JP2001113743A - Image forming device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To realize smoothness of an image at a low density. A data control unit (20) outputs image data of each pixel for each LD into upper bits (D1a, D2a) and lower bits (D1b, D2b), and outputs reference voltages (Vr1, Vr2). The upper bit control unit 31 of the LD modulation unit 30 outputs a pulse width modulation signal P1 according to D1a, and an identification signal L indicating whether D1a is the lowest value.
1 is also output. The D / A1 current setting section 32 sets P based on Vr1.
1, a current value for power modulation is set according to D1b, and D /
The A2 addition current setting unit 33 sets a current value for power modulation addition according to D1b based on Vr2 when D1a is recognized as the lowest value from L1. The current addition unit 34 sets the current value for power modulation to The added current value is added, and the LD driving unit 35
Causes the LD 1a to emit light by pulse width modulation and power modulation according to the added value. The LD modulator 40 performs substantially the same processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a laser printer, a digital copying machine, and a facsimile apparatus for writing (forming) an image (electrostatic latent image) using a multi-beam.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a laser printer or a digital copier, a laser beam output from a single laser light source (laser diode) is rotated by a polygonal motor. The electrostatic latent image is formed by scanning the surface of the photoreceptor (photoreceptor surface) moved in the sub-scanning direction in the main scanning direction by periodically deflecting the image using a "mirror"). When high performance is required in such an image forming apparatus, the rotation speed of the polygon motor or the image signal (image data)
Needs to be faster.

However, the number of rotations of the polygon motor and the frequency of the image signal are limited, and the processing cannot always be performed at a desired processing speed. Therefore, an image forming apparatus has been proposed which has a plurality of laser light sources at substantially the same position in the main scanning direction and separated by a predetermined distance in the sub-scanning direction.

In this type of image forming apparatus, a plurality of laser beams output from a plurality of laser light sources are periodically deflected by using a polygon mirror rotated by a polygon motor, and are moved in a sub-scanning direction. An electrostatic latent image is formed by scanning the surface of the body in the main scanning direction with a positional difference in the sub-scanning direction (writing by a multi-beam).

In the multi-beam writing method, the amount of information that can be recorded simultaneously increases, so that the rotation speed of the polygon motor and the frequency of the image signal can be reduced, and a stable image can be processed at high speed. Will be possible.

On the other hand, as a modulation method for the laser light source, a pulse width modulation method (a method of controlling the on-duty time while keeping the light output of the laser light source constant) and a power modulation method (a method of controlling the light output of the laser light source). System) has been considered, and a modulation system combining the two modulation systems has also been proposed.

In an image forming apparatus using a modulation system combining the pulse width modulation system and the power modulation system and a multi-beam writing system, for example, a data control unit, a plurality of upper bit control units for a plurality of laser light sources, A setting unit and an LD driving unit are provided, and they perform the following processing.

The data control unit outputs image data for each pixel for each laser light source, divided into upper bit data and lower bit data, and outputs a common reference voltage to each laser light source. Each upper bit control section outputs a pulse width modulation timing signal according to the upper bit data for each pixel from the data control means.

Each of the current setting sections respectively converts a timing signal for each pixel from an upper bit control section corresponding to a common reference voltage from the data control section and a lower bit data for each pixel from the data control section. A current value for power modulation is set and output accordingly. Each LD drive unit emits light by performing pulse width modulation and power modulation on the corresponding laser light source (LD) according to the current value for power modulation from the corresponding current setting unit.

[0010]

However, in an image forming apparatus using a modulation method in which a pulse width modulation method and a power modulation method are combined, switching of the modulation method occurs, and the linearity of gradation is changed by the switching. May break. Therefore, smoothness is lost particularly at a low-density gradation change. In addition, in the case of using a multi-beam writing method, if there is a power difference between the laser light sources, the difference is conspicuous especially in a low-density portion, which causes image deterioration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been developed in an image forming apparatus using a modulation method combining a pulse width modulation method and a power modulation method and a multi-beam writing method. An object is to realize smoothness of an image.

