JPH0846795A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image with optimum quality by selecting a photoreceptor charging voltage or the like when multi-gradation image is formed by a copying machine mode means and a binary image is formed by a printer mode means. CONSTITUTION:In the case of the copying machine mode, usual copying processing is implemented. That is, image data read by a CCD is processed by an image data processing section 56. On the other hand, when the image data are sent via a connector, the print mode is selected. The image forming device stores the sent image data to an image memory 58a or 59a and when the image data of a prescribed amount are sent, the print processing is conducted. It is required to revise the process condition of image forming between the copying machine mode and the printer mode. As the process conditions, there are charging voltage, development bias voltage, toner density, laser output intensity and laser output width or the like and they are selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is capable of both printing a multi-tone image obtained by scanning an original and printing a binary (two-tone) image sent from a computer or a facsimile (FAX). The present invention relates to an improvement capable of improving image quality in an image forming apparatus that can be performed.

[0002]

2. Description of the Related Art In recent years, an electrophotographic image forming method has been applied to various apparatuses and has also come to be used in electrostatic copying machines, printers connected to computers, fax machines, and the like. In addition, data from a computer or FAX is input to a digital electrostatic copying machine that converts image data into laser light and writes the image on the photoconductor with the laser light, prints the copied image, and outputs it from the computer. A multi-functional peripheral capable of performing printing, printing of FAX data, and the like with a single device is also considered.

[0003]

By the way, copying image data for copying an original, a computer, a FAX, and the like.
It is completely different from the print image data such as. That is, the image data for copying is data (multi-valued data) read in multiple gradations by scanning an original, whereas the image data for printing is binary data processed by a computer or FAX. is there. The difference between the image data to be printed being multi-valued data and the binary data is that the required image quality is an image with gradation that sufficiently reproduces halftones in the case of multi-valued data. In the case of binary data, the contrast is solid, the black density is high, and the image lines are solid.

However, in the conventional structure, the image forming condition (process condition) is not changed depending on whether it is multi-valued data or binary data, and as a result, both of them can obtain only half-finished quality images. There wasn't.

In a digital electrostatic copying machine, it is known as a well-known technique to change process conditions such as charging voltage and developing bias voltage depending on whether a document image is a character document or a photographic document. There is. For example, in the case of a text original, the process conditions are set so as to make the contrast clear, whereas in the case of a photo original, the process conditions are set so that the halftone reproducibility can be obtained. In this way, it is possible to obtain a copy image of quality corresponding to each original type. However, this is merely a change in the process conditions in the multi-valued data, and the above problems could not be solved.

Further, in the conventional configuration, the amount of toner actually transferred to the paper may not change so much even if the amount of toner attached to the photoconductor changes (increases) due to the change of process conditions. However, due to the change in the process conditions, it becomes difficult for the paper to be peeled off from the photoconductor and paper jam occurs.

An object of the present invention is to obtain a high-quality image regardless of whether multi-valued image data for copying is printed or binary image data for printing such as a computer or FAX is printed. An image forming apparatus capable of improving not only the quality of the image formed on the photoconductor but also the quality of the image actually formed on the paper and preventing the occurrence of paper jam. The purpose is to provide.

[0008]

According to a first aspect of the present invention, there is provided means for converting image data into laser light and switching the laser light output in accordance with a gradation step of the image data, and the laser light output. In an electrophotographic image forming apparatus including an image forming unit that forms a toner image having a corresponding density, data obtained by reading an original image image is stored as multi-tone image data, and the image data is displayed in tone steps. A copying machine mode means for converting a laser beam of a corresponding output to form an image and image data represented by binary data sent from a facsimile, a computer or the like are stored, and the binary image data is stored as described above. A printer mode means for converting the laser light output into only two output states of on / off to form an image, and a photosensitizer for forming a multi-gradation image by the copying machine mode means. Process condition switching means for switching between process conditions such as charging voltage and developing bias voltage and process conditions such as photoconductor charging voltage and developing bias voltage when performing binary image formation by the printer mode means. It is characterized by that.

According to a second aspect of the present invention, a density detecting means for forming a toner patch on a photoconductor under a predetermined process condition and detecting the density of the toner patch, and the density detecting means detect the density. The image forming apparatus according to claim 1, further comprising: a correction unit that compares the toner patch density with a previously stored reference density and corrects the process condition based on the comparison result. When the process condition is corrected based on the above, the change rate of the process condition when the multi-gradation image formation is performed by the copying machine mode unit and the process condition when the binary image formation is performed by the printer mode unit Is provided with a means for switching between the change rate and the change rate.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the photosensitive member is exposed in accordance with a change in the amount of toner adhering to the photosensitive member according to the process condition set by the process condition switching means. A means for setting a transfer output for transferring the toner on the body to a sheet, a means for detecting the humidity in the main body of the image forming apparatus, a means for storing the relationship between the humidity and the transfer output, and a means for adjusting the detected humidity. And a means for correcting the transfer output.

