JP2013148668A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner able to set quantities of beam light emitted from a light source such that the quantities have appropriate values when detecting a writing position on a target scan surface in a main scanning direction and when starting the scanning of the target scan surface in the main scanning direction.SOLUTION: An optical scanner comprises: an SOS sensor configured to receive at a predetermine position beam light deflected by a polygon mirror 14 and to output an SOS signal used as a reference signal when the writing timing in the main scanning direction of the target scan surface of a photoreceptor drum 60 is set; and a control circuit 51 configured to control a driving section 70 provided to drive a light source such that a quantity of beam light is equal to a first quantity of light when an SOS sensor 18 is caused to receive beam light and output an SOS sensor and to control the driving section 70 such that until a predetermined time passes after the SOS signal is input from the SOS sensor 18, a quantity of beam light when scanning in the main scanning direction of the scanned surface is started is equal to a second quantity of light, which differs in value according to each position in the sub-scanning direction of the scanned surface.

Description

  The present invention relates to an optical scanning device.

  Some optical scanning devices use a so-called surface emitting laser that emits a plurality of beams from a plurality of light emitting points as a light source. In an optical scanning device equipped with this surface emitting laser, the reflectivity of the mirror that folds the beam emitted from the surface emitting laser and makes it incident on the scanned surface of the photosensitive drum varies depending on the polarization direction of the beam. There is a problem that the amount of light when the surface to be scanned is scanned in the main scanning direction differs for each beam. For this reason, image defects such as uneven density and horizontal stripes occur in the main scanning direction of the formed image. It is also known that uneven density occurs due to uneven charging or dirt on the photosensitive drum in the sub-scanning direction.

Japanese Patent Application Laid-Open No. 2004-133620 discloses an open loop control that corrects a light amount variation caused by a scanning optical system.
Patent Document 2 discloses a configuration for switching the laser emission output, because if the sensitivity of the photoconductor is different for each product, even if the laser emission output is controlled to be constant, the drawing density varies among the products. (0003 paragraph)

Japanese Patent No. 3840794 Japanese Patent No. 3231436

  According to the present invention, when detecting the writing position in the main scanning direction of the surface to be scanned of the image carrier and starting scanning in the main scanning direction of the surface to be scanned, the light amount of the light beam of the light source is appropriately set. An object of the present invention is to provide an optical scanning device capable of controlling a drive unit that drives a light source so as to have a small value.

  In order to achieve this object, an optical scanning device of the present invention deflects a light source having a plurality of light emitting points and a plurality of light beams emitted from the light source in the main scanning direction of the surface to be scanned of the image carrier. And a detecting means for receiving the beam light deflected by the deflecting means at a predetermined position and outputting a synchronization detection signal that serves as a reference signal for setting the writing timing of the surface to be scanned in the main scanning direction. When the detection means receives the light beam and outputs the synchronization detection signal, the driving unit that drives the light source is controlled so that the light amount of the beam light becomes the first light amount, and the synchronization detection signal is The amount of beam light when starting scanning in the main scanning direction of the surface to be scanned is the position in the sub-scanning direction of the surface to be scanned after a predetermined time elapses after input from the detection means. With different amount of light for each And control means for controlling the driving unit such that the second light quantity that.

  In the optical scanning device, a storage means for storing correction data for correcting the light amount of the beam light at the plurality of light emitting points for each of the main scanning direction and the sub-scanning direction of the surface to be scanned, and a clock signal A clock signal to be output to a counter that counts the number of clocks is selected from the first clock signal and the second clock signal, and correction data in the main scanning direction and the sub-scanning direction are respectively stored from the storage means. The control means for outputting an up signal for instructing up-counting or a down signal for instructing down-counting to the counter according to read and read correction data, and a first clock signal output from the control means Alternatively, the second clock signal is up-counted or down-counted according to the up signal or the down signal. And a digital-analog conversion means for inputting a count value of the counter and outputting a correction instruction signal for correcting the amount of light emitted from the light emitting point to a drive unit for driving the light source in accordance with the input count value. The control means includes a second control signal to the counter from the second clock signal during a period from when the synchronization detection signal is input from the detection means to when scanning in the main scanning direction of the surface to be scanned is started. When a first clock signal having a high frequency is output and scanning of the surface to be scanned in the main scanning direction is started, the second clock signal is output to the counter.

