JP3160310B2 - Image forming apparatus and image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser printer, a digital copying machine, and a facsimile apparatus and an image forming method .

[0002]

2. Description of the Related Art Generally, in an image forming apparatus such as a laser printer or a digital copying machine, for example, a dither method, a density pattern method, an error diffusion method, and the like are used as a recording method for improving image quality of a half tone. ing.

However, when using these recording methods,
Even if the reproduction of halftones is good, problems such as a decrease in resolution, generation of moiré, generation of texture, and generation of jaggedness in oblique lines or curved portions occur.

Therefore, in an image forming apparatus using laser exposure, pulse width modulation in which laser light (laser beam) is modulated in a time of one pixel or less has been proposed to compensate for these disadvantages.

[0005] Further, pulse width modulation has been developed with the aim of further improving the image quality of oblique lines or curved portions.
It has been proposed to specify the position of the pulse. As a circuit for realizing this pulse width modulation and pulse position designation, a combination of a plurality of triangular wave generation circuits, a D / A converter and a comparator (see Japanese Patent Application No. 1-79571), a combination of a delay line and a logic circuit (See Japanese Patent Application No. 2-65857).

[0006]

However, in the former method, the analog waveforms of a plurality of triangular wave generating circuits having different shapes are selected according to the position designation of the pulse, so that each analog waveform differs from the ideal shape. In such a case, there are problems that the gradation characteristics are different depending on the position designation of the pulse, and that a beautiful oblique line or curve cannot be reproduced.

The latter method has the disadvantage that the circuit scale becomes large when the number of tones to be expressed is large, and the circuit operation becomes unstable when the image frequency becomes high.

Accordingly, the present invention provides a circuit which can reproduce beautiful oblique lines and curves without depending on the gradation position depending on the position of a pulse, and can be used even when the number of gradations to be expressed is large or the image frequency is high. Image forming apparatus and image forming that are not so large and can stably perform pulse width modulation of laser light
The aim is to provide a method .

[0009]

An image forming apparatus according to the present invention irradiates a light beam onto an image carrier to form an image in pixel units. Output means for outputting a position signal indicating the position of the target pixel signal, for the pixel signal to be image-formed by the image forming means, based on the position signal output from the output means, inversion processing or Processing means for performing non-inverting processing; generating means for generating a reference signal whose output changes with the passage of time; and comparing the pixel signal processed by the processing means with the reference signal generated by the generating means A comparison unit, and a control unit that controls an image forming operation by the image forming unit according to a comparison result compared by the comparison unit and a position signal output from the output unit. There. The image forming method of the present invention includes:
By irradiating a light beam on the image carrier, the image is
Image forming apparatus having image forming means for forming in units
A pixel to be subjected to image formation by the image forming means.
A position signal indicating the position of the signal is output to the image forming means.
The position signal with respect to the pixel signal to be image-formed.
Performs inversion or non-inversion based on
Generates a reference signal whose output changes over time.
The pixel signal subjected to the inversion processing or the non-inversion processing and the above
Compare with the reference signal and compare the comparison result with
The image forming operation by the image forming means in accordance with the position signal.
It is characterized by controlling.

[0010]

According to the present invention, an image is formed in a pixel unit by an image forming means by irradiating a light beam onto an image carrier, and a position signal indicating a position of a pixel signal to be subjected to the image formation is outputted by an output means. And inverting or non-inverting processing is performed by the processing unit on the basis of the position signal output from the output unit with respect to the pixel signal to be image-formed by the image forming unit. A reference signal whose output changes together with the generation means is generated by the generation means, and the pixel signal processed by the processing means is compared with the reference signal generated by the generation means. The comparison result is output from the output means. The image forming operation of the image forming means is controlled in accordance with the position signal.

[0011]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a sectional view of a full-color recording apparatus as an image forming apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a photosensitive drum as an image carrier which rotates counterclockwise. Around the photosensitive drum 1, a charger 2, a first developing device 9, a second developing device 10, a third developing device 11, a fourth developing device 1
2. A transfer drum 15 as a transfer material support, a static eliminator 13 before cleaning, and a photoconductor cleaner 14 are arranged.

A polygon mirror 7 for scanning a laser beam (laser beam) from a semiconductor laser (laser diode 45, 46) to be described later, and a polygon motor for driving the polygon mirror are provided between the charger 2 and the first developing device 9. 8, an exposure unit 3 including a lens 6, a mirror 5, and a mirror 4. The developing units 9 to 12 develop the electrostatic latent image on the photosensitive drum 1 with four different colors of toner. For example, the first developing unit 9 is magenta, the second developing unit 10 is cyan, and the third developing unit 11 Is a yellow toner, and the fourth developing device 12 has a black toner.

