JP2000305328A - Image forming device - Google Patents

Abstract

(57) [Problem] To provide an image forming apparatus capable of preventing a decrease in image density. SOLUTION: The supply of toner to the developing device is controlled based on a result of comparing a detected toner concentration in the developing device with a predetermined reference value VTref. Then, based on the detected image density VSP of the reference image formed on the photoconductor and the detected toner density VT in the developing device (steps S5 and S6), the reference value VT is obtained.
ref is corrected (steps S10 and S18). When the reference image has been formed (step S2), the reference value VTref after the previous correction (steps S10 and S18) is changed to a preset default value of the reference value VTref (step S3).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art In such an image forming apparatus, since the toner density in a developer affects the image density, it is desirable to keep the toner density constant. It largely depends on environmental conditions such as temperature and humidity, development conditions, and the like. Therefore, usually, a reference image is formed on the photoconductor by a development potential that is a difference between a predetermined surface potential of the photoconductor and a development bias,
This reference image is detected by a reflective photosensor called a P sensor, and based on the detection result, the control level of a magnetic permeability sensor called a T sensor provided in the developing device is corrected, and the target T sensor is corrected. A technique for obtaining a stable image by determining a toner density as an output value is known.

In this case, as shown in FIG. 7, the control point of the P sensor is set at a developing potential of 400 V and the output value ratio vs.
p / vsg = 0.1 (Vsp: P sensor output value of reference image, vsg:
Assuming that the P sensor output value at the non-image forming portion of the photoconductor is used, when the developer is not deteriorated and has a charging ability, a developing potential -ID (arrow A in FIG. 7) is used. An image density) curve is obtained, and a target image density is obtained. However, when the developer deteriorates over time and the charging ability decreases, a potential-ID curve as shown by an arrow B in FIG. 7 results, and a target image density cannot be obtained. Therefore, conventionally, a threshold value is provided for the output of the T sensor, and the output value is controlled so that the toner concentration does not fall below a predetermined toner concentration TC.

[0004] This is performed, for example, as follows.
That is, at each image forming operation, the toner concentration in the developing device is detected by the T sensor, and the toner supply amount is controlled using the output value VT as a control reference value. A reference image is formed on the photoreceptor every time a predetermined number of images are formed, the image density is detected by a P sensor, and a correction amount ΔVT of the control reference value VTref is calculated based on the output value. Then, the correction amount ΔVT and the output value of the T sensor when the reference image is created
The control target value VTref is determined by VT and VTref = VT + ΔVT, and when the corrected control target value is smaller than the threshold, the control target value VTref is set as a corrected control value. If the corrected control value is larger than the threshold value, the threshold value is set and used for toner density control until the next reference image formation.

[0005]

However, in the prior art, as shown in FIG. 8, if the image forming apparatus is not used for a long time and left in a high-temperature and high-humidity environment (eg, during a summer vacation). Before and after leaving, the output value of the T sensor is detected to be a high value at the start of the image forming operation, and if this value is used as the detection output value, the toner concentration TC detected by the T sensor becomes low. I will. It has been found that the cause of the increase in the output value VT value of the T sensor due to being left is that the bulk density of the developer has changed. Even if such fluctuations can be corrected initially by the detection output value of the P sensor, if the toner is stirred for about 5 minutes, the output value VT value of the T sensor returns to the normal value. However, there is a problem that the image density is reduced without supplying toner.

An object of the present invention is to provide an image forming apparatus capable of preventing a reduction in image density.

[0007]

According to the first aspect of the present invention, there is provided an exposure apparatus for forming an electrostatic latent image on a photoreceptor, a developing apparatus for developing the formed electrostatic latent image with toner, A replenishing device for replenishing toner to the developing device, a toner concentration sensor for detecting a toner concentration in the developing device, and controlling the replenishing device based on a result of comparing the detected toner concentration with a predetermined reference value. Replenishment control means, reference image forming means for controlling the exposure device and the developing device to form a reference image from a toner image, an image density sensor for detecting the image density of the reference image, Correction means for correcting the reference value based on the detected toner density; a stirring device for stirring the toner in the developing device; and a reference value after the previous correction when the reference image is formed. And default setting means for changing the default value of the reference value set in advance, an image forming apparatus includes a.

Accordingly, when the reference image is formed again on the photoreceptor, the corrected new reference value is changed to a preset default value for the reference value, so that toner agitation is performed. Accordingly, it is possible to cope with the return of the output value of the toner density sensor to a normal value, and it is possible to prevent a decrease in image density.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the correction means sets the correction amount of the reference value in the direction of decreasing the toner density to be less than the sensitivity of the toner density sensor.

