JP2006047388A - Image forming apparatus and developer supplying method in its developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and a developer supplying method in its developing device preventing deterioration in working efficiency by making a compulsive consumption quantity for refreshing developer smaller than before even when printing ratio is low and by making the intervals longer between the compulsive consumptions of the developer. <P>SOLUTION: A means to count the number of image formed sheets, a means to count the accumulated number of dots in a formed image and a control means to calculate average printing ratio of the formed image from the counted number of image formed sheets and the accumulated number of dots and varying the developer supplying interval from a developer supplying means to a developer containing means according to the average printing ratio are provided in the apparatus. The control means makes the developer supplying interval from the developer supplying means to the developer containing means shorter according to the average printing ratio when the average printing ratio is less than a standard printing ratio which is determined beforehand and the developer quantity in the developer containing means exceeds the specified quality determined according to the printing ratio. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention 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 method, and a developer supplying method in the developing apparatus. In particular, an image is formed with original data having a low printing rate. The present invention relates to an image forming apparatus which prevents toner deterioration and a developer supply method in the developing apparatus.

  In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a composite machine using an electrophotographic system, a latent image formed on a photoconductor is developed so as to face the photoconductor and be placed in a developer storage chamber. A developer carrying member that carries the contained developer and transports it to the development region is used. At this time, for example, the amount of developer used for actual image formation with respect to the amount of developer (number of dots) used when the entire surface of the formed image is black solid (in the case of color, solid for each color used) When the ratio of (number of dots) is defined as the printing rate, this printing rate is about 5% in a normal image. However, when this printing rate is low, less developer is transported from the developer carrier to the photosensitive member. Therefore, the replacement of the developer particles in the developing device is reduced, the developer becomes excessively charged, the external additive for charge control is peeled off or is embedded in the developer, and the charging becomes unstable, as shown in FIG. As described above, image density reduction and fogging occur.

  The graph shown in FIG. 10 is a graph obtained by examining the change in image density depending on the number of printed sheets when the document printing rate is 5%, 4%, 2.5%, 1.5%, and 0.5%. Yes, the horizontal axis represents the number of printed sheets, and the vertical axis represents the image density (Macbeth density (measured using a reflection density meter RD918 manufactured by Macbeth), 0.00 means white and 1.60 means black). From this graph, it can be seen that when the document printing rate is 2.5% or less, the image density decreases with the number of printed sheets.

  In particular, in an image forming apparatus having a plurality of developing devices such as a color image forming apparatus, various printing is performed from a case of a high printing rate such as a photograph or a graphic image to a low printing rate such as only a logo mark. Rate images are handled, and the printing rate is often different for each developing device. Therefore, conventionally, improvements have been made to stabilize the charge control ability of the developer by optimizing the surface shape, material and external additives of the toner and improving the surface material of the developer carrier. In this case, the developer is excessively charged and the above phenomenon occurs.

  Therefore, Patent Documents 1 and 2 are provided with a printing rate calculation means for calculating the printing rate and a control means for instructing a forced consumption operation of the developer to the photosensitive member, and the printing rate calculated by the printing rate calculation means is used as a reference. When the printing rate is smaller than the predetermined reference printing rate, the developer is forcibly consumed, and the same effect as that in which the image formation is performed at a predetermined printing rate is obtained (hereinafter referred to as this). The technique is abbreviated as developer refresh.

JP-A-4-68370 JP-A-4-88641

  However, the developer refresh techniques disclosed in Patent Documents 1 and 2 consume a large amount of developer due to forced consumption of the developer, and the developer is consumed even though it is not used from the user's perspective. There is also a problem that work efficiency deteriorates because a certain time is required for this forced consumption.

  Therefore, in the present invention, even if the printing rate is low, the forced consumption of the developer can be reduced as compared with the conventional one, and the working efficiency is deteriorated by making the forced consumption interval of the developer large. An object of the present invention is to provide an image forming apparatus and a developer supplying method in the developing apparatus that can prevent this.

In order to solve the above problems, a developer supplying method in the developing device of the image forming apparatus according to the present invention is as follows.
A developing device comprising: a developer carrying member that conveys the developer to the developing region facing the photosensitive member; and a developer containing unit that supplies the developer to the developer carrying member; and the developer containing in the developing device. A developer supplying method in the developing device of the image forming apparatus, the developer supplying means for supplying the developer to the means from the outside,
The image forming apparatus includes a means for counting the number of image formations and a means for counting the cumulative number of dots of the formed image, and calculates an average printing rate based on the counted cumulative dot number and the number of image formations. When the printing rate is lower than a predetermined reference printing rate, the developer supply interval by the developer supplying unit to the developer containing unit is shortened.

In order to solve the above problems, a developer supplying method in the developing device of the image forming apparatus according to the present invention is as follows.
A developing device comprising: a developer carrying member that conveys the developer to the developing region facing the photosensitive member; and a developer containing unit that supplies the developer to the developer carrying member; and the developer containing in the developing device. A developer supplying method in the developing device of the image forming apparatus, the developer supplying means for supplying the developer to the means from the outside,
The image forming apparatus includes a means for counting the number of image formations and a means for counting the cumulative number of dots of the formed image, and calculates an average printing rate based on the counted cumulative dot number and the number of image formations. When the printing rate is lower than a predetermined reference printing rate, the developer supply to the developer containing unit by the developer supplying unit is determined according to the amount of developer in the developer containing unit corresponding to the printing rate. It is characterized by carrying out so that it may become more than the specified amount.

In order to solve the above problems, an image forming apparatus according to the present invention includes:
A developing device comprising: a developer carrying member that conveys the developer to the developing region facing the photosensitive member; and a developer containing unit that supplies the developer to the developer carrying member; and the developer containing in the developing device. An image forming apparatus having developer supplying means for supplying the developer to the means from the outside,
The image forming apparatus calculates the average printing rate of the formed image from the means for counting the number of image formations, the means for counting the cumulative number of dots of the formed image, and the counted number of image formations and the cumulative number of dots, A control unit that changes a developer supply interval from the developer supply unit to the developer storage unit in accordance with the average printing rate, and the control unit that changes the developer supply interval has the average printing rate set in advance. When smaller than a predetermined reference printing rate, the developer supply interval from the developer supply unit to the developer storage unit is controlled to be short according to the average printing rate, and the amount of developer in the developer storage unit is It is characterized in that the amount exceeds a specified amount corresponding to the printing rate.

  In this way, the average print rate of the formed image is calculated from the cumulative number of dots of the formed image and the number of formed images, and when the average print rate is smaller than a predetermined reference print rate, the average print rate depends on the average print rate. The developer supply interval from the developer supply means to the developer storage means is controlled to be short so that the amount of developer in the developer storage means becomes equal to or greater than a predetermined amount corresponding to the printing rate. Thus, when the highly charged developer on the developer carrying member returns to the developer containing means, it can be mixed with more developer. For this reason, excessive charging of the developer described above and the external additive for charge control in the developer are peeled off or embedded in the developer to prevent charging from becoming unstable and reducing image density and fogging. can do. That is, it is known that a two-component development system using a carrier as a developer has an effect of preventing charge-up by increasing the toner-to-carrier ratio. When there is a large amount of developer in the means, there is an effect of lowering the charge of the developer returned without being used for development. In addition, by gradually replenishing the developer in the developer accommodating means, it is possible to prevent the occurrence of image defects such as fogging and image density reduction due to changes in toner characteristics during toner replacement.

  The developer supply interval from the developer supply means to the developer accommodating means is determined in advance by the development amount calculated based on the cumulative dot number calculated by the cumulative dot number counting means for each specific printing rate range. By setting the interval to reach the predetermined value, the developer amount corresponding to the printing rate can always be ensured in the developer accommodating means.

Further, the image forming apparatus is configured so that when the number of image formations counted by the image formation number counting unit reaches a predetermined number and the calculated average printing rate is lower than a printing rate that is a predetermined reference, A predetermined amount of developer is developed on the photosensitive member and consumed.
Further, the control means is configured to provide an amount corresponding to the average printing rate when the image forming number counted by the image forming number counting unit reaches a predetermined number and the calculated average printing rate is lower than a predetermined reference printing rate. The developer is controlled to be developed from the developer containing means onto the photosensitive member via the developer carrying member.

  In this way, in addition to controlling the developer supply interval from the developer supply means to the developer containing means to be short, development is performed when the number of image formation reaches a predetermined number and the average print rate is lower than the reference print rate. The developer is refreshed by developing and consuming the developer in the developer accommodating means by an amount corresponding to the printing rate. However, the developer in the developer containing means is replenished at short intervals when the printing rate is low. Since the developer is prevented from being charged up, the amount of developer consumed in this refresh can be less than in the case where the conventional refresh is performed alone, and the forced consumption (refresh) interval of the developer can be increased. In addition, it is possible to provide an image forming apparatus that can prevent work efficiency from deteriorating and a developer supplying method in the developing apparatus.

  When the image forming apparatus develops and consumes the developer on the photosensitive member, a bias voltage for conveying the developer from the developer carrying member to the photosensitive member is set for each specific printing rate range. By making the bias larger than the bias, it becomes possible to reliably consume the developer charged and charged up with a strong power.

