JP5173373B2 - Image forming apparatus and method of controlling image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that employs an electrostatic system, an electrophotographic recording system, and the like, and a control method for the image forming apparatus.

  Hereinafter, the background art of the present invention will be described by dividing it into a transfer stabilization technique and a color stabilization technique.

<Transfer stabilization technology>
Conventionally, an image forming apparatus having a plurality of image forming units is known.

  Each image forming unit forms an electrostatic latent image on an image carrier such as a photosensitive drum by irradiating light with a laser beam light-modulated according to image information or a light emitting element such as an LED. Thereafter, the electrostatic latent image is developed as a toner image by developing means containing developer (toner), and the toner image is transferred onto a transfer material (recording medium) or intermediate transfer member conveyed by the transfer material carrier. Transcript.

  The plurality of image forming units form toner images of different colors, and the transfer material transport member sequentially multiplexes the toner images of the respective colors onto the transfer material while sequentially transporting the transfer material to a predetermined position of each image forming unit. An image forming apparatus that forms a color image by a transfer method has been proposed. In addition, there has been proposed an image forming apparatus that forms a color image by a method (intermediate transfer method) in which a toner image of each color is transferred onto an intermediate transfer member in a multiple transfer and then transferred onto a transfer material. As the intermediate transfer member, an endless intermediate transfer belt that is stretched by a driving roller for transmitting driving and at least one driven roller and whose surface moves is used.

  In this type of image forming apparatus, it is required to optimally set the primary transfer current in order to increase transfer latitude (transfer efficiency) from a photosensitive drum (hereinafter referred to as “drum”) as an image carrier to an intermediate transfer belt. Is done. However, when the primary transfer current is low, transfer failure tends to be caused when the primary transfer current is high, and it is difficult to set the primary transfer current optimally.

  Therefore, a primary transfer latitude is increased by providing a peripheral speed difference between the photosensitive drum and the intermediate transfer belt. Due to this difference in peripheral speed, transfer is performed using a shearing force that scoops out the toner image on the photosensitive drum, thereby improving and stabilizing the primary transfer latitude when the toner image on the photosensitive drum is primarily transferred. A technique for achieving this has been proposed. This technique prevents the occurrence of uneven density in the image and the loss of line images and character images due to a decrease in the primary transfer latitude. In this technique, in particular, the center of the secondary color fine line does not fall out and the transfer latitude is improved, but a frictional force is always generated between the photosensitive drum and the intermediate transfer belt due to the difference in peripheral speed. For this reason, the coefficient of friction changes between when there is toner between the photosensitive drum and the intermediate transfer belt and when there is no toner, and the rotational speed of the photosensitive drum varies. As a result, exposure is blurred when an electrostatic latent image is formed on the photosensitive drum, and image streaks are generated.

  This phenomenon is the image formation in which a plurality of developing units are associated with one image carrier, toner images of a plurality of colors are sequentially formed on the image carrier, and the toner images are superimposed on the intermediate transfer member to form an image. It also occurs in the device. It also occurs in a system that directly transfers a toner image from a photosensitive drum to a transfer material conveyed to a transfer material conveyance body. Here, the transfer material conveyance body and the intermediate transfer body are collectively referred to as transfer movement means.

  Therefore, a peripheral speed difference is provided between the rotational speed of the plurality of image forming units and the rotational speed of the transfer moving means such as an intermediate transfer member or a transfer material transport member onto which toner images are transferred. Then, an image that forms a dot dispersion image (dot pattern) on the transfer moving means by dispersing a dot developer image (dot toner image) with predetermined predetermined minute dots superimposed on a normal toner image, that is, a normal image. A forming apparatus has been proposed (for example, Patent Document 1).

  In this way, even in the image forming apparatus in which the circumferential speed difference is provided between the rotational speeds of the photosensitive drum and the transfer moving unit, it is possible to provide an image forming apparatus that can perform more stable image formation and print a high-quality image.

  Further, as described in Patent Document 2, for example, even in an image forming apparatus that does not provide a peripheral speed difference between the image carrier and the transfer moving unit, an unintended speed difference occurs due to eccentricity of the drive roller, and the like. As a result, color misregistration occurs. Therefore, as in Patent Document 1, a more stable image formation is performed by forming a dot pattern on the transfer moving unit by dispersing a dot toner image with predetermined predetermined fine dots overlaid with a normal image, High quality images can be printed.

<Color stabilization technology>
On the other hand, in recent years, the demand for a direct imaging printer that does not require a plate has increased. Many companies adopt direct imaging printers because of the short finishing time, service to each customer, and environmental problems such as mass production and disposal. Among direct imaging printers, the price, the inkjet system suitable for photographic printing, and the power of electrophotographic printers with high productivity and close to the finish of offset printing are on the rise. In such situations, color stability is the most important alternative to conventional offset printing and photography.

  In order to ensure color stability, stabilization control is performed in the printer apparatus. More specifically, a technique for reading a toner density detection patch pattern formed on a photoreceptor with a density sensor and feeding it back to a toner density control unit in the developing device to control the toner density appropriately (toner before fixing) (Patent Document 3).

  In general, although toner patches can be easily created and erased, only information on toner density before toner fixing can be obtained. Therefore, when control based on the toner patches is performed, the steps after the fixing step are performed. The effect is not reflected in the toner density.

  In view of this, it has been proposed to read an image printed by a reader portion of a so-called copying machine incorporated in the apparatus main body and perform image control (read patch reader after fixing) (Patent Document 4).

  However, this technique has to move the recording medium on which the output image is formed by the user's hand to the reader unit, and has poor operability. Due to the troublesomeness of the user, the density adjustment is not regularly performed in most cases. As a technique for eliminating such annoyance, a technique for sensing an output image by mounting a sensor in the middle of conveyance of a recording medium after fixing has been disclosed (Patent Document 5).

  Also, a technique (patent color sensor reading after fixing) that adjusts the balance (gray balance) of achromatic colors that is sensitive to human visibility in response to detection of a color image has been disclosed (Patent Document 6).

