JP6631334B2 - Optical writing device and image forming device - Google Patents

Description

  The present invention relates to an optical writing apparatus and an image forming apparatus, and more particularly to a technique for reducing a memory capacity required for light quantity correction in an optical writing apparatus using an organic LED.

In recent years, the demand for miniaturization of electrophotographic image forming apparatuses has been increasing. Therefore, in order to further reduce the size of optical writing devices that form an electrostatic latent image by exposing the surface of the photoconductor, optical scanning devices that use laser diodes (LDs) as light-emitting Switching to a line optical type in which dot light emitting elements are arranged in a line.
In the case of a line optical type optical writing device, when a semiconductor LED is used as a light emitting element, the light emitting section (LED array) and a drive circuit section for controlling each light emitting element are formed on separate substrates for manufacturing reasons. Inevitably, the cost increases. For this reason, an OLED-PH (OLED Print Head) has been proposed in which a single substrate is formed by using an organic LED (OLED: Organic Light Emitting Diode) to reduce the cost.

However, the OLED has a deterioration characteristic in which the light emission efficiency decreases as the light emission time increases, and it is known that this deterioration characteristic changes according to the amount of emitted light and the environmental temperature. In the OLED-PH, even if the light amount differs between OLEDs by only a few percent, uneven streaks are visually recognized in the printed image, and the image quality is not practical.
For this reason, for example, the history data of the light emission time and the ambient temperature are stored for each light emission amount for each OLED constituting the OLED-PH, and when the OLED is caused to emit light, the desired light emission amount is determined from the light emission time and the environmental temperature. Has been proposed for estimating the amount of drive current that can obtain (see, for example, Patent Document 1). Further, a technique has been proposed in which the number of times of light emission is counted for each OLED, and when the count value exceeds a certain value, the driving voltage is increased (for example, see Patent Document 2).

  By applying these light amount correction techniques, excellent image quality can be maintained irrespective of a decrease in luminous efficiency due to deterioration of the OLED.

JP 2003-029710 A JP 2005-329634 A

  Although not specifically disclosed in the above prior art, it is necessary to prepare a light amount correction table in order to obtain a desired drive current amount and drive voltage from a combination of a light emission amount, a light emission time, and an environmental temperature. Further, since there is an individual difference between OLEDs, it is necessary to prepare a light quantity correction table for each luminous efficiency of the OLEDs, for example. Further, in order to correct the light amount with high accuracy, it is necessary to adjust the drive current amount and the like slightly, so that the light emission time in the light amount correction table must be finely divided.

Then, since the size and number of the light amount correction tables must be enormous, the storage capacity required for storing the light amount correction tables becomes enormous, the size of the optical writing device increases, and the component cost increases. And may rise.
The present invention has been made in view of the above-described problems, and has an optical writing device and an image writing method capable of accurately performing light amount correction accompanying deterioration of an OLED without unnecessarily increasing a storage capacity. It is an object to provide a forming device.

In order to achieve the above object, an optical writing device according to the present invention causes a current-driven light-emitting element, which deteriorates with an increase in the number of times of light emission, and deteriorates faster as the amount of light emission increases, to emit light at a plurality of set light amounts. An optical writing device that performs optical writing by using a threshold value storage unit that stores a threshold value common to at least two or more set light amounts of the plurality of set light amounts, and stores a coefficient value corresponding to the set light amount during light emission. Coefficient value storage means for storing, and when the light emitting element emits light at one of the two or more set light amounts, the one set light amount is selected from the coefficient values stored by the coefficient value storage means. Is specified, and the number adjusted using the specified coefficient value is counted as a count value corresponding to the cumulative number of times of light emission of the light emitting element that has emitted light, and the count value is compared with a threshold value. , The degree of deterioration of the light emitting element emit light when the count value exceeds the threshold allowed to proceed for a predetermined frequency, a current is corrected to increase the drive current to be supplied to the light emitting element in accordance with the advanced degree of deterioration current Correction means.

With this configuration, instead of storing the threshold value for each set light amount, a threshold value common to the set light amounts and a coefficient value having a smaller data amount than the threshold value are stored, so that it is necessary to correct OLED deterioration. Storage capacity can be reduced.
In this case, each time the light-emitting element emits light with the set light amount of 1, the counting means adds the coefficient value to a count value or subtracts the coefficient value from the count value. When the difference between the count value and its initial value reaches the threshold value, the current correction may be performed.

Further, the coefficient value storage unit stores a plurality of integer values as the coefficient value related to the one set light amount, and the counting unit sequentially stores the plurality of integer values each time the light emitting element emits light. The count value may be switched to be used for the calculation of the count value, or the coefficient value may be composed of an integer part and a decimal part.
Each time the light-emitting element emits light at the set light amount of 1, the sub-count value is counted up or down by one, and the difference between the sub-count value and its initial value is the coefficient value related to the set light amount of 1. A sub-counting means for resetting the sub-count value to an initial value each time the count value reaches, and a main count value each time a difference between the sub-count value and the initial value reaches the coefficient value relating to the set light amount of 1 A main count unit that counts up or down by one, and the current correction unit may perform the current correction when a difference between the main count value and an initial value thereof reaches the threshold value.

In this case, the coefficient value storage means stores a plurality of integer values as coefficient values for each set light amount, and the sub-count means sets a difference between the sub-count value and its initial value as the coefficient value. The plurality of integer values may be sequentially switched each time the number reaches the predetermined value.
Further, the threshold value storage means may store one threshold value common to all of the plurality of set light amounts.

Also, with a drive current supplied to the light emitting element, a current quantity relationship storage means for storing the LUT or function correlates the light emission amount of the light emitting element when supplied with the drive current, pre-SL current correction The means may perform the current correction using the LUT or the function.
Furthermore, the current quantity relationship storage means, in accordance with the deterioration degree of the light emitting element, and stores the LUT or function, before Symbol current correcting means may perform the current correction in accordance with the deterioration degree .