  As described above, according to the present invention, since the forced consumption interval of the developer can be increased, work efficiency can be prevented from being deteriorated, and the amount of the developer discharged by the forced consumption can be reduced as compared with the prior art. Therefore, it is possible to provide an efficient image forming apparatus and a developer supplying method in the developing apparatus.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  FIG. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention, FIG. 2 is a schematic control block diagram for implementing a developer supply method in the developing apparatus according to the present invention, and FIG. 3 is a developing apparatus according to the present invention. FIG. 4 is a flowchart of developer refresh when the developer supply method in the developing device according to the present invention is used, and FIG. 5 is a flowchart of the developer supply method in the developing device according to the present invention. A table listing the parameters in the first embodiment, such as the printing rate, the start of replenishment of the developer, the replenishment amount, and the consumption at the time of refreshing when performing the developer refresh, FIG. 6 shows the implementation of the first embodiment. FIG. 7 is a graph showing the relationship between the number of printed sheets and the image density at various printing rates. FIG. 7 is a graph showing the correction of the printing rate and the developer when the developer supplying method and the developer refresh in the developing device according to the present invention. A table listing the parameters in the second embodiment such as start, replenishment amount, consumption during refresh, etc. FIG. 8 shows the relationship between the number of printed sheets and the image density at various printing rates. FIG. 9 is a graph in which the relationship between the number of printed sheets and the image density at various printing rates is examined by performing only developer refresh.

  In FIG. 1, reference numeral 1 denotes a photoreceptor (image carrier) drum formed of a-Si (amorphous silicon), and an exposure device 3 using a charging device 2, for example, a laser scanning unit, is arranged around the drum. Furthermore, 7a, 7b, 7c, 7d in the developing device 4 indicated by black (BK) 4a, magenta (M) 4b, cyan (C) 4c, and yellow (Y) 4d are provided on the photosensitive drum (image carrier). A rotary type developing device 4 is provided so that the developer carrying members shown in FIG. Each developer unit 4 is provided with a developer storage chamber of black (BK) 41a, magenta (M) 41b, cyan (C) 41c, and yellow (Y) 41d, and each developer storage chamber 41a, 41b, 41c, and 41d have a capacity of about 30 g, for example, and when an image is formed at a standard printing rate (about 5%), the developer provided outside when the developer is reduced to 20 g. When the developer is supplied from the storage units 42a, 42b, 42c, and 42d by a developer supply means (not shown) and is supplied up to about 28 g, the supply is terminated by detecting it with a sensor (not shown). It is like that. In the following description, a case where the toner in the developer is a positively charged toner and a toner having a volume average particle diameter of 5.0 to 8.0 μm is used will be described as an example.

  5 is an intermediate transfer belt for transferring the toner images of the respective colors formed on the photosensitive drum 1 in an overlapping manner, and 51 is a primary transfer roller for transferring the toner image formed on the photosensitive drum 1 to the intermediate transfer belt 5. , 6 is a cleaning device for the photosensitive drum 1, 8 is a secondary transfer roller for transferring the toner image on the intermediate transfer belt 5 to the recording medium 9, 10 is a fixing device, 11 is a cleaning device for the intermediate transfer belt, and 12 is a recording device. In the following description, the present invention will be described by taking a color image forming apparatus using the rotary type developing device 4 and the intermediate transfer belt 5 as an example. If the image forming apparatus has a structure capable of supplying the developer from the developer storage unit 42 provided outside as needed, such as a monochrome image forming apparatus or a tandem color image forming apparatus. It may be in the form image forming apparatus such as it is of course.

  In FIG. 2, 20 is a control device for the entire image forming apparatus, 21 is image data to be formed, 22 is a counter for the number of image formations counted by the control device 20, and 23 is a color image shown in FIG. In the case of a forming apparatus, the number of dots in the image data 21 counted for each color to be used (for each developing device 4a, 4b, 4c, 4d) is accumulated for each color (for each developing device 4a, 4b, 4c, 4d). For example, as shown in FIG. 5, the accumulated dot number counter 24 that stores the cumulative dot amount (printing rate (%) for replenishing the developer is multiplied by the number of images formed as the developer replenishment interval. 1), a developer supply amount storage device 25 according to a printing rate storing the replenished developer amount at the time of replenishment, the consumed developer amount at the time of refreshing, the developing bias, etc., although not shown in FIG. Part 42a 42b, 42c, 42d is a developer supply device for supplying the developer to the developer containing chambers 41a, 41b, 41c, 41d, 26 is a charge control device of the charging device shown by 2 in FIG. 1, and 27 is 3 in FIG. An exposure control device for sending image data 21 to the exposure device shown by, 28 is a development bias control device for controlling the development bias between the developer carriers 7a, 7b, 7c and 7d and the photosensitive drum 1, and 29 is a photosensitive device. A primary transfer bias controller 30 applies a toner image formed on the body drum 1 to a primary transfer roller for transferring the toner image to the intermediate transfer belt 5. The toner image transferred to the intermediate transfer belt 5 is applied to the recording medium 9. This is a control device for the secondary transfer bias applied to the secondary transfer roller to be transferred.

