JP4356706B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus having a function of detecting a color registration error representing a color shift when a color image is obtained by superimposing images of different colors.

  In recent years, the creation of documents in offices has rapidly progressed in colorization, and in response to this, devices such as copying machines, printers, and facsimiles are also required to support colorization. Further, when the colorization of these devices is advanced, it is required to improve the image quality of the output image and increase the output speed.

  However, when trying 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 by the temperature change inside the device, the impact when replenishing the recording paper, the external force when a person hits the device, the position of the parts inside each unit If the above changes slightly, this slight change in position causes deterioration in color registration when attempting to increase the speed.

  Therefore, Patent Document 1 and Patent Document 2 disclose a technique for measuring a color registration error amount and improving the image quality while correcting the error amount. This is because a color registration pattern corresponding to each color is formed on the image carrier, these color registration patterns are optically read by a reading means, and an interval between the color registration patterns of each color is calculated based on the read signal. The position of each color image forming unit and the image formation start timing are corrected so that this becomes equal to the reference value.

  FIG. 13 is a configuration diagram illustrating an image forming apparatus 1 ′ having a function of measuring such a color registration error. That is, the image forming apparatus 1 ′ includes a pattern generating unit 2 ′ that generates a predetermined color registration pattern 11 ′ corresponding to each color, and a color registration pattern 11 ′ corresponding to each color on a conveyance belt that is the image carrier 10. The image forming units 3a to 3d to be formed as images, the color registration pattern 11 ′ on the image carrier 10 to be optically read and converted into an electric signal, and the electric signal read by the reading unit 4 An error detection unit 5 for obtaining an error amount of color registration based on the image data, an image temporary storage unit 6 for temporarily storing image data corresponding to each color, and a controller 7 for controlling each unit. ing.

  In order to execute an image forming mode that is a normal image output by the image forming apparatus 1 ′, first, general image data 20 is stored in the image temporary storage unit 6. The general image data 20 is for superimposing four color images of Black, Yellow, Magenta, and Cyan to form a multicolor image. Each color image data is “K” in the image temporary storage unit 6. , “Y”, “M”, and “C”. Next, a sheet (not shown) is fed onto the image carrier 10 by the driving roller 10a and the driven roller 10b and conveyed.

  On the image carrier 10, image forming units 3a to 3d corresponding to the respective colors are arranged, and the sheet transported on the image carrier 10 is in a state of passing under the image forming units 3a to 3d. At this time, the leading edge of the conveyed paper reaches the transfer point immediately below the black image forming portion 3d and the leading edge of the image formed by the image forming portion 3d simultaneously reaches the transfer point. As described above, the image forming unit 3d sequentially reads image data from “K” in the image temporary storage unit 6 and forms an image.

  As a result, the images formed by the image forming unit 3d are sequentially transferred onto the paper at the transfer points. Similarly, the Yellow image forming unit 3c, the Magenta image forming unit 3b, and the Cyan image forming unit 3a correspond to “Y”, “M”, and “C” in the temporary image storage unit 6 corresponding to the conveyance of the sheet. The image data of the colors to be read are sequentially read out to form an image. In this way, the images are formed by the image forming units 3a to 3d while sequentially taking the timing, whereby the images of the respective colors are superimposed on the paper, and a color image is formed.

  Next, the execution of the color registration correction mode in which the color registration error amount is measured by the image forming apparatus 1 'to correct the positions of the image forming units 3a to 3d and the image forming timings of the respective colors will be described. First, a command is issued to each unit by the controller 7 to notify that it is in the color registration correction mode. Upon receiving this notification, the pattern generating unit 2 ′ outputs the image data of the color registration pattern 11 ′ corresponding to each color to the image temporary storage unit 6.

  In this color registration correction mode, only the image carrier 10 is rotated by driving the driving rollers 10a and 10b without conveying the paper. In this state, the image forming units 3a to 3d corresponding to the respective colors perform the same operation as the image forming mode described above at the same timing, and directly correspond to the respective colors on the image carrier 10 that is not transporting the sheet. The color registration pattern 11 'thus transferred is transferred.

  14 and 15 are diagrams 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 the direction perpendicular to the moving direction of the image carrier 10 (see the arrow in the figure). Has been. These color registration patterns 11 a ′ to 11 d ′ are used for measuring the color registration error amount in the moving direction of the image carrier 10.