According to a fourth aspect of the present invention, in the first aspect of the invention, the peeling output for peeling the sheet from the photoconductor is set according to the charging voltage set by the process condition switching means. Means for detecting humidity in the main body of the image forming apparatus, means for storing a relationship between humidity and peeling output, and means for correcting peeling output according to the detected humidity. To do.

[0012]

According to the first aspect of the invention, when the image forming is performed based on the image data of the original by the copying machine mode means and the image forming is performed by the printer mode means based on the image data of the computer or FAX. The process conditions such as the charging voltage and the developing bias voltage are switched depending on the time. The scan data of the original is multi-gradation (multi-value) image data, and in this case, it is preferable that the gradation level is emphasized and the halftone is sufficiently reproduced. It is desirable that the concentration of toner adhering to the photoconductor is suppressed. Therefore, process conditions are shifted in that direction. For example, the charging voltage, the developing bias voltage, the toner concentration in the developing device, the laser output intensity are low, and the laser output width is shifted to be narrow. On the other hand, the print data of the computer and the fax are binary image data, and in this case, the image density (toner density attached to the photoconductor is such that the black and white contrast of the image is strong and the black portion is sufficiently black. ) Is desirable. Therefore, the process conditions are shifted in that direction, and, for example, the charging voltage, the developing bias voltage, the toner concentration in the developing device, and the laser output intensity are high,
The laser output width is shifted to be wider.

The operation of the invention described in claim 2 will be described.
In general, the density of a toner image formed on a photoconductor fluctuates under the influence of changes over time of the photoconductor, the developer, etc. and changes in the surrounding environment. On the other hand, multivalued image data for copying,
In order to maintain good quality of binary image data for computer and FAX printing, it is necessary to maintain suppressed image density and sufficiently dark image density, respectively, as described in the action of claim 1. . Therefore, in the invention described in claim 2, the toner patch is formed on the photoconductor under a predetermined condition, and the process condition is changed based on the relationship between the density of the toner patch and the reference density stored in advance.
At this time, the change rate of the process condition at the time of forming a multi-valued (multi-tone) image and the change rate of the process condition at the time of forming a binary image are switched, and the process condition for forming a multi-valued image is changed. Is improved so that the gradation reproducibility is improved, and the process conditions for forming a binary image are corrected so as to improve the contrast.

According to the third aspect of the invention, the transfer output is changed according to the change in the amount of toner adhering on the photosensitive member by changing the process condition. If the amount of toner on the photoconductor increases, in order to transfer all the toner to the paper,
It is also necessary to increase the transfer output. In the present invention, for example, the process condition for forming the image of the multivalued image data for copying by the process condition switching means described in claim 1 is set so that the toner adhesion amount on the photoconductor is reduced. If so, the transfer output is reduced accordingly. In addition, the process condition switching means allows a computer,
When the process condition for forming an image of binary image data for FAX printing is set so that the toner adhesion amount on the photoconductor is large, the transfer output is increased accordingly. As a result, necessary and sufficient toner transfer is performed. Also, the transfer performance from the photoconductor to the paper is affected by the ambient humidity. A major factor is that the paper absorbs moisture to lower the electric resistance, which lowers the transfer rate.
Therefore, by correcting the transfer output according to the humidity, it is possible to obtain the transfer output for transferring the toner on the photoconductor to the paper as necessary and sufficient.

According to the fourth aspect of the invention, the peeling output is changed according to the set charging voltage. If the charging potential of the photoconductor rises, the attraction force between the photoconductor and the paper becomes large, so that the peeling output also needs to be increased. In the present invention, for example, when the charging voltage when forming the image of the multivalued image data for copying is set to be low by the process condition switching means described in claim 1, the peeling is performed accordingly. The output is reduced. If the process condition switching means sets the charging voltage for forming an image of binary image data for computer and FAX printing to be high, the peeling output is increased accordingly. This facilitates peeling of the paper. Further, the peeling performance of the paper is affected by the ambient humidity. This is because the paper absorbs moisture to lower the electric resistance, which may reduce the peeling performance and cause a paper jam. Therefore, by correcting the peeling output according to the humidity, it is possible to prevent deterioration of the peeling performance.

[0016]

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

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

The digital image forming apparatus of this embodiment comprises a scanner unit 1, a laser printer unit 2, a multistage unit 3 which is a paper feeding device, and a sorter 4.

The scanner unit 1 includes a document placing table 11 made of transparent glass and a double-sided automatic document feeder (RDF) 1.
2 and a scanner unit 13.
When scanning a document placed on the document table 11, the scanner unit 1 is configured to read a document image while moving the scanner unit 13 along the lower surface of the document table 11, and the RDF 12 If you use
With the scanner unit 13 stopped at a predetermined position below the DF 12, the document image is read while the document is being conveyed.

The RDF 12 sets a plurality of originals at once and automatically feeds the originals one by one to the upper side of the scanner unit 13 so that one side or both sides of the original can be scanned according to the operator's selection. 13 is configured to be read.

