JP6435928B2 - Optical writing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical writing apparatus and an image forming apparatus, and more particularly to a technique for realizing high image quality by suppressing unevenness in light quantity during job execution in an optical writing apparatus using an OLED.

In recent years, in the field of image forming apparatuses, application of OLEDs (Organic Light Emitting Diodes) as light emitting elements has been studied in order to reduce the cost of optical writing apparatuses.
The OLED has a characteristic that the light emission efficiency decreases due to deterioration over time. For this reason, for example, a technique for boosting the drive voltage supplied to the OLED when the drive time of the OLED exceeds a certain time has been proposed (see, for example, Patent Document 1). In this way, even if the OLED deteriorates with time, the OLED can emit light stably at a desired light emission amount, so that deterioration of image quality can be prevented.

JP 2005-329634 A

However, if the OLED drive time exceeds a certain time during the execution of the print job, the drive voltage cannot be increased during the execution of the print job, so the light emission amount decreases until the print job is completed. Will continue to do. In particular, when a print job with a large number of printed sheets is executed, there is a possibility that the driving time of the OLED becomes long and the emission amount is significantly reduced.
Also, the drive time may differ between OLEDs for each print job. For example, the OLED driven on the previous page has a significantly reduced light emission, while the OLED driven only on the last page does not decrease the light emission so much, so that the light amount difference between the OLEDs becomes large. In such a case, uneven stripes occur, and the deterioration of image quality becomes particularly significant.

  The present invention has been made in view of the above-described problems, and provides an optical writing apparatus and an image forming apparatus that realize excellent image quality by suppressing a decrease in light amount during execution of a print job. Objective.

  In order to achieve the above object, the optical writing device according to the present invention increases the driving current amount of the light emitting element every time the cumulative light emission time reaches a preset threshold value for each light emitting element. A writing device, for each job, determination means for determining whether or not the threshold is reached during the execution period of the job, and for each light emitting element determined by the determination means to reach the threshold In place of the threshold value, current control means for performing control to increase the drive current of the light emitting element before the start of the job or after the completion of the job according to the threshold time and the light emission time of the light emitting element during the execution period; It is characterized by providing.

  In this way, if the threshold is present during the job execution period, the drive current is set at the start of the job or at the completion of the job according to the light emission time of the light emitting element during the execution period instead of the threshold. Therefore, even when a job with a large number of printed sheets is executed, high image quality can be realized.

1 is a diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. 6 is a cross-sectional view illustrating an optical writing operation by the optical writing device 100. FIG. It is a schematic plan view of the OLED panel part 200, and the sectional view in the AA 'line and the sectional view in the CC' line are also shown. 2 is a block diagram showing a main configuration of a TFT substrate 300. FIG. FIG. 3 is a circuit diagram showing main configurations of a selection circuit 401 and a light emitting block 402. 3 is a block diagram illustrating a main hardware configuration of a control unit 102. FIG. 3 is a block diagram illustrating a main functional configuration of a control unit 102. FIG. 3 is a flowchart showing the operation of a control unit 102. It is a graph which illustrates transition of drive current amount I concerning a prior art. It is a graph which illustrates the error from the ideal amount of the drive current amount I which can occur in the prior art. It is a graph which illustrates transition of drive current amount I concerning an embodiment of the invention. It is a table | surface which illustrates the current increase timing which concerns on embodiment of this invention. 13 is a graph showing an execution period of the job illustrated in FIG. It is a graph which illustrates transition of the actual electric current amount in which the error from the ideal electric current amount can be accumulated. It is a block diagram which shows the main function structures of the control part 102 which concerns on the modification of this invention. It is a flowchart showing operation | movement of the control part 102 which concerns on the modification of this invention. 6 is a graph illustrating a case where a current increase timing is corrected every time a print job is executed three times. It is a graph which illustrates transition of drive current amount I when current increase timing is carried up at the time of a job start. It is a graph which illustrates transition of drive current amount I concerning a modification of the present invention. It is a flowchart showing the characteristic operation | movement of the control part 102 which concerns on the modification of this invention.

Embodiments of an optical writing device and an image forming apparatus according to the present invention will be described below with reference to the drawings.
[1] Configuration of Image Forming Apparatus FIG. 1 is a diagram illustrating a main configuration of an image forming apparatus according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 is a so-called tandem color printer. The image forming units 101 </ b> Y to 101 </ b> K included in the image forming apparatus 1 form toner images of Y (yellow), M (magenta), C (cyan), and K (black) colors under the control of the control unit 102.

