JPH11119562A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the register of a transfer material, to simplify and miniaturize the device, and to obtain satisfactory transfer performance by providing detection means between upstream and downstream image-forming means in the direction of the carrying of the recording material for detecting the position of the front end of the recording material. SOLUTION: Four transfer means, transfer rollers 7a-7d, are arranged opposite the electrophotographic photoreceptor-drums 1a-1d of the image-forming means A-D respectively. Also, between the positions of transfer formed by nips between the photoreceptor drums 1a-1d and the corresponding transfer rollers 7a-7d in the direction of the carrying of the recording material P, recording-material- front-end detection sensors 9a-9c are provided as the detection means for detecting the position of the front end of the recording material P. By carrying out an image transfer operation by the independent image-forming means A-D and transfer rollers 7a-7d according to detection information obtained by the detection sensors 9a-9c, the register of the recording material P is facilitated even in the case the device is equipped with the plurality of image forming means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer, and more particularly to an image forming apparatus having a plurality of image forming means.

[0002]

2. Description of the Related Art Conventionally, in a copying machine or a laser beam printer using an electrophotographic process, as shown in FIG.
Four image forming units A to D of yellow, magenta, cyan and black are provided adjacently from the upstream side to the downstream side in the conveying direction of the recording material P, and these image forming units A to D are provided.
D, one transfer belt 51 faces the image forming units A to
D, the photosensitive drums 1a to 1d are stretched over the entire range facing each other.
Electrodes 52a to 52d to which a transfer voltage is applied are arranged on the back side of the transfer belt 51 opposed to .about.1d.

Then, the recording material P is fed out by a feeding roller 6, separated and fed one by one by a separating means (not shown), and is placed between the photosensitive drum 1a and the transfer belt 51 arranged at the most upstream side. When entering, the photosensitive drum 1a rotating in the direction of the arrow in FIG. 4 is charged to a predetermined potential by the charging device 2a, and then, an image forming exposure optical system based on color separation of a color original image, and a time series of image information Receiving optical image information from an exposure device 3a comprising a scanning exposure optical system or the like by a laser scanner for outputting a laser beam modulated in accordance with an electric digital pixel signal, the image is statically corresponding to a yellow component image of a target color image. An electrostatic latent image is formed.

Then, the electrostatic latent image is developed into a yellow color by the developing device 4a. The yellow developed image on the photosensitive drum 1a is electrostatically attracted by applying a predetermined transfer voltage to an electrode 52a disposed on the back side of the transfer belt 51, and is transferred to the recording material P on the transfer belt 51. You. The residual developer is cleaned by the cleaning device 5a.

The image forming means B for the magenta component, the image forming means C for the cyan component, and the image forming means D for the black component are sequentially visualized in the same process as the image forming means A for the yellow component, and are transferred. The four types of toner images are electrostatically transferred onto the recording material P conveyed by the belt 51 in a superimposed manner to form a composite color toner image corresponding to the target color image.

On the other hand, the registration of the recording material P is performed by fine adjustment, for example, by slightly changing the angle of a mirror used in the optical system.

The recording material P on which the color image has been transferred is fixed to a fixing roller 8a and a pressure roller 8b which are heated to a predetermined temperature.
The toner image is permanently fixed to the recording material P and is discharged outside the apparatus by being heated and pressurized in the fixing device 8.

[0008]

However, in the above-mentioned conventional example, the recording material P is conveyed to a position corresponding to the four image forming means A to D by one transfer belt 51,
The registration of the recording material P becomes difficult, and a registration adjustment mechanism is separately required, which causes a problem that the apparatus becomes complicated and large.

Further, since it is necessary to guarantee the resistance value of the transfer belt 51 over the entire circumference, there is a problem that it takes a long time to inspect the resistance value, which leads to a decrease in yield and an increase in cost.

[0010] The present invention is to solve the above problems,
An object of the present invention is to provide an image forming apparatus in which even when a plurality of image forming units are provided, registration of a recording material is easy, the apparatus can be simplified and downsized, and good transfer performance can be obtained. It will not be provided.

