JP2010128190A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that eliminates unnecessary drive and prevents toner deterioration by controlling the drive time of a developing drive section prior to image formation according to a charged state of toner. <P>SOLUTION: The image forming apparatus 1 includes: a developing unit 14 that charges toner and develops a latent image formed on a photoreceptor drum 11 by using the toner; a storage section 53 that stores the first time at which the image is finally formed; and a control section 52 that changes a development aging time Tc prior to a developing process, on the basis of the time Tb that has elapsed from the first time and the drive time Ta of the developing unit 14 when the image is finally formed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic system.

  Conventionally, in an image forming apparatus using an electrophotographic method, an electrostatic latent image is formed on a photoconductor when the photoconductor is irradiated with laser light based on image data of an original, and is formed on the photoconductor. The electrostatic latent image is developed by a developing device. Prior to development, a developing driving unit such as a developing roller is driven to charge the developer. In general, the development drive unit is linked with the driving of the fixing device and the photosensitive member, and therefore the drive time is set long. In recent years, in order to save energy, the frequency with which the apparatus is turned off in the power saving mode or the sleep state is increasing. Each time the device is turned on from the power saving mode or the sleep state, the development drive unit is driven and the developer is frequently charged. As a result, the developer deteriorates, causing problems such as a decrease in density and image fogging. May occur. In addition, the charge amount of the developer decreases according to the drive stop time of the development drive unit. If the stop time of the apparatus is short, the charge amount of the developer does not change much, but after the development drive unit stops driving for a long time, the charge amount of the developer is greatly reduced, and a stable image cannot be obtained. .

  Therefore, in Patent Document 1, the first time when the image forming process (development process) is executed last is counted with a clock. When the image forming process is started again, a drive stop time that is the difference between the first time and the current time is calculated. When the drive stop time is equal to or greater than a predetermined value, the development unit such as the development sleeve and the developer supply roller is driven in advance by the development drive unit for a predetermined time determined based on the drive stop time, and then the image A forming process is performed. In this way, the charge amount of the developer that has decreased during the drive stop is recovered.

However, in the above-described conventional technology, the drive time of the development drive unit is changed based on the drive stop time, but the image formation state of the last image formation process (development process), for example, The developer charge amount also changes depending on the time required for the development processing, so that even if the developer charge amount is corrected based only on the drive stop time, the developer is stable during the next image formation. In this case, there is a problem in that a problem such as a decrease in density and image fogging occurs.
JP 2001-147630 A (paragraph [0048], FIG. 1)

  The present invention has been made in order to solve the above-described problems, and wasteful driving can be achieved by controlling the driving time of the development driving unit prior to image formation in accordance with the charged state of the developer. An object of the present invention is to provide an image forming apparatus that eliminates the deterioration of the developer.

  In order to achieve the above object, the present invention relates to an electrophotographic image forming apparatus for forming an image on paper, in which a developer is charged and a latent image formed on a photoconductor is developed using the developer. A charging process prior to the development process based on the storage unit, the storage unit storing the first time at which the image was last formed, the elapsed time from the first time, and the state of the last image formation. And a control unit for changing the time.

  According to this configuration, as the elapsed time from the first time increases, the charge amount of the developer decreases. However, depending on the state of the last image formation, the charge amount of the developer at the first time Therefore, even when the elapsed time from the first time is the same, the degree of decrease in the charge amount of the developer is different. Based on the degree of the decrease, the charging time is corrected prior to the developing process, so that the developer charge amount is always appropriate regardless of the last image formation state and the elapsed time.

  According to a second aspect of the present invention, the control unit changes the time for the charging process based on the elapsed time from the first time and the number of output sheets when the image is formed last. It is said. According to this configuration, since the charge amount of the developer at the first time differs depending on the number of output sheets when the image is formed last, even if the elapsed time from the first time is the same, the developer The degree to which the amount of charge decreases is different. By correcting the charging processing time prior to the development processing based on the degree of this decrease, the developer charge amount is always appropriate regardless of the last image formation state and elapsed time.

  According to a third aspect of the present invention, the control unit determines the time for the charging process based on the elapsed time from the first time and the driving time of the developing device when the image is formed last. It is characterized by changing. According to this configuration, since the charge amount of the developer at the first time varies depending on the driving time of the developing device when the image is formed last, even if the elapsed time from the first time is the same. The degree of decrease in the charge amount of the developer is different. Based on the degree of the decrease, the charging time is corrected prior to the developing process, so that the developer charge amount is always appropriate regardless of the last image formation state and the elapsed time.

