JP6617507B2 - 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 accurately correcting light amount unevenness between a large number of OLEDs with a small storage capacity.

In recent years, for the purpose of reducing the size and cost of an image forming apparatus, technological development for reducing the cost of an optical writing apparatus using an organic light emitting diode (OLED) has been advanced.
A typical light emitting circuit of an OLED is a circuit in which a driving thin film transistor (TFT) 1902 is connected in series to an OLED 1901, as shown in FIG. Supplied to OLED 1901. Further, when the gate-source voltage Vgs applied to the driving TFT 1902 is changed in a state where the predetermined voltage Vdd is applied to the series circuit, the driving current Id changes, so that the light amount L of the OLED 1901 is adjusted.

  The light quantity L of the OLED not only changes according to the drive current Id, but also changes depending on the temperature of the OLED itself and deterioration with time. Furthermore, the progress of deterioration of the OLED changes depending on the drive current Id and temperature during light emission. Therefore, it is necessary to determine the drive current Id of each OLED in consideration of these factors in order to emit light with high accuracy so that unevenness in the amount of light does not occur between a large number of OLEDs arranged in the optical writing device. is there.

In order to suppress the unevenness of the light amount of the OLED, a feedback control method that feedback-controls the light amount L of the OLED measured using the light amount sensor, or a prediction that corrects the drive current Id by predicting a light amount change in consideration of the above factors. There is a correction method (see, for example, Patent Documents 1 and 2).
The predictive correction method is suitable not only for suppressing the unevenness of the light amount of the OLED but also for the purpose of adopting the OLED for reducing the cost in the sense that a light amount sensor is not required.

Japanese Patent No. 5343073 JP 2003-029710 A

  In the prediction correction method, in order to specify the gate-source voltage Vgs applied to the TFT in order to cause the OLED to emit light with the desired light amount L, the light amount L-forward voltage as illustrated in FIG. With reference to the Vel table, the forward voltage Vel of the OLED for obtaining the desired light quantity L is calculated. Furthermore, the gate-source voltage Vgs of the TFT corresponding to the forward voltage Vel is calculated with reference to the forward voltage Vel-source-gate voltage Vgs table illustrated in FIG. In this way, the gate-source voltage Vgs of the TFT for causing the OLED to emit light with a desired light quantity L can be obtained.

  In the prediction correction method, conventionally, linear interpolation is performed when calculating the forward voltage Vel of the OLED and the gate-source voltage Vgs of the TFT. Therefore, in the light quantity L-forward voltage Vel table of FIG. The forward voltage Vel is stored for the amount of light L, and the gate-source voltage Vgs is stored for the forward voltage Vel at regular intervals in the forward voltage Vel-gate-source voltage Vgs table of FIG.

  FIG. 21A is a graph showing the relationship between the light amount L and the forward voltage Vel and the relationship between the forward voltage Vel and the gate-source voltage Vgs. As shown in FIG. 21A, the range of the light amount L of the OLED used in the prior art is a linear region in which the forward voltage Vel of the OLED is substantially proportional to the light amount L. For this reason, even if the forward voltage Vel is stored for the light quantity L at a constant interval as described above, the error in the linear interpolation can be sufficiently reduced (FIG. 21B).

  However, since the demand for image formation speed is not necessarily high in a low-cost machine, it is necessary to suppress the light amount L of the OLED when the exposure time for each pixel on the outer peripheral surface of the photosensitive drum is long. Further, the optimum image forming speed varies depending on the paper type of the recording sheet used for image formation. For example, in the case of thick paper, it takes a heat amount to fix the toner image, so it is necessary to slow down the image forming speed.

  As shown in FIG. 21B, in the range where the light amount L of the OLED is small (non-linear region), the light amount L and the forward voltage Vel have a non-linear relationship. If the light amount L-forward voltage Vel table and the forward voltage Vel-gate-source voltage Vgs table are created by fitting the data in a small range (non-linear region), an error in linear interpolation in the non-linear region increases.

On the contrary, if the interval of the light amount L in the linear region is narrowed in accordance with the non-linear region, the interval of the light amount L is also narrowed in the linear region, so the light amount L-forward voltage Vel table or forward voltage Vel-gate-source voltage. The Vgs table becomes too large. As a result, the storage capacity for storing these tables increases, and the cost of the image forming apparatus increases.
The present invention has been made in view of the above-described problems, and provides an optical writing device and an image forming apparatus that can perform optical writing with a low light amount without causing unevenness in light amount or increase in storage capacity. The purpose is to do.

In order to achieve the above object, an optical writing device according to the present invention includes an OLED characteristic table in which correspondence between a forward voltage or drive current supplied to an OLED and a light amount is discretely described, and the OLED as a thin film transistor. A forward direction corresponding to the indicated light amount by linearly interpolating the discrete light amount described in the OLED characteristic table. An optical writing device that controls a gate-source voltage of the thin film transistor so as to calculate a voltage value or a driving current value and supply the forward voltage value or the driving current value to the OLED. The discrete light quantity described has a large light quantity value on the OLED characteristic curve representing the relationship between the forward voltage or drive current and the light quantity. In addition to the region where the change in the directional voltage or the drive current changes linearly, the value of the light amount is small, and the change is also taken in a non-linear region. The discrete density is set densely compared to the linear region, and when the forward voltage value or the drive current value is calculated from the OLED characteristic table, the discrete forward voltage or the drive described in the TFT characteristic table is calculated. A gate-source voltage corresponding to a calculated value of the forward voltage or drive current value is obtained by linear interpolation of the amount of current, applied to the thin film transistor, and the forward voltage or drive current in the OLED characteristic table; The forward voltage or the drive current in the TFT characteristic table is different in discrete distribution .

In this way, since the discrete density of the light amount is set densely in the non-linear region as compared with the linear region, the OLED characteristic table performs optical writing even at a low light amount without causing unevenness of the light amount or increase in storage capacity. it is possible.

In this case, provided with a temperature detection means for detecting an index indicative of the temperature of the pre-Symbol OLED, the OLED characteristic table, a plurality to correspond to different temperatures of the OLED, is provided, wherein the OLED emission When there is an instruction indicating the amount of light to be emitted, a forward direction corresponding to the indicated amount of light by linearly interpolating the discrete amount of light described in the OLED characteristic table corresponding to the temperature nearest to the temperature indicated by the index A voltage value or a drive current value may be calculated.