  First, the outline of the present invention will be briefly described. An image forming apparatus according to the present invention is a black (BK), magenta (M), cyan (C), or yellow (Y) developer constituting the rotary developing device 4. From developer storage chambers 42a, 42b, 42c, 42d provided outside the rotary developing device 4 to developer storage chambers 41a, 41b, 41c, 41d provided corresponding to 4a, 4b, 4c, 4d The developer can be supplied. Normally, the developer supply to the developer storage chamber 41 in such an image forming apparatus is performed by detecting the amount of developer using, for example, an optical sensor and starting supply when the amount of developer decreases by a certain amount. In many cases, the replenishment method is used until the output is stabilized. However, in the present invention, the average printing rate is calculated from the cumulative number of dots of the image obtained from the image data and the number of formed images, and the printing based on the average printing rate is used. If the rate is lower than the rate, the developer replenishment timing is controlled so as to shorten the developer supply interval from the cumulative number of dots according to the average printing rate, and the developer amount in the developer storage chambers 41a, 41b, 41c, 41d is The developer that has become highly charged on the developer carriers 7a, 7b, 7c, and 7d due to the low printing rate so that the amount is equal to or more than a specific amount that corresponds to the printing rate is the developer storage chamber 41a, 41b, 41 , When you return to 41d, it is obtained to be able to mix with more developer.

  In this way, it is known that a two-component development system using a carrier as a developer has an effect of preventing charge-up by increasing the toner-to-carrier ratio. However, if the amount of the developer in the developer accommodating chambers 41a, 41b, 41c, and 41d is large, there is an effect of reducing the charge of the developer that has been returned without being used for development, and the developer accommodating means is little by little. By replenishing the toner, it is possible to prevent the occurrence of image defects such as fogging and a decrease in image density due to changes in the characteristics of the developer when the developer is replaced.

  In the present invention, when the calculated average printing rate is lower than the reference printing rate after a specific number of images are formed, the developer carriers 7a and 7b are not charged and exposed to the photosensitive drum 1. , 7c, and 7d, the developer in the developer storage chambers 41a, 41b, 41c, and 41d is used as described above. Thus, the charge replenishment is prevented by the developer replenished at a short interval, so that the amount of developer discharged in this refresh operation can be smaller than in the case of performing the refresh alone, and the forced consumption of the developer ( Since the (refresh) interval can be long, it is possible to prevent the work efficiency from deteriorating.

  The above is the outline of the present invention. Before describing the details of the present invention, the image forming apparatus to which the present invention is applied will be described with reference to FIG. 1. In the standby state, the rotary developing device 4 in FIG. For example, the developer carrying member 7 a of the black (BK) developing device 4 a is set at a developing position facing the photosensitive member (image carrying member) drum 1. Then, when the image data 21 is sent to the control device 20 in FIG. 2, the image data 21 is converted to black (BK), magenta (M), cyan (C), and yellow (Y) by the control device 20. On the other hand, the photosensitive drum (image carrier) drum 1 is uniformly charged to about +300 V by the charging device 2 by the charging control device 26 shown in FIG.

  Then, black (BK) data is given from the exposure control device 27 to the exposure device 3 by the control device 20, and the photosensitive drum (image carrier) drum 1 is exposed to form a latent image. At this time, the surface potential of the photosensitive drum 1 after the exposure is about + 10V. This latent image is applied between the photosensitive drum 1 and the developer carrier 7 by the developing bias control device 28. For example, the DC of Vdc is 160V, Vpp is 1.5kV, frequency is 2.5kHz, duty The toner is developed with a developer flying on the photosensitive drum 1 by a developing bias with a 30% alternating electric field superimposed thereon to form a toner image. Further, the toner image is transferred to the intermediate transfer belt 5 by the primary transfer roller 51 to which a primary transfer bias having a potential difference of −100 to −600 V applied by the primary transfer bias controller 29 is applied. The developer (toner) remaining after the formed toner image is transferred to the intermediate transfer belt 5 is cleaned by the cleaning device 6, and the next image formation is performed. The secondary transfer roller 8 and the cleaning device 11 that are in contact with the intermediate transfer belt 5 are separated from the intermediate transfer belt 5 until the toner images of all colors are transferred onto the intermediate transfer belt 5 by the control device 20. It has been made.

  When the black (BK) toner image is thus formed, the rotary developing device 4 rotates counterclockwise in the figure, and the next magenta (M) developing device 4b faces the photosensitive member (image carrier) drum 1. The image data of magenta (M), which has been previously decomposed, is given to the exposure device 3 for exposure. Then, a latent image is formed on the photosensitive member (image carrier) drum 1, and this is developed with a developer (toner) carried by the developing roller 7b provided in the developing device 4b to become a toner image, and an intermediate transfer belt. 5 is superimposed and transferred onto a black (BK) toner image transferred onto the toner image 5.