  According to the first aspect of the present invention, as the elapsed time from the first time becomes longer, the charge amount of the developer decreases, but at the first time according to the state of the last image formation. Since the charge amount of the developer is different, the degree of decrease in the charge amount of the developer is different even if the elapsed time from the first time is the same. Based on the degree of this decrease, by correcting the charging process time prior to the development process, the developer charge amount is always appropriate regardless of the last image formation state and elapsed time. Deterioration can be prevented, and useless driving of the developing device can be eliminated.

  According to the second aspect of the present invention, since the charge amount of the developer at the first time varies depending on the number of output sheets when the image is formed last, the elapsed time from the first time is the same. Even so, the degree of decrease in the charge amount of the developer is different. Based on the degree of this decrease, by correcting the charging process time prior to the development process, the developer charge amount is always appropriate regardless of the last image formation state and elapsed time. Deterioration can be prevented, and useless driving of the developing device can be eliminated.

  According to the third aspect of the present invention, since the charge amount of the developer at the first time varies depending on the driving time of the developing device when the image is formed last, the elapsed time from the first time Even when the time is the same, the degree of decrease in the charge amount of the developer is different. Based on the degree of this decrease, by correcting the charging process time prior to the development process, the developer charge amount is always appropriate regardless of the last image formation state and elapsed time. Deterioration can be prevented, and useless driving of the developing device can be eliminated.

  Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. The embodiment of the present invention shows the most preferable form of the invention, and the use of the invention and the terms shown here are not limited thereto.

(First embodiment)
FIG. 1 is a schematic plan view showing an overall configuration of an image forming apparatus according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 1 includes a sheet feeding unit 2 disposed in a lower portion thereof, a sheet conveying unit 3 disposed on a side of the sheet feeding unit 2, and the sheet conveying unit 3. The image forming unit 4 disposed above the image forming unit 4, the fixing unit 5 disposed on the discharge side of the image forming unit 4, and the image disposed above the image forming unit 4 and the fixing unit 5. A reading unit 6 is provided.

  The paper feed unit 2 includes a plurality of paper feed cassettes 7 for containing paper 9, and the paper 9 is fed from the selected paper feed cassette 7 among the plurality of paper feed cassettes 7 by the rotation of the paper feed roller 8. Each sheet is surely sent out to the sheet transport unit 3.

  The paper 9 sent to the paper transport unit 3 is transported toward the image forming unit 4 via the paper supply path 10. The image forming unit 4 forms a toner image on a sheet 9 by an electrophotographic process, and a photosensitive drum 11 rotatably supported in a predetermined direction (the arrow direction in the drawing), and the photosensitive drum 11. A charging unit 12, a developing device 14, a transfer unit 15, a cleaning unit 16, and a charge eliminating unit 17 are provided around the body drum 11 along the rotation direction.

  The charging unit 12 includes a charging wire to which a high voltage is applied. When a predetermined potential is applied to the surface of the photosensitive drum 11 by corona discharge from the charging wire, the surface of the photosensitive drum 11 is uniformly charged. . Then, when light based on the image data of the document read by the image reading unit 6 is irradiated to the photosensitive drum 11 by the exposure unit 13, the surface potential of the photosensitive drum 11 is selectively attenuated, and the photosensitive drum. 11 An electrostatic latent image is formed on the surface. Next, the developing device 14 develops the electrostatic latent image on the surface of the photosensitive drum 11, and a toner image is formed on the surface of the photosensitive drum 11. The toner image is transferred to the paper 9 supplied between the photosensitive drum 11 and the transfer unit 15 by the transfer unit 15.

  The sheet 9 on which the toner image has been transferred is conveyed toward the fixing unit 5 disposed on the downstream side of the image forming unit 4 in the sheet conveying direction. In the fixing unit 5, the paper 9 is heated and pressed by the heating member 18 and the pressure roller 19 as a pressure rotating body, and the toner image is melted and fixed on the paper 9. Next, the fixed sheet 9 is discharged onto the discharge tray 21 by the discharge roller pair 20. After the transfer by the transfer unit 15, the toner remaining on the surface of the photoconductive drum 11 is removed by the cleaning unit 16, and the residual charge on the surface of the photoconductive drum 11 is removed by the charge eliminating unit 17. Then, the photosensitive drum 11 is charged again by the charging unit 12, and thereafter image formation is performed in the same manner.

  Next, the developing device will be described with reference to FIG. FIG. 2 is a diagram schematically showing a developing device and structural members related to the developing device in the image forming apparatus according to the embodiment of the present invention.

