JP2005262478A - Light beam emission controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light source driving device that prevents streaklike irregularities due to luminous energy correction both in a main scanning direction and a subsidiary scanning direction. <P>SOLUTION: Low pass filters 110A and 110B are provided for correction data in a main scanning direction and correction data in a subsidiary scanning direction, respectively. The main scanning direction correction data is used for luminous energy correction in a luminous energy correction section 106 through the low pass filter 110A and a signal indicting the subsidiary direction correction data is used for luminous energy correction through the low pass filer 110B. Consequently streaklike irregularities due to the luminous energy correction do not occur in any of the main scanning direction and the subsidiary scanning direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, a light beam emitted from a light source is main-scanned based on image data, and an electrostatic latent image is formed on an image carrier that relatively moves in a sub-scanning direction that is a direction orthogonal to the main scanning. The present invention relates to a light beam emission control device that is used in an image forming apparatus that forms an image by developing and transferring an image onto a recording medium. The light emission control device controls light emission of a light beam emitted from the light source.

  Conventionally, there is an image recording apparatus that records an image by scanning and exposing an image carrier with a light beam. A general operation of such an image recording apparatus will be described with reference to FIG. In the image recording apparatus 200 shown in FIG. 9, the laser LD is subjected to ON / OFF control based on the image data after the light amount is controlled so that the output light amount corresponds to the reference voltage. Thereby, the light beam LB having a light amount corresponding to the reference voltage is modulated and output from the laser LD based on the image data.

  The light beam LB output from the laser LD is irradiated onto the drum-shaped photosensitive member 206 while performing main scanning in the axial direction through a scanning optical system 204 including a polygon mirror 202. At this time, by rotating the photosensitive member 206, sub scanning of the light beam is performed in a direction orthogonal to the main scanning direction, and an image (electrostatic latent image) is formed on the photosensitive member.

  Thus, when the photosensitive member is scanned and exposed by the light beam, ideally, it is desirable that the light quantity distribution of the laser be constant regardless of the scanning position of the laser. However, in actuality, the laser light that has passed through the periphery of each lens due to the characteristics of the optical system such as the mirror and the lens causes unevenness in the light amount distribution in the main scanning direction on the surface of the photosensitive member. Cause uneven density. Such light amount unevenness in the main scanning direction stores correction data for each position in the main scanning direction obtained in advance based on the light amount unevenness in the main scanning direction, as proposed in Patent Document 1. When the laser is ON / OFF controlled based on the image data, the laser output light amount is corrected based on the correction data corresponding to the main scanning position within one main scanning (specifically, the duty of the ON / OFF control). Alternatively, the problem can be solved by correcting the drive current value supplied to the laser.

  At this time, if the correction data is changed by digital-to-analog conversion (hereinafter referred to as D / A conversion) of the digital correction signal, the amount of light changes in a step-like manner as the correction data changes. The amount of light changes abruptly, causing streaking in the sub-scanning direction on the image. For this reason, in Patent Document 1, a low-pass filter is inserted into correction data (correction control voltage) output after the D / A change to smooth the light amount change.

  On the other hand, even in the sub-scanning direction, unevenness in the amount of light occurs due to uneven charging or dirt on the photoreceptor.

  Such light amount unevenness in the sub-scanning direction is stored in advance as correction data for each position in the sub-scanning direction obtained based on the light amount unevenness as proposed in Patent Document 2. This can be solved by correcting the reference voltage based on correction data corresponding to the sub-scanning position every time.

Therefore, in order to eliminate unevenness in the amount of light in both the main and sub-scan directions, as shown in FIG. 10, the light amount control unit 210 that performs light amount control based on the reference voltage Vref and the laser LD are driven (lighted). A light amount correction unit 214 that performs light amount correction based on correction data in the main scanning direction is provided between the drive unit 212 and correction data in the main scanning direction is input to the light amount correction unit 214 via a low-pass filter (LPF) 216. In addition to the input, the reference voltage Vref used in the light amount control of the light amount control unit 210 may be changed based on the correction data in the sub-scanning direction.
JP 11-291548 A JP-A-6-164037

  However, it is not suitable to correct the reference voltage in order to eliminate unevenness in the amount of light in the sub-scanning direction because the following problems occur.

  That is, normally, the image recording apparatus is provided with a sensor 220 (see FIG. 9) for detecting the light beam LB that travels outside the image recording range within the scanning (main scanning) range of the light beam LB. The main scanning timing of the light beam LB is detected by detecting the light beam LB with the sensor 220. Then, in synchronization with the detected main scanning timing, image writing timing in the main scanning direction (start timing of laser ON / OFF control based on image data for one line) is controlled.

