JPH05107886A - Image forming device - Google Patents

Abstract

PURPOSE:To keep the reproducibility of a fine line by a digital exposing means excellent, regardless of the size of the dot diameter, etc., of the digital exposing means, in an image forming device provided with an analog and the digital exposing means. CONSTITUTION:When the dot diameter, etc., of the digital exposing means L1 is changed, and the ratio of the output interval of a dot to its diameter exceeds a fixed value, a detecting means 60 detects the fact. When the digital exposing means L1 forms a latent image, a control means 61 changes at least either of a latent image condition or a developing condition based on a signal from a detecting means 60 to make developing contrast wide.

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 provided with an analog exposure means and a digital exposure means, and more specifically, a laser beam irradiation width of the digital exposure means (hereinafter referred to as an irradiation width).
Regardless of the size of the dot width), it relates to a mechanism for improving the reproducibility of fine lines.

[0002]

2. Description of the Related Art As one of image forming apparatuses, a so-called digital image forming apparatus having both an analog exposure unit and a digital exposure unit is used.
Ana copier is known. Similar to a general analog copying machine, the image forming unit of this copying machine is provided with a charging unit using corona discharge, a developing unit containing a developer (toner), and the like around the photosensitive member, as in a general analog copying machine. A latent image is formed on the surface of the photoconductor charged by the charging unit by the analog exposure unit or the digital exposure unit, the latent image is developed by the developer (toner) of the developing unit, and then the sheet material is toner-coated. Transfer the image.

The analog exposure means for forming a latent image on the photoconductor has a light source such as a halogen lamp for illuminating a document on a document table, and an optical path from the light source to the photoconductor is formed by a reflection mirror, an optical lens and the like. is doing. As a result, the analog exposure unit forms a latent image on the photoconductor that is true to the original image.

On the other hand, the digital exposure means is composed of a laser light source, a polygon mirror, an optical lens and the like, and by appropriately repeating ON / OFF of the laser light source for scanning the photoconductor, a predetermined photoconductor is formed on the photoconductor. Form a digital latent image. This laser light is originally emitted synchronously by pulse width modulation, and at the same time, the laser light is scanned by the polygon mirror in the rotational axis direction (main scanning direction) of the photoconductor, so microscopically the photoconductor The laser light is emitted in a dot shape on the top. A predetermined digital latent image is formed on the photosensitive member by controlling ON / OFF of the irradiation of such dot-shaped laser light. In general, the number of dots per inch in the main scanning direction is expressed in units of DPI, and the number of dots per inch in the rotation direction of the photoconductor (sub scanning direction) is expressed in units of DLI.

The drive signal for the laser light source is input from a computer, for example, by communication, characters, characters, date, etc. stored in the copying machine itself are input, and further, the same light source as the analog exposure means is provided. Alternatively, the reflected light from the original may be input from a digital reading unit that reads an image with an image reader such as a CCD (charge coupled device).

The development of a latent image in such a digital / ana copying machine is different from the development of an LBP (laser beam printer) attached to a computer or a word processor in the reversal development system, and is different from the charging polarity of the photoconductor. Regular development using a developer (toner) of opposite polarity is generally adopted. Therefore, when a latent image is formed on the photoconductor by digital exposure, part of the analog exposure preceding the latent image is blocked, and the area on the photoconductor where the exposure is blocked is digitally exposed by the background scan (image Part of the latent image charge is left and scanning is performed to erase the latent image charge in the non-image area), and a writing image is formed by regular development.

[0007]

By the way, when the above-mentioned dot density is increased in such digital exposure, the ratio of the portion where one dot overlaps the next dot increases. In the digital exposure by the background scan as described above, the dots corresponding to the image forming portion on the photoconductor are not irradiated with laser light,
The laser light is applied only to the dots corresponding to the portions other than the image forming portion. Therefore, even in a dot-shaped portion which is desired to be in a dark state without being irradiated with laser light for image formation, the laser light is irradiated to the end portion thereof, and the thin line is thin especially when the thin line is desired to be output. There will be a problem that it will not be output or will not be output.