Further, the light emitting element may be an organic EL.
Further, an image forming apparatus according to the present invention includes the optical writing device according to the present invention. By doing so, the above-described effects can be obtained.

FIG. 1 is a diagram illustrating a main configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram showing a main configuration of the optical writing device 100. FIG. 3 is a schematic plan view of the OLED panel 200, and also shows a cross-sectional view taken along line BB ′ and a cross-sectional view taken along line CC ′. FIG. 3 is a block diagram illustrating a main configuration of a TFT substrate 300. FIG. 3 is a circuit diagram showing a pair of selection circuits 401 and a light-emitting block 402. 5 is a timing chart illustrating an active driving method. FIG. 3 is a block diagram illustrating a main functional configuration of the ASIC 310. (A) illustrates a drive current value table, and (b) illustrates an addition value table. (A), (b), and (c) illustrate a luminous efficiency table, a set light amount table, and a deterioration degree table in order. 5 is a flowchart illustrating an operation of the ASIC 310. (A) illustrates a dot count threshold value table according to the related art, and (b) is a table for trial calculation of the data amount of the table. It is a table | surface which compares the deterioration speed for every set light quantity. FIG. 7A is a table for trial calculation of the data amount of the addition value table according to the first embodiment, and FIG. It is a figure which illustrates the addition value table concerning a 2nd embodiment. In the addition value table according to the second embodiment, (a) is a table for trial calculation of a data amount, and (b) is a table for trial calculation of a correction error. FIG. 13 is a block diagram illustrating a main functional configuration of an ASIC 310 according to a third embodiment. FIG. 14 is a diagram illustrating a threshold table according to the third embodiment; 13 is a flowchart illustrating an operation of the ASIC 310 according to the third embodiment. In the threshold table according to the third embodiment, (a) is a table for trial calculation of a data amount, and (b) is a table for trial calculation of correction accuracy.

Hereinafter, embodiments of an optical writing device and an image forming apparatus according to the present invention will be described with reference to the drawings.
[1] First Embodiment First, a first embodiment of the present invention will be described.
(1) Configuration of Image Forming Apparatus First, the configuration of the image forming apparatus according to the present embodiment will be described.

As shown in FIG. 1, the image forming apparatus 1 is a so-called tandem type color printer. The image forming stations 110Y, 110M, 110C, and 110K included in the image forming apparatus 1 form toner images of Y (yellow), M (magenta), C (cyan), and K (black) under the control of the control unit 101. Form.
For example, when forming a yellow toner image in the image forming station 110Y, the charging device 112 uniformly charges the outer peripheral surface of the photosensitive drum 111. The optical writing device 100 forms an electrostatic latent image by exposing the outer peripheral surface of the photoconductor drum 111.

  The developing device 113 supplies yellow toner to the outer peripheral surface of the photoconductor drum 111, develops (appears) the electrostatic latent image, and forms a yellow toner image. The primary transfer roller 114 electrostatically transfers (primary transfer) the toner image from the outer peripheral surface of the photosensitive drum 111 to the outer peripheral surface of the intermediate transfer belt 102. The toner remaining on the outer peripheral surface of the photosensitive drum 111 after the primary transfer is removed by the cleaner 115 and discarded.

The intermediate transfer belt 102 is stretched around a secondary transfer roller pair 103 and a driven roller 104, and rotates in the direction of arrow A while carrying a toner image.
Similarly, the magenta, cyan, and black toner images formed by the image forming stations 110M, 110C, and 110K are primary-transferred onto the outer peripheral surface of the intermediate transfer belt 102 at the same timing so as to overlap the yellow toner image. To form a color toner image. The intermediate transfer belt 102 conveys the color toner image to the secondary transfer roller pair 103.

The sheet cassette 120 contains a bundle of recording sheets S, and the pickup roller 121 sends out the recording sheets S one by one. When the recording sheet S reaches the timing roller 122, the conveyance is temporarily stopped, and then conveyed to the secondary transfer roller pair 103 in synchronization with the conveyance of the color toner image by the intermediate transfer belt 102.
The secondary transfer roller pair 103 electrostatically transfers (secondarily transfers) the toner image on the intermediate transfer belt 102 onto the recording sheet S. After the secondary transfer, the toner remaining on the intermediate transfer belt 102 is scraped off by the cleaner 105 and discarded. The recording sheet S to which the toner image has been transferred is heat-fixed by the fixing device 106 to the toner image, and is then discharged onto a discharge tray 108 by a discharge roller 107.

An operation panel (not shown) is connected to the control unit 101, and presents information to the user of the image forming apparatus 1 and receives an instruction input from the user.
(2) Configuration of Optical Writing Device 100 Next, the configuration of the optical writing device 100 will be described.
(2-1) Overall Configuration As shown in FIG. 2, the optical writing device 100 has an OLED panel 200 and a rod lens array 202 housed in a holder 203, and the OLED panel 200 has 15,000 pieces. OLEDs 201 are arranged in a line. The light beam L emitted from the OLED 201 is condensed on the outer peripheral surface of the photosensitive drum 111 by the rod lens array 202. The rod lens array 202 is an optical element in which a large number of rod lenses are integrated, and may be an SLA (SELFOC Lens Array; SELFOC is a registered trademark of Nippon Sheet Glass Co., Ltd.) or an MLA (Micro Lens Array). May be used.

  The positional relationship between the individual rod lenses constituting the rod lens array 202 and the individual OLEDs 201 is various, and the light collection rate of each OLED 201 is not constant. The exposure amount of each OLED 201 on the outer peripheral surface of the light emitting device 111 becomes uneven. In order to prevent such unevenness from occurring, in the present embodiment, the light emission amount is adjusted for each OLED 201.

(2-2) Schematic Configuration of OLED Panel 200 FIG. 3 is a schematic plan view of the OLED panel 200, and also shows a cross-sectional view taken along line BB ′ and a cross-sectional view taken along line CC ′. 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. 15,000 OLEDs 201 are arranged on the TFT substrate 300 along the main scanning direction. These OLEDs 201 are arranged in a row or in a zigzag pattern so that the condensing points are arranged at a pitch of 21.2 μm (1200 dpi) on the outer peripheral surface of the photosensitive drum 111.

  A sealing plate 301 is attached to a surface of the TFT substrate 300 on which the OLED 201 is provided, with a spacer frame 303 interposed therebetween. Thus, the OLED 201 and the like mounted on the TFT substrate 300 are sealed in a state where dry nitrogen or the like is sealed so as not to be exposed to the outside air. In addition, you may enclose a hygroscopic agent together. The sealing plate 301 may be sealing glass or may be made of a material other than glass.

  The driver IC 302 is mounted outside the sealing region of the TFT substrate 300. The control unit 101 includes an ASIC (Application Specific Integrated Circuit) 310 for driving the optical writing device 100. The control unit 101 is connected to the driver IC 302 via a card wire (FFC: Flexible Flat Card) 311, and inputs image data to the driver IC 302 using the ASIC 310. The driver IC 302 converts the image data and outputs a luminance signal. A driving current according to the luminance signal is supplied to the OLED 201, and the light emission amount is controlled. The luminance signal may be a current signal or a voltage signal.

The driver IC 302 has a built-in temperature sensor 304. The internal temperature of the driver IC 302 detected by the temperature sensor 304 as the environmental temperature of the OLED 201 is correlated with the temperature of the OLED 201 itself. The control unit 101 can refer to the temperature detected by the temperature sensor 304 incorporated in the driver IC 302.
As described above, in the OLED-PH, the OLED and the TFT can be formed on the same substrate, so that the light emitting unit (LED array) and the control circuit unit (drive IC, etc.) have to be provided on different substrates. Cost can be reduced compared to PH.

(2-3) Configuration of TFT Substrate 300 The OLED 201 has a light quantity temperature characteristic in which luminous efficiency changes with a change in environmental temperature, and the density of the entire image changes depending on the level of the environmental temperature. In addition, the OLED 201 has a deterioration characteristic in which the light emission amount decreases as the integrated light emission time becomes longer. On the other hand, since the integrated light emission time of each OLED 201 varies depending on the image data, the light amount deterioration degree differs for each OLED 201 and the luminance is different. It will vary.

With respect to such a problem, it is necessary to adjust the drive current amount for each OLED 201 in order to keep the print image uniform and the image quality constant. For this reason, the driver IC 302 writes the luminance signal generated for each OLED 201 to the drive circuit using the DAC, so that the light emission amount for each OLED 201 is adjusted.
Further, in the present embodiment, a plurality of OLEDs 201 share a DAC, and an active drive system in which a luminance signal is written from the DAC while sequentially switching these OLEDs 201 is adopted, thereby reducing the circuit scale. In the active driving method, the luminance signal written by the DAC is held until the next writing is performed after the main scanning period (1H period) elapses (for example, when light emission data is written, light emission is performed for about 1H period). to continue).

As shown in FIG. 4, in the TFT substrate 300, 15,000 OLEDs 201 are grouped into 150 light-emitting blocks 402, each of which is 100 pieces. Further, 150 DACs 400 are built in the driver IC 302 and correspond to the light-emitting blocks 402 one-to-one.
When the driver IC 302 receives the image data from the control unit 101, the driver IC 302 distributes the input to each DAC 400 for every 100 pixels for each scanning period. A selection circuit 401 is provided on any circuit from the DAC 400 to the light-emitting block. Each DAC 400 converts the image data into a luminance signal, and sequentially outputs a luminance signal to the 100 OLEDs 201 under its control.

  FIG. 5 is a circuit diagram showing a pair of the selection circuit 401 and the 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 includes one capacitor 521, one driving TFT 522, and one OLED 201. The selection circuit 401 includes a shift register 511 and 100 selection TFTs 512.

  The shift register 511 is connected to the respective gate terminals of the 100 selection TFTs 512 and turns on the selection TFTs 512 in order. The source terminal of the selection TFT 512 is connected to the 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 driving TFT 522.

With the shift register 511 turning on the selection TFT 512, a luminance signal from the DAC 400 is input to the first terminal of the capacitor 521 (charge), and is held until reset (hold).
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 line 531.

The drain terminal of the driving TFT 522 is connected to the anode terminal of the OLED 201, forming a series circuit. The cathode terminal of the OLED 201 is connected to the ground wiring 532. The power supply line 531 is connected to the constant voltage source AVDD received from the power supply unit 612, and the ground wiring 532 is connected to the ground terminal GND.
The constant voltage source AVDD is a supply source of the drive current supplied to the OLED 201. The drive TFT 522 is a voltage held between the first and second terminals of the capacitor 521, in other words, the drive TFT 522 A drain current corresponding to the source-gate voltage is supplied to the OLED 201 as a drive current. Needless to say, the higher the source-gate voltage, the more the driving TFT 522 supplies more driving current, and the more the OLED 201 emits light.

  For example, when a luminance signal corresponding to Hi is written to the capacitor 521, the driving TFT 522 is turned on, and the OLED 201 emits light with a light amount corresponding to the driving current. When a luminance signal corresponding to Low is written to the capacitor 521, the driving TFT 522 is turned off, and the OLED 201 does not emit light. Thus, by changing the activation signal output by the DAC 400, the light emission amount of the OLED 201 can be controlled.

  A reset circuit 540 is connected to the write wiring 530. When the reset circuit 540 is turned on, the wiring from the current DAC 400 to the selection TFT 512 is reset to a predetermined voltage. The predetermined voltage may be the same voltage as the constant voltage source AVDD, or may be the same voltage as the installation voltage. Further, these intermediate voltages may be used, and it is desirable to select an appropriate voltage. The reset circuit 540 may be built in the driver IC 302. Further, the reset may be performed by changing the polarity of the DAC between the reset and the write.

