JP4540966B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using a two-component developer, such as a copying machine, a facsimile machine, and a printer.

  In this type of image forming apparatus, maintaining the image density constant is an important issue. In order to maintain the image density constant, generally, the toner density of the developer is controlled. As a method for controlling the toner density, a toner density sensor (hereinafter referred to as “T sensor”) is installed in the developing device, and the toner replenishment amount is determined based on the comparison result between the detected value of the T sensor and the target value. A method of adjusting is known. According to this method, it is possible to control the toner concentration in the developer so that the detection value of the T sensor becomes a predetermined target value. However, even if the detection value of the T sensor is the same, the image density differs depending on the surrounding environment (temperature, humidity, etc.) of the developer and the use conditions of the developer (degradation degree of toner, carrier, etc.). Therefore, even if toner density control is performed using only the T sensor, the image density may not be maintained constant.

  2. Description of the Related Art Conventionally, image forming apparatuses that perform toner density control using a pattern density sensor (hereinafter referred to as “P sensor”) that detects the density of a toner pattern on a latent image carrier such as a photoconductor in combination with a T sensor are known. (See Patent Document 1 and Patent Document 2). In this image forming apparatus, a pattern latent image for image density detection is formed on a latent image carrier, and this is developed by a developing device to form a toner pattern. The density of the toner pattern is detected by the P sensor, and the target value of the T sensor is corrected based on the detection result. If the detection result of the P sensor is used, it is possible to directly grasp the image density. Therefore, even if the surrounding environment and usage conditions of the developer change, the target value of the T sensor can be corrected to an appropriate value based on the detection result of the P sensor. As a result, the toner density of the actual developer can be kept constant at the target density without being affected by the surrounding environment of the developer and use conditions, and the image density can be maintained at the target density. become.

  On the other hand, as a toner for an image forming apparatus using a two-component developer, a toner using a modified polyester resin as a base material is known. This toner can be produced, for example, as follows. In an organic solvent, a modified polyester resin capable of reacting with a compound having at least an active hydrogen group, a colorant and a release agent are dissolved or dispersed. The solution or dispersion thus obtained is dispersed in an aqueous medium containing resin fine particles and reacted with at least one of a crosslinking agent and an extender. Then, the organic solvent is removed from the resulting dispersion, and the resin fine particles are washed to obtain a toner. Such a toner is easier to control the shape of the toner as compared with the case where the toner is produced by a suspension polymerization method. As a result, the removal efficiency when the residual toner on the image carrier is cleaned with a blade is easily improved. There are benefits. Further, there is an advantage that the surfactant does not remain inside the toner as in the case of the emulsion polymerization toner, and the charging of the toner is not inhibited by contaminating the photoreceptor or the developing roller. However, there is a demerit that when the toner is deteriorated by stirring, the fluidity of the developer is easily deteriorated.

When a toner based on a modified polyester resin having such disadvantages is used in an image forming apparatus that controls toner density by using both the P sensor and the T sensor, the following problems occur.
As the T sensor, a magnetic permeability sensor that measures the magnetic permeability of a carrier (magnetic material) existing in a predetermined region in the developer is widely used. The toner density detection method using the T sensor is as follows. That is, when the toner concentration in the developer increases, as shown in FIG. 11A, a large number of toners are interposed between the carriers, and as a result, the distance between the carriers increases. Therefore, the magnetic permeability of the carrier existing in the detection area of the T sensor is lowered, and the output voltage of the T sensor is lowered. On the other hand, when the toner concentration in the developer is lowered, as shown in FIG. 11 (b), the amount of toner interposed between the carriers is reduced, so that the distance between the carriers is reduced and the T sensor is within the detection area. The permeability of the existing carrier is increased. As a result, the output voltage of the T sensor increases. Therefore, if the output voltage of the T sensor is low, it can be determined that the toner concentration is high, and if the output voltage of the T sensor is high, it can be determined that the toner concentration is low.

  The toner based on the modified polyester resin has a demerit that it easily deteriorates the fluidity of the developer as described above due to deterioration. For this reason, for example, when a large number of images with a small image area ratio are formed, a large amount of deteriorated toner exists in the developer, so that the fluidity of the developer is considerably deteriorated. When the fluidity deteriorates as described above, gaps (voids) in the developer increase as shown in FIG. In this case, even if the toner density of the actual developer is decreased, the distance between the carriers is not changed from that before the gap is increased. Therefore, since the output voltage of the T sensor indicates the target value, the toner supply operation is stopped. As a result, the image density is lowered even though the output voltage of the T sensor indicates the target value. However, such a decrease in image density is detected by the P sensor. Based on the detection result of the P sensor, the target value of the T sensor is corrected to be lower than the current value. In other words, the distance between the carriers is corrected to the target value corresponding to a state where the distance between the carriers is wider than before the correction. As a result, the output voltage of the T sensor becomes higher than the corrected target value, and it is determined that the toner is insufficient, and the toner supply operation is resumed. By detecting the toner pattern density by the P sensor and correcting the target value of the T sensor, the actual toner density of the developer is maintained constant even if the developer fluidity deteriorates, and the image density is reduced. The target concentration is maintained.

Japanese Patent Laid-Open No. 10-186830 JP-A-11-305497

However, if the developer is deteriorated in fluidity, such as after a large number of images having a low image area ratio are continuously formed, if left untreated for a long time, scumming or toner scattering will occur after the image is left untreated. It was confirmed that the problem of occurrence occurred. And as a result of earnest research, the present inventor found the reason as follows.
That is, for example, consider a case where the image forming apparatus is turned off with the developer fluidity deteriorated, and the image forming apparatus is turned on the next morning to perform image formation. In this case, the developer having deteriorated fluidity is allowed to stand overnight without being stirred. The developer immediately before being left is in a state with many gaps as shown in FIG. At this time, the toner density of the actual developer is an appropriate density. However, in the next morning, the developer is in a so-called tight state, and the gap is small as shown in FIG. Therefore, the distance between the carriers is narrower than that immediately before leaving. In this state, the image forming apparatus operates and image formation is performed. The target value of the T sensor at the start of operation of the image forming apparatus is a value immediately before being left, that is, a value corrected so as to be optimal for a state where the distance between carriers is wide. Accordingly, the target value of the T sensor at this time is not optimal for the developer immediately after being left in a state where the distance between the carriers is narrow. As a result, the detection value of the T sensor becomes higher than the target value, and it is determined that the toner is insufficient, and the toner replenishment is performed even though the actual toner concentration of the developer is an appropriate concentration. Will be done. As a result, the toner density of the actual developer becomes too high, causing background contamination and toner scattering.

