JPH04355486A - Image forming device - Google Patents

Abstract

PURPOSE:To provide a copying machine capable of keeping a state possible to provide a satisfactory transfer image even if the thickness of a sheet is changed. 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, a transfer roller 31 for transferring the developed image pressed onto the photosensitive drum 9 to a sheet, and a paper thickness sensor 21 for detecting the thickness of the sheet. In this device, the nipping width (n) by the photosensitive drum 9 and the transfer roller 31 can be changed by a cam mechanism on the basis of the detection result by the paper thickness 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

2. Description of the Related Art An image forming apparatus (for example, a copying machine) includes a photoreceptor drum, an optical system that forms a latent image on the photoreceptor drum according to image information, and an optical system that forms a latent image formed on the photoreceptor drum. A device is already known that includes a developing device for developing and a transfer roller for transferring the developed image onto paper (see, for example, Japanese Patent Laid-Open Nos. 1-265282 and 1-269969). 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.

[0003] In this device, the transfer roller presses the paper against the photoreceptor drum and the bias voltage applied to the transfer roller causes the photoreceptor drum to be moved between the photoreceptor drum and the transfer roller. The upper toner image 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.

0004

SUMMARY OF THE INVENTION In the above-described image forming apparatus, paper having various thicknesses can be used. When the thickness of the paper changes, the nip width that occurs when the paper is sandwiched between the photosensitive drum and the transfer roller changes. That is, when a thick sheet of paper is sandwiched, the nip width increases, and when a thin sheet of paper is sandwiched, the nip width becomes small.

[0005] As described above, when the nip width changes, it becomes impossible to maintain an appropriate pressure contact state of the paper against the photosensitive drum, and good image transfer becomes impossible.

An object of the present invention is to provide an image forming apparatus that can maintain a state in which a good transferred image can be obtained even if the thickness of the transfer sheet changes.

[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 the developed image to the transfer sheet by pressing against the transfer sheet; a thickness detection means that detects the thickness of the transfer sheet; and a width of the nip between the image bearing drum and the transfer roller is changed based on the detection result by the thickness detection means. nip 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.

Prior to this image transfer operation, the thickness detection means detects the thickness of the transfer sheet. Then, 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 thickness detecting means. As a result, the width of the nip is set so that it has an appropriate value for image transfer while sandwiching the transfer sheet whose thickness has been detected. Therefore, in this case, even if the thickness of the transfer sheet changes, a state in which a good transferred image can be obtained can be maintained.

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. 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.

A paper thickness sensor 21 is provided in the paper transport path 17 for detecting the thickness of the paper supplied to the image forming section constituted by the photosensitive drum 9 and the like. As shown in FIG. 2, the paper thickness sensor 21 includes a semiconductor laser 22 and a light projection lens 2 for irradiating the paper A with laser light.
3, a photo position detection element (PSD) 24 that receives light reflected from the surface of the paper A, and a light receiving lens 25. A drive circuit 26 is connected to the semiconductor laser 22, and a signal amplification circuit 27 is connected to the optical position detection element 24.

As shown in FIG. 3, the transfer device 13 has a case 30 that rotates in the direction of arrow X about a rotation center O1. A transfer roller 31 is supported in the upper part of the case 30 so as to be rotatable about a rotation center O2. The transfer roller 31 is made of an elastic material having a specific resistance of about 106 angstroms.cm. Note that the upper part of the transfer roller 31 is connected to the photoreceptor drum 9 as shown in FIG.
It is in pressure contact with the bottom surface of.

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 31 rotatable about a rotation center O3 is arranged on the lower surface of the case 30. This cam 3
4 rotates around the center O3, the transfer device 13 rotates in the X direction. In addition, each center O1, O2, O
3 are parallel to each other.

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 paper thickness sensor 21 is connected to the control unit 40.
A signal corresponding to the paper thickness can be input from the paper thickness sensor 21 to the control section 40 . Further, a cam drive unit 41 including a stepping motor and the like for rotationally driving the cam 30 is connected to the control unit 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 . An electrostatic latent image is formed on the photoreceptor drum 9 based on the read image information. Photosensitive drum 9
After unnecessary portions of the electrostatic latent image formed thereon are removed by a blank lamp, the electrostatic latent image is visualized with toner by a developing device 12. The toner image formed on the photosensitive drum 9 in the developing device 12 is transferred onto the supplied paper by the transfer device 13. 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 photosensitive drum 9 after the transfer is cleaned by a cleaning device 14.

In the above-described copying operation, while the paper passes through the paper transport path 17, the paper thickness sensor 21 precisely measures the distance to the paper surface, thereby measuring the thickness of the paper. Then, based on the measured thickness, the cam drive unit 4
1 is driven to set the cam 34 at a position corresponding to the thickness. FIG. 5 illustrates the position of the transfer roller 31 moved by this setting operation. In FIG. 5, position P is the position when thin paper is used, position Q is the position when medium thickness paper is used, and position R is the position when thick paper is used. Note that the center O4 is the rotation center of the photoreceptor drum 9.

In FIG. 5, at position R, which is set when the paper is thick, the transfer roller 31 is in pressure contact with the photosensitive drum 9 at the most downstream side in the paper conveyance direction, and the paper discharge direction Y is at the most upward position. be. Then, as the position changes from position Q to position P, the pressure contact position of the transfer roller 31 against the photoreceptor drum 9 shifts to the upstream side in the paper conveyance direction (FIG.
(to the right). At the same time, the paper ejection direction Y is downward. Further, as the position moves from the position R to the position P, the nip width n between the transfer roller 31 and the photosensitive drum 9 gradually increases from the width n1 to the width n2 to the width n3. Note that the amount of change in the nip width n is set so that the optimum nip width for the transfer operation is formed when the paper is sandwiched between the nip portions.

In this embodiment, since the pressure contact position of the transfer roller 31 against the photosensitive drum 9 and the nip width n change as described above, an appropriate transfer operation can be maintained depending on the thickness of the paper. That is, here, the nip width n is controlled so that when thicker paper is used, the nip width n becomes smaller, and when the thinner paper is used, the nip width n becomes larger. Therefore, in this case, even if the thickness of the paper used changes, the optimum nip width is always formed and a good transfer operation can be maintained.

Moreover, in this embodiment, as the thickness of the paper becomes thinner, the paper ejection direction Y becomes downward, so even if the paper is weak (that is, thin), it can be reliably separated from the photoreceptor drum 9. It will be held on. In addition, in the case of stiff (that is, thick) paper, it is ejected relatively upward, so that its leading edge is smoothly guided to the paper ejection conveyance device 18 side. In this manner, in this embodiment, the pressure contact position of the transfer roller 31 against the photosensitive drum 9 is also appropriately changed based on the paper thickness detected by the paper thickness sensor 21.

Next, a specific control example will be explained. The diameter of the photosensitive drum is 78 mm, and the diameter of the transfer roller 31 is 16 mm.
The experiment was conducted using mm. The paper used at this time was postcard with a thickness of 0.22 mm, thick paper with a thickness of 0.13 mm, regular paper with a thickness of 0.08 mm, and paper with a thickness of 0.05 mm.
It was a thin paper.

The copying operation was performed under control such that the sum of the amount of penetration of the transfer drum 31 into the photosensitive drum 9 and the thickness of the paper was 0.3 mm (that is, the nip width during the transfer operation was 3.97 mm). That is, in the case of postcards, the amount of bite of the transfer roller 31 is 0.05 mm (that is, the nip width is 1.63 mm), and in the case of thick paper, the amount of biting is 0.15 mm (that is, the nip width is 2 mm).
．． 81 mm), and the amount of intrusion for regular paper is 0.
The copying operation was performed with the transfer roller 31 biting in at 0.25 mm (ie, nip width 3.63 mm) when thin paper was used. As a result, good copy images were obtained on all types of paper.

[Other Embodiments] (a) Instead of the above embodiment, a configuration shown in FIG. 6 may be adopted. In FIG. 6, the rotation center O1 of the transfer device 13 is located near the rotation center O4 of the photoreceptor drum 9. In FIG. Further, the cam 34 is in pressure contact with the side wall surface of the case 30. A coil spring 35 has one end fixed to the copying machine main body 1 side, and the other end of the coil spring 35 fixed to the lower part of the case 30. This coil spring 35 is arranged in an expanded state, thereby always elastically biasing the case 30 toward the left side in FIG. 6.

In the configuration shown in FIG. 6, when the cam 34 rotates, the case 30 rotates in the X direction about the center O1. As a result, as shown in FIG. 7, the nip width n changes from n1 to n2 and then to n3.

With this configuration as well, the nip width and paper feeding direction can be set according to the paper thickness, similar to the operation of the above-described embodiment.

(b) Instead of the above embodiment, the configuration shown in FIG. 8 may be adopted. In FIG. 8, the transfer device 1
The rotation center of 3 is common to the rotation center O4 of the photoreceptor drum 9. In this transfer device 13, a transfer roller 30 is supported by a case 30 that is rotatable around a rotation center O4. A cam 34 is in contact with the left side surface of the case 30 in the figure. Furthermore, a coil spring 35 is arranged in the extended state in the same manner as in the embodiment of FIG. In this case, a subcase 36 is disposed within the case 30, and the subcase 36 can move in the radial direction of the photosensitive drum 9 (in the direction of arrow Z). The transfer drum 31 is rotatably supported by this subcase 36. Furthermore, a second
A cam 37 is arranged. The second cam 37 can move the sub case 36 up and down in the Z direction by rotating. With this configuration as well, the nip width and paper feeding direction can be set according to the paper thickness, similar to the above-described embodiment.

[0029]

In the image forming apparatus according to the present invention, the width of the nip between the image bearing drum and the transfer roller is changed based on the detection result by the thickness detection means. Therefore, according to the present invention, even if the thickness of the transfer sheet changes, a state in which a good transferred image can be obtained can be maintained.

[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 block diagram of the paper thickness sensor.

FIG. 3 is a schematic vertical cross-sectional view of the transfer device.

FIG. 4 is a schematic block diagram of the control unit.

FIG. 5 is a schematic diagram showing its operating state.

FIG. 6 is a schematic side view of another embodiment.

FIG. 7 is a schematic diagram showing the operating state of the embodiment of FIG. 6;

FIG. 8 is a schematic side view of yet another embodiment.

[Explanation of symbols]

8 Exposure device 9 Photoreceptor drum 10 Main charging device 12 Developing device 13 Transfer device 21 Paper thickness 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 a transfer sheet; and detecting the thickness of the transfer sheet. An image forming apparatus comprising: a thickness detecting means; and a nip width changing means for changing the width of a nip between the image bearing drum and the transfer roller based on a detection result by the thickness detecting means.