JP2006227474A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus capable of accurately detecting a line for measuring color slurring by making good use of transmitted light and detecting the difference of the transmitted light. <P>SOLUTION: A photodetector part 9 is constituted of a 1st optical sensor unit 9A for detecting the position of the A-side end of the line for measuring color slurring 21, and a 2nd optical sensor unit 9B for detecting the position of the B-side end of the line for measuring color slurring 21. The 1st and the 2nd optical sensor units 9A and 9B are arranged perpendicularly to a transfer belt 6, and both ends of the line for measuring color slurring 21 are detected by the two optical sensor units. The positions of the 1st and the 2nd optical sensor units 9A and 9B are set on the outside from the maximum width of recording paper. The 1st and the 2nd optical sensor units 9A and 9B include one light emitting element and two light receiving elements at transparent parts at both ends of the transfer belt 6 respectively so that the light emitting element may be arranged above and the light receiving elements may be arranged below in a state where the respective transparent parts are held in between. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention develops an image on a plurality of photoconductors using an electrophotographic process, forms a color image by superimposing and transferring a plurality of single-color images on an image transfer region of a transfer belt, and then forming the color image on a recording paper. The present invention relates to a color image forming apparatus such as a color printer, a digital color copying machine, and a color facsimile that perform transfer.

  Conventionally, as a color image forming apparatus for forming a color image at a high speed, a photosensitive drum is provided for each color toner of black (K), yellow (Y), magenta (M), and cyan (C) along a conveying belt. Then, the recording paper is sequentially transported by the transport belt to sequentially transfer the images of each color, or the images of each color are sequentially transferred onto the image transfer area of the transfer belt so as to overlap each other. There is a so-called tandem method for transferring images.

  One of the main difficult problems in this tandem color image forming apparatus is that color misregistration of each color image is likely to occur. Examples of the color shift include a shift in the scanning direction (main scanning direction), a shift in the belt conveyance direction (sub-scanning direction), and an inclination in the scanning direction (main scanning direction).

  The color misregistration of each color is adjusted so as to be equal to or less than an allowable value at the time of shipping the apparatus. However, when maintenance such as replacement of the photosensitive drum is performed, or because of changes in the environment (such as internal temperature and internal humidity) between adjustment and use, the latent image that forms a latent image on the photosensitive drum is displayed. The relative positional relationship among the image forming unit, the photosensitive drum, and the transfer belt is slightly changed, and the color misregistration of each color becomes an allowable value or more.

  Therefore, this type of color image forming apparatus generally corrects color misregistration in a correction mode. In this correction mode, a color shift measurement line is formed for each color on the image transfer area of the transfer belt, the color shift measurement line is detected, and the image formation timing of each color is adjusted based on the detection signal. By doing so, the color shift of the color image is corrected.

For example, the color image forming apparatus disclosed in Patent Document 1 forms a color misregistration measurement line for each color on the image transfer region of the transfer belt in the correction mode, and the color misregistration measurement line is formed as a reflection type. It is detected by light detection means.
Japanese Patent No. 3469768

  However, the colors of the transfer belt substrate and the color misregistration measurement line may be approximated. In this case, there is a problem that when detecting the color misregistration measurement line, there is almost no difference in contrast between the two, and erroneous detection is likely to occur.

  Further, on the image transfer area of the transfer belt, due to long-term use, dirt due to toner formed as an image or scratches generated when the toner is scraped off by a cleaner occurs. Due to the occurrence of these stains and scratches, there is a problem that there is almost no difference in contrast between the transfer belt and the color misregistration measurement line, and erroneous detection is likely to occur.

  In Patent Document 1, since reflected light is used, stains or scratches are generated when the color of the transfer belt substrate and the color misalignment measurement line are approximate, or on the image transfer area of the transfer belt. In this case, there is almost no difference in contrast between the transfer belt and the color misregistration measurement line, and erroneous detection of the color misregistration measurement line is likely to occur.

  The present invention is intended to solve such a conventional problem, and uses a transmitted light to detect a difference in the transmitted light, thereby enabling a color image for accurately detecting a color shift measurement line. An object is to provide a forming apparatus.

  The color image forming apparatus of the present invention has the following configuration in order to solve the above problems.

(1) an image forming section in which a plurality of image forming stations including a photosensitive member and a developing unit that develops a latent image formed on the photosensitive member are arranged in a row;
Latent image forming means for forming a latent image on each of the photoreceptors of the plurality of image forming stations;
A transfer belt onto which a monochrome image formed on each photoreceptor of the plurality of image forming stations is transferred;
A color image forming apparatus comprising: a control unit that measures a color shift of an image formed in each of the image forming stations and executes a correction mode for correcting the color shift at a predetermined time.
The transfer belt has transparent portions at both ends,
Photodetecting means comprising a light-emitting element and a light-receiving element disposed with the transparent parts sandwiched between the transparent parts at both ends of the transfer belt,
In the correction mode, the control means outputs a control signal for forming a color misregistration measurement line in the main scanning direction to the transparent portions at both ends of the transfer belt to the latent image forming means, and the light detection means The color shift is measured based on the detection signal.

  The color image forming apparatus is, for example, a color printer, a digital color copying machine, or a color facsimile. The predetermined time is, for example, when the environment changes more than a certain value, immediately after maintenance of the apparatus main body is performed, or when a certain time has elapsed. The environment is, for example, the temperature inside the device and the humidity inside the device.

  The light detection means emits light from a light emitting element to a color misregistration measurement line formed in a transparent part at both ends of the transfer belt, and detects light transmitted from the transparent part by a light receiving element.

