JPH08286457A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device which recognizes a color registration pattern easily and correctly even in case linear scratch and soil are caused on an image carrier in the direction of its movement. CONSTITUTION: The image forming device 1 comprises a pattern producing part 2, image forming parts 3a-3d, a part 4 for reading a color registration pattern 11, an error detection part 5 for detecting an amount of error in color registration, a line-width setting part 8 for setting the line width of the color registration pattern 11 greater than the widths of soil and scratch, and a low pass filter 9 which recognizes the color registration pattern 11 and sends the result to the error detection part 5. It further comprises a detection part 12 which detects the widths of soil and scratch.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a function of detecting a color registration error which indicates the degree of color deviation when images of different colors are superposed to obtain a color image.

[0002]

2. Description of the Related Art In recent years, document production in offices has been rapidly changed to color, and accordingly, it has been required for devices such as copying machines, printers and facsimiles to support colorization. Further, when the colorization of these devices is promoted, high image quality of output images and high speed output are required.

However, if an attempt is made to increase the output speed, it becomes difficult to maintain the high quality of the output image due to the deterioration of the color registration. Also, the position of the unit for forming images of each color due to the temperature change inside the device, the impact when refilling recording paper, the external force when a person bumps into the device, and the position of the parts inside each unit. When the speed and the like are attempted to be increased, the slight change in the position causes deterioration of the color registration.

Therefore, Japanese Unexamined Patent Publication No. 64-88471 and Japanese Unexamined Patent Publication No. 1-83676 disclose a technique for measuring an error amount of color registration and correcting it to improve image quality. . This is to form a color registration pattern corresponding to each color on the image carrier, optically read these color registration patterns by a reading means, and calculate the interval between the color registration patterns of each color based on the read signal. The position of the image forming unit of each color and the image formation start timing are corrected so that this becomes equal to the reference value.

FIG. 13 is a block diagram illustrating an image forming apparatus 1'having a function of measuring such a color registration error. That is, the image forming apparatus 1 ′ has a predetermined color registration pattern 11 ′ corresponding to each color.
And a color registration pattern 11 ′ corresponding to each color are formed as an image on the transport belt which is the image carrier 10, and a color on the image carrier 10. A reading unit 4 that optically reads the registration pattern 11 ′ and converts it into an electric signal, and an error detection unit 5 that obtains an error amount of color registration based on the electric signal read by the reading unit 4 are provided. An image temporary storage unit 6 that temporarily stores image data corresponding to each color and a controller 7 that controls each unit are provided.

In order to execute the image forming mode which is a normal image output by the image forming apparatus 1 ', first, general image data 20 is stored in the image temporary storage section 6.
The general image data 20 includes Black, Yellow,
The image data of each color is “K”, “Y”, “M” in the image temporary storage unit 6, and is used to form a multicolor image by superimposing images of four colors of Magenta and Cyan.
Each is stored in "C". Next, the drive roller 10a and the driven roller 10b feed a sheet of paper (not shown) onto the image carrier 10 and convey it.

Image forming units 3a to 3d corresponding to respective colors are arranged on the image carrier 10, and a sheet conveyed on the image carrier 10 passes under the image forming units 3a to 3d. Becomes At this time, the leading edge of the conveyed paper is black.
Of the image forming unit 3d such that the image forming unit 3d reaches the transfer point immediately below and the tip of the image formed by the image forming unit 3d reaches the transfer point at the same time.
The image data is sequentially read from “K” of the image temporary storage unit 6 by d, and an image is formed.

As a result, the images formed by the image forming section 3d are sequentially transferred onto the paper at the transfer points. Similarly, the yellow image forming unit 3c, the image forming unit 3b of Magenta and Cy corresponding to the sheet conveyance.
The image forming unit 3a of “an” is “Y” in the image temporary storage unit 6,
Image data of corresponding colors are sequentially read from "M" and "C" to form an image. In this manner, the images are formed by the image forming units 3a to 3d while the timings are sequentially taken, so that the images of the respective colors are superposed on the paper to form a color image.

Next, the amount of color registration error is measured by the image forming apparatus 1 ', and the image forming portion 3a for each color is measured.
Execution of the color registration correction mode for correcting the position of 3d and the timing of image formation will be described. First, the controller 7
Then, a command is issued to each unit to notify that it is in the color registration correction mode. Upon receiving this notification, the pattern generation unit 2 ′ outputs the image data of the color registration pattern 11 ′ corresponding to each color to the image temporary storage unit 6.