  According to the first aspect of the present invention, the beam light of the light source is detected when the writing position in the main scanning direction of the surface to be scanned of the image carrier is detected and when scanning in the main scanning direction of the surface to be scanned is started. It is possible to control the drive unit that drives the light source so that the respective light amounts become appropriate values.

  According to the second aspect of the present invention, even when the digital-analog conversion means is used as the means for outputting the correction instruction signal for correcting the light emission amount of the light emitting point to the driving unit of the light source, the synchronization detection signal is generated. When outputting to the detection means, the light amount of the light emitting point is controlled to the first light amount, and when starting the scanning of the surface to be scanned in the main scanning direction, the light amount of the light emitting point is controlled to the second light amount. Can do.

(A) is a plan view of the optical scanning device, and (B) is a diagram showing an XX cross-sectional view of the optical scanning device and a photosensitive drum that is irradiated with laser light L from the optical scanning device. It is a figure for demonstrating the several light emitting element with which VCSEL is provided. It is a figure which shows an example of a structure of a VCSEL driver. It is a figure which shows an example of a structure of a correction | amendment control voltage generation part. (A) shows the main scanning direction and the sub-scanning direction of the surface to be scanned of the photosensitive drum, and (B) shows the change in the amount of light between A-B and C-D shown in (A). It is a figure which shows an example. It is a figure which shows a mode that the optical scanning apparatus is equipped with the light quantity correction data of a subscanning direction for every line from which the position of a subscanning direction differs. It is a figure for demonstrating operation | movement with a control part and a correction | amendment control voltage generation part. It is a flowchart explaining the operation | movement procedure of an optical scanning device.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. First, the configuration of the embodiment will be described with reference to FIG. 1A shows a plan view of the optical scanning device 10 to which the present invention is applied, and FIG. 1B shows an XX sectional view of the optical scanning device 10 and a laser beam L from the optical scanning device 10. 2 shows a photosensitive drum 60 that receives the irradiation of.

  The optical scanning device 10 is referred to as a surface emitting laser (hereinafter referred to as VCSEL (Vertical Cavity Surface Emitting LASER)) in which a plurality of light emitting elements (light emitting points) forming a minute spot diameter are two-dimensionally arranged in a plane as a laser light source. ) 11. The VCSEL 11 is disposed in the housing 20 together with the scanning optical system. The optical scanning device 10 includes, as a scanning optical system, a collimator lens 12, a cylindrical lens 13, a rotary polygon mirror (polygon mirror) 14 (corresponding to the deflecting means of the present invention) formed with a regular hexahedron, an fθ lens 15, and a cylindrical lens. A mirror 16, a reflection mirror 17, and an SOS (Start Of Scan) sensor (corresponding to the detection means of the present invention) 18 are provided.

  The divergent laser light L emitted from the VCSEL 11 is converted into parallel light by the collimator lens 12. The laser light L converted into parallel light is imaged as a long line image in the main scanning direction in the vicinity of the deflection reflection surface 14a of the polygon mirror 14 by the cylindrical lens 13 having refractive power only in the sub-scanning direction. The laser beam L is reflected by the deflecting / reflecting surface 14a of the polygon mirror 14 that rotates at a high speed at a constant speed, and is scanned counterclockwise (in the direction of the arrow C) at an equal angular velocity.

  The laser light L passes through the fθ lens 15 and then enters the cylindrical mirror 16. The cylindrical mirror 16 has refractive power only in the sub-scanning direction, and the laser light L that has passed through the fθ lens 15 has a cylindrical shape so that the imaging position in the sub-scanning direction coincides with the outer peripheral surface of the photosensitive drum 60. Reflected by the mirror 16. Then, the surface of the photosensitive drum 60 is exposed by scanning exposure by irradiating the outer peripheral surface of the photosensitive drum 60 from the exposure port 19 formed in the housing 20.

  The fθ lens 15 has a function of equalizing the scanning speed of the light spot of the laser light L. Further, the above-described line image is formed in the vicinity of the deflecting / reflecting surface 14a of the polygon mirror 14, and the fθ lens 15 causes a light spot on the surface of the photosensitive drum 60 with the deflecting / reflecting surface 14a as an object point in the sub-scanning direction. Since the image is formed, this scanning optical system has a function of correcting the surface tilt of the deflecting / reflecting surface 14a. Furthermore, the cylindrical mirror 16 also has a surface tilt correction function that conjugates the outer peripheral surfaces of the polygon mirror 14 and the photosensitive drum 60 in the sub-scanning direction.

