JP2005140917A - Development device, image forming apparatus and developing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of adjusting image density, while maintaining image quality and further restraining toner or power from being consumed wastefully and time from being wasted, and to provide an image forming apparatus equipped with the development device and a developing method. <P>SOLUTION: The image density is adjusted by setting the ratio of circumferential speed (the ratio of the circumferential speed of the developing roller to the photoreceptor drum), based on the operation experience information of the developing device (one or several pieces of information from among of cumulative operating time, the cumulative number of developing times, the cumulative time of supplying the developer to a developer tank and the cumulative number of times thereof, elapsed time from finishing the last operation until starting next operation, the time elapsed from starting of the operation, and the time elapsed after the latest supply of the developer, when intermittently supplying the developer to the developing tank) (S5 to S8, and S10); setting the ratio of the circumferential speed based on the humidity of ambient air (S9 and S10); or setting the ratio of the circumferential speed based on comparison between the detected value of magnetic permeability, when finishing the operation the last time and the detected value of magnetic permeability at the present time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a developing device that develops an electrostatic latent image on an image carrier with a developer, an image forming apparatus including the developing device, and a developing method.

In an electrophotographic image forming apparatus, an electrostatic latent image on a photosensitive drum is developed by a developing device. The developing device includes a developing roller disposed opposite to a rotating photosensitive drum (image carrier) on which an electrostatic latent image is formed, and a developing tank that stores a developer. The electrostatic latent image on the photosensitive drum is developed by conveying the developer in the developing tank to the photosensitive drum side.
Since the density of an image developed by the developing device varies depending on various factors, it is necessary to adjust the density in order to maintain a constant image quality.
Conventionally, density adjustment in a developing device is performed by forming a reference patch image (test image) on a photosensitive drum, a transfer belt, or the like, detecting the density, and calculating the difference between the detected density and a preset reference density. In general, the developing bias (voltage) is adjusted accordingly.
On the other hand, it is known that the image density can be adjusted by adjusting the peripheral speed ratio of the developing roller to the photosensitive drum.
For example, Patent Document 1 discloses that a reference patch image is formed and the peripheral speed ratio between the photosensitive drum and the developing roller is determined based on the density.
Further, Japanese Patent Application Laid-Open No. H10-228561 discloses a method for determining the peripheral speed ratio between the drum and the developing roller, depending on the desired image density (setting by a person).
JP-A-10-90960 JP-A-5-204236

However, in the density adjustment by adjusting the developing bias, the cleaning field fluctuates, so that a so-called fog phenomenon is developed in which an area that should not be developed is developed, and the image quality deteriorates.
Further, when the density adjustment is performed based on the density of the test patch image, there is a problem that the toner and power required for outputting the patch image and the processing time are wasted. This is contrary to the recent demand for energy saving.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to adjust image density while maintaining image quality and suppressing wasteful consumption of toner, power, time, and the like. It is an object of the present invention to provide a developing device capable of performing the above, an image forming apparatus including the developing device, and a developing method.

In order to achieve the above object, the present invention includes a developing roller that rotates opposite to a rotating image carrier on which an electrostatic latent image is formed, and a developing tank that contains a developer, and the developing roller stores the developing roller. In a developing device that develops the electrostatic latent image by transporting an agent, an operation result detecting unit that detects operation result information of the developing device, and a detection result of the operation result detecting unit is applied to the image carrier. And a first peripheral speed ratio setting means for setting a peripheral speed ratio of the developing roller.
Here, the operation result information includes the accumulated operation time of the developing device, the accumulated number of times of development, the accumulated time and number of times of developer replenishment to the developing tank, from the end of the previous operation to the start of the current operation. Information on one or more of the following elapsed time, the elapsed time from the start of operation, and the most recent elapsed time after the developer supply to the developer tank is intermittently supplied.
These pieces of information are correlated with the development density.
For example, when a two-component developer is used, if development is performed under the same conditions, the carrier tends to deteriorate and the image density tends to increase as the cumulative operation time increases. Similarly, even when a one-component developer is used, the external additive deteriorates as the operation time becomes longer, and the amount of toner having a small particle size remaining in the developing tank increases, so that the image density increases. There is a tendency. In addition, the cumulative operation time is approximately proportional to the cumulative number of development times, the cumulative time of developer replenishment to the developing tank, and the cumulative number of times, and can be substituted by these.
Further, as the elapsed time from the end of the previous operation to the start of the current operation (hereinafter referred to as the standing time) becomes longer, the charge amount of the developer decreases due to the discharge, so that the image density tends to increase. On the other hand, the developer is agitated by the start of operation (for example, rotation of the developing roller or operation of the agitator), and the charge amount of the developer increases as the elapsed time from the start of operation increases. Tend to go down.
In addition, when developer is replenished intermittently (intermittently replenished), the charge amount in the developer tank is insufficient (or uncharged) immediately after the latest developer replenishment. The developer ratio tends to increase and the development density tends to increase. Then, since the charge amount of the developer increases with time by stirring, the developing density gradually decreases.
Each of the above information is information that does not require special processing by interrupting the development process in order to obtain it. Therefore, if the development density is adjusted based on this information, toner, power, time, etc. The development density can be adjusted without causing unnecessary consumption.
Further, since the development density is adjusted by setting the peripheral speed ratio, it is possible to prevent the occurrence of the fog phenomenon that occurs when the development bias voltage is adjusted, and to maintain the image quality.

