JP6277855B2 - Optical writing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical writing device and an image forming apparatus.

Some image forming apparatuses such as printers use an optical writing device in which minute light emitting elements are arranged in a line and an image is written on a photosensitive member by a light beam emitted from each light emitting element.
Patent Document 1 discloses a line head in which a large number of organic light emitting diodes (OLEDs) as light emitting elements are arranged on a substrate along the main scanning direction as an optical writing device.

  The line head has a configuration in which a parallel circuit in which each of the plurality of first light emitting elements for writing is connected to the power supply line on the anode side and connected to the ground line on the cathode side is arranged on the substrate. . Each first light-emitting element is connected in parallel with another second light-emitting element (having the same characteristics as the first light-emitting element) that is not used for writing. A pair of light emitting elements forms a single light emitting unit.

  For each light emitting unit, current is supplied to the first light emitting element during light writing (light emission), no current is supplied to the second light emitting element, and current is not supplied to the first light emitting element during non-writing (lights off). The circuit configuration is such that current is supplied to the second light emitting element. With this circuit configuration, the amount of current supplied to each light emitting unit is constant regardless of whether the first light emitting element emits light or turns off.

Therefore, as in the configuration in which the second light emitting element is not provided, the magnitude of the current flowing through the power supply line varies depending on whether each first light emitting element is turned on or off. It can suppress that the emitted light quantity of each 1st light emitting element varies.
In the above circuit configuration, since the current is supplied to the second light emitting element and the second light emitting element emits light while the first light emitting element is turned off, the light when the second light emitting element emits light is applied to the photoreceptor. It is necessary to configure so that it is not irradiated. As an example of this configuration, Patent Document 2 discloses a configuration in which a metal film for shielding light emitted from a second light emitting element is provided on a substrate.

JP 2005-144687 A JP 2010-201800 A

However, in the above circuit configuration, one second light emitting element and its current supply line are required as a set for each first light emitting element, and as the number of first light emitting elements increases, The cost burden on the second light emitting element that is not for writing increases.
SUMMARY An advantage of some aspects of the invention is that it provides an optical writing device and an image forming apparatus including the optical writing device that can reduce the cost burden while suppressing variations in the amount of emitted light. Yes.

  In order to achieve the above object, an optical writing device according to the present invention selects light from among a plurality of first light emitting elements for each optical writing timing and emits light, and writes on the photosensitive member by the light beam. A writing device, comprising: one second light emitting element provided corresponding to a light emitting element group composed of at least two or more first light emitting elements among the plurality of first light emitting elements; and the second light emitting element. A light-shielding member that shields a light beam emitted toward the photoconductor and a first light-emitting element included in the light-emitting element group and one power line, and controls a current from the power line A driving circuit that outputs a current to be supplied to the corresponding first light emitting element, and of each first light emitting element that performs optical writing among the first light emitting elements included in the light emitting element group at each optical writing timing. For each On the other hand, the output current of the corresponding drive circuit is supplied. On the other hand, the supply of the output current of the corresponding drive circuit is cut off for each of the remaining first light-emitting elements that are not subjected to optical writing. And a switching circuit for switching a supply destination of the output current of each of the drive circuits so that a total current of the output current of the circuit is supplied to the second light emitting element.

  In addition, a substrate having a light emitting element formation region on which the plurality of first light emitting elements and the one or more second light emitting elements are provided is provided, and each first light emitting element has a first direction in the light emitting element forming region. A plurality of element arrays arranged in a line along the first line are provided adjacent to each other in a second direction orthogonal to the first direction, and each of the two element arrays constituting the adjacent elements is provided. The first light emitting elements may be arranged in a staggered pattern in which the positions in the first direction are alternately shifted in a plan view of the substrate.

  Here, the substrate further includes a drive portion forming region in which the plurality of drive circuits are provided, and a lead-out wiring for receiving the output current of the corresponding drive circuit for each of the first light emitting elements. The light emitting element formation region and the drive portion formation region are provided in a positional relationship that is elongated along the first direction and adjacent to the second direction in a plan view of the substrate, The lead-out wiring is extended from the drive part formation region toward each first light emitting element in the light emitting element formation region, and two or more first light emitting elements constituting an element row closest to the drive part formation region Among the two first light emitting elements adjacent to each other in the first direction, there are P lead-out lines corresponding to the first light emitting elements constituting the other element rows in the plan view. If the one The number N of the first light emitting element constituting the light element group, [(P + 1) × M] (where, M is a positive integer) may be set to.

Further, the second light emitting element may have a characteristic that a current density is smaller when a current having the same magnitude flows than the first light emitting element.
The second light emitting element may have a larger area than the first light emitting element.
Furthermore, the first light emitting element and the second light emitting element may have different shapes.
The second light emitting element may have a larger rated current than the first light emitting element.

Furthermore, a light-shielding wiring for supplying a current to each of the drive circuits or each of the first light-emitting elements is provided, and the light-shielding member is the wiring, and when viewed from the photoconductor side, Two light emitting elements may be hidden behind the wiring.
The first light emitting elements may be made of the same material with the same shape and size.

Further, each of the first light emitting element and the second light emitting element may be an organic LED.
An image forming apparatus according to the present invention is an image forming apparatus that writes an image on a photosensitive member by a light beam from an optical writing unit, and includes the optical writing device described above as the optical writing unit.

  With the above configuration, at any timing of optical writing, in any combination of N (plurality) first light emitting elements constituting one light emitting element group and those not performing optical writing. Even when (N + 1) light emitting elements including N first light emitting elements and one second light emitting element are used as one light source unit, the light source unit is supplied from the power supply line. The total amount of current will not change.

  Accordingly, variation in the amount of emitted light can be suppressed, and the total number of second light emitting elements provided in the optical writing device can be reduced as compared with the configuration in which the first light emitting elements and the second light emitting elements are provided in one-to-one correspondence. , It will be possible to reduce the cost burden.

1 is a diagram illustrating a main configuration of an image forming apparatus according to Embodiment 1. FIG. It is a figure for demonstrating the optical writing operation | movement by an optical writing part. It is a figure which also shows the sectional view in an AA 'line, and the sectional view in a CC' line in addition to the schematic plan view of an OLED panel. It is a figure which shows the circuit structure of an OLED panel. It is a figure which shows the circuit structure of an OLED panel. (A) is a schematic top view which expands and shows a part when a light source part is seen from the surface side on the opposite side to the light extraction surface of a TFT substrate, (b) is D shown to (a). It is arrow sectional drawing of the TFT substrate in the -D 'line. It is a timing chart for demonstrating the light emission control method of the OLED panel by rolling drive. (A) is a schematic plan view of the TFT substrate which concerns on an Example, (b) is arrow sectional drawing in the BB 'line shown to (a). (A) is a schematic plan view of the TFT substrate which concerns on a comparative example, (b) is arrow sectional drawing in the EE 'line shown to (a). 6 is a schematic plan view of a light source unit according to a modification of the first embodiment. FIG. (A) is a schematic plan view which expands and shows a part of TFT substrate of the structure based on Embodiment 2, (b) is arrow sectional drawing in line FF 'shown to (a). . It is a schematic plan view of the light source part in the structural example at the time of making the shape of a 2nd light emitting element into an ellipse. It is a graph which shows the relationship between the lifetime of a light emitting element, and a rated drive current.

Hereinafter, embodiments of an optical writing apparatus and an image forming apparatus will be described with reference to the drawings.
<Embodiment 1>
(1) Configuration of Image Forming Apparatus FIG. 1 is a diagram illustrating a main configuration of the image forming apparatus according to the present embodiment.

As shown in FIG. 1, the image forming apparatus 1 is a so-called tandem color multifunction peripheral, and includes a document reading unit 100, an image forming unit 110, and a paper feeding unit 130.
The document reading unit 100 optically reads a document placed on the document table tray 101 while the automatic document feeder 102 transports the document, and generates image data. The image data is stored in the control unit 112 described later.

  The image forming unit 110 includes image forming units 111Y, 111M, 111C, and 111K, a control unit 112, an intermediate transfer belt 113, a secondary transfer roller 114, a fixing device 115, a discharge roller pair 116, a discharge tray 117, and a cleaning blade 118. And a timing roller pair 119. Further, the image forming unit 110 is equipped with toner cartridges 120Y, 120M, 120C, and 120K that supply toner of each color of Y (yellow), M (magenta), C (cyan), and K (black).

