JPH05323790A - Image density control method for image forming device - Google Patents

Abstract

PURPOSE:To prevent the overreplenishing of toner caused by reduction in the quantity of the toner stuck to a reference image due to environmental fluctuations, etc., and the scattering of the toner from a developing unit, in a copying machine forming the reference image on a photosensitive body whenever 10 copies are made, detecting the density of the reference image by an optical detector, and controlling the replenishment of the toner to a developing room from a hopper part by the rotation of an agitator, based on the result of the detection. CONSTITUTION:The increasing rate of the density of a toner image is obtained from the variation of the density of the reference image before and after 10 copies made by using the detection value of the density of the reference image by the optical detector 7, and a difference between the quantity of the toner consumed from the developing unit while 10 copies are made, and the quantity of the toner replenished to the developing room by the rotation of the agitator 46, and when the obtained increasing rate becomes a prescribed level or below, the reduction in the density of the reference image is judged by a factor except a toner concentration, and a toner replenishment control level value is changed over to a value so as not to excessively increase the toner concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image density control method for an image forming apparatus such as a copying machine, a facsimile, a printer or the like.

[0002]

2. Description of the Related Art For example, in an image forming apparatus using an electrophotographic system, the image density formed on the electrostatic latent image bearing is maintained at a constant density, and a low contrast character portion of image information can be reproduced well. In addition, it is a requirement to clearly reproduce the background portion to form a high quality image. In order to satisfy this requirement, in an image forming layer equipped with a developing device using a two-component developer consisting of a carrier and a toner,
It is necessary to satisfactorily control the toner concentration (% by weight of toner in the developer).

Therefore, in the field of this type of image forming apparatus, various methods for controlling the toner density in the developing device have been put into practical use and proposed. For example,
In Japanese Patent Laid-Open No. 53-12336, a reference toner image for detecting a specific intermediate density is formed on a part of an electrostatic latent image carrier, the density of this toner image is detected, and based on this density. A method of controlling the toner supply amount of the developing device has been proposed. Further, in Japanese Patent Laid-Open No. 63-34565, in order to control the toner replenishment amount with higher accuracy, the density of the reference toner image and the density of the background portion of the electrostatic latent image carrier on which the reference toner image is not formed. A method has been proposed in which the toner replenishment amount of the developing device is controlled based on the ratio of the detected values of the two. As a device configuration for carrying out these methods, for example, an optical sensor may be added to detect the density of the reference toner image formed on the electrostatic latent image carrier, and a relatively simple configuration. It can be implemented at low cost. These basically control the toner density in the developing device in order to guarantee the image density.

[0004]

However, the amount of developing toner on the electrostatic latent image bearing member, which greatly affects the image density, is not limited to the fluctuation of the toner concentration in the developing device, but also the electrostatic latent image bearing during development. It also depends on changes in the development potential, which is the potential difference between the potential on the body and the potential of the developing electrode member, and environmental changes. Therefore, in the above configuration, even when the cause of the change in the density of the reference toner image is the change in the development potential or the environmental change, the feedback is made to the toner density in the developing device. Therefore, in an image forming apparatus in which the amount of developing toner on the electrostatic latent image carrier changes greatly due to environmental changes, for example,
To ensure the image density, the toner density in the developing device fluctuates greatly, and the toner density becomes too low, causing carrier adhesion to the background, and conversely, the toner density becomes too high and development is performed. There is a risk of causing problems such as toner scattering outside the device.

In order to avoid such a problem, for example, a sensor for monitoring various characteristic values other than the image density such as an environmental sensor or a potential sensor is added, and the cause of the image density change is identified by these sensors, Although it may be possible to feed back to the condition that caused the problem, such a method complicates the control and increases the cost, and is not suitable for a small and inexpensive device.

The present invention has been made in view of the above problems. An object of the present invention is to obtain the toner by determining the change in the toner adhesion amount on the latent image carrier with respect to the toner supply amount of the developing device. By determining whether the control limit of the replenishment control is reached or not, and before a problem occurs due to an abnormal amount of toner in the developing device, switching to proper image density control will cause an abnormal amount of toner. An object of the present invention is to provide a method for controlling the image density of an image forming apparatus, which is capable of preventing defects caused by a large amount and ensuring the image density.

[0007]

In order to achieve the above object, the invention of claim 1 forms a reference latent image on a latent image carrier and develops the reference latent image with a developing device to form a reference. An image density control method for an image forming apparatus, comprising forming a toner image, detecting a density of the reference toner image, comparing a detection value of the reference toner image with a reference value, and setting a toner replenishing operation of the developing device. , The degree of increase in the density of the reference toner image with respect to the difference between the toner replenishment amount of the developing device and the toner consumption amount from the developing device within a predetermined period is calculated. The value is changed to a value corresponding to a relatively small density, and the toner replenishing operation of the developing device is set based on the detected value of the reference toner image.

According to a second aspect of the present invention, a reference latent image is formed on a latent image carrier, the reference latent image is developed by a developing device to form a reference toner image, and the density of the reference toner image is detected. In the image density control method of the image forming apparatus for setting the toner replenishing operation of the developing device based on the detected value of the reference toner image, the toner replenishing amount of the developing device and the toner consumption from the developing device within a predetermined period. The degree of increase in the density of the reference toner image with respect to the difference from the amount is obtained, and when the degree of increase is less than or equal to a predetermined level, the image forming conditions at the time of forming the reference toner image are changed so that the developing potential becomes relatively small. Forming the reference toner image, detecting the density of the reference toner image, and setting the toner replenishing operation of the developing device based on the detected value of the reference toner image.

According to a third aspect of the present invention, a reference latent image is formed on the latent image carrier, the reference latent image is developed by a developing device to form a reference toner image, and the density of the reference toner image is detected. In the image density control method of the image forming apparatus for setting the toner replenishing operation of the developing device based on the detected value of the reference toner image, the toner replenishing amount of the developing device and the toner consumption from the developing device within a predetermined period. The degree of increase in the density of the reference toner image with respect to the difference from the amount is calculated, and when the degree of increase is below a predetermined level, the image forming conditions other than the toner density in the developing device are set so that the image density becomes relatively high. It is characterized by changing to.

