JP2010093048A - Light-emitting device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of problems due to variations in characteristics of light emitting elements when performing multiple exposure.
Organic EL elements (811, 812,...) Arranged along the X direction, and one or more organic EL elements (for example, 821, 831, 841) arranged along the Y direction with each of them leading. An organic EL element group (8G1, 8G2,...), A power value measuring means for measuring each power value of light for each organic EL element group, and variations in the power values determined based on the measurement results. And a correction value setting means for setting each correction value corresponding to each light emitting element group so that each power value is constant, and driving for driving the light emitting element based on the correction value. Correction means for correcting the signal.
[Selection] Figure 5

Description

  The present invention relates to a light emitting device such as an organic EL (Electro Luminescence) device and an image forming apparatus.

  As a thin and light-emitting source, OLED (Organic Light Emitting Diode), that is, an organic EL element has attracted attention. The organic EL element has a structure in which at least one organic thin film formed of an organic material is sandwiched between a pixel electrode and a counter electrode. The organic EL element emits light when a predetermined current is supplied between the pixel electrode and the counter electrode.

  A light-emitting device including such a light-emitting element such as an organic EL element is used for a printer head for an image forming apparatus such as a line printer of a tandem method or a 4-cycle method. Here, the image forming apparatus includes, for example, an image carrier such as a photosensitive drum, a charger, a developing device, a transfer device, and the like in addition to the printer head. The image carrier is charged by a charger and then exposed to light emitted from a light emitting element that forms part of the printer head. By this exposure, an electrostatic latent image is formed on the surface of the image carrier. Thereafter, the electrostatic latent image is developed with toner supplied from a developing device, and the toner is transferred to a transfer medium such as paper by a transfer device. As a result, a desired image is formed on the transfer medium.

As a light emitting device incorporated in such an image forming apparatus or the like, for example, those disclosed in Patent Documents 1 and 2 are known.
JP 2007-125705 A JP 2008-87197 A

By the way, since the light emitting device as described above usually has a configuration in which a plurality of light emitting elements such as the organic EL elements are provided, there is a problem in that variations in light emission intensity occur between these elements.
In addition, there is a problem in that the light emission characteristics (for example, light emission efficiency) of these light emitting elements deteriorate with time in accordance with the degree of light emission in the past (for example, the number of times of light emission). In particular, there are cases where a plurality of images having a common form are continuously output (for example, when a large number of similar images are printed by the image forming apparatus in which the light emitting device is employed as the printer head). Although the light emitting element always emits light, the other light emitting element is traced to emit little light, and there is a high possibility that the variation in the deterioration of the characteristics of each light emitting element increases with time.
When this is the case, the degree of deterioration of each light emitting element on one light emitting device is different (although “deterioration” per light emitting element itself is of course a problem). One light-emitting element in each light-emitting element still has a sufficient light-emitting capability, but another light-emitting element has a disadvantage in that it can no longer emit light at an earlier stage. In short, there arises a problem that the “lifetime” of the light emitting element varies.

  The aforementioned Patent Document 1 discloses a technique for dealing with such a problem. That is, in Patent Document 1, “pulse width determining means” that determines the pulse width of the driving signal of the light emitting element by “first coefficient and gradation data”, and the current value of the driving signal by “second coefficient” are determined. So that the “first coefficient” and the “second coefficient” are substantially the same as the “mode of change in the light emission characteristics” of the plurality of light emitting elements, etc. A technique selected under the above-mentioned objective is disclosed (refer to [Claim 1] of Patent Document 1 etc. for the above). According to such a technique, the effect that “the effect of suppressing unevenness in luminance (gradation) can be maintained over a long period of time” can be achieved (refer to [0007] of Patent Document 1 or (See FIG. 2 and its description [0022] et seq.).

  Such a technique of Patent Document 1 is very effective in solving the above-described problem. In addition, Patent Document 1 discloses a technique in which the first coefficient or the like is set for the purpose of making the light amounts (light emission energy) of the respective light emitting elements substantially coincide with each other. An effect different from the above, that is, (gradation) unevenness suppression (see [0007] of Patent Document 1) (that is, the technique of Patent Document 1 not only suppresses uneven gradation unevenness over time). It also realizes the suppression of synchronicity.)

However, there are still challenges.
That is, as disclosed in Patent Document 2 described above, the image forming apparatus or the like has a technique for performing multiple exposure on the exposure surface of the image carrier (Claim 1 of Patent Document 2). reference). In Patent Document 2, on the premise of such a technique, by appropriately setting the positioning of “fourth light source” from “first light source” included in each of “first light source column” and “second light source column”, A technique is disclosed in which the size and energy of an exposure area (spot area) by these light sources is made uniform, thereby suppressing image resolution and gradation unevenness (the above is disclosed in Patent Document 2 [0004] to [0005] [0037]. [FIG. 8] etc.).
According to such Patent Document 2, it is true that such effects as gradation unevenness suppression are effectively exhibited.

  However, also in this Patent Document 2, a new problem caused by overlapping the multiple exposure technique and the above-described variation between the light emitting elements or the variation in characteristic deterioration over time is specially disclosed. There is no particular consideration. For example, when focusing on two points on the image carrier, multiple exposure is performed on one of the three points by three light emitting elements (first group), and another three points are emitted on the remaining point. Considering the case of performing multiple exposure with the element (second group), it is usually assumed that these six light emitting elements have the above-described characteristic variations, so that the same gradation expression is expressed at the two points. Even if an attempt is made to perform the above, there is a possibility that a gradation difference will occur between an image formed based on the first group and an image formed based on the second group.

  It is an object of the present invention to provide a light emitting device and an image forming apparatus that can solve at least a part of the above-described problems.

  In order to solve the above-described problem, the light-emitting device according to the present invention includes first, second,..., N-th light-emitting elements (n is a positive integer) arranged in the first direction, The first, second,..., Nth light emitting element groups, and the first, second,..., Nth light emitting element groups arranged in the second direction intersecting the first direction, and the first, second,. For each nth light emitting element group, each correction corresponding to each light emitting element group is made constant based on the variation of each power value of light emitted from each light emitting element group. Correction value setting means for setting a value; and correction means for correcting a drive signal for driving the light emitting element based on the correction value.

According to the present invention, first, it is assumed that there is a power value for each of the first, second,. Therefore, this power value can also be distinguished from the “first, second,..., N-th” power values, similarly to the numbering for the light emitting element group. The correction means determines a correction value for each light emitting element group so as to eliminate variations in the first, second,..., Nth power values. Therefore, this correction value can also be distinguished from the “first, second,..., Nth” correction values.
The drive signal for driving each light emitting element is corrected by such a correction value, but in this case, it is most preferably included in the pth light emitting element group (p = 1, 2,..., N). It is preferable that the plurality of light emitting elements to be corrected simultaneously with the p-th correction value (that is, correction is performed after the correspondence between the light emitting element group and the correction value is achieved).
For this reason, in the present invention, even if each of the light emitting elements has a variation in the light emission characteristics as described above, the power value emitted from each light emitting element group is the total light emitting element group. Over a certain range. In addition, according to the present invention, since the correction for each light emitting element is not performed for each light emitting element but for each light emitting element group, the correction process can be speeded up. It is done.
In any case, the present invention has one of the major features that the correction of the drive signal is not performed for each light emitting element but for each light emitting element group. As a result, speeding up of the correction processing described above can be achieved, or an effect of enabling image formation with practically sufficient quality despite such effects can be enjoyed at the same time. To get.

