JP2009090525A - Image forming apparatus and its adjusting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, wherein uneven density in a formed image is reduced by suppressing quantitative variation of light emitted to the surface of a photoreceptor drum due to laser light emission delay. <P>SOLUTION: This image forming apparatus uses an OFS type optical system, wherein the light amount emitted to the surface of the photoreceptor drum when the laser light emitting element is driven at a prescribed duty ratio is measured, and correction data to correct every pixel in a single scanning line to have the prescribed light amount is determined and previously stored. During the image forming period, this image forming apparatus is allowed to correct the driving current of the laser light emitting element by using the previously stored correction data. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus such as a laser printer or a digital copying machine that forms an electrostatic latent image on a photosensitive drum, and an adjustment method thereof.

  In general, an electrophotographic image forming apparatus irradiates a laser beam to form an electrostatic latent image on a photosensitive drum. As a method for scanning and exposing a photosensitive drum, a raster scanning method is generally used, in which a laser is formed in a beam shape and a photosensitive surface is scanned and exposed by an optical system.

  Conventionally, the UFS (Under Field Scanner) method shown in FIG. 13 has been generally adopted among the raster scan methods. However, at present, in order to meet the demand for higher speed, an optical system of the OFS (Over Field Scanner) system shown in FIG. 14 is adopted as a system for scanning the photosensitive drum at a higher speed than the UFS system. Yes. In these two methods, the UFS method irradiates the polygon mirror with a light beam smaller than the reflection surface of the polygon mirror, whereas the OFS method irradiates a light beam larger than the reflection surface of the polygon mirror. There is a difference.

  Compared with the UFS method, this OFS method increases the number of polygon mirror surfaces, increases the number of scanning lines that can be drawn in one rotation, and increases the rotation speed of the polygon mirror (miniaturization of the polygon mirror). Can be speeded up. By adopting such a configuration, the OFS method is more advantageous than the UFS method in terms of noise, rotational speed, heat generation, and rising speed, but there is a problem that the irradiation distribution in the main scanning direction becomes non-uniform. Has surfaced. This non-uniformity of the irradiation distribution in the main scanning direction is due to the change in the amount of reflected light caused by the change in the angle of the reflecting surface of the polygon mirror as shown in FIG.

  The laser light emitted from the laser diode has a non-uniform light intensity distribution characteristic called FFP (Far Field Pattern) characteristic. When a light beam wider than the width of the reflection surface of the polygon mirror is incident on the polygon mirror, regions having different light quantity distributions in the light beam are reflected depending on the angle of the polygon mirror reflection surface as shown in FIG. Accordingly, the amount of reflected light within one scanning period varies due to uneven distribution due to the FFP characteristics.

  Due to this change in the amount of reflected light, the amount of light decreases near the end in the main scanning direction with a large angle, rather than near the center in the main scanning direction with a small angle. Therefore, when an image is formed, there arises a problem that the density decreases at the end in the main scanning direction as shown in FIG. In addition to increasing the speed of the image forming apparatus, high image quality and long life (high durability) are required, so it is necessary to correct this density change to form a uniform image without density change.

  In Patent Document 1, correction values relating to density changes at the time of resolution conversion are stored in a storage unit, various correction values corresponding to image coordinates and image data are integrated, and the emission intensity of laser light is controlled as correction data. An image forming apparatus is proposed. Patent Document 2 proposes an image forming apparatus in which the density is corrected by changing the γ curve in order to correct the print density in accordance with the density setting for the purpose of further optimizing the density.

  The density unevenness in the OFS method is corrected by changing the amount of laser light in the main scanning direction. There are two main methods for changing the laser light quantity. One is to equalize the amount of light irradiated to the surface of the photosensitive drum by optical components such as a lens, a reflecting mirror, and an aperture. The other is to make the amount of light irradiated to the surface of the photosensitive drum uniform by electrically changing the light emission current of the laser. Since it is difficult to adjust the correction amount individually for the former, it is disadvantageous for the characteristics variation of laser chips having different characteristics. It is used a lot.

In the method of performing electrical laser emission control, the amount of drive current in one main scanning period is changed. At this time, the amount of drive current at the center of the image is decreased from the end of the image. By controlling this driving current, the main scanning illuminance distribution on the drum surface is controlled to be constant. When such control is performed, correction is normally performed using a constant drive current change curve in one main scanning period as shown in FIG.
Japanese Patent Laid-Open No. 2005-070069 JP 2002-172817 A

  However, in the prior art, it is necessary to consider the light emission delay of the laser diode for the following reason. FIG. 18 is a diagram showing the LI characteristics of the laser diode. In order to cause the laser diode to oscillate, it is necessary to apply a drive current that is equal to or greater than a threshold current. Further, the laser diode has a capacitance component, and the laser drive circuit has a parasitic capacitance. In addition to the influence of the capacitance component, the laser driving circuit requires a time of several ns to several tens of ns in order to give the laser diode a driving current equal to or higher than the threshold current. Accordingly, since a loss time occurs from when the laser current is started to when the laser actually oscillates, a light emission delay as shown in FIG. 19 occurs. The length of this light emission delay mainly depends on the amount of laser current.

