JP3693547B2 - Toner density control device for electrophotographic apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention detects the magnetic permeability in a two-component developer composed of toner and carrier, obtains the toner concentration in the developer based on the detected value, and the toner concentration in the developer is a predetermined toner concentration. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner density control device of an electrophotographic apparatus for adjusting a toner replenishment amount to control a toner density, and in particular, a color electrophotographic apparatus having a plurality of developing devices having different developer colors. The present invention relates to a toner concentration control device suitable for a developing device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in image forming apparatuses such as copying machines and laser printers that employ an electrophotographic process, image quality compensation control (hereinafter referred to as process control) is performed in order to prevent deterioration in image quality due to changes over time. ing. That is, when an image is always formed under the same conditions in the image forming apparatus, the image quality state gradually deteriorates. The deterioration of the image quality is such that the initial image density cannot be obtained due to a change with time, for example, the charging property of the photoconductor as a recording medium according to the number of image formations. Further, in the background (background), image deterioration in which toner adheres to an area where toner or the like should not adhere occurs. For this reason, process control is required. Such process control is disclosed in detail in, for example, Japanese Patent Laid-Open No. 10-213928.
In addition, in an image forming apparatus using a two-component developer composed of a toner and a carrier, in addition to the process control described above, the toner concentration (mixing ratio of carrier and toner) of the developer in the developing device is set. Toner density control is also performed to keep it constant.
That is, as shown in FIG. 10A, the amount of toner adhering to the electrostatic latent image is substantially proportional to the toner concentration in the developer, and the toner concentration in the developer is the image density (ID) of the recorded image. This directly affects the image quality. For this reason, the above-described toner density control is performed.
[0004]
In the conventional toner density control, the toner density of the developer in the developing device is detected, and when the toner density is lower than a predetermined target toner density value, a toner replenishment mechanism is set so that the target toner density value is obtained. Is used to replenish the toner in the developing device and stop the toner replenishment when the target toner density value is reached.
[0005]
In general, a magnetic permeability sensor is used as a toner concentration detecting means provided in the developing unit and for detecting the toner concentration in the developer. This magnetic permeability sensor detects the magnetic permeability of the developer that changes in accordance with the amount of toner (toner mixing ratio) adhering to the magnetic carrier due to frictional charging, as the magnitude of the inductance of the coil placed close to the developer. . There is a correlation between the toner concentration in the developer and the magnetic permeability of the developer, in which the magnetic permeability decreases as the toner concentration in the developer increases, and the magnetic permeability increases as the toner concentration decreases. By detecting the magnetic permeability of the toner, the toner concentration can be obtained.
[0006]
However, when the developer fluidity and the toner charge amount change due to the influence of temperature and humidity, the output value (magnetic permeability) of the magnetic permeability sensor changes even though the toner concentration is the same. was there.
That is, as shown in FIG. 10B, even if the toner concentration in the developer is constant, the output value of the magnetic permeability sensor changes when the temperature of the developer changes. Specifically, the output value of the magnetic permeability sensor decreases as the temperature decreases and increases as the temperature increases.
[0007]
Further, the magnetic permeability of the developer changes depending on the amount of toner attached to the magnetic carrier, and the amount of toner attached to the carrier changes depending on the amount of toner charged. Therefore, the output value (magnetic permeability) of the magnetic permeability sensor also changes depending on the charge amount of the toner. Specifically, the charge amount of the toner is particularly low at high humidity and high at low humidity.
That is, as shown in FIG. 10C, the magnetic permeability sensor outputs a predetermined sensor output (TD) at normal temperature / normal humidity (N / N) in the detection of a predetermined target toner concentration. Although adjusted, the sensor output increases under the high temperature / high humidity (H / H) environment due to the influence of the charge amount due to the friction of the toner, and conversely, under the low temperature / low humidity (L / L) environment. Sensor output decreases.
[0008]
FIG. 11 shows changes in the output of the magnetic permeability sensor (ATC sensor) with respect to the toner specific density (toner density in the developer). As shown in FIG. 11, the output of the magnetic permeability sensor with respect to the toner specific concentration shifts higher than the normal temperature state in the humid state and shifts lower than the normal temperature state in the low temperature state.
For this reason, in the H / H environment, as shown in FIG. 12B, although the toner density has not changed at all, the apparent toner density is lowered, so that toner replenishment is achieved. The toner is supplied until the sensor output is the same as N / N. Therefore, excessive toner is supplied to the carrier, and the actual toner density increases excessively. In FIG. 12B, the toner supply start point is indicated by C, and the toner supply end point is indicated by D.