The scanner unit 13 includes a lamp reflector assembly 14 for exposing a document, a plurality of reflection mirrors 15 for guiding a reflected light image from the document to a photoelectric conversion element (CCD) 17, and a reflected light image from the document on the CCD 17. A plurality of lenses 16 for forming an image are provided.

The image data obtained by reading the original image with the scanner unit 13 is sent to the image processing unit and subjected to various processing, and then temporarily stored in the memory of the image processing unit. The image data in this memory is given to the laser printer unit 2 in response to an output instruction, and an image is formed on a sheet.

The laser printer unit 2 includes a manual feed tray 21, a laser writing unit 22, and an electrophotographic process unit 23 for forming an image.

The laser writing unit 22 is a semiconductor laser 24 which is a light output section for emitting light according to the image data from the memory of the image processing section, a polygon mirror for deflecting the laser light at an equal angular velocity, and a laser which is deflected at an equal angular rate. It has an f-θ lens or the like for correcting the light so that the light is deflected at a constant velocity on the electrophotographic process section photosensitive drum 25.

The electrophotographic process section 23 includes a photoconductor drum 25, and a charger 25a, a developing device 25b, a transfer device 25c, and a peeling device 25 arranged around the photoconductor drum 25.
d, a cleaning device 25e, a static eliminator 25f, and the like, and further, a fixing device 26 is arranged in the transport system to heat and fix the toner on the peeled paper. A gate flapper 27 is arranged on the paper output side of the fixing device 26 to switch the path of the image forming paper to either the sorter 4 or the multi-stage paper feeding unit 3 side arranged below the laser printer unit 2. There is.

The laser printer section 2 is further provided with a connector section 28 for inputting print data from a computer or FAX (not shown). For example, RS-232-C or the like is used to input the print data.

In the laser writing unit 22 and the electrophotographic process section 23, the image data read from the memory of the image processing section is stored in the laser writing unit 22.
By scanning with a laser beam, an electrostatic latent image is formed on the surface of the photosensitive drum 25, and is visualized by a developing device using toner. This toner image is electrostatically copied and fixed on the surface of the sheet conveyed from the multi-stage sheet feeding unit 3. The sheet on which the image is formed in this manner is sent to the sorter 4 or again to the multi-stage sheet feeding unit 3.

The multi-stage sheet feeding unit 3 has a reversing conveyance path 31 arranged below the fixing device 26, a double-sided / composite conveyance path 32 arranged below the reversal conveyance path 31, and a double-sided / composition conveyance path 32. First, second, and third cassettes 33, 34, and 35, which are arranged underneath, and are used as paper storage units, a fourth cassette 36 that can be added by selection, and each cassette 33, 34, 3
And a conveyance path 37 for conveying the paper from the papers 5, 36 to the photosensitive drum 25. During image formation processing, each cassette 3
The sheet is conveyed to the photoconductor drum 25 from any one of 3, 34, 35, and 36 or through the double-sided / composite conveying path 32, and the toner image is transferred onto the sheet.

The sorter 4 is provided with a multi-stage discharge tray 41, and discharges paper onto the uppermost discharge tray 41 when the number of copies or prints is only a part. On the other hand, when the number of copies or prints is plural, the sheets are partially discharged onto the respective discharge trays 41.

FIG. 2 is a block diagram of a control unit of the image forming apparatus. The entire image forming apparatus is controlled by the central controller 51. The central control unit 51 collectively controls the control units of the above-described operation units. The RDF control unit 52 controls the conveyance of the document by the RDF 12. The scanner control unit 53 controls the moving direction of the scanner unit 13,
The moving speed and the like are controlled so that the CCD 17 can stably read an image. The transport system control unit 54
First to fourth cassettes 33, 34, 35, 36,
Paper from the paper, transporting the paper with the toner image transferred,
Control emissions, etc.

The image forming process control section 55 is a section for controlling the rotation control of the photosensitive drum 52 and the image forming process in the laser printer section 2. In order to improve the image quality, the charging potential by the charger 52a and the developing process are performed. Bowl 25b
Control the developing bias voltage, the toner concentration in the developing device 25b, the transfer output by the transfer device 25c, the peeling output by the peeling device 25d, and the like.

The image data processing unit 56 processes the image data for copying of 256 gradations / dots read by the CCD 17 through several steps such as histogram processing, error diffusion processing, compression processing, etc., to obtain 16 gradations. / Dot image data and stored in the image memory 56a. When printing this image data for copying,
The image data is read from the image memory 56a and output to the laser output controller 57.

The FAX data processing unit 58 includes a connector 28.
An image memory 58a for storing FAX image data input via the is provided. FAX data processing unit 58
When printing the FAX image data, reads out the image data from the image memory 58a and outputs the image data to the laser output control unit 57.

The print data processing unit 59 is a unit for processing the print data of the computer input through the connector, and if the image data for the computer to be sent is binary data, the image memory 59a as it is.
To store. However, the print data processing unit 59
A character code data expansion function may be provided. In that case, when the character code is sent, the character code is expanded into binary data and then stored in the image memory 59a. When printing image data for a computer, the image data is read from the image memory 59a and output to the laser output control unit 57.