As described above, even in a direct imaging type image forming apparatus, color stability is one of the most important issues, and attention is focused on stabilization control using a sensor provided after image formation.
JP 2004-118076 A JP-A-11-52758 Japanese Patent Laid-Open No. 1-309082 JP-A 63-185279 JP-A-10-19389 JP 2002-344759 A

  However, if a dot dispersion image for stabilizing the transfer is formed on the entire surface of the paper when forming a patch image for stabilizing these colors, the measured value is measured by the method of measuring the toner density before fixing the toner. However, it is affected by the increase in toner due to the dot dispersion image.

  On the other hand, in the method of reading a toner patch after toner fixing, since the dot dispersion image is transferred as it is onto the paper, the read data is affected by the dot dispersion image when the patch image is read by the reader unit or the color sensor. .

  For example, since a dot dispersion image of yellow is superimposed on a cyan halftone patch image, a yellow toner component is included in the read data when the patch is read by a reader unit or a color sensor. Further, in order to avoid this influence, if the formation of the dot dispersion image is stopped at the time of forming these patch images, streaks occur in the patch image due to a change in the friction coefficient, and the read value fluctuates as shown in FIG. Can not read accurately.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus and an image forming apparatus that can avoid the influence of dot dispersion images on a patch image while suppressing the occurrence of streak unevenness during patch image formation for color stabilization. It is to provide a control method.

In order to solve this problem, an image forming apparatus of the present invention includes a dot dispersed image forming unit that forms a dot dispersed image in which a plurality of dot developer images having an area of at least one dot unit are dispersed on an image carrier. A patch image forming unit that forms a patch image to be read by the reading unit to adjust the image in any region on the image carrier , and is read by the reading unit in the region of the patch image. The dot dispersion image forming means is controlled so that the dot dispersion image is formed outside the area, and the dot dispersion image is formed in the area of the patch image and in the reading area by the reading means. and control means for controlling the pre-Symbol dot dispersion image forming means so as not to, characterized in that it comprises a.

The image forming apparatus control method according to the present invention includes a dot dispersed image forming step for forming a dot dispersed image in which a plurality of dot developer images each having an area of at least one dot unit are dispersed on an image carrier, and a reading unit. A patch image forming step for forming a patch image for image adjustment in any area of the image carrier , and within the area of the patch image and outside the reading area by the reading unit. the controls the dot dispersion imaging process as dot dispersion image is formed, in the region of the patch image, the and the reading means by reading area, prior to the no dot dispersion image is formed characterized in that it comprises a control step of controlling the serial dot dispersion imaging process.

Furthermore, a program for executing the steps of the control method of the image forming apparatus to the computer, and storing the program, provides a readable storage medium in the computer.

  According to the present invention, at the time of forming a patch image for stabilizing the color, it is possible to avoid the influence of the dot dispersion image on the patch image while suppressing the occurrence of uneven stripes, that is, to stabilize the transfer. It becomes.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the following first to fourth embodiments, a method of forming a dot toner image when forming a patch image on a sheet will be described. In these embodiments, a case is described in which a patch image is read by a color sensor mounted in the printer, but in an image adjustment method for reading a patch image by setting a sheet on which a patch image is formed in a reader unit, The same applies.

<Example of Configuration of Image Forming Apparatus of Embodiment>
FIG. 1 is a cross-sectional view of a main part of an image forming apparatus according to an embodiment of the present invention.

  In the present embodiment, the image forming apparatus is an electrophotographic system, and includes a reader unit 1R and a printer unit 1P.

  The reader unit 1R optically reads a document image, converts it into an electrical signal, and transmits it to the printer unit 1P.

  The printer unit 1P includes four image forming units 10 (10a, 10b, 10c, and 10d) arranged side by side, a paper feeding unit 20, an intermediate transfer unit 30, a fixing unit 40, a cleaning unit 50, and a registration sensor 60. And a control unit 80.

  The four image forming units 10 (10a to 10d) arranged side by side have the same configuration. The image forming units 10a to 10d are image forming units for black, cyan, magenta, and yellow, respectively. In the image forming unit 10 (10a to 10d), a drum-shaped electrophotographic photosensitive member as the first image carrier, that is, the photosensitive drum 11 (11a to 11d) is rotatably supported and driven to rotate in the arrow direction. Is done. A primary charger 12 (12a to 12d), an exposure unit 13 (13a to 13d), and a folding mirror 16 (16a to 16d) are arranged in the rotation direction opposite to the outer peripheral surfaces of the photosensitive drums 11a to 11d. Further, a developing device 14 (14a to 14d) and a cleaning device 15 (15a to 15d) are arranged.

  In the primary chargers 12a to 12d, charges of a uniform charge amount are given to the surfaces of the photosensitive drums 11a to 11d. Next, the exposure units 13a to 13d are exposed on the photosensitive drums 11a to 11d via the folding mirrors 16a to 16d with light beams such as laser beams modulated according to the recording image signal from the reader unit 1R. An electrostatic latent image is formed there.

  Further, the electrostatic latent images are visualized by developing devices 14 a to 14 d each containing developer of four colors such as black, cyan, magenta, and yellow (hereinafter referred to as “toner”). A visualized visible image (toner image) is a belt-like intermediate transfer member as a second image carrier constituting the intermediate transfer unit 30 in the image transfer regions Ta, Tb, Tc, Td, that is, intermediate transfer Transfer to the belt 31. The intermediate transfer unit 30 will be described in detail later.

  On the downstream side of the image transfer areas Ta, Tb, Tc, Td, the cleaning devices 15a, 15b, 15c, 15d are not transferred to the intermediate transfer belt 31 by the cleaning devices 15a, 15b, 15c, 15d to scrape off the toner remaining on the photosensitive drums 11a-11d. Clean the surface. By the process described above, image formation with each toner is sequentially performed.

  The paper feed unit 20 includes cassettes 21a and 21b for storing the transfer material P, a manual feed tray 27, and pickup rollers 22a, 22b and 26 for feeding the transfer material P one by one from the cassettes 21a and 21b or the manual feed tray 27. . The paper feed unit 20 includes a paper feed roller pair 23 that further conveys the transfer material P fed from the pickup rollers 22a and 22b, and a paper feed guide 24. Further, the paper feeding unit 20 includes registration rollers 25a and 25b that send the transfer material P to the secondary transfer region Te in accordance with the image forming timing of each image forming unit 10.

  Here, the intermediate transfer unit 30 will be described in detail.