  At this time, if the reference voltage is changed and the amount of light beam is changed, the beam spot diameter of the light beam is changed. Therefore, the detection timing of the main scanning timing by the sensor 220 is shifted and the image writing timing is changed. In other words, if the reference voltage is corrected to eliminate unevenness in the amount of light in the sub-scanning direction, the image writing position on the photoreceptor is shifted line by line.

  Therefore, as shown in FIG. 11, two-dimensional correction data composed of correction data in the main scanning direction and the sub-scanning direction is input to the light amount correction unit 214 via the low-pass filter 216, and the main scanning direction is also applied in the sub-scanning direction. It is conceivable that the same light amount correction is performed. However, the correction data in the sub-scanning direction naturally changes more slowly (at a lower frequency) than the correction data in the main scanning direction that performs correction within one main scan, so that the correction data in the main scanning direction is smoothed. Therefore, the low-pass filter 216 cannot properly smooth the correction data in the sub-scanning direction. Therefore, the light amount change is abrupt for correction in the sub-scanning direction, and the light amount unevenness correction causes streak unevenness in the main scanning direction (step-like light amount unevenness that occurs when correction data fluctuates).

  An object of the present invention is to obtain a light beam emission control device that can prevent the occurrence of streak-like unevenness due to light amount unevenness correction in both the main scanning direction and the sub-scanning direction in consideration of the above facts.

  In the present invention, a light beam output from a light source is subjected to main scanning on an image carrier, and the image carrier is moved in a sub-scanning direction orthogonal to the main scanning direction to expose an image on the image carrier. A light source driving device for driving the light source for recording, and a light amount control means for controlling the light amount of the light source so as to obtain a predetermined output light amount, and an image is recorded on the image carrier by exposure. The first correction data for correcting the light amount unevenness in the main scanning direction and the second correction data for correcting the light amount unevenness in the sub-scanning direction are input, and the input first correction data And based on the second correction data, the light quantity correction means for correcting the output light quantity of the light source after the light quantity control by the light quantity control means, and the first correction data used for correction by the light quantity correction means are smoothed. First smoothing And stage is characterized by having, a second smoothing means for smoothing the second correction data used for correction in the light amount correction means.

  According to the present invention, the output of the light source is controlled by the light amount control means so as to become the predetermined light amount. Thereafter, when the first correction data for correcting the light amount unevenness in the main scanning direction and the second correction data for correcting the light amount unevenness in the sub-scanning direction are input to the light amount correcting unit during the image forming period. Based on the first and second correction data, the output light quantity of the light source after the light quantity control is corrected by the light quantity correction means. The first correction data and the second correction data used for correction by the light amount correction unit are smoothed by the first smoothing unit and the second smoothing unit respectively provided for exclusive use. In other words, since the means for smoothing the first (main scanning direction) correction data and the second (sub-scanning direction) correction data are respectively provided, the respective correction data can be appropriately smoothed. In both the main scanning direction and the sub-scanning direction, streak-like unevenness does not occur due to light amount unevenness correction.

  In the above light source driving apparatus, the light amount correction unit multiplies the control amount obtained by the light amount control of the light amount control unit by the first correction data and the second correction data to obtain a correction amount. Can be obtained.

  In this case, the light quantity correction unit is configured to multiply the control amount by the first correction data or the second correction data, a multiplication result by the first multiplication unit, and the second or And a second multiplying unit that multiplies the first correction data. The light amount correcting unit includes the first correction data and the second correction unit. You may make it provide the 1st multiplication means which multiplies 2nd correction data, and the 2nd multiplication means which multiplies the multiplication result by the said 1st multiplication means, and the said control amount.

  In addition, since the multiplication unit included in the light amount correction unit performs the multiplication by analog data processing, the output after the multiplication of the two correction data after smoothing and the control amount obtained by the light amount control also fluctuates smoothly. And image streaks can be prevented. In this case, it is preferable that the light amount correction unit has a function of executing calibration at a predetermined timing. This is because the analog multiplier means varies the output voltage at the time of clearing (at the time of zero signal input) due to individual variations in transistor characteristics, etc., so that calibration is performed to set the output voltage at the time of zero signal input to the reference voltage. This is because correction can be performed with high accuracy.

