JP2010089367A - Light emitting device, image formation device, and drive method of light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress variation of each organic EL element. In addition, the service life is extended.
A plurality of organic EL elements (8) driven by a drive signal defined by a current value and a pulse width, a current measuring means (14) for measuring each current value flowing through each of the organic EL elements, and a measurement result thereof Each of the organic EL elements includes a current value setting means for setting a current correction value that makes each current value constant based on the variation of each current value caused by the first cause, which is determined based on A power sensor (23) for measuring each power value of the emitted light, and based on the variation of each power value caused by the second cause, which is determined based on the measurement result, the power value is made constant. Pulse width setting means for setting a pulse width correction value. The present invention is characterized in that the current correction value and the pulse width correction value are determined according to a first cause and a second cause that are conceptually distinguished.
[Selection] Figure 5

Description

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

  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 2007-130963 A JP 2007-125705 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.

Patent Documents 1 and 2 described above disclose techniques for dealing with such problems.
That is, Patent Document 1 uses “first gradation data” and “second gradation data” generated based on “first gradation data” as data “designating each gradation value of a light emitting element”, and In addition, a technique for changing the light emission period based on each of them is disclosed (refer to [Claim 1] and the like of Patent Document 1 in the above). According to such a technique, since “the degree of light emission is made uniform for a plurality of light emitting elements” compared to “when each light emitting element is driven based only on the first gradation data”, each light emitting element The effect that the variation in the amount of light due to the deterioration of the light over time can be suppressed ”is obtained (as described above, [0006] of Patent Document 1 or [FIG. 2] and the description thereof [0025] and the like. ,reference).
Japanese Patent Laid-Open No. 2004-228688 determines “pulse width determining means” for determining the pulse width of the drive signal of the light emitting element based on “first coefficient and gradation data”, and determines the current value of the drive signal based on “second coefficient”. 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. The technique selected under the purpose of the above is disclosed (refer to [Claim 1] etc. of Patent Document 2 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 (see Patent Document 2 [0007], or (See FIG. 2 and its description [0022] et seq.).

  Such techniques of Patent Documents 1 and 2 are extremely effective in solving the above-described problems. In addition, in Patent Document 1, on the basis of the dependency of the second gradation data on the first gradation data, that is, the substantial reduction in the number of handled data, etc., the circuit scale is prevented from being enlarged, the storage capacity is reduced, The effects different from those described above are obtained (see [0004] [0003] of Patent Document 1). Patent Document 2 also discloses a technique in which the first coefficient and the like are set for the purpose of making the light amounts (light emission energy) of the respective light emitting elements substantially coincide with each other. (Tone) Another effect of suppressing unevenness (see [0007] of Patent Document 2) (that is, the technique of Patent Document 2 not only suppresses gradation unevenness over time, but also It also achieves temporal suppression.)

However, there are still challenges.
In other words, the light-emitting device is usually hardly considered to be used alone, and is usually used as one element constituting some larger system such as the image forming apparatus. . In this case, the light emitted from the light-emitting elements constituting the light-emitting device is not often used as it is. For example, according to the example of the printer described above, an optical system composed of a lens having an appropriate shape is installed between the light emitting element and the image carrier, thereby collecting light energy, or The utilization efficiency can be improved.
However, if it does so, it is appropriate to evaluate the problem of the synchronic brightness | luminance (gradation) variation in a light emitting element, or the change with the passage of time from the viewpoint which looks at such a system as a whole. This is because there may be some variation in the optical system depending on each light emitting element. In this case, even if there is no variation in the light transmitted through the optical system, the image carrier If attention is paid to the light immediately before entering the light, the possibility of uneven brightness (gradation) will not be denied. In some cases, the state of change with time is not considered to be different from the case of viewing the light emitting device alone when viewed in the entire system.
In other words, the solution of the problem may be more effective when performed from such an overall perspective.

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

  In order to solve the above-described problems, a light-emitting device according to the present invention includes a substrate, a plurality of light-emitting elements formed on the substrate and driven by a drive signal defined by a current value and a pulse width, and the plurality of light-emitting devices. For each of the light emitting elements, a first measurement unit that measures each current value that flows when driven by a predetermined same drive signal, and each of the currents caused by the first cause that is determined based on a measurement result by the first measurement unit Current value setting means for setting each current correction value corresponding to each current value so as to make each current value constant based on variation in values, and each of the light emitted by each of the plurality of light emitting elements Based on the variation of each power value caused by the second cause, which is determined based on the second measurement means for measuring the power value and the measurement result by the second measurement means, the power values are made constant. The pulse width setting means for setting each pulse width correction value corresponding to each power value, and the current value and pulse width defining the drive signal are corrected based on the current correction value and the pulse width correction value. Correction means.

According to the present invention, the variation in the current value caused by the “first cause” is corrected by the current correction value, and the variation in the power value caused by the “second cause” distinguished from the “first cause”. Is corrected with the pulse width correction value. In this case, the “second cause” may include, for example, “variation related to the optical system” as described above, but in the present invention, such variation is corrected by the pulse width correction value. It turns out that.
Thus, in the present invention, the technical significance or mission of “pulse width correction value” or “pulse width setting means” and that of “current correction value” or “current value setting means” They are classified according to the categories of “1 cause” and “second cause”.
For this reason, according to the present invention, the occurrence of variations among a plurality of light emitting elements from the viewpoint of the entire system can be suitably suppressed.
Further, according to the present invention, the lifetime of the light emitting element can be extended as compared with the case where the luminance (gradation) of the light emitting element is corrected only by the current correction value, for example. This is because if the correction based on the increase / decrease (especially increase) of the current is performed, there is a high possibility of shortening the lifetime of the light emitting element.