  The same operation is repeated with cyan (C) and yellow (Y) image data, and when all color toner images are transferred to the intermediate transfer belt 5 to form a full-color toner image, the controller 20 The secondary transfer roller 8 and the cleaning device 11 that have been separated from the intermediate transfer belt 5 are brought into contact with the intermediate transfer belt 5 to feed the recording medium 9 to the secondary transfer position where the secondary transfer roller 8 is located. A secondary transfer bias is applied to the secondary transfer roller 8 by the transfer bias control device 30, and the full-color toner image is transferred to the recording medium 9.

  The recording medium 9 onto which the full-color toner image has been transferred in this manner is further sent to the fixing device 10 where it is fixed by heat and pressure and discharged to the discharge unit 12. The developer (toner) remaining on the intermediate transfer belt 5 is cleaned by the cleaning device 11 and prepared for the next image formation.

  In such an image forming apparatus, in the present invention, the developer supply to the developer storage chamber 41 and the refresh of the developer are the printing rate and the start of replenishment of the developer when the developer supply method and the developer refresh are performed. The table shows a list of parameters in the first embodiment such as the replenishment amount and the consumption amount at the time of refresh, and the values shown in FIG. 5 are used, and the processing is performed according to the flow shown in FIGS.

  In the table of FIG. 5, “printing ratio A (%)” indicates that the amount of developer (cumulative dot number) required for forming an image on a predetermined number of sheets is solid black on the entire image (in the case of color). Is a value calculated for the ratio to the amount of developer used (number of dots) when it is set to be solid for each color used. When the calculated printing rate is lower than the reference printing rate (5% in this case) after image formation, the developer carrying members 7a, 7b, The amount of developer consumed, “development bias setting value” when performing a refresh operation for causing the developer on 7c, 7d to fly to the photosensitive drum 1 to be discharged, consumed, is the DC development bias (Vdc) during this refresh operation. Value of `` replenishment start The “total dot amount” is the average printing rate in the range indicated by the printing rate A when the printing rate A is 3.0% or less (for example, 1.5 when A is 1.0 to 2.0), When it exceeds 3.0%, the maximum printing rate (for example, 4.0 when A is 3.0 to 4.0) is multiplied by the value of “developer replenishment interval (sheets)” at the right end of the table. The cumulative dot amount of the image to be formed is counted by the value, and when the count value reaches this value, the developer storage chambers 41a, 41b, 41c, 41d are developed from the developer storage units 42a, 42b, 42c, 42d. Supply agent. “Reduced developer amount at start of replenishment” indicates the amount of developer consumed by the image formed up to the start of supply of this developer (40 mg at a printing rate of 5% per A4 sheet). Developer shall be consumed).

  First, the developer supply to the developer storage chamber 41 will be described based on the flow of FIG. 3. When the power of the image forming apparatus is turned on, the control device 20 in FIG. The contents of the counter 22 and the cumulative dot number counter 23 are reset. When the image data 21 is sent, the control device 20 counts the number of image formations sent by the image formation number counter 22 in step S42, and then the number of print dots in the image data 21 sent in step S43. Is added to the cumulative dot number counter 23. In the next step S44, the control device 20 divides the content of the cumulative dot number counter 23 by the content of the image forming number counter 22, calculates the number of dots per image forming sheet, and the number of dots is calculated on the entire surface of the image. Is calculated as a percentage, that is, an average printing rate A is calculated.

  In the next step S45, the control device 20 determines which one of the average printing rates A corresponds to that shown in steps S46 to S51. The blocks shown in steps S46 to S51 correspond to the column of the printing rate A in FIG. 5 described above. For example, when the average printing rate is 2.5%, the process proceeds to step S48. Then, the control device 20 reads the replenishment start accumulated dot amount (in this case, 400) corresponding to the 2.5% printing rate stored in the developer supply amount storage device 24 according to the printing rate in FIG. In step S54, it is determined whether or not the content of the cumulative dot number counter 23 has reached the replenishment start cumulative dot amount (in this case, 400).

  When the content of the cumulative dot number counter 23 has reached the replenishment start cumulative dot amount (in this case, 400), the process proceeds to the next step S59, and the control device 20 in FIG. Instructed to supply 3.2 g of the developer shown in 5 at the start of replenishment to the developer storage chambers 41a, 41b, 41c, and 41d from the developer storage units 42a, 42b, 42c, and 42d. . Therefore, 3.2 g of developer is supplied from the developer storage units 42a, 42b, 42c, and 42d to the developer storage chambers 41a, 41b, 41c, and 41d, and the process returns to step S41. If the content of the cumulative dot number counter 23 has not reached the replenishment start cumulative dot amount (in this case, 400) in step S54, the process returns to step S42 and the same is repeated, but during this time, the average printing is performed. Needless to say, when the rate fluctuates greatly, the determination in step S45 may proceed to a step different from the previous step among the blocks shown in steps S46 to S51.

