JP7459705B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

In an image forming apparatus, a predetermined tension is applied to a recording medium such as a sheet of paper during conveyance, thereby suppressing meandering of the recording medium. In an electrophotographic image forming apparatus, a recording medium is conveyed while applying a predetermined tension, an image is transferred onto the recording medium by a transfer roller, and then the transferred image (transfer image) is fixed by a fixing roller.

In order to apply a certain tension to the recording medium between the transfer roller and the fixing roller, the fixing speed needs to be equal to or faster than the transfer speed, and ideally the fixing speed and the transfer speed would be the same. On the other hand, if the fixing speed is too fast compared to the transfer speed, the tension of the recording medium becomes too high, so that the vibration of the fixing roller (fixing drive vibration) is easily transmitted to the transfer roller via the recording medium, and the fixing drive vibration causes blurring of the transferred image. To address this problem, for example, Patent Document 1 discloses an image forming device in which the speed ratio between the transfer roller's transport speed and the transfer roller's transport speed is variable.

JP 2004-101925 A

If the speed ratio of the conveyance speed is adjusted as in Patent Document 1, blurring of the transferred image can be reduced. However, when suppressing blur in a transferred image by adjusting the conveyance speed, the allowable speed difference between the fixing speed and the transfer speed is extremely small, so fine adjustment is required, and failure in adjustment leads to deterioration of image quality.

The present invention has been made in consideration of the above. That is, the objective of the present invention is to provide an image forming device that can easily reduce blurring of a transferred image and form an image with excellent quality.

(1) An image forming apparatus having a vibration absorbing unit between a transfer roller and a fixing roller, and a control unit that calculates the spring constant of the elastic mechanism of the vibration absorbing unit so that the resonance frequency of the elastic mechanism is equal to or less than 1/√2 of the frequency of the fixing drive vibration generated by the fixing roller.

(2) An image forming device as described in (1) above, comprising a transport unit for transporting continuous paper.

(3) The image forming device of (1) or (2), wherein the vibration absorbing section further comprises a roller having an elastic member.

(4) The image forming apparatus according to any one of (1) to (3), wherein the elastic mechanism includes an air cylinder mechanism whose spring constant is adjustable.

(5) an image analysis unit that acquires an image formed by the image forming apparatus and calculates a frequency of image unevenness in the image; The image forming apparatus according to any one of (1) to (4) above, which calculates a spring constant and adjusts the spring constant of the elastic mechanism.

(6) The control unit further calculates the spring constant of the elastic mechanism so that the resonance frequency of the elastic mechanism is 1/2 or less of the frequency of the fixing drive vibration generated by the fixing roller (2). The image forming apparatus according to any one of (5) to (5).

The image forming device of the present invention makes it easy to reduce blurring of the transferred image, and can form images with excellent quality.

1 is a system diagram showing an overall configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a configuration diagram schematically showing an image forming apparatus according to an embodiment of the present invention. 11 is a schematic diagram showing an elastic mechanism according to a comparative example. FIG. FIG. 2 is a schematic diagram showing a vibration absorbing section according to an embodiment of the present invention. 5A and 5B are schematic diagrams illustrating an example of an elastic mechanism according to an embodiment of the present invention. 7 is a graph showing the influence of the relationship between the resonance frequency of the elastic mechanism and the fixing drive frequency on the vibration transmissibility. 3 is a flowchart showing the flow of control of the elastic mechanism according to the embodiment of the present invention.

The following describes embodiments of the present invention with reference to the drawings. The present invention is not limited to the following embodiments. In addition, the components in each embodiment can be combined in part or in whole as appropriate.

An image forming apparatus according to an embodiment of the present invention will be described. The image forming apparatus according to this embodiment is a so-called tandem color image forming apparatus, and forms a full-color image on a recording medium. The recording medium in this embodiment is paper. Note that the present invention is applicable not only to the image forming apparatus of this embodiment but also to an electrophotographic image forming apparatus that includes a fixing roller and a transfer roller. Also, a recording medium other than paper may be used.