  The laser light L is incident on the SOS sensor 18 via the reflection mirror 17 prior to scanning exposure on the surface of the photosensitive drum 60. In other words, the first laser beam L of each scanning line is incident on the SOS sensor 18 every time the laser beam L performs main scanning on the surface of the photosensitive drum 60. The SOS sensor 18 detects the irradiation timing for each scanning line on the surface of the photosensitive drum 60 and generates a signal (hereinafter referred to as an SOS signal) indicating the irradiation start timing in the main scanning direction. The SOS sensor 18 outputs the generated SOS signal to the control unit 50.

Further, a VCSEL driver 30 that controls driving of the VCSEL 11 is connected to the VCSEL 11. The VCSEL driver 30 is input with various control signals such as image data for writing output from the image processing unit 40 and a light amount instruction and a light amount control execution instruction output from the control unit 50.
At the time of image formation, the VCSEL driver 30 outputs a drive signal to the VCSEL 11 according to the control signal input from the control unit 50 and the image data for writing input from the image processing unit 40, and controls turning on / off of each light emitting element.

  Further, the VCSEL driver 30 controls the light quantity of the VCSEL 11 so that the light quantity of each light emitting element of the VCSEL 11 is constant and does not vary. During this light amount control, the control unit 50 outputs to the VCSEL driver 30 a signal that instructs lighting of one of the light emitting elements of the VCSEL 11 and a signal that instructs execution of the light amount control as control signals. The VCSEL driver 30 detects the light quantity of the laser light by the photodetector 101 shown in FIG. 3 in a state where the corresponding light emitting element is turned on according to the control signal. The VCSEL driver 30 supplies the corresponding light emitting element so that the signal of the voltage corresponding to the light amount of the laser light output from the photodetector 101 and the signal of the reference voltage indicating the light amount of the laser light substantially coincide with each other. The drive current value to be adjusted is adjusted. The reference voltage is a voltage for instructing the amount of laser light when setting the reference image density. By performing this operation for all the light emitting elements, the output light amount of all the light emitting elements can be controlled. The VCSEL driver 30 holds the adjusted drive current value after the light amount control, and supplies the adjusted drive current value to the light emitting element at the time of lighting.

Next, the VCSEL 11 will be described with reference to FIG.
The VCSEL 11 has a plurality of light emitting elements (light emitting points) arranged two-dimensionally in a plane and can output a plurality of laser beams simultaneously. In this embodiment, the number of light emitting elements is 32, but the number of light emitting elements is not limited to 32. The optical scanning device 10 can simultaneously scan a plurality of laser beams L by using such a VCSEL 11 as a light source.

Next, a schematic configuration of the VCSEL driver 30 will be described with reference to FIG. FIG. 3 shows a schematic configuration of the VCSEL driver 30.
A photodetector 101 is provided in the vicinity of a plurality of light emitting elements LD1 to LD32 (hereinafter simply referred to as LD when it is not necessary to distinguish each light emitting element) provided in the VCSEL 11. One photodetector 101 is provided for a plurality of light emitting elements LD. The photodetector 101 includes a photoelectric conversion element that detects the amount of light beam emitted from the light emitting element LD and converts it into an electrical signal. For this reason, the output of the photodetector 101 has a voltage value corresponding to the amount of light emitted from the light emitting element LD.

  The output signal line 102 of the photodetector 101 is connected to the inverting input terminal of the differential amplifier 104 via a current-voltage conversion circuit (I / V) 103. A reference value (reference voltage Vref) 105 is input to the non-inverting input terminal of the differential amplifier 104. A reference voltage and a detection voltage are input to the differential amplifier 104, and the differential amplifier 104 outputs a voltage (hereinafter referred to as a control voltage) such that the difference between the two is zero. The control voltage output from the differential amplifier 104 is input to the drive unit 70. Thirty-two driving units 70 are provided corresponding to the respective light emitting elements LD1 to LD32. In order to distinguish each driving unit 70, the driving unit 70 corresponding to LD1 is referred to as a driving unit 70 (1), and the driving unit 70 corresponding to LD2 is referred to as a driving unit 70 (2). Similarly, the other drive units 70 are expressed as drive units 70 (3),..., Drive unit 70 (32). Moreover, since each drive part 70 (1)-(32) is provided with the same structure, in the following description, the drive part 70 (1) is demonstrated as a representative.

