JP2011098485A - Exposure head, and control method of exposure head - Google Patents

Abstract

Provided is a technique for realizing a long life of an exposure head by suppressing the frequency of light quantity correction.
A first light emitting element, a second light emitting element, an optical unit that images light emitted from the first light emitting element, and an image that images light emitted from the second light emitting element; A measurement unit for measuring a light amount of one light emitting element to obtain a first measured light amount, measuring a light amount of the second light emitting element to obtain a second measured light amount, and a second measured light amount being a first threshold value The determination unit determines whether or not the light amount correction of the second light emitting element is necessary based on the first measurement light amount, and if the determination unit determines that the light amount correction is necessary, the light amount of the second light emitting element And a correction unit that does not execute the light amount correction of the second light emitting element when the determination unit determines that the light amount correction is unnecessary.
[Selection] Figure 10

Description

  The present invention relates to an exposure head that performs exposure using light from a light emitting element and a method for controlling the exposure head.

  Conventionally, there has been proposed an exposure head that includes a plurality of light emitting elements arranged in the main scanning direction and performs exposure using light emitted from each light emitting element (Patent Document 1). Incidentally, in such an exposure head, the light emitting element deteriorates as it repeatedly emits light, and as a result, the light amount of the light emitting element may decrease. Therefore, the exposure head described in Patent Document 1 appropriately measures the light amount of each light emitting element using an optical sensor, and corrects the light amount of the light emitting element when a light emitting element whose light amount has decreased due to deterioration is detected. In this way, the light amount of the deteriorated light emitting element can be raised to the target light amount.

JP 2009-034943 A

  By the way, in order to perform such light amount correction, it is necessary to increase the level of a signal applied to a deteriorated light emitting element (for example, the value of a current applied to the light emitting element). However, the deterioration of the light emitting element tends to be accelerated as the signal level increases. For this reason, the life of the exposure head may be shortened every time the light amount is corrected. Therefore, it is not preferable to frequently perform such light amount correction from the viewpoint of extending the life of the exposure head.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for realizing a long life of an exposure head by suppressing the frequency of light amount correction.

  In order to achieve the above object, the exposure head according to the present invention forms an image of light emitted from the first light emitting element, the second light emitting element, and the first light emitting element, and the second light emitting element An optical unit that forms an image of the emitted light, and a measuring unit that measures the light quantity of the first light emitting element to obtain the first measured light quantity, and measures the light quantity of the second light emitting element to obtain the second measured light quantity When the second measured light amount is equal to or less than the first threshold, the determination unit that determines whether the second light emitting element needs to be corrected based on the first measured light amount, and the determination unit needs to correct the light amount. A correction unit that executes light amount correction of the second light emitting element when the determination unit determines that correction of light amount is unnecessary, and a correction unit that does not perform light amount correction of the second light emitting element. It is said.

  In order to achieve the above object, the exposure head control method according to the present invention provides a first exposure head for performing exposure by forming an image of light from the first light emitting element and the second light emitting element by an optical unit. A first step of measuring a light amount of one light emitting element to obtain a first measured light amount, measuring a light amount of the second light emitting element to obtain a second measured light amount, and a second measured light amount being a first The second step of determining whether or not the light amount correction of the second light emitting element is necessary based on the first measured light amount, and the second step when the second step determines that the light amount correction is necessary. And a third step of performing the light amount correction of the second light emitting element when the second step determines that the light amount correction is unnecessary. .

  In the invention configured as described above (exposure head, exposure head control method), the light amount of the light emitting element may decrease due to deterioration. Therefore, also in the present invention, the light quantity of the light emitting element is measured to correct the light quantity of the light emitting element. However, in the present invention, in order to suppress the frequency of light amount correction, the necessity of light amount correction is determined, and light amount correction is performed according to the determination result. Specifically, it is as follows. First, the first measurement light amount is obtained by measuring the light amount of the first light emitting element, and the second measurement light amount is obtained by measuring the light amount of the second light emitting element (measurement unit, first step). . If the second measured light amount is equal to or less than the first threshold value, whether or not the second light emitting element needs to be corrected is determined based on the first measured light amount (determination unit, second step). The light amount of the second light emitting element is corrected according to the determination result (correction unit, third step). That is, even if the light amount of the light emitting element (second light emitting element) decreases due to deterioration, the light amount of the light emitting element (second light emitting element) decreases depending on the light amount of another light emitting element (first light emitting element). In some cases, the influence on the exposure of the light emitting element (second light emitting element) can be allowed to be reduced without affecting the exposure. Therefore, the present invention determines whether or not the light amount correction of the light emitting element (second light emitting element) is necessary based on the measured light amount (first measured light amount) of another light emitting element, and according to the necessity determination. The light amount of the light emitting element (second light emitting element) is corrected. In this way, it is possible to extend the life of the exposure head while suppressing the frequency of light quantity correction.

  Specifically, the determination unit determines that the light amount correction of the second light emitting element is unnecessary when the light amount index value indicating the value corresponding to the first measured light amount is equal to or greater than the second threshold value. You may comprise so that it may not exist. That is, even if the light amount of the second light emitting element is reduced due to deterioration, the second light amount index value indicating a value corresponding to the first measured light amount of the first light emitting element is equal to or larger than the second threshold value. The influence of the decrease in the light amount of the light emitting element on the exposure is not conspicuous, and it can be determined that the light amount correction of the second light emitting element is unnecessary. Then, by executing the light amount correction of the second light emitting element according to the necessity determination, it is possible to suppress the frequency of the light amount correction and to extend the life of the exposure head.

  Furthermore, a third light-emitting element is provided, the measurement unit measures the light amount of the third light-emitting element, and the correction unit measures the third light amount measured by the measurement unit and the third light amount of the third light-emitting element. The light quantity index value may be obtained by averaging one measurement light quantity.

  In addition, a storage unit that stores the target light amount of the first light emitting element is provided, and the correction unit corrects the light amount of the first light emitting element to the target light amount when the first measured light amount is less than the target light amount. You may comprise. Thus, it is possible to execute good exposure with a sufficient amount of light by correcting the light amount decrease of the first light emitting element.