FIG. 1 is a system diagram showing the overall configuration of an image forming apparatus X according to this embodiment. The image forming apparatus X includes a control section 1, a storage section 400, a data acquisition section 500, a display operation section 600, an image forming section 100, a paper transport section 200, and an image analysis section 300. The control unit 1 includes a CPU (Central Processing Unit) and the like, and controls the operation of the image forming apparatus X.

The storage unit 400 includes a nonvolatile storage medium such as a ROM (Read Only Memory) and an HDD (Hard Disk Drive), a RAM (Random Access Memory), and the like. The storage unit 400 stores data etc. acquired by the data acquisition unit 500, and also functions as a work area when the control unit 1 executes a program. The storage unit 400 also stores the frequency of vibration (fixing drive frequency) generated from the fixing rollers 19A and 19B (described later in FIG. 2). If there are multiple fixing rollers, the fixing drive frequency is stored for each fixing roller.

The data acquisition unit 500 acquires data of the image to be formed. In this embodiment, the data acquisition unit 500 includes a document reading device SC (described later in FIG. 2), but the form of the data acquisition unit 500 is not limited to this. The data acquisition unit 500 may receive data via a network (not shown), may acquire data by connecting to an external storage device (not shown), or may acquire data in some other way.

The display operation unit 600 is composed of a touch panel display or the like, and displays an operation screen while accepting various inputs from the user. Note that instead of the display operation unit 600, a display unit and an operation unit may be provided separately.

The image forming section 100 includes image forming units 1Y, 1M, 1C, 1K, a primary transfer roller, transfer rollers (secondary transfer rollers) 16, 17, fixing rollers 19A, 19B (described later in FIG. 2), and a data acquisition section. An image is formed on the paper based on the data acquired by 500.

The paper transport unit 200 is a transport unit that includes a paper transport roller 20 (described later in FIG. 2) and a vibration absorbing unit 201, and transports the paper while applying tension. The vibration absorbing unit 201 includes a vibration absorbing roller 211 and an elastic mechanism 212 (see FIG. 3), and is installed between the transfer rollers 16 and 17 and the fixing rollers 19A and 19B to absorb vibrations transmitted to the recording medium.

The image analysis unit 300 optically reads the image formed on the paper by the image forming unit 100, analyzes the image, and calculates the drive vibration (fixing drive vibration) of the fixing rollers 19A and 19B from the blur of the image. The image reading mechanism of the image analysis unit 300 is not particularly limited, and may be, for example, a device similar to the document reading device SC of the data acquisition unit 500.

FIG. 2 is a configuration diagram schematically showing the image forming apparatus X according to the present embodiment. As shown in FIG. 2, the image forming apparatus ), cyan (C), and black (K) images, image forming units 1Y, 1M, 1C, and 1K, transfer rollers (secondary transfer rollers) 16 and 17, fixing rollers 19A and 19B, and vibration absorbing unit 201. Equipped with.

The paper feeder 210 is disposed upstream of the image forming device X in the paper feed direction and feeds rolled continuous paper (hereinafter referred to as paper) to the image forming device X. The winder 220 is disposed downstream of the image forming device X in the paper feed direction and winds up the paper on which an image has been formed by the image forming device X. The image analysis unit 300, also described in FIG. 1, is installed between the image forming device X and the winder 220 and analyzes the image formed by the image forming device X.

A plurality of paper transport rollers 20 transport the paper on a transport path between a paper feeder 210 and a winder 220. Each paper transport roller 20 is constituted by a pair of rollers pressed against each other, and at least one of the rollers is rotationally driven by an electric motor (not shown) serving as a driving means. The paper transport roller 20 transports the paper by rotating while holding the paper. These electric motors (not shown) and paper transport rollers 20 function as a transport section that transports continuous paper.

In addition to being configured with a pair of rollers, the conveyance means can widely adopt a configuration consisting of a pair of rotating members, such as a combination of belts or a combination of a belt and a roller. Further, the image forming apparatus It is also possible to form an image on a sheet of paper by providing a paper feed tray without including the device 220.

