JPS61105570A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To obtain photographic images of high quality with a certain density by controlling the exposure intensity to a photosensitive surface in an exposure part in accordance with the reduction of sensitivity due to the elapse of time after the operation start of a photosensitive body. CONSTITUTION:In the print operation for the first page just after the operation start, the collector current value of a transistor TR 34 is low because the terminal voltage of a capacitor 40 of an integrating circuit 41 is low. Consequently, the current flowed to a laser beam emitting element 51 is large, and the exposure intensity is a high value. This exposure intensity is reduced along a reduction characteristic curve determined by the time constant of the integrating circuit 41 in accordance with the elapse of time after the operation start time. This reduction characteristic curve is set so as to correspond to the reduction characteristic curve of the sensitivity of the photosensitive surface of a photosensitive drum 2. As the result, the lightness of character images formed by laser beam scanning on the photosensitive surface is held at an approximately certain value, and photographic images of high quality with a certain density level are always obtained just after the operation start as well as a certain time after the operation start.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electrophotographic apparatus that forms an image on the photosensitive surface of a charged photoreceptor in an exposure section and develops it in a development section to obtain a photographic image. In particular, the present invention relates to an electrophotographic apparatus that compensates for a decrease in sensitivity of a photoreceptor over time by reducing exposure intensity in response to the lapse of time.

[Prior Art] In general, in an electrophotographic apparatus, a charging section consisting of a charging charger emits a laser beam along the circumference of a photosensitive drum rotating at a constant speed in response to a character code input from the outside. an exposure section, a development section, a transfer section, which scans the
A static eliminator is placed in each. In addition, near the transfer part,
A paper insertion section that feeds paper to the transfer section and a fixing section that fixes the character image transferred by the transfer section are provided.

In such an electrophotographic apparatus, when a character code for printing a photograph on paper is input from the outside, character pattern data corresponding to this character code is read out from the character generator, and a laser beam is directed onto the photoreceptor based on this character pattern data. By scanning the charged photosensitive surface, a character image corresponding to the input character code is created on the photosensitive surface. Then, the character image formed by this laser beam is developed at the next developing section, and further transferred to the paper fed from the abrasive section at the next transfer section. Then, the paper onto which the character image has been transferred is fixed in a fixing section. In addition,
The character image remaining on the transferred photosensitive surface is neutralized by the static eliminating section.
Waits for the next charge.

[Problems to be Solved by the Invention] However, the electrophotographic apparatus configured as described above has the following problems. The sensitivity of the photoreceptor used in such an electrophotographic device, that is, the surface potential due to charging with respect to the charging voltage applied by the charging charger, is as shown in Figure 5, immediately after the power is turned on and the operation starts. shows a very high value. However, charging, exposure, and development.

When characters are photographically printed on a large number of sheets of paper by repeating transfer and static elimination, the sensitivity of the photoreceptor decreases over time and reaches a substantially constant value after a certain period of time. Then, for example, when the operation is stopped for several hours or more, the photoreceptor sensitivity returns to its original high value.

Therefore, if the charging voltage applied by the charging charger is a constant value, the surface potential due to charging will be abnormally high immediately after the start of operation, and image formation by laser beam exposure will be relatively insufficient. Become. As a result, the resulting photographic character image becomes too dark. Further, after a certain period of time has elapsed, the surface potential due to charging becomes low due to the low sensitivity of the photoreceptor, and the charging is canceled by exposure, resulting in the resulting photographic character image becoming too bright. Therefore, there is a problem in that uniform photographic images with constant density cannot always be obtained.

The present invention was made based on the above circumstances, and its purpose is to reduce the exposure intensity in response to the decrease in sensitivity of the photoreceptor, thereby reducing the image formed on the photoreceptor surface after exposure. It is an object of the present invention to provide an electrophotographic apparatus that can maintain the brightness of an image at a more or less constant value and can always obtain high-quality photographic images of constant density.

[Means for Solving the Problems] The present invention forms an image on the photosensitive surface of a photoreceptor charged by a charging unit in an exposure unit, develops it in a developing unit to obtain a photographic image, and further creates a photographic image in a static eliminating unit. In an electrophotographic device, the exposure intensity on the photosensitive surface in the exposure section is changed over a predetermined period of time from the start of operation in response to a decrease in sensitivity over time after the start of operation of the photoreceptor. In response to this, the temperature is lowered, and after a certain period of time, the value is reduced to a substantially constant value.