[0012]

According to the present invention, a plurality of laser beams output from a plurality of laser light sources are periodically deflected by using a rotating polygon mirror, and are deflected on a photosensitive member surface moved in a sub-scanning direction. An image forming process in which an electrostatic latent image is formed by scanning the photosensitive member surface in the main scanning direction with a positional difference in the sub-scanning direction, and the electrostatic latent image is developed with toner to form a toner image In order to achieve the above object, the apparatus is characterized as follows.

According to the first aspect of the present invention, the image data of each pixel for each laser light source is separately output into upper bit data and lower bit data, and a first reference voltage and a common reference voltage common to each laser light source are output. A data control means for outputting a common second reference voltage, a timing signal for pulse width modulation in accordance with the upper bit data of the image data for each pixel, and the upper bit data indicating the lowest value An upper bit control means for each laser light source for outputting an identification signal for identifying whether or not a power modulation current value is set in accordance with the timing signal and the lower bit data based on the first reference voltage; Current setting means for each laser light source to be output; Only when it is recognized that show the,
Addition current setting means for each laser light source for setting and outputting a current value for power modulation addition according to the lower bit data with reference to the second reference voltage; Current addition means for each laser light source for adding the current value for the addition and outputting the current value after the addition, and performing pulse width modulation and power modulation on the corresponding laser light source according to the current value after the addition, respectively. And driving means for emitting light.

According to a second aspect of the present invention, image data for each pixel for each laser light source is separately output into upper bit data and lower bit data, and a common reference voltage and an individual reference A data control means for outputting a voltage, a timing signal for pulse width modulation in accordance with the upper bit data of the image data for each pixel, and identification for identifying whether or not the upper bit data indicates the lowest value. An upper bit control unit for each laser light source that outputs a signal, and a current for each laser light source that sets and outputs a current value for power modulation according to the timing signal and the lower bit data based on the common reference voltage Setting means, and that the upper bit data indicates the lowest value from the identification signal, respectively. Only when recognized, is the addition current setting means for each laser light source for setting and outputting an addition current value for power modulation in accordance with the lower bit data based on the individual reference voltage, and Current adding means for each laser light source for adding the added current value to the current value for use and outputting the added current value, and performing pulse width modulation on the corresponding laser light source according to the added current value, respectively. And a driving unit that emits light by power modulation.

According to a third aspect of the present invention, in the image forming apparatus of the second aspect, the data control means generates specific image data for forming a process pattern for density adjustment on the surface of the photosensitive member. And outputting specific image data generated by the means to the higher-order bit control means, current setting means, and addition current setting means corresponding to each laser light source, so that a process pattern is formed on the surface of the photoconductor by image forming processing. A process pattern forming unit to be formed; and a density detecting unit for sequentially detecting the density of each process pattern sequentially formed for each laser light source by the unit. The individual unit according to each density detection result by the density detecting unit. Reference voltages are individually output.

[0016]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 2 is a perspective view showing a configuration example of a mechanism of the multi-beam writing device in the image forming apparatus according to the embodiment of the present invention.

In this multi-beam writing apparatus, reference numeral 1 denotes a laser diode (hereinafter referred to as "L") which is a plurality of laser light sources.
D ") in one package, and image data (image signals) from each LD.
Is emitted (output) according to. The plurality of laser beams are shaped into a laser beam having a narrow cross section with a predetermined shape by a collimator lens 2, an aperture 8, and a cylindrical lens 3 constituting a scanner as an optical scanning means, and the polygon mirror 4 Is irradiated.

That is, the plurality of laser beams are:
The collimated lens 2 converts the light beam into a parallel light beam, and then an extra laser beam is cut by an aperture 8 having a slit corresponding to the size of a writing dot (scan density). Each parallel light beam shaped by the aperture 8 is
Each laser beam for writing an image in the main scanning direction is condensed by the cylindrical lens 3 to have a predetermined size on the surface (photosensitive surface) of the photosensitive drum 7 which is moved (rotated) in the sub-scanning direction. Irradiates the polygon mirror 4.

Since the polygon mirror 4 is continuously rotated at a constant speed by a polygon motor (not shown), the laser beam incident on the polygon mirror 4 is periodically deflected and passes through the reflection mirror 9 in the main scanning direction (photosensitive). It is repeatedly moved and scanned in X) (axial direction of the body drum 7). At this time,
The laser beam deflected by the polygon mirror 4 is subjected to conversion from equiangular motion to constant-velocity motion by a pair of Fθ lenses 5 and correction of surface tilt by a lens 6 for correcting surface tilt.
The angle is changed by the reflection mirror 9 and an image is formed on the surface of the photosensitive drum 7 in a spot shape with a predetermined beam diameter.

Since the LD array 1 has a plurality of LDs, a plurality of LDs having a pitch (position difference) in the sub-scanning direction (rotation direction of the photosensitive drum 7) Y on the surface of the photosensitive drum 7 are provided. Of the laser beam irradiation is drawn. The photosensitive drum 7 is rotated in the sub-scanning direction by a main motor (not shown), and the surface is uniformly charged by a charging device (not shown).

Thereafter, the charged surface of the photosensitive drum 7 is exposed by repetition of scanning of a plurality of laser beams by the polygon mirror 4, and an electrostatic latent image (electrostatic image) corresponding to image data is formed thereon. . The electrostatic latent image is visualized by developing with a toner from a developing device to become a toner image, transferred to one sheet of paper fed by a paper feeding device by a transfer device, and further thermally transferred by a fixing device. Be established. The sheet on which the toner image has been thermally fixed is discharged out of the apparatus, and the image forming process for one sheet is completed.

FIG. 3 is an enlarged perspective view of the LD array 1 of FIG. In the heterodyne junction surface 1A of the LD array 1,
A plurality of (two in this example) LDs are formed, and the laser beams output from each LD are B1 and B2 as shown in the figure. In this embodiment, the LD array 1 having two LDs is provided, but an LD array having three or more LDs or two or more single LD units may be provided instead. .

In FIG. 2, a laser beam immediately before scanning on the photosensitive drum 7 is provided in a laser beam path on the main scanning start point side outside the main scanning writing area (outside a predetermined main scanning width) with respect to the surface of the photosensitive drum 7. Since the laser beam passes through the synchronous detection sensor 11 via the synchronous mirror 10, the synchronous detection sensor 11 detects the laser beam and generates and outputs a synchronous detection signal for defining a write start position in the main scanning direction. I do. Then, a control unit (not shown) uses the synchronization detection signal from the synchronization detection sensor 11 to control the emission start timing of the laser beam for image writing for each scan (periodically).

FIG. 1 is a block diagram showing a configuration example of a main part of a control unit of an image forming apparatus provided with the multi-beam writing device. The data control unit 20 corresponds to the data control unit of claim 1, and writes image data for each pixel for each of the LDs 1 a and 1 b of the LD array 1, which is input from the outside, to an internal memory (not shown). The image data of each pixel for the LD 1a is transferred to the upper bit data D1a at the optimum timing according to the synchronization detection signal from
And lower bit data D1b, and outputs
The image data for each pixel with respect to D1b is divided into upper bit data D2a and lower bit data D2b and output.

Further, a common first reference voltage (reference voltage) Vr1 and a common second reference voltage (reference voltage) Vr2 are output to each of the LDs 1a and 1b. In this case, the first reference voltage Vr1 is set to the D / A1 current setting unit 32 of the LD modulation unit 30 and the D / A1 current of the LD modulation unit 40.
The second reference voltage Vr2 is commonly output to the current setting unit 42, and the second reference voltage Vr2 is commonly output to the D / A2 addition current setting unit 33 of the LD modulation unit 30 and the D / A2 addition current setting unit 43 of the LD modulation unit 40.

The LD modulating unit 30 includes an upper bit control unit 31, a D / A1 current setting unit 32, a D / A2 addition current setting unit 33, a current adding unit 34, an LD driving unit 35, and the like for the LD 1a. . In the LD modulation section 30, the upper bit data D1a for each pixel from the data controller 20 for the LD1a is input to the upper bit controller 31.

The high-order bit control section 31 corresponds to the high-order bit control means of the first aspect, and includes a pulse width modulation method (LD1a
(A method of controlling the on-duty time while keeping the optical output of the upper bit data constant).
1a, the timing signal P1 for pulse width modulation is set to D /
A1 is output to the A1 current setting unit 32 and an identification signal L1 for identifying whether or not the upper bit data D1a indicates the lowest value.
Is output to the D / A2 addition current setting unit 33.

The D / A1 current setting section 32 corresponds to the current setting means of claim 1 and is a circuit for realizing a power modulation method (a method of controlling the optical output of the LD 1a), and controls the first reference voltage Vr1. Based on the timing signal P1 and the lower bit data D1b, a current value for power modulation is set as a reference and output to the current adding unit 34.

The D / A2 addition current setting section 33 corresponds to the addition current setting means of the first aspect, and only outputs the second reference signal when the identification signal L1 recognizes that the upper bit data D1a indicates the lowest value. Based on the voltage Vr2, a current value for power modulation addition is set according to the lower bit data D1b, and output to the current addition unit 34.

The current adding section 34 corresponds to the current adding means of claim 1, and adds the added current value to the power modulation current value, and outputs the added current value to the LD driving section 35.
The LD driving unit 35 corresponds to the driving unit of claim 1 and emits light by performing pulse width modulation and power modulation on the LD 1 a in accordance with the current value after the addition.

The LD modulating section 40 includes an upper bit control section 41 for the LD 1b, a D / A1 current setting section 42, a D / A2 addition current setting section 43, a current addition section 44, an LD driving section 45, and the like. . In the LD modulator 40, the upper bit data D2a for each pixel for the LD1b from the data controller 20 is input to the upper bit controller 41.

The upper bit control section 41 corresponds to the upper bit control means of claim 1 and is a circuit for realizing a pulse width modulation method, and outputs a pulse width modulation timing signal P2 according to the upper bit data D2a. In addition to outputting to the / A1 current setting section 42, the identification signal L2 identifying whether or not the upper bit data D2a indicates the lowest value is output to the D / A2 addition current setting section 43.

The D / A1 current setting section 42 corresponds to the current setting means according to claim 1 and is a circuit for realizing a power modulation method. The D / A1 current setting section 42 uses the first reference voltage Vr1 as a reference and the timing signal P2 and the lower bit data D2b. The current value for power modulation is set and output to the current adding unit 44 in accordance with.

The D / A2 addition current setting unit 43 corresponds to the addition current setting means of the first aspect, and performs the second reference only when it is recognized from the identification signal L2 that the upper bit data D2a indicates the lowest value. Based on the voltage Vr2, a current value for power modulation addition is set according to the lower bit data D2b, and output to the current addition unit 44.

The current adding section 44 corresponds to the current adding means of claim 1, and adds the added current value to the power modulation current value, and outputs the added current value to the LD driving section 45.
The LD driving unit 45 corresponds to the driving unit of claim 1 and emits light by performing pulse width modulation and power modulation on the LD 1b according to the current value after the addition.

FIG. 4 shows image data output from the data control unit 20 and currents output from the D / A1 current setting units 32 and 42, the D / A2 addition current setting units 33 and 43, and the current addition units 34 and 44. FIG. 4 is a diagram illustrating a relationship with a value. As can be seen from FIG. 4, in the D / A1 current setting units 32 and 42, the output current value is increased or decreased according to the image data (lower-order bit data D1b and D2b).
And the rate of increase of A2 increases.

The slope of the output current value of each of the D / A2 addition current setting sections 33 and 43 is determined by the value of the second reference voltage Vr2, and while the upper bit data D1a and D2a indicate the lowest value, the lower bit data D1b and D2b increase or decrease. The output current value of the current adders 34 and 44 is D / A1
The output current values of the D / A2 addition current setting units 33 and 43 are added to the output current values of the current setting units 32 and 42, and the rate of increase of A1 and A2 at the time of switching the modulation method approaches linear.

FIG. 5 is a block diagram showing another example of the configuration of the main part of the control section of the image forming apparatus provided with the multi-beam writing apparatus shown in FIG. 2, and the same parts as those in FIG. It is attached.

The data control unit 20 ′ includes a first reference voltage Vr 1 common to each of the LDs 1 a and 1 b of the LD array 1 and second and third reference voltages Vr 1
Of the reference voltage Vr2, Vr3. In this case, the first reference voltage Vr1 is
The D / A1 current setting unit 32 and the D / A1 current setting unit 42 of the LD modulation unit 40 commonly output the second reference voltage Vr2 to the D / A2 addition current setting unit 33 of the LD modulation unit 30 and the third reference voltage Vr2. Is output to the D / A2 addition current setting unit 43 of the LD modulation unit 40. The other processing is the same as that of the data control unit 20, and the description is omitted.

