JP4584726B2 - Developing device, image forming apparatus, and image forming method - Google Patents

Description

  The present invention relates to a developing device, an image forming apparatus, and an image forming method, and more particularly to replacement control of a deteriorated developer.

  In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a printing machine, an electrostatic latent image formed on a photosensitive member that is a latent image carrier is subjected to a visible image processing by a developing device, and a visible image is obtained. A recording output can be obtained by transferring to a sheet or the like.

  In addition to the configuration in which one photoconductor is provided for only a single color, there is a configuration in which a plurality of photoconductors are provided for forming images of a plurality of colors. In the latter case, a multicolor image including a full color image is formed. Used in cases.

By the way, as a developer used for development, there is a two-component developer in which a toner and a carrier are mixed in addition to a one-component developer containing only a magnetic or non-magnetic toner.
The two-component developer is composed of a toner and a carrier that carries the toner, and the toner can be charged by a frictional charging action that occurs during agitation and mixing so that the toner can be electrostatically attracted to the electrostatic latent image on the photoreceptor. Is done.

  The toner and the carrier may be contaminated by a part of the toner that is repeatedly rubbed and collided by stirring and mixing, and the carrier coating layer may be peeled off. When such a phenomenon occurs, the charging ability of the carrier with respect to the toner gradually decreases, and the fogging phenomenon of the image due to the charging failure of the toner tends to occur. In this case, the fog phenomenon means a phenomenon in which toner charged to a reverse polarity due to a decrease in the charge amount of the developer adheres to a non-image portion of the photoreceptor, and this may cause a decrease in image quality.

  Conventionally, the decrease in toner concentration that causes a decrease in image quality is to detect the magnetic permeability that changes depending on the mixing ratio of the toner with respect to the magnetic carrier when using a two-component developer in which the toner and the magnetic carrier are mixed. The toner density is stabilized by replenishing the toner when the change in magnetic permeability corresponds to the shortage of toner (for example, Patent Document 1). Further, as a configuration used for toner density control, there is a configuration in which a pattern image for density detection is formed separately from the image portion, and toner supply control is performed based on detection of the image density (for example, Patent Document 2). .

  On the other hand, the charging function of the carrier contained in the developer is deteriorated due to a phenomenon such as peeling off of the surface coating layer as described above. For this reason, it is necessary to replace the developer separately from the replenishment of the toner. However, if the replacement is performed for all the developers in the developing device, maintenance labor and cost are increased, and further image formation can be performed. Inconveniences such as an increase in waiting time for the user due to no downtime occur.

  Conventionally, instead of replacing all of the developer described above when preventing image quality degradation, in addition to replenishing new toner, a part of the developer is forced to overflow from the developing device, resulting in a decrease in charging performance The developer is discharged from the developer container, and the developer is replaced by newly replenishing the carrier and the toner, so that the charging performance of the developer is maintained and the deterioration in image quality is suppressed. (For example, patent document 3).

In the configuration disclosed in Patent Document 3, a new carrier is replenished in the developing device separately from the replenishment of consumed toner, and the developer in the developing device that has become excessive is provided on the wall surface of the developing device. The developer is discharged from the developer outlet and is collected in the developer collection container. By sequentially repeating such supply and discharge of the carrier and the deteriorated developer, the developer that is contaminated and deteriorated in the developing device is sequentially replaced with newly supplied toner and carrier. As a result, the charging performance of the developer is maintained, and the deterioration of the image quality is suppressed.
However, in the configuration of the above-described conventional invention, the carrier is replenished to the developing device in such a manner that the carrier is replenished at the same ratio as the toner replenishment amount. For this reason, since carrier replenishment is performed regardless of the use method and use conditions of the image forming apparatus, the degree of deterioration of the carrier differs depending on the use situation, and the image to be developed also differs. For example, when the deterioration of the carrier is so severe that it is not in time for replenishment / discharge of the carrier depending on the use situation, there is a possibility that problems such as deterioration of image quality and background stains may occur. On the other hand, when the carrier is hardly deteriorated, the carrier is replenished / discharged in proportion to the amount of toner consumption, so that the carrier is wasted.

  Therefore, a configuration in which the carrier replenishment is controlled by the operation time of the developing device (for example, Patent Document 4) and a developer replenishment / discharge control according to the number of image formations, targeting the actual developing operation state. (For example, patent document 5) is proposed.

Japanese Patent Laid-Open No. 10-213928 (paragraph “0011” column) Japanese Patent Laid-Open No. 3-206471 (from page 4, lower right column, line 4 to page 5, upper left column, line 15) JP 2001-183893 (paragraph “0045” column) JP-A-9-297462 (paragraph "0012" column) JP 2003-337469 A (paragraph "0013" column)

However, as disclosed in Patent Document 4, in the carrier replenishment control in the case where the developing device is actually operated , due to a difference in driving conditions such as whether the developing device was continuously operated or due to environmental fluctuations. The difference in carrier deterioration is not taken into consideration, and the replenishment / discharge control according to the number of image formations as disclosed in Patent Document 5 uses the development bond usage rate, that is, the difference in image area rate and image pattern. The difference in carrier deterioration due to is ignored.
For this reason, it is necessary to accurately detect developer replenishment / discharge control based on the actual deterioration of the developer in order to stabilize the charging ability of the developer and to suppress deterioration in image quality.