In the color registration correction mode, the sheet is not conveyed and only the image carrier 10 is rotated by driving the drive rollers 10a and 10b. Then, in this state, the image forming units 3a to 3d corresponding to each color perform exactly the same operation as the above-described image forming mode at the same timing, and directly correspond to each color on the image carrier 10 that does not convey the sheet. The color registration pattern 11 'is transferred.

14 and 15 are views showing examples of color registration patterns transferred onto the image carrier 10. That is, in the example shown in FIG. 14, the color registration patterns 11a ′ to 11d ′ of the respective colors are sequentially transferred to both ends of the image carrier 10 along a direction perpendicular to the moving direction of the image carrier 10 (see the arrow in the figure). Has been done. These color registration patterns 1
1a ′ to 11d ′ are used to measure the amount of color registration error in the moving direction of the image carrier 10.

Further, in the example shown in FIG. 15, the color registration patterns 11a 'to 11d' of respective colors are sequentially transferred to both ends of the image carrier 10 along the moving direction of the image carrier 10 (see the arrow in the figure). . These color registration patterns 11a '
11d 'are used for measuring the color registration error amount in the direction perpendicular to the moving direction of the image carrier 10.

Any of the color registration patterns 11a'-1
Even if it is 1d ′, after being transferred onto the image carrier 10, it is optically read by the reading unit 4 and converted into a predetermined electric signal. The error detection unit 5 obtains an electric signal from the reading unit 4 and uses the color registration patterns 11a ′ to 11a corresponding to each color.
The interval of d ′ is compared with a reference value, and the difference in color registration error amount is notified to the controller 7.
The controller 7 corrects the positions of the image forming portions 3a to 3d for each color and the image forming start timing so that the color registration error amount becomes zero. This ends the color registration correction mode.

The effect that the color registration error is corrected in this way will appear in the next image forming mode.

[0015]

However, such an image forming apparatus has the following problems. That is, after the image forming apparatus is used for a long period of time, the environment for measuring the error amount of color registration is deteriorated and the measurement accuracy is lowered. In particular, the image carrier that forms the color registration pattern easily deteriorates,
Easy to get dirty and scratched. For example, as shown in FIG. 16, when the image carrier 10 is linearly scratched (similarly for dirt) along the moving direction (see the arrow in the figure), the position of the color registration pattern 11a ′ is accurately determined. Difficult to detect.

FIG. 17 is a diagram showing an example of an output signal from the reading section in the C section in FIG. Thus, in the reading unit 4 (see FIG. 16), the color registration pattern 1
An accurate color registration error amount cannot be detected unless both the signal from 1a 'and the signal from a flaw are read and which signal from the color registration pattern 11a' is distinguished.

Therefore, the present invention provides an image forming apparatus capable of easily and accurately recognizing a color registration pattern even when linear scratches or stains are formed on the image carrier along its moving direction. The purpose is to provide.

[0018]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus configured to achieve the above object. That is, the image forming apparatus of the present invention comprises a pattern generating means for generating a color registration pattern for measuring a color registration error, an image forming means for forming the color registration pattern as an image on an image carrier, and an image forming means. It has a reading means for optically reading the color registration pattern formed on the carrier and converting it into an electric signal, and an error detecting means for obtaining an error amount of color registration based on the electric signal obtained by the reading means. In addition, based on the electric signal obtained from the line width setting means for setting the line width of the color registration pattern to be thicker than the width of the linear stains or scratches along the moving direction of the image carrier, and the electric signal obtained from the reading means. And a recognition means for recognizing the color registration pattern and passing the result to the error detection means. Further, the image forming apparatus is also provided with a stain / scratch width detecting means for detecting the width of a linear stain or scratch along the moving direction of the image carrier.

[0019]

According to the present invention, the line width of the color registration pattern is set by the line width setting means to be thicker than the width of the linear stains or scratches along the moving direction of the image carrier, and the line width is set by the pattern generating means. A color registration pattern with the specified line width is generated. Therefore, the color registration pattern formed on the image carrier by the image forming means is thicker than the width of stains and scratches. Further, since the line width of the color registration pattern is thicker than the width of stains or scratches, the recognition unit accurately distinguishes the color registration pattern based on the electric signal obtained from the reading unit and the stains or scratches from the signal difference. , The result is passed to the error detecting means. Further, in the case where the dirt scratch width detecting means is provided, the width of linear dirt and scratches on the image carrier is detected in advance. This makes it possible to form a color registration pattern having a line width thicker than the width of the stain or scratch on the image carrier, depending on the width of the stain or scratch.

[0020]

Embodiments of the image forming apparatus of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus 1 includes, for example, Black, Yellow, M
This is a device for recording a multicolor image by superimposing four-color images composed of agent and Cyan, and has a function of correcting an error amount of color registration.

Therefore, the image forming apparatus 1 forms the color registration pattern 11 and the pattern generating section 2 for generating a predetermined color registration pattern 11 corresponding to each color as an image on the conveyor belt which is the image carrier 10. Image forming unit 3a
3d, a reading unit 4 that optically reads the color registration pattern 11 and converts the color registration pattern 11 into an electric signal, an error detection unit 5 that obtains a color registration error amount based on the electric signal, and image data corresponding to each color. An image temporary storage unit 6 for temporarily storing the image, a controller 7 for controlling each unit, a line width setting unit 8 for setting the line width of the color registration pattern 11 to a predetermined thickness, and a reading unit. 4 and a low-pass filter 9 which is a recognition means for recognizing the color registration pattern 11 on the basis of the electric signal from 4.

The pattern generating section 2 has a built-in storage means (not shown) and stores image data of the color registration pattern 11 having a predetermined line width set by the line width setting section 8. As the storage means, a ROM, a hard disk, or the like that does not disappear even when the power of the image forming apparatus 1 is turned off is used.

2 and 3 are diagrams showing examples of color registration patterns generated by the pattern generating section 2. As shown in FIG. In the example shown in FIG. 2, the color registration patterns 11a to 11d of the respective colors are sequentially transferred to both ends of the image carrier 10 along a direction perpendicular to the moving direction of the image carrier 10 (see the arrow in the drawing). . These color registration patterns 11a to 11d
Is used to measure the amount of color registration error in the moving direction of the image carrier 10.

Further, in the example shown in FIG. 3, the color registration patterns 11a to 11d of the respective colors are sequentially transferred to both ends of the image carrier 10 along the moving direction of the image carrier 10 (see the arrow in the figure). These color registration patterns 11a to 11d
Is used to measure the amount of color registration error in the direction perpendicular to the moving direction of the image carrier 10. All of the color registration patterns 11a to 11d are optically read by the reading unit 4 after being transferred onto the image carrier 10.

The image forming sections 3a to 3d are for forming images corresponding to respective colors. In the image forming mode, an image based on general image data 20 is formed on a sheet (not shown), and color registration is performed. In the correction mode, an image is formed based on the image data of the color registration pattern 11 sent from the pattern generating section 2. Therefore, the image forming unit 3a
Denoted at 3d are those for forming an image by an electrophotographic method by combining a photoconductor, a scanning optical system and a developing means, those for forming an image by transferring pigments or the like of an ink ribbon by heat or impact force, and ink scattering. Any unit may be used as long as it forms an image, such as a unit that forms an image by doing so. The image forming units 3a to 3d corresponding to each of these colors are usually installed at substantially equal intervals.

The reading section 4 is a color registration pattern 1 formed on the image carrier 10 by the image forming sections 3a to 3d.
1 is optically read and converted into a predetermined electric signal. As shown in the enlarged cross-sectional view of FIG. 4, the reading unit 4 includes a window 41 that takes in light that is transmitted to the upper side of the image carrier 10 from the illuminating means 40 that is arranged below the image carrier 10, and a window 41. An image forming optical system 42 that forms an image of the captured light, a photoelectric conversion unit 43 that receives the light formed by the image forming optical system 42, and a drive circuit board 44 that fixes the photoelectric conversion unit 43 and that includes a drive circuit. And is housed in the housing 45.

The illuminating means 40 applies the color registration pattern 11 (see FIG. 1) formed on the image carrier 10 to the image carrier 1.
Illuminate from the bottom of 0. Therefore, for example, an LED, a halogen lamp, a fluorescent lamp, or the like that can secure a sufficient amount of light is used. In this example, it is assumed that the image carrier 10 is a translucent member, and the illumination means 40 is arranged below the image carrier 10 (transmissive illumination system), but the image carrier 10 is opaque. When used as a member, the illuminating means 40 is arranged diagonally above the image carrier 10 to reflect light (reflection type illumination system).

