JPH05204224A - Color image forming device - Google Patents

Abstract

PURPOSE:To obtain a small size, high printing speed color image forming device capable of expressing clear full-color with a projector such as an OHP. CONSTITUTION:In the color image forming device which carries out transfer and fixing after plural toner images are superposed on a photosensitive drum 2 by superimposing plural toner images successively on a photosensitive drum 2 rotates at every rotation of the drum 2, the speed of the process of superimposing a final toner image is made slower by 1/n of the speed in an ordinary process. The transfer of image data in the reduced processing-speed is thinned according to the reduced processing-speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly to an overhead projector (hereinafter referred to as OHP).
The present invention relates to a color image forming apparatus capable of forming a toner image on a transparent member (hereinafter referred to as OHP paper).

[0002]

2. Description of the Related Art Conventionally, when forming an image on OHP paper or thick paper, the toner of each color is sufficiently melted so that reflection at the boundary surface of the toner does not occur, thereby preventing color turbidity and producing a vivid color image. For this purpose, there is a device in which the linear velocity is decreased and the fixing nip time is increased. (JP-A-60-808
85, JP-A-60-86574).

In these prior arts, when an image is formed on a photoconductor, it is executed at a normal speed as in the case of normal paper, and the linear speed is reduced after the rear end of the OHP paper passes through the transfer section. Has been switched to.

[0004]

The above-mentioned conventional technique has an advantage that image defect unevenness can be eliminated without requiring switching of process conditions in the middle of an image, but has the following problems. is there.

(1) Switching the linear velocity during the exposure or developing process is not suitable because it tends to cause image distortion and unevenness. Therefore, the velocity switching is performed after the image transfer onto the recording paper is completed. There is. For this reason, a distance longer than the length of the OHP paper must be provided between the transfer unit and the fixing unit without fail, which leads to an increase in the size of the apparatus.

(2) Similarly, a paper transport mechanism is required between the transfer section and the fixing section, which complicates the apparatus and increases the cost.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is a compact full-color printer capable of expressing vivid full-color in an OHP projector, and a printing speed not much different from the conventional one. It is about realizing Copier.

[0008]

The above object is to form a color image in which toner images are sequentially superposed every time the image forming body is rotated and a plurality of toner images are superposed on the image forming body, and then transfer and fixing are carried out. In the apparatus, the process speed is set to 1 / us of the normal process speed from the step of superimposing the last toner image.
The color image forming apparatus is characterized in that the transfer of the image data at a slower process speed is performed at a slower speed of n (n is an integer).

[0009]

First, the outline of the present invention will be described.

On the image forming body (hereinafter referred to as a photosensitive drum), for example, Y (yellow), M (magenta), and C (cyan) are imagewise exposed and developed at a normal process speed in the order of K (black). The process speed is switched to 1 / n of the normal speed from the fourth rotation in which the image exposure of (1) is performed, and the transit time of the fixing unit is increased to improve the smoothness and the transparency of the toner.

When the process speed is changed, the image data for forming the electrostatic latent image is transferred by thinning out n-1 scans every n scans. As a result, it is not necessary to change the transfer speed of the image data or the writing speed of the writing unit, so that complicated process control is not necessary and the fixing performance can be improved without reducing the printing speed.

Further, there is no need to secure a distance between the fixing portion and the transfer portion as in the conventional case, which is a great advantage in developing a small-sized apparatus. Further, a complicated mechanism for feeding the recording paper in the horizontal direction such as belt conveyance can be eliminated, which is advantageous in cost.

In the process control, basically, the rotation speed of the developing sleeve of the developing device is switched in proportion to the process speed change, and the voltage applied to the transfer roller is changed to a condition that the transfer can be surely transferred to the OHP paper at a low speed. Only need be. When the fixing conditions are controlled at the same time, the temperature of the heat roller is switched to a temperature suitable for the fixing nip time to promote the deformation of the toner and prevent the occurrence of offset. The switching of the fixing temperature is preferably performed at the time of starting the operation in the OHP mode or before that. That is, since the fixing roller has a large heat capacity, it takes some time after the switching to reach the desired temperature range of the roller temperature. Therefore, it is most preferable to start printing after reaching the desired control temperature region after switching the roller temperature.

Further, by adopting a scorotron charger as the charger, the greed voltage can be changed and the surface potential of the photoconductor can be kept uniform and constant even when the line speed is changed. The stability can be improved by switching the roller voltage to an appropriate value.
Further, it is preferable that the process speed is not changed during image formation of a specific color (charging, image exposure, development) but during image formation.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a color image forming apparatus 1 according to the present invention.
It is a figure which shows the structure of an Example.

The present embodiment is a non-contact developing type full-color laser copier for four colors of Y, M, C and K.

In this embodiment, when forming an image on OHP paper or thick paper, the process speed and the fixing speed are switched under the control of the control unit 17. When selecting OHP or thick paper as the recording paper, the operator presses the OHP mode selection key 18 to switch from the normal mode to the OHP mode.

First, the basic structure (basic operation) of the color copier body will be described.

Before being exposed by the laser writing unit 1, a photosensitive drum (drum diameter 99.7
The entire surface of (mm) 2 is adjusted to a predetermined potential by the charger 13. The charger 13 is a scorotron charger, the grit voltage is -550 V, and the charging potential of the photoconductor is -600 V. This condition does not change regardless of the normal mode / OHP mode.
By adopting this scorotron charger, the surface potential of the photosensitive drum 2 and the electric charge of the toner can always be kept uniform and constant even if the process speed is switched as described later. Further, in this embodiment, in addition to the charger 13, the pre-charger 11
By providing the photosensitive drum 2 with a pre-charge, the potential decrease due to the memory carrier at the time of forming each color image is prevented, and the surface potential of the photosensitive drum 2 is further stabilized.

On the photosensitive drum 2 which has been primary charged,
An electrostatic latent image is sequentially formed by the laser writing unit 1, and the latent image is developed by each of the Y, M, C, and K developing units 3, 4, 5, and 5.
6 sequentially develops. In the case of full color, the photosensitive drum 2 rotates once for each color development, and a total of four rotations are performed, so that toner images of a plurality of colors are overlapped and formed on the photosensitive drum 2.

In this exposure and development process, the transfer roller
The 10 (belt 9) and the conductive brush (fur brush) 12 for cleaning are in a non-contact state, and when the photosensitive drum 2 enters the fifth rotation, the transfer roller 10 and the cleaning device 12 are pressed against each other. The reason why the transfer roller 10 and the like are pressed after the multicolor image is completely formed in this way is to prevent image fluctuation due to an increase in load during image formation.

The recording paper set in the paper feed tray 7 is fed through the second paper feed roller 8 and, when passing over the transfer roller 10, the multicolored images formed in duplicate are transferred at one time. It As will be described later, the transfer voltage is the normal paper mode and OHP.
Can be switched between paper mode.

The fixing process is performed using the pair of heat rollers 14a and 14b. A heater 31 is built in the heat roller 14a, and the fixing temperature is controlled by switching the operating time of the heater 31. This temperature control is performed by two kinds of uniform switching according to the recording paper mode and negative feedback control based on the environmental temperature measurement result by the temperature sensor 16.

After the fixing process, the recording paper is sent upward through the paper discharge roller 15 and discharged.

Next, the control unit 17 will be described.

The control unit 17 is a functional block (CPU
As a result of the operation according to the software program), a recording material detection unit 19, a fixing temperature control unit 20, a counter 22, and a process switching control unit.
21, a speed control means 23, a transfer / cleaning pressure contact control means 24, and a transfer roller voltage switching means 25. The switching control means 21 comprehensively controls the switching of the process speed and the switching of the transfer roller voltage.

As a drive system block, a three-phase stepping motor (photosensitive drum 2, second paper feeding roller 8,
29, which drives the heat rollers 14a, 14b, etc. of the fixing unit, and the drive system (pulse generator 26,
It has a pulse sequencer 27 and a drive circuit 28).

The pulse sequencer 27 receives the pulse train output from the pulse generator 26 and sends the control pulse of the stepping motor 29 to the drive circuit 28. This control pulse is also supplied to the counter 22, which receives the command from the switching control means 21 to start pulse counting and notifies the switching control means 21 of the count value. As a result, the rotation amount of the stepping motor 29 can be grasped, and as a result, the switching control means 21 accurately recognizes the phase of the photosensitive drum 2 and the position of the recording paper, and when the predetermined phase is reached, the speed control means 23. Etc. to send the switching command to switch the process conditions.

A constant voltage source 30 is provided for supplying a transfer voltage to the transfer roller 10, and a switch Sw1 for switching the transfer voltage is provided in the constant voltage source 30. When the image formation on the OHP paper is selected by the mode selection key 18, the recording material detection means 19 detects this and notifies the switching means 21 and the fixing temperature control means 20. In this case, the recording material detecting means 19 itself may be provided with a function of automatically detecting the material of the recording paper.

Upon being notified of the OHP mode, the switching control means 21 resets the counter 22 to the initial state and then starts counting the number of control pulses supplied to the stepping motor 29, and a predetermined count value. To become and,
The speed control means 23 is instructed to significantly reduce the process speed, and the transfer roller voltage switching means 25 is instructed to switch the transfer voltage to the low voltage side. That is, the switch Sw1 of the constant voltage source 30 is switched to the C terminal side by the instruction of the transfer roller voltage switching means 25. This allows
Transcription adapted to the reduction in process speed is carried out.

When the fixing temperature is also controlled, the switching control means 21 instructs the fixing temperature control means 20 to switch the fixing temperature to set the optimum fixing temperature condition. This switching is performed before the start of copying (printing) so that printing is started after the temperature of the heat roller pair 14a, 14b reaches a desired area.

Next, the operation of this embodiment will be described in detail with reference to the timing charts of FIGS.

The contents of the process speed and transfer condition switching in this embodiment are as follows.

Example of speed switching In the case of normal paper mode From the first rotation to the end of printing ... No change at 75 mm / sec.

In the case of mono-color in the OHP mode From the second rotation to the end of printing ... Switching to 15 mm / sec and thinning out the transfer of image data.

In the case of full color in the OHP mode From the first rotation to the end of the third rotation ... 75 mm / sec From the fourth rotation to the end of the printing ... Switching to 15 mm / sec and forward transfer of the image data.

Example of transfer condition switching Normal mode, mono-color: + 1.5KV Normal mode, full-color: + 2.0KV OHP mode, mono-color and full-color: + 1.0KV Fig. 2 (normal-mode full-color Case) When a copy key (not shown) is pressed and a start command is issued, the rotation of the photosensitive drum 2 is started at time t ₁ . By the instruction of the switching control means 21, the speed control means 23,
Control the process speed to 75 mm / sec. Further, since the switch Sw1 of the constant voltage source 30 is on the A terminal side (highest voltage, +2 KV) as shown in FIG. 1, the transfer roller voltage is not switched.

Each time the photosensitive drum 2 makes one rotation, Y,
Image exposure and development of M, C, and K are sequentially performed, and when four rotations are completed, a superposed multicolor image is formed on the photosensitive drum 2. The grid voltage of the scorotron charger 13 is −550.
V, and the surface potential of the photosensitive drum 2 is -600V.

The photosensitive drum 2 is further rotated, and at the time t ₂ of the fifth rotation, the transfer roller 10 is pressed against the photosensitive drum 2 under the control of the transfer / cleaning pressure contact control means 24, and after a short delay, at time t _3. A conductive fur brush (cleaning device) 12 is pressure-bonded to the.

The pre-charger 11 and the charger 13 are always on, and the fixing temperature is not switched because it is in the normal mode.

FIG. 3 (OHP mode in full color) When the mode selection key 18 is pressed to select the OHP mode, control including switching of process conditions is started in order to improve fixing performance. That is, first, at time t ₀ , the fixing temperature control means 20 starts fixing temperature control, and
The optimum fixing temperature for HP paper is set. Fixing roller pair
Since 14a and 14b have a considerable heat capacity, the desired temperature range cannot be reached immediately even if the fixing temperature is switched. Therefore, at time t ₁ when the temperature reaches the desired temperature range, a start command is issued and the printing operation is started.

The exposure and development process is as shown in FIG. 2 until the third color.
However, when the photosensitive drum 2 enters the fourth rotation for forming the final toner image, the process speed is switched from 75 mm / sec to 1/5 of 15 mm / sec at time t _3. And a significant speed reduction is performed. When this speed decreases, the rotation of the developing sleeve of the black developing device also decreases. This keeps the image density constant. Further, the rotation speed of the rotary polygon mirror, which is the deflection means of the laser light of the laser writing unit 1, is kept constant without being changed. The development of the third color is completed before this speed.

At time t ₄ , the switch Sw1 of the constant voltage source 30 is moved to the C terminal side (+1.0 K by the transfer roller voltage switching means 25).
Then, the transfer roller 10 is pressure-bonded at time t ₅ .

When the speed reduction is executed, the image data is transferred to the laser writing unit 1 only for one scanning every five scannings of the laser writing unit 1, and the white data is transferred for the remaining four scannings. To do. That is, the image data when the process speed is changed to 1 / n is thinned out every n scans of the laser writing unit 1 and transferred to the laser writing unit 1. By doing so, the writing density of image exposure can be kept constant regardless of the process speed without changing the rotational speed of the rotary polygon mirror of the laser writing unit 1.

For example, in the case of a color image forming apparatus provided with an image reading device having a color CCD or the like, the scanning speed of the image reading device is switched to a low speed of ⅕ from the time t ₃ to read the image. Done. Therefore,
Read scanning is performed at a density of 5 times higher. On the other hand, the operating speed of the laser writing unit 1 does not change and is kept constant. Therefore, the image data obtained by the image reading apparatus is transferred every n scans by discarding n-1 image data or converting the image data into white data. As a result, similarly to the above, the writing density of image exposure can be kept constant regardless of the process speed without changing the rotational speed of the rotary polygon mirror of the laser writing unit 1.

The sequence control in this case is as shown in FIG.

A color CCD 151, which is a kind of color scanner of the image reading apparatus, is used to set the horizontal direction B of the document.
Color information of (blue), G (green), and R (red) is read, and an analog video signal is output.

This signal is converted to A by the A / D conversion circuit 152.
After the D / D conversion, a shading correction is performed by the data processing circuit 153 to remove color information and distortion caused by the optical system, and Y (yellow), M (magenta), C
Extraction of black component (UCR) from each data of Y, M, and C after complementary color conversion to (cyan) and gradation correction
Is performed and separated into a chromatic color component and an achromatic color component.

Here, Y, M, and C which are chromatic color components are color-corrected and gradation-corrected together with the black component (K), and then input to the selector A154. The toner is sequentially sent to the selector B155 by the selector A154 in the order of toner image formation. In the sector B155, the mode selection key 18
According to the mode selected by, in the normal mode, it is sent to the laser writing unit 1 as it is. Also OHP
In the mode, the image data for n-1 scans of the image data is thinned from the time when the process speed is changed to 1 / n, and n
The data is sequentially sent to the laser writing unit 1 for each scan for one scan. The white data input from the white data generation circuit 156 may be sent out in place of the n-1 minute image data subtracted from the time. FIG. 4 (in the case of mono-color red in the normal mode) Although almost the same as the case of FIG. 2, exposure and development are performed for Y color and M color. Further, at time t ₇ , the constant voltage source 30
The switch Sw1 is switched to the terminal B side (+1.5 KV), and the transfer roller voltage is switched. At that time,
At time t ₈ , the transfer roller 10 is pressed. The switching control of the process speed and the fixing temperature is not performed.

FIG. 5 (OHP mode for mono-color red) Although almost the same as the case of FIG. 3, the developing and exposing steps are performed for Y color and M color. Because it is in OHP mode,
At time t ₉ when the image exposure of the second color M is started, the process speed is switched to a low speed (for example, 1/5 speed), and at time t ₁₀ , the switch Sw1 of the constant voltage source 30 is switched to the C terminal. It is switched to the side (+1.0 KV) and the transfer roller voltage is controlled. At time t ₁₁ , the transfer roller 10 is pressure-bonded.
As the process speed decreases, the rotation of the developing sleeve of the M developing device also decreases. As for the image data at this time, as in the case of FIG. 3, the image data is transferred only for one scan every five scans of the laser writing unit 1.

Although the embodiment of the present invention has been described above, the control of the fixing roller temperature is not always necessary for switching the fixing condition, that is, the toner is smoothed only by changing the fixing nip time by switching the process speed. The degree and transparency can be improved.

[0053]

As described above, in the OHP mode, the color image forming apparatus of the present invention has a process speed of 1 times the normal speed from the step of superimposing the last toner image.
Since the image data is decimated to n / n and transferred by thinning out n-1 scans, the overall printing speed is much faster than the conventional device while keeping the device small and slightly smaller than the normal printing. It was possible to realize a color image forming apparatus that can be slow.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a color image forming apparatus of the present invention.

FIG. 2 is a timing chart showing an operation of the apparatus of FIG. 1 in a normal mode (full color).

3 is a timing chart showing an operation of the apparatus of FIG. 1 in an OHP mode (full color).

4 is a normal mode of the apparatus of FIG. 1 (mono color red)
It is a timing chart which shows operation at the time.

5 is a timing chart showing an operation of the apparatus of FIG. 1 in an OHP mode (monocolor red).

FIG. 6 is a diagram showing sequence control of image formation according to the present invention.

[Explanation of symbols]

 1 Laser Writing Unit 2 Image Forming Body (Photosensitive Drum) 3, 4, 5, 6 Developer 8 Second Paper Feed Roller 10 Transfer Roller 12 Conductive Brush (Cleaning Device) 13 Charger (Scorotron Charger) 14a, 14b Heat roller pair 16 Temperature sensor 17 Control unit 18 Mode selection key 19 Recording material detection means 20 Fixing temperature control means 21 Switching control means 22 Counter 23 Speed control means 24 Transfer / cleaning pressure control means 25 Transfer roller voltage switching means 26 Pulse generator 27 Pulse sequencer 28 Drive circuit 29 Stepping motor 30 Constant voltage source Sw1 Transfer voltage selector switch

Claims (3)

[Claims] 1. A color image forming apparatus that sequentially superimposes toner images for each rotation of an image forming body and superimposes a plurality of toner images on the image forming body, and then transfers and fixes the last toner image. A color image forming apparatus characterized by slowing the process speed of the superposing step. 2. The slowing process speed of claim 1 is 1 / n of the normal process speed.
Color image forming apparatus. However, n shows an integer here. 3. The color image forming apparatus according to claim 1, wherein the transfer of the image data at the slowed process speed according to claim 1 is performed by thinning according to the slowed process speed.