  The drive unit 70 (1) includes a control voltage superimposing unit 71 (1), a sample hold capacitor 72 (1), and a driver 73 (1). The output terminals of the differential amplifier 104 are control voltage superimposing units 71 (1), 71 (2) provided in the driving units 70 (1), 70 (2),. .., connected to 71 (32). The aforementioned control voltage is held in the sample-and-hold capacitor 72 (1) as holding means via the control voltage superimposing unit 71 (1). Based on the control voltage held in the sample-and-hold capacitor 72 (1), the light emitting element LD () is generated based on the voltage generated in the voltage source in the driver 73 (1) and the current (drive current) generated in the current source. 1) emits light.

For example, when the light emission amount of the light emitting element LD is small, the detection voltage input to the differential amplifier 104 is low, and the reference voltage is higher. As the output of the differential amplifier 104, a voltage obtained by increasing a voltage corresponding to this voltage difference is output, which becomes a control voltage at the time of light emission of the light emitting element LD, and the light amount of the light emitting element LD increases.
Conversely, when the amount of light emitted from the light emitting element LD is large, the detection voltage input to the differential amplifier 104 is high, and the reference voltage is lower. As the output of the differential amplifier 104, a voltage obtained by reducing a voltage corresponding to this voltage difference is output, which becomes a control voltage at the time of light emission of the light emitting element LD, and the light amount of the light emitting element LD decreases.

  In addition, a correction control voltage for correcting the above-described control voltage is input to the control voltage superimposing unit 71 (1) of the driving unit 70. The correction control voltage is generated by the correction control voltage generator 80. The control voltage superimposing unit 71 (1) superimposes the correction control voltage output from the correction control voltage generating unit 80 on the control voltage output from the differential amplifier 104. The control voltage on which the correction control voltage is superimposed by the control voltage superimposing unit 71 (1) is held in the sample hold capacitor 72 (1).

  Thirty-two correction control voltage generation units 80 are also provided corresponding to the light emitting elements LD1 to LD32 and the driving units 70 (1) to 70 (32). The correction control voltage generation unit 80 is also expressed as correction control voltage generation units 80 (1), 80 (2),..., 80 (32) in order to distinguish each correction control voltage generation unit 80. 3 shows a configuration in which 32 correction control voltage generation units 80 are provided in association with the drive units 70 (1) to 70 (32). However, the correction control voltage generation unit 80 is provided with the drive unit 70. One (1) to 70 (32) may be provided, and one correction control voltage generation unit 80 may output the correction control voltage to each of the drive units 70 (1) to 70 (32).

Next, the correction control voltage generation unit 80 (1) and the control unit 50 that controls the correction control voltage generation unit 80 (1) will be described with reference to FIG. The other correction control voltage generation units 80 (2) to 80 (32) have the same configuration as the correction control voltage generation unit 80 (1), and are similar to the correction control voltage generation unit 80 (1) from the control unit 50. Therefore, the description of the correction control voltage generation unit 80 (1) is replaced with the description of the other correction control voltage generation units 80 (2) to 80 (32).
The control unit 50 includes a control circuit 51 and a storage unit 52. The control circuit 51 includes a CPU (Central Processing Unit), a ROM (Read Only Memory) (both not shown) and the like, and the CPU performs data processing according to a program recorded in the ROM, whereby the correction control voltage generator 80, The operation of the drive unit 70 is controlled. The storage unit 52 includes, for example, a memory such as a RAM (Random Access Memory) or a hard disk device.

The storage unit 52 corrects the density unevenness in the main scanning direction, which is obtained based on the density unevenness that occurs in the main scanning direction, and the sub-scanning direction that is obtained based on the density unevenness that occurs in the subscanning direction. It stores correction data for correcting density unevenness. The correction data is light amount data necessary for correcting density unevenness or control voltage (current) data for obtaining a light amount output.
Here, density unevenness in the main scanning direction will be described with reference to FIG. 5A shows the main scanning direction and the sub-scanning direction of the surface to be scanned of the photosensitive drum 60, and FIG. 5B shows the section between A and B shown in FIG. 5A. , An example of the change of the light quantity between C-D is shown.

