JPH08224912A - Color printer - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent misalignment when a plurality of toner images formed on a photoconductor are superposed and transferred on an intermediate transfer drum. An intermediate transfer drum is supported so as to be in contact with a photoconductor and to rotate following the photoconductor, and a rotation speed of a photoconductor drive motor is controlled by a control device so that one rotation period of the intermediate transfer drum becomes a predetermined period. Control. In determining the rotational speed of the photoconductor when forming the electrostatic latent image of the first color during printing, the rotational time of the intermediate transfer drum during printing of the previous page was measured, and the electrostatic latent image , The rotation time of the intermediate transfer drum and the rotation of the intermediate transfer drum after the predictive correction, which is calculated by the actual measurement value and the predicted rotation fluctuation amount, by predicting the rotation fluctuation amount due to the fluctuation of the intermediate transfer drum load that occurs during the development and transfer processes. The speed difference from the reference time is corrected by the speed control drive circuit of the photoconductor. By doing so, a plurality of toner images can be accurately superimposed and transferred onto the surface of the intermediate transfer drum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser printer, and more particularly, to a color printer configured to obtain a color image by superimposing and transferring toner images of different colors on an intermediate transfer member.

[0002]

2. Description of the Related Art A conventional color laser printer is of a type that forms a color image by transferring a plurality of different-color toner images formed on a photoconductor onto an intermediate transfer body in an overlapping manner. In the above-mentioned method, a photoconductor including a photoconductive photoconductive drum or photoconductive belt is rotated at a predetermined speed to uniformly charge the surface of the photoconductor, and the light is deflected in a direction perpendicular to the rotating direction of the photoconductor. Exposure control for forming an electrostatic latent image is performed by intermittently controlling a scanned laser beam in accordance with video data corresponding to an image for each color to be printed. The electrostatic latent image formed on the surface of the photoconductor by the exposure is developed to form a toner image, and the toner image is transferred to the intermediate transfer member that rotates while partially contacting the photoconductor. A color toner image is formed on the intermediate transfer member by repeating the above process a plurality of times. The color toner image formed on the intermediate transfer member is collectively transferred to a sheet and then fixed to realize color image printing. As described above, in the laser printer including the photoconductor and the intermediate transfer body, the alignment accuracy of the toner images of the respective colors on the intermediate transfer body becomes an important problem in obtaining a high-definition color image. Therefore, as described in JP-A-62-195687, each driving means for driving the photosensitive member and the intermediate transfer member is controlled in synchronization with a common basic clock signal, and the basic clock signal is used to control the driving means. A control means for controlling the timing of exposure and transfer of each color has been proposed. In addition,
63-81370, the speed of each photosensitive drum driving means is detected by detecting the speed of the transfer paper conveying belt which is rotated by being driven by the photosensitive drums while being in contact with a plurality of photosensitive belts one after another. Controlled color printers have been proposed.

[0003]

The speed control means of the photosensitive member in the conventional color printer is not sensitive to the photosensitive member and the intermediate transfer member when the load fluctuation occurs when the photosensitive member or the intermediate transfer member rotates or when the transfer paper is conveyed. The speed of the intermediate transfer member changes, causing a deviation between the preset rotation speed of the photosensitive member and the execution rotation time of the intermediate transfer member, resulting in a positional deviation between the electrostatic latent image of the previous color within the page. To do.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color laser printer in which the speed control method of the photosensitive drum rotation driving means is optimized in order to improve the above problems.

[0005]

According to the present invention, in the speed control of the photosensitive member, the speed load fluctuation occurs due to the relationship between the rotation time measurement timing of the intermediate transfer member and the speed load fluctuation of the intermediate transfer member due to the printing process. In the case of the rotation time measurement timing of the intermediate transfer member, the rotation time difference due to the load fluctuation predicted in advance is corrected with respect to the measured rotation time, and the corrected rotation time result is used. Then, a time difference is calculated by comparing the rotation measurement time or the corrected rotation time result with a predetermined rotation reference time, and the speed of the photosensitive member in the color superimposing process at the next printing is the rotation time difference. Is provided with a control means for changing the speed of the photoconductor in a direction for correcting

[0006]