  The specific structure and material of the “light emitting element” in the present invention can be basically determined freely. For example, an element in which a light emitting layer made of an organic EL material or an inorganic EL material is interposed between electrodes. The light emitting device of the present invention can be employed. Furthermore, various light emitting elements such as an LED (Light Emitting Diode) element and an element that emits light by plasma discharge can be used in the present invention.

The light emitting device of the present invention further includes a drive circuit for driving the light emitting element, and the drive circuit includes a common circuit portion common to a plurality of light emitting elements included in one of the light emitting element groups. You may comprise as follows.
According to this aspect, since the common circuit portion is provided as if it corresponds to each light emitting element group, simplification of the circuit configuration of the drive circuit, reduction in circuit scale, and the like are realized. . Such an effect can be grasped more clearly when the “driving circuit” referred to in this aspect is configured, assuming that the circuit is formed so as to individually correspond to each light emitting element. . In this aspect, since the circuit configuration is shared for a plurality of light emitting elements included in at least one light emitting element group (that is, a common circuit portion is provided), the above-described effect is effectively enjoyed. It is.

In this aspect, the drive circuit further includes a current source element that supplies a drive current for the light emitting element, and the common circuit portion is for the current source element for adjusting the magnitude of the drive current. A control signal supply circuit that supplies the control signal to the current source element may be included.
In this embodiment, first, the “current source element” includes, for example, a transistor used in a saturation region, and a device that changes the magnitude of the drain-source current according to the voltage applied to the gate. It is. In this case, the “voltage” referred to here corresponds to an example of the “control signal” in this aspect.
And according to this aspect, the said common circuit part contains the control signal supply circuit which supplies such a control signal to a current source element.
As described above, this aspect provides a suitable example in which the above-described common circuit portion is more specific.
More specifically, the “control signal supply circuit” of this aspect can include, for example, a DA converter (Digital Analog Converter) or the like. An example of such a form will be described in a later embodiment.

In the light emitting device of the present invention, the drive signal is defined by a current value and a pulse width, and the correction unit corrects the drive signal by correcting at least one of the current value and the pulse width. You may comprise as follows.
According to this aspect, the light emission mode of the light emitting element or the control related to the correction is suitably performed.

Particularly in this aspect, the correction means may be configured to correct the drive signal by correcting the current value.
According to this aspect, the light emission mode of the light emitting element or the control related to the correction is performed with the current value supplied thereto (in this case, the “correction value” in the present invention is the “current correction value”). It can also be said.)
By the way, the correction by the correction means according to the present invention is preferably performed simultaneously with the p-th correction value for a plurality of light-emitting elements included in the p-th light-emitting element group, as described above. If it redraws to this aspect, about the several light emitting element contained in the pth light emitting element group, the correction | amendment by the same electric current correction value will be performed.
Therefore, when the plurality of light emitting elements in this case are used for, for example, multiple exposure, the plurality of light emitting elements are driven with the same current value during that time.
For example, this increases the possibility of slowing down the deterioration rate of the whole of the plurality of light emitting elements constituting the “light emitting device” according to the present invention, as compared with the case where each light emitting element is individually corrected. This is because when performing individual correction for each light emitting element, there is a high risk of causing variations in the lifetime of each light emitting element, and therefore, among the light emitting elements included in a certain light emitting element group, the lifetime is quickly increased. This may lead to the appearance of a light emitting element that becomes unable to emit light (= multiple exposure that was originally planned is no longer possible), but in this embodiment, light emission included in one light emitting element group This is because the elements are supplied with the same drive current in the above-mentioned meaning, and therefore, the deterioration rate related to them can be made constant.

In the light emitting device of the present invention, the light emitting device further includes an exposure surface facing the light emitting element, and the exposure of the exposure surface by the light emission of the light emitting element includes a plurality of light emitting elements included in one of the light emitting element groups. It may be configured to be performed by multiple exposure by light emission over time.
According to this aspect, one of the most preferable usage examples of the “light emitting device” according to the present invention is provided.
That is, in the multiple exposure, “the light emission over time of a plurality of light emitting elements included in one of the light emitting element groups” is performed as described above. Therefore, the effects according to the present invention described above, or various aspects thereof. (For example, the power value observed for each light emitting element group can be made uniform, or the same driving current is supplied to the light emitting elements included in one light emitting element group. Various effects such as that the life of the battery can be extended) are most effectively enjoyed.

Further, in the light emitting device of the present invention, for each of the first, second,..., Nth light emitting element groups, power value measuring means for measuring each power value of the light emitted from each of the light emitting element groups is further provided. You may comprise so that it may be equipped.
According to this aspect, since each power value for each light emitting element group is suitably measured, the correction of the drive signal referred to in the present invention is also suitably performed.

On the other hand, the image forming apparatus according to the present invention includes the various light emitting devices described above in order to solve the above-described problems.
The image forming apparatus of the present invention includes the above-described various light emitting devices, that is, a light emitting device that can suitably suppress variation in light emission characteristics between the light emitting elements. There is almost no possibility of generating so-called streaks on the print medium.
The concept of “image forming apparatus” in the present invention includes, for example, a so-called organic EL display.
Alternatively, the concept of “image forming apparatus” according to the present invention includes a so-called printer or the like provided with an image carrier such as a photosensitive drum, a charger, a developing device, a transfer device, and the like as in the above-described example. A more specific configuration example in this case will be described again in <Application Example> of the later embodiment.
In the former case, “image formation” means that an image is output on an image display surface on which organic EL elements that are “light emitting elements” are arranged. For example, an image is output on a transfer medium such as the above. In short, the “image forming apparatus” in the present invention means a general apparatus capable of “forming” an image that can be recognized by a human being in some sense.

  Hereinafter, embodiments according to the present invention will be described with reference to FIGS. 1 to 5. In addition to FIGS. 1 to 5 mentioned here, in each drawing referred to below, the ratio of dimensions of each part may be appropriately different from the actual one.

  FIG. 1 is a perspective view showing a partial configuration of an image forming apparatus using the light emitting device 10 as an optical head (light emitting device). As shown in the figure, the image forming apparatus includes a light emitting device 10, a converging lens array 15, a photosensitive drum 110, and a control unit CU.

  Among these, the light emitting device 10 includes a plurality of organic EL elements (light emitting elements) arranged along the longitudinal direction in FIG. Each of these organic EL elements emits light downward in FIG. 1 (see the broken line in the figure). This light is incident on a converging lens array 15 to be described later. A more detailed configuration of the light emitting device 10 will be described later.

