JPH08202093A - Electrophotographic image forming device - Google Patents

Abstract

PURPOSE: To provide the image of proper density whether it is a printing mode or a copying mode. CONSTITUTION: This device possesses a photoreceptor drum 31, a reading writing light source 33b, a liquid crystal shutter array 33c, a transparent original platen 33a, a reflection mirror 33d and a developing bias control circuit 6. In the copying mode, image forming is performed by irradiating the photoreceptor drum 31 with reflected light from an original 5 by way of the liquid crystal shutter array 33c, and in the printing mode, the image forming is performed by irradiating the photoreceptor drum 31 with the reflected light from the reflection mirror 33d by way of the liquid crystal shutter array 33c. In the copying mode, the developing bias control circuit 6 sets the bias potential of a developing sleeve 35 to a value which is αV lower than that in the printing mode so as to compensate weak reflected light from the original 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying / printing electrophotographic image forming apparatus using a liquid crystal shutter array.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses having both printing and copying functions have been known. Such a device is disclosed in, for example, Japanese Patent Application Laid-Open No. 1-142572. Figure 6
FIG. 4 is an explanatory view for schematically explaining the operation principle of the image forming apparatus described in the above publication, in which light A from a light source 101 is transmitted through a transparent document table 102. In the copy mode, the light transmitted through the document table 102 is reflected by the surface of the document 103 placed on the document table 102, and the reflected light B corresponding to the shade of the surface of the document 103 is reflected by the document table 102.
To reach the liquid crystal shutter array 105. In this copy mode, since all the micro shutters constituting the liquid crystal shutter array 105 are controlled to be in the transmission state, the reflected light B irradiates the photosensitive drum 106 without being blocked by the liquid crystal shutter array 105. , Manuscript 1
The electrostatic latent image 03 is formed on the photoconductor drum 106.
This electrostatic latent image is visualized by development (toner adhesion), and the obtained toner image is transferred to the recording paper 107.

On the other hand, in the print mode, the document table 1
Since the original 103 is not provided on the second sheet 2, the light A from the light source 101 passes through the original table 102, is reflected by the reflection mirror 104, and evenly reaches the liquid crystal shutter array 105, but the print sent from the computer is transmitted. An image signal to be applied is applied to the micro-shutters forming the liquid crystal shutter array 105, and the opening and closing of each micro-shutter is controlled based on the image signal. Therefore, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 106. This electrostatic latent image is visualized by development (toner adhesion), and the obtained toner image is transferred to the recording paper 107.

[0004]

However, the conventional apparatus described in the above publication has a problem that the light amount (irradiation intensity) illuminating the photosensitive drum is significantly different between the copy mode and the print mode. That is, in the copy mode, the light weakly reflected on the surface of the original illuminates the photosensitive drum, whereas in the print mode, the strong light almost completely reflected by the reflection mirror illuminates the photosensitive drum. Therefore, if the reference of the image density (toner image density) is adjusted to that in the print mode, it tends to be light in the copy mode, and conversely, if it is adjusted in the copy mode, the print mode tends to be dark. Was there.

The present invention has been made in view of the above circumstances, regardless of the print mode or the copy mode.
It is an object of the present invention to provide an electrophotographic image forming apparatus capable of obtaining an image having an appropriate density.

[0006]

In order to solve the above-mentioned problems, the invention according to claim 1 provides a photosensitive drum for forming an electrophotographic image, a light source for reading and writing, and a liquid crystal shutter array for image information. Is provided on the same side of the transparent document table, and a reflection mirror for reflecting the light incident from the light source toward the liquid crystal shutter array is provided on the back side of the document placed on the other surface of the document table. In the copy mode, the reflected light from the original is irradiated onto the photosensitive drum via the liquid crystal shutter array to form an image, and in the print mode, the reflected light from the reflection mirror is passed through the liquid crystal shutter array. An electronic image forming apparatus for both copying and printing, which irradiates an image on a photosensitive drum to form an image, wherein a developing means is provided with a first bias voltage in order to compensate weak reflected light from an original in a copying mode. Set, or print mode, and characterized by being obtained by adding a developing bias voltage control means for setting the developing means to suppress the strong reflected light from the reflecting mirror to the second bias voltage value.