Upper bit controller 31 of LD modulator 30
Is a circuit for realizing the pulse width modulation method, which corresponds to the high-order bit control means of claim 2.
In response to the pulse width modulation timing signal P1 according to D / A1
Output to the current setting unit 32 and the upper bit data D
An identification signal L1 for identifying whether 1a indicates the lowest value is
Output to the D / A2 addition current setting unit 33.

The D / A1 current setting section 32 corresponds to the current setting means of claim 2 and is a circuit for realizing a power modulation method. The D / A1 current setting section 32 uses the first reference voltage Vr1 as a reference to set the timing signal P1 and the lower bit data D1b. The current value for power modulation is set and output to the current adding unit 34 in accordance with.

The D / A2 addition current setting section 33 corresponds to the addition current setting means of the present invention. The D / A2 addition current setting section 33 outputs the second reference signal only when it is recognized from the identification signal L1 that the upper bit data D1a indicates the lowest value. Based on the voltage Vr2, a current value for power modulation addition is set according to the lower bit data D1b, and output to the current addition unit 34.

The current adding section 34 corresponds to the current adding means of claim 2, and adds the added current value to the power modulation current value, and outputs the added current value to the LD driving section 35.
The LD driving unit 35 corresponds to the driving unit of claim 2 and emits light by performing pulse width modulation and power modulation on the LD 1 a in accordance with the current value after the addition.

Upper bit controller 41 of LD modulator 40
Is a circuit for realizing a pulse width modulation method, which corresponds to the high-order bit control means of claim 2.
The timing signal P2 for pulse width modulation is changed to D / A1
Output to the current setting unit 42 and the upper bit data D
An identification signal L2 for identifying whether or not 2a indicates the lowest value
Output to the D / A2 addition current setting unit 43.

The D / A1 current setting section 42 corresponds to the current setting means of claim 2 and is a circuit for realizing a power modulation system. The D / A1 current setting section 42 has a timing signal P2 and lower bit data D2b based on a first reference voltage Vr1. The current value for power modulation is set and output to the current adding unit 44 in accordance with.

The D / A2 addition current setting section 43 corresponds to the addition current setting means of the present invention. The D / A2 addition current setting section 43 applies the third reference only when it is recognized from the identification signal L2 that the upper bit data D2a indicates the lowest value. Based on the voltage Vr3, a current value for power modulation addition is set according to the lower bit data D2b, and output to the current addition unit 44.

The current adding section 44 corresponds to the current adding means of the present invention, and adds the added current value to the power modulation current value, and outputs the added current value to the LD driving section 45.
The LD driving section 45 corresponds to the driving means of claim 2, and emits light by performing pulse width modulation and power modulation on the LD 1b according to the current value after the addition.

As described above, the D / A2 addition current setting unit 33 of the LD modulation unit 30 sets the D / A2 addition current setting unit 43 of the LD modulation unit 40 to the third reference voltage based on the second reference voltage Vr2. Each process is performed based on Vr3. Here, the light output (light emission power) of each of the LDs 1a and 1b.
Is different, the image degradation is conspicuous, especially when there is a difference in low density, so that the second and third reference voltages V
By adjusting r2 and Vr3 individually, it is possible to reduce the difference between the light emission powers of the LDs 1a and 1b due to the lower bit data D1b and D2b.

Further, if a process pattern is formed on the surface of the photosensitive drum 7 for each of the LDs 1a and 1b and its density is adjusted, it is not necessary to select the LDs 1a and 1b or perform detailed power adjustment. In addition, it is also possible to eliminate the low density difference between the LDs 1a and 1b that normally occurs due to the deterioration of the portion (engine) of the image forming apparatus that executes the image forming process or the environmental change, and thus it is possible to prevent the image from deteriorating.

Therefore, processing including formation of a process pattern for each of the LDs 1a and 1b and adjustment of its density will be described.
This will be described in more detail. In this case, the data control unit 2
0 'also functions as a specific image data generating means, a process pattern forming means, and a density detecting means.