The illumination means 40 is controlled by an illumination control means (not shown) so that the amount of illumination light can be adjusted. As a result, the light amount is reduced due to the deterioration of the illumination unit 40, the transmittance of the image carrier 10 is reduced, the sensitivity of the photoelectric conversion unit 43 is reduced, and the illumination unit 40 and the window 4 are used.
Even if the quantity of light is reduced due to the adherence of the stain 1, the photoelectric conversion means 43 can be kept in the optimum light receiving state. If the reading unit 4 is arranged in a sufficiently bright place, the illuminating unit 40 may be omitted.

Further, the imaging optical system 4 in the reading section 4
Reference numeral 2 is a SELFOC lens array, an achromatic lens, a phorogram lens, or the like, and may be anything as long as it keeps the surface of the image carrier 10 and the photoelectric conversion means 43 in a conjugate relationship.

The photoelectric conversion means 43, which is a main component of the reading section 4, reads an image of the color registration pattern 11 (see FIG. 1) formed by the imaging optical system 42 and converts it into an electric signal. It is composed of an image sensor such as an image sensor and a photoelectric conversion element such as a photodiode. The drive circuit board 44 has a circuit for driving the photoelectric conversion means 43 and also has an interface function of outputting the electric signal output from the photoelectric conversion means 43 to the low-pass filter 9 shown in FIG.

The case 45 is for accommodating the image forming optical system 42, the photoelectric conversion means 43, and the drive circuit board 44, and an opening for allowing the light from the illumination means 40 to enter inside is provided in the lower part thereof. A window 41 for preventing the entry of toner, dust, etc. is attached to this opening. A cover is attached to the upper part of the housing 45.

Next, the error detector 5 will be described. As shown in the block diagram of FIG. 5, the error detection unit 5 receives the signal band-limited by the low-pass filter 9 and calculates the interval of the color registration pattern 11 (see FIG. 1) corresponding to each color, and uses this as a reference. The controller 7 (see FIG. 1) is notified of the color registration error amount 55, which is the difference between the value and the value.

Therefore, the error detector 5 processes the signal from the low-pass filter 9 to produce the color registration pattern 11
(See FIG. 1) Pattern position calculation means 51 for calculating each pattern position, pattern position memories 52a to 52d for temporarily storing the calculation result for each color, and the number of calculations of the pattern position calculation means 51 are counted. The end signal generating means 54 notifying that all of the color registration pattern 11 has passed under the reading section 4 (see FIG. 1) and the content of the pattern position memories 52a to 52d in response to the end signal of the end signal generating means 54 are displayed. The color registration error calculating means 53 is provided which calculates the interval between the color registration patterns 11 of the respective colors while referring to the reference value and obtains the color registration error amount 55.

The error detecting section 5 includes color registration patterns 11a to 11d corresponding to each color as shown in FIGS.
Is calculated, and the color registration error amount 55 corresponding to each direction is calculated. That is, in the case of the color registration patterns 11a to 11d shown in FIG. 2, the color registration error is based on the design value of the interval (the interval along the moving direction of the image carrier 10) of the color registration patterns 11a to 11d of each color. The amount 55 is calculated, and in the case of the color registration patterns 11a to 11d shown in FIG. 3, the design of the spacing between the color registration patterns 11a to 11d of each color (the spacing in the direction perpendicular to the moving direction of the image carrier 10) is designed. The color registration error amount 55 is calculated based on the value, that is, zero.

The image temporary storage unit 6 of the image forming apparatus 1 shown in FIG. 1 temporarily stores general image data 20, and
The image data of the color registration pattern 11 is temporarily stored, and both are selected according to the image forming mode or the color registration correction mode. Therefore, the image forming apparatus 1 is used in a DRAM, an SRAM, a hard disk, or the like, in which the power may be turned off and data may be lost. Further, the controller 7 notifies each part of the start of the image forming mode and the color registration correction mode, and at the end of the color registration correction mode, the color registration error amount 55 (see FIG. 5) output from the error detection part 5 is displayed. Then, the work of correcting the positions of the image forming portions 3a to 3d and the image forming start timing corresponding to the respective colors is performed so that this becomes zero.

