JPH07147634A - Image forming device and image reader - Google Patents

Abstract

PURPOSE:To enable optimum double face image formation by removing image density shift caused by back print. CONSTITUTION:An original (a), where an image in green is formed on the front side, and an original (b), where an image in yellow is formed on the rear side, are read and the image density correction of a slanting line part 91 (c) overlapped on the front and rear sides is performed. Namely, concerning the image density on the front side, double face images are formed with the same image density as an original document at a part which is not the slanting line part 91 and with the image density correcting the density of the yellow component lower than that of the original document while considering the back print at the slanting line part 91.

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 and an image reading apparatus, and more particularly to an image reading apparatus for performing density correction based on image densities of a front surface and a back surface and an image forming apparatus for forming a double-sided image. .

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus having a double-sided image forming function is configured to form different images on the front surface and the back surface of one transfer medium.

[0003]

However, in the above-described conventional example, there is a problem in that, during image output, show-through occurs depending on the thickness of the transfer medium, and an image different from the intended image density is output. Was. The present invention has been made to solve the above problems, and provides an image forming apparatus and an image reading apparatus capable of removing image density deviation due to show-through and performing optimum double-sided image formation and double-sided image reading. To aim.

[0004]

In order to achieve the above object, the image forming apparatus of the present invention has the following constitution. An image forming apparatus that has a double-sided image forming function, performs density correction based on image densities on the front and back sides, and forms a double-sided image, including a reading unit that reads a front side document and a back side document
A density correction unit is provided for performing density correction based on the image densities of the front surface and the back surface read by the reading unit.

[0005]

In such a structure, the front side document and the back side document are read, density correction is performed based on the read image densities of the front side and the back side, and a double-sided image is formed by the double-sided image forming function.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described in detail below with reference to the drawings. [Description of Image Forming Process] FIG. 1 is a schematic configuration diagram illustrating the configuration of an image forming apparatus according to an embodiment of the present invention.
The embodiment is an image forming apparatus capable of forming full-color images of four colors using magenta, cyan, yellow, and black toners. Four image forming apparatuses corresponding to magenta, cyan, yellow, and black are provided independently of each other. It has an imaging station. Each station has photosensitive drums 101a to 101d as an image carrier, and each photosensitive drum has a primary high voltage charger and a grid high voltage unit 103.
The surface is uniformly charged by a to 103d. After uniform charging, an image corresponding to each color is exposed on the photosensitive drum by the laser scanning systems 102a to 102d based on the image information of each color scanned by the laser optical system 107 to form an electrostatic latent image. The latent image corresponding to each color image information is developed into a toner image by the developing devices 104a to 104d having toners of magenta, cyan, yellow, and black,
By the transfer chargers 105a to 105d, the toner image is transferred onto the transfer medium carried on the transfer belt 108 which is a document carrying means. The residual toner on each photosensitive drum is removed by the cleaning devices 106a to 106d.

[Description of Double-sided Image Forming Sequence] Next, a double-sided image forming sequence in the embodiment will be described by using an example in which paper is fed from an upper cassette. Simultaneously with the “ON” of the image formation start signal, the first paper feed roller solenoid (not shown) is turned “ON”, and the feeding operation of the transfer media P stacked in the paper feed cassette 110a is started. The transfer medium P fed from the cassette is conveyed by the registration roller 11
3, 114, and the first registration roller 115.
A predetermined loop is formed in the state where the front end of the transfer medium P has abutted against and is temporarily stopped.

On the other hand, at the same time when the image formation start signal is turned "ON", the original document on the platen is read by the CCD 116, and the read image signal is sent to the image processing section 11.
Sent to 7. After the image data read into the image memory of the image processing unit 117 is ready for laser scanning,
The driving of the first registration roller 115 is started. By this drive, the transfer medium P is adsorbed and conveyed to a predetermined position on the transfer belt for image formation. The image of each color is transferred onto the transfer medium P as described in the above [Description of image forming process]. At this time, the image information of the original document stored in the memory is magenta, cyan, and yellow. , And is written on the photosensitive drum of each color by the laser optical system 107 so as to be superimposed and transferred onto the transfer material medium at each timing of passing through each black station.
The transfer medium P, which has passed through four stations in sequence and has multiple transferred images, is then fixed with a toner image by fixing means 10 for fixing the toner.

On the other hand, at the time of the front side copy, at the same time when the image forming start signal is turned “ON”, the re-feeding roller release solenoid (not shown) is turned “ON”, and the re-feeding roller 112 is raised in preparation for double-sided image formation. To do. Further, by turning on a sheet conveying path deflecting plate solenoid (not shown), the first sheet deflecting plate 114 operates to form a sheet conveying path for double-sided image formation. At the same time, the paper stopper plate solenoid SL (not shown) in the intermediate tray section 118 is turned on, and the paper stopper plate in the intermediate tray (not shown) is operated.

At the same time, the second conveying section drive solenoid SL (not shown) is turned on, and the second conveying section, that is, the roller pair 115 starts driving. When the fixing operation for the first side is completed, the transfer medium P is conveyed to the double-sided path by the above-described first sheet deflecting plate 114, and is conveyed to the conveying roller 115. The transfer medium P is a switchback unit (paper reversing unit) 1
After passing the paper reversal detection sensor 119 provided in 17, the forward / reverse rotation roller 116 rotates in the reverse direction. As a result, the transfer medium P is switched back and is sent to the second transport unit (transport roller 120). Deflection plates 121 and 122 for each paper size convey the transfer medium P conveyed into the intermediate tray 118 by driving the paper deflection plate solenoids SL7 and SL8 (not shown) according to the size of the transfer medium P. Change the route.

When the first transfer medium P is conveyed into the intermediate tray, the re-feed roller release solenoid (not shown) is temporarily turned off, and the re-feed roller 11 is rotating.
2 is lowered onto the transfer medium P. The transfer medium P conveyed by this is abutted against a paper stopper plate (not shown). By the series of operations, the transfer medium on which the image formation on the first side is completed is sequentially stacked in the intermediate tray 111, and becomes a standby state in preparation for the image formation on the second side.

In this state, the second paper feed roller 11
No. 2 descends onto the transfer medium loaded in the tray. In this state, when the image forming start signal for the second side is transmitted, the image forming operation for the second side is started. That is, the second conveying unit drive solenoid (not shown) is turned “ON”, the re-feeding roller 112 rotates, and the transfer medium P in the tray is re-fed from the top. When the first transfer material starts to be fed, that is, when it is started to be conveyed by the conveyance roller 122, the second paper feed roller moves up. When the feeding of the first transfer medium is completed, the rotating second feeding roller is lowered at a predetermined timing to feed the next transfer medium (second sheet). The sheet re-feeding roller 112 repeats this up and down operation. The re-fed transfer material is conveyed by the conveying roller 114, the leading end hits the first pair of registration rollers, forms a predetermined loop, and is temporarily stopped, as in the case of forming an image on the first surface. After being fixed and transported on the transporting unit 108 at a predetermined timing, the second surface image is formed after passing through the first to fourth stations and the second surface image is fixed. On the other hand, when the image formation of the second side is started, the above-mentioned first sheet deflection plate solenoid (not shown) is “OFF”, so the image formation of the second side is completed and the transfer after the fixing is completed. The medium is guided to the paper ejection roller and ejected and stacked on the paper ejection tray. After ejecting the final transfer medium, the series of operations is completed.

[Description of Image Processing Unit] FIG. 2 shows the flow of the image signal from the image processing circuit unit 117, which processes the image information read by the CCD 116 as an electric signal and outputs it as a print signal. It is a thing. CCD1
The image data picked up at 17 is sampled and held by the circuit 202, A / D converted, and converted into a digital signal of three colors of RGB. The separation data of each color is the circuit 20
Shading correction and black correction are performed at 3 and circuit 2
After the NTSC correction in 04 and the LOG conversion in the circuit 205, a signal corresponding to the toner signal used in the printer is generated by the masking / UCR circuit 206, and each generated signal is stored in the memory unit 207 as image data. Is stored. The image data stored in the memory unit 207 is read out, subjected to γ correction in the circuit 208, edge-enhanced in the circuit 209, and sent to the printer unit.

FIG. 3 is a diagram showing the flow of image data in the printer section. M sent from the above reader
The CYK image signal is γ-corrected by the γ-correction circuit 301 according to the sensitivity of each photoconductor. Thereafter, the image data M and C are passed through the FIFO 302, converted into a pulse width according to the gradation data by the pulse width modulation circuit 304, and the laser driver 305 emits a laser according to the pulse width. The image signals Y and K are converted into γ and then Y, K
Laser is scanned in M and C as a mirror image.
The main scanning data is inverted by the O circuit 302 and converted into a pulse width according to the pulse width modulated gradation data, and the laser driver 305 emits a laser according to the pulse width.

[Description of Image Synchronous Control] FIG. 4 is a diagram showing a positional relationship between the photosensitive drums 101a to 101d. The photosensitive drums are arranged side by side by a distance d1. Further, the transfer belt 108 conveys the transfer medium at the speed Vb. Laser scanning system L1 based on image information of each color
.About.L4 (102a to 102d), the distance from the position where the image corresponding to each color is exposed on the photosensitive drum to the transfer belt contact position is d3. The distance from the registration roller 115 to the center of the photosensitive drum 101a is d2. At this time, the timing at which the image information of the original document stored in the memory is written on the photosensitive drum of each color so that the image information of the original document is superimposed and transferred onto the transfer material medium at each timing of passing each station of magenta, cyan, yellow, and black. Is shown in FIG.

In order to send the transfer medium stopped by the registration rollers onto the transfer belt, the image pattern formation start signal is turned "ON" at the same time when the registration rollers are started. The rising edge of the enable signal for each color rises from the rising edge of the image pattern forming signal as shown by the following equation: Tm = (d2-d3) / Vb Tc = Tm + d1 / Vb Ty = Tc + d1 / Vb Tbk = Ty + d1 / Vb It falls according to the length of the medium in the sub-scanning direction.

FIG. 6 is a diagram showing a circuit for generating an enable signal. In the embodiment, as a clock for the counter or the like, HSYNC which is synchronously generated each time the laser scans one line is used. Reference numeral 601 is a 14-bit counter, which counts the number of HSYNCs in synchronization with HSYNC. A register 602 stores a value to be loaded into the counter when a LOAD signal is generated, and data is written by a CPU (not shown). In the embodiment, "0" is written. Reference numerals 603 to 606 are comparators for comparing the image enable rising times of the respective colors, and the CPU (not shown) writes the HSYNC count numbers corresponding to the above-mentioned Tm, Tc, Ty, and Tbk in the registers 607 to 610, and the 14-bit counter When it matches the output, a match signal is output. Further, 611 to 614 are comparators for comparing the image enable fall times of the respective colors, and 615 to 61
The above-mentioned Tm + T by the CPU not shown in the register of 8
The HSYNC count number corresponding to p, Tc + Tp, Ty + Tp, Tbk + Tp is written, and when the output of the 14-bit counter matches, a match signal is output. Here, Tp is represented by Tp = L / Vb, where L is the length of the paper.

The above-mentioned image pattern formation start signal is input to CNT_START shown in FIG. 6, and when the rising signal of the image pattern formation start signal is detected by the two D latches, it is input to LOAD of the counter 601. The counter is cleared and the counting operation starts. The counter 601 cumulatively counts HSYNC, and when the count value corresponding to the rising edge of the magenta enable is reached, the comparator 603 detects a match and generates a match signal. The coincidence signal is input to the J terminal of the 619 JK flip-flop, and the magenta sub-scan enable MVEN rises to Hi. When the count further progresses and the number of falling edges of the enable is reached, the comparator 611 detects a match and outputs a match signal, the match signal is input to the K terminal of the JK flip-flop 619, and the magenta sub-scan enable MVEN rises to Low. Go down. The sub-scan enable is generated for cyan, yellow, and black in the same manner.

[Explanation of Image Area Editing Control] In the embodiment, since the image area processing is performed, the area is designated by the editor as shown in FIG. Also, it is possible to assign different functions to each area. FIG. 7 is a diagram showing the image area enable signal and the function, showing the generation of the area enable signal for the main scanning and the sub scanning and the output state of the function code in the area when the area 1 and the area 2 are selected by the editor. It is shown.

FIG. 8 is a diagram showing an image signal editing processing circuit. The image signal that has been input is used to create image-through data that does not undergo image processing and mirror image data.
03 LIFO and each output data is input to the A and B inputs of the image signal selector 802. Also,
The data written in the register 804 by the CPU (not shown) is input to the C input of the image signal selector 802. Here, the area edit signal generation circuit 801 counts the sub-scanning synchronization signal HSYNC and the main scanning synchronization clock VCLK, and internally generates the above-mentioned main / sub-area enable signal as shown in FIG. Also, a function code is generated for each area, and the image signal selector 802 is generated according to this signal.
By switching the input of, it is possible to output data that is not processed, mirror image data, fixed value data, etc. for each area. Then, the signal from the image signal selector 802 is input to the FIFO of 805, and the output from the FIFO 805 is output as an edited image signal.

[Application Example] Next, as shown in FIG. 9A, a document having a green image formed on the front surface thereof and a document having a yellow image formed on the back surface thereof as shown in FIG. 9B. One embodiment of the present invention will be described by taking as an example the case of outputting a double-sided image original from an original. When the originals (a) and (b) shown in FIG. 9 are read, as shown in FIG.
In No. 1, there is a portion where the front surface area and the back surface area overlap.
A process for correcting the image density of the overlapped shaded portion 91 will be described.

The image data of (a) and (b) shown in FIG. 9 is stored in the memory as described in [Description of image processing section]. Next, the density of each pixel on the front surface and the back surface is read from the memory by a CPU (not shown). Since the read pixel density is color-separated by the toner signal, density values can be obtained for each pixel for magenta, cyan, yellow, and black. For example, for the green image in (a) shown in FIG.
Density values of magenta 0%, cyan 100%, yellow 100%, and black 0% are obtained, and for the yellow image of (b), magenta 0%, cyan 0%, and yellow 100%.
%, Black 0% density values are obtained. Here, the following calculation is performed for each pixel to correct the density value of the image corresponding to the front original.

M '= Ma (1-α) + Mbα C' = Ca (1-α) + Cbα Y '= Ya (1-α) + Ybα Bk' = Bka (1-α) + Bkbα where suffix a is the surface Indicates the suffix b
Indicates the back side. The dash 'indicates the result after the calculation. For example, Ma represents the image density of magenta on the front side, Mb represents the image density of magenta on the back side, and M ′ represents the calculation result of magenta. And α is 0
The show-through coefficient takes a value of ≦ α ≦ 1 and is set according to the thickness of the transfer paper.

The above calculation is performed for each pixel, and the calculation result is stored again in the memory as the image density. When this series of processing is repeated, the image density on the surface is the same as the original original image density in the portion other than the shaded portion 91 in FIG. 9C. The density of the component is stored in the memory with the image density corrected and set lower than that of the original document. Then, the image data stored in the memory is subjected to double-sided image formation and output, as described in the above [double-sided image formation sequence].

As described above, according to the embodiment, the front surface and the back surface of the original double-sided original are read, and the density value is corrected by the calculating means based on the read front surface image density and the back surface image density. Even if is used, it is possible to remove the image density deviation regardless of show-through and form a color image faithfully to the original. <Modification> In the above-described embodiment, the correction calculation is performed by the CPU.
However, it may be performed by a hardware circuit for speeding up.

FIG. 10 is a block diagram of the image processing unit when this show-through density correction is performed by a hardware circuit.
As shown in FIG. 10, at the latter stage position of the memory unit 207, γ
The show-through density correction circuit 100 is provided at the position before the correction circuit 208.
1 is set. Similar to the above-described embodiment, the read images on the front surface and the back surface are stored in the memory. The stored image is processed by the show-through density correction circuit 1001 according to the above-described embodiment in hardware according to the printing of the front side and the printing of the back side, and the corrected data is sent to the γ conversion circuit.
After that, image processing is performed in the same sequence as in the above-described embodiment.

The show-through correction circuit described above will be described below. FIG. 11 is a diagram showing a show-through density correction circuit. The show-through density correction circuit has circuits for four colors which are toner signals, but each circuit is the same, and the circuit of M which is a magenta signal will be described here. here,
Since the same processing as the equation M ′ = Ma (1-α) + Mbα shown in the above-described embodiment is performed, first, 8-bit image density data Ma on the surface is read out, and the selector 1101 passes through the A side and the multiplier 1102. Is output to the B side of. This data is multiplied by the data from the register 1103 on the A side in the multiplier 1102 and stored in the DQ register 1104. At this time, data obtained by multiplying (1−α) by 256 is set in the register 1103 by a CPU (not shown). As a result, the DQ register 1104 stores the calculation result corresponding to the first term on the right side of the above equation. Next, the selector 11
From 01, the back surface density data Mb is output to the A side of the multiplier 1105. This data is multiplied by the data from the register 1106 on the A side in the multiplier 1105, and added by the adder 1107.
Is output to the B side of. At this time, the register 1106 has
Data obtained by multiplying α by 256 is set by a CPU (not shown). As a result, the multiplier 1105 performs an operation corresponding to the second term on the right side of the above equation.

In this way, the operations corresponding to the first and second terms are performed and added by the adder 1107. After the addition of the image density data of 8 bits, the lower 8 bits are truncated and the data is output in 8 bits. As described above, according to the modified example, the show-through density correction can be performed at high speed by the hardware circuit.

The present invention may be applied to a system including a plurality of devices or an apparatus including a single device. Further, it goes without saying that the present invention can also be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0030]

As described above, according to the present invention,
It is possible to eliminate the image density shift due to show-through and perform optimum double-sided image formation or reading.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment.

FIG. 2 is a diagram showing a flow of images in an image processing unit.

FIG. 3 is a diagram showing a flow of images in a printer unit.

FIG. 4 is a diagram showing an arrangement of image forming stations.

FIG. 5 is a timing chart of an image forming section enable signal.

FIG. 6 is a diagram showing a circuit for forming an image forming section enable signal.

FIG. 7 is a timing chart of an area enable signal for an edit area.

FIG. 8 is a diagram showing an image editing circuit for an area signal.

FIG. 9 is a diagram illustrating an example of show-through correction.

FIG. 10 is a diagram showing an image flow of an image processing unit according to a modification.

FIG. 11 is a diagram showing a show-through correction circuit according to a modification.

FIG. 12 is a diagram showing an editing area designating unit in the embodiment.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location 9191-5L G06F 15/68 310 J

Claims (2)

[Claims] 1. An image forming apparatus having a double-sided image forming function, which performs density correction based on image densities of a front surface and a back surface to form a double-sided image, comprising a reading unit for reading a front surface original and a rear surface original. An image forming apparatus comprising: a density correction unit that performs density correction based on the image densities of the front surface and the back surface read by the reading unit. 2. An image reading device comprising: a reading unit for reading a front side image and a back side image; and a density correcting unit for correcting the density based on the densities of the front and back side images read by the reading unit. apparatus.