The data control unit 20 ′ operates at a predetermined timing, for example, between sheets (after the image forming process for one sheet is completed and before the image forming process for the next sheet is started). Specific image data for forming a process pattern for adjustment (usually a simple quadrangular solid pattern) on the surface of the photosensitive drum 7 is generated, and the specific image data corresponds to each of the LDs 1a and 1b. LD
Upper bit control units 31, 41 of the modulation units 30, 40, D / A1
Current setting units 32 and 42, D / A2 addition current setting units 33 and 43
To perform image forming processing.

Thus, a process pattern is sequentially formed on the surface of the photosensitive drum 7 for each of the LDs 1a and 1b. The data control unit 20 'sequentially detects the density of each process pattern sequentially formed for each of the LDs 1a and 1b using a density sensor (not shown), and outputs a second reference voltage which is an individual reference voltage according to each density detection result. , And third reference voltages Vr2 and Vr3 are individually output (at this time, the second and third reference voltages Vr2 and Vr3 are output so that the density of each process pattern becomes the target density).
The third reference voltages Vr2 and Vr3 are individually set and changed) to perform low-density density adjustment.

[0053]

As described above, according to the image forming apparatus of the first aspect of the present invention, the data control means converts the image data of each pixel for each laser light source into upper bit data and lower bit data. And outputs a common first reference voltage and a common second reference voltage to each laser light source, and the high-order bit control means for each laser light source outputs the high-order bit data of the image data for each pixel. A timing signal for pulse width modulation is output according to the bit data, and an identification signal for identifying whether the upper bit data indicates the lowest value is output. Based on the reference voltage, a current value for power modulation is set and output according to the timing signal and the lower bit data, and each level is output. Only when the addition current setting means for the light source recognizes from the identification signal that the upper bit data indicates the lowest value, the power modulation for the power source is performed in accordance with the lower bit data based on the second reference voltage. Current output means for each laser light source adds the current value for the addition to the current value for power modulation, and outputs the current value after the addition, The driving means causes the corresponding laser light source to emit light by pulse width modulation and power modulation according to the current value after the addition, thereby realizing smoothness of an image at a low density.

According to the image forming apparatus of the second and third aspects, the data control means divides the image data for each pixel for each laser light source into upper bit data and lower bit data and outputs the data. A common reference voltage and an individual reference voltage are output to the laser light source, and the high-order bit control means for each laser light source outputs a timing signal for pulse width modulation in accordance with the high-order bit data of the image data for each pixel. Output and an identification signal for identifying whether the upper bit data indicates the lowest value, and the current setting means for each laser light source outputs the timing signal and the lower bit data based on the common reference voltage. A current value for power modulation is set and output in accordance with the sum. Only when each of the identification signals recognizes that the upper bit data indicates the lowest value, sets a current value for power modulation addition in accordance with the lower bit data based on the individual reference voltage. Output, and a current adding means for each laser light source,
The current value for the addition is added to the current value for the power modulation, and the current value after the addition is output. The driving unit drives the corresponding laser light source according to the current value after the addition by pulse width modulation. And power modulated to emit light,
By individually adjusting the individual reference voltages, it is possible to reduce the difference in the light emission power of each laser light source due to the lower bit data (match the low density of each laser light source). Therefore, smoothness of the image at a low density can be realized for each laser light source.

Further, according to the third aspect of the present invention, the data control means generates specific image data for forming a process pattern for density adjustment on the surface of the photoreceptor, and generates the specific image data for each laser light source. By outputting to upper bit control means, current setting means, and addition current setting means,
By forming a process pattern on the photoreceptor surface by image forming processing, sequentially detecting the density of the process pattern for each laser light source, and individually outputting the individual reference voltages according to the respective density detection results, each laser It is also possible to eliminate a low density difference between the light sources, and to prevent image deterioration without selecting each laser light source or performing detailed power adjustment.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a main part of a control unit of an image forming apparatus including the multi-beam writing device illustrated in FIG.

FIG. 2 is a perspective view illustrating a configuration example of a mechanism of a multi-beam writing device in the image forming apparatus according to an embodiment of the present invention.

FIG. 3 is an enlarged perspective view of the LD array 1 of FIG.

