JPH05341610A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce an amount of waste toner by changing the size of a toner image formed outside an image forming area according to an original image signal. CONSTITUTION:Image exposure is carried out, at the same time the image of an original is read by a one-dimentional image sensor 23, such as the CCD of a digital reading system, to be stored in a storage circuit 15, an image ratio is decided by a comparison circuit 16, the length of a time (t) while blank exposure is turned off during the postrotation is determined, and that the length of a time while it is turned on is controlled by a laser driver circuit 17. By turning off the blank exposure only for (t) seconds during the postrotation, electrostatic charges on an image carrier 1 are not destaticized only for its part, so that this latent image part is formed with a toner image by a developing unit 3. An amount of waste toner as a result of remaining of transfer is estimated by reading the image signal, the amount of waste toner per one copy is kept almost constant by changing the size of the toner image outside the image forming area, and damage to the surface of the image carrier, filming and image flowing, etc., can be prevented.

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 or a printer.

[0002]

2. Description of the Related Art FIG. 6 is a sectional view of a conventional general electrophotographic copying machine. The electrostatic latent image formed on the image carrier 1 by the primary charging device 2 and the image exposure I is visualized as a toner image by the developing device 3 and then transferred onto the transfer material by the transfer charging device 4. The material is a series of separation steps 5a, 5
It is separated from the surface of the image carrier 1 by b and 5c. on the other hand,
Since the image carrier 1 such as a photoconductor is repeatedly used, the toner remaining on the surface after transfer is removed by the cleaner 6. In such a system in which the endless image carrier is repeatedly used, the cleaner 6 plays a very important role. The cleaner 6 basically has a main role of removing the residual toner as described above, but in addition to the residual toner, powder such as paper dust transferred from the transfer material is also present on the image carrier. It is contaminated by foreign substances and discharge products such as Nox generated in each charger, and causes a defective image such as image deletion unless it is removed or cleaned from the image carrier. Therefore, conventionally, the cleaner 6 is often provided with an auxiliary cleaning means such as a cleaning blade 61 for removing residual toner and a cleaning roller 62 for cleaning the paper dust and Nox. Most of these auxiliary means are located on the upstream side of the cleaning blade 61 and come into contact with the image carrier to perform cleaning by mechanically rubbing on the image carrier while removing residual toner paper powder and Nox. .. However, these cleaning blade 61 and cleaning roller 6
The rubbing force of 2 and the like depends on the amount of toner, paper dust, etc. held by each cleaning means. In most cases, the distribution of residual toner and the like in the longitudinal direction of each cleaning means is non-uniform, so that the amount of toner and the like retained in each cleaning means is also non-uniform, resulting in a rubbing force of each cleaning means in the longitudinal direction. Is uneven, the cleaning effect becomes uneven, and image deletion partially occurs, the surface of the image carrier is damaged due to excessive local rubbing force, and filming caused by this causes spots on the transfer material. The harmful effects such as the state-like contamination will occur. Among them, the purpose is to remove paper powder, Nox, etc. together with the residual toner,
This tendency was large in the auxiliary cleaning means.

Therefore, a uniform rubbing force is provided in the longitudinal direction of the cleaning means to prevent damage to the image carrier due to excessive local rubbing force and filming caused thereby, and to partially There has been proposed an image forming apparatus capable of preventing image deletion and obtaining a good image.

That is, an image carrier which forms a toner image on its surface and moves endlessly, a developing means for forming a toner image on its surface, a transfer means for transferring this toner image onto a transfer material, and a transfer means. A cleaning unit for removing residual toner remaining on the surface of the image carrier later, and a toner image pattern forming unit for forming a continuous toner image in the longitudinal direction of the cleaning unit in front of the image forming area on the surface of the image carrier. The image forming apparatus.

[0005]

However, in the above-mentioned conventional example, since the toner image of the same size is always formed in the longitudinal direction of the cleaning means, it corresponds to the toner image collected by the cleaning means. The amount of waste toner is almost constant at all times.However, as residual toner is added to the waste toner, the amount of waste toner increases when a large number of images with a high image ratio are copied, and the waste toner storage container fills up early. There was a problem that became.

The present invention is intended to solve the above problems. That is, according to the present invention, the amount of waste toner per sheet is kept substantially constant, and the surface of the image carrier is damaged.
An object is to provide an image forming apparatus capable of preventing filming, image deletion, and the like.