  FIG. 20 is a diagram showing the relationship between the image data and the drum surface light amount at each laser current amount. As shown in FIG. 20, when the amount of laser current decreases, the light emission delay increases. Therefore, the amount of light (drum surface light amount) irradiated to the surface of the photosensitive drum when the laser is driven with the same image data decreases as the laser current amount decreases.

  In the OFS method, as described above, a method of performing electrical laser emission control is used, and the amount of laser drive current in one main scanning period is changed. At this time, in order to eliminate the characteristics of the OFS method shown in FIG. Therefore, the laser light emission delay amount at the center of the image is increased. When the laser diode is pulse-lit, the irradiation distribution in the main scanning direction decreases the amount of laser light at the center of the image as shown in FIG. When image formation is performed, a decrease in the amount of laser light at the center of the image caused by this laser current difference causes image density unevenness, causing a problem that the density at the center of the image becomes lighter than at the edge of the image.

  The present invention has been made in view of the above-described problems, and suppresses variations in the amount of light applied to the surface of a photosensitive drum due to laser light emission delay, thereby reducing density unevenness in the formed image. An object is to provide an apparatus.

  The present invention includes, for example, a laser light emitting unit that emits light, and a rotating polygon mirror that converts light emitted from the laser emitting unit into scanning light for an image carrier. This can be realized as an image forming apparatus that irradiates a light beam having a width larger than one mirror surface width of the mirror. The image forming apparatus drives the laser light emitting means at a predetermined duty ratio, controls drive current for driving the laser light emitting means, and coordinates corresponding to each pixel in one scanning line of the image carrier. The main scanning that indicates the light quantity for each coordinate of the light irradiated to the image carrier when the laser light emitting means is driven at a predetermined duty ratio A correction data determining means for measuring the irradiation light quantity and determining correction data to be multiplied by the drive current so that the measured main scanning irradiation light quantity becomes a target light quantity at each coordinate; and for performing image formation at the time of image formation Drive current correction means for correcting the drive current input to the laser emission means by multiplying the drive current by the determined correction data. .

  Further, the present invention includes, for example, a laser light emitting unit that emits light, and a rotating polygon mirror that converts light emitted from the laser emitting unit into scanning light to the image carrier, Image formation for correcting the drive current input to the laser light emitting means by irradiating a light beam having a width larger than one mirror surface width of the rotary polygon mirror and multiplying the drive current for driving the laser light emitting means by the correction data This can be realized as an adjustment method related to the apparatus. In the adjustment method, the laser emission means is driven at a predetermined duty ratio, and a drive control step for controlling a drive current for driving the laser emission means, and coordinates corresponding to each pixel in one scanning line of the image carrier are set. A coordinate measurement step for measuring in accordance with the driving of the laser light emitting means, and main scanning irradiation indicating the amount of light for each coordinate of the light emitted to the image carrier when the laser light emitting means is driven at a predetermined duty ratio And a correction data determining step for determining correction data to be multiplied by the drive current so that the measured main scanning irradiation light quantity becomes a target light quantity at each coordinate.

  The present invention can provide, for example, an image forming apparatus that suppresses variations in the amount of light applied to the surface of a photosensitive drum due to a delay in laser light emission and reduces density unevenness in the formed image.

  An embodiment of the present invention is shown below. The individual embodiments described below will help to understand various concepts, such as superordinate concepts, intermediate concepts and subordinate concepts of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

[First Embodiment]
The first embodiment will be described below with reference to FIGS. 1 to 6. FIG. 1 is a diagram illustrating a configuration of a printer 100 according to the first embodiment. In the present embodiment, a printer 100 that is a laser beam printer will be described as an application example of the image forming apparatus. However, the present invention is not limited to a laser beam printer as an image forming apparatus, but can be applied to a facsimile, a scanner, or a multifunction machine using an electrophotographic system. In the following, description will be given mainly on the components related to the present invention. Therefore, the printer 100 according to the present invention may be configured to include other components.

  The printer 100 includes a semiconductor laser 1, an image signal generation unit 2, a laser drive control unit 3, a drive current correction unit 4, a collimator lens 5, a rotary polygon mirror 6, an fθ lens 7, a mirror 8, a main scanning synchronization unit 9, and a photosensitive drum. 10 includes a laser light quantity detection unit 11 and a CPU 13. The optical system applied in this embodiment is the OFS optical system shown in FIG. Therefore, the light flux width of the parallel light a after passing through the collimating lens 5 is wider than the width (mirror face width) of one reflecting mirror surface of the rotary polygon mirror 6.

  The semiconductor laser 1 functions as a laser emission unit, and emits a laser beam according to a drive current supplied from the laser drive control unit 3. The image signal generation unit 2 outputs a laser emission signal (hereinafter referred to as an image signal b) to the laser drive control unit 3 in accordance with image data of an image formed on the recording material. The laser drive control unit 3 functions as drive control means, drives the semiconductor laser 1 with a predetermined duty ratio, and controls the amount of emitted light by controlling the drive current according to the image signal b.

  The drive current correction unit 4 functions as drive current correction means, and outputs correction data for controlling the amount of light emitted from the semiconductor laser 1 to the laser drive control unit 3. Specifically, the drive current correction unit 4 corrects the drive current input to the semiconductor laser 1 by multiplying the determined correction data by the drive current for performing image formation during image formation.