The image forming units 111Y to 111K receive toner supply from the toner cartridges 120Y to 120K, respectively, and form toner images of each color of YMCK under the control of the control unit 112.
For example, the image forming unit 111Y includes a photosensitive drum 121, a charging device 122, an optical writing device 123, a developing device 124, and a cleaning device 125. Under the control of the control unit 112, the charging device 122 uniformly charges the outer peripheral surface of the photosensitive drum 121.

The control unit 112 includes a built-in ASIC (Application Specific Integrated Circuit; hereinafter referred to as “brightness signal output unit”) based on image data for printing included in the received job, for example, image data read by the document reading unit 100. )), A digital luminance signal for causing the optical writing device 123 to emit light is generated.
As will be described later, the optical writing device 123 includes a plurality of OLED light-emitting elements arranged in the main scanning direction, and causes each light-emitting element to emit light according to the digital luminance signal generated by the control unit 112. Optical writing is performed on the outer peripheral surface of the photosensitive drum 121 by the light beam L emitted from each light emitting element to form an electrostatic latent image (exposure of the photosensitive drum 121).

The developing device 124 supplies toner to the outer peripheral surface of the photoconductive drum 121 to develop (visualize) the electrostatic latent image.
A primary transfer voltage is applied to a primary transfer roller 126 disposed opposite to the photoconductive drum 121 via the intermediate transfer belt 113, and toner carried on the outer peripheral surface of the photoconductive drum 121 by electrostatic action. The image is electrostatically transferred (primary transfer) to the intermediate transfer belt 113.

The cleaning device 125 scrapes off the toner remaining on the outer peripheral surface of the photosensitive drum 121 with a cleaning blade, and further removes the electric charge by illuminating the outer peripheral surface of the photosensitive drum 121 with a static elimination lamp.
Similarly, each of the image forming units 111M to 111K forms a corresponding color toner image. These toner images are sequentially primary transferred (multiple transfer) onto the intermediate transfer belt 113 so as to overlap each other, thereby forming a color toner image. The intermediate transfer belt 113 is an endless belt-like rotator, and rotates in the direction of arrow A to convey the primarily transferred toner image toward the secondary transfer roller 114.

  Each of the sheet feeding units 130 includes a sheet feeding cassette 131 that stores recording sheets S for each sheet size, and supplies the sheets S to the image forming unit 110 one by one. The supplied sheet S is carried out in parallel with the intermediate transfer belt 113 carrying the toner image, and is carried to the secondary transfer roller 114 via the timing roller pair 119. The timing roller pair 119 is configured so that the time when the color toner image on the intermediate transfer belt 113 reaches the secondary transfer roller 114 coincides with the time when the sheet S reaches the secondary transfer roller 114. The conveyance timing to the next transfer roller 114 is adjusted.

The secondary transfer roller 114 is applied with a secondary transfer voltage, and forms a transfer nip portion with the intermediate transfer belt 113.
When the sheet S conveyed from the timing roller pair 119 passes through the transfer nip portion, the color toner image on the intermediate transfer belt 113 is electrostatically transferred (secondary transfer) onto the sheet S. The sheet S after the color toner image is secondarily transferred is conveyed to the fixing device 115. Further, after the secondary transfer, the residual toner remaining on the intermediate transfer belt 113 is further conveyed in the direction of arrow A, and then scraped off by the cleaning blade 118 and discarded.

The fixing device 115 heats and melts the color toner image on the sheet S conveyed from the secondary transfer roller 114 and fixes the color toner image on the sheet S. The sheet S that has passed through the fixing device 115 is discharged onto the discharge tray 117 by the discharge roller pair 116.
The control unit 112 comprehensively controls operations such as document reading by the document reading unit 100, formation of a color image on the sheet S by the image forming unit 110, and feeding of the sheet S by the sheet feeding unit 130, and the like. Smoothly execute various jobs.

The control unit 112 is communicably connected to an external terminal such as a personal computer (PC) (not shown) via a network. When a print job is received from the external terminal, the control unit 112 performs printing based on the image data. Can be executed.
(2) Configuration of Optical Writing Device 123 FIG. 2 is a diagram for explaining an optical writing operation by the optical writing device 123.

As shown in FIG. 2, the optical writing device 123 is one in which the OLED panel 20 and the rod lens array 22 are accommodated in a housing 23, and a plurality of light emitting elements 61 are arranged in the main scanning direction on the OLED panel 20. They are arranged in a line along the line (perpendicular to the drawing).
Each of the plurality of light emitting elements 61 individually emits a light beam L.
The rod lens array 22 forms an image on the surface of the photosensitive drum 121 with the light beams L emitted from the respective light emitting elements 61.

FIG. 3 is a schematic plan view of the OLED panel 20, and a cross-sectional view taken along the line AA ′ and a cross-sectional view taken along the line CC ′ are also shown. Moreover, the schematic plan view part has shown the state which removed the sealing plate mentioned later.
As shown in FIG. 3, the OLED panel 20 includes a TFT (thin film transistor) substrate 30 on which an OLED is integrally formed, a sealing plate 31, a source IC 32, and the like.

A plurality of light emitting elements 61 arranged in a line along the main scanning direction are arranged on the TFT substrate 30.
The substrate surface 34 of the TFT substrate 30 on the side where the light emitting element 61 is disposed is a sealing region, and the sealing plate 31 is attached with the spacer frame 33 interposed therebetween. As a result, the sealing region is sealed in a state in which dry nitrogen or the like is sealed so as not to touch the outside air. In order to absorb moisture, a hygroscopic agent may be enclosed in the sealing region. Moreover, the sealing plate 31 may be sealing glass, for example, and may consist of materials other than glass.

The surface 35 of the TFT substrate 30 opposite to the side on which the light emitting element 61 is disposed serves as a light extraction surface, and the light beam L emitted from each light emitting element 61 passes through the TFT substrate 30 and the light extraction surface 35. Is emitted downward from the figure (exposure of the photosensitive drum 121).
A source IC 32 is mounted outside the sealing region of the TFT substrate 30. The luminance signal output unit 135 of the control unit 112 outputs a digital luminance signal to the source IC 32 via the flexible wire 36. The source IC 32 converts the received digital luminance signal into an analog luminance signal, and outputs the analog luminance signal to a driving circuit provided for each light emitting element 61. The drive circuit generates a drive current for the light emitting element 61 in accordance with the received analog luminance signal.

(3) Circuit Configuration of OLED Panel 20 FIG. 4 is a diagram showing a circuit configuration of the OLED panel 20, specifically, a sample hold circuit (hereinafter referred to as “S / H circuit”) 50 in the TFT substrate 30. The connection relationship among the drive unit 55, the plurality of light source units 21, and the source IC 32 is shown.
As shown in FIG. 4, each light source unit 21 includes four light emitting elements 61 (first light emitting elements) for writing and one light emitting element 62 (first light emitting element) that is different from these and not for writing. 2 light-emitting elements).

Each of the light emitting elements 61 and 62 is composed of a current driven type light emitting element in which the amount of emitted light changes according to the amount of current supplied (the magnitude of the current). Here, the light-emitting element 61 and the light-emitting element 62 are formed of the same material (raw material), have the same shape and size, and are formed to have the same characteristics such as the relationship between current and amount of emitted light and electrical resistance characteristics. ing.
The drive unit 55 corresponds to each thin film transistor 56 provided corresponding to each of the plurality of light emitting elements 61, here a P-type field effect transistor (FET), and each drive circuit 56. The switch 57 provided is provided. Hereinafter, the thin film transistor is referred to as a drive circuit.

The source IC 32 includes a synchronization signal generation circuit (Sync) 40, a DAC circuit 41, and a VIDEO circuit 42.
A DAC (Digital to Analogue Converter) circuit 41 converts the digital luminance signal received from the luminance signal output unit 135 of the control unit 112 into an analog luminance signal, and outputs the converted analog luminance signal SG to the S / H circuit 50. .

The S / H circuit 50 is a circuit that switches a holding element 54, which is provided corresponding to each of a plurality of light emitting elements 61, here a capacitor by a selector 51.
The selector 51 includes a shift register 52 and a switch 53 provided for each of the plurality of holding elements 54.
The shift register 52 turns on the switches 53 one by one in synchronization with the pulse signal output from the synchronization signal generation circuit 40 of the source IC 32. While one switch 53 is on, all other switches 53 are off.