[0011]

An image forming apparatus according to the present invention for achieving the above object is an image forming apparatus having a plurality of image forming means using an electrophotographic process. Transfer means for transferring the toner image formed on the recording material to the plurality of image forming means, respectively, and an image forming means on the upstream side in the recording material transport direction,
A detecting means for detecting the leading end position of the recording material is provided between the image forming means and the subsequent image forming means on the downstream side in the recording material conveyance direction.

According to the present invention, as described above, transfer means are provided to face a plurality of image forming means, respectively, and the image forming means on the upstream side in the recording material conveying direction and the downstream part in the recording material conveying direction following the image forming means are provided. A detecting means for detecting the leading end position of the recording material between the image forming means and the image forming means on the side, so that the image transferring operation can be performed independently by the image forming means and the transferring means in accordance with information detected by the detecting means. Accordingly, even when a plurality of image forming units are provided, the registration of the recording material becomes easy, and the respective toner images can be superimposed without displacement.

In other words, the transfer performance of the other image forming means is improved as in the case where the recording material P is conveyed to the positions corresponding to the four image forming means A to D by one transfer belt 51 shown in the above-mentioned conventional example. Considering complicated transfer control is necessary,
Alternatively, the problem that the controllable standard width is limited is solved, and the arrangement of each image forming unit and the transfer unit can be freely set, so that the detecting unit for detecting the leading end position of the recording material between each image forming unit can be freely set. It is possible to dispose the toner images without complicated control for registration of the recording material, and it is possible to superimpose each toner image without displacement by a simple detecting means.

In the case where the transfer control is performed such that the transfer charge amount applied to the recording material of the plurality of transfer means increases as the toner images are superimposed, the transfer direction in the recording material conveyance direction in which the plurality of toner images are superimposed on each other. In the image forming means on the side, a sufficient electrostatic attraction force can be ensured, so that scattering of the toner image is prevented, image defects are prevented, and good transfer can be performed.

Further, the resistance values of the plurality of transfer means are arranged such that the resistance becomes lower as the toner images are superimposed in order from the highest, and the resistance is fixed to the transfer means facing a predetermined image forming means when there is no recording material. And a transfer voltage determining means for determining a transfer voltage to be applied when the recording material passes based on the bias voltage applied at the time of the constant current, and transferring the transfer voltage determined by the transfer voltage determining means to another transfer voltage. It is characterized in that the voltage is applied to all the transfer units arranged opposite to the image forming unit.

According to the above configuration, by applying the same transfer voltage to all transfer means, the amount of transfer charge applied to the recording material increases as the toner images are superimposed, and the electrostatic attraction force increases. Sufficient electrostatic attraction force can be ensured even in the image forming means on the downstream side in the recording material conveyance direction where a plurality of toner images are superimposed, so that scattering of toner images is prevented, image defects are prevented, and good transfer is achieved. Can be implemented.

Further, the image forming apparatus has at least two components.
An image forming apparatus in which one transfer step is controlled by one transfer voltage control circuit, wherein the lower the resistance of the plurality of transfer units controlled by the one transfer voltage control circuit, the lower the resistance, the more the toner images are superimposed. And a constant current is applied to the transfer means when there is no recording material using one of the transfer means, and is applied when the recording material passes based on the bias voltage applied at the constant current. A transfer voltage determining means for determining a transfer voltage is provided, and the transfer voltage determined by the transfer voltage determining means is applied to other transfer means.

According to the above configuration, by applying the same transfer voltage to a plurality of transfer means controlled by one transfer voltage control circuit, the amount of transfer charge applied to the recording material increases each time a toner image is superimposed. As a result, a sufficient electrostatic attraction force can be secured even in the image forming means on the downstream side in the recording material conveyance direction where a plurality of toner images are superimposed, so that scattering of the toner image is prevented. Defects can be prevented and good transfer can be performed.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of an image forming apparatus according to the present invention will be specifically described with reference to the drawings. FIG. 1 is a schematic sectional view showing the configuration of the first embodiment of the image forming apparatus according to the present invention.

