JP2006192678A - Light-emitting device, image forming apparatus, and driving method for light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain the uniform distribution of quantity of light by correcting a difference between the quantities of light of light-emitting elements of a line head through the use of the simple constitution of a circuit. <P>SOLUTION: Firstly, driver connection data are determined by using data on the quantity of light from all the light-emitting elements of the line head 2, which are prestored in an EE-PROM 6, so that driver connection for controlling reference power of each driver IC 3 can be performed. In the driver connection, uniform approximate correction for each of the drivers ICs 3 is applied to the light-emitting element driven and controlled by each of the driver ICs 3. Next, a correction coefficient K between the respective light-emitting elements is determined by making any one of all the light-emitting elements serve as a reference light-emitting element. The difference between the quantities of the light of the light-emitting elements, which is left after the driver correction, is corrected by using the correction coefficient K, so that the quantity of the light of the light-emitting device 1 can be uniformized. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light emitting device, an image forming apparatus, and a light emitting element driving method using light emitting elements arranged in a line.

An electrophotographic image forming apparatus that performs printing by using a line head provided with a large number of light emitting elements in the line direction as an exposure means has been developed. The line head is composed of a large number of single elements such as light emitting diodes (LEDs) and a plurality of arrays, is modularized including a plurality of driver ICs for driving them, and is built into the image forming apparatus as a light emitting device. It has become. In order to use such a light emitting device for printing purposes such as an image forming apparatus, it is required to reduce the light amount difference generated between the light emitting elements of the line head to a level that can be ignored.
For this reason, it has been proposed to use an organic electroluminescence (organic EL) element capable of accurately producing the light emission quantity of several thousand light emitting points necessary for the image forming apparatus as the light emitting element of the line head as described above. . However, when the condensing lens array is provided on the light emitting element, there is a problem that a difference in light amount between the light emitting elements is enlarged.

  In the electrophotographic image forming apparatus (line printer) as described above, the radiated light from the line head is usually applied to the SELFOC (registered trademark) lens array (trade name of Nippon Sheet Glass; hereinafter, SELFOC (registered trademark) lens. Is passed through SL and a SELFOC (registered trademark) lens array is referred to as an SL array), and an image is formed on the photosensitive drum and exposed. The SL array enables a wide range of images to be formed by a configuration in which a large number of cylindrical SL elements for erecting equal-magnification images are arranged. The images made by the SL array are made by overlapping the images made by each SL element (erecting equal-magnification imaging), and the SL elements have a light intensity distribution that halves football. Yes. Therefore, in the SL array, there is a problem that periodic light amount unevenness occurs with the arrangement pitch of each SL element. In addition, light amount unevenness due to optical variation for each SL element and position variation with the line head also occurs. Therefore, if there is a light amount difference due to such light amount unevenness, when the line head and the SL array are combined, the uniformity of the light intensity in the main scanning direction deteriorates due to the light amount unevenness of the SL array. As a result, the exposure accuracy is lowered, and the print quality of the image forming apparatus is impaired.

FIG. 8 is a light amount distribution diagram of a conventional light emitting device showing the above problem.
In FIG. 8, the light emitting device 201 includes a line head 2 in which a plurality of light emitting elements are integrated, and a driver IC 202. In addition, by the combination in which one of the driver ICs 202 drives the m organic EL elements EL11 to ELm1, the n driver ICs 202 share and drive the mxn organic EL elements EL11 to ELmn. ing. The Pdata which is the light amount data in FIG. 8 varies with the inclination and periodicity with respect to the position of each organic EL element due to the above-mentioned causes, and the light amount difference range R1 which is the difference between the maximum value and the minimum value is a large value. It has become.

Therefore, it has been proposed to correct the light amount difference R1 between the light emitting elements of the line head by means of drive control.
For example, Patent Document 1 describes a configuration in which light emission amounts of a large number of LED elements are selected and combined with a driver IC for each rank of light emission amount. Further, Patent Document 2 includes an example in which a line head is configured by using a plurality of LED arrays having a small light amount difference between LED elements in the same chip, and then an adjustment unit that adjusts the light amount for each array is provided. Are listed. Further, Patent Document 3 stores light amount data obtained by individually measuring the light amounts of all the elements of the line head in a state including a lens array, and corrects the light amount difference by reading the light amount data from the memory. It is described.

Japanese Patent Laid-Open No. 5-506653 JP-A-10-157194 Japanese Patent Laid-Open No. 2002-370401

  However, the technique described in Patent Document 1 has a problem in that since the line head is configured by selecting a single light emitting element, the yield is low, and the selection cost is also required, which is expensive. The technique described in Patent Document 2 also has a problem that the yield is low and the cost is high because the line head is configured by selecting the LED array under the condition that the light amounts of the individual light emitting elements are uniform. It was. In addition, the technique described in Patent Document 3 corrects a large light amount difference between all light emitting elements, so that the control range necessary for the correction is large, the configuration of the drive and control circuit is complicated, and the image forming apparatus is expensive. There was a problem of becoming.

  The present invention has been made in view of the above-described problems of the prior art, and can correct a light amount difference of a light emitting element of a line head using a light emitting element with a simple circuit configuration to obtain a uniform light amount distribution. It is an object of the present invention to provide a light emitting device, an image forming apparatus, and a light emitting element driving method.