  In the example shown in FIG. 15, the color registration patterns 11 a ′ to 11 d ′ 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 11 a ′ to 11 d ′ are used for measuring a color registration error amount in a direction perpendicular to the moving direction of the image carrier 10.

  Any of the color registration patterns 11a 'to 11d' is transferred onto the image carrier 10 and then optically read by the reading unit 4 and converted into a predetermined electric signal. The error detection unit 5 obtains an electrical signal from the reading unit 4, compares the interval between the color registration patterns 11 a ′ to 11 d ′ corresponding to each color with a reference value, and notifies the controller 7 of the color registration error amount that is the difference between them. To do. The controller 7 corrects the positions of the image forming units 3a to 3d for the respective colors and the image formation start timing so that the color registration error amount becomes zero. This ends the color registration correction mode.

  The effect of correcting the color registration error in this way appears in the next image forming mode.

JP-A 64-88471 Japanese Patent Laid-Open No. 1-83676

  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 color registration error amount deteriorates, resulting in a problem that the measurement accuracy is lowered. In particular, an image carrier that forms a color registration pattern is easily deteriorated and is likely to be stained or scratched. For example, as shown in FIG. 16, when a scratch (same as dirt) is linearly formed along the moving direction of the image carrier 10 (see the arrow in the figure), the position of the color registration pattern 11a ′ is accurately set. It becomes difficult to detect.

  FIG. 17 is a diagram illustrating an example of an output signal from the reading unit in the C unit in FIG. As described above, the reading unit 4 (see FIG. 16) reads both the signal from the color registration pattern 11a ′ and the signal from the scratch, and must distinguish which is the signal from the color registration pattern 11a ′. Thus, an accurate color registration error amount cannot be detected.

  Accordingly, the present invention provides an image forming apparatus capable of easily and accurately recognizing a color registration pattern even when a linear scratch or stain is attached along the moving direction on an image carrier. With the goal.

The present invention has been made to achieve such an object. That is, the present invention provides 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 the image carrier, and an image on the image carrier. An image forming apparatus having a reading unit that optically reads a formed color registration pattern and converts it into an electrical signal, and an error detection unit that obtains an error amount of color registration based on the electrical signal obtained by the reading unit. Then, the error detection means calculates the centroid position of the area exceeding the preset threshold value for the waveform of the electric signal obtained from the reading means, and obtains the position of the color registration pattern from the centroid position. Further, in addition to the above configuration, a stain wound width detecting means for detecting the width of linear stains and scratches along the moving direction of the image carrier, and a line width wider than the width detected by the stain scratch width detecting means The image forming apparatus includes a line width setting unit that sets a color registration pattern. Further, according to the present invention, the error detection unit sets a threshold value for a plurality of waveforms in the electrical signal obtained from the reading unit according to a difference in the size of the plurality of waveforms, and the color information is obtained from information on a region exceeding the threshold value. The position of the registration pattern is obtained. At this time, the threshold is a value between the signal bottoms of the plurality of waveforms, and the level difference between the signal bottoms of the plurality of waveforms is the first level difference and the second level difference smaller than the first level difference. If the second level difference is greater than the first level difference, the threshold value that is variable according to the level difference is set so that the signal bottom level is converted into a ratio and closer to the deep side. .

  In 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 line-like dirt and scratches along the moving direction of the image carrier, and the line set by the pattern generation means is set. A width color registration pattern is generated. For this reason, the color registration pattern formed on the image carrier by the image forming means is thicker than the width of dirt or scratches. In addition, since the line width of the color registration pattern is wider than the width of the dirt or scratch, the recognition means accurately distinguishes the color registration pattern based on the electrical signal obtained from the reading means and the dirt or scratch from the signal difference. The result is passed to the error detection means. In the case where the dirt / scratch width detecting means is provided, the width of the linear dirt / scratch attached to the image carrier is detected in advance. This makes it possible to form a color registration pattern having a line width wider than the width of the image bearing member in accordance with the width of dirt or scratches attached to the image carrier. In addition, the error detection means calculates the center of gravity position of the region exceeding the preset threshold for the waveform of the electric signal obtained from the reading means, and obtains the position of the color registration pattern from the center of gravity position. Scratches can be accurately distinguished from the signal difference.

  Therefore, the image forming apparatus of the present invention has the following effects. That is, when measuring the color registration error, even if the image carrier is soiled or scratched, the simple and inexpensive configuration ensures that the color registration pattern is not affected by the soiling or scratching. It becomes possible to recognize the position. In addition, by detecting the width of dirt and scratches attached to the image carrier and setting the line width of the color registration pattern according to this, the dirt and scratches that change as the image forming apparatus is used can be reduced. Accordingly, it is possible to measure the color registration error. As a result, the color registration error can be measured with high accuracy over a long period of time, so that a high-quality image output can always be provided.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus 1 is an apparatus that records a multicolor image by superimposing four color images including, for example, Black, Yellow, Magenta, and Cyan, and has a function of correcting an error amount of color registration. .

  Therefore, the image forming apparatus 1 forms an image on the pattern generating unit 2 that generates a predetermined color registration pattern 11 corresponding to each color, and the color registration pattern 11 on the conveyance belt that is the image carrier 10. Units 3a to 3d, a reading unit 4 that optically reads the color registration pattern 11 and converts it into an electrical signal, an error detection unit 5 that obtains an error amount of color registration based on the electrical signal, and an image corresponding to each color An image temporary storage unit 6 for temporarily storing data; a controller 7 for controlling each unit; and a line width setting unit 8 for setting the line width of the color registration pattern 11 to a predetermined thickness; A low-pass filter 9 that is a recognition unit that recognizes the color registration pattern 11 based on an electrical signal from the reading unit 4 is provided.

  The pattern generation unit 2 includes a storage unit (not shown) and stores image data of the color registration pattern 11 having a predetermined line width set by the line width setting unit 8. As the storage means, a ROM, a hard disk, or the like that does not lose data even when 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 unit 2. FIG. In the example shown in FIG. 2, the color registration patterns 11 a to 11 d of each color 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). . These color registration patterns 11a to 11d are used for measuring the color registration error amount in the moving direction of the image carrier 10.

  In the example shown in FIG. 3, the color registration patterns 11 a to 11 d 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 drawing). These color registration patterns 11a to 11d are used for measuring a color registration error amount in a direction perpendicular to the moving direction of the image carrier 10. Any of the color registration patterns 11 a to 11 d is optically read by the reading unit 4 after being transferred onto the image carrier 10.

  The image forming units 3a to 3d are for forming images corresponding to the respective colors. In the case of the image forming mode, the image forming units 3a to 3d form an image based on general image data 20 on a sheet (not shown), and in the color registration correction mode. In this case, an image based on the image data of the color registration pattern 11 sent from the pattern generator 2 is formed. For this reason, the image forming units 3a to 3d are configured to form an image by an electrophotographic method by combining a photoconductor, a scanning optical system, and a developing unit, or to transfer an ink ribbon pigment or the like by heat or impact force. Any unit can be used as long as it forms an image, such as a unit that forms an image by scattering ink. The image forming units 3a to 3d corresponding to these colors are usually installed at substantially equal intervals.

  The reading unit 4 optically reads the color registration pattern 11 formed on the image carrier 10 by the image forming units 3a to 3d and converts the color registration pattern 11 into a predetermined electric signal. As shown in the enlarged 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 an illumination unit 40 that is disposed below the image carrier 10, and a window 41. An imaging optical system 42 that forms an image of the captured light, a photoelectric conversion means 43 that receives light imaged by the imaging optical system 42, a drive circuit board 44 that fixes the photoelectric conversion means 43 and includes a drive circuit; These are housed in the housing 45.

  The illumination unit 40 illuminates the color registration pattern 11 (see FIG. 1) formed on the image carrier 10 from the lower side of the image carrier 10. For this reason, the thing which can ensure sufficient light quantity, such as LED, a halogen lamp, a fluorescent lamp, is used, for example. In this example, it is assumed that the image carrier 10 is a translucent member, and the illumination means 40 is disposed below the image carrier 10 (transmission illumination system), but the image carrier 10 is opaque. In the case of a member, the illumination means 40 is disposed obliquely above the image carrier 10 so as to reflect light (reflection 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, even if a decrease in the amount of light due to deterioration of the illumination unit 40, a decrease in the transmittance of the image carrier 10, a decrease in sensitivity of the photoelectric conversion unit 43, a decrease in the amount of light due to contamination of the illumination unit 40 and the window 41, etc. occurs. 43 can be maintained in an optimum light receiving state. If the reading unit 4 is arranged in a sufficiently bright place, the illumination unit 40 may be omitted.

  The imaging optical system 42 in the reading unit 4 may be anything as long as it includes a selfoc lens array, an achromatic lens, a holographic lens, etc., and 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 unit 4 reads an image of the color registration pattern 11 (see FIG. 1) created by the imaging optical system 42 and converts it into an electrical signal. For example, a CCD image sensor or the like. The image sensor and a photoelectric conversion element such as a photodiode. The drive circuit board 44 includes a circuit that drives the photoelectric conversion unit 43 and also has an interface function that outputs an electric signal output from the photoelectric conversion unit 43 toward the low-pass filter 9 illustrated in FIG. 1.

  The housing 45 is for housing the imaging optical system 42, the photoelectric conversion means 43, and the drive circuit board 44, and an opening for allowing light from the illumination means 40 to enter the interior is provided below the housing 45. A window 41 is attached to the opening to prevent toner and dust from entering. A cover is attached to the top of the housing 45.

  Next, the error detection unit 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, calculates the interval of the color registration pattern 11 (see FIG. 1) corresponding to each color, and uses this as a reference The color registration error amount 55, which is a difference between the two values, is notified to the controller 7 (see FIG. 1).

  For this reason, the error detection unit 5 processes the signal from the low-pass filter 9 to calculate individual pattern positions of the color registration pattern 11 (see FIG. 1), and temporarily calculates the calculation result for each color. The pattern position memories 52a to 52d to be stored and the end signal generating means 54 for notifying that all the color registration patterns 11 have passed under the reading unit 4 (see FIG. 1) by counting the number of calculation times of the pattern position calculating means 51. In response to the end signal from the end signal generating means 54, the interval between the color registration patterns 11 of the respective colors is calculated while referring to the contents of the pattern position memories 52a to 52d, and this is compared with the reference value to determine the color registration error. The color registration error calculating means 53 for obtaining the quantity 55 is provided.

  The error detector 5 calculates the positions of the color registration patterns 11a to 11d corresponding to the respective colors as shown in FIGS. 2 and 3, and calculates a color registration error amount 55 corresponding to each direction. 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 (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 interval between the color registration patterns 11a to 11d of each color (the interval in the direction perpendicular to the moving direction of the image carrier 10). A 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 or temporarily stores image data of the color registration pattern 11. Both are selected depending on the registration correction mode. For this reason, the image forming apparatus 1 is used in a DRAM, SRAM, hard disk, or the like that may lose data when the power is turned off. Further, the controller 7 notifies each unit of the start of the image formation mode and the color registration correction mode, and the color registration error amount 55 (see FIG. 5) output from the error detection unit 5 at the end of the color registration correction mode. In response, the position of the image forming units 3a to 3d corresponding to each color and the image formation start timing are corrected so that this becomes zero.

  The image forming apparatus 1 according to the first embodiment includes a line width setting unit 8 for setting the line width of the color registration pattern 11 (see FIG. 1), and the color registration pattern 11 based on an electric signal from the reading unit 4. It is characterized in that a low-pass filter 9 is provided as a recognition means for recognizing.

  The line width setting unit 8 is configured so that the width of the color registration pattern 11 to be formed is larger than the width of dirt or scratches that are linearly attached along the moving direction of the image carrier 10 due to the characteristics (mechanism) of the image forming apparatus 1. Settings are made to increase the line width. The pattern generation unit 2 generates a color registration pattern 11 having a line width set by the line width setting unit 8 and passes the image data to the image temporary storage unit 6.

  FIG. 6 is a band characteristic diagram of a Laplacian filter which is an example of the low-pass filter 9 (see FIG. 1). For example, when an 11-tap Laplacian filter is used, the coefficients are set to -0.05471, -0.01167, 0.08416, 0.14778, 0.21466, 0.23956, 0.21466, 0.14778, 0. If the values are set to 08416, −0.01167, and −0.05471, the band characteristics shown in FIG. 6 are obtained, and the low-pass characteristics can be obtained.

  Note that the low-pass filter 9 may be configured by a program process, or may be configured by a commercially available coil and capacitor, so that desired characteristics can be obtained by optimally designing the order and element constants. Good. Further, 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, a procedure for measuring a color registration error amount in the image forming apparatus 1 having the above-described configuration will be described. Here, as shown in FIG. 7, an example of reading when there is a scratch (width h) along the moving direction of the image carrier 10 will be described. First, the color registration patterns 11 corresponding to the respective colors are formed along the moving direction of the image carrier 10 by the image forming units 3a to 3d shown in FIG. As a result, as shown in FIG. 7, color registration patterns 11a to 11d are sequentially formed on both ends of the image carrier 10 corresponding to the respective colors along the moving direction. The line width H of the color registration patterns 11a to 11d is set larger than the width h of the scratch by the line width setting unit 8 (see FIG. 1) described above.

  Next, the image carrier 10 on which the color registration patterns 11 a to 11 d are formed is moved, and signals based on the color registration patterns 11 a to 11 d are sequentially read by the reading unit 4. FIGS. 8A and 8B are diagrams showing examples of output signals from the reading unit 4. FIG. 8A corresponds to reading at the A part in FIG. 7 and FIG. 8B corresponds to reading at the B part in FIG. In each drawing, the portion where the amount of received light is reduced indicates a portion where 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 unit 4 is passed to the low-pass filter 9 (see FIG. 1) to perform band limitation. FIG. 9 is a diagram illustrating an example of an output signal from the low-pass filter 9. 9A is obtained by passing the read output signal (see FIG. 8B) at the position of FIG. 7B through the low-pass filter 9. FIG. In this example, since the scratch width h shown in FIG. 7 is about 0.1 mm (basic frequency is 5 Line-pair / mm), the band characteristic shown in FIG. Since the line width H of the pattern 11a is about 0.5 mm (fundamental frequency 1 Line-pair / mm), the gain is almost “1”. For this reason, as shown in FIG. 9A, 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 if the difference between the width of the scratch and the line width of the color registration pattern 11a ′ is small as in the prior art, it is possible to cause a difference in waveform by passing through the low-pass filter 9, and the position of the color registration pattern Can be easily recognized.

  Next, this output signal is passed to the error detector 5 shown in FIG. The error detection unit 5 receives this signal by the pattern position calculation means 51 shown in FIG. 5, and sets each threshold 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 scratch, about 50% is set as the threshold value, and the pattern position calculating means 51 (See FIG. 5) calculates the barycentric position of the hatched portion in FIG. 9 (a) that exceeds this threshold. This is the position of the color registration pattern 11a.

  Further, as shown in FIG. 9B, when there is no significant difference between the waveform of the color registration pattern 11a and the waveform of the scratches, a threshold value of about 80% is set, and this threshold value is similarly exceeded. (B) The center-of-gravity position of the middle hatched portion is calculated. 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.

  The positions of the color registration patterns 11a to 11d of the respective colors calculated by the pattern position calculation unit 51 shown in FIG. 5 are temporarily stored in the pattern position memories 52a to 52d. This temporary storage operation is repeated for all the color registration patterns 11 a to 11 d formed on the image carrier 10. The total number of the color registration patterns 11a to 11d is an integral multiple of the types of the normal image forming portions 3a to 3d (see FIG. 1), and is often set to a length that can be formed over the entire circumference of the image carrier 10.

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

  Next, the color registration error calculating means 53 that has received the end signal from the end signal generating means 54 calculates the intervals between the color registration patterns 11a to 11d in the respective colors while referring to the contents of the pattern position memories 52a to 52d. 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 values of the “K” pattern position memory 52a in which the position of the black color registration pattern 11a is stored are sequentially read out and the average 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 is obtained. This is also performed for the “M” pattern position memory 52c and the “C” pattern position memory 52d, and the difference between them is obtained.

  For example, taking Black as a reference, the 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 “K And the difference between the average value of the “C” pattern position memory 52a 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 calculation means 53 sets the intervals between the color registration patterns 11a to 11d corresponding to the previously calculated colors as predetermined reference values (the intervals between the color registration patterns of the respective colors in the moving direction of the image carrier 10). This is a design value and is zero in a direction perpendicular to the moving direction of the image carrier 10), and a color registration error value 55, which is the difference, is notified to the controller 7 shown in FIG. 1.

  The controller 7 corrects the positions of the image forming units 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 perform color registration error correction.

  The low-pass filter 9 shown in FIG. 1 has an independent configuration for easy understanding of the description, but the same applies to the configuration built in the reading unit 4 and the error detection unit 5. Further, in this embodiment, an example in which an electrical filter is used as the low-pass filter 9 has been described. However, the optical low-pass filter 9 can be realized by devising the optical system of the reading unit 4.

  For example, rubbing glass or the like is placed 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 that forms an image on the photoelectric conversion means 43 (FIG. 1). The characteristic of the low-pass filter can be optically obtained by blurring the image of (see). This can be easily realized by changing the window 41 from transparent glass to rubbing glass.

  As another means, as shown in the enlarged 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 and the photoelectric conversion are converted. By slightly breaking the conjugate relationship with the means 43, the color registration pattern 11 (see FIG. 1) imaged on the photoelectric conversion means 43 can be blurred, and the characteristics of the low-pass filter can be optically obtained.

  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 larger than the width of the scratches and dirt, and the color registration is accurately performed by the action of the low-pass filter 9. The position of the pattern 11 can be recognized, and a satisfactory error amount measurement of color registration can be performed.

  Next, the image forming apparatus 1 in 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 includes a dirt / flaw width detecting unit 12, a characteristic changing unit 13, and a pattern width changing unit 14.

  The dirt wound width detection unit 12 can monitor the output signal from the reading unit 4 to the low-pass filter 9 and detects a period during which the output signal falls below a predetermined threshold value. It is configured to measure the width of dirt and scratches. The comparison between the output signal and the threshold value is performed by a comparator (not shown) constituted by an analog or digital comparator. The measurement during the period when the output signal falls below the threshold is performed by a counter (not shown) that receives the output of the comparator. The dirt / scratch width detection unit 12 notifies the characteristic changing unit 13 and the pattern width changing unit 14 of the measured width of dirt and scratches.

  The characteristic changing unit 13 has a built-in look-up table having several kinds of coefficients to be set for the low-pass filter 9, and after receiving a signal of dirt and flaw width from the flaw / flaw width detecting unit 12, the characteristic changing unit 13 performs a lookup. A coefficient corresponding to the width of the dirt or scratch is referred to by a table, and the characteristics of the low-pass filter 9 can be changed and set by the referenced coefficient. This look-up table is stored in a ROM or hard disk that does not lose data even when the image forming apparatus 1 is powered off.

  The pattern width changing unit 14 is built in the pattern generating unit 2, and is a storage unit (not shown) that stores several types of color registration patterns 11 (see FIG. 1) of different thicknesses that are also built in the pattern generating unit 2. ), The line width of one color registration pattern 11 can be set based on the signal of the width of dirt and scratches obtained from the dirt / scratch width detector 12.

  Next, a color registration error correction procedure in the image forming apparatus 1 according to the second embodiment having such a configuration will be described. First, when a command is issued to each part by the controller 7, the dirt / scratch width detection unit 12 shifts to an operation for detecting the width of the dirt / scratch on the image carrier 10. At this time, the pattern generating unit 2, the image temporary storage unit 6, and the image forming units 3a to 3d are temporarily in a resting state, and only the image carrier 10 on which the color registration pattern 11 is not formed is rotated.

  Next, the reading unit 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 dirt wound width detection unit 12 monitors the output signal from the reading unit 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 falls below the threshold is measured. The predetermined threshold value is set in advance to about half of the received light amount 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 this as the dirt / scratch width, and notifies the characteristic changing unit 13 of the value. .

  The characteristic changing unit 13 receives the dirt / scratch width signal obtained from the dirt / scratch width detection unit 12 and calculates a coefficient such that the cut-off frequency is two to three times the basic frequency of the dirt / scratch width. Corresponding coefficients are selected from the look-up table so that the low-pass filter 9 is set. Then, the selected coefficient is changed and set for the low-pass filter 9.

  Similarly to the characteristic changing unit 13, the pattern width changing unit 14 receives a signal of the width of dirt and scratches from the dirt / scratch width detecting unit 12, and the line width of the color registration pattern 11 is about the width of the dirt and scratches. The color registration pattern stored in the storage means is selected to be about 5 times. As a result, a color registration pattern 11 having a line width larger than the width of dirt or scratches attached to the image carrier 10 can be formed on the image carrier 10 from the image forming units 3a to 3d, and at the reading unit 4 The low-pass filter 9 can be set so that the position of the color registration pattern 11 can be reliably recognized based on the read signal.

  After the characteristic change of the low-pass filter 9 and the line width of the color registration pattern 11 are thus changed, the color registration error amount is measured in the same manner as described in the first embodiment. As a result, even when the image carrier 10 is deteriorated by long-term use and the state of the fouling due to the attached dirt changes, it is possible to always perform good color registration error measurement accordingly.

  As an application example of the image forming apparatus 1 in the second embodiment, when detecting the width of dirt and scratches, the low-pass filter 9 for dirt and scratches is detected by the pattern position calculation means 51 (see FIG. 5) of the error detector 5. The signal bottom is detected by detecting the signal bottom, and in the color registration correction mode, the pattern position is intermediate between the bottom of the output signal of the low-pass filter 9 and the signal bottom of the dirt or scratch obtained previously. The threshold value of the calculation means 51 is set.

  This makes it possible to reliably distinguish the position of the color registration pattern 11 from the position of dirt or scratches even when the measurement environment for color registration errors due to dirt or scratches has deteriorated. Registration error can be measured.

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

It is a block diagram explaining 1st Example of this invention. FIG. 3 is a first diagram illustrating an example of a color registration pattern. FIG. 6 is a second diagram illustrating an example of a color registration pattern. It is an expanded sectional view explaining a reading part. It is a block diagram explaining an error detection part. It is a band characteristic figure of a Laplacian filter. It is a figure explaining the state with a crack. It is a figure which shows the example of the output signal from a reading part. It is a figure which shows the example of the output signal from a low-pass filter. It is an expanded sectional view explaining another example. It is a block diagram explaining 2nd Example of this invention. It is a figure which shows the example of an output signal at the time of reading a dirt wound. It is a block diagram explaining a prior art example. It is a figure (the 1) which shows the example of the conventional color registration pattern. FIG. 10 is a second diagram illustrating an example of a conventional color registration pattern. It is a figure which shows the state into which the damage | wound was entered. It is a figure which shows the example of the output signal from a reading part.

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 DESCRIPTION OF SYMBOLS ... Low pass filter, 10 ... Image carrier, 11 ... Color registration pattern, 12 ... Dirt wound width detection part, 13 ... Characteristic change part, 14 ... Pattern width change part

Claims (3)

Pattern generating means for generating a color registration pattern for measuring an error in color registration, image forming means for forming the color registration pattern as an image on the image carrier, and a color formed on the image carrier An image forming apparatus comprising: a reading unit that optically reads a registration pattern and converts it into an electrical signal; and an error detection unit that obtains an error amount of color registration based on the electrical signal obtained by the reading unit,
The error detecting means includes
The waveform of the electrical signal obtained from said reading means, when a plurality of waveform is obtained, as set threshold is between the signal bottom of the plurality of waveforms,
When there is a first level difference and a second level difference smaller than the first level difference as the level difference between the signal bottoms of the plurality of waveforms, the second level difference is more than the first level difference. However , the threshold value that varies according to the level difference is set so that the signal bottom level is converted into a ratio and is closer to the deep side,
An image forming apparatus characterized in that the position of the color registration pattern is obtained from information of an area exceeding the set threshold value. Pattern generating means for generating a color registration pattern for measuring an error in color registration, image forming means for forming the color registration pattern as an image on the image carrier, and a color formed on the image carrier An image forming apparatus comprising: a reading unit that optically reads a registration pattern and converts it into an electrical signal; and an error detection unit that obtains an error amount of color registration based on the electrical signal obtained by the reading unit,
The error detecting means includes
For the waveform of the electrical signal obtained from the reading means, as a threshold setting between the waveform bottom of both the waveform of the color registration pattern and the waveform of the dirt and scratches attached to the image carrier ,
When there is a first level difference and a second level difference smaller than the first level difference as the level difference between the signal bottoms of both waveforms, the second level difference is more than the first level difference. , Set the threshold that varies according to the level difference so that the signal bottom level is converted into a ratio and closer to the deep side,
An image forming apparatus, comprising: calculating a barycentric position of an area exceeding the set threshold and determining the position of the color registration pattern from the barycentric position. Dirt wound width detecting means for detecting the width of linear dirt and scratches along the moving direction of the image carrier;
The image forming apparatus according to claim 2, further comprising: a low-pass filter that limits a band of an electric signal obtained from the reading unit in accordance with a width detected by the dirt wound width detecting unit.

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