The document reader SC scans and exposes the image of the document using the optical system of the scanning exposure device, and obtains an image signal by reading the reflected light using a line image sensor. This image signal is then subjected to A/D conversion, shading correction, compression, and other processes, and then input to the control unit 1 (see Figure 1) as image data.

The image forming unit 1Y that forms a yellow (Y) image includes a photosensitive drum 14Y, a charging section 10Y arranged around the photosensitive drum 14Y, an optical writing section 11Y, a developing device 12Y, and a drum cleaner 13Y. Similarly, the image forming units 1M, 1C, 1K include photoreceptor drums 14M, 14C, 14K, charging sections 10M, 10C, 10K arranged around them, optical writing sections 11M, 11C, 11K, developing devices 12M, 12C, 12K and drum cleaners 13M, 13C, 13K. Note that in FIG. 2, for convenience of explanation, the photoreceptor drum 14Y and the image forming unit 1Y are shown separately, but the photoreceptor drum 14Y is one component of the image forming unit 1Y.

The surfaces of the photoconductor drums 14Y, 14M, 14C, and 14K are uniformly charged by the charging units 10Y, 10M, 10C, and 10K. A latent image is formed on the photoconductor drums 14Y, 14M, 14C, and 14K by scanning exposure by the optical writing units 11Y, 11M, 11C, and 11K. Furthermore, the developing devices 12Y, 12M, 12C, and 12K visualize the latent images on the photoconductor drums 14Y, 14M, 14C, and 14K by developing them with toner. As a result, an image (toner image) of a predetermined color corresponding to one of yellow, magenta, cyan, and black is formed on the photoconductor drums 14Y, 14M, 14C, and 14K.

The images formed on the photoreceptor drums 14Y, 14M, 14C, and 14K are transferred sequentially to predetermined positions on the intermediate transfer belt 18 by the primary transfer rollers. The intermediate transfer belt 18 is an endless belt that is stretched over multiple rollers including the transfer roller 16 and the belt driven roller 15. These rollers are arranged along the paper width direction that intersects (almost perpendicular to) the paper transport direction, and the roller axis direction and the paper width direction correspond to each other.

The transfer roller 16 is in pressure contact with the inner peripheral surface of the intermediate transfer belt 18, and is disposed opposite the transfer roller 17 via the intermediate transfer belt 18. The belt driven roller 15 is in pressure contact with the inner peripheral surface of the intermediate transfer belt 18 and supports the intermediate transfer belt 18 from the inside. The belt driven roller 15 is positioned upstream of the primary transfer roller corresponding to black in the rotation direction of the intermediate transfer belt 18.

The image made up of each color transferred onto the intermediate transfer belt 18 is transferred by the transfer roller 17 onto the paper transported at a predetermined timing by the paper transport roller 20. This transfer roller 17 is a roller-shaped rotating member that is pressed against the outer circumferential surface of the intermediate transfer belt 18, and transfers the image transferred onto the intermediate transfer belt 18 onto the paper.

The fixing rollers 19A and 19B are rotatably configured gears, and are driven to rotate through a drive motor (not shown) serving as a drive means, thereby applying pressure to the image transferred to the paper (transfer image). The fixing roller 19A includes a heater 191 as a heating section. Heater 191 applies heat to the transferred image. In this way, the fixing rollers 19A, 19B and the heater 191 fix the image on the paper by applying pressure and heat to the transferred image. Although only one set of fixing rollers 19A and 19B is shown in FIG. 2, a plurality of sets of fixing rollers having different numbers of teeth may fix the image.

The vibration absorbing section 201 is provided on the transport path between the transfer rollers 16, 17 and the fixing rollers 19A, 19B, and absorbs vibrations transmitted to the paper. The vibration absorbing mechanism is explained using Figures 3A and 3B.

Figure 3A shows a vibration absorbing section 201A of a comparative example. The vibration absorbing section 201A includes a vibration absorbing roller 211 with an elastic member, and an elastic mechanism 212A. The elastic mechanism 212A is, for example, a spring. When the rotation speed of the fixing rollers 19A, 19B is faster than that of the transfer rollers 16, 17 and tension is applied to the paper, the vibration of the fixing rollers 19A, 19B (fixing drive vibration) is easily transmitted to the transfer rollers 16, 17 via the paper. Therefore, the vibration absorbing section 201A includes an elastic mechanism 212A as shown in Figure 3A, and absorbs the fixing drive vibration.