The laser output control section 57 controls the laser output output from the laser writing unit 22. The laser output control unit 57 includes the image data processing unit 56,
Alternatively, the image data input from the FAX data processing unit 58 or the print data processing unit 59 is modulated into laser light, which is output to the photosensitive drum 25. At the time of this output, the output intensity of the laser light and the laser output width are appropriately changed according to the type of image data.

The operation unit 60 is an operation panel provided on the upper surface of the main body of the image forming apparatus, and is provided with a print switch for inputting an image formation start command, a ten-key pad for inputting the number of prints, and the like.

The main operation during image formation will be described.

The image forming apparatus is normally in the copying machine mode, and is switched to the print mode when FAX image data or computer image data is transmitted via the connector 28.

In the copying machine mode, normal copying processing is performed. That is, when the print switch is operated after the image forming conditions such as the number of prints and the density setting are input, the document scanning process is executed. And CCD1
The image data read by the image data processing unit 56
Process. After that, the image data is output to the laser writing unit 22, and the copy image is formed based on the image data.

On the other hand, when image data for FAX or image data for computer is transmitted through the connector 28, it is switched to the print mode. When an instruction to print is issued by a FAX device, a microcomputer, or the like (not shown), these devices determine the vacant state of the image forming apparatus. Then, in the empty state, that is, in the state where the copying process or other printing process is not executed,
The FAX machine and the microcomputer execute data transmission to the image forming apparatus. The image forming apparatus is switched to the printer mode, and the copy processing cannot be executed. The image forming apparatus stores the transmitted image data in the image memory 58a or 58a. Then, the print process is executed every time a predetermined amount of image data is transmitted. The predetermined amount is, for example, when one image data is received or when all the image data is received, and this is set appropriately by the device.

By the way, the required image quality is different between the copying machine mode and the printer mode. In the case of original copy in the copier mode, the gradation of copy image quality,
That is, halftone reproducibility is required. In addition, the density of black solid may be sacrificed in order to obtain sufficient reproducibility of light-colored portions. On the other hand, FAX or computer image data in the printer mode is binary data of “white” and “black”, and the required image quality is high black density, expressiveness of dots, firmness of lines, etc. Is.

Due to the difference in the required image quality, it is necessary to change the image forming process conditions between the copying machine mode and the printer mode. The process conditions include charging voltage, developing bias voltage, toner concentration, laser output intensity, laser output width and the like. FIG.
Shows an example of setting these process conditions, and each process condition will be described below.

First, an example of changing the charging voltage and the developing bias voltage as process conditions will be described.

FIG. 4 is a diagram showing the relationship between the original density and the density of the toner image formed on the photoconductor when the grayscale original is copied in the copying machine mode. When the copy image density exceeds 1.4, it is determined to be pure black. In this experiment, in examining the relationship between the document density and the copy image density,
The copying process was performed by changing the charging voltage and the developing bias voltage. FIG. 5 shows an example of setting the charging voltage and the developing bias voltage in that case. It should be noted that if only one of the charging voltage and the developing bias is changed, the density of the image becomes darker or lighter as a whole, and the image contrast cannot be obtained. By changing both of them at the same time, the density of the entire image is adjusted and the contrast is not destroyed.

As can be seen from FIG. 4, under the condition of the combination 1 in which the charging voltage and the developing bias voltage are high, the density of the original image is about 1.0 or less, and the toner image density is
A high concentration of 1.4 or more can be obtained. In such a state, the above-mentioned conditions necessary for the copying process are not satisfied. This is because the toner image becomes too dark as a whole, and a region having a particularly light density becomes almost unreproducible.

On the other hand, the conditions of combination 2 and combination 3
Under the condition of 3, the maximum density of the toner image gradually decreases, and under the condition of the combination 3, the maximum density of the toner image does not reach 1.4, and a light image is obtained on the entire document. It turns out that This is preferable for the copied image because it is possible to obtain the reproducibility of the light density region in accordance with the above-mentioned conditions of the copied image. In particular, good reproducibility can be obtained under the conditions of combination 2 and combination 3.

On the other hand, the FAX image data and the computer image data are binary data of black and white, and it is preferable that the black portion has a density as dark as possible.
Looking at the combination of the charging voltage and the developing bias voltage shown in FIG. 5, the copy image densities for solid black (1.4 original density) are 1.43, 1.40, and 1.35 in combinations 1 to 3, respectively. And the combination 1
It can be seen that in the state of the combination 2, sufficient black solid density can be obtained.

When the print processing was executed for the binary image data under the conditions of the above combinations 1, 2, and 3, the dot reproducibility of the image under the conditions of the combination 1 was very good, and the combination 2 It was possible to obtain almost good dot reproducibility even under the condition of. From this, it is understood that it is preferable to execute image formation under the conditions of combination 1 and combination 2 in the printer mode.

An example of changing the toner density in the developing device as the process condition will be described.