  When the detection by the P sensor is first performed after the operation of the image forming apparatus is started in this way, it is understood from the detection result that the image density is too high. Therefore, the target value of the T sensor is corrected based on this detection result, that is, in a direction suitable for a state where the distance between carriers is narrow. However, correction of the target value of the T sensor based on the detection result of the P sensor corrects a slight error from the optimum value of the target value of the T sensor caused by changes in the surrounding environment and usage conditions of the developer during operation of the image forming apparatus. Is to do. Therefore, in order to correct the large error caused by the above-mentioned neglect, the detection by the P sensor and the target value correction of the T sensor must be repeated many times. Moreover, in order to perform detection by the P sensor, as described above, it is necessary to form a pattern latent image on the latent image carrier and develop it with a developing device to form a toner pattern. Therefore, if detection by the P sensor is performed at a very short time interval, the normal image forming operation is delayed. Therefore, the detection interval by the P sensor is normally set to be performed about once every 30 image formations.

FIG. 13 is a graph showing a conventional toner density control operation when the developer is left overnight with the fluidity of the developer deteriorated and the operation of the image forming apparatus is started the next morning. In this graph, the horizontal axis represents the number of sheets passed immediately after the start of operation of the image forming apparatus, and the vertical axis represents the detection value of the T sensor and the toner replenishment operation time. This graph also shows the target value of the T sensor.
In this example, the detection operation of the P sensor is performed once every 30 sheets of paper and the target value of the T sensor is corrected. Since the target value at the start of operation remains the target value immediately before being left, it is a relatively low value. On the other hand, as a result of leaving the gap between the developers reduced and the distance between the carriers narrowed, the detection value of the T sensor increases more and more. As shown in the figure, the target value of the T sensor is corrected so as to increase stepwise by the detection operation of the P sensor. However, while the detection value of the T sensor is increasing, the toner replenishing operation is continued and the toner is replenished excessively. This excessive toner supply operation is finally stopped by performing detection by the P sensor and correction of the target value of the T sensor four times in this example. Therefore, the toner is excessively supplied over a long period of time, from the start of operation the next morning until 120 images are formed. As a result, the toner density of the actual developer keeps increasing, and in addition to the period for forming 120 images after starting operation the next morning, the toner density of the actual developer is set to the target after that. Until the density is reduced to near the density, scumming or toner scattering occurs.

It should be noted that not only the situation in which the developer fluidity has deteriorated but the situation where the developer is left for a long period of time, the situation in which the detection value of the T sensor increases despite toner replenishment, that is, the toner concentration is high. In a situation where it is perceived that the toner has been lowered, similarly, there arises a problem that background contamination or toner scattering due to excessive toner supply occurs.
Further, such a problem is not limited to the case of using a toner based on a modified polyester resin, and can similarly occur if the toner has a characteristic that tends to deteriorate the fluidity of the developer due to deterioration. is there.
Further, if the T sensor detects a parameter related to the developer density for a part of the developer accommodated in the developing device, the above-described problem may occur without being limited to the magnetic permeability sensor.

  The present invention has been made in view of the above-described problems, and the object of the present invention is to provide scumming or toner scattering due to excessive toner replenishment even when toner that tends to deteriorate the fluidity of the developer is used. It is an object of the present invention to provide an image forming apparatus capable of suppressing the occurrence of the above.

In order to achieve the above object, the invention of claim 1 develops a latent image on a latent image carrier with a developer containing a toner and a carrier by a developing device, and finally obtains a toner image obtained thereby. The toner is transferred onto a recording material to form an image, and a toner replenishing device that replenishes the developer in the developing device with the toner consumed by the image formation, and is housed in the developing device. A toner density sensor that detects a parameter related to the developer density for a part of the developer, and a pattern latent image for image density detection is formed on the latent image carrier and developed by the developing device. A pattern density sensor that detects the density of the obtained toner pattern, and a replenishment operation control that controls the toner replenishment operation of the toner replenishing device based on the detection result of the toner density sensor so that the detected value matches the target value. And a target value correction for executing a correction process for correcting the target value so that the toner replenishment operation is performed so that the density of the toner pattern detected by the pattern density sensor becomes a target density. In the image forming apparatus provided with the means, the parameter detected by the toner density sensor during the toner replenishment operation tends to be reduced with respect to the toner concentration even though the toner is replenished by the toner replenishment operation of the toner replenishment device. In this case , the parameter detected by the toner density sensor during the toner replenishment operation is decreased with respect to the toner density even though the toner is replenished by the toner replenishing device. when it is determined that indicates that there is a tendency for a predetermined period of time, the toner concentration in the toner supply operation Than normal indicating that the parameter has been detected tends to increase the toner density in the capacitors, it is characterized in that the shorter the interval of the correction process.
According to the second aspect of the present invention, the latent image on the latent image carrier is developed with a developer containing a toner and a carrier by a developing device, and the resulting toner image is finally formed on a recording material. The toner is transferred to form an image, and a toner replenishing device that replenishes the developer in the developing device with the toner consumed by the image formation, and a part of the developer contained in the developing device. A toner density sensor for detecting a parameter related to the developer density, and a density of a toner pattern obtained by forming a pattern latent image for image density detection on the latent image carrier and developing the pattern latent image on the latent image carrier. A pattern density sensor for detecting toner, a replenishment operation control means for controlling the toner replenishment operation of the toner replenishing device based on the detection result of the toner density sensor so that the detected value matches the target value, and the pattern And a target value correcting means for performing correction processing for correcting the target value at a predetermined timing so that the toner replenishing operation is performed so that the density of the toner pattern detected by the degree sensor becomes a target density. Whether the parameter detected by the toner density sensor during the toner supply operation is decreasing with respect to the toner density even though the toner is supplied by the toner supply operation of the toner supply device in the image forming apparatus. Even if the toner is replenished by the toner replenishing device, the parameter detected by the toner density sensor during the toner replenishing operation tends to decrease with respect to the toner density. when it is determined that shown for a predetermined period, it is configured such that the toner replenishing operation is forcibly stopped It is an feature.
According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the toner replenishment device replenishes the toner when the correction processing execution interval is shortened or the toner replenishment operation is forcibly stopped. Despite this, the parameter detected by the toner density sensor during the toner replenishment operation tends to decrease with respect to the toner density, and the toner pattern density detected by the pattern density sensor has a predetermined threshold density. It is the time when it is over.
According to a fourth aspect of the present invention, in the image forming apparatus of the first, second or third aspect, the end of the predetermined period is when the density of the toner pattern detected by the pattern density sensor becomes a reference density. It is characterized by.
According to a fifth aspect of the present invention, in the image forming apparatus of the first, second, third, or fourth aspect,
A magnetic carrier is used as the carrier, and a magnetic permeability sensor that detects the magnetic permeability of the developer, which is a parameter related to the developer density, is used as the toner concentration sensor.
According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect, a toner based on a modified polyester resin is used as the toner.