  By supplying the developer from the developer storage units 42a, 42b, 42c, and 42d to the developer storage chambers 41a, 41b, 41c, and 41d in this manner, it can be understood by looking at the replenishment start cumulative dot amount column in FIG. As described above, when the average printing rate is low, the developer is supplied in a shorter period of time, and the developer amount in the developer storage chambers 41a, 41b, 41c, and 41d is equal to or more than a specific amount that is determined according to the printing rate. As described above, since there are many developers in the developer accommodating chambers 41a, 41b, 41c, and 41d, there is an effect of reducing the charge of the developer that is returned without being used for development. It is also possible to prevent the occurrence of image defects such as fogging and a decrease in image density due to changes in the characteristics of the developer during agent replacement.

  Next, in the refresh operation shown in FIG. 4, when the image forming apparatus is powered on, the controller 20 in FIG. 2 first resets the contents of the image forming number counter 22 and the accumulated dot number counter 23 in step S71. To do. When the image data 21 is sent, the control device 20 counts the number of image formations sent by the image formation number counter 22 in step S72, and then print dots in the image data 21 sent in step S73. The number is added to the cumulative dot number counter 23. Then, in the next step S74, the control device 20 determines whether or not the number of formed images has reached 200. If not, the control device 20 returns to step S72 to repeat the same, and if it has reached, proceeds to step S75. The content of the cumulative dot number counter 23 is divided by the content of the image formation number counter 22 to calculate the number of dots per image formation, and what percentage corresponds to the case where the total number of dots is solid, ie, An average printing rate A is calculated.

  Then, in the next step S76, the control device 20 determines which one of the average printing rates A corresponds to that shown in steps S77 to S80. The blocks shown in steps S77 to S80 correspond to the column of the printing rate A in FIG. 5 described above. For example, when the average printing rate is 2.5%, the process proceeds to step S79. Here, the control device 20 reads the refreshed consumption developer amount (in this case, 1200 mg) corresponding to the 2.5% printing rate stored in the developer supply amount storage device 24 according to the printing rate in FIG. .

  Then, the controller 20 does not charge and expose the photosensitive drum 1 in the next step S83 during non-image formation, but applies it between the photosensitive drum 1 and the developer carrier 7 by the developing bias controller 28. As shown in the development bias setting value of FIG. 5, the voltage Vdc is 50 V higher than normal (160 V), and 210 V, Vpp is 1.5 kV and the frequency is 2.5 kHz. Then, an alternating electric field with a duty ratio of 30% is applied in a superimposed manner. Therefore, the developer can be transported to the photosensitive drum 1 in a short time and discharged. When the predetermined amount of developer is discharged in this way, the process returns to step S71 and the same thing is repeated.

  The above is the refresh operation in the image forming apparatus of the present invention. In the conventional developer refresh, as described above, the printing rate for a normal image is set to 5%, for example, and the printing rate for every 100 sheets of image formation is, for example, When the printing rate is lower than the standard printing rate, the developer is forcibly consumed to make it become the standard printing rate in a pseudo manner. However, in the present invention, the toner is replenished at short intervals as described above. Since the developer is prevented from being charged up, the amount of developer discharged in this refresh operation can be smaller than in the case where the conventional refresh alone is performed, and the forced consumption (refresh) interval of the developer can be increased.

  For example, if refresh is performed every 200 sheets and 40 mg of developer is consumed at a printing rate of 5% per A4 sheet, the developer consumption when printing 200 sheets at a printing rate of 5% is as follows: 8000 mg. For this reason, when the printing rate is 1%, the amount of developer consumed is 8 mg per sheet, which is 1600 mg for 200 sheets. Therefore, in the conventional refresh, it is necessary to discharge 6400 mg of developer. Conventionally, if the refresh operation is not performed for a long time, as described above, the developer is excessively charged, or the charge control external additive in the developer is peeled off or is embedded in the developer, thereby stabilizing the charging. Since the image density is lowered and fogging occurs, the image formation is performed on about 100 sheets.

  However, in the present invention, the refresh may be performed at intervals of about 200 sheets, and 2800 mg when the average printing rate A is 1.0% or less as shown in the column of refreshed consumed developer amount in FIG. 2000 mg in the case of 1.0 to 2.0%, 1200 mg in the case of 2.0 to 3.0%, 0 in the range of 3.0 to 4.0%, greatly reduced ing.

  In the above description, the refresh interval has been described as every 200 sheets of image formation, but it goes without saying that this value can be arbitrarily set. The image forming number counter 22 and the cumulative dot number counter 23 have been described as being the same as those used in the developer supply operation to the developer storage chamber 41, but the developer supply operation and the refresh operation are the same. Since there is a high possibility of being performed at different times, it is preferable to use a dedicated one for each.