The developing device 25b contains a toner and a carrier as a two-component developer, and the ratio of the toner in this is the toner concentration. Toner density of 3.5
%, 4.0%, and 4.5%, and the grayscale copying process was performed in the same manner as in the above example. FIG. 6 shows the result. As can be seen from the figure, the higher the toner density in the developing device, the higher the density of the copy image,
Looking at the density of the toner image with respect to the density of 1.4 on the gray scale, the toner density of 4.0 is almost 1.4, and the toner density of 4.
5, a copy density of 1.45 was obtained with a toner density of 3.5, and 1.35 with a toner density of 3.5. From this relationship with the image quality required in the copying machine mode and the image quality required in the printer mode, the optimum toner density under the copying machine mode is about 3.5 to 4.0%, It can be seen that the optimum toner density below is about 4.0 to 4.5%.
As a result, the reproducibility of halftones can be improved in the copying machine mode, and a high density image with clear dots can be obtained in the print mode.

An example of changing the output intensity of the laser light as the process condition will be described.

The laser light output from the laser writing unit 22 is divided into 16 laser output widths so as to correspond to the print processing in the copying machine mode. That is, since the image data for copying is represented by 16 gradations (16 values) / dot as described above, it is divided into 16 (time division) to correspond to it. As a result, for example, when the density of a certain dot is the fourth gradation, laser light having a 4/16 width is output, and when the density of a certain dot is the 13th gradation, the laser light is
Laser light with a width of 3/16 is output. In the printer mode, the value is binary / dot, the laser output when the density is 0 is 0/16, and the laser output when the density is 1 is 16/16.

When changing the output intensity of the laser light,
Change the output intensity of laser light of the same width. For example, the illuminance of the full width of the laser light on the surface of the photosensitive drum is changed. In this example, the illuminance on the surface of the photosensitive member for the full width (16/16) of the laser light was set to three levels of 0.8 mW, 0.9 mW, and 1.0 mW. The toner image density with respect to the gray scale in this case is shown in FIG. From this figure, in the copying machine mode, the range of 0.8 to 0.9 mW in which the toner image density with respect to black solid (gray scale density 1.4) does not reach 1.4 is preferable, and in the printer mode. 0.9 to 1.0 m capable of obtaining a sufficient black solid density (toner image density 1.4 or more) with respect to black solid (gray scale density 1.4)
It can be seen that the range of W is preferable.

By changing the laser output intensity for canceling the charge on the photosensitive drum,
The density of the toner image formed on the photosensitive drum changes because the relative potential difference between the dark portion (the area not exposed to the light) and the bright portion (the area exposed to the light) causes a change in the density on the photosensitive drum. It is considered that this is because the adhered state of the toner changes.

An example of changing the output width of the laser light as the process condition will be described.

In order to change the output width of the laser light, the maximum output width of the laser light is set to χ, and the output width is changed within this χ. In this example, the maximum output width χ is divided into 32, and the 16th block, the 24th block, and the 32nd block are set as the output widths of the laser light.

For example, as shown in FIG. 8, when the output width is set up to the 16th block, when the image density of dots is the fifth gradation in the copying machine mode, 32 is set.
When the laser light is turned on in the range of the 1st to 5th blocks of the division and the gradation is the 14th, the 1st of the 32 divisions
The laser light is turned on in the range of the 14th block. When the dot image density is "1" in the printer mode, the laser light is turned on in the range of the first to sixteenth blocks.

On the other hand, when the output width is set up to the 32nd block, the laser beam remains off when the image density of the dots is the 0th gradation in the copying machine mode, but the first floor is used. When the tone is a tone, the laser beam is turned on in the range of 1st to 17th blocks in the 32 divisions, and when it is the 14th gradation, the laser beam is turned on in the range of 1st to 30th blocks of the 32 divisions. To do. Further, when the image density is "0" in the printer mode, the laser light remains off, but when it is "1", all 32/32 blocks are turned on.

When a gray scale copying experiment was conducted by changing the output width of the laser light in this way, the results shown in FIG. 9 were obtained. As can be seen from this figure, when the output width of the laser beam is changed, the slope of the copy image density with respect to the gray scale density changes accordingly, and the maximum density also changes. The maximum density is about 1.4 when the output width of the laser beam is 24/32 blocks with respect to the black solid of the grayscale original, and the output width of the laser beam is 32/32 blocks. When it was done, a higher concentration was obtained. On the contrary, the output width of the laser beam is 16/3
When it was reduced to 2 blocks, the overall density became light. From this, the output width of the laser beam in the copier mode is preferably 16/32 to 24/32.
Laser beam output width in printer mode is 24 / 32-3
It turns out that it is preferable to set it to 2/32.

The density of the toner image formed on the photosensitive drum changes by changing the laser output width, as in the case where the laser output intensity is changed. It is considered that this is because the adhered state of the toner on the photosensitive drum changes due to the potential difference.

As described above, by changing the process conditions such as the charging voltage and the developing bias voltage between the copying machine mode and the printer mode, it is possible to form an image having a quality suitable for each mode.