  In this way, by providing a transparent portion at both ends of the transfer belt and forming a color shift measurement line in the transparent portion, even when the colors of the transfer belt substrate and the color shift measurement line are approximated, , The contrast between the two becomes clear. Therefore, the color misregistration measurement line can be detected with high accuracy.

  Further, by using the transmitted light to detect the color misregistration measurement line, the light emitting element can be disposed above the image transfer region of the transfer belt and the light receiving element can be disposed below. On the other hand, when using reflected light, all of the light emitting element and the light receiving element must be arranged above the image transfer area of the transfer belt.

  Therefore, when the light emitting element and the light receiving element are disposed, the space restriction above the image transfer area of the transfer belt is less likely to be restricted as compared with the case where reflected light is used. Therefore, an increase in the size of the apparatus main body can be avoided.

(2) Based on the detection signal of the light detection means, the control means detects the inclination of the color deviation measurement line with respect to a preset reference line in the main scanning direction and the color deviation measurement line from the reference line. Deviation is measured as the color deviation.

  In this configuration, the deviation of the color deviation measurement line from the preset reference line is a deviation in the scanning direction (main scanning direction) from the reference line and a deviation in the belt conveyance direction (sub scanning direction) from the reference line. is there.

  The control means specifies the position of the color misregistration measurement line based on the detection signal of the light detection means. Based on the position of the color misregistration measurement line, the control means determines whether the color misregistration measurement line has a tilt in the main scanning direction with respect to a preset reference line and the misregistration measurement line from the reference line. Measure as

(3) The light detection means includes the light-emitting element and the light-receiving element so that the optical axes between the light-emitting element and the light-receiving element intersect at least two points in the main scanning direction with the transparent portions at both ends of the transfer belt. A light receiving element is arranged.

  In this configuration, one light emitting element is arranged on either the upper side or the lower side of the transparent part between the transparent parts at both ends of the transfer belt, and two light receiving elements are arranged on the other side (4). And a structure in which two light emitting elements are arranged on either the upper side or the lower side with the transparent parts sandwiched between the transparent parts at both ends of the transfer belt, and two light receiving elements are arranged on the other side. Can be considered.

  Either configuration can be implemented, but the configuration shown in (4) described later is more economical because one light emitting element is less. In addition, it is advantageous to receive light from one light-emitting source because variations in light emission can be reduced.

  In addition, in this configuration, since two light receiving elements are used, the difference in the amount of received light can be detected by a differential amplifier circuit, so that the transfer belt transparent portion is contaminated or scratched by long-term use. However, it is possible to distinguish the color deviation measurement line with higher accuracy.

(4) In the light detection means, one light emitting element is disposed on either the upper side or the lower side with the transparent parts sandwiched between the transparent parts at both ends of the transfer belt, and two light receiving elements are provided on the other side. Has been placed.

  In this configuration, compared to the case where one light emitting element is arranged on either the upper side or the lower side with the transparent parts sandwiched between the transparent parts at both ends of the transfer belt and one light receiving element is arranged on the other side. The detection accuracy of the color misregistration measurement line is increased.

(5) The light detection means is disposed on the most downstream side of the transfer belt.

(6) The transparent portions at both ends of the transfer belt are provided outside the preset image forming range of the maximum usable recording paper.

  On the image transfer area of the transfer belt, the image forming range of the maximum usable recording paper that is set in advance is the image area, and is outside the preset image forming range of the maximum usable recording paper. That is, the transparent portions at both ends of the transfer belt are divided as color misregistration measurement areas for forming a color misregistration measurement line.

  By separating the image area that is frequently used and the area for measuring color misregistration, the area for measuring color misalignment is less susceptible to the effects of dirt and scratches that have occurred over many years of use. Can be measured.

(7) An environment measuring means for measuring the environment of the apparatus body is provided.
The control means executes the correction mode when the environment changes more than a certain level.

  In this configuration, the environment is, for example, the temperature inside the device and the humidity inside the device. The time when the environment changes more than a certain value is when, for example, the temperature inside the apparatus has increased by 10 degrees. If the temperature in the apparatus rises by 10 degrees, the relative positional relationship between the latent image forming means, the photosensitive drum, and the transfer belt becomes delicate due to the difference in coefficient of thermal expansion among the latent image forming means, the photosensitive drum, and the transfer belt. Misalignment and color misalignment occurs. In addition, since the quality of the toner changes due to a change in the internal temperature of the apparatus and a change in the internal humidity of the apparatus, this may cause color misregistration.

  The control means automatically performs color misregistration correction when the environment changes beyond a certain level. The user does not need to manually input color misregistration correction to the apparatus main body, thus improving the usability of the user.

(8) The control means executes the correction mode immediately after the maintenance of the apparatus main body is performed or when a certain time has elapsed.

  In this configuration, the maintenance is, for example, replacement of the photosensitive drum. When maintenance of the apparatus main body is performed, the relative positional relationship among the latent image forming unit, the photosensitive drum, and the transfer belt is slightly shifted, and color shift occurs.

  The certain time is, for example, one day or one week. It is conceivable that the relative positional relationship among the latent image forming means, the photosensitive drum, and the transfer belt is slightly shifted due to the use for a certain period of time, resulting in color shift.

  The control means automatically executes correction of color misregistration immediately after the maintenance of the apparatus main body is performed or when a certain time has elapsed. The user does not need to manually input color misregistration correction to the apparatus main body, thus improving the usability of the user.

  According to the present invention, even when the colors of the transfer belt substrate and the color misregistration measurement line are approximate, the color misregistration measurement line can be accurately detected.

  In addition, even if dirt or scratches occur on the transparent portion of the transfer belt after many years of use, there is an effect that it is possible to distinguish the color deviation measurement line with higher accuracy.