  By the way, as described above, according to the present invention, even if the light amount of the light emitting element (second light emitting element) is reduced due to deterioration, depending on the light amount of another light emitting element (first light emitting element), This utilizes the fact that the influence on the exposure of the decrease in the light amount of the light emitting element becomes inconspicuous. In short, according to the present invention, the influence of the light amount reduction of the light emitting element (second light emitting element) on the exposure is made inconspicuous by another light emitting element (first light emitting element). Therefore, the optical unit irradiates light from the first light emitting element and light from the second light emitting element to the exposed surface moving in the second direction orthogonal to the first direction. The light irradiated by the first light emitting element and the light irradiated by the second light emitting element may be configured such that a range adjacent to the exposed surface in the first direction can be exposed. . In other words, in such a configuration, the range on the exposed surface irradiated with light from the first light emitting element is adjacent to the range on the exposed surface irradiated with light from the second light emitting element. . Therefore, the above effect of making the influence of exposure to the exposure of the light amount reduction of the light emitting element (second light emitting element) inconspicuous by another light emitting element (first light emitting element) is more effectively achieved. It is possible to increase the allowable range of the light amount reduction of the light emitting element. Accordingly, it is possible to further reduce the frequency of light quantity correction and to further extend the life of the exposure head.

  Here, the optical unit may form the light emitted from the first light emitting element and the light emitted from the second light emitting element by an optical system that forms an erect image, or may be optical. The unit may be configured to form the light emitted from the first light emitting element and the light emitted from the second light emitting element by an optical system that forms an inverted image.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. The perspective view which shows the structure of a line head. The fragmentary sectional view which shows the structure of a line head. The top view which shows arrangement | positioning of the light emitting element and optical sensor which were provided in the head board | substrate. FIG. 3 is a plan view showing the arrangement of spots formed on the surface of the photosensitive drum. The block diagram which shows the structure of a Y line head control circuit. The figure which illustrated the parameter calculated | required at the time of line head shipment as a table | surface. The figure which shows an example of light quantity correction | amendment. The flowchart which shows the operation | movement which a light emission control circuit performs. The figure which illustrates the result of having measured the light quantity of each light emitting element.

First Embodiment FIG. 1 is a diagram showing an embodiment of an image forming apparatus provided with a line head to which the present invention is applicable. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus uses a color mode in which four color toners of yellow (Y), magenta (M), cyan (C) and black (K) are superimposed to form a color image, and only black (K) toner. Thus, the image forming apparatus can selectively execute a monochrome mode for forming a monochrome image. In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory, etc., the main controller MC gives a control signal to the engine controller EC, and based on this, an engine The controller EC controls each part of the device, such as the engine unit EG and the head controller HC, and executes predetermined image forming operations, and responds to image forming commands on recording sheets such as copy paper, transfer paper, paper, and OHP transparent sheets. The image to be formed is formed.

  In the housing main body 3 included in the image forming apparatus according to this embodiment, an electrical component box 5 that includes a power circuit board, a main controller MC, an engine controller EC, and a head controller HC is provided. An image forming unit 2, a transfer belt unit 8, and a paper feed unit 7 are also disposed in the housing body 3. In FIG. 1, a secondary transfer unit 12, a fixing unit 13 and a sheet guide member 15 are disposed on the right side in the housing body 3. The paper feed unit 7 is configured to be detachable from the housing body 3. The paper feeding unit 7 and the transfer belt unit 8 can be removed and repaired or exchanged.

  The image forming unit 2 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan) and 2K (for black) that form a plurality of images of different colors. In FIG. 1, since the image forming stations of the image forming unit 2 have the same configuration, only some of the image forming stations are denoted by reference numerals for convenience of illustration, and the reference numerals are omitted for other image forming stations. To do.

  Each image forming station 2Y, 2M, 2C, and 2K is provided with a photosensitive drum 21 on which a toner image of each color is formed. Each photoconductor drum 21 is arranged such that its rotation axis is parallel or substantially parallel to the main scanning direction MD (direction perpendicular to the paper surface of FIG. 1). Each photosensitive drum 21 is connected to a dedicated drive motor and is driven to rotate at a predetermined speed in the direction of arrow D21 in the figure. As a result, the surface of the photosensitive drum 21 is conveyed in the sub-scanning direction SD that is orthogonal or substantially orthogonal to the main scanning direction MD. A charging unit 23, a line head 29, a developing unit 25, and a photoconductor cleaner 27 are disposed around the photoconductive drum 21 along the rotation direction thereof. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. When the color mode is executed, the toner images formed by all the image forming stations 2Y, 2M, 2C, and 2K are superimposed on the transfer belt 81 provided in the transfer belt unit 8 to form a color image. When the monochrome mode is executed, only the image forming station 2K is operated to form a black monochrome image.

  The charging unit 23 includes a charging roller whose surface is made of elastic rubber. The charging roller is configured to rotate in contact with the surface of the photosensitive drum 21 at the charging position, and is driven to rotate as the photosensitive drum 21 rotates. The charging roller is connected to a charging bias generator (not shown). The charging roller is supplied with the charging bias from the charging bias generator and is charged at a charging position where the charging unit 23 and the photosensitive drum 21 come into contact with each other. The surface of 21 is charged to a predetermined surface potential.

  The line head 29 is arranged such that its longitudinal direction LGD is parallel or substantially parallel to the main scanning direction MD, and its width direction LTD is parallel or substantially parallel to the sub-scanning direction SD. The line head 29 includes a plurality of light emitting elements arranged in the longitudinal direction LGD, and is disposed to face the photosensitive drum 21. Then, light is emitted from these light emitting elements toward the surface of the photosensitive drum 21 charged by the charging unit 23 to form an electrostatic latent image on the surface.

  FIG. 3 is a perspective view showing the structure of the line head. In the drawing, the configuration on the back surface side of the head substrate 294 is shown, and the configuration on the front surface side is omitted. Of the two surfaces of the head substrate 294, the upper surface in the figure is the front surface, and the lower surface in the figure is the back surface. FIG. 4 is a partial cross-sectional view showing the structure of the line head. FIG. 5 is a plan view showing the arrangement of light emitting elements and optical sensors provided on the head substrate. 3 and 4, the light emitting element is denoted by the symbol E, whereas in FIG. 5, a numerical value n is indicated in parentheses denoted by the symbol E in order to number the light emitting elements E in order in the main scanning direction MD. -9, n-8,..., N-1, n, n + 1,. Here, n is a positive integer. 3 and 4, the light emission direction of the light emitting element E (in other words, the direction from the line head 29 toward the photosensitive drum 21) is a direction orthogonal to the main scanning direction MD and the sub-scanning direction SD. Are attached with the optical axis direction Doa.

