JP5114886B2 - Exposure equipment - Google Patents

Description

  The present invention relates to an exposure apparatus capable of scanning a light beam from a light source by separating it into a plurality of optical paths.

  In recent years, in an image forming apparatus that forms an electrostatic latent image by scanning a photosensitive member with a laser beam, a plurality of laser beams are respectively converted into Y (yellow), M (magenta), C (cyan), and K (black). It has been proposed to perform scanning exposure by separating the light paths guided onto the photoreceptors of the respective colors.

  Conventionally, as a technique for performing appropriate control of a semiconductor laser while reducing the number of control lines for controlling a plurality of semiconductor lasers in a multi-beam scanning device, for example, there is a technique as disclosed in Patent Document 1. .

  That is, the controller unit outputs a plurality of duty signals for controlling a plurality of semiconductor lasers to a scanning unit unit including a drive circuit for driving each semiconductor laser corresponding to each semiconductor laser. Output side by side on the axis. In the scanning unit unit to which such a duty signal is input, the duty signal corresponding to each semiconductor laser is detected and converted into a duty voltage, and is input as a reference voltage to a drive circuit corresponding to the semiconductor laser.

Thereby, a plurality of semiconductor lasers can be individually controlled by one control line.
JP 2003-248368 A

  However, when the technique described in Patent Document 1 is applied, in order to recognize the distinction of each color by the difference in frequency, it is necessary to have a plurality of frequencies, and a circuit for duty adjustment is required for each frequency. Therefore, there has been a problem that the circuit scale becomes large and complicated.

  Further, when the technique described in Patent Document 1 is applied, it is necessary to transmit both the clock signal and the image data in order to recognize the frequency difference, and there is a possibility that the crosstalk may adversely affect each other.

  An object of the present invention is to provide an exposure apparatus that can quickly adjust the light amount without complicating the control circuit.

In order to solve the above-mentioned problems, the invention of claim 1 is an exposure apparatus that performs scanning exposure by separating a plurality of light beams emitted from a light source into optical paths reaching a plurality of photoconductors. A generating means for generating a reference voltage common to the plurality of photoconductors for emitting a light beam of a predetermined light amount, and a light beam of a light amount necessary for forming an electrostatic latent image on each photoconductor A difference between a deriving unit for deriving an appropriate reference voltage for each photoconductor, an appropriate reference voltage derived by the deriving unit, and a reference voltage common to the plurality of photoconductors generated by the generating unit. Correspondingly, correction means for correcting the drive current of the light beam corresponding to each photoconductor is provided.

  The invention of claim 2 further comprises a light amount adjusting means for adjusting the light amount of the light beam to the predetermined light amount according to the invention of claim 1, wherein the correcting means adjusts the light amount by the light amount adjusting means. The correction is not performed.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the information processing apparatus further includes an acquisition unit that acquires a change amount of the drive current when the reference voltage value generated by the generation unit is changed by a predetermined amount. The correction means derives a correction value for the drive current based on the difference between the reference voltage and the appropriate reference voltage and the amount of change acquired by the acquisition means.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the detection means for detecting an operating environmental condition of the exposure apparatus and a predetermined condition according to the environmental condition detected by the detection means. Setting means for stepwise setting the reference voltage value generated by the generating means within the range of the reference voltage value.

  According to a fifth aspect of the present invention, in the invention according to the fourth aspect, the acquisition means includes a drive current when a maximum value of the reference voltage value range that can be set by the setting means is set, and a minimum value of the range. Based on the difference between the driving current when the value is set and the driving current when the value is set, the driving current when the reference voltage value set by the setting means is changed in one step is obtained as a unit driving current. The correction unit derives a difference between the appropriate reference voltage value derived by the deriving unit and the reference voltage value by the number of steps, and multiplies the number of steps by the unit drive current to obtain a correction value. To derive.

  According to a sixth aspect of the present invention, in the first to fifth aspects of the invention, the number of the light beams is larger than the number of the photoconductors.

  The invention according to claim 7 is the invention according to any one of claims 1 to 6, wherein the derivation of the appropriate reference voltage by the derivation means is executed for each process control.