However, the fixing drive vibration is not constant, but changes depending on, for example, the printing linear speed. Also, if fixing rollers 19A, 19B are gear-shaped, large vibrations occur periodically each time one tooth of the gear presses against the paper, and when image forming device X is provided with multiple fixing rollers with different numbers of teeth, the frequency of the fixing drive vibration changes depending on which fixing roller the vibration comes from. Therefore, when the fixing drive vibration changes, an elastic mechanism with a constant resonance frequency will not only be unable to absorb the vibration, but will actually increase the vibration, causing blurring in the transferred image and potentially degrading image quality.

Therefore, in this embodiment, a vibration absorbing section 201 as shown in FIG. 3B is provided. The vibration absorber 201 includes a vibration absorber roller 211 including an elastic member and an elastic mechanism 212 . The elastic mechanism 212 is an elastic mechanism that can control the resonance frequency by changing a spring constant, and is an air cylinder mechanism as shown in FIG. 4, for example. The air cylinder mechanism shown in FIG. 4 can adjust the elasticity of the operating part by adjusting the internal air pressure. By changing the spring constant of the elastic mechanism 212, the vibration absorbing unit 201 suppresses the fixing drive frequency and the resonance frequency of the elastic mechanism from matching, thereby reducing blur in the transferred image and improving the image quality. be able to.

Adjustment of the resonance frequency of the elastic mechanism will be explained using FIG. 5. FIG. 5 is a graph showing the relationship between the vibration transmissibility (db) and the frequency (Hz) of the elastic mechanism for each elastic mechanism having a different resonance frequency when the fixing drive frequency is 20 Hz. If the vibration transmissibility is higher than the 0 db vibration transmissibility line, the vibration transmissibility is increasing, and if it is lower than the line, the vibration transmissibility is decreasing.

The dashed line indicates a sample in which the resonance frequency of the elastic mechanism is set to 10 Hz, which is 1/2 of the fixing drive frequency. The solid line indicates a sample in which the resonance frequency of the elastic mechanism is set to 14.1 Hz, which is 1/√2 of the fixing drive frequency. The dotted line indicates a sample in which the resonance frequency of the elastic mechanism was set to 20 Hz, which coincides with the fixing drive frequency.

As shown by the dotted line, when the resonance frequency of the elastic mechanism coincided with the fixing drive frequency, the vibration transmission rate increased by 15 db. As shown by the solid line, when the resonance frequency of the elastic mechanism was 1/√2 of the fixing drive frequency, the vibration transmission rate did not increase or decrease. As shown by the dashed line, when the resonance frequency of the elastic mechanism was 1/2 of the fixing drive frequency, the vibration transmission rate decreased by 10 db.

From the above, the spring constant of the elastic mechanism 212 is adjusted so that the resonance frequency of the elastic mechanism is equal to or less than 1/√2 of the fixing drive frequency, and preferably adjusted so that it is equal to or less than 1/2 of the fixing drive frequency. By adjusting the resonance frequency of the elastic mechanism in this way, it is possible to significantly reduce the transmission of the vibrations of the fixing rollers 19A and 19B to the transfer rollers 16 and 17. Such adjustment has the effect of improving image quality in general image forming apparatuses having a fixing roller and a transfer roller, but is particularly effective in printing on continuous paper where the influence of vibration of the fixing roller tends to be large.

A method of setting the resonant frequency to a predetermined value will be explained. The general formula for the resonant frequency is shown in formula (1). Fo represents the resonance frequency (Hz), K represents the spring constant (N/m), and M represents the mass (kg).

Since the resonant frequency and the spring constant have the relationship shown in formula (1), the spring constant that realizes the intended resonant frequency of the elastic mechanism can be calculated based on that resonant frequency as shown in formula (2).