  The intermediate transfer belt 31 serves as a winding roller, a driving roller 32 that transmits driving to the intermediate transfer belt 31, a driven roller 33 that is driven by the rotation of the intermediate transfer belt 31, and a secondary transfer region across the intermediate transfer belt 31. It is wound around a secondary transfer counter roller 34 facing Te. A primary transfer plane A is formed on the intermediate transfer belt 31 between the driving roller 32 and the driven roller 33.

  The intermediate transfer belt 31 is an endless belt made of an elastic material such as rubber or elastomer as a raw material, and the Young's modulus in the circumferential direction is “107 Pa” or more. The thickness of the intermediate transfer belt 31 is preferably “0.3 mm to 3 mm” from the viewpoints of ensuring thickness accuracy and strength and realizing flexible rotational driving. Further, the intermediate transfer belt 31 is adjusted to a desired resistance value (preferably a volume resistance value of “1011 Ωcm” or less) by adding a conductive agent such as metal powder (carbon or the like). Further, the rotational speed of each of the photosensitive drums 11a to 11d and the rotational speed of the intermediate transfer belt 31 are set to a difference of about several percent so that the intermediate transfer belt is fast.

  The drive roller 32 is coated with rubber (urethane or chloroprene) having a thickness of several millimeters on the surface of the metal roller to prevent slippage between the drive roller 32 and the intermediate transfer belt 31. The drive roller 32 is rotationally driven in the direction of arrow B by a pulse motor (not shown). The photosensitive drums 11 a to 11 d are disposed so as to face the primary transfer plane A of the intermediate transfer belt 31. Therefore, the primary transfer areas Ta to Td are positioned on the primary transfer plane A.

  In the primary transfer regions Ta to Td where the photosensitive drums 11 a to 11 d and the intermediate transfer belt 31 face each other, a primary transfer charger 35 (35 a to 35 d) is disposed on the back of the intermediate transfer belt 31. A secondary transfer roller 36 is disposed to face the secondary transfer counter roller 34, and a secondary transfer region Te is formed by a nip with the intermediate transfer belt 31. The secondary transfer roller 36 is pressed against the intermediate transfer belt 31 with an appropriate pressure. A cleaning blade 51 for cleaning the image forming surface of the intermediate transfer belt 31 and a waste toner box 52 for storing the removed waste toner are provided downstream of the secondary transfer region Te on the intermediate transfer belt 31. .

  The fixing unit 40 includes a fixing roller 41a provided with a heat source such as a halogen heater therein, and a roller 41b that is pressed against the roller 41a (the roller 41b may also include a heat source). The fixing unit 40 includes a guide 43 for guiding the transfer material P to the nip portion of the roller pair 41 (41a, 41b). In addition, it has an inner discharge roller 44, an outer discharge roller 45 for guiding the transfer material P discharged from the roller pair 41 to the outside of the apparatus, and a discharge tray 48 on which the transfer material P is stacked.

  Further, a color sensor 62 that detects a patch image on the sheet is disposed after the fixing unit 40. Two color sensors 62 are mounted on the front 62a and the back 62b in the main scanning direction, and two patch images can be read simultaneously. In response to an instruction from an operation panel (not shown), a patch image is formed on the transfer material P, the patch image is read by the color sensor 62 while paper is conveyed, and maximum density adjustment, gradation adjustment, and the like are executed.

  The control unit 80 includes a CPU (not shown) for controlling the operation of the mechanism in each unit, a registration correction circuit (not shown), a motor driver unit (not shown), and the like. When an image forming operation start signal is issued from the control unit 80, feeding of the transfer material P is started from the paper feeding stage selected according to the selected paper size or the like.

  Next, the operation of the image forming apparatus having the above configuration will be described.

  When an image forming operation start signal is issued from the control unit 80, first, the transfer material P is sent out one by one from the cassette 21a by the pickup roller 22a. The transfer material P is guided between the paper feed guides 24 by the paper feed roller pair 23 and conveyed to the registration rollers 25a and 25b. At that time, the registration rollers 25a and 25b are stopped, and the leading edge of the paper hits the nip portion. Thereafter, the registration rollers 25a and 25b start to rotate in accordance with the timing when the image forming units 10a to 10d start to form an image. The rotation of the registration rollers 25a and 25b is performed so that the transfer material P and the toner image primarily transferred onto the intermediate transfer belt 31 from the image forming units 10a to 10d coincide with each other in the secondary transfer region Te. Is set.

  On the other hand, in the image forming unit 10d, when an image forming operation start signal is issued from the control unit 80, the toner image formed on the photosensitive drum 11d is changed to 1 by the primary transfer charger 35d to which a high voltage is applied. Primary transfer is performed on the intermediate transfer belt 31 in the next transfer region Td. The primarily transferred toner image is conveyed to the next primary transfer region Tc. In this case, image formation is performed with a delay of the time during which the toner image is conveyed between the image forming units, and the next toner image is transferred onto the previous image with registration (image position) aligned. The same process is repeated for the primary transfer areas Ta, Tb, and Tc of the other colors, and eventually, the four color toner images are primarily transferred onto the intermediate transfer belt 31.

  Thereafter, when the transfer material P enters the secondary transfer region Te and contacts the intermediate transfer belt 31, a high voltage is applied to the secondary transfer roller 36 in accordance with the passing timing of the transfer material P. Then, the four color toner images formed on the intermediate transfer belt 31 by the above-described process are collectively transferred onto the surface of the transfer material P. Thereafter, the transfer material P is accurately guided to the nip portion of the fixing roller pair 41 by the conveyance guide 43. The toner image is fixed on the paper surface by the heat of the fixing roller pair 41 and the pressure of the nip. Thereafter, the transfer material P is conveyed by the inner discharge roller 44 and the outer discharge roller 45, and discharged to the outside of the apparatus.

  The printer unit 1P is provided with a registration sensor 60 for correcting a registration shift of each color image formed on each of the photosensitive drums 11a to 11d, that is, a color shift. The registration sensor 60 is installed on the transfer area A surface and at a position downstream of all the image forming units 10 and before the belt 31 is folded back by the driving roller 32. The cause of the color misregistration (registration misregistration) is due to a mechanical attachment error between the photosensitive drums 11a to 11d, an optical path length error or optical path change of the laser beam light generated by each exposure unit 13a to 13d, or an environmental temperature of the LED. Warping and the like.