In the image forming apparatus 1 according to the first embodiment,
In particular, a line width setting unit 8 that sets the line width of the color registration pattern 11 (see FIG. 1) is provided, and a low-pass filter 9 that is a recognition unit that recognizes the color registration pattern 11 based on an electric signal from the reading unit 4 is provided. The feature is that it is equipped.

The line width setting unit 8 forms the color registration which is formed more than the width of a stain or a scratch linearly formed along the moving direction of the image carrier 10 which is expected in terms of the characteristics of the image forming apparatus 1 (mechanism). The setting is made to thicken the line width of the pattern 11.
The pattern generating section 2 generates the color registration pattern 11 having the line width set by the line width setting section 8 and transfers the image data to the image temporary storage section 6.

FIG. 6 shows a low-pass filter 9 (see FIG.
FIG. 4 is a band characteristic diagram of a Laplacian filter which is an example of a reference). For example, when an 11-tap Laplacian filter is used, its coefficient is -0.05471, -0.
01167, 0.08416, 0.14778, 0.2
1466, 0.23956, 0.21466, 0.14
778, 0.08416, -0.01167, -0.0
If it is set to 5471, the band characteristic as shown in FIG. 6 is obtained, and the low pass characteristic can be obtained.

Even if the low-pass filter 9 is constructed by a program process, an element is composed of a coil and a capacitor which are generally commercially available, and the order and the constant of the element are optimally designed to obtain a desired characteristic. You may Moreover, since the output of the reading unit 4 (see FIG. 1) is usually an analog signal, when a Laplacian filter is adopted, an A / D conversion means (not shown) is provided in advance to convert it into a digital signal. There is a need.

Next, the procedure for measuring the color registration error amount in the image forming apparatus 1 having such a configuration will be described. Here, as shown in FIG. 7, the image carrier 1
An example of reading is when there is a scratch (width h) along the moving direction of 0. First, the image forming units 3a to 3a shown in FIG.
By 3d, the color registration pattern 11 corresponding to each color is formed along the moving direction of the image carrier 10. This allows
As shown in FIG. 7, the color registration patterns 11a to 11 are provided on both ends of the image carrier 10 along the moving direction of the image carrier 10 for each color.
d are formed in sequence. In addition, this color registration pattern 1
The line width H of 1a to 11d corresponds to the line width setting unit 8 described above.
(See FIG. 1), it is set thicker than the width h of the scratch.

Next, the color registration patterns 11a-11
The image carrier 10 on which d is formed is moved to sequentially read signals based on the color registration patterns 11a to 11d.
Read by. FIG. 8 is a diagram showing an example of an output signal from the reading unit 4, (a) is a portion A of FIG. 7, and (b) is a diagram.
Corresponds to the reading at the portion B in FIG. In each drawing, the portion where the amount of received light is reduced indicates the portion where the light from the illumination means 40 (see FIG. 4) is blocked. For example, in the case of FIG. 8A, the color registration pattern 11a (see FIG. 7), and in the case of FIG. 8B, the color registration pattern 11a and the scratched portion.

Next, the output signal from the reading section 4 is passed to the low-pass filter 9 (see FIG. 1) to limit the band. FIG. 9 is a diagram showing an example of an output signal from the low pass filter 9. That is, FIG. 9A is obtained by passing the read output signal (see FIG. 8B) at the position shown in FIG. 7B through the low-pass filter 9. In this example,
The width h of the scratch shown in FIG. 7 is 0.1 mm (fundamental frequency is 5 Li
Since the band characteristic shown in FIG. 6 has no gain, the line width H of the color registration pattern 11a is about 0.5 mm (fundamental frequency 1 Line-pair / mm). Therefore, the gain is almost "1". Therefore, in FIG.
As shown in (a), a large waveform difference occurs between the color registration pattern and the scratch.

Similarly, FIG. 9B shows an output signal obtained by passing the read signal at the position C in FIG. 16 through the low-pass filter 9 in FIG. Even when the difference between the scratch width and the line width of the color registration pattern 11a ′ is small as in the conventional case, it is possible to cause a difference in waveform by passing the light through the low-pass filter 9. Can be easily recognized.

Next, this output signal is passed to the error detector 5 shown in FIG. In the error detecting section 5, the pattern position calculating means 51 shown in FIG. 5 receives this signal and sets the respective threshold values as shown in FIG. As shown in FIG. 9A, when there is a large difference between the waveform of the color registration pattern 11a (see FIG. 7) and the waveform of the flaw, the threshold value is set to about 50%, and the pattern position calculating means 51 is set. (See FIG. 5) calculates the position of the center of gravity of the hatched portion in FIG. This is the position of the color registration pattern 11a.

