JP2924906B2 - Color image forming method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming method, and in particular, multiple transfer of each color toner image formed on the surface of a photoreceptor onto a recording medium, and onto the recording medium after the transfer. The present invention relates to a color image forming method for fixing a color image.

(Prior Art) In a color image forming method executed in a color copying machine or the like, each step of charging, exposure and development is performed on the surface of a photoconductor conveyed at a predetermined linear speed, and these processes are performed. Through each process, each color toner image is formed on the photoreceptor, and the recording medium is conveyed to a transfer unit at a predetermined linear speed by a conveyance system including a paper feed roller, and the photoreceptor is agitated in this transfer unit. The formed toner images of each color are multiplex-transferred onto a recording medium. Further, the recording medium after the transfer is transferred to a fixing step while being conveyed at a predetermined linear speed, whereby a final color image is formed.

In recent years, in such a color image forming method, various methods for improving the transparency and surface gloss of an image have been proposed. For example, in Japanese Patent Application Laid-Open No. 60-211483, a high image quality is obtained by lowering the conveying speed of the recording medium, that is, the rotation speed of the fixing roller in the fixing step after the transfer of the toner image, from that during normal image formation. It has been proposed. Such a reduction in the rotation speed of the fixing roller is also performed in color copying for monochrome copying or copying on an OHP transparent sheet for color copying.

However, when the fixing speed is reduced as described above,
The transport speed of the recording medium differs between the contact portion and the fixing portion of the photoconductor, and the recording medium may be moved at different transport speeds, causing the recording medium to sag or rub the toner image. For this reason, in the conventional apparatus, the position at which the recording medium is separated from the transfer unit and the arrangement position of the fixing unit are sufficiently separated from each other, and the length of the recording medium to be used is restricted to be short. I have. Therefore, the conventional apparatus for lowering the fixing speed is increased in size or limited in paper size.

(Object) Accordingly, the present invention provides a color image forming method capable of reducing the size of an image forming apparatus that performs a fixing operation at a low speed and eliminating the size limitation of a recording medium used. The purpose is to:

(Structure) In order to achieve the above object, the present invention forms a toner image for each color with a plurality of color toners on the surface of a photoconductor conveyed at a predetermined linear velocity, and rotates these toner images by a transfer drum. The transfer is performed for each color on a recording medium that is held and conveyed at a predetermined linear velocity, and the recording medium after the transfer is fixed in the fixing step while being conveyed at a linear velocity lower than the linear velocity in the transfer step of the transfer drum. In the color image forming method adapted to execute the operation, the length from the transfer position where the toner image is transferred to the recording medium to the fixing position where the fixing operation of the toner image onto the recording medium is performed is determined by the recording medium. , The entire recording medium is rotated and held on the transfer drum until the transfer operation of the final toner image is completed, and all the transfer operations of the final toner image to the recording medium are completed. Later, until the fixing step is started,
The transport speed of the recording medium by the transfer drum is reduced so as to be synchronized with the transport speed of the recording medium in the fixing step.

Further, the present invention forms a toner image for each color with a plurality of color toners on the surface of the photoconductor conveyed at a predetermined linear speed,
These toner images are transferred for each color onto a recording medium held rotatably by a transfer drum and conveyed at a predetermined linear velocity, and the recording medium after the transfer is transferred at a linear velocity lower than the linear velocity in the transfer step of the transfer drum. In a color image forming method in which a fixing operation is performed in a fixing step while being conveyed at a speed, a transfer position at which a toner image is transferred to a recording medium is moved to a fixing position at which a toner image is fixed to a recording medium. A high image quality fixing mode is provided in which the length of the recording medium is shorter than the length of the recording medium, and the conveying speed of the recording medium in the fixing step is lower than that of the normal mode for performing normal image formation. In this high image quality fixing mode, the entire recording medium is rotated and held on the transfer drum until the transfer operation of the final toner image is completed, and the final transfer to the recording medium is performed. After all the image transfer operations are completed and before the fixing step is started, the conveying speed of the recording medium by the transfer drum is synchronized with the conveying speed of the recording medium in the fixing step. In the normal mode, the transfer speed of the recording medium by the transfer drum is constant and equal to the transfer speed of the recording medium in the fixing step, and the fixing step is started at the time of the final toner image transfer operation. Features.

Further, according to the present invention, in the color image forming method according to claim 1 or 2, the length of the recording medium is shorter than the circumferential length of the transfer drum.

In the color image forming method having such a configuration, the recording medium is moved at the same operation speed in any part. As a result, the recording medium is not moved at a different transport speed as in the related art, so that the recording medium is prevented from becoming slack or rubbing the toner image.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, an outline of a laser full-color copying machine shown in FIGS. 6 and 7 will be described as an example of a color image forming apparatus to which the present invention is applied.

The light emitted from the laser writing unit 1 is modulated by image information for each color sent from an image reader (not shown), and is exposed to the surface of the photosensitive drum 3 which is initially charged by the charger 2. You. As a result, an electrostatic latent image for each color is formed on the surface of the photosensitive drum 3, and the electrostatic latent image is
The image is developed by 5, 6, and 7, and a visible image of each color toner is obtained. The respective color developing devices 4, 5, 6, 7 are a yellow developing device, a magenta developing device, a cyan developing device, and a black developing device, respectively. The toner images obtained by these color developing devices are multiplex-transferred by a corona discharge action of a transfer charger 10 to a recording paper as a recording medium wound around a transfer drum 8 and held by a clamper 9.
The recording paper is sent out toward a transfer section of the transfer drum 8 by a paper feed system including a paper feed cassette 11, a call roller 12, a paper feed roller 13, and the like. The recording paper on which multiple transfer of the visible image of each color toner has been performed is separated from the transfer drum 8 by the separation charger 14 and the separation claw 15 and then sent to the fixing device 17 by the transport belt 16. In the fixing device 17, a fixing operation of the toner image on the recording paper is performed by a heating / pressing process using a heating roller 17a and a pressing roller 17b. The recording paper on which the fixing has been performed is sent out onto a discharge tray 19 by a discharge roller 18. In the above-described apparatus, four color toners of yellow, magenta, cyan, and black are used.
In order to obtain an image, four photosensitive drums 3 and four transfer drums 8 are used.
It is designed to be rotated.

The photoreceptor drum 3 in the above-described apparatus is rotationally driven by a DC motor (not shown), and the DC motor has a drive shaft of a transfer drum 8 via a helical gear train having a reduction ratio set to 1. Are linked. Thus, the photosensitive drum 3 and the transfer drum 8 are driven to rotate in synchronization with each other, and the photosensitive drum 3 and the transfer drum 8 are rotated at a relative speed of 0 in the transfer section. . Further, the developing operation by each color developing device 4, 5, 6, 7 is performed at each position of DY, DM, DC, DBK shown in FIG.
The transfer drum 8 is provided with a release mechanism for retracting the transfer drum 8 to a position indicated by a broken line in the figure. When the release mechanism is operated, the clamp 9 makes the photosensitive drum 3 contact with the side of the photosensitive drum 3. That is to be avoided. In FIG. 8, the symbol T indicates the transfer position,
Symbol L indicates an exposure position, and symbol DP indicates a separation position.

In the laser writing unit 1, as shown in FIG. 9, after the modulated light beam emitted from the laser generator 21 is polarized at an equal angular velocity by the optical deflector 22, f
A scanning surface on the photosensitive drum 3 is irradiated with a predetermined spot diameter through an imaging lens 23 having a θ characteristic, and is scanned at a constant speed. Some light beams are mirrored
The light is reflected at 24 and guided to the synchronization detecting device 25, from which a line signal indicating the end of the image is emitted. The photosensitive drum 3 is rotated by one pixel pitch in a cycle of scanning the optical scanning beam by one line. Therefore, the surface portion of the photosensitive drum 3 is raster-scanned by the optical scanning beam without any gap.

As shown in FIG. 4, by each control means 32, 33, 34, 35 placed under the control of the main CPU 31 of the above device,
A driving motor 36 for driving the photosensitive drum 3 to rotate, a driving motor 37 for driving the heating roller 17a and the pressing roller 17b of the fixing device 17 to rotate, a driving system 38 for the separation charger 14, and a clamper for holding the recording paper on the transfer drum 8 9
Are operated at predetermined timings. Further, a mode instruction signal is sent from the operation panel 41 to the main CPU 31 via the operation panel display control means 42. Also, the photosensitive drum 3 has
A rotary encoder is provided, and an encoder pulse generated from the rotary encoder is used as a basic clock for sequence timing.