In the image forming apparatus according to the first to seventh aspects, a parameter related to the developer density is detected for a part of the developer accommodated in the developing device, and the toner density of the developer is determined from the detection result. Here, normally, when toner is replenished, the parameter detected by the T sensor (toner density sensor) indicates an increase in toner density. However, when the toner tends to deteriorate the fluidity of the developer, as described above, the parameter detected by the T sensor shows a decrease in the toner density even though the toner is replenished by the toner replenishing device. An unusual situation can occur. In such a situation, although the actual toner density of the developer is appropriate, the toner replenishment operation is continued and the toner is excessively replenished, resulting in background smudges and toner scattering.
Therefore, the image forming apparatus according to the first aspect of the present invention shortens the execution interval of the correction process for a predetermined period compared to the normal time when the abnormal situation occurs. That is, the execution interval of the process of correcting the target value of the T sensor based on the detection result of the toner pattern by the P sensor (pattern density sensor) is shortened. As a result, the time interval for reviewing the target value of the T sensor is shortened, and the target value can be corrected to an appropriate value more quickly than before. As a result, the toner replenishment operation can be continued for a shorter time than before, and excessive toner replenishment can be stopped quickly.
The image forming apparatus according to claim 2 forcibly stops the toner supply operation when the abnormal situation occurs. As a result, it is possible to suppress the situation where the toner replenishing operation is continued even though the actual toner concentration of the developer is appropriate, and to quickly stop the excessive toner replenishment.
The image forming apparatus according to claim 4 measures the non-operation time of the developing device, and determines whether or not the measurement time exceeds the reference time. When the non-operating time of the developing device becomes long, as described above, the gap in the developer is reduced, and the parameter detected by the T sensor is decreased due to the toner being replenished by the toner replenishing device at the time of re-operation. An abnormal situation can occur that indicates When the image forming apparatus according to the fourth aspect determines that the measurement time exceeds the reference time as a result of the determination, the image forming apparatus sets the execution interval of the correction processing for a predetermined period as in the image forming apparatus according to the first aspect. Keep it short . I it, in the image forming apparatus according to claim 4, the excessive toner replenishment can occur after standing a gap is large developer can be stopped quickly.

  As described above, according to the first to eighth aspects of the present invention, excessive toner replenishment that can occur when toner that tends to deteriorate the fluidity of the developer can be quickly stopped. In addition, there is an excellent effect that the occurrence of toner scattering can be suppressed.

Hereinafter, an embodiment in which the present invention is applied to a copying machine as an image forming apparatus will be described. In the present embodiment, a monochrome image forming apparatus will be described as an example, but the present invention can be similarly applied to a known color image forming apparatus.
First, the configuration of the copying machine according to the present embodiment will be described.
FIG. 2 is a schematic configuration diagram of the entire copying machine according to the present embodiment. In FIG. 2, an image reading apparatus 200 is mounted on the copying machine main body 100 and placed on a sheet bank 300. Mounted on the image reading apparatus 200 is an automatic document feeder 400 configured to be rotatable about the back side (the back side of the paper in the figure) as a fulcrum.

  Inside the copying machine main body 100, a drum-shaped photoconductor 10 is provided as a latent image carrier. Around the photoconductor 10, a charging device 11 using a charging roller, a developing device 12, a transfer device 13, and a cleaning device 14 are sequentially arranged along a rotation direction A (counterclockwise direction in the drawing) A. Arranged. The developing device 12 uses a polymerized toner produced by a polymerization method as a toner, and attaches the polymerized toner to an electrostatic latent image on the photoconductor 10 using a developing roller as a developer carrier. Visualize. The transfer device 13 includes a transfer belt 17 wound around two rollers 15 and 16, and the transfer belt 17 is pressed against the peripheral surface of the photoconductor 10 at the transfer position B. Further, the copying machine main body 100 is provided with a toner replenishing device 20 for replenishing the developing device 12 with new toner on the left side of the charging device 11 and the cleaning device 14 in the drawing. Further, the copying machine main body 100 is provided with a sheet conveying device 60 that conveys the sheet S sent from the sheet cassette 61 of the sheet bank 300 to the stack unit 39 via the transfer position B. The sheet conveying apparatus 60 conveys the sheet S along the supply path R1 or the manual feed path R2 and the sheet conveyance path R. On the sheet conveyance path R, a registration roller 21 is provided upstream of the transfer position B in the sheet conveyance direction. On the other hand, a thermal fixing device 22 is provided on the downstream side in the sheet conveyance direction of the sheet conveyance path R with respect to the transfer position B. The heat fixing device 22 performs heat and pressure fixing by sandwiching the sheet S between a heating roller (heating member) 30 and a pressure roller (pressure member) 32. A discharge branch claw 34, a discharge roller 35, a first pressure roller 36, a second pressure roller 37, and a stiffness roller 38 are provided further downstream in the sheet conveyance direction of the heat fixing device 22. A stack unit 39 is also provided for stacking sheets on which images have been formed through the thermal fixing device 22. Further, the copying machine main body 100 is provided with a switchback device 42 on the right side in the drawing. The switchback device 42 reverses the reversing path R3 branched from the position where the discharge branch claw 34 of the sheet conveying path R is arranged, and the position of the registration roller 21 on the sheet conveying path R again after passing the reversing path R3. The sheet S is conveyed along the re-conveying path R4 that leads to the point. A pair of switchback rollers 43 and a plurality of other rollers 66 are provided in the reversing path R3 and the re-transport path R4. Further, the copying machine main body 100 is provided with a laser writing device 47 on the left side of the developing device 12 in the drawing. The laser writing device 47 includes a scanning optical system such as a laser light source (not shown), a rotary polygon mirror 48 for scanning, a polygon motor 49, and an fθ lens (not shown).

