JP2008185914A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and surely perform appropriate density correction by preventing sampling timing from being lagged even when an intermediate belt is elongated and contracted. <P>SOLUTION: A pattern for position detection and a pattern for density correction are plotted on the surface of the intermediate belt with the lapse of fixed time, and the pattern for density correction is detected with the lapse of fixed time after detecting the pattern for position detection. Next, the pattern for density correction is removed. Then, a spot (background) of the surface of the belt from which the pattern for density correction is removed is detected with the lapse of fixed time after the pattern for position detection is detected again, and density correction is performed based on comparison of the pattern for density correction detected previously with the background. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer or a copier capable of color printing by an intermediate transfer method using an intermediate belt, and more particularly to an image forming apparatus capable of correcting the density of an image formed on the intermediate belt. It is.

  In an image forming apparatus such as a printer or a copying machine, the image quality may differ even when the same toner image is output depending on the temperature and humidity (use environment) or depending on the operation of the developing device and the photosensitive drum. In such a case, the calibration is performed when the temperature inside the machine at power-on falls below a certain value, or when a certain number of prints have been made since the last calibration. Generally, a method of adjusting the toner density so as to obtain image quality, that is, correcting the density and reducing the degree of difference in image quality is generally performed.

In particular, in an image forming apparatus that forms a color image by an intermediate transfer method, a density measurement pattern is formed on an intermediate belt, the density of this pattern is sampled, and, for example, on the intermediate belt after one round (one rotation) Of the surface where no image is formed at the same place where the density measurement pattern is sampled, and the density correction is performed based on the difference (comparison) of these sampling values one to one. By performing this, calibration with high accuracy becomes possible. In order to perform the one-to-one difference, it is necessary to grasp the rotational position of the intermediate belt. For example, information about the distance that the intermediate belt makes one revolution or rotation timing is stored in advance as a fixed value. Alternatively, it is necessary to attach a so-called “feather” or the like (position detecting member) to a predetermined position of the intermediate belt.
JP 2004-294471 A

  However, the intermediate belt may expand and contract depending on the operating temperature conditions and the usage level (usage time, etc.) (it may be possible to make the belt not expand / contract at a higher cost). When the distance is stored as a fixed value, if the intermediate belt expands or contracts, a one-to-one difference cannot be obtained at an appropriate position, and accurate density correction cannot be performed. In addition, when a belt or any other device that can detect the position is attached to the intermediate belt, the belt can be expanded and contracted, but the cost is increased.

  On the other hand, in Patent Document 1, the position detection time from the calibration pattern exposure start timing to the photosensitive drum to the detection timing of the calibration pattern tip on the conveyor belt is measured, and the deviation from the position reference time is measured. A technique for adjusting the mutual alignment of each calibration pattern (monochromatic image) formed on the conveyance belt for each process unit (image forming unit) by obtaining is disclosed. However, all of these techniques are based on detecting each calibration pattern actually formed on the conveyance belt. The sampling timing of the density measurement pattern forming unit and the density measurement pattern are the same. Adjustment that matches the sampling timing of the pattern forming portion for non-density measurement after the intermediate belt wraps at the position cannot be performed.

  The present invention has been made in view of the above circumstances, and even if the intermediate belt expands and contracts depending on the use temperature condition and use level (usage time, etc.), the belt can be expanded and contracted without cost. It is an object of the present invention to provide an image forming apparatus that can prevent occurrence of a sampling timing shift and can perform appropriate density correction easily and reliably.

  An image forming apparatus according to the present invention is an image forming apparatus configured to be capable of image formation by an intermediate transfer method using an intermediate transfer belt and having a density correction function for correcting the density of an image in the image formation. A belt rotating unit that rotates the intermediate transfer belt endlessly, a density correction pattern that is a predetermined pattern image for density correction, and a density correction pattern on the belt surface of the intermediate transfer belt that rotates endlessly. Pattern forming means for forming a position detection pattern, which is a predetermined pattern image for detecting a position, and after forming the position detection pattern, forming the density correction pattern at a predetermined time interval; A position pattern for detecting the position detecting pattern on the belt surface of the endlessly rotating intermediate transfer belt; A density pattern detecting means for detecting the density correction pattern on the belt surface of the intermediate transfer belt that rotates endlessly after a predetermined time has elapsed after the position detecting pattern is detected by the output means and the position pattern detecting means; And after the density correction pattern is detected by the density pattern detection means, a removal means for removing the density correction pattern from the belt surface, and after the density correction pattern is removed by the removal means, Belt surface detection for detecting belt surface information of the belt surface where the density correction pattern is removed after a certain period of time after the position detection pattern is detected again by the position pattern detection means. And information on the density correction pattern detected by the density pattern detecting means and the bell Characterized in that it comprises a density correction means for performing the density correction based on a comparison of the belt surface information detected by the surface detector.