FIG. 6 shows a flow of controlling the elastic mechanism 212 to improve the image quality of the image forming apparatus X. In step S101, the user operates the display operation unit 600 to select a mode of the image forming apparatus X. When the normal print mode is selected (step S101: normal print mode), the control unit 1 moves to step S102.

In step S102, the control unit 1 determines the fixing vibration frequency for the current printing from among the fixing drive frequencies stored in the storage unit 400 based on the printing speed and the number of gears of the fixing rollers 19A, 19B. . If there are multiple fixing rollers, the fixing vibration frequency is determined based on the number of gears of the fixing roller that is expected to produce the maximum vibration. By processing in this way, it is possible to suppress large vibrations from being transmitted to the transfer rollers 16 and 17 even in the normal print mode, and improve image quality.

In step S103, the control unit 1 calculates a spring constant based on the determined fixing drive frequency so that the resonance frequency of the elastic mechanism 212 is equal to or less than 1/√2 of the fixing drive frequency. The air pressure of the elastic mechanism 212 is adjusted to achieve this. In step S104, the control unit 1 executes printing and ends the process.

In step S101, the user selects the evaluation feedback mode if he or she desires to improve the print image quality (step S101: evaluation feedback). If the evaluation feedback mode is selected, the control unit 1 moves to step S105. In step 105, the control unit 1 executes printing. In step S106, the image analysis unit 300 acquires the printed image.

In step S107, the image analysis unit 300 analyzes the acquired image to detect image unevenness. In step S108, the frequency of the blurring that appears in the detected image unevenness (image unevenness frequency) is calculated.

In step S109, the image analysis unit 300 checks whether the image unevenness frequency matches any of the fixing drive frequencies in the memory unit 400. If there is a match (step S109: Yes), the image analysis unit 300 determines that the matching image unevenness frequency is the fixing drive frequency and proceeds to step S110. In step S110, the image unevenness frequency is set to the fixing vibration frequency and proceeds to step S103. By processing in this manner, it becomes possible to adjust the spring constant of the elastic mechanism to match the fixing drive frequency of the fixing roller that is causing the vibration, and image quality can be improved more reliably.

If the image unevenness frequency does not match any of the fixing drive frequencies stored in the storage unit 400 (step S109: No), the image unevenness is not caused by the fixing drive vibration, but is caused by the vibration of another device such as a drum. It is thought to have originated from Therefore, the control unit 1 moves to step S102, and thereafter performs printing in the same manner as in the normal print mode.

Note that the present invention is not limited to the above-described embodiments, and can be modified without departing from the spirit thereof.

Image forming device
Control part 1
Storage section 400
Data acquisition section 500
Display operation section 600
Image forming section 100
Transfer roller (secondary transfer roller) 16, 17
Fixing roller 19A, 19B
Paper transport section (transport section) 200
Conveyance roller 20
Vibration absorber 201
Vibration absorbing roller 211
Elastic mechanism 212
Image analysis department 300

Claims (6)

a vibration absorbing section between the transfer roller and the fixing roller;
a control unit that calculates a spring constant of the elastic mechanism so that the resonance frequency of the elastic mechanism of the vibration absorbing unit is 1/√2 or less of the frequency of the fixing drive vibration generated by the fixing roller; Forming device. The image forming apparatus according to claim 1, further comprising a transport section that transports continuous paper. The image forming apparatus according to claim 1 or 2, wherein the vibration absorbing section further includes a roller having an elastic member. The image forming apparatus according to claim 1, wherein the elastic mechanism includes an air cylinder mechanism whose spring constant is adjustable. An image analysis unit that acquires an image formed by the image forming apparatus and calculates a frequency of image unevenness of the image,
5. The image forming apparatus according to claim 1, wherein the control unit further calculates an appropriate spring constant of the elastic mechanism from a frequency of the image unevenness, and adjusts the spring constant of the elastic mechanism. The control unit further calculates a spring constant of the elastic mechanism so that the resonance frequency of the elastic mechanism is 1/2 or less of the frequency of the fixing drive vibration generated by the fixing roller. The image forming apparatus according to item 1.

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