  In addition, since it is not easily affected by dirt, scratches, and the like generated by long-term use, there is an effect that it is possible to measure color shift stably over a long period of time.

  In addition, there is an effect of improving user convenience.

  A digital color copying machine that is a color image forming apparatus according to an embodiment of the present invention will be described below.

  FIG. 1 is a front sectional view showing a main configuration of a digital color copying machine according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the configuration of the light detection unit of the digital color copying machine according to the embodiment of the present invention.

  The digital color copying machine 1 includes a control unit 2 that controls the main body of the apparatus, and laser light modulated based on image data of each color of K (black), Y (yellow), M (magenta), and C (cyan). Are charged by a laser light source (not shown) that emits light, a laser scanner unit 3K, 3Y, 3M, 3C having a rotary polygon mirror (not shown) that deflects the emitted light, and a charger (not shown), The photosensitive drums 4K, 4Y, 4M, and 4C that form an electrostatic latent image on the surface by rotating while receiving laser light exposure from the laser scanner units 3K, 3Y, 3M, and 3C, and the photosensitive drums 4K, 4Y, Development units 5K, 5Y, 5M, and 5C that develop electrostatic latent images formed on 4M and 4C with toners of colors K, Y, M, and C, and photosensitive drums 4K, 4Y, 4M, and 4C, respectively. developing The transfer belt 6 to which the toner image is transferred, the transfer belt 6 is stretched, and a driving roller 6A and a driven roller 6B that rotate the transfer belt 6 in the direction of the arrow by a driving device (not shown), and each photoconductor. Transfer devices 7K, 7Y, 7M, and 7C that transfer toner images developed on the drums 4K, 4Y, 4M, and 4C to the transfer belt 6, and K on the photosensitive drums 4K, 4Y, 4M, and 4C according to instructions from the control unit 2 The color misregistration measurement lines 21K, 21Y, 21M, and 21C transferred onto the transfer belt 6 by forming toner images of the color misregistration measurement lines 21K, 21Y, 21M, and 21C with the respective colors Y, M, and C are displayed. The light detection unit 9 for detecting, the transfer roll 8 for transferring the image image formed on the image area 23 (see FIG. 3 described later) on the transfer belt 6 to the recording paper 11, and the temperature in the apparatus. A temperature sensor 10 to a constant, a storage unit 12 for use in correcting the color shift, and is configured and a cleaner 13 for removing the toner on the transfer belt 6.

Each image forming station _{P K, P Y, P M} , P C has substantially the same structure are arranged in a row. Each image forming station _{P K, P Y, P M} , P C , the photosensitive drum 4K, 4Y, 4M, and 4C, and includes the developing unit 5K, 5Y, 5M, and 5C, respectively.

  As shown in FIG. 2 or FIG. 3 described later, the transfer belt 6 has transparent portions at both ends. The transparent portions at both ends are provided outside the preset image forming range of the maximum usable recording paper. When the color deviation measuring lines 21K, 21Y, 21M, and 21C are formed in the transparent portion, the color of the substrate of the transfer belt 6 and the color deviation measuring lines 21K, 21Y, 21M, and 21C is approximated. However, the contrast between the two becomes clear. Accordingly, the color misregistration measurement lines 21K, 21Y, 21M, and 21C can be detected with high accuracy.

Above the transfer belt 6, the first image forming station P _K , the second image forming station P _Y , the third image forming station P _M , and the fourth image forming station P are close to the transfer belt 6. _C and the light detection unit 9 are arranged in parallel from the upstream side of the transfer belt 6.

  The light detection unit 9 is disposed on the most downstream side of the transfer belt 6 as shown in FIG. As shown in FIG. 2 or FIG. 3 to be described later, the light detection unit 9 includes a first optical sensor unit 9A that detects the position of the A side end of the color misregistration measurement lines 21K, 21Y, 21M, and 21C. It comprises a second optical sensor unit 9B that detects the position of the B-side end of the deviation measurement lines 21K, 21Y, 21M, and 21C. The first optical sensor unit 9A and the second optical sensor unit 9B are arranged perpendicular to the transfer belt 6, and the color deviation measuring lines 21K, 21Y, 21M, and 21C are arranged by these two optical sensor units. Detect both ends. Here, the positions of the first optical sensor unit 9A and the second optical sensor unit 9B are located outside the maximum width of the recording paper.

In the first optical sensor unit 9A and the second optical sensor unit 9B, one light emitting element is disposed above the transparent part at both ends of the transfer belt 6 with each transparent part interposed therebetween, and the light receiving element is provided below. Are arranged. The first optical sensor unit 9A includes a light emitting element LED _A, made from the light-receiving element PD _A1, PD _A2, the second optical sensor unit. 9B, the light-emitting element LED _B, consisting of the light receiving element PD _B1, PD _B2.

  That is, the light detection unit 9 includes the light emitting element and the light receiving element so that the optical axis between the light emitting element and the light receiving element intersects at least two points in the main scanning direction with the transparent parts at both ends of the transfer belt. ing.

When the light emitting elements LED _A and LED _B and the light receiving elements PD _A1 , PD _A2, PD _B1 , and PD _B2 are arranged, the space restriction above the image transfer region of the transfer belt 6 is limited as compared with the case of using reflected light. It is hard to receive. This is because when the reflected light is used, the light emitting elements LED _A and LED _B and the light receiving elements PD _A1 , PD _A2, PD _B1 , and PD _B2 must all be arranged above the transfer belt 6. Therefore, there is an effect that the apparatus main body 1 is not increased in size.

  In the embodiment of the present invention, one light emitting element is arranged above and two light receiving elements are arranged below the transparent parts at both ends of the transfer belt 6. May be arranged with one light emitting element below and two light receiving elements above. Moreover, when performing, you may arrange | position two light emitting elements above, and may arrange | position two light receiving elements below.

  Although it is possible to implement both the configuration in which one light emitting element is disposed or the configuration in which two light emitting elements are disposed, the former configuration is more economical because one light emitting element is less. In addition, it is advantageous to receive light from one light-emitting source because variations in light emission can be reduced.

The light receiving elements PD _A1 and PD _A2 and the light receiving elements PD _B1 and PD _B2 are arranged in parallel to the main scanning direction of the transfer belt 6, and detect the color misregistration measurement lines 21K, 21Y, 21M, and 21C. Making it easy.

In addition, the first optical sensor unit 9A emits light from the light emitting element LED _A , and the transmitted light transmitted from the transparent portion of the transfer belt 6 is received by the light receiving element PD _A2 . Since the transmitted light does not pass through the color deviation measurement lines 21K, 21Y, 21M, and 21C of the transfer belt 6, the light receiving element PD _A1 does not receive the transmitted light. Since the two light receiving elements PD _A2 and PD _A1 are used, the difference in the amount of received light can be detected by a differential amplifier circuit (see FIG. 4 to be described later). Even if dirt or scratches are generated on the top, it is possible to distinguish the color deviation measurement lines 21K, 21Y, 21M, and 21C with higher accuracy. The operation of the second photosensor unit 9B is the same. In order to reduce measurement errors, it is preferable to use a plurality of light receiving elements having the same characteristics as these light receiving elements.

  The temperature sensor 10 is composed of, for example, an electronic thermometer. The temperature sensor 10 measures the temperature in the apparatus and gives the temperature to the control unit 2.

  The storage unit 12 specifies the positions of the color misregistration measurement lines 21K, 21Y, 21M, and 21C on the transfer belt 6 and corrects the color misregistration with 66 dots (00 to 65) in the main scanning direction. Color misregistration correction coordinates are set in a part of the storage area in the direction 7 lines (00 to 06) (see FIG. 9 described later). That is, the present invention includes storage means for setting color misregistration correction coordinates that specify the detection position of the color misregistration measurement line, and the control means uses the color misregistration correction coordinates of the storage means in the correction mode. This is a color image forming apparatus that performs the correction.

  In addition, the storage unit 12 stores in advance reference lines 22K, 22Y, 22M, and 22C, which are virtual lines, in order to grasp the reference positions of the color deviation measurement lines 21K, 21Y, 21M, and 21C for each color (described later). FIG. 3). The coordinates of the reference lines 22K, 22Y, 22M, and 22C are the center of the color misregistration correction coordinates, that is, the 03 to 63 dots in the main scanning direction and the 03 lines in the sub scanning direction (see FIG. 9 described later).

  That is, the color shift measurement lines 21K, 21Y, 21M, and 21C are formed at the timing of forming the reference lines 22K, 22Y, 22M, and 22C.

Control unit 2, the image forming stations _{P K, P Y, P M} , to execute a correction mode for correcting the measured color shift of the image formed in the P _C the color deviation to a predetermined time (to be described later 6 reference). The predetermined time is, for example, when the temperature inside the apparatus changes more than a certain value, or immediately after maintenance of the apparatus main body is performed, or when a certain time has elapsed.

  The time when the temperature inside the apparatus changes more than a certain value is when, for example, the temperature inside the apparatus rises by 10 degrees. If the internal temperature rises by 10 degrees, the laser scanner units 3K, 3Y, 3M, and 3C and the photosensitive drums 4K, 4Y, 4M, and 4C and the transfer belt 6 have different coefficients of thermal expansion. The relative positional relationship between 3Y, 3M, and 3C and the photosensitive drums 4K, 4Y, 4M, and 4C and the transfer belt 6 is slightly shifted, and color shift occurs. In addition, since the quality of the toner changes due to a change in the internal temperature of the apparatus and a change in the internal humidity of the apparatus, this may cause color misregistration.

  In the normal mode, the control unit 2 monitors the in-device temperature given from the temperature sensor 10, and executes the correction mode when it is determined that the in-device temperature has changed beyond a certain level (see FIG. 6 described later).

  The maintenance is, for example, replacement of the photosensitive drum. When maintenance of the apparatus main body is performed, the relative positional relationship between the laser scanner units 3K, 3Y, 3M, and 3C and the photosensitive drums 4K, 4Y, 4M, and 4C and the transfer belt 6 is slightly shifted, and color shift is caused. Arise.

  When determining that the maintenance has been performed, the control unit 2 executes the correction mode (see FIG. 6 described later).

  Moreover, the fixed time is, for example, one day or one week. It is considered that the relative positional relationship between the laser scanner units 3K, 3Y, 3M, and 3C and the photosensitive drums 4K, 4Y, 4M, and 4C and the transfer belt 6 may be slightly misaligned and color misalignment may occur due to the use for a certain period of time. It is done.

  When the control unit 2 determines that the predetermined time has elapsed, the control unit 2 executes the correction mode (see FIG. 6 described later).

  In the above description, optical writing is performed on the photosensitive drums 4K, 4Y, 4M, and 4C by scanning and exposing a laser beam with the laser scanner units 3K, 3Y, 3M, and 3C. However, a writing optical system (LED head) including a light emitting diode array and an imaging lens array may be used instead of the laser scanner unit. The LED head is smaller than the laser scanner unit and has no moving parts and is silent. Therefore, it can be suitably used in an image forming apparatus such as a tandem digital color copying machine that requires a plurality of optical writing.

Here, the digital color copying machine 1 corresponds to the “color image forming apparatus” of the present invention. The laser scanner units 3K, 3Y, 3M, and 3C correspond to the “latent image forming unit” of the present invention. Image forming station _{P K, P Y, P M} , all _{P C} corresponds to the "image forming part" of the present invention. The developing devices 5K, 5Y, 5M, and 5C correspond to the “developing unit” of the invention.

  FIG. 3 is a top view of the transfer belt on which the color misregistration measurement line is formed in the digital color copying machine according to the embodiment of the present invention as seen from above.

  On the transfer belt 6, an image area 23 (a central portion of the transfer belt 6) that is an image formation range of a recording paper having a preset maximum usable width, and a preset maximum usable width recording. It is divided into color misregistration measurement areas 24A and 24B (transparent portions on both ends of the transfer belt 6) that are outside the paper image forming range, that is, transparent portions on both ends of the transfer belt 6.

  That is, the color misregistration measurement areas 24A and 24B are areas for forming the color misregistration measurement lines 21K, 21Y, 21M, and 21C, and the image area 23 is an area for forming an image image.

  By dividing the image area 23 having a high frequency of use and the areas 24A and 24B for measuring color misregistration, the color misregistration measuring areas 24A and 24B are not easily affected by dirt and scratches caused by long-term use. The color misregistration can be measured stably.

  The color misalignment measurement lines 21K, 21Y, 21M, and 21C for each color have color misalignments as shown in FIG. 3 with respect to the respective reference lines 22K, 22Y, 22M, and 22C. There are three main color shifts: (1) shift in the main scanning direction, (2) shift in the sub-scanning direction, and (3) tilt in the main scanning direction.

  The color misregistration measurement line 21K shown in FIG. 3 corresponds to the “(3) inclination in the main scanning direction”. The color misregistration measurement line 21M corresponds to the “(2) Deviation in the sub-scanning direction”. The color misregistration measurement line 21C corresponds to the “(1) Deviation in the main scanning direction”.

  (1) Misalignment in the main scanning direction is caused by misalignment of the photosensitive drums 4K, 4Y, 4M, and 4C in the axial direction or the exposure scanning start positions of the laser scanner units 3K, 3Y, 3M, and 3C. .

  (2) The deviation in the sub-scanning direction is exposed on the photosensitive drums 4K, 4Y, 4M, and 4C as the deviation of the image leading end line, or on the photosensitive drums 4K, 4Y, 4M, and 4C. This is caused by the exposure positions of the laser scanner units 3K, 3Y, 3M, and 3C.

  (3) The inclination in the main scanning direction is the inclination of the photosensitive drums 4K, 4Y, 4M, and 4C axes or the mounting parallelism between the photosensitive drums 4K, 4Y, 4M, and 4C and the laser scanner units 3K, 3Y, 3M, and 3C. This is caused by the deviation of the degree.

  FIG. 4 is a circuit diagram showing a circuit for processing a detection signal detected by the light detection unit in the digital color copying machine according to the embodiment of the present invention. FIG. 5 is a diagram showing a deviation in the main scanning direction of the color deviation measurement line in the digital color copying machine according to the embodiment of the present invention.

  A circuit for measuring the color misregistration (1) to (3) will be described with reference to FIG. As described above, the first optical sensor unit 9A and the second optical sensor unit 9B disposed at the transparent portions at both ends of the transfer belt 6 are connected to both ends of the color misregistration measurement lines 21K, 21Y, 21M, and 21C for each color. Part. On the other hand, the transfer belt 6 rotates at a predetermined image forming speed in the direction of the arrow in FIG.

Here, as shown in FIG. 4, when the first color misregistration measurement line 21K passes through the positions of the respective optical sensor units 9A and 9B, the output signals of the respective light receiving elements PD _A1 and PD _A2 are respectively circuits 30A. And is converted into an appropriate signal by a voltage level conversion circuit (not shown). Similarly, the output signals of the light receiving elements PD _B2 and PD _B1 are differentially amplified by the circuit 30B and converted into appropriate signals by a voltage level conversion circuit (not shown). The appropriate signals are led to the A / D conversion inputs A / D2A and A / D2B of the control unit 2, respectively.

  The control unit 2 determines the signal level from the input A / D conversion input signal, and recognizes that the color misregistration measurement line 21K has passed through the positions of the optical sensor unit 9A and the optical sensor unit 9B.

In this way, by taking the difference between the transmitted light in the two light receiving elements PD _A2 and PD _A1 , even if dirt or scratches occur on the transparent portion of the transfer belt 6 due to long-term use, the color deviation measurement line 21K. There is an effect that it is possible to make a distinction with a higher accuracy.

  The same operation is performed when the color misregistration measurement lines 21Y, 21M, and 21C pass in order.

  With the above configuration and operation, one light emitting element is arranged on either the upper side or the lower side with the transparent parts sandwiched between the transparent parts at both ends of the transfer belt 6, and one light receiving element is arranged on the other side. Compared to the case, the detection accuracy of the color misregistration measurement lines 21K, 21Y, 21M, and 21C is higher when one light emitting element is arranged on one side and two light receiving elements are arranged on the other side.

  Further, the differential amplification & voltage level conversion circuits 30A and 30B are each provided with hysteresis so as not to sense a minute input difference by a circuit (not shown). As a result, the detection of the color misregistration measurement lines 21K, 21Y, 21M, and 21C can be detected more clearly by making it possible to adjust the sensing width appropriately.

On the other hand, when (1) the color misregistration measurement line 21C shifted to the right in the main scanning direction passes through the positions of the respective photosensor units 9A and 9B (see FIG. 5B), the respective light receiving elements PD _A1 The output signal of PD _A2 is differentially amplified by the circuit 30A and converted into a voltage level conversion signal, but the voltage level conversion signal level is zero. Similarly, the output signals of the light receiving elements PD _B1 and PD _B2 are differentially amplified by the circuit 30B and converted into a voltage level conversion signal, but the voltage level conversion signal level is zero. Therefore, the respective conversion signals are not led to the A / D conversion inputs A / D2A and A / D2B of the control unit 2.

However, the output signal of the light receiving element PD _B2 is guided to the control unit 2 A / D conversion input A / D2D. The output signal of the light receiving element PD _A1 is not guided to the A / D conversion input A / D2C of the control unit 2.

  The control unit 2 recognizes that the color misregistration measurement line 21C is misaligned to the right in the main scanning direction because it is not input to A / D2C but is input to A / D2D.

  Conversely, (1) even when a color misregistration measurement line that is shifted to the left in the main scanning direction passes through the position of each of the optical sensor units 9A and 9B, the control unit 2 performs the same operation as described above. (1) It can be recognized that there is a shift to the left in the main scanning direction.

  FIG. 6 is a flowchart showing the operation of the controller of the digital color copying machine according to the embodiment of the present invention. This operation is an operation showing a process in which the digital color copying machine 1 shifts from a normal mode in which printing is performed on the recording paper 11 to a correction mode.

  The digital color copying machine 1 determines whether or not it is a predetermined time (s1). As described above, the predetermined time is, for example, when the temperature inside the apparatus changes more than a certain value, or immediately after maintenance of the apparatus main body is performed, or when a certain time has passed. If it is determined that it is not the predetermined time, the digital color copying machine 1 returns to s1 and continues the processing.

  On the other hand, if it is determined that it is a predetermined time, the digital color copying machine 1 executes a correction mode (color shift detection / correction routine) (s2), returns to s1, and continues the processing.

  In the correction mode, first, (1) deviation detection / correction in the main scanning direction is performed (see FIG. 7), and then (2) deviation in the sub-scanning direction and (3) inclination in the main scanning direction are detected. Correction is performed (see FIG. 8 described later).

  Hereinafter, on behalf of the color misregistration measurement lines 21K, 21Y, 21M, and 21C, (1) detection of misregistration in the main scanning direction of the color misregistration measurement line 21C (see FIG. 3) that is misaligned in the main scanning direction. -Explain the correction.

  The digital color copying machine 1 forms a color misregistration measurement line 21C on the transfer belt 6 (s101), and starts detecting the color misregistration measurement line 21C (s102).

  The digital color copying machine 1 determines whether or not the first optical sensor unit 9A has detected the A side end of the color misregistration measurement line 21C (s103).

  Here, in order to detect the color misregistration measurement line 21C in s103, it is necessary to shift the color misregistration measurement line 21C by the number of dots shifted from the reference line 22C in the main scanning direction in s107 described later.

The determination of s103 is performed as follows. If both PD _A1 and PD _B2 of the optical sensor unit 9A detect the color misregistration measurement line 21C, the control unit 2 determines that the color misregistration measurement line 21C has no misalignment in the main scanning direction (FIG. 4, see FIG. 5 (a)). If the PD _A1 in the optical sensor unit 9A detects the color misregistration measurement line 21C, and the PD _B2 does not detect the color misregistration measurement line 21C, the control unit 2 performs the color misregistration measurement line 21C. It is determined that 21C has a deviation in the main scanning direction (rightward in FIG. 5B) (see FIGS. 4 and 5B).

  Here, the color misalignment measurement line 21C in FIG. 5A is assumed to be a position detected after shifting by the number of dots shifted from the reference line 22C in the main scanning direction in s107 described later.

  In the above, the case where the position is shifted to the right (main scanning direction) with respect to FIG. 5A is measured, but the position is shifted to the left (main scanning direction) with respect to FIG. The case is measured in the same way.

  If it is determined that the A-side end of the color misregistration measurement line 21C has not been detected, the digital color copying machine 1 moves the color misregistration measurement line 21C 1 in the main scanning direction (leftward in FIG. 5B). A color misregistration measurement line 21C is once again formed on the transfer belt 6 at the dot shifted position (s107), and the process returns to s103 to continue the processing.

  If it is determined that the A-side end of the color misregistration measurement line 21C is detected, the digital color copying machine 1 sets the detection position of the color misregistration measurement line 21C as the correction line 40C in the storage unit 12. (S104).

  With the setting of s104, (1) correction for deviation in the main scanning direction ends. After the correction mode is completed, an image image is formed on the transfer belt 6 based on the correction line 40C.

  The digital color copying machine 1 determines whether or not the correction lines 40K, 40Y, 40M, and 40C are set in the color misregistration measurement lines 21K, 21Y, 21M, and 21C for all colors (s105). If it is determined that the correction lines 40K, 40Y, 40M, and 40C are not set in the color misregistration measurement lines 21K, 21Y, 21M, and 21C for all colors, the digital color copying machine 1 returns to s103 and continues the processing.

  If it is determined that the correction lines 40K, 40Y, 40M, and 40C are set in the color misregistration measurement lines 21K, 21Y, 21M, and 21C for all colors, the digital color copying machine 1 determines the inclination in the correction main scanning direction and the sub-scanning. The process proceeds to a direction deviation detection / correction routine (see FIG. 8 to be described later) (s106), and this process ends.

  As described above, (1) correction of the color misregistration measurement line 21 </ b> C having misalignment in the main scanning direction is completed.

  FIG. 8 shows a case where (1) the detection and correction of the deviation in the main scanning direction is finished in the correction mode, and (2) the detection and correction of the deviation in the main scanning direction and (3) the deviation in the sub scanning direction are executed. 3 is a flowchart showing an operation of a control unit of the digital color copying machine according to the embodiment of the present invention. FIG. 9 is a diagram showing a correction example for the inclination in the main scanning direction and the deviation in the sub scanning direction in the digital color copying machine according to the embodiment of the present invention.

  Hereinafter, on behalf of the color misregistration measurement lines 21K, 21Y, 21M, and 21C, (2) the color misregistration measurement line 21K tilted in the main scanning direction (see FIG. 3) and (3) the misregistration in the sub scanning direction. A description will be given of (2) inclination in the main scanning direction and (3) deviation detection / correction in the sub-scanning direction with respect to the color misregistration measurement line 21M (see FIG. 3).

  In FIG. 7, (1) the digital color copying machine 1 which has completed the detection and correction of the deviation in the main scanning direction again forms the color deviation measurement lines 21K and 21M on the transfer belt 6 (s201), and the color deviation measurement. Detection of the work lines 21K and 21M is started (s202). S201 and s202 in FIG. 8 are substantially the same as s201 and s202 in FIG.

  The digital color copying machine 1 determines whether one of the two optical sensor units 9A and 9B has detected the color misregistration measurement lines 21K and 21M (s203). If it is determined that one of the two optical sensor units 9A and 9B has not detected the color misregistration measurement lines 21K and 21M, the digital color copying machine 1 advances the transfer belt 6 one line downstream in the sub-scanning direction. (S208), the process returns to s203 and continues.

  Here, until the color misregistration measurement line 21K and the color misregistration measurement line 21M are detected in either one of the two optical sensor units 9A and 9B in s203, the transfer belt 6 is moved downstream in the sub scanning direction in s208. Will advance one line at a time.

  Further, since the color misregistration measurement line 21K has an inclination in the main scanning direction, only the A-side end of the color misregistration measurement line 21K is first detected by the optical sensor unit 9A. Since the color misregistration measurement line 21M has no inclination in the main scanning direction, both ends of the color misregistration measurement line 21M are detected simultaneously by both of the two optical sensor units 9A and 9B.

  On the other hand, if it is determined in s203 that either one of the two optical sensor units 9A and 9B detects the color misregistration measurement lines 21K and 21M, the digital color copying machine 1 includes the two optical sensor units 9A and 9A. Both 9B determine whether or not the color misregistration measurement lines 21K and 21M have been detected (s204). If both the optical sensor units 9A and 9B determine that the color misregistration measurement lines 21K and 21M are not detected, the digital color copying machine 1 advances the transfer belt 6 one line downstream in the sub-scanning direction (s209). ) And return to s204 to continue the processing.

  Here, since the color misregistration measurement line 21K has an inclination in the main scanning direction, only the end portion on the A side of the color misregistration measurement line 21K is first detected by the optical sensor unit 9A. Then, until the B side end of the color misregistration measurement line 21K is detected by the optical sensor unit 9B, the line is advanced line by line in the sub-scanning direction in s209.

  Further, since the color misregistration measurement line 21M has no inclination in the main scanning direction, both ends of the color misregistration measurement line 21M are simultaneously detected by the two optical sensor units 9A and 9B.

  On the other hand, if it is determined in s204 that both the two optical sensor units 9A and 9B have detected the color misregistration measurement lines 21K and 21M, the digital color copying machine 1 uses the color misregistration correction coordinates of the storage unit 12 as the coordinates. On the other hand, the detection positions of the color misregistration measurement lines 21K and 21M are recorded (s205).

  For example, the position of the color misregistration measurement line 21K is recorded as 03 to 63 dots in the main scanning direction and 00 to 06 lines in the sub scanning direction (see FIG. 9A).

  Further, the position of the color misregistration measurement line 21M is recorded as 03 to 63 dots in the main scanning direction and 01 to 01 lines in the sub scanning direction (see FIG. 9B).

  The digital color copying machine 1 sets correction lines 41K and 41M (s206).

  Unlike the correction lines 40K and 40M, the correction lines 41K and 41M go through (1) detection and correction of deviation in the main scanning direction, (2) inclination in the main scanning direction and (3) detection and correction of deviation in the sub-scanning direction. This is the final correction line determined by

  s206 will be described in detail. The control unit 2 calculates the inclination in the main scanning direction from the color misregistration measurement line 21K and the reference line 22K, and the color with the reference line 22K as an axis with respect to the color misregistration correction coordinates in the storage unit 12. A correction line 41K that is symmetrical to the deviation measurement line 21K is calculated and set (see FIG. 9A). As shown in FIG. 9A, the position of the correction line 41K is 03 to 63 dots in the main scanning direction and 06 to 01 lines in the sub scanning direction.

  Further, the control unit 2 calculates a deviation in the sub-scanning direction from the color deviation measurement line 21M and the reference line 22M, and a color deviation measurement line with the reference line 22M as an axis with respect to the color deviation correction coordinates in the storage unit 12. A correction line 41M symmetrical to 21M is calculated and set (see FIG. 9B). As shown in FIG. 9B, the positions of the correction lines 41M are 03 to 63 dots in the main scanning direction and 05 to 05 lines in the sub scanning direction.

  That is, since the color misregistration measurement line 21M is formed two lines after the reference line 22M, the correction is made by setting the image formation timing two lines ahead of the current color misregistration measurement line 21M formation position. It becomes possible.

  With the setting of s206, the correction for (2) the color misregistration measurement line 21M having a deviation in the sub-scanning direction and (3) the color misregistration measurement line 21K having an inclination in the main scanning direction is completed. After the correction mode is completed, an image image is formed on the transfer belt 6 based on the correction lines 41K and 41M.

  The digital color copying machine 1 determines whether or not the correction lines 41K, 41Y, 41M, and 41C are set in the color misregistration measurement lines 21K, 21Y, 21M, and 21C for all colors (s207). If it is determined that the correction lines 41K, 41Y, 41M, and 41C are not set in the color misregistration measurement lines 21K, 21Y, 21M, and 21C for all colors, the digital color copying machine 1 returns to s203 and continues the processing.

  If it is determined that the correction lines 41K, 41Y, 41M, and 41C are set in the color misregistration measurement lines 21K, 21Y, 21M, and 21C for all colors, this process ends.

  As described above, the correction of (2) the color misregistration measurement line 21M having a deviation in the sub-scanning direction and (3) the color misregistration measurement line 21K having an inclination in the main scanning direction is completed.

  Therefore, in the present embodiment, first, (1) the main shift direction, or (2) the main scan direction inclination, or (3) the color shift measurement line having the sub-scan direction shift, the (1) main scan direction line. The final correction line can be determined by detecting and correcting the deviation in the scanning direction, and then detecting and correcting (2) the inclination in the main scanning direction and (3) the deviation in the sub-scanning direction.

  Even when the color misalignment measurement line has a combination of (1) misalignment in the main scanning direction, (2) inclination in the main scanning direction, and (3) misalignment in the sub-scanning direction, first, (1) main misalignment The final correction line can be determined by detecting and correcting the deviation in the scanning direction, and then detecting and correcting (2) the inclination in the main scanning direction and (3) the deviation in the sub-scanning direction.

  By performing the configuration and control as described above, there is an effect that the color misregistration measurement line can be detected with high accuracy even when the color of the transfer belt substrate and the color misregistration measurement line is approximate.

  In addition, even if dirt or scratches occur on the transparent portion of the transfer belt after many years of use, there is an effect that it is possible to distinguish the color deviation measurement line with higher accuracy.

  In addition, since it is not easily affected by dirt, scratches, and the like generated by long-term use, there is an effect that it is possible to measure color shift stably over a long period of time.

  In addition, there is an effect of improving user convenience.

1 is a front sectional view showing a main configuration of a digital color copying machine according to an embodiment of the present invention. Sectional drawing which shows the structure of the photon detection part of the said digital color copying machine Top view of the transfer belt on which a color misregistration measurement line is formed in the digital color copying machine as seen from above. A circuit diagram showing a circuit for processing a detection signal detected by a light detection unit in the digital color copying machine. The figure which shows the shift | offset | difference in the main scanning direction of the line for a color shift measurement in the said digital color copying machine A flowchart showing the operation of the controller of the digital color copying machine. Flow chart showing operation of correction mode (color shift detection / correction routine) Flowchart showing the operation of the correction mode (detection and correction of tilt in the correction main scanning direction and deviation in the sub scanning direction). The figure which shows the example of correction | amendment with respect to the inclination of a main scanning direction, and the shift | offset | difference of a subscanning direction in the said digital color copying machine.

Explanation of symbols

1-digital color copying machine 2-control unit 3-laser scanner unit 4-photosensitive drum 5-developing device 6-transfer belt 7-transfer device 8-transfer roll 9-light detection unit 10-temperature sensor 11-recording paper 12 -Memory 13-Cleaner 21-Color shift measurement line 22-Reference line 23-Image area 24-Color shift measurement area 30-Circuit 40-Correction line 41-Correction line

Claims (8)

An image forming section having a plurality of image forming stations arranged in a line, each including a photoconductor and a developing unit that develops a latent image formed on the photoconductor;
Latent image forming means for forming a latent image on each of the photoreceptors of the plurality of image forming stations;
A transfer belt onto which a monochrome image formed on each photoreceptor of the plurality of image forming stations is transferred;
A color image forming apparatus comprising: a control unit that measures a color shift of an image formed in each of the image forming stations and executes a correction mode for correcting the color shift at a predetermined time.
The transfer belt has transparent portions at both ends,
Photodetecting means comprising a light-emitting element and a light-receiving element disposed with the transparent parts sandwiched between the transparent parts at both ends of the transfer belt,
In the correction mode, the control means outputs a control signal for forming a color misregistration measurement line in the main scanning direction to the transparent portions at both ends of the transfer belt to the latent image forming means, and the light detection means A color image forming apparatus that measures the color misregistration based on a detection signal.   The control means determines, based on a detection signal of the light detection means, an inclination of the color deviation measurement line in a main scanning direction with respect to a preset reference line and a deviation of the color deviation measurement line from the reference line. The color image forming apparatus according to claim 1, wherein the color misregistration is measured as the color misregistration.   The light detecting means includes the light emitting element and the light receiving element such that an optical axis between the light emitting element and the light receiving element intersects at least two points in the main scanning direction with the transparent portions at both ends of the transfer belt. The color image forming apparatus according to claim 1, wherein the color image forming apparatus is disposed.   The light detecting means has one light emitting element arranged above or below the transparent parts at both ends of the transfer belt, and two light receiving elements arranged on the other side. The color image forming apparatus according to claim 1.   The color image forming apparatus according to claim 1, wherein the light detection unit is disposed on the most downstream side of the transfer belt.   The color image forming apparatus according to claim 1, wherein the transparent portions at both ends of the transfer belt are provided outside a preset image forming range of the maximum usable recording paper. An environment measuring means for measuring the environment of the device body is provided,
The color image forming apparatus according to claim 1, wherein the control unit executes the correction mode when the environment changes more than a certain level.   8. The color image forming apparatus according to claim 1, wherein the control unit executes the correction mode immediately after maintenance of the apparatus main body is performed or when a predetermined time has elapsed.

Images