  As shown in FIG. 2, the developing device 14 includes a housing 22 that houses a magnetic one-component developer, stirring members 23 and 24 that stir and convey the developer (hereinafter, sometimes referred to as “toner”), A developing roller 26 for conveying the toner to the photosensitive drum 11 and a regulating member 28 are provided. The toner tank 31 supplies toner to the developing device 14.

  The agitating members 23 and 24 are disposed at the bottom of the housing 22 and include spiral blades provided on a support shaft extending in the axial direction. When the stirring members 23 and 24 rotate, the toner circulates and mixes between the stirring members 23 and 24 and is conveyed to the developing roller 26.

  The developing roller 26 includes a magnet that generates a magnetic field toward the developing roller 26 at a position adjacent to the stirring member 24, and is rotatably supported by the housing 22. The developing roller 26 is exposed from the opening of the housing 22 and faces the photosensitive drum 11 with a certain interval. The toner is conveyed from the developing roller 26 to the photosensitive drum 11 at a portion adjacent to the developing roller 26 and the photosensitive drum 11.

  The regulating member 28 regulates the toner carried on the surface of the developing roller 26 to a predetermined layer thickness, and is attached substantially above the developing roller 26 with a predetermined interval from the surface of the developing roller 26.

  Further, the image forming apparatus 1 includes a development driving unit 51 such as a motor that rotationally drives the developing roller 26, a drum driving unit 55 such as a motor that rotationally drives the rollers of the photosensitive drum 11 and the fixing unit 5, and during development. A bias power source 56 that applies a bias to the developing roller 26, a control unit 52 that controls driving of each of the drive units 51 and 55 and the bias power source 56, a clock 54 that is connected to the control unit 52, and a control unit 52. And a storage unit 53.

  The toner conveyed from the stirring member 24 is carried on the surface of the developing roller 26 by the magnetic force in the developing roller 26. The carried toner is regulated to a certain height by the regulating member 28 and is conveyed toward the photosensitive drum 11 by the rotation of the developing roller 26 by the development driving unit 51. In accordance with the bias applied to the developing roller 26 by the bias power source 56 and the potential on the surface of the photoconductive drum 11, the toner is conveyed to the surface of the photoconductive drum 11 at a portion near the developing roller 26 and the photoconductive drum 11. The

  Next, the operation of warming up the apparatus and the subsequent image forming operation will be described with reference to FIGS. 3 is a warm-up time chart in the image forming apparatus, and FIG. 4 is an image forming time chart.

  As shown in FIG. 3, when the main SW (power supply) of the apparatus is turned on or when the sleep state or the power saving mode is shifted to the output enabled state, the drum driving unit 55 drives the photosensitive drum and the fixing roller for a predetermined time and develops The driving unit 51 rotates the developing roller 26 for a time according to the control described later, charges the toner carried on the developing roller 26 (hereinafter sometimes referred to as “developing aging”), and warms up.

  As shown in FIG. 4, when the warm-up is completed, the development driving unit 51 and the drum driving unit 55 are driven for a period of time Ta, and a desired number of images are formed. When the formation of the desired number of images is completed, the driving of the development driving unit 51 and the drum driving unit 55 is stopped. , The clock 54 measures the first time when the driving of the development driving unit 51 is stopped, and the storage unit 53 holds the first time via the control unit 52 and also sets the time Ta to the developing device. Is held as the driving time. Thereafter, the apparatus is turned off.

  When power is turned on when image formation is started again, the control unit 52 calculates a difference Tb between the first time stored in the storage unit 53 and the second time at the current power-on. Based on the elapsed time Tb from the first time and the developing device driving time Ta previously held in the storage unit 53, the developing aging time Tc prior to the current image formation is determined.

  The determination of the development aging time Tc will be described with reference to FIGS. FIG. 5 is a diagram showing the relationship between the elapsed time Tb from the first time (unit is hours) and the toner charge amount (unit is μC / g), and FIG. 6 is the development aging time Tc (unit is seconds). ) And the toner charge amount (unit: μC / g).

