JP2010201827A - Image forming apparatus, image forming method, and image forming program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a high speed and high accuracy image formation by corresponding to the skew of a recording medium which is conveyed thereto. <P>SOLUTION: An image forming apparatus, which controls a side edge detecting means, interlocking with the position of a recording medium guiding means, includes: a skew amount detecting means which detects the skew amount of the recording medium from detection information obtained by the side edge detecting means and conveyance information of the recording medium; a skew history storage means which stores a plurality of skew amount detection results obtained by the skew amount detecting means; a skew tendency calculating means which calculates an average value and a variation amount of the skew from a plurality of skew data stored by the skew history storage means; and an image shape correcting means which corrects an image shape formed on the recording medium by corresponding to the skew tendency calculation result by the skew tendency calculating means and image forming conditions at the time of the skew tendency calculation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, an image forming method, and an image forming program, and in particular, an image forming apparatus and an image forming apparatus for realizing high-speed and high-precision image formation corresponding to a skew of a recording medium being conveyed. The present invention relates to a method and an image forming program.

  Conventionally, an inkjet image in which a plurality of nozzles are arranged in a nozzle row direction, which is a direction (main scanning direction) orthogonal to a recording medium conveyance direction such as paper, is configured as a line type recording head. Forming devices are known. In such an image forming apparatus, the direction perpendicular to the conveyance direction of the recording medium, that is, the side edge in the width direction of the recording medium is recorded due to a skew of the recording medium, a positional deviation caused by the conveyance means, a designation error in the formed image, and the like. There is a problem that, when the size is deviated from the medium size, an image to be formed protrudes or the protruding image contaminates the conveying unit.

  In view of the above problems, there is known a technique of providing a skew correction mechanism such as mechanically correcting a skew of a recording medium on a conveyance path before image formation (for example, Patent Documents 1 to 3). 3).

  Patent Document 1 discloses an edge for detecting a side edge of a recording medium in front of a skew correction mechanism for the purpose of eliminating positional deviation after the recording medium skew correction by the skew correction mechanism without reducing the productivity of the image forming apparatus. A sensor is provided to detect the side edge of the recording medium a plurality of times to determine the skew state of the recording medium, and from the result, the amount of positional deviation in the main scanning direction of the recording medium after passing through the skew correction mechanism is determined. A method for correcting the writing position in the scanning direction is disclosed.

  Japanese Patent Application Laid-Open No. 2004-228688 aims to simplify the operation of the mechanical skew correction mechanism (recording medium temporary stop) in order to prevent image shift (position and tilt) due to skew of the recording medium and to cope with high speed. A system is disclosed in which the skew of a recording medium is detected at the leading end of the recording medium, and the read order of stored formed images is changed in accordance with the amount of skew to rotate and deform the image.

  In Patent Document 3, for the purpose of enabling the skew of the recording medium to be detected with high accuracy and at high speed, the skew detection of the lateral edge of the recording medium is performed to detect the skew with high accuracy. The difference between the skew amount of the horizontal edge is calculated from the image, and when it is less than the predetermined amount (when the straight line travels), the image reading means (= tip / horizontal edge) is calculated from the skew amount of the leading edge obtained from the leading edge detection and the skew amount of the horizontal edge. A method of calculating the attachment angle of the detection means) and correcting the skew amount of the tip is disclosed.

  However, the skew correction mechanism described above has a problem that high positional accuracy is required for its attachment, or that the correction cannot be completely performed due to further increase in the speed of the conveying means or the type of the recording medium.

  The present invention has been made in view of the above-described problems. Even in various recording media and image forming environments, high-speed and high-accuracy image formation corresponding to the skew of the recording media being conveyed. It is an object to provide an image forming apparatus, an image forming method, and an image forming program for realizing the above.

  In order to solve the above problems, the present invention employs means for solving the problems having the following characteristics.

  In the present invention, the recording medium guide means for setting the position of the side end portion in the width direction orthogonal to the conveyance direction of the recording medium, and the recording medium that is provided and operable in the direction orthogonal to the conveyance direction are provided. An image forming apparatus that controls the side end detection unit in conjunction with the position of the recording medium guide unit, and includes a side end detection unit that detects the position of the side end unit. A skew amount detecting means for detecting the skew amount of the recording medium based on the obtained detection information and the conveyance information of the recording medium, and a skew history storage for storing a plurality of skew amount detection results obtained by the skew amount detecting means. A skew tendency calculating means for calculating an average value and a change amount of the skew based on a plurality of skew data stored in the skew history storage means, and the skew Skew tendency calculation result of direction calculation means, and having an image shape correction means for correcting the image shape in correspondence with the image forming condition at the time of skewing tendency calculation is formed on the recording medium.

  In the present invention, image data storage means for storing at least one page of image data is provided, and the image shape correction means corrects the image shape in advance using a skew tendency calculation result that matches the image forming conditions. The corrected image shape is stored in the image data storage means.

  In the present invention, the image shape correcting unit compares the skew change amount obtained by the skew tendency calculating unit with a threshold value, and stops the image forming process when the threshold value is exceeded.

  In the present invention, the skew tendency storage means for storing the skew tendency calculation result calculated by the skew tendency calculation means and the image forming condition, and the skew change amount obtained by the skew tendency calculation means and the threshold value are compared. If the value is equal to or less than the threshold value, a newly calculated skew tendency calculation result is stored in the skew tendency storage means, and the image shape corresponding to the latest skew tendency calculation result is stored in the image data storage means corresponding to another page. Image data switching means for storing the corrected image data and switching the image formation data after completion of the correction is provided.

  Further, in the present invention, the skew tendency calculating means uses a moving average value calculated from preset past skew data as a skew average value.

  Further, in the present invention, the skew tendency calculating means uses a deviation amount from a detection value immediately before the latest skew data as a skew change amount.

  Further, in the present invention, the skew tendency calculating means uses a standard deviation calculated from a preset number of past skew data as a skew change amount.