  The present invention has an excellent effect that light amount adjustment can be performed quickly without complicating the control circuit.

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

  FIG. 1 schematically shows a configuration of an image forming apparatus 10 according to the present embodiment. As shown in the figure, the image forming apparatus 10 includes an endless belt-like intermediate transfer belt 14 that is stretched around a plurality of winding rollers and conveyed in the direction of arrow E by driving a motor (not shown). A plurality of image forming units 15 (details will be described later) are arranged along the longitudinal direction.

  Note that the image forming apparatus 10 in the present embodiment also supports color image formation, and toners corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (K). Image forming units 15Y, 15M, 15C, and 15K that form images are provided. Hereinafter, the members provided for each color are shown by adding alphabets (Y / M / C / K) indicating the respective colors at the end of the reference numerals. The description will be made by omitting the alphabet at the end of the code.

  As shown in the figure, the image forming unit 15 includes a photosensitive drum 16 that is disposed in contact with the intermediate transfer belt 14 and rotates at a predetermined speed in the arrow F direction.

  Formed on the peripheral surface of each photosensitive drum 16 is a charging roller 18 for charging the photosensitive drum 16, an exposure unit 20 for forming an electrostatic latent image on the photosensitive drum 16, and the photosensitive drum 16. The developed electrostatic latent image is developed with toner of a predetermined color (yellow / magenta / cyan / black) to form a toner image, and the toner image on each photosensitive drum 16 is transferred to the intermediate transfer belt 14. Each transfer roller 25 is provided.

  By rotating in the direction of arrow F, the photosensitive drum 16 is sequentially subjected to various processes by the charger 18, the exposure unit 20, the developing unit 22, and the transfer roller 25, and a toner image is formed on the peripheral surface.

  The different color toner images formed by the image forming units 15 are transferred onto the intermediate transfer belt 14 so as to overlap each other on the belt surface of the intermediate transfer belt 14. As a result, a color toner image is formed on the intermediate transfer belt 14. In this embodiment, the toner image in which the four color toner images are transferred in a superimposed manner is referred to as a final toner image.

  On the downstream side of the four image forming units 15 in the conveying direction of the intermediate transfer belt 14, a transfer device 26 including two rollers 26A and 26B facing each other is disposed. The final toner image formed on the intermediate transfer body belt 14 is sent between the rollers 26A and 26B, taken out from the paper tray 29 provided at the bottom of the image forming apparatus 10, and is similarly supplied to the rollers 26A and 26B. The paper that has been conveyed in between is transferred.

  In addition, a fixing device 30 including a pressure roller 30A and a heating roller 30B is disposed in the conveyance path of the sheet on which the final toner image is transferred. The sheet conveyed to the fixing device 30 is nipped and conveyed by the pressure roller 30A and the heating roller 30B, whereby the toner on the sheet is melted and pressed against the sheet to be fixed. Thereby, a desired image (color image) is formed on the paper. The paper on which the image is formed is discharged out of the apparatus.

  FIG. 2 shows a cross section orthogonal to the cross section of the exposure unit 20 shown in FIG. As shown in FIGS. 1 and 2, four light beams LY, LM, LC, and LK are emitted from a single casing, and four photosensitive drums 16Y corresponding to yellow, magenta, cyan, and black are used. , 16M, 16C, and 16K are respectively subjected to scanning exposure.

  The exposure unit 20 includes a circuit board 44 having a laser array (LD array) 40 having a plurality of light emission points as a light source, and light beams are emitted from the light emission points of the LD array 40, respectively.

  A collimator lens 50, a half mirror 52, a cylindrical lens 54, and a polygon mirror 56 are arranged on the optical path of the light beam emitted from the LD array 40, and the light beam emitted from the LD array 40 is converted into a collimator lens. The light converted into substantially parallel light by 50 and transmitted through the half mirror 52 is incident on the polygon mirror 56 with the light beam being narrowed by the cylindrical lens 54.

  An f-θ lens 58 is provided on the optical path in the reflection direction of the polygon mirror 56, and the scanning speed by the rotation of the polygon mirror 56 is made substantially constant by the f-θ lens 58, and the light beam is emitted.