The converging lens array 15 is disposed between the light emitting device 10 and the photosensitive drum 110. The converging lens array 15 includes a large number of gradient index lenses arranged in an array with each optical axis facing the light emitting device 10. Light emitted from each organic EL element of the light emitting device 10 reaches the outer surface of the photosensitive drum 110 after passing through each gradient index lens of the converging lens array 15.
As the converging lens array 15, specifically, for example, SLA (Selfoc Lens Array) available from Nippon Sheet Glass Co., Ltd. can be used (Selfoc: SELFOC is a registered trademark of Nippon Sheet Glass Co., Ltd.). ). If this is used, the light from the light emitting device 10 forms an erecting equal-magnification image on the photosensitive drum 110.

The photosensitive drum 110 has a substantially cylindrical shape. The central axis is provided with a rotation axis. The photosensitive drum 110 rotates about the rotation axis in the sub-scanning direction, which is the direction in which the recording material (transfer medium) is conveyed (see the arrow in the figure). Note that the extending direction of the rotation axis coincides with the main scanning direction.
The photosensitive drum 110 and the light emitting device 10 are controlled so that a predetermined relationship is established between the rotation timing of the photosensitive drum 110 and the light emission timing of each organic EL element of the light emitting device 10. The For example, along the main scanning direction, light emission / non-light emission of each organic EL element is controlled according to the brightness of one line of the image to be formed, and for one line along the sub scanning direction. The rotation of the photoconductive drum is controlled such that the photoconductive drum rotates by a predetermined angle after the completion of the photosensitivity process for the image. In the present embodiment, multiple exposure is performed as will be described later. The relationship between this multiple exposure and the rotation control described above will be described later.
In this way, a latent image (electrostatic latent image) corresponding to a desired image is formed on the outer surface of the photosensitive drum 110.

The power measuring device 23H includes a measuring unit 231 and a support unit 232 as shown in FIG. 1 or FIG.
The measurement unit 231 can be disposed so as to be positioned between the converging lens array 15 and the photosensitive drum 110. The measurement unit 231 includes a power sensor (light sensor) 23 made of, for example, a photodiode.
On the other hand, as shown in FIG. 2, one end of the support portion 232 is fixed to the left end of the measurement portion 231 in the figure, and the other end is attached to the first frame F1. Between the support part 232 and the 1st flame | frame F1, the translation operation | movement mechanism which consists of a linear motor etc. is provided, for example. Accordingly, the support portion 232 can travel along the direction penetrating the paper surface of FIG. 2, and thus the power measuring device 23 </ b> H can travel along the arrangement direction of the organic EL elements (see also FIG. 1). ).
In the present embodiment, the power measurement device 23H can be retracted to an area other than the installation area of the light emitting device 10 by this traveling function (see the broken line in FIG. 1). Accordingly, when the light emitting device 10 forms an electrostatic latent image on the photosensitive drum 110, the power measuring device 23H does not get in the way.
In addition, the distance between the focusing lens array 15 and the photosensitive drum 110 may not be sufficient due to the performance of the focusing lens array 15 or the like. It is preferable to provide a photosensitive drum moving mechanism or the like for making the variable. According to this, the traveling function is better secured.
With the above configuration, the power measurement device 23H can measure each power value for the light emitted from the light emitting device 10, particularly the light emitted from each organic EL element constituting the light emitting device 10.

The control unit CU includes a CPU (Central Process Unit), a RAM (Random Access Memory) that stores necessary information, and a ROM (Read that stores programs necessary for operating the image forming apparatus). Only memory). The control unit CU can also synchronize the rotation timing of the photosensitive drum 110 and the light emission timing of the light emitting device 10.
In addition, the control unit CU obtains a current correction value for driving the organic EL element 8 through measurement of the power value using the power measuring device 23H, and performs current correction based on the correction value. This point will be described later.
In addition, the control unit CU controls operations of the various elements so that the various elements constituting the image forming apparatus according to the present embodiment operate in a harmonious manner.

More specifically, the above-described light emitting device 10 has a structure or configuration as shown in FIGS.
In FIG. 2 and the like, the light emitting device 10 includes an element substrate 7 and a cover substrate 12. Among them, the element substrate 7 is a plate-like member having a substantially rectangular shape in plan view as shown in FIG. The element substrate 7 is made of a light-transmitting material such as glass, quartz, or plastic.
As shown in FIG. 2, such a light emitting device 10 is mounted on the surface of the ceiling that forms the shape of the hook in the second frame F <b> 2 having the shape of a cross-section. Further, a flexible printed circuit board 53 is attached to the second frame F2 so as to follow the left bar in FIG. One end of the flexible printed circuit board 53 is connected to the circuit element thin film 801, and the other end is connected to the circuit board 51 (hereinafter, the numbers [I] and [II] will be attached in this order). .)

[I] The circuit element thin film 801 constitutes a part of the light emitting device 10 and is a thin film formed on the element substrate 7 composed of various circuit elements including the organic EL element described above. Although depicted in a very simplified form in FIG. 2, the circuit element thin film 801 includes a plurality of organic EL elements 8, a plurality of drive circuits 9, and the like, as shown in FIG.
Note that the number and arrangement of the organic EL elements 8 and drive circuits 9 shown in FIG. 3 and the like are merely examples. In the present embodiment, in particular, the arrangement of the organic EL elements 8 shown in each drawing such as FIG. 3 is determined for the purpose of simplifying the explanation regarding the multiple exposure described later. There is.

Among these, the drive circuit 9 is composed of a drive transistor Tr1 or a switching transistor (hereinafter abbreviated as “SW transistor”) Tr2 shown in FIG. 5 to be referred to later, and is involved in driving the organic EL element 8. To do.
On the other hand, the organic EL element 8 includes two electrodes facing each other and a light emitting functional layer including at least an organic light emitting layer between the two electrodes (both not shown in FIG. 3). A common line 16 is connected to one of the two electrodes, and a power line (not shown in FIG. 3) is connected to the other electrode via a drive circuit 9.
In particular, in the present embodiment, such organic EL elements 8 are arranged according to a matrix arrangement on the element substrate 7 as shown in FIG. This matrix array includes first, second,..., Nth organic EL elements 811, 812,..., 81 n arranged along the X direction in FIG. , N happens to be “10”.) Secondly, the matrix array includes three organic EL elements 8 that start from each of these organic EL elements 811, 812,..., 81 n and are arranged along the Y direction in FIG. It is. For example, the organic EL elements 821, 831 and 841 are arranged with the organic EL element 811 at the head (in this specification, the reference “8” is the reference “811”, “812”,..., “81n”, “821”,..., “841” etc. are used as a generic code.
At this time, in this embodiment, the “organic EL element group 8G” is considered in the matrix arrangement. That is, for example, in addition to the organic EL element 811 positioned at the head, the four organic EL elements 8 including the organic EL elements 821, 831, and 841 constitute the “organic EL element group 8G1”. Hereinafter, similarly, the organic EL element group 8G2 is constituted by organic EL elements 812, 822, 832, and 842, the organic EL element group 8G3 is constituted by organic EL elements 813, 823, 833, and 843, and so on. (Note that in this specification, the code “8G” is used as a generic code for all or part of the codes “8G1”, “8G2”,. .
Such an organic EL element group 8G plays a central role in this embodiment, which will be described later.