According to a fourth aspect of the present invention, in the image density control method of the image forming apparatus according to the first, second or third aspect, the reference toner image, the density detection of the reference toner image, which is performed after the change,
With the setting of the toner replenishing operation of the developing device based on the detected value of the reference toner image, the reference toner image with respect to the difference between the toner replenishing amount of the developing device and the toner consumption amount from the developing device within a predetermined period is set. The feature is that the degree of increase in the density is obtained, and when the degree of increase is equal to or lower than a predetermined level, the shortage of the replenishment toner is notified.

According to a fifth aspect of the present invention, in the image density control method for an image forming apparatus according to the first, second or third aspect, the reference toner image is detected after the change, and the density of the reference toner image is detected.
With the setting of the toner replenishing operation of the developing device based on the detected value of the reference toner image, the reference toner image with respect to the difference between the toner replenishing amount of the developing device and the toner consumption amount from the developing device within a predetermined period is set. If the degree of increase in density is determined and the degree of increase is equal to or higher than a predetermined level, the reference value, the image forming condition when forming the reference toner image, or the image forming condition other than the toner density in the developing device is changed. It is characterized by returning to the previous one.

According to a sixth aspect of the present invention, in the image density control method of the image forming apparatus according to the first, second, third, fourth or fifth aspect of the image forming apparatus for digital writing, the number of pixels to be imaged is counted and predetermined. It is characterized in that the toner consumption amount is obtained based on the counting result of the number of pixels formed in the period.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. FIG. 1 is a schematic configuration diagram of a main part of a laser beam writing type image forming apparatus utilizing the present invention. This embodiment uses a reversal development system that uses a negatively charged organic photoreceptor as an image bearing member and a two-component developer including a negatively charged toner and a carrier as a developer. In FIG. 1, the photoconductor 1 first rotates in the direction of the arrow and is uniformly negatively charged by the charger 2. Next, the laser beam 3 corresponding to the image information is scanned and exposed in the direction orthogonal to the rotation direction of the photoconductor 1. The electrostatic latent image formed on the photoreceptor 1 by this is
It is visualized by the developing device 4. The visible toner image formed on the photoconductor 1 is transferred to the transfer material 6 fed by the registration roller 10 by the transfer charger 5, and then toward the fixing device 11 together with the transfer material 6 separated from the photoconductor 1. It is conveyed and fixed on the transfer material 6 by the fixing device 11. On the other hand, the toner remaining on the photoconductor 1 after the above-mentioned transfer is removed from the photoconductor 1 by the cleaning device 8. After the cleaning, the electric charge remaining on the photoconductor 1 is removed by the discharge light of the lamp 9. After the photoconductor 1 is thus cleaned, the above-mentioned steps are repeated again, and the image forming operation of the next image information is executed. Here, in the image forming area of the photoconductor 1,
The dark portion potential (background potential) VD is set to −850 [v], the exposed portion potential (image portion potential) VL is set to −100 [v], and the exposed portion potential (image portion potential) VL (−10).
0 [v]) and the bias potential VB (−600 [v]) of the developing roller 41 (see FIG. 2) of the developing device 4 VL−VB = 500 [v]. The electrostatic latent image is developed.

The developing device 4 for developing the electrostatic latent image formed on the photoconductor 1 is housed in the developing roller 41 for supplying toner to the photoconductor 1 and the developing device 4 as shown in FIG. Agitating roller 42 for agitating the developed developer, separator 43 for transferring the developer remaining on developing roller 41 toward agitating roller 42 again, developing roller 4
1, a doctor blade 44 that regulates the amount of developer supplied to a predetermined amount of developer, a toner container 45 that stores new toner to be replenished in the developing device 4, and the toner container 4
An agitator 46 for agitating the toner in 5 and replenishing it in the developing device 4 is provided. And the developing roller 4
1 and the like and the developing chamber in which the developer including the toner and the carrier is stored and the toner storage portion 45 are partitioned by a partition plate 47, and the toner in the toner storage portion 45 is partitioned by the rotation of the agitator 46 in the partition plate. A hole 47a for replenishing the developing chamber with the developing chamber is formed.

In this image forming apparatus, in order to control the toner density in the developing device 4 at a portion other than the image forming area of the photoreceptor 1, for example, a reference image patterned as shown in FIG. 12 is formed at a predetermined timing. As the reference image 12, an image pattern which becomes a solid image after the electrostatic latent image of the image information formed on the photoconductor 1 is visualized can be effectively used. In this example, as will be described later, the density of the reference image 12 is detected by an optical detection means having an output characteristic as shown in FIG. Therefore, in order to use the range in which the detection characteristic of the optical detecting means is good, the toner adhesion amount per unit area of the reference image 12 on the photoconductor 1 is 0.3 to 0.6 [mg / cm ² ]. It is desirable that it becomes a degree. Therefore, in this embodiment, the reference image 1
The developing bias VP when forming 2 is about -340
It is set to [v], and the reference image 12 is formed by the potential difference VL−VP = 240 [v] from the exposed portion potential (image portion potential) VL.

The reference image 12 for controlling the toner density, which is formed outside the image forming area of the photoconductor 1, is optically sensed so as to be opposed to the photoconductor 1 as shown in FIG. 3A. Detected by means. As shown in FIG. 3, the optical detecting means is a reflection type density detecting sensor 7 (optical sensor) including a light emitting element 7a such as a light emitting diode having an emission wavelength peak of 950 mm and a light receiving element 7b such as a phototransistor. It is configured. The density detection sensor 7 detects the detection signal voltage V corresponding to the reflectance of the reference image 12.
It is configured to output the detection signal voltage VSG corresponding to the reflectance of the surface of the photoconductor 1 without the SP and the reference image 12.

