JP2008296443A - Optical printing head correcting method, optical printing head, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress printing irregularity when using an optical printing head for printing while emitting light onto a photosensitive medium such as a photo conductor. <P>SOLUTION: The optical printing head 3 comprises an image forming optical system 32 for forming an image of light emitted from a plurality of emitting elements 34 arranged in rows in a main scanning direction, on the photosensitive medium 1. This method is provided for correcting the light quantity of the plurality of emitting elements 34 in accordance with light quantity correcting data. The light quantity correcting data includes spot diameter-derived correcting data which is created on the basis of a measured angle highly correlative between the dispersion of the diameter of a beam spot in the main scanning direction when exposing the photosensitive medium 1 and the dispersion of the exposure amount (the printing concentration) of the photosensitive medium 1 in the main scanning direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention includes an optical print head used to expose a photosensitive medium such as an electrophotographic printer, a facsimile machine, a copying machine, or a photosensitive medium such as photosensitive paper, a correction method thereof, and an optical print head. The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus employing an electrophotographic method, an optical print head is sometimes used as an exposure unit for exposing a photoreceptor. An optical print head, for example, irradiates and images light from a plurality of light emitting elements arranged in a straight line on a circuit board as a plurality of light spots via a lens array such as a rod lens array on the surface of the photosensitive member. It is something to be made.

  A plurality of light emitting elements used in an optical print head are manufactured by a semiconductor manufacturing technique, and it is difficult to make the light emitting characteristics of these light emitting elements uniform. For this reason, even if the same amount of power is supplied to a plurality of light emitting elements, the amount of emitted light differs from light emitting element to light emitting element, so that the size of the light spot formed on the photoconductor and the amount of irradiation light may vary. Such variations cause unevenness in the image and make it difficult to accurately express gradation.

  In order to solve this problem, correction data for correcting the amount of light according to the light emission characteristics is created so that the amount of light emitted from each light emitting element to the photosensitive member is constant, and light emission is performed based on this correction data. A technique for adjusting the light emission amount by adjusting the drive time of the element (pulse width at the time of power supply) has been proposed (for example, see Patent Document 1).

  However, in the correction method for adjusting the light emission amount, it is difficult to sufficiently suppress unevenness in the print density because the variation in the shape of the light spot due to the manufacturing tolerance or assembly tolerance of the lens array cannot be suppressed.

  Moreover, the shape of the light spot on the photoconductor may be an ellipse or the like due to the aberration of a plurality of lenses constituting the lens array (see, for example, Patent Document 2). In such a case, the print density differs depending on whether the direction in which the long axis of the light spot extends is close to the screen direction (near parallel) or if the long axis of the light spot is close to the direction perpendicular to the screen direction. Become. For this reason, when there is no uniformity in the direction of the major axis of the plurality of light spots on the photosensitive member, this also causes uneven print density.

  An object of the present invention is to suppress printing unevenness when printing is performed by irradiating a photosensitive medium such as a photosensitive body with light using an optical print head.

JP-A-2-62257 Japanese Patent Laid-Open No. 11-241194

  In the first aspect of the present invention, a plurality of light emitting elements arranged in a line in the main scanning direction, and an imaging optical system for imaging light emitted from the plurality of light emitting elements on a photosensitive medium, In the optical print head provided, the light amount of the plurality of light emitting elements is corrected by light amount correction data, wherein the light amount correction data includes a variation in a beam spot diameter in the main scanning direction and the main scanning. Including spot diameter-derived correction data created on the basis of a measurement angle having a high correlation with print density in the direction or variation in exposure amount in the photosensitive medium, and the diameter of the beam spot is A cutting length when the beam spot is cut by a first straight line passing through the center of the beam spot, and the measurement angle is relative to a second straight line passing through the center of the beam spot. Characterized in that it is a crossing angle of the first straight line, the light quantity correcting method for an optical print head is provided.