The photosensitive drum 1 whose surface is uniformly charged by the charger 2 is exposed by the above-described exposure unit 3 scanned by image data, forms an electrostatic latent image, and corresponds to the image data. The toner is developed by the developing devices 9 to 12 and is sequentially transferred by the transfer charger 17 to the transfer material electrostatically attracted to the transfer drum 15. The untransferred toner on the photoconductor drum 1 is cleaned by a pre-cleaning static eliminator 13 and after the static elimination, the photoconductor cleaner 14.

On the other hand, paper as a transfer material is stored in a cassette 23.
The paper is sent out by the paper feed roller 24 and the registration roller 25
Once aligned. The transfer material is transferred from the transfer drum 15
Suction roller 2 provided at a position corresponding to the suction position of
6. The sheet is sent to the attraction charger 16 by the registration roller 25 and is electrostatically attracted onto the transfer drum 15 by the attraction charger 16. Thereafter, as described above, the color toner on the photosensitive drum 1 is transferred by the transfer charger 17 provided at a position facing the photosensitive drum 1. When performing multicolor printing, the above-described development process and transfer process are repeated up to four times. Then, the transfer material is separated from the transfer drum 15 by the separation unit 27, and is discharged to the tray 31 via the conveyance belts 28 and 29 and the fixing unit 30. Next, a control system of the full-color printing apparatus will be briefly described with reference to FIG.

In FIG. 1, reference numeral 41 denotes an external device, which is connected to the full-color printing apparatus via an interface circuit 42. Examples of the external device 41 include a color scanner, a computer, a word processor,
Examples include a personal computer and an image processing device.

The following are prepared as the interface signals of 42. That is, the IHSYNO signal is a horizontal synchronizing signal which is output from this device to the external device 41 prior to the transfer of image data for one scan. IVC
The LKO signal is a clock signal output from the external device 41 to this device. The IVDATs 70 to 00 are image data, which are transferred from the external device 41 to this device in synchronization with the aforementioned IVCLKO signal.

The IVDATs 70 to 00 are image data corresponding to the operation (color stage) of this apparatus. That is, since this apparatus has four developing devices 9 to 12 built-in as described above, for example, when the recording operation is performed using the magenta developing device 9, the magenta image data is stored in the IVDAT70. The signal is transferred from the external device 41 to this device in response to the ~ 00 signal. Similarly, when the recording operation is performed in the cyan developing device 10, the cyan image data is transmitted to the black developing device 12 when the recording operation is performed in the yellow developing device 11. When the recording operation is performed, the black image data is transferred from the external device 41 to this device.

In addition, various signals necessary for control are prepared between the external device 41 and this device.
The external device 41 can control this device using these signals.

The interface circuit 42 has a plurality of line buffers for temporarily storing image data sent from the external device 41, so that the image data can be processed asynchronously with the external device 41. I have.

An image signal processing circuit 43 reads out the image data stored in the line buffer of the interface circuit 42 and performs an appropriate process (details will be described later).
The HSYNO signal is a signal equivalent to the above-described IHSYNO signal. The RDCLKO signal is output from the interface circuit 4
2 is a read clock for reading out image data from a line buffer built in 2.

VDATs 70 to 00 are image data read from the line buffer. The BDO signal is a signal obtained by inverting a BD1 signal described later, and is a laser drive circuit 44.
Are sent to the image processing circuit 43. The above I
The HSYNO signal and the HSYNO signal are created based on the timing of the BDO signal. SHARPO
The signal is a signal for selecting a laser beam that scans the photosensitive drum 1. That is, when the SHARPO signal is at a low level (hereinafter abbreviated as L level), a laser beam having a small beam diameter (light energy is concentrated) scans the photosensitive drum 1.

On the other hand, when the SHARPO signal is at a high level (hereinafter abbreviated as H level), a laser beam having a large beam diameter (light energy is dispersed) scans the photosensitive drum 1. The LDO signal corresponds to the image data VDAT70.
This is a laser drive signal that changes on the basis of .about.00.

When the LDO signal is at the L level, the laser diode 45 or 46 emits light, and when the LDO signal is at the H level, it does not emit light. The SMPO signal is a signal for forcing the laser diode 45 or 46 to emit light. This SMP
When the O signal is at the L level, the laser diode 45 or 46 emits light. The SMPO signal is a signal for forcibly emitting light from the laser diode 45 or 46 outside the image forming area to measure the emission power and to obtain the reference signal BD1 (BDO) from the photodiode 48.

The laser drive circuit 44 is a circuit that causes the laser diode 45 or 46 to emit light in response to the SHARPO signal, LDO signal, and SMPO signal from the image signal processing circuit 43 and receives the reference signal BD1 from the photodiode 48. IFA is a signal for causing the laser diode 46 to emit light, and ISA is a signal for causing the laser diode 46 to emit light.
Is a monitor signal of the light emission power of FIG. Similarly, IFB is a signal for causing the laser diode 45 to emit light, and ISB is a monitor signal of the emission power of the laser diode 45.

The laser drive circuit 44 monitors the light emission power of the laser diode 45 or 46 and controls the laser diode 45 or 46 to emit light at a certain power designated by the control circuit 49.
47 is a half mirror and a laser diode 45 or 4
6 is arranged so that the laser light generated from any one of them reaches the photosensitive drum 1.

