JPH01296274A - Color image forming device - Google Patents

Abstract

PURPOSE:To form a color image without deviation by carrying out the image transfer, after carrying a transfer material, which is carried in circulation, at a low speed and positioning at a specified position. CONSTITUTION:When the tip of the transfer paper, which is carried in circulation through transfer material paths 86A and 87, is detected by a paper tip detecter 83, a driving source is controlled by CPU and a driving roll 89b is controlled to move at a low speed. Then the transfer paper is carried at a low speed and its tip is detected by a photo sensor 84, and the transfer paper is positioned at a fixed position D, which has a transfer position C as reference. Later, in the same way, the transfer paper is carried at a fixed speed and each color image is layered without deviation by repeated transferring, and a color image of good quality without color deviation can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a color image forming apparatus, which has a means for circulating a transfer material, and a color toner image formed on an image forming body using the means. The present invention relates to a color image forming apparatus in which a color image is formed by repeating the process of transferring and fixing color toner images, and in particular, the timing of transporting a transfer material is improved in order to improve the overlay accuracy of color toner images.

[Conventional technology]

2. Description of the Related Art Conventionally, as an apparatus for forming a color image by an electrophotographic method, there is one described, for example, in Japanese Patent Laid-Open No. 163978/1983. In this publication, a document is scanned to obtain recording signals for each color such as yellow, Y1, magenta, M1, cyan, Cy, black, Bk, etc., and the recording signals are written onto an image forming body via a laser beam for each color to form an electrostatic latent image. The electrostatic latent image is developed with a developer containing a corresponding color toner to form a color toner image, and this process is repeated to transfer it onto a transfer material on a transfer drum. A color image is formed by separating the transfer material from the image and fixing it.

In such a color image forming apparatus, (1) when the transfer material is attached to and removed from the transfer drum, misalignment in the timing of attachment and detachment, twisting or bending of the transfer material, poor fixing, etc. may cause toner image transfer deviations, transfer omissions, etc.

(2) When the toner images of each color are superimposed and transferred onto the transfer material on the transfer drum, the subsequent toner images are superimposed on the unfixed toner images, which may cause damage or blurring, resulting in poor image quality. This may cause problems such as being damaged.

Furthermore, for example, Japanese Patent Application Laid-Open No. 60-76766 discloses a color image forming apparatus which forms toner images of each color superimposed on an image forming body and transfers them all at once onto a transfer material conveyed by a normal conveying means. is proposed.

In this color image forming apparatus, toner images of each color are formed on an image forming body in a superimposed manner and transferred onto a transfer material at the same time, so there is little transfer deviation, which is advantageous in terms of color image formation. However, there are the following problems.

(1) The usual developing method of developing by rubbing the surface of the image forming body cannot be used. Therefore, it is necessary to use a special development method such as a non-contact development method in which toner is caused to fly through a gap for development, or a cloud development method.

(2) Since it is necessary to transfer a plurality of color toner images onto a transfer material at once on an image forming body, the transfer efficiency is poor in a normal transfer method, and special measures are required.

(3) When forming the second and subsequent toner images on the formation body, since the previous toner image exists, the conditions for transfer, cleaning, static elimination, charging, exposure, etc. are different from normal electrophotographic processes, and their control is becomes complicated.

(4) Since the previous toner image exists on the image forming body, it cannot be used as a demand type, and the apparatus cannot be made compact.

Therefore, for example, Japanese Patent Laid-Open No. 62-230160 proposes a two-color image forming apparatus having means for circulating transfer material.

In the above publication, the image information stored in the memory is read out for each color, the laser beam is modulated by the image information, writing is performed on the image forming body, development is performed with a developer containing the corresponding color toner, and the obtained color is The process of transferring and fixing the toner image onto the transfer material can be repeated, and the transfer material on which the first color toner image has been transferred and fixed is conveyed in circulation, and then the next color toner is placed on top of it. The image is transferred and fixed to form a two-color image. According to such an image forming apparatus, a color image can be formed by using a normal image forming process as is except for the circulation conveyance means, and therefore, it is possible to form a color image by using the normal image forming process as is.
Problems in the No. 2 publication, etc. are resolved.