  Further, a density sensor 61 that measures the density of the patch during density control is disposed in the vicinity of the registration sensor 60. When density control is performed, the density sensor 61 measures the density of each patch.

(Register misalignment correction example)
Hereinafter, the registration error correction operation will be described with reference to FIG.

  FIG. 2 is a partial cross-sectional view of the printer unit 1P of FIG.

  In FIG. 2, the image forming unit 10 a is shown, but the following operations are similarly executed by the image forming units 10 b, 10 c, and 10 d.

  The control unit 80 is a control unit that is commonly used for controlling the image forming units 10b, 10c, and 10d. A registration correction pattern image (color misregistration detection image) is created on the transfer belt 31 from each of the photosensitive drums 11a to 11d by a signal from the registration correction pattern generation unit 81 in the control unit 80. Further, a toner density adjustment pattern image is created on the transfer belt 31 from each of the photosensitive drums 11 a to 11 d by a signal from the toner density adjustment pattern generation unit 82 in the control unit 80.

  The registration sensor 60 includes a light emitting element and a light receiving element (not shown), reads a registration correction pattern image Sa created on the transfer belt 31, and registers on the photosensitive drums 11a to 11d corresponding to the respective colors. Detect deviation.

  Based on the detection result, the control unit 80 applies an electrical correction to the image signal to be recorded or drives the folding mirrors 16a to 16d provided in the laser beam optical path. The optical path length change of the beam or the optical path change correction is performed.

(Configuration example of concentration sensor)
FIG. 3 is a schematic configuration diagram of the density sensor 61.

  The density sensor 61 includes an infrared light emitting element 3051 such as an LED, light receiving elements 3052a and 3052b such as a photodiode and Cds, an IC (not shown) that processes received light data, and a holder (not shown) that accommodates these. And.

  A toner density adjustment pattern image is transferred from each of the photosensitive drums 11a to 11d onto the transfer belt 31 by a signal from the toner density adjustment pattern generation unit 82 in the control unit 80, that is, a toner patch 3064 is created.

  The light receiving element 3052a detects the intensity of irregularly reflected light from the toner patch 3064 on the intermediate transfer belt 31, and the light receiving element 3052b detects the intensity of regular reflected light from the toner patch 3064. By detecting both the regular reflection light intensity and the irregular reflection light intensity, the density of the toner patch 3064 from a high density to a low density can be detected. The light receiving elements 3052a and 3052b execute A / D conversion (10 bits) for changing the output value in accordance with the detected amount of light. After being converted into a digital signal, it is converted into density information by a luminance-density conversion table. The Based on the density information, various controls described later are executed to ensure color stability.

(Color sensor configuration example)
FIG. 4 is a schematic configuration diagram of the color sensor 62.

  The color sensor 62 that detects the color of the patch after fixing is arranged downstream of the fixing unit 40 in FIG. 1 in the transfer paper conveyance direction, reads the patch 3061 after fixing formed on the transfer material P, and performs RGB. Detect the output value.

  The color sensor 62 includes a white LED (light emitting element) 3053, a charge storage type sensor (light receiving element) 3054a with RGB on-chip filter, and a light receiving unit 3054 having a photodiode (PD) 3054b used for a trigger signal. .

  The light beam of the white LED 3053 is incident on the transfer material P on which the patch image 3061 is formed at an angle of 45 degrees, and the irregular reflection light intensity in the 0 degree direction is detected by the charge storage type sensor 3054a with an RGB on-chip filter. The charge storage type sensor 3054a with an RGB on-chip filter is configured to receive each color of RGB. The charge storage sensor of the charge storage sensor 3054a with RGB on-chip filter may be a photodiode. A plurality of RGB 3-pixel filter sets may be provided.

  Further, the arrangement of the white LED (light emitting element) 3053 and the light receiving unit 3054 may be changed so that the incident angle of the light beam of the white LED (light emitting element) 3053 is 0 degree and the reflection angle is 45 degrees. . Furthermore, instead of the configuration including the white LED (light emitting element) 3053 and the light receiving unit 3054, a configuration including an LED that emits light of three RGB colors and a sensor without a filter may be used.

  The color sensor 62 configured as described above detects the RGB output value of the patch image 3061 on the transfer material P, returns it to the printer controller, and performs various image controls.

<Example of Image Data Creation in First Embodiment>
The generation method of the first embodiment of image data input from the control unit 80 during normal image formation to the exposure unit 13d of the image forming unit 10d will be described with reference to FIG.

  FIG. 5 is a schematic configuration diagram of the control unit 80 and the exposure unit 13d of the image forming unit 10d according to the first embodiment.

  In the figure, the most upstream image forming unit 10d on the primary transfer plane A is defined as a Y station (Yellow). The image forming unit 10d superimposes a minute dot toner image on a yellow (Y) image. This is because a dot toner image is added to the image of the most upstream image forming unit 10d, and the dot toner image undergoes frictional force fluctuation during the temporary transfer of all the downstream image forming units (10a, 10b, 10c). Because it works to relax. That is, the dot toner image functions to reduce transfer shock. Also, yellow dots are less noticeable after being transferred to the recording medium than other M, C, and K dots. The dot toner image is a dot dispersed image in which a plurality of dot developer images having an area of at least one dot unit are dispersed. The formation of the dot dispersion image is referred to as dot dispersion image formation processing.

  In FIG. 5, the image information input from the host PC 101 or the reader unit 1R is processed by the image processing unit 103 of the control unit 80, and is output as an image density signal (a) for driving the laser unit.

  The control unit 80 includes a dot pattern formation unit 106, a logical operation circuit 110-1, and an area signal generation unit 108-1, and executes control on the Y station that is the yellow image formation unit 10d.

  In the dot pattern forming unit 106, a dot pattern signal (b) for forming a minute dot toner image is generated and transmitted to the density determination circuit 104. When the dot pattern signal (b) is “1”, the density determination circuit 104 transmits the image density signal (a) to the PWM circuit 107 as it is. On the other hand, when the dot pattern signal (b) is “0”, an image density signal indicating a predetermined density value defined for the dot pattern is transmitted to the PWM circuit 107 of the exposure unit 13d.

