JP2011083963A - Apparatus and method for forming image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology which enables formation of a good image by stabilizing potential variation of a photoreceptor for the variation in spectral distribution of light emitting elements. <P>SOLUTION: An image forming apparatus includes an exposure head having the light emitting elements and an emission control part which controls the light emitting elements to emit light in response to a control signal, the photoreceptor which senses the light emitted from the light emitting elements of the exposure head to form a latent image, a development part which develops the latent image formed on the photoreceptor, a detection part which detects the quantity of light of the light emitting elements, and a correction part which corrects the control signal based on a first correction value determined from the detection results of the detection part and a second correction value determined from the spectral distribution of the light emitting elements. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method for forming a latent image by exposing a photosensitive member to light from a light emitting element.

  2. Description of the Related Art Conventionally, there has been proposed an image forming apparatus that forms a latent image on a photosensitive member by utilizing the property that the photosensitive member is exposed to light to cause a potential change. For example, in the image forming apparatus disclosed in Patent Document 1, an exposure head including a plurality of light emitting elements arranged in a predetermined direction is disposed so as to face the photosensitive member, and light from each light emitting element is irradiated onto the surface of the photosensitive member in a spot shape. As a result, the potential of the irradiated portion changes. Then, the latent image can be formed on the surface of the photosensitive member by changing the potential of the portion corresponding to the latent image to be formed by light irradiation. Further, the image forming apparatus develops the latent image as an image by attaching toner to the latent image thus formed.

JP 2008-238633 A JP 2008-2011136 A

  Incidentally, the amount of toner adhering during development depends on the amount of potential change on the surface of the photoreceptor. Therefore, in order to form an image satisfactorily, it is important to accurately control the amount of change in the potential of the photoreceptor due to light irradiation of the light emitting element. This is because if the amount of potential change is significantly different from the predetermined amount of change, an appropriate amount of toner cannot be attached, and as a result, the desired image cannot be obtained because the image density is greatly shifted. It is.

  On the other hand, since the light amount of the light emitting element changes with the temperature change or deterioration of the light emitting element, the potential change amount may deviate from the predetermined potential change amount due to the light amount change of the light emitting element. . Therefore, the exposure head disclosed in Patent Document 2 detects the light amount of the light emitting element using an optical sensor and corrects the light amount of the light emitting element based on the detection result.

  However, even if the light amount of the light emitting element is corrected in this way, it may still be difficult to accurately control the amount of change in potential of the photoconductor. The cause is variation in the spectral distribution of the light emitting element. That is, since the manufacturing accuracy of the light emitting elements is limited, it is difficult to make the spectral distributions of all the light emitting elements to be manufactured uniform. Therefore, the spectral distribution of the light emitting element varies depending on the light emitting element, for example, the spectral distribution shifts in the wavelength axis direction or the shape of the spectral distribution itself changes. As a result, the amount of change in potential of the photoreceptor is not stable, and there is a possibility that good image formation cannot be performed.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of forming a good image by stabilizing the potential change amount of the photoconductor with respect to variations in the spectral distribution of the light emitting elements. And

  In order to achieve the above object, an image forming apparatus according to the present invention is sensitive to light emitted from a light emitting element and an exposure head having a light emission control unit that emits light according to a control signal, and light emitted from the light emitting element of the exposure head. Then, the photosensitive member on which the latent image is formed, the developing unit that develops the latent image formed on the photosensitive member, the detecting unit that detects the light amount of the light emitting element, and the first detection result obtained from the detection result of the detecting unit And a correction unit that corrects the control signal based on the second correction value obtained from the correction value and the spectral distribution of the light emitting element.

  In addition, in order to achieve the above object, the image forming method according to the present invention provides the first correction value obtained from the detection result of the detection unit for detecting the light amount of the light emitting element and the second distribution obtained from the spectral distribution of the light emitting element. A first step of correcting a control signal for controlling light emission of the light emitting element based on the correction value of the light source, and exposing the photosensitive member to light from the light emitting element that emits light according to the control signal corrected in the first step. The second step of forming a latent image on the photosensitive member and the third step of developing the latent image formed in the second step are provided.