[II] On the other hand, as shown in FIG. 2, the circuit board 51 is along the inner surface of the left bar in FIG. It is attached as follows.
As shown in FIG. 5, the circuit board 51 includes a control unit CU, a gradation value control circuit 19, a current value setting memory 11, a DA converter (an example of a “control signal supply circuit” in the present invention) 1D, 2D, 3D,..., A light emission control circuit 21, a power sensor 23, and the like. 5 also shows a circuit configuration example of the organic EL element 8 or a drive circuit 9 for driving the organic EL element 8.

First, the drive circuit 9 shown in FIG. 5 is a circuit configuration example of the drive circuit 9 described above. As shown in the figure, the drive circuit 9 has the same configuration regardless of whether each organic EL element 8 is different.
Therefore, the drive circuit 9 will be described with reference to the drive circuit 9 shown in the upper left corner of the figure. The drive circuit 9 includes two transistors, that is, a drive transistor (an example of the “current source element” in the present invention) Tr1, and an SW transistor. Tr2 and one capacitor C1 are provided.
Among these, the source of the driving transistor Tr1 is connected to the power supply line Vel, and the drain thereof is connected to the source of the SW transistor Tr2. One electrode of the capacitor C1 is connected to the gate of the drive transistor Tr1, and the source of the drive transistor Tr1 is connected to the other electrode of the capacitor C1. The gate is also connected to the DA converter 1D. This drive transistor Tr1 is assumed to be used in the saturation region.
On the other hand, the drain of the SW transistor Tr2 is connected to the pixel electrode of the organic EL element 811. The gate of the SW transistor Tr2 is connected to the light emission control circuit 21. The SW transistor Tr2 is assumed to be used in the linear region.

With the above configuration, first, electric charge is stored in the capacitor C1 in accordance with the level of the gradation signal sent from the gradation value control circuit 19 or the DA converter 1D, and the gate transistor driving transistor Tr1 is set to that level. A corresponding voltage is applied. As a result, the drive transistor Tr1 functions as a current source that supplies a current corresponding to the level.
Secondly, under this situation, when a light emission command signal is sent from the light emission control circuit 21 to the gate of the SW transistor Tr2, the SW transistor Tr2 is turned on. A predetermined value of current is supplied from the driving transistor Tr1 functioning as a current source. In this case, the light emission command signal also has a meaning of designating a period during which the SW transistor Tr2 is maintained in an ON state. Therefore, a period during which the current is to be supplied to the organic EL element 811 (that is, a pulse width) It also has a meaning to define.
The “drive signal” referred to in the present invention is a concept including the light emission control signal in addition to the gradation signal. The former defines the current value of the “drive signal”, and the latter defines the pulse width.

As is apparent from FIG. 5, the other drive circuits 9 have the same configuration as described above, and the same light emission control is performed on them.
However, in the present embodiment, among the various elements described above, the DA converters 1D, 2D, 3D,... Are not provided so as to individually correspond to the respective organic EL elements 8. These DA converters 1D, 2D, 3D,... Are provided so as to correspond to each of the organic EL element groups 8G described above as shown in FIG. For example, paying attention to the organic EL element group 8G1 in FIG. 5, the gates of the four drive transistors Tr1 connected to each of the organic EL elements 811, 821, 831, 841 included therein are commonly used, A DA converter 1D is connected. The same applies to the other organic EL element groups 8G2, 8G3,.

Next, various other elements constituting the circuit board 51 described above will be described.
The power sensor 23 measures the power value when the organic EL element 8 shown in FIG. In this case, the power sensor 23 measures the power value for each organic EL element group 8G described above. That is, the power sensor 23 is not related to the plurality of organic EL elements 8 included in the same organic EL element group 8G. If there are measured power values P1, P2, P3,..., The power sensor 23 grasps that each of them corresponds to the organic EL element groups 8G1, 8G2, 8G3,.
The power values P1, P2, P3,... Measured here are variations in various characteristic values such as the threshold voltage Vth or mobility of the drive transistor Tr1, variations in the characteristics of the light emitting functional layers constituting the organic EL element 8, Alternatively, the light transmission efficiency between the organic EL elements 8 due to the positioning error of each lens in the converging lens array 15 (for example, an error related to the relative positional relationship between each lens and each organic EL element 8). Depending on various factors such as variations in

The current value setting memory 11 stores the measurement result of the power value related to each organic EL element group 8G by the power sensor 23 and the current correction value determined according to the instruction of the control unit CU corresponding thereto. In response to the power sensor 23 measuring the inherent power values P1, P2, P3,... For each organic EL element group 8G as described above, the current value setting memory 11 is also 1 Current correction values J1, J2, J3,... For one organic EL element group 8G are stored (the symbols “J1, J2, J3,...” Are not shown in FIG. 5).
The purpose of the current correction values J1, J2, J3,... Is that when the current corrected by the current correction values J1, J2, J3,. The aim is to emit light with the same power value.

  In addition, based on the measured power values P1, P2, P3,..., A method for obtaining current correction values J1, J2, J3,. Various methods such as a method using an appropriate arithmetic expression are conceivable, but basically, anything within the scope of the present invention. As a most preferable example, a method of preparing a predetermined table or correspondence table that defines the relationship between the measured power value and the current correction value in the control unit CU or the like is from the viewpoint of processing speed or the like. Is this good.

When the gradation value control circuit 19 receives an input of a gradation signal for a specific organic EL element 8 sent from the control unit CU, the current correction value J1 for the corresponding organic EL element group 8G is received. , J2, J3,..., The gradation signal is corrected with the current correction values J1, J2, J3,..., And the corrected gradation signal is converted into the DA converters 1D, 2D, To 3D.
The DA converter 1D converts a gradation signal that is a digital signal corresponding to a certain organic EL element group 8 sent from the gradation value control circuit 19 into a gradation signal that is an analog signal, and converts the gradation signal into an analog signal. 8 is supplied to the gate of the drive transistor Tr1 corresponding to 8.

The light emission control circuit 21 supplies light emission control signals L11, L12,..., L21, L22,..., L31, L32,. Toward the gate of the SW transistor Tr2 in the drive circuit 9 corresponding thereto. As described above, the light emission control signals L11, L12,... Define a period during which the SW transistor Tr2 should be in an ON state or a period during which a current should be supplied to the organic EL element 8.
As a backside of the above circumstances, the light emission control signals L11, L12,... Naturally shift the SW transistor Tr2 in the ON state to the OFF state (that is, stop the light emission of the organic EL element 8). Also used when.

  The “drive circuit” referred to in the present invention is a broader concept including the control unit CU, the gradation value control circuit 19, the DA converters 1D, 2D, 3D,. This is not necessarily the same as “driving circuit 9” in the present embodiment.

Next, the operation and effect of the light emitting device 10 according to this embodiment having the above-described configuration will be described with reference to FIGS. 6 to 9 in addition to FIGS.
First, the control unit CU performs initial setting related to the current correction value (step S101 in FIG. 6). This initial value setting includes processing for making the current correction values J1, J2, J3,... Stored in the current value setting memory 11 equal. That is, J1 = J2 = J3 =.