Although color image forming apparatuses have been improved as described above, as copying technology has become more sophisticated in recent years, there has been a demand for further improvements in the image quality of color images. For this purpose, it is important that the toner images of each color formed on the image forming body are always transferred onto the transfer material in a timely manner. However, in general, blank paper is used as a transfer material, which is weak and prone to deformations such as folds, twists, and wrinkles, and is also prone to skewing or wrapping during the conveyance process. Furthermore, since the transfer material expands and contracts due to changes in temperature and humidity, there are many problems in the conveyance of conventional transfer materials, and improvements are needed in the layer.

For example, conventionally, in order to convey a transfer material to a transfer area, the transfer material conveyed from a cassette hits a timing roll, forms a loop, and is temporarily stopped. Next, the timing roll is driven by the original scanning start signal, and the transfer material is conveyed to the transfer area in synchronization with the image forming process. However, this method has the following problems.

(1) The position of the leading edge of the transfer material stopped by the timing roll varies and is not constant.

(2) Since the transfer material is not sufficiently wrapped around the timing roll, the transfer material slips when the roll is driven.

For example, Japanese Patent Application Laid-open No. 52-75332 discloses a method in which a transfer material is conveyed, the leading edge of the transfer material reaches a specific position that has been aligned in advance, and a conveyance roll is driven by a scanning start signal of the original. A technique has been proposed in which a transfer material is conveyed from the specific position to a transfer area to perform a toner image transfer process. The outline of the specific contents is as above.

First, as shown in FIG. 8, the transfer material P fed from the cassette 2 by the paper feed roll 3 abuts against the timing roll 4 which is in a temporarily stopped state to form a loop.

Next, the roll 4 is rotated, and the skew of the transfer material is corrected by the paper pressure of the loop, and the transfer material is conveyed, reaches a pre-aligned position, and is stopped. By the way, the conveyance of the transfer material after the paper feed cassette is stopped by a clutch mechanism under time control by a microcomputer (CPU).
The transfer material is turned on and off, but the transfer material is stopped at the aligned point D by being detected by the paper leading edge detection sensor S2. As the ground detection sensor S2, a photo sensor, a microswitch, an ultrasonic detector, or the like may be used.

On the other hand, the optical system 7 that scans the document and reads its information is
The transfer material P runs a distance of QO from the home position H and reaches the reading start point A, but by this time the leading edge of the transfer material P has reached the aligned position.

On the other hand, the optical system 7 reads the document after point A, and the optical information thereof is written through the first mirror M1, the second mirror M2, etc., at the point B and after on the image forming body 1 rotating at a constant speed. Further, when the optical system 7 reaches point A, the first mirror M1 of the optical system 7
Microswitch S1 is activated by the action of cam 8 connected to
The timing roll 4 and the conveyance roll 5 are driven by the signal, the transfer material P is conveyed to the transfer area, and the toner image on the image forming body I is transferred.

Here, the 0 point is the transcription start point, BCCa2 and CD length Q2.
Point D is aligned so that they are equal.

[Problem to be solved by the invention]

The inventors of the present invention have further investigated the technique described in the above-mentioned publication and have found the following problems.

In FIG. 8, the timing roll 4 is rotated,
When the transfer material P is conveyed to an aligned position, some positional deviation always occurs. That is, even if the leading edge of the transfer material P is detected by the sensor S2 and the drive is stopped by actuating the clutch mechanism based on the signal, the transfer material P will not stop at a predetermined position but will continue to move for a while, causing an error. As a result, it has been found that the conveyance of the transfer material P and the timing of image formation are not sufficiently matched, resulting in a timing shift, making it impossible to obtain a truly desired transferred image.

As a result of extensive studies, the inventors of the present invention found that the timing deviation due to the movement error of the transfer material at a predetermined position is affected by the material, thickness, size of the transfer material, humidity of the atmosphere, etc., but is particularly affected by the conveyance speed. He realized that the influence was important and completed the present invention.

[Means to solve the problem]

An object of the present invention is to provide an improved transfer paper conveying means to superimpose and transfer the toner images of each color formed on an image forming body onto a transfer material, and to avoid timing deviations, color shifts, etc., and to achieve stable transfer. An object of the present invention is to provide a color image forming apparatus that can produce high quality color images.

