JP2007017778A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus where, in the case the paper to be printed and a printing mode in printing indication are different, the defect in fixing such as offset caused by the overquantity/underquantity of heat in a fixing device can be reduced. <P>SOLUTION: In the image forming apparatus comprising: a transferring unit; a fixing device; and a driving source of carrying paper, voltage is applied to paper, the flowing electric current is measured, a paper carrying velocity is accelerated/decelerated, and, in accordance with the change of the paper carrying velocity, the transferring voltage to be applied and heater lighting time are changed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to sheet conveyance speed control of the apparatus.

  Conventional image forming apparatuses support a wide variety of paper types, such as papers with different paper materials such as plain paper, OHP, glossy paper, and label paper, and papers with different paper thickness and basis weight such as thin paper, recycled paper, and thick paper. For this reason, the print mode is subdivided and the user designates a print mode that matches the paper to be printed.

  Each printing mode is set so that a good image result can be obtained with a paper transport condition according to the target paper type, a transfer condition for transferring toner onto the paper, and a fixing condition for fixing toner onto the paper. Yes.

  Recent image forming apparatuses are becoming cheaper and often do not include a sensor for detecting the type of paper or a sensor for detecting the paper size in order to reduce costs. In addition, since there are many types of corresponding paper, the print mode is subdivided, and it is not easy to specify a print mode suitable for the paper to be actually printed. With such a configuration, when the type of paper to be printed is different from the type of paper in the print mode instructed to print, the amount of heat when fixing toner to the paper due to transfer failure due to transfer voltage mismatch when transferring toner to the paper This causes a defect such as fixing failure due to mismatching of fixing conditions such as offset due to excessive / low.

  Paper setting failure when the print mode is thick and the print mode instructed to be thin is thin, or the print mode instructed to be printed is thin and the print mode instructed to print is different from the print mode Occasionally, the amount of heat in the fixing device is excessive / insufficient, which may cause defects such as toner offset, or toner melting too much and the paper cannot be peeled off from the fixing roller.

  An object of the present invention is to change the rotation speed of a motor serving as a drive source of a sheet by changing the rotation speed of a motor before the sheet is conveyed into the fixing device when the printing sheet and the printing mode instructed to print are different. It is an object of the present invention to provide an image forming apparatus that can reduce fixing defects such as offset due to excessive / insufficient heat quantity in the fixing device by changing the above.

  The above object is to apply a voltage to a sheet in an image forming apparatus having a transfer unit having a transfer roller provided with an electrode for transferring toner to the sheet, a fixing device, and a motor that is a power source for sheet conveyance. This is achieved by determining the type of paper based on the value of the flowing current and varying the paper transport speed.

  According to the present invention, when a paper setting failure occurs such as when the type of printing paper does not match the type of printing mode instructed to print, the value of the current flowing through the paper is measured by the voltage applied to the leading edge of the printing paper, and the type of paper is determined. By discriminating and varying the rotation speed of the motor that is the drive source for paper conveyance, it is possible to reduce the offset due to excessive / insufficient heat quantity in the fixing device. Further, by changing the sheet conveyance speed, the transfer failure can be reduced by adjusting the second transfer voltage. By changing the paper transport speed and reducing the offset in the fixing device, it is possible to prevent the paper from being soiled with unfixed toner adhering to the fixing roller due to the offset, and it is not possible to peel off the fixing roller due to the influence of the unfixed toner. Paper jams such as wrapping around the fixing roller can be prevented.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic longitudinal section of the overall configuration of an image forming apparatus according to an embodiment of the present invention, and FIG. 2 shows details of the control device of FIG.

  As shown in FIG. 1, the photosensitive belt 1 is uniformly charged by a charger 2 while being rotated around a guide roller 4 at a constant speed, and laser light emitted from an exposure device 3 according to an image signal of each color. The electrostatic latent images corresponding to the respective colors are sequentially formed by the exposure, and the electrostatic latent images are sequentially selected by selecting the developing devices using the developers of the corresponding colors of the four developing devices 13, 14, 15, and 16. Each color toner image is formed.

The color toner images on the surface of the photosensitive belt 1 are transferred onto the surface of the intermediate transfer unit 5 that rotates synchronously while being in contact with the surface of the photosensitive belt 1. Become.
The paper 17 that is a recording medium stored in the paper feed cassette 8 is extracted and conveyed by the paper feed roller 9 and sent to the registration roller 18, and the color toner image on the surface of the paper 17 and the intermediate transfer unit 5 by the registration roller 18. Are fed toward the transfer roller 10 after being controlled so as to be matched with each other.