According to a second aspect of the invention, there is provided the electrophotographic image forming apparatus according to the first aspect, wherein the developing bias voltage control means controls the bias potential applied to the developing means and the photosensitive drum. It is characterized in that the bias voltage of the developing means is controlled so that the potential difference from the potential in the exposure region is substantially the same in the copy mode and the print mode.

According to a third aspect of the present invention, a photosensitive drum for forming an electrophotographic image, a light source for reading and writing, and a liquid crystal shutter array for image information are provided on the same surface side of a transparent document table. A reflecting mirror for reflecting the light incident from the light source toward the liquid crystal shutter array is provided on the back side of the document placed on the other surface of the document table, and in the copy mode, the reflection mirror from the document is read. An image is formed by irradiating the photosensitive drum with the reflected light through the liquid crystal shutter array, and in the print mode, the reflected light from the reflecting mirror is irradiated onto the photosensitive drum through the liquid crystal shutter array to form an image. An electronic image forming apparatus which is also used for printing, wherein the light source is set to a first output value in order to compensate for the weak reflected light from the original in the copy mode, or the light is reflected in the print mode. Is characterized in that the light source in order to suppress the strong reflected light from the color formed by adding the light source control means for setting the second output value.

According to a fourth aspect of the present invention, in the electrophotographic image forming apparatus according to the third aspect, the light control means determines whether the exposure intensity for the photosensitive drum is in the copy mode or the print mode. It is characterized in that the output of the light source is controlled so as to be substantially equal.

According to a fifth aspect of the present invention, a photosensitive drum for forming an electrophotographic image, a light source for reading and writing, and a liquid crystal shutter array for image information are provided on the same surface side of a transparent document table. A reflecting mirror for reflecting the light incident from the light source toward the liquid crystal shutter array is provided on the back side of the document placed on the other surface of the document table, and in the copy mode, the reflection mirror from the document is read. An image is formed by irradiating the photosensitive drum with the reflected light through the liquid crystal shutter array, and in the print mode, the reflected light from the reflecting mirror is irradiated onto the photosensitive drum through the liquid crystal shutter array to form an image. In an electronic image forming apparatus which is also used for printing, in the copy mode, the liquid crystal shutter array is set to the first transmittance level in order to compensate the weak reflected light from the original, or When Ntomodo, are characterized by being obtained by adding a shutter control means for setting the liquid crystal shutter array so as to suppress the strong reflected light from the reflecting mirror to the second transmission level.

According to a sixth aspect of the present invention, in the electrophotographic image forming apparatus according to the fifth aspect, the liquid crystal shutter array is composed of a large number of micro-shutters capable of multivalued expression. It has a feature.

[0012]

According to the structure of the present invention, the developing bias voltage control means sets the developing means to the first bias voltage value in order to compensate the weak reflected light from the original in the copy mode (or in the print mode). , The developing means is set to the second bias voltage value in order to suppress the strong reflected light from the reflecting mirror). At this time, the developing bias voltage control means, for example, makes the potential difference between the bias potential applied to the developing means and the potential in the exposure area of the photosensitive drum substantially equal in the copy mode and the print mode. Controlling the bias voltage of the developing means (structure according to claim 2). Therefore, the toner of substantially the same amount adheres to the photosensitive drum regardless of the print mode or the copy mode, so that it is possible to always obtain an image of an appropriate density.

According to the third aspect of the invention, the light source control means sets the light source to the first output value in order to compensate the weak reflected light from the original in the copy mode (or from the reflection mirror in the print mode). The light source is set to the second output value in order to suppress the strongly reflected light of. At this time, the light control means controls the output of the light source so that the exposure intensity with respect to the photosensitive drum is substantially equal in the copy mode and the print mode (claim 4).