  The solid line shown in FIG. 5 is the case where the developing device drive time Ta is relatively long, and the toner charge amount is high at the first time (when the elapsed time Tb in FIG. 5 is 0). A chain line is a case where the developing device drive time Ta is relatively short, and the toner charge amount is low at the first time. The broken line in FIG. 5 indicates that the developing device drive time Ta is in the middle of the above two, and the toner charge amount is also in the middle of the above two. As the elapsed time Tb becomes longer, the toner charge amount of these three members decreases, but the degree to which the toner charge amount decreases differs depending on the toner charge state at the first time. Therefore, for example, assuming that the toner charge amount necessary for proper image formation is 28 μC / g, when the elapsed time Ta is 6 hours, the three toner charge amounts are approximately 29 μC / g, 26 μC from the highest. / G and 23 μC / g, it is difficult to achieve an appropriate charge amount only by the elapsed time Tb from the first time, and an appropriate toner charge amount is included including the drive time Ta of the previous developer. Thus, it is necessary to determine the development aging time Tc.

  As shown in FIG. 6, the toner charge amount before image formation (when the development aging time Tc in FIG. 6 is 0 second) is determined by the previous developer driving time Ta and the elapsed time Tb from the first time. In some cases, high charging shown by a solid line, medium charging shown by a broken line, and low charging shown by a one-dot chain line. When these three members are developed and aged, the toner charge amount increases. The amount of increase varies depending on the level of toner charge before image formation, and the development aging time for achieving an appropriate toner charge varies. For example, if an appropriate toner charge amount is 28 μC / g (line T in FIG. 6), development aging of about 40 seconds is required to make the low charge toner indicated by the one-dot chain line in FIG. 6 an appropriate toner charge amount. In addition, in order to make the medium charged toner indicated by the broken line in FIG. 6 have an appropriate toner charge amount, development aging of approximately 20 seconds is required. Further, in the case of the highly charged toner indicated by the solid line in FIG. Is no longer necessary. Therefore, when the previous driving time Ta of the developing device is short, the developing aging time is lengthened. When the previous driving time Ta of the developing device is long, the toner charge amount is high, so the developing aging time is shortened. To be.

Therefore, for example, the relationship between the elapsed time Tb, the developing device drive time Ta, and the development aging time Tc shown in Table 1 is defined.

  In this table, when the elapsed time Tb is longer, the development aging time Tc is lengthened, and even when the elapsed time Tb is the same, if the previous drive time Ta of the developing device is short, the development aging time Tc is It is determined to be long. Further, when the elapsed time Tb exceeds a predetermined time, the developing aging time Tc is set to be constant regardless of the previous driving time Ta of the developing device. In this way, the reduced toner charge amount is recovered regardless of the state of the previous image formation or the elapsed time from the previous image formation.

  This table is stored in the storage unit 53 in advance. Prior to image formation, the control unit 52 drives the developing roller 26 to rotate for the development aging time Tc based on this table from the previous driving time Ta and the elapsed time Tb of the developing device stored in the storage unit 53. Thereby, development aging is performed.

  According to the first embodiment, the image forming apparatus 1 charges the toner, uses the toner to develop the latent image formed on the photosensitive drum 11, and finally forms the image. 1 based on the storage unit 53 that stores the time 1, the elapsed time Tb from the first time, and the driving time Ta (image formation state) of the developing device 14 at the time of the last image formation. Prior to this, a control unit 52 for changing the development aging time (charging processing time) Tc is provided.

  According to this configuration, since the toner charge amount at the first time varies depending on the driving time Ta of the developing device 14 when the image is formed last, even if the elapsed time Tb from the first time is the same. The degree of toner charge reduction is different. Based on the degree of this decrease, the development aging time (charge processing time) Tc is corrected prior to the development process, so that the drive time Ta (image formation state) of the developing device 14 and the elapsed time Tb are finally related. Since the toner charge amount is always appropriate, toner deterioration can be prevented, and unnecessary driving of the developing device 14 can be eliminated.

(Second Embodiment)
FIG. 7 is a diagram schematically showing a developing device and components related to the developing device in the image forming apparatus according to the second embodiment of the present invention. In the second embodiment, the number of output sheets for image formation is used as the last image formed state, and the development aging time is corrected based on the number of output sheets and the elapsed time from the first time. Hereinafter, the description of the same part as that of the first embodiment is omitted.

  The image forming apparatus 1 includes a development driving unit 51 such as a motor that rotationally drives the developing roller 26, a drum driving unit 55 such as a motor that rotationally drives the rollers of the photosensitive drum 11 and the fixing unit 5, and a developing roller during development. 26, a bias power source 56 for applying a bias to the control unit 26, a control unit 52 for controlling the driving of each of the drive units 51 and 55 and the bias power source 56, a clock 54 connected to the control unit 52, and a memory connected to the control unit 52 And a sheet number counter 57 connected to the control unit 52.