FIG. 3B shows the relationship between the toner adhesion amount per unit area of the reference image 12 and the output of the density detection sensor 7. Based on this relationship, in the present embodiment, the detection signal voltage VS of the surface of the photoconductor 1 without the reference image 12
The toner density control level to be compared with the output voltage ratio VSP / VSG of G and the detection signal voltage VSP of the reference image 12 is set in advance. Then, the reference image 12 is formed at a predetermined detection timing of the reference image 12, for example, every 10 copies, and the detection signal voltage VSG of the surface of the photoconductor 1 without the reference image 12 and the detection signal voltage VSP of the reference image 12 are set. Of the output voltage ratio VSP / VSG and the toner density control level are compared, and based on the comparison result, it is necessary to replenish the toner to the developing device 4 by rotating the agitator 46 until the next detection timing of the reference image 12. And a toner replenishment condition called a replenishment amount is set. For example, normally, 0.5 / 4.0 is used as the toner density control level, and the output voltage ratio V
When SP / VSG> 0.5 / 4.0, it is determined that toner replenishment is necessary, and conversely, when VSP / VSG ≦ 0.5 / 4.0, it is determined that toner replenishment is unnecessary.

The above construction is basically the same as the conventionally known toner replenishment control method using the reference image 12. In the toner replenishment control method using the reference image 12 as described above, there is a possibility that problems such as toner scattering and carrier adhesion may occur as described in the section of the related art. Hereinafter, this point will be described in detail. 4 (a) to 4 (c)
3 shows a relationship (adhesion amount γ characteristic) between the development potential and the toner adhesion amount in each environment of the image forming apparatus of this embodiment. (A) is low temperature and low humidity, 10 ° C, 20
%, (B) is the laboratory environment (25 ± 3 °
C, 46 ± 4%), (c) is high temperature and high humidity at 27 ° C,
80%, showing the relationship under each environment. In each figure, the results a, b, and c when the toner density is changed by three levels are also shown (a in FIG. 9A: 3.3 [wt].
%], B; 2.295 [wt%], c; 1.53 [wt
%], (B): a; 3.32 [wt%], b; 2.16
5 [wt%], c; 1.335 [wt%], in (c) a;
3.14 [wt%], b; 2.05 [wt%], c; 1.3
6 [wt%]). From this, it can be seen that the adhered amount γ characteristic changes depending on the toner concentration, but changes due to the environmental difference, which is larger than the change width. Figure 4 (d) shows
Development potential when the reference image 12 is formed (240
[V]) the relationship between the toner concentration and the toner adhesion amount (T
C and characteristics) are shown for each environment of a high temperature and high humidity, b normal temperature and normal humidity, and c low temperature and low humidity. From this as well, it can be seen that the variation in the amount of adhesion due to the environment is large. Further, it can be seen that the adhered amount with respect to the toner concentration tends to be saturated in a region where the toner concentration is high. For example, the rate of increase of the adhered amount with respect to the toner concentration is about 3.5 [wt.
%] Or more), the toner concentration is 1.0 [wt%], 0.05 [mg / cm ² ] at high temperature and high humidity, and 0.04 at normal temperature and normal humidity.
[Mg / cm ² ] and about 00.2 [mg / cm ² ] at low temperature and low humidity.

As shown in FIGS. 4 (a) to 4 (d), in the low temperature and low humidity environment, under the condition that the developing potential is low, that is, the toner is hard to be developed, the reference image 1 as described above is obtained.
Even if a relatively large amount of toner is replenished by the toner replenishment control using the detection result of No. 2, it is easily inferred that the control may run away because the toner adhesion amount does not increase so much.

FIGS. 5A to 5F show the control of detecting the density of the reference image 12 and feeding back the toner density to the toner density control level value of 0.5 / 4.
The results of simulating the changes in the toner density and the amount of toner adhered to the image portion when 0 is used in consideration of various factors that are actually expected when the image forming apparatus is used. is there. Here, in general, various fluctuation factors include environmental fluctuations, exposure dose fluctuations, temporal fluctuations (charge potential, photoconductor sensitivity, etc.). Of these, Figure 5
In (a) to (f), the center is -850 [v].
Variation of charging potential VD in the range of 750 to -900 [v], exposure amount E of ± 10% centered on 16 [crg / cm ² ]
Fluctuation, the photoconductor sensitivity E _{1/10 in} the range of 1.00 to 1.35 [Lux · sec] centered on 1.15 [Lux · sec] (even if the predetermined charging potential is attenuated to 1/10 (Indicated by the required amount of light), and three environmental changes of 10 ° C. 20%, the above-mentioned laboratory environment, and 27 ° C. 80% are considered. Then, for example, in the upper limit line of the fluctuation range indicated by reference numeral i in FIG. 5A, the development potential becomes the lowest due to the combination of the fluctuation factors (the charging potential VD is -900.
[V] and the sensitivity E _{1/10 of the} photoconductor is 1.35 [Lux · se
c]), the lower limit line of the fluctuation range indicated by the symbol j has the highest development potential due to the combination of each fluctuation factor (the charging potential VD is −750 [v], and the photoconductor sensitivity E _{1 / 10} indicates 1.00 [Lux · sec]). From the simulation results shown in FIGS. 5A to 5C,
The toner concentration fluctuates in the range of 1.1 to 5.8 [wt%], and the toner adhesion amount in the image area is 0.65 to 0.55 from the simulation results shown in FIGS. 0.
It is estimated to fluctuate within the range of 85 [mg / cm ² ]. (Hereinafter, blank space) In the case of the present image forming apparatus, the proper range of the toner density is 1.0 to 4.0 in which no abnormality such as carrier adhesion and toner scattering occurs.
[Wt%], the optimum range is 1.5 to 3.0 [wt%], so according to the above simulation, as expected,
In a low-temperature and low-humidity environment, the toner density becomes abnormally high under the condition that the developing potential is low (In the case of the image forming apparatus, the proper range of the toner adhesion amount on the image portion is 0.6 to
It is 0.9 [mg / cm ² ], which is sufficiently satisfactory. ).

