JPS6059376A - Adjusting device of image density - Google Patents

Abstract

PURPOSE:To take a high-quality copy having no irregularity of density regardless of a copy history by adjusting the amount of exposure according to the characteristic distribution of a photosensitive body perpendicular to a moving direction, and adjusting the density. CONSTITUTION:A surface electrometer 8 is provided to a scanner 9. When a motor 13 rotates, the electrometer 8 scans on the surface of the photosensitive body 5 in the direction of a shaft 5a to measure the potential. An image density adjusting filter 4 is made of, for example, translucent black polyethylene and wound around a shaft 17. The tip of the filter 4 is drawn with wires 18a and 18b. The wires 18a and 18b are wound around the shaft 17. When some potential difference on the photosensitive body 5 is recognized by the measurement of the electrometer 8, the filter 4 is moved and stopped at the difference part. Thus, the filter 4 is set where image density should be adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image density adjusting device for an image forming apparatus such as an electronic copying machine, and particularly to a device for adjusting the density of one image so as to correct the charging characteristics or sensitivity characteristics of a photoreceptor.

In conventional copying machines, the following image@density unevenness often occurs in the copied image f. After making many copies with a width narrower than the maximum possible copy width, there will be a difference in the charging ability and sensitivity of the photoreceptor between the part of the photoreceptor that is used for copying and the part that is not, and the charging characteristics of the photoreceptor will become unstable. η increases uniformly. If a large width copy is subsequently made, a density step will occur at the boundary of the copied image corresponding to the size of the previous multiple copies. This phenomenon is particularly noticeable in halftone (/--ftone) images.

The appearance of this level difference differs depending on the characteristics of the photoconductor, and the causes are: (1) Differences in the charging history of the photoconductor depending on whether there is an original or not.

■ Differences in development B history on the photoconductor caused by differences in the amount of developer attached depending on whether or not development is performed.

(2) This is thought to be due to residual developer or deposits on the surface of the photoreceptor, which causes differences in the exposure history of one image of the static elimination exposure tube, resulting in differences in the charging characteristics, sensitivity characteristics, etc. of the photoreceptor.

For example, after making 5,000 consecutive copies of A4 size, which is slightly smaller than this, using a copying machine that uses a Se photoreceptor and a one-component pressure fixing developer and is capable of maximum copying of B4 size,
B4 size 7-ftone original (original density = 0.
4) Copied. When the density of the close-up image was measured using a Macbeth densitometer RD-514 (trade name), the density of the copy image in a portion corresponding to A4 size was D5000p and H were 06. Copy image density D5000 in non-compatible areas
S, HIr'r, was 0.3.

In this example, the portion corresponding to the portion with a large copy history had a higher density than the other portions. photoreceptor, developer,
In some cases, the opposite level difference may appear due to factors such as electrostatic charge and light.

Such density unevenness l'j in one image makes it difficult to read the number of copied strokes and degrades its quality.

An object of the present invention is to provide an image density adjustment device that eliminates the above-mentioned drawbacks of conventional image forming devices and provides an image forming device that can make high-quality copies without uneven image density regardless of the copy history. With the goal.

In order to achieve this object, the present invention provides an image density adjusting device for an image forming apparatus that exposes one image while the exposure position on the photoreceptor moves. This image density adjustment device is characterized in that it adjusts the exposure amount according to distribution characteristics and adjusts the density of one image to be formed.

Examples of the present invention will be described in detail below. FIG. 1 is a schematic diagram of an embodiment of an electronic machine H equipped with an image density adjusting device to which the present invention is applied.

An optical path RAY is irradiated onto a document 1 from an exposure lamp 2. The optical paths R and AY are reflected by the original 1, passed through the optical system 3, and are irradiated onto the photoreceptor 5vc via the distribution correction filter 4, so that an image of a copy is formed on the surface of the photoreceptor 5. The entire photoreceptor 5 is charged in advance by a charger 6. The positive charges are partially removed by the subject image, forming an electrostatic latent image.

This electrostatic a1 image is developed in a developing device 7, transferred to copy paper, and then fixed by a conventional known means to obtain a copy.

The surface electrometer 8 does not operate in such Nishinomiya copying process. For example, it operates when about 1000 copies have been made and it is necessary to adjust the density of one image.

FIG. 2 is a perspective view showing details of an image density adjusting device comprising a surface electrometer 8 and an image density adjusting filter 4. As shown in FIG.

A surface electrometer 8 is attached to a scanner 9.

The scanner 9 is engaged with a guide rod 25 by a pole screw that engages with a threaded rod 10. The threaded rod 10 is connected to the motor 1 through gears 11 and 12.

When the motor 13 rotates, the first surface electrometer 8 scans the surface of the photoreceptor 50 in the direction of the axis 5a to measure the surface potential.

A pulse plate 14 and a photoelectric sensor 15 are attached to the motor 16. There is also a scanner 9 at the back and front of the guide rod 25.
Several microswitches 16a and 16b are arranged at a distance corresponding to the scanning width.

The image density adjustment filter 4ri is made of, for example, semi-transparent black polyethylene and is wound around a shaft 17. The tips of the filter 4 are connected to wires 18a and 18b, and the wires 18a and 18b are wound around a shaft 17 via an idle shaft 19.

The shaft 17 is connected to and driven by the step motor 2 OK gears 21 and 22. An exposure optical system 6 is located above the photoreceptor 50.
(omitted in this figure) is arranged, and a filter 4 blocks a part of the optical path. Note that the wires 18a and 18b are located outside the exposure optical path and do not affect the formation of one image.

In the back direction of the drum 5, the upper tail photoelectric sensor 2 of the filter 4
7 is provided to detect the presence or absence of the filter 4.

FIG. 6 is a control block diagram of the image density adjustment device. The copying process of the electronic copying machine is carried out by the main body sequence control CP.
Controlled by U30. Image 1 The signal at the start of the image density adjustment and the signal at the end are the image (image a degree adjustment control Cl) U? ) is connected between 2.

The CPU 32 is a microcomputer including a microprocessor, ROM-RAM, and an input/output interface. The CPU 32 includes a tarlock pulse of the photoelectric sensor 15, a clock pulse of the photoelectric sensor 24, a measured potential of the surface electrometer 8, an on/off signal of the switch 16a, and a clock pulse of the photoelectric sensor 24.
The on/off signal of the sensor 27 and the on/off signal of the sensor 27 are respectively converted into digital signals and inputted as necessary. Also CPU3
From 2, a forward rotation or reverse rotation drive signal is sent to the motor 13, and a motor 2
A drive signal for forward or reverse rotation is output to 0. The ROM of the CPU 32 stores an execution program for this control system.

A flowchart diagram of the program is shown in FIG.

In the figure, a dotted line 50 is a part of the execution program of the main body CPU 30, and the two-image density adjustment is performed every 1000 sheets. CPU
This process may be carried out at any time when the copy number counter of 32 is 1000 (in order to remove unnecessary charge, toner, etc. on the photoreceptor).

At the beginning, the filter 4 is wound around the shaft 17. In step 101, it is determined whether the sensor 27 detects the filter 4 or not. Since the sensor 27 has detected the filter 4 including 0FF72, the motor 20 is reversed (
Step 102), the filter 4 is wound around the shaft 17, and when the sensor 27 is turned on, the motor 20 is stopped (step 106). With this, the fill is removed from the optical path RAY of the 4H1ilE optical system 6. Next, the surface potential is measured by scanning with a surface electrometer 8. Since the electrometer 8 was returned to the back side in the previous image density adjustment, the motor 16 is rotated in the normal direction (step 104) to scan from the back to the front. Read the surface potential Vl (potential of the back side of the photoreceptor) at the beginning of scanning into register 1 (step 105).
. The sensor 15 starts counting pulses from the pulse plate 14 of the motor 16 (step 106). While counting, the surface potential V2 at that time is read into the register R2 (step 107). A step appears in the surface potential and +R1-I'!
2 becomes 100V or more (step 108), it is necessary to adjust the image density using the filter 4. R1-R2
If <100, the switch 16b turns ON on the electrometer 8 (step 109), and j! Scanning is then stopped until it comes to the front of rl (step 11o).

While scanning, counting and measuring the surface voltage v2 are continued. Then, in step 108, R1-R,2≧100
When the position is reached, extend the filter 4 to that position.

Since it is no longer necessary to scan the surface electrometer 8, the motor 13 is stopped (step 111). The position where a step appears in the surface potential L1 = aT, (a is the scan speed) is calculated (step 112). The motor 20 is rotated forward to extend the filter to that position (step 113). While counting the pulses of the motor 20 & 23 with the sensor 24 (step 114)
), position 112 of filter 4 = 12 (b is filter 4
(moving speed). This step 114-115
While repeating this, when TJ2≧LIK'fx (step 116), that is, when the filter 4 has moved to a point where there is a step in the surface potential.

The motor 20 is stopped (step 117). The filter 4 has now reached the adjustment position.

Next, return the electrometer 8 to its original position at the back. The motor 13 is reversed (step 118), and when the switch 16a detects the potential control 8 (step 119).

Stop the motor 13.

With the above steps, the filter 4 is placed at the position where the image density is to be adjusted, and the electrometer returns to the home position I'X side') ItC, and the process is completed. An end signal is output from the CPU 32 to the main body sequence control roller CPU 6Q, and the copying machine becomes ready for normal copying again.

If the image is copied in such a state, an extremely high quality photocopied image without uneven density can be obtained.

In the embodiment, image density adjustment filters may be provided in multiple layers. In that case, after the filter in tube 1 moves to the concentration adjustment position, the first filter is fixed at that position as long as the release signal is
The drive source of the second filter receives the signal from U and moves the second filter. When the surface potential of the photoreceptor has multiple steps, the previously adjusted uniforming effect of the first filter continues, and the uniformizing effect of the second filter is added. The maintenance cycle of the photoreceptor extends to d].

The above example is an example of automatic control using a microcomputer to drive the filter of the device, but when a difference occurs in the charging characteristics of the photoreceptor, Zarpisman manually adjusts the surface potential of the photoreceptor. Even if I do, I won't cut it.

Examples of the exposure amount distribution correcting means at that time are shown in FIGS. 5 to 8.

In FIG. 5, 41 is a filter, which is fixed to the opening frame 42 with Velcro tapes 43a and 44a and 43b and 44b, and can be adjusted steplessly in the longitudinal direction of the opening. Note that since the tip portion 41a of the filter 41 has a thicker light transmittance than the tip portion 41b, steps at the correction boundary are prevented when correction is performed using the filter according to the characteristics of the photoreceptor.

FIG. 6 shows a second filter 45 in addition to the first filter 41.
This is an example of overlapping the . When there are two levels of image density, the density can be adjusted at each position.

FIG. 7 shows an example in which the exposure adjustment means on each side are filters, but are replaced with light shielding adjustment plates 46 and 47. That is,
Adjustment plates 46 and 47 protrude into the slit portion of the opening frame 42 and are fixed with screws 48 through elongated holes. Depending on the greeting size frequently used by the user 9 For example, if a large number of B5 size copies are used, the exposure distribution is corrected by narrowing the aperture with both adjustment plates 46 and 47, and A4 size copies are When used frequently, the adjustment plate 47 is used alone to narrow the aperture and correct the exposure distribution.

FIG. 8 similarly uses a light-shielding adjustment plate, but this is an effective configuration when parts with little copy history are more likely to be charged to a higher potential than parts with many copies. The width of the light shielding plate 49 attached to the aperture frame 42 is wider than the light shielding plates 50 and 51, so as to cover more of the portion of the photoreceptor with a large copy history.

The image density adjustment device described above is a Se photoreceptor.

When applied to a copying machine using a one-component pressure fixing developer and actually copied, the following satisfactory results were obtained.

After making 5,000 consecutive copies of A4 size copy paper, B
The halftone manuscript was cohesive using 4 sizes of copy paper, and the density was measured using a Macbeth densitometer RD-514. In the area corresponding to A4 size, the copied image density was D5000P and H was 06, and in the non-compatible area, the copied image density was D5000S and H was 0.3 before using this apparatus. When the filter was placed between A4 size and B4 size, the copy density was 0 in both the A4 size area and the non-A4 size area.
6, and a uniform image was obtained.

As explained above, by using the image density adjusting device of the present invention, it is possible to obtain an image forming apparatus that can produce high-quality copies of 75 ≦ without density unevenness in copied images, regardless of the copy history of the photoreceptor. .

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an electronic copying machine equipped with an image density adjustment device to which the present invention is applied, Fig. 2 is a partial perspective view of a main part thereof, and Figs. 7 and 8 are a partial front view of another embodiment. It is a diagram. 6 is an exposure optical system, 4 is a filter, and 5 is a photoreceptor. 8 is a surface electrometer. Patent applicant Canon Co., Ltd.

Claims (1)

[Scope of Claim] In an image density adjustment device of an image forming apparatus that exposes an image while moving an exposure position on a photoreceptor. An image density adjustment device that adjusts the density of an image to be formed by adjusting an exposure amount according to a characteristic distribution of a photoreceptor in a direction perpendicular to the moving direction.