In the structure according to the fifth aspect, the shutter control means sets the liquid crystal shutter array to the first transmittance level in order to compensate the weak reflected light from the original in the copy mode (or in the print mode). , The liquid crystal shutter array is set to the second transmittance level in order to suppress the strong reflected light from the reflecting mirror). In the structure according to the fifth aspect, the liquid crystal shutter array is composed of a large number of micro shutters capable of multi-valued expression.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a sectional view showing the overall construction of the electrophotographic image forming apparatus according to the first embodiment of the present invention, and FIG. 2 shows the construction of the essential parts of the electrophotographic image forming apparatus. FIG. The electrophotographic image forming apparatus of this example relates to an electrophotographic image forming apparatus for both copying and printing using a liquid crystal shutter array, and as shown in FIG. 1, the recording sheets set in a tray are separated one by one. Paper feed unit 1 that sends it to the transport path
And a toner image based on an image signal is formed on the photosensitive drum by the Carlson process (electrophotographic method), and then,
The image forming unit 3 transfers the toner image onto the recording paper 2 sent from the paper feeding unit 1, and the fixing unit 4 thermally fixes the toner image transferred onto the recording paper 2.

The image forming unit 3 has a photosensitive drum 31 provided on the surface thereof with a photoconductive layer exhibiting characteristics of an electric insulator in a dark place and an electric conductor in a bright place, and the surface of the photosensitive drum 31 has a predetermined polarity. A main charger (scorotron charger) 32 for uniformly charging to a potential (about -700 V in this example);
An optical reading / writing device (exposure device) 33 that exposes the uniformly charged surface of the photosensitive drum 31 to form an electrostatic latent image, and the electrostatic latent image formed on the surface of the photosensitive drum 31 to the toner tank 3.
4, a developing sleeve 35 for developing (visualizing) toner 34a, a transfer charger (corona charger) 36 for electrostatically transferring the toner image formed by this development onto the recording sheet 2, and a transfer. A cleaner 37 for scraping and collecting the toner 34a remaining on the surface of the photosensitive drum 31 after that is roughly configured.

As shown in FIG. 2, the optical reading / writing device 33 includes a transparent manuscript table 33a, a slit-shaped light source 33b installed below the manuscript table 33a in the figure, and the manuscript table 33a. A liquid crystal shutter array 33c disposed below and facing the photosensitive drum 31, and a document table 3
And a reflection mirror 33d installed above the light source 3a. White light emitted in a slit shape from the light source 33b is transmitted through the document table 33a and then reflected by a reflection mirror 33d. It is adjusted to irradiate 33c. Here, the light source 33b has a sidelight structure in which a light bulb type halogen lamp is placed at one end of the quartz lot, and has the same function as a rod-shaped light source that illuminates the entire length of the liquid crystal shutter array 33c. The liquid crystal shutter array 33c is a two-frequency drive liquid crystal panel in which about 2000 micro shutters having an opening size of about 100 μm are arranged in a staggered pattern. Each micro-shutter reduces the light transmittance when a low-frequency electric field of several kHz is applied, and the shutter closes at 200 kH.
When the application of the high frequency electric field of z is switched, the light transmittance starts to increase, the shutter is opened, and the light transmitted through the shutter is incident on the surface of the photosensitive drum 31. Each micro shutter corresponds to one pixel.

The original table 33a and the reflection mirror 33d are configured to be movable in a direction orthogonal to the longitudinal direction of the slit-shaped light source 33b and the liquid crystal shutter array 33c, and are synchronized with the rotation of the photosensitive drum 31 in the copy mode. do it,
By moving the document table 33a to the right in the figure, the document 5
All of are read.

The developing sleeve 35 is provided with a developing bias control circuit 6 for controlling the developing bias voltage. Specifically, the developing bias control circuit 6 determines the bias voltage in the copy mode in consideration of the fact that the light amount (irradiation intensity) illuminating the photosensitive drum is significantly different between the copy mode and the print mode. Set lower than that in print mode.

Next, the operation of this example will be described. When the device having the above configuration is operated as a printer, the light source 3
The slit-shaped light emitted from 3b reflects the reflection mirror 33d.
Reflected almost 100% by the liquid crystal shutter array 33.
Head to c. In the liquid crystal shutter array 33c, a drive circuit having an integrated circuit structure creates an open / closed state for each micro shutter based on an image signal sent from a computer, and only light transmitted through the opened micro shutter is exposed. The drum 31 is illuminated to create an electrostatic latent image according to the soft original. This electrostatic latent image is developed (toner 34
The toner image obtained by being visualized by (a) is transferred to the recording paper 2 by the transfer charger 36.

