JPH05281881A - Image forming device - Google Patents

Abstract

PURPOSE:To very efficiently clean residual toner without using a precleaning charger. CONSTITUTION:A cleaning device 9 has a fur brush 11 made of conductive fiber in a roll form, and brought into contact with a photosensitive body 1, to be rotated, in the prescribed direction, power source means 11A and 11B for selectively applying two kinds of voltages to the fur brush 11, and a switching means S1 changing over two kinds of voltages, and a timing control means 25 control the discharging timing of a transfer charger 6 and a separating charger 7, and the changing over timing of the switching means S1, so that a region (c) where a visible pattern for adjusting an image density is formed, does not receive corona discharge by the transfer charger 6 and the separating charger 7, a region (b) except a latent image forming region and the visible pattern forming region, does not receive the corona discharge by the separating charger 7, and simultaneously, a voltage applied to the fur brush 11, is changed over at the time of when the region (c) passes a fur brush position, and at the time except it.

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, and more particularly to an image forming apparatus using a photoconductive photoconductor. This invention can be applied to a copying machine and an optical printer.

[0002]

2. Description of the Related Art A photoconductive, drum-shaped or belt-shaped photosensitive member is rotated to form an electrostatic latent image, the electrostatic latent image is developed, and the visible image obtained by the development is transferred onto a transfer paper. After the electrostatic transfer to the surface, the transfer paper is separated from the photoconductor by the separation charger, the visible image is fixed on the transfer paper to obtain the formed image, and after the transfer paper is separated, the photoconductor is cleaned. The device is well known in the past in relation to copiers and optical printers. Further, in such an image forming apparatus, a latent image pattern for image density adjustment is formed on a photoconductor, the latent image pattern is developed into a visible pattern, and the optical density of the visible pattern is detected. It is also well known to adjust the image density of the formed image based on the image forming process.

FIG. 2 schematically shows a copying apparatus which is one conventional example of an image forming apparatus having an image density adjusting function. The outline and problems of image formation and image density adjustment will be described with reference to this apparatus example.

In the drawings, reference numeral 1 indicates a photoconductive photosensitive member. The photoconductor 1 is formed in a drum shape, is driven to rotate clockwise, and is uniformly charged by the charger 2 to have a predetermined polarity (for the sake of concreteness of description, a positive polarity). The original to be copied is placed flat on the original glass 17 and scanned by the scanning type exposure optical system indicated by reference numeral 3. The exposure optical system image-projects the light image of the document on the peripheral surface of the photoconductor 1,
As a result, an electrostatic latent image corresponding to the original is formed.

Next, the eraser 4 operates to operate the photoconductor 1
Eliminate the unnecessary parts above. The electrostatic latent image formed on the photoconductor 1 is developed by the developing device 5, and a visible image is formed on the photoconductor 1 by the toner 22. The toner 22 is normally negatively charged. The transfer paper S is fed from a cassette (not shown), is sent to a transfer unit, that is, a facing portion between the photoconductor 1 and the transfer charger 6, in synchronization with the movement of the visible image, and is superposed on the visible image. At this time, the transfer charger 6 performs corona discharge having a polarity opposite to that of the toner forming the visible image, that is, a positive polarity, and transfers the visible image onto the transfer sheet S. The transfer paper S on which the visible image has been transferred is neutralized by the AC corona discharge biased to the negative polarity by the separation charger 7 and separated from the surface of the photoconductor. Then, after that, the image is sent to a fixing device (not shown) to fix the visible image, and then discharged to the outside of the device. The corona discharge of the transfer charger 6 and the separation charger 7 is performed only while the charger and the transfer paper S are facing each other.

After the transfer paper is separated, the photoconductor is subjected to corona discharge from the pre-cleaning charger 8 and then cleaned by the cleaning device 9, and is further initialized by receiving static elimination from the static elimination charger 15 and the static elimination lamp 16.

Now, in FIG. 1, the reference pattern 1 having a predetermined image density is provided at the left side of the original glass 17.
8 is provided so that the image of the reference pattern is projected on the photoconductor 1 prior to the image exposure of the photoconductor by the original light image.