By the way, the image quality formed by the electrophotographic image forming apparatus is affected by environmental changes, changes over time, and the like. For example, when an OPC photosensitive member is used as the photosensitive drum, the surface potential at room temperature is 100 when compared to the surface potential at room temperature due to the temperature dependence of the mobility of the photo carrier in a low temperature environment.
A voltage drop of ~ 150V may occur. Also, Se
In the case of a photoreceptor, the surface potential increases by about 50 V in a low temperature environment due to the temperature dependence of the amount of thermally excited carriers generated in the photosensitive layer, and the surface potential decreases by about 50 to 100 V in a high temperature environment. Further, in the case of an OPC photosensitive member, as the number of copied sheets increases, mechanical stress (polishing action of a cleaner blade) is received, the photosensitive layer is reduced in film thickness, the film thickness is decreased, and the surface potential is gradually decreased. There is a tendency to go down.

In addition to this, for example, the developer is affected by humidity. When the humidity is low, the electric resistance of the developer itself is high, the charge holding power of the triboelectrically charged toner is high, and the density of the formed image is high. The opposite is true when the humidity is high. Further, the developer, particularly the carrier, may be peeled off the coat or the amount of the toner may be increased due to the spent on the carrier due to a change with time, which may change the toner chargeability.

As a result, the quality of the formed image is affected by environmental changes and changes over time. Therefore,
Conventionally, the process of changing process conditions according to environmental changes and changes over time has been executed. The main part of the procedure will be described.

As shown in FIG. 1, a reflective toner density sensor 29 is arranged on the peripheral surface of the photosensitive drum 25 between the developing device 25b and the cleaning device 25e. This detects the density of the toner patch formed on the photosensitive drum 25b.

The correction processing of the process conditions is performed, for example, during warm-up when the power of the image forming apparatus main body is turned on, at regular intervals during the power-on of the image forming apparatus main body, and a predetermined time has elapsed without executing the image forming processing. It is executed every so often. When the process condition correction timing comes, first, the process conditions such as the charging voltage and the developing bias voltage are set to a predetermined state to form a toner patch. This toner patch is moved to the position of the reflection type toner density sensor 29 as it is without being transferred to the paper,
The density is detected by the reflective toner density sensor 29.
The toner patch density thus obtained is compared with the reference density, and the process conditions such as the charging voltage and the developing bias voltage are corrected based on the comparison result.

A method of correcting individual process conditions will be described.

When correcting the charging voltage and the developing bias voltage, the charging voltage and the developing bias voltage are changed while maintaining a constant difference, and other process conditions such as laser output are set to the values in the copying machine mode. As a result, a toner patch is formed and the toner density is detected. On the other hand, as the reference density, the toner patch density detected under the same process condition under the standard environment at the initial stage of the apparatus is used.
When the state of the combination shown in is adopted, the reference density is 1.35. Therefore, of the conditions under which the charging voltage and the developing bias voltage are changed, the charging voltage and the developing bias voltage with which the density of 1.35 is obtained are set.
As a result, the appropriate charging voltage in the copier mode,
The developing bias voltage is required.

Now, by the above control, the charging voltage in the copying machine mode is increased by -100 V to -500 + (-10
It is assumed that a result of correcting 0) = − 600 V is obtained. On the other hand, in the printer mode, assuming that the correction factor in the copying machine mode is 1.0, printer mode correction factor = (− 600) / (− 500) =
From 1.2, it is necessary to perform 1.2 times the correction amount in the copier mode. That is, the charging voltage in the printer mode is −600 + (− 120) = − 720. In this way, by changing the correction rate for each mode, it is possible to perform correction according to each mode.

The developing bias voltage is set to have a constant difference with respect to the charging voltage, and the developing bias voltage = the charging voltage-(-150).

The toner density correction is performed as follows.

The toner patch forming conditions for correcting the toner density are the same as the charging voltage and the developing bias voltage. However, when the toner density is corrected, the toner density in the copying machine mode is determined based on the relationship between the toner density and the difference between the reference density and the detected toner patch density, which is obtained in advance and stored as a table. The toner density correction amount is obtained.

When the toner density correction rate in the copying machine mode is 1.0, the toner density correction rate in the printer mode is printer mode correction rate = 4.0 / 3.5 = 1.14. Therefore, the correction amount in the printer mode can be obtained by multiplying the toner concentration correction amount in the copying machine mode obtained based on the above table by 1.14.

A method of correcting the laser output intensity will be described.

When the laser output intensity is corrected, the laser output intensity is changed in a plurality of steps, and other process conditions such as the charging voltage and the developing bias voltage are set to the values of the copy mode. The laser output intensity changing step is, for example,
Although it is set to three stages of 0.9, 1.0, and 1.1, the number of stages is not limited to this, and for example, stages of higher values may be set. Under this condition, a toner patch is formed on the photosensitive drum 25, and the laser output intensity when the detected toner patch density reaches the reference density (about 1.35) is obtained. Thereby, the corrected laser output intensity for the copying machine mode is obtained.

