JP3160933B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is an electrophotographic copying machine, relates to an image forming apparatus such as a laser printer, in particular, an image to obtain a constant image density regardless of changes in developing conditions
The present invention relates to a forming apparatus.

[0002]

2. Description of the Related Art In an electrophotographic apparatus, an electrostatic latent image is formed by exposing a photosensitive member to light and then exposing the photosensitive member, and a visible image is obtained by developing the latent image. In this image formation, the contrast potential of the electrostatic latent image is adjusted so that the same developing density can be obtained in the solid portion regardless of the change in the developing conditions for the same original density. . Note that the contrast potential means a potential difference between a bright portion potential and a dark portion potential. In order to automatically perform this density adjustment, a patch having a constant potential is formed on the photoreceptor, and the density when the patch is developed is detected by a density sensor, so that the detected density matches the reference density. It is also known to automatically adjust the contrast potential. In general, a solid, that is, solid black development patch obtained by uniformly charging a rectangular area having a certain area at a certain potential and developing the charged area is used as the patch.

However, when a solid black developing patch is used, the density-sensor output characteristic of the density sensor is saturated in a high density portion, so that it is necessary to use a low-density developing patch. In order to form this low-density development patch, the charging potential for forming the patch must be lowered as compared with the normal state, and the control system of the charging device becomes complicated.

Therefore, a halftone dot pattern or a linear pattern is used as a development patch. In a development patch using a non-solid pattern such as a halftone dot pattern, toner image portions and white spots are alternately arranged, and the detection diameter of the density sensor is sufficiently larger than the pitch of the halftone dot pattern or the like. Therefore, even if the density of the toner image portion is high, the average density detected by the density sensor is low. Therefore, a developing patch suitable for density control can be formed without switching the operation of the charging device.

However, when a development patch such as the above-described halftone dot pattern is used, a new problem as described below occurs.

For example, a sectional view of a potential pattern of an electrostatic latent image having a different contrast potential for forming a development patch having an area ratio of 75% is shown in FIG. The horizontal axis indicates the image position, and the vertical axis indicates the image potential. In the figure, and indicate potential patterns whose contrast potentials are 700 V, 550 V, and 350 V, respectively. The width of the valley of the potential pattern corresponds to the width of a white spot between each point or each line, and both sides thereof are shown. This corresponds to a toner image portion. Patches with these potential patterns
When development is performed at the development bias level V _BIAS indicated by the broken line, the cross section of the pattern after development is as shown in FIG. That is, as the contrast potential increases, the width of the toner image portion increases, and the width of the blank portion decreases.

On the other hand, the density sensor detects the density of the development patch based on the amount of light reflected from the photoconductor. That is,
When the density is low, that is, when the amount of toner is small, the amount of reflected light is large due to specular reflection on the surface of the photoconductor, but when the density is high, that is, when the amount of toner is large, the amount of reflected light is covered because the surface of the photoconductor is covered with toner. , The density of the development patch can be detected based on the amount of reflected light from the photoconductor.

[0008]

However, when the cross section of the toner image is stacked in the height direction shown in FIG. 15 from the reference state shown in FIG.
After one layer of toner is developed on the photoreceptor, the change in the amount of reflected light is small even if toner is further laminated. On the other hand, when the toner spreads in the horizontal direction as shown by the increase in the toner amount, the area of the toner image portion changes, and the change in the amount of reflected light is large. Therefore, when using a non-solid development patch such as a halftone dot pattern,
Unlike the solid development patch, there is room for the toner image portion to spread around each halftone dot or line. Therefore, the density sensor detects the spread of the developed image in the horizontal direction as shown in FIG. However, the sensitivity is low in the height direction as shown in FIG. However, it is assumed that the amount of toner of the developed image shown in FIG. 15 is equal to that of the developed image shown in FIG.
In FIG. 16, E4 is the density sensor output when the developed image in the reference state shown in FIG. 15 is measured, E5 is the density sensor output when the developed image is extended in the height direction,
E6 is the density sensor output when the developed image indicated by extends in the horizontal direction.

