding period of time during which the holding signal Anode1 is at the “H” level. The organic EL element 34 of the pixel is turned on.

  Similarly, during the second period, the pixels a2, b2,..., F2 in each pixel group are in a period in which the selection signal Select2 is “H” level, and in each pixel group in the period in which the selection signal Select3 is “H” level. .., F3, and the pixels a4, b4,..., F4 in each pixel group in the period when the selection signal Select4 is at the “H” level, respectively, The current corresponding to the divided image data) is output from the data driver 21, and the corresponding pixels are turned on during the period in which the subsequent holding signals Anode2 to 4 are at "H" level.

  Thus, according to the present embodiment, one line time provided for each pixel group is divided into a plurality of, for example, two divided periods, and the duty ratio of the lighting time for each pixel of the pixel circuit is set small. Since writing is performed at low gradation in the divided period and the drive current value is increased by that amount, the time required for charging the pixel circuit is always shortened regardless of the gradation of the image data to be printed. It is possible to increase the throughput by realizing a high printing speed in the apparatus.

  In addition, in the above embodiment, the duty ratio of the lighting time for each pixel in each pixel group is made different for each of the plurality of divided periods. Therefore, when the image data has a low gradation, the duty is The signal charge is written to the pixel circuit and the light emission is driven on the divided period side where the ratio is smaller, and the signal charge is written to and lighted on the pixel circuit on the divided period side where the duty ratio is higher when the gradation is high. In order to do this, the switching or combination of the period with respect to the gradation of the image data is set in advance so that the driving current value at the low gradation is sufficiently high to maintain the required writing speed and at the high gradation. Can be suppressed, and the degree of freedom in designing each element of the pixel circuit can be increased.

  In the above-described embodiment, the case where one line time is divided into two divided periods of first and second has been described. However, the present invention is not limited to this, and one line time is divided into three or four or more divided periods. The organic EL element that is a light emitting element may be driven to emit light.

  In the above embodiment, the case where an organic EL element is used as the light emitting element has been described. However, the present invention is not limited to this, and the exposure amount can be variably set by driving control based on the effective value according to the light emission luminance and the light emission time. The present invention can be similarly applied even when other light emitting elements are used.

  In addition, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the implementation stage. Further, the functions executed in the above-described embodiments may be combined as appropriate as possible. The above-described embodiment includes various stages, and various inventions can be extracted by an appropriate combination according to a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, if the effect is obtained, a configuration from which the constituent requirements are deleted can be extracted as an invention.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a diagram showing a configuration of a drive circuit of an exposure head unit according to the same embodiment. FIG. FIG. 3 is a view showing the configuration of an equivalent circuit of a part of the exposure head substrate according to the embodiment. 4 is a timing chart showing a general driving method in the equivalent circuit of FIG. 3. 4 is a timing chart showing a driving method in the equivalent circuit of FIG. 3 according to the embodiment. FIG. 5 is a diagram illustrating a relationship of drive currents corresponding to multiple gradations in the timing chart of FIG. 4. The figure which shows the relationship of the drive current according to the multi-gradation in the timing chart of FIG. 5 which concerns on the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 2 ... Exposure apparatus, 2A ... Case part, 2B ... Rod lens array part, 3 ... Charging roller, 4 ... Eraser light source photoconductor, 5 ... Cleaning member, 6 ... Developing device, 7 ... Printing paper, DESCRIPTION OF SYMBOLS 8 ... Transfer roller, 9 ... Fixing roller, 11 ... Conveyance belt, 20 ... Data analysis / timing control unit, 21 ... Data driver, 22 ... Select generation unit, 23 ... Exposure head substrate, 24 ... Anode generation unit, 30 ... Holding Transistor 31, drive transistor 32, holding capacitor 33 33 selection transistor 34 organic EL element 35, 36 reset transistor

Claims (11)

An exposure apparatus that performs exposure according to image data on a photosensitive drum,
A plurality of pixels having light emitting elements are arranged in a line, and a light emitting element array that performs exposure according to the image data on the photosensitive drum;
One line time in which one line is exposed on the photosensitive drum by the light emitting element array is divided into a plurality of divided periods having different lighting times of the light emitting elements of the light emitting element array, An image data processing unit that generates a plurality of divided image data corresponding to a duty ratio composed of a ratio of the lighting time to the one line time corresponding to a divided period;
An exposure apparatus comprising: a drive signal generation circuit that generates a plurality of drive signals according to the plurality of divided image data and supplies the plurality of drive signals to the corresponding light emitting element array in each of the corresponding divided periods.   2. The exposure apparatus according to claim 1, wherein the plurality of pixels in the light emitting element array are divided into a plurality of pixel groups having a predetermined number, and the pixels of the pixel groups are driven in a time division manner.   3. The exposure apparatus according to claim 1, wherein the drive signal generation circuit generates a drive current having a current value corresponding to the divided image data as the drive signal.   The image data processing unit supplies the light emitting element to the photosensitive drum when the light emitting element is lit for a time corresponding to the corresponding duty ratio at a luminance corresponding to the divided image data corresponding to each of the divided periods. 4. The exposure apparatus according to claim 1, wherein the sum of the light energy to be obtained is a value that provides light energy corresponding to the image data. 5. The image data processing unit sets the one line time to a first divided period in which the duty ratio is set to a first value and a second value in which the duty ratio is smaller than the first value. Divided into second divided periods,
The divided image data includes first divided image data corresponding to the first divided period and second divided image data corresponding to the second divided period,
The first divided image data is set to zero when the gradation value of the image data is lower than a predetermined first gradation value, and the second divided image data is the gradation value of the image data. 5. The exposure apparatus according to claim 1, wherein the exposure apparatus is set to zero when higher than a predetermined second gradation value.   6. The exposure apparatus according to claim 5, wherein at least one of the first divided image data and the second divided image data is set to zero. An image forming apparatus that performs printing according to image data,
A photosensitive drum;
A plurality of pixels having light emitting elements are arranged in a line, and a light emitting element array that performs exposure according to the image data on the photosensitive drum;
One line time in which one line is exposed on the photosensitive drum by the light emitting element array is divided into a plurality of divided periods having different lighting times of the light emitting elements of the light emitting element array, An image data processing unit that generates a plurality of divided image data corresponding to a duty ratio composed of a ratio of the lighting time to the one line time corresponding to a divided period;
An image forming apparatus, comprising: a drive signal generation circuit that generates a plurality of drive signals according to the plurality of divided image data and supplies the drive signals to the corresponding light emitting element arrays in the corresponding divided periods.   The image forming apparatus according to claim 7, wherein the drive signal generation circuit generates a drive current having a current value corresponding to the divided image data as the drive signal.   The image data processing unit supplies the light emitting element to the photosensitive drum when the light emitting element is lit for a time corresponding to the corresponding duty ratio at a luminance corresponding to the divided image data corresponding to each of the divided periods. 9. The image forming apparatus according to claim 7, wherein a sum of the light energy to be produced within the one line time is set to a value that provides light energy corresponding to the image data. The image data processing unit sets the one line time to a first divided period in which the duty ratio is set to a first value and a second value in which the duty ratio is smaller than the first value. Divided into second divided periods,
The divided image data includes first divided image data corresponding to the first divided period and second divided image data corresponding to the second divided period,
The first divided image data is set to zero when the gradation value of the image data is lower than a predetermined first gradation value, and the second divided image data is the gradation value of the image data. The image forming apparatus according to claim 7, wherein the image forming apparatus is set to zero when the value is higher than a predetermined second gradation value.   The image forming apparatus according to claim 10, wherein at least one of the first divided image data and the second divided image data is set to zero.

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