JPH02132473A - Electrophotography device - Google Patents

Abstract

PURPOSE:To correct uneven printing density in the rotational direction of a photosensitive drum and to contrive the stabilization of density of a small-size device which is constrained so much especially by providing a control part for executing a control so that an exposure value of an image exposure device is varied in accordance with a rotational position of the photosensitive drum. CONSTITUTION:In the case of increasing the toner supply quantity to three stages toward the latter half of one page at the time of heavy duty, a clock is generated from a clock generator 80 by turn-on of a motor start/stop signal and a step-motor 13 is driven, and a photosensitive drum 1, etc., rotate. Simultaneously, a light emission time control part 88 generates the lowest signal to an LED array 3 and controls the light emission time. Also, this clock is counted by a first and a second counters 82, 85 and detects a rotational position of the drum 1. In such a way, by increasing an exposure value of the array 3 by the rotational position of the drum 1 in accordance with a toner supply quantity characteristic of a developing device 4, the printing density can be corrected to the prescribed density.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial field of application Prior art (Figure 6) Means for solving the problem to be solved by the invention (Figure 1) Working example (a) 1 Description of Examples (Figures 2 to 4) (b)
Description of other embodiments (Fig. 5) Effects of the invention [Summary] An object of the present invention is to prevent uneven printing density in the rotational direction of the photosensitive drum in an electrophotographic apparatus that controls the exposure amount according to the rotational position of the photosensitive drum. In an electrophotographic apparatus in which a photosensitive drum charged by a charger is exposed to an image by an image exposure device, developed by a developing device, and transferred to a printing medium by a transfer device, the photosensitive drum is transferred to a photosensitive drum according to the rotational position of the photosensitive drum. A control section was provided to control the exposure amount of the image exposure device to vary.

[Industrial application field]

The present invention relates to an electrophotographic apparatus that controls the amount of exposure depending on the rotational position of a photosensitive drum.

Electrophotographic devices are widely used in printers, facsimile machines, copying machines, and the like.

This electrophotographic apparatus has many process units such as a photosensitive drum, a pre-charger, a developer, an exposure device, a static eliminator, and a cleaner, so the apparatus tends to be large.

However, recently, from the perspective of use in OA equipment, etc.
The need for small electrophotographic devices is increasing.

In order to miniaturize electrophotographic apparatuses, restrictions on the configuration and arrangement of each process unit are increasing.

When such restrictions increase, density unevenness tends to occur in the toner image on the photosensitive drum, and countermeasures are desired.

[Conventional technology]

FIG. 6 is an explanatory diagram of the prior art.

As shown in FIG. 6(A), in an electrophotographic apparatus, a rotating photosensitive drum 1 is charged with a front charger 2, exposed to an image by an exposure device 3 such as an LED, and then a developing device (sleeve) 4 is used. The toner image on the photosensitive drum L is transferred to a printing medium (paper) PP using a transfer charger 5, and then an optical charge remover (LED for charge removal)
) 6 for photostatic discharge, and a cleaner 7 for cleaning.

The exposure amount of the exposure device 3 was determined depending on the process conditions and was constant.

[Problem to be solved by the invention]

However, with the downsizing of the apparatus, restrictions on each process unit have become greater, resulting in uneven print density in the rotation direction of the photosensitive drum 1, that is, in the conveyance direction of the paper PP.

For example, in order to downsize the developing device 4, it is necessary to downsize the developing device 4, but in this case, the sleeve (supply roller) of the developing device 4 must also be made small, and the amount of toner supplied becomes small.

In such cases, the printer is designed to supply enough toner to obtain sufficient density for normal printing;
For heavy-duty printing such as all-solid printing, as shown by the solid line in FIG. 6(B), the amount of toner supplied cannot keep up, and the density gradually becomes lighter within one page.

Furthermore, depending on the sequence, the surface potential of the photosensitive drum may not be uniform in the rotational direction, which also causes density unevenness.

For example, when a thermal fixing device is disposed close to the photosensitive drum 1, the photosensitive drum 1 is rotated only during printing, so that certain parts of the photosensitive drum 1 are exposed to heat while the photosensitive drum 1 is stopped. The sensitivity of that part will change.

In such a case, the surface potential of a specific portion of the photosensitive drum 1 decreases, and the density becomes thinner, as indicated by the dotted line in FIG. 6(B).

Further, the same applies when static elimination is not performed.

As described above, in the conventional technology, as the apparatus becomes smaller, a problem arises in that printing density unevenness occurs in the rotational direction of the photosensitive drum 1.

Therefore, an object of the present invention is to provide an electrophotographic apparatus that can prevent uneven printing density in the rotational direction of a photosensitive drum.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle of the present invention.

As shown in FIG. 1A, in the present invention, a photosensitive drum 1 charged by a charger 2 is exposed to an image by an image exposure device 3, developed by a developing device 4, and printed on a printing medium PP by a transfer device 5. In an electrophotographic apparatus that transfers images to a photosensitive drum 1, depending on the rotational position of the photosensitive drum
a control unit 8 that controls the exposure amount of the image exposure device 3 to change;
It has been established.

[Effect]

The present invention changes the exposure amount of the image exposure device 4 so as to correct the uneven printing density since such uneven printing density occurs with certain characteristics with respect to the rotational direction of the photosensitive drum 1.

For example, if the print density characteristics before correction are shown as the dotted line in FIG. It is.

〔Example〕

(a) Description of one embodiment FIG. 2 is a configuration diagram of an embodiment of the present invention.

In the figure, the same parts as shown in Figures 1 and 6 are:
They are shown with the same symbols.

The photosensitive drum 1 has a diameter such that one page can be printed in three rotations, and is made of an aluminum drum coated with a photosensitive material.

The exposure device W3 is composed of a row of LED arrays.

The developing device 4 has a rotating sleeve 4l to which a carrier is attached around the mag roll 40, and frictionally charges the toner Tn in the toner box 43 by the rotational movement of an agitator 42, and supplies the toner Tn to the sleeve 4l. , The static eliminator 6 is an optical static eliminator composed of an LED array.

The cleaner 7 includes a pred cleaner 70 that contacts the photosensitive drum 1 and a waist toner box 71 that stores residual toner scraped off by the blade cleaner 70.

Reference numeral 9 denotes a conveyance roller, which conveys the print medium PP conveyed from a hopper (not shown); 10 denotes a transfer guide roller, which guides the print medium PP during the transfer operation by the transfer charger 5; and 11, a conveyance roller. A conveyance guide guides the print medium PP after transfer, and a fixing roller 12 fixes the transferred toner image on the print medium PP.

The photosensitive drum 1, the developing device 4, and the cleaner 7 are integrally formed as a unit, and each of the integrally formed units can be replaced.

Further, the developing device 4 is miniaturized, and the diameter of the sleeve 41 is small.

If the rotation speed of the sleeve 41 is increased, the amount of toner supplied will increase accordingly, but if the rotation speed is increased, the toner will be more likely to scatter and the load torque will also increase, so it is necessary to suppress the speed to a certain level. Therefore, the amount of toner supplied can be reduced accordingly.

FIG. 3 is a block diagram of a control section according to an embodiment of the present invention.

In the figures, the same parts as those shown in FIGS. 1, 2, and 6 are indicated by the same symbols.

13 is a step motor that drives each part of the electrophotographic apparatus (photosensitive drum 1, conveyance roller 9, fixing roller 12, developing sleeve 41, agitator 42, etc.); 14 is a step motor drive circuit; The step motor 13 is driven in accordance with the phase switching signal.

80 is a clock generator which generates a driving clock for the step motor 13 that drives each part of the electrophotographic apparatus in response to a motor start/stop signal; 8l is a phase switching unit which generates a driving clock for the step motor 13 that drives each part of the electrophotographic apparatus; 13 excitation phase switching is performed.

82 is a first counter that counts the clock of the clock generator 80 and indicates the position of the step motor 13, that is, the rotational position of the photosensitive drum 1; 83 is a first reference device that measures the exposure amount; The distance r to the first position where
A is stored, and 84 is a first comparator, which compares the counted value of the first counter 82 and the reference distance ra of the first reference device 83, and generates the control signal B. .

85 is a second counter, which counts the clock of the clock generator 80 and indicates the rotational position of the photosensitive drum 1; 86 is a second reference device, which measures the second position at which the exposure amount is changed; 87 is a second comparator that stores the distance rb from the second counter 85 to the second comparator 87.
The control signal C is generated by comparing the reference distance rb of the reference device 86.

Reference numeral 88 is a light emitting time control unit, which uses a motor start/stop signal as a control signal A, and together with control signals B and C as L.
It outputs a light emission time control signal (light emission strobe signal) for the ED array 3.

FIG. 4 is an explanatory diagram of the operation of one embodiment of the present invention.

In this example, the amount of toner supplied during heavy duty does not catch up with the consumption toward the second half of one page, as shown in the figure, so the exposure amount is increased in three steps toward the second half of one page. ing.

When the motor start/stop signal (signal A) is turned on, a clock is generated from the clock generator 80, the step motor 13 is driven, and the photosensitive drum 1 and the like are rotated.

Along with this, the light emission time control section 88 controls the light emission time of the LED array 3 by setting the light emission time control signal to the lowest value a.

Therefore, the LED array 3 emits light according to the write data with the light emission strobe width a.

Also, this clock is used by the first and second counters 82 and 85.
, and the rotational position of the photosensitive drum l is detected.

In this way, the photosensitive drum 1 is rotated and a printing operation is performed.

When the photosensitive drum 1 rotates by ra from the start, the first
The control signal B from the comparator 84 is turned on.

Thereby, the light emission time control section 88 sets the light emission time control signal to b (a<b) and changes the light emission time of the LED array 3.

Therefore, the LED array 3 emits light according to the write data with the light emission strobe width b.

Further, the photosensitive drum 1 moves from the start to rb(ra<r
b), the control signal C from the second comparator 87 turns on.

Thereby, the light emission time control section 88 sets the light emission time control signal to c (b<c) and changes the light emission time of the LED array 3.

Therefore, the LED array 3 emits light according to the written data with the emission stroke width C.

When the printing of one page is completed, the motor start/stop signal is turned off, the clock of the clock generator 80 is stopped, the step motor 13 is stopped, the photosensitive drum 1 etc. are also stopped, and the LED array 3 is turned off. The output of the time control signal is also stopped.

In this way, the light emitting time of the LED array 3, which is an exposure device, is increased in accordance with the toner supply amount characteristics of the developing device 4, the amount of exposure to the photosensitive drum 1 is increased, and the print density is corrected to a constant value. .

(b) Description of other embodiments FIG. 5 is an explanatory diagram of another embodiment of the present invention.

The example in FIG. 5 shows an example in which the turbidity of a specific portion of the photosensitive drum 1 decreases due to the heat of the fixing device, the charging potential decreases, and uneven printing density occurs. Indicates that one page will be printed with rotation.

In this case, the rotational position at which the charged potential decreases may be measured in advance, and the light emission time may be controlled as shown in FIG. 5 in accordance with the rotational position of the photosensitive drum 1, similar to the example shown in FIG.

In the embodiment shown in FIG. 3, the control section 8 is composed of a counter, etc., but these can also be composed of a microprocessor and executed by a program.Also, in the example of FIG. You can also use it as

Further, although the exposure device W3 has been described using an LED array, it can also be applied to a device using a well-known laser light source or the like.

12 Although the present invention has been described above with reference to examples, the present invention can be modified in various ways according to the gist of the present invention, and these are not excluded from the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, since the exposure amount of the image exposure device is controlled according to the rotational position of the photosensitive drum,
It corrects the density unevenness that appears in the vertical direction of the paper due to the characteristics of the electrophotographic process, and has the effect of achieving uniform print density, contributing to the stabilization of print density especially in small electrophotographic equipment where there are many restrictions on the process unit. There's a lot to do.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of the present invention, Fig. 2 is a configuration diagram of an embodiment of the invention, Fig. 3 is a block diagram of a control section of an embodiment of the invention, and Fig. 4 is an operation of an embodiment of the invention. FIG. 5 is an explanatory diagram of another embodiment of the present invention, and FIG. 6 is an explanatory diagram of a prior art. In the figure, 1-photosensitive drum, 2-charger, 3-image exposure device, 4-developing device, 5-transfer device, 8-control unit.

Claims (1)

[Claims] (1) The photosensitive drum (1) charged with the charger (2),
In an electrophotographic device that exposes an image with an image exposure device (3), develops it with a developer (4), and transfers it to a printing medium (PP) with a transfer device (5), depending on the rotational position of the photosensitive drum (1). An electrophotographic apparatus characterized in that a control section (8) is provided for controlling the exposure amount of the image exposure device (3) to be changed.