  For example, in the image forming unit 101Y, the charging device 111 uniformly charges the outer peripheral surface of the photosensitive drum 110. As will be described later, the optical writing device 100 includes light emitting elements (OLEDs) arranged in a line in the main scanning direction, and causes each OLED to emit light according to the digital luminance signal generated by the control unit 102. As a result, optical writing is performed on the outer peripheral surface of the photosensitive drum 110, and an electrostatic latent image is formed.

The developing device 112 supplies toner to the outer peripheral surface of the photosensitive drum 110 to develop (develop) the electrostatic latent image. The primary transfer roller 113 electrostatically transfers (primary transfer) the toner image from the photosensitive drum 110 to the intermediate transfer belt 103.
In this way, the YMCK color toner images formed by the image forming units 101Y to 101K are primarily transferred onto the intermediate transfer belt 103 at a timing so as to overlap each other, and become a color toner image. As the intermediate transfer belt 103 conveys the color toner image to the secondary transfer roller pair 104, the recording sheet S supplied from the paper feed cassette 105 is also conveyed to the secondary transfer roller pair 104.

The secondary transfer roller pair 104 electrostatically transfers (secondary transfer) the toner image on the intermediate transfer belt 103 onto the recording sheet S. The recording sheet S to which the toner image has been transferred is thermally fixed on the toner image by the fixing device 106 and then discharged outside the apparatus.
Note that the optical writing device 100 performs optical writing not only when a print job is executed, but also when executing an image stabilization process, for example.

[2] Configuration of Optical Writing Device 100 Next, the configuration of the optical writing device 100 will be described.
As shown in FIG. 2, the optical writing device 100 includes an OLED panel 200 and a rod lens array (SLA: Selfoc Lens Array; registered trademark of Nippon Sheet Glass) 202 accommodated in a holder 203. Is mounted with an OLED 201. The light beam L emitted from the OLED 201 is condensed on the outer peripheral surface of the photosensitive drum 110 by the rod lens array 202. Note that an MLA (Micro Lens Array) may be used instead of the SLA. Further, illustrations of cables and the like for connecting to necessary portions of the image forming apparatus 1 are omitted.

FIG. 3 is a schematic plan view of the OLED panel 200, and a cross-sectional view taken along the line BB ′ and a cross-sectional view taken along the line CC ′ are also shown. The schematic plan view shows a state in which a sealing plate 301 described later is removed.
As shown in FIG. 3, the OLED panel 200 includes a TFT (Thin Film Transistor) substrate 300, a sealing plate 301, a driver IC (Integrated Circuit) 302, and the like. On the TFT substrate 300, a large number of OLEDs 201 are arranged in a line along the main scanning direction. These OLEDs 201 may be arranged in a line or in a staggered arrangement.

  The substrate surface of the TFT substrate 300 on which the OLED 201 is disposed serves as a sealing region, and the sealing plate 301 is attached with the spacer frame 303 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 outside air. In order to absorb moisture, a hygroscopic agent may be enclosed in the sealing region. Further, the sealing plate 301 may be, for example, sealing glass or may be made of a material other than glass.

A driver IC 302 is mounted outside the sealing region of the TFT substrate 300. The control unit 102 inputs a digital luminance signal to the driver IC 302 via the flexible wire 310. The control unit 102 incorporates a dedicated ASIC (Application Specific Integrated Circuit) for generating a digital luminance signal.
The driver IC 302 converts the digital luminance signal into an analog luminance signal (hereinafter simply referred to as “luminance signal”) and inputs it to the driving circuit for each OLED 201. The drive circuit generates a drive current for the OLED 201 in accordance with the luminance signal. The luminance signal may be a current signal or a voltage signal.

  As shown in FIG. 4, in the TFT substrate 300, 15,000 OLEDs 201 are grouped into 150 light emitting blocks 402 in units of 100. The OLEDs 201 may be arranged in a line at a pitch of 21.2 μm in the main scanning direction, or may be in a staggered arrangement. In addition, 150 DACs 400 are built in the driver IC 302 and correspond to the light emitting blocks 402 on a one-to-one basis. The DAC 400 is a variable voltage source that can be digitally controlled.