[Function] With an electrophotographic apparatus configured in this way, the exposure intensity is high immediately after the start of operation and decreases as time passes, so that the decrease in sensitivity of the photoreceptor over time is equivalently compensated for, and the exposure The brightness of the image formed on the surface becomes almost constant.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing the general structure of an electrophotographic apparatus according to an embodiment. In the figure, reference numeral 1 denotes a housing, and a photosensitive drum 2 having a photosensitive surface formed along its outer periphery is installed in the center of the housing 1. The photosensitive drum 2 is rotated at a constant speed by a motor (not shown). A charging charger 3 that forms a charging section along the circumference of the photosensitive drum 2. A laser beam generator 5 that outputs a scanning laser beam 4 that forms an exposure area. Developing section 6. Transfer section 7 having a transfer charger. A static eliminating lamp 8 and a wiping roller 9 forming a static eliminating section are provided.

An insertion slot 1 for a paper feed cassette 10 is provided at the lower side of the housing 1.
1 is formed between the insertion opening 11 and the transfer section 7, and a paper feed roller 13 and a paper feed guide 14 for guiding the paper 12 stored in the paper feed cassette 10 to the transfer section 7. It is provided. Note that a paper insertion section 15 for manually feeding paper is provided on the side surface of the housing 1. A conveyor 16 and two fixing rollers 17 are provided on the opposite side of the transfer section 7 to the paper feed guide 14.
A fixing section 18 consisting of 8.17b is provided.

As shown in FIG. 2, the laser beam generator 5 includes:
A laser beam light emitting element 51 that turns on and off in response to character pattern data information read from a character generator, a rotating polygonal AI 52 and an fθ lens 53 that horizontally scan the laser beam from the light emitting element 51, A scanning start position detector 54, a scanning end position detector 55, a reflection 156, 57 for irradiating a laser beam onto these multi-position detectors 54, 55, and a mirror for directing the laser beam to the photosensitive surface of the photosensitive drum 2. 58
It is made up of.

FIG. 3 is a block diagram showing a schematic configuration of the electrophotographic apparatus, and 20 in the figure is a CPU that executes various calculation information processing. The CPU 20 is connected to a ROM 22.22, which stores fixed data such as control programs, via a path line 21 consisting of a data bus, an address bus, etc. A character generator 23 that stores character pattern data corresponding to character codes input from the outside. A RAM 24 that temporarily stores variable data such as character codes input from the outside. For example, an interface 25 for receiving character codes sent from an external host computer via a transmission path. It also controls the I10 port 26, etc., which transmits and receives control signals and data to and from each part.

This I10 boat 26 includes various sensors 27, 54, 55, etc. inside the laser beam generator 5. Various lamps 28, such as the static elimination lamp 8; various chargers 29, such as the charging charger 3 and the transfer charger; and the photosensitive drum 2° rotation polygon 152. Fixing roller 17
a, 17b, conveyor 16. Various motors 30 and the like that rotationally drive the paper feed roller 13 and the like are connected. The I10 boat 26 also sends each character pattern data read from the character generator 23 to the laser beam generator f5.

In the character generator 23, each character pattern is vertically divided into a large number of parts, and each divided pattern is displayed and stored as scan data.

In the RAM 24, there is a 1 to be printed input from an external host computer via an interface 25.
A page print data buffer that stores character codes for a page, and a line data buffer that stores one line of scan data that has been read out from this page print data buffer 1 and converted into the aforementioned multiple scan data by the character generator 23. is formed.

Further, the laser beam generator 5 has a circuit configuration as shown in FIG. That is, the 7-node terminal of the laser beam emitting element 51 that emits a laser beam is connected to the drive power supply terminal 32 that supplies a DC drive voltage of +■D via the current limiting resistor 31, and the cathode terminal is grounded. ing.

A switching transistor 33 is connected between the 7-node terminal of the laser beam emitting element 51 and ground, and the base terminal of the switching transistor 33 is connected to the scanning data output terminal of the I10 port 26.

Furthermore, the anode terminal of the laser beam emitting element 51 is connected to the collector terminal of an amplifying transistor 35 via a resistor 34, and the emitter terminal of the transistor 35 is grounded via a resistor 36. In addition, the transistor 35
The base terminal of is connected via a resistor 37 to a connection point between a resistor 39 and a capacitor 40 of an integrating circuit 41 consisting of a resistor 39 and a capacitor 40 connected in series between a +5V control power supply terminal 38 and ground. Note that a diode 42 for preventing backflow is connected between both terminals of the resistor 39.