By controlling the rotational speed of the intermediate transfer member by measuring the rotation time of the intermediate transfer member for each printed page, it is possible to follow the rotational fluctuation of the intermediate transfer member with the elapse of the number of printed sheets. This makes it possible to form a toner image on the intermediate transfer member with improved color superposition accuracy.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a cross section of the main part of a laser printer. The printing portion of the laser printer 27 includes a photosensitive belt 5 wound around rotating wheels 1 and 2 so as to rotate at a constant speed in the arrow direction, and the rotating wheel 1 for rotating the photosensitive belt 5. , 2 for driving the photosensitive belt 5 at a constant speed, and a position sensor for reading a reference position mark formed on the outer peripheral surface of the photosensitive belt 5 in order to generate a reference position signal in the sub-scanning direction of the photosensitive belt 5. 14, a charger 7 that uniformly charges the surface of the photosensitive belt 5, and a scanning exposure device that exposes the uniformly charged surface of the photosensitive belt 5 to form an electrostatic latent image on the surface of the photosensitive belt 5. 8 and four developing devices 9, 10, 1 for developing the electrostatic latent image to form a toner image
1, 12 and a cleaner 13 for removing the toner remaining on the surface of the photosensitive belt 5 after transferring the toner image, and the photosensitive belt 5
An erase lamp 17 for removing electric charges remaining on the surface is provided. The scanning exposure device 8 is configured to irradiate the surface of the photosensitive belt 5 with a laser beam 39 according to video data and expose the surface of the photosensitive belt 5 by scanning the laser beam 39. The scanning exposure device 8 detects the timing when the beam spot passes the reference position for starting the deflection scanning in each deflection scanning. Developing device 9, 10, 11, 12
Are four developing devices using four color developers respectively, and each developing device 9, 10, 11, 12 has a developing function imparted or eliminated by controlling the developing bias voltage. The intermediate transfer drum 15 is used to superimpose a plurality of toner images of different colors formed on the surface of the photosensitive belt 5 to form one color toner image and transfer the formed color toner image to a sheet.

The intermediate transfer drum 15 uses the photosensitive belt drive motor 6 as a drive source, and the driving force is transmitted by frictional force and electrostatic attraction force at one contact portion with the photosensitive belt 5, and the surface of the photosensitive belt 5 is moved in the arrow direction. It rotates at a speed synchronized with.

Further, in order to remove the toner remaining on the surface of the intermediate transfer drum 15, a cleaner 16 capable of controlling contact and separation is arranged on the surface of the intermediate transfer drum 15.

A reference position mark is formed on the outer peripheral surface of the intermediate transfer drum 15, and a position reference sensor 23 generates a read reference position signal TPS. Further, the outer peripheral surface and the like are configured such that the deflection scanning start reference detection signal BDT1 output from the scanning exposure device 8 is always generated an integral number of times during the period in which the intermediate transfer drum 15 makes one rotation. Cassette 1
8 stores the paper 19, the paper feed roller 20 extracts the paper 19 and supplies it to the registration roller 21, and the registration roller 21 temporarily stops the conveyance of the paper 19 sent by the paper feed roller 20 to perform alignment. Adjust the paper feed timing.

The transfer device 22 is a region where the paper 19 conveyed from the registration rollers 21 contacts the intermediate transfer drum 15, and applies a transfer charge to the back surface of the paper 19 to form a toner image on the surface of the intermediate transfer drum 15. Transfer to No. 19. Further, the static eliminator 23 separates the paper 19 from the surface of the intermediate transfer drum 15.

The fixing device 24 is configured to fix the toner image on the sheet 19 by passing the sheet 19 on which the toner image is transferred between the heating roller and the pressure roller.

The paper discharge roller 25 is for discharging the paper on which the toner image is fixed to the outside of the machine. The control device 26 is connected to a higher-level information processing device, exchanges control information and print data with the information processing device, and controls the constituent means inside the laser printer 27 to execute printing.

FIG. 2 is a block diagram showing the internal structure of the control device 26. The control device 26 is composed mainly of a CPU 28, a RAM 37 storing a program, a laser control circuit 29 for controlling blinking of the semiconductor laser 8a, a beam detector for detecting a timing at which a beam spot passes a deflection scanning start reference position, and an amplification. Circuit 8g,
A scanning reference signal generation circuit 30, which generates a scanning synchronization reference signal based on the deflection scanning start reference detection signal BDT1 and the sub-scanning direction reference position signal HPS, an oscillator 31, and a reference position signal TPS of the intermediate transfer drum 15 are input. Detection signal processing circuit 3 for measuring the rotational speed of the intermediate transfer drum 15
3, a clock supply circuit 34 which is a photosensitive belt drive motor rotational speed adjusting means for adjusting the rotational speed of the photosensitive belt driving means by supplying a reference clock signal which is controlled by the CPU 28 and serves as a reference of the rotational speed of the photosensitive belt driving means. The oscillator 32 and the control drive circuit 35 for controlling the internal components of the laser printer 27 are provided.

Next, the print control process executed by the CPU 28 will be described with reference to FIG.

When the information processing device generates a print request signal, the CPU 28 in the control device of the laser printer 27
In response to the print request signal, the print control process according to the control program stored in the ROM 40 is started.

First, the control drive circuit 35 is operated to rotate the photoconductor 5 and the intermediate transfer drum 15, and the erase lamp 17, the charger 7, and the transfer device 22 are put into operation. Next, the developing devices 9, 10, 11, 12 to be operated are confirmed based on the information given from the information processing device.

The input of the reference position signal HPS in the sub-scanning direction on the surface of the photosensitive belt 5 is monitored, and the photosensitive belt 5 rotates to the writing reference position and the reference signal HPS in the sub-scanning direction.
Occurs, the print permission signal Vsync in the sub-scanning direction is generated after T1.

Then, the print permission signal Vsync in the sub-scanning direction
Within the generation period, the print permission signal Hsync in the main scanning direction is generated after a specified time from the generation timing of the main scanning synchronization reference signal BDT1.

Thereafter, the video data transmitted from the information processing device is received in synchronization with the generated print permission signal Vsync in the sub-scanning direction, and is transmitted to the laser control circuit 29 to control the semiconductor laser 39 to blink. An electrostatic latent image for one scanning line is formed on the surface of the photosensitive belt 5 by the semiconductor laser blinking control.

When the electrostatic latent image for one scanning line is completed, it is confirmed whether or not it is within the print permission signal Vsync generation period T2 in the sub-scanning direction, and the print permission signal Vsync generation period T2 in the sub-scanning direction is confirmed.
Within the range, the generation of the main scanning synchronization reference signal BDT1 is monitored, and when the next main scanning synchronization reference signal BDT1 is generated,
The video data transmitted from the information processing device is received in synchronization with the print permission signal Vsync in the sub-scanning direction, transmitted to the laser control circuit 29, and the semiconductor laser 8a is controlled to blink.

When the print permission signal Vsync generation period T2 in the sub-scanning direction ends, the print permission signal Vsync in the sub-scanning direction disappears, and the exposure of the toner image of the corresponding color ends.
The electrostatic latent image formed by the exposure is developed by the developing device 9, 10, 11, 12 of the corresponding color, and after the development, the developing function of the developing device is lost.

The toner image of the corresponding color thus formed is transferred and held on the surface of the intermediate transfer drum 15 when coming into contact with the intermediate transfer drum 15. In the printing process for two colors or more, instead of the input waiting process for the reference position signal HPS in the sub-scanning direction, the print permission signal Hsync in the main-sub-scanning direction for the time T0 when the intermediate transfer drum 15 makes one revolution,
Difference Tr between Vsync occurrence period T1 and T2 total T1 + T2
Is controlled to perform the above-described exposure and development operations.

In this way, the toner images of two or more colors are also transferred and held on the surface of the intermediate transfer drum 15 so as to be superimposed on the toner image of the previous color.

In this way, the paper feed roller 20 is used to transfer the toner image on the surface of the intermediate transfer drum 15 onto the paper 19.
Is rotated to extract the paper 19, the paper 19 is supplied to the registration roller 21, and the rotation of the paper feed roller 20 is stopped.

Next, the paper feed timing is adjusted so that the paper 19 aligns with the toner image and contacts the intermediate transfer drum 15, and the leading end of the paper 19 conveyed by the rotation of the registration roller 21 becomes the intermediate transfer drum 15. The transfer device 22 is energized at the timing when the intermediate transfer drum 1 comes into contact with the intermediate transfer drum 1.
5 The toner image on the surface is electrostatically transferred to the paper 19.

Further, the paper 19 on which the color toner image is transferred has the toner image on the paper 1 while passing through the fixing device 24.
The sheet is fixed on the sheet No. 9, and is ejected outside the apparatus by the sheet ejection roller 25.

Next, referring to FIGS. 4 and 5, the color superposition speed control method by the photosensitive belt driving means according to the present invention will be described.

As described with reference to FIG. 3, in order to accurately form the color-superimposed toner image on the intermediate transfer drum, the electrostatic latent image formed on the photosensitive belt at the electrostatic latent image cycle time (T0) is used. The developed toner image must be accurately intermediate-transferred for each rotation of the intermediate transfer drum. Further, in the print process mechanism of the present embodiment, there is a characteristic that the rotation of the intermediate transfer drum changes when the intermediate transfer drum cleaning mechanism portion is operated when cleaning the surface of the intermediate transfer drum. Hereinafter, four-color printing control is shown in FIG. 4, and two-color printing control is shown in FIG.
This will be described below.