  In the PWM circuit 107, the image density signal received from the density determination circuit 104 is converted into a pulse width signal by a PWM table that generates a pulse width corresponding to the image density signal as shown in FIG. Sent to. The toner image formed on the photosensitive drum 11d is obtained by superimposing image information and a minute dot pattern. In this example, either image information or a minute dot pattern is formed for each pixel.

  The area signal generation unit 108-1 generates an area signal for instructing an area in which the dot pattern forming unit 106 forms a dot pattern. This area signal includes a main scanning paper area signal (c), a sub scanning paper area signal (d), a main scanning dot pattern area signal (e), and a sub scanning dot pattern area signal (f).

  The logical operation circuit 110-1 receives these four signals. Then, the dot pattern enable signal (g-1) is output to the dot pattern forming unit 106 under the following logical conditions. The logical condition is that the main scanning and sub-scanning paper area signals (c) and (d) are “0”, and the main scanning dot pattern area signal (e) or the sub-scanning dot pattern area signal (f) is “0”. This is the case.

That is, when expressed by a logical expression,
/ g = / c and / d and (/ e or / f), (/ means negative logic)
It becomes.

  When the dot pattern enable signal (g-1) is “0” in the dot pattern forming unit 106, dot pattern formation is executed.

  During normal image formation, the paper area signals (namely, signals (c) and (d)) and the dot pattern area signals (namely, signals (e) and (f)) are substantially in the same state. Therefore, a dot pattern is formed over the entire surface of the paper, and the normal image and the dot pattern are overlaid as shown in FIG.

(Configuration and operation example of dot pattern forming unit)
The processing of the dot pattern forming unit 106 will be described with reference to FIGS.

  FIG. 8 is a schematic configuration diagram of the dot pattern forming unit 106, and FIG. 9 is a timing chart showing the operation of the dot pattern forming unit 106.

  As an example, it is assumed that the number of dots in the main scanning direction of the minute region forming the dot pattern is 8 dots, the number of dots in the sub-scanning direction is 6 dots, and the number of shift dots is 1. The number of dots formed in the minute area is only one, and the position is (X, Y) = (3, 0) in the minute area.

  The dot pattern forming unit 106 includes a counter 201, a counter 202, a counter 203, and a lookup table (LUT) 204.

  The counter 201 counts the position in the main scanning direction, and repeats counting from 0 to 7 with an image clock as an input. The counter 201 can load an initial value. The output of the counter 203 is used as an initial value, and the main scanning top signal is used as a load signal. The counter 202 is a counter that counts up using the main scanning top signal as a clock, and repeats counting from 0 to 5. The counter 203 is a counter that counts the initial value at the time of shift. The counter 203 counts up whenever the counter 202 overflows. When the main scanning top signal is input, the count value is loaded into the counter 201. When the count value of the counter 201 and the count value of the counter 202 are input to the LUT 204 and the combination matches the value set by the LUT 204, the output of the LUT 204 becomes “High” and a minute dot pattern is formed.

  FIG. 10 is a diagram illustrating an example of a toner image on which a minute dot pattern is formed.

  Each small square in FIG. 10 is a pixel, and a toner image with a dot pattern is formed on the hatched pixel.

  Since the main scanning position of the minute area is shifted by one dot every six main scanning lines in the opposite direction to the main scanning direction, the main scanning position where the minute dots are formed becomes uniform. As a result, there is no problem that vertical streak stains occur on the secondary transfer roller, toner accumulates at a specific position of the cleaning blade, or the dot toner image transferred to the recording medium becomes noticeable.

  In this embodiment, the number k of shift dots is set to 1. However, when the size m of the micro area in the main scanning direction is 8 dots, the value of the number k of shift dots (for example, 3, 5, 7 etc.) is adopted so that the greatest common divisor of m and k is 1. However, the main scanning position where the minute dots are formed can be made uniform.

(Patch image and dot pattern formation example during image adjustment according to the first embodiment)
Next, a method for forming a patch image and a dot pattern at the time of image adjustment by the color sensor will be described.

  The patch image is generated by the toner density adjustment pattern generator 82 shown in FIG. As described above, since two color sensors 62 are mounted in the main scanning direction (front color sensor 62a and back color sensor 62b), two patches can be read simultaneously. Therefore, for example, magenta patch images are formed in a row with different densities in the sub-scanning direction and read by the front color sensor 62a. On the other hand, with the color sensor 62b on the back side, it is possible to read cyan patch images formed in a line with different densities in the sub-scanning direction. The patch image at this time is formed as shown in FIG. An elliptical dotted line portion in each quadrangular patch image is an area actually read by the color sensor 62.

  At the time of patch image formation, the area signal generator 108-1 receives area signals (that is, a main scanning dot pattern area signal (e) and a sub scanning dot pattern area signal (f )) Is output. For this reason, the dot toner image of yellow toner and the patch images of cyan and magenta toner do not overlap, and the yellow dot toner image is not affected when the color sensor 62 reads the patch image. Further, since the dot toner image is formed by the most upstream image forming unit 10d, there is an effect of suppressing the change of the friction coefficient in the image forming units 10a to 10c below that.

  FIG. 12 shows an example in which the patch image and the dot toner image do not overlap at all, but it is sufficient that the dot toner image is not affected when the patch image is read.

  The patch image of FIG. 12 is shown in detail in FIG. 13A, but the patch image formation is performed so that the dot toner image is not formed only at the reading position (patch image reading area) of the color sensor 62 surrounded by the broken line as shown in FIG. 13B. The unit 109 may be controlled.

  According to the first embodiment, the area signal generation unit 108-1 and the logical operation circuit 110-1 control the dot pattern formation unit 106. Then, the dot pattern is prevented from overlapping the patch image generated by the toner density adjustment pattern generator 82 or the patch image reading area. As a result, when forming a patch image for color stabilization, it is possible to avoid the influence of the dot dispersion image on the patch image while suppressing the occurrence of streak unevenness.

<Example of Image Data Creation in Second Embodiment>
The second embodiment is different from the first embodiment in that the dot toner image is formed in a band shape in the sub-scanning direction. As in the first embodiment, the case of forming a color sensor patch image will be described as an example.

  The generation method of the second embodiment of the image data input to the exposure unit 13d during patch image formation will be described with reference to FIG.

  FIG. 14 is a schematic configuration diagram of the image forming unit 10d and the exposure unit 13d according to the second embodiment. The difference from FIG. 5 is that the area signal generation unit 108-2 does not output the sub-scanning dot pattern area signal (f) to the logic operation circuit 110-2.

  In FIG. 14, image information input from the host PC 101 or the reader unit 1 </ b> R is processed by the image processing unit 103. Image information for the patch image is generated by the toner density adjustment pattern generation unit 82 and processed by the image processing unit 103. The processed image information is output as an image density signal (a) for driving the laser unit.

  The control unit 80 includes a dot pattern forming unit 106, a logical operation circuit 110-2, and an area signal generation unit 108-2, and executes control on the Y station that is the yellow image forming unit 10d.

  In the dot pattern forming unit 106, a dot pattern signal (b) for forming a minute dot toner image is generated and transmitted to the density determination circuit 104. When the dot pattern signal (b) is “1”, the density determination circuit 104 transmits the image density signal (a) to the PWM circuit 107 as it is. On the other hand, when the dot pattern signal (b) is “0”, an image density signal indicating a predetermined density value defined for the dot pattern is transmitted to the PWM circuit 107.

  In the PWM circuit 107 of the Y station 10d, the image density signal received from the density determination circuit 104 is converted into a pulse width signal by a PWM table that generates a pulse width corresponding to the image density signal as shown in FIG. It is sent to the laser unit 105. The toner image formed on the photosensitive drum 11d is obtained by superimposing image information and a minute dot pattern. In this example, either image information or a minute dot pattern is formed for each pixel.

  The area signal generation unit 108-2 generates an area signal for instructing an area in which the dot pattern forming unit 106 forms a dot pattern. This area signal includes a main scanning paper area signal (c), a sub-scanning paper area signal (d), and a main scanning dot pattern area signal (e).

  The logical operation circuit 110 receives these three signals. When the main scanning paper area signal (c) and the sub scanning paper area signal (d) are “0” and the main scanning dot pattern area signal (e) is “0”, the dot pattern enable signal (g− 2) is output to the dot pattern forming unit 106.

That is, when expressed by a logical expression,
/ g = / c and / d and / e, (/ means negative logic)
It becomes.

  When the dot pattern enable signal (g-2) is “0” in the dot pattern forming unit 106, dot pattern formation is executed.

  In the second embodiment, as shown in FIG. 15, the dot toner image is formed in a strip shape in the sub-scanning direction. A main scanning dot pattern area signal (e) is output so that the dot toner image does not overlap the patch image. Therefore, the area where the dot toner image is formed becomes narrow, but the dot toner image exists at any position in the sub-scanning direction within the dot pattern area. Thereby, it is possible to prevent stripe unevenness in the patch image.

  In the second embodiment, as in the first embodiment, an example in which the patch image and the dot toner image do not overlap at all is shown. However, it is sufficient that the dot toner image is not affected when the patch image is read. Therefore, it is not always necessary to avoid overlapping. The patch portion of the method of FIG. 15 is shown in detail in FIG. 16A, but only the color sensor reading portion (patch image reading region) surrounded by a broken line as shown in FIG. 16B is controlled not to form a dot toner image. You may do it.

  According to the second embodiment, the dot pattern forming unit 106 does not overlap the patch image generated by the toner density adjustment pattern generating unit 82 or the patch image reading area so that the dot pattern does not overlap. A toner image is formed in a strip shape in the sub-scanning direction. As a result, when forming a patch image for color stabilization, it is possible to avoid the influence of the dot dispersion image on the patch image while suppressing the occurrence of streak unevenness.

<Example of Image Data Creation in Third Embodiment>
The third embodiment is different from the first embodiment in that the dot toner image is formed in a strip shape in the main scanning direction. As in the first embodiment, the case of forming a color sensor patch image will be described as an example.

  The generation method of the third embodiment of the image data input to the exposure unit 13d at the time of patch image formation will be described with reference to FIG.

  FIG. 17 is a schematic configuration diagram of the image forming unit 10d and the exposure unit 13d according to the third embodiment. The difference from FIG. 5 is that the area signal generation unit 108-3 does not output the main scanning dot pattern area signal (e) to the logic operation circuit 110-3.

  In FIG. 17, image information input from the host PC 101 or the reader unit 1 </ b> R is processed by the image processing unit 103. Image information for the patch image is generated by the toner density adjustment pattern generation unit 82 and processed by the image processing unit 103. The processed image information is output as an image density signal (a) for driving the laser unit.

  The control unit 80 includes a dot pattern formation unit 106, a logical operation circuit 110-3, and an area signal generation unit 108-3, and executes control on the Y station that is the yellow image formation unit 10d.

  In the dot pattern forming unit 106, a dot pattern signal (b) for forming a minute dot toner image is generated and transmitted to the density determination circuit 104. When the dot pattern signal (b) is “1”, the density determination circuit 104 transmits the image density signal (a) to the PWM circuit 107 as it is. On the other hand, when the dot pattern signal (b) is “0”, an image density signal indicating a predetermined density value defined for the dot pattern is transmitted to the PWM circuit 107.

  In the PWM circuit 107 of the Y station 10d, the image density signal received from the density determination circuit 104 is converted into a pulse width signal by a PWM table that generates a pulse width corresponding to the image density signal as shown in FIG. It is sent to the laser unit 105. The toner image formed on the photosensitive drum 11d is obtained by superimposing image information and a minute dot pattern. In this example, either image information or a minute dot pattern is formed for each pixel.

  The area signal generation unit 108-3 generates an area signal for instructing an area in which the dot pattern forming unit 106 forms a dot pattern. This area signal generates a main scanning paper area signal (c), a sub scanning paper area signal (d), and a sub scanning dot pattern area signal (f).

  The logical operation circuit 110-3 receives these three signals. When the main scanning paper area signal (c) and the sub scanning paper area signal (d) are “0” and the sub scanning dot pattern area signal (f) is “0”, the dot pattern enable signal (g− 3) is output to the dot pattern forming unit 106.

That is, when expressed by a logical expression,
/ g = / c and / d and / f, (/ means negative logic)
It becomes.

  In the dot pattern forming unit 106, when the dot pattern enable signal (g-3) is "0", the dot pattern is formed.

  In the third embodiment, the patch image is generated by the toner density adjustment pattern generator 82 shown in FIG. As shown in FIG. 18, a dot toner image is formed in a strip shape in the main scanning direction. Since the sub-scanning dot pattern area signal (f) is output so that the dot toner image does not overlap the patch image, the area where the dot toner image is formed becomes narrow. However, since a dot toner image or a patch image exists at any position in the sub-scanning direction in the paper area, unevenness of the patch image can be prevented by the effect of the dot toner image. However, in this case, the difference in friction generated between the paper and the transport roller between the area where the dot toner image is formed and the area where the patch image is formed, for example, by increasing the width of the patch image. It is necessary to prevent this from occurring.

  In the third embodiment, as in the first embodiment, the example in which the patch image and the dot toner image do not overlap at all is shown. However, it is sufficient that the dot toner image is not affected when the patch image is read. Therefore, it is not always necessary to avoid overlapping. FIG. 19A shows the details of the patch portion of the method of FIG. 18, but only the color sensor reading portion (patch image reading region) surrounded by a broken line as shown in FIG. 19B is controlled not to form a dot toner image. You may do it.

  According to the third embodiment, the dot pattern forming unit 106 uses the dot pattern forming unit 106 so that the dot pattern does not overlap the patch image generated by the toner density adjustment pattern generating unit 82 or the patch image reading area. A toner image is formed in a strip shape in the main scanning direction. As a result, when forming a patch image for color stabilization, it is possible to avoid the influence of the dot dispersion image on the patch image while suppressing the occurrence of streak unevenness.

<Example of Image Data Creation in Fourth Embodiment>
The difference between the fourth embodiment and the first to third embodiments is that although the patch image is formed on the intermediate transfer member, it is not transferred to the transfer material. The patch image formed on the intermediate transfer member is read by the density sensor 61 and then cleaned by a cleaning unit.

  The generation method of the fourth embodiment of the image data input to the exposure unit 13d at the time of patch image formation will be described with reference to FIG.

  FIG. 20 is a schematic configuration diagram of the image forming unit 10d and the exposure unit 13d according to the fourth embodiment. The difference from FIG. 5 is that the area signal generation unit 108-4 does not output the main scanning paper area signal (c) and the sub scanning paper area signal (d) to the logical operation circuit 110-4.

  In FIG. 20, image information input from the host PC 101 or the reader unit 1 </ b> R is processed by the image processing unit 103. Image information for the patch image is generated by the toner density adjustment pattern generation unit 82 and processed by the image processing unit 103. The processed image information is output as an image density signal (a) for driving the laser unit.

  The control unit 80 includes a dot pattern formation unit 106, a logical operation circuit 110-4, and an area signal generation unit 108-4, and controls the Y station, which is the yellow image formation unit 10d. Good.

  In the dot pattern forming unit 106, a dot pattern signal (b) for forming a minute dot toner image is generated and transmitted to the density determination circuit 104. When the dot pattern signal (b) is “1”, the density determination circuit 104 transmits the image density signal (a) to the PWM circuit 107 as it is. On the other hand, when the dot pattern signal (b) is “0”, an image density signal indicating a predetermined density value defined for the dot pattern is transmitted to the PWM circuit 107.

  In the PWM circuit 107 of the Y station 10d, the image density signal received from the density determination circuit 104 is converted into a pulse width signal by a PWM table that generates a pulse width corresponding to the image density signal as shown in FIG. It is sent to the laser unit 105. The toner image formed on the photosensitive drum 11d is obtained by superimposing image information and a minute dot pattern. In this example, either image information or a minute dot pattern is formed for each pixel.

  The area signal generation unit 108-4 generates an area signal for instructing an area where the dot pattern forming unit 106 forms a dot pattern. This area signal includes a main scanning dot pattern area signal (e) and a sub-scanning dot pattern area signal (f).

  The logical operation circuit 110-4 receives these two signals. When the main scanning dot pattern area signal (e) or the sub scanning dot pattern area signal (f) is “0”, the dot pattern enable signal (g-4) is output to the dot pattern forming unit 106.

That is, when expressed by a logical expression,
/ g = / e or / f, (/ means negative logic)
It becomes.

  When the dot pattern enable signal (g-4) is “0” in the dot pattern forming unit 106, dot pattern formation is executed. The area where the dot pattern is formed is controlled so that the dot pattern is formed from the front of the patch image so as not to cause streak unevenness with respect to the patch image.

  In the fourth embodiment, the area signal generation unit 108-4 performs the main scanning dot pattern area signal (e) and the sub scanning dot pattern area signal so as to avoid the patch image as shown in FIG. Output (f). Therefore, the dot toner image made of yellow toner and the patch image do not overlap, and the yellow dot toner image is not affected when the density sensor 61 reads the patch image.

  FIG. 21 shows an example in which the patch image and the dot toner image do not overlap at all. However, since it is sufficient that the dot toner image is not affected at the time of reading the patch image, it is not always necessary to avoid the overlap. The relationship between the patch image and the dot toner image does not necessarily have to be as shown in FIG. 13A, and may be as shown in FIG. 13B, or the dot toner image may be formed in a strip shape as shown in FIGS. The effect is obtained.

  According to the fourth embodiment, the area signal generation unit 108-4 and the logical operation circuit 110-4 control the dot pattern formation unit 106. Then, the dot pattern is prevented from overlapping the patch image generated by the toner density adjustment pattern generator 82 or the patch image reading area. As a result, when forming a patch image for color stabilization, it is possible to avoid the influence of the dot dispersion image on the patch image while suppressing the occurrence of streak unevenness.

<Another embodiment>
In this embodiment, an example in which a patch image for density detection is formed on the intermediate transfer member has been described. However, a patch image for density detection is formed on the photosensitive member, and the patch image on the photosensitive member is The technology of each of the above embodiments can also be used when the concentration sensor detects.

  Image streaks due to changes in frictional force are not limited to color image formation, but also occur when, for example, a black image is formed by a color image forming apparatus. Therefore, high-quality image formation can be performed by using the present invention even when forming a monochrome image.

  Further, in an image forming apparatus that does not use an intermediate transfer body, the present invention can also be applied to a configuration in which a developer image is transferred directly from an image carrier to a transfer material mounted on a transfer material conveyance body or the like. In that case, a peripheral speed difference is often provided in the moving speed between the transfer material conveyance body and the image carrier. Further, the present invention can be applied to a configuration in which there is no peripheral speed difference between the moving speeds of the transfer material conveyance body and the image carrier when an unintended speed difference occurs due to eccentricity of the drive roller.