The control circuit 49 is composed of a microcomputer and its peripheral circuits, and performs various data processing and various controls. The main functions of the control circuit 49 are listed below.

(1) The information from the interface circuit 42, that is, the command from the external device 41 is decoded, and each section of the device is controlled according to the instruction. Also, the status corresponding to the command is output to the external device 41 through the interface circuit 42. (2) The display content is output to a display LED (not shown) or a 7-segment display (not shown) of the control panel 53. (3) On / off control of the various solenoids 51,... (4) Information from various switches and the sensor 52 is taken in and processed. (5) Various parameters are set to the image signal processing circuit 43 and internally generated pattern data is transmitted. (6) The mirror motor driver 54 is turned on and off by the mirror motor 8. (7) The laser drive circuit 44 sets the power of the laser emission and monitors the power.

(8) Control of the high voltage power supply 56 is performed.
That is, output on / off control and output power setting for the charger 2, output on / off control for the transfer charger 17 are performed.
OFF control and output power setting, output on / off control and output power setting for developing bias, output on / off control and output power setting for adsorption charger 16, other output on / off control and power for high voltage output Make settings. It also monitors whether each output is operating normally. (9) ON / OFF control of the photoreceptor drum motor driver 57 and the transfer drum motor driver 58 and monitoring of whether or not a steady rotation is performed. (10) On / off control of various fan motors 50 is performed. (11) ON / OFF control of a pre-exposure lamp (not shown) is performed. (12) Monitor the temperature of the heat roller of the fixing unit 30;
On / off control of the heater lamp is performed. (13) The operation timing of this device is controlled by a signal from the reference timing creation circuit 59. (14) The toner supply motor driver 215 is controlled to operate the toner supply motor of the color that needs to be supplied among the four toner supply motors. As described above, the control circuit 49 corresponds to the command section of this device. Next, a drive system for the photosensitive drum 1 and the transfer drum 15 will be briefly described.

As shown in FIG. 1, the photosensitive drum 1, the photosensitive drum motor 61, and the photosensitive drum motor encoder 6
0 is coaxial. Therefore, the output of the photoconductor drum motor encoder 60 can be used as rotation information of the photoconductor drum 1.

Similarly, the transfer drum 15, the transfer drum motor 63, and the transfer drum motor encoder 62 are coaxial. Therefore, the output of the transfer drum motor encoder 62 can be used as rotation information of the transfer drum 15. The outputs of the photosensitive drum motor encoder 60 and the transfer drum motor encoder 62 are both input to the reference timing creation circuit 59.

The sensor 64 and the sensor 65 are both located on the sides of the transfer drum 15 and output a signal when the transfer drum 15 reaches a specific rotation position. For example, a projection is provided at the end of the transfer drum 15, and a photo interrupter is installed at a point where the projection passes. The outputs of the two sensors 64 and 65 are input to a reference timing creation circuit 59.

Next, the exposure section (optical system) 3 of the apparatus will be described in detail. This device has two laser diodes 45 and 46 mounted thereon as described above, and according to an image to be recorded, a laser diode 4 suitable for the image is provided.
Exposure is performed at 5, 46. The positional relationship between the two laser diodes 45, 46, the half mirror 47, and the polygon mirror 7 will be described with reference to FIG.

As shown in FIG. 3, the laser light generated from the laser diode 45 is reflected by the half mirror 47 and reaches the polygon mirror 7. On the other hand, the laser diode 4
The laser light generated from 6 passes through the half mirror 47,
The light reaches the polygon mirror 7. At this time, polygon mirror 7
The optical path (optical axis) to the laser beam is adjusted so that the laser beam generated from the laser diode 45 and the laser beam generated from the laser diode 46 are exactly the same.

The distance DB between the laser diode 45 and the half mirror 47 is set to be shorter by about 3 mm than the distance DA between the laser diode 45 and the half mirror 47. Therefore, the optical path length to the photosensitive drum 1 is larger for the laser diode 45 than for the laser diode 4.
It is about 3 mm shorter than 6.

FIG. 4 is an enlarged view showing a state in which the photosensitive drum 1 is exposed by the laser beams generated from the laser diodes 45 or 46 having different optical path lengths. As shown in FIG. 4, the laser beams a1 and a2 gradually become thinner from the exposure unit 3 to expose the photosensitive drum 1. The laser beam a1 shown in FIG. 4 corresponds to the laser beam generated from the laser diode 45 when the photosensitive drum 1 is exposed at the point where the laser beam is thinnest.

The laser light a2 shown below is thicker on the photosensitive drum 1 than the laser light a1. This laser light corresponds to the laser light generated from the laser diode 46. In this laser beam a2,
The distance d from the point at which the laser light becomes thinnest to the surface of the photosensitive drum 1 is about 3 mm.
It is equal to the difference in the optical path length between the laser diodes 45 and 46 and the photosensitive drum 1.