6A to 6F show toner density control level values VSP / VSG in the above simulation.
= 0.5 / 4.0 instead of the toner density control level value VS
The results of similar simulations using P / VSG = 0.8 / 4.0 are shown. Various variation factors here are the same as those in the above simulation. This Figure 6
From the simulation results shown in (a) to (c), the toner concentration varies in the range of 0.9 to 4.0 [wt%],
Further, from the simulation results shown in FIGS. 6D to 6F, the toner adhesion amount of the image portion is 0.5 to 0.7 [mg].
/ cm ² ]. Thus, the toner density control level value VSP / VSG = 0.8 / 4.
6 is different from the case of using the toner density control level value VSP / VSG = 0.5 / 4.0 in FIGS. 5A to 5F when 0 is used. As can be seen from f), under the conditions of high temperature and high humidity and high development potential, that is, under the condition that the toner is easily developed, the toner concentration becomes low and carrier adhesion occurs, or the toner adhesion amount decreases and image density becomes insufficient. Expected to do. As described above, the toner replenishment control method using the reference image 12 may cause problems such as toner scattering and carrier adhesion as described in the section of the related art.

Therefore, in the embodiment according to the first aspect of the present invention, normally, the toner concentration does not abnormally decrease due to various fluctuation factors as in the simulations of FIGS. 5A to 5F. The toner replenishment control is performed by using the density control level value, for example, VSP / VSG = 0.5 / 4.0, and the toner density is abnormal due to the control using the toner density control level value due to the variation of various fluctuation factors. At the time when there is a fear of an increase, as in the simulations of FIGS. 6A to 6F, a toner density control level value that does not cause an abnormal increase in toner density due to fluctuations of various fluctuation factors, for example, VSP / VSG = 0.8 / 4.
The toner supply control is performed by switching to 0.

A more specific description will be given below. The timing of switching the toner concentration control level value is obtained by calculating the toner image density increase rate (toner adhesion amount increase rate) with respect to the toner increase amount in the developing chamber. Here, the toner increase amount in the developing chamber is a difference between the toner amount replenished in the developing chamber by the rotation of the agitator 46 (toner replenishment amount) and the toner amount consumed in the developing chamber by development (toner consumption amount). The toner supply amount into the developing chamber is, for example,
Since the toner supply amount to the developing chamber per one rotation of the agitator 46 is almost constant, it can be obtained by counting the number of rotations of the agitator 46.
FIG. 7A shows the toner replenishment amount per one rotation (one toner replenishment operation) of the agitator 46 with respect to the remaining amount of toner in the toner container in the image forming apparatus. Except when the toner container is almost 100% full of toner and when the toner is running low
It can be seen that about 0.1 [g] of toner is supplied per revolution of the agitator 46. From this, when the signal is fed back to the toner density by the image density detection, how many times the toner replenishing operation is performed (how many times the agitator 46 is rotated) is stored.
By multiplying the replenishment amount (0.1 g) per time, it is possible to roughly estimate how much toner has been replenished before the next image density detection. Further, the toner consumption amount from the developing chamber can be estimated by, for example, assuming the average toner consumption amount per one image, and the number of image formation times the average toner consumption amount. Therefore, the increase amount of toner in the developing device can be obtained from the toner supply amount-toner consumption amount. Then, the toner image density increase rate is calculated by checking how much the detected density of the reference image changes with respect to this toner increase amount compared to the previous time. When the toner image density increase rate calculated in this way becomes equal to or lower than a preset predetermined level, the toner density control level value is switched.

For example, when the toner density control level value VSP / VSG = 0.5 / 4.0 shown in FIGS. 5A to 5F is used, if the developing potential is lowered due to low temperature and low humidity, the toner is reduced. The rate of increase in image density decreases. Here, according to the results shown in FIG. 4D, when the M / A change rate with respect to the toner concentration is less than 0.02 [mg / cm ² / wt%], FIGS. The toner density control level value VSP / VSG = 0.8 / 4.0 shown in FIG. As a result, an abnormal increase in toner density can be suppressed, and good images can be stably obtained. Here, the developer capacity is 100 [g] and the toner is 0.1
Replenishment of [g] corresponds to an increase in toner density of 0.1%, and the relationship between the toner adhesion amount and the image density is shown in FIG.
It is as shown in (b). Further, in this case, the toner amount consumed for forming one image is assumed to be 0.07 [g / cm ² ] as the average toner consumption amount. At this time, the toner density and the amount of toner adhering to the image portion are as shown in FIGS.
Together, toner concentration TC 1.0 to 4.0 [wt%],
Toner adhesion amount on image area M / A = 0.6 to 0.8 [mg / c
m ² ].

FIG. 8 is a flow chart of a specific example of the above toner replenishment control. First, a reference image is formed immediately after the main switch is turned on, and the amount of reflected light at the reference image portion and the background portion of the photoconductor is detected (steps 1, 2, 3). Next, the ratio of the output values of both detections is calculated and stored in the register R _1, and the first reference value 0.5 / 4.
0 is stored in the register R (steps 4 and 5). Then, the contents of both registers R ₁ and R are compared (step 6). If it is determined that the output value ratio is larger, that is, if the density is insufficient, the toner replenishing operation is set to K rotations of the agitator during the subsequent 10 copy operations. If the ratio of the output values is equal to or less than the reference value, that is, if it is determined that the density is sufficient, the toner replenishing operation is set as the setting (step 7). The number of rotations of the agitator is set to 0 (step 8). The rotation of the agitator during the operation of copying 10 sheets may be performed in a dispersed manner for each copy, or if possible, the rotation of the agitator K times may be performed along with the first copy of the first sheet. You may complete it. Further, this K times may be a variable that changes depending on the difference between the output value ratio and the reference value, for example.

Next, after a manual copy start by pressing a copy start button (not shown) or an automatic copy start for the second and subsequent copies of continuous copy,
Whether or not it is the timing to form the reference image is determined depending on whether or not the copy is the multiple of 10, such as 10 or 20, for example (steps 9 and 10). If it is determined that it is not the timing to form the reference image, the next copy start is awaited. On the contrary, when it is determined that it is the timing to form the reference image, the reference image is formed, and the reflected light amount of the reference image portion and the background portion of the photoconductor are detected as in the case immediately after the main stitch is inserted. The ratio of the output values is calculated and stored in the register R ₁ (step 1
1, 12, 13).