By exposure with the reference pattern image, a "latent image pattern" corresponding to the reference pattern is formed on the photoreceptor 1. The latent image pattern is developed by the developing device 5 into a "visible pattern", and its optical density is detected by the sensor 19
Detected by. That is, specifically, the optical density is detected by irradiating the light of the light emitting element on a visible pattern and receiving the reflected light by the light receiving element. Based on this optical density, the density of the formed image to be formed by the image forming structure is adjusted.

Specifically, the image density is adjusted by controlling the charging potential by the charger 2, the original illumination intensity by the exposure optical system, the developing bias, etc. based on the optical density. Further, based on the above optical density, the toner replenishing device 21
Of the toner 2 to the developing device 5 by controlling the replenishment clutch 20 of
2 replenishments are made.

The cleaning device 9 removes residual toner and minute transfer paper fragments remaining on the photoconductor after the transfer paper is separated. The "residual toner" can be roughly classified into three types: transfer residual toner, untransferred toner, and visible pattern forming toner. What is "transfer residual toner"?
The toner that constitutes the visible image to be transferred and is not transferred to the transfer paper. The “untransferred toner” is a toner that adheres to the surface of the photoconductor that does not overlap with the transfer when the visible image is transferred. "Visible pattern composition toner"
Is a toner that constitutes a visible pattern as its name implies.

The "transfer residual toner" is negatively charged at the development stage, but when the transfer paper is separated from the photoconductor, it is strongly positively charged by discharging with the transfer paper which is strongly positively charged. Since it remains on the photoconductor by being charged, it is strongly positively charged after the transfer paper is separated.
The charge distribution is as shown in (A).

"Untransferred toner" is toner that adheres to the photoconductor area that has been neutralized by the eraser. However, these are abnormal toner charges (the toner that should have been negatively charged originally is in the development stage). It is positively charged) and is attached to the surface of the photoconductor by an adhesive force such as Van der Waals force. Therefore, the untransferred toner includes positively charged ones and negatively charged ones, and its charge distribution is shown in FIG.
As shown in (B), it straddles positive and negative.

The "visible pattern forming toner" is not transferred to the transfer paper and is not negatively affected by corona discharge by the transfer charger 6 and the separation charger 7. Therefore, the "visible pattern forming toner" is charged to the original negative polarity. It has a charge distribution as shown in FIG. The amount of visible pattern toner is large, and therefore the peak of the distribution due to the charge distribution is high.

FIG. 3 shows the pre-cleaning charger 8 and the cleaning device 9 in the apparatus example of FIG. The cleaning device 9 includes a fur brush 11 made of conductive fibers, a blade 23, a bias roller 12, a scraper 13, a carrier tool 14, and a power supply means 1.
The main constituent elements are 1A and 12A. Reference numeral 10 indicates a seal for closing the inlet side of the cleaning device.

The above-mentioned three types of residual toner remaining on the surface of the photoconductor after the transfer paper is separated are in different charged states as described above, and the entire residual toner is required to be electrically cleaned by the fur brush 11. Is preferably aligned to the same charge polarity. In that case, the charge polarity to be aligned should be the same as the charge polarity (negative polarity in the example in the description) of the "visible pattern toner", which has the largest amount of residual toner. After that, the fur brush 11 to which a positive voltage is applied
It is better to clean with.

The pre-cleaning charger 8 is for aligning the charging polarities of the residual toner as described above, and at the position immediately before the cleaning device 9, the AC corona discharge biased to the residual toner is negative. Give.

However, it is difficult to make the polarity of the residual toner completely negative by the AC corona discharge of the pre-cleaning charger 8. For example, the “transfer residual toner” having the charge distribution as shown in FIG. 4A and the “untransferred toner” having the charge distribution as shown in FIG. 4B have been subjected to corona discharge by the pre-cleaning charger. After that, as shown in FIGS. 3D and 3E, some toners are still positively charged.

When the residual toner in such a state is cleaned by the fur brush 11 to which a positive voltage is applied from the power supply means 11A, the toner in the shaded portions in FIGS. 4D and 4E is removed from the photoconductor. It remains unremoved. These must be removed by the blade 23, but in order to obtain a sufficient cleaning effect, the pressure of the blade 23 against the surface of the photoconductor must be increased considerably, and the blade 23 adversely affects the life of the photoconductor. There is a fear of giving.

[0019]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and is a novel image forming apparatus capable of extremely efficiently cleaning residual toner without the need for a pre-cleaning charger. For the purpose of providing.

[0020]

SUMMARY OF THE INVENTION The image forming apparatus of the present invention is "a photoconductive drum-shaped or belt-shaped photosensitive member is rotated to form an electrostatic latent image, and the electrostatic latent image is developed by a developing device. After the development, the visible image obtained by the development is electrostatically transferred onto the transfer paper by the corona discharge of the transfer charger, and then the transfer paper is separated from the photoconductor by the corona discharge of the separation charger to transfer the visible image. It is an apparatus that carries out an image forming process of fixing the image on paper to obtain a formed image, and cleaning the photoconductor after separating the transfer paper. " The formation of the electrostatic latent image
As in the example described above, it may be performed by an image exposure method in which a light image of an original is projected onto a uniformly charged photoreceptor.
An electrostatic latent image may be formed by performing optical writing on the uniformly charged surface of the photoconductor.

An image forming apparatus according to a first aspect of the invention has an image density adjusting mechanism and a timing control means. The "image density adjusting mechanism" forms a latent image pattern for adjusting the image density outside the electrostatic latent image forming area of the photoconductor, develops this latent image pattern with a developing device to form a visible pattern, and This mechanism detects the optical density and adjusts the image density of the formed image in the image forming process based on the detection result.
The “electrostatic latent image forming area” refers to a photoconductor area to be superposed on the transfer paper when the visible image is transferred. The "outside of the electrostatic latent image forming area" in which the latent image pattern for adjusting the image density is formed means a portion other than the latent image forming area in the direction in which the surface of the photoconductor moves in the image forming structure.

As the image density adjusting mechanism, various conventionally known ones can be appropriately used. Therefore, the "latent image pattern" may be formed by the method of projecting the image of the reference pattern as in the above-mentioned example, by utilizing the optical writing, or by the method of controlling the charging voltage of the charger. good. Furthermore, the optical density detection of the visible pattern for controlling the image density does not necessarily have to be performed for each image forming process, and may be performed once for a plurality of times. In this case, if the formed latent image pattern is unnecessary, it may be erased by an eraser.

Outside the latent image forming area, the photoconductor area other than the latent image pattern (and also the portion where the latent image pattern is formed when the latent image pattern is unnecessary) is used as a part of the electrostatic latent image forming process. The charge is removed by the eraser.

The "timing control means" controls at least the timing of the transfer charger, the separation charger and the cleaning device.

In the image forming apparatus according to claim 1,
The "cleaning device" includes a fur brush formed of conductive fibers in a roll shape and rotating in a predetermined direction in contact with the photoconductor, and a power supply unit for selectively applying two kinds of voltages to the fur brush. And a switching means for switching the above two types of voltages.

The "timing control means" ensures that the visible pattern is not subject to corona discharge by the transfer charger and the separation charger, and that the photoconductor portion other than the visible pattern is not subject to the corona discharge of the separation charger outside the latent image forming area. , And the applied voltage to the fur brush,
"When the visible pattern passes through the fur brush position,
At other times ”, the discharge timing of the transfer charger and the separation charger and the switching timing of the switching means are controlled.

The cleaning device may have a "cleaning blade whose edge is in contact with the peripheral surface of the photoconductor after cleaning with a fur brush" (claim 2). In addition, in order to remove the toner transferred to the fur brush from the fur brush, various methods known in the related art can be used, but "a conductive bias roller to which a voltage is applied is brought into contact with the fur brush. It is possible to electrically transfer the toner from the fur brush and bring the scraper into contact with the bias roller to remove the transferred toner from the bias roller ”(claim 3). In this case, the voltage can be applied to the fur brush via the bias roller (claim 4).

[0028]

As described above, in the present invention, among the toners constituting the residual toner, the "transfer residual toner" reaches the cleaning portion due to the corona discharge of the transfer charger and the separation charger, and the "untransferred toner" is transferred. Receiving the corona discharge of only the charger and reaching the cleaning section,
The "visible pattern toner" reaches the cleaning portion without being subjected to corona discharge by the transfer and separation chargers.