With such a configuration, a luminance signal is written as follows. As shown in FIG. 6, when the shift register 511 first turns on the first selection TFT 512, a luminance signal from the DAC 400 is input to the first capacitor 521 with the ON period as a charge period.
Next, when the shift register 511 turns off the first selection TFT 512, a drive current corresponding to the voltage held by the first capacitor 521 is supplied to the first OLED 201, and the OLED 201 is turned on (hold period). .

With the first selection TFT 512 turned off, the second selection TFT 512 is turned on, and a luminance signal is input to the second capacitor 521. When such an operation is performed up to the 100th selection TFT 512, the operation returns to the first selection TFT 512 and the above operation is repeated.
Note that, in the present embodiment, the case where the driving TFT 522 is a p-channel TFT is described as an example, but it goes without saying that an n-channel driving TFT 522 may be used. The write wiring 530, the power supply line 531 and the ground wiring 532 are all thin-film wirings.

(3) Functional Configuration of ASIC 310 Next, the functional configuration of the ASIC 310 will be described.
As shown in FIG. 7, the ASIC 310 includes a drive current correction unit 700 and a dot count unit 710, and the dot count unit 710 includes a dot counter 711 for each OLED 201.

When the corresponding OLED 201 emits light once in the main scanning period unit, the dot counter 711 adds a predetermined count value.
The drive current correction unit 700 stores a drive current value table, an addition value table, and a temperature correction coefficient.
As shown in FIG. 8A, the drive current value table stores the drive current value using the luminous efficiency, the set light amount, and the degree of deterioration as parameters. The luminous efficiency is represented by the ratio of the light emission amount to the drive current value. If the drive current value is the same, the light emission efficiency is higher as the light emission amount is larger, and if the light emission amount is the same, the light emission efficiency is smaller as the drive current value is smaller. high.

The set light amount is a target light amount that the OLED 201 should emit. The set light amount is specified for each OLED, and is changed as needed. For example, when the system speed of the image forming apparatus 1 is switched depending on whether the type of the recording sheet S is plain paper or thick paper, the set light amount is also switched.
The degree of deterioration is a parameter indicating the degree of deterioration of the OLED 201 due to light emission. In the present embodiment, the luminous efficiency is 10 types, the set light amount is 5 types, and the degree of deterioration is 200 steps from 1.000 to 1.400 in 0.002 increments. The degree of deterioration of the OLED 201 is also set to 1.000.

As shown in FIG. 8B, the addition value table stores the addition value of the dot counter 711 using the luminous efficiency, the set light amount, and the degree of deterioration as parameters, and stores the dot count threshold value using the luminous efficiency and the degree of deterioration as parameters. Is stored. The addition value is an integer value added to the dot counter 711 each time the OLED 201 emits light once.
In the present embodiment, two addition values are stored for each combination of the luminous efficiency, the set light amount, and the degree of deterioration. For example, when the light emission efficiency is 01, the degree of deterioration is 1.002, and the set light amount is 500 W / m ² , 18 and 19 are stored as the added values. When the set light quantity is 100 W / m ² , 200 W / m ² , 300 W / m ² , 400 W / m ² and 500 W / m ² , the data amount of the added value stored is 1 bit × 2, 2 bits × 2 3 bits × 2, 4 bits × 2 and 5 bits × 2.

The dot count threshold is an integer value indicating the timing at which the degree of deterioration is increased by one step (0.002 in the present embodiment). When the count value of the dot counter 711 reaches the dot count threshold, the OLED 201 deteriorates. The degree is increased by one step.
The drive current correction unit 700 further stores a luminous efficiency table, a set light amount table, and a deterioration degree table. As shown in FIG. 9, the luminous efficiency table stores the luminous efficiency for each OLED 201, and the set light amount table stores the set light amount for each OLED 201. The deterioration degree table stores the deterioration degree for each OLED 201.

(4) Operation of ASIC 310 Next, the operation of the ASIC 310 will be described.
As shown in FIG. 10, the ASIC 310 first acquires the luminous efficiency, the set light amount, and the degree of deterioration corresponding to each OLED 201 from the luminous efficiency table, the set light amount table, and the degree of deterioration table (S1001). Next, the ASIC 310 acquires a drive current amount corresponding to the acquired luminous efficiency, the set light amount, and the degree of deterioration from the drive current amount table (S1002). An addition value and a dot count threshold value corresponding to a combination of the luminous efficiency and the degree of deterioration are acquired from the addition value table (S1003).

For example, when the luminous efficiency is luminous efficiency 01, the degree of deterioration is 1.002, and the set light amount is 200 W / m ² , the value of 3 is obtained from the additional value table illustrated in FIG. 4 is read. When the set light quantity is 100 W / m ² , the added value may be unconditionally set to 1.
Thereafter, when the OLED 201 is caused to emit light (S1004: YES), the driver IC 302 is instructed to supply the driving current to the OLED 201 (S1005). Then, the addition value is added to the count value of the dot counter 711 corresponding to the OLED 201 to obtain a new count value (S1006). In this case, the ASIC 310 alternately adds two addition values corresponding to the light emission efficiency, the set light amount, and the degree of deterioration each time the OLED 201 emits light.

When the new count value is equal to or larger than the dot count threshold value (S1007: YES), the deterioration degree of the OLED 201 is updated (S1008). In the present embodiment, the degree of deterioration is increased by 0.002.
After the process of step S1008 is completed, or when the new count value is smaller than the dot count threshold (S1007: NO), the process proceeds to step S1004 and the above process is repeated.

(5) Data Amount Required for Deterioration Correction Next, a data amount required for deterioration correction is compared with that of the related art.
In the prior art, similarly to the present embodiment, the degree of deterioration increases by 0.002 from 1.000 to 1.400, and the light amount is corrected every time the degree of deterioration increases by 0.002. The set light quantity is classified into five types, and the luminous efficiency is classified into ten types. In the related art, 1 is added to the dot count value each time the OLED 201 emits light once, and when the dot count value exceeds the dot count threshold value, the drive current value is updated.

Also, in the related art, the same drive current value table as the drive current value table according to the present embodiment is used. Therefore, the data amount of the drive current value table is the same in both the conventional technology and the present embodiment.
(5-1) Data amount required in the conventional technology In the conventional technology, the addition value of the dot counter is always 1, so that the addition value table is unnecessary. A dot count threshold value table that stores a dot count threshold value for each combination is required (FIG. 11A).

The data amount of the dot count threshold value table can be estimated as follows. FIG. 11B is a table exemplifying a dot count threshold, which is the number of times of light emission to be counted from the initial deterioration degree of 1.000 to the next deterioration degree of 1.002 until the deterioration degree is updated. The dot count threshold value becomes maximum when the set light amount is 100 W / m ² , the value is 8,819,812,090, and the data amount is 34 bits. Further, the dot count threshold becomes minimum when the set light amount is 500 W / m ² , the value is 478, 986, 887, and the data amount is 29 bits.

The luminous efficiency is 10 types, the set light amount is 5 types, and the degradation degree is 200 steps from 1.000 to 1.400.
Since (10 types) × (200 steps) × (29+... +34 bits) ≒ 312 kilobits, a huge recording capacity is required, which causes an increase in the cost of the optical writing device.
(5-2) Data amount of addition table Next, the data amount of the addition table is trially calculated under the same conditions as in the above-described conventional technique.

As shown in FIG. 12, the speed at which the degree of deterioration advances by one step from 1.000 to 1.002 (deterioration speed) is set based on the deterioration speed when the set light amount is 100 W / m ^2. When the light amount is 200 W / m ² , the ratio becomes 3.51 times from the dot count threshold ratio. Similarly, when the set light quantity is 500 W / m ² , the deterioration speed is 18.41 times.
In the present embodiment, paying attention to the ratio of the deterioration speeds, instead of using the dot count threshold value table according to the related art, a common dot count threshold value is used regardless of the set light amount and the addition value table is used. To reduce the amount of data.

Further, in the present embodiment, two added values are used for each set light amount in order to secure the accuracy of the degree of deterioration. In other words, as illustrated in FIG. 13A, for the light amount of 200 to 500 W / m ² , the added value has ^two values, a count UP value a and a count UP value b, and is switched and added for each light emission. . When the set light quantity is 500 W / m ² , the count UP value a is held at 18, and the count b is held at 19, and is switched and added for each light emission, and 18.5 is added on average for each light emission. Is done.

In the above prior art, when the set light quantity is 500 W / m ^2, it is necessary to store a 29-bit dot count threshold, whereas in the present embodiment, 5 bits × 2, that is, 10 bits Since only the data needs to be stored, the amount of data that must be stored can be reduced. When the set light quantity is 100 W / m ² , 200 W / m ² , 300 W / m ² and 400 W / m ² , the data amount of the added value stored is 1 bit × 2 (= 2 bits) and 2 bits × 2, respectively. (= 4 bits), 3 bits × 2 (= 6 bits) and 4 bits × 2 (= 8 bits).

Therefore, the data amount of the addition value table is
(10 types) × (200 steps) × ｛34 bits + (2+... +10 bits)｝ ≒ 124 kilobits, which is compressed to less than half of the estimated value according to the prior art.
(5-3) Accuracy of Deterioration Degree Next, the estimation accuracy of the degree of deterioration in the present embodiment will be described.

As described above, in the present embodiment, the degree of deterioration is estimated by updating the count value using two addition values for each set light amount. Assuming that the set light amount is 200 W / m ² , as an example, the estimation accuracy of the degree of deterioration is such that when addition values 3 and 4 are alternately added, an average of 3.5 is added in one light emission. The number of flashes whose degree is updated from 1.000 to 1.002 is
8,819,812,909 ÷ 3.5 ≒ 2,519,946,311
And the difference from the exact threshold is
2,515,330,403-2,529,946,311 = 4,615,908
Therefore, the correction error is
4,615,908 ÷ 2,515,330,403 ≒ 0.18%
It is. If this correction error is repeated until the light emission amount of the OLED 201 for the same drive current decreases by 20%, the accumulated error becomes
0.002 × 0.18% × (20% ÷ 0.2%) ≒ 0.04%
It becomes. With such an error, it is not visually recognized in the printed image. Even when the set light amounts are 300 W / m ² , 400 W / m ^2, and 500 W / m ² , when the accumulated error is similarly calculated, as shown in FIG. 13B, −0.52%, −0 0.33% and -0.09%, which are levels that are not visually recognized in the printed image.

Note that, in the present embodiment, an example in which the number of added values is two has been described. However, three or more added values may be switched. A plurality of the same addition values may be included. For example, if three addition values 3, 3 and 2 are used, 2.67 can be approximated with high accuracy.
[2] Second Embodiment Next, a second embodiment of the present invention will be described.

The image forming apparatus according to the second embodiment has substantially the same configuration as the image forming apparatus according to the first embodiment, but differs in the data format of the added value in the added value table. The following description focuses on differences from the image forming apparatus according to the first embodiment. Note that the same reference numerals are given to members and the like common to the first embodiment.
(1) Addition Value Table In the addition value table according to the present embodiment, as shown in FIG. 14, each addition value has an integer part and a decimal part. For example, in a column where the set light quantity is 100 W / m ² , an addition value of a total of 3 bits, in which the integer part is 1 bit and the decimal part is 2 bits, is stored, and in this embodiment, any degree of deterioration is stored. The added value is 1.00.

In addition, in the column where the set light quantity is 200 W / m ² , an addition value of a total of 4 bits, that is, 2 bits for both the integer part and the decimal part, is stored. When the degree of deterioration is 1.002, 3. 50 are stored. Similarly, in the columns of the set light amounts of 300 W / m ² , 400 W / m ² and 500 W / m ² , the data size of the added value is 5, 6 and 7 bits.
(2) Data amount of addition table Next, the data amount of the addition table is estimated.

For example, when the set light quantity is 500 W / m ² , the conventional technique estimated in the first embodiment needs to store a 29-bit dot count threshold, whereas FIG. As shown, in the present embodiment, since the count UP value approximating to the second decimal place only needs to be stored by 7 bits, the amount of data to be stored can be reduced. When the set light amount is 100 W / m ² , 200 W / m ² , 300 W / m ² and 400 W / m ² , the data amount of the added value stored is 1 bit, 4 bits, 5 bits and 6 bits, respectively.

Therefore, the data amount of the addition value table is
(10 types) × (200 steps) × {34 bits + (1+... +7 bits)} 112 kilobits. Taking into account 30 kilobits to extend the fractional 2 bits,
Since 112 kilobits + 30 kilobits = 142 kilobits, it is compressed to less than half of the estimated value 312 kilobits relating to the prior art.

(3) Estimation Accuracy of Deterioration Degree Next, the estimation accuracy of the deterioration degree in the present embodiment will be described.
The estimation accuracy of the degree of deterioration in the present embodiment is, assuming that the set light amount is 200 W / m ² as an example, as shown in FIG. 15B, an average of 3.5 additions per light emission. Therefore, the number of flashes whose deterioration degree is updated from 1.000 to 1.002 is
8,819,812,909 ÷ 3.5 ≒ 2,519,946,311
And the difference from the exact threshold is
2,515,330,403-2,529,946,311 = 4,615,908
Therefore, the correction error is
4,615,908 ÷ 2,515,330,403 ≒ 0.18%
It is. If this correction error is repeated until the light emission amount of the OLED 201 for the same drive current decreases by 20%, the accumulated error becomes
0.002 × 0.18% × (20% ÷ 0.2%) ≒ 0.04%
It becomes. With such an error, it is not visually recognized in the printed image. Even when the set light amounts are 300 W / m ² , 400 W / m ^2, and 500 W / m ² , when the accumulated error is similarly calculated, as shown in FIG. 15B, −0.52%, −0 0.33% and -0.09%, which are levels that are not visually recognized in the printed image.

In the present embodiment, the case where the precision of the added value is 0.25 by setting the decimal part to 2 bits has been described as an example. However, the precision of the added value is set to 3 bits or more. May be set to 0.125 or less.
[3] Third Embodiment Next, a third embodiment of the present invention will be described.

  The image forming apparatus according to the third embodiment has substantially the same configuration as the image forming apparatus according to the above embodiment, while the dot counter 711 for each OLED 201 includes a main counter and a sub counter, The difference is that each threshold value of the main counter and the sub counter is specified for each set light amount. The following description focuses on differences from the image forming apparatus according to the above embodiment. Note that the same reference numerals are given to members and the like common to the above embodiment.

(1) Functional Configuration of ASIC 310 First, the functional configuration of the ASIC 310 will be described.
As shown in FIG. 16, in the present embodiment, a dot counter 711 for each OLED 201 includes a main counter 1601 and a sub counter 1602. As described later, the sub-counter 1602 is incremented by one each time the corresponding OLED 201 emits light once. When the count value of the sub-counter 1602 reaches the sub-counter threshold, the main counter 1601 is incremented by one, and the count value of the sub-counter 1602 is reset to zero.

In the present embodiment, drive current correction section 700 stores a threshold value table instead of the addition value table.
As shown in FIG. 17, the threshold table stores two sub-counter thresholds using the luminous efficiency, the set light amount, and the degree of deterioration as parameters, and stores a dot count threshold using the luminous efficiency and the degree of deterioration as parameters.

  As described above, when the count value of the sub-counter 1602 reaches one of the two sub-counter thresholds, the count value of the main counter 1601 increases by one and the count value of the sub-counter 1602 becomes zero. Is reset to The sub-counter threshold to be referred to is switched each time the count value of the sub-counter 1602 is reset to 0.

When the above process is repeated and the count value of the main counter 1601 reaches the dot count threshold, the degree of deterioration increases by 0.002, and the count value of the main counter 1601 is reset to zero.
In the example of FIG. 17, for example, when the set light amount is 100 W / m ² and the degree of deterioration is 1.002, 18 and 19 are stored as the sub-counter thresholds. For example, when the OLED 201 emits light 18 times, the count value of the sub-counter 1602 reaches one sub-counter threshold, the count value of the main counter 1601 is increased by 1, and the count value of the sub-counter 1602 is reset to 0.

When the count value of the main counter 1601 reaches the dot count threshold value, the degree of deterioration is updated from 1.002 to 1.004, and the count value of the main counter 1601 is reset to 0.
(2) Operation of ASIC 310 Next, the operation of the ASIC 310 will be described. Steps common to those in FIG. 10 are denoted by the same reference numerals such as S1001.

  As shown in FIG. 18, the ASIC 310 first acquires the luminous efficiency, the set light amount, and the degree of deterioration corresponding to each OLED 201 from the luminous efficiency table, the set amount of light table, and the degree of deterioration table (S1001). Next, the ASIC 310 acquires a drive current amount corresponding to the acquired luminous efficiency, the set light amount, and the degree of deterioration from the drive current amount table (S1002). Further, the ASIC 310 sets two sub-counter thresholds from the threshold table. At the same time as reading (S1801), the dot count threshold is read (S1802).