Next, the control unit CU performs power variation measurement (step S102 in FIG. 6). That is, the control unit CU is emitted from each organic EL element 8 by driving the power measurement device 23H or scanning the power sensor 23 on the organic EL element 8 (see FIG. 1 and the like). Measure the power value of light.
At this time, an appropriate relationship is set between the scanning speed (or moving speed) of the power sensor 23 and the light emission timing of each organic EL element 8. In particular, in this embodiment, the light emission timing of the organic EL element 8 at the time of power measurement is governed for each organic EL element group 8G. For example, when the power sensor 23 reaches the organic EL element group 8G1, the organic EL elements 811, 821, 831, and 841 included in the organic EL element group 8G1 emit light at the same time, and the next organic EL element group When reaching above 8G2, the organic EL elements 812, 822, 832, and 842 included in the organic EL element group 8G2 emit light at the same time, and at the same time, the preceding organic EL elements 811, 821, 831, and 841 are simultaneously turned off. And so on. In this way, the power sensor 23 (or the control unit CU) grasps the correspondence relationship between the measured power value and each organic EL element group 8G.
In this case, it is important that all the organic EL elements 8 are driven under the same drive signal (especially under the same current value condition).
From this and the fact that the current correction values J1, J2, J3,... Are equalized in step S101, theoretically, each organic EL element 8 should emit light with the same power value. Therefore, the power value observed for each organic EL element group 8G should be the same. However, the power values P1, P2, P3,... Actually observed with respect to each organic EL element group 8G are the variations in various characteristic values such as the threshold voltage Vth of the drive transistor Tr1 as described above, and within the converging lens array 15. May vary depending on various factors such as variations in light transmission efficiency between the organic EL elements 8 due to the positioning errors of the lenses (rather, it is natural). “Power variation measurement” in this processing implies such a background.

  Next, the control unit CU determines whether or not the measured power values P1, P2, P3,... Vary within a predetermined range (step S103 in FIG. 6). That is, given the predetermined lower limit value PL and upper limit value PU, the truth of PL <P1 <PU, PL <P2 <PU, PL <P3 <PU,... For each of the measured power values P1, P2, P3,. Judgment is false. And when this judgment is denied, for example, when P1 ≦ PL or PU ≦ P1 is established with respect to P1, a current correction value setting process for the P1 is performed (step S103 in FIG. 6; step from NO to step S103) S105). That is, the current correction value J1 is newly determined to correspond to this P1. For example, qualitatively, if P1 is larger, a current correction value J1 is set such that a smaller drive current is caused to flow through the organic EL element 8 to decrease it, and if P1 is smaller, this is increased. It seems that a current correction value J1 opposite to that described above is determined in order to achieve this.

  The power value measurement process and the current correction value setting process described above are performed for all organic EL element groups 8G included in the light emitting device 10 (step S104 in FIG. 6). As a result, current correction values J1, J2, J3,... Relating to all the organic EL element groups 8G are determined and stored in the current value setting memory 11. If an affirmative determination is made in step S103 in FIG. 6 (step S103 in FIG. 6; YES), the current correction value setting process in step S105 is not performed, but in this case, the organic EL element group concerned For 8G (Z) (Z is a natural number whose upper limit matches the number of organic EL element groups 8G), the initial value set in step S101 is used as the current correction value J (Z) as it is. become.

  Through this process, all the organic EL element groups 8G have substantially the same value that does not exceed a certain range as long as the organic EL element groups 8G are driven under the same drive signal. Will be supplied.

Based on the above, in the light emitting device 10 according to the present embodiment, when an electrostatic latent image is formed on the photosensitive drum 110, multiple exposure as described below is performed. Hereinafter, this will be described with reference to FIGS.
First, as shown in FIG. 7, an electrostatic latent image SZ as a set of pixels D11, D12, D13,... Each having a unique gradation value is formed on the photosensitive drum surface (exposure surface) 110S. Is placed on the premise. The electrostatic latent image SZ is formed by arranging pixels D11, D12, D13,... In a matrix, and in the matrix arrangement, as shown in the figure, one row of images, two rows of images. It is possible to think of a group of pixels arranged in the up and down direction in the figure taken, while conceiving a group of pixels arranged in the left and right direction in the figure one line, picture two lines,. Is possible. In the former, for example, “image 1 column” is composed of pixels D11, D21, D31,..., And in the latter, for example, “image 1 row” is composed of pixels D11, D12, D13,.

In order to form such an electrostatic latent image SZ, each organic EL element 8 shown in FIG. 5 and the like is driven by a drive signal having the contents shown in FIG.
That is, first, in the first stage, each organic EL element 811, 812, 813,... Positioned at the head of each organic EL element group 8G is made up of the pixels D11, In order to form D12, D13,..., Gradation values D11, D12, D13,... (Hereinafter, the symbols “D11”, “D12”,. It is also used as an expression to express.). Therefore, in this case, the control unit CU supplies the gradation value control circuit 19 with gradation signals SD11, SD12, SD13,... Corresponding to the gradation values D11, D12, D13,. 19 supplies gradation signals, each of which has been corrected by the current correction values J1, J2, J3,..., To the organic EL elements 811, 812, 813,.
As a result, as shown in FIG. 9A, the light emitted from the organic EL element 811 is irradiated on the photosensitive drum surface 110S, so that the pixel D11 is part of the electrostatic latent image SZ. Formed as.

Next, in the second stage, each organic EL element 821, 822, 823,... Kept in the next stage (next line) of each organic EL element 811, 812, 813,. Are driven by a drive signal having gradation values D11, D12, D13,... As their contents (see FIG. 8).
In this second stage, each of the organic EL elements 811, 812, 813,... Has gradation values so as to form the pixels D21, D22, D23,. It is driven by a drive signal whose contents are D21, D22, D23,. At this time, in order to stop the light emission in the first stage, the light emission control circuit 21 once turns off the SW transistor Tr2 corresponding to each of the organic EL elements 811, 812, 813,. Considering the above, the SW transistor Tr2 is turned on again.
In parallel with the control of the light emission mode of each of the organic EL elements 811, 812, 813,..., The control unit CU shows the photosensitive drum 110 in FIG. Rotate by the distance of one pixel. As a result, as shown in FIG. 9B, a pixel D21 resulting from the light emission of the organic EL element 811 is formed as a part of the electrostatic latent image SZ next to the pixel D11.
At the same time, the pixel D11 is irradiated with light emitted from the organic EL element 821 driven based on the gradation value D11. That is, the formation part of the pixel D11 on the photosensitive drum surface 110S is subjected to multiple exposure.

In the first stage, although not shown in FIG. 9A, the pixels D12, D13,... Are statically placed by the organic EL elements 812, 813,. That is, it is formed as a part of the electrostatic latent image SZ.
Similarly, also in the second stage, the pixels D22, D23,... Are part of the electrostatic latent image SSZ by the organic EL elements 812, 813,. This means that the pixels D12, D13,... Are subjected to multiple exposure by the organic EL elements 822, 823,.
7 is formed corresponding to each of the organic EL element groups 8G1, 8G2,... Shown in FIGS. It will be done.