  The analog luminance signal (signal indicating the light emission amount) SG output from the DAC circuit 41 is input to one terminal of the holding element 54 via the switch 53 that is turned on among the plurality of switches 53. The other terminal of the holding element 54 is connected to a power supply line 71 extending from the constant voltage source 70. Therefore, when the signal SG output from the DAC circuit 41 is input to the holding element 54, the charge corresponding to the voltage difference between the voltage of the signal SG and the voltage at the connection point on the power supply line 71 is held. (Accumulated).

  The accumulation of electric charges in the holding elements 54 is executed in order for each holding element 54 in synchronization with an operation in which the switches 53 are sequentially turned on one by one. Accumulation of charge in the holding element 54 is referred to as charging, and the time required for charging one holding element 54 (time during which one switch 53 is turned on) is referred to as a charge period. Charging for each holding element 54 is performed in order for each holding element 54, and to the holding element 54 for the first light emitting element 61 among n (plurality) of light emitting elements 61 as described later (FIG. 7). The period from the start of charging (t1) to the end of charging of the last n-th light emitting element 61 to the holding element 54 (t2) is one main scanning period (hereinafter simply referred to as “scanning period”). .

  In each of the plurality of drive circuits 56, the source terminal S is connected at a connection point 72 on the power supply line 71, and the gate terminal G is connected to one terminal of the corresponding holding element 54. Since the other terminal of the holding element 54 is connected to the power supply line 71, the potential difference (hereinafter referred to as “gate voltage Vg”) between the gate terminal G and the source terminal S of the drive circuit 56 is the same. It becomes equal to the voltage between the terminals at both ends of the holding element 54, that is, a voltage corresponding to the amount of charge held in the holding element 54.

The drive circuit 56 is a voltage input type circuit that controls the current from the power supply line 71 input to the source terminal S according to the magnitude of the gate voltage Vg and outputs it from the drain terminal D.
Therefore, the magnitude of the output current of the drive circuit 56 is determined by the amount of charge held in the holding element 54, that is, the magnitude of the voltage of the output signal of the DAC circuit 41. That is, the output signal SG of the DAC circuit 41 is a signal indicating the magnitude of the output current of the drive circuit 56 (drive current to be supplied to the light emitting element 61).

Therefore, the output signal of the DAC circuit 41 is provided for each holding element 54 corresponding to each light emitting element 61 so that a driving current corresponding to the light amount suitable for light emission is supplied to each light emitting element 61 from the driving circuit 56. By individually adjusting the SG voltage, each light emitting element 61 can emit light stably.
For example, when a difference occurs in the input voltage to the other terminal for each holding element 54 due to a potential drop in the length direction of the power supply line 71, the voltage from the constant voltage source 70 is not affected as much as possible. As the distance increases, it is possible to perform control for adding the voltage of the output signal SG to the original voltage by an amount corresponding to the difference for each holding element 54.

In addition, when the light emitting element 61 has a light amount deterioration characteristic in which the light amount decreases with an increase in the accumulated light emission time and a light amount variation characteristic in which the luminance changes with an environmental temperature variation, the voltage of the output signal SG is increased based on the characteristics. If the height is corrected for each light emitting element 61, it becomes possible to always maintain the light emission quantity of each light emitting element 61 at an appropriate amount irrespective of the light quantity deterioration characteristic or the like.
The current output from the drain terminal D of each drive circuit 56 is supplied to the switch 57 corresponding to the drive circuit 56 as the current to be supplied to the light emitting element 61 corresponding to the drive circuit 56.

  Each switch 57 includes a first state in which the drain terminal D of the corresponding driving circuit 56 and the lead-out wiring 91 connected to the anode of the light emitting element 61 corresponding to the driving circuit 56 are connected, and the drain of the driving circuit 56. The second state in which the terminal D and the lead-out line 92 connected to the anode of the light emitting element 62 are connected is switched according to the signal output from the VIDEO circuit 42 of the source IC 32. The cathode of each light emitting element 61 and the cathode of each light emitting element 62 are connected to the ground terminal 80 via the ground wiring 81.

FIG. 4 shows an example in which all the switches 57 corresponding to each of the four light emitting elements 61 are switched to the first state in one light source unit 21 representatively shown among the plurality of light source units 21. ing.
Based on the image data used for printing, the VIDEO circuit 42 exposes (emits light) the photosensitive drum 121 for each light emitting element 61 in units of scanning period (at each optical writing timing) (not for exposure) ( Select the item to be turned off. For each light emitting element 61 that emits light, a signal for switching to the first state is output to the switch 57 corresponding thereto, and for the light emitting element 61 that is extinguished, to the switch 57 corresponding thereto. To output a signal for switching to the second state.

  As a result, the current output from the drain terminal D of the drive circuit 56 corresponding to the light emitting element 61 corresponding to the switch 57 that is switched to the first state in a certain scanning period in units of the scanning period is the light emitting element. It flows to the ground wiring 81 through 61. By supplying current to the light emitting element 61, the light emitting element 61 emits light, and the light beam L from the light emitting element 61 is used for exposure of the photosensitive drum 121.

On the other hand, in the same scanning period, the current output from the drain terminal D of the drive circuit 56 corresponding to the light emitting element 61 corresponding to the switch 57 switched to the second state is supplied to the light emitting element 61. Instead, the total current of the output currents from the respective drive circuits 56 flows to the ground wiring 81 through the light emitting element 62.
The current supply to the light emitting element 62 causes the light emitting element 62 to emit light, but light emitted from the light emitting element 62 is shielded by a light shielding member 65 (FIG. 6), which will be described later. Does not reach the photosensitive drum 121, and the photosensitive drum 121 is not exposed.

  In the example shown in FIG. 4, all the switches 57 corresponding to the four light emitting elements 61 included in one light source unit 21 are in the first state. As a result, the leftmost light emitting element 61 is supplied with the output current Ia of the driving circuit 56 corresponding thereto, and the second light emitting element 61 from the left end is supplied with the output current Ib of the driving circuit 56 corresponding thereto. . Similarly, the output current Ic of the driving circuit 56 corresponding to the third light emitting element 61 from the left end is supplied, and the output current Id of the driving circuit 56 corresponding to the fourth light emitting element 61 from the left end is supplied. Supplied. The output current of any drive circuit 56 is not supplied to the light emitting element 62.

In this case, each of the four light emitting elements 61 emits light with a light emission amount corresponding to the output current, but the light emitting element 62 is turned off.
In contrast, in the example illustrated in FIG. 5, in one light source unit 21, among the four light emitting elements 61, the switches 57 corresponding to the leftmost light emitting element 61 and the second light emitting element 61 from the left end are provided. In the first state, the respective switches 57 corresponding to the third and fourth light emitting elements 61 from the left end are switched to the second state.

  As a result, the output currents Ia and Ib of the drive circuit 56 are supplied to the left end and the second light emitting element 61, but the output current Ic of the drive circuit 56 corresponding to the third and fourth light emitting elements 61 is supplied. , Id are not supplied, and a current Ie obtained by adding the output currents Ic and Id is supplied to the light emitting element 62. In this case, the left end and the second light emitting element 61 emit light, the third and fourth light emitting elements 61 are turned off, and the light emitting element 62 emits light.

In both the example shown in FIG. 4 and the example shown in FIG. 5, the total current amount It supplied from the power supply line 71 to one light source unit 21 for each scanning period is the output current of each corresponding drive circuit 56. It becomes the same with the total value Iw of Ia to Id, that is, (Ia + Ib + Ic + Id). This is the same except in the cases shown in FIGS.
Specifically, for example, when only the leftmost light emitting element 61 emits light among the four light emitting elements 61 and the remaining three are turned off, the following is performed.

That is, the output current Ia of the corresponding drive circuit 56 is supplied to the light emitting element 61 that emits light, and the three light emitting elements 61 that are turned off emit light without being supplied with the output currents Ib to Id of the corresponding drive circuit 56. It is supplied to the element 62. Therefore, the total amount of current It supplied to the light source unit 21 is a value Iw obtained by summing the output currents Ia to Id.
For example, when all of the four light emitting elements 61 are extinguished, the output currents Ia to Id of the corresponding drive circuits 56 are not supplied to any of the light emitting elements 61, and the current Iw obtained by adding them is the current Iw. The light is supplied to the light emitting element 62. Accordingly, also in this case, the total current amount It is the same as the total value Iw of the output currents Ia to Id. This is the same for each of the other light source units 21.