First, the speed control method of the photosensitive belt drive motor in the four-color (YMCK) overprinting process will be described with reference to FIG.

The photosensitive belt speed control at the time of forming the electrostatic latent images of the first color (Y) and the second color (M) is controlled by the preset photosensitive belt drive motor speed set value F0.

When the electrostatic latent image of the third color (C) is formed, the diameter of the intermediate transfer drum increases due to the adhesion of the toner image to the intermediate transfer drum 15, and the intermediate transfer drum 15 driven by the photosensitive belt makes one revolution. Time increases. With this in mind,
A photosensitive belt drive motor speed set value F1 obtained by adding a speed set correction value f (correction amount corresponding to a rotation time delay due to an increase in the diameter of the intermediate transfer drum due to adhesion of the toner image) to the photosensitive belt drive motor speed set value F0. It is controlled by (= F0 + f).

When the electrostatic latent image of the fourth color (K) is formed, it is controlled by the photosensitive belt drive motor speed setting value F2 (= F1 + f) to which the speed setting correction value f is further added. Further, in parallel with the electrostatic latent image forming process of four colors, the rotation time of the intermediate transfer drum is measured at the timing shown in the figure.

After the formation of the four-color electrostatic latent image, the rotation measurement time t1, t for one rotation of the intermediate transfer drum 15 at the time of the second color transfer and the third color transfer in which the load fluctuation of the intermediate transfer drum 15 is small.
2 is averaged, and the average value (t1 + t2) / 2 is compared with the intermediate transfer drum rotation reference time T0, and the photosensitive belt drive motor speed set value F0 is corrected to correct the time deviation from T0. The subsequent photosensitive belt drive motor speed setting value F0 'is executed as the photosensitive belt speed setting value at the time of forming the electrostatic latent image of the first color of the next print page. Thereafter, the photosensitive belt drive motor speed control is executed for each print page.

The speed switching timing by the speed control of the photosensitive belt drive motor is performed at the end of the formation of the electrostatic latent image of each color.

In the case of three-color printing (example: YMC) (not shown), the photosensitive belt speed control at the time of forming the electrostatic latent images of the first color (Y) and the second color (M) is set in advance. It is controlled by the photosensitive belt drive motor speed setting value F0.

When the electrostatic latent image of the third color (C) is formed, the one rotation time of the intermediate transfer drum 15 is increased due to the adhesion of the toner image to the intermediate transfer drum 15, as described above. In consideration of this, the photosensitive belt drive in which the speed setting correction value f (correction amount corresponding to the rotation time delay due to the increase in the diameter of the intermediate transfer drum due to the adhesion of the toner image) is added to the photosensitive belt drive motor speed setting value F0 Motor speed set value F
It is controlled by 1 (= F0 + f).

The rotation time of the intermediate transfer drum is measured in parallel with the three-color electrostatic latent image forming process. After the electrostatic latent images of three colors have been created, the second variation in the load on the intermediate transfer drum 15 is small.
The rotation measurement time t1 for one rotation of the intermediate transfer drum 15 at the time of color transfer is compared with the intermediate transfer drum rotation reference time T0, and the photosensitive belt drive motor speed setting value F0 is set so as to correct the time lag from T0. The corrected photosensitive belt drive motor speed setting value F0 ′ is executed as the photosensitive belt speed setting value at the time of forming the electrostatic latent image of the first color of the next print page. Thereafter, the photosensitive belt drive motor speed control is executed for each print page. In the case of two-color printing (example: YM) (see FIG. 5), the rotation fluctuation time (tm) due to cleaning of the intermediate transfer drum is corrected from the rotation measurement time t0 for one rotation of the intermediate transfer drum 15 for the first color transfer. , Corrected rotation time t
0 '(= t0-tm) is the intermediate transfer drum rotation reference time T0
The photosensitive belt drive motor speed set value F0 is corrected so as to correct the time lag from T0, and the corrected photosensitive belt drive motor speed set value F0 ′ is set to the static value of the first color of the next printed page. It is executed as a photosensitive belt speed setting value at the time of forming an electrostatic latent image.

In the case of one-color printing, an electrostatic latent image is created with the photosensitive belt drive motor speed setting value F0 fixed.