Thereafter, in each of the third and subsequent stages, as is apparent from FIGS. 8 and 9C and 9D, processing similar to the above is sequentially performed. To summarize this, the four organic EL elements 8 belonging to a certain organic EL element group 8G are driven based on a drive signal determined according to the same gradation value in order or with time. The organic EL element 8 that has been driven by the drive signal is driven on the basis of the drive signal determined according to the gradation value for expressing the pixel in the next row on the electrostatic latent image SZ. Will be repeated.
In the present embodiment, as a result of such an operation, quadruple multiple exposure is performed.
The advantage of such multiple exposure is that, for example, even if the light emission energy of each organic EL element 8 is not sufficient, it is possible to give a relatively sufficient energy to the surface 110 of the photosensitive drum. The electrostatic latent image SZ can be formed.

The light emitting device 10 described above has the following effects.
(1) According to the light emitting device 10 according to the present embodiment, first, the four organic EL elements 8 included in the Zth organic EL element group 8G (Z = 1, 2,..., 10) Since the correction is performed simultaneously by the Zth current correction value J (Z) corresponding to the element group 8G, each of the organic EL elements 8 has a variation factor as described above. However, the power value emitted from the organic EL element group 8G is within a certain range over all the organic EL element groups 8G1, 8G2,.
Therefore, as described above, the power values between the columns “image 1 column”, “image 2 column”,... In FIG. 7 are formed corresponding to each of the organic EL element groups 8G1, 8G2,. Therefore, the variation of the power value seen in the entire electrostatic latent image SZ is also within the predetermined range. Therefore, when an image is formed on the print medium based on the electrostatic latent image SZ formed as a result, there is very little possibility that a print defect such as streak unevenness will occur.
According to the present embodiment, the occurrence of problems due to variations among the plurality of organic EL elements 8 can be suitably suppressed in the above sense.

(2) According to the light emitting device 10 according to the present embodiment, the correction related to each organic EL element 8 is not performed for each organic EL element 8, but is performed for the organic EL element group 8G as one unit. There is also an advantage that processing can be speeded up.

(3) In the light emitting device 10 according to the present embodiment, one DA converter (1D) corresponding to one organic EL element group 8G and common to the four organic EL elements 8 included therein. , 2D, ...) are connected.
As described above, in this embodiment, the circuit configuration is shared for the four organic EL elements 8 included in one organic EL element group 8G (that is, a common circuit portion is provided). Therefore, as apparent from the comparison with the case where each of these four organic EL elements 8 is individually provided with a DA converter, the circuit configuration of the drive circuit for driving the organic EL elements 8 is simplified. , Circuit scale reduction, etc. are realized.

(4) According to the light emitting device 10 according to the present embodiment, when attention is paid to one pixel D11,... (See FIG. 7), the organic EL element 8 involved in the multiple exposure for the pixel D11,. In the meantime, all are driven with the same drive current based on the same current correction value.
For example, this increases the possibility of slowing down the deterioration rate of the plurality of organic EL elements 8 constituting the light emitting device 10 as compared with the case where each organic EL element 8 is individually corrected. This is because when individual correction is performed for each organic EL element 8, there is a high possibility that the lifetime of each organic EL element 8 will vary, and therefore, the organic EL elements included in one organic EL element group 8G. 8, it may lead to the appearance of the organic EL element 8, which has a lifespan and becomes unable to emit light early (= the multiple exposure originally planned is no longer possible), but in this embodiment, The organic EL elements 8 included in one organic EL element group 8G are supplied with the same drive current in the above-mentioned meaning, and therefore, the deterioration rate related to them can be made constant. It is.

Although the embodiments according to the present invention have been described above, the image forming apparatus or the light emitting apparatus according to the present invention is not limited to the above-described embodiments, and various modifications can be made.
(1) In the above-described embodiment, the organic EL elements 8 are arranged so as to form a regular lattice as shown in FIG. 3 or FIG. 4, but the present invention is not limited to such a form.
For example, as shown in FIG. 10, an arrangement in which the organic EL elements 8 arranged in each adjacent row are deviated to a certain extent along the row direction can also be adopted in the present invention.
The arrangement form as shown in FIG. 10 can also be called a kind of matrix-like arrangement. In such a matrix-like arrangement, first, first, second,... Nth arrayed along the X direction in FIG. Organic EL elements 811 ′, 822 ′, 813 ′, 824 ′,. Here, the difference from the case of FIG. 3 is that these organic EL elements 811 ′, 822 ′, 813 ′, 824 ′,... Are not arranged in a straight line, but are arranged in steps as shown. It is like that. It goes without saying that such a case also corresponds to “aligned along the first direction” in the present invention.
Secondly, in the matrix arrangement, each of the organic EL elements 811 ′, 822 ′, 813 ′, 824 ′,... Is the top, and one organic EL element is arranged along the Y direction in FIG. 8 is included. For example, the organic EL element 831 ′ is arranged with the organic EL element 811 at the head (in particular, in the description of FIG. 10, the symbol “8” is the symbol “811 ′” as described above). , “812 ′”,..., Etc., are used as generic symbols.
Even in such a form, the “organic EL element group 8G ′” is conceived in the matrix arrangement. That is, for example, the two organic EL elements 8 including the organic EL element 811 ′ positioned at the head and the organic EL element 831 ′ constitute “organic EL element group 8G′1”. The same applies hereinafter. In FIG. 10, “organic EL element group 8G′8” is shown as an example (in the description of FIG. 10, in particular, reference numeral “8G ′” is the reference numeral “8G′1” as described above). ","8G'2",.

In such a form, as described above, the organic EL elements 811 ′, 822 ′, 813 ′, 824 ′,... This is slightly different from the case of FIG. That is, the organic EL elements 8 (hereinafter referred to as “even-numbered column leading elements”) positioned at the top of the even-numbered columns of the second column, the fourth column,... Are the odd-numbered columns of the first column, the third column,. The organic EL element 8 (hereinafter referred to as “odd-column first element”) positioned at the top of the head is positioned at a deeper position as viewed from above in the figure. Further, the even-numbered column leading elements constitute the first row, and the odd-numbered column leading elements constitute the second row. In the following, the organic EL elements 8 positioned in the second and subsequent rows from the top in the odd columns constitute the third row, the fifth row,..., And are positioned in the second and subsequent rows from the top in the even columns. The organic EL elements 8 to be formed constitute the fourth row, the sixth row,.
In short, such a form can be said to be an example in a case where the organic EL elements 8 are arranged in a “staggered pattern” or a “checkered pattern”.

In the arrangement mode of FIG. 10 as well, the multiple exposure as described in the above embodiment can be similarly executed by using the organic EL element group 8G ′ as a reference unit. In FIG. 10, it is visually expressed that the organic EL elements 811 ′ and 831 ′ or the organic EL elements 824 ′ and 844 ′ are involved in multiple exposure (in particular, double exposure in this embodiment).
And even in such a form, it is obvious that the operational effects that are not essentially different from the operational effects achieved by the above-described embodiment are exhibited.