The image reading apparatus 200 includes a light source 53, a plurality of mirrors 54, an imaging optical lens 55, an image sensor 56 such as a CCD, and the like, and a contact glass 57 is provided on the upper surface thereof.
The automatic document feeder 400 is provided with a document setting table (not shown), and a document stacking table (not shown) is provided at the document discharge position. The automatic document transport device 400 includes a plurality of document transport rollers, and the document transport rollers transport the document from the document setting table to the document stack table through the reading position on the contact glass 57 of the image reading device 200. The
The sheet bank 300 is provided with a plurality of sheet cassettes 61 for storing sheets S such as paper and OHP film as recording materials. Each sheet cassette 61 is provided with a call roller 62, a supply roller 63, and a separation roller 64, respectively. On the right side of the sheet cassette 61 in the drawing, the above-described supply path R1 leading to the sheet conveyance path R of the copying machine main body 100 is formed. Several sheet conveying rollers 66 for conveying the sheet are also provided in the supply path R1.
Further, the copying machine main body 100 is provided with a manual feed unit 68 on the right side in the drawing. The manual feed unit 68 is provided with a manual feed tray 67 that can be opened and closed. The manual feed path R <b> 2 that guides the manual sheet set on the manual feed tray 67 to the sheet conveyance path R is formed. Similarly to the sheet cassette 61, the manual feed unit 68 is also provided with a calling roller 62, a supply roller 63, and a separation roller 64.

Next, the operation of the copying machine will be described.
When making a copy using the copying machine, first, a main switch (not shown) is turned on, and a document is set on a document setting table of the automatic document feeder 400. In the case of a book document, the automatic document feeder 400 is opened, a document is set directly on the contact glass 57 of the image reading device 200, and the automatic document feeder 400 is closed and pressed. When a start switch (not shown) is pressed, when an original is set on the automatic document feeder 400, the original is moved onto the contact glass 57 through the document feeding path by the document feeding roller, and then the image reading device 200 is driven. Then, the document contents are read and discharged onto the document stacking table. On the other hand, when the document is set directly on the contact glass 57, the image reading device 200 is immediately driven to read the content of the document. When reading the content of the original, the image reading apparatus 200 irradiates the original surface on the contact glass 57 with light from the light source 53 while moving the light source 53 along the contact glass 57. Then, the reflected light is guided to the imaging optical lens 55 by a plurality of mirrors 54 and put into the image sensor 56, and the document content is read by the image sensor 56.

  On the other hand, simultaneously with the reading of the document content, the photoconductor 10 is rotated by a photoconductor drive motor (not shown). First, the surface of the photoconductor 10 is uniformly charged by the charging device 11, and then writing is performed by irradiating the laser beam from the laser writing device 47 in accordance with the content of the original read by the image reading device 200 described above. Then, an electrostatic latent image is formed on the surface of the photoconductor 10. Thereafter, the developing device 12 attaches toner to the electrostatic latent image to make it visible.

  At the same time as the start switch is pressed, the sheet S is sent out by the calling roller 62 from the one corresponding to the selected size among the plurality of sheet cassettes 61 provided in the sheet bank 300. Then, the fed sheet S is separated one by one by the supply roller 63 and the separation roller 64, and the one sheet is guided to the supply path R 1, and is guided to the sheet conveyance path R by the sheet conveyance roller 66. The sheet S conveyed to the sheet conveyance path R hits the registration roller 21 and is stopped. When the manual paper feed unit 68 is used, the manual feed tray 67 is opened and the sheet S is set on the manual feed tray 67. In this case as well, only one sheet S is conveyed to the manual feed path R2 by the calling roller 62, the supply roller 63, and the separation roller 64, and is guided to the sheet conveyance path R by the sheet conveyance roller 66. Stopped by hitting. In this way, the sheet S stopped by the registration roller 21 starts to rotate at the timing when the leading end of the visible toner image of the photoreceptor 10 enters the transfer position B. 21 to the transfer position B.

The sheet S fed to the transfer position B is transferred with the toner image on the photoreceptor 10 by the transfer device 13 and carries the image on the surface thereof. Residual toner remaining on the surface of the photoconductor 10 after the transfer is removed by the cleaning device 14, and the residual potential on the photoconductor 10 is also removed by a neutralization device (not shown) to prepare for the next image formation starting from the charging device 11. . On the other hand, the sheet S carrying the image is conveyed by the transfer belt 17 and enters the heat fixing device 22. Then, heat and pressure are applied while being conveyed between the heating roller 30 and the pressure roller 32, and the image on the sheet S is fixed. After that, the sheet S is discharged onto the discharge stack unit 39 with a stiffness by the discharge roller 35, the first pressure roller 36, the second pressure roller 37, and the roller with stiffness 38, and is stacked there. The
When images are formed on both sides of the sheet S, the discharge branch claw 34 is switched, and the toner image is transferred to one side of the sheet S. Then, the toner image is transferred from the sheet conveying path R to the reversing path R3. The sheet S is conveyed by the sheet conveying roller 66 and put into the switchback position 44, and then switched back by the switchback roller 43. This time, the sheet S is put in the re-conveying path R4, and the sheet conveying roller 66 again conveys the sheet. It is led to the path R. Then, the toner image is transferred to the opposite surface of the sheet in the same manner as described above.

FIG. 3 is a perspective view of the toner bottle 23 set in the toner replenishing device 20.
The toner bottle 23 includes a cylindrical bottle body 24 and a cap portion 25. A storage space for storing replenishing toner is formed inside the bottle main body 24, and a spiral protrusion is formed in the storage space. When the toner bottle 23 is set in the toner replenishing device 20, first, the bottom portion of the bottle body 24 (the opposite end portion of the cap portion 25) and the drive shaft of the bottle drive motor 26 are engaged. At the same time, the cap unit 25 is fixed to the toner supply device 20. When the lever 25a provided in the cap unit 25 is operated, the toner discharge port 25b formed in the cap unit 25 is opened. After the setting, when the bottle drive motor 26 is driven, the bottle main body 24 rotates, and the toner in the accommodation space is conveyed into the cap portion 25 by the spiral protrusion. The toner in the cap unit 25 is conveyed into the developing device 12 from the toner discharge port 25b. With such a configuration, the amount of toner (toner replenishment amount) supplied to the developing device 12 can be adjusted by controlling the driving of the bottle drive motor 26.

Next, toner concentration control by the toner concentration control apparatus in the present embodiment will be described.
FIG. 4 is a block diagram showing the configuration of the toner concentration control apparatus in the present embodiment.
In the present embodiment, a toner density sensor (T sensor) 102 is provided in the developing device 12, and a pattern density sensor (P sensor) 103 is provided so as to face the surface of the photoreceptor 10. The T sensor 102 detects the magnetic permeability in a part of the developer, and is a general magnetic permeability sensor in which the output voltage (detection value) increases as the magnetic permeability increases. In this embodiment, a magnetic permeability sensor is used as the T sensor. However, if a parameter related to the developer density can be detected for a part of the developer accommodated in the developing device 12, this is used. Not limited. The P sensor 103 is a reflective optical sensor, and detects the density of the toner pattern on the photoconductor 10 from the amount of reflected light that varies depending on the change in the amount of toner. The output voltage of the P sensor 103 is lower as the toner amount is smaller, that is, as the toner pattern density is lower. The P sensor is not limited to this as long as the density of the toner pattern on the photoconductor 10 can be detected. The output signals of these sensors 102 and 103 are input to the control unit 101 as supply operation control means and target value correction means.

  In this toner density control apparatus, the detection timing by the T sensor 102 is preferably when the developer is being stirred, and is therefore performed between images during an image forming operation or during continuous image formation. Since it is desirable that the detection interval by the T sensor 102 be as short as possible, in this embodiment, it is performed for each image forming operation. On the other hand, the detection operation by the P sensor cannot be performed during the image forming operation because a toner pattern needs to be formed on the photoreceptor 10. Therefore, the detection timing by the T sensor 102 is performed between images during non-image forming operation or continuous image formation. However, in the detection operation by the P sensor 103, while the toner pattern is formed on the photoconductor 10, the normal image formation operation is made to wait, so this detection operation is performed between images during continuous image formation, for example. In this case, the continuous image forming speed is reduced. Therefore, the detection operation by the P sensor 103 cannot be performed as frequently as the T sensor 102. Therefore, in this embodiment, it is set so that the detection operation by the P sensor 103 is performed once every 30 images are output. The detection timing by the P sensor 103 is preferably changed as appropriate according to the system and required specifications.

Whenever the image forming operation is performed, the control unit 101 receives the detection value Vt from the T sensor 102 and compares the detection value Vt with the target value Vtref. If it is determined that the detected value Vt is equal to or greater than the target value Vtref, a control signal for driving the bottle drive motor 26 is output. As a result, the bottle drive motor 26 is driven to supply toner to the developer in the developing device 12. On the other hand, if it is determined that the detected value Vt is lower than the target value Vtref, a control signal for stopping the driving of the bottle drive motor 26 is output. As a result, the driving of the bottle drive motor 26 is stopped, and the toner supply is stopped.
The control unit 101 receives the detection value Vsp from the P sensor 103 every time 30 images are output, and corrects the target value Vtref. Specifically, if it is determined that the detected value Vsp is lower than a specified value (target toner pattern density) Vspref, the target value Vtref is corrected to be low. As a result, even if the detection value Vt of the T sensor 102 has been below the target value Vtref so far, if it is equal to or greater than the corrected target value Vtref, the toner supply operation is started and the image density increases. On the other hand, if it is determined that the detection value Vsp of the P sensor 103 is greater than or equal to the specified value Vspref, the target value Vtref is corrected so as to increase. As a result, even if the detection value Vt of the T sensor 102 has been equal to or higher than the target value Vtref so far, if the target value Vtref after correction falls below the corrected target value Vtref, the toner supply operation is stopped and the image density is lowered.

  Here, the toner used in the present embodiment uses a modified polyester resin as a base material. Specifically, it is manufactured as follows. That is, a modified polyester resin, a colorant, and a release agent that can react with at least a compound having an active hydrogen group are dissolved or dispersed in an organic solvent. The solution or dispersion thus obtained is dispersed in an aqueous medium containing resin fine particles and reacted with at least one of a crosslinking agent and an extender. Then, the organic solvent is removed from the resulting dispersion, and the resin fine particles are washed to obtain a toner. As described above, this toner has a demerit that it easily deteriorates the fluidity of the developer. For example, if the toner is left after the image formation is continuously performed, the gaps existing before the toner is reduced. As a result, there may occur a situation in which toner supply continues excessively while the detection value Vt of the T sensor 102 is equal to or higher than the target value Vtref even though the toner supply device 20 supplies toner. Therefore, in the present embodiment, control as described in each of the following control examples is performed.

[Control example 1]
FIG. 1 is a flowchart showing a control flow for suppressing excessive toner supply in the first control example.
In this control example 1, the detection operation interval m of the P sensor 103 is initially set to 30 sheets (S1). As described above, the control unit 101 controls the toner supply operation using the detection values of the T sensor 102 and the P sensor 103. During this control, when the toner replenishing operation is performed (S2), the control unit 101 determines whether or not the detection value Vt of the T sensor 102 is increasing (S3). At this time, if the detection value Vt of the T sensor 102 does not tend to increase, the detection value of the T sensor 102 is normal because it indicates an increase in toner density. On the other hand, if it is determined that the detection value Vt of the T sensor 102 is increasing, this indicates that the detection value of the T sensor 102 indicates a decrease in toner density even though the toner is replenished. It is a situation. However, even if the detection value Vt of the T sensor 102 tends to increase during the toner replenishment operation, there may be a situation in which the image density also decreases depending on circumstances. For example, when images with a very high image area ratio are continuously formed, the toner replenishment amount cannot catch up with the toner consumption amount, and the detection value of the T sensor 102 is the toner value even though the toner is replenished. It can show a decrease in concentration. This is normal. Therefore, in this control example 1, for further confirmation, it is also determined whether or not the detection value Vsp of the P sensor 103 is higher than a specified value Vspref that is a predetermined threshold concentration (S4). As a result of this determination, when the detection value Vsp of the P sensor 103 is higher than the specified value Vspref, the image density is also increased, so that it can be confirmed that excessive toner supply is performed.