The terminal voltage of the capacitor 40 of this integrating circuit 41 changes from one control power supply terminal 38 to the other when the device is powered on and becomes operational.
Since a DC voltage of +5■ is applied from , the voltage increases according to a time constant determined by the values of the resistor 39 and the capacitor 4o. This time constant is set so that the increase characteristic of the terminal voltage of the capacitor 40 corresponds to the characteristic curve A of FIG. 5, in which the photoreceptor sensitivity on the photosensitive surface of the photosensitive drum 2 decreases with respect to the elapsed time after the start of operation. Since the base terminal voltage of the transistor 35 corresponds to the terminal voltage of the capacitor 40, the collector current increases as the terminal voltage of the capacitor 40 increases. Therefore, the collector current has a low value immediately after the start of operation of the device, becomes high as time elapses, and becomes a substantially constant value after a certain period of time has elapsed.

In an electrophotographic apparatus configured as described above, when the apparatus is turned on in order to continuously print photographic character images on a certain number of sheets of paper or more, an error occurs as shown in the figure.
111 Kara + 5 V (7) il N 'II
The pressure 1fi i'J m 'RII is applied to the integrating circuit 41 via the ift element 38. As a result, capacitor 4
0 terminal voltage, that is, the collector current of transistor 35 starts to rise according to the above-mentioned time constant determined by resistor 39 and capacitor 40.

Immediately after the start of operation of the apparatus, scan data is not sent out and the output signal of the scan data output terminal of the I10 port 26 is at L level, so the switching transistor 33 is in a cut-off state.

Therefore, a current is supplied to the laser beam emitting element 51 from the +■D drive power supply terminal 32 via the current limiting resistor 31, and the laser beam emitting element 51 emits a laser beam. The intensity of the laser beam, that is, the intensity of exposure to the photosensitive surface corresponds to the value of the current flowing through the laser beam emitting element 51. Immediately after the start of operation, the aforementioned collector current value is small, so the exposure intensity takes a high value.

In this state, when the character code for one page is input from the external host computer via the interface 25,
This input character code for one page is temporarily stored in the page print data buffer in the RAM 24, and then sequentially printed one line at a time, converted into one line of scan data by the character generator 23, and then stored in the line data buffer in the RAM 24. Store in.

When a printing command is input, the photosensitive drum 2 starts rotating at a constant speed, and at the same time, a charging command is sent from the I10 boat 26 to the charging section, and the photosensitive surface is charged by the charging charger 1-.
Charge with jar 3. Next, the row of RAM24
'One line of scanning data stored in the data buffer is sequentially read out and sent to the laser beam generator 5 via the scanning data output terminal of the I10 port 26. In the laser beam generator 5, the input scanning data is input to the base terminal of the switching transistor 33, so the switching transistor 33 repeats on/off operations in response to information included in the scanning data. When the switching transistor 33 is on, the laser beam emitting element 5
Since almost no current flows through 1, the laser beam emitting element 51 outputs a laser beam that repeatedly turns on and off in response to the information of each scan data, and this laser beam 4 hits the charged photosensitive surface of the photosensitive drum 2. scanned against. As a result, a character image for one line corresponding to the character code for one line is formed on the photosensitive surface.

When a character image for one line is created, the character code for the next line is read from the page print data buffer of the RAM 24 and converted into scan data for one line by the character generator 23 in the same manner as described above. Store in row data buffer. Then, the laser beam generator 5 forms the next line of character images on the photosensitive surface.

In this way, character images are sequentially formed on the photosensitive surface of the photosensitive drum 2, which is rotated at a constant speed.

The character image for one page formed on the photosensitive surface of the photosensitive drum 2 is
As described above, the image is developed in the developing section 6 and transferred onto the paper 12 fed from the paper feed cassette 10 in the transfer section 7 .

The photographic character image transferred onto the paper 12 is fixed by fixing rollers 17a and 17b of the fixing section 18. Then, the paper 12 on which one page of photographic character images has been formed is discharged from the fixing section 18 to the outside of the housing 1.