  According to the above configuration, the image forming apparatus is configured to be capable of image formation by an intermediate transfer method using an intermediate transfer belt, and has a density correction function for correcting image density in image formation. The intermediate transfer belt is rotated endlessly by the belt rotating unit, and the density correction pattern, which is a predetermined pattern image for density correction, is formed on the belt surface of the intermediate transfer belt that is rotated endlessly by the pattern forming unit. A position detection pattern, which is a predetermined pattern image for detecting a position, is formed. After the position detection pattern is formed, a density correction pattern is formed at a predetermined time interval. The position pattern detection means detects the position detection pattern on the belt surface of the intermediate transfer belt that rotates endlessly, and after the position detection pattern is detected by the position pattern detection means by the density pattern detection means, a predetermined time is passed. A density correction pattern on the belt surface of the intermediate transfer belt that rotates endlessly is detected. Further, after the density correction pattern is detected by the density pattern detecting means by the removing means, the density correction pattern is removed from the belt surface, and after the density correction pattern is removed by the removing means by the belt surface detecting means. In this case, after the position detection pattern is detected again by the position pattern detection means, the belt surface information of the place where the density correction pattern on the belt surface is removed is detected after a certain period of time. Then, the density correction unit performs density correction based on the comparison between the density correction pattern information detected by the density pattern detection unit and the belt surface information detected by the belt surface detection unit.

  That is, with respect to the intermediate transfer belt that rotates endlessly, a position detection pattern and a density correction pattern are formed on the belt surface at a predetermined time interval, and after the position detection pattern is detected, The density correction pattern is detected at the timing when the same time as the predetermined time has elapsed. Thereafter, only this density correction pattern is removed. After detecting the position detection pattern again, the belt surface information where the density correction pattern has been removed is detected at the same time as the fixed time at the time of pattern formation. Even if the intermediate belt expands and contracts according to the operating temperature conditions and the usage level (usage time, etc.), it is possible to prevent the occurrence of sampling timing deviation due to the belt expansion and contraction without cost. The information of the density correction pattern forming unit and the non-density correction pattern forming unit (background) in the same place, with the detection position (detection time) of the position detection pattern as a reference position, can be compared on a one-to-one basis. Therefore, it is possible to easily and surely perform appropriate density correction.

  In the above-described configuration, the removing unit may rotate the endless intermediate transfer belt after a position detection pattern is detected by the position pattern detection unit or after a density correction pattern is detected by the density pattern detection unit. The belt is separated from the belt surface by a predetermined time between a passage time until the position detection pattern on the belt surface passes the removal position by the removal means and a time obtained by adding the fixed time to the passage time. It is preferable to remove the density correction pattern.

  According to this, the position on the belt surface of the intermediate transfer belt that rotates endlessly after the position detection pattern is detected by the position pattern detection unit or after the density correction pattern is detected by the density pattern detection unit. The density correction pattern is removed from the belt surface at a predetermined time between a passage time until the detection pattern passes the removal position by the removal means and a time obtained by adding the predetermined time to the passage time. Therefore, the removal of the density correction pattern after the density correction pattern is detected can be reliably performed with a simple structure.

  Further, in the above configuration, the pattern forming unit may include the position detection pattern and the density correction pattern in which an end side in the endless rotation direction is a straight line parallel to a direction orthogonal to the endless rotation direction. It is preferable to form on the surface.

  According to this, since the pattern forming means forms on the belt surface a position detection pattern and a density correction pattern in which the edge in the endless rotation direction is a straight line parallel to the direction orthogonal to the endless rotation direction. Measurement of time from detection of position detection pattern to detection of density correction pattern, or time from detection of position detection pattern or density correction pattern to removal of density correction pattern It is possible to easily and surely take timings in measurement and the like, and it becomes possible to easily and reliably detect each of these patterns, and thus it is possible to perform density correction with higher accuracy.

  According to the present invention, even when the intermediate belt expands and contracts according to the use temperature condition and the use level (usage time, etc.), the sampling timing shift occurs due to the belt expansion and contraction without incurring cost. Therefore, appropriate density correction can be performed easily and reliably.

  A printer as an example of an image forming apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a printer according to an embodiment of the present invention. As shown in FIG. 1, the printer 1 includes image forming units 2M, 2C, 2Y, and 2K arranged in parallel for each color of magenta (M), cyan (C), yellow (Y), and black (K) in the printer body. Has been.

  The image forming units 2M, 2C, 2Y, and 2K (collectively referred to as the image forming unit 2) form (print) a color image on a sheet. For example, the photosensitive drum 3 made of amorphous silicon and the photosensitive drum 3 are used. A charging unit 4, an exposure unit 5, a developing unit 6, and a photoconductor cleaning unit 7 are provided around the body drum 3.