  In the invention (image forming apparatus and image forming method) configured as described above, a latent image is generated by changing the electric potential of the photosensitive member by light emitted to the photosensitive member by causing the light emitting element to emit light according to a control signal. Form. And this invention controls based on not only the 1st correction value calculated | required from the detection result of the detection part which detects the light quantity of a light emitting element but also the 2nd correction value calculated | required from the spectral distribution of a light emitting element. The signal is corrected. As a result, it is possible to stabilize the potential change amount of the photosensitive member against variations in the spectral distribution of the light emitting elements and form a good image.

  At this time, the correction unit may be configured to correct the control signal based on the spectral sensitivity of the photoconductor at the centroid wavelength of the spectral distribution. That is, since the centroid wavelength of the spectral distribution tends to change according to the dispersion of the spectral distribution, the control signal for controlling the light emission of the light emitting element is corrected based on the spectral sensitivity of the photoconductor at the centroid wavelength of the spectral distribution. As a result, the amount of potential change of the photosensitive member can be stabilized against variations in the spectral distribution of the light emitting elements.

  Further, the correction unit calculates the second correction value from the correlation between the centroid wavelength and the density of the image obtained by developing the latent image formed by the light emitting element having the spectral distribution having the centroid wavelength. You may comprise so that it may require | require. In this way, by obtaining the second correction value from the correlation between the gravity center wavelength of the spectral distribution and the image density, the image density can be more reliably stabilized against variations in the spectral distribution, and good image formation can be achieved. Is possible.

  Further, the control signal may be corrected based on a value obtained by multiplying the first correction value by the second correction value. With this configuration, it is possible to stabilize the potential change amount of the photoconductor with respect to variations in the spectral distribution of the light emitting elements, and to form a good 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 block diagram which shows the structure of a Y line head control circuit. The figure which showed an example of the spectral sensitivity of a photoreceptor as a graph. Explanatory drawing of the light emission control which a spectral sensitivity ratio data storage part and a correction circuit perform. The figure which showed an example of spectral distribution measurement as a table | surface. The figure which showed an example of the measurement result of the gravity center wavelength of spectral distribution with the graph. The figure which showed an example of the correlation of a gravity center wavelength and image density as a graph. The figure which showed the relative density of the image formed with the light emitting element E whose centroid wavelength is 660 [nm]. The block diagram which shows the modification of a structure of a Y line head control circuit. The figure which showed the data etc. which are memorize | stored in Y line head control circuit as Table 1. FIG. The figure which showed the gravity center wavelength vs density | concentration correlation data as Table 2. FIG. The block diagram which shows the head panel module provided in the line head. 4 is a timing chart illustrating an example of lighting time control of a light emitting element.

First Embodiment FIG. 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 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. In these drawings, the optical axis extends in the direction perpendicular to the main scanning direction MD and the sub-scanning direction SD and in 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). A direction Doa is attached.

  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. Each light emitting element E emits light in response to application of a drive current.

  Further, an optical sensor SC is provided on the back surface 294-t of the head substrate 294 (FIG. 4). The optical sensor SC is provided to detect a change in the light amount of the light emitting element E due to temperature change or 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. Is done.

  Further, a gradient index rod lens array RLA (hereinafter abbreviated as “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. Thus, the light emitted from the light emitting element E is imaged at an equal magnification by the lens array RLA, and the surface of the photosensitive drum 21 is irradiated with the spot SP. Then, the irradiation area of the spot SP on the surface of the photosensitive drum 21 is exposed, 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, the photosensitive drum 21, the charging unit 23, the developing unit 25, and the photosensitive cleaner 27 of each of the image forming stations 2Y, 2M, 2C, and 2K are unitized as a unit. The cartridge is configured to be detachable from the apparatus main body. Each cartridge is provided with a nonvolatile memory for storing information related to the cartridge. Then, wireless communication is performed between the engine controller EC and each cartridge. Thus, information about each cartridge 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 and the lifetime of consumables are managed.

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

  FIG. 5 is a block diagram showing the configuration of the Y line head control circuit. The Y line head control circuit CC includes a correction circuit CC1, a light amount correction data storage unit CC2, and a spectral sensitivity ratio data storage unit CC3, and video data VD− for yellow (Y) sent from the main controller MC. Based on Y and the like, data TD-Y (data signal) indicating the light emission period of the light emitting element E and a current value ID-Y (current value signal) of the drive current supplied to the light emitting element E are generated.