FIG. 4 shows image data output from the data control unit 20 of FIG. 1 and currents output from the D / A1 current setting units 32 and 42, the D / A2 addition current setting units 33 and 43, and the current addition units 34 and 44. FIG. 4 is a diagram illustrating a relationship with a value.

5 is a block diagram illustrating another configuration example of a main part of a control unit of the image forming apparatus including the multi-beam writing device illustrated in FIG. 2;

[Explanation of symbols]

 1: LD array 1a, 1b: LD (laser diode) 4: Polygon mirror 7: Photoreceptor drum 20, 20 ': Data control unit 30, 40: LD modulation unit 31, 41: Upper bit control unit 32, 42: D / A1 current setting unit 33, 43: D / A2 addition current setting unit 34, 44: current addition unit 35, 45: LD driving unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA07 AA54 BA56 CA11 CB73 2H045 AA01 BA02 BA23 BA32 CB33 5C072 AA03 BA15 BA19 HA02 HA06 HA13 HB02 HB06 HB20 QA14 UA16 XA01 XA05 5C074 AA02 H0307H DD DD

Claims (3)

[Claims] A plurality of laser beams output from each of a plurality of laser light sources are periodically deflected by using a rotating polygon mirror, and the laser beams are moved in a sub-scanning direction with a positional difference in the sub-scanning direction. An image forming apparatus that forms an electrostatic latent image by scanning the photoconductor surface in the main scanning direction and develops the electrostatic latent image with toner to form a toner image. Data control means for dividing the image data of each pixel into upper bit data and lower bit data and outputting the same, and outputting a common first reference voltage and a common second reference voltage to each laser light source; A timing signal for pulse width modulation is output according to the upper bit data of the image data for each pixel, and the upper bit data is set to the lowest value. An upper bit control unit for each laser light source that outputs an identification signal for identifying whether or not the power supply is indicated, and setting a current value for power modulation according to the timing signal and the lower bit data based on the first reference voltage. Current setting means for each laser light source to output the light, and only when it is recognized from the identification signal that the upper bit data indicates the lowest value, based on the lower bit data based on the second reference voltage. Addition current setting means for each laser light source for setting and outputting an added current value for power modulation, and respectively adding the added current value to the power modulation current value, and calculating the added current value. Current adding means for each laser light source to be output; and pulse width modulation of the corresponding laser light source according to the current value after the addition. An image forming apparatus characterized in that a driving means for emitting light by power modulation and. 2. A plurality of laser beams output from a plurality of laser light sources are periodically deflected by using a rotating polygonal mirror, and the laser beams are moved in the sub-scanning direction with a positional difference in the sub-scanning direction. An image forming apparatus that forms an electrostatic latent image by scanning the photoconductor surface in the main scanning direction and develops the electrostatic latent image with toner to form a toner image. Data control means for outputting image data for each pixel by dividing into upper bit data and lower bit data, and outputting a common reference voltage and an individual reference voltage to each laser light source; A timing signal for pulse width modulation is output according to the upper bit data of the data, and whether or not the upper bit data indicates the lowest value is determined. An upper bit control unit for each laser light source that outputs an identification signal for identifying the same, and setting and outputting a power modulation current value according to the timing signal and the lower bit data based on the common reference voltage. Current setting means for a laser light source, and addition for power modulation according to the lower bit data based on the individual reference voltage only when each of the identification signals recognizes that the upper bit data indicates the lowest value. Addition current setting means for each laser light source that sets and outputs a current value for each laser light source; and each laser light source that adds the current value for the addition to the current value for power modulation and outputs the current value after the addition. Current addition means for the pulse width modulation and power of the corresponding laser light source according to the current value after the addition. An image forming apparatus characterized in that a driving means for emitting light by tone. 3. The image forming apparatus according to claim 2, wherein the data control unit generates specific image data for forming a process pattern for density adjustment on the photoconductor surface, By outputting the specific image data generated by the means to the higher-order bit control means, the current setting means, and the addition current setting means corresponding to each of the laser light sources, the image forming process allows the process to be performed on the photosensitive member surface. A process pattern forming unit for forming a pattern; and a density detecting unit for sequentially detecting the density of each process pattern sequentially formed for each of the laser light sources by the unit. Wherein the individual reference voltages are output individually.