[0007]

In order to achieve the above object, the present invention provides an image carrier which forms a toner image on the surface thereof and moves endlessly, and a developing which forms a toner image on the surface of the image carrier. And a transfer means for transferring the toner image onto a transfer material, a cleaning means for removing residual toner remaining on the surface of the image carrier after transfer, and a longitudinal direction of the cleaning means outside the image area on the surface of the image carrier. In an image forming apparatus having a toner image pattern forming unit for forming a toner image over the entire area and a unit for reading a document image, the size of the toner image outside the image forming area is changed according to the read document image signal. To have means.

[0008]

According to the present invention, the amount of waste toner due to the transfer residue is estimated by reading the image signal, and the size of the toner image outside the image forming area is changed to make copy 1.
It is possible to prevent damage to the surface of the image carrier, filming, image deletion, etc., while keeping the amount of waste toner per sheet substantially constant.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrophotographic copying machine will be described as a first embodiment of the present invention with reference to FIG.

In FIG. 1, an image carrier 1 is a primary charger 2
Are uniformly charged by the corona, and an electrostatic latent image is formed by the exposing means described later, which is visualized by the first developing device 3 containing the black toner or the second developing device 24 containing the color toners, and the transfer charging device 4 After being transferred onto the transfer paper by means of the separating charger 5 and separating the transfer paper from the image carrier 1, the fixing device 34 fixes the image on the transfer paper. Further, the residual toner on the image carrier 1 is removed by the cleaner 6, the charges on the image carrier are uniformly erased by the pre-exposure lamp 7, and then the above process is repeated.

An illumination lamp 22 for illuminating an original on the original table glass 21 is provided above the image carrier 1, and reflected image light obtained by irradiation of the illumination lamp 22 is moved to movable mirrors 8, 9, 10. The image forming lens 12 and the fixed mirror 11 constitute a first exposure unit L ₁ which leads to the image carrier 1.

Further, the surface of the image carrier 1 is neutralized before and after the exposure of the document by the first exposure means L ₁ , and at the same time, an arbitrary character is formed or the reflected light of the document is read by the CCD 23, and the laser is generated according to the image signal. A second exposure unit L ₂ as a digital exposure unit including a laser unit 18 capable of outputting a beam and a mirror 19 for guiding the laser beam to the image carrier 1 is provided.

The sequence of the copying operation will be described below with reference to FIG. When the user completes various mode settings such as the number of sheets and magnification, the copy operation is started by pressing a copy button (not shown) (copy ON). To describe the case of continuous copying of two sheets, first, the image carrier 1 starts to rotate and at the same time, a blank exposure is performed as a laser unit 1.
The light beam modulated by the semiconductor laser 26 in FIG. 8 is collimated by the collimator lens 27 and then incident on the polygon mirror 28, and the reflected light exits from the laser unit 18 via the fθ lens 29 and is reflected by the reflection mirror. Incident on 19,
The electrostatic charge on the surface of the image carrier 1 is removed to remove the electrostatic charge, and the optical system including the lens moves to a position corresponding to the set magnification, and the transfer material stands by in front of the image carrier 1. It is the front rotation until it enters the state. During this period, a voltage is applied to the primary charger 2 and the image carrier 1 is uniformly charged. However, since the laser unit 18 is driven during this pre-rotation, the electrostatic charge on the image carrier 1 is removed. It

Subsequently, image exposure is performed by the first exposure means L ₁ , and an electrostatic latent image corresponding to the original is formed on the image carrier 1. The subsequent process is as described above.

Simultaneously with this image exposure, the original image is read by a one-dimensional image sensor 23 such as a CCD of a digital reading system as shown in FIG. 3 and stored in a storage circuit 15, and an image ratio is determined by a comparison circuit 16. Then, the time t for turning off the blank exposure at the time of post-rotation is determined, and the laser driver circuit 17 controls the lighting time.

When the blank exposure is extinguished for t seconds during the post-rotation, the electrostatic charge on the image carrier 1 is not eliminated, so that the latent image portion forms the toner image 70 as shown in FIG. To be done. Here, FIG. 4 shows the image forming area 7.
1 is a development view of an image carrier surface 1a showing a first example of a toner image 70 formed behind 1. Since the transfer material has already been transferred at this point, the toner image 70 is not transferred and is directly supplied to the cleaner 6, and the cleaning roller 62 and the cleaning blade 61 are uniformly coated with the toner.