In addition, since the dot size is susceptible to various influences, it is the current situation that it varies from copying machine to copying machine.
Therefore, even if the dot density (DPI) is set to a constant value, the reproducibility of fine lines differs from copy machine to copy machine.

Therefore, according to the present invention, at least one of the latent image condition and the developing condition at the time of digital image formation is changed from the condition at the time of analog image formation according to the size of the dot width at the time of digital image formation. It is an object of the present invention to provide an image forming apparatus having good reproducibility of thin lines.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is an analog exposure unit that exposes a photoreceptor charged by a charging unit to form a latent image, and the analog exposure unit. In the image forming apparatus including a digital exposure unit that forms a latent image and a developing unit that develops the latent image, the digital exposure unit continuously performs dot-shaped exposure to form a latent image. And a detection unit that detects whether the ratio between the output interval of these dots and the dot width exceeds a certain value, and at least the latent image condition or the development condition based on the signal from the detection unit. And a control unit that changes one of them when forming a digital image.

[0011]

According to the above structure, when the dot diameter or the like changes and the ratio between the dot output interval and the diameter exceeds a certain value,
When the detection means detects it, and in such a case, when the digital exposure means forms a latent image, the control means changes at least one of the latent image condition and the development condition based on the signal from the detection means. ..

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a so-called digital-ana copying machine. This digital-ana copying machine has two exposure means (digital exposure means and analog exposure means) L.
1 and L2 are combined, and by appropriately using or combining both exposure units, characteristic image formation such as multicolor copying and partial writing of additional information, which cannot be obtained by the analog exposure unit L1, is performed. Is possible.

The copying machine main body C of FIG. 1 has a photosensitive drum 1 rotatably supported in the direction of the arrow. The photosensitive drum 1 is a laminated organic photoreceptor (OPC) having a charge generation layer (CGL) and a charge transport layer (CTL) on the surface of a cylindrical aluminum cylinder. Around the photosensitive drum 1, a primary charger 2 that uniformly charges the photosensitive drum 1 along the direction of rotation (arrow), analog and digital exposure means that forms an electrostatic latent image on the photosensitive drum 1. L ₁ ,
L ₂ , developing devices 24 and 3 for converting the electrostatic latent image into a visible image with toner, a transfer charger 4 for transferring the visible image onto a sheet material P, and a separation charger 5 for separating the sheet material P from the photosensitive drum 1. A cleaner 6 for removing the residual toner on the photosensitive drum 1 and a pre-exposure lamp 7 for removing the potential of the photosensitive drum 1 are provided. The developing units 3 and 24 store, for example, black toner and red toner, respectively, and form black and red toner images on the photosensitive drum 1.

The front side of the copying machine body 1 (right side in FIG. 1)
, A plurality of paper feed cassettes 31 accommodating sheet materials P of different sizes are detachably attached, and the plurality of paper feed cassettes 31 are separated one by one near the upper front edge thereof. Paper feed rollers 31a for feeding the respective sheets are arranged. In addition, these paper feed rollers 31
a from the side of the photosensitive drum 1 to the left side of FIG.
A registration roller 44, a conveyor belt 33, and a fixing roller 34 are arranged in this order, and a paper discharge tray 36 is attached to the left side of the copying machine main body C. All of these registration rollers 44 and the like are rotationally driven by a driving device (not shown), and the registration rollers 44 synchronize the conveyance timing of the sheet material P and the rotation of the photosensitive drum 1 and also the sheet material P. The fixing roller 34 is heated by a heating means (not shown) to fix the toner adhering to the sheet material P.

The flapper 35 is provided with the paper discharge tray 36.
The sheet material P that has been fed is distributed to the paper discharge tray 36 or the intermediate tray inside the copying machine main body C. From the flapper 35 to the intermediate tray 3
The feeding rollers 38, 39, 40, 41 are arranged between 7 and 7, and the feeding rollers 38, 39, 40,
All 41 are rotatably driven by a drive device (not shown). Further, a paper feed roller 42 is arranged above the intermediate tray 37, and the sheet material P sent out by the paper feed roller 42 passes through the paper path 43 and is fed again by the registration rollers 44. Is becoming By using this intermediate tray 37, it is possible to make multiple copies on the same sheet material P. That is, for example, when only black copy is required, the paper feed cassette 31
The sheet material P supplied from the photosensitive drum 1 from the developing device 3
It is sufficient that the black visible image formed by is transferred to the paper discharge tray 36 immediately after being transferred. On the other hand, when the red copy is required in addition to the black copy, the sheet material P after the black copy is finished, By switching the flapper 35, it is carried into the intermediate tray 26, is re-fed to the photosensitive drum 1 from here, and this time the red visible image formed by the developing device 24 is transferred, and is discharged to the paper discharge tray 36. Just do it.

Next, the analog exposure means L ₁ will be described.

A platen glass 2 is provided on the upper surface of the copying machine main body C.
1 is installed, and an illumination lamp 22 capable of scanning along the glass 21 is arranged below the platen glass 21. Further, mirrors 8, 9, 10, 11 and an imaging lens 12 are provided between the glass 21 and the photosensitive drum 1.
Is arranged so that the light emitted by the illumination lamp 22 is reflected by a document (not shown) placed on the platen glass 21 and reaches a predetermined area on the outer peripheral surface of the photosensitive drum 1. Has been done. In addition, these mirrors 8,
The three mirrors 8, 9, 10 on the front side of the optical path (left side in FIG. 1) among 9, 10, 11 move in the direction of arrow a (FIG. 1) in synchronization with the rotation speed of the photosensitive drum 1. Further, the shutter 1 is provided between the mirror 11 at the final stage and the photosensitive drum 1.
3 is provided, and the shutter 13 is configured to block the optical path by driving a light shielding member that is swingably supported by a solenoid or the like. By opening / closing the shutter 13, analog exposure of the photosensitive drum 1 can be switched ON / OFF.

A lamp regulator 14 for adjusting the amount of light is connected to the illuminating lamp 22, and the lamp regulator 14 is provided with a D / A converter 15 in sequence.
The microcomputer 16 and the memory circuit 17 are connected. Further, a developing bias control circuit 20 and a developing bias power source 25 are connected to the D / A converter 15 in order, and the developing bias of the developing units 3 and 24 is controlled by these (described later).

On the other hand, the digital exposure means L ₂ is
It has a laser unit 18 and a digital reader R. Among these, the laser unit 18 has a laser diode 26, and the laser diode 26 turns on / off a laser beam according to a laser drive signal from a laser drive circuit (not shown) which is created based on a video signal. A collimator lens 27 is arranged near the laser diode 26, and the laser light emitted from the laser diode 26 is collimated by the collimator lens 27. The polygon mirror 28 is in the shape of a polygonal column that is rotatably supported, and is rotated at a high speed by a driving device (not shown). An f / θ lens 29 and a mirror 19 are arranged in the optical path of the laser light reflected by the polygon mirror 28. The laser light is applied to the photosensitive drum 1 in a dot shape as described above, but the detection means 60 has a ratio “b / a” (FIG. 3) between the dot output interval a and the dot width b. The control means 61, which is connected to the detection means 60, changes the latent image condition or the development condition by receiving a signal from the detection means 61. ..

The video signal to the laser unit 18 is based on the information input from the outside of the copying machine by communication or the information of characters, characters and date stored in the inside of the copying machine. Some are based. FIG. 2 shows a view of the digital reader R as seen from above. The digital reading device R is disposed at substantially the same height as the image forming lens 12 of the analog exposure means L1 (FIG. 1), and has a specific wavelength band transmission filter 50, 51, a reading lens 52, a photoelectric conversion element (for example, a photoelectric conversion element). CCD) 53. The filters 50 and 51 are two types of color separation filters (for red and blue). Each filter 5
The reading lens 52 is arranged so as to face 0 and 51. The photoelectric conversion element 53 is functionally divided into two parts, half of which converts light passing through the filter 50 into an electric signal, and the other half of which converts light from the filter 51 into an electric signal (FIG. 2). The mirrors 8, 9, 10 and the like on the optical path front side of the filters 30, 31 share the analog exposure means L ₁ . Laser light is emitted from the laser unit 18 based on the original reading information of the photoelectric conversion element 53. In order to form a suitable latent image on the surface of the photosensitive drum 1 by the laser light, the reading information of the photoelectric conversion element 53 is read. On the other hand, known black correction, shading correction, etc. are added.