  Furthermore, the present invention provides the recording medium guide means for setting the position of the side end portion in the width direction orthogonal to the conveyance direction of the recording medium, and the recording that is provided and operably provided in the direction orthogonal to the conveyance direction. In the image forming method, wherein the side edge detection unit is configured to control the side edge detection unit in conjunction with the position of the recording medium guide unit. A skew amount detecting step for detecting the skew amount of the recording medium based on the detection information obtained by the means and the conveyance information of the recording medium, and a skew for storing a plurality of skew amount detection results obtained by the skew amount detecting step Skew tendency calculation for calculating a mean value and a change amount of a skew based on a history storage step and a plurality of skew data stored in the skew history storage step An image shape correction step for correcting an image shape formed on the recording medium in correspondence with a skew tendency calculation result in the skew tendency calculation step and an image forming condition at the time of skew tendency calculation. And

  Furthermore, in the image forming program, the present invention provides a computer operably operating in a direction perpendicular to the transport direction, recording medium guide means for setting the position of the side end in the width direction perpendicular to the transport direction of the recording medium. The side edge detection means for detecting the position of the side edge of the conveyed recording medium, the skew of the recording medium based on the detection information obtained by the side edge detection means and the conveyance information of the recording medium A skew amount detecting means for detecting an amount; a skew history storing means for storing a plurality of skew amount detection results obtained by the skew amount detecting means; and an average skew based on a plurality of skew data stored by the skew history storing means. A skew tendency calculating means for calculating a value and an amount of change, a skew tendency calculating result in the skew tendency calculating means, and a skew In correspondence to the image forming conditions at the time trends calculated to function as the image shape correction it means for correcting the image shape formed on the recording medium.

  According to the present invention, even in various recording media and image forming environments, it is possible to realize high-speed and high-precision image formation corresponding to the skew of the recording medium being conveyed.

1 is a diagram illustrating an example of a schematic configuration of an image forming apparatus according to an exemplary embodiment. It is a figure which shows an example of the control block structure in a main control means. It is a figure which shows an example of the structure which provided the image data switching means in the control block structure. It is a figure which shows an example of the head unit of a line head. It is a figure for demonstrating the structure which a side edge part detection means operate | moves in conjunction with a recording medium guide means. It is a figure which shows the example of image correction from skew amount. It is a figure which shows an example of the skew amount detection in a skew amount detection means. It is a figure which shows an example which calculates a skew tendency from the skew amount in a skew tendency calculation means. It is a figure which shows an example which calculates an average value using a moving average method. It is a figure which shows typically the internal structure of a skew tendency memory | storage means. It is a figure for demonstrating the state in which the amount of skew changes exceeded the predetermined value. 6 is a flowchart illustrating an example of a control procedure of image forming processing in the present embodiment. 10 is a flowchart illustrating an example of a processing procedure for acquiring skew tendency data during image formation in the present embodiment. 6 is a flowchart illustrating an example of a control procedure from when skew tendency data is updated during image formation according to the present embodiment until image processing is performed in response thereto.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments in which an image forming apparatus, an image forming method, and an image forming program according to the present invention are suitably implemented will be described with reference to the drawings.

<Schematic configuration example of image forming apparatus>
FIG. 1 is a diagram illustrating an example of a schematic configuration of an image forming apparatus according to the present embodiment. In this embodiment, an ink jet printer is used as an example of the image forming apparatus, but the scope of application of the present invention is not limited to this.

  As shown in FIG. 1, a side edge detection unit 10, a detection unit control unit 11, a registration roller pair 12, a recording medium separating unit 13, and a recording medium calling roller as an image forming apparatus 1 used as an inkjet printer. (Rotating body) 14, recording medium guide means 15, recording medium stacking section 16, conveying means 17, main control means 18, recording medium pressing roller (rotating body) 19, temperature / humidity detecting means 20, The conveyance amount detection means 21 is included.

  FIG. 1 also shows a line head 31, a stacked recording medium 32, a deflection forming recording medium 33, and an image forming recording medium 34, and further includes a line head drive control signal 35 and a side end. The flow (direction) of the part detection information 36, the detection part position control signal 37, the recording medium size information 38, the temperature / humidity information signal 39, and the transport amount information signal 40 is shown.

  Here, the conveyance means 17 in this embodiment shown in FIG. 1 shows an example of an air suction belt conveyance system. There are four color (Y, M, C, K) line heads 31-1 to 31-4 above the transport means 17, which are controlled by a line head drive control signal 35 from the main control means 18.

  Further, the recording medium 32 is loaded on the recording medium stacking section 16, and the side end position is regulated by the recording medium guide means 15 that sets the position of the side end in the direction orthogonal to the transport direction.

  The recording medium 32 is pressed against the recording medium separation unit 13 by the recording medium calling roller 14, and is frictionally separated by the separation roller 13 a and the separation pad 13 b constituting the recording medium separation unit 13 and conveyed to the registration roller pair 12. .

  In the registration roller pair 12, the recording medium is abutted between the registration roller pairs 12 a and 12 b, and the recording medium 33 is temporarily stopped to form the bend-formed recording medium 33, thereby making the recording medium skew (tilt). Is removed. Thereafter, the deflection forming recording medium 33 passes between the registration roller pairs 12 a and 12 b and is conveyed to the recording medium pressing roller 19 on the conveying means 17.

  On the transport unit 17, the side end detection unit 10 that detects the side end of the recording medium 34 before entering the line heads 32-1 to 32-4 is operable in a direction orthogonal to the transport direction. Is provided. Further, the side edge detection unit 10 is controlled by the detection unit control unit 11.

  The detection unit control means 11 controls the movement and stop of the recording medium size information 38 from the recording medium stacking part 16 by inputting it to the main control means 18 and the detection part position control signal 37 output in accordance with the subsequent calculation processing. Is done.

  Although not shown in FIG. 1, the main control means 18 is provided with an image area limiting means to be described later, and the size of the recording medium from the recording medium stacking section 16 is the same as the control of the detecting section control means 11. Based on the information 38 and the side edge detection information 36 from the side edge detection means 10, the image area to be ejected is calculated and reflected in the line head drive control signals 35-1 to 35-4 for each color. .

  Similarly, on the main control unit 18, a skew amount detection unit, a skew history storage unit, a skew tendency calculation unit, an image formation condition detection unit, a skew tendency storage unit, an image shape correction unit, and an image data storage unit, which will be described later, are provided. Etc. are mounted. Here, the recording medium type information for supporting various recording medium types and the image forming condition information such as the image forming speed are the operation panel of the image forming apparatus or the image forming apparatus not explicitly shown in FIG. In the host computer to which is connected, the user designates and is taken into the main control means 18.

  Further, the temperature / humidity of the image forming apparatus, which is image forming environment information for dealing with various image forming environments, is detected information from the temperature / humidity detecting means 20 via the temperature / humidity information signal 39. And stored together with the recording medium type information, the image forming speed, etc., in the skew tendency storage means. At the time of image shape correction, a skew tendency calculation result that matches these detected image forming conditions is read from the skew tendency storage means, and image shape correction is executed.