Next, an embodiment of the image forming method of the present invention using the above-described color copying machine will be described below.

FIG. 5 is a timing chart illustrating a normal image forming process. As shown in the figure, when the print button is pressed at time t0, a print signal is generated, whereby the drive motor for driving the photosensitive drum 3 and the transfer drum 8 starts operating, and at the time t8
, The call roller 12 is turned on and the sheet feeding operation is started. At the time t0, since the position of the transfer drum 8 is not clear, the photosensitive drum 3 and the transfer drum 8
Is driven to rotate for a fixed time, and at time t1, a drum HP detection signal is issued by the position sensor.
The drum HP detection signal gives a timing at which the clamper 9 reaches the transfer point. The rising of the drum HP detection signal activates the clamper release mechanism, and the falling of the drum HP detection signal causes the photosensitive drum to fall. The transfer drum 8 comes into contact with the drum 3 again. The fall of the drum HP detection signal gives a timing at which the leading edge of the image reaches the transfer point. Such a drum HP detection signal is used as a reference in the following sequence.

After confirming that the registration of the recording paper has been detected at time t9, the paper feed roller 13 is turned on at time t10 to perform the paper feed operation. Then, at time t12, the clamper 9 is turned on, the leading end of the recording paper is held on the transfer drum 8 by the clamper 9, and the recording paper is wound around the transfer drum 8.

Next, assuming that the linear velocity of the photosensitive drum 3 is v, the formation of the electrostatic latent image corresponding to each color image is started by the generation of the LGATE signal at times t26, t28, t30, and t32. Each of the times t26, t28, t30, and t32 is the photosensitive drum 3
Distance between the exposure position L, the black development position DBK, and the transfer position T (see FIG. 8) on the outer circumference of the circle For Is set to satisfy.

The electrostatic latent images corresponding to the respective colors formed in this manner are developed by causing the developer to stand on the respective developing sleeves in the respective color developing devices 4, 5, 6, and 7. When the developing device is in the off state, the position of the scissoring magnet provided in the developing sleeve is changed, so that the scissoring state is achieved. The four color developing devices 4, 5, 6, and 7 are sequentially operated without being simultaneously turned on, and one color development is executed each time the photosensitive drum 3 rotates once. Each time t16, t18, t20, t22 giving the timing of the development start, Are set so as to satisfy respectively.

FIG. 5 shows a case where the development of four colors is performed, but a single color output or a two-color output can also be performed. In that case, the transfer rotation speeds corresponding to those modes are set, the developing color code for selecting the developing device to be used is set, and the sequence control is performed based on the drum HP detection signal counter. .

The transfer charger 10 is turned on from time t24 to time t25, and the transfer process is always executed when each color toner image reaches the transfer point T.

The photosensitive drum 3 is rotated 5 times from the beginning (time t5 to
At t6), the four-color latent image writing step, the developing step, and the transfer step are completed. Immediately after the transfer step of the yellow toner image, which is the final toner image, the process is shifted to the recording paper separating step. Go. That is, at the time t34, the separation charger 14 is turned on, and at the time t36
The separation claw 15 is turned on. At this time, the transfer is still performed on the recording paper, but the separation starts from the leading end of the image after the transfer is performed.
The leading end of the separated recording paper is sent to the fixing device 17. At this time, if the size of the recording paper is relatively large, the transfer process may not be completed yet, but each drive is performed such that the linear velocity of the roller in the fixing device 17 becomes the same as the linear velocity of the photosensitive drum 3. Since the motors are synchronized, the recording paper is moved at the same transport speed in any part, and the recording paper is not moved at a different transport speed, so that the recording paper may be slackened or the toner image may not be moved. There is no rubbing.

FIG. 1 is a flowchart illustrating an image forming process in the high image quality fixing mode.

First, in step 1, when the high image quality fixing mode is selected with the input button on the operation panel, in step 2, the high image quality fixing mode flag (HF flag) is set. When the print is turned on in step 3,
The transfer rotation speed NT and the development color code are set in steps 4 and 5, respectively, according to the number and type of development colors that have already been set by other inputs. Next, in step 6, the drum detection counter NHP is reset, and in step 7, the encoder counter of the photosensitive drum 3 is reset, and in step 8, each drive motor is turned on. Then, the routine proceeds to a drum HP detection monitoring routine of step 9.