  The light quantity correction data storage unit CC2 is provided for correcting the light quantity of the light emitting element E accompanying the temperature change or deterioration based on the detection result of the optical sensor SC. The light quantity correction data storage unit CC2 And the correction circuit CC1 cooperate to execute light amount correction. That is, as described above, in this embodiment, the surface of the photosensitive drum 21 is electrostatically irradiated by irradiating the surface of the photosensitive drum 21 with light from each light emitting element E and changing the potential of the irradiated portion of this light. A latent image is formed. At this time, the amount of potential change on the surface of the photosensitive drum 21 depends on the light amount of the light emitting element E. Therefore, when the light quantity of the light emitting element E changes with temperature and deterioration, the potential change amount deviates from a desired change amount, and an appropriate image may not be formed. Therefore, the following light amount correction is executed to deal with such a problem.

  First, parameters necessary for correcting the light amount are measured in advance when the line head 29 is shipped from the factory. That is, at the time of factory shipment, the line head 29 is attached to a light quantity measuring jig that detects the light quantity emitted from each light emitting element E using a light quantity detector. The light quantity measuring jig causes the light emitting elements E arranged in the main scanning direction MD to emit light in order, and the light quantity Pg (of each light emitting element E (1), E (2),..., E (n),. 1), Pg (2),..., Pg (n),... Are detected by a light quantity detector and stored. Further, in parallel with the operation of storing the detection result of the light amount detector, the light amount measuring jig detects the light amounts Ph (1), Ph detected by the light sensor SC of the line head 29 while the light emitting elements E are sequentially turned on. (2), ..., Ph (n), ... are stored. A light amount correction coefficient Pg (n) / Ph (n) is calculated for each light emitting element E from the parameters Pg (n) and Ph (n) thus determined. Then, the line head 29 is shipped in a state where the light quantity correction coefficient Pg (n) / Ph (n) is stored in the light quantity correction data storage unit CC2.

  Here, the numerical value in parentheses attached to the light emitting element E is an identification number of the light emitting element E, and is attached to each light emitting element E in order from the main scanning direction MD. The light amount Pg (n) indicates the light amount of the light emitting element E (n) detected by the light amount detector of the light amount measuring jig, and the light amount Ph (n) indicates the light emitting element E (detected by the optical sensor SC of the line head 29. The amount of light of n) is shown. The same applies to parameters (parameters Pj (n), etc.) with identification numbers in parentheses used in the following description.

  Then, after the line head 29 is shipped, the light amount correction is executed at a timing such as when the image forming apparatus is powered on or between image formations. That is, in this light quantity correction, the correction circuit CC1 causes each light emitting element E to emit light in order, and the light quantity Pj (1), E (n),... Of each light emitting element E (1), E (2),. Pj (2),..., Pj (n),... Are detected by the optical sensor SC and stored. The correction circuit CC1 then obtains a value Pj (n) × Pg (n) / Ph (n) obtained by multiplying the detected light amount Pj (n) of the photosensor SC by a light amount correction coefficient Pg (n) / Ph (n). Estimated as the actual light quantity of the light emitting element E (n).

  Since the actual light amount Pj (n) × Pg (n) / Ph (n) of the light emitting element E (n) can be estimated in this way, the light emitting element E (( The correction amount of the light quantity of n) is obtained. Then, a drive current value supplied to the light emitting element E (n) is obtained so as to correct the light quantity of the light emitting element E (n) by this correction amount (light quantity correction).

  Incidentally, the amount of potential change on the surface of the photosensitive drum 21 due to light irradiation from the light emitting element E depends not only on the light amount of the light emitting element E but also on the spectral distribution of the light emitting element E. That is, since the manufacturing accuracy of the light emitting element E is limited, it is difficult to make the spectral distributions of all the light emitting elements E to be manufactured the same. Therefore, the spectral distribution of the light emitting element E varies due to the light emitting element E shifting the spectral distribution in the wavelength axis direction or changing the shape of the spectral distribution itself. On the other hand, as disclosed in Japanese Patent No. 4115253, the spectral sensitivity of the photoconductor generally varies with the wavelength of light (FIG. 6). Therefore, when the spectral distribution of the light emitting element E varies, the potential change amount of the photosensitive drum 21 may not be stable. This will be described in detail as follows.