  In FIG. 9, only the developer refresh is performed for every 100 sheets of the image formed by the above-described conventional method, and the original print ratio is 5%, 4%, 2.5%, 1.5%, 0.5%. FIG. 10 is a graph showing changes in the number of printed sheets and image density in the same manner as in FIG. 10, where the horizontal axis represents the number of printed sheets, the vertical axis represents the image density (Macbeth density, 0.00 means white, and 1.80 means black. ). When the developer is refreshed as described above, the image density is stable as compared with the case where the refresh shown in FIG. 10 is not performed. However, when the printing rate is 2.5% or less, the image density starts from about 5000 sheets. The concentration is gradually decreasing.

  On the other hand, in FIG. 6, the developer supply and the developer refreshing are performed according to the printing rate into the developer storage chamber 41 described above, and the document printing rate is 5%, 4%, 2 as in FIG. The graph shows the change in the number of printed sheets and the image density when .5%, 1.5%, and 0.5%. The horizontal axis represents the number of printed sheets and the vertical axis represents the image density. As can be seen from this graph, unlike the case of only refreshing in FIG. 9, the printing rate is stable without any decrease in image density, indicating that the method of the present invention is highly effective. ing.

  FIG. 7 shows the second embodiment of the present invention in which the refreshing consumption amount and the developing bias setting value are changed among the parameters of the first embodiment shown in FIG. The operation is exactly the same as in the embodiment, and the operation is exactly the same as the flow shown in FIGS. FIG. 8 is a graph showing changes in the number of printed sheets and image density when the developer shown in FIG. 7 is used and the developer is supplied to the developer storage chamber 41 and the developer is refreshed. Is the number of printed sheets, and the vertical axis is the image density (Macbeth density, 0.00 means white and 1.60 means black).

  As can be seen from the graph of FIG. 8, the print rate is stable without any decrease in image density as in the graph of FIG. 6, but as can be seen from the list of FIG. “Refresh consumption amount” is smaller than that in the first embodiment shown in FIG. 5, and in the present invention, it is shown that the effect is large even when the amount of developer discharged is small during refresh.

  As described above, according to the present invention, when the average printing rate of the formed image is calculated from the cumulative number of dots of the formed image and the number of formed images, and this average printing rate is smaller than a predetermined reference printing rate. The developer supply interval from the developer supply means to the developer storage means is controlled to be short according to the average print rate, and the amount of developer in the developer storage means is determined according to the print rate By setting the amount to be greater than or equal to the amount, when the highly charged developer on the developer carrying member returns to the developer containing means, it can be mixed with more developer. For this reason, excessive charging of the developer described above and the external additive for charge control in the developer are peeled off or embedded in the developer to prevent charging from becoming unstable and reducing image density and fogging. can do. In addition, by gradually replenishing the developer in the developer accommodating means, it is possible to prevent the occurrence of image defects such as fogging and image density reduction due to changes in toner characteristics during toner replacement.

  In addition to controlling the developer supply interval from the developer supply means to the developer storage means to be short, when the number of image formation reaches a predetermined number and the average printing rate is lower than the reference printing rate, The developer is refreshed by developing and consuming the developer in an amount corresponding to the printing rate, so that the developer in the developer storage means is supplied by the developer replenished at short intervals when the printing rate is low. Since charge-up is prevented, the amount of developer consumed in this refresh can be smaller than in the case where the conventional refresh is performed alone, and the forced consumption (refresh) interval of the developer can be increased, so that the work efficiency is improved. It is possible to provide an image forming apparatus capable of preventing deterioration and a developer supplying method in the developing apparatus.

  According to the present invention, it is possible to provide an image forming apparatus capable of maintaining a good image over a long period of time even when the document printing rate is low, and a developer supplying method in the developing device.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. It is a general | schematic control block diagram which implements the developer supply method in the developing device which becomes this invention. It is a flowchart of the developer supply method in the developing device according to the present invention. It is a flowchart of a developer refresh when the developer supplying method in the developing device according to the present invention is used. A table listing the parameters in the first embodiment, such as the printing rate, the start of replenishment of the developer, the replenishment amount, and the consumption amount at the time of refreshing when performing the developer refreshing method and developer refreshing in the developing device according to the present invention. It is. 6 is a graph showing the relationship between the number of printed sheets and the image density at various printing rates in the first embodiment of the present invention. Table showing a list of parameters in the second embodiment, such as the printing rate, the start of supply of the developer, the supply amount of the developer, the supply amount at the time of refresh, and the like when the developer supply method and developer refresh in the developing device according to the present invention are performed. It is. 6 is a graph showing the relationship between the number of printed sheets and the image density at various printing rates by implementing the second embodiment of the present invention. 6 is a graph showing the relationship between the number of printed sheets and image density at various printing rates by performing only developer refresh. 6 is a graph showing the relationship between the number of printed sheets and image density at various printing rates without performing developer refreshing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive body (image carrier) drum 2 Charging device 3 Exposure device 4 Rotary developing device 4a Black (BK) developing device 4b Magenta (M) developing device 4c Cyan (C) developing device 4d Yellow (Y) developing device 41a Black (BK) Developer storage chamber 41b Magenta (M) developer storage chamber 41c Cyan (C) developer storage chamber 41d Yellow (Y) developer storage chambers 42a, 42b, 42c, 42d Developer storage unit 5 Intermediate transfer belt 51 Primary transfer roller 6 Cleaning device 7a, 7b, 7c, 7d Developer carrier 8 Secondary transfer roller 9 Recording medium 10 Fixing device 11 Cleaning device 12 Discharge unit 20 Control device 21 Image data 22 Image forming number counter 23 Cumulative number of dots Counter 24 Developer supply amount storage device by printing rate 25 Developer supply device 26 Charge control device 27 Controller 28 developing bias control device 29 the primary transfer bias control device 30 a secondary transfer bias controller