  Similarly, a temperature detecting means for detecting an index indicating the temperature of the OLED is provided, and a plurality of the TFT characteristic tables are provided corresponding to different temperatures of the OLED, respectively. When the directional voltage value or the drive current value is calculated, the discrete forward voltage or drive current amount described in the TFT characteristic table corresponding to the temperature closest to the temperature indexed by the index is linearly interpolated and A gate-source voltage corresponding to the calculated value may be obtained and applied to the thin film transistor.

  Furthermore, it comprises temperature detecting means for detecting an index indicating the temperature of the OLED, and a plurality of the OLED characteristic tables are provided corresponding to different temperatures of the OLED, and the TFT characteristic table is A plurality of OLED characteristics tables corresponding to different temperatures of the OLED and corresponding to the temperature closest to the temperature indicated by the index when there is an instruction indicating the amount of light to be emitted by the OLED. When the forward voltage value or the drive current value corresponding to the indicated light quantity is calculated by linear interpolation with the discrete light quantity described in the above, and the forward voltage value or the drive current value is calculated from the OLED characteristic table, Linear interpolation is performed for the discrete forward voltage or drive current amount described in the TFT characteristic table corresponding to the temperature closest to the temperature indicated by the index. Gate corresponding to the calculated value - seeking source voltage may be applied to the thin film transistor.

  Further, in the OLED characteristic table, the correspondence between the forward voltage or drive current supplied to the OLED and the light amount is described discretely for each predetermined cumulative light emission time of the OLED, and the light amount that the OLED should emit light When there is an instruction indicating the forward light voltage value corresponding to the indicated light quantity by linearly interpolating the discrete light quantity described in the OLED characteristic table corresponding to the cumulative light emission time nearest to the cumulative light emission time of the OLED. Alternatively, the drive current value may be calculated.

An optical writing device according to an embodiment of the present invention includes an OLED characteristic table in which correspondence between a forward voltage or drive current supplied to an OLED and a light amount is discretely described, and the OLED connected to a thin film transistor. A forward voltage value corresponding to the indicated light amount by linearly interpolating the discrete light amount described in the OLED characteristic table when there is an instruction indicating the light amount to be emitted by the OLED. Or an optical writing device that controls a gate-source voltage of the thin film transistor so as to calculate a driving current value and supply the forward voltage value or the driving current value to the OLED, and is written in the OLED characteristic table. The discrete light quantity has a large light quantity value on the OLED characteristic curve representing the relationship between the forward voltage or drive current and the light quantity. Alternatively, in addition to the region where the change from the drive current changes linearly, the value of the amount of light is small and the change is nonlinear, and the non-linear region has a discrete density of the amount of light. Are set more densely than the linear region, and the OLED characteristic table shows that the correspondence between the forward voltage or drive current supplied to the OLED and the amount of light is discrete for each predetermined cumulative emission time of the OLED. When there is an instruction indicating the amount of light to be emitted by the OLED, linear interpolation is performed on the discrete amount of light described in the OLED characteristic table corresponding to the accumulated light emission time closest to the accumulated light emission time of the OLED. Then, a forward voltage value or a drive current value corresponding to the indicated light amount is calculated.
In this case, there is provided a TFT characteristic table in which the correspondence between the gate-source voltage of the thin film transistor and the forward voltage or drive current supplied to the OLED is discretely described, and is described in the TFT characteristic table. The discrete forward voltage or drive current has a large forward voltage or drive current on the TFT characteristic curve representing the relationship between the gate-source voltage and the forward voltage or drive current. In addition to the region where the change between the gate voltage and the gate-source voltage changes linearly, the value of the forward voltage or the drive current is small and the change is non-linear. The discrete density of the forward voltage or drive current is set more densely than the linear region, and the forward voltage value or drive current is determined from the OLED characteristic table. When the value is calculated, the gate-source voltage corresponding to the calculated value is obtained by linearly interpolating the discrete forward voltage or the drive current amount described in the TFT characteristic table, and applied to the thin film transistor. Also good.
In addition, a temperature detection unit that detects an index indicating the temperature of the OLED is provided, and a plurality of the OLED characteristic tables are provided corresponding to different temperatures of the OLED, and the amount of light that the OLED should emit light When there is an instruction indicating the forward voltage value corresponding to the indicated light quantity by linearly interpolating the discrete light quantity described in the OLED characteristic table corresponding to the temperature nearest to the temperature indexed by the index, or A drive current value may be calculated.
Similarly, a temperature detecting means for detecting an index indicating the temperature of the OLED is provided, and a plurality of the TFT characteristic tables are provided corresponding to different temperatures of the OLED, and the OLED characteristic table is arranged in order from the OLED characteristic table. When the directional voltage value or the drive current value is calculated, the discrete forward voltage or the drive current amount described in the TFT characteristic table corresponding to the temperature closest to the temperature indexed by the index is linearly interpolated, and A gate-source voltage corresponding to the calculated value may be obtained and applied to the thin film transistor.
Furthermore, it comprises temperature detecting means for detecting an index indicating the temperature of the OLED, and a plurality of the OLED characteristic tables are provided corresponding to different temperatures of the OLED, and the TFT characteristic table is A plurality of OLED characteristics tables corresponding to different temperatures of the OLED and corresponding to the temperature closest to the temperature indicated by the index when there is an instruction indicating the amount of light to be emitted by the OLED. When the forward voltage value or the drive current value corresponding to the indicated light quantity is calculated by linear interpolation with the discrete light quantity described in the above, and the forward voltage value or the drive current value is calculated from the OLED characteristic table, Linear interpolation of discrete forward voltage or drive current amount described in the TFT characteristic table corresponding to the temperature closest to the temperature indicated by the index Gate corresponding to the calculated value - seeking source voltage may be applied to the thin film transistor.
In the OLED characteristic table, the discrete density of the predetermined cumulative light emission time that discretely describes the correspondence between the forward voltage or drive current supplied to the OLED and the light quantity is set more densely as the cumulative light emission time is shorter. It is desirable.
Similarly, in the TFT characteristic table, the correspondence between the gate-source voltage of the thin film transistor and the forward voltage or driving current supplied to the OLED is discretely described for each predetermined cumulative light emission time of the OLED. When the forward voltage value or the drive current value is calculated from the OLED characteristic table, the discrete forward voltage or the discrete forward voltage described in the OLED characteristic table corresponding to the cumulative light emission time closest to the cumulative light emission time of the OLED or A gate-source voltage corresponding to the calculated value may be obtained by linear interpolation of the drive current amount and applied to the thin film transistor.

Even in this case, the TFT characteristic table includes a discrete density of the predetermined cumulative light emission time that discretely describes the correspondence between the gate-source voltage and the forward voltage or drive current. It is desirable to set it closely.
An image forming apparatus according to the present invention includes the optical writing device according to the present invention.