  The charging unit 4 uniformly charges the surface of the photosensitive drum 3 to a predetermined potential. The exposure unit 5 irradiates the surface of the photosensitive drum 3 with a laser beam (LED light) generated based on image data transmitted from an image data storage unit 30 or the like, which will be described later. It forms an image. The developing unit 6 makes the electrostatic latent image appear as a toner image by attaching the toner supplied from the toner supply unit 61 to the electrostatic latent image formed on the photosensitive drum 3. The photoconductor cleaning unit 7 cleans the toner on the surface of the photoconductor drum 3 after the primary transfer of the toner image to the intermediate belt 10 described later.

  Below the image forming units 2M to 2K, an intermediate transfer roller 9 (primary transfer roller) and an intermediate belt (intermediate transfer belt) for performing an intermediate transfer (primary transfer) of the toner image that has become apparent on the surface of the photosensitive drum 3 are provided. 10 is disposed. The intermediate belt 10 is formed of a predetermined belt body and is configured to rotate endlessly by driving rollers 11 to 13 in a state where the intermediate belt 10 is pressed against the photosensitive drum 3 by an intermediate transfer roller 9 disposed to face each photosensitive drum 3. Has been. The toner images of the respective colors formed on the photosensitive drum 3 are transferred and superimposed on the intermediate belt 10 that is rotated endlessly in order of magenta, cyan, yellow, and black at the same timing. As a result, a color image composed of four colors Y, M, C, and K is formed on the intermediate belt 10.

  A secondary transfer roller 14 is provided via the intermediate belt 10 at a position facing the drive roller 13. The secondary transfer roller 14 transfers a color image on the intermediate belt 10 to a sheet by a transfer bias from a control unit 100 described later.

  The printer 1 also includes a paper feed unit 15 that feeds paper toward the image forming units 2Y to 2K. The paper feed unit 15 includes a paper feed cassette 151 that stores paper of each size, a transport path 152 that is a path through which the paper is transported, a transport roller 153 that transports the paper in the transport path 152, and the like. The sheets taken out from the cassette 151 one by one are conveyed toward the image forming units 2Y to 2K, that is, the position of the secondary transfer roller 14. The paper feeding unit 15 conveys the paper subjected to the secondary transfer process to the fixing unit 16 and discharges the paper subjected to the fixing process to the paper discharge tray 17 at the upper part of the printer main body.

  A fixing unit 16 is provided at an appropriate position downstream of the secondary transfer roller 14 in the conveyance path 152. The fixing unit 16 fixes the toner image transferred to the paper. The fixing unit 16 includes a heat roller 161 and a pressure roller 162. The heat on the paper is melted by the heat of the heat roller 161, and the pressure is applied by the pressure roller 162 to fix the toner on the paper.

  The printer 1 also includes a static elimination cleaning 18 and a density sensor 19. The neutralization cleaning 18 removes (collects) the toner (residual toner) on the intermediate belt 10. For example, as shown in the enlarged schematic view of FIG. 2, the static elimination cleaning 18 includes a cleaning electrode 181 and a cleaning brush 182 (rotating brush). A cleaning bias having a polarity opposite to the charged charge of the toner is applied to the cleaning brush 182 by the cleaning electrode 181. The toner is removed by moving the toner on the intermediate belt 10 to the cleaning brush 182 by the applied electrostatic force. The charge removal cleaning 18 is also used to remove a density correction pattern 202 when performing calibration, which will be described later. However, the neutralization cleaning 18 removes a certain portion of the toner on the endless rotating intermediate belt 10 and passes the neutralization cleaning 18 without removing a certain portion of the toner. It is possible to switch between removal and non-removal.

  The density sensor 19 measures the density on the surface of the intermediate belt 10 (hereinafter referred to as “belt surface” as appropriate), and continuously detects the density of each part of the belt surface according to the endless rotation of the intermediate belt 10. Sensing operation can be performed at all times. However, the “density” here indicates not only the density of the toner actually present on the belt surface but also the meaning of the density of the belt surface itself (referred to as the background) when the toner is removed. . That is, in the present embodiment, the density sensor 19 particularly detects the density of a position detection pattern 201 described later, the density of a density correction pattern 202, and the density of the belt surface after removal of the density correction pattern 202. The density sensor 19 may not be used. For example, a sensor capable of capturing an image including grayscale information may be used as long as density detection is possible.

  FIG. 3 is a block configuration diagram illustrating an example of a schematic configuration of the printer 1. As shown in FIG. 3, the printer 1 includes a network I / F (interface) unit 30, an image data storage unit 40, an operation panel unit 50, a recording unit 60, a cleaning unit 70, a sensor unit 80, and a main control unit 100. ing. The network I / F unit 30 controls transmission / reception of various data to / from an information processing apparatus (external device) such as a PC connected via a network such as a LAN. The image data storage unit 40 temporarily stores image data transmitted from a PC or the like via the network I / F unit 30. The operation panel unit 50 is provided on the front unit of the printer 1 and functions as an input key for inputting various instructions by the user or displays predetermined information.