  FIG. 6 is a graph showing an example of the spectral sensitivity of the photoconductor. The horizontal axis represents the light wavelength [nm] and the vertical axis represents the sensitivity [m × m / mJ]. In the figure, the spectral sensitivity of the photoconductor using a-Si (amorphous silicon), OPC (Organic Photo Conductor), and Se-Te (selenium-tellurium) as materials is shown. It can be seen that the spectral sensitivity of any of the photoconductors varies with the wavelength of light. Here, the OPC photoconductor will be described as an example. In the vicinity of a wavelength of 700 [nm], the longer the wavelength, the more the OPC. The spectral sensitivity of the photoreceptor is good, and the potential changes with less energy (in other words, a latent image is formed). For example, when two light emitting elements E having different spectral distributions are compared, each light emitting element E The light-emitting element E having a spectral distribution that contains more long wavelength components changes the potential of the photoconductor more greatly, even though the amount of light (corresponding to the value obtained by integrating the spectral distribution with the wavelength) is the same. For this reason, even if the light amount correction of the light emitting element E described above is performed, if the spectral distribution of each light emitting element E of the line head 29 varies, the amount of change in potential of the photosensitive member varies, which is favorable. There was a risk that image formation could not be performed.

  Therefore, the line head control circuit CC of the present embodiment includes a spectral sensitivity ratio data storage unit CC3, and the spectral sensitivity ratio data storage unit CC3 and the correction circuit CC1 cooperate to perform light emission control of the light emitting element E. It addresses this issue.

  FIG. 7 is an explanatory diagram of light emission control performed by the spectral sensitivity ratio data storage unit and the correction circuit. In the graph shown in the figure, the horizontal axis represents the wavelength [nm] of light and the vertical axis represents intensity, and the spectral distribution of each of the light emitting elements E (n) and E (m) and the photosensitive drum 21. The spectral sensitivity of is shown. Note that the spectral sensitivity of the photosensitive drum 21 in FIG. 7 is different from the spectral sensitivity of the photosensitive member illustrated in FIG. 6, and is the spectral sensitivity of the photosensitive drum 21 used in this embodiment. In the same graph, the spectral sensitivity of the optical sensor SC is also shown. It can be seen that the spectral sensitivity of the photosensor SC is relatively constant.

  As shown in the figure, it can be seen that the spectral sensitivity of the photosensitive drum 21 is not constant, and that the spectral sensitivity is reduced from the position exceeding 600 [nm]. Accordingly, the light emitting element E having a spectral distribution including more long wavelengths has a smaller potential change amount to be changed. On the other hand, in the example of the figure, the light emitting element E (n) and the light emitting element E (m) have different spectral distributions. That is, the spectral distributions of the light emitting elements E (n) and E (m) are substantially the same at the peak PK, but the spectral distribution of the light emitting element E (n) is the spectral distribution of the light emitting element E (m). In comparison, it contains more long wavelengths. Therefore, the amount of potential change due to the light emitting element E (n) tends to be smaller than the amount of potential change due to the light emitting element E (m). Therefore, in this embodiment, the spectral sensitivity ratio data storage unit CC3 and the correction circuit CC1 control the light emission of the light emitting element E in order to suppress the variation in the potential change amount due to the variation in the spectral sensitivity. Based on the spectral distribution of E.

  First, parameters necessary for performing such light emission control are measured in advance when the line head 29 is shipped from the factory. That is, at the time of factory shipment, the line head 29 is attached to a spectral distribution measurement jig that measures the spectral distribution of each light emitting element E using a spectroscope. The spectral distribution measuring jig causes the light emitting elements E arranged in the main scanning direction MD to emit light in order, and each light emitting element E (1), E (2),..., E (m),. n) Measure the spectral distribution of.

で重心波長が求められる。こうして、各発光素子Ｅ(1)、Ｅ(2)、…、Ｅ(m)、…、Ｅ(n)、…の重心波長Ｇ(1)、Ｇ(2)、…、Ｇ(m)、…、Ｇ(n)、…が求められる。 FIG. 8 is a table showing an example of spectral distribution measurement. As shown in the table, the wavelength range for measuring the spectral distribution is set to 550 [nm] to 850 [nm]. This is because the spectral distribution is measured in a wavelength region (FIG. 7) in which the spectral intensity is sufficiently reduced. In this case, if the measurement wavelength resolution of the spectrometer is 10 [nm], 31 pieces of data are acquired. Then, the centroid wavelength of the spectral distribution is obtained from the measurement result. Specifically, the following formula:

The center of gravity wavelength is obtained. Thus, the center-of-gravity wavelengths G (1), G (2),..., G (m) of the light emitting elements E (1), E (2),. ..., G (n), ... are required.