The above object is to provide a means for writing color-specific recording signals obtained by reading a color original onto an image forming member to form an electrostatic latent image, and a means for developing the electrostatic latent image with a developer containing a corresponding color toner. and means for conveying a transfer material for transferring the color toner image to a transfer area and transferring the color toner image onto the transfer material, and each of the above-mentioned means is necessary. In a color image forming apparatus that repeatedly forms a multicolor toner image on the transfer material, in the process of conveying the transfer material to the transfer area, the transfer material is conveyed at a low speed and its leading edge is moved to a predetermined position. means for conveying the transfer material aligned at the predetermined position to a transfer area to transfer and fix the color toner image formed on the image forming body; - This is achieved by a color image forming apparatus characterized by having means for circulating and conveying the fixed transfer material.

[Structure and operation of the invention]

The features of the color image forming apparatus of the present invention can be summarized as follows.

That is, the color image forming apparatus of the present invention is an apparatus that writes recording signals for each color obtained by reading a color original onto an image forming body, and forms a color image by repeating development, transfer, and fixing. , it has a means for circulating and transporting a transfer material carrying a fixed toner image obtained by developing, transferring and fixing, and it has an improved paper feeding means for transporting the transfer material to the transfer area in a timely manner. There are characteristics.

Since the transfer material is circulated and conveyed to form a color image, the troublesome transfer drum described above is not required, and the image formation process can be performed by utilizing the conventional technology of white and black as is. This brings about many advantages.

Furthermore, since the means for feeding the transfer material to the transfer area has been improved as shown in FIG. 1, the transfer material is transported in sufficient timing with the image forming process. As a result, there is no timing shift, and since the toner images of each color are sufficiently aligned, a high-resolution color image without color shift can be obtained.

In FIG. 1, a transfer material PA or PB is fed by driving a paper feed roll 3A or 3B from a paper feed cassette 2A or 2B based on a copy start signal. It is transported while being prevented from running, and is transported to the timing roll 4 which is stopped at -.

Here, the tip of the transfer material PA or PB is on the timing roll 4.
It is struck by the object, forming a loop and stopping it. Next, under the control of the CPU, the timing roll starts rotating at a low speed after a certain period of time to slowly convey the transfer material, and the leading edge of the transfer material is detected by a leading edge detection sensor S2 placed at a predetermined position point. and stopped.

The transfer material PA or PB is transported at a low speed of 100 mm/s.
ec or less, preferably 1 to 80 mm/sec, more preferably 5 to 50 mm/sec. Here, if it exceeds 100 mm/sec as in the conventional case, the transfer material slips during low-speed conveyance and the conveyance is delayed, or the leading edge of the transfer material is detected by the leading edge detection sensor S2, and that signal is used to stop the transfer material from being conveyed at the low speed. Even when the transfer material is stopped at point D, a large inertial force acts on the transfer material, so that the conveyance is not stopped and the transfer material passes past point D, causing problems such as increased variation in the stopping position.

If the transfer material is conveyed at a low speed as described above, the above-mentioned disadvantages will be eliminated, and the transfer material will be conveyed while being sufficiently matched with the image forming timing.

Next, the timing roll 4 and the conveyance roll 5 are driven by a scan start signal from the microswitch S1 of the scanning optical system, and the sheet is conveyed to the transfer area C at a normal conveyance speed.

Furthermore, although the above explanation is for the case where the paper is conveyed from the paper feed cassette 2A or 2B to the transfer area in order to transfer the first color toner image, after the first color toner image is transferred and fixed, it is circulated and conveyed. For example, when the paper reaches the intermediate tray 14 and waits there, the subsequent transport is the same as the transport from the cassette.

Note that the distance over which the transfer material is conveyed at low speed to the predetermined position by the timing roll 4 is usually 1 to 20 mm.

The speed at which the transfer material is transported to the transfer area C after the low-speed transport is:
It is usually the same as the circumferential speed of the image forming drum, in which case DC
The distance therebetween is made equal to the circumference Q between the writing point B on the image forming body and the transfer area C.

By the way, in the explanation of FIG. 1, as an example of the means for conveying the transfer material P, the transfer material P conveyed from the previous process is brought into contact with a timing roll and stopped, and then conveyed at a low speed to a predetermined position iD.
The image forming apparatus stops when it reaches this position, and is conveyed to the transfer area in accordance with the image forming timing using this predetermined position as a reference point. According to this method, the transfer material P can be conveyed at a constant speed without difficulty, and the stopping at the predetermined position can be performed with high precision without variation.

Further, as another example of a means for conveying the transfer material P that is applicable to the present invention, as described in Japanese Patent Application Laid-Open No. 62-208065, the transfer material P conveyed from the previous process is first conveyed by a timing roll. The transfer material is continuously conveyed to the position, and without stopping at the first position, the transfer material is conveyed at a low speed to the second position to increase the speed, and from the second position as a base point, the transfer material is moved to the transfer area in accordance with the image forming timing. There is also one for conveying paper, and it may be similarly used in the paper feeding means of the present invention.

Next, the general structure of the color image forming apparatus of the present invention and its image forming process will be explained with reference to the block diagram of FIG.

As shown in FIG. 2, it is composed of a reading section A, a writing section B, a recording section C, and a control section. In the reading section A, optical information obtained by optically scanning a color document with a light source such as a halogen lamp or a fluorescent lamp is divided into multiple pieces by color separation means such as a color filter, a dichroic ink mirror, a dichroic ink prism, etc. The signals are separated into colors, converted into electrical signals by photoelectric conversion means such as a plurality of line image sensors (hereinafter referred to as CCD), and digitized by A/D conversion means. The obtained color-specific digital signals are converted into color signals to be recorded by an image processing device, subjected to various corrections necessary for color recording, and multi-valued by a multi-value conversion means to produce color-specific recording signals. is obtained.

This recording signal is output to the writing section, and is written on the image forming body by the writing section B, which is a laser beam optical device, to form an electrostatic latent image. Thereafter, image formation is performed by the recording section C.

This recording section C includes a plurality of developing devices, a paper feeding device including a transfer material circulation conveyance device, a color toner image transfer/separation device, a cleaning device, etc. The above-mentioned improvements have been made to ensure accurate matching.

The electrostatic latent image is developed by a first developer containing toner developer of a color corresponding to the recording signal to form a first color toner image. This color toner image is transferred and fixed onto a transfer material fed from a paper feed cassette in synchronization with the image formation, and is then transported by a transfer material circulating means. A second color toner image formed on the image forming body by writing and developing a recording signal of the next color on the conveyed transfer material is transferred and fixed onto the first color toner image. This process of transfer, fixing, and circulating conveyance is repeated as many times as necessary to form a color image.

As the timing roll for conveying the transfer material, an elastic member such as urethane rubber, butadiene rubber, or chloroprene rubber with a rubber hardness of 60 to 90° is used to easily balance the tip of the transfer material and to prevent slipping during conveyance of the transfer material. The same roll is used.

Further, as the sensor S2 for detecting the leading edge of the transfer material at the above-mentioned point, a photo sensor, a microswitch, an ultrasonic detector, or other known paper detection sensor is used. Further, as the means for switching the low-speed conveyance of the transfer material, a known speed change means such as a speed change motor, a clutch mechanism, a gear change, etc. is used.

By the way, regarding the color image forming apparatus of the present invention, the signal processing in the reading section A explained in FIG.
Publications No. 78 to 59-163980, JP-A-62-9
Those described in Japanese Patent Application Publication No. 7467 and Japanese Patent Application Laid-Open No. 62-230160 can be used. Although the above explanation uses a color original as an example, it is also possible to use a black and white original, specify an area, perform partial color conversion, and then develop the specified area with color toner to form a color image. The present invention also includes cases where

〔Example〕

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the embodiments of the present invention are not limited thereto.

(Example 1) Fig. 3 is a cross-sectional view of a color image forming apparatus for explaining this embodiment, Fig. 4 is a block diagram for explaining signal processing of reading section A, and Fig. 5 is a sectional view of a color image forming apparatus for explaining this embodiment. Characteristic diagram,
FIG. 6 is a sectional view of the laser optical device, and FIG. 7 is a sectional view of the paper feeding device.