Thus, in the present embodiment, each light source unit 21 associates one light emitting element 62 with a plurality of light emitting elements 61, in other words, the plurality of light emitting elements 61 share one light emitting element 62. ing.
In each scanning period, the output current of the corresponding driving circuit 56 is supplied to each of the light emitting elements 61 that emit light (performs optical writing), while the remaining light emitting elements that are extinguished (not perform optical writing). For each of 61, the supply of the output current of the corresponding drive circuit 56 is cut off (not supplied), and instead the total current of the output current of each of the drive circuits 56 is supplied to the light emitting element 62. A circuit configuration is provided in which each switch 57 as a switching circuit for switching the supply destination of the output current of each drive circuit 56 and a VIDEO circuit 42 for controlling the switch 57 are provided.

  Thereby, for each light source unit 21, even if the combination of the light emitting element 61 and the light emitting element out of the plurality of light emitting elements 61 included in the light source unit 21 is changed between a certain scanning period and the next scanning period, respectively. If the gate voltage Vg of the driving circuit 56 does not change, the output currents Ia to Id of the respective driving circuits 56 become the same, so the total amount of current It supplied from the power supply line 71 does not change.

  The fact that the total amount of current It supplied from the power supply line 71 for each light source unit 21 does not change in units of scanning periods means that the magnitude of the current flowing in the power supply lines 71 does not vary in units of scanning periods. . The fact that the magnitude of the current flowing through the power supply line 71 does not change means that the potential drop caused by the fluctuation, that is, the magnitude of the potential gradient on the power supply line 71 that decreases as the distance from the constant voltage source 70 increases. It also means that it does not fluctuate.

If the magnitude of the potential drop of the power supply line 71 varies for each scanning period, the light emission amount of the light emitting element 61 may vary as follows.
That is, it is assumed that a signal indicating the same light emission amount is output from the DAC 41 to the holding element 54 corresponding to a certain light emitting element 61 every scanning period. In this case, the voltage of the signal from the DAC 41 is input to one terminal of the holding element 54, and the voltage of the power supply line 71 is input to the other terminal.

  For example, the voltage of a signal input from the DAC 41 to one terminal of the holding element 54 is constant during the charge period in the previous scanning period and the current scanning period, whereas the holding voltage is held from the power supply line 71. If the voltage input to the other terminal of the element 54 fluctuates due to the fluctuation of the magnitude of the potential gradient of the power supply line 71, it is held by the same holding element 54 in the previous scanning period and the current scanning period. The amount of charge will be different.

If the amount of charge held in the holding element 54 during the charge period differs every scan period, the gate voltage Vg of the corresponding drive circuit 56 also varies.
As described above, the drive circuit 56 is a voltage-driven drive driver that outputs a current corresponding to the magnitude of the gate voltage Vg. Therefore, even if a signal indicating the same light emission amount is output from the DAC 41 for each scanning period, if the gate voltage Vg varies due to the potential variation of the power supply line 71, it is output from the drive circuit 56 during each scanning period. The amount of current supplied to the light emitting element 61 is also different, and the amount of light emitted from the current driven light emitting element 61 varies for each scanning period.

  On the other hand, when the circuit configuration of the present embodiment is adopted, the magnitude of the potential gradient on the power supply line 71 does not vary greatly every scanning period as described above. Therefore, if a signal indicating the same light emission amount is output from the DAC 41 to the holding element 54 every scanning period, the amount of charge held in the holding element 54 does not vary from scanning period to scanning period, and the corresponding driving circuit 56 The gate voltage Vg does not fluctuate.

In this case, since the output current of the drive circuit 56 does not fluctuate every scanning period, when the light emitting element 61 emits light, the amount of current supplied to the light emitting element 61 does not fluctuate and the amount of emitted light varies. Does not occur.
As described above, in the circuit configuration of the present embodiment, one light emitting element 62 is provided for a plurality of light emitting elements 61 while suppressing variations in the amount of light emitted from each light emitting element 61 due to fluctuations in the potential drop of the power supply line 71. , The total number of the light emitting elements 62 can be reduced and the cost burden can be reduced as compared with the configuration in which the light emitting elements 61 and 62 are provided on a one-to-one basis.

(4) Configuration of Light Source Unit 21 FIG. 6A is a schematic plan view showing an enlarged part of the light source unit 21 when viewed from the side of the surface 35 a opposite to the light extraction surface 35 of the TFT substrate 30. FIG. 6B is a cross-sectional view of the TFT substrate 30 taken along the line DD ′ shown in FIG.
Here, FIG. 6 shows only main members necessary for explanation, and main members that are hidden behind other members when the TFT substrate 30 is viewed from the surface 35a side (hereinafter referred to as “plan view”). Is indicated by a broken line. In addition, the horizontal direction in the figure corresponds to the main scanning direction. These are the same in each figure described below.

As shown in FIG. 6 (a), element rows 21a, 21b, 21c, and 21d, in which a plurality of light emitting elements 61 are arranged in a line along the main scanning direction, are sub-scanning directions orthogonal to the main scanning direction. Are arranged in this order (adjacent).
Among the element rows 21a to 21d, the positions of the light emitting elements 61 constituting one of the adjacent element rows and the light emitting elements 61 constituting the other element row 21b are alternately shifted in the main scanning direction. It is configured to be arranged in a staggered pattern. By forming the staggered pattern, the number of the light emitting elements 61 arranged per unit length in the main scanning direction can be increased, and the degree of integration of the light emitting elements 61 can be increased and the resolution can be increased. Note that the positional relationship between the light emitting element 61 and the light emitting element 62 is not limited to the above.

  In a plan view, among the plurality of light emitting elements 61 constituting each of the element rows 21 a and 21 b, four light emitting elements 61 that are adjacent to each other and the positions surrounded by these four light emitting elements 61 are arranged. In addition, one light source unit 21 is configured by one light emitting element 62. A plurality of light source portions 21 are arranged in a line along the main scanning direction, and this row is referred to as an element row 21e.

  Similarly, in plan view, among the plurality of light emitting elements 61 constituting each of the element rows 21c and 21d, four light emitting elements 61 that are adjacent to each other and positions surrounded by these four light emitting elements 61 One light source unit 21 is composed of one light emitting element 62 arranged in the light emitting element 62. A plurality of light source portions 21 are arranged in a line along the main scanning direction, and this row is referred to as an element row 21f.

Assuming that the region 21g where the element rows 21e and 21f are arranged on the TFT substrate 30 is a light emitting element forming region, two drive unit forming regions 55a and 55b are arranged on both sides of the light emitting element forming region 21g in the sub-scanning direction. Is provided.
One drive portion formation region 55a is a region where the drive circuit 56 and the switch 57 corresponding to each of the light emitting elements 61 constituting the element row 21e are formed, and the other drive portion formation region 55b is the element row 21f. This is a region where a drive circuit 56 and a switch 57 corresponding to each of the light emitting elements 61 constituting the light emitting element 61 are formed.

Each of the drive portion formation regions 55a and 55b is elongated along the main scanning direction, and lead-out wirings 91 and 92 connected to the respective switches 57 in each region extend toward the light emitting element formation region 21g. Has been.
Of the lead wires 91 and 92 connected to each switch 57, the lead wire 91 extends to the corresponding light emitting element 61 for each light source unit 21, and the lead wire 92 extends to the corresponding light emitting element 62. Has been. By these lead wires 91 and 92, the output current of the drive circuit 56 is supplied to the light emitting element 61 or the light emitting element 62 through the switch 57.

Note that the cathode-side terminal of each light-emitting element 61 and the cathode-side terminal of each light-emitting element 62 are configured to be connected to the ground wiring 81 as described above. The terminals and wiring are omitted.
The cross-sectional configuration of the TFT substrate 30 is such that the light emitting layer 150 is laminated on the glass substrate 140 via the wiring layer 160 as shown in FIG. 6B.

The glass substrate 140 is formed of a light-transmitting material, and the wiring layer 160 includes wiring (extracted wirings 91 and 92 and the power supply line 71) and the light shielding member 65 inside the light-transmitting inorganic insulating film. Is formed. A surface 35 of the glass substrate 140 opposite to the side on which the wiring layer 160 is laminated is a light extraction surface.
The wiring layer 160 has a structure in which three inorganic insulating films are stacked in the thickness direction. Of the three layers, the layer closest to the light emitting layer 150 is the first wiring layer 161 and the layer closest to the glass substrate 140 is the first. The third wiring layer 163 and the layer interposed between the first wiring layer 161 and the third wiring layer 163 are the second wiring layer 162. Hereinafter, the thickness direction may be referred to as the vertical direction.

  In the first wiring layer 161 and the second wiring layer 162, wirings such as lead-out wirings 91 and 92 are provided. The lead-out wiring 91 provided in the second wiring layer 162 below the first wiring layer 161 and the light-emitting element 61 provided in the light-emitting layer 150 above the first wiring layer 161 are the first wiring. They are electrically connected through through holes (not shown) provided in the layer 161. On the other hand, in the third wiring layer 163 below the second wiring layer 162, a light blocking member 65 is provided at a position immediately below each light emitting element 62.

The light shielding member 65 is a film formed of a light-shielding metal such as aluminum or copper, and is used for shielding a light beam emitted from the light emitting element 62.
The light emitting layer 150 above the wiring layer 160 is made of an organic insulating film, and the light emitting element 61 and the light emitting element 62 are provided. In the figure, the upper end side of each light emitting element is the cathode side, the lower end side is the anode side, and a state in which the transparent electrode 63 is provided on the anode side is shown. The transparent electrode 63 is connected to the lead wiring 91 or 92.

Each of the light emitting element 61 and the light emitting element 62 has a light emitting portion on the anode side, and a light beam is emitted toward the wiring layer 160.
The light beam L emitted from the light emitting element 61 passes through the wiring layer 160 and the glass substrate 140 each having translucency, and is emitted from the light extraction surface 35 of the glass substrate 140. The emitted light beam L becomes a light beam for exposing the photosensitive drum 121.

  On the other hand, a light beam (not shown) emitted from the light emitting element 62 attempts to enter the third wiring layer 163 via the first wiring layer 161 and the second wiring layer 162, but is provided in the third wiring layer 163. The light shielding member 65 is shielded from light. Accordingly, the light beam emitted from the light emitting element 62 does not reach the glass substrate 140, but is prevented from being emitted from the light extraction surface 35 of the glass substrate 140 toward the photosensitive drum 121.

  Wiring such as the lead wires 91 and 92 and the power supply line 71 is provided on the first wiring layer 161 and the second wiring layer 162 of the wiring layer 160, and a light shielding member 65 made of a light shielding metal is provided on the third wiring layer 163. Can be performed by using an existing film formation manufacturing method. Note that the size, shape, thickness, etc. of the light shielding member 65 are determined in advance by experiments or the like so that the light beam emitted from the light emitting element 62 can be shielded.

(5) About the light emission control method in each light source part 21 FIG. 7: is a timing chart for demonstrating the light emission control method in each light source part 21, and has shown the light emission control method by what is called rolling drive.
Here, in the figure, in order to distinguish each of the plurality of switches 53, they are represented as 53-1,... (N-1), n, and in order to distinguish each of the plurality of switches 57, 57-1, 2 ··· (n-1), n. Moreover, in order to distinguish each of the some light emitting element 61 which consists of OLED, it represents as OLED-1, ... (n-1), n. Those with the same numerical value added to each correspond to each other. The luminance signals SG1, 2,... N are output in time order from the DAC circuit 41 shown in FIG.

  As shown in FIG. 7, only the switch 53-1 is turned on in synchronization with the luminance signal SG1 being output, and the luminance signal SG1 is turned on while the switch 53-1 is on. It is written in the holding element 54 corresponding to OLED-1. If the switch 53-1 is the leftmost switch 53 shown in FIG. 4, the luminance signal SG <b> 1 is written in the holding element 54 connected to the switch 53. In this case, the left side light emitting element 61 shown in FIG. 4 corresponds to the OLED-1 shown in FIG. 7, and the writing period of the luminance signal SG1 becomes the charging period of the luminance signal SG1 for the OLED-1.

  When the output of the luminance signal SG1 is completed, the switch 53-1 is turned off (OFF). Subsequently, only the switch 53-2 is turned on in synchronization with the output of the luminance signal SG2, and the switch 53-1 is turned on. The luminance signal SG2 is written to the holding element 54 corresponding to OLED-2. If the switch 53-2 is the second switch 53 from the left end shown in FIG. 4, the luminance signal SG <b> 2 is written to the holding element 54 connected to the switch 53. In this case, the second light emitting element 61 from the left end shown in FIG. 4 corresponds to the OLED-2 shown in FIG. 7, and the writing period of the luminance signal SG2 becomes the charging period of the luminance signal SG2 for the OLED-2.

Thereafter, writing of the corresponding luminance signals SG3, SG4,... SG (n-1), SGn is shifted in time order to the respective holding elements 54 corresponding to OLED-3, 4,... (N-1), n. Done.
For each OLED, a period in which the corresponding switch 53 is on is a charge period, and a period other than the charge period is a hold period.

The gate voltage Vg is determined by the voltage of the luminance signal SG written to the holding element 54 in the charge period, and a current corresponding to the gate voltage Vg in the charge period is output from the drive circuit 56 in the hold period subsequent to the charge period. Is done. When the hold period ends, the operation proceeds to the next charge period, and the operation after the charge is charged to the holding element 54 is repeated.
A period from the start t1 of the charge period for OLED-1 to the end t2 of the charge period for OLED-n is one scanning period (1Hsync). This one scanning period is determined in advance as the optical writing timing required for forming an electrostatic latent image for one line in the main scanning direction on the photosensitive drum 121.

  The switches 57-1,..., (N−1), n are in a first state (exposure period: at the time of optical writing) and a second state (non-exposure) in response to a signal from the VIDEO circuit 42 for each scanning period. (Period: non-writing). FIG. 7 shows an example in which only the switches 57-3 and 57-4 are switched to the second state and all the other switches 57 are switched to the first state in a certain scanning period (time points t1 to t2).

As described above, the OLED corresponding to the switch 57 in the first state emits light, but the OLED corresponding to the switch 57 in the second state does not emit light.
Accordingly, in the example of FIG. 7, among the OLEDs 1 to n, the OLEDs 3 and 4 corresponding to the switches 57-3 and 4 in the second state are turned off during the period from the time t1 to the time t2. Each of the OLEDs emits light, and the photosensitive drum 121 is exposed by the light beam L from the OLED. For OLED-3 and 4, the photosensitive drum 121 is not exposed. From this, the scanning period shown between the time points t1 and t2 corresponds to non-writing time (period in which optical writing is not performed) for OLED-3 and OLED-3, and optical writing time (lighting time) for each of the other OLEDs. This corresponds to the period during which writing is performed.

  When one scanning period (t1 to t2) ends, the transition to the next scanning period is repeatedly executed, and the OLED-1 to n rotate by the exposure operation of the respective photosensitive drums 121 for each scanning period. An electrostatic latent image for one line along the main scanning direction is formed on the photosensitive drum 121. As a result, an electrostatic latent image corresponding to an image for one page is formed in the rotation direction (sub-scanning direction) of the photosensitive drum 121.

(6) Comparison between a configuration in which one light emitting element 62 is associated with a plurality of light emitting elements 61 and a configuration in which one light emitting element 62 is associated with one light emitting element 61 FIG. FIG. 8A is a schematic plan view of the TFT substrate 30, and FIG. 8B is FIG. 8A. FIG. 8A is a diagram illustrating an example of a configuration in which one light emitting element 62 is associated with 61. The arrow directional cross-sectional view in the BB 'line shown in FIG.

As shown in FIG. 8A, in the configuration according to the embodiment, one light emitting element 62 is associated with three light emitting elements 61, and the plurality of light emitting elements 61 are arranged along the main scanning direction. Three element rows 21m, 21n, and 21p arranged in a line are arranged in this order in the sub-scanning direction, that is, arranged in an adjacent positional relationship.
Each of the light emitting elements 61 constituting the three element rows 21m to 21p is arranged in a staggered manner in which positions in the main scanning direction are alternately shifted.

The light emitting element 62 is disposed at a substantially intermediate position between two adjacent light emitting elements 61 among the plurality of light emitting elements 61 constituting the second element row 21n.
The drive portion formation region 55c is a region in which a plurality of drive circuits 56 and a plurality of switches 57 are provided on the substrate 30, and is elongated along the main scanning direction in plan view, and the element array 21p. Is arranged on the opposite side of the element array 21n.