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 figure explaining OLED201, Comprising: (a) shows the structure of OLED201, (b), (c) is a graph which shows a temperature characteristic and a light quantity characteristic, respectively. 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 400. FIG. FIG. 3 is a circuit diagram showing main configurations of a selection circuit 501 and a light emitting block 502. It is a block diagram which shows the main structures of ASIC510. It is a figure which illustrates the setting light quantity table which the drive current correction | amendment part 600 of ASIC510 memorize | stores. It is a figure which illustrates the (a) Vel initial table and (b) Vel correction coefficient table which the drive current correction | amendment part 600 of ASIC510 memorize | stores. It is a graph which shows the relationship between the light quantity L of OLED201, and the forward voltage Vel, (a) illustrates the division | segmentation of the light quantity L which balances suppression of a linear interpolation error, and saving of storage capacity, (b) is a graph of OLED201. Explain the effect of temperature. It is a flowchart which shows the procedure which divides | segments the light quantity L. FIG. It is a graph which illustrates the procedure which divides | segments the light quantity L in order from (a) to (e). It is a flowchart which shows the procedure which estimates the forward voltage Vel. It is a figure which illustrates the (a) initial Id table and (b) Id correction coefficient table which the drive current correction | amendment part 600 of ASIC510 memorize | stores. It is a figure which illustrates the gate-source voltage Vgs table which the drive current correction | amendment part 600 of ASIC510 memorize | stores. 7 is a graph showing the relationship between the gate-source voltage Vgs and the forward voltage Vel, wherein (a) illustrates the division of the gate-source voltage Vgs that achieves both linear interpolation error suppression and storage capacity saving; ) Explains the effect of temperature. It is a flowchart which shows the procedure which estimates the gate-source voltage Vgs. 5 is a graph illustrating a characteristic change according to the accumulated light emission time of the OLED 201, where (a) shows the relationship between the light amount L and the forward voltage Vel, and (b) shows the relationship between the gate-source voltage Vgs and the forward voltage Vel. Indicates. It is a circuit diagram which shows the typical light emission circuit of OLED. It is data for causing the OLED to emit light with a desired light amount, where (a) shows a light amount L-forward voltage Vel table, and (b) shows a forward voltage Vel-gate-source voltage Vgs table. It is a figure explaining the error in linear interpolation, Comprising: (a) is a graph showing the relationship between the light quantity L and the forward voltage Vel, and the relationship between the forward voltage Vel and the gate-source voltage Vgs, (b). FIG. 4 is a graph illustrating a linear interpolation error in a linear region and a nonlinear region.

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 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 color printer. The image forming units 101Y, 101M, 101C, and 101K included in the image forming apparatus 1 receive toner images of respective colors Y (yellow), M (magenta), C (cyan), and K (black) under the control of the control unit 102. Form.

  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 and develops (visualizes) the electrostatic latent image to form a Y-color toner image. The primary transfer roller 113 electrostatically transfers (primary transfer) the toner image from the outer peripheral surface of the photosensitive drum 110 to the outer peripheral surface of the intermediate transfer belt 103. The intermediate transfer belt 103 is stretched around the secondary transfer roller pair 104 and the driven roller 105 and rotates in the direction of arrow A.

  Similarly, the MCK toner images formed by the image forming units 101M, 101C, and 101K are primarily transferred onto the outer peripheral surface of the intermediate transfer belt 103 so as to be superimposed on the Y toner image to form 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 106 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 107 and then discharged onto the discharge tray 109 by the discharge roller 108.
When the recording sheet S is thick paper, more heat is required to fix the toner image than when it is plain paper. For this reason, the image forming apparatus 1 switches the conveyance speed (system speed) of the recording sheet S according to the paper type of the recording sheet S, conveys the recording sheet S at full speed, and conveys the recording sheet S at half speed when using thick paper. To do. Since the rotation speed of the photosensitive drum 110 is switched according to the system speed, the exposure time per pixel becomes longer and shorter, so the optical writing device 100 switches the light amount of the OLED.

[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 202 accommodated in a holder 203, and the OLED 201 is mounted on the OLED panel 200. 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. The rod lens array 202 is an optical element in which a large number of rod lenses are integrated, and an SLA (SLA: Selfoc Lens Array) or an MLA (Micro Lens Array) may be used. Note that cables and the like for connecting to necessary portions of the image forming apparatus 1 are not shown.

  As shown in FIG. 3A, the OLED 201 includes an anode 302 that is a transparent electrode made of indium oxide (ITO), an organic layer 303 made of at least one layer, and aluminum (Al The cathode 304 made of a metal such as The OLED 201 emits light with a light amount corresponding to the drive current and drive voltage supplied from the current source 310 via the anode 302 and the cathode 304.

  In addition, the light emission efficiency of the OLED 201 decreases as the accumulated light emission time increases, but the rate of decrease is under the influence of the temperature and light amount of the OLED 201. For example, as shown in FIG. 3B, the light emission efficiency decreases faster as the temperature of the OLED 201 during light emission is higher. Further, as shown in FIG. 3C, when the drive current of the OLED 201 is large or when the drive voltage is high, the light amount of the OLED 201 increases, but the light emission efficiency decreases faster as the light amount increases.

In the optical writing device, the accumulated light emission time for each OLED 201 varies, and the temperature and light quantity at the time of light emission can also differ for each OLED 201. Therefore, in order to suppress the light quantity unevenness of the OLED 201, each of the factors depends on these factors. It is necessary to correct the light quantity of the OLED 201.
FIG. 4 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. Moreover, the schematic plan view part has shown the state which removed the sealing plate 401 mentioned later.

  As shown in FIG. 4, the OLED panel 200 includes a TFT substrate 400, a sealing plate 401, a driver IC (Integrated Circuit) 402, and the like. On the TFT substrate 400, 15,000 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 manner as long as the condensing points are 21.2 μm pitch (1200 dpi) on the outer peripheral surface of the photosensitive drum 110.

Since the positional relationship between each OLED 201 and the rod lens array 202 is not constant, the light collection rate by the rod lens array 202 is different for each OLED 201. For this reason, the difference in condensing rate is compensated by adjusting the amount of light for each OLED 201.
The substrate surface of the TFT substrate 400 on which the OLED 201 is disposed is a sealing region, and the sealing plate 401 is attached with the spacer frame 403 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 401 may be, for example, sealing glass or may be made of a material other than glass.