The density unevenness generated in the main scanning direction is unevenness mainly caused by the characteristics of the optical system. Therefore, the density unevenness in the main scanning direction that occurs between A and B parallel to the main scanning direction shown in FIG. 5A and the density unevenness in the main scanning direction that similarly occurs between CDs parallel to the main scanning direction are shown. As shown in FIG. 5B, they are almost the same. Therefore, the correction data for correcting the density unevenness in the main scanning direction is different for each line in the main scanning direction (for example, the line between AB and the line between CD shown in FIG. 5A). The same correction data can be used for each line in the main scanning direction.
When only density correction in the main scanning direction is performed, the light amount of the light emitting element LD at the writing position in the main scanning direction may be always set to the same value. Normally, it is sufficient to set a reference light amount at the time of initial APC (auto power control) (APC will be described later) operation, that is, a light amount for setting a reference image density (referred to as 100% light amount). This is because, as described above, the density unevenness in the main scanning direction caused by the characteristics of the optical system causes the same density unevenness in each line in the main scanning direction.

  Next, correction data for correcting density unevenness in the sub-scanning direction will be described. The uneven density in the sub-scanning direction is caused by uneven charging or dirt on the photosensitive drum 60, unevenness of the developer generated on the conveying member that conveys the developer to the developing position on the photosensitive drum 60, and the like. Therefore, the same density unevenness does not occur in each line in the main scanning direction unlike the density unevenness in the main scanning direction, and density unevenness correction in the sub-scanning direction is performed in addition to correction of density unevenness in the main scanning direction. For this purpose, as shown in FIG. 6, it is necessary to provide correction data for each position (each line) in the sub-scanning direction. FIG. 6 shows how correction data 1 to 10 in the sub-scanning direction are prepared for each position in a different sub-scanning direction. Each of the correction data 1 to 10 in the sub-scanning direction has correction data for correcting the light amount of the light emitting element LD for each position in the main scanning direction.

Returning to FIG. 4, the controller 50 and the correction control voltage generator 80 (1) will be described.
The control circuit 51 outputs a SOS signal output from the SOS sensor 18, a first clock signal (also referred to as CLK1) supplied from, for example, an image forming apparatus as a host device on which the optical scanning device 10 is mounted, A 2-clock signal (also expressed as CLK2) is input. The SOS signal is a signal indicating the irradiation start timing of the laser light L in the main scanning direction on the surface to be scanned, and the laser in the main scanning direction after a predetermined time T has elapsed after the control circuit 51 inputs the SOS signal. Irradiation with light L is started.

  The control circuit 51 selects the first clock signal (hereinafter referred to as CLK1) input from the host device for a predetermined time T (see FIG. 7) after inputting the SOS signal, and selects CLK1 as the selected clock ( Hereinafter, it is output to the up / down counter 81 as “selected CLK”. Further, when a predetermined time T elapses after the input of the SOS signal, the control circuit 51 selects CLK2 instead of CLK1, and outputs the selected CLK2 to the up / down counter 81 as the selected CLK. Furthermore, the control circuit 51 stops outputting the selected CLK to the up / down counter 81 when a predetermined time W (see FIG. 7) has elapsed since the SOS signal was input. Then, the control circuit 51 outputs a reset signal for resetting the counter of the up / down counter 81 to the up / down counter 81.

  In addition, the control circuit 51 reads the correction data in the main scanning direction and the correction data in the sub-scanning direction from the storage unit 52, and increases the correction control voltage to a voltage corresponding to the correction data read from the storage unit 52. Outputs an up signal or a down signal to the down counter 81. The light amount of the light emitting element LD at the image writing position in the main scanning direction is set to a light amount considering density unevenness in the sub scanning direction.

  The correction control voltage generation unit 80 (1) includes an up / down counter 81, a D / A (digital-analog) converter 82, and a filter unit 85. The filter unit 85 includes a resistor 86, a switch 87, and a capacitor 88.

  The up / down counter 81 receives the selection CLK output from the control circuit 51, a reset signal, and an up signal or a down signal. The up / down counter 81 includes a counter. When the signal input from the control circuit 51 is an up signal, the up / down counter 81 counts up the counter in synchronization with the selected CLK. The up / down counter 81 counts down the counter in synchronization with the selected CLK signal when the signal input from the control circuit 51 is a down signal. The up / down counter 81 outputs the count value of the counter to the D / A converter 82.

  The D / A converter 82 converts the digital count value output from the up / down counter 81 into an analog signal. The D / A converter 82 outputs the count value converted into the analog signal to the subsequent filter unit 85.