Claims (8)

A developing device comprising: a developer carrying member that conveys the developer to the developing region facing the photosensitive member; and a developer containing unit that supplies the developer to the developer carrying member; and the developer containing in the developing device. A developer supplying method in the developing device of the image forming apparatus, the developer supplying means for supplying the developer to the means from the outside,
The image forming apparatus includes a means for counting the number of image formations and a means for counting the cumulative number of dots of the formed image, and calculates an average printing rate based on the counted cumulative dot number and the number of image formations. A developer supply method in a developing device of an image forming apparatus, characterized in that, when a printing rate is lower than a predetermined reference printing rate, a developer supply interval from the developer supplying unit to the developer containing unit is shortened.   The developer supply interval from the developer supply means to the developer accommodating means is determined in advance by the development amount calculated based on the cumulative dot number calculated by the cumulative dot number counting means for each specific printing rate range. The developer supplying method in the developing device of the image forming apparatus according to claim 1, wherein the interval reaches a value. A developing device comprising: a developer carrying member that conveys the developer to the developing region facing the photosensitive member; and a developer containing unit that supplies the developer to the developer carrying member; and the developer containing in the developing device. A developer supplying method in the developing device of the image forming apparatus, the developer supplying means for supplying the developer to the means from the outside,
The image forming apparatus includes a means for counting the number of image formations and a means for counting the cumulative number of dots of the formed image, and calculates an average printing rate based on the counted cumulative dot number and the number of image formations. When the printing rate is lower than a predetermined reference printing rate, the developer supply to the developer containing unit by the developer supplying unit is determined according to the amount of developer in the developer containing unit corresponding to the printing rate. A developer supplying method in a developing device of an image forming apparatus, wherein the developing method is performed so that the amount exceeds a specified amount.   In the image forming apparatus, when the image forming number counted by the image forming number counting unit reaches a predetermined number and the calculated average printing rate is lower than a predetermined printing rate, a predetermined printing rate range is previously set. 4. A developer supplying method in a developing device of an image forming apparatus according to claim 1, wherein a predetermined amount of the developer is developed on the photosensitive member and consumed.   When the image forming apparatus develops and consumes the developer on the photosensitive member, a bias voltage for conveying the developer from the developer carrying member to the photosensitive member is set based on a bias at the time of image formation for each specific printing rate range. The developer supply method in the developing device of the image forming apparatus according to claim 4, wherein the developer is enlarged. A developing device comprising: a developer carrying member that conveys the developer to the developing region facing the photosensitive member; and a developer containing unit that supplies the developer to the developer carrying member; and the developer containing in the developing device. An image forming apparatus having developer supplying means for supplying the developer to the means from the outside,
The image forming apparatus calculates the average printing rate of the formed image from the means for counting the number of image formations, the means for counting the cumulative number of dots of the formed image, and the counted number of image formations and the cumulative number of dots, A control unit that changes a developer supply interval from the developer supply unit to the developer storage unit in accordance with the average printing rate, and the control unit that changes the developer supply interval has the average printing rate set in advance. When smaller than a predetermined reference printing rate, the developer supply interval from the developer supply unit to the developer storage unit is controlled to be short according to the average printing rate, and the amount of developer in the developer storage unit is An image forming apparatus, wherein the image forming apparatus is configured to have a specific amount or more determined in accordance with a printing rate.   The control means develops an amount corresponding to the average printing rate when the image forming number counted by the image forming number counting unit reaches a predetermined number and the calculated average printing rate is lower than a predetermined reference printing rate. 7. The image forming apparatus according to claim 6, wherein control is performed to develop the developer from the developer containing means onto the photosensitive member via the developer carrying member.   The control by the control means to develop the developer from the developer containing means to the photosensitive member via the developer carrying member is performed by applying a bias voltage for conveying the developer from the developer carrying member to the photosensitive member, and an image. The image forming apparatus according to claim 7, wherein the image forming apparatus is controlled to be larger than a bias at the time of formation.

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