JP6281331B2 - Optical writing apparatus, image forming apparatus, and optical writing method - Google Patents

Description

  The present invention relates to an optical writing device, an image forming apparatus, and an optical writing method.

  As an image forming apparatus such as a digital copying machine, a printer, and a facsimile machine, an electrophotographic image forming apparatus is widely used because a high-quality image can be recorded at a high speed. An electrophotographic image forming apparatus uses a laser diode (semiconductor laser) as a light source, forms an electrostatic latent image on a photosensitive member by a laser beam emitted from the laser diode, and develops the electrostatic latent image. A toner image is formed, and the toner image is transferred to a recording material such as paper to form an image.

  In such an electrophotographic image forming apparatus, in order to improve the image quality, it is necessary to keep the output of the laser diode constant. Conventionally, APC (Auto Power Control) is used. A circuit is used to keep the output of the laser diode constant.

  That is, since the light output characteristics of the laser diode are sensitive to changes in the ambient temperature, even if the laser diode is driven with a constant current, the light output fluctuates due to changes in the ambient temperature, self-heating, or the like. In order to suppress this fluctuation in optical output, a photodiode that monitors the optical output of the laser diode is incorporated in the laser diode package, and the drive current of the laser diode is feedback controlled based on the detection result of the photodiode. It has been practiced to control the light output of the laser diode to be constant.

  In recent years, there has been an increasing demand for higher speed and higher definition of images in image forming apparatuses. To meet these demands, a plurality of light sources (laser diodes) arranged at predetermined intervals in the sub-scanning direction. ) Is provided. Such an image forming apparatus scans the photosensitive member simultaneously with a laser beam from a plurality of light sources and writes image data of a plurality of lines simultaneously by one scanning of the scanning optical system.

  By the way, in such an image forming apparatus using a plurality of light sources, from the viewpoint of cost, a harness or the like is provided from one power supply unit to a light source control board on which a plurality of light sources and a light source control unit that drives these light sources are mounted. Power is supplied through a transmission line (hereinafter referred to as a power transmission line).

  On the other hand, in an image forming apparatus using a plurality of light sources, the lighting timing of each light source is independently performed by image data, and the lighting timing of each light source is controlled independently. Therefore, when power is supplied from a single power supply unit to a plurality of light sources, the drive current of the light source and the current consumption of the light source control unit change according to the number of lighting of the light source. Here, since the drive current of the light source is a load current of the light source control unit, the sum of the drive current of the light source and the consumption current of the light source control unit becomes the consumption current of the light source control board (= input current of the light source control board). .

  When the current consumption of the light source control board changes, a voltage drop and GND floating occur due to the impedance of the power transmission line that supplies power from the power supply unit to the light source control board, so that the power supply unit supplies the light source control unit and the light source. The level of the power supply voltage and the level of the reference voltage signal supplied to the light source control board for APC control change. As a result, the amount of light emitted from the light source varies depending on the number of light sources to be turned on. In addition, regardless of the number of light sources, the amount of light emitted from the light sources deviates from the target amount of light. The image quality deteriorates due to such a change (fluctuation, deviation) in the light amount of the light source.

  As an invention proposed to solve such a problem, there are an optical writing device, an image forming apparatus, and an optical writing control method described in Patent Document 1. This optical writing device has a plurality of light sources that can be turned on and off individually, and a light source that is turned on simultaneously when a plurality of light sources are combined and a plurality of light sources are turned on simultaneously. A memory for storing a light amount correction value, which is correction information for correcting a light amount difference from the individual light emission amount. When a plurality of light sources are turned on simultaneously, the memory is referred to, and the emission light quantity of the simultaneously lit light sources is corrected and controlled based on the light quantity correction value corresponding to the light sources to be turned on simultaneously.

  However, in the optical writing device described in Patent Document 1, the cost is increased by mounting a memory for storing a correction light amount. Further, it is necessary to perform complicated control by referring to the memory to acquire the light amount correction value and reflect it in the light source driving current.