  An object of the present invention is to provide a stable image quality, resource saving, and cost by utilizing a developer without waste and maintaining the characteristics of the developer stably for a long period of time in view of the problems in the conventional development described above. It is an object of the present invention to provide a developing device, an image forming apparatus, and an image forming method capable of achieving the reduction.

According to the first aspect of the present invention, in the developing device capable of replenishing the developer composed of only the carrier or the mixture of the carrier and the toner, and discharging the excess developer and replacing the developer, the developer Is used for detecting the deterioration state of the developer from the degree of background contamination by comparing the density detection result in the non-image portion on the latent image carrier side supplied with the lower limit value of the preset detection output. and a density sensor, said image density sensor is connected to the input side, the output side and a control unit developer supply means being connected, the control unit may land in the non-image portion by the image density sensor The background potential at the time of stain detection is set lower than that at the time of image formation, and a state in which weakly charged toner is likely to adhere to the non-image area is set, and in this state, the lower limit value of the detection output by the image density sensor is used as a reference. Together determine the deteriorated state of the developer on the basis of background contamination state of said at non-image portion by comparing the detection output from the non-image portion, the replenishment amount of the developer according to this determination result, one of emissions or It is characterized by controlling both.

According to a second aspect of the present invention, in the developing device capable of replenishing the developer composed of only the carrier or a mixture of the carrier and the toner while discharging the excess developer and replacing the developer, the developer Is used for detecting the deterioration state of the developer from the degree of background contamination by comparing the density detection result in the non-image portion on the latent image carrier side supplied with the lower limit value of the preset detection output. and a density sensor, said image density sensor is connected to the input side, the output side and a control unit developer supply means being connected, the control unit may land in the non-image portion by the image density sensor during stain detection, increasing the toner concentration weakly charged toner and adhered easily state to the non-image portion by a certain amount of toner supply, based on the lower limit of detection output in the image density sensor in this state Serial determine the deteriorated state of the developer based on the result of detecting the scumming of the non-image portion on the latent image carrier by determining the deteriorated state of the developer by comparing the detected output from the non-image portion According to the determination result, one or both of the developer replenishment amount and the discharge amount are controlled .

According to a third aspect of the present invention, in the developing device according to the first or second aspect, the control unit has a lower limit value of a detection output of the image density sensor in a state where weakly charged toner tends to adhere to the non-image portion. When comparing the detection output from the non-image portion with reference to the above, the toner density in the developer is set to a state where the toner density is maintained at a constant density .

According to a fourth aspect of the present invention, the control unit detects from the non-image part based on a lower limit value of a detection output of the image density sensor in a state where weakly charged toner is likely to adhere to the non-image part. When performing output comparison, a lower limit value in which information relating the length of the development drive stop time until the detection output comparison is performed and the toner adhesion state to the non-image portion due to this length is used for the comparison in advance. The correction information is used as correction information .

According to a fifth aspect of the present invention, in the developing device according to the first or second aspect , the control unit has a lower limit value of a detection output of the image density sensor in a state in which weakly charged toner tends to adhere to the non-image portion. When comparing the detection output from the non-image part with reference to the reference value, the developer agitation supply is continued for a certain period of time, and then the lower limit value of the detection output from the image density sensor is used as a reference. It is characterized in that the deterioration state of the developer is discriminated by comparing the detection output from the image portion .

According to a sixth aspect of the present invention, in the developing device according to any one of the first to fifth aspects, the control unit outputs the non-image portion from the non-image portion on the basis of a lower limit value of a detection output of the image density sensor. When determining the deterioration of the developer by comparing the detection output, the detection output from the non-image part and the lower limit value are compared a plurality of times, the tendency of the comparison result of a plurality of times is obtained, and the development is performed based on the tendency. It is characterized by judging deterioration of the agent .

According to a seventh aspect of the present invention, in the developing device according to the sixth aspect , the control unit detects the background contamination detected during a certain period of time from the start of the development driving, and the agitation time is constant. In this case, the developer deterioration determination process is terminated at that time when the value becomes the specified value or less in a shorter time .

According to an eighth aspect of the present invention, in the developing device according to any one of the first to seventh aspects, the developer deterioration detection start timing is set based on a determination result when the previous deterioration detection is performed. It is a feature.

According to a ninth aspect of the present invention, in the developing device according to the eighth aspect , the control unit sets a shortest value for the interval of the deterioration detection start timing of the developer, and as a result of the deterioration detection at the shortest interval, When it is determined that the developer has deteriorated continuously for a predetermined number of times, the developer replenishment / discharge operation is stopped and a warning operation is selected.

According to a tenth aspect of the present invention, in the developing device according to any one of the first to ninth aspects, the specified value of the background contamination used for the developer deterioration judgment performed in the control unit is an image quality requested by a user. It can be changed according to the characteristics.

According to an eleventh aspect of the present invention, the developing device according to any one of the first to tenth aspects is used in an image forming apparatus.

The invention of claim 12 wherein is characterized in that an image forming method for performing developer deterioration judgment by the developing device according to one of claims 1 to 10.

According to the present invention, when the deterioration of the developer is determined by detecting the background stain in the non-image portion using the existing image density sensor, the developer that is present at a position that does not contribute to the image is targeted. By directly detecting the deterioration state, it is possible to determine the developer deterioration by using a position that does not contribute to the image. In particular, when detecting the deterioration state, the background potential at the time of detecting the deterioration of the developer is made smaller than that at the time of image formation, so that the detection sensitivity to the deterioration of the developer can be increased, and the accuracy of the deterioration detection is increased. This makes it possible to keep the developer charging ability stable by making it possible to supply and discharge the developer with higher accuracy.