  FIG. 9 is a graph showing an example of the measurement result of the centroid wavelength of the spectral distribution. In the graph, the horizontal axis indicates the light emitting element number n and the ordinate indicates the centroid wavelength [nm]. As shown in the figure, in the range indicated by the arrows in the graph, the center-of-gravity wavelength is shifted to the longer side, and the amount of potential change due to the light emitting element E in the range is reduced. Moreover, at the boundary of the range, the latent image formed by the light emitting element E having a long spectral center of gravity wavelength and the latent image formed by the light emitting element E having a short spectral center of gravity wavelength are adjacent to each other across the boundary. It will be. Therefore, when the latent image formed without considering the dispersion of the spectral distribution is developed, the difference in lightness and darkness appears remarkably at this boundary.

  In order to deal with such a problem, in the present embodiment, the photosensitive drum 21 at each of the center-of-gravity wavelengths G (1), G (2),..., G (m),. Spectral sensitivities I (1), I (2),..., I (m),. Then, one reference light-emitting element E (ref) is selected from each light-emitting element E, the spectral sensitivity I (ref) corresponding to this reference light-emitting element E (ref), and each light-emitting element E (1), Ratio of spectral sensitivities I (1), I (2), ..., I (n), ... corresponding to E (2), ..., E (n), ... I (1) / I (ref), I (2) / I (ref),..., I (n) / I (ref),... Are obtained as spectral sensitivity ratio data. The spectral sensitivity ratio data I (1) / I (ref), I (2) / I (ref), ..., I (n) / I (ref), ... are stored in the spectral sensitivity ratio data storage unit CC3. In this state, the line head 29 is shipped from the factory.

  In the actual latent image forming operation after the shipment of the line head 29, the correction circuit CC1 performs light emission control of the light emitting element E based on the spectral sensitivity ratio data stored in the spectral sensitivity ratio data storage unit CC3. That is, the light emitting element E () with the light quantity obtained by multiplying the light quantity Pj (n) × Pg (n) / Ph (n) estimated from the detection value of the photosensor SC by the spectral sensitivity ratio data I (n) / I (ref). The drive current value ID-Y is determined so that n) emits light. Then, during the light emission period indicated by the data TD-Y obtained from the video data VD-Y, the drive current having the current value ID-Y is supplied to the light emitting element E (n) to cause the light emitting element E (n) to emit light. By executing such light emission control on each light emitting element E, it is possible to stabilize the amount of potential change due to light irradiation of each light emitting element E.

  As described above, in the first embodiment, the estimated light amount Pj (n) × Pg (n) / Ph (n) (first correction) obtained from the detection result of the optical sensor SC that detects the light amount of the light emitting element E. Value) as well as the spectral sensitivity ratio data I (n) / I (ref) (second correction value) obtained from the spectral distribution of the light-emitting element E, the drive current value ID-Y of the light-emitting element E (Control signal) is corrected. As a result, it is possible to stabilize the potential change amount of the photosensitive drum 21 with respect to the variation in the spectral distribution of the light emitting element E and form a good image.

  The first embodiment is preferably configured to correct the drive current value ID-Y (control signal) based on the spectral sensitivity of the photosensitive drum 21 at the centroid wavelength of the spectral distribution. In other words, the centroid wavelength of the spectral distribution tends to change according to the variation of the spectral distribution. Therefore, by correcting the drive current value ID-Y (control signal) of the light emitting element E based on the spectral sensitivity of the photosensitive drum 21 at the center of gravity wavelength of the spectral distribution, the dispersion of the spectral distribution of the light emitting element E can be reduced. On the other hand, the amount of potential change of the photosensitive drum 21 can be stabilized.

  In addition, it is particularly preferable to apply the present invention to a configuration in which an organic EL element is used as the light emitting element E as in the first embodiment. That is, the organic EL element has a large variation in spectral distribution as compared with other elements such as LEDs (Light Emitting Diodes), and thus the above-described problem is likely to occur. Therefore, it is preferable to achieve good image formation by applying the present invention to a configuration using an organic EL element as the light emitting element E.