[0009]
Further, in the L / L environment, as shown in FIG. 12A, the apparent toner density is increased, and thereafter, the toner is mixed with the carrier until the same sensor output as N / N is obtained. Even if the amount is insufficient, it is not replenished at all. Therefore, the toner is insufficient with respect to the carrier, and the actual toner density is too low. In FIG. 12A, A indicates the point where the toner density is apparently increased by A, and toner is not replenished in the section from A to B.
That is, conventional toner concentration control that detects the magnetic permeability of the developer and replenishes the toner so that the toner concentration that can be obtained from the magnetic permeability is maintained at a predetermined target toner concentration (target mixing ratio). Thus, it is impossible to follow environmental changes such as humidity and temperature as described above, and the toner concentration of the developer in the developing device cannot be adjusted accurately.
[0010]
In view of such problems, various toner density controls have been conventionally proposed in consideration of environmental changes such as temperature and humidity.
For example, Japanese Patent Application Laid-Open No. 57-116370 and Japanese Patent Application Laid-Open No. 56-101166 describe a technique for performing correction control according to relative humidity, particularly regarding humidity conditions. However, there are cases where such a method cannot obtain a sufficient correction effect.
[0011]
That is, as shown in FIG. 10C, in the environment of high temperature / low humidity (relative humidity) and low temperature / high humidity (relative humidity), the same magnetic permeability sensor as in the case of normal temperature / normal humidity (relative humidity). It becomes an output, and it looks like it maintains a predetermined toner density. Therefore, if the toner density correction control is performed simply by referring to the relative humidity, the correction control may be incorrect depending on the environmental conditions, which adversely affects the image density. For this reason, there is a case where a sufficient correction effect cannot be obtained by the method of performing the correction control according to the relative humidity.
[0012]
Japanese Patent Application Laid-Open No. 6-282166 discloses a change in environmental state, particularly a change in humidity, and the toner / carrier mixing ratio of the developing device according to the detection result (= target toner concentration = target magnetic permeability sensor). A technique for controlling the output) is described. In this publication, there is provided a means for detecting the humidity in the image forming apparatus, in particular, the absolute humidity, and the developer mixing ratio for a high absolute humidity based on the developer mixing ratio target value at normal humidity. An apparatus is disclosed that controls toner supply so that the target value (TD) is lowered and the developer mixture ratio target value (TD) is increased when the absolute humidity is low. For this reason, it is possible to control to maintain a constant density when developing a latent image formed on the photoreceptor in response to a change in humidity, and to stabilize the image quality.
[0013]
[Problems to be solved by the invention]
In the technique described in the above-mentioned Japanese Patent Application Laid-Open No. 6-282166, in order to compensate for the fact that an incorrect correction may be performed with respect to a change in magnetic permeability due to an environmental change at a relative humidity, a sufficient correction cannot be performed. The absolute humidity is detected, and based on this, the developer mixing ratio is controlled.
However, when such a control method is adopted, a sensor for detecting the absolute humidity must be installed, and the sensor is very expensive, which increases the manufacturing cost.
[0014]
By the way, the adverse effect when the toner density control cannot be performed accurately due to the environmental change described above is more conspicuous in the color machine than in the monochrome machine.
That is, in a monochrome machine, considering the influence of the surrounding environment, the image density changes with respect to the area where the image density does not change even if the amount of toner attached to the electrostatic latent image changes somewhat, that is, the change in the toner attached amount. Development characteristics are set in a saturated area. For this reason, the image density does not change much even if the amount of toner attached to the electrostatic latent image slightly changes due to a change in the surrounding environment.
[0015]
On the other hand, a color machine forms a color toner image by superimposing a plurality of color toner images on the surface of a photoconductor, and transfers and fixes it on a recording sheet to create a color image print. For this reason, when the layer thickness of the toner image of each color changes, the hue of the color image changes, or the light transmittance when printed on the OHP sheet changes, thereby degrading the image quality. In general, the hue of a color image and the development characteristics that improve the transmittance when printed on an OHP sheet are not the saturation region in a monochrome machine, but the amount of toner attached to the electrostatic latent image changes. Since it is in the unsaturated region where the image density changes, the image density changes when the amount of toner attached to the electrostatic latent image changes due to a change in environmental conditions.
[0016]
Furthermore, in the case of a color machine, in addition to the influence due to the change in the environmental conditions as described above, the difference in the characteristics (mainly chargeability) between the colors of the developer is also related. Y (yellow), M (magenta) There is also a problem that it is very difficult to match the charging characteristics between the colors because the charging characteristics when the environmental conditions are changed greatly due to differences in the colorants used for C, C, and K (black). (Refer FIG. 12 (a) (b)).
[0017]
However, in the conventional techniques such as the above-mentioned publications, consideration is given to the environment, but the difference in charging characteristics when the environment changes in each color of the developer is not compensated. In other words, the conventional correction control method can correct the environment, but does not correct the environmental characteristics for each color of the developer, so that the effect of improving the stability of the image density against environmental changes is not sufficient.
[0018]
The present invention has been proposed in view of the above-described circumstances. When the ambient environment changes, the charging characteristics of the developer are prevented from changing, and the toner density is prevented from changing. An electrophotographic apparatus capable of obtaining a color image of good quality by performing correction control that approximates to an actual measurement value in consideration of environmental characteristics for each color of the developer based on toner density information. The purpose is to provide.
[0019]
[Means for Solving the Problems]
The toner density control device for an electrophotographic apparatus according to the present invention has the following features in order to achieve the above-described object.
[0020]
  That is, the toner concentration control device of the electrophotographic apparatus according to the present invention includes a magnetic permeability sensor for detecting magnetic susceptibility, and detects the magnetic permeability of the two-component developer composed of toner and carrier by the magnetic permeability sensor, Toner replenishment is performed so that the detected permeability becomes a target permeability determined based on a predetermined toner concentration.UdenIn a toner density control device of a child photographic device,Relative humidity and temperature as operating environment conditionsEnvironment detection means for detecting, and an environmental correction that divides the operating environment state detectable by the environment detection means into a plurality of areas and represents a change in permeability according to the permeability in the operating environment state for each area Value andWhen the developer is changedThe storage means for storing the output value of the magnetic permeability sensor in the operating environment, and the storage means stored based on the operating environment state detected by the environment detection meansFor each areaSelect the corresponding environmental compensation value, and select the environmental compensation valueWhen the developer is changedA target permeability calculating means for calculating the target permeability from an environmental correction value in an operating environment state, the target permeability calculating means including the selected environmental correction value and theWhen the developer is changedThe difference value with the environmental correction value in the operating environment state is the output value of the magnetic permeability sensor and theWhen the developer is changedThe operating environment when the output value of the magnetic permeability sensor is replaced with the developer instead of the environmental correction value when the difference is greater than a predetermined value than the difference between the output value of the magnetic permeability sensor in the operating environment state. The target permeability is calculated from the output value of the permeability sensor in a state.
[0022]
The electrophotographic apparatus on which the toner density control device is mounted is a color electrophotographic apparatus having a plurality of developing devices having different developer colors, and the change value of the magnetic permeability stored in the storage means. Is set for each developing unit, and the target permeability calculating means preferably corrects the target permeability for each developing unit.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of a toner density control device of an electrophotographic apparatus according to the present invention will be described with reference to the drawings.
[0024]
FIG. 2 is a schematic longitudinal sectional view of an electrophotographic apparatus provided with a toner concentration control apparatus according to an embodiment of the present invention. The embodiment shown in FIG. 2 shows a color printer as an example of a typical electrophotographic apparatus. However, the present invention is not limited to a color printer, and the electrophotographic image forming apparatus in general. Can be applied.
[0025]
As shown in FIG. 2, a color printer including a toner density control device according to the present invention includes a drum-shaped photosensitive member 1 that is a latent image carrier, and the photosensitive member 1 has a direction indicated by an arrow in the drawing. Is driven to rotate. The photoreceptor 1 is first uniformly charged to a specific polarity by a charger 2 and then exposed to a laser beam from an LSU (laser beam scanner unit) 3, whereby an electrostatic latent image is formed on the surface according to the image. Is formed. Development units 4a, 4b, 4c, and 4d, which are development devices capable of performing four-color development of yellow, cyan, magenta, and black, are sequentially arranged on the downstream side of the laser beam exposure position. In addition, for each exposure, one developing unit is selectively driven to perform development.
[0026]
Each developer contained in each developing unit is a two-component developer composed of a carrier and a toner. In the developing unit, a stirring roller for stirring the developer and a developing roller for supplying the developer supplied by the stirring roller to the photoreceptor 1 from the opening of the unit are provided. Each developing unit is provided with a magnetic permeability sensor (ATC sensor) for detecting the toner density (toner specific density) of the developer in the developing unit. Further, each developing unit includes A toner cartridge for supplying toner to the developing unit is connected.
[0027]
The toner image on the photoreceptor 1 formed by the developing unit is transferred to a sheet of plain paper or the like held on the transfer drum 5 that is rotationally driven at the same peripheral speed as the photoreceptor 1. The transfer drum 5 is rotationally driven by a motor that drives the photosensitive member 1 and rotates in the direction of the arrow in the figure, and electrostatically attracts the sheet to the surface by a voltage applied to the drum base. The sheets are stored in a sheet feeding cassette 6 and are fed one by one from the sheet feeding cassette 6 and conveyed.
[0028]
The toner image formed on the photoreceptor 1 is transferred to the sheet on the transfer drum 5 at the contact point between the photoreceptor 1 and the transfer drum 5. At this time, the toner remaining on the photosensitive member 1 without being transferred is removed by the photosensitive member cleaner 7, and the surface of the photosensitive member 1 is discharged by the discharging lamp 8.
[0029]
When the transfer of the first color toner image to the sheet is completed in this way, the next color toner image is formed in the same manner as described above, and transferred onto the sheet adsorbed on the transfer drum 5. Thereafter, when the formation of the toner images of all four colors and the transfer to the sheet are completed, the sheet is separated from the transfer drum 5 by the peeling claw 9 and conveyed to the fixing device 10. The toner image is heated and fixed by the fixing device 10 and then discharged to the discharge tray 11.
[0030]
Next, a control device for controlling the toner density (toner specific density) provided in the above-described color printer will be described with reference to FIG.
FIG. 3 is a block diagram illustrating a schematic configuration of the control device.
As shown in FIG. 3, the control device 21 for controlling the toner density includes a CPU having functions of a calculation device 23 and a storage device 22. The control device 21 receives input signals from the humidity sensor 12 and the ATC sensor 13 and controls the toner cartridge drive motor 14 to thereby develop the yellow, cyan, magenta, and black developing units 4a, 4b, 4c, and 4d. Toner supply from the toner cartridge is controlled.
[0031]
The amount of toner replenished to each developing unit 4a, 4b, 4c, 4d is determined by the ON time of the toner cartridge drive motor 14. That is, the control device 21 monitors the output value from the ATC sensor 13 provided for each of the developing units 4a, 4b, 4c, and 4d, and when the toner is consumed and the toner concentration in the developer decreases, Toner is supplied to the developing units 4a, 4b, 4c, and 4d.
[0032]
More specifically, when the toner is consumed, the control device 21 replenishes the toner so that the output value from the ATC sensor 13 becomes a target sensor output (TD) corresponding to a predetermined reference toner density. The control is performed so as to keep the toner density of the developer in each of the developing units 4a, 4b, 4c, and 4d constant.
[0033]
As described above, the magnetic permeability, which is the output value from the ATC sensor 13, is greatly influenced not only by the change in the toner concentration but also by the change in the fluidity of the developer. Further, the fluidity of the developer is greatly influenced by the temperature and humidity that are the operating environment. Therefore, the color printer is provided with a humidity sensor 12 (see FIG. 2). The humidity sensor 12 detects an environmental state where the color printer is installed, outputs a measurement result to the CPU constituting the control device 21, and changes the output from the ATC sensor 13 based on the environmental change. 21 is corrected.
[0034]
The humidity sensor 12 measures temperature and relative humidity, and outputs the measurement result to the control device 21. The control device 21 refers to the absolute humidity calculation table stored in the storage device 22, and sets the environmental state where the color printer is installed based on the measurement result of the humidity sensor 12 to the numbers “1” to “93”. It is expressed by assigning a humidity value consisting of
[0035]
The absolute humidity calculation table stored in the storage device 22 is a table in which the temperature and the relative humidity are associated with each other and represented as a value corresponding to the absolute humidity, as shown in FIG.
[0036]
The storage device 22 stores an environmental correction value table (hereinafter referred to as LUT) as shown in FIG. In this LUT, output values “1” to “93” of the humidity sensor 12 are changed from “1” to “6”, “7” to “18”, “19” to “35”, “36” to “ 56 ”,“ 57 ”or more, and is divided into five humidity areas A, B, C, D, and E in order from the lowest humidity value. Area C is an N / N environment at normal temperature and humidity.
[0037]
  Environmental correction used to correct the target sensor output for each humidity areavalueThis is set for each color of the developer used. thisEnvironmental compensation valueIs256Given in count valueYes. That isThe ATC sensor 13When the maximum voltage is 5V5V / 255The0.02VIs 1 countIt has become.
[0038]
  thisEnvironmental compensation valueIs the target sensor output(TD)For example, the developer is replaced.In the state (operating environment state as the standard)If the toner density in the initial developer detected by the ATC sensor 13, that is, the sensor output of the reference toner density is 2 V in the area C of the N / N environment, 2 V is set as the reference sensor output. A value obtained by adding a difference with respect to “50” which is the TD correction value in the area C of the / N environment is the target sensor output, that is, TD.
[0039]
  For example, if you look at the black developer,When the reference operating environment is area C and the target sensor output (TD) is 2VIn the area B where the humidity is lower than the area C, about 1.8 V obtained by 2V − {(50−40)} × 0.02 is the TD correction value. At low humidity, even if the toner concentration is the same, the output value of the ATC sensor 13 is low (apparent toner concentration UP), so at the same voltage of the ATC sensor 13 as in area C, the TD value becomes high and the toner is insufficient. Thus, by changing the voltage of the ATC sensor 13 and lowering the TD, the change in the output value of the ATC sensor 13 due to the environmental change can be corrected.
[0040]
On the other hand, in the area D where the humidity is higher than the area C, the TD correction value is about 2.3 V obtained by 2V − {(50−65)} × 0.02. At high humidity, the output value of the ATC sensor 13 becomes high even when the toner density is the same (apparent toner density drop), so the TD value is too low at the same voltage of the ATC sensor 13 as in area C, and the toner is excessive. Although the supply occurs, the output value change of the ATC sensor 13 due to the environmental change can be corrected by increasing the TD by increasing the voltage of the ATC sensor 13 in this way.
[0041]
In the area A where the humidity is lower than the area B, the TD correction value is set smaller. On the other hand, in the area E of higher humidity than the area D, a larger TD correction value is set.
[0042]
Similarly, the TD correction value for each humidity area is set in consideration of the charging characteristics of the toner based on the color differences of black, cyan, magenta, and yellow. Such a TD correction value is set based on empirical data or experimental data.
[0043]
As the number of humidity areas in such an LUT is finely divided, TD can be corrected more finely. However, in this embodiment, since the environmental correction value is set for each color of the developer, the capacity of the storage means increases according to the number of colors of the developer, and there is a limit to subdividing the area. Therefore, in this embodiment, the area is divided into five humidity areas, and a TD correction value is set for each color for each humidity area, and the TD is corrected based on the TD correction value. ing.
[0044]
Here, although the humidity area is different, the actual state in the developing unit is not changed enough to correct the TD, or conversely, even if the humidity area is the same or a difference of one area. Actually, it is assumed that TD correction is absolutely required, or that there is a serious state change that requires a larger correction instead of correction for one area.
[0045]
For example, in FIG. 4, when the temperature is 15 ° C. and the relative humidity is 80%, the absolute humidity value is “35”, and since this absolute humidity value “35” belongs to the C area, it is added to the reference TD value. The TD correction value is “50”. Here, when only the relative humidity changes to 20% and the absolute humidity value becomes “7”, the absolute humidity value “7” belongs to the B area, and the TD correction value becomes “40”. However, the TD correction value used here is the absolute humidity value “20” when the temperature is 15 ° C. and the relative humidity is 50%, and the absolute humidity value “16” when the temperature is 15 ° C. and the relative humidity is 40%. Is the same as the TD correction value, the TD correction amount is insufficient in the former, and the TD correction amount is excessive in the latter. That is, since the LUT is set to be the most optimal TD correction value at the central humidity value of each humidity area, in the case of the humidity value belonging to the vicinity of the boundary of the humidity area, the correction becomes excessive, Or correction will be insufficient. Of course, such a problem can be solved by subdividing the area, but it is practically impossible due to the capacity of the storage means.
[0046]
Therefore, in the toner density correction device according to the present embodiment, the arithmetic device 23 obtains the actual change amount of the output value of the ATC sensor 13 and performs TD correction using the change amount and the LUT. Yes.
[0047]
Next, a control procedure of toner density correction by the above-described toner density correction apparatus will be described.
FIG. 1 is a flowchart showing a control procedure of toner density correction. Note that the flowchart shown in FIG. 1 also includes an image quality compensation control procedure. In FIG. 1, “tonacon” represents toner control (toner density compensation control), and “procon” represents process control (image quality compensation control).
[0048]
In the toner density correction apparatus according to the present embodiment, as a first step of toner control, in order to store the initial toner density in the storage device 22, the replacement status of each developing unit is confirmed with respect to the color printer.
[0049]
Therefore, first, it is determined whether or not the developer has just been replaced (S1). Here, when the developing unit is detected as a new one, the developer is stirred for 1 minute, the toner and the carrier are sufficiently mixed, and the toner mixing ratio, that is, the toner concentration in the developer is stable. Then, the ATC sensor 13 is read and stored in the storage device 22 as a reference value (S2). The output value of the humidity sensor 12 at this time is also stored in the storage device 22 as an initial humidity value (S3). Here, the above-described reference sensor output is determined based on the detected reference value. The initial humidity value and the reference sensor output are retained even after the power is turned off.
[0050]
On the other hand, after the processing (S2, S3) immediately after the replacement of the developer is completed, or when the developer is not immediately after the replacement (No in S1), it is determined whether or not it is time to perform process control (No. S4). The timing for performing process control in the color printer according to the present embodiment is when the power is turned on. It is also possible to perform process control every time the number of printed sheets reaches a predetermined number.
[0051]
If it is time to perform process control, the output value of the humidity sensor 12 is read (S5), and process control is executed (S6). Details of this process control are described in detail in Japanese Patent Application Laid-Open No. 10-213928 filed earlier by the applicant of the present application.
[0052]
When the process control is completed, it is determined whether or not the current output value of the humidity sensor 12 has changed with respect to the corresponding humidity area when the toner mixing ratio reference value (TD) is set (S7). ). If it is not time to perform process control (No in S4), the above steps (S5 to S7) are skipped.
[0053]
  Here, if the humidity area has changed, the output value of the ATC sensor 13 is read and is set as “S1” (S11). Subsequently, the previous output value “S” of the ATC sensor 13 stored in the storage device 22 is read (S12). Here, immediately after the replacement of the developer, the value obtained in step (S2) described above is “S”. If the time has elapsed since the developer was replaced, the value read at the time of toner density control performed before turning off the power of the previous day becomes “S0”. In addition, LUTIn step (S7) described above, Move to step (S7)When judgingIt is the difference value of the environmental correction value“Z” is read (S13).
[0054]
  Next, the magnetic permeability change amount “Y” which is the output difference between the previous and current ATC sensors 13 is obtained as “S−S1”.Convert the calculated permeability change into a count value corresponding to the environmental correction value, and the value"Y" was read from the LUTDifference value of environmental compensation valueIs compared with "Z" (S14). here,Difference value of environmental compensation valueWhen the difference “Z−Y” between “Z” and the permeability change amount “Y” is larger than a predetermined threshold value, the obtained permeability change amount “Y” is assumed to be reliable, and this permeability The amount of change “Y” isEnvironmental compensation value(S15).That is, as in the case of the LUT environmental correction value, the target sensor output (TD) is obtained from the previous and current output values of the ATC sensor 13.
[0055]
  on the other hand,Difference value of environmental compensation valueWhen the difference “Z−Y” between “Z” and the magnetic permeability change amount “Y” is less than a predetermined threshold value, the obtained magnetic permeability change amount “Y” is determined to be unreliable. Without using the magnetic permeability change amount “Y”, the LUT read in the above step (S13)Difference value of environmental compensation value“Z” is used (S16).
[0056]
In the toner density correction apparatus according to this embodiment, the above-described threshold value is set to “5”. Here, this threshold value will be described.
[0057]
As shown in FIG. 13, the output change of the ATC sensor 13 increases as the humidity becomes higher. The TD correction value in each humidity area uses the TD change in the humidity at the center of each humidity area. For this reason, as the humidity becomes higher, the TD change after correction based on the humidity value becomes less reliable. In order to correct this, a threshold value is provided in the toner density correction apparatus according to the present embodiment. Note that the threshold value is set to “5” when the humidity value is “20” or more in FIG. This is because the output change width of the sensor 13 is about 10, and by setting the threshold value to “5”, it is possible to improve the correction accuracy at the upper and lower humidity in each humidity area on the high humidity side. Thus, the threshold value may be determined based on the sensitivity of the ATC sensor 13 to be used and the output change of the ATC sensor 13 with respect to the humidity.
When the environmental correction value is determined (S15 or S16), the value selected as the correction value is added to the reference sensor output described above, and this is used as the TD correction value.
[0058]
Subsequently, toner supply is performed based on the new TD. That is, until the output value of the ATC sensor 13 is determined to be equal to or less than TD, the toner cartridge driving roller is rotated to replenish the toner in the developing unit (S9, S10).
[0059]
Further, when it is not the process control timing (No in S4) and when the humidity area is not changed (No in S7), the above-described steps (S8 to S10) are performed.
Although the above-described flowchart shows compensation control for one developing unit, since the toner density correction device according to the present embodiment is used in a color printer, the four developing units 4a, 4b, 4c, and 4d are used. Compensation control is performed for each.
[0060]
  Next, the above-described correction of toner density will be described with a specific example. For example, it is assumed that the process control timing is reached after the developer (black) is replaced. If the environment at the time of developer replacement is area C, the value “S” read in step 12 (S12) is “50" On the other hand, if the output value read by the humidity sensor 12 in step 5 (S5) is shifted to D, the output value is read in step 13 (S13).Difference value of environmental correction value of LUT“Z” becomes “65-50”.
[0061]
  In addition, the output value of the ATC sensor 13 read in step 11 (S11) increases as the humidity area increases, and in step 14 (S14)Permeability change"S-S1"Is converted into the count value corresponding to the environmental compensation value,"Y" is "5" and "ZY" is "65-50-5 = 10". Since “10” obtained here exceeds the threshold value “5”, it was obtained in step 13 (S13).Difference value “Z” of LUT environmental correction valueInstead ofThe target sensor output (TD) is obtained from the previous and current output values of the ATC sensor 13..
[0062]
6A and 6B, only the LUT is used, and when the TD correction is performed by the environmental change and the toner density control is performed, the image density (ID) and the fog (BG) in which the toner is scattered in the solid white portion are illustrated. ) Shows the result of examining the state of occurrence. Similarly, FIGS. 7A and 7B show the results of examining the image density and the state of occurrence of fog when the toner density correction apparatus according to this embodiment is used.
[0063]
As can be seen by comparing FIG. 6A and FIG. 7A, in the TD correction relying only on the LUT, the phenomenon that the image density greatly changes due to the difference in environment is the actual change in magnetic permeability. This is improved by using the quantity “Y”.
The fog phenomenon is not a problem at L / L where the toner is insufficient, but is greatly affected at H / H. As can be seen by comparing FIG. 6B and FIG. 7B, in the TD correction relying only on the LUT, the fog phenomenon caused by H / H is caused by using the actual permeability change amount “Y”. It has been improved.
[0064]
FIG. 8 shows a conventional image forming apparatus that uses TD correction that relies only on the LUT and an image forming apparatus that includes the toner density correction device according to the present embodiment that uses the actual magnetic permeability change amount “Y”. The result of investigating the variation of the toner density in the developer generated for each humidity area is shown.
[0065]
As is apparent from FIG. 8, in the conventional image forming apparatus using only the LUT, variations of 2 to 4% occur in the respective colors of black, cyan, magenta, and yellow. On the other hand, in the image forming apparatus including the toner density correction apparatus according to the present embodiment, the black, cyan, magenta, and yellow colors are accommodated with a variation of about 1%, and the toner density variation is greatly improved. You can see that
[0066]
FIG. 9 shows a conventional image forming apparatus that uses TD correction that relies only on the LUT, and an image forming apparatus that includes the toner density correction device according to the present embodiment that uses the actual magnetic permeability change amount “Y”. Fig. 5 shows the result of examining the variation in ID generated for each humidity area.
As is clear from FIG. 9, there is no significant variation in black even when only the LUT is used, but the variation in ID is greatly improved in each color of cyan, magenta, and yellow. Understand.
[0067]
【The invention's effect】
Since the toner density control device 21 of the electrophotographic apparatus according to the present invention has the above-described configuration, the following effects can be obtained.
That is, according to the toner concentration control device 21 of the electrophotographic apparatus according to the present invention, the operating environment state is divided into a plurality of areas, and the amount of change in magnetic permeability is stored for each area.
[0068]
For this reason, even if there is a slight change in the operating environment state and there is almost no need to correct the target permeability, the correction is not performed, and the target permeability is corrected only after some environmental change occurs. .
Therefore, it is possible to avoid the inconvenience of correcting the target permeability even though the temperature and humidity are slightly changed and the adjustment of the target permeability is not actually required.
[0069]
Further, the target permeability calculating means can calculate the difference value between the magnetic permeability detected last time and the magnetic permeability detected this time, that is, the actual magnetic permeability change amount except when the developer is replaced. Based on the above, the target permeability is calculated.
For this reason, the target permeability is a value according to the actual environment. Therefore, the target magnetic permeability is not corrected even though it is not necessary, and the correct target magnetic permeability is corrected based on actual measurement at an appropriate timing. Control becomes possible. As a result, although the toner concentration is adjusted based on the magnetic permeability of the developer, the accuracy is as if the mixing ratio of the toner to the carrier of the developer is directly detected, except for the influence of the magnetic permeability environment. High toner density control is possible.
[0070]
Further, according to the toner concentration control device 21 of the electrophotographic apparatus according to the present invention, the difference value, which is an actual change amount obtained by detecting the magnetic permeability of the developer, is concerned only when the difference value is not less than a predetermined threshold value. The target permeability is corrected using the difference value. Therefore, when the obtained difference value is less than the threshold value, the target permeability is corrected based on the change value corresponding to each environmental area stored in the storage unit. For example, if a reliable value is greater than or equal to a predetermined value X based on the output fluctuation of the magnetic permeability sensor, this value X is set as a threshold value. Then, only when the difference value, which is the actual change amount obtained by detecting the magnetic permeability, is reliable, correction is performed using the difference value, and the difference value is low in reliability. Can correct the target permeability more accurately by adopting a correction value stored in the storage means, that is, a correction value based on experimental data or experience data.
[0071]
Further, according to the toner density control device 21 of the electrophotographic apparatus according to the present invention, it is possible to compensate for the difference in charging characteristics when the environment changes in each color of the developer in addition to the correction for the environment. In other words, in addition to the correction for the environment, the environmental characteristics of each color of the developer are also corrected. Therefore, the stability of the image density against the environmental change is improved, and an excellent color electrophotographic apparatus can be obtained.
[Brief description of the drawings]
FIG. 1 is a flowchart illustrating a control procedure for toner density correction.
FIG. 2 is a schematic longitudinal sectional view of an electrophotographic apparatus provided with a toner concentration control device 21 according to an embodiment of the present invention.
3 is a block diagram illustrating a schematic configuration of a control device 21. FIG.
4 is an explanatory diagram of an absolute humidity calculation table stored in a storage device 22. FIG.
FIG. 5 is an explanatory diagram of an environment correction value table stored in a storage device 22;
FIG. 6 shows the result of examining the image density and the occurrence state of fog in which toner is scattered in a white solid portion when TD correction is performed by environmental change using only the environmental correction value table and toner density control is performed. It is explanatory drawing shown.
FIG. 7 is an explanatory diagram showing the results of examining the image density and the state of occurrence of fog when the toner density correction apparatus according to the present embodiment is used.
FIG. 8 shows the result of examining the variation in the toner density in the developer generated in each humidity area in the conventional image forming apparatus and the image forming apparatus provided with the toner density correction device according to the present embodiment. It is explanatory drawing.
FIG. 9 is an explanatory diagram showing a result of examining variations in IDs generated in each humidity area in a conventional image forming apparatus and an image forming apparatus including a toner density correction device according to the present embodiment.
FIG. 10 is a graph (a) showing a change in the amount of toner adhering to an electrostatic latent image with respect to toner density, a graph (b) showing a change in permeability sensor output with respect to humidity, and a change in permeability sensor output with respect to development stirring time. It is a graph (c) which shows.
FIG. 11 is a graph showing changes in the output of the magnetic permeability sensor with respect to the toner specific concentration.
FIG. 12 is a graph showing a relationship between a change in environmental state and an ATC sensor output.
FIG. 13 is a graph showing a change in sensor output with respect to an absolute humidity value.
[Explanation of symbols]
1 Photoconductor
2 Charger
3 LSU (Laser Beam Scanner Unit)
4a to d Development unit
5 Transfer drum
6 Sheet feeding cassette
7 Photoconductor cleaner
8 Static elimination lamp
9 Peeling nails
10 Fixing device
11 Discharge tray
12 Humidity sensor
13 ATC sensor
14 Toner cartridge drive motor
21 Control device
22 Storage device
23 Arithmetic unit

Claims (2)

A magnetic permeability sensor for detecting magnetic permeability is provided, and the magnetic permeability of the two-component developer composed of toner and carrier is detected by the magnetic permeability sensor, and the detected magnetic permeability is determined based on a predetermined toner concentration. in the toner density control device line power sale child photographic apparatus toner supply so that the target permeability,
Environment detecting means for detecting relative humidity and temperature in the electrophotographic apparatus as an operating environment state ;
When the operating environment state that can be detected by the environment detecting means is divided into a plurality of areas, and an environmental correction value that represents a change in magnetic permeability according to the magnetic permeability in the operating environment state for each area is replaced with a developer. Storage means for storing the output value of the magnetic permeability sensor in the operating environment at
Based on the operating environment state detected by the environment detection means, select a corresponding one of the environmental correction values for each area stored in the storage means,
A target permeability calculating means for calculating the target permeability from the selected environment correction value and the environment correction value in the operating environment when the developer is replaced ;
The target permeability calculating means is configured such that the difference value between the selected environmental correction value and the environmental correction value in the operating environment state when the developer is replaced , the output value of the magnetic permeability sensor and the developer are replaced. In the case where the output value of the magnetic permeability sensor is replaced with the environmental correction value instead of the environmental correction value when the difference is greater than the difference between the output value of the magnetic permeability sensor in the operating environment at the time and the developer. A toner concentration control device for an electrophotographic apparatus, wherein the target magnetic permeability is calculated from an output value of the magnetic permeability sensor in an operating environment state of the electrophotographic apparatus.   The electrophotographic apparatus on which the toner density control device is mounted is a color electrophotographic apparatus having a plurality of developing devices having different developer colors, and the change value of the magnetic permeability stored in the storage means is: 2. The toner density control device of an electrophotographic apparatus according to claim 1, wherein the target magnetic permeability calculation means is set for each developing device, and the target magnetic permeability calculating means corrects the target magnetic permeability for each developing device.

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