  The collimating lens 5 converts the laser light emitted from the semiconductor laser 1 into parallel light a. The rotary polygon mirror 6 converts the parallel light a into scanning light g that scans the photosensitive drum 10 in the main scanning direction. The fθ lens 7 corrects the optical distortion and scanning speed of the scanning light g. The mirror 8 reflects the scanning light g and irradiates the surface of the photosensitive drum 10. The main scanning synchronization unit 9 generates a main scanning synchronization signal (hereinafter referred to as BD signal d) by receiving the laser light reflected by the rotary polygon mirror 6. The laser light quantity detector 11 receives the laser light emitted from the semiconductor laser 1 as monitor light e. The CPU 13 outputs a control signal k for driving the semiconductor laser 1 to the laser drive control unit 3.

  The CPU 13 comprehensively controls the above-described components. Further, according to the present embodiment, the CPU 13 functions as correction data determination means. Specifically, the CPU 13 measures a main scanning irradiation light amount (main scanning irradiation distribution) indicating a light amount for each coordinate of light irradiated on the photosensitive drum 10 when the semiconductor laser 1 is driven at a predetermined duty ratio. To do. Further, the CPU 13 determines correction data to be multiplied by the drive current so that the measured main scanning irradiation light amount becomes the target light amount at each coordinate.

  Hereinafter, details of each component will be described in accordance with a procedure for forming an electrostatic latent image on the photosensitive drum 10 as an image carrier. When receiving a print command from the controller or the host computer, the printer 100 starts image formation. Here, the controller comprehensively controls the printer 100 and outputs a print command to the CPU 13. As a case where the controller outputs a print command, for example, an image read from an original by a scanner provided in the printer 100 may be printed. The host computer is an external device connected to the printer 100 via a network, and transmits a print command to the printer 100.

  When the print command is transmitted, the CPU 13 outputs a control signal k to the laser drive control unit 3. The laser drive control unit 3 drives the semiconductor laser 1 to emit laser light. Here, the main scanning synchronization unit 9 generates the BD signal d by receiving the laser beam reflected by the rotary polygon mirror 6. The BD signal d is output to the laser drive control unit 3, the drive current correction unit 4, and the image signal generation unit 2 as shown in FIG.

  When the semiconductor laser 1 emits laser light, the laser light quantity detection unit 11 receives the laser light as monitor light e and generates a PD signal h. The PD signal h is output to the laser drive control unit 3 and the CPU 13. Here, a method of detecting the monitor light e as the rear beam light of the semiconductor laser is generally used, but it can also be configured by a method of separating and detecting the front beam light with a splitter, a half mirror, or the like. When the laser drive control unit 3 receives the PD signal h, the laser drive control unit 3 performs APC control (Auto Power Control control), and controls the amount of light emitted from the semiconductor laser 1 to be constant.

  When receiving the BD signal d, the image signal generator 2 outputs the image signal b to the laser drive controller 3 in synchronization with the BD signal d. Further, the drive current correction unit 4 outputs correction data c to the laser drive control unit 3 in synchronization with the BD signal d. Here, the correction data c includes coordinate position data in the main scanning direction, and a drive current value, a drive current correction amount, or a drive current correction rate at each coordinate position. The laser drive control unit 3 controls the emission of the semiconductor laser 1 based on the image signal b and the correction data c.

  Laser light emitted from the semiconductor laser 1 is converted into parallel light a by the collimator lens 5 and converted into scanning light g by the rotating polygon mirror 6. Further, the scanning light g is corrected by the fθ lens 7 for optical distortion such as surface tilt and scanning speed. The scanning light g optically corrected by the fθ lens 7 is reflected by the mirror 8 and then irradiated on the surface of the photosensitive drum 10 to form an electrostatic latent image. Thereafter, the printer 100 according to the present embodiment selectively attaches the developer to the electrostatic latent image formed on the photosensitive drum 10, transfers it to the recording material, and heats the recording material and the developer. To fix and print.

  Next, detailed components of the drive current correction unit 4 will be described with reference to FIG. FIG. 2 is a diagram illustrating a control configuration of the drive current correction unit 4 according to the first embodiment. Note that the control configuration described below is an application example and is not limited to this configuration. For example, components included in the drive current correction unit 4 described below do not need to be included in the drive current correction unit 4 and may be connected to the drive current correction unit 4.

  The drive current correction unit 4 includes a coordinate measurement counter 21, a reference voltage generation unit 22, a memory 23, and a correction data generation unit 25. In the memory 23 that functions as a storage unit, correction data for each pixel is stored in the nonvolatile memory 24. The drive current correction unit 4 includes an increase / decrease unit (not shown) that can increase / decrease the reference voltage value or the correction data of all pixels in one scanning line by a control signal.

  The coordinate measurement counter 21 functions as a coordinate measurement unit. When the BD signal e is input to the drive current correction unit 4, the coordinate measurement counter 21 measures the coordinate position of each pixel with respect to the main scanning direction based on the BD signal e. Specifically, the coordinate measurement counter 21 measures the coordinates corresponding to each pixel in one scanning line of the photosensitive drum 10 in accordance with the driving of the semiconductor laser 1. Based on the measurement result of the coordinate measurement counter 21, correction data corresponding to each coordinate position (each pixel) is read from the memory 23 and output to the correction data generation unit 25.

  In the reference voltage generation unit 22, the reference voltage Vref is generated and output to the correction data generation unit 25. The correction data generation unit 25 multiplies the correction data and the reference voltage Vref to generate correction data c. The multiplied correction data c is output to the laser drive control unit 3. The correction data stored in the nonvolatile memory 24 can be rewritten by a control signal from the CPU 13. Further, the drive current correction unit 4 can perform ON / OFF control of correction data output and control whether or not the correction data is multiplied by the reference voltage.

  Next, a method for determining drive current correction data in the present embodiment will be described with reference to FIGS. The correction data is determined before shipment from the factory. The determined correction data is stored in the nonvolatile memory 24. FIG. 3 is a diagram showing a laser current and an irradiation distribution on the photosensitive drum 10 when the semiconductor laser 1 is driven at a predetermined duty (DUTY) ratio according to the first embodiment. Further, (a) shows a case where the correction data output (light quantity correction output) is set to OFF before shipment from the factory. On the other hand, (b) shows the case where the correction data output is set to ON. Note that the drum irradiation distribution shown in FIG. 3 indicates the integrated light amount of the laser light amount irradiated to the photosensitive drum 10. Hereinafter, the drum irradiation distribution is also referred to as a main scanning irradiation distribution or a main scanning irradiation light amount.

  As shown in FIG. 3A, in the factory, the semiconductor laser 1 is driven at a predetermined duty ratio before product shipment, and the drum irradiation distribution is measured. Here, the predetermined duty ratio indicates a pulse ON / OFF ratio when the laser drive control unit 3 outputs a drive current (laser current) to the semiconductor laser 1 as a pulse. Therefore, the duty ratio when one scan line is driven with one pulse is 100% because the pulse output is always ON.

  When the drum irradiation distribution is measured, correction data that makes the drum irradiation distribution constant at the target light amount is calculated. Here, the correction data is a value for controlling the drive current for correcting the light quantity measured at each coordinate position to the target light quantity. For example, when the measured light quantity is larger than the target light quantity, a value for reducing the drive current is calculated. On the other hand, when the measured light quantity is smaller than the target light quantity, a value for increasing the drive current is calculated. Therefore, as shown in FIG. 3A, a correction value for reducing the drive current is set for the coordinates of the image area exceeding the target light amount in the drum irradiation distribution. FIG. 3B shows the laser current distribution and the drum irradiation distribution when the drive current amount is controlled based on the calculated correction data.

  Here, in the printer 100 according to the present embodiment, the problems described above with reference to FIGS. 18 to 20 can be solved. Specifically, as described above, by setting the target light amount to be output at a predetermined duty ratio before product shipment, it is possible to obtain a drive current correction value that also considers the influence of light amount attenuation due to light emission delay. it can. These correction data may be calculated by a predetermined formula, or may be adjusted while repeating a plurality of measurements. Thus, the derived correction data is stored in the non-volatile memory 24 and is read and used at the time of image formation. Note that it is desirable that the printer 100 periodically adjust the correction data even after product shipment in consideration of wear of the photosensitive drum 10 and the like.

  FIG. 4 is a diagram illustrating a relationship between the duty ratio and the drum surface light amount after calculating the drive current correction data according to the first embodiment. In FIG. 4, the horizontal axis indicates the duty ratio when the semiconductor laser 1 is driven, and the vertical axis indicates the drum surface light quantity. Here, the predetermined duty ratio described in FIG. 3 is A%. Note that the solid line shown in FIG. 4 indicates the relationship between image edges. A dotted line indicates the relationship in the center of the image.

  As shown in FIG. 4, the semiconductor laser 1 is driven at a duty ratio of A%, and correction data is calculated so that the drum irradiation distribution at this time is uniform with the target light quantity. The target light amount when driven at a duty ratio of A% is a laser light amount of B% compared to the laser light amount when driven at a duty ratio of 100%. However, as shown in FIG. 4, in the vicinity where the duty ratio is 100%, the drum surface light quantity at the center of the image increases compared to the drum surface light quantity at the image end. The effect of the increase in the drum surface light amount due to the duty ratio near 100% is reduced by applying it to the image forming apparatus described below. As a result, the influence of density unevenness due to the laser drive current difference is reduced. can do.

  FIG. 5 is a diagram illustrating the relationship between the drum surface light amount and the drum potential when the image forming apparatus according to the first embodiment is laser-driven at each duty ratio. In FIG. 5, the horizontal axis indicates the drum surface light amount at each duty ratio, and the vertical axis indicates the drum potential.

  As shown in FIG. 5, the closer the drum surface light amount is to 0%, the greater the drum potential gradient, and the more sensitive the drum sensitivity. Further, the closer the drum surface light amount is to 100%, the smaller the gradient of the drum potential, and the lower the drum sensitivity.

  By adopting the photosensitive drum 10 having such characteristics to the printer 100, in the region where the drum sensitivity is sensitive, although the drum potential gradient is large, the laser light amount attenuation due to the laser light emission delay is reduced. Can reduce the effects of Further, in the region where the drum sensitivity is insensitive, the amount of drum surface light in the vicinity of a duty ratio of 100% is increased as shown in FIG. 4, but the drum potential is small, so that it is hardly affected by density unevenness. Therefore, by adopting the photosensitive drum 10 having such characteristics, it is possible to reduce the influence of density unevenness due to the laser drive current difference.