As shown in FIG. 1, a full-color image forming apparatus as an embodiment of the image forming apparatus according to the present invention comprises four image forming means A to D for yellow, magenta, cyan and black, each of which is a recording material P. The image forming units A to D are provided adjacent to each other from the upstream side to the downstream side in the transport direction.
Of each of the electrophotographic photosensitive drums 1a to 1d of FIG.
Transfer rollers 7a to 7d serving as two transfer units are arranged.

Around the photosensitive drums 1a to 1d, charging devices 2a to 2d, exposure devices 3a to 3d, developing devices 4a to 4d, and cleaning devices 5a to 5d are arranged, respectively.

Further, in the conveying direction of the recording material P, a leading end position of the recording material P is detected between each transfer position formed by a nip portion between each of the photosensitive drums 1a to 1d and each of the transfer rollers 7a to 7d. Recording material leading edge detection sensor 9a serving as detection means
To 9c.

Then, the recording material P is fed out by the feed roller 6, separated and fed one by one by a separating means (not shown), and placed between the photosensitive drum 1a and the transfer roller 7a which are arranged at the most upstream side. When the photosensitive drum 1a enters, the photosensitive drum 1a rotating in the direction of the arrow in FIG. 1 is charged to a predetermined potential by the charging device 2a, and then, an image forming exposure optical system based on color separation of a color original image, and a time series of image information. Receiving optical image information from an exposure device 3a comprising a scanning exposure optical system or the like by a laser scanner for outputting a laser beam modulated in accordance with an electric digital pixel signal, the image is statically corresponding to a yellow component image of a target color image. An electrostatic latent image is formed.

Next, the electrostatic latent image is visualized in yellow by the developing device 4a. The yellow developed image on the photosensitive drum 1a is electrostatically transferred by applying a DC voltage to the core of the transfer roller 7a from a power source (not shown). In the present embodiment, since a negatively charged toner is used, the voltage applied to the metal core of the transfer roller 7a is a positive voltage.
Note that the residual developer is cleaned by the cleaning device 5a.

Next, the recording material P is conveyed to the image forming means B, and the magenta component image is transferred in the same manner as in the above-described image forming means A. However, it is necessary to register the image so that the writing position of the image is aligned. . Therefore, the leading edge position of the recording material P is detected by the recording material leading edge detection sensor 9a, and a control unit (not shown) determines the toner image writing position of the image forming unit B from the transport length of the recording material P and the electrophotographic process speed.

Similarly, for the cyan component image of the image forming means C and the black component image of the image forming means D, the position of the recording material P is similarly detected by the recording material leading edge detection sensors 9b and 9c, and a control unit (not shown) is used. The writing position of the toner image is determined based on the signal.

In the transfer method, a positive voltage is applied from a power source (not shown) to the cores of the transfer rollers 7b to 7d to electrostatically develop the toner on the recording material P in the same manner as in the case of the yellow developed image described above. Transfer the image.

The transfer method will be described in more detail. The resistance value of the transfer rollers 7a to 7d is 1 × 10 ⁶ to 1 ×.
And used as a 10 ⁹ Omega, transcriptional control a constant current is applied to one of the core metal of the transfer roller 7a~7d when no recording material P, on the basis of the applied bias voltage at the time of constant current A method is used in which a constant bias voltage determined by a transfer voltage determining means (not shown) that determines a bias voltage to be applied when the recording material P passes is applied when the recording material P passes.

In this embodiment, when there is no recording material P, +2 μm
A constant current of A is applied, and each of the transfer rollers 7a to 7a when the recording material P passes a transfer voltage of 1.25 times the bias voltage thereof.
7d is applied to the core metal.

As for the recording material leading end detection sensors 9a to 9c, a mechanical sensor of a mold is arranged, and an optical sensor (not shown) for detecting the presence or absence of light transmission when the sensor falls due to the passage of the recording material P is separately provided (not shown). The start position of each toner image is determined by software-controlling the timing.

As described above, the yellow component image forming unit A, the magenta component image forming unit B, the cyan component image forming unit C, and the black component image forming unit D are sequentially visualized in the above-described process. Each photosensitive drum 1a-1
d and the transfer rollers 7a-7d, the four types of toner images are electrostatically transferred onto the recording material P conveyed in a superimposed manner to form a composite color toner image corresponding to the target color image.

The recording material P on which the color image has been transferred is fixed to a fixing roller 8a heated to a predetermined temperature and a pressure roller 8b.
The toner image is permanently fixed to the recording material P and is discharged outside the apparatus by being heated and pressurized in the fixing device 8.

As described above, the four image forming units A to D
By making the respective transfer rollers 7a to 7d independent, it is possible to provide the recording material leading edge detection sensors 9a to 9c between the respective image forming means A to D in the conveying direction of the recording material P. As in the example, fine adjustment such as slightly changing the angle of a mirror used in the optical system for each of the image forming units A to D for registration is unnecessary, and the registration registration mechanism is inexpensive and simple.

The detecting means for detecting the position of the leading end of the recording material P is not limited to the present embodiment.
May be configured to directly detect the tip position of the light.

Next, a second embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 2 is a schematic sectional view showing the configuration of the second embodiment of the image forming apparatus according to the present invention. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

In the first embodiment, the transfer rollers 7a to 7a
The resistance value of 7d, the transfer voltage applied to the core metal of the transfer rollers 7a to 7d, or the amount of transfer charge on the back side of the recording material P are not particularly specified in the image forming units A to D. In the present embodiment, the transfer control is performed so that the transfer charge amount applied to the recording material P of the transfer rollers 7a to 7d increases as the toner images are superimposed, thereby improving the transferability when the toner images are superimposed.

In FIG. 2, the resistance values of the transfer rollers 7a to 7d are in the range of 1 × 10 ⁶ to 1 × 10 ⁹ Ω. In particular, the resistance value of the transfer roller 7a Ra> the resistance value R of the transfer roller 7b
b> the resistance value Rc of the transfer roller 7c> the resistance value Rd # of the transfer roller 7d.

The method of determining the transfer voltage applied to the core metal of each of the transfer rollers 7a to 7d is as follows. Only the transfer roller 7a is provided with a transfer voltage control circuit 21 also serving as a transfer voltage determination means, and the other transfer rollers 7b to 7d Are connected in parallel to the transfer voltage control circuit 21 via the switch S1.

First, the transfer voltage to be applied to the metal core of the transfer roller 7a when there is no recording material P is determined in the same manner as in the first embodiment with the switch S1 turned off. Next, the switch S1 is connected when the recording material P sequentially passes through the image forming units A to D, so that the same transfer voltage is applied to the transfer rollers 7a to 7d.

With the above configuration, each of the transfer rollers 7a to 7d
Is a relation of {Ra>Rb>Rc> Rd} and the transfer voltage applied to the core metal of the transfer rollers 7a to 7d is the same, the transfer charge amount given to the back surface of the recording material P is ｛ Image forming unit A <Image forming unit B <Image forming unit C <
The number increases in the order of the image forming means D #.

On the other hand, when another toner image is superimposed and transferred on an already formed toner image, the toner image is directly transferred onto the surface of the recording material P by the thickness of the previously formed toner. Therefore, a large amount of transfer charge is required.

Therefore, in this embodiment, the amount of transfer charge applied to the back surface of the recording material P increases in the order of {image forming means A <image forming means B <image forming means C <image forming means D}, and toner images are superimposed. Since the electrostatic attraction force increases each time, a sufficient electrostatic attraction force can be ensured even in the image forming means on the downstream side in the conveying direction of the recording material P on which a plurality of toner images are superimposed, so that the toner image is scattered. To prevent image loss and perform good transfer.

For example, in the above configuration, the transfer rollers 7a-7
If a separate transfer voltage control circuit 21 is provided for each d and independently controlled, this leads to an increase in the size and cost of the apparatus.
In the present embodiment, only one transfer voltage control circuit 21 is required, and the apparatus can be reduced in size with a simple configuration and the cost can be reduced.

In this embodiment, an example is shown in which the transfer voltage control circuit 21 is provided only on the transfer roller 7a of the image forming means A. However, the transfer rollers 7b-7d of the other image forming means B-D are shown. May be provided with a transfer voltage control circuit 21 and the remaining transfer rollers may be connected in parallel to the transfer voltage control circuit 21 via the switch S1 in substantially the same manner as described above. The charge amount is as follows:
<Image forming unit B <Image forming unit C <Image forming unit D #
And the same effect as described above can be obtained.

Next, a third embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 3 is a schematic sectional view showing the configuration of the third embodiment of the image forming apparatus according to the present invention. The same components as those in the first and second embodiments are denoted by the same reference numerals, and description thereof is omitted.

In the second embodiment, by providing one transfer voltage control circuit 21 for the four transfer rollers 7a to 7d, the structure is simple and the size and cost of the apparatus can be reduced. On the other hand, transfer rollers 7a to 7
The resistance value of d needs to be set widely, and there is a problem in that including layers, it becomes complicated in terms of manufacturing.

Therefore, in this embodiment, the image forming means A and B are constituted as one set, and the image forming means C and D are constituted as another set, and the transfer voltage control circuit 31, which also serves as the transfer voltage determining means, is used for each set. 32 are provided one by one, and each transfer roller 7a-
The resistance value of 7d is set to {Ra> Rb}, {Rc> Rd}.

In this embodiment, the transfer voltage control circuit 31 is provided on the transfer roller 7a of the image forming means A, and the image forming means B
The transfer voltage control circuit 31 is connected to the transfer roller 7b via a switch S2. Similarly, a transfer voltage control circuit 32 is provided on the transfer roller 7c of the image forming means C, and the transfer voltage control circuit 32 is connected to the transfer roller 7d of the image forming means D via a switch S3.

With the above configuration, the resistance of the transfer rollers 7a to 7d can be set regardless of Ra / Rb and Rc / Rd, so that the manufacturing complexity of the transfer rollers 7a to 7d can be reduced. Other configurations are the same as those of the first and second embodiments, and substantially the same effects can be obtained.

As another configuration, the transfer voltage control circuit 31
Is provided on the transfer roller 7b of the image forming means B, and the transfer voltage control circuit 31 is connected to the transfer roller 7a of the image forming means A via the switch S2. The image forming means C provided on the transfer roller 7d
Even when the transfer voltage control circuit 32 is connected to the transfer roller 7c via the switch S3, substantially the same effect as described above can be obtained.

[0051]

Since the present invention has the above-described configuration and operation, a transfer unit is provided in opposition to a plurality of image forming units, and the image forming unit on the upstream side in the recording material conveyance direction and the subsequent image forming unit are provided. The detecting means for detecting the leading end position of the recording material is provided between the image forming means and the image forming means on the downstream side in the recording material conveying direction, so that the independent image forming means and the transferring means can be used in accordance with the information detected by the detecting means. By performing the image transfer operation, even when a plurality of image forming units are provided, the registration of the recording material becomes easy, and the respective toner images can be superimposed without displacement.

Therefore, the problem that complicated transfer control is required in consideration of the transfer performance of other image forming means as in the conventional example, or that the controllable standard width is limited, is solved. Since the arrangement of the forming means and the transfer means can be freely set, a detecting means for detecting the leading end position of the recording material can be freely arranged between the image forming means, and complicated control is required for the registration of the recording material. In addition, each toner image can be superimposed without displacement by a simple detecting means, and furthermore, the size and cost of the apparatus can be reduced.

In the case where the transfer control is performed so that the amount of transfer charge applied to the recording material of the plurality of transfer means increases as the toner images are superimposed, the transfer direction in the recording material conveying direction in which the plurality of toner images are superimposed is reduced. In the image forming means on the side, a sufficient electrostatic attraction force can be ensured, so that scattering of the toner image is prevented, image defects are prevented, and good transfer can be performed.

Further, the resistance values of the plurality of transfer means are arranged so that the resistance becomes lower as the toner images are superimposed in order from the highest, and the resistance is fixed to the transfer means facing a predetermined image forming means when there is no recording material. A current is supplied, and a transfer voltage determining means for determining a transfer voltage to be applied when the recording material passes based on the bias voltage applied at the time of the constant current is provided. The same transfer voltage determined by the transfer voltage determining means is provided. By applying the voltage to all the transfer units disposed opposite to the other image forming units, the amount of transfer charge applied to the recording material increases as the toner images are superimposed, and the electrostatic attraction force increases. In the image forming means on the downstream side in the recording material conveyance direction where a plurality of toner images are superimposed, a sufficient electrostatic attraction force can be secured, so that scattering of toner images is prevented, image defects are prevented, and good transfer is realized. Can.

Further, the image forming apparatus has at least two
An image forming apparatus in which one transfer step is controlled by one transfer voltage control circuit, wherein the lower the resistance of the plurality of transfer units controlled by the one transfer voltage control circuit, the lower the resistance, the more the toner images are superimposed. And a constant current is applied to the transfer means when there is no recording material using one of the transfer means, and is applied when the recording material passes based on the bias voltage applied at the constant current. A transfer voltage determining means for determining a transfer voltage is provided, and the same transfer voltage determined by the transfer voltage determining means is applied to a plurality of transfer means controlled by one transfer voltage control circuit to give the recording material. Since the amount of transfer charge increases each time a toner image is superimposed and the electrostatic attraction force is increased, sufficient electrostatic attraction can be achieved even in the image forming means on the downstream side in the recording material conveyance direction where a plurality of toner images are superimposed. It is possible to secure an image defect is prevented to prevent the scattering of toner images can implementation good transfer.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a configuration of a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic sectional view illustrating a configuration of an image forming apparatus according to a second embodiment of the invention.

FIG. 3 is a schematic sectional view illustrating a configuration of a third embodiment of the image forming apparatus according to the invention.

FIG. 4 is a diagram illustrating a conventional example.

[Explanation of symbols]

1a to 1d: photosensitive drum, 2a to 2d: charging device, 3
a to 3d exposure apparatus, 4a to 4d developing apparatus, 5a to 5
d cleaning device, 6 feeding roller, 7a to 7d
Transfer roller, 8: Fixing device, 8a: Fixing roller, 8b: Pressure roller, 9a to 9d: Recording material leading edge detection sensor, 21, 3
1, 32: transfer voltage control circuit, A to D: image forming means, P
... Recording material, S1, S2, S3 ... Switch

Claims (4)

[Claims] 1. An image forming apparatus having a plurality of image forming means using an electrophotographic process, wherein the transfer means for transferring a toner image formed on each of the image forming means to a recording material is provided by the plurality of image forming means. Detecting means for detecting the position of the leading end of the recording material is provided between the image forming means on the upstream side in the recording material transport direction and the image forming means on the downstream side in the recording material transport direction subsequent thereto. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the transfer control is performed such that the amount of transfer charge applied to the recording material of the plurality of transfer units increases as the toner images overlap. 3. The transfer device according to claim 1, wherein the plurality of transfer units are arranged such that the resistance is lower as the toner images are superimposed on the transfer unit in descending order. And a transfer voltage determining means for determining a transfer voltage to be applied when the recording material passes based on the bias voltage applied at the time of the constant current, and transferring the transfer voltage determined by the transfer voltage determining means to another transfer voltage. The image forming apparatus according to claim 1, wherein the voltage is applied to all transfer units arranged to face the image forming unit. 4. An image forming apparatus in which at least two transfer processes are controlled by one transfer voltage control circuit,
A plurality of transfer means controlled by one transfer voltage control circuit are arranged so that the resistance becomes lower as the toner images are superimposed in descending order, and one of the transfer means is used when there is no recording material. A constant current is supplied to the transfer means, and a transfer voltage determining means for determining a transfer voltage to be applied when the recording material passes based on the bias voltage applied at the constant current is provided, and the transfer determined by the transfer voltage determining means is provided. The image forming apparatus according to claim 1, wherein the voltage is applied to another transfer unit.