  On the light exit side of the f-θ lens 58, first reflection mirrors 59Y, 59M, 59C, 59K, second reflection mirrors 60Y, 60M, 60C and cylindrical mirrors 61Y, 61M, 61C, 61K provided for each color are provided. Is provided. The light paths of the plurality of light beams emitted from the f-θ lens 58 are separated for each color by the first reflecting mirrors 59Y, 59M, 59C, and 59K. The separated light beams pass through the second reflecting mirrors 60Y, 60M, 60C and the cylindrical mirrors 61Y, 61M, 61C, 61K disposed on the optical paths corresponding to the respective colors, and the photosensitive drums 16Y, 16M corresponding to the respective colors. , 16C, 16K. At this time, the light beam is scanned on the photosensitive drums 16Y, 16M, 16C, and 16K by the rotation of the polygon mirror 56, thereby performing the main scanning, and the sub scanning is performed by the rotation of the photosensitive drums 16Y, 16M, 16C, and 16K. Is done.

  On the other hand, the light beam emitted from the light source 44 and transmitted through the collimator lens 50 and reflected by the half mirror 52 is incident on the monitor photodiode (MPD) 64 through the condenser lens 62, and is emitted from the LD array 40 by the MPD 64. The light quantity of the emitted light beam is monitored.

  In addition, a reflection mirror 66 is provided between the cylindrical mirror 61K and the photosensitive drum 16K in a non-image forming area on the photosensitive drum 16 and on a path reaching the vicinity of the scanning start position. The light reflected by the reflecting mirror 66 enters the SOS sensor 68, and the scanning start timing is synchronized based on the detection timing of the light beam by the SOS sensor 68.

  FIG. 3 is a view showing an example of an arrangement of a plurality of light emitting points of the LD array 40 of the exposure unit 20 according to the embodiment of the present invention.

  The exposure unit 20 according to the embodiment of the present invention has 32 light emitting points and emits 32 light beams, as shown in FIGS. 3A and 3B, for example.

  As shown in FIG. 3 (A), the arrangement of the 32 light emitting points is a 4 × 8 array, and as shown in FIG. 3 (A), reflection mirrors 59Y, 59M, 59C and 59K separate the optical paths to the first to eighth lasers, the ninth to sixteenth lasers, the seventeenth to twenty-fourth lasers, and the twenty-fifth to thirty-second lasers, and the first to eighth lasers correspond to yellow. The photosensitive drum 16Y is irradiated, the 9th to 16th lasers are irradiated to the photosensitive drum 16M corresponding to magenta, the 17th to 24th lasers are irradiated to the photosensitive drum 16C corresponding to cyan, and the 25th to 25th lasers are irradiated. You may make it irradiate the photosensitive drum 16K corresponding to black with the 32nd laser.

  Alternatively, as an 8 × 4 array, as shown in FIG. 3 (B), the first laser to the 32nd laser in order from the upper left of FIG. 3 (B), and the reflection mirrors 59Y, 59M, 59C, and 59K are used in the same manner as described above. The optical paths may be separated from each other, or other arrangements may be used.

  FIG. 4 shows the configuration of a control system related to exposure processing by the exposure unit 20 of the image forming apparatus 10 according to the embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 10 includes an environment sensor 46, a control unit 70 that controls the operation of the entire image forming apparatus 10, and an LD driver 80 for driving the LD array 40. Has been.

  The environmental sensor 46 is provided in the image forming apparatus 10 and can detect the temperature and humidity in the image forming apparatus 10.

  The control unit 70 includes an image processing unit 71, a reference voltage value setting unit 72, and a reference voltage generation unit 74.

  The image processing unit 71 is connected to the SOS sensor 68 and the LD driver 80. The image processing unit 71 generates a video signal for each color of Y, M, C, and K based on the input image data.

  The image processing unit 71 outputs a video signal for one main scanning to the LD driver 80 at a scanning start timing based on the detection timing of the light beam from the SOS sensor 68.

  The image processing unit 71 outputs not only a video signal based on the image data but also a video signal for generating an electrostatic latent image (potential patch) having a predetermined size and shape used in density correction processing described later. To do.

  Further, the image processing unit 71 also outputs an APC_ENB signal that permits execution of a light amount adjustment process for feedback control so that the light amount of each laser of the LD array 40 becomes uniform (details will be described later).

  The reference voltage value setting unit 72 is connected to the environment sensor 46, the reference voltage generation unit 74, and the LD driver 80, and the reference voltage generation unit 74 is connected to the LD driver 80.

  The reference voltage value setting unit 72 sets a reference voltage value to be output to the LD driver 80. The reference voltage specifies a use range of the reference voltage value according to the temperature and humidity detected by the environment sensor 46, and determines an intermediate value of the specified use range as a reference reference voltage value (Vref_b).

  FIG. 5A shows an example of the use range of the reference voltage value. As shown in the figure, the environment is classified into any one of environment 1 to environment 3 according to the detected temperature and humidity, and use ranges A to CZone appropriate for each environment are used.

  In the present embodiment, environment 1 is set when high temperature and humidity are high, environment 3 is low temperature and low humidity, and environment 2 is set between environment 1 and environment 3, respectively.

  In addition, the set values of 0 to 1023 shown in the figure are set values indicating the reference voltage Vref. The setting value 0 corresponds to Vref = 0 (V), and the setting value 1023 corresponds to Vref = 2.00 (V). Accordingly, the setting values and the reference setting values corresponding to each use range are as shown in Table 1 below.

リファレンス電圧値設定部７２は、起動時やプリント終了後、環境が変化した場合等の予め定められたタイミングでリファレンス電圧値の設定を実行する。このリファレンス電圧値の設定時には、まず、環境条件に応じて決定したリファレンス電圧値の使用範囲の最大の電圧値（Ｖｒｅｆmax）を示す設定値をリファレンス電圧生成部７４に出力し、その後に最小の電圧値（Ｖｒｅｆmin）を示す設定値をリファレンス電圧生成部７４に出力してから、最終的にプリントを実行するためのリファレンス電圧値として、環境に応じて選択された使用範囲の基準設定値をリファレンス電圧生成部７４に出力する。

The reference voltage value setting unit 72 sets the reference voltage value at a predetermined timing such as when the environment changes after startup or after printing is completed. At the time of setting the reference voltage value, first, a set value indicating the maximum voltage value (Vrefmax) in the use range of the reference voltage value determined according to the environmental condition is output to the reference voltage generation unit 74, and then the minimum voltage is set. After the set value indicating the value (Vrefmin) is output to the reference voltage generation unit 74, the reference set value of the usage range selected according to the environment is used as the reference voltage value for finally executing printing. The data is output to the generation unit 74.

  Note that the range of use as shown in the figure provides the amount of light that achieves the desired concentration under each environmental condition obtained by experiments using actual machines, simulations using computers based on product specifications, and the like. It is preferable to set an optimal range of values. Also, the set values 0 to 299 (Vref: 0V to 0.58V) are in the non-use range.

  The reference voltage generation unit 74 generates a voltage corresponding to the input set value as Vref and outputs it to the LD driver 80.

  On the other hand, as shown in FIG. 4, the LD driver 80 includes a drive circuit 84. The drive circuit 84 is configured on the circuit board 44 and is connected to the image processing unit 46 and the LD array 40.

  The drive circuit 84 drives the first to thirty-second lasers of the LD array 40 in accordance with the video signal input from the image processing unit 46.

  As shown in the figure, the LD driver 80 includes an APC (Automatic Power Control) circuit 82 that adjusts the amount of light emitted by each laser of the LD array 40. The APC circuit 82 is connected to the drive circuit 84, the MPD 64, the image processing unit 71, and the reference voltage generation unit 74.

  When the APC_ENB signal is input, the APC circuit 82 drives the drive circuit using Vref input from the reference voltage generation unit 74 to execute the light amount adjustment processing. The drive circuit 84 is operated so as to sequentially emit the first to thirty-second lasers of the LD array 40, and the light amount of the light beam emitted from each laser is made uniform using the detection result of the light beam amount by the MPD 64. Adjust by feedback control so that

  Note that the output of the APC_ENB signal permitting execution of the light amount adjustment by the APC circuit 82 from the image processing unit 71 is a drive circuit at the time of setting the reference voltage by the reference voltage value setting unit 72 (see FIG. 7) or at the time of image formation. 84 is output every time the video signal for one main scan is completed (see FIG. 8). At the time of image formation, the APC_ENB signal is output to the LD driver 80 only for a predetermined period within a range in which the light beam emitted from the LD array 40 is guided to the non-image portion on the photosensitive drum 16. .

  In the image forming apparatus 10, a potential sensor 48 that detects a potential at a predetermined position in the main scanning direction on the photosensitive drum 16 is provided between the exposure position and the developing position of the photosensitive drum 16. Further, the control unit 70 includes a difference deriving unit 76 and an appropriate reference voltage value deriving unit 78.

  The appropriate reference voltage value deriving unit 78 is connected to the potential sensor 48 and the difference deriving unit 76. The appropriate reference voltage value deriving unit 78 derives the density after development from the potential detected by the potential sensor 48. Further, based on the derived density after development, a reference voltage value for obtaining the desired density after development is derived as Vref_r, and similarly to the reference voltage value setting unit 72, the derived Vref_r is set. The value is output to the difference deriving unit 76.

  The difference deriving unit 76 is connected to the appropriate reference voltage value deriving unit 78 and the reference voltage value setting unit 72. The difference deriving unit 76 derives a difference ΔP (ΔP is an integer, −128 <ΔP <128) between the setting value indicating Vref_b and the setting value indicating appropriate Vref_r, and outputs the difference ΔP to the LD driver 80.

  Here, the relationship between the reference voltage and the drive current is a proportional relationship as shown in FIG. Further, the amount of light beam emitted from each laser is proportional to the drive current.

  For this reason, the LD driver 80 includes a unit drive current deriving unit 86, a parameter holding unit 88, and a drive current setting unit 90.

  That is, the drive current setting unit 90 emits a light beam having a desired light amount by correcting the drive current by an amount corresponding to the difference ΔP. The drive current setting unit 90 is configured to be able to correct the drive current in 255 steps.

  Therefore, the unit drive current deriving unit 86 derives the amount of change Istep of the drive current per step in the drive current setting unit 84. In the present embodiment, Istep is derived by operating the drive circuit 84 using Vrefmax and Vrefmin temporarily generated by the reference voltage generation unit 74 when the reference voltage value setting unit 72 sets the reference voltage value. The difference between the drive currents Imax and Imin at this time is the number of steps when the drive current setting unit 90 corrects the drive current (in this embodiment, 255, which is the same as the number of Vref set values in each use range). Execute by dividing. The unit drive current Istep derived by the unit drive current deriving unit 86 is held in the parameter holding unit 88.

  The drive current setting unit 90 derives a drive current correction value Icorr (= ΔP × Istep) for each color in accordance with the differences ΔP and Istep held in the parameter holding unit 88, and sets the drive current of each laser to the correction value Icorr. Only the correction is made and output to the drive circuit 84.

  The drive circuit 84 corrects the drive current in accordance with the correction value Icorr input from the drive current setting unit 90 and drives the LD array 40.

  The correction of the drive current according to the correction value Icorr is executed only at the time of scanning exposure based on the video signal according to the image data, and at the time of light amount adjustment by the APC circuit 82 executed outside the image forming area every time scanning is completed. The drive circuit 84 is driven with a drive current that does not take into account Icorr.

  The operation of the present embodiment will be described below.

  FIG. 6 shows a flow of printing processing executed based on a print job input from the outside to the image forming apparatus 10. Hereinafter, the printing process according to the present embodiment will be described with reference to FIG.

  First, in step 200, the in-machine environment is detected by the environment sensor 46, and in the next step 202, the use range of the reference voltage Vref for driving the LD array 40 is determined based on the detected in-machine environment. Here, in addition to the use range of Vref, process conditions relating to image formation such as process speed, voltage during charging, development, and transfer are set.

  In the next step 204, the maximum value Vrefmax of the determined use range of Vref is set as Vref to be output to the LD driver 80. As a result, a voltage of Vrefmax is generated by the reference voltage generation unit 74 and supplied to the LD driver 80. Further, the image processing unit 71 outputs an APC_ENB signal to the LD driver 80.

  Thereafter, the process proceeds to step 206, and the light amount adjustment by the APC circuit 82 is executed while operating the drive circuit 84 at Vrefmax, and then the process proceeds to step 208.

  The light amount adjustment by the APC circuit 82 is executed by sequentially emitting the first to thirty-second lasers of the LD array 40 with Vref input from the control unit 70 and performing feedback control of the respective light amounts detected by the MPD 64. Is done.

  In step 208, the drive current Imax of each laser is held, and then the process proceeds to step 210.

  In step 210, the minimum value Vrefmin of the Vref usage range is set as the value of Vref output to the LD driver 80, and the process proceeds to the next step 212. At this time, the image processing unit 71 outputs the APC_ENB signal to the LD driver 80 as in the case where Vrefmax is set in step 204.

  In step 212, the light amount adjustment by the APC circuit 82 is executed while operating the drive circuit 84 with Vrefmin, and then the process proceeds to step 214.

  In step 214, the drive current Imin of each laser is held, and thereafter, the process proceeds to step 216.

  In step 216, a unit drive current Istep for each laser is derived, and then the process proceeds to step 218 to hold the derived unit drive current Istep. In the present embodiment, a case where the drive current of the drive circuit 84 can be changed in 255 steps will be described. For this reason, in this embodiment, the unit drive current Istep of each laser is changed when the drive current is changed by the difference between the drive current Imax of each laser held in step 208 and the drive current Imin of each laser held in step 214. It is derived by dividing by the number of steps (256).

  In the next step 220, the reference voltage Vref_b in the use range of Vref set in step 202 is set as Vref to be output to the LD driver 80. Even when Vref_b is set, the image processing unit 71 outputs an APC_ENB signal.

  In the next step 222, the light amount adjustment by the APC circuit 82 is executed while operating the drive circuit 84 with Vref_b, and then the process proceeds to step 224.

  In step 224, the drive circuit 84 is operated by Vref_b to drive the LD array 40, and a light beam is scanned on the photosensitive drum 16 to form a potential patch having a predetermined size and shape for each color.

  In the next step 226, an appropriate reference voltage Vref_r is derived for each color. The derivation of Vref_r is executed by detecting the potential of the potential patch of each color by the potential sensor 48 and deriving a reference voltage that becomes a predetermined potential. In addition, as the predetermined potential, a potential obtained by an experiment using an actual machine, a simulation using a computer based on the specifications of the actual machine, or the like that can obtain a desired density after development can be applied. In addition, the desired density and the potential at which the desired density is obtained may be different for each color.

  In the next step 228, a difference ΔP between the setting value indicating Vref_b and the setting value indicating Vref_r is derived, and then the process proceeds to step 230. In step 230, the correction value Icorr to be set is derived, and then the process proceeds to step 232 to hold the derived correction value Icorr. The correction value Icorr is the product of ΔP and Istep.

  In the next step 234, printing is executed according to the input print job. In this printing, as shown in FIG. 8, the image processing unit 71 outputs a video signal for each scan, and at the position where the light beam reaches the outside of the image forming area every time one scan is completed, the APC circuit 82 Execute the light amount adjustment by.

  As shown in FIG. 8, when the light amount adjustment is performed by the APC circuit 82, the drive circuit 84 is driven by the drive current Ib corresponding to Vref_b, and at the time of image formation, the drive circuit 84 is driven by the drive current corrected by the correction value Icorr. To do.

  In the next step 236, after the in-flight environment is detected by the environment sensor 46, the process proceeds to step 238.

  In step 238, based on the temperature and humidity detected by the environment sensor 46, it is determined whether it is necessary to change the currently set environment group. If the determination is affirmative, the process returns to step 202 again.

  If the determination in step 238 is negative, the process proceeds to step 240 to determine whether or not to form a potential patch. If the determination is affirmative, the process returns to step 208 again.

  Note that the formation of the potential patch is executed every time a predetermined number of images are formed, every predetermined period, at the time of process control, in consideration of the balance of productivity, stability, toner consumption, and the like.

  If the determination in step 240 is negative, the process proceeds to step 242 to determine whether printing based on the print job has been completed. If the determination is negative, the process returns to step 236 again.

  As a result of the determination in step 238 or step 240, when shifting to step 202 or step 224, it is preferable to shift at a timing that does not interfere with image formation such as an inter-image or between pages, and printing is performed as necessary. Interrupt.

  If the determination at step 242 is affirmative, the printing process is terminated.

  As described above in detail, according to the present embodiment, when the 32 light beams emitted from the LD array 40 are separated into optical paths reaching the four photosensitive drums 16 for scanning exposure, the LD A reference voltage Vref_b for emitting a light beam having a predetermined light amount from the array 40 is generated, and an appropriate reference for emitting a light beam having a light amount necessary for forming an electrostatic latent image on each photosensitive drum 16 is generated. The voltage value Vref_r is derived for each photoconductor drum 16, and the drive current of the light beam corresponding to each photoconductor drum 16 is corrected according to the difference between the appropriate reference voltage value Vref_r and the reference voltage Vref_b. Therefore, there is no need to set a different reference voltage value for each laser corresponding to each photosensitive drum 16, and a reference voltage for each color. The control circuit as compared with the case where the different is not complicated.

  Further, in the light amount adjustment of the light beam using the APC circuit 82, it is not necessary to change the reference voltage value for each color, so there is no need to wait for the stabilization of the voltage value accompanying the change of the reference voltage value, and the light amount can be quickly Adjustments can be performed.

  In this embodiment, since the drive current is not corrected, the APC circuit 82 adjusts the light amount so that the light amounts of all the light beams become the light amounts corresponding to the input reference voltage values as usual. Therefore, even if the configuration for correcting the drive current is adopted, the APC circuit 82 need not be changed.

  Further, the operating environment conditions (temperature and humidity) of the exposure unit 20 are detected by the environment sensor 46, the use range of the reference voltage value is selected according to the detected environmental condition, and the reference voltage value generated within the selected range. Is set step by step. In such a configuration, the drive current when the reference voltage is changed by one step is obtained as the unit drive current Istep, and the correction value is derived using the step number difference ΔP between Vref_b and Vref_r and the unit drive current Istep. Therefore, it is easy to derive the correction value.

  In the present embodiment, the unit drive current Istep includes the drive current Imax when the maximum value Vrefmax of the reference voltage value use range is set and the drive current when the minimum value Vrefmin of the range is set. It is derived by dividing the difference from the drive current Imin when set by the number of steps corresponding to the use range of the reference voltage value. Thereby, an average unit drive current can be derived with high accuracy.

  In the present embodiment, the number of steps when setting the drive current has been described as being the same as the number of Vref setting values in each usage range, but the present invention is not limited to this. . If the number of steps for setting the drive current is different from the number of Vref setting values for each usage range, the arithmetic expression for deriving Icorr may be adjusted.

  In the present embodiment, the Vref usage range is divided into three and the range to be used is selected according to environmental conditions. However, the present invention is not limited to this.

  That is, for example, as shown in FIG. 10, the use range of Vref can be adjusted to the entire range of environment 1 to environment 3 regardless of the environmental conditions so as to be adjusted by the drive current.

  The configuration of the image forming apparatus 10 according to the above-described embodiment (see FIGS. 1 to 4) is an example, and can be changed as appropriate without departing from the spirit of the present invention.

  For example, in the present embodiment, the mode in which the reference voltage Vref and the difference ΔP are separately transmitted in the light intensity control of the LD array has been described (see FIG. 4), but the present invention is not particularly limited to the data transmission mode. . For example, as shown in FIG. 9, data including a reference voltage value and difference data is generated by the data generation unit 96 and is collectively output to the LD driver 80. In the LD driver 80, the reference is separated by the data separation unit 98. The data may be separated into data indicating the voltage Vref and data indicating the difference ΔP.

  Further, for example, in the present embodiment, the description has been given of the form in which the exposure unit 20 configured to separate the optical path of the light beam from one LD array 40 and guide it onto the four photosensitive drums 16 is applied. Is not limited to this.

  In other words, it is sufficient that the light beam from one light source is separated into a plurality of optical paths, and the exposure unit is configured to separate the optical paths of the light beams from the two light sources into two and guide them to four photosensitive members. It can also be applied to. In this case, the number of polygon mirrors may be one or two.

  Furthermore, it goes without saying that the number of photoconductors is not limited to four but may be two or more.

  The flow of each process according to the above embodiment (see FIG. 6) is also an example, and can be appropriately changed without departing from the gist of the present invention.

  For example, in the above-described embodiment, the description has been given of the mode in which the potential of the potential patch is detected by the potential sensor, and the appropriate reference voltage value is derived based on the detection result. However, the present invention is not limited to this, and the toner is not limited thereto. It is also possible to create a patch, detect the density of the toner image with a density sensor, and derive an appropriate reference voltage value based on the detection result.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. It is the schematic which shows the structure of the exposure unit which concerns on embodiment. It is a figure which shows the example of an arrangement | sequence of the light source of LD array applicable to the exposure unit which concerns on embodiment. It is a block diagram regarding the light quantity control of the LD array which concerns on embodiment. (A) is explanatory drawing which shows the use range of the reference voltage according to an environment group, (B) is a graph which shows the drive current (light quantity) when a reference voltage is changed. 6 is a flowchart showing a flow of printing processing according to the embodiment. 6 is a timing chart relating to driving of the LD array when setting a reference voltage according to the embodiment. 5 is a timing chart relating to driving of the LD array during image formation according to the embodiment. It is a block diagram regarding the light quantity control of the LD array which concerns on another form. It is a figure which shows the other setting example of the use range of a reference voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 14 Intermediate transfer body belt 16 Photosensitive drum 18 Charging roller 20 Exposure unit 22 Developer 46 Environment sensor 48 Potential sensor 72 Reference voltage value setting part (setting means)
74 Reference voltage generator (generator)
76 Difference derivation unit 78 Proper reference voltage value derivation unit (derivation means)
82 APC circuit (light intensity adjustment means)
86 Unit drive current deriving unit (acquisition means)
90 Drive current setting section (correction means)

Claims (7)

An exposure apparatus that performs scanning exposure by separating a plurality of light beams emitted from a light source into optical paths reaching a plurality of photosensitive members,
Generating means for generating a reference voltage common to the plurality of photoconductors for emitting a light beam of a predetermined light amount from the light source;
Deriving means for deriving an appropriate reference voltage for each photoconductor for emitting a light beam having a light amount necessary for forming an electrostatic latent image on each photoconductor;
The driving current of the light beam corresponding to each photoconductor is corrected according to the difference between the appropriate reference voltage derived by the deriving unit and the reference voltage common to the plurality of photoconductors generated by the generating unit. Correction means;
An exposure apparatus comprising: A light amount adjusting means for adjusting the light amount of the light beam to the predetermined light amount;
The exposure apparatus according to claim 1, wherein the correction unit does not execute the correction when the light amount is adjusted by the light amount adjustment unit. An acquisition unit for acquiring a change amount of the drive current when the reference voltage value generated by the generation unit is changed by a predetermined amount;
The correction means derives a correction value of the drive current based on a difference between the reference voltage and the appropriate reference voltage and a change amount acquired by the acquisition means. 2. The exposure apparatus according to 2. Detecting means for detecting an operating environment condition of the exposure apparatus;
Setting means for stepwise setting the reference voltage value generated by the generating means within a range of the reference voltage value determined in advance according to the environmental condition detected by the detecting means;
The exposure apparatus according to claim 1, further comprising: The acquisition unit is configured to set a driving current when the maximum value of the reference voltage value range that can be set by the setting unit is set and a driving current when the minimum value of the range is set. Based on the difference with the drive current, the drive current when the reference voltage value set by the setting means is changed by one step is obtained as a unit drive current,
The correction unit derives a difference between the appropriate reference voltage value derived by the deriving unit and the reference voltage value by the number of steps, and multiplies the number of steps by the unit drive current to derive a correction value. 5. An exposure apparatus according to claim 4, wherein:   6. The exposure apparatus according to claim 1, wherein the number of the light beams is larger than the number of the photoconductors.   7. The exposure apparatus according to claim 1, wherein the derivation of the appropriate reference voltage by the derivation unit is executed for each process control.

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