Of these three types of residual toner, the "transfer residual toner" and the "visible pattern forming toner" are oppositely charged. The "untransferred toner" is charged to the same polarity as the "transfer residual toner" by the action of corona discharge by the transfer charger.

Therefore, in the state of reaching the fur brush, the "transfer residual toner and untransferred toner" are charged to the same polarity,
The "visible pattern toner" is charged opposite to the other residual toner, and the three types of residual toner can be cleaned by switching the voltage applied to the fur brush.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A shows only a characteristic part of an image forming apparatus to which the present invention is applied to the image forming apparatus described with reference to FIG. In order to avoid complication, the same reference numerals as those in FIGS. 2 and 3 are used for those which are not considered to be confused.

Also in this example, the photoconductor 1 is positively charged, and an electrostatic latent image is formed by projecting and irradiating an original light image, and the toner is negatively charged and used for development. To do. Therefore, the corona discharge having the positive polarity is performed in the transfer charger 6, and the AC corona discharge biased to the negative polarity is performed in the separation charger 7.

In the steps from the transfer of the visible image to the cleaning, the transfer charger 6, the separation charger 7,
The state change of the fur brush 11 is as shown in FIG. In this figure, the area a is the "electrostatic latent image forming area", the area b is the "area other than the latent image pattern forming area" outside the electrostatic latent image forming area, and the area c is the "latent image pattern forming area". .. As shown in the figure, the positive corona discharge by the transfer charger 6 is generated in the regions a and b, and the negative corona discharge corona discharge by the separation charger is generated only in the region a. Therefore, when reaching the cleaning device 9, the charge distribution of the residual toner is as shown in FIG. That is, "transfer residual toner"
Has been positively charged as described above after being subjected to the corona discharge of the transfer charger 6 and the separation charger 7, and its charge distribution is as shown by the curve 1-1 in FIG. The curve is the same as the charge distribution in FIG. 4 (A)). As shown in FIG. 4 (B), the “untransferred toner” is a mixture of positively and negatively charged toner. However, when the transfer charger 6 receives the positive corona discharge,
As shown by the curve 1-2 in (C), the charge distribution has a positive polarity, and the distribution is close to that of the "transfer residual toner" (curve 1-1). On the other hand, the “visible pattern constituent toner” is the same as that at the beginning of development, and the curve 1-3 of FIG.
As shown in Fig. 4, the negative charge distribution (this distribution is shown in Fig. 4C).
Is the same as the charge distribution of).

On the other hand, the polarity of the voltage applied to the fur brush 11 is such that when the regions a and b are cleaned as shown in FIG. 1B (when the regions a and b are in contact with the fur brush 11). ) It has a negative polarity. Therefore, the untransferred toner and the untransferred toner are electrically adsorbed by the fur brush 11 and removed from the surface of the photoconductor. At this time, since the charge distributions of the untransferred toner and the untransferred toner are substantially the same,
Both can be cleaned extremely well.

The visible pattern forming toner is the fur brush 1.
In the position 1, the positive voltage is applied to the fur brush 11, and the negatively-charged “visible pattern forming toner” is satisfactorily removed. The residual toner remaining after being removed by the fur brush 11 is completely removed by the blade 23.

The residual toner electrically adsorbed on the fur brush 11 from the photosensitive member 1 comes into contact with the fur brush 11 and rotates clockwise.
(The voltage is applied from the power supply 12A or 12B), and the scraper 13 made of urethane whose edge is brought into contact with the bias roller 12 is scraped off to the bottom of the housing of the cleaning device, and the transfer means. 14 (in this example, a coil-shaped rotating body) is transferred in the direction orthogonal to the drawing and is collected by the collecting unit.

The voltage applied to the fur brush 11 is switched by switching the power sources 11A and 11B connected to the conductive core portion in which the conductive fibers are planted in a brush shape with the switch S1. Similarly, the voltage applied to the bias roller 12 is switched by switching the power supplies 12A and 12B connected to the bias roller 12 with the switch S2. The power supplies 11A, 11B, 12A and 12B constitute power supply means, and the switches S1 and S2 are "switching means".
Make up. The switches S1 and S2, which are switching means,
The switching control is controlled by the timing control means 25 like the discharge of the transfer charger 6 and the separation charger.