  Further, the main control means 18 receives the carry amount information for detecting the skew amount from the carry amount detection means 21 disposed in the carry means 17 via the carry amount information signal 40, and detects the skew amount. Sent to the means.

<Main control means 18>
Next, a specific configuration of the above-described main control unit will be described with reference to the drawings. FIG. 2 is a diagram showing an example of a control block configuration in the main control means. 2 includes a skew amount detection unit 51, a skew history storage unit 52, an image formation condition detection unit 53, a skew tendency calculation unit 54, a skew tendency storage unit 55, and an image shape correction unit 56. , Image data storage means 57, image area restriction means 58, and drive control signal generation means 59.

  2 shows a line head drive control signal 35, side edge detection information 36, detection unit position control signal 37, recording medium size information 38, temperature / humidity information signal 39, transport amount information signal 40, and recording medium type information. 60, the flow (direction) of signals of the image data 61 and the ejection timing information 62 is shown.

  First, the skew amount detection unit 51 determines the skew amount of the recording medium 34 being conveyed (for example, from the side end detection information 36 from the side end detection unit 10 and the conveyance amount information signal 40 from the conveyance amount detection unit 21). , Main scanning direction shift amount, direction, inclination amount, etc.) are detected. The detected skew amount is stored in the skew history storage unit 52 for a plurality of preset times. Note that the stored number of times may be set in advance, for example, to a number obtained through experiments, or may be configured so that the number of stored times can be set in advance.

  Next, the skew tendency calculating unit 54 calculates the average value and the change amount from the plurality of skew amounts stored in the skew history storage unit 52. At the same time, the image forming condition detection unit 53 uses the recording medium size information 38, the temperature / humidity information signal 39, the transport amount information signal 40, and the recording medium type information 60, for example, so that the image forming apparatus 1 calculates the skew tendency. The image forming condition is detected. Further, the skew tendency calculation means 54 stores the skew tendency calculation result in the skew tendency storage means 55 together with the skew tendency calculation result.

  The image shape correcting unit 56 receives the image data 61 that is data to be printed, and based on the detection information from the image forming condition detecting unit 53, the skew shape storing unit 55 receives the type, size, and image formation of the recording medium. Skew tendency calculation results that match various image forming conditions such as environmental temperature and humidity, image forming speed, etc. are read, and image data 61 is subjected to rotational deformation and jaggy correction according to the values of various image forming conditions (image edge portion Correction processing such as smoothing is executed. That is, the image shape correcting unit 56 uses the skew tendency data that matches the image forming conditions for image formation from the skew tendency storing unit 55 to correct the image shape in advance by deformation or the like, and stores the corrected image shape. I can keep it. As a result, it is possible to deal with a wider variety of recording medium types and image forming environments. Furthermore, it is possible to cope with skew correction while maintaining high image quality more reliably.

  The image data 61 whose image shape has been corrected by the image shape correcting unit 56 is sequentially stored in the image data storage unit 57. The image data stored in the image data storage means 57 is sequentially output to the image area restriction means 58, for example, by a start signal generated inside the image forming apparatus 1. The image data storage means 57 can store at least one page or more of image data.

  The image shape correcting unit 56 reads the skew tendency data stored in the image forming apparatus 1, compares it with newly calculated latest skew data, and further sets a preset skew fluctuation allowable value (threshold). Comparison is made to determine whether the value is within the allowable value. Here, the image shape correcting means 56 stores the latest skew amount if it is within the allowable value, and if it exceeds the allowable value, determines that it is in an error state, proceeds to image formation stop processing, and performs processing. Can be controlled to end.

  The image area limiting means 58 limits (masks) the image area formed for each line by the side edge detection information 36, the recording medium size information 38, and the transport amount information signal 40, and discharge timing signals for each head. In accordance with 62, the signal is output to the drive control signal generating means 59.

  The drive control signal generation unit 59 is configured to distribute and output the line heads 31 for each color based on the image data in which the image area is limited. Here, a detection unit position control signal 37 for moving and stopping the side edge detection unit 10 in accordance with the recording medium size information 38 is output from the image area limiting unit 58.

  As an image region restriction method in the image region restriction means 58, for example, a rough image region is determined from the recording medium size information 38 and the restriction is first applied. Next, the size (width) of the image to be formed is compared with the side edge detection information 36. If the side edge detection information 36 of the recording medium 32 is smaller, the side edge detection information 36 is out of the width. The method of deleting the image (making it a white image) is taken.

<Other embodiments: Configuration example in which image data switching means is provided in the control block configuration>
Next, as another embodiment of the control block configuration of the main control unit 18 described above, an example in which an image switching unit is provided will be described with reference to the drawings. FIG. 3 is a diagram showing an example of a configuration in which image data switching means is provided in the control block configuration. In the configuration shown in FIG. 3, the same reference numerals are given to the components that perform substantially the same processing as in FIG. 2 described above, and a specific description thereof is omitted here.

  The main control means 18 shown in FIG. 3 has a configuration in which the image data switching means 70 and a plurality of image data storage means 57 are provided in addition to the block configuration example shown in FIG. In the example of FIG. 3, two image data storage units 57 (image data storage units 57-1 and 57-2) are provided in the example of FIG. 3, but the present invention is not limited to this, and three or more. It may be provided.

  In this embodiment, the image shape correction is performed again on the image data held in the image data storage unit 57 with the new skew tendency calculation result even during image formation. Note that the processing content up to the image shape correcting unit 56 is the same as the above-described content, and thus the description thereof is omitted here.

  As a new part in the embodiment shown in FIG. 3, the skew tendency calculating unit 54 first determines whether or not the skew state has changed based on the skew history information from the skew history storage unit 52. As a result, the skew tendency calculating unit 54 outputs a re-correction command 72 to the image shape correcting unit 56 when it is determined that the skew state has changed.

  The image shape correcting means 56 receives an image forming signal 71 for notifying whether or not an image is being formed. If an image is being formed at that time, the image forming operation after the image data storage means 57 is performed. In parallel with this, another image data storage means (for example, the image data storage means 57-2) is provided according to the skew tendency data obtained from the new skew tendency calculation result. Then, the image data stored in the image data storage means 57-1 is corrected again and stored.

  Here, the newly provided image data switching means 70 receives the image forming signal 71 and the re-correction completion signal 73 for notifying the completion of re-correction from the image shape correcting means, and the image area limiting means 58. The image data to be output to is switched to recorrection data.