In addition , according to the second aspect of the present invention, it is possible to make a situation in which background contamination easily occurs by detecting the deterioration of the developer after supplying a certain amount of toner. Can be increased.

According to the third aspect of the present invention, by detecting the scumming with the toner concentration kept constant, it is possible to detect the deterioration of the developer in the scumming by eliminating the difference in the charge amount of the developer due to the difference in the toner concentration. This makes it possible to improve the accuracy of detection of deterioration.

According to the fourth aspect of the present invention, based on the relationship between the development stop time before detection of deterioration set in advance and the background contamination of unused developer, the development stop time before detection of background contamination and deterioration in the non-image area. Thus, the deterioration state of the developer is judged, so that the difference in the development stop time before the deterioration is detected, that is, the charge amount of the developer is the same as immediately after the continuous printing and immediately after the first printing of the day. It is possible to prevent the deterioration detection accuracy of the developer from differing from the actual deterioration state of the developer due to the difference depending on the difference in the stirring time.

According to the invention described in claim 5 , since the deterioration detection of the developer is performed after the development processing is performed for a certain time, the difference in the charge amount is eliminated by eliminating the difference in the stirring time due to the difference in the development time. In addition, it is possible to detect the deterioration of the developer after it has been eliminated, thereby preventing the deterioration of the deterioration detection accuracy.

According to the sixth aspect of the invention, by setting two detection timings at the start of development driving and after a lapse of a fixed time, the difference in charging state due to the difference in stirring time is eliminated, and the state of occurrence of scumming is stabilized. In addition, the deterioration of the developer can be detected. In addition, by stabilizing the charged state of the developer obtained by actual stirring by comparing the change rate of the background stain obtained by continuing detection of the background stain for a certain period of time from the start of development driving. Developer deterioration can be detected, and detection accuracy can be improved.

According to the seventh aspect of the present invention, the detection of developer deterioration is stopped when the detected value of the background stain reaches the specified value or less in a shorter time than the fixed stirring time, so that the detection time is wasted. Can be prevented.

According to the eighth aspect of the present invention, since the start timing for detecting the deterioration of the developer is set based on the detection result obtained when the previous execution was performed, the detection start timing can be changed according to the deterioration state of the developer. In this way, it is possible to prevent unnecessary deterioration detection from starting or deterioration detection that does not follow the deterioration depending on when the deterioration is slow or early.

According to the ninth aspect of the present invention, since the shortest detection start timing is set and a warning can be given in the case of deterioration detection at this shortest interval, scumming due to factors other than developer deterioration occurs. Therefore, it is possible to prevent the developer from being continuously supplied and discharged continuously at a short interval.

According to the tenth aspect of the present invention, the development occupant deterioration determination criterion can be changed according to the user's request, so that it is possible to detect the deterioration according to the use state of the developer for the required image quality.

According to the eleventh and twelfth aspects of the present invention, it is possible to directly detect the deterioration of the developer for the background contamination existing in the non-image portion of the latent image carrier in the determination of the developer deterioration state that leads to the deterioration of the image quality. Therefore, unlike the developer replenishment / discharge control based on the operating status of the device, rather than the developer deterioration for dirt, the developer charging performance can be improved according to the actual developer deterioration state, and the image quality It is possible to prevent the decrease.

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

  FIG. 1 is a schematic diagram showing a main part of an image forming apparatus to which an image forming method using a developing device according to an embodiment of the present invention is applied. The image forming apparatus described as the present embodiment includes a copying machine, a printer, a facsimile machine, a printing machine, and the like.

  In FIG. 1, an image forming apparatus 1 has a configuration related to the present embodiment, a photosensitive member 2 that is a latent image carrier that carries an electrostatic latent image to be developed, and an electrostatic latent image on the photosensitive member 2. And a developing device 3 for processing a visible image. In addition to the photoreceptor 2 and the developing device 3, the image forming apparatus 1 includes a charging device, a writing device, a transfer device, a cleaning device, and a fixing device for fixing an image after transfer, although not shown. It is.

The developing device 3 uses a two-component developer in which a toner and a magnetic carrier are agitated and mixed to carry a charged toner on the carrier.
The developing device 3 includes a casing 3A that forms a casing of the device, a developing sleeve 3B that is disposed at a position facing the photoreceptor 2 in the casing 3A, and each space that is partitioned by a partition wall 3A1 in the casing 3A. Rotating transport augers 3C and 3D which are arranged inside and have a lead direction capable of transporting the developer in opposite directions, and a doctor blade 3E which defines the layer thickness of the developer carried on the developing sleeve 3B. And.

  In the developing device 3, the electrostatic latent image carried on the photosensitive member 2 is contacted with the developer on which the toner that has been agitated and mixed by the conveyance augers 3C and 3D and frictionally charged is attached to the carrier, The visible image processing of the electrostatic latent image is performed by electrostatically attracting the toner to the electrostatic latent image.