Next, a method for determining the rotation fluctuation time (tm) due to the cleaning of the intermediate transfer drum will be briefly described. The color laser printer must heat up the fixing device to enable fixing, clean the surface of the photosensitive belt and the surface of the intermediate transfer drum, and perform various initialization processes from the power-on to the ready-to-print state. I won't. During execution of the initial operation, the intermediate transfer drum cleaning time when cleaning the intermediate transfer drum surface is measured and the intermediate transfer drum rotation time is measured, and the rotation time difference between the two is measured. It is stored in the memory as (tm) and used at the time of speed control of the photosensitive belt drive motor in the printing process described above.

By the above control processing, the distortion of the photosensitive belt 5 and the intermediate transfer drum 15 caused by the environment such as temperature, the change of the rotation characteristic with the lapse of the number of sheets to be printed, the change of the rotation characteristic of the intermediate transfer drum due to the change over time, etc. Can be followed and the problem due to the thickening of the intermediate transfer drum 15 in the case of multi-color printing can be solved. Further, it is possible to eliminate the positional deviation of the toner images of a plurality of colors in the sub-scanning direction on the intermediate transfer drum 15 due to the load variation in the rotational direction of the intermediate transfer drum 15.

[0043]

According to the present invention, the intermediate transfer member is rotated by obtaining a driving force by a frictional force or an electrostatic attraction force from one contact portion with the photosensitive member, so that the intermediate transfer member is rotated during the printing process. When the transfer member rotation time is measured, and in the case of a measurement timing at which load fluctuation due to the printing process occurs, the rotation measurement time is corrected in consideration of the rotation fluctuation time predicted in advance, and the intermediate transfer member at the time of the next printing is corrected. By controlling the photosensitive member drive speed so as to feed back the rotational speed, the rotation time of the intermediate transfer member can be optimized for each printed page.

The amount of load fluctuation due to the printing process is
By providing a function of actually measuring the rotation fluctuation time at the time of initial processing operation when the power is turned on, it is possible to follow the change in the load fluctuation amount due to machine difference, environment, and temporal change. Therefore, when a plurality of toner images of different colors are transferred onto the intermediate transfer body in an overlapping manner, the toner images of the respective colors can be accurately polymerized when a color toner image is obtained, and a high-definition color image can be obtained. .

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a main part of a color laser printer of the present invention.

FIG. 2 is a block diagram of a control device in the color laser printer of the present invention.

FIG. 3 is a print control time chart of the color laser printer of the present invention.

FIG. 4 is a color matching control time chart during four-color printing in the color laser printer of the present invention.

FIG. 5 is a color matching control time chart during two-color printing in the color laser printer of the present invention.

[Explanation of symbols]

5 ... Photosensitive belt, 6 ... Photosensitive belt drive motor, 8 ... Scanning exposure device, 9-12 ... Developing device, 15 ... Intermediate transfer drum, 26 ... Control device, 27 ... Color laser printer, 3
3 ... Detection signal processing circuit, 34 ... Clock supply circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Taketani 1-1-1 Higashitaga-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Electric Appliances Division Taga Headquarters (72) Inventor Katsu Nakano Tsuchiura-shi, Ibaraki 502, Machi

Claims (2)

[Claims] 1. A photosensitive member which is rotated by a photosensitive member driving means, and an exposing means which forms an electrostatic latent image on the surface of the photosensitive member,
A developing unit for forming a toner image on the electrostatic latent image; an intermediate transfer drum for rotating the toner image on the photosensitive member to transfer the toner image on the photosensitive member; and a frame body for assembling these members. In the color laser printer, the toner image of different colors is repeatedly formed on the photoconductor, the toner images of the respective colors are sequentially transferred, and the color image is formed by stacking the toner images on the intermediate transfer body. Rotation time measuring means for measuring the rotation time of the intermediate transfer member at the time of forming the color image of the previous page in determining the rotation speed of the photosensitive member when forming a latent image,
A fluctuation amount predicting unit that predicts a rotation fluctuation amount due to a load fluctuation of the intermediate transfer member that occurs during an electrostatic latent image, a development process, and a transfer process, and a predicted correction amount calculated from the measured value and the predicted rotation fluctuation amount. A color laser printer having speed correction means for speed-correcting using a time difference between a rotation time of the intermediate transfer body and a preset rotation reference time of the intermediate transfer body. 2. The rotation time measuring means according to claim 1, wherein the rotation time measuring means rotates the intermediate transfer member when a load is applied and a load is reduced when executing an initial control process for shifting from a power-on state to a printable state. A color laser printer characterized by measuring time and determining the predicted rotation fluctuation amount from the measured value by the fluctuation amount prediction means.