  The recording unit 60 includes the image forming unit 2, the paper feeding unit 9, the fixing unit 16, and the transfer unit 61, and performs image printing on a sheet based on image data stored in the image data storage unit 40. is there. However, the transfer unit 61 includes the intermediate belt 10, the driving rollers 11 to 13, the secondary transfer roller 14, and the like, and transfers the toner image on the photosensitive drum 3 to the sheet via the intermediate belt 10. . The cleaning unit 70 includes the static elimination cleaning 18 (including the photosensitive member cleaning unit 7). The sensor unit 80 includes various sensors of each unit of the printer 1, particularly the density sensor 19.

  The main control unit 100 reads out and executes a ROM (Read Only Memory) that stores various control programs, a RAM (Random Access Memory) that temporarily stores data or functions as a work area, and the control programs. The microcomputer 1 is configured to transmit and receive various control signals to and from the respective functional units, and control operation of the entire printer 1.

  By the way, the printer 1 has a function of performing print density correction, that is, a calibration for density correction of a toner image (image) formed on the belt surface. Hereinafter, the calibration for density correction will be described. To do. Regarding this calibration, the main control unit 100 includes a belt rotation control unit 101, a density sensor sampling unit 102, a sampling data storage unit 103, a pattern drawing control unit 104, a position detection data acquisition unit 105, a time measurement unit 106, and a density correction unit. A data acquisition unit 107, a cleaning control unit 108, a background data acquisition unit 109, and a density correction unit 110 are provided.

  The belt rotation control unit 101 controls endless rotation driving of the intermediate belt 10 by controlling rotation driving of the driving rollers 11 to 13. The density sensor sampling unit 102 performs sampling (or image reading) on density measurement data (referred to as a density sensor value) transmitted from the density sensor 19. Data acquired by this sampling is referred to as “density sampling data”. The sampling data storage unit 103 stores density sampling data acquired by the density sensor sampling unit 102 (for example, the RAM). A position detection pattern 201 and a density correction pattern 202 shown in FIG. 4 described later are sampled in the time t-axis direction shown in the figure by the density sensor 19 as the intermediate belt 10 rotates.

  Here, in the upper view indicated by reference numeral 210 in FIG. 4, the position (image formation, primary transfer) drawn on the belt surface by the image forming unit 2, that is, the image forming units 2M, 2C, 2Y, and 2K during the calibration. An example of the detection pattern 201 and the density correction pattern 202 is shown. However, the X-axis direction in the figure is the endless rotation direction of the intermediate belt 10, and the Y-axis direction is a direction orthogonal to the direction (belt width direction of the intermediate belt 10). In the following description, a case where the calibration is performed on, for example, the image forming unit 2M in the image forming units 2M, 2C, 2Y, and 2K will be described. The same applies to the other image forming units 2.

  The position detection pattern 201 (position detection patch; position detection pattern image) is, for example, a strip extending in the Y-axis direction (which may be considered as a strip having a certain width extending in the X-axis direction) or a rectangular shape ( A toner image drawn in a rectangular shape (which may be a square shape).

  The density correction pattern 202 (density correction patch; density correction pattern image) has, for example, the same constant width as the width of the position detection pattern 201 in the Y-axis direction (which may be different from each other), and the X-axis. It is a toner image drawn in a strip shape or a quadrangular shape (rectangular shape; may be square shape) extending in the direction. The density correction pattern 202 includes, for example, a plurality of block regions having different densities (or resolutions; dpi), that is, different degrees of pixel thinning. Here, the density gradually decreases like block areas B1, B2, B3... B12. Specifically, the block areas B1, B3, B5... And B2, B4, B6. It consists of twelve block areas whose density gradually decreases at alternate positions. The position detection pattern 201 and the density correction pattern 202 are collectively referred to as a “pattern set” hereinafter. Regarding the pixel thinning (density), the position detection pattern 201 is assumed to have a predetermined density, for example, a normal pixel density (for example, the same density as the block region B1) in which pixels are not thinned. In the present embodiment, both end sides in the X-axis direction of the position detection pattern 201 and the density correction pattern 202 are drawn so as to be parallel to the Y-axis direction, that is, the direction orthogonal to the endless rotation direction.

  Returning to FIG. 3, the pattern drawing control unit 104 controls the drawing of the position detection pattern 201 and the density correction pattern 202 on the intermediate belt 10. Specifically, the pattern drawing control unit 104 performs endless rotation of the intermediate belt 10 at a predetermined position on the belt surface at the time of calibration, that is, for example, when the execution of calibration is instructed by the user from the operation panel unit 50. Accordingly, a toner image of the position detection pattern 201 is first formed, and after the toner image of the position detection pattern 201 is formed, a predetermined time t1 (waiting time t1) is waited, that is, the waiting time t1 is separated (constant). After the time t1, the image forming operation of the image forming unit 2M is controlled so as to form the toner image of the next density correction pattern 202 (note that the formation of the toner image of the pattern “draws the pattern” "Also expressed).