The developing device 3 in this embodiment has a configuration in which the developer is replaced with a new developer. Hereinafter, this configuration will be described.
In FIG. 1, the casing 3A has a developer replenishing section 4 in the upper part of the space where the conveyance auger 3D adjacent to the conveyance auger 3C that conveys the developer toward the developing sleeve 3B, and the conveyance auger 3D. Developer collecting portions 5 are respectively provided on the wall portions away from the developing sleeve 3B in the rotation direction (in the direction of the arrow in the drawing). The developer supply unit 4 and the developer recovery unit 5 are communicated with a space in which the transport auger 3D is disposed through an opening that penetrates the casing 3A.

FIG. 2 is a diagram showing the configuration of the developer replenishing unit 4 and the developer collecting unit 5 for the developing device 2, in which the developer replenishing unit 4 is a toner feeding pipe for feeding only toner. One end of 4A1 and one end of developer feeding pipe 4B1 for feeding a developer consisting of a carrier alone or a carrier mixed with a small amount of toner are connected to a replenishing opening 3A2 provided in casing 3A.
Each of the toner feeding pipe 4A1 and the developer feeding pipe 4B1 is provided with a conveying screw (indicated by reference numeral 4A10 for only one conveying screw in FIG. 1). The toner can be transported while being agitated and mixed in the axial direction by being rotationally driven by a toner transport motor 4A2 and a developer transport motor 4B2 provided at the other end of each of the pipes 4A1 and 4B1.

In FIG. 2, a toner cartridge 4A and a carrier cartridge (including a case where a developer mixed with a small amount of toner is used) 4B are connected in the middle of each of the feed pipes 4A1 and 4B1, and are accommodated inside. A developer replenishing unit 4 that discharges only the toner or carrier that is being mixed or a developer mixed with a small amount of toner, and the discharged toner, carrier, or developer communicates with the inside of the casing 3A as the conveying screw rotates. It is designed to be conveyed.
As shown by an arrow A in FIG. 1, the toner or carrier or developer from the developer replenishing section 4 is dropped into the space where the conveyance auger 3D is arranged.

On the other hand, the developer recovery unit 5 includes a recovery chamber 5A having a space communicating with a space where the transport auger 3D in the casing 3A of the developing device 3 is disposed. One end of the pipe 6 is connected. Disposed inside the developer discharge pipe 6 is a discharge screw 5C that is rotationally driven by a developer discharge motor 5B.
The other end of the developer discharge pipe 6 communicates with the inside of a developer recovery container 7 that is detachably attached to the developing device 3. For collecting the developer, instead of providing the collecting chamber 5A, a weir is provided on the casing 3A side of the developing device 3, and the developer exceeding the weir overflows and flows into the developer discharge pipe. A configuration is also possible. In this case, the developer overflow that occurs when the developer is replenished can be used.
The developer discharge motor 5B sets the rotation time and the rotation amount in a control unit (a member denoted by reference numeral 100 in FIG. 3), which causes the developer filled in the developer discharge pipe 6 to be filled. The developer can be recovered by moving it toward the developer recovery container 7. In this embodiment, the toner cartridge 4A, the carrier cartridge 4B, and the developer collection container 7 provided in the developer collection unit provided in the developer supply unit 4 are all detachable from the developing device 3. The toner cartridge 4A and the carrier cartridge 4B are replaced with new ones when the stored toner, carrier or developer is consumed, and the developer recovery container 7 is full. Emptyed out.

The toner concentration of the developer accommodated in the developing device 3, that is, the mixing ratio of the toner in the developer, is a toner concentration sensor embedded in the casing 3A and having a detection surface facing the outer peripheral portion of the transport auger 3D. 8 is determined by detecting a change in magnetic permeability. When the mixing ratio is determined, toner replenishment control is executed according to this result.
Further, the detection of the image density is performed by the image density sensor 9 facing the photoconductor 2, and toner replenishment control is performed when it is determined that the toner density is low according to the result. The image density sensor 9 used in this embodiment is an optical sensor that can detect light irradiated from a light emitting element and reflected on the photoreceptor 2.

  The image density sensor 9 is composed of an optical sensor having a light emitting part and a light receiving part using an LED or the like. It is used to change the set value. When the reference pattern density is high according to the detection result, the toner density in the developer is lowered. When the reference pattern density is low, the toner in the developer is used. It has a function capable of correcting using the detection result of the toner density sensor 8 arranged on the developing device 3 side so as to increase the density.

  Usually, the image density sensor 9 using an optical sensor often detects the toner density in the image area, but in this embodiment, by detecting the amount of reflected light on the non-image area of the photosensitive member 2, the image density sensor 9 other than the image area is detected. It is used to determine the degree of developer deterioration by detecting the amount of poorly charged toner adhering to the toner. Details of this configuration will be described later.

  As a means for conveying toner and developer for the feeding pipes 4A1 and 4B1 and the developer discharging pipe 6 provided in the developer replenishing section 4 and the developer collecting section 5, suction is used instead of a screw. It is also possible to adopt a conveyance form using negative pressure by a pump.

  In FIG. 2, the toner concentration sensor 8 is disposed on a substantially bottom surface of the casing 3 </ b> A corresponding to the lower side in the gravity direction of the casing 3 </ b> A, and is provided at a position where the developer is easily collected when the developer moves. This makes it possible to inevitably make contact with the developer by utilizing the movement of the developer in the direction of gravity, and accurately detects a change in permeability determined by the mixing ratio of the toner with respect to the carrier. Yes.

