JPH04355485A - Image forming device - Google Patents

Abstract

PURPOSE:To provide a copying machine capable of keeping a satisfactory image quality even if the characteristic of a transfer sheet is changed in accordance with an environmental change and being manufactured at low cost. CONSTITUTION:A copying machine has a photosensitive drum 9, a latent image forming part for forming a latent image on the photosensitive drum 9 according to an image information, a developing device 12 for developing the latent image on the photosensitive drum 9, and a transfer roller 31 pressed onto the photosensitive drum 9 to transfer the developed image onto a sheet. This device also has a humidity sensor 21 and a nipping width changing part for changing the nipping by the photosensitive drum 9 and the transfer roller 31 on the basis of the detection result by the humidity sensor 21.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to an image forming apparatus, particularly,
The present invention relates to an image forming apparatus for forming an image on a transfer sheet according to image information.

0002

[Prior Art] As an image forming apparatus (for example, a copying machine),
A photoconductor drum, an optical system that forms a latent image according to image information on the photoconductor drum, a developing device that develops the latent image formed on the photoconductor drum, and a developed image produced by the development onto paper. A device equipped with a transfer roller for transferring is already known (see Japanese Patent Laid-Open No. 1-265282). In this device, a bias voltage having a polarity opposite to the charge of the toner on the photoreceptor drum is applied to the transfer roller.

In this image forming apparatus, the paper fed between the photosensitive drum and the transfer roller is pressed by the transfer roller and the bias voltage applied to the transfer roller. The toner image on the photoreceptor drum is transferred. The paper onto which the toner image has been transferred is separated from the surface of the photoreceptor drum and supplied to a fixing device. After the fixing process is performed in the fixing device, the paper is discharged.

Furthermore, this image forming apparatus is configured to detect environmental changes such as humidity that cause changes in the resistance of the paper, and control the transfer bias voltage based on the detected environmental changes to maintain stable image quality.

[0005]

[Problems to be Solved by the Invention] In the conventional configuration,
Since a configuration is required to change the transfer bias voltage in accordance with changes in paper characteristics due to environmental changes, a bias voltage control circuit and an associated high voltage transformer are required, which increases manufacturing costs.

An object of the present invention is to provide an image forming apparatus that can maintain good image quality even if the characteristics of the transfer sheet change due to environmental changes and can be manufactured at low cost.

[0007]

An image forming apparatus according to the present invention is an apparatus for forming an image on a transfer sheet according to image information. This device includes an image-bearing drum, a latent-image forming means for forming a latent image on the image-bearing drum according to image information, a developing means for making the latent image on the image-bearing drum visible, and a a transfer roller that transfers a developed image onto a transfer sheet by contact with the transfer sheet; an environment detection device that obtains data regarding the environment; and a nip that changes the width of the nip between the image bearing drum and the transfer roller based on the detection results of the environment detection device. width changing means.

[0008]

[Operation] In the image forming apparatus according to the present invention, the latent image forming means forms a latent image on the image bearing drum according to image information. Then, the developing means visualizes the latent image on the image bearing drum. A transfer roller that is in pressure contact with the image bearing drum transfers the developed image onto a transfer sheet.

During this image transfer operation, the nip width changing means changes the width of the nip between the image bearing drum and the transfer roller based on the detection result by the environment detecting means. As a result, even if the characteristics of the transfer sheet change due to changes in the environment, the nip width is adjusted in accordance with the change, so that appropriate image transfer can be performed. As a result, good image quality can be maintained even if environmental changes occur. Moreover, in this case, expensive components such as a high voltage transformer are not required, so the image forming apparatus is low cost.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a copying machine as an embodiment of the present invention. In FIG. 1, a document table 2 is fixed to the upper surface of a copying machine main body 1, and a document presser 3 that can be opened and closed is arranged on the document table 2. As shown in FIG. A bypass tray 4 and a pair of paper feed cassettes 5 and 6 are removably installed on the right side of the copying machine main body 1 in the figure.

Inside the copying machine main body 1, an exposure device 8 for reading originals is provided at the top. This exposure device 8 is composed of a light source, a mirror, a lens, etc. Further, a photosensitive drum 9 on which an electrostatic latent image is formed is arranged in the center of the copying machine main body 1. Around the photoreceptor drum 9, there are a main charging device 10 that charges the photoreceptor drum 9 to a predetermined charge, a blank lamp 11 that erases the charge on unnecessary areas on the photoreceptor drum 9, and a photoreceptor drum 9.
a developing device 12 for developing the upper electrostatic latent image with toner;
A transfer device 13 that transfers the toner image on the photoreceptor drum 9 onto paper, and a cleaning device 14 that removes residual toner on the photoreceptor drum 9 are arranged.

Bypass tray 4 and paper feed cassettes 5 and 6
A paper transport path 17 and a paper discharge transport path 18 for transporting paper are provided between the image forming section and the image forming section constituted by the photosensitive drum 9 and the like, and downstream of the image forming section, respectively. In the paper transport path 17, the paper feed cassette 5,
A humidity sensor 21 for detecting humidity as one of the environmental factors is provided in a portion near 6. On the downstream side (on the left side in the figure) of the paper ejection transport path 18, there is a fixing device 19 for fixing the transferred image on the ejected paper, and a fixing device 19 for ejecting the paper fixed by the fixing device 19 to the outside. A discharge roller 20 is provided.

As shown in FIG. 2, the transfer device 13 has a case 30 that can move up and down in the direction of arrow X. A transfer roller 31 is supported in the upper part of the case 30 so as to be rotatable about a rotation center O1. This transfer roller 3
1 is made of an elastic body with a specific resistance of approximately 106 angstrom cm. Note that the upper part of the transfer roller 31 is in pressure contact with the lower surface of the photoreceptor drum 9, as shown in FIG.

A fur brush 32 is disposed below the transfer roller 31 in the case 30 and is in pressure contact with the lower surface of the transfer roller 31. The fur brush 32 is rotationally driven by a drive mechanism (not shown), and the fur brush 32 is rotated by a drive mechanism (not shown).
1 Clean the top. The tip of a blade 33 fixed to the inner wall surface of the case 30 bites into the lower part of the fur brush 32. The blade 33 is for scraping off toner adhering to the fur brush 32 from the fur brush 32.

A cam 34 rotatable about a rotation center O2 is arranged on the lower surface of the case 30. This cam 3
4 rotates around the center O2, the transfer device 13 moves in the X direction. Note that the center O2 is parallel to the center O1.

This copying machine has a control section 4 as shown in FIG.
It has 0. The control unit 40 includes a CPU, ROM, and R.A.
It includes a microcomputer consisting of M, etc. The above-mentioned humidity sensor 21 is connected to the control unit 40,
A signal corresponding to humidity can be input from the humidity sensor 21 to the control unit 40 . Further, a cam drive section 41 including a stepping motor and the like for rotationally driving the cam 34 is connected to the control section 40 . With this cam drive section 41,
The rotational posture of the cam 34 changes. Furthermore, a transfer voltage application section 42 for applying a bias voltage to the transfer roller 31 is connected to the control section 40 . The transfer voltage applying section 42 can apply a bias voltage having a polarity opposite to the charge of the toner on the surface of the photoreceptor drum 9 to the transfer roller 31.

Next, the operation of the above embodiment will be explained. When a copying operation is started, paper is conveyed from a selected portion of the bypass tray 4 and the paper feed cassettes 5 and 6 to the photosensitive drum 9 via the paper conveyance path 17. on the other hand,
Exposure device 8 reads image information from a document placed on document table 2 . Then, an electrostatic latent image is formed on the photoreceptor drum 9 based on the read image information. After unnecessary portions of the electrostatic latent image formed on the photoreceptor drum 9 are removed by a blank lamp 11, the electrostatic latent image is visualized with toner by a developing device 12. The toner image formed on the photoreceptor drum 9 in the developing device 12 is transferred to the transfer device 13.
The image is transferred onto the supplied paper. The paper onto which the toner image has been transferred is subjected to a fixing process in a fixing device 19, and then is discharged to the outside by a discharge roller 20. The surface of the photoreceptor drum 9 after the transfer is cleaned by a cleaning device 1.
4.

In the above copying operation, the humidity sensor 21
measures the humidity near the bypass tray 4 and paper feed cassettes 5 and 6. Then, based on the measured humidity, the cam drive section 41 operates to set the cam 34 at a position corresponding to the humidity.

When the humidity is high, the resistance of the paper is low, so the transfer roller 31 is driven upward, and a wide nip width n1 is set as shown by the dashed line in FIG. This compensates for the tendency for the image density (ID) to decrease due to the decrease in paper resistance, and provides a good transferred image.

On the other hand, when the humidity is low, the resistance of the paper increases, so the transfer roller 31 is lowered as shown by the solid line in FIG. 5, and a narrow nip width n2 is set. When the resistance of the paper increases, the ID tends to become too high.
In this case, by setting a small nip width n2, the ID is corrected and a good transferred image can be obtained.

While the copying operation is not performed, the transfer roller 31
is arranged at the position indicated by the two-dot chain line in FIG. 4, and is separated from the photosensitive drum 9. Thereby, deformation of the transfer roller 31 can be prevented and the durability of the transfer roller 31 can be improved. Furthermore, in the state indicated by the two-dot chain line in FIG. 4, the transfer roller 31 is separated from the photosensitive drum 9, so maintenance work such as replacing the transfer roller 31 can be easily performed.

Table 1 shows the results of an example in which the nip width was changed in accordance with changes in humidity, and the results of a comparative example in which the nip width was not changed.

[Table 1]

As is clear from Table 1, in the case of the example in which the nip width was set appropriately in accordance with changes in humidity (RH), the ID could be maintained at a good value. On the other hand, in the case of the comparative example in which the nip width was not changed, I
D became too low and a good transferred image could not be obtained.

[Other Embodiments] (a) Instead of the above embodiment, a configuration shown in FIG. 5 may be adopted. In FIG. 5, the transfer device 13 is housed in a swing case 50, and the transfer roller 31 can move up and down within the swing case 50. The rotation center O3 of the swing case 50 is common to the photoreceptor drum 9, and the swing case 50 can swing in the Y direction about the center O3. Further, the other end of a coil spring 51, one end of which is fixed to the copying machine main body 1 side, is fixed to the lower end of the swing case 50. This coil spring 51 is arranged in an expanded state, thereby always elastically biasing the swing case 50 toward the left side in FIG. 5. Further, a cam 52 is in contact with the lower part of the swing case 50 from the left side in FIG. This rotation of the cam 52 causes the swing case 50 to spring into the coil spring 51.
It can be rotated in the Y direction against the

According to the configuration shown in FIG. 5, the transfer roller 31 is
By moving the swing case 50 in the Y direction, it is possible to not only respond to changes in humidity, but also to respond to changes in paper thickness by rotating the swing case 50 in the Y direction. Note that the posture of the swing case 50 may be automatically changed by detecting the thickness of the supplied paper using a paper thickness sensor.

(b) In the above embodiment, humidity was used as an environmental factor, but the present invention is not limited thereto, and control may be performed based on other environmental factors such as temperature.

[0027]

In the image forming apparatus according to the present invention, the nip width between the image bearing drum and the transfer roller is changed based on the detection result by the environment detection means. Therefore, according to the present invention, good image quality can be maintained even if the characteristics of the transfer sheet change due to environmental changes. Moreover, since there is no need to employ expensive parts such as a high voltage transformer, manufacturing can be performed at low cost.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional view of a copying machine to which the present invention is adopted.

FIG. 2 is a schematic vertical cross-sectional view of the transfer device.

FIG. 3 is a schematic block diagram of the control unit.

FIG. 4 is a schematic diagram showing its operating state.

FIG. 5 is a schematic side view of another embodiment.

[Explanation of symbols]

8 Exposure device 9 Photoreceptor drum 10 Main charging device 12 Developing device 13 Transfer device 21 Humidity sensor 30 cases 31 Transfer roller 34 Cam 40 Control section 41 Cam drive part

Claims (1)

[Claims] 1. An image forming apparatus for forming an image on a transfer sheet according to image information, the apparatus comprising: an image bearing drum; and a latent image forming apparatus for forming a latent image on the image bearing drum according to the image information. a developing means for developing a latent image on the image bearing drum; a transfer roller that is in pressure contact with the image bearing drum and for transferring the developed image onto the transfer sheet; and an environment detection device for obtaining data regarding the environment. and a nip width changing means for changing the width of the nip between the image bearing drum and the transfer roller based on the detection result by the environment detecting means;
An image forming apparatus equipped with