The laser beam a1 on the photosensitive drum 1
Is about 10 μm in the main scanning direction, and the beam diameter φ2 of the laser beam a2 in the main scanning direction is about 50 μm. Next, the distribution of light energy when images are formed with laser beams having different beam diameters in the main scanning direction and the images will be described with reference to FIGS.

FIG. 5A shows a laser driving pulse (LDO) signal, a light energy distribution, and an image of an image when the laser light is emitted for a certain unit time in a state where the light energy of the laser light is concentrated. It shows the relationship. FIG.
As shown in the figure, the light energy has a steep peak distribution.

Since it is difficult to consider such a light energy distribution in the form of a mountain, the light energy distribution is simply modeled as a square wave, and the image is modeled as a rectangle, as shown in the right figure. In this case, the SHARPO signal output from the image signal processing circuit 43 is at the L level, and the laser beam on the photosensitive drum 1 corresponds to the most narrowed position while the laser diode 45 is emitting light. As shown in FIG. 4, the laser beam is thin as indicated by the beam diameter φ1.

FIG. 6 shows the distribution of light energy and the appearance of an image when a laser drive pulse (LDO) signal having a pulse width modulated as shown in FIG. . As is apparent from FIG. 6, when an image is formed in a state where light energy is concentrated, a clear black and white image that is faithful to the laser drive pulse (LDO) signal is given.

Note that P in the figure represents time and distance corresponding to one pixel, and it is assumed that the laser beam is scanning from left to right. As a result, an image as shown in FIG. 7B can be obtained for an image to be expressed as shown in FIG. Therefore, it is possible to print an image having no gradation, such as a character or a diagram, with good image quality.

On the other hand, FIG. 8 shows a laser drive pulse (LD) when a laser is emitted for a certain unit time in a state where the light energy distribution of the laser light is spread more smoothly than in FIG.
O) shows the relationship between the signal, the light energy distribution, and the image. As shown in the figure, the light energy has a gentle mountain distribution, and the total light energy is the same as the case where the light energy shown in FIG. 5 is concentrated.

The image has a lower density than the case of FIG. 5 because the light energy per unit area is weak. If this situation is modeled in the same manner as in FIG. 5, the light energy distribution can be considered to be approximated as a long rectangular wave and the image approximated to a square as shown in the right figure. In this case, SHARP output from the image signal processing circuit 43
The O signal is at the H level, and the laser diode 46
In the state where the light is emitted, the laser light on the photoconductor 20 corresponds to a position deviated from the most narrowed position, and the laser light is in a thick state like the beam diameter φ2 shown in FIG.

FIG. 9 shows the case where the same signal as the pulse width modulated laser drive pulse (LDO) signal shown in FIG. 6 is given by using a laser beam in which light energy is dispersed to some extent as shown in FIG. Is a model of the light energy distribution and the state of the image. As can be seen from this figure, when the light energy is dispersed, the light energy is distributed in a mountain-like manner, and an intermediate energy level not shown in FIG. 6 can be output. When the photoconductor 1 is exposed and developed with such a light energy distribution, a halftone (halftone) can be expressed. The image in FIG. 9 shows that the higher the light energy, the higher the image density. Therefore, an image having gradation, such as a photograph, can be printed with good image quality.

As described above, the shape of the laser beam for writing an image can be changed according to the type of image to be recorded. That is, the beam shape of the laser beam for writing the image is small when recording an image such as a character or a diagram, and when recording an image having a gradation such as a photograph,
By increasing the size, any image can be reproduced with high image quality.

As shown in FIG. 10, the image processing circuit 43 comprises a timing circuit 71, a laser beam shape emission timing control signal generation circuit 72, a conversion table 73, a pulse generation circuit 74, and a toner consumption count circuit 75. ing. The configuration of the timing circuit 71 is shown in FIG.
Next, the timing charts are shown in FIGS.
Shown in

As shown in FIG. 11, the timing circuit 71 includes a waveform shaping circuit 81, a crystal oscillator 82, a clock phase synchronizing circuit 83, a frequency dividing circuit 84, an AND gate 85, and a pulse generating timing signal generating circuit 86. Have been.

The timing circuit 71 is for generating a reference signal required by each circuit from the BDO signal and MGOUT0. The BDO signal is formed based on the BD1 signal and is scanned by a polygon mirror.・
It is low during periods when the beam is passing through the photodiode, and high during other periods.

By the waveform shaping circuit 81, the BDO signal is converted to an H level of a constant pulse width of a negative level with respect to the leading or trailing edge thereof.
The SYN0 signal is output. The crystal oscillator 82 is a clock generation source, and always outputs a clock at a stable frequency. The clock phase synchronization circuit 83 synchronizes the phase of the clock of the crystal oscillator 82 with the rising timing of the HSYN0 signal, and the synchronized clock always has a fixed phase relationship with the rising of the HSYNO signal. ing. The synchronized clock is frequency-divided by half by the frequency dividing circuit 84.