In FIG. 3, a color original 21 on an original table 22 is optically scanned by an optical system. This optical system includes a light source 23
．． 24 and a carriage 26 provided with a reflecting mirror 25
．． It is composed of a movable mirror unit 28 provided with V mirrors 27A and 27B. The carriage 26 and the movable mirror unit 28 are caused to travel on the slide rail 31 at predetermined speeds and directions, respectively, by a stepping motor 29. Original 21 by light sources 23 and 24
The optical information (image information) obtained by irradiating the reflection mirror 25. The light is guided to the optical information conversion unit 32 via mirrors 27A and 27B.

In addition, when scanning color originals, commercially available warm white fluorescent lamps are used as the light sources 23 and 24, and anti-flicker lamps are used to prevent emphasis or attenuation of specific colors. Therefore, these light sources 23 and 24 are turned on and driven by a high frequency power source of about 40 KHz.

In addition, in order to maintain a constant temperature of the tube wall or promote warm-up, the tube wall is kept warm by a heater using a thermistor.

[A standard white plate 39 is provided on the back side of the left end of one unit 22. This is because the image signal is normalized to a white signal by optically scanning the standard white plate 39.

The optical information conversion unit 32 includes a lens 30. prism 33
．． Two dichroic mirrors 34, 35, a CCD 36 for capturing a red color-separated image, a CCD 37 for capturing a green color-separated image, and a C0 for capturing a blue color-separated image.
D38.

Optical signals obtained by the optical system are collected by a lens 30, and separated into blue optical information and yellow optical information by a dichroic mirror 34 provided in the prism 33 described above. Furthermore, the yellow optical information is color-separated into red optical information and green optical information by the dichroic mirror 35. In this way, the color optical image is decomposed by the prism 33 into three-color optical information of red, R, green, and blue.

Each color separation image is formed on the light receiving surface of each CCD, thereby obtaining an image signal converted into an electrical signal.

After the image signal is processed by a signal processing system, recording signals of yellow Y, magenta M, cyan Cy, and black Bk are obtained, and the recording signals of each color are outputted to the writing section B.

The above is the color document reading section A, and its signal processing system is shown in FIG.

That is, as described above, the color image information of the color original 21 is converted into red R by the two dichroic mirrors 34 and 35.
The image is separated into three color separated images: green (G) and blue (B). Therefore, as shown in Part 5, the cutoff wavelength of the dichroic mirror 34 is about 450 to 520 nm, and the cutoff wavelength of the dichroic mirror 35 is about 550 to 6 nm.
A 20 nm one is used. As a result, the green component becomes the transmitted light, the blue component becomes the first reflected light, and the red component becomes the second reflected light.

The color separated images of red R1, green G, and blue B are supplied to image reading means, such as CCD sensors 36, 37, and 38, and image signals of only the red component, green component G, and blue component B are output from each image reading means, for example, CCD sensors 36, 37, and 38.

The image signals R, G, and B are supplied to A/D converters 40, 41, and 42, and are converted into digital signals having a predetermined number of bits, 8 bits in this example. Shading correction is performed simultaneously with A/D conversion. 43, 44, and 45 indicate a shading correction circuit. In this correction circuit, a standard white plate 39
The white signal obtained by scanning is used as a reference signal to correct distortion during image exposure.

The digital image signal subjected to the shading correction is extracted by the gate circuits 46, 47, and 48 only for the signal corresponding to the maximum original size width, and is supplied to the color correction circuit 49 at the next stage. When the maximum document width to be handled is A3 size, the size signal A3 generated by a timing signal generating means (not shown) of the system is used as the gate signal.

Here, if the shading-corrected digital image signals are VR, VG, and VB, respectively, then these image signals VR
, VG, and VB are supplied to a color correction circuit 49 and converted into color signals for an image output device.

In this embodiment, the color of the image output device is Y (yellow).
9M (magenta), C (cyan), K (black)
is configured to be.

Each converted color signal contains color code data (2-bit data) indicating each color information and its density data.
(6-bit, 7-bit data).

Data for each of these color signals is stored in a color correction map in a ROM configuration.

The color-corrected image data is transferred to a color image processing step.

First, the color code data is supplied to the next-stage color ghost correction circuit 50, and is divided into 7×1 pixels in the main scanning direction (horizontal scanning direction) and 1×7 pixels in the sub-scanning direction (drum rotation direction).
Color ghosts are corrected at pixels.