  The line head 29 includes a head substrate 294 that is a glass substrate inside a main body 291, and a plurality of light emitting elements E are arranged in the main scanning direction MD (longitudinal direction LGD) on the back surface 294-t of the glass substrate 294. The two lines are lined up in a staggered pattern. Each light emitting element E is a so-called bottom emission type organic EL (Electro-Luminescence) element, and emits light upon receiving a drive current.

  A plurality of photosensors SC are provided on the back surface 294-t of the head substrate 294. The optical sensor SC is provided to detect a change in the light amount of the light emitting element E due to deterioration, and the current value of the drive current applied to the light emitting element E is corrected based on the detection result of the optical sensor SC.

  Further, a gradient index rod lens array RLA (hereinafter abbreviated as a lens array RLA) faces the light emitting element E provided on the back surface 294-t of the head substrate from the head substrate surface 294-h side. Therefore, the light emitted from the light emitting surface of the light emitting element E passes through the head substrate 294 and enters the lens array RLA. The light emitted from the light emitting element E is imaged at the same magnification by the lens array RLA, and the surface of the photosensitive drum 21 is irradiated with the spot SP (FIG. 6).

  FIG. 6 is a plan view showing the arrangement of spots formed on the surface of the photosensitive drum. In the drawing, in order to indicate which light emitting element E each spot SP is formed on, the numbers n-9 and n of the light emitting elements E in which the spot SP is formed in parentheses attached to the spot SP. -8, ..., n-1, n, n + 1, ... are marked. As can be seen from FIGS. 5 and 6, the light emitting elements E and E whose positions in the main scanning direction MD are adjacent form spots SP and SP so that the positions in the main scanning direction MD are adjacent. For example, the spots SP (n−1) and SP (n) formed by the light emitting elements E (n−1) and E (n) whose positions in the main scanning direction MD are adjacent are positioned in the main scanning direction MD. Adjacent to each other. The adjacent spots SP and SP thus expose a range adjacent to the main scanning direction MD. Then, the area exposed to the spot SP on the surface of the photosensitive drum 21 is exposed to light, and an electrostatic latent image is formed on the surface of the photosensitive drum 21.

  Returning to FIG. 1, the description of the apparatus configuration will be continued. The developing unit 25 has a developing roller 251 that carries toner on the surface thereof. The charged toner is developed at a developing position where the developing roller 251 and the photosensitive drum 21 come into contact with each other by a developing bias applied to the developing roller 251 from a developing bias generator (not shown) electrically connected to the developing roller 251. Moves from the developing roller 251 to the photosensitive drum 21, and the electrostatic latent image formed on the surface thereof is visualized.

  The toner image made visible at the development position is transported in the rotational direction D21 of the photosensitive drum 21, and is then primarily transferred to the transfer belt 81 at the primary transfer position TR1 where the transfer belt 81 and each photosensitive drum 21 abut. .

  A photoreceptor cleaner 27 is provided in contact with the surface of the photoreceptor drum 21 on the downstream side of the primary transfer position TR1 in the rotation direction D21 of the photoreceptor drum 21 and on the upstream side of the charging unit 23. The photoconductor cleaner 27 abuts on the surface of the photoconductor drum to remove the toner remaining on the surface of the photoconductor drum 21 after the primary transfer.

  The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. 1, and an arrow D81 illustrated by rotation of the driving roller 82 stretched between these rollers. And a transfer belt 81 that is circulated in the direction (conveyance direction). Further, four transfer belt units 8 are arranged on the inner side of the transfer belt 81 so as to be opposed to each of the photosensitive drums 21 included in the image forming stations 2Y, 2M, 2C, and 2K when the cartridge is mounted. Primary transfer rollers 85Y, 85M, 85C and 85K. Each of these primary transfer rollers is electrically connected to a primary transfer bias generator (not shown).

  When the color mode is executed, as shown in FIGS. 1 and 2, all the primary transfer rollers 85Y, 85M, 85C, and 85K are positioned on the image forming stations 2Y, 2M, 2C, and 2K, so that the transfer belt 81 is imaged. A primary transfer position TR1 is formed between each photosensitive drum 21 and the transfer belt 81 by being pushed and brought into contact with the photosensitive drum 21 included in each of the forming stations 2Y, 2M, 2C, and 2K. Then, by applying a primary transfer bias from the primary transfer bias generating unit to the primary transfer roller 85Y or the like at an appropriate timing, the toner images formed on the surface of each photosensitive drum 21 are respectively transferred to the corresponding primary transfer positions. Transfer is performed on the surface of the transfer belt 81 in TR1. That is, in the color mode, the single color toner images of the respective colors are superimposed on the transfer belt 81 to form a color image.

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed on the downstream side of the black primary transfer roller 85K and on the upstream side of the driving roller 82. The downstream guide roller 86 is common to the primary transfer roller 85K and the black photosensitive drum 21 (K) at the primary transfer position TR1 formed by the primary transfer roller 85K contacting the photosensitive drum 21 of the image forming station 2K. It is configured to contact the transfer belt 81 on the tangent line.

  The paper feed unit 7 includes a paper feed unit having a paper feed cassette 77 capable of stacking and holding sheets and a pickup roller 79 that feeds the sheets one by one from the paper feed cassette 77. The sheet fed from the sheet feeding unit by the pickup roller 79 is adjusted in sheet feeding timing by the registration roller pair 80, and then the drive roller 82 and the secondary transfer roller 121 abut along the sheet guide member 15. Paper is fed to the secondary transfer position TR2.

  The secondary transfer roller 121 is provided so as to be able to come into contact with and separate from the transfer belt 81 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). The fixing unit 13 includes a heating roller 131 that includes a heating element such as a halogen heater and is rotatable, and a pressure unit 132 that presses and biases the heating roller 131. The sheet on which the image is secondarily transferred is guided to a nip formed by the heating roller 131 and the pressure belt 1323 of the pressure unit 132 by the sheet guide member 15, and in the nip, a predetermined value is formed. The image is heat-fixed at temperature. The pressure unit 132 includes two rollers 1321 and 1322 and a pressure belt 1323 stretched between them. A nip portion formed by the heating roller 131 and the pressure belt 1323 by pressing the belt tension surface stretched by the two rollers 1321 and 1322 against the peripheral surface of the heating roller 131 out of the surface of the pressure belt 1323. Is configured to be widely taken. Further, the sheet thus subjected to the fixing process is conveyed to a paper discharge tray 4 provided on the upper surface portion of the housing body 3.

  The drive roller 82 described above circulates and drives the transfer belt 81 in the direction of the arrow D81 in the figure, and also serves as a backup roller for the secondary transfer roller 121. A rubber layer having a thickness of about 3 mm and a volume resistivity of 1000 kΩ · cm or less is formed on the peripheral surface of the drive roller 82. Secondary transfer is omitted by grounding through a metal shaft. The conductive path of the secondary transfer bias supplied from the bias generation unit via the secondary transfer roller 121 is used. Thus, by providing the driving roller 82 with a rubber layer having high friction and shock absorption, image quality deterioration caused by transmission of the impact to the transfer belt 81 when the sheet enters the secondary transfer position TR2. Can be prevented.

  Further, in this apparatus, a cleaner portion 71 is disposed to face the blade facing roller 83. The cleaner unit 71 includes a cleaner blade 711 and a waste toner box 713. The cleaner blade 711 removes foreign matters such as toner and paper dust remaining on the transfer belt 81 after the secondary transfer by bringing the tip of the cleaner blade 711 into contact with the blade facing roller 83 via the transfer belt 81. The foreign matter removed in this way is collected in a waste toner box 713. Further, the cleaner blade 711 and the waste toner box 713 are configured integrally with the blade facing roller 83.

  In this embodiment, in each color image forming station 2Y, 2M, 2C, and 2K, the photosensitive drum 21, the charging unit 23, the developing unit 25, and the photosensitive cleaner 27 are integrally formed with the cartridge CR (FIG. 2). ) As a unit. The cartridges CR for each color Y, M, C, and K are configured to be detachable from the apparatus main body. Each cartridge CR is provided with a nonvolatile memory for storing information related to the cartridge CR. Then, wireless communication is performed between the engine controller EC and each cartridge CR. In this way, information about each cartridge CR is transmitted to the engine controller EC, and information in each memory is updated and stored. Based on these pieces of information, the usage history of each cartridge CR and the lifetime of consumables are managed.

  The above is the schematic configuration of the image forming apparatus. Next, light emission control of the light emitting element E executed in the present embodiment will be described. This light emission control is executed by a line head control circuit CC provided in the head controller HC (FIG. 2). Therefore, hereinafter, the configuration and operation of the line head control circuit CC will be described. The line head control circuit CC is provided for each of the colors Y, M, C, and K. However, since the configuration and operation of the circuit CC are common to the colors Y, M, C, and K, yellow is used here. A description will be given taking the Y line head control circuit CC for (Y) as an example.

  FIG. 7 is a block diagram showing the configuration of the Y line head control circuit. The Y line head control circuit CC is provided with a light emission control circuit CC1 and a light quantity correction data storage unit CC2. The light emission control circuit CC1 supplies data TD-Y indicating the light emission period of the light emitting element E to the light emitting element E based on the video data VD-Y for yellow (Y) sent from the main controller MC. The current value ID-Y of the drive current is determined from each light emitting element E (1),..., E (n-1), E (n), E (n + 1),. ) Etc.). Then, the light emission control circuit CC1 applies the drive current having the current value ID-Y to each light emitting element E (n) or the like only during the period indicated by the data TD-Y. As a result, each light emitting element E (n) or the like emits light of a light amount corresponding to the current value ID-Y for a period indicated by the data TD-Y.

  However, at this time, the light emission control circuit CC1 refers to the data stored in the light amount correction data storage unit CC2 in order to cause each light emitting element E (n) to emit light with a substantially uniform light amount. A current value ID-Y is generated. That is, in the light quantity correction data storage unit CC2, the current value ID-Y obtained for causing each light emitting element E (n) to emit light with a substantially uniform light quantity is stored as an 8-bit digital signal. The current value ID-Y, which is a digital signal, is obtained in advance at the time of shipment of the line head 29 and stored in the light amount correction data storage unit CC2, and is appropriately updated after the shipment of the line head 29. This will be described in detail as follows.

  When the line head 29 is shipped, an initial correction signal value Ci (n), which is an 8-bit digital signal, is stored as a current value ID-Y in the light amount correction data storage unit CC2. The initial correction signal value Ci (n) is obtained in advance when the line head 29 is shipped from the factory, and is stored in the light quantity correction data storage unit CC2.

  FIG. 8 is a diagram illustrating parameters obtained at the time of shipment of the line head as a table. In the table of the figure, the initial signal value Si (n), the initial light quantity Lsi (n), the initial correction signal value Ci (n), and the initial correction light quantity Li (n) are respectively shown for the light emitting element E (n) and the like. It is written. The initial signal value Si (n) and the initial correction signal value Ci (n) are both 8-bit digital values indicating the current value ID-Y of the drive current applied to the light emitting element E (n), and the value Si (n) , Ci (n) multiplied by a predetermined proportionality constant is the drive current value actually applied to the light emitting element E (n). The initial light amount Lsi (n) is a light amount when the light emitting element E (n) emits light with the current value indicated by the initial signal value Si (n). The initial correction light amount Li (n) is the initial correction signal. This is the amount of light when the light emitting element E (n) emits light at the current value indicated by the value Ci (n).

  At the time of factory shipment, the line head 29 is first attached to a light quantity measuring jig. The light quantity measuring jig includes a light quantity detector that can detect the quantity of light emitted from the light emitting element E at a position facing the light emitting element E, and the light quantity emitted from each light emitting element E using the light quantity detector. Is detected. That is, the light quantity measuring jig causes the light emitting elements E (n) and the like arranged in the main scanning direction MD to emit light in order, and the light emitting elements E (1), E (2),. , Lsi (n),... Are detected by a light amount detector and stored. At this time, the jig for measuring light quantity gives the drive current of the initial signal value Si (n) of the same level 127 to each light emitting element E (n) and the like. As can be seen from the table, the initial light amount Lsi (n) of each light emitting element E (n) varies even though the signal Si (n) of the same level is given. This is due to manufacturing variations of the light emitting elements E (n) and the like. Therefore, in order to correct such light quantity variation, the initial correction signal value Ci (n) is obtained from the initial signal value Si (n) and the initial light quantity Lsi (n) and stored in the light quantity correction data storage unit CC2. . As can be seen from the table, by driving the light emitting element E (n) with this initial correction signal value Ci (n), the light quantity Li (n) of each light emitting element E (n) and the like is made to be approximately 1.000. be able to.

  In this way, in the subsequent exposure operation of the line head 29, each light emitting element E (n) is driven based on the initial correction signal value Ci (n) stored in the light quantity correction data storage unit CC2, so that each light emitting element E The amount of light such as E (n) can be made substantially uniform. However, as described above, the current value ID-Y stored in the light quantity correction data storage unit CC2 is appropriately updated after the shipment of the line head 29. The reason for this is as follows.

  That is, even if the light amount of each light emitting element E (n) is made substantially uniform at the time of shipment of the line head 29, each light emitting element E (n) etc. In some cases, the light amount of each light emitting element E (n) or the like may decrease due to deterioration. In addition, depending on the image to be formed, the light emission frequency of each light emitting element E (n) or the like is different. The degree of deterioration is greater. Therefore, the light emission control circuit CC1 performs light amount correction of each light emitting element E (n) at the timing of turning on the power of the image forming apparatus or between image formations, and is stored in the light amount correction data storage unit CC2. The current value ID-Y is updated. In this light amount correction, the light sensor SC detects the light amount of each light emitting element E (n) that sequentially emits light, and the light emission control circuit CC1 updates the correction signal value Cc (n) based on this detected light amount. The value ID-Y is obtained and stored in the light quantity correction data storage unit CC2.

  Note that the optical sensor SC is disposed away from each light emitting element E (n) and the like, and detects light traveling through the head substrate 294 from each light emitting element E (n) and the like. That is, the optical sensor SC does not detect the light amount of each light-emitting element E (n) or the like at the facing position of the light-emitting element E (n) or the like, unlike the light amount detector provided in the above-described light amount measurement jig. . Therefore, in the light amount correction, if the detected light amount itself of the optical sensor SC is handled as the light amount of each light emitting element E (n), the light amount correction may not be performed with sufficient accuracy.

  Therefore, the light amount correction data storage unit CC2 stores the light amount detected by the optical sensor SC at the time of shipment of the line head 29 as the initial detected light amount Pi (n). More specifically, when the above-described initial correction signal value Ci (n) is obtained at the time of shipment of the line head 29 from the factory, the drive current having a current value corresponding to the initial correction signal value Ci (n) is changed to each light emitting element. Sequentially given to E (n) and the like. The detected light amounts Pi (1), Pi (2),..., Pi (n),... Detected by the optical sensor SC from the light emitting elements E (n) that sequentially emit light are stored in the light amount correction data storage unit. Stored in CC2. Thereby, in the light amount correction after shipment of the line head 29, the initial correction light amount Li (n) and the initial detected light amount are detected with respect to the detected light amount of each light emitting element E (n) and the like by the optical sensor SC in the light amount correction. By multiplying the ratio Pi (n), the light quantity of each light emitting element E (n) and the like after shipment of the line head 29 can be measured with high accuracy. Based on the above, the details of the light amount correction will be described.

  FIG. 9 is a diagram illustrating an example of light amount correction. In the figure, the value applied to the light emitting element E (n) is represented by the horizontal axis of the digital signal value indicating the current value applied to the light emitting element E (n) and the measured light quantity of the light emitting element E (n) is represented by the vertical axis. Light quantity characteristic lines LL0 and LL1 indicating the relationship between the current value and the light quantity of the light emitting element E (n) are shown. Here, the light quantity characteristic line LL0 is that of the light emitting element E (n) at the time of shipment of the line head 29, and the light quantity characteristic line LL1 is that of the light emitting element E (n) after being changed due to deterioration.

  In the light amount correction, first, drive currents corresponding to two different digital signal values Cl and Ch are sequentially applied to the light emitting element E (n), and at this time, the detected light amount Pl (n), Ph (n) is obtained. The light emission control circuit CC1 multiplies the detected light amount Pl (n) by the ratio of the initial corrected light amount Li (n) and the initial detected light amount Pi (n) to determine the light amount of the light emitting element E (n). That is, the light amount Ll (n) of the light emitting element E (n) is obtained as Pl (n) × Li (n) / Pi (n). Similarly, the actual light amount Lh (n) of the light emitting element E (n) with respect to the digital signal value Ch is obtained as Ph (n) × Li (n) / Pi (n). Then, from the digital signal values Cl and Ch and the light amounts Ll (n) and Lh (n) of the light emitting element E (n), the slope of the light amount characteristic line LL1 (Lh (n) −Ll (n)) / (Ch− Cl) is required. In this way, the digital signal for causing the deteriorated light emitting element E (n) to emit light with the initial correction light amount Li (n) by obtaining the slope of the light amount characteristic line LL1 and approximating the light amount characteristic line LL1 as a linear function. The value Cc (n) can be determined. The digital signal value Cc (n) is obtained for each light emitting element E (n) and the like.

  By the way, performing such light amount correction increases the level of the signal applied to the deteriorated light emitting element E (n) (that is, the value ID-Y of the current applied to the light emitting element). However, the deterioration of the light emitting element E (n) tends to be accelerated as the signal level increases. Therefore, the life of the line head 29 may be shortened each time the light amount is corrected. Therefore, in order to suppress the frequency of light amount correction, the light emission control circuit CC1 determines whether or not the light amount correction of each light emitting element E (n) is necessary, and each light emitting element E (( Perform the light amount correction of n).

  FIG. 10 is a flowchart showing an operation executed by the light emission control circuit. First, in step S101, the light emission control circuit CC1 causes each light emitting element E (n) to emit light and measures the light quantity of each light emitting element E (n). Specifically, a drive current having a current value corresponding to the initial correction signal value Ci (n) is applied to the light emitting element E (n), and the detected light amount Pd (n) of the photosensor SC at this time is obtained. . The light emission control circuit CC1 multiplies the detected light amount Pd (n) by the ratio of the initial corrected light amount Li (n) and the initial detected light amount Pi (n), that is, Pd (n) × Li (n). / Pi (n) is obtained as the light amount Ld (n) of the light emitting element E (n). Thus, the result of measuring the light quantity Ld (n) for each light emitting element E (n) is shown in FIG. Here, FIG. 11 is a diagram illustrating the result of measuring the light quantity of each light emitting element. In the example of the figure, the light amount of all the light emitting elements E is lower than the initial light amount. In addition, the light emitting element E (n) has a particularly sharp decrease in light amount, and is more deteriorated than the other light emitting elements.

  Subsequent to step S101, steps S102 to S104 are executed for each light emitting element E (n) and the like. In step S102, it is determined whether or not the measured light amount Ld (n) of the light emitting element E (n) is equal to or less than the threshold value Lth1. When the measured light amount Ld (n) of the light emitting element E (n) is larger than the threshold value Lth1 (in the case of “NO” in step S102), it can be determined that the deterioration of the light emitting element E (n) has not progressed so much. The light amount correction of the element E (n) is not executed. On the other hand, when the measured light amount Ld (n) of the light emitting element E (n) is equal to or less than the threshold Lth1 (in the case of “YES” in step S102), it is considered that the deterioration of the light emitting element E (n) has progressed to some extent. . However, even in this case, in the present embodiment, the light amount correction is not performed immediately, and whether or not the light amount correction of the light emitting element E (n) is necessary is determined in step S103.

  That is, in step S103, it is determined whether the light amount average Lav of the peripheral light emitting elements of the light emitting element E (n) is equal to or greater than the threshold value Lth2. The average light amount of the peripheral light emitting elements is the two light emitting elements E (n−1), E whose positions in the main scanning direction MD are adjacent to the light emitting element E (n) that is a target for determining whether or not light amount correction is necessary. (n + 1) It is obtained as an average value of the respective light amounts Ld (n-1) and Ld (n + 1) (that is, Lav = (Ld (n-1) + Ld (n + 1)) / 2). Incidentally, the threshold value Lth2 is larger than the threshold value Lth1. When the average light amount Lav of the peripheral light emitting elements is equal to or greater than the threshold value Lth2 (in the case of “YES” in step S103), it is determined that the light amount correction of the light emitting element E (n) is unnecessary and is not executed. On the other hand, when the average light amount Lav of the peripheral light emitting elements is less than the threshold value Lth2 (in the case of “NO” in step S103), the light amount correction of the light emitting element E (n) is executed.

  As described above, the present embodiment measures the light amount of each light emitting element E (n) and measures the light amount of the light emitting element E (n) in order to cope with the decrease in the light amount of each light emitting element E (n) due to deterioration. to correct. However, in this embodiment, in order to suppress the frequency of light amount correction, the necessity of light amount correction is determined, and light amount correction is performed according to the determination result. Specifically, it is as follows. First, the amount of light Ld (n) is obtained by measuring the amount of light of each light emitting element E (n). If the measured light quantity Ld (n) (second measured light quantity) of a light emitting element E (n) is equal to or smaller than the threshold value Lth1 (first threshold value), whether or not the light quantity correction of the light emitting element E (n) is necessary. Is judged. At this time, the necessity of the light amount correction is determined based on the measured light amounts of the other light emitting elements E (n−1) and E (n + 1) different from the light emitting element E (n) to be subjected to the light amount correction (first measurement). Light quantity). Then, according to the determination result, the light amount of the light emitting element E (n) is corrected. That is, even if the light amount Ld (n) of the light emitting element E (n) decreases due to the deterioration, the light amounts Ld (n−1) and Ld (of the other light emitting elements E (n−1) and E (n + 1). When the number n + 1) is sufficiently large, the light amount reduction of the light emitting element E (n) may be allowed without being noticeable, and the light amount reduction of the light emitting element E (n) may be allowed. Therefore, in the present embodiment, the light emitting element E (n) is based on the measured light amounts Ld (n−1) and Ld (n + 1) of the other light emitting elements E (n−1) and E (n + 1). The necessity of light quantity correction is determined, and the light quantity correction of the light emitting element E (n) is performed according to the necessity judgment. In this way, it is possible to extend the life of the line head 29 by suppressing the frequency of light quantity correction.

  Specifically, in the present embodiment, an average value Lav (light quantity index value) of light quantities Ld (n-1) and Ld (n + 1) of other light emitting elements E (n-1) and E (n + 1). ) Is equal to or greater than the threshold value Lth2 (second threshold value), the light amount correction of the light emitting element E (n) is determined to be unnecessary and is not performed. That is, even if the light amount of the light emitting element E (n) is reduced due to the deterioration, the light amount average value Lav of the other light emitting elements E (n−1) and E (n + 1) is equal to or larger than the threshold value Lth2, The influence on the exposure of the light amount reduction of the element E (n) is not conspicuous, and it can be determined that the light amount correction of the light emitting element E (n) is unnecessary. Then, by executing the light amount correction of the light emitting element E (n) according to the necessity determination, it is possible to suppress the frequency of the light amount correction and to extend the life of the line head 29.

  By the way, as described above, in the present embodiment, even if the light amount of the light emitting element E (n) is reduced due to deterioration, depending on the light amount of another light emitting element, the influence on exposure of the light amount reduction of the light emitting element E (n). Is to make use of the inconspicuousness. In short, in the present embodiment, the influence of the light amount reduction of the light emitting element E (n) on the exposure is made inconspicuous by another light emitting element. Therefore, in the present embodiment, light emitting elements E (n−1) and E (n + 1) are used as the other light emitting elements. That is, the range of exposure of the spots SP (n-1) and SP (n + 1) by the light emitting elements E (n-1) and E (n + 1) and the spot SP (n) by the light emitting element E (n). Is exposed in the main scanning direction MD. Therefore, the above-described action of making the influence on the exposure of the light amount reduction of the light emitting element E (n) inconspicuous by another light emitting element E (n-1), E (n + 1) is more effectively achieved, It is possible to make a large allowable range of the light amount reduction of the light emitting element E (n). Therefore, the frequency of light amount correction can be further suppressed, and the life of the line head 29 can be further extended.

Others As described above, in the above-described embodiment, the line head 29 or the line head 29 and the head controller HC cooperate to function as the “exposure head” of the invention, and the light emitting elements E (n−1), E (n + 1) corresponds to the “first light emitting element” of the present invention, the light emitting element E (n) corresponds to the “second light emitting element” and “third light emitting element” of the present invention, and the rod lens array RLA It corresponds to the “optical unit” of the present invention, and the light emission control circuit CC1 and the optical sensor SC cooperate to function as the “measurement unit” of the present invention, and the light emission control circuit CC1 functions as the “determination unit” of the present invention. The light emission control circuit CC1 and the light amount correction data storage unit CC2 function as the “correction unit” of the present invention. Further, the light quantity correction data storage unit CC2 corresponds to the “storage unit” of the present invention. The surface of the photosensitive drum 21 corresponds to the “exposed surface” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described one without departing from the spirit of the present invention. That is, in the above embodiment, the two light emitting elements E (n−1) and E (n + 1) are used as the peripheral light emitting elements of the light emitting element E (n) whose light amount is to be corrected. The number is not limited to this. For example, four light emitting elements E (n-2), E (n-1), E (n + 1), and E (n + 2) may be used as the peripheral light emitting elements. Alternatively, only one light emitting element E (n + 1) may be used as the peripheral light emitting element.

  In the above embodiment, the average value Lav of the peripheral light emitting elements and the threshold value Lth2 are compared to determine whether or not the light amount correction of the light emitting element E (n) is necessary. However, the necessity of light amount correction of the light emitting element E (n) may be determined by comparing the maximum value Lmax of the peripheral light emitting elements with the threshold value Lth2. Further, it may be determined whether or not the light amount correction of the light emitting element E (n) is necessary based on the dispersion of the light amount of the peripheral light emitting elements.

  In the above embodiment, the light amount correction is not performed for the light emitting element E (n−1) or the like whose measured light amount is larger than the threshold value Lth1. However, the light quantity correction may be performed for the light emitting elements E (n−1) and the like. Specifically, the initial light amount (target light amount) of each light emitting element E is stored in a storage unit such as the light amount correction data storage unit CC2, and the measured light amount of the light emitting element E (n-1) is less than the initial light amount. In some cases, the light amount of the light emitting element E (n-1) may be corrected to the initial light amount. In this way, by correcting the decrease in the light amount of the light emitting element E (n-1) or the like, it is possible to execute good exposure with a sufficient amount of light.

  Further, in the above embodiment, the light quantity Pl (n) detected by the optical sensor SC is multiplied by the ratio of the initial correction light quantity Li (n) and the initial detected light quantity Pi (n) to each light emitting element E (n) or the like. It was calculated as the measurement light quantity. However, the detected light amount Pl (n) itself of the optical sensor SC may be obtained as the measured light amount of each light emitting element E (n). In such a case, it is not necessary to store the initial correction light quantity Li (n) in the light quantity correction data storage section CC2, and therefore the light quantity correction data storage section CC2 is configured by a relatively inexpensive memory with a small storage capacity. Therefore, the cost of the line head 29 can be reduced.

  Further, in the configuration in which the detected light amount Pl (n) itself of the optical sensor SC is obtained as the measured light amount of each light emitting element E (n), the following changes are added to the flowchart in the above embodiment, It is possible to determine whether or not the light amount correction of the light emitting element E (n) is necessary. That is, instead of determining whether or not correction is necessary in step S103 of the flowchart of FIG. 10 of the above embodiment, for example, each light emitting element E is calculated from the detected light amount Pd (n) of the optical sensor SC and the initial detected light amount Pi (n). Deterioration rate Rd (n) = (Pi (n) −Pd (n)) / Pi (n) such as (n) is obtained, and light emission adjacent to the light-emitting element E (n) that is a determination target of correction necessity The necessity of light amount correction of the light emitting element E (n) may be determined from the deterioration rate Rd (n-1) of the element E (n-1). Specifically, when the deterioration rate Rd (n-1) of the adjacent light emitting element E (n-1) is less than the reference deterioration rate Rrf, the light amount of the light emitting element E (n) is corrected and the adjacent light emitting element If the deterioration rate Rd (n-1) of E (n-1) is equal to or higher than the reference deterioration rate Rrf, it may be determined not to correct the light amount of the light emitting element E (n).

  In the above embodiment, since the line head 29 is provided with a plurality of optical sensors SC, the sum of the detection values of two or more optical sensors SC may be used as the detected light amount of each light emitting element E (n). . Specifically, the sum of the detection values of the two optical sensors SC (m) and SC (m + 1) can be used as the detected light amount of the light emitting element E (n) by the optical sensor SC.

  Incidentally, in the above embodiment, the light amount detection of each light emitting element E (n) by the optical sensor SC is performed at two timings, that is, when the line head 29 is shipped and when the light amount is corrected after the line head 29 is shipped. At this time, in consideration of variations in characteristics of each photosensor SC, the combination of the light emitting element E (n) and two or more photosensors SC that detect the light quantity of the light emitting element E (n) is common at each timing. It is preferable to keep them.

  As the optical sensor SC, various known ones can be used. For example, a silicon PN type photodiode can be used. In general, a photodiode has a dark current, and an amplifier that converts the output current of the photodiode into a voltage also has an offset voltage, so that the output value does not become zero even when no light is incident on the photodiode. . In order to eliminate this influence, the offset value of the amplifier output of each optical sensor SC is measured in advance with all the light emitting elements E (n) turned off, and the offset from the amplifier output value when the light is detected is offset. What subtracted the value may be used as the detection value.

  In the above embodiment, a plurality of optical sensors SC are disposed on the back surface 294-t of the head substrate 294 (FIG. 4). However, the arrangement positions of the plurality of optical sensors SC are not limited to this, and various changes can be made. Therefore, for example, a plurality of optical sensors may be provided on the surface 294-h of the head substrate 294.

  Further, the optimum values of the threshold values Lth1 and Lth2 described above vary depending on the image type, resolution, and the like. Therefore, various images are formed while changing each of the threshold values Lth1, Lth2, and from these results, optimum values of the threshold values Lth1, Lth2 corresponding to the various images are obtained in advance, and storage units such as a light quantity correction data storage unit CC2 You may remember it.

Further, in the light amount correction described with reference to FIG. 9, when obtaining the slope of the light amount characteristic line LL1, drive currents corresponding to two different digital signal values Cl and Ch are sequentially applied to the light emitting element E (n). In addition, the detected light amounts Pl (n) and Ph (n) of the photosensor SC at this time were obtained. However, at this time, the initial correction signal value Ci (n) may be applied instead of the digital signal value Cl to determine the slope of the light quantity characteristic line LL1. In this case, the digital signal value Cc (n) for causing the deteriorated light emitting element E (n) to emit light with the initial correction light amount Li (n) is expressed by the following equation:
Cc (n) = Ci (n) + (Li (n) -Ll (n)) * (Ch-Ci (n)) / (Lh-Ll (n))
Given in.

  Further, when the slope of the light quantity characteristic line LL1 does not change significantly before and after the deterioration of the light emitting element E (n), the light quantity characteristic line LL1 is assumed to be a constant value, and the light quantity characteristic line LL1 is approximated by a linear function. May be.

  In addition, the light amount when performing the exposure operation by the line head 29 is not necessarily the initial correction light amount Li (n) at the time of shipment of the line head 29, and is a light amount different from the initial correction light amount Li (n) or the like. Each light emitting element E (n) or the like may emit light.

  In the above embodiment, a bottom emission type organic EL element is used as the light emitting element E. However, the type of the light emitting element E is not limited thereto, and for example, a top emission type organic EL element may be used as the light emitting element E.

  Further, the line head 29 used in the present invention is not limited to the one having the above-described refractive index distribution type rod lens array RLA as an optical system. Therefore, for example, a line head described in JP 2008-36937 A can also be used. In other words, in the line head of this document, the imaging optical systems that are formed of convex lenses and form an inverted image are arranged in an array, and light emitting elements are grouped by a predetermined number facing each imaging optical system. Light-emitting element groups are arranged. Therefore, the light emitted from each light emitting element of the light emitting element group is imaged as a spot by the imaging optical system. In the line head described in Japanese Patent Application Laid-Open No. 2009-45917, a technique for correcting the light amount of the light emitting element in a configuration in which an imaging optical system for forming an inverted image is disposed opposite to the light emitting element group has been proposed. Therefore, the present invention can also be applied to light amount correction of a light emitting element in such a line head.

  By the way, the light quantity reduction of the light emitting element E used with the line head 29 may be caused by the temperature change of the surrounding environment and the power supply voltage fall besides the deterioration of the light emitting element E. However, since the light quantity reduction of the light emitting elements E due to the temperature change or the power supply voltage drop occurs uniformly for all the light emitting elements E, the light quantity of each light emitting element E is increased by increasing the driving current by a certain amount for each light emitting element E. Can be kept properly. Further, as described above, since the light amount decrease due to temperature change and power supply voltage reduction occurs uniformly for all the light emitting elements E, since the light amount of all the light emitting elements E is kept substantially uniform even after the light amount decrease, In some cases, this reduction in the amount of light does not matter, and in such a case, the correction operation of increasing the driving current for each light emitting element E by a certain amount can be omitted.

  21 ... photosensitive drum, 29 ... line head, CC ... line head control circuit, CC1 ... light emission control circuit, CC2 ... light quantity correction data storage unit, E, E (n-1), E (n), E (n + 1) ... light emitting element, RLA ... rod lens array, SC ... light sensor, MD ... main scanning direction, SD ... sub-scanning direction, SP ... spot

Claims (8)

A first light emitting element;
A second light emitting element;
An optical unit that images light emitted from the first light emitting element and images light emitted from the second light emitting element;
A measuring unit for measuring a light amount of the first light emitting element to obtain a first measured light amount, and measuring a light amount of the second light emitting element to obtain a second measured light amount;
A determination unit that determines whether or not the light amount correction of the second light emitting element is necessary based on the first measurement light amount when the second measurement light amount is equal to or less than a first threshold;
When the determination unit determines that light amount correction is necessary, the light amount correction of the second light emitting element is performed, and when the determination unit determines that light amount correction is not necessary, the light amount correction of the second light emitting element is performed. And the correction part that does not
An exposure head comprising:   The determination unit determines that correction of the light amount of the second light emitting element is unnecessary when a light amount index value indicating a value corresponding to the first measured light amount is equal to or greater than a second threshold value. The exposure head described in 1. A third light emitting element,
The measurement unit measures the amount of light of the third light emitting element;
3. The exposure according to claim 2, wherein the correction unit obtains the light amount index value by averaging a third measured light amount measured by the measurement unit and the first measured light amount with respect to the light amount of the third light emitting element. head. A storage unit for storing a target light amount of the first light emitting element;
4. The exposure according to claim 1, wherein the correction unit corrects the light amount of the first light emitting element to the target light amount when the first measured light amount is less than the target light amount. 5. head. The optical unit irradiates light from the first light emitting element and irradiates light from the second light emitting element to an exposed surface moving in a second direction orthogonal to the first direction,
The light irradiated by the first light emitting element and the light irradiated by the second light emitting element can expose a range adjacent to the first direction of the exposed surface. 5. The exposure head according to any one of 4 above.   6. The exposure head according to claim 5, wherein the optical unit forms the light emitted from the first light emitting element and the light emitted from the second light emitting element by an optical system that forms an erect image.   6. The exposure head according to claim 5, wherein the optical unit forms the light emitted from the first light emitting element and the light emitted from the second light emitting element by an optical system that forms an inverted image. The light from the first light emitting element and the second light emitting element is imaged by an optical unit to measure the light quantity of the first light emitting element of the exposure head that performs exposure, and the first measured light quantity is obtained. A first step of measuring a light quantity of the two light emitting elements to obtain a second measured light quantity;
A second step of determining, based on the first measured light quantity, whether the second light quantity is equal to or less than a first threshold value, based on the first measured light quantity;
When the second step determines that the light amount correction is necessary, the light amount correction of the second light emitting element is executed. When the second step determines that the light amount correction is unnecessary, the second light emitting element is corrected. A third step that does not perform light amount correction;
An exposure head control method comprising:

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