  That is, the image shape correcting unit 56 compares the skew change amount obtained by the skew tendency calculating unit 54 with the preset skew fluctuation allowable value (threshold value) described above, and when it is equal to or smaller than the allowable value, the skew tendency storing unit. The image data subjected to the image shape correction corresponding to the latest skew tendency calculation result stored in is stored in the image data storage means corresponding to another page. The image data switching unit 70 switches the image formation data after the correction is completed.

  As a result, even if there is a change in the stored skew amount, all the processing is performed by performing rotational deformation and jaggy correction on the mounted image data page memory without interrupting image formation. When the process is completed, the formation image data is switched to prevent the productivity from being lowered. Therefore, it is possible to correct the recording medium skew at high speed and with high accuracy.

<Example of head unit of line head 31>
Here, a head unit example of the above-described line head will be described with reference to the drawings. FIG. 4 is a diagram illustrating an example of a head unit of a line head. In addition, the line head 81 shown in FIG. 4 has shown the structure corresponding to one line as an example.

  As shown in FIG. 4A, the line head 81 has two head modules 82-1 and 82-2, and each head module 82-1 and 82-2 has a recording medium width direction. A plurality of head units 83 are arranged in a zigzag manner.

  Here, for example, the mounting position accuracy of each head unit 83 as shown in FIG. 4A, that is, the nozzle position accuracy between a plurality of head units constituting a line, is the ink droplet landing position accuracy as it is. Therefore, if the degree is severe, it may appear as an abnormal image. Therefore, as shown in FIG. 4B, in the plurality of nozzles 84 included in each head unit 83, the nozzle rows of adjacent head units are slightly overlapped in the same nozzle row direction as the recording medium width direction. A head unit is arranged by providing the nozzle overlap area 85, and correction processing such as distributing image data to both head units is performed on the portion where the nozzle rows overlap. As a result, the positional deviation between the two is difficult to understand.

  Further, as shown in FIG. 4C, in the recording medium conveyance direction 86, the ejection timing of the head unit 83 is originally set in order to cope with the displacement due to the configuration of the head unit 83 (staggered arrangement, multi-line arrangement, etc.). The discharge timing adjusting means for adjusting is provided in the main control means 18 for each head unit 83. The ejection timing adjustment means controls the odd-numbered head unit ejection timing adjustment amount 87 and the even-numbered head unit ejection timing adjustment amount 88, respectively. As a result, even with respect to a slight misalignment due to the mounting position accuracy of the head unit, fine adjustment can be performed using the discharge timing adjusting means.

<Configuration in which the side edge detection means 10 operates in conjunction with the recording medium guide means 15>
Next, a configuration in which the side edge detection unit 10 operates in conjunction with the recording medium guide unit 15 will be described with reference to the drawings. FIG. 5 is a diagram for explaining a configuration in which the side edge detection unit operates in conjunction with the recording medium guide unit. FIG. 5 shows a top view of the image forming apparatus 1 described above. Specifically, the side edge detection unit 10, the detection unit control unit 11, the registration roller pair 12a, and the recording medium separation unit. 13 shows a separation roller 13a, a recording medium calling roller 14, a recording medium guide means 15, a recording medium stacking portion 16, a recording medium pressing roller 19, a line head 31, and a recording medium 32. Yes.

  In FIG. 5, the side edge detection means 10 includes a left edge detection means 10a and a right edge detection means 10b, and the recording medium guide means 15 includes a recording medium left guide means 15a and a recording medium right guide means 15b. And have.

  Further, in FIG. 5, left side edge detection information 36 and right side edge detection information 36b detected by the left edge detection means 10a and the right edge detection means 10b, respectively, as side edge detection information 36, and detection unit position control A detection unit left position control signal 37a and a detection unit right position control signal 37b for controlling the detection unit control unit 11 as a signal 37, and a recording medium left guide unit 15a and a recording medium right guide unit 15b as recording medium size information 38. The recording medium left size information 38a and the recording medium right size information 38b that are respectively regulated are shown.

  As shown in FIG. 5, the recording medium guide means 15 is composed of a recording medium left guide means 15a and a recording medium right guide means 15b, and is operable left and right with reference to the center of the conveying means. Here, the operating range of the recording medium left guide unit 15 a and the recording medium right guide unit 15 b is within the range of the size of the recording medium 32 that can be conveyed in the conveying direction 74 by the image forming apparatus 1. When the recording medium 32 is loaded, the alignment is performed manually or automatically.

  The aligned position information is output to the above-described main control unit 18 as recording medium left size information 38a and recording medium right size information 38b.

  The main control unit 18 recognizes the size of the recording medium 32 loaded in the recording medium stacking unit 16 from the recording medium left size information 38a and the recording medium right size information 38b, and the image area limiting unit 58 and the detection unit described above. Recording medium size information 38 is output to the control means 11.

  The image area restricting means 58 compares the recording medium size information 38 with the size of the image to be formed, and deletes an image outside the area of the recording medium 32 when the recording medium 32 is smaller (to a white image). To do).

  Further, in the main control unit 18, the detection unit is arranged so that it is at the center of the detection range of the left end detection unit 10a and the right end detection unit 10b at a preset position where the side end of the recording medium 32 passes. The left position control signal 37a and the detection unit right position control signal 37b are output to the detection unit control unit 11, and the detection unit control unit 11 moves the left end detection unit 10a and the right end detection unit 10b.

  Next, when image formation is started, the left edge detection information 19a and the right edge detection information 19b of the recording medium 32 are transferred from the left edge detection means 10a and the right edge detection means 10b to the main control means 18. The image outside the area of the recording medium 32 is deleted (made a white image) by the image area limiting means 58 in the main control means 18 that is output.

<Example of image correction from skew amount>
Next, an image correction example based on the skew amount will be described with reference to the drawings. FIG. 6 is a diagram illustrating an example of image correction based on the skew amount. 6A shows a correction example in which the formed image is rotated and deformed, and FIG. 6B shows a correction example in which jaggy correction is performed.

  In FIG. 6, N1 to N16 indicate numbers for identifying the nozzles 84 provided in the head unit 86, dX indicates a displacement amount of the formation position (= used nozzle shift amount), and dθ and dθ ′ A skew angle is indicated, X indicates a main scanning direction (= nozzle row direction), Y indicates a sub-scanning direction (= conveyance direction), a indicates a medium size pixel, and b indicates a small size pixel.

  As shown in FIG. 6A, the used nozzle is shifted and the ejection timing is shifted from the skew amount of the recording medium (formation position deviation dX and angle dθ) (FIG. 6A → FIG. 6B). )), Deform the formed image. That is, in FIG. 6A, the formed image is easily rotated and deformed by changing the reading order of the stored image data.