  In a second aspect of the present invention, a plurality of light emitting elements arranged in a line in the main scanning direction, an imaging optical system for imaging light emitted from the plurality of light emitting elements on a photosensitive medium, and the plurality Light having a data holding means capable of holding light quantity correction data for correcting the light quantity of the light emitting elements, and a drive control means for controlling the driving of the plurality of light emitting elements based on the light quantity correction data In the print head, the light amount correction data has a correlation between a variation in the diameter of the beam spot in the main scanning direction and a variation in the print density in the main scanning direction or the exposure amount in the photosensitive medium. Spot diameter derived correction data created with a high measurement angle as a reference is included, and the diameter of the beam spot is determined by the first straight line passing through the center of the beam spot. An optical print head is provided, wherein the measurement angle is a crossing angle of the first straight line with respect to a second straight line passing through the center of the beam spot. Is done.

  According to a third aspect of the present invention, there is provided an image forming apparatus comprising the optical print head.

  The second straight line is, for example, a straight line extending along the main scanning direction. Of course, the second straight line may be a straight line extending in the sub-scanning direction, or may be another straight line.

  The correlation may be, for example, the covariance in the main scanning direction between the beam spot diameter and the print density or the exposure amount, and the standard deviation of the beam spot diameter variation and the print density. Or the correlation coefficient divided by the product of the standard deviation of the variation in the exposure amount.

  The correlation coefficient is preferably 0.4 or more in absolute value, and more preferably 0.6 or more in absolute value.

  The light quantity correction data preferably includes the spot diameter-derived correction data created corresponding to each of a plurality of screen angles. In this case, the drive control means drives the plurality of light emitting elements based on the spot diameter-derived correction data created according to the screen angle.

  The imaging optical system includes, for example, a plurality of rod lenses arranged in the main scanning direction. The plurality of rod lenses are arranged in a staggered manner, for example.

  The light quantity correction data may include outgoing light quantity derived correction data for making the emitted light quantity from the plurality of light emitting elements uniform within a desired range.

  According to the present invention, a spot created based on a measurement angle having a high correlation between a variation in the diameter of the beam spot and a variation in print density (exposure amount) in the main scanning direction on the photosensitive medium. Based on the diameter-derived correction data, the light amounts of the plurality of light emitting elements are corrected. For this reason, even if the light spots on the photosensitive medium such as the photoconductor are non-circular, such as an ellipse, even if the direction of the major axes of the light spots is not uniform, Can be suppressed.

  Hereinafter, an image forming apparatus and an optical print head according to the present invention will be specifically described with reference to the accompanying drawings.

  The image forming apparatus X shown in FIG. 1 includes an electrophotographic photosensitive member 1, a charging device 2, an optical print head 3, a developing device 4, a transfer device 5, a fixing device 6, a cleaning device 7, and a static eliminating device 8. It is.

  The electrophotographic photosensitive member 1 forms an electrostatic latent image and a toner image based on an image signal, and is rotatable in the direction of arrow A in FIG. As shown in FIG. 3, the electrophotographic photoreceptor 1 has a photosensitive layer 11 formed on the outer peripheral surface of a cylindrical substrate 10.

  The cylindrical substrate 10 has conductivity at least on its surface, and is formed of, for example, aluminum.

  The photosensitive layer 11 has a structure in which a photoconductive layer made of an inorganic semiconductor such as amorphous silicon or an organic semiconductor is deposited. When the photoconductive layer is irradiated with light from the optical print head 3, the photoconductive layer 11 is photoconductive. The specific resistance of the layer is rapidly reduced to form a predetermined latent image on the photoconductive layer. The photosensitive layer 31 may also be provided with a carrier injection blocking layer for blocking carrier injection from the cylindrical substrate 10 and a surface layer for protecting the surface of the electrophotographic photosensitive member 1.

  The charging device 2 is for charging the surface of the electrophotographic photoreceptor 1 uniformly to a positive polarity or a negative polarity according to the type of the photoconductive layer. The charging potential of the electrophotographic photosensitive member 1 is usually 200 to 1000V.

  As shown in FIGS. 2 and 3, the optical print head 3 is used to form an electrostatic latent image on the surface of the electrophotographic photosensitive member 1, in accordance with an image signal, the electrophotographic photosensitive member 1 (photosensitive layer 11). The surface is irradiated with light. The optical print head 3 is disposed substantially parallel to the electrophotographic photosensitive member 1 so as to be separated by a predetermined distance. The optical print head 3 includes a case 30, a circuit board 31, and a rod lens array 32.

  The case 30 is for holding the circuit board 31 and the rod lens array 32, and is formed, for example, by resin molding using a black resin.

  The circuit board 31 is formed by mounting a plurality of light emitting element array chips 34 and driving ICs 35 in an array on an insulating substrate 33 and forming conductive wiring in a predetermined pattern.

  The insulating substrate 33 is formed in a long rectangular shape from an electrically insulating material such as glass epoxy resin, glass, or ceramics.

  The plurality of light emitting element array chips 34 are arranged in a row along the longitudinal direction (main scanning direction) of the insulating substrate 33, and the plurality of light emitting elements (not shown) are, for example, 600 dpi (dot per inch). ) In a straight line with a density of The light emitting element array chip 34 includes a plurality of connection pads (not shown), and is connected to the driver IC 35 via conductive wiring (not shown).

  The light emitting element is made of, for example, a GaAlAs-based or GaAsP-based LED, and has a configuration in which a p-type semiconductor and an n-type semiconductor are pn-junctioned. When power is applied to each light-emitting element from the outside through circuit wiring, connection pads, etc., electrons are injected into the p-type semiconductor and holes are injected into the n-type semiconductor, respectively. Light is emitted with a predetermined luminance by recombination in the vicinity of the pn junction and converting the energy generated during the coupling into light. That is, each light emitting element emits light for a predetermined time corresponding to the image data by applying predetermined energy from the outside based on the image data.

  The driver IC 35 is for individually controlling the lighting state of the light emitting elements based on image data from the outside, and is electrically connected to the light emitting element array chip 34 through conductive wiring. As shown in FIG. 4, the driver IC 35 includes a gradation control unit 36, a light amount correction unit 37, and a plurality of constant current power supplies 38.

  The gradation control unit 36 is a shift register for serially transferring gradation image data from the outside that controls the gradation level of light, a latch for temporarily storing these gradation image data, and a strobe signal. Is supplied to the constant current power supply 38 based on the gradation image data in the latch. The gradation control unit 36 varies the energization time of the current supplied from the constant current power supply 38 to the light emitting element based on the gradation image data in the latch, for example, so that the print density level can be adjusted according to the light emitting time of the light emitting element. Perform key control.

  The light quantity correction unit 37 includes a shift register for serially transferring the light quantity correction data, a latch for temporarily storing the light quantity correction data, and the like, and is determined based on the light quantity correction data stored in the latch. The light emission amount of the light emitting element is adjusted by switching the current value of the current supplied from the current power supply 38 to the light emitting element. Details of the light amount correction data will be described later.

  The plurality of constant current power supplies 38 are provided in one-to-one correspondence with the light emitting elements, and the current value is adjusted based on the light amount correction data stored in the latch of the light amount correction unit 37.

  On the other hand, the rod lens array 32 is for irradiating and imaging the light from the light emitting element on the external electrophotographic photosensitive member 1, and holding a plurality of rod lenses 32A on a holder 32B. The plurality of rod lenses 32A are arranged in a staggered manner in the longitudinal direction (main scanning direction) of the insulating substrate. For example, the diameter is 0.3 mm to 1.1 mm, and the length is 4 mm to 17 mm. It is a cylindrical shape.

  The developing device 4 shown in FIG. 1 is for developing an electrostatic latent image on the electrophotographic photosensitive member 1 to form a toner image. The developing device 4 holds a developer and includes a developing sleeve 40.

  The developer is for constituting a toner image formed on the surface of the electrophotographic photoreceptor 1, and is triboelectrically charged in the developing device 4. As the developer, a two-component developer composed of a magnetic carrier and an insulating toner or a one-component developer composed of a magnetic toner can be used.

  The developing sleeve 40 plays a role of transporting the developer to a developing region between the electrophotographic photosensitive member 2 and the developing sleeve 40.

  In the developing device 4, the toner frictionally charged by the developing sleeve 40 is conveyed in the form of a magnetic brush adjusted to a constant spike length, and this toner is used in the developing area between the electrophotographic photosensitive member 1 and the developing sleeve 40. The electrostatic latent image is developed to form a toner image. The charge polarity of the toner image is opposite to the charge polarity on the surface of the electrophotographic photosensitive member 1 when image formation is performed by regular development, and the image formation is performed when reversal development is performed. The charged polarity of the surface of the body 1 is the same as the charged polarity.

  The transfer device 5 is for transferring a toner image onto a recording paper P fed to a transfer region between the electrophotographic photosensitive member 1 and the transfer device 5, and includes a transfer charger 50 and a separation charger 51. I have. In the transfer device 5, the back surface (non-recording surface) of the recording paper P is charged with a polarity opposite to that of the toner image in the transfer charger 50, and the electrostatic charge between the charged charge and the toner image causes the recording paper P to be charged. The toner image is transferred. In the transfer device 5, simultaneously with the transfer of the toner image, the back surface of the recording paper P is AC-charged in the separation charger 51, and the recording paper P is quickly separated from the surface of the electrophotographic photoreceptor 1.

  As the transfer device 5, it is also possible to use a transfer roller that is driven by the rotation of the electrophotographic photosensitive member 1 and disposed with a small gap (usually 0.5 mm or less) from the electrophotographic photosensitive member 1. It is. The transfer roller in this case is configured to apply a transfer voltage that attracts the toner image on the electrophotographic photosensitive member 2 onto the recording paper P by, for example, a DC power source. When such a transfer roller is used, a transfer material separating device such as the separation charger 51 can be omitted.

  The fixing device 6 is for fixing the toner image transferred to the recording paper P, and includes a pair of fixing rollers 60 and 61. In the fixing device 6, the toner image is fixed to the recording paper P by heat, pressure, or the like by passing the recording paper P between the pair of rollers 60 and 61.

  The cleaning device 7 is for removing toner remaining on the surface of the electrophotographic photoreceptor 1, and includes a cleaning blade 70. In the cleaning device 7, the toner remaining on the surface of the electrophotographic photosensitive member 1 is scraped and collected by the cleaning blade 70. The toner collected in the cleaning device 7 may be recycled into the developing device 4.

  The static eliminator 8 is for removing the surface charge of the electrophotographic photosensitive member 1. The static eliminator 8 is configured to remove the surface charge of the electrophotographic photosensitive member 2 by, for example, light irradiation.

  Next, a correction method of the optical print head 3 will be described together with a determination method of correction parameters for creating light amount correction data to be stored in the latch of the driver IC 35.

  First, before assembling the optical print head 3 into the image forming apparatus 1, the light emission output of each light emitting element in the light emitting element array 34 is measured, and based on this measurement result, the light emission output of each light emitting element falls within a required range. First correction parameters for making uniform are created. The first correction parameter can be created based on the light amount of each light emitting element measured using, for example, the beam measuring device 9 shown in FIG.

  The beam measuring device 9 is configured to observe light from a light emitting element in the optical print head 3 with a CCD camera 90 via a rod lens array 32. The CCD camera 90 can be moved along a row of light emitting elements by a drive system. An image picked up by the CCD camera 90 is subjected to image processing in an information processing device 91 such as a personal computer. The information processing device 91 obtains a predetermined power value necessary to fill the difference between the light emission output of each light emitting element and the average value (reference value) based on the intensity distribution of the plurality of light emitting elements. A first correction parameter is created in correspondence with.

  The correction target value when the light amount correction is performed using the first correction parameter is determined within a correctable range in consideration of, for example, the photosensitivity of the electrophotographic photosensitive member 1 and the printing speed. The correction target value is usually set in the vicinity of the average value of the light amounts of the plurality of light emitting elements before correction, for example, the variation in the light emission output of each light emitting element 3 is within ± 15%, preferably within ± 7%. The

  The correction target value is set in such a range when the variation in the light emission output is too large, the shape of the light emission intensity distribution of each light emitting element varies greatly when creating the second correction parameter described later. This is because the correction value in the second correction parameter is greatly changed, and high-accuracy correction may not be possible.

Here, when 16-level gradation expression is performed for each color, a correction parameter of 4 bits (2 ⁴ = 16) is required for each dot, and when 64-level gradation expression is performed for each color, one dot is required. 6-bit (2 ⁶ = 64) light quantity correction data is required. The gradation expression can be performed by, for example, the magnitude of applied power (for example, current value or application time). In this case, when expressing gradation of 16 steps (4 bits / dot), for example, by adjusting each gradation with a power width of 3%, it is possible to perform power adjustment with a width of about 45%. On the other hand, when expressing gradations of 64 levels (6 bits / dot), for example, by adjusting each gradation with a power width of 1.2%, it is possible to perform power adjustment with a width of about 75%. Note that the increment of the power adjustment width of each gradation may be determined by, for example, the design of the light emitting element or IC, and is not necessarily limited to the above-described increment width.

  Next, a second correction parameter is created based on the correlation between the variation in the beam spot diameter and the variation in the print density in the main scanning direction at various measurement angles. The second correction parameter is an image obtained by moving the CCD camera 90 and moving the beam spot when each light emitting element of the light emitting element array chip 34 emits light with substantially the same luminance based on the first correction parameter. It can be created by processing.

  More specifically, the information processing apparatus 91 calculates the beam spot diameter and light emission intensity of each light emitting element by processing an image captured by the CCD camera 90.

  As shown in FIG. 6, the beam spot Bs of each light emitting element has an aberration (image formation) of each rod lens 32A when the rod lens array 32 has a configuration in which a plurality of rod lenses 32A are arranged in a staggered manner. The difference between the position and the distance to the center of the rod lens), and the inclination θ1 of the principal axis L of the beam spot Bs continuously changes as shown in FIG. Here, as shown in FIG. 8, the inclination θ1 of the main axis L means the inclination of the major axis of the beam spot Bs with respect to the main scanning direction (the arrangement direction of the rod lenses 32A), and in the illustrated example, it is counterclockwise. The direction is positive.

  As shown in FIGS. 9A and 9B, the diameter D of the beam spot Bs is a cut in a cross section when the beam spot Bs is cut along a straight line (cut line) S passing through the center of the beam spot Bs. Defined as length. The measurement angle θ2 is defined as the slope of a straight line (cut line) S with respect to the main scanning direction. In the illustrated example, the clockwise direction of the measurement angle θ2 is a positive direction. Further, the beam spot Bs for measuring the diameter D of the beam spot Bs is preferably in the range of 2% to 25%, for example, as shown in FIG. Is a beam spot Bs at a position selected from a range of 2% to 10%.

  Here, as shown in FIG. 10, for example, when dots are formed in odd rows for odd columns, while dots are formed in even rows for even columns (screen angle θ3 = 45 °), for example, Due to the continuous change in the inclination θ1 of the main axis L of the beam spot Bs, the print density can change continuously in the main scanning direction.

  Therefore, as a result of intensive studies on parameters that can correlate with changes in the print density in the main scanning direction, the present inventor has found that changes in the print density change in the diameter of the beam spot Bs at a specific measurement angle in the main scanning direction. We found that there is a correlation.

  As shown in FIG. 11, when the screen angle is 45 ° and the measurement angle θ2 (see FIG. 9A) is 0 °, there is a correlation between the change in the print density in the main scanning direction and the change in the diameter of the beam spot Bs. Sex was not seen. On the other hand, when the measurement angle θ2 (see FIG. 9A) is 105 °, a high correlation was observed between the change in the print density in the main scanning direction and the change in the diameter of the beam spot Bs.

  In FIG. 11, the vertical axis is shown as a change (variation) in print density, but for example, the same tendency can be seen when the vertical axis is the exposure amount for the electrophotographic photosensitive member 1.

  Therefore, the correlation between the change in the print density in the main scanning direction and the change in the diameter D of the beam spot Bs with respect to various measurement angles θ2 (see FIG. 9A) was examined. The result shown in FIG. was gotten. In FIG. 12, the correlation is shown as a correlation coefficient. Here, the correlation coefficient in FIG. 12 is obtained by dividing the covariance between the diameter D of the beam spot Bs and the print density by the product of the standard deviation of the variation in the diameter D of the beam spot Bs and the standard deviation of the variation in the print density. It is a thing.

  As can be seen from FIG. 12, the correlation coefficient changed according to the measurement angle θ2 (see FIG. 9A), and the absolute value increased when the measurement angle θ2 was around 60 ° and around 105 °. Since the correlation coefficient is higher as the absolute value is closer to 1, the correlation density changes in the main scanning direction and the diameter D of the beam spot Bs when the measurement angle θ2 is around 60 ° and around 105 °. It shows that the correlation of the change is high. Therefore, in the example shown in FIG. 12, the measurement angle θ2 is in the vicinity of 60 ° and 105 °, for example, the main scanning direction at the measurement angle θ2 in which the correlation coefficient is 0.4 or more, preferably 0.6 or more in absolute value. It can be seen that variation in the print density in the main scanning direction can be suppressed by controlling the driving of each light emitting element and adjusting the diameter D of the beam spot according to the change in the diameter D of the beam spot Bs. That is, the second correction parameter corresponds to the change in the diameter D of the beam spot Bs at the measurement angle θ2 where the change in the print density in the main scanning direction and the change in the diameter D of the beam spot Bs are highly correlated. It is created to make the variation in the diameter D of the spot Bs uniform. For example, when the diameter D of the beam spot Bs is adjusted by the power applied to the corresponding light emitting element, the second correction parameter is the diameter D of the beam spot Bs corresponding to each light emitting element and the average value thereof. A predetermined power value required to fill the difference from the (reference value) is obtained, and is created as a value corresponding to this value.

  The first and second correction parameters created in this manner reflect the light emission characteristics or print characteristics of the optical print head 3. In the optical print head 3, a plurality of constant currents are printed at the time of printing based on the emission light amount-derived correction data created based on the first correction parameter and the spot diameter-derived correction data created based on the second correction parameter. The light emission state of the light emitting element is controlled by controlling the current value of the power source 38 and the application time. As a result, when image formation is performed using the optical print head 3, variations in print density are suppressed. Also, appropriate gradation expression can be achieved by suppressing variations in print density.

  The first and second correction parameters may be stored in the driver IC 35, may be stored in a memory different from the driver IC 35, and may be mounted on the circuit board 33, or the optical print head 3 may be stored in a memory provided outside. Further, the emission light amount-derived correction data and the spot diameter-derived correction data based on the first and second correction parameters may be created in the optical print head 3 or outside the optical print head 3. In the latter case, the emission light amount-derived correction data and the spot diameter-derived correction data are created in advance before the optical print head 3 is incorporated into the image forming apparatus and stored in the driver IC or memory of the optical print head 3. Also good.

  The present invention is not limited to the embodiments described above, and can be variously modified. For example, FIGS. 11 and 12 show an example in which the screen angle θ3 is 45 ° (see FIG. 10), but the same method as described above is also used when the screen angle θ3 is other than 45 °. Thus, the second correction parameter can be created. In addition, second correction parameters are generated for a plurality of screen angles, and spot diameter-derived correction data is generated based on the second correction parameters corresponding to the screen angles at the time of printing, and It is also possible to correct the amount of light.

  When performing color printing, for example, a plurality of types of light emitting elements having different peak wavelengths of emission intensity are used, and the first and second correction parameters are individually set for each of the plurality of types of light emitting elements having different peak wavelengths. Should be created.

  The present invention is not limited to an optical print head using a rod lens array in which a plurality of rod lenses are arranged in a staggered manner, or an optical print head using a rod lens array in which a plurality of rod lenses are arranged in a row, or It can be applied to an optical print head using a convex lens instead of the rod lens.

  The present invention is not limited to an image forming apparatus that employs an electrophotographic method, and may be applied to an image forming apparatus that forms an image on a photosensitive medium by irradiating a photosensitive medium such as photosensitive paper with light. it can.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. It is a disassembled perspective view which shows an example of the optical print head concerning this invention. FIG. 3 is a cross-sectional view of the optical print head shown in FIG. 2. FIG. 3 is a circuit diagram of a driver IC in the optical print head shown in FIG. 2. It is a schematic block diagram of the beam measuring device used for producing a correction parameter. It is a top view for demonstrating the relationship between the shape of a beam spot, and a rod lens array. It is a graph which shows the change of the inclination of the principal axis of the beam spot in the main scanning direction. It is a figure for demonstrating the inclination of the principal axis of a beam spot. It is the schematic for demonstrating the diameter of a beam spot. It is a figure which shows the example of formation of the printing dot when a screen angle is 45 degrees. It is a graph which shows the correlation of the diameter of the beam spot in the main scanning direction, and the variation in printing density. It is a graph which shows the correlation coefficient of the measurement angle of the diameter of a beam spot, and printing density.