  As described above, according to the present invention, the means for smoothing the first (main scanning direction) correction data and the second (sub-scanning direction) correction data are provided for the respective corrections. The data can be smoothed appropriately, and the control voltage used for correction from the analog multiplier having the calibration function according to the correction data is smoothly output according to the correction data. In both the scanning directions, it is possible to prevent the occurrence of streak-like unevenness due to light amount unevenness correction and to perform two-dimensional light amount correction with high accuracy.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a basic configuration of a light source driving apparatus 100 to which the present invention is applied. The light source driving apparatus 100 can be used, for example, to drive a laser LD that is a light source of the image recording apparatus 200 shown in FIG. 9, and this case will be described below.

  As shown in FIG. 1, the light source driving device 100 includes a drive unit 102 that drives (lights) the laser LD, a light amount control unit 104 that performs light amount control so that the output light amount of the laser LD becomes a predetermined light amount, and unevenness in light amount. A light amount correction unit 106 that corrects the output light amount of the laser LD based on correction data for correcting the light source, and a controller 108 that controls the overall operation of the light source driving device 100. As for the controller 108, the function can be provided in a control device provided outside the light source driving device 100, for example, in the main body of the image recording device 200.

  The drive unit 102 supplies a drive current to the laser LD. When a drive current is supplied from the drive unit 102, the laser LD emits light with a light amount corresponding to the supplied drive current value and outputs a light beam. Although not shown in the drawing, a lighting signal is input from the controller 108 to the driving unit 102, and the laser LD is turned on / off based on the lighting signal by turning on / off the driving current to the laser LD. Turns ON / OFF of.

  The drive unit 102 is connected to the light amount control unit 104 via the light amount correction unit 106. The light quantity control unit 104 corresponds to the light quantity control means of the present invention, and controls the drive current value supplied from the drive unit 102 to the laser LD so that the output light quantity of the laser LD becomes the reference light quantity.

  Specifically, the reference voltage Vref is input from the controller 108 to the light amount control unit 104. The light amount control unit 104 adjusts the drive current value supplied from the drive unit 102 to the laser LD so that the output light amount of the laser LD becomes a light amount corresponding to the reference voltage Vref (hereinafter referred to as a reference light amount). Since the drive unit 102 holds the drive current value when the reference light amount is obtained even after the light amount control, the laser LD can emit light with the reference light amount during subsequent image recording.

  The light amount correction unit 106 is connected to the controller 108, and from the controller 108, correction data in the main scanning direction (corresponding to the first correction data of the present invention) and correction data in the sub-scanning direction (second correction of the present invention). Signal corresponding to data) is input.

  Here, the correction data output from the controller is D / A converted based on the digital correction signal and output as a control voltage for controlling the light amount correction. In the present embodiment, a low-pass filter (LPF) 110A that smoothes and outputs an input signal between the controller 108 and the light amount correction unit 106 as the first smoothing means and the second smoothing means of the present invention. 110B, the correction data in the main scanning direction output from the controller 108 passes through the low-pass filter 110A, and the signal representing the correction data in the sub-scanning direction passes through the low-pass filter 110B to the light amount correction unit 106. Each is designed to be entered.

  The low-pass filters 110A and 110B are each designed to have a cut-off frequency suitable for fluctuations in correction data in the main scanning direction and fluctuations in correction data in the sub-scanning direction. The low pass filter 110B is suitable for relatively smoothing a low frequency signal.

  Therefore, the correction data in the main scanning direction and the correction data in the sub scanning direction are appropriately smoothed by the low-pass filters 110A and 110B, respectively, and then input to the light amount correction unit 106.

  The light amount correction unit 106 corresponds to the light amount correction unit of the present invention, and calculates the drive current value supplied from the drive unit 102 to the laser LD based on the input correction data in the main scanning direction and correction data in the sub scanning direction. By correcting, the output light amount of the laser LD is corrected (hereinafter referred to as two-dimensional light amount correction).

In order to perform two-dimensional light amount correction, the light amount correction unit 106 combines two multipliers 120 and 122 (see FIG. 2 and FIG. 3), and sets correction data in the main scanning direction as X and correction data in the sub-scanning direction. Y is provided with an analog circuit that obtains a correction amount by multiplying X × Y × Z, where Z is the output (control amount) of the light amount control unit 104 obtained by execution of the light amount control.
The multipliers 120 and 122 perform multiplication with analog data, and the light amount correction unit 106 obtains the multiplication result as an analog value. This is because, when a multiplier that performs multiplication with digital data is used, the multiplication result becomes a digital value and changes in a step shape. As a result, the light amount correction by the light amount correction unit 106 changes the light amount in a step shape. This is because streaky irregularities are generated.

  Further, a multiplier that performs multiplication with analog data is affected by individual variations in transistor characteristics and the output voltage of the multiplier, that is, the reference voltage of the multiplier output varies among the individual even in a clear state (at the time of zero input). . For this reason, the light amount correction unit 106 has a function of calibrating each multiplier by inputting a reset signal from the outside (in this example, the controller 108 as an example), and can perform correction with high accuracy without variation. it can. . The calibration is a process for setting the output voltage when zero is input as a reference.

  Here, there are two possible combinations of the two multipliers 120 and 122 in the light amount correction unit 106, that is, X × Y × Z.

  In the first multiplication method (hereinafter referred to as multiplication method 1), as shown in FIG. 2, Z and Y (or X) are input to a multiplier 120 (corresponding to the first multiplication means of claim 3). The output of the multiplier A and X (or Y) are input to the multiplier 122 (corresponding to the second multiplication means of claim 3), and the light amount correction is performed so that the output of the multiplier 122 is input to the drive unit 102. The unit 106 is configured to multiply Z by Y (or X), and then multiply Z × Y by X (or Z × X by Y).

  In the second multiplication method (hereinafter referred to as multiplication method 2), as shown in FIG. 3, X and Y are input to the multiplier 120 (corresponding to the first multiplication means of claim 4), and the multiplier 122 The light quantity correction unit 106 is configured so that the output of the multiplier 120 and Z are input to (corresponding to the second multiplication means of claim 4), and the output of the multiplier 122 is input to the drive unit 102, and X and Y is multiplied first, and then X × Y is multiplied by Z.

  The light amount correction unit 106 may be configured to perform multiplication by any of the multiplication methods 1 and 2. However, when a plurality of lasers (for example, a surface emitting laser (VCSEL)) is used as a light source in order to perform simultaneous scanning with a plurality of light beams, the multiplication method 1 requires multipliers 120 and 122 for each laser. On the other hand, in the multiplication method 2, as shown in FIG. 4, the multiplier 120 at the first stage is shared by a plurality of lasers, and the output of the multiplier 120 is branched to provide multipliers 122_1 to 122_1 provided for each laser. It is sufficient to input to n, which is preferable because the circuit scale can be made smaller than the multiplication method 1.

  The controller 108 stores in its internal memory (not shown) correction data in the main scanning direction obtained based on unevenness in the amount of light in the main scanning direction and in the subscanning direction obtained based on unevenness in the amount of light in the subscanning direction. Correction data is stored in advance.

  At the time of image recording, the controller 108 outputs signals representing correction data in the main scanning direction and correction data in the sub-scanning direction according to the scanning position of the light beam based on these correction data stored in the internal memory. Each is generated and output. Thus, at the time of image recording, the drive current value determined by the light amount control unit 104 is corrected by the light amount correction unit 106 based on the correction data in the main scanning direction and the correction data in the sub scanning direction, and the output of the laser LD The amount of light changes. On the other hand, at the time of light amount control, the controller 108 outputs a signal indicating correction stop (for example, a signal indicating correction data = 0), and is output as it is without correcting the control amount output by the light amount control unit 104. A light quantity serving as a reference for correction is set.

  Next, the operation of the light source driving apparatus 100 will be described with reference to FIG. FIG. 5 is a flowchart showing the basic operation of the light source driving device 100.

  That is, the light amount correction unit 106 performs calibration of the multipliers 120 and 122 (step S1), and the light amount control unit 104 performs light amount control of the laser LD (step S2). By this light amount control, the drive current value supplied from the drive unit 102 to the laser LD is determined so that the laser LD emits light with a reference light amount corresponding to the reference voltage Vref. Thereafter, when it is time to record an image, the controller 108 starts outputting correction data in the main scanning direction and correction data in the sub-scanning direction according to the scanning position of the light beam (step S3). The correction data in the main scanning direction and the correction data in the sub-scanning direction are respectively smoothed by the corresponding low-pass filters 110A and 110B (step S4) to become correction data X and Y (analog signals), and the light amount correction unit 106. Is input.

  The light amount correction unit 106 multiplies (X × Y × Z) the X, Y and the output control amount Z of the light amount control unit 104 obtained by the light amount control to obtain a correction amount, and the laser is based on the correction amount. The drive current value supplied to the LD is corrected (step S5). The drive unit 102 supplies the corrected drive current to the laser LD and turns on / off the supply of the drive current based on the image data (step S6). Accordingly, the laser LD is turned on / off based on the image data while the light amount is corrected based on the correction data in the main scanning direction and the correction data in the sub scanning direction corresponding to the scanning position.