Since the toner amount of the developed image is equal to the toner amount of the developed image indicated by the symbol, a difference occurs in the output of the density sensor although the density after fixing on the recording paper is equal.

For this reason, if the density of the developed patch is detected by a density sensor and the toner supply amount is controlled so that the detected density becomes a constant reference value, the developed image in a pattern having a high contrast potential may be horizontally oriented. The output of the density sensor becomes darker than the actual copy density because it is wider and wider, and it operates to match the output of the density sensor by lowering the density. As a result, the density of the output image becomes lower. I will. Conversely, in the case of a low contrast potential, the density of the output image increases. FIG. 17 shows the relationship between the contrast potential and the output image density. However, the output of the density sensor is constant.

As described above, if the contrast potential of the electrostatic latent image is different, the automatic density adjusting mechanism does not operate properly and the density of the output image changes.

When a halftone dot pattern or the like is used as a development patch, as described below, the copy density fluctuates due to the influence of humidity.

In general, the charge of a developer becomes lower at high humidity, and the amount of development increases for the same electrostatic latent image. Therefore, the developed image corresponding to the halftone dot or linear pattern not only spreads in the horizontal direction (reference) but also increases in the height direction (reference), similarly to the cross section shown in FIG. As described above, the density sensor has high sensitivity to the spread of the developed image in the horizontal direction, but has low sensitivity in the height direction. At high humidity, the height of the developed image is higher, so the density is detected lower than the actual density.As a result, the density of the output image becomes higher. It is detected at a higher level, resulting in a lower density of the output image. FIG. 18 shows an example of the relationship between relative humidity and concentration.

The present invention has been devised to solve the above problems, and has as its object to obtain an image having a stable density irrespective of changes in image forming conditions, environmental changes, and the like.

[0015]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method of forming a non-solid pattern developing patch.
By detecting and comparing the detection result with the concentration reference value,
Influences development density in image forming apparatus that performs density control
Fluctuation detection means for detecting fluctuations that cause
To change the contrast potential to control the contrast potential
Control means, and according to a detection result of the fluctuation detecting means.
To control the contrast potential and the density control reference.
Value of non-solid pattern due to contrast potential change
It is characterized in that errors due to shape variations are corrected. Ma
In addition, the density control reference value is accompanied by a change in contrast potential.
Corrects errors due to shape fluctuations of non-solid patterns
Alternatively, an offset may be added. Influence on development density
The fluctuations that give rise to humidity or developer fatigue or
There is a difference in developer characteristics .

[0016]

When performing automatic density adjustment in an electrophotographic copying machine, a development patch formed on a photoreceptor or a transfer drum is compared with a reference density, and a means for controlling the development density so that the two coincide with each other. For example, a toner dispenser is controlled. Further, in order to correct the density fluctuation due to the influence of the density or the like, the contrast potential of the electrostatic latent image formed on the photoconductor is controlled. When a non-solid pattern such as a halftone dot pattern is used as a development patch, if the contrast potential is changed, an error occurs in the output of the density sensor with respect to the actual density change. Therefore, in the present invention,
The reference density is corrected according to the contrast potential, and the detection error in the density sensor is corrected.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be specifically described below based on embodiments with reference to the drawings.

FIG. 1 is an explanatory view schematically showing a first embodiment of the electrophotographic apparatus of the present invention.

Around the drum-shaped photoreceptor 1, a charger 2, an exposure unit 3, a developing unit 5 equipped with a toner dispenser 4, a density sensor 6, a transfer unit 7, a cleaning device 8, a static elimination lamp 9, and the like are sequentially arranged. Are located. Further, a fixing device 10 is arranged in the middle of a paper path through which the recording paper A after the transfer passes.

