JP3050390B2 - Toner density control method and image forming apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner density control method for an electrophotographic apparatus and an image forming apparatus.

[Conventional technology]

A toner density control method has been widely proposed in which a toner adhesion amount of a toner adhesion pattern formed on a photoreceptor is detected by a toner density detection unit, and toner supply is turned on and off based on a result of comparison with a control reference value. .

FIG. 4 is a characteristic diagram of the toner density sensor output with respect to the toner density, and the relationship between the toner density and the sensor output is linear in a certain toner density area. Than this, a reference value of the sensor output for example V _T1 provided, so that the sensor output becomes the V _T1, by controlling the driving motor of the toner replenishing roller to be described later, that the toner density in the developing device T ₁ It can be kept constant.

FIG. 5 is a characteristic diagram of the output of the optical sensor with respect to the amount of adhered toner. The relationship between the amount of adhered toner and the output of the optical sensor can be generally expressed by an exponential function. As a result, the sensor output V _R0 when the toner adhesion is 0 (that is, the photoconductor background portion) is obtained.
It is determined, and automatically output V _R1 of the toner adhesion amount M ₁ can be determined.

As will be described later, the toner concentration sensor is provided in the developing device, and the optical sensor is provided downstream of the developing device so as to face the photoconductor.

FIG. 6 is a conceptual diagram showing the overall control of the toner density. The first quadrant shows the characteristics of the original density and the photoconductor potential obtained thereby, and the second quadrant shows the characteristics obtained after the development with respect to the photoconductor potential. The relationship between the toner adhesion amounts to be applied.

As shown in the figure, it determines the certain document density OD1, when attention is paid to the toner adhesion amount of the photosensitive member potential V ₁ by it, even if controlling the toner concentration of the developer constant, with respect to the initial development characteristic a For example, the development characteristics b
It changes like

This is generally due to a change in the charging ability of the developer, especially the carrier, for the toner. Here, the case where the developing ability is lowered is described, but the reverse case is of course also possible. In order to detect the change in the development characteristic and to keep the development characteristic constant, a method of checking the toner adhesion amount of OD1 at certain intervals and controlling the toner concentration based on the result is adopted.

For example, as shown in FIG. 6, when the developing characteristic decreases as indicated by b, the toner adhesion amount decreases from M _{1 to} M ₂ . This means that the optical sensor output increased from V _R1 → V _{R2 in} FIG.
If on the basis of the _R1, it detects that the toner adhesion amount is reduced by the output of the V _R2. As shown in FIG. 4 Accordingly, the reference value of the toner density sensor V _T1 → (change) shifts to V _T2 can control the toner concentration can be raised to T ₁ → T _2, the results in The development characteristics can be improved. When the developing characteristic is increased, the operation is reversed.

[Problems to be solved by the invention]

In the case of maintaining the developing characteristics by the toner density shift as described above, if the shift is applied in the direction of increasing the toner density, the toner replenishment will be continued accordingly. It has recently been found that a problem such as toner adhesion to the body surface or toner scattering from the developing device may occur, which is a problem.

In addition, the detection timing of the optical sensor is usually provided at a certain interval, and parameters such as the number of copies and time are selected. By the way, the change in development characteristics does not appear equally for all devices,
It differs depending on the user of the device, the environment in which it is placed, and the like. Therefore, since the development characteristics that change during the detection interval differ from device to device, if the shift amount is a constant value, there is a problem that correction is insufficiently corrected in one device and excessively corrected in another device. Atsuta.

An object of the present invention is to solve the problem that when the amount of change of the control reference value is large, the amount of toner replenishment increases and the rise of the charge of the replenishment toner cannot be made in time. An object of the present invention is to provide a toner density control method and an image forming apparatus that can prevent background contamination and toner scattering caused by toner replenishment without considering a change amount and can always obtain a stable image.

[Means for solving the problem]

An object of the present invention is to provide a toner density control method for detecting a toner adhesion amount on a photoreceptor and changing a control reference value of a toner density control means for controlling a toner density of a developing device in accordance with the detection result. This is achieved by a first means which performs the detection stepwise a plurality of times for one detection of the toner adhesion amount on the photoconductor.

Further, the above object is to detect a toner adhesion amount in a toner concentration control method of detecting a toner adhesion amount of a specific toner adhesion pattern and changing a control reference value of a toner concentration detection unit provided in a developing device according to the result. The change amount of the control reference value of the toner density sensor is changed according to the difference between the detected value and the reference adhesion amount, and the control amount is divided into a plurality of levels according to the difference, and the change amount is set for each level. This is achieved by two means.

The object of the present invention is to provide an image forming apparatus which detects a toner adhesion amount on a photoreceptor and changes a control reference value of a toner density control means for controlling a toner density of a developing device according to the result. The change of the value is achieved by a third means which is performed stepwise a plurality of times for one detection of the toner adhesion amount on the photoconductor.

Further, the above object is to provide an image forming apparatus which detects a toner adhesion amount of a specific toner adhesion pattern and changes a control reference value of a toner density detection means provided in a developing device according to the result. The change amount of the control reference value of the toner density sensor is changed according to the difference between the detected detection value and the reference adhesion amount, the change amount is divided into a plurality of levels according to the magnitude of the difference, and the change amount is set for each level. This is achieved by a fourth means.

[Action]

According to the first and third means, when the shift is executed in the direction in which the toner concentration increases, the shift amount is executed stepwise a plurality of times with respect to one detection of the toner adhesion amount on the photoconductor. As a result, it is possible to solve a start-up failure due to rapid toner supply, and to eliminate problems such as background contamination and toner scattering.

According to the second and fourth means, the amount of change of the control reference value of the toner density sensor is changed in accordance with the difference between the detection value of the optical sensor and the reference adhesion amount, and the level is changed to a plurality of levels according to the magnitude of the difference. Since the amount of change is separately set for each level, toner correction according to the amount of change in development characteristics is realized.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a control block diagram of a copying machine in which the control method of the present invention is implemented, wherein 1 is a photosensitive member, 2 is a developing device, 3 is a developing sleeve, 4 is a toner supply roller, 5 is a casing,
6 is a toner density sensor, 7 is a drive motor of the toner replenishing roller 4, 8 is a toner hopper, 9 is an optical sensor, 10 is a detection signal of the toner density sensor 6 and the optical sensor 9, and
Also, an I / O unit that outputs commands to the drive motor 7, 11 is a CP
U and 12 are ROMs storing sequence programs, and 13 is a RAM storing various data and variables.

In such a configuration, the fluctuation of the toner adhesion amount is detected by the optical sensor 9, and based on the result, the control is performed so that the control toner density value of the toner density sensor 6 located in the developing device 2 is shifted.

FIG. 1 is a flowchart showing the control contents of the first embodiment of the toner density control method according to the present invention. After the copy start (1-1), for example, once every 1000 copies (Y in 1-2) ), to form a toner deposition pattern corresponding to the document density OD1, detects the deposition amount M ₂ by the optical sensor 9, M ₂ is detected as an electric signal V _R2 (1-3), I
Sent from the / O unit 10 to the CPU 11. RAM1 in CPU11
The reference value V _R1 of the optical sensor 9 stored in
_R2 is compared (1-4).

As described above, when the developing characteristic is reduced, the toner adhesion amount is reduced, and the sensor output has a relationship of _VR1 < _VR2 (Y in 1-4). When such a relationship is obtained
CPU11 changes the control reference value V _T1 of the toner concentration sensor 6, which is memory RAM13 to V _T2, increases the control toner density.

In this case, when changing V _T1 to V _T2 , V _T2 −V _T1 = Δ at one time
Instead of shifting the V _T, dividing the ΔV _T to n times, ΔV _T / n
(= A [Delta] T) by gradually transferred to V _T2 with a certain interval. That is, n = 1 (1-5), and first, the toner density control reference value is set to V _T1 + nΔT (1-6). Thereafter, toner replenishment control is performed (1-7), and when the actual toner density increases by ΔT (Y in 1-8), the next ΔT is shifted (N, 1-10 in 1-9). In this flow, the number of shifts is set to five, and when the shift is completed (Y in 1-9), the end is made.

For V _R1> V _R2 also (Y at 1-11), the optical sensor 9
Must be lowered, but in this case, it is sufficient to shift at once (5) at a time ΔT which is 5 times (1-12).

FIG. 2 is a flow chart showing the control contents of a second embodiment of the toner density control method according to the present invention. Steps 2-1 to 2-4 correspond to steps 1-1 to 1--1 in FIG. Same as up to 4.

