JPS63267977A - Electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To form a uniform halftone screen pattern image free from variance of irradiation by setting the slit width (the length in the moving direction of a photosensi tive body) of a halftone pattern exposure device to a value which is integer-number of times as long as the length for which the photosensitive body is moved by one tooth of a gear or a pulley which drives the photosensitive body. CONSTITUTION:Relations l1=nl2 [(n) is an integer] are satisfied between the length l2 for which photosensitive bodies 11, 14, and 17 are moved by one tooth of the gear or the pulley which drives these photosensitive bodies and the slit width of irradiation (the length l1 in the moving direction of photosensitive bodies) of a halftone pattern exposure device 31. Irradiation of the halftone pattern exposure device 31 is performed intermittently at intervals of a time corresponding to movement for the irradiation slit width l1 of photosensitive bodies 11, 14, and 17, and the halftone screen pattern image is developed and transferred after being formed on a required position of the surface of the photosensitive body before or after original image exposure. Consequent ly, halftone pattern images each of which has the slit width l1 exposed on surfaces of photosensitive bodies 11, 14, and 17 do not overlap neither are separated, and regular images are obtained. Thus, a uniform halftone pattern for gradation improvement free from variance of irradiation is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a mesh pattern exposure device for improving image quality in an electrophotographic copying machine.

[Prior Art] In an effort to improve copy image quality in electrophotographic copying machines, many methods and devices have been proposed for exposing a mesh screen pattern image separately from original exposure, mainly as a means for improving gradation.

As a typical example, (1)...The mesh pattern image is exposed on the entire surface at the same time.

(2)...Image-forming exposure of a mesh pattern cylinder rotating synchronously with the photoreceptor.

3)... A fixed band-shaped mesh pattern is exposed intermittently.

There are methods and devices such as

However, the devices in (1) and (2) above are large,
It is complicated and expensive, and if the relationship between the intermittent exposure timing and the actual moving distance of the photoreceptor during the intermittent exposure is not appropriate, the device described in (3) cannot produce accurate mesh screens at pattern joints. There was a problem in that a pattern was not formed and striped unevenness occurred in this part.

Therefore, Japanese Patent Application Laid-Open No. 53-8142 proposes a configuration in which the exposure timing is determined intermittently based on the signal from a photodetector using a disc with irregularities provided on the shaft of the photoreceptor. A plate-based photodetector (optical encoder) requires extremely high precision, making the device complex and expensive.

[Objective] It is an object of the present invention to economically provide a copying machine that forms a uniform net screen pattern image without uneven irradiation using a simple device.

[Structure] In an electrophotographic copying machine, the present invention provides an arbitrary light body movement distance corresponding to one tooth of a gear or pulley that drives a photoreceptor! (Dan 2)
and the irradiation slit width (length 01 in the direction of photoconductor movement) of the net pattern exposure device (nl = nf12), and the intermittent irradiation timing of the net pattern exposure device is set to the time for every nl movement of the irradiation slit width of the photoconductor. The halftone screen pattern image is formed at a required portion of the photoreceptor surface before or after exposure of the original image, and then developed and transferred.

[Example] An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an overall side view of an electrophotographic copying machine equipped with a mesh pattern exposure apparatus according to the present invention.

The document on the document table 1 is illuminated by an illumination unit consisting of an irradiation lamp 2 and a reflector 3, and the reflected light is
Mirror 4, second mirror 5, third mirror 6, fourth mirror 7
, lens 8, and fifth mirror 9 to the sixth mirror IO.

At the sixth mirror IO, component light of one color among blue light, green light, and red light (here, it is assumed to be blue light) is reflected, and component light of the other two colors is transmitted. The blue light reaches the first S light belt 11, and the blue light projection position 12
image is formed.

On the other hand, the green light and red light that have passed through the sixth mirror IO reach the seventh mirror 13 (where the green light is reflected and the red light is transmitted), and the green light is transmitted to the second photoreceptor belt 1.
The image is formed at the green light projection position 15 of No. 4.

The red light that has passed through the mirror 13 reaches the third photoreceptor belt 17 by the mirror 16 and forms an image at the red light projection position 18, whereby the colors are separated onto the surface of each photoreceptor belt. An electrostatic latent image is formed. Next, a net screen pattern image is exposed by the net pattern exposure device 31 overlapping this electrostatic latent image.

The first to third photoreceptor belts 11, 14, and 17 are driven in the direction of the arrow in the drawing by the clockwise rotation of the respective drive rollers 20.

As each photoreceptor belt moves, the developing process begins. Since the first photoreceptor belt 11 has been exposed to blue light, the developing device 19 uses yellow toner, which is a complementary color, to develop the image. be converted into Similarly, the second photoreceptor belt 1
4 is exposed to green light, so the developing device 21 uses magenta toner, which has a complementary color relationship with this, and the third photoreceptor belt 17 has received red exposure, so the developing device 22 uses magenta toner, which has a complementary color relationship with this toner. It is visualized using cyan toner.

These photoreceptor surfaces on which toner images are formed are
The charges are removed by pre-transfer charge eliminators 23, 24, and 25, and each toner image is arranged so as to be transferred to the same position on the transfer paper as it advances to each transfer position 12°, 15', and 18'.

On the other hand, the transfer paper 26 is driven in the direction of the arrow in the drawing by the counterclockwise rotation of the drive roller 30 at a timing that matches the leading edge position of the toner image on the third photoreceptor belt 17. It is supplied onto the conveyor belt 27.

A cyan toner image is transferred onto the transfer paper 26 fed onto the transfer paper conveyance belt 27 by the transfer charger 28 at the transfer position 18° of the third photoreceptor belt 17, and then the cyan toner image is transferred onto the transfer paper 26 fed onto the transfer paper conveyance belt 27 by the transfer charger 28. The magenta toner image on the belt 14 and the yellow toner image on the first photoreceptor belt 11 are superimposed and transferred at the transfer position 12' by the respective transfer chargers.

In this embodiment, the mesh pattern exposure device 31 is placed after exposing the original image, but it may be placed before exposing the original image.

Next, the mesh pattern exposure device 31 will be explained with reference to FIGS. 2 and 3.

The net pattern exposure device 31 includes an illumination lamp unit 32, a diffuser plate 33 for making the brightness uniform, a slit plate 34 (the inside of the slit is indicated by 1) for regulating the irradiation on the photoreceptor surface, and a net screen pattern filter 35. , and a lens 36 for forming an image of the net screen pattern of the net screen pattern filter 35 on the surface of the photoreceptor.

The illumination lamp unit 32 emits light intermittently, and in this embodiment is an LE lamp with a bar lens to improve illumination efficiency.
A D element array unit is used. As shown in FIG. 4, the mesh screen pattern filter 35 has light transmitting parts 35a having an area ratio of 10 to 40 arranged in a row on a predetermined pattern line, and the remaining 60 to 90 parts are non-transparent. The light transmitting part 35a and the non-transmitting part 35b form a regular pattern (screen angle θ=45 degrees).

Incidentally, as shown in FIGS. 2 and 3, the ill state is set in the photoreceptor surface exposure slit.

At least a net screen pattern filter 35 is fixed to the slit plate 34 by adhesive or the like, integrated with the slit plate 34, and pressed by a spring member 38 to form a film surface of the lens 36 and the net screen pattern filter 35 (the slit plate
The lens 36 is housed in the holder 37 such that the distance from the lens 36 (the surface side of the lens 4) matches the specification value of the lens 36.

Further, the distance between each photoreceptor belt 11, 14, 17 and the lens 36 is fixed by adjusting the position of the entire mesh pattern exposure device 31 including the holder 37 within the machine so that the distance = L.

The slit plate 34 has a tapered shape with a width larger than 111 on the side of the diffuser plate 33, as shown in FIG. 2, so that the entire area of the slit 1 has uniform brightness.

The above mesh screen pattern filter 35 is attached to the slit plate 3
4 is shown as a plan view (a) and a side view (b) in Fig. 5, the mesh screen pattern is in the same row at the front and rear edge A and A' positions of u1 in the slit. It is configured to be in a state.

Then, the illumination lamp unit 32 is blinked intermittently at a period of time tl in which the photoreceptor 11, 14, 17 moves one distance, and the charges on the photoreceptor surface in the portion corresponding to the light transmitting portion 35a are erased. A regular erase pattern (u1(a), dan2(b), r13(c)-1) is formed in the middle direction and in the advancing direction (see FIG. 6).

However, the moving speed of the photoreceptor is not always constant, but fluctuates in a meshing cycle for each gear such as a drive gear or a pulley.

In other words, the speed of the photoreceptor (Vp) is determined by its center speed <
It usually has fluctuation components of VO) and Shizuko.

In such a state, if the illumination lamp unit 32 is operated with the blinking cycle tl once 1/VO without any effort, the moving distance of the photoreceptor during the time tl will not be constant. As a result, as shown in Fig. 7, dan 1 (a), fl 1 (b), dan 1 (c)...
A gap (.DELTA.n>) or an overlapping state (.DELTA..degree.) may occur at the boundary between each erase area, resulting in an irregular erase pattern.

Furthermore, when the illumination lamp unit 32 emits light intermittently, the distance the photoreceptor moves during the light emission time differs depending on whether the speed of the photoreceptor is fast or slow, and the size of the erase dot changes (U- 1(a), n 1(b), 1
1 (c)...Differences occur in each area),
A copy developed and transferred from this image has the disadvantage that it becomes an image with uneven shading in the form of horizontal stripes at the fil pitch.

Therefore, in order to solve the above problem, the present invention configures the net pattern device 31 as follows.

FIG. 8 shows an overall side view of the photoreceptor drive device, and the transfer paper conveyance drive roller 30 has a worm wheel 41 driven by a worm gear 46 provided on a drive shaft 45.
are fixed coaxially. Further, the drive gear 42 of the registration roller 40 is fixed coaxially with the worm wheel 41, and is connected to the registration roller clutch 4 via an idle gear 43.
4 and the registration roller 4°.

Further, the fixing roller drive gear 49 is also connected to the worm wheel 4.
1 and transmits power from the drive shaft 45 to the fixing roller via the idle gear 50.

The worm wheel 41... is a worm gear 46 fixed in parallel on one extended drive shaft 45.
...and they are intertwined with each other. This single drive shaft 45 is horizontally supported in relation to the registration roller 40, the photoreceptor drive roller 20, the transfer paper conveyance belt drive roller 30, and the fixing roller drive mechanism, and extends long. and is interlocked with the output shaft of one electric motor 47 via a timing belt 48. By driving one long drive shaft 45 with a single electric motor 47 in this way, the worm wheels 41 that mesh with the worm gears 46 fixedly attached to the drive shaft 45 are rotated all at once. Registration roller 40
, first to third photoreceptor belts, transfer paper conveyance belt 27
and drives all of the fuser rollers. Then, one rotation of the worm wheel 41 causes the photoreceptor belt drive roller 20 to
The worm wheel 4 also rotates once, but here, the worm wheel 4
1, the number of teeth is Z, and the circumference of the drive roller 20 is πD (however,
D is the roller diameter), then the photoreceptor for one tooth is πD/Z
move on. If the moving distance of the photoreceptor for one tooth is 2, and the center speed of the photoreceptor movement is 0, then the meshing period (t2) for each tooth becomes t2 = l /VO.

Further, the photoreceptor velocity waveform is shown in FIG. 10(a), and according to this, the photoreceptor moves a certain distance u2 in time t2 from any point in time.

Therefore, it is set so that the mesh screen pattern exposure period regulated by the slit plate 34 is set to be the same as 112, and the light emitting period t1 of the illumination lamp unit 32 is set to the same timing as t2 (see FIG. 10(b)). . Then t
The distance traveled by the photoreceptor during time l is constant, and furthermore,
The speed of the photoreceptor at the time of light emission is also constant.

From this, the slit width at is set to be an integral multiple (9 times) of the photoreceptor belt 1.0y2 for one tooth. That is, if the irradiation timing tl is an integer multiple of the meshing period for each tooth of the worm wheel, and tl = n-t2, the net pattern images for each slit width exposed on the photoreceptor surface will overlap or have gaps. There is no such thing, resulting in a regular image.

However, even if the relationship between ul and u2 (that is, the relationship between tl and t2) is not an exact integer multiple, if it is approximately approximated, then fil( for one erase area and the area before and after it (n 1(b)) There are almost no problems between a) and fil(c)). That is, ∆° and ∆° in Fig. 7 are close to zero, the speeds at the time of light emission of the illumination lamp unit 32 are also similar, and the sizes of the erase dots are also almost the same, so that in practice there is no adverse effect on the image. do not have.

For example, when the number of teeth of the worm wheel 41 is Z=62, and the circumferential length πD of each drive roller 20 is 75 mm, then 2=1.21 mm.

Therefore, by setting tan l = 1.211 Im, the screen angle is 4
A mesh screen pattern filter 35 of 120 lines/inch was installed in the mesh pattern exposure device 31 so that the mesh screen pattern was aligned in the same row on the line AA' in FIG. Then V O = 120mm/see
and t l =0.01 sec, t (ON) = 0
．． As a result of blinking each illumination lamp unit 32 with one pulse oscillator (not shown) under the condition of 0.003 sec, it was possible to obtain an excellent copy with no unevenness in density.

In this example, we have explained the case where it is installed in a color copying machine that uses a plurality of belt-shaped photoreceptors, but it can also be installed in a monocolor copying machine or a color copying machine that uses a single belt-shaped or drum-shaped photoreceptor. A similar effect can be obtained.

[Effects] As described above, the present invention relates the dimensions of the mesh screen pattern exposure to the photoreceptor movement distance of one tooth of the worm wheel that drives the photoreceptor belt, thereby achieving complicated,
A uniform gradation-improving net pattern without uneven irradiation can be formed without requiring any expensive special equipment.

4. Brief description of the drawings FIG. 1 is a schematic diagram of an electrophotographic copying machine according to the present invention, FIG. 2 is a sectional view of a mesh pattern exposure device, FIG. 3 is an explanatory perspective view of the mesh pattern exposure device, and FIG. 4 5 is a partially cutaway view of the mesh screen pattern filter, FIG. 5 is an explanatory diagram of the mesh screen pattern filter attached to the slit plate, and FIG.
7 is an explanatory diagram of erase pattern formation on the photoreceptor surface,
FIG. 8 is a side view of the entire photoreceptor driving device, FIG. 9 is a sectional view taken along the line B--B in FIG. 8, and FIG. 10 is a graph showing the photoreceptor speed waveform and the irradiation timing of the irradiation lamp.

Il, 14.17... Photoreceptor belt, 12.15
．． 18...Each light projection position, 12", 15', 18
'...Transfer position, 19.21.22...Developing device, 20...Photoconductor drive roller, 31...Mesh pattern exposure device, 32...Illumination lamp unit, 34 ... Slit plate, 35 ... Net screen pattern filter, 4
5... Drive shaft, 48... Pulley, Dan1...
...Irradiation slit width, r12...Photoconductor movement distance for one tooth of the photoconductor drive gear.

Claims (2)

[Claims] (1) After the photoreceptor is uniformly charged, a mesh screen pattern image is intermittently irradiated by a mesh pattern exposure device before or after exposing the original image to form a mesh screen pattern image with the width of the irradiation slit on the required part of the photoreceptor surface. After that, in an electrophotographic copying machine configured to perform development and transfer, the photoconductor is moved by one tooth of a gear or pulley that drives the photoconductor, changing the slit width (length in the direction of photoconductor movement) of the mesh pattern exposure device. An electrophotographic copying machine characterized in that the width is an integer multiple of the distance to be scanned. (2) The electrophotographic copying machine according to claim 1, wherein the intermittent irradiation timing of the mesh screen pattern image of the mesh pattern exposure device is set to a time interval of movement of the irradiation slit width of the photoreceptor.