(2) In the above embodiment, the current correction values J1, J2, J3,... Are generated, whereby the gradation signal is corrected. However, the present invention is not limited to such a form.
For example, since the light emission control signal emitted from the light emission control circuit 21 can have a meaning as a signal for instructing the pulse width as described above, in some cases, the light emission control signal is corrected (that is, pulse width correction). A mode may be employed in which variation is suppressed between the organic EL element groups 8G by applying. In addition, a mode in which such pulse width correction and the current value correction in the above embodiment coexist in an appropriate relationship may be employed.

(3) In the above-described embodiment, an example in which the drive circuit 9 is formed on the element substrate 7 together with the organic EL element 8 has been described. However, the present invention is not limited to such a form.
For example, there may be a mode in which an organic EL element driver having a circuit configuration equivalent to that of the drive circuit 9 is provided on the flexible printed board 53 that connects the organic EL element 8 and the circuit board 51 (see FIG. "EL element driver" is not shown). In addition, in FIG. 5 and the like, an example in which the circuit board 51 includes the control unit CU and other various elements (11, 19, 23,...) Is disclosed. Which of the various elements in the circuit 9 is configured as a “circuit board” or configured as a part in the light emitting device 10 is basically a matter that can be freely determined.

(4) The light emitting device 10 according to the above-described embodiment is a so-called bottom emission type in which light emitted from the organic EL element 8 passes through the element substrate 7 and reaches the photosensitive drum 110. The invention is not limited to such a form. The “light emitting device” referred to in the present invention may be a top emission type or a dual emission type.

<Application example>
Next, application examples to which the light emitting device according to the present invention is applied will be described.
<Image forming apparatus>
The light emitting device according to each of the above aspects can be used as a line type optical head for writing a latent image on an image carrier in an image forming apparatus using an electrophotographic system. Examples of the image forming apparatus include a printer, a printing part of a copying machine, and a printing part of a facsimile. FIG. 11 is a longitudinal sectional view showing an example of an image forming apparatus using the light emitting device 10 as a line type optical head. This image forming apparatus is a tandem type full color image forming apparatus using a belt intermediate transfer body system.

  In this image forming apparatus, four organic EL arrays 10K, 10C, 10M, and 10Y having the same configuration are exposed to four photosensitive drums (image carriers) 110K, 110C, 110M, and 110Y having the same configuration. It is arranged at each position. The organic EL arrays 10K, 10C, 10M, and 10Y are the light-emitting devices 10 according to any one of the embodiments exemplified above.

  As shown in FIG. 11, the image forming apparatus is provided with a driving roller 121 and a driven roller 122. An endless intermediate transfer belt 120 is wound around these rollers 121 and 122, and an arrow indicates As shown, the periphery of the rollers 121 and 122 is rotated. Although not shown, tension applying means such as a tension roller that applies tension to the intermediate transfer belt 120 may be provided.

  Around the intermediate transfer belt 120, four photosensitive drums 110K, 110C, 110M, and 110Y each having a photosensitive layer on the outer peripheral surface are arranged at a predetermined interval. The subscripts K, C, M, and Y mean that they are used to form black, cyan, magenta, and yellow visible images, respectively. The same applies to other members. The photosensitive drums 110K, 110C, 110M, and 110Y are rotationally driven in synchronization with the driving of the intermediate transfer belt 120.

  Around each photosensitive drum 110 (K, C, M, Y), there is a corona charger 111 (K, C, M, Y), an organic EL array 10 (K, C, M, Y), and development. A device 114 (K, C, M, Y) is arranged. The corona charger 111 (K, C, M, Y) uniformly charges the outer peripheral surface of the corresponding photosensitive drum 110 (K, C, M, Y). The organic EL array 10 (K, C, M, Y) writes an electrostatic latent image on the charged outer peripheral surface of the photosensitive drum. Each organic EL array 10 (K, C, M, Y) is installed such that the arrangement direction of the plurality of light emitting elements P is along the bus (main scanning direction) of the photosensitive drum 110 (K, C, M, Y). Is done. The electrostatic latent image is written by irradiating the photosensitive drum with light by the plurality of light emitting elements P described above. The developing device 114 (K, C, M, Y) forms a visible image, that is, a visible image on the photosensitive drum by attaching toner as a developer to the electrostatic latent image.

  The black, cyan, magenta, and yellow developed images formed by the four-color single-color image forming station are sequentially transferred onto the intermediate transfer belt 120 to be superimposed on the intermediate transfer belt 120. As a result, a full-color image is obtained. Four primary transfer corotrons (transfer devices) 112 (K, C, M, Y) are arranged inside the intermediate transfer belt 120. The primary transfer corotron 112 (K, C, M, Y) is disposed in the vicinity of the photosensitive drum 110 (K, C, M, Y), and the photosensitive drum 110 (K, C, M, Y). The electrostatic image is electrostatically attracted from the toner image to transfer the visible image to the intermediate transfer belt 120 passing between the photosensitive drum and the primary transfer corotron.

  A sheet 102 as an object on which an image is to be finally formed is fed one by one from the sheet feeding cassette 101 by the pickup roller 103, and between the intermediate transfer belt 120 and the secondary transfer roller 126 in contact with the driving roller 121. Sent to the nip. The full-color visible image on the intermediate transfer belt 120 is secondarily transferred to one side of the sheet 102 by the secondary transfer roller 126 and fixed on the sheet 102 through the fixing roller pair 127 as a fixing unit. . Thereafter, the sheet 102 is discharged onto a paper discharge cassette formed in the upper part of the apparatus by a paper discharge roller pair 128.

  Next, another embodiment of the image forming apparatus according to the present invention will be described. FIG. 12 is a longitudinal sectional view of another image forming apparatus using the light emitting device 10 as a line type optical head. This image forming apparatus is a rotary developing type full-color image forming apparatus using a belt intermediate transfer body system. In the image forming apparatus illustrated in FIG. 12, a corona charger 168, a rotary developing unit 161, an organic EL array 167, and an intermediate transfer belt 169 are provided around the photosensitive drum 165.

  The corona charger 168 uniformly charges the outer peripheral surface of the photosensitive drum 165. The organic EL array 167 writes an electrostatic latent image on the charged outer peripheral surface of the photosensitive drum 165. The organic EL array 167 is the light emitting device 10 of each aspect exemplified above, and is installed so that the arrangement direction of the plurality of light emitting elements P is along the bus line (main scanning direction) of the photosensitive drum 165. The electrostatic latent image is written by irradiating the photosensitive drum 165 with light from these light emitting elements P.

  The developing unit 161 is a drum in which four developing units 163Y, 163C, 163M, and 163K are arranged at an angular interval of 90 °, and can rotate counterclockwise about the shaft 161a. The developing units 163Y, 163C, 163M, and 163K supply yellow, cyan, magenta, and black toners to the photosensitive drum 165, respectively, and attach the toner as a developer to the electrostatic latent image, thereby the photosensitive drum 165. A visible image, that is, a visible image is formed.

  The endless intermediate transfer belt 169 is wound around a driving roller 170a, a driven roller 170b, a primary transfer roller 166, and a tension roller, and is rotated around these rollers in a direction indicated by an arrow. The primary transfer roller 166 transfers the visible image to the intermediate transfer belt 169 that passes between the photosensitive drum and the primary transfer roller 166 by electrostatically attracting the visible image from the photosensitive drum 165.