  When the development driving unit 51 and the drum driving unit 55 are driven to form a desired number of images, the number counter 57 counts the number of sheets on which the image is formed, and the storage unit 53 is connected via the control unit 52. This output number P is held. When the formation of the desired number of images is completed, the driving of the development driving unit 51 and the drum driving unit 55 is stopped. The clock 54 measures the first time when the driving of the development driving unit 51 is stopped, and the storage unit 53 holds the first time via the control unit 52. Thereafter, the apparatus is turned off. When the power supply is turned on when starting image formation again, the control unit 52 determines the difference between the first time stored in the storage unit 53 and the second time at the current power-on (first time). Elapsed time) Tb is calculated.

  When the number of output sheets P increases, the rotation driving time of the developing roller 26 increases, and the charge amount of the toner carried on the developing roller 26 increases. On the other hand, when the number of output sheets P decreases, the rotation driving time of the developing roller 26 increases. The toner becomes shorter and the charge amount of the toner carried on the developing roller 26 is low. As described in the first embodiment, as the elapsed time Tb increases, the toner charge amount decreases. Therefore, when the previous output number P is small, the development aging time is lengthened. When the previous output number P is large, the toner charge amount is high, so that the development aging time is shortened. Time Tc is determined.

Therefore, for example, the relationship between the elapsed time Tb, the previous output number P, and the development aging time Tc shown in Table 2 is defined.

  In this table, as the elapsed time Tb becomes longer, the development aging time Tc is lengthened, and even if the elapsed time Tb is the same, the development aging time Tc becomes longer when the number P of previous output is small. It is determined as follows. Further, when the elapsed time Tb is equal to or longer than a predetermined time (12 hours), the development aging time Tc is set to be constant regardless of the previous output number P. In this way, the reduced toner charge amount is recovered regardless of the state of the previous image formation or the elapsed time from the previous image formation.

  This table is stored in the storage unit 53 in advance. Prior to image formation, the control unit 52 drives the developing roller 26 to rotate for the development aging time Tc based on this table from the previous output number P stored in the storage unit 53 and the elapsed time Tb. Thereby, development aging is performed.

  According to the second embodiment, the image forming apparatus 1 charges the toner, and uses the toner to develop the latent image formed on the photosensitive drum 11, and finally the image forming apparatus 1 forms the image. Based on the storage unit 53 that stores the time of 1, the elapsed time Tb from the first time, and the number of output sheets P (the image formed state) when the image was last formed, the development process is performed prior to the development process. And a control unit 52 that changes the aging time (charge processing time) Tc.

  According to this configuration, the toner charge amount at the first time differs depending on the number of output sheets P when the last image is formed. Therefore, even if the elapsed time Tb from the first time is the same, the toner charge amount is the same. The degree of decrease is different. Based on the degree of this decrease, the development aging time (charge processing time) Tc is corrected prior to the development process, so that the number of output sheets P (image formed state) and the elapsed time Tb when the image is formed last. Regardless, since the toner charge amount is always appropriate, toner deterioration can be prevented, and unnecessary driving of the developing device 14 can be eliminated.

  The present invention can be used for an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic system.

1 is a schematic plan view showing an overall configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram schematically showing a developing device and structural members related to the developing device in the image forming apparatus according to the first embodiment of the present invention. These are time charts for warm-up in the image forming apparatus according to the first embodiment of the present invention. These are time charts of image formation in the image forming apparatus according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating an elapsed time from a first time and a toner charge amount in the image forming apparatus according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating a charging processing time and a toner charge amount in the image forming apparatus according to the first embodiment of the present invention. These are the figures which show schematically the developing device in the image forming apparatus which concerns on 2nd Embodiment of this invention, and the structural member relevant to a developing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Photosensitive drum 14 Developing device 26 Developing roller 51 Development drive part 52 Control part 53 Memory | storage part 54 Clock 57 Sheet counter

Claims (3)

In an electrophotographic image forming apparatus that forms an image on paper,
A developer that charges the developer and develops the latent image formed on the photoreceptor using the developer;
A storage unit for storing a first time when an image is formed last;
An image forming apparatus comprising: a control unit configured to change a charging processing time prior to a developing process based on an elapsed time from the first time and a state in which an image is finally formed.   2. The image forming apparatus according to claim 1, wherein the control unit changes a charging process time based on an elapsed time from the first time and an output number of sheets when an image is formed last. .   2. The charging unit according to claim 1, wherein the control unit changes a charging process time based on an elapsed time from the first time and a driving time of the developing device when an image is formed last. Image forming apparatus.

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