A high voltage from a high voltage generating circuit 11 is applied to the charger 2 and a laser raster output scanner (not shown) comprising a laser light source, a rotary polygon mirror, a lens, etc. (Indicated by laser ROS in the figure) 12
From the laser beam L. A patch pattern signal from a patch pattern generation circuit 13 or an image signal from an image signal source 14 is selectively supplied to the laser raster output scanner 12. In the vicinity of the photoconductor 1,
A humidity sensor 15 for detecting relative humidity is provided as an environment sensor for detecting an environment in the housing of the electrophotographic apparatus.

The density sensor 6 is a reflected light type density sensor as schematically shown in FIG. 2, and irradiates light from a light emitting element 6a such as a light emitting diode onto the surface of the photosensitive member 1 to cause it to emit light. The amount of reflected light from the surface is detected by a light receiving element 6b such as a phototransistor. That is, as the density of the development patch B formed on the surface of the photoconductor 1 increases, the amount of reflected light decreases.
By measuring the output of b, the density of the development patch B can be detected. 5a is a developing roll of the developing device 5, and C is a developer layer formed on the outer periphery of the developing roll 5a.

The output of the density sensor 6 and the output of the humidity sensor 15 are supplied to an arithmetic circuit 16, and the toner supply time in the developing device 5 is determined based on an arithmetic expression described later, and the motor drive circuit is determined based on the toner supply time. 17 to rotate a dispense motor (not shown) provided in the toner dispenser 4.

The toner dispenser 4 is provided adjacent to the developing device 5, and as shown in FIG. 3, a toner tank 4a for storing the toner D and a toner tank 4a for stirring the toner D in the toner tank 4a. An agitator 4b and a dispense roll 4c for supplying the toner D from the toner tank 4a into the developing device 5 are provided. A dispense motor (not shown) is connected to the dispense roll 4c.
Is rotated to supply an amount of toner according to the rotation time.

Next, a basic operation of the above-described electrophotographic apparatus will be described. In this specification, the term “developing patch” is used for any image in an electrostatic latent image state or a visible image state.

When the image forming operation is started, in FIG. 1, the photosensitive member 1 starts rotating in the direction of the arrow, and a constant voltage is applied from the high voltage generating circuit 11 to the charger 2.
The surface of the photoconductor 1 is uniformly charged. Next, the photoconductor 1
Is exposed to the laser light L from the laser raster output scanner 12 to form an electrostatic latent image of the development patch. The electrostatic latent image is developed by the developing device 5 to form a visible development patch, and the density of the development patch is detected by the density sensor 6,
This developing patch density is compared with a developing patch density target value Radcmax in an arithmetic circuit 16, and the toner dispenser 4 is controlled via a motor drive circuit 17 in accordance with the comparison result. Is controlled.

Here, in the present embodiment, correction is applied to the development patch density target value Radcmax in advance in accordance with the humidity of the environment in which the electrophotographic apparatus is installed.

That is, after the power is turned on and before the image forming cycle starts, the relative humidity in the housing of the electrophotographic apparatus is detected by the humidity sensor 15, and the relative humidity is detected from a preset humidity correction table as shown in Table 1. Offset value AD of development patch density target value Radcmax corresponding to humidity value
Coffset is required. Incidentally, A ₁ to A ₂₀ represents a respective offset value. Then, this offset value ADCoffset is added to the development patch density target value Radcmax.

[0028]

[Table 1]

That is, since the output density increases as the humidity increases, the ADC offset value is such that the intermediate humidity is 0, the high humidity side is positive, the low humidity side is negative, and the absolute value increases as the distance from the center increases. Set to a value.

In the patch forming cycle, the surface of the photoconductor 1 is first uniformly charged by the charger 2 as described above,
Next, the laser light L from the laser raster output scanner 12
Is irradiated on the inter-image portion of the photoconductor 1, and the photoconductor 1
An electrostatic latent image for a development patch is formed thereon. As shown in FIG. 4, the inter-image portion includes an image area F where an electrostatic latent image E on the photoconductor 1 corresponding to an image to be output on the recording paper A is formed, and the image area F And the inter-image portion does not come into contact with the recording paper A.

For example, when a development patch having a halftone dot pattern as shown in FIG. 5 is formed, a patch pattern signal as shown in FIG. 6 is generated by the patch pattern generation circuit 13 during the development patch period. May be used to modulate the laser beam L from the laser raster output scanner 12. When forming a development patch having a linear pattern as shown in FIG. 7, a patch pattern signal as shown in FIG. 8 may be used. FIGS. 5 to 8 schematically show development patches and signals in a simplified manner for easy understanding, and do not show the temporal relationship between actual development patch patterns and patch pattern signals. Absent. To give an example of an actual development patch, the size of the development patch is about 30 mm × 30 mm, and the pitch of halftone dots or lines is 1 mm.
It is about 00 to 200 μm. In this case, the detection diameter of the density sensor 6 is about 3 mm.

By the irradiation of the laser beam L, an electrostatic latent image corresponding to the development patch is formed on the photoreceptor 1, and this electrostatic latent image is visualized as a toner image by a developer in a developing unit 5. Is done. The density of this development patch is
And is supplied to the arithmetic circuit 16.

The arithmetic circuit 16 controls the toner dispenser 4 so that the density of the development patch becomes (Radcmax + ADCoffset). Specifically, based on the following formula,
The ON time SUMadc of the dispense motor provided in the toner dispenser 4 is obtained in units of 100 ms, and the motor drive circuit 17 determines the ON time SUMadc for this time.
Of the developing device 5 by rotating the dispensing motor of
Is supplied with a predetermined amount of toner.

SUMadc = (Radcpatch− (Radcmax + ADCoffset)) × Kadc where Radcpatch = (Vpatch / Vclean) × 200 Vpatch: output voltage of the density sensor at the developing patch portion Vclean: output voltage of the density sensor at the clean surface Kadc: toner supply Amount calculation coefficient Note that the value of Radcpatch decreases as the concentration increases.

Therefore, as schematically shown in FIG.
When the density of the developing patch detected by the density sensor 6 is high, the value of Radcpatch becomes small, and the on-time SUMadc of the dispense motor becomes short. Therefore, the supply amount of the toner is reduced, and the development density is changed to a lower direction. As a result, basic automatic density control is performed. Furthermore, since the offset value ADCoffset is set to a larger positive value as the humidity is higher, the on-time SUMadc of the dispense motor is shorter as the humidity is higher.
Therefore, even if the density of the development patch detected by the density sensor 6 is constant, a smaller amount of toner is supplied as the humidity becomes higher, and the development density in the subsequent development decreases. As a result, the disadvantage that the copy density becomes high at the high humidity described in the section of the related art can be solved.

Since the development patch is formed in the inter-image portion G as described above and does not come into contact with the recording paper A, the development patch after development is not transferred to the recording paper A and the cleaning device is used. 8, and the residual charge of the photoconductor 1 is removed by the discharge lamp 9 to prepare for the next image forming cycle.

When the patch forming cycle is completed, an image forming cycle is started, and the charging step, the exposing step, and the developing step are repeated as in the above-described patch forming cycle. However, in the image forming cycle, an image signal from the image signal source 14 is supplied to the laser raster output scanner 12, and the laser light L is modulated by a signal corresponding to an image to be output. Is formed, and the electrostatic latent image is developed to obtain a toner image H.
At the time of this development, the automatic density adjustment is performed with the density of the development patch detected earlier as a reference and corrected in accordance with the humidity, so that an output image with the optimum density is always obtained.