In FIG. 6A, the two drive part formation regions 55a and 55b are in a positional relationship of sandwiching the light emitting element formation region 21g in the sub-scanning direction. However, in the example of FIG. In other words, the light emitting element forming region 21g and the drive unit forming region 55c are long in the main scanning direction and aligned in the sub scanning direction.
The lead wires 91 and 92 connected to each switch 57 provided in the drive unit formation region 55c are extended toward the light emitting element formation region 21g.

The wiring layer 160 has a two-layer structure of a first wiring layer 161 and a second wiring layer 162 as shown in FIG.
The first wiring layer 161 is provided with a plurality of light emitting elements 61 constituting the element rows 21p and 21n, and lead lines 91 and 92 for the plurality of light emitting elements 62, respectively. The second wiring layer 162 has an element row. A lead-out wiring 91 for each of the plurality of light emitting elements 61 constituting 21 m and a light shielding member 65 corresponding to each of the plurality of light emitting elements 62 are provided.

On the other hand, FIG. 9 is a diagram showing a configuration according to a comparative example in which one light emitting element 62 is associated with one light emitting element 61, and FIG. 9A is a schematic plan view of the TFT substrate 30. FIG. 9B is a cross-sectional view taken along line EE ′ shown in FIG.
Here, the comparative example shown in FIG. 9 is an example in which a plurality of light emitting elements 61 are provided under the same conditions (the number per unit area and the arrangement position) as in the above embodiment.

As shown in FIG. 9A, in the configuration according to the comparative example, the total number of light emitting elements 61 and the total number of light emitting elements 62 are the same. Here, a set of one light emitting element 61 and one light emitting element 62 adjacent to each other constitutes one light source unit.
All the three element rows 21m to 21p are configured such that one second light emitting element 61 is disposed between two adjacent light emitting elements 61. Therefore, if the distance between the two light emitting elements 61 adjacent to each other in the main scanning direction on the TFT substrate 30 (corresponding to the resolution of the formed image in the main scanning direction) is the same as that in the above embodiment, the comparative example has However, it is necessary to increase the number of light emitting elements and lead-out lines per unit area on the TFT substrate 30.

  Since the number of light emitting elements and lead wires per unit area in plan view is increased, the comparative example has a wiring layer as shown in the cross-sectional view of FIG. The number of layers is increased by 160. Unless the number of wiring layers 160 is increased, it is necessary to provide a large number of lead-out wirings so that the intervals per unit area in the main scanning direction are as small as possible, and the spacing between two adjacent lead-out wirings is narrow. This is because if it becomes too large, the insulation between the wirings may not be secured.

In this way, increasing the number of wiring layers 160 increases the number of light emitting elements 62 and their lead-out wirings 92, such as the addition of manufacturing processes and the increase in the amount of forming materials. The cost burden at the time will increase.
In contrast, in the configuration of the example according to the present embodiment, the total number of the light emitting elements 62 and the lead-out wirings 92 is reduced as compared with the comparative example in which the plurality of light emitting elements 61 are arranged under the same conditions. The number of layers can be reduced, and the cost burden can be reduced accordingly.

Further, since the number of light emitting elements 62 per unit area can be reduced in plan view as compared with the configuration of the comparative example, it becomes possible to reduce the interval in the main scanning direction of each light emitting element 61 (increase the density), Accordingly, it is possible to increase the resolution in the main scanning direction.
<Modification according to Embodiment 1>
FIG. 10 is a schematic plan view of the light source unit 21 according to the modification, and members such as a light shielding member that are not necessary for the description are omitted.

As shown in the figure, one light source unit 21 includes two light emitting elements 61 and one light emitting element 62.
A plurality of light emitting elements 61 arranged in the main scanning direction are arranged so that element rows 21a to 21d are arranged in the sub scanning direction, and the positions of the respective light emitting elements 61 in the main scanning direction are arranged in a staggered manner. This point is the same as the configuration according to the first embodiment.

Each of the plurality of light emitting elements 62 is arranged at a position between two adjacent light emitting elements 61 among the plurality of light emitting elements 61 constituting the element row for each of the element rows 21b and 21c.
The drive part formation regions 55a and 55b are basically the same as the drive part shown in FIG. In other words, the drive portion formation region 55a is a region where the drive circuit 56 and the switch 57 corresponding to each of the light emitting elements 61 constituting the element rows 21a and 21b are formed, and the drive portion formation region 55b is the element row 21c. And a drive circuit 56 and a switch 57 corresponding to each of the light emitting elements 61 constituting 21d.

Lead wirings 91 and 92 for the light emitting element 61 and the light emitting element 62 are extended from the driving part forming regions 55a and 55b, respectively, and a driving current is supplied through the lead wirings 91 and 92, respectively.
Although a circuit configuration for this modification is not shown, a circuit in which two light-emitting elements 61 out of four light-emitting elements 61 are deleted for each light source unit 21 with respect to the circuit configuration shown in FIG. 4 according to the embodiment. The configuration can be the circuit configuration according to this modification. Of course, the drive circuit 56 and the switch 57 corresponding to the deleted light emitting element 61 are also unnecessary.

In this modified example, since one light emitting element 62 is associated with two light emitting elements 61, if the currents supplied to the two light emitting elements 61 are Ia and Ib, When both of the two light emitting elements 61 are turned off simultaneously, the current Ie flowing through the light emitting element 62 is (Ia + Ib), which is the maximum value.
In the embodiment, since one light emitting element 62 is associated with four light emitting elements 61, the current Ie that flows through the light emitting element 62 when all the four light emitting elements 61 are simultaneously turned off. Becomes (Ia + Ib + Ic + Id) as described above, which is the maximum value. Therefore, if each of Ia to Id has the same value, the maximum value of the current Ie flowing through the light emitting element 62 is about half that of the configuration according to the embodiment if the configuration of this modification is taken. It can be reduced to the value of.

Usually, many light emitting elements such as OLEDs have the characteristic that the thermal load increases and deteriorates as the amount of current flowing increases, so that the lifetime tends to be shortened. Therefore, the maximum value of the current flowing through the light emitting element 62 Can be kept low, the life of the light emitting element 62 can be extended accordingly.
Although the light emitting element 62 is not used for exposure (image writing) of the photosensitive drum 121, it plays a central role in suppressing variations in the amount of emitted light accompanying current fluctuations in the power supply line 71. The longer the life of the element 62, the longer the effect of suppressing the variation in the amount of emitted light can be maintained over a long period of time, and the deterioration in the image quality of the formed image due to the variation in the amount of emitted light can be suppressed.

In the above description, the light emitting element 61 and the light emitting element 62 having the same characteristics are used. However, it is needless to say that the light emitting element 61 and the light emitting element 62 are not completely the same. Variations in the characteristics are allowed.
For example, in each light source unit 21, the difference between the total current values flowing through the plurality of light emitting elements 61 and one light emitting element 62 included in the light source unit 21 is within a predetermined range in which light emission variation can be tolerated for each scanning period. If it fits in. In order to realize this, the material, shape, size, and the like of each light emitting element can be determined in advance by experiments or the like.

<Embodiment 2>
In the first embodiment, the configuration example in which the light emitting element 61 and the light emitting element 62 have the same shape and the same size is described. However, in the second embodiment, the size of the light emitting element 62 is larger than that of the light emitting element 61. This is different from the first embodiment in this respect. Hereinafter, in order to avoid duplication of description, the description of the same contents as those of Embodiment 1 is omitted, and the same components are denoted by the same reference numerals.

FIG. 11A is an enlarged schematic plan view showing a part of the TFT substrate 30 having the configuration according to the second embodiment, and FIG. 11B is a line FF ′ shown in FIG. FIG.
As shown in FIG. 11A, each of the plurality of light source units 21 includes four light emitting elements 61 and one second light emitting element 61.

Each of the four light emitting elements 61 has the same shape and the same size.
The light-emitting element 62 has the same shape as the light-emitting element 61, but is larger than the light-emitting element 61. Here, the area is larger in plan view.
The reason why the area of the light-emitting element 62 is larger than that of the light-emitting element 61 is that the current of the light-emitting element 62 is larger than that of the light-emitting element 61 compared to the case of the same size. This is to reduce the current density.

That is, when a circuit configuration in which one light emitting element 62 is associated with a plurality of light emitting elements 61 is used, the light emitting element 62 includes a drive current for each light emitting element 61 when all of the plurality of light emitting elements 61 are simultaneously turned off. The total current flows as the maximum current.
Both the light-emitting element 61 and the light-emitting element 62 have a characteristic that the lifetime is likely to be shortened when the thermal load or the like due to current supply increases as described above. It tends to end up reaching the end of its life.

In order to prevent the light emitting element 62 from reaching the end of its life as early as possible, a burden such as a thermal load applied to the light emitting element 62 may be reduced as much as possible.
Since the thermal load of the light emitting element 62 increases as the amount of current (current density) per unit area increases, the current density can be reduced as much as possible to reduce the thermal load. If the maximum current is constant, the area of the light emitting element 62 may be increased.

Thus, in the present embodiment, the area in plan view is made larger than that of the light emitting element 61 so that the volume of the light emitting element 62 is larger than that of the light emitting element 61.
Also in the present embodiment, as in the configuration example of FIG. 8 described above, the drive unit forming region 55c and the light emitting element forming region 21g that are long in the main scanning direction are adjacent to each other in the sub scanning direction. .
Each drive circuit 56 provided in the drive portion formation region 55c includes a plurality of light emitting elements 61 and four light emitting elements 62 constituting the four element rows 21a to 21d provided in the light emitting element formation region 21g. Each is configured to supply a drive current.

In order to correspond to this configuration, the wiring layer 160 has a three-layer structure of a first wiring layer 161, a second wiring layer 162, and a third wiring layer 163 as shown in FIG.
The first wiring layer 161 is provided with a lead wiring 92 for each of the plurality of light emitting elements 62, and the second wiring layer 162 is provided with a lead wiring 91 for each of the plurality of light emitting elements 61, and the third wiring layer. A light shielding member 65 is provided at 163.

As described above, the number of light emitting elements 61 corresponding to one light emitting element 62 (the number to be shared) is increased. In this case, the number of light emitting elements 62 provided on the TFT substrate 30 is increased to four. The lifetime of the light-emitting element 62 can be extended by making the light-emitting element 62 larger than the light-emitting element 61 while reducing the manufacturing cost.
Note that, as a method for reducing the current density of the light emitting element 62, the configuration in which the light emitting element 61 and the light emitting element 62 have the same shape in plan view and the area of the light emitting element 62 is larger than the area of the light emitting element 61 has been described above. However, it is not limited to this.

  For example, as shown in FIG. 12, the light emitting element 61 may have a circular shape while the light emitting element 62 has an elliptical shape in plan view. The configuration in which the shapes of the light emitting element 61 and the light emitting element 62 are different increases the degree of design freedom, and the light emitting element 62 can be provided using a space on the TFT substrate 30 where the light emitting element 61 is not provided. It is possible to reduce the size of the TFT substrate 30 by suppressing an increase in panel size such as increasing the area of the TFT substrate 30 in order to provide the element 62.

  Further, the shape in plan view is not limited to an elliptical shape, and other shapes, for example, an elongated shape may be used. Forming the light-emitting element 62 in an elliptical shape or a long shape can be realized by performing a process such as patterning of a predetermined shape at the time of manufacturing the TFT substrate 30, as in the case of forming a circular shape. Needless to say, the shape of the light blocking member 65 needs to be a shape that can block the light emitted from the light emitting element 62 in accordance with the shape of the light emitting element 62.

In the above, the configuration example in which the area of the light emitting element 62 in plan view is increased to reduce the current density of the current flowing through the light emitting element 62 has been described, but the present invention is not limited thereto.
For example, although the area in plan view is the same as that of the light emitting element 61, the thickness of the light emitting element 62 may be larger than that of the light emitting element 61 in the thickness direction of the TFT substrate 30. Further, both the area and the thickness may be increased.

If the size of the light emitting element 62 is increased in this way, the current density of the current flowing through the second light emitting element can be reduced as much as the maximum value of the supplied drive current is the same. Thus, it is possible to reduce a load applied to the light emitting element 62 such as a thermal load caused by a current flowing through the light emitting element 62, thereby extending the life of the light emitting element 62.
Further, instead of making the size of the light emitting element 62 larger than that of the light emitting element 61, for example, a configuration in which the light emitting element 62 has a rated current larger than that of the light emitting element 61 can be used.

  FIG. 13 is a graph showing the relationship between the life of the light emitting element and the rated drive current. For example, a light emitting element with a rated drive current of I1 has a life of Z1, while light emission with a rated drive current of I2 (> I1). It shows that the lifetime of the element extends to Z2 (> Z1). From this graph, it can be seen that the light emitting element has a characteristic that the life is longer as the rated drive current is larger. This is because it is considered that the larger the rated drive current is, the greater the margin for thermal load such as heat resistance, and the longer the life is likely to be delayed due to the progress of deterioration.

Therefore, for example, by using the light emitting element 61 having a rated drive current of I1 and the light emitting element 62 having a rated drive current of I2, the light emitting element 62 having a maximum supply current larger than that of the light emitting element 61 is used. Can be prevented from reaching the end of its life early. Note that the magnitude of the rated current can be adjusted by, for example, the forming material or thickness of the light emitting element.
<Modification>
As described above, the present invention has been described based on the embodiment. However, it is needless to say that the present invention is not limited to the above-described embodiment, and the following modifications may be considered.

(1) In the above embodiment, a plurality of element rows 21a to 21d in which two or more light emitting elements 61 are arranged in a line along the main scanning direction are arranged so as to be adjacent to each other in the sub scanning direction in plan view. Although the example of a structure which demonstrated was demonstrated, it is not restricted to this. For example, a configuration in which only one element row is provided may be employed.
(2) In the above embodiment, the light shielding member 65 is made of a metal film, but is not limited thereto.

For example, an existing wiring provided on the TFT substrate 30, specifically, a power supply line 71 for supplying a current to each driving circuit 56 or a lead-out wiring 91 for supplying a current to each light emitting element 61 is shielded. A configuration can also be used as 65.
Specifically, for the lead-out wiring 91 provided in the wiring layer 162 shown in FIG. 6B, a portion having a light-shielding property and a portion located immediately below the light emitting element 62 is widened, and the widened portion is provided. Thus, a configuration in which light from the light emitting element 62 is blocked is conceivable.

  When the light extraction surface 35 of the TFT substrate 30 is viewed from the photoconductor side, the wiring method, the wiring width and thickness, the wiring and each light emission so that each light emitting element 62 is hidden behind the light shielding wiring. This can be realized by preliminarily determining the relative positional relationship and size relationship with the element 62 through experiments. In this way, wiring such as the power supply line 71 originally formed in the manufacturing process of the OLED panel 20 can also be used as a light shielding member, so that it is possible to reduce manufacturing effort and cost.

  Here, the above-mentioned photoconductor side corresponds to the light extraction surface 35 side in the embodiment, and when the optical writing device 123 is mounted on the image forming apparatus 1, the photoconductor side with respect to the optical writing device 123. In the case of a single unit that is not yet mounted, it means the side on which the photoconductor is positioned with respect to the optical writing device 123 when it is assumed that it is mounted. Further, when viewed from the photosensitive member side, it can be rephrased as viewed from the direction opposite to the traveling direction of the light beam emitted from the light emitting element.

The light shielding member 65 can be formed of a material other than metal (such as resin) as long as it has a light shielding property. If possible, the light shielding member 65 is replaced with a configuration in which the light shielding member 65 is provided in the wiring layer. For example, there may be a configuration in which the light emitting element 62 is provided at the light beam exit or on the surface 35 of the glass substrate 140.
(3) In the above embodiment, one light source is formed by (N + 1) light-emitting elements including N (two or more) light-emitting elements 61 and one light-emitting element 62 constituting one light-emitting element group. As an example of configuring the unit 21, the case where N = 2 in FIG. 10, N = 3 in FIG. 8, and N = 4 in FIGS. 6 and 11 has been described, but is not limited thereto.

There may be a plurality of values of N, for example, 5 or more. Furthermore, if the value of N is a value indicating the total number of the plurality of light emitting elements 61 formed on the substrate 30 if possible, all the light emitting elements 61 share one light emitting element 62. Also good.
The arrangement of the light emitting element 61 and the light emitting element 62 on the substrate 30 can also be expressed as follows.

For example, in FIG. 11A, among the plurality of light emitting elements 61 constituting the element row 21d closest to the drive unit formation region 55c in plan view, the other light emitting elements 61 adjacent to each other in the main scanning direction In this arrangement, three lead wires 91 corresponding to three light emitting elements 61 among the plurality of light emitting elements 61 constituting 21a to 21c in this case pass.
One light source 61 and one light emitting element 62 in each of the element rows 21a to 21d constitute one light source unit 21. In this case, the number N of light emitting elements 61 included in one light source unit 21 is four.

  On the other hand, in the example shown in FIG. 10, one light emitting element in another element row 21 c is disposed between two light emitting elements 61 adjacent in the main scanning direction in the element row 21 d closest to the drive unit formation region 55 b in plan view. One lead-out wiring 91 corresponding to 61 passes through, and one light-emitting element 61 and one light-emitting element 62 in each of the element rows 21c and 21d constitute one light source unit 21. In this case, the number N of light emitting elements 61 included in one light source unit 21 is 2.

  In the example shown in FIG. 8A, two element rows 21m and 21n are disposed between two light emitting elements 61 adjacent to each other in the main scanning direction in the element row 21p closest to the drive unit formation region 55c in plan view. Two lead-out wirings 91 corresponding to the light emitting elements 61 pass through, and one light source section 21 includes one light emitting element 61 and one light emitting element 62 in each of the element rows 21m, 21n, and 21p. It is configured. In this case, the number N of light emitting elements 61 included in one light source unit 21 is three.

  That is, between the two light emitting elements 61 adjacent to each other in the main scanning direction in the element row closest to the drive unit forming region 55a (or 55b, 55c), the light emitting elements 61 constituting the other element rows are seen in plan view. When the number of lead wirings to be passed is P, the number N of the plurality of light emitting elements 61 included in one light source unit 21 is expressed as [(P + 1) × M] (where M is a positive integer). can do.

8 shows a configuration example (N = 3) when P = 2 and M = 1, and FIG. 10 shows a configuration example (N = 2) when P = 1 and M = 1. Is a configuration example (N = 4) when P = 3 and M = 1. FIG. 6 shows a configuration example (N = 4) in the case of P = 1 and M = 2.
Even if the value of N is 4, the arrangement (layout) of the light-emitting elements 61 and 62 is different when the value of P is 1 as shown in FIG. 6 and when the value of P is 3 as shown in FIG. Since it changes, it becomes possible to make the arrangement of the light emitting elements more suitable by determining a combination of values of P and M suitable for the apparatus configuration by experiments or the like.

(4) In the above embodiment, a plurality of light source sections 21 including N (plurality) light emitting elements 61 and one light emitting element 62 are provided, and the number of light emitting elements 61 included in each light source section 21 is provided. However, the present invention is not limited to this. For example, the light source unit 21 may have a different N value.
(5) In the above embodiment, a configuration example of a so-called bottom emission type (bottom emission type) in which the light beam L emitted from the light emitting element 61 passes through the wiring layer 160 and the glass substrate 140 toward the photosensitive drum 121. However, the present invention is not limited to this.

For example, the light emitting layer 150 and the transmissive wiring layer 160 are laminated on the glass substrate 140 in this order, and the light beam L emitted from the light emitting element 61 of the light emitting layer 150 passes through the wiring layer 160 and is a photosensitive drum. A configuration toward 121 can also be assumed.
(6) In the above-described embodiment, the configuration example using the organic LED (OLED) as the light emitting element has been described. However, the configuration is not limited thereto, and for example, an LED may be used. Each of the plurality of drive circuits 56 provided between each light emitting element 61 and one power supply line 71 connected to the constant voltage source 70 is composed of an FET. Other types of circuits may be employed as long as they can be executed.

Furthermore, although the example which uses the glass substrate 140 as a base material for arrange | positioning a light emitting element and wiring was demonstrated, as a base material, what is necessary is just what a light emitting element and wiring are arrange | positioned on it, for example other than glass These materials can also be used as a base material.
(7) In the above embodiment, the configuration example in which the optical writing device is used in the color multifunction peripheral has been described, but the present invention is not limited to this. For example, the present invention is applied to an image forming apparatus such as a copying machine or a printer having a photosensitive member such as a photosensitive drum 121 in which an image such as an electrostatic latent image is written by a light beam from an optical writing unit, and an optical writing device used therefor. it can. Further, the present invention is not limited to an image forming apparatus, and can be applied to a general apparatus that writes on a photosensitive member with a light beam. In this case, for example, a plurality of element rows in which two or more light emitting elements 61 are arranged in a line along the first direction are arranged so as to be adjacent to each other in the second direction orthogonal to the first direction. You can also.

  Further, the contents of the above embodiment and the above modification may be combined as much as possible.

  The present invention can be widely applied to an optical writing device and an image forming apparatus including the same.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 21 Light source part 21a, 21b, 21c, 21d, 21e, 21f, 21m, 21n, 21p
Element array 21g Light emitting element formation region 30 TFT substrate 35a Light extraction surface 42 VIDEO circuit (switching circuit)
55 Drive part 55a, 55b, 55c Drive part formation area 56 Drive circuit 57 Switch (switching circuit)
61 Light emitting element (first light emitting element)
62 Light emitting element (second light emitting element)
65 Light-shielding member 71 Power supply line 91, 92 Lead-out wiring 112 Control unit 121 Photosensitive drum 123 Optical writing device

Claims (11)

An optical writing device that selects and emits some of the plurality of first light emitting elements for each optical writing timing, and writes on the photosensitive member by the light beam,
One second light emitting element provided corresponding to a light emitting element group consisting of at least two or more first light emitting elements among the plurality of first light emitting elements;
A light shielding member that shields a light beam emitted from the second light emitting element and directed to the photosensitive member;
Provided between each of the first light emitting elements included in the light emitting element group and one power supply line, and controls the current from the power supply line to output a current to be supplied to the corresponding first light emitting element. A driving circuit to
At each optical writing timing, among the first light emitting elements included in the light emitting element group, the output current of the corresponding driving circuit is supplied to each of the first light emitting elements that perform optical writing, while optical writing is performed. For each of the remaining first light emitting elements, the supply of the output current of the corresponding driving circuit is cut off, and instead, the total current of the output currents of the respective driving circuits is supplied to the second light emitting element. A switching circuit for switching the supply destination of the output current of each driving circuit;
An optical writing device comprising: A substrate having a light emitting element formation region in which the plurality of first light emitting elements and the one or more second light emitting elements are provided;
In the light emitting element formation region,
A plurality of element rows in which the respective first light emitting elements are arranged in a line along the first direction are provided so as to be adjacent to each other in a second direction orthogonal to the first direction,
The first light-emitting elements constituting the two adjacent element rows are arranged in a staggered manner in which the positions in the first direction are alternately shifted in a plan view of the substrate. The optical writing device according to claim 1. The substrate further includes:
A drive portion forming region provided with the plurality of drive circuits, and a lead-out wiring for receiving the output current of the corresponding drive circuit for each of the first light emitting elements;
The light emitting element formation region and the drive part formation region have a positional relationship that is elongated along the first direction and adjacent to the second direction in a plan view of the substrate,
Each of the lead-out wirings extends from the drive unit formation region to each first light-emitting element in the light-emitting element formation region,
Among the two or more first light emitting elements constituting the element row closest to the drive unit formation region, another element row is arranged between the two first light emitting elements adjacent in the first direction in the plan view. In the case of a configuration in which P lead-out lines corresponding to the first light emitting element to be configured are passed,
3. The optical writing device according to claim 2, wherein the number N of the first light emitting elements constituting the one light emitting element group is [(P + 1) × M] (where M is a positive integer). . The second light emitting element includes:
4. The optical writing device according to claim 1, wherein a current density is smaller when a current of the same magnitude flows than the first light emitting element. 5. The second light emitting element includes:
The optical writing device according to claim 4, wherein the area of the first light emitting element is larger than that of the first light emitting element.   6. The optical writing device according to claim 4, wherein the first light emitting element and the second light emitting element have different shapes.   The optical writing device according to claim 1, wherein the second light emitting element has a rated current larger than that of the first light emitting element. A light-shielding wiring for supplying a current to each driving circuit or each first light-emitting element;
The light shielding member is the wiring;
8. The optical writing device according to claim 1, wherein when viewed from the photosensitive member side, all the second light emitting elements are hidden behind the wiring. 9.   9. The optical writing device according to claim 1, wherein each of the first light emitting elements has the same shape and size and is made of the same material.   The optical writing device according to claim 1, wherein each of the first light emitting element and the second light emitting element is an organic LED. An image forming apparatus for writing an image on a photosensitive member by a light beam from an optical writing unit,
An image forming apparatus comprising the optical writing device according to claim 1 as the optical writing unit.

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