A part of the conveyance auger 3D that faces the toner density sensor 8 is provided with a scraping member 10 that can scrape off the developer and foreign matters adhering to the detection surface of the toner density sensor 8.
FIG. 3 is a block diagram for explaining a control unit for performing developer replenishment / discharge control in accordance with the deterioration of the developer used in the developing device 3. In FIG. 3, the control unit 100 performs image formation. This is a part that executes a sequence program for the entire processing. As members related to the present embodiment, a developing device start detecting means 101, a toner density sensor 8, an image density sensor 9, and a timer 102 are connected to the input side and output. On the side, the driving unit 103 of the transport augers 3C and 3D of the developing device 3, the toner transport motor 4A2, the carrier transport motor 4B2, and the alarm unit 104 located on the developer supply unit 4 side used as developer supply means. Each is connected.
The developing device start detection means 101 is a means for detecting the operating state of the developing device, and for example, a print start switch on the operation panel side or a start switch of the image forming apparatus is used. The timer 102 is used for measuring the drive stop time of the developing device 3 and the like.

The control unit 100 detects weakly charged toner adhering to the background portion by detecting the background stain on the non-image portion of the photoreceptor 2 by the image density sensor 9, and based on this result, the degree of deterioration of the developer is detected. And the developer replenishment / discharge control. The contents of control will be described below.
FIG. 4 is a graph showing the relationship of the toner adhesion amount to the non-image portion of the photoreceptor 1 with respect to the output value of the image density sensor 9.
Since the image density sensor 9 is a reflection density sensor, the larger the toner adhesion amount, the lower the reflectance and the smaller the output value. The smaller the toner adhesion amount, the higher the reflectance and the larger the output value. From this relationship, the toner adhesion amount (background stain) can be detected by the image density sensor.

On the other hand, FIG. 5 is a diagram showing the results of experimental determination of the degree of background contamination on the photoreceptor 2 with respect to the charge amount of the carrier. As can be seen from FIG. 5, there was little background stain when the charge amount of the developer was high, and there was a tendency for the background stain to become worse when the charge amount was low. The following reasons are conceivable.
As a result, when the charging ability of the carrier is low, the charge amount of the developer is low, and the toner with a small charge amount (weakly charged toner) increases in the developing device. For this reason, the amount of toner that easily separates from the developing roller 15 increases, and even in non-image areas, the toner adheres and tends to appear as background stains.
Similarly, when the charging ability of the carrier is high, the toner is sufficiently charged, so that the amount of weakly charged toner is small, the amount of toner that is easily detached from the developing sleeve 3B is reduced, and as a result, the occurrence of scumming is reduced. Since there is such a relationship between the carrier and the charging capability, the charging capability of the carrier can be detected by detecting the ground stain.
From the relationship shown in FIGS. 4 and 5, the detection output of the image density sensor 9 with respect to the charge amount of the developer is as shown in FIG. That is, when the charge amount of the developer is small, the output value of the image density sensor is small, and when the charge amount of the developer is large, the output value of the image density sensor is large.

From these relationships, by detecting the output value of the image density sensor 9, it is possible to detect scumming and determine the chargeability (deterioration) of the carrier.
In order to perform the developing operation while maintaining the image quality, it is necessary to keep the charging ability of the carrier at a certain value or more. Therefore, in FIG. 6, the lower limit value of the output value V of the image density sensor 9 is defined as A, and the deterioration detection is performed by comparing the output value V and A of the image density sensor 9 in the non-image portion on the photoreceptor 2. To do.

When V <A, the charging ability of the carrier is lower than the specified value, and it can be determined that the carrier is deteriorated. Therefore, carrier replenishment / discharge operations are performed.
When V> A, since it can be determined that the carrier has not deteriorated, the carrier replenishment / discharge operation is not performed.
Deterioration detection timing is performed in accordance with the number of printed sheets, development drive time, toner supply timing, and the like.

  In this embodiment, based on such a principle, processing for further improving the accuracy of determination of the deterioration state of the developer is performed, and this processing is to detect scumming under conditions where scumming is likely to occur. It is in. That is, when the deterioration detection is performed under the condition that the background stain is not likely to occur, the change in the output value of the image density sensor 9 in the relationship between the charge amount and the image density sensor output shown in FIG. It becomes difficult to accurately detect changes in the charge amount. On the other hand, if the deterioration detection is performed under the condition in which the background stain is likely to occur, the change in the output from the image density sensor 9 according to the change in the charge amount of the developer tends to appear remarkably, and the developer changes with good sensitivity. It is possible to accurately detect the degree of deterioration of.

  As a method for making the background easy to cause stains, (1) a method for reducing the background potential of the photosensitive member 2 so that weakly charged toner easily adheres, and (2) a toner by supplying a certain amount of toner. There is a method of increasing the density and decreasing the charge amount of the toner.

The method described in (1) corresponds to the embodiment of the invention described in claim 1 and can detect a small difference in the degree of deterioration of the developer. The accuracy of replenishment / discharge control can be increased to maintain stable developer charging.
The method described in (2) corresponds to the embodiment of the invention described in claim 3, and the charging ability is lowered by increasing the toner concentration, whereby weakly charged toner tends to adhere to the background portion. As a result, it is possible to improve the deterioration accuracy of the developer and to stabilize the charging property by improving the supply / discharge control accuracy of the developer.

By the way, when the above configuration is used, the charge amount of the developer may differ depending on factors other than the deterioration of the developer, and in this case, the background stain may also differ depending on those factors. For this reason, the detection output from the image density sensor 9 includes a change due to factors other than the deterioration of the developer, and an erroneous determination may occur when determining the original deterioration state of the developer. Therefore, in this embodiment, the charging property of the developer is stabilized by using the following methods (3) to (5).
(3) A method of detecting deterioration under a condition where the developer concentration is constant.
(4) The start and end of the development drive are continuously detected, and the ground on the non-image portion of the photoreceptor 2 is determined based on the relationship between the preset development stop time before the detection of deterioration and the background contamination of the unused developer. A method of judging the deterioration state of the developer based on the stain detection and the development stop time before the ground stain detection.
(5) A method of detecting deterioration after a developing operation, that is, a stirring operation for a certain time.

The method described in (3) corresponds to an embodiment of the invention described in claim 2 , and the toner density of the developer is made constant by detecting it with the toner density sensor 8, and the image density sensor 9 based on the difference in toner density is used. Therefore, it is possible to detect the deterioration of the actual developer. In this case, the toner density is set to a high value so that the background contamination is likely to occur by the methods described in (1) and (2).

The method described in (4) corresponds to the embodiment of the invention described in claim 4 , and the difference in the charge amount of the developer may be caused by the length of the development drive stop time before detecting the deterioration of the developer. As a difference, it is assumed that the detection result of the image density sensor 9 is changed. That is, it is considered that the influence of the difference in the developer charge amount due to the difference in the developer agitation time, such as at the end of continuous development and at the first use, affects the detection by the image density sensor 9. For this reason, with regard to unused developer, the relationship between the length of the development drive stop time before the deterioration detection and the background stain is obtained in advance through experiments, calculation processing, or simulation, and the development drive stop time is determined based on the length of the development drive stop time. Calculate the specified value for dirt. The specified value in this case corresponds to the lower limit value A of the image density sensor 9 described above. Thus, when the deterioration is detected, the length of the development drive stop time is used as one of the detection determination parameters, the length of the development drive stop time is detected, and a predetermined value for this length is detected from the image density sensor 9. By comparing the output with the developer, even when the developer charge amount due to the development drive stop time changes, it is possible to determine the deterioration state of the developer corresponding to the drive stop time. In this case, the developing device start detection unit 101 and the timer 102 in the control unit 100 shown in FIG. 3 are used.

The method described in (5) corresponds to the embodiment of the invention described in claim 5 , and in this case as well, it is possible to prevent the difference in charge rising with respect to the developer from being determined by the detection output of the image density sensor 9. It is taken into consideration. In other words, since the difference in developer agitation time affects the difference in developer charge amount, it is assumed that the charged state is made constant by eliminating the unevenness of the agitation time by performing the development operation for a certain period of time. As a result, the difference in the degree of deterioration of the developer can be clearly discriminated, and the accuracy of detection of the developer deterioration can be improved. In this case, the development operation for a certain period of time is controlled by the timer 102 connected to the control unit 100.

By the way, with regard to the charge rise of the developer, the charge rise is poor at the initial stage of stirring, and the so-called predetermined charge amount is not reached. For this reason, although the developer is not deteriorated as a detection result by the image density sensor 9, a determination condition that the deterioration is obtained is obtained. In this embodiment, therefore, the deterioration of the developer can be accurately determined by detecting the background contamination by the image density sensor and simultaneously detecting the change in background contamination with respect to the stirring time.
That is, from the relationship between the charge amount of the developer and the background stain shown in FIG. 5, the developer is in an unstable state at the initial stage of stirring when the charge has not risen. When you stand up, it is thought that dirt will improve. Therefore, it is considered that the relationship between the output value of the image density sensor and the stirring time is as shown in FIG.

  On the other hand, since the rising property of charging varies depending on the degree of deterioration of the developer separately from the stirring time, the change rate of the image density sensor output with respect to the stirring time represents the degree of deterioration of the developer. However, since this includes changes due to the development drive time and development stop time before the deterioration detection as well as the degree of deterioration, both the output value of the image density sensor is detected simultaneously with the change rate. As a result, judging the deterioration based on both the rising property of the charge and the charge amount is useful for improving the accuracy of the deterioration detection.

As a method for this,
(6) The developer deterioration is detected twice at the start of development and every certain time, and the difference between the two detection results and the result of the second detection value or both are compared with the specified value. how to.
(7) The developer density detection by the image density sensor is continued for a certain time from the start of the development driving, and the image density when the background is reduced and the developer is stirred for a certain time. This is a method of comparing a detection value from a sensor with a specified value.

The method described in (6) corresponds to the embodiment of the invention described in claim 7. In FIG. 7, the output value of the image density sensor at the time of developing driving start T1 and at the time of driving for a fixed time T2 is V1. The lower limit value A of the output value after driving for a predetermined time and the minimum value Vmin of the change amount of the sensor output in the time from T1 to T2 are determined in advance.
First, when V2 is compared with A and V2> A, it is determined that the background contamination is not more than the specified value and the developer is not deteriorated, and the deterioration detection operation is terminated.
When V2 <A, (V2−V1) is compared with Vmin.
When (V2−V1)> Vmin, the background stain is not less than the specified value at the time of T2, but it is determined that the background stain has been greatly improved in a certain time and the rising property of charging is good. it can. For this reason, it is determined that the developer has not deteriorated, and after further stirring, V2 and A are compared again, and unless V2 <A, the replenishment / discharge operation is not performed.
If (V2−V1) <Vmin, the background stain after stirring for a certain time also exceeds the specified value (V2 <A), and the rising property of charging is poor, so that the developer is deteriorated. I can judge. Therefore, a developer replenishment / discharge operation is performed.