The drum HP detection monitoring routine is shown in FIG.
First, in step 11, it is confirmed whether or not the drum HP detection is standing, and then, in step 12, the transfer drum is released. Then, after the drum detection counter NHP is advanced by one in step 13, it is determined in step 14 whether or not the drum detection counter NHP is 1, and if it is 1, the paper feed clamping operation is performed in step 15. Done. Further, in step 16, the drum detection counter NHP is compared with the transfer rotation speed NT. Until the drum detection counter NHP becomes equal to the transfer rotation speed NT, the above-described ordinary toner image forming process and transfer process are executed in step 17. . If the drum detection counter NHP exceeds the transfer rotation speed NT, for example, when the transfer rotation speed NT is 4, the drum detection counter NHP becomes 5
In step 18, the high image quality fixing mode flag (HF flag) is referred to. If the HF flag is set, it is confirmed in step 19 that the drum detection counter NHP is one more than the transfer rotation speed NT. In step 20, the speed of the drive motor is switched to a low speed. That is, instead of performing the recording paper separating operation in the normal image forming mode, the overall image forming speed is reduced while the recording paper is clamped. In step 19, the drum detection counter NHP determines the transfer rotation speed N.
If it is confirmed that the value is not equal to the number obtained by adding 1 to T, a recording sheet separating operation is performed in step 21. If the high image quality fixing mode flag (HF flag) is not set in step 18, the recording paper is separated in step 22, and in step 23, the number obtained by adding 2 to the transfer rotation speed NT is equal to the drum detection value. It is set to the counter NHP and returned.

In FIG. 1, at step 24 after the drum HP detection monitoring routine is executed, the drum detection counter N
When it is confirmed that the HP is greater than the transfer rotation number NT by 2; that is, when the drum detection counter NHP reaches 6, the recording paper is discharged, the motor is turned off in step 25, and the print standby state is set in step 26. Will be migrated.

FIG. 3 shows a timing chart in the high image quality fixing mode described above. In this example, the rotation speeds of the photosensitive drum 3 and the transfer drum 8 are switched to half of the normal speed from time T6. At the same time, the roller rotation speed of the fixing device 17 and the conveyance speed of the recording paper conveyance system are also reduced so that the photosensitive drum 3 is synchronized with the switching of the speed. in this case,
Since the rotation speed of the photosensitive drum 3 is reduced by half, the frequency of the encoder pulse is also reduced by half, so that the operation timing of each step is delayed as a whole.

In the present embodiment, the drive motors are separately provided for each system, so that the roller speed of the fixing device 17 can be changed at the same time as referring to the high-quality fixing mode signal at the time of print-on. I have.
On the other hand, an embodiment in which the rotation drive of all the systems is performed by the main motor is also possible.

In the image forming method in such an embodiment, the operation of switching the speed of the drive motor of the photosensitive drum 3 is performed when the transfer drum 8 rotates after the transfer process is completed. That is, the high-quality fixing mode for lowering the fixing speed is executed after the transfer operation of the final toner image is completed, and the fixing step is performed separately from other image forming apparatus steps such as the transfer step. Therefore, each step that is easily affected by the linear velocity, such as the electrostatic latent image forming step, the developing step, and the transfer step, is executed at a normal linear velocity. Further, each of the transport speed of the photosensitive drum 3 and the transport speed of the recording paper by the transport system is reduced so as to be synchronized with the fixing transport speed, and the transport operation in the fixing process is synchronized with the transport operation by another transport system. It is done while. Therefore, the recording paper is moved at the same transport speed in any part, and the recording paper is not moved at a different transport speed as in the related art. as a result,
The recording sheet is satisfactorily conveyed even in the low-speed fixing process, and the recording sheet does not sag or the toner image does not rub.

The present invention, in which the rotation speed of the fixing roller is reduced in the fixing step, can be used for color copying for black-and-white copying or copying on an OHP transparent sheet for color copying.

(Effects) As described above, according to the present invention, the transfer speed of the recording medium on the transfer drum is not reduced until the transfer is completed, so that the transfer can be performed promptly. The conveyance speed of the recording medium is reduced so as to be synchronized with the conveyance speed of the recording medium in the fixing step. Therefore, regardless of the length of the conveyance path from the transfer position of the recording medium to the fixing position, the recording medium sags or the toner image It is possible to perform good fixing without causing rubbing, and to use a transport path in which the length from the transfer position to the fixing position is shorter than the length of the recording medium. Applicable.