If the OLED 201 is to emit light (S1004: YES), the driver IC 302 is instructed to supply the driving current to the OLED 201 to emit light (S1005), and the count value of the sub counter 1602 is increased by 1 (S1803). ). Next, the count value of the sub-counter 1602 is compared with the sub-counter threshold.
If the count value of the sub-counter 1602 has reached the sub-counter threshold (S1804: YES), the count value of the main counter 1601 is increased by 1 (S1805). Note that the sub-counter threshold value to be compared with the count value of the sub-counter 1602 is switched every time the count value of the sub-counter 1602 reaches the sub-counter threshold value.

Next, the count value of the main counter 1601 is compared with the dot count threshold value. If the count value has reached the dot count threshold value (S1806: YES), the deterioration degree is updated (S1807). In the present embodiment, the degree of deterioration is increased by 0.002.
After the process of step S1807 is completed, or when the count value of the sub counter 1602 is less than the sub counter threshold (S1804: NO), when the count value of the main counter 1601 is less than the dot count threshold (S1806: NO) Proceeds to step S1004 and repeats the above processing.

(3) Threshold Table The amount of data of the threshold table according to the present embodiment is estimated.
As illustrated in FIG. 19A, the threshold table stores two sub-counter thresholds for each combination of the luminous efficiency, the set light amount, and the degree of deterioration. For example, in the column of the set light amount of 100 W / m ² , both the sub-counter threshold a and the sub-counter threshold b are 5 bits, and in the column of the set light amount of 200 W / m ² , the sub-counter threshold a and the sub-counter threshold are set. b is 3 bits.

The threshold table also stores a 29-bit dot count threshold. In the present embodiment, since the deterioration speed when the set light amount is 500 W / m ² is used as a reference, compared with the case where the deterioration speed when the set light amount is 100 W / m ² is used as a reference, The data amount of the count threshold can be reduced.
Therefore, the data amount of the threshold table is
(10 types) × (200 steps) × {29 bits + (5 bits × 2 +... +2 bits × 2)} 106 kilobits. This is approximately one third of the prior art table size of 312 kilobits.

(4) Estimation Accuracy of Deterioration Degree Next, estimation accuracy of the deterioration degree in the present embodiment will be described.
In the first embodiment, as shown in FIG. 12, the deterioration speed at another set light amount is obtained by setting the deterioration speed when the set light amount is 100 W / m ² to 1.00. On the other hand, in the present embodiment, as shown in a column 1900 of FIG. 19A, when the set light amount is 500 W / m ² , the deterioration speed is set to 1.00, and the other set light amounts are used. Is determined. The sub-counter thresholds a and b are expressed as follows using the deterioration speed V.

(Sub counter threshold a) = [V]
(Sub counter threshold b) = [V] +1
Here, [•] is a Gaussian symbol, and represents an integer value obtained by truncating a decimal part of a numerical value in the symbol. If the sub-counter thresholds a and b are used alternately, the deterioration speed can be approximated by the average value of the sub-counter thresholds a and b.

Taking the case where the set light quantity is 100 W / m ² as an example, since the sub-counter thresholds a and b are 18 and 19, an accurate degradation rate 18.41 is approximated using the average value 18.5.
For this reason, as shown in FIG. 19 (b), the estimation accuracy of the deterioration degree is an average of 3.5 added in one light emission, so that the deterioration degree is updated from 1.000 to 1.002. The number of flashes is
478,986,887 × {(18 + 19)} 2｝ ≒ 8,861,257,419
And the difference from the exact threshold is
8,861,257,419-8,819,812,090 = 41,445,329
Therefore, the correction error is
41,445,329 ÷ 8,819,812,090 ≒ 0.47%
It is. If this correction error is repeated until the light emission amount of the OLED 201 for the same drive current decreases by 20%, the accumulated error becomes
0.002 × 0.47% × (20% ÷ 0.2%) ≒ 0.09%
It becomes. With such an error, it is not visually recognized in the printed image. Even when the set light amounts are 200 W / m ² , 300 W / m ^2, and 400 W / m ² , when the accumulated error is similarly calculated, as shown in FIG. 19B, −0.95%, −0 .17% and 0.03%, which are levels that are not visually recognized in the printed image.

  Note that, in the present embodiment, an example in which the number of sub-counter thresholds is two has been described. However, three or more sub-counter thresholds may be switched. May include a plurality of the same sub-counter thresholds. For example, when three sub-counter thresholds 5, 5, and 6 are used, 5.33 can be more accurately approximated than when two sub-counter thresholds are used.

[4] Modifications Although the present invention has been described based on the embodiments, it goes without saying that the present invention is not limited to the above-described embodiments, and the following modifications can be made. .
(1) In the first embodiment, the case where the degree of deterioration is updated each time the OLED 201 emits light by the number of times obtained by dividing the dot count threshold by the average value of the two added values has been described as an example. Further, in the second embodiment, the case where the degree of deterioration is updated each time the OLED 201 emits light by the number of times obtained by dividing the dot count threshold value by the addition value having the integer part and the decimal part has been described.

Further, in the third embodiment, the case where the degree of deterioration is updated each time the OLED 201 emits light the number of times that the dot count threshold is multiplied by the sub-counter threshold has been described as an example.
In these first and second embodiments, the accuracy of the deterioration correction is the same even if an addition value table in which the addition value and the dot count threshold are both multiplied by the same multiplier is used. Further, since the dot count threshold value is shared between the set light amounts, the effect of the present invention can be obtained.

In the third embodiment, if the divisor for dividing the dot count threshold is the same as the multiplier for multiplying the sub-counter threshold, the accuracy of the deterioration correction is the same. Further, since the dot count threshold value is shared between the set light amounts, the effect of the present invention can be obtained.
(2) In the above embodiment, the case where the dot counter 711, the main counter 1601, and the sub-counter 1602 count up from the initial value 0 to the threshold has been described as an example, but it goes without saying that the present invention is not limited to this. If the difference between the initial value and the final value is equal to the threshold value, the initial value need not be 0.

Alternatively, the countdown may be performed by reversing the magnitude relationship between the initial value and the final value. In this case, the above addition value is subtracted from the count value as a subtraction value. For example, the threshold may be counted down to 0 as the initial value by a subtraction value.
(3) In the above embodiment, a case where a common dot count threshold is used for all five types of set light amounts from 100 W / m ² to 500 W / m ^{2 has} been described as an example, but the present invention is not limited to this. Needless to say, a common dot count threshold may be used for at least two types of set light amounts.

If a common dot count threshold value is used between the set light amounts, the types of dot count threshold values that need to be stored for deterioration correction can be reduced, so that the data amount required for deterioration correction can be reduced. Naturally, the data amount can be reduced most by using a common dot count threshold value among all the set light amounts.
(4) In the above embodiment, the dot count threshold value at which the added value corresponding to any one of the set light amounts is equal to 1 is used, but it is needless to say that the present invention is not limited to this. The effect of reducing the data amount of the addition value table can be obtained even if a dot count threshold value whose corresponding addition value does not become 1 is used.

For example, in the addition value table of FIG. 8B, even if a dot count threshold value and a value obtained by doubling all of the addition values are used instead of the original values, the same correction accuracy as in the first embodiment can be obtained. This can be achieved, and the data amount can be reduced as compared with the related art, though not as much as in the first embodiment.
In order to minimize the data amount of the addition value table, it is desirable to use a dot count threshold value at which the addition value corresponding to any one of the set light amounts is equal to 1.

  (5) In the above embodiment, the case where the drive current value according to the degree of deterioration of the light emitting element is acquired using the drive current value table has been described as an example, but it is needless to say that the present invention is not limited to this. , The drive current value may be calculated using an appropriate function instead of an LUT (Look Up Table). Such a function, for example, according to the above-described embodiment, causes the drive current value to be calculated using the luminous efficiency, the degree of deterioration, and the set light amount as variables.

  (6) In the above embodiment, the case where the image forming apparatus 1 is a 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. Or a monochrome printer. Further, it may be a copying machine having a scanner or a facsimile machine having a communication function. Further, even if the present invention is applied to a multi-function peripheral (MFP) having these functions, effects can be obtained.

  INDUSTRIAL APPLICABILITY The optical writing apparatus and the image forming apparatus according to the present invention are particularly useful as an apparatus in which the memory capacity required for light quantity correction is reduced in an optical writing apparatus using an organic LED.

1. Image forming apparatus 110 Image forming station 100 Optical writing apparatus 101 Control unit 200 OLED panel 201 OLED
310 …… ASIC
700 drive current correction section 710 dot count section 711 dot counter 1601 main counter 1602 sub-counter

Claims (11)

An optical writing device that performs optical writing by causing a current-driven type light emitting element that deteriorates with an increase in the number of times of light emission and emits light at a plurality of set light amounts to rapidly deteriorate as the amount of light emission increases,
Threshold storage means for storing a threshold common to at least two or more set light amounts of the plurality of set light amounts,
Coefficient value storage means for storing a coefficient value corresponding to a set light amount at the time of light emission ,
When the light-emitting element emits light at one set light amount of the two or more set light amounts, a coefficient value corresponding to the one set light amount is specified from the coefficient values stored by the coefficient value storage means. The number adjusted using the specified coefficient value is counted as a count value corresponding to the cumulative number of times of light emission of the light emitting element that has emitted light, and the count value is compared with a threshold value. Current correction means for advancing the degree of deterioration of the light-emitting element that emits light by a predetermined number of times and increasing the drive current to be supplied to the light-emitting element according to the degree of deterioration that has progressed. Characteristic optical writing device. Each time the light-emitting element emits light with the set light amount of 1, the count value is added to the coefficient value, or a counting means for subtracting the coefficient value from the count value,
2. The optical writing device according to claim 1, wherein the current correction unit performs the current correction when a difference between the count value and the initial value reaches the threshold value. The coefficient value storage unit stores a plurality of integer values as the coefficient value related to the one set light amount,
3. The optical writing apparatus according to claim 2, wherein the counting unit sequentially switches the plurality of integer values each time the light emitting element emits light and uses the plurality of integer values for calculating the count value. The optical writing device according to claim 2, wherein the coefficient value includes an integer part and a decimal part. Each time the light emitting element emits light at the set light amount of 1, the sub-count value is counted up or down by one, and the difference between the sub-count value and its initial value reaches the coefficient value related to the set light amount of 1 A sub-counting means for resetting the sub-count value to an initial value each time;
Main count means for counting up or down the main count value by one each time a difference between the sub count value and its initial value reaches the coefficient value relating to the set light amount of 1;
2. The optical writing device according to claim 1, wherein the current correction unit performs the current correction when a difference between the main count value and an initial value thereof reaches the threshold value. The coefficient value storage means stores a plurality of integer values as coefficient values for each set light amount,
6. The optical writing device according to claim 5, wherein the sub-counting means sequentially switches the plurality of integer values each time a difference between the sub-count value and its initial value reaches the coefficient value. The optical writing apparatus according to claim 1, wherein the threshold storage unit stores one threshold common to all of the plurality of set light amounts. A drive current supplied to the light-emitting element, and a current-light-amount relationship storage unit that stores an LUT or a function that associates a light emission amount of the light-emitting element when the drive current is supplied,
Before SL current correcting means, an optical writing device according to any one of claims 1 to 7, characterized in that performing the current correction using the LUT or function The current light quantity relation storage means stores the LUT or the function according to the degree of deterioration of the light emitting element,
Before SL current correcting means, an optical writing device according to claim 8, characterized in that the current correction in accordance with the deterioration degree. 10. The optical writing device according to claim 1, wherein the light emitting element is an organic EL. An image forming apparatus comprising the optical writing device according to claim 1.