In order to achieve the above object, a light-emitting device includes a line head in which a plurality of light-emitting elements are arranged and a plurality of driver ICs, and each driver IC drives a plurality of light-emitting elements. A first drive control unit that controls a reference power that defines the drive power of the element, and a second drive control unit that individually controls the drive power of each light emitting element are provided.
According to the present invention, the first drive control unit that controls the reference power that defines the drive power of the light emitting element for each driver IC using the light amount data, and the second that individually controls the drive power for each light emitting element. The drive control unit is hierarchized to correct the light amount difference of the light emitting elements. Therefore, the configuration of the control circuit that corrects the light amount of the light emitting element and emits light becomes easy, and for example, the number of bits of each drive control unit can be reduced. In particular, since the second drive control unit needs to drive and control the light emitting element at high speed, the effect of reducing the number of bits is great.
Here, in the present invention, the electric power for driving the light emitting element is referred to as driving power, and the light emission amount output from the driven light emitting element is referred to as light quantity.

In addition, the first drive control unit described above is controlled using a first correction value based on light amount data obtained by measuring the light amount of the light emitting element of the line head in advance, and the second drive control unit includes the light amount. Control is performed using a second correction value based on the data and the first correction value.
According to the present invention, the second drive control unit that individually controls the drive power for each light emitting element following the light emission information input from the outside has a large correction amount due to the correction of the first drive control unit. Reduced to Therefore, it becomes easy to follow the light emission information inputted from the outside, and the configuration and speeding up of the control circuit can be easily realized.

Further, the minimum light amount in the light emitting elements driven by each of the driver ICs is selected from the light amount data, and the first correction value is obtained based on the value of the minimum light amount.
According to this invention, it becomes easy to obtain the correction values of the first drive control unit and the second drive control unit from the light amount data. Therefore, the calculation for calculating the correction value by a controller such as an image forming apparatus is facilitated.

In addition, the driving method in which the first drive control unit drives the light emitting element is a method in which the driver IC controls the driving voltage or driving current of the light emitting element, and the second drive control unit controls the light emission. The driving method for driving the element is a pulse width modulation method.
According to this invention, a suitable drive system can be selected for each of the first drive control unit and the second drive control unit.

In addition, a measurement unit that measures environment data of an environment in which the light emitting device is installed is provided, and the first drive control unit is further corrected and controlled using the environment data measured by the measurement unit.
In this case, environmental data of the light emitting device, such as ambient temperature, can be measured and fed back to the reference power of the driver IC to control the light emitting device in an appropriate state.

Further, a line head of the same chip using an organic EL element as the light emitting element is configured, and a lens is provided in the line head.
In this case, the light-emitting device intended by the present invention can be realized more easily.

Next, an image forming apparatus according to the present invention includes a photoconductor, a charging unit that uniformly charges the photoconductor, and the above-described light emitting device, and exposing the photoconductor to electrostatically form an image to be formed. An exposure unit that forms a latent image on the photoconductor; a developing unit that develops the electrostatic latent image on the photoconductor as a toner image; and a transfer unit that transfers the toner image on the photoconductor to a transfer material; And a fixing unit for fixing the toner image on the transfer material.
According to the present invention, it is possible to more easily realize an image forming apparatus with high image quality and suitable for natural image printing.

A measuring unit configured to measure environmental data of an environment in which the image forming apparatus is installed; and further correcting and controlling the first drive control unit using the environmental data measured by the measuring unit. To do.
In this case, the temperature inside or around the image forming apparatus can be measured and fed back to the light emitting device, and the image forming apparatus can be controlled in an appropriate state.

The image forming apparatus may further include a measurement unit that measures elapsed time data used, and the correction control is further performed on the first drive control unit using the elapsed time data measured by the measurement unit. .
In this case, it is possible to feed back the prediction data of the light amount change of the line head calculated from the elapsed use time of the image forming apparatus to the light emitting apparatus and control the image forming apparatus in an appropriate state.

Next, a driving method of a light emitting element according to the present invention is a driving method of a light emitting device including a line head in which a plurality of light emitting elements are arranged and a plurality of driver ICs, and each driver IC drives a plurality of light emitting elements. A reading step of reading the light amount data of the plurality of light emitting elements measured and stored in advance, and a reference power for defining the driving power of the light emitting element for each driver IC by a first correction value based on the light amount data. A first control step for correcting, and a second control step for individually correcting the driving power of each light emitting element by a second correction value based on the light amount data and the first correction value.
Thereby, an effect | action and effect equivalent to the light-emitting device of this invention are acquired.

Further, the minimum light quantity in the light emitting element driven by each of the driver ICs described above is selected from the light quantity data, and the first correction value is obtained based on the value of the minimum light quantity.
Thereby, an effect | action and effect equivalent to the light-emitting device of this invention are acquired.

  Hereinafter, the present invention will be described with reference to the drawings.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. 1 to 5 are diagrams showing a first embodiment according to the present invention.

First, the configuration of the light emitting device according to the present embodiment will be described with reference to FIG.
FIG. 1 is a block diagram of a light emitting device 1 according to an embodiment of the present invention. The light emitting device 1 includes a line head 2 in which light emitting elements of mxn organic ELs EL11 to ELmn are arranged, and a driver IC (1) to a driver IC (n that drives m light emitting elements that are continuous in the line head 2. ) N driver ICs 3, a memory EE-PROM 6, and a power supply circuit 7.