Next, the operation of the above embodiment will be described.

A case in which the original image includes a black portion and a red portion and the image reading device R is used to automatically perform two-color copying on the sheet material P will be described.

When an operator places an original on the platen glass 21 of the copying machine main body C and presses a copy start button (not shown), the illumination lamp 22 is scanned in the direction of arrow a by a driving device (not shown). Then, the light from the illumination lamp 22 is applied to the entire document. Then, the light reflected from the document is reflected by the mirrors 8, 9 and 10 to change its optical path, passes through the imaging lens 12 and the red filter, and is finally irradiated onto the photosensitive drum 1. This photosensitive drum 1 is 1
Since it is uniformly charged by the secondary charger 2, the surface potential of the photosensitive drum 1 in the exposed portion is lowered according to the amount of light, and an electrostatic latent image is formed. Since the red filter is used in the exposure as described above, only the latent image corresponding to the black portion of the original image is formed on the surface of the photosensitive drum 2, and the latent image corresponding to the red portion is formed. Not done. Further, since the developing device 3 contains charged black toner, the charged toner adheres to the portion of the photosensitive drum 1 where the electrostatic latent image is formed to form a visible image.

On the other hand, the sheet material P is sent out from the sheet feeding cassette 31 by the sheet feeding roller 31a, and the registration roller 44 moves the sheet material P between the lower surface of the photosensitive drum 1 and the transfer charger 4 in accordance with the rotation of the photosensitive drum 1. Delivery in the meantime. The transfer charger 4 is charged with a polarity opposite to that of the charged toner, so that the toner is attracted by an electric force, and as a result, the visible image on the photosensitive drum 1 is transferred onto the sheet material P. To be done. Further, since the separation charger 5 removes the charge of the toner adhering on the sheet material P by neutralization, the sheet material P does not adhere to the photosensitive drum 1. The sheet material P is conveyed by the conveyor belt 33 and fixed by the fixing roller 34. The flapper 35 is the output tray 3
In order to block the path to the sheet 6, the sheet material P is
It is fed by 9, 40, 41 and temporarily placed on the intermediate tray 37. A cleaner 6 provided on the outer periphery of the photosensitive drum 1 removes toner remaining on the photosensitive drum 1 after transfer, and a pre-exposure lamp 7 exposes the photosensitive drum 1 to cause the primary charger 2 to operate. The potential that remains charged is removed.

Next, an image forming process for the red portion of the original is performed.

Next, the red portion is read using the digital reading device R as described above. The black portion of the original D is erased as blank exposure by laser irradiation of the digital exposure means L2, and the red portion of the original D is read by the photoelectric conversion element 23.
The laser exposure is performed according to the output of to form an image. Here, the exposure amounts of the analog exposure unit L ₁ , the illumination lamp 22 constituting the digital exposure unit L ₂ , and the laser unit 18 are adjusted to the standard exposure conditions so that the image does not have light and shade. For example, the latent image potential on the photoconductor 1 by the exposure of the illumination lamp 22 is VL1, and the latent image potential on the photoconductor drum 1 by the exposure of the laser unit 18 is VL2.
Then, the dark potential V = −650V on the surface of the photosensitive drum 1.
On the other hand, the exposure amount of the illumination lamp 22 and the laser unit 18 is adjusted so that VL1 = VL2 = −150V, and each set value is stored in the storage circuit 17.