Then, the ratio of both output values and the reference value stored in the register R are compared (step 14). here,
When the ratio of the output values is equal to or less than the reference value, that is, when it is determined that the density is sufficient, the number of rotations of the agitator during the copying operation period of the subsequent 10 sheets is set to 0, and the content of the register R ₁ is set. Updated the data of the ratio of the detection value related to the latest detection,
Wait for the next copy start (steps 15 and 16). On the contrary, when it is determined that the output value ratio is larger, that is, the density is insufficient, the toner replenishment amount replenished in the developing device after the immediately preceding reference image forming timing is calculated, and the calculation result is calculated. Then, the toner image density increase rate is calculated from the toner consumption amount after the immediately preceding reference image forming timing (steps 17 and 18).

Then, it is judged whether or not the toner image density increase rate is larger than a predetermined value 0.02 (step 1).
9). Here, if it is determined that the density of the reference image is lower than the predetermined value, that is, the cause of the lowering of the density of the reference image is mainly the lowering of the toner density in the developing device, the agitator of the subsequent 10-sheet copying operation is performed. The number of rotations is set to K times, the content of the register R ₁ is updated to the data of the ratio of the detection value related to the latest detection, and the next copy start is waited (steps 20 and 1).
6). On the other hand, if it is determined that the toner density in the developing device may be abnormally increased due to fluctuations of various fluctuation factors or less, that is, the contents of the register R may be set to an image density lower than the first reference value. Second standard value corresponding to 0.8 / 0.4
(Step 21).

Then, it is again judged whether or not the ratio of the detection values relating to the latest detection stored in the register R ₂ is larger than the second reference value (step 22). Here, if it is determined that the density is higher than the second reference value, that is, the density of the reference image relating to the latest detection is lower than the lower second comparative density corresponding to the second reference value, the subsequent 10 The number of rotations of the agitator is set to K times during the copy operation of the sheets, the content of the register R is switched to the first reference value,
The content of the register R ₁ is updated to the data of the ratio of the detection value related to the latest detection, and the next copy start is waited (step 2
3, 24, 16). On the contrary, when it is determined that the value is less than or equal to the second reference value, the number of rotations of the agitator during the subsequent 10 copy operations is set to 0, and the content of the register R is switched to the first reference value. , The content of the register R ₁ is updated to the data of the ratio of the detection value related to the latest detection, and the next copy start is waited (steps 25, 24, 16).

Next, an embodiment according to the invention of claim 2 will be described. In the present embodiment, the toner image density increase rate with respect to the toner replenishment amount is obtained as described above, and when the toner image density increase rate becomes equal to or lower than a predetermined level, the forming condition of the reference image 12 is changed and the reference image is changed again. The image 12 is formed, and the toner density is detected and the toner replenishment condition is set based on the detected density, thereby preventing the toner density in the developing chamber from rising abnormally. This is because instead of switching the toner density control level value as in the above embodiment, the toner density fluctuation and the toner adhesion amount fluctuation on the image portion can be changed, for example, by changing the formation condition of the reference image 12. 5 (a) to (f) to FIG.
This is because it is possible to perform the same thing as changing to those shown in (a) to (f). For example, in FIGS. 9A to 9F, only the developing bias VP at the time of forming the reference image 12 is −34 as compared with the conditions of FIGS. 5A to 5F.
FIG. 7 shows simulation results of toner density and toner adhesion amount of an image portion when changing from 0 [v] to −390 [v]. From these, it can be seen that the same simulation result as in FIGS. 6A to 6F can be obtained when the predicted control value of the toner density control level value is VSP / VSG = 0.8 / 4.0. As a specific example of the present embodiment, for example, normally, a toner density control level value that does not cause an abnormal decrease in toner density due to various fluctuation factors, as in the simulations of FIGS. 5A to 5F, for example, The toner replenishment control is performed using VSP / VSG = 0.5 / 4.0, and the control using this toner concentration control level value due to fluctuations of various fluctuation factors may cause an abnormal increase in toner density. At this point, as shown in the simulations of FIGS. 9A to 9F, the developing bias VP at the time of forming the reference image is changed to −390 [v] so that the toner density does not abnormally increase even if the seed variation factor changes. Toner replenishment control is performed. As a result, the toner density and the toner adhesion amount in the image area are shown in FIGS. 5 and 9 together, the toner density TC is 1.0 to 4.0 [wt%], and the toner adhesion amount in the image area M / A = 0.6. It was controlled to ˜0.8 [mg / cm ² ].

FIG. 10 is a flow chart of a specific example of the above toner replenishment control. Also in this example, the toner replenishing operation is set using the reference image immediately after the main switch is turned on, and thereafter, the reference image is used every time the copy becomes a multiple of 10 such as 10 sheets or 20 sheets. The basic point of setting the toner replenishing operation is the same as the control of the above-described embodiment shown in FIG. 8, and the corresponding steps are designated by the same reference numerals. This control differs from the control in FIG. 8 in the following points. That is, in the control of FIG. 8, in order to switch the toner density control level value, processing for switching the toner density control level value using the register R (steps 5, 21, 24 in FIG. 8) is performed. On the other hand, in this control, the development potential V at the time of forming the reference image
In order to switch P, the processing for switching the development potential VP using the register VP (A in FIG. 10).
1, A2, A6). Further, in the control of FIG. 8, when the toner concentration control level value is switched, the ratio of the latest detected reference image and the output value of the background portion of the photoconductor is compared with the reference value (steps 21 and 22 in FIG. 8). In contrast, in this control, after the development potential VP is switched,
Again, using the development potential VP after switching, the reference image 12 is formed, the amount of reflected light from the reference image and the background portion of the photoconductor is detected, and the output values of both detections are stored in the register R ₁ , and both outputs are output. The ratio of the values and the reference value (0.5 / 0.4 remain unchanged) are compared (steps A3, A4 in FIG. 10).
A5).

Next, an embodiment according to the invention of claim 3 will be described. In the present embodiment, the toner image density increase rate with respect to the toner replenishment amount is obtained as described above, and when the toner image density increase rate becomes equal to or lower than a predetermined level, toner is attached to the image portion instead of toner replenishment. The normal image forming conditions other than the toner density are switched so as to increase the amount to improve the density of the image area, thereby preventing the toner density in the developing chamber from rising abnormally.

FIG. 11 is a flowchart of a specific example of control for switching the developing bias VB during normal image formation in order to improve the amount of toner attached to the image portion. Also in this example, the toner replenishing operation using the reference image is set immediately after the main switch is turned on, and then the copy operation is performed, for example, 10 times.
The basic point of setting the toner replenishment operation using the reference image every time the number of sheets is a multiple of 10 such as 20 sheets is similar to the control of the above-described embodiment shown in FIG. The same steps are denoted by the same reference numerals. This control differs from the control shown in FIG. 8 in the following points. That is, FIG.
In order to switch the toner density control level value in the control of step 1, processing for switching the toner density control level value using the register R (steps 5, 21, 24 in FIG. 8)
On the other hand, in this control, the register V is used to switch the developing potential VB during normal image formation.
Processing for switching the development potential VB using B (B1 and B3 in FIG. 10) is performed. Further, in the control of FIG. 8, at the time of switching the toner density control level value, the ratio of the latest detected reference image and the output value of the photoconductor background portion is compared with the reference value after switching, and based on the comparison result. While the toner replenishing operation is set (steps 21, 22, 23 and 25 in FIG. 8), the present control detects the latest reference image and the background portion of the photoconductor when switching the development potential VB. Regardless of the ratio of output values,
The toner supply frequency is set to 0 (steps 19 and 25 in FIG. 11).

Next, an embodiment according to the invention of claim 4 will be described. The present embodiment is characterized by the toner end detection method applicable to each of the embodiments according to the inventions of claims 1 to 3. That is, as described above, the toner image density increase rate with respect to the toner replenishment amount is lower than the predetermined level, and therefore, after the toner density control level value or the image forming condition at the time of the standard image formation or the normal image formation is switched, When the toner image density increase rate falls below a predetermined level continuously again, it is determined that the toner is exhausted, and the toner end display is performed.

FIG. 12 and FIG. 13 are flow charts of specific control in which this toner end detection method is applied to the specific example of the toner replenishment control of FIG. 8 described above. First, after detecting that the toner image density increase rate is below a predetermined level after the main switch is turned on, the toner density control level value is switched, and the ratio of the latest detected reference image and the output value of the background portion of the photoconductor is detected. As a result of comparing with the reference value after switching,
Until it is determined that the replenishment operation is necessary and the number of times of toner replenishment is set to K times, it is the same as the control in FIG. 8, and the same reference numerals are given to each step. This control is different from the control shown in FIG.
In the control of FIG. 8, the toner density control level value is first switched after the main switch is turned on, and the result of comparing the detected latest reference image and the output value ratio of the background portion of the photoconductor with the reference value after switching, When it is determined that the replenishment operation is necessary and the number of times of toner replenishment is set to K times, the toner concentration control level value is immediately returned to the first reference value (step 2 in FIG. 8).
1, 22, 23, 24), in this control, in this case, the flow shown in FIG. 13 is entered (step 2 in FIG. 12).
3 to step C1) in FIG. 13, the following operation is performed. That is, also in the flow shown in FIG. 13, thereafter, the reference image is formed and compared with the reference value every time the copy becomes a multiple of 10, such as 10 or 20, for example. However, this reference value is the second reference value VSP / VSG = 0.8 / 4.
0 is used. Then, this second reference value VSP / VSG =
Whether the toner density is judged to be sufficient by comparison with 0.8 / 4.0 (N in step C7 in FIG. 13), or the toner image density increase rate is higher than the predetermined level (0.02) Unless it is determined that the agitator has become smaller, the number of rotations of the agitator during the subsequent 10 copy operations is set to K (steps C1, C2, C3, C4, C5, C in FIG. 13).
6, C7, C9, C10, C11, C12). And
If it is determined that the toner density is sufficient by comparison with the second reference value, after setting the toner replenishment count 0,
12 to return the toner density control level value to the first reference value (steps C7, C8 in FIG. 13, FIG. 12).
Step 24). As described above, when it is determined that the toner image density increase rate is smaller than the predetermined level (0.02) before it is determined that the toner density is sufficient by the comparison with the second reference value, the toner is When it is determined that the toner has run out, the toner end display is performed (step C11 in FIG. 13,
C13).

Next, an embodiment according to the invention of claim 5 will be described. This embodiment relates to a modification of each embodiment according to the inventions of claims 1 to 3. In the specific example of the embodiment of the invention of claim 1 or 2, as described above, the toner image density increase rate with respect to the toner replenishment amount falls below a predetermined level, and the toner density control level value or the image forming condition at the time of forming the reference image is formed. In the case of switching, the original toner density control level value or the like is returned before the toner image density increase rate is determined at the next reference image forming timing. That is, in the specific example of claim 1 (FIG. 8), immediately after the toner replenishing operation is set by using the toner density control level value after switching, and in the specific example of FIG. 2 (FIG. 10), the development bias after switching is set. Immediately after the setting of the toner replenishing operation using the reference image formed by the VP, the original toner density control level value is restored (step 24 in FIG. 8, FIG. 10).
Step A6). Further, in the specific example (FIG. 11) of the embodiment of the invention of claim 3, as described above, the toner image density increase rate with respect to the toner replenishment amount is lower than a predetermined level, and the image forming condition at the time of normal image formation is set. When the switching is performed, the original image forming condition may be returned to before the determination of the toner image density increase rate at the next reference image forming timing (steps 14, 15, B1 in FIG. 11). Also, when the original image forming condition is restored after the toner image density increase rate is determined (steps 19, 20, 1 in FIG. 11).
6, B1), the comparison value to be compared with the toner image density increase rate is
Normal image forming conditions (developing bias VB = -600
Comparative value (0.02) for determining whether or not it is necessary to switch from (v)) to the image forming condition (developing bias VB = -650 [v]) when there is a risk of abnormal increase in toner density
Is the same as. Therefore, these specific examples (Fig. 8, 1
0, 11), the control response may be poor, or the timing for returning to the original toner concentration control level value may not be appropriate. Therefore, in the present embodiment, when the toner image density increase rate with respect to the toner replenishment amount falls below a predetermined level and the toner density control level value or the image forming condition at the time of reference image formation is switched, the toner image density increase rate is changed thereafter. The obtained toner density control level value and the like are compared with a comparison value for determining whether to return to the original toner density control level value or the like, and based on the result, the original toner density control level value or the like is returned. In the image forming apparatus according to the present exemplary embodiment, as the upper limit value of the toner image density change rate, the toner density of 1.0 is obtained from FIG.
A suitable change rate is 0.05 [mg / cm ² ] of toner adhesion amount per [wt%], and a stable image is obtained by using this value as the above comparison value.

FIGS. 14 and 15 are flow charts of control in which this control is applied to the specific example of the toner replenishment control of FIG. 8 described above. Detecting that the toner image density increase rate is below a predetermined level, switching the toner density control level value, and comparing the latest detected reference image and the output value of the background of the photoconductor to the reference value after switching. As a result of comparing
Set replenishment operation (step 23 or step 25)
Up to the above, the control is the same as that of FIG. 8, and the same reference numerals are given to each step. This control differs from the control in FIG. 8 in that the toner concentration control level value is immediately returned to the first reference value after the replenishment operation is set in the control in FIG. 8 (FIG. 8).
In contrast to the steps 23, 24, and 25) in the middle, in the present control, the following operation is performed after the setting of this replenishing operation. That is,
First, the content of the register R ₁ is updated to the data of the ratio of the detection values related to the latest detection (step D1 in FIG. 15), and thereafter, 10 copies such as 10 copies or 20 copies are performed.
The calculation of the toner image density increase rate using the reference image and the comparison with the above-mentioned comparison value (0.05) are performed every time when the number of sheets becomes a multiple of (steps D2, D3, D4, D5, D6 in FIG. 15).
D7, D8, D9). Unless it is determined in this comparison that the toner image density increase rate is larger than the comparison value, that is, the toner image density increase rate exceeds the upper limit of the toner image density (see FIG. 15).
As long as it is N in step D14, the toner replenishing operation is set using the second reference value which is the toner density control level after switching (steps D10 and D1 in FIG. 15).
1, D1, D12). When it is determined that the toner image density increase rate is larger than the comparison value in comparison with this comparison value, that is, the toner image density increase rate exceeds the upper limit value of the toner image density, the toner density control level value is set to the first reference value. Back to the value,
The toner supply operation is set using this first reference value, and the process proceeds to step 16 in FIG. 14 (steps D14, D15, D16 in FIG. 15).

Next, an embodiment of the invention of claim 6 will be described. In the present embodiment, the toner consumption amount required to obtain the toner image density increase rate in the embodiments of claims 1 to 5 is obtained more precisely. As described above, in each of the above-described embodiments, the toner increase amount in the developing chamber is expressed by (number of replenishment operations × toner replenishment amount per replenishment operation) − (number of image formation times × average toner consumption amount per image). Seeking
Here, since the average toner consumption amount per image is largely different depending on the output image, a general average value (average 0.07 [g / sheet] per sheet in each of the above examples) was assumed. .. In this embodiment, the number of pixels (dots) to be imaged is counted according to the image information, and the toner consumption amount is calculated by (the image formation pixel number × toner consumption amount per pixel). That is, the toner replenishment amount is accurately obtained by (number of replenishment operations × toner replenishment amount per replenishment operation) − (number of image forming pixels × toner consumption amount per pixel). As a result, the toner replenishment control can be performed more accurately. In the image forming apparatus using the digital writing system, various techniques are known for calculating the toner consumption amount by counting the image data by a pipe or the like. Therefore, the toner consumption amount is also calculated in the present embodiment. These techniques can be used.

Although each of the above embodiments uses a two-component developer, the present invention can be applied to an image forming method using a one-component developer. A developing device using a one-component developer is provided with a developing chamber containing a developing roller and the like, and a hopper portion 45 containing toner to be supplied to the developing chamber, like the developing device 4 in FIG. It is known to supply toner from 45 to the developing chamber. The amount of toner carried by the developing roller 41 in the developing chamber 41 and conveyed to the area facing the photoconductor 1 is controlled, and the amount of toner supplied from the hopper 45 to the developing chamber is carried by the developing roller 41. When controlling the charge amount (Q / M) of the toner to be generated, the reference image 12 is formed on the photoconductor, and the toner replenishment from the hopper unit 45 to the developing chamber is controlled based on the detection result. Is effective. Even when such a one-component developer is used, the toner adhesion amount on the image portion changes due to various factors such as the environment. Therefore, when the toner adhesion amount to the photoconductor is changing mainly due to the variation factors such as the environment, it is attempted to control the toner adhesion amount to the photoconductor only by the toner replenishment control from the hopper unit 45. Due to excessive toner supply to the developing chamber, problems such as toner scattering from the developing device may occur. Therefore, in the image forming method using the one-component developer, which forms the reference image 12 on the photoconductor and controls the toner replenishment from the hopper unit 45 to the developing chamber based on the detection result, the image forming method may also be used. Similarly to the embodiment of the invention described above, the toner image density increase rate (the rate of increase in toner image density with respect to the amount of toner supplied to the developing chamber) is calculated. It is effective to switch the control reference level of the toner replenishment control, assuming that the toner adhesion amount varies due to the factor. Further, the bias applied to a toner supply roller that supplies toner to the developing roller 42 while frictionally charging it or a blade that frictionally charges the toner by frictionally charging the toner on the developing roller 42 to form a thin toner layer is controlled. In the case of controlling the image density by controlling the layer thickness of the one-component toner layer carried on the developing roller 42 and the toner Q / M, the density of the reference image is detected to obtain the toner image density increase rate. The bias may be controlled based on the above.

[0040]

As described above, according to the present invention, only the sensor for detecting the toner adhesion amount (image density) on the latent image carrier can be used.
It is possible to properly control the toner concentration and the toner adhesion amount with a simple and inexpensive configuration that does not use other environment sensors, potential sensors, or the like. In particular, according to the inventions of claims 1 to 3, even if there are environmental fluctuations, potential fluctuations, and the like, it is possible to reduce carrier adhesion, toner scattering, etc. due to abnormal toner density, and to stabilize the output image with high quality. You can control the image quality. According to the invention of claim 4, it is possible to inform the user of the toner end state accurately and promptly, and it is possible to prevent defective image quality and malfunction due to the toner end. Further, according to the invention of claim 5 or 6, it is possible to control the toner concentration and the toner adhesion amount in an appropriate range with higher accuracy, and always respond to various usages of the user with stable and high quality. You can control the image quality.

[Brief description of drawings]

FIG. 1 is a front view showing a schematic configuration of a copying machine to which the present invention can be applied.

FIG. 2 is an enlarged view of a developing device of the copying machine.

FIG. 3A is an explanatory diagram of reference image detection of the copying machine,
FIG. 7B is a characteristic diagram of the output of the sensor used for detecting the reference image.

4A to 4C are toner adhesion amounts γ of the copying machine.
FIG. 3D is a characteristic diagram showing the relationship between the toner concentration and the toner adhesion amount in the developing device of the copying machine.

5A to 5C are characteristic diagrams showing variations in toner concentration when toner replenishment control is performed at a certain toner concentration control level, and FIGS. 5D to 5F show the same toner replenishment control. FIG. 6 is a characteristic diagram showing a variation in toner adhesion amount in the case.

6A to 6C are characteristic diagrams showing variations in toner concentration when toner replenishment control is performed at other toner concentration control levels, and FIGS. 6D to 6F are the same toner replenishment control. FIG. 4 is a characteristic diagram showing a variation in toner adhesion amount when the toner is attached.

FIG. 7A is a characteristic diagram showing a toner replenishing ability by an agitator of a developing device of the copying machine, and FIG. 7B is a characteristic diagram showing a relationship between the toner adhesion amount and the image density of the copying machine.

FIG. 8 is a flowchart of a control example of the embodiment of the invention of claim 1;

9A to 9C are characteristic diagrams showing variations in toner concentration when toner replenishment control is performed using a reference image formed with a developing bias having a certain value, and FIGS. FIG. 6 is a characteristic diagram showing a variation in toner adhesion amount when the toner replenishment control is performed.

FIG. 10 is a flow chart of a control example of the embodiment of the invention of claim 2;

FIG. 11 is a flowchart of a control example of the embodiment of the invention of claim 3;

FIG. 12 is a part of a flowchart of a control example of the embodiment of the invention of claim 4;

FIG. 13 is another part of the flowchart of the control example of the embodiment of the invention of claim 4;

FIG. 14 is a part of a flowchart of a control example of the embodiment of the invention of claim 5;

FIG. 15 is another part of the flowchart of the control example of the embodiment of the invention of claim 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 4 Developing device 7 Optical detector 41 Developing roller 45 Hopper part 47 Agitator

Claims (6)

[Claims] 1. A reference latent image is formed on a latent image carrier, the reference latent image is developed by a developing device to form a reference toner image, the density of the reference toner image is detected, and the reference toner image is detected. In a method of controlling the image density of an image forming apparatus, in which the toner replenishing operation of the developing device is set by comparing the detection value of the developing device with the reference value, the toner replenishing amount of the developing device and the toner consumption from the developing device within a predetermined period The degree of increase in the density of the reference toner image with respect to the difference from the amount is obtained, and when the degree of increase is below a predetermined level, the reference value is changed to a value corresponding to a relatively small density, and the reference toner image is detected. An image density control method for an image forming apparatus, wherein a toner replenishing operation of a developing device is set based on a value. 2. A reference latent image is formed on a latent image carrier, the reference latent image is developed by a developing device to form a reference toner image, the density of the reference toner image is detected, and the reference toner image is detected. In the image density control method of the image forming apparatus, which sets the toner replenishing operation of the developing device based on the detection value of, the difference between the toner replenishing amount of the developing device and the toner consuming amount from the developing device within a predetermined period is calculated. When the degree of increase in the density of the reference toner image is obtained, and when the degree of increase is less than or equal to a predetermined level, the image forming condition at the time of forming the reference toner image is changed so that the developing potential becomes relatively small. Formation, density detection of the reference toner image, and
An image density control method for an image forming apparatus, wherein a toner replenishing operation of a developing device is set based on a detected value of the reference toner image. 3. A reference latent image is formed on a latent image carrier, the reference latent image is developed by a developing device to form a reference toner image, the density of the reference toner image is detected, and the reference toner image is detected. In the image density control method of the image forming apparatus, which sets the toner replenishing operation of the developing device based on the detection value of, the difference between the toner replenishing amount of the developing device and the toner consuming amount from the developing device within a predetermined period is calculated. When the degree of increase in the density of the reference toner image is obtained, and when the degree of increase is less than or equal to a predetermined level, the image forming conditions other than the toner density in the developing device may be changed so that the image density becomes relatively high. A characteristic image density control method for an image forming apparatus. 4. The developing device within a predetermined period according to the setting of the reference toner image after the change, the density detection of the reference toner image, and the toner replenishing operation of the developing device based on the detected value of the reference toner image. The degree of increase in the density of the reference toner image with respect to the difference between the toner replenishment amount and the toner consumption amount from the developing device is calculated, and when the degree of increase is below a predetermined level, the shortage of the replenishment toner is notified. An image density control method for an image forming apparatus according to claim 1, 2 or 3. 5. The developing device within a predetermined period according to the setting of the reference toner image after the change, the density detection of the reference toner image, and the toner replenishing operation of the developing device based on the detected value of the reference toner image. The degree of increase in the density of the reference toner image with respect to the difference between the toner replenishment amount and the amount of toner consumed from the developing device is calculated, and when the increase degree is equal to or higher than a predetermined level, the reference value and the reference toner image are formed. 2. The image forming conditions according to claim 1 or the image forming conditions other than the toner density in the developing device are returned to those before the change.
2 or 3 is an image density control method for an image forming apparatus. 6. An image forming apparatus for digital writing, wherein the number of pixels to be imaged is counted, and the toner consumption amount is obtained based on the counting result of the number of pixels imaged within a predetermined period. Item 1. An image density control method for an image forming apparatus according to item 1, 2, 3, 4 or 5.