In addition, the concept of “first cause” and “second cause” in the present invention is basically unlimited except that there is a meaning that a temporary distinction is established between them (note that “Temporary distinction” means, for example, that “first cause” is classified into smaller “first (1) cause, first (2) cause,..., First (n) cause”. If the “second cause” is also possible to be classified into smaller “second (1) cause, second (2) cause,..., 2 (m) cause”, A common part between the first (1) cause and the second (1) cause, for example, the first (1) cause = the second (1) cause, etc. Even if there is, there is a difference in at least one of the causes (for example, first (2) cause ≠ second (2) cause) Including the case cormorant (since, but still "distinction" This is because it is possible.).).
However, in the present invention, the variation in the current value is caused by “first cause” and the variation in the power value is caused by “second cause”. There is no denying that it has significant significance. Specific examples that reflect such significance will be described immediately later (for example, “variation in characteristics of drive transistors” described later is a specific example of “first cause”, and “variation in optical transmission efficiency of the optical system”). "Is a specific example of" second cause ".)
As described above, the “first cause” and the “second cause” are basically unlimited concepts, but are not contentless.

  In addition, the specific structure and material of the “light-emitting element” in the present invention can be basically freely determined. 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 drive transistors that supply all or part of the drive signal to each of the plurality of light-emitting elements, and the first cause is each of the plurality of light-emitting elements. You may comprise so that the variation in the characteristic of a drive transistor may be included.
According to this aspect, the variation in the characteristics of the drive transistor is corrected by the current correction value. The variation mentioned here implies that various characteristic values such as the threshold voltage Vth or mobility of the driving transistor vary. Such variation greatly affects the increase / decrease in the amount of current supplied to the light emitting element, and therefore it is preferable to deal with the current correction value.

The light-emitting device of the present invention further includes an optical system arranged to face each of the plurality of light-emitting elements, and the second measuring unit transmits the light emitted from the light-emitting element through the optical system. In this case, the second cause may include a variation in light transmission efficiency of the optical system for each of the plurality of light emitting elements.
According to this aspect, for example, variation in light transmission efficiency of an optical system including one or more lenses having an appropriate shape is corrected by the pulse width correction value. Therefore, according to this aspect, first, the effect of suppressing the variation between the light emitting elements from the viewpoint of the entire system described above is more effectively achieved.
Further, the variation referred to in the present embodiment is not absolutely impossible to correct with the “current correction value” referred to in the present invention (rather, it can be said that it is an ordinary method from a conventional viewpoint). In the present embodiment, this is dealt with by a pulse width correction value. As a result, the opportunity for current correction does not increase unnecessarily, and the effect of prolonging the lifetime of the light-emitting element can be achieved more effectively.

The light-emitting device of the present invention further includes a translucent semi-reflective layer and a reflective layer formed on the substrate so as to sandwich the light-emitting element when viewed along the normal direction of the surface of the substrate. The translucent semi-reflective layer and the reflective layer constitute a resonator structure that increases the intensity of light emitted from the light emitting element, and the second cause is the resonator structure for each of the plurality of light emitting elements. You may comprise so that the variation of the distance between the said semi-transparent semi-reflective layer and reflective layer may be included.
According to this aspect, first, since the resonator structure is configured, the light emitted from the light emitting element can be repeatedly reflected, thereby having a specific wavelength component in the finally extracted light. The intensity of light can be increased.
Further, according to this aspect, the variation related to the resonator structure is corrected by the pulse width correction value. For example, as described above, the variation includes a variation in the distance between the translucent semi-reflective film and the semi-reflective layer constituting the resonator structure as described above, or any substance sandwiched between these layers (in the embodiments described later, “ The light-emitting functional layer 18 ”corresponds to a variation in the refractive index.
Therefore, this aspect also has the effect of suppressing variation between light emitting elements from the viewpoint of the entire system described above. In other words, it can be said that this aspect has a significance that the effect obtained by the above-described resonator structure can be more effectively realized by accompanying such pulse width correction.

Further, in the light emitting device of the present invention, the pulse width setting means once sets the pulse width correction value, and then newly adds the pulse width correction value based on the measurement result of each power value again by the second measurement means. The pulse width correction value may be set.
According to this aspect, for example, a case where a cause that changes over time is included in the “second cause” can be suitably dealt with. That is, in such a case, even if the variation can be initially suppressed within a certain range by the correction based on the pulse width correction, a variation exceeding the range may occur later. Then, “each power value” is measured “again” and a “new pulse width correction value” is set, and correction based on it can be performed. Therefore, the variation is confined to the range again. It is possible.
Note that “again” and “newly” in this aspect mean that the power value is measured or the pulse width correction value is set at least twice. That is, these measurements and settings may be performed any number of times as long as the light emitting device of the present invention is used.

In the light emitting device of the present invention, each of the plurality of light emitting elements is arranged along a predetermined straight line, and the second measuring means travels along the extending direction of the predetermined straight line. It may be configured to include possible optical sensors.
According to this aspect, the power can be measured by scanning the light sensor on the light emitting element. At the same time, after the measurement, the light sensor is removed from the region where the light emitting elements are arranged. Can be suitably positioned in the area. According to the latter, in particular, the optical sensor does not interfere with the progress of light emitted from the light emitting element. In addition, if the light emission timing of each light emitting element is adjusted in synchronization with the above-described scanning, the power related to each light emitting element can be preferably measured.

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 has variations in luminance (gradation) of the light emitting elements by the current value correction and the pulse width correction corresponding to the above-described various light emitting devices, that is, “first cause” and “second cause”. Therefore, for example, there is almost no risk of so-called streaks on the image-formed print medium output by the image forming apparatus.
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.

  On the other hand, a driving method of a light emitting device according to the present invention is a driving method of a light emitting device including a plurality of light emitting elements driven by a driving signal defined by a current value and a pulse width in order to solve the above-described problem. For each of the plurality of light emitting elements, a first measurement step of measuring each current value that flows when driven by a predetermined same drive signal, and a first cause that is determined based on a measurement result of the first measurement step, A current value setting step of setting each current correction value corresponding to each current value so as to make each current value constant based on the resulting variation in each current value; and each of the plurality of light emitting elements A second measurement step of measuring each power value of the light emitted by the light source, and a variation of each of the power values caused by the second cause, which is determined based on a measurement result of the second measurement step. A pulse width setting step for setting each pulse width correction value corresponding to each power value so that the value is constant, and the drive signal is defined based on the current correction value and the pulse width correction value A correction step of correcting the current value and the pulse width.

  According to the present invention, it is apparent that the operational effects that are not essentially different from the operational effects exhibited by the above-described light emitting device according to the present invention are exhibited.

In the driving method of the light emitting device according to the present invention, the second measuring step includes a step of measuring a power value of light transmitted through an optical system facing the light emitting element among light emitted from the light emitting element, The second cause may include a variation in light transmission efficiency of the optical system for each of the plurality of light emitting elements.
According to this aspect, among the various aspects of the light-emitting device according to the present invention described above, it is apparent that the operational effects that are not essentially different from the operational effects exhibited by the aspects including the “optical system” are achieved. .

In the light emitting device driving method according to the present invention, the second measurement step and the pulse width setting step may be repeatedly performed with a predetermined period in between.
According to this aspect, among the various aspects of the above-described light emitting device according to the present invention, the “effect and effect obtained by the aspect that the“ pulse width setting means ”sets“ new pulse width correction value ”are essentially obtained. It is clear that there is an effect not different from the above.
Note that “repetition” in this aspect means that measurement of a power value or setting of a pulse width correction value is performed at least twice. That is, these measurements and settings may be performed any number of times as long as the light emitting device of the present invention is used.
In addition, the “predetermined period” includes, for example, the case where the power value measurement of the first time, the second time,... Is performed, and the period between them is constant, and the time period varies. Or when the image is drawn at a certain point in time desired by the user.

  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, a power measuring device 23H, 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.

A converging lens array (corresponding to an example of the “optical system” in the present invention) 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.

When such a converging lens array 15 is used, in addition to the above-described formation of an erecting equal-magnification image, it is possible to improve the utilization efficiency of light and the like. Image formation is preferably performed. However, since the converging lens array 15 is an optical element that transmits light emitted from the light emitting device 10, it is inevitable that the light is attenuated to a certain extent. Further, in this case, for example, due to the presence of positioning errors of each lens in the converging lens array 15 (for example, errors relating to the relative positional relationship between each lens and each organic EL element) and the like, The light transmission efficiency may be different for each.
According to the above, there is a possibility that the light emission intensity varies on the photosensitive drum 110. In the present embodiment, such a problem is preferably solved, but a description of this point will be given later.

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 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 may be disposed so as to be positioned between the converging lens array 15 and the photosensitive drum 110. The measurement unit 231 has a power sensor (optical sensor) having a measurement surface (the latter is preferably larger than the former) having an appropriate size as compared with the size of one of the organic EL elements. ) 23 is provided. The power sensor 23 is composed of, for example, one or more photodiodes.
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.
The control unit CU obtains a pulse width correction value and a current correction value through measurement of a power value using the power measurement device 23H, measurement of a current value supplied to the organic EL element, and the like, and Pulse width correction and current correction based on these correction values are performed. 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 120. 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. The number of the organic EL elements 8 shown in each drawing such as FIG. 3 is determined by convenience such as ease of viewing the drawing and the size of the paper.

Among them, the drive circuit 9 is composed of switching transistors Tr12, Tr22, Tr32 (hereinafter sometimes referred to collectively as “switching transistor Tr X2”) shown in FIG. concern.
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 the present embodiment, the organic EL elements 8 are arranged along a straight line extending in the longitudinal direction of the element substrate 7 as shown in FIG. Here, the “straight line” happens to be compared with the common line 16 in FIG.

Such an organic EL element 8 constitutes a part of a laminated structure 250 formed on an element substrate 7 as shown in FIG. 4, for example.
In FIG. 4, the laminated structure 250 includes, in order from the element substrate 7, the semiconductor layer 1, the gate insulating film 300, the gate metal 3, the first interlayer insulating film 301, the signal line 6 and the relay line 61, and the second interlayer insulation. The film 302, the pixel electrode 13, the third interlayer insulating film 303, the light emitting functional layer 18, and the counter electrode 5 are included.
The above-described switching transistor (hereinafter sometimes abbreviated as “SW transistor”) Tr X2 includes the semiconductor layer 1, the gate insulating film 300, and the gate metal 3 among them. A signal line 6 is connected to the source region in the semiconductor layer 1 through a contact hole 361, and a relay line 61 is connected to the drain region through a contact hole 362. Note that the contact holes 361 and 362 are both formed so as to penetrate the first interlayer insulating film 301.
The organic EL element 8 includes a pixel electrode 13, a light emitting functional layer 18, and a counter electrode 5. Among these, the pixel electrode 13 and the counter electrode 5 correspond to the “two electrodes” described above. In the present embodiment, the pixel electrode 13 has a translucent and semi-reflective function, and the counter electrode 5 has a reflective function (the difference between the two is only a degree difference, but the former transmits more light, There is a difference that the latter transmits far less light than that). Such a difference in function can be realized by providing a difference in material between the pixel electrode 13 and the counter electrode 5 or providing a difference in thickness.
The pixel electrode 13 is connected to the above-described relay line 61 through the contact hole 363. Thereby, the pixel electrode 13 is electrically connected to the SW transistor Tr X2. The contact hole 363 is formed so as to penetrate the second interlayer insulating film 302. The counter electrode 5 is connected to the common line 16 (not shown in FIG. 4).
Further, the light emitting functional layer 18 includes an organic light emitting layer, and the organic light emitting layer is further made of an organic EL material that emits light by combining holes supplied from the pixel electrode 13 and electrons supplied from the counter electrode 5. It is configured. In addition to the organic light emitting layer, the light emitting functional layer 18 includes a part or all of an electron blocking layer, a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, and a hole blocking layer. Also good.

  Such an organic EL element 8 emits light L1 or light L2. As shown in FIG. 4, the light L <b> 1 is emitted from the light emitting functional layer 18 downward in the figure and directly proceeds downward while passing through the laminated structure 250 and the element substrate 7. Light. In addition, the light L2 that travels upward in the figure from the light emitting functional layer 18 is reflected by the counter electrode 5, and then travels downward in the figure while passing through the laminated structure 250 and the element substrate 7. (See also FIG. 1 for the above). Furthermore, among the light emitted from the light emitting functional layer 18, there is also light extracted outside after being repeatedly reflected a plurality of times between the pixel electrode 13 and the counter electrode 5, as shown as light L3 in the figure. The third interlayer insulating film 303 has a function of regulating the light emitting region of the organic EL element 8 by covering a part of the pixel electrode 13.

In the above case, if the optical distance between the pixel electrode 13 and the counter electrode 5 is appropriately set, the intensity of light having a specific wavelength component can be increased. That is, in this case, the pixel electrode 13 as a translucent semi-reflective layer and the counter electrode 5 as a reflective layer constitute a kind of resonator, and reflection like light L3 is repeated, or The intensity of light having a specific wavelength component that is finally extracted can be increased by the occurrence of amplifying interference between the lights L1 and L2. The “optical distance” is obtained as (refractive index) × (physical distance) (in the case of FIG. 4, only the light emitting functional layer 18 exists between the pixel electrode 13 and the counter electrode 5. This is relatively simple as the product of the refractive index and its physical thickness.)
The optical distances as just described should be set equal to each other as long as each of the organic EL elements 8 emits light of the same color. Due to the influence, each of the organic EL elements 8 may be different. Then, the degree of light amplification differs for each organic EL element 8, and as a result, there is a possibility that the emission intensity varies on the photosensitive drum 110. In the present embodiment, such a problem is preferably solved, but a description of this point will be given 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 current value setting memory 11, a data switching circuit 12, a DA converter (Digital Analog Converter) 13, a current measuring means 14, a pulse width setting memory 21, a pulse width. A correction circuit 22 and a power sensor 23 are provided. 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 organic EL elements 81, 82, 83,... Shown in FIG. 5 are equivalent to the organic EL element 8 described above (hereinafter referred to as “81, 82, 83,. When collectively called, the symbol “8” may be used as a representative).
5 is an example of the circuit configuration of the drive circuit 9 described above (hereinafter, reference numerals “91, 92, 93,...” Are all or a part of them). When collectively referred to, it may be represented by the symbol “9”.) These drive circuits 91, 92, 93,... Have the same configuration regardless of the organic EL elements 81, 82, 83,.

Therefore, the drive circuit 91 will be described with reference to the drive circuit 91 shown on the leftmost side in the drawing. The drive circuit 91 includes three transistors, that is, the drive transistor Tr11, the SW transistor Tr12, the write transistor Tr13, and one A capacitor C1 is provided.
Among these, the source of the driving transistor Tr11 is connected to the power supply line Vel via the current measuring means 14, and the drain thereof is connected to the source of the SW transistor Tr12. Further, one electrode of the capacitor C1 is connected to the gate of the drive transistor Tr11, and the source of the drive transistor Tr11 is connected to the other electrode of the capacitor C1. The gate is also connected to the drain of the writing transistor Tr13. The drive transistor Tr11 is assumed to be used in the saturation region.
On the other hand, the drain of the SW transistor Tr12 is connected to the pixel electrode 13 of the organic EL element 81 (see FIG. 4). The gate of the SW transistor Tr12 is connected to the pulse width correction circuit 22. On the other hand, the write transistor Tr13 has a gate connected to the control unit CU and a source connected to the DA converter 13. It is assumed that the SW transistor Tr12 and the writing transistor Tr13 are used in a linear region.

With the above configuration, first, when the write command signal Wrt1 is sent from the control unit CU to the gate of the write transistor Tr13, the write transistor Tr13 is turned on, and the DA converter 13 is turned on. The electric charge is stored in the capacitor C1 according to the level of the gradation signal sent from, and the voltage corresponding to the level is applied to the gate of the drive transistor Tr11. Thus, the drive transistor Tr11 functions as a current source that supplies a current corresponding to the level.
Secondly, under this situation, when the pulse width command signal PLS1 is sent from the pulse width correction circuit 22 to the gate of the SW transistor Tr12, the SW transistor Tr12 is turned on, whereby the organic EL element 81 is turned on. Is supplied with a predetermined current from the drive transistor Tr11 functioning as a current source. In this case, the pulse width command signal PLS1 also has a meaning of designating a period during which the SW transistor Tr12 is maintained in an ON state. Therefore, a period during which the current is to be supplied to the organic EL element 81 (that is, the length of the pulse width) ).
The “drive signal” referred to in the present invention is a concept including the pulse width command 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 92, 93,... Have the same configuration as that related to the drive circuit 91, and the same light emission control is performed on them.

Next, various other elements constituting the circuit board 51 described above will be described.
The current measuring means 14 measures the magnitude of the current flowing through each of the organic EL elements 81, 82, 83,... Shown in FIG. In this case, the current measuring means 14 can grasp which organic EL element 8 corresponds to the measured current value. That is, if there are measured current values I1, I2, I3,..., The current measuring means 14 grasps that each corresponds to the organic EL elements 81, 82, 83,.
The current values I1, I2, I3,... Measured here may vary depending on the threshold voltage Vth of the drive transistors Tr11, Tr21, Tr31,. .

The current value setting memory 11 stores a current value measurement result flowing through each organic EL element 8 by the current measuring unit 14 and a current correction value determined according to an instruction from the control unit CU corresponding thereto. Corresponding to the fact that the current measuring means 14 measures the specific current values I1, I2, I3,... For each of the organic EL elements 8 as described above, this current value setting memory 11 also has 1 Current correction values J1, J2, J3,... For each organic EL element 8 are stored (the symbols “J1, J2, J3,...” Are not shown in FIG. 5).
The purpose of the current correction values J1, J2, J3,... Is the same as that of each organic EL element 8 when the current corrected by the current correction values J1, J2, J3,. The purpose is to allow current to flow. In other words, if the current values after correction are assumed to be JI1, JI2, JI3, etc., even if I1 ≠ I2 ≠ I3 ≠ ..., the correction aims at JI1 = JI2 = JI3 =. It is.

In addition, based on the measured current values I1, I2, I3,..., 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 preferred example, a method of preparing a predetermined table or correspondence table that defines the relationship between the measured current 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.
The same can be said for the pulse width setting memory 21 described later.

  When the data switching circuit 12 receives the input of the gradation signals On1, On2, On3,... Sent from the control unit CU for a specific organic EL element 8, the data switching circuit 12 Referring to the current correction values J1, J2, J3,..., The gradation signals On1, On2, On3,... Are corrected with the current correction values J1, J2, J3,. The gradation signals JOn1, JOn2, JOn3,... Are supplied to the DA converter 13 in the subsequent stage (note that the symbols “JOn1, JOn2, JOn3,...” Are not shown in FIG. 5). In short, the data switching circuit 12 converts the gradation signal into the organic signal while switching the organic EL element 8 to be supplied with the gradation signal (that is, switching between On1, On2, On3,...). It supplies toward the EL element 8 or toward the drive circuit 9 corresponding to the organic EL element 8.

The DA converter 13 receives the gradation signal JOn (p) (p is an upper limit value corresponding to the number of organic EL elements 8), which is a digital signal corresponding to a certain organic EL element 8 sent from the data switching circuit 12. Is converted to a gradation signal KK (p) which is an analog signal, which is supplied to the writing transistors Tr13, Tr23, Tr33 in the drive circuit 9.
In the present embodiment, since the data switching circuit 12 exists as described above, only one DA converter 13 is sufficient, and the circuit configuration is further simplified. it can.

On the other hand, the power sensor 23 measures the power value when each of the organic EL elements 81, 82, 83,... Shown in FIG. In this case, the power sensor 23 can grasp the correspondence between the measured power value and each organic EL element 8 as in the current measuring means 14.
The pulse width setting memory 21 stores the measurement result of the light emission power value of each organic EL element 8 by the power sensor 23 and the pulse width correction value determined according to the instruction of the control unit CU accordingly. In this case, the pulse width measurement memory 21 stores the pulse width correction values W1, W2, W3,... For each organic EL element 8 in the same manner as the current value setting memory 11 (note that Symbols “W1, W2, W3,...” Are not shown in FIG.
The purpose of the pulse width correction values W1, W2, W3,... Is when each of the organic EL elements 8 is supplied with a current corrected by the pulse width correction values W1, W2, W3,. Is to emit light with substantially the same power value.
The pulse width correction circuit 22 supplies pulse width command signals PL1, PL2, PL3,... Corresponding to each organic EL element 8 to the organic EL elements 8 based on the pulse width correction values W1, W2, W3,. Toward the gate of the SW transistor Tr12 in the drive circuit 9 corresponding thereto. As described above, the pulse width command signals PL1, PL2, PL3,... Define a period during which the SW transistor Tr12 should be in an ON state or a period during which a current should be supplied to the organic EL element 8.

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 current variation measurement (step S102 in FIG. 6). That is, the control unit CU sequentially supplies the current to each organic EL element 8 by sequentially controlling each drive circuit 9 corresponding to each organic EL element 8, and at the same time, the current measuring unit 14 A current value related to the target organic EL element 8 is measured. Thereby, the current measuring means 14 (or the control unit CU) grasps which organic EL element 8 a certain current measurement value corresponds to.
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).
If this is the same as the current correction values J1, J2, J3,... In step S101, the same current should theoretically flow through each organic EL element 8. However, the current values I1, I2, I3,... That actually flow through each organic EL element 8 are the threshold voltages Vth of the drive transistors Tr11, Tr21, Tr31,. Depending on the variation, it can vary (rather it is natural). “Current variation measurement” in the present process implies such a background.

  Next, the control unit CU determines whether or not the measured current values I1, I2, I3,... Vary within a predetermined range (step S103 in FIG. 6). That is, given a predetermined lower limit value IL and upper limit value IU, IL <I1 <IU, IL <I2 <IU, IL <I3 <IU,... For each of the measured current values I1, I2, I3,. Judgment of authenticity. When this determination is denied, for example, when I1 ≦ IL or IU ≦ I1 is satisfied with respect to I1, a current correction value setting process for the I1 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 I1. For example, qualitatively, if I1 is larger, a negative current correction value J1 is determined to decrease it, and if I1 is smaller, a positive current correction value J1 is determined to increase it. It seems that.

  The above current value measurement processing and current correction value setting processing are performed for all organic EL elements 8 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 elements 8 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 8 is concerned. For (p), the initial value set in step S101 is used as it is as the current correction value J (p).

Through such processing, all the organic EL elements 8 have substantially the same value that does not exceed a certain range as long as the organic EL elements 8 are subsequently driven under the same drive signal. Current will be supplied.
This is visually represented in FIG. That is, FIG. 8 shows an example in which different current values I1, I2, and I3 (I2 <I1 <I3) are measured for the organic EL elements 81, 82, and 83 at the time of the current measurement process. ing. Such variations are caused by differences in the characteristics of the drive circuits 91, 92, 93 associated with the organic EL elements 81, 82, 83, for example, variations in the characteristics of the drive transistors Tr11, 21, 31 described above.
The current correction values J1, J2, and J3 are determined based on the measured current values I1, I2, and I3 (see the middle stage of FIG. 8). The current correction values J1, J2, and J3 are determined based on the organic EL elements 81, It acts on the drive signal for driving 82 and 83. Here, if it is considered that the same drive signal is supplied to all of these organic EL elements 81, 82, 83, all the organic EL elements 81, 82, 83 have the current correction values J1, J2, J3. Due to the action, a current having the same value JI1 = JI2 = JI3 flows (see the lower part of FIG. 8).

  Subsequently to the above, the control unit CU performs initial setting related to the pulse width correction value (step S201 in FIG. 7). This initial setting includes processing for equalizing the pulse width correction values W1, W2, W3,... Stored in the pulse width setting memory 21. That is, W1 = W2 = W3 =.

Next, the control unit CU performs power variation measurement (step S202 in FIG. 7). 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. For example, when the power sensor 23 reaches a certain organic EL element 8, the organic EL element 8 emits light. When the power sensor 23 reaches the next organic EL element 8, the organic EL element 8 emits light and simultaneously the previous organic EL element 8 emits light. It seems that the EL element 8 is turned off. In this way, the power sensor 23 (or the control unit CU) grasps the correspondence between the measured power value and each organic EL element 8.
In this case, it is important that all the organic EL elements 8 are driven under the same drive signal (especially under the same pulse width condition).
If this is the same as the pulse width correction values W1, W2, W3,... In step S201, the power values observed for each organic EL element 8 should theoretically be the same. It is. However, the power value actually observed for each organic EL element 8 is the difference in light transmission efficiency between the organic EL elements 8 due to the positioning error of each lens in the converging lens array 15 as described above. Alternatively, it varies depending on variations such as a difference in distance between both electrodes (13, 5) related to each organic EL element 8 related to the resonator structure (see FIG. 4) constituted by the pixel electrode 13 and the counter electrode 5. There is a possibility (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 S203 in FIG. 7). 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. If this determination is negative, for example, regarding P1, if P1 ≦ PL or PU ≦ P1 is established, a pulse width correction value setting process for P1 is performed (from step S203 in FIG. 7; NO). Step S205). That is, the pulse width correction value W1 is newly determined to correspond to this P1. For example, qualitatively, if P1 is larger, a smaller pulse width correction value W1 is determined to decrease it, and if P1 is smaller, a larger pulse width correction value W1 is determined to increase it. It seems to be.

  The power value measurement process and the pulse width correction value setting process described above are performed for all the organic EL elements 8 included in the light emitting device 10 (step S204 in FIG. 7). As a result, pulse width correction values W1, W2, W3,... For these all organic EL elements 8 are determined and stored in the pulse width setting memory 21. If an affirmative determination is made in step S203 of FIG. 7 (step S203 of FIG. 7; YES), the pulse width correction value setting process of step S205 is not performed, but in this case, the organic EL element concerned For 8 (p), the initial value set in step S201 is used as it is as the pulse width correction value W (p).

Through this process, all the organic EL elements 8 have almost the same power value that does not exceed a certain range as long as the organic EL elements 8 are driven under the same drive signal thereafter. It will emit light.
This is visually represented in FIG. That is, FIG. 9 shows an example in which different power values P1, P2, P3 (P2 <P1 <P3) are measured for the organic EL elements 81, 82, 83 at the time of the power value measurement process. Has been. Such variations are caused by variations such as differences in the converging lens 15 or the resonator structure as described above. In FIG. 9, the power value is expressed by the product of the light emission intensities H1, H2, and H3 and the light emission time (that is, pulse width) T0.
The pulse width correction values W1, W2, and W3 are determined based on the measured power values P1, P2, and P3 (see the middle part of FIG. 9). Acts on a drive signal for driving the EL elements 81, 82, 83, and generates pulse width command signals PLS1, PLS2, PLS3,. Here, if it is assumed that the same drive signal as in the previous power measurement process is supplied to each of the organic EL elements 81, 82, and 83, all the organic EL elements 81, 82, and 83 have the pulse width correction value. By the action of W1, W2, and W3, light is emitted with the same power value PE (see the lower part of FIG. 9). In FIG. 9, by chance, the organic EL element 81 is set to have a pulse width T1 (> T0) larger than the previous pulse width T0 for the organic EL element 81 based on the power value P3 for the organic EL element 83. For the element 82, an example is shown in which the power values for all the organic EL elements 81, 82, 83 are aligned by setting a pulse width T2 (> T1) that is larger than that.

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, variations in the current values I1, I2, I3,... Due to variations in the characteristics of the drive transistors Tr11, Tr21, Tr31,. It is corrected with J1, J2, J3,. Further, according to the light emitting device 10, the power values P 1, P 2, P 3,... Caused by the variations in the organic EL elements 8 of the converging lens array 15 or the resonator structure described with reference to FIG. The variation is corrected by the pulse width correction values W1, W2, W3,.
As described above, in the present embodiment, the technical significance or mission of the current correction and the pulse width correction are varied according to each cause of various variations. That is, the former mainly plays a role of suppressing variations based on internal factors such as variations in characteristics or performance of each drive circuit 9 associated with each organic EL element 8, and the latter mainly plays a role in each organic EL element 8. After light is emitted from the EL element 8, it can be called a variation based on external factors such as a variation that the light is caused to reach on the photosensitive drum 110 (or a variation related to light extraction efficiency). )).
For this reason, according to the present embodiment, the occurrence of variations among the plurality of organic EL elements 8 from the viewpoint of the entire system can be suitably suppressed.

(2) Further, according to the light emitting device 10 according to the present embodiment, for example, as apparent from the comparison with the case where the luminance (gradation) of the organic EL element 8 is corrected only by the current correction value, The lifetime of the EL element 8 can also be extended. This is because if the correction based on increase / decrease (especially increase) in the current is performed, there is a high possibility that the lifetime of the organic EL element 8 is shortened (in general, a larger current value is applied to the organic EL element 8). When a driving signal having a constant pulse width is supplied and a driving signal having a larger pulse width (a constant current value) is compared, the former is more organic than the latter. 8 is fast.) In the present embodiment, the pulse width correction is performed in combination with the current value correction. In other words, the scene or situation where the current value correction is performed is limited. The risk of accelerating the deterioration rate is greatly reduced.

In addition, regarding these points, whether the driving mode of the organic EL element 8 is controlled by the current value or the pulse width depends on the result, which is finally a unified index such as the emission intensity. (Or, in the end, the organic EL element 8 is not subject to the current value correction and the pulse width correction in a superimposed manner). Otherwise there is no possibility of misunderstanding.
However, as in the present embodiment, the scenes in which the current value correction and the pulse width correction are performed are distinguished according to each cause distinguished by a certain standard (for example, “internal factor” and “external factor” described above). This technical idea must be recognized as having a technical significance that is significantly different from the prior art.

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, no particular mention is made as to how many times the current value correction or the pulse width correction value is performed, but the present invention is not particularly limited in this respect.
However, regarding pulse width correction, if this is performed twice or more, it can be said that a more favorable result is obtained. This is because, according to the example of the above-described embodiment, the purpose of performing the pulse width correction is that the power value of each organic EL element 8 is due to variations based on “external factors” or “variations related to light extraction efficiency”. However, the variation based on such “external factors” may include causes that change over time as the usage time of the light emitting device 10 increases. Because. In this case, if the pulse width correction is performed twice or more, it is possible to confine the power value variation generated after a certain period of time again within a certain range.
The same thing may be applied to the current value correction to some extent. Therefore, in such a case, it may be assumed that the current value correction is performed twice or more.
After all, in the present invention, the current value correction or the pulse width correction can be basically performed any number of times.

(2) In the above-described embodiment, variations in the characteristics of the drive transistors Tr11, Tr21, and Tr31 are given as specific examples of the “first cause” in the present invention. Convergence is given as a specific example of the “second cause”. Although variations relating to the lens array 15 or the resonator structure of FIG. 4 are mentioned, the present invention is not limited to such examples.
For example, in order to drive the organic EL element 8, various circuit configurations other than the circuit configuration shown in FIG. 5 are conceivable, but even in this case, the characteristics of various circuit elements in the circuit configuration are considered. Naturally, this variation can occur. The “first cause” in the present invention basically includes all such cases.
Further, the structure for causing the light emitting device 10 to face the photosensitive drum 110 may be a structure other than the structure shown in FIG. 2, or the structure shown in FIG. However, the manner in which the light-emitting device 10 is attached to the second frame F2 causes variations between the organic EL elements 8 (for example, some organic EL elements 8 are closer to the photosensitive drum 11 and other organic EL elements 8 are more There is a possibility that it may be positioned far away). The “second cause” in the present invention basically includes all such cases.

(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, the circuit board 51 is provided with a control unit CU, various elements (11 to 14) for current correction, and various elements (21 to 22) for pulse width correction. However, which of these various elements, further various elements in the drive circuit 9 is configured as a “circuit board”, or is configured as a part in the light emitting device 10, etc. Basically, it 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.
Further, in the above embodiment, the organic EL elements 8 are arranged so as to be aligned in a straight line along a predetermined straight line. However, the present invention is not limited to this. For example, the organic EL elements 8 are “staggered”. May be arranged in a line.

<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. 10 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. 10, this 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. 11 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 shown in FIG. 11, 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. 10 and 11 uses the light emitting element as the exposure unit, the apparatus can be made smaller than when the 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 sectional drawing regarding one 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 a drive current variation correction process. It is a flowchart which shows the flow of light emission power variation correction processing. It is explanatory drawing which expressed the flow of the drive current variation correction process notionally and visually. It is explanatory drawing which expressed the flow of the light emission power variation correction process notionally and visually. 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, 120 ... Cover substrate, 8, 81, 82, 83 ... Organic EL element, 13 ... Pixel electrode, 18 ... Light emitting functional layer, 5 ... Counter electrode, 9, 91, 92, 93 ... drive circuit, 15 ... focusing lens array, 23H ... power measuring device, 110 ... photoconductor drum, CU ... control unit, 51 ... circuit board, 11 ... current Value setting memory, 12 ... Data switching circuit, 13 ... DA converter, 14 ... Current measuring means, 21 ... Pulse width setting memory, 22 ... Pulse width correction circuit, 23 ... Power sensor, Tr11, Tr21, Tr31 ... Drive transistor, J1, J2, J3 ... Current correction value, PLS1, PLS2, PLS3 ... Pulse width command signal

Claims (10)

A substrate,
A plurality of light emitting elements formed on the substrate and driven by a drive signal defined by a current value and a pulse width;
For each of the plurality of light emitting elements, first measurement means for measuring each current value that flows when driven by a predetermined same drive signal;
Each current correction corresponding to each current value such that each current value is made constant based on the variation of each current value caused by the first cause, which is found based on the measurement result by the first measuring means. Current value setting means for setting a value;
Second measuring means for measuring each power value of light emitted from each of the plurality of light emitting elements;
Each pulse width corresponding to each power value such that each power value is constant based on the variation of each power value caused by the second cause, which is determined based on the measurement result by the second measuring means. A pulse width setting means for setting a correction value;
Correction means for correcting the current value and the pulse width defining the drive signal based on the current correction value and the pulse width correction value;
A light emitting device comprising: Each drive transistor for supplying all or part of the drive signal to each of the plurality of light emitting elements,
The first cause is
Including variations in characteristics of the drive transistors for each of the plurality of light emitting elements,
The light-emitting device according to claim 1. An optical system disposed to face each of the plurality of light emitting elements;
The second measuring means measures a power value of light transmitted through the optical system among light emitted from the light emitting element,
The second cause is
Including variations in light transmission efficiency of the optical system for each of the plurality of light emitting elements,
The light-emitting device according to claim 1 or 2. A translucent semi-reflective layer and a reflective layer formed on the substrate so as to sandwich the light emitting element as seen along the normal direction of the surface of the substrate,
These semi-transparent semi-reflective layer and reflective layer constitute a resonator structure that increases the intensity of light emitted from the light-emitting element,
The second cause is
Including variation in the distance between the translucent semi-reflective layer and the reflective layer constituting the resonator structure for each of the plurality of light-emitting elements,
The light-emitting device according to any one of claims 1 to 3. The pulse width setting means includes
After setting the pulse width correction value once,
Based on the result of re-measurement of each power value by the second measuring means,
A new pulse width correction value is set.
The light emitting device according to claim 1, wherein the light emitting device is a light emitting device. Each of the plurality of light emitting elements is arranged along a predetermined straight line,
The second measuring means includes
An optical sensor capable of traveling along the extending direction of the predetermined straight line;
The light emitting device according to claim 1, wherein the light emitting device is a light emitting device. The light-emitting device according to claim 1 is provided.
An image forming apparatus. A driving method of a light emitting device including a plurality of light emitting elements driven by a driving signal defined by a current value and a pulse width,
A first measurement step of measuring each current value flowing when each of the plurality of light emitting elements is driven by a predetermined same drive signal;
Each current correction corresponding to each current value such that each current value is constant based on the variation of each current value caused by the first cause, which is determined based on the measurement result of the first measurement step. A current value setting process for setting a value;
A second measurement step of measuring each power value of light emitted from each of the plurality of light emitting elements;
Each pulse width corresponding to each power value such that each power value is constant based on the variation of each power value caused by the second cause, which is determined based on the measurement result of the second measurement step. A pulse width setting step for setting a correction value;
Based on the current correction value and the pulse width correction value, a correction step for correcting the current value and pulse width defining the drive signal;
A method for driving a light emitting device, comprising: The second measuring step includes a step of measuring a power value of light transmitted through an optical system facing the light emitting element among light emitted from the light emitting element,
The second cause is
Including variations in light transmission efficiency of the optical system for each of the plurality of light emitting elements,
The method for driving a light emitting device according to claim 8. The second measurement step and the pulse width setting step are repeatedly performed with a predetermined period in between.
The method for driving a light emitting device according to claim 8 or 9, wherein:

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