JPS63271389A - Image forming device - Google Patents

Abstract

PURPOSE:To remove high-frequency abnormal noises uncomfortable to the ears so that a silent operation can be made by providing a mass increase part to the end face of a photosensitive drum off the center of rotation thereof. CONSTITUTION:The mass increase part such as projection is provided on the part of the end face of the photosensitive drum 1 off the center of rotation thereof. Namely, for example, a projection 11 which constitutes the mass increased part is integrally provided on the end face 1a of the drum 1 in the part off the center of rotation thereof. This projection 11 may be single or plural. The oscillation mode of the drum 1 is thereby increased in oscillation amplitude at the end part thereby and, therefore, the drum 1 becomes extremely rigid to the torsional oscillation of an even order mode in which friction energy is liable to enter; consequently, the friction energy cannot enter the same and even if the friction force is negative attenuation, the self-excited oscillation is not generated and the generation of the abnormal noises is prevented.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Field of Application) The present invention relates to image forming apparatuses such as laser printers and electronic copying machines, and particularly relates to image forming apparatuses such as laser printers and electronic copying machines, and in particular to the development process that remains on the surface of a photosensitive drum after image transfer. The present invention relates to an image forming apparatus including a cleaning device that scrapes off toner with a cleaning blade.

(Prior Art) In image forming apparatuses such as laser printers and electronic copying machines, photoconductors are used as printing media. This photoconductor is applied to the outer peripheral surface of a cylindrical photosensitive drum made of a conductor such as aluminum.

Taking a laser printer as an example, the printing process will be described. First, the photoconductor is uniformly charged. For example, in the case of organic photoconductor (OPC), -70
Charging is performed to a negative potential of 0V. Next, line scanning is performed while turning the laser beam on and off in accordance with the printed dot data, and by sending the photoconductor at a constant speed in a direction perpendicular to this line scanning, two-dimensional light is produced on the photoconductor. form an image. This two-dimensional optical image is an electrostatic latent image in which the charged potential of the portion irradiated with the laser beam is reduced.

A charged developer (toner) is then contacted onto the surface of the photoconductor. For example, when a developer of the same polarity as the electrostatic potential on the photoconductor is brought into contact, the developer will adhere to the de-charged areas of the photoconductor.

This development process gives the surface of the photoconductor an eye (
A visible developer image is formed.

Thereafter, a sheet of paper is applied to the front surface of the photoconductor, and a potential opposite to the charged potential of the developer is applied from the back side of the sheet to transfer the developer on the photoconductor to the sheet of paper. Then, heat or pressure is applied to the developer image transferred to the paper to fix the image on the paper. The developer remaining on the photoconductor without being transferred to the paper is scraped off and cleaned by a cleaning blade brought into contact with the photoconductor, and the process returns to the charging step again.

In this way, image forming devices such as laser printers perform printing through charging, exposure, development, fixing, and cleaning processes, so compared to impact printers, they can print arbitrary characters, graphics, etc. faster and with higher quality. It has the characteristics of being able to print with low noise.

(Problem to be Solved by the Invention) However, although such image forming apparatuses are capable of low-noise operation in principle, they have the disadvantage that they sometimes generate abnormal high-frequency noise that is very harsh to the ears. . This noise usually has a clear ``chee'' tone and is different from other mechanical noises, such as those caused by motors, gears, paper feed, etc., and is effective because the cause of its occurrence was previously unknown. No countermeasures have been taken, and there has been a strong desire to reduce or even eliminate such abnormal noise. This invention has been made with attention to these points, and an object of the present invention is to provide an image forming apparatus that can effectively remove abnormal high-frequency noise using simple means. .

[Structure of the Invention (Means for Solving Problems)] The present inventor has discovered that abnormal high-frequency noise in an image forming apparatus such as a laser printer can cause frictional force between the photosensitive drum and the cleaning blade during the cleaning process. It was discovered that self-excited vibration occurred in the photosensitive drum due to this, and that the sound of this self-excited vibration was abnormal high-frequency noise. Such a vibration system is a torsional vibration of the photosensitive drum, and its vibration mode is an even-order mode. This is related to the fact that the photosensitive drum is a thin cylinder with flanged structures at both ends, and a frictional force uniformly distributed in the axial direction acts on the cylindrical surface in the circumferential direction. In this case, energy is likely to enter the photosensitive drum in even-order mode torsional vibration, and it also acts on this (if the frictional force has negative damping, that is, if the first derivative number of friction with respect to the sliding speed is negative) The inventor has discovered that this frictional force becomes the limit of energy supply, and that self-excited vibration occurs in the photosensitive drum as described above in the even-order mode of torsional vibration. Since it is in the frequency range, it becomes noise.

Therefore, in the present invention, a mass increasing portion made of a protrusion or the like is provided on the end face of the photosensitive drum and at a portion away from the center of rotation.

(Function) In general, when a simple pendulum of mass m and length is mounted at a position R from the center of rotation of a rotating body, the ratio of the frequency of torsional vibration of the rotating body to the rotational angular velocity of the rotating body is n. , a simple pendulum is equivalent to a flywheel with a moment of inertia of m (R+J) 2/ (1-(]/R)n').

The natural frequency of the problematic torsional vibration of a photosensitive drum in an image forming apparatus such as a laser printer is several KHz.
As above, since the number of rotations is number+rpm (approximately 1 rps or less), the frequency ratio n becomes a very large value. As a result, if the value approaches zero, the equivalent moment of inertia becomes infinitely large. Providing a mass increasing portion on the end face of the photosensitive drum away from the center of rotation produces an effect similar to this. The vibration mode of the photosensitive drum has a large vibration amplitude at its ends and is therefore very effective. In other words, since the photosensitive drum becomes extremely rigid against torsional vibrations in even-order modes in which frictional energy easily enters, frictional energy can enter. Even if the frictional force is negatively damped, self-excited vibration will not occur. First, the occurrence of abnormal noise is prevented.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

In the figure, reference numeral 1 denotes a photosensitive drum, and around this photosensitive drum 1, a charging device 2, an exposure device 3, a developing device 4, a transfer device 5, a peeling device 6, and an afterimage erasing device 7 are arranged in the direction of rotation of the photosensitive drum 1. They are arranged sequentially. Then, the cleaning device 7 moves a cleaning blade 9, and this cleaning blade 9 comes into contact with the circumferential surface of the photosensitive drum 1, and due to this contact, the developer remaining on the surface of the photosensitive drum 1 is removed as the photosensitive drum 1 rotates. It is scraped off and cleaned.

The photosensitive drum 1 is formed into a cylindrical shape as shown in FIG. The photoconductor described above is uniformly applied to the outer peripheral surface of the photosensitive drum 1. And end surface 1a of this photosensitive drum 1
For example, a protrusion 11 constituting a mass increasing portion is integrally provided at a portion away from the center of rotation. This protrusion 11 may be singular or plural.

When the frequency of the sound generated during the cleaning process was analyzed in the photosensitive drum 1 without the protrusion 11 as a mass increasing part on the end surface 1a, as shown in FIG. 3(a), abnormal high frequency noise of 10.65 KHz was found. There has occurred.

On the other hand, when the protrusion 11 is provided as a mass increasing part on the end surface 1a of the photosensitive drum 1, as shown in FIG. Ta.

[Effects of the Invention] As explained above, according to the present invention, the unpleasant high-frequency abnormal noise can be reliably removed by providing a mass increasing portion on the end face of the photosensitive drum away from the center of rotation. This has the effect of achieving quiet operation.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, with FIG. 1 being a sectional view of a photosensitive drum, and FIG. 2 being a sectional view of main parts of a laser printer.
FIG. 3 is an analysis diagram of sound frequencies. 1... Photosensitive drum, 7... Cleaning device, 9...
...Cleaning blade, 11...Protrusion (mass increasing part). Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (4)

[Claims] (1) In an image forming apparatus having a process of applying a developer to a photosensitive drum to form a desired image, and a process of transferring the image formed in this process to a recording material, an end surface of the photosensitive drum is provided. An image forming apparatus characterized in that a mass increasing portion is provided in a portion away from the center of rotation. (2) The image forming apparatus according to claim 1, wherein the mass increasing portion is a projection. (3) The image forming apparatus according to claim 2, wherein the number of projections is one. (4) The image forming apparatus according to claim 2, wherein there is a plurality of protrusions.