JP2001027832A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a waiting time in the case of forming a color image and to smoothly perform image forming operation without delay by switching the mode of a carrying belt before finishing forming a monochrome image in the case of forming the color image succeedingly to forming the monochrome image. SOLUTION: In the case of forming the color image succeedingly after consecutively forming the black monochrome image, whether or not forming the monochrome image is performed to a final sheet is judged. When forming the monochrome image is performed to the final sheet, an instruction for switching to the color mode is outputted from a controller 17 in order to start the printing of the color image without requiring the waiting time. At this time, forming the monochrome image is not finished yet but the carrying belt 9 makes respective image forming stations 1C, 1M, 1Y and 1Bk come in contact with a photoreceptive drum 2. At the time of performing switching operation, forming the monochrome image is still performed but a transfer condition in the station 1Bk is maintained still in a proper state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a color image forming apparatus applied to a tandem process full-color copying machine or printer which can also be used for monochrome printing. More specifically, the present invention relates to a color image forming apparatus that reduces a time loss associated with switching when a monochrome image and a color image are continuously formed.

[0002]

2. Description of the Related Art In a tandem process full-color image forming apparatus for both monochrome use, when forming a monochrome image, it is advisable to retreat the transport belt from an image forming station other than one used. This is to extend the life of an image carrier such as a photosensitive drum and a transport belt that transports a sheet in an image forming station for each color.

[0003] Therefore, for example, a technique as disclosed in Japanese Patent Application Laid-Open No. 9-292758 has been proposed. This technology has a color mode in which an image is formed by bringing a conveyor belt into contact with each photosensitive drum, and a monochrome mode in which an image is formed by contacting only one photosensitive member using a conveyor belt. The mode is switched according to the image. That is, the color mode is used when forming a color image, and the monochrome mode is used when forming a monochrome image. When a color image is formed after the formation of a monochrome image, the mode is switched after the formation of the monochrome image is completed.

[0004]

However, the above-described conventional color image forming apparatus has a problem that a considerable waiting time occurs when a color image is formed after a monochrome image is formed. This will be described with reference to FIG. FIG. 4 shows timings when a color image is formed successively after four monochrome images are formed. In FIG. 4, the paper feed interval between the sheets for monochrome images is the sum of the time corresponding to the paper length and the time corresponding to the space between the papers. Here, when a sheet for a new monochrome image is fed, it is read from the figure that the leading end of the immediately preceding sheet has reached the third Y (yellow) image forming station.

However, the feeding interval between the last sheet for monochrome images and the first sheet for color images is much longer than the feeding interval between sheets for monochrome images. The reason is that the time T1 required from the time when the final sheet for monochrome image is fed to the time when the sheet passes through the Bk (black) image forming station at the last stage, and the time T2 required for the mechanical switching operation from the monochrome mode to the color mode. Is required. During this time, the color image forming operation cannot be started. Such a loss of time is a major problem for a tandem process full-color image forming apparatus that aims to increase the speed.

The present invention has been made to solve the above-mentioned problems of the conventional color image forming apparatus. That is, an object of the present invention is to provide a color image forming apparatus capable of reducing a waiting time when a color image is formed after a monochrome image is formed continuously and smoothly performing an image forming operation without delay. Is to do.

[0007]

SUMMARY OF THE INVENTION A color image forming apparatus according to the present invention, which has been made to solve this problem, comprises a plurality of color image forming stations arranged in parallel, and a plurality of color image forming stations arranged opposite to each image forming station. Transport belt that moves and passes through them, and a transport belt that switches between a monochrome mode in which the transport belt contacts only one of the image forming stations and a color mode in which the transport belt contacts all of the image forming stations. The switching means and the switching of the monochrome mode and the color mode are instructed to the conveyance belt switching means, and when the color image formation is performed after the monochrome image formation, the conveyance belt mode switching is performed before the end of the monochrome image formation. And a mode selecting means for setting the mode.

Further, the case where the conveyor belt faces the image forming station is not limited to the case where both are in contact with each other as in the case of the color mode or the single case of the monochrome mode. This also includes the case where both are separated to some extent, such as the case other than the one in the monochrome mode. Here, the term “contact” is not limited to the case of strict contact, but also includes the case of close proximity.