Further, in the same developing device, a magnetic permeability detecting means for detecting the magnetic permeability of the developer in the developing tank, a detected value of the magnetic permeability detecting means at the end of the previous operation, and the current magnetic permeability detecting means And a second peripheral speed ratio setting means for setting a peripheral speed ratio of the developing roller with respect to the image carrier based on a comparison with the detected value. Things can be considered.
As described above, since the developer charge amount decreases as the standing time increases, if development is performed under the same conditions as the previous operation immediately after the start of operation, over-density development is usually performed. , After starting the operation of the developing device (starting the rotation of the developing roller), the development is started after a certain warm-up time for sufficiently charging the developer.
On the other hand, when a two-component developer is used, the toner concentration used as an input for toner replenishment control is generally detected by the permeability of the developer. This permeability depends on the charge amount of the developer in addition to the toner concentration. Also fluctuate. That is, when the charge amount of the developer decreases, the repulsive force between the particles of the developer decreases, and as a result, the bulk density increases, and as a result, the detected value of magnetic permeability increases.
Therefore, if no significant change in toner density due to toner replenishment occurs during standing and for a while after the start of operation, the transparency at the end of the previous operation (for example, when the agitator is stopped or when the rotation of the developing roller is stopped). By setting the peripheral speed ratio according to a comparison (for example, difference) between the magnetic permeability detection value, that is, the magnetic permeability detection value of a sufficiently charged developer and the current magnetic permeability detection value, the warm-up time is eliminated, or Even if shortened, an appropriate image density (image quality) can be maintained. This effect can be obtained in the same manner even if the peripheral speed ratio is set based on the above-described leaving time and elapsed time from the start of operation.
Furthermore, in this case, it is not necessary to keep time counting while the developing device is stopped, and the power consumption of the time measuring means such as a clock transmitter can be suppressed.
As described above, even if the development density is adjusted based on the detected value of magnetic permeability, wasteful consumption of toner, power, time, etc. is not caused. Further, since the development density is adjusted by setting the peripheral speed ratio, the image quality can be maintained.

In the same developing device, a humidity detecting means for detecting the humidity of the surrounding air, and a third peripheral speed for setting a peripheral speed ratio of the developing roller with respect to the image carrier based on a detection result of the humidity detecting means. It is also possible to consider a developing device characterized in that it comprises a ratio setting means.
When the ambient air humidity is high (low), the amount of discharge from the developer increases (decreases), so the charge amount of the developer decreases (rises) and the image density increases (decreases). Therefore, by setting the peripheral speed ratio based on the humidity, the image quality (image density) can be maintained regardless of the change in the charge amount due to the humidity change.
Thus, even if the development density is adjusted based on the detected humidity value, wasteful consumption of toner, power, time, etc. will not occur. Further, since the development density is adjusted by setting the peripheral speed ratio, the image quality can be maintained.

Further, if one or more of the first to third peripheral speed ratio setting means are provided, it is possible to adjust the density corresponding to more various situations.
Further, the present invention may be an image forming apparatus provided with each of the developing units.
In this case, the test image forming means for forming the test image, the image density detecting means for detecting the image density of the test image, the setting of the peripheral speed ratio based on the detection result of the image density detecting means, and And / or output corresponding density adjusting means for setting the developing bias voltage in the developing device at a predetermined timing, and one or more of the first to third peripheral speed ratio setting means are configured to output the output It is conceivable that the peripheral speed ratio is set during a period between timings when the processing by the corresponding density adjusting means is performed.
Since the first to third peripheral speed ratio setting means perform density adjustment (peripheral speed ratio setting) based on indirect information or detection value correlated with image density, there is a deviation from the actual situation. It can happen.
Therefore, according to the above configuration, it is possible to maintain a constant image density by performing processing by the first to third peripheral speed ratio setting means (density adjustment using an indirect index) at a relatively high frequency, and The deviation can be corrected by adjusting the density based on the density (direct index) of the test image (patch image) at a relatively infrequent timing.
As a result, the image density can be kept constant while minimizing wasteful consumption of toner, power, time, and the like.

Further, the present invention may be understood as a developing method corresponding to processing executed by the developing device.
That is, one of them is that the electrostatic latent image is formed by transporting the developer from a developer tank containing the developer by a developing roller that rotates against an image carrier on which the electrostatic latent image is formed. In the developing method for developing the developing device, the operation result information of the developing device is detected, and the peripheral speed ratio of the developing roller with respect to the image carrier is set based on the detection result. .
The second is that the electrostatic latent image is formed by transporting the developer from a developer tank containing the developer by a developing roller that rotates against an image carrier on which the electrostatic latent image is formed. In the developing method for developing, when the developer in the developing tank is a two-component developer containing toner and carrier, the toner concentration is detected by the magnetic permeability of the developer, and the toner at the end of the previous operation is detected. The developing method is characterized in that a peripheral speed ratio of the developing roller to the image carrier is set based on a comparison between the detected density value and the current detected toner density value.
The third is that the electrostatic latent image is formed by transporting the developer from a developer tank containing the developer by a developing roller that is rotated opposite to the rotating image carrier on which the electrostatic latent image is formed. In the developing method for developing, the humidity of ambient air is detected, and the peripheral speed ratio of the developing roller to the image carrier is set based on the detection result.

  According to the present invention, the peripheral speed ratio of the developing roller to the image carrier is set based on the operation record information, the developer permeability detection value, and the ambient humidity detection value. Since the development density can be adjusted without processing, it is possible to adjust the development density while suppressing wasteful consumption of toner, power, time, and the like. Further, since the development density is adjusted by setting the peripheral speed ratio, it is possible to prevent the occurrence of the fog phenomenon that occurs when the development bias voltage is adjusted, and to maintain the image quality.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a schematic sectional view of an image forming apparatus A provided with the developing device X according to the embodiment of the present invention, FIG. 2 is a schematic sectional view of the developing device X, and FIG. FIG. 4 is a graph showing the relationship between the peripheral speed ratio and the image density, FIG. 5 is a graph showing the relationship between the standing time and the elapsed time after the start of operation, and the charge amount of the developer, and FIG. FIG. 7 is a graph showing the relationship between the time and elapsed time after the start of operation and the output value of the developer permeability sensor. FIG. 7 is a graph showing the relationship between the humidity and toner concentration and the developer permeability. FIG. It is a graph showing the relationship between the number of sheets, image density, and peripheral speed ratio setting.

