JPH0620225B2 - Color misregistration correction device in image forming apparatus - Google Patents

Description

Detailed Description [Table of Contents] Outline Industrial field of application Conventional technology (Figs. 4 and 5) Problems to be solved by the invention Means for solving problems (Fig. 1) Operation Embodiments (FIGS. 2 and 3) Advantageous Effects of the Invention [Outline] In the color image forming apparatus, in order to prevent positional deviation of images of respective colors to be combined, the present invention synchronizes with the rotation of the image carrier and synchronously. The misregistration amount of the recorded dot is stored, and the latent image formation timing of the image of each color is corrected based on this, so that the misregistration of each color is eliminated over the entire image and a good color image is obtained. It is a thing.

[Industrial application field]

The present invention relates to a color misregistration correction device in an image forming apparatus such as an electrophotographic recording device, and more particularly to accurately correcting color misregistration of toner images of a plurality of colors.

[Conventional technology]

A color electrophotographic recording apparatus, for example, as shown in FIG.
Chargers 21, 24, 27, and exposure LED (Light Emitting Diode) arrays 22, 2 are arranged on the periphery of the photosensitive drum 20.
5, 28, yellow developing device 23, magenta developing device 2
6. A cyan developing unit 29 is arranged, and the exposure LED arrays 22, 25, 28 are caused to emit light in accordance with the data stored in the separately prepared image memory to form a latent image for each color, Yellow, magenta, and cyan toner images obtained by developing with a yellow developing device 23, a magenta developing device 26, and a cyan developing device 29, respectively, are sequentially formed in position as the photosensitive drum 20 rotates. A color image can be recorded by combining them to form a color image and transferring the color image to the recording paper 31 by the transfer device 30. Reference numeral 32 is a cleaner, and a driver is provided in the block of each exposure LED array 22, 25, 28.

At this time, if the positions of the yellow, magenta, and cyan toner images are displaced, the colors expressed by the combination of these three colors are also displaced, and the image quality is degraded. Therefore, it is necessary to accurately record the positions of the toner images of the respective colors to be combined.

Therefore, in the conventional color image recording apparatus, as shown in FIG. 5, the increment output pulse signal from the rotary encoder 41 directly connected to the photosensitive drum shaft moves one recording dot by the rotation of the surface of the photosensitive drum 20. Frequency divider 42, so that one pulse output is obtained each time
Each exposure LED array 21, 24 divided by 45, 48,
It is used as a light emission timing clock of 27. In each of the exposure LED arrays 21, 24, 27, image information is read from the image memories 44, 47, 50 according to the values of the clock signals counted by the counters 43, 46, 49, and data for one dot line is read. Is transmitted to the exposure LED arrays 21, 24 and 27.

At this time, when the exposure LED array 21 for yellow is made to emit light first so that the timings may be different depending on the mounting positions of the exposure LED arrays 21, 24, 27 that perform image exposure for each color of yellow, magenta, and cyan. Shifts the numerical values of the counters 46 and 49 so as to delay the image recording timing by the exposure LED array 24 for magenta and the exposure LED array 27 for cyan.

[Problems to be solved by the invention]

By the way, in such a conventional color image recording apparatus, an incremental output from a rotary encoder is used as a light emission timing clock signal for each exposure LED array 21, 24, 27 for recording an image of each color of yellow, magenta, and cyan. A signal obtained by dividing the pulse signal at equal intervals is used.

However, in reality, due to the eccentricity of the photosensitive drum, the difference in the rotation angle due to the misalignment of the photosensitive drum and the rotary encoder, or the pitch error of the rotary encoder,
Pitch unevenness occurs relatively between the movement amount of the photosensitive drum surface and the light emission timing clock pulse.

The pitch unevenness is periodical in synchronization with the rotation of the photosensitive drum, but the phase of the pitch unevenness is shifted due to the difference in the mounting positions of the LED arrays for exposure, so that yellow,
There is a problem in that the positions of the recording dots are deviated between magenta and cyan, resulting in color misregistration.

Therefore, it is an object of the present invention to provide an image forming apparatus that does not have such color shift.

[Means for solving problems]

In order to achieve the above object, according to the present invention, as shown in FIG. 1, when the dot YT of the yellow toner is used as a reference, the dot M of the magenta toner is formed on the dot line 1 which coincides with the dot YT.
T and cyan toner dots CT are arranged so that color misregistration is corrected to correct the degree of misalignment. First
In the state shown in the figure, the dot MT of magenta toner shows a state delayed by 3 pulses from the output pulse of the rotary encoder with respect to the reference dot line 1, and the dot CT of cyan toner shows a state advanced by 2 pulses. . Therefore, in such a case, the light emission timing of the exposure LED array for magenta is advanced by 3 pulses by the output pulse of the rotary encoder, and the light emission timing of the exposure LED array for cyan is delayed by 2 pulses. Such correction is performed over one round of the photosensitive drum.

[Action]

This makes it possible to accurately match the developing positions of the respective colors over the entire image.

〔Example〕

The configuration of an embodiment of the present invention will be described based on FIGS. 2 and 3 with reference to other drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a ROM (Read Only) in which correction information according to the present embodiment is written.
Memory) is an example.

In FIG. 2, 1 is a rotary encoder, 2 is a frequency divider, 3 is a counter, 4 is an image memory in which image data for yellow is written, 5 is an exposure LED array for yellow, 6 is a counter, and 7 is Image memory in which image data for magenta is written, 8 is an exposure LED for magenta
Array, 9 is a counter, 10 is an image memory in which image data for cyan is written, and 11 is an exposure LE for cyan.
D array, 12 is a counter for counting the increment output pulse output from the rotary encoder 1, 1
3 is a ROM for magenta correction, 14 is an R for cyan correction
Since these ROMs 13 and 14 are OM and are characteristic parts of the present invention, they will be described later in detail.

In this embodiment, the recording dot pitch is 400 dpi,
The diameter of the photosensitive drum is 218 mm, and the rotary encoder 1 outputs a pulse signal of 43200 pulses in one rotation. The frequency divider 2 outputs 43200 pulse signals per one rotation, that is, one pulse signal obtained by dividing one rotation into 43200 equal parts.
The frequency is divided into / 4 to generate a light emission timing clock. In addition, a driver exists in the illustrated blocks of each exposure LED array 5, 8, 11.

The counter 12 counts 43,200 pulse signals per revolution output from the rotary encoder 1, that is, increment output pulses, and is set by a zero signal generated when the rotary encoder 1 makes one revolution.

The ROM 13 is a ROM in which data for magenta correction is written, and the output pulse of the rotary encoder 1 indicating the absolute rotation position of the photosensitive drum, that is, 4 pulses per rotation.
It is accessed by the output of counter 12 which counts 3200 increment output pulses. FIG. 3A illustrates the ROM 13 in the case of correcting the state of the magenta toner MT in FIG. That is, in FIG. 1, the rotary encoder 1 is determined from the yellow toner dot YT with the magenta toner MT as a reference.
Since there is a delay of 3 pulses in the increment output pulse of, if there is no delay, the absolute rotation device m of the photosensitive drum, that is, the counter 12 that counts the increment output pulse of the rotary encoder 1 When the dot MT of the magenta toner of the image with respect to the dot YT is to be developed, "1" is written in the address of m-3, which is advanced by 3 pulse positions, so that the exposure LED array 24 for magenta is displayed. It is configured to emit light earlier by the amount of deviation.
The next light emission timing is m + 1.

ROM14 has R written with data for cyan correction
OM, which is accessed by the output of the counter 12 like the ROM 13. FIG. 3B illustrates a case where correction is performed on the state of the dot CT of the cyan toner of FIG. That is, as shown in FIG. 1, since it advances from the yellow toner dot YT by two pulses, if there is no advance, the cyan dot recorded at the absolute rotation position n will be developed with two pulses delayed, n +.
"1" is written in the address of 2, so that the exposure LED array 27 is delayed so that the cyan dot is delayed by 2 pulses.
The light emission timing of is corrected.

By the way, the correction data of the ROMs 13 and 14 are entered as follows.

First, in the same manner as in the conventional case shown in FIG. 5, three exposure LED arrays 21, 24, 27 are recorded over the entire circumference of the photosensitive drum by using the light emission timing clocks at the same intervals as those 21, and each of them is recorded. Check the recording state of color toner by partially enlarging it.

As a result, at a certain position, as shown in FIG. 1, if accurate, each dot of yellow, magenta, and cyan, which should be lined up in the axial direction of the photosensitive drum, is recorded while being displaced in the photosensitive drum rotation direction. The number of pulses is measured with respect to the output pulse interval of the rotary encoder 1 based on the amount of deviation based on the yellow dot.

As a result, when the absolute rotational position of the photosensitive drum is m when the absolute rotational position is magenta and n when the photosensitive drum is cyan, when they are deviated as shown in FIG.
Fill in. Of course, conversely, the correction position may be set to “0”, the other to “1”, and “0” may be set to the light emission timing.

Such operations are distributed evenly over the entire circumference of the photosensitive drum, and interpolation is performed at, for example, several tens of points, and the light emission timing of the exposure LED array for recording magenta and cyan is written in each ROM to generate a light emission timing clock. The means.

Of course, the counters 6 and 9 are counted up by this light emission timing clock.

As a result, the light emission timings of the magenta exposure LED array 8 and the cyan exposure LED array 11 are corrected, and based on the image data read from the image memories 7 and 10 by the outputs of the counter 6 and the counter 9, A latent image is formed and developed at an accurate position, and the recording dot positions of the respective colors are matched with each other with high accuracy, whereby a good color image can be obtained.

In the above embodiment, an example of combining three colors of yellow, magenta and cyan has been described as a color image recording method, but the present invention is not limited to this, and other colors may be combined. The number of colors to be combined can be two, or four or more.

Further, the means for detecting the rotational position of the photosensitive drum is not limited to the rotary encoder, and other means having an equivalent function can be used.

〔The invention's effect〕

In the image forming apparatus, the surface of the photosensitive drum is moved due to the eccentricity of the photosensitive drum, the difference in the rotation angle due to the axis deviation between the photosensitive drum and the rotational position detecting means such as the rotary encoder, or the pitch error of the rotational position detecting means. The amount, the output pulse of the rotational position detecting means, and the clock pulse at equal intervals generate relative pitch unevenness.

This pitch unevenness is periodic in synchronization with one rotation of the photosensitive drum, and the phase is different for each image writing unit whose position is different in the circumferential direction.

Therefore, in the present invention, latent image formation position correction information corresponding to the absolute rotation position of the photosensitive drum is stored in advance over one round of the photosensitive drum, and the image formation timing is corrected by referring to this information according to the rotation position of the photosensitive drum. As a result, it is possible to eliminate the positional shift over the entire image.

As described above, according to the present invention, it is possible to accurately match the recording dot positions of the images of the respective colors to be combined with each other by an extremely simple means, so that good color image recording without color misregistration over the entire image area can be performed. A possible imaging device can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is a structural diagram of an embodiment of the present invention, FIG. 3 is an explanatory diagram of a ROM in which correction information is written in the present invention, and FIG. 4 is a color electrophotographic recording apparatus. And FIG. 5 is an explanatory view of a conventional example. 1 ... Rotary encoder, 2 ... Frequency divider 3 ... Counter, 4 ... Image memory 5 ... Exposure LED array for yellow 6 ... Counter 7 ... Image memory 8 ... Exposure LED array for magenta 9 ... Counter 10 ... Image memory 11 ... Exposure LED array for cyan 12 ... Counter 13 ... ROM 14 ... ROM

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location G06K 15/12 C H04N 1/23 103 C 9186-5C

Claims (1)

[Claims] 1. An image forming apparatus for forming a toner image on an endless image carrier (20) by a plurality of developing means, and transferring an already-synthesized toner image onto a recording sheet at a time to record an image. The rotational position detection means (1) for detecting the absolute rotational position of the image carrier and the storage means for storing the latent image forming position correction information corresponding to the absolute rotational position of the image carrier over the entire circumference of the image carrier are provided. A color misregistration correction apparatus in an image forming apparatus, wherein a latent image formation timing signal is output based on information.