The control circuit 49 generates an MGOUT0 signal (L level in the image area and H level in the areas other than the image area) based on the clock VDCLK0 synchronized with the HSYNC0 signal. )
Occurs. The VDCLK0 signal is input to an AND gate 85, and is gated with a signal obtained by inverting the signal MGOUT0 representing an image area to produce RDCLK0. RD
CLK0 is output only in the image area and serves as a reference clock for reading image data.

Pulse generation timing signal generation circuit 86
Is a synchronized clock (clock phase synchronization circuit 8
3) and an HSYN0 signal to generate an enable signal, a trigger signal, a reset signal, a latch selection signal, and the like as various timing signals required for the pulse generation circuit 74.

The laser beam shape emission timing control signal generating circuit 72 adjusts the pulse position of the print pixel, that is, the laser emission timing within one pixel to the left or according to the print pixel and image data adjacent before and after the print pixel. High-quality printing is enabled by selecting right-justified or by narrowing down the laser beam shape or increasing it by blurring.

The conversion table 73 stores the image data VDATs 70 to 00 sent from the interface circuit 42.
Is a conversion table for converting the data into pulse width modulation data PWDAT7-0. In this conversion table 73,
The color of the toner used for development, the type of image such as text and photos, laser power, various process conditions, aging,
The contents of an arbitrary table can be selected according to changes in other conditions, and the contents of the table can be rewritten from the control circuit 49 to arbitrary data.

Next, the pulse generating circuit 74 will be described with reference to FIG.
3, and will be described with reference to FIGS. FIG. 13 is a block diagram of the pulse generation circuit 74, and FIG. 15 is a timing chart thereof.

As shown in FIG. 13, the pulse generation circuit 74
Is composed of the following. That is, the pulse width data PWDAT7-0 are converted to the pulse position designation signal LEFT.
A data inversion / non-inversion selection circuit 110 for selecting whether or not to invert according to the level of 1, and two sets of latches for latching the data output from the data inversion / non-inversion selection circuit 110 and the pulse position designation signal LEFT1 Circuits 111, 1
12, two D / A converters 114 and 116 for converting the 8-bit data from the latch circuits 111 and 112 into analog signals, and two ramp generators 113 and 115 for generating triangular waves at different timings. Two comparators 117 and 118 for comparing the outputs of the D / A converters 114 and 116 with the outputs of the ramp generators 113 and 115, respectively, and the latch circuit 11
, And two XOR circuits 119 and 120 having the outputs of the comparators 117 and 118 as inputs, and the outputs of these XOR circuits 119 and 120 and the timing circuit 7.
AND circuits 121 and 122 for inputting a signal from
NO with the outputs of AND circuits 121 and 122 as inputs
And an R circuit 123.

As is apparent from FIG. 13, the signals after the data inversion / non-inversion selection circuit 110 have the same circuit in two systems and operate in the same manner. However, the operation timing differs depending on the signal from the timing circuit 71.

FIG. 14 shows a data inversion / non-inversion selection circuit 11.
FIG. 2 is a diagram showing a specific example of a circuit configuration of 0, which is configured by a non-inverting buffer 131, an inverting buffer 132, a buffer 133, and an inverter circuit 134. FIG.
As shown in FIG. 4, when the pulse position designation signal LEFT1 is at the L level, the non-inverting buffer 131 is selected, and the pulse width data PWDAT7 to PWDAT0 remain non-inverting and the latch circuit 11
1, 112. On the other hand, the pulse position designation signal L
When EFT1 is at the H level, the inversion buffer 132 is selected, and the pulse width data PWDAT7-0 are inverted,
The data is transferred to the latch circuits 111 and 112.

Here, pulse width data PWDAT7-0
The relationship between the pulse position designation data LEFT1 signal, the laser emission, and the output image will be described. In the pulse width data PWDAT7-0, PWDAT7 is M
SB and PWDAT0 are LSB.

The pulse width data PWDAT7-0
The relationship between the laser emission time and the laser emission time is as follows: when PWDAT7-0 is "FFH", the laser emission time is 100%
Laser emission time is 0% when DAT7-0 is OOH
(No light emission). Here, 100% means
This means all the time allocated to one pixel.
That is, the pulse width data PWDAT7 to PWDAT0 are, for example, "4
In the case of “FH”, the laser emission time for that pixel is approximately 31% according to the following equation. 4FH / FF
H = 79/255 = 0.3098

The pulse position designation signal LEFT1 is
When the laser emits light for 100% or less of the time, this signal is used to specify at what timing the laser is emitted for successive pixels. That is, when the pulse position designation signal is at the H level, the laser is continuously emitted from the immediately preceding pixel, and when the pulse position designation signal is at the L level, the laser is emitted continuously from the immediately succeeding pixel.