Explanation of symbols

X Image forming device 1 Electrophotographic photosensitive member (photosensitive medium)
3 Optical print head 32 Rod lens array (imaging optical system)
32A rod lens 35 driver IC (data holding means, drive control means)
Bs Beam spot D Beam spot diameter θ2 Measurement angle θ3 Screen angle

Claims (17)

Light quantity correction in an optical printhead comprising a plurality of light emitting elements arranged in a line in the main scanning direction and an imaging optical system for imaging light emitted from the plurality of light emitting elements on a photosensitive medium According to data, a method of correcting the light quantity of the plurality of light emitting elements,
The light amount correction data is based on a measurement angle having a high correlation between the variation in the diameter of the beam spot in the main scanning direction and the variation in the print density in the main scanning direction or the exposure amount in the photosensitive medium. Contains the created spot diameter-derived correction data, and
The diameter of the beam spot is a cutting length when the beam spot is cut by a first straight line passing through the center of the beam spot,
The method according to claim 1, wherein the measurement angle is an intersection angle of the first straight line with respect to a second straight line passing through the center of the beam spot.   The light quantity correction method for an optical print head according to claim 1, wherein the second straight line is a straight line extending along the main scanning direction.   The correlation indicates the covariance of the beam spot diameter and the print density or the exposure amount in the main scanning direction, the standard deviation of the beam spot diameter variation and the variation of the print density or the exposure amount. The light quantity correction method for an optical print head according to claim 1, wherein the correlation coefficient is divided by a product of standard deviations.   The light quantity correction method for an optical print head according to claim 3, wherein the correlation coefficient is 0.4 or more in absolute value.   5. The light quantity correction method for an optical print head according to claim 1, wherein the light quantity correction data includes the spot diameter-derived correction data created corresponding to each of a plurality of screen angles.   The light quantity correction method for an optical print head according to claim 1, wherein the imaging optical system includes a plurality of rod lenses arranged in the main scanning direction.   The light quantity correction method for an optical print head according to claim 6, wherein the plurality of rod lenses are arranged in a staggered manner.   The light quantity correction method according to claim 1, wherein the light quantity correction data includes emission light quantity-derived correction data for making the emitted light quantity from the plurality of light emitting elements uniform within a desired range. . A plurality of light emitting elements arranged in a line in the main scanning direction, an imaging optical system for forming an image of light emitted from the plurality of light emitting elements on a photosensitive medium, and a light amount of the plurality of light emitting elements are corrected. An optical print head comprising: data holding means capable of holding light quantity correction data for driving; and drive control means for controlling driving of the plurality of light emitting elements based on the light quantity correction data,
The light amount correction data is based on a measurement angle having a high correlation between the variation in the diameter of the beam spot in the main scanning direction and the variation in the print density in the main scanning direction or the exposure amount in the photosensitive medium. Contains the created spot diameter-derived correction data, and
The diameter of the beam spot is a cutting length when the beam spot is cut by a first straight line passing through the center of the beam spot,
The optical print head according to claim 1, wherein the measurement angle is an intersection angle of the first straight line with respect to a second straight line passing through a center of the beam spot.   The optical print head according to claim 9, wherein the second straight line is a straight line extending along the main scanning direction.   The correlation indicates the covariance of the beam spot diameter and the print density or the exposure amount in the main scanning direction, the standard deviation of the beam spot diameter variation and the variation of the print density or the exposure amount. The optical printhead of claim 9 or 10, wherein the optical printhead is the correlation coefficient divided by the product of the standard deviation.   The optical print head according to claim 11, wherein the correlation coefficient is 0.4 or more in absolute value. The light amount correction data includes the spot diameter-derived correction data created corresponding to each of a plurality of screen angles,
The optical print head according to claim 9, wherein the drive control unit drives the plurality of light emitting elements based on the spot diameter-derived correction data created according to the screen angle.   The optical print head according to claim 9, wherein the imaging optical system includes a plurality of rod lenses arranged in the main scanning direction.   The optical print head according to claim 14, wherein the plurality of rod lenses are arranged in a staggered manner.   The optical print head according to claim 9, wherein the light quantity correction data includes emission light quantity-derived correction data for making the emitted light quantity from the plurality of light emitting elements uniform within a desired range. . An image forming apparatus comprising the optical print head according to claim 9.

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