  A voltage is applied to the leading edge of the paper 17 sent to the transfer roller 10 to detect the current value flowing through the paper 17. The type of paper is determined based on the detected current value, and before the paper 17 is conveyed to the fixing device 12, the speed of the motor that is the drive source of the paper conveyance is changed. Further, when the paper transport speed is changed, the second transfer voltage to be applied when the toner latent image on the transfer belt 22 is transferred to the paper 17 is changed.

  Thereafter, a mechanical pressing force and a transfer electric field are applied from the back surface of the sheet 17 by the transfer roller 10 while the sheet 17 is in contact with the intermediate transfer unit 5, and the color toner image on the surface of the intermediate transfer unit 5 is transferred to the sheet 17. .

  The transfer roller 10 is pulled up so as not to act in the process of forming the toner images of the respective colors on the photosensitive belt 1 on the surface of the intermediate transfer unit 5. The sheet 17 on which the color toner image has been transferred is sent out toward the fixing roller 11. The fixing roller 11 constitutes a part of the fixing device 12, and the color toner image is heat-fixed on the surface of the paper 17 while the fed paper 17 passes through the fixing roller 11. The sheet 17 on which the color toner image is thermally fixed is discharged onto a discharge tray 21 via a discharge roller 19.

  The transfer belt cleaner 20 cleans the toner remaining on the surface of the intermediate transfer unit 5. The transfer belt cleaner 20 is pulled up so that the cleaning operation does not work in the process of forming a color toner image by repeatedly transferring a single color toner image to the surface of the intermediate transfer unit 5, and transfers the completed color toner image to the paper 17. After that, it is pressed so as to act on the surface of the intermediate transfer unit 5.

  In FIG. 2, the control device 100 is mainly composed of a central processing unit (hereinafter abbreviated as CPU) 101, a ROM 102 storing a control program for the CPU 101, and a work memory RAM 103 necessary for the CPU 101 to execute the control program. The above-described components are controlled in accordance with an input signal from the operation panel 201 and an input signal from an information processing apparatus to be described later.

  An input / output interface (I / F) 104 mediates communication of the CPU 101 with the information processing apparatus 200 such as the operation panel 201 or a personal computer, and print data generated by the information processing apparatus 200 is sent to the exposure control unit 105. introduce. The exposure control unit 105 controls the exposure apparatus 3 to generate laser light.

  The mechanism control unit 106 is a control unit group for controlling a group of mechanisms in the image forming process, and is controlled by the CPU 101 to output a motor drive instruction signal S1, a transfer roller control signal S2, and a transfer voltage control signal S3. In addition, signals for controlling the developing unit 106b, the cleaner unit 106c, the charging unit 106d, the fixing unit 106e, and the like are input and output.

  The motor control unit 107 is connected to control the motor 20 that drives the photosensitive belt 1, the paper feed roller 9, the fixing device 12, and the like, and a drive signal S7 according to a motor drive instruction signal S1 given from the motor unit 106a. And a detection signal S8 for detecting the amount of angular displacement generated from the encoder 21 directly connected to the rotating shaft of the motor 20 is input. Further, the motor control unit 107 transmits the detection signal S8 from the encoder 21 to the CPU 101 via the interrupt control unit 108 as the rotation angle signal S9 of the photosensitive belt 1. The transfer roller control unit 108 is connected to a clutch that brings the transfer roller 10 into contact with the transfer belt 22 by a transfer roller control signal S4. The transfer voltage control unit 109 is configured such that a voltage is applied to the transfer unit 5 by a transfer voltage control signal S5.

  The sheet type determination, sheet conveyance speed, and transfer voltage selection processing in the image forming apparatus having the above-described configuration will be described with reference to the flowchart of FIG.

  First, after receiving the print data, the image forming apparatus uses the developer of the corresponding color of the four developing devices 13, 14, 15, 16 on the photosensitive belt 1 by the first transfer process (step 701). A developing device is selected to form a toner image, and a color toner image is formed on the surface of the intermediate transfer unit 5 that rotates in synchronization with the surface of the photoreceptor belt 1. After a color toner image is formed on the surface of the transfer belt 22 of the transfer unit 5, the paper 17 is conveyed to the registration roller 18 by the paper feed roller 9.

  The registration roller 18 conveys the sheet 17 toward the transfer roller 10 so that the leading end of the sheet 17 and the leading end of the color toner image on the surface of the transfer belt 22 are aligned. In the transfer belt current detection process (step 702), the transfer roller 10 is brought into contact with the surface of the transfer belt 22 and a voltage of 0.8 KV is applied when the sheet is not fed before the sheet is conveyed to the transfer roller 10, and the transfer is performed. The current Ir flowing through the belt 22 is measured. In the paper tip application voltage determination process (step 703), the voltage Vp to be applied to the paper tip is determined from the measured transfer belt current Ir from the paper tip application voltage table divided for each paper type.