Therefore, in this control example 1, the detection operation interval m by the P sensor 103 is made shorter than usual, the interval of correction processing of the target value Vtref of the T sensor is made fine, and this target value Vtref is quickly set to an appropriate value. Correct it.
Specifically, first, the detection operation interval m is shortened and the number of times of detection by the P sensor 103 (hereinafter referred to as “the number of suppression operations”) K is set to 10 (S5). Then, the detection operation interval m by the P sensor 103 is set to 10 sheets (S6). In this state, the correction processing of the target value Vtref in the toner density control described above is executed until the suppression operation frequency K becomes 0 (S6). S7 to S9). When the number of suppression operations K becomes 0, the detection operation interval m is returned to 30 sheets at the initial setting (S10). By performing such control, when the above abnormal situation occurs, the correction processing of the target value Vtref of the T sensor 102 can be executed three times more than usual per the number of times of image output. As a result, as shown in FIG. 5, after the abnormal situation described above, the excessive toner supply operation could be stopped when the image output was about 50 sheets. Therefore, as shown in FIG. 13, compared to the conventional case where the excessive toner replenishment operation is not stopped until the image output is about 120 sheets, the period during which the excessive toner replenishment is performed is in units of the number of image output sheets. When it thinks in, it became less than half. In addition, scumming and toner scattering were significantly suppressed as compared to the conventional case.
In this control example 1, the number of suppression operations K is set to 10. However, this number is preferably as small as possible from the viewpoint of suppressing a decrease in the continuous image formation speed. According to the result shown in FIG. 5, the number of suppression operations K can be set to about 5.

[Control example 2]
FIG. 6 is a flowchart showing a control flow for suppressing excessive toner supply in the present control example 2.
Also in the second control example, the process for confirming that excessive toner replenishment is performed is the same as in the first control example (S11 to S14). In this control example 2, when it is confirmed that excessive toner supply is performed, the toner supply operation is forcibly stopped, and subsequent toner supply is prohibited (S15). Then, the detection operation by the P sensor is repeated every 30 image outputs until the detection value Vsp of the P sensor becomes equal to or less than the specified value Vspref (S16, S17). During this time, the correction process of the target value Vtref of the T sensor 102 is not performed. When image formation is performed in a state where toner replenishment is prohibited, as a result of toner consumption, the image density decreases and the detection value Vsp of the P sensor decreases. When the detected value Vsp becomes equal to or less than the specified value Vspref, the toner pattern density has decreased to the target density. Therefore, the target value Vtref of the T sensor 102 is detected by the T sensor 102 at this time. The value Vt is set (S18). Then, the prohibited toner replenishing operation is released (S19), and then the above-described toner density control is performed based on the newly set target value Vtref (S20).

  As a result, as shown in FIG. 7, after the abnormal situation described above, the excessive toner replenishment operation could be stopped when about 100 image outputs were made. Therefore, as shown in FIG. 13, compared to the conventional case where the excessive toner replenishment operation is not stopped until the image output is about 120 sheets, the period during which the excessive toner replenishment is performed is in units of the number of image output sheets. In other words, background contamination and toner scattering were suppressed compared to the conventional case.

[Control Example 3]
FIG. 8 is a block diagram showing the configuration of the toner density control device in the third control example.
In the present control example 3, a timer 104 as a time measuring means for measuring the standing time is added to the configuration of the toner density control apparatus of the above embodiment shown in FIG. The timer 104 is connected to the control unit 101 and starts time measurement in response to a measurement start command from the control unit 101. When the measurement time T reaches a predetermined reference time Tref, the timer 104 is controlled. Notification to the unit 101.

FIG. 9 is a flowchart showing a control flow for suppressing excessive toner supply in the third control example.
This control example 3 is a process for confirming that excessive toner replenishment is performed from the detection value Vt of the T sensor 102 and the detection value Vsp of the P sensor 103 as in the control example 1 and the control example 2 described above. do not do. Instead, the timer 104 measures the developer leaving time, and determines whether or not the leaving time exceeds the reference time. Then, if the standing time exceeds the reference time, it is assumed that excessive toner replenishment is performed in the subsequent image forming operation, and the target value Vtref of the T sensor is set in the same manner as in the above control example 1. The target value Vtref is quickly corrected to an appropriate value by narrowing the interval of the correction process.
Specifically, also in this control example 3, the detection operation interval m of the P sensor 103 is initially set to 30 sheets (S21). As described above, the control unit 101 controls the toner supply operation using the detection values of the T sensor 102 and the P sensor 103. During this control, the control unit 101 monitors whether or not the developing device 12 is being driven (S22). When the driving of the developing device 12 is stopped, a measurement start command is output to the timer 104, and the timer 104 measures time (S23). Before the measurement time T of the timer 104 reaches the reference time Tref (S24), when the driving of the developing device is resumed (S22), the control unit 101 outputs a measurement stop command and a reset command to the timer 104. On the other hand, when the measurement time T of the timer 104 reaches the reference time Tref (S24), the control unit 101 sets the number of suppression operations K to 10 (S25), as in the above control example 1, and the P sensor 103. After the detection operation interval m is set to 10 (S26), the target value Vtref correction processing in the toner density control described above is executed until the suppression operation count K becomes 0 (S27 to S29). When the suppression operation count K becomes 0, the detection operation interval m is returned to 30 sheets at the time of initial setting (S30).

It has been confirmed that when the developer is left for a long period of time, as described above, the abnormal situation occurs. In this control example 3, it is confirmed whether or not the abnormal situation occurs by determining whether or not the developer leaving time exceeds the reference time Tref. This determination can be performed more easily than determining the increasing tendency of the detection value Vt of the T sensor 102 as in the above control example 1, and does not require complicated determination and control. In the third control example, as in the first control example, as shown in FIG. 5, after the developer is left for a long period of time and the abnormal situation occurs, Thus, the excessive toner replenishing operation can be stopped, and background contamination and toner scattering are considerably suppressed as compared with the conventional case. Therefore, according to the third control example, with respect to the abnormal situation caused by leaving the developer for a long time, it is possible to suppress background contamination and toner scattering with simpler processing than in the first control example.
In this control example 3, the number of suppression operations K is set to 10. However, as in the case of the control example 1, the suppression operation frequency K is set to about 5 based on the result shown in FIG. Is also possible.

[Control Example 4]
FIG. 10 is a flowchart illustrating a control flow for suppressing excessive toner supply in the present control example 4.
This control example 4 is performed using the toner density control device including the timer 104 as in the above control example 3, and measures the developer leaving time (S31 to S34). If the standing time exceeds the reference time, it is assumed that excessive toner replenishment is performed in the subsequent image forming operation, and the toner replenishment operation is forcibly performed as in Control Example 2 above. The operation is stopped, and the subsequent toner supply is prohibited (S35). Then, until the detection value Vsp of the P sensor becomes equal to or lower than the specified value Vspref, the operation of performing the detection operation by the P sensor is repeated for every 30 image outputs (S36, S37), and the detected value Vsp becomes equal to or lower than the specified value Vspref. Then, the target value Vtref of the T sensor 102 is set to the detection value Vt (S38). Thereafter, the prohibited toner replenishing operation is released (S39), and then the above-described toner density control is performed based on the newly set target value Vtref (S40).

  As a result, as shown in FIG. 7, after the developer is left for a long time and the above abnormal situation occurs, the excessive toner supply operation can be stopped when the image output is about 100 sheets. As a result, soiling and toner scattering were suppressed as compared with the conventional case. Also in this control example 4, with respect to the abnormal situation caused by leaving the developer for a long time, it is possible to suppress background stains and toner scattering by simpler processing than in the case of the control example 2.

As described above, in the copying machine according to the present embodiment, the latent image on the photosensitive member 10 as the latent image carrier is developed by the developing device 12 using the developer containing the toner and the carrier, and the toner image obtained thereby. Is finally transferred onto a sheet S as a recording material to form an image. This copying machine has a toner supply device 20 for supplying toner in the developing device 12 to the amount of toner consumed by image formation, and a part of the developer contained in the developing device 12 is related to the developer density. A toner pattern obtained by developing a pattern latent image for detecting the image density on the photoconductor 10 and developing the pattern latent image on the photoconductor 10 with the T sensor 102 as a toner density sensor for detecting the magnetic permeability that is a parameter to be developed. And a P sensor 103 as a pattern density sensor for detecting the density of the. Further, the control unit 101 provided in the copying machine controls the toner supply operation of the toner supply device 20 based on the detection result of the T sensor 102 so that the detected value Vt matches the target value Vtref. And a correction process for correcting the target value Vtref so that the toner supply operation is performed so that the density (detected value Vsp) of the toner pattern detected by the P sensor 103 becomes the target density (specified value Vspref). , Functioning as a target value correcting means executed at a predetermined timing (every 30 image outputs).
In the above control example 1, when the toner detected by the T sensor 102 shows a decrease in toner density even though the toner is replenished by the toner replenishing device 20, the toner is replenished for a predetermined period. The execution interval of the correction process is shortened compared to the normal time when the magnetic permeability detected by the sensor 102 indicates an increase in toner density. As a result, as described above, it is possible to shorten the period during which excessive toner replenishment occurs in an abnormal situation where the magnetic permeability detected by the T sensor 102 indicates a decrease in toner density despite the toner replenishment, Background contamination and toner scattering can be considerably suppressed as compared to the conventional case.
Further, in the above control example 2, when the magnetic permeability detected by the T sensor 102 indicates a decrease in toner density even though the toner is supplied by the toner supply device 20, the toner supply operation is forcibly performed for a predetermined period. Stop. Also with this configuration, as described above, background contamination and toner scattering can be suppressed as compared with the conventional case.
In particular, in the control example 1 and the control example 2 described above, the magnetic permeability detected by the T sensor 102 in spite of the toner replenishment by the toner replenishing device 20 not only indicates a decrease in toner density but also detected by the P sensor 103. When the detected value Vsp exceeds a predetermined threshold density (specified value Vspref), the correction processing execution interval is shortened or the toner supply operation is forcibly stopped. As a result, it is possible to reliably confirm that excessive toner supply is performed.
On the other hand, in the above control example 3, a timer 104 is provided as a time measuring means for measuring the non-operation time of the developing device 12, and when the measured time T of the timer 104 exceeds the reference time Tref, the same as in the above control example 1. In addition, the execution interval of the correction process is made shorter than when the measurement time T is equal to or shorter than the reference time Tref for a predetermined period. According to this configuration, it is possible to shorten the period during which the excessive toner replenishment that occurs under the above-described abnormal situation that can occur when the developer is left for a long period of time, and considerably suppress scumming and toner scattering compared to conventional ones. it can.
In the control example 4, when the measurement time T of the timer 104 exceeds the reference time Tref, the toner supply operation is forcibly stopped for a predetermined period, as in the control example 2. Even with this configuration, as described above, it is possible to shorten the period during which excessive toner replenishment that occurs under the above-described abnormal situation that may occur when the developer is left for a long period of time, and to prevent background contamination and toner scattering. It can be suppressed compared.
In the control example 2 and the control example 4, the end of the predetermined period is set when the density (detected value Vsp) of the toner pattern detected by the P sensor 103 becomes the reference density (specified value Vspref). It is. Thereby, when the toner density of the actual developer reaches the optimum density, the correction processing execution interval is shortened or the excessive toner replenishment suppressing operation of forcibly stopping the toner replenishing operation is terminated. Can do. Therefore, the period during which the excessive toner replenishment suppressing operation is performed can be minimized. In the control example 1 and the control example 3 described above, the suppression operation for excessive toner replenishment is terminated when the set number of suppression operations (10 times) is completed. Similar to the control example 2 and the control example 4, when the density of the toner pattern (detected value Vsp) detected by the P sensor 103 reaches the reference density (specified value Vspref), the operation for suppressing excessive toner supply is finished. You may comprise. Conversely, the control example 2 and the control example 4 may be configured to end the excessive toner replenishment suppression operation when the set number of suppression operations (10 times) is completed.
In this embodiment, a magnetic carrier is used as the carrier, and a magnetic permeability sensor that detects the magnetic permeability of the developer, which is a parameter related to the developer density, is used as the T sensor 102. As a result, in the configuration using the T sensor that has been widely used conventionally, the above-described excessive toner replenishment suppressing operation can be employed, and background contamination and toner scattering can be suppressed as compared with the conventional case.
In this embodiment, a toner based on a modified polyester resin is used as the toner. As described above, such a toner has advantages that it is easy to improve the removal efficiency when cleaning with a blade, and that the surfactant does not remain inside the toner or inhibit charging of the toner. However, on the other hand, there is a demerit that the fluidity of the developer is likely to be deteriorated, the above-mentioned abnormal situation is likely to occur, and the above-described background contamination and toner scattering are likely to occur. However, this can be sufficiently suppressed by adopting the above-described excessive toner replenishment suppressing operation, and therefore, the above-mentioned merit can be enjoyed in a state in which background contamination and toner scattering are suppressed.