There are two types of toner collected by the cleaner, that is, the toner image 70 and the transfer residual toner that remains without being transferred. The inner transfer residual toner is about 10% of the amount of toner developed as an image, and varies depending on the image ratio. In this embodiment, the image carrier 1 is rotated at a process speed of 200 mm / sec to obtain an image ratio of 10
% Of the original, the turn-off time t after rotation after blank exposure is 0.01 seconds, and if the original has an image ratio of 10% or more and less than 20%, t = 0.005 seconds. In the case of t = 0, 100,000 copies of originals having different image ratios were repeated, but problems such as image deletion, drum scratches, and filming did not occur, and the amount of waste toner was smaller than that before carrying out the present invention. I was able to make it less than 70%.

A second embodiment of the present invention will be described. In the above-described embodiment, the image ratio of the document is calculated as a ratio to the total area of the document, but the rotation axis direction of the image carrier is divided into a plurality of parts, and the image ratio in each divided region is calculated. The width of the toner image may be controlled.

FIG. 5 shows an example of a toner image outside the image forming area when the number of divisions is 6. According to the present embodiment, even if there is a large difference in the image ratio in the rotation axis direction of the image carrier (for example, when the back side is black and the front side is white),
The toner is always supplied uniformly along the longitudinal direction of the cleaner, and good cleaning performance is maintained.

A third embodiment of the present invention will be described. In the embodiment, the image ratio is calculated for each copy and the size of the toner image outside the image forming area is controlled. However, the image forming area is calculated according to the value obtained by integrating the image ratio for each copy. The size of the outer toner image may be controlled. The size of the toner image may be determined based on the determined integral value for each of a plurality of sheets, or the fixed number of toner images may be set when the integral value reaches the determined value without determining the number of sheets. Alternatively, a method of forming

The integrated value of the image ratio may be grasped not in relation to the number of copies but in relation to the number of rotations of the image carrier. That is, when converted as an image ratio per number of rotations of the image carrier, it is possible to compensate for a difference in the number of rotations of the image carrier per copy depending on the copy size.

A fourth embodiment of the present invention will be described. As shown in FIG. 1, when developing with different toners in a device having a plurality of developing devices, the physical properties of the toners are often different, and the amount of toner supplied to the cleaner for each toner is also different for each toner. You may need to change to. Therefore, the two types of filters 30, 31 (for example, red and blue filters) used in the digital reading system of FIG. 3, the reading lens 32, and the CCD 23 detect the color of the original document, and the color is detected by the two developing devices. When developing, it is possible to detect both the color and the image ratio and control the size of the toner image outside the image forming area.

[0023]

As described above, according to the present invention,
Since the size of the toner image formed outside the image forming area is changed according to the original image signal, that is, when the image ratio is large, the toner image is small, and when the image ratio is small, the toner image is supplied to the cleaner. It is possible to reduce the amount of waste toner while keeping the amount substantially constant.

Therefore, according to the present invention, damage to the surface of the image carrier, filming, image deletion, etc. can be prevented and
The amount of waste toner can be reduced as much as possible, and the device can be downsized.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of an operation of the image forming apparatus of FIG.

FIG. 3 is a plan view showing the digital reading system of FIG. 1.

FIG. 4 is a development view of the surface of an image carrier showing one example of the toner image formed behind the image forming area.

FIG. 5 is a development view of the surface of an image carrier showing another example of the toner image formed behind the image forming area.

FIG. 6 is a sectional view showing an example of a conventional image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier 2 ... Primary charging device 3 ... Developing device 4 ... Transfer charging device 6 ... Cleaner 15 ... Storage device 16 ... Comparison circuit 17 ... Laser driver circuit 23 ... CCD

Claims (1)

[Claims] 1. An image carrier that forms a toner image on the surface and moves endlessly, a developing unit that forms the toner image on the surface of the image carrier, and a transfer unit that transfers the toner image onto a transfer material. Cleaning means for removing residual toner remaining on the surface of the image carrier after transfer, and toner image pattern forming means for forming a toner image outside the image area on the surface of the image carrier along the longitudinal direction of the cleaning means. An image forming apparatus having means for reading a document image, further comprising means for changing a size of a toner image outside the image forming area according to a read document image signal.