That is, as shown in FIG. 3A, in this print mode, the photosensitive drum 31 has the main charger 32.
Is charged to about -700V. Photosensitive drum 3
When light is radiated to the No. 1 through the liquid crystal shutter array 33c, it behaves as a good electric conductor in the radiated region (pixel), so that the potential rises to about -70V. on the other hand,
Toner 34a having a negative potential is attached to the developing sleeve 35, and the developing bias control circuit 6 causes the developing bias control circuit 6 to generate a voltage of -300V.
Is applied. Therefore, at the time of development, when viewed from the toner particles, the developing bias is -300V, while the developing bias is -300V.
Appears as (+), the toner 34a is
Move up. In this way, development visualization is performed.

Next, when operating as a copying machine, all the micro shutters constituting the liquid crystal shutter array 33c are opened. The light from the light source 33b passes through the transparent document table 33a and strikes the document (hard document) 5.
The light reflected on the surface of the original passes through the liquid crystal shutter array 33c, which is in a completely transparent state, and is irradiated onto the photosensitive drum 31 to form an electrostatic latent image. However, in the copy mode, since the reflection on the document surface is weak, the exposure is incomplete. Therefore, the irradiation area (pixel) of the photosensitive drum 31
Then, as shown in (b) of the same figure, since it does not rise to −70 V and stays at − (70 + α) V (α> 0), the adhesion rate of the toner to the photosensitive drum 31 decreases as it is. , The image density decreases. In order to prevent this, in this example, the developing bias voltage is applied to the developing sleeve 35 by the developing bias control circuit 6 in the copy mode.
(300 + α) V is applied.

As described above, according to the structure of this example, the operation of the developing bias control circuit 6 adjusts the potential difference between the developing sleeve and the irradiation area on the photosensitive drum 31 so that it is always substantially constant. . Therefore, the print mode,
Since the toner of substantially the same amount adheres to the photosensitive drum 31 regardless of the copy mode, it is possible to always obtain an image of an appropriate density regardless of the mode.

Second Embodiment FIG. 4 is a sectional view showing the arrangement of the main parts of an electrophotographic image forming apparatus according to the second embodiment of the present invention. In the figure,
The light source control circuit 7 controls the light quantity of the light source 33b, and in the copy mode in which the quantity of light reflected from the document 5 is weak, controls so as to increase the quantity of light emitted from the light source 33b in advance as compared with the print mode. Therefore, also according to the second embodiment, it is possible to obtain an image having an appropriate density regardless of the print mode or the copy mode. 4, the same components as those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

[Third Embodiment] FIG. 5 is a sectional view showing the arrangement of the essential parts of an electrophotographic image forming apparatus according to the third embodiment of the present invention. In the figure,
The liquid crystal shutter array 8 is composed of a micro shutter capable of gradation expression (multi-value expression), and a shutter control circuit 9 gradation-controls the transmittance of each micro shutter in response to an image signal. In this example, the shutter control circuit 9 controls so that the amount of transmitted light (transmittance) of each micro shutter slightly decreases in the print mode, and controls so as to completely transmit the light in the copy mode. Also according to the third embodiment, it is possible to obtain an image having an appropriate density regardless of the print mode or the copy mode.

Although the embodiment of the present invention has been described in detail above with reference to the drawings, the specific structure is not limited to this embodiment, and there are design changes and the like within the scope not departing from the gist of the present invention. Also included in the present invention. For example, although the liquid crystal shutter array is arranged between the document table and the photosensitive drum in the above-mentioned embodiment, it may be arranged between the document table and the light source. Further, instead of moving the document table, an optical system such as a light source or a liquid crystal shutter array may be moved.

[0027]

[0023]

As described above, according to the electrophotographic image forming apparatus of the present invention, an image having an appropriate density can be obtained regardless of the print mode or the copy mode.

[Brief description of drawings]

FIG. 1 is a sectional view showing an overall configuration of an electrophotographic image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a main part of the electrophotographic image forming apparatus.