In this embodiment in which the laser beam is scanned from left to right with respect to the output image, the pulse position designation signal L
When the EFT1 is at the H level, the laser emits light continuously to the left pixel in the pixel, and when the EFT1 is at the L level, the laser emits light so as to continue to the right pixel. In the case of this embodiment, the configuration is such that toner adheres to the portion exposed by the laser beam.

Next, the signal flow of the pulse generation circuit 74 will be described with reference to FIGS. As a specific example, a case where the pulse width data PWDAT7 to PWDAT0 are "4FH" and the pulse position designation signal LEFT1 changes from L level to H level to L level as shown in FIG. As described above, whether the data input to the data inversion / non-inversion selection circuit 110 is inverted or non-inverted depending on the level of the pulse position designation signal LEFT1.

As shown in FIG. 15B, the pulse position designation signal LEFT1 for the pulse width data PWDAT7-0 of the first two pixels is at the L level, and the pulse position for the pulse width data PWDAT7-0 of the third pixel is L level. Designation signal LEFT1 is at H level. Furthermore, the fourth pixel,
The pulse position designation signal LEFT1 for the pulse width data PWDAT7-0 of the fifth pixel is at the L level. Therefore, the data output from the data inversion / non-inversion selection circuit 110 is “4FH” for the first, second, fourth, and fifth pixels, and “BOH” for the third pixel.

The data output from the data inversion / non-inversion selection circuit 110 and the pulse position designation signal LEFT1
Is latched by the latch circuits 111 and 112. The latch timing is determined by the latch circuit 111 and the timing circuit 7.
1 is determined by the signal LTA1 from the latch circuit 1
12 is determined by the signal LTB1 from the timing circuit 71. The LTA1 signal and the LTB1 signal are alternately output from the timing circuit 71 for each pixel.

As shown in FIG. 15D, the first pixel,
The LTA1 signal is output to the third pixel and the fifth pixel, and the data output from the inversion / non-inversion selection circuit 110 for that pixel is latched in the latch circuit 111 as shown in FIG. It indicates that Note that LTB1 is used for the data of the second and fourth pixels.
A signal is output, and output data from the inverting / non-inverting selecting circuit 110 is latched in the latch circuit 112, but is omitted in this timing chart.

Hereinafter, the signal flow will be described using the data latched by the latch circuit 111. The operation of the data latched by the latch circuit 112 is exactly the same as the operation of the data latched by the latch circuit 111, and a description thereof will be omitted.

The data for each pixel latched by the latch circuit 111 is output to the D / A converter 114,
Converted to analog level. D / A converter 114
Changes the level of an output analog signal in accordance with the number of input digital data. That is, when the input to the D / A converter 114 is “FFH”, the output level (voltage) of the analog signal is maximum, and when the input is “OOH”, the output level (voltage) of the analog signal is minimum.

Therefore, when "4FH" is input as an input, the output level of the analog signal of the D / A converter 114 is about 31% when the maximum output is 100% and the minimum output is 0%. Becomes When "BOH" is input as an input, the output level is about 69%.

The analog signal output from the D / A converter 114 is input to the comparator 117. The comparator 117 compares the analog signal output from the D / A converter with the analog signal output from the ramp generator 113, and outputs the result as an H level or an L level.

That is, as shown in FIG. 15 (j),
If the analog signal output from the D / A converter 114 is larger than the analog signal output from the ramp generator 113 (if the voltage is high), the output is set to H.
Output the level, and vice versa
Analog signal output from the D / A converter 1
If the signal is larger than the analog signal output from 14 (if the voltage is high), an L level is output as an output.

Next, the ramp generators 113 and 115
Will be described. Trigger inputs TRGA1, TRG1, TRG1
B1 and reset inputs RSTA1 and RSTB1 are input. When the trigger input TRGA1 or TRGB1 is input, the output level (voltage level) of the ramp generator 113 or 115 starts to gradually decrease.

When the reset input RSTA1 or RSTB1 is inputted, the output level (voltage level) of the ramp generator 113 or 115 is obtained.
Returns to the level before the trigger input was input.
That is, the lamp generators 113 and 115 are charge / discharge circuits that start discharging by a trigger input and are charged to the original potential by a reset input. Further, the potential drop due to this discharge is proportional to time.

FIG. 15I shows this operation of the ramp generator 113. (I) of FIG.
As apparent from FIG. 15, the TRG shown in FIG.
The rising edge of A1 causes the ramp generator 11
The output (voltage) of 3 starts to drop. And this gradient is constant.

Next, when the reset input RSTA1 shown in FIG.
Output (voltage) quickly returns to the original level. The ramp generator 113 repeats this operation at a cycle of two pixels. Note that the trigger inputs TRGA1, TRG1,
B1 and reset inputs RSTA1 and RSTB1 are both
This signal is output from the timing circuit 71 in a two-pixel cycle. Although the operation of the ramp generator 115 is not shown in FIGS. 15A to 15P, the operation is out of phase with the ramp generator 113 by one pixel. That is, TRGA1 and TRGB1
, And the phases of RSTA1 and RSTB1 are also shifted by one pixel. That is, the ramp generators 113 and 115 are circuits that output a part of a triangular wave (an analog waveform that repeats charging and discharging).

As shown in FIG. 15 (j), the output of the comparator 117 is the result of comparison between the output level of the D / A converter 114 and the output level of the ramp generator 113. Therefore, the comparator 117 when the input data to the D / A converter 114 is “4FH”
Is compared with the output of the comparator 117 when the input data to the D / A converter 114 is "BOH", the former has a shorter H level. The output of the comparator 117 and the latch circuit
The exclusive OR of the LEFT1 signal (f) latched at 111 is calculated by the XOR circuit 119 as shown in FIG.
Output. Therefore, the latch circuit 111
When the input LEFT1 signal (f) is at the H level, the output of the comparator 117 is inverted and output from the XOR circuit 119.

On the other hand, the latch
When the LEFT1 signal (f) is at the L level, the output of the comparator 117 is output from the XOR circuit 119 as it is. The output of the XOR circuit 119 is
21 and is logically ANDed with the ENA1 signal from the timing circuit 71 shown in FIG. EN
The A1 signal is a square wave of two pixel periods that goes high only while the output of the XOR circuit 119 is valid.

The AND circuit 121 thus obtained
As shown in FIG. 15 (m), while the output is at the H level, the laser emits light. Therefore, when focusing on the output of the AND circuit 121 for the first pixel in which the pulse width data PWDAT7 to 0 are “4FH” and the pulse position designation signal LEFT1 is at the L level, the laser is approximately 31 It is understood that the signal is such that the laser emits light in%.

The output of the AND circuit 121 for the third pixel in which the pulse width data PWDAT7-0 is “4FH” and the pulse position designation signal LEFT1 is at the H level is approximately 31% of the first half of the pixel, that is, the left side. It can be seen that the signal emits light.

On the other hand, a laser drive signal is output to the output of the AND circuit 122 for the second pixel and the fourth pixel by the same circuit operation. By taking the logical sum of the outputs of the AND circuit 121 and the AND circuit 122, a laser drive signal for all the pixels can be obtained.

As described above, the pulse generation circuit 7
By inputting the pulse width data PWDAT7 to 0 and the pulse position designation signal LEFT1 to the pixel 4, the laser emission time and timing can be freely controlled within the time allocated to the pixel.

Further, since the circuit configuration shown in FIG. 13 includes an analog circuit, variation between elements becomes a problem. Therefore, the accuracy can be further improved by configuring these elements in the same IC. That is, the pulse generating circuit 74 is configured by one IC provided on the substrate 140 as shown in FIG.

The toner consumption count circuit 75 counts the amount of toner consumed when printing is performed based on the input pulse width modulation data PWDAT71 to 01 and the pulse position signal LEFT1 based on these image signals. By reading the result, the control circuit 49 can perform toner supply, toner density control, and the like.

As described above, the selection circuit 110 inverts or non-inverts the image data of the pixel to be image-formed by the pulse position designating signal corresponding to the image data of the pixel to be image-formed and the adjacent pixels before and after the pixel. The inverted or non-inverted image data and the ramp generator 1
13 and a part of the triangular wave generated by the comparator 1
Then, the laser driving circuit 44 drives the laser diodes 45 and 46 in accordance with the exclusive OR signal of the comparison result and the pulse position designation signal in the XOR circuit 119.

As a result, the gradation characteristics do not depend on the pulse position designation, a beautiful diagonal line or curve can be reproduced, and the circuit scale can be reduced even when the number of gradations to be expressed is large or when the image frequency is increased. It is not so large, and the pulse width modulation of the laser beam can be performed stably.

The pulse generating circuit has a circuit configuration capable of specifying a pulse position by using an analog waveform having the same shape, and all circuits for converting the image information into a pulse signal for driving a laser. Is mounted on a one-chip IC. That is,
This IC chip includes, for example, a selection circuit for selecting whether to invert or not invert the pulse width data according to a position designation signal, a plurality of latch circuits for latching the pulse width data and the position designation signal from the selection circuit, and a latch circuit. To convert pulse width data from the D / A into an analog level signal
An A converter, a plurality of ramp generators for forming an analog waveform, a plurality of comparators for comparing the output of the D / A converter with the output of the ramp generator, an exclusive OR of the output from the comparator and the position designation signal from the latch circuit. It comprises a plurality of gates and a logic circuit for synthesizing the output from the gates. As a result, the same waveform is generated on the same one-chip IC as the analog waveform, so that the waveforms are the same so as not to cause any problem, and the operations related to pulse width modulation and pulse position designation are all performed on one chip. Because of the operation, it is also excellent in high speed.

As described above, by constructing the functions necessary for laser pulse width modulation and pulse position designation on a single IC chip, differences in characteristics among elements can be eliminated, multi-gradation expression is possible, and high-speed expression is possible. Thus, accurate pulse width modulation of laser light can be stably performed.