6 is a flowchart showing a control flow for suppressing excessive toner replenishment according to Control Example 1 executed in the copier according to the embodiment. 1 is a schematic configuration diagram of the entire copier. FIG. 3 is a perspective view of a toner bottle set in a toner supply device included in the copier. FIG. 3 is a block diagram illustrating a configuration of a toner density control device used in Control Example 1 and Control Example 2. The graph which shows the control result in the control example 1 and the control example 3. FIG. 9 is a flowchart illustrating a control flow for suppressing excessive toner supply according to a control example 2; The graph which shows the control result in the control example 2 and the control example 4. FIG. FIG. 6 is a block diagram illustrating a configuration of a toner density control device used in Control Example 3 and Control Example 4. 10 is a flowchart illustrating a control flow for suppressing excessive toner supply according to Control Example 3. 10 is a flowchart showing a flow of control for suppressing excessive toner supply according to a control example 4; (A) is explanatory drawing which shows the state where the toner density | concentration in a developer is high. FIG. 6B is an explanatory diagram illustrating a state where the toner concentration in the developer is low. (A) Explanatory drawing which shows the state which the fluidity | liquidity of the developer deteriorated. (B) is explanatory drawing which shows the mode of the developer after leaving the developer of the state of the figure (a) to stand overnight. 6 is a graph showing a conventional toner density control operation when an image forming apparatus is started to operate in the next morning after being left overnight with the developer fluidity deteriorated.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Photoconductor 12 Developing device 20 Toner replenishing device 23 Toner bottle 26 Bottle drive motor 101 Control part 102 T sensor 103 P sensor 104 Timer

Claims (6)

The latent image on the latent image carrier is developed by a developing device using a developer containing toner and carrier, and the resulting toner image is finally transferred onto a recording material to form an image. There,
A toner replenishing device that replenishes the developer in the developing device with the amount of toner consumed by image formation;
A toner concentration sensor for detecting a parameter related to developer density for a part of the developer contained in the developing device;
A pattern density sensor for forming a pattern latent image for image density detection on the latent image carrier and detecting the density of a toner pattern obtained by developing the pattern latent image with the developing device;
Replenishment operation control means for controlling the toner replenishment operation of the toner replenishing device based on the detection result of the toner concentration sensor so that the detected value matches the target value;
Target value correcting means for executing correction processing for correcting the target value at a predetermined timing so that a toner replenishing operation is performed so that the density of the toner pattern detected by the pattern density sensor becomes a target density; In the provided image forming apparatus,
Means for determining whether or not the parameter detected by the toner concentration sensor during the toner replenishment operation is decreasing with respect to the toner concentration even though the toner is replenished by the toner replenishment operation of the toner replenishing device; When the determination means determines that the parameter detected by the toner density sensor during the toner supply operation is decreasing with respect to the toner density even though the toner is supplied by the toner supply device. a predetermined period, than the normal parameters detected by the toner concentration sensor during the toner supply operation to indicate that an upward trend for the toner density, image forming, characterized in that shortened the interval of the correction process apparatus. The latent image on the latent image carrier is developed by a developing device using a developer containing toner and carrier, and the resulting toner image is finally transferred onto a recording material to form an image. There,
A toner replenishing device that replenishes the developer in the developing device with the amount of toner consumed by image formation;
A toner concentration sensor for detecting a parameter related to developer density for a part of the developer contained in the developing device;
A pattern density sensor for forming a pattern latent image for image density detection on the latent image carrier and detecting the density of a toner pattern obtained by developing the pattern latent image with the developing device;
Replenishment operation control means for controlling the toner replenishment operation of the toner replenishing device based on the detection result of the toner concentration sensor so that the detected value matches the target value;
Target value correcting means for executing correction processing for correcting the target value at a predetermined timing so that a toner replenishing operation is performed so that the density of the toner pattern detected by the pattern density sensor becomes a target density; In the provided image forming apparatus,
Means for determining whether or not the parameter detected by the toner concentration sensor during the toner replenishment operation is decreasing with respect to the toner concentration even though the toner is replenished by the toner replenishment operation of the toner replenishing device; When the determination means determines that the parameter detected by the toner density sensor during the toner supply operation is decreasing with respect to the toner density even though the toner is supplied by the toner supply device. a predetermined period, the image forming apparatus characterized by being configured such that the toner replenishing operation is forcibly stopped. The image forming apparatus according to claim 1 or 2,
The reason why the correction processing execution interval is shortened or the toner replenishment operation is forcibly stopped is that the parameter detected by the toner density sensor during the toner replenishment operation despite the toner replenishment operation. indicates that the toner density tends to decrease, and the image forming apparatus, wherein the concentration of the toner pattern detected by the pattern density sensor is when it exceeds a predetermined threshold concentration. The image forming apparatus according to claim 1, 2 or 3.
The end of the predetermined period is when the density of the toner pattern detected by the pattern density sensor becomes a reference density. The image forming apparatus according to claim 1, 2, 3, or 4.
Using a magnetic carrier as the carrier,
An image forming apparatus using a magnetic permeability sensor that detects a magnetic permeability of a developer, which is a parameter related to a developer density, as the toner density sensor. The image forming apparatus according to claim 5.
An image forming apparatus using a toner based on a modified polyester resin as the toner.

Images