Further, according to the present invention, the transfer operation of the final toner image is completed in the high image quality fixing mode so that the fixing step in the high image quality fixing mode is performed separately from other image forming apparatus steps such as the transfer step. And the conveyance speed of the photosensitive member and the conveyance of the recording medium by the general conveyance system so that the conveyance operation of the recording medium in the fixing step of the high-quality fixing mode is performed in synchronization with the conveyance operation by another conveyance system. Since the speed is reduced so as to be synchronized with the fixing conveyance speed, any part of the recording medium is moved at the same conveyance speed even in the high-quality fixing mode in which low-speed fixing is performed. The recording medium is no longer moved at different transport speeds as in the past,
As a result, the recording medium is satisfactorily conveyed even in the fixing step, and no slack or rubbing of the toner image occurs. Therefore, according to the present invention, it is not necessary to sufficiently separate the position where the recording medium is separated from the transfer unit and the arrangement position of the fixing unit, or to limit the length of the recording medium to be used to be short. It is possible to reduce the size of the image forming apparatus performing the high-quality fixing mode in which the operation is performed at a low speed, and to eliminate the size limitation of the recording medium used.

[Brief description of the drawings]

1 and 2 are flowcharts showing a high image quality fixing mode in one embodiment of the present invention, FIG. 3 is a timing chart showing a high image quality fixing mode, and FIG. 4 is a block diagram showing a control system. FIG. 5 is a timing chart showing a normal image forming apparatus mode, FIGS. 6 and 7 are side views showing an example of a color image forming apparatus to which the present invention is applied, and FIG. FIG. 9 is a schematic perspective view showing a configuration of a laser writing system, showing a release mechanism. 3 ... Photoconductor drum, 4,5,6,7 ... Each color developing device, 8 ...
... Transfer drum, 9 ... Clamper, 10 ... Transfer charger, 14 ... Separation charger, 15 ... Separation claw, 17 ... Fixing device.

Claims (3)

(57) [Claims] An image forming apparatus includes: a plurality of toner images formed on a surface of a photoconductor conveyed at a predetermined linear speed; a toner image for each color; The color is transferred on the recording medium conveyed in each color, and the fixing operation is performed in the fixing process while the recording medium after the transfer is conveyed at a linear speed lower than the linear speed in the transfer process of the transfer drum. In the image forming method, a conveyance path having a length from a transfer position where a toner image is transferred to a recording medium to a fixing position where a toner image is fixed to the recording medium is shorter than the length of the recording medium. The entire recording medium is rotated and held on the transfer drum until the transfer operation of the final toner image is completed, and after the transfer operation of the final toner image onto the recording medium is completed, the fixing step is started. Until a color image forming method characterized by the conveying speed of the recording medium by the transfer drum, reducing them to synchronize conveyance speed of the recording medium in the fixing step. 2. A method according to claim 1, wherein a plurality of color toner images are formed on the surface of the photoconductor conveyed at a predetermined linear speed, and the toner images are rotatably held by a transfer drum at a predetermined linear speed. The color is transferred on the recording medium conveyed in each color, and the fixing operation is performed in the fixing process while the recording medium after the transfer is conveyed at a linear speed lower than the linear speed in the transfer process of the transfer drum. In the image forming method, a conveyance path having a length from a transfer position where a toner image is transferred to a recording medium to a fixing position where a toner image is fixed to the recording medium is shorter than the length of the recording medium. A high-quality fixing mode in which the conveying speed of the recording medium in the fixing step is set lower than a normal mode for performing normal image formation. In the high-quality fixing mode, The entire recording medium is rotated and held on the transfer drum until the transfer operation of the final toner image is completed, and after the transfer operation of all the final toner images to the recording medium is completed, the above-described fixing process is started. The transport speed of the recording medium by the transfer drum is decreased so as to be synchronized with the transport speed of the recording medium in the fixing step. In the normal mode, the transport speed of the recording medium by the transfer drum is constant and A color image forming method, wherein the fixing step is started at the same time as the transfer speed of the recording medium in the fixing step and during a transfer operation of a final toner image. 3. The color image forming method according to claim 1, wherein a length of the recording medium is shorter than a circumferential length of the transfer drum.