The digital image at this time is usually formed by so-called background scanning. Therefore, 1
To represent a thin line having a dot width, as shown in FIG. 3, the central dot is not illuminated, but only the dots on both sides are illuminated. Since each dot has an overlapping portion, the thin line output as an image is a line thinned by the overlapping portion.

In the present embodiment, in order to solve this problem, when the dot output interval is a and the dot width is b (FIG. 3), it is determined that the ratio "b / a" exceeds a certain value. When the detection unit 60 detects, the latent image condition and the developing condition that are different between the analog image formation and the digital image formation are used, and the development contrast of the digital value is widened to suppress the thinning of the fine line.

For example, when an analog image is formed, V _D = -650 V | V _D -V _DC |; Development contrast V _DC = -200 V V _DC ; Current bias DC
Min performs image formation on the condition that, at the time of digital imaging, an image is formed on the condition that _{V D = -680V V DC = -50V} . As described above, by widening the development contrast and digital, it is possible to suppress the thinning of the fine line. Further, by changing the latent image condition, it is possible to solve the problem (for example, increase in the potential V _L ) that occurs when the organic semiconductor is used as a photoconductor.

A plurality of dot densities (DPI) may be set when forming a digital image. In this case, the dark potential (V _D ) and the developing bias DC component (V _DC ).
The relationship with is as shown in FIG.

Although the dark potential (V _D ) and the developing bias DC component (V _DC ) are both changed in the above embodiment, only the latter may be changed. In this case, when it is possible to set a plurality of dot densities (DPI),
The relationship between the dot density and the difference between the developing bias DC component (V _DC ) is shown in FIG.

Note that this graph is only an example, and may be appropriately changed when the developing characteristics and the spot diameter change.

In this embodiment, the developing condition is switched when the dot width is b / a = 1.1. However, another value may be used depending on the developing condition in analog.

Next, another embodiment of the present invention will be described with reference to FIGS.

FIG. 6 shows the voltage waveform of the developing bias during analog image formation. The voltage waveform of the developing bias alternates between the + side and the-side at a constant cycle. In this device, the toner is charged to a positive potential, so
When the developing bias voltage is on the positive side, the toner is transferred from the developing device onto the photosensitive drum, and the toner adheres to the dark portion having the potential of -650V. On the other hand, when the developing bias voltage is on the one side, the toner attached to areas other than the dark portion is returned to the developing device again by the electric force.

On the other hand, FIG. 7 shows the voltage waveform of the developing bias during digital image formation. Such a developing bias voltage waveform reduces the duty ratio (for example,
20%), the voltage peak on the + side is increased to increase the amount of toner adhered to the dark portion of the photosensitive drum and suppress the thinning of fine lines.

In the present embodiment, the duty ratio is switched, but the voltage V _PP (difference between the plus side peak voltage and the one side peak voltage in the voltage waveform of the developing bias) is set to that during analog image formation. It may be switched when the digital image is formed. FIG. 8 is a diagram showing the relationship between V _PP and dot density. When a plurality of dot densities (DPI) at the time of digital image formation can be set, the relationship between V _pp and the dot density is as shown in FIG. When the developing bias DC component (V _DC ) is also changed, the relationship shown in FIG. 9 is used. By increasing the voltage V _PP at the time of digital image formation, the amount of toner adhered to the dark portion on the photosensitive drum increases, and it is possible to suppress thinning of fine lines.

FIG. 10 shows an example in which, unlike the multicolor image forming process including transfer twice, the image forming process is performed once without cleaning the photosensitive drum after the completion of the first development. That is, this is a process of distinguishing a black image area and a color (for example, red) image area by one irradiation of the illumination lamp 22 and visualizing them by the corresponding developing devices 3 and 24. For example, the red toner image is superimposed on the previously developed image (for example, the black toner image).

In this embodiment, a color process is used in which recharging and second image exposure / development are successively performed after the first development. The analog exposure H1 is configured as reflected light from the original table 30 as in the above-described embodiment, and the digital exposure H2 is similarly generated by a digital reading system or a laser optical system commanded to drive by an external image signal. 1 Surface is irradiated.