  The waiting time t1 is a time (separation) that ensures at least a distance W (a separation distance between the position detection pattern 201 and the density correction pattern 202) that can suitably clean the density correction pattern 202 described later. If the distance is too short, it is not possible to secure a time until the operation for removing the density correction pattern 202 after the position detection pattern 201 passes the static elimination cleaning 18, as will be described later). May be. The information on the waiting time t1 may be stored in advance as a fixed value, for example, in the time measuring unit 106 described later.

  The position detection data acquisition unit 105 acquires information of the position detection pattern 201 from the density sampling data obtained by the density sensor sampling unit 102. That is, the position detection data acquisition unit 105 detects the position detection pattern 201 (the position of the position detection pattern 201) on the belt surface. Specifically, the position detection data acquisition unit 105 stores, for example, a comparison pattern having the same shape as the position detection pattern 201, and the same pattern as this comparison pattern is detected from the density sampling data. The information of the position detection pattern 201 is acquired.

  The timer 106 measures time (performs time counting). Specifically, the time measuring unit 106 has elapsed time from when the position detection pattern 201 is drawn to when drawing of the density correction pattern 202 is started, that is, after the drawing of the position detection pattern 201 is finished. From this, it is measured that time has elapsed by the waiting time t1. Further, the time measuring unit 106 measures the elapse of time by the waiting time t <b> 1 after the position detection pattern 201 is detected by the position detection data acquisition unit 105.

  The density correction data acquisition unit 107 acquires the information of the density correction pattern 202 from the density sampling data when the elapsed time t1 is measured by the time measuring unit 106 after the position detection pattern 201 is detected. To do. That is, the density correction data acquisition unit 107 detects the density correction pattern 202 (position of the density correction pattern 202) on the downstream side (time t-axis direction in FIG. 4) of the position detection pattern 201 on the belt surface. To do.

  The cleaning control unit 108 removes (cleans) the toner on the belt surface by controlling the cleaning operation of the static elimination cleaning 18 (cleaning unit 70). Here, the cleaning control unit 108 controls the operation of the static elimination cleaning 18 so as to remove the density correction pattern 202. Specifically, after the position detection pattern 201 is detected by the position detection data acquisition unit 105 (or after the density correction pattern 202 is detected by the density correction data acquisition unit 107), The cleaning operation of the static elimination cleaning 18 is started after a predetermined time, and this cleaning operation is continued for the time required for the density correction pattern 202 to move in the X-axis direction (longitudinal direction) along with the endless rotation of the photosensitive drum 3. And then finish this. By controlling the operation in this way, only the density correction pattern 202 is removed, leaving the position detection pattern 201 in the pattern set, as shown in the lower diagram of FIG. The background indicated by reference numeral 203 from which the density correction pattern 202 has been removed is the background (background 203).

  The “predetermined time” after the position detection pattern 201 or the density correction pattern 202 is detected in FIG. 1 means that the position detection pattern 201 or the density correction pattern 202 on the intermediate belt 10 in FIG. With the rotation, the position detection pattern 201 is detected by the position detection data acquisition unit 105 at the position of the density sensor 19, and then the position of the neutralization cleaning 18 (toner removal position; cleaning position; or the cleaning brush 182 and the intermediate belt 10. Is a fixed value that is determined in advance by measurement or the like. For the information on the time required for passing, a measured value or the like is stored in advance in, for example, the time measuring unit 106.

  After the density correction pattern 202 is detected by the density correction data acquisition unit 107, the background data acquisition unit 109 detects the position detection pattern 201 again and then waits for the waiting time t1. Is obtained from the density sampling data (referred to as background data). That is, the density correction data acquisition unit 107 detects background data of the same place where the density correction pattern 202 exists on the downstream side of the position detection pattern 201 on the belt surface (hereinafter referred to as “back” as appropriate). It is expressed as “detecting the ground 203”.

  As shown in FIG. 4, both end sides in the X-axis direction of the position detection pattern 201 and the density correction pattern 202 are parallel to the Y-axis direction, that is, the direction orthogonal to the endless rotation direction. Detection of the edge (edge) of each pattern figure moved by endless rotation, that is, detection of the above-described “wait time t1” and “predetermined time” can be performed easily and reliably. Thereby, the accuracy of density correction can be further increased.

  The density correction unit 110 compares the density correction pattern 202 detected by the density correction data acquisition unit 107 with the background 203 detected by the background data acquisition unit 109, that is, the density correction pattern 202 and A one-to-one difference is taken between image portions corresponding to the background 203, and a predetermined density correction process is performed based on the difference (comparison) information.

  FIG. 5 is a flowchart illustrating an example of calibration relating to density correction according to the present embodiment. For example, when the user instructs execution of calibration from the operation panel unit 50, the pattern drawing control unit 104 draws the position detection pattern 201 on the belt surface of the intermediate belt 10 that rotates endlessly. After the position detection pattern 201 is drawn, the density correction pattern 202 is drawn with a waiting time t1 (step S1). (This results in a pattern set as indicated by reference numeral 210 in FIG. 4.) The drawn pattern set is moved to the position of the density sensor 19 along with the endless rotation of the intermediate belt 10, and the density sensor value by the density sensor 19 is moved. Based on this, the position detection pattern 201 is detected by the position detection data acquisition unit 105 (step S2). Time measurement after the position detection pattern 201 is detected is performed by the time measuring unit 106 (NO in step S3), and when it is measured that the same waiting time t1 has passed (YES in step S3). The density correction pattern 202 is detected by the density correction data acquisition unit 107 (step S4).

  The time measuring unit 106 performs time measurement after the position detection pattern 201 is detected by the position detection data acquisition unit 105 or the density correction pattern 202 is detected by the density correction data acquisition unit 107 ( In step S5, when it is measured that a predetermined time, for example, the required passage time has elapsed (YES in step S5), that is, after the position detection pattern 201 has passed the cleaning position by the charge removal cleaning 18, the cleaning control unit The density correction pattern 202 is cleaned by 108 (static elimination cleaning 18) (the position detection pattern 201 is not cleaned by the static elimination cleaning 18) (step S6). (This results in a position detection pattern 201 and a background 203 as indicated by reference numeral 220 in FIG. 4.) Next, the position detection pattern 201 and the background 203 become a density sensor along with the endless rotation of the intermediate belt 10. The position detection pattern 201 is detected again by the position detection data acquisition unit 105 based on the density sensor value of the density sensor 19 (step S7). Time measurement after the position detection pattern 201 is detected is performed by the timer 106 (NO in step S8), and when it is measured that the same waiting time t1 has elapsed (YES in step S8). The background 203 is detected by the background data acquisition unit 109 (step S9). Then, the density correction unit 110 performs a predetermined density correction process based on the information of the density correction pattern 202 and the background 203 (step S10).

  As described above, according to the image forming apparatus (printer 1) of the present invention, it is possible to form an image by the intermediate transfer method using the intermediate belt 10 (intermediate transfer belt) and to correct the image density in the image formation. The intermediate transfer belt is rotated endlessly by the belt rotation control unit 101 or the drive rollers 11 to 13 (belt rotation means), and the pattern drawing control unit 104 or the image forming unit 2 (pattern formation) is provided. The density correction pattern 202, which is a predetermined pattern image for density correction, and a predetermined position for detecting (identifying) the position of the density correction pattern 202 are formed on the belt surface of the intermediate belt 10 that rotates endlessly. After the position detection pattern 201 that is a pattern image is formed and the position detection pattern 201 is formed, Density correction pattern 220 at a constant time (e.g. waiting time t1) is formed. The density sensor 19 and the position detection data acquisition unit 105 (position pattern detection means) detect the position detection pattern 201 on the belt surface of the intermediate belt 10 that rotates endlessly, and the density sensor 19 and the density correction data acquisition unit. After the position detection pattern 201 is detected by the position pattern detection means 107 (density pattern detection means) 107, the density correction on the belt surface of the intermediate belt 10 that rotates endlessly after a certain time (the waiting time t1). A pattern 202 is detected. In addition, after the density correction pattern 202 is detected by the density pattern detection unit by the cleaning control unit 108 or the static elimination cleaning 18 (removal unit), the density correction pattern 202 is removed from the belt surface. After the density correction pattern 202 is removed by the removing means and after the position detecting pattern 201 is detected again by the position pattern detecting means, the density on the belt surface is separated by a certain time (the waiting time t1). Belt surface information (background 203) where the correction pattern 202 has been removed is detected. Then, the density correction unit performs density correction based on a comparison between the information of the density correction pattern 202 detected by the density pattern detection unit and the background 203 detected by the belt surface detection unit.

  That is, for the intermediate belt 10 that rotates endlessly, the position detection pattern 201 and the density correction pattern 202 are formed on the belt surface at a predetermined time (wait time t1), and the position detection pattern 201 is detected. After that, the density correction pattern 202 is detected at the timing when the same time as the predetermined time at the time of pattern formation has elapsed. Thereafter, only the density correction pattern 202 is removed. Then, after detecting the position detection pattern 201 again, the belt surface information (background 203) where the density correction pattern 202 is removed at the same time as the fixed time at the time of pattern formation has passed. Since it is configured to detect, even if the intermediate belt 10 expands and contracts according to the operating temperature condition and the usage level (usage time, etc.), the sampling timing shift due to the belt expansion and contraction without cost. The density correction pattern 202 forming portion and the non-density correction pattern forming portion (background 203) in the same place, with the detection position (detection time) of the same position detection pattern 201 as a reference position. Information can be compared on a one-to-one basis, and appropriate density correction can be performed easily and reliably. To become.