  The present invention has been made to solve such a problem, and an object thereof is to include a light source control board on which a light source and a light source control unit that supplies a light source driving current to the light source are mounted, and the light source In an optical writing device to which a power source for the light source and the light source control unit and a reference voltage signal for controlling the light source driving current are supplied from the outside of the control board, consumption of the light source control board according to a change in an operation state of the light source It is to reduce the light quantity change of the light source due to the change of current by an inexpensive and simple means.

  The optical writing device of the present invention has a light source control board on which a light source and a light source control unit that supplies a light source driving current to the light source are mounted, and the power source of the light source and the light source control part from outside the light source control board, An optical writing device to which a reference voltage signal for controlling the light source driving current is supplied, and an energized part mounted on the light source control board and energized for a predetermined period including a period in which the light source driving current flows. And a current control unit that controls a current flowing through the current-carrying unit so that a current consumption of the light source control board is constant during the period.

  According to the present invention, it has a light source control board on which a light source and a light source control unit for supplying a light source driving current to the light source are mounted, and the light source and the power source of the light source control part from outside the light source control board, and the light source In an optical writing apparatus to which a reference voltage signal for controlling a drive current is supplied, a change in the amount of light of the light source caused by a change in current consumption of the light source control board in accordance with a change in the operating state of the light source is inexpensive and simple. It can be reduced by means.

1 is a diagram illustrating a schematic configuration of a laser printer as an image forming apparatus according to an embodiment of the present invention. It is a perspective view of the principal part of the optical writing part in FIG. FIG. 2 is an electrical block diagram of a main part of the optical writing unit in FIG. 1. FIG. 4 is a timing diagram for explaining an operation when no additional current is passed through a variable resistor on the light source control board in FIG. 3. FIG. 4 is a timing diagram for explaining an operation in a case where an addition current flowing through a variable resistor on a light source control board in FIG. 3 is made constant. FIG. 4 is a timing diagram for explaining an operation when an addition current flowing through a variable resistor on the light source control board in FIG. 3 is changed. FIG. 4 is a timing diagram for explaining an operation when a period in which an addition current is supplied to the light source control board in FIG. 3 is a sub-scanning period and is changed.

Embodiments of the present invention will be described below with reference to the drawings.
<Schematic configuration of image forming apparatus>
FIG. 1 is a diagram showing a schematic configuration of a laser printer as an image forming apparatus according to an embodiment of the present invention.

  As illustrated, the laser printer 1 includes an image forming unit 2 and a fixing unit 3. Although not shown, an image processing unit that performs necessary image processing on print data, a paper feeding unit that supplies printing paper to the image forming unit 2, an image is formed by the image forming unit 2, and an image is formed by the fixing unit 3. A paper discharge unit that discharges the fixed printing paper to a paper discharge tray, a data reception unit that receives print data from an external device (such as a personal computer or a scanner), operation keys for setting various operation modes of the laser printer 1, An operation display unit having a display or the like for displaying various information is provided.

  In the image forming unit 2, a charging unit 11, an optical writing unit 12, a developing unit 13, a transfer unit 14, a separation unit 15, a cleaning unit 16, and the like are disposed around the photoconductor 10 that is rotationally driven.

  In the image forming unit 2, the charging unit 11 uniformly charges the photosensitive member 10, and then the optical writing unit 12 irradiates the photosensitive member 10 with a laser beam modulated based on the image data. 10 forms an electrostatic latent image. Next, toner (developer) is attached to the photosensitive member 10 by the developing unit 13 to form a toner image as a developer image. Next, the transfer unit 14 transfers the toner image on the photoconductor 10 from a paper supply unit through a paper supply path 17 to a printing sheet as a recording medium fed between the photoconductor 10 and the transfer unit 14. . Next, the separation unit 15 separates the printing paper onto which the toner image has been transferred from the photoreceptor 10 and conveys the printing paper to the fixing unit 3.

  The fixing unit 3 includes a heating roller that is rotated and heated to a predetermined fixing temperature, a pressure roller that contacts the heating roller and rotates together with the heating roller, a heater that heats the heating roller to a predetermined fixing temperature, and the like. ing. Then, the printing paper on which the toner image is transferred is conveyed while being heated and pressurized by a heating roller and a pressure roller, and the toner image is fixed on the paper to form an image.