  When the driver IC 302 receives a digital luminance signal (image data) from the control unit 102, the input is distributed to each DAC 400 by 100 pixels for each scanning period. A selection circuit 401 is disposed on each circuit from the DAC 400 toward the light emitting block. Each DAC 400 sequentially outputs luminance signals to the subordinate 100 OLEDs 201 by so-called rolling driving.

  FIG. 5 is a circuit diagram showing a pair of selection circuit 401 and light emitting block 402. As shown in FIG. 5, the light emitting block 402 includes 100 light emitting pixel circuits, and each light emitting pixel circuit has a capacitor 521, a driving TFT 522, and an OLED 201. The selection circuit 401 includes a shift register 511 and 100 selection TFTs 512.

  The shift register 511 is connected to the gate terminal of each of the 100 selection TFTs 512, and sequentially turns on the selection TFTs 512. The source terminal of the selection TFT 512 is connected to the current DAC 400 via the write wiring 530, and the drain terminal is connected to the first terminal of the capacitor 521 and the gate terminal of the OLED driving TFT 522.

When the shift register 511 turns on the selection TFT 512, the output voltage of the DAC 400 is applied to the first terminal of the capacitor 521 and held. The first terminal of the capacitor 521 is also connected to the gate terminal of the driving TFT 522, and the second terminal of the capacitor 521 is connected to the source terminal of the driving TFT 522 and the power supply wiring 531.
The anode terminal of the OLED 201 is connected to the drain terminal of the driving TFT 522, and the cathode terminal of the OLED 201 is connected to the ground wiring 532. The power supply wiring 531 is connected to the constant voltage source Vpwr, and the ground wiring 532 is connected to the ground terminal.

  The constant voltage source Vpwr is a supply source of the drive current supplied to the OLED 201, and the drive TFT 522 supplies the OLED 201 with a drive current corresponding to the voltage held between the first and second terminals of the capacitor 521. To do. For example, when a signal corresponding to H is written to the capacitor 521, the driving TFT 522 is turned on and the OLED 201 emits light. When a signal corresponding to L is written to the capacitor 521, the driving TFT 522 is turned off and the OLED 201 does not emit light.

In this embodiment, the case where the driving TFT 522 is a p-channel is described as an example, but needless to say, an n-channel driving TFT 522 may be used.
[3] Hardware Configuration of Control Unit 102 Next, the hardware configuration of the control unit 102 will be described.

As shown in FIG. 6, the control unit 102 includes a CPU (Central Processing Unit) 601 and a ROM (Read Only Memory) 602.
When the image forming apparatus 1 is powered on, the CPU 601 reads and starts a boot program from the ROM 602, and then reads from a HDD (Hard Disk Drive) 604 using a RAM (Random Access Memory) 603 as a working storage area. A program such as an OS (Operating System) is executed.

  The CPU 601 communicates with other apparatuses using a NIC (Network Interface Card) 605 via a communication network such as a LAN (Local Area Network), and receives a print job. Further, the CPU 601 controls the TFT substrate 300 via the ASIC 606, presents information to the user using an operation panel (Operation Panel) 607, and receives an instruction input.

[4] Functional Configuration of Control Unit 102 Next, a functional configuration of the control unit 102 will be described.
The control unit 102 increases the drive current amount I by a preset current amount ΔI for each predetermined number of times of light emission in accordance with a decrease in light emission efficiency due to deterioration with time of the OLED 201, so that the OLED 201 has a constant irradiance (setting The drive current amount I is controlled so as to emit light with a light amount.

As shown in FIG. 7, the control unit 102 includes a light emission time counting unit 701, a threshold time calculating unit 702, and the like.
The light emission time counting unit 701 counts, for example, the cumulative number of times of light emission of the OLED 201 since the factory shipment of the image forming apparatus 1 as the cumulative light emission time count for each OELD 201. The accumulated light emission time count may be stored in the HDD 604 that is a nonvolatile storage device, or when a writable nonvolatile semiconductor memory is mounted on the control unit 102, the accumulated light emission time is stored in the semiconductor memory. You may memorize count.

The threshold time calculation unit 702 calculates a threshold time Th that is a light emission time during which the drive current amount I of the OLED 201 should be increased. Instead of calculating the threshold time Th, all the threshold times Th may be stored in advance, and an appropriate threshold time Th may be selected from the stored threshold times Th.
Advance time calculation unit 703 calculates the advance time T _adv obtained by subtracting the threshold time Th from the cumulative emission time count before starting a print job for each OLED201.