In this color image forming apparatus, when a color image is formed, the color mode is selected by the mode selecting means, and the transport belt is brought into contact with all the image forming stations by the transport belt switching means.
On the other hand, when forming a monochrome image, the monochrome mode is selected by the mode selection means, and the conveyance belt is brought into contact with only one image forming station by the conveyance belt switching means.

When a color image is to be formed following the formation of a monochrome image, switching from the monochrome mode to the color mode is instructed by the mode selection means before the monochrome image forming operation is completed. Therefore, the formation of the color image can be started earlier than in the case where the mode is switched after the formation of the monochrome image is completed. Therefore, the waiting time from the end of the formation of the monochrome image to the start of the formation of the color image can be reduced. Therefore, the total image forming operation can be performed smoothly without delay.

The present invention is particularly significant when applied to a color image forming apparatus in which the image forming station used in the monochrome mode is the last one. In this case, the mode selection means switches the mode of the transport belt when performing color image formation subsequent to monochrome image formation more than the end of monochrome image formation (where one point of the transport belt is the first point). It is desirable to complete the process at least a time given by (time required for traveling from the image forming station to the last image forming station)-(time corresponding to sheet interval).

In this case, after the last sheet for the monochrome image is fed, the first sheet for the color image is fed at a sheet feeding interval equal to the sheet feeding interval between the sheets for the monochrome image. it can. For this reason,
When performing color image formation subsequent to monochrome image formation, the user is not made aware of the waiting time due to mode switching.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a color image forming apparatus according to the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, the electrophotographic color printer according to the present embodiment has four image forming stations 1 arranged in parallel in a printer main body, that is, a first color image forming station (cyan) 1 (C). ), A second color image forming station (magenta) 1 (M), a third color image forming station (yellow) 1 (Y), and a final color image forming station (black) 1 (Bk). .

Each of the image forming stations 1 (C), 1
Each of (M), 1 (Y), and 1 (Bk) is provided with a photosensitive drum 2 as an image carrier. Around the periphery of each photoconductor drum 2, a charger 3 for uniformly charging the photoconductor drum 2 is scanned, and an original is scanned and the image is read.
An optical system 4 for exposing the image, a developing device 5 for developing the electrostatic latent image formed by the exposure, and a transfer charger 6 for transferring the developed visible image to the print sheet 11 are provided. However, in the black image forming station 1 (Bk), instead of the transfer charger 6, a transfer roller 7 also serving as a drive roller of a transport belt 9 for transporting the print sheet 11 is provided. Further, the transport belt 9 is stretched between a transfer roller 7 as a driving roller and a driven roller 8, and is driven clockwise (in the direction of the arrow in the drawing) by the rotation of the driving roller 7. Note that a voltage having a polarity opposite to that of the toner of the developing device 5 is applied to the transfer charger 6 and the transfer roller 7 for transfer.

A cam 10 is located between the driven roller 8 and the image forming station 1 (C) and inside the conveyor belt 9. The cam 10 is in contact with the inner peripheral surface of the conveyor belt 9 at two locations on the outer periphery and substantially in the diameter direction. When the cam 10 is at the position shown by the solid line in FIG.
(C), 1 (M), 1 (Y), and 1 (Bk) are in contact with the transfer positions of the photosensitive drum 2. In each image forming station, appropriate transfer conditions are maintained. This state is the color mode.

On the other hand, when the cam 10 is at the position shown by the broken line, the transport belt 9 is
(C), 1 (M), and 1 (Y), separated from the transfer position of the photosensitive drum 2 and contacted only with the photosensitive drum 2 of the image forming station 1 (Bk). In the image forming station 1 (Bk), appropriate transfer conditions are maintained. This state is the monochrome mode. That is, the cam 10 is a means for switching the mode of the transport belt 9 and is controlled by the controller 17.

Further, a paper feed cassette 12 containing the print sheets 11, a paper feed unit 13 for taking out the print sheets 11 one by one from the paper feed cassette 12 and sending them out onto a transport belt 9, and a print sheet separated from the transport belt 9 A fixing device 14 for fixing the visible image on the fixing device 11 and a discharge tray 15 for receiving the print sheet 11 passing through the fixing device 14 are provided.

In the color printer constructed as described above, when the cam 10 is in the color mode shown by the solid line, the print sheet 11 sent from the paper supply unit 13 is attracted onto the transport belt 9 and transported. , Each image forming station 1 (C), 1 (M), 1 (Y), 1 (B
The images formed on the respective photosensitive drums 2 are sequentially transferred by k). Thereafter, the print sheet 11 is sent to the fixing device 14 where the transferred image is fixed, and is discharged onto the paper discharge tray 15. That is, a color image is formed.

On the other hand, when the cam 10 is rotated to be in the monochrome mode shown by the dashed line, each image is printed on the printing sheet 11 which is sent from the sheet feeding unit 13 and is adsorbed on the conveying belt 9 and conveyed. Forming station 1
(C), 1 (M), and 1 (Y), the image is not transferred, and the image formed on the photosensitive drum 2 is transferred only by the image forming station 1 (Bk). Thereafter, the print sheet 11 is sent to the fixing device 14 where the transferred image is fixed, and is discharged onto the paper discharge tray 15. That is, a black monochrome image is formed. Note that a monochrome image can be formed even when the cam 10 is in the color mode. For example, when a color image is formed, a single monochrome image is continuously formed, and a color image is subsequently formed, it is better to form a monochrome image while the cam 10 is in the color mode.

Subsequently, in the color printer of FIG.
First, a description will be given of control in a case where several black monochrome images are successively formed and subsequently a color image is formed. FIG. 2 shows the flowchart. First # 1
Then, the mode of the transport belt 9 is switched by the cam 10. In this case, the mode is switched to the monochrome mode. That is, the transport belt 9 shown by a broken line in FIG. 1 is separated from the photosensitive drums 2 of the image forming stations 1 (C), 1 (M), and 1 (Y). And # 2
To form a monochrome image. At this time, the number of printed monochrome images is counted. Next, in # 3, it is determined whether the formation of the monochrome image has reached the final sheet. This determination is made based on the number of prints counted in # 2. If the last sheet has not yet been reached (# 3: No), the process returns to # 2 and printing of a monochrome image is continued. If the last sheet is reached (# 3: Yes),
Go to # 4.

In step # 4, an instruction to switch to the color mode is issued from the controller 17. At this point, the formation of the monochrome image has not been completed yet, but printing of the subsequent color image is started without waiting time. As a result, the conveyor belt 9, shown by a solid line in FIG. 1, is moved to each of the image forming stations 1 (C), 1 (M), 1 (Y), 1 (B
k) is in contact with all the photosensitive drums 2.
At the time of this switching operation, although a monochrome image is still formed, no problem occurs because the transfer conditions in the image forming station 1 (Bk) are maintained at an appropriate level. In step # 5, printing is performed on the final print sheet 11 for monochrome images. In the following # 6, it is determined whether or not the final print sheet 11 for a monochrome image has passed the first color image forming station 1 (C). If it has not passed yet (# 6: No), the determination is repeated. If it has passed (# 6: Yes), proceed to # 7,
Printing of the color image is started.

The switching timing will be further described with reference to FIG. FIG. 3 shows timings of various operations when a monochrome image is continuously formed on four print sheets and a color image is continuously formed. Note that each print sheet is of the same size. In FIG. 3, t1, t2, t3, and t4 are timings for feeding four print sheets for forming a monochrome image. As can be understood from these figures, these paper feed intervals are the sum of the length of the print sheet and the sheet interval. Also, when a new print sheet is fed,
It can be seen that the leading end of the previous print sheet has reached around the third color image forming station 1 (Y). At this time, the rear end of the previous sheet passes through the first color image forming station 1 (C).

When the fourth (final) print sheet for a monochrome image is fed at timing t4, the determination of # 3 in FIG. 2 becomes Yes. For this reason, a mode switching instruction is issued in # 4. Based on this instruction, mode switching of the cam 10 is started at timing t5 in FIG. Then, the rear end of the fourth print sheet for the monochrome image is the first print sheet.
After passing through the color image forming station 1 (C), FIG.
The judgment of # 6 in the inside is Yes. At this point, the cam 10
The switching of the transport belt 9 to the color mode has been completed. Therefore, the leading print sheet for the color image is fed at timing t6 in FIG. 3 (# 7 in FIG. 2).

The interval between the feed timing t4 of the last print sheet for a monochrome image and the feed timing t6 of the first print sheet for a color image is the feed interval of each print sheet for a monochrome image. (T1,
(t2, t3, t4 intervals, hereinafter referred to as normal intervals). Therefore, the user hardly notices the extra waiting time accompanying the mode switching.

In order to make this possible, the cam 10 and the conveyor belt 9 must be in the color mode when the first print sheet for a color image is to be fed at regular intervals. This timing is, assuming that the sheet interval is 0, the end timing of monochrome image formation (the trailing end of the final print sheet for monochrome image is the image forming station 1 (B
k), the trailing edge of the sheet is the first
This timing is a timing retroactive to the time required to travel from the color image forming station 1 (C) to the final color image forming station 1 (Bk).

However, in practice, a certain amount of sheet interval is inevitable for the reliability of the sheet transport system.
That can be delayed. Therefore, when the mode is switched from the end timing of the monochrome image formation, (one point of the conveyor belt 9 is changed from the first color image forming station 1 (C) to the final color image forming station 1 (Bk)
(Time required to travel to)-(time corresponding to the sheet interval) must be completed by the timing of going back. Each criterion in FIG. 2 and each timing in FIG. 3 are determined so as to satisfy these.

As described in detail above, in the electrophotographic color printer according to the present embodiment, when a monochrome image is formed continuously and then a color image is formed, the final color image for the monochrome image is formed. When a print sheet is fed, switching from the monochrome mode to the color mode is started without waiting for the end of forming a monochrome image on the print sheet. When the first print sheet for the color image is to be fed at regular intervals, the mode switching is completed. This realizes a color image forming apparatus that can smoothly continue image formation without making the user aware of an extra wait time accompanying the mode switching.

The present embodiment is merely an example, and does not limit the present invention. Therefore, naturally, the present invention can be variously modified and modified without departing from the gist thereof.

[0029]

As is apparent from the above description, according to the present invention, the waiting time for forming a color image after continuously forming a monochrome image is reduced, and the image forming operation is smoothly performed without delay. And a color image forming apparatus that can perform the image processing.

[Brief description of the drawings]

FIG. 1 is a sectional view of a color printer according to an embodiment.

FIG. 2 is a flowchart illustrating switching of a position of a conveyor belt.

FIG. 3 is a timing chart illustrating switching of the position of a conveyor belt.

FIG. 4 is a timing chart illustrating the conventional switching of the position of a conveyor belt.

[Explanation of symbols]

1C, 1M, 1Y, 1Bk Image forming station 9 Conveyor belt 10 Cam (conveyor belt switching means) 17 Controller (mode selecting means)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akihiro Hayashi 2-3-13 Azuchicho, Chuo-ku, Osaka-shi Osaka International Building Minolta Co., Ltd. (72) Inventor Katsuaki Goto 2-3-3 Azuchicho, Chuo-ku, Osaka-shi No. 13 Osaka International Building Minolta Co., Ltd. F term (reference) 2C061 AQ06 AR01 AS02 CF03 CF05 CK08 HH08 HJ03 HK11 HN06 2H027 EC09 ED17 ED24 EE05 FA28 FA30 FA35 FA37 FB05 FB07 2H030 AB02 AD05 AD08 AD17 BB02 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB23 BB02

Claims (2)

[Claims] 1. An image forming station of a plurality of colors arranged in parallel, a transport belt arranged to face each of the image forming stations and moving through the same, and the transport belt is attached to the image forming station. Conveyor belt switching means for switching between a monochrome mode for contacting only one of the forming stations and a color mode for contacting all of the image forming stations; and a conveyor belt for switching between the monochrome mode and the color mode. A color selecting means for instructing the switching means and, when performing color image formation following monochrome image formation, performing mode switching of the conveyor belt before completion of monochrome image formation. Forming equipment. 2. The color image forming apparatus according to claim 1, wherein said image forming means used in said monochrome mode is a last stage, and said mode selecting means performs color image formation subsequent to monochrome image formation. The mode switching of the transport belt in the case of performing is performed more than the end of monochrome image formation (the time required for one point of the transport belt to travel from the first image forming station to the last image forming station). A color image forming apparatus, wherein the image forming apparatus is completed before the time given by (time corresponding to the sheet interval).