The method described in (7) corresponds to the embodiment of the invention described in claim 8 and is deteriorated not by the change amount Vmin of the sensor output in a certain time but by the change rate (slope) a of the sensor output with respect to the stirring time. Judging.
First, similarly to the method described in (6), the output value V2 after stirring for a predetermined time is compared with A. If V2> A, it is determined that the developer has not deteriorated, and the deterioration detection operation is terminated. .
In the case of V2 <A, it is considered that the rising property of charging is good in the case of a> amin with respect to the predetermined lower limit value amin of the change rate. Therefore, it is determined that the developer is not deteriorated, and a <amin In this case, it is determined that the developer has deteriorated.

In this method, it is necessary to continuously detect the sensor output for a certain period of time, but instead, if the sensor output V at a certain point satisfies V> A, even if a certain period of time has not elapsed, the detection of deterioration is immediately terminated. can do.
In other words, when the scumming value falls below the specified value of scumming after stirring for a certain period of time, the developer degradation detection can be completed to shorten the time required for the degradation detection. Uptime can be shortened, and user work efficiency is not delayed. This corresponds to an embodiment of the invention described in claim 9.

The deterioration detection timing is changed according to the deterioration detection result, so that even when the degree of deterioration is large, it is possible to cope with the increase in the number of times of developer replenishment / discharge. That is, deterioration detection timing is initially determined according to the number of prints, development drive time, toner replenishment timing, etc., but other than the initial timing, the timing is determined based on the previous deterioration detection result. For example, when the initial timing is determined by the development drive time, when the first deterioration detection is performed after the drive time T1, the timing of the nth deterioration detection is Tn = from the (n−1) th deterioration detection operation. It is performed after time Tn indicated by n · Tn−1. At that time, n is determined that the developer has deteriorated at the time of (n-1) -th deterioration detection, and when the developer replenishment / discharge operation is performed, n <1 and the deterioration has occurred. If it is determined that there is no, n = 1.
Here, in the case where the deterioration detection timing is other than the time such as the number of prints, the deterioration detection timing can be determined by replacing T with the number of prints P, the toner replenishment amount G, and the like.
Usually, when the deterioration of the developer progresses, the margin regarding the charging ability of the developer becomes small, and therefore the frequency of occurrence of background contamination increases. For this reason, in order to improve the deterioration of the developer and prevent the chargeability of the developer from decreasing, it is necessary to replenish and discharge the developer following the deterioration. It is an important factor to reduce the detection interval. On the other hand, if it is determined that there is no deterioration, it can be said that there is some margin in the charging capacity of the developer, so if the deterioration detection interval is reduced, deterioration detection will be performed unnecessarily. In this case, the deterioration detection interval is set to the same state as before .

As described above, the deterioration detection interval can be changed according to the degree of deterioration of the developer. However, a minimum value is set in advance, that is, a deterioration detection timing interval is set in advance, and deterioration is detected at the shortest interval. In other words, in the relationship shown in FIG. 6, if the relationship of V <A is obtained, the charging ability of the carrier is lower than the specified value, and it is determined that the carrier is deteriorated, the development is performed. Degradation of salting agent as a result of detection due to a factor different from developer deterioration due to detection of developer deterioration when the specified timing is not reached, which is one of the conditions for judging the deterioration state of the agent. It is determined that the output value of the image density sensor 9 due to a problem or malfunction other than the above is less than a specified value, and a warning is given to the user via the alarm unit 104 shown in FIG. As a result, it is possible to prevent the developer from being replenished / discharged when the detected value of the image density sensor 9 is less than or equal to a predetermined value due to a factor different from the deterioration of the developer itself. Maintenance work or the like can be performed before a problem due to a cause other than the deterioration of the developer becomes large. This corresponds to an embodiment of the invention described in claim 9 .

On the other hand, in this embodiment, the specified value of the background stain when determining the deterioration of the developer can be changed according to the user's image quality selection. In other words, the configuration is such that the specified value for judging deterioration can be selected by the user.
At this time, it is difficult for the user to select a prescribed value for developer deterioration, which results in an increase in user effort. Therefore, the prescribed value for developer deterioration is set so as to change accordingly when the user selects image quality. For example, when the user selects high image quality, the lower limit value A in FIG. 6, the lower limit value A in FIG. 7, the change rate Vmin, amin, and the like are set to large values. Thereby, the charge amount of the developer is stabilized at a high value, so that image formation can always be performed with high image quality. At the same time, the deterioration detection timing may be reduced. Conversely, when the user does not select high image quality, the lower limit value A in FIG. 6, the lower limit value A in FIG. 7, and the change rates Vmin and amin are set small. As a result, the allowable range of scumming is widened, and the charging ability of the developer is stabilized when it is reduced to a certain extent, but instead the deterioration detection time is shortened, so the device warm-up time can be shortened and the user's work efficiency Can be improved. Since the number of times of replenishment / discharge of the developer is expected to be reduced, the consumption of the developer can be reduced, and the waste of the developer can be reduced.
In this way, by selecting the required image quality by the user himself, the required image quality can be maintained according to the user and the developer consumption can be maintained according to the user. Can be the least.

1 is a cross-sectional view illustrating a configuration of a main part of an image forming apparatus to which a developing device according to an embodiment of the present invention is applied. It is a figure which shows the structure of the developer supply part and developer collection | recovery part used for the image development apparatus by the Example of this invention. It is a block diagram for demonstrating the structure of the control part used for the image development apparatus shown in FIG. FIG. 6 is a diagram for explaining a relationship between an amount of toner attached to a non-image portion and an image density sensor output. It is a diagram for explaining the relationship between the degree of background stain and the charge amount of the developer. It is a diagram for explaining the relationship between the charge amount of the developer and the image density sensor output. It is a diagram for explaining the relationship of the image density sensor output with respect to the stirring time of the developer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photoconductor 3 Developing apparatus 3C, 3D Conveying auger 4 Developer supply part 4A Toner cartridge 4B Carrier cartridge 5 Developer collection part 7 Developer collection container 8 Toner density sensor 9 Image density sensor 100 Control part 101 Development drive Starting means 102 Timer 103 Drive unit 104 Alarm unit V Image density sensor output A Specified value

Claims (12)

In a developing device in which a developer composed of only a carrier or a mixture of a carrier and a toner is replenished while an excess developer is discharged and the developer can be replaced.
In order to detect the deterioration state of the developer from the degree of background contamination by comparing the density detection result in the non-image area on the latent image carrier to which the developer is supplied with a lower limit value of a preset detection output. An image density sensor used ; and
The image density sensor is connected to the input side, and the output side includes a control unit to which developer replenishing means is connected;
The control unit sets a state in which weakly charged toner is likely to adhere to the non-image portion by setting the background potential at the time of detection of background contamination in the non-image portion to be lower than that at the time of image formation by the image density sensor. By comparing the detection output from the non-image area on the basis of the lower limit value of the detection output from the image density sensor, it is possible to determine the deterioration state of the developer based on the background contamination state in the non-image area. A developing device that controls one or both of a supply amount and a discharge amount of a developer according to a result. In a developing device in which a developer composed of only a carrier or a mixture of a carrier and a toner is replenished while an excess developer is discharged and the developer can be replaced.
In order to detect the deterioration state of the developer from the degree of background contamination by comparing the density detection result in the non-image area on the latent image carrier to which the developer is supplied with a lower limit value of a preset detection output. An image density sensor used ; and
The image density sensor is connected to the input side, and the output side includes a control unit to which developer replenishing means is connected;
When the background density is detected in the non-image area by the image density sensor , the controller increases the toner density by supplying a certain amount of toner so that weakly charged toner is likely to adhere to the non-image area. By comparing the detection output from the non-image portion with reference to the lower limit value of the detection output from the image density sensor, the deterioration state of the developer is determined to thereby determine the ground of the non-image portion on the latent image carrier. A developing device characterized by determining a deterioration state of a developer based on a result of detecting dirt and controlling one or both of a developer replenishment amount and a discharge amount according to the determination result . The developing device according to claim 1 or 2,
The control unit performs the comparison of the detection output from the non-image part based on the lower limit value of the detection output of the image density sensor in a state where weakly charged toner is likely to adhere to the non-image part. A developing device characterized by setting a state in which a constant toner density is set for a developer. The developing device according to claim 1 or 2,
The control unit preliminarily compares the detection output from the non-image part with reference to the lower limit value of the detection output of the image density sensor in a state where weakly charged toner is likely to adhere to the non-image part. The information relating the length of the development drive stop time until the comparison of the detection output and the toner adhesion state to the non-image part due to this length is used as correction information for the lower limit value used for the comparison. A developing device. The developing device according to claim 1 or 2,
When the control unit compares the detection output from the non-image part with reference to the lower limit value of the detection output of the image density sensor in a state where weakly charged toner is likely to adhere to the non-image part, After the developer agitation supply is continued for a period of time, the deterioration state of the developer is determined by comparing the detection output from the non-image area with reference to the lower limit value of the detection output from the image density sensor. A developing device. The developing device according to any one of claims 1 to 5 ,
The control unit compares the detection output from the non-image part with the lower limit of the detection output from the image density sensor as a reference, and determines the deterioration of the developer from the non-image part. A developing apparatus characterized in that a comparison with the lower limit value is performed a plurality of times, a tendency of a comparison result of a plurality of times is obtained, and deterioration of the developer is determined based on the tendency . The developing device according to claim 6 .
In the process that has continued for a certain period of time from the start of development driving , the control unit detects when the detected value of the background contamination is less than the specified value in a shorter time than the constant agitation time. A developing device characterized in that the developer deterioration judging process is terminated . The developing device according to one of claims 1 to 7,
The developer deterioration detection start timing is set based on a determination result when the previous deterioration detection is performed . The developing device according to claim 8, wherein
In the control unit , the shortest value is set for the interval of the developer deterioration detection start timing, and the case where it is determined that the developer has deteriorated as a result of the deterioration detection at the shortest interval is continuously specified times. If determined, the developer supply / discharge operation is stopped and a warning operation is selected . The developing device according to any one of claims 1 to 9,
2. A developing apparatus according to claim 1, wherein the specified value of background contamination for determining the deterioration of the developer performed in the control unit can be changed according to the image quality requested by the user . An image forming apparatus using the developing device according to claim 1. Image forming method and performing developer deterioration judgment by the developing device according to one of claims 1 to 10.

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