A driver IC 402 is mounted outside the sealing region of the TFT substrate 400. The control unit 102 inputs a digital luminance signal to the driver IC 402 via the flexible wire 410. The control unit 102 incorporates a dedicated ASIC (Application Specific Integrated Circuit) for generating a digital luminance signal.
The driver IC 402 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. The driver IC 402 has a temperature sensor 420 built therein.

Since the driver IC 402 is mounted on the TFT substrate 400 like the OLED 201, the temperature T detected by the temperature sensor 420 is substantially equal to the temperature of the OLED 201 itself. Instead of the temperature sensor 420, a temperature sensor that detects the ambient temperature around the OLED 201 may be used.
As shown in FIG. 5, in the TFT substrate 400, 15,000 OLEDs 201 are grouped into 150 light emitting blocks 502 in units of 100. The driver IC 402 includes 150 DACs 500, which correspond to the light-emitting blocks 502 on a one-to-one basis. The DAC 500 is a digitally controllable variable voltage source, and supplies a current while maintaining a specified voltage.

When the driver IC 402 receives a digital luminance signal (image data) from the ASIC 510 built in the control unit 102, the input is distributed to each DAC 500 by 100 pixels every scanning period. Further, the ASIC 510 acquires the temperature T detected by the temperature sensor 420 from the driver IC 402.
A selection circuit 501 is provided on each circuit from the DAC 500 toward the light emitting block. Each DAC 500 sequentially outputs luminance signals to the subordinate 100 OLEDs 201 by so-called rolling driving.

  FIG. 6 is a circuit diagram showing a pair of selection circuit 501 and light emitting block 502. As shown in FIG. 6, the light emitting block 502 includes 100 light emitting pixel circuits, and each light emitting pixel circuit includes a capacitor 621, a driving TFT 622, and an OLED 201. The selection circuit 501 includes a shift register 611 and 100 selection TFTs 612.

  The shift register 611 is connected to the gate terminals of the 100 selection TFTs 612, and sequentially turns on the selection TFTs 612. The source terminal of the selection TFT 612 is connected to the current DAC 500 via the write wiring 630, and the drain terminal is connected to the first terminal of the capacitor 621 and the gate terminal of the driving TFT 622.

  With the shift register 611 turning on the selection TFT 612, the output voltage of the DAC 500 is applied to the first terminal of the capacitor 621 and held. The first terminal of the capacitor 621 is also connected to the gate terminal of the driving TFT 622, and the second terminal of the capacitor 621 is connected to the source terminal of the driving TFT 622 and the power supply wiring 631.

The anode terminal of the OLED 201 is connected to the drain terminal of the driving TFT 622, and the cathode terminal of the OLED 201 is connected to the ground wiring 632. The power supply wiring 631 is connected to the constant voltage source Vpwr, and the ground wiring 632 is connected to the ground terminal GND.
The constant voltage source Vpwr is a supply source of the drive current supplied to the OLED 201, and the drive TFT 622 generates a drain current corresponding to the voltage held between the first and second terminals of the capacitor 621 as the drive current. To the OLED 201. For example, when a signal corresponding to H is written to the capacitor 621, the driving TFT 622 is turned on and the OLED 201 emits light. When a signal corresponding to L is written to the capacitor 621, the driving TFT 622 is turned off and the OLED 201 does not emit light.

  Note that a reset circuit 640 is connected to the DAC 500. The reset circuit 640 may be built in the driver IC 402 or a TFT may be used. Further, the reset circuit 640 may switch the polarity of the DAC between reset and write. When the reset circuit 640 is turned on, the wiring from the DAC 500 to the selection TFT 612 is reset to a predetermined voltage. This predetermined voltage may be the power supply voltage Vdd or the ground voltage GND. Also, an appropriate intermediate potential may be used.

Note that although the case where the driving TFT 622 is a p-channel is described as an example in this embodiment mode, it is needless to say that an n-channel driving TFT 622 may be used.
[3] Configuration of ASIC 510 First, the configuration of the ASIC 510 will be described.

As shown in FIG. 7, the ASIC 510 includes a drive current correction unit 700 and a dot count unit 710. The dot count unit 710 includes a dot counter 711 for each OLED 201. The dot counter 711 increases the count value by 1 when the corresponding OLED 201 emits light once.
The drive current correction unit 700 stores six LUTs (Look Up Tables) including a set light amount table, an initial Vel table, a Vel correction coefficient table, an initial Id table, an Id correction coefficient table, and a TFT characteristic table.

(3-1) Set Light Amount Table As shown in FIG. 8, the set light intensity table is a table in which the set light intensity L is recorded for each system speed for each of 15,000 OLEDs 201.
The set light amount L is a light amount set in advance as a light amount to be emitted from the OLED 201, and is represented by a radiation divergence [W / m ² ] in the present embodiment.

Since the OLED 201 has a different light collection rate (optical system efficiency) depending on the positional relationship with the rod lens array 202, it is necessary to adjust the amount of light for each OLED 201 in order to align the exposure amount on the outer peripheral surface of the photosensitive drum 110. is there. For this reason, the set light amount L of the OLED 201 having a high light collection rate is small, and the set light amount L of the OLED 201 having a low light collection rate is set large.
Further, when the recording sheet S is a thick paper, the amount of heat necessary for fixing the toner image is larger than when the recording sheet S is a plain paper. For this reason, when the conveyance speed (system speed) of the recording sheet S is switched according to the paper type of the recording sheet S, the rotation speed of the photosensitive drum 110 during exposure is also switched, so that the exposure time per pixel is increased or decreased. .

Regardless of the length of the exposure time, the set light amount for each OLED 201 is adjusted in order to align the exposure amount per pixel. That is, the set light amount is set to be small when the exposure time is long, and the set light amount is set to be large when the exposure time is low.
For this reason, the set light amount table stores, for each OLED 201, the set light amount L when the system speed of the image forming apparatus 1 is full speed and the set light amount L when the system speed is half speed. Since the exposure time for each pixel is switched when the system speed is switched, the exposure amount for each pixel is made uniform by switching the set light amount L for each OLED 201.

In FIG. 8, the set light amount L when the system speed is full speed and the set light amount L when the system speed is half speed are stored for each OLED 201. Needless to say, the system speed is not limited to two stages of full half speed, and may be three or more stages.
(3-2) Initial Vel Table and Vel Correction Coefficient Table The initial Vel table is a table that stores the initial value of the forward voltage Vel for each light quantity L for each of 15,000 OLEDs 201. In the initial Vel table illustrated in FIG. 9A, the initial value of the forward voltage Vel of each OLED 201 is stored for each of the _nine light amounts L _{0 to} L ₉ . Thereby, the range of the light quantity L is divided into eight sections (FIG. 10A).