  At this time, the correction data in the main scanning direction and the correction data in the sub scanning direction are appropriately smoothed through the dedicated low-pass filters 110A and 110B, respectively, and then used for light amount correction. In both directions, streak-like unevenness due to light amount unevenness correction (step-like light amount unevenness that occurs when correction data fluctuates) does not occur.

  Thus, in the present embodiment, dedicated low-pass filters 110A and 110B are provided in the main scanning direction and the sub-scanning direction, respectively, and correction data in the main scanning direction is corrected data in the sub-scanning direction via the low-pass filter 110A. Is used for the light amount correction in the light amount correction unit 106 after passing through the low-pass filter 110B. As a result, each correction data can be appropriately smoothed, and the control voltage used for correction is smoothly output according to the correction data from an analog multiplier having a calibration function based on the correction data. Therefore, in the main scanning direction and the sub-scanning direction, the occurrence of streak-like unevenness due to light amount unevenness correction can be prevented, and two-dimensional light amount correction can be performed with high accuracy. Further, since the reference voltage Vref is not changed, there is no concern that the image writing position is shifted.

  Next, the operation of the light source driving apparatus 100 will be described in detail using a specific example. In the following, description will be made on the assumption that two-dimensional light amount correction is performed as follows as an example.

  FIG. 6A shows the relationship between the output light amount (vertical axis) of the laser LD and the drive current (horizontal axis). In the two-dimensional light amount correction, as shown in FIG. 6A, there are two types of light amount control (APC1) for making the reference light amount L00 corresponding to the reference voltage Vref and light amount control (APC2) for making the second reference light amount Lff. The amount of light is controlled by linear interpolation between the two points L00 and Lff. Note that L00 <Lff, and in this example, the maximum light amount in the correction range is Lff.

  The light amount L after the light amount correction is determined by the multiplication result shown in the following equation (1) as correction data αx in the main scanning direction and correction data αy in the sub-scanning direction.

L = αx / 16 × αy / 16 × (Lff−L00) + L00 (1)
However, 0 ≦ αx / 16 ≦ 1 and 0 ≦ αy / 16 ≦ 1.

  In this example, 4-bit data indicating αx and αy is output from the controller 108, and the subscript xy attached to L in FIG. 6A is 4-bit data of αx and αy, respectively. Is shown in hexadecimal.

  In FIG. 6B, the reference light amount L00 = 10 and the second light amount Lff = 26, and the correction data αx in the main scanning direction changes from 1 → 16 → 1 according to the scanning position of the light beam in the main scanning direction. An example of two-dimensional light amount correction that is executed when the correction data αy in the sub-scanning direction changes from 0 to 1 according to the scanning position of the light beam in the sub-scanning direction is shown. In FIG. 6B, in the first main scanning (sub-scanning position = 1) of the light beam, αy = 0, so that the light amount becomes L00 in the main scanning direction, and the second and subsequent main scanning (sub-scanning positions). In ≧ 2), it can be seen that the light amount changes in a mountain shape in which the light amount gradually increases from the main scanning direction end portion to the central portion, and the peak increases as the number of scans increases. That is, the light amount is two-dimensionally corrected according to the positions in the main scanning direction and the sub-scanning direction.

(Example 1)
First, as Example 1, the operation of the light source driving apparatus adopting the multiplication method 1 will be specifically described. FIG. 7 shows an example of the analog circuit configuration of the light source driving device in this case. Hereinafter, the operation of this analog circuit will be described based on the symbols shown in the figure.
First, in order to execute APC1, the switches SW10 and SW11 are turned ON, and correction data αx and αy = 0. At this time, the switches SW51 to SW53 are turned on by turning on the reset signal, and the multipliers 120 and 122 are calibrated simultaneously with the APC1.
The correction data αx and αy are converted from digital signals to analog signals by the D / A converters DAC1 and DAC2, respectively, and then converted into correction data X and Y via the low-pass filters 110A and 110B. Although input to the input 1 of 122, since the correction data αx and αy = 0, that is, X and Y = 0, the operations of the multipliers 120 and 122 can be ignored. Note that the multipliers 120 and 122 multiply the respective inputs 1 and 2. The inputs 2 of the multipliers 120 and 122 each have two input terminals, and the input 2 is inputted with a differential voltage between these two input terminals.

Further, when the switches SW10 and SW11 are turned on, a drive current is supplied from the current source CS to the laser LD, and the laser LD is turned on. Then, the output light of the laser LD is detected by the photodiode PD, and a voltage corresponding to the detected light amount (detected light amount voltage) is input to the comparator COMP. The comparator COMP compares the detected light amount voltage with the reference voltage Vref, and the capacitor C3 is charged according to the comparison result. At this time, since the switches SW51 and SW52 are ON, the capacitors C41 and C42 are similarly charged according to the comparison result of the comparator COMP.
Here, when the correction data αx and αy = 0, that is, when X and Y = 0, the outputs of the multipliers 120 and 122 should be 0, but actually there is an offset output voltage. Therefore, the capacitor C3 is charged with reference to the offset output voltage of the multiplier 122. Since the switch SW53 is ON, the offset output voltage of the multiplier 120 is charged to C43.

  Finally, at the end of APC1, the capacitor C3 is charged with the control voltage of the current source CS for causing the laser LD to emit light with the reference light amount L00 with reference to the offset output voltage of the multiplier 122, and the capacitor C41, C42 is also charged with the same voltage as this control voltage. When APC1 ends, the switch SW11 is turned off, and the switches SW51 to SW53 are also turned off when the reset signal is turned off.

  Next, in order to execute APC2, the switches SW10 and SW51 are turned ON (the switches SW52 and 53 are OFF), and the correction data αx and αy = f are set.

  The correction data αx and αy are converted from digital signals to analog signals by the D / A converters DAC1 and DAC2, respectively, and then converted into correction data X and Y via the low-pass filters 110A and 110B. It is input to the input 1 of 122. Further, when the switch SW10 is turned on, a drive current is supplied from the current source CS to the laser LD, and the laser LD is turned on. Then, the output light amount of the laser LD is detected by the photodiode PD, and the comparator COMP compares the voltage corresponding to the detected light amount with the second reference light amount (maximum light amount) Vref2. Since the switch SW51 is ON, the capacitor C41 is charged according to the comparison result.

  Therefore, the difference voltage between the charging voltage of the capacitor C41 and the charging voltage of the capacitor C42 charged by the APC1 is input to the input 2 of the multiplier 120. The multiplier 120 multiplies the difference voltage by the correction data X (= f) input to the input 1A. A difference voltage between the output voltage indicating the multiplication result of the multiplier 120 and the charging voltage of the capacitor C43 charged by the APC1 is input to the input 2 of the multiplier 122. As a result, as the output voltage of the multiplier 120, a voltage corresponding to the fluctuation from the offset output voltage serving as a reference can be input to the input 2 of the multiplier 122.

The multiplier 122 multiplies the input voltage input to the input 2 by the correction data Y (= f) input to the input 1. Due to this multiplication result (that is, the multiplication result of the two multipliers 120 and 122), the control voltage of the current source CS is shifted by changing the potential at the point E. As a result, the drive current value supplied to the laser LD changes. To do. Due to the change in the drive current value, the output light amount of the laser LD changes and is fed back via the comparator COMP.
At the end of APC2, the capacitor C41 is charged with the control voltage of the current source CS for causing the laser LD to emit light with the second light amount Lff. When APC2 ends, the switch SW51 is turned off.

  Therefore, after execution of APC1 and APC2, the capacitor C41 is charged with Lff, and the capacitor C42 is charged with a control voltage corresponding to L00. The capacitor C3 is charged with a control voltage corresponding to L00 with reference to the offset output voltage of the multiplier 122, and the capacitor C43 is charged with the offset output voltage of the multiplier 120.

Therefore, a voltage (this voltage corresponds to the output control amount Z) corresponding to (Lff−L00) shown in the equation (1) is input to the input 2 of the multiplier 120. Therefore, the multipliers 120 and 122 Multiplication of αx × αy × (Lff−L00) is performed.
At the time of image recording, the correction data αx and αy corresponding to the scanning position are sequentially output from the controller 108, and if the switch SW10 is turned on / off based on the image data, the multipliers 120 and 122 allow the αx × αy × (Lff -L00) is multiplied, and the control voltage of the current source CS is shifted from the control voltage corresponding to L00 charged in the capacitor C3 by the multiplication result. That is, based on the correction data in the main scanning direction and the sub-scanning direction, the correction amount is calculated in a directly proportional relationship, the control voltage of the current source CS is corrected by the correction amount, and the drive current value of the laser LD changes. To do. As a result, the drive current value supplied from the current source CS to the laser LD is corrected so that the amount of light shown in Expression (1) is obtained, and the light source driving device 100 corrects the light quantity according to Expression (1). The laser LD can be turned on / off based on the image data.

(Example 2)
First, as Example 2, the operation of the light source driving apparatus adopting the multiplication method 2 will be specifically described. FIG. 8 shows an analog circuit configuration example of the light source driving device in this case. Hereinafter, the operation of this analog circuit will be described based on the symbols shown in the figure. In FIG. 8, the same members as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  First, in order to execute APC1, as in the first embodiment, the switches SW10 and SW11 are turned on and the correction data αx and αy = 0. At this time, when the reset signal is turned ON, the switches SW51 to SW52 are turned ON, and the multiplier 122 is calibrated simultaneously with APC1.

  The correction data αy is input to the D / A converter DAC1 via the D / A converter DAC2 and the low pass filter 110B. The correction data αx is also input to the D / A converter DAC1, where multiplication of the correction data αx and the correction data Y and analog signal conversion are performed. This output is input to the input 1 of the multiplier 122 via the low-pass filter 110B. At this time, since the correction data αx and αy = 0, that is, X and Y = 0, the operation of the multiplier 122 is as follows. Can be ignored. However, the output of the multiplier 122 does not actually become 0, and an offset output voltage exists.

  Further, when the switches SW10 and SW11 are turned on, a drive current is supplied from the current source CS to the laser LD, and the laser LD is turned on. Then, the output light amount of the laser LD is detected by the photodiode PD, and a voltage corresponding to the detected light amount is compared with the reference light amount Vref in the comparator COMP. In accordance with the comparison result, the capacitor C3 is charged with the offset output voltage of the multiplier 122 as a reference. At this time, since the switches SW51 and SW52 are ON, the capacitors C41 and C42 are similarly charged.

  Finally, at the end of APC1, the capacitor C3 is charged with the control voltage of the current source CS for causing the laser LD to emit light with the reference light amount L00 with reference to the offset output voltage of the multiplier 122, and the capacitor C41, C42 is also charged with the same voltage as this control voltage. When APC1 ends, the switch SW11 is turned off, and the switches SW51 to SW52 are also turned off when the reset signal is turned off.

  Next, in order to execute APC2, the switches SW10 and SW51 are turned on (the switch SW52 is turned off), and the correction data αx and αy = f are set.

  The correction data αy becomes correction data Y via the D / A converter DAC2 and the low-pass filter 110B, is input to the D / A converter DAC1, is multiplied by the correction data αx, and the result is output as an analog signal. Through the low-pass filter 110A, an X × Y multiplication result is input to the input 1 of the multiplier 122. That is, the difference from the first embodiment is that the D / A converter DAC1 for the main scanning direction varies the dynamic range according to the correction data Y, that is, the function of the multiplier 120 is provided.

Further, when the switch SW10 is turned on, a drive current is supplied from the current source CS to the laser LD, and the laser LD is turned on. Then, the output light amount of the laser LD is detected by the photodiode PD, and the comparator COMP compares the voltage corresponding to the detected light amount with the second reference light amount (maximum light amount) Vref2. Since the switch SW51 is ON, the capacitor C41 is charged according to the comparison result.
Therefore, the difference voltage between the charging voltage of the capacitor C41 and the charging voltage of the capacitor C42 charged by the APC1 is input to the input 2 of the multiplier 122. The multiplier 120 multiplies the difference voltage by the input voltage of the input 1 (= X × Y = f × f), and the control voltage of the current source CS is changed by changing the potential at the point E according to the multiplication result. As a result, the drive current value supplied to the laser LD changes. Due to the change in the drive current value, the output light amount of the laser LD changes and is fed back via the comparator COMP. At the end of APC2, the capacitor C41 is charged with the control voltage of the current source CS for causing the laser LD to emit light with the second light amount Lff. When APC2 ends, the switch SW51 is turned off.
Therefore, after execution of APC1 and APC2, the capacitor C41 is charged with Lff, and the capacitor C42 is charged with a control voltage corresponding to L00. The capacitor C3 is charged with a control voltage corresponding to L00.

  Therefore, a voltage corresponding to (Lff−L00) shown in Expression (1) (this voltage corresponds to the output control amount Z) is input to the input 2 of the multiplier 122. Multiplication of αx × αy × (Lff−L00) is possible by the D / A converter DAC1 including the multiplier 122 and the multiplier 122.

  At the time of image recording, if the correction data αx and αy corresponding to the scanning position are output from the controller and the switch SW10 is turned on / off based on the image data, the main scanning direction and the sub-scanning direction are the same as in the first embodiment. Based on the correction data, the correction amount is calculated in a directly proportional relationship, the control voltage of the current source CS is corrected, and the drive current value of the laser LD changes. As a result, the drive current value supplied from the current source CS to the laser LD is corrected so that the amount of light shown in Expression (1) is obtained, and the light source driving device 100 corrects the amount of light according to Expression (1). The laser LD can be turned on / off based on the image data.

  As described above, in any of the first and second embodiments, the light amount correction of the laser LD can be performed to eliminate the uneven light amount based on the correction data in the main scanning direction and the sub scanning direction. At this time, the correction data in the main scanning direction and the sub-scanning direction are used for multiplication for obtaining the correction amount after passing through the dedicated low-pass filters 110A and 110B, respectively. (Step-like unevenness in the amount of light that occurs when correction data fluctuates) does not occur.

  In the above description, the present invention is applied to a light source driving device having a function (light amount correction unit 106) that performs light amount correction by correcting a drive current value supplied to the laser LD based on correction data. The invention is not limited to this. The present invention can also be applied to a light source driving device having a function of correcting the amount of light by correcting the ON / OFF duty of the laser LD.

It is a block diagram which shows the basic composition of the light source drive device which concerns on embodiment of this invention. It is a block diagram which shows the internal structure of the light quantity correction | amendment part which multiplies by the multiplication method 1. FIG. It is a block diagram which shows the internal structure of the light quantity correction | amendment part which multiplies by the multiplication method 2. FIG. It is a block diagram which shows the internal structure of the light quantity correction | amendment part which multiplies by the multiplication method 2, when using a several laser as a light source. It is a flowchart which shows the basic operation | movement of the light source drive device which concerns on embodiment of this invention. (A), (B) is a graph for demonstrating two-dimensional light quantity correction | amendment. 1 is a circuit diagram illustrating a detailed configuration example of a light source driving device when a multiplication method 1 is employed (Example 1). FIG. (Example 2) which is a circuit diagram which shows the detailed structural example of the light source drive device at the time of employ | adopting the multiplication method 2. FIG. 1 is a diagram illustrating a general configuration of an image recording apparatus. It is a block diagram which shows the structure for performing the conventional light quantity nonuniformity correction | amendment. It is a block diagram which shows the structure for inputting two-dimensional correction data and performing light quantity correction | amendment similar to a main scanning direction also about a subscanning direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Light source drive device 102 Drive part 104 Light quantity control part (Light quantity control means)
106 Light quantity correction unit (light quantity correction means)
108 Controller 110A Low-pass filter (first smoothing means)
110B low-pass filter (second smoothing means)
120 multiplier (first multiplication means)
122 multiplier (second multiplication means)
LD laser

Claims (6)

Based on image data, a light beam emitted from a light source is main-scanned, an electrostatic latent image is formed on an image carrier that is relatively moved in a sub-scanning direction that is orthogonal to the main scanning, and then developed. A light beam emission control device that is used in an image forming apparatus that forms an image by transferring an image onto a recording medium and controls light emission of a light beam emitted from the light source,
A light amount control means for performing light amount control of the light source so as to have a predetermined output light amount determined in advance;
First correction data for correcting light amount unevenness in the main scanning direction when an image is formed on the image carrier and second correction data for correcting light amount unevenness in the sub-scanning direction are input and input. A light amount correction unit that corrects an output light amount of the light source after the light amount control by the light amount control unit, based on the first correction data and the second correction data.
First smoothing means for smoothing the first correction data used for correction by the light quantity correction means;
Second smoothing means for smoothing the second correction data used for correction by the light quantity correction means;
A light beam emission control device comprising:   2. The light amount correction unit according to claim 1, wherein the control amount obtained by the light amount control of the light amount control unit is multiplied by the first correction data and the second correction data to obtain a correction amount. The light beam emission control device described. The light amount correction means is
First multiplying means for multiplying the control amount by the first correction data or the second correction data;
Second multiplication means for multiplying the multiplication result by the first multiplication means and the second correction data or the first correction data;
The light beam emission control device according to claim 2, further comprising: The light amount correction means is
First multiplication means for multiplying the first correction data and the second correction data;
Second multiplication means for multiplying the multiplication result by the first multiplication means and the control amount;
The light beam emission control device according to claim 2, further comprising:   5. The light beam emission control device according to claim 2, wherein the multiplication unit included in the light amount correction unit performs the multiplication by analog data processing. 6. 6. The light beam emission control device according to claim 5, wherein the multiplication unit included in the light amount correction unit has a function of executing calibration at a predetermined timing.

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