Completion time calculation unit 704 adds cumulative light emission time (for example, the number of times of light emission) necessary for executing the print job to cumulative light emission time count at the start of the job (hereinafter, “job completion time”). that.) the T _job is calculated for each OLED201.
The delay time calculation unit 706 calculates a delay time T _pst obtained by subtracting the threshold time Th from the job completion time T _{job for} each OLED 201.

The change necessity determination unit 705 confirms, for each OLED 201, whether or not the cumulative light emission time reaches the threshold time Th during the execution period of the print job, thereby increasing the drive current amount I of the OLED 201 (hereinafter, referred to as “the change time”). , “Current increase timing”) is determined. When the threshold time Th is reached during the execution period of the print job, the carry time T _adv and the carry time T _pst are different in sign, and in this embodiment, the carry time T _adv and the carry time T _pst are This is determined by whether the sign of the product of is positive or negative.

The timing determination unit 707 compares the carry time T _adv and the carry time T _{pst for} each OLED 201 and selects the one having the smaller absolute value. Thus, it is determined whether the current increase timing is before the start of the print job or after the completion.
The drive current amount control unit 708 increases the drive current amount I for each OLED 201 at the current increase timing according to the determination of the timing determination unit 707. Therefore, even in the same print job, the current increase timing may be different for each OLED 201.

[5] Operation of Control Unit 102 Next, the operation of the control unit 102 will be described.
As shown in FIG. 8, the control unit 102 initializes the accumulated light emission time count to 0 in the light emission time counting unit 701 at the time of factory shipment (S801). Thereafter, when executing a new print job (S802: YES), first, the completion time calculation unit 704 calculates the job completion time _Tjob (S803). The job completion time T _job for each OLED 201 is calculated by first calculating a light emission time for causing the OLED 201 to emit light in order to execute the print job, and adding the obtained light emission time to the cumulative light emission time count.

  Next, the threshold time calculation unit 702 calculates the threshold time Th for each OLED 201 using Expression (1) (S804).

ここで、［・］はガウス記号であって、記号内の数値の整数部分を表している。従って、上式は、累積発光時間ｃｏｕｎｔを、駆動電流量Ｉを増加させる周期ｐｅｒｉｏｄで割った値の整数部分に１を加算して、更に電流増加周期ｐｅｒｉｏｄを乗算することによって閾値時間Ｔｈを求めるようになっている。

Here, [•] is a Gaussian symbol and represents the integer part of the numerical value in the symbol. Therefore, in the above expression, the threshold time Th is obtained by adding 1 to the integer part of the value obtained by dividing the accumulated light emission time count by the period period for increasing the drive current amount I and further multiplying by the current increase period period. It is like that.

For example, when the value of the current increase period period is 100, the threshold time Th is 100 if the cumulative light emission time count is in the range from 0 to 99, and the cumulative light emission time count is from 100 to 199. The threshold time Th is 200.
In the present embodiment, the threshold time Th is calculated using only the accumulated light emission time count and the current increase period period regardless of whether or not the drive current amount I is increased at a current increase timing other than the threshold time Th. Is done.

Advance time calculation unit 703 calculates the cumulative emission time count from subtracting the threshold time Th advance time T _adv as in Equation (2) (S805).

繰下げ時間算出部７０６は、式（３）のようにジョブ完了時間Ｔ_jobから閾値時間Ｔｈを差し引いて繰下げ時間Ｔ_pstを算出する（Ｓ８０６）。

The deferral time calculation unit 706 calculates the deferral time T _pst by subtracting the threshold time Th from the job completion time T _job as shown in Expression (3) (S806).

変更要否判定部７０５は、累積発光時間が当該印刷ジョブの実行期間中に閾値時間Ｔｈに達するかを、繰上げ時間Ｔ_advと繰下げ時間Ｔ_pstとの積の符号から判定する。具体的には、当該符号が正である場合には（Ｓ８０７：ＮＯ）、累積発光時間が当該印刷ジョブの実行期間中に閾値時間Ｔｈに達しないと判断されるので、そのまま印刷ジョブを実行し（Ｓ８１１）、印刷ジョブが完了したら（Ｓ８１２：ＹＥＳ）、ジョブ完了時間Ｔ_jobを新たな累積発光時間ｃｏｕｎｔとする（Ｓ８３０）。

Change necessity determination unit 705 determines whether the cumulative emission time reaches the threshold time Th during execution of the print job, from the sign of the product of the time T _pst deferred and advance time T _adv. Specifically, when the sign is positive (S807: NO), it is determined that the accumulated light emission time does not reach the threshold time Th during the execution period of the print job, so the print job is executed as it is. (S811) When the print job is completed (S812: YES), the job completion time _Tjob is set as a new accumulated light emission time count (S830).