The applied voltages to the fur brush 11 and the bias roller are "transfer residual toner and untransferred toner" sequentially transferred from the photoconductor 1 to the bias roller 12 through the fur brush 11 when cleaning the areas a and b. So that the photoconductor 1 to the fur brush 11,
Further, the potential is sequentially applied to the bias roller in the “positive direction”, and when cleaning the area c, the “visible pattern forming toner” is transferred from the photoconductor 1 to the bias roller 12 via the fur brush 11. The transfer is sequentially performed from the photoconductor 1 to the fur brush 11 and then to the bias roller so that the potential is sequentially increased in the “negative direction”.

According to the experiment, the cleaning efficiency by the fur brush 11 is extremely high, and the use of the blade 23 can be omitted in some cases. Even if the potential of the electrostatic pattern is set to be somewhat low and the amount of toner forming the visible pattern is not so large, the blade 23 may be omitted without causing any problem.

In the above example, the fur brush 11 and the bias roller 12 are separately applied with voltage, but the power supplies 11A and 11B are omitted and the bias roller 12 is directly applied with voltage. A cleaning voltage may be applied to the fur brush 11 via the fur brush 11.

As described above, it is not always necessary to form the latent image pattern in each image forming step, and when the latent image pattern is not formed during the image forming step,
It goes without saying that it is not necessary to switch the applied voltage of the fur brush 11.

[0042]

As described above, according to the present invention, a novel image forming apparatus can be provided. Since the present invention is configured as described above, an extremely good cleaning effect can be realized even without using the pre-cleaning charger required in the conventional cleaning device. Further, since the pre-cleaning charger becomes unnecessary and ozone is not generated by the charger, the amount of ozone generated in the entire image forming apparatus can be effectively reduced.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a conventional image forming apparatus.

FIG. 3 is a diagram showing a cleaning unit in the apparatus of FIG.

FIG. 4 is a diagram for explaining a problem of the conventional technique.

[Explanation of symbols]

 1 Photoconductor 6 Transfer Charger 7 Separation Charger 11 Fur Brush 11A, 11B Power Supply Means S1 Switching Means a Electrostatic Latent Image Forming Area c Latent Image Pattern Forming Area

Claims (4)

[Claims] 1. A photoconductive, drum-shaped or belt-shaped photosensitive member is rotated to form an electrostatic latent image, the electrostatic latent image is developed by a developing device, and a visible image obtained by the development. Is electrostatically transferred onto the transfer paper by the corona discharge of the transfer charger, then the transfer paper is separated from the photoconductor by the corona discharge of the separation charger, and the visible image is fixed on the transfer paper to obtain a formed image. An apparatus for performing an image forming step of cleaning the photoconductor after separation, which forms a latent image pattern for image density adjustment outside the electrostatic latent image forming area of the photoconductor, and forms the latent image pattern on the developing device. To develop a visible pattern, detect the optical density of the visible pattern, and adjust the image density of the formed image in the image forming step based on the detection result; and at least the transfer char. Charger, a separation charger, and timing control means for controlling the timing of the cleaning device. The cleaning device includes a fur brush that is formed of conductive fibers in a roll shape and that contacts the photoconductor and rotates in a predetermined direction. The fur brush has a power supply means for selectively applying two kinds of voltages and a switching means for switching the two kinds of voltages, and the visible pattern receives corona discharge by the transfer charger and the separation charger. When the visible pattern passes through the fur brush position, the photosensitive drum portion other than the visible pattern is not subjected to corona discharge of the separation charger outside the latent image forming area, and the applied voltage to the fur brush is And the discharge of the above-mentioned transfer charger and separation charger by switching at other times. The switching timing of the timing and the switching means, the image forming apparatus is characterized in that so as to control by the timing control means. 2. The image forming apparatus according to claim 1, wherein the cleaning device has a cleaning blade having an edge in contact with the peripheral surface of the photoconductor after cleaning with a fur brush. 3. The image forming apparatus according to claim 1, wherein a conductive bias roller to which a voltage is applied contacts the fur brush to transfer toner from the fur brush.
An image forming apparatus characterized in that a scraper comes into contact with the bias roller to remove the transferred toner from the bias roller. 4. The image forming apparatus according to claim 3, wherein voltage application to the fur brush is performed via a bias roller.