  For example, if the application of the light emitting device 1 is an image forming apparatus that prints A3 size paper, a line head width of 12 inches is required, and if the resolution is 600 dpi, mxn that is the number of light emitting elements is 7200. It becomes. For example, if the number of drive terminals of the driver IC that drives the line head is 200, 7200/200 = 36 driver ICs are required. Therefore, m = 200 and n = 36.

  The EE-PROM 6 is a non-volatile memory, and after the line head 2 is manufactured, light amount data as shown in FIG. 8 in which all the light emitting elements are measured is written, and the light amount when necessary through the interface of the light emitting device 1. Data can be read out. As the light amount data, the light amount of the light emitting element with respect to a predetermined unit driving power is used. Note that the light amount data is measured using a predetermined measurement device (not shown). In the measurement, each light emitting element is caused to emit light at the same time and measured by a light receiving element of a measuring device that faces the light emitting element on a one-to-one basis, or each light emitting element is sequentially emitted under the same conditions to measure the light quantity. Measure by method.

  The power supply circuit 7 performs constant voltage and constant current necessary for each driver IC 3 to drive and control the line head 2 based on the supply power supplied to the light emitting device 1.

The controller 10 is a part of the image forming apparatus and includes a correction calculation unit 11 and a measurement unit 14 to control the entire light emitting device 1. The correction calculation unit 11 individually corrects the inter-driver correction data for correcting the reference power that defines the driving power of the light emitting element for each driver IC 3 and the driving power for each light emitting element, using the light amount data of the EE-PROM 6. A correction value of inter-element correction data is calculated. The inter-driver correction data and the inter-element correction data are hierarchized with the inter-driver correction data as a higher level and are used to correct the light amount difference of the light emitting elements.
The correction calculation unit 11 calculates driver correction data and inter-element correction data using the light amount data of the EE-PROM 6, and then stores the correction data in the driver correction table 13 and the inter-element correction table 12. The stored driver correction data is sent to the light emitting device 1 as each drive IC correction data (DRV-DATA). The inter-element correction data is combined with the input image data in the correction calculation unit 11 and sent to the light emitting device 1 as graphic data (GR-DATA). The measurement unit 14 measures environmental data related to the light emitting device and the image forming apparatus, and reflects the measurement result in the correction calculation unit 11.

The calculation method of the driver correction data and the inter-element correction data will be described in detail later with reference to FIGS. 3 to 5. However, the driver correction data is substantially corrected by controlling the reference power of the individual driver IC 3 and the remaining light emission The light quantity difference between the elements is corrected by the correction data between elements. Therefore, since the amount of GR-DATA correction calculation that requires high-speed calculation and output for each element is reduced for new image data, a control circuit can be configured more easily than in the past. On the other hand, correction by DRV-DATA can be handled with a fixed value even when image data is newly input, so that high speed is not required, and a simple circuit can be used.
For example, in the case of the configuration as disclosed in Patent Document 3, if 6-bit correction data is added to image data having 6-bit gradation, 12-bit gradation data is required after correction. When used, it is possible to reduce GR-DATA, which is gradation data after correction, from 12 bits to 9 bits by distributing 3 bits to DRV-DATA.

  In the present embodiment, a suitable method can be selected for each of the drive control method corresponding to GR-DATA and the drive control method corresponding to DRV-DATA. Since the high speed is required for the former, the pulse width control (PWM) method is used, and for the latter DRV-DATA, the drive voltage of the entire driver IC 3 is changed. The drive control for changing the drive voltage of the entire driver IC 3 can be easily realized by adding a relatively simple circuit to the driver IC 3.

  Further, the drive control method for changing the drive voltage of the entire driver IC 3 can be easily added and combined with correction data based on another parameter. In the present invention, the configuration may be such that the environmental data of the measurement unit 14 is multiplied by a predetermined ratio and added to DRV-DATA. The environmental data of the measurement unit 14 includes temperature, humidity, change with time, characteristics of printing paper on which the image forming apparatus is to perform printing, and the like.

  The light emitting device 1 and the controller 10 are separate units in the image forming apparatus and can be replaced in units. Therefore, when assembling and manufacturing the image forming apparatus, it is easy to replace the light emitting device 1 in which a problem has occurred or to replace the light emitting device 1 that has been used for a long time and has reached the end of its life. Since the unique light quantity data is stored in the EE-PROM 6 of the new light-emitting device 1 that has been replaced, the correction calculation unit 11 reads the new light quantity data, and based on this, the driver correction table and the inter-element correction table are read out. It is supposed to replace the data.

  The storage unit for storing the DRV-DATA output to each driver IC 3 is included in the correction calculation unit 11. However, the storage unit is provided inside the light emitting device 1, and the DRV-DATA stored in the storage unit is stored in the storage unit. You may make it input into each 3. Thereby, since control which sets DRV-DATA to the light-emitting device 1 is closed by the light-emitting device 1, the interface of the light-emitting device 1 and the controller 10 can be reduced. In this case, as storage means for storing DRV-DATA in advance, a method of using a part of the EE-PROM 6, a method of adding a memory IC dedicated to storage of DRV-DATA, or an individual driver IC 3 A method of providing storage means can be applied.