Second Embodiment The line head control circuit CC of the first embodiment corrects the current value ID-Y and the like of the drive current based on the spectral sensitivity ratio data stored in the spectral sensitivity ratio data storage unit CC3. On the other hand, the line head control circuit CC of the second embodiment stores the correlation between the gravity center wavelength of the spectral distribution and the image density, and based on this correlation, the current value ID-Y of the drive current, etc. Correct. Hereinafter, the second embodiment will be described in detail with reference to FIGS.

  FIG. 10 is a graph showing an example of the correlation between the center-of-gravity wavelength and the image density. The horizontal axis represents the center-of-gravity wavelength [nm] of the spectral distribution, and the vertical axis represents the relative density. The relative density on the vertical axis is formed with light having a spectral distribution in which the centroid wavelength is the value on the horizontal axis with respect to the density of the halftone image formed with light having a spectral distribution with a centroid wavelength of 660 [nm]. The density of the generated halftone image is shown as a relative ratio. From the figure, it can be seen that the relative density increases as the centroid wavelength increases.

  FIG. 11 shows the relative density of a halftone image formed when a driving current corresponding to the relative current on the horizontal axis is applied to the light emitting element E that emits light having a spectral distribution with a centroid wavelength of 660 [nm]. FIG. The abscissa in the figure shows the drive current value ID-Y and the like when the current value when only the light amount correction based on the detection value of the photosensor SC is performed is “1”. In addition, the vertical axis in the figure shows the halftone image density when the halftone image density formed when the light emitting element E is driven with the relative current “1” is “1”. Here, when the relative current is x and the relative density is y, the relational expression y = 4x−3 is established.

  In the second embodiment, the correlation shown in FIG. 10 is stored in the line head control circuit CC in order to make the image density constant regardless of the center-of-gravity wavelength of the spectral distribution of the light emitting element E. Based on this, the drive current value ID-Y and the like are corrected. More specifically, the density (reference density) of a halftone image formed with light having a spectral distribution with a reference centroid wavelength of 650 [nm] is formed with light having a spectral distribution with each centroid wavelength. In order to match the densities of the halftone images, the drive current value ID-Y is corrected. According to FIG. 10, in order to make them coincide with each other, for example, the driving current value ID− is set so that the density of the halftone image by the light having the spectral distribution with the center of gravity wavelength 660 [nm] falls to 0.97 in terms of the relative density ratio. Y must be corrected. Therefore, when the relative current is obtained from the relational expression y = 4x−3 described above, (3 + 0.97) /4=0.9925 is obtained. Therefore, the current value obtained only by correcting the light amount based on the detection value of the optical sensor SC is multiplied by this coefficient (= 0.9925) to obtain a drive current value ID-Y, etc. It is possible to make the image density constant regardless of the centroid wavelength of the spectral distribution.

  The correction of the drive current value ID-Y will be described with reference to FIGS. 12, 13 and 14 as follows. Here, FIG. 12 is a block diagram showing a modification of the configuration of the Y-line head control circuit. FIG. 13 is a table showing data stored in the Y-line head control circuit and values calculated from the data as Table 1. FIG. 14 is a diagram showing the gravity center wavelength vs. concentration correlation data as Table 2. Although only yellow (Y) will be described here, the same applies to other colors.

  The light emission current after light amount correction is a drive current value [uA] to each light emitting element E when only light amount correction based on the detection value of the optical sensor SC is performed, and is obtained in the same manner as in the first embodiment. It is stored in the light quantity correction data storage unit CC2. The centroid wavelength is obtained for each light emitting element E at the time of factory shipment of the line head 29 in the same manner as in the first embodiment, and is stored in the CC4 and centroid wavelength data storage unit CC4. The print density is a value obtained by the correction circuit CC1 for each light emitting element E from the barycentric wavelength in Table 1 and the print density in Table 2. The density ratio calculation value is obtained by dividing the reference density of 0.592 (the density of the halftone image formed by the light having the reference centroid wavelength of 650 [nm]) by the printing density shown in Table 1 so that the correction circuit CC1 has each light emitting element E. This is the value obtained every time. Further, the current correction coefficient is a coefficient obtained by (3 + concentration ratio calculation value) / 4 as described with reference to FIG. The light emission current after wavelength correction is a value obtained by the correction circuit CC1 for each light emitting element E by multiplying the light emission current after light amount correction in Table 1 by the current correction coefficient in Table 1.

  That is, the correction circuit CC1 reads the centroid wavelength of the spectral distribution of each light emitting element E from the centroid wavelength data storage unit CC4. Then, the print density corresponding to the centroid wavelength is obtained for each light emitting element E from the read centroid wavelength and the correlation data (Table 2) stored in the centroid wavelength vs density correlation data storage unit CC5. Furthermore, the light emission current after wavelength correction is multiplied by the density ratio calculation value obtained by dividing the reference density by the print density to obtain the light emission current after wavelength correction as a drive current value ID-Y. Then, the current having the drive current value ID-Y is applied to the light emitting element E.

  As described above, in the second embodiment, the estimated light amount Pj (n) × Pg (n) / Ph (n) (first correction) obtained from the detection result of the optical sensor SC that detects the light amount of the light emitting element E. The drive current value ID-Y (control signal) of the light emitting element E is corrected based not only on the value) but also on the concentration ratio calculated value (second correction value) obtained from the spectral distribution of the light emitting element E. As a result, it is possible to stabilize the potential change amount of the photosensitive drum 21 with respect to the variation in the spectral distribution of the light emitting element E and form a good image.

  In the second embodiment, the correlation between the centroid wavelength and the density of the image obtained by developing the latent image formed by the light emitting element E having the spectral distribution having the centroid wavelength by the developing unit 25 (Table 2). From this, the calculated density ratio value (second correction value) is obtained, which is preferable. That is, in this way, the density ratio calculation value is obtained from the correlation between the center-of-gravity wavelength of the spectral distribution and the image density, and the driving current value ID-Y (control signal) is corrected based on the density correction value. The image density can be more reliably stabilized against variations in distribution, and good image formation is possible.

Third Embodiment By the way, in the first and second embodiments, the drive current value ID-Y is calculated based on the spectral sensitivity ratio data I (n) / I (ref) or the calculated concentration ratio in the above embodiment. It was corrected. However, the data TD-Y indicating the light emission period of the light emitting element E may be corrected based on the spectral sensitivity ratio data I (n) / I (ref) or the concentration ratio calculation value.

  FIG. 15 is a block diagram showing a configuration of a head panel module provided in the line head. The head panel module HPM causes the light emitting element to emit light based on the data TD-Y. The head panel module HPM is provided in each of the line heads 29 of each color Y, M, C, K. However, since the configuration of the head panel module HPM is common to each color, here, the Y (Y) line of yellow (Y) is used. The head panel module HPM provided in the head 29 will be described as an example.

  The head panel module HPM is provided with a driver DV for supplying a drive current to the light emitting element E at an appropriate light emission timing. The driver DV has a shift register for storing the data TD-Y, a latch circuit for latching the data TD-Y, and controls the lighting time of the light emitting element E according to the latched data TD-Y. Built-in lighting control circuit.

  Each driver DV receives a Start pulse that gives a trigger for starting the shift register. The Start pulse is generated by the Y line head control circuit CC based on the synchronization signal Sync from the main controller MC and supplied to the driver DV. Then, the shift register activated by receiving the Start pulse shifts the data TD-Y in synchronization with the Data Clock, so that the data TD-Y for one line is stored across the shift registers of the plurality of drivers DV. The Thereafter, during the lighting time indicated by the data TD-Y latched by the Latch signal, the drive current having the current value ID-Y is supplied to the light emitting element E in synchronization with the PWM Clock. In this way, the lighting time of each light emitting element E is controlled (FIG. 16). Here, FIG. 16 is a timing chart showing an example of lighting time control of a light emitting element, and latch timing of data for 48 outputs of one driver DV and one light emitting element E connected to each of 48 outputs. The light emission timing is shown. In the example of the figure, a certain light emitting element E is turned on for a time Te (1) according to the data corresponding to the data TD (1), and then corresponds to the data TD (2) following the data TD (1). A case where a lighting operation of lighting for a time Te (2) according to data is executed is shown. At this time, each light emission duty is given by Te (1) / Th, Te (2) / Th,..., And the amount of energy given to the surface of the photosensitive drum 21 by the light emitting element E is adjusted by increasing or decreasing the light emission duty. can do. Here, the period Th is a period (one line scanning period) required to form a latent image of one line.

  Therefore, in this embodiment, instead of correcting the drive current value ID-Y based on the spectral sensitivity ratio data I (n) / I (ref) or the concentration ratio calculation value, data indicating the light emission period of the light emitting element E. TD-Y is corrected, and thereby the light emission duty of the light emitting element E is adjusted. By executing such light emission control on each light emitting element E, it is possible to stabilize the amount of potential change due to light irradiation of each light emitting element E.

  As described above, in the third embodiment, the estimated light amount Pj (n) × Pg (n) / Ph (n) (first correction) obtained from the detection result of the optical sensor SC that detects the light amount of the light emitting element E. Data TD-Y (control signal) is corrected based not only on (value) but also on the spectral sensitivity ratio or concentration ratio calculated value (second correction value) obtained from the spectral distribution of the light emitting element E. The light emitting element E emits light according to the data TD-Y. As a result, it is possible to stabilize the potential change amount of the photosensitive drum 21 with respect to the variation in the spectral distribution of the light emitting element E and form a good image.

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 present invention, and the photosensitive drum 21 becomes the “photosensitive member” of the present invention. The line head control circuit CC corresponds to the “light emission control unit” and the “correction unit” of the present invention, the development unit 25 corresponds to the “development unit” of the present invention, and the optical sensor SC Part. In the first and second embodiments, the drive current value ID-Y corresponds to the “control signal” of the present invention, and in the third embodiment, the data TD-Y corresponds to the “control signal” of the present invention. ing.

  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. For example, in the first and second embodiments, a specific configuration for supplying a drive current to the light emitting element E, that is, a configuration like the head panel module HPM in the third embodiment is not mentioned. However, in carrying out the first and second embodiments, if the head panel module HPM is provided in the line head 29 and the corrected drive current value ID-Y and the like are stored in the head panel module, The light emitting element E can be made to emit light with the corrected drive current value ID-Y.

  In the second embodiment, the example in which the coefficient 0.09925 is obtained by calculation has been described. However, the coefficient for the relative density ratio is stored in a table in advance, and the coefficient for the relative density ratio is read as appropriate to correct the light amount. The drive current value may be corrected by multiplying the current value.

  In the third embodiment, the case where the line head control circuit CC and the head panel module HPM are configured separately has been described. However, these may be realized as an integrated circuit.

  In the above embodiment, a bottom emission type organic EL element is used as the light emitting element E. However, 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 be used. That is, in the line head of the same document, the imaging optical system composed of convex lenses is arranged in an array, and a light emitting element group in which a predetermined number of light emitting elements are grouped facing each imaging optical system. Is arranged.

  21 ... photosensitive drum, 29 ... line head, HC ... head controller, CC ... head control circuit, ID-Y, ID-M, ID-C, ID-K ... drive current value, TD-Y, TD-M, TD-C, TD-K ... data, SC ... light sensor

Claims (5)

An exposure head having a light emitting element and a light emission control unit that emits light according to a control signal;
A photoreceptor on which a latent image is formed in response to light emitted by the light emitting element of the exposure head;
A developing unit for developing the latent image formed on the photoreceptor;
A detection unit for detecting a light amount of the light emitting element;
A correction unit that corrects the control signal based on a first correction value obtained from a detection result of the detection unit and a second correction value obtained from a spectral distribution of the light emitting element;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the correction unit corrects the control signal based on the spectral sensitivity of the photoconductor at a centroid wavelength of the spectral distribution.   The correction unit has a correlation between the centroid wavelength and the density of an image obtained by developing the latent image formed by the light emitting element having a spectral distribution having the centroid wavelength with the developing unit. The image forming apparatus according to claim 1, wherein a correction value is obtained.   The image forming apparatus according to claim 1, wherein the control signal is corrected based on a value obtained by multiplying the first correction value by the second correction value. A control signal for controlling the light emission of the light emitting element based on the first correction value obtained from the detection result of the detection unit for detecting the light amount of the light emitting element and the second correction value obtained from the spectral distribution of the light emitting element. A first step of correcting,
A second step of forming a latent image on the photosensitive member by exposing the photosensitive member to light from the light emitting element that emits light according to the control signal corrected in the first step;
A third step of developing the latent image formed in the second step;
An image forming method comprising:

Images