JP6642015B2 - Light beam scanning device and light beam scanning method - Google Patents

Description

  The present invention relates to a light beam scanning device and a light beam scanning method.

  2. Description of the Related Art In a conventional electrophotographic image forming apparatus, the amount of laser light emitted from a light source (such as a laser diode) is detected from the output of a light receiving element, and control is performed to bring the amount of laser light closer to a target amount of light. Further, it is known that the laser diode changes its IL (current-light amount) characteristic due to a temperature change.

  For example, in the related art, a technique is known in which the temperature inside the apparatus main body is measured, and the limit value of the current supplied to the laser light source at the time of automatic light intensity adjustment is changed according to the measured temperature.

  The light amount control in the above-described conventional image forming apparatus does not take into account the detection error of the light amount by the light receiving element, the error generated in the internal circuit for controlling the light amount, and the like. For this reason, conventionally, the light amount of the laser beam is controlled while including these errors, and a change in the light amount due to the errors causes a change in the density of the image, which may degrade the image quality. .

  The disclosed technology aims to suppress fluctuations in image density.

The disclosed technology detects a light amount of light emitted from a light source based on an output of a light receiving element that receives the light, and outputs a command value for outputting a current supplied to the light source according to the detected light amount. A light amount control unit that outputs the light amount, and a light source driving unit that supplies a current corresponding to the command value output from the light amount control unit to the light source, wherein the light amount control unit detects the light amount in a first period. When the fluctuation amount of the light amount and the light amount detected in the second period is equal to or more than the fluctuation upper limit value, the current that fluctuates the light amount detected in the first period by the fluctuation upper limit value and A corresponding command value is output , and when the fluctuation width of the light amount detected in the first period and the light amount detected in the second period is less than the fluctuation upper limit, in the first period The detected light amount Serial is a light beam scanning apparatus which outputs a corresponding command value to the current varying fluctuation width of.

  Variation in image density can be suppressed.

FIG. 1 is a diagram illustrating an outline of a configuration of an image forming apparatus according to a first embodiment. FIG. 2 is a diagram illustrating a writing unit of the image forming apparatus according to the first embodiment. FIG. 3 is a diagram illustrating a light source driving unit according to the first embodiment. 5 is a flowchart illustrating an operation of the writing unit according to the first embodiment. FIG. 3 is a diagram illustrating functions of an APC control unit according to the first embodiment. It is a figure showing an example of IL characteristic. 5 is a flowchart illustrating processing of an APC control unit according to the first embodiment. 5 is a timing chart illustrating control by the APC control unit according to the first embodiment. It is a figure explaining the function of the APC control part of a 2nd embodiment. 9 is a flowchart illustrating processing of an APC control unit according to the second embodiment. 9 is a timing chart illustrating control by the APC control unit according to the second embodiment.

(First embodiment)
Hereinafter, a first embodiment will be described with reference to the drawings. FIG. 1 is a diagram schematically illustrating the configuration of the image forming apparatus according to the first embodiment.

  The image forming apparatus 100 according to the present embodiment includes an image forming unit 200 and a fixing unit 300.

  In the image forming apparatus 100 according to the present embodiment, the image forming unit 200 forms an image on a print sheet based on image data obtained by performing necessary image processing on the print data, and the fixing unit 300 forms the image on the print sheet. The formed image is fixed.

  Note that the image forming apparatus 100 according to the present embodiment includes a paper feed unit that feeds print paper, a paper discharge unit that discharges print paper after an image is fixed to a paper discharge tray, and data acquisition that acquires print data. And an operation display unit having an operation key for setting and operating various operation modes of the image forming apparatus 100 and a display for displaying various information.

  The image forming unit 200 according to the present embodiment includes a photoconductor 210, a cleaning unit 220, a charging unit 230, a writing unit 240, a developing unit 250, a transfer unit 260, a separation unit 270, and a paper feed path 280.

  The photoconductor 210 of the present embodiment is driven to rotate. Further, the charging unit 230, the writing unit 240, the developing unit 250, the transfer unit 260, and the separation unit 270 of the present embodiment are each disposed around the photoconductor 210.

  In the image forming unit 200, after the photoconductor 210 is uniformly charged by the charging unit 230, the writing unit 240 irradiates the photoconductor 210 with laser light (light) modulated based on image data. Then, an electrostatic latent image is formed on the photoconductor 210. Details of the writing unit 240 will be described later.