Next, the line head module will be described. This line head module is used as an exposure unit of an image forming apparatus.
FIG. 2 is a side sectional view of the line head module 101 according to the present embodiment. The line head module 101 of the present embodiment includes a line head 2 in which a plurality of organic EL elements are arranged in alignment, and an SL array 131 in which SL elements 131a that image the light from the line head 2 are erecting at an equal magnification. The head case 152 is supported at a predetermined interval. The line head 2 and the SL array 131 are held in the head case 152 in an aligned state, whereby the SL array 131 concatenates the light from the line head 2 to a photosensitive drum described later at an equal magnification. It is supposed to be imaged.

  The line head 2 is formed by integrally forming a light emitting element array (light emitting portion line) formed by arranging a plurality of organic EL elements on a long and thin rectangular element substrate. Further, the organic EL elements may be arranged in two rows in a staggered manner. In that case, the pitch of the organic EL elements in the element arrangement direction of the line head 2 can be reduced, and the resolution of the image forming apparatus described later can be improved.

  The organic EL element has a configuration in which at least an organic light emitting layer is sandwiched between a pair of electrodes, and emits light by supplying a current from the pair of electrodes to the organic light emitting layer. One electrode in the organic EL element is connected to a common ground, and the other electrode is connected to the drive line of the corresponding driver IC 3. In this line head 2, an organic EL element is used as the EL element, but it goes without saying that an inorganic EL element may be used instead.

The SL array 131 is an aggregate in which convergent rod lenses are accommodated. Each SL element 131 a is accommodated and fixed by a black silicone resin, and the aggregate is attached to the head case 152. The SL element 131a has a parabolic refractive index distribution from the center to the periphery. Therefore, the light incident on the SL element 131a travels while meandering in the inside thereof at a constant period. Therefore, if the length of the SL element 131a is adjusted, an image can be formed upright at an equal magnification. In this way, in the SL element 131a that forms an erecting equal-magnification image, it is possible to superimpose images formed by adjacent SL elements 131a, and a wide range of images can be obtained. Therefore, the SL array 131 shown in FIG. 2 can accurately form light from the entire line head 2 on the exposed surface.
However, in the line head module 101 having the above-described configuration, the light amount distribution varies greatly depending on the arrangement form of the line head 2 and the SL array 131. For example, as shown in FIG. 8, not only the variation in the light amount but also a periodic change in the line direction of the SL array 131 occurs. Therefore, even if the light emission amount variation of the line head 2 itself is corrected and uniform light is made incident on the SL array 131, the amount of light emitted from the line head module 101 has a periodic distribution, and further the line The alignment accuracy between the head 2 and the SL array 131 is also greatly affected.

  The luminance correction method according to the present embodiment includes the light amount variation caused by the structure of the SL array 131 and the light amount variation caused by the alignment with the line head 2 as the light amount difference between the elements of the line head 2. It is to correct.

Next, a correction method for driving the light emitting element of this embodiment will be described.
FIG. 3 is a corrected light amount distribution diagram of the light emitting device according to the present embodiment, FIG. 3A is a light amount distribution diagram after driver correction, and FIG. 3B is a light amount after inter-element correction. A distribution chart is shown. FIG. 3 shows a case where the light amount difference is corrected using the Pdata in the light amount distribution diagram of FIG. 8 as an example.

  In FIG. 3, the horizontal axis indicates the position of the light emitting element of the line head 2 and corresponds to the drive terminal position of each driver IC 3 of the light emitting device 1. The power on the vertical axis indicates the amount of light that is actually output from the SL array 131 by the light emission of the light emitting element. The driver IC 3 includes a DRV-DATA input terminal for controlling the reference power, and the output of each drive terminal is controlled. Since the horizontal axis in FIG. 3B is the same as the horizontal axis in FIG. 3A, the display indicating the drive terminal position of each driver IC 3 is omitted.

  First, driver correction is performed as the first step correction. For this purpose, the light quantity data of the light emitting element is read from the EE-PROM 6, and the minimum light quantity of the light emitting element in each driver IC 3 of the driver IC (1) to driver IC (n) is obtained as LP, and LP1 to LPn Ask for. Next, a value with the lowest light quantity among LP1 to LPn is defined as Cmin, and a value obtained by dividing this Cmin by the value of each LP is defined as a driver correction coefficient C of each drive IC3. By this calculation, driver correction coefficients C1 to Cn, which are correction values for each driver IC 3, are determined, and a driver correction table storing each value of C1 to Cn is generated.

  FIG. 3A is a post-correction light amount distribution diagram after correcting the driver IC (1) to the driver IC (n) with the driver correction coefficients C1 to Cn. By the calculation method for correcting the reference power of each driver IC 3 described above, the minimum light amount in each driver IC 3 is aligned with P0, and the light amount difference range R2 is several minutes compared to the light amount difference range R1 when correction is not performed. Is reduced to 1. Here, the control for correcting the amount of light is based on the idea that the driving power of the light emitting element having a high amount of light is reduced to make the entire level uniform. This prevents the light emitting element having a low light amount from being excessively driven to shorten its life.

  Next, by performing inter-element correction on the light quantity distribution diagram after driver correction in FIG. 3A, the light quantity of all the light emitting elements is corrected to be P0. This inter-element correction in the second step will be described later using the inter-element light quantity correction diagram of FIG. As described above, the driver correction coefficient can be obtained with a simple algorithm by the calculation method of the present embodiment in which LP, which is the minimum light amount for each driver IC 3, is obtained.