This type of correction is performed because unnecessary color ghosts occur during color correction, especially around black characters. Depending on the configuration of the color correction map, red or blue color appears around the edges of black characters. Image quality is improved by removing color ghosts.

Color ghost processing applies only to color code data.

51 is an MTF correction circuit for correcting resolution.

Since resolution correction is contour correction, the target image data for processing is density data.

The color data selector circuit 52 receives a processing designation signal that instructs what kind of image processing is to be performed from the display/operation unit, and y, which indicates the color that must be currently captured and output.
M, cy, and sk multiplied signals are input, and a selection is made as to whether or not to send the resolution-corrected density data to the next multi-value conversion means 53 based on these and the above-mentioned input signals.

For example, when simply copying, only images with the same color as the Y, M, Cy, and Bk signals are output, and when performing color swapping for the entire document, for example, changing magenta to cyan and cyan to magenta. When attempting to perform color conversion, first, magenta image data is output when printing cyan, and cyan image data is output when printing magenta.

The image data (density data) output from the color data selector circuit 52 is multi-valued by the multi-value conversion means 53. In this example, the 6-bit density data is 0 to 3.
Exchanged into bit data (4-value data). Threshold data (6 bits) serving as a standard for 4-value conversion is set manually or automatically.

Therefore, the threshold value selection circuit 54 includes a manual threshold value determination means 56 for manual setting, and an automatic threshold value determination means 55 for automatic setting. The manual threshold value determining means 56 is configured to be able to independently determine a threshold value for each color, outputs an externally specified threshold value, and performs binarization using this threshold value.

The automatic threshold value determining means 55 is configured to use an RO in which a predetermined threshold value is stored.
Consists of M. Switching between manual and automatic is performed by an EE release signal. Normally, it is automatic setting mode l' (EE mode). Further, Y, M, Cy, and Bk signals indicating which color is to be selected in which sequence are also supplied.

The image data converted into four values by the multi-value conversion circuit 53 is output to the writing section B via the interface circuit 58. The details of the signal processing system of the reading section A described above can be found in Japanese Patent Application No. 16413/1983 filed by the applicant of the present application.
Color Image Processing System”. As the writing section B, a semiconductor laser device 59 shown in FIG. )62.

The semiconductor laser device 59 has a laser oscillator 63, and the laser beam emitted from the oscillator 63 is transmitted to the mirror 6.
5.66, the light enters a deflector 61 consisting of an octahedral rotating polygon mirror or the like. The laser beam is deflected by this polygon, and this is reflected by the f-theta lens 6 for imaging.
7 and onto the surface of the photoreceptor 62.

68 and 69 are cylindrical lenses for correcting inclination angles.

The polygon 61 rotated at a constant speed by the drive motor 60 causes the laser beam to scan the surface of the photoreceptor 62 at a constant speed in a predetermined direction a, and by such scanning, image exposure corresponding to the recording signal for color printing is performed. will be done.

Note that the f-θ lens 67 is used to adjust the beam diameter on the photoreceptor 62 to a predetermined diameter.

As the deflector 61, a galvanometer mirror 1 optical crystal deflector or the like can be used. When deflection scanning is started by the laser beam, the laser beam index sensor 6
4, beam scanning is detected and beam modulation using the first color recording signal (yellow signal) is started. The modulated beam is scanned by a charger 71 over a photosensitive drum 62 to which a negative charge is applied.

Here, an electrostatic latent image corresponding to the first color signal Y is formed on the photoreceptor 62 by the main scanning by the laser beam and the sub-scanning by the rotation of the photoreceptor 62.

This electrostatic latent image is subjected to contact reversal development by an ML developing device 72 containing a yellow developer (to be described later) to form a yellow toner image. The image is transferred onto the paper P by the action of the transfer pole 101.

Here, as the photoreceptor 62, an OPC photoreceptor for negative charging, which will be described later, is used, and as the developer, one containing a negatively charging yellow toner is used. Therefore, from the bias power supply
A bias voltage of C-500 to -600 V is applied to perform contact reversal development, and the spot exposed portion of the laser beam based on the Y recording signal is developed.

The yellow toner image transferred onto the transfer paper P as described above is separated by the action of the separation pole 102, and then transferred to the conveyor belt 10.
3, the image is carried into the fixing device 104 where it is heated and fixed. The transfer material P after fixing is controlled by a flipper 106 while being transported by a transport roller 105, and is further controlled by a transport roller 107.
and transported to the circulation transport route +08. In the circulation conveyance path 108, the conveyance roll 109.1
10 to the intermediate tray Ill, and is stopped and placed in a standby state. On the other hand, after the yellow toner image has been transferred, the photoreceptor 62 is cleaned by the cleaning blade 91 of the cleaning device 90, re-charged by the charger 71, and then transferred to the recording signal of the second color (magenta signal) obtained by the reading section A. A magenta toner image is formed through beam scanning based on this image and development by a second developing device 73 containing magenta developer. On the other hand, the transfer material P placed in a standby state on the intermediate tray lit is transferred to the intermediate tray 111 by a paper feed signal from the CPU.
From there, it is transported to the timing roll 89 by transport rolls 112, 113, and 114. Thereafter, the paper is transported to the transfer area in synchronization with image formation by the paper feeding method shown in FIG. The image is transferred and fixed.

In a similar process, writing based on the third recording signal (cyan signal), development by the third developing device 74 (cyan developing device), and writing based on the fourth recording signal (black signal),
By repeating development using the fourth developing device 75 (black developing device), a color image in which the toner images of each color are fixed and superimposed on the transfer paper P is obtained. The transfer paper P carrying this color image is controlled by the 7-resoper 106 and is ejected to a paper ejection tray via an ejection roll 115.

Here, the color image may be formed by operating one, two, or three of the four developing devices to form a monochromatic, two-color, or three-color image.

When making multiple copies from the same original, the transfer material P on which the yellow toner image has been formed is stacked and stopped on the intermediate tray lit, and when transferring the next magenta toner image,
The transfer material P on which the yellow toner image has been formed is sequentially taken out from the lower side of the intermediate tray 111 in accordance with the timing of image formation, and conveyed to transfer and transfer the magenta toner image.
The fixing process may be similarly repeated for cyan toner images and black toner images to efficiently form a large number of color images.

By the way, in this embodiment, 85 plain paper fed horizontally is used as the transfer material P. A paper feeding device shown in FIG. 7 is used to convey the transfer material P to the transfer area. That is, the transfer material P
is from the paper feed cassette 80 or intermediate tray Ill to the CPU
Paper feed roll 81, drive roll 8 based on the paper feed signal from
2a1 Sabaki roll 82b1, idler 82c1, and limiter 82d, or the transport rolls 112-114 transport the sheet to the timing roll 89 via the passage 86 or 87 at a transport speed of 150 mm/see. A paper leading edge detector (photointerrupter using infrared rays) 83 is disposed on the timing roll 39, and detects the leading edge of the conveyed transfer material P. Based on the signal, the paper feeding roll 81 and The rotation of the drive roll 82a of the double-feed prevention means stage 82 is stopped, and the transfer material P is brought into contact with the surface of the timing roll 89 and stopped. At this time, a loop is formed at the leading end of the transfer material P due to the delay in stopping the paper feed roll 81 and the drive roll 82a.

Next, under the control of the CPU, the driving roll 89b and driven roll 89a of the timing roll 89 are rotated at a low speed to achieve the above-mentioned rule.
60 m of transfer paper P whose tip asymmetry has been corrected by paper pressure
It is conveyed 9 mm at a conveyance speed of m/sec, and its tip reaches point D. The transfer material P is stopped at point D by detecting the leading edge of the transfer material P by the photosensor 84 and stopping the driving of the drive source based on the detection signal.

Next, the driving roll 89b is driven by the M number S from the scanning start point of the original scanning optical system (point A in Figure 1), and the driving roll 89b is driven for 200 m.
It is transported to the transfer area at m/sec (same speed as the circumferential speed of the photoreceptor 62). Note that the distance between the localization value point and the transfer position C is set to be the same as the circumference of the photoreceptor 62 from the writing start point B to the transfer position C, as in the case of FIG.

In addition, in the case of circulating conveyance of the transfer material P after toner image transfer and fixing, the distance of 200 mm to the conveyance roll 107 after transfer and fixation is
/sec, but after that it is transported to intermediate tray Ill by 3
The paper is transported at a high speed of QOmm/sec, and the transport from the intermediate tray ill is the same as when feeding from the paper feed cassette 80.
It is assumed to be 50 mm/sec.

Also, speed changes in each sheet feeding process are performed by gear clutch switching, and the timing is controlled by the CPU.

The effect of making the transfer material P move at a particularly low speed from the timing roll 89 to the fixed position point in this embodiment is that in an image forming apparatus that involves circulating conveyance of the transfer material P carrying a fixed toner image as in this embodiment. Especially big. In other words, even though the original flexibility of the paper is reduced due to fixation and the conveyance performance is deteriorated, the paper can be conveyed to a predetermined position and stopped without bending, skewing, slipping, etc. transfer to the next transfer area is achieved accurately. Furthermore, the resulting color image has less color shift and a high-resolution copy image can be obtained.

(Example 2) A color image was formed by feeding B4 transfer paper from a paper feed force Cera 1-80A (B4 portrait) instead of the paper feed force Cera 80 (B5 landscape) in Example 1. In this case, as in Example 1, the transfer material PA on the paper feed cut 80A is transported at 150 mm/sec via the transport path 86A by the paper supply roll 81A and the transport roll 82A (which also serves to prevent double feeding). It abutted against the timing roll 89 and was controlled by the paper leading edge detection signal to form a loop and stop. However, the subsequent low-speed conveyance from the timing roll 89 to the positioning value is 4
0mm/sec, and the conveyance from 1 position value is 202mm/sec, which is slightly faster than the circumferential speed of the photoconductor, which is 200mm/sec.
It was set as e. This is to cope with the fact that in the case of 84 paper, the paper is fed vertically and the size length is large, causing a conveyance delay and a delay in the timing of transfer.

The rest was the same as in Example 1, and a high-resolution four-color image could be produced without any color shift.

〔Effect of the invention〕

As is clear from the above description, according to the color image forming apparatus of the present invention, when a color image is formed by superimposing and transferring toner images of each color onto a transfer material, the transfer material is supplied to the transfer area. The timing of paper and conveyance is accurate and stable, resulting in effects such as obtaining high-resolution color images without color shift.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of a paper feeding device, FIG. 2 is a configuration explanatory diagram of a color image forming apparatus, FIG. 3 is a sectional view of the color image forming apparatus, FIG. 4 is a block diagram of a signal processing system of a reading section, FIG. 5 is a dichroic mirror spectral absorption characteristic diagram, FIG. 6 is a sectional view of a laser optical device, FIG. 7 is a sectional view of a paper feeding device, and FIG. 8 is an explanatory diagram of a conventional paper feeding device. 1.62... Image forming body (photoreceptor) 21... Original 22
,...Original table 23, 24...Light source 25.27A, 27B...Reflection mirror 30...
・Lens 34.35...Dichroic mirror 36.
37.38...CCD 40.41.42...A/D converter 49...
・Color correction circuit 53...Multi-value conversion means 58...Interface circuit 59...Semiconductor laser device 72.73.74.75...Developer 80.8OA...Paper feed cassette 81.81A... ...Paper feed roll 82...Double feeding prevention means 82a...Drive roll 83...Paper leading edge detector 84...Photo sensor 86.86A, 87...Transfer material path 89...Timing roll 89b...Drive roll +01...Transfer device 104...Fixer 106...Flipper

Claims (1)

[Claims] (1) A means for writing color-specific recording signals obtained by reading a color original onto an image forming member to form an electrostatic latent image, and developing the electrostatic latent image with a developer containing a corresponding color toner. a means for forming a color toner image; a means for conveying a transfer material for transferring the color toner image to a transfer area; and a means for transferring the color toner image onto the transfer material; In a color image forming apparatus that repeatedly forms a multicolor toner image on the transfer material, in the process of conveying the transfer material to the transfer area, the transfer material is conveyed at a low speed and its leading edge is moved to a predetermined position. means for conveying the transfer material aligned at the predetermined position to a transfer area to transfer and fix the color toner image formed on the image forming body; - A color image forming apparatus characterized by having a means for circulating and conveying a fixed transfer material.