The filter unit 85 is a filter for removing high frequency noise generated when the output of the D / A converter 82 is switched. The high frequency noise is superimposed on a signal or the like for correcting the light amount of the light emitting element LD, and thus causes uneven density.
As shown in FIG. 4, the filter unit 85 includes a low-pass filter having a resistor 86 and a capacitor 88. The correction control voltage filtered by the filter unit 85 is output to each of the drive units 70 (1) to 70 (32). In addition, the filter unit 85 is provided with a switch 87 that switches on and off the low-pass filter during APC control (APC control will be described later). The switch 87 is turned on / off by a switching signal output from the control circuit 51. That is, during APC control, the switch 87 is controlled to be off so that the filter unit 85 is invalid, and when it is not APC control, the switch 87 is controlled to be on so that the filter unit 85 is valid. The signal line connecting the control circuit 51 and the switch 87 is not shown.

The control of the correction control voltage generation unit 80 by the control circuit 51 will be described in more detail with reference to FIG. In addition, since the following control is control applied to all the correction control voltage generation parts 80 (1) -80 (32), it describes with the correction control voltage generation part 80. FIG.
The control circuit 51 determines the detection of the writing position in the main scanning direction of the surface to be scanned of the photosensitive drum 60 based on the SOS signal output from the SOS sensor 18. For example, the writing of image data in the main scanning direction is started 10 μsec after the control circuit 51 inputs the SOS signal. However, the sensitivity and responsiveness of the SOS sensor 18 change when the amount of light input to the SOS sensor 18 changes. Since the SOS signal output from the SOS sensor 18 is an analog signal, if the sensitivity or responsiveness of the SOS sensor 18 changes, the rise or fall of the SOS signal may be slow, or the output timing of the SOS signal may be shifted. There is also a case. Therefore, if the light amount of the light emitting element LD for detecting the writing position in the main scanning direction on the surface to be scanned is changed, there may be a case where an accurate SOS signal cannot be supplied to the control circuit 51. For this reason, when detecting the writing position in the main scanning direction of the surface to be scanned, it is necessary to always set the light amount of the light emitting element LD to the same light amount, for example, the above-mentioned 100% light amount (the first light amount of the present invention). is there.

  Further, since the writing of image data in the main scanning direction of the surface to be scanned is started after a predetermined time T (for example, 10 μsec) after the control circuit 51 inputs the SOS signal, the predetermined time after the SOS signal is output. During T, it is necessary to set the light amount of the light emitting element LD to a correction light amount (hereinafter referred to as a second light amount) according to correction data in the sub-scanning direction. That is, when only the density correction in the main scanning direction is performed, it is sufficient to always set the light amount of the light emitting element LD to 100% at the writing position of each line in the main scanning direction. However, when the light amount correction in the sub-scanning direction is performed, as described above, the light amount of the light emitting element LD must be set to a different second light amount for each line writing position in the main scanning direction.

  The current value of the drive current of the light emitting element LD is raised or lowered by the D / A converter 82 based on the count value of the up / down counter 81. That is, the D / A converter 82 changes the correction control voltage based on the selection CLK, the up signal, and the down signal output from the control circuit 51. If the D / A converter 82 is operated with a clock that is too fast, noise called glitch is generated. Therefore, the output of the D / A converter 82 is controlled to change stepwise with a clock of about 1 MHz. ing. That is, the circuits (correction control voltage generation units 80 (1) to 80 (32)) that correct the light amount of the light emitting element in the image area of the photosensitive drum 60 (the area where the image is written) do not get noise. It is designed to move slowly and is not intended to move quickly. Nevertheless, when the light amount correction in the sub-scanning direction is performed, the light amount of the light emitting element LD may have to be changed instantaneously for a predetermined time T after the control circuit 51 inputs the SOS signal. . For this reason, if the light quantity of the light emitting element LD is set from 100% light quantity (first light quantity of the present invention) to the second light quantity using a clock used for image writing, the D / A converter The operation of 82 is not in time. That is, the light amount of the light emitting element LD may not be switched from the 100% light amount to the second light amount during a predetermined time T (for example, 10 μsec). For example, assuming that the period from the input of the SOS signal by the control circuit 51 to the start of image writing in the main scanning direction is 10 μsec and the clock frequency is 1 MHz, only 0.15% at 1 clock and 1.5% at 10 μsec. The light quantity of the light emitting element LD cannot be changed. However, the light amount correction in the sub-scanning direction may be corrected in units of 10% and 20%.

Therefore, when the SOS signal output from the SOS sensor 18 is input to the control circuit 51 (timing (a) shown in FIG. 7), CLK1 is selected as the selected CLK for a predetermined time T after the input of the SOS signal. Output to the down counter 81. The predetermined time T is the time from when the SOS signal is output from the SOS sensor 18 until the start of image writing based on the image data in the image area of the photosensitive drum 60. Note that the frequency of CLK1 is set to 20 MHz in this embodiment. During the period from the input of the SOS signal to the writing of the image in the main scanning direction, the writing of the image to the image area of the photosensitive drum 60 is not performed, so the D / A converter 82 with a high-speed clock of 20 MHz. Even if is operated, the image is not affected. For example, if the predetermined period T is 10 μsec and the clock frequency is 20 MHz, the light amount of the light emitting element LD can be changed by 30% during 10 μsec.
Further, the control circuit 51 outputs CLK1 as the selected CLK to the up / down counter 81 and outputs an up signal or a down signal to the up / down counter 81 according to the amount of light at the line writing position in the main scanning direction. . That is, if the light amount at the writing start position of the line in the main scanning direction is lower than 100% light amount, a down signal is output to the up / down counter 81, and if it is higher than 100% light amount, the up signal is output to the up / down counter 81. Output.

  When a predetermined time T has elapsed since the input of the SOS signal (timing (b) shown in FIG. 7), the control circuit 51 selects CLK2 instead of CLK1, and uses the selected CLK2 as the selected CLK, and the up / down counter 81 Output to. CLK2 is a clock used when an image is written in the image area of the photosensitive drum 60, and the frequency is set to 1 MHz so that the above-mentioned glitch noise does not occur. Further, the control circuit 51 stops outputting the selected CLK to the up / down counter 81 when a predetermined time W has elapsed since the SOS signal was input (timing (c) shown in FIG. 7). Then, the control circuit 51 outputs a reset signal for resetting the counter of the up / down counter 81 to the up / down counter 81 (timing (c) shown in FIG. 7). By resetting the counter of the up / down counter 81, the light amount of the light emitting element LD is reset to 100%.

As described above, in this embodiment, when the SOS sensor 18 receives the laser light of the light emitting element LD and outputs the SOS signal, the light amount of the light emitting element LD is set to 100%, and the main scanning direction of the surface to be scanned is set. When starting this scanning, the light amount of the light emitting element LD can be set to a light amount having a different value for each position in the sub-scanning direction. Therefore, it is possible to set the light amount of the light emitting element LD to be an appropriate value.
Even when the driving unit 70 uses the D / A converter 82 as means for outputting a correction control signal for correcting the light amount of the light emitting element LD, the SOS signal is output to the SOS sensor 18. Controls the light amount of the light emitting element LD to 100% light amount, and when starting the scanning of the surface to be scanned in the main scanning direction, the light amount of the light emitting element LD is different in light amount for each position in the sub scanning direction. Can be controlled.

Here, APC will be described.
The APC of the optical scanning device includes “initial APC” performed during a predetermined period before image formation and “line APC” performed for each scan. “Initial APC” is performed to control the light amount of each beam to the required light amount, and “Line APC” is performed to maintain the light amount.
The initial APC is a mode that is executed when the image forming apparatus is started up or after a print instruction, and each of LD1 to LD32 is turned on in time series, and the light quantity of the laser light is detected by the photodetector 101 shown in FIG. To do. The VCSEL driver 30 supplies the corresponding light emitting element so that the signal of the voltage corresponding to the light amount of the laser light output from the photodetector 101 and the signal of the reference voltage indicating the light amount of the laser light substantially coincide with each other. The drive current value to be adjusted is adjusted. By performing this operation for all the light emitting elements, the output light amount of all the light emitting elements is controlled. Since this initial APC takes time to converge (until the light intensity adjustment is completed) because the control voltage of the internal circuit (the driving units 70 (1) to 70 (32)) is reset, the initial APC is performed several times. APC is executed. The VCSEL driver 30 holds the adjusted drive current value after the light amount control, and supplies the adjusted drive current value at the time of lighting.
The line APC is a mode executed in an area (APC area) other than the image area where image formation is performed within one main scanning period (SOS signal interval), and the held control voltage leaks or the like. The amount of light fluctuation due to the environment and the passage of time is adjusted, for example, the amount of light decreases and the amount of light changes. Since these fluctuations are small between one line, one APC operation is usually performed. The drive current values corresponding to all the light emitting elements set at the end of the line APC are read out, all the light emitting elements are turned on based on the drive current value, and the output light amount of all the light emitting elements is controlled.

Next, the processing procedure of the optical scanning device 10 will be described with reference to the flowchart shown in FIG.
First, the optical scanning device 10 performs initial APC during a predetermined period before image formation (step S1). When the initial APC is completed and the light amounts of the respective LD1 to LD32 are set to the reference light amount that is a preset light amount, the control circuit 51 starts an SOS search (step S2). In the SOS search, the control circuit 51 causes the light emitting elements LD corresponding to lines in the main scanning direction to write an image to emit light with 100% light quantity. When receiving the SOS signal output from the SOS sensor 18, the control circuit 51 outputs CLK 1 to the up / down counter 81 of the correction control voltage generation unit 80. Further, the control circuit 51 outputs an up signal or a down signal to the up / down counter 81 according to the light amount at the writing position in the main scanning direction, and the light amount of the light emitting element LD is set to the writing position of the line for writing the image. The light quantity is set (step S3).

  The control circuit 51 selects CLK2 and outputs it to the up / down counter 81 when an image is written to the image area of the photosensitive drum 60 after the predetermined time T has elapsed. Further, the control circuit 51 controls the light emission amount of the light emitting element LD by switching the signal output to the up / down counter 81 to an up signal or a down signal, and forms an image in the image area of the photosensitive drum 60 ( Step S4). When the writing of the image to the line in the main scanning direction is completed, the control circuit 51 stops outputting the selected CLK to the up / down counter 81 and outputs a reset signal to the up / down counter 81. As a result, the count value of the up / down counter 81 is reset to the initial value, and the light amount of the light emitting element LD is set to 100%.

  When the writing of the line image data to the photosensitive drum 60 is completed (step S5 / NO), the control circuit 51 performs line APC (step S6), and the light amounts of the light emitting elements LD1 to LD32 are set by the initial APC. The light amount of the light emitting elements LD1 to LD32 is controlled so as to be the reference light amount. When the line APC is completed, the control circuit 51 returns to step S2, and performs an SOS search to write an image of the next line (step S2). Further, when the writing of the image data on the photosensitive drum 60 and the printing on the printing paper are finished for all the image data (step S5 / YES), this process is finished.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Optical scanning device 30 VCSEL driver 40 Image processing part 50 Control part 60 Photosensitive drum 70 Drive part 80 Correction control voltage generation part

Claims (2)

A light source having a plurality of luminous points;
Deflecting means for deflecting a plurality of light beams emitted from the light source in the main scanning direction of the scanned surface of the image carrier;
Detecting means for receiving the beam light deflected by the deflecting means at a predetermined position and outputting a synchronization detection signal serving as a reference signal when setting the writing timing in the main scanning direction of the surface to be scanned;
When causing the detection means to receive beam light and output the synchronization detection signal, the driving unit that drives the light source is controlled so that the light amount of the beam light becomes the first light amount, and the synchronization detection signal is The amount of light of the beam when starting scanning in the main scanning direction of the surface to be scanned after the input from the detection means until a predetermined time elapses for each position in the sub-scanning direction of the surface to be scanned Control means for controlling the drive unit so as to obtain a second light amount which is a light amount having different values.
An optical scanning device comprising: Storage means for storing correction data for correcting the light amount of the beam light at the plurality of light emitting points for each of the main scanning direction and the sub-scanning direction of the scanned surface;
A clock signal to be output to a counter that counts the number of clock signals is selected from the first clock signal and the second clock signal, and correction data for the main scanning direction and the sub-scanning direction are stored from the storage unit. The control means for outputting to each of the counters an up signal for instructing up counting or a down signal for instructing down counting according to the read correction data,
The counter that counts up or down the first clock signal or the second clock signal output from the control means according to the up signal or the down signal;
Digital-analog conversion means for inputting a count value of the counter and outputting a correction instruction signal for correcting a light emission amount of a light emitting point to a drive unit that drives the light source according to the input count value;
The control means has a frequency higher than that of the second clock signal in the counter from when the synchronization detection signal is input from the detection means to when scanning in the main scanning direction of the surface to be scanned is started. 2. The optical scanning according to claim 1, wherein a high first clock signal is output, and when the scanning of the surface to be scanned in the main scanning direction is started, the second clock signal is output to the counter. apparatus.

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