FIG. 3 is an explanatory diagram for explaining the operation of the same embodiment.

FIG. 4 is a cross-sectional view showing a configuration of a main part of an electrophotographic image forming apparatus according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a configuration of a main part of an electrophotographic image forming apparatus according to a third embodiment of the present invention.

FIG. 6 is an explanatory diagram of an electrophotographic image device using a conventional liquid crystal shutter array.

[Explanation of symbols]

31 photosensitive drum 33b light source 33c, 8 liquid crystal shutter array 33a document table 33d reflecting mirror 6 developing bias control circuit (developing bias voltage control means) 7 light source control circuit (light source control means) 9 shutter control circuit (shutter control means)

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G03G 15/06 101

Claims (6)

[Claims] 1. A photosensitive drum for forming an electrophotographic image, a light source for reading and writing, and a liquid crystal shutter array for image information are provided on the same surface side of a transparent document table, and the other surface of the document table is provided. A reflection mirror for reflecting the light incident from the light source toward the liquid crystal shutter array is provided on the back side of the document placed on the document, and in the copy mode, the reflected light from the document is transmitted through the liquid crystal shutter array. In the print mode, the image is formed by irradiating the photosensitive drum with the photosensitive drum to irradiate the reflected light from the reflection mirror onto the photosensitive drum via the liquid crystal shutter array to form an image. Therefore, in the copy mode, the developing means is set to the first bias voltage value to compensate for the weak reflected light from the original, or in the print mode, the strong reflection from the reflection mirror is set. Electrophotographic image forming apparatus characterized by comprising adding a developing bias voltage control means for setting the developing means to the second bias voltage value so as to suppress light. 2. The developing bias voltage control means makes the potential difference between the bias potential applied to the developing means and the potential in the exposure area of the photosensitive drum substantially equal in the copy mode and the print mode. The electrophotographic image forming apparatus according to claim 1, wherein the bias voltage of the developing unit is controlled. 3. A photosensitive drum for forming an electrophotographic photograph, a light source for reading and writing, and a liquid crystal shutter array for image information are provided on the same surface side of a transparent document table, and the other surface of the document table is provided. A reflection mirror for reflecting the light incident from the light source toward the liquid crystal shutter array is provided on the back side of the document placed on the document, and in the copy mode, the reflected light from the document is transmitted through the liquid crystal shutter array. In the print mode, the image is formed by irradiating the photosensitive drum with the photosensitive drum to irradiate the reflected light from the reflection mirror onto the photosensitive drum via the liquid crystal shutter array to form an image. Therefore, in the copy mode, the light source is set to the first output value to compensate for the weak reflected light from the original, or in the print mode, the strong reflected light from the reflection mirror is suppressed. Electrophotographic image forming apparatus characterized by comprising adding a light source control means for setting the light source to the second output value so as to. 4. The light control means is configured to control the output of the light source so that the exposure intensity with respect to the photosensitive drum is substantially equal in the copy mode and the print mode. The electrophotographic image forming apparatus according to claim 3, which is characterized in that. 5. A photosensitive drum for forming an electrophotographic photograph, a light source for reading and writing, and a liquid crystal shutter array for image information are provided on the same surface side of a transparent document table, and the other surface of the document table is provided. A reflection mirror for reflecting the light incident from the light source toward the liquid crystal shutter array is provided on the back side of the document placed on the document, and in the copy mode, the reflected light from the document is transmitted through the liquid crystal shutter array. In the print mode, the image is formed by irradiating the photosensitive drum with the photosensitive drum to irradiate the reflected light from the reflection mirror onto the photosensitive drum via the liquid crystal shutter array to form an image. Therefore, in the copy mode, the liquid crystal shutter array is set to the first transmittance level in order to compensate the weak reflected light from the original, or in the print mode, the reflection mirror is set. Et strong reflected light electrophotographic image forming apparatus characterized by comprising adding shutter control means for setting the liquid crystal shutter array in a second transmission level in order to suppress. 6. The electrophotographic image forming apparatus according to claim 5, wherein the liquid crystal shutter array comprises a large number of micro shutters capable of multi-valued expression.