  Next, the image forming section 200 causes the developing section 250 to attach toner (developer) to the photoreceptor 210 to form a toner image as a developer image.

  Next, the image forming unit 200 causes the transfer unit 260 to transfer the toner image on the photoconductor 210 between the photoconductor 210 and the transfer unit 260 through the paper feed path 280 as a recording medium (print paper). Transfer to Next, the image forming unit 200 separates the printing paper on which the toner image has been transferred from the photoconductor 210 by the separating unit 270 and conveys the printing paper to the fixing unit 300.

  The fixing unit 300 includes a heating roller that is driven to rotate and is heated to a predetermined fixing temperature, a pressing roller that contacts the heating roller and rotates together with the heating roller, a heater that heats the heating roller to a predetermined fixing temperature, and the like. ing. Then, the fixing unit 300 conveys the printing paper to which the toner image has been transferred while heating and pressurizing the printing paper with a heating roller and a pressing roller, and forms an image by fixing the toner image to the paper.

  Further, the image forming unit 200 removes the charge of the photoreceptor 210 on which the transfer of the toner image is completed by the cleaning unit 220, cleans the residual toner, uniformly charges the toner by the charging unit 230, and forms the image again. .

  Next, the writing unit 240 of the present embodiment will be described with reference to FIG. FIG. 2 is a diagram illustrating a writing unit of the image forming apparatus according to the first embodiment.

  The writing unit 240 according to the present embodiment includes a writing control unit 310, a light source driving unit 320, a light source 330, a synchronization detection sensor 340, and a polygon mirror 350. In addition, the writing unit 240 of the present embodiment includes an fθ lens, a reflection mirror, a synchronous reflection mirror, and the like in addition to the above-described units. In FIG. 2, broken arrows indicate laser light.

  The writing control unit 310 of this embodiment controls the rotation of the polygon mirror 350 and the light source driving unit 320 based on the image data. Specifically, write control section 310 outputs a DATA signal and an XAPC signal to light source drive section 320. The DATA signal is a signal for turning on / off the light source 330 based on image data. The XAPC signal is a signal that determines the timing at which the light source driving unit 320 controls the amount of laser light emitted from the light source 330.

  The light source driving unit 320 of the present embodiment controls the amount of laser light emitted from an LD (Laser Diode) 331 of the light source 330 based on the XAPC signal. Further, the light source driving unit 320 of the present embodiment controls turning on / off of the LD 331 based on the DATA signal.

  The light source 330 has an LD 331 and a PD (Photo Diode) 332. The LD 331 is a light source that emits a laser beam of an amount corresponding to the current supplied from the light source driving unit 320 to the polygon mirror 350. The PD 332 is a light receiving element that receives the laser light emitted from the LD 331, and outputs a current corresponding to the received light amount to the light source driving unit 320.

  The synchronization detection sensor 340 has, for example, a photodiode, and generates a synchronization detection signal that is a pulse output when a laser beam is incident. In the present embodiment, the writing control unit 310 sets an effective scanning period, which is a period during which an image is written on the photoconductor 210, based on the synchronization detection signal.

  The polygon mirror 350 of the present embodiment rotates at an angular velocity according to the image density of the image forming apparatus 100.

  In the present embodiment, the laser light emitted from the LD 331 is reflected by the polygon mirror 350, passes through the fθ lens, and reaches the reflection mirror. Then, the light is reflected by the reflection mirror and forms an image on the photoconductor 210.

  In this embodiment, when the polygon mirror 350 rotates, the incident position (reflection position) of the laser beam on the reflection mirror moves in the direction of arrow Y, and the image formation position on the photoconductor 210 moves in the direction of arrow Y. Moving. The direction of arrow Y is the direction of the generatrix of the cylinder that is the shape of the photoconductor 210, and is the main inspection direction of the image.

  In the present embodiment, a part of the laser light transmitted through the fθ lens also enters the synchronous reflection mirror. The synchronous reflection mirror is disposed on a scanning line of the laser beam of the photoconductor 210 and close to a position outside the image forming area. The synchronous reflection mirror reflects the incident laser light to the synchronous detection sensor 340.

  As described above, the writing unit 240 according to the present embodiment corresponds to a light beam scanning device that emits laser light from the LD 331 and scans the photoconductor 210.

  Next, the light source driving unit 320 of the present embodiment will be described with reference to FIG. FIG. 3 is a diagram illustrating a light source driving unit according to the first embodiment.

  The light source driving unit 320 of the present embodiment controls the light amount of the laser beam emitted from the LD 331 to approach a target value based on the current detected from the PD 332.

  The light source drive unit 320 of the present embodiment includes a comparator 321, an ADC (Analog to Digital Converter) 322, an APC (Automatic Power Control) control unit 323, a DAC (Digital to Analog Converter) 324, and an LD drive unit 325.

  The output of the PD 332 is supplied to one input of the comparator 321, and the reference current value Vref corresponding to the target light amount is supplied to the other input. The reference current value Vref is a predetermined value, and is a value corresponding to a target value (target light amount) of the light amount emitted from the LD 331. The output of the comparator 321 is the difference between the output of the PD 332 and the reference current value Vref, and is supplied to the ADC 322.

  The ADC 322 converts an input analog value into a digital value and outputs the digital value. The output of the ADC 322 is supplied to the APC control unit 323 as a difference signal.

  The APC control unit 323 determines a command value for outputting the current value supplied to the LD 331 based on the difference signal output from the ADC 322 so that the light amount of the light emitted from the LD 331 approaches the target light amount. Is output to the LD drive unit 325. That is, the APC control unit 323 of the present embodiment functions as a light amount control unit that controls the light amount of the LD 331. The output of the APC control unit 323 is supplied to the DAC 324. In the following description, the control performed by the APC control unit 323 is called APC control.

  The DAC 324 converts the command value output from the APC control unit 323 into an analog value, and supplies the analog value to the LD driving unit 325. The LD driver 325 outputs a current corresponding to the input analog value to the LD 331.

  The light source driving unit 320 according to the present embodiment turns on the LD 331 in each of the three divided regions in one main scan line based on the XAPC signal and the DATA signal. The XAPC signal is supplied to the APC control unit 323, and the DATA signal is supplied to the LD driving unit 325.

  In the following description, lighting in each of the three areas is referred to as APC lighting, image area lighting, and synchronous lighting.

  The light source drive unit 320 controls the amount of laser light emitted from the LD 331 during APC lighting. Specifically, the light source driving unit 320 supplies the difference between the output of the PD 332 and the reference current value Vref to the APC control unit 323 via the ADC 322 during APC lighting.

  The APC control unit 323 samples the supplied value during a period in which the XAPC signal is valid, and calculates a command value corresponding to the light amount of the LD 331.

  In the APC control unit 323 of the present embodiment, when changing the light amount of the LD 331, an upper limit value is provided for the fluctuation width. In the present embodiment, by providing an upper limit value for the fluctuation range of the light amount, it is possible to significantly change the light amount due to, for example, a detection error of the light amount by the PD 332 or an error generated inside the light source driving unit 320. Suppress. Note that the upper limit value of the fluctuation range of the light amount in the present embodiment is a preset value. In addition, the fluctuation range of the present embodiment is a value represented by an absolute value including both the increase and the decrease. Details of the upper limit of the fluctuation range will be described later.

  Further, the light source driving unit 320 forms an electrostatic latent image of an image drawn on the paper surface on the photoconductor 210 when the image area is lit, and controls the irradiation position of the laser beam in the main scanning direction with the synchronous lighting. . In the synchronous lighting, the laser light is adjusted to be incident on the synchronization detection sensor 340 by an optical configuration, and the synchronization detection sensor 340 on which the laser light is incident generates a synchronization signal.

  Next, the operation of the writing unit 240 of the present embodiment will be described with reference to FIG. FIG. 4 is a flowchart illustrating the operation of the writing unit according to the first embodiment.

  When printing by the image forming apparatus 100 is started, the writing unit 240 of this embodiment causes the writing control unit 310 to start rotating the polygon mirror 350 (step S401). Subsequently, the writing unit 240 causes the writing control unit 310 to turn on the LD 331 of the light source 330 via the light source driving unit 320 (step S402).

  Subsequently, the light source driving unit 320 performs APC control by the APC control unit 323 (Step S403). Details of the APC control in step S403 will be described later.

  Next, the writing control unit 310 causes the light source driving unit 320 to turn on the LD 331 in accordance with the DATA signal, and forms an image (step S404). Subsequently, the writing control unit 310 determines whether the printing has been completed (step S405).

  If the printing has not been completed in step S405, the writing control unit 310 returns to step S403. If printing has been completed in step S405, the writing control unit 310 turns off the LD 331 via the light source driving unit 320 (step S406). Subsequently, the writing control unit 310 stops the rotation of the polygon mirror 350 (step S407), and ends the processing.

  Next, the APC control of the present embodiment will be described with reference to FIGS. FIG. 5 is a diagram illustrating the function of the APC control unit according to the first embodiment.

  The APC control unit 323 according to the present embodiment includes a fluctuation upper limit value storage unit 341, an LD characteristic storage unit 342, an IL characteristic detection unit 343, an LD control unit 344, and a command value output unit 345.

  The fluctuation upper limit storage unit 341 of the present embodiment stores the upper limit of the fluctuation width.

  The LD characteristic storage unit 342 stores information indicating an IL (current-light amount) characteristic of the LD 331.

  The IL characteristic detecting unit 343 detects the IL characteristic of the LD 331 when the LD 331 is turned on before performing image formation, and stores the IL characteristic in the LD characteristic storage unit 342. Specifically, the IL characteristic detecting unit 343 detects the IL characteristic when the LD 331 is turned on in step S402 in FIG.

  The LD control unit 344 refers to the LD characteristic storage unit 342, and determines, in the IL characteristic detected by the IL characteristic detection unit 343, that the light amount of the LD 331 is less than a threshold value for determining that the LD 331 is turned on. Supply values. Details of the LD control unit 344 will be described later.

  The command value output unit 345 changes the amount of light emitted from the LD 331 according to the output of the ADC 322 (difference signal) so that the current value detected from the PD 332 approaches the reference current value Vref. Specifically, the command value output unit 345 outputs a command value indicating a current value supplied from the LD driving unit 325 to the LD 331 according to the difference signal.

  For example, when increasing the current value supplied to the LD 331 during APC control, the command value output unit 345 of the present embodiment outputs a command value for outputting the increased current value to the LD driving unit. 325 may be output. Further, for example, when the current value supplied to the LD 331 is reduced when the APC control is performed, the command value output unit 345 of the present embodiment outputs the command value for outputting the reduced current value to the LD value. The data may be output to the drive unit 325.

  FIG. 6 is a diagram illustrating an example of the IL characteristic. In FIG. 6, the vertical axis indicates the light amount, and the horizontal axis indicates the current.

  In the case of a general LD, when the light amount emitted from the LD is equal to or less than the light amount P corresponding to a current value not exceeding the threshold current Ith, it is determined that the LD is not turned on. Also, the LD is determined to be turned on when it emits a light amount corresponding to the current value applied exceeding the threshold current Ith. The relationship between the amount of light and the current applied exceeding the threshold current Ith has an approximately proportional correlation.

  The IL characteristic changes depending on the temperature of the LD. Generally, as the temperature rises, the threshold current Ith increases, and the slope of the curve indicating the relationship between the light amount and the current becomes gentle.

  FIG. 6 shows the IL characteristics of the LD 331. As shown in FIG. 6, when the temperature is 25 ° C., the IL characteristic of the LD 331 detected by the IL characteristic detecting unit 343 is as indicated by a solid line 61. When the temperature is 50 ° C., the IL characteristic detected by the IL characteristic detecting unit 343 is as indicated by a solid line 62.

For example, when the temperature of the LD 331 is 25 ° C., the LD 331 of the present embodiment is turned on when the threshold current Ith is supplied to the LD 331 and the light amount of the LD 331 becomes P ₀ or more. In other words, in order to light the LD 331, it is necessary to supply a current having a value larger than the threshold current Ith to the LD 331.

Therefore, when not turning on the LD 331, the LD control unit 344 of the present embodiment sets the current supplied to the LD 331 to a bias current smaller than the threshold current Ith. In the present embodiment, by leaving supplying a bias current to LD331, when receiving a lighting instruction of LD331, it can be promptly P ₀ or the amount of the LD331, to improve the followability to lighting indication Can be.

  The temperature change of the LD 331 is a long-term change such as printing a plurality of sheets, and the IL characteristic does not change significantly during the APC control period (at least 1 ms or less). Therefore, during the period in which the APC control is being performed, the light amount of the LD 331 does not greatly change.

  For this reason, in the APC control, the case where the fluctuation of the light amount of the LD 331 becomes large is considered to be caused by, for example, an error in detecting the light amount of the LD 331 by the PD 332 or an error in converting the analog value into the digital value by the ADC 322. .

  In the present embodiment, attention is paid to this point, and in the APC control by the APC control unit 323, an upper limit value is set for the fluctuation width of the light amount. In the following description, the upper limit of the fluctuation range is referred to as a fluctuation upper limit.

  The fluctuation upper limit value in the present embodiment is a value set in advance. The variation upper limit value in the present embodiment is a value corresponding to the maximum image density difference that cannot be perceived by human eyes. That is, the fluctuation upper limit value of the present embodiment is a command value for supplying a current for changing the amount of light so as to generate a maximum density difference among image density differences that cannot be sensed by human eyes.

  In the present embodiment, a command value supplied from the APC control unit 323 to the LD driving unit 325 is changed little by little, and an experiment is performed in advance to determine whether or not a person can sense a density difference of an image. A command value corresponding to the fluctuation width immediately before the image density difference can be sensed may be used as the fluctuation upper limit value.

  Next, APC control by the APC control unit 323 of the present embodiment will be described with reference to FIG. FIG. 7 is a flowchart illustrating processing of the APC control unit according to the first embodiment.

  The APC control unit 323 of the present embodiment uses the command value output unit 345 to detect the amount of light emitted by the LD 331 from the output from the ADC 322 (Step S701). Specifically, the command value output unit 345 detects a current value (digital value) corresponding to the light amount of the light emitted from the LD 331 from the difference signal output from the ADC 322 and the target light amount.

  Subsequently, the command value output unit 345 calculates a fluctuation range of the current value supplied to the LD 331 from the difference signal output from the ADC 322 (Step S702).

  Subsequently, the command value output unit 345 determines whether the calculated fluctuation range is equal to or larger than the fluctuation upper limit value stored in the fluctuation upper limit storage unit 341 (Step S703).

  If the fluctuation range is smaller than the fluctuation upper limit value in step S703, the process proceeds to step S705 described later.

  If the fluctuation width is equal to or more than the fluctuation upper limit value in step S703, the command value output unit 345 sets the fluctuation upper limit value as the fluctuation width (step S704). Subsequently, the command value output unit 345 calculates a command value reflecting the fluctuation range, outputs the command value to the LD drive unit 325 via the DAC 324 (step S705), and ends the process. Specifically, the command value output unit 345 outputs to the LD driving unit 325 a command value for outputting a current value obtained by fluctuating the current value currently supplied to the LD 331 by the fluctuation width. The LD drive unit 325 of the present embodiment changes the current value supplied to the LD 331 according to the command value output from the command value output unit 345.

  The APC control unit 323 of the present embodiment repeats the processing in FIG. 7 at the timing when the XAPC signal becomes valid in the area where the APC is turned on. Hereinafter, the operation of the APC control unit 323 will be further described with reference to FIG.

  FIG. 8 is a timing chart illustrating control by the APC control unit according to the first embodiment. In FIG. 8, control of image area lighting and synchronous lighting performed during a period in which the XAPC signal is invalid is omitted to explain the APC control.

  The APC control unit 323 of this embodiment performs APC control when the XAPC signal and the DATA signal become valid. In FIG. 8, the XAPC signal is valid at a low level (hereinafter, L level) and invalid at a high level (hereinafter, H level). In FIG. 8, the DATA signal is invalid at L level and valid at H level.

  FIG. 8 shows an example in which the fluctuation upper limit value is α, and the detected current value (digital value) B = command value A + 3α.

  In FIG. 8, APC control is performed at timings T0, T1, T2, T3, and T4 at which the XAPC signal becomes L level (valid).

  At the timing T0, the current value (digital value) corresponding to the light amount detected by the command value output unit 345 is A. At the timing T0, the command value output to the LD driving unit 325 is also A. Therefore, the command value output unit 345 outputs the command value A to the LD drive unit 325 during a period K1 from the timing T0 to the timing T1 at which the next APC control is performed.

  Next, at the timing T1, the current value (digital value) corresponding to the light amount detected by the command value output unit 345 is B. At this time, the command value output unit 345 compares the command value A in the period K1 with the current value (digital value) B, and determines whether or not the fluctuation width is equal to or more than the fluctuation upper limit α.

  In the example of FIG. 8, the current value (digital value) B = command value A + 3α, and the difference between the command value A and the current value (digital value) B is equal to or greater than the fluctuation upper limit value α.

  Therefore, the command value output unit 345 outputs the command value A + α obtained by adding the fluctuation upper limit value α to the command value A in the period K1 to the LD driving unit 325, and from the timing T1 to the timing T2 when the next APC control is performed. In the period K2, a current value corresponding to the command value A + α is supplied to the LD 331.

  In this embodiment, when the fluctuation of the command value corresponding to the light amount is equal to or more than the upper limit value, the current value supplied to the LD 331 is changed by the predetermined fluctuation upper limit value.

  Next, at the timing T2, the current value (digital value) B corresponding to the light amount detected by the command value output unit 345 remains. At this time, the command value output unit 345 compares the command value A + α in the period K2 with the current value (digital value) B, and determines whether the fluctuation width is equal to or larger than the fluctuation upper limit α.

  In the example of FIG. 8, the current value (digital value) B = command value A + 3α, and the difference between the command value A + 3α and the current value (digital value) value B is equal to or greater than the fluctuation upper limit value α. Therefore, the command value output unit 345 outputs the command value A + 2α obtained by adding the fluctuation upper limit value α to the command value A + α in the period K2 to the LD driving unit 325, and from the timing T2 to the timing T3 at which the next APC control is performed. In the period K3, a current value corresponding to the command value A + 2α is supplied to the LD 331.

  In the example of FIG. 8, the current value (digital value) corresponding to the amount of light detected by the command value output unit 345 remains at B even at the timing T3. Therefore, the command value output unit 345 compares the command value A + 2α in the period K3 with the current value (digital value) B, and determines whether the fluctuation width is equal to or larger than the fluctuation upper limit α.

  In the example of FIG. 8, the difference between the command value A + 2α and the current value (digital value) B is equal to or larger than the fluctuation upper limit α. Therefore, the command value output unit 345 outputs the command value A + 3α obtained by adding the fluctuation upper limit α to the command value A + 2α in the period K3, that is, the current value (digital value) B to the LD drive unit 325, and from the timing T3, A current value corresponding to the current value (digital value) B is supplied to the LD 331 during a period K4 until the timing T4 when the APC control is performed.

  As described above, in the present embodiment, when the fluctuation width is equal to or more than the fluctuation upper limit value, the light amount is changed stepwise by the fluctuation upper limit value. Can be suppressed.

  Although not shown in FIG. 8, for example, when the difference between the command value A and the current value (digital value) B is γ (increase) less than the fluctuation upper limit α, the command value output unit 345 outputs the command value. The value A + γ is output to the LD drive unit 325, and a current value corresponding to the command value A + γ is supplied to the LD 331 during the period until the next APC control is performed.

  As described above, the APC control unit 323 according to the present embodiment performs the upper limit variation corresponding to the density variation that cannot be sensed by human vision when the variation range of the light amount causes the variation in density that can be sensed by human vision. Do not change more than the width.

  Therefore, according to the present embodiment, even when the current value (analog value) output from the PD 332 is greatly varied from the current value corresponding to the light amount of the LD 331 due to, for example, the influence of disturbance, the LD 331 The light amount fluctuates only by an amount corresponding to the density difference of the image in a range that cannot be sensed by a person.

  Further, even if a difference signal that does not match the difference between the current value (analog value) output from the PD 332 and the reference current value Vref is supplied to the APC control unit 323 due to a problem such as the resolution of the ADC 322, Can be prevented from causing a change in density that can be visually recognized.

  Therefore, according to the present embodiment, it is possible to suppress a change in image density caused by a change in the amount of light emitted from the LD 331.

  In the present embodiment, the command value output unit 345 of the APC control unit 323 outputs a command value corresponding to the current value supplied from the LD driving unit 325 to the LD 331, but is not limited thereto.

  The command value output unit 345 of the present embodiment also outputs to the LD drive unit 325 a command value corresponding to a difference signal indicating a difference between the current value (analog value) output from the PD 332 and the reference current value Vref. good. In this case, the LD driving unit 325 may change the value of the current supplied to the LD 331 based on the command value corresponding to the difference signal.

(Second embodiment)
Hereinafter, a second embodiment will be described with reference to the drawings. The second embodiment is different from the first embodiment in that the variation upper limit value is changed in accordance with the change in the target light amount. Therefore, in the following description of the second embodiment, components having the same functional configuration as those of the first embodiment will be denoted by the same reference numerals as those used in the description of the first embodiment. Is omitted.

  In the present embodiment, a plurality of change upper limit values are held as stepwise values, and the change upper limit value is changed according to a change in the target light amount. In the present embodiment, the light amount of the LD 331 can be quickly brought close to the target light amount by changing the fluctuation upper limit value in accordance with the change in the target light amount.

  It should be noted that the largest variation upper limit value among the plurality of variation upper limit values in the present embodiment is a current that changes the amount of light so as to generate the largest density difference among the density differences of the image that cannot be sensed by human eyes. This is a command value (variation upper limit α) for supplying a value.

  In the present embodiment, by defining the maximum value of the variation upper limit value as described above, it is possible to suppress a variation in image density due to a variation in light amount.

  FIG. 9 is a diagram illustrating the function of the APC control unit according to the second embodiment. The APC control unit 323A of the present embodiment has a target light amount changing unit 346 in addition to the components of the APC control unit 323 of the first embodiment.

  The target light amount changing unit 346 of the present embodiment changes the target light amount when a predetermined condition is satisfied, for example, when a setting related to image formation in the image forming apparatus 100 is changed. The predetermined condition is, for example, when the printing speed in the image forming apparatus 100 is changed. Specifically, the target light amount changing unit 346 of this embodiment changes the value of the reference current value Vref to change the reference current value corresponding to the target light amount when a change or the like that matches the condition for changing the target light amount is performed. Change the current value.

  Further, a plurality of fluctuation upper limit values are stored in the fluctuation upper limit storage unit 341 of the present embodiment, each of which is associated with a target light amount. When the target light amount is changed, the target light amount changing unit 346 of the present embodiment selects a change upper limit corresponding to the changed target light amount.

  The variation upper limit value stored in the variation upper limit value storage unit 341 of the present embodiment supplies a current value that changes the amount of light so as to generate a maximum density difference among image density differences that cannot be sensed by human eyes. Command value for

  In the following description, the variation upper limit value stored in the variation upper limit storage unit 341 of the present embodiment will be described as α and β.

  The variation upper limit value α in the present embodiment is a command value for supplying a current value that changes the amount of light so as to generate a maximum density difference among image density differences that cannot be sensed by human eyes. Further, the variation upper limit value β of the present embodiment is a value smaller than the variation upper limit value α. In other words, the fluctuation upper limit value β is a command value for supplying a current value that changes the amount of light so as to generate a density difference smaller than the maximum density difference among the density differences of the image that cannot be sensed by human eyes. .

  FIG. 10 is a flowchart illustrating processing of the APC control unit according to the second embodiment. FIG. 10 shows a process of changing the fluctuation upper limit value when the target light amount is changed.

  The APC control unit 323A of the present embodiment determines whether the target light amount changing unit 346 has changed the target light amount (Step S101).

  If the target light amount is changed to a larger value in step S101, the target light amount changing unit 346 sets the upper limit fluctuation value to α (step S102), and ends the processing. When the target light amount is changed to a smaller value in step S101, the target light amount changing unit 346 sets the upper limit fluctuation value to β which is a value smaller than α (step S103), and ends the process. If the target light amount has not been changed in step S101, the target light amount changing unit 346 terminates the processing.

  The APC control unit 323A of the present embodiment may perform the processing in FIG. 10 before starting the APC control, for example, or may perform the processing in FIG. 10 when the target light amount is changed.

  FIG. 11 is a timing chart illustrating control by the APC control unit according to the second embodiment.

  In FIG. 11, in the period K1, the target light amount is changed (increased) from the light amount corresponding to the current value (digital value) A to the light amount corresponding to the current value (digital value) C. The case where the upper limit is also changed from β to α is shown.

  In FIG. 11, the command value D is a value larger than the command value A + α, and the current value (digital value) C is a value smaller than the command value A + α and larger than the command value A. Further, the current value (digital value) D in FIG. 11 is a value including an error due to the influence of, for example, disturbance.

  In the example of FIG. 11, only the period K2 includes an error in the detection of the light amount of the LD 331.

  At the timing T1, the current value (digital value) corresponding to the light amount detected by the command value output unit 345 is D. In the period K1 before the timing T1, the command value output to the LD driving unit 325 is A. At this time, the command value output unit 345 compares the current value (digital value) D with the command value A, and determines whether the fluctuation width is equal to or larger than the fluctuation upper limit α.

  In FIG. 11, the current value (digital value) D is a value larger than the command value A + α. Therefore, the command value output unit 345 outputs the command value A + α obtained by adding the fluctuation upper limit value α to the command value A in the period K1 to the LD driving unit 325, and from the timing T1 to the timing T2 when the next APC control is performed. In the period K2, a current value corresponding to the command value A + α is supplied to the LD 331.

  At the next timing T2, the current value (digital value) corresponding to the light amount detected by the command value output unit 345 is C. In the period K2 before the timing T2, the command value output to the LD driving unit 325 is A + α. At this time, the command value output unit 345 compares the current value (digital value) C with the command value A + α, and determines whether or not the fluctuation width is equal to or larger than the fluctuation upper limit α.

  In the example of FIG. 11, the current value (digital value) C is a value smaller than the command value A + α and larger than the command value A. Therefore, the fluctuation range between the current value (digital value) C and the command value A + α is smaller than the fluctuation upper limit α. Therefore, the command value output unit 345 outputs the command value C (command value A + α−γ) obtained by subtracting the variation γ from the command value A + α to the LD driving unit 325 at the timing T2, and in the period K3, the command value C A current value corresponding to C is supplied to the LD 331.

  As described above, in the example of FIG. 11, the variation upper limit value is changed from the variation upper limit value β set in the period K1 to α, which is larger than β, in accordance with the change in the target light amount in the period K1. . Therefore, according to the present embodiment, the light amount of the LD 331 can be brought closer to the target light amount more quickly than when the APC control is performed with the fluctuation upper limit being kept at β.

  As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the requirements described in the above embodiments. Regarding these points, the gist of the present invention can be changed within a range that does not impair the gist, and can be appropriately determined according to the application form.

REFERENCE SIGNS LIST 100 image forming apparatus 200 image forming unit 210 photoreceptor 220 cleaning unit 230 charging unit 240 writing unit 250 developing unit 260 transfer unit 270 separation unit 300 fixing unit 310 writing control unit 320 light source driving unit 321 comparator 322, 324 ADC
323 APC control unit 325 LD drive unit 330 Light source 331 LD
332 PD
341 Fluctuation upper limit storage unit 345 Command value output unit 346 Target light amount change unit

JP 2006-76216 A

Claims (6)

A light amount control unit that detects a light amount of light emitted from a light source based on an output of a light receiving element that receives the light, and outputs a command value for outputting a current supplied to the light source according to the detected light amount. When,
A light source driving unit that supplies a current corresponding to the command value output from the light amount control unit to the light source,
The light amount control unit includes:
When a fluctuation range between the light amount detected in the first period and the light amount detected in the second period is equal to or more than a fluctuation upper limit, the light amount detected in the first period is changed to the fluctuation upper limit. Outputs the command value corresponding to the current that fluctuates by the value ,
When the fluctuation range between the light amount detected in the first period and the light amount detected in the second period is less than a fluctuation upper limit value, the light amount detected in the first period is changed by the fluctuation. A light beam scanning device that outputs a command value corresponding to a current that varies by a width . A storage unit that holds a plurality of the fluctuation upper limit values,
The fluctuation upper limit is:
The light beam scanning device according to claim 1, wherein when a target value of the amount of light emitted from the light source is changed, the light beam scanning device is changed according to the change of the target value. The plurality of fluctuation upper limit values are command values for outputting a current corresponding to a light amount that generates a density difference of an image that cannot be visually sensed by a human,
3. The light beam scanning device according to claim 2, further comprising a command value for outputting a current corresponding to a light amount that generates a maximum density difference among density differences of an image that cannot be visually sensed by a human. The light source and the light beam scanning apparatus according to any one of claims 1 to 3 having a light receiving element. An image forming apparatus having a light beam scanning apparatus according to any one of claims 1 to 4. A light beam scanning method using a light beam scanning device,
A light amount control procedure for detecting a light amount of light emitted from a light source based on an output of a light receiving element for receiving the light, and outputting a command value for outputting a current supplied to the light source according to the detected light amount When,
A light source driving procedure for supplying a current corresponding to the command value output in the light quantity control procedure to the light source,
The light amount control procedure includes:
When a fluctuation width between the light amount detected in the first period and the light amount detected in the second period is equal to or larger than a fluctuation upper limit, the light amount detected in the first period is changed to the fluctuation upper limit. Outputs the command value corresponding to the current that fluctuates by the value ,
When the fluctuation width between the light amount detected in the first period and the light amount detected in the second period is less than a fluctuation upper limit, the light amount detected in the first period is changed by the fluctuation. A light beam scanning method for outputting a command value corresponding to a current fluctuating by a width .

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