When the relationship of V _R1 <V _R2 is obtained (Y at 2-4), CP
U11 is changed control reference value V _T1 of the toner concentration sensor 6, which is memory RAM13 to V _T2, varying the control toner density.

At this time, the value of the difference between the detection value V _R2 of the optical sensor 9 and the reference value V _R1 is divided into three stages, and the difference is divided into three stages.
Shift amount of the control reference value (V _T2 -V _T1) allocating as the table below.

As shown in this table, when the Y (the case of level 1) in 2-5 down only [Delta] V _T to the new toner density control standard value V _T2 (2-6). Similarly, in 2-7 and Y (For Level 2), 2.DELTA.V _T down (2-
8). If N is 2-7 (level 3), 3
ΔV _T down (2-9).

On the other hand, if V _R1> V _R2 (Y 2-10), when Y 2-11 (level 1), the [Delta] V _T up-, when Y in 2-13 (level 2), 2.DELTA.V _T Up. In 2-13, N
When (level 3) is 3DerutaV _T UP-.

As described above, a stable image can be always obtained by correcting the toner density according to the amount of change in the development characteristics.

〔The invention's effect〕

As described above, according to the first and third aspects of the present invention, the control reference value is changed stepwise a plurality of times with respect to one detection of the toner adhesion amount on the photoconductor. ,
When the change amount of the control reference value becomes large, the toner replenishment amount becomes large and the rise of the charge of the replenishment toner cannot be completed in time. And the like can be eliminated.

According to the second and fourth aspects of the present invention, the change amount of the control reference value of the toner density sensor is changed in accordance with the difference between the detected value of the toner adhesion amount and the reference adhesion amount, and a plurality of values are changed in accordance with the difference. , And the amount of change is set for each level, so that toner density correction according to the amount of change in development characteristics can be realized, and a stable image can always be obtained.

[Brief description of the drawings]

FIG. 1 is a flow chart showing control contents of a first embodiment of a toner density control method according to the present invention, and FIG. 2 is a flow chart showing control contents of a second embodiment of a toner density control method according to the present invention. FIG. 3 is a control block diagram of a copying machine embodying the present invention, FIG. 4 is a characteristic diagram of a toner density sensor output with respect to a toner density, FIG. 5 is a characteristic diagram of an optical sensor output with respect to a toner adhesion amount, and FIG. FIG. 3 is a conceptual diagram showing the entire toner density control. DESCRIPTION OF SYMBOLS 1 ... Photoreceptor, 2 ... Developer, 4 ... Toner supply roller, 6 ... Toner density sensor, 9 ... Optical sensor, 11 ...
…CPU.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-186280 (JP, A) JP-A-1-1333071 (JP, A) JP-A-1-163785 (JP, A) JP-A 64-64 40967 (JP, A) JP-A-1-169468 (JP, A) JP-A-63-131152 (JP, A) JP-A-61-46565 (JP, U)

Claims (4)

(57) [Claims] 1. A toner density control method for detecting a toner adhesion amount on a photoreceptor and changing a control reference value of a toner density control means for controlling a toner density of a developing device according to a result of the detection. Is performed stepwise a plurality of times for each detection of the amount of toner adhering to the photoreceptor. 2. A toner density control method for detecting a toner adhesion amount of a specific toner adhesion pattern and changing a control reference value of a toner density detection means provided in a developing device according to the result. The change amount of the control reference value of the toner density sensor is changed according to the difference between the value and the reference adhesion amount, the change amount is divided into a plurality of levels according to the magnitude of the difference, and the change amount is set for each level. Characteristic toner density control method. 3. The image forming apparatus according to claim 1, wherein the control unit further controls a toner density control unit for controlling a toner density of a developing unit according to a result of detecting a toner adhesion amount on the photoconductor. The image forming apparatus is characterized in that the change is performed stepwise a plurality of times with respect to one detection of the toner adhesion amount of the photoconductor. 4. An image forming apparatus which detects a toner adhering amount of a specific toner adhering pattern and changes a control reference value of a toner concentration detecting means provided in a developing device according to the result. The change amount of the control reference value of the toner density sensor is changed in accordance with the difference between the detected value and the reference adhesion amount, and the control amount is divided into a plurality of levels according to the magnitude of the difference, and the change amount is set for each level. An image forming apparatus comprising: