JP3265576B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a scanning unit for setting a plurality of exposure units on a photoreceptor and forming an image on each of the exposure units, and a plurality of scanning units corresponding to the respective exposure units. Having a color toner developing unit,
The present invention relates to an image forming apparatus in which a plurality of images can be selected by a pass and output by overlapping.

[Conventional technology]

In recent years, with the digitization of color copiers, several different types of color copiers, such as two-color and full-color, have been offered at relatively reasonable prices according to user demands. The conventional two-color copying machine executes two development steps, but the present applicant separately proposes a so-called one-pass two-color copying machine that performs two-color copying in one development step ( Japanese Patent Application No. 1-338597: "Image Recording Apparatus"). The outline is described below.

The one-pass two-color copying machine is equipped with, for example, a two-color toner developing device composed of red and black, and performs all red or all black image reproduction by selecting one of the developing devices. The two-color image reproduction is performed by the operation. In this case, a first exposure unit and a second exposure unit are set with a certain gap in the photoconductor, and a scanning unit for forming an image on each exposure unit, a developing unit for red toner and a developing unit for black toner The containers are arranged to form a two-color image of one pass and two colors.

FIG. 3 is a block diagram showing an overall configuration of a two-color image forming apparatus of a one-pass two-color system, FIG. 4 is a diagram showing a schematic configuration of an image processing unit, and FIG. FIG. 6 is a diagram showing a configuration example of the unit, FIG. 6 is a diagram showing the configuration of the ROS, and FIG. 7 is a diagram for explaining image reproduction characteristics of the first developing device and the second developing device.

For example, red (sub color) and black (main color) 2
A so-called one-pass two-color type two-color image forming apparatus for reproducing a color image includes an image processing unit as shown in FIG.
20 and an image output unit 110. The image processing unit 20 reads the two-color original image of red and black, generates two sets of image data as a pair of density data D and a color flag CF, appropriately processes the data, and outputs the processed data. An image output unit that reproduces two sets of image data from a pair of the density data D and the color flag CF from the image processing unit 20 and visualizes them.

As shown in FIG. 4, the image processing unit 20 includes a full-color sensor 30 and a sensor interface circuit 40 that constitute an image reading unit, and a color image information generation circuit that processes the output.
70, an editing / processing circuit 90, and an interface circuit 100.

The full-color sensor 30 optically scans a document, and the sensor interface circuit 40 converts a read signal sequentially output from the full-color sensor 30 in a time-division manner for each cell in color component data (a predetermined pixel unit). B: blue, G:
Green, R: red) and output them in parallel. The color image information generation circuit 70 is for determining which color original data each color component data (BGR) from the sensor interface circuit 40 is, and corresponds to the density data D of 256 gradations of each pixel and the red image. The sub color flag SCF and the main color flag MCF corresponding to the black image are generated. The editing / processing circuit 90 performs editing and processing such as enlargement, reduction, and color inversion on the density data D and the color flags SCF and MCF from the color image information generation circuit 70. In this case, 8 bits of density data D and color flags SCF, M
Since it is only necessary to perform editing and processing for two bits of CF, the circuit configuration of the editing and processing circuit 90 is simplified as compared with a type in which editing and processing are performed on two systems of image data (8 bits each). can do. Then, the density data D and the color flag SC from the editing / processing circuit 90 are output.
F and MCF are sent to the laser printer 110 via the interface circuit 100. FIG. 5 shows a configuration example of the image output unit 110.

In FIG. 5, reference numeral 120 denotes a positively charged photoconductor,
Is a charging corotron that charges the photoconductor 120 in advance, and 122 is a dual beam scanning unit (hereinafter referred to as ROS [Raster Output S
123, a first developing device using, for example, a positive red toner, a second developing device using, for example, a negative black toner, and 125 aligning the polarity of the toner image on the photoconductor 120. Transfer pretreatment corotron, 126, a transfer corotron for transferring the toner image on photoconductor 120 to recording sheet 127, 128, recording sheet 12 electrostatically attached to photoconductor 120 side
7, a cleaner 129 for removing residual toner on the photoconductor 120; 130, an eraser lamp for removing residual charges on the photoconductor 120; 131, a toner image on the recording sheet 127 after the transfer process; A fixing device for fixing.

Note that the image reproduction characteristics of the recorded image density with respect to the input image density of the first developing device 123 and the second developing device
They are different as shown by Ys and Ym in the figure.

 Further, details of the ROS 122 will be described with reference to FIG.

141 is a first color image forming semiconductor laser, 142 is a second color image forming semiconductor laser, 143 is both lasers 141,
A polygon mirror that reflects the beam Bm from 142 at different angles, a polygon motor 144, an fθ lens 145, and a beam 146 from the laser 141 of the first color 141
A mirror 147 that guides the first exposure unit E1 located in front of the first developing unit 123 to the second exposure unit 147 that transmits the beam Bm from the laser 142 of the second color to the photosensitive member 120 at a stage subsequent to the first developing unit 123. Mirrors 148 and 149 leading to the unit E2 are SOS sensors for detecting the scanning start positions of the first and second color laser beams, respectively.

The drive control system of the ROS 122 is configured as follows.

In FIG. 5, the image processing unit 20 outputs red (first color) and black (second color) multi-tone image data in a state separated into density data D and a color flag CF as described above. The data distribution circuit 150
Based on the density data D and the color flag CF sent from the image processing unit 20, the data is distributed to two systems of image data Ds and Dm. 1st TRC (Tone Reproduction Cont
roler) 151 and the second TRC 152 are the data distribution circuit 1
The density levels of the image data Ds and Dm distributed at 50 are converted according to the reproduced image density characteristics. First screen generator 153 and second screen generator 1
54 processes the respective image data Ds and Dm separately and generates image density codes SOs and SCm corresponding to the respective image data. The FIFO 155 stores the image density codes SCs from the first screen generator 153. Is stored once and output,
The gap memory 156 stores the image density code SCm from the second screen generator 154 for a scanning time corresponding to the gap Gp between the first exposure unit E1 and the second exposure unit E2, and outputs it. 1st ROS controller 157
The second ROS controller 158 drives and controls the first color laser 141 and the polygon motor 144, and the second ROS controller 158 drives and controls the second color laser 142.
And 160. Reference numeral 161 denotes a motor driver of the polygon motor 144.

Note that the first ROS controller 157 controls the lasers 141 and 142 so that the exposure unit is an image unit, and the second ROS controller 158 is an unexposed unit as an image unit.

Next, a basic operation of the laser printer 110 will be described.

FIG. 8 is a diagram for explaining an image forming process of the image output unit.

First, the density data D and the color flag CF from the image processing unit 20 are distributed to two systems of image data Ds and Dm by the data distribution circuit 15, and are subjected to data conversion by the TRCs 151 and 152. 153, 154
Are converted into two systems of image density codes SCs and SCm. Thereafter, the data is transmitted to the first and second ROS controllers 157 and 158 via the FIFO 155 or the gap memory 156.

At this time, first, the first ROS controller 157
Then, the polygon motor 144 is driven to form a latent image Z1 having an exposed portion as an image portion as shown in FIG. 8A on the first exposed portion E1 of the photosensitive member 120. Then, this latent image Z1 is
When the image is developed at 123 under the first phenomenon bias VB1, a first toner image T1 is formed as shown in FIG.

Thereafter, the second ROS controller 158 drives the laser 142 to form a latent image Z2 in which the non-exposed portion becomes an image portion as shown in FIG. 8B in the second exposed portion E2 of the photoconductor 120. . When the latent image Z2 is developed by the second developing device 144 under the second developing bias VB2, as shown in FIG.
A toner image T2 is formed.

Then, after the toner images T1 and T2 are made uniform in polarity by the pre-transfer treatment corotron 125, they are transferred to the recording sheet 127 by the transfer corotron 126, and then fixed by the fixing device 131. ing.

FIG. 9 is a diagram showing a specific configuration of the data distribution circuit 150.

The data distribution circuit 150 includes two selection circuits 171 and 172. The selection circuits 171 and 172 control the
One of the input signals (A, B) of the system is selected. The color flag CF is used as a control input, and the density data D
Is input to the input terminal B of the selection circuit 171 and the input terminal A of the selection circuit 172, respectively, and the data of “0” is input to the selection circuit 17.
The signal is input to the input terminal A on the opposite side of 1 and the input terminal B on the opposite side of the selection circuit 172, respectively. Then, the color flag CF (in this example, pixels in the background area are handled as being included in the main color area, and pixels in the sub color area are at high level, and pixels in other areas are at low level. The input signal on the A side is selected at a low level and the input signal on the B side is selected at a high level depending on the state of (1). In the data distribution circuit 150, the output of one of the selection circuits 171 is transferred as sub-color density data Ds and the output of the other selection circuit 172 is transferred as main color density data Dm to the subsequent stage in pixel units.

 FIG. 10 is a diagram for explaining the characteristics of TRC.

The first TRC 151 cooperates with the first ROS controller 157 to
A desired image reproduction characteristic of the developing device 123, for example, the first
Sub-color conversion table (look-up table) for correcting the characteristics shown in FIG. 0 to a linear one like the first quadrant
The sub-color density data Ds is converted in advance before coding by the first screen generator 153. 2T
RC152 cooperates with the second ROS controller 158 and the first TRC151
7 is a main color conversion table (lookup table) for correcting the recorded image reproduction characteristic of the second developing device 124 to a desired one. 1TRC151, assuming that the density data corresponding to the input image density, for example, the density data Ds corresponding to the sub-color density is a curve like the fourth quadrant in FIG. The density conversion is performed as shown by a dotted line in the third quadrant of FIG. In this case, the conversion data is converted into the first screen generator 153.
When the pulse width modulation is performed by the first ROS controller 157 via the interface, the characteristic (SG-IOT characteristic) between the input density data and the output image density of the screen generator becomes as shown by the dotted line in the second quadrant of FIG. Consequently, a linear characteristic as shown in the first quadrant of FIG. 10 is obtained.

The screen generators 153 and 154 convert the input image data of 256 density gradations (including the zero density level) into image density codes SC (SCs, SCs in FIG. 5) of 4 to 7 gradations (including the zero density level). SCm).

FIG. 11 is a block diagram showing a basic configuration of the screen generators 153 and 154. In the figure, 8-bit input image data DT (corresponding to Ds and Dm in FIG. 5) is buffered.
Error diffusion circuit 200 once stored in 180
Sent to The error diffusion circuit 200 and the comparison circuit 240 include a threshold pattern setting circuit 190.
The threshold pattern THP set in is input and error diffusion processing and comparison processing are respectively performed. The output from the comparison circuit 240 is input to the density code generator 250, where a predetermined conversion is performed and the image density code SC (see FIG. 5)
SCs and SCm).

The threshold pattern setting circuit 190 sets a plurality of thresholds in encoding the multi-tone image data DT, and for example, a different A-sequence pattern for each adjacent pixel,
It has a B-sequence pattern.

FIG. 12 is a diagram showing a schematic configuration of the first ROS controller 157 and the second ROS controller 158.

The first ROS controller 157 receives a predetermined V clock signal VCK
Signal generating circuit 261 for generating the
And a FIFO synchronized with the V clock signal VCK from the synchronization signal generation circuit 261.
An image density code SC (corresponding to SCs) from 155 is taken in, and a multi-level modulation circuit 265 for modulating the pulse width of the image density signal SD in accordance with the image density code SC is provided.

The synchronizing signal generation circuit 261 is connected to the V clock signal VCK from the video clock generator 262 and the sensor amplifier.
This is to generate a synchronization signal in which the detection signal of the first SOS sensor 148 amplified in 263 is phase-matched. Further, the polygon motor controller 264 controls the motor control clock signal S
By transmitting M to the motor driver 161, the driving of the polygon motor 144 is controlled. Further, the multilevel modulation circuit 265 drives and controls the first laser 141 by transmitting the image density signal SD to the laser driver 159.

Further, the second ROS controller 158 has basically the same configuration as the first ROS controller 157 except that the polygon motor controller 264 is not provided, and the VROS from the video clock generator 272 and the sensor amplifier 273 A synchronization signal is generated in phase with the amplified detection signal of the second SOS sensor 149, and the gap signal is generated at the timing of the synchronization signal.
A synchronizing signal generation circuit 271 which takes in and outputs the image density code SC (corresponding to SCm) from 156, and an image density signal SC based on the image density code SC output from the synchronizing signal generation circuit 271
And a multi-level modulation circuit 275 for modulating the pulse width of the SD.

[Problems to be solved by the invention]

As described above, in the two-color color copying machine of the one-pass two-color system, since there is a gap between the first exposure unit and the second exposure unit, a gap memory is prepared and an image corresponding to the gap is prepared. It is necessary to store the density code and perform registration adjustment.

Although there are various evaluation factors of a copying machine, the reproducibility occupies a large weight, along with the number of copies per unit time. In this case, in a digital copying machine using pixel modulation, increasing the number of gradations per pixel is one of the improvement means.

However, in the above one-pass two-color copying machine,
The size of the gap memory increases in proportion to the number of gradations per pixel, and there is a problem that it is difficult to improve reproducibility.

An object of the present invention is to solve the above-described problems, and to provide an image forming apparatus capable of increasing the number of gradations per pixel according to an operation mode without increasing the size of a gap memory. Is what you do.

Means for Solving the Problems For this purpose, the present invention provides an image forming apparatus for forming an image with a plurality of color materials, an image input unit for inputting image data of a plurality of color materials, A plurality of image forming units for performing image formation for each of the plurality of color materials by changing the number of gradations of an image according to the obtained image data, and an image forming unit at a rear position among the image input unit and the plurality of image forming units And a gap memory that stores data corresponding to a gap between the image forming units corresponding to an image forming unit located behind the preceding image forming unit, and bypasses the gap memory. A bypass circuit for controlling the bypass circuit to be in the bypass mode when the operation mode is a single-color operation mode, and controlling the number of gradations of an image formed by the image forming unit of a color material used for image formation. And a control circuit for switching and controlling the number of color materials used for formation to a higher gradation number than in a plurality of operation modes.

[Action]

In the image forming apparatus of the present invention, the screen generator generates an image density code of the image data corresponding to each exposure unit, and the gap memory stores the image density code corresponding to the gap of the exposure unit at the rear position with respect to the preceding exposure unit. The data is stored, registration is adjusted, the scanning unit is driven, and a two-color image is reproduced. And, in the image output mode by single color,
By controlling the bypass circuit, the gap memory is bypassed. Therefore, in the image output mode with single color,
The number of gradations of the screen generator can be increased regardless of the size of the gap memory.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a diagram for explaining an embodiment of the image forming apparatus according to the present invention, and FIG. 2 is a diagram for explaining an example of changing the number of gradations.

In FIG. 1, screen generators 1 and 2
The first screen generator 153 described with reference to FIG.
And the same as the second screen generator 154, the number of gradations per pixel can be changed, and each of the image data Ds and Dm is processed separately, and the image density codes SCs and Generate SCm. The gap memory 3 also stores the image density code SCm from the screen generator 2 for a scanning time corresponding to the gap Gp between the first exposure unit and the second exposure unit and outputs the same, as in FIG. ROS controllers 4 and 5 are 5th
In the same manner as in the figure, the laser and the polygon motor (not shown) for the first and second colors are driven and controlled. The bypass circuit 6 outputs the output of the screen generator 1 to ROS
The gap memory 3 is connected directly to the input of the controller 4.
Is to bypass. The control circuit 7 controls the switching of the number of gradations per pixel of the screen generators 1 and 2 and the bypass of the gap memory 3 by the bypass circuit 6 according to the operation mode.

Now, the screen generators 1 and 2 are, for example, the second
The configuration is such that the number of gradations per pixel can be switched between 2 bits as shown in FIG. 3A and approximately 3 bits as shown in FIG. 3B. In such a case,
As shown in the figure, 4 gradations including 0 for 2 bits and 0 for 3 bits
, Image density codes SCs and SCm of seven gradations are generated corresponding to the respective image data. Therefore, if the size of the gap memory 3 is set so that registration can be adjusted when the screen generators 1 and 2 are operated with the number of gradations per pixel being 2 bits, 1
In the operation mode for reproducing a two-color image of pass two colors, the screen generators 1 and 2 are selected so that the number of gradations is 2 bits. However, in the operation mode for reproducing an all-black image, since only the pixel data Dm is output through the screen generator 2, the gap memory 3, and the ROS controller 5, there is no need to perform registration adjustment with the reproduced image of the image data Ds. A bypass circuit 6 can be passed instead of the gap memory 3. Therefore, there is no restriction on the number of gradations due to the size of the gap memory 3. The same applies to the operation mode for reproducing an all-red image. Therefore, the control circuit 7 sets the number of gradations of the screen generators 1 and 2 to 2 bits in order to perform registration adjustment by the gap memory 3 for the one-pass two-color operation mode, and opens the bypass circuit 6. In this state, the gap memory 3 is connected between the screen generator 2 and the ROS controller 5, and the number of gradations of the screen generators 1 and 2 is set to 3 for the all-red or all-black operation mode.
The value is increased to bit -1 and the gap memory 3 is
Is controlled so as to bypass.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above embodiment, the gap memory 3 is bypassed by connecting the screen generator 2 and the ROS controller 5 with the bypass circuit 6, but the output of the screen generator 1 is switched from the ROS controller 4 to 5 and connected. May be configured. In this case, it is needless to say that the characteristics of the data distribution circuit and the TRC described with reference to FIG. In addition, the TRC and screen generator were divided into systems for each color through the data distribution circuit, but the TRC and screen generator were shared, parameters were switched by flags and operation modes, and the bypass circuit was controlled. Is also good.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, 1
For a two-color copying machine of the pass two-color system, all red,
In the case of the operation mode of a single color such as all black, the gap memory is bypassed, so that the gradation per pixel in the single color operation mode can be achieved without increasing the size of the gap memory by a simple circuit configuration change. The number can be increased to improve the image quality.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining one embodiment of an image forming apparatus according to the present invention, FIG. 2 is a diagram for explaining an example of changing the number of gradations, and FIG. FIG. 4 is a block diagram showing an overall configuration of a color image forming apparatus, FIG. 4 is a diagram showing a schematic configuration of an image processing unit, FIG. 5 is a diagram showing a configuration example of a one-pass two-color laser printer, and FIG. FIG. 7 is a diagram showing the configuration of the ROS, FIG. 7 is a diagram for explaining the image reproduction characteristics of the first developing device and the second developing device, FIG. 8 is a diagram for explaining the image forming process of the image output unit, FIG. FIG. 9 is a diagram showing a specific configuration of the data distribution circuit 150, FIG. 10 is a diagram for explaining the characteristics of the TRC, and FIG. 11 is a screen generator.
FIG. 12 is a block diagram showing the basic configuration of 153 and 154, and FIG.
FIG. 4 is a diagram illustrating a schematic configuration of a controller 157 and a second ROS controller 158. 1 and 2 ... screen generator, 3 ... gap memory, 4 and 5 ... ROS controller, 6 ... bypass circuit, 7 ... control circuit.

Continuation of the front page (51) Int.Cl. ⁷ identification code FI H04N 1/46 B41J 3/00 A 1/60 B (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/23-1 / 31 H04N 1/46-1/64 G03G 15/01-15/01 117

Claims (1)

(57) [Claims] An image forming apparatus for forming an image with a plurality of color materials, comprising: an image input unit for inputting image data of a plurality of color materials; and a gradation number of an image based on the image data input from the image input unit. A plurality of image forming units for variably performing image formation for each of the plurality of color materials; and a preceding image arranged between the image input unit and an image forming unit at a rear position among the plurality of image forming units. A gap memory for storing data corresponding to a gap between the image forming units corresponding to an image forming unit at a position behind the forming unit; a bypass circuit for bypassing the gap memory; In this case, the bypass circuit is controlled to the bypass mode, and the number of gradations of the image formed by the image forming unit of the color material used for image formation is determined by a plurality of operation modes. An image forming apparatus characterized in that a higher control circuit for controlling switching to the gradation number than when the de.