JPH032879A - Image forming device - Google Patents

Abstract

PURPOSE:To maintain a fixed image quality regardless of any environmental fluctuation, etc., by switching an exposure quantity based on control information different between when a photosensitive body exposing quantity is increased and when it is decreased. CONSTITUTION:The exposure amount is switched based on the control information different between when the photosensitive body exposing quantity is increased and when it is decreased. For example, at the time of obtaining a required potential contrast of the potential Vc, the exposure quantity is not switched even when the potential contrast becomes the value Vc after once the exposure quantity is switched from a Lo side to a Hi side. It is not until the potential contrast lowers to a value VB lower than the VC that the switching operation is carried out. Thus, even when the potential contrast slightly flactuates because of such as the environmental fluctuation, the exposure quantity is not switched, and therefore, a fixed image quality can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an image forming apparatus that forms an image by an electrophotographic process such as a copying machine, a laser beam printer, etc.
In particular, the present invention relates to one in which the surface condition of a photoreceptor can be controlled in accordance with changes in the atmosphere and the like.

(Prior Art) Conventionally, this type of device is known to form images under optimal conditions against environmental changes by controlling the grid voltage of the corona charger and the amount of exposure to the photoreceptor. ing.

That is, as shown in FIG. 6, the method adopted in this conventional example is a method for controlling the potential contrast on the surface of the photoreceptor as an image forming condition. By changing the bias, the surface potential (Vo) of the photoreceptor is changed, thereby obtaining the required potential contrast (VD - VL).

Here, Vo indicates the dark potential of the photoconductor, and vL indicates the bright potential of the photoconductor.

However, the surface potential of the photoreceptor ■. Even if you change the potential contrast (V
, -VL), therefore, when the range of change in potential contrast required is wide, a method is used in which the exposure amount is switched between a low contrast side and a high contrast side.

That is, for example, when the required potential contrast (Va VL) in FIG. 6 is larger than the value at point B, an operation is performed to switch the exposure amount from Lo to Hl as shown in FIG. 7. In this case, in order to obtain the target potential contrast (V D-vLL)lI)) at point C, the grid bias potential is lowered as the exposure amount changes, and the potential contrast (-VL) is lowered as the exposure amount changes. are made the same (FIG. 6 BB'), then the surface potential V of the photoreceptor. The plan is to perform control to increase the

In this way, when changing the potential contrast (vo VL) to a high value, the exposure amount is switched from Lo to HI, and the grid bias potential is changed so that it shifts in the order of A→B-B'-C in FIG. on the other hand,
When changing the potential contrast (vo vt,) to a lower value, switch the exposure amount from H to Lo and change the grid bias potential so that it shifts in the order of C-B'-B-A in the same figure. By doing so, the potential contrast (vo VL) was controlled over a wide range.

(Problem to be Solved by the Invention) However, in the case of such a conventional example, in the region of potential contrast where the exposure amount changes, that is, between B and B′ in FIG. 6, the potential contrast is the same when the exposure amount is changed. Even if controlled so that The disadvantage is that the gender changes.

That is, FIG. 8(a) shows the EV characteristics of a typical photoreceptor such as OPC (organic optical semiconductor). In this case, the change in potential is not linear with respect to the exposure amount, and therefore, the actual EV characteristic changes as shown in FIG. 8(b) depending on the maximum exposure amount used.

Therefore, by the method described above, point B (B'
) If the photoreceptor is controlled to obtain a potential contrast of The problem was that it changed. However, although gradation correction has conventionally been performed when switching the exposure amount, it has been difficult to stabilize the image quality by making corrections that are commensurate with changes in the exposure amount. In particular, in a full-color image forming apparatus in which gradation is important, it is necessary to stabilize gradation.

The present invention has been made to solve the problems of the prior art described above, and its purpose is to suppress changes in image quality due to exposure switching and maintain a constant image quality regardless of environmental changes. An object of the present invention is to provide an image forming apparatus that can perform the following steps.

(Means for Solving the Problems) In order to achieve the above object, the present invention switches the amount of exposure to the photoreceptor during image formation based on control information of the surface condition of the photoreceptor on which an image is to be formed. In the image forming apparatus, the exposure amount is switched based on different control information depending on whether the exposure amount to the photoreceptor is increased or decreased.