  In the present embodiment, the light amounts L0 and L9 are selected so that the minimum light amount L0 matches the minimum set light amount L in the set light amount table and the maximum light amount L9 matches the maximum set light amount L. As long as the light quantity L0 is less than or equal to the minimum set light quantity L and the maximum light quantity L9 is greater than or equal to the maximum set light quantity L, the forward voltage Vel can be estimated by linear interpolation as described later.

In the present invention, it goes without saying that the light quantity L is not limited to 9 levels, and may be 8 levels or less or 10 levels or more. However, increasing the type of light quantity L increases the table size and increases the storage capacity. Therefore, it is desirable to reduce the type within a range where errors due to linear interpolation can be tolerated.
Amount L _i, for example, can be determined as the flow chart of FIG. 11. First, the value of the number i of the light amount is initialized to 0 (S1101), the amount of light L _i Namely minimum light amount L0 minimize the set amount of light L _min (S1102). Next, to increase the number i of the light quantity by 1 (S1103), obtains the light amount L _i where the absolute value of the linear interpolation error between the light quantity L _i and the light amount L _i-1 is equal to the upper limit value (S1104).

If the obtained amount of light L _i is smaller than the maximum set amount of light L (S1105: NO), the above processing is repeated proceeds to step S1103. In this way, as illustrated in FIGS. 12A to 12C, the light amounts L ₁ and L ₂ can be obtained sequentially starting from the light amount L ₀ . Further, since the linear interpolation quantity L ₀ to the upper limit value as a reference for the absolute error, L _1, L ₂ ... the obtaining, narrows the spacing amount L _i when the curvature of the characteristic graph 1201 of OLED201 is large, The forward voltage Vel can be calculated with high accuracy. Moreover, the spacing of the light amount L _i is widened when the curvature is small, it is possible to suppress an increase in the storage capacity of the table.

When the obtained light amount L _i is equal to or _larger than the maximum set light amount L _max (S1105: YES), the light amount L _i is multiplied by the ratio of the light amount L _{i to} the maximum set light amount L _max by each light amount _Li. Are proportionally distributed (S1106), and the process is terminated.
Assuming that the maximum value of the light quantity number i is N, the light quantities L _i from the numbers 0 to N are proportionally distributed as shown in equation (1).

このように比例配分すれば、比例配分前のＬ_Nが最大の設定光量Ｌ_maxよりも大きい場合には、すべての区間（Ｌ_i、Ｌ_i+1）を狭めることができるので線形補間の誤差の上限を更に小さくすることができる。

If proportional distribution is performed in this way, when L _N before proportional distribution is larger than the maximum set light amount L _max , all the sections (L _i , L _{i + 1} ) can be narrowed. Can be further reduced.

That is, before the proportional distribution, as shown in FIG. 12D, the light amount L _N is in an unnecessary range exceeding the maximum set light amount L _max , whereas after the proportional distribution, the light amount L _N in FIG. as such, just enough amount L _i the range corresponding to the set amount of light L is covered. Moreover, since all the sections (L _i , L _{i + 1} ) are narrower than before the proportional distribution, the linear interpolation error can be reduced.
As shown in FIG. 10B, the relationship between the light amount L of the OLED 201 and the forward voltage Vel changes depending on the temperature of the OLED 201. A Vel correction coefficient table is used to correct this change. The Vel correction coefficient table is a table group provided for each temperature of the OLED 201, and each table is a correction coefficient (hereinafter, “Vel correction”) of the forward voltage Vel for each combination of the light amount L of the OLED 201 and the accumulated light emission time E. "Coefficient") is stored.

The Vel correction coefficient table illustrated in FIG. 9B is provided every 10 degrees from 0 degrees Celsius to 80 degrees Celsius. Each Vel correction coefficient table stores a Vel correction coefficient for each of the _nine light quantities L _{0 to} L ₉ every 50 hours from 0 hour to 1000 hours.
In this embodiment, a Vel correction coefficient table is provided every 10 degrees. However, also for this temperature interval, the temperature range where the characteristic change is large is narrow and the temperature range where the characteristic change is small is wide. The interval may be determined. In this way, the linear interpolation error can be reduced and the storage capacity for storing the Vel correction coefficient table can be saved.

  Similarly, in this embodiment, the cumulative light emission time is divided every 50 hours, but the cumulative light emission time may be determined so that the period in which the characteristic change is large is narrow and the period in which the characteristic change is small is wide. Good. For example, the linear interpolation error can be reduced and the Vel correction coefficient table can be stored if the interval between the cumulative light emission times is narrowed at the beginning of use and the end of the lifetime when the characteristic change is large, and the interval between the cumulative light emission times is widened during the middle period. It is possible to save storage capacity.

When calculating the forward voltage Vel corresponding to the set light amount L of the OLED 201 during the cumulative light emission time T, as shown in FIG. 13, first, the light amount closest to the set light amount L is smaller than the set light amount L. The maximum light amount L _i and the minimum light amount L _{i + 1} among the light amounts larger than the set light amount L are selected (S1301). Then, by referring to the initial Vel table, the initial value Veli _i, reads Veli _{i + 1} (S1302) corresponding number of the OLED201 light amount L _i, the set of the L _{i + 1,} equation (1) Thus, the initial value VelI is estimated by linear interpolation (S1303).

次に、温度センサー４２０を参照して検出温度Ｔを取得して（Ｓ１３０４）、検出温度Ｔに直近の温度のＶｅｌ補正係数テーブル、すなわち、検出温度Ｔよりも低温のＶｅｌ補正係数テーブルのうち最も高温のＶｅｌ補正係数テーブル（温度Ｔ_jとする）と、検出温度Ｔよりも高温のＶｅｌ補正係数テーブルのうち最も低温のＶｅｌ補正係数テーブル（温度Ｔ_j+1とする）を選択する（Ｓ１３０５）。

Next, the detected temperature T is acquired by referring to the temperature sensor 420 (S1304), and the most recent Vel correction coefficient table of the temperature closest to the detected temperature T, that is, the Vel correction coefficient table lower than the detected temperature T is the most. A low temperature Vel correction coefficient table (referred to as temperature T _{j + 1} ) is selected from among a high temperature Vel correction coefficient table (referred to as temperature T _j ) and a Vel correction coefficient table higher than the detected temperature T (S 1305). .