Therefore, it is possible to prevent a decrease in image density due to excessive correction.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the image forming apparatus 1 of the present embodiment is configured such that a photoconductor 2 is rotatable, and a charger 3 that charges the photoconductor 2 in order around the photoconductor 2. An exposure device 4 for exposing the photoreceptor 2, a developing device 6 having a toner replenishing roller 5 as a replenishing device, and a T sensor 7 as a toner density sensor for detecting the toner density in the developing device 6. Is provided.
Further, behind the developing device 6, a paper feeding device 8 for transporting the transfer paper to the photoconductor 2 and a toner image formed on the photoconductor 2 are transferred to the transfer paper, and thereafter, the transfer paper is separated from the photoconductor 2. And a P sensor 10 serving as an image density sensor for forming a reference image for detecting image density on the photoconductor 2 and detecting a toner image density (toner adhesion amount) on the photoconductor 2. And a cleaning device 11 are provided. Further, the developing device 6 is provided with a stirring device (not shown) for stirring the developer therein.

FIG. 2 is a block diagram showing the electrical connection of the control system of the image forming apparatus 1. The control system includes a CPU 12 for centrally controlling the entire image forming apparatus 1, a ROM 13 storing various control programs, tables (described later) shown in FIGS. A RAM 14 for storing and serving as a work area of the CPU 12 is connected by a bus 17. The bus 17 is connected to a motor driver 15 of a motor 16 for driving the T sensor 7, the P sensor 10, and the toner supply roller 5,
Various sensors and actuators (not shown) constituting the image forming apparatus are connected.

FIG. 3 is a flow chart of toner supply control using the T sensor 7 and the P sensor 10. 3 is started by turning on a main switch (not shown) of the image forming apparatus 1. First, a reference image is formed as a toner image on the photoconductor 2 (step S1), and the toner density of the reference image is detected by the P sensor 10 (step S2).
Then, the control reference value VTref of the T sensor 7 (control reference value of the toner density in the developing device 6) is set to a predetermined default value (step S3), and the output of the P sensor 10 in the reference image is set. The ratio Vsp / Vs between the value Vsg and the output value Vsp of the P sensor 10 in the non-image forming portion of the photoconductor 2
g and T sensor 7 at the time of detection by P sensor 10
Is obtained (step S4). The difference between the control reference value VTref of the T sensor 7 and the VT at the start of the image forming operation is larger than the predetermined threshold α (Y in step S5), and the control reference value VPref of the P sensor 10 and the start of the image forming operation Vsp / Vsg
Is greater than a predetermined threshold β (Y in step S6)
At this time, the operation enters the developer agitation mode, and the developer agitation time and the correction amount ΔVT of the reference value VTref are obtained according to the tables shown in FIGS. 4 and 5 (step S).
7). Then, the agitation time is stored in the RAM 14 (step S8), and the correction amount ΔVT is also stored in the RAM 14 (step S9). Then, a new control reference value VTref according to the stirring time is obtained from the obtained correction amount ΔVT (step S10). Thereafter, a copy operation is started (step S
11) to determine the toner supply time t (second) (“VTref−V
T ") (step S12), the toner supply roller 5 is turned on for t (seconds) (step S1).
3) The toner is supplied into the developing device 6. Then, while subtracting the stirring time of the developer (step S15),
The developer is stirred (Step S14).

On the other hand, the difference between the control reference value VTref of the T sensor 7 and the VT at the start of the image forming operation is smaller than the threshold value α (N in step S5), or the control reference value VPre of the P sensor 10
When the difference between f and Vsp / Vsg at the start of the imaging operation is smaller than the threshold value β (N in step S6), the correction amount ΔVT of the control reference value VTref is determined using the table of FIG. 4 (step S17). ), A new reference value VTref is determined (step S)
18). Then, a copy operation starts (step S1).
9) The toner supply time t (sec) is determined (“VTref−V
T ") (step S20), the toner supply roller 5 is turned on for t (sec) (step S2).
1) The toner is supplied into the developing device 6. And 1
If the job has ended, the process ends (Y in step S21), otherwise, the process returns to step S9 (step S9).
21 N). Steps S13 and S21 implement a supply control unit, step S2 implements a reference image forming unit, steps S10 and S18 implement a correction unit, and step S3 implements a default setting unit.

FIG. 6 shows the toner concentration TC of the developing device 6 and T
7 is a graph showing a relationship with an output value of a sensor 7. When the initial developer is supplied, the developing device 6 is idled for a predetermined time, the output of the T sensor 7 is stabilized, and the toner density is controlled by comparing the output with the reference value VTref. In this example, the toner concentration of the initial agent is 4.0 wt%, and the reference value Vtref of the T sensor 7 is set.
(That is, the default value of step S3) is set to 2.5V. The toner supply control is performed in accordance with the tables shown in FIGS. FIG. 4 shows the correction amount of the output of the T sensor 7 based on the output of the P sensor 10, and S in the table indicates the sensitivity (V / wt%) of the T sensor 7, and in this example, about
0.4V. For example, when the output value VT of the T sensor 7 is 2.7 V and the output value Vsp / Vsg of the P sensor 10 is 0.17, the reference value Vtref of the next T sensor 7 becomes 2.5-S / 4 = 2.4 V,
Until the next detection by the P sensor 10, the toner supply time t
(= F (Vtref-VT)) is supplied for sec. Similarly, when the output value VT of the T sensor 7 is 2.9 V, the output value Vsp / V of the P sensor 10 is obtained.
If sg = 0.07, enter the developer stirring mode and
The stirring time is stored, and the reference value Vtref =
2.5 + 0.4 = 2.9V. When the copy operation proceeds and the remaining time is 150 seconds, the reference value Vt of the T sensor 7 is used.
ref = 2.5 + 0.2 = 2.7 V, and the toner supply time t (= f
(Vtref-VT)) Replenished for seconds. In this example, the detection of the toner concentration TC by the T sensor 7 is performed on the transfer paper 1
Although the detection is performed for each sheet, the image density detection of the reference image by the P sensor 10 employs a transfer roller as a transfer method. Performed when the power is turned on.

As described above, according to the image forming apparatus 1 of the embodiment of the present invention, the reference value VTre of the T sensor 7
f and the VT at the start of the imaging operation, and the P sensor 10
Based on the difference between the reference value VPref and the output value Vsp / Vsg, the reference value VTref is corrected, and a toner stirring mode is provided to stably control toner with respect to environmental fluctuations and aging fluctuations. It can be carried out.

The reference value VTref and the VT at the start of the image forming operation
, The reference value VPref of the P sensor 10 and the output value Vsp / Vs
The above object is achieved by setting each threshold value for the difference from g and setting the developer to the stirring mode when each threshold value is greater than or equal to the threshold value.

Further, as shown in the flowchart of FIG. 3, every time the reference image is formed (step S2), the correction amount of VTref (steps S10 and S18) is deleted each time, and the default value is 2.5 V (step S3). To use
The toner replenishment control is performed without being affected by the change in VT due to environmental fluctuations, and there is no excessive replenishment of toner, thereby preventing background contamination and toner scattering.

In addition, the correction amount of the reference value VTref in the direction of lowering the toner density is set to be less than the sensitivity S of the T sensor 7, especially
Since it is 2 or less (see FIG. 3), it is possible to prevent a decrease in image density due to excessive correction of the reference value Vtref.

[0020]

According to the first aspect of the present invention, the new reference value after correction is changed to a default value preset for the reference value when a reference image is formed on the photosensitive member again. By doing so, it is possible to respond to the return of the output value of the toner density sensor to a normal value due to the toner agitation, and it is possible to prevent a decrease in image density.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, it is possible to prevent a decrease in image density due to excessive correction.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a configuration around a photoconductor of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating electrical connection of a control system of the image forming apparatus.

FIG. 3 is a flowchart illustrating toner supply control of the image forming apparatus.

FIG. 4 is a table of a correction amount of a T sensor output by a P sensor output in the image forming apparatus.

FIG. 5 is a table showing a relationship between a stirring time of a developer and a correction value of an output of a T sensor in the image forming apparatus.

FIG. 6 is a graph showing a relationship between toner density and T sensor output in the image forming apparatus.

FIG. 7 is a graph showing a relationship between a development potential and an image density in a conventional image forming apparatus.

FIG. 8 is a graph showing the relationship between the number of copies and the output of a T sensor in a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photoconductor 4 Exposure apparatus 6 Developing apparatus 7 Toner density sensor 10 Image density sensor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Jiji Mizuishi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Ken Amamiya 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Inside Ricoh Company (72) Inventor Hiroshi Mizusawa 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company (72) Inventor Mayumi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company ( 72) Inventor Kenzo Tatsumi 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Toshitaka Yamaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Hideki Yoshinami 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H027 DA10 DD07 EA06 EC03 EC06 HB09 2H077 DA04 DA10 DA42 DB01

Claims (2)

[Claims] An exposure device for forming an electrostatic latent image on a photoreceptor; a developing device for developing the formed electrostatic latent image with toner; a replenishing device for replenishing the developing device with toner; A toner density sensor for detecting a toner density in the developing device, a replenishment control means for controlling the replenishing device based on a result of comparing the detected toner density with a predetermined reference value, and the exposing device and the developing device. A reference image forming means for controlling to form a reference image from a toner image; an image density sensor for detecting an image density of the reference image; and a correction for correcting the reference value based on the detected image density and the detected toner density Means, a stirring device for stirring the toner in the developing device, and when the reference image has been formed, a previous reference value after the correction is decomposed to a predetermined reference value. An image forming apparatus comprising: a default setting unit that changes a default value. 2. The image forming apparatus according to claim 1, wherein the correction unit sets the correction amount of the reference value in the direction of decreasing the toner density to be equal to or less than the sensitivity of the toner density sensor.