Further, it is preferable that the control information is a surface potential contrast.

(Function) In the present invention having the above configuration, when controlling the photoreceptor to a predetermined surface condition, after the exposure amount has been switched, the photoreceptor may change due to slight environmental changes. Even if the surface condition changes, the exposure amount is not changed. Therefore, it is possible to significantly reduce the number of times the exposure amount is changed based on the surface condition control information, and it is possible to suppress changes in image quality as much as possible.

(Example) Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a diagram illustrating the configuration of a full-color image forming apparatus showing an embodiment of the present invention. Reference numeral 1 denotes a laser control unit that generates a laser beam modulated in accordance with an input image signal. Reference numeral 2 denotes a polygon mirror having a rotating polygon mirror, which is rotated at a constant speed by a scanner motor (not shown) to deflect an incident laser beam. 3 is an imaging lens, which is an optical lens having f/θ characteristics.

Reference numeral 4 denotes a photosensitive drum as a photosensitive member, which is exposed to an incident laser beam to form an electrostatic latent image. Note that the photosensitive drum 4 rotates in the direction of the arrow. Reference numeral 5 denotes a static elimination lamp that eliminates static potential on the surface of the photosensitive drum 4 to make it uniform. A corona charger 6 uniformly charges the surface of the photosensitive drum 4. Reference numeral 7 denotes a grid electrode, which acts as a control electrode when uniformly charging the surface of the photosensitive drum 4.

8a, 8b, 8c, and 8d are developing means that develop the electrostatic latent image formed on the photosensitive drum 4 with each developer (magenta, cyan, yellow, and black) according to the developing bias applied to each developing sleeve 5axSd. Visualize it. Reference numeral 9 denotes a transfer drum that carries transfer paper fed from a paper feed cassette 10.

A transfer charger 11 transfers the toner image formed on the photosensitive drum 4 onto a transfer paper carried on a transfer drum 9. 1
Reference numeral 2 denotes a peeling claw that separates the transfer paper onto which the toner images of each color have been transferred from the transfer drum 9.

A fixing device 13 fixes the toner image on the transfer paper. Reference numeral 14 denotes a paper discharge tray on which transfer paper on which image formation has been completed is placed. A cleaning device 15 collects toner remaining on the photosensitive drum 4.

A potential sensor 16 is provided close to the photosensitive drum 4 at a position after laser beam irradiation, and detects the potential of the latent image. 17 is an A/D converter which converts the analog output of the potential sensor 16 into a digital output. Reference numeral 18 denotes a voltage control section comprised of a microcomputer, which includes a RAM serving as data storage means and control data storage means, a bias calculation means, a CPU serving as control means, and the like.

19 is a D/A converter that converts the control information determined by the voltage control unit 18 into analog data, and controls the high voltage control unit 20a that controls the voltage applied to the charger 6 and the voltage applied to the grid electrode 7. The control data is sent to the high voltage control unit 20b which controls the developing devices 88 to 8d, and the developing bias data is sent to the developing bias voltage control circuits 21a to 21d which control the developing devices 88 to 8d.

Next, the potential control operation on the surface of the photosensitive drum 4 will be explained based on FIGS. 2 and 3.

In this embodiment, as in the case of the conventional example, the image forming conditions are set based on the information obtained by the potential sensor 16 by controlling the voltage applied to the grid electrode 7 of the corona charger 6. Furthermore, when the range of the forming conditions, that is, the required potential contrast (■.-VL) exceeds the control range of the grid voltage, the amount of laser beam exposure to the photosensitive drum 4 is switched to increase the brightness of the drum surface. By changing the partial potential vL (Vwu.-vLLLo,), a wider range of potential contrast can be obtained (FIG. 2).

However, when the exposure amount is switched, the image quality, particularly the gradation, changes due to the influence of the EV characteristics of the photosensitive drum 4, so it is desirable to avoid switching the exposure amount as much as possible.

Therefore, in this embodiment, as shown in FIG. 3, the point of potential contrast at which the exposure amount is switched is made different between when switching from the L0 side to the H1 side and when switching from the H1 side to the L0 side. We are trying to solve this problem. That is, in this embodiment, when switching the exposure amount from the Lo side to the H side, the operation is performed when the required potential contrast (vo - VL) reaches a predetermined value VL (C→ C'), when switching from the H side to the LO side, the switching operation is not performed even if this value ■ is reached, and the exposure amount is reduced when it reaches an even lower value ■ (B'-B) It is said that In other words, the exposure amount switching characteristic with respect to the required potential contrast (-VL) is given a hysteresis characteristic. Then,
By performing such control, for example, when obtaining the required potential contrast of vc, after switching the exposure amount from the L0 side to the H side, even if the potential contrast returns to this value V, the exposure amount will not change. No switching takes place, and only when this drops to vll, which is a value lower than Vc, does a switching operation take place. Therefore, even if the potential contrast changes slightly due to environmental changes, the exposure amount will not be changed.
As a result, it becomes possible to maintain a constant image quality.

Incidentally, in the above embodiment, the exposure amount is switched in two stages, but the present invention is not limited to this, and can also be applied to an apparatus that performs multi-stage switching.

FIG. 4 is a graph showing changes in the exposure amount of an apparatus that switches the exposure amount in six stages with respect to the required potential contrast (V 0 VL). If you switch the exposure amount frequently in this way, the rate of exposure change at the time of switching will decrease, so
Fluctuations in comfort caused by the EV characteristics of the photosensitive drum 4 can be reduced. However, since the number of switching points increases accordingly, exposure amount switching is performed frequently even due to slight environmental changes, resulting in a decrease in image quality.

However, as shown in Figure 5, if the exposure amount is controlled using the method described above so that it has hysteresis characteristics at each switching point, the exposure will remain constant after one switching unless a large environmental change occurs. The quantity is maintained. Therefore, if the present invention is applied to such an apparatus, it becomes possible to form an image of very high quality, in addition to the small change in gradation when changing the exposure amount.

It goes without saying that the present invention can be applied to any device that performs exposure amount switching in multiple stages other than the two stages and six stages described above.

(Effects of the Invention) As described above, according to the present invention, changes in image quality due to exposure switching can be suppressed as much as possible, and as a result, a constant image quality can be maintained despite any environmental changes. It becomes possible.

Therefore, in a full-color image forming apparatus in which comfort is particularly important, it is possible to always form high-quality images without color shift or the like.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention, and FIGS. 2 and 3 show control operations for the surface potential of a photosensitive drum in the same embodiment. A graph showing the relationship between the grid bias potential of the corona charger and the surface potential of the photosensitive drum; FIG. 3 is a graph showing the relationship between the required potential contrast of the photosensitive drum and the amount of exposure;
4 and 5 are graphs showing the relationship between the required potential contrast and the exposure amount on the photosensitive drum to show the control operation of another embodiment of the present invention, and FIGS. This figure shows the control operation of the surface potential of the photoreceptor in the forming device. Figure 6 is a graph showing the relationship between the grid bias potential of the charger and the surface potential of the photoreceptor, and Figure 7 is the required potential on the photoreceptor. Graphs showing the relationship between contrast and exposure amount. FIGS. 8(a) and 8(b) are graphs showing the relationship between exposure amount and surface potential of the photoreceptor. Explanation of symbols l... Laser control unit 4... Photosensitive drum (photosensitive member) 6... Corona charger 7... Grid electrode 8a,
8b, 8c, 8d - Developing means 16... Potential sensor 18... Voltage control section 20a
, 20b...high pressure control units 21a, 21b, 21
c, 21d=・Development bias voltage control circuit Fig. 2 Fig. 3 Fig. 4 Fig. j History 1) Electric Uko last VD+ vL Fig. 5/10,000! Den-Iko contrast Vo -1/L Fig. 6 Grid, unbiased @ITL Fig. 7-VJv'qn-1 contrast Fig. 8 (O) (b)

Claims (2)

[Claims] (1) In an image forming apparatus equipped with means for switching the amount of exposure to the photoreceptor during image formation based on control information of the surface state of the photoreceptor on which an image is to be formed, the amount of exposure to the photoreceptor is increased; An image forming apparatus characterized in that the exposure amount is switched based on different control information depending on when the exposure amount is decreased. (2) The image forming apparatus according to claim 1, wherein the control information is surface potential contrast.