If the sign is negative (S807: YES), the carry time T _adv and the carry time T _pst are compared to determine which absolute value is smaller.
When the advance time _Tadv has a smaller absolute value (S808: YES), the drive current amount I is immediately increased (S810), and the print job is executed (S811). Thereafter, when the print job is completed (S812: YES), the job completion time _Tjob is set as a new accumulated light emission time count (S830).

Otherwise (S808: NO), the print job is immediately started (S820). Thereafter, when the print job is completed (S821: YES), the drive current amount I is increased (S822), and the job completion time _Tjob is set as a new accumulated light emission time count (S830).
When the accumulated light emission time count is updated, the process proceeds to step S802 and the above processing is repeated.

[6] Comparison with Prior Art Next, the effect of the present invention will be described by comparing with the prior art.
(1) Prior Art First, the prior art will be described by taking as an example a case where the current increase period period is 100 light emission times.

In the prior art, as shown in FIG. 9, the driving current amount I is increased by a preset current amount ΔI as shown by a solid line graph 901 every 100 times of light emission,
The light intensity is corrected. On the other hand, the drive current amount I for causing the OLED 201 to emit light with the set light amount increases in proportion to the light emission time as indicated by a dotted line graph 902.

In order to minimize the absolute value of the difference between the graphs 901 and 902, in FIG. 9, the integrated value (for example, area 911) of the current amount difference during the period when the graph 901 falls below the graph 902 is shown, and the graph 901 is the graph 902. The drive current amount I is controlled so as to be equal to the integrated value (for example, area 912) of the current amount difference in a period exceeding the period.
If such control is performed in parallel with the execution of the print job, every time one line is scanned, all 15,000 OLEDs 201 must be individually controlled, and the drive current amount I is controlled. Therefore, it is practical to control the drive current amount I only between jobs.

  However, when the conventional technology is applied as it is, when the current increase timing is reached during execution of the print job, the drive current amount I is increased after the print job is completed, so that the current increase timing is set as shown in FIG. After the elapse, the drive current amount I is maintained without being increased until the print job is completed. For this reason, unevenness occurs due to an insufficient amount of light emitted from the OLED 201, and the image quality deteriorates.

(2) On the other hand this embodiment, in the present embodiment, when the absolute value than it is deferred time T _pst of advance time T _adv is small, increases the amount of drive current I at the beginning of the print job. For example, as shown in FIG. 11, when the absolute value than it is deferred time T _pst of advance time T _adv is small, advancing the current increase timing at the start of the print job. In this way, compared to the case where the drive current amount I is increased after the print job is completed, the drive current amount I (graph 1101) and the drive current amount (graph 1102) for causing the OLED 201 to emit light with the set light amount. Therefore, the image quality can be prevented from deteriorating.

FIG. 12 is a table showing examples of print jobs executed at various timings and determining whether or not light amount correction is necessary, and FIG. 13 is a graph illustrating print jobs a to c. All of the print jobs a to c are executed in the cumulative light emission period in which the threshold time Th is close to 300 times.
As shown in FIG. 12A, the print job a is deferred because the accumulated light emission time at the start is 290 times, the advance time _Tadv is -10 times, and the accumulated light emission time at the completion is 350 times. Time T _pst is 50 times. Therefore, since the sign of the product of the carry time T _adv and the carry time T _pst is negative and the carry time T _adv has a smaller absolute value, the drive current amount I is increased at the start.

In print job b, as shown in FIG. 12B, the accumulated light emission time at the start is 250 times, so the advance time _Tadv is -50 times, and the accumulated light emission time at the completion is 310 times, so it is decremented. Time T _pst is 10 times. Therefore, since the sign of the product of the carry time T _adv and the carry time T _pst is negative and the carry time T _pst has a smaller absolute value, the drive current amount I is increased upon completion.

Furthermore, in print job c, as shown in FIG. 12C, the accumulated light emission time at the start is 230 times, so that the advance time _Tadv is -70 times, and the accumulated light emission time at the completion is 290 times. Therefore, the reduction time T _pst becomes −10 times. Therefore, since the sign of the product of the carry time T _adv and the carry time T _pst is positive, the drive current amount I is increased according to the threshold time Th, not at the start time or at the completion time.

[7] Modifications As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and the following modifications can be implemented. .
(1) In the above embodiment, the threshold time Th is determined using only the accumulated light emission time count and the current increase period period regardless of whether or not the drive current amount I is increased at a current increase timing other than the threshold time Th. The case where it is calculated has been described as an example.

  When the drive current amount I is increased at a current increase timing other than the threshold time Th and then the drive current amount I is increased for each period from the current increase timing, as illustrated in FIG. Error of the actual drive current amount (hereinafter referred to as “actual amount”) 1402 with respect to an ideal drive current amount (hereinafter referred to as “ideal amount”) 1401 that emits light with the set light amount.

As for this deviation, the shaded areas 1411, 1413 and 1415 having a smaller actual amount 1402 than the ideal amount 1401 have a larger area than the shaded areas 1412 and 1414 having a larger actual amount 1402 than the ideal amount 1401. It is clear from that. For this reason, the moving average of the actual amount 1402 deviates from the ideal amount 1401.
On the other hand, according to the above-described embodiment, as shown in the shaded areas 1111 to 1113 in FIG. Therefore, compared with the case of FIG. 14, the moving average of the actual amount 1101 is closer to the ideal amount 1102 in FIG.

The OLED 201 has a characteristic that the light emission efficiency decreases faster as the drive current amount increases. For this reason, as the actual amount deviates from the ideal amount, the deterioration rate of the OLED 201 deviates from the deterioration rate in the ideal amount. For this reason, even if the drive current amount I is increased by the increase amount ΔI set assuming the ideal amount, the OLED 201 may not be able to emit light with the set light amount.

Therefore, according to the above embodiment, it is possible to control the light emission amount of the OLED 201 with higher accuracy than in the case of determining the current increase timing as shown in FIG.
However, if the current increase timing is raised or lowered by execution of the print job, there is a difference between the actual amount and the ideal amount at that time. If such a difference accumulates, there is a risk that the accuracy of the amount of emitted light may also decrease.

Since the OLED has a characteristic that the light emission efficiency decreases quickly as the drive current amount increases, if the difference between the ideal amount and the actual amount occurs, the decrease rate of the light emission efficiency deviates from the decrease rate of the ideal amount. In such a case, the OLED cannot emit light with the set light amount with high accuracy even if the drive current amount I assuming the rate of decrease in the light emission efficiency at the ideal amount is supplied.
In this modification, the following countermeasures can be taken against such a problem.

FIG. 15 is a block diagram illustrating a functional configuration of the control unit 102 according to the present modification. As shown in FIG. 15, the control unit 102 according to this modification includes an integrated time update unit 1501 and a correction time determination unit 1502 in addition to the functions shown in FIG. 7.
Integration time updating unit 1501, a time T _adv accelerated if the current increase timing is at the start of the print job, also integrated time a deferred time T _pst if the current increase timing is at the completion of the print job Add to _Tacm .

The correction time determination unit 1502 determines whether or not the accumulated light emission time obtained by subtracting the accumulated time _Tacm from the threshold time Th is set as a new current increase timing instead of the threshold time Th.
FIG. 16 is a flowchart showing the operation of the control unit 102 according to the present embodiment. The processes common to those in the flowchart of FIG. Also, portions that are not necessary for the description of the present modification are omitted from the processes common to the flowchart of FIG. Hereinafter, description will be made by paying attention to the characteristic processing in this modification.

First, as an initialization process, the accumulated light emission time count is initialized to 0, and the accumulated time update section 1501 initializes the accumulated time _Tacm to 0 (S1601).
If the absolute value of the carry-down time T _pst is smaller than the carry-up time T _adv (S808: YES), the accumulated time update unit 1501 adds the carried time T _adv to the accumulated time _Tacm (S1611). Otherwise (S808: NO), the accumulated time update unit 1501 adds the decrement time T _pst to the accumulated time _Tacm (S1612).

If there is no new print job (S802: NO) and the correction time determination unit 1502 determines that it is the correction time (S1621: YES), the threshold value Th is used instead of the threshold time Th. with increasing amount of drive current I to the cumulative emission time obtained by subtracting the integrated time T _acm from the time Th (S1622), and initializes to 0 the integration time T _acm (S1623).
As described above, when the print job is not executed, the drive current amount I is increased at a current increase timing different from the threshold time Th, and the actual amount and the ideal amount are made to coincide with each other, so that the OLED 201 can be obtained with higher accuracy. Can emit light.

The correction time determination unit 1502 may determine that the correction time has come when the absolute value of the accumulated time T _acm exceeds a predetermined upper limit value, or initialize the accumulated time T _acm to 0 and then _{execute a} print job. If it is executed a predetermined number of times, it may be determined that the correction time has come. Moreover, integration time T _acm may determine that the OLED201 is initialized to 0 becomes the correction timing When light is emitted a predetermined number of times.

FIG. 17 is a graph illustrating a case where the current increase timing is corrected every time the print job is executed three times. In the example of FIG. 17, the current increase timing is incremented by 30 from the threshold time 100 by the execution of the print job to be the cumulative light emission time 70, and is incremented by 20 from the threshold time 200 to be the cumulative light emission time 180. The accumulated light emission time 320 is reduced by 20 times. Therefore, the accumulated time T _acm is

となる。これによって、次の閾値時間４００から積算時間Ｔ_acm（＝−３０）を減算した累積発光時間４３０が次の電流増加タイミングとされる。

It becomes. Thus, the accumulated light emission time 430 obtained by subtracting the accumulated time T _acm (= −30) from the next threshold time 400 is set as the next current increase timing.

In this way, on the graph, the areas 1711 to 1714 where the actual amount exceeds the ideal amount and the areas 1721 to 1724 where the actual amount is less than the ideal amount can be balanced. Therefore, unevenness in the amount of light can be prevented by causing the OLED 201 to emit light with higher accuracy, so that the image quality can be improved.
(2) In the above modification, the case where the deviation between the actual amount of the drive current amount and the ideal amount is eliminated by adjusting the current increase timing has been described, but it goes without saying that the present invention is not limited to this. Instead of or in addition to this, the following may be performed.

  In the case where the threshold time Th is set so as to balance the excess and deficiency of the actual amount with respect to the ideal amount, as illustrated in FIG. The area 1811 in which the actual amount 1802 is insufficient with respect to the amount 1801 is reduced, while the area of the region 1812 in which the actual amount 1802 is excessive with respect to the ideal amount 1801 is increased. For this reason, the balance between the excess and deficiency of the actual amount 1802 with respect to the ideal amount 1801 is broken.

On the other hand, in this modification, as illustrated in FIG. 19, the increase amount ΔI of the drive current amount I at the start of the print job is decreased from the original D ₀ to D ₁ . In this way, the area 1812 of FIG. 18 is reduced to the area 1901 of FIG. Since the actual amount 1802 becomes equal to the area 1901 in which the actual amount 1802 becomes excessive, excess / shortage of the actual amount 1802 with respect to the ideal amount 1801 is balanced.

FIG. 20 is a flowchart illustrating processing added to the flowcharts of FIGS. 8 and 16 in the operation of the control unit 102 according to the present modification. As shown in FIG. 20, in this modification, after the process of step S807, the increase amount ΔI of the drive current amount I is calculated so that the excess and deficiency of the actual amount with respect to the ideal amount is balanced (S2001).
In this way, since the excess or deficiency of the actual amount with respect to the ideal amount can be balanced, the light emission amount of the OLED 201 can be brought closer to the set light amount with higher accuracy. Accordingly, since any OLED 201 can emit light with a light emission amount close to the set light amount, a light amount difference between the OLEDs 201 can be suppressed, and unevenness and the like can be suppressed to achieve high image quality.

  (3) In the above embodiment, the case where the control unit 102 controls the drive current amount I for each OLED 201 has been described. Needless to say, the present invention is not limited to this. The drive current amount I may be controlled in the optical writing device 100 such as the IC 302. The effect of the present invention can be obtained regardless of the device that controls the drive current amount I.

(4) In the above embodiment, the case where the current increase timing of the drive current amount I is raised at the start of the print job or lowered at the completion of the print job has been described as an example. However, it goes without saying that the present invention is not limited to this. Alternatively, the following may be used.
That is, when the current increase timing is advanced, it is not necessary to exactly match at the start of the print job, and it may be increased before the start of the print job. Also, when the current increase timing is deferred, it does not have to coincide exactly when the print job is completed, and the effect of the present invention can be obtained by deferring after the completion of the print job.

Further, in order to determine the current increase timing, although it is best to compare the magnitude of the absolute value of the advance time T _adv a deferred time T _pst as in step S808 of FIG. 8, the present invention Needless to say, the present invention is not limited to this, and the following may be used instead.
That is, a positive number alpha a deferred absolute value to the addition value of the time _{T pst (T pst + α)} , carry is compared with the absolute value of the time T _adv, when advancing greater in absolute value of the time T _adv Alternatively, the current increase timing may be advanced. In this way, the probability of decrementing the current increase timing is increased, and the drive current amount I supplied to the OLED 201 can be suppressed, so that the deterioration rate of the OLED 201 can be suppressed and the power consumption can be suppressed.

  (5) In the above embodiment, the case where the image forming apparatus 1 is a so-called tandem type color printer has been described as an example. However, it is needless to say that the present invention is not limited to this. The present invention may be applied to a monochrome printer. The same effect can be obtained by applying the present invention to a copying machine equipped with a scanner, a facsimile machine equipped with a communication function, and a multi-function peripheral (MFP) equipped with these functions. Can do.

  The optical writing apparatus and the image forming apparatus according to the present invention are useful as an apparatus that uses an OLED to realize high image quality regardless of the number of output sheets for each job.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 100 ... Optical writing apparatus 102 ... Control part 201 ... OLED
701 ... Light emission time counting unit 702 ... Threshold time calculation unit 703 ... Advance time calculation unit 704 ... Completion time calculation unit 705 ... Change necessity determination unit 706 ... Decrease time calculation unit 707 ... Timing determination unit

Claims (12)

An optical writing device that performs optical writing by increasing the drive current amount of the light emitting element each time the accumulated light emission time reaches a preset threshold value for each light emitting element,
Determination means for determining whether the threshold is reached during the execution period of the job for each job;
For each light emitting element determined to reach the threshold by the determination means, instead of the threshold, depending on the threshold time and the light emission time of the light emitting element during the execution period, before the job start or after the job completion And a current control means for performing control to increase the drive current of the light emitting element. The current control means includes a job start time and a job completion time.
If the accumulated light emission time is closer to the threshold at the start of the job, increase the drive current before starting the job,
2. The optical writing apparatus according to claim 1, wherein when the job is completed and the accumulated light emission time is closer to the threshold, the drive current is increased after the job starts. 3. The optical writing apparatus according to claim 1, wherein the determination unit performs the determination using a preset threshold value regardless of whether or not the current control unit performs the control. 4. The determination means determines whether the advance time obtained by subtracting the threshold value from the accumulated light emission time at the start of the job and the advance time obtained by subtracting the threshold value from the accumulated light emission time at the completion of the job have different signs. Make the determination,
4. The optical writing device according to claim 1, wherein the current control unit performs the control with an accumulated light emission time according to a smaller absolute value of the advance time and the delay time. 5. . Integration means for integrating the advance time and the advance time;
5. The optical writing device according to claim 4, further comprising: a second current control unit configured to perform control to increase a driving current amount at a correction timing that is a cumulative light emission time obtained by subtracting the integrated value from the threshold value. . The second current control means includes
6. The optical writing apparatus according to claim 5, wherein the correction timing is calculated when the absolute value of the integrated value is equal to or greater than a predetermined value. The second current control means includes
6. The optical writing apparatus according to claim 5, wherein the correction timing is calculated every time a predetermined number of jobs are executed. The second current control means includes
6. The optical writing apparatus according to claim 5, wherein the correction timing is calculated for each predetermined cumulative light emission time. The second current control means includes
Compared to increasing the drive current amount at the threshold,
When performing the control before the job starts, the amount of drive current after the control is small,
When performing the control after completion of the job, the amount of drive current after the control is large,
The optical writing apparatus according to claim 5, wherein the control is performed as follows. The current control means includes
10. The control according to claim 5, wherein when the sign of the integrated value is positive, the control is performed so that the amount of increase in the drive current amount is smaller than when the sign is negative. The optical writing device according to claim 1. The optical writing device according to claim 1, wherein the light emitting element is an OLED. An image forming apparatus comprising the light emitting device according to claim 1.

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