  Further, the image forming unit 2 discharges the photosensitive member 10 after the transfer of the toner image by the cleaning unit 16 to clean the residual toner, and then uniformly charges the charging unit 11 to form an image again. .

<Perspective view of the main part of the optical writing unit>
FIG. 2 is a perspective view of a main part of the optical writing unit 12 in FIG. In this figure, a dashed arrow indicates a laser beam.

  The optical writing unit 12 includes an LD (laser diode) unit 21 as a light source that emits a laser beam, a polygon mirror 22 that rotates at an angular velocity corresponding to the image density of the laser printer 1, an fθ lens 23, a reflection mirror 24, and a synchronous reflection mirror. 25 and a synchronization detection element 26.

  The laser beam emitted from the LD unit 21 is reflected by the polygon mirror 22, passes through the fθ lens 23, and reaches the reflection mirror 24. Then, the light is reflected by the reflection mirror 24 and forms an image on the photosensitive member 10.

  As the polygon mirror 22 rotates in the direction of arrow 31, the incident position (reflection position) of the laser beam on the reflection mirror 24 moves in the direction of arrow 32, and the image formation position on the photoconductor 10 moves in the direction of arrow 33. Move to. The direction of the arrow 33 is the direction of the cylindrical bus that is the shape of the photoconductor 10, and is the main scanning direction of the image.

  A part of the laser beam that has passed through the fθ lens 23, that is, the laser beam on the photosensitive member 10, is also incident on a synchronous reflection mirror 25 that is disposed in the vicinity of a position outside the image forming area. The synchronous reflection mirror 25 reflects the incident laser beam to the synchronous detection element 26.

  The synchronization detection element 26 includes, for example, a photodiode, and generates a synchronization detection signal that is a pulse output when a laser beam is incident thereon. Based on this synchronization detection signal, an effective scanning period, which is a period during which an image is written on the photoconductor 10, is set.

<Electric block diagram of optical writing unit>
FIG. 3 is a diagram showing a first example of an electrical block diagram of a main part of the optical writing unit 12 in FIG.

  The optical writing unit 12 includes a writing control board 100 and a light source control board 110. Between the writing control board 100 and the light source control board 110, a reference voltage signal transmission line 131, an image area signal transmission line 132, an LD1 lighting control signal transmission line 133, and an LD2 lighting control signal transmission line as control signal transmission lines. 134, and a power line 135 as a power transmission line and a GND line 136.

  The write control board 100 is connected to the power supply unit 120 inside or outside the optical writing unit 12, and power is supplied from the power supply unit 120 to the write control board 100, and the light source control board is connected via the power transmission line. Power is supplied to 110.

  A write control unit 101 is mounted on the write control board 100. On the light source control board 110, a light source control unit 111, an LD unit 21, and a variable resistor 113 are mounted.

  The light source control unit 111 includes a comparator 111a, an analog control unit 111b, and transistors 111c and 111d. The LD unit 21 includes a first LD 21a, a second 21b, and a PD (photodiode) 21c. Here, an LD unit having two (two channels) LDs is used as a light source, but the number of channels and the number of light sources are not limited thereto.

  The reference voltage signal, the image area signal, and the LD1 lighting control signal are respectively transmitted from the writing control unit 101 through the reference voltage signal transmission line 131, the image area signal transmission line 132, the LD1 lighting control signal transmission line 133, and the LD2 lighting control signal transmission line 134. The LD2 lighting control signal is transmitted to the light source control unit 111. The image area signal is asserted at the start of printing and negated with the job end. That is, this signal is active only during the period of the paper surface in the sub-scanning direction of the printing paper. The writing control unit 101 functions as an image area signal supply unit.

  The light source control unit 111 recognizes the image area in the sub-scanning direction of the printing paper based on the image area signal, and determines the timing for lighting the first LD 21a and the second LD 21b based on the LD1 lighting control signal and the LD2 lighting control signal. The lighting light amount (light intensity) is controlled by the reference voltage signal.