Further, referring to the dot counter 711 corresponding to the OLED 201 (S1306), the cumulative light emission time N is acquired, and the cumulative light emission time that is shorter than the cumulative light emission time N as the cumulative light emission time nearest to the cumulative light emission time N of the OLED 201 is obtained. The largest accumulated light emission time N _k of the time and the smallest accumulated light emission time N _{k + 1} among the accumulated light emission times longer than the accumulated light emission time N are selected (S1307).

Then, referring to the Vel correction coefficient table of the temperatures T _j and T _{j + 1} , eight correction coefficients VelCC corresponding to the sets of the light amounts L _i and L _{i + 1} and the accumulated light emission times N _k and N _{k + 1. i, j, k,} etc. are read out (S1308), and a correction coefficient is estimated by linear interpolation (S1309). That is, first, the correction coefficient VelCC _{j, k} is estimated for the accumulated light emission time N _k as shown in Equation (2),

同様の式を用いて補正係数ＶｅｌＣＣ_j,k+1を推算した後、これらを用いて式（３）のように補正係数ＶｅｌＣＣ_jを推算する。

After estimated correction coefficient VelCC j, a k + ₁ using the same formula, to estimate the correction coefficient VelCC _j by the equation (3) using these.

同様に、温度Ｔ_j+1のＶｅｌ補正係数テーブルを参照して、補正係数ＶｅｌＣＣ_j+1を推算した後、これらの補正係数を用いて補正係数ＶｅｌＣＣを式（４）のように推算する。

Similarly, the correction coefficient VelCC _{j + 1} is estimated with reference to the Vel correction coefficient table of the temperature T _{j + 1} , and then the correction coefficient VelCC is estimated as in Expression (4) using these correction coefficients.

以上のようにして、推算された初期値ＶｅｌＩと補正係数ＶｅｌＣＣとを用いて式（５）のように順方向電圧Ｖｅｌが推算される（Ｓ１３１０）。

As described above, the forward voltage Vel is estimated as shown in the equation (5) using the estimated initial value VelI and the correction coefficient VelCC (S1310).

なお、設定光量Ｌに一致する光量、検出温度Ｔに一致する温度、累積発光時間Ｎに一致する累積発光時間がある場合には、言うまでもなく線形補間を行わずに直値を用いる。
（３−３）初期ＩｄテーブルとＩｄ補正係数テーブル
初期Ｉｄテーブルは、１５，０００個あるＯＬＥＤ２０１のそれぞれについて駆動電流Ｉｄの初期値を光量ごとに記憶するテーブルである。図１１（ａ）に例示する初期Ｉｄテーブルにおいては、９つの光量Ｌ₀〜Ｌ₉のそれぞれについて、１５，０００個のＯＬＥＤ２０１毎に駆動電流Ｉｄの初期値が記憶される。光量Ｌ₀〜Ｌ₉の選び方は初期Ｖｅｌテーブルと同様である。

If there is a light amount that matches the set light amount L, a temperature that matches the detected temperature T, and a cumulative light emission time that matches the cumulative light emission time N, it goes without saying that a direct value is used without performing linear interpolation.
(3-3) Initial Id Table and Id Correction Coefficient Table The initial Id table is a table that stores the initial value of the drive current Id for each of the 15,000 OLEDs 201 for each light quantity. In the initial Id table illustrated in FIG. 11A, the initial value of the drive current Id is stored for each of the 15,000 OLEDs 201 for each of the _nine light amounts L _{0 to} L ₉ . The method of selecting the light amounts L _{0 to} L ₉ is the same as in the initial Vel table.

The relationship between the light amount L of the OLED 201 and the drive current Id also changes depending on the temperature of the OLED 201. The Id correction coefficient table used for this temperature correction is a table group provided for each temperature of the OLED 201, and each table is a correction coefficient IdCC for the drive current Id for each combination of the light amount L of the OLED 201 and the accumulated light emission time E. Is remembered. The Id correction coefficient table illustrated in FIG. 11B is provided every 10 degrees from 0 degrees Celsius to 80 degrees Celsius. Each Id correction coefficient table stores an Id correction coefficient IdCC for each of the _nine light quantities L _{0 to} L ₉ every 50 hours from 0 hour to 1000 hours.

Similarly to the case where the forward voltage Vel is estimated using the initial Vel table and the Vel correction coefficient table, the drive current Id is estimated by linear interpolation using the initial Id table and the Id correction coefficient table.
(3-6) Gate-Source Voltage Vgs Table The gate-source voltage Vgs table is a table group provided for each temperature of the OLED 201, and as shown in FIG. A gate-source voltage Vgs is stored for each combination of the forward voltage Vel and the drain current (drive current) Id. This is because the relationship between the forward voltage Vel and the gate-source voltage Vgs varies depending on the temperature of the OLED 201 as shown in FIG.

Further, as shown in FIG. 16 (a), the gate - source voltage Vgs table, although nonuniform forward voltage Vel into seven sections by the forward voltage Vel ₀ ～Vel _7, six You may unequally divide into the following or eight or more areas. The same applies to the drain current Id.
The selection of the forward voltage Vel and the drain current Id, for example, the minimum amount the minimum forward voltage Vel ₀ to L ₀ can be calculated from, sandwiched between the maximum forward voltage Vel ₈ that the maximum can be calculated from the amount of light L ₉ The intermediate forward voltages Vel1 to Vel7 may be selected so that the linear interpolation error of the gate-source voltage Vgs is within the allowable range within the determined interval.

When the gate-source voltage Vgs is estimated from the forward voltage Vel and the drive current Id, first, the forward currents Vel _i and Vel _{i + 1} that are closest to the forward voltage Vel and the drive current that is closest to the drive current Id. Id _j and Id _{j + 1} are selected (S1701). Next, referring to the gate-source voltage Vgs table, the gate-source voltages Vgs _{i, j} corresponding to the combinations of the forward voltages Vel _i , Vel _{i + 1} and the drive currents Id _j , Id _{j + 1} are determined. Read (S1702).

Then, the gate-source voltage Vgs _j is estimated using Equation (7).

同様に、ゲート−ソース電圧Ｖｇｓ_j+1も推算する（Ｓ１７０３）。
更に、式（８）を用いてゲート−ソース電圧Ｖｇｓを推算する（Ｓ１７０４）。

Similarly, the gate-source voltage Vgs _{j + 1} is also estimated (S1703).
Further, the gate-source voltage Vgs is estimated using equation (8) (S1704).

ＡＳＩＣ５１０が１ライン走査する毎にＯＬＥＤ２０１毎に上述のようにゲート−ソース電圧Ｖｇｓを推算すると、ＤＡＣ５００がキャパシター６２１に当該ゲート−ソース電圧Ｖｇｓを書き込む。そして、当該ゲート−ソース電圧Ｖｇｓが駆動用ＴＦＴ６２２のゲート−ソース端子間に印加されると、駆動電流ＩｄがＯＬＥＤ２０１に供給され、ＯＬＥＤ２０１が所望の光量Ｌで発光する。

When the gate-source voltage Vgs is estimated for each OLED 201 as described above every time the ASIC 510 scans one line, the DAC 500 writes the gate-source voltage Vgs to the capacitor 621. When the gate-source voltage Vgs is applied between the gate and source terminals of the driving TFT 622, the driving current Id is supplied to the OLED 201, and the OLED 201 emits light with a desired light amount L.

[5] 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) Although not particularly mentioned in the above embodiment, the OLED 201 and the driving TFT 622 both deteriorate as the accumulated light emission time becomes longer, and the characteristics change. For example, as shown in FIG. 18A, in order to accurately estimate the forward voltage Vel by linear interpolation when the curvature radius of the characteristic graph is smaller in the initial stage than after the deterioration of the OLED 201, the initial characteristic is used. Accordingly, it is necessary to narrow the interval of the light amount L. This is because if the interval of the light quantity L is widened according to the characteristics after deterioration, the linear interpolation error of the forward voltage Vel becomes too large in the initial stage.

Further, as shown in FIG. 18B, even when the gate-source voltage Vgs is estimated from the forward voltage Vel, the interval of the forward voltage Vel is determined according to the initial characteristic having a small curvature radius in the characteristic graph. This is effective for keeping the linear interpolation error of the gate-source voltage Vgs within an allowable range.
Furthermore, if the interval of the light quantity L is determined individually for each of the initial stage and after the deterioration, the linear interpolation error can be suppressed by narrowing the interval of the light quantity L in the initial stage, and the light quantity after the deterioration. By increasing the interval L, the table size can be kept small.

  (2) In the above embodiment, the case where the gate-source voltage Vgs table is provided for each temperature has been described as an example. However, it goes without saying that the present invention is not limited to this, and instead of temperature or temperature In addition, a gate-source voltage Vgs table may be provided for each accumulated light emission time of the OLED 201. Also in this case, as in the above embodiment, the gate-source voltage Vgs corresponding to the accumulated light emission time of the OLED 201 is estimated by linear interpolation.

  The characteristics of the OLED 201 and the driving TFT 622 are large in the initial use, and the characteristics tend to decrease as the deterioration progresses. For this reason, in the Vel correction coefficient table, the Id correction coefficient table, and the gate-source voltage Vgs table, the linear interpolation error can be suppressed small by narrowing the interval of the accumulated light emission time in the initial use. Further, if the interval of the accumulated light emission time is widened after the deterioration in which the accumulated light emission time becomes long, the table size can be suppressed small.

  (3) 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, and a color printer other than the tandem type is used. There may be a monochrome printer. The same effect can be obtained even if the present invention is applied to a copying machine equipped with a scanner, a facsimile machine equipped with a facsimile communication function, and a multi-function peripheral (MFP) having these functions. Can do.

  The optical writing apparatus and the image forming apparatus according to the present invention are useful as an apparatus that accurately corrects unevenness in the amount of light between a large number of OLEDs with a small storage capacity.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 101 ... Image forming part 102 ... Control part 100 ... Optical writing device 201 ... OLED
420 ... Temperature sensor 402 ... Driver IC
510 ... ASIC
622 ... Driving TFT
700: Driving current correction unit 710 ... Dot counting unit 711 ... Dot counter

Claims (14)

An OLED characteristic table in which the correspondence between the forward voltage or drive current supplied to the OLED and the amount of light is discretely described, and a series circuit in which the OLED is connected to a thin film transistor,
When there is an instruction indicating an instruction light amount that the OLED should emit, a forward voltage value or a drive current value corresponding to the instruction light amount is obtained by linearly interpolating a discrete light amount described in the OLED characteristic table. And a gate-source voltage of the thin film transistor so as to supply a forward voltage value or a driving current value to the OLED.
The discrete light amount described in the OLED characteristic table has a large light amount value on the OLED characteristic curve representing the relationship between the forward voltage or drive current and the light amount, and the light amount and the forward voltage or drive current In addition to the region where the change changes linearly, the value of the light amount is small and the change is also taken into a non-linear region, and
In the non-linear region, the discrete density of the light amount is set densely compared to the linear region,
A TFT characteristic table in which the correspondence between the gate-source voltage of the thin film transistor and the forward voltage or drive current supplied to the OLED is discretely described;
The discrete forward voltage or drive current described in the TFT characteristic table has a forward voltage or drive current value on the TFT characteristic curve representing the relationship between the gate-source voltage and the forward voltage or drive current. In addition to the linear region where the change between the forward voltage or the drive current and the gate-source voltage is linear, the nonlinear region where the forward voltage or the drive current is small and the change is nonlinear And also adopted
In the non-linear region, the discrete density of the forward voltage or drive current is set densely compared to the linear region,
When the forward voltage value or the drive current value is calculated from the OLED characteristic table, the forward voltage or the drive current value is calculated by linearly interpolating the discrete forward voltage or the drive current amount described in the TFT characteristic table. A gate-source voltage corresponding to the calculated value is obtained and applied to the thin film transistor,
Wherein said forward voltage or a driving current in an OLED characteristic table, and the forward voltage or a driving current in the TFT characteristics table, the optical writing device you characterized by discrete distributions are different. Temperature detecting means for detecting an index indicating the temperature of the OLED;
A plurality of the OLED characteristic tables are provided corresponding to different temperatures of the OLED,
When there is an instruction indicating the amount of light to be emitted by the OLED, the discrete amount of light described in the OLED characteristic table corresponding to the temperature closest to the temperature indicated by the index is linearly interpolated to obtain the indicated amount of light. 2. The optical writing device according to claim 1, wherein a corresponding forward voltage value or driving current value is calculated. Temperature detecting means for detecting an index indicating the temperature of the OLED;
A plurality of TFT characteristic tables are provided corresponding to different temperatures of the OLED,
When the forward voltage value or the drive current value is calculated from the OLED characteristic table, the discrete forward voltage or the drive current amount described in the TFT characteristic table corresponding to the temperature closest to the temperature indicated by the index the gate corresponding to the calculated value by linear interpolation - seeking source voltage, the optical writing device according to claim 1, characterized in that applied to the thin film transistor. Temperature detecting means for detecting an index indicating the temperature of the OLED;
A plurality of the OLED characteristic tables are provided corresponding to different temperatures of the OLED,
A plurality of TFT characteristic tables are provided corresponding to different temperatures of the OLED,
When there is an instruction indicating the amount of light to be emitted by the OLED, the discrete amount of light described in the OLED characteristic table corresponding to the temperature closest to the temperature indicated by the index is linearly interpolated into the indicated amount of light. Calculate the corresponding forward voltage value or drive current value,
When the forward voltage value or the drive current value is calculated from the OLED characteristic table, the discrete forward voltage or the drive current amount described in the TFT characteristic table corresponding to the temperature closest to the temperature indicated by the index the gate corresponding to the calculated value by linear interpolation - seeking source voltage, the optical writing device according to claim 1, characterized in that applied to the thin film transistor. In the OLED characteristic table, the correspondence between the forward voltage supplied to the OLED or the driving current and the amount of light is discretely described for each predetermined cumulative light emission time of the OLED.
When there is an instruction indicating the amount of light to be emitted by the OLED, the indicated amount of light is obtained by linearly interpolating the discrete amount of light described in the OLED characteristic table corresponding to the accumulated light emission time closest to the accumulated light emission time of the OLED. the optical writing device according to any one of claims 1 to 4, characterized in that to calculate the forward voltage value or driving current value corresponding to. An OLED characteristic table in which the correspondence between the forward voltage or drive current supplied to the OLED and the amount of light is discretely described, and a series circuit in which the OLED is connected to a thin film transistor,
When there is an instruction indicating the amount of light that the OLED should emit, linear interpolation of the discrete amount of light described in the OLED characteristic table to calculate a forward voltage value or drive current value corresponding to the indicated amount of light, An optical writing device that controls a gate-source voltage of the thin film transistor to supply a forward voltage value or a driving current value to the OLED,
The discrete light amount described in the OLED characteristic table has a large light amount value on the OLED characteristic curve representing the relationship between the forward voltage or drive current and the light amount, and the light amount and the forward voltage or drive current In addition to the region where the change changes linearly, the value of the light amount is small and the change is also taken into a non-linear region, and
In the non-linear region, the discrete density of the light amount is set densely compared to the linear region,
In the OLED characteristic table, the correspondence between the forward voltage or drive current supplied to the OLED and the amount of light is discretely described for each predetermined cumulative light emission time of the OLED.
When there is an instruction indicating the amount of light to be emitted by the OLED, the indicated amount of light is obtained by linearly interpolating the discrete amount of light described in the OLED characteristic table corresponding to the accumulated light emission time closest to the accumulated light emission time of the OLED. optical writing device you and calculates the forward voltage value or driving current value corresponding to. A TFT characteristic table in which the correspondence between the gate-source voltage of the thin film transistor and the forward voltage or drive current supplied to the OLED is discretely described;
The discrete forward voltage or drive current described in the TFT characteristic table has a forward voltage or drive current value on the TFT characteristic curve representing the relationship between the gate-source voltage and the forward voltage or drive current. In addition to the region where the forward voltage or drive current and the gate-source voltage change linearly, the region where the forward voltage or drive current is small and the change is non-linear Taken and
In the non-linear region, the discrete density of the forward voltage or drive current is set densely compared to the linear region,
When the forward voltage value or the drive current value is calculated from the OLED characteristic table, the forward voltage or the drive current value is calculated by linearly interpolating the discrete forward voltage or the drive current amount described in the TFT characteristic table . The optical writing device according to claim 6 , wherein a gate-source voltage corresponding to the calculated value is obtained and applied to the thin film transistor. Temperature detecting means for detecting an index indicating the temperature of the OLED;
A plurality of the OLED characteristic tables are provided corresponding to different temperatures of the OLED,
When there is an instruction indicating the amount of light to be emitted by the OLED, the discrete amount of light described in the OLED characteristic table corresponding to the temperature closest to the temperature indicated by the index is linearly interpolated into the indicated amount of light. 8. The optical writing device according to claim 6 , wherein a corresponding forward voltage value or driving current value is calculated. Temperature detecting means for detecting an index indicating the temperature of the OLED;
A plurality of TFT characteristic tables are provided corresponding to different temperatures of the OLED,
When the forward voltage value or the drive current value is calculated from the OLED characteristic table, the discrete forward voltage or the drive current amount described in the TFT characteristic table corresponding to the temperature closest to the temperature indicated by the index The optical writing device according to claim 7 , wherein a gate-source voltage corresponding to the calculated value is obtained by linear interpolation and applied to the thin film transistor. Temperature detecting means for detecting an index indicating the temperature of the OLED;
A plurality of the OLED characteristic tables are provided corresponding to different temperatures of the OLED,
A plurality of TFT characteristic tables are provided corresponding to different temperatures of the OLED,
When there is an instruction indicating the amount of light to be emitted by the OLED, the discrete amount of light described in the OLED characteristic table corresponding to the temperature closest to the temperature indicated by the index is linearly interpolated to obtain the indicated amount of light. Calculate the corresponding forward voltage value or drive current value,
When the forward voltage value or the drive current value is calculated from the OLED characteristic table, the discrete forward voltage or the drive current amount described in the TFT characteristic table corresponding to the temperature closest to the temperature indicated by the index The optical writing device according to claim 7 , wherein a gate-source voltage corresponding to the calculated value is obtained by linear interpolation and applied to the thin film transistor. In the OLED characteristic table, the discrete density of the predetermined cumulative light emission time that discretely describes the correspondence between the forward voltage supplied to the OLED or the drive current and the amount of light is set more densely as the cumulative light emission time is shorter. The optical writing device according to claim 5 , wherein the optical writing device is an optical writing device. In the TFT characteristic table, the correspondence between the gate-source voltage of the thin film transistor and the forward voltage or driving current supplied to the OLED is discretely described for each predetermined cumulative light emission time of the OLED.
When the forward voltage value or the drive current value is calculated from the OLED characteristic table, the discrete forward voltage or the drive current described in the OLED characteristic table corresponding to the accumulated light emission time closest to the accumulated light emission time of the OLED. gate the amount by linear interpolation corresponding to the calculated value - seeking source voltage, the optical writing according to any one of claims 1 to 5, 7, 9 and 10, characterized in that applied to the thin film transistor apparatus. The TFT characteristic table discretely describes the correspondence between the gate-source voltage and the forward voltage or drive current. The discrete density of the predetermined cumulative light emission time is set more densely as the cumulative light emission time is shorter. The optical writing device according to claim 12 , wherein: An image forming apparatus comprising the optical writing device according to any one of claims 1 to 13.

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