In an electrophotographic apparatus configured as described above, during the printing operation for the first page (sheet) immediately after the apparatus is turned on and started operating, the terminal voltage of the capacitor 40 of the integrating circuit 41 shown in FIG. is low, so transistor 34
The collector current value of is also low. Therefore, the current flowing through the laser beam emitting element 51 is large, and the exposure intensity is a high value as shown in FIG. Then, as the FR interval passes from the operation start time, the exposure intensity decreases according to a decreasing characteristic curve B determined by the time constant of the integrating circuit 41 as shown in the figure. This deterioration characteristic curve 8 corresponds to the photosensitive drum 2 in FIG.
It is set so as to correspond to the photoreceptor sensitivity reduction characteristic curve A of the photoreceptor surface. Therefore, when the photoconductor sensitivity is high immediately after the start of operation, the exposure intensity of the laser beam 4 outputted from the laser beam generator 5 to the photoconductor surface is high, and decreases as the photoconductor sensitivity decreases.
The relationship between the surface potential of the photosensitive surface charged by the charging charger 3 and the exposure intensity is always constant. As a result, the brightness of the character image formed by laser beam scanning on the photosensitive surface is maintained at a substantially constant value.

As a result, high-quality photographic images with a constant density level can always be obtained even immediately after the start of operation and even after a certain period of time has elapsed.

Note that when the printing of photographic characters on a certain number of sheets of paper is finished, the power to the device is turned off, the operation is stopped, and a downtime of several hours has elapsed, the photoconductor sensitivity of the photoconductor drum 2 returns to its original value as described above. Return to

At the same time, the charge stored in the capacitor 40 of the integrating circuit 41 is also discharged, so that the base terminal voltage of the transistor 35 returns to the original low voltage.

Note that the present invention is not limited to the embodiments described above. In the embodiment, at the same time as the power is turned on, the integration circuit 41
Although the voltage supply is started for the first page (first sheet), the voltage supply may be started in synchronization with the print command for the first page (first sheet).

[Effects of the Invention] As explained above, according to the present invention, the exposure intensity in the exposure section is adjusted to a predetermined value from the start time of operation in response to a decrease in photoreceptor sensitivity over time after the start of operation of the photoreceptor. During a certain period of time, it is decreased in response to the elapsed time, and after the certain period of time has elapsed, it is controlled to a substantially constant value. Therefore, the reduction in photoreceptor sensitivity of the photoreceptor can be compensated for, the brightness of the image formed on the photoreceptor surface after exposure can be maintained at a substantially constant value, and a high-quality photographic image with a constant density can always be obtained.

[Brief explanation of drawings]

The drawings show an electrophotographic apparatus according to an embodiment of the present invention, in which Fig. 1 is a schematic cross-sectional view showing the whole, Fig. 2 is a perspective view showing the schematic configuration of the laser beam generator, and Fig. 3 is a block diagram. 4 is a circuit diagram of the laser beam generator, the fifth factor is a sensitivity characteristic diagram of a photoreceptor, and FIG. 6 is an exposure intensity characteristic diagram of a laser beam on a photosensitive surface. DESCRIPTION OF SYMBOLS 1... Housing, 2... Photosensitive drum, 3... Charger, 4... Laser beam, 5... Laser beam generator, 6... Developing section, 7... Transfer section , 8...
- Static elimination lamp, 9... Wiping roller, 10... Paper feed cassette, 12... Paper, 18... Fixing unit, 20
...CPU, 23...Character generator, 2
4...RAM125...Interface, 26.
・・I10 port, 29...Charger, 33-・
・Switching transistor, 35...Transistor, 39...Resistor, 40...Capacitor, 41...
Integrating circuit, 51... laser beam light emitting element.

Claims (2)

[Claims] (1) At least a charging section, an exposing section, a developing section, and a static eliminating section are sequentially disposed along the moving direction of the photoconductor, and the exposure section is used to form an image on the photosensitive surface of the photoconductor charged by the charging section. image,
Furthermore, in an electrophotographic apparatus in which a photographic image is obtained through development in the developing section, and the photoreceptor is neutralized in the static eliminator to wait for the next charging, the exposure intensity to the photosensitive surface in the exposure section is set to In response to a decrease in sensitivity due to the passage of time after the body starts working, the sensitivity is reduced in response to the elapsed time within a predetermined certain time from the start time of work, and after the certain time has passed, the sensitivity is reduced to a substantially constant value. An electrophotographic apparatus comprising an exposure intensity control means. (2) The electrophotographic apparatus according to claim (1), wherein the exposure intensity control means includes an integrating circuit consisting of a resistor and a capacitor.