  The control of the light quantity is performed as follows. Part of the laser beam emitted from the first LD 21a and the second LD 21b is detected by the PD 21c and input to the comparator 111a. The comparator 111a compares the output level of the PD 21c with the level of the reference voltage signal, and outputs the difference as a comparison result to the analog control unit 111b. Based on the comparison result, the analog control unit 111b controls the output currents of the transistors 111c and 111d, that is, the drive currents of the first LD 21a and the second LD 21b.

  For example, when the level of the reference voltage signal decreases, the light amounts of the first LD 21a and the second LD 21b are decreased so that the output level of the PD 21c decreases. Conversely, when the level of the reference voltage signal increases, the light amounts of the first LD 21a and the second LD 21b are increased so that the output level of the PD 21c increases. Thereby, the light amounts of the first LD 21a and the second LD 21b are controlled so as to always correspond to the change of the reference voltage signal.

  The variable resistor 113 is a part to be energized for consuming current supplied from the power supply unit 120 to the light source control board 110. Hereinafter, the current flowing through the variable resistor 113 is referred to as an addition current. As will be described in detail later, the light source control unit 111 can variably control the period and current value for supplying the addition current to an arbitrary value by changing the resistance value of the variable resistor 113.

<Operation when no additional current flows>
FIG. 4 is a timing diagram for explaining the operation when no additional current is passed through variable resistor 113 on light source control board 110 in FIG. This operation is performed when the control signal is not supplied from the light source control unit 111 to the variable resistor 113 and is turned off, and the resistance value is infinite (open state).

  When the first LD 21a and the second LD 21b are not lit, the current consumption of the light source control board 110 is 0 mA. As for the lighting period, when only one LD is lit (LD1 lighting period, LD2 lighting period), the lighting timings of the first LD 21a and the second LD 21b overlap, and both of them are lit. (LD1 & 2 lighting period) is 20 mA. Here, the shortest value of the lighting period (in the figure, the first LD1 lighting period and LD2 lighting period) is one pixel period. The current consumption of the light source control board 110 is the sum of the current consumption of the light source control unit 111 and the current consumption of the LD unit 21 (= light source driving current).

  When the current consumption of the light source control board 110 increases due to the lighting of the first LD 21a and the second LD 21b, the voltage drop and the GND floating occur due to the resistance of the harness that constitutes the power supply line 135 and the GND line 136.

  For example, the potential on the write control substrate 100 in the power supply line 135 and the GND line 136 is 5.0 V and 0 V, respectively, and the reference voltage signal is 1.0 V. When the voltage drop in the power supply line 135 when only one LD is lit and the GND floating in the GND line 136 are both 0.01 V, the power supply voltage in the light source control board 110 is 4.98 V, and the reference voltage signal is 0. .99V. Further, the voltage drop and GND floating when both LDs are lit are 0.02V, the power supply voltage on the light source control board 110 is 4.96V, and the reference voltage signal is 0.98V.

  Here, the level of the reference voltage signal supplied to the light source control unit 111 and the amount of light of the LD are in a proportional relationship, and when a reference voltage signal of 1.0 V is supplied, the amount of light corresponding to 10 mW power consumption (hereinafter, It emits light with a light quantity of 10 mW).

  However, due to fluctuations in the level of the reference voltage signal, the analog control unit 111b in the light source control unit 111 causes the light source driving current corresponding to the 0.99V or 0.98V reference voltage signal to flow instead of 1.0V. 111c and 111d are driven. Further, since the voltage applied between the collectors and emitters of the transistors 111c and 111d changes due to fluctuations in the level of the power supply voltage, the light source driving current amount to be supplied to the LD corresponds to the reference voltage signal of 0.99V or 0.98V. It will also change from the amount of drive current.