Further, as shown in FIG. 9B, when there is no large difference between the waveform of the color registration pattern 11a and the waveform of the scratch, a threshold value of about 80% is set, and this threshold value is set in the same manner. The position of the center of gravity of the hatched portion in FIG. Such position calculation is calculated for each of the color registration patterns 11a to 11d. As a result, even if the image carrier 10 is scratched (including dirt), only the position of the color registration pattern 11 can be accurately extracted.

Color registration patterns 11a to 11 of the respective colors calculated by the pattern position calculating means 51 shown in FIG.
The position of d will be temporarily stored in the pattern position memories 52a to 52d. In addition, the operation of this temporary storage,
This is repeated for all the color registration patterns 11a to 11d formed on the image carrier 10. The total number of color registration patterns 11a to 11d is the same as that of the normal image forming units 3a to 3
The length is often an integral multiple of the type of d (see FIG. 1) and can be formed over the entire circumference of the image carrier 10.

Therefore, the total number or the time required for the color registration patterns 11a to 11d to pass under the reading section 4 is uniquely determined. Utilizing this property, the end signal generating means 54 shown in FIG. 5 has the number of operations of the pattern position calculating means 51 or the color registration patterns 11a to 1a.
Monitoring the time elapsed since the first detection of 1d,
When these exceed a predetermined value, an end signal is sent to the color registration error calculation means 53.

Next, the color registration error calculating means 53 which has received the end signal of the end signal generating means 54,
The interval between the color registration patterns 11a to 11d for each color is calculated with reference to the contents of the pattern position memories 52a to 52d, and this is compared with a reference value to obtain a color registration error amount 55. The procedure for calculating the color registration error amount 55 is as follows.

First, the value of the pattern position memory 52a for "K" in which the position of the black color registration pattern 11a is stored is sequentially read and the average thereof is obtained, and then the position of the yellow color registration pattern 11b is stored. The value of the "Y" pattern position memory 52b is read and the average thereof is calculated. The pattern position memory 52c for "M" and the pattern position memory 52d for "C"
And calculate the difference between them.

For example, taking Black as a reference,
Difference between the average value of the "Y" pattern position memory 52b and the average value of the "K" pattern position memory 52a, the average value of the "M" pattern position memory 52c and the average value of the "K" pattern position memory 52a And the difference between the average value of the “C” pattern position memory 52d and the average value of the “K” pattern position memory 52a. This is the interval between the color registration patterns 11a to 11d corresponding to each color.

Next, the color registration error calculating means 53 sets the interval of the color registration patterns 11a to 11d corresponding to each color calculated previously to a predetermined reference value (the color registration pattern of each color in the moving direction of the image carrier 10). Is a design value of the interval, which is zero in the direction perpendicular to the moving direction of the image carrier 10, and notifies the controller 7 shown in FIG. 1 of the color registration error value 55, which is the difference between them. To do.

The controller 7 corrects the positions of the image forming portions 3a to 3d (see FIG. 1) of each color and the image formation start timing so that the color registration error value 55 (see FIG. 5) becomes zero. This makes it possible to correct the color registration error.

The low-pass filter 9 shown in FIG.
In order to make the description easy to understand, is independent, but the same applies to the configuration incorporated in the reading unit 4 or the error detection unit 5. Further, although an example in which an electrical one is used as the low-pass filter 9 has been described in this embodiment, the optical low-pass filter 9 can be realized by devising the optical system of the reading unit 4.

For example, frosted glass or the like is put in the optical system between the image carrier 10 and the photoelectric conversion means 43 shown in FIG. 4, and the color registration pattern 11 on the surface of the image carrier 10 is focused on the photoelectric conversion means 43. The characteristics of the low-pass filter can be optically obtained by blurring the image (see FIG. 1). This can be easily realized by changing the window 41 from transparent glass to frosted glass.

As another means, as shown in the enlarged cross-sectional view of FIG. 10, the positional relationship among the image carrier 10, the imaging optical system 42, and the photoelectric conversion means 43 is intentionally shifted so that the image carrier 10 is moved. The color registration pattern 1 that forms an image on the photoelectric conversion means 43 by slightly breaking the conjugate relationship between the photoelectric conversion means 43 and
It is also possible to blur the image of No. 1 (see FIG. 1) and optically obtain the characteristics of the low-pass filter.

As described above, in the image forming apparatus 1 according to the first embodiment, the line width setting unit 8 makes the line width of the color registration pattern 11 thicker than the width of scratches and stains, and the low pass filter 9 works properly. Since the position of the color registration pattern 11 can be recognized, it is possible to measure the error amount of good color registration.

Next, the image forming apparatus 1 according to the second embodiment of the present invention will be described. FIG. 11 is a configuration diagram illustrating the image forming apparatus 1 according to the second embodiment. That is, the image forming apparatus 1 is characterized in that it is provided with the stain scratch width detecting unit 12, the characteristic changing unit 13, and the pattern width changing unit 14.

The stain flaw width detection unit 12 is capable of monitoring the output signal from the reading unit 4 to the low-pass filter 9, and detects the period when this output signal is below a predetermined threshold value. The width of the stains and scratches on 10 can be measured. The comparison between the output signal and the threshold value is performed by a comparator (not shown) including an analog or digital comparator. The measurement of the period when the output signal is below the threshold value is performed by a counter (not shown) that receives the output of the comparator. The dirt / scratch width detecting unit 12 determines the width of the measured dirt or scratches by the characteristic changing unit 1
3 and the pattern width changing unit 14 are notified.

The characteristic changing section 13 includes a low-pass filter 9
Incorporating a look-up table having several kinds of coefficients to be set for, the dirt and scratch width signals are received by the look-up table after the dirt and scratch width signal is received from the dirt and scratch width detection unit 12. It is configured so that the characteristic of the low-pass filter 9 can be changed and set by referring to the corresponding coefficient. The look-up table is stored in a ROM or a hard disk that does not lose the data even when the image forming apparatus 1 is powered off.

The pattern width changing section 14 is built in the pattern generating section 2 and also has a storage means (see FIG. 1) for storing several kinds of color registration patterns 11 (see FIG. 1) which are also built in the pattern generating section 2 and have different thicknesses. (Not shown), the line width of one color registration pattern 11 can be set based on the signal of the width of the stain or the scratch obtained from the stain scratch width detection unit 12.

Next, a procedure for correcting a color registration error in the image forming apparatus 1 of the second embodiment having such a configuration will be described. First, the controller 7
When a command is issued to each part by the
Shifts to the operation of detecting the width of a stain or scratch on the image carrier 10. At this time, the pattern generation unit 2, the image temporary storage unit 6, and the image forming units 3a to 3d temporarily enter a rest state, and only the image carrier 10 on which the color registration pattern 11 is not formed is rotated.

Next, the reading section 4 performs an operation of reading the image carrier 10 on which the color registration pattern 11 is not formed, in the same manner as when the color registration pattern 11 is formed. As a result, signals from dirt and scratches on the image carrier 10 are read.

Next, the stain flaw width detecting section 12 monitors the output signal from the reading section 4 to the low-pass filter 9 to obtain an output signal as shown in FIG. Then, this is compared with a predetermined threshold, and the period during which the output signal is below the threshold is measured. The predetermined threshold value is preset to about half the amount of received light with respect to the bottom of the signal when the color registration pattern 11 is read. The dirt / scratch width detection unit 12 performs this operation over the entire circumference of the image carrier 10, obtains the maximum value of the detected dirt / scratch, sets it as the width of the dirt / scratch, and notifies the characteristic changing unit 13 of the value. .

The characteristic changing section 13 receives the signal of the width of the stain or the scratch obtained from the stain / scratch width detecting section 12 so that the cutoff frequency becomes 2 to 3 times the basic frequency of the width of the stain or the scratch. A corresponding coefficient is selected from the look-up table so that the low coefficient is set to the low pass filter 9. Then, the selected coefficient is changed and set for the low-pass filter 9.

Further, the pattern width changing unit 14 receives the signal of the width of the stain or scratch from the stain scratch width detecting unit 12 like the characteristic changing unit 13, and the line width of the color registration pattern 11 indicates the stain or scratch. The color registration pattern stored in the storage means is selected so as to have a width of about 5 times. As a result, the color registration pattern 11 having a line width thicker than the width of stains or scratches on the image carrier 10 is formed on the image forming portions 3a to 3a.
It is possible to set the low-pass filter 9 that can be formed on the image carrier 10 from 3d and that can surely recognize the position of the color registration pattern 11 based on the signal read by the reading unit 4.

After changing the characteristics of the low-pass filter 9 and the line width of the color registration pattern 11 in this manner, the error amount of color registration similar to that described in the first embodiment is measured. As a result, even if the image carrier 10 deteriorates due to long-term use and the state of scratches due to adhered dirt changes, it is possible to always perform good color registration error measurement accordingly.

Further, the image forming apparatus 1 in the second embodiment.
As an application example of the above, when detecting the width of dirt or scratches, the pattern position calculating means 51 (see FIG. 5) of the error detection unit 5 monitors the signal after passing through the low-pass filter 9 for dirt or scratches, and detects the signal bottom. Is detected and the threshold value of the pattern position calculating means 51 is set in the middle between the bottom of the output signal of the low-pass filter 9 and the signal bottom of the stain or scratch previously obtained in the color registration correction mode. .

As a result, even if the measurement environment of the color registration error due to stains or scratches deteriorates, the position of the color registration pattern 11 can be reliably distinguished from the position of stains or scratches. It is possible to perform a good color registration error measurement.

In this embodiment, Black,
The image forming apparatus 1 that records a multicolor image by superimposing images of four colors of Yellow, Magenta, and Cyan has been described as an example, but the present invention is not limited to this, and another color (including monotone) is superimposed. The same applies to an apparatus that also forms an image.

[0070]

As described above, the image forming apparatus of the present invention has the following effects. That is, when measuring the color registration error, even if the image bearing member has stains or scratches, the simple and inexpensive structure ensures that the color registration pattern is not affected by the stains or scratches. It becomes possible to recognize the position. Moreover, by detecting the width of stains and scratches on the image bearing member and setting the line width of the color registration pattern according to the detected width, stains and scratches that change with the use of the image forming apparatus can be detected. Accordingly, it is possible to measure the color registration error correspondingly. As a result, it is possible to measure the color registration error with high accuracy over a long period of time, so that it is possible to always provide a high quality image output.

[Brief description of drawings]

FIG. 1 is a configuration diagram illustrating a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a color registration pattern (No. 1)
Is.

FIG. 3 is a diagram showing an example of a color registration pattern (No. 2)
Is.

FIG. 4 is an enlarged cross-sectional view illustrating a reading unit.

FIG. 5 is a block diagram illustrating an error detection unit.

FIG. 6 is a band characteristic diagram of a Laplacian filter.

FIG. 7 is a diagram illustrating a scratched state.

FIG. 8 is a diagram showing an example of an output signal from a reading unit.

FIG. 9 is a diagram showing an example of an output signal from a low pass filter.

FIG. 10 is an enlarged cross-sectional view illustrating another example.

FIG. 11 is a configuration diagram illustrating a second embodiment of the present invention.

FIG. 12 is a diagram showing an example of an output signal when a stain scratch is read.

FIG. 13 is a configuration diagram illustrating a conventional example.

FIG. 14 is a diagram (part 1) showing an example of a conventional color registration pattern.

FIG. 15 is a diagram (No. 2) showing an example of a conventional color registration pattern.

FIG. 16 is a diagram showing a scratched state.

FIG. 17 is a diagram showing an example of an output signal from a reading unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Pattern generation part 3a-3d Image formation part 4 Reading part 5 Error detection part 6 Image temporary storage part 7 Controller 8 Line width setting part 9 Low pass filter 10 Image carrier 11 Color registration pattern 12 Stain scratch width detection part 13 Characteristic change part 14 Pattern width change part

Claims (2)

[Claims] 1. A pattern generating means for generating a color registration pattern for measuring a color registration error, an image forming means for forming the color registration pattern as an image on an image carrier, and an image forming means on the image carrier. Image formation having a reading unit for optically reading the color registration pattern formed on the substrate and converting it into an electric signal, and an error detecting unit for obtaining an error amount of color registration based on the electric signal obtained by the reading unit. An apparatus, wherein the line width of the color registration pattern is set to be thicker than the width of linear stains or scratches along the moving direction of the image carrier, and the line width setting unit is obtained from the reading unit. An image forming apparatus comprising: a recognizing unit that recognizes the color registration pattern based on an electric signal and transfers the result to the error detecting unit. 2. The image forming apparatus according to claim 1, further comprising: a stain flaw width detection unit that detects a width of a linear stain or flaw along the moving direction of the image carrier.