  Further, as shown in FIG. 6B, it is only necessary to rotationally deform the formed image by shifting the use nozzle and the ejection timing from the skew amount of the recording medium (shift amount dX of formation position and angle dθ). In addition, the image is corrected by interpolating the image edge portion of the rotated and deformed image with pixels whose pixel size has been changed from FIG. 6A to FIG. (FIG. 6 (c) → FIG. 6 (d)).

  Note that the simple skew correction method shown in FIG. 6A can cope with a higher speed, but since correction is performed in units of pixels, there is a possibility that the expression of the image edge portion becomes rough. In addition, the complex skew correction method as shown in FIG. 6B can obtain a high-quality image, but requires some time for the processing.

  Therefore, in the present embodiment, the image forming apparatus can further cope with the skew of the conveyed recording medium with high image quality even when the image forming apparatus is further increased in speed, and various recording medium types and image forming environments. In order to provide

<Example of skew amount detection in the skew amount detecting means 51>
An example of skew amount detection in the skew amount detecting means 51 described above will be described with reference to the drawings. FIG. 7 is a diagram showing an example of skew amount detection in the skew amount detection means. In the following processing, in order to simplify the description of detecting the skew amount in the skew amount detection means 51, only the left end detection means 10a is described as the side end detection means 10, but in the present invention. However, the present invention is not limited to this. For example, in order to improve the detection accuracy, the same detection and calculation can be performed for the right end detection means 10b, and both detection results can be used.

  In the skew amount detection method, the coordinates (x1, y0) of the front end portion of the recording medium 32 are first detected by the side end detection means 10a when the conveyance direction 74 is as shown in FIG. Here, the center (x max / 2) of the left end detection range (left end information) 75 in the side end detection means 10a is moved and arranged so as to be an ideal side end passage position of the recording medium 32. Has been. Therefore, when the recording medium 32 is skewed, there is a high possibility that the recording medium 32 is deviated from the ideal side edge passing position, and the deviation amount (shift amount) in the main scanning direction is “Δx0 = x1− (x max / 2) ".

  Here, the negative sign attached to the calculated result Δx0 means that it shifts to the left side in the figure from the ideal side end passage position. Further, y0 indicates a point in time when the recording medium 32 crosses the side edge detection unit 10a, and this is set as a reference position in the transport direction 74.

  Next, after a predetermined recording medium transport distance y1 is transported in advance, the side edge detection means 10a performs side edge detection again, thereby detecting the position x2. Here, the predetermined recording medium transport distance y1 set in advance is, for example, a skew set by the user from an operation panel that can also receive the image forming apparatus 1 or a host computer connected to the image forming apparatus 1 via a communication network. It is calculated from the set value of the detection distance and the recording medium size information 38 loaded on the recording medium stacking unit 16.

From the coordinates (x2, y1) detected by this re-detection, the coordinates (xn, yn) of the left rear end of the recording medium taking into account the size of the recording medium 32 being conveyed are calculated. Note that the above calculation formula is obtained by the following formula.
xn = (Δx / Δy) · L
yn = (Δy / Δx) · xn
(However, L = length in the conveyance direction of the recording medium, Δx = x1-x2, Δy (conveying means feed amount) = y1-y0)
As described above, the skew amount of the recording medium 32 is expressed by the leading edge coordinates (Δx0, y0) and the trailing edge coordinates (xn, yn) on the left side, the right side, or both ends, and the obtained skew amount is the image. Applied to rotational deformation processing. Further, the skew amount detected in the present invention is not limited to the expression in coordinates as described above, and may be expressed by a rotation angle calculated from the front end coordinates and the rear end coordinates, for example. Further, it may be expressed by a slope a and an intercept b in the case where the main scanning direction is a Y-axis and the sub-scanning direction is an X-axis and the linear equation Y = aX + b.

  As shown in FIG. 7, the skew amount is detected by the coordinates of the front end portion and the rear end portion of the recording medium 32. At this time, the leading end coordinate y0 in the transport direction 74 (sub-scanning direction) of the recording medium 32 is set as a reference when the leading end of each recording medium 32 passes, and therefore, rather than a value for calculating a skew tendency. Used to adjust the discharge timing at the time of formation.

  Also, with respect to the rear end coordinate y1 of the recording medium 32 in the sub-scanning direction, if the recording medium 32 is a standard size generally used and its size L is known, the rear end main scanning direction coordinate xn In this embodiment, the recording medium type and its size are stored together as data classification items as image forming conditions. Therefore, it is not used as a skew tendency value. Therefore, the values indicating the skew tendency in the present invention are the leading end main scanning direction coordinate Δx0 and the trailing end main scanning direction coordinate xn.

  Here, FIG. 8 is a diagram showing an example of calculating the skew tendency from the skew amount in the skew tendency calculating means. Moreover, FIG. 9 is a figure which shows an example which calculates an average value using a moving average method.

  As shown in FIG. 8, the leading end main scanning direction coordinate Δx 0 indicates the amount of deviation in the main scanning direction from the ideal side end passing position of the recording medium 32. Δx0 passes from the ideal side end passage position to the left side in the case of “Δx0 <0” (negative sign) from the relationship between (x max / 2) and x1, In the case of “x0> 0” (positive sign), it indicates that the right side is passed from the ideal side edge passing position.

  Further, the rear end main scanning direction coordinate xn indicates how much the rear end of the recording medium 32 that has been shifted by Δx0 passes from Δx0. Also, xn is based on the relationship between x1 and x2, and in the case of “xn <0” (negative sign), the rear end passes through the left side of Δx0, and in the case of “xn> 0” (positive sign) Indicates that the rear end portion passes on the right side of Δx0.

  Next, as shown in FIG. 9, for example, the skew tendency calculating means 54 stores the two skew amount detection values (front end main scanning direction coordinates Δx0, rear end main scanning direction coordinates xn) as skew history storage means. A plurality of times are stored in 52 and calculated as an average value of the two main scanning direction coordinate values. In FIG. 9, as an example, the respective average values are calculated by the moving average method using the latest five data.

  The average value calculation method may be a moving average method that is calculated using the latest data for a plurality of times. Further, as shown in FIG. 9, a past average value (An -1 avg., Bn-1 avg.) (For example, 90% in the example of FIG. 9) and the specific gravity of the latest values (An, Bn) (for example, 10% in the example of FIG. 9), Formulas set in advance according to the setting contents (for example, “An avg. = (An−1 avg. × 9 + An) / 10”, “Bn avg. = (Bn−1 avg. × 9 + Bn) in the example of FIG. 9) / 10 ")).

  Furthermore, the method of calculating the average value in the present invention is not limited to the above contents, and for example, not only the average value described above but also a skew change amount can be used as a value indicating a skew tendency, for example. In this case, it is indicated by the difference between the average value of the past several times and the current value. Furthermore, as another method, for example, a standard deviation calculated from a plurality of preset data may be calculated as the amount of change.

  Here, FIG. 10 is a diagram schematically showing the internal structure of the skew tendency storage means. FIG. 10 schematically shows the internal structure of the skew tendency storage means 55 for storing the skew tendency calculation result calculated as described above and the image forming conditions at the time of calculation. The items of the internal structure of the skew tendency storage means 55 include, for example, “type”, “size”, “direction”, “both sides presence / absence”, “temperature”, “humidity”, “skew tendency calculation value (Δx0). [Mm], xn [mm]) "and the like.

  As shown in FIG. 10, the skew tendency result calculated using the above-described contents is obtained by using other image forming conditions such as image forming speed (conveying speed of the conveying unit), internal temperature of the image forming apparatus, humidity, and recording medium type. In other words, it is stored in the skew tendency storage means 55 for each condition such as size, presence / absence of double-sided printing.

  As a result, when image formation is performed again under the same conditions, the skew tendency storage unit 55 refers to the skew tendency data having the same image formation conditions. In addition, assuming that the image formation under the same conditions has not been performed in the past, the data obtained in the basic experiment in advance can be stored in each image formation condition at the time of factory shipment.

  FIG. 11 is a diagram for explaining a state in which the skew change amount exceeds a predetermined value. In the skew amount transition in FIG. 11, the vertical axis represents main scanning coordinates [mm], and the horizontal axis represents the number of acquisitions (history). Further, the “♦” mark in FIG. 11 indicates the leading end main scanning direction coordinate Δx detected at that time, and the solid line in FIG. 11 indicates 5 data obtained by averaging the past five data from that time. The section moving average value is shown.

  In addition, the dotted line and the alternate long and short dash line shown in FIG. 11 indicate that the five-section moving standard deviation (3σ) is added to the five-section moving average value up to (n−1) immediately before that point (+) and minus (−). It is the value. The previous average value ± 3σ range shows a predetermined value, and error determination is performed when the latest detected value deviates from this range. If the detected latest value is within this range, the 5-section moving average value at that time (including the latest value) is effective, and this value is used as the skew tendency value together with the image forming conditions and the skew tendency. At the same time as being stored in the storage means 55, it is used by the image shape correction means 56 as a value for image rotation deformation.

<Image formation program>
Here, the above-described image forming apparatus 1 can also perform image formation according to the present invention with the dedicated apparatus configuration described above, but an execution program (image for causing a computer to execute the processing in each configuration of each apparatus described above) The image forming process according to the present invention can be realized by generating a forming program) and installing the program in, for example, a general-purpose image forming apparatus.

  The execution program installed in the computer main body can be provided by a recording medium such as a CD-ROM. In this case, the recording medium in which the execution program is recorded is set in a drive device or the like provided in the computer, and the execution program included in the recording medium is installed from the recording medium to the auxiliary storage device or the like provided in the computer via the drive device. .

  As a recording medium, other than a CD-ROM, for example, a recording medium that records information optically, electrically, or magnetically, such as a flexible disk or a magneto-optical disk, a ROM (Read Only Memory), a flash memory, or the like As described above, various types of recording media such as a semiconductor memory for electrically recording information can be used.

  The computer also includes a network connection device that can be connected to a communication network, and obtains an execution program from another terminal connected to the communication network or the execution result obtained by executing the program or The execution program itself in the invention can be provided to other terminals.

  The auxiliary storage device provided in the computer is a storage means such as a hard disk, and can store the execution program in the present invention, a control program provided in the computer, and perform input / output as necessary. The memory device included in the computer stores an execution program read from the auxiliary storage device by the CPU. The memory device includes a ROM, a RAM (Random Access Memory), and the like.

  The computer also has a CPU (Central Processing Unit), and controls the overall processing of the computer, such as various operations and input / output of data between each component, based on a control program such as an OS (Operating System) and an execution program. Thus, each processing can be realized.

  As a result, a special apparatus configuration is not required, and the image forming process can be efficiently realized at a low cost. Further, the image forming process can be easily realized by installing the program.

  Next, the image form processing in the present embodiment will be specifically described. FIG. 12 is a flowchart illustrating an example of a control procedure of image forming processing in the present embodiment. FIG. 12 shows a control flow from when the image forming apparatus according to this embodiment receives a start command to when image formation is executed.

  First, the image forming apparatus 1 for performing printing processing in the present embodiment is initially in a standby state, but an image forming start signal (command) from an operation panel (not shown) or an electrically connected host computer. It is determined whether or not it has been received. Specifically, for example, the determination is made based on whether or not the start button is turned on (S01). If the start button is not turned on (NO in S01), the process waits until the start button is turned on. In the process of S01, when the start button is turned on (YES in S01), various conditions for printing, in this embodiment, the ambient temperature and humidity (temperature / humidity) in the image forming apparatus, the paper type ( (Recording medium type), size, printing speed (image forming speed), etc. are acquired from each detecting means or setting means (S02).

  Here, it is determined whether or not the acquisition is complete (S03). If the acquisition is not complete (NO in S03), the process returns to S02 until the acquisition is completed, and the process is repeated. When the acquisition is completed (YES in S03), the skew tendency data stored in advance in the storage unit that matches the condition is read (S04). Next, using the read skew tendency data, the image data is subjected to rotation processing and jaggy correction processing, and then stored in the image formation data storage means (S05).

  Here, it is determined whether or not the image formation preparation process has been completed (S06). If the process has not been completed (NO in S05), the process returns to S04 and the process is repeated. When the process is completed (YES in S05), the side edge detection unit is moved to the detection position from the recording medium size information described above, and preparation for starting image formation (image formation preparation) is made (S07). .

  At this time, it is determined whether or not the image formation preparation in S07 is OK (S08). If the preparation is not OK (NO in S08), the process returns to S07 and waits until the image formation preparation is completed. In the case of preparation OK (YES in S08), the recording medium size information is read next (S09), and it is determined whether or not the side edge detection position is OK (S10). If the detection position is shifted (not OK) (NO in S10), the side edge detection means is moved (S11), and the process returns to S09 to repeat the process. If the side edge detection position is OK (YES in S10), the side edge detection means is stopped (S12), image formation is performed (S13), and the process ends.

  That is, the procedure shown in FIG. 12 is a flowchart for performing image rotation processing and jaggy correction processing for the first image formation by using skew tendency data that matches the printing conditions stored in the apparatus. Here, as skew tendency data immediately after manufacturing, that is, in an unused state, a recording sheet passing test of a predetermined number of sheets or more may be performed under all printing conditions in the manufacturing process, and stored in the image forming apparatus in advance. Skew tendency data obtained in experiments can be stored as default values.

  Next, a procedure for acquiring skew tendency data during image formation in the present embodiment will be described using a flowchart. FIG. 13 is a flowchart illustrating an example of a processing procedure for acquiring skew tendency data during image formation in the present embodiment. In the example of FIG. 13, the control procedure for detecting the skew amount from the recording medium such as paper conveyed during the image formation and acquiring it as skew tendency data in the image forming apparatus of the present embodiment is shown. .

  First, the image forming apparatus of the present invention determines whether or not the detected position is the leading edge of the recording medium based on the side edge detection information from the side edge detecting means during image formation (S21). In the case (NO in S21), the process waits until the tip is detected. In the case of the front end of the recording medium (YES in S21), the front end side end is detected (S22).

  Next, it is determined whether or not the recording medium has passed a preset distance (S23). If the recording medium has not passed the preset distance (NO in S23), the process of S23 is repeated until the preset distance is passed. Do. Further, in the process of S23, when the set distance is passed (YES in S23), the rear end side end is detected (S24), and the above-described two side end data (front end side end, rear end side) The skew data of the recording medium is calculated from the end portion (S25). In other words, the side edge position data of the recording medium is acquired from the obtained recording medium leading edge passage information, and at the same time, the measurement of the movement amount of the conveying section is started.

  Next, when a predetermined moving distance is passed, the side edge position data of the recording medium is acquired again, and the skew data of the recording medium is calculated from the two side edge data described above.

  Next, skew tendency data stored in the image forming apparatus is read (S26), compared with the calculated skew data described above, and further compared with a preset skew fluctuation allowable value (threshold value). It is determined whether it is within (S27).

  If it is within the allowable value (YES in S27), the oldest skew amount is deleted (S28), and the latest skew amount is stored at the same address (S29). Further, the skew tendency data is calculated from the total skew amount (S30), the skew tendency data is stored (S31), and the skew tendency data update flag indicating that the preset skew tendency data has been updated is turned ON. (S32), the process returns to S21, and the process is continued until the transported recording medium is completed or the image formation stop process is performed. If the allowable value is exceeded in the process of S27 (NO in S27), it is determined as an error state, the process proceeds to an image formation stop process (S33), and the process ends.

  That is, in the above-described processing, if it is within the allowable value, first, the oldest stored skew data is erased, and newly calculated skew data is stored there. Next, skew trend data is calculated from the stored skew data, including the newly calculated skew data, and stored. Further, a flag indicating that the skew tendency data has been updated is set, and control is performed to return to the leading edge detection state of the recording medium again.

  Next, a control procedure from when the skew tendency data is updated during image formation to when image processing is performed will be described with reference to a flowchart. FIG. 14 is a flowchart illustrating an example of a control procedure from when the skew tendency data is updated during image formation according to the present embodiment until image processing is performed.

  In FIG. 14, the image forming apparatus according to the present embodiment detects the update of the skew tendency data using the update flag as shown in FIG. 13 described above, and then performs image processing and reflects it as image formation. The control procedure up to is shown.

  In FIG. 14, it is determined whether or not an update flag indicating that the skew tendency data has been updated is set to ON (S41). If the update flag is not set to ON (NO in S41), the process waits. It becomes a state. If the update flag is set to ON in S41 (YES in S41), the skew tendency data update flag is reset (set to OFF) (S42), and the updated skew tendency data is read. (S43).

  Next, in order to reflect the updated skew tendency data, the next image formation data is read (S44), image rotation processing and jaggy correction processing are executed, and the processed image formation data is saved (S45).

  Here, it is determined whether or not all image corrections have been completed and the process has been completed (S46). If the process has not been completed (NO in S46), the process returns to S45 to repeat the subsequent processes. In the process of S46, when the process is completed (YES in S46), detection of the next image formation timing, that is, detection of a timing that can be reflected in the image forming apparatus is started (S47), and the corresponding timing is reached. (S48), if it is not the timing (NO in S48), the system waits until that timing is reached. Further, in the process of S48, when the timing is reached (YES in S48), the memory area outputting the image forming data is switched (S49), and the process is terminated. Thereby, it is possible to switch the image formation data. Here, the image forming data that reflects the updated skew tendency data is calculated back from the time required for the correction processing time and the image forming plan set at that time in the main control means of the image forming apparatus. It is preferable to determine compatible image formation data.

  As described above, according to the present invention, high-quality, high-speed, and high-accuracy image formation can be performed even in various recording medium types and image forming environments, corresponding to the skew of the recording medium being conveyed. Can be realized.

  Specifically, in the present invention, the side edge detection means for detecting the side edge of the recording medium is provided so as to be operable in a direction orthogonal to the conveyance direction of the recording medium. In the present invention, for example, when a recording medium is loaded in the recording medium stacking section, the recording medium is operated in conjunction with recording medium guide means for setting the position of the side end in the width direction of the recording medium. As a result, it is possible to mount an inexpensive sensor with a narrow detection range instead of an expensive sensor that can be detected over the entire width of the recording medium.

  In the present invention, the skew amount of the recording medium is detected with high accuracy by using the conveyance information from the recording medium conveyance unit and the detection result from the side edge detection unit. Thereby, detection error factors such as variations in sensor mounting angle are reduced compared to when detecting the tip, and detection can be performed with high accuracy.

  In the present invention, for example, the recording medium is mechanically corrected by passing the recording medium through a pair of registration rollers, and the skew amount detection result obtained from the recording medium conveying means and the side edge detecting means is obtained. Skew history storage means for storing is provided, and further skew tendency calculation means for calculating an average value and a change amount of the skew amount from a plurality of detection results stored in the skew history storage means is provided. From this skew tendency calculation result, the writing position (main scanning / sub-scanning) of the formed image is changed and rotational deformation is performed, and then correction processing such as jaggy correction is performed. As a result, it is possible to cope with skew correction while more reliably maintaining high image quality.

  In addition, since the skew of the recording medium also changes depending on various conditions such as the type and size of the recording medium, the temperature and humidity of the image forming environment, and the image forming speed, in the present invention, with respect to the skew tendency calculation result described above, By storing the history data for each of various preset conditions, even when an image is formed again, a skew tendency calculation result corresponding to the various conditions is read and image correction is performed. As a result, it is possible to deal with a wider variety of recording medium types and image forming environments. Further, the present invention stores a skew tendency calculation result for each of various conditions in image formation, so that even when an image is formed anew, a recording medium can be obtained from stored data (for example, the above-described various conditions and skew amount). Therefore, it is possible to perform rotational deformation and jaggy correction corresponding to the skew amount at the time of capturing an image to be formed (image processing) into the apparatus, and it is possible to cope with high speed.

  In addition, even if there is a change in the stored skew amount, rotation deformation and jaggy correction are performed on the mounted image data page memory without interrupting image formation, and all processing is performed. By switching the formed image data at the time of completion, a decrease in productivity can be prevented.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and various modifications, within the scope of the gist of the present invention described in the claims, It can be changed.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Side edge part detection means 11 Detection part control means 12 Registration roller pair 13 Recording medium separation part 14 Recording medium calling roller (rotating body)
DESCRIPTION OF SYMBOLS 15 Recording medium guide means 16 Recording medium stacking part 17 Conveyance means 18 Main control means 19 Recording medium press roller (rotary body)
DESCRIPTION OF SYMBOLS 20 Temperature / humidity detection means 21 Conveyance amount detection means 31, 81 Line head 32 Stacked recording medium 33 Deflection formation recording medium 34 Image formation recording medium 35 Line head drive control signal 36 Side edge detection information 37 Detection part position control signal 38 Recording medium size information 39 Humidity information signal 40 Conveyance amount information signal 51 Skew amount detecting means 52 Skew history storing means 53 Image forming condition detecting means 54 Skew tendency calculating means 55 Skew tendency storing means 56 Image shape correcting means 57 Image data storing means 58 Image area limiting means 59 Drive control signal generating means 60 Recording medium type information 61 Image data 62 Discharge timing information 70 Image data switching means 71 Image forming signal 72 Re-correction command 73 Re-correction completion signal 74 Conveyance direction 75 Left end detection Range (Left edge information)
82 Head module 83 Head unit 84 Nozzle 85 Nozzle overlap area 86 Recording medium conveyance direction 87 Odd-number row head unit discharge timing adjustment amount 88 Even-number head unit discharge timing adjustment amount

Claims (9)

Recording medium guide means for setting the position of the side end portion in the width direction orthogonal to the conveyance direction of the recording medium, and provided on the side edge portion of the conveyed recording medium provided to be operable in the direction orthogonal to the conveyance direction. In the image forming apparatus that includes a side edge detection unit that detects a position, and controls the side edge detection unit in conjunction with the position of the recording medium guide unit.
Skew amount detection means for detecting a skew amount of the recording medium based on detection information obtained by the side edge detection means and conveyance information of the recording medium;
Skew history storage means for storing a plurality of skew amount detection results obtained by the skew amount detection means;
Skew tendency calculating means for calculating an average value and a change amount of skew based on a plurality of skew data stored by the skew history storing means;
Image shape correction means for correcting an image shape formed on the recording medium in correspondence with a skew tendency calculation result in the skew tendency calculation means and an image forming condition at the time of skew tendency calculation. Forming equipment. Image data storage means for storing at least one page of image data;
The image shape correcting unit corrects an image shape in advance using a skew tendency calculation result that matches the image forming condition, and stores the corrected image shape in the image data storage unit. Item 2. The image forming apparatus according to Item 1. The image shape correcting means
The image forming apparatus according to claim 1, wherein a skew change amount obtained by the skew tendency calculating unit is compared with a threshold value, and if the threshold value is exceeded, the image forming process is stopped. Skew tendency storage means for storing a skew tendency calculation result calculated by the skew tendency calculation means and the image forming conditions;
The skew change amount obtained by the skew tendency calculating means is compared with a threshold value, and if it is equal to or less than the threshold value, a newly calculated skew tendency calculation result is stored in the skew tendency storing means, and the image corresponding to another page is stored. 3. An image data switching means for storing image data subjected to image shape correction corresponding to the latest skew tendency calculation result in the data storage means, and for switching the image formation data after the correction is completed. The image forming apparatus according to 3. The skew tendency calculating means includes:
5. The image forming apparatus according to claim 1, wherein a moving average value calculated from skew data set in the past several times is set as a skew average value. The skew tendency calculating means includes:
The image forming apparatus according to claim 1, wherein a deviation amount from a detection value immediately before the latest skew data is set as a skew change amount. The skew tendency calculating means includes:
6. The image forming apparatus according to claim 1, wherein a standard deviation calculated from preset skew data of the past several times is used as a skew change amount. Recording medium guide means for setting the position of the side end portion in the width direction orthogonal to the conveyance direction of the recording medium, and provided on the side edge portion of the conveyed recording medium provided to be operable in the direction orthogonal to the conveyance direction. An image forming method for controlling the side edge detection means in conjunction with the position of the recording medium guide means, and a side edge detection means for detecting a position;
A skew amount detection step of detecting a skew amount of the recording medium based on detection information obtained by the side edge detection means and conveyance information of the recording medium;
A skew history storing step for storing a plurality of skew amount detection results obtained by the skew amount detecting step;
A skew tendency calculating step of calculating an average value and a change amount of skew based on a plurality of skew data stored in the skew history storing step;
An image shape correction step of correcting an image shape formed on the recording medium in correspondence with a skew tendency calculation result in the skew tendency calculation step and an image forming condition at the time of skew tendency calculation. Forming method. Computer
Recording medium guide means for setting the position of the side end in the width direction perpendicular to the conveyance direction of the recording medium;
A side end detection means provided to be operable in a direction orthogonal to the transport direction and detecting a position of a side end of the transported recording medium;
A skew amount detection means for detecting a skew amount of the recording medium based on detection information obtained by the side edge detection means and conveyance information of the recording medium;
Skew history storage means for storing a plurality of skew amount detection results obtained by the skew amount detection means;
A skew tendency calculating means for calculating an average value and a change amount of the skew based on a plurality of skew data stored by the skew history storing means; and
An image forming program for functioning as an image shape correcting unit for correcting an image shape formed on the recording medium in correspondence with a skew tendency calculation result in the skew tendency calculating unit and an image forming condition at the time of skew tendency calculation.

Images