In this process, the photosensitive drum 1 is uniformly charged by the first charger 2, and the analog exposure H1 is applied to form the first latent image. Development is performed by the developing device 3 containing the component type black toner B1. Then, the toner image on the photosensitive drum 1 is charged by the second charger 2 ', and the second exposure beam H2 is emitted as the digital exposure to form the second latent image.
Development is performed by the developing device 24 that is arranged close to the photosensitive drum 1 and that contains the one-component red toner R1. In this way, the steps of charging, image exposure, and development are repeated to form toner images of a plurality of colors on the photosensitive drum 1, and the toner images are collectively transferred to the transfer material.

The black toner B1 and the red toner R1 in the developing devices 3 and 24 are supplied to the developing sleeves B4 and R4 by the fur brushes B2 and R2. The fur brushes B2, R2 not only agitate the toner in the developing devices 3, 24, but also disturb the toner on the developing sleeves B4, R4 after development to prevent so-called sleeve ghost.

Developing bias power sources B7 and R5 are connected to the developing sleeves B4 and R4, respectively, and a DC electric field is formed between the photoconductor 1 and the developing rollers B4 and R4. The toners B1 and R1 on the developing sleeves B4 and R4 are the rubber blades B3 and
It is regulated by R3 and a thin layer of toner is formed and used for development.

Also in this embodiment, the dot output interval a
When the ratio of the dot width b to the dot width b is a certain value or more, the development contrast during digital image formation is set to be wider than that during analog image formation, whereby an image without thin lines can be obtained.

[0045]

As described above, in the digital / ana copying machine,
Since the control unit changes the latent image condition and the like in response to the signal from the detection unit, the dot-exposure area exposed by the digital exposure unit is large, so that there is a possibility that the dot overlaps with the adjacent dot. Even if it is large, the development contrast can be maintained wide. Therefore, even when it is desired to output a thin line by digital exposure by background scanning, it is possible to prevent the thin line from becoming thin or not being output.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus according to the present invention.

FIG. 2 is a plan view showing an image reading device.

FIG. 3 is an explanatory view showing an irradiation area of a laser beam irradiated on a photosensitive drum at the time of forming a digital image.

FIG. 4 Dark potential (V _D ) and development bias DC component (V
Figure showing the relationship with _DC ).

FIG. 5 is a diagram showing a relationship between a difference in dark potential (V _D ) and dot density.

FIG. 6 is a diagram showing a voltage waveform of a developing bias at the time of forming an analog image.

FIG. 7 is a diagram showing a voltage waveform of a developing bias during digital image formation.

FIG. 8 is a diagram showing the relationship between the peak voltage V _{PP of the} developing bias and the dot density.

FIG. 9 is a diagram showing a relationship between development contrast and dot density.

FIG. 10 is a diagram showing another embodiment according to the present invention.

[Explanation of symbols]

 1 Photosensitive Body (Photosensitive Drum) 2 Charging Means (Primary Charging Device) 3 Developing Means (Developing Machine) 14 Lamp Regulator 18 Laser Unit 28 Polygon Mirror 31 Paper Feed Cassette 60 Detecting Means 61 Control Means C Copy Machine Main Body L1 Analog Exposure Means L2 digital exposure means R digital reader

Front page continuation (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location G03G 15/01 117 Z 7818-2H 15/04 120 9122-2H H04N 1/29 H 9186-5C

Claims (1)

[Claims] 1. An analog exposure unit for exposing a photoreceptor charged by a charging unit to form a latent image, and a digital exposure unit for forming a latent image similarly to the analog exposure unit.
In an image forming apparatus provided with a developing means for developing the latent image, the digital exposing means forms a latent image by continuously performing dot-like exposure, and the output interval of these dots and the dot width A detection means for detecting whether or not the ratio of the latent image and the development condition exceeds a certain value, and a control means for changing at least one of the latent image condition and the developing condition on the basis of a signal from the detection means during digital image formation. An image forming apparatus comprising: