JP2000211185A - Optical scanner and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To select or switch sub-scanning direction image resolution and the number of gradations from a plurality of combinations. SOLUTION: A sub-scanning direction image resolution switching signal (c) responsive to a desired sub-scanning resolution and a number-of-gradations switching signal (d) responsive to the number of gradations of input image data are generated and output from an image data controller 600. A lighting time control signal generator 602 generates timing control signal lighting time control signal 3 for controlling timing of ΦI at each optical writing line based on the signals (c), (d). A drive signal controller 603 variably sets a duty ratio of the ΦI at each sub-scanning line is response to the number of the gradations.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device and an image forming apparatus, and more particularly, to an optical scanning device in which a plurality of heads each having a plurality of light emitting elements are arranged in a line and a photosensitive member is exposed by the optical scanning device. The present invention relates to an image forming apparatus having a configuration.

[0002]

2. Description of the Related Art Conventionally, an SLED (self-scanning LED array: hereinafter referred to as SLED) is disclosed in
JP, JP-A-2-2008067, JP-A-2-2-267
JP-A-12170, JP-A-3-20457, JP-A-3-194978, JP-A-4-5872, JP-A-4-23367, JP-A-4-2965
No. 79, Japanese Unexamined Patent Publication (Kokai) No. 5-84771, and a proposal of a light emitting element array for an optical printer in which a Japanese hard copy '91 (A-17) drive circuit is integrated, and the Institute of Electronics, Information and Communication Engineers ('90 .3.5) PNPN. It has been introduced in the proposal of a self-scanning light-emitting element (SLED) using a thyristor structure, and has attracted attention as a recording light-emitting element of an electrophotographic image forming apparatus.

FIG. 9 shows an example of this SLED, and its operation will be described.

As shown in FIG. 9, the SLED has a thyristor 1 'to 5' for transfer connected in cascade and a thyristor 1 to 5 for light emission connected in cascade. The gate signals of the respective thyristors are common as shown in the figure, and the gates of the first thyristors 1 and 1 'are connected to the signal input of ΦS. The gates of the second thyristors 2 and 2 'are connected to the cathodes of diodes connected to the terminals of ΦS, and the third thyristors 3 and 2'
The gate of 3 'is connected to the cathode of the next diode.

FIG. 10 is a timing chart showing a control signal for controlling the above SLED and ON / OFF of the thyristor, and shows an example in which all elements are turned on. The transfer and light emission will be described with reference to the timing chart of FIG.

The transfer is started by changing ΦS (FIG. 10A) from 0V to 5V. When ΦS becomes 5V, Va = 5V, Vb = 3.7V (the forward voltage drop of the diode is assumed to be 1.3V), and Vc = 2.4.
V, Vd = 1.1 V, and 0 V after Ve. The gate voltage of the transfer thyristor 1 'changes from 0V to 5V, the gate voltage of the transfer thyristor 2' changes from 0V to 3.7V, and so on.

In this state, by changing Φ1 (FIG. 10 (B)) from 5V to 0V, the potential of each terminal of the transfer thyristor 1 'becomes 5V for the anode, 0V for the cathode, and 3.7V for the gate. Meet. When the transfer thyristor 1 'is turned on, the thyristor 1' is in the on state even if ΦS is changed to 0V in this state, and Va ≒ 5V is maintained. This is because ΦS is applied via a resistor (not shown) and the potential between the anode and the gate becomes almost equal when the thyristor is turned on.

Therefore, even if ΦS is set to 0V, the ON condition of the first thyristor is maintained, and the first shift operation is completed. When the ΦI signal (FIG. 10D) for the light emitting thyristor is changed from 5 V to 0 V in this state, the condition becomes the same as the condition where the transfer thyristor is turned on, so that the light emitting thyristor 1 is turned on and the first LED is turned on. Will be. In the first LED, when ΦI is returned to 5 V, the potential difference between the anode and the cathode of the light emitting thyristor disappears, and the minimum holding current of the thyristor cannot flow, so the light emitting thyristor 1
Turns off.

Next, the transfer of the thyristor on condition from 1 'to 2' will be described.

[0010] Even if the light emitting thyristor 1 is turned off, Φ1 is 0V.
Therefore, the gate voltage of the transfer thyristor 1 ′ is Va ≒ 5 V and Vb = 3.7 V with the transfer thyristor 1 ′ kept on. In this state, Φ2 (FIG. 10)
By changing (C)) from 5V to 0V, the potential of the transfer thyristor 2 'becomes 5V for the anode and 5V for the cathode.
0V, gate = 3.7V. This turns on the transfer thyristor 2 '. By changing Φ1 from 0 V to 5 V after the transfer thyristor 2 ′ is turned on, the transfer thyristor is turned off in the same manner as the light emitting thyristor 1 is turned off.

Thus, the on state of the transfer thyristor is 1 '.
From 2 to 2 '. When ΦI is changed from 5 V to 0 V, the light emitting thyristor 2 is turned on to emit light. In addition,
The reason that only the light emitting thyristor corresponding to the on transfer thyristor can emit light is that when the transfer thyristor is not on, the gate voltage is 0 V except for the thyristor next to the on thyristor, so that the thyristor is on. This is because it is not a condition. Since the potential of φI becomes 3.4 V (a forward voltage drop of the light emitting thyristor) when the light emitting thyristor is turned on, the adjacent thyristor is turned on because there is no potential difference between the gate and the cathode. Can not do it.

Although it has been described above that the light emitting thyristor is turned on and emits light by setting ΦI to 0 V,
In an actual image forming operation, it is naturally necessary to control whether or not to actually emit light at that timing in accordance with image data. Image data D in FIG.
p, φD in FIG. 10 (F) is a signal indicating this, and SLED
Is logically ORed externally with the ΦI and the image data Dp, and only when the image data Dp is 0V, the ΦI terminal of the SLED actually becomes 0V and emits light, and when the image data Dp is 5V, the SLED ΦI terminal remains at 5 V and does not emit light.

Here, a method of configuring the SLED array head will be described with reference to an external view of the head shown in FIG.

An SLED is provided on a base substrate 212 using a printed wiring board made of glass epoxy material, ceramic material, or the like.
The semiconductor chip 211 is mounted. The lighting control circuit (driver IC) 214 is supplied with an external control signal,
A lighting control signal for the SLED semiconductor chip 211 is generated. An external control signal and power are input from the connector 213 and supplied to each semiconductor. SLED semiconductor chip 2
11 is connected to a bonding wire 215, whereby output signals Φ1Φ, Φ1Φ from the driver IC 214 are output.
2, ΦS, IΦ and negative side power supply (GND in this example)
Enter each. Reference numeral 216 denotes a positive power supply pattern (+5 V in this example) drawn on the base substrate 212.
Reference numeral 217 denotes a silver paste for providing electrical conductivity between the positive power supply pattern 216 and the back surface electrode of the SLED semiconductor chip 211 and bonding and fixing the same.

Recently, there has been developed an image forming apparatus in which four colors of yellow, magenta, cyan and black are image-formed on a photosensitive drum for each color, superimposed on one sheet, transferred, fixed, and output. Has been put to practical use.

FIG. 12 is a side view showing a schematic configuration of the whole of such a color image forming apparatus. First, the configuration of the color reader unit will be described with reference to FIG.

The CCD 101 is mounted on the substrate 311. Reference numeral 312 denotes a printer processing unit, and reference numeral 301 denotes a platen glass (platen). Reference numeral 302 denotes a document feeder. Alternatively, a mirror pressure plate (not shown) or a white pressure plate (not shown) may be mounted in place of the document feeder 302. Halogen lamps or fluorescent lamps are used as the light sources 303 and 304 to illuminate the original. The reflecting umbrellas 305 and 306 are
The light of No. 04 is focused on the document. Reference numerals 307 to 309 denote mirrors. The lens 310 condenses reflected light or projected light from the document on the CCD 101.

The carriage 314 includes the halogen lamp 3
03, 304, reflectors 305, 306 and a mirror 307 are accommodated. The carriage 315 includes mirrors 308 and 309
To accommodate. 313 is another IPU (image processing unit)
3 shows an interface (I / F) unit with the like. Note that the carriage 314 has a velocity V, and the carriage 315 has a velocity V.
At / 2, the entire surface of the document is scanned (sub-scanning) by mechanically moving the CCD 101 in a direction perpendicular to the electrical scanning (main scanning) direction.

Next, the configuration of the printer unit in FIG. 10 will be described.

Reference numeral 317 denotes a magenta (M) image forming unit;
8 is a cyan (C) image forming unit, and 319 is a yellow (Y)
An image forming unit 320 is a black (K) image forming unit. Since the configuration of each image forming unit is the same, the M image forming unit 317 will be described in detail here, and the description of the other image forming units will be omitted.

In the M image forming section 317, a latent image is formed on the surface of the photosensitive drum 342 by the light from the LED array 210. The primary charger 321 is connected to the photosensitive drum 3
The surface of 42 is charged to a predetermined potential to prepare for latent image formation. The developing device 322 develops the latent image on the photosensitive drum 342 to form a toner image. Note that the developing device 322 has a sleeve 3 for applying a developing bias to perform development.
45 are included.

The transfer charger 323 is connected to the transfer material transport belt 3.
The toner image on the photosensitive drum 342 is transferred to a recording paper or the like on the transfer material conveying belt 333 by discharging from the back surface of the transfer roller 33. In the present embodiment, a configuration having good transfer efficiency is assumed (for example, by optimizing the physical properties of the toner). Therefore, the cleaner is not provided, but it goes without saying that the cleaner may be attached. .

Next, a procedure for transferring a toner image onto a transfer material such as recording paper will be described.

Transfer materials such as recording paper stored in the cassettes 340 and 341 are picked up by rollers 339 and 338.
Is supplied onto the transfer material transport belt 333 by the paper feed rollers 336 and 337 for each sheet. The supplied recording paper is charged by the adsorption charger 346. Transfer material transfer belt
The transfer material transport belt 333 is driven by the roller 348, and the recording paper or the like is charged in a pair with the attraction charger 346, and the recording paper or the like is attracted to the transfer material transport belt 333. Note that the transfer material transport belt roller 348 may be a drive roller for driving the transfer material transport belt 333, and a drive roller for driving the transfer material transport belt 333 is arranged on the opposite side. Is also good.

The paper leading edge sensor 347 detects the leading edge of the recording paper or the like on the transfer material transport belt 333. The detection signal of the paper leading edge sensor 347 is sent from the printer unit to the color reader unit, and is used as a sub-scan synchronization signal when a video signal is sent from the color reader unit to the printer unit.

Thereafter, the recording paper and the like are transferred to the transfer material transport belt 3.
The toner image is formed on the surface of the image forming units 317 to 320 in the order of M, C, Y, and K. The transfer material such as recording paper that has passed through the K image forming unit 320 is separated from the transfer material transport belt 333 after the charge is removed by the charge removing charger 349 in order to facilitate separation from the transfer material transport belt 333. The peeling charger 350 can prevent image disturbance due to peeling discharge when the recording paper or the like is separated from the transfer material transport belt 333. The separated recording paper or the like is charged by pre-fixing chargers 351 and 352 in order to supplement the toner attraction force and prevent image disorder, and after the toner image is thermally fixed by the fixing device 334, the recording paper is discharged. The paper is discharged to the paper tray 335.

Next, the LED arrays 210, 211, 21
2, 213 will be described.

When an SLED chip is used as an LED array, each LED array needs the above-mentioned four light emission control signals. That is, the start clock ΦS for returning the light emitting position to the first bit, the transfer clocks Φ1 and Φ2 for switching the light emitting position one bit at a time, and the light emitting thyristor for actually emitting light at the selected light emitting position. ΦI which is a lighting timing signal.

The light emission control signal generating circuit will be described with reference to the block diagram of FIG. 13 and the timing chart of FIG.

Reference numeral a denotes an image enable signal, which is sent from a main controller (image data controller, not shown) of the image forming apparatus, and starts at a recording paper passage timing detected by the paper edge sensor 347. When forming an image at a predetermined position on the recording paper, L
The ED array is a sub-scanning synchronization signal for notifying the timing to start writing. The delay circuit 501 delays the image enable signal a by a separately specified timing described later to correct the variation in the position of the light emitting point array of the LED array head in the sub-scanning direction, and delays the image enable signal a ′. Is output.

Variations in the light emitting point sequence of the LED array head in the sub-scanning direction are caused by various positional accuracy variations on the LED array head side and positional accuracy variations and variations of each unit positioning member on the image forming apparatus side. It occurs due to a number of causes, such as a variation in the relative position between the LED array unit and the image forming apparatus during the mounting operation and the transportation of the apparatus. If the writing position on the photoreceptor by the LED array fluctuates or fluctuates in the sub-scanning direction due to the above reasons, a color image is formed in which the four color images are superimposed with their amounts shifted in the sub-scanning direction. Of course, a good output image cannot be obtained.

Therefore, the LED which has been recognized by various methods in advance
A delay time corresponding to the amount of displacement of the array of light emitting points in the sub-scanning direction in the array is set in each of the above-described delay circuits, thereby performing correction for delaying the sub-scanning direction synchronization signal from the apparatus main body by a predetermined timing.

The timing chart of FIG. 14 shows this correction. In the figure, δY, δM, δC, δK
Indicates a delay amount controlled by the setting, and differs for each color.

Returning to the block diagram of FIG.
Reference numeral 516 indicates one LED array head as a whole.
Reference numeral 3 denotes an SLED chip.

The image enable signal a 'delayed as described above is provided to the LED array drive signal generation circuit 503. The LED array drive signal generation circuit 503 is composed of a combination sequential circuit, and the delayed image enable signal a '
The light emission control signal Φ
S, Φ1, Φ2, and ΦI are generated.

When receiving the delayed image enable signal a ', the block 503 returns an image data request clock b to a main controller (not shown). The parallel image data Dp 'is input from the main controller to the yellow LED array head 516 in synchronization with the request clock b.

In the LED array head in this example, one head uses 56 SLED chips, and the light emitting point in one chip is 128 bits. For this reason, originally, the image data corresponding to each chip position is converted from 1 bit to 12 bits.
56 signals serialized up to 8 bits must be input in parallel. However, the LED array head has 56
Providing the data input line leads to an increase in the number of connection cables, and there are also problems in handling of the cables and cost.

For this reason, a system is used in which data is transmitted and received eight times with seven parallel signals within one bit lighting timing to transfer data of a total of 56 bits.
A data conversion block 510 in FIG. 13 converts the image data Dp 'so that the parallel data is distributed to 56 chips.

Reference numeral 511 denotes a gate circuit block, which outputs an OR of the image data Dp distributed to each chip by the data conversion block 510 and the light emission control signal ΦI. Thus, the L signal of ΦI is supplied to the SLED chip only for the chip whose image is on. In this example, when the image data φD is H, the SLED
The ΦI terminal of the chip 513 is kept at H and does not emit light. When the image data φD is L, the φI signal from the LED array drive signal generation circuit 503 passes through the gate circuit block 511 as it is, and during the L period, the φI terminal of the SLED chip 513 is at L level.
It emits light when falling.

Reference numeral 512 denotes a buffer block, and LE
The output signals of φS, 1 and 2 from the D array drive signal generation circuit 503 are distributed to 56 SLED chips 513. Since the ΦI signal is independently generated for each chip 513 by the gate circuit block 511, in this example, the ΦI signal
The signal does not include an internal buffer.

The above configuration is provided independently for one LED array head. The configuration of FIG.
Although the same elements are provided for each of the C and K colors, only the yellow color has been described in detail here. The same configuration as described above is independently adopted for the other three colors for magenta, cyan, and black.

[0042]

In the above-mentioned conventional LED array head, when giving a gradation to a write pixel, the light-emitting current (drive current) of each light-emitting element is adjusted at the timing when φI in FIG. It is necessary to independently modulate based on the multi-level image data, or to independently modulate the length or duty ratio of the L period of ΦI based on the multi-level image data. To perform such modulation, 1
Light emitting current modulating means or light emitting duty modulating means for the number of light emitting pixels which emit light simultaneously by one head are required, and the configuration provided with these means has a problem that the drive circuit becomes complicated and large-scale.

In the above-mentioned self-scanning LED array, one light emitting enable signal is input to one LED array chip, so that the number of modulating means required is equal to the number of mounted LED array chips. There was a problem.

Further, in the above-described self-scanning LED array head, since the scanning operation is performed independently by the light emission of each LED array chip, the LED array head is rotated as the photosensitive drum rotates in the sub-scanning direction. The write line formed on the photosensitive drum by the
It becomes oblique for each D array chip. As a result,
There is a problem that one scanning line (main scanning line) becomes saw-toothed.

The above problem will be described with reference to FIGS.

FIG. 15 is an explanatory view schematically showing a photosensitive member and an optical writing section of an electrophotographic image forming apparatus using an LED array head as optical writing means.

The cylindrical photosensitive drum 342 rotates at a predetermined speed in the direction of the arrow at the time of image formation (peripheral speed V).
d). Reference numeral 210 denotes the LED array head described with reference to FIG. 12, which is disposed to face the photosensitive drum 342. The LED array head 210 is provided with a plurality of LED array chips 211. The arrangement direction of the LED array chips 211 is substantially the axial direction of the photosensitive drum 342, and the light-emitting pixels are arranged in a straight line in a plurality (128 dots in this example) in parallel with the chip longitudinal direction. The LED array chips 211 are arranged and mounted on a base substrate (not shown), and necessary drive signals are supplied from the substrate through bonding wires (not shown). A plurality (12 in this example, for simplicity) of LED array chips 211 are aligned on the base substrate.

Each LED array chip 211 scans the light emitting point in the direction of the arrow, that is, shifts the light emitting pixels sequentially. According to the light emission of the LED array chip 211,
Optical writing (exposure) is performed on the photosensitive surface of the photosensitive drum 342 at the opposing position. According to the rotation of the drum, the above main scanning is repeated (sub scanning).

FIG. 16 is an explanatory diagram showing an example of the optical writing line formed on the photosensitive drum together with the LED array chip.

It is assumed that the peripheral speed of the photosensitive drum is Vd, the repetition cycle of the sub-scan is Ts, and the resolution of the main scan (= light emitting pixel pitch) is Pm. Generally, the repetition cycle of the sub-scan is set according to the relationship expressed by the following equation, and the resolution (repetition cycle) of the sub-scan is adapted to the resolution of the main scan.

[0051]

Pm = Vd * Ts However, the scanning line by each chip is actually Vd *
A sawtooth scan line including a step in the sub-scanning direction represented by Ts (= Pm) is obtained as shown in FIG. This step corresponds to one pixel pitch of the main scanning light emitting pixels. If there is a step portion of the saw, for example, when a ruled line or a character in the main scanning direction is printed, an unnatural step occurs in the peripheral portion,
Further, when a screen-processed gray image is written, there may be a problem that a beat is visually generated at the stepped portion and the screen image frequency.

The problem due to the saw-tooth difference is, of course, not unique to an image forming apparatus using a self-scanning LED array head. An LED array head configured to perform optical scanning by independently performing moving scanning of a light emitting point in each of a plurality of divided areas of the head has the same problem as described above.

Accordingly, the present invention has been made in view of the above-mentioned problems, and an optical scanning device which solves the above-mentioned problems and an image forming apparatus having a configuration in which optical writing is performed on a rotating photosensitive member by the optical scanning device are provided. The purpose is to provide.

[0054]

According to a first aspect of the present invention, there is provided a light emitting device having a plurality of light emitting elements arranged in a main scanning direction and a plurality of light emitting means arranged in the main scanning direction. An array head and an optical writing line on a rotating photoreceptor that is driven to rotate about a rotation axis substantially parallel to the main scanning direction by performing main scanning for causing the plurality of light emitting elements to emit light in accordance with image data. A scan for optically scanning such that the formed optical writing line is relatively moved at a predetermined speed on the rotating photoconductor in a sub-scanning direction substantially perpendicular to the main scanning direction. The optical writing line is repeated by the scanning means at a speed corresponding to n times the arrangement pitch of the light emitting elements, and further, image data of a predetermined gradation is input. Input means for generating light emission signals for controlling light emission of the plurality of light emitting means in common; and changing timing of the light emission signals in accordance with a desired sub-scanning resolution and the number of gradations of the input image data. And a selecting means for selecting the number of gradations of an image formed by the optical writing line from binary to 2 ⁿ values.

According to a second aspect of the present invention, in the first aspect, the selecting means includes means for generating a resolution selection signal corresponding to the desired sub-scanning resolution, and a gradation of the input image data. Means for generating a gradation selection signal corresponding to the number, and means for generating a timing control signal for controlling the timing for each optical writing line based on the resolution selection signal and the gradation selection signal. And a light emission control unit that varies a duty ratio of the light emission signal in accordance with the number of gradations according to the generated timing control signal.

According to a third aspect of the present invention, in the second aspect, image data to be written for each of the optical writing lines is selected according to the desired sub-scanning resolution based on the image data from the input means. An optical scanning device is further provided, which further comprises:

According to the fourth aspect of the present invention, a plurality of light emitting means in which a plurality of light emitting elements are arranged in the main scanning direction, a light emitting array head in which the light emitting elements are arranged in the main scanning direction, A rotating photoreceptor having a substantially parallel rotation axis, a driving unit for rotationally driving the rotating photoreceptor, and a main scan for causing the plurality of light emitting elements to emit light in accordance with image data; Means for repeatedly forming an optical writing line so that the formed optical writing line is relatively moved at a predetermined speed on the rotating photoconductor in a sub-scanning direction substantially perpendicular to the main scanning direction. An image forming apparatus having a scanning unit for optical scanning,
By the scanning means, the formation of the optical writing line is repeated at a speed corresponding to n times the arrangement pitch of the light emitting elements,
An input unit for inputting image data of a predetermined gradation; a light emission control unit for generating a light emission signal for controlling light emission of the plurality of light emitting units in common; a desired sub-scanning resolution and the number of gradations of the input image data; Selecting means for selecting the number of gradations of an image formed by the optical writing line from binary to 2 ⁿ values by changing the timing of the light emission signal in accordance with Provide equipment.

According to a fifth aspect of the present invention, in the fourth aspect, the selecting means includes means for generating a resolution selection signal corresponding to the desired sub-scanning resolution, and a gradation of the input image data. Means for generating a gradation selection signal corresponding to the number, and means for generating a timing control signal for controlling the timing for each optical writing line based on the resolution selection signal and the gradation selection signal. And a light emission control unit that varies a duty ratio of the light emission signal according to the number of gradations in accordance with the generated timing control signal.

According to a sixth aspect of the present invention, in the fifth aspect, the image data to be written for each of the optical writing lines is selected according to the desired sub-scanning resolution based on the image data from the input means. An image forming apparatus further comprising:

[0060]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an example of an optical writing line formed on a photosensitive drum when the sub-scanning repetition rate is doubled in one embodiment of the optical scanning apparatus and the image forming apparatus according to the present invention. It is explanatory drawing shown with an LED array chip. The repetition cycle of the sub-scanning is 1/2 of the conventional one, that is, Ts / 2 since the repetition rate is twice. Therefore, the size of the sawtooth step in the sub-scanning direction is

[0062]

## EQU2 ## Vd * Ts / 2, which is 1/2 of the conventional value. At this time, the amount of movement of the photosensitive drum in the sub-scanning direction during one scanning line corresponds to half (1/2 pixel) of the main scanning image pitch.

Therefore, in the present embodiment, in the above state,
By controlling the image data and the LED array drive signal as described below, the image resolution and the number of gradations in the sub-scanning direction can be selected and switched from a plurality of combinations.

FIG. 2 is a circuit diagram showing a configuration of an image signal and LED array drive signal control block according to the present embodiment. 2, the same elements as those in FIG. 13 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. Also,
Although the configuration of FIG. 2 includes the same elements for each of the colors Y, M, C, and K, here, only yellow is shown and described. The same configuration as described above is independently adopted for the other three colors for magenta, cyan, and black. The above configuration is based on one LED array head 516
Independently.

Reference numeral 600 denotes an image data controller, and an image resolution switching signal c and a gradation number switching signal d from the image data controller 600 in the sub-scanning direction.
Is provided to the lighting time control signal generation circuit 602. The two switching signals c and d correspond to a resolution selection signal and a gradation selection signal, and the lighting time control signal generating circuit 602 generates a later-described lighting time control signal e corresponding to a timing control signal according to the two resolution gradation selection signals. The drive signal is provided to a drive signal controller 603 including the same configuration as the LED array drive signal generation circuit 503. Main control block of the image forming apparatus,
Alternatively, the image data controller 600 sends the lighting time control signal to the lighting time control signal generation circuit 602 based on a sub-scanning direction image resolution switching signal c and a gradation number switching signal d from outside (both not shown). e.

In response to the lighting time control signal e, the drive signal controller 603 controls the lighting time of the lighting enable signal ΦI common to all chips to a value corresponding to a predetermined number of gradations. As a result, selection of image resolution and number of gradations,
Switching is performed. The procedure of the lighting time control will be described in more detail by exemplifying various operating conditions.

For example, here, the main scanning image resolution (light emitting pixel pitch) is set to 600 dpi, and the scanning repetition speed of the sub-scanning is equivalent to 1200 dpi (the main scanning image resolution is 2 dpi).
An example of a combination of the image resolution in the sub-scanning direction and the number of gradations that can be specifically configured in the case of (double) will be described with reference to the timing charts of FIGS.

First, in the first example, the sub-scanning image resolution is 600
dpi and the number of gradations are binary. FIGS. 3 and 4 show timing charts at this time. 3 is for an odd line ((2m-1) th line) and FIG. 4 is for an even line (2mth line). Light emission control for main scanning at the timing shown in both figures is performed for each sub-scan. Are executed alternately.

The lighting time control signal e does not change every sub-scan as shown in FIGS. 3G and 4G, but outputs a constant value (H in this example). The LED array drive signal controller 60 responds to the H level lighting time control signal e.
Numeral 3 outputs a light emission enable signal .PHI.I (FIG. 3 (D) and FIG. 4 (D)) which is a pulse signal whose duty does not change every sub-scanning line and which is common to all chips. Here, the light emission enable signal φI has a uniform duty ratio of 70%, but is not limited to this value.

At this time, based on binary image data transmitted from the main control block of the image forming apparatus or from outside (both are not shown), the image data controller 600 outputs the same data (ΦD = 1 or 0) is set to the LED array drive signal controller 603.
Send to

By the light emission control as described above, the sub-scanning image resolution of 600 for the two scanning lines for the case of the first example.
It is possible to realize a dpi and a binary number of gradations.

Subsequently, in the second example, the sub-scanning image resolution is 60
0 dpi, and the number of gradations is four. FIGS. 5 and 6 show timing charts at this time. FIG. 5 shows an odd-numbered line ((2m-1) th line), and FIG. 6 shows an even-numbered line (2mth line). Light emission control for main scanning at the timings shown in FIGS. Are executed alternately.

The lighting time control signal e alternates between H and L for each sub-scan as shown in FIGS. 5 (G) and 6 (G).
In response to the level change of the lighting time control signal e, the light emission enable signal .PHI.I common to all the chips to the LED array head 516 has a duty ratio every sub-scan as shown in FIGS. 5 (D) and 6 (D). It changes to two types. In the illustrated example, the first (odd line) is 70%, and the next (even line) is 35%.
It is. The two values of the duty are not limited to these values.

At this time, based on the quaternary image data transmitted from the main control block of the image forming apparatus or from the outside (neither is shown), the image data controller 600 sets the first time for each scan line and the second time for each scan line. Is weighted as 1, A data signal is transmitted to the LED array drive signal controller 603 as shown in FIG. With the above light emission control, the sub-scanning image resolution is 600 dpi and the number of gradations is 4 in two scanning lines.
Value can be realized.

Finally, in the third example, the sub-scanning image resolution is 12
00 dpi and the number of gradations is binary. FIGS. 7 and 8 show timing charts at this time. FIG. 7 shows an odd-numbered line ((2m-1) th line), and FIG. 8 shows an even-numbered line (2mth line). Light emission control for main scanning at the timing shown in both figures is performed for each sub-scan. Are executed alternately.

The lighting time control signal e does not change every sub-scan as shown in FIGS. 7G and 8G, but outputs a constant value (H in this example). The LED array drive signal controller 60 responds to the H level lighting time control signal e.
Numeral 3 outputs a light emission enable signal ΦI (FIG. 7 (D) and FIG. 8 (D)) which is a pulse signal for every sub-scanning line and whose duty does not change, which is common to all chips. Here, the light emission enable signal φI has a uniform duty ratio of 70%, but is not limited to this value.

At this time, the image data controller 600 transmits 1200 dpi, which is transmitted from the main control block of the image forming apparatus or from outside (both are not shown).
Based on the binary image data, data (ΦD = 1,
Or 0) is set to the LED array drive signal controller 60
Send to 3.

With the above-described light emission control, the sub-scanning image resolution of 120 for one scanning line in the case of the second example.
0 dpi and a binary number of gradations can be realized.

As described above, in the above embodiment according to the present invention, the sub-scanning repetition speed of the optical writing line on the photosensitive drum is set to twice the main scanning resolution.
All the LED chips are commonly driven by using the light emission enable signal in common, and the on-time is switched to a predetermined value by changing the duty ratio every time the sub-scan is repeated, and the number of input image gradations is changed from binary. Switch to four values. Therefore, the amount of the writing line step in the sub-scanning direction can be reduced as described above. Also,
One luminescence current modulation means without direct luminescence current modulation or luminescence duty modulation for each individual luminescence pixel,
Alternatively, the image resolution and the number of gradations in the sub-scanning direction can be selected and switched from a plurality of combinations (for example, the first to third examples in the above embodiment) only by the light emission duty modulation unit.

[0080]

As described above, according to the optical scanning apparatus and the image forming apparatus of the present invention, the main scanning for causing the plurality of light emitting elements to emit light in accordance with the image data is performed, whereby the rotation axis substantially parallel to the main scanning direction is obtained. Means for repeatedly forming an optical writing line on a rotating photoreceptor which is driven to rotate about a rotation center, wherein the formed optical writing line is formed at a predetermined speed in a sub-scanning direction substantially perpendicular to the main scanning direction on the rotating photoreceptor. The scanning unit that optically scans the light-emitting elements so as to be formed by relative movement repeats the formation of the optical writing line at a speed equivalent to n times the arrangement pitch of the light-emitting elements, and further emits a light-emitting signal that controls the light-emission of a plurality of light-emitting units in common. A light emission control unit for generating the light emission signal according to a desired sub-scanning resolution and changing the timing of the light emission signal in accordance with the number of gradations of the input predetermined gradation image data; 2 ⁿ gradation number of the image to be formed from the binary
Selection means for selecting between the values to reduce the amount of step in the sub-scanning sawtooth writing line, and to directly modulate the light emission current and the light emission duty for each individual light emitting element. Instead, the image resolution in the sub-scanning direction and the number of gradations are selected from a plurality of combinations with only one light emission current modulation means or light emission duty modulation means,
There is a feature that can be switched.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical scanning device and an image forming apparatus according to an embodiment of the present invention for controlling light emission of an LED array.

FIG. 2 is a circuit diagram showing an image signal and LED array drive signal control block configuration in an embodiment of the optical scanning device and the image forming apparatus according to the present invention.

FIG. 3 is a timing chart showing an LED array light emission control operation in an embodiment of the optical scanning device and the image forming apparatus according to the present invention.

FIG. 4 is a timing chart showing an LED array light emission control operation in an embodiment of the optical scanning device and the image forming apparatus according to the present invention.

FIG. 5 is a timing chart showing an LED array light emission control operation in an embodiment of the optical scanning device and the image forming apparatus according to the present invention.

FIG. 6 is a timing chart showing an LED array light emission control operation in an embodiment of the optical scanning device and the image forming apparatus according to the present invention.

FIG. 7 is a timing chart showing an LED array light emission control operation in one embodiment of the optical scanning device and the image forming apparatus according to the present invention.

FIG. 8 is a timing chart showing an LED array light emission control operation in one embodiment of the optical scanning device and the image forming apparatus according to the present invention.

FIG. 9 is a circuit diagram showing an example of a basic configuration of a conventional self-scanning LED array (SLED).

FIG. 10 is a timing chart for controlling a conventional SLED.

FIG. 11 is an external perspective view showing an example of a mounting configuration of a conventional SLED array head.

FIG. 12 is a side view showing an example of a color image forming apparatus using a conventional LED array head.

FIG. 13 is a circuit configuration diagram for controlling light emission of a conventional LED array head.

FIG. 14 is a timing chart for explaining misregistration correction in the sub-scanning direction in the circuit configuration of FIG. 13;

FIG. 15 is an explanatory diagram for explaining a problem of a conventional example.

FIG. 16 is an explanatory diagram for explaining a problem of a conventional example.

[Explanation of symbols]

 211 LED array chip 342 Photosensitive drum 501 Delay circuit 510 Data conversion block 511 Gate circuit block 512 Buffer block 513 SLED chip 516 LED head 600 Image data controller 602 Lighting time control signal generation circuit 603 Drive signal controller a Image enable signal a 'Delayed image enable signal b Image data request clock c Sub-scanning direction image resolution switching signal d Tone number switching signal e Lighting time control signal

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C162 AE12 AE14 AE21 AE28 AE47 AF13 AF44 AF57 AF60 AF62 AF71 AF79 FA04 FA17 5C051 AA02 CA08 DA03 DB02 DB29 DE02 DE29 EA02 EA03 FA01

Claims (6)

[Claims] 1. A plurality of light emitting means in which a plurality of light emitting elements are arranged in a main scanning direction; a light emitting array head in which the plurality of light emitting elements are arranged in the main scanning direction; Means for repeatedly forming an optical writing line on a rotating photosensitive body that is driven to rotate about a rotation axis substantially parallel to the main scanning direction by performing scanning, wherein the formed optical writing line is A scanning unit for optically scanning the body so as to be formed by relatively moving at a predetermined speed in a sub-scanning direction substantially perpendicular to the main scanning direction, the scanning unit comprising: Repeating the formation of the optical writing line at a speed equivalent to n times the arrangement pitch,
An input unit for inputting image data of a predetermined gradation; a light emission control unit for generating a light emission signal for controlling light emission of the plurality of light emitting units in common; a desired sub-scanning resolution and the number of gradations of the input image data; Selecting means for selecting a gradation number of an image formed by the optical writing line from a binary value to a 2 ⁿ value by changing a timing of the light emitting signal in accordance with the optical scanning line. apparatus. 2. The image processing device according to claim 1, wherein the selection unit generates a resolution selection signal according to the desired sub-scanning resolution, and outputs a gradation selection signal according to the number of gradations of the input image data. Means for generating, and means for generating a timing control signal for controlling the timing for each of the optical writing lines based on the resolution selection signal and the gradation selection signal, the light emission control means comprising: An optical scanning device, wherein a duty ratio of the light emission signal is varied according to the number of gradations in accordance with the timing control signal. 3. The apparatus according to claim 2, further comprising: a unit that selects image data to be written for each of the optical writing lines in accordance with the desired sub-scanning resolution based on the image data from the input unit. Optical scanning device. 4. A rotary photosensitive device having a plurality of light emitting means in which a plurality of light emitting elements are arranged in a main scanning direction, a light emitting array head in which the light emitting elements are arranged in the main scanning direction, and a rotation axis substantially parallel to the main scanning direction. A driving unit for driving the rotary photoreceptor to rotate, and a main scan for causing the plurality of light emitting elements to emit light in accordance with image data, thereby repeatedly forming an optical writing line on the rotating rotary photoreceptor. Scanning means for optically scanning such that the formed optical writing line is relatively moved at a predetermined speed in the sub-scanning direction substantially perpendicular to the main scanning direction on the rotating photoreceptor. In the image forming apparatus, the scanning unit repeats formation of the optical writing line at a speed corresponding to n times the arrangement pitch of the light emitting elements,
An input unit for inputting image data of a predetermined gradation; a light emission control unit for generating a light emission signal for controlling light emission of the plurality of light emitting units in common; a desired sub-scanning resolution and the number of gradations of the input image data; Selecting means for selecting the number of gradations of an image formed by the optical writing line from binary to 2 ⁿ values by changing the timing of the light emission signal in accordance with apparatus. 5. The image processing apparatus according to claim 4, wherein the selection unit generates a resolution selection signal corresponding to the desired sub-scanning resolution, and outputs a gradation selection signal corresponding to the number of gradations of the input image data. Means for generating, and means for generating a timing control signal for controlling the timing for each of the optical writing lines based on the resolution selection signal and the gradation selection signal, the light emission control means comprising: An image forming apparatus that varies a duty ratio of the light emission signal in accordance with the number of gradations in accordance with the timing control signal. 6. The image processing apparatus according to claim 5, further comprising: a unit that selects image data to be written for each of the optical writing lines in accordance with the desired sub-scanning resolution based on the image data from the input unit. Image forming apparatus.