  Specifically, in the first rotation of the photosensitive drum 165, an electrostatic latent image for a yellow (Y) image is written by the organic array 167, and a developed image of the same color is formed by the developing unit 163Y. The image is transferred to the transfer belt 169. Further, in the next rotation, an electrostatic latent image for a cyan (C) image is written by the organic array 167, a developed image of the same color is formed by the developing device 163C, and an intermediate transfer is performed so as to overlap the yellow developed image. Transferred to the belt 169. Then, during the four rotations of the photosensitive drum 165, yellow, cyan, magenta, and black visible images are sequentially superimposed on the intermediate transfer belt 169. As a result, a full-color visible image is formed on the transfer belt 169. It is formed. When images are finally formed on both sides of a sheet as an object on which an image is to be formed, the same color images of the front and back surfaces are transferred to the intermediate transfer belt 169, and then the front and back surfaces are transferred to the intermediate transfer belt 169. A full-color visible image is obtained on the intermediate transfer belt 169 by transferring the visible image of the next color.

  The image forming apparatus is provided with a sheet conveyance path 174 through which a sheet passes. The sheets are picked up one by one from the paper feed cassette 178 by the pick-up roller 179, advanced through the sheet transport path 174 by the transport roller, and between the intermediate transfer belt 169 and the secondary transfer roller 171 in contact with the drive roller 170a. Pass through the nip. The secondary transfer roller 171 transfers the developed image to one side of the sheet by electrostatically attracting a full-color developed image from the intermediate transfer belt 169 collectively. The secondary transfer roller 171 can be moved toward and away from the intermediate transfer belt 169 by a clutch (not shown). The secondary transfer roller 171 is brought into contact with the intermediate transfer belt 169 when a full-color visible image is transferred onto the sheet, and is separated from the secondary transfer roller 171 while the visible image is superimposed on the intermediate transfer belt 169.

  The sheet on which the image has been transferred as described above is conveyed to the fixing device 172 and is passed between the heating roller 172a and the pressure roller 172b of the fixing device 172, whereby the visible image on the sheet is fixed. The sheet after the fixing process is drawn into the discharge roller pair 176 and proceeds in the direction of arrow F. In the case of double-sided printing, after most of the sheet passes through the paper discharge roller pair 176, the paper discharge roller pair 176 is rotated in the reverse direction and introduced into the double-sided printing conveyance path 175 as indicated by an arrow G. The Then, the visible image is transferred to the other surface of the sheet by the secondary transfer roller 171, the fixing process is performed again by the fixing device 172, and then the sheet is discharged by the discharge roller pair 176.

  Since the image forming apparatus illustrated in FIGS. 11 and 12 uses a light emitting element as an exposure unit, the apparatus can be made smaller than when a laser scanning optical system is used. Note that the light-emitting device of the present invention can also be adopted in an electrophotographic image forming apparatus other than those exemplified above. For example, the light emitting device according to the present invention is applied to an image forming apparatus that directly transfers a visible image from a photosensitive drum to a sheet without using an intermediate transfer belt, and an image forming apparatus that forms a monochrome image. Is possible.

  Further, the application range of the light emitting device according to the present invention is not limited to the “image forming apparatus” as described above. For example, the light emitting device according to the present invention is also used as an illumination device in various electronic devices other than the electronic device such as the image forming apparatus. Examples of such electronic devices include facsimile machines, copiers, multifunction machines, and printers. For these electronic devices, a light emitting device in which a plurality of light emitting elements are arranged in a planar shape is suitably employed.

1 is a perspective view illustrating a configuration of a part of an image forming apparatus including a light emitting device according to an embodiment as an optical head. It is sectional drawing which shows the light-emitting device of FIG. 1, and its surrounding structure. It is a top view of the light-emitting device of FIG. It is explanatory drawing which shows notionally the arrangement | sequence aspect of the organic EL element on the light-emitting device of FIG. It is a circuit diagram regarding the various circuit elements which comprise the circuit board (51) of FIG. It is a flowchart which shows the flow of light emission power variation correction processing. It is explanatory drawing which shows the mode of the pixel which comprises an electrostatic latent image, and its gradation value. It is explanatory drawing which shows the relationship between the content of the drive signal for forming the electrostatic latent image of FIG. 7, and each organic EL element. It is explanatory drawing which shows a mode that the organic EL element driven according to FIG. 8 forms an electrostatic latent image on the surface of a photoreceptor drum. It is a figure of the same meaning as FIG. 3, Comprising: It is a top view of the light-emitting device used as the aspect different from the figure. 1 is a longitudinal sectional view illustrating an example of an image forming apparatus. It is a longitudinal cross-sectional view which shows another example of an image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Light-emitting device, 7 ... Element substrate, 12 ... Cover substrate, 8 ... Organic EL element, 8G ... Organic EL element group, 9 ... Drive circuit, 15 ... Converging lens array, 23H ... Power measuring device 110 ... photosensitive drum 110S ... photosensitive drum surface, CU ... control unit 51 ... circuit board 11 ... current value setting memory 19 ... tone value control circuit 1D, 2D, 3D: DA converter, 21: Light emission control circuit, 23: Power sensor, Tr1: Drive transistor, J1, J2, J3: Current correction value

Claims (8)

1st, 2nd,..., Nth light emitting elements (n is a positive integer) arranged along the first direction, and 1 arranged along the second direction crossing the first direction with each of them as the head A first, second,..., Nth light emitting element group consisting of one or more light emitting elements;
Corresponding to each light emitting element group such that each power value is constant based on variation of each power value of light emitted from each of the first, second,..., Nth light emitting element groups. Correction value setting means for setting each correction value;
Correction means for correcting a drive signal for driving the light emitting element based on the correction value;
A light emitting device comprising: A drive circuit for driving the light emitting element;
The drive circuit is
Including a common circuit portion common to a plurality of light emitting elements included in one of the light emitting element groups,
The light-emitting device according to claim 1. The drive circuit is
A current source element for supplying a driving current for the light emitting element;
The common circuit portion is
A control signal supply circuit for supplying a control signal for the current source element for adjusting the magnitude of the drive current to the current source element;
The light-emitting device according to claim 2. The drive signal is defined by a current value and a pulse width,
The correction means includes
By correcting at least one of the current value and the pulse width,
Correcting the drive signal;
The light-emitting device according to any one of claims 1 to 3. The correction means corrects the drive signal by correcting the current value.
The light-emitting device according to claim 4. Further comprising an exposure surface facing the light emitting element,
Exposure to the exposure surface by light emission of the light emitting element,
By multiple exposure by light emission over time of a plurality of light emitting elements included in one of the light emitting element groups,
Done,
The light emitting device according to claim 1, wherein the light emitting device is a light emitting device. Each of the first, second,..., Nth light emitting element groups further comprises power value measuring means for measuring each power value of light emitted from each of the light emitting element groups.
The light emitting device according to any one of claims 1 to 6. The light-emitting device according to claim 1 is provided.
An image forming apparatus.

Images