On the other hand, assuming that the laser output intensity correction rate in the copying machine mode is 1.0, the laser output intensity correction rate in the printer mode is printer mode correction rate = 1.0 / 0.8 = 1.25. By multiplying the laser output intensity correction amount in the copying machine mode obtained as described above by 1.25, the correction amount of the laser output intensity in the printer mode can be obtained.

A method of correcting the laser output width will be described.

When the laser output width is corrected, the laser output width is set in a plurality of stages, and other process conditions such as the charging voltage and the developing bias voltage are set to the values in the copy mode. The laser output width is, for example, 14/32, 16/3
Although it is set to three stages such as 2, 18/32, this stage is not limited to this, and a larger number of stages may be set, and the range of the laser output width should be wider. It may be set to. The laser output width when the density of the toner patch formed under such conditions becomes the reference density (approximately 1.35) is obtained. This is the corrected laser output width in the copier mode.

Now, it is assumed that the appropriate laser output width in the copier mode is required to be 15. On the other hand, the laser output width correction factor in the printer mode with respect to the correction factor in the copying machine mode is printer mode correction factor = 32/16 = 2. Therefore, the correction amount in the copier mode is 16
When there is one step from / 32 to 15/32, the correction amount of the laser output width in the printer mode has two steps from 32/32 to 30/32. In this embodiment, when the correction is performed to increase the laser output width,
Since no further correction is possible in the printer mode, only the laser output width in the copying machine mode may be corrected and the laser output width in the printer mode may be fixed at 32/32. Also, in advance, the initial value of the laser output width in the printer mode should not be the maximum value of the laser output width that can be set (for example, not 32/32 but 28/32).
It may be set and a range that can be corrected later may be provided.

As described above, each process condition is corrected, and it becomes possible to form a toner image of an appropriate density on the photosensitive drum 25 without being affected by changes over time, changes in the environment, and the like.

Next, the toner image formed on the photosensitive drum 25 is transferred to a sheet, or the sheet is transferred to the photosensitive drum 25.
The transfer output and peeling output when peeling from the sheet will be described.

First, the transfer output will be described.

FIG. 10 is a diagram showing the transfer output required according to the density of the image formed on the photosensitive drum 25. Since the amount of toner per unit area increases as the image density on the photosensitive drum increases, it is necessary to increase the transfer output for transferring the toner on the photosensitive drum 25 to the paper. In the printer mode, since the image density is binary and the toner density of the area to which the toner is attached is the maximum density (black solid 1.4), in order to transfer the toner image of 1.4 density , A transfer output of about 180 μA is required.

On the other hand, in the copying machine mode, the image density is 16 values, and the transfer output is set so that good toner transfer is performed in the entire range from the low density area to the high density area. There is a need to. Therefore, it is necessary to set the value lower than the upper limit of the allowable range in the low density region and higher than the lower limit of the allowable range in the high density region. Therefore, in the copier mode, as shown in FIG.
It is preferable to set the transfer output to about 30 to 150 μA. In this way, by switching the transfer output between the copying machine mode and the printer mode, the photosensitive drum 2
It is possible to almost certainly transfer the toner attached on the sheet 5 to the sheet.

On the other hand, the peeling output is set as follows.

FIG. 11 shows the dark portion voltage of the photosensitive drum 25 (charging voltage = area not exposed to light = voltage of the area where toner is attached) and the paper on which the toner is transferred is peeled from the surface of the photosensitive drum 25. It is a figure showing the relationship with the output of the peeling device 25d required for. When the dark portion potential on the photoconductor drum 25 is high, the suction force between the surface of the photoconductor drum 25 and the toner is correspondingly increased. Therefore, it is necessary to set a high peeling output for separating the paper and the toner from the surface of the photosensitive drum 25. As a result, as shown in FIG. 11, the peeling voltage required depending on the dark space voltage also becomes high.

Here, as described above, the charging voltage required in the copying machine mode is approximately -500 to 550V. Therefore, the optimum peeling output required for peeling is approximately -2.
It becomes about 00 to -250V. On the other hand, the charging voltage required in the printer mode is about -550 to -600V, and the optimum peeling output required for peeling is about -250 to.
It is about -300V. By switching the peeling output according to the copying machine mode and the printer mode in this manner, the paper can be reliably peeled from the photosensitive drum 25, and the paper jam can be prevented. Note that the peeling output normally outputs both AC and DC. Also in this example, the AC output is fixed at 5.0 KV and only the DC output is changed.

By the way, the transfer performance and the peeling performance hardly change with time, but they are easily affected by environmental changes, especially humidity. The change in electric resistance due to moisture absorption of the paper has a great influence. Therefore, the transfer output and the peeling output are corrected according to the humidity in the main body of the image forming apparatus.

As shown in FIG. 1, the image forming apparatus main body is provided with a humidity sensor 30 for detecting the humidity in the apparatus. The transfer output and the peeling output are corrected according to the detection value of the humidity sensor 30.

FIG. 12 shows the results of obtaining the relationship between the relative humidity and the optimum transfer output in each of the copying machine mode and the printer mode. This relationship is stored in advance, and the transfer output is corrected according to the detected humidity.

FIG. 13 shows the result of the relationship between the relative humidity and the optimum peeling output obtained in each of the copying machine mode and the printer mode. This relationship is stored in advance and detected. An appropriate peeling output can be obtained by correcting the peeling output according to the obtained humidity.

The correction processing is executed at the same timing as the correction timing of the process condition, for example. By such a correction, good toner transfer and paper peeling can be executed even when the environmental humidity changes.

[0093]

According to the first aspect of the present invention, the image data of any of multi-gradation image data obtained by scanning a document and binary image data which is computer or FAX data can be obtained. The image formation is executed under the process conditions suitable for the above, and an image of optimum quality can be obtained.

According to the invention described in claim 2, the photoconductor,
When the density of the toner image formed on the photoconductor changes due to changes in the developer or the like over time or environmental changes, the process conditions are changed to prevent the density change of the toner image. At this time, since the change rate is switched between the multivalued process condition and the binary process condition, it is possible to prevent the toner image density from changing in each of the multivalued image data and the binary image data. According to the third aspect of the present invention, the toner on the photoconductor is adjusted by adjusting the transfer output even when the amount of toner adhered on the photoconductor is changed by changing the process condition during image formation. Can be sufficiently transferred onto paper. Further, the toner transfer can be maintained in a sufficient state even when the environmental humidity changes.

According to the invention described in claim 4, even when the attraction force between the photoconductor and the paper is changed by changing the charging voltage at the time of image formation, the peeling output is adjusted to adjust the photoconductor. The paper and the paper can be reliably separated. Further, even if the environmental humidity changes, the paper can be reliably peeled off.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus that is an embodiment of the present invention.

FIG. 2 is a block diagram of a control unit of the image forming apparatus.

FIG. 3 is a diagram showing an example of setting various process conditions.

FIG. 4 shows a relationship between a document density (gray scale) and a toner image density when the charging voltage and the developing bias voltage are changed.

FIG. 5 is a diagram showing a setting example of a charging voltage and a developing bias voltage.

FIG. 6 shows the relationship between the document density and the toner image density when the toner density in the developing device is changed.

FIG. 7 shows the relationship between the document density and the toner image density when the laser output intensity is changed.

FIG. 8 is a diagram showing a setting example of a laser output width.

FIG. 9 shows the relationship between the document density and the toner image density when the laser output width is changed.

FIG. 10 is a diagram showing a relationship between an image density to be transferred onto a sheet and a transfer output for transferring a toner image.

FIG. 11 is a diagram showing a relationship between a charging potential of a photosensitive drum and a peeling output for peeling a sheet.

FIG. 12 is a diagram showing a relationship between humidity and required transfer output.

FIG. 13 is a diagram showing a relationship between humidity and required peeling output.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Motoyuki Itoyama 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka Prefecture Sharp Corporation (72) Hiroo Naoi 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka Within the corporation

Claims (4)

[Claims] 1. A means for converting image data into laser light and switching the laser light output according to the gradation level of the image data; and an image forming means for forming a toner image having a density according to the laser light output. In an electrophotographic image forming apparatus equipped with, the data obtained by reading a document image is stored as multi-gradation image data, and this image data is converted into an output laser beam according to the gradation step to form an image. Image data represented by binary data sent from a facsimile machine, a computer or the like is stored, and the binary image data is output in two stages of ON / OFF of the laser light output. Printer mode means for performing image formation by converting only into the image forming means, and a process such as a photoconductor charging voltage and a developing bias voltage for forming multi-tone images by the copying machine mode means. An image forming apparatus comprising: a process condition switching unit that switches between a condition and a process condition such as a photosensitive member charging voltage and a developing bias voltage when performing binary image formation by the printer mode unit. . 2. A density detecting means for forming a toner patch on a photosensitive member under a predetermined process condition, and detecting the density of the toner patch, a toner patch density detected by the density detecting means, and a pre-stored value. The image forming apparatus according to claim 1, further comprising: a correction unit that compares the reference density that has been set, and corrects the process condition based on the comparison result, wherein the process condition is corrected based on the comparison result. When doing
There is provided means for switching between a change rate of process conditions when performing multi-gradation image formation by the copying machine mode means and a change rate of process conditions when performing binary image formation by the printer mode means. An image forming apparatus characterized by the above. 3. A means for setting a transfer output for transferring the toner on the photoconductor onto a sheet according to a change in the amount of toner adhering to the photoconductor according to the process condition set by the process condition switching means. A unit for detecting the humidity inside the image forming apparatus main body, a unit for storing the relationship between the humidity and the transfer output, and a unit for correcting the transfer output according to the detected humidity, The image forming apparatus according to claim 1. 4. A means for setting a peeling output for peeling a sheet from a photoconductor in accordance with a charging voltage set by the process condition switching means, and a means for detecting humidity in an image forming apparatus main body. The image forming apparatus according to claim 1, further comprising: a unit that stores a relationship between humidity and a peeling output; and a unit that corrects the peeling output according to the detected humidity.