  The dimensions, materials, shapes, and relative positions of the components of the image forming apparatus described above are not intended to limit the scope of the present invention only to those unless otherwise specified.

  Another object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus. This can also be achieved by the computer (or CPU, MPU, etc.) of the system or apparatus reading and executing the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code and the storage medium storing the program code constitute the present invention. .

  As a storage medium for supplying the program code, for example, a floppy (registered trademark) disk, a hard disk, or a magneto-optical disk can be used. Further, optical disks such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD + RW, magnetic tape, nonvolatile memory card, ROM, and the like can be used. Alternatively, the program code may be downloaded via a network.

  The functions of the above-described embodiments are not only realized by executing the program code read by the computer. In some cases, an OS (operating system) or the like running on the computer performs part or all of the actual processing based on the instruction of the program code, and the functions of the above-described embodiments are realized by the processing. included.

  Further, the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instruction of the program code, a CPU or the like provided in the extension board or extension unit with the extension function performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing. Cases are also included.

1 is a cross-sectional view of a main part of an image forming apparatus according to an embodiment of the present invention. It is a fragmentary sectional view of the printer part of FIG. It is a schematic block diagram of a density sensor. It is a schematic block diagram of a color sensor. It is a schematic block diagram of the image formation part and exposure part which concern on 1st Embodiment. It is a figure which shows an example of the PWM table which shows the relationship between an image density signal and a pulse width. It is a figure which shows the state in which the dot pattern is formed over the paper whole surface. It is a schematic block diagram of a dot pattern formation part. It is a timing chart which shows operation | movement of a dot pattern formation part. FIG. 6 is a diagram illustrating an example of a toner image on which a minute dot pattern is formed. It is a figure which shows the relationship between a patch image and the reading area of a color sensor. It is a figure which shows the relationship between the patch image and dot toner image which concern on 1st Embodiment. FIG. 13 is a diagram illustrating a state where the patch image and the dot toner image do not overlap in FIG. 12. FIG. 13 is a diagram illustrating a state in which the patch image and the dot toner image do not overlap in the reading area of the color sensor in FIG. 12. It is a schematic block diagram of the image formation part and exposure part which concern on 2nd Embodiment. It is a figure which shows the relationship between the patch image and dot toner image which concern on 2nd Embodiment. FIG. 16 is a diagram illustrating a state where the patch image and the dot toner image do not overlap in FIG. 15. FIG. 16 is a diagram illustrating a state in which the patch image and the dot toner image do not overlap in the color sensor reading region in FIG. 15. It is a schematic block diagram of the image formation part and exposure part which concern on 3rd Embodiment. It is a figure which shows the relationship between the patch image and dot toner image which concern on 3rd Embodiment. FIG. 19 is a diagram illustrating a state in which the patch image and the dot toner image do not overlap in FIG. FIG. 19 is a diagram illustrating a state in which the patch image and the dot toner image do not overlap in the color sensor reading region in FIG. 18. It is a schematic block diagram of the image formation part and exposure part which concern on 4th Embodiment. It is a figure which shows the relationship between the patch image and dot toner image which concern on 4th Embodiment. It is a figure which shows the relationship between the reading density and reading position of the conventional color sensor.

Explanation of symbols

1R reader unit 10 image forming unit 13 exposure unit 30 intermediate transfer unit 34 secondary transfer counter roller 35 (35a to 35d) primary transfer charger 36 secondary transfer roller 80 control unit 81 registration correction pattern generation unit 82 toner Density adjustment pattern generator 101 Host PC
DESCRIPTION OF SYMBOLS 103 Image processing part 104 Density determination circuit 105 Laser unit 106 Dot pattern formation part 107 PWM circuit 108 Area signal generation part 110 Logic operation circuit

Claims (10)

Dot dispersed image forming means for forming a dot dispersed image in which a plurality of dot developer images having an area of at least one dot unit are dispersed on an image carrier;
Patch image forming means for forming a patch image to be read by the reading means and performing image adjustment in any region on the image carrier;
The dot dispersion image forming means is controlled so that the dot dispersion image is formed within the patch image area and outside the reading area by the reading means, and within the patch image area and the reading. the read area by means, the image forming apparatus characterized by comprising a control means for controlling the pre-Symbol dot dispersion image forming means so that the no dot dispersion image is formed. Wherein, prior Kipa Tsu as the dot dispersed image to a strip-shaped area in the main scanning direction including the reading area by the reading unit Ji image is not formed, wherein the controller controls the dot dispersion image forming means The image forming apparatus according to claim 1 . It said control means, prior to the dot dispersion image in the sub-scanning direction of the strip-shaped area including the reading area by the reading means Kipa pitch image is not formed, wherein the controller controls the dot dispersion image forming means The image forming apparatus according to claim 1 . When the image forming apparatus forms a color image, the dot dispersion image forming means, the image forming apparatus according to claims 1, characterized in that to form the dot dispersion images of yellow to any one of the 3 . The image forming apparatus according to any one of 4 claims 1, characterized in that it comprises a removal means to remove the patch image the reading means is Tsu read from said image bearing member. A dot dispersion image forming step of forming a dot dispersion image in which a plurality of dot developer images each having an area of at least one dot unit are dispersed on the image carrier;
A patch image forming step of forming a patch image to be read by a reading unit and performing image adjustment in any region of the image carrier;
The dot dispersion image forming process is controlled so that the dot dispersion image is formed within the patch image area and outside the reading area by the reading unit, and within the patch image area and the reading. the read area by means control method of the image forming apparatus characterized by comprising a control step of controlling the pre-Symbol dot dispersion imaging process such that the dot dispersion image is not formed. The dot dispersion image forming step is controlled in the control step so that the dot dispersion image is not formed in a belt-like region in a main scanning direction including a reading region of the patch image by the reading unit. Item 7. The control method according to Item 6. The dot dispersion image forming step is controlled in the control step so that the dot dispersion image is not formed in a band-like region in a sub-scanning direction including a reading region of the patch image by the reading unit. Item 7. The control method according to Item 6. A program for causing a computer to execute the method according to claim 6 . A computer-readable storage medium storing the program according to claim 9 .

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