  That is, the light amount varies between a light amount of approximately 9.9 mW and a light amount of 9.8 mW between when one LD is lit and when two LDs are lit. In addition, when one is lit and when two are lit, the light amount is shifted to approximately 9.9 mW or 9.8 mW instead of the target light amount of 10 mW. These changes (variations and deviations) in the amount of light are not preferable because they change the density of the printed image.

Note that the voltage drop and GND float can be calculated by the following equations.
Voltage drop = Current consumption / Number of harnesses of power supply line 135 x Harness length x Harness unit resistance GND float = Current consumption / Number of harnesses of GND wire 136 x Harness length x Harness unit resistance

For example, if the current consumption is 200 mA, the number of harnesses of the power line 135 is 2, the number of harnesses of the GND line 136 is 2, each harness length is 0.1 m, and each unit resistance is 1 Ω / m,
Voltage drop = GND float = 200 mA / 2 × 0.1 m × 1Ω / m = 100 mA × 0.1Ω = 10 mV
It becomes.

<Operation when the addition current is constant>
FIG. 5 is a timing diagram for explaining the operation when the addition current flowing through the variable resistor 113 on the light source control board 110 in FIG. 3 is made constant. Here, during the period when power is supplied from the power supply unit 120 to the light source control board 110, an additional current of 100 mA flows constantly. That is, the “predetermined period including the period during which the light source driving current flows” in the present invention is a period during which power is supplied from the power supply unit 120 to the light source control board 110.

  This 100 mA added current causes a voltage drop of 0.1 V and a GND float. In consideration of the voltage drop and GND floating for the steady addition current, the power supply voltage output from the power supply unit 120 to the power supply line 135 is 5.2V, and the reference voltage signal output from the write control board 100 is 1.1V. Then, when the LD is not lit, the power supply voltage on the light source control board 110 is 5.0V and the reference voltage signal is 1.0V.

  In addition, when one LD is lit (LD1 lighting period, LD2 lighting period), the current consumption of the light source control board 110 increases by 10 mA to 110 mA, so that a voltage drop of 0.01 V and GND floating occur. Therefore, the power supply voltage on the light source control board 110 is 4.98V, and the reference voltage signal is 0.99V. When two LDs are lit (LD1 & 2 lighting period), the current consumption of the light source control board 110 increases by 20 mA to 120 mA, and a voltage drop of 0.02 V and GND floating occur. Therefore, the power supply voltage on the light source control board 110 is 4.96V, and the reference voltage signal is 0.98V.

  That is, by increasing the level of the power supply voltage and the reference voltage signal, it is possible to avoid the influence of the voltage drop for the added current and the GND floating, but due to the change in the current consumption of the light source control board 110 that changes due to the lighting of the LD. The effects of voltage drop and GND floating that cannot be avoided.

<Operation when adding current is changed>
Therefore, the optical writing device according to the present embodiment further performs current control as shown in the following diagram.
FIG. 6 is a timing chart for explaining the operation when the addition current flowing through the variable resistor 113 on the light source control board 110 in FIG. 3 is changed.

  As shown in the figure, in order to eliminate the change in the current consumption of the light source control board 110 due to the lighting of the LD, the addition current value is changed in accordance with the lighting of the LD. Decrease.

  The light source control unit 111 reduces the current value corresponding to the level of the reference voltage signal (10 mA for one LD in the figure) from the added current in accordance with the timing of “lighting” of the LD lighting control signal. The current consumption on the control board 110 is always kept constant. That is, the added current value when one LD is lit (LD1 lighting period, LD2 lighting period) is 90 mA, and the added current value when both LDs are lit (LD1 & 2 lighting period) is 80 mA. To do.

  By doing so, the current consumption of the light source control board 110 becomes a constant value of 100 mA and does not change regardless of whether or not the LD is turned on, and the voltage drop and the GND floating are also unchanged and constant. For this reason, the levels of the power supply voltage and the reference voltage signal input to the light source control unit 111 do not change and become constant values of 5.00 V and 1.00 V, respectively, so that fluctuations in the light amount of the LD can be eliminated.