  In addition, after the position detection pattern 201 is detected by the position pattern detection unit or the density correction pattern 202 is detected by the density pattern detection unit by the removal unit, the position of the intermediate belt 10 that rotates endlessly on the belt surface. The density from the belt surface is separated by a predetermined time between a passage time until the detection pattern 201 passes the removal position by the removal means and a time obtained by adding the waiting time t1 (fixed time) to the passage time. Since the correction pattern 202 is removed, the removal of the density correction pattern 202 after the density correction pattern 202 is detected can be reliably performed with a simple structure.

  In addition, this embodiment can be paraphrased as follows. That is, the density correction pattern 202 is formed on the intermediate belt 10, the density of the formed pattern is sampled, and no image is formed on the intermediate belt 10 at the sampled value of this density and the same sampled position. In the calibration method in which density correction is performed based on the difference between the sampled value and the sampled value, the position detection pattern 201 is drawn before the density correction pattern 202 is drawn. 201, and the position detection pattern 201 is not cleaned from the intermediate belt 10 and the position detection pattern 201 is detected even in the second round (or more than the third round), that is, the position detection pattern. By detecting 201 twice, the pattern is drawn after this position detection pattern 201. A timing for sampling the density of the density correction pattern 202, it is possible to anything to the background 203 that is not drawn (concentration of the belt surface itself) is matched with the timing for sampling the intermediate belt 10.

  As a result, the timing for sampling the density correction pattern 202 and the timing for sampling the background 203 are both a fixed time after the position detection pattern 201 is detected. Sampling at the same position can be performed, sampling timing shift due to belt expansion / contraction does not occur (sampling timing shift due to belt expansion / contraction can be corrected), and optimal density correction can be performed. In addition, this invention can also take the following deformation | transformation aspects.

  (A) In the above embodiment, as shown in FIG. 4, after the position detection pattern 201 is drawn, the time until the density correction pattern 202 is drawn is measured by the rear end of the position detection pattern 201 (reference numeral From the edge position indicated by reference numeral 204) to the tip of the density correction pattern 202 (edge position indicated by reference numeral 205), for example, from the tip (edge position indicated by reference numeral 206) of the position detection pattern 201 (this edge position). The time from the time when the image of the front end is detected to the front end of the density correction pattern 202 may be measured. In short, after the position detection pattern 201 is drawn, it may be timed by the time measuring unit 106 so that a certain time is separated (a certain time is left) before the density correction pattern 202 is drawn.

  (B) The installation positions of the static elimination cleaning 18 and the concentration sensor 19 around the intermediate belt 10 are not limited to the positions shown in FIG. However, the neutralization cleaning 18 needs to be disposed upstream of the image forming unit 2 (2M) in the endless rotation in order to remove residual toner on the belt surface during normal printing. In the calibration for correction, after the density correction pattern 202 is detected by the density sensor 19 and removed by the static elimination cleaning 18, it is necessary to dispose the density sensor 19 upstream of the static elimination cleaning 18. Any arrangement may be used as long as these conditions are satisfied. It should be noted that, after the density correction pattern 202 is detected by the density sensor 19, the static elimination cleaning 18 and the density sensor 19 are more arranged so that there is no measurement error of the time required for passing, which takes timing until the pattern is removed by the static elimination cleaning 18. It is preferable to arrange at a short distance.

  (C) In the above embodiment, from the viewpoint of shortening the calibration time, the intermediate belt 10 is rotated once (1) after the position detection pattern 201 and the density correction pattern 202 are detected at the position of the density sensor 19. The position detection pattern 201 and the background 203 are detected after the rotation). However, the position detection pattern 201 and the background 203 may be detected after a plurality of rounds (multiple rotations) such as two rounds after one round.

  (D) The method of removing the density correction pattern 202 is performed by the static elimination cleaning 18 at a timing when a predetermined time elapses after the position detection pattern 201 or the density correction pattern 202 is detected by the density sensor 19 as in the above embodiment. For example, the removal timing may be measured by providing a sensor exclusively for cleaning position detection (providing another concentration sensor) in the static elimination cleaning 18. In the above-described embodiment, only the location of the density correction pattern 202 is cleaned (removed), but conversely, the location of the position detection pattern 201 may not be cleaned. That is, for example, when the pattern set approaches, the cleaning operation for the belt surface is started, the cleaning operation is stopped when the position detection pattern 201 reaches the static elimination cleaning 18, and the cleaning operation is performed after the passage of the position detection pattern 201 is completed. You may make it resume. In short, any configuration and removal method may be used as long as they are removed after the density correction pattern 202 is detected.

  (E) The shape of the position detection pattern 201 is not limited to the above-described embodiment, and for example, any shape other than a circle (perfect circle or eccentric circle) or a square shape can be employed. Moreover, it does not need to be comprised from one shape part, and may consist of two or more types of shape parts. For example, a shape such as a one-dimensional barcode or a two-dimensional barcode may be used. In short, what is necessary is just to be detected as a position detection pattern. However, as described above, it is preferable that the end side in the endless rotation direction (the end side at the position indicated by the reference numerals 204 and 206) be a straight line parallel to the direction orthogonal to the endless rotation direction. In this regard, it is also preferable that the density correction pattern 202 has a linear shape whose end in the endless rotation direction is parallel to the direction orthogonal to the endless rotation direction. Accordingly, the time from the detection of the position detection pattern 201 to the detection of the density correction pattern 202 is measured, or the density correction pattern 202 is detected after the position detection pattern 201 or the density correction pattern 202 is detected. It is possible to easily and reliably (accurately) take the timing for measuring the time until removal, etc., and the detection operation of each pattern can be easily and reliably performed. It becomes possible.

1 is a schematic configuration diagram of a printer according to an embodiment of the present invention. It is a schematic diagram of the cleaning part in the printer. FIG. 2 is a block configuration diagram illustrating an example of a schematic configuration of the printer. It is a schematic diagram showing an example of a position detection pattern and a density correction pattern drawn on the belt surface. It is a flowchart which shows an example of the calibration regarding the density correction which concerns on this embodiment.

Explanation of symbols

1 Printer (image forming device)
2, 2M, 2C, 2Y, 2K Image forming unit (pattern forming means)
3 Photosensitive drum 9 Intermediate transfer roller 10 Intermediate belt 11 to 13 Driving roller (belt rotating means)
14 Secondary transfer roller 18 Static elimination cleaning (removal means)
181 Cleaning electrode 182 Cleaning brush 19 Density sensor (position pattern detection means, density pattern detection means, belt surface detection means)
101 Belt rotation control unit (belt rotation means)
102 density sensor sampling unit 103 sampling data storage unit 104 pattern drawing control unit (pattern forming means)
105 Position detection data acquisition unit (position pattern detection means)
106 Timekeeping Unit 107 Density Correction Data Acquisition Unit (Density Pattern Detection Unit)
108 Cleaning control unit (removal means)
109 Background data acquisition unit (belt surface detection means)
110 Density correction unit (density correction means)
201 Position detection pattern 202 Density correction pattern 203 Background (where the density correction pattern on the belt surface is removed in claim 1)
t1 waiting time

Claims (3)

An image forming apparatus configured to be capable of image formation by an intermediate transfer method using an intermediate transfer belt, and having a density correction function for correcting the density of an image in the image formation,
Belt rotating means for rotating the intermediate transfer belt endlessly;
A density correction pattern that is a predetermined pattern image for density correction and a position detection signal that is a predetermined pattern image for detecting the position of the density correction pattern on the belt surface of the endless rotating intermediate transfer belt. Pattern forming means for forming a pattern, and after forming the position detection pattern, pattern forming means for forming the density correction pattern at a predetermined time interval;
Position pattern detection means for detecting the position detection pattern on the belt surface of the endless rotating intermediate transfer belt;
A density pattern detecting means for detecting the density correction pattern on the belt surface of the intermediate transfer belt that rotates endlessly after the predetermined time interval after the position detection pattern is detected by the position pattern detecting means;
A removal means for removing the density correction pattern from the belt surface after the density correction pattern is detected by the density pattern detection means;
After the density correction pattern is removed by the removing means, and after the position detection pattern is detected again by the position pattern detecting means, the density correction pattern on the belt surface is separated after a certain period of time. Belt surface detection means for detecting belt surface information of the place where the pattern is removed;
Density correction means for performing density correction based on a comparison between density correction pattern information detected by the density pattern detection means and belt surface information detected by the belt surface detection means. Image forming apparatus. The removing means includes
After the position detection pattern is detected by the position pattern detection means or after the density correction pattern is detected by the density pattern detection means, the position detection pattern on the belt surface of the endlessly rotating intermediate transfer belt is The density correction pattern is removed from the belt surface at a predetermined time between a passage time until it passes through the removal position by the removing means and a time obtained by adding the predetermined time to the passage time. The image forming apparatus according to claim 1. The pattern forming means includes
2. The position detection pattern and the density correction pattern in which an end side in the endless rotation direction is a straight line parallel to a direction orthogonal to the endless rotation direction are formed on the belt surface. Or the image forming apparatus according to 2;

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