  FIG. 6 is a flowchart illustrating a procedure for calculating correction data according to the first embodiment. The processing described below is centrally controlled by the CPU 13.

  In step S601, the CPU 13 sets the duty ratio to A% and causes the laser drive control unit 3 to emit the semiconductor laser 1 based on this duty ratio. Next, in step S <b> 602, the CPU 13 measures the drum surface irradiation distribution irradiated on the surface of the photosensitive drum 10. Specifically, the CPU 13 measures the drum surface irradiation distribution by a sensor capable of measuring the laser beam irradiated on the surface of the photosensitive drum 10. Here, the sensor capable of measuring laser light is, for example, an optical sensor that has a light receiving element and outputs a signal corresponding to the amount of light received when the laser light is received. Further, the CPU 13 measures the drum surface irradiation distribution corresponding to the coordinate position in the main scanning direction based on the BD signal d.

  Subsequently, in step S603, the CPU 13 calculates correction data such that the drum surface light amount is uniform with the target light amount. In step S604, the CPU 13 stores the calculated correction data in the nonvolatile memory 24 in association with each coordinate position. Thereafter, at the time of image formation, the drive current correction unit 4 reads the correction data stored in the nonvolatile memory 24 and multiplies it by the reference voltage Vref to drive the semiconductor laser 1 with the corrected drive current.

  As described above, the printer 100 according to the present embodiment measures the main scanning irradiation distribution (main scanning irradiation light amount) when the laser is driven with a predetermined duty ratio, and the main scanning irradiation distribution is the target light amount in each pixel. Correction data to be multiplied by the drive current is calculated so as to be uniform. As a result, the printer 100 can generate correction data that takes into account the influence of laser light emission delay, which is a problem in an image forming apparatus employing the OFS method. Therefore, the printer 100 can reduce the light amount attenuation due to the laser light emission delay and reduce the influence of density unevenness. In this embodiment, the correction data is calculated by setting the duty ratio to a predetermined duty ratio. However, it is only necessary to provide at least one laser emission OFF period such as the frequency of the image data and the dot unit.

  The present invention is not limited to the above embodiment, and various modifications can be made. For example, the printer 100 may include a memory (storage unit) that stores the determined correction data. Accordingly, the printer 100 can set correction data in a factory before product shipment, and can reduce processing at the time of initial startup.

[Second Embodiment]
Next, a second embodiment will be described with reference to FIGS. In the present embodiment, a method of reducing light amount attenuation due to laser light emission delay when the correction data is determined by measuring the main scanning irradiation distribution (main scanning irradiation light amount) in a state where the duty ratio is 100% will be described. In addition, description is abbreviate | omitted about the technique which overlaps with 1st Embodiment.

  Since the schematic configuration of the printer 100 according to the present embodiment is the same as that of the first embodiment, description thereof is omitted. The configuration of the drive current correction unit 4 according to the present embodiment is the same as that in FIG. However, in the present embodiment, in addition to the correction data of each pixel, a delay attenuation factor indicating a relative value at which the laser light amount attenuates due to the laser light emission delay of each pixel is stored in the nonvolatile memory 24.

  At the time of image formation, based on the measurement result of the coordinate measurement counter 21, correction data and delay attenuation rate corresponding to each coordinate position are read from the memory 23 and output to the correction data generation unit 25. The correction data generation unit 25 multiplies the reciprocal of the delay attenuation rate, the correction data, and the reference voltage Vref to generate correction data c. The correction data stored in the memory 23 is data calculated before shipment from the factory so that the main scanning irradiation distribution is uniform with the target light amount when the laser drive is performed with a duty ratio of 100%.

  Hereinafter, the delay attenuation rate will be described with reference to FIG. FIG. 7 shows the duty ratio and drum surface light amount when drive current control is performed using correction data that makes the main scanning irradiation distribution uniform with the target light amount when laser driving is performed with the duty ratio set to 100%. FIG. In FIG. 7, the horizontal axis represents the duty ratio, and the vertical axis represents the drum surface light amount. Also, the solid line in the figure indicates the measurement result at the edge of the image, and the dotted line indicates the measurement result at the center of the image.

  As shown in FIG. 7, when the laser is driven at a duty ratio of A%, the laser light amount at the image end is C%, and the laser light amount at the center of the image is D%. Here, the delay attenuation rate according to the present embodiment indicates the relative value of the laser light amount (C%) at the image end and the laser light amount of each pixel. In other words, the delay attenuation rate is a ratio for setting the laser light amount at the image end as the target light amount and controlling the light amounts in other pixels to the target light amount. In the case of the pixel at the center of the image, the delay attenuation rate can be calculated from C%, which is the relative value of the laser light amount at the edge of the image, and D%, which is the relative value of the laser light amount at the center of the image. The delay attenuation rate of each pixel calculated in this way is calculated before factory shipment, and is stored in the nonvolatile memory 24 in association with each coordinate position.

  Since the relationship between the duty ratio and the drum surface light amount when controlling the drive current based on the delay attenuation rate of each pixel and the correction data in this embodiment is the same as that in FIG. 4 described in the first embodiment, Omitted. Therefore, the printer 100 according to the present embodiment controls the drive current using the delay attenuation rate of each pixel and the correction data that makes the main scanning irradiation distribution uniform with the target light amount at a duty ratio of 100%. An effect equivalent to that of the first embodiment can be obtained.

  FIG. 8 is a flowchart showing a procedure for calculating the correction data and the delay attenuation rate according to the second embodiment. The processing described below is centrally controlled by the CPU 13.

  First, in step S801, the CPU 13 sets the duty ratio to 100% and drives the semiconductor laser 1 with the correction data output turned OFF. Next, in step S802, the CPU 13 measures the drum surface irradiation distribution (main scanning irradiation distribution). Furthermore, in step S803, the CPU 13 functions as correction data determination means, and calculates correction data that makes the drum surface irradiation distribution uniform with the target light amount. In step S <b> 804, the CPU 13 stores the calculated correction data for each pixel in the nonvolatile memory 24. Further, the CPU 13 sets the delay attenuation rate of each pixel to 1 and stores it in the nonvolatile memory 24.

  Next, in step S805, the CPU 13 controls the drive current based on the correction data stored in step S804 with the output of the correction data turned on, sets the duty ratio to A%, and sets the semiconductor laser 1 to ON. Drive. In step S806, the CPU 13 measures the main scanning irradiation distribution of the laser light emitted in step S805. Further, the CPU 13 functions as a delay attenuation rate calculating unit, and calculates the delay attenuation rate from the laser light amount at the image end and the laser light amount of each pixel with reference to the laser light amount at the image end. Subsequently, in step S807, the CPU 13 overwrites the nonvolatile memory 24 with the delay attenuation rate in each pixel calculated in step S806. Here, the CPU 13 functions as a changing unit that changes the delay attenuation rate. In step S604, the CPU 13 stores the calculated correction data in the nonvolatile memory 24 in association with each coordinate position. Thereafter, at the time of image formation, the drive current correction unit 4 reads the correction data and the delay attenuation rate stored in the nonvolatile memory 24 and multiplies them by the reference voltage Vref, so that the semiconductor laser 1 is corrected with the corrected drive current. Drive. Note that the delay attenuation rate is converted into an inverse of the delay attenuation rate and multiplied by the reference voltage Vref.

  As described above, the printer 100 according to the present embodiment has the correction data in which the main scanning irradiation distribution becomes uniform with the target light amount when the semiconductor laser 1 is driven with the duty ratio set to 100%, and each pixel. The delay attenuation rate at each coordinate position is stored in advance. Accordingly, the printer 100 can obtain the same effect as that of the first embodiment by controlling the drive current based on the correction data and the delay attenuation rate, and the density caused by the different drive current in each pixel. The influence of unevenness can be reduced. In this embodiment, since the correction data and the delay reduction rate are calculated by setting the duty ratio to 100%, the pulse driving at the time of measuring the main scanning irradiation amount can be omitted, and the processing is performed. It can be simplified.

[Third Embodiment]
Next, a third embodiment will be described with reference to FIGS. 9 to 12. When the threshold current of the semiconductor laser 1 fluctuates greatly due to the influence of temperature change, the influence of density unevenness caused by the laser drive current difference may not be alleviated if the delay attenuation rate is constant. In this embodiment, even when the threshold current of the semiconductor laser 1 greatly fluctuates due to the temperature change, an appropriate delay attenuation rate is set to reduce the influence of density unevenness caused by different drive currents in each pixel. How to do will be described. Note that a description of the same technique as in the first and second embodiments is omitted. As a precondition, the threshold current of the semiconductor laser 1 according to the present embodiment depends on the temperature. Further, at the time of factory shipment, correction data and delay attenuation rate for each pixel are stored in advance in the nonvolatile memory 24 of the printer 100.

  FIG. 9 is a diagram illustrating a configuration of the printer 100 according to the third embodiment. As shown in FIG. 9, the printer 100 according to the present embodiment further includes a temperature detection unit 12 in addition to the same configuration as in the first and second embodiments. The temperature detection unit 12 is disposed inside the printer 100 and measures the internal temperature of the printer 100. Information on the measured in-machine temperature is output to the CPU 13 as a temperature signal j. Further, the temperature detection unit 12 may be disposed on the surface of the printer 100 and measure an environmental temperature that is a temperature outside the printer 100.

  FIG. 10 is a diagram showing the relationship between the drive current of the semiconductor laser 1 and the light output at each temperature according to the third embodiment. In FIG. 10, the horizontal axis indicates the drive current, and the vertical axis indicates the light output. 1001 indicates a threshold current at 20 ° C. Reference numeral 1002 denotes a threshold current at 40 ° C. Further, 1003 indicates a threshold current at 60 ° C. As the temperature rises, the threshold current increases. On the other hand, the threshold current decreases as the temperature decreases. Therefore, it is necessary to set an optimum delay attenuation rate according to the temperature change.

  FIG. 11 is a diagram illustrating a relationship between the in-machine temperature of the printer 100 according to the third embodiment and the rate of change of the delay attenuation rate. In FIG. 11, the horizontal axis indicates the in-machine temperature (° C.), and the vertical axis indicates the rate of change (%) in the delay attenuation rate. The rate of change of the delay decay rate is a rate at which the delay decay rate at the in-machine temperature of 25 ° C. is 100% and the delay decay rate changes due to the influence of the temperature change.

  As shown in FIG. 11, when the temperature inside the machine rises, the threshold current increases, so that the delay decay rate becomes smaller. Further, when the in-machine temperature decreases, the threshold current decreases, so that the delay attenuation rate increases. The printer 100 according to the present embodiment measures the temperature change by measuring the relationship between the in-machine temperature and the rate of change of the delay attenuation rate in advance, and changing the optimum delay attenuation rate according to the change in the in-machine temperature. The semiconductor laser 1 can be driven with a corresponding driving current. Hereinafter, the rate of change of the delay decay rate depending on the in-machine temperature is referred to as the delay rate of change.

  In the drive current correction unit 4 according to the present embodiment, the delay attenuation rate and the delay change rate of each pixel are stored in the nonvolatile memory 24 in addition to the correction data of each pixel. Therefore, at the time of image formation, the correction data, delay attenuation rate, and delay change rate corresponding to each coordinate position are read from the nonvolatile memory 24 based on the measurement result of the coordinate measurement counter 21 and output to the correction data generation unit 25. The The correction data generation unit 25 multiplies the inverse of the delay attenuation rate, the inverse of the delay change rate, the correction data, and the reference voltage Vref to generate correction data c.

  As the correction data and the delay attenuation rate stored in the nonvolatile memory 24, values equivalent to those in the second embodiment are stored. However, with regard to the delay attenuation rate, the delay attenuation rate calculated using the in-machine temperature of 25 ° C. as a reference temperature is stored. The delay change rate is a delay change rate with respect to the in-machine temperature. For example, when the in-machine temperature is 25 ° C., a value of 100% is stored in the nonvolatile memory 24. The relationship between the delay change rate and the temperature change is measured in advance, and when the internal temperature changes by a predetermined temperature, the CPU 13 rewrites the optimum delay change rate. In the present embodiment, the delay change rate is measured at a predetermined temperature increment from 10 ° C. to 60 ° C. (for example, 5 ° C. increments) with 25 ° C. as a reference, and a table (change rate) defining the delay change rate every 5 ° C. increments. Table) is stored in the memory 23.

  The CPU 13 selects a delay change rate corresponding to the in-machine temperature from the delay change rate table stored in the memory 23 based on the detection result of the temperature detection unit 12. The selected delay change rate is stored in the nonvolatile memory 24 by the CPU 13. Specifically, when the in-machine temperature changes by 5 ° C. from the reference temperature or the previously changed temperature, the CPU 13 changes the delay attenuation rate using the change rate table. The drive current correction unit 4 generates correction data c from the delay change rate stored in the nonvolatile memory 24, the delay attenuation rate of each pixel, the correction data of each pixel, and the reference voltage Vref.

  FIG. 12 is a flowchart showing a procedure for setting an optimum delay change rate in accordance with the in-machine temperature according to the third embodiment. The processing described below is centrally controlled by the CPU 13.

  In step S <b> 1201, the CPU 13 detects the in-machine temperature by the temperature detection unit 12. Subsequently, in step S1202, when the CPU 13 detects that the in-machine temperature has changed by 5 ° C. or more from the detection result of the temperature detection unit 12, the delay corresponding to the in-machine temperature is determined by the delay change rate table stored in the memory 23. Select the rate of change. Further, in step S1203, the CPU 13 stores the selected delay change rate in the nonvolatile memory 24.

  As described above, the printer 100 according to the present embodiment sets the delay change rate according to the in-machine temperature, so that the influence of density unevenness caused by different drive currents in each pixel does not depend on the temperature change. Can be reduced. In the present embodiment, the temperature detection unit 12 is provided and the rate of change of the delay attenuation rate is set according to the in-machine temperature, but is not limited to this. The threshold current of the semiconductor laser 1 changes due to durability deterioration due to the light emission time. For example, the printer 100 may be provided with a timer (timer) for measuring the laser emission time, and the change rate of the delay attenuation rate may be set according to the laser emission time.

1 is a diagram illustrating a configuration of a printer 100 according to a first embodiment. It is a figure which shows the control structure of the drive current correction | amendment part 4 which concerns on 1st Embodiment. 2 is a diagram showing a laser current and an irradiation distribution on a photosensitive drum 10 when the semiconductor laser 1 is driven at a predetermined duty (DUTY) ratio according to the first embodiment. FIG. It is a figure which shows the relationship between the duty ratio after calculating the correction data of the drive current which concerns on 1st Embodiment, and a drum surface light quantity. FIG. 6 is a diagram illustrating a relationship between a drum surface light amount and a drum potential when laser driving is performed at each duty ratio in the image forming apparatus according to the first embodiment. It is a flowchart which shows the procedure which calculates the correction data which concern on 1st Embodiment. It is a figure which shows a duty ratio and drum surface light quantity when drive current control is performed using the correction data in which the main scanning irradiation distribution is uniform with the target light quantity when the duty ratio is set to 100% and laser driving is performed. . It is a flowchart which shows the procedure which calculates the correction data and delay attenuation factor which concern on 2nd Embodiment. It is a figure which shows the structure of the printer 100 which concerns on 3rd Embodiment. It is a figure which shows the relationship between the drive current and optical output of the semiconductor laser 1 in each temperature which concerns on 3rd Embodiment. It is a figure which shows the relationship between the in-machine temperature of the printer 100 which concerns on 3rd Embodiment, and the change rate of a delay attenuation factor. It is a flowchart which shows the procedure which sets the optimal delay change rate according to the internal temperature which concerns on 3rd Embodiment. It is a figure which shows the structure of a UFS optical system. It is a figure which shows the structure of an OFS optical system. It is a figure which shows the light quantity fluctuation | variation of an OFS optical system. It is a figure which shows the light quantity fluctuation | variation of an OFS optical system. It is a figure explaining the light quantity fluctuation correction method. It is a figure which shows the forward current and optical output characteristic of the semiconductor laser. It is a figure explaining a laser light emission delay. It is a figure which shows the relationship between the duty ratio in each laser current amount, and a drum surface light quantity. It is a figure which shows the influence by a laser light emission delay.

Explanation of symbols

100: printer 1: semiconductor laser 2: image signal generation unit 3: laser drive control unit 4: drive current correction unit 5: collimating lens 6: rotary polygon mirror 7: fθ lens 8: mirror 9: main scanning synchronization unit 10: photosensitive Drum 11: Laser light quantity detector 13: CPU

Claims (8)

A laser emitting unit that emits light, and a rotating polygon mirror that converts the light emitted from the laser emitting unit into scanning light for an image carrier, and the rotating polygon mirror includes one of the rotating polygon mirrors. An image forming apparatus that irradiates a light flux having a width larger than one mirror surface width,
A drive control means for driving the laser light emitting means at a predetermined duty ratio and for controlling a drive current for driving the laser light emitting means;
Coordinate measuring means for measuring coordinates corresponding to each pixel in one scanning line of the image carrier in accordance with driving of the laser light emitting means;
When the laser emitting means is driven at the predetermined duty ratio, the main scanning irradiation light amount indicating the light amount for each coordinate of the light irradiated to the image carrier is measured, and the measured main scanning irradiation light amount is Correction data determining means for determining correction data to be multiplied by the drive current so as to obtain a target light amount in coordinates;
Drive current correction means for correcting the drive current input to the laser light emission means by multiplying the determined correction data by the drive current for image formation at the time of image formation. An image forming apparatus. The drive current correction means includes
Storage means for storing the determined correction data in correspondence with the coordinates measured by the coordinate measuring means;
The image forming apparatus according to claim 1, wherein correction data corresponding to coordinates measured by the coordinate measuring unit during image formation is read from the storage unit to correct the driving current. The correction data determining means includes
When the correction data is determined from the main scanning irradiation light amount measured in a state where the predetermined duty ratio is set to 100%, measurement is performed using a predetermined duty ratio that is not 100% and the determined correction data. A delay attenuation rate calculating means for calculating a delay attenuation rate that is a ratio of the main scanning irradiation light amount and the target light amount for each coordinate;
The drive current correction means includes
The drive current input to the laser emission unit is corrected by multiplying the drive current for performing image formation by the reciprocal of the calculated delay attenuation rate together with the determined correction data. The image forming apparatus according to claim 1. The drive current correction means includes
Storage means for storing the determined correction data and the calculated delay decay rate in association with the coordinates measured by the coordinate measurement means;
The image forming apparatus according to claim 3, wherein correction data and a delay attenuation rate corresponding to coordinates measured by the coordinate measuring unit at the time of image formation are read from the storage unit to correct the driving current. A temperature detecting means for detecting an internal temperature of the image forming apparatus or an external environmental temperature;
The storage means further stores in advance a rate-of-change table that defines a rate of change of the delay decay rate that changes according to the internal temperature or the environmental temperature,
The correction data determining means includes
5. The apparatus according to claim 4, further comprising a changing unit that changes the delay attenuation rate stored in the storage unit using the change rate table when the internal temperature or the environmental temperature changes. The image forming apparatus described. The rate of change table defines the rate of change in increments of a predetermined temperature from a reference temperature as a reference,
The said change means changes the said delay attenuation factor using the said change rate table, if the in-machine temperature or environmental temperature changes 5 degreeC from the reference temperature or the temperature changed last time. Image forming apparatus. Further comprising time measuring means for measuring the time when the laser light emitting means is driven,
The storage means further stores in advance a rate-of-change table that defines a rate of change of the delay attenuation rate that changes according to the time when the laser light-emitting means is driven,
The correction data determining means includes
5. The apparatus according to claim 4, further comprising a changing unit that changes the delay attenuation rate stored in the storage unit by using the change rate table in accordance with a time measured by the time measuring unit. Image forming apparatus. A laser emitting unit that emits light, and a rotating polygon mirror that converts the light emitted from the laser emitting unit into scanning light for an image carrier, and the rotating polygon mirror includes one of the rotating polygon mirrors. An image forming apparatus that corrects the drive current input to the laser light emitting means by irradiating a light flux having a width larger than one mirror surface width and multiplying the drive current for driving the laser light emitting means by correction data An adjustment method,
A drive control step of driving the laser emission means at a predetermined duty ratio and controlling a drive current for driving the laser emission means;
A coordinate measuring step of measuring coordinates corresponding to each pixel in one scanning line of the image carrier in accordance with driving of the laser light emitting means;
When the laser emitting means is driven at the predetermined duty ratio, the main scanning irradiation light amount indicating the light amount for each coordinate of the light irradiated to the image carrier is measured, and the measured main scanning irradiation light amount is And a correction data determining step for determining correction data to be multiplied by the drive current so as to obtain a target light amount in coordinates.

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