First, the configuration of the image forming apparatus A on which the developing device X according to the embodiment of the present invention is mounted will be described using the cross-sectional view of FIG.
The image forming apparatus A converts an image read by the image reading apparatus and data from a device externally connected to the image forming apparatus A (for example, a host device such as a personal computer) into an image by the electrophotographic method. It is a printer that records and outputs.
In the image forming apparatus A, each process unit responsible for each function of the image forming process is arranged around the photosensitive drum 3, and an image forming unit is formed by these. Around the photosensitive drum 3, a charging unit 5, an optical scanning unit 11, a developing device X, a transfer unit 6, a cleaning unit 4, and a charge removal lamp 12 are sequentially arranged.
The surface of the photosensitive drum 3 is uniformly charged by the charging unit 5, and the optical image is scanned on the uniformly charged photosensitive drum 3 by the optical scanning unit 11 to write an electrostatic latent image. Further, the electrostatic latent image written by the optical scanning unit 11 is visualized with toner by the developing device X. The consumed toner is supplied from the toner supply tank 7 to the developing tank 21 by the toner supply device 2.
Next, the image visualized on the photosensitive drum 3 is transferred onto the recording sheet by the transfer means 6, and the developer remaining on the photosensitive drum 3 is removed by the cleaning unit 4. A new image can be recorded on the photosensitive drum 3. The static elimination lamp 12 removes the electric charge on the surface of the photosensitive drum 3.
Below the image forming apparatus A, a supply tray 10 provided in the main body of the image forming apparatus A is disposed. The supply tray 10 is a recording material storage tray that stores recording sheets. The recording sheets stored in the supply tray 10 are separated one by one by the pickup roller 16 and the like, conveyed to the registration roller 14, and timed with the image formed on the photosensitive drum 3 by the registration roller 14. , Are sequentially supplied between the transfer means 6 and the photosensitive drum 3. The image recorded and reproduced on the photosensitive drum 3 is transferred onto the recording sheet. The supply of the sheet to the supply tray 10 is performed by pulling out the supply tray 10 to the front side (operation side, front side of the drawing) of the image forming apparatus A.

The lower surface of the image forming apparatus A is sent from a desk device having a multi-stage recording sheet supply tray (not shown) prepared as a peripheral device and a large-capacity recording material supply device capable of accommodating a large number of recording sheets. A sheet receiving port 13 is provided for receiving the incoming recording sheets and sequentially supplying the recording sheets toward the image forming unit.
A fixing device 8 is disposed in the upper part of the image forming apparatus A. The fixing device 8 sequentially receives the sheet on which the image has been transferred, and fixes the developed image transferred onto the recording sheet by heat and pressure by the fixing roller 81, the pressure roller 82, and the like. Thereby, an image is recorded on the recording sheet.
The recording sheet on which the image is recorded is further conveyed upward by the conveying roller 17 and passes through the switching gate 9. When the recording sheet discharge tray is set to the stacking tray 15 provided in the exterior of the image forming apparatus A, the recording sheet is discharged to the stacking tray 15 by the reverse roller 18. On the other hand, when double-sided image formation or post-processing is designated, the recording sheet is once discharged halfway toward the stacking tray 15 by the reversing roller 18, and then reversed after being stopped with the sheet trailing edge held. The roller 18 is reversed. Then, the sheet is reversely conveyed in the reverse direction, that is, in the direction in which the recording material refeeding conveyance apparatus and the post-processing apparatus that are selectively mounted for double-sided image formation and post-processing are mounted.
At this time, the switching gate 9 is switched from the solid line state in FIG. 2 to the broken line state. When performing double-sided image formation, the reversely conveyed sheet is supplied to the image forming apparatus A again through a recording material refeeding and conveying apparatus (not shown). When post-processing is performed, the recording material re-transport device is transported to a post-processing device via a relay transport device (not shown) at another switching gate, and post-processing is performed. FIG. 1 shows an example in which the recording material re-feeding / conveying device and the post-processing device are not mounted.
In the upper and lower space of the optical scanning unit 11, a control unit 110 for accommodating a circuit board for controlling the image forming process, an interface board for receiving image data from an external device, etc., and the various interface boards, and the image A power supply device 111 and the like for supplying electric power to each part to be formed are arranged.

FIG. 2 is a cross-sectional view illustrating a schematic configuration of the developing device X and the toner replenishing device 2 according to the embodiment of the present invention. The developing device X uses a developer (two-component developer) made of toner and carrier.
The developing device X includes a developing roller 24 that rotates to face a photosensitive drum 3 (an example of the image carrier) on which an electrostatic latent image is formed, a developing tank 21 that contains a developer, and a developing tank 21. A stirring rotary blade 22 and a stirring roller 23 for stirring the developer inside are provided. When the developing roller 24 rotates, the developer is conveyed from the developing tank 21 to the photosensitive drum 3, thereby developing the electrostatic latent image on the photosensitive drum 3.
The developer in the developing tank 21 is agitated and charged by the rotation of the developing roller 24, the agitating rotary blade 22 and the agitating roller 23. Further, a developing bias voltage is applied to the developing roller 24 in order to provide a potential difference from the photosensitive drum 3.
Further, the developing device X includes a magnetic permeability sensor 25 for detecting the magnetic permeability of the developer in the developing tank 21 and a humidity sensor 26 for detecting the humidity of the ambient air of the developing device X, and development is performed based on the detected value. The toner concentration in the agent and the surrounding humidity are detected.

On the other hand, the toner replenishing device 2 includes a toner replenishing tank 7 for storing toner to be replenished in the developing tank 21, a paddle 71 for pumping up the toner by rotating in the inside thereof, and a toner for transporting the pumped toner. A conveyance roller 72 and a toner replenishment roller 73 for replenishing toner conveyed from the toner conveyance roller 72 into the developing tank 21 through a replenishing port Q are provided.
In the toner replenishing device 2, the toner replenishing roller 73 rotates when the toner concentration detected by the magnetic permeability sensor 25 becomes lower than the low setting level, and becomes higher than the high setting level (> low setting level). The toner replenishing roller 73 stops. As a result, the toner is replenished intermittently.
A toner bottle 30 filled with toner is attached to the toner supply tank 7, and toner is supplied from the toner bottle 30 to the toner supply tank 7 as needed.
The operation control of the developing device X (start and stop, setting of the rotation speed of the developing roller 24, etc.) and the operation control of the toner replenishing device 2 (rotation drive control of the toner replenishing roller 73 based on the toner density) are controlled. This is performed by the unit 40. The control unit 40 includes a CPU, a ROM for storing a program executed by the CPU, and other peripheral devices, and the CPU executes each process described later by executing the program stored in the ROM. Further, the control unit 40 includes a clock transmitter, and thereby has a function of time lapse.
Further, the developing device X includes a data storage unit 50 including an SRAM or the like in which various parameters and formulas (coefficients of formulas) used for the processing of the control unit 40 are stored.

Next, before describing the developing process of the developing device X, various characteristics of the developing device X will be described first.
FIG. 4 shows the ratio of the peripheral speed Vd of the developing roller 24 to the peripheral speed Vp of the photosensitive drum 3 (hereinafter simply referred to as the peripheral speed ratio) and the image density (non-dimensionalized) of the image formed on the recording sheet. It is a graph showing the relationship with an index value.
As shown in FIG. 4, the image density increases as the peripheral speed ratio increases, and is in a substantially proportional relationship. This shows that the image density can be adjusted by setting the peripheral speed ratio. The following three forms are conceivable as a method for setting the peripheral speed ratio. (A) a method in which only the rotation speed (circumferential speed) of the developing roller 24 is variable; (b) a method in which only the rotation speed (circumferential speed) of the photosensitive drum 3 is variable; and (c). In this method, both rotation speeds are variable.
Here, since changing the rotational speed of the photosensitive drum 3 affects the writing speed of the electrostatic latent image and the image forming speed, in this embodiment, the peripheral speed ratio is set in the form (a). Shall be set.

When a two-component developer is used and development is performed under the same conditions, as described above, the carrier tends to deteriorate and the image density tends to increase as the cumulative operation time increases.
Similarly, even when a one-component developer is used, the external additive deteriorates as the operation time becomes longer, and the amount of toner having a small particle size remaining in the developing tank 21 increases, so that the image density is reduced. It tends to be higher.
Therefore, if the development density is adjusted based on the cumulative operation time of the developing device X, the change in image density over time due to carrier deterioration or the like can be prevented, and the image quality can be maintained. Here, the relationship between the accumulated operation time and the development density is experimentally measured in advance, and can be stored in the data storage unit 50 in advance as a peripheral speed ratio correction formula or correction table corresponding to the relationship. That's fine.
Here, the cumulative operation time is substantially proportional to the cumulative number of development times, the cumulative time of developer replenishment to the developing tank, and the cumulative number of times, and can be substituted by these.
FIG. 8A is a graph showing the relationship between the cumulative number of printed sheets (that is, the cumulative number of development times), which is an index corresponding to the cumulative operation time, and the image density. As shown in FIG. 8A, if no adjustment is made, the image density increases exponentially as the cumulative number of printed sheets increases.
FIG. 8B is a graph showing a situation in which the peripheral speed ratio is lowered exponentially as the cumulative number of printed sheets increases in correspondence with the graph shown in FIG.
FIG. 8C is a graph showing changes in image density when the peripheral speed ratio setting is corrected according to the increase in the cumulative number of printed sheets in accordance with the graph of FIG. 8B.
As shown in FIG. 8C, it can be seen that the image density can be maintained substantially constant by appropriately setting the peripheral speed ratio in accordance with the cumulative number of printed sheets.

FIG. 5A is a graph showing the relationship between the elapsed time from the end of the previous operation of the developing device X to the start of the current operation, that is, the standing time and the charge amount of the developer in the developing tank 21. is there.
As shown in FIG. 5A, the charging amount of the developer decreases due to discharge as the standing time increases. Since this is a discharge phenomenon, the charge amount decreases exponentially.
Therefore, if the peripheral speed is set (adjusted) for a while after the start of the operation, the image density until the developer is sufficiently charged after the start of the operation can be properly maintained. Can do.
On the other hand, FIG. 5B shows the relationship between the elapsed time from the start of operation (after the operation has been stopped) after leaving the developing device X (after the operation is stopped) and the charge amount of the developer. It is a graph showing.
Since the developer is stirred (stirring by driving the developing roller 24, the stirring roller 23, etc.) at the start of operation, as shown in FIG. 5 (b), the developer becomes longer as the elapsed time after the start of operation becomes longer. The amount of charge increases exponentially.
Therefore, if the peripheral speed is set based on the elapsed time after the start of operation, the image density until the developer is sufficiently charged after the start of operation can be properly maintained.
Here, the charge amount at the start of operation (initial value of the charge amount) depends on the leaving time until that time as shown in FIG. It is desirable to perform in combination with the peripheral speed ratio setting based on the elapsed time. That is, it is preferable to set an initial value of the correction amount of the peripheral speed ratio at the start of operation based on the standing time, and to correct the initial value of the correction amount based on the elapsed time after the start of operation.

FIG. 6 (a) shows the leaving time of the developing device X (the elapsed time from the end of the previous operation to the start of the current operation) and the detected value (output voltage, “sensor output” in the figure) of the magnetic permeability sensor 25. It is a graph showing the relationship between these.
As shown in FIG. 5A, the developer charge amount decreases exponentially as the standing time increases, and the detected value of the magnetic permeability sensor 25 increases exponentially. This is because the bulk density of the developer increases as a result of the reduction in the repulsive force between the particles of the developer as the charge amount decreases.
FIG. 6B is a graph showing the relationship between the elapsed time from the start of operation after leaving the developing device X (the elapsed time after the start of operation) and the detected value of the magnetic permeability sensor 25.
As shown in FIG. 5 (b), as the elapsed time after the start of operation becomes longer, the charge amount of the developer increases exponentially. Therefore, contrary to that shown in FIG. 6 (a), The detected value of the magnetic permeability sensor 25 falls exponentially.
Conventionally, after the start of operation of the developing device, the development is controlled to start after a lapse of warm-up time until the developer is sufficiently charged. This warm-up time is set, for example, as a warm-up time until a predetermined time sufficient for charging is set based on prior measurements, or until the detected value of the magnetic permeability sensor 25 falls below a preset set level. It was controlled.
Here, if no significant change in toner density occurs due to toner replenishment during standing and for a while after the start of operation, the detected magnetic permeability at the end of the previous operation, that is, the permeability of the sufficiently charged developer. By setting the peripheral speed ratio according to the comparison (for example, difference) between the detected value and the current permeability detected value, an appropriate image density (image quality) can be maintained even if the warm-up time is eliminated or shortened. .
For example, first, after the operation of the developing device X, the warm-up time is controlled until the detected value of the magnetic permeability sensor 25 falls below a set level higher than the conventional set level (development is performed during the warm-up time). Absent). After the warm-up time ends, the peripheral speed ratio is corrected according to the difference between the magnetic permeability detection value at the end of the previous operation and the current magnetic permeability detection value.
By such control, when the leaving time is long, the warm-up time is shortened as compared with the prior art by the amount that the setting level of the magnetic permeability sensor 25 is higher than the conventional level. In addition, when the neglected time is short and the magnetic permeability detection value is already lower than the set level at the start of operation, warm-up is omitted.
Thereby, the waiting time at the start of operation can be shortened while maintaining the image quality.

FIG. 7A is a graph showing the relationship between the humidity of the surrounding air and the detected value (output voltage) of the magnetic permeability sensor 25 when the actual toner concentration of the developer is constant (weight concentration 4%). is there.
As shown in FIG. 7A, when the ambient air humidity is high, the amount of discharge from the developer increases, so the charge amount of the developer decreases and the permeability detection value increases. At this time, the image density also increases.
FIG. 7B is a graph showing the relationship between the actual toner concentration of the developer in the developing tank 21 and the detected value of the magnetic permeability sensor 25. In the figure, the graph indicated by the thick solid line represents the case of normal humidity, the graph indicated by the alternate long and short dash line represents the case where the humidity is higher than the normal humidity, and the graph indicated by the broken line represents the case where the humidity is lower than the normal humidity.
When the humidity is constant, the actual toner concentration and the permeability detection value (sensor output) have a negative proportional relationship. However, even if the actual toner concentration is constant, the permeability detection value changes if the humidity changes.
Therefore, by setting the peripheral speed ratio based on the humidity, the image quality (image density) can be maintained regardless of the change in the charge amount due to the humidity change.

Next, the procedure of the developing process by the developing device X will be described using the flowchart shown in FIG. This process is implemented by the control unit 40 executing a control program. In the following, S1, S2,... Represent processing procedure (step) numbers.
(S1)
When the print data is received from the host device, the control unit 40, such as the previous operation end time and accumulated operation time, the reference speed Nd0 (reference rotation speed) of the developing roller 24, etc. from the data storage unit 50. Initial processing such as data reading and recording (storage) of the operation start time in the data storage unit 50 is executed.
(S2)
Next, drive systems such as the developing roller 24 and the stirring roller 23 are driven to rotate. Thereby, stirring of the developer in the developing tank 21 is started. At this time, the developing roller 24 is rotationally driven at the reference speed Nd0 read from the data storage unit 50. Further, in conjunction with the operation of the developing device X, the control unit 40 also drives the photosensitive drum 3 to rotate at a predetermined constant rotation speed.
As a result, the developing device X enters a warm-up operation state.

(S3)
Next, the control unit 40 maintains the current warm-up operation state until the warm-up is completed.
The criterion for determining the end of warm-up is that the warm-up has been completed if the detected value of the magnetic permeability sensor 25 (toner concentration sensor) is equal to or less than (reference magnetic permeability + α), and that it has not been determined otherwise. To do.
As shown in FIGS. 5B and 6B, as for the magnetic permeability of the developer, as the time after the start of operation elapses, the charge amount increases due to stirring, and the detected magnetic permeability value decreases.
Here, the reference magnetic permeability is a magnetic permeability corresponding to a state in which the developer is sufficiently charged when the toner density is a normal density (a density that does not require toner replenishment). Conventionally, the warm-up operation is continued until the detected magnetic permeability value is equal to or lower than the reference magnetic permeability.
However, in this developing apparatus X, the image density is adjusted by setting the peripheral speed ratio, which will be described later.

(S4)
Next, the control unit 40 performs image density correction (hereinafter, output corresponding density correction) based on the test image (patch image) output from an operation input unit such as a sheet key provided in the image forming measure A. Check whether the operation has been performed.
(S21 to S23, an example of processing of the output corresponding density adjusting means)
In S4, when it is detected that an operation for executing the output-corresponding density correction has been performed, the control unit 40 determines that the charging unit 5, the optical scanning unit 11 and the developing device X (these are the above-described operations). By controlling an example of the test image forming unit, a predetermined test image (patch image) is output (developed) on the photosensitive drum 3 (S21).
Next, the image density of the test image is detected by a reflection-type image density sensor 60 (an example of the image density detection means) composed of an illumination lamp and a CCD that photoelectrically converts the reflected light. As shown in FIG. 2, the image density sensor 60 is disposed, for example, on the rear stage side (downstream in the rotational direction) of the developing device X around the photosensitive drum 3 and outputs (develops) it on the photosensitive drum 3. The image density of the test image (patch image) is detected (S22).
Further, the control unit 40 sets the reference speed N0 of the developing roller 24 based on the density detection result of the image density sensor 60, and stores (updates) this in the data storage unit 50 (S23), Thereafter, the process proceeds to S14 described later.
The reference speed N0 is set by, for example, calculating a difference between a reference image density (preset image density) that is an original image density of the test image and a detected density of the image density sensor 60. Setting based on a conversion table from the difference to the reference speed N0 can be considered. This conversion table can be obtained from the relationship between the image density and the peripheral speed ratio shown in FIG. That is, since the peripheral speed ratio value to be corrected according to the difference (that is, the speed correction value of the developing roller 24) is obtained from the graph of FIG. 4, the speed correction value thus obtained is used as a conversion table. The data storage unit 50 may be stored in advance.

(S5: An example of the process of the first peripheral speed ratio setting means (when the operation result information is the elapsed time from the start of operation))
On the other hand, in S4, when the operation for executing the output-corresponding density correction is not detected, the control unit 40 determines the elapsed time after the start of the operation of the developing device X (that is, the elapsed time from the start of the operation). Time) and a correction value N1 of the rotational speed of the developing roller 24 is set based on the elapsed time.
Here, the elapsed time after the start of operation is calculated by subtracting the current operation start time recorded in the initial process (S1) from the current time.
The correction value N1 is set based on a “conversion table from the elapsed time after the start of operation to the correction value N1” stored in the data storage unit 50 in advance.
As shown in FIGS. 5B and 6B, as for the magnetic permeability of the developer, as the time after the start of operation elapses, the charge amount increases due to stirring, and the detected magnetic permeability value decreases. Accordingly, in the graph shown in FIG. 5B, appropriate correction can be performed by obtaining a conversion table in which the charge amount (vertical axis) is converted into the correction value N1.

(S6: An example of the processing of the first peripheral speed ratio setting means (when the operation result information is the elapsed time from the end of the previous operation to the start of the current operation))
Next, the control unit 40 calculates the leaving time before the operation of the developing device X (that is, the elapsed time from the end of the previous operation to the start of the current operation), and based on the leaving time, A correction rate R1 of the rotation speed of the developing roller 24 is set.
Here, the neglected time is calculated by subtracting the previous operation end time read out in the initial process (S1) from the current time.
The correction rate R1 is set based on the “conversion table from the neglected time to the correction rate R1” stored in the data storage unit 50 in advance.
As described above, in S5, a conversion table based on the graph of FIG. However, the graph of FIG. 5B represents the change in the charge amount after the start of the operation after the developing device X is left for a sufficiently long time. Varies with time. For example, if the leaving time is 0, the charge amount is almost flat even if the time has elapsed after the start of operation.
Therefore, in the process of S6, the correction rate R1 for correcting the correction value N1 in the range of 0 to 1 times is set according to the standing time until then.
Specifically, in the graph of FIG. 5A, the value (charge amount) on the vertical axis when the leaving time = 0 is converted to the correction factor R1 = 0, and a sufficient leaving time (for example, the leaving time = A conversion table obtained by converting the value of the vertical axis at 8Hr) to the correction factor R1 = 1 is obtained, and the correction factor R1 is set based on the conversion table.
As a result, it is possible to perform appropriate correction according to the leaving time.

(S7: An example of the processing of the first peripheral speed ratio setting means (when the operation result information is the accumulated operation time))
Next, the control unit 40 sets a correction value N2 for the rotational speed of the developing roller 24 based on the accumulated operation time of the developing device X read in the initial processing of S1.
Here, the correction value N2 is set based on the “conversion table from the cumulative operation time to the correction value N2” stored in the data storage unit 50 in advance.
In this conversion table, the relationship between the cumulative operation time and the development density is experimentally measured in advance, and the conversion table corresponding to the relationship may be stored in the data storage unit 50 in advance.
(S8: Example of processing of the first peripheral speed ratio setting means (when the operation result information is the elapsed time after the latest developer replenishment))
Next, the control unit 40 calculates an elapsed time after the latest developer replenishment, and sets a correction value N3 for the rotation speed of the developing roller 24 based on the elapsed time.
As described above, the toner replenishment tank value 2 sets the correction value N3 according to the elapsed time from the most recent replenishment time in order to intermittently replenish the developer to the developing tank 21. .
Here, the elapsed time after the latest developer replenishment is calculated by subtracting the latest developer replenishment time recorded (stored) in the data storage unit 50 in S12 described later from the current time.
The correction value N3 is set based on “a conversion table from the elapsed time after the latest developer replenishment to the correction value N3” stored in advance in the data storage unit 50.
In this conversion table, the relationship between the elapsed time immediately after the developer replenishment and the development density is experimentally measured in advance, and the conversion table corresponding to the relationship may be stored in the data storage unit 50 in advance. .
The above-described processes of S5 to S8 are performed by the control unit 40 on the operation result information of the developing device X (the elapsed time from the start of operation, the elapsed time from the end of the previous operation to the start of the current operation, the cumulative operation Process of the first peripheral speed ratio setting means for detecting the time and the elapsed time after the latest developer replenishment (an example of the process of the operation result detecting means) and setting the peripheral speed ratio based on the detection result It is an example.

(S9: An example of processing of the third peripheral speed ratio setting means)
Next, the control unit 40 sets a correction value N4 for the rotation speed of the developing roller 24 based on the detected value (humidity of the ambient air) of the humidity sensor 26.
Here, the correction value N4 is set based on a “conversion table from humidity to the correction value N4” stored in the data storage unit 50 in advance.
This conversion table may be stored in advance in the data storage unit 50 by converting the vertical axis (permeability sensor output) of the graph shown in FIG. 7A into the correction value N4.
(S10)
Further, the control unit 40 sets the rotation speed Nd of the developing roller 24 based on the correction value and correction rate set in S5 to S6. Thereby, since the rotational speed of the photosensitive drum 3 is constant, the peripheral speed ratio is set (the peripheral speed ratio is changed).
Here, the rotational speed Nd is set as Nd = N0 + (R1 × N1 + N2 + N3 + N4) / 4, for example.
As described above, by performing the processes of S5 to S9 and S10 (an example of a plurality of processes of the first to third peripheral speed ratio setting means), the density adjustment (peripheral speed) corresponding to more various situations is performed. Ratio setting). Of course, even if any one of the processes of S5 to S9 is performed, a certain effect can be obtained.

(S11-S15)
Next, the control unit 40 starts development at the set peripheral speed ratio (S11, continuation of development when the process is repeated after returning from the process of S13 described later).
As a result, development and image formation on the recording sheet are performed in a state where the density is adjusted by the peripheral speed ratio.
Then, the control unit 40 checks whether or not toner replenishment has been performed in the toner replenishing device 2. If it is detected that toner replenishment has been performed, the control unit 40 stores the latest stored in the data storage unit 50. While the developer replenishment time is updated to the current time, the toner replenishment time is not updated (S12). This time is the time used in S8 described above.
Next, the control unit 40 checks whether or not the development is completed (S13). If the development is not completed, the control unit 40 returns to S5 and repeats the above-described processing.
On the other hand, when the development is completed, the driving system such as the developing roller 24 and the stirring roller 23 is stopped (S14).
Further, the control unit 40 performs an end process such as updating the previous operation end time (for calculating the neglected time in S6) and the accumulated operation time (used in S7) stored in the data storage unit 50. After execution (S15), the development process is terminated.
Here, the previous operation end time is updated to the current time, and the accumulated operation time is obtained by adding the time obtained by subtracting the operation start time stored in the initial processing of S1 from the current time to the original accumulated operation time. Update.

The peripheral speed ratio setting process of S5 to S10 (an example of the process of the first to third peripheral speed ratio setting means) is a density adjustment (peripheral speed) based on indirect information or detection value correlated with image density. The ratio setting) may cause a deviation from the actual situation.
On the other hand, the peripheral speed ratio setting (S21 to S23) based on the detection result of the image density sensor (an example of the image density detection means) that detects the image density of the test image by the development processing shown in FIG. The setting of the reference speed of the developing roller by the above process and an example of the process of the output corresponding density adjusting means) are performed at the timing when the operation to execute the output corresponding density correction is performed (an example of the predetermined timing). In the period between the timings (when there is no operation), the setting of the peripheral speed ratio (correction of the peripheral speed ratio) is performed by the processing of S5 to S10.
Accordingly, the peripheral speed ratio setting process (concentration adjustment by an indirect index, an example of one or a plurality of processes of the first to third peripheral speed ratio setting means) is performed at a relatively high frequency. While it is possible to maintain a constant image density, the deviation from the actual situation depends on the processing of S21 to S23, that is, the density (direct index) of the test image (patch image) at a relatively infrequent timing. Correction can be made by performing density adjustment processing.

In the example shown in FIG. 3, the example in which the peripheral speed ratio is set by the processing of S21 to S23 is shown. However, for example, the processing may be replaced with the processing for setting the developing bias voltage to be applied to the developing roller 24 in the developing device X. Alternatively, it may be possible to replace the processing with a combination of this and peripheral speed ratio setting (an example of processing of the output corresponding density adjusting means).
Further, in the process of S7 in FIG. 3, the correction value N2 based on the accumulated operation time is set. This accumulated operation time includes the accumulated number of development times, the accumulated developer supply time to the developer tank, and the accumulated number of times. Since they are almost proportional to each other, they can be substituted. The accumulated number of developments can also be detected by the control unit 40.
The cumulative number of developments can be obtained, for example, by accumulating and counting the number of pages on which images have been formed. The cumulative time of developer replenishment to the developing tank and the cumulative number of times are, for example, those of the toner replenishing device 2 It can be obtained by accumulating the driving time and the number of times of driving of the toner supply roller 73 and the like.

Further, in the example shown in FIG. 3, the peripheral speed ratio setting process (correction process) based on the elapsed time from the start of operation and the leaving time is performed in S5 and S6. As an alternative, it is conceivable to replace the peripheral speed ratio processing based on the detected value of the magnetic permeability sensor 25.
That is, the processes of S5 and S6 in FIG. 3 are compared with the detected value of the magnetic permeability sensor 25 (an example of the magnetic permeability detecting means) at the end of the previous operation and the current detected value of the magnetic permeability sensor 25. Based on this, it is replaced with a process for setting a peripheral speed ratio (peripheral speed ratio of the developing roller 25 with respect to the photosensitive drum 3) (an example of the process of the second peripheral speed ratio setting means). This can be realized by the following processing, for example.
First, in the end process of S15 in FIG. 3, the detected value of the magnetic permeability sensor 25 at the end of the operation is stored in the data storage unit 50, and this is stored in the initial process of S1 in FIG. Read as the permeability detection value at the end of operation.
Next, instead of the processing of S5 and S6 in FIG. 3, the difference between the current permeability detection value (detection value of the permeability sensor 25) and the permeability detection value at the end of the previous operation (hereinafter referred to as permeability). And a correction value N5 of the rotation speed of the developing roller 24 is obtained based on the difference. Then, in the process of S10 in FIG. 3, a process is performed in which (R1 × N1) in the calculation formula of the developing roller speed Nd described above is replaced with N5.
Here, the setting of the correction value N5 based on the magnetic permeability difference is performed based on the “conversion table from the magnetic permeability difference to the correction value N5” stored in advance in the data storage unit 50.
As shown in FIGS. 6 (a) and 6 (b), the detected value of the magnetic permeability sensor 25 increases exponentially according to the standing time and functions according to the elapsed time from the start of operation. To drop. Therefore, the difference between the current permeability detection value and the permeability detection value at the end of the previous operation is the change in charge amount (that is, the change in image density) taking into account both the standing time and the elapsed time from the start of operation. ).
Therefore, the relationship between the difference in magnetic permeability and the speed to be corrected by the developing roller 24 (the correction value N5) in order to make the image density constant is measured in advance, and this is stored in the data storage unit 50 as the conversion table. Just remember.
According to such a process, it is not necessary to keep time counting while the operation of the developing device X is stopped, and the power consumption of the clock transmitter in the control unit 40 can be suppressed.

  The present invention can be applied to a developing device in an electrophotographic image forming apparatus.

1 is a schematic cross-sectional view of an image forming apparatus A that includes a developing device X according to an embodiment of the present invention. 2 is a schematic sectional view of the developing device X. FIG. 5 is a flowchart showing a procedure of development processing by the developing device X. The graph showing the relationship between a peripheral speed ratio and image density. The graph showing the relationship between the standing time and the elapsed time after the start of operation, and the charge amount of the developer. The graph showing the relationship between the leaving time and the elapsed time after the start of operation, and the output value of the developer permeability sensor. 6 is a graph showing the relationship between humidity and toner concentration and developer permeability. 6 is a graph showing the relationship between the cumulative number of printed sheets, image density, and peripheral speed ratio setting.

Explanation of symbols

X ... developing apparatus 2 ... toner replenishing apparatus 3 ... photosensitive drum 7 ... toner replenishing tank 21 ... developing tank 24 ... developing roller 25 ... magnetic permeability sensor (image density sensor)
26 ... Humidity sensor 40 ... Control unit 50 ... Data storage unit 73 ... Toner replenishing rollers S1, S2, ... Processing procedure (step)

Claims (10)

The electrostatic latent image is developed by transporting the developer from the developer tank containing the developer to the image carrier side by a developing roller that rotates against the rotating image carrier on which an electrostatic latent image is formed. In the developing device
An operation result detecting means for detecting operation result information of the developing device;
First peripheral speed ratio setting means for setting a peripheral speed ratio of the developing roller with respect to the image carrier based on a detection result of the operation performance detection means;
A developing device comprising:   The operation result information includes the cumulative operation time of the developing device, the cumulative number of times of development, the cumulative time and number of times of developer replenishment to the developing tank, the elapsed time from the end of the previous operation to the start of the current operation, The information on one or more of an elapsed time from the start of operation and an elapsed time after the most recent developer replenishment in the case where developer replenishment to the developer tank is intermittently replenished. Development device. The electrostatic latent image is developed by transporting the developer from the developer tank containing the developer to the image carrier side by a developing roller that rotates against the rotating image carrier on which an electrostatic latent image is formed. In the developing device
Magnetic permeability detecting means for detecting the magnetic permeability of the developer in the developing tank;
A second rotation for setting a peripheral speed ratio of the developing roller with respect to the image carrier based on a comparison between a detection value of the magnetic permeability detection means at the end of the previous operation and a current detection value of the magnetic permeability detection means. Speed ratio setting means;
A developing device comprising: The electrostatic latent image is developed by transporting the developer from the developer tank containing the developer to the image carrier side by a developing roller that rotates against the rotating image carrier on which an electrostatic latent image is formed. In the developing device
Humidity detection means for detecting the humidity of the surrounding air;
Third peripheral speed ratio setting means for setting a peripheral speed ratio of the developing roller with respect to the image carrier based on a detection result of the humidity detecting means;
A developing device comprising: The electrostatic latent image is developed by transporting the developer from the developer tank containing the developer to the image carrier side by a developing roller that rotates against the rotating image carrier on which an electrostatic latent image is formed. In the developing device
One or more of the operation performance detection means, the magnetic permeability detection means and the humidity detection means;
One or more of the first to third peripheral speed ratio setting means;
A developing device comprising:   An image forming apparatus comprising the developing device according to claim 5. A test image forming means for forming a test image;
Image density detecting means for detecting the image density of the test image;
Output corresponding density adjusting means for setting the peripheral speed ratio and / or developing bias voltage in the developing device at a predetermined timing based on the detection result of the image density detecting means,
The one or more of the first to third peripheral speed ratio setting means perform peripheral speed ratio setting in a period between timings when processing by the output corresponding density adjusting means is performed. Image forming apparatus. The electrostatic latent image is developed by transporting the developer from the developer tank containing the developer to the image carrier side by a developing roller that rotates against the rotating image carrier on which an electrostatic latent image is formed. In the developing method to
A developing method comprising: detecting operation result information of the developing device; and setting a peripheral speed ratio of the developing roller to the image carrier based on the detection result. The electrostatic latent image is developed by transporting the developer from the developer tank containing the developer to the image carrier side by a developing roller that rotates against the rotating image carrier on which an electrostatic latent image is formed. In the developing method to
The developing roller for the image carrier is detected based on a comparison between the detected value of the magnetic permeability at the end of the previous operation and the detected value of the current permeability at the end of the previous operation. A developing method characterized in that the peripheral speed ratio is set. The electrostatic latent image is developed by transporting the developer from the developer tank containing the developer to the image carrier side by a developing roller that rotates against the rotating image carrier on which an electrostatic latent image is formed. In the developing method to
A developing method comprising: detecting a humidity of ambient air; and setting a peripheral speed ratio of the developing roller to the image carrier based on a detection result.

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