  Next, when the leading edge of the paper 17 conveyed from the registration roller 18 in the paper leading edge voltage application processing (step 704) reaches the transfer roller 10, the voltage Vp determined in the paper leading edge voltage determination processing (step 703) is used. Apply to the leading edge of the paper 17. In the paper front end current measurement process (step 705), the paper current Ip of the current flowing through the paper is measured with the voltage Vp applied to the front end of the paper 17. The paper current Ip is a level representation of the current flowing through the paper and ranges from “0” to “255”.

  As the output level approaches “255”, the current flowing through the paper 17 is large, indicating that the paper thickness is thin. Further, as the output level approaches “0”, the current flowing through the paper 17 is small, indicating that the paper thickness is thick. Based on the output level of the sheet current, the voltage level to be applied in the second transfer is determined from the second transfer applied voltage table for each sheet type in the transfer voltage determination process (step 706). In the paper type determination process (step 707), the type of the paper 17 being conveyed is determined based on the paper current Ip. Even if the printing mode of thin paper / plain paper is designated, if the paper current Ip obtained in the paper leading edge current measurement process (step 705) is small, the thick paper system is printed.

  Even if the thick paper type printing mode is designated, the paper type is determined that the thin paper / plain paper type is printed if the paper current Ip is large. The paper conveyance speed is changed based on the paper type determined in the paper type determination process (step 707). As the paper current Ip increases, the paper resistance value decreases as the paper current Ip increases, so the transport speed approaches 1/1 speed, and as the paper current Ip decreases, the paper resistance value increases, so the transport speed decreases.

Plain paper, and when the conveying speed of the thin paper and 1/1 speed, 1/2 speed cardboard up to a basis weight 90~163g / m ^2, a basis weight 164 g / ^{m 2} or more thick 1/4 speed, OHP1 / 4 speed. In order to change the sheet conveying speed, in the motor speed changing process (step 708), the motor that is the driving source of the sheet conveying is instructed to change the speed, and the deceleration / acceleration is finished before the sheet is conveyed to the fixing device. . Next, in the transfer voltage re-determination process (step 709), the second transfer application voltage is reselected in accordance with the change in the sheet conveyance speed. Based on the duty of the voltage Vp applied to the leading edge of the sheet and the current sheet current Ip flowing through the leading edge of the sheet, the sheet is selected again from the second transfer applied voltage table of the sheet type selected in the sheet determination type determination process (step 707).

  Next, the heater heating time is adjusted in order to reduce the cause of defects in the fixing device 12 by changing the sheet conveyance speed by the fixing control operation mode changing process (step 710). When the paper transport speed is reduced, the amount of heat applied to the paper increases, so the heater heating time is shortened. When the paper transport speed is accelerated, the amount of heat applied to the paper decreases, so the heater heating time is extended. As a result, offset and jam in the fixing device 12 are reduced.

  After the paper type determination process (step 707) is executed, the same paper type is printed until the paper cassette 8 as the same paper source is inserted and removed, and the paper conveyance speed, transfer conditions, and fixing are performed. We will control the conditions.

  In this way, when the type of paper to be printed is different from the print mode instructed to print, the current value flowing at the voltage applied to the paper 17 is measured, and the paper transport speed in the print mode instructed to print is changed to thereby fix the fixing device 12. It is possible to reduce jamming such as offset due to excessive / insufficient heat quantity and paper winding.

1 is a schematic longitudinal sectional view of an overall configuration of an image forming apparatus. It is detail drawing of a control apparatus. FIG. 10 is a flowchart of a series of operations including a paper conveyance speed change process of the image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photosensitive belt, 2 ... Charger, 3 ... Exposure apparatus, 4 ... Guide roller, 5 ... Intermediate transfer body unit, 6 ... 1st roller, 7 ... 2nd roller, 8 ... Paper feed cassette, 9 ... Paper feed Roller, 10 ... Transfer roller, 11 ... Fixing roller, 12 ... Fixing device, 13, 14, 15, 16 ... Developing device, 17 ... Paper, 18 ... Registration roller, 19 ... Discharge roller, 20 ... Transfer belt cleaner, 21 ... paper discharge tray, 22 ... transfer belt, 100 ... control device.

Claims (4)

  An image forming apparatus having a transfer unit, a fixing device, and a drive source for transporting paper, measuring a current flowing by applying a voltage to the paper and accelerating / decelerating the paper transport speed.   The image forming apparatus according to claim 1, wherein the transfer voltage to be applied is changed in accordance with the change in the sheet conveyance speed.   The image forming apparatus according to claim 1, wherein the heater lighting time is changed in accordance with the change in the sheet conveyance speed. The image forming apparatus according to claim 1, wherein a condition for changing a sheet conveyance speed is maintained until the sheet feeding cassette is inserted and removed.

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