  The light source control unit 111 that functions as a current control unit performs the control for changing the addition current in this way. That is, the analog control unit 111b in the light source control unit 111 calculates a current value corresponding to the level of the reference voltage signal input to the light source control unit 111 from the added current value (100 mA in the figure) when the LD is not lit. The resistance value is changed so that the subtracted current flows through the variable resistor 11 3.

  Here, the added current value when the LD is not lit is 100 mA, but is not limited to this value. It is desirable that more than the amount of current when all the LDs (two in FIG. 3) are lit with the maximum light amount can flow constantly.

<Operation when the period during which the additional current flows is the sub-scanning period and is changed>
FIG. 7 is a timing chart for explaining the operation when the period in which the addition current is supplied to the light source control board 110 in FIG. 3 is the sub-scanning period and is changed. That is, the “predetermined period including the period during which the light source driving current flows” in the present invention is defined as the sub-scanning period.

  As shown in the figure, an additional current is allowed to flow only during a period in which the image region signal indicating the sub-scanning period (= printing operation period) is valid, so that no extra current flows at a timing other than the printing operation period in which the image forming operation is performed. To control.

  That is, first, when the image area signal changes from invalid to valid (asserted), the addition current is changed from 0 mA to 100 mA. Thereafter, when one LD is lit (LD1 lighting period, LD2 lighting period), the additional current value is reduced to 10 mA to 90 mA, and when both LDs are lit (LD1 & 2 lighting period) The value is reduced to 20 mA to 90 mA.

  Thus, as in the case of FIG. 6, the current consumption of the light source control board 110 does not change and remains constant at 100 mA, regardless of whether or not the LD is lit, so that the voltage drop and GND floating also change. It becomes constant. For this reason, the levels of the power supply voltage and the reference voltage signal input to the light source control unit 111 do not change and become constant values of 5.00 V and 1.00 V, respectively. Misalignment can be eliminated.

  DESCRIPTION OF SYMBOLS 1 ... Laser printer, 10 ... Photoconductor, 12 ... Optical writing part, 21 ... LD unit, 100 ... Write control part, 110 ... Light source control board, 111 ... Light source control part, 113 ... Variable resistance.

JP 2010-194443 A

Claims (7)

A light source control board on which a light source and a light source control unit for supplying a light source drive current to the light source are mounted; a power source for the light source and the light source control unit from outside the light source control board; and a reference for controlling the light source drive current An optical writing device to which a voltage signal is supplied,
An energized part mounted on the light source control board and energized in a predetermined period including a period in which the light source driving current flows;
A current control unit for controlling a current flowing in the energized unit so that a current consumption of the light source control board is constant in the period;
An optical writing device. The optical writing device according to claim 1,
The optical writing device, wherein the energized portion is a variable resistor. The optical writing device according to claim 1,
The optical writing apparatus, wherein the predetermined period is a period in which power is supplied to the light source control board. The optical writing device according to claim 2,
The optical writing device, wherein the current control unit changes a resistance value of the variable resistor in accordance with a level of the reference voltage signal. A photosensitive member is irradiated with a laser beam modulated based on image data from an optical writing unit to form an electrostatic latent image, and a developer image obtained by developing the electrostatic latent image on the photosensitive member with a developer is formed. An image forming apparatus that forms an image by transferring to a recording medium,
An image forming apparatus comprising the optical writing device according to claim 1 as the optical writing unit. The image forming apparatus according to claim 5.
An image forming apparatus, comprising: an image region signal supply unit that supplies an image region signal corresponding to a sub-scanning period of the image to the light source control unit, wherein the predetermined period is the sub-scanning period. Light source control including a light source, a light source control unit that supplies a light source driving current to the light source, and an energized unit, and a power source for the light source and the light source control unit and a reference voltage signal that controls the light source driving current are supplied from the outside An optical writing method executed by an optical writing device having a substrate,
An energization step of passing a current through the energized part, and a light source driving step of supplying a light source driving current from the light source control unit to the light source,
A light that performs the energization step during a predetermined period including a period during which the light source driving step is performed, and controls a current flowing through the energized portion so that a current consumption of the light source control board is constant during the period. Writing method.

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