Further, since the processing in the pulse generation circuit is performed alternately by different circuits for odd-numbered pixels and even-numbered pixels, the processing speed can be increased, and the gradient of the analog waveform generated by the ramp generator can be improved. Can be compared using a fixed portion, and it can be prevented that a problem occurs in the gradation characteristics and that a beautiful oblique line or curve cannot be reproduced.

[0089]

As described in detail above, according to the present invention, the gradation characteristics do not depend on the pulse position designation, and a beautiful diagonal line or curve can be reproduced. It is possible to provide an image forming apparatus and an image forming method capable of stably performing pulse width modulation of a laser beam even when the frequency is increased without a large circuit scale.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an overall control system of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a vertical sectional side view of the image forming apparatus of FIG. 1;

FIG. 3 is a diagram for explaining a main part of an exposure unit in FIG. 1;

FIG. 4 is a diagram for explaining a beam shape of laser light when an optical path length is changed.

FIG. 5 is a diagram showing a relationship between a laser driving pulse, a light energy distribution, and an image.

FIG. 6 is a diagram showing a relationship between a laser driving pulse, a light energy distribution, and an image.

FIG. 7 is a diagram showing an image when an image to be expressed and an image are formed in a state where light energy is concentrated.

FIG. 8 is a diagram illustrating a relationship between a laser driving pulse, a light energy distribution, and an image.

FIG. 9 is a diagram showing a relationship between a laser driving pulse, a light energy distribution, and an image.

FIG. 10 is a block diagram showing a configuration of the image signal processing circuit of FIG. 1;

FIG. 11 is a block diagram showing a configuration of the timing circuit of FIG. 10;

FIG. 12 is a timing chart for explaining the operation of the timing circuit of FIG. 10;

FIG. 13 is a block diagram illustrating a configuration of a pulse generation circuit in FIG. 10;

FIG. 14 is a block diagram showing a configuration of a data inversion / non-inversion selection circuit in FIG. 13;

FIG. 15 is a timing chart illustrating the operation of the pulse generation circuit of FIG. 13;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum (image carrier), 3 ... Exposure part (exposure means), 9-12 ... Developer, 15 ... Transfer drum, 41 ...
External device, 42 interface circuit, 43 image signal processing circuit, 44 laser driving circuit (driving means), 4
5, 46: laser diode (generation means), 48: photodiode (second output means), 49: control circuit, 53: control panel, 71: timing circuit (third output means), 72: laser beam Shape light emission timing control signal generation circuit (first output means), 7
3 conversion table, 74 pulse generation circuit, 75 toner consumption count circuit, 81 waveform shaping circuit, 82 crystal oscillator, 83 clock phase synchronization circuit, 84 frequency divider circuit, 85 AND gate, 86 ... Pulse generation timing signal generation circuit, 110 ... Data inversion / non-inversion selection circuit (data inversion / non-inversion means), 111, 112 ... Latch circuit, 113, 115 ... Ramp generator (triangle wave generation means), 114, 116 ... Converters (conversion means), 117, 118 ... comparators (comparison means), 1
19, 120... XOR circuit (exclusive OR means), 12
1, 122 ... AND circuit, 123 ... NOR circuit, 131
.., Non-inverting buffer, 132, inverting buffer, 133, buffer, 134, inverter circuit, 140, substrate.

Continuation of the front page Examiner Masaaki Sudo (56) References JP-A-62-140550 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/44 G03G 15/04 H04N 1 / 23 103

Claims (4)

(57) [Claims] 1. An image forming means for forming an image in pixel units by irradiating a light beam onto an image carrier, and a position signal indicating a position of a pixel signal to be formed by the image forming means. Output means for outputting a pixel signal to be subjected to image formation by the image forming means, a processing means for performing inversion processing or non-inversion processing based on a position signal output from the output means, Generating means for generating a reference signal whose output changes over time; comparing means for comparing the pixel signal processed by the processing means with the reference signal generated by the generating means; And control means for controlling an image forming operation by the image forming means according to a comparison result obtained by the comparison and a position signal output from the output means. 2. The method according to claim 1, wherein the generating unit, the comparing unit, and the controlling unit include:
2. The image forming apparatus according to claim 1, further comprising first and second units, wherein the first and second units are driven in alternate pixel units. 3. The image forming means, the output means, the processing means,
2. The image forming apparatus according to claim 1, wherein the generation unit, the comparison unit, and the control unit are configured in the same IC. 4. A method for irradiating a light beam on an image carrier.
Image having image forming means for forming an image in pixel units
In the forming apparatus, a pixel signal to be subjected to image formation by the image forming means
And outputs a position signal indicating the position of the pixel signal.
Inverting or non-inverting processing based on the position signal
To generate a reference signal whose output changes over time
And the pixel signal subjected to the inversion processing or the non-inversion processing is
The reference signal is compared with the reference signal, and according to the comparison result and the position signal,
An image forming method , comprising: controlling an image forming operation by an image forming unit .