Next, a method for controlling the reference power and the driving power for each light emitting element will be described.
FIG. 4 is a block diagram of the driver IC 3 and its surroundings, and includes a reference control unit 20, a line head 2, and an element control unit 27. Further, a temperature sensor 22 which is one form of the measurement unit 14 in FIG. 1 is input to the reference control unit 20 via the correction calculation unit 11. The reference control unit 20 and the element control unit 27 are preferably configured as the driver IC 3 on the same IC chip for wiring connection, but may be separate chips depending on conditions such as the chip size.

The reference control unit 20 is a first drive control unit, and controls the reference power of the driver IC 3.
In the reference control unit 20, DRV-DATA including the driver correction coefficient C as a coefficient is input to the D / A conversion circuit 21, and the reference control unit 20 outputs a voltage value corresponding thereto. The output voltage of the D / A conversion circuit 21 is input to each of the buffers 23, determines the source voltage of each switching transistor (SwTr) 24, and controls the light emission intensity of the light emitting element. For example, the light emitting element EL11 connected to the drain of the SwTr 24 emits light when the SwTr 24 is on, and the intensity of light emission is controlled according to the source voltage.

  The output of the D / A conversion circuit 21 changes linearly according to DRV-DATA, and controls the reference power that defines the drive power of the entire reference control unit 20 as described above. Accordingly, the entire m light emitting elements connected to the reference control unit 20 are controlled based on DRV-DATA. Further, the light emission time of the light emitting element is a time during which the SwTr 24 is turned on, and is controlled by a gate input to the SwTr 24. The driving power of the light emitting element is obtained by multiplying the light emission time by the above light emission intensity.

  The SwTr 24 may be a bipolar transistor or a MOS transistor. In the case of a MOS transistor, it can be used for both the P channel and the N channel. In the case of the P channel, the gate voltage is turned on in the negative direction from the source potential. It is controlled by m PWM outputs Wj (where j = 1 to m, j is a natural number) so as to be turned on.

The element control unit 27 is a second drive control unit and controls drive power for each light emitting element.
GR-DATA which is gradation data having PWM time width information of about 10 bits is input to the element control unit 27, and the element control unit 27 converts it into m pulses of the PWM output Wj and outputs it. The SwTr 24 is turned on for the duration of each pulse width.

  The element control unit 27 includes a shift register and a latch circuit (not shown) in which the same number as the number of bits of GR-DATA is parallel, and each shift register includes m stages. For example, if the number of parallel bits of GR-DATA is 9 bits, 9-bit parallel data for generating each Wj signal is sent by the shift register. The element control unit 27 includes m PWM generation counters (not shown). The m PWM generation counters are configured to generate m PWM outputs Wj each having a pulse width based on 9-bit parallel data. Is generated. Therefore, by reducing the number of bits of GR-DATA according to the present embodiment, the configuration of the element control unit 27 having a large number of circuit elements can be facilitated.

  The temperature sensor 22 is installed in the vicinity of the light emitting device 1 and can detect the temperature of the line head 2. The temperature data detected via the correction calculation unit 11 is input to the D / A conversion circuit 21 so that driver correction is performed, and the entire line head 2 can be temperature corrected. When the temperature data is digital output, it is digitally calculated as DRV-DATA, and when it is analog data, it is only necessary to perform simple arithmetic processing for controlling the output voltage of the D / A conversion circuit 21. Accordingly, correction corresponding to the operating temperature can be performed very easily, so that when applied to an image forming apparatus, print quality can be improved.

Next, a method for correcting the light amount between elements will be described.
FIG. 5 is a schematic diagram of the inter-element light amount correction of the light emitting device according to the present embodiment. FIG. 5 (a) shows a state before correction of the inter-element light amount correction, and FIG. 5 (b) shows the inter-element light amount correction. It shows after correction.

FIG. 5 shows three light emitting elements EL11, EL21, and EL31 that are driven by the driver IC (1) and are adjacent to each other as an example. The vertical axis in FIG. 5 represents the light amount, and the horizontal axis represents the PWM pulse width for driving each light emitting element.
Since FIG. 5A is before the inter-element light amount correction, EL11, EL21, and EL31 all have gradations of values given by the image data input to the controller 10. Hereinafter, a case will be described as an example in which the PWM pulse width of the gradation is assumed to be T0 and EL11, EL21, and EL31 are corrected to emit light with the same luminance.

  Here, the state before the start of inter-element light amount correction will be described in detail. FIG. 5A shows a state after the driver correction has already been performed, and therefore, P1, P2, and P3 are all values obtained by multiplying the original light amount by the same driver correction coefficient C. For example, C = 1 in the driver IC (1) related to P1, P2, and P3. The light amount difference between the light emitting elements in each driver IC 3 still remains, and the light amount correction between the elements is performed by the method shown in the following steps for the purpose of correcting this light amount difference.

  First, the light amount difference data stored in the EE-PROM 6 is multiplied by the light amount data of all the light emitting elements corresponding to each driver IC 3 by the driver correction coefficient C of the driver correction table, and this is used as the driver corrected light amount data. . P1, P2, and P3 in FIG. 5 are values of the driver-corrected light amount data, indicating that the light emission power is large in the order of P2> P1> P3, and the light amount of P2 is the highest.

  Next, an inter-element correction coefficient K is obtained. For this purpose, first, any one of the light emitting elements is set as a reference light emitting element. The reason that the setting can be made by selecting from all the light emitting elements is that the correction between the driver ICs is completed by the driver correction. In this case, it is preferable to select a light emitting element with an average light amount as a reference light emitting element so that the pulse width of PWM control after correction is not too wide or conversely too narrow.

  In the example of FIG. 5, the light emitting element EL11 having an intermediate light amount is selected as the reference light emitting element. Since the light quantity of EL11 is P1, when this P1 is divided by the light quantity of each light emitting element, the inter-element correction coefficient K is obtained. By using this inter-element correction coefficient K, the drive time is corrected by reducing the drive time of a light emitting element having a high light amount and increasing the drive time of a light emitting element having a low light amount. In FIG. 5A, the inter-element correction coefficient K2 = 0.8 for EL21 and K3 = 1.2 for EL31. In the reference light emitting element EL11, naturally, K1 = 1.

  By the above calculation, the correction coefficient K between the respective elements is obtained for all the light emitting elements, and this data can be stored as an inter-element correction table to perform inter-element light amount correction. For example, as shown in FIG. 5, if the gradation value of the input image data is T0 in PWM pulse width, the PWM pulse width after inter-element correction for EL11, EL21, EL31 is K = 1. The values are obtained by multiplying 0.8 and 1.2, respectively, and T1 = T0, T2 = 0.8T0, and T3 = 1.2T0. In this way, the light amounts of all the light emitting elements are corrected as shown in FIG. In this case, since EL11 is selected as the reference light emitting element, the correction is made based on the light quantity P1.

  In FIG. 5, the gradation value of the image data is exemplified as T0 that is the same for EL11, EL21, and EL31. However, in general, the input gradation of each light emitting element of the image data is arbitrary. For example, if the PWM pulse width of the EL11 image data is T0, T21 for EL21, and Ty for EL31, the PWM pulse width after inter-element correction for EL11, EL21, EL31 is T1 = T0, T2 = 0.8Tx. , T3 = 1.2Ty.

  In this way, in the present embodiment, the light amount data of the light emitting elements of the line head 2 stored in advance in the EE-PROM 6 is used to perform driver correction for controlling the reference power of each driver IC 3, and then The light amount difference between the light emitting elements remaining after the driver correction is corrected so as to be uniformed by the light amount correction between the elements. This reduces the correction range that requires inter-element light amount correction and reduces the correction processing. Therefore, the configuration of the correction circuit that requires a large circuit size and high speed, and the calculation processing for correction can be performed. It has the advantage of being easy.

  Further, there is an advantage that the overall characteristic of the light emitting device 1 can be corrected by adding a simple configuration and feeding back the parameter relating to the environmental characteristic to the driver correction.

  In addition, since the variation in the driving capability between the driver ICs 3 is not zero, the driving capability data of each driver IC 3 may be included in the light amount data when combined with the line head 2. Thereby, the correction accuracy of the light emitting device 1 is further improved.

  In addition, in correcting the inter-element light amount, one reference light emitting element is selected from all the light emitting elements, and the inter-element correction coefficient K of all the light emitting elements is obtained by this reference light emitting element. It is also possible to correct the light amount between elements by grouping related light emitting elements. Specifically, for each group, the light emitting element having the lowest light quantity LP can be used as a reference light emitting element, and the light quantity correction between elements can be performed within each group. Thus, the calculation of the light amount correction between elements can be divided for each driver IC 3 to reduce the calculation amount. In this case, the inter-element correction coefficient K is obtained by dividing the value of the minimum light quantity LP for each driver IC 3 by the light quantity of the other light emitting elements.

  Further, a CPU may be provided inside the light emitting device 1, and the light emitting device 1 may incorporate a part of the correction calculation unit 11. Accordingly, the light emitting device 1 can be handled as a single unit, and the control of the light emitting device 1 can be separated from the controller 10. Therefore, it is easy to create a processing program for the controller 10, and it is possible to contribute to speeding up the operation of the controller 10.

  The installation location of the sensor such as the temperature sensor 22 may be built in the light emitting device 1 instead of outside the light emitting device 1.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to the drawings.

  FIG. 6 is a diagram showing a second embodiment according to the present invention. The difference from the first embodiment is the configuration of the driver IC. Hereinafter, a different part from the said 1st Embodiment is demonstrated, and the code | symbol same about the part which overlaps with the said 1st Embodiment is attached | subjected, and description is abbreviate | omitted. The configuration in which m PWM signals Wj (where j = 1 to m, j are natural numbers) from the element control unit 37 is input to the gate of the SwTr 35 and the SwTr 35 is turned on is the same as in the case of FIG.

FIG. 6 is a block diagram of the driver IC 4 according to the present embodiment and its surroundings. The driver IC 4 includes the reference control unit 30, the line head 2, and the element control unit 37. Further, a temperature sensor 22 which is one form of the measurement unit 14 in FIG. 1 is input to the reference control unit 30 via the correction calculation unit 11. The reference control unit 30 and the element control unit 37 are preferably configured as the driver IC 4 in the same IC chip for wiring connection, but may be separate chips depending on conditions such as the chip size.
The configuration around the driver IC 4 in FIG. 6 is significantly different from the configuration in FIG. 4 of the first embodiment in that the reference control unit 30 is current controlled. As is well known, the organic EL element is a current driving element and has a characteristic that the intensity of light emission is proportional to the driving current. Therefore, current control is more suitable for performing high-precision light emission control. Therefore, the reference control unit 30 of the present embodiment is configured to convert DRV-DATA into a current value.

  The D / A conversion circuit 31 includes a plurality of reference voltage generation circuits and a selection circuit (not shown). The reference voltage generation circuit includes a plurality of resistors connected in series between the power supply voltage Vcc and the ground, and the power supply voltage Vcc is divided by these resistors to generate a plurality of reference voltages. The selection circuit selects one of a plurality of reference voltages based on DRV-DATA and outputs it as an analog voltage signal Vgref.

  Next, the transistor 33 of Qr2 has a function of converting a voltage into a current. The transistor 33 allows a current corresponding to the value of the analog voltage Vgref to flow as the analog current signal Iref. Therefore, the analog current signal Iref corresponding to the DRV-DATA digital data is generated. The analog current signal Iref is applied to the gate and drain of the current setting transistor 32 of Qr1, and the drain output Vg of the current setting transistor 32 is input to the gate of the drive current source transistor 34 (Q1 to Qm) of each light emitting element. The drive currents I1 to Im are supplied. Therefore, the drive currents I1 to Im have current values corresponding to the digital data of DRV-DATA.

  In this way, in this embodiment, the light amount data of the light emitting elements of the line head 2 stored in advance in the EE-PROM 6 is used, the reference power of each driver IC 4 is subjected to driver correction by current control, and then The light amount difference between the light emitting elements remaining after the driver correction is corrected so as to be uniformed by the light amount correction between the elements. As a result, the correction range that requires light amount correction between elements is greatly reduced, and the configuration of the correction circuit and the arithmetic processing for correction are facilitated. Further, the light amount of the line head 2 is controlled with high accuracy. It has the advantage of being able to.

(Application examples)
A tandem image forming apparatus using the light emitting device of the present invention will be described. FIG. 7 is a schematic configuration diagram of a tandem image forming apparatus. An image forming apparatus 80 shown in FIG. 7 includes line head modules 101K, 101C, 101M, and 101Y having the same configuration as the line head module 101 of the previous embodiment. Body) 41K, 41C, 41M, and 41Y are arranged as exposure apparatuses, respectively, and are configured as a tandem system.

  The image forming apparatus 80 includes a driving roller 91, a driven roller 92, and a tension roller 93. The intermediate transfer belt 90 is stretched around these rollers so as to circulate and drive in the direction of the arrow (counterclockwise) in FIG. Is. Photosensitive drums 41K, 41C, 41M, and 41Y are arranged at predetermined intervals with respect to the intermediate transfer belt 90. These photosensitive drums 41K, 41C, 41M, and 41Y have a photosensitive layer as an image carrier on the outer peripheral surface thereof.

  Here, K, C, M, and Y in the symbols of the photosensitive drum mean black, cyan, magenta, and yellow, respectively, and indicate that the photosensitive members are black, cyan, magenta, and yellow, respectively. . The meanings of these symbols (K, C, M, Y) are the same for the other members. The photosensitive drums 41K, 41C, 41M, and 41Y are driven to rotate in the arrow direction (clockwise) in FIG. 7 in synchronization with the driving of the intermediate transfer belt 90.

  Around each photosensitive drum 41 (K, C, M, Y), charging means (corona charger) 42 for uniformly charging the outer peripheral surface of the photosensitive drum 41 (K, C, M, Y), respectively. (K, C, M, Y) and rotation of the photosensitive drum 41 (K, C, M, Y) on the outer peripheral surface uniformly charged by the charging means 42 (K, C, M, Y) The line head module 101 (K, C, M, Y) of the present invention that sequentially scans the line in synchronism with each other is provided.

  Further, a developing device 44 (K, C) that applies a toner as a developer to the electrostatic latent image formed by the line head module 101 (K, C, M, Y) to form a visible image (toner image). , M, Y). Then, primary transfer rollers 45 (K, C, M, and Y) as transfer means for sequentially transferring the toner images developed by the developing devices 44 (K, C, M, and Y) to the intermediate transfer belt 90 that is a primary transfer target. Y) and a cleaning device 46 (K, C, M, Y) as a cleaning means for removing toner remaining on the surface of the photosensitive drum 41 (K, C, M, Y) after being transferred. Is provided.

  Here, each line head module 101 (K, C, M, Y) is installed such that the arrangement direction of the organic EL elements is along the bus line of the photosensitive drum 41 (K, C, M, Y). The light emission energy peak wavelength of each line head module 101 (K, C, M, Y) and the light intensity peak wavelength of the photosensitive drum 41 (K, C, M, Y) are set so as to substantially match. Yes.

  The developing device 44 (K, C, M, Y) uses, for example, a non-magnetic one-component toner as a developer, and the one-component developer is conveyed to the developing roller by a supply roller, for example, and adheres to the surface of the developing roller. The film thickness of the developed developer is regulated by a regulation blade. Then, the developer is attached in accordance with the potential level of the photosensitive drum 41 (K, C, M, Y) by bringing the developing roller into contact with or pressing the photosensitive drum 41 (K, C, M, Y). And developed as a toner image.

  The black, cyan, magenta, and yellow toner images formed by the four-color single-color toner image forming station are intermediated by the primary transfer bias applied to the primary transfer roller 45 (K, C, M, Y). Primary transfer is sequentially performed on the transfer belt 90. Then, the toner images that are sequentially superposed on the intermediate transfer belt 90 to become a full color are secondarily transferred to a recording medium P such as paper by a secondary transfer roller 66 as a secondary transfer unit, and further, a fixing unit serving as a fixing unit. The toner is fixed on the recording medium P by passing through the roller pair 61 and then discharged onto a paper discharge tray 68 formed on the upper part of the apparatus by the paper discharge roller pair 62.

  In FIG. 7, reference numerals indicate a paper feeding cassette 63 in which a large number of recording media P are stacked and held, a pickup roller 64 that feeds the recording media P from the paper feeding cassette 63 one by one, and a secondary transfer roller 66. The gate roller pair 65 defines the supply timing of the recording medium P to the secondary transfer portion. Further, a secondary transfer roller 66 that forms a secondary transfer portion with the intermediate transfer belt 90, and a cleaning blade 67 as a cleaning unit that removes toner remaining on the surface of the intermediate transfer belt 90 after the secondary transfer. is there.

  The image forming apparatus provided with the line head module of the present invention is not limited to the above, and various modifications are possible. For example, a four-cycle image forming apparatus or a monochrome image forming apparatus may be used.

1 is a block diagram of a light emitting device according to a first embodiment of the present invention. The side sectional view of a line head module. The light quantity distribution map after correction | amendment of a light-emitting device. (A) is a light quantity distribution diagram after driver correction, and (b) is a light quantity distribution diagram after inter-element correction. The driver IC and its surrounding block diagram. The schematic diagram of the light quantity correction between elements of a light-emitting device. (A) shows before correction of inter-element light amount correction, (b) shows after correction of inter-element light amount correction. The driver IC which concerns on the 2nd Embodiment of this invention, and its surrounding block diagram. 1 is a schematic configuration diagram of a tandem image forming apparatus to which a light emitting device is applied. The light quantity distribution figure of the conventional light-emitting device.

Explanation of symbols

EL11-ELmn ... Organic EL element as light-emitting element, 1 ... light emitting device, 2 ... line head, 3, 4 ... driver IC, 6 ... EE-PROM, 11 ... correction calculation unit, 12 ... inter-element correction table, 13 ... Driver correction table, 14 ... measurement unit, 20, 30 ... reference control unit as first drive control unit, 21,31 ... D / A conversion circuit, 22 ... temperature sensor, 27, 37 ... second drive control unit 80, an image forming apparatus, 101, a line head module, 131, an SL array, 131a, an SL array element.

Claims (11)

A light emitting device including a line head in which a plurality of light emitting elements are arranged and a plurality of driver ICs, each driver IC driving the plurality of light emitting elements,
A first drive control unit that controls a reference power that defines the drive power of the light emitting element for each driver IC;
A second drive control unit for individually controlling the drive power for each light emitting element;
A light-emitting device comprising: The first drive control unit is controlled using a first correction value based on light amount data obtained by measuring in advance the light amount of the light emitting element of the line head,
The light emitting device according to claim 1, wherein the second drive control unit is controlled using a second correction value based on the light amount data and the first correction value.   3. The first correction value is obtained based on the minimum light quantity value selected from the light quantity data, and the first correction value is obtained based on the minimum light quantity value among the light emitting elements driven by each of the driver ICs. Light-emitting device. The driving method in which the first drive control unit drives the light emitting element is a method in which the driver IC controls the driving voltage or driving current of the light emitting element,
4. The light emitting device according to claim 1, wherein the second driving control unit drives the light emitting element by a pulse width modulation method. 5. It has a measuring unit that measures the environmental data of the environment where the light emitting device is installed,
5. The light emitting device according to claim 1, wherein the first drive control unit is further subjected to correction control using environmental data measured by the measurement unit.   The light-emitting device according to claim 1, wherein a line head of the same chip using an organic EL element as the light-emitting element is configured, and the line head includes a lens. A photoreceptor,
A charging unit for uniformly charging the photoreceptor;
An exposure unit comprising the light emitting device according to any one of claims 1 to 6, and exposing the photosensitive member to form an electrostatic latent image of an image to be formed on the photosensitive member;
A developing unit that develops the electrostatic latent image on the photoreceptor as a toner image;
A transfer portion for transferring a toner image on the photoreceptor to a transfer material;
A fixing unit for fixing a toner image on the transfer material;
An image forming apparatus comprising: A measurement unit that measures environmental data of an environment in which the image forming apparatus is installed;
The image forming apparatus according to claim 7, wherein the first drive control unit is further subjected to correction control using environmental data measured by the measurement unit. A measuring unit that measures elapsed time data used by the image forming apparatus;
The image forming apparatus according to claim 7, wherein the first drive control unit is further subjected to correction control using elapsed time data measured by the measurement unit. A driving method of a light emitting device including a line head in which a plurality of light emitting elements are arranged and a plurality of driver ICs, each driver IC driving a plurality of light emitting elements,
A reading step of reading the light amount data of the plurality of light emitting elements which are measured and stored in advance;
A first control step of correcting a reference power defining a driving power of the light emitting element for each driver IC by a first correction value based on the light amount data;
A second control step of individually correcting the driving power for each light emitting element by a second correction value based on the light amount data and the first correction value;
A method for driving a light emitting element, comprising: 11. The first correction value is obtained based on the minimum light quantity value selected from the light quantity data, and the first correction value is determined based on the minimum light quantity value among the light emitting elements driven by each of the driver ICs. Driving method of the light emitting element.

Images