Since the toner image H on the photosensitive member 1 is formed at a position where it can come into contact with the recording paper A, when the toner image H passes through the transfer unit 7, The transferred recording paper A is transferred to the fixing device 10 and the toner image H is fixed thereon. The toner remaining on the photoconductor 1 after the transfer is removed by the cleaning device 8, and the residual charge is removed by the charge removing lamp 9.

Next, a second embodiment of the present invention will be described with reference to FIG.
0 will be described. The members and the like corresponding to those of the first embodiment shown in FIG.

In the second embodiment shown in FIG. 10, the high voltage generating circuit 11 is connected to the arithmetic circuit 16, and the output voltage of the high voltage generating circuit 11 is controlled by the arithmetic circuit 16.

In the second embodiment, the relative humidity in the casing of the electrophotographic apparatus is detected by the humidity sensor 15 after the power is turned on and before the image forming cycle starts, and is set in advance as shown in Table 2. From the humidity correction table, a predetermined contrast potential is selected to supplement the developability at the relative humidity. B _{1 to} B ₂₀ indicate respective contrast potentials.

[0042]

[Table 2]

That is, as described in the section of the prior art, when the humidity changes, an error occurs in the output of the density sensor 6, and as a result, the density becomes high at high humidity and becomes low at low humidity. However, by selecting the contrast potential according to the humidity, an error in the output of the density sensor 6 is corrected as a result. For example, in high humidity, by increasing the target value of the contrast potential and giving an instruction to the high voltage generation circuit 11, the voltage applied from the high voltage generation circuit 11 to the charger 2 is increased, and the electrostatic latent image on the photoconductor 1 is increased. Has a higher contrast potential. Therefore, the width of the toner image portion after development is increased, the sensitivity of the density sensor 6 is increased, and the output of the density sensor 6 is larger than a normal value. As a result, the toner dispenser 4 is controlled so that the output density decreases, and a toner image having a normal density is formed.

Next, according to the table shown in Table 3, the target value of the development patch density Rad corresponding to the target value of the contrast potential is shown.
An offset value ADCoffset of cmax is obtained. In addition,
C _{1 to} C ₆ indicate respective offset values. Then, this offset value ADCoffset is added to the development patch density target value Radcmax.

[0045]

[Table 3]

The reason why the offset amount ADCoffset is changed according to the target value of the contrast potential is to correct an error generated in the output of the density sensor 6 due to the level of the contrast potential, as described above.

Thereafter, similarly to the first embodiment, the density of the development patch on the photosensitive member 1 is detected by the density sensor 6, and the toner dispenser 4 is controlled so that the detected density becomes (Radcmax + ADCoffset).

Thus, for example, even in an electrophotographic apparatus in which the contrast potential is changed in order to correct a change in density caused by a change in humidity, a density sensor generated by changing the contrast potential Since the output error is corrected, the optimum image density can be always maintained.

Next, a third embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. The members and the like corresponding to those of the first embodiment shown in FIG.

In the third embodiment shown in FIG. 11, the transfer drum 18 is pressed against the photosensitive member 1 and the recording paper A is wound around the outer periphery of the transfer drum 18. In the transfer drum 18, a light-transmitting cylindrical synthetic resin film (not shown) is supported between a pair of flanges (not shown). A tie bar (not shown) for securing the mechanical strength of the transfer drum 18 is connected between the pair of flanges, and there is no synthetic resin film at the tie bar. In addition, the tie-bar portion falls down to the inner diameter side from the surface of the synthetic resin film, so that it does not directly contact the photoconductor 1. Further, the density sensor 6 is disposed on the downstream side in the vicinity of the transfer section so as to face the transfer drum 18.

In the third embodiment, after the development patch formed on the photosensitive member 1 is once transferred onto the recording paper A wound on the transfer drum 18, the density of the development patch is detected by the density sensor 6. Is different from the first embodiment. Other operations are the same as those in the first embodiment, and a description thereof will be omitted.

In the third embodiment shown in FIG. 11, a light transmission type sensor can be used as the density sensor 6. That is, the light-emitting element and the light-receiving element can be arranged opposite to each other with the synthetic resin film of the transfer drum 18 interposed therebetween, and the density can be detected based on the amount of transmitted light.

In the second embodiment shown in FIG. 10, the transfer drum is pressed against the photosensitive member in the same manner as in the third embodiment shown in FIG. 11, and the image is developed on the recording paper wound around the transfer drum. A patch may be formed, and the density of the developed patch may be detected.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. The members and the like corresponding to those of the first embodiment shown in FIG.

The fourth embodiment shown in FIG. 12 shows a color electrophotographic apparatus, in which a transfer drum 18 is pressed against the photosensitive member 1. Further, as developing units, yellow, magenta, cyan and black color developing units 19Y and 19, respectively.
A rotary developing device 19 including M, 19C, and 19K is used.

The developing patch forming operation of the color electrophotographic apparatus shown in FIG. 12 will be described below.

First, the photoreceptor 1 is charged by the charger 2, and is then exposed by the laser light L from the laser raster output scanner 12 to form an electrostatic latent image of a development patch on the photoreceptor 1. The electrostatic latent image is first developed, for example, by the yellow developing unit 19Y to form a yellow developing patch, and the density of the yellow developing patch is detected by the density sensor 6. The development patch is the photoconductor 1
Since the developing patch is formed at a position corresponding to the tie bar position of the transfer drum 18, even when the developing patch comes to the transfer position, it is not transferred to the transfer drum 18. The yellow developing patch that has passed the transfer position is removed by the cleaning device 8 and the residual charge is removed by the charge removing lamp 9 to prepare for the next image forming cycle.

Next, the rotary developing device 19 is rotated so that the magenta developing device 19M faces the photosensitive member 1,
As in the case of yellow, a magenta development patch is formed on the photoreceptor 1 by the respective steps of charging, exposure and development, and the density is detected by the density sensor 6.

Similarly, for cyan and black, developing patches of each color are formed on the photosensitive member 1 while rotating the rotary developing machine 19, and the density is detected by the density sensor 6.

Next, automatic density control using the four color development patches will be described.

After the power is turned on, the relative humidity in the housing of the electrophotographic apparatus is detected by the humidity sensor 15 before the image forming cycle starts, and the relative humidity is obtained from a preset humidity correction table as shown in Table 4. A predetermined contrast potential is selected in order to supplement the developability in the above. Incidentally, D ₁ to D ₁₀ denotes the various contrast potential. For example, D ₆ = 450 V, D ₇ = 430 V, D ₈ = 41
0V.

[0062]

[Table 4]

Next, at the selected contrast potential, for example, four color development patches of yellow, magenta, cyan and black with an area ratio of 60% are formed on the photosensitive member 1 in the above-described steps for each color. Then, the densities of the development patches of each color are sequentially detected by the density sensor 6, and the detection results for each color Radcpatch (Y), Radcpatch (M), Radcpatch (C), Radcpatch (C)
atch (K) and target patch densities Radcmax (Y), Radcmax of each color
(M), Radcmax (C), Radcmax (K) difference D (Y), D (M), D (C),
Find D (K).

D (Y) = Radcpatch (Y) −Radcmax (Y) D (M) = Radcpatch (M) −Radcmax (M) D (C) = Radcpatch (C) −Radcmax (C) D (K) = Radcpatch (K) −Radcmax (K) Next, the arithmetic circuit 16 calculates an average value M of these differences.

M = (D (Y) + D (M) + D (C) + D (K)) / 4 From the average value M of these four colors, a contrast potential required to bring the patch density close to the target density is obtained. The potential target value is corrected again.

As described above, by performing the common automatic density adjustment of the four colors by using the average of the densities of the development patches of the four colors, the detection errors when detecting the densities of the development patches are averaged, and each color is independent. Errors are reduced as compared with the case where the density of each color is adjusted by detecting the density of the development patch. In addition, if the development patch is formed for each color a plurality of times and the density is measured and the average of the density of each development patch is obtained for each color, the error is reduced. For example, if the development patch is formed four times for each color, In this case, the density must be measured by forming a development patch 16 times in total, and there is a disadvantage that it takes time to measure the density.

Next, an image forming cycle will be described.

First, the photoreceptor 1 is charged and then exposed by the laser light L modulated by a yellow image signal, so that an electrostatic latent image is formed on the photoreceptor 1. The electrostatic latent image is first developed, for example, by a yellow developing unit 19Y to form a yellow toner image, and the yellow toner image is transferred onto the recording paper A wound on the transfer drum 18. .

Next, the developing device 19M of magenta is
, And charged and charged as in the case of yellow.
Through each of the exposure and development steps, a magenta toner image is formed on the photoconductor 1, and this magenta toner image is transferred over the yellow toner image previously transferred onto the recording paper A. .

Similarly, cyan and black are transferred onto the recording paper A in a superimposed manner. That is, the toner image of yellow, magenta, cyan, and black is multiplex-transferred onto the recording paper A by four rotations of the transfer drum 18 to form a color image.

At the time of forming each color image described above, the high voltage generation circuit 11 is controlled based on the previously obtained contrast potential target value, so that the density of the toner image of each color formed on the photoreceptor 1 is Is appropriate, and the density and hue of the color image formed on the recording paper A wound on the transfer drum 18 are also appropriate.

In the embodiment shown in FIG. 12, the density of the development patch formed on the photosensitive member 1 is detected.
The development patches of each color may be transferred onto the recording paper A wound on the transfer drum 18 and the density of the development patches may be detected. In this case, as shown by a broken line in FIG.
8 to detect the density of the developed patch after transfer. When the density of the development patch after transfer is detected, the development patch is applied to the photosensitive member 1 when the development patch is exposed.
, That is, at a position excluding the position corresponding to the tie bar position of the transfer drum 18.

As described above, when detecting the density of the developed patch after transfer, charging, exposure, development, and transfer are performed for each color, and four colors of development are recorded on the recording paper by four rotations of the transfer drum. Patches are formed, and the density of each development patch is detected for each rotation. The operation after the density detection is the same as the operation described above, and thus the description is omitted. However, in the embodiment shown in FIG. 12, instead of controlling the density by the toner dispenser, the density is controlled by changing the charging potential and the contrast potential.

It should be noted that, of the above embodiments, in the embodiment in which the developing density is controlled by the toner dispenser, the developing bias is changed by changing the developing potential or by changing the contrast potential. You may make it control.

Further, in the above-described embodiment, the case where the relative humidity is detected and the target contrast potential is changed in order to correct the fluctuation of the developing property due to the humidity has been described as an example. May be used to detect the absolute humidity.

The causes of the fluctuation of the developing property include, in addition to the humidity, the fatigue of the developer, the characteristic difference due to the difference in the color of each color developer in the case of the color developer, and the like. In order to correct the fluctuation of the developing property caused by the fatigue of the developer, a timer indicating the usage time of the developer is provided, and the target contrast potential is changed according to the usage time of the developer measured by the timer. do it. Further, in order to correct the fluctuation of the developing property caused by the characteristic difference of each color of the color developer,
The target contrast potential may be changed according to the color of the color developer.

[0077]

As described above, according to the present invention, in an electrophotographic copying machine that performs automatic density adjustment using a non-solid developing patch such as a halftone dot patch, fluctuations in developability due to various causes are eliminated. When the correction is performed by changing the contrast potential, the development density reference value is corrected according to the contrast potential. This makes it possible to correct a density detection error peculiar to the use of a non-solid development patch. Therefore, an output image having an optimum density is always obtained regardless of external conditions.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a first embodiment of the electrophotographic apparatus of the present invention.

FIG. 2 is a schematic cross-sectional view for explaining an operation of detecting a development patch density by a density sensor.

FIG. 3 is a schematic sectional view of a toner dispenser.

FIG. 4 is a diagram for explaining an inter-image unit.

FIG. 5 is an explanatory diagram schematically showing an example of a development patch based on a halftone dot pattern.

6 is a waveform diagram schematically showing a pattern signal for forming the developing patch shown in FIG.

FIG. 7 is an explanatory diagram schematically showing an example of a development patch using a linear pattern.

8 is a waveform diagram schematically showing a pattern signal for forming the development patch shown in FIG.

FIG. 9 is a graph for explaining reference density correction at the time of automatic density adjustment.

FIG. 10 is an explanatory view schematically showing a second embodiment of the electrophotographic apparatus of the present invention.

FIG. 11 is an explanatory view schematically showing a third embodiment of the electrophotographic apparatus of the present invention.

FIG. 12 is an explanatory view schematically showing a fourth embodiment of the electrophotographic apparatus of the present invention.

FIG. 13 is a graph showing an example of a potential pattern of an electrostatic latent image.

FIG. 14 is a graph showing a relationship between a toner image portion and a blank portion of a toner image after development.

FIG. 15 is an explanatory diagram illustrating a change state of the cross-sectional pattern of the toner image when the density increases.

FIG. 16 is a diagram for explaining a difference in sensitivity of the density sensor due to a difference in a change state of a sectional pattern of a toner image.

FIG. 17 is a graph showing a relationship between contrast potential and density.

FIG. 18 is a graph showing the relationship between relative humidity and concentration.

[Explanation of symbols]

Reference Signs List 1 photoreceptor, 2 charger, 3 exposure section, 4 toner dispenser, 4a toner tank, 4b agitator, 4
c Dispense roll, 5 developing unit, 5a developing roll, 6 density sensor, 6a light emitting element, 6b light receiving element, 7 transfer unit, 8 cleaning device, 9 static elimination lamp, 10 fixing unit, 11 high voltage generation circuit, 12 laser ROS, 13 Patch pattern generation circuit, 14 image signal source, 15 humidity sensor, 16 arithmetic circuit, 17 motor drive circuit, 18 transfer drum, 19 rotary development device, A recording paper, B development patch, C developer layer, D
Toner, E electrostatic latent image, F image area, G inter-image part, H toner image, L laser beam

Continuation of the front page (56) References JP-A-1-101563 (JP, A) JP-A-1-319054 (JP, A) JP-A-58-30773 (JP, A) JP-A-63-65461 (JP, A) JP-A-3-95569 (JP, A) JP-A-1-232360 (JP, A) JP-A-59-116768 (JP, A) JP-A-56-159671 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/00 G03G 21/00

Claims (3)

(57) [Claims] An image of a non-solid pattern developing patch is formed.
Detected by the concentration control by comparing the detection result and the density reference value
Detecting means for detecting a change affecting development density in an image forming apparatus for performing
And a controller that controls the contrast potential by changing both the dark and light areas.
Trust potential control means, and a contrast potential according to a detection result of the fluctuation detecting means.
Control and the contrast control reference value
Error due to shape change of non-solid pattern due to position change
An image forming apparatus that corrects an image . 2. Developing a non-solid pattern developing patch
Detected by the concentration control by comparing the detection result and the density reference value
Detecting means for detecting a change affecting development density in an image forming apparatus for performing
And a controller that controls the contrast potential by changing both the dark and light areas.
Trust potential control means, and a contrast potential according to a detection result of the fluctuation detecting means.
Control and the contrast control reference value
Error due to shape change of non-solid pattern due to position change
Characterized by adding an offset to compensate for
Image forming device . 3. The image according to claim 1 or claim 2.
